Photochemistry (Specialist Periodical Reports) (Vol 13)

Photochemistry Volume 13

A Specialist Periodical Report

Photochemistry Volume 13

A Review of the Literature published between July 1980 and June 1981

Senior Reporter D. Bryce-Smith, Department of Chemistry, University of Reading Reporters

N. S. Allen, Manchester Polytechnic A. Cox, University of Warwick J. D.Coyle, The Open University R. B. Cundall, University of Salford G . Hancock, The University of Oxford W. M. Horspool, University of Dundee J. M. Kelly. Trinity College, University of Dublin C. Long. Trinity College. University of Dublin L. M. Peter, University of Southampton S. T. Reid, The University of Kent A. J. Roberts, The Royal Institution, London M. Wyn-Jones, Allen Clark Research Centre, Towcester

The Royal Society of Chemistry Burlington House, London, WIV OBN

ISBN 0-85 186- 1 15-6 ISSN 0556-3860

Copyright @ 1983 The Royal Society of Chemistry All Rights Reserved N o part of this book may be reproduced or transmitted in any form or by any means-graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems-without written permission from The Royal Society of Chemistry

Organic formulae composed by Wright’s Symbolset method

Typeset and printed by John Wright & Sons (Printing) Ltd. at The Stonebridge Press, Bristol.

Contents Introduction and Review of the Year By D. Bryce Smith

Part I

xv

Physical Aspects of Photochemistry

Chapter 1 Developments in Instrumentation and Techniques By A. J. Roberts 1 Introduction 2 Plasma Sources

3

3 3

3 Laser Sources Molecular Gas Infrared Lasers Solid-state Lasers Dye Lasers Picosecond Pulsed Dye Lasers Laser Dyes Visible and U.V.Gas Lasers Frequency Conversion Techniques

4 4 5 7 8 9 10 11

4 Detection and Monitoring of Laser Radiation Monochromators and Detectors

12

5 Spectroscopic Techniques U.v.-Visible Absorption Spectroscopy Intracavity Laser Absorption Spectroscopy Infrared Spectroscopy Tunable Diode Laser Spectroscopy Fourier Transform Infrared Spectroscopy Remote Atmosphere Monitoring Optical and Infrared Double-resonance Spectroscopy Photoacoustic Spectroscopy Multiphoton Excitation Raman Spectroscopy Emission Spectroscopy Chemiluminescence

16 16 17 18 18 19

20

6 Transient Absorption Spectroscopy Nanosecond Flash Photolysis Measurements Picosecond Transient Absorption Measurements

29 30 31

13

21 21

23 24

25 29

vi

Contents

7 Transient Emission Spectroscopy

32

8 Chemical Techniques

36

Chapter 2 Photophysical Processes in Condensed Phases By R. B. Cundall and M. Wyn-Jones

39

1 Introduction

39

2 Singlet-state Processes Quenching Processes Energy Transfer Micellar Systems Macromolecule Systems Biologically Related Systems

39 75 80 82 85 87

3 Triplet-state Processes Biological Aspects Esr., Microwave, and Related Studies

92 102 103

4 Physical Aspects of some Photochemical Studies Photolysis and Related Reactions Photo-oxidation Photoisomerization Photochromism Chemiluminescence and Bioluminescence

105 105 111 113 114 115

Chapter 3 Gas-phase Photoprocesses By G. Hancock

117

1 Aliphatic Hydrocarbon Molecules, Ions, and Radicals

117

2 Aromatic Hydrocarbons

119

3 Organic Compounds Containing Oxygen

120

4 Sulphur-containing Compounds

125

5 Nitrogen-containing Compounds

127

6 Halogen-containing Compounds

131

7 Atom Reactions

136

8 Infrared Photochemistry

139

vii

Contents 9 Photochemistry of Atmospherically Important Species H Atoms, H,, and H, 0 Atoms, 02,0,, and HO, N Atoms, N,,land NO,

10 Miscellaneous

149 153 155 158 162

Part I/ Photochemistry of fnorganic and Organometallic Chemistry Chapter 1 The Photochemistry of Transition-metal Complexes By A. Cox

171

1 Introduction

171

2 Titanium

171

3 Vanadium

171

4 Chromium

172

5 Molydenum and Tungsten

176

6 Manganese

177

1 Iron

177

8 Ruthenium

178

9 Osmium

184

10 Cobalt

184

11 Rhodium

186

12 Iridium

188

13 Nickel

188

14 Palladium and Platinum

189

15 Copper

190

...

Contents

Vlll

16 Lanthanides

191

17 Uranium

193

18 Actinides

195

Chapter 2 The Photochemistry of Transition-metal Organometallic Compounds, Carbonyls, and Lowoxidation-state Compounds By J. M. Kelly and C. Long

196

1 General

196

2 Titanium and Zirconium

196

3 Vanadium and Niobium

197

4 Chromium, Molybdenum, and Tungsten

198

5 Manganese and Rhenium

20 1

6 Iron, Ruthenium, and Osmium

203

7 Cobalt and Rhodium

207

8 Nickel, Palladium, and Platinum

209

9 Copper and Silver

210

10 Mercury

210

11 Lanthanides and Actinides

210

Chapter 3 Photochemistry of Compounds of the Main Group Elements By J. M. Kelly and C. l o n g

21 1

1 Group 3 Elements

21 1

2 Silicon and Germanium

212

3 Tin and Lead

216

ix

Contents 4 Nitrogen and Phosphorus

217

5 Oxygen, Sulphur, and Selenium

218

6 Other Elements

219

Part Ill Organic Aspects of Photochemistry Chapter 1 Photolysis of Carbonyl Compounds By W. M. Horspool

223

1 Introduction

223

2 Norrish Type I Reactions

224

3 Norrish Type I1 Reactions

230

4 Oxetan Formation

234

5 Fragmentations and Miscellaneous Reactions

236

Chapter 2 Enone Cycloadditions and Rearrangements: Photoreactions of Cyclohexadienones an'd Quinones By W. M. Horspool

24 1

1 Cycloaddition Reactions Intramolecular Intermolecular

24 1 24 1 245

2 Enone Rearrangements

255

3 Photoreactions of Thymines etc.

268

4 Photochemistry of Dienones Cross-conjugated Dieones

274 275

5 1,2-, 1,3-, and 1,rl-Diketones

278

6 Quinones

290

Contents

X

Chapter 3 Photochemistry of Olefins, Acetylenes, and Related Compounds By W. M. Horspool

297

1 Reactions of Alkenes Addition Reactions Hydrogen Migrations and Abstractions Fission Processes cis-trans Isomerization

297 297 299 300 300

2 Reactions involving Cyclopropane Rings

302

3 Diene Isomerization

314

4 Reactions of Trienes and Higher Polyenes

319

5 [2 + 2]Intramolecular Additions

322

6 Dimerization, Intermolecular Cycloaddition, and Reactions of Acetylenes

325

7 Miscellaneous Reactions

328

Chapter 4 Photochemistry of Aromatic Compounds By J. 0.Coyle

333

1 Introduction

333

2 Isomerization Reactions

333

3 Addition Reactions

339

4 Substitution Reactions

353

5 Intramolecular Cyclization Reactions

369

6 Dimerization Reactions

386

7 Lateral-Nuclear Rearrangements

389

Chapter 5 Photo-reduction and -oxidation By A. Cox 1 Reduction of Carbonyl Group

394

394

xi

Contents

2 Reduction of Nitrogen-containing Compounds

396

3 Miscellaneous Reductions

398

4 Singlet Oxygen

400

5 Oxidation of Aliphatic Compounds

402

6 Oxidation of Aromatics

41 1

7 Oxidation of Nitrogen-containing Compounds

416

8 Miscellaneous Oxidations

419

Chapter 6 Photoreactions of Compounds Heteroatoms other than Oxygen By S. T. Reid

containing 422

1 Nitrogen-containing Compounds Rearrangements Addition Miscellaneous Reactions

422 422

2 Sulphur-containing Compounds

457

3 Compounds Containing Other Heteroatoms

463

Chapter 7 Photoelimination By S. T. Reid

444 454

469

1 Introduction

469

2 Elimination of Nitrogen from Azo-compounds

469

3 Elimination of Nitrogen from Diazo-compounds

477

4 Elimination of Nitrogen from Azides

484

5 Photodecomposition of Other Compounds having N-N Bonds

489

6 Photoelimination of Carbon Dioxide

49 1

xii

Contents

7 Fragmentation in Organosulphur Compounds

492

8 Miscellaneous Decomposition and Elimination Reactions

495

Part lV Polymer Photochemistry

50 1

By N. S. Allen 1 Introduction

50 1

2 Photopolymerization Photoinitiated Addition Polymerization Photografting Photocrosslinking

50 1 502 513 514

3 Optical and Luminescence Properties

519

4 Photodegredation and Photo-oxidation Processes Poly olefins Poly(viny1 halides) Polystyrenes Poly acrylics Polyamides Poly(2,6-dimethyl- 1,4-phenylene oxide) (PPO) Polyurethanes Rubbers Natural Polymers Miscellaneous Polymers

529 529 53 1 534 536 537 538 538 539 54 1 54 1

5 Photosensitized Degredation Photosensitive Polymers Photoactive Additives

544 544 546

6 Photostabilization

546

7 Photochemistry of Dyed and Pigmented Polymers

55 1

8 Appendix: Review of Patent Literature Photopolymerizable Systems Review Tables

554 554 555

...

Contents

Xlll

Part V Photochemical Aspects of Solar Energy Conversion

569

By L. M. Peter 1 Introduction

569

2 Biological Systems

57 1

3 Homogeneous and Microheterogeneous Photochemical Systems

573

4 Photogalvanic Cells

579

5 Photoelectrolysis with Semiconductor Electrodes

582

6 Liquid-junction Solar Cells Cadmium Chalcogenides Gallium Arsenide Gallium Phosphide Indium Phosphide Layer-type Dichalcogenides Silicon Other Semiconductors Photosensitization

586 586 587 587 588 589 594 595 595

7 Advances in Theory and Techniques of Semiconductor Electrochemistry

595

8 Organic Solid-state Systems

598

Author Index

600

Introduction and Review of the Year For this, and probably also for subsequent Volumes, the separate treatment of purely theoretical and spectroscopic aspects is being discontinued. This step has been taken partly to keep the length, and thence the price, to a reasonable level and partly because of organizational difficulties. Readers will however find many of these aspects incorporated within the more ‘physical’ sections of this Report. We are pleased to welcome Dr. A. J. Roberts who has contributed a section on Instrumentation and Techniques covering the period July 1980-July 1981, inclusive. Many references to spectroscopic techniques are included. Despite the development of lasers, synchrotron sources, etc., most photochemists still employ conventional mercury or xenon discharge lamps for photochemical (as distinct from photophysical) studies: nevertheless the use of lasers often leads to different chemistry (see Letokhov, Turro, inter afia).Gough and Sullivan have developed a controlled temperature-gradient U.V. lamp. The high intensity and sharp emission lines pro.vide the possibility of particularly valuable applications in atomic absorption spectroscopy. Laser sources continue to be actively developed, often with great ingenuity, and now dominate spectral calibration applications in the physical and infrared regions; but plasma sources still prove attractive for the vacuum ultraviolet. Synchrotron radiation, being completely tunable, is finding increasing applications, notably in biochemical and biophysical research (see e.g. Castellani and Quercia). Fork, Green, and Shank have obtained dye laser pulses of 90 fs, the shortest yet reported, by the interaction of two oppositely directed pulses in a saturable absorber within a ring system. In laser absorption spectroscopy, major increases in sensitivity have been obtained by use of the intracavity absorption techniques now under active development by several groups. Nordal and Kanstad have derived absorption spectra by photothermal radiometry (PTR), a technique whereby the absorption of amplitude-modulated light causes pulsating surface temperatures and hence a pulsed thermal reradiation. Applications of this technique to biological materials such as blood and leaves have been demonstrated. The use of microprocessors in absorption and emission spectroscopy can provide major improvements in the signal-to-noise ratio (Hannah and Coates; Edgell, Schmidlin, and Balk; Saito et af.,Christmann et al., inter afia). Wren’s observation that many commonly used materials for optical components in vacuum U.V. spectrometers exhibit strong luminescencewhen irradiated at short wavelengths should be noted by workers in the field of V.U.V. fluorescence. Arbeloa has developed an improved and simplified method for quantum yield measurements. The use of 9,lO-diphenylanthracene as a singlet counter has been questioned: 9,lO-dibromoanthracene seems to be preferable (Adam et al.). xv

xvi

Introduction and Review of the Year

Room-temperature phosphorescence (RTP) techniques in which the sample is adsorbed onto an inert solid support are proving valuable in the analysis of traces of polynuclear aromatic compounds (Parker et al.; Vo-dinh et al.). Useful techniques are being developed for the hitherto troublesome resolution of ncomponent fluorescence decays (Weber and Jameson; Slifkin and Darby). The successful use of a pulsed laser in conjuction with conductivity measurements to study the photochemistry of [Cr(en),13 + represents an interesting new approach which probably has wider potential applications (Waltz et al.). Boule et al. report that the practical yields in some photoreactions can be usefully increased by employing a poor solvent for the reactants: this gives the advantages of high dilution without the normal associated disadvantages. In the field of techniques, one of the more unusual reports during the year is a new photochemical method for the analytical determination of carbon in organic compounds involving the formation of carbon dioxide by Ce(SO&sensitized photo-oxidation (Ivanov and Atanov). Brauchle et al. have described a new technique termed ‘holographic photochemistry’, and have used it to study Habstraction by benzophenone in a polymer host. The theoretical understanding of radiationless transitions has been extended in an important paper by Sarai and Kakitani. Among numerous studies on intermolecular energy-transfer mechanism in fluid media, attention is particularly drawn to the very detailed classical treatment by Balzani et al., and Dewey and Hammes’ study of systems having donors and acceptors on surfaces. This latter is relevant to membrane biochemistry. Zemel and Hoffman have used zinc- and magnesium-substituted haemoglobins to make the first detailed study of longrange Forster-type energy transfer in which both the separation and orientation of the donor and acceptor are accurately known. Zimmerman et al. have described energy transfer between chromophores at the termini of rod-like linked bicyclo[2,2,2]octane units. There is considerable continuing interest in the possible role of charge transfer in fluorescence quenching phenomena. Watkins has concluded that oxygen-quenching of fluorescence of aromatic hydrocarbons in methyl cyanide does not involve charge transfer to give radical ions even though such a process is energetically favourable in principle. The process appears to be that conventionally assumed, namely

+ 02(?Zg-) T , + 02(?Eg-) T , + 02(3Zg-) So + 0 2 ( l A g ) .

S,

-+

-+

It does however appear that oxygen-quenching of porphyrins and metalloporphyrins does at least partly proceed via charge transfer (Cox, Whitten, and Gianotti). Prutz and Maier have reported the following energy-pooling reaction of singlet oxygen. ‘Ag + ‘Ag-+ ‘Zg+ + 3CgTheir emission lifetime of ca. 35ps for the ‘C,+ state does however seem surprisingly long. In this connection it is interesting to note that singlet oxygen generated by photochemical dye-sensitization does not react with simple acetylenes, but does react with these in the presence of dicyanoanthracene: thus diphenylacetylene gives benzil (Berenjian et al.; Mattes and Farid). The reaction is

Introduction and Review of the Year xvii thought to involve O2 ; but an alternative possibility would involve addition of singlet oxygen to a charge-transfer complex of dicyanoanthracene with the acetylene. Myers and Birge have derived a simple expression for the effect of solvent polarizability on the oscillator strength of a solute. Various improved procedures (including the use of microcomputer-aided systems) for determining luminescence quantum yields have been described in addition to the development by Arbeloa already mentioned (see Kirkbright; Cahen; Ritter; Christman; Knorr; and Weber, inter alia.). There is increased interest in the effects of pressure on luminescence phenomena (Drickamer; Paladini and Weber; Sonnenschein; inter a h ) . In some systems the effects are similar to those of increasing solvent polarity. Pressure can certainly shift the relative positions of energy levels relative to each other. Fischer continues his deeply probing studies on the photophysics and photochemistry of 1,2-diarylethyIenes,and has reported interesting effects of excitation wavelength on the flourescence quantum yield. Becker et al. have reported some strong effects of solvent viscosity in these systems. Lewis and Holman report what appears to be the first example of divergent reactions from two almost isoenergetic excited singlet states ('La and 'Lb)in the photoaddition of 1-cyanonaphthalene to 1,2-dimethylcyclopentene.This is of course the photochemical equivalent of dual fluorescence. Murai et al. have made the first observation of a quintet-state triplet-triplet radical pair (cf: Huber and Schwoerer). van der Waals complexes of rare gases continue to attract considerable interest. For example, the complexes of argon and krypton with pentacene (P) have been studied by a supersonic expansion technique (Amirav, Even, and Jortner). It appears that two isomers of each complex may exist. The shorter life-times of PKr, than PAr, species are attributed to the promotion of S, + T, crossing by the 'external heavy-atom effect'. Coherent anti-Stokes Raman scattering (CARS) provides a promising method for examining vibrationally excited intermediates formed in isomerization reactions of polyatomic molecules. The technique may permit kinetic spectroscopy of single vibrational levels during fast reactions (Luther and Wieters). Much remains to be understood about the photochemical behaviour of formaldehyde and related species despite further work published this year. For example, the question of the possible formation of the isomeric hydroxycarbene (CHOH) remains unresolved. The following tautomeric equilibrium between singlet a-oxocarbenes (1) formed by photolysis of the corresponding adiazoketones (2, R = Me, Et, Pr') has been reported by Tomioka et al. Ph<-COR

rPhCO-CR..

The rearranged carbenes can be trapped by alkenes: see also Blaustein and Berson. Incidentally, the reaction to give (3) described by Munro and Sharp provides an unusual example of diazoalkane photolysis that does not involve a carbene intermediate.

Introduction and Review of the Year

xviii

Replacement of the aldehydic hydrogen by ,H in C H S C H O reduces the

TI+ So intersystem crossing rate by a factor of 2.4 (Briihlmann, Russegger, and Huber). On the other hand, Hirata and Lim report that ring deuteriation of benzaldehyde increases intersystem crossing and internal conversion rates. h& ;=

hv

0 Ph

(3)

Evidence for orthogonally twisted triplet states of enones has come from laser flash studies, though the precise degree of twist in particular cases is dependent on the flexibility of the molecule (Gioia at al.). The rates of unimolecular decomposition of tetramethyldioxetane from various vibrational levels to ground- and excited-state acetone molecules have been measured by an elegant procedure (Cannon and Crim). The infrared photochemistry of SF, continues to attract considerable interest. One important study involves excitation of SF, in high-resolution diode-infrared laser double resonance experiments. At high intensities, and 30 ps infrared pulses, ‘spectral hole burning’ is observed at energies corresponding to the absorption of between 4 and 5 photons per molecule (Reiser et al.; cf. Sharp et al.). Among various reports of relevance to environmental chemistry, the finding by Wallace et al. that tropospheric concentrations of ozone are increased near the plumes of power plants emitting sulphur dioxide is of particular interest. The effect is not caused by photoreactions of SO, alone, but occurs with SO, in the presence of Cl,. A chain process involving C100- radicals may be involved. Of more distant relevance is the observation by Ferris and Benson that photolysis of PH, to P,H4 appears to play a part in the atmospheric photochemistry of the planet Jupiter. D-line emission from Na(3,P) formed by the reaction of F with Na, is considerably broadened. It may be that observations of this type will provide direct information about the properties of a transition state or species formed in a chemical reaction; in this case FNaNa and FNaNa* (Arrowsmith et al.). Interest in organosilicon photochemistry continues to develop, with particular reference to the photochemical generation of R,Si intermediates. Stable silacyclopropenes have been prepared by a photochemical route (Ishikawa et al.), and clear evidence for the formation of tetramethyldisilene, Me,Si=SiMe,, has been obtained by trapping as a [2 + 4]cycloadduct with cyclopentadiene (Nakadaira et al.), The irradiation of iodosilanes may produce cationic together with radical intermediates (Eaborn et al.): cf. vinyl iodides. The organotin radical species Bu,Sn formed by laser-flash photolysis of Bu,SnH in di-t-butyl peroxide solution is surprising in showing strong absorption in the visible region (Scaiano). Growing interest has been focussed on transition-metal photochemistry in view of its potential relevance to the problem of solar energy fixation. Among the more general developments however, a new formalism of ‘bond indexes’ proposed by Vanquickenborne and Ceulemans promises to rationalize the photochemistry of hexaco-ordinate complexes of transition metals. The ligand most readily expelled is deemed to be that having the smallest bond index. Vogler and Kunkely have

Introduction and Review of the Year xix provided the first example of the photo-oxidation of a ligand in a transition-metal (Ni or Pt) complex under conditions in which the oxidation state of the metal remains unchanged. Using [Ru(bipy),]* as donor, Rosenfeld-Gruenwald and Rabani have demonstrated what appears to be the first example of electrontransfer to the photoexcited uranyl ion in a reversible system: UOZ2+acts as an electron acceptor in both ground and excited states. A 'long-range electron transfer' mechanism has been proposed for the UOZ2+-and Fe2+-catalysed photo-oxidation of alkenes (Murayama, Kohda, and Sato). The luminescence of Eu" is increased more than sixhundred-fold by complexation with crown ethers (Adachi et al.). In another application of crown ether photochemistry, the reaction (4) -+ ( 5 ) involves a change of cavity size on irradiation, giving a crown ether which can complex alkali-metal cations. The rate of thermal reversion in the complexed photoproduct varies with the metal ion involved (Yamashita et al.). +

7

quantitative' hv

i

The possibility of a new type of information storage system has been suggested by the irreversible photodisplacement of chloride ion from a polymer-bound chlororuthenium complex deposited on an electrode (Haas, Kriens, and Voss). Photochromic systems are also of potential use in infcrmation storage. The platinum complex (6) undergoes a novel type of photochromism involving photodisplacement of solvent to give the complex (7): reversion occurs by a 'dark' reaction with the solvent (Rohly and Mertes). Heller and his group have described some interesting and potentially commercially useful developments in the field of photochromic fulgides, including a new fulgide-based re-usable actinometer for the visible and near-u.v. Anjaneyulu et al.

Soh. (6)

(7)

(Soh.= Me,SO, MeCN)

Introduction and Review of the Year

xx

have employed similar species in the quite different field of lignan synthesis. Tomachewskii et al. have described some interesting reversible photochromic systems based on the conversion of azomethine imines into diaziridines. The photochemistry of micellar systems is also .one of the more notable growth areas of the subject, being of interest in both photobiology and solar energy conversion. For example, relatively stable charge separation (i.e.retardation of the back reaction) has been achieved in the micellar system, *Ru(bpy)32+ + C,,MV2+

+ R ~ ( b p y ) ~+~ C,,MV+ +

where C,,MV is methylviologen bearing a C,,chain (Brugger and Gratzel). Several groups have devised interesting systems based on the conformational changes that occur on irradiation of azo-compounds. Thus, artificial photoresponsive membranes have been produced by incorporation of alkylammonium salts containing azobenzene chromophores into dipalmitoyl-phosphatidylcholine liposomes (Kano et al.): photochemical control of micellar catalysis has been achieved in a related manner using a photosensitive surfactant (Shinkai et al.; cf. Ueno et al.). The same group have used photoisomerizations in modified crown ethers to achieve photochemical control of ion-transport processes: cf. Yamashita et al. In a particularly interesting study, Moriarty et al. have attempted to mimic in vivo conditions by comparing the irradiation of 7,8-dehydrocholesterol in various ordered lipid multilayers with the results of irradiation in thin films. Notable differences emerged, favouring the lipid media. Irradiation in hexane solution gives mainly tachysterol, which is only a minor product from the lipid reactions. Turning now to the more general field of solar energy conversion, we may note the valuable broad but well-focussed classification of various approaches to the problem provided by Nozik. Good progress is being made in the development of efficient photoelectrochemical systems, particularly by a group at Bell Laboratories. Hybrid biological systems are beginning to look interesting. For example Ochiai et al. have prepared a ‘living electrode’ incorporating a living blue-green alga which can function as a photoanode. Groby and Hall, and Adams et al. have used immobilized chloroplasts and enzymes to achieve photolytic hydrogen generation, and Bhardwaj et al. have described an interesting photocell incorporating chloroplasts. As noted above, Gratzel’s group in Lausanne continue to provide innovation in this field. They have now reported bifunctional semiconductor redox catalysts for the photodissociation of water: for example, they have catalysed the photochemical formation of both hydrogen and oxygen in systems containing n-dodecylmethylviologen and [Ru(bpy),]. Controversy continues about the precise role of the platinum catalysts commonly used in important systems of this type (and sometimes about reproducibility), although Miller and McLendon have obtained evidence that the dispersed platinum particles act as ‘microelectrodes’. Japanese workers have reported that ruthenium tris-bipyridyl complexes with polymers containing electron-accepting viologen groups generate hydrogen from water on solar photolysis. Electron migration along the polymer chain is believed to occur (Nishyima et al.; Shimizu and Fukui; Kamogawa et al.). In yet another variant system for the photodecomposition of water, Gratzel et al. have reported improved quantum yields using niobium-doped Ru0,-n-TiO, containing platinum.

Introduction and Review of the Year

xxi

Ultraviolet irradiation of Ti"' compounds in aqueous ethanol provides yet another hydrogen-generating system. The use of C,'H,OH leads to equimolar proportions of H, and 2H2 (Potapov et al.). But Giro et al. report that in aqueous HC1, visible light is also effective if [Ru(bpy)J2+ is also present. Sutin has challenged this claim, and has reported details of an alternative related system said to generate hydrogen using 450 nm light. Cu2 crown-ether complexes appear promising as electron relays in photoredox systems relevant to solar energy conversion (Humphrey-Baker et al.: CJ Monserrat et al.). Goldstein's cell containing rubidium crown-ether complexes also looks promising. The now classical, but in practical terms disappointing, iron-thionine system still has its devotees, including Brokken-Zijp, Dung, and Mesmaeker (yes, really!). Albery estimates that photogalvanic cells have a limiting maximum efficiency of 5%. If this is correct, such cells have little if any prospects of practical utility in solar energy storage; but time will tell, for the prediction of a limit often stimulates attempts to exceed it. p-Lutetium rhodate (LuRhO,) in conjunction with n-TiO, provides a photoelectrolysis cell that produces hydrogen and oxygen without external bias and has a sufficient excess of power for a small load (Jarrett et al.). Guruswamy et al. have reported a 2% solar efficiency for a related photoelectrolysis cell using p-LaCrO,: a considerable improvement on the performance of TiO,/GaP cells. Our Reporter, Dr. Laurence Peter, nominated GaAs as the 'material of the year' for Volume 12. This year, the award goes to p-type InP, largely on the basis of work carried out at the Bell Laboratories. Thus Heller et al. have described the first really efficient p-type photoelectrochemical cell based on pInP/VCl,-VC1,-HCl/C. After treatment of the InP photocathode with alkaline peroxide, and then aqueous potassium cyanide, the solar efficiency rose to 11.5%. The stability of such cells, coupled with the ability to function well under intense irradiation, makes them some of the more promising candidates for future largescale use. Further developments will be awaited with great interest. Gray et al. have reported a very interesting cyclic process for the photoreduction of water to hydrogen at 546nm based on use of a rhodium complex and the dissociation of HC1 to hydrogen and chlorine atoms. The theoretical treatment of the transport and kinetics of minority carriers at illuminated semiconductor electrodes by Albery et al. is likely to be applied widely. The cluster ion (Mo,C1,J2- has been suggested to be potentially useful in systems for solar storage (Maverick and Gray). We come now to some of the more notable developments in organic photochemistry. Dauben and Kellogg have provided further examples of systems in which the conformation of the electronic ground-state speciesappears important in determining the course of photoreactions. +

Introduction and Review of the Year xxii The acid-catalysed photoisomerization of the indene (8) to (9) has some interesting mechanistic features in that it occurs via a singlet mechanism, yet HCl does not quench the fluorescence (Morrison and Giachero). The photochemical migration of aryl groups, as in the indene (lo), giving (1 l), is suggested by Manning et al. to involve an ‘internal exciplex’ rather than the radical-like transition state previously proposed by Zimmerman et al. New examples of photochemical synthesis of the whimsically named ‘betweenanenes’ (1 2) by irradiation of the cis-isomers are reported by Marshall et al.: cf- Nakazaki et al., in Vol. 9. Ring sizes range from 8 to 26 carbon atoms. Inoue et al. report that the cis-trans photoisomerization of cyclo-octene sensitized by

methyl benzoate is anomalous and shows features of a singlet process. This study should stimulate greater interest in the use of aryl esters as sensitizers. Mukai et al. report that ZnO or CdS can catalyse the photodissociation of certain cyclobutanes to ethylenes: cf- Takamuku and Schnabel. The elusive trans-cyclohexene remains a questionable entity despite further work by Kropp el al. on the xylene-sensitized photodimerization of cyclohexene. Borden et al. have described a 1,5-sigmatropic rearrangement which leads to inversion at the migrating carbon for both thermal and photoprocesses. This seems to be a case in which preservation of orbital symmetry is of less dominating importance than the adoption of a ‘least motion pathway’. Dauben and Olsen have provided other examples of ‘least motion’ control in the ring-opening of cyclohexa- 1,3-dienes. Kitamura et al. have described the following extremely interesting cyclization process dependent upon trapping by azide of a vinylic carbocation (1 3) formed by photoionization of a vinylic halide (14).

R p-MeOC,H,

XBr

R

R

p-MeOC,H,

-;:- ’ R>d+

+dimethyl N,fumarate

’

iv

Me0,C

N

p-MeOC,H,

‘COzMe

Charlton et al. have provided evidence for photoionization of an allylic iodide, so the behaviour of vinylic halides can no longer be considered unique. In the field of aromatic photochemistry, Maier and Schneider report that the Dewar-benzene (15) is more thermodynamically stable than the benzene (1 6) into

Introduction and Review of the Year

xxiii which it is converted on irradiation. Although it is now orthodox to invoke benzvalene intermediates in photochemical ring-transposition reactions of benzene derivatives, Scott and Highsmith's suggestion that similar intermediates are involved in the thermal ring transpositions of the three difluorobenzenes at temperatures above 1000 "C must be regarded as highly controversial: one wonders whether some limited population of the S , state might occur under such extreme conditions. Kobayashi et al. have obtained the heterobenzvalene (17) by a photochemical procedure. The compound is stable at room temperature, and is in fact the first heterobenzvalene to be isolated and characterized. Rather surprisingly, excited benzene does not appear to form an exciplex with tertiary amines at CN

low concentrations (Beecroft and Davidson). Attention is drawn to two important papers on photoaddition, photosubstitution, and photocleavage reactions of fluorobenzenes and other substituted benzenes with amines (Gilbert, Krestonosich, and Westover), to an unusual 1,3-addition of toluene to 1,Il-dicyanonaphthalene, giving (18) (Albini et a/.), to detailed studies of photoadditions of dienes and monoenes to the benzene ring (Gilbert et al.), and to corresponding intramolecular additions (Gilbert and Taylor). Aromatic photonucleophilic substitution continues to be an active area of research. Among many reports, the photocyanation of naphthalene and other aromatic hydrocarbons by cyanide ion in the presence of p-dicyanobenzene as electron acceptor, and also preferably oxygen, is of special interest since nucleophilic substitution in hydrocarbons is normally rather uncommon (Yasuda et a/.). The aromatic radical cation seems to be involved. In contrast, the aromatic radical anions (which eliminate cyanide) are believed to be intermediates in the photosubstitution of cyano groups by hydrogen (Tada et al.). Semmelhack and Bargar have reported some interesting intramolecular photonucleophilic substitutions by enolate anions that give up to Cl0 rings in useful yield: for example, (19) + (20).

<=

H d5CMe2COMe Bu'OK

0

(19)

Wald et al. report that dibromomaleimides [e.g. (21)] photoreact with many aromatic systems in processes, which could well prove of synthetic utility in building ring systems [e.g. (22)j. Turning now to the carbonyl compounds, the declining interest in the photolysis of simple carbonyl compounds noted in previous Reports appears to be continuing; but some notable work continues to appear, for example the use of micellar systems as a means of improving regiospecificity. Turro, Bauer, et al. report that

Introduction and Review of the Year

xxiv

the photodecarbonylation of trans-2,3-dimethylcyclobutanone is stereospecific, whereas that of the cis-isomer is not. Attention is drawn to the interesting paper by Murray and Ford on the sometimes dramatic effect of methyl constituents in the photolysis of cyclic ketones. Suzuki et al. report that certain phosphonates can undergo a photoreaction analagous to Norrish Type 1 fission of ketones, i.e. (23) + (24). But Norrish Type 2 reactions tend to dominate with ethyl and higher alkylphosphonates. Dankowski et al. have also reported a Norrish Type 1 process involving fission of a C-P bond, viz (23) --+ (26). 0 II CI,CP(OMeJ,

-

0 0

II

1

(Me0)2P- (OMe),

Muthuramu and Ramamurthy have reported the first example of Norrish Type 1 cleavage in a thione, or more specifically a dithiolactone. The synthesis of dodecahedranes by Paquette et al. is a considerable achievement in molecular engineering, and involves several carbonyl photolysis steps as described in Part I11 Chapters 1 and 2. Much of the current work on thermally reversible intramolecular photoformation of strained systems seems to stem from the interest in developing energy-storage systems. Several examples are described this year involving intramolecular addition of an ethylenic bond to a carbonyl or enone moiety, but these unfortunately involve ultraviolet rather than visible light. The main practical utility of such reactions will probably continue to lie in the field of synthesis, though it is probably easier to obtain research grants these days for work on energy storage. Wiesner's empirical rules for enone cycloaddition have been criticized by de Mayo and Loutfy, but Wiesner has now produced further supporting evidence for them. Serebryakov has reported an unusual ene-type photoaddition of acetylene to the enone moiety of cholestenone (27), which gives (28)-

Ketone-sensitized photoadditions of aldehydes to a/3-unsaturated esters gives 4oxoalkanoic acids in variable but sometimes excellent yields (Cerfontain and van Noort: cf. Rosenthal and Chow). Insoluble benzoylated polystyrene is effective as

Introduction and Review of the Year

xxv

a sensitizer for photoaddition of maleic anhydride to cyclohexene, in place of benzophenone (Bourdelaude et ul.). The procedure may simplify work-up since the sensitizer does not contaminate the products. Current thinking about the mechanism of photoreduction of benzophenone by benzhydrol is challenged by new findings from Schuster and Karp. Fredericks and Wrighton describe a new process for the sensitization for ketone photoreduction, which involves a low-lying metal-to-ketone charge-transfer state, and also provide the first example of a metal(Re)-to-ligand charge-transfer photoprocess in which the ligand undergoes ;he redox reactions, reduction in this case. Attention is drawn to an interesting key photocyclization step in a new synthesis of ( f)-oestrone by Quinckert et al., and a /?-lactamphotosynthesis described by Aoyama et af., viz (29) + (30). CHMe2

Ph+%

HMe2

0 (29)

hv

PhSEMe

MdH

'CHMe2 (30)

Wolner has described a remarkably regioselective photochlorination (of a steroid) by PhICl,. Bookbinder and Wrighton have described highly efficient and reversible photoreduction processes on p-type silicon electrodes derivatized with a siliconcontaining quaternary salt of 4,4'-bipyridyl. Many thousands of redox cycles are reported to be possible wjthout significant deterioration. Phenyl fulminate, PhON&, the first example of an organic fulminate, appears to be formed on irradiation of (3 1) in argon at 10 K (Wentrup et af.).Leuenberger et al. have used a photochemical route to provide the first authenticated example of a triaziridine (32). Aziridine diones (33) have been prepared for the first time by low-temperature irradiation of the ozonides (34) of diphenylmaleimides (Aoyama et d.). They are thermally unstable. Irradiation of (34) at room temperature gives RNCO, CO, and (PhCO),O.

Introduction and Review of the Year xxvi In the field of polymer photochemistry, our Reporter Dr. Allen has himself been very productive this year. His Chapter cites over 740 references together with numerous patents which are listed in the Appendix. Japanese patents in this area now exceed in number the combined totals from Europe and the United States. Note that the review period, for this Chapter only, runs from June 1980 to May 1981 inclusive. Charge-transfer initiator systems are attracting increased interest, as is cationic photopolymerization. Photopolymers of acetylenes and polyacetylenes are of potential importance as conductors and semiconductors, for example in solar cell applications (Fouassier et al., Yee, Day, et al., inter a h ) . Fouassier et al. report that vinyl polymerization photosensitized by aromatic ketones can proceed faster in a micellar system through enhanced initiation rather than propagation. Dolotov et al. have photopolymerized formaldehyde at low temperatures to give poly oxymethylene. Photografting techniques have been used to prepare crease-resistant cotton fabrics (Reinhardt and Arthur, inter alia), and flame-resistant textiles have been obtained by photografting using a vinyl phosphonate (Harris et d.). Damen and Neckers have described what appears to be the first example of a photochemical template effect whereby styrene-divinylbenzenecopolymers guide the stereochemistry of a subsequent photoprocess. Despite a vast amount of work, the mechanism@) for initiation of the airoxidation of polyolefins remains a matter of continued debate. Polyene structures seem to play a key role in the photodegradation of poly(vinylch1oride): see Owen et al., Yang et al.; cf. Yamamoto et al. The environmentally desirable photodegradable polyethylene has been prepared by doping with radiation-modified atactic polypropylene (Omichi and Hagiwara) and hydroxyethylferrocene(Borodulina et al.).The photostabilizationof polymers by hindered piperidines is proving of great technological importance. Of the related mechanistic studies, those by Allen and McKellar, Son, Sedlar et al.. Scott et al., and Hodgeman are particularly notable. D . Bryce-Smith.

Part I PHYSICAL ASPECTS OF PHOTOCHEMISTRY

1 Developments in Instrumentation and Techniques BY A. J. ROBERTS

1 Introduction This article is concerned with the developments in instrumentation and techniques in photochemistry and spectroscopyduring the period July 1980-June 1981. Such a wide ranging topic is impossible to review at all critically, nor is it feasible to consider every publication concerning photochemical instrumentation. Consequently, many reports concerned merely with the application of established techniques have been omitted. In this respect, it should be noted that the relative brevity of some sections (for example plasma sources, u.v.-visible spectroscopy) in no way reflects the use or application of these techniques, but merely their advanced state of development. Further it is apparent that, during the past decade, a swing away from developments in instrumentation for conventional photochemistry in favour of spectroscopy and laser photochemistry has occurred. This has been reflected in the following discussion. The author would like to thank Dr. Mike West for several helpful discussions during the preparation of this manuscript.

2 PlasmaSources Several reports - have discussed a modified version of a commercially available Grimm’s glow discharge lamp for use as a hollow cathode emission source. Aluminium, copper, and graphite cathode materials were investigated. The modification of large diameter (Perkin Elmer) hollow cathode lamps for a small diameter lamp housing (Instrumentation Laboratory model 75 1 spectrophotometer) has been de~cribed.~ The selective spectral enhancement of arc discharge lamps with the addition of metal halides has been demonstrated,’ and the highenergy conversion into narrow wavelengths suggests an application as CW-laser pump sources. A controlled temperature-gradient lamp has been shown to perform better (sharper emission lines and higher intensity) than an electrodeless discharge lamp for atomic absorption spectroscopy.6The design of a lithium heatpipe arc lamp for use as a laboratory source has been discussed.’ Although laser sources are rapidly dominating spectral calibration in the visible and infrared regions, plasma sources are still attractive for the vacuum U.V. A

’ ’

S. Caroli, A. Alimonti, and 0. Senofonte, Spectrosc. Lett., 1980, 13, 451. 0. Senofonte, S. Caroli, and A. Alimonti, Spectrosc. Lptt., 1981, 14, 195. A. Alimonti, S. Caroli, and 0. Senofonte, Specfrosc. Lett., 1980, 13, 307. D. E. Nixon, R. C. Singer, and A. F. Skidmore, Appl. Specirosc., 1980, 34, 605. W. Bamberg, E.O.S.D., 1981, 13, 59. D. S. Gough and J. V. Sullivan, Anal. Chim. Acta, 1981, 124, 259. R. W. Boyd and D. J. Harter, Appl. Opi., 1980, 19, 2660.

3

Photochemistry

4

deuterium discharge lamp has been developed as a radiance transfer standard between 115 and 370nm.8 Although magnesium fluoride windows were used in this application, a later r e p ~ r t in , ~ which an argon mini-arc was utilized for standardization in the region 92-200 nm, suggested that problems may arise due to the formation of colour centres. The errors introduced due to the polarization of the irradiance standard source are often neglected since, in many cases, the required data are unavailable. Consequently the characteristic polarization of a DXW-type filament lamp (General Electrics 1000W) has been tabulated.” Synchrotron radiation provides an attractive, completely tunable, moderately intense source for spectroscopy, and several facilities are currently available, or are in development, for such application. The use of synchrotron radiation in biophysical and biochemical research has been discussed in a collection of 28 papers.” Its use in vacuum-u.v. spectroscopy and the design of suitable optical components has been considered.

3 Laser Sources

Molecular Gas Infrared Lasers.-Two brief reviews have been published on infrared laser sources and their applications. l4 A compact high-pressure ( 5 atm.) C02 laser has been designed and operated at pulse repetition rates up to 50 Hz.15 Single-mode power densities of 300 MW 1- were achieved, although the short sealed-off lifetime of the laser limited its usefulness as a spectroscopicsource. A shock tube driven C0,-Ar gas dynamic laser provided a 4ms, 2 W pulse at 1 8 . 4 ~ r n . I4~W output was also obtained from a 1.2cm active length of laser medium using a conical nozzle for mixing CO, and nitrogen.” Pre-ionization of the discharge medium has been found to improve the performance of transverse electric atmospheric (TEA) C 0 2lasers. l a * Advantages were gained both from a three-fold increase in output power and better pulse-to-pulse reproducibility. A CW waveguide C02 laser, with transverse radiofrequency pumping was found to be 8.5% efficient with up to 4.6 W output power.2o3-W output was obtained from a CO waveguide laser with chilled, flowing gas.21 Gold electrodes have been utilized in a sealed CO laser producing 28.5W output power.22 The laser was shown to have a long operational life. 37

lo I’

l2

’* l6

l8

l9

2o 21 22

P. J. Key and R. C. Preston, J. Phys. E., 1980, 13, 866. R. C. Preston, C. Brookes, and F. W. J. Clutterbuck, J . Phys. E., 1980, 13, 1206. R. K. Kostuk, Appl. Opt., 1980, 19, 2274. ‘Synchrotron Radiation Applied to Biological and Biochemical Research’, ed.A. Castellani and I. F. Quercia, NATO Advanced Study Institutes Series, Series A: Life Sciences, Vol. 25, Plenum, New York, 1980. M. R. Howells, Appl. Opt., 1980, 19, 4027. S. D. Smith, Opt. Laser Technol., 1980, 12, 199. ‘New Infrared Sources’, Laser Focus, 1981, Feb., 76. P. E. Dyer and B. L. Tait, Appl. Phys., 1980, 37, 356. A. A. Vedeneev, A. Yu. Volkov, A. I. Demin, E. M. Kudriavtsev, J. Stanco, J. Milewski, and M . Brunne, Appl. Phys. Lett., 1981,38, 199. H. Hara and A. Fujisawa, Appl. Phys. Lett., 1981, 38, 65. I. W. Lee and S. S. Lee,Appl. Ph-vs. Lett., 1980, 37, 871. D.B. Cohn, Appl. Phys. Lett., 1980, 37, 771. G.Allcock and D. R. Hall, Opt. Commun., 1981, 37. 49. J. P. Hauck and E. H. Huffman, Rev. Sci. Instrum., 1980, 51, 1265. P. J. M. Peters, W. J. Witteman, and R. J. Zuidema, Appl. Phys. Lett., 1980, 37, 119.

Developments in Instrumentation and Techniques

5

A compact frequency stabilized TEA-CO, laser was operated at a pulse repetition rate of 100Hz with pulse energies of 80mJ.23 Active frequency and amptitude stabilization was achieved for a CW C 0 2 laser.24A bandwidth of less than 300kHz and a power fluctuation less than 3 x were obtained. Some interest has been displayed in the possibility of short pulse production by modelocking C 0 2 lasers. The introduction of a short pulse into a high-power oscillator at a time close to the lasing threshold produces injection mode-locking. This has been demonstrated for a non-dispersive 30 J TEA-C02 laser operating on the 10pm and 9 pm bands.25Injection mode-lockinghas been employed together with a saturable absorber to produce reliable sub-nanosecond pulse trains from a large aperture TEA-C02 laser.26 The longitudinal mode structure in a mode-locked CO, laser has been investigated using a scanning Fabry-Perot interfer~meter.~’ A line-narrowed TEA-CO, laser has been developed as an enhanced pump for optically pumped molecular gas laser systems such as the 1 6 p transition in CF,.28 160mJ output at 12.8pm was obtained from a C0,-laser-pumped ammonia laser.29The device was designed for ease of construction and should be usable with other gases also. Sub-nanosecond pulses were derived from NH, and C2D2lasers pumped using an injection mode-locked CO, laser.30 Greater than 1 MW pulse energies were recorded. An optically pumped NSF laser provided tunable output in the range 6 18-658 cm Perchloryl fluoride (FC10,) with C 0 2 laser excitation generated 34 lines between 16.3 and 17.7pm with output powers up to 4mJ.32 Single-mode 100 kW output powers were found for D 2 0in a ring laser configuration.33 Picosecond pulses tunable from 2700 to 32000cm-1 were obtained using a travelling wave parametric process.34 The temporal jitter between two systems operating together could be reduced to less than 1 ps.

’. ’

Solid-state L~wTs.-F,(II) colour centres in alkali halides were utilized to produce tunable-i.r. laser radiation in the ranges 1.7-2 pm (KBr),35 2.42-2.9 pm (KCl-Li),36 and 2.55-3.28 pm (RbC1-Li).36 A similar system, pumped using a Nd-YAG laser, produced 5 ns wide pulses with energies of 100 p.J.37The Iaser was tunable over the range 3685-3697 cm- with 0.3 - bandwidth. A review of InGaAsP laser diodes, suitable for operation over the range 1.01.7 pm, has been published.38 9mW of laser output were obtained from a CdS

24

P. W. Pace and J. M. Cruickshank, IEEE J . Quantum. Electron., 1980, 16. 937. D. Curtois, C. Thiebeaux, A. Delanaigue. E. Merienne, and P. Jouve, O p t . Laser Technol., 1981. 13.

”

P. Bernard, P. Mathieu, and P. A. Belanger, O p t . Comntun., 1980, 34, 1980.

”

155. 26 ”

’’ 29 ’O

” ”

’’ 34 j5

’’ ’’

’’

P. E. Dyer and I. K. Perera, Appl. Ph-vs., 1980, 23, 245. B. J. M. Bormans and A. H. M. Olbertz. O p t . Commun.. 1980,34, 431. P. V. Gatenby, K. C. Hawkins, and H. N. Rutt, J . Phys. E., 1981, 14, 56. R. G. Harrison, P. K. Gupta. A. Kar, and M. R. Taghizadeh. O p t . Commun., 1980, 34,445. B. K. Deka, P. E. Dyer, and I. K. Perera, O p t . Commun., 1981, 37, 127. T.A. Fisher, J. J. Tie, and C. Wittig. Appl. Phys. Lett., 1980, 37, 592. H.H. Rutt, Opt. Commun., 1980. 34, 454. W. A. Peebles, D. Umstadter, D. L. Brower, and N. C. Luhmann, Appl. Pliys. L e / / . , 1981, 38, 851. A. Seilmeir and W. Kaiser, Appl. Phys., 1980, 23, 113. W. Getterman, F. Luty, K. P. Koch, and H. Welling, O p t . Commun., 1980, 35, 430. R. Berigang, Opt. Commun., 1980, 34, 249. A. S. Subdo, M. M. T. Loy. P. A. Roland, and R. Beigang, O p t . Commun., 1981, 37, 417. G.H. Olsen. Opt. Eng.. 1981, 20. 440.

6

Photochemistry

platelet optically pumped using an Ar’ laser.39 The same system was also operated in a synchronously pumped mode with a mode-locked argon ion laser, producing pulses as short as 8ps with 3.2mW average power.40 Considerable effort has been expended in producing short pulses by mode-locking GaAs (and related) semiconductor lasers. 28 ps wide pulses were produced at a repetition rate of 2.5 GHz by a gain-switching method.41 Streak-camera pulse monitoring has demonstrated that an actively mode-locked angled strip GaAlAs laser was capable of producing bandwidth-limitedpulses of 16ps duration with 1 W peak power and ATAv = 0.36.42 Amplified spontaneous emission (ASE) in GaAs without a resonant cavity, pumped using two-photon excitation from a mode-locked Nd-glass laser, produced lops wide pulses;43 but synchronous pumping of a similar system resulted in a 7 ps pulse A passively mode-locked modified strip buried heterostructure GaAlAs diode laser, with an extended resonator, has been shown to produce pulses with a width of 5.1 ps, close to the transform limit.45 At a repetition rate of 850 MHz average powers of 5 mW were obtained. Finally, pulses less than 1 ps wide have been produced by gain-switching a GaAs laser with pumping using a synchronously pumped mode-locked dye laser.46 Neodymium lasers remain a favourite source for photochemical applications providing high power outputs at 1.06 pm (and in the visible and ultraviolet region with frequency conversion). The relative performance of flashlamp-pumped Nd,La, -,P5OI4laser rods has been evaluated with x = 1.O, 0.75, and 0.20.47The maximum laser efficiency was found for NdP5014.Regenerative amplification of a 40 ps Nd-YAG laser pulse produced gigawatt output with no degradation of the temporal and spatial characteristic^.^^ 3.4TW pulses with 100ps width were generated using Nd-phosphate glass disc amplifier^.^' Many applications require short ( < 100ps) high intensity pulses and several reports have been concerned with reliable mode-locking of these lasers. For example, slow Q-switching of a passively mode-locked Nd-glass laser was found to result in a more stabilized output pulse train. Passive mode-locking was achieved using saturable absorbing dyes and a thermally compensated phosphate glass rod. 5 2 Both systems produced pulses with approximately 4 ps duration. An intracavity etalon incorporated into a Nd-Y AG oscillator enabled passive mode-locking, forming pulses 12 ps long.’ Active mode-lockingwas achieved in a Q-controlled feedback-stabilized Nd-glass ’ ~ high laser resulting in loops pulses with energies of 1 mJ at 1.06~ m . The 3y

40 41

42 43 44 45

46 47

48

49

s2 53 54

C. B. Roxlo, D . Beebelaar, and M. M. Salour, Appl. Phys. Lett., 1980, 38, 507. C. B. Roxlo and M. M. Salour, Appl. Phys. Lett.. 1981, 38, 738. J. AuYeung. Appl. Phys. Lett., 1981, 38, 308. M. B. Holbrook, W. E. Sleat, and D. J. Bradley, Appl. Phys. Lett., 1980, 37, 59. W.-L. Cao, A. M . Vaucher, and C. H. Lee, Appl. Phys. Lett., 1981, 38, 306. W.-L. Cao, A. M. Vaucher, and C. H. Lee, Appl. Phys. Lett., 1981, 38, 653. E. P. Ippen, D . J . Eilenberger. and R. W. Dixon, Appl. Phys. Lett., 37, 267. M. A. Duguay, T. C. Damen. J. Stone, J. M . Wiessenfeld, and C. A. Burrus, Appl. Phys. Letr., 1980, 31, 369. S. R. Chinn and W. K. Zwicker, J . Appl. Phys., 1981, 52, 66. C. Joshi and P. B. Corkum, O p t . Commun., 1981. 36. 8 2 . Y. Kato, K. Yoshida, J. Kuroda, and C. Yamanaka, Appl. Phys. Lett., 1981, 38, 72. M. C. Marconi, 0. E. Martinez, and F. P. Diodati, Appl. Phys. Lett., 1980, 37, 684. R. R. Alfano, N . H. Schiller, and G. A. Reynolds, IEEE J. Quantum. Electron., 1981, 17, 290. T. R. Royt, O p t . Commun., 1980, 35, 271. H. Graener and A. Labereau, Opt. Commun., 1981, 37, 138. R. Fedosejeves and M . C. Richardson, IEEE J . Quuntum. Electron., 1980, 16, 985.

De\tdopnzents in Instrumentution and Techniques 7 temporal stability should permit synchronization with other pulsed laser systems. Injection of a single sub-nanosecond pulse into a latent ring oscillator enabled 12ps and 3 ps pulses to be derived from Nd-YAG and Nd-glass lasers re~ p e c t i v e l y and ; ~ ~ 120 ps pulses were compressed to 15ps using a saturable dye in a regenerative amplifier.56A Pockels cell was utilized to vary rapidly the resonator output coupling in a Nd-YAG oscillator producing 600 ns long pulses with little loss of energy.57 Smooth long pulse emission (1 80 ps, 100W) was also obtained from a frequency-doubled Nd-YAG laser, at a pulse repetition rate of 50 Hz.” A short-cavity passively @switched laser was capable of generating pulses time’ disadvantage of Nd-YAG lasers is their low tunable between 2 and 17 n ~ . ~One maximum pulse repetition rate. Efficient burst mode operation of a Q-switched flashlamp-pumped laser generated a 35mJ output with a pulse repetition rate of 1 kHz.60 The combination of an acousto-optic and frustrated total internal reflectance modulator enabled the pulse repetition rate of a high-power Nd-YAG laser to be increased into the kHz region.61Synchronization was achieved between a Q-switched mode-locked Nd-YAG laser and a mode-locked argon ion laser with less than 18 ps jitter.62 A Q-controlled actively mode-locked ruby laser produced 35ps wide pulses which could be synchronized with another mode-locked laser with less than loops jitter.63

Dye Lasers.-Since their development in the mid-1970s CW and pulsed dye lasers have been increasingly applied in photochemistry and spectroscopy. Flashlampand laser-pumped systems will be considered here, with a discussion of picosecond-pulsed systems referred to a !ater section. Transverse excitation with an atmospheric pressure lamp has been faund to offer extended operating times whem compared with conventional systems.64 Higher quality output has been obtained as a result of thermally isolating the dye cell from the flashlamp and ensuring a symmetrical dye flow? Co-axial and pre-ionized linear flashlamps have been compared for use as excitation sources for high-power repetitive pulsed dye lasers.66 The efficient operation of pre-ionized flashlamps has been con~ i d e r e dGas . ~ ~pressure and bore diameter were found to be important parameters. Excimer lasers would seem to offer a useful excitation source for near-u.v. dye lasers and a dye cell designed for this purpose has been reported.68 The dye solvent was found to influence the photochemical stability of such a laser pumped using 308 nm radiation from an XeCl source.69 1 W output was obtained at 100 Hz. ” ”

’’ s9

6o 61

62

63 64

65 66 67 68 69

K.-J. Choi and M. R. Topp, J . Opt. SOC.Am., 1981. 71, 520. J. E. Murray and D. J . Kuizenga, Appl. PIiys. Lett., 1980, 37. 27. W. E. Schmidt, IEEE J . Quuntum. Electron.. 1980, 16, 791. A. Koeneke and A. Hirth. Opt. Commun., 1980.34, 245. S . Jackel. H. M. Ioebenstein, A. Zigler, H. Zmord, and S. Zweigenbaum, J . Phys. E., 1980, 13, 995. R. C. Knight, R. J. Dewhurst, and S. A. Ramsden, J . Pliys. E., 1980, 13, 1339. E. M.Wood, Soc. Photo-opt. Instrum. Eng., 1980, 247, 124. G. T. Harvey, C. W. Gabel, and G.Movrou, O p t . Commun., 1981.36, 213. F. M. B. Greek and H. Pepin, Rev. Sci. Instrunr., 1980, 51. 1656. Z. KOnefal and J. Szcepdnski, Opt. Commun., 1981,36, 331. T. B. Lucatoro, T. J. McIlrath, S. Mayo. and H. W. Furumoto, Appl. Opt., 1980, 19, 3178. A. Hirth. T. Lasser, R. Meyer, and K. Schetter. O p t . Commun.. 1980, 34, 223. A. Hirth, R. Meyer, and K. Schetter, Opt. Commun.. 1980, 35, 255. D. S. Bethune, Appl. Opt., 1981, 20, 1897. P. Cassard, P. B. Corkum. and A. J. Alcock, Appl. Phys., 1981, 25, 17.

8

Photochemistry

Automatic wavelength control of a ns-pulsed dye laser has been de~cribed.~' Tuning to any visible wavelength was possible with a near-transform limitedbandwidth of 450 MHz. Similar bandwidths were obtained using an intracavity etalon and a grating set at grazing incidence." - 7 3 Holographic gratings were found to be favourable owing to their higher efficiency.7 3 Nitrogen-laser-pumped dye lasers have also been tuned using Fizeau wedges,74*7 5 linewidths of 0.01 nm were obtained with tuning over a 10 nm range.75A double prism arrangement was found to reduce the bandwidth of a N,-laser-pumped coumarin 500 dye laser to less than 10-3.76A Michelson mode-selector was incorporated in an argon-ionlaser-pumped dye laser providing single-mode operation with 1 W A single longitudinal mode N,-laser-pumped dye laser, with a linewidth of .~~ narrow-linewidth operation 0.02 cm - * has also been d e m o n ~ t r a t e dHigh-power has been achieved in several reports using a ring dye laser configuration. For example, a unidirectional optically stable ring laser operated with a single longitudinal mode with only a grating, at grazing incidence, for tuning.79 An external reference Fabry-Perot cavity in a single-mode CW ring laser provided high output powers with 150 kHz linewidths.80 Radiation at 292-305 nm with a 2MHz linewidth, 7GHz scan range, and 500pW power was obtained with an intracavity frequency doubled, actively stabilized ring dye laser.81 Picosecond Pulsed Dye Lasers.-loops Pulses with lOOkW peak powers were obtained from amplified spontaneous emission in a nitrogen-laser-pumped dye laser system.82 Passive mode-locking of a flashlamp-pumped dye laser, with dye amplification cells pumped using nitrogen and excimer lasers, and frequency shifting by stimulated Raman scattering in Cs vapour produced pulses of 1-3 ps duration with 1-20 MW peak power in the 3.3-8.4 pm region.83 Active/passive mode-locking of a flashlamp-pumped system provided 2.5 pJ pulses with widths less than 1 0 ~ sPicosecond . ~ ~ GaAs and GaP switches, combined with a Pockels cell enabled active mode-locking of a coumarin dye laser producing 50ps pulses with 500 kW peak powers.85 Intracavity interferometers have been used both for tuning and mode-locking of CW dye lasers.86*87With pulse amplification in nitrogen-laser-pumped dye cells 50 MW peak powers have been reported for a 2 ps pulse.87 55 mJ and 15 mJ outputs were reported for rhodamine and coumarin dye T. Suzuki. H.Kato. Y. Adachi. N . Konishi. and T. Kasuya. Appl. PIiys.. 1981. 24, 331. T. Chang and F. Y. Li, Appl. Opt., 1980, 19, 3651. 7 2 L. A. Godfrey. W. G. Egbert. and R. S. Meltzer, Opt. Comntun.. 1980, 34, 108. '' S. Mory, A. Rosenfeld, S. Polze, and G. Kom, Opt. Commitn., 1981, 36. 342. '4 M. N . Nenchev and Y . H . Meyer. Appl. Plt,~~s., 1981, 24, 7. '' Y . H . Meyer and M. N. Nenchev. Opt. Conwtirrt..1980, 35. 115. '' F. J. Duarte and J. A. Piper, Opt. Contmim., 1980, 35, 100. '-C. G. Aminoff and M. Kaivola, Opt. Commun.. 1981. 37. 133. M. K. Iles, A. P. D'Silva, and V. A. Fassell, Opt. Cornntwi., 1980, 35. 133. S. G. Dinev. 1. G. Koprinkov, K. V. Staminov. and K. A. Stankov, Opt. Contniun., 1980. 35, 403. 80 S. M . Jarrett and A. G. Jacobson, SOC.Photo-opt. Instrunt. Eng., 1980, 247, 64. E. R . Elieh. W. Hogervorst. K . A. H . van Leeuwen. and B. H . Post. Opr. Coniniutt.. 1981, 36, 366. Cubeddu. S. desilvestrie. and 0. Svelto. Opt. Coniiiiun.. 1980. 34. 461. '-' R. R . Wyatt and D . Cotter. Opt. Cuniniiiri.. 1981. 37, 421. " M . D. J . Burgess, R . Fedosejevs. P. A . Jaanimapi. and M . C. Richardson, I E E E J . Qucmruni. Electron., I98 1. 17. 496. '' W. Margulis. W. Sibbett. and J. R. Taylor, Opt. C'onzrnitn.. 1980, 35. 153. Hh E. Mannero and J. Jasny, Opr. Coninturi.. 1981. 36. 66. '-E. E. E. Mannero and F. P. Schafer. Appl. Ph.rs., 1980. 23, 135. 70

"

Developments in Instrumentation and T e c hiques

9

lasers with three-stage dye cell amplification.88A 165mJ output was obtained in a single pulse at 589nm using a two-stage amplification process.89 33% Second harmonic generation was possible with such high powers. Synchronously pumped CW dye lasers have become a popular source of high repetition rate ultra-short pulses. An opto-electronic feedback system has been used to increase the power stability by a factor of 5.90 Improved performance of a cavity-dumped synchronously pumped dye laser was reported following the addition of a saturable absorber to the laser dye ~olution.’~Bandwidth-limited pulses of 2.5ps duration were obtained with energies in the range 4-8nJ. The conditions for perfect operation have been investigation by second harmonic correlation t e c h n i q ~ e sThe . ~ ~best pulse shape was found to correspond to perfect synchrony between dye laser and argon ion laser (obtained with precise matching of cavity lengths). A scheme for active stabilization by control of the dye laser cavity length has been proposed.93 The operation of a cavity-dumped synchronously pumped laser has been described.94 The quality of the dye laser pulses was found to depend critically upon the mode-locking of the argon ion laser. 20mW average power was obtained in the region 710-770 nm with 0.7 ps pulse widths by synchronously pumping oxazine- 1 with rhodamine 6G output in a tandem c~nfiguration.’~ The interaction ot two oppositely directed pulses in a saturable absorber in a ring dye laser (colliding pulse mode-locking) has provided the shortest dye laser pulses reported to date ( 9 0 f ~ )The . ~ ~methods for measuring these short pulse durations will be discussed later. Laser Dyes.-A catalogue of available laser dyes, alternative names, literature references, and chemical abstracts numbers has been compiled.97 4,7-(2-phenyl4H-1-benzothiopyran-4-ylidine)-4-choro-benzpthiopyryliumperchlorate has been shown to be a superior dye for the region 1.15-1.24 pm when compared with the commercially available dye DNTPC.98Oxazine 720 and Carbazine 720 have been shown to be suitable for single-frequency operation in the range 690-700nm,99 and DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran) has been utilized for synchronously pumped lasers over 605-725 nm. O0 DCM appears to offer a promising alternative to cresyl violet, having an efficiency comparable with that of rhodamine 6G. O0 Nitrogen-laser-pumped rhodamine 6G-safranin-T mixtures have been found to be tunable over 31 nm with 100 kW pump powers.lO’ The effects of solvent pH on the gain and tunability of 8R 8y

” ” Y3

”

” 96

” ”

F. R. Wallenstein and H.Zacharias, Opt. Commun., 1981. 32, 429. F. Bos, Appl. Opt., 1981, 20, 1887. R.E. Russo, R. Withnell, and G. M. Hieftje, Rev. Sci. Instrum., 1981, 52, 772. M.J. Wirth. M. J . Saunders, and A. C . Koskelo. Appl. Phys.. 1981, 38.295. D. B. McDonald, D. Waldeck. and G. R. Fleming. Opt. Commun., 1980. 34, 127. N. Frigo, C. Hemenway. and H.Mahr. App. Phys. Lett., 1980. 37. 981. V. Sundstrom and T. Gilbro, Appl. Phys.. 1981. 24, 233. F. Minami and K. Era, Opt. Coniniun., 1980. 35, 393. R. L. Fork, B. 1. Greene, and C. V. Shank, Appl. PIiI-s. Lett., 1981, 38, 671. J . M. Kauffman. Appl. Opt.. 1980. 20, 3431. W. Kranitzky, B. Kopownski, W. Kaiser, K. H. DreXhdge, and G. A. Reynolds, Opt. Commun., 1981.

36, 149. yy

P. E. Jessop and A. Szabo. I E E E J. Quuiitut?i. Electron.. 1980, 16. 812. E. G. Marason. 0 p 1 . Commun., 37, 56. P. J. Sebastian and K. Sathianandan, Opt. Coinmuit.. 1981. 32. 422.

Ion

’”*

10

Photochemistry

fluorescein dyes has been studies. lo' Acid conditions were found to give reduced gain but an increase in tunability. Lasing in the 490-530nm region, with the efficiencyof rhodamine 6G, was found for derivatives of 2-aminobenzopyran. O3 Pyridylphenyloxazoles have been shown to be suitable flashlamp-pumped laser dyes for the blue-green spectral region.'04 A 1 : 1 mixture of propylene glycol carbonate and ethylene glycol has been found to a satisfactory solvent for polymethine dyes, replacing the potentially hazardous solvent DMS0.'05

'

Visible and U.V.Gas Lasers.-357, 380.5, and 405.9 nm radiation (pulse duration 150, 400, and 400 ns, respectively) was obtained from an electron-beam-excited nitrogen laser.'06 Improvements were found on the addition of excess He and Ne to the nitrogen-argon gas mixture. A 19 ns pulse with energy of 30 mJ was derived from a nitrogen-laser system."' With pre-ionization, a grooved electrode and partial screening of the discharge, pulse reproducibility was found to be good. Near threshold two-mode operation of an argon ion laser lead to a modulated output at 500---900MH~.'~~ Passive mode-locking of an argon ion laser was achieved using rhodamine 6G as a saturable absorber. Io9 Detector-limited pulses shorter than 1 ns were observed. A recent review has discussed the available hollow cathode metal ion lasers providing CW output in the 220-320nm and 800-2000nm regions."' Laser lines at 248.6, 250.6, 259.1, and 260.0nm are reported for a H e - C u ' hollow cathode laser,' ' and the U.V. output of a Cu"cylindrical hollow cathode laser has been investigated. Several emission lines at 579.9,645.4,719.1, 1061,1074,1193, 1302, 1346, and 1361 nm have been found for a hollow cathode tin laser.' A highpulse repetition rate (5 kHz) compact neutral lead vapour laser has been found to generate 90 MW of average power at 722.9 nm.' l4 Lasing in the range 650-720nm has been reported for an optically pumped iodine monofluoride laser.'I5 The same system in discharge excited He, Ar, CFJ, and NF, produced 24 kW output in a 15 ns long pulse between 480 and 496 nm.'16 280.4, 354.5, and 490.8 nm radiation has been produced in transversely excited ClF, BrF, and IF lasers, respectively, with mJ output powers.'" Two reviews have been published concerned with excimer laser developments and application.

''

'

T. Govidanunny and B. M. Sivaram, Opt. Commun., 1981,32,425. M. 1. Dzyvbenko, V. V. Maslov, I . G. Naumenko, and V. P. Pelipenko, Opt. Spektrosk., 1980,49,

lo'

lo' lo' log 'lo

'Is l7

764. L. A. Lee and R. A. Robb, IEEE J. Quantum. Electron., 1980, 16, 777. J . M. Herbelin and J. A. McKay, Opt. Commun., 1981, 36, 63. M . 4 . Chou and G . A. Zawadzkas, IEEE J . Quantum. Electron., 1981, 17, 7 7 . U. Rebhan, J. Hildebrandt, and G . Skoop, Appl. Phys., 1980, 23, 341. K. Berndt and E. Klose, Opt. Commun., 1980, 35, 417. W. Dietel, E. Dopel, and D. Kuhlke, Opt. Commun., 1980, 35, 445.

D. C. Gerstenberger, R. Solanki, and G . J. Collins, IEEE J . Quantum. Electron., 1980, 16, 820. C.-Z. Wu, Y.-A. Mo, Y. Yang, and S.-D. Zheng, Wu Li, 1980,9, 299. H. J. Eichler, H. Koch, J. Salk, and C. Skrobol, Opt. Commun., 1980, 34, 228. K. Gnadig and L. Fu-Cheng, Opt. Commun., 1980, 34, 219. M. C. Gokay and L. A. Cross. IEEE J. Quantum. Electron., 1981, 17, 11. S. J. Davis and L. Hanko, Appl. Phys. Lett., 1980, 37, 692. M. L. Dlabal, S. B. Hutchinson, J. G . Eden, and J. T. Verdeyen, Appl. Phys. Lett., 1980, 37, 873. M. Diegelmann, H. P. Grieneisen, K. Hohla, X.-J. Hu, J. Krasinski, and K. L. Kampa, Appl. Phys., 1980, 23, 283.

M. R. H. Hutchinson, Appl. Opt.. 1980, 19, 3883. P. N . Mace. SOC.Photo-opt. Instrum. Eng., 1980, 247, 108.

Developments in Instrumentation and Techniques

11

A medium scale high-current-density co-axial electron-beam device for excimer laser pumping has been described. 2o The efficient operation (400 mJ at 308 nm) of a Blumlein-discharge-excited XeCl laser was reported. l 2 100 ns pulses were obtained from a microwave-pumped XeCl laser. 2 2 A U.V.pre-ionized transversedischarge-excited XeCl laser was mode-locked by injection mode-locking using a frequency-doubled passively mode-locked rhodamine 6G dye laser. 23 150 M W pulse energies were obtained in a 7 ps long pulse. 50 mJ pulses at 308 nm were produced by two-pass amplification in XeCl. 24 Lasing in the range 380-480 nm was generated in an electron-beam-excited Ar-Kr-NF, mixtures. 12’ 5 kW powers were reported. Optical pumping at 193nm by an ArF excimer laser has been employed to produce 377.6 nm lasing in a TlBr photodissociation laser,126 and 342nm radiation from I, excited into the D-X absorption band.12’ An iodinephotodissociation laser was pumped using either XeCl or KrF cxcimer lasers. 12’ Pulses were obtained with durations between 2.6-12 ns with 0.5 MW powers.

Frequency Conversion Techniques.-Harmonic generation in non-linear crystals and stimulated Raman scattering techniques have been widely applied for the generation of laser light in hitherto unavailable spectral regions. The generation of coherent vacuum U.V. and X-ray U.V.radiation by non-linear methods has been Type 1 5th-harmonic generation at 212.8nm has been reported reviewed.12g*lJo for a neodymium laser using a 5mm crystal of urea.131 Average powers of 320 mW were obtained. High efficiency third- and second-harmonic generation has been reported using, respectively, a type I1 KDP crystal 132 and a LiNb03 crystal in which quasi-phase-matching for the non-linear optical coefficient d 3 , was achieved. 3 3 Efficient conversion of 1.06 pm radiation into the spectral region 450 nm-1.5 pm at specific frequencies was performed in a multi-mode, gradedindex optical fibre.’ 34 130mW average power at 2.3 pm with 1.6 M W peak power was obtained by mixing in LiNbO,, fundamental light at 1.06 pm with near4.r. laser emission obtained from a dye laser pumped using the second harmonic of the Nd-YAG 1 a ~ e r . lA~ ~ stabilized CW 5pm source was obtained by frequency doubling the output from a C 0 2 laser using a tellurium Frequency variation, at discrete wavelengths, was possible over the range 4.6-5.5 pm.

’

’’’ lZ6

’”

G. L. Oomen and W. J. Witteman, Opt. Commun., 1981, 32, 461. C. Jianwen, F. Shufen, and L. Miaohang, Appl. Ph-vs. Lett., 1980, 37, 883. A. J. Mendelsohn, R. Normandin, S. E. Harris, and J. F. Young, Appl. Phys. Left., 1981, 38, 603. G. Reksten, T. Varghese, and D. J. Bradley, Appl. Phvs. Lett., 1981, 38, 513. T. L. Pacala, J. B. Laudenslager, and C. P. Christensen, Appl. Phys. Lett., 1980, 37, 366. F. K. Tittel. M. Smayling, W. L. Wilson, and G. Marowsky, Appl. Phys. Lett., 1980, 37, 862. P. Burkhard, W. Luthy, and T. Gerber, Opt. Commun., 1980,34,451. M. J. Shaw,C. B. Edwards, F. ONeill, C. Fotakis, and R. J. Donovan, Appl. Phys. Left., 1980,37, 346.

131 13’

133

134

E. E. Fill, W. Skrlac, and K.-J. Witte, Opt. Commun., 1981, 37, 123. J. Reintjes, Appl. Opt., 1980, 19, 3889. C. R. Vidal, Appl. Opt., 1980, 19, 3897. K. Kato. IEEE J. Quantum. Electron., 1980, 16, 810. W. Seka, S. D. Jacobs, J. E. Rizzo, R. Boni, and R. S. Craxton, Opt. Commun.. 1980, 34,469. D. Feng, N.-B. Ming. J.-F. Hong, Y.4. Yang, J.-S. Zhu, Z. Yang, and Y.-N.Wang, Appl. Ph-vs. Lett., 1980, 37. 607. K. 0. Hill, D. C. Johnson, and B. S . Kawasaki. Appl. O p t . , 1981, 20, 1075. K. Kato, IEEE J . Quantum. Electron., 1980, 16, 1017. A. Delahaigue, C. Thiebeaux, and P. Jouve. Appl. Phvs., 1981, 24, 21.

12

Photochemistry

238-249 nm CW radiation has been obtained from standing-wave and ring dye lasers operating with coumarin 102 dye and'intracavity lithium formate monohydrate crysta1s.l3' Up to 70 pW of U.V. output at 244nm were reported. A similar ring laser system with a cooled ADP crystal was used to generate output at 254 nm with 120 pW (multi-mode) and 60 pW (single-mode) powers.'38 The 314-31 8 nm range has been covered using a RDP crystal intracavity in a rhodamine B dye laser. 39 Frequency doubling in a synchronously pumped mode-locked laser has been performed using intracavity ADP and LiIO, crystals. 140 Conversion effifor LiIO, were reported with 36pW ciencies (at 295nm) of up to 9 x average power and 1.7 ps pulse widths. A review of sum-frequency-conversion possibilities using noble gases suggests that the major part of the 106-150nm spectral region may be covered. 14' The laser output from a substituted-terphenyl dye laser was trebled in frequency in pure Xe gas generating 106nm light with 9 x 10- ' power-conversion efficiency.14' Sum and difference frequencies, at 239 and 434nm, have been obtained in KDP with the combination of XeCl and Nd-YAG lasers.'42 35% conversion into first Stokes radiation has been reported using non-resonant stimulated Raman scattering in a high-pressure H, cell.'43 The XeF laser output at 353 nm was shifted to 414 and 499 nm. The use of stimulated Raman scattering to generate light in the range 1-10 pm has been demonstrated using a ruby-laserpumped dye laser. 144 30 ps long pulses from a frequency-doubled mode-locked Nd-YAG oscillator at 532nm have been Raman shifted to 2.38pm in Cs vapour. 1 4 5 0.4 mJ pulse energies were reported. The 4s-3D transition in potassium vapour has been used for a similar purpose. '41 4 Detection and Monitoring of Laser Radiation The problems of accurately detecting pulsed and CW laser radiation in the range 0.5-1.1 pm has been disc~ssed.'~'Calorimeters are described for CW (4-10 W) and pulsed (0.2-0.8 J in 0.1-1 ms) lasers. An absolute power meter, depending upon the deflection of a suspended mirror by the momentum of the laser beam, has been constructed.148 A foil of refractory material has been employed to convert 1-10W i.r. radiation into visible light, which was then detected with a conventional photometric device. 149 1 ns CO, laser pulses with energies in the range 0 . 0 1 4 . 1 J have been detected by monitoring the e.m.f. generated by the plasma formed by focussing the radiation onto a metal surface. The detector is claimed 13' 138

L39

I4O 141

14'

S. J. Bastow and M. J. Dunn, Opt. Commim., 1980, 35. 259. C. R. Webster, L. Woste, and R. N. Zare, Opt. Commun.. 1980, 35,435. S. Runge and N. Wooffer. Opt. Commim., 1981, 32, 489. D. Welford, W. Sibbett, and J. R. Taylor, Opt. Commun., 1980, 35,283. W.Zapka, D. Cotter, and U. Brackmann, Opt. Commun., 1981, 36, 79. V. L. Lyutskanov, S . D. Savov. S . M. Saltiel. K. V. Stamenov, and I. V. Tomov, Opt. Commun., 1981,

37. 149.

143 144

145

L46 14' 148 149

150

D.W. Trainor, H. A. Hyman, I. Itzkan, and R. M. Heinrichs, Appl. Phys. Lett., 1980, 37, 440. A. deMartino. R. Frey, and F. Pradere. IEEE J. Quantum. Electron., 1980, 16. 1184. R. Wyatt and D. Cotter, Opt. Commun., 1981, 32,481. P. Bernage, P.Niay, and R. Houdart, Opt. Commun., 1981. 36, 241. J. G. Edwards. SOC.Phot-opt. Instrum. Eng., 1980, 234, 12. G.Roosen and C. Imbert, Opt. Eng., 1981, 20, 437. L. J. Hendricks, Rev. Sci. Instrum.. 1980. 51, 1659. E. E. Bergmann, E. J. McLellan, and J. A. Webb, Appl. Phys. Lett., 1980, 37, 18.

13

Developments in Ins trunientut ion and Techniques

to be indestructable. A potassium ferrioxalate actinometer has been used to measure the U.V. output from a nitrogen laser in the power range 10-900mJ.'51 No change in quantum yield was observed up to a power density of lo8 W cm-'. Several photodiode systems have been discussed for the measurement of subnanosecond laser pulses. A detector suitable for such pulses in the wavelength range from the U.V.to > I pm has been fabricated from a commercially available Si avalanche photodiode.' 5 2 A risetime of 200 ps was reported. An edge-incident Si photodiode was shown to have a similar temporal response, 53 and in addition, as a phototransistor it responded to CW radiation with current gain. An n+-InP/n-GaInAsP/n-InP/p+-InPstructure was found to operate out to 1.25 pm with a risetime -c1 6 0 ~ s .A' ~p-type ~ In,~,,Ga,~,,As was shown to be suitable for the region 1.0-1.7 pm.'" The response was 70ps (FWHM) with a 45 ps rise and decay time. A strontium barium niobate pyroelectric detector for ps laser pulses in the wavelength regions ~ 4 0 nm 0 and 7 pm-I mm was investigated using an 'upconversion' technique in which birefringence in a CS, Kerr cell, induced by a pulse from a CO, laser, allowed light from an argon ion laser to be detected using a ps streak camera.' 5 6 The time response, linearity, and other properties of germanium, silicon, and vacuum photodiodes were investigated using ps pulses from a Ramantuned mode-locked Nd-YAG laser. 5 7 Single-photon avalanche diodes (SPADS) have been utilized to monitor 15Ops (FWHM) laser pulses, although it would seem that the response of the SPAD should be significantly faster than this. Several mounting schemes have been investigated for thin-film photoconductors. 5 9 Risetimes approaching 25 ps (detector limited) were obtained. Non-linear autocorrelation techniques still remain the only viable method for monitoring laser pulses with true picosecond resolution. Several rapid scanning schemes for a Michelson interferometer have been proposed, allowing autocorrelation measurements in real time, thus greatly assisting the alignment of synchronously pumped dye laser systems. Length variation was achieved using (a) a rotating slab of quartz,16* (6) a rotating two mirror system,16' or (c) a mirror fixed to a loudspeaker cone. 162 The interpretation of autocorrelation measurements has been discussed by McDonald et aLg2with the conclusion that the true pulse width may be up to 2 x longer than previously assumed. The profile of ps ruby laser pulses has been detected using two-photon absorption. 163

'

Monochromators and Detectors.-A basic review of spectrometer types and design, suitable perhaps as undergraduate tutorial material, has been pubIs'

"*

H. Gruter, ./. Appl. Phys., 1980, 51, 5204. J . M . Harris. W. T. Barnes, T. L. Gustafson. T. H . Burshaw, and F. E. Lytle, Rev. Sci. Instrum.. 1980, 51, 988.

15' Isti

Is'

161

Iti3

C. W. Chen and T. K. Gustafson, Appl. Phys. Lett., 1980, 37, 1014. V. Diadiuk, S. H. Groves, and C. E. Hurwitz, Appl. Phys. h i t . , 1980, 37, 807. J . Degani. R. F. Leheny, R. E. Nahomy, M. A. Pollack, J. P. Heritage, and J. C. Dewinter, Appl. Phys. Lett., 1981, 38,27. E. J. McLekan and S. C. Stotlar, Opt. Spectrosc., 1981, 15, 55. P. Valat, G . Ripoche, M. Nail, and J. P. Gex, Opt. Commun., 1981, 36, 378. S. Cova, A. Longoni, and A. Andreoni, Rev. Sci. Instrum., 1981, 52, 408. P. R. Smith, D. H. Austin, and A. M. Johsnon, Rev. Sci. Instrum., 1981.52, 138. S. N. Ketkar, J. W. Keto. and C. H. Holder, Rev. Sci. Instrum., 1981, 52, 405. Z. A. Yasa and N. A. Amer, Opt. Commim., 1981, 36, 406. K. L. Sala, G . A. Kenney-Wallace, and G . E. Hall, I E E E J . Quantum. Electron., 1980, 16, 990. W. Blau and A. Penzkofer, Opt. Commun., 1981, 36, 419.

14

Photochemistry

lished.164A spectrometer designed to monitor the spectral output from CO, lasers has been described. 165a Fifty pyroelectric detectors were positioned for the various P and R lines and a substantial increase in sensitivity over conventional methods was reported. Unwanted reflections and coma were eliminated in a mid-resolution infrared spectrometer by placing the entrance and exit slits above and below the grating. 1 6 5 b Several systems for automation of spectrometers have been discussed. A computer-controlled Echelle monochromator allowed wavelength increments of 0.01 nm. A wavelength-scan and lamp-intensity control scheme for the popular Bausch and Lomb high-intensity monochromator has been described.' 67 The accurate synchronization of monochromator wavelength-scan and chart-recorder speed,168and the possibility of rapid scanning allowing spectra to be displayed in real time on an oscilloscope,169 has also been discussed. Details have been provided for the modification of a commercially available mirror mount (Oriel model 1450) for use as a stepper-motor controlled grating mount.170 A method for the alignment of Ebert-Fastie monochromators, by observing the Fresnel diffraction pattern from a He-Ne laser has been described.17' A deuterium lamp with MgF windows has been employed for the calibration of a vacuum-u.v. monochromator over the region 115-340 nm.' 7 2 A 5 m Echelle vacuum-u.v. monochromator was found to display diffraction-limited resolution in the U.V. and visible spectral regions, falling to 54% of the diffraction limit at 120nm. The temporal broadening of a 10ps laser pulse on passing through a monochromator system has been investigated using a streak-camera-video readout device.174Periodic errors in the dispersion of a scanning U.V. monochromator (McPherson model 225-1 m vacuum-u.v.), amounting to kO.01 nm with a period of 2.5 nm, have been reported. 175 A mechanically (rather than holographically) prepared concave grating was utilized in a high-efficiency aberation-corrected monochromator. 76 Highfrequency plane holographic gratings, however, were found to be preferable for vacuum-u.v. applications in the wavelength range 120-450 nm. 177 The efficiency of gratings for wavelength selection in dye lasers has been found to be improved by dielectric coating. 78 The generation of surface gratings with periods less than 100nm, by doubling the spatial frequency, has been demonstrated.17' Some other recent optical developments of possible interest include MgF, multiplate resonant 16*' 165 166

167 168

169

170 171 172

173 175

176 177

E. F. Young, O p t . Spectra, 1980, 14, 44. ( a ) J. G . Edwards, R. Jefferies, and J. D. Ridgen, J . Phys. E., 1981, 14, 731; ( b ) R. LeDoucen, V. Menoux, M. Larvor, and C. Haeuster, Appl. Opt., 1980, 19, 31 10. D. L. Anderson, A . R. Forster, and M. L. Parsons, Anal. Chem., 1981, 53, 771. D. C. Look and J. W. Farmer, Rev. Sci. Instrunt., 1980, 51, 968. S.Mil'shtein and D. Mordowicz, J . Phys. E., 1981, 14, 682. R. Angus, O p t . Spectra, 1980, 14, 49. T. W. Carman, P. E. Dyer, and P. Monk, J . Phys. E.. 1980. 13, 718. C. Julien and C. Hirlmann, J . Phys. E., 1980, 13, 923. D. H. Nettleton and R. C. Preston, Appl. Opt., 1981, 20, 1274. H. Nubbermeyer and B. Wende, Appl. Phys., 1980,23, 259. N . H. Schiller and R. R. Alfano, O p t . Commun., 1981, 35, 451. R. DeSerio, Appl. Opt., 1981, 20, 1781. T. Harada and T. Kita, Appl. Opt., 1980, 19, 3987. A . J. Caruso, G . H. Mount, and B. E. Woodgate, Appl. Opt., 1981, 20, 1764. D. Mayster, J. P. Laude, P. Gascoin, D. Lepere. and J. P. Priou, Appl. Opr., 1981, 19, 3099. L. F. Johnson and K. A. Ingersol, Appl. Phys. Lett., 1981. 38, 532.

Developments in Instrumentation and Techniques

15

reflectors for the vacuum-u.v.,180a high-performance thin liquid film MacNeille prism polarizer for the u.v.4.r. regions,'81 and a 6-sided prism designed to transmit a particular wavelength without spatial deviation. Several precautions for safe operation of photomultiplier tubes have been discussed. 183 After-pulsing in photomultipliers due to helium poisoning was examined for the RCA 4522 tube. 84 In applications in which exposure to helium cannot be avoided, purging with nitrogen may be desirable. The effect of after-pulsing on photon-correlation experiments has been discussed. 8 5 With careful calibration procedures the problems may be largely overcome. A wider dynamic range for light intensity measurements using photomultiplier tubes has been obtained by simultaneously monitoring and controlling the anode current and dynode voltages. 86 An application involving the simultaneous measurement of absorption and circular dichroism spectra was proposed. An inexpensive pulse amplifier4iscriminator suitable for photon counting detection systems operating at high repetition rates and avoiding pulse pile-up effects has been reported. 18' Pulse repetition rates up to 250 MHz were possible with 10 ns pulse pair resolution. The various methods for the detection of infrared radiation have been reviewed. For broad-band detection with moderate sensitivity, thermal devices were recommended. However, for increased sensitivity photon detectors should be employed. PbS,Se, -, and Pb,Sn, -,Se photodiodes have been shown to have high quantum efficiencies over the range 1-10 pm.18gA p+-nGe avalanche photodiode has been found to provide a low noise, low dark current detector for the region 1.3-1.55 pm.19' The performance of a Gao~4,1n,~,3Asphotodiode has been evaluated and shown to be a most sensitive detector in the 1-1.7pm range."' The response of metal-oxide-metal diodes for the detection of i.r. and visible radiation was found to be temperature dependent. l g 2 Suggestions for improving the response of such systems are given. The noise from a Ge: Cu photoconductive detector in an i.r. absorption spectrometer was found to be reduced with the use of a grating cooled to 90 K. 1 9 3 The construction of a Ge detector for low light intensities in the wavelength range 1-1.6pm has been reported by McLaren and Wayne.lg4 Fast amplifiers for low background Ge :Hg detector^"^ and a photovoltaic indium antimonide detector in the 3.5-4.2 pm range' 9 6 have been described. The acousto-optic interaction with a thermally

'

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lS7 lS8

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W. R. Hunter, M. H. R. Hutchinson. and M. R. 0. Jones, Appl. Opt., 1981, 20, 770. J. A. Dobrowolski and A. Waldorf, Appl. Opr., 1981. 20. I 1 1. M. V. R. K. Murtly and R. P. Shukla, Opt. Eng., 1980, 19. 621. C. Tassell, Opt. Laser Terhnol., 1980, 12. 271. D. F. Bartlett. A. L. Duncan, and J. R. Elliot, Rev. Sci. Instrum., 1981, 52, 265. H . C. Burstyn, Rev. Sci. hutrum.. 1980. 51, 1431. H. Hayashi, H. Tdchibana, and A. Walda, Rev. Sri. Instrum., 1980, 51. 1501. R. A. Borders, J. W. Birks, and J. A. Borders, Anal. Chem., 1980. 52. 1273. P. N. J. Dennis, SOC.Photo-opt. Instrum. Eng.. 1980. 234, 27. R. B, Schoolar, J. D. Jensen, G. M. Black. S. Foti, and A. C. Bouley, Infrared Pliys.. 1980, 20, 271. S . Kagawa, T. Kdneda. T. Mikawa. Y. Banaba, Y. Toydma, and 0.Mikami. Appl. Phys. Lett.. 1981. 38.429.

19'

T. P. Pearsill. IEEE J . Quantum. Electron.. 1980, 16. 709.

"' M. I, Kostenko, V. I. Stroganov, and A. I. Kondratyev, Opt. Commun.. 1981, 36. 140. 193 194 19' 196

0. Bernard, C. Deloupy. and M. Palpacuer, J . Phys. E . . 1981, 14, 299. I. A. McLdren and R. P. Wayne, J . Phoiochem., 1981, 16, 9. J. D. McDonald. Rev. Sci. Instrum.. 1980. 51, 1270. J. Altmann, S. Kohler. and W. Lahmann. J . Phys. E., 1980, 13. 1275.

16

Photochemistry

induced grating in an optical waveguide has been employed to measure the 1 ms pulse from a CO, Iaser.19' CsTe solar blind tubes, semi-transparent bi-alkali diodes, and bi-alkali image intensifiers have been compared as detectors for the vacuum-u.v. region.I9* The optogalvanic effect has been utilized to enable the detection of relatively low intensities of resonance light by the measurement of ionization currents in high concentrations of atomic vapours. 199The system has been specifically designed for the 253.7nm Hg line, and the high resolution and good tolerance to stray light characteristics suggest it may offer a useful detector for atomic absorption spectroscopy. 5 Spectroscopic Techniques

review of currently available U.v.-Visible Absorption Spectroscopy.-A u.v.-visible spectrophotometers and accessories has been compiled by Tayler,'" Several sample cells have been reported allowing absorption spectra to be recorded under non-ambient sample conditions. A high-temperature cell, designed for a Cary model 15 spectrophotometer, has been employed in an investigation of the octahedral-tetrahedral equilibrium in aqueous solutions of cobalt(I1) compounds. 201 A cell for a double-beam instrument (Beckman Acta M-VII) enabled studies of aqueous systems with temperatures up to 325 "C at maximum pressures of 12 MPa.202Sample pressure and temperature variation was also possible in a study of volatile uranyl complexes in the gas phase using a home-built spectroph~tometer.~~~ Synchroton radiation has been employed as a spectral source for a study of the absorption of HCN and DCN in the wavelength range 80-120nm.204 A vacuum-u.v. spectrophotometer for absorptions in the region 105-200 nm has been described.20s Solid-, liquid-, and gas-phase samples could be analysed at temperatures from -200 to 100°C and at pressures between 0 and 150 atmospheres. The absorption spectrum of trans-di-imide in the vacuum-u.v. has been measured.206First-derivative U.V.spectroscopy has been employed in the analysis of Watts nickel plating solutions for trace amounts of ~accharin.~" Impurity levels of 0.1 p.p.m. have been recorded. A wavelength modulated derivative spectrophotometer with a multi-pass absorption cell has been developed for the automatic analysis of atmospheric Traces of SO2, NO, and NOz were detected with limits of 15, 13, and 8 p.p.b., respectively. A double-beam single-detector absorption spectrometer has been Independence I"

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T. D. Black a n d V. A. Komotskii. Appl. P/i,r.s.Left.. 1981. 38, 113. G. H. C. Freeman, Soc. Photo-opt. Itistrutii. Dig.. 1980, 234, 84. R. Stephens. Cm. J. Client.. 1980, 58, 1621. C. Tayler. L f h . E4irip. Dig., 1981. 19, Feb.. 65. T. W . Swaddle a n d L. Fabes, Cuti. J . Clienr., 1980. 58, 1418. N. J. Susak. D. A. Crerar, T. C. Forseman, and J. L. Haas. Rev. Sci. Itisrrutii., 1981. 52. 429. A. Ekstroin. H. J . Hurst. C . H. Randall, and H . Loch, J . Ph!,s. C l m i . , 2980, 84, 2626. T. Nalapa. T. Kondow. Y. Ozaki. and K. Kuchitsu. Cl~cvii.P/~I..F.. 1981. 57. 45. P. Laporte. J. L. Subtil. M. Bon, and H. Damany, A p p l . Opr.. 1981. 20. 2133. P. S. Neudorful. R. A. Black, a n d A . E. Douglas, Can. J . Clrmi., 1981. 59. 506. G . L. Fin and J . D. Pollack. Atid. Chetii., 1980, 52. 1589. T. I m n i and K . Nahaniur;i. J. P/ij.s. E.. 1981. 14. 105. S.-Y.Shaw and J . T. Lue, ./. P/i,rs. E.. 1980. 13, 845.

Developments in Instrumentation and Techniques

17 from spectral distributions of the source was achieved using an electronic automatic gain control. The system performed well when used for derivative spectroscopy. For the comparison of two absorption spectra, the method of weighted least-squares fitting, with a two-parameter model, has been utilized and improved Using the procedures described, effects due to stray light and flicker may be eliminated. Problems, owing to deviations from Beer's law, encountered when the excitation-source bandwidth is greater than that of the absorber may be overcome with the use of a fluorescence cell placed after the sample permitting selective monitoring of the absorption at the centre of the source line.211Using a flashlamppumped dye laser for the source, rovibronic transitions in H 2 C 0were observed by this method. The absorption spectrum of Cs vapour at 0.1 Torr has been measured by observing the perturbations of the electromagnetic impedence owing to absorption of light.2l 2 The absorption of amptitude-modulated light causes pulsating surface temperatures in a sample and, hence, a pulsed thermal reradiation. By monitoring the variation of radiant emission with the wavelength of the incident light, the absorption spectrum may be derived. Such photothermal radiometry (PTR) has been performed on such various substances as Nd,O, powder, blood, and a leaf.213 Intracavity Laser Absorption Spectroscopy.-Considerable signal enhancement may be expected when using intracavity absorption methods. A CW dye laser was employed for the intracavity measurement of broad-band absorbing species in aqueous solutions.214Enhancements of 6 x 10' were obtained for absorbances in the range 5 x 10-5-10-3. Spectra for H,O and I, were recorded in a CW dye laser intracavity spectrometer in which several tuning mechanisms, cavity lengths, and pumping powers were investigated.2 The sensitivity enhancement was found to be independent of cavity length and pumping power, but to increase with the bandwidth of the tuning element. A CW dye laser was also employed to measure HCl ( 5 4 ) and ( 7 4 ) overtone vibration-rotation bands.216 An intracavity absorption spectrometer has been described using a broad-band uncoded LiF-F, +.colour centre laser, pumped using a pulsed excimer laser, suitable for the range 880-970 nrn3.,l7High sensitivity has been reported for intracavity absorption spectroscopy of dimethyl-sym-tetrazine and I,, which were rotationally and vibrationally cooled in a supersonic molecular beam.218A delay in the onset of lasing following pumping, because of the increased loss, is resultant upon the inclusion of an absorbing species in the cavity. The measurement of this delay, rather than the optical loss, has been shown to be capable of resolving absorbances of 1 0 - 3 . 2 ' 9

'

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2'2

K. L. Ratzlaff, Atiul. Cheni.. 1980. 52. 1415. P. W. Fairchild, N . L. Garland, W. E. Howard, and E. K. C. Lee, J . Cheni. P1i.w.. 1980.73, 3046. C. Stanciulescu, R. C . Bobulescu, A. Surmeian, D. Popescu, I. Popescu. and C. B. Collins, Appl. P/IJ*.s. LcJt/.,1980. 37, 888.

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P. E. Nordal and S. 0. Kanstad, Appf. Phys. Lett.. 1981, 38,486. J. S. Shirk, T. D. Harris, and J. W. Mitchel. Anal. Client., 1980. 52, 1701. S. J . Harris and A. M . Weiner. J . Chern. PiiFs.. 1981. 74. 3673. K. V . Reddy, J . Mot. Spectrosc.. 1980, 82. 127. V. M . Bacv. H . Schroder, and P. E. Toschak, Opt. Coniniun., 1981, 36, 57. W. R. Lambert. P. M . Felker, and A. H. Zewail, J . Chent. Plijs., 1981. 74. 4732. J . M . Rainsey and W. B. Whitten. A t i d . Client.. 1980, 52, 2192.

18 Photochemistry Infrared Spectroscopy.-A review of commercially available i.r. spectrometers has been published.220A 3 m vacuum grating instrument with digital data recording has provided resolution of 0.025 cm - I : computerized deconvolution of spectra improved this to 0.010cm-1.221Similar resolution was reported for a 5 m focal length littrow vacuum grating spectrometer when used for the 2v, band of 13CH, at 1.67 pm.222Line positions were determined with a precision of +0.002cmThe application of microprocessors to infrared spectroscopy has been discussed by Hannah and C o a t e ~ A. ~computer-controlled ~~ instrument has been constructed and found to offer substantial improvement in signal-to-noise.224 A 1 m multipass cell for i.r. spectroscopy, utilizing two parallel concave mirrors, has allowed path lengths up to 150m to be achieved.225For a study of collisioninduced simultaneous transitions in binary gas mixtures, a 2m sample cell has been constructed that allows pressure variation up to 1500 bar.226A cell has been designed for pressures up to 10Kbar and temperature variation over the range 10-300K.227 A Pfund-type cell has been constructed for i.r. spectroscopy with sample temperatures of 1300 K,228and a dual purpose cell, for i.r. absorption and electrical conductivity measurements, allowing temperatures to be achieved in the range 293-773 K, has been employed in a study of adsorbed gases on solids.229A reaction cell has been designed to enable i.r. spectroscopy of heterogeneously catalysed gas-phase reactions at elevated temperatures under reaction conditions. ’O Second-derivative i.r. spectroscopy has enabled the separation of sharp peaks from broad structureless Spectra of trace C 0 2 are used as illustrations. A useful bibliography of published data for i.r. spectroscopy has been provided by Oliver and M a r ~ d e n . ~The , ~ problem of searching an i.r. reference library using a computer has also been ~onsidered.~,’

’.

Tunable Diode Laser Spectroscopy.-During the past few years, tunable diode lasers have emerged as an important spectral source for infrared spectroscopy. A review of this field, dating back to 1976 has been published.234 A dual beam tunable diode laser spectrometer for mid-i.r. measurements has been described.235 Successive sweeping of the current-modulated laser permitted signal averaging and hence a good signal-to-noise ratio. Similar improvements were obtained by a scanning mechanism in which the laser output was modulated and the current

221

222

223 224

225

226

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”*

229

230

232 233 234

235

‘Ranging into the Infrared’, Lab. Equip. Dig., 1981, 18. Dec., 78. D. B. Braund, A. R.H. Cole, J. A. Cugley, F. R. Honey. R. E. Pulfrey. and G. D. Reece, Appl. O p t . , 1980, 19, 2146. K. Fox, G. W. Halsey, and D. E. Jennings, J. Mol. Spectrosc., 1980, 83, 213. R. W. Hannah and J. P. Coates, Eur. Spectrosc. N e w , 1980, 32, 30. W. F. Edgell, E. Schmidlin, and M.W. Balk, Appl. Spectrosc., 1980, 34, 420. J. Altmann, R. Baumgart, and C. Weitkamp, Appl. Opt., 1981. 20, 995. C. Brodbeck, J.-P. Bouanich, P. Figuiere, and H. Szwarc, J. Chem. Phys., 1981.74, 77. F. D. Medina, Infrared Phys., 1980, 20. 297. W. S. Dalton and H. Sakai, Appl. Opt., 1980, 19, 2145. P. T. Walsh, S. J. Gentry, A. Jones, and T. A. Jones, J . Phys. E., 1981. 14, 309. P. C. M. vanwoerkom, P. Blok, H. J. vanveenendaal, and R. L. de Groot, Appl. Opt., 1980,19,2547. M. R. Whitbeck, Appl. Spectrosc., 1981, 35, 93. R. W. A. Oliver and B. Marsden, Eur. Spectrosc. News, 1980, 33, 33. R. H. Shaps and J. F. Sprouse, Eur. Spectrosc. News, 1980, 32, 39. R. S. Eng, J. F. Butler, and K. J. Linden, O p t . Eng., 1980, 19, 945. D. E. Jennings, Appl. Opt., 1980, 19, 2695.

Developments in Instrumentation and Techniques

19

advanced during the dark time.236A computer-controlled spectrometer for the range 2.2-3.3 pm was constructed using a CW colour centre laser.237 Tunable diode laser spectroscopy has been employed in order to observe the Zeeman effect in the i.r. absorption of molecules with no electromagnetic moment, due to differences between the excited- and ground-state g - f a ~ t o r s . ~Doppler~' limited resolution was obtained for I3CH3I and 12CH2DIin the region 820866cm-' with a resolution of 0 . 0 0 0 6 ~ r n - ' 240 . ~ ~In ~ ~addition, the relative abundance of 1291 with respect to I2'I was found to be 0.032, comparing well with mass spectroscopic data. Doppler-limited resolution was also reported for ['H,]-ethylene in the 2174-2227 cm- region.241Other systems that have been investigated include NH, (931-954cmMoF, ( v 3 Q branch, 7407 5 0 ~ m - ' ) , ~H2"C0 ~~ and H213C0 (band centres 1746.009cm-' and 1707.981cm- l , the radicals C35Cl, C37C1,245and CF,246 and HNO, (430 transitions in the region 1690--1727~m-').~~~ The i.r. spectrum of ,'O14N was investigated over the sample temperature range 800-1050 0C.248 Eight ozone absorption lines around 1068.7cm-' were resolved using a Pb salt diode laser and heterodyne frequency measurements after mixing the laser output with that from a C 0 2 laser.249A long optical path absorption cell was used in a study of the v , transition in UF, at 16 pm.250A tunable far-i.r. optically pumped laser was used to measure the absorption of water vapour between 8 and 1 0 4 ~ m - l The . ~ ~ absorption ~ of SO2 was monitored at 20 lines from a DF laser.252

Fourier Transform Infrared Spectroscopy.-New Fourier transform (FT) spectrometers recently described in the literature include a double-beam optically compensated spectrometer suitable for weak i.r. absorptions (0.5-1%) 2 5 3 and a system based upon a refractively scanned interferometer, in which the optical path length variation is achieved by translating a wedge of refractive material across one of the arms.254Such a design should permit lower construction costs and improved ruggedness. A FT i.r. spectrometer designed around a polarizing Michelson interferometer has been shown to offer several advantages over 236 "'l

238 239 240

241 242 243 244

245 246 247

24g 249

250

2s1 252 253 2s4

J. N.-P. Sun, M. L. Olsen, D. L. Grieble, and P. R. Griffiths, Appl. Opt., 1980, 19, 2762. G. Litfin, C. R. Pollock, J. V. V. Kasper, R. F. Curl, and F. K. Tittle, IEEE J. Quantum. Electron., 1980,16, 1154. V. G. Koloshinikov, Y. A. Kuritsyn, I. Pak, N. I. Ulitskiy, B. M. Kharlamov, A. D. Britov, I. I. Zasavitsky, and A. P. Shotov, Opt. Commun., 1980, 35, 213. P. P.Das, V. M. Devi, and K. N. Rao, J. Mol. Spectrosc., 1981, 86, 202. M. Wahlen and G. Tucker, Opt. Commun., 1981, 36, 39. N. Ohashi, K. Kawaguchi, and E. Hirota, J. Mol. Spectrosc., 1981, 85, 427. G. Baldachini, S. Marchetti, and V. Montelatici, J. Mol. Spectrosc., 1981, 86, 115. J. C. Cummings, J. Mol. Specrrosc., 1980, 83, 417. D. M. Sweger and R. L. Sams, J. Mol. Spectrosc., 1981, 87, 18. C. Yamada, K. Nagai, and E. Hirota, J. Mol. Spectrosc., 1981,85, 416. K. Kavaguchi, C. Yamada, Y.Hamadd, and E. Hirota, J. Mol. Spectrosc., 1981, 86, 136. A. G. Maki and J. S. Wells, J. Mol. Spectrosc., 1980, 82, 427. A. G. Maki and F. J. Lovas, J. Mol. Spectrosc., 1981, 85, 368. M. Lyszyk, J. C. Depannemaecker, J. G. Bantegnie, F. Herlemont, J. Lemaire, and Y . Riant, Opt. Cornmun., 1981, 37, 53. K. C. Kim and W. B. Person, J . Chem. Phys., 1981, 74, 171. 0. A. Simpson, R. A. Bohlander, J. J. Gallagher, and S. Perkowitz, J. Phys. Chem., 1980, 84, 1753. J. Altmann and P. Pokrowsky, Appl. Opt., 1980, 19, 3449. S.C. Shen, T.Welker, J. Kuhl, and L. Genzel, Infrared Phys.. 1980, 20, 277. W. M. Doyle, B. C. McIntosh, and W. L. Clarke, Appl. Specfrosc., 1980, 34, 599.

20

Photochemistry

conventional systems for dual beam Fourier transform, circular dichroism, and reflectance ellipsometric i.r. s p e c t r o ~ c o p y . For ~ ~ this application suitable i.r. grid polarizers for the range 5&700 cm- have been described, along with several suggestions for improving the performance of polarizing interferometers. 2 5 6 The technique of rapid scanning FT time-resolved infrared spectroscopy has been discussed with particular emphasis on the practical aspects and care required for such m e a s ~ r e m e n t s . ~ ~ ’ Improvements in the detection limits of FT i.r. spectroscopy are possible with the application of least-squares spectral regression techniques. 2 5 With base-line fitting and use of all the information available from a reference spectrum, trace gas levels may be detected even if the individual spectral features lie below the noise level. Target factor analysis has been applied in order to determine the number and identity of components in a series of related multicomponent mixtures.259FT i.r. spectroscopy has been employed in order to identify HOCH,OCHO as an intermediate in the gas-phase reaction of 0,and C2H4.260A long path (180 m) cell was used to detect glycoaldehyde, at the p.p.m. level, among products in the photolysis of C,H4, NO, and R O N 0 (R = aryl group).261 A method for continuously monitoring the total gaseous effluent from a heterogeneously catalysed reaction, using mid4.r. FT spectroscopy, has been described.262 Products may be identified and analysed semi-quantitatively and changes in the reactor performance diagnosed. FT i.r. spectroscopy has been used to determine the solvent-induced frequency of the FT i.r. shifts for the C-H stretching bands of n - ~ c t a n e . Measurement ~~, spectra for HCl and DCl over the range 2 8 4 0 - 8 4 5 0 ~ m - ’ , and ~ ~ ~for HI and DI over the range 3000-10 380 cmallowed accurate prediction of the TC1 and TI spectra. For D2160,the high resolution (5 x 10-3cm-1) available using FT i.r. spectroscopy enabled an extended and more precise set of rotational levels to be derived for the vibrational states (000), (020), (loo), and (O01).266Rotational constants and vibrational term values were evaluated for 13CS2 from FT i.r. measurements between 250-430 cm- with 0.01 cm- res01ution.~~’1988 lines were observed for ozone recorded using a FT i.r. spectrometer with a solar source. 268 Remote Atmospheric Monitoring.-Several techniques for remote atmospheric monitoring of pollutants, trace gases, etc. by LIDAR (Light Detection And Ranging) have become popular over recent years. Of these, DIAL (Differential Absorption Lidar) spectroscopy would seem to be of most interest to the 25s

25h 257 258 259

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M. J. Dignam and M. D . Baker, App/. Specfrosc., 1981.35. 187. W. A. Challener, P. L. Richards, S. C. Zilio, and H. L. Garvin, Infrared Phys., 1980, 20, 215. A. A. Garrison, R. A . Crocombe. G. Mamantov, and J. A. deHaseth. Appl. Specfrosc., 1980,34,398. D. M. Haaland and R. G . Easterlang, Appl. Specfrosc., 1980, 34, 539. M. McCue and E. R. Malinowski, Anal. Chim. Arfa. 1981, 133, 125. H. Niki, P. D. Maker, C. M. Savage, and L. P. Breitenbach, J . Phys. Chem., 1981, 85, 1025. H. Niki, P. D . Maker, C. M. Savage, and L. P. Breitenbach. Chem. Phys. Lett.. 1981, 80, 499. D . D. Saperstein, Anal. Chem., 1980, 52, 1565. D. G . Cameron. S. C. Hsi, J. Umemura, and H. H . Mantsch, Can. J . Chem., 1981, 59. 1357. G. Guelachvili, P. Niay, and P. Bernage. J . Mol. Spectrosr., 1981, 85, 271. G . Guelachvili, P. Niay, and P. Bernage, J . Mol. Spectrosc., 1981, 85, 253. N . Papineau. J.-M. Flaud, and C. Camy-Peyret, J . Mu/. Specfrosc.. 1981, 87. 219. J . Kauppinen and K. Jolma, J. Mol. Specfrosc.. 1981, 85, 314. A . Barbe, C. Secroun. P. Jouve, A. Goldman, and D. G. Murray, J. Mu/. Spectrosr., 1981,86, 287.

Developments in Instrumentation and T e c hiques

21

photochemist. The advantages of using two lasers for DIAL, with one tuned to a known absorption line of the molecule of interest and the other serving as a reference, have been discussed.269In the same report, the effects of atmospheric turbulence were considered. DIAL instruments have been constructed using two simultaneously pulsed C 0 2 lasers (for sensing of ozone at 9 . 5 ~ m ) , ~and ~ ’ two Nd-YAG-pumped dye lasers (for the monitoring of water v a p o ~ r ) A . ~single ~~ CO, laser, operated at two wavelengths using an angle-modulated diffraction grating, was suggested to be an ideal source for DIAL.272A single XeCl laser was used to determine vertical ozone distributions in the stratosphere from 15 to 25 km.273Descriptions of a mobile g r ~ u n d - b a s e d , ~and ’ ~ an orbiting 2 7 5 DIAL system have been reported. The possibilities for remote sensing of H 2 0 and methane (from natural gas spills) by laser Raman and atmospheric alkali atoms, OH, NO, and NO, by fluorescence LIDAR 2 7 7 have also been examined and reviewed. Optical and Infrared Double-resonance Spectroscopy.-Sub-Doppler optical spectroscopy of BaO has been performed using two CW dye lasers.278A crossed-beam i.r.-u.v. double-resonance spectrometer has been described for observing electronic hot-band spectra of molecules vibrationally excited by a C 0 2 laser.279 Vibrational relaxation from NO (v = 1) has been studied by exciting at 5.3pm using a C 0 2 laser and then monitoring the resonance U.V.fluorescence induced using a discharge lamp.280An i.r.-u.v. double-resonance technique has revealed vibrational energy redistribution times in HFB of 30-100 ns.281Two 30ps pulses from 2 tunable C 0 2 lasers were used in a pump-probe ps double resonance study of SF6.282A deep-hole burning feature was observed at the pump wavelength. An apparatus has been described for the investigation of isomerization reactions using C0,-laser-induced fluorescence and i.r. doubleresonance absorption spectroscopy.283 Photoacoustic Spectroscopy.-Photoacoustic spectroscopy (PAS) and its applications have been recently reviewed.284A single-beam i.r. PAS spectrometer has been constructed for the range 800--4000cm- using a broad-band carbon rod spectral source in preference to a laser.285A double-beam in-time PAS instrument has been described,286in which a single microphone was used to monitor both the 269 ’’O

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D. K. Killinger and N. Menyuk. Appl. PAYS. Lett.. 1981, 38. 968. R. W. Stewart and J. L. Bufton. Opt. Eng.. 1980. 19. 503. E. V. Browell. A. F. Carter. and T.D. Wilkerson. Opt. Eng.. 1981, 20, 85. M. Hamza, T. Kobayasi, and H. Inaba. Opt. Quantum. Electron., 1981, 13, 187. 0. Uchino, M. Maeda, T. Shibata, M. Hirono, and M. Fujiwara, Appl. Opr., 1980, 19, 4175. J. G. Hawley, Laser Focus, 1981, Mar., 60. V. J. Abreu, Opt. Eng.. 1980, 19, 489. D. A. Leonard. Opt. Eng., 1981, 20, 91. T. J. McIlrath, Opt. Eng.. 1980, 19, 495. R . A . Gotscho, P. S. Weiss, and R. W. Field. J . Mol. Spectrosc., 1980, 82. 283. M. B. Robin and N. A. Kuebler. Chem. PIijs. Lett., 1981, 80, 512. J . Kosanetzky, U. List. W. Urban, H. Vormann, and E. H. Fink, Chem. Phys.. 1980. 50, 361. S. Speiser and E. Grunwald, Chem. PIiys. Lett., 1980. 73, 438. R. C. Sharp, E. Yablonovitch, and N. Bloembergen. J . Chem. Phys., 1981, 74, 5357. I. Glatt and A. Yogev, Chem. Phps. Lett., 1981, 77. 228. G . F. Kirkbright, and S. L. Castleden, C h m . Br., 1980. 16. 661. M. J. D. Low and G . A. Parodi, Injrared Phys., 1980. 20, 333. M.F. Cox. G . N. Coleman, and T. W. McCreary. Anal. CIieni., 1980, 52, 1421.

22 Photochemistry reference and sample signals, which were 180" out of phase. Real-time compensation for intensity source vibrations were possible by this method. A highperformance photoacoustic cell has been used over the temperature range 9 0 320 K.287The frequency dependence of the photoacoustic signal was investigated using carbon black for a reference. The instrument was applied to investigations of the photocycle in a bacteriorhodopsin system, and to excitonic levels in semiconductors.288A cell for PAS for samples on t.1.c. plates has also been described.289Q Several carbon black samples were examined for suitability as reference standards for PAS.289bNorbit A decolourizing carbon was found to be most satisfactory. However, the problems associated with using carbon black for a reference has led to abandonment of the method and, instead, calibration of the spectrometer by a direct measurement of the emission spectrum of the excitation source has been used.290 The absorption spectrum 291 and quantum yields of fluorescence2 9 2 - 293 of solutions with high optical densities have been determined using PAS. An improvement in the responsivity of PAS to trace gas absorptions was obtained with a Helmholtz resonator attached to the sample cell.294Low C 0 2 levels were monitored by PAS using a 1mW diode laser and exciting into the 4.803 pm line.295 Photoacoustic detection with C 0 2 laser excitation permitted the detection of several hydrazines and oxidation products at the p.p,b. A theoretical and experimental study has compared methods for detecting low absorption in liquid nitrogen by either PAS or a photorefractive technique.297 PAS has been found to be an ideal technique for the study of surfaces and adsorbed species. In studies of optically thin samples, pulsed laser excitation has 299 The degree of been shown to enable sensitivities of to be obtained.298* chemical modification of silica gel surfaces has been monitored by PAS.300A linear relationship between the photoacoustic signal and the amount of carbon or nitrogen adsorbed on the surface was found. PAS has also been used to study the photoinduced transient formed when eosine Y was adsorbed onto ZnO p~wder,'~'and the thin oxide layers (<4nm thick) on a copper electrode.302An investigation of layered samples has shown that PAS may be capable of depth discrimination.30 287

289

290 291

292

293 294 295 296 297 298 299

300 301 jo2

303

P. S. Bechthold, M. Campagna, and J. Chatzipetros, Opt. Commun., 1981, 36, 369. P. S. Bechthold, M. Campagna, and J. Chatzipetros, Opt. Commun., 1981, 36, 373. ( a ) V. A. Fishman and A. J. Bard, Anal. Chem., 1981,53, 102; (6) C. H. Lochrnuller, R. Rohl, and D. B. Marshall, Anal. LRtt., 1981, 14, 41. M. J. D. Low and G. A. Parodi, Spectrosc. Lett., 1980, 13, 663. U. Madvaliev and R. E. Shikhlinskaya. Opt. Specrrosc.. 1980,49, 250. D. Cahen. H. Garty, and R. S. Becker, J . Phys. Chem., 1980. 84. 3384. M. J. Adams, J. G. Highfield, and G. F. Kirkbright. Anal. Chem., 1980, 52, 1260. W. A. McClenny, C. A. Bennett, G. M. Russwurm, and R. Richmond, Appl. Opt., 1981, 20, 650. T. H. Vansteenkiste, F. R. Faxvog, and D. M. Roessler, Appl. Specrrosc., 1981, 35, 195. G. L. Loper, A. R. Calloway, M. A. Stamps, and J. A. Gelbwachs, Appl. Opt., 1980, 19, 2726. S. R. J. Brueck, H . Kildal, and L. J. Belanger, Opt. Commun.,1980, 34, 199. A. Rosencwaig and J. B. Willis, J. Appl. Ph-vs., 1980, 51, 4361. A. Rosencwaig and T. W. Hindley, Appl. Opi., 1981, 20,606. C. H. Lochmuller and D. R. Wilder, Anal. Chim. A d a , 1980, 118, 101. T. Iwasaki, S. Oda, T. Sawada, and K. Honda, J. Phys. Chem., 1980,84, 2800. U. Sander, H. H. Strehblow, and J. K. Dohrmann, J . Phys. Chem., 1981, 85,447. P. Helander, I. Lundstrom, and D. McQueen, J . Appl. Phys., 1981, 52, 1146.

Developments in Instrumentat ion and Techniques

23

A Michelson interferometer with the facility for step and integrate, and rapid scan operation has been used for Fourier transform PAS.304The merits of the two methods were considered. The versatility of this technique for the measurement of the infrared spectra of powdered samples has been demonstrated.3o5*306 Some possible reasons for the distortion of such measurements have been discussed.307 FT-PAS has enabled discrimination between Kl4No3 and K”N03 and has shown the technique to be suitable for quantitative analysis of solid mixtures.308 Vibrational energy relaxation in methyl halides has been investigated using opto-acoustic methods.309In one system the phase-lag between the pressure wave and the modulated excitation source was monitored, while in the other pulsed excitation was employed and the transient photoacoustic signal was observed.

Multiphoton Excitation.-Reviews of multiphoton spectroscopy (including Raman and CARS) and the possibilities of reaching vacuum-u.v. transitions by this m e t h ~ dl ,1 ~have been published recently. The multiphoton i.r. absorption of SF, has been investigated using a TEA-CO, laser and pyroelectric dete~tion.~’, The effects of pressure variation over the range 10-3-1 Torr were determined with the findings that under collisionless conditions, multiphoton absorption was dependent upon the laser-pulse intensity, while the energy fluence became more important at higher pressures. A thermionic diode with a shielded auxilliary compartment was used to detect two-photon absorptions under Doppler-free condition^;^ two- and three-photon excitations were induced in I, using a dye laser tunable over the 450-610nm region.314 A method for determining two-photon absorption cross-sectionsusing a low intensity CW laser has been reported,315along with some results for a Rhodamine B solution. A fluorimeter suitable for two-photon excitation using a tunable dye laser has been de~cribed.”~ Spectra of diphenylbutadiene in an EPA glass at 77K were used for illustration. Two-photon excited fluorescence was also observed for OsO, l 7 and UF, 318 with excitation using a C 0 2 and Raman frequency-shifted dye laser, respectively. Polarization effects on two-photon excitation have been examined. * *

’

L. B. Lloyd, S. M. Riseman, R. K. Burnham, E. M. Eyring, and M. M. Farrow, Rev. Sci. Instrum., 1980,Sl. 1488. M.G.Rockley, Appl. Spectrosc., 1980,34, 405. jo6G. Laufer, J. T. Huneke, B. S. H. Royce, and Y. C. Teng, Appl. Phys. Le/t.. 1980,37,517. 307 M. G . Rockley, Chem. Phys. Lett., 1980,75, 371. M. G. Rockley, D. M. Davis, and H. H. Richardson, Appl. Spectrosc., 1981,35, 185. ’09 J. Schurman and G . H. Wegdam, Chem. Phys. Lett., 1980,73,429. 310 M.Ito and N. Mikami, Appl. Spec. Rev., 1980, 16,299. 311 P. Lambropoulos, Appl. Opr., 1980, 19.3926. ’I2 R. V. Ambartzumian, G. N. Makarov, and A. A. Puretzky, Opt. Commun., 1980,34, 81. 3 ’ 3 K. C. Harvey. Rev. Sci. Instrum.. 1981. 52, 205. 314 K. Kasotani, Y. Tanaka, K. Shibuya, M. Kawasaki, K. Obi, H. Sato, and I. Tanaka, J . Cheni. Phys., 198I , 74, 895. ’I5 I. M.Catalan0 and A. Cingolani. Appl. Phys. Left.. 1981,38, 745. J. A. Bennett acd R. R. Birge, J . Chem. Phys.. 1980,73,4234. ’I7 M.N. R. Ashfold, C. G . Atkins, and G. Hancock, Chem. Pliys. Lett.. 1981,80, 1. 318 E. R. Bernstein and P. M. Kennedy, J . Chem. Phys.. 1981,74, 2143. 319 M.J. Wirth, A. Koskelo, and M. J. Sanders, Appl. Spectrosc.. 1981.35, 14. ’O K. Kasdtdni. M. Kawasaki, H. &to, Y. Murasawa. K. Obi, and I. Tanaka, J . Chem. Phys., 1981,74, 3 164. 304 305

24 Photochemistry Multiphoton ionization spectroscopy has been reviewed in two recent articles.321.322 An apparatus has been described for constant intensity multi23 A sensitive molecular vapour detection system photon ionization ~pectroscopy.~ utilizing resonance+nhanced two-photon ionization has been used to monitor naphthalene to a limit of 5 x 104m~lecule~cm-1.324 Excitation was achieved using a frequency-doubled Nd-YAG-pumped dye laser at 287.5nm and the authors postulated single-molecule detection limits using such a system. Resonance-enhanced multiphoton ionization (REMPI) methods have been reviewed along with a description of a computer-controlled high-resolution time-offlight laser mass spectrometer system.325 Multiphoton ionization combined with mass spectroscopy has been proposed as a sensitive tool for analysis of trace gases to a detection limit of 2 parts in 109.326 Flashlamp- and ni trogen-laser-pumped dye lasers have been used for REMPI detectors for gas chromatography. 327 Aromatic hydrocarbons could be detected at the 10 pg level. The necessity for constant peak energy as well as CW power, for multiphoton ionization studies has been discussed.328

Raman Spectroscopy.-The second and third harmonic light from a Nd-YAG laser, converted into the wavelength range 395-500 nm by Raman scattering in a high-pressure H, cell, has been shown to be an ideal spectral source for Raman spectroscopy.329 3.2 ns pulses from an N,-laser-pumped dye laser have been utilized in a spectrometer capable of probing both ps and ps processes.330Two counter-propagating pulsed dye lasers have been used in order to measure highresolution, fluorescence-free, stimulated Raman gain spectra without the need for optically dispersive devices.33 The non-resonant background was reduced in a coherent Raman spectrometer using a novel technique.332 Two short pulses at frequencies W , and W, excited molecular vibrations at the frequency ( W,- Ws). Once the fast non-linear reaction of the electrons had decayed, a delayed pulse probed the remaining excitation by coherent Raman spectroscopy. Modulation techniques have been shown to be capable of increasing the signalto-noise ratio for Raman spectroscopy, this being illustrated for the resonanceenhanced inverse Raman effect.3 3 Inverse Raman spectroscopy enables spectra of highly luminescent systems to be recorded. A suitable spectrometer has been described in which a resolution of 1 cm- was achieved with scan rates dependent only upon the scan speed of the dye laser used for e ~ c i t a t i 0 n . jA~ ~100-fold increased sensitivity was reported with the use of a multiplex spectrometer for

’

’

321

V. S. Antonov and V. S. Letokhov, Appl. Phys., 1981, 24. 89. P. M. Johnson. Appl. Opt.. 1980, 19, 3920. G . 0. Uneberg. P. A. Campo, and P. Johnson, J . Chem. Pliys.. 1980. 73, 1110. C. Klimcak and J . Wessel. Appl. Phy.7. Lett., 1980. 37, 138. 3zi D . A. Lichtin. S. Datta-Ghosh. K. R . Newton. and R. B. Burnstein, Chem. Phys. Lett.. 1980.75214. 32h U. Boesl. H. J . Neusser, and E. W. Schlag. Chem. Phys.. 1981. 55. 193. ”C. M . Klimcak and J . E. Wessel, A n d . Chcni.. 1980, 52, 1233. 328 I-. J . Rothberg. D. P. Gerrity, and V . Vaida. J . C/ieni. Phys.. 1980, 73. 5508. R . P. vanDuyne and K . D. Parks. C h i . P h j : ~ Lctf.. . 1980. 76. 196. D. Nicollin, P. Bertels, and J . A . Koningstein. Cm. J . Clirrn.. 1980. 58. 1334. 33’ J . R. Nester. Appl. Spectrosr., 1981. 35. 81. W . Zinth. Opt. (’oniniun.. 1980, 34,479. 333 J. P. Haushlater, C. E. Butfett. and M . D. Morris. A n d . C/icni.. 1980, 52, 1284. 334 C. E. Ruffett and M . D . Morris, Appl. Spcctrosc.. 1981. 35. 203. 322

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’”

’’’

’”

’-”

Developments in Instrumentation and Techniques

25 Raman measurements.335 Two high-pressure cells for Raman spectroscopy have been reported allowing pressures up to 345Kbar with some temperature variation.336*3 3 7 Considerable interest has recently been focused on surface-enhanced Raman spectroscopy (SERS). It has been shown to have the potential for observing the interaction of electrode materials. (Au, Ag, Cu) with adsorbates from an . ~In ~ addition, ~~ great enhancement of the Raman electrolyte (CN -, p ~ r i d i n e )340 spectrum of ethylene and propylene adsorbed onto silver has been suggested to be due to SERS.341 The observation of the effect for pyridine, benzene, and cyclohexane adsorbed onto a mercury surface has shown that a roughened solid surface is not necessary.342 The angular dependence of SERS has been investigated using fibre-optic probes for both the laser excitation source and the detector.343A surface picosecond Raman gain spectrometer has been described in which the beat frequency from two synchronously pumped dye lasers induces the vibrational transitions.344 A method for measuring derivative spectra of Raman vibrations of molecules adsorbed on a surface has been described and illustrated for carbonate ions on silver.345A 2nm surface layer of silicon on sapphire was detected using stimulated Raman gain spectroscopy.346 Three modulations and demodulations were used in order to extract the signal that displayed a high signalto-noise ratio.

Emission Spectroscopy.-Fluorescence spectroscopy is now a versatile and wellestablished technique, and most photochemical laboratories have commercially available instruments. For critical work, however, many workers prefer a purposebuilt fluorimeter optimized for the problems of current interest. Although the literature abounds with descriptions of such systems it was felt that little use would be gained from a list of variations on the lamp/monochromator/cell/monochromator/detector theme: consequently, this article has concentrated upon instrumental developments of a more general nature. In many instances the laser is replacing the conventional discharge lamp as a spectral source for fluorescence spectroscopy. For example, a nitrogen-laser-pumped dye laser has been used in a fluorescence excitation spectroscopic study of 2,12-dimeth~ltridecahexaene,~~~ and a spectrometer capable of recording excitation and fluorescence spectra has been used for low-pressure vapour-phase samples.348 Other examples will be discussed when considering applications for fluorescence spectroscopy. A Xe flashlampboxcar integrator system has been used for excitation, fluorescence, and ti me-resolved fluorescence studies of h igh-tern pera t ure 33s 336

"' '" 339 34"

'" 343 344 345

346 34'

J. J. Freeman. J. Heaviside. P. J. Hendra, J. Prior, and E. S. Reid, Appl. Specirosc., 1981, 35, 197. A. H . Abdullah and W. F. Sherman, J . Pli.vs. E.. 1980. 13, 1154. K . R. Hirsch and W . B. Holzdpfel. Rev. Sri. Instrum., 1981. 52, 52. H. Wetzel, B. Pettinger. and U. Wenning. Chem. Phys. Lett.. 1980. 75, 173. K. von Raben, R. K. Chang, and B. L. Laube, Client. Phys. Leii.. 1981, 79.465. C. S. Allen, G . C. Schatz. and R. P. van Duyne, Clirni. Pliys. Left., 1980, 75. 201. M. Moskovits and D. P. Dilella, Client. P / i w . Lett.. 1980, 73, 500. R. Naaman, S. J . Buelow, 0. Cheshnovsky, and D. R . Herschback, J . Phys. Chem., 1980,84, 2692. G . R . Trott and T. E. Furtak. Rev. Sci. hisirum., 1980. 51, 1493. J. P. Heritage and D . L. Allara. Cltcni. Phys. Lett.. 1980, 74, 507. J. P. Heritage and J . G . Bergman. Opt. Cuntntun.. 1980, 35, 373. B. F. Levine, C. G . Bethea, A. R. Tretold, and M. Korngor. Appl. Phys. Leii., 1980, 37, 595. R. A. Auerbach. R . L. Christensen. M . F. Granville, and B. E. Kohler, J . Cheni. Phys., 1981,74,4. H . Baba, M . Fuiita. and K . Uchida. Cliem. P/iI.s. Lei!., 1980, 73. 425.

26

Photochemistry

v a p ~ u r s . ~A~temperature-controlled ’ cell suitable for use over the range - 30 to 80°C (kO.1“C) for corrosive gases such as UF, has been reported.350 Other fluorescence cells recently described include (i) a high-pressure (up to 5 Kbar) cell with temperature control from - 20 to 90 0C,35(ii) a multipass cell for gas-phase samples with dye laser excitation,352and (iii) a cell with electromagnet, enabling the effect of magnetic fields on radiationless deactivation processes to be examined. A computer-controlled spectrophotometer has been described that permits the simultaneous recording of fluorescence and absorption spectra. A microprocessor has also been employed in a fluorimeter designed to overcome many of the problems associated with self absorption in high-optical-density s ~ l u t i o ns50 .~ Corrections were made using the cell-shift methods.355bA modulated excitation source, together with a rotating polarizer and lock-in detection, has been used to measure steady-state fluorescence polarization spectra with good signal-tonoise.356A chopper system has also been employed in order to separate excitation and fluorescence signals when the emission wavelength lies near the absorption line and the decay of luminescence is longer than 20 P S . ~ ” Of possible concern to any worker observing vacuum-u.v. fluorescence signals are Wren’s observations that SI-U.V.quartz, U.V.grade sapphire, MgF,, and BaF, (commonly used materials for vacuum-u.v. optical components) show strong luminescence when excited above 200 nm.358 The deconvolution of multicomponent fluorescence spectra may be accomplished using a ratio method providing spectral regions may be located where the luminescence is due to one species only.359 Several xanthene and coumarin derivatives dispersed in polymer matrices have been suggested as possible quantum counters for fluorescence spectroscopy.360 The temperature dependence of the fluorescence quantum yield standards, rhodamine B and rhodamine 101, has been investigated.361Rhodamine 101 would seem to be preferable owing to the invarience of its quantum yield with temperature over the range studied. Errors of up to 80% may be introduced in quantum yield determinations if the intensity distribution within the exciting light band, and the spectral dependence of the absorption within this band, are neglected.362 A method for correcting for re-absorption and re-emission effects in quantum yield determinations when applied to processes having high quantum yields, has been 349

350 351

352

353 354 355

356 357

358 359

360 361

3b2

J. A. Caird, W. T. Carnall, J. P. Hessler. and C. W. Williams, J . Chem. Phys., 1981, 74, 798; J. A. Caird, J. P. Hessler, W. T. Camall, and C. W. Williams, J . Chem. Piiys., 1981, 74, 805. R. N. Shelton, W. W. Rice, F. B. Wampler, and J. J. Tree. Rev. Sci. Instrum.. 1981, 52, 576. D. R. Dawson and H. W. Offen, Rev. Sci. Instrum., 1980, 51, 1348. K . G. Spears and L. D. Hoffland, J. Chem. Phys., 1981,74, 4765. C. Michel and C. Tric, Chern. Phys., 1980, 50, 341. Y . Saito, H. Tachibana, H . Hayashi, and A. Wdda, Phofochem. Photobiol., 1981, 33, 289. ( ( I ) D. R. Christmann, S. R. Crouch,, and A. Timnick Anal. Chem., 1981, 53, 276; (6) A. Novak, Collect. C x c h . , Clicwi. Commun.. 1978. 43. 2869. R. A. Hann, J . Phys. E., 1981, 14, 152. H. C. Basso and M. A. Aegerter, Appl. Opt., 1981, 20, 12. D. J . Wren, Appl. Specrrosc.,1980, 34,627. M. P. Fogarty and I. M. Warner, Anal. Chem., 1981, 53, 259. K. Mandal, T. D. L. Pearson, and J. N . Demas, Anal. Chem., 1980, 52, 2184. T.Karstens and K. Kobs, J . Phys. Chem., 1980,84, 1871. J. Bendig, D. Kreysig, and R. Schoneich, Opt. Spektrosk., 1980, 49, 56.

Developments in Instrumentation and Techniques

27

proposed.363 The method, although considerably simpler, has been found to produce results in good agreement with other techniques. A method for evaluating quantum yields of fluorescence for samples in high-optical-density films less than 0.01 cm thick has been described.364 The high sensitivity of fluorescence spectroscopy has suggested that 'the technique may provide a powerful analytical tool for the analysis of species present only in trace quantities. For example, a nitrogenlaser-pumped dye laser was used together with pulse-gated detection electronics to detect rhodamine 6G at a concentration of 0.04 ngdm-3.365 Laser fluorimetry with photon-counting detection has demonstrated a detection limit of 2 pg dmfor a europium(II1) complex.366For the analysis of fluorescent drugs at the trace level, high- and low-powered laser fluorimetry has been shown to provide useful data. 367 A multiple-wavelength fluorimeter incorporating an intensified diode array detector has been employed for the rapid analysis of thiamine and riboflavin.368 For the analysis of crude oil mixtures, synchronous scanning fluorescence spectroscopy, in which both excitation and fluorescence wavelengths are varied simultaneously, has been suggested.369The comparison of oil samples with reference spectra has been carried out using a vector solution.370 A photofragmentation laser-induced fluorescence method has been proposed for the detection of atmospheric trace gases.371Two lasers were employed, one for photolysis and the other for the electronic excitation of the fragment, which was then monitored by fluorescence. Discrimination against Raman and Rayleigh scattering effects and background luminescence was possible. Laser-induced fluorescence (LIF) methods have been widely applied to the study of small molecular species in the gas phase. The second harmonic of a Nd-YAG laser was used, together with a boxcar integrator for detection, in order to determine the cross-sections for collision-free fluorescence from NO,. 3 7 2 LIF was used to monitor vibrational energy transfer from CO, to alcohols.373 The CO, was contained in the intracavity region of a @switched C 0 2 laser. Vibrationally hot azulene molecules were generated by electronic excitation using a dye laser, and subsequent internal conversion back to the ground state.374The resulting infrared luminescence was observed using a HgCdTe detector, and it was found that a stepladder model adequately described the vibrational deactivation by collisions. LIF from D,O excited at 9.26 pm using a TEA-CO, laser was detected using a Cu-Ge detector cooled in liquid helium. 3 7 Vibrational relaxation rates for collisions with D,O, D,, HD, H,, He, and Ar were evaluated. Ozone photolysis and laser-

"' I . L. Arbeloa, J . Photochem., 1980, 14, 97. 364

365

D. Krenske, S. Abado, H. van Damme, M. Cruz, and J. J. Fripiat, J . P/7ys. Chem., 1980, 84, 2447. K. Miyaishi, M. Kunitake, T. Imasaka, T. Ogawa, and N. Ishibashi, Anal. Chim.Acta., 1981, 125, 161.

366 367

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372 373 374 375

S. Yamada, F. Miyoshi, K. Kano, and T. Ogawa, Anal. Chin?. Acta, 1981, 127, 195. N. Strojny and J. A. F. de Silva, Anal. Chem., 1980, 52, 1554. M. A. Ryan and J. D. Ingle, Talanta, 1981, 28, 225. P. John and I. Soutar, Chem. Br., 1981, 17, 278; M. M. Corfield, H. L. Hawkins, P. John, and I. Soutar, Analyst (London), 1981, 106, 188. T. J. Killeen, D. L. Eastwood, and M . S. Hendrick, Talanta, 1981, 28, 1. M. 0. Rodgers, K. Asdi, and D. D. Davis, Appl. Opt., 1980, 19, 3597. C. S. Dulcey, T. J. McGee, and T. J. McIlrath, Chem. Phys. Lett., 1980, 76, 80. P. R. Rao, S. V. Babu, V. S. Rao, and Y. V. C. Rao, Chein. Phys., 1981, 55, 215. G . P. Smith and J. R. Barker, Chem. PhJx Lett., 1981, 78, 253. S. S. Miljanic and C. B. Moore, J . Chem. Phys., 1980, 73, 226.

28 Pho tockem istry induced OH fluorescence spectroscopy were accomplished using a frequencydoubled dye laser in the range 281-295nm.376 A similar system was used to monitor NH fragments from the photodissociation of NH3.377 A multipass fluorescence cell was used, with a Xe lamp (28 cm- bandwidth) for excitation, in order to measure single vibronic level (SVL) fluorescence spectra from p-difluorobenzene under collision-free conditions. 7 8 Frequency-doubled dye lasers have also been used to determine SVL fluorescence spectra for p y r a ~ i n e ~, y~ r~i d~ i n e , ~and ~ ’ S 0 2 . 3 8 1The combination of laser excitation with rotational and vibrational cooling of the sample using a supersonic molecular beam has been widely used for high-resolution spectroscopy of isolated species, and has been reviewed.382 SVL fluorescence spectra were recorded for naphthalene in a supersonic jet with excitation using a frequency-doubled dye 3 8 4 Several fluorobenzene cations were prepared by electron-impact ionization of the parent species in seeded supersonic molecular beams. 3 8 5 * 386 Ionization did not seem to have any effect upon the rotational and vibrational cooling of the samples, so the LIF spectra obtained were greatly simplified when compared with conventional gas-phase studies. Other species that have been investigated include aniline,387 t h i ~ p h o s g e n e p, ~h ~t h~a l ~ c y a n i n e ,styrene,390 ~~~ and n-alkylbenzenes. 3 9 1 Quantum beats were observed in the dye-laser-excited fluorescence of biacetyl in a supersonic jet.392 A review of the recent developments of phosphorescence spectroscopy for the analysis of low concentrations of organic species considered low- and roomtemperature methods together with synchronous scanning, derivative, and phaseresolved techniques.393 In particular, room-temperature phosphorescence (RTP) measurements, in which the organic sample is adsorbed onto an inert solid support material, are finding increasing application for analysis of aromatic compounds at the trace In an extended review, technical details are presented together with a list of compounds that display RTP.395Polynuclear aromatic compounds found in synthetic fuel oils were analysed using RTP.396 The selectivity was enhanced by synchronously scanning the emission and excitation wavelengths and

’’’ M. 0. Rodgers. K. Asai, and D. D. Davis. Chem. Pliys. Lett.. 1981, 78, 246. L. G. Piper, R. H. Krech, and R. L. Taylor, J. Chenr. Phys., 1980, 73, 791. ’” R. A. Coveleski and C. S. Parmenter. J. Mol. Specrrosc., 1981. 86. 86. ’’’ D. B. McDonald and S. A. Rice, J. Chem. Phys., 1981, 74, 4893. R. J. Shaw, J. E. Kent, and M. F. O‘Dwyer, J. Mol. Spectrosc., 1980. 82. 1 . ”’ Y. Mochizuki. K. Kaya. and M. Ito. Cliem. Phjs.. 1981. 54. 375. 377

382 383 jar

3R5 386 387 388 3R9 3’)0 391

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396

Y. T. Lee and Y. R. Shen, P h j s . Today. 1980. Nov., 52. S. M. Beck, D. E. Powers, J. B. Hopkins, and R. E. Smalley, J . Client. Phys.. 1980. 73, 2019. S. M. Beck, J. B. Hopkins. D. E. Powers, and R. E. Smalley. J. Clrem. Plijs., 1981. 74. 43. R. C. Tuckett, Cliem. Phjs.. 1981, 58, 151. T. A. Miller. B. R. Zegdrski, T. J. Sears, and V. E. Bondybey. J . Phys. Chem., 1980, 84, 3155. N. Mikami, A. Hiraya. I. Fujiwara, and M. Ito, Chem. Phys. Lett., 1980, 74, 531. R. Vasudev, Y. Hirata, E. C. Lim, and W. M. McClain, Chrrn. Phys. Leri., 1980, 76, 249. P. S. H. Finch, C. A. Hayman, and D. H. Levy. J. Cliem. Phys., 1980, 73, 1065. R. J. Hemley, D. G. Leopold. V. Vaida, and J. L. Roebber, J . Plijs. Clieni., 1981. 85, 134. J. B. Hopkins, D . E. Powers, and R. E. Smalley, J. Chem. Pliys., 1980. 73, 683. W. Henke, H. L. Selzle, T. R. Hays, S. H. Lin, and E. W. Schlag. Chem. Plijs. Lett., 1980, 77, 448. J . L. Ward, G. L. Walden. and J. D. Winefordner. Talanta. 1981. 28. 201. R. T. Parker, R. S. Freedlander, and R. B. Dunlop, Anal. Cliim. Acta, 1980, 119, 189. R. T. Parker. R. S. Freedlander. and R. B. Dunlop, A n d . Cliim. Acro, 1980, 120. 1. T. Vo-dinh. R. B. Gammage, and P. R. Martinez. Anal. C h i i ~Acra, . 1980, 118. 313.

Developments in Inst rumentat ion und Techiques

29

by the use of heavy-atom perturbers. RTP has also been employed for the analysis of workplace air samples for polynuclear aromatic hydrocarbons.398 Chemi1uminescence.-It has been suggested that problems which occur in the determination of yields of bio- and chemi-luminescencemay be due to the sample cell.399Errors of 25% may be caused by reflection and refraction from interfaces, and, consequently, frosted containers and point-source geometries were recommended. Several authors have concentrated on the use of sensitizers for the enhancement of chemiluminescence. The heavy-atom effect was found to operate in the energy transfer from enzyme-generated acetone to xanthene dyes.4009,lODiphenylanthracene (9,IO-DPA) has been suggested to be a poor singlet counter for chemiluminescence as some triplet states were also counted.401 In another report, 9,lO-dibromoanthracene was found to be a more effective enhancer, when compared with 9,1O-DPA, for chemiluminescence from a cyclic Luminol chemiluminescence was employed in the analysis of Cr"' ions in seawater.403 Enhancement with bromide ions enabled detection limits of 3.3 x ~ O - ' M to be achieved. A crossed molecular beam apparatus was described for the study of chemiluminescent reactions such as F, + I, and Br, + Cl,.404 The effects of collision energy and beam pressure on the chemiluminescence were evaluated. A fast-flow system has been utilized for investigation of bimolecular reactions with rates up to 5 x 10l3mol-' cm3 s - ' . ~ " For an illustration of the method, the kinetics of the chemiluminescent reaction of H,B.N(CH,), with O ( 3 f )atoms were determined. Other reactions that have been investigated using chemiluminescence include N + + C0406 and the quenching of O('D) by N,O and NZs4O7 Chemiluminescence, laser-induced fluorescence spectra, and fluorescence lifetimes were recorded for the HSO radical in the gas phase.408 6 Transient Absorption Spectroscopy Few instrumental developments have appeared in the field of conventional (p) flash photolysis, so the description of this technique will be limited to a selection of applications illustrating the diverse use and results obtained from the method. A long-lived transient was observed following the excitation of C,H, using a 3000 J 5 ps flash in N,.409A 2 ps spectroscopic flash, triggered by a set delay after excitation, monitored the transient absorption in the wavelength region 140157 nm. The reactions of OH and OD with butane, [2H1,]-butane, and ~ e n t a n e , ~ ~ '

398

''' 400 401

402 403 404 *05

406 407 408

409 410

T. Vo-dinh, R. B. Gammage. and P. R. Martinez. Anal. Cheni., 1981. 53, 253. E. S. Rich, C. H. Groover, and J. E. Wampler, Photochem. Photobiol., 1981, 33, 727. N. Duran and G. Cliento. Phorochem. Photobiol.. 1980. 32, 113. W. Adam. G . Cliento. and K. Zinner, Phoroc'hem. Phofobiol., 1980, 32, 87. W. Adam, C. Cardilla, 0. Cueto, and L. 0. Rodriguez, J . Ant. Chem. Soc'., 1980, 102, 4802. C. A. Chang, H. H. Pattersen, L. M. Mayer. and D. E. Bause, A n d . Clieni., 1980, 52, 1264. C. C. Kahler and Y. T. Lee, J. Client. Phys., 1980, 73, 5122. P. M. Jeffers and S. H. Bauer, Chem. Phys. Lptt,, 1981,80, 29. D. Neuschafter, C. Ottinger, and S. Zimmermann, Clwn. Phys., 1981,55, 313. L. Lam, D. R. Hastie, B. A. Ridley, and H. 1. Schiff, J . Pliorocheni., 1981, 15, 119. M. Kawasaki, K . Kasatani, and H . Sato. Client. Phys. Let/., 1980, 75, 128. A. H. Laufer, J . Client. Phys., 1980, 73, 49. G . Pdrasbevopoulas and W. S. Nip, Can. J . Chent., 1980, 58, 2146.

30

Photochemistry and CH,O, with NO, NO2, and CH,O, 4 1 1have been investigated using ps flash photolysis. The photolysis of benzyl halides and the subsequent decay kinetics of the benzyl radical have been studied using conventional flash photolysis 412 as have the reactions of benzyl, o-methylbenzyl, and p-methylbenzyl radicals with O2 and NO.413In an investigation of the quenching of NH, by ozone, the radicals were prepared using a flash from a Xe lamp and the system monitored using a 2 5 p pulse from a rhodamine 6G dye laser.414 The electronic spectrum of the 1s6W160 molecule formed by photolysis of W(CO)6 vapour was recorded in the region 260-680 nm.415 Other applications include monitoring the evolution of C1, from NaCl aqueous solutions4'6 and an investigation of the photolysis of purine, an important light-absorbing species in DNA.41

Nanosecond Flash Photolysis Measurements.-A computer-controlled ns flash photolysis spectrometer has been described.418 The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2-3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets.419 A PDP I1 computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe configuration with up to 10011s probe delay.420A method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption Decay times comparable to or shorter than the excitation flash may be determined by this method. For an investigation of the dynamics of fast reactions, such as laser-induced explosions in NH,-ND, mixtures, a time-resolved infrared spectroscopic photographic method has been developed.422 Light from a pulsed dye laser was converted to an infrared continuum by stimulated Raman scattering in a Rb vapour cell. Following absorption the remaining radiation was 'up-converted' to the visible by means of a 4-wave mixing process in a second Rb cell. This visible light was then easily photographed. Many varied laser systems have been used for ns-flash photolysis experiments. For example, the kinetics of the electron-transfer quenching of triplet methylene

''I

'I2 413 414 415

'16 417

''* 419

420

421

422

S. P.Sander and R. T. Watson, J. Phys. Chem., 1980, 84, 1664. F. Bayraceken, Chem. Phys. Lett., 1980, 74, 298. T. Ebata, K. Obi, and I. Tenaka, Chem. Phys. Lett.. 1981, 77,480. V. P.Bukdtov, A. A. Buloyan, S. G. Cheskis, M. Z. Kozliner, 0.M. Sarkisov, and A. I. Trostin, Chem. Phys. Lett., 1980, 74, 288. A. N. Samoilova, Y.M. Efremov, and L. V. Gurvich, J. Mol. Spectrosc., 1981, 86, I . D. Wu, D. Wong, and B. D. Bartolo, J. Pliotocheni., 1980. 14, 303. R. Arce, L. A. Jimenez, V. Rivera, and C. Torres, Photochem. Photobiol., 1980, 32, 91. J. C. Scaiano, J. Am. Chem. Soc., 1980, 102, 7747. P. K. Das and S. N. Bhattacharyya, J. Phys. Chem., 1981, 85, 1391. J. Jasney and J. Sepiol, J . Phys. E., 1981, 14,493. J. C. Scaiano, J. Photochem., 1981, 16, 71. P. Avouris, D. S. Bethune, J. R. Lankard, J. A. Ors. and P. P. Sorokin, J. Chem. Phys., 1981, 74, 2304.

31 blue by iron(1ir) complexes423 and ground-state dye molecules 424 have been studied using a @switched ruby laser at 694.3 nm. A frequency-doubledruby laser was used for a flash photolysis study of the reduction of benzophenone by aliphatic a m i n e ~ The . ~ ~ collisional ~ dissociation of I, by 0, ( b ' Z g + ) was monitored by the appearance rate and amptitude of the transient absorption due to I(,P3,,) using a Nd-YAG-laser-pumped dye laser frequency-converted to 763 nm in a high-pressure H, A nitrogen-laser-pumpeddye laser was used for a pump-probe and a signal-gain measurement of the excited-state absorption properties of the laser dye, POPOP.427 The triplet state of azobenzene was investigated using 3.5 ns pulses at 337.1 nm from a pulsed N, laser.428Intermolecular vibrational energy-transfer rates for highly excited CFjI and the rates of conformational conversion for 2,3-dihydropyran raised to 1400K,430were determined using ns flash photolysis measurements with a pulsed CO, laser. For flash photolysis in the vacuum-u.v. excimer lasers would seem to offer an attractive source. A KrF laser was used for the gas-phase photolysis of benzene at 248 nm.431*432 A Xe lamp was used for a monitoring beam and evidence was presented for transient absorptions in the wavelength region 210-930nm431 and for cluster formation on the ns times~ale.~~, Other applications of laser flash photolysis have included (a) a study of the bimolecular rate constant for the reaction between singlet oxygen and several lipidsoluble substances,433(b) an investigation of quenching, solvent, and temperature effectson the photolysis of in dole^,^^^ (c) the time dependence of the quenching of aromatic hydrocarbons by tetramethylpiperidine N - o ~ i d e , ~and ~ ' (4 the kinetics of the geminate recombination of aromatic free radicals.436 Finally, flash photolysis has been utilized in order to examine the feasibility of a tunable IF laser (479-498 nm) and an IC1 laser (430nm).437 Picosecond Transient Absorption Measurements.-Several picosecond excitation and probe experiments have been recently described. A 0 . 5 ~ spulse from a passively mode-locked dye laser was utilized to excite and subsequently monitor the singlet absorption in tetra~henylethylene.~~' A 5 ps relaxation time, ascribed to twisting around the ethylene double bond, and a long-lived twisted intermediate were observed. The involvement of an intermediate exciplex in the photoinduced hydrogen-atom transfer reaction of pyrene with diphenylamine was demonstrated Developments in Instrumentation and Techniques

4L3 424 425

426 427 428 02' 430

431 432 433 434

435 436 437

"'

T. Ohno and N. N. Lichtin, J . Am. Chem. Soc.. 1980. 102, 4636. P. V. Kamat and N. N . Lichtin. J . Phys. Chem.. 1981, 85. 874. S. Inbar. H. Linschitz. and S. G . Cohen. J . Am. Chem. Soc., 1981, 103, 1049. D. F. Muller, R. H. Young, P. L. Houston, and J. R. Wiesenfeld, Appl. Phys. Lett.. 1981, 38. 404. G. Marowsky and H. Schomburg, J. Photocliem., 1980, 14. 1. S. Monti, E. Cardini, P. Bortolus, and E. Amouyal, Chern. Phys. Lett., 1981, 77, 115. Y . A. Kudriavtsev and V. S. Letokhov, Chem. Phys., 1980. 50, 353. D. Garcia and E. Grunwald, J . Am. Chem. Soc., 1980. 102, 6407. N. Nakashima. H. Inoue, M. Sumitani. and K. Yoshihara. J . Chem. Phys., 1980. 73, 5976. N. Nakashima, H. Inoue, M. Sumitani, and K. Yoshihara, J . Cliem. Phys., 1980, 73. 4693. B. A. Lindig and M.A. J. Rodgers, Photocheni. Photobiol.. 1981. 33. 627. R . Klein, I. Tdtischeff. M. Bazin, and R. Santus, J . Phys. Chem., 1981, 85, 670. J. C. Scaiano, Ciieni. Phys. Lett., 1981, 79, 441. I. V. Khudyakov, Y. I. Kiryukhin, and A. 1. Yasmenko. Cliem. Phys. Lett., 1980, 74, 462. M.Dlabal and J. G . Eden, Appl. Phys. Lett., 1981, 38,489. B. I. Green.Chem. fhys. Lett.. 1981. 79. 51.

32

Photochemistry

using ps time-resolved absorption The sample was excited using the second harmonic of a pulsed ruby laser and probed by a 2ps continuum generated by the laser pulse in a heated polyphosphoric acid solution cell. The probe was detected using a polychromator and photodiode array. The formation of the long-lived transient in trans-thioindigo at 600nm was observed on a ps timescale using transient absorption measurements with a 30 mJ, 6 ps A 5ps pulse from a mode-locked Nd-glass laser was used to excite the first singlet state of rhodamine 6G in ethanol.441 Probing lops later and monitoring the anisotropy of the transient absorption enabled the polarization of the S,-S4 transient moment to be determined. 40 ps pulses from a frequency-doubled ruby laser have been used to probe the excited singlet state absorptions of several laser dyes.442Other pump-probe experiments have observed the 1.6 ps recovery time for the 625 nm charge-transfer absorption band of azurin following bleaching,443and the effects of excess vibrational energy on the cis-trans isomerization of stilbene in A dual beam optical arrangement, with videcon detection, was used to monitor the ps transient absorption spectrum of bathorhodopsin after 150ps and 500 ps following excitation at 347.2 nm.445 Problems that may be encountered due to external birefringence effects in the anisotropic absorption method of Shank and Ippen 446a have been discussed.446b In the event of these interferences being unavoidable, methods have been described to allow the rotational reorientation times of the dye molecules in fluid solution to be determined.446.447 The accumulated 3-pulse stimulated photon-echo method 448a was used in order to monitor vibrational relaxation times of the first excited electronic state of p e n t a ~ e n e . ~ "Two * ~ amplified dye lasers were used to perform ps photon-echo measurements on pentacene and naphthalene samples, which established that pseudo-local photon scattering was responsible for optical dephasing in vibronic transitions.449 A mode-locked cavity-dumped synchronously pumped dye laser system was used to demonstrate long coherence times for the delocalized optical excitation of dimer states, by ps photon-echo

7 Transient Emission Spectroscopy Despite their potential for high time-resolution, phase methods in which the measured phase-lag between the fluorescence and the modulated excitation source T. Okada, N . Tashita, and N . Mataga, Chem. f h y s . Lett., 1980, 75. 220. S. A. Krysanov and M. V . Alfimov. Chem. f h w . L e f t . . 1980. 76. 221. "I A. Penzkofer and J. Wieldmann, Opt. Conimun.. 1980, 35. 81. ldZ D. Magde, S. T . Gaffney. and B. F. Campbell. IEEE J . Qunrituni. Electron., 1981. 17. 489. J . M . Wiesenfeld. E. P. Ippen. A. Corin, and R . Bersohn. J . An?. Chent. Soc., 1980, 102. 7256. 444 F. E. Doany. B. I . Greene. and R. M . Hochstrasser, Chent. fhys. Lett., 1980. 75, 206. 445 K . Suzuki. T. Kobayashi. H. Ohtani. H. Yesaka, S. Nagakura. Y . Shichida, and T . Yoshizawa, 43y 440

44b

'" "" 'Jq

""

Pliotoc.lier?t. Pliotohiol.. 1980. 32. 809. C . v. Shank and E. 1. Ippen. Appl. Pliys. Lett.. 1975.26.62; C. V. Shank, E. P. Ippen, 0.Teschke, and K. B. Eisenthal. J . CIiem. P l i ~ s . 1978, , 67. 5547: ( h )D. Waldeck. A. J. Cross. D. B. McDonald. and G. R . Fleming. J . Chem. fliys.. 1981. 74. 3381. G. S. Beddard and M . J . Westby. Cltrrii. Pliys.. 1981. 57. 121. ( ( I ) W. H . Hesselink and D. A. Wiersma. f1ij.s. Rev. Lvit., 1979.43. 1991; ( h )J . Client. fhys.. 1981.74. 886. W. H. Heshelink and D. A. Wiersina, J . Clieni. fh,w..1980. 73. 648. R . W. Olson. F. G. Patterson. H. W. H . Lee. and M. D. Fayer. Cheni. f1iy.v. Lett.. 1981. 79, 403.

(N)

Developments in Ins t rumenrut ion und Techniques

33

is utilized in order to evaluate the emission decay time, seem to have been little used. One problem has been the inability of the method to identify heterogenous fluorescence decays. However, methods involving the use of n different modulation frequencies promise to overcome this disadvantage and enable resolution of n component fluorescence decays.45 The technique has been applied to the heterogenous decay of tryptophan in solution.452 Slifkin and Darby have presented a theory for the analysis of double and triple exponential decays measured using the phase and modulation method.453 The authors predict that the technique should be capable of resolving 4-component decays also. Time-resolved single-photon counting (SPC) remains by far the most popular method for measuring fluorescence decay times occurring on the nanosecond and subnanosecond time scale. Conventionally the sample is excited using a nanosecond spark discharge lamp. For example, a flashlamp-SPC system was used for several drugs such as benzimidazoles and barbiturates, showing that time-resolved fluorescence measurements enable similar species to be identified.454 Nonexponential fluorescence decays are easily identified and analysed by the conventional SPC technique. For example, heterogeneous decays were observed for phthalimides in polar vitrifying solutions 4 5 5 and tryptophan at pH values less than 7.456 However, the low intensities available from nanosecond spark discharge lamps have precluded high wavelength resolution of fluorescence decays, and many uses of more intense high stability CW pulsed lasers for excitation for SPC have been reported. For example, frequency-doubled, cavity-dumped synchronously pumped mode-locked dye lasers have been used for excitation in the wavelength region around 300nm.457-459A CW mode-locked (not cavitydumped) laser was used for sub-nanosecond decay time The usual end-on photomultiplier tube was replaced by a side-on tube and ic comparators were used in place of constant fraction discriminators. The photophysics of aqueous tryptophan were studied using a CW pulsed dye laser, with pulse selection using a Pockels cell and SPC detection.461 One disadvantage of laser excitation sources is their limited tunability and so, for a study of the timeresolved fluorescence from NO fragments resulting from the photolysis of methyl A relatively simple method for nitrite, a synchrotron radiation source was deriving dual fluorescence decay times using SPC, applicable when the two decay times are well separated, has been The various methods available for

'

"'

"' 453

454

G . Weber, J . Phys. Chem.. 1981. 85, 949.

G . Weber and D. M. Jameson, J . Phys. Chem.. 1981. 85. 953. M . A. Slifkin and M . 1. Darby. J . Phys. E., 1980. 13. 896. L. J. Clinelove and L. M. Upton. Anal. Chini. A m , 1980. 118, 325. V. T. Koyava. V . S. Pavlovich. L. G. Pikulik. V. I. Popechits, and A. M. Sarzhevskii, Opt. Spektrsk., 1980. 49, 296.

"' E. Gudpin. R. Lopez-Delgado. and W. R . Ware. Crm. J . C'llcm., 1981. 59, 1037. 45A. C . Jones. K . Janecka-Sturcz. D . A. Elliot, and J . 0. William. Client. Pliw. k t l . , 1981, 80, 413. R. M . Brewer and M. Nicol. J . Lumin., 1980, 21, 367. jS9A. K. Jameson and E. C. Lim. Clwm. Phys. Lett., 1981, 79, 326. 4h0 S. Kinoshita. H. Ohta. and T. Kushida. Rev. Sci. Instrum.. 1981. 52, 572. 461 R. J . Robbins, G . R. Fleming, G. S. Fkddard, G . W. Robinson, P. J. Thistlethwaite, and G. J. Woolfe. J . Ant. Client. Soc.. 1980, 102, 6271. F. Lahmani. C. Lardeux. and D. Solgadi. J . Cliem. Phys., 1980. 73, 4433. 463 T. Wilson and A. M . Halpern. J . Am. Cliem. Sot.., 1980. 102, 7272.

34

Photochemistry

the measurement of wavelength- and time-resolved fluorescencespectra have been critically The measurement of the time-dependentdepolarization of the fluorescencefrom molecules rotating on a time-scale comparable to the fluorescence decay time, enables information to be derived concerning the molecular reorientation motion. A review of these techniques has been published.46sA method involving an optical delay line has been used to record time-resolved fluorescence depolarization methods using only 1 photodetector, and thus some of the possible instrumental distortions are removed.466 The apparently straightforward method of monitoring the fluorescence using a fast photomultiplier tube with the output displayed on a storage oscilloscope still finds many applications. For example, the fluorescence from pyrene samples excited using a frequency-doubled ruby laser and quenched with added multivalent metal ions,467 and the emission polarization anisotropy and fluorescence decay for several dyes excited using a pulsed argon ion have been investigated using this method. An extension of this technique involves the use of a transient digitizer in place of the storage oscilloscope.469- 4 7 1 For fluorescence decay measurements down to a few picoseconds, streak cameras have been extensively used. A synchronously pumped dye laser was used, in conjunction with a synchronously scanned streak camera, to measure dual component fluorescence decays from polymethine dyes with ps re~olution.~’~ Although synchronously scanned streak cameras together with CW mode-locked dye lasers, offer the highest time resolution, the majority of experiments of this type employ ‘single-shot’excitation (invariably using the second or third harmonic of a mode-locked solid-state laser). In this case, a significant reduction in the time jitter associated with the streak deflection may be achieved using a laser-activated cryogenic Si-switch to trigger the camera.473 The increased stability enabled several hundreds of laser ‘shots’ to be averaged and, even with 20ps excitation pulses, fluorescence decay times as short as 2ps were resolved. A pulsed laser-streak camera system has been proposed for quantitative f l ~ o r i m e t r y .47~ ~ ~ ’ Some applications of time-resolved fluorimetry using streak cameras will now be considered in order to illustrate the various possibilities available to the photochemist. The ps decay of the acridine singlet state has been determined as a function of temperature 476 and solvent 477 using the third harmonic of a mode464

465 466 467 460 469

470 471 472

473 474

475 476 477

s. R. Meech, D. V. O’Connor, A. J. Roberts, and D. Phillips, Photochem. Photobiol., 1981,33, 159. K. P. Ghiggino, A. J. Roberts, and D . Phillips, Adv. Polym. Sci., 1981, 40,66. R. W. Winaendts van Resandt, and L. DeMaeyer, Chem. Phys. Lett., 1981,78, 219. F. Grieser and R. Tausch-Treml, J . Am. Chem. Soc., 1980, 102, 7258. R. K. Bauer and A. Balter, Opt. Commun., 1980,34, 379. G. E. Berovic, Z. Ludmer, and L. Zeiri, Chem. Phys. Lett., 1981, 80, 409. W. W. Rice, R. C. Oldenborg, P. J. Wantuck, J. J. Tiee, and F. B. Wampler, J. Chem. Phys., 1980,73, 3560. R. G. Aviles, D. F. Muller, and P. L. Houston, Appl. Phys. Lett., 1980, 37, 358. D. Welford, W. Sibbet, and J. R. Taylor, Opt. Commun., 1980,34, 175; W. Sibbett, J. R. Taylor, and D. Welford, IEEE J. Quantum. Electron., 1981, 17, 500. M. Stavola, G. Mourou, and W. Knox, Opt. Commun., 1980, 34, 404. G. L. Walden and J. D. Winefordner, Spectrosc. Lett., 1980, 13, 785. G. L. Walden and J. D. Winefordner, Spectrosc. Lett., 1980, 13, 793. S. L. Shapiro and K. R. Winn, J. Chem. Phys., 1980,73, 1469. S. L. Shapiro and K. R. Winn, J . Chem. Phys., 1980,73, 5958.

Developments in Instrumentation and Techniques

35

locked Nd-YAG laser for excitation. Time-dependent fluorescence shifts and spectral shape changes together with non-exponential fluorescence decays for tetraphenylethylene in solution were observed using a frequency-tripled modelocked Nd-glass laser, with 5 ps time resolution.478Steady-state spectra were recorded under identical experimental conditions using a videcon and optical multichannel analyser. Similar laser-streak camera systems were employed in studies of (i) intramolecular exciplex formation between anthroyl and amine moieties,479* 480 (ii) excited-state relaxation and proton-transfer effects for 2-(2hydroxyphenyl)-benzothiazole,48 (iii) photodissociation of diphenyl diazomethane and subsequent energy relaxation in the diphenylcarbene fragment,482and (iv) the effects of the excitation pulse intensity on the quantum yield and fluorescence decay of phyc~biliproteins.~~~ A three-pulse technique using a synchronously pumped mode-locked dye laser together with a modified Michelson interferometer has been described.484By this technique, ps fluorescence decay times may be evaluated without the disadvantages of up-conversion or Kerr cell methods. The suitability of the system for the analysis of low. optical quality samples was suggested. An injection mode-locked Nd-YAG ring laser was used as an excitation source for a zero-background fluorescence study of the time evolution of the emission from large hydrocarbons with 12ps resolution.485 Correlation based approaches to time-resolved fluorimetry have been reviewed by Hieftje and H a ~ g e nDespite . ~ ~ ~the apparent low costs of the equipment and the reasonable time resolution, little application of the methods were evident. Single exponential time constants for emission decays may be determined simply using two discriminators set at different levels.487The time delay between the triggering times allows computation of the lifetime. A dual beam amplitudemodulated method has been described in which ns fluorescence decays may be compared with 20 ps time resolution.488Asano and Koningstein have suggested that a consideration of the dependence of the sample transmission upon laser intensity may allow evaluation of the fluorescence decay time.489 A method for measuring fluorescencequantum yields and cascade free lifetimes for open shell cations has been reported. The lifetimes are calculated from the coincidencebetween undispersed fluorescencephotons and energy selected photoe l e c t r o n ~ . ~A~similar * system has been used to evaluate the fluorescence lifetimes of CO,+ and CSz+,491and fluorobenzene cations.492 478

479 480 481 48f

483

484 485 486 40’

488 489 490 491

492

P. F. Barbara, S. D. Rand, and P. M. Rentzepis, J . Am. Chem. Soc., 1981, 103,2156. M. K. Crawford, Y. Wang, and K. B. Eisenthal, Chem. P h y ~Lett., . 1981, 79, 529. Y. Wang, M. K. Crawford, and K. B. Eisenthal, J . Phys. Chem., 1980,84, 2696. P. F. Barbara, L. E. Brus, and P. M. Rentzepis, J. Am. Chem. SOC.,1980, 102, 5631. C. Dupuy, G . M. Korenowski, M. McAuliffe, W. M. Hetherington, and K. B. Eisenthal, Chem. Phys. Lett., 1981, 77, 272. D. Wong, F. Pellegrino, R. R. Alfano, and B. A. Zilinskas, Phofochem. Phorobiol., 1981, 33, 651. H. Mahr, A. G. Sagan, C. P. Hemenway, and N. J. Frigo, Chem. Phys. Letr., 1981.79, 503. K.-J. Choi, B. P. Boczar, and M. R. Topp, Chem. Phys., 1981, 57, 415. G . M. Hieftje and G . R. Haugen, Anal. Chem., 1981,53, 755A. W. P. Carver, Rev. Sci. Insrun., 1981, 52,607. H. Gugger and G . Calzaferri, J . Phofochem., 1981, 16, 31. M. Asano and J. A. Koningstein, Chem. Phys.. 1981,57. 1. J. P. Maier and F. Thommen, Chem. Phys., 1980, 51, 319. R. C. Dunbar and D. W. Turner, Chem. Phys., 1981,57. 377. J. P. Maier and F. Thommen, Chem. Phys., 1981,57, 319.

36

Photochemistry

Criteria for evaluating the degree of fit between measured fluorescence decay curves and trial decay functions have been 494 In some instances plots of weighted residuals were found to be sufficient, but a generalized statistical test was proposed for all other cases.493An analysis of the statistical distribution of noise in fluorescence decay measurements by SPC has shown, as expected, that Poisson statistics dominate.495A method for obtaining decay information from pulse fluorimetry without the need for consideration of the excitation pulse, has been described.496

8 Chemical Techniques Of the vast number of reports concerning photoinitiated chemical reactions, the majority have involved the use of conventional Xe and Hg lamps for excitation and thus offer little of interest to a review of recent developments in instrumentation for photochemistry. consequently, this discussion will concentrate mainly upon the use of novel excitation sources, especially lasers. For excitation in the vacuum-u.v. region, several atomic resonance lamps have been employed. Hg, Zn, and Cd emission lines were used in the photolysis of gaseous tetramethylethylene over the excitation range 185-230 nm.497 The photolysis of methylsilane (at 147 nm) 498 and pent-1-ene (at 123.7 nm) 499 was performed using xenon and krypton resonance lamps, respectively. Synchrotron radiation is also a useful source for the vacuum-u.v. The photodissociation of nitrates and CF3N0 in the wavelength range 120-170nm was performed using such a source.5oo The photodissociation of C H 3 0 N 0 (1 10-160 nm) and ozone (170-240) has also been achieved using a synchrotron source. A short review of laser-induced chemical processes has been presented by L e t o k h ~ v In . ~many ~ ~ instances photolysis using lasers leads to products which differ from those found using conventional excitation. For example, new products were observed following the KrF laser excitation of diphenyldiazomethane and tetraphenyloxirane and following the ps photodecomposition of protoporphyThe photolysis of SF, using both a u.v.(ArF) excimer laser and an rin IX.505 i.r.(COJ laser resulted in enhanced photodissociation when compared with results obtained using only U.V. excitation.506 Excimer lasers seem to be gaining popularity as excitation sources for photochemistry. ArF lasers (operating at 193nm) have been employed in studies of the photodissociation of chloroethyl493 494

495 496 49 7 498 499

503 ’04

505

J. A . Irvin, T. I. Quickenden, and D. F. Sangster, Rev. Sci. Instrum., 1981, 52, 191. D. V. O’Connor. A. J. Roberts, and D. Phillips, Ann. N. Y . Acud. Sci., 1981, 366, 109. A. Andreoni, R. Cubeddu, S. desilvestri, and P. Laporta, Rev. Sci. Instrum., 1981, 52, 849. J . Rickd, Rev. Sci. Instrum., 1981, 52, 195. G. J . Collin, H. Deslauriers, and A . Wieckowski, J . Phys. Chem., 1981, 85, 944. P. A. Longeway and F. W. Lampe, J . Photochem., 1980, 14, 31 1. J. Niedzielski and J. Gawlowski, J . Phorochem., 1980. 14, 323. F. Lahmani, C. Lardeux, and D. Solgadi, J . Phorochem., 1981, 15, 37. F. Lahmani, C. Lardeux, M. Lavollee, and D. Soligadi, J . Chem. Phys., 1980, 73, 1187. L. C. Lee, G . Black, R. L. Sharpless, and T. G . Slanger, J . Chem. Phys., 1980, 73, 256. V. S. Letokhov, Phys. Today, 1980, 33, Nov., 34. N. J. Turro, M. Aikawa, J. A. Butcher, and G . W. Griffin, J. Am. Chem. SOC.,1980, 102, 5127. T. I. Karu, P. G . Kryukov, V. S. Letokhov, Y. A. Matveetz, and V. A. Semchishen, Appl. Phys., 1981, 24, 245. J. J. Tiee. F. B. Wampler, and W. W. Rice, Chem. Phys. Lett., 1980, 76, 230.

Developments in Inst rument at ion and Techniques

37

enes '07 and H2S and D2S.'08 Fe(CO),(PF,),, Fe(CO),(PF&, and Fe(CO),PF, species were identified as products following the photolysis of Fe(CO),-PF, mixtures using a KrF excimer laser at 248 nm.'09 The photodissociation of dimethylnitrosamine using a XeF laser was also investigated.' l o The photolysis of CH212and 1,1-C2H412using a frequency-doubled dye laser was found to produce I, as a significant photoproduct. However, the primary photolysis step was shown to be the production of I atoms. The self-sensitized photo-oxidation of potassium rubrene-2,3,8,9-tetracarboxylatewas investigated using the 488 nm output from a CW argon ion laser.512 The multiphoton i.r. laser-induced decomposition of [2H6]-acetonewas studied in order to check the applicability of the 'classical' thermal decomposition mechanism to account for the observed products. A discharge flow apparatus, together with a grating tuned C 0 2 laser, was used in an investigation of 13C isotope enrichment.' l 4 The initial selectivity achieved upon excitation of '2CH,F-13CH3F mixtures was maintained in the excited vibrational state even following molecular collisions. A frequency-doubled dye laser was used to investigate the high-resolution absorption spectra for 14CH20 and 12CH,0 between 290 and 345r1m:"~ thirty lines suitable for selective photolysis of 14CH20were determined. A monoisotopic lamp was used for the separation of the rare lg6Hg isotope by hydrogen halide scavenging of excited Hg(,P,) atoms: 22% enriched samples could be prepared at a rate of 23 mg h-'.'16 The i.r. multiphoton decomposition of enriched "BCl, and "BCl, was investigated using the output from a TEA-C02 laser at 944.2cm-1.517 The ratio of decomposition rates determined for the pure enriched samples was found to be greater than for naturally occurring BCl,, owing to vibrational energytransfer effects. The kinetics of the multiphoton excitation of BCl, and subsequent reaction with H2S were determined using a TEA-C02 laser.' l 8 Isotope selectivity was found to be increased with incident energy. A 250mJ pulse from a C 0 2 laser was used to decompose UF, in a UF,-SF6 mixture.519Care was taken to adjust the laser fluence to 1 Jcm-2 so that multiphoton ionization could occur without dielectric breakdown of either species. Problems may be encountered in photochemical synthesis when high concentrations of reactants are used. So it is interesting that the yield of reactions at low concentrations of reactants has been increased, without the usual disadvantages, using a poor solvent for the reactants and a conventional dynamic reactor.520

''

'

'I0 511

513

'" 'I4

'16 517

"' 519

s20

M. G. Moss, M. D. Ensminger, and J. D. McDonald, J. Chern. Phys., 1981,74, 6631. W. G. Hawkins and P. L. Houston, J . Chem. Phys.. 1980, 73, 297. G. Nathanson, B. Gitlin, A. M. Rosan, and J. T. Yardly, J . Chem. Phys., 1981, 74, 361. G. Geiger, H. Stafast, U. Bruhlmann, and J. R. Huber, Chem. Phys. Left., 1981,79, 521. G. Schmitt and F. J. Comes, J . Photochem., 1980, 14, 107. J. M. Aubry, J. Rigaudy, and N. K. Cuong, Photorhem. Photobiof., 1981, 33, 155. W. Brdun and J. R. McNesby, J . Phys. Chem.. 1980, 84, 2521. D. S. Y. Hsu and T. J. Manuccia, Chem. Phys. Lett., 1980, 76, 16. R. E. M. Hedges, P. Ho, and C. B. Moore, Appl. Phys., 1980. 23, 2 5 . C. R. Webster and R. N. Zare, J . Phys. Chem.. 1981, 85, 1302. Y. Ishikawa, 0. Kurihara, R. Nakane, and S Arai. Chern. P h ~ s .1980, , S2, 143. K. Takeuchi, 0. Kurihdra, and R. Nakane, Chem. Phvs.. 1981,54. 383. R. S. Karve, S . K. Sdrker, K. V. S. Rama Rdo, and J. P. Mittal, Chem. Phys. Letr., 1981, 78, 273. P. Boule, J.-P. Jedndrau, J.-C. Grdmain, and J. Lamaire, J . Photochem., 1981, 16, 67.

38 Photochemistry Methods have been proposed to enable the determination of quantum yields for chemical reactions in solution for the case where the photoproducts also compete for the excitation light.”l An interesting technique has been developed for the determination of the kinetics of photochemical reactions using holography. 522 The time course of the reaction is monitored by measuring the growth of an interference pattern in the sample caused by the overlap of two laser beams. The method has been used to study the two-photon dissociation of dimethyl-sym-tetrazine 5 2 3 * 524 and the hydrogen-abstraction reaction benzophenone in a poly(methylmethacry1ate) matrix.523.5 2 5

sz2

523

“‘ 52s

N . J . Bunce. J. Pliotocliem., 1981 15, I . D. M . Burland. G . C. Bjorklund, and D. C. Alvarez, J . Am. Chem. SOC.,1980, 102, 7117. G. C. Bjorklund, D. M . Burland, and D. C. Ahdrez, J . Chem. fhys., 1980, 73, 4321. C. Brauchle. D. M. Burland. and G. C. Bjorklund, J. Am. Chem. SOC.,1981, 103, 2515. C. Brauchle, D. M . Burland, and G. C. Bjorklund. J. Phys. Chem., 1981,85, 123.

2 Photophysical Processes in Condensed Phases BY R. B. CUNDALL AND

M. W.

JONES

1 Introduction

The year under review has shown continual progress in elucidating the detailed behaviour of excited singlet and triplet states. This has been largely due to the improvement of experimental equipment especially in the very short time domains. The need for a complete understanding of photophysical processes in any application of excited-state properties is now fully accepted, particularly in analytical applications of luminescence and biochemistry. 2 Singlet-state Processes The number of theoretical papers attempting to provide a unified explanation of experimental data appears to have declined. This may be due to the fact that excited states are more difficult to describe theoretically because electron correlation plays a more important role. Schweig and Thiel show that the MNDOC treatment is superior to other methods although application to photochemical problems requires caution. One of the relatively few papers dealing with radiationless transitions is that of Sarai and Kakitani in which the effect of a large nuclear rearrangement is investigated. This would appear to be an important advance on most of the theories published hitherto. In the condensed phase the effect of the environment is of great importance and an interesting review has been provided by Kasha et a/.’ Myers and Birge4 have derived a simple expression for the effect of solvent on the oscillator strength of a solute, which involves the refractive index of the solvent and another factor depending on the molecular shape and orientation of the transition moment. The theory successfully predicts the effect of solvent polarizability on the oscillator strength of the n* t n transition of p-carotene and the n* t n transition in p yrazine. During the year under review there has been more emphasis on the improvement of experimental technique than theory. Bunce’ has analysed the determination of quantum yields for reactions, particularly those in which excimers may be involved. The measurement of fluorescence quantum yields is not generally

’

A. Schweig and W. Thiel, J . Ant. C l i m . Sot.. 1981, 103, 1425. A. Sarai and T. Kakitani, Chrrti. Plijx. Loti.. 1981. 77. 427. M. Kasha. B. Dellinger, and C. Brown, Bioluminescence and Chemiluminescence, Basic Chemistry and Analytical Applications, ed. M. de Luca and W. D. McElroy, Academic Press,New York, 1981, p. 3. A. B. Myers and R . R. Birge. J . Clirwi. P h ~ x 1980, , 73, 5314. N . J. Bunce. J . Photoc.ltem.. 1981. 15. I .

39

40

Photochemistry

very accurate for various reasons. Arbeloa has presented a method for correcting for the effects of re-absorption and emission which he has applied to the fluorescein dianion. Photoacoustic spectroscopy would appear to offer many advantages for measuring the luminescence quantum yields, especially in solid systems. The potential of the technique has been demonstrated by Kirkbright and co-workers who have measured the luminescence quantum efficiency of 1,1,4,4tetraphenylbuta- 1,3-diene, Yellow Liumogen, and sodium salicylate with an accuracy of about 1%. A critical examination of the technique has been made by Cahen, Garty, and Becker in experiments made with concentrated solutions of sodium fluorescein and cresyl violet perchlorate. The application of the microcomputer to the problems of fluorescence data acquisition is clearly appropriate. A detailed account of a system for determination of corrected, derivative, and differential spectra and quantum yields shows how the commonly used methods can be i m p r ~ v e dAnother .~ paper describes the use of microcomputer to shift the position of fluorescence sample cell. l o The ability to handle large amounts of data increases the information available and this is well illustrated by the resolution of overlapping emission spectra accomplished by increasing the dimensionality of the use a fluorescence decay time-emission measurement. Knorr and Harris wavelength data matrix to do this. Time-resolved emission spectra are potentially one of the most informative of all photophysical measurements. Experimental and computational aspects are assessed in the paper by Meech et a/.’ Lahri l 3 has reviewed the determination of acidity constants in excited singlet states as well as providing an extensive compilation of pK* data. Schulman, Vogt, and Lovell l4 have measured rate constants for the protonation of the excited base and deprotonation of the weak base acridone by fluorimetric titrations in moderately concentrated acid media using bromide ion as a quencher. An unusual suggestion that photochemical processes can be influenced by surface conditions has been made by Nitzan and Brus.” The effect is not unexpected if a model in which a dipole interacts with a dielectric sphere is assumed. This paper draws attention to the possibility that photochemistry at interfaces may proceed differently from the homogeneous counterpart. Environmental pollution requirements have been responsible for the interest in analysis of polyaromatic hydrocarbons (PAH). John and Soutar l 6 have reviewed the problems of using luminescence techniques for examination of oil spill. Various methods have been devised to deal with the analysis of complex mixtures involved. Synchronous fluorescence is a useful method using comparatively simple equipment. Rank annihilation methods applied to data acquired as an

’’

I. L. Arbeloa. J . Pliotocheni., 1980. 14, 97.

’ M . J. Adams, J. G . Highfield, and G. F. Kirkbright. A t i d . C l i m . , 1980. 52, 1260. lo

I’

l3 l4

l6

D . Cahen, H. Garty. and R. S. Becker. J . P h j x Clierii.. 1980. 84. 3384. A. W. Ritter, P. C. Tway, L. J. Cline Love, and H . A. Ashworth, A n d . Chetii.. 1981. 53, 280. D. R . Christman, S. R. Crouch, and A. Timnick. A t i d . Cliwi.. 1981, 53, 276. F. J. Knorr and J. M. Harris. A n d . Client.. 1981. 53. 272. S. R . Meech, D . V. O’Connor, A . J. Roberts. and D. Phillips, Pliotockcw. Photohiol.. 1981. 33. 159. S. Lahiri. J . Sri. Ind. Res.. 1979. 38, 492. S. G. Schulman, B. S. Vogt, and M. W. Lovell. Clioii. Pli.~*s.Lett.. 1980, 75, 224. A. Nitzan and L. E. Brus, J . Client. Phj*s.. 1981, 74, 5321. P. John and 1. Soutar. C l i ~ mBv.. . 1981. 278. J . B. F. Lloyd. I . W. Evett. and J. M. Dubeny. J . Foretisic Sci.. 1980, 25, 589.

Photopliysicai Processes in Condensed Piiuses

41 emission-excitation matrix have been successfully applied to six-component mixtures and the methodology clearly defined in a paper by Ho et a1.’* The analytical problems are considerably reduced by the application of high-pressure liquid chromatography. The recently published volumes of ‘Modern Fluorescence Spectroscopy’, edited by Wehry,’ review this and other topics in fluorimetry. Spilled oil characterization2’ and shale oil2 have been examined. Compounds other than PAH (polycyclic aromatic hydrocarbons) may also be analysed, e.g. nitrogen heterocycles.22A full analytical procedure is given by Colin and V i ~ n . ~ ~ The quantitative possibilities are enhanced by the high spectral resolution that can be achieved by using Shopolski s p e c t r o ~ c o p yThis . ~ ~ is facilitated by the use of laser fluorimetric detection:25selectivity and sensitivity are improved by this technique and two-photon excitation increases the spectroscopic range. The sharp-line absorption spectra (full width at half maximum of 1-1 0 cm- ’) facilitate selective excitation with a tunable dye laser 26 and a series of multialkylated aromatic isomers has been examined. Figures 1 and 2 show this for benz[a]anthracene and alkylated derivatives in n-octane. Maple and Wehry 2 7 have detailed the technique further by examination of several hydroxynaphthalenes. Much greater spectral resolution is obtained in vapour deposited annealed n-heptane deposits and the full potential of laser tunability can be achieved.28 Laser excitation has also been used for the application of time-resolved fluorescence to h.p.l.~.,~’ using different delays it has been shown possible to detect 5-5Ofmol quantities of PAH. Fluorescence polarization methods have been long used for characterization of excited states and examination of molecular dynamics. Development of techniques, both instrumental and computational, have extended their areas of research during the course of the recent year. Johansson and Lindblom 30 have reviewed the state of the art for measurements the orientation and mobility of molecules in membranes studied by polarized light spectroscopy. Liquid crystals provide excellent media in which to study the effects of chromophore ordering as well as providing model systems for biological situations. Theoretical analyses have been given by N a q ~ i , and ~ ’ Dozov and P e n ~ h e vA. ~method ~ for measuring second rank order parameters using fluorescence detected linear dichroism has been described 3 3 Stretched poly(viny1 alcohol) films have been used for similar studies on anisotropic systems. A comparison of films and systems studied has

’” IY

’’ ’’ ”

23

” ” ” ” ” ”

’’

30 j2

3-3

C.-N. Ho. G . D. Christian. and E. R. Davidson. A i i d . C h i l i . . 1980, 52. 1071. P. Froechlich and E. L. Wehry, Modem Fluorescence Spectroscopy’, Plenum Press, New York and London, 1981, Vol. 3, p. 35. K . Higashi and K . Hagiwara, Friwniirs‘ Z : A n d . Cliivti.. 1980. 302, 281. R. J . Hurtubise and J . D . Phillip, A m / . Cltini. Acro, 1979. 110, 245. C. D. Ford and R. J . Hurtubise. A n d . Lrit.. 1980. l3(A6). 485. J . M . Colin and G . Vion, Antrlirsis. 1980. 8. 224, J . M. Colin, G . Vion. M. Lamotte. and J. Joussot-Dubien. J. Cliroriiotogr.. 1981. 204, 135. E. S. Yeung and M . J. Sepaniak. A n d . Clicwr.. 1980. 52. 1465A. Y. Yang. A. P. D‘Silva. and V. A. Fassel. A n d . C/IPI?I.. 1981. 53, 894. J. R. Maple and E. L. Wehry. A n d . Clieni.. 1981, 53. 266. J. R. Maple. E. L. Wehry. and G . Mamantov. Alitrl. C h i i . . 1980, 52. 920. J. H. Richardson. K . M. Larson. G . R. Haugen. D. C. Johnson. end J . E. Clarkson. Aiitrl. C h h . At,tci. 1980, 116, 407. L. B.-A. Johansson and G. Lindblom. Qiuir/. Rev. Bioph~-s.,1980. 13, 63. K . R. Naqvi. J. Clicw. f l t j x . 1981. 74, 2658. 1. N . Dozov and I. 1. Penchev. J. Lutiiiii.. 1980. 22. 69. L. B.-A. Johansson. G. Lindblom. and K . R. Naqvi. J . Cliwi. Plij..s.. 1981. 74. 3771.

42

Photochemistry

i n s -366.5

R, L

nm

I----------1

I 6.8-DM-

B (01 A

t

A 2

t

L

W

2 a w

a Il-M-B to1 A

1

1

1

I

1

370

365

]

,

315

,

,t

L

I

I 385

1

I

390

WAVELENGTH Inm) EXCITATION SPECTRA EMISSION SPECTRA

Figure 1 Selectively e.wited.f[uorescencespectra of the individual components in a misture of 6,8-dimetli~~lhenz[a]anthracene and 1 I -metkylhen~[u]anthracene in n-octane (Reproduced by permission from Anal. Chew., 1981. 53. 896).

8

I

383

1

1

1

385

387

1

7

1

6.

1

I

389.

WAVELENGTH

391 396

398

400

Inm)

Figure 2 Spectral positions of 0-0 nzultiplets of benzralanthracene and several alkylated henz[a]anthracenesin n-octane (Reproduced by permission from Anal. Cltem., 1981, 53. 896).

Photopliysicul Processes in Condensed Pliusa

43 been made by Fiksinski and F r a ~ k o w i a kThe . ~ ~polarized absorption and emission of chlorophyllin, phycoerythrobilin, and phycocyanobilin in stretched poly(viny1 and a alcohol) films,'35the effect of photoselection in uniaxial liquid general theory of polarized fluorescence emission in uniaxial crystals have also been presented. In liquid crystals the physical properties of a solute become anisotropic, and the effect of this is the circularly polarized fluorescence (CPF) of achiral molecules dissolved in cholesteric liquid crystals. The CPF of perylene, pyrene, azulene, and diphenylhexatriene have been examined by Stegemeyer et ~ 1 . ~Two-photon ' processes in uniaxial samples have been discussed by Michl and T h ~ l s t r u pPhotophysical .~~ studies have been assisted by various types of systems that use lasers, for example, a system capable of generating 2ps duration pulses from 400-700nm using a CW dye laser tuned and actively mode-locked by an interfer~meter.~'Absorption and emission processes can be made by optical molecular dephasing with coherent laser s p e c t r o ~ c o p yThe . ~ ~ techniques by which subpicosecond light pulses can be applied to the problems of chemistry, physics, and biology have been reviewed.42Walden and Winefordner 44 have illustrated the use of the streak camera for quantitative fluorometry and time-resolved fluorimetry. The use of pressure as a variable is becoming increasingly exploited and the review of high-pressure luminescence in liquids, polymer films, and crystalline studies by Drickamer 4 5 surveys the effects on radiative and non-radiative processes. An interesting example is the study of the polarization of the intrinsic fluorescence and fluorescence of dansyl conjugates of en01ase.~~ The effects of pressure on the fluorescence spectra and polarization are shown in Figures 3 and 4. The increase of hydrostatic pressure promotes the formation of dimers. The authors point out that the pressure perturbation of fluorescence polarization is a method of general applicability to studies of protein aggregation and it can also be of value in characterizing the effect of ligands on the aggregation of oligomeric proteins. Pulse fluorometry has been favoured over phase techniques since hitherto no general method has been available for determining the proportions and lifetimes of fluorescence components in complex systems. Weber 47 has presented an exact solution of the problem using the values of the phase shifts and relative modulation of the overall fluorescence of as many light-modulation frequency as there are components. The simplicity and speed of the numerical methods involved 433

34 35 36

3' 38 39

*' 42

43 44 O5

46 47

K . Fiksinski and D. Frackowiak. Spectrosc. Lett., 1980, 13, 873. D. Frackowkak, K . Fiksinski, and H. Pienkowska. Pliotocheni. Photohiol., 1981, 2. 21. K. R. Naqvi, J. Chem. Phys., 73,3019. A. Szdbo, J . Clieni. PI~JY..1980, 72. 4620. H . Stegemeyer, W. Stille, and P. Pollmann. Isr. J . Clietii.. 1979. 18, 312. J . Michl and E. W. Thulstrup. J . Clieni. PIixs.. 1980. 72, 3999. E. E. Mariner0 and F. P. Schlfer, Appl. Pli,vs.. 1980, 23, 135. A. H . Zewail, Ace. Cliem. Rcs., 1980, 13, 360. C . V. Shank. E. P. Ippen, R. L. For, A. Migus. and T. Kobayashi, Pliilos. Trrins. R. Soc. London. Ser. A, 1980. 298. 303. G. L. Walden and J. D . Winefordner. Spectrosc. Lett., 1980, 13. 785. G . L. Walden and J . D . Winefordner, Spectrosc. Lett.. 1980. 13, 793. H . G. Drickamer, Rev. Pliys. Cliem. Jpn.. 1980, 50, I . A. A. J. Paladini and G . Weber. Bioclieni.. 1981, 20. 2587. G. Weber, J . P1i.w. Cliem.. 1981. 85. 949.

44

X

(nm)

Red s h i f i s of .f/iiori~.s(’ptii’(i spectrti of‘ m o l ~ i . stnuintuincd ~ ut room tetiipc~roture. inhrcctl bj. chnge,s in ionic stroigth iind prcssurcJ. ( - ) EnoImt’, 5 x 10- M. in 0.05 M Tris, pH 7 . 0 ; (- - -) cwolme. 5 x lo-‘ M, in 0.05 M - Litid 1 M-KCl, pH 7 . 0 (nortiicrli:ctl); (-.-) cviolosr. 5 x M,in 0.05 M Tris, pH 7 . 0 , tit 2 kbar. i,, = 980 nm (Reproduced by permission from Biodietiiistrj-. I98 I. 20. 2587). Figure 3

!

in the phase-shift method should stimulate the use of this method especially in biological systems, which are virtually always heterogeneous. Aliphatic hydrocarbons are not the subject of extensive photophysical investigation in spite of unique character of 0 electron excitation involved. The effect of polarization on the lowest excited states have been theoretically investigate? by

Photot~Ii~.siccrl Proc~cssc~s in Contleviscd PI1ri.w.v

45

INDO method^.'^ Dipole moments of states as a function of twist around bonds are examined and predictions made of photoisomerization effects. Energies, dipoles, and non-adiabatic couplings have also been computed for diradical and zwitterion states of ethylene and ~ r o p e n eConformational .~~ analysis of flexible truiis-dienes can be made by the technique of polarization spectroscopy 5 0 in stretched polymer films as has already been mentioned. Vitamin D and its derivative have been selected as examples of the use of the technique. Simple benzenoid systems have not been as extensively reported as in previous years. West and Miller 5 ' have studied the fluorescence from dilute solutions of benzene in cyclohexane induced by protons and alpha particles. A model for interpretation of the data involving intratrack quenching by products of the irradiation is not fully adequate. Gibson and Rest 5 2 have measured quantum yields of fluorescence and phosphorescence in various frozen gas matrices and from these yields and lifetime data have calculated the photophysical rate constants for C,H, and C,D, at 12 K, which are given in Tables 1, 2, and 3. The fluorescence rate constants obtained in matrices at 12 K are comparable with those

kF/(

lobs- '1 3.57 3.85 3.70 3.64 4.00 3.48

kl,-/( 10's- ') 6.63 6.56 6.30 9.35 6.00 18.26

-

-

-

-

kp/( 1 0 - I ~ -I ) 6.05 6.4I 7.03 10.70 6.34 7.87 125 5000

kNR/(10- 3

-I)

3.97 4.35 I .33 7.98 11.19 3.94 -

Table 2 Culculuted rute constants j b r ,fluoresceticv ( k F), intersy~teni crossing (k,,) , phosphorescence ( k p), unci tron-ruciiutive ciecuy ,from the triplet stute (kNR).for C6D6 in vurious gus mitrices ut 12 K k,/( 10' s - I ) 2.87 3.10 2.94 2.92 3.17 2.89 -

-w

A,,-/( 10' S - I ) 3.50 4.65 3.90 5.93 4.96 12.27 -

k,/( 10- 's - I ) 4.75 4.74 5.17 10.38 3.99 5.25 I I8 5000

kNR/(10 - 3

- I

)

I .79 I .63 0.92 4.87 3.56 2.73 -

I. Bdraldi. M . C. Bruni, F. Momicchioli. and G. Ponterini. Cltcw. Plijx., 1980. 52, 415. M . Persico, J . Ant. Cliiwi. Soc., 1980, 102. 7839. M . Sheves. N . Friedman. D. Levendis. L. Margulies. and Y . Mazur. Isr. J . Climi.. 1979. IS. 359. M. L. West and J. H . Miller, Cltiwi. Pltj-s. Let[., 1980. 71. 110. E. P. Gibson and A. J. Rest, J . Clictit. Soc.. Frrrtickiv Trcirts. 2, 1981. 77. 109.

'" ''

46

Photochemistry

Table 3 Comparison of rate constants for fluorescence (kF), intersystem crossing ( k I C ) ,phosphorescence (kp), and non-radiative decay from the triplet state (kNR).for C6H6 and C6D6 in various environments Solution Vupour CH4 Glass (300 K) (300 K) (77 K) (12K)" k,/106s-' C6H6 3.57 1.7' 1.73b 2.5' 2.20' C6D6 2.87 1.37' 3.5d 1.75' 6.6' k,,/ 106 s C6H6 6.63 8.0b 9.7d C6D6 3.50 8.7' 6.tld 3.5' k p/ 10 - 2 s C6H6 6.05 4.17b 4.75 3.5' C6D6 k , , / w S-' C6H,j 3.96 40Ib 123' C6D6 1.79 68' " Ref. 52. Methylcyclohexdne. 'R. Li and E. C. Lim. J . C k m . P/I.I-s.~ 1972,57, 605; 5 : 5 : 2 by volume ethyl ether, isopentane, and ethanol. *R.B. Cundall and S. McD. Oglive, in 'Organic Molecular Photophysics', ed. J. B. Birks, Wiley, London, 1975, Vol. 2; 10-20 Torr. 'Single vibronic level emission,

'

'

0.1 Torr

in the vapour phase at 300K. Perdeuteriation causes the photophysical rate constants to decrease, consistent with a reduction of the Franck-Condon factors. Nakashima et al.53have used a K r F excimer laser to obtain transient absorption of dilute benzene solutions and measured S,, t S, and T,, t T, absorptions between 220 and 850 nm. The absorption band at 500 nm observed previously by other workers disappears upon dilution and consequently is assigned to the 0.003), 540-325nm excimer band. Other assignments were 620nm ('Elu, F ( I 'E,,, F 0.04), and 270nm (2'E2,, F 0.12). The observed energies from the ground state to the 1 ' E 2 , and 21E2sstates were 7.8 and 9.2eV, respectively. The T, t T I spectrum shows a single peak at 235nm (F 0.35) and a shoulder around 3 10 nm (F 0.12). Vibronic mechanisms in the two-photon spectrum of benzene 5 4 and also toluene, halobenzenes, and aniline 5 5 have been studied by Goodman and co-workers. Two-photon excitation of benzene crystals at 4.2 K has been recorded in the 200 nm second absorption system.56The data suggest that the transition is 'Blu t ' A , , in which the vibronic intensity is derived from the ' E l , , state in the one photon and IE,, in the case of two-photon excitation. Spectral solvent effects on toluene have been reported by M a ~ o v e i . ~Traverso ' and Brunet 5 8 have examined the S, t So transition in biphenyl and confirmed the earlier conclusion that this is a forbidden process. Polynuclear hydrocarbons remain a source of much basic information in establishing the principles of photophysics. The enhancement of weakly allowed vibronic bands in the fluorescence and absorption spectra of 1,12-benzoperylene, 1,2,3,4-dibenzanthracene,naphthalene, and 1-methylnaphthalene have observed in polar solvents at room temperatures. 5 9 Since no convincing correlation between

-

-

-

53

''

55

56

57

59

-

N. Nakashima, M. Sumitani, 1. Ohmine, and K. Yoshihara, J . Client. PIys.. 1980. 72, 2226. L. Goodman and R. P. Rava, J . CItent. Phys.. 1981. 74, 4826. R. P. Rava. L. Goodman, and K . Krogh-Jesperson, J . Chent. fltys., 1981, 74, 273. A. Bree. C. Taliani. and T. Thirunamachandran, Clt~nr.f l t j x . 1981, 56, 123. V. Macovei, Rev. Rouni. Chin?.,1980, 25, 651. G . Traverso and J. E. Brunet, Spectrosc. Let,.. 1980. 13, 657. A. Mukhopadhyay and S. Georghiou, Pltotocheni. Photohiol.. 1980, 31. 407.

Photophysical Processes in Condensed Phases

47

the solvent effect and the solvent dielectric constant, or Kosower's Z value, is found the formation of symmetry reducing complexes between the solvent and excited state is suggested. The angular dependence of the fluorescence polarization spectra of anthracene has been investigated in polyethylene films.60 The b3gnontotally-symmetric ring vibration at 1655cm- has been assigned by this method and the modulation polarization technique. Theoretical studies have been reported on the formation of dimers and excimers of naphthalene, anthracene, and pyrene.6' The analysis suggests that the conformations of triplet excimers are different from those of the corresponding singlet excimers. Steady-state and timeresolved fluorescence measurements have been used to study the kinetics of excimer formation in dinaphthylalkanes.62The extensive kinetic data suggests that intramolecular excimer formation is directly controlled by rotational relaxation processes that lead to the excimer conformation. The results indicate that the isotactic sequence in vinyl polymers plays an important role in intramolecular excimer formation. Luminescence has been used to show that the geometry change between the ground- and excited-states of naphthalene is important in modifying the energies of multiplet components in S , -+ So and T , -+ So transitions in argon matrices.63 The energies and oscillator strengths of exciton transitions in crystalline naphthalene, anthracene, tetracene, and pentacene have been cal.~~ culated using second quantized boson theory by Schlosser and P h i l p ~ t tGustav et have calculated the geometries of 1-phenyl- and 2-phenyl-naphthalenes in the electronic So and S , states. The transitions in 2-phenylnaphthalene are forbidden and this explains the differences in fluorescence lifetimes. The dynamics of electron-hole recombination and prompt and delayed components in the electroluminescence of anthracene have been theoretically analysed.66 Anderson 6 7 has used 7 ps 355 nm pulses to study the vibrational relaxation of the S, state of anthracene in 3-methylpentane at room temperature. Unrelaxed vibronic states exist well into the picosecond range and they may participate in processes competitive with the main electronic relaxation processes in polynuclear hydrocarbons. A few studies of the effect of pressure have been reported. The first singlet exciton state of anthracene single crystals has been observed at pressures up to 30Kba1-.~* The pressure effect on the exciton shift is small compared with the strong pressure dependence of the Davydov splitting. Figures 5 and 6 show the fluorescence spectra of 1 ,l'-binaphthyl, 2,2'-binaphthyl, and 2,2'-dimethoxy- 1 ,1 'binaphthyl which have also been studied up to 3 0 K b a 1 - . ~ ~ Alkyl substituents, apart from lowering the melting points and increasing the

" " 3' '4

" " " " "

T. Terada, M. Koyanagi. and Y . Kanda. Bull. C/iiw. Soc. J / J I ~ 1980, .. 53. 2399. E. J. Padma Malar and A. K . Chandra. htlirrri J . Chcrii., Srcr. A . 1980. 19. 283. S . Ito. M. Yamamoto. and Y . Nishijima. Btrll. C/iiwi. Srw. JIJN..1981. 54. 35. J. Najbdr. and A. M . Turek. C/tlWi. Phys. Lclt.. 1980. 73. 536. D. Schlosser and M . R. Philpott, Chern. Phys., 1980, 49, 181. K . Gustav. U . Kempka. and J . Suhnel, C/i~nt.P/tj*.s.Lctr.. 1980, 71, 280. L. Altwegp and 1. Zschokke-Grlnacher, J. Cliiwt. P h y . . 1980, 73, 213. R. W. Anderson, 'Picosecond Phenomena 11. Proc. 2nd Int. Conf. Picosecond Phenomena', ed. R . Hochstrasser. W. Kaiser. and C. V. Shank. Springer-Verlag. Berlin, Heidelberg, and New York, 1980. R. Sonnenschein. K. Syassen, and A. Otto, J . C/7lJit7.Ph!..s.. 1981. 74, 4315. Y . Hard and M . F . Nichol. Bull. Clinii. Soc. J p i . . 1978. 51. 1985.

48

Photochemistrjv

3.60

I

I

I

8

28000 340 (cm-9

(eV)

B 320

26000

Z

W

3.00 24000

2.80

10

20 30 40 50 PRESSURE(K bar) Figure 5 Pressure dependence of the excitronic transition energies for thejrst singlet state of

0

unthrucene (Reproduced by permission from J. P/iys. Chem., 198 1, 74, 43 15).

solubility of scintillators, reduce self-quenching and quenching by heavy atoms. This has been shown with 26 selected scintillator molecules.70i7 1 In many cases photophysical effects are much influenced by photochemical reaction. The fluorescence of naphthacene is affected by dimerization and oxidation. 7 2 Interaction with anthracene and quinones also occurs. The adiabatic pho to1y tic cycloreversion of substituted lipidopterenes in to intramolecular exciplexes shows an example involving anthracene derivatives.7 3 A series of very detailed papers on conformational effects on the fluorescence and photochemistry of [2n] 9,lO-anthracenophanes have been published by Ferguson and coIt is not possible in this review to summarize this very detailed work S. Gershuni, M. Rabinovitz, I. Agrandt, and I. B. Berlman, J . Pfiys. Chem.. 1980, 84, 517. S. Gershuni, M. Rabinovitz, I. Agranat, and I. B. Berlman, ‘Liquid Scintillation Counting Recent Applications and Development, Vol. 1, Physical Aspects, Academic Press Inc., New York, 1980, p. 43. 7 2 M. Furusawa, M. Tachibana. and T. Tsuchiya. Bunseki Kagciku. 1980, 29, 592. 7 3 H.-D. Becker, K. Sandros, and K. Andersson. Cliem: P l i w Lett.. 1981, 77, 246. 7J A. Durand, J. Ferguson, M. Puza, and G. B. Robertson, J. Am. Chem. Soc., 1980. 102, 3524. A. Durdnd. J. Ferguson. and G. B. Robertson. Client. P l t w . 1980, 53, 215. l6 A. Durand, J. Ferguson, M. Puza, and G. B. Robertson, Chem. Phys., 1980, 53, 225. ”’ J . Ferguson, Client. PIiys. Lett.. 1981, 79, 198.

70

”

’’

PJiotophysical Processes in Condensed PJiuses PRESSURE (kbar)

30

10

0

49

60

n

'E

-500

V

W

t

LL

I

s

-lo00

U

w w

O

z

O 0 --O1 0-'2

\;

-1 500

- 2000

1.0

1.1 DENSITY

12

1.3

9/90

Figure 6 Shift qf rlir wntres qfgruvity qftlir 0 (@), 0-1 (0).unnd 0-2 (0)vihronic. h u n h oj' lint ltrucene (Reproduced by permission from J . P h j x Clieni., 1981. 74, 4315).

in any satisfactory fashion. Measurements of the fluorescence spectra and fluorescence quantum yields associated with 1,3-bis(9-anthyryl)-I,1,3,3tetramethyl disiloxane (1) and its photoisomer (2) indicate that photochemistry occurs from an unsymmetrical e ~ c i m e rThis . ~ ~work follows upon earlier work on fluorescence and photocyclomerization measurements on a series of a,o-(bis-9anthry1)n-alkanes in methyl cyclohexane and ethanol. 79

78 i9

J . Ferguson. A. Castellan. J.-P. Des Vergne. and H . Bouas-Laurent, CIim. P h ~ sLcw., . 1981.78.446. A. Castellan. J.-P. Des Vergne, and H . Bouas-Laurent. C h m . Phys. Lcw.. 1980. 76. 390.

"

n'

1 .oo

(20°C) 2.03 1.83 1.90 2.25 I .85 I .88 2.02 1.85 1.81 2.05

In perfluoro-n-hexane solvent

Solvent Cyclohexane Ethyl ether Propan-2-01 Benzene Ethanol Ethyl acetate Dioxan Acetone Acet oni trile Dimethylformamide Vapour

(ns) 430 415 386 31 I 373 367 309 324 340 280 210

5F

0.09 0.148 0.152 0.151 0.156 0.176 0.184 0.188 0.207 0.203 0.070

1.51 1.59 1.68 2.47 1.93 1.99 2.04 1.91 2.06 2.50 0.67

(0.65) 0.66 0.65 0.77 0.72 0.73 0.63 0.62 0.70 0.70 0.14"

lop6 ,p-0

X

(s-l)

4F

kF (s-') I .35 2.35 2.56 3.76 3.01 3.38 3.75 3.60 4.26 5.10 0.47

kFO-O

10-5

8.16 8.50 9.1 1 7.45 7.50 7.34 12.0 11.8 8.8 10.7 30.9

10-5

1.38 1.36 1.42 2.09 1.63 1.65 1.67 1.55 I .63 1.99 0.62

k,,

(s-l)

10-6

W')

kdiff

Table 4 Radiative transition probabilities for pyrene in various oxygen_free solvents ut 25 "C

Piiotopiiysicul Proc*cwesiri Coiidcmcd Piitrscs

51 Picosecond photon-echo experiments have been used to study delocalized electronic excitation of pentacene dimers in a p-terphenyl host8' The fluorescence spectra and temperature dependence of amorphous anthracene films doped with naphthacene show structural changes in amorphous films.8 Fluorescence decay of 9-methylanthracene has been used by Tan and Treloar to study the coiling of poly(methacry1ic acid) in water. Hara and Ware83 have studied the influence of solvent on the radiative probablity from the 'Blustate of pyrene. The fraction of fluorescence in the 0-0 parallels the extinction coefficient change for the 0-0 band. The Ham band also decreased with temperature, an effect correlated with the decrease in dielectric constant with temperature. There is also evidence that a solvent-solute interaction is involved in Ham band effects in alcohols and aromatic solvents. Use of the integrating sphere eliminates any uncertainty in the conventional instrumental refractive index correction. Some of the data obtained is given in Table 4. Pyrene shows emission from the S2 state. Nickel and RodenE4 have distinguished the S , + So and S , -+ So emissions of pyrene in delayed fluorescence caused by triplet-triplet annihilation. The strong S , -+ So DF is quenched by compounds like N-diethylamine or triethylamine which do not quench T , or S , , Figure 7. Hot-band emission from S l a is t not readily quenched however. Pyrene and some of its derivatives are being extensively used as probes of biological and macromolecular structures. Lianos el have compared the properties of two main classes of pyrene derivatives. The first includes those in which the substituent weakly perturbs the n-electron cloud, the second involve quite different behaviour

Figure 7 Corrected spectra of' prrene (1.0 x 10-'M) in M C H (----), M) DEA ( 1 .O M) in M C H (-) rind cihsorption spectrum o/'p!-rcwc~in ( I .O x M C H ( - - - ) ~ l 193 t K (Reproduced by permission from Ckeni. Pliys. Lett., 1980, 71, 238).

+

'' 82

" " ' 5

R. W. Olson, F. G. Patterson. H. W. H. Lee, and M . D. Fayer, Clicwi. P/I.v.F.Lrtt.. 1981. 79. 403. Y. Maruyama and K . Takamiya-lchikawo. In/.J . Qiuiiitiiiu Clicni.. 1980. 18, 587. K. L. Tan and F. E. Treloar. Client. f I y s . k t t . , 1980, 73, 234. K . Hara and W. R. Ware. Chew. fliys.. 1980. 51, 61. B. Nickel and G . Roden, Clienl. P1iy.v. Lett.. 1980, 71, 238. P. Lianos, B. Lux, and D. Gerard. J . Cliitn. Ph!:s., 1980. 77. 907.

E(S2)

conlpowld

Azulene

['HJ Azulene Guaiazulene I .3-Dichloroazulene

I .3-Dibronioazulene 5.6-Dichloroazulene

Sol\wrt

3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH

(cm - I ) S , + So and S , -+ S , 28200 S , -+ So and S 2 -+ S , 28 300 S2 -+ So and S , + S , 28 200 S 2 + So and S2 -+ S , 28 300 S 2 + So and S2 + S , 26950 S 2 + So and S , -, S, 27000 S , -+ So and S , S , 27040 S , + So and S 2 + S , 27 120 S 2 + So and S , + S , 26920 S2 + So and S , -+ S , 27000 S , -, So and S , -+ S , 27230 S , --, So and S , + S , 27300 €ir~i.ssion.sohsvriwl

-+

Table 6 Rute constunts of processes originuting ,fioni S , ,frozen solutions

Coriipoiind Azulene

Ruilititirc riitc k," (s-l) 2.4 x 107 2.4 x 1 0 7 2.4 x 107 2.4 x 107 3.5 x 107 3.5 x 107 3.5 x lo7 3.5 107 3.5 x 1 0 7 3.5 x 107 2.4 x 1 0 7 2.4 x 107

Solllent

3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH 3MP EtOH

['H,]Azulene Guaiazulene I .3-Dichloroazulene 1.3-Dibromoazulene 5.6-Dichloroazulene

AE(S,-S,) (cm - ') 13930 I3 890 I3 960 14000 13 700 13 740 14235 14200 13860 13.830 13470 13510

5,

(ns) 1.63 1-69 2.55 2.60 0.45 0.60 1.18 1.05

0.34 0.36 1.08 1.19

of' uzulenc. conipoundr in

Non-ruiliLitire Stltt' EliNR (s-!) 5.90 x lo8 5.68 x 10, 3.68 x 10, 3.61 x lo8 2.19 x 10' 1.63 x 10" 8.12 x 10, 9.17 x 10, 2.91 x 10" 2.74 x 10" 9.02 x lo8 8.16 x 10,

" A t rooin temperature. assumed to be temperature independent

Table 7 Spectrul und kinetic dutu of the ,fluorescence emissions oj' curbonjV derivatives (3)-(5) of uzuiene at 77 K COnlpoLlnd

'Aldehyde' (3) 'Ketone' (4)

E(S,) Etnission.v ohservrtl (mi-) EtOH S, So and S , -+ So 17600 n-hexane S 2 -+ So and S , + So 16 800 Sz-+ So and S , --t So 17200 EtOH n-hexane S , + So and S , So 16000 EtOH S 2 -+ So and S , So 16600 Solwnt

-+

-+

1-Trichloroacetyl-

azulene (5)

--+

T2

T1

(ps)

( ps)

(50 400 k 40 (50 < 150 <50 200 k 50 (50 < 150 <50
PI1ot oph~*sii~cit Proc~c~.ssc.s ir 1 Cor 1ei(vi.rcvl Phcrscs

53

owing to the proximity of (n,n*)and (n,n*)states. An extensive study of the decay kinetics of pyrene in artifical and natural membrane vesicles has been studied by pulse fluorometry.86 Three exponential decays are determined and interaction of the excited state with the environment as well as with a ground-state molecule in the excimer is indicated. Intramolecular excimer fluorescence can be used to probe fluidity changes and phase transition in phosphatidylcholine bilayer~.~'Intramolecular excimer formation has the advantage of making the interaction an unimolecular process, independent of concentration. The properties of azulene and derivatives continue to be fruitful subjects of research. Griesser and WildE8 have studied the S , --+ So and S , 4 S , fluorescence spectra of azulene in energy-selection experiments at low temperature ( 7 K ) in 3-methylpentane glass using laser excitation into the S , state. The first emission shows a sharp zero-photon line spectrum, containing broad vibronic bands. Data shown in the paper are for 1,3-dichloroazulene. The effect of the energy-gap dependence of the radiationless transition rates in azulene and its derivatives has been examined by the same authors.89 The fluorescence transition S , + S , , observed for the first time in azulene derivatives, gives an indication of the effect of substitution on the S , - S , energy gap. The S2 4 S1 internal conversion is the most important decay mechanism and the small effect of deuteriation indicates that most of the energy is accepted by C-C skeletal stretching modes than C-H stretching modes; see Tables 5 and 6 . Spectral and kinetic data have also been obtained for three carbonyl derivatives (3)-(5).90 These are shown in Table 7. Me

The S , lifetimes are smaller than 50 ps as expected in view of the large decrease in the S,-S, energy gap relative to azulene. No evidence was found for significant participation of triplet states in the deactivation of both singlet states. Spectral data indicate that the carbonyl group interacts only very weakly with the azulene chromophore, the main effect being a shift of the S , state to higher energies. Picosecond-timescale experiments on stilbene have been reported by Hochs t r a ~ s e r . ~Vibrational ' relaxation is faster than isomerization: the findings in hexane are summarized in Figures 8 and 9.

M . Lui. H. C. Cheung, K.-H. Chen. and M . S. Habercom. Biop/t.r.s. C h ~ n i .1980, , 12, 341. "

Zachariasse. W. Kuhnle. and A. Weller. CAaii. P l t ~ x .t c i f . . 1980, 73. 6. "'KH.. AJ . .Griesser and U. P. Wild. J . Cltcwi. PhJ-s.. 1980. 73. 471 5. "

''

H . J. Griesser and U . P. Wild, C I I P ~Ph,rs., I. 1980. 52. I 1 7. H . J . Griesser and U . P. Wild, J . flmmcltcwi., 1980. 13. 309. R. Hochstrasser. f w c App'pl. C/tcw.. 1980. 52, 2638.

54

Photochemistry

A (nm) I

1.0 -

O4

I

I

I

M t -stiltmw / b a n e xcxc= 306 nm

1

--- 12 ps -58

t

ps

b

0.6 -

04

-

I

I

450

500

1

550 A (nm)

600

650

Figure 8 Trunsient absorption spectrfi qf stilbene (a).for 265 nm escitcition, (b) ,for 308 nm excitation (Reproduced by permission from Pure Appl. Clieni.. 1980, 52, 2683).

Photophysical Processes in Condensed Phases

55

EXCITED STATE SURFACE / / '\

1

/

/

/

/I

< 20 ps

1

1

'\

hv

?,' \ \

\

\

GROUND STATE SURFACE

Figure 9 Sclremaric dirrgrrrni of ihe stilbene civnomics (Reproduced by permission from Pure Appl. Chem., 1980. 52. 2683).

By monitoring the fluorescence generated by two consecutive picosecond light pulses it has been possible to measure rate constants for the cisjtrans isomerization of ~ t i l b e n e The . ~ ~ main reaction occurs in the singlet manifold via a perpendicular singlet state with lifetime shorter than a few picoseconds. Greeneg3 has observed rapidly disappearing (z = 5ps) and a longer-lived ( 5 = 3.0 ns) absorptions following 0.5 ps excitation of tetraphenylethylene. The former appears owing to the singlet state, which disappears by twisting. The longer-lived absorption is less certain in origin and could arise from a radical. Ghiggino 94 has examined the time-resolved fluorescence of trans- 1,2-di(2naphthy1)ethylene (6).The dependence of the fluorescence emission on excitation wavelength is ascribed to the participation of conformers. The fluorescence decay is non-exponential. The time-resolved spectra are consistent with the involvement

" " "

M . Sumitani. N . Nakashima. and K . Yoshihara, CIICIII.Ph,r.s. Lv/f., 1979, 68. 255. B. 1. Greene, C ~ P I IPI h. j x Lcfi., 1981, 79. 51. K . P. Ghiggino. J . P/intoc.hcrii.. 1980. 12. 173.

56 Photochemistry of conformers but there is no indication of any conformational change or reaction in the excited state. Fischer 9 5 responds to the claims of Russian workers 96 by pointing out that the only trans- I ,2-diarylethylenes in which a pronounced variation of fluorescence quantum yield with E,, has been shown to exist are I-phenyl-2-(2-naphthyl)-and 1 ,2-di(2-naphthyl)-ethylene1 most probably because two or three almost isoenergetic conformers exist in equilibrium. Fischer 9 7 has reported that the emission spectra of solutions of trans- 1,2-diarylethylenes, where at least one of the aryls is 2phenanthryl or 2-benzo[c]phenanthryl1 vary with excitation wavelength. There is a little dependence on solvent or temperature. These observations are explained as arising from the almost isoenergetic conformers as mentioned above. I t is instructive to note that confusion can arise where effects due to aggregation in poor solvents are not recognized. Becker, Sandros, and Hansent 9 8 have reported some excited state properties of cis- and trans- Il2-di(9-anthryl)ethylenes.The very marked dependence of the fluorescence spectra of such derivatives on viscosity is shown in Figure 10. trans-2-Styrylnaphthalene in n-hexane at 20°C is shown to be a mixture of two c o n f o r r n e r ~ .Bush ~ ~ and Scott"' have reported absorption, emission spectra, and fluorescence quantum yields for distyrylbenzene and substituted derivatives. The fluorescence quantum yields were very high, most approaching unity, Table 8, and in contrast to earlier studies showed very little solvent dependence. Saltiel and Eakerl'' show by azulene and oxygen quenching of photosensitized production of triplet states that triplet states are not involved in the photoisomerization of 1-phenyl-2(2-naphthyl)ethylene. The triplet lifetime of 104-1 50 ns determined by these workers is much longer than cu. 20ns previously assigned. The latter is reassigned to the longer lived of two non-equilibrating isomeric excited transoid singlet states. A singlet pathway has also been suggested for the direct photoisomerization of 4-cyanostilbenes in solution by Gorner. ' Extensive direct and triplet-sensitized isomerization data together with fluorescence and intersystem crossing measurements are presented for 4-cyanostilbene1 4,4'-dicyanostilbene, 4-cyano-4'-methoxystilbene, and 4cyano-4'-dimethylaminostilbene in several solvents, varying quencher concentration, temperature, and viscosity. The excited state properties of [ 5 H ] dibenzo[u,d]cycloheptene, (7), which corresponds to cis-stilbene, have been examined. O 3 Both the fluorescent singlet and triplet-triplet absorption have been measured.

''

'

(7) E. Fischer. J . Phi..s. Chiwi., 1981. 85. 1770. "" N . P. Kovalenkd. M . V . Altiiiiov. A . Abduk;tdiro\. mid Y . B. Shekk. /:I). .4krrt/. N m k . S S S R . . SCY Khim.. 1979. 6. 1247. ''- E. Fischer. J . Phj..,. Chiwt.. 1980. 84. 403. '' H.-D. Becker. K . Siindros. and L. Hanstii. J . Urg. Chiw.. 1981. 46. 821. y'' J . B. Birks. G. Bitrtocci. G. G. Aloisi. S. Dellonte. and E. Barigclleti. Chivn. P/tj.s.. 1980. 51. 113. ""' T. E. Bush and G . W. Scott. J. Wtj..s. C//iw/.. I98 I . 85. 144. l"' J . Sitltirl i i i d D. W. Eiiker. C / / i , / j t . P//I..\. /A//.. 1980. 75. 209. "" H. G i i r ~ r J. . P//oloihiwt.. 19x0. 13. 269. "" A . R. Witthins iiiid F. Biiyrahceken. J . /-wuiu. 1980. 21. 3 Y .

57

Pliotopliysical Processes in Conclcnsecl P1iusc.s EMISSION SPECTRA

OF

trans 1.2 -Dl ( 10- ACE TOX Y - 9 -ANTHRY L ) ETHYLENE

450

500

550

600

65onm

Figure 10 Etuissioii spectrrr of trans- 1 .'-his( 1O-rrc~to.~~~-9-~inthr~:,.l)et/?l.lmL' ui vurjing vism i ( ! * in cylohesunr (curve I ). his( 2 - r t l i ~ ~ l l i c . ~ ~ ~ l ) p k(curves t h ~ i l u t2~- 4 ) . and nietlirlcyclol i ~ ~ s c i i i ~ ~ ~ r l ~(cI c :i l 1 i i)i glriss ( c u r w 5 ) (Reproduced by permission from J . 01-x.Clieni.. 1981, 46, 821).

Table 8 Fluorescence yuuntuni yidcr's (y;,)

Dist yrylbenzene Bis('-met hylst yrylbenzene) Bis(4-inethylst yrylbeenzene) Bis(2-methyl-o-styryl benzene)

102.6 f 6.0 98.0 _+ 6.0 104.0 f 6.0 94.0 2.5

104.6 & 3.0 99.5 f 2.3

91.4 & 2.1 87.0 _+ 2.1

Bennett and Birgelo4 have determined a two-photon excitation spectrum of all-trans 1+diphenylbuta- 1,3-diene in EPA glass at 77 K. The system origin of the lowest 'A,*- nn*stateisobservedat 27900f20cm-', 130cm-' below thesystem origin of the strongly allowed 'B,,*+ state. The short intrinsic lifetime of fluorescence is associated with strong vibronic coupling of the 'A,*- state with the nearby lB,*+ state. The spectral data are shown in Figure 11.

"''

J. A . Bennett aind

R. R. Birge. J . C ' / r c w . P/r,rs.. 1980. 73. 4234.

58

Photochemistry

I '

1

1

I

I

1

1

1

r

J

4

I \

'' II

FLUORESCENCE

310

320

330

340

WAVELENGTH

350

360

370

(nm)

Figure 11 One-photon absorption,Jluorescence, and two-photon excitation spectra of diphenylhutadiene in EPA at 77 K. The iwo-photon excitation spectrum is plotred v ~ r s i ~2J2, s where i,,, is the wavelength of the laser escitation (Reproduced by permission from J . Cltem. Pliys., 1980, 73, 4231).

'

Sowada and Holroyd O 5 have used a combined X-ray-visible-dye-laser doublepulse technique to determine the photodetachment spectra of the anions of biphenyl, trans-stilbene, pyrene, perylene, benzperylene, coronene, and nitrobenzene in non-polar solvents. More attention is being given to the photophysics of non-hydrocarbons. There is also increasing awareness of conformational factors and the involvement of excited state complexes in photochemical processes. Nitromethane is excited by n + n* transitions but fluorescence and phosphorescence cannot be detected. ' 0 6 The photochemistry of simple aliphatic aldehydes in the presence of olefins and hydrogen donors has been studied using fluorescence quenching.' O 7 The quenching efficiency of olefins relates to differences in ionization potentials and electron affinities of olefin and aldehyde. Energy migration between chromophores in I74-aliphatic diketones has also been established.'0a This occurs at rates of about 2-3 x l o a s - ' in both singlet and triplet states. Also the lack of a dependence on solvent viscosity indicates that molecular rotation is not involved. The effect of hydrogen bonding on the n + n* blue shift in a,P-unsaturated ketones has been examined theoretically. l o g Another theoretical paper of interest deals with the spectroscopic properties of higher excited states of retinal isomers.' l o This work allows identification of the cis (fi)

lo'

'OH

'lo

U . Sowada and R. A. Holroyd, J . P/ij:s. Client., 1981. 85, 541. B. Marciniak, J. Koput and S. Paszyc, Bull. A c d . Pol. Sci.,1979, 27, 843. M. V. Encina, E. A. Lissi, and F. A. Olea. J . Plioroclieni.. 1980, 14, 233. E. A. Lissi. M . V. Encina, F. Castaneda. and F. A. Olea. J . P1i.r.s. Client., 1980, 84, 251 A. F. Beecham. A. C . Hurley, and C. H . J . Johnson, Alcsr. J . Chent., 1980, 33, 699. B. Honig, U . Dinur, R. R . Birge, and T. G. Ebrey, J . Am. Client. Soc., 1980. 102, 488.

Pliotopliysicul Processes in Concierisecl Phuses

59 and y-bands in the spectrum of both rhodopsin and bacteriorhodopsin. Becker et ul. '' ' have identified a weakly allowed state of 'A,* character in the spectra of 2,4,6,8,10-dodecapentaenal.A similar result has been obtained with the Schiffs base derivative o f ' this linear polyenal. The photophysics of hydrogen-bonded complexes of retinoic acid and its 9-cis- and 13-cis-isomers have also been studied especially with regard to the effects of hydrogen bonding on radiative and nonradiative processes. Tautomerization in 2-(2-pyridinyl)- 1-(3-pydrinyl)ethanone has been studied by, amongst other techniques, fluorescence emission.' ' The dependence of the fluorescence in both the solvent and temperature is interpreted as a solvent cage effect as well as rapid intramolecular and/or intermolecular hydrogen exchange. Both electronic absorption and emission spectra of biphenylene-2,3-dione has been reported by Kuboyama. l4 Phosphorescence but no fluorescence spectra are reported. Halpern and Wryzykowka ' ' have made a detailed study of the fluorescence quenching of a representative saturated amine, N,N-diethylmethylamine in n-hexane at 25 "C. It appears that the fluorescence quenching of aliphatic amines can occur by several mechanisms which may operate simultaneously. These include energy transfer, electron transfer, and hydrogen bonding: exciplex formation may also occur. Laser-induced fluorescence of the 1,3-difluorobenzene radical cation has been reported.' l 6 Three papers on photoprocesses in phenol have appeared. Grabner 'I7 in steady-state photolysis studies reports quantum yields of fluorescence, hydrated electron, and H-atom formation from excited phenol in aqueous solution at excitation energies of 254 and 229nm corresponding to the two lowest excited singlet states between 10 and 65 "C.The mechanisms postulated are indicated in Scheme 1. Zechner et a/.' '* have studied solvent effects on the primary photoprocess of phenol in several solvents. Data on product yields are exemplified in Table 9. A study of electron ejection in aqueous phenol and phenolate solution used 27ps pulses at 265 nm.' l 9 The phenolate undergoes extremely rapid electron ejection,

'

so Scheme 1 I I

"* 'IJ

Is l6

'IR 119

R. S. Becker, P. K . Das. and G. Kogdn, Cltrrti. P l i ~ s Lcit., . 1979. 67, 463. T. Takemura, K . Chihara. R . S. Becker, P. K. Das, and G . L. Hug, J . Ant. Cliertt. Soc.. 1980, 102.. 2604. M. Melzig, S. Schneider, F. Dorr, and E. Daltrosso. Bcr-. Birriscngc~s.P I i j x . C/imt., 1980. 84. 1108. A. Kuboyama, Bull. Client. Sor.. Jpn.. 1981. 54. 873. A. M. Halpern and K. Wryzykowska. J . Pliotoclwru.. 1981. 15. 147. V. E. Bondybey, J. H. English. and T. A. Miller, Cli~rtt.Plr.~:v.L1,ri.. 1979. 66, 165. G. Grabner. G. Kohler. J. Zechner. and N. Getoff, J . Plijx C/wni.. 1980. 84. 300. J. Zechner, G. Kohler. G. Grabner, and N . Getoff, Cm. J . Clicni., 1980. 54. 2006. J. C. Mialocq. J. Sutton. and P. Goujon. J . Clit~nt.P/iIx., 1980. 72. 6338.

Water Cyclohexanc Methanol Propan-2-01 t-Butyl alcohol

Solvent

0.2 1 0.22 0.22

0.18

QJS1) 0.14

0.7 1 0.37 0.93 0.93 0.93

P”” 10-3 1.8 x 1 0 - ~ 4.5 x lo-“ 5.7 x 10-4

0.02 I

Qe254

0.033 < 10-3 (1.80 f 0.1) x 10-3 1 x 10-3 1 10-3

QF”

< 10-3 < 10-3

-

0.18 -

xc

0.002 0.1 I 0.001

Q,,?54

0.064 0.55 0.003

QII”Y

Table 9 Quuntuni yields offluorescence (QF). solvuted electrons (Q,), und H utonis (QH), uncl rvr1uc.s o#’p. re.U phenol in vurious solsents ut 30 “C

0.002

0.06 0.51

31I

zH.#Or J I ~

Pho t ophjxiccil Procxmes in Coti c k n s c d PI]trsL>S

61 but in the phenol molecule it is slower with a delay of about 12 ps. Two-photon processes are probably involved in hydrated electron formation. Nanosecond and picosecond photochemical kinetics of quinoid fluorescence produced by excitation of the enol form salicylideaniline have been investigated in various environments. ' 2o An excited-state tautomeric proton transfer occurs within 5 ps at temperatures above 4 K in both protic and aprotic solvents. Ford et al. l 2 have measured fluorescence lifetimes for the 450 nm excitation of methyl and phenyl salicylate in various solvents. Quenching studies on the short wavelength fluorescence band at 340 nm point to the existence of three distinct ground-state conformers. Lopez-Delgado and Lazare 2 2 have also studied methyl salicylate in the gas, liquid, and solution phases. They conclude that the dual fluorescence arises from two conformers (or rotamers) in the ground state. The blue fluorescence arises from excitation of the more abundant conformer, and the U.V. fluorescence arises from the other. Emission and intersystem crossing of aniline in various solvents have been measured using tris(dibenzy1methano)europium as a ~ c e p t 0 r . lThe ~ ~ results are listed in Tables 10-12.

'

Table 10 Egect of various solvents on aniline emission parameters Aiiilitic

TctllI / > C ~ U -

cottcviitrrrtic~ti 3g1-1

3gl-I 3g1-1 3z1-l

8 8 8 8 8

10-5M 10-5M 10-5M x 10-5M

x x x

x 1 0 - 5

Solrent

Cyclohexane Ethanol MP EPA Cyclohexane Ethanol MP EPA ~ EPA

A,, (nm) 265-310 265-300 265-290 265-290 265-295 275-295 275-300 290 290

tiire

20 C 20 c 77 K 77 K 20 C 20 c 77 K 77 K 77 K

hFmix

bmax

(nm) 315 339 330 340 315 339 330 340 340

(nm)

420 420

420 420 420

@F

0.08 0.10 0.08 0.10 0.17 0.10 0.17 0.10 0.10

@P

0.074 0.76

0.65 0.85 0.50

A hsorption

Solrcw t

Cyclohexane Diethyl ether Benzene Dioxan Tetrahydrofuran Butanol Propanol Ethanol Methanol Water " I"

Dielectric c*onstcrrtI

2.023 4.335 2.284 2.209 7.39 17.8 20. I 24.3 33.62 80.37

'-ma,

'.ma x

(nm) 287.5 289 289 290 290.5 286 285.5 284 282 280

t:

1760 1920 1800 2260 1840 1480 1440 1480 1430 1300

(nm) 315 33 1 327 339 335 340 340 340 340 342

E i i q g y of' Mhrind

''Illax

(cm-I) 31746 30211 30581 29498 29850 29411 29411 29411 29411 29239

@F

0.17 0.13 0.14 0.13 0.12 0.11 0.10 0.10 0.09 0.12

P. F. Barbara. R. M. Rentzepis. and L. E. Brus. J. A i i i . Cliiw. Soc.. 1980. 102. 2786. D. Ford. P. J. Thistlewaite. and G. J . Woolfe. Cliiwi. f h ! x Lctt., 1980, 69, 246. R. Lopez-Delgado and S. Lazare. J. f/i.r.s. C l i m . . 1981. 85. 763. G. Perichet. R. Chapelan, and B. Pouyet. J. f l i o t o d i i w i . , 1980, 13, 67.

(cm - I ) 32 937 32 255 -

31 992 31 923 32 062 32 062 32 062 32 132 -

Aniline solution in MP (77 K ) Aniline solution in cyclohexane (20"C ) Aniline solution in EPA (77K) Aniline solution in ethanol (20 "C)

-

0.85

-

3.9

2.7

2.7

0.10

0.10

~ d n s ) Qp 3.9 0.65

0.17

0.17

@F

-

5.4

-

4.2

T~/(S)

0.90

-

0.75

-

QlC

0.83

3.7 x 107

-

0.17

lo7

3.7 x

-

-

lo7

4.3 x

0.18

kp"/(S - I )

kFC/(s-') 4.3 x 107

0.81

.r,"/(ms) -

-

1.0 x

-

5.1 x

k,"/(s-

1)

3.3 x lo8

-

1.9 x lo8

-

k,,%(s-

Table 12 Calculated rate constants,for fluorescence (kF),intersystem crossing (kIC),and phosphorescence (kp).for vurious aniline solutions

Photophysical Processes in Condensed Phases 63 Picosecond spectroscopy has been used to study diffusion-limited processes in pdimethylaminobenzaldehyde (8)’ 24 and the related species (9), which exhibit dual or multiple fluorescences.

’’

Me,

,Me N

Me,

N

,CH,-CH,-CH,,

N

,Me

Ground-state aggregation, solvent-assisted relaxation, and excimer formation are responsible for long-wavelength fluorescence bands. Roy et al. 26 have studied the time-resolved emission from benzil and naphthil in semi-solid glasses to show that the relaxed excited triplet shows a growth followed by decay. This shows a geometrical relaxation occurs in the excited states. The fluorescence of relaxed and unrelaxed states of benzil.’” The unrelaxed emission exhibits a mirror image with absorption and blue shift in hydroxylic solvents. The fluorescence properties of ophthaldehyde derivatives of iodinated amino-acids have been studied by Miller and Thakrar. 1 2 * The photochemical aspects of carbonyl photochemistry remain important subjects of research. Wagner and Thomas’29 have used CIDNP to elucidate Irradiation of benzophenone radical formation from z,a,a-trifluoroacetophenone. and its derivatives in the presence of molecules with abstractable hydrogen atoms can give rise to intensely fluorescent compounds. This effect may interfere with the observation of nanosecond-domain kinetics. Quantum yields and kinetic isotope effects in nanosecond flash studies of the reduction of benzophenone by aliphatic amines have been measured by Inbar et Rate constant data are given in Tables I3 and 14. Winnik and Maharaj 32 have studied the reaction of benzophenone with n-alkanes through hexane to hexatriacontane EA is 3.9f0.2kcal for all chain lengths.I3’ The effects of substituents on the benzophenone on these reactions have also been examined.133 The reactions of phenylacetophenone when used as polymerization initiator have been reviewed by Merlin and Fouassier. 34 Harris and Selinger 35* 36 have, in two papers, studied the proton-induced fluorescence quenching of 1- and 2-naphthol. The respective rate constants for

’ ’

2*

125

12’

I”) I3O

13’ 13’

13’

I34 13’

E. Heumann, A h . Mol. Rcl~rsolioiiPro(*cwc~s.1979, 15, 297. S. Dlhne. W. Freyer. K . Teuchner. J . Dobkowski. and Z . R . Grabowski, J .

O i r i i k . . 1980. 22, 37. D. S. Roy, K . Bhattacharyya. S. C. Berd. and M. Chowdhury. Clicin. fliys. Lelt., 1980, 69, 134. K. Bhattacharyya, D . Roy. and M. Chowdhury. J . Lirriiin., 1980. 22. 95. J . M. Miller and H. Thakrar. Aritrl. Cliiiii. Actcr. 1981. 124. 221. P. J . Wagner and M. J . Thomas. J . Ant. Chmi. So(,.. 1980, 102, 4173. A. Lamire. A. Mar, U. Maharaj. D. C . Dong, S.-T. Cheung, and M. A. Winnick. J . Plii)/ocliorii.. 1980, 14. 265. S. Inbar. H. Linschitz. and S. G . Cohen, J . Am. Climi. Soc.. 1981. 103. 1048. M . A. Winnick and U. Maharaj. M~ic.r.oiiinl.c.irlc.s,1979. 12, 902. U . Maharaj, M . A, Winnick. B. Dors. and H . J. Schlfer. Mcrc.i.oc.o/(~cirl(~.s. 1979. 12, 905. A. Merlin and J.-P. Fouassier. J . Cliiwi. Pliys., 1981. 78. 267. C. M . Harris and B. K . Selinger. J . Pli,r.s. Clicni., 1980, 84. 1366. C . M . Harris and B. K . Selinger. J . P/il..v. Clicvii.. 1980. 84. 891.

64

Plto tochemistry

Table 13 Pulsed-her photolysis of 0.004M henzoplienone-~i~~nor systems

Cotiipountl

Solvenr C6H6

0.002-0.02

C6H6

0.002-0.02

CHJN

0.001--0.01

C6H6

0.0014.0 I

CH,CN

0.0014.01 0.0001-0.005 0.00014.005 0.000 06-0.003 0.00005--0.0006

'bH6 C6H6 C6H6 C6H6

C,H6:CH3CN (3:2)

ki,/(M - s- I ) 9.0 x 10'. 7.5 x 10' 6.4 x 107,7.0 x lo7 1 . 1 x lo8 2.3 x lo8,2.5 x lo8 3.0 x lo8 3.3 x lo8 3.4 x 109 3.0 x lo9,2.3 x lo9 4.5 x 109 8.9 x lo9

Table 14 Pulsed-her pltotolysis of0.004 M henzophenone-primary umine sj'stems. Effects of N-D and a-C-D Atiiine

k,,/(M - s - I ) 3.6 x 107 6.4 x lo7 3.0 x 1 0 7 5.6 x 107

Concentrution (M) 0.01-0.08 0.014.08 0.01 4 . 0 5 0.01 4 . 0 5 0.01-0.06 0.0 1-O.06 0.0 1 4 . 0 6

1.7 x

lo8 lo8 lo8 lo8

2.4 x 1.86 x 1.80 x 2.25 x lo8 2.31 x lo8

0.014.06

k,,/k,

1.8 I .9

I .4 1.2 1.3

"In benzene saturated with D20. 'In benzene saturated with H 2 0

quenching of ROH* and RO-* by Haq+ are 1.7 f 0.5 x 1 0 9 s - ' M - ' and 2.8 f 0.5 x 1 0 ' o s - l M - ' for I-naphthol, and 2.4 & 0.3 x I O 7 s - ' M - I and 6 f 1 x l O9 s - ' M - ' for 2-naphthol. The neglect of these effects has led to errors in the rate constants for protonation and deprotonation. The effect of nitrile geometry (linear or bent) on the singlet-state properties of benzonitrile and p-dimethylaminobenzonitrile has been investigated by INDO/S calculations. 1 3 ' A previously low-lying hidden state is the bent form. Solvent viscosity has a marked effect on the fluorescence yield of p-N,N-dialkylaminobenzylidenemalononitrile.3 8 The yield is increased by decreasing molecular rotation of surrounding molecules and so the molecule can be used as probe of microenvironments. Two papers have appeared on the photoionization of N,N,N',N'-tetramethyl-pphenylenediamine (TMPD) in various solvents. 39* Em ission and absorption spectra of some substituted 4-hydroxypyridines as well as pK and pK* values have

'

'

I-'-

I.' I.'

I"'

F. D. Lewis and B. Holnian. 111. J. P/rj..v. Chcrn., 1980. 84. 2326. K . Y . Law. < ' / / C W / . P//l.s. LcJtt..1980. 75. 545. K. Sioiiios. G . Kourouklis. L. G . Christophorou. and J . G . Carter. R d i w . P h j x Chwr.. 1980. 15. 313. K . Lee and S. Lipsky. R(/t/itr/.f/r,r\. ~ ' / r w r . . 19x0. 15. 305.

Pliotopliysicd Processes in Condensed Pliases 65 been r e ~ 0 r t e d . I ~This ' paper discusses the relevance of tautomerism to DNA structure. The fluorescence spectra of 4-cyanobiphenyl and 4 ' 4 kyl- or 4 ' 4 koxysubstituted liquid crystals have been examined as a function of solvent polarity and solute concentration. 142 The fluorescence originates from the planar ' L astate polarized along the long axis of the molecule. A red shift in fluorescence with increasing solvent polarity is due to orientation relaxation. Excimers which have not been reported to form in the first excited ' L astate of biphenyl are observed in concentrated solutions of cyanobiphenyl derivatives. Pande et at. 43 have studied the red-edge effect in excited-state reactions of 2-naphthylamine. The effect appears due to the participation of some non-promoting out-of-plane modes which slow proton transfer in the excited state. Picosecond and nanosecond pulse methods have been used to measure the timeresolved absorption spectra of 9-nitroanthracene, 9-benzoyl- 10-nitroanthracene, and 9-cyano- 10-nitroanthracene. 144 The long build-up time for triplet-triplet absorptions (72-86 ps) suggests that these do not represent the lifetimes of the singlet states but are the rates of internal conversion within the triplet manifold and that indirect intersystem crossing S,(n,n*) -+ T,(n,n*)+ T,(n,x*) is the most important process for populating T,. The fluorescence quantum yields of pyrene- 1-carboxaldehyde in water and methanol are 0.98 and 0.07,14' an effect attributed to solvent effects on x,n* and n,n* states. Cycloaddition reactions of 1-naphthonitrile to 1,2-dimethylcyclopentene are attributed to both ' L a and ' L , states.146It is pointed out that although dual fluorescence is known, this is the first example of divergent reaction from two nearly isoenergetic singlet states. An analysis of the U.V. spectra of some acyl pyridines, 4 7 including a theoretical examination of the molecular geometry, and excited states of bipyrimidine compounds'48 have also been made. Phototautomerism and the fluorescence of the cation of 4-aminopyrazole[3,4-dJpyrimidine, an analogue of adenine, has been published by Wierzchowski et al. 149 Intramolecular heteroexcimer formation in p-(CH,),NC6H4(CH2),(9-anthryl) and P - ( C H , ) ~ N C ~ H ~ ( C H1-pyrenyl) ~),( in hexane and propan-2-01 have been investigated by picosecond time-resolved fluorescence measurements.I 5 0 Two types of heteroexcimer (loose and sandwich) are postulated. The scheqe put forward is: A * m D %loose heteroexcimer e sandwich heteroexcimer. INDO/S calculations on excited states of aza-analogues of stilbene show the lowest excited states to be n,n*, the n,n* states being slightly higher. Extensive experimental studies on the reactivity, fluorescence, and photoisomerization as a function of substitution 5 2 and

'

'

''

D . Sen and C. H. J . Wells, SpiJi,troi,/iiiii.Acrrr. Purr A . 1980, 36, 563.

'" C. David and D. Baeyens-Volant. M o l . CrIw. Liq. CrIxr., 1980. 59. 181. 'L' U. Pande. N . B. Joshi. aiid D. D. Pont. Clicvrt. P/IJ.s.Lcrr.. 1980. 72. 209. '" K . Hmaiioue. S. Hirayama. T . Nakayama, and H. Teranishi. J . P/iI:s. C/icin., 1980. 84, 2074. IJ5 IJh

''-

'" 151

'sI

J . Oton and A. U. Acuna. J . P/ioloihiw.. 1980. 14. 341. F. D. Lewis aiid B. Holman, 111. J . P1i.r.s. C/iivii.. 1980. 84, 2328. W. Pietrzycki. P. Tomasili. and A. Sucharda-Sobczyk. J . M o l . Slriiiv.. 1981. 73. 49. J . Siihnel. U. Kenipka. and K . Gustav. J . M o l . Srrir1.r.. 1981. 76. 213. J . Wierzchowski. M. Szczesniak. and D . Shugar. Z . N~itrrrfimch.1980, 35. 878. M. Migita. T. Okada. N . Mataga. N . Nakushima. K . Yoshihara, Y. Sakata. and S. Misumi. C h c ~ i . P/i.rs. L c / [ . . 1980. 72, 229. 6. Orlaiidi. G. Poggi. and G . Marconi, J . Clicrii. SOL. .. FrrrcitkiJ. Trms. 2. 1980. 76. 598. G. Bartocci. U . Mazzucato. F. Masetti. and G. Galiazzo, J . PhI:c.. Chcwi.. 1980, 84, 847.

66

Pho tocliernistrey

protonation I s 3 have been made by another group. The asymmetric photochemistry occuring under the influence of circularly polarized light has been studied by Horman er a/. 54 Keto-enolization in 2-( l'-hydroxy-2'-naphthyl)benzothiazolehas been studied by laser flash photolysis.Is5 The photochemical properties of the group of compounds loosely described as dyes continues because of the interests in laser technology as well as textiles, photography, etc. The light stability and photodegradation of dyes has been the subject of a recent review.'56 The low energy of n,n* absorption spectra of anthraquinones has been analysed by Kuboyama.157The spectra of the lowest 'n,n* and 'n,n* states of phenazine and acridine have been studied in a biphenyl matrix at 2 K . I 5 * Electronic origins and vibrational analyses can be made in the biphenyl matrix, which allows clear separation of differently polarized spectra. Fluorescence spectroscopy provides evidence for hydrogen bonding of catecholamines, resorcinolamines, and related compounds with phosphate and other anionic species in water.159 Siegmund and Bendig'" have measured the absorption and fluorescence spectra of acridine, N-methylacridine, and N-phenylacridine at 298 K in 35 solvents. The polarity of the excited states and intersystem crossing efficiency are related to solvent properties. Absorption and fluorescence spectra, fluorescence lifetimes, and fluorescence quantum yields for 5,l O-dimethyl5,IO-dihydrophenazine (1 0), 9,14-dimethy1-9,14-dihydrodibenzo[a,c]phenazine ( I l), 9,14-dimethy1-9,14-dihydrophenanthro[4,5-abc]phenazine (1 2), and 6,13-dihydrodibenzo[b,i1phenazine (1 3) have been measured in benzene at room temperature.I6' The spectra are shown in Figure 12 and fluorescence data in Table 15. The long natural radiative lifetimes and large separation between Me I

Me 1

I Me (10)

Ifr3

I" 15'

'" Is' 'sI I6O "'

G . Bartocci. G. Favaro. and G. G. Aloisi. J . Phoroc./irrii.. 1980. 13, 165. M. Htiriiiann. D. Ufermann. M. P. Schneider. and H. Rau. J . P / i o / o c / w i . , 1981. 15, 259. A. Graness. H. Hartman. and J. Kleinschmiett. Z . Plijx Clicwi. ( L ~ i p z i g )1980. . 261, 946. R . S. Sinclsir. Photochriii. Photohid.. 1980. 31. 627. A. Kuboyarna, Birll. CIieni. Sot.. Jpii,. 1979. 52. 329. D. L. Harva and D. S. McClure. C/tcw. Phjx., 1981. 56, 167. J . de Vente, P. J. M. Bruyn, and J. Zaagsma, J . Pharm. Pharmacol., 1981, 33, 290. M. Siegmund and J. Bendig. Z. Narurforsch., Teil A , 1980, 35, 1076. G. 9. Schuster, S. P. Schmidt. and B. G . Dixon. J . P / ~ j xC'hiwi.. . 1980, 84. 1841.

67

Photophysicul Processes in Condensed Phuses

A (nm)

Figure 12 Absorption (A) und jluorescent'e (F) spectru of 5,1O-chnetli~l-5,IO-diIiyclrophencrzine (a), 9.14-ciiniethyl-9.14-ciil~~~tlro~liben;o[cc,c.17l1ena~ine (b), 9,14-dimetli~I-9,14dihydrophenanthro[4,5-abclphenazine (c), and 6,13-dimethy1-6,13-dihydrodibenzo[b,4 plrenazine (d) in benzene ut 24 T. Tlir ortiinutr sccili~scrpply to the uhsorpiion spectru: niusittiirni ,f[uoressCence intensities cwe arbitrury (Reproduced by permission from 1. Phj*s. Cliem., 1980,84,1841).

Table 15 Culculuted und esperimentul opticul transitions of' ( 10) und ( 13) (C2,,) Wuvelengt h /( nm ) Ctilc.

Ohs."

419 385 342 300 288 346 322 312 278 245

397

(

- 296 370) 337

(-315) 266 248

Oscill~itor strength Cuk.. Ohs. 0.95 0.15

0 0 0 0.17 0 0.22 0.0I 0.16 0.83

0.37 0.22 0.07 0.67

In benzene solution at 24 C. hother work. Experimental values were determined in 3-methylpentane at 77 K

"

absorption and emission maxima suggest that the first transition is symmetry forbidden for ( lo)-( 12). The photophysical behaviour of (1 3) is different, so state ordering must be changed in this compound. Excited-state absorption spectra of p-phenylene-bis(5-phenyl-2-oxazole) (POPOP) in dioxan have been obtained over the spectral range 310-760nm. In

Plio t ochniiis t q* 68 the gas phase and in solution S , - S , and not S , + S , absorption is the most probable cause of fluorescence quenching in dye laser operation. Jaraudias has studied the effect of solvent on the relaxation processes of 3,3’-diethyloxadicarbocyanine iodide (DODCI). Solvent viscosity and specific interactions, depending o n the nature of the solvent, are involved in the excited-state relaxation. Picosecond fluorescence measurements have been made on acridine by Shapiro and Winn. 64 The fluorescence lifetime depends upon the excitation and emission wavelengths in some solvents: see Table 16. The lifetime is a sensitive function of temperature and medium. The results are complex but differences of hydrogen bonding with the solvents are important. The \’&& v’ = I vibrational relaxation of sjw-tetrazine in n-hexane has been shown to occur within 8ps although weakly coupled.’65 Harriman and Mills have confirmed that the triplet state of anthraquinone-2,6-disodium sulphonate reacts with water to produce a photosolvate. Anomalous S , + So fluorescence and T2 + So phosphorescence have been found in the triphenyl methane derivatives (14)-(20): 16’ the results are shown in Table 17. The gap between the S2 and S , levels is large, 14000cm-’. The coordination of a lanthanide ion quenches in several cases the S , + Sofluorescence, but the S , + So emission is not significantly affected. The time-resolved fluorescence spectrum of Quinacrine Mustard at pH 4.6 shows three exponential components whose amplitudes depend on both excitation This behaviour is tentatively assigned to the and observation wavelenghts. formation of three protonated species of the excited molecule. The merocyanine dye ( 1 -methyl-4-hydroxystyryl)pyridiniumbetaine (21) shows in rigid ethanol an excitation wavelength-dependent fluorescence. 69 This is interpreted as arising from differentsolute-solvent orientations. In fluid solutions at room temperature there is rapid orientational and translational relaxation of the solvent cage. Three species of 3-hydroxycoumarin can be characterized by their absorption spectra. 7 0 The neutral molecule and cation are fluorescent, whereas the anion is not. First excited singlet state pK, values were calculated using the Forster-Weller equation but the values obtained by fluorimetry, Table 18, are in complete agreement with the ground-state data indicating a rapid excited-state deactivation prior to protolytic equilibration. A very thorough study of the solvent acid acidity dependence of the absorption and fluorescence of the plant estrogen coumestrol(22), has been made by Wolfbeis and Schaffner. ” In aqueous solution, five different species (dianion + dication) can be involved. Other related compounds have also been examined. The yellowgreen luminescence from quercetin and 3-hydroxyflavone at room temperature has

’

’

G. Marowsky and H. Schomburg, J. Pltotochiwt.. 1980, 14, I . J. Jaraudias. J . P/totochm?..1980, 13, 3 5 . S. L. Shapiro and K. R. Winn. J . Cliwt. Plijx. 1980, 73. 5958. Ihi P. F. Barbara. L. E. Brus, a n d P. M. Rentzepis. Cltcvit. Pliys. Lett., 1980, 69, 447. Ihh A. Harriman a n d A . Mills, Pltotochmi. Pltorohiol., 1981, 33. 619. lh7 A. Jarowski and J. Rzeszotarska, J. Ltrriiin.. 1980. 21. 409. IhH A . Andreoni. R. Cubeddu. S. de Silvestri, and P. Laporte. Opt. Cotiirni~ti.. 1980, 33, 277. IhY K . A. AI-Hassan and M . A. El-Bayoumi. Clttvit. P1i.v.v. Lc//.. 1980. 76, 121. ”() 0.S . Wolfbeis, Z . Phys. Chem. (Frankfurt am Main), 1981, 125, 15. I 0. S. Woltbeis and K. Schatfner. Pltotocltiwt. Photohiol.. 1980, 32, 143. lh2 lh3

Menthanol Methanol Ethanol Ethanol Isopropanol Butanol Decanol Ethylene glycol Glycerol Water Carbon tetrachloride Hexane Benzene Acetonitrile

Solvent

Escitntion iiuvelengrli/(nm) 355 396 355 396 355 355 355 355 355 355 355 355 355 355

328 f 50ps 346 f 50ps 339 f 50ps 539 f 50ps 723 f 50ps 1 1.6 ns 60 f 15ps 46 f lops 53 f lops 46 f lops

-

371 f 50ps 21 ns 350 f 50ps

T, 450 nm

-

> 580nm

407 f 50ps 904 k 80ps 375 _+ 50ps 817 & 80ps 346 f Sops 396 f 50ps 325 & 50ps 1.87ns+ Ions 1.92 ns +long tail 28.4 ns

T

Table 16 Dependence 0f:fiuorescence lifetime of ucriiiine upon severul purunwters T.

2.02 ns I .49 ns

5 ns

(450nm 77 K)

-

77 ps

33 ps

-

-

-

I23 ps

-

200: 1 ns 250 ps

Tripkt rim.

jiirtii.

50

+_

6; 38ps

10 13; 27 & 3; 30ns

3.2 ns

0.8 ns: 0.9 ns 350 ps; 0.8 ns; 0.7 ns 0.9 ns 0.9 ns (ri-propanol)

Privioiis rtiiis.vion

9 7~

k

2

5

Y \

2

2.

Photochemistry

70

HOOC OH (14)

Me

H03s0 0 HOOC

OH

(19)

Me

Me

Me

Me

c'fY1

HO,S

\

Me

(21)

been shown by Sengupta and Kasha 7 2 to arise from a tautomer produced by proton transfer in the excited state. At 77K in 2-methylbutane glass, where tautomerization cannot occur, a normal U.V. fluorescence corresponding to the U.V.absorption is observed. 4-Phenylumbelliferone (4-PU), is a model for several natural compounds, which fluoresce from a species formed in acidic solution by an P. K. Sengupta and M.Kasha, Chem. Phys. Lett.,

1979,68, 382.

‘

(cm-’) 18900 19 200 17100 I7 150 I8 700 I8 700 17600

1’

1700 800 55000 9500 I 00 I 00 28000

c

A hsorpt ioti

--*

s,

(cm-I) 20 850 23 300 23 800 22 700 22 000 22 000 21 500

s, +

Fiuorescmw r s, so (ns) (cm-’) 6.5 6.3 16950 1 16500 3.2 I7 400 6.4 10.0 6.4 I6 500

5.7

I 1.7

r (ns) -+

T, so 23 200 23 800 23200 22 800 23 800 23 500 23800 22300 22300 21 700 21500 22500 22500 21800

21 I50 20800 20500 19750 21300 20800 21000

19500 18700 16000 19750 21300 20800 13700

95 1540 230 210 340 290 280

13400 I3 300 I5 200 I6 450 12 900 I2 900 I6 400

Energy

5

p

Table 17 Musiniu qf uhorption spectru in the visible (and corresponding molar ubsorptivities E) , .fluorescence, und phosphorescence sspc’c-tru,Iifitinws qf S , -, So und S, -+ S,,fluorescence and T2 + So phosphorescence, undS2 + S , energy gups estimuted,from 2 the absorption spectru ,for compounds ( 14)-(20) s

Plio t ochsmis t rjv 72 Table 18 Ground und first excited singlet stute dissociution constunts of 3hjdro.yycoumarin at 22 "C 0-0 \Imaxabs

Species

Anion Neutral molecule Cation

pKa(So) 7.16 f 0.04 -3.9

0.2

mitisition

\~m,xf'u

(cm- ') (cm- I ) (24 165) (27349) (estimatedy 32616 26247 29431

(cm- ') 30534

29455

23529

PKa(S,1 PKa(S1) by F&sfer,fluoriWr//rr-cri/c. merrictill~ 2.6 7.2 2.5

- 3.9

26492

"Assuiiiing the same Stoke's shift as for the cation

adiabatic photoreaction of the excited state [Scheme 2, path (b)]."3 This could be enrichment a tautomer or more likely a quinoid keten phototautomer: provides evidence for the latter. Path (a) is preferred in slightly acidic solution. anion(S,)

A

4-PU(S,) (b) phototautomer (exciplex)

I -

1

photochemical ring-opening

517nm flu

anion(S,)

111;

/enw

4-PU(S0) 4Ruorescence

keten tautomer

(?)

Scheme 2

Lumichrome [7,8-dimethylalloxazine, (23)], a flavin tautomer, has two fluorescence emissions with maxima at 440 and 540 nm in pyridine-dioxan mixtures.' 7 4 Nanosecond time-resolved fluorescence shows fast growth of the latter due to proton transfer from N-1 of the excited lumichrome (23*) to N-10 during the lifetime of lumichrome singlet, and emission occurs from the excited flavinic chromophore (24*). Quinizarin and daunorubicin (an anti-cancer drug) have been studied to obtain information on transition-moment direction. 7 5 Quinizarin has been examined in

(23) I-' I''

(24)

0. S. Wolfbeis. E. Lippert mid H. Schwarz. Bcr. Bwi.scvigc~.v. P/i.~x.Chcrii.. 1980. 84. I 1 IS J . D. Choi. R. D. Fugate. and P.-S. Song. J . A m . C/ICW.SOL. 1980, 102, 5293. R. N . Ci~pps;111dM . Viilit. P h ~ ~ f ~ ~Photohid.. c h ~ i . 1981. 33. 673.

..

Pliotoplysical Processes in Condensed Phmes

73 Shopolski and EPA matrices. The first four electronic transitions are assigned and fluorescence is due to the ' B , (nn*) -, ' A transition. Since the n + n* transitions are higher in energy, intersystem crossing is inefficient, as observed. The natural pigment, 2-amino-4-pteridinone, has been the subject of an intense photophysical investigation and the photosensitizing properties have also been studied. 7 6 Picosecond fluorescence kinetics and polarization anisotropy measurements have been obtained from anthrocyanin pigments and in vivo samples.'77 Evidence of quenching and non-random orientational order in in vivo systems has been indicated. Fleming and co-workers have examined the birefringence and dichroism of dye solutions during picosecond pulse excitation. Rotational reorientation times for oxazine-725, cresyl violet, rhodamine B, and DODCI measured were 144 f 10, 223 & 12, and 153 & 8ps, respectively. The rotational motion of small chromophores has been measured by a combination of steadystate polarization and single-photon lifetime measurements, in which there is simultaneous delection of two polarization directions. 7 9 Nemet et ul. ''O have measured a fluorescence decay time of 4.1 & 0.1 ns for rhodamine 6G. The same dye has been the subject of two papers dealing with its properties as a laser dYe*'". 1 8 2 Karstens and Kobs ' 8 3 have compared rhodamine B (25) and rhodamine 101 (26) as fluorescence quantum yield reference substances. For rhodamine 101 the quantum yield was 1.0 at all the temperatures investigated. This was not true for rhodamine B, and at room temperature OF d 0.5. A number of luminescence quantum counters based on organic dyes in polymer matrices have been described. 184 Poly(viny1 alcohol) films are suitable for water-soluble dyes, and poly(viny1pyrrolidone) is compatible with dyes soluble in organic solvents. The photoionization of 9-anilino- I -naphthalenesulphonate (ANS) is shown to occur through a biphotonic process. '" An intermediate charge-transfer complex

'

' ''

i

'$7

C , Ch.'I h'tdt. M. Aubailly. A. Motnzikolf. M. Bazin. and R . Santus. P l r o ~ o i h ~Pliotohiol.. r~~. 1981, 33, '

641.

F. Pellegruno. P. Sekuler. and R. R. Alfaro. P l i ~ t ~ ~ l i cPlrotohioplrjx., ~ti. 1981. 2, 15. D. Waldeck. A . J. Cross, jun.. D. B. McDonald. and G . R . Fleming, J . Chcw. P/ij*s..1981.74, 3381. R. W. Wijnnendts van Resandt and L. De. Maeyer. C'lrcw. Phjx Lotr.. 1981, 78. 249. "" N . Nemet. K. Szues. M. Hilbert. and L. Kozina. Ac./ir P/rI..s. C/IP/JI.. 1979. 25. 103. P. R. Hanimond. lEEE J . Qiwrituiir Elviwoii.. 1980. 1 I . I 157. In' P. R. Haintnond and R . Nelson, lEEE J . Qirtrririrrii E/li1'/~O/7.. 1980, 1 I , 1161. l n 3 T. Karstens and K. Kobs. J . P l i j x C ~ J I J 1980. ~ . . 84. 1871. In' K . Maiidal. T. D. L. Pearson. and J. N . Demas. Ant//. Chivir.. 1980. 52. 2184. I n s H. Nakaniura. J . Tonakii. N . Nakashimii. and K . Yoshihara. Clrcwi. P/rj*.s.Lit//.. 1981. 77, 419. I--

IiH

I-'

74 Pl~otoc.liPniisri.!. involving the solvent is reported. The pressure dependence of excited-state proton transfer equilibria has been examined in several substituted naphthalene dyes, in particular 1-dimethylamino-naphthalene-5-sulphonic acid (DANS). 8 6 High pressure has been used in the luminescence of intramolecular charge transfer compounds by Rollinson and D r i ~ k a m e r . To ' ~ ~a large extent the increase of pressure alters luminescence in a way similar to an increase of solvent polarity. The technique is obviously a powerful one for elucidating systems where n,n* and n,n* states can be involved as well as proton transfer and solvent cage effects. Pollis and Drickamer188 have made high-pressure luminescence measurements on metalloporphyrins in polymeric media. This very interesting paper shows how pressure can be used to control the relative rates along the various paths available since pressure shifts energy levels with respect to one another. The energy-level diagram for Cu-octaethylporphyrin in Figure 13 illustrates this. An investigation of Group 3A phthalocyanines using laser photophysics has been made by Brannon and Magde. ' 8 9 Fluorescence yield and lifetime and triplet yields have been measured at room temperature. LOW PRESSURE

HIGH PRESSURE

Absorption spectra and decay kinetics of electron adducts of proflavin and acridine yellow in aqueous solution have been studied and the rates of transfer to different electron acceptors measured. '90 Electron injection from xanthene dyes and tetraphenylporphines into ZnO and TiO, has been shown to compete with fluorescence. ' 'I Picosecond spectroscopy has been used to determine excited-state absorption spectra and decay mechanisms in photostabilizers. ' 9 2 Fluorescence I"'

InIxx

"" 1"'' '"I

I"'

C . J . M;istritllpelo i i d H.W . Otfen. J . Sdliiio/i C ' h ~ i . 1980. . 9. 325. A. M. Rolliiisoii and H . G . Drickamer. J . C'licwi. P/I.IT..1980. 73. 5981. T . G. Politis and H . G . Drickamer. J . C ' / i w i . f / i j x . , 1981. 74. 263. J . H . Briinnoii iund D. Magde. J . Am. C ' h ~ ~ iSoc.. ~ i . 1980. 102. 62. M. T. Neiiadovic. 0. 1. Micic. and M . M. Kosanic. R d i i i [ . fli,r.y. C/icwi., 1981. 17, 159. M. Miitsumura. K . Mitsuda. N . Yoshizawa. mid H . Tsubomura. Bull. Clirrti. Soc. Jpz.. 1981. 54. 692. A. L. Huston, C. D. Merritt, G . W. Scott, and A. Gupta, Proc. 2nd Int. Conf. on Picosecond

Phenomena, ed. R. Hochstrasser. W. Kaiser, and C. V. Shank, Springer-Verlag, Berlin, Heidelberg, and New York, 1980, p. 232.

Photopi1j i c d Psoc~c~ssc~s iiI Cor I ~icwse~l Pit iisc.v 9

s

75

has been used to determine constants between riboflavin and a series of phenothiazines. 1 9 3 Cline Love and Upton 19' propose that measured and natural fluorescence lifetimes can be used for the selective determination of drugs and metabolites. Quenching Processes.-Complexes formed between excited states and ground states are now recognized to be very widespread in all aspects of photochemistry. Consequently they are the subject of numerous papers. Large rates of quenching by different states of fluorescent solvent excited state liquid cis-decalin and cyclohexane as observed by pulse radiolysis are caused by large reaction radii.195Values of 14, 13, and I5 A are found for the quenching of the excited state is cis-decalin by CCI,, in cyclohexane by CCI, and 0,. respectively. Aliphatic aldehydes undergo self-quenching ( k 2: 1O9 M - ' s - ') from the singlet state leading to a dimeric a-ketol. l g 6 Quenching of fluorescence by dienes has a rate constant of about the same value ( e u . 4 x lo9 M - ' s - ') giving rise to the formation of oxetans. Watkins '91 has concluded that, although energetically favourable, quenching of the fluorescence or aromatic hydrocarbons by oxygen in acetonitrile does not produce radical ions. The experiments support earlier views that 0, quenching involves reactions ( I ) and (2). Deuteriation has

little effect on the rate of oxygen quenching. By contrast, quenching of porphyrin and metalloporphyrin excited states by oxygen in protic and aprotic solvents has been shown by spin-traps to form both superoxide and singlet oxygen.198The

quenching of the fluorescence of naphthylalkyl halides (27) and (28) by haiogen group is dependent on the length of the chain and nature of the halogeno-group (see Table 19).'99 Triplet yields are dependent upon the orientation of the halogenogroup with respect to the aromatic nucleus. Ramakrishnan and his colleagues have studied the interaction of excited anthracene and carbon tetrachloride, 2oo fluorescence quenching of anthracene by acrylonitrile, 201 and solvent effects on the I43 IYS IYS

1Yh

1Y7

14H I4Y

200

E. Martin. F. R. Mowgon. and A. PdrdO. Aiiril. @rim. Rivrl. Sou. Esp. Fi.s. Quirii.. 1980. 76. 77. L. J. Cline Love and L. M . Upron. A d . Clrirrr. ,4c.fr,. 1980. 118. 325. L. H. Luthjens. H . D . F. Codee. H . C. de Leng. and A. Huinmel. CIrcvrr. P / I , I ~Lc.tr.. . 1981. 79. 444. J . Kossanyi. G . Daccord. S. Sabbah. B. Furth. P. Chaquin. J . C. Andre. and M . Buchy. N o m . J . Chiiii.. 1980. 4. 337. A. R . Watkins. C/rwi. Phyv. Lc,rr.. 1979. 65. 380. G. S. Cox. D. G . Whitten. and C. Gianotti. Clrc~rir.P/I.I.S.Lcvr.. 1979. 67. 51 I . R. S. Davidson. R. Bonneau. J . Jousott-Dubien. and K . R . Trethwey. C/r[wi.P h ~ xLcrr.. 1980. 74. 318. N . Se1var:ijan. M . M . Panicker. S. Vaidyanathitn. and V . Rumakrishnan. Iiiclicrri J . Clrcwi.. 1979. 18.

23. 20I

N . Selvarajan and V . Riimakrishnan. Irrrliciri J. CIrewi. See,.. Scc.r. A. 1979. IS. 340.

I -methylnaphthaleiie (27). I? = I . x = c1 (27). I ? = 2. x = c1 (27). I? = 3. x = CI (27). I I = 2. X = Br (27).I 1 = 2. x = I 2-met hy I n ;ip ht hale ne (28). I 1 = 2. x = CI (28). I I = 2. X = Br (28). I? = 2. x = I

0.044 0.10 0.20 0.06 0.55 0.30 0.03 0.06 0.18 <:0.15

0.85 0.034 0.255 0.57 0.05 0.025 0.6 0.1 < 0.05 <0.015

2.5 0.23 1.6 2.0 0.27 0.29 2.4 I .7 0.37 0.07

0.1 17 0.45

0.17 0.07 2.14 1.06 0.03 0.04 20.5 23.16

"Calculation of/;,, requires a knowledge of k , . This was obtained from being obtained from oxygen quenching nieiisurenients

0.28 3.9 0.46 0.43 1.56 2.4 0.39 0.56 22 2 12

4, =

4.9 x los 2.8 x 10" 10.6 x loh 1.6 x 10" x 10' x

14.3 7.8 3.67 198 >23 >7

loh

x 10'

x lo6 x loh x loh

k , ~ , .the values of

T,

photoreaction of anthracene with acrylonitrile.202 Time-resolved absorption spectra of pyrene-aromatic amine systems have been measured by picosecond laserspectroscopy.203The heteroexcimer was detected with a lifetime of about 200 ps, in good agreement with the rise time of the I-hydro-1-pyrenyl radical. Picosecond dynamics of the intramolecular exciplex anthracene-(CH,),-N,N-dimethylaniline have been measured in a c e t ~ n i t r i l eTwo . ~ ~ ~processes can occur: (i) very rapid (7 & 1 ps) electron transfer for molecules in extended conformation, producing solvated ion pairs without passing through the exciplex state, or (ii) folded conformers yield exciplexes with 2 ps, having a lifetime of 580 & 30 ps. The details are shown in Figure 14. The photophysical behaviour of a series of intramolecular exciplexes of 1 -amino-3-(9-anthryl)propanes have been studied as a function of solvent and structure.205Similar measurements have been made on the intramolecular exciplex fluorescence of N-phenyl-N-methyl-3-(9-anthryl)-I-aminopropalie in saturated hydrocarbons of different viscosity.'06 Multiple fluorescence is also found in the N-trimethylene-bridged p-N-methylaminoben~aldehyde.~~~ The influence of restricted internal motion on the intramolecular exciplex of 1 -@dimethylaminophenyl)-3-(9-anthryl)propane has been studied by Gusten et ~ 1 . ~ ' ~ Loutfy 209 has proposed using b-(N,N-dialkylamino)benzylidene]malonitrilesas fluorescence probes for measuring the extent of polymerization of methyl methacrylate. Fluorescence quenching of 2-methylnaphthalene with aliphatic amines has been used to measure the thermodynamics and kinetics of exciplex formation and the results interpreted by the Marcus theory.'" The effects of electron acceptors on the fluorescence and truns -+ cis-isomerization of 2-styrylN. Selvarajan and V. Ramakrishnan. h / i i i / i J. CI~PIII. Sol... Swt. A , 1979. 18, 331. T. Okada. N . Tashita. arid N . Mataga, C I ~ P IPI I/ ~. , I XLctr.. . 1980, 75. 220. 'OJ M . K . Crawford. Y . Wang, and K . B. Eisenthal. CIIPIII. P/I,Ix.L.ctl.. 1981. 79. 529. F. Pragst. H.-J. Hiimann. K . Teuchner. and S. Daehne. J . L w ~ i n . 1978. . 17, 425. N. Yang. S. B. Neoh. T. Naito, L . - K . Ny, D. A. Chernofi. and D. B. McDonald. J . Am. C h w i . SOC.. 1980. 102. 2806. '07 W. Freyer, K . Teucher. and S. Diihne. J. Prtrkt. C/icw.. 1981. 323. 324. "" H . Gusten. R . Meisner. and S. Schoef. J . Phorochrwi.. 1980. 14, 77. 'OL) K. 0. Loutfy, M r / i ~ r . o r l t o / c , c ~ i r 1981. l. 14. 270. '") F. Meeus. M. Van der Auweraer. and E. C. De Schryver. J . Atit. Cliiwt. Soc. 1980. 102. 4017. 201

?03

..

77 I

I

I

A- D I

FOLDED

EXTENDED 1 FOLDED EXTENDED CONFORMATONICONFORMATION CON FOR MA TI^ ACETONITRILE 2 - METHYLBUTANE

CONFORMATION f

Figure 14

=184

6

=37

E ~ i c ~ - 1iwl.v g j * crtitl r[i*tititnii.s(~~'trtitIir.trc~i~tic-(CH ),-N.N-tliriic~th!.lti~iilitic~ in hotli

loi t.- trritl high-poltrritj- soli~cwt.Rchtiiv cvii~rsqiev iirc

ti

qutilittitiiv

(Reproduced by permission from Cliiwi. P1ij.s. Lett.. 1981. 79, 529).

naphthalene have been reported by Gennari e t u / . ~' ' A similar investigation has been made by Aloise et d.212 The fluorescence quenching of stilbene, styrylnaphthalenes, and some aza-analogues by aliphatic amines has been studied in organic solvents. The quenching is associated with exciplex emission, and the Stern-Volmer quenching coefficient increases with a decrease in the ionization potential of the amine. truns 4 cis Photoisomerization shows that Qcis is reduced less than OFas induced intersystem crossing, through charge-transfer association, leads to isomerization in the triplet manifold. Parola and Cohen 2 1 3 have studied the effect of solvent on the photoreduction and quenching of benzophenone by amines, an effect attributed to interaction with the triplet state. Picosecond spectroscopy has been used to study the photodissociation of 1,-aromatic complex and the formation of iodine atom-aromatic complexes.2 l J Shizuka, Nakamura, and Morita " have studied the anion-induced fluorescence of aromatic molecules. Electron transfer from the anion to the excited aromatic seems to be the key step (Table 20). Triplet formation has also been studied by nanosecond laser spectroscopy. The rate constants are shown in Table 21. The fluorescence of 2-ethoxynaphthalene is quenched by methyl benzoate through an exciplex.216The importance of the rate of formation of exciplexes and radical ions in the encounters of excited aromatic esters with aliphatic amines has been stressed by Costa and M a c a n i k 2'' A charge-transfer mechanism is clearly demonstrated in the quenching of excited aromatic esters by triethylamine.2 'I1 'I'

2'3

'Is 'I5

'" 'I7 'IH

G . Gennari. G . Cauzzo. G . Galiazzo. and M. Folin. J . P/ioioc.hcrii. 1980. 14. I I . G. Aloise. G . Bartocci. G. Favaro. and U . Mazzueato. J . P/ij*.s.C/wii.. 1980, 84. 2020. A. H . Parola and S. G. Cohen. J . P/iotoc~hcii~.. 1980. 12. 41. C . A. LanghotT, K . Gnadig. and K . B. Eisenthal, C/ic,m. P h j x . . 1980, 46, 117. H. Shizuka. M . Nakamura, and T. Monita. J . PIiJs. C/iiwi.. 1980. 84. 989. S. Murata, J . Pliotoihiwi.. 1980. 14. 167. S. M. de B. Costa and A. L. Macanita. J . Plioioihiwi., 1979. I I . 429. S. M . de B. Costa, A . L. Macanita, E. C . C. Mela. and M . J . Prieto. J . Pliorochcwi.. 1979. I I . 361.

2.1 2.2, I .8 9.3, 6.3, 4.3 0.34 0.136 3.58 5. I 5.46 I .40

0.28, 0.088 0.06, 7.9, 5.8, 0.12 2.8, x 5.1 x lo-' 0.70, 3.6 5.59 1S O h

6.07 1 .87h

0.10, 0.08, 6.8, 4.2, 0.42, 2.3 x 2.0, x 0.67

4.8 x 3.0 x 5.4, x 5.8, 1.4, 0.2 I , 1.0 x lo-' 2.56 x 7.03 X 0. I6 6.24 2.0 10-3

0.13 6.59 2.29

0.96 2.4 x < 2 x 10-3

5.6,

2.8, x

7.07 2.55

1 x

+

2.25b 2.32' 2.20' 1.62' 1.61' 1.70' 2.22b 2.45' 2.41' 2.46'

3.99d 3.87' 3.79' 3.8,' 3.73' 3.30' 3.58d 3.33d 4.12d 4.28'

74 _+ 2 12.2 & 0.6 12.4 & 0.5 5.4 f 0.3 16.4 f 0.5 4.2 0.2 53.5 f 1.0 420 f 7 6.7 f 0.4 13 f I

5

:*

3 5

a

::

Experimental errors within 5",,except for the anthracene-CI- system (errors within lo:;,). Data taken from S. Wawzonek and H. A. Laitinen, J . Ant. CI1en7.Soc., 1942. 64. 2365. ' Ref. 21 5 . Data taken from J. B. Birks 'Photophysics of Aromatic Molecules', Wiley-lnterscience, London, 1970. ''Data taken from 1. Berlman, 'Handbook of Fluorescence Spectra of Aromatic Molecules'. Academic Press. New York, 1965. 'Data taken from M. J. Blandamer and M. Fox Clieni. Rev., 1970,-70, 59. g V . M. Berdnikov and N. M. Bazhin, RII.EY. J . P/I,I:Y.Clr~ni.,1970, 44. 395. "Calculated values from the equation E(ccts) = 1.35E(X-iX ' ) 3.55 in eV units. 'Vs. the standard hydrogen electrode u4.

Naphthalene 1 -Methoxynaphthalene 2-Methoxynaphthalene 1-Cyanonaphthalene 2-Cyanonapththalene Anthracene Phenanthrene Pyrene Fluorene Biphenyl E(ctts)f/(eV) E( X -/X * )g. '/(eV)

*

Table 20 Rate constants .for the anion-induced.fluorescence quenching ( kq), lijetimes ( T ~ ) ,halfltoave potentials of' aromatic molecules (E,,,), oxidation potentials [ E ( X - / X )], and CTTS transition energies [E(ctts)]of inorganic anoins, and excited singlet energy levels (EA*)in 50% EtOH-H,O solutions at 300 K

Pliotopliysical Processes in Condensed Pliuses Table 21 Anion-induced intersystem crossing rate k,c, 'A Anthracene

Phenanthrene

'XIN,BrIN,Br-

'kq/(M-'s-') 4.3 (f0.2) x lo9 4.3 ( f 0 . 2 ) x lo8 2.2(fO.l) x lo8 3.4 (kO.1) x lo8 2.3(_+0.1)x lo7 I . O ( + O . l ) x lo7

,c,lk,c) (M-l) 26.4 1.80 1.3, 20., 0.1, 0.53

79

klc,/(M - I s - I ) " 3.9, ( f 0 . 3 ) x lo9 2.6, ( k 0 . 2 ) x lo8 1.94( f O . l ) x lo8 2.8,(*0.1) x 108 1.2(*0.4) x 10' 7.6 ( k 0 . 4 ) x lo6

;'* 0.91 0.62 0.88 0.84 0.05 0.76

"The k,,. values for anthracene and phenanthrene were evaluated assuming klc to be 1.4, x 10' and 1.4, x IO's-', respectively. *;' = k,J1kq (errors within lo",,)

Emissions from intra- and inter-molecular exciplexes between benzophenone and N,N-dimethylaniline have been studied in detail by Japanese Lim et a1.220have presented evidence that singlet-triplet intersystem crossing from the charge-transfer state of electron-donor-acceptor complexes is efficient only when a locally excited triplet state of a component molecule (donor or acceptor) lies below the charge-transfer singlet state. The influence of starting conformations on intramolecular exciplex formation in a-phenyl-r,-N,Ndimethylaminoalkanes has been extensively investigated.221 Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds.222 Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2N,N-dimethylaminopyridineinduced by p-nitroaniline is also caused by exciplex formation.223 The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.224A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons.2 2 5 The N-isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.226 Photoinduced electron-transfer in the p phenylenediamine-paraquat complex yields the paraquat cation. The quenching of thionine fluorescence by metal cations has been studied.228 Complex formation between thionine and SO,'- ions has also been established. Quenching of Methylene Blue by Fe"' has also been examined.229 Fluorescence from intramolecular charge-transfer states of aromatic silanes is reported by Shizuka et 0 1 . ~ ~ '

"'

219

"" "'

--77.9

224 225

22b

"' 'IH 129

230

H. Masuhara. Y. Masda, H. Nakajo. N . Mataga. K . Tomita, H. Tatemitsu. Y. Sakata. and S. Misumi. J . Am. Clicni. Soc., 1981. 103. 634. B. T. Lim. S. Okajima. A . K . Chandra. and E. C . Lim. Clicvii. PIijx. Lcvt.. I98 I. 79. 22. M. Van der Auweraer, A. Gilbert. and F. C. De Schryver. J . Am. CIi~wi.Sot,., 1980, 102. 4007. N . Iked. T. Okada. and N . Matagd. Bid/. C/im. Sol.. Jpu.. 1981, 54. 1025. J . Wollebeu and A. C . Testa. J . Photoc/icwi., 1980. 13, 215. G . E. Johnson. J . P/ij..s. Cliiwi.. 1980. 84, 2940. A. Ahinad and G . Durucher. Cwi. J . Spwrosc., 1981, 26. 19. U . Lachish and D. J . Williams. Clicni. P/ij.s. Lctt.. 1980. 72. 225. A. T. Pulos. C. K . Kelley. and R . Sumane, J . f / i j : s . Chcvii.. 1981. 85. 823. G . Kohler. S. Solar. and N. Getoff, Z . N(lfiirjiJr.s~h., To;/ A . 1980. 35. 1201. T. Ohno and N. N . Lichtin. J . P/ij:s. C/rm.. 1980. 84. 3485. H . Shizuka. H . Obuchi. M . Ishikawa. and M . Kumada, J . C/icwi. Sol,.. Chew. Coiwiiiui.. 19x1. 405.

80

Photoc.lieniistr.?i

The electron-donor aspect of molecules such as porphyrins can be used to induce charge-transfer photogeneration in surfaces.231.2 3 2 An interesting situation is the enhancement of fluorescence of x-napthoxyacetic acid in y-cyclodextrin by the space regulating role of c y c l o h e ~ a n o l .Excimer ~~~ formation also occurs in these systems. Energy Transfer.-In this area, theory attracts more effort than experiment. B ~ r s h t e i nhas ~ ~examined ~ the influence of migration mechanism of approaching particles on energy transfer between them. A very detailed treatment of exchange energy transfer in fluid solution is given by Balzani, Bolletta, and S c a n d ~ l aThe . ~ ~treatment ~ is classical and has been designed for treating vertical and ‘non-vertical’ transitions. Blumen et ul.236have considered energy transfer amongst impurity molecules in disordered systems. Blumen 2 3 7 has also presented expressions for the ensemble-averaged decay of the excitation of a donor owing to the energy transfer viu anisotropic dipolar interaction to randomly distributed acceptors. Huber238 has studied coherent transfer in systems with a low concentration of quencher. Other papers deal with excitation transfer from donor to acceptors in condensed media239 and dynamics of non-random energy accumulation viu excitation transfer in random The theory of impurity trapping and self-trapping is developed using the theory of exciton-photon coupling. 241 Kopelman and Argyrakis 242 have developed the theory of diffusive and lattice migration of excitons. The theory of exciton annihilation in molecular crystals has been extended by Kenkre.243 Kenkre and Wong244 have extended exciton-transport theory for direct migration experiments. The same authors have analysed other aspects of exciton migration.245 Kosloff and Rice 246 have considered quantum effects in the mechanism of intramolecular energy transfer. More related to general photochemistry are the papers which have appeared o n wholly or partly diffusion-controlled reactions. The effect of a very short lifetime of the donor on the calculation of fluorescence quantum yields and lifetimes has . ~ ~ et~ ul.248analyse the kinetics of energy been analysed by Viriot et ~ 1 1 Andre transfer to an acceptor when there are two different excited states capable of acting as donors and when interaction between these states is possible. The exchange interaction contribution to energy transfer between ions in the rapid diffusion limit R. 0. Loutt’y and E . R. Mcnzel. J . A m . C k w 7 . Soc.. 1980. 102. 4967. T . Taniniurii. T . Kawai. and T . Sakata. J. P/r~..v.Clwm.. 1979. 83. 2639. A. Veno. K . T;ihah;ishi. Y. Hino. and T. 0 s ; i . J . C / r w ~Sou.. . Cliiw. Comrmtrr.. 1981. 194: A. Veno. K. Takahiishi. and T . Osa. hid.. 1980. 92 I. A . I . Burshlein. J . Lw~irr..1980. 21. 317. ’.’.’ V. Balzani. F. Bolletta. iind F. Scandola. J . .4ur. C ’ / w u . Soc-.. 1980. 102. 21 52. A . Blunien. J . Klafter. iind R. Silbey. J . C ’ h c w r . PhI.5.. 19x0. 72. 5 3 2 0 . ’37 A . Blumen. J . C h c ~ r . P//I..v. . 1981. 74. 6920. 13H D. L. Huber. P/IJ..v.Rcr. B. 19x0. 22. 1714. ”’) A. Blumen, Nuovo Ciniento, 1981, 63B,50. ”” A. Blumen, J. Manz, and G. Zumofen, Nuovo Cinwnto, 1981, 63B, 59. D. P. Craig. L. A . Dissado. and S. H.Wiilnisley. C/rcw. PhI.s.. 1980. 46. 87. . 19x0. 75. 3053. R. Kopelnian and P. Argyrukib. J. C / I W / P/rI..v.. ”.’ V. M. Kenlive. Phj..v. RcI.. B. 1980, 22. 2089. 2-L4 Y . M . W o n g iind V. M. Kenkre. P/r~.v.Her. B. 19x0. 22. 3072. V. M. Kenkre and Y. M. Wong. PhIx. KCI B. 1980. 22. 5710. ”” R. Koslotfand S. A . Rice. C’lwrrr. /VI.I..\. / A , / / . . 19x0. 69. 209. ”M. L. Viriot. J . C . Andre. and W. R . Ware. ./. P/rofoc,/fc,rlf..1980. 14. 133. J . C. Andre. M . HoLiCIl>.. ;ind W. R. Wiirc. J . P / I ~ J / ~ K / W1980; / ~ / . 14. . 177.

’”

’’’

”’

81

Photoplij~.siidProcesses in Comimseci Phases

has been analysed by Meanes, Yeh, and S t r ~ e r The . ~ ~effect ~ of diffusion on transfer processes mediated by dipolar and quadrupolar interactions has been examined by Allinger and B l ~ m e n . ~ ~ ~ Since energy transfer is important in biochemical systems Dewey and Hammes 2 5 have developed a general method for estimating fluorescence resource energy between distributions of donors and acceptors on surfaces. Models of interest for membrane biochemistry are (a) an infinite plane, (b) parallel infinite planes, (c)the surface of a sphere, (d) the surfaces of concentric spheres, and (e) the surfaces of two separated spheres. Energy transfer in solid alkanes at 4 and 7 7 K has been studied by pulse very r a d i o l y ~ i s .A~ ~ ~ rapid transfer from excited alkane to toluene is shown. Energy transfer between diethylmethylamine and benzene occurs with either acting as donor.253The singlet energy of the amine is about 700cm-' higher than the S , state of benzene; a value of 430cm- is deduced from measured energy transfer rates. The participation of an exciplex is possible. Beecroft and Davidson 2 5 4 find that 2-phenylethylarnines exhibit fluorescence owing to an intramolecular exciplex in cyclohexane. The excited state of benzene at low concentrations does not form an exciplex with tertiary amines. Instead sensitized amine fluorescence is observed. The authors speculate on this effect which clearly relates closely to the effect described in reference 253. Energy transfer at 5 K in crystalline anthracene doped with 2-methylanthracene has been studied by fluorescence spectroscopy and time-resolved spectrofluorim e t r ~ . The ~ ' ~ dopant induces two distinct traps that can be assigned to specific orientations of the guest. Energy transfer from naphthalene to anthracene on polymer chains is enhanced by nearly 102-fold.256This requires the lifetime of naphthalene excited states to be extended. Intramolecular energy transfer in molecules containing phenanthrene and r-diketone moieties connected by chains of 5 methylene groups has been studied.257From the effect of exciting wavelength and temperature it is demonstrated that energy is transferred very efficiently to the r-diketone chromophore from the phenanthrene group. A more extended description is given in a second paper.258 Zimmerman and co-workers 2 5 9 have synthesized rod-like molecules composed of bicylco[2,2,2]octane units bonded bridgehead to bridgehead. Various end chromophores were placed at the terminal bridgehead sites of [I]-rods and [2]rods. Rate studies revealed intramolecular singlet-energy transfer from the naphthyl moieties to acetyl. cyclohexanecarbonyl, and benzoyl groups with shortening of the naphthyl S , chromophore lifetime. The dependence on distance was greater than the anticipated sixth power, an effect discussed in terms of an

'

'

"-)

15" '5'

"' 2i-7

'i4 2ii

-7 .j 2ih

2iv

C . F. Meanes. S. M . Yeh. and L. Stryer. J. A n i . C/icvii.So(... 1981, 103, 1607. K . Allinger and A . Bluiiien. C/icvrr. P/I,I..Y.Lilt/.. I9X I . 79. 494. T. G . Dewey and C . G. Hitmiiies. Biop/i~~.s. J.. 1980. 32. 1023. T. Miyazaki. I. Shigetu. and K . Fueki. Rtditrr. Ph?..). C/iiwi.. 1980. 16. 107. A. M. Halpern and K . Wryzkowska. C'lwrit. P/IJ..\. I.(,//.. 1981. 77. 82. R . A . Heccrol't and R . S. Davidson. C / / c w i . P/iI..s.L o / / . . 1981. 77. 7 7 . N. J . B ~ . ~ d gaild c D. P. Solomans. J. C / / c / i l . Soc... f > / r c u / ( /Trt//~.s. ~. 2, 1980. 76. 472. D. A . Holden and J . E. Guillet. .~lfic.roiiio/~,c.lr/c'.\. 1980. 13. 289. D. Get/. A . Ron. and S. Speiser. J. M o l . S/rr/c.f..1980, 61. 61. D. Getz. A. R o n . M . B. Rubin. und S. Speiwr. J . P/iI.,\. Chcvir.. 1980. 84. 768. H . E. Zimiiirmian. T. D. Goldiii~iii.7'. K . Hirzel. and S. P. Schmidt. J . Oyq. Chcwi.. 19x0, 45. 3933.

82

Photochemistry

Scheme 3

overlap delocalization in the case of the [ I]-rods. The kinetic pathway used for the discussion is shown in Scheme 3. Energy transfer between coumarin 1 and coumarin 314 has been demonstrated.260The dye mixture is more efficient in laser action than coumarin 314 alone. In studies of energy transfer between dyes with closely located S , levels using steady-state and picosecond studies, rhodamine 6G and 3,3'-diethylthiocarbocyanine iodide mixtures have been examined. 2 6 1 Picosecond spectroscopy shows the rate of energy transfer to be essentially that predicted by Forster theory. R, was measured to be 73.2 A. Fluorescence decay times and quantum yields in the rhodamine 6G (donor)/malachite green (acceptor) system have been reported by Bojarski and Grabowska.262The theory of concentration depolarization in dye solutions has been extended by Cherek.263Mobius and Kuhn 264 report energy transfer from oxacyanine to a thiocyanine dye in monolayer assemblies and fully examine the theory and nature of the monolayer assemblies. Fluorescence decays of a monolayer of rhodamine B on singlet crystals of anthracene, phenanthrene, and naphthalene have been studied with a pulsed picosecond laser.265Electron and energy transfer are involved in producing two different decay characteristics. Amorphous films or amorphous solid films of porphyrins on metal substrates have been examined.266The absorption spectra resemble those in solution but the lifetime of the S , states are reduced by non-radiative decay. Forster energytransfer to the metal substrate explains most of the quenching observed but exciton transfer is also involved. Micellar Systems.-The application of photophysical methods to the study of micellar phenomena is the most rapidly developing aspect of this subject at the. present time. Apart from the intrinsic interest to the problems of colloid chemistry the effects on energy and electron transfer are very pronounced. These latter aspects may contribute very significantly to the technology of solar energy conversion. Lindig and Rodgers 2 6 7 have reviewed the subject and given a 260

262 263

2hJ 265

"' 267

A. J. Cox and B. K. Matise. Chcwi. Ph.rs. Lctt.. 1980. 76. 125. Y. Kusumato, H. Sato. K. Maeno. S. Yahiro. a n d N. Nakashima, Bull. Clicni. SOC.Jpn.. 1981.54.60, C. Bojarski and E. Grabowska, Z . N(itiwtorscli., T d A. 198 I . 35. 1030. H . Cherek, J . Luniin., 1980, 22, 103. D. Mobius and H . Kuhn, Isr. J. Chmi., 1979. 18, 375. N . Nakashima. K. Yoshihara. and F. Willig. J . Clwrii. Phxs., 1980, 73, 3553. K . Tanimura, T. Kawai, and T. Sakata, J . P1i~:s.C l m i . , 1980, 84, 751. B. A. Lindig and M . A. J. Rodgers. Plioiochvti. Photobiol., 1980. 31, 617.

Photophysical Processes in Condensed Phases

83 comprehensive list of references from 1979. Van der Auweraer et aE.268have made a theoretical analysis of fluorescence quenching in micelles. A model assuming that quenching proceeds in a spherical shell at or near the micelle surface is used. The implications for diffusion and non-diffusion controlled reactions are discussed. Fendlert6’ reviews membrane-mimetic photochemistry. The molecular organization of logical systems can be simulated by microemulsions, micelles, and vesicles. In such systems all the characteristics of biochemical processes can be achieved. Ziemiecki, Holland, and Cherry 2 7 0 have described a method for evaluating binding constants of solutes to micelles. The method involves quenching of a probe but has the advantage that the lifetime of the probe need not be known. Binding constants for Cu2 and 1,5-dimethyIhexa-2,4-dieneare reported. The quenching of pyrene fluorescence by metal ions in micellar solutions shows that the more highly charged the metal ion the greater its tendency to bind to the micelle ~ u r f a c e7 .1 ~Intramicellar quenching constants were obtained for Cu2 and Eu3+ in some systems. Another detailed examination of the quenching of pyrene and pyrene derivatives by metal ions in SDS micelles has been made by Dederen et An empirical and theoretical model for first-order micellar quenching rate constants are compared. Lianos and Zana273use the fluorescence decay of micelleincorporated pyrene to determine the aggregation number upon the addition of butanol, pentanol, and hexanol. The latter change the aggregation by solubilization. The same authors use time-resolved fluorescence analysis of micellesolubilized pyrene to show that the aggregation number of SDS micelles increases rapidly with NaCl concentrations above 0.45 M.274Turro et al.275use an indolelabelled probe to study micelle structure by use of absorption, fluorescence, and quenching by NO2- and Co2+ ions. Turro and Lee276 have studied the 1cyanonaphthalene excimer in micellar solutions and conclude that the excimer is relatively polar (dipole moment -4 D) and that it is solubilized mainly in the Stern layer of detergent micelles. has measured quantum yields of blue fluorescence of acridine in protic and aprotic homogeneous solvents of different polarity and in alkaline solutions of different types of detergent. Water penetration and solubilization of acridine can be deduced from these measurements Miller et al.’ 7 8 have also used kinetic fluorescence spectroscopy to follow excimer formation of pyrene in SDS and follow aggregation as a function of ionic strength. Miller 2 7 9 employs this technique to measure microviscosity in SDS micelles. Addition of n-hexanol can lower the microviscosity very markedly. Deaggregation of dyes and dye-detergent aggregation has been studied in the 3,3’-diethylthia+

+

Zh8

M . Van der Auweraer, J. C. Dederen. E. Gelade, and F. C. De Schryver. J . Clin??.f / i j , s . . 1981. 74. 1140.

J . H. Fendler. J .

f h j x . Clicrti.. 1980. 84. 1485. H . W. Ziemiecki. R. Holland. and W. R. Cherry. C ’ / r i w . P / r j * s .Lc/r.. 1980, 73. 145. F. Grieser and R. Tausch-Treml. J . A i i i . (’hcvir. Soc,.. 1980. 102. 7258. 272 J. C. Dederen. M . Van der Auweraer. and F. C. De Schryver. J . P/ij..s. Chcrii., 1981, 85, 1198. 273 P. Lianos and R. Zana, C h ~ i if~h j.* s . Lrtr., 1980. 76. 62. P. Lianos and R. Zana. J . Plijx. Chon.. 1980. 84. 3339. 275 N . J . Turro. Y . Taaimoto. and G. Gabar. Photochcrn. Pliotohiol.. 1980. 31. 527. 27h N . J . Turro and P. C. C. Lee. Pliotoc~lirru.Photohiol., 1980. 32. 327. ”’ T. Wolff. Ber. B~rn.si~rigr~.s. P h ~ ~ s ~ C h c w1981. r . . 85. 145. 27x D. J. Miller. U . K . A. Klein, and M . Hauser. Ber. Burwrigc.s. PIijx. C//lW.. 1980, 84, 1135. 17’ D. J . Miller. Bcr. Buii.soigc,.s.P/I,I~s. Clicvri.. 198 I . 85. 337. 2h9

Pliotochemistry carbocyanine iodide-sodium lauryl sulphate system.280Microemulsion formation has been used to examine photophysical effects.281 Pyrene carboxyaldehyde resides on the surface, whereas pyrene resides in the microemulsion interior. Reactions of pyrene and pyrene butyrate with thallous ions are used to compare micelles and microemulsions. Almgren 2 8 2 describes a stopped-flow technique to determine the rate of migration of pyrene molecules between single-wall lipid vesicles. The limiting step is the rate of exit of pyrene from the vesicles into the aqueous environment. Fluorescence quenching of pyrene and pyrene decanoic acid by various anline derivatives has been studied in dipalmitoylphosphatidylcholine liposomes in gel phase.283 N,N-Dimethylaniline and p-isopropyl-N,Ndimethylaniline caused anisotropic diffusional quenching, whereas N,N-dicetylaniline, a less-mobile quencher, causes static quenching predominantly. These observations make it possible for the location of pyrene and derivatives in the liposome membranes to be deduced. Halide ion quenching and enhancement of the fluorescence of fluoranthrene solubilized in cetyltrimethylammonium bromide Only halides present in the Stern micelles has been examined by Burrows et layer are effective quenchers. Fluorescence combined with 3C n.m.r. and lightscattering techniques has been used for structural studies of oil-in-water emulsions.2g5 Energy-transfer experiments have also been used to study the properties of colloidal systems. A fluorescence stopped-flow technique has been used to monitor excitation energy-transfer of the Forster type between pyrene and perylene and deduce the migration of these probes between lipid vesicles in aqueous solutions.286As suggested in another report 2 8 2 migration occurs through the aqueous phase with exit from the vesicle as the limiting process. A picosecond study of energy transfer between rhodamine 6G and 3,3’-diethylthiacarbocyanineiodide in sodium lauryl sulphate in the premicellar region.287The energy transferred is of the Forster type. The quenching of the fluorescent donor 1 ,Sdimethylnaphthalene by cyclic azoalkanes, which are fluorescent acceptors, has been used to study the properties of micellar systems, in particular binding constants, residence times of quenchers, and aggregation number.288Rodgers 2 8 9 has used picosecond fluorescence to measure the decay of Rose Bengal fluorescence in aqueous micelles. Water molecules near the micellar interface have different protonicity from those in bulk solution. Also at low surfactant concentration multiple occupancy of probe molecules may lead to S , - S , mutual annihiliation. Charge separation is a light-induced effect of great interest because of its deployment as a means for utilization in solar energy conversion. A micellar system has been reported in which this achieved by bringing about a retardation of 84

””

H. Sato. M. Kauns,aki. K . Kasatani. Y. Kusuinoto. a n d N. Nakashima. Chew. Lcrt.. 1980, 1529. M. Almgrcn. F. Griescr. a n d J. K . Thomas. J . Am. C ’ l i c w . So(,.. 1980. 102. 3188. M. Almgrrn. C’lrcvri. P//,I,A. Lcrt.. 1980. 71. 539. 2x3 K . Kmo. H . K a u m u m i . T. Ognwa. and J . Sunaiiioto. C//o/ir.f h ) x Lctt.. 1980. 74. 51 I . H . D. B L I ~ ~ o wS.\ . J . Foriiiosinho. M. F. J . R . Pawa. and E. J . Rasburii. J . C/im1. SOC .. Firrotk~!, T/W\. 2. 1980. 76. 685. 2h5 Y. Tricot. .I. Kiwi. W. Niederbrrger. a n d M . Gritrttl. J . P/j),,\. Chwi.. 19x1. 85, 867. ”” M. Alliigreli. J . : 1 ~ i .( ’ h c ~ l i . SOC..1980. 102. 7882. ”H. Sato. Y. Kuzuinoto. N. Nakashimu. :tiid K . Yoshihara. Chew. P/jj..s. Lctr., 1980. 71. 326. IXc M . Aikaua. A . Yekta. J . - M . Lui. a n d N . J . Turro. P h o r o c h l i . P/io,ohio/.. 1980. 32, 197. ”’) M . A . J . R0dg~1-s.(‘//(,///. P//,l.\. f - c / t . . 1981. 78. 509. 2x2

Photcipliysicul Processes in Condensed Phuses

-

85

the back reaction that is based on the excited-state redox system in equation (3). “Ru(bipy)32+

+ MV2+

MV+

+ R~(bipy)~~+

(3)

Instead of simple methylviologen (MV”), Brugger and Gratzel 290 use the amphiphilic derivative C , ,MV2 as an electron acceptor. The comparatively stable charge separation is brought about by organization of the reactants at molecular level and interplay of hydrophobic and electrostatic forces. Exciplex formation can also be responsible for quenching in micellar solutions, for example, the fluorescence quenching in aromatic hydrocarbondicyanobenzene and -N,N-dimethylaniline system^.^" The photoinduced electron-transfer reaction of duroquinone (DQ) -N-ethylcarbazole (ECz) system (equation 4), has been investigated in micellar solutions and micro emulsion^.^^^ +

DQ

+ ECz

’I”

DQ;

+ ECz:

products

(4)

The heterogeneity of the system serves to prevent the back-electron transfer. In a more detailed report on work, which was briefly described in ref. 290, Gratzel and co-workers 2 9 3 report on systems in which the electron back-transfer rate constant is reduced at least 500-fold by the positive surface potential of the aggregates. This type of study and its implications for H, and 0, production from water by photochemical methods have been reviewed by G r a t ~ e I . ~ ~ , Primary photoprocesses and photochemical behaviour of proflavin have been investigated in aqueous and anionic micellar solutions.29sMicellar environments affect the pK of the singlet and triplet excited states owing to differences in surface and bulk pH. The photoredox behaviour is due to monophotonic photoionization and triplet-triplet annihilation gives rise to oxidized and reduced proflavin radicals in water, whereas biphotonic photoionization occurs in micelles. Photoredox processes have also been studied in Zn-tetraphenylporphyrinmethylviologen surfactant assemblies.296 Photochemical processes in heterogeneous systems, and across micelle boundaries in particular, clearly has great potential. The photolysis of amphipathic alkylcobaloximes in mixed micelles shows a co-operative effect owing to structure.297The photoreduction of anthraquinone in aqueous micellar solution has been compared with that in non-aqueous solution.298The dimerization of 3(n-buty1)cyclopentenone is solvent-dependent and the ratio of isomeric products depends on surfactant c ~ n c e n t r a t i o n .It, ~is~ suggested that this can be used as a means of critical micellar concentration determination. Macromolecule Systems.-The photochemistry of polymers is treated elsewhere, but some properties of macromolecules pertinent to this chapter will be quoted.

”)’

P.-A. Brugger and M . Griitzel. J . A m . C/iwi. S i r . . 1980, 102. 2461.

K . Hamamoto. and N . Mataga. Chcwi. PIijx. Lctt., 1979. 62. 364. ”‘ YY .. Waka. Yamaguchi. T. Miyashita. and M . Matsuda. J . Ph,w. Ch~m..1981, 85, 1369. P.-A. Brugger. P. P. Infelta. A. M . Braun. and M . Gritzel. J . A m . Clicrii. Soc., 1981, 103, 320. ”)‘ . Griitzel, fsr. J . Ch~wi.,1979. 18. 364. ”)’M M.-P. Pileni and M. Gritzel, J. P/i,w. Clicwi., 1980, 84. 2402. ’’)’M.-P. A. M . Braun, and M . Griitzel. Pliotochlwi. Photohii)l.. 1980. 31, 423. ”’- D. A . Pileni. Lerrer. F. Ricchiero, and C. Giannotti. J . f / i r . s . C / i m . , 1980. 84. 3007. ”)’V. Swayainbunathan and N. Periasamy, J . P/iotcdiciii., 1980, 13. 325. 2yy

K . H. Lee and P. de Mayo.

Pliotodioii. Plrotohiol.,

1980. 31. 31 I .

86 Piio tockemistry For example, Gupta et find that in poly(vinylnaphtha1ene)about 84% of the excitation energy is dissipated by internal conversions. This contrasts with naphthalene itself and involves the excimer. This work and also that of Demeyer et ~ 1 . ~shows ' ~ that there are at least two excimer-formation processes and that simple excimer kinetics analoguous to those in homogeneous solution do not apply. Excimer formation in the same polymer is used to determine polymer miscibility properties. 302 Excimer formation kinetics as a function of environment have been studied by Aspler and G ~ i l l e tA. ~series ~ ~ of papers dealing with the multiexponential fluorescence decay in polymeric systems show how time-resolved fluorescence can be used successfully for the analysis of complex kinetics.304*3 0 5 Excimer kinetics and singlet- and triplet-energy migration have also been examined in a series of three papers.306-308Excimer formation has been studied in poly(N-vinylcarbazole) 309 and in bis-anthracene polymer^.^ '' A full investigation of the photophysics of poly(N-vinylcarbazole) in solution has been made by a Japanese group.31' The photophysical processes involved change markedly with the fluorescent state involved. Charge-transfer effects consequent upon addition of electron-acceptor effects are also reported. Ghiggino et have used picosecond fluorescence to study the formation and decay of emitting species in the same system. Exciplex formation has been reported by Hoyle and G ~ i l l e t , ~and they report evidence for an exciplex consisting of two carbazole chromophores and one molecule of dimethyl terephthalate. Exciplex formation and electron transfer have been examined in polar solvents using a p-N,Ndimethylaminostyrene-p-cyanostyrenec ~ p o l y m e rl 4. ~Energy migration, a feature of polymer systems, has also been studied by fluorescence techniques3 l 5 - 3 1 ' Pyrene excimer formation has been used as an environmental probe, in particular, the dynamics of end-to-end cyclization in polystyrene has been measured by ' Winnik et '0°

302 303 '04

A. Gupta, R. Liang, J. Moacanin, D. Kliger, R. Goldbeck, J. Horowitz, and V. M. Miskowski, Eur. Polriti. J.. 1981. 17. 485. K. Demeyer. M. Van der Auweraer, L. Aerts. and F. C. De Schryver, J. Cliim. Piiys., 1980,77.493. S. N. Semerak and C. W. Frank, Mmroniolec.ules, 1981, 14, 443. J. S. Aspler and J. E. Guillett, Mricromolecules. 1979, 12, 1082. D. Phillips, A. J. Roberts, and I. Soutar, J. Pollni. Sci., Po[vm. Pliys. Ed., 1980, 18. 240; P o f w e r , 1981. 22. 293.

'07

D. Phillips, A. J. Roberts, and 1. Soutar, Eur. Polym. J., 1981, 17, 101. T. Nakahira. I. Maruyama, S. Iwabuchi, and K. Kojima. Mucromol. Client., 1979, 180, 1853. T. Nakahira, S. Ishizuka, S. Iwabuchi, and K. Kojima, Macromol. Ciiem., Rcrpicl Comniun., 1980. 1.

'08

T. Nakahira, S. Ishizuka. S. Iwabuchi, and K. Kojima. Macrocmol. Clieni., RapidConiniun., 1980. 1,

309

G. Rippen, G. Kaufmann. and W. Klopffer, Clicm. fliys., 1980, 52, 165. J.-P. Desvergne. A. Castella. and R. Leclaux. Ciieni. Pliys. Lett., 1980, 71, 228. H. Mashuhara, S. Ohwada, N. Mataga, A. Itaya, K. Okamoto, and S. Kusabayashi, J. Phys. Clieni., 1980. 84, 2363. K. P. Ghiggino, D. A. Archibald, and P. J. Thistlethwaite, J. Polym. Sci., Pofvm. Lett. Ed., 1980, 18,

'05

437. 759. 310

673. 3L3 314

'I5

318

C. E. Hoyle and J. E. Guillet, Mm~romolecules,1979, 12, 956. K. Iwai, M. Furue. S. Nozakura. Y.Shirota. and H. Mikawa, Poiym. J.. 1980. 12, 97. P. K. Das. M. W. Encinas, and J. C. Scaiano. J. Piiorociiem., 1980, 12, 357. R. F. Reid and 1. Soutar. J. Polym. Sci.. 1970, 18. 457. R. A. Anderson, R. F. Reid, and I. %mar, Eur. Pofym. J., 1980, 16, 945. M. A. Winnick, T. Redpath, and D. H. Richards, Mcicromolecules, 1980. 13, 328.

87

Pkotopliysicul Processes in Condensed Phases

Biologically Related Systems.-The application of photophysical methods to biochemical problems is not new, but increased activity is now apparent. Equipment and techniques are now widely available and it happens that the time scales especially amenable to study by photophysical methods are those in which many of the most important biochemical processes occur. Studies on the photophysics of indole-containing compounds are important because of the common occurrence of tryptophan residues in proteins. The photophysics of the indole chromophore has been the subject of considerable controversy. In this short review it is impossible to do justice to the subject. A study of singlet- and triplet-energy transfer from indole to anthracene has allowed estimates of OT = 0.43 f 0.05 and OF = 0.49 & 0.05 to be made for indole in cy~lohexane.~The mechanism of the well known photoionization of indole derivatives is still obscure. The confusion over the fluorescence properties of tryptophan seems to have been considerably (it would be unwise to say completely) clarified by Gudgin et al.320This group have systematically measured the decay of tryptophan fluorescence in aqueous solutions as a function of pH. Below pH7.0 the decay appears to be a double exponential with a subnanosecond component confirming the previous findings of Rayner and S ~ a b o In . ~the~ low ~ pH region when the proton concentration becomes kinetically significant tryptophan fluorescence is quenched by H + with a diffusion-controlled rate and no experimental evidence is found for emission from a cationic form. At pH >O the decay becomes triple exponential with the appearance of a long component whose contribution to the total emission intensity increases rapidly with increasing pH at the expense of the other two emissions (Tables 22-24). The authors do not consider the mechanisms or states giving rise to the emission. The widely held view has been that 'Laand ' L , states, uncoupled to each other, but coupled to the ground state, are involved, although Rayner and Szabo 322 have recently suggested an alternative mechanism involving the coexistence of different rotational conformers in the ground state. Another possibility is the existence of different ionic species. Gudgin et al. criticize the work of

'

Table 22

Tryptophan fluorescence lifetimes and relative emission intensities in aqueous solution in function of p H : citric acid-sodium phosphate bufler. ien 280nm; emission through 350nm cut-offfilter, T = 20°C

-

Citric acid

'I9 320 321

322

PH

T l / W

I1

2.55 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.8

2.33 k 0.15 2.57f0.13 2.65 f 0.12 2.76 f 0.1 2.87 f 0.1 2.95 0.1 2.98 & 0.1 3.07 k 0.1 3.16 f 0.1

0.89 0.92 0.94 0.93 0.93 0.94 0.93 0.94 0.93

r2/(ns) 0.38 f 0.15

0.44fO.15 0.49 & 0.15 0.45 f 0.15 0.50 f 0.15 0.52 f 0.15 0.40 f 0.15 0.55 f 0.15 0.59 f 0.15

12

( M x 102)

0.11 0.08 0.06 0.07 0.07 0.06 0.07 0.06 0.07

8.86 7.95 6.97 6.15 5.46 4.85 4.30 3.68 2.27

R. Klein, I. Tatischeff, M. Bazin, and R. Santus, J . PIiys. CIicrn.. 1981, 85, 670. E. Gudgin, R. Lopez-Delgado, and W.R. Ware, Con. J . Chem., 1981,59, 1037.

D. M. Rayner and A. G.Szabo. Cum J . Clieni., 1978,56, 743. A. G.Szabo and D.M.Rayner, J . Ant. Clicni. Sor., 1980, 102, 554.

Pho t ocheniist rj

88 Table 23

-

H' 3.5 2.0 1.6 I .45 I .28 1.21 1.1 1 .o 0.84

7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

2.5 3.5 5.25 6.2 7.9

x x x x x

=2

'51

(MIL) 3.2 x 10-4

PH

Table 24

9

Trj*ptoipIiun,f[uosewence lifetimes und relutive eniission intensities in HCl-wuter solutions us u .function of' pH. jLeX 280 nm; eniission through 305 nm cut-off,filter, T = 20 PC

lo-'

lo-' lo-'

lo-' 0. I45

(ns) 3.2 f 0.1 1.70 k 0.1 1.20 f 0.15 1.05 f 0.15 0.80 f 0.15 0.75 f 0.2 0.51 f 0.2 0.49 f 0.2 0.34 f 0.25

(ns) 0.52 f 0.15 0.43 & 0.15 0.40 f 0.15 0.37 f 0.20 0.31 f 0.25 0.13 f 0.4 -

1, 0.94 0.80 0.65 0.70 0.80 0.85

1 .oo 1 .oo

-

1.00

1'

0.06 0.20 0.35 0.30 0.20 0.15 -

-

Tryptophun fluorescence lifetime vulues and relutive emission intensities 280 nm; in sodium tetruborute bufjer solutions us a.functionof pH. E., eniission through 305 nm cut-off.filter, T = 20 "C

3.19 3.08 3.16 3.20 3.15 3.16 3.15 3.1 1

f 0.1 f 0.1 k 0.1 f 0.1 rf: 0.1 f 0.1 0.2 f 0.4

0.94 0.9 1 0.855 0.735 0.495 0.255 0.10 0.03

"Because of the increasing activity of

0.60 f 0.15 0.55 f 0.15 0.55 f 0.15 0.50 f 0.20 0.47 & 0.30 (0.5 f 0.5)" (0.5 f 0.5)" (0.5 f 0.5)" T ~ .the

0.06 0.05 0.045 0.035 0.025 -0.015 <0.01 <0.01

precision on the

T~

9.1 9.1 9.0 9.2 9.2 9.1 9.18 9.0

f 0.5 0.3 f 0.2 k 0.1 f 0.1 f 0.1 f 0.1 f 0.1


-0.03 0.10 0.23 0.485 0.73 0.89 0.96

measurement becomes very poor

Robbins et ul.323on tryptophan and 3-methylindole since powerful solid-state laser excitation was used. Jameson and Weber 324 have resolved the fluorescence of tryptophan by phase and modulation fluorometry in terms of emission from the zwitterion and anion present in amounts determined by the pH of the solution. The forms interconvert more slowly than fluorescence processes and have similar absorption and emission spectra. Measurements were made with excitation frequencies of 6, 18, and 30MHz in the pH range 8-10, in which the relative zwitterion concentration varies from 0.82-4.09. Resolved lifetimes were 3.1 0.4 ns for the zwitterion and 8.7 f 0. I ns for the anion. The agreement with Gudgin et a/. seems satisfactory. T r ~ o n g has ~ ~ studied ' tryptophan in aqueous 4.5 M-CaC1, and characterized the charge-transfer complex, [Trp' . . . nH20-], formed within the solvent cage at 300 and 77K. A subsequent paper326 shows that photoionization of the CT complex can be brought about by visible light (A >, 434nm): the energetics and mechanism of photoionization of tryptophan are discussed in detail. Lumry and 313

325 32h

R . J . Robbins, G. R. Fleming, G. S. Beddard, G. W. Robinson, P. J . Thistlethwaite, and G. J . Woolfe. J . Am. Chcm. Soc.. 1980, 102, 6271. D. M. Jameson and G. Weber, J . fhjx Clrertr., 1981, 85, 953. T. B. Truong. J . f l r j x . CIrm.. 1980, 84, 960. T.B. Troung. J . fhjx Clreni., 1980. 84, 964.

Photopl~~~sicul Processes in Cotidensd Phuses

89 his co-workers327 have presented a consistent picture of the formation and behaviour of indole-type exciplexes. In the case of 3-methylindole and n-butanol, exciplexes of 1 : 1 and 1 :2 stoicheiometry can be formed, each with a red shift of the emission maximum of 15 nm (Figure 15). This indicates behav'iour that should be related to tryptophan and tryptophanyl residues in proteins. 1

I

WOVOIWWJ~.

nm

Figure 15 Fluorescence spectra qf'3-nietlirlinifolein n-heptune at 6.8 "C with vurious amounts ?in-hutmiol udded: (a) 0.0 M; (b) 3.75 mM; ( c ) 1 1.2 mM; (d) 14.8 mM. The spectrci were normulized to huve the sume intensitj. at 293 nm (Reproduced by permission from Photochetn. Pltotohiol.. 198 I , 33, 609).

Tran and Fendler 328 have used steady-state and nanosecond time-resolved spectroscopy to study excimer formation for N-[4-( 1-pyrene)butanoyl]-D-and -Ltryptophan methyl esters and their racemate pyr-DL-Trp in methanol and in optically active octanol. Appreciable differences in the kinetics and thermodynamic of excimer formation are observed. The efficiencies of excitation energy transfer from tyrosine to tryptophan residues in globular proteins in native and denatured states has been measured by studying the wavelength dependence of the fluorescence quantum yield.329The results are summarized in Table 25. Unlike findings from earlier work, energy transfer is almost completely absent in the denatured state. Examples of investigations on proteins are the study of rapid relaxation processes in pig heart lipoamide dehydrogenase revealed by subnanosecond resolved f l ~ o r o m e t r y 'and ~ ~ ~ relaxation in apomyoglobin using the 2-ptoluidylnaphthalene-6-sulphonicacid (TNS) as a fluorescent probe.33' Phase fluorometry was used in both these investigations. Fluorescence has been used to study conformational changes of haemoglobins 3 3 2 and laser photolysis to examine oxygen binding in haemerythrin 3 3 3 and photodissociation of carboxyhaemoglobin. 34* 32'

3ZR 3") 330 331 331 333

334

335

M. V. Hershberger. R. Lumry. and R. Verrall. P/ioroclic.ni. Photohiol.. 1981. 33. 609. C. D. Trdn and J . H. Fengler, J . An?. Clicvii. Soc.. 1980, 102. 2923. Y. Saito, H . Tachibdna. H. Hayashi, and A. Wada. Pliotochcm. Pliorohiol.. 1981. 33, 289. A. J . W. G . Visser. H. J . Grande. and C. Veeger. Biopliys. C h i . . 1980. 12. 35. J. R. Lakowicz and H. Cherek. Biot.lic*iri.Biophys. Rex Conintun.. 1981. 99. 1173. R. E. Hirsch and R. L. Nagel. J . Biol. C l ~ n i . 1982, . u6. 1080. N . Alberding. D. Lovelette, and R . H . Austin. Proc. N d . Acad. Sci. USA., 1981, 78, 2307. D. A. Duddell, R. J . Morris. and J . F. Richards. Bioclieni. Biopli,w. Acto, 1980, 621, 1 . J. Lindqvist. S. El Mohsni. F. Ttibel, B. Alpert. and J . C. Andre, C/ie.rii.PIiys. Lcrr.. 1981; 79. 525

150

103

14.3 20. I 23.2 25.1 34.4 45.8

4 6

Trp

15 14

0.267 0.428

No. o f residueS Tyr Trp/Tyr" 2 3 4 0.5 10 0.4 4 2 0.37 19 8 0.25

0.06

0.01 i: 0.09

0.24 f 0.09 0.07 f 0.16 f 0.06 i: 0.08

0.10 f 0.10

0.04 -0.04 0.09 0.02 0.12 0.01

0.69

f 0.11

f 0.28 i: 0.11 f 0.07 f 0.12 f 0.04

0.30 f 0.06

0.48 0.38 0.29 0.17 0.55 0.22

0.43

0.81 f 0.06 0.286

0.18

0.16 f 0.05

1.07 f 0.07

Eficiency of energy transferb Present study329 Previous study Native Denatured Native Denatured

'The ratio of the number of Trp residues to that of Tyr residues in a protein. The amount of error is the standard deviation of t ( i ) at wavelengths between 275 and 290 nm.The high Trp/Tyr ratio makes the value I - A(R) very small and consequently will result in a large error in the value of the efficiency, so this deviation is roughly related to the Trp/Tyr ratio. 'The mol wt. and Trp and Tyr contents were derived from amino-acid sequences summarized in the literature

Protein Lysozyme Trypsin inhibitor Trypsin x-Chymotrypsin Carboxypeptidase A Phosphoglycerate kinase Hexokinase Alcohol dehydrogenase

Mol wt.c ( x lo3)

Table 25 The molecular weight, the contents of tryptophan and tyrosine, and the @ciencies of energy transfer

Photophysical Processes in Condensed Phases

91 Fluctuations observed in the polarized fluorescent of rhodamine-labelled myosin have been used in the detailed study of muscle contraction.336 An extremely fast relaxation of the 625 nm charge-transfer absorption band of the blue copper protein, azumin, has been studied by subpicosecond light The blue protein solution is transiently bleached but the absorption reversibly reappears with a time constant of 1.6 & 0.2 ps) owing to reverse chargetransfer. A fast transient ( c 0.5 ps) is attributed to excited-state vibrational relaxation/internal conversion. Hydrophobic properties of phtyochrome have been examined using 8-anilinonaphthalene- 1-sulphonate as probe.338 Fluorescence depolarization anisotropy of ethidium bromide bound to DNA has been used to examine the torsion dynamics of this linear macromolecule.33g The kinetics of the photoisomerization of bilirubin has been studied because of the relevance to phototherapy. 340 The fluorescence of bilirubin increases on binding to human serum albumin.341This and other primary photoprocesses have been investigated by picosecond spectroscopy. Karvaly 342 has put forward a new photochemical mechanism for energy conversion in bacteriorhodopsin. An extensive review of the photophysics of light transduction in rhodopsin and bacteriorhodopsin has been made by Birge.343 The dynamics of cis-trans isomerization in rhodopsin has been analysed by INDO-CISD molecular orbital theory.344 Similar calculations on polyenes and cyanine dyes have also been A new picosecond resonance Raman technique shows that a distorted all-trans-retinal appears within 30 picoseconds after excitation of rhodopsin or isorhodopsin. 346 This suggests that isomerization is nearly completed within picoseconds of absorption. Time-resolved studies of protein fluorescence during the photochemical cycle of bacteriorhodopsin have been reported by Fukumoto et Photosynthesis provides another source of stimulation for investigations in photophysics. The photochemistry of manganese prophyrins have been investigated because of their relevance to photosystem II.348* 349 Related to this are the studies on the quenching of fluorescence of tetraphenylp~rphine.~~', 351 Freed 352 has given a quantum mechanical description of the radiative and nonradiative characteristics of the lowest singlet states in chlorophyll hydrated dimers.

33h

337

338 334 3J0 3J1 342

343 34J 345

3*6

'" 3J8 3Jy 350 351

352

J. Borejdo, S. Putnam, and M. F. Morales, Proc. Notl. A c d . Sci. USA. 1979, 76. 6346. J. M. Wiesenfeld. E. P. Ippen. A. Corin. and R. Bersohn. J . Ant. Cltrwt. Soc.. 1980, 102, 7256. T.-R. Hahn and P . 4 . Song, Biocltc~rnistrj~, 1981. 20. 2602. J. C. Thomas. S . A. Allison. C. J. Appelof. and J. M . Schurr. Biopliys. Cltcwi., 1980, 12, 177. K. Isobe and S. Onishi, Biochvit. J . . I98 I , 193, 1029. B. I. Greene. A. A. Lamola, and C. V. Shank. Proc. N u t / . Acrrtl. Sci. U S A , 1981. 78. 2008. B. Karvaly. B i o c h w . Biop1i.n. Rcs. Conmnm.. 1980. 93, 1042. R. R. Birge. Araiu. Rev. Biop1t.r.~.Biorwg.. 198 I. 10. 31 5. R. R. Birge and L. M . Hubbard, J . Arii. Clitwi. Soc., 1980. 102. 2185. U . Dinur. B. Honig. and K. Schutten. Cltcvn. P/tj:v. Lett., 1980. 72, 493. G. Hayward. W. Carlsen. A. Siegman. and J. Stryer, Scicwcv. 198 I. 21 1, 942. J. M. Fukumoto. W. D. Hopewell, B. Karvaly. and M . A. El-Sayed, Proc.. Nrrtl. A c d S c i . U S A , 1981, 78, 252. 1. A . Duncan. A. Harriman. and G. Porter. J . Clicwi. Soc.. F(irrrrlrij*Trons 2, 1980. 1415. A. Harriman. and G. Porter. J . C/tr~rit.Sol.., Frrrrrilr?,~Trcrns 2, 1980. 76, 1429. A . Harriinan and R. J. Hosie. J . Photoclt~nt..1981, 15, 163. V. J. Godik. M . Urbanova. A . Y. Boresov, and K. Vacek, Stud. Biop1i.w ~ B d i r i 1981. ~. 82. 179. K . F. Freed. J . Ant. Cltiw~.Sol,.. 1980. 102, 3130.

92

Photochemistry

Chlorophyll u in polystyrene has been studied by fluorimetry as a model of lightharvesting antenna in p h o t o ~ y n t h e s i s .Lifetimes ~~~ of chlorophyll a have been measured by Cermak and Kaplanova353and the effects of reabsorption on the concentration dependence reported.354 Naqvi 3 5 5 proposes that the lightharvesting function of carotenoids in photosynthesis requires electron exchange between the energy donor (carotenoids) and acceptor (chlorophyll). The photosynthetic pigments chlorophylls a and c, and bacteriochlorophyll a have been studied in a nematic liquid-crystal by polarized absorption and fluorescence as a function of applied electric field.356Picosecond studies have been made of charge separation in photosynthesis by Windsor and H ~ l t e n . ~A~n ' example of the application of picosecond laser methods to cellular systems is the study of energy transfer in the alga Anacystis n i d u l a n ~ . ~ ~ ~ Dynamics in cellular systems are well adapted to study by photophysical methods. Related to solar energy conversion also is a report of photosensitized electron transport from ethylenediaminetetracetic acid or Fe2 to Fe(CN)63across a liquid membrane containing both a surface-active ruthenium" complex and vitamin K,. 5 9 The incorporation of a surface-active nicotinamide chloride markedly enhances the rate of electron transport. The permeation of liposomal bilayers has been studied by pyrene-labelled lecithin. 360 Liposome fusion has been monitored by quenching of pyrene group probes with 4-dodecyl-N,N-dimethylaniline.36 Liposomal bilayers have also been studied by the fluorescence polarization of N-dansylhexadecylamine. 362 Pulse fluorometry has used to study changes in the environment of N-(l-pyrenesulphonyl)dipalmitoyl-L-a-phosphatidylethanolamine in concanavalin A-stimulated human lymphocytes.3 6 3 Luminescence properties of biochemically significant compounds can be used for analysis. The properties of thiamine derivatives published by Gibson and Turnbull 3 6 4 are typical of the information needed for this purpose. +

3 Triplet-state Processes Winefordner and co-workers 3 6 5 review the development of phosphorimetry since 1975 for the quantitative measurement of low concentrations of organic molecules. The authors cover such areas as low-temperature and roomtemperature phosphorimetry as well as advances in source and detection systems. Recalculation of phosphorescence oscillator strength has been carried o u t and correction terms obtained.366 Phosphorescence spectroscopy has been developed 355 jSh

3s7

"' 354

3h')

'" .''.I

.'''

K. Cerinak and M . Kaplanova, c':c~cli.J. f l i w . . 1980. B30, 713. M. Kaplanova and K. Cerinak. J. f / i ( i t o c / i ~ w i . 1981, . 15, 313. K. R. Naqvi. P/iotoc/i~wi.Pliotohiol.. 1980. 31. 523. D. Bauman and D. Wrobel. Biopl~~*.v. Climi.. 1980. 12. 83. M. W. Windsor and D. Hotten. Philos. Trtrri.5. R. Soc. LomIo/i, Scr. A. 1980, 298. 335. S. S. Brody. G. Porter. C. J. Tredwell. and J. Barber. Pliotochwi. fliotohiopli,r.v . 1981. 2. I I . T. Sugimoto. J. Miyazaki. T. Kokubo. S. Taninioto.M . Okano. and M. Matsumoto. J . Clicnr. So(,.. Chwi. Coriir~iirri..I98 I , 2 10. J . Sunamoto. T . Nomura. and H. Okainoto. Bull. Chem. SOC.Jpn., 1980, 53, 2768. J. Sunamoto. K. Iwamoto. H . Iwamoto. H. Kondo. K. Kano. and T. Ogawa. Cliorii. Lrtr.. 1981, 15. K . lwamoto and J. Sunanioto. Bid/. Chiwi. Soc. J p . . I98 I 54. 399. N . Kido. F. Tanaka. N . Kaneda. and K. Yagi. Biochcrii. Biop/iIx Acttr, 1980. 603. 255. E. P. Gibson and J. H. Turnbull. J . Clwrr. Soc., Perkin Trans. 2, 1980, 1288. T. L. Ward. G. L. Walden. and J. D. Winefordtier. Tcrlcrrircr. 1981. 28. 201. R. Wollt'iind F. Mark. Momr.s/i. Clwri.. 1980, 111. 591. ~

Pliotopliysical Processes in Condensed Pliases

93 for crude oil identification using synchronous excitation and total contour spectra.367This technique shows promise for differentiation of crude oil samples and this technique can be enhanced and extended by use of external 'heavy-atom' quenchers. INDO calculations have been performed on the ground and triplet ~ ~ ~ calculations provide estimates of the relative states of b i p h e n ~ l e n e .Such energies and geometries of the T , and S , excited states. Changes in geometry on excitation are also discussed. A kinetic study by means of zero-field flash experiments and Zeeman experiments are reported on the phosphorescence of palladiumporphin in single crystals of n-octane between I .2 and 4.2 K.369 The results show an e, vibration, which appears owing to intensity borrowing through spin-orbit and vibronic coupling and involves an intermediate charge-transfer state. Najbar and co-workers 3 7 0 have reported on the phosphorescence of naphthalene in rare-gas matrices and on the photophysical behaviour of chloroq ~ i n o l i n e . Luminescence ~~ spectra, quantum yields, and phosphorescence lifetimes are presented for the latter in various solvent systems (Tables 26-28). The motion of triplet excitons has been measured in p-terphenyl crystals at room temperat~re.~ The ' ~ motion is anisotropic in the ab plane, with diffusion tensor components D,, = (0.3 & 0.1) x IO-'and D,, = (1.3 f 0.1) x 1015cm2s-'. Table 26 Energies oftlie lobrqest S(n,n*)and T electronic states of chloroquinolines Molecule Quinoline 2-Chloroquinoline

E,(crn-') 32000'. 31 860' 3 1 390", 3 I 430'

4-Chloroquinoline 6-Chloroquinoline 7-Chloroquinoline 2.4-Dichloroquinoline 4.6-Dichloroquinoline

3 I 040".3 1 620' 31 140". 31 250' 31 210' 31 580", 31 120, 30 620". 30 8 1 0'

Methylcyclohexane : isopentane ( 1 : I ). energies of different sites are given

Ethanol.

ETJ(cm-9 21 755, 21 590'. 21 91jd 22210, 22 110, 21 990, 21 955, 2 1 835', 22 120" 21 440d,21 450" 21 615, 21 480, 21 34W, 21 650" 21 680, 21 535' 21 &IOU, 21 730, 21 705, 21 6ood 21 340", 21 270, 21 175d Hexane.

Iso-octane. For crystalline matrices

Table 27 The luniinescence quuntum yields of cliloroquinolines @'ph

Molecule 2-Chloroquinoline 4-Chloroquinoline 6-Chloroquinoline 7-Chloroquinoline 2.4-Dichloroquinoline 4.6-Dichloroquinoline

95 K 0.35 k 20;, 0.10 0.20 0.15 0. I2 0.07

wMeQ 2-. 4-. 6-. and 7-methylquinoline. 3b7

"" "(' "' "')

j7'

"

%I@:

77 K 0.32 & 1O:b 0.1 I 0.40 0.10 0.20 0.2 1

o p b

@Fl@P"

77 K 0.22 k 10% -

n-MeQ 77K 3.3 0.84 4.5 0.95 -

0.03 -

Methylcyclohexane: nopentane.

'Ethanol

M . M. Cortield. H. L. Hawkins, P. John, and 1. Soutar, Anrili:s/ (London). 1981, 106. 188. J. C. Rayez and J . J. Dannenberg. J . M i d . S m c f . , 1980. 68. 235. G. W. Canters and J. A. Kooter. Mol. Phys.. 1980, 41, 1431. A. M. Turek and J. Najbar. A r m fhys. Po/. A. 1980. 58. 317. J . Najbar. B. M . Trzcinska, Z. H. Urbanek, and L. M . Proniewicz, Acrrr fhys. Pol. A , 1980,58, 331. A. Fort and V. Ern. Clirw. f l i i x Lrari., 1980. 14. 579.

94

Photochemistry

Table 28

The phosphorescence lifetimes rT(s) of chloroquinolines and methylquinolines at 77 K

Molecule Quinoline 2-Chloroquinolinef 4-Chloroquinoline 6-Chloroquinoline 7-Chloroquinoline 2,CDichloroquinoline 4,6-Dichloroquinoline

7Tb

?TC

1.30 f 0.05 0.77 f 0.01 0.40 f 0.01 0.26 f 0.01 0.31 f 0.01 0.36 & 0.01

0.86 f 0.01 0.62 f 0.02 0.30 f 0.01 0.26 f 0.02 0.27 f 0.01 0.32 & 0.02

7Te

7Td

0.90 0.62 0.29 0.26 0.28 0.31

f 0.01 f 0.02 0.01 & 0.01 f 0.01 f 0.01

0.52 0.21 0.19 0.25 0.24

?T

n-MeQ"

f 0.01 f 0.01 f 0.01 f 0.01 f 0.02

1.42 11.52 1.05 1.35

0.14 f 0.01 0.16 f 0.02 0.15 f 0.02 0.12 f 0.02

"n-MeQ = 2-, 4-, 6-, and 7-methylquinoline. 'Ethanol. chloride. /rT (in durene) = 0.24 & 0.02s

Hexane.

Iso-octane. 'Carbon tetra-

Ziebig and P r a g ~ report t ~ ~ ~on the electrogeneration of triplet states of intramolecular anthracene-amine systems. A critical assessment of roomtemperature phosphorescence as an analytical technique in aqueous micellar solution has been presented and results reported for naphthalene, pyrene, and biphenyl in T 1/Na and Ag/Na mixed-counterion lauryl sulphate micelles. 74 Experimental problems associated with circular dichroism (CD) measurements of photoexcited triplet states have been presented and Tetreau and Lavalette report on the first observation of the CD of an excited triplet molecule (Figure 16).375 Heat-pulse-induced delayed phosphorescence has been observed via the internal and reverse internal conversion processes in the phosphorescent levels of xanthone in n-pentane at 1.5 and 4.2 K.376The positions of three phosphorescence levels of xanthone in n-pentane are shown in Figure 17. Solutions of azulene and fluoranthrene in isopentane show delayed fluorescence resulting from heterotriplet-triplet annihilation.377Triplet lifetimes values in the temperature range 131-201 K have been obtained and the results explained in terms of thermallyactivated intersystem crossing followed by internal conversion. The extrapolated 2ps. low-temperature triplet lifetime is 48 Phosphorescence studies on p-benzoquinone (PBQ) at 4.2 K in isostructural crystals such as p-dichlorobenzene and p-bromochlorobenzene have been reported, and the results are interpreted in terms of anisotropic local field effects of the host environmental molecules.378 A first observation of a quintet state triplet-triplet radical pair formed in the pairwise interaction of two triplet-state benzoylphenylmethylenes has been made.379 Rate constants for the intersystems crossing from singlet excited states to the individual triplet sublevels have been determined for a series of halonaphthalenes. 380 The results are conveniently summarized in Table 29. The positional 373 374 375

376 377

378 379

R. Ziebig and F. Pragst, Cliem. P1iy.s. Let(., 1980, 70, 544. L. J. Cline Love, M . Skrilec, and J. G. Harbarta, Anal. Chem., 1908. 52, 754. C. Tetreau and D. Lavalette, Nouv. J . Cliim., 1980, 4, 423. T. Terada, M. Koyanagi, and Y . Kanda, Cliem. P I i p . Lett.. 1980, 72, 408. H. J. Kray and B. Nickel, Cliem. Pliys., 1980, 53, 235. Y. Miyagi, M. Koyanagi. and Y. Kanda, Bull. CIiem. SOC.Jpn., 1980,53. 2502. H. Murai, M. Torres, and 0. P. Strausz, J . Am. Chem. Sot.., 1980, 102, 5104. H . Saigusa, T. Azurii, M. Sumitani, and K. Yoshihard, J . Chem. Phys., 1980, 72, 1713.

95

Photopliysical Processes in Condensed Pliuses

0.0

I

I

I

1

1

23

24

25

26

V~lO-~crn-'

i',js

$'

h

k2

K, Kl3

,

$1

cm-'

t5cm-1

96

'r

4

.? 4

0,

f

0

4

P,

' r

4

U

Y

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4 bc

.s

9,

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b)

QJ

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x x x g

x +I +I +I

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Pliotoplij~sic.ulProcc~ssesin Conclctisc~clPhases

97 The room-temperature phosphorescence (RTP) of benzolflquinoline and phenanthridine shows enhancement by spotting HBr-ethanol solutions of the compounds onto silica gel chromatographic plates,383 Acridine however showed no RTP emission but gave strong fluorescence. Possible interaction effects of the compounds with the substrate are discussed. The mechanism of the photoinduced decarboxylation of pyruvic acid has been reinvestigated and accounted for viu electron transfer from an excited to a ground state molecule. Quantum yields of triplet production at 295 K in deoxygenated benzene, acetonitrile, and water are 0.65, 0.88, and 0.22, respectively.384 The long wavelength ( i > 240 nm) photolysis of thiirane results in intersystem crossing to the lowest excited triplet state with a quantum yield of about 0.86.385 It is reported that r,x-dinaphthylalkanes form triplet excimers instantaneously with excitation by laser Investigations of the temporal characteristics and chain-length dependence of this triplet excimer suggest that the precursor is a ground state van der Waals force bound dimer. Enhanced phosphorescence is shown in intramolecular exciplex systems [carbazole(CH,),-(terephthalic acid methyl ester)] owing to electron transfer that causes fluorescence quenching of the carbazole residue.387 Wilson and H a l ~ e r report n ~ ~ on ~ exciplex formation between a triplet alkanone and alkylbenzene, and thus reaffirm the role of exciplexes in the quenching of triplet carbonyl compounds by olefimc and aromatic hydrocarbons. The effect of the heavy-atom substituents, bromine and iodine, on the electrondonor aniline in the electron-transfer reaction with thiopyronine triplet has been investigated by flash spectroscopy in solvents of different viscosity and polarity.389 Triplet quenching and radical yields are presented in Table 30. The results are analysed in terms of decay constants of an intermediate triplet exciplex. The influence of an external heavy-atom effect on the phosphorescence spectra of quinoxaline and 2,3-dichloroquinoxaline has also been reported.390The influence of chloride ion on the decay rate of Methylene Blue triplet in 0.01 M acid in the

Table 30 Triplet quenching parameters of tkiopyronine with N,N-dimethylated unilines ( D M A ) p - Br-D M A

DMA

k,U

Solvent Acetonit rile Water (50% acetonitrile) "Quenching constant ( IO9M-'s-I ). quenching

383

8.2

2.3

@,"

1 .o 0.93

k,"

orb

8.0 2.5

0.88 0.13

Radical yield per triplet under conditions of complete triplet

R. J. Hurtubise, Trrlcrrttci. 1981, 28. 145.

R. S. Ddvidson, D. Goodwin, and P. F. de Violet. Cltcwi. P1ij.s. Lett.. 1981. 73, 471. "' E. M. Lown. K . S. Sidhu. A. W. Jackson. A. Jodham. M. Green. and 0.P. Stransz. J . PIiys. Clicwi., 1981.85, 1089.

"' D. Webster, J.

F. Baugher. B. T. Lim, and E. C. Lim.. C/iem. P l i w Lett., 1981, 77, 294. Y. Hatano, M . Yamamoto, and Y . Nishijima, CIreni. P/r.r.y. Lett.. 1981, 77, 299. "' T. Wilson and A. M . Halpern. J . Ant. Client. Soc.. 1981. 103. 2412. 389 G. Winter and U . Seiner, Bey. Bunsenges Pltjx. Clieni.. 1980. 84, 1203. 390 S. Yamauchi, H. Saigusa. and T. Azumi. J . C/iiwt. Pli.~*s.,1981, 74. 5335. 387

98

Photochemistry

presence of ferrous ions has been investigated by means of laser flash photol y ~ i sChloride . ~ ~ ~ ions weakly accelerate decay of 3MBH2+in aqueous solution in the absence of Fe". Quenching of 3MBH2+ by Fe" is more strongly catalysed by Cl- in both water and SOv/v% aqueous CH3CN. A possible role of chloride is as a bridging species in quenching via electron transfer between 3MBH2+and Fe" is examined. Further reports of the quenching of triplet Methylene Blue by complexes of cobalt(I1) have also been presented and the results discussed in terms of a reversible electron-transfer Rate constants for the energy-transfer quenching of the lowest excited triplet states of anthracene, acridine, and naphthalene by Cr"' have been presented.393Low k, values were obtained and are attributed to low values of the pre-exponential factor of the energy transfer rate constants. A detailed analysis has been presented by Zemel and Hoffman394of the longrange (Foster-type) triplet-to-triplet energy transfer between the photoexcited triplet states of the zinc and magnesium protoporphyrin IX chromophores of Znand Mg-substituted haemoglobin. This difficult observation was made on fluid media and at ambient temperature by monitoring the time dependence of triplet-triplet absorption. This work represents the first detailed study of a longrange energy-transfer process, where both distances between the acceptor and donor and their orientations are accurately known. Further evidence of Forster-type energy-transfer effects has been obtained for several excited triplet-state donors and several ground-state doublet nitroxyl radicals.395Critical transfer distances of the order of 12-20 8,were measured and were on good agreement with calculated values. Several papers have been presented on various spectroscopic energy transfer studies involving triplet ketones. Wilson and Halpern have presented a detailed kinetic study of sensitized 9,lO-dibromoanthracene (DBA) fluorescence produced by energy transfer from triplet ketones involving a ~ e t o p h e n o n and e ~ ~acetone397 ~ as donor. The results indicate that DBA is a sensitive probe for triplet ketones. Quenching results have also been presented for acetone phosphorescence by a series of aryl alkyl ketones possessing lower triplet energies than acetone.398 Quenching constants for phenyl alkyl ketones are considerably lower than for a diffusion-controlled process (k, = lo8-lo9 M - s- l), whereas those for quenchers with high electronaffinity are close to diffusion-controlled rates (k, = 10" M - ' s - l ) . Quenching of the benzophenone triplet and its derivatives with electron-attracting substituents by aryl ketones bearing electron-releasing substituents reveal a dependence of the quenching rate parameter on the structure of the two interacting partners.399 Excitation-resonance energy-transfer 39' 392 393 394 395

396 397

398 399

T. L. Osif and N . N. Lichtin, Pltotochmt. Pltotohiol.. 1980. 31. 403. T. Ohno and N. N. Lichtin. J . P h p . C'hent., 1980, 84. 3019. V. Balzami, M. T. Indelli, M. Maestri, D. Sandrini. and F. Scandola. J . Pltys. CIieni.. 1980,84, 852. H. Zemel and B. M. Hoffman, J . Am. CItent. Soc.. 1981, 103. 1192. N. N. Quan and A. V. Guzzo. J . P/t,~s.CIient.. 1981. 85, 140. T. Wilson and A. M. Halpern, J . A m . Clieni. Soc.. 1980. 102, 7272. T. Wilson and A. M. Halpern. J . Ant. Client. Soc.. 1980. 102. 7279. M. F. Mirbach. V. Ramamurthy. M . J. Mirbach. N. J. Turro. and P. J. Wagner. Noicv. J . Chint.. 1980, 4, 47 I . G. Favaro and F. Masetti. J . Pltotochem., 1981. 15. 241.

Photophysical Processes in Condensed Phases 99 efficiencies in n-hexane from 3(n, n*) and 3(n,n*) states of seven aromatic ketones to dienes have been mea~ured.~"The results indicate that excitation energy migration within the benzoyl sensitizer is sufficiently rapid to make state differences of little importance during excitation-resonance energy transfer. Experiments show that in the photoreduction of acetophenone by 1-phenylethanol, half of the ketone triplets are quenched by reaction with the OH bond rather than the conventionally accepted reaction with the a-C-H bond.401 The quantum yield for the photoreduction in benzene was 0.59 and 0.50 in acetonitrile. Laser flash photolysis techniques have been used in energy-transfer studies of aromatic hydrocarbons and ketones to di-t-butyl peroxide.402Rate constants for triplet quenching in benzene at 25°C are 7.9 x lo6, 3.4 x lo6, and 7.ox 1 0 4 ~ 4 s - for p-methoxypropiophenone, benzophenone, and benz[a]anthracene, respectively. The kinetics of triplet quenching are shown in Table 31. Aromatic ketones, made water soluble by ionic substituents, have also been employed in the photosensitized cis-trans isomerization in the maleicfumaric acid system.403The photostationary state cis : trans ratio was dependent on the triplet energy of the sensitizer and the pH of the medium.

Table 31 Kinetics of triplet quenching by di-t-butyl peroxide. TT

Sensit t e r Propiophenone p-Methox ypropiophenone Benzophenone Benzophenone Phenanthrene Phenanthrene Naphthalene Benzil Fluorenone Benz[a]anthracene Anthracene "Units of M-'s-'. at 25°C.

Solvent benzene benzene benzene acetonit rile benzene acetonitrile benzene benzene benzene benzene benzene

k,"

9.6 7.9 3.4 3.7 1.8 3.0 1.1 2.8 2.4 7.0 9.7

(perox)b

x x x

lo6 lo6

x x x x x x

lo6 lo6 lo6 lo6

lo6

lo4 105

x 104 x lo4

11'

23 60

0.57 0.72

98

0.85

150 3000 680 2200 1500

0.62

nanoseconds, in neat peroxide. 'Efficiency to t-butoxy radical generation neglecting any differences in cage recombination between direct and sensitized photodecompositions

The triplet-triplet energy transfer from aromatic hydrocarbons to trans- and cis-stilbene has been investigated by applying the Ulstrup and Jortner quantum mechanical description of electron-transfer This analysis accounts well for the experimental results, the main features of the energy-transfer process being determined by the (low-frequency) twisting mode and the (high-frequency) stretching C=C mode of donor and acceptor molecules. Further work, using flash kinetic spectroscopy, has been reported on the rate constants for triplet-energy transfer from indeno[2,l-O]indene to a ~ u l e n e . Energy ~ ~ ' transfer was studied as a 'O0 *O' *02

Oo3 40' '05

R. B. Abakerli and V. G. Toscano. J . Pliotochiwi.. 1981. 15, 229. P. J. Wagner and A. E. Puchalski, J . Am. Clteni. Soc., 1980, 102, 7138. J. C. Scaiano and G. G. Wubbels, J . Am. C'limt. Soc.. 1981, 103, 640. A. Gupta, R. Mukhtar. and S . Seltzer. J . Pliss. Cltc~iii.,1980. 84. 2356. G. Orlandi. S. Monti. F. Barigelletti. and V. Balzani. Clicin. Pliys., 1980. 52, 313. J. Saltiel, P. T. Shannon. 0. C . Zafiriou. and A. K . Uriotte, J . An?. Chcm. Soc.. 1980. 102. 6799.

100

Photochemistry

function of both temperature and solvent and the results critically assessed in terms of the Debye equation for diffusion controlled process. Scaiano406reports on the temperature dependence of the quenching of seven aromatic hydrocarbon triplets by tetramethylpiperidine N-oxide. The results indicate that the change in rate constants in the triplet energy range I .28-2.90 eV is largely caused by entropic factors. Sciano407 has also examined solvent effects in the photochemistry of xanthone. Both the lifetime and the rate constants for the interaction of xanthone triplets with hydrogen donors are dependent on solvent. The change is attributed to the effect of hydrogen bonding in bringing about an inversion of n, n* and n,n* triplet states. Effects on xanthone triplet lifetime and rate constant are shown in Tables 32 and 33. Table 32 Kinetic parameters .for triplet decay in severul solvents ~~/(ns)a 8300 I 7 200 1300 71 700 22 60 370 270

Sol vent Acetonit rileb Water-acetonitrile' Methanol Benzene Carbon tetrachloride Cyclohexane n-Heptane 2-Propanol CI,C (0.05 M-propan-2-01)

k s Q / ( M - ' s-')" 4.5 x lo8 4.2 x 107 2.1 x lo8 4.3 x lo8 9 x lo8 d 4 x 109= 2.5 x 10' 7.5 x lo8

"At 22 C ; typical errors in k,, are IS',,. According to the manufacturer's specifications. the sample used contained 0.04",, water. A 1 : 1 mixture in volume. Not measured. Error could be as large as 3 0(,

Table 33 Rate constants ,for the interaction qf xanthone triplets \+ith severul hydrogen donors Suhstrcite Bu,SnH Pr'OH Pr'OH Pr'OH n-Heptane Cyclohexane Cyclohexane Cyclohexane

Medicr C1,C Cl,C I : I. CI,C-Pr'OH Pr'OH n-heptane CI,C methanol cyclohexane

-

"At 22 C. 'Typical errors are 10--15",, approximate figures (preceded by )

k,/(M-' 1.5 x 109 1.1 x lo8 4.1 x 105 2.2 x 105 2.5 x lo6 7.7 x lo6 -2 x 105 -5.4 x lo6 s - ' ) u v b

for most values and about 30:',, for those indicated as

Watkins408 has also reported on the solvent effects on the quenching of aromatic hydrocarbons by tetramethylpiperidone N-oxide. N o correlation of quenching efficiency with the charge-transfer properties of the aromatic hydrocarbon free-radical collision complex was found. Other work by Watkins409 has been concerned with the quenching of aromatic hydrocarbons by stable carbon free radicals. The results are summarized in Table 34. The author proposes that J . C. Scdiano. C'h~nr./'hj..\. Lett.. 1981. 79. 44 I . J. C. Scaiano. J . Ant. C/rcm. Sol .. 1980. 102. 7747. JOR A. R. Watkins. C h o n . f l t r s . Lc~rr..1980. 70. 262. "' A. R. Watkins. Cltcwt. PIIVJ.Lcrr.. 1980. 75. 230. 'Oh do-

Photopiiysical Processes in Condensed Phases 101 Table 34 Bimolecular rate contants k , .for quenching of aromatic hydrocarbon triplet states by bis-biphenylene ally1free radicals in methylcyclohexane A roniutic

hydrocurbon Biphenyl Fluorene Tri phenylene Phenanthrene Naphthalene Coronene Fluoranthene Pyrene 1,2-Benzanth racene I , 12-Benzperylene Ant hracene Perylene An thanthrene Tetracene

Triplet energy (ev) 3.01 2.98 2.90 2.69 2.63 2.41 2.30 2.10 2.05 2.01 1.82 1.56 I .45 1.28

k,/(109

~ - 1 s - 1 )

(1)

(11)

9.3 11.4 7.3 11.3 2.6 1.31 3.4 3.0 3.2 2.6 2.8 2.0 1.92

4.7

(111) 5.7

-

-

6.1 7.3 7.4 8.2

5.1 5.3 0.63

-

-

4.3 3.6 3.6 4.5 2.8 2.8

1.58 3.9 1.88 1.62 0.46 3.7 3.2

the mechanism leading to quenching is based on an exchange interaction between the free radicals and the triplet state. The triplet-triplet annihilation of Nmethylcarbazole (NMC) leads to primary population of upper excited singlet states which is detected by delayed fluorescence. In toluene, energy transfer from the upper excited states of NMC to toluene is The effects of ring substitution and the effect of aromatic quenchers on the photoreduction by toluene of r,r,a-trifluoroacetophenonehave been pre~ented.~' The results are interpreted in terms of differing reactivities of the nn* and n,n* triplets. The quenching of the monoprotonated lowest state of Methylene Blue, 3MBH2+by the ground state of the dye MB+ has been investigated by laser flash p h o t o l y ~ i s . ~Rate ' ~ constants for quenching were found to be of the order 1 x 1O8MP1s- in water, aqueous acetonitrile, and aqueous ethanol. Electrontransfer reactions between triplet Methylene Blue and ferrocenes in acetonitrile have also been reported.413Rate constants and radical yields are presented and the results explained in terms of a heavy-atom-induced intersystem crossing in the triplet exciplex. The photophysical properties of the lowest triplet state of Nmethylthioacridone (NMTN) have been examined, including the effect of oxygen quenching of the thione triplet.414 The quenching of triplet excitons on poly(N-vinylcarbazole) by biacetyl has also been examined and delayed fluorescence (20-50 ns) observed indicating some exciton mobility occurs even after triplet-triplet annihilation has become in~ignificant.~'An exciton-trapping model is used to describe the results. Further

'

'

'

*I"

'I'

8 . Nickel and G. Roden. Cliaii. P l i j - . ~ .1980, , 53. 243. P. J . Wagner and H . M . H. Lam. J . Ant. Cliivii. Soc.. 1980. 102. 4167. P. V. Kamat and N . N . Lichtin, J . P l i ~ x Cliiwi.. . 1981, 85. 814. S. Tamura. K . Kikuchi. H . Kokubin, and A. Weller. P1iy.v. Cliiwi.. 1980, 121. 165. A. Safarzadeh-Amiri. D. A. Condirston. R. E. Verrall. and R . P. Steer, Cliciii. Pltys. Let/.. 1981, 77,

415

S. E. Webber and P. Arots-Avotins. J . Clicwi. Pl1y.v.. 1980. 72. 3773,

*I'

'I2 *I3

99.

102

Pliotocliemisrrv

papers of interest concern the quenching of phenanthrene triplets by conjugated dienes in anionic m i ~ e l l e s quenching ,~~~ of benzophenone by o l e f i n ~ , ~tripletenergy transfer from the disodium salt of naphthalene disulphonic acid to the acridinium ion,418 and from aromatic hydrocarbons to trans- and cisa~obenzene.~” An interesting paper by Turro and Aikawa4” reports the first observation of delayed fluorescence and phosphorescence of 1-chloronaphthalene (CI-N)in conventional anionic and cationic micelles. The authors give experimental evidence of prompt fluorescence, phosphorescence, delayed fluorescence, and delayed excimer fluorescence. The delayed fluorescence is shown to arise predominantly from triplet-triplet annihilation within a single micelle.

’’

Biological Aspects.-The lowest excited triplet states of all-trans-p-carotene produced by pulse radiolysis has been studied by time-resolved resonance Raman spectro~copy.”~’ Six transient Raman bands at 965, 1009, 1125, 1188, 1236, and 1496cm-’ were observed and assigned to the triplet state of /?-carotene. The authors conclude that the molecule may be substantially twisted, presumably at the 15,15’ band in the triplet state. Further work has also been carried out by the same workers on the triplet state of a l l - t r a n ~ - r e t i n a l .The ~ ~ ~results indicate increased n-electron delocalization in the triplet state and propose that the relaxed excited triplet-state exists in either all-trans or 9-cis conformation. Das and B e ~ k e r have “ ~ ~ also employed pulse radiolysis and laser flash photolysis to study several photophysical properties of the triplet states of the series of polyenals (29)-(33) related to retinal (31) as homologues (Table 35). Results are presented

‘lh

*I7 ‘I’

‘” ‘” ‘” *” ‘13

J . C . Selwyn and J . C . Scaiano, Crrri. J . Chmi., 1981. 59, 663. A. Mar and M. A. Winnick. Clwii. PIij-s. LPII.,1981, 77, 73. Y. Nishida, K. Kikuchi, and H. Kokubun, J . Pliotochern., 1980, 13, 75. S. Monti, E. Gardini. P. Bortolus. and E. Amouyal, Clieni. Pliys. Li.tt., 1981, 77, 115. N . J. Turro and M . Aikawa, J . Ant. Client. Soc.. 1980, 102, 4866. N . H. Jensen. R. Wilbrandt, P. B. Pagsberg, A. H. Sillesen, and K . B. Hausen, J . Ani. Cliem. Sol.., 1980, 102, 7441. R. Wilbrandt and N . H. Jensen. J . Ant. Ckern. Soc.. 1981, 103. 1036. P. K . Das and R. S. Becker, J . Ant. Clieni. Soc.. 1979. 101, 6348.

Photopliysicul Processes in Condensed Phases 103 Table 35 Triplet-state photopliysicalproperties of polyenals in various solvents Tripfet-triplet absorption All-transpolyenal (29)

(30)

(31)

(32)

(33) fl

Sol W i l t Hexane Methanol Cyclohexane Benzene Ace toni t rile Methanol Hexane Benzene Acetonit rile Methanol Cyclohexane Benzene Acetoni trile Methanol Cyclohexane Methanol

Band ma.\(nmfl) 385 400 410 430 440 440 445 460 470 460 470 490 490 475 500 510

E-winction coefi at band maxb*C

(M-'cm-' x 3.85 (3.4)' 6.3 6.3 (7. I)' 5.1 (6.1)' 5.1 (5.7)' 7.8 6.7 (6.2)' 5.9 (6.7)' (3.38)E 12. I (I 1.9)' (11.2)' (14.9)' 20. I 13.6

f 5 nm. & IS",. 'Obtained from calculations.

Triplet state decay constant

(ccs-')d 10

5.3 0.16 0.1 1

0.094 0.092 0.11 0.1 1 0.083 0.062 0. I4 0.12 0.084 0.097 0.14 0.12

4r,b 0.42 -0.45 0.66 0.72 0.51 0.4 1 0.4-0.7 0.58 0.16 0.08 0.54 -0.038 -0.095 -0.033 0.018 GO.01

1074

on the effects of various solvents (nonpolar, polar, and hydrogen bonding) on the photophysical behaviour of two longer and two shorter homologues of retinals, and are discussed in relation to possible state orders and intersystem crossing. The dependence of quantum yields on wavelength have been reported for the rhodopsin system at 77K.424 These measurements provide an insight into the primary photochemistry and photoisomerization of retinal in cattle and sea squid rhodopsin. It is shown that a photoequilibrium can be established between rhodopsin, bathorhodopsin, and isorhodopsin according to Scheme 4. rhodopsin (1 1 -cis)

bathorhodopsin (all-trans)

\Ivvvr

m . um

isorhodopsin (94s)

Scheme 4

The naphthalene-sensitized formation of triplet-excited chlorophyll a (chl a) and all-trans B-carotene has been investigated by pulse radioly~is.~~' Rate constants for transfer of triplet energy from naphthalene to chl a and all-trans pcarotene in benzene at 25°C are 3.6 f 0.6 x 109M-'s-' and 10.7 f 1.2 x lo9 M - ' s - ', respectively. Rate constants for triplet-triplet annihilation are 1.4 f 0.3 x 109M-'s- forchl uand 3.6 & 0.4 x 109M-'s-' for all-trans /3-carotene.

'

E.s.r., Microwave, and Related Studies.-E.s.r. studies of phosphorescent triplet states of 2,2'-bipyridyl, 3,3'-, 4,4'-, 5,5'-, and 6,6'-dimethyl-2,2'-bipyridyls and 2,2'-

424

'I5

T. Suzuki and R . H. Callender, Biopltys. J . . 1981. 34,261. N. H. Jensen. R. Wilbrandt. and P. B. Pagsberg, Pitorochem. Pliotobiol., 1980. 32. 719.

104

Pliotoc.hc~tiiistr?.

biquinolyl have been carried out in ethanol glasses.426E.s.r. spectra of both the Eand 2-conformers were observed in poly(viny1 alcohol) films and their assignment examined by changing the direction of applied magnetic field. The conformations of the phosphorescent triplet states of molecules were confirmed to be all E in ethanol glasses. Huber and Schwoerer 4 2 7 describe e.s.r. experiments which show the existence of quintet states ( S = 2) after U.V. irradiation at 4.5 K in perdeuteriated p-toluenesubstituted diacetylene. Nine e.s.r. transitions per quintet were detected and were attributed to bicarbenes of short oligomers. E.s.r. has also been applied to the study of photochemical reactions of fluoro-substituted ketones with amines, tetraphenylborates, and o r g a n o m e t a l ~ . ~ ~ ~ Time-resolved e.s.r. is shown to be a useful technique in the direct observation of k -+k ' scattering in a one-dimensional triplet exciton system, 1,2,4,5-tetrachlor ~ b e n z e n e . "This ~ ~ technique appears to be well suited to the determination of time constants involved in the scattering process. Two papers have been presented on the photochemistry of 5-methylphenazinium salts in aqueous solution."30*4 3 Fluorescence, optical flash photolysis, and electron paramagnetic resonance (e.p.r.) techniques have been used to elucidate various aspects of product formation and quantum yield. Two products have been identified, namely the 5-methyl- 10-hydrophenazinium cation radical cation (PyH +) (MPH ?) and the pyocyanine (I-hydroxy-5-methyl-phenozinium) in a stoicheiometric ratio of 2 : 1. The quantum yield of formation of (MPH ?) was found to be 0.29 & 0.03 at pH 7.0 and 1.1 f 0.1 at pH 3.0. The triplet state of MP' ( T , )has also been detected by triplet-triplet absorption and is found to have a lifetime of 0.5 ns. Flash photolysis and e.p.r. have also been used to study a geminate triplet radical pair obtained from hydrogen abstraction by excited triplet acetone from propan-2-01."~~The authors demonstrate that the geminate pairs contribute most of the polarization in photochemically-induced dynamic electron polarization (CIDEP) as compared with free random-phase pairs. An e.p.r. optical study has been made on randomly oriented triplets of magnesium tetraphenylporphyrin (MgTPP) and zinc tetraphenylporphyrin in solvents ethanol, toluene, and t~luene-pyridine."~~ A strong temperature dependence was observed over the narrow range 100-180 K, and these observations are interpreted in terms of an equilibrium process between two or three photoexcited triplet forms. Hutchinson and Kemple 434 report e.p.r. and ENDOR spectroscopic measurements for the lowest triplet state of ['H ,]biphenyl molecules in [2H ,,]biphenyl singlet crystals at 1.9 K. Information pertaining to the relative orientations of these triplet-state molecules are given. Further papers of interest relate to the dynamic behaviour of transient e.p.r. signals following

-

'''

J . Higuchi. M . Yagi, T. Inaki. M. Bunden. K . Tanigaki. and T. Ito, Bid/. Clicw. Soc. J p . , 1980. 53, 890. R. Huber and M . Schwoerer, Cliiwi. f/i,r.s. Lcvt., 1980, 72. 10. K . S. Chen. T. Foster and J . K . S. Wan, Cciri. J . Cli~ni..1980, 58, 591. 'lY A. J . Van Strient. J. F. C. Van Kooten, and J . Schmidt. Client. P/~.I:T. Lett.. 1980. 76, 7 . *'" V. S. F. Chew and J . R. Bolton. J . fli.r.9. Clrm.. 1980, 84. 1903. V. S. F. Chew, J . R. Bolton, R. G . Brown, and G . Porter, J . fhys. Clrcvii.. 1980. 84, 1900. *32 K . Wong. T. M. Chen. and J. R. Bolton. J . fhys. Clicwi., 1981. 85, 12. *'.' S. A. Scherz and H . Levanon. J . Plivs. Clicrtt.. 1980, 84, 324. "* C. A. Hutchinson and M. D. Kemple. J . C ~ B I Ifh!:v.. I. 1981, 74. 192.

*"

"'

105 laser excitation of molecular triplet states in single crystals of 9,9-[ 'H,][2H,]fluorene.S3s A time resolution of 15 ns is demonstrated. Also an e.p.r.. study of triplet states of porphyrins, chlorophyll u, and the covalently linked dimer of Zn pyrochlorophyllide u, in a liquid crystal, has been The nearest-neighbour excited-state exchange matrix elements in dimers of 1,2,4,5-tetrachIorobenzene(TCB) have been independently obtained using highresolution phosphorescent - microwave double resonance (p.m.d.r.) and 0.d.m.r. technique^."^' The authors conclude that the matrix element for energy transfer in the triplet state of TCB is not the same for dimer and exciton states. Schutz and co-workers 438. 439 report on the use of 0.d.m.r. experiments at zerofield monitoring the delayed fluorescence (DF) and phosphorescence signals. The lowest triplet state in anthracene single crystals has been investigated and the following zero-field splitting (ZFS) parameters obtained D , = 0.06 967, E , = 00793, D, = 0.0694, and E , = 0.00808. Further investigations have been made on the metastable triplet excitons in 1 : 1 CT crystal anthracenetetracyanobenzene. Exciton ZFS values of D = 2019.5 and E = -248 MHz were obtained. Both the radiative and non-radiative properties of the lowest triplet state T , of a series of pyrene derivatives have also been determined by 0.d.m.r. techniques. 440 The assignment of the orbital symmetry of the phosphorescent triplet state of N,N,N',N'-tetramethyl-p-phenylenediamine(TMPD) has been studied by microwave-induced delayed phosphorescence (M IDP) and the assignment of B,, for the orbital symmetry established.441 Kinoshita, Iwasaki and Nishi442 have provided an interesting review of the molecular spectroscopy of the triplet state through optical detection of 0.d.m.r. The authors provide an interesting account of triplet-singlet excitation spectroscopy together with a compliation of the data available on ZFS parameters and decay rates. Steiner 443 provides a theoretical treatise of the effect of magnetic field on the sublevels of a triplet exciplex and shows how this modulates the radical dissociation yield of the exciplex. Triplet-triplet energy transfer in the system quinoxalene in ethanol studied by 0.d.m.r. reveals that such energy transfer takes place at concentrations above 2 x lo-, M dm-3.444 Photc)pli!.sic~trlProc~esse~s it1 Cotidevisctl Phtrsus

4 Physical Aspects of Some Photochemical Studies

Photolysis and Related Reactions.-The phosphorescent decays of the triplet-state sublevels in ketones has been investigated by generation through photolysis of J35

436 437

*" 43y ,

440

'*I

'" 443

"'

R. Furrer and M. C. Thurnaver, Cliivii. fliys. Lett., 1981. 79. 28. V. Crebel and H . Levanon. Clicwi. P1i.1-s.LiJtt., 1980, 72, 218. W. G. Breiland, T. E. Altman, and J. S. Voris, Clicwi. Pliys. Lptt.. 1979, 67,30. J. U.Von Schutz. F. Guckel. W. Steudle. and H . C. Wolf. Clicwi. f l i j - s . . 1980. 53. 365. J. U . Von Schutz. W . Stendle. H. C. Wolf, P. Reineker. and U . Schinid, Clicni. P1iy.v. Lctt., 1981. 79. I . C. Brauchle. H . Kabza, and J. Voitlander. Cliem. f l i j x . 1981. 55. 137. K. Matsui. H. Morita. N . Nishi, M . Kinoshita, and S. Nagakura, J . Cliiwi. Pli.~*.v..1980. 73, 5514. M. Kinoshita. N. Iwdsaki, and N. Nishi, Appl. Spctrosc. Rev.. 1981. 17, I . U. Steiner. Ber. Bittis~vigi~s Pl1.1-s.Clicwi., I98 I , 85, 228. A. Inoue. N. Nishi. M. Kinoshita. and N . Ebara. J . Cltmi. Soc.. Jpn.. 1980. 53. 2466.

106

Photochemistry

substituted 1 , 2 - d i o ~ e t a n s . ~ The ~ ' results indicate that the only source of triplet ketones in the dioxetan photolysis is through intersystem crossing from the excited singlet state of the ketone. No evidence was given for a metastable intermediate form of dioxetan. Laser flash photolysis has also been employed in the study of the excited singlet state of benzene, toluene, p-xylene, polystyrene, and poly(xm e t h y l ~ t y r e n e )Some . ~ ~ ~ of the physical properties of these compounds are given in Table 36. Flash photolysis has been used to elucidate the photochromic

Table 36 Physical properties

of

the singlet states First-order decuy constant ( 1 0 7 s- 1 ) 3.2 3.2 2.9 2.9 5.0 4.2

A hsorp t ion muximu (nm)

Cotnpound Benzene

620 480 640 630 530 520

Toluene p-Xylene Polystyrene Poly-methylst st yrene

Assignment

'El,, c ' E l , , +'El,c 'El,, c lElu t 'El, t

B,,(monomer) ' B , , (excimer) B,, (monomer) ' B t u (monomer) 'B1,(excimer) ' B , , (excimer)

behaviour of triphenylformazan 447 and on the study of electron-transfer reactions from phenolate ions to various carbonyl triplets.448 Rate constants for electron transfer are in the range 2 x lo9 to 1 x 1 0 l 0 M - ' s - The quantum yields of primary photoproducts (phenoxy-radicals and radical anions of carbonyl compounds) are essentially unity. Laser flash photolysis of more substituted azobenzenes has shown the existence of a triplet state whose behaviour is viscosity dependent.449It is suggested that this transient species be assigned to the lowest (71, n*) triplet state of the trans-4-nitroazobenzenes (34 a-g) investigated (Table 37). The temperature dependence of the photochemistry of o-methylacetophenone

R

(34)

R a; NO, b; CN c; NO, d; NO, e; Br 445

446 44 7

448

449

R'

RZ

R3

R4

Br Br CI H H

NHCOMe NHCOMe NHCOMe NHCOMe H

(HOCH,CH,)N(CH,CH,CN) (HOCH,CH,)N(CH,CH,CN) (HOCHzCH2)N(CH,CH,CN) (HOCH,CH,)N(CH,CH,CN) NMe,

OMe OMe OMe OMe H

D. C. Doetschman, J. L. Fish, P. Lechtken, and D. Negus. Clietit. f/?w.,1980, 51, 89. S. Tagdwa and W. Schnakel. Climi. Plij-s. Lett., 1980, 75, 120. U . W. Grummit and H . Langbein. J . fltotoclien~.,1981. 15, 329. P. K. Dds and S. N. Blattocharyya. J . f l i w . Client.. 1981, 85, 1391. H . Corner, H . Gruen. and D. Schulte-Frohlinde. J . fhys. Clieni.. 1980,84. 3031.

17 9 4.7 5

2.9 2.2 0.6 0.60 0.55 0.35

o-Terphenyl-diphenyl ether ( I : 1) 1 -Phenylethanol Diphenyl-diphenyl ether ( 1 : 3) GT

Propan-2-01 1.3-Dibromobenzene MTHF Benzene Methanol Acetonitrile PMMA DNBT GT DNBT GT DNBT GT PMMA PMMA Toluene Toluene

17 5 17 5 17 5

17

q, CP

DNBT

Solvent

j.,,,

(nm) 353 530 694 530 530 530 353 530 694 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530

--

680 (740) 400, 685 400, 685 (780) 400, 690 (770) 400, 695 (780) 700 700 660 690 780 750

h h h

(nm) 400, 695 (760) 400, 700 (750) 710 (760) 400, 695 (780) 400, 700 (780) 420. 700 (800) 700 400. 695 (770) 710 700-800 390, 700 (780) 700-800

R,," 107

4.4 7 3.6 5 28

2 12

3.8 4.0 10 8 12 9 8 27 8 10

s-I

kObS

.o

8

10

d 0.005

0.01

0.2 0.15 0.03

1

0.05 0.2 0.0 1 c 0.005 < 0.005 c0.005

0.05

0. I 0.1 0.07

0.3

OD

Absorption maxima, decay rate constants, and yield of the transient of substituted trans-azobenzenes in various solvents at room temperature

lues in parenthesis refer to weak absorption maximum o r a shoulder. No discernable absorption between 700 and 800 nm

P

ound

37

.4

-.

. I :

. I :

n ,

.-

n

108 Photochemistry has been examined by laser flash p h o t o l y s i ~Data . ~ ~ ~are presented on the decay of the biradical generated in the photoenolization of o-methylacetophenone. A temperature study of the triplet state of iodonaphthalene and iodobiphenyl indicates that an intramolecular energy relocation process is inhibited as the temperature is lowered from 20 "C with a resulting increase in triplet lifetime.451 The activation energies for this process in toluene are given as 5.9, 4.8, and 3.4 kcal mol for 1-iodonaphthalene, 2-iodonapththalene and, 4-iodobiphenyl, respectively. Both laser flash photolysis and flash photolysis have been used to elucidate the transient species produced from solutions of a series of hydra zone^."^^ These compounds were synthesized from substituted 1,3-diones coupled to substituted aromatic amines. These compounds exists as the two distinct stereoisomers (35a) and (35b), for which the transient characteristics are summarized in Table 38.

Brauer and co-workers report on the photolysis of endoperoxide (PO) of heterocoerdianthrone (HCD = dibenzo[q]perylene-8,1 t j - d i ~ n e ) . ~4'5~4 . Two photoreactions were observed, vk, irreversible decomposition of PO with a quantum yield Qdec = 0.006, probably from T,(n,n*), and secondly a photoreversible cleavage of PO into HCD and 0, from the S,(n,n*) state with a maximum quantum yield of 0.26. The disodium salt of 9,l O-anthracenediproprionic acid (ADPA) has been used as a singlet-oxygen monitor.455 ADPA is bleached to an endoperoxide on reaction with singlet oxygen and the change in absorbance followed by time-resolved laser photolysis experiments. The rate constant for ADPA bleaching in 'H,O is given as 8.2 = lo7 M - s- and is the bimolecular rate constant for quenching of singlet oxygen by ADPA. The behaviour of the scintillation emission from 2,5-diphenyloxazole in liquid cyclohexane has been investigated by use of a picosecond ( - lops) electron The subsequent emission was detected by streak camera and attributable to the fluorescence from excited 2,5-diphenyloxazole. Energy transfer was observed from excited cyclohexane molecules to 2,5-diphenyloxazole with a rate constant of 4 x 10" M - ' s - ' . The lifetime of the excited singlet state of cyclohexane was 300ps. Further photolysis studies have been made on liquid oxepan with particular emphasis being placed on the dependence on ring Scaiano. Clictn. P/i,~*s. Lctt.. 1980. 73, 3 19. '" J.F. C.Grieser J. K. Thomas, J. Clwii. P/I,I*s.,1980. 73, 21 15. '" J . McVie. Aand Mitchell. R. S. Sinclair. and T. G. Truscott. J . Clion. Soc.. P d i n Trtms. -7, '" R. Schmidt.. D. W. Dreus. and H. D. Brauer, J . Am. Clieni. So c.. 1980, 102, 2791. "('

"' W. Dreus. R. Schmidt. and H. D. Brauer. Climi. P h j x . L ~ t t .1980, . 70, 84. '" 9. A. Lindip. M. A. J. Rodgers. and A. P. Schaap. J. Am. Cliwii. Soc.. 1980. 102. 5590. J5h

4s7

Y. Katsumura, S. Tagawa, and Y. Tabata. J . Pli1.s. Clic~n.,1980. 84. 833. H. P. Schuchmann and C. Von Sonntag. J. Photochcni., 1980. 13. 347.

1980. 286.

Me Me Me Me Me Me Me Ph

Me Me Me Ph Ph Ph p-N02C,H4 Ph

Sliort-lived trunsients In hesane In ethanol R a e of decuy Rate of cieccy 10-5k/(s-') imax/(nm) 1 0 - ~ k / ( s - ' ) i,,,/(nm) 460 0.10 452 4.4 455 0.10 470 4.4 470 0.08 480 2.8 455 0.12 455 1.4 0.12 * 455 445 0.14 470 17.3 0.14 470 27.7 460 462 0.15 468 10.0

Transient characteristics in hesane and ethanol solution

Isomer (35a) is rapidly converted into (35b) in a polar solvent

(35) (35) (35) (35) (35) (35) (35) (35)

Table 38

42 1 42 I 425 425

I .4 I .4 0.4 0.4

1.7 2.2 5.8

450 420

*

436

110 Pliot o d i mi istrj Transient species with lifetimes of several nanoseconds have been observed in the laser photolysis of en one^.'^^ These transient species have been identified as orthogonol or twisted triplet states, the angle of twisting varying with the rigidity of the molecule. Bonneau discusses the nature of the reactive triplet state involved in the photochemistry of some enones. Photolysis of [2,2]paracyclophane in glassy solvents at 77 K produces a species with two benzyl radicals linked by an ethylene bridge.459 From studies of excitation spectra and emission lifetime a broad band was observed, which is attributed to intramolecular excimer fluorescence of this radical pair. Photolysis experiments have elucidated the mechanism for the efficient production of phenyl benzoate, the geminate product, from direct and sensitized irradiations of dibenzoyl peroxide in solution.460Photolysis has also been used to obtain rate constants for addition ( k , ) of benzothiazole-2-thiyl radical to vinyl monomers.46' Rate constants of 6.3 x I O5 to 2.5 x 1 O8 M - ' s- ' were obtained for reactions with vinyl acetate and styrene monomers. The effect of concentration, temperature, and solvent on the photodegradation of benzothiazolinospiropyrans using flash photolysis has been presented.462transCyclo-octene is shown to be the major product in the photolysis of cis-cyclo-octene ~ ~ ~ on with a quantum yield of 0.34.463Hamanoue and c o - w o r k e r ~report intersystem crossing and lowest triplet states of 4-chromanone, chromone, and flavone and of some nitroanthracene derivative^.'^^ For the latter long build-up times for triplet-triplet absorption were observed (72-86 psec) and represent the effect of the rates of internal conversion (T,, Tl). Indirect intersystem crossing to higher levels of the triplet manifold is most important in these systems. Intermolecular hydrogen abstraction by benzophenone in a poly(methy1 methacrylate) host has been studied by an argon laser using a new technique of holographic p h o t ~ c h e m i s t r y ,which ~ ~ ~ involves the absorption of two laser photons. A benzophenone triplet state abstracts a hydrogen atom from the host to produce a ketyl radical. Subsequent reaction with the host produces a long-lived intermediate. Hydrogen abstraction occurs only from the higher nn* triplet state. Further investigations have been reported on the extinction coefficients for the triplet-triplet absorption of benzophenone and naphthalene in benzene solution and of anthracene in benzene, ethanol, and cyclohexane solution.467 Rate constants for several processes involved in the photochemistry of a series of substituted benzophenones have been obtained by laser spectroscopy.468 The results are discussed in relation to photoinduced vinyl polymerization. The effect of oxygen on the photocyclization of N-methyldiphenylamine to Nmethylcarbazole in n-hexane, water, and aqueous surfactants has been studied by +

45q

"" I '" 46

463

"' '6S

'" '" 46 i

R. Bonneau, J. A m . Clicwi. Sol.., 1980. 102, 3816. S. Ishikawa, J . Nakamura, and S. Nagakura, Birll. Clieni. Soc. Jpn., 1980, 53, 2476. A . Kitamurd. H. Sakuragi, M. Yoshida, and K. Tokumaru. Bull. Clicni. Soc. Jpii.. 1980, 53. 1393. 0. Ito. K. Nagami, and M. Matsuda, J. P1i.w. Cli~wi..1981. 85, 1365. D. Gaude. R. Gautron. R. Ouglielmetti, and J. C . Dully. Bull. Soc. Cliifn. R., 1981, 11. 14. H . P. Schuchmann and C . Von Sonntag. J. Plioioc~l~cwi.. 1981. 15, 159. K. Hamanoue, T. Nakayama, T. Miyake, and H. Teranishi. Clien~.Lett., 1981, 39. K. Hamanove. S. Hirayama. T. Nakayama, and H. Teranishi. Client. b i t . , 1980. 407. C. Brauchle. D. M. Burland, and G. C. Bjorklund. J. P h ~ xClicvn., 1981, 85, 123. R. H. Compton, K. T. V. Grattan. and T. Morrow. J. Plioioclilwi., 1980. 14. 61. A. Merlin, D.-J. Lougnot, and J.-P. Fouassier. Polwii. Bull., 1980. 2 , 847.

PIIo t ophj *.Y icul Proc~c~ssc~s ii I Cot 1ticvised PI1c~.sc~.s 111 steady-state and flash photolysis The reaction sequence in micelles involves the same intermediate steps as in homogeneous solutions. The biinolecular dehydrogenation of the intermediate dihydro-N-methylcarbazoleby oxygen is enhanced in aqueous and micellar solutions, whereas the quenching rate of triplet intermediates by oxygen is not affected. Laser photolysis has also been used to study the photoinduced electron transfer from zinc tetraphenylporphyrin to acceptors solubilized either in the lipid interior or aqueous bulk of anionic oilcorrelation has been established in-water m i c r ~ e m u l s i o n s .A~ ~quantitative ~ between isotopic enrichment parameters and photochemical efficiencies of dibenzyl ketone in micellar s ~ l u t i o n . " ~The ' radical anions and cations of 1,6diphenylhexatriene (DPH) have been produced and characterized in both homogeneous and micellar solutions by pulse radiolysis and laser flash p h o t o l y ~ i s . ~ ~ ~ Both radical ions show intense ( c z lo5 M - ' cm-') absorption peaks at 600650nm. Electron transfer in micelles and vesicles and from the radical anion of biphenyl to carotene and DPH and from the radical anions of these to inorganic acceptors has also been studied. Reaction kinetics of ligand binding to myoglobin (M b), haemoglobin (Hb), horseradish peroxidase (HRP), and microperoxidase- 1 1 (MP-I 1 ) down to a temperature of -90 "C in supercooled mixed solvents, using dye laser and flash photolysis, have been reported.473 The photodissociation kinetics were characteristic of a case geminate transient diffusion-controlled reaction. Photo-oxidation.-Turro and c o - w o r k e r ~ 'report ~ ~ the rate constants for quenching of singlet molecular oxygen ( '0,) by several strained molecules. The authors also discuss a non-photochemical method for determination of quenching constants of singlet oxygen involving thermolysis of 1,4-ditnethylnaphthalene-1,4endoperoxide. Laser flash photolysis has been used to determine the bimolecular rate constants for the reaction between 0, ( 'A,) and several lipid-soluble and water-soluble substrate^."^^ 1,3-diphenylisobenzofuranand 9,lO-anthracene dipropionic acid disodium salt were used as singlet oxygen monitors. Prutz and Maier 4 7 6 report on the time dependence of various fluorescence bands from 0, ('Zg+).O2 ('Z,') was produced by an energy-pooling reaction from O 2 (*A,) (equation 5). 'C,-

'A,

+

'A,

-

-

'Z,+

+ 3zg-

-

fluoresces at 765 nm in liquid 0, with a fluorescence lifetime of 35 p, which is much longer than the lifetime 5 of the 'Xg+state which is about 8ps. Further experimental work is necessary to explain on the long emission lifetime now attributed to the 'Zg+ state in the liquid phase. Khan477 further reports on the first observation of emission corresponding to both the 'Ag N . Roessler and T. Wolff. Pliotoclt~ni.Pltotohiol.. 1980. 31, 547. M.-P. Pileni. Clirvtt. PIt,rs. Let/.. 1980. 75. 540. B. Kraeutler and N. J. Turro. C/ti.nt. P1i.r.s. Lr>ti.. 1980, 70, 266. 472 M. Almgren and J . K . Thomas. Pltotoclier~t.Pltotohiol.. 1980. 31. 329. 473 B. Hasinoft. J . PIijx. CItrw.. 1981, 85, 526. "' B. N . J . Turro. M . F. Chow. S. Kaufer. and M. Jacobs, Tim~rltcclrortLcti.. 1981. 22. 3. 475 B. A. Lindig and M . A . J. Rodgers. Pltotoc*hi~rtt.Photohid.. 1981. 33, 627. 47h R. Protz and M. Maier. J . Cltrw. Plt~s..1980. 73. 5464. A. U. Khan. Cltc~rti.P/i,~:v.Lrtt.. 1980. 72. 112.

470 471

'"

112

Photochemistry

= 0) -P 'Xg-(v'' = 0) and the 'An (v' = 0) -, 'Zg- (v" = 1) transitions of molecular oxygen in liquid solutions at room temperature. These observations were made possible by the use of a specially built highly sensitive near-i.r. spectrophotometer. An example of such emission is shown for the classic H,O,-OCI - chemiluminescence reaction in which singlet oxygen was first detected as a chemical intermediate (Figure 18). Of further interest are papers

(1,'

I

lo00

B

I

B

I

1200 1400 WAVELENGTH nm

e

I

0

Figure 18 Cliemilirniinescen~espectrum of H,O,-OCI - reuction at room remperuture. (a) lnstrunientul background rind (b) eniission ut 1.27 pm and 1.58 pm (Reproduced by permission from Clteni. f l z j s . Lett.. 1980, 72, 112).

relating to the ene reaction between singlet oxygen and 01efins.~'~ The potential usefulness of photosensitized oxygenations of olefins has been realized for some time and some examples are given in Scheme 5. Various spectroscopic techniques have been applied to unravel the nature of the reactive intermediate present in these reactions. The authors summarize the various theories put forward to explain these reactions and concentrate on data available for the ene reaction.478 Photoreduction and photo-oxidation reactions of porphyrin compounds have been further i n ~ e s t i g a t e d ; ~also ~ ' the photoperoxidation of unsaturated organic molecules.480*48 It is shown that photoperoxidation of 1,3-diphenyIisobenzofuran (DPBF) in benzene is accompanied by molecular oxygen consumption on a 1 : 1 stoicheiometric basis consistent with the formation of the endoperoxide as a L. M . Stephenson, M. J. Grdina, and M . Orfanopoulos, Acc. Chem. Res., 1980. 13, 419. Y . Hare1 and J. Manassen, Pliotochiwi. Pliolohiol.. 1980, 31. 457. '"" B. Stevens and K . L. Marsh, J . Charii. RPS.,1980, 290. ''I B. Stevens, J . A. Ors, and C . N . Christy, J . PI1.r.s. Clicwi.. 1981. 85, 210.

478

Photophysicul Processes in Condensed Phases

113

'

1

Me/fMe OOH

Scheme 5

-

primary product. Triplet DPBF reacts with the endoperoxide with a rate constant of 10' M - ' s - ' to form unidentified secondary products.

Photoisomerization.-Birge and H ~ b b a r d analyse ~ ~ * the molecular dynamics of cis-trans isomerization in the visual pigment rhodopsin using INDO-CISD molecular orbital theory and semiempirical molecular dynamic theory. The analysis predicts that the excited-state species is trapped during isomerization in an activated complex that has a lifetime of - 0 . 5 ~ s . This activated species oscillates between two components which preferentially decay to form isomerized product (bathorhodopsin) or unisomerized 1 1-cis-chromophore (rhodopsin) within 1.9-2.3 ps. The authors further conclude that the chromophore in bathorhodopsin has a distorted all-trans-geometry and is the most realistic model for the first intermediate in the bleaching cycle of rhodopsin. In the photoisomerization of 13-desmethylretinal it is shown that the hitherto unseen 13-cis-isomer is also present to an extent of 7% in addition to the 7-cis-, 9cis-, and 1 1- c i ~ - i s o m e r s The . ~ ~ ~photoisomerization processes of polyenes have been investigated using a theoretical approach and results of calculations for the potential energy surfaces with particular references to radiationless transitions presented.484 The monoanion of bromothymol blue shows reversible spectral changes in organic solvents, which are attributed to photoinduced rotational isomerizat i ~ n Transient . ~ ~ ~ species involved in direct photoisomerization of transthioindigo have been investigated using picosecond spectroscopy.486 The longlived transient absorption band at 600nm is shown to be formed on a picosecond time scale. Such ultrafast formation is inconsistent with the earlier assignment of this band to triplet-triplet absorption. A photoisomerization quantum yield for thioindigo of nearly unity has been observed at temperatures of around 180 K.487 A detailed analysis indicates that an isomerization via the singlet as well as via the triplet state is possible. 482

484

485 486 487

R. R. Birge and L. M. Hubbard, J . Am. Cltem. Soc.. 1980. 102, 2195. W. Gartner, H . Hopf. W. E. Hull, D. Oesterhelt, D. Scheutzow. and P. Towner, Tetrcrltedron Left., 1980, 21. 347. I. Ohrnire and K . Morokuma, J . Cliem. Plijs., 1980, 73, 1908. U. W. Grummit, A h . Mol. Rekcmition Processes, 1980, 18, 181. S. A. Krysanov and M. V. Alfirnov. Client. PItys. Lett., 1980, 76. 221. R. Memming and K. Kobs, Ber. Bunsenges PIiJs. Client., 1981. 85, 238.

114

Photochemistry

Photochromism.-Heller and co-workers have described various photochromic properties of heterocyclic In their first report the authors present the rearrangement reactions of (E)-r-3-furylethylidene(isopropylidene) succinic anhydride (36). It is shown that compound (36) undergoes conrotatory and thermal disrotatory ring-closure to give red 7,7a-dihydro-4,7,7-trimethylbenzo[b]furan-5,6-dicarboxylic anhydride (37) in near quantitative yield. The

&o

&i0

Me /

Me Me

(36)

(37)

reverse process occurs on exposure to white light. Analogous electrocyclic reactions of the pale yellow (E)-r-2,5-dimethyl-3-furylethylidenesuccinic anhydrides, which photocyclize on exposure to ultraviolet light, give thermally-stable deep red (37).The reverse process is shown on exposure to white light (Scheme 6).

R' = H, R2 = Me b; R' = Me, R 2 = Et c; R' = R2 = Me a;

Scheme 6 488

489 490

H . G. Heller, J . Chmi. Soc.. Prrkin Trcrns. 1, 198 I . 198. P. J . Dords, H . G . Heller, P. J . Strydom, and J. Whittall, J . Clrc~m.Soc.. Perkin Trrms. I, 1981, 202. H . G. Heller and J. R . Langan, J . C/itw. Sw., Pcrkin Trcms. 2. 1981, 341.

Photoplipic*uI Processes in Condensed Phusi~s

115

Further uses of the anhydride as a chemical actinometer are discussed. Acyclic azines having higher condensed aromatic and heterocyclic substituents are shown to be photochromic and show both thermal and photochemical isomerization with 492 Seventeen different substituted azines were investigated large spectra shifts.491* and were found to vary with respect to their reaction mechanism. The azines can therefore be divided into four reaction groups depending on the substituents. The differing behaviour can be rationalized if a photochemically induced E-2 isomerization about a C=N bond is involved. The sensitized as well as unsensitized photochemical E-Z and Z-E isomerization of benzophenone-9anthraldehyde azine have been investigated and the S , state of the E isomer is shown to be reactive. Sensitization of the triplet state does not induce the reaction. Chemiluminescence and Bioluminescence.-The chemiluminescent properties of several imino- 1,2-dioxetans, prepared by photosensitized oxygenation of ketenimines at - 78 "C, reveal that their decomposition to the corresponding ketones and isocyanates proceeds viu a biradical mechanism.493 Chemiluminescence is shown to be a convenient monitor of the lipid peroxidation reactions.494 Chemiluminescence is indeed induced or enhanced by conditions that normally increase lipid peroxidation or that create a peroxidative stress. The synthesis of fluorescein hydrazide and the study of the chemiluminescence accompanying its oxidation in protic as well as aprotic solvents has recently been Of further interest is the synthesis of anthracene derivatives bearing a -COCHgroup and measurement of their direct chemiluminescence on air oxidation in alkaline The chemiluminescence is explained in terms of a chemically-initiated electron-exchange luminescence mechanism. Direct chemiluminescence has been found from the air oxidation of 3-acyl-9methyl~arbazole.~~' The chemiluminescence of dioxetanone has been investigated theoretically and the results provide insight into the structure, reactivity, and properties of peroxides.498 The electrogenerated chemiluminescence (ECI) of five 1-amino-3-anthryl-9propane derivatives has been studied in t e t r a h ~ d r o f u r a n .Emission ~~~ from intramolecular exciplexes in ECI spectra and weak emission from the locally excited anthracene moiety were observed. The influence of triplet state interaction in ECI emission is discussed. The cheiniluminescent decomposition of three SIperoxy-lactones gives C O , and the corresponding ketone in high yield.500 The chemiluminescent species produced has been investigated in some detail by measurements of lifetime, energy-transfer activation parameters, and photochemical reactions. *"

K . Appenroth, M. Reichenbacher, and R. Paetzold, J . Plrotoclicwi.. 1980, 14. 39. K. Appenroth, M. Reichenbacher, and R. Paetzold. J . Plrotoc*lierii.. 1980, 14. 51. Y. Ito. H. Yokoyd, K . Kyono, S . Yamamurd, Y . Yamada. and T. Matsuura, J . Chiwi. So(..,Chcm. Coinrnuri., 1980, 807. ")' A. Boveris. E. Cadenas. and B. Chance, Fed. Proc.. 1981, 40. 195. '95 J. Nokokavouras, J. Zois, G. Vassilopoulos. and A. Perry, J . Piidit. C ~ P I ?1981. ~ . . 323. 21. 'y6 T. Hiramatsu. T. Harada, and T. Yamafi, Bull. Clicwi. Soc. Jprt.. 1981. 54, 985. 4y7 I. Kamiya and T. Sugimoto. BtrN. Cltc~ni.Soc. Jpn., 1981. 54. 25. *" S. P. Schmidt. M . A. Vincent, C. E. Dykstra, and G. B. Schuster, J . Ant. Cherii. So(,..1981. 103, 1292. *99 R. Ziebig, H. J . Hamann, W. Jugelt, and F. Pragst, J . Luniin., 1980, 21, 353. 500 N. J. Turro and M.-F. Chow, J . Ani. Clicmi. Soc., 1980, 102, 5058.

*"

Pho t oc*lwiristq* The quenching of peroxidized luminol chemiluminescence by reduced pyridine nucleotides has been r e p ~ r t e d . ~ ' 'Neither superoxide nor hydroxyl radical scavengers were found to quench the chemiluminescence of luminol in the presence of horseradish peroxidase and H 2 0 2 . Both chemi- and bio-luminescence of firefly luciferin have been investigated and a dioxetanone mechanism proposed for the light-producing pathway.'02 The relation between structure and triboluminescence has been investigated in two polymorphic systems, viz, hexaphenylcarbodisphosphorane and anthranilic acid.jo3Only one phase is triboluminescent. A correlation between triboluminescence and unit cell symmetry groups is given. The detection and possible applications of lyoluminescence are described in an interesting paper by Ettinger c't a/. I t is shown that lyoluminescence can be used to measure the radical scavenging activity of chemical compounds, particularly those with potential for use as radioprotective agents. 116

'''' '("

'O.'

504

J . K . Wong and M . L. Salin. Plrotoi~licwi.Pliotohiol.. 1981. 33. 737. E. H . White. M . G . Steinmetz. J . D. Miano. P. D. Wildes. and R . Morland, J . h i . C/i~wi. Soc.. 1980. 102. 3199. G. E. Hordis. W. C. Kaska. B.-P. Chandra. and J . I. Zink. J . ,4111.Clicwi. Soc., 1981. 103, 1074. K. V. Ettinger, J. R. Mallard, C. I. Anunuso, E. D. V. Filho, C. Regen, and S. Srirath, Nucl. h s t . Mct,~. .. 1980. 175. 136.

3 Gas- phase Photoprocesses BY

G. HANCOCK

1 Aliphatic Hydrocarbon Molecules, Ions, and Radicals Fluorescence spectroscopy of the ovalene molecule, C3,H 14, seeded in a supersonic beam of rare gas atoms, has been used to unravel the dynamical behaviour of the first (S,)and second (S,) excited singlet states.' The S, t So transition shows a sparse, well resolved vibrational structure, with S , lifetimes indicating that its decay is almost wholly radiative. In contrast, the fluorescence decay times following S2 t So excitation are some 200 times larger than those expected from measurements of the oscillator strength of this transition, and this has been interpreted in terms of S2 - S , interstate mixing, with the number of states in the S , background manifold coupling with the S2electronic origin (only 1800 cm higher in energy than the S, origin) as -3 x lo5 for this huge isolated molecule. Supersonic expansion of another polycyclic hydrocarbon, pentacene (C2,H 36) in Ar and Kr has, in contrast been used to study the properties of van der Waals complexes formed between pentacene (P) and rare gas (R) species., PAr, and PKr, complexes each show a pair of features in the vibrationless fluorescence excitation spectrum separated by 4 and 7cm- respectively, thought to arise from two separate isomers of each PR, complex. Spectral shifts between the isolated P molecule electronic origin and the vibrationless excitation of PR, do not obey simple additivity rules as a function of n, in contrast to the behaviour seen in complexes formed between iodine and rare gases, I,R,,. As expected, lifetimes of excited PKr, species are considerably shorter than those of PAr,, a nice illustration of the 'external heavy-atom effect' promoting S , --+ T , intersystem crossing (and hence reducing the fluorescence lifetime) in the decay kinetics of an isolated molecule. Infrared irradiation of van der Waals complexes containing ethylene has been used to measure absorption linewidths and hence predissociation rates of the vibrationally excited specie^.^ Predissociation lifetimes were found to be in the range 0.3 ps for large ethylene clusters, to 0.9 ps for C,H4*C,F4, corresponding to between 9 and 26 vibrational periods before dissociation. Coherent anti-Stokes Raman scattering, CARS, appears to be a promising spectroscopic method of investigating vibrationally excited intermediates formed in isomerization reactions of large polyatomic molecule^.^ The S, state of cycloheptatriene and its 7-methyl derivative, formed by absorption at 266 nm,

',

' A. Amirav. U. Even. and J. Jortner. J. Chem. Phys.. 1981, 74. 3745. Amirdv, U. Even, and J. Jortner, J. Pliys. Chem.. 1981, 85, 309. ' A. M. P. Casassa, D. S. Bomse. and K. C. Janda. J. Chem. Phys.. 1981, 74, 5044. K.Luther and W. Wieters, J. Chem. Phys.. 1980, 73, 4131.

117

118

Plio t oclieniistr!,

rapidly undergo internal conversion (IC) to So species with high vibrational energies: before these transient molecules isomerize into aromatic products (e.g. cycloheptatriene into toluene) their CARS spectra can be observed. The authors suggest that as this technique can be used on the ps time scale, kinetic spectroscopy of single vibrational levels during fast reactions should prove p ~ s s i b l e . ~ End-product analyses have been used to investigate the far-u.v. photolyses of several aliphatic hydrocarbons. Elimination of CH, is the predominant process in the photolysis of 1 ,1 -dimethylcyclopropane at both 147 and I24 nm (primary quantum yields of 0.34 and 0.39, respectively): nine additional reaction channels were identified. Tetramethylethylene (TME) photolysed at various wavelengths between 185-229nm shows products that can be divided into two groups, according to whether the quantum yield falls or rises with increasing total pressure.6 The former group is thought to originate from loss of either H or CH,, with the resultant vinylic (CH,),&H, or allylic (CH,), e&H,&, fragments either decomposing further, or being stabilized by collision. The latter group, a set of isomers of the parent compound, is believed to result from a collisionally induced pre-isomerization mechanism ( 1) competing with collisionless removal TME*

M

A*

A

processes (fluorescence or IC). CH, formation is the most important radical process in the far-u.v. photolysis of but-I-yne ' and b ~ t - 2 - y n e . ~ The decay mechanisms of cations of several unsaturated hydrocarbons have been investigated by coincidence techniques (photoelectron-photon and photoelectron-ion l o * I ) and by laser-induced fluorescence. I' Radiative and nonradiative contributions to the rate constants for removal of the first excited states of the cations of diacetylene and several substituted derivatives l o * l 2 have been evaluated, with radiative decay apparent in some of these species containing up to 0.4 eV internal energy, even though competing fragmentation channels can also be detected.12 For the buta-1,3-diene cation (C4H6+), the dependence of the unimolecular decomposition rate constant upon internal energy of the parent ion has been determined.' Rate constants for reaction of the CH radical with a number of atomic l 3 and molecular collision partners have been reported, with multiple-photon dissociation of suitable precursor molecules using either infrared or ultraviolet l 4 laser radiation used as the pulsed photolysis source, and laser-induced fluorescence near 431 nm employed as a sensitive time-resolved detection method. A similar technique has been used to measure removal rates of a"A, CH, and CD, with

'

'

J. B. Binkewicz, M. Kaplan, and R . D . Doepker. Crm. J. Client., 1981, 59. 537.

' G . J . Collin, H . Deslauriers. and A. Wieckowski. J . fliys. Client.. 1981, 85, 944. '

"

' lo

" l2 13

l4

H . Deslauriers, J . Deschenes. and G. J . Collin. C m . J. Clicwi., 1980, 58. 2100. J. DeschOnes. H. Deslauriers. and G . J . Collin, Cm. J . Clieni.. 1980. 58. 2108. J. P. Maier and F. Thommen. J . Clieni. Plgx., 1980. 73, 5617. J . Dannacher. J . P. Stadelmann. and J . Vogt, J . Client. Pliys.. 1981. 74, 2094. J . Dannacher, J. P. Flamme. J. P. Stadelmann, and J. Vogt, Cliem. Pl1.m.. 1980, 51. 189. J . P. Maier and L. Misev, CIieni. Pliys., 1980. 51, 311. I . Messing, T. Carrington. S. V. Filseth. and C. M. Sadowski, Cliem. PIiys. k i t . , 1980, 74, 56; I. Messing. S. V. Filseth, C. M. Sadowski. and T. Carrington. J. Clieni. P l i p . . 1981, 74. 3874. J . E. Butler, J . W. Fleming, L. P. Goss, and M. C. Lin. Clieni. Pliys., 1981. 56, 355.

119 various reactive and non-reactive collision partners. Absolute rate constants were measured to be an order of magnitude larger than those previously accepted, although relative values were in agreement with earlier results. The singlet-triplet separation in methylene retains its fascination, with the latest calculated value of 10.5kcal mol- agreeing with other theoretical treatments and values obtained from various photochemical and photodissociation studies. The recurrent problem is the considerably higher value (19.5 kcal mol- I ) found from photodetachment measurements on CH,-. and a careful reconsideration of the experimental data has revealed no reason to change this to the more popular smaller value. There is agreement upon at least one aspect concerning CH,, that any relativistic contribution to the calculated singlet-triplet energy separation is a negligible one. Gus-phase Plz(~tol?r.oc’c.~sc..s

’

2 Aromatic Hydrocarbons A two-laser photoionization method has been used to measure the collision-free

lifetime of benzene triplets produced in a molecular beam.” Excitation of the 6, level of S , benzene at 259 nm is followed by rapid ( 80 ns) ISC to vibrationally excited TI, and the decay of this (by ISC to S o * ) can be followed by monitoring C6H6+ions formed by 193-nm photoionization as a function of time following the initial S , excitation. The triplet states, possessing 1.1 eV of vibrational energy, were found to decay with a lifetime of 470 ns. Measurements of triplet decay for benzene, C6D6, and various alkylbenzenes by sensitized phosphorescence of biacetyl have highlighted differences between the short lifetimes seen in the gas phase and long lifetimes in low-temperature matrices, and the different decay paths in these media have been discussed.” Vibrational relaxation within S, benzene has been measured by observations of the changes in the fluorescence spectrum brought about by added collision partners.21Pulsed laser excitation of benzene at 248nm leading to production of molecular clusters via what are believed to be single-photon absorption processes has been reported,22 and emission from electronically excited CN has been seen following irradiation of toluene-NO mixtures at 266 nm, apparently resulting from chemical reaction involving fragments produced by multiple-photon dissociation. 2 3 A series of n-alkylbenzenes, cooled by supersonic expansion and excited to what are initially well localized ring distortion vibrations within the first excited singlet states, show fluorescence spectral behaviour that is dependent upon the alkyl chain length.24 For the first three members of the series (toluene to n-propylbenzene) resonance fluorescence from the initially pumped mode in S , was observed, but for

-

I’

19

’*

22 23 24

M . N . R. Ashfold. M. A. Fullstone. G . Hancock. and G . W. Ketley. Client. Pliys., 1981, 55, 245. P. Saxe, H. F. Schaefer. 111, and N. C. Handy, J . Pliys. Climi., 1981, 85, 745. P. C . Engelking. R. R. Corderman. J . J . Wendoloski, G . B. Ellison, S. V. O’Neil, and W. C. Lineberger, J . Cliem. Phys., 1981. 74, 5460. E. R. Davidson, D. Feller, and P. Phillips, C l i ~ n t Pliys. . L f r r . . 1980, 76, 416; C. P. Wood and N. C. Pyper. Mol. Pliys.. 1980. 41, 149. M. A. Duncan, T. G . Dietz. M. G. Liverman. and R. E. Smalley, J . Pliys. Cliem., 1981, 85, 7. K . W. Holtzclaw and M. D. Schuh, Chm. Pliys.. 1981, 56. 219. L. M. Logan, 1. Buduls, A. E. W. Knight, and 1. G. Ross. J . Cliem. Pliys., 1980, 72, 5667. N . Nakashima, H. Inoue, M . Sumitmi. and K . Yoshihara. J . Cliem. Pliys.. 1980. 73, 4693. J. B. Lurie and M. A. El-Sdyed, J . P l i . ~ Cliem.. . 1980, 84. 3348. J. B. Hopkins, D. E. Powers, and R. E. Smalley, J. Cliem. Pliys., 1980. 73, 683.

120 Photochemistry longer alkyl chains the fluorescence showed no resonant features, indicating that intramolecular vibrational relaxation (IVR) was essentially complete. Rates of these IVR processes were estimated to be on the sub-nanosecond time scale. Similar processes in isolated naphthalene molecules, excited to levels of S , containing up to 4000 cm- of vibrational energy, were again found to take place on a time scale much faster than f l ~ o r e s c e n c e . ~ ~ Laser flash photolysis has been used to prepare vibrationally excited Solevels of azulene, viu rapid IC from the initially populated S , state.26 Decay of infrared emission in the 3.3pmC-H stretch region was used to monitor rates of vibrational energy removal from So,and a stepladder model used to calculate the average amount of energy transferred per gas kinetic collision. The surprising result was that azulene - azulene collisions transfer 3500cm-’ of energy, a large amount in comparison with that normally expected for gas-phase collisional processes. Observations of laser-induced fluorescence of several polycyclic aromatic hydrocarbons in atmospheric pressure flames at 1200-1 500 K have been reported,,’ with spectra not differing greatly from those obtained at lower temperatures, indicating little net change in vibration on excitation of these molecules. 3 Organic Compounds Containing Oxygen Although many experimental and theoretical investigations have been carried out on formaldehyde, the dynamics of the behaviour of the first excited singlet state are still not completely understood. A recent review has highlighted several aspects of this topic, in particular the problems of the fast ‘collisionless’ non-radiative decay of S , , and the time lag observed at higher pressures for the appearance of products.28 The authors report that no experiment has yet demonstrated conclusively that S , dissociates at the zero-pressure limit, although theory suggests that it does, as the molecule is not large enough to undergo non-radiative nondissociative S , decay. A significant experimental point is made, that surprisingly low pressures are required for collision-free conditions to apply.28 Under these low-pressure conditions (0.1-1 mTorr) single rotational level lifetimes have been measured in the 4’ states of S , H 2 C 0 and D,CO. In H,CO, the lifetimes vary between 20 ns-3.1 ps, whereas in D 2 C 0 they cluster around 6.2 ps, thought to be close to the pure radiative lifetime. Higher vibrational levels of S , D,CO, 43,and 2143 show shorter lifetimes, which again fluctuate with rotational quantum number. A collisionless sequential decay mechanism (2) is invoked to explain the S1

-So

H,(DJ

+ CO

(2)

results, in which the last step may, for low vibrational levels of S , , involve tunnelling through a barrier to dissociation. Coupling between S , and So cannot be satisfactorily explained in terms of a smooth continuum of So states, as

25 26

” 28

S. M. Beck, J. B. Hopkins, D. E. Powers, and R. E. Smalley, J . Chem. Phys., 1981, 74,42. G . P. Smith and J. R. Barker, Chem. Pliys. Lett., 1981. 78, 253. D. S. Coe and J. 1. Steinfeld, Cliem. PIiys. Left.. 1980, 76, 485. W. M. Gelbart, M. L. Elert. and D. F. Heller, G e m . Rev., 1980, 80, 403.

Gas-phase Photoprocesses

121

electric 2 9 and magnetic 30 field effects can change the fluorescence 2 9 9 30 and photodissociation 30 rates appreciably. Thus the continuum of So levels is thought to possess local structure, at least near the S , origin:,' clearly Stark shifting at higher vibrational levels would be of interest in providing further details of this. Collisional relaxation of formaldehyde following single rotational level excitation has been reported by several groups. Curvature of the Stern-Volmer plots at pressures between and lo3 Torr for electronic quenching of both H 2 C 0 and D,CO, and the increase in quenching rate by Ar, C o t , and CH,F on deuteriation are factors that appear to have no simple quantitative e ~ p l a n a t i o n .An ~~ important clue would be identification of the elusive intermediate state between S , and the dissociation products populated by collisions: is it So, T,, or possibly HCOH? Calculations show that similar barriers exist for formaldehyde dissociation to H, + CO, and for isomerization to the HCOH intermediate; however for HFCO, the fluorohydroxycarbene species has a much higher energy barrier for its formation than does the dissociation step to H F + C 0 . 3 2Unfortunately the U.V. spectrum of fluoroformaldehyde only sets in above 1 10 kcal mol- higher than barriers to either process, and thus there exists no simple means of excitation of HFCO to energies between the two barriers in order to probe the importance of the isomerized form of the molecule in the dissociation dynamics. Following excitation of 4l S , H,CO, rotational and vibrational relaxation by collisions to levels of different lifetimes to that initially pumped make a major contribution to the observed curvature of the Stern-Volmer plots.31 For the corresponding vibrational level in S , D,CO, rotational relaxation by self collision appears to be , ~ ~is still somewhat slower than the very rapid 4' -, 4O vibrational ~ e l a x a t i o nyet five times faster than gas kinetic.33*34 Collision-induced rotational state changes of A J = & 1 are observed to p r e d ~ m i n a t eevidence ,~~ for a long-range dipole-type mechanism controlling the interaction. Finally, the lifetime of the electronically excited cation of deuteroformaldehyde, D,CO+(A2B,) has been measured, and the rate-determining step in the fragmentation of this ion to give DCO+ is thought to be IC to the electronic ground state.3s Low-pressure studies in glyoxal have shown that the S1state has a significant dissociation decay channel at the zero-pressure limit.36 Fluorescence intensity following CW Ar' laser irradiation at 454.4 nm shows a gradual decline with time with a rate constant that is independent of glyoxal pressure in the range 0.483.2mTorr, and that increases linearly with laser power. The primary quantum yield of dissociation is estimated to be 20.1. 3 6 Collision-induced S , + T, ISC in glyoxal has been studied in the presence of various added gases, with the relative magnitudes of the collision cross-sections found to be dependent upon the value of the intermolecular well depth between S1 glyoxal and the collision partner.,' Such

',

30

31

32

33 34

35 36 3'

J. C. Weisshaar and C. B. Moore, J . Chem. Phys., 1980.72, 5415. N. I. Sorokin, V. I. Makarov. N. L. Lavrik, Y. M. Gusev, G . I. Skubnevskaya, N. M. Bazhin, and Y. N. Molin, Chem. Phys. Left., 1981, 78, 8. J. C. Weisshaar, D. J . Bamford, E. Specht, and C. B. Moore, J. Chem. Phvs., 1981, 74, 226. K. Morokuma, S. Kato, and K. Hirao, J . Chem. Phys., 1980, 72, 6800. P. W. Fairchild and E. K. C. Lee, J . Pliys. Chem., 1980, 84, 3346. B. J. Orr, J. G. Haub. G. F. Nutt, J. L. Steward, and 0. Vozzo, Chem. Pli-vs. Left., 1981, 78, 621. R. Bombach, J. Ddnndcher, J. P. Stadelmann, and J. Vogt, Chem. Phys. Left., 1981,77, 399. G . W. Loge, C . S. Parmenter, and B. F. Rordorf. Chem. Phys. Left., 1980, 74, 309. C. S. Parmenter and M. Sedver, Cliem. Phys., 1980. 53. 333.

122

Photochemistry

behaviour has now been observed in several sets of rapid gas-phase quenching processes (for example in the removal rates of ;‘A CH, by non-reactive collision partners lS) and provides evidence for the long-range attractive part of the intermolecular potential dominating the collision process. Low-energy collisions at a translational temperature of 0.5-0.1 K between He and S , glyoxal expanded in a supersonic jet appear to be some 20-30 times more efficient at causing ISC than those at room t e m p e r a t ~ r e Furthermore, .~~ there appears to be essentially no dependence of the ISC rate upon the initially prepared rovibronic state of S , g l y o ~ a l which, , ~ ~ for rotational states, is consistent with theoretical prediction^.^' No distinct propensity rules for changes in K appear to apply in collisions transferring rotational energy in S , glyoxal with ground-state species or with CO;40 other studies on this molecule include a discussion of the retention of polarization in collision-free fluorescence excited by a polarized source, and its effect on measurements of relative rotational state populations via the Honl-London factor^,^' and further observation of the magnetic quenching of fluorescence in both glyoxal 4 2 and m e t h y l g l y ~ x a l . ~ ~ Quantum beats observed in biacetyl following pulsed irradiation in a molecular beam have been analysed to obtain the density of vibrationally hot triplet states interacting with the initially pumped singlet levels,44 and the effects of collisions and magnetic fields on such quantum beats have been studied, yielding the first direct measurements of cross-sections for dephasing collision^.^^ The kinetics of quenching of 3 A , biacetyl have been studied for several collision partners.46*47 Negative temperature-dependences for quenching by O 2 and NO are cited as evidence for the formation of collision complexes, whereas, for acetaldehyde, the magnitudes of the Arrhenius parameters are similar to those expected for freeradical H-atom abstraction reactions, possibly implying that triplet biacetyl acts as a biradical in the gas phase.47 ISC in biacetyl from T I -, S , , the reverse of that normally observed, has been seen in an experiment in which CO, laser radiation was used to pump triplet molecules (produced near the T , origin by initial excitation to S , , followed by ISC and vibrational relaxation) by multiple-photon absorption to S,.48 Figure 1 shows the effect of the i.r. pulse on the phosphorescence and fluorescence signals from biacetyl: the phosphorescence is seen to be rapidly and irreversibly quenched, and simultaneously a strong S , fluorescence signal is observed. Since the triplet-singlet energy separation in biacetyl is 2100cm- the generation of the fluorescence signal sets a lower limit of two CO, laser photons absorbed per triplet molecule excited.48 A similar reduction in the

,

’,

39 40

41

42 43 44

45 46

47 48

C. Jouvet and B. Soep, J . Chem. Phys.. 1980,73,4127. F . A. Novak and S. A. Rice, J . Cliem. Phys., 1980, 73, 858. H. M . Tenbrink, J . Langelaar, and R. P. M . Rettschnick, Cliem. Phys. Lett., 1980, 75, 115. G. W. Loge and C. S. Parmenter, J . Chem. Phys., 1981, 74, 29. C. Michel and C. Tric, Chem. Phys., 1980, 50, 341. K . Hashimoto, S. Nagakura, J . Nakamura, and S. Iwata, Cliem.Pliys. Lett., 1980, 74, 228. J . Chaiken, M. Gurnick, and J. D. McDonald, J . Chem. Phj-s., 1981, 74, 106, 117. W . Henke, H. L. Selzle, T. R. Hays, S. H . Lin, and E. W. Schlag, Chem. Plivs. Lett.. 1981, 77, 448. C. O’Concheanainn and H. W. Sidebottom, J. Photochem., 1980, 13, 175; M. B. Foley and H. Sidebottom. ;bid.. 1981, 15, 59. C. O’Concheanainn, M. B. Foley. and H . W. Sidebottom, J . Photochem., 1981, 15, 185. J . Y . Tsao, J . G . Black, E. Yablonovitch, and I . Burak, J . Cliem. Pli.vs., 1980, 73, 2076.

123

Gas-phase Pho topro cesses

I

2

6

4

8

10

crs

Figure 1 The efSect of i.r. radiation on the phosphorescence (upper trace, a) and.fltlorescence (lower trace, b) signals,from biacetyl. Time zero corresponds to optical excitation at 405 nm from a dye laser pulse, and the time of introduction of the 9.6 pm CO, laser pulse is indicated by the arrow

phosphorescence quantum yield caused by i.r. multiple-photon absorption by propynal triplets has been reported.49 The zero-pressure decay rates of H C S - C H O and HC&-CDO triplet states have been measured to be 3.1 x lo3 and 1.7 x lO3sd1, respe~tively.~~ Subtracting the contribution from radiative decay (0.71 x lo3s-' in each case) yields the T , --+ So ISC rates, and these show that the substitution of an 49

H . Stafast, J . Opitz, and J . R. Huber, Chem. PIiys., 1981, 56. 63. U. Briihlmann. P. Russegger, and J. R. Huber. Cliem. Pliys. Lerr., 1980, 75. 179.

I24 Pho t oc‘hemist iyq aldehydic hydrogen by deuterium reduces the ISC rate by a factor of 2.4. Calculations using either the v l 0 or v4 vibrations of propynal So as the dominant accepting mode for ISC [vl0 is the CH(D) aldehyde wag, v4* the C L O stretch] are able to reproduce this deuteriation effect.50 Multiple-photon ionization of acetaldehyde, and end-product analysis of the single-photon photolysis of CCI3CHOS2 have been reported. Emission between 250-450 nm in the ’ A , - X’E transition in the methoxy-radical C H 3 0 occurs in the reaction of metastable rare-gas atoms with CH,0H,53 and laser-induced fluorescence of single vibrational levels of the vinyloxy-species CH,=CHO has been detected.54 The collisional relaxation of vibrationally excited C F 3 0 - ions, formed in an ICR cavity, has been studied by using i.r. multiple-photon dissociation of these species by process (3) as a time-resolved method for their d e t e ~ t i o nAs . ~ ~the ease of the CF,O-

11/11’

---+

F-

+ CF,O

(3)

multiple-photon dissociation step (and hence the yield of F-) depends upon the internal energy content of the parent C F 3 0 - , the fraction of ions decomposed by the laser decreases as the vibrationally excited ions relax, thus yielding information upon rates of these de-excitation proce~ses.~’ An elegant experiment that measures directly the unimolecular decomposition rate of process (4)has been r e p ~ r t e d . ’Tetramethyldioxetan ~ is excited in the near-

i.r. to high overtones of the C-H stretching vibrations, u = 4 and 5, corresponding to internal energies of 32 and 39 kcal mol- respectively, and exceeding the energy barrier to dissociation, some 27 kcal mol - Part of the decomposition pathway yields electronically excited acetone, and observations of time-resolved fluorescence from this enables rates of unimolecular decay of state-selected tetramethyldioxetan to be found: these are 0.12 x lo6 and 3.4 x 106s-’ for u = 4 and 5, re~pectively.’~ Measurements of phosphorescence intensities in gas-phase benzaldehyde have shown that S, -, T , ISC dominates over S , + So IC at low to moderate vibrational energy content of the initially prepared S, state, whereas IC becomes important at higher energie~.~’ Deuteriation of ring hydrogens changes both ISC and IC rates dramatically, but these are only moderately affected by deuteriation of the aldehydic hydrogen, and the possible identities of the vibrational modes which couple the electronic states to yield this unexpected behaviour have been suggested.” Studies of intramolecular redistribution of excess energy within T ,

’,

“ 52

s3

’‘ 55

” 57

G. J . Fisanick, T. S. Eichelberger, B. A. Heath. a n d M . B. Robin, J. Cheni. PhFs., 1980, 72, 5571. T. Ohta and I. Mizoguchi, Int. J. Chm. Kitzc.r.. 1980, 12, 717. M. Sutoh, N. Washida, H. Akimoto, M. Nakamura. and M. Okuda, J. Clieni. Phys., 1980, 73, 591. G. Inoue and H.Akimoto, J. C/iwi. Ph1.s.. 1981. 74, 425. J. M. Jasinski and J. 1. Brauman. J . Clicw. fl1y.s.. 1980, 73. 6191. B. D. Cannon and F. F. Crim, J. C / m i . P/~ys..1980, 73. 3013. Y. Hirata and E. C. Lim, J. Cllcwi. P / I ~ S1980. .. 72, 5505.

125

Gas-phase Photoprocesses

states of aryl alkyl ketones have shown that energy flow between carbonyl and ring vibrations is significantly slower for molecules wi!h bulky alkyl groups.58 Deuteriation of ring hydrogens decreases the T , + So ISC rate by a factor of four, a far smaller effect that the three orders of magnitude difference caused by a similar deuteriation in ben~aldehyde.~'An alternative interpretation of the behaviour of vibrationally excited triplet states TI* formed following excitation of acetophenone has been suggested,59 the dissociation step ( 5 ) instead of the conventionally assumed ISC process (6).58 The emission behaviour of 1,4-

C6H,COCH3(Tl*)

-

C,H,eO + e H 3 C6H5COCH3 (so)

(5)

(4)

naphthoquinone and its 2-methyl derivative,60 and the 'dual fluorescence' caused by the two possible forms of intramolecular hydrogen-bonded rotamers of methyl salicylate 6 1 have been investigated.

4 Sulphur-containing Compounds Thiiran, C,H,S, when irradiated at wavelengths > 240 nm, undergoes ISC to T , with high efficiency (a = 0.86).62The triplet state has a long radiative lifetime and is resistant to collisional de-excitation, and can undergo reversible addition to alkenes, inducing their geometrical isomerism without energy transfer and subsequent quenching of the triplet state. Process (7) is believed to take place in the

observed cis-trans isomerism of butene. Product analyses of the U.V. photolyses of tri- and tetra-methylene sulphoxide 6 3 - 64 have been used to model their dissociation pathways. In trimethylene ~ u l p h o x i d e ,the ~ ~ cyclopropane product appears to be formed with a non-random distribution of internal energy, and this has been used to suggest that the SO fragment is formed in the metastable 'A state, reaction (8). Collision-induced electronic quenching of S , thioformaldehyde n

L'

s\. +

'* 59 6o 61

62

63 64

hv

-A

+

SO('A)

Y. Hirdta and E. C. Lim, J . Cltetn. Pliys., 1980, 73, 3804. A. R. Rennert and C. Steel, Clteni. Phys. Lett., 1981, 78, 36. T. Itoh and H. Bdba, Cltem. fhys.. 1980. 51, 179. A. U. Acuna. J. Catalan. and F. Toribio. J. PItys. Cheni.,1981. 85, 241; R. Lopez-Delgardo and S. Lazare, ibid., 1981, 85, 763. E. M. Lown. K. S. Sidhu, A. W. Jackson. A. Jodhan, M.Green, and 0. P. Strausz. J . P1ty.v. Client., 1981, 85, 1089. F. H. Dorer and K. E. Salomon, J . PIiys. Client., 1980, 84, 3024. F. H.Dorer and K. E. Salomon, J. P l i w Clieni., 1980, 84. 1302.

126

Pho t ockcmistry H,CS is seen to dominate over vibrational and rotational relaxation, as the fluorescence spectra of S , show that the species retain their memory of the initially excited rovibronic levels at relatively high pressure^.^^ Fluorescence excitation of jet-cooled thiophosgene, Cl,CS, has been reported.66 Vibrational and rotational energy disposal in the CS(A l7) fragment of the monochromatic V.U.V.dissociation of CS, shows that a high proportion (1530%) of the available energy is found in product vibration, with most or all energetically possible vibrational levels populated.67 Electronic quenching of CS (A'n,v' = 0-5) by CS2 and Xe shows rates which are intensive to v', and too fast to allow collisional rotational and vibrational redistribution, although these relaxation processes do occur for other gases.68Quenching of CS(A l7, u' = 0) by 0 atoms shows a distinct rotational state d e p e n d e n ~ e with , ~ ~ levels which are perturbed by nearby triplet states being selectively removed. A model for quenching via the formation of a collision complex, followed by reaction or ISC, is invoked to explain the observations. Photolysis of CS, at 193nm yields S('D), which has been observed directly by time-resolved resonance fluorescence, and rate constants for quenching of the excited S atom with CS,, OCS, and CH, have been m e a s ~ r e d . 'The ~ primary quantum yield of S( ' D ) was estimated as % I5%, considerably lower than that previously reported by less direct photofragment spectroscopy studies '' at the same wavelength. The co-product of 193nm photolysis, C S ( X ' C + ) , has also been observed.72 In the 193-nm photolysis of H,S, around 20 000 cm - of energy is available for partitioning within the ground-state fragments, yet the SH radical is found to have only -320cm-' internal energy.73 A model for recoil of the departing H atom along the original H-SH bond direction can be used to explain the data: the recoil will be orthogonal to the remaining S-H vibrational mode and this is unlikely to couple effectively to it, and considerations of angular-momentum conservation preclude high rotational-state population in SH. The laser-induced fluorescence technique has been used to study the B3Cu-X3C,- transition in S,, revealing details of the perturbing Bn3nustate,74 and the 2 'A'--f2A'' transition in HSO, with the latter radical formed by reaction of discharged O2 with H,S.75 Fluorescence quantum yields and lifetimes of various sulphur-containing ions have been measured,76 and V.U.V.photoionization efficiencies reported for formation of CS2+ from the parent CS2.77

'

'

" 66

67

68 69 70

7'

72 73 74 75

'' 77

D . J . Clouthier, C. M. L. Kerr. and D. A. Ramsay, Ciicni. PIiys., 1981, 56. 73. R. Vasudev, Y. Hirata. E. C. Lim, and W. M. McClain. Clieni. Phys. Lett., 1980, 76. 249. M. N . R. Ashfold, A. M. Quinton. and J. P. Simons. J . Ciieni. Sot.. Fnrcitkny Trcins. 2, 1980,76, 905. M. N. R. Ashfold, A. M. Quinton, and J. P. Simons, J . Clieni. Sot..Fcircickciy Trcins. 2, 1980, 76, 915. A. J . Hynes and J . H. Brophy, Ciieni. Pliys. Lett., 1980. 75. 52. M. C. Addison, R. J. Donovan. and C. Fotakis. Ciieni. PIiys. Lett., 1980, 74. 58. S. C. Yang, A. Freedman. M. Kawasaki, and R. Bersohn, J . Cliem. Pliys.. 1980, 72, 4058. J . E. Butler, W. S. Drozdoski. and J. R. McDonald. Ciieni. P I i w . . 1980, 50. 413. W. G . Hawkins and P. L. Houston, J . Cheni. Phys., 1980, 73, 297. D. A. Peterson and L. A. Schlie, J . Chem. Phys., 1980, 73, 1551; C. R. Quick, jun. and R. E. Weston, jun., ibid., 1981, 74, 4951. M . Kawasaki, K . Kasatani, and H. Sato. Clicwi. PIiys. Lett., 1980, 75, 128. J . P. Maier and F. Thommen, Clieni. Phys., 1980, 51, 319. Y . Ono, S. H. Linn. H. F. Prest, M. E. Cress. and C. Y. Ng. J . Ciiem. fiiys., 1980, 73. 2523.

127

Gus-phuse Pho toprocesses

5 Nitrogen-containing Compounds Emission accompanying excitation of Hg-NH mixtures with XeI exciplex radiation (253.2nm) has been studied in the Hg pressure range 1-40 Torr.” At low pressures ( < 1 Torr), the familiar U.V.emission of the HgNH, complex at 342nm is seen, whereas at higher Hg concentrations this is replaced by a strong green emission band near 500 nm. Lifetime measurements on this band eliminate Hg3* as the emitter, and its identity is suggested as Hg,NH,*: potential gain on this system does not appear promising as the carrier absorbs throughout the green emission band. Multiple-photon ionization of expansion-cooled NH, has been carried out, with 2- and 3-photon absorption features being identified, and the state confirmed.” Similar studies on previously reported position of the pyrroles 8o and on trimethylenediamine have been reported, with ‘two colour’ excitation demonstrating the usefulness of the technique in elucidating pathways for the resonantly enhanced MPI processes.8’ One-*,, 8 3 and t ~ o - p h o t o nexcitation ~~ of trialkylamines has been observed. For trimethylamine, S1 appears to radiate following excitation at wavelengths where both S , and S2 are populated ”* 8 3 and the fluorescence shows a dual exponential decay at pressure low enough to ensure that collisional relaxation is not of imp~rtance.’~ Relaxation of two different vibronic distributions in S , , one formed directly by excitation, and the other by rapid IC from S,, is invoked to explain this behaviour, with these isoenergetic levels having different fluorescence lifetime^.'^ Rapid quenching of S , trimethylamine by 0, and NO has been interpreted as due to complex formation between the colliding species.’’ Product analyses of the 193 nm photolysis of methylamine show that the major decomposition route involves formation of HCN.86 Single vibrational levels of the ‘ B , state of aniline, formed by excitation within a He-aniline molecular beam, have been shown to relax in low-energy collisions with the He diluent at rates which are markedly dependent upon the identity of the vibrational mode excited.” Intramolecular vibrational energy transfer within the ‘ B , state induced by collision with H,O and CH,F is also mode specific,*’ and rates for these processes are of the same order for these two collision partners and considerably faster than for energy transfer caused by Ar. Within p-alkylanilines, collisionless intramolecular vibrational relaxation from the initially excited NH, inversion mode to the alkyl chain modes appears to be complete within 1 n ~ , ’ ~

e’

’’

’’ A. Mandl and H. A. Hyman, J. Clrem. Phys.. 1981, 74, 3167. 79

’’ 83 84

’’ 86

” 89

J. H. Glownia, S. J. Riley, S. D. Colson, and G. C. Nieman, J. Cliem. Phys., 1980, 72, 5998; J. H. Glownia, S. J. Riley, S. D. Colson, and G. C. Nieman, ibid,, 1980, 73, 4296. C. D. Cooper, A. D. Williamson. J. C. Miller, and R. N. Compton, J. Chem. Phvs., 1980, 73, 1527. K. R. Newton, D. A. Lichtin, and R. B. Bernstein, J. Pliys. Cliem., 1981, 85, 15. Y.Matsumi and K. Obi, Chem. Phys., 1980, 49. 87. C. G. Cureton, D. V. OConnor. and D. Phillips, Clteni. Pliys. Left., 1980, 73, 231. K. Kasatani. M. Kawaskak, H. Sato, Y. Murasawa. K. Obi, and 1. Tanaka, J . Chem. Phys., 1981,74, 3164. K. Obi and Y. Matsumi, Cliem. f l i y s . , 1980. 49, 95. N. Nishi. H.Shinohara, and I. Hanazaki. Clretii. PI7y.s. Lerf.. 1980. 73. 473. J. Tusa, M. Sulkes, and S. A. Rice, J. Clrcm. f I 7 . 1 x . 1980. 73, 5897. M. Vandersall, D. A. Chernoff. and S. A. Rice, J . Cliem. Phys., 1981, 74, 4888. D. E. Powers, J. B. Hopkins, and R. E. Smalley, J. Chcni. Phys., 1980, 72, 5721.

128

Photochemistry

with little vibronic isolation being provided by the benzene ring between these two functional groups. Continuous irradiation of pentafluoropyridine (1) in the near-u.v. forms a product identified as the Dewar isomer (2), which was found to revert to (1) in a period of 5 days." Two short-lived transients, with half lives of 22 and 3 ms were detected by flash photolysis, and assigned to the two fulvene isomers, (3) and (4). Pyrazine excited in its 'B,,(nz*) t ' A , transition shows a marked variation of

-

mF F

F

FfJF

F

F

&F

F&F F

F

F

fluorescence quantum yield over the limited wavelength range of a vibrational absorption band c o n t ~ u r , ~apparently ' due to ISC rates being enhanced with increasing rotational quantum number. A K2 dependence of the non-radiative rate fits the data.92 Rates of collision-induced vibrational energy transfer within 'B,, pyrazine have been measured, with both energy defect considerations and propensity rules being found necessary to explain their observed magnitudes.', Lifetime measurements of various vibrational levels of 'B,(nn*)pyrimidine show that the v 1 totally symmetric ring stretch is the predominant accepting mode for the biexponential fluorescence decay rates observed being explained by mixing of nn* and nn* low-lying states. 9 5 Phosphorescence from pyrimidine has been reported for the first time.96 Photofragment vapour (@ = spectroscopy of sym-tetrazine at 266nm ('B2, t 'A,) shows that one HCN molecule formed [reaction (9)] receives considerable translational excitation, yet C2N,H2 ('B,,)

-

2HCN

+ N,

(9)

the second is translationally co0L9' This suggests stepwise rather than concerted HCN elimination, with the recoil direction (estimated from the angular distribution of photofragments) determined by the parent molecular geometry. Interestingly, photolysis at 532 nm ('B,, + ' A , ) yields exactly the same photodissociation dynamics as at 266nm, implying that a two-photon absorption step is necessary 90

" " 93 '4

" '6

''

E. Ratajczak, B. Sztuba, and D. Price, J . Pliotochem.. 1980, 13, 233. H . Baba, M . Fujita, and K. Uchida, Clirm. P l i j x Left., 1980, 73, 425. G. ter Horst, D. W. Pratt. and J. Kommandeur, J . Chem. Phys., 1981,74, 3616. D. B. McDonald and S. A. Rice, J . Clieni. Pliys., 1981, 74, 4907. A. K. Jameson and E. C. Lim, Chem. Pliys. Leff., 1981, 79, 326. W. A. Wassam and E. C. Lim, Clieni. Pliys., 1980, 48, 299. T. Takemura, K. Uchida, M. Fujita, Y. Shindo, N . Suzuki. and H. Babd. Cliem. Phys. Lett., 1980,73. 12. J . H . Glownia and S. J. Riley, Clieni. Plijx Lett., 1980, 71. 429.

Gas-phase Photoprocesses 129 for decomposition in the visible, and that the truly isolated B,, state of tetrazine is photochemically stable.” For dimethyltetrazine, fluorescence quantum yield measurements have shown that although decomposition is observed following visible excitation, it does not take place directly from the ‘B,, state, and that an intermediate (and unidentified) state is involved.98aFurther low-pressure studies on these systems will clearly be stimulated by these observations. The wavelength dependence of the quantum yield of I(2P,) formation in the photodissociation of ICN has been measured in the region 240-280 nm.98bFigure 2 shows the ICN absorption spectrum in this region (the A continuum), together

’

100

80 W

--

I

’

-

60-

;L’

B

5

C .c a8 L

g

40

1

A’

ii

-

‘0

/. ’‘o-l a\

1

! \

-

O,

/ 20-

- ,ooor I O3.5

\. \.

\ ; \=\

/

/

-

’ ’

.@A\.

/./ ,-‘

c

.g

‘Pi’ I

/

‘ 0

1

-\ ‘ 0

I 37

I

I

39

1

-I

41

-

-0

I

I

43

I 45

with the contribution to this from dissociation to form I(’P+) [the product of E~~~ and the I(’p+) quantum yield], and the difference between these two curves, with the last of these giving the contribution from dissociation to ground-state I atoms (2P3,2).As can be seen from the Figure, at least three electronic states are responsible for the A continuum absorption in ICN. Vibrational and rotational energy disposal in the CN(A211iand BZZ+)products of v.u.v. photodissociation of ClCN, BrCN, and ICN has been determined from observations of fragment 98

99

(a)M . Paczkowski, R. Pierce, A. B. Smith, and R. M. Hochstrasser, Chem. Ph-vs. Lett., 1980, 72, 5; (6) W. M. Pitts and A. P. Baronavski, hid.. 1980, 71, 395. M. N.R. Ashfold, A. S. Georgiou, A . M . Quinton, and J. P. Simons, J. Chem. Sor.. Faraday Trans.2, 198 1, 77, 259.

130

Photochemistry

fluore~cence,~~ The nature of the cyanogen halide excited state (either directly dissociative, formed by an intravalence electronic transition, or predissociative, formed via a Rydberg transition) influences these energy distributions, and qualitatively the Franck-Condon description of the dissociation process explains the data.99Cross-sections for CN production in the 105-155 nm dissociation of HCN have been measured,loOand several calculations have been carried out of energy disposal following dissociation of bent and linear triatomic molecules, with specific application to those fragmenting to give CN. lo' Photolysisof cyanogen has been used to produce CN(A211i) and to observe the B2C+ t A211 transition by laser-induced fluorescence. O 2 Vibrational and rotational distributions in N0(217) formed in the visible photodissociation of CF,NO have been measured.l o 3 The NO production rate is equal to the rate of decay of excited CF,NO molecules (the fluorescence lifetimes of which have been recently determined lo4) showing that although predissociation of the initially populated CF,NO(A) state results in the photofragments, no long-lived intermediate state is involved: 95% of the NO product is formed in u = 0, and vibrationally excited state populations do not fit a linear surprisal plot, possibly indicating the existence of more than one predissociation mechanism. Vacuum-u.v. photolysis of CF2CIN0, leading to formation of electronically excited NO and CF, radicals, has been reported."' The near-u.v. photolysis of methyl nitrite yields methoxy radicals [equation (lo)] with a quantum yield of unity.lo6 Reaction rate constants of CH,O with 0, CH,ONO

+ hv

-

CH,O

+ NO

(to yield formaldehyde+ HO, lo6) and NO (forming HNO, detected by laserinduced fluorescence lo') have been measured. Vacuum-u.v. photolysis of CH,ONO yields NO in the A 2 Z + , C 2 n , and D 2 Z + states (albeit with low quantum yields lo'), and the distributions of energy within the vibrational levels of NO (A'C') produced by photolysis of this l o g and other nitrites ' l o have been discussed in terms of statistical models of energy partitioning. Dimethylnitrosoamine, excited to S , by absorption at 363.5nm, dissociates with unit quantum yield to form NO, and vibrational excitation in the product has been detected by i.r. emission.l 1 U.V. photolysis of HN, at wavelengths around 290nm yields metastable NH (a'A), and observations of the rate of removal of this species (by laser-induced fluorescence) have resulted in a rate constant for reaction (1 1) of NH(a'A) loo

lo3 lo4 lo'

Io6 lo'

lo' lo9

'lo

+ HN,

A

NH2(A2Al)+ N,

(11)

L. C. Lee, J . Chem. Phys., 1980, 72, 6414. M. D. Morse and K. F. Freed, Chem. Phys. Lett., 1980, 74, 49; M. D. Morse and K. F. Freed, J . Chem. Phys., 1981, 74, 4395; K. Takatsuka and M. S. Gordon, ibid., 1981, 74, 5718, 5724. C. Conley, J. B. Halpern, J. Wood, C. Vaughn, and W. M . Jackson, Chem. Phys. Lett., 1980,73,224. M. P. Roellig, P. L. Houston, M. Assher, and Y. Haas, J . Chem. Phys., 1980, 73, 5081. K. G. Spears and L. D. Hoffland, J . Chem. Pl7y.s.. 1981,74. 4765. C. A. F. Johnson and H. J. Wright, J . Chem. SOC., Faraday Trans. 2, 1980,76, 1409. R. A. Cox, R. G. Derwent, S. V. Kearsey, L. Batt, and K. G . Patrick, J . Phorochem.. 1980. 13, 149. N. Sanders, J. E. Butler, L. R. Pdsternack, and J . R. McDonald, Chem. Phys., 1980, 48, 203. F. Lahrnani. C. Lardeux, M. Ldvollke, and D . Solgadi, J. Chem. Phys., 1980, 73, 1187. F. Lahrnani, C. Lardeux, and D. Solgadi, J . Chem. Phys., 1980,73, 4433. F. Lahmdni, C. Lardeux, and D . Solgddi, J . Photochem., 1981, 15, 37. G. Geiger, H. Stafast, U. Bruhlmann, and J. R. Huber. Chem. Phys. Left., 1981, 79; 521.

Gas-phase Photoprocesses

131

1.8 x 10-'ocm3 molecule-'s-' l 2 Absolute cross-sections for the absorption of HNO,, and quantum yields for the formation of OH('C) in the wavelength region 110-190 nm have been reported,'13 the excess energy in the OH* fragment appearing mainly in rotation with an approximately Boltzmann distribution, in sharp contrast with that for dissociation of H,O and H,O, at the same wavelength. Laser-induced fluorescence of the J1At'-z1A' transition in the HNO radical has been comprehensively studied, with the predissociation mechanism evaluated from the observed S (but not K' or u') dependence of the fluorescence quantum Finally in this Section , the fluorescence excitation spectrum of phthalocyanine in a supersonic-free jet has been analysed, with vibrational structure in this large molecule resolved for the first time,"' and studies of exciplex formation l 6 and quenching behaviour ' of 9,lO-dicyanoanthracene have been reported.

'

6 Halogen-containing Compounds In the 248 nm photolysis of methyl iodide, i.r. fluorescence from the CH, fragment has shown that this is formed with vibrational excitation in the out-of-plane bending mode, but that higher frequency C-H stretching modes are not A calculation for this dissociation process using an assumed populated. potential energy surface for the excited CHJ state implies that the vibrational distribution in the CH, 'umbrella mode' peaks at u = 2, and the results are seen to fit recent photofragment spectroscopy measurements of the total fragment internal energies in CH,I photolysis.119Quantum yields for the production of I(,P+) from CH,I and CH,I, have been measured at 248 and 308nm: at the former wavelength, i.r. emission from the CH,I product in CH,I, photolysis was seen, peaking near the C-H stretching and CH, bending vibrations, but present at all other i.r. wavelengths, indicating that the fragment is produced with excitation into a high density of internal states, nearing the vibrational quasicontinuum.' l 8 I, elimination does not appear to be of importance in the near-u.v. photolysis of CH,I,,120 although some emission from excited I, (3nau) is seen in photolysis at V.U.V. wavelengths.12' From studies of the 147nm photolyses of CH,CHCl,, and CH,ClCH,Cl evidence is presented for the elimination of 2 C1 atoms, either simultaneously, or by C1,* formation and subsequent decomposition. Photolyses of HCC1, in the u.v.',, and of vibrationally excited cations of fully halogenated methanes by i.r. radiation 124 have been studied, and the spectral 'I2 'I3

'I4 'I5 'I6

'I7 'I8

'I9 12' 122

L. G. Piper, R. H. Krech, and R. L. Taylor, J . Chem. f l i p . , 1980, 73, 79. H.Okabe, J. Chem. fIiys., 1980, 72, 6642. R. N. Dixon, K. B. Jones, M. Noble, and S. Carter, Mol. fliys., 1981, 42, 455. P. S. H. Fitch, C. A. Hayndm, and D. H. Levy, J . Chem. fliys., 1980, 73, 1064.

S . Hirayama and D. Phillips, J. fhys. Chem., 1981, 85, 643. S. Hirayama, Chem. fliys. Lett., 1981, 79, 174. S. L. Baughcum and S. R. Leone, J. Chem. fhys., 1980, 72, 6531. M. Shapiro and R . Bersohn, J. Chem. fhys., 1980, 73, 3811. G. Schmitt and F. J. Comes, J. fhotochem., 1980, 14, 107. H. Okabe, M. Kawasaki. and Y. Tanaka, J. Cliem. fhys., 1980, 73, 6162. T. Yano, K. H. Jung, and E. Tschuikow-Roux, J. fliys. Cliem., 1980, 84, 2146; T. Yano and E. Tschuikow-Roux, ibid, p. 3372. S . Hautecloque, J. fhofochem., 1980, 14, 157. M.J. Coggiola. P. C. Cosby, and J. R. Peterson, J. Chem. fliys., 1980, 72, 6507.

132

Photochemistry

dependences of I('P*) and ( , P 3 , 2 ) formation in the photolyses of various perfluoroalkyl iodides have been reported.' 2 5 Intramolecular redistribution in S , p-difluorobenzene 'has been studied directly by observations of the fluorescence spectra in the presence of increasing concentrations of an efficient electronic quenching gas (in this case, 0,). 2 6 Under these conditions, emission is observed only from molecules that radiate during the interval between absorption and quenching, which, at high pressures of added gas (up to 30 kTorr), can be reduced to the ps time scale. Redistribution of vibrational energy is seen to take place with a rate constant of 10' s- 1 . 1 2 6 Spectroscopic and kinetic studies of several triatomic halogenated carbene radicals have been reported in the past year, with detection of these in their ground electronic states by laser-induced fluorescence a common experimental technique. X'A' C H F has been formed by infrared multiple-photon dissociation of CF,HCI, with the laser excitation spectrum of the J ' A " - f ' A ' transition recorded, and radiative lifetimes of four vibronic states measured to lie in the range 1.92.5 p.'2 7 Emission has been seen from HCF and DCF produced electronically excited in methane-F, flames. '2 8 Reaction rates of ground-state CFCl and CCl, radicals with various scavengers ' 29, 30 have been reported, with the radicals generated either by U.V.photodissociation of a suitable halogenated hydrocarbon,'29 or, in the case of CFCl, by chemical reaction between oxygen atoms and CF,CFCI:'30 laser-induced fluorescence was used in both cases to monitor the radical concentrations. For the CFCl + NO reaction (the only one common to both studies for which a removal rate was quantitatively determined), rate constants differing by almost an order of magnitude have been reported, 1 x 10- l 4 and 1.4 x 10- l 5 cm3molecule- s- (refs. 129 and 130, respectively). The radiative lifetime of the A state of CFBr has been measured as 1 150 & 50 ns,' and U.V.emission from the corresponding state of CF, seen in reactions of metastable He atoms with CF,CI,.' 32 The dissociation of several alkali halides in the near U.V.has been studied by three different groups using the technique of photofragment spectroscopy.' 3 3 - 3 5 Contributions to the absorption spectrum from parallel and perpendicular transitions (corresponding, at least for the heavier halides, to upper electronic states with quantum numbers fi = 0 or 1) can be determined from the anisotropy of the dissociation yield with respect to the polarization of the laser beam, and this has been accomplished for KI and NaI (300-337nm),'33 KBr and NaBr (265310nm),'33 Na, K, Rb, and Cs iodides at 347.1 nm,134 and the corresponding chlorides at 266 nm. 35 Dissociation energies for several of these molecules have been reported.' 3 3 * ' 35 Photodissociation of HgBr, at 193nm yields excited HgBr

'

-

'

'

'

'

'

125

Iz6

I29

V. S . Ivanov, A. S. Kozlov, A. M . Pravilov. and E. P. Smirnov, Kvantovayo Electron., 1980,7, 993. R. A. Coveleskie, D . A. Dolson. and C. S. Parmenter, J . Chem. Phys., 1980, 72, 5774. M . N. R. Ashfold, F. Castano, G. Hancock, and G. W. Ketley, Cltem. Pltys. Lett.. 1980, 73, 421. R. I. Patel, G . W. Stewart, K. Casleton, J. L. Cole, and J. R. Lombardi, Cliem. Phys., 1980,52,461. J. J . Tiee, F. B. Wampler, and W. W. Rice, Clrem. Pltys. Lett., 1980, 73, 519. H. Meunier, J. R. Purdy, and B. A. Thrush, J. Clirm.Soc., F(imday Trans. 2 , 1980, 76, 1304. J. R. Purdy and B. A. Thrush, Chem. Phys. Lett., 1980.73. 228. T. Ishiguro, Y. Hamada, and M. Tsuboi, Bull. Chern. Soc. Jpn., 1981, 54, 367. N. J. A. van Veen, M. S. de Vries, J. D. Sokol, T. Bailer, and A. E. de Vries, Cliem. Pliys., 1981,56,81. W. R. Anderson, B. M . Wilson. R. C. Ormerod, and T. L. Rose. J . Cltem. Phvs., 1981, 74, 3295. T. M. R. Su and S. J . Riley, J . Cliem. Phys., 1980, 72, 6632.

*'' 135

Gus-pkusse Photoprocesses

133

(B'C') with almost unit quantum yield, 136 and the nascent vibrational distributions of both HgI and HgBr from photolyses of the corresponding dihalides at this wavelength have been determined. 3 7 The distributions were separable into relative contributions from processes forming ground-( 2P3,2)and excited-(,Pt) state halogen atoms, X: production of X( P312) was accompanied by vibrational population inversion in HgX(B), and X('P,) by a Boltzmann-like HgX(B) state distribution. Quenching of the vibrational levels of HgBr(X) with He has been shown to be an efficient process, and thus the HgBr (B + X ) laser can extract energy efficiently if He is present to remove the terminating laser level by vibrational relaxation. '38 Another publication describing laser action on this transition has appeared. 39 Photofragment spectroscopy of thallium halides has helped characterization of the upper electronic states involved in the U.V.absorption spectra.14' For TIBr, photolysis at I93 nm produced population inversions in neutral TI transitions, and photon efficiency) has been r e ~ 0 r t e d . l ~Two-photon ' lasing (with 2 x absorption of KrF radiation at 248 nm by InCl and InBr yields excited states of In,142and similar processes take place in the 193nm photolysis of SnI,, SbI,, Ge14,'43 PbI,, and PbBr,.'44 One- 145 and two-photon 146 absorption processes in UF, have been studied in some detail, with the quenching behaviour of the fluorescent state(s) produced being, not surprisingly, somewhat complex. This year's group of publications upon the rare-gas halides includes a careful study of the ordering of the B and C states in XeCI, XeBr, and KrCl by observation of the temperature dependences of the C + A and B + A emission^.'^^" For KrCI, the alphabetic ordering of the states is confirmed, whereas the B state is found to lie above the C for the xenon halides.147uThe value of E,--E, for XeC1,'47u -130 & 35cm-' differs considerably from that estimated from XeCl fluorescence measurements carried out at room temperature, 5.4 &- 25cm- 1.1476 The determination of the correct ordering of these states is of some importance, not only for overall modelling of the rare-gas halide laser systems, but also because if the C state lies sufficiently below the B, then lasing on the C -+ A transition becomes possible, as has been shown in the successful operation of the XeF (C + A ) laser at 470 nm. Measurements of the polarization of fluorescence from XeF(B) produced by 193nm photolysis of XeF, has been

'

136

13' ''13

140

14' 14' 144

lo5

'46

14'

B. E. Wilcomb, R. Burnham. and N. Djeu, Client. Pliys. Lett., 1980, 75. 239. J. A. McGarvey. jun., N. H. Cheung, A. C. Erlandson, and T . A. Cool, J. Client. Pliys.. 1981, 74. 5133. H. Helvajian and C. Wittig, Appl. Pliys. Lett., 1981, 38, 731. R. T. Brown and W. L. Nighan. Appl. PIiys. Lett., 1980. 37. 1057. M. S. de Vries, N. J. A. van Veen, T. Baller, and A. E. de Vries. Client. Pliys. Lett., 1980, 75, 27; N. J. A. van Veen. M. S . de Vries, T. Baller, and A. E. de Vries, Cliem. Pliys., 1981, 55. 371. P. Burkhard. W. Liithy. and T. Gerber. Opt. Commun., 1980, 34, 451. T. A. Cool and J. B. Koffend. J. Clieni. Pliys.. 1981, 74. 2287. H. Hemmati and G. J. Collins. IEEE J. Quantum Electron., 1980, 16, 1014. H. Hemmati and G. J. Collins. IEEE J . Quantum Electron.. 1980. 16, 594. E. Borsella, F. Catoni, and G. Freddi, J. Cliem. Pliys., 1980.73, 316; W. W. Rice, R. C. Oldenborg, P. J. Wantuck. J. J. Tiee. and F. B. Wampler. ibid., p. 3560; K. C. Kim, M. Reisfeld, and D. Seitz, ibid.,p. 5605. E. R. Bernstein and P. M . Kennedy, J. Cliem. Pliys., 1981, 74, 2143. (a)J. Tellinghuisen and M.R. McKeever. Client. Pliys. Lett., 1980, 72, 94; ( h ) J . Bokor and C . K. Rhodes, J. Client. Pliys., 1980. 73, 2626.

134

Photochemistr~*

used to suggest the symmetry of the parent molecule's dissociative state Collisional depolarization and electronic quenching rates for the XeF(B) state were determined in this and formation and quenching processes involved in the XeCI(B) state have also been investigated.'49 Lasing has been seen from the Kr,F exciplex at 430nm,'50 and emission spectra have been recorded from various mixed rare-gas halide trimers (e.g. KrXeCI). ' ' Vibrational relaxation of I, (311,,+)in very low-energy collisions with He and Ne in a seeded molecular beam is found to be an extremely efficient process, with cross-sections at least as large as hard-sphere collision values.'s2 Models incorporating orbiting or rotational resonances of the colliding pair are found to fit the data, and it is suggested that this mechanism will be quite a common one for relaxation process at low energies. 5 2 Excitation and dispersed fluorescence spectra of several van der Waals molecules containing I, have been reported. 1 5 3 - 1 5 5 For I ,Ar,Heb complexes, additivity rules predict the shift of the absorption band from that of free I, to be of the form Aa + Bb, where A and B are constants (in contrast to the behaviour described earlier in this Report for pentacene complexes2). An increase in the number of rare-gas atoms in the complex resulted in a more than proportional increase in the number of vibrational quanta per rare-gas atom required for dissociation.' 53 Evidence for anisotropy in the intermolecular potential between I, and H, has been found from similar studies on the 12-H2 complex, with different absorption spectra seen for ortho- and para-H,, and different product-state distributions observed when orthoand para-H, complexes predissociate.' 5 5 For o-H,--I,, the relatively high van der Waals stretching frequency (100cm- ') couples well with the I, vibrational frequency (128 cm- ' in the B state), and hence makes vibrational predissociation rapid, an 18 ps lifetime being obtained from bandwidth measurements. The influence of rotations upon the vibrational predissociation rate of the HeI, complex has been explored theoretically.' 5 6 30% Conversion of 193 nm photons to 342 nm laser output in molecular iodine has been found in irradiated I,-SF, mixtures. " Relatively high pressures of buffer gas, to induce collisional energy transfer from the initially populated D state to the lasing 3112e levels, is the key to achieving high efficiencies.'s7 Recombination of I atoms formed by photolysis at 694.3 nm at relatively high pressures (up to l00atm.) of various buffer gases has been used to test models of the cage effect, and to determine second-order rate constants for atomic recombination. 5 8 Photofragment spectroscopy of the products of multiple-photon ionization has

'

'

'

'41 149

Is' Is'

153

is4

Is'

Is6 Is'

Is'

G . W. Loge and J. R. Wiesenfeld, Client. Pliys. Left., 1981, 78. 32.

T. G . Finn, R. S. F. Chang. L. J . Palumbo. and L. F. Champagne, Appl. Phys. L e f t . , 1980,36, 789. F. K . Tittel, M . Smayling. W. L. Wilson, and G. Marowsky. Appl. Pliys. Lerf.. 1980, 37, 862. H . C. Brashears, D. W. Setser, and Y. C. Yu, J . Climt. P/I.I~.Y.. 1981. 74. 10. M. Sulkes, J. Tusa. and S. A. Rice, J . Chm7. Phys., 1980, 72, 5733. K. E. Johnson, W. Sharfin. and D. H . Levy, J . CIi~ni.PIiys., 1981, 74. 163. K. E. Johnson and D. H . Levy, J . CIwrn. Pliys., 1981. 74. 1506. J . E. Kenny, T. D. Russell, and D. H . Levy, J . Clwm. Pliys.. 1980, 73, 3607. J. E. Beswick and G . Delgardo-Barrio, J . C h m . Phys., 1980. 73, 3653. M . J. Shaw, C. B. Edwards, F. O'Neill, C. Fotakis, and R . J. Donovan, Appl. Phys. Lett., 1980.37. 346. J. M . Zellweger and H . van den Bergh. J . Cliem. Pltys., 1980.72, 5405.

135

Gus-phuse Plwropr.oc*esses

been achieved, with positive and negative ions and neutral products observed in the high-intensity irradiation of I, in a molecular beam. l s 9 Extensive studies of the kinetic behaviour of the B3lIo,,+states of Br, and C1, have been reported.16'- 1 6 5 For Br,, rates of electronic quenching and internal energy transfer within the B state have been measured for several collision partners, 6o with the role of collision-induced predissociation responsible for removat of Br,* molecules discussed in detail.'60 The absence of fluctuations in the experimentally observed fluorescence lifetimes of predissociating states as a function of vibrational quantum number can be explained if the repulsive parts of the potential curves of the bound and predissociating states are approximately parallel, and an analytical interpretation of the predissociation behaviour under this assumption has been presented.16' Radiative lifetimes of the B states of Br, and C1, are 12.4 162 and 305 164* 165 ps, respectively, and the dependence of predissociation rates upon rotational quantum number in these states has been explored and shown to be consistent with a heterogenous predissociation mechanism involving the B state and one or more 'n(1u)states.'63*1 6 5 Discharge pumping of mixtures of NF,, CF,l, and rare gases gives rise to laser action between 480--490nm on the E -+ A(311) transition in IF.'66 Franck-Condon pumping of the B state of IF (formed in the I, + F, reaction) with a broad-band laser source at 500 nm results in red-shifted stimulated emission between 650-720 nm.' 67 Photofragment spectroscopy of ICl and IBr ,has provided Landau-Zener parameters for avoided crossings within the excited states of these molecules, and, in ICl, resolution of transitions originating from different vibrational levels of the electronic ground state has provided some information on the repulsive part of the 311potential curve.168Radiative lifetimes have been measured 169 and a and collisional relaxation rates of BrF(B 3110+) detailed report on the dependence of the isotopically selective addition of ICl(A311) to acetylene on buffer gas pressure and excitation wavelength has appeared. 70 Relaxation of the ,P, states of I and Br 1 7 2 in collisions with H, has been studied by optoacoustic spectroscopy 7 1 and by i.r. emission techniques,' 7 2 respectively. The optoacoustic method allows determination of whether translational energy is absorbed or released in the collision process, and with H, it is found that absorption occurs, i.e. there is net translational cooling. The formation

'

-

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159

'6l 16' 16'

164 165

'" '61

17' 17'

'

M. S. de Vries, N. J. A. van Veen, T. Baller. and A. E. de Vries, Client. PIiys., 1981. 56. 157. M . A. A. Clyne, M. C. Heaven, and S. J. Davis, J . Clieni. Soc., Furadciy Trans. 2, 1980, 76, 961. M. S. Child, J . PIiys. B . . 1980. 13, 2557. M. A. A. Clyne. M. C. Heaven, and E. Martinez. J . Clieni. Soc., Furaday Truns. 2, 1980, 76, 405. R. Luypaert. G . de Vlieger, and J. van Craen, J . Clieni. f l i p . , 1980, 72, 6283. M. A. A. Clyne and E. Martinez, J . Cliem. Soc., Fnrnduy Trcins. 2, 1980,76, 1275. M. A. A. Clyne and E. Martinez, J . Clieni. SOC..Faraduy Trans. 2, 1980,76, 1561. R. J. de Young, Appl. Pliys. Lett., 1980,37,690; M . L. Dlabal. S. B. Hutchinson, J. G. Eden, and J. T. Verdeyen, ibid.. p. 873. S. J. Davis and L. Hanko, Appl. P1ty.v. LRtt., 1980. 37, 692. M. S. de Vries. N. J. A. van Veen. M . Hutchinson, and A. E. de Vries. Client. Pltjs., 1980. 51, 159. M. A. A. Clyne and J. P. Liddy. J . Climi. Soc.. Furaduy Truns. 2, 1980, 76, 1569. M . Stuke and E. E. Marinero. Bcr. Birrisenges. Pliys. Clieni., 1980, 84. 657. T. F. Hunter and K. S. Kristjansson, Cliem. PIiys. L ~ t t . 1980, , 75. 456. D. J. Nesbitt and S. R. Leone, J . Climi. P1ij.s.. 1980. 73, 6182.

136

Photochemistry

of H,(v = 2) by the slightly endothermic process (12) is thought to be responsible. ' 7 1 An efficient near resonant E- Venergy transfer also takes place in the

0) ---+ I(,P3/,) + H,(u = 2), A E = 119cm-' (12) Br('P+)-H, system, and measurements of the rates of quenching of Br(,P+) with H, need to take the formation of the equilibrium process (13) into a ~ c 0 u n t . l ~ ~ I('P,)

+ H,(v

=

+

Br(2P,) + H2(u = 0) Br(,P,/,) H,(u = 1) (13) When this is done, a rate constant for the forward process of 6.3 x 10- cm3 molecule- s- is obtained, and discrepancies in the previously reported values are probably due to neglect of the reverse processes taking place.172 For the corresponding ,P, state in atomic fluorine, diode laser measurements of the absorption cross-section of the ,P, t 'P3/, transition at 404 cm - ' yields a radiative lifetime of 660 s for the upper spin-orbit state.' 7 3

'

7 Atom Reactions Associative ionization of Na atoms [equation (14)] takes place in the presence of laser radiation tuned to either member of the sodium D line doublet Na(3s)

+ Na(3s) + 2hv1 Na(3p) + Na(3p)

-

Na(3p)

----+

Na'

Na,'

+ Na(3p) +e

]

(14)

(*P+,3/2 +- 'S,).' 74 However, at moderately high laser powers, when the 3p t 3s transition is saturated, a further photon is seen to be absorbed from the field. A true laser-induced ionization process (15) forming N a + is thought to be 2Na(3s)

+ 2hv1 + hv,

+ Na + e

(1 5 )

responsible for this, with resonant photon absorption hv, by both colliding partners followed by absorption of another photon hv, during the course of the collision. Enhancement of N a + formation was also observed when v2 was tuned off resonance with the 3p t 3s transition. 74 The ion-exchange process (1 6 ) has

H+

+ Na

--+

H(n = 2)

+ Na+

(16)

also been found to be enhanced when Na is in the 3p state, and this has been studied as a function of relative kinetic energy of the colliding pair.175Measurements of E-V exchange between Na(3p) and CO show the final distribution of vibrational levels in CO is near Poisson, peaking at u = 2, and is insensitive to effects of temperature. 76 The results are consistent with a curve-crossing mechanism, involving the formation of a N a +CO- ionic complex. Flames of H,-0,-N, containing Na can lead to chemical reaction between excited Na states (2P+,3,2)and H,O or H2.177 Measurements of Na atom concentrations via laserinduced fluorescence of the 3p-3s transition can thus be affected by substantial chemical removal of the 3p atom population, and this needs to be taken into

'

173 174

17' 17' '77

A. C. Stanton and C. E. Kolb, J . Cliem. P1i.w.. 1980, 72, 6637. J. Weiner and P. Polak-Dingels, J . Cliem. Pliys.. 1981, 74, 508. V. S. Kushawaha, C. E. Burkhardt, and J. J. Leventhal, Phys. Rev. Lett., 1980, 45, 686. D. S. Y. Hsu and M . C. Lin, J . Cliem. Phys., 1980, 73, 2188. C . H . Muller, 111, K. Schofield, and M . Steinberg, J . Cliem. Pliys., 1980, 72, 6620.

Gas-phase Photoprocesses

137

account, particularly when saturated absorption of laser radiation is used as a quantitative probe of atom concentrations.' 7 7 Studies on the higher members of the alkali family include measurements of rates of quenching of the spin-orbit states of several atomic levels of Rb 7 8 - ' and Cs, 'O with, in the case of 5,P +, 3,2 Rb, the temperature dependence of the cross-section in collisions with CH, and its deuteriated derivatives indicating that quenching takes place via an E-R energytransfer process. 7 8 Quenching of Mg(3s3p3PJ)by H, is found to increase sharply with temperature Inefficient E to V, R energy transfer is thought to take in the range 612-841 K. place in competition with chemical reaction to form MgH, with the activation energy for the latter process being equal to the reaction endothermicity. Theoretical studies of this process indicate that side attack of Mg* on the H-H bond is favoured. 8 2 Electronic energy redistribution in collisions between two excited Mg atoms ( 3 P J )has been studied, with consideration given to its effect upon limiting the energy-storage capabilities of possible Group I1 excimer lasers at relatively high excited-atom densities.183 Electronic energy partitioning in chemical reactions of Mg* and Ca* ( 3 P )with F, and C1, has been measured (with the results not in accord with those expected on adiabatic correlation arguments),' 84 and rates of quenching of the Ca* ( 3 P ) state by Ca, Mg, and inert gases have been determined by a phase-shift method. 8 5 The near resonant spin-forbidden energy-transfer process (17) is found to be efficient, with the 3 P , state

'

'

'

'"

'

'

Ca(4s5p'P1)

+ Ar

---+

Ca(4s5p3P,,,,,)

+ Ar

preferentially populated with a state-specific rate constant of 5.2 x 10- l 1 cm3 molecule-' s - '.lg6 Rates for similar processes involving4s4p 'P and P states of Ca and Sr have also been measured. l g 7 Chemiluminescence in the reactions of metastable ('D) Ca with 0, 18' and of Ca and Sr with HCl has and Sr 192 been observed, ground-state reactions of Mg with FOz 190 and Ba with hydrogen halides have been reported, and the Hanle effect has been used to measure the lifetime of the 5d6p 3D, state of Ba (10.2 ns). 193 Spin-forbidden quenching of Cd (5S5p1P1) to the metastable 'Po, l , z levels occurs with high efficiency for many collision partners, despite the existence of several energetically available chemical or additional energy-transfer processes. 194

'''

184

190

19* 193 194

R. A. Phaneuf and L. Krduse, Can. J . Phys.. 1980, S8, 1047. M. Glodz, J. B. Atkinson, and L. Krause, Can. J. Chem., 1981, 59, 548. P. Munster and J. Marek, J . Phys. El., 1981, 14, 1009. W. H. Breckenridge and W. L. Nikolai, J . Chem. Phys., 1980, 73, 2763. N. Adams, W. H . Breckenridge, and J. Simons, Chem. Phys.. 1981,56, 327. W. H. Breckenridge, W. L. Nikolai, and J . Stewart, J . Chem. Phys.. 1981, 74, 2073. A. Kowalski and M. Menzinger. Chem. Phys. Lett., 1981, 78, 461. R. J. Malins and D. J. Benard, Chem. Phys. Lett., 1980, 74, 321. W. H. Pence and S. R. Leone, J . Chem. Pliys.. 1981,74, 5707. J. J. Wright and L. C. Balling, J . Chem. Phys., 1980, 73, 1617. J. A. Irvin and P. J. Dagdigian, J . Chem. Phys., 1980, 73, 176. U. Brinkmann, V. H. Schmidt, and H. Telle, Chem. Phys. Lett., 1980, 73, 530. R. D. Coombe and R. K. Home, J . Pliys. Chern., 1980,84, 2085. A. Gupta, D. S. Perry, and R. N. Zare, J . Chem. Phys.. 1980,72,6237; A. Siege1 and A. Schultz, ibid., p. 6227. A. Gupta. D. S. Perry, and R. N. Zare, J. Chem. Phys., 1980, 72, 6250. G. Brink, A. Glassman, and R. Gupta, Opt. Commun., 1980,33, 17. W. H. Breckenridge and 0. K. Malmin, J . Chem. Phys., 1981,74, 3307.

138

Photochemistry Chemical reaction does take place with H2,1g5 producing CdH ( v = 0) in rotational states well represented by a Boltzmann distribution at a temperature of 5200 K. Rate constants for quenching of Cd(3P0,,)lg6 and lifetime measurements of several excited Cd states have been reported. Spin conservation is not seen to be a major constraint in the quenching of Zn (43P1) by ground-state Ca, with states with approximateelectronic energy exchange creating Ca (4lP,) and (53s1) ly equal probability. 198 Quenching rates of Hg(3P,) with several simple gases have been measured from deconvolution of the P, fluorescence decay curves, lg9 and a conventional photochemical separation scheme of Hg isotopes, in which iHg(3P,), excited in an isotopically selective fashion by 253.7 nm radiation from a iHg lamp, reacts with hydrogen halides, has been revitalized, with the authors pointing out a timely reminder to all those who carry out laser isotope separations that experiments of a similar nature were being successfully carried out almost fifty years ago.200 Fluorescence from electronically excited fragments formed in collisions of rotor accelerated beams of metastable rare-gas atoms with Br, and BrCN has been measured and used to probe the mechanisms of the processes involved. Polarization of fluorescence from KBr (B) and Br,*, produced in the Kr(3P,,o) + Br, system shows that rotational alignment perpendicular to the relative velocity vectors of the colliding partners is retained in both inelastic and reactive scattering processes.2o' No such polarization is observed in the fluorescence of CN(B2Z+) formed in reaction (18), and this can be explained by a two-stage harpooning Xe(3P2,0)+ BrCN

Xe('So)

+ CN(B2C+) + Br

(18)

mechanism, in which an excited (Xe+CN-)* intermediate is formed.,', More conventional studies have measured vibrational and rotational distributions in electronically excited CN formed in the reaction of BrCN with metastable Ar (3P0,,).,03 Calculations of the potential curves of ArH have been carried out, with estimates made of curve-crossing parameters for the states involved in the rapid quenching process of metastable Ar( P) with H atoms.204 Penning ionization predominates in the quenching of Ne and Ar (3P0,2)by Hg, whereas for Kr(3P,), excitation transfer to metastable Hg(3P,) is the major step. All processes take place with very large c r o s s - s e ~ t i o n s .Penning ~~~ ionization is also observed in collisions between metastable He(23s) and Ne(3Po,,) with CS 206 and CS2.207 Reactions of Xe(3P,) with various Br- and I-containing species, leading to 195

196

'91

19' 199

'O0 '01

'O' '03 *04 '05 '06 '07

W. H. Breckenridge and D. Oba, Chem. Phys. f u t t . , 1980,72,455. H.Umemoto, T. Kyogoku, S. Tsunashima, and S. Sato, Chem. Phys., 1980,52, 481. B. Cheron, J. Jarosz, and P. Vervisch, J . Phys. B., 1980, 13, 2413; M. Chantepie, J. L. Cojan, J. Landais, and B. Laniepce, J . Phys. Lett., 1980,41, L433; H. Kerkhoff, M.Schmidt, U. Teppner, and P. Zimmermann. J . P h p . B.. 1980, 13, 3969. R. D.Coombe, F. J. Wodarczyk, and R. K. Home, J. Chem. Phys.. 1981, 74, 1044. T. Hikida, M. Santoku, and Y. Mori, Rev. Sri. Instrum., 1980,51, 1063. C. R. Webster and R. N. Zare, J . Phys. Chem., 1981, 85, 1302. R. J. Hennessy and J. P. Simons, Chem. Phys. Lett., 1980. 75. 43. R.J . Hennessy, Y. Ono, and J. P. Simons, Chem. Pliys. Lett., 1980,75,47. A. J. Yencha, Y. Ozaki, T. Kondow. and K. Kuchitsu, Chem. Phys., 1980,51, 343. R. L. Vance and G . A. Gallup, J . Chem. Phys., 1980,73. 894. D.J. Wren and D. W. Setser, J. Chem. Ph.vs., 1981, 74,2331. H. Obase, M. Tsuji, and Y. Nishimura, Chem. Phys., 1981,57, 89. A. J. Yencha and T. Wu, Chem. Ph.vs., 1980,49, 127.

Gas-phase Photoprocesses 139 emission from Band C state XeBr and XeI, have been studied, with rate constants, electronic branching ratios, and vibrational energy distributions reported;208 kinetic parameters for quenching of several excited Kr states have been measured,209 and collisions between Ar(4s3P,,,) and Fe(CO), have been shown to lead to emission from electronically excited Fe atoms.210 Chemiluminescence from CaX species (X = halogen) arises from the reaction of copper with X, molecules. For Cu + F,, ground-state copper atoms (,S)react to produce A, B, and C states of CuF, with an inversion of population of the C state relative to the B state observed,211whereas metastable Cu atoms ('0)are responsible for chemiluminescent reactions with the other halogem2l 2 Emission is seen in reactions of the ground-state Group IIIa atoms from GaF and InF (311) with F2,,13 with population inversions formed in the vibrational levels of these excited states; the products of ground-state reactions of Y,'14 SC,''~,2 1 5 and Yb216 atoms with various molecular species have been studied by and laser-induced fluorescence 2 1 4 * * techniques. chemiluminescence 14. Laser excitation of atomic levels in S ~ I , ~ Zr,"' '' Dy,219and U 2 2 0 has been carried out, with lifetime measurements,2 quenching rates,217and chargeexchange reactions 2 1 of the excited species reported.

'

"9

8 Infrared Photochemistry The majority of past publications on infrared photochemistry have made use of observations upon the yields of products of multiple-photon dissociation (MPD) to infer details of the multiple-photon absorption (MPA) processes taking place. The appeal of such experiments is that they are relatively straightforward, at least by end-product analysis techniques, although sophistication in the methods inevitably (and very successfully) has crept in: molecular-beam photofragment spectroscopy and laser-induced fluorescence detection of photofragments are examples of this. In many aspects, MPA experiments are harder, as interesting effects tend to take place at low average numbers of i.r. photons absorbed per molecule, and these are difficult to measure by standard calorimetric techniques. However, significant progress is now being made, with optoacoustic methods of detection of energy deposition, and, particularly, with spectroscopic 'pump and probe' techniques to monitor the time-resolved behaviour of specific sets of internal energy levels of molecules excited by MPA. Sulphur hexafluoride still commands considerable attention. Single-photon excitation of v 3 = 1 has been studied in high-resolution diode-infrared laser '09

*Io 'I' '13

'I4 '15

'" 'I9 O''

K. Tdmagake, D . W. Setser, and J . H. Kolts, J . Ciiem. Piiys., 1981, 74, 4286. R. S. F. Chang, H. Horiguchi, and D. W. Setser, J . Ciiem. Piiys., 1980, 73, 778. J. Kobovitch and J. Krenos, J . Ciipm. Piips., 1981. 74, 2662. R. W. Schwenz and J. M. Parson, J . Ciiem. Piiys., 1980, 73, 259. R. W. Schwenz and J . M. Parson, Cliem. Pliys. Lett., 1980, 71, 525. R. W. Schwenz, L. C. Geiger, and J. M. Parson, J . Chem. Ph.vs.. 1981.74, 1736. H. C. Brayman, D. R. Fischell, and T. A. Cool, J . Chem. Phys., 1980,73, 4247, 4260. J. L. Gole and S. A. Pace, J . Chem. Piiys., 1980, 73, 836. R. Dirscherl and H. U. Lee, J . Chem. Phys., 1980. 73, 3831. J. A. Gelbwachs, R. S. Nesbitt, and R. P. Frueholz, Chem. Pliys. Lett., 1981, 77. 222. P. Hannaford and R. M. Lowe, J . Phys. B, 1980, 14, L5. B. Burghardt, R. Harzer, G. Meisel, and S. Penselin, Opt. Cummun.. 1980. 33, 169. P. Benetti, M . Broglia, and P. Zampetti, Opt. Commun.. 1981, 36,218.

140

Pho t oc&m ist rj’ double-resonance experiments, with the observed line shapes able to be reproduced theoretically.221N o evidence of intramolecular coupling at this low level of excitation is seen. At higher intensities, double-resonance experiments using very short (30ps) i.r. pulses show evidence of deep and narrow spectral hole burning at the pump wavelength at energies corresponding to 4-5 photons absorbed per molecule, in contrast to previous ns time scale experiments, for which a broad bleaching had been found to occur to high and low wavelengths of the pump line.222The existence of this saturation effect seems to point to a bottleneck in the absorption process due to discrete vibrational states at these levels of excitation: raising the pump fluence decreases the hole burning, as molecules are pumped into the quasicontinuum where saturation effects became insignificant. Furthermore, an extraordinarily fast collisional process repopulating the absorbing level was observed taking place with a rate constant of 1.5 x 10-8cm3m01ecule-1s-1. This emphasises the need for use of very low pressures and short pulse lengths in order to probe truly collision-free absorption processes in SF,, and accounts for the behaviour previously observed at similar pressures with only ns time Quantitative optoacoustic spectroscopy measurements of MPA processes are generally limited to pressures 2 0. I Torr, and thus for collision-free conditions to apply during the pumping process, the pulse length needs to be SlOOns for collisions with gas kinetic cross-sections, and considerably shorter than this if processes as rapid as those described above for SF, apply. At lower pressures, 10-3-10Torr, MPA in SF, has been measured by using a pyroelectric detector offset from the path of a CO, laser beam in a static sample of gas, and acting as a bolometer for the detection of vibrationally excited molecules impinging upon its 2 2 4 MPA cross-sections can be quantitatively estimated by this novel surface.223* technique: it is found that at low pressures ( < 10-2Torr) and low fluences ( < 10- J cmP2,where little MPD takes place), laser intensity (W cm-2) plays the essential role in the absorption process, whereas in the presence of collisions at higher pressures the fluence is the dominant parameter.224Pressure and fluence effects upon the MPA of C O , laser radiation in CF312 2 5 and of H F laser radiation by molecules containing OH groups 226 have been measured in a higher pressure regime by optoacoustic spectroscopy. Double-resonance experiments involving i.r. pumping followed by visible or U.V.laser probing of the vibrationally excited species have been reported by several groups. Laser-induced fluorescence of thiophosgene following MPA of CO, radiation at intensities > 3 MWcm-2 has shown that the vibrational populations of u = 0 4 , 6 , and 8 of the v4 mode are depleted or not populated under collisionfree conditions when the initially pumped mode is 2v4, and only at lower laser intensities are population increases in these levels observed.227It appears that all

”’ 222

223 224

*”

2’6

227

C. Reiser. J. I . Steinfeld. and H . W. Galbraith, J . C I i ~ n iPhys., . 1981, 74, 2189. R. C. Sharp, E. Yablonovitch, and N . Bloembergen, J . Cliem. Pliys., 1981, 74, 5357. R. V. Ambartzumian, L. M . Dorozhkin, G. N. Maliarov, A . A. Puretzky, and B. A. Chayanov, Appl. Phys., 1980, 22, 409. R . V. Ambartzumian, G . N. Makarov. and A . A . Puretzky, Opt. Contntun.. 1980. 34. 81. J. M . Weulersse and R. Genier, Appl. PliJs., 1981, 24, 363. R. D. McAlpine, D. K . Evans, and F. K. McClusky, J . Chm. Phys., 1980, 73, 1153. D. M. Brenner, J . Clic~ni.fliys.. 1981, 74, 2293.

Gus-phase Pltotoprowsses 141 rotational levels are able to interact with the laser field at the intensities used and no bottlenecking of vibrational populations occurs in this molecule, in contrast to the behaviour of propynal 2 2 8 studied under similar conditions. Clearly the extent of pumping of the low levels of these small molecules will depend crucially upon their spectroscopic features, as well as on the laser intensities employed. Depletion of fluorescence from the A ' A , state of thiophosgene has been seen following excitation of state selected vibronic levels by MPA to predissociating levels 2 2 9 (a similar experiment to that reported earlier for biacetyl and propynal 49). No obvious dependence of the fluorescence depletion upon the total vibrational energy of the initially produced ' A , state was observed: it is suggested that this method could be employed for quantitative measurements of absorption crosssections of vibrationally excited molecules in electronically excited states.229 Cross-sections for absorption of 193nm radiation in SF, are found to be considerably enhanced following i.r. MPA;230time-resolved observations of hotband absorption following MPA in C6F, 2 3 1 and CF31232 have been used to measure rates of collisional redistribution of vibrational energy. MPA of two different laser wavelengths in CCI, appears to have markedly different effects near the dissociation threshold.233 CO, laser excitation at 980cm-' interacts initially with the v 1 + v 2 + v4 combination mode, and at the threshold for dissociation ( 120J cm - ,), approximately 28 photons are measured to be absorbed per molecule. Radiation from an ammonia laser at 794cm- is initially absorbed by the v 3 fundamental in CCI,. The threshold for dissociation is considerably lower, 1.2 Jcm-2, and at this point 60 photons are absorbed, i.e. far more energy is required at this wavelength to dissociate the molecule. The authors appear to put the view that as the combination mode contains the C - C I stretch, v l , this contributes more efficiently to dissociation than does the pure v 3 2 3 3 . Bond selectivity arguments of this kind have been advanced before, but it has been shown that alternative plausible explanations can just as easily explain the experimental observations:234 developments in this case are eagerly awaited. Irradiation of C2H,CI at non-CO, laser wavelengths, in this case around 3.3 pm, shows resonances in the MPD yield at wavelengths corresponding to peaks in the fundamental and overtone absorption At this relatively high photon energy, it is shown that for many rotational states the quasicontinuum is reached after absorption of only two photons: absorbed energy increases almost linearly with fluence with no bottlenecking, in contrast to the behaviour observed at 10 pm, and a simple rate equation treatment of absorption in the quasicontinuum is shown 22a

229

230 23' 232 233

234

235

D. M. Brenner, K. Brezinsky. and P. M. Curtis, Ciiem. P i i n . Leii.. 1980. 72. 202. D. M. Brenner. J . Pliys. Cliem.. 1980, 84. 3341. J. J. Tiee, F . B. Wampler, and W. W. Rice, Clirwi. Pli,w. Lcti.. 1980. 76. 230. S. Speiser and E. Grunwald, Client. PIiw. Lei(.. 1980. 73. 438. Y. A. Kudriavtsev and V. S. Letokhov, Clieni. Pliys., 1980. 50, 353. B. I. Vasilev. N. A. Vishnyakov. V. T. Galochkin, A. Z. Grasyuk. A. P. Dyadkin, A. K. Zhugalkin. V. A. Kovalevskii, V. N. Kosinov, A. N. Oraevskii, A. N. Sukhanov, and N. F. Starodubtsev, Sov. Pliys. JETP Letr.. 1980. 30. 25. M. N. R. Ashfold and G . Hancock. "Infrared Multiple Photon Excitation and Dissociation; Reaction Kinetics and Radical Formation", in 'Gas Kinetics and Energy Transfer', ed. P. G . Ashmore and R. J. Donovan (Specialist Periodical Reports). The Royal Society of Chemistry, London, 1981, Vol. 4, p. 73. H.L. Dai, A. H.Kung, and C. B. Moore, J . Client. Plijs.. 1980, 73, 6124.

142

Photochemistry

to be valid also for the discrete levels in this molecule.235 Narrow peaks in the MPA spectrum of ethylene (taken with a high-pressure continuously tunable CO, laser) have been observed within the relatively low intensity range 40-600 kW ern-,, and ascribed to stepwise multiple-photon absorption resonances. 36 Laser-induced fluorescence detection of radical fragments formed by i.r. M P D is now an established technique, and its ability in determining quantum states of such species has been exploited in measurements of their internal energy distribution^.,^^ The CN fragment, formed in the M P D of C,H,CN has been studied in some detail, with particular emphasis upon the effect of the intensity of the CO, laser pulse upon the rotational energy distribution in the X2C’ (u” = 0) ground When molecules are excited during the laser pulse to levels above the dissociation limit, unimolecular decomposition can compete with further photon absorption, and, as the rate of the latter process depends upon the laser intensity, higher intensity pulses will access a higher range of internal states in the dissociating species, and hence provide more energy for distribution in the internal states of the fragments. Figure 3 illustrates experimental evidence for this.237Time-resolved measurements of the C N (X2C’,u” = 0) rotational state distribution show that fragments produced during the high-intensity peak of a CO, laser pulse are hotter than those formed late in time by the low-intensity tail despite the fact that for the latter species dissociation arises from absorption at a considerably higher laser fluence.2 3 7 Similar conclusions have been reached in experiments using single and multimode pulses of the same fluence: CN fragments have more internal energy for the higher intensity multimode p ~ l s e s39. ~All distributions are well represented by Boltzmann temperatures, as can be seen from the data in Figure 3. Intensity effects have also been reported for the partitioning of energy in the (O,O,O) and (0,1,0) vibrational levels of ‘CH, produced in the MPD of acetic anhydride and acetic acid, with again Boltzmann distributions observed by laser-induced fluorescence in the rotational states of the radical fragments.240 When two or more competing dissociation pathways occur for molecules excited by MPA, as the relative rates of dissociation from the two transition states will, in general, change with increasing energy, laser intensity will in a similar way affect the relative product yields. Such an effect has been seen for the competing pathways eliminating H F and HCl in the M P D of CH,=CClF.241 However in the MPD of C,F,H, competition between channels eliminating H F and breaking the C-C bond is found to be invariant with laser fluence (and hence intensity) and this has been interpreted in terms of a simple ‘threshold fluence’ model appropriate for the focused beam geometries employed.242Competing channels in the M P D of cyclobutanone have been characterized,243* 244 and an attempt made to explain 236 237

239 240 24’

242 243 244

1. N . Knyazev, N. P. Kuzmina, V. S. Letokhov, V. V. Lobko, and A. A. Sakisyan, Appl. Opt.#1980, 22, 429. M . N. R. Ashfold, G . Hancock, and M . L. Hardaker, J . Phofochcm., 1980, 14, 85. C. M. Miller and R. N. Zare, Chem. Phys. L c f f . , 1980. 71, 376. A. M. Renlund, H . Reisler, and C. Wittig, Cliem. Phys. LRff., 1981, 78, 40. A. J. Grimley and J. C. Stephenson, J . CIiem. Pliys., 1981, 74, 447. W. A. Jalenak and N . S. Nogar, J . PIiys. Clicm.. 1980, 84, 2993. P. A. Hackett, C. Willis, M . Drouin, and E. Weinberg, J . Phys. Chem., 1980, 84, 1873. S. Koda, Y. Ohnuma, T. Ohkawii, and S. Tsuchinya, Bull. Cliem. SOC.Jpn., 1980, 53, 3447. V. Starov, N. Selamoglu, and C. Steel, J . Phys. Cliem.. 1981, 85, 320.

+

c c

6

0

L

250

N"(N"t 1)

500

750

I

1000

Figure 3 Rotational distributions of CN(X'C+, v" = 0)produced in the i.r. MPD of lOmTorr C,H,CN. On the left are$uorescence excitation spectra taken at times of 160 ns (upper trace) and 3 ps (lower trace)from the peak of the C 0 2laser pulse. The pulse shape, with these times indicated by arrows, is illustrated to the upper right of the Figure. The plots of ln{Z/(N" + 1)) against N"(N" + 1) to the upper right of each excitation spectrum represent the populations of the (X'C', v" = 0) state rotational levelsplotted in such a way that a straight line would indicate a Boltzmann distribution. As can be seen from the Figure, the rotational distributions can be well represented by Boltzmann temperatures, but with very different values, 970 K and 435 K for the 160 ns and 3 ps observations, respectively. TheJEuenceswere 18 J cm-2 at 16011s and 55 J cm-' at 3 ps

C

5-

.+

2

1

-2

+

Photochemistry the discordant results presently in the literature for the variation of relative product yields with precursor pressure. 244 The effects of magnetic 2 4 s and electric 246 fields have been found to increase the M P D yields of CF2HCI.The effects are most pronounced at low values of the laser fluence (and hence for the pulses of constant temporal shapes used, of the laser intensity) and is illustrated for the electric field in Figure 4.246Breakdown of the

144

R

Fluence (Jcm-* 1 Figure 4 The ratio R of the fraction of CF,HCl dissociated by i.r. MPD per laser pulse in the irradiated volume with and without the electric jield, as a function of the laser ,fluenee (J cm- 2). The electricfield strength was 4.2 kV cm- and the CF,HCI pressure 300 mTorr

’,

angular momentum selection rules caused by the field is believed to cause the effective density of states to increase at low values of the total absorbed i.r. energy, and this removes the effect of a low-energy bottleneck limiting the absorption efficiency.246At higher fluences this bottleneck is eliminated by the increased laser intensity,246 and hence an increase in the field has a smaller (and eventually negligible) effect on the MPD yield. MPD of n-butyl vinyl ether at 9.6 and 10.6pm produce different sets of dissociation products; for example, acetylene is found at 9.6pm, yet not at the longer ~ a v e l e n g t h . ~The ~ ’ authors point out however that this does not necessarily justify the assumption of a bond- or mode-selective dissociation process, since acetylene may be formed by wavelength-dependent dissociation of a product of the MPD of the parent molecule.247 245 246 25’

R. Duperrex and H . van den Bergh, J . CIiem. Phj-s., 1980,73, 585. P. Gozel and H. van den Bergh, J . Chem. Phys., 1981, 74, 1724. H . Hofmann, W. Klopffer. G . Schafer, and J . Gloor, Ckem. P/iys., 1981, 56. 337.

Gas-phase Photoprocesses

145

1.r. emission has been seen from the vibrationally excited CO, product of MPD of vinylacetic and pyruvic from hydrogen halides formed by chemical reaction of Cl, with H atoms produced in the MPD of various hydrocarbon^,^^' and of HBr with F and C1 atoms formed in the MPD of CF,C1.250 Infrared fluorescence from C,F,Cl following MPA shows emission from both discrete levels and the quasicontinuum, with efficient intramolecular vibrational redistribution out of the pumped mode evident after absorption of only 2-3 photons.251Emission in the i.r. has been seen following MPA in N,F,,252 and has been used to study the interconversion of perfluorocyclobutene to perfluorobutadiene isomers following MPA.25 Further isomerization reactions induced by CO, lasers have been reported.254 Comprehensive studies have been carried out on the MPD of hexafluoroacetone as a function of laser fluence, frequency and substrate pressure,255 and the influence of collisional effects on the formation of CF, in the MPD of CF2CFC12 5 6 and CF,HCl 2 5 7 has been experimentally measured and theoretically modelled. Fluence dependences of the H F laser-induced decomposition of 2,2,2trifluor~ethanol,’~~ and the 9.4pm CO, laser MPD of C,F,Cl 2 5 9 have been reported, and triethylphosphite joins the increasing list of molecules dissociated by CO, laser radiation.260 Several instances of visible emission accompanying collisionless MPA have now been described in the literature, and recently some of the examples have now been studied in detail. In OsO, the emitting species is believed to be the parent molecule in an (unidentified) electronically excited state 2 6 1 formed by intramolecular vibrational to electronic energy transfer (‘inverse electronic relaxation’, IER). Identification of the emitter in these cases is no easy task: however a method has been recently described 262 that allows distinction to be made unambiguously between emission from parent molecules and from fragments formed by MPD, and this has been applied to the luminescence accompanying MPA in CrO,Cl,. A molecular beam of the parent molecule is crossed with a pulsed CO, laser beam, and the angular dependence of the emitting species with respect to the original beam direction is detected in a time-resolved fashion. If the emission is solely from excited parent molecules then the angular distribution should lie along the original

248

249 251

252

253 254

255

256

J. L. Buechele, E. Weitz, and F. D. Lewis, Chem. Phys. Lett.. 1981, 77, 280. C. R. Quick, A . B. Horwitz, R. E. Weston, and G. W. Flynn, Chem. Ph-ys. Lett., 1980, 72, 352. A. B. Horwitz, J. M. Preses. R. E. Weston, and G. W. Flynn, J . Chem. Phys., 1981, 74, 5008. J. W. Hudgens and J. D. McDonald, J . Chem. Phys., 1981, 74, 1510. C. Kleinermanns and H. Gg. Wagner, Z . Phys. Chem., 1980, 119, 159. I. Glatt and A. Yogev. Chem. Phys. L e r r . , 1981, 77, 228. A. Ben-Shad and Y. Haas, J . Chem. Phys.. 1980, 73, 5107; D. Garcia and E. Grunwald, J . Am. Chem. Soc., 1980, 102, 6407. P. A. Hackett, M. Gauthier, W. S. Nip, and C. Willis, J . Phys. Chem., 1081, 85, 1147; P. A. Hackett, V. Malatesta, W, S. Nip. C. Willis, and P. B. Corkum, J. Phys. Chem., 1981, 75, 1152. J. Stone, E. Thiele, M. F. Goodman, J. C. Stephenson, and D . S . King, J . Chem. Phys., 1980, 73, 2259.

257 258 259

260 261 262

A. C. Baldwin and H. van den Bergh, J . Chem. Phys., 1981, 74, 1012. D. Anderson, R. D. McAlpine, D . K. Evans, and H. M. Adams, Chem. Phys. Let[., 1981,79, 337. K. Nagai and M. Katayama, Jpn. J. Appl. Phys., 1980, 19, 1235. C. N . Merrow and N . S. Nogar, Chem. Ph-vs. Lett., 1981, 79, 69. A. A. Makarov, G. N. Makarov, A. A. Puretzky, and V. V. Tyakht, Appl. Phys., 1980 23, 391. T. A. Watson, M. Mangir, C. Wittig, and M. R. Levy, J . Phys. Chem., 1981, 85, 154.

146

Photochemistry

molecular beam axis. In fact in CrO,Cl, considerable off-axis emission occurs, which can only be attributed to luminescencefrom fragments presumably formed in their ground electronic state that subsequently absorb CO, laser radiation and then undergo IER: parent electronic excitation is a minor channel.262 More conventional bulb studies of the emission accompanying MPA of CrO2C1,, while demonstrating the collisionless nature of the IER process, were unable to determine the identity of the emitting species.263 Differences and similarities in the behaviour of reactions induced thermally and by CO, laser radiation at relatively high pressures have been described in several cases. Decomposition of CH,CF,Cl with a CW laser source takes place with a rate constant equal to the thermal value at 200 Torr, but vibrational and translational degrees of freedom appear not to be completely equilibrated at lower pressures.264 In the irradiation of perdeutero-acetone, a classical thermal mechanism does not explain the results, but what is believed to happen is that decomposition of the parent molecule takes place near the laser focus, a rapid temperature rise results from the recombination of CD, radicals, and the subsequent chemistry is largely the thermal decomposition of C,D, at temperatures approaching 1900 K.265Laser heating of N,H,-H2S mixtures,266of pure NH, (leading to NH 311and NH, under collisional conditions emission) 267 and of HN,-DN,-HCl mixtures have been reported, with, in the last of these, the temperature of the reacting mixture being monitored by time-resolved i.r. spectral photography (TRISP) of the internal state distribution of the HCl ‘thermometer’.268CW irradiation of lowpressure C2H, is reported to produce triplet-state molecules,269and excitation of SF, near the nozzle of a supersonic expansion molecular beam leads to the production of translationally cool but internally excited SF, molecules.270 Sensitized decomposition of C0C1,,271 UF6,272and tetralin (ClOHl2)2 7 3 by CO, lasers has been carried out, with, in the case of tetralin, different products being found from those produced in pyrolysis experiment^,,'^ and this has been attributed to the laser-induced process reducing heterogeneous decomposition effects. The photodissociation rate of the cyanobenzenecation at 568 nm is found to be significantly increased in the presence of CW CO, laser radiation.,’, Without the laser present, the dissociation is via a sequential two-step mechanism (19), and the

263 264

’” 265

267

I. Burak and J. Y. Tsao, Chem. Phys. Lett., 1981,77, 536. R. N. Zitter, D. F. Koster, A. Cantoni, and A. Ringwelski, Chem. Phys., 1981, 57, 1 1 . W. Braun and J. R. McNesby, J . Phys. Chem., 1980. 84, 2521. S. F. Bureiko, A. P. Burtsev, N. S. Golubev, I. L. Danilov, and Y . M. Ladvishchenko, High Energy Chem., 1980, 14, 282. I. Hanazaki, K. Kasantani, and K. Kuwata, Cheni. Phys. Lett., 1980, 75, 123. P. Avouris, D. S. Bethune, J. R. Lankard, J. A, Ors, and P. P. Sorokin, J . Chem. Pliys., 1981, 74, 2304.

’O

X. de Hemptinne and D. de Keuster, J . Chem. fhys.. 1980, 73, 3170. D. R. Coulter, F. R. Brabiner, L. M. Casson, G. W. Flynn, and R. B. Bernstein, J . Chem. Phys., 1980,

2’1

73, 281. C. Riley and L. MacLean, J . Am. Chem. SOC.,1980, 102, 5108.

269

272 273

274

R. S. Karve, S. K. Sarkar, K. V. S. Rama Rao, and J. P. Mittal, Chem. Phys. Lett., 1981, 78, 273. M. R. Berman, P. B. Comita, C. B. Moore, and R. G . Bergman, J . Am. Chem. Soc., 1980,102,5692. C. A . Wight and J . L. Beauchamp, Chem. Ph-vs. Lett., 1981, 77, 30.

Gas-phase Photoprocesses

147

enhancement is believed to be due to vibrationally excited ground-state molecules, produced by IC from the (C6H5CN+)*species, absorbing CO, laser photons and undergoing MPD. The wavelength dependence of this effect exhibits a pronounced peak at 970cm- and is believed to probe the molecule within its quasicontinuum of states. A similar increase in the 610nm photodissociation rate of the iodobenzene cation with CO, laser radiation has been seen, but with little i.r. wavelength selectivity.275The ion molecule reaction (20) is markedly affected by

',

+

(CH,OH)H '(OH,) + CH30H CW CO, laser irradiati~n.,'~The rate constant for the forward reaction is increased by a factor of > 1000 to 2.6 x 10- cm3molecule- s - under conditions in which each (CH,OH),H+ species absorbs an average of - 4 photons from the laser. The CW laser-induced MPD of (CH,),Cl+ and its deuteriated derivatives 2 7 7 and of CF31+278 have been reported, and saturation effects in the pulsed MPD of CH,OHF- 2 7 9 have been investigated. Steady-state rate coefficients for unimolecular decomposition can be extracted from measurements of the fluence dependence of the MPD yield, providing that laser intensity effects are unimportant in the MPA process.280Application of the Pauli master equation and the energy-grained master equation to MPD have been presented, and the effects of unimolecular decomposition rates 2 8 3 and laser pulse shapes284on the dissociation yields and energy distributions in the products have been considered theoretically. Models for the MPA process involving a single active absorbing oscillator coupled to a heat bath,28s and two non-linearly coupled oscillators interacting with the laser field 286 have been presented. Calculations have been made of the dependence of the fraction of SF, molecules excited below the dissociation limit on the laser fluen~e,,~'and of the role of transfer of angular momentum in the MPA process,288 and further theoretical papers have described a Bloch equztion derivation of rate expressions for MPA,289and the effect of mixing ground-state quantum levels in the presence of the laser field, enabling a large number of rotational states to be pumped at moderate laser inten~ities.~~' 275

276

277 278 279

280

"'

283

284

286

287 288

289

290

R. C. Dunbar, J. D . Hays, J . P. Honovich, and N . B. Lee, J . Am. Chem. Soc., 1980, 102, 3950. D. S. Bomse and J. L. Beauchamp, J . Am. Chem. Soc., 1980, 102, 3967. D . S . Bomse and J . L. Beauchamp, Chem. Phys. Lett., 1981, 77, 25. L. R . Thorne and J . L. Beauchamp, J , Chem. Phys.. 1981.74, 5100. R. N. Rosenfeld, J. M. Jasinski, and J. I. Brauman, Chem. Phvs. h i t . . 1980, 71, 400. M . Quack, P. Humbert, and H. van den Bergh, J . Chem. Phys., 1980,73, 247. J. Troe, J . Chem. Phvs., 1980, 73, 3205. A. C. Baldwin and J. R. Barker, J . Chem. Phys., 1981, 74, 3813, 3823: W. D. Lawrance, A. E. W. Knight, R. G. Gilbert, and K. D. King, Cheni. Phys.. 1981, 56, 343. E. Thiele, J. Stone, and M. F. Goodman, Chem. Phys. h i t . , 1980. 76, 579; J . C. Stephenson, S. E. Bialkowski, D. S . King, E. Thiele, J. Stone, and M. F. Goodman, J . Chem. Phys., 1981, 74, 3905; E. Zamir and R. D . Levine, Chern. Phys., 1980, 52, 253. E. Thiele, M. F. Goodman, and J. Stone, Chem. Phys. Lett.. 1980, 72, 34. P. G . Harper, I. Mackie, and S. D. Smith, Opt. Commun.. 1980,32,41 I ; J. J . Chou and E. R. Grant, J . Chem. Phys.. 1981, 14. 384. R. Ramaswamy, P. Siders, and R. A. Marcus. J . Chem. P h j x , 1981, 74. 4418. D. Poppe, J . Chem. Phys., 1981, 74, 5326. D. Poppe, Chem. Phys. Lett., 1980, 75, 264. H. Friedmann and V. Ahiman, Opt. Commun.. 1980, 33, 163. M. V. Kuzmin, Opt. Commun., 1980, 33, 26.

148

Photochemistry

Most experiments carried out to date in isotope separation using pulsed infrared lasers have been restricted to relatively low pressures, 1 Torr, in order to reduce 100 ns pulse width. For collision-induced isotopic scrambling during the economic separation of deuterium, higher pressures are needed in order to reduce reactor size and gas pumping costs, and thus lower pulse lengths are needed. Pulses of 2 ns duration have been used in the MPD of several deuteriated fluorocarbons at pressures up to 1 atmosphere, and these studies have shown that both difluoromethane and tritluoromethane are photochemically satisfactory as starting materials for large scale deuterium isotope separation by MPD.291Tritium separation from CTF, has been considered, with i.r. absorption spectra of the parent molecule Isotopically selective MPD of the 'UO,(hexafluoroacetylacetonate),.tetrahydrofuran complex in a molecular beam is found to increase in efficiency at lower temperatures, and the factors governing isotopic selectivity in large molecules of this kind have been discussed.293 Carbon-isotope separation schemes involving pulsed and CW C 0 2 lasers have received considerable attention. In the MPD of 'CF,I, scavenging of 'CF, by HI improves the dissociation yield by preventing rapid recombination of the radicals with I Improvements in isotopic selectivity by a factor of 20 are seen by increasing the temperature in the MPD of 'CF2C12at specific wavelengths to the blue of the 927 cm- vs fundamental;295temperature- (and wavelength-) dependent MPA rates competing with collisional scrambling processes are invoked to explain the results.295 Pulsed CO, irradiation of C,F,CI 2 9 6 and CF,Br 297 leads to isotopically selective MPD, and CW pumping of 'CH,F and its subsequent reactions with Br atoms has been seen to retain isotopic selectivity even when states above u = 1 are populated.298 Single visible photon absorption of high overtones of CH stretching frequencies in 'CH,NC leads to isotopically selective i s ~ m e r i z a t i o nCW , ~ ~ CO, ~ laser dissociation of ethylene clusters is suggested as a potential method for isotope separation,300and a review has appeared of recent work on laser isotope separation at the Los Alamos fa~ility.~"Several isotope enrichment processes involving BCI, have been described, with scavenging of dissociation fragments or of vibrationally excited parent molecules by reaction with 0 , , , 0 2 H2S,303and N(CH,), ,04 reported. Isotopically selective MPD of

--

"I

292

293 294 295

296 297 298

299

'01 '02

'03

'04

J . B. Marling, 1. P. Herman, and S. J. Thomas, J . Cliem. Pli~s.,1980, 72, 5603. I. P. Herman and J . B. Marling, J . Pltys. Chem., 1981, 85, 493. J . A . Horsley, D. M . Cox, R. B. Hall, A. Kaldor, E. T. Maas, jun., E. B. Priestley, and G. M. Kramer, J . Chem. Phys., 1980, 73, 3660. C. N . Plum and P. L. Houston, Appf. Phys.. 1981. 24. 143. J . S. J. Chou and E. R. Grant, J . Client. Pliys., 1981, 74, 5679. E. Borsella. R. Fantoni. A . Giardini-Guidoni, and G . Sanna, Chem, Phjx Lett., 1980, 72. 25. M. Neve de Mevergnies and P. del Marmol. J . Cheni. Pliys., 1980, 73, 301 I . D. S. Y. Hsu and T. J. Manuccia, Cliem. Pliys. Lctt., 1980, 75, 16. K. V. Reddy and M. J . Berry, Clieni. Phys. Lett., 1980, 12, 29. M. P. Casassa, D. S. Bomse, J . L. Beauchamp, and K. C. Janda, J . Cliem. Phys., 1980, 72, 6805. R. J . Jensen, J. A. Sullivan, and F. T. Finch, Sep. Sci. Technol., 1980, 15, 509. Y . Ishikawa, 0. Kurihara, R. Nakane, and S. Arai, Cliem. Phys., 1980, 52, 143; H. Kojima, T . Fukumi, K . Fukui, and K. Naito, J . P h j x Cliem., 1980, 84, 2528. K. Takeuchi, 0. Kurihara, and R. Nakane, Chem. Phys., 1981, 54, 383. G. A. Kapralova, L. E. Makharinskii, E. M. Trofimova, and A. M . Chaikin, Sov. Phys. JETP Lett., 1980. 31, 504.

Gas-phase Photoprocesses

149

another B-containing compound, 2-chlorovinyldichlorodiborane,has been carried Measurements of the rates of removal of small free radicals, produced by pulsed i.r. MPD and detected by laser-induced fluorescence, have been carried out by several research groups, and the results of recent experiments have been reviewed.234The C, radical in its ground X'Z; and low-lying first excited a 3 n , state has been investigated in detail by this method.306*,07 Oxygen is found to cause equilibration between the two states at a rate that is faster than overall removal by reaction,306 and for many other species, both reactive and collision-induced ISC rates have been quantitatively determined.," C2(a31J,) removal rates have also been measured by using U.V.MPD (by means of an excimer laser) as a photolysis source,3o8and the rate constant for recombination of CF, radicals formed in their ground electronic state by i.r. MPD, has been measured by a mass spectrometric technique. ,09 Finally in this Section on infrared photochemistry, the i.r. laser-induced reaction of SF, with a Si surface has been described.310Pulsed CO, laser radiation in the absence of SF, causes momentary heating of a Si target, but no Si removal: in the presence of a few Torr of SF,, etching of the Si is observed. The mechanism for the process is yet to be established, but it appears that both the reactions of excited species produced by the laser, and the effect of the laser radiation at the gas-surface interface are of importance., l o 9 Photochemistry of Atmospherically Important Species An estimate of the global burden of CHF2C1 (Freon 21) has been made from measurements of its atmospheric concentration. The result indicates that the total amount released from anthropogenic sources has been underestimated by almost a factor of 2. In clean background tropospheric air its concentration is virtually immeasurably small (0.1-2.5 p.p.t.v.), and it seems that a potential route for its production by reaction of CFCI, (Freon 11) on tropospheric aerosols is not of importance., l 2 The interpretation of CFCI, and CCI, measurements at Harwell has been debated with regard to the proximity of the site to local sources of these species.313Concentrations of C10 have been measured for the first time by a landbased experiment, by monitoring the J = 11/2 + J = 9/2 emission line.314The C10 column density was lower than that found from balloon flights, and a greater vertical gradient was obtained than that predicted from theoretical models. '05 '06 '07

309

'I0 'I1

"' "*

R. J. Jensen, J. K. Hayes, C. L. Cluff, and J. M. Thorne. IEEE J. Quantum Electron., 1980.16, 1352. M. S. Mangir, H. Reisler, and C. Wittig, J. Chem. Phys., 1980, 73, 829. H. Reisler, M. S. Mangir, and C. Wittig, J. Cheni. Phys.. 1980. 73, 2280. L. Pasternack, A. P. Baronavski, and J. R. McDonald, J. Chem. Phys., 1980,73,3508; L. Pasternack, W. M. Pitts and J. R. McDonald. Client. Phys., 1981, 57. 19. R. I. Martinez, R. E. Huie, J. T. Herron, and W. Braun, J. Phys. Chem., 1980, 84, 2344. T. J. Chuang, J. Chem. Phys., 1980, 72, 6303. R. A. Rasmussen, M. A. K. Khalil, S. A. Penkett, and N. J. D. Prosser, Geophys. Res. Lett.. 1980.7. 809. S . A. Penkett, N. J. D. Prosser, R. A. Rasmussen, and M. A. K. Khalil. Nature (London), 1980,286, 793. D. M. Cunnold, F. N. Alyed, and R. G. Prinn, Atmos. Environ., 1980. 14, 617; S. A. Penkett, K. A. Brice, R. G. Derwent, and A. E. J. Eggleton, ibid., p. 618. A. Parrish, R. L. de Zafra, P. M. Solomon, J. W.Barrett, and E. R.Carlson, Science. 1981,211,1158.

I50

Pho t o c h w is t r j * HCI 3 15 - 3 1 6 and H F 3 1 6 mixing ratios in the stratosphere, and total atmospheric CI and Br concentrations have been reported.317Further measurements have been made of NO,318* 3 1 9 NO 2, 319* 320 N 0 321 0 atoms,322H2C0,323 and alkanes324 in various regions of the atmosphere, and the results of a field sampling program of a wide range of tropospheric gases and aerosols have been published.325 Photolysis of ozone within the Hartley continuum does not appear to produce O ( ' D ) with unit quantum yield: @O('D) has been measured as 0.85 0.02 at 248 nm 3 2 6 and 0.88 0.02 at 266nm 3 2 7 from experiments monitoring O ( 3 P )by The U.V.absorption time-resolved absorption 326 and resonance spectrum of 0, 3 2 8 and its photolysis rate to produce O( 'D)329 both show changes when the parent molecule is vibrationally excited. At wavelengths above 310 nm 'Ag)],vibrational excitation [the energy threshold for production of O(' D)+ 02( increases the cross-section for O(' D)production by two orders of magnitude, and this effect was found to diminish as the energy of the dissociating photon was increased.329At shorter wavelengths ( 1 70-240 nm) the production of O('S) from 0, photolysis has an upper limit of O.l(%, and so any contribution from this excited state in, for example, the atmospheric OH production rate is thought to be insignificant . 3 3 0 The effects of low concentrations of sulphur dioxide upon the rates of 0, and N O formation in irradiated mixtures of NO, and air have been investigated, in an effort to determine the reasons for formation of increased tropospheric concentrations of 0, near the plumes of power plants emitting N o such effects were observed for SO, concentrations up to 10 p.p.m.; when the experiments were repeated with added CI, however an increase in the O3 concentration was observed, and a chain-reaction mechanism involving formation of the ClOO species has been suggested to explain the observations.331 Further twodimensional modelling calculations of 0,depletion rates have been described.332 The importance of establishing the fraction F of the removal rate of O(' D)by N,O 2

'I5

317 'IH

31y

"'

9

K . V. Chance. J . C. Brasunas, and W . A. Traub, Gmp/i,rs. Res. Lett.. 1980. 7. 704: P. Marche. A. Barbe. C. Secroun. J . Corr. and P. Jouve. G1wphy.v. Ros. L ~ t t .1980, , 7. 869. H. Libuijs, G. L. Vail. G. Tremblay. and D. J . W . Kendall, Gcop/i.rs. Res. Lett.. 1980, 7, 205. W. W. Berg. P. J. Crutzen. F. E. Grahek, S. N. Gitlin. and W. A. Sedlacek. Gcwppliys. Res. Lett., 1980, 7. 937. N . lwagami and T. Ogawa. P h c i Spircv Sci., 1980, 28. 867. H . K . Roscoe. J . R. Drummond, and R. J . Jarnot. Proc. R. Sot. London. SLT. A . 1981, 375, 507. B. B. McMahon and E. L. Simmons. Nutiiri> (Lonilon). 1980.287,710: J . P. Naudet, P. Rigaud. and D. Huguenin. Gwp/i,rs. Ros. Lett.. 1980, 7. 70 I . P. S. Connell. R. A. Perry. and C. J . Howard, GiwpIgx. RPS.Lett.. 1980. 7, 1093. W . E. Sharp. Gcopli.rs. Rcs. Lcw.. 1980. 7. 485. V. Neitzert and W. Seiler. Gaoph,r.s. Rev. Lett., 1981, 8, 79.

"' "' R . Eichrnann. G . Ketseridis, G. Schebeske, R . Jaenicke, J . Hahn. P. Warneck, and C. Junge. Atnios. 1980. 14, 695. '" DEni*iron.. . D. Davis. J . GwpIijx. RPS..1980. 85, 7285.

S. T. Amimoto, A. P. Force, J . R. Wiesenfeld, and R. H . Young, J . Clicni. Pliys.. 1980, 73. 1244. J. C . Brock and R . T. Watson. CIi~vii.P h ~ x Lctt.. . 1980, 71. 371. 3 2 n 1. C. McDade and W . D . McGrath. C l i m . Ph,rs. Lett., 1980, 72. 432; I . C. McDade and W . D. McGrath, C h m . PIiys. Lett.. 1980, 73, 413. "' P. F. Zittel and D. D. Little, J . Cliem. PIij:v.. 1980. 72. 5900. 3 3 0 L. C. Lee, G. Black, R. L. Sharpless. and T. G . Slanger. J . C h ~ n i Plijx.. . 1980. 73. 256. 3 3 ' J. S. Wallace. G. S. Springer, and D . H . Stedman. .4tnio.s. Emiron. 1980, 14, 1147. 3 3 2 J. A. Pyle and R. G . Derwent. Ncrturt I Lonilon). 1980. 286,373; C. Miller, J . M. Steed, D . L. Filkin, and J . P. Jesson. N(itiirc (Lontlori). 1980. 288, 461. 32h

"'

151 G ~ ~ v -(isc p h PI]0 tO ~oCC~SSCS S leading to formation of 2 N 0 molecules upon the 0, depletion rate by halocarbon release has been stressed in a recent publication:333a 1% variation in the NO production rate via this mechanism is expected to result in a 0.43Xchange in the 0, depletion. Measurements of F at different temperatures and total pressures have been carried out.,,, The involvement of excited 0, species (produced in an unspecified state by 0 + O2 recombination) in formation processes of N 2 0 in the atmosphere has been p r ~ p o s e d34, ~the wavelength dependences of 0, absorption coefficientshave been measured,335and the rate for the 0, +CH, reaction has been determined. 3 3 6 Photolysis of 0, in the Hartley bands leads to 02('A,) production, with 60% formed vibrationally excited,,,' and under atmospheric conditions quenching is found to be a rapid process. Rates of formation of O,('A,) by this mechanism in the upper atmosphere of Venus have been calculated and compared with those determined by observations of the O,( 'Ag) emission at 1.27 pm: for the values to agree, the previously accepted ozone concentrations would have to be revised upwards by a factor of In the terrestrial atmosphere, the photolysis of 160180 at wavelengths between 170-205 nm could be an important source of odd oxygen in the high stratosphere and mesosphere, as solar radiation not absorbed by discrete I6O, features may penetrate these regions and photolyse the minor isotopic constituent (present as 4 ' : ~of naturally occurring 0,).339 Laser-induced fluorescence measurements of atmospheric OH have been carried out now for several years, and shown to be capable of detecting extremely low concentrations of the radical. It has been pointed out however that interference from laser-generated OH could affect the results considerably: 340 the wavelength used for OH excitation, 282nm, generates O('D) from 0,photolysis, and this reacts with H,O to form OH in the troposphere in a time ( - I ns) which is shorter than the laser pulse width. Calculations and experimental assessments of the importance of this effect have been described.340*3 4 1 The reaction of OH with CS, has been shown to be too slow to act as either a substantial sink for CS,, or a source for OCS in the troposphere,342 and the OH+OCS reaction, the rate constant of which is < 8.8 x 10-'5cm3 molecule- s- ' at room temperature is a similarly minor degradation path for OCS.3 4 3 The role of reaction (21) in atmospheric chemistry is now well recognized, and general agreement upon the value of its rate constant, of critical importance for modelling calculations of the stratospheric ozone balance, now appears to be H02+N0 333 334

335 336 33i

338 33y

"' 3J2

343

-

OH + N O ,

(21)

L. Lam, D. R. Hastie, B. A . Ridley, and H. 1. Schiff. J . Pltoroclient., 1981, 15, 119. S. S. Prasad, Natirw (London). 1981, 289, 386. J. J . DeLuisi. Gropltys. Res. Lett., 1980, 7. 1102. N . Washida. H. Akimoto. and M . Okuda, J . Chrm. Pli,v.s., 1980, 73, 1673. 0. Klais, A . H . Laufer. and M . J . Kurylo, J . Client. Pli,w.. 1980, 73, 2696. J. P. Parisot and G . Moreels, f c u r ~ v1980. , 42. 46. R. J . Cicerone and J. L. McCrumb, Gcwp/i,w.Rcs. Lett.. 1980. 7 , 251. G . Ortgies. K. 11. Gericke, and F. J . Comes, Gcopltj:~.Res. Lctt., 1980, 7, 905. D. D. Davis, M . 0. Rodgers, S. D. Fischer, and K . Asai, Gcwp/i.w. Res. Lett., 1981, 8, 69; D. D. Davis. M. 0. Rodgers. S. D. Fischer. and W . S. Heaps. GcopliJx Res. Lert., 1981. 8. 73. P.H . Wine, R. C . Shah, and R. Ravishankara. J . fliys. Clicnt.. 1980, 84, 2499; R. S. Iyer and F. S. Rowland, Gcophjx Rcs. LPII. 1980, 7. 197. A. V. Ravishankara, N . M . Kreutter, R. C . Shah. and P. H. Wine. Gcopltjx Rcs. Lett., 1980.7, 861.

Photochenzistry reached amongst several sets of investigators. Measurements of both forward and reverse rates of (21) have now fixed the previously uncertain heat of formation of HO, as AH,' (298) = 2.5 & 0.6 kcal mol- ', and this has established the thermochemistry of other reactions involving HO, of potential importance in the atm~sphere.~"" The forward rate constant for reaction (21) has been shown to be independent of pressure in the region 2-1 7 rnbar.,"' The catalytic cycle reactions (22) and (23) removes odd oxygen in the stratosphere, and is of particular

152

HO,

+ 0,

+

-

OH

+ 20,

+

OH 0, HO2 0, (23) importance at altitudes below 25km, as it does not involve oxygen atoms (in contrast to similar cycles involving nitrogen oxides or chlorine species). The rate constant for reaction (22) has now been measured directly for the first time over the temperature range 245--365 K,346and extrapolation of the Arrhenius plot to 220 K yields a value five times larger than that previously assumed for atmospheric modelling calculations. Further quantitative studies of reactions of atmospheric importance include measurements of the temperature dependences of process (24)347and of the recombination rate of methylperoxy radicals with NO,,348and

CI

+ HOCl

-

HCI

+ C10

(24)

an estimation of an upper limit for the reaction between C10 and H2C0,349not fast enought to be an appreciable sink for C10 radicals. The photolysis rate of atmospheric NO, has been measured, and its dependences upon parameters such as the solar zenith angle and the amount of cloud cover have been evaluated.350The photochemistry of small molecules containing sulphur, and its implications for the atmospheric S cycle have been discussed,351 as has the role of stratospheric 'reactive nitrogen' as a source for species such as NO and HNO, in the unpolluted t r ~ p o s p h e r e . ~Ammonia '~ concentrations have been calculated in the atmospheres of both Earth 3 5 3 and Saturn;354the far-u.v. photolysis of mixtures of NH, with methane results in the formation of amines and nitriles, and the relevance of these results to the evolution of primitive atmospheres has been discussed. Ions of the form HfX,(H20)m,where X has mass 41, have been detected in the stratosphere, and recent laboratory experiments on clustering equilibria for these species suggest that X is acetonitrile, CH,CN.356The stratospheric chemistry of J44

'" "-

'" '" "'

''' "' 353

355 35h

C. J . Howard. J . Am. Ciiwi. Soc., 1980, 102, 6937. W. Hack, A. W. Preuss, F. Temps, H . Gg. Wagner. and K . Hoyermann. I t i t . J . Chcrii. Kinet.. 1980. 12, 851. M. S. Zahniser and C. J. Howard, J . Ciicwi. P/i?*s., 1980. 73, 1620. J. L. Cook. C. A . Ennis. T. J . Leck. and J. W. Birks, J . Chcni. P l i ~ s . ,1981, 74, 545. A . R. Ravishankara. F. L. Eisele, and P. H . Wine, J . Chnii. PIIJs., 1980, 73, 3743. G. Pulet, G. Le Bras, and J. Combourieu, G c o p h ~ sRcs. . Lrt1., 1980, 7. 413. F. C. Bahe. U . Schurath. a n d K . H. Becker. Atnios. Etzviron.. 1980, 14, 71 I . N . D. Sze and M . K . W . KO,Atnios. Environ.. 1980, 14, 1223. H . Levy, J . D. Mahlman, and W. J. Moxim. Gcwph~x.Rcs. Li>tt., 1980, 7,441. J . S. Levine, T . R. Augustsson, and J . M. Hoell, Gcoph~*s.Res. Let[., 1980, 7. 317. S. K . Atreya, W. R. Kuhn, and T. M . Donahue. G e o p l i ~ ~Rrs. s . L P I I . .1980. 7, 474. A . Bossard and G. Toupance, Klitiire (Lonilon). 1980, 288, 243. H. Bohriiiger and F. Arnold. Ntrlurc lLonrlon), 1981, 290, 321.

153 metal atoms (formed by aircraft emission or meteoroid ablation) has been described,357 and measurements of intensities of Na(D) lines in the upper atmosphere have led to the suggestion of the mechanism for formation of the excited species being reaction ( 2 5 ) , with NaO formed from Na + 03.358a Gas-phase Photoprocesses

NaO

+0

----+

Na('P)

+ 0,

(25)

Reaction (26) is believed to be the major source of O('D) above 150 km in the daytime thermosphere, and the influence of this previously unconsidered reaction N(,D)

+ 0,

-

NO

+ O('D)

(26)

on the O('D) 630 nm emission rate has been calculated.358bThe auroral chemistry of N('D), formed by dissociative excitation of N, by fast electrons,359 and of N,O, formed in the reaction of N,(A3C,+) with 0, 360 has been reported. H Atoms, H,, and H,.-Reactions of ground-state H atoms with the following molecules and radicals have been reported: HBr,361HN3,362C2H4,363i-C4H8,364 T,,365 CF3Br,366 dimethyl s ~ l p h i d e ,368 ~ ~ dimethyl ~. ether,368 NF2,369- 3 7 1 03,372 - 3 7 5 and various fluorine- and bromine-containing compounds.376 Hotatom studies of the H + CH3C1 reaction have determined the apparent energy threshold for the process as 47 14kJmoi-',377 and D atom reactions include measurements of the internal energy distribution in OD formed from D + and of the rates and kinetic isotope effects in the D + Cl, and Br, systems.379Reaction (27) is believed to produce NF(a'A) highly selectively, with a

-

H + NF, NF(a'A) + H F (27) quantum yield of 20.9,369-371 and subsequent reactions of this with H atoms, process (28) is again selective in populating the N('0) state.369The radiative lifetimes of metastable NF(a'A) is estimated to be H

+ NF(a'A)

----+

N('0)

+ HF

(28)

The contribution of the reaction channel (29) to the removal rate of 0, by H atoms has been estimated by several ~ ~ r k e rHigh ~ yields . ~ ~of O ~ ( 3-P )have ~ ~ ~ H 357 358

359 360

+ 0,

-

HO,

+ O(3P)

E. Murad, W. Swider, and S. W. Benson. Ncrturv (London), 1981, 289, 273. D. R. Bates and P. C. Ojha, Ntrrure (London), 1980,286,790; ( b ) D. G. Torr, P. G. Richards, and M. R . Torr, Geophjx Res. Lett., 1980, 7, 410. J . C. Gerard and 0. E. Harang, J . Gropliys. Res., 1980, 85, 1757. E. C. Zipf, NCrtiwv (London), 1980.287. 523; E. C. Zipfand S. S. Prasad, Nature (London), 1980,287, (N)

'" J.525.L. Jourdain, G. Le Bras, and J. Combourieu. Clreni. P/I.Y.S.Lett., 1981, 78, 483. 362

365 366

368 369 370

37' 372

(29)

0. Kajimoto, T. Kawajira, and T. Fueno, Cheni. Ph)*s. Lett., 1980, 76, 315. K. Sugawara, K. Okazaki, and S. Sato, CIimi. P l i j x Lett., 1981, 78, 259. C . E. Canosa, R. M. Marshall, and A. Sheppard, Int. J . Cliem. Kinet., 1981, 13, 295. G . H . Kwei and V. W . S. Lo, J . Chem. PI1y.s.. 1980, 72, 6265. D. M. Silver and N . de Haas, J . Cheni. Phys.. 1981, 74, 1745. M . M . Ekwenchi, A. Jodhan, and 0. P. Strausz, Int. J . Chsm. Kinet., 1980, 12, 431. J. H . Lee, R . C. Machen, D. F. Nava, and L. J. Stief, J . CIieni. Phys., 1981, 74, 2839. C. T. Cheah and M . A. A. Clyne, J . CIieni. So(,.,Frrrrrdq* Trrrns. 2, 1980, 76, 1543. R . J. Malins and D. W. Setser, J . Phj-s. Clrem., 1981, 85, 1342. C. T. Cheah and M. A. A. Clyne, J . P/rotoc/ieni., 1981, 15, 21. A. P. Force and J. R . Wiesenfeld, J . Cliem. Phj-s., 1981, 74, 1718.

154

Ptiotochemistrj*

been detected by time-resolved atomic absorption spectroscopy 3 7 2 and by laser paramagnetic resonance 3 7 3 in this reaction system. Failure to observe HO, radicals however has led to an estimate of 5 2 % of the H + 0, reaction leading to their formation, and the participation of vibrationally excited OH * (formed by H + 0,) reacting with either H atoms or 0,, process (30) is suggested as the Time-resolved observations indicate that if O(,P) is produced source for O(3P).373 by reaction (30) then its rate constant would need to be increased by an order of

OH* +03

-

OH

+ 0, + O(3P)

(30)

magnitude over the presently accepted value for the de-excitation of OH* by 0,.372 Further measurements upon the role of OH* in this system are promised. 3 7 2 The effects of isotopic substitution 3 8 0 * 3 8 1 and of internal and kinetic on the calculated cross-section for the H + H, reaction on an accurate potential energy surface have been described. At a given translational energy, vibrational energy in H, increases the reaction rate, whereas rotational energy has the opposite effect near the threshold for reaction.383 Classical trajectory studies of the H + 0, reaction have reproduced values of the experimental rate constant over a wide temperature range,384and the temperature dependence of the effect of third-body stabilization of the excited HO, species formed in this system have been similarly calculated.385Approximate theories of thermal rate constants have been used to estimate that for the H + F, reaction, with comparisons made of this value with that calculated quantally for colinear collisions on an accurate potential energy surface. Agreement between variational transition-state theory and the quanta1 results is found to be within 5% over a wide temperature range.386 Theoretical investigations of reactions of H atoms with HC0,388and C2H4 3 8 9 have also been described. Frequency tripling of KrF laser output in Xe results in radiation near 83nm, tunable over a region of 0.5 nm, and this has been used to measure absorption line profiles in the B”lX,+ +-- XIZg+ system in H,, and the corresponding B” t X 373

374 375 376

377 37H

379

3x0 381

382

383 384 38s

386

387

’*’

389

B. J. Finlayson-Pitts, T. E. Kleindienst, M . J. Ezell, and D. W. Toomey, J . Cliem. Ph!*s., 1981, 74, 4533. N. Washida, H. Akimoto, and M . Okuda, J. CIILWI. P/tj..c., 1980, 72, 5781. B. J. Finlayson-Pitts and T. E. Kleindienst, J. Clietni. P / i j 3 . , 1981, 74, 5643. R. J. Malins and D. W. Setser, J . Ckem. P l i j x . , 1980, 73. 5666. P. L. Gould, G. A. Oldershaw, and A. Smith, Cheni. f / i y . s . Left., 1980, 76, 319. E. J. Murphy, J . H. Brophy. G . S. Arnold, W. L. Dimpfl, and J . L. Kinsey, J . Chem. Pliys., 1981, 74. 324. S. Jaffe and M. A. A. Clyne, J . Chem. So(,.,Frrrcidqv Trrms. 2. 1981, 77, 531. H. R. Mayne, J . Clieni. PIiys.. 1980, 73, 217; B. C. Garrett, D. G . Truhlar, R. S. Grev, and R. B. Walker, ibid., p. 235. J. C. Sun, B. H. Choi, R. T. Poe, and K . T. Tang, J . Cheni. Phys., 1980, 73, 6095. C. D. Barg, H. R. Mayne, and J . P. Toennies, J. Chrm. Pl1j.s.. 1981, 74. 1017. M. Baer, H . R. Mayne, V. Khare, and D. J. Kouri. Clwm. Phys. Lett., 1980, 72, 269. J. A. Miller, J . Clieni. Pli?v., 1981, 74, 5120. R. J. Blint, J . Cliern. PhJx., 1980. 73, 765. H. C. Garrett, D. G . Truhlar, R. S. Crev, A. W. Magnuson, and J. N. L. Connor, J . C‘/lcn?.Phj-s.. 1980, 73, 1721. B. C. Garrett. D. G. Truhlar, and R. S. Grev, J . Pliys. Chetn., 1980, 84, 1749. S. C. Farantos and J . N . Murrell, Mol. Ph?.s., 1980, 40, 883. W. L. Hase, D. M. Ludlow, R. J . Wolf, and T. Schlick, J . Phys. Chem. 1981, 85. 958.

Gas-phase Pliotoprocvsses

155

transition in HD.390Predissociation takes place viu crossing to the repulsive limits of the B"C,* state above its dissociation limit, and an analysis of the B t X linewidths and asymmetries has shown that the rate of this process depends significantly upon the Franck-Condon factors for the B"--B' interaction.390 Spectroscopic constants for the i.r. 2Al'-2E' transitions in H, and D, near 3600cm-' have been measured, and these states have been found to be the upper levels of the 602.5 and 710nm bands previously observed for these triatomic radicals.391

0 Atoms, 02,0,,and H0,-Rate constants for bimolecular reactions of groundstate 0 atoms with the following substrates have been measured: H2,392HCN,393 CH30H,394i ~ o b u t a n e , ~CF,HC1,396 ~' f l ~ o r e t h y l e n e s OH,398 , ~ ~ ~ CH3,399propane,400OCS,401CH,SSCH3,402and SO,.403In the 0 + H, reaction, measurements at 298 K have provided further evidence for curvature at the low temperature end of the Arrhenius plot, and the influence of vibrationally excited H, on this reaction has been carefully considered.392 Calculations on the 0 + H, reaction 405 with the properties of various potential energy surfaces have been reported,404* for the reaction evaluated.405Hydrogen abstraction in the 0 + C H 3 0 H reaction takes place from the methyl group,394whereas for 0 + isobutane, the H attached to the tertiary carbon atom is preferentially removed.395The rate constant for the latter process, 1.0 x 10- l 3 cm3 molecule- s- l , is in agreement with that predicted from a sum rule of the rates of attack on individual H atoms.395The dynamics of the 0 + C,F,,406 C2F,I,407 and C3F,1408 reactions have been studied by molecular beam scattering; OH product distributions have been measured 409 and calculated 410 for various 0 + alkane reactions. CO vibrational distributions have been determined in the 0 + HC=CCH,X reactions (X = C1, Br),411the temperature dependence of the third-body recombination of 0 + 0, has been

390

M. Rothschild, H. Egger, R. T. Hawkins, H. Pummer. and C. K. Rhodes, Chcm. P h j x . Lctr., 1980,

72, 404. G. Herzberg, H . Lew, J. J. Sloan. and J. K . G . Watson, C m . J . PItys., 1981, 59, 428. 3q2 G . C. Light and J. H. Matsumoto. Int. J . C/tcwi. KincJt.. 1980. 12. 451. 393 P. Roth, R. Lohr. and H. D. Hermanns, B w . Bunscwgc>s.Plty.s. C'/tc.nt.. 1980, 84, 835. 394 H. H. Grotheer and Th. Just, Cltcwi. P h ~ sL. P I I . .198 I . 78, 71. 395 N. Washida and K. D. Bayes. J . P h j ~ Chcwt., . 1980, 84, 1309. 396 V. I. Egorov, S. M. Temchin, N. 1. Gorbdn, and V. P. Balakhin, Kinat. Critril.. 1979, 20, 850. 397 K. Sugawara, K. Okazaki, and S. Sato, Bull. Cltcwt. Sot. J p n . , 1981. 54. 358. 398 R.S. Lewis and R. T. Watson, J . PIIJS.C / t m . *1980, 84, 3495. 399 N. Washida, J . CAem. Phys., 1980, 73. 1665. 4oo S. P. Jewell, K. A. Holbrook, and G . A. Oldershaw, f n t . J. Cheni. Kinct.. 1981, 13, 69. jol J . S. Robertshaw and I. W . M. Smith, Int. J . Client. Kinat., 1980, 12, 729. 402 J . H. Lee and I. N. Tang, J . Chem. Phys., 1980, 72, 5718. jo3 M. Slack and A. Grillo, J . Cheni. Pltys., 1980, 73. 987. 404 D. C. Clary and J . N. L. Connor, M o f . Phys.. 1980, 41, 689. jo5 A. F. Wagner, G . C. Schatz. and J . M. Bowman, J . Clieni. Pltys., 1981,74,4960; G . C. Schatz, A. F . Wagner. S. P. Walch. and J . M. Bowman, J . Cltctn. P h ~ * s .1981, . 74, 4984. 406 P. A . Gorry, R. J. Browett, J. H. Hobson, and R. Grice, M o l . P l i j x . 1980, 40, 1325. jo7 R. J. Browett, J. H. Hobson, P. A . Gorry. C. V. Nowikow. and R. Grice, Mol. Pltys., 1980,40. 1315. 408 R.J. Browett, J. H. Hobson, and R. Grice, Mol. Phys., 1981, 42, 425. P. Andresen and A. C. Luntz, J . C/tm, P/tys., 1980, 72, 5842. 410 A. C. Luntz and P. Andresen. J . Clicni. P/IJ*s.,1980. 72, 5851. jl' G. T. Fujimoto, M. E. Umstead. and M. C. Lin, Cheni. P h ~ : s . .1980. 51. 399. 391

156

Photoc.hc~iiistr.?,

further investigated.412and a theoretical study of the 0 + acetylene reaction has been r e p ~ r t e d . " ' ~ Energy distributions in the OH(X2ni) products of the O ( ' D ) reaction with H,0,414-417H2,418HCL4I9 NH3,420and saturated hydrocarbons 4 2 1 have been measured by laser-induced fluorescence 4 1 s - - 4 2 and resonance absorption technique~.~ In' ~the O ( ' D ) + H,O reaction [equations (31) and (32)], bimodal O('D)

+ H20

-

20H H2

+

(31) 0 2

(32)

rotational state distributions in OH ( u = 0) have been observed, corresponding to rotational temperatures of 400 and 1900 K,"14 500 and 2500 K,41s and 360 and 4200 K "' in three separate experiments. The origin of the colder fragments has been ascribed both to direct reaction 4 1 4 * 41 and to partial rapid rotational relaxation of the hot species formed."16 Isotopic labelling of the oxygen atom in H 2 0 has demonstrated that the vibrational energy in the new OH bond is significantly greater than that in the old, and this has been interpreted in terms of H-atom abstraction (or stripping) dynamics rather than 0-atom insertion into the bond.416 OH formation [equation (31)] appears to be the major water 0-H channel in this reaction, with process (32) accounting for 510% of the overall O ( ' D ) removal rate at 298 K."17 Bimodal rotational distributions in the OH product of the O ( ' D ) + alkane reactions have been interpreted as due to contributions from insertion (leading to a broad distribution of high rotational states) and abstraction (leading to population of a few rotational states only).42' Insertion dominates for small hydrocarbons (CH, and C2H6), whereas for C,H, these results are consistent and C(CH3), abstraction is of greater imp~rtance:"~' with recent crossed molecular beam studies of the O ( ' D ) + CH, reaction, in which mainly CH,O + H products were Rates of collisional removal of O(' 0 ) with atmospheric gases 4 2 3 and halogenated methanes 4 2 4 have been measured, with in the latter case observations of the O ( 3 P )product allowing estimations of the contributions from quenching and chemical reaction to be determined. The rapid near resonant equilibration process (33) is thought to be responsible 02(lAg)

for pumping I('P,,,)

+

1(2p3,2)

in the 0,-iodine

0 2 ( 3 2 g - ) + I(2p1j2) (33) energy-transfer laser. Production of

'" 0. Klais. P. C. Anderson, and M . J. Kurylo. hi/.J. CI76~77.K k p / . , 1980, 12. 469. B. Harding, J . Phj.s. C/?Cm..1981, 85, 10. "' L. K. H . Gericke and F. Comes, Chiwi. P/rj..s. Lctt., 1980. 74, 63. 'I3

'I5

M . 0. Rodgers, K . Asai. and D. D. Davis. Cllc~7.P/II.s. f>c>tt.,1981, 78. 246. J. E. Butler. L. D. Talley. G. K. Smirh. and M . C . Lin, J . C/~cnl.P h j ~ . 1981. . 74, 4501. R. Zellner, G. Wagner, and B. Hiinme. J . PIrJx. Ch~w7..1980. 84, 3196. 'Ix G. K. Smith and J. E. Butler. .I. CIww. Phj-.s.. 1980. 73. 2243. 'Iq A . C . Luntz. J . C ' l i c ~ r v . Plijx., 1980. 73, 5393. "" D. Sanders. J. E. Butler. and J . R . McDonald, J . C ~ C WPhI..v., I. 1980, 73, 5381. '" AN .. C. Luntz, J . Clroii. PIrjx., 1980. 73, 1143. Casavecchia, R. J . Buss, S. J . Sibener. and Y . T. Lee. J . C ' h ~ n i .P h j ~ . 1980, . 73, 6351. "' P. P. H . Wine and A . R. Ravishankara. Chon. P h j . ~ Lc.rt., . 1981, 77, 103. "' A. P. Force and J. Wiesenfeld, J . P/IJ..c.Chrn7.. 1981. 85. 782. 41 7

GUS -phU.W Ph o t O

--

157 ground-state iodine atoms has been assigned to process (34), with O,('c,+) being ~ 0VI'CSSIJS

+

O,('C,+) I, 0 2 ( 3 z ~+ /2~1 ( )2 p 3 ; 2 ) (34) formed either by the energy pooling reaction of two O,( 'Ae) molecules, or by the energy-transfer process (35). However, measurements of the rate of de-excitation of 02(1A(8)

+ r(2p3/2)

02(1cg+)

+

r(2p3/2)

(35)

O,('C,+) by I, have suggested that process (34) is of minor importance, and that an alternative source of iodine atoms in this system must be identified.425 The temperature dependences of process (35) and of the 02('Ag) energy-pooling reaction have been determined;426 'dimol' emission resulting from collisions between two O,( 'A,) molecules has also been i n v e ~ t i g a t e d . ~Vibrational ~' relaxation rates of O2(lAe, v = 1) have been measured at high temperatures in a shock sensitized ernision from SeO, Se,, and SeS produced in the b'C+ states by near-resonant energy exchange with O2(lAs)appears to hold promise for the production of electronic population inversions in these systems,429and a search for O,( 'A,) by photoionization mass spectrometry in the products of the reactions of 0, H, and NO with ozone has failed to detect it in significant concentration^.^^^ Quenching rates of the b'Xg+ 4 3 1 and A%:,' 432 states of O2 have been reported. Photofragment spectroscopy of 0 3 + between 457.9-752.5 nm has determined energy partitioning in the 0' and 0, photofragments formed from ground and vibrationally excited (in the v 1 symmetric stretching mode) parent rn01ecules.~~~ 4 3 5 states of O,+ has been studied. Predissociation of the b4X,- 434 and f4ng Reactions of ground-state OH radicals with H2,436 H,02,437 HCH0,438 NH3,439C0,440 HN03,442and various hydrocarbons 4 3 6 * 443 and their J25

J26

"' 'lfl

"' 431 432

J33 J3J

J35

436 J37

438

439

"O

441

D. F. Muller, R. H. Young, P. L. Houston, a n d J. R. Wiesenfeld, Appl. f / i j * . s . Lerr., 1981, 38, 404. R. F. Heidner, C. E. Gardner. T. M. El-Sayed. G. I. Segal, and J. V. V. Kasper, J. C / W J IPhj*s.. . 1981, 74, 5618. P. M . Borrell, P. Borrell. and K . R. Grant, J. Chcv~7.Soc.. Ftrrrrtkrj. Trtr17.s. 2. 1980. 76, 1442; G . A. Fisk and G. N . Hays. CIiwi. Pl7j.s. Lctt., 198 I . 79. 33 I . P. M. Borrell, P. Borrell. and K . R. Grant, J. C/wrt7.Sot,.. Fwrrticry Truris. 2 , 1980, 76, 923. R. Winter. I. Barnes, E. H. Fink. J. Wildt. and F. Zabel. C/itv~i. P h ~ : s .Lrtt.. 1980. 73, 297. N. Washida, H. Akimoto, a n d M . Okuda, Bull. c/?C'/?7. Sol.. J p . , 1980, 53. 3496. R . G. Aviles. D. F. Muller, and P. L. Houston, A p p / . P h ~ . s Lctr.. . 1980. 37, 358. R. D. Kenner and E. A. Ogryzlo, Int. J . Chci~7.K i n c f . , 1980, 12, 501. J. T. Moseley, J. B. Ozenne, and P. C. Cosby, J . Chcvii. P h j x . 1981. 74. 337. M. Carre, M . Druetta, M. L. Gaillard, H . H . Bukow. M . Horani, A. L. Roche, and M. Velghe, Mol. Ph.rs., 1980. 40, 1453; J. C. Hansen. M . M . Graff. J. T. Moseley. and P. C . Cosby, J. C ~ U Jfhj*s.. I. 1981. 74, 2195. H. Helm, P. C. Cosby. and D. L. Huestis. J . C h ~ 7fhys., . 1980. 73, 2629. F. P. Tully and A. R. Ravishankara, J. PIiJs. C h ~ n i .1980. , 84, 3126. U. C. Sridharan, B. Reimann, and F. Kaufman. J. Chmt. fhjx., 1980. 73, 1286; L. F. Keyser. J. P h ~ s . Chcm., 1980, 84. 1659. B. M.Morrison. jun., and J . Heicklen. J. f h o r o c l i m . . 1980. 13. 189; L. J. Stief, D. F. Nava. W. A . Payne, and J. V. Michael, J. Chcr~i.Phj:s.. 1980. 73, 2254. J. A. Silver and C. E. Kolb, C/wm f h j - s . Lett.. 1980,75, 191; K . J. Niemitz. H. Gg. Wagner. and R. Zellner, Z. PI7j.s. C/iuJ7., 1981, 124, 155. C . M. Stevens. L. Kaplan, R. Gorse, S. Durkee. M . Compton. S. Cohen. and K . Bielling, Irzt. J . Cheni. Kinrt., 1980, 12, 935. L. G . Anderson, J. f l 1 j . s . C l i m . . 1980, 84, 2 152. H . H . Nelson, W. J. Marinelli, and H . S. Johnston, Chern. Phjx. Lett., 1981. 78. 495. G. Paraskevopoulos and W. S. Nip, Ctnr. J . CIJPIJI.. 1980, 58, 2146; G . K . Farquharson and R. H. Smith. Airst. J. C / J W ~1980.33. ., 1425; J . V. Michael. D. F. Nava. R.P. Borkowski, W. A. Payne, and L. J. Stief. J . C/icv~i.f h j . s . , 1980. 73, 6108.

I58 Photochemistry halogenated derivatives 444 have been studied. Two recent determinations of the rate constants of process (36) ds a function of temperature in the region OH

+ H,O,

-

HO,

+ H20

(36)

245-460 K are in substantial agreement,',' but find values of k , , a factor of 2 higher at 298 K and factors of 3-5 higher at temperatures corresponding to 1030 km altitude than those previously accepted. The effect of these new values upon atmospheric modelling calculations is liable to be ~ o n s i d e r a b l e . Trajectory ~~ calculations upon the OH + H, surface have been carried out, with the effect of vibrational energy on product-state distribution and reaction enhancements evaluated.445The use of laser-induced fluorescence of the A-X transition in OH to monitor flame temperatures has been predissociation linewidths in the A 2 C + states have been calculated 447 and lifetimes of the B and C states of the radical measured.448 The first three-dimensional quantum mechanical calculations of triatomic photodissociation has been performed on H 2 0 , with calculated extinction coemcients in the region 130-1 35 nm agreeing well with experimentally observed features.449 Mechanistic 4 5 0 and kinetic 4 5 1 details of the reactions of HO, with itself 4 5 1 and with OH radicals 4 5 1 have been reported. 4503

N Atoms, N,, and NO,.-Resonance fluorescence methods have been used to study the reactions of ground-state N atoms (4S) with several molecular collision 4 5 3 The question whether N atoms react with unsaturated hydrocarpartners.452* bons has been raised. Removal rates of N(4S) by C,H4 have been seen to increase with N, pressure in time-resolved experiments, and the reaction is presumed to be third order;452at a total pressure of 3 Torr the calculated removal rate is however over two orders of magnitude larger than that estimated from flow-discharge and the discrepancy between these results, both using direct methods of N(4S) observation, remains unexplained. Energy partitioning in the NO product of the slow N(4S) + 0, reaction has been studied, with absolute values of the rate constants into vibrational levels u = 2-7 determined.454A minimum energy path calculation has been made for this reaction on quartet and doublet surfaces, with comparisons of experimental activation energies with theoretical barrier heights showing that reaction on the doublet appears to predominate.455The excitation rates of ground-state N atoms in collisions with Ar metastables have been determined,456and both quenching and reactions of

'" D. 445

44h JAi

448 449

45 I

452 453 454

455

'"

L. Singleton. G. Paraskevopoulos, and R . S. Irwin, J. Phys. Cliem., 1980, 84, 2339; G. Paraskevopoulos, D. L. Singleton, and R. S. Irwin, ihid., 1981, 85, 561. G. C . Schatz and H. Elgersma. Climr. Pli.v.7. Leif., 1980, 73, 21: G. C. Schatz, J . Clienr. P/r?9s.,1981, 74. 1133. c'. Chan and J . W. Daily, Appl. Opr., 1980, 19, 1963. M . L. Sink. A . D. Bandrauk, and R. Lefebvre, J . Cliem. P l i ? ~ .1980, , 73. 4451. T. Bergeman, P. Erman, and M. Larsson, Cliem. Pli?*s., 1980, 54, 55. E. Segev and M. Shapiro. J . Cli~wr.P h ~ s . .1980, 73, 2001. H . Niki, P. D. Maker, C . M. Savage, and L. P. Breitenbach, Clicwr. Pliys. krr.,1980, 73, 43. C. J. Hochanadel, T. J . Sworski. and P. J. Ogren. J . Pliys. Clrcm., 1980, 84, 3274. D. Husain and N. K . H. Slater, J . Clim. Soc., Frrrrirkij* Trrins. 2, 1980, 76, 606. J . V. Michael, Ciiem. Phys. Lcfi.. 1980, 76, 129. A. Rahbee and J . J . Gibson, J . CIiem. PA?..s.. 1981, 74, 5142. G. Das and P. A. Benioff, Cliem. P1iy.s. I,ctt.. 1980, 75, 519. L. G. Piper, M. A. A. Clyne, and P. B. Monkhouse, C l i ~ mPliys., . 1980. 51, 107.

Gas-phase Photoprocesses 159 ~ ~ e.s.r. ~ , ~detection ~ ~ of excited N atoms ( 2 D and ’ P ) have been s t ~ d i e d , with N(’D) being utilized for the first time in kinetic experiments.458 Measurements of the removal rates of N2(A3Z:,+)by various small molecules have been r e p ~ r t e d . ~ Modelling ~ ~ - ~ ~ lof the HgX(X = Br, C1) lasers requires knowledge of such rate constants, as the addition of N, to the mercury halide laser system is found to increase the efficiency and output energy by an order of magnitude, and the potential mechanism for this is dissociative excitation with HgX2.459 The energy-pooling reaction of reactions of N2(A3Zu+) 2N,(A3&,+) molecules has been shown to generate the near-i.r. Herman band system of nitrogen, yet the states linked by this transition have yet to be assigned.461The fluorescence decay behaviour of the N2(B31’I,)462 and (C3n,)463 states have been studied, and the mechanism for vibrational relaxation within the A2n,state of N 2 + has been shown to involve collision-induced transitions into and out of high vibrational levels of the X 2 Z , + ground state.464 Fine details of the effect of internal states of NO upon the cross-section for its reaction with 0, are starting to emerge.465.466 No dependence of the chemiluminescence yield of the NO2* product upon the electronic fine structure states of NO (21’1, and 2113,2) is 466 but an increase in rotational energy increases the cross-section appreciably: the development of molecular beam electric field focusing techniques is such that J and m, state-selected beams of NO are now able to be used in reactive studies.466Theoretical studies of the effects of vibrational energy in this reaction show no mode-specific enhancement of the cross-section for various model potential energy surfaces, although the presence of energy is more effective in overall vibration than in t r a n ~ l a t i o n . ~Lifetimes ~’ of the A , B, and D states of NO have been measured.468 In the multiple-photon ionization of rotationally cooled NO seeded in a molecular beam of He, high laser powers have been seen to produce appreciable line broadening Figure 5 shows the MPI spectra at high and low intensities in the beam, together with a high intensity spectrum from a room-temperature ‘bulb’ sample, both sets of spectra showing features due to the two-photon A 2 Z + t X211,(0, 0) transition, with the A state then ionized by further absorption. Rotational cooling is evident in the beam, and the broadening effect is seen to be absent in the ‘bulb’ sample of NO. An explanation offered for this is that in the presence of the laser field, low-energy NO-He collisions (similar to those 457 458 459

460

46’ 462

463 464 465

466 467 468 469

M. P. Iannozzi and F. Kaufman, J . Cliem. Pliys.. 1980, 73, 4701; K. Sugawara, Y. Ishikawa, and S. Sato, Bull. Chem. SOC.Jpn., 1980, 53, 3159. B. Fell, I. V. Rivas, and D. L. McFadden, J . Pliys. Chem., 1981, 85, 224. T. D. Dreiling and D. W. Setser. Chem. Pltys. Lett., 1980, 74, 21 1 . W. G. Clark and D. W. Setser. J . Pliys. Cliem., 1980, 84, 2225; L. G. Piper, G. E. Caledonia, and J. P. Kennedly. J . Cliem. Phys., 1981, 74, 2888. I. Nadler, D. W. Setser, and S. Rosenwaks, Cliem. Phys. Lett., 1980, 72, 536. N. Sadeghi and D. W. Setser, Cliem. PIiys. Lett.. 1981, 77, 304. E. I. Asinovskii, L. M. Vasilyak, and Y. M. Tokunov, High Temp., 1979, 17, 719. D. H. Katdyatna, T. A. Miller, and V. E. Bondybey, J . Chem. Phys., 1980, 72, 5469. S. L. Anderson, P. R. Brooks, J. D. Fite, and 0. V. Nguyen, J . Chem. P h p . , 1980, 72, 6521. D. van den Ende and S. Stolte, Chem. Pliys. Lett., 1980, 76, 13. S. Chapman, J . CIiem. Phys., 1981, 74, 1001. T. Hikida, S. Yagi, and Y. Mori, Cliem. Phys., 1980. 52, 399. (a) R. E. Demaray, C. Otis, K. Aron, and P. Johnson, J . Chem. Phys., 1980,72, 5772; (b) C. E. Otis and P. M. Johnson, Chem. Phys. Lett., 1981,83, 73.

160

Plz o tochemist rq’

I

4 52.2

I

I

I

452.4 Laser wavelength/ nm

Figure 5 ( a ) Multiple-photon ionizution spectruni qf’tlieNO A’C’ t X2111(0,0)hund at lou~ Iuser intensitl?in N tnolechr henm q f ” 0 seeded in He. This is (I two-photon resonance in N ,four-photon ionizution process ut this h e r wvelength. Onlj. three lines, representing AN = 0, I , and 2 trimsitions ure seen, indicating that the rotutional temperature in the heam is less thun I K . (b) Scan of the suine spec.trril region US (a) except NI higher loser power, showing broadening. (c) Room-temperature spectrum of pure NO in the same region with the same intensity as (b)showing laser resolution limited linewidths

reported earlier in beams of glyoxa13*and aniline87 in He) cause crossings between the potential energy curves of a real excited state and a two-photon ‘dressed’ state produced by the laser field. Subsequent experiments however have shown that AC Stark broadening rather than laser-enhanced collisions are responsible for this effect,469band its absence in the higher-pressure experiments [Figure 5(c)] is yet to be explained. Fluorescence spectroscopy of NO, has been used to determine the onset of predissociation in the and to measure the absolute cross-section for emission following monochromatic excitation at 532 nm,47 and the temperature dependences of both the NO, fluorescence spectral distribution and its collisional ”(’

C. H . Chen. D . W. Clark. M . G . Payne, and S. D. Kramer, Opt. C o m r n ~ t .1980, . 32, 391 C. S. Dulcey. T. J . McGee. and T. J. McIlrath. C h m . PItjx. Lcrt.. 1980. 76. 80.

161

Gus-phuse Photoprocesses

quenching behaviour have been measured.472 The dynamics of the photodissociation of NO, at 337 nm have been investigated by measurements of the energy distribution in the NO fragment using laser-induced fluore~cence.~'Figure 6 shows rotation-vibration population distributions for both for spin-orbit states of NO, with a strong vibrational population inversion apparent, and with rotational energies appearing non-statistical, with some evidence of a bimodal rotational of laser-induced fluorescence from photofragments d i s t r i b ~ t i o n .Detection ~~~ such as NO in this fashion can be a useful method for measurements of low concentrations of non-fluorescing molecular species.474 Electronically excited NO, (produced by absorption of Ar' radiation) abstracts tertiary H atoms directly from isobutane, with t-nitrobutane formed as the major product by subsequent reaction of the t-butyl radicals.475 Internal Energy Distribution "%IS

i

0,015

NO,+ hv -NOW

A,,,=

* n)+O(3p)

337.1 nm 0

0

I

0 0 0

I

0

Internal energy/cm-'

Figure 6 Population distribution of the NO-fragments (is a,function of the internal energy of their specific rotation-vibration states, produced by photodissociution of NO, ut 337.1 nm. Open circles denote the 2111, ground electronic state,jlled circles the 2n3,2 state

The photochemistry of the nitrate radical, NO,, needs to be incorporated into realistic models of the chemistry of the stratosphere: NO, arises mainly from the reaction of NO, with 0,, and its photolysis products can take part via reactions (37) and (38) in the photochemical cycles upon which the balance of stratospheric

NO,

+ hv

-

+ 0,

(37)

NO, + O

(38)

NO

ozone depends. Accurate measurements of the absorption cross-section are a first requirement, and a value of 1.21 x 10-'7cm2 at 294K at the absorption maximum, 663nm, has been derived from an experiment in which known

"'

D. G. Keil, V. M . Donnelly. and F. Kaufman. J . Clwni. P h ~ : s . .1980, 73. 1514. M . Geilhaupt, K . Meicr, and K . H. Welge, J . C/imi. Ph,vs., 1981, 74. 218. "' HM.. Zacharias, 0. Rodgers. K . Asai, and D. D. Davis, Appl. U p . , 1980. 19. 3597. M. E. Urnstead. J. W. Fleming. and M. C. Lin, IEEE J. Q w t i i u t ? i E k t r o t i . . 1980, 16. 1227.

162 Photochemistry concentrations of NO, were quantitatively converted into N 0 3 . 4 7 6Processes (37) and (38) have photochemical thresholds at wavelengths of 8 pm and 580nm, respectively,476 and their relative rates by solar photolysis over the wavelength region 470-700 nm favour process (38) by a factor of 10 over (37), the quantum yield of 0 atoms being close to unity at wavelengths below 580nm.477In the photodissociation of N,O at vacuum-u.v. wavelengths, excited-state NO (B21T) and N, (B311) products have been observed, and their quantum yields and mechanisms of formation investigated.478

-

SO, and COX.-Collision-induced rotational relaxation within the 2' A , excitedstate manifold of SO, has been studied.479,480 Excitation of single rovibronic levels of the 2 state near 304.3nm yields single exponential decays, in contrast with previous reports of double exponential decay behaviour when broader band excitation sources were used. Interference from the underlying continuous ' B , state appears to be the cause of the latter behaviour, and narrow band excitation can remove this problem.479Total removal rates of the selected levels by SO, have cross-sections of 500 state-to-state rotational energy transfer crosssections of 50 A' are observed, with dipole-like propensity rules (AKa = 1) occuring from these collision processes.48o Near-u.v. emission from SO, has been seen following infrared multiple-photon absorption by the ground-state molecule, with subsequent 'inverse electronic relaxation', possibly assisted by collisions, populating the $ A , and BIB, emitting states.481 Excitation of CO in the A'n(v' = 13) t-X'C+(v" = 0) transition has been accomplished using tunable V.U.V.radiation at 123 nm produced by frequency tripling the output of a dye laser in Kr gas. The production of the excited state was detected by its subsequent ionization to form CO+ at 266 nm.482Lifetimes of the d3A state of CO have been measured by a delayed coincidence A method of calculating bound-free Franck-Condon factors has been applied to the photodissociation of C02;484reactions of ground-state C,O (Z3C-) with NO, O,, and isobutene have been studied using time-resolved laser-induced fluorescence to monitor the radical concentration^.^^^

- -

*

10 Miscellaneous Rotational relaxation within the first excited states (A'C,') of Li, 486 and Na, 4 8 7 has been studied with several collision partners. For Li,, a strong asymmetry in the ratios of cross-sections for upward and downward AJ changes is observed,486 in contrast to the Na, work, in which little dependence of this kind is seen.487 A

'" D. N. Mitchell, R. P. Wayne, P. J. Allen, R. P. Harrison, and R. J . Twin, J . Chiwt. Soc., Formk/!Tucrns. 2 , 1980. 76, 785. 47'

F. Magnotta and H. S. Johnston. Geoplij-s. Rc~s.Lett., 1980, 7, 769. 478 I. P. Vinogradov and V. V. Firsov, Higli Eticrgj. Clietn., 1980, 14. 16. 479 D. L. Holtennann, E. K . C. Lee. and R. Nanes, Cl7en7. Plys. Lctt., 1980. 75, 91. D. L. Holtermann, E. K . C. Lee, and R. Nanes, Clrrwi. Pl7j.s. L c r r . . 1980. 75, 249. G. L. Wolk. R. E. Weston, jun., and G. W. Flynn, J . Chc~rti.Phj-s., 1980, 73, 1649. 482 H. Zacharias, H . Rottke, and K . H. Welge, Opt. Comrnun., 1980, 35. 185. W. C . Paske. J . R. Twist, A. W. Garrett, and D. E. Golden, J . Cliem. Pliys., 1980, 72, 6134. 4H4 K . C. Kulander and J. C. Light, J . Cliuti. P/7j-x., 1980, 73, 4337. V. M . Donnelly, W. M . Pitts, and J . R. McDonald. Clw77. Phys., 1980, 49, 289. 4 X h Ch. Ottinger and M . Schroder, J . PAjx. B , 1980, 13. 4163. '" T. A. Brunner, N. Smith. A. W. Karp. and D. E. Pritchard. J . C h m ~Phrs., . 1981. 74. 3324.

'"

Gas-phase Photoprocesses 163 simple exponential energy-gap dependence of the cross-section is found to be inadequate in explaining the data in both m o l e c ~ l e s4,8 ~7 and ~ ~ ~empirical scaling laws have been reported, which fit a large range of experimental results extremely For the C'll and D ' n states of NaK, energy transfer from single rotational levels has been studied using polarized laser fluorescence, and crosssections have been measured for transfer of orientation as well as population;488 the former is believed to be a valuable indication of anisotropy in the intermolecular potentials. Collisional effects determining the internal energy distributions in ground-state Na, expanded in a low-pressure free jet of sodium vapour have been determined.489 A Boltzmann distribution is observed at the nozzle exit, yet deviations from this occur downstream, indicating that relaxation processes away from the nozzle are of importance. Dissociation and predissociation of alkali-metal dimers in one-490-492 and two-photon 493 absorption processes have been investigated experimentally 490, 49 493 and t h e ~ r e t i c a l l y .The ~ ~ ~fluorescence from Na('P,) atoms formed in the dissociation of Na, via excitation of the B'n, c X'&+ transitions is found to be polarized,490 and its magnitude and direction (with respect to the electric vector of the laser beam) are in accord with earlier theoretical predictions of this effect. Predissociation products from the C and D states of Rb2491and from the states reached by two-photon absorption in Csz 493 have been identified. Emission in the d3n1-a3C+494 and D'rI-a3Z+ 495 bands of NaK has been analysed spectroscopically, and comparisons have been made between observed and calculated emission bands of LiCa 496 (produced in the reaction between Ca atoms and electronically excited lithium dimers). Bound-free transitions in alkalimetal dimers have been i n v e ~ t i g a t e d , ~and ~ ' dispersed laser-excited fluorescence used to obtain rotational and vibrational constants for the ground states of the monohydrides and deuterides of sodium and potassium.498 Rotational relaxation studies have been carried out on BaO radicals in the A 'Z+ with scaling laws again developed for the rates of rotational redistribution brought about by collisions with Ar and CO,, and simultaneous measurements of line-shapes in the C'C+ t A ' C + transition have allowed the centre of mass scattering angle distribution, brought about by velocity changing collisions, to be characterized. Collisions with CO, cause significantly smaller angle scattering than do those with Ar, although for both species scattering is predominantly forward in the centre of mass frame. Small changes in rotational quantum number J result in small centre-of-mass deflection angles and larger 3 '

488

489

490 491

492

493 494

495 496

497 4y8 499

J . McCormack and A. J. McCaffery, Cliem. Phys., 1980, 51. 405. F. Aerts and H . Hulsman, Chem. Phys. Lett.. 1980, 72,237. E. W . Rothe, U. Krduse, and R. Duren, Chem. Phys. Lett., 1980, 72, 100. E. J. Breford and F. Engelke, Cliem. Pliys. Lett., 1980, 75, 132. T.Uzer and A. Dalgarno, Chem. Pliys.. 1980, 51, 271.

C. B. Collins, J. A. Anderson, D. Popescu. and I. Popescu, J . Cliem. Plips., 1981, 74, 1053, 1067. H . Kato and C. Noda, J . Chem. Pliys., 1980. 73,4940. C. L. Chi0 and H . Chang, Cheni. P l i j ~ Left., . 1980, 73, 167. D.K. Neumann. D. J. Benard, and H . H. Michels, Chem. Pltys. Lett., 1980, 73, 343. J. Tellinghuisen, G. Pichler, W. L. Snow, M. E. Hillard, and R. J. Exton, Chem. Pliys., 1980,s. 3 13; D. D. Konowalow and P. S. Julienne, J . Chem. Phys., 1980, 72, 5815. M. Giroud and 0. Nedelec, J . Cliem. P l y . , 1980, 73,4151. R. A. Gottscho, R . W. Field, R . Bacis, and S. J. Silvers, J . Cliem. Pliys., 1980, 73, 599.

Pho t o c h i v I~is trj*

164

changes in J result in large deflections, implying that these distinct processes are controlled by the long- and short-range parts, respectively, of the intermolecular potential.499 The radiative lifetime of the C'C' state BaO has been measured as 10.5 1 n ~ ; ~ ' 'similar measurements on the A2n states of BO, and BO 5 0 1 have been reported. The 147 nm photolysis of Si,H, has been carried out by classical photochemical technique^."^ Three primary processes are suggested, all of which result in the formation of H atoms, and of which reaction (39) has the largest quantum yield 5 0 1 3 5 0 2

Si,H,

+ hv

-----+

SiH,

+ SiH, + H

(39)

(@ = 0.61). The U.V. photolysis of PH, has been reinvestigated, with the

formation of P,H4 (from PH, recombination) in the subsequent chemical reactions emphasized, particularly with respect to its role in the photochemistry of the atmosphere of Jupiter.504 Laser-induced fluorescence studies of PbS have produced lifetimes for the A , a, and B state^;''^ linewidth measurements on the C10, J2A2t f 2 B , transition have been used to study the predissociation mechanism as a function of spin and rotational angular momentum, and vibrational quantum numbers. 506 Laser transitions operating with the ' S state of Se as the upper level are currently of interest, as the possibility of storing considerable amounts of energy in this optically metastable state implies that high-power pulsed output on the ' S - ' D , and ' S - , P , transitions at 776.8 and 488.7nm will result. Photolysis of OCSe at 172nm forms Se('S) with a quantum yield of 0.63.507 Substantial quantities of free electrons are formed [by photoionization of Se('S)] and these quench the ' S state extremely rapidly (at a rate constant of 1.2 x l0-'cm3 molecule- s-');~'' this undesirable effect can be controlled by addition of SF6,507q which itself undergoes an efficient electron-attachment process. Laser output on both transitions corresponding to 0.3 photons per OCSe molecule in the irradiated volume has been achieved.508 At 193nm, the Se('S) quantum yield is lower (0.25) 5 0 9 but this wavelength may be a more suitable one for OCSe photolysis, as the ArF laser is more efficient than the Xe,* 172nm source, and photoionization of Se('S) is not possible at 193 nm. Substantial formation of one of the lower lasing levels t 3 P 1 )is found (a = 0.25) but this can be rapidly removed by quenching collisions with CO or C0,.509 Lifetime and quenching behaviour of SeO, excited at 288.8 nm has been reported."' The spectroscopic and kinetic behaviour of rare-gas excimer states have been studied in some detail. Rapid quenching of He,(a3C,+) by several collision

'*

500 50 I

503 504

5"5

'07

'')' 50y

'lo

Y. C. Hsu. B. Hegemann, and J . G. Pruett, J . C'heni. P / i . ~ x 1980, . 72, 6437. M . A. A. Clyne and M. C . Heaven, Client. Phj-s., 1980, 51, 299. S. McIntosh. R. A. Beaudet, and D. A. Dows, Ckem. P/ij.s. Lett., 1981, 78, 271. G. G. A . Perkins and F. W. Lampe, J . A m . Cliiwt. Soc.. 1980, 102, 3764. J. P. Ferris and R. Benson, J . An?. CAiwi. Soc., 1981, 103, 1922. 9. Burtin, M . Carleer, R. Cocin, C . Dreze. and T. Ndikumana, J . PIiys. B . 1980, 13, 3783. S. Michielsen, A. J. Merer. S. A. Rice. F. A. Novak. K . F. Freed, and Y . Hamada, J . Chm7. PIij~s., 198I , 74, 3089. W. M. Trott, J . K . Rice, and J. R. Woodworth, J . Chem. Pliys., 1981, 74, 518. H . T. Powell and 9. R. Schleicher, J . Chetn. Phj-s.. 1980, 73, 5059. M . J . Shaw, M. C . Gower, and S. Rolt, Cliiwt. PIiys. Lett., 1980. 73, 478. A . W. Miziolek. Climi. Phys. Lett., 1980, 74, 32.

Gus-pliuse Ph o t cipr oc ~ ~ s s e . s

165

partners has been quantitatively o b ~ e r v e d ,*~high excited Rydberg states (11 < 25) of He, have been found by absorption from the CI state and detected by collisional or autoionization processes,512and the kinetics of removal of the He2(d3X:,') state by He have been studied.513Neon,"4 k r y p t ~ n , " ~ and " xenon 5 1 5 b dimers have received spectroscopic 4- 5 1 5 h and kinetic 5 u attention. Exciplexes of MgXe j 1 and CdHg 5 1 7 have been investigated with the aim of determining their potential as candidates for lasing action: neither appears promising owing to the large excitation energies needed to produce the Mg* excited-state precursor^,^ and to absorption of potential lasing wavelengths by the upper ( a )CdHg state,5l 7 respectively. Green emission produced in the pulsed excitation of Hg-N, mixtures at 253.7 nm has been ascribed to the Hg3* species, and its spectroscopy and kinetic behaviour have been investigated experimentally. Considerable research effort is presently directed towards the photodissociation of metal carbonyls, partially because population inversions and laser action has been achieved upon the atomic metal vapours formed. The mechanisms of the fragmentation processes are naturally of interest. For Fe(CO),, irradiation at 248 nm produces Fe(CO),, Fe(CO),, and Fe(CO), from single-photon absorption at fractional yields of 0.55,0.35, and 0. 1 , 5 1 9 and it is thought that at this and other wavelength^,^^' sequential loss of CO from highly internally excited fragments formed results in the observed products. The intensity and spectral distribution of Fe* fluorescence produced by multiplephoton absorption of 248 nm radiation in Fe(CO), is highly dependent upon conditions of excitation, and could explain the varying results obtained in different laboratories.521The detection of metal atoms by multiple-photon ionization following their production by multiple-photon dissociation of volatile precursor molecules is now a common technique, and has been reported for the Fe,522Cr,523W,523and Mn 5 2 4 carbonyls, f e r r ~ c e n e ,5~2 5~ ~ . and n i ~ k e l o c e n e . ~Plasma ,~ formation has been seen in the C 0 2 laser irradiation of Fe, Ni, and Cr c a r b o n y l ~ . ' ~ ~ The effect of non-resonant laser fields upon the cross-section for simple chemical reactions ('laser-assisted collisions') is currently of theoretical interest,527- 5 3 0 and 511

512

'I3 '14 515

516 'I7

'I9 ''O

'" '" '" '" 523

52b

''' 529

530

S. Takao, M. Kogoma. T. Oka, M. Imamura. and S. Arai, J . Cli~~nt. P l i j x . . 1980, 73, 148. R. Panock, R. R. Freeman, R. H. Storz, and T. A. Miller, Cltem. Pltj*.s. Lett., 1980, 74, 203. J. W. Parker, L. W. Anderson, W. A. Fitzsimmons, and C. C. Lin, J. Client. Pltjs., 1980, 73, 6179. Y. Tanaka and W. C. Walker, J . Clieni. Pli.rs., 1981, 74, 2760. ((1) Y. Salamero. A. Birot, H. Brunet, H. Dijols, J. Galy, P. Millet. and J. P. Montagne, J. Clieni. P I y . , 1981,74,288; ( b )0. Dutuit, M. C. Castex, J. Le Calvt, and M. Lavollee, ibid., 1980,73. 3107. L. Schumann, D. Wildman, and A. Gallagher, J. Clteni. Phj*s., 1980, 72. 6081. M. W. McGeoch, J. Clteni. Pl~ys.,1980, 73, 2534. A. B. Callear and D. R. Kendall, Cltem. Pltys., 1981, 57, 65. G . Nathanson, B. Gitlin, A. M. Rosan, and J. T. Yardley, J. Ciiem. Phys.. 1981, 74, 361. J. T. Yardley. B. Gitlin, G. Nathanson. and A. M. Rosan, J. Cliem. Pltj,s., 1981. 74, 370. J. Krasinski, S. H. Bauer, and K. L. Kompd, Opt. Contniun., 1980, 35, 363. P. C. Engelking, Clteni. Pl1y.s. Lett.. 1980, 74, 207. D. P. Gerrity, L. J. Rothberg, and V. Vaida. Clieni. Plijx Lett., 1980, 74, 1. L. J. Rothberg. D. P. Gerrity, and V. Vaida, J . Cltem. P l t j x , 1981, 74, 2218. S. Leutwyler, U. Even, and J. Jortner, Cliem. Pltys. Lett., 1980, 74, 1 I . Y. Langsam and A. M . Ronn, Cheni. Ph?~s.,1981, 54, 277. I. H. Zimmerman. T. F. George. J. R. Stallcop. and B. C. F. M. Laskowski, Clieni. Pliys.. 1980, 49, 59. J. Weiner, J. Chenr. Pltys., 1980, 72, 5731. A. E. Ore1 and W. H. Miller, J . Cltem. Phys., 1980, 73, 241. M. Crance and S. Stenholm. J . Pl1j.s. B . 1980. 13. 1563.

166

Photochemistry

calculations upon the predicted enhancements for several systems have appeared, for example Br + H 2 , 5 2 7Hg + C12,528and H + LiF.529Clear experimental evidence for such processes is difficult to obtain, but this does seem to have been achieved for reaction (40).531The channel to form electronically excited HgBr K

+ HgBr,

-

KBr

+ HgBr

(40)

(B2C') becomes energetically feasible if energy corresponding to a photon of wavelength < 606 nm is added to the system. In the presence of 595 nm laser light, emission attributed to the HgBr(B) state is seen, despite the fact that neither reagents nor products absorb at this wavelength, and the cross-section for this process is estimated to be -10-'7cm2 at a laser intensity of ~ M W C ~ ~ ~ Experiments of this kind may provide direct details of the properties of the transition state for a chemical reaction: an alternative approach is to observe the effects of 'pressure broadening' of a spectroscopic transition in an atom or molecule formed by chemical reaction as it is in the vicinity of its co-product. For reaction (41) such an effect has been observed.532D-line emission from Na(2P)

F

+ Na,

-

FNaNa* ------+ I

I

h(a)

NaF I

+ Na(32P)

(41)

I

-

Figure 7 Spectral distribution of the radiation in the wings of the sodium D lines (589.0 and 589.6nm) recorded a1 a total D line intensity IN=*of'(2.4 0.2) x 106countss-'. Each lo point on the wing represents -3QQcounts repeated once or twice: error bars give iieviution. Intensities Icere corrected fbr instrument sensitivity

-

53'

P. Hering, P. R. Brooks, R. F. Curl,jun., R. S. Judson, and R. S. Lowe, Phys. Rev. Lett., 1980, 44, 687.

532

P. Arrowsmith. F. E. Bartoszek, S. H. P. Bly, T. Carrington, P. E. Charters, and J. C. Polanyi, J . Clwni. Plij*s., 1980, 73, 5895.

Gus-phuse Photoprocesses 167 formed is seen to be considerably broadened, the wings of the emission profile extending asymmetrically to several tens of nm on either side of the pure atomic transitions, as can be seen from the data of Figure 7. In principle this provides information upon the relative position of the emitting FNaNa* and the lower FNaNa states on the potential energy surfaces connecting reagents and products.532 Laser-induced predissociation in the presence of a surface magnetic field,533and dissociation dynamics in the presence of an intense laser field 5 3 4 have been treated theoretically. The dynamics of unimolecular decomposition and its relation to statistical theories of energy partitioning in fragments have been investigated. 5 3 5 The effect of reagent vibrational energy on the addition reactions between hydrogen halides and unsaturated hydrocarbons has been calculated: HX vibration is found to enhance the reaction probability, but not to an extent that suggests full utilization of the energy in overcoming the activation barrier.536 A threedimensional quantum treatment of vibrational predissociation in van der Waals molecules has been de~cribed,’~’theories have been proposed to explain intramolecular vibrational energy transfer in statistical 5 3 8 , 5 3 9 and intermediate 5 3 8 case molecules, and a review of laser-induced photoionization has appeared.540

533 534 535

53h 537 538

539 540

D. K. Bhdttacharyya, K . S. Lam, and T. S. George, J . Chem. Phys., 1980, 73, 1999. J. Weiner, Chem. Pliys. Lett., 1980, 75, 241; A. D. Bandrauk and M. L. Sink, J . Client. Phys.. 1981, 74, 1110. B. A. Waite and W. H. Miller, J. Ciiem. Phys., 1980, 73, 3713; ibid., 1981, 74, 3910. E. Zamir, Y. Haas, and R. D. Levine, J . Chem. Phys., 1980, 73, 2680. J. A. Beswick and A. ReqUend, J. Chem. PhJs., 1980,73, 4347. K. F. Freed and A. Nitzan, J . Ciiem. Phys.. 1980, 73, 4765. S. Mukamel and R. E. Smalley, J . Chem. Phys., 1980, 73, 4156. V. S. Antonov and V. S. Letokhov, Appl. Pliys.. 1981, 24, 89.

Part 11 PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS

1 The Photochemistry of Transition-metal Complexes BY A. COX

1 Introduction Topics, which have formed the subjects of reviews this year, include the luminescence kinetics of metal complexes in solution, photochemical rearrangements of co-ordination compounds,2 photochromic complexes of heavy metals with diphenylthiocarbazone derivative^,^ the photochemistry of actinide^,^ actinide separation processes,' and light-induced electron-transfer reactions in solution and organized assemblies.6 A discussion has also appeared on assigning excited states in inorganic photochemistry.'

2 Titanium

Hydrogen has been reported to be formed together with Ti'" compounds on irradiation of aqueous-EtOH solutions of Ti'" at wavelengths greater than 3 10nm. In C,D,OH, equimolar amounts of H, and D, were produced.' Ti'" compounds also arise on photoreduction of Ti(OR),, R = alkyl, in the presence of a r n i n e ~ . ~ 3 Vanadium Following excitation of the CT bands at 313 nm, quantum yields of photoreduction and fluorescence have been obtained for the V" alcoholates of MeOH, EtOH, and PrOH. Absorption, emission, and excitation spectra of the V"' alcoholates are presented and the photochemical reaction mechanism and emission processes of V"' alcoholates are discussed.l o Low-temperature experiments have shown" the existence of radical transients in the formation of V" by photolysis of aqueous VCl, in alcoholic solvents. These transients are the products of one-electron oxidation of the alcoholic ligand in the V"-HOR complex. The

' ' * lo

T. J. Kemp, Prog. React. Kinet., 1980, 10, 301. F. Scandola, Org. Chem., 1980, 42, 549. A. Fabrycy and J. Soroka, Wiad. Chem., 1980,34,47. L. M. Toth, J. T. Bell, and H. A. Friedman, ACS Symp. Ser., 1980, 117, 253. G. L. Depoorter and C. K. Rofer-Depoorter. ACS Symp. Ser., 1980, 117, 267. D. G. Whitten, P. J. DeLaive, T. K. Foreman, J. A. Mercer-Smith, R. H. Schmehl, and C. Gianotti, Sol. Energy: Chem. Convers. Storage,[Symp.], ed.,R. R. Hautala, B. R. King, and C. Kutal, Humana Press Inc., Clifton, N.J, 1978, p. 117. A. W. Adamson, Gov. Rep. Announce. Index (U.S.), 1981,81, 61. I. A. Potapov, M. B. Rozenkevich, and Yu.A. Sakharovskii, Koord. Khim., 1981,7, 229. I. Kijima, Jpn. Kokai Tokkyo Koho. 1980,80, 139 392. Y. Doi and M. Tsutsui, Fundam. Res. Homogeneous Catal., 1979, 3, 859. B. V. Koryakin and T. S. Dzhabiev, Izv. Akud. Nuuk SSSR, Ser. Khim., 1980, 1769.

171

172 Photochemistry oxalato-vanadium(Ir1) complex, V(C204)2- is reported to sensitize the decomposition of oxalic acid in aqueous solution at 254nm, giving C 0 2 and CO as products. Following CT excitation, V" and the oxalate radical are produced and the latter decomposes to the formic acid radical, which is then reduced by V" to CO. A study l 3 of the mechanism of phototransformations of co-ordination compounds of vanadium in alcohol solutions has shown the existence of a stepwise redox process involving reduction of the metal atom and oxidation of solvent molecules. Trichloro-oxovanadium undergoes a similar phototransformation in alcoholic media,', and at low temperature a V"' compound is stabilized. Photolysis of VO(OR),, R = Me, Et, Pri, Pr, Bu, and amyl, brings about reduction only to the V"' level. l 5 This observation contrasts with the behaviour of chlorine-containing complexes and is a result of the greater tendency of the alkoxides to associate. Following photoreduction, the products derived from the alkoxides are more easily reoxidized by 0, than those containing C1. The effect of alcohol additives on the photoreduction of Vv ions and the liberation of hydrogen from aqueous solution has been examined,16 and found to decrease in the order Pr'OH > EtOH > PrOH > MeOH > Bu'OH. Irradiation of ethanolic solutions of acetylacetonate complexes of vanadium of the type VO(acac),OEt brings about two-electron reduction of the Vv ion.'' At shorter wavelengths (Airr = 254nm), ligand substitution occurs in CCl, to give VO(acac),Cl. This undergoes further photoreduction by visible light to VO(acac),. 4 Chromium

Measurements have been made of the room-temperature luminescence quantum yields of various Cr"' ammine and ethylenediamine complexes in water. l 8 Most emission was phosphorescence, but some fluorinated complexes emitted delayed fluorescence.The range of quantum yields was accounted for in terms of processes degrading the 2E state. Radiationless decay rates for the 4T2g + 4A2gtransition have been obtained for several Cr"' compounds in different glassy hosts and these have revealed a discrepancy in the 4T2g behaviour between crystals and glasses.l 9 It is suggested that this has its origin in the Cr"' site symmetry. The solid-state emission lifetimes of deuteriated and undeuteriated [Cr(NH3),I3 and [Cr(en),13 have been used as a probe to study the back intersystem-crossing deactivation pathway for these compounds.20 General agreement is found between the evidence presented and recent suggestions concerning a direct photochemical role for the 2 E state. Measurements of the temperature dependence of the +

+

'

l2

'' l4

l5 l6 l7

l9

2o 21

A. Matsumoto, H. Kumafuji, and J. Shiokawa, Inorg. Chim. Acta, 1980, 42, 149. A. I. Kryukov, S. Ya. Kuchmii, A. V. Korzhak, Z . A. Tkachenko, and V. A. Il'yushenok, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim., 12th, 1977, p. 218. A. V. Korzhak and S. Ya. Kuchmii, Tezisy Dokl. Resp. Konf. Molodykh Uch. Khim., 2nd, 1977, p. 31. S. Ya. Kuchmii and A. I. Kryukov, Ukr. Khim. Zh.. 1980, 46, 1052. I. S. Shchegoleva, S. Ya. Kuchmii, T. I. Serdyukova, and A. I. Kryukov, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim., 12th, 1977, p. 226. S. Ya. Kuchmii, A. M . Turchaninov, and A. I. Kryukov, Ukr. Khim. Zh., 1980,46,806. A. D . Kirk and G. B. Porter, J . Phys. Chem., 1980, 84, 887. L. J. Andrews, A. Lempicki, and B. C. McCollurn, Chem. Phys. Lett., 1980, 74, 404. N. A. P. Kane-Maguire, G. M. Clonts, and R. C. Kerr, Inorg. Chim. Acta, 1980, 44, L157. R. Fukuda, R. T. Walters, H. Macke, and A. W. Adamson, J . Phys. Chem., 1979, 83, 2097.

173 The Photochemistry of Transition-metal Complexes luminescence lifetimes of Cr"' complexes have been made in various media.22 These have enabled an expression to be developed for the rate constant of the luminescence decay. The activation energy of the temperature-dependent nonradiative term was found to be strongly solvent-dependent and this has lead to a chemical mechanism being suggested for deactivation of the 2E,state rather than simply accounting for it in terms of back intersystem-crossing. In another study, luminescence, time-resolved luminescence, and decay-time measurements over the range 4-100 K have enabled the exchange interaction parameters in several trinuclear Cr"' complexes of the type fCr,O(RCOO),(H,O),]X .nH,O (R = Me or Et) to be determined.23 Pulsed laser conductivities have been used 24 to study the photobehaviour of [Cr(en),13'. The method depends on measuring conductivity changes associated with reaction (1) following laser excitation. This is a new [Cr(en),(en)(H,0)I3+

+ H+

___+

[Cr(en),(enH)(H,O)l4+

(1)

approach and may be generally helpful in avoiding complications with excitedstate absorption. In a series of Cr'"-alkylamine complexes with CrN, skeletons, a correlation has been shown to exist between the radiationless transition rate and the number of active hydrogens attached to the donor atoms.25 The authors also report an expression that predicts the dependence of the non-radiative rates from the vibrational degeneracy and the displacement of the maximum frequency modes. A new formalism, namely bond indexes, Z(ML) has been developed which explains photolabilization and photosubstitution reactions of some hexacoordinated complexes of transition metals such as Cr, Co, and Rh. These bond indexes have been applied to ground and excited states, and the rule established that the leaving ligand is the one characterized by the smallest value of the bond index I*(ML). In the complex trans-[Cr(en),NCSF]+, thiocyanate photoaquation is quenched in parallel with the emission, and (en) photoaquation is quenched in a wavelength-dependent manner. " The differential quenching suggests participation by two quartet ~ t a t e s , ~and E 4B,together with some doublet participation, and accords with theoretical predictions as well as with known behaviour in other systems. The quantum yield of photoracemization of [Cr(en),I3+ has been found to be independent of pH. Although some of the data obtained suggest that the twist mechanism of photoracemization might be preferred, it has not proved possible to discriminate definitively between this and the bond-rupture mechanism.28 In aqueous HC1 solutions, irradiation of [Cr(en)J3 or [Cr(NH,Me),13 is reported to lead to substitution of one ligand by water.*' Photoaquation also occurs in

',,

+

22

23 24 25 26

2'

29

+

S. R. Allsopp, A. Cox, T. J. Kemp, W. J. Reed, S. Sostero, and 0.Traverso, J . Chem. SOC..Faraday Trans. I , 1980, 76, 162. M. Morita and Y. Kato, In?. J . Quantum Chem.. 1980,18, 625. W. L. Waltz, R. T. Walters, R. J. Woods, and J. Lilie, Inorg. Chim. Acta. 1980, 45, L153. K. Kuehn, F. Wasgestian, and H. Kupka, J . Phys. Chem., 1981, 85, 665. L. G. Vanquickenborne and A. Ceulemans, Inorg. Chem., 1981, 20, 110. A. D. Kirk, L. A. Frederick, and S. G. Glover, J. Am. Chem. SOC.,1980, 102, 7120. M. C. Cimolino, N. J. Shipley, and R. G. Linck, Inorg. Chem., 1980, 19, 3291. Yu. N. Shevchenko, V. A. Krasnova, A. A. Svezhentsova, V. V. Sachok, and A. I. Kryukov, Zh. Neorg. Khim., 1980, 25, 1834.

174

Photochemistry

NaClO,-HClO, solutions. By contrast, however, photolysis of [Cr(en),]' in aqueous HCl-KCl results in formation of cis-[Cr(en),Cl,]+. Irradiation of trans-[Cr(en),FiJ in aqueous solution gives [Cr(en)(enH)(H20)F2l3+, plus an isomer of [Cr(en)(enH)(H,0)F,l3 and cis-[Cr(en),F(H,0)J2+, of which the first is the dominant product.30 Thus, although the net stereochemistry of the starting material is retained, there is still some stereochemical inversion. These results appear to be in conflict with those of other workers.31 The products obtained from the photoaquation of trans-[Cr(NH,),F,I2 are consistent with the edge-displacement model and also with recent suggestions invoking a dissociative symmetry-restrictedphotoprocess.32 Results obtained in a similar investigation of the cis-isomer are consistent with only the symmetryrestricted photoreaction. A study has been made 3 3 of the ligand-fieldphotolysis of [Cr(tren)F,]+ in acidic solution, and release of F- is found to occur with a quantum yield of 0.21. the same aquofluoro isomer is formed in this process as is generated in the acid- or base-catalysed thermal reaction, and it is concluded that the photochemistry of this complex does not fit the current theoretical models of LF photochemistry of d3 centres. Under the stimulus of interest in the photoactive excited state of a Crnr C,, complex, the ligand-field photochemistry of [Cr(NH,),(CN)12 + has been examined in acidic solution.34 Aquation of NH, occurred and CN- was released thermally. Adamson's rules and other theoretical models were found to be helpful in interpreting these observations, and the product distribution suggests that equatorial photoaquation takes place with partial stereochemical change. The role of the doublet state in the photochemistry of Reinecke's ion, trans-[Cr(NH,),(NCS),] - ,continues to stimulate interest. It has now been tentatively suggested35 for Reinecke's ion itself, and indeed for Cr"' ammine complexes generally, that the doublet state disappears by chemical reaction rather than by intersystem crossing to the first quartet thexi state. The photochemistry of trans-Cr(tfa), has been studied in non-aqueous solvents by both continuous and flash experiment^.^^ For Airr >, 366 nm the dominant process is trans --+ cis isomerization, whereas at iirr = 254nm both isomerization and redox decomposition occur, being markedly solvent dependent. The existence of the photoredox process suggests at least a qualitative similarity between the photochemistry of this complex and that of other first-row transitionmetal b-diketonate complexes. Photoinduced bridge-cleavage has been reported for the rhodo complex [Cr(NH,),0HCr(NH3)5]C15 in acid solution at 254nm. A model is suggested in which all of the photoreactions arise from the CT state or the third quartet state, L,. The quantum yields of photolysis of [Cr(NH,),I3' in 1 0 ~ aqueous NaOH at 77 K and 365 or 436 nm have been observed to decrease with continued irradiation.,* However, warming the solution briefly to the devitrification temperature, restores the quantum yields to their original value. It is +

+

+

+

,

30 31

32 33 34

35

36

37 38

S. C. Pyke and R. G. Linck, Inorg. Chem., 1980, 19, 2468. M. F. Manfrin, D. Sandrini, A. Juris, and M. T. Gandolfi, Inorg. Chem., 1978, 17, 90. A. D. Kirk and L. A. Frederick, Inorg. Chern., 1981, 20, 60. M. J. Saliby, P. S. Sheridan, and S. K. Madan, Inorg. Chem., 1980, 19, 1291. P. Riccieri and E. Zinato, Inorg. Chem., 1980, 19, 3279. A. W. Adamson and A. R. Gutierrez, J. Phys. Chem., 1980,84, 2492. C. Kutal, D. B. Yang, and G. Ferraudi, Inorg. Chem., 1980, 19, 2907. R. R. Ruminski and W. F. Coleman, Inorg. Chem., 1980, 19,2185. A. Kh. Vorob'ev and V. S. Gurman, Kinet. Katal., 1979, 20, 1439.

The Photochemistry of Transition-metal Complexes

175

believed that this is because some ions which absorb light do not undergo a photochemical reaction because of their particular environment. There is still widespread interest in the photochemistry of [Cr(bipy),13 + and related complexes. The ' E and 4T, electronic excited states of this complex have been studied by Raman scattering in aqueous solution.39Similarities were noted between the 2E and ground-state spectra, but differences between the intensities and shifts of corresponding vibrational Raman bands of 4T2 and 4A, [Cr(bipy),13+ are more pronounced. The 4T2 -+ ' E intersystem-crossing rates have been determined using photoaquation quantum yield data for the two complexes [CrL313+,(L = bipy and 1,lO-phen) and both were found to be approximately unity.40 This result is in agreement with that obtained by KaneMaguire and Langford 41 from oxygen-quenching studies of the photoracemization of optically active [ C r ( ~ h e n )+. ~ ]The ~ values of for [Cr(bipy),13+ in H,O and D 2 0have been determined as 1.O and 0.23 with no change being noticed in the lifetime of the emitting state.42These results are taken to imply a change in the efficiency of the intersystem crossing from 4Tz,and is thought to arise from the rigidity of the phen ligands, which reduces the distortion of the 4T, state. Formation of thermally equilibrated Cr"' excited state and formation of Cr" have now been shown to be competitive processes that occur following irradiation of polypyridyl complexes of Cr" in alcoholic media.43The Cr' complexes arise as a result of oxidation of the solvent by the upper excited state and this kind of solvent-dependent photoredox process has now been found in various coordination complexes. Evidence has also appeared for the existence of a Cr" intermediate in the photolysis of [Cr(bipy),13 in DMF.44 An autocatalytic reaction is implicated in which a Cr"-bipy complex acts as the chain carrier. Luminescencequantum yields and a wavelength dependence have been reported 45 for the photohydrolysis of [Cr(bipy)J3+ over the wavelength range 488.0610.0nm. At about 590nm a crossover appears to exist at which disc decreases. The rate of ISC must, therefore, be fast enough to compete with relaxation within the quartet manifold, and at long wavelength the quartets mainly relax to ground state. Oxidation of [Cr(bipy)3]2' by Sz082- and T13+has been found 46 to lead to the generation of an excited state of [ C ~ ( b i p y ) ~ ]which ~ + , luminesces between 700-750 nm, and which forms with pseudo-first-order kinetics. Oxidations using H,O, did not lead to any chemiluminescence. Chromic acid esters have been photolysed in aqueous solutions of potassium chromate in 40% alcohol (MeOH, EtOH, 2-PrOH) in the presence of aquoamine cobalt(m) and the reaction appears to involve formation of CrVin the first step.47 It is also reported 48 that CrVoccurs as a short-lived species in the photoreduction of Crvl in the liquid phase; in rigid glasses it has been detected by e.s.r. However, +

39 40 4*

42 43 44 4s O6

47 48

M. Asano, J. A. Koningstein, and D. Nicollin, J . Chem. Phys., 1980, 73, 688. N. Serpone, M. A. Jamieson, and M. Z. Hoffman, J. Chem. SOC.,Chem. Commun., 1980, 1006. N. A. P. Mane-Maguire and C. H. Langford, tnorg. Chem., 1976, 15,464. R. Sriram, M. Z. Hoffman, and N. Serpone, J . Am. Chem. SOC.,1981, 103,997. G. J. Ferraudi and J. F. Endicott, Inorg. Chim. Acta, 1979, 37, 219. G. B. Porter and J. van Houten, tnorg. Chem., 1980, 19, 2903. R. L. P. Sasseville and C. H. Langford, tnorg. Chem.. 1980, 19, 2850. F. Bolletta, A. Rossi, and V. Balzani, tnorg. Chim. Acta, 1981, 53, L23. H. Hennig, P. Scheibler, R. Wagener, and D. Rehorek, fnorg. Chim. Acta. 1980, 44, L231. P. Rusev, M. Mitewa, P. Bonchev, and A. Malinovski, Dokl. Bolg. Akad. Nauk, 1980, 33, 519.

176 Photochemistry irradiation of [CrO,Cl]-[HPy] +-DMF induces a two-electron-transfer process with generation of Cr" as a transient. In the Crv'-oxalic acid-DMF-MeCN system, the photoreactions were found 49 to be solvent dependent: CrVwas again produced and Cr" and Cr"' were intermediates. A red luminescence of low quantum efficiency has been detected from chromate in some specific host lattices. Complexes of CrVand Cr"' are produced 5 1 in the photoprocess leading to the hardening of chromated poly(viny1 alcohol). Methods have also been reported for the determination of chromium by a luminescence methods2 and by a photochemical titration procedure.53 For other reports on chromium see references 65, 78, and 98. 5 Molybdenum and Tungsten It is reported that the Mo" cluster ion [MO,C~,,]~-is phosphorescent in solution at room temperature with a lifetime <200 ps, and electron acceptors such as methylviologen and chloranil are both observed to accept an electron from its excited state.', This ion is potentially useful in solar energy storage systems. Photooxidation of octacyanomolybdate(1v) occurs on irradiation of [(RC6H4),I], [Mo(CN),], (where R = H, p-C1, orp-Me) in the solid phase and in dilute benzene solution to give [MO(cN)8]3- together with aryl radical^.'^ The Mo" complex is probably produced by electron transfer to the diaryliodonium ion. Evidence has also been presented that suggests that photolysis of the same complexes in solution leads to the formation of two new MoV compound^.'^ The photoreduction of MoV'on silica gel has been studied in a CO atmosphere at room temperature using wavelengths less than 340 nm. Surface ions Mo" and COz were produced, and the Mo"-SiO, was found to have strong redox proper tie^.'^ Mo"' ions are reported following irradiation into the charge-transfer band of MoCl, in an ethanol glass at 77 K. A study has been made 5 9 of the effect of wavelength on the extent of dinitrogen exchange in bis(dinitrogen) complexes of Mo and W. It is concluded that photodissociation occurs on the population of the lowest LF state and may also arise from other excited states. The aquoheptacyanotungstate(v1)ion has been synthesized photochemically and the kinetics of its thermal reactions studied. A general scheme for the photoreactions of W(CN)84- has been proposed:60 this contributes to a better understanding of the [M(CN),]"-, (M = Mow, W", or Nb"') system as a whole. Molybdenum and tungsten are also discussed in reference 170. 49

50 51

52

53 54 55

56

"

59

6o

P. Rusev, P. R. Bonchev, M. Miteva, and A. Malinovski, Inorg. Nucl. Chem. Lett., 1980, 16, 121. G. A. M . Dalhoeven and G. Bfasse, Chem. Phys. Lett., 1980, 76, 27. V. P. Sherstyuk, L. E. Mazur, and L. M . Karachunskaya, Zh. Nauchn. Prikl. Fotugr. Kinematogr., 1980, 25, 40. I . P. Alimarin, A. M. Medvedeva, and G . P. Tikhonov, Zh. Anal. Khim., 1980, 35, 1946. E. 1. Dodin, A. M. Pavlova, and I. P. Kharlamov, Zh. Anal. Khim., 1980, 35, 926. A. W. Maverick and H. B. Gray, J . Am. Chem. SOC.,1981, 103, 1298. H. Hennig, D. Rehorek, J. Salvetter, and A. Hantschmann, Proc. Conf. Coord. Chem., 7th, 1978, p.61. D. Rehorek, J. Salvetter, A. Hantschmann, H. Hennig, Z. Stasicka, and A. Chodkowska, Inurg. Chim. Acta. 1979, 37, L471. A. N. Pershin, B. N. Shelimov, and V. B. Kazanskii, Kinet. Katal., 1980, 21, 494. T. I. Sardyukova, S. Ya. Kuchmii, and A. I. Kryukov, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim., i2th, 1977, p. 222. L. J. Archer and T. A. George, Inorg. Chim. Acta, 1980, 44, L129. B. Sieklucka and A. Samotus, J. Inorg. Nucl. Chem., 1980, 42, 1003.

177 The Photochemistry of Transition-metal Complexes 6 Manganese The luminescent properties of the complexes of manganese(@ chloride with 4benzylpyridine, (ClzHlzN)MnCl, and (C,,H,,N),MnCI,, have been measured 6 1 and the results compared with those obtained using a model of parabolic configurational curves. An investigation is also reported 62 of the mechanism of photolysis of the oxalate complexes of manganese(Irr), K3Mn(Cz0,), and K[Mn(CzO4)z(HzO)21-

7 Iron Irradiation of FeSO4-HZSO4or FeS04-Na2S04(HzS0,) leads to Fe"' and Hz. It has been found 63, 64 that a linear correlation exists between the irradiation time and the rate of Fe"' formation, and that for more concentrated solutions of Fe" and H,SO,, the rate of photo-oxidation is lower. The results suggest the presence in solution of ion pairs or sulphate complex structures. Saturated aqueous solutions of carbon dioxide are reported6' to be reduced to formic acid and to formaldehyde on 254 nm irradiation in the presence of transition-metal ions such as Fe", Co", Cr", and Run. However, photoreduction of methanol proved to be sluggish and only low yields of methane were obtained. Relative efficiencies of the reduction step parallel the abilities of the intermediates to capture solvated electrons, suggesting that these species participate in the reduction process. The photooxidation of Fe" to Fe"' has been examined66 for systems of iron chlorocomplexes in Me,CO-MeOH mixtures using excited Fe"' complexes or tetracene as sensitizer. Stern-Volmer constants were measured. The S1 state of methylene blue is reported 6 7 to be quenched by [Fe(Hzo),I3 mainly by the static mechanism (k, = 1.7 x 10" MS-'). A new method has been announced68 for the determination of oxalate by gas chromatographic measurement of the COz evolved in the photodecomposition of Fe"' oxalate and is based upon the photoredox reaction of the Fe'" mono-oxalate complex [equation (2)]. A study of the photolysis of [Fe(CZO4),l3- has been made +

2FeC204

hv

2Fe2+

+ 2C0, + CZO4'-

(2)

in aqueous solution and in the presence of o-phenanthr~line.~'Quantum yields of photolysis of [Fe(C,04),13- were also determined in the presence of an excess of C204'-, thus preventing formation of appreciable quantities of [Fe(C,O,),(phen)]-. Irradiation of an aqueous solution of the Fe"' complex of pyridine-2-carboxylicacid leads to the formation of pyridine and the 2,2'-bipyridine Fe" complex.70 The corresponding complex of pyridine-3-carboxylic acid gave the 61

" 64 65

'' 68 69

'O

F. Lignou, H. Payen de la Garanderie, K. Nikolic, and 1. Buric, Fizika (Zagreb), 1980, 12, 27. V. E. Stel'mashok and A. L. Poznyak, Dokl. Akad. Nauk. BSSR. 1980, 24, 53. S. Papp and L. Vincze, Inorg. Chim. Acta, 1980, 44, L241. L. Vincze and S. Papp, Proc. Conf. Coord. Chem., 8th, 1980, p. 439. B. Aakermark, U. Eklund-Westlin, P. Baeckstroem, and R. Loef, Acta Chem. Scand., Ser. B, 1980,34, 27. J. Sima, H. Zliechovcova, and J. Gazo, Chem. Zvesti, 1980, 34, 172. T. Ohno and N. N. Lichtin, J . Phys. Chem., 1980, 84, 3485. J. M. Cooley and B. Kratochvil, Can. J. Chem., 1980, S, 627. H. Funayama, K. Ogiwara, T. Sugawara, and H. Ohashi, Kokagaku Toronkai Koen Yoshbhu, 1979, 70. K. Takada, T. Kimura, and A. Sugimori, Kokagaku Toronkai Koen Yoshishu, 1979, 206.

178

Photochemistry

Fe" complex of 2,2'-bipyridine-3,5'-dicarboxylicacid but the pyridine-4-carboxylic acid was observed not to be photosensitive in the presence of Fe" ions. The photochemistry of low-spin Fe"' complexes with macrocyclic ligands continues to be a field that attracts interest. Irradiation of the charge-transfer bands of [Fe(TIM)(OMe)(MeOH)]2+ (TIM = 2,3,9,lO-tetramethyl-1,4,8,11tetraazacyclotetradeca- 1,3,8,1O-tetraene) and of [Fe(DMG),(OMe>(MeOH)] (DMG = dimethylglyoxime), was found to lead to oxidation of the co-ordinated MeOH and reduction of the metal centre.71 These photoreactions have been attributed to the population of methoxy-to-Fe"' CT states. In the presence of organic ligands such as potassium tartrate and citric acid, the photolysis of aqueous ferric nitrate has been examined 7 2 at 350 nm. Temperature and nitrate ions were without effect on (bFell in the photoreduction process, but a sensitivity to pH was observed. It is suggested that the FerlI complex is partially decomposed during the simultaneous bond-rupture and electron-transfer process. The photoreactions of [FeCl,]- have been studied 73 in concentrated solutions of HC1 and HClO,. Addition of alcohols to the HClO, solutions leads to increases in the quantum yield, which then becomes a constant equal to the photoreduction of this complex in pure alcohols. U.V. irradiation of the hexamolybdoferrate (NH,),[H,FeMo,O,,] in water or aqueous methanol brings about photoreduction of Fe"' to Fe". It is also reported 74 that photodecomposition of aryldiazonium cations occurs in the presence of an H2C204solution containing (NH,),[H,FeMo,O,,], but this is not observed in the absence of the salt. The photochemistry of K,[Fe(CN),]. 3H,O has been studied 7s in an alkali halide matrix at 77 K and found to give [Fe(CN)J4- in a thermally irreversible process. Alkoxy radicals have been detected 76 in the irradiation of alcoholic solutions of K,Fe(CN),. For other reports on iron see references 78 and 170. 8 Ruthenium65 Reviews have appeared of light-induced electron-transfer reactions of ruthenium complexes containing nitrogen heterocycles.77*7 8 Examination of luminescence data of [Ru(bipy),12+ in PMM and EPA at temperatures below about 90K has shown that the molecule does not have D , symmetry throughout the absorption-mission process.79 Moreover, photoselection spectra of the complex suggest that in rigid matrices the molecular symmetry of the excited state and/or the ground state is lower than D,. In an electron-transfer experiment using S,OS2- as an oxidizing agent, the quantum yields of formation of the MLCT state of [Ru(bipy),12+ and [Ru(phen),12+ have been determined 8 o as unity and the phosphorescence quenching constants found 71

72 l3

l4

l5 7h

"

'' 79

G. Ferraudi and C. Carrasco, Inorg. Chem., 1980, 19, 3466. A. J. Mahmood, Q. N. Hossain, and M . A. Chowdhury, Dacca Univ. Stud., Part B, 1979, 27, 71. V. F. Plyusnin and N. M. Bazhin, Izv. Sib.Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1980, 8. V. P. Sagalovich, T. N . Tikhonova, N. B. Kupletskaya, and L. A. Kazitsyna, Zh. Obshch, Khim., 1980, 50, 1424. G. B. Porter and A. J. Rest, J . Chem. SOC.,Chem. Commun., 1980, 869. D. Rehorek, Z . Chem., 1980, 20, 312. H. Yoneda, U. Sakaguchi, and A. Miyanaga, Kagaku (Kyoto), 1980,35, 148. N. Sutin and C. Creutz, Pure Appl. Chem., 1980, 52, 2717. K . W. Hipps, Inorg. Chem., 1980, 19, 1390. F. Bolletta, J. Juris, M. Maestri, and D. Sandrini, Inorg. Chim. Acta, 1980, 44, L175.

179

The Photochemistry of Transition-metal Complexes

'

to be 5.33 x lo8 and 5.63 x lo8M - s - ' from Stern-Volmer plots. The effect of pressure on the lifetime and quenching of transition-metal complex ion phosphorescence has been investigated.8 Phosphorescence emission from [Ru(bipy),j2+, [Cr(en),13+, and [Cr(bipy),13 was unaffected up to pressures of 2.9 kbar, as was the quenching of [Ru(bipy),12+ phosphorescence by oxygen. In the case of Co(acac), and methylviologen, however, the quenching constants were found to be increased by about 40% at 2.9 kbar. This is consistent with an electrontransfer quenching process. [Ru(bipy),I2+ has been shown to transfer singlet energy to Rhodamine 101: the efficiency of the transference is solvent dependent and highest in deoxygenated methanol. 8 2 Both diffusional contact exchange and long-range resonance Forster energy-transfer seem to operate depending on the solvent viscosity. cis-transIsomerization of some alkenes including stilbene and CI- and p-styrylnaphthalene has been achieved using the photoexcited [Ru(phen),12 ion in acetonitrile. In the photosensitization of oxygen-bridged dicobalt(rI1) cations by the excited state of [Ru(bipy),12+, energy transfer is thought to account for 10% of the quenching events and electron transfer for 90%. Following energy transfer, there is a dark redox reaction that leads to the products formed in the steady-state photolysis studies.84 The kinetics of this reaction have also been measured.85 Substituted bis(ethy1enediamine) complexes of osmium, e.g. trans-[OsO,(en),]"', cis[0s(en),H2l2 +,and cis-[Os(en),Cl,]+ have been used 8 6 to study the luminescence quenching rates of [Ru(bipy),I2'. A parallelism was observed between the relative quenching efficiencies and the susceptibilities of the complexes to redox processes, indicating an electron-transfer mechanism; quenching by energy transfer may also occur. The temperature quenching of the [Ru(bipy),]' emission by Cu" and Eu"' has been investigated8' over the range 290-350K. For Cu" complexes, the quenching does not obey Marcus theory in that the rate constants are only slightly dependent on AGO, and the results are interpreted in terms of a rate-determining step, which involves a configuration change in the encounter pair. Linear Stern-Volmer plots have been obtained for the quenching of the luminescent state of [Ru(bipy)J2+ by penta-ammine cobalt(rr1) complexes of p-nitrobenzoate, onitrobenzoate, benzoate, and acetate as a function of the concentration of the Co complex.88 In the case of the last two complexes, quenching occurs by electron transfer to the cobalt atom and a competition is found to exist between cage dissociation leading to Co" and cage recombination which results in regeneration of the reactants. Further reports of photoreductive quenching of polypyridine complexes of Ru" have appeared. Irradiation of [Ru(bipy),12 , of other Ru" complexes, and of complexes of Fe" in aqueous solution containing Et,N gives MeCHO by irreversible oxidation of the amhe.*' However, in anhydrous Et,N, [Ru(bipy),12

'

+

+

+

+

+

81

83 84

86

87 88 89

A. D. Kirk and G. B. Porter, J . Phys. Chem., 1980, 84, 2998. K. Mandal, T. D. L. Pearson, and J. N. Demas, J . Chem. Phys., 1980, 73,2507. G. Gennari, G. Galiazzo, and G. Cauuo, Gazz. Chim. Ital., 1980, 110, 259. K. Chandrasekaran and P. Natarajan, Inorg. Chem., 1980, 19, 1714. K. Chandrasekaran and P. Natarajan, J . Chem. Soc., Dalton Trans., 1981, 478. J . M. Malin, Inorg. Chim. Acta, 1980, 45, 87. J. E. Baggott and M. J. Pilling, J. Phys. Chem., 1980, 84, 3012. W. Boettcher and A, Haim, J . Am. Chem. SOC.,1980, 102, 1564. P. J. DeLaive, T. K. Foreman, C. Giannotti, and D. G. Whitten, J . Am. Chem. Soc., 1980, 102,5627.

180

Photochemistry

did not give permanent photoreduction nor did any of the Fe" complexes studied. Dithio-anions such as diethyldithiocarbamate (dtc-) in solution in MeCN are reported to quench the luminescence of photoexcited [Ru(bipy),12 to give the disulphide (dtc),. In one case, both static quenching and specific ion effects seem to be involved; and if electron acceptors such as anthraquinone or dinitrobenzenes are present, their radical ions are generated in sufficient concentrations to enable their spectroscopic properties to be examined. Benzenethiolate also quenches the excited state of [Ru(bipy),I2 by electron transfer." Irradiation of [Ru(bipy),12 in aqueous solution at pH 7 leads to a low quantum yield phot~racemization.~~ This reaction, which occurs via a phosphorescing state, also shows chiral effects if quenching is carried out using Co(acac),. The photoreactive state is probably a triplet state or some other state in thermal equilibrium with it. Photoanation of [Ru(bipy),I2+ in DMF at 458nm is reported 93 to yield two products, [Ru(bipy),(DMF)Br]+ and [Ru (bipy),Br,], in a process that is based on ion pairs and ion triplets as the photoactive species. Ligand substitution also occurs when the same substrate is irradiated in degassed MeCN. The product under these conditions is [RuCl(MeCN)(bipy),]Cl and similarly in Me,O and CH,Cl, as solvent there is complete conversion to RuCl,(bipy),. In the presence of oxygen, however, the photoreaction in MeCN was substantially Electrodes, derivatized with [Ru(bipy),Cl( poly(4viny1pyridine))lClhave been irradiated and exchange of the co-ordinated C1- with H,O, ClO,-, and MeCN found to occur.95 This is claimed to be the first observation of a photosubstitution on a surface-attached system and since the process is irreversible it offers the possibility of information storage, The preparation of ~is-[Ru(bipy)~(CO)Cl]C10, - has been reported 96 together with its photoreactions with neutral ligands, such as MeOH, pyridine, MeCN, PEt,, and PPh,. In all cases the product was of the form cis-[Ru(bipy),ClL]+. Photolysis of the Ru'" complexes cis- and trans-[Ru(en),Cl]+ leads to C1- loss, aquation, and geometric isomerization to give mixtures of cis- and trans[R~(en),(H,o)Cl]~ +,which themselves are photointer~onvertible.~~ Several new chemiluminescent reactions of co-ordination compounds have been announced 98 and involve complexes such as [Ru(bipy),13+, [Cr(bipy),I2+, [Rh(bipy),]+, [Ir(phen),]+, and (OC),Re-Re(CO),(phen). Reaction of strong reductants, formed during the oxidation of oxalate, with electrogenerated [Ru(bipy),13 gives a strong chemiluminescence corresponding to emission by [Ru(bipy),12+. This same emission could also be observed following reaction of Ru"' complexes with ~ x a l a t e .Similarly, ~~ certain organic acids, e.g. pyruvic, +

+

+

+

+

90 91

92 93 94 95

96

"

99

A. Deronzier and T. J. Meyer, inorg. Chem., 1980, 19, 2912. T. Miyashita and M. Matsuda, Kokagaku Toronkai Koen Yoshishu, 1979, 246. G. B. Porter and R. H. Sparks, J . Photochem., 1980, 13, 123. W. M. Wallace and P. E. Hoggard, inorg. Chem., 1980, 19, 2141. R. F. Jones and D. J. Cole-Hamilton, inorg. Chem. Acta, 1981, 53, L3. 0. Haas, M. Kriens, and J. G . Vos, J . Am. Chem. SOC.,1981, 103, 1318. J . M. Clear, J. M. Kelly, C. M. O'Connell, J. G. Vos, C. J. Cardin, S. R. Costa, and A. J. Edwards, J . Chem. SOC.,Chem. Commun., 1980, 750. M. E. Rerek and P. S. Sheridan, Inorg. Chem., 1980, 19, 2646. A. Vogler, L. El-Sayed, R. G. Jones, J. Namnath, and A. W. Adamson, inorg. Chim. Acta, 1981, 53, L35. I. Rubinstein and A. J. Bard, J . Am. Chem. SOC.,1981, 103, 512.

The Photochemistry of Transition-metal Complexes

181 malonic, and lactic, following oxidation by Ce", also gave intermediates that are chemiluminescent on reaction with [Ru(bipy),13+. The photoinduced splitting of water into its elements continues to be a topic attracting a great deal of interest. An investigation has been reported loo of the effect of transition-metal catalysts on the kinetics of the photo-oxidation of water to 0, by reagents such as [Ru(bipy),I3+ and [Fe(bipy),13+. Visible light irradiation of an aqueous HC1 solution of [Ru(bipy),12+ containing Ti"' is claimed to lead to hydrogen evolution. l o l The reaction is thought to involve electron-transfer quenching of the 'CT state of [Ru(bipy),12+ to form Ti", which in acid solution reacts very rapidly to give hydrogen, so suppressing the back reaction between Ti" and Ru"'. However, these observations have been challenged l o 2 by Sutin who has detected virtually no molecular hydrogen using this system. It is also claimed that the quenching of the excited state of [Ru(bipy),12 by Ti"' occurs predominantly by energy transfer.lo3 Hydrogen peroxide is generated in the irradiation of an aqueous HC1 solution of [Ru(bipy),I2+ and Sb'". Experiments suggest that electron transfer in this case occurs to a dissolved oxygen molecule.lo4 Numerous other processes have also been reported. These include the photo-oxidation of water in the presence of a cobalt catalyst using [IrC1,12- or [M(bipy),I3+ (M = Os, Fe, or Ru) as oxidizers 'OS* l o 6 and the synthetic iron-sulphur complex [Fe,S,(SCH,Ph),]'as electron carrier. lo' Improvements in the quantum yield for the photodecomposition of water have been recorded lo' using a 0.1% Ru0,n-TiO,(Nb-doped) metal oxide loaded with Pt particles. The quenching rate constants (k,) for *[Ru(bipy),lz+ by a series of viologen salts having different redox potentials (E+) have been measured log at pH 5 in deaerated solution, and k, found to decrease with increasing -E+. A correlation was also established between k, and AG that is consistent with the Rehm-Weller model for electron-transfer reactions.' l o The rate of hydrogen production from a mixture of bis(2,2'-bipyridine)(diethyl-2,2'-bipyridine-4,4'-dicarboxylate)ruthenium(m), edta, methyl viologen, and a platinum catalyst was found to be lower than when [Ru(bipy),]'+ is used."' This is thought to be due to electron withdrawal by the ester groups and to bimolecular quenching by water. In reactions such as these, the possibility of the existence of a particle-size dependence on the release of hydrogen has been investigated.ll2 However, within the range < 100-1000 A none has been found. The details of the mechanism of hydrogen production on irradiation of a mixture of [Ru(bipy),]'+, [Rh(bipy)J3+, and triethanolamine (TEOA) in the presence of a platinum catalyst at pH 8,25 "C, and +

N. K. Khannanov and V. Ya. Shafirovich, Kinet. Katal., 1981, 22, 248. G. Giro, G. Casalbore, and P. G . Di Marco, Chem. Phys. Lett., 1980, 71,476. lo'B. S. Brunschwig and N. Sutin, Chem. Phys. Lett., 1981, 77, 63. lo3 B. S. Brunschwig and N. Sutin, Inorg. Chem., 1979, 18, 1731. lo4 Y. Kurimura and R. Onimura, Inorg. Chem., 1980, 19, 3516. lo' V. Ya. Shafirovich, N. K. Khannanov and V. V. Strelets, Dokl. Akad. Nauk, SSSR, 1980,250, 1197. V. Ya. Shafirovich, N. K. Khannanov, and V. V. Strelets, N o w . J . Chim., 1980, 4, 81. lo' T. Okuno and 0. Yonemitsu, Chem. Leu., 1980,959. lo*J. Kiwi, E. Borgarello, E. Pelizzetti, M. Visca, and M. Graetzel, Angew. Chem., Int. Ed. Engl., 1980,

loo lo'

19, 646.

E. Amouyal, B. Zidler, P. Keller, and A. Moradpour, Chem. Phys. Lett., 1980, 74, 314. 'loD. Rehm and A. Weller, Ber. Bunsenges. Phys. Chem., 1969, 73, 834. ' 1 1 0. Johansen, A. Launikonis, A. W. H. Mau, and W. H. F. Sasse, Aust. J . Chem., 1980, 33, 1643. 11' P. Keller and A. Moradpour, J. Am. Chem. SOC.,1980, 102, 7193. lo9

182

Photochemistry

using 450nm light have been published.'13 The main features are summarized in Scheme 1.

Some earlier kinetic results 'I4 on the photoreduction of methylviologen have been challenged on the ground that several important reactions have been neg1ected.'15 The complex [Ru(SPZ),l2+, BPZ = bipyrazyl, has been investigated and shown to have emission and absorption properties comparable with those of the analogous bipyridine complex, but a longer triplet-state lifetime.'16 In the presence of TEOA it is capable of photoreducing methylviologen with a quantum yield of 77%. A review has appeared of attempts to increase charge separation between geminate ion pairs by using micellar systems for photoreduction mediated by [Ru(bipy),12 , benzylviologen, or zinc tetraphenylporphin. Time-resolved measurements of the luminescence of the excited state of [Ru(bipy),12+ have been used to examine the photoredox reactions between this species and N-alkylviologen ions in micellar media.' l 8 Even under conditions where non-exponential behaviour is expected, exponential decay is observed and is understandable in terms of the quenching process occurring within the diffuse double layer of the micelles. In reverse micelles, and using duroquinone as quencher, the duroquinone partitions into the aqueous pool and no phase transfer of electrons or product ions occurs. The luminescence of [Ru(bipy),12 is reported to show an increased intensity in an aqueous solution of sodium poly(styrene sulphate) and this is attributed to a co-operative effect due to both the binding of the Run with the pendant styrene sulphate anions, and interaction between Ru" and neighbouring pendant styrene groups. I9 Abnormal decay kinetics have been observed for the excited state of [Ru(bipy),12 in surfactant solutions. These show that in solutions containing sodium dodecyl sulphonate (SDS) at concentrations below the critical micellar concentration, [Ru(bipy),]' + forms complexes with SDS containing +

+

+

113

114 11s 116

117

118 119

S.-F. Chan, M. Chou, C. Creutz, T. Matsubara, and N. Sutin, J . Am. Chem. SOC.,1981, 103, 369. I. Okura, S. Nakamura, K. T. Nguyen, and K. Nakamura, J. Mol. Catal., 1979, 6, 261. S. Oishi and K. Nozaki, J. Mol. Cutul., 1980, 9, 231. R. J. Crutchley and A. B. P. Lever, J . Am. Chem. SOC.,1980, 102, 7128. T. Matsuo, K. Kano, and T. Nagamura, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20, 1087. M. A. J. Rodgers and J. C. Becker, J . Phys. Chem., 1980,84,2762. K. Kurimura and E. Tsuchida, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20,622.

The Photochemistry of Transition-metal Complexes

183 several of the ruthenium ions.12* The very fast decay suggests self quenching within such a cluster. Photoreduction of the amphipathic viologens (1) may be brought about 12' in the presence of edta using the Ru" complex (2). Bilayer systems gave the best yields

(1) n = 10, 12, 14, 16

and electron transport across the lipid bilayer was examined using several electron carriers of which dialkylalloxazines were found to be the most satisfactory. The same workers have also examined photoinduced electron-transfer reactions for [Ru(bipy) 3] and the amphipathic derivative bis(2,2'-bipyridine)]4,4'bis(dodecylcarbamoyl)2,2'-bipyridine] ruthenium(I1) in various micellar systems. 2 2 , 23 Photoinduced electron-transfer between an amphipathic ruthenium(1r) complex and N-butylphenothiazine has been examined in various microenvironments. 24 [Ru(bipy),12 and Zn tetrabis(N-methylpyridy1)porphyrin have been used as sensitizers in the photoreduction of a homologous series of amphiphilic viologens such as N-alkyl-N'-methyl-4,4'-dipyridinium (C,MV2 +), (C, = dodecyl, tetradecyl, hexadecyl. or octadecyl). Pathways were established by means of which micellar assemblies couid prevent the back reaction of important photoredox processes.12s Oxidative quenching of [Ru(bipy)# + by a polymer incorporating the viologen group has been shown to lead to radical dimers of the viologen unit and electron migration along the electron chain has been proved using e.s.r.126The synthesis has been described of polystyrene pendant tris(bipyridine)ruthenium complex'27-129 and the complex is reported to show catalytic activity in the photoreduction of methylviologen in aqueous dmf using triethanolamine as reducing agent. Photosensitized formation of hydrogen peroxide has been described in the [Ru(bipy)$ +-ascorbic acid system.' 30 The reactions are initiated by electrontransfer from the deprotonated ascorbic acid to the lowest excited state of the +

' '

+

120 12' 122

123 124

lZ5 lZ6

12' 12* 129

130

J. H. Baxendale and M. A. J. Rodgers, Chem. Phys. Lett., 1980,72, 424. T. Matsuo, K. Takuma, K. Itoh, and K. Sakura, Kokagaku Toronkai Koen Yoshishu. 1979, 244. T. Matsuo, K. Takuma, K. Sakura, and T. Sakamoto, Nippon Kagaku Kaishi, 1980,486. T . Matsuo, K. Takuma, Y. Tsutsui, and T. Nishijima, J . Coord. Chem., 1980, 10, 187. T. Takayanagi, T. Nagamura, and T. Matsuo, Ber. Bunsenges. Phys. Chem., 1980, 84, 1125. P. A. Brugger, P. P. Infelta, A. M. Braun, and M. Gratzel, J . Am. Chem. Soc., 1981, 103, 320. T. Matsuo, T. Sakamoto, and T. Nishijima, Kokagaku Toronkui Koen Yoshishu. 1979, 98. M. Kaneko, A. Yamada, S. Nemoto, and M. Yokoyama, Kobunshi, Ronbunshu, 1980, 37, 685. M. Kaneko, S. Nemoto, A. Yamada, and Y. Kurimura, Inurg. Chim. Acta, 1980,44, 289. M. Kaneko, A. Yamada, and Y. Kufimura, Inorg. Chim. Acta, 1980, 45, L73. Y. Kurimura, H. Yokota, and Y. Muraki, Kokagaku Toronkui Koen Yoshishu, 1979, 66.

Photochemistry

184

ruthenium complex. Photocatalysis of the homogeneous water-gas shift reaction has been investigated '3 1 using the complex [RuCl(CO)(bipy),]Cl, and the photochemistry reported 1 3 2 of some nitroso-transition-metal complexes of the form [M(N0)X,l2- (M = Re, Ru, Os, or Ir; X = C1, Br, I, or SCN). 9 Osmium

Energy-level gaps and both radiative and radiationless decay constants have been '~~ obtained for a series of 0s" complexes containing n-conjugated l i g a n d ~ . This has been done by computer analysis of the intensity and decay time of the photoluminescence. An ion-parent coupling model has been used to rationalize the empirical parameters and the emitting levels shown to have d-n*(a,) CT configuration. Lifetimes and emission energies have been reported 1 3 4 for the metal to polypyridine ligand in a series of highly luminescent bis-2,2'-bipyridine and bis1,lO-phenanthroline complexes of 0 s " containing acceptors such as MeCN. Systematic variations with the added ligand were noticed and the excited states were found to undergo both oxidative and reductive quenching. 10 Cobalt

A review has appeared 135 of the CT photochemistry of cobalt(II1) complexes.

'

Experimental confirmation has now become available 36 of the theoretical prediction that for complexes of the type MA4XY trans-cis-isomerization is to be expected when X is a better c donor than A. This evidence has emerged from a study of the ligand-field photolysis of trans-[Co(en),(CN)Cl] and trans[Co(en),(CN)H,Ol2+. The photochemical behaviour of all the CN cis-isomers of dicyano(ethy1enediamine-NN'-diacetato)- (3) and dicyanobis(g1ycinato)cobaltate(n1) (4)complexes have been examined at room temperature and at 77K.'37 Photoproducts were only observed to arise by excitation of the CTLM 222 nm). In acidified solution room-temperature photolysis of (3) leads band (A,, to a cobalt(rI1) complex having a C-bonded amino-acid residue and CH,fiH,R, which arises from elimination of CO,. At 77K the products are cobalt(Ir1) complexes in which the CH,NHR residue is co-ordinated to the central metal atom through the C and N atoms. Compound (4)behaves similarly. Chargetransfer photolysis of ethylenediamine-NN'-diacetato(ethylenediamine)cobalt(rrI) at 0-5 "C is reported 1 3 * to give (5) as the principal product. However, at room temperature only isomers and racemates of the original compound were formed. 365 nm, the In a study of the photoredox reactions of cis-[Co(en),(NO,),]+ at lirr cobaltous ion and the linkage isomer are the only products.139 These seem to arise in a solvent-assisted reaction of the excited state, which may be formulated as +

13' 13'

133 134

13' 136

13'

13'

139

D. J. Cole-Hamilton, J. Chem. Soc., Chem. Commun., 1980, 1213. A. B. Nikol'skii, and A. M. Popov, Dokl. Akad. Nauk SSSR, 1980, 250,902. D. E. Lacky, B. J. Pankuch, and G . A. Crosby, J . Phys. Chem., 1980, 84, 2068. E. M. Kober, B. P. Sullivan, W. J. Dressick, J. V. Caspar, and T. J. Meyer, J . Am. Chem. Soc., 1980, 102, 7383. J. H. Kim and S. C. Shim, Hwahak Kyoyuk, 1980,7, 65. K. F. Purcell, S. F. Clark, and J. D. Petersen, Inorg. Chem., 1980, 19, 2183. A. L. Poznyak and V. I. Pavlovskii, Z . Anorg. Allg. Chem., 1980, 465,159. A. L. Poznyak and V. E. Stel'mashok, Koord. Khim., 1979,5, 1670. A. Radhakrishnan and P. Natarajan, Indian J . Chem., Sect. A , 1979, 18, 165.

The Photochemistry of Transition-metal Complexes

185

shown in Scheme 2. Cis-[(en),Co(S,O,),]- has been oxidized 140 to the stable compound trans-[(en),Co(0H,)(S30,)]+.The latter complex, which contains the very reactive ligand disulphane monosulphonate, is sensitive to laboratory fluorescent light and undergoes photolysis with a half-life of about 60 minutes.

-

ci.~-[Co(en),(NO~)~]+

cis-[Co(en),(NO,)ONO] +

hv

*cis-[Co(en),(NO,),]'

Co2+ + 2(en)

+ 2N0,

Scheme 2

Irradiation of the S-bonded complex [CO(~~),(SO,CH,CH,NH,)]~in aqueous solution is reported141 to lead to the corresponding 0-bonded isomer. This complex slowly reverts thermally to the starting material (t+-600 h at room temperature) and is the first example of an 0-sulphinato complex of cobalt(1rr). Photolysis of carboxylatopenta-ammine complexes of the type [CO(NH,)~O,CR]~+(R = CH,Br, CH2C0,H, CH(OH)Ph, and CH,Ph) in frozen solution leads 14* to decarboxylation and formation of the corresponding organometallic ions [Co(NH,),)R]+. In some related the same author reports that photoinduced loss of one propionate residue occurs from ethylenediaminetetrapropionate. Spectroscopic investigations of the Co"' complex produced indicate some Co(N),(O), binding. In the case of cobalt(m) complexes with aminopolycarboxylic acids and N-heterocyclic ligands such as bipyridine or phenanthroline, photoredox decomposition also occurs to give organometallic Co'" compounds.144 The effect of anions of the second co-ordination sphere upon the photoredox reactions of [Co(phen),C,O,]+RCO,- (R = H, Me Et, Me,C, CCl,, CF,, or Ph) has been studied 145 using a spin-trappingtechnique. In MeOH, the photoreduction corresponds to an outer-sphere mechanism, whereas in EtOH, the carboxylate ions in the second co-ordination sphere act as electron donors in the photoredox process. Complexes of the type [CoL,(C,O,)]X, (L = bipy; X = F, C1, Br, I, ClO,, BF,, Ph,B, SCN, OCN, HCO,, and OAc) have been prepared and p h ~ t o l y s e d . ' In ~ ~ the solid state CO, is evolved to give Con complexes that are identical with the thermolysis products. +

140 14' 14* 143

144 14s 146

J. P. Mittleman, J. N. Cooper, and E. A. Deutsch, J . Chem. Soc., Chem. Commun., 1980, 733. H. Maecke, V. Houlding, and A. W. Adamson, J . Am. Chem. Soc., 1980, 102, 6888. A. L. Pomyak and V. V. Pansevich, Vestsi Akad. Navuk BSSR, Ser. Khim. Navuk, 1980, 18. V. E. Stel'mashok and A. L. Poznyak, Koord. Khim., 1980,6, 144. V. I. Pavlovski and A. L. Pomyak, Dokl. Akad. Nauk, BSSR, 1980, 24, 1103. D. Rehorek and H. Hennig, Z . Chem., 1980, 20, 109. H. Hennig, R. Benedix, J. Lerchner, and K. Jurdeczka, 2.Anorg. Allg. Chem., 1979, 458, 139.

186

Photochemistry

Following direct triplet excitation of [co(CN),l3 - in aqueous Solution, [Co(CN),(H,0)l2- is generated with the same quantum yield as following the shorter wavelength singlet excitation. 147 Intersystem crossing from the initially formed excited singlets to lower energy triplets appears, therefore, to be approximately unity. This conclusion is consistent with that drawn from studies on several heavier metal d6 complexes, namely that there is efficient interconversion to the lowest energy ligand-field state, (3 Tlg) from which ligand labilization or nonradiative deactivation to the ground state can occur. Compounds of the type K,[Co(CN),L], where L = one of a variety of N-heterocycles, show no lowenergy MLCT bands or any significant n-back-bonding in the ground state. On photolysis at 365 nm, photoaquation of L occurs 14' (# = 0.17-4.40). Comparisons made between [Fe"(CN),I3 - and [CO"(CN),]~- show that the quantum yields are smaller in the latter case. This is attributed to the greater difficulty in breaking the M-L bond in the excited state of the doubly-charged [CO"'(CN),]~metal centre than in the triply-charged [Fen(CN),l3 - centre. The photochemistry of the binuclear complex [(CN),CoCNMo(CN),(OH), - J 7 - , formed in aqueous solution from [CO(CN),]~-and [MO(CN)8]4-, has been examined.',' Visible light irradiation of an aqueous solution of [RU(CN)6I4- and trans-i-[Co(~-His),] leads to the development of an intense red-orange colour.' However, whereas [Fe(CN),I4- and [Co(His),] react thermally at room temperature, no dark reaction was apparent, with the ruthenium complex. It is suggested that a mixed valence compound is formed in which Co"' and Ru" are linked by a cyano bridge; trans-amine-[Co(~-His)~]+ and all-cis-[Co(~-His)(~-His)] both appear to exhibit the same reaction pattern as the trans-imidazole isomer. A new method for determining CO" based on the chemiluminescence of Co"-luminol-acetylacetone mixtures has been announced and the formation of CO" complexes of fluorescein have been reported.lsZ For other reports on cobalt see references 25, 65, 168, and 170. +

+

+

'

11 Rhodium 2 6 , 7 8 9 98 Emission spectra and emission lifetimes of the complexes [M(2=phos),] ClO,,[M = Rh'? Ir'; k p h o s = cis- 1,2-bis(diphenylphosphino)ethylene] have been measured as a function of temperature and the results interpreted in terms of a two-level emitting manifold.' 5 3 Similar experiments have also been carried out on [RhA,X](ClO,), (A = NH, or ND,; X = C1, Br, or A) in the solid state.'', In the two-term rate law derived to fit the observations, one term dominates below about 150 K and the second dominates at 295 K. Ligandfield excitation of the Rh"' complex trans-[Rh(NH,),(OH)Y]"+, (Y = C1- or Br -) induces photoisomerization and ligand labilization giving l S 5 cis[Rh(NH,)4(HzO)(OH)]2 +.Following excitation, Y is thought to dissociate to give 14' 148

149 15* 15' 152

153

'51

M. Nishazawa and P. C. Ford, Inorg. Chem., 1981, 20, 294. H. D. Wohlers, K. D. Van Tassel, B. A. Bowerman, and J. D . Petersen, Inorg. Chem., 1980, 19,2837. L. I. Kirkovskii, M. B. Rozenkevich, and Yu. A. Sakharovskii, Koord. Khim., 1979, 5, 1359. S. Bagger, Acta Chem. Scand., Ser. A , 1980, 34, 63. G. Angelova, A. Panova, and D. Bakurdzhieva, Metalurgiya (Sojid) 1979, 34,27. B. Agarwal, B. V. Agarwala, and A. K. Dey, J . Indian Chem. SOC.,1980,57, 130. W. A. Fordyce, H. Rau, M. L. Stone, and G. A. Crosby, Chem. Phys. Lett., 1981,77,405. M. A. Bergkamp, R. J. Watts, and P. C. Ford, J. Phys. Chem., 1981, 85, 684. L. H. Skibsted and P. C. Ford, Inorg. Chem., 1980, 19, 1828.

The Photochemistry of Transition-metal Complexes

I87 an electronically excited, square-pyramidal complex [Rh(NH3)40H]2 , which subsequently reacts with water to produce the observed cis-product. In some related work156 cis- and trans-[Rh(en),XI]"+, (X = I, NH,, or H 2 0 ) photoaquate to ~rans-[Rh(en),(H,O)I]~+,and the stereochemistry of the photoproducts is consistent with the arguments of Vanquickenborne and Ceulemans. l s 7 Three separate reaction channels have been observed for trans- and cis[Rh(en),(NH,)II2+ with a strong preference for the Rh"' metal centre not to break a RhU1-enbond in a LF excited state. Further support for the Vanquickenborne and Ceulemans model has been forthcoming from a study of the photoisomerization of cis- and tr~ns-[Rh(en),(NH,)(H~O)]~at 313 nm and in aqueous HClO, at pH3.5. The results also show that the stereochemical course of a d6 substitution reaction can be driven and controlled by light, heat, or their combination. The photoluminescence spectrum, lifetime, quantum yield, and ligand photosubstitution reaction quantum yield have been reported for [Rh(NH,),C1I2+ in various solvents at room temperature. In water, LF excitation leads mainly to C1- substitution but in DMF, Me2S0, and MeOH as solvent, it is mainly NH, that is lost. Rate constants for various excited-state processes are determined and from these the conclusion is drawn that it is the rate of C1substitution with solvent variation that largely influences the nature of the predominant photoreaction. In aqueous solution, the emission of [Rh(NH,),BrI2 is quenched 160 by HO - according to Stern-Volmer kinetics, k , = 2.7 x 10" M s- at 5 "C. The photochemistry of this complex involves both NH, and Br- aquation and the results show that quenching of the emission also quenches the NH, aquation. These observations strongly suggest that the emitting state is involved in the NH, aquation process. A report has appeared lcil of the results of energy-transfer and electron-transfer quenching experiments involving the ,A2" excited state of some binuclear rhodium isocyanide complexes, e.g. [Rhz(br)J2 ,where br = 1,3-di-isocyanopropane, and [Rh2(TMB),I2 + , and TMB = 2,5-dimethyl-2,5-di-isocyanohexane.Detailed +

+

+

-

+

+ TMPD *[Rh(TMB),]'+ + TMPD *[RhZ(TMB),]'+ + PQz+ *[Rh(br),12+

+ TMPDf [Rh,(TMB),]+ + TMPD' [Rh2(TMB),I3+ + PQf [Rh,(br),]+

(3) (4) (5)

studies were made of the reactions (3H5), where TMPD = NNN'Mtetramethyl-p-phenylenediamine and PQ2 = paraquat. One-electron oxidation of [Rhz(br)4]2 by PQ2 is also observed but the kinetics of the back reaction are complex. Irradiation of a solution of [Rh2(br)4]2+, where br = 1,3-diisocyanopropane, in HC1 at 546nm leads 162 to the formation of Rh" and evolution of hydrogen. A cyclic process capable of splitting water has been shown +

+

lS6

+

lS8

S. F. Clark and J. D. Petersen, Inorg. Chem., 1980, 19, 2917. L. G. Vanquickenborne and A. Ceulemans, Inorg. Chem., 1978, 17, 2730. S. F. Clark and J. D. Petersen, Inorg. Chem.. 1981, 20, 280. M. A. Bergkamp, R. J. Watts, and P. C. Ford, J . Am. Chem. Soc., 1980, 102, 2627. M. T. Larson, A. W. Adamson, and R. C. Rumfeldt, Cov. Rep. Announce. Index (U.S.), 1980,80,

161

3576. S. J. Milder, R. A. Goldbeck, D. S. Kilger, and H. B. Gray, J . Am. Chem. Soc., 1980, 102, 6761.

H. B. Gray, V. M. Miskowski, S. J. Milder, T. P. Smith, A. W. Maverick, J. D. Buhr, W. L. Gladfelter, I. S. Sigal, and K. R. Mann, Fundam. Res. Homogeneous Catal., 1979, 3, 819.

188

Photochemistry

to be involved, as well as a solar chemical cycle that results in the conversion of a hydrohalic acid into hydrogen and free halogen. 12 Iridium 7 8 , 9 8 9 1 5 3

An investigation of solvent effects on the photoluminescence of cisdichlorobis( 1,10-phenanthroline)iridium(m) chloride and cis-dichlorobis(4,4dirnethyl-Z,2'-bipyridine)iridium(111) chloride over the range 2-77K has shown 163 that the luminescing excited state of each species is MLCT. The sensitivity of this method for assigning orbital characters of luminescing states is such as to establish cis-[IrC1,(4,4-Me2bipy),]C1 as a model CT emitter in place of cis-[IrCl,phen,)]Cl. Emission quantum yields, lifetimes, and photosolvation yields have been measured for cis-[IrCl,(bipy),] + and ~is-[IrCl,([~H,]-bipy),]+in several solvents including H,O, MeOH, DMF, and CH,CN. Both CT and LF states seem to be involved and photosolvation occurs by a dissociative or dissociative interchange mechanism.164 The photoreactions of [Ir(NH3)5X]3+(X = C1-, Br-, or I-), [Ir(NH,),LI3+ (L = NH,, H,O, MeCN, or PhCN), trans[IT(NH,)~I,]+,and tran~-[Ir(NH,),(H,O)1]~ have been examined in aqueous solution and the quantum yields of photoaquation and product distributions found to be independent of wavelength. It is concluded that LF excitation is followed by efficient ISC to give a common excited state, which is the lowest energy triplet LF state. Qualitatively the photochemistry of Ir"' ammine complexes appears to be similar to that of the Rh"' analogues. In some related work,166LF excitation of cis- and trans-[Ir(en),XY]+ (X = C1-, Br-, or I-; X = HO-; Y = C1-) in aqueous solution leads to labilization of the halide ligand. The transdichloro-complexes undergo p ho toaqua tion with complete reten tion, whereas with the cis-analogues, some photoisomerization is observed. These and other results are explicable in terms of a model proposed for the photostereochemistry of Rh"' tetra-ammine complexes. A facile photoreaction between hexachloroiridate(1v) and tetra-alkyltin in acetonitrile and at low temperatures has been reported. 16' Irradiation brings about cleavage of the tin alkyls probably by quenching of the photoexcited hexachloroiridate(1v) in an electron-transfer process [equation (6)]. +

*[IrCl,]'-

+ R,Sn

-

[IrC1J3-

+ R,Snt

(6)

13 Nickel The quenching of the luminescence of anthracene, biacetyl, and 1-bromonaphthalene has been studied using the complexes ML,(NCS), (M = Co, Mn, or Ni; L = 4-picoline), in both liquid and glassy solution. In the case of anthracene, a diffusion-controlled process seems to operate, for biacetyl the quenching is encounter-controlled, and for the BrC, ,H,-NiL,(NCS), system a dipolar and/or exchange-quenching process is involved. Irradiation of M[oC6H4(NH2)2]2,(M= Ni or Pt) in CHC1, at 350nm leads to photo-oxidation via 163 164

16' 166

16'

16'

T. L. Cremers and G . A. Crosby, Chem. Phys. Lett., 1980, 73, 541. B. Divisia, P. C. Ford, and R. J. Watts, J . Am. Chem. Soc., 1980, 102, 7264. M . Talebinasab-Sarvari, A. W. Zanella, and P. C. Ford, Inorg. Chem., 1980, 19, 1835. M . Talebinasab-Sarvari and P. C. Ford, Inorg. Chem., 1980, 19, 2640. S. Fukuzumi and J. K. Kochi, Inorg. Chem., 1980, 19, 3022. A. Guarino, E. Possagno, and R. Bassanelli, J. Chem. SOC..Faraday Trans. I , 1980, 76, 2003.

The Photochemistry of Transition-metal Complexes

189 an excited intraligand state giving the cation M[o-C6H4(NH),],+ and CHC1, :. This appears to be the first report of a photoreaction occurring in which the ligands are oxidized while the oxidation state of the metal remains unchanged.'69 The photoreduction of water has now been observed17' to occur in neutral aqueous THF solution in the presence of transition-metal dithiolene complexes (6) R = CN, Me, or Ph; M = Co, Fe, Pd, Pt, Mo, Ni, or W; n = 2 or $ 2 = 0, 1-,

or 2 - . Evolution of hydrogen has also been observed from solutions of the Ni complex (7) in dry THF. Photopolymerization of acrylonitrile in NiC1,-C,H4-glycol-HC1 and NiC1,-DMF-HCl systems at - 78 "C is reported to be initiated by a NiC1,-acrylonitrile complex formed in these systems.17' 14 Palladium and Platinum 16'* 170 The quantum yield of photoinduced trans-cis-isomerization of the four-coordinate planar complex trans-[PdX,(PPr,),] (X = C1, Br, or I) has been found to decrease in the order C1 > Br > I and to be independent of the wavelength of the exciting radiati~n."~ Increases in dipole moment also bring about increases in the amount of cis-isomer. In the particular case of the irradiation of trans[Pd(PPr,)Cl,] in MeNO,, the cis-configurationof the product has been established by X-ray analysis.173 The transformation appears to occur by an intramolecular mechanism involving a tetrahedral intermediate, which can collapse to a squareplanar form. Examination of the temperature-dependence of the luminescence of single crystals of the chain compound BaPd(CN),a4H2O has revealed the presence of two component^.'^^ One is short-lived (1011s) and is centred at -26 x l0,cm-l and one is long-lived (2ms at 5K) and is centred at 19 x lo3cm-'. A smaller spin-orbit coupling is more evident in Pd compounds than in Pt compounds, and this causes differences of lifetimes and emission energies between the two metals. An investigation of the photoisomerization of the Pt" complexes, cis- and trans(Et,P),PtPhCl, in MeCN has shown 176 that the cis-trans and trans-cis conversions occur by different mechanisms. The former appears to proceed by an intramolecular twisting in a low-lying LF state and the latter by a dissociative pathway from a CT state. The platinum complex (8) has been reported to display a

'',

-

169

170 17'

173 174 175

17'

A. Vogler and H. Kunkely, Angew. Chem. fnt. Ed. Engl.. 1980, 19, 221. R. Henning, W. Schlamann, and H. Kisch, Angew. Chem., Int. Ed. Engl., 1980, 19, 645. S.I. Mah, Hanguk Swnyu Konghakhoe Chi, 1979, 16, 215. M. Cusamano, G. Guglielmo, V. Ricevuto, S. Sostero, 0. Traverso, and T. J. Kemp, J. Chem. SOC., Dalton Trans., 1981, 302. N. W. Alcock, T. J. Kemp, F. L. Wimmer, and 0. Traverso, Inorg. Chim. Acra, 1980, 44,L245. N. W. Alcock, T. J. Kemp, and F. L. Wimmer, J. Chem. SOC.,Dalton Trans., 1981, 635. W. D. Ellenson, A. K.Viswanath, and H.H. Patterson, Inorg. Chem., 1981, 20, 780. L. L. Costanzo, S. Giuffrida, and R. Romeo, Znorg. Chim. Acta, 1980, 38, 31.

Photochemistry

190

hv S

s

CI

(8) S = Me,SO, MeCN

(9)

novel photochromic process.177 This consists of displacement of solvent on irradiation, and solvolysis of the product (9) in the dark in which the terminal aldehyde group reacts with a solvent molecule. A 5-co-ordinate intermediate is most probably involved in the thermal solvolysis and possibly also in the photosubstitution. 15 Copper Reviews have appeared of the photochemistry of copper complexes,17' the luminescence properties of copper(1) compounds,' 79 and of the mutual influence of ligands in co-ordination complexes.''O, The first emission and emission-quenching studies of bis(2,g-dimethyl-1,lOphenanthroline)copper(r) in fluid solution have been described,182 and at room temperature in CH2C12 the lifetime and quantum yield were found to be 54 & 10ns and 2 x respectively. Donor solvents such as MeOH, EtOH, and CH,CN tend to quench the emission, possibly by interaction with the metal centre. Luminescence spectra and decay times of emission have been measured 1 8 3 down to liquid helium temperatures for the complex [Cu(PPh,),(phen)]+ . The decay time at low temperatures suggests the involvement of a triplet level of the CT state and the radiative processes have to be described in terms of at least a threelevel system. A monoclinic form of the Cu' iodide pyridine complex has been prepared 84 but unlike the cubane tetrameric modification, this isomer does not show luminescence thermochromism. The photochemistry of copper@)chloride has been examined at 3 13 nm and 77 K in ethanol and HCl solutjon and has shown transient radical complex formation between Cu' and CH3CHOH. Photolysis of.DMF solutionsof [CuC1412- is reported 186 to lead to formation of the radical,CH,(CH,)NCHO, (10) and the Cu'-(lO) complex. At higher concentrations of [CuCl4l2-, photooxidation of (10) by excited [CuC1,J2- predominates. The photochemistry of the 177 178 179 180 181

182 I83 184 185

186

W. G. Rohly and K. B. Mertes, J . Am. Chem. SOC.,1980, 102, 7939. G. Ferraudi and S. Muralidharan, Coord. Chem. Rev., 1981,36, 45. H. D. Hardt and A. Pierre, Ann. Univ. Sarav., Math.-Naturwiss. Fak., 1980, 15, 7. J. Gazo, Proc. Conf. Coord. Chem., 8th, 1980, p. 99. J. Sykora, J. Sima, D. Valigura, E. Horvath, and J. Gazo, Proc. Conf. Coord. Chem., 8th, 1980, p. 393. M. W. Blaskie and D. R. McMillin, horg. Chem., 1980, 19, 3519. G. Blasse and D. R. McMillin, Chem. Phys. Left., 1980, 70, 1. E. Eitel, D. Oelkrug, W. Hiller, and J. Straehle, 2.Naturforsch., Teil B, 1980, 35, 1247. V. F. Plyusnin, N. M. Bazhin, and 0. B. Kiseleva, Zh. Fiz. Khim., 1980, 54, 672. V. F. Plyusnin, N. M. Bazhin, and 0. M. Usov, Koord. Khim., 1980, 6, 856.

The Photochemistry of Transition-metal Complexes

191

halocuprates has also been investigated 8 7 in connection with photochemical solar energy conversion. In particular, a study of their photo-oxidation in acidic media has included such topics as the nature of the optical transition and also of the photolysis intermediates, medium effects, and an evaluation of the efficiency of CTTS transitions. The intermediate produced in the flash photolysis of copper(I1) oxalato complexes in deaerated aqueous solution has been identified 18* as CuCO,. This species, which is also generated by pulse radiolysis of the Cu'I-oxalate-formate system, decays by first-order kinetics. A dependence of the rate constant on pH and on the concentrations of Cu" and oxalate ions is established and this is interpreted in terms of competing reactions of CuCO, [equations (7) and (8)]. CuCO,

+ 2H+

cuco, + CU"

-

Cu"

+ HC0,H

(7)

2cu'

+ co,

(8)

The copper(m) tetraglycinate complex [Cu(H- ,Gly,)] - is reported ls9 to be photodecomposed to triglycinamideand tetraglycine (Gly,). Product distributions vary with pH, and in neutral solution room light is found to cause substantial reaction. Another Cu"' complex Cu(H-,Aib,) in which the ligand is the tripeptide of cc-aminoisobutyric acid is known to undergo a similar photocatalysed decarboxylation, and an analogous decarboxylation leading to Gly is proposed in the case of the photolysis of [Cu(H-,Gly,)]-. Rate constants have been determined I g l for the photochemical bleaching of the thionine cation in salts such as Q5[Cu8LSH].1 1.5H20 (Q = Cu, Mn, or Mo containing Cu' and Cu"'; H,L = maleonitriledithiol; and Q,[Mo,L,O,(OH),] - 7.6H20, H,L' = toluene3,4-dithiol. The results show that incorporation of the thionine cation into the complexes increases its photoreactivity.

,,

16 Lanthanides A discussion has appeared of the mechanism of sensitization of Tb" luminescence by Ce"' in CaF,. As part of a search for reversible, photoinduced, oneelectron-transfer reactions of the type shown in equation (9), which can in hv

Ce3+(aq) + A"+(aq)7 Ce" A

+ A("-')+(aq)

(9)

principle generate a photogalvanic current, the photoinduced electron-transfer between Ce"aq and Cu"aq ions has been investigated Ig3 by ps flash photolysis. The primary photochemical step appears to be bimolecular collision of the lowest energy 4d -+ 5fexcited state of Ce"' with Cu" leading to CeIV and Cu' as the la'

"' la9

190 191

D. D. Davis, R. K. Thamburaj, K. L. Stevenson, and C. R. Davis, Energy Res. Abstr., 1980,5, Abstr. No. 330. S. Das and G. R. A. Johnson, J. Chem. Soc.. Faraday Trans. 1. 1980, 76, 1779. J. S. Rybka, J. L. Kurtz, T. A. Neubecker, and D. W. Margerum, Inorg. Chem., 1980, 19, 2791. S. T. Kirksey, T. A. Neubecker, and D. W. Margerum, J . Am. Chem. SOC.,1979, 101, 1631. M. Kaneko, H. Araki, and A. Yamada, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979,20, 1053.

192

193

M. S. Orlov, E. A. Pudovik, A. L. Stolov, and V. D. Shcherbakov, Paramagnitn. Rezonans, fKazan), 1978, 81. R. P. Asbury, G. S. Hammond, P. H.P. Lee, and A. T. Poulos, Inorg. Chem., 1980, 19, 3461.

192

Photochemistry

photoproducts. A method of determining organic carbon has been reported 194 using chemical and photochemical oxidation of the organic material with Ce(SO,), as sensitizer. In this procedure CO, is liberated and is determined coulometrically. Eu" ions are photo-oxidized in aqueous solutions of HC1 at room temperature by a mechanism that involves transfer of an electron from the excited ion to a proton or other acceptor.lg5 At Airr = 250 or 365nm, the reaction efficiency is increased with the acidity of the soluiion; Eu"' ions were observed to have an inhibiting effect. In frozen solutions of hydrohalic acids at 77K the photooxidation occurs by a similar r n e c h a n i ~ m , 'and ~ ~ under these conditions the rate constant measured for luminescence quenching was found to be in good agreement with the theoretical value.lg7 Ed' complexes of crown ethers and polyethylene glycols luminesce with an intense blue emission, which in the case of 15-crown-5 is over 600 times as strong as that of methanolic EuCl,. This enhancement is attributed to a reduced internal quenching rate. 19' A time-resolved study of the emission from Na3Eu(C4H,05), .2NaC10,. 6H20-europiumdiglycolatehas shown lg9 that following excitation to the 5D2(E) state, the emission from ' D o exhibits a fast and a slow build-up. This is interpreted in terms of two independent decay modes for 5D,.The luminescence of the complex formed between Eu"' and 2-propionylindan-1,3-dione has been studied 2oo at pH 4.0-4.5 and this forms the basis of a luminescence method for the determination of europium. Fluorescence measurements have been made 2o on Dy"', Er"', Eu'", and Sm"' salts of methacrylic acid-methyl methacrylate copolymer, and copolymers of acrylic acid with styrene, 1-vinylnaphthalene, and 1-vinylanthracene.In the case of Eu"', the results suggest the formation of ionic aggregates. The fluorescence intensity decreases in the order methacrylate > styrene > naphthalene > anthracene suggesting that the aromatic groups successfully compete with the exciting radiation and that there is negligible energy transfer from aromatic groups to the Eu"' ions. The coordination and solvation of Ed1' and Tb"' ions have been investigated 202 using fluorescence quenching and other techniques in anhydrous CH,CN (CD,CN) and DMF. In MeCN, Eu(NO,), is not dissociated whereas in DMF both ionic and coordinated NO, - are present. Similar results are obtained for Tb"'. Complexes of the form Ln(N0,)3(4-bipy),.4H,0 Ln = Eu, Tb, Lu, and LnC1,(4bipy),.6H20, Ln = Eu, Tb, Lu, or Y have been prepared 203 and all are found to be luminescent in the solid state. Similarly the fluorescence spectra of [EuL(NO,),]. H 2 0 and [EuL,](ClO,), -2H,O, L = 2,2"2""erpyridine-1,1',1''trioxide, have also been reported. 204 CPL (circularly polarized luminescence) 194

195 196 19'

19* 199

*O0 201 *02 203 '04

T. N. Ivanov and A. N. Atanov, Zh. Anal. Khim, 1980,35, 588. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Khim. Vys. Energ., 1980, 14,542. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Zh. Fiz. Khim., 1981,55, 138. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Zh. Fiz. Khim., 1981,55, 144. G.Adachi, K. Tomokiyo, K. Sorita, and J. Shiokawa, J . Chem. Soc., Chem. Commun., 1980,914. D.S.Roy, K. Bhattacharyya, A. K. Gupta, and M. Chowdhury, Chem. Phys. Lett., 1981,77,422. S.V. Bel'tyukova, N. S. Poluektov, T. B. Kravchenko, and L. I. Kononenko, Zh. Anal. Khim., 1980, 35, 1103. E. Banks, Y. Okamoto, and Y. Ueba, J . Appl. Polym. Sci., 1980,25, 359. J. C. G. Buenzli, J. R. Yersin, and M. Vuckovic, Rare Earths Mod. Sci. Technol., 1980,2, 133. D.M.Czakis-Sulikowska and J. Radwanska-Daczekalska, Pol. J . Chem., 1979,53,2439. A. Musumeci, R. P. Bonomo, and A. Seminara, Inorg. Chim. Acta. 1980,45,L169.

The Photochemistry of Transition-metal Complexes

193 measurements have been made 2 0 5 of the ternary complexes formed between pyridine-2,6-dicarboxylic acid (DPA), Tb"', and some amino-acids (AA). In Tb(DPA),(AA), a weak unipositive CPL was observed when the amino-acid was co-ordinated in a unidentate manner. For bidentate co-ordination, a doublesigned CPL was observed, and in the region pH8-10 this was also the case for most amino-acids. The fluorescence properties of several europium and samarium P-diketonates have been measured and assignments of the transitions made. 206 Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to The luminescence of the heptafluoroheptane-2,4-dionecomplexes of Sm, Eu, and Tb has been measured 208 in dilute ethanol at pH 8 and 610nm; mixed-ligand complexes with 1,lO-phenanthrolineexhibited an enhanced luminescence. Photolysis of the Tb"' chelate of 2,2,6,6-tetramethylheptane-3,5-dionehas been examined 209 at 3 1 1 nm in various alcohols, and loss of one P-diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 17 Uranium A review of the photochemistry of uranium compounds has appeared.210 In a paper discussing ground- and excited-state interaction between aquauranyl(v1) and nitrate ion, the structure and thermodynamic formation functions of photoexcited (UO,NO,)+ are shown to differ from those in the ground state.211 Exchange of the nitrato-ligand in excited (U02N03)+occurs faster than U022-Idecays, and the rate of deactivation, quantum yield, and radiative probability are higher than those of *UOZ2+.The luminescence of U 0 2 2 +in aqueous acidic NO3- and C10,- has been investigated in terms of acidity, temperature, selfquenching, and H-donor concentration. 'I2 Complex processes in which *[UO2HI2' and *[U2O4HI4+are formed adiabatically appear to be involved, and more than one mechanism may be necessary to explain the results. Another study of the luminescence lifetime of U 0 2 2 + ,reports 213 it to be strongly temperaturedependent at room temperature, but largely independent of temperature at 77 K. Both effects are sensitive to [2H]-substitution in such solvents as water, mildly acidic water, concentrated aqueous LiCl, and methanol. The low-temperature deactivation mechanism was concluded to be a physical process. The Ag +-induced quenching of U 0 2 2+ luminescence has been investigated l4 and analysed in terms of outer- and inner-sphere models. A mechanism is suggested in which electron transfer leads to formation of an excited-state inner-sphere complex of significant 205

206 207 208

209 210

212 '13 214

H. G. Brittain, J . Am. Chem. SOC.,1980, 102, 3693. H. G. Huang, K. Hiraki, and Y. Nishikawa, Nippon Kagaku Kaishi, 1981, 66. V. E. Karasev, N. I. Steblevskaya, and R. N. Shchelokov, Koord. Khim., 1981, 7 , 147. L. I. Konenko, T. B. Kravchenko, S. V. Bel-tyukova, V. E. Kuz'min, and E. S. Suprinovich, Ukr. Khim. Zh.. 1980, 46, 427. H. G. Brittain, J. Phys. Chem.. 1980,84, 840. R. T. Paine and M. S. Kite, ACS Symp. Ser., 1980, 131. M. D. Marcantonatos, M. Deschaux, and F. Celardin, Chem. Phys. Lett., 1980,69, 144. M. D. Marcantonatos, J. Chem. SOC.,Faraday Trans. 1, 1980, 76, 1093. A. Cox, T. J. Kemp, W. J. Reed, and 0. Traverso, J . Chem. SOC.,Faraday Trans. 1, 1980,76, 804. M. D . Marcantonatos and M. Deschaux, Chem. Phys. Left.,1980, 76, 359.

194

Photochemistry

binding energy. The first direct demonstration of electron transfer to the photoexcited uranyl ion in a reversible system appears to have been made.215 *U022+is quenched by [Ru(bipy),]'+ to give [Ru(bipy),13+ and conversely, . [Ru(bipy),13+ is observed to be the *[Ru(bipy),]'+ is quenched by U 0 2 2 + Again product showing that UO," is an electron acceptor in both its excited and ground state. Values have been determined 2 1 6 for the luminescence quenching of uranyl ions by inorganic ions such as Co2+,Pb2+,Cu2+,Ce3+,Hg22+,Tl', Ag', Mn2+,CNS-, C1-, Br-, I-, and NO2- in aqueous solution at pH2.3 and room temperature. The values suggest that quenching occurs by intermolecular electrontransfer. In the cases of Cu2+,Co2+,Mn2+, and NO,'-, however, quenching by an energy-transfer mechanism is also possible. A mechanism (Scheme 3) has been

Scheme 3

proposed * 1 7 for the UOZ2+-or Fe2'-catalysed photo-oxidations of olefins for which the term 'long-range electron-transfer mechanism' has been suggested. It involves interligand electron-transfer from the electron-donating ligand (HO- or C1-) to O2 through the metal ion and olefin molecule, and is similar to the pathway already suggested * for the TiC1,-catalysed photoreactions of ketones with methanol. Support for this comes from the establishment of a correlation between reactivities and product ratios with half-wave reduction potentials of the polyhalogenated compounds. The results of a study219 of the photolysis of the uranyl-malonic acid-bimalonate system suggest that the primary photosensitive species is a (1 : 1) uranyl bimalonate complex, which forms as a precipitate. Kinetic and other evidence supports the mechanism shown in equations (1 O H 1 3), where Ma1 = malonate. UOZ2++ HMal-

UO,(HMal)+

UO,(HMal)+

(10)

, 2 UO,*(HMal)+

(1 1)

hv

dark

UVb,*(HMal)+ UVO2+

+ &,CO,H

UVO2++ &,CO,H

+ CO,

Uv'022+ + CH,CO,-

(12) (13)

Several interesting photoreductions of the excited uranyl ion have appeared. Irradiation of U 0 2 2 + in MeCN or PrCN solution using wavelengths above 400nm brings about reduction by a first-order process, which is in competition with physical quenching pathways.220 No ground-state complex seems to be involved, and the reduction proceeds by an a-H-abstraction from the nitrile '16 217 2'8

219

220

T. Rosenfeld-Gruenwaldand J. Rabani, J. Phys. Chem., 1980,84, 2981. G. I. Romanovskaya, V. I. Pogonin, and A. K. Chibisov, Zh. Prikl. Spektrosk., 1980, 33, 850. E. Murayama, A. Kohda, and T. Sato, J . Chem. Sac., Perkin Trans. 1, 1980, 947. T. Sato, S. Yoshiie, T. Imamura, K. Hasegawa, M. Miyahara, S. Yamamura, and 0.Iro, Bull. Chem. SOC.Jpn., 1977, 50, 2714. A. G. Brits, R. Van Eldik, and J. A. Van den Berg, Inorg. Chim. Acta, 1980, 39, 47. A. S. Brar, R. Chander, and S. S. Sandhu, Indian J . Chem., Sect. A , 1979, 17, 554.

195

The Photochemistry of Transition-metal Complexes

molecule. Photoreduction of U 0 2 2 +is also reported 2 2 2 to occur on irradiation of solutions containing either Ph,P or Ph,Bi and gives UIV and Ph,PO or Ph,BiO, respectively. An exciplex seems to be formed in both reactions followed by oxygen-atom transfer. The structure of tetra(glycinato)uranium(Iv) dihydrate, a photoreduction product of U022fin the presence of glycollic acid, has been determined by X-ray cry~tallography.~~~ A study of the luminescence of uranates and of energy-transfer processes involving these compounds has been reported 224 and the excitation spectra of the luminescence of the uranate group has been described for various U-doped corn pound^.^^^ The decay of UF, fluorescence following 375 nm excitation has been reviewed,226and UF, also undergoes 227 decomposition following irradiation with a TEA-CO, laser in the presence of SF,. 221v

18 Actinides The photochemistry of the Np'", NpV,and Np"' ions has been investigated 228 in HNO, solutions at 254 and 300 nm. All oxidation states were converted to Np". In the presence of urea and mild reducing agents, the quantum efficiencies were found to vary widely and to be a function of pH, wavelength, and reaction conditions. The Np"' ion will undergo 2 2 9 photo-oxidation to Np"'" in aerated solution and in A decrease in the rate of this transformation was the presence of K2S208. observed with increasing concentrations of LiOH or an addition of NO,-. 47

221

222

223 224 225

226 227 228

229

A. S. Brar, A. S. Sarpal, and S. S. Sandhu, Indian J. Chem.. Sect. A , 1980, 19, 413. A. S. Brar, A. S. Sarpal, and S. S. Sandhu, Indian J. Chem., Sect. A , 1980, 19, 902. N. W. Alcock, T. J. Kemp, S. Sostero, and 0. Traverso, J . Chem. SOC.,Dalton Trans., 1980, 1182. D. M. Krol, INIS Atomidex, 1980, 11, Abstr. No., 550026. K. C. Bleijenberg, J. Chem. Phys.. 1980, 73, 617. R. Cubeddu, Quad. Ric. Sci., 1980, 105, 27. R. S . Kame, S. K. Sarkar, K. V. S. Rao, and J. P. Mittal, Chem. Phys. Lett., 1981, 78, 273. L. M. Toth and H. A. Friedman, Radiochim. Acta, 1980,27, 173. V. P. Shilov, E. S. Stepanova, and N. N. Krot, Radiokhimiya, 1980, 22, 5 3 .

2 The Photochemistry of Transition-metal Organometallic Compounds, Carbonyls, and Low-oxidation-state Compounds BY J. M. KELLY AND C. LONG

1 General The photoactivation of organometallic catalysts and the infrared laser photochemistry in low-temperature matrices have been the subject of recent reviews.

,

2 Titanium and Zirconium Previous studies (especially using deuterium-labelled compounds and solvents) have revealed that photo-excitation of dialkyltitanocenes Cp2MR2leads to several products including RH formed by hydrogen-atom abstraction from the cyclopentadienyl ring. A recent investigation of CIDNP observed during irradiation of Cp,MMe, (M = Ti or Zr) in solution both in the presence and absence of trapping agents such as oxygen, thiophenol, and nitroxides provides much useful information on the nature of the initial steps in this type of r e a ~ t i o n .It~ was observed, for example, that during irradiation of Cp,TiMe, or (MeCp),TiMe, in oxygen-free solution there were no changes in the n.m.r. spectrum of the sample. However, if traces of oxygen were present, enhanced absorption of the metalbound methyl group of the starting material, a very small emission signal from ethane, and a small enhancement for methane were detected. On the basis of Kaptein’s rules it was shown that (i) a singlet excited state was responsible for the observed reaction, (ii) the recombination [equation (l)] is highly efficient, and (iii) methane is formed from caged radicals whereas ethane is produced from escaped methyl radicals. In the presence of methanol, the n.m.r. signal of the metal-bound methyl of the product Cp,TiMeOMe is seen in emission, consistent with the reaction of methanol with the caged radical pair rather than with the escaped products [equation (2)]. Cp,TiMe, Cp,TiMe

+ Me’ + MeOD

hv

~

-4

---+

-

Cp,TiMe

+ Me’

Cp,TiMe(MeOD)

------+ Cp,TiMeOMe

+ Me’

+ MeD

(2)

M . S. Wrighton, J. L. Graff, C. L. Reichel, and R. D. Sanner, Ann. NY Accid. Sci.,1980, 333, 188. M. Poliakoff and J. J. Turner, in ‘Chemical and Biochemical Applications of Lasers’, ed. C. B. Moore, Vol. 5, p. 175. P. W. N. M. Leeuwen, H. Van der Heijden, C. F. Roobeek. and J. H. G. Frijns, J . Orgrinomet. Chem.. 1981, 209, 169.

196

The Photochemistrj~qf Transition-metal Organonietallic Cornpounds

197

Photoinduced insertion of ethylene into the M-Me bond is observed for Cp,ZrMe, [equation (3)], but not for c ~ , T i M e , . ~Upon irradiation Cp,TiR, Cp,ZrMe,

+ C,H,

I1 1s

Cp,ZrPr"Me

(3)

(R = Me, Bz, or Ph) are converted into catalysts for the hydrogenation of olefins, the reaction being truly photocatalytic for Cp,TiMe, and Cp,TiBz, and photoassisted for c ~ , T i P h , . In ~ each case the initiating step has been identified as homolysis of the Ti-C bond, and the Ti"' species was monitored by e.s.r. Either styrene or methyl methacrylate can be caused to polymerize by irradiating (Bu'CH2),Ti in their presence. The molecular-weight distribution in both cases is bimodal suggesting that both the (Bu'CH,),Ti and the neopentyl radical may initiate the polymerization.

A mixture of q4-diene zironocene complexes (1) and (2) is formed on photolysis of Cp,ZrPh, with 1,3-dienes at - 30 oC.6It was further observed that the sym-cisform could be completely transformed into the sym-trans- form by irradiation. Although photosubstitution of Cp,Ti(CO), by PF, proceeds readily, that of its analogue (C,Me,),Ti(CO), does not occur under similar conditions.' 3 Vanadium and Niobium Photocleavage of the M-Me bond is observed for Cp,VMe, Cp,NbMe,, and Cp,VMe,.' The first two complexes yield only methane as the organic product, whereas about 36% ethane is formed from Cp,VMe,. Labelling experiments reveal that the ethane is formed by both inter- and intra-molecular processes, whereas the hydrogen abstracted in the production of methane can come from a methyl group, the Cp-ring, or the solvent.' Cp,V,(CO),, which may be considered to contain a V-V bond, was prepared by photolysis of CpV(CO), in t.h.f.9 Photocleavage of this bond is not observed: photosubstitution of carbon monoxide (e.g. by phosphines) occurs instead. The photochemical formation of CpV(NO),CO by irradiation of CpV(CO), and [Co(NO),Br], has been described." Photolysis of CpNb(CO), in hexane solution gives the unusual cluster Cp,Nb,(C0)7,", whereas in t.h.f. the useful reagent 4

5 6

7 8

9 10 11

E. Samuel, J. Organomet, Chem., 1980, 198, C65. J. C. W. Chien, J.-C. Wu, and M. D. Rausch, J. Am. Chem. SOC.,1981, 103, 1180. G. Erker, J. Wicher, K. Engel, F. Rosenfeldt, W. Dietrich, and C. Krueger, J . Am. Cliem. Soc., 1980, 102,6344. D. J. Sikora. M. D. Rausch, R. D. Rogers, and J. L. Atwood, J . A m . Chem. Soc., 1981, 103, 982. D. F. Foust, M. D. Rausch, and E. Samuel, J. Organomel. Chem.. 1980, 193, 209. L. N. Lewis and K. G. Caulton, fnorg. Chem., 1980, 19, 1840. F. Nlumann and D. Rehder, J. Orgunornet. Chem., 1981, 204, 411. W. A. Herrmann, M. L. Ziegler, K. Weidenhammer. and H. Biersack, Angew. Chem. Int. Ed. Engl., 1979, 18, 960.

12

W. A. Herrmann, H. Biersack, M. L. Ziegler, K. Weidenhammer. R. Siegel, and D. Rehder, J . Am. Cliem. SOC.. 1981, 103, 1692.

198

Photochemistry

CpNb(CO),(t.h.f.) is formed: this has been employed to yield I3CO and phosphine derivatives, ' and sulphur-bridged binuclear complexes. ' [V(CO) (m.t .h.f.)] - and cis-[V(CO),(m. t .h. f.)2]- have been characterized in low-temperature solvent glasses following photodissociation of [v(Co),] - in the presence of methyltetrahydrofuran (m.t.h.f.)." Compound (3) is formed by irradiation of [v(co),]- and 3-chlorocyclohex- 1-ene.

,

4 Chromium, Molybdenum, and Tungsten The photochemistry of the Group VI hexacarbonyls in low-temperature solvent glasses continues to attract attention.". 1 7 - l 9 The infrared spectra of M(CO), (hydrocarbon) in methylcyclohexane ' and methylcyclohexane-isopentane l 5 glasses, as well as the spectra of M(CO),(arene).I7 M(CO),(H,0),'8 and M(CO),L (L = m.t.h.f., Me,CO, MeCHO, and MeOH) have been recorded. U.V. irradiation of M(CO), in hydrocarbon glasses for extended periods gives M(CO), and M(CO), as well as M(CO),.' 8, l 9 Irradiation at longer wavelengths causes partial reversal of M(CO), to M(CO), and of M(CO), to M(CO),. C0,laser-induced decomposition of metal carbonyls including Cr(CO), has been studied. 2o (q2-L)M(CO), and (q2-L),M(CO), (M = Mo or W) (L = methyl acrylate or dimethyl acrylate) are formed by irradiation of M(CO), in the presence of the ligand.2' Irradiation of Mo(CO), with 3,4-dimethylphosphole or l-phenylphosphole gives the dimer complexes (4)and (5) as well as the expected Mo(CO), derivatives. 22

(4)R l3

l4 l6 I' l9 'O 21

22

=

Me, P h , or But

(5)

W. A. Herrmann and H. Biersack, J. Organomet. Chem., 1980, 191, 397. W. A. Herrmann, H. Biersack, M. L. Ziegler, and B. Balbach, J. Organornet. Chern., 1981, 206, C33. J. D. Black, M. J. Boylan, P. S. Braterman, and A. Fullarton, J. Chem. Soc., Dalton Trans., 1980, 1651. U. Franke and E. Weiss, J. Organornet. Chern., 1980, 193, 329. D. R. Tyler and D. P. Petrylak, J. Organomet. Chem., 1981, 212, 389. M. J. Boylan, J. D. Black, and P. S. Braterman, J . Chem. Soc., Dalton Trans., 1980, 1646. J. D. Black and P. S. Braterman, Inorg. Chim. Acta, 1980, 44,L181. Y. Langsam and A. M. Ronn, Chem. Phys., 1981, 54, 277. F. W. Grevels, M. Lindemann, R. Benn, R. Goddard, and C. Krueger, Z. Naturforsch., Teil 5 , 1980, 35, 1298. C. C. Santin, J. Fischer, F. Mathey, and A. Mitschler, J. Am. Chem. Sac., 1980, 102, 5809.

The Photochemistry of Transition-metal Organometullic Compounds 199 The nature of the intermediate species formed on photolysis of mixtures of M(CO), and CCl,, (a useful initiating system for olefin metathesis 23 and acetylene polymerization 24) have been further investigated using spin-trapping reagents.25 It is known from the work of Wrighton et that for W(CO), L complexes the luminescence properties in solvent glasses at 77K and the photochemical behaviour in fluid solution at room temperature are determined by the relative energies of the LF and MLCT excited states. In that work it was shown that when the LF state is lowest the complex undergoes CO-photosubstitution efficiently and exhibits short-lived emission (- 1 ps) in EPA glasses at 77 K, whereas when the CT state is lowest photosubstitution is much less efficient' and the observed lifetime much longer ( 15-30 ps). It has now been reported that relatively weak emission = 640nm; z = 360ns) even in may be observed from W(C0),(4-CNpy) (A, fluid solution and this has allowed a comparison of the photochemical and emission properties of this complex." It undergoes relatively inefficient (a = 0.021 at 25 "C) CO-photosubstitution with an apparent activation energy of 32 kJ mol- '. Both the emission and the photoreaction may be quenched by anthracene and the same Stern-Volmer constant is found in both cases, indicating that the same state (i.e. the MLCT species) is involved in both processes. However, another attractive explanation is that the photoreaction takes place from the LF state reached by thermal activation from the lowest but non-reactive MLCT state. Recent studies with other M(CO),L complexes 2 8 - 3 2 reveal that there are substantial differences between their photochemical and photophysical properties in low-temperature matrices, solvent glasses, and fluid solution, which is due, at least in part, to the temperature dependence of the non-radiative processes. W(CO)5L (L = py, 3-Br-py, and piperidine) all show two emission bands (at about 420 and 530 nm, respectively) in argon or methane matrices at 12 K, whereas + ' A , phosphorescence) is only the lowest-energy emission (assigned as the recorded in solvent glasses at 77K.28 The higher energy band is assigned to ' E + 'A, fluorescence, and it is assumed that the observation of the fluorescence is due to the markedly reduced rate of internal conversion at 12 K. The phosphine complexes W(CO),PMe, and W(CO),PCl, show only weak fluorescence and no phosphorescence in 12K matrices, possibly because the triplet state is not appreciably p ~ p u l a t e d . ~The ' photochemical behaviour of Cr(CO),PMe, and Cr(CO),PCl, in argon matrices differs strikingly, CO-loss being predominant for the former and PC1,-expulsion for the latter.29 These results have been explained by the existence of two photoactive excited states, whose relative position is dependent on the ability of the unique ligand to undergo x-backbonding with the

-

23 24

" " 28

F. Garnier and P. Krausz, J . Mol. Catal., 1980,8,91. T. Masuda, Y. Kuwane, K. Yamamoto, and T. Higashimura, Polym. BUN. (Berlin), 1980,2 , 823. R. G.Gasanov and R. Kh. Freidlina, Dokl. Akad. Nauk SSSR, 1980,254, 113. M.S.Wrighton, H. B. Abrahamson, and D . L. Morse, J . Am. Chem. SOC.,1976,%, 4105. A. J. Lees and A. W. Adamson, J . Am. Chem. Soc., 1980, 102,6874. G.Boxhoorn, A. Oskam, E. P. Gibson, R. Narayanaswamy, and A. J. Rest, fnorg. Chem., 1981,20,

783. 30

G.Boxhoorn, G . C. Schoemaker, D. J. Stufiens, and A. Oskam, fnorg. Chim. Acta, 42, 241. G.Boxhoorn, G. C. Schoemaker, D. J. Stufkens, A. Oskam, A. J. Rest, and D. J . Darensbourg, fnorg.

31

Chem., 1980, 19,3455. G.Boxhoorn, G. C. Schoemaker, D. J. Stufkens, and A. Oskam, Inorg. Chim. Acta, 1981,53,L121.

29

'' G . Boxhoorn, D. J. Stufkens, and A. Oskam, J. Mol. Strurt., 1980,60,321.

200

Photochemistry

metal. The sensitivity of the photochemistry of M(CO),L in argon or methane matrices to irradiation wavelength has been exemplified by studies with M(CO),(pip) (M = Cr, Mo, or W) 30 and Cr(CO),(pyrida~ine).~'The latter case is particularly interesting as it appears to suggest that MLCT states can be photoreactive even when thermal activation is unlikely. The photochemical behaviour of Cr(CO),NMe, has been found to depend on the temperature of the xenon matrix.32 MCD studies of M(CO),EPh, (M = Cr or W; E = P, As, or Sb) 3 3 and M(CO), (alkylamine) 34 confirm that the lowest-energy spin-allowed band arises from a ' E t ' A , transition. Photoexcitation of W(CO), CPh, appears to yield diphenylcarbene as this has been trapped by diethyl f ~ m a r a t e . ~In ' the absence of trapping agents Ph,C=CPh, is formed, probably by reaction of the carbene with W(CO),CPh,. A full report has been published on the resonance Raman spectra of M(CO), (di-imine) (M = Cr, Mo, or W), and their relevance to the photosubstitution reactions of the complexes has been discussed.36 It was observed that the complexes are only photoactive if v, (COcis) shows resonance enhancement of Raman intensity. This enhancement is a result of the CT transition causing delocalization of the negative charge over the cis-carbonyls and hence reduction of n-backbonding with the metal and weakening of the M - C O bond. A useful polymer-bound catalyst has been prepared by photolysis of Cr(CO),(norbornadiene) in the presence of polystyrene-containing pendant PPh, groups. 3 7 Photodecarbonylation of (arene)Cr(CO), derivatives has been employed in the preparation of (phenanthrene)(Cr(CO), bound to phosphinated p ~ l y s t y r e n e ,in ~ ~the synthesis of the structurally unusual (C6Et6)Cr(CO),PPh,,,' and in the formation of the cluster (~6-PhMe)CrCo,(yS-C,Me,),(CO)4.40 In the presence of 6,6-dimethylfulvene, photolysis of (arene)Cr(CO), leads to both carbon monoxide and arene elimination and the consequent formation of (6).41

The principal reaction induced by photoexcitation of CpM(CO),Et (M = Mo ~ or W) is olefin elimination with the consequent formation of C P M ( C O ) , H . ~In the presence of PMe,, the product is CpM(CO)(PMe,),M(CO),Cp. The nitrene complex (7) is formed in low yield by irradiation of CpMo(CO),Me in the 33 34

35 3h

37 38 3y

" 42

A. F. Schreiner, S. Amer, W. M . Duncan, and R. M. Dahlgren, J . Phys. Chem., 1980, 84, 2688. A. F. Schreiner, S. Amer, W. M. Duncan, G. Ober, R. M . Ddhlgren, and J. Zink, J . Am. Chem. SOC., 1980, 102, 687 1 . B. H . Edwards and M. D. Rdusch, J . Orgunomel. Chem., 1981, 210, 91. R. W. Balk, T. Snoeck, D . J. Stufkens, and A . Oskam, Inorg. Chem., 1980, 19, 3015. H . B. Gray and C. C. Frazier, US P, 4228035, 1980 (Chem. Ahsfr., 1981, 94, 37 128). D. Tatarsky, D. H. Kohn, and M . Cais, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1387. G. Hunter. D . J. Iverson, K. Mislow, and J. F. Blount, J. Am. Chem. Soc., 1980, 102, 5942. L. M. Cirjak, J . 3 . Huang, Z.-H. Zhu, and L. F. Dahl, J . Am. Chem. Soc., 1980, 102, 6623. F. Edelmann, D. Wormsbaecher, and U. Behrens, Chem. Ber., 1980, 113, 3120. H. G. Alt and M. E. Eichner, J . Orgunomer. Chem.. 1981, 212, 397.

The Pli o tochemis t ry of Transition-metal Organome tallic Compounds

20 1

presence of BzN,.,~ Photo-induced 1,2-methyl migration to yield CpM(CO),Me (M = Mo or W) has been observed for CpM(CO),PbMe,, whereas with the corresponding triethylplumbane derivative the product is [CpM(C0)3]2PbEt,.44 The photochemistry of Cp,Cr,(CO), and ($-C,Me,),Cr,(CO),, which contain Cr-Cr triple bonds, has been in~estigated.~’ The observed photoreaction is expulsion of carbon monoxide and not cleavage of the C d r bond. The increasing quantum yield for CO-dissociation at shorter wavelengths indicates that an upper excited state is involved. Irradiation of Cp,Mo,(CO),(EtC&Et) in the presence of hydrogen and EtCECEt yields (8).46 Oxidation of the 17-electron species CPW(CO)~generated by photolysis of [CpW(CO)3]2has been

(8)

The spectroscopic properties and photochemistry of Cr( 1-norbornyl), have been studied.48 The primary process is loss of a norbornyl radical following the homolytic cleavage of the metal-alkyl bond, although the identity of the final chromium-containing product is still uncertain. The photoactive state appears to be a LMCT species as quantum yields in the U.V. are quite high (@366 = 0.036), whereas visible light excitation of the LF states is inefficient in inducing the reaction ( @ 5 5 0 = 2-3 x lo-,).

5 Managanese and Rhenium The photocleavage of Mn,(CO),, or Re,(CO),, has been carried out in the presence of ferricenium ions, substituted ferricenium ions, and other mild oxidants.47 Relative rates for the oxidation of the initial photoproduct M(CO), compared with the rate of chlorine abstraction from CCI, have been obtained. Products identified following photolysis of Mn,(CO),, or Re,(CO),, in the presence of 3,5-di-t-butyl-1,Zbenzoquinone (DBQ) are Mn(DBQ), 49 and Re(CO),(DBQ).’O Initial formation of Mn(CO), is also implicated in the photochemical synthesis of [Mn(CO),EPh], (E = Se or S) from Mn,(CO),, and from Ph,E, 5 1 and of the polynuclear complex { Rh,L,[Mn(CO),],)(PF,), Mn,(CO),, and Rh,L4PF, (L = 2,4-dimethyl-2,5-di-i~ocyanohexane).~~ 43 44 45 46 47

48 49

R. Korswagen and M. L. Ziegler, Z. Naturforsch., Teil B, 1980, 35, 1196. K. H.Pannell and R. N. Kapoor, J. Organomet. Chem., 1981, 214, 47. J. L. Robbins and M. S. Wrighton, Inorg. Chem., 1981, 20, 1133. S. Slater and E. L. Muetterties, Inorg. Chem., 1981, 20, 946. A. F. Hepp and M. S. Wrighton, J. Am. Chem. SOC.,1981, 103, 1258. H. B. Abrahamson and E. Dennis, J. Organomet. Chem.. 1980, 201, C19. M. W. Lynch, D. N. Hendrickson, B. J. Fitzgerald, and C. G. Yierpont, J. Am. Chem. SOC., 1981,103, 3961.

50 51

52

K. A. M. Creber and J. K. S . Wan, J . Am. Chem. SOC.,1981, 103, 2101. P. Jaitner, J. Organomet. Chem., 1981, 210, 353. D. A. Bohling, T. P. Gill, and K. R.Mann, fnorg. Chem., 1981, 20, 194.

202

Photochemistry

The primary photoproduct of U.V.photolysis of Mn(CO),X and Mn(CO),R ( X = C1, Br, or I;,, R = Me or MeCO 54) in argon or methane matrices at 12 K is the trigonal bipyramidal complex [Mn(CO),X or Mn(CO),R] in which the unique ligand occupies an equatorial position. The u.v.-induced photoreaction of Mn(CO),Me as in equation (4) may be reversed using longer wavelength Mn(CO),Me

-

Mn(CO),Me

+ CO

(4)

radiation. However an analogous reverse reaction is not observed with Mn(CO),COMe. Instead it was noted that this species rearranges to Mn(CO),Me, thereby offering some support for the theory that in solution the decarbonylation of Mn(CO),COMe to Mn(CO),Me may proceed by a dissociative mechanism. Examination of the chemical, electrochemical, and spectroscopic behaviour of R,EM(CO),L (R = Ph or Me, E = Ge or Sn, M = Mn or Re, L = phen or bpy) reveals that the lowest state is one in which an electron has been transferred from the HOMO, which has sigma E-M bonding character to the LUMO which is mainly localized on L.55The rhenium complexes emit in fluid solution at room temperature, and the luminescence may be quenched by both electron acceptors and electron donors, as in reactions ( 5 ) and (6). No net photochemistry is observed

+Q Ph,Sn-Re(CO),(phen)* + Q

Ph,Sn-Re(CO),(phen)*

-

[Ph,Sn-Re(CO),(phen)l+ [Ph,Sn-Re(CO),(phen)l-

+ Q+ Q'

(5)

(6)

for reductive quenching (6),whereas the cation formed by oxidative quenching ( 5 ) decomposes to give [Re(CO),(phen)]+ and Ph,Sn, as predicted from cyclic voltammetry experiments. MLCT state offac-[XRe(CO),L,] (X = C1, L = 4-PhCOpy; X = I, L = 4MeCOpy) is quenched by NEt, via an electron-transfer mechanism. Photolysis eventually leads to reduction of the co-ordinated ketone to the corresponding alcohol and oxidation of NEt, to Et,NH and MeCHO. As the irradiated alcohol slowly exchanges with free ketone in solution this photoreaction can be exploited to effect the reduction of ketones to alcohols using visible light. Data from resonance Raman experiments confirm that the lowest-energy absorption bands of various Re(CO),(di-imine)X complexes are MLCT in ~ h a r a c t e r . ~ ' The infrared spectra of the decarbonylation photoproducts of CpMn(CO),, (MeCp)Mn(CO),, and CpMn(CO),(CS) in low-temperature solvent glasses have been recorded.58 In general the rate of photolysis of these starting materials is less than that for M(CO), suggesting that rapid CO-recombination may be occurring. In alcohol glasses two CpMn(CO),(ROH) species, probably rotamers, have been observed. The preparation of MnCo, clusters by the photoreaction of CpMn(CO), and (C,Me,),Co,(CO), has been de~cribed.~'Photolysis of CpMn(CO),CPh, liberates the carbene CPh,, and the organic products obtained

''

53

''

'' 56 57

5N

T. M . McHugh, A. J. Rest, and D. J. Taylor, J . Chem. Soc., Dulfon Trans., 1980, 1803. T. M . McHugh and A. J. Rest, J . Chem. Soc., Dalton Trans., 1980, 2323. J . C. Luong, R. A. Faltynek, and M . S. Wrighton. J . Am. Cliern. SOC.,1980, 102, 7892. S. M . Fredericks and M. S. Wrighton, J . Am. Chem. Soc., 1980, 102, 6166. R . W. Balk, D. J. Stufkens, and A. Oskam, J . Cliem. SOC.,Dalton Trans., 1981, 5 , 1124. J. D. Black, M. J. Boylan, and P. S. Braterman, J . Chem. Soc., Dalron Trans., 1981, 673.

203

The Pliotocliemistry of Transition-metal Orgunometallic Compounds

in hexane solution include hydrogen-abstraction products Ph,CH, and Ph,CHCHPh,, and its dimer Ph2C=CPh2.35 Both the emission lifetime and quantum yield of D,Re,(CO), are greater than those of H4Re,(C0),2 owing to the decreased rate of non-radiative decay in the lowest triplet state of the deuteriated complex.59 A similar but somewhat larger effect is noted for [H6Re4(C0)12]2- and [D6Re4(CO)12 ] 2 - , the increased magnitude of the effect being possibly attributable to the H atoms in [H,Re,(CO), 2]2being edge-bridging, whereas those in H,Re,(CO) are face-bridging. Dihydrogen is eliminated upon U.V.irradiation of ReH 3(Ph2PCH2CH2PPh2)2, and the resulting reactive fragment ReH(Ph,PCH,CH,PPh,), has been trapped by N,, CO, C2H4, or C2H2.60If the irradiation is carried out in C6D6 solution, deuterium is exchanged between solvent and the complex presumably via the rapid insertion and elimination reactions (7) and (8). In ReH,(PMe,Ph),, efficient

,,

,

ReH( Ph ,PCH ,CH PPh,)

, + C6D,

-

ReH D(C D5)( Ph,PCH ,CH 2PPh,)

ReHD(C,D 5)( Ph ,PCH ,CH ,CH ,PPh,), ReD(Ph,PCH,CH,PPh,), ____+

,

(7)

+ C,D,H

(8)

photo-induced exchange between the metal-hydride protons and those of benzene or the phenyl group of the phosphine ligand occurs.61 However in this case the primary photoprocess is expulsion of a phosphine ligand and not elimination of dihydrogen. In the absence of excess phosphine, the products are H,Re,(PMe,Ph), or H,Re(PMe,Ph),. 6 Iron, Ruthenium, and Osmium

Photo-oxidation of ferrocene by CC1, in solution can normally only be effected by U.V.irradiation. However it has been observed that the reaction may be carried out with visible light in cetyltrimethylammonium chloride micelles, albeit with low quantum yield.62 It is suggested that the main effect of micellization may be an increase in the oxidation potential of ferrocene or alternatively that a CTTS state of ferrocene is involved under these conditions. The ring substitution of ruthenocene by irradiation in 1 : 1 (v/v) solutions of ethanol with CCl,, CHCl,, or CH2C12proceeds by a mechanism similar to that previously found for f e r r ~ c e n e . ~ , Other reports consider the synthesis of ferrocenyl thioesters 64 and the photooxidation of f e r r ~ c e n e . ~ ' Visible (A > 400nm) excitation of [CpFe(p-xylene)]+PF,- in the presence of a suitable ligand L, e.g. isonitriles, phosphines, or CO, leads to expulsion of the pxylene and formation of [CpFeL3]+.66In acidic aqueous solution the product is Fe2 . +

59

6o 61 62

63 64 65

66

J . L. Graff and M. S. Wrighton, J . A m . Chem. Soc., 1981, 103, 2225. M . G. Bradley, D. A. Roberts, and G. L. Geoffroy, J. Am. Chem. Soc., 1981, 103, 379. M. A. Green, J. C. Huffman, and K. G. Caulton, J . Am. Chem. Soc., 1981, 103, 695. D. M. PdpSUn, J. K. Thomas, and J. A. Labinger, J . Organomel. Chem., 1981, 208, C36. A. Sugimori, M. Matsui, T. Akiyama, and M . Kajitdni, Bull. Chem. Soc. Jpn., 1980, 53, 3263. C. Gotzmer, US P, 4219490, 1980 (Chem. Abstr., 1980, 93, 239659). M . Yokota and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 192; Chem. Abstr., 1980,93,25561. T. P. Gill and K. R. Mann, Inorg. Chem., 1980, 19, 3007.

204

Photochemistry

Two transients have been observed following flash photolysis of Cp,Fe,(C0),.67 From a study of their spectra, kinetics, and reactivity towards CO, phosphines, or CCI,, they have been assigned as CpFe(CO), and Cp,Fe,(CO), This finding should help to reconcile the uncertainties of the primary photoprocesses of Cp,Fe,(CO), discussed in last year’s Report. Photolysis of Cp,Fe,(CO), in the presence of 2-3-diazanorbornene (dnb) yields Cp,Fe,(CO),(q’-dnb) and Cp,Fe,(CO)2(q2-dnb).68 Carbene complexes (9) are formed by photolysis of a mixture of Cp,Fe,(CO), and N,CHCO,R (R = Et or

(9)

(10)

Recent reports on the photochemistry of CpFe(CO),-derivatives include the observation of CpFe(CO),Me following irradiation of CpFe(CO),PbMe,,” the formation of the orthometallated derivative (10) and the elimination of Ph,MeSiH upon irradiation of CpFe(CO),SiMePh, and P(OPh),,’ the photodecarbonylation of CpFe(CO),(trans-COCH=CHR) (R = Me or Ph) to give the corre~ the observation sponding alkenyl complex C p F e ( C 0 ) , ( t r a n ~ - C H 4 H R ) , ’and of CpFe(C0) (m.t.h.f.)I upon photolysis of CpFe(CO),I in methyltetrahydrof ~ r a n . ’ ~The photoelimination of ethylene from CpFe(CO),Et, giving CpFe(CO),H, has been monitored in low-temperature matrices. 7 3 In the same report it is also shown that the initial photoprocess in the conversion of (1 1) into

(13)

(14)

(15)

( 1 2) is CO-expulsion, with the methyl migration from the cyclopentadiene ring to

the metal occurring either when the matrix is allowed to warm or when it is further ”

”

‘’ ’()

”

’’ ’.’

J. V. Caspar and T. J . Meyer, J . Am. Chem. SOL-.,1980, 102, 7794. R . Battaglia, P. Mastropasqua, and H . Kisch, Z . Noturforsck., Teil B, 1980, 35, 401. W. A. Herrman, J . Plank, I. Bernal, and M. Creswick, 2. Nnrurfbrsciz., Teil B, 1980, 35, 680. K. H . Pannell, J. Orgnnomet. Ciiern., 1980, 198, 37. G. Cerveau, G . Chauviere, E. Colomer, and R. J. P. Corriu, J . Orgnnomet. Chem., 1981, 210, 343. S. Quinn and A. Shaver, Inorg. Ciiini. Acta, 1980, 38, 243. W.Gerhartz, G. Ellerhorst. P. Dahler, and P. Eilbracht, Liebigs Ann. Chem., 1980, 1296.

The Photochemistry of' Transit ion-me tul 0rgctnometullic Compounds

205

irradiated.73With (13) the final product is (14), the reaction probably proceeding riu ( 1 5 ) , which however did not build up in appreciable concentration probably because of its high photosensitivity. The yields of Fe(CO), (n = 1-4) produced by laser excitation of Fe(CO), in the gas phase at ;1. = 352 nm, 248 nm, or 193 nm have been measured by trapping the species with PF3.74* 7 5 The striking conclusion is that the lower carbonyls are formed in high yields [e.g. at 248 nm the quantum yields for Fe(CO), and Fe(CO), are 0.55 and 0.35, whereas that for Fe(CO), is only 0.101 even though the decomposition is induced by single-photon absorption. It is not clear whether these species are produced directly from the excited state [e.g. equation (9)] or by Fe(CO),* Fe(CO),* Fe(CO),+ Fe(CO),+

-

+ 3CO Fe(CO),t + CO Fe(CO),t + CO Fe(CO), + CO

Fe(CO),

(9) (10) (1 1) (12)

stepwise decomposition of the vibrationally excited fragments (steps 10-12), although the latter process seems more likely. These observations could have important consequences for the photochemistry of Fe(CO), in condensed phases, although it is likely that in solution cage recombination and removal of excess vibrational energy by the solvent will greatly reduce the yield of the lower carbonyls. Other papers describe the production of excited iron atoms from multiphoton U.V.excitation of Fe(CO), or sensitized with excited argon atoms,77and the multiphoton C0,-laser induced excitation of Fe(CO),.,' E.s.r studies on u.v.-irradiated pentane solutions of Fe(CO), under 30 atm. of hydrogen reveal the presence of HFe,(CO),, which is also produced if H,Fe,(CO), is ph~tolysed.'~ The same species as well as [(CH,CHCH,)Fe(CO),]' is also formed if Fe(CO), is irradiated in the presence of cyclopropane. More data on the highly reactive catalytic species responsible for the Fe(CO),photocatalysed isomerization of pent-1-ene have been obtained both by laser and flash photolysis methods,79 and by Fourier Transform i.r. spectroscopy.*' Very high quantum yields (>>I)and high turnover rates are found. As an induction period for the process is observed it appears that the active catalyst is not formed from Fe(CO), by a one-photon process and the sequence (13) was suggested WCO),

hv

+ Fe(CO),(pentene)

hv

Fe(CO),(pentene) (13)

earlier. Other authors have suggested that the active catalysts are CO-bridged dimeric iron species on the basis of their studies with Fe(CO),(PF,), --n (n = 0-5) as photocatalysts for pentene isomerization. They observed a gradual decrease in activity as II decreased from 5 to 1, and a sudden fall to zero activity for Fe(PF,),. 74

G . Nathanson, B. Gitlin, A. M. Rosan, and J. T. Yardley, J. Chem. Phys.. 1981, 74, 361.

'' J . T. Yardley, B. Gitlin. G . Nathanson, and A. M. Rosan, J . Chem. Phys., 1981, 74, 370. l6

J . Krasinski, S. H. Bauer, and K . L. Kompa, Opt, Commun., 1980, 35, 363.

'' J. Kobovitch and J. Krenos, J . Clrem. Phys., 1981, 74, 2662, 78

79

*'* O

P. J. Krusic, J. Am. Chem. SOC.,1981, 103, 2131. J. C. Mitchener and M . S. Wrighton, J . Am. Chem. SOC..1981. 103, 975. D. B. Chase and F. J. Weigert, J . Am. Clzem. Soc., 1981, 103, 977. G. L. Swartz and R. J. Clark, Inorg. Chem.. 1980, 19, 3191.

206

Photochemistry

Pentene isomerization and hydrosilylation have also been induced by irradiation of phosphinated polystyrene-bound Fe(CO), complexes.82 The photochemistry of Fe(CO), with dienes or olefins in polytetrafluoroethylene has been 84 1.r. evidence for (diene)Fe(CO),, (diene),FeCO, and for (ethylene)Fe(CO), is presented, and it has been found that the stability of these complexes towards air oxidation is much higher in the polymer matrix than in solution. Hydrosilylation of butadiene may be induced by photolysis of the diene with R,SiH (R = Me, Ph, or Et) and Fe(C0),.85 With Me,SiH the observed products are trans- 1-butenyl-, trans-2-butenyl-, and cis-2-butenyl-trialkylsilanes.The reaction appears to proceed‘through (1 6), which may be independently synthesized by irradiation of (butadiene)(FeCO), and R,SiH.

(H,C=CH)3SiCH=CH,

I

‘‘7 I \

I (19)

Recent synthetic applications of the photochemical reactions of Fe(CO), are the formation of (17) from (18),86 and of (19) from di~henylketen.~’ Fe(CO), and presumably dihydrogen are formed upon U.V.irradiation of H,Fe(CO), in argon matrices.88Upon exposure to Nernst glower radiation the reverse process [oxidative addition of hydrogen to Fe(CO),] takes place. Oxidative addition in low-temperature matrices has also been observed upon irradiation (1 < 360nm) of Fe atoms in methane, the species MeFeH being identified by its i.r . spectrum. Photoexpulsion of the axial CO group is observed for Fe(CO),NMe, or Fe(CO),py in rare-gas matrices, the effect being reversed by warming the matrix or by i.r. p h o t o l y ~ i s .The ~ ~ photodissociation spectrum of Fe(CO),- (to give Fe(CO), -) has been measured in an ion cyclotron resonance s p e c t r ~ m e t e r . ~ ~ 82

83 84

85

86

’’ ’* 89 90

R. D . Sanner, R. G. Austin, M.S. Wrighton, W. D. Honnick, and C. U. Pittman, jun,, Adv. Chem. Ser., 1980, 184, 13. M . A. De Paoli, S. M. De Oliveira, and F. Galembeck, J . Orgunomet. Chem., 1981, 193, 105. M. A. De Paoli, J . Macromof. Sci.,Chem., 1981, 16, 1359. I. Fischler and F.-W. Grevels, J . Orgunomet. Chem., 1981, 204, 181. A. S. Batsanov, Yu. T. Struchkov, G . V. Nurtdinova, A. A. Pogrebnyak, L. V. Rybin, V. P. Yur’ev, and M . I. Rybinskaya, J . Organomet. Chem., 1981, 212, 211. W. A. Herrmann, J. Gimeno, J. Weichmann, M. L. Ziegler, and B. Balbach, J . Orgunomet. Chem., 198 1, 213, C26. R. L. Sweany, J . Am. Chem. Soc., 1981, 103, 2410. W. E. Billups, M. M . Konarski, R. H. Hauge, and J. L. Margrave, J . Am. Chem. Soc., 1980,102,7393. C . M . Rynard and J. I. Brauman, fnorg. Chem., 1980, 19, 3544.

207 In CO-saturated acetonitrile solution, [Fe(CO), 1]2- appears to be quite photo~table.~’ However in the presence of triphenylphosphine, Fe(CO),(PPh,), and [Fe(CO),]’ - are formed. These findings, and the observed photodecomposition [equation (14)] in alkaline aqueous solution, may be rationalized by The Photochemistry of Transition-metal Organometallic Compounds

[Fe,(CO), J 2 -

+ 4H20

[F%(CO)1 11

I11’

[Fe(CO),]’-

k

hv

+ 2Fe(OH), + 2H2 + 7CO

+ [Fe3(C0),,]2-

-

+ CO

(14) (15)

assuming that the initial photoreaction is CO-extrusion [equation (15)] and not cluster fragmentation. New cluster compounds have been formed by the irradiation of mixtures of Fe(CO), or (q4-cyclobutadiene)Fe(CO), and (q5C5Me5)2C02(C0)2,40 and of Fe(CO), or Ru,(CO),, and H , O S , ( C O ) ~ ~Photo.~~ lysis of mixtures of (20) and Sn2Me, or Co,(CO), yield (21) and (22).93 Me I

Me-Sn Se-

x ,/

,(CO)Fe-

Se

(20)

\

Fe(CO),

se/

‘se

LxJ (OC),Fe-Fe (21)

(CO),

co (COh (22)

7 Cobalt and Rhodium

The photochemistry of Co(CO),(NO) has been studied both in the gas phase and in solution.94 Reaction with gaseous HCl produces N 2 0 [equation (Mi)].This Co(CO),NO

hv

HCI

CoCl,

+ N 2 0 + H,O + CO

(16)

suggests that the excited state has a bent ‘ N 4 - l i k e ’ M-N-0 unit rather than a linear ‘N-0’-like’ M-N-0 unit. In the latter case the product might be expected to be NOC1. In solution it was noted that the quantum yield for substitution with phosphines, arsines, or pyridine was strongly dependent on the type of entering ligand, suggesting associative attack by the ligand on the ‘bent’ excited state species. The i.r. bands of the species obtained on photolysis of HCo(CO), in argon matrices, previously assigned to HCO(CO),,~~ are now considered to be characteristic of c0(co)4.96This is expected to arise from photohomolysis of the Co-H bond in HCo(CO),, and the presence of H’ and Co(CO), has also been verified by e.s.r. measurements. A study of the reaction conditions for conversion of Co,(CO), to C O , ( C O ) , notes ~ that the reaction may be photoassisted although the quantum yield is ” 92 93 94

’*

96

”

D. R. Tyler and H. B. Gray, J . Am. Chem. SOC.,1981, 103, 1683. E. W. Burkhardt and G . L. Geoffroy, J. Organomet. Chem., 1980, 198, 179. D. Seyferth and R. S. Henderson, J . Organomet. Chem., 1981, 204, 333. W. Evans and J. 1. Zink, J . Am. Chem. SOC..1981, 103, 2635. P. Werner, B. S. Ault, and M. J. Orchin, J . Orgunomet. Chem., 1978, 162, 189. R. L. Sweany, inorg. Chem., 1980, 19, 3512. M. F. Mirbach, A. Saw, A. M. Krings, and M. J. Mirbach, J . Organomet. Chem., 1981, 205, 229.

Photochemistry

208

In solution CO-dissociation is the main photoreaction upon U.V. excitation of Co(CO),SiR, (R = Me or Ph).98The co-ordinatively unsaturated Co(CO),SiR, produced may be trapped by P(OPh), or by pentene, and it may also reversibly oxidatively add R,SiH [e.g.equation ( I 7)]. R,SiCo(CO), is a photocatalyst for the isomerization or hydrosilylation of pent- I-ene. Co(CO),SiPh,

+ Et,SiH

Co(CO),(SiPh,)(SiEt,)(H)

.------

Co(CO),SiEt,

+ SiPh,H

(17)

Wilkinson's compound CIRh(PPh,), has been found to be a useful photocatalyst for the hydrosilylation of olefins in the presence of oxygen.99The primary photoprocess is phosphine expulsion, which generates the suspected catalytically active species ClRh(PPh,),. Hydrogen evolution has been observed upon photolysis of HRh(PPr',), in aqueous phosphoric acid. l o o More information on the properties and photoreactions of the isocyanidebridged complexes [Rh2b4I2' [b = CN(CH,),NC] have been published.lO'- l o 4 Polarized single-crystal studies and time-resolved resoname Raman spectra reveal that the 3 A 2 uexcited state has a much stronger Rh-Rh bond than the ground state. The ,A2" state may be quenched by azulene and other low-energy quenchers, allowing its ET to be estimated as about 164 kJmol- ' . I o 3 The excited state may also undergo electron transfer, and the species formed, either from oxidative quenching (e.g. with methylviologen) or by reductive quenching (e.g. with amines) have been characterized by flash photolysis. The photoproduction of hydrogen by reaction of [Rh2b4I2+has been shown to proceed in two steps, namely a thermal reaction (1 8) and a photoinduced process (19) of the tetranuclear complex. O4 2[Rh2b4I2+ + 2HC1 [Rh4b,C1,]4+

+ 2HC1

""

[Rh4b,C1J4+

+ H,

2[Rh2b4Cl2I2+ + H,

(18)

(19)

Compound (23) undergoes photo-elimination of nitrogen and the formation of product (24).lo' The reaction proceeds via an intramolecular pathway, possible by insertion of an initially formed co-ordinated nitrene into the ortho-CH bond of the neighbouring group. The photochemistry of surfactant alkylcobaloximes in sodium lauryl sulphate (SLS) or cetyltrimethylammonium bromide (CTAB) micelles has been described. l o 6 The quantum yield for anaerobic photohomolysis of the Co-C bond was found to be three times larger in saturated micelles compared with those containing only 1 or 2 cobaloximes. This effect is possibly caused by a co-operative 99 '()"

I"'

'(''

I 05 'Oh

C . L. Reichel and M. S. Wrighton, fnorg. Chem., 1980, 19, 3858. R. A. Faltynek, fnorg. Chem., 1981. 20, 1357. R. F. Jones and D. J . Cole-Hamilton, J . Chem. Soc., Chem. Commun., 1981, 58. S . F. Rice and H . B. Gray, J . Am. Chem. Soc.., 1981, 103, 1593. R. F. Dallinger, V. M. Miskowski, H. B. Gray, and W. H . Woodruff, J . Am. Chem. Sor., 1981, 103, 159.5. S. J . Milder, R. A. Goldbeck, D. S. Kliger, and H. B. Gray, J . Am. Ckem. Soc., 1980, 102, 6761. I. S. Sigat K . R. Mann, and H . B. Gray, J . Am. Chem. SOC.,1980, 102, 7252. M . E. Gross and W. C. Trogler, J . Orgrmomet. Cliem., 1981, 209, 407. D. A. Lerner, F. Ricchiero, and C . Giannotti, J . Phys. Cliem., 1980, 84, 3007.

The Photochemistry of Transition-metal Organometallic Compounds

209

(24)

(23)

effect owing to the organization of the cobaloximes in the micelle. Other work on models for B,, includes the photochemistry of alkyl derivatives of cholestanocobaloximes,l o 7 and of dehydrocorrins.lo*

8 Nickel, Palladium, and Platinum Excitation of the charge transfer (5d-n&,,) state of cis- or trans[PtC1,(C,H4)(4Mepy)] by 254 nm radiation causes ethylene expulsion and the resultant formation of the dimer [PtC12(4Mepy)],. O9 The cis-trans isomerization reactions that occur with modest quantum efficiencies (0.07 for cis + trans; 0.01 for trans -,cis) have been ascribed to reactions of d-d excited states. The photoisomerisation of trans-[PdCl,(PR,),] (R = Et, Pr", or Bu") proceeds predominantly by an intramolecular process with only a few per cent involving The trans -, cis isomerization of intermolecular phosphine exchange. Pd(CNMe),(SCN), has been reported to take place upon irradiation into C?' bands.", Irradiation of q3-allylpalladiumcomplexes results in the formation of 1,5-dienes [e.g. (25) from (26)], products presumably of the coupling of ally1 radicals.' The '"3

(25)

(26)

p h oto-induced oxidative addition of CH,Cl, to (Ph3P),PtC2H4, giving cis- and trans-[(Ph3P),PtCl(CH ,el)] and cis-[PtCl,(PPh,),], is quenched by radical traps.' l 4 Ultraviolet irradiation of acidic solutions of M(PEt,), (M = Pd or Pt) results in the formation of [M(PEt3)3(H20)]2'and hydrogen.'" The dissociation of Ni(CO), by multiphoton i.r. laser excitation 2o or sensitized by excited argon atoms 1 1 5 has been described. lo'

'08 lo9 ''O

''I

'I3

'I5

M. Fountoulakis and J. Retey, Chem. Ber., 1980, 113, 650. Y. Murakami, Y. Aoyama, and K. Tokunaga, J. Am. Chem. SOL'.,1980, 102, 6736. R. Rumin and P. Courtot, J. Organomet. Chem., 1980, 193, 407. N. W. Alcock, T. J. Kemp, F. L. Wimmer, and 0. Traverso, Inorg. Chim. Acta, 1980, 44, L245. N. W. Alcock, T. J. Kemp, and F. L. Wimmer, J. Chem. Soc., Dalton Trans., 1981, 635. L. L. Costanzo, S. Giuffrida, G. Condorelli, A. Giuffiida, and G. Guglielmo, Congr. Naz. Chim. Inorg., [Atti], 13th, 1980, 206 (Chem. Abstr., 1981, 94,217457). J. Muzart and J. P. Pete, J. Chem. SOL'., Chem. Commun., 1980, 257. 0. J . Scherer and H. Jungmann, J. Organomet. Cliem., 1981, 208, 153. J. S. Winn, Faraclny Svmp. Chem. SOC.,1980, 14, 102.

210

Photochemistry 9 Copper and Silver

A review of the photochemical properties of copper complexes includes a survey of the photocatalysed reactions of copper-olefin complexes. l6 The addition of acetonitrile to norbornene may be induced by irradiation in the presence of silver ions. The reaction appears to involve excitation of a LMCT excited state of the norbornene-silver complexes and the formation of norbornene radical cations. The detection of CuH and CuMe in methane matrices at 12 K following the 320nm photolysis of copper atoms has led to the proposal that optically excited copper atoms insert into the C-H bond of methane. l 1 The HCuMe species thus produced undergoes secondary photolysis to give CuH and methyl radicals and also CuMe and hydrogen atoms. The photoproperties of silver atoms in matrices have been studied in detail. l 9

'

'

'

10 Mercury

The photo-induced substitution reactions of alkenylmercury compounds appear to proceed by a free-radical chain mechanism [e.g.reactions (20)]. 120 Photolysis of Bu'CH=CHHgCl

+ SPh'

Bu"CHCH(SPh)HgCI

-----+ B u ' C H d H S P h

+ HgCl

(20)

1-alkenylmercury halides in the presence of sulphinate ions provides a useful route to a,B-unsaturated sulphones. 2 1 The effect on the triplet state kinetics of binding MeHg' to tryptophan or benzimidazole has been monitored using 0.d.m.r. and polarized phosphorescence excitation measurements. * **

'

11 Lanthanides and Actinides Irradiation of t.h.f. solutions of Cp,UR (R = Me or Bun) gives CpJU t.h.f., although elevated temperatures ( e . g . 60 "C) are required for efficient reaction.',, Homolytic cleavage of the U-R bond is presumed to be the first step. Photoinduced cleavage of the Yb-Me bond allows the conversion of [(MeCp),YbMej, into (MeCp),Yb.' 24

'Ih

'" '"

l9 ''I 12'

"'

G . Ferraudi and S. Muralidharan, Coord. Cliem. Rev.,1981, 36, 45. J. W. Bruno, T. J. Marks, and F. D. Lewis, J . Am. Chem. Soc., 1981, 103, 3608. G. A. Ozin, D. F. Mcintosh, S. A, Mitchell, and J . Garcia Prieto, J . Am. Clrem. Sot,., 1981, 103, 1574. S . A . Mitchell, J. Farrell, G . A. Kenney-Wallace, and G. A. Ozin, J. Am. Chem. Soc., 1980, 102, 7702. G . A. Russell and J. Hershberger, J . Am. Chem. Soc., 1980, 102, 7603. J. Hershberger and G . A. Russell, Synthesis, 1980, 475. R . R. Anderson and A. H. Maki, J . Am. Chem. Soc., 1980, 102, 163. E. Klahne, C. Giannotti, H . Marquet-Ellis, G. Folcher, and R. D. Fischer, J . Orgcinomet. Cliem., 1980, 201, 399. H A . Zinnen, J. J . Pluth, and W. J . Evans, J . Ckem. Soc., Chem. Commun., 1980, 810.

3 Photochemistry of Compounds of the Main Group Elements BY J. M. KELLY AND C. LONG

1 Group 3 Elements A detailed quantum yield study of the photocyclization of anilinodimesitylboranes [ e g . (l)] in the presence of iodine has been published.' When the iodine concentration is less than lop3M, the major product is (2), whereas at high iodine concentrations (3) predominates. It is proposed that the initial step in the formation of (2) is an electron transfer to iodine from the excited state of ( I ) , and that the cation so produced then cyclizes and subsequently loses a methyl group. At higher concentrations the iodine appears to act as a heavy-atom quencher of the excited state of (1) which produces the cation. and iodine also seems to promote the methyl group migration required for the formation of (3).

H\

H

\

4

N -3 I

There have been several recent papers on i.r. laser-induced decomposition of boron trichloride in the presence of other substances, e.g. phosgene2 and hydrogen sulphide. 3, At 15 K in argon matrices, gallium and indium atoms undergo photochemical insertion into water. Dimers also photoreact giving bridged species, which may then undergo a further photodecomposition (equations 1 and 2).

' '

M . E. Glogowski and J. L. R. Williams, J . Orgrmomef. Cltem., 1980, 195, 123. C. Riley and L. Maclean, J . A m . Chem. Soc., 1980, 102, 5108. K . Takeuchi, 0. Kurihara, and R. Nakane. Cltem. Phys.. 1981,54, 383. K. Takeuchi, 0. Kurihard, and R . Nakane, J . Chem. Eng. Jpn., 1980, 13, 246. R. Hauge, J. W. Kauffman, and J . L. Margrave, J . Ant. Clrem. Soc., 1980. 102, 6005.

21 1

212

Piio toc'iieniis t ry

The luminescence of TI' in lithium chloride6 and in potassium iodide' has been further studied.

2 Silicon and Germanium Several primary photoprocesses have been identified for MeSiH, excited by 147 nm radiation in the gas phase. Of these the processes represented in equations (3)-(5) have quantum yields greater than 0.2.8

11\%

MeSiH, MeSiH, MeSiH,

/I

v

Me

+ H + SiH,

(3)

+ H,

(4)

MeSiH

I1 \!

-----+ CH,SiH,

+ H,

(5)

For polysilanes in 2,3-dimethylbutane solution, photolysis induces a net disproportionation (e.g. Si,H, and Si,H,, from If acetone is present then isopropoxysilanes [e.g. Me,CHOSiH(SiH,), from SI,H8] are formed. ' The insertion of CCI into the Si-H bond of silanes has been studied.' Upon photoexcitation, either in the gas phase or as liquid, SiMe, undergoes mainly two primary photoprocesses (6) and (7) (@ = 0.55 and 0.22, respectively).' The Me,SiCH,, so formed, may react further by dimerization to give the 1, 1,3,3-tetramethyl-1,3-disiIacyclobutane (4a). However in the gas phase the

,

(4)a; R = Me b:R=H

majority of the silaolefin species are intercepted by radicals, and this accounts for the lower yield of (4a) in the gas phase compared with that found in the liquidphase photolysis reaction, where cage recombination of the radicals produced in reaction (6) may occur. SiMe, SiMe,

I?\'

-----+ SiMe, I1 \!

+ Me

Me,SiCH,

+ CH,

(6) (7)

' M . U . Belyi, S. E. Zelenskii. B. A . Okhrimenko, and V. P. Yashchuk, Ukr. Fiz. Zh. (Russ.Ed.). 1981, 102. ' 26, D. J . Simkin, J . P. Martin, M . Authier-Martin, K. Oyama-Gannon, P. Fabeni, G . P. Pazzi, and A. ' lo I ' 12

Ranfagni. P h j s . Rev. B, 1981, 23, 1999. P. A. Longeway and F. W . Lampe. . I Pliotoc,lieni., . 1980, 14. 31 I . F. Feher and I. Fischer, Z . Anorg. Allg. CAem., 1980, 466, 23. F. Feher. I. Fischer, a n d D. Skrodzki, Z . Anorg. A&. Ciimi., 1980, 466, 29. F. C. James, H. K. J . Choi, 0. P. Strausz, a n d T. N. Bell, Chem. PIi.vs. L e i f . , 1979, 68,131. E. Bastian. P. Potzinger, A. Ritter, H . P. Schuchmann, C . Von Sonntag, and G . Weddle, Bcr. Bunscngcs. P h ~ . s Chcm., . 1980, 84, 56.

Plio t oc~henzisty*of' Conzpmds qf

'

tl i p

Mairi Groi11, Eliw ien ts

21 3

SiMe,, may be conveniently generated by photolysis of cyclo-Si,Me, ,, and this method has been used in the study of its insertion into Si-H bonds (e.g. in Me,SiH),13* l 4 S i - 0 bonds (e.g. Me,Si0Et),I3 and into HCI.l4 I n lowtemperature matrices it has been shown that SiMe, may be converted by visible light (A = 450nm) into MeHSi=CH2.l5 Annealing the photolysed matrix yields (4b). In Several workers have studied the photochemistry of silacyclobutanes. E, < 210nm) excitation of 1,l-dimethylsilacyclothe gas phase, U.V.(185nm butane causes elimination of ethylene and the formation of Me,Si = CH,.', This silaolefin, when formed, has an internal energy which is probably in excess of the Si-C 7r-bond energy, and it may be that its reactivity is different from that of Me,Si=CH, generated thermally or in solution. In particular it is possible that its isomerization to Me,HSicH occurs and this might be an explanation for the substantial amounts of polymer that accompany the ethylene and 1,1,3,3tetramethyl- 1,3-disilacycIobutane as products. Mass spectrometric measurements show that the products from octamethyl- 1,2-disilacyclobutane are mainly 2,3dimethylbut-2-ene and hexamethylsilacyclopropane. ' The primary photoprocess is probably that shown in equation (8).

-=

-

I

Me,CCMe,SiMe,SiMe,

Me,C----CMe,

+ Me,Si=SiMe,

(8)

The products of photolysis of substituted silacyclobutanes in methanol solution are either those derived from initial formation of the silaolefin [e.g.equation (9)] or by cleavage of the Si-C bond [e.g. equation ( 10)].18 A similar sensitivity to the nature of the substituent is observed with 1,3-disilacyclobutanes, where it is 1,3-disilacyclobutane undergoes observed that l,l93,3-tetramethy1-2,4-diphenylphotocleavage of a Si-C bond, whereas 1,1,3,3-tetraphenyl-1,3-disilacyclobutane is stable.

-

Ph,SiCH,CH,CHPh

Bu',SiCH,CH,CHPh

hv

h 1' MeOH

Ph,Si(OMe)Me

+ PhCH = CH,

Bu',Si(OMe)CH,CH,CH,Ph

(9) (10)

An examination of the photoproducts formed from Me,SiSiMePhSiMe, and dienes reveals that the initial reactive species formed on photodecomposition of the trisilane are ( 5 ) and MePhSi:.I9 The adduct formed from (5) and 2,3dimethylbuta-l,3-diene, which was earlier" thought to be (6) is now assigned the more reasonable structure (7). The silylene MePhSi: reacts with the diene to give the alkenylsilacyclopropane (8). This species builds up to a substantial concentration if a low-pressure mercury lamp is used, whereas if a high-pressure mercury lamp is employed, (8) photoisomerizes to (9) and (10). l3

l4 I'

l9

2o

T. Y. Gu and W. P. Weber, J . Orgcmomcf. Client.. 1980. 195, 29. 1. M . T. Davidson and N. A. Ostah, J . Orgnnomct. Cliem., 1981, 206, 149. T. J . Drahnak, J. Michl, and R. West, J . Am. Chem. Soc., 1981, 103, 1845. H . C. Low and P. John, J . Orgcmomet. Cliem., 1980, 201, 363. I . M . T. Davidson, N. A. Ostah, D. Seyferth, and D. P. Duncan, J . Orgcmomet. Chem., 1980, 187,297. P. Jutzi and P. Langer, J . Organamet. Clteni., 1980, 202, 401. M. Ishikawa, K . Nakagawa, R. Enokida, and M. Kumada, J . Orgcmonier. Chem., 1980, 201, 151. M . Ishikawa, F. Ohi, and M . Kumada, J . Orgunomet. Cheni., 1975. 86, C23.

214

Photochemistry

In low-temperature matrices (1 1) undergoes a photoreversible di-.n-methane photorearrangement to give (1 2).2' Tetramethylsilene, which could be formed by photoelimination from (1 l), is not observed at low temperatures but is produced in cyclohexane solution at room temperature where it has been trapped by dienes.21

Ye x

SiMel I Si (Me)- C H

Ph SiMe,

SiMe,

Me,Si-Si-CH

Me

Me

Ph

Me

Me

Me

g

F M e Me-Si-H

/ \

X

Me

I

/ \

Ph (9)

Ph

Me

An interesting series of photochemical interconversions of unsaturated silane derivatives starting from the alkynyldisilane (1 3) has been described (Scheme 1).22

Me3Si

I

I

/SiMe3 c-c

\

\ /

Si

/ \

Ph Ph

hi*

Me,Si

\

C=C= SiPh2 Me3SiC~CSiPh2SiMe35 / (13) Me Si .~

,

Me3Si

SiMe,

\ /

Me Si\ ,C=C=C Me,Si

C

/ \

SiPh,

\Si/

hi,, heat

Ph,

Me3Si

Me3Si-C

I

\c-c

SiMe, I /C-SiMe,

I. I Ph, Si-SiPh,

Scheme 1

Unlike most silacyclopropenes the mesityl-substituted compounds (1 4), which are formed by irradiation of the alkynyldisilanes (1 5 ) are remarkably stable towards oxygen and moisture and therefore particularly suitable for photochemical 21

22

J. D. Rich, T. J. Drahnak, R. West, and J. Michl., J . Urganomet. Chern., 1981, 212, C1. M, Ishikawa, D . Kovar, T. Fuchikami, K. Nishimura, M . Kumada, T. Higuchi, and S. Miyamoto, J . Am. Chem. SOL-.,1981, 103, 2324.

21 5

Photochemistry of Compounds of the Main Group Elements

studies.’, With (14a) (R = Ph) extrusion of the silylene is the only observed reaction, whereas with (14b) (R = SiMe,) photoisomerization to the alkyne (15b) and formation of a silapropadiene are also found.

R

SiMe,

\

RC =C f i Si Me,

/

(14) a; R = Ph

b; R

=

(15) a; R = Ph b; R = SiMe,

SiMe,

The cis-trans-photoisomerization of Me,SiCR = CRSiMe, (R = SiMe,Ph)24 and the reaction of singlet oxygen with 1,l-dimethyl-1-silacyclopent-3-enezshave been described. A short review in Japanese of the photochemistry of organosilicon compounds including acylsilanes has been published.26 Sensitization and quenching experiments show that the triplet state of acetyltrimethylsilane is involved in reaction (ll).” Furthermore, as the lifetime of the triplet state (z 13ns) does not vary

-

MeCOSiMe,

+ Pr’OH

-----+

MeCH(OPr’)OSiMe,

(1 1)

with the concentration of propan-2-01, it is clear that the excited state decomposes to give some other species, probably MecOSiMe,, which then reacts with the alcohol. By contrast it has been demonstrated that reaction of the acetylsilane with dimethyl fumarate proceeds by direct attack of either the singlet or the triplet state of MeCOSiMe, on the electron-acceptor olefin.28A possible mechanism is given in Scheme 2. Photolysis of 1,l -dimethyl-1-sila-2-cyclopenianonein t-butylalcohol gives the cyclic acetal product expected from a siloxycarbene intermediate.” 0

II MeCSiMe,

+

h I’

C0,Me

Me SiMe,

M e OSiMe3 V C 0 , M e -+ M e , S i O d c o z M e ‘C0,Me 23 24

25 26

” 29

Me

‘CO2Me

Scheme 2 M. Ishikawa, K. Nishimura, H . Sugisawa, and M. Kumada, J . Orgunornet. Cliem., 1980, 194, 147. H. Sakurai, H. Tsbita, M. Kird, and Y. Nakadaira, Angew. Chem., 1980,92, 632. A. Laporterie, J. Dubac, and P. Mazerolles, J. Orgmomet. Chem.. 1980, 202, C89. H. Sakurdi, Y. Ndkadaira, and H. Tobita, Kngaku N o Ryoiki, 1979, 33, 879. R. A. Bourque, P. D. Davis, and J. C. Dalton, J . Am. Clzem. Soc.. 1981, 103, 697. J. C. Dalton and R. A. Bourque, J . Am. Chem. Soc., 1981, 103, 699. A. Hassner and J. A. Soderquist, Tetrcrhedron Lett., 1980, 21, 429.

216

Photochemistry

However the germanium analogue (16) forms Me,HGe(CH,),CO,Bu‘ apparently by initial photochemical cleavage of the Ge-acyl bond and subsequent formation of the ketene Me,Ge(CH,),CH=C==O.

Other publications consider the photochemical reactions of Hg(SiMe,), with f l u o r o - ~ l e f i n s ,the ~ ~ photo-induced reaction of Me,SiCI, -,(n = 1-3) with S0,C12,31the e.s.r. properties of photochemically produced substituted triarylsilyl radicals,32 and a comparison of the phosphorescence spectra of SiPh,, GePh,, SnPh,, and PbPh,.,,

3 Tin and Lead From e.s.r. and l19Sn CIDNP measurements it is clear that photolysis of Me,SnSnR,SnMe, (R = Me or Et) leads to both Sn-Sn and Sn-C bond cleavage [equations (12) and ( 13)].,“ The polarization and enhancement factors observed for the CIDNP signals agree with those calculated for the triplet state of the tristannane as the precursor for both reactions Me,SnSnR,SnMe, Me,SnSnR,SnMe,

I1 11

----+

Me,Sn

+ SnR,SnMe,

hv -----+ (Me,Sn),SnR

+R

(12) (13)

Irradiation of (17) causes elimination of SnMe,, and the consequent production of (18).35The stannylene produced extracts a tellurium atom from (17) to yield (1 9). Laser flash photolysis of di-t-butylperoxide solutions of Bu,SnH produces Bu,Sn, which rather surprisingly absorbs strongly in the visible.36 The photoreactions of Et,SnCH,CH=CH, and thiols have been described.,’

30 31

32 33 34

3s 36

”

A. K . Datta, R. Fields, and R. N . Haszeldine, J. Cliem. Res. ( S ) , 1980, 1, 2. N. N. Voronkov, S. A. Bolshakova, V. P. Baryshok, A. I. Albanov, and B. Z. Shternberg, Dokl. Aknd. Ncruk SSSR, 198I, 256, 90. H. Sakurai, H. Umino, and H. Sugiyama, J. Am. Chem. Soc., 1980, 102, 6837. H. Mie and T. Azumi, Koen Yoshishu-Bunshi Kozo Sogo Toronkai, 1979, 384. C. Grugel, M . Lehnig, W. P. Neumann, and J. Sauer, Tetrnhedron Lett., 1980, 21, 273. B. Mathiasch, J. Orgunomet. Cliem., 1980, 194, 37. J. C. Scaiano, J. Am. Cliem. Soc., 1980, 102, 5399. M. G. Voronkov, V. I. Rakhlin, S. Kh. Khangazheev. R. G. Mirskov, and A. I. Albanov, Zh. Ohshch. Kliim., 1980, 50, 1771.

Photochemistry of Compounds of the Main Group Elements

21 7 Photoassisted lead tetra-acetate oxidation of alcohols38 and laser-induced fluorescence of gaseous lead ~ u l p h i d e ,have ~ been the subject of recent reports. 4 Nitrogen and Phosphorus

-

Conductometric methods have been used to follow the reactions of the transient species formed by flash photolysis (A 200nm) of nitrate ions in aqueous ~ o l u t i o n . ~The ' initial excited state produced was shown to decay by two routes either to give HOONO or to give a lower energy excited state. Other reactions observed, and also those described previously by other workers, are summarized in Figure 1. A study of the photolysis of HN, induced by 290 nm dye-laser pulses has been reported.41The isomerization of N,F, in the presence of fluorine and oxygen has been initiated p h o t ~ c h e m i c a l l y . ~ ~

NO,*

-

(200) N03*-(300)+OH

I

0

4-l + NO2 =@N,O4--

H2O 10-3s

hu

Figure 1 Kinetic pathways in the photolysis of nitrate ions in aqueous solutions (Reproduced by permission from Z . Phys. Chem., 1980, 123, 1). 38

39 'O 4'

42

M. Lj. Mihailovic, V. Andrejevic. and A. V. Teodorovic, Glas. Hem. Drus. Beogrcicl, 1980, 45, 327. B. Burtin, M. Carleer, R. Colin, C. Dreze, and T. Ndikumana. J . Phy. B., 1980, 13, 3783. I. Wagner, H . Strehlow, and G. Busse, Z . Pliys. Client. (Wieshaden), 1980, 123, 1. L. G. Piper, R . H . Krech, and R. L. Taylor, J . Chem. Phys., 1980, 73, 791. A. A. Kibkalo and V. I . Vedeneev, Kinet. Katal., 1980, 21, 850.

Photochemistry

218

U.V. photolysis of phosphine gives diphosphine as the initial product = 1.78).43 Although a detailed analysis of the reacLion course was hampered by the accumulation of red phosphorus as the reaction proceeded, it is clear that reactions (14)--(16) are important processes. The photochemical decomposition of PPh, has been monitored by 31P n.m.r.44 The reaction proceeds via the triplet state and evidence was also found for the production of benzyne from the phenyl radical produced in the initial photoreaction.

(aPzH4 = 0.80 : @ - p H 3

PH, H

+ PH,

I1v

PH,

+H

(14)

PH,

+ H,

(1 5 )

5 Oxygen, Sulphur, and Selenium Rate constants for the reaction of hydrogen, methane,45 or ammonia 46 with hydroxyl radicals generated by flash photolysis of water in the gas phase have been determined. The photoreactions of SO, in argon, nitrogen, or oxygen matrices at 12 K have been studied."' Only in oxygen matrices are photoproducts (SO,) observed and it was demonstrated that the dimer (SO,),, but not monomeric SO,, was reactive. In the gas-phase photochemistry of both CH2(CH2),S04*and CH2(CH,),S049 the primary photoprocess appears to be rupture of a C-S bond to give a diradical that subsequently ejects SO. A very detailed laser-molecular beam study of the multi-i.r.-photon dissociation of SF, has been reported." The translational energy distribution and the dissociation lifetime of the excited SF, have been studied as a function of the laser intensity and energy influence, and it has been demonstrated that the dissociation of the excited SF, (to SF, and F) is in good agreement with the predictions of RRKM theory. The photo-induced cyclizations of the selenol esters (20) and (21) to give (22) and (23), respectively, have been described. Photolysis of benzyl phenyl selenide (24a) or of the phenyl ribosyl derivative (24b) yield the corresponding diselenides (25).52The photoreduction of acetophenone by H2Se has been in~estigated.~,

- -

43 44

" 46

'' 48

"

s2

s3

J. P. Ferris and R. Benson, J . Ani. Clwm. Soc., 1981, 103, 1922. Y. A. Levin, E. I. Gol'dfarb, and E. I . Vorkunova, Zh. Ubshdi. Kiiim., 1980, 50. 1981. F. P. Tully and A. R. Ravishankara, J . Plija. Clwmi., 1980, 84, 3126. K. J. Niemitz, H . G . Wagner, and R. Zellner, 2.Phys. Client. (Wiesbrrden), 1981, 124, 155. J. R. Sodeau and E. K. C. Lee, J. PlIj*s. Ciieni., 1980, 84, 3358. F. H. Dorer and K. E. Salomon, J. Phys. Cliem., 1980, 84, 3024. F. H . Dorer and K. E. Salomon, J . Plijs. Client., 1980. 84, 1302. P. A. Schulz, A. S. Sudboe, E. R. Grant, Y . R. Shen, and Y. T. Lee, J . Chem. Plijs., 1980, 72, 4985. K. Beelitz. K. Prdefcke, and S. Gronowitz, J. Organonlet. Chem.. 1980. 194, 167. J.-L. Fourrey. G. Henry, and P. Jouin, Tetraliedron Lett., 1980, 21. 455. N. Kambe, K. Kondo, and N. Sonoda, Clreni. Lefr., 1980, 1629.

Photochemistry of Compounds of the Main Group Elements

& S e 0o M e

0

(20)

AcOH2C =

Me

(22)

(24) a; R = CH2C,H5

b; R

219

9

Se -Sd (25)

AcO OAc

6 Other Elements The quantum yield for the photodissociation of iodine and the rate of recombination of the iodine atoms so produced have been determined in alkane solvents at pressures up to 3 kbar.54The higher pressure causes an increase in the viscosity ( q ) of the solvent, and it was shown that the quantum yield (i.e. the fraction of iodine atoms escaping from the solvent cage) depends on q - ’. The photoinduced reaction of fluorine and methane in low-temperature matrices yields a hydrogen-bonded species MeF...HF. A study of the effect of infrared radiation on the interaction of XeF, and silicon surfaces56 and a report on excited states of xenon produced by vacuum-u.v. irradiation” have been published.

J. Schroeder, J. Troe, and U. Unterberg, J. Phys. Chem., 1980, 84, 3072. ’’ KG.. Luther, L. Johnson and I. Andrews, J. Ant. Chenr. Soc., 1980, 102, 5737. T. J. Chuang, J . C h m . Plivs., 1981, 74, 1461. ’’ G. Di Stefano, M. Lenzi, A. Margani. and C. N . Xuan, J. Clwni. Pli>ts., 1981, 74, 1552 ” 56

Part I11 ORGANfC ASPECTS OF PHOTOCHEMISTRY

1 Photolysis of Carbonyl Compounds BY W. M. HORSPOOL

1 Introduction The decline of interest over past years in the photochemistry of simple carbonyl compounds now seems to have reached a deficiency state. The number of research groups actively studying in this area appears to be diminishing very quickly, and the quantity of really important advances has decreased dramatically. Much of the remaining interest has switched from the synthetic aspects of carbonyl photochemistry to more physical studies involving energy transfer and excited-state lifetime measurements. Typical of this area of study is the account by Zimmerman and his co-workers of the details of their studies of energy transfer in rod-like molecules (e.g., 1,2). A detailed study of the photochemical reaction of

(1)

4

R 2= 1-naphthyl R' = Me, R2 R' = C6H4, R2 = I-naphthyl R' = Me, R2 = 2-naphthyl. R' = C,H,,, R2 = 2-naphthyl

R2

(2) R' = Me, R2 = 1-naphthyl R' = Ph, R2 = I-naphthyl

excited acetophenone in the presence of l-phenylethanol has shown that half of the ketone triplets are quenched by the OH bond rather than by reaction with a C-H bond.2 Earlier work by Wagner and Schott also focused attention on the interpretation of the results of ketone photolysis in alcohol solution. Wagner and his co-workers have also studied charge-transfer quenching of triplet trifluroroacetone. The CIDNP effects in this system were also reported.' Albini has reviewed the useful synthetic reactions achieved by energy-transfer I

*

H. E. Zimmerman, T. D. Goldman, T. K. Hirzel, and S. P. Schmidt, J . Org. Chem., 1980, 45,3933. P. J. Wagner and A. E. Puchalski, J . Am. Chem. SOC., 1980, 102, 7138. P. J. Wagner and H. N. Schott, J . Am. Chem. Soc., 1969, 91, 5383. P. J. Wagner and H. M. H. Lam, J. Am. Chem. SOC., 1980, 102,4167. P. J. Wagner and M. J. Thomas, J. Am. Chem. Suc., 1980, 102,4173. A. Albini, Synthesis, 1981, 249.

223

224

Photochemistry

and electron-transfer photosensitization, and Warrener review.

' has published

a short

2 Norrish Type I Reactions

Turro and Mattay * have studied the photochemistry of 1,2-diphenyl-2,2dimethylpropan-1-one (3) in micellar solution. The products formed from this reaction are the olefin (4,23%) and benzaldehyde (5,23%). Trace amounts of other products (Scheme 1) were detected. The reaction appears to be dominated by the P h q P h Me Me

+

+

PhCHO ( 5 ) 23%

Me i PhC=CH, (4) 23%

+

PhCH(CH,), trace

+

PhC(CH,),C(CH,),Ph trace

(3)

Scheme 1

Norrish Type I reaction leading to radicals (PheO and PhMe,C*) from which the products are formed. Another study in micellar solution has examined the photochemical decomposition of 1,3-diphenylpropan-2-0ne(6).' P

h y Ph 0 (6)

Turro and Kraeutler l o have reviewed the state of the art of magnetic field and magnetic isotope effects in the study of organic reactions. A study of the photochemical behaviour of phenyladamantyl ketone (7) in benzene has shown that the reactions are dominated by fission processes (a Norrish Type I reaction) to yield the products shown in Scheme 2." When the irradiation is carried out in hexadecyltrimethylammonium chloride (HDTCI) solution, adamantane (AdH) is the main product. There is a poor mass balance in this experiment which is thought to be due to interaction of the PhCO radical with the miceller medium. When Cu2 is used as a radical trap a different distribution of products is observed (Scheme 2, third entry). +

0 PhAAd

Ad = I-adamantyl

(7) (7)

(7)

A PhCHO C A

-L HDTCI

75% 7%

+

PhCOPh 6%

-

+

AdH

+

I-PhAd

+

33%

35%

Ad-Ad 3%

60"L

-

-

AdOH 3%

+

PhCOCOPh 3% AdCI 33%

+

PhCO,H 45%

Scheme 2

' lo

l1

R. W. Warrener, Chem. Aust., 1980, 47, 163 (Chem. Abstr., 1980, 93, 149009). N. J. Turro and J. Mattay, Tetrahedron Lett., 1980, 1799. H. Hayashi, Y.Sakaguchi, and S . Nagakura, Chem. Lett., 1980,1149 (Chem.Abstr., 1981,94, 102414). N. J. Turro and B. Kraeutler, Acc. Chem. Res., 1980, 13, 369. N. J. Turro and C.-H. Tung, Tetrahedron Lett., 1980, 4321.

225

Photolysis of Curbonyl Compounds

Irradiation of acetoxystyrene (8) in hexane solution affords acetophenone (one of the products of a-fission: presumably the other product, acetaldehyde is also present) and the diketone (9) (formed by what is formally a [1,3]-acetyl migration) as the primary photoproducts. Continued irradiation of the reaction mixture brings about cleavage of this diketone (9) into radical pairs (10, 11) which can either reform starting material [from radical pair (lo)] or produce acetophenone as well as yielding isopropenyl benzoate (12) and benzoic acid [from radical pair (1 l)].

A study of the wavelength and temperature dependence of the photochemistry of the cyclobutanone (13) has been reported. The reactions normally encountered in the photochemistry of such species are a-cleavage leading to decarbonylation, cycloelimination yielding olefins and ketenes, ring expansion to a carbene intermediate, and recyclization to the starting material (Scheme 3). The present

deca rbonylation

b, +

4

cis

+ CH,CO,R + 7+ CH,CH,CO,R

cycloelimination

ring expansion

OR and trans

Scheme 3

work has shown that reformation of the starting material does not arise to a significant extent. The stereospecificity of the cycloelimination and ring-expansion paths is high at 25 "Cand 3 13 nm. Decarbonylation of the trans-isomer (13) is also stereospecific but only moderate stereospecificity is shown for the decarbonylation of the cis-isomer (1 3). Such high stereospecificity is indicative of the involvement of the singlet state but there is obviously leakage from S , to T , in the case of the cis-compound with the resultant loss of stereospecificity. Decrease in the wavelength from 313 + 254nm brings about only a small change in the reaction H . Garcia, R. Martinez-Utrilla, and M. A. Miranda, Tetrahedron Left., 1980, 3925. N . J. Turro, D. Bauer, V. Ramamurthy, and F. Warren, Tetrahedron Lett., 1981, 611.

226

Photochemistry

pattern. With change in temperature from 25 to -78 "Cthe yield of the cyclization product (reformed starting material) is enhanced at the expense of the cycloelimination and decarbonylation. Stereospecificity of the reactions does not appear to be greatly effected by such temperature change apart from a slight decrease in the stereospecificity of the decarbonylation process. Interest in the ring-expansion process for its synthetic potential has also been reported. Photolysis of the ketones (14a-c) in methanol afforded the ring-expanded acetals (1 5 a - c ) via the now wellexemplified route of ring expansion to a carbene intermediate (e.g., 16) which l 5 In competition with this subsequently is trapped by solvent (methan~l).'~? reaction is the cleavage of the four-membered ring (in 1 4 a - c and 17) to yield the olefin products (18 and 19, respectively). When the ring-opening process was applied to the ketones (14b, d, e) by irradiation in aqueous tetrahydrofuran high yields of the lactols (20) were obtained without the competition of ring opening to olefins. It is clear that in this instance the change of solvent has a profound effect on the outcome of the photochemical reaction.

c;: 0

R2

(14)

R'

Te

9

:

CAR]

0

R2

R2

' 0

Q 0 ,..I1

R'

0

(1 5 ) (16) (17) a; R' = CHSMe=CHSMe, R 2 = OH b; R' = CH=CHCHOHC5H11, R2 = OH c; R' = CH=CHCH(OSiMe,Bu') C,H,;, R2 = OSiMe2But d; R' = R2 = H e; R' = Bun, R 2 = OH

$OH

R' (18)

(19)

R' (20)

Population of the triplet nz* state of the esters (21) results in the conversion to the unsaturated aldehydes (22) by an a-fission process.'6*17 The reaction is sometimes complicated by the intervention of Norrish Type I1 reactivity dependent on the length of the alkyl substituent. The singlet state of the compounds is unreactive. 1-Menthone (23) is photochemically active and yields, on prolonged irradiation, the acid (24) following Norrish Type I fission and disproportionation of the R. F. Newton, D. P. Reynolds, N . M. Crossland, D. R. Kelly, and S. M. Roberts, J . Chem. Soc., Perkin Trans. I , 1980, 1583. For reviews see D. R. Morton and N. J. Turro, Adv. Photochem., 1974, 9, 197; P. Yates and R. D. Loutfy, Arc. Chem. Res., 1975, 8, 209. J. Kossanyi, I. Kawenoki, B. Furth, and V. Meyer, J . Photochem., 1980,12,305 (Chem. Abstr., 1980, 93, 167 207).

See also J. Kossanyi, J. Perales, A. Laachach, I. Kawenoki, and J. P. Morizur, Synthesis, 1979, 279.

Photolysis of Carbonyl Compounds

227

0

0

QR (21) n = I or 2

R

@C02&

C0,Et =

H , Me, Et, Pr, Pr’CH,

(22)

resultant biradical.’ Other products, (25) and (26), are also formed and arise from the decarbonylation and the Norrish Type I1 cyclization of (23). The other two products (27) and (28) encountered presumably arise by secondary processes. The ester (29) is the only volatile photoproduct obtained from the irradiation of the

(23)

(24)

(25)

(26)

(27)

(28)

ketone (30a) in methanol.” An analogous path (that of a-fission) is followed by the ketone (31), which yields the ester (32) on irradiation under similar conditions. The reason for the apparent preferred fission of bond ‘a’ in the ketones (30a and

R’

(29)

(30) a; R’ = RZ = Me b; R 1 = Me, R2 = H c;,R’ = R2 = Me

(31)

3 1) is not instantly obvious and the authors l 9 investigated the influence of methyl substitution upon the photochemical reaction of (30). When a single methyl substituent is included in ketone (30b) products (33) and (34) are obtained from the two possible paths of a-fission leading to the biradicals (35) and (36) (Scheme 4). However, when two substituents were incorporated as in (30c) the compound was only very slowly reactive and failed to yield identifiable products. The influence of methyl substitution can be overwhelming, as with the bicyclic ketone (37), which yields only products (38) and (39) derived from Norrish Type I fission towards the more stable biradical (40).’ Norrish Type I reactivity can also lead to photoepimerization as has been reported for the conversion of (41) into (42).20 The photoconversion of the silane (43) into the acetal(44) in propan-2-01 can be sensitized and quenched.’l A kinetic study has shown that the triplet lifetime of l9 2o

R. K.Baslas, Int. Congr. Essent. Oils,(Pap.), 7th. 1977, 7 , 484. R. K. Murray, jun. and T. M. Ford, J . Am. Chem. Soc., 1980, 102, 3194. I. Kitagawa, T. Kamigauchi, K. Yonetani, and M. Yoshihdra, Chem. Pharm. Bull., 1980, 28, 2403 (Chem. Absrr., 1981, 94, 84324). R. A. Bourque, P. D. Davis, and J. C. Dalton, J . Am. Chem. Soc., 1981, 103, 697.

GOB

228

Photochemistry

(30b)

--+

4

(35)

(34)

(36)

i Me

(33)

Scheme 4

the silane (43) is not affected by changing the concentration of the alcohol. Thus the mechanism for the formation of the acetal involves the excitation of the silane to its triplet state followed by transformation into the carbene (45). This carbene is then trapped by the solvent. Such a mechanism is in agreement with that proposed earlier by Brook et ~ 1Photoaddition . ~ ~ of the silane (43) to dimethyl fumarate gives the trans-cyclopropane (46).23No evidence was found for the presence of the

doAc ***

...Me

JoA=

Me

OMe (42)

(41)

0 II Me-C -SiMe3 (43)

OPri I Me-C-OSiMeJ

I

H

Me-E-OSiMe3 (45)

(44) 22

23

A. G . Brook and J. M . J. Duff, J . Am. Chem. Soc., 1967, 89, 454;Can. J . Chem., 1973, 51, 2869. J. C . Dalton and R. A. Bourque, J. Am. Chem. Soc., 1981, 103,699.

Photolysis of Carbonyl Compounds

229 0. .,CO2Me

C0,Me MeflCO,Me OSiMe,

C0,Me MeflCO,Me OSiMe,

Me-iJC02Me SiMe

Me-74C0,Me OSiMe (49)

cis-product (47); but this is formed along with the trans-adduct (46) in a ratio of 2 : 3 from the photoaddition of the silane (43) to dimethyl maleate. From a careful study of the reaction the authors23 suggest that the formation of the product involves the addition of the excited triplet or singlet state of the silane (43) to give a short-lived biradical(48), which rearranges to the 1,3-biradica1(49),prior to ring closing to the cyclopropane. No evidence was collected for the intermediacy of the carbene (45) in this reaction. The phosphonates (50) are photochemically reactive and lead to products dependent upon the nature of the substituents.24 Irradiation of the phosphonate (50a) yields the product (51a) as a result of a photoreaction analogous to a Norrish Type I process. An analogous product (51b) is also encountered in the photolysis of phosphonate (50b). In this instance however other products (52b) and (53b) are produced as a result of Norrish Type I1 reactivity and fission of the resultant biradical. Norrish Type I1 fission dominates the photoreactions of (5Oc) and (50d) yielding the monoester (52c, d) and the olefin (53c, d). Fission of the C-P bond to afford the radical (54) and products derived from it is the result of irradiation of the phosphine (55).25 0 II CI,CP(OR)2 (50) a; R = Me

b; R = Bu' c; R = Pr" d; R = Et

p

(OR 1

0

j

(51) a; R = Me

b; R = Bu'

II I

C1JCP-OH

OR (52) b;

R = Bu'

c; R d; R

(54)

= Pr" = Et

RifR2 (53) b: R1 = R2 = Me c; R' = Me, R2 = H d; R' = R2 = H

(55)

The formation of chromones (56) from the photolysis of acetates (57) is brought about by a free-radical path involving the fission of a C-0 bond to yield the radical intermediate (58).26 24 25

N. Suzuki, T. Kawai, S. Inoue, N. Sano, and Y. Izawa, Bull. Chem. Soc. Jpn., 1980, 53, 1421. M. Dankowski, K. Praefcke, J.-S. Lee and S. C. Nyburg, Phosphorus Sulphur, 1980.8, 359 (Chem. Abstr., 1981, 94, 29797). H. Garcia, R. Martinez-Utrilla, and M. A. Miranda, Tetrahedron Lett., 1981, 1749.

Photochemistry

230

"Ac (57)

(56)

R' R'

= =

R2 = H; R'

(58)

H, R2 = OMe, Cl,lor Me; M e 0 or OH, R2 = H; R' = R2 = Me =

3 Norrish Type I1 Reactions Wagner 2 7 has reviewed the photochemistry of simple carbonyl compounds and the rearrangements involving 1,4-biradicals produced by, for example, Norrish Type I1 behaviour of ketones. A study of the photochemistry of alkanals in dilute solution and in the presence of H-donors or olefins has been reported by Encina et a1.28The behaviour towards unsaturated compounds appears to be related to the difference in the ionization potentials and electron affinities. Kossanyi et al.29have reported their studies into the quenching of aldehyde singlet states by dienes. The influence of naphthalene on the photoreaction of 4-methylpentan-2-one in solution has been e~aluated.~' A detailed study of the photoelimination reactions of the racemic trifluoroacetates (59,60) has been reported by Gano and Chien.3' A kinetic analysis

(59)

of the reaction was carried out to evaluate the contribution of the triplet and the singlet processes to the overall formation of the products (61), (62), and (63) (Table 1). The alternative fate, i.e. other than elimination of the 1,4-biradical formed by a Norrish Type I1 process, is the formation of cyclobutanols. Such is the outcome of the irradiation of the gibberellin derivative (64a) which yields the cyclobutanol (65). Treatment of this derivative with a tritium or deuterium donor affords the labelled derivative (64b).32 Azetidinols (66) are formed on irradiation of the ketones (67) in ethereal solution. The azetidinols (66) arise by way of the Norrish 27

28

29

30 31

32

P. J. Wagner, Org. Chem., 1980, 42, 381. M. V. Encina, E. A. Lissi, and F. A. Olea, J . Photochem., 1980, 14, 233 (Chem. Abstr., 1981, 94, 102431). J. Kossanyi, G. Daccord, S. Sabbdh, B. Furth, P. Chaquin, J. C. Andre, and M. Bouchy, N o w . J . Chim., 1980, 4, 337 (Chem. Abstr., 1981, 94, 29792). W. Augustyniak, J . Photochem., 1980, 12, 99 (Chem. Abstr., 1980,93, 167 238). J. E. Gano and D. H.-T. Chien, J . Am. Chem. Soc., 1980, 102, 3182. M. Lischewski and G . Adam, Br. Pat. Appl., 2022077 (Chem. Abstr., 1980, 93, 132654).

P ho t olysis of Carbony 1 Compounds

23 1

Table 1 Stereospecificity of product formation from triuoroacetates (59) and (60) 3 1 Ester

Product

(59)

(62) (61) (63) (61) + (62) (63)

(60)

Regioselectivity Singlet Triplet 6.6 7.38 7.38 6.6 4.32 3.5 4.39 3.5

+

Stereospecificity Singlet Triplet

0.88

0.56

0.74

0.02

Type I1 process via intermediate (68).33 Minor products are also produced in the reaction by cleavage of the biradical (68). An analogous cyclization is also reported for the ketones (69) yielding the products (70).34

(64) a; R b:R

(66)

= =

H DorT

(67) Ar' = ArZ = Ph

Arl Ar' Ar' Ar' Ar' Ar'

= = =

= = =

(68)

MeOC,H,, ArZ = C,H, C,H5CbH4, Arz =C,H, C,H,, ArZ = CIC,H, C6H5, Arz = MeOC,H, C,H,, Ar2 = MeC,H, 2-naphthy1, Ar2 = C,H,

0H

d-"

Me

N

Ph (69) R = 2-fury1, benzo[b]furan-2-y1, 2-thienyl, pyrrol-2-yl, 1 -methylpyrrol-2-yl, 2, 4-dimethylthiazol-5-y1, or 3-pyridyl

Ph

A laser flash study of the behaviour of o-methylacetophenone has been reported in a study of the hydrogen-abstraction process leading to the quinomethide intermediate.35The ketones (7 1) also undergo photochemical conversion into a quinomethide intermediate, which cyclizes to the cyclobutenols (72) with reasonable efficiency. It is interesting that, although these ketones (71) undergo complete conversion on prolonged irradiation, the conversion of ketone (7 1, X = COC,H,Pr3'-2,4,6) yields a mixture of the cyclobutenol (72, 33

34

35

K . L. Allworth, A. A. El-Hamamy, M. M . Hesabi, and J. Hill, J . Cliem. Soc., Perkin Trans. I, 1980, 1671. M. M. Hesabi, J. Hill, and A. A. El-Hamarny, J . Chem. Soc., Perkin Trims. I , 1980, 2371. J. C . Scaiano, Chem. PIiys. Lett., 1980, 73, 319.

Photochemistry

232

(71) (72) X = OMe, Me, Bu', H, C8O2H,CO,Me, CF,, or CN

X = COC,H,Pr,'-2,4,6) and the starting material. This arises as a result of photoconversion of the cyclobutenol into starting material. The formation of cyclobutenols (72) was quenched using 2,5-dimethylhexa-2,4-dieneand the triplet lifetime thereby calculated. It was readily demonstrated that a Hammett plot of log zH/zx against otwas linear and gave a negative value for p. It was concluded that there is a strong effect exercised on the reaction by the presence of the bulky ortho-sub~tituents.~~ Quinkert and his co-workers 37 have reported a photochemical route to the synthesis of (_+)-oestrone(73). The reaction involves photoexcitation of the keto-olefin (74), which is transformed into the o-quinomethide (75) and then undergoes intramolecular addition to afford (76). Subsequent chemical transformation yields the product (73). The extension of this process to the synthesis of (+)-oestrone was also reported.38

HO

w \

Irradiation of the furanone derivative (77a) affords the two products (78) and (79) shown in Scheme 5.39 When the oxygen function at C-2 is not methylated (77b), irradiation yields the products (80, 81) (Scheme 6). In this case a different rearrangement mechanism is permitted as a result of the relative ease of opening of the furanone ring. The route to product (80) is thought to involve a Norrish Type I1 process of the carbonyl group with the proximate methoxy function. Subsequent rearrangement via the spiro intermediate (82) ultimately provides the product (80). In the first example (Scheme 5 ) the formation of (78) also involves 36 37

38 39

Y. Ito, Y. Umehard, Y . Yamada, and T. Matsuura, J . Chem. SOC., Chem. Commun., 1980, 1160. G. Quinkert, W.-D. Weber, U. Schwartz, and G. Durner, Angew. Chem.,hi.Ed. Engl., 1980,19, 1027. G.Quinkert, U. Schwartz, H. Stark, W.-D.Weber, H. Baier, F.Adam, and G. Durner, Angen. Chem. Int. Ed. Engl., 1980, 19, 1029. J. H. van der Westhuizen, D. Ferreira, and D . G. Roux, J . Chem. SOC.,Perkin Trans. I , 1980, 1540.

Photolysis of Carbonyl Compounds

233 _ ,,r. _ *~M

M & -yM m eJJe

c\ o

W

O

M

e

\

Me0

HOCH, (774

(78)

t

OMe

Me (79)

Scheme 5

M

e

o

\

w

o

M

e &

OH

I

OH 0

OMe

Me M e 0 Ho

Scheme 6

the spiro intermediate but the presence of a 2-alkoxy group prevents further rearrangement.

The Norrish Type I1 reaction, while commonly following a path that yields a 1,6biradical, can sometimes yield 1,5-or higher biradicals. A 1,5-biradical path is the key to the cyclization involved in an approach to the synthesis of dodecahedrane and its derivatives reported by Paquette and his co-~orkers.~' The photocyclization of the aldehyde (83) yields, after oxidation, the ketone (84). Further 40

L. A. Paquette, D. W. Balogh, and J. F. Blount, J . Am. Chem. SOC.,1981, 103,228.

234

Photochemistry

irradiation of this material yields the alcohol (85) via an analogous 1,5-biradical intermediate. Higher biradical species are discussed in a review by Breslow 41 of his work in the area of biomimetic control of chemical stereoselectivity.

Me

Me

(83)

(84)

(85)

4 Oxetan Formation

The gas-phase irradiation of hexafluoroacetone and 1,2-dichlorofluoroethylene (mixture of 2 and E isomers) gives the two oxetans (86) and (87) in a ratio of 55 : 45.42

F 3FC T \ H CI c1

F 3H C T i CI C1 F

(87)

(86)

Photoaddition of benzophenone to the methylene ketone derivatives (88) yields . ~ ~ biradical (90) the oxetan derivatives (89a) in 28 and 26% yield, r e ~ p e c t i v e l yThe is presumed to be the intermediate in the formation of these compounds. The authors 43 suggest that there are two competing pathways for reaction within this biradical, one leading to the oxetans (89), and another by rearrangement through Z

0

0

Me

Mi (88) R = H or Me

(89) a; Z . = 0; R b; R = H; Z

Ph Ph H or Me H , OH

= =

(90)

TPh2

I

,o

MC

(92) Z = HOor H 41

42

''

(93)

R. Breslow, Acc. Chem. Res., 1980, 13, 170. M . G. Barlow, B. Coles, and R. N. Haszeldine, J . Fluorine Chem., 1980, 15, 381. M . Nitta, T. Kuroki, and H. Sugiyama, J . Chem. Soc., Chem. Commun., 1980, 378.

Photolysis of Carbonyl Compounds

235

(91) to yield adducts of the type (92). This route manifests itself in the photoreaction of the ene-ol (93) to yield the oxetan (89b) and the rearranged adduct (92). Another account of the photoaddition of benzophenone to norbornadiene has been reported.44 The products encountered (94,95,96a) seem to differ little from earlier reports 4 5 of this addition. The same products are formed from benzophenone and quadricyclane. The addition of (97) to norbornadiene yields the adducts (98, 62%) and (96b, 38%).

(95)

o=c/C0,Me

(96) a; R b; R

4 0

= =

Ph C0,Me

C0,Me

\

C0,Me

C0,Me

(97)

(98)

A detailed study of the photoaddition of trans-dicyanoethylene to the ketones (99-101) has been published.46 The results indicate that the cycloaddition is

b; R'-R2

N :@

C;

= CH,-CH, = Me

R 1 = R2

(102)

stereospecific, yielding in each case two oxetans (102), the result of em-attack on the carbonyl group. Minor products are also obtained where the oxetan is produced by endo-attack. The quantum yield measurements appear to indicate 44

45

46

K. Shima, M. Ikenoue, and K . Kamei, Kokagaku Toronkai Koen Yoshishu, 1979, 162 (Chem. Abstr., 1980, 93, 7263). T. Kubota, K. Shima, and H. Sakurai, Chem. Lett., 1972, 343; A. A. Gorman and R. B. Leyland, Tetrahedron Lett., 1972, 5345; A. G . Barwise, A. A. Gorman, R. B. Leyland, C. T. Parekh, and P. G. Smith, Tetrahedron, 1980, 36, 397. N. J. Turro and G . L. Farrington, J . Am. Chem. Soc., 1980, 102, 6056.

236

Photochemistry

that the cycloaddition from the em-face is enhanced by increasing steric hindrance: the relative quantum yield for the formation of oxetans from ketone (99) is 3.4 times higher than that for ketone (100). Reasonable yields of the adducts (103) are obtained when acetone is irradiated Compounds of in the presence of 2,3-dihydro- and 2-methyl-2,3-dihydro-furan. this structure can also be obtained by the photocyclization of the vinyloxy ketones (104a) and (104b),. which yields the adducts (105a) and (105b), re~pectively.~’ Intramolecular cycloaddition is also encountered in the photoreactions of the cyclic alkanones (106).48However the reaction favours the formation of the crossed adduct (107) in all the cases studied. The accompanying products are the alternative oxetan (108) and the products from Norrish Type I fission.

M Me e Rr (103) a; R b; R

n H = Me

=

R (104) a; R = H

(105) a; R = H

b; R

b; R

R (106) n

=

n =

1-3, R = H 2,R = MeorH

=

Me

R

=

Me

R

(107)

5 Fragmentations and Miscellaneous Reactions The diene (109) is formed when the keto-diene (110) is irradiated in various solvents using 1 = 254nm.49 The Diels-Alder activity of the diene (109) was

investigated. A detailed study of the photochemical gas-phase decarbonylation of bicyclic ketones (111, 112) has been reported (Scheme 7).50 The photodecarbonylation of the sugar derivatives (1 13, 1 14) yields the products (1 15, 1 16) shown in Scheme 8.’l Irradiation (A < 220 nm) of the saturated esters (1 17, 1 18, and 1 19) and acids results in two p h o t o p r o c e s s e ~ The . ~ ~ ester ( I 17) undergoes elimination of acetic

‘’ 49

’’ 50

s2

H. A. J. Carless and D. J. Haywood, J. Chem. Soc., Chem. Commun., 1980, 1067. J. Kossanyi, P. Jost, B. Furth, G. Daccord, and P. Chaquin, J. Chem. Res. (S), 1980, 368. L. Schwager and P. Vogel, Helv. Chim. Acta, 1980, 63, 1176. P. S . Mariano, E. Bay, D. G. Watson, T. Rose, and C. Bracken, J . Org. Chem., 1980, 45, 1753. K. Heyns, H.-R. Neste, and J. Thiem, Chem. Ber., 1981, 114, 891. G. Wolff and G. Ourisson, Tetrahedron Lett., 1981, 1441.

Photolysis of Carbonj4 Compounds

H

237

H

Me

Me

Me

Me

Scheme 7

(113)

R' = Me = R2 R * = Ph. R2 = H

(1 14)

Scheme 8

acid, presumably via a process akin to the Norrish Type I1 reaction, yielding the olefin (120). The same olefin (120) is obtained from the irradiation of the ester (121) presumably by a similar mechanism. Similar elimination reactions are encountered for the bile acids (1 18) and (1 19) (Scheme 9). A detailed analysis of the photosolvolysis of the chiral acetate (122) has been carried The products formed from the reaction are shown in Scheme 10 for the two solvents used. The results indicate that there is partitioning of the excited state between an allowed I ,3-sigmatropic shift of the benzyl group on the acetate system and the involvement of heterolytic and homolytic pathways. An electron-transfer mechanism is used to explain the formation of products (123-125) (Scheme 11) resulting from the photolysis of ester (126).54 The products are formally obtained by the loss of an acetyl group (C-0 bond fission) and hydrogen abstraction by the resultant ally1 radical. 53 54

D. A. Jaeger and G. H . Angelos, Tetrahedron LRtt., 1981, 803. K. Tsujimoto, Y. Kamiyama, Y. Furukawa, and M . Ohashi, Kokagaku Toronkai Koen Yoshishu, 1979, 208 (Chern. Abstr., 1980, 93, 70 529).

(1 19)

Scheme 9 Ar

Ar / I 1’

M e t H IR

\

OCOCH, (1 22)

Ar

I

1

MeC-H

f

I

I R

OR a ; R = H b i r r = Me

+

MeC-H

Ar

Ar = 3,5-diMeOC,H,

a ; R = H b; R = Me

CF,CH,OH

Ar

I

+

Me-C-H

I

I I

Me-C-H

R

OCH2CF3

R = H or Me Scheme 10

&OAC

R&Me Me

-t

R& Me

+

Me ( 126)

(123; 779

(124; 14:i)

(125; 3%)

R = 2-naphthyl

Scheme 11

The photolysis of the ether (127) in n-heptane yields free radicals in a first-order reaction.55The lactone (128) and the 3-tetrahydropyrone (129) are formed when the compound (1 30) is subjected to solution-phase irradiation.s6 55

56

V. Cermak, P. Vetesnik, and P. Pecen, Chern. Prum., 1979, 29, 642 (Chern. Abstr., 1980.92, 197550). C. Bernasconi, L. Cottier, G. Descotes, M. F. Grenier, and F. Metras, J . Heterocycl. Chern., 1980, 17, 45.

Phot olysis of Carbony1 Compounds

(127)

(1 28)

239

( 130)

( 129)

From the results (Scheme 12) obtained from the irradiation of the halocyclohexanones (1 3 I), the authors suggest that both free-radical and ionic paths are operative. They have further shown that sensitized reaction leads to radical products derived from the reaction of an nn* triplet state, whereas the singlet state leads to the ionic product^.^'

’’

(131) X

X X

X

=

C1, R = H

= C1, R = Me = Br,R = H = I, R = H

28% 16% 90% 70% Scheme 12

59%

13% 26% 10% 30%

58% -

A study of a series of bis-sulphenylated keto compounds has revealed a remarkable solvent effect.58Thus irradiation of, for example, (1 32) in acetonitrile yields ( 1 33, 43%) as the major product accompanied by two minor products (134, 25%) and (135,23%). But in benzene the products (1 34,63%) and (1 35,4973 were produced with no evidence for the formation of the cyclized material (1 33). Several examples of the reaction are cited. The photodegradation of some sulphonamides (e.g., 136) has been studied.59

(132)

(133)

(134)

(135)

The epoxycholestanone (1 37) undergoes conversion into the isomer ( 1 38) when irradiated at 254 nm.60 The irradiation of mixtures of 1,2-diarylketones and benzhydrylamine has been reported.61 The products encountered in this reaction are thought to arise from free radicals produced by hydrogen abstraction from the amine by the excited carbonyl compound. Caronna et ~ 1have . reported ~ ~ the formation of the adduct 5’ 58 59

P. C. Purohit and H. R. Sonawane, Tetruhcdron, 1981, 37. 873. T. Sasaki, K. Hayakawa, and S. Nishida, Tetrahedron Left., 1980. 3903. B. Weiss, H. Durr, and H. J. Haas, Angeir, Chem., I n / . Ed. Engl., 1980, 19, 648. P. Morand and S. A. Samad, Bangladesh J. Sci. Inn. Res., 1979, 14, 265 (Chem. Abstr.. 1980, 92, 181 481).

61

62

K. N. Mehrotra and G. P. Pandey, Bull. Chem. Soc. Jpn., 1980, 53, 1081. T. Caronna, S. Morrocchi, and B. M. Vittimberga, J. Heterocjd. Chent., 1980. 17. 399.

Plzot ochemistry

240

R' /

R3 (136) R L = H , R 2 = Ph, R3

R' R'

R1

= = =

R'

=

Me

PhCO, R 2 = Ph. R 3 = M e H , R 2 = 2-thiazolyl. R 3 = N H ,

'H '8H o

&HI7

HO

=

R 2 = Ph, R3 = M e H , R 2 = PhCO, R3 = M e

6

,,,

0

( 137)

( 138)

(1 39) from the irradiation of 2-pyridinecarbonitrile with benzophenone in non-

acidic solution. When the irradiation is carried out in acidic propan-2-ol-H20 the adduct (1 39) is accompanied by the reduced cyclized material (140). Ph

( 139)

ph

( 140)

Cycloaddition occurs when the silacyclobutenes (141) are irradiated in the presence of aldehydes and ketones.63 The preferred reaction mechanism for the process involves photoexcitation of the carbonyl compound followed by attack of the carbonyl oxygen at silicon. This yields two biradical intermediates (142) and (143) that lead to the two isolated products (144) and (145) (Scheme 13).

I R; ( 144) Scheme 13 b3

R. Okazaki, K.-T. Kang, and N. Inamoto, Tetruhedron Lett., 1981, 235.

3

L

Enone Cycloadditions a nd Rearrangement s: Photoreactions of Cyclohexadienones and Quinones BY W. M. HORSPOOL

1 Cycloaddition Reactions Intramolecular.-A full account of the synthetic approaches' using intramolecular cycloaddition of enones (1) eventually to yield the hirsutane skeleton (2, Scheme 1) has supplemented the material originally published in note form.2

Intramolecular cycloaddition can often provide an easy synthetic entry to novel strained compounds. Thus the photocycloaddition of the butenolides (3) yields the adducts shown in the Scheme 2. Irradiation of the enone (4)at 330 nm affords the 0

total yield 62"/,; ratio m 3 : l

Scheme 2

'

J. S. H. Kueh, M. Mellor, and G. Pattenden, J . Chem. SOC..Perkin Trans. I , 1981, 1052. J. S. H. Kueh, M. Mellor, and G. Pattenden, J. Chem. Soc., Chem. Commun., 1978, 5 . W. R. Baker, P. D. Senter, and R. M. Coates, J. Chem. SOC.,Chem. Commun., 1980, 1011.

24 1

242

Photochemistry

tricyclic product (5) in good yield (67%).4 Subsequent thermal reactions transformed this compound into (6), a derivative of tricyclo[4,2,0,0 1, 4]octane.

(5)

(4)

(6)

The photocyclization of the enone (7) to yield (8) has been used as an approach to the synthesis of the spiro(4,5)decane system.’ The tetracyclic product (9a) is obtained from the photo-induced intramolecular cyclization of the pyridone (10a)6, Increase in the chain length involving (lob) resulted in the formation of

(7)

(8)

the head-to-head adduct (1 la). However with an intermediate chain length (1Oc) the irradiation afforded the two adducts (9b) and (1 1b) in a ratio of 7 : 1. When intermolecular cycloadditions were effected between (12) and a range of olefins (1 3), the addition took place in a head-to-tail fashion affording (14)?

(9) a; n = 1 b;n=2

(10) a; n = 1 b;n=3 c;n=2

RCH =CH

H (12)

0

(13) R = OAC, CN, CO,Me, or CH

a:

(11) a; n = 3 b;n=2

K.

H (14)

The cage compounds (1 5) are produced from the enones (1 6) by irradiation in benzene solution.’ The identity of the products from the reactions was established

’ a

S. Wolff and W. C. Agosta, J. Chem. Soc., Chem. Commun., 1981, 118. W. Oppolzer, L. Gorrichon, and T. G. C. Bird, Helv. Chim. Acta, 1981, 64, 186. C. Kanoeka, T. Naito, H . Fujii, K. Shiba, M . Ito, and M. Somei, Kokagaku Toronkai Koen Yoshishu, 1979, 108 (Chem. Abstr., 1980, 93, 70805). C. Kaneoka, T. Naito, and M. Somei, J. Chem. SOC.,Chem. Commun., 1979, 804. G. Gowda and T. B. H. McMurry, J . Chem. SOC.,Perkin Trans. 1, 1980, 1516.

243

Enone Cycloadditions and Rearrangements

by spectroscopic and chemical means. The current interest in cage compounds is prompted by energy conservation i.e., the ability to trap energy in a strained molecule from which it can be recovered at a later stage. The cage compound (1 7) is formed on irradiation of the cyclopentadienone dimer (18).9 Fuchs l o has also R2 .R'

3: Me

(16)

(15) a; R' = H , R2 = Me

b; R'

=

Me U

(17) R

=

2-fury1 or 2-thienyl

Me, R2 = H

(18b) R'

(1 8a)

= R2 =

R 3 = H ; R'

=

R2 = H, R 3 = Ph; = R2 = Me, R 3 = Ph

R' = Me, R2 = H, R3 = Ph; R'

reported on the photochemical transformations of cyclopentadienone dimers (18b). Hamada et a!.' 1* l 2 have reported the synthesis of the cage compounds (19a) by the irradiation of the adducts (19b) using Pyrex-filtered light as the actinic source. The conversion could be carried out with wavelengths up to 360nm. For longer wavelengths, up to 390nm, the adducts (20) were useful and could be readily converted into the cage compounds (21). The X-ray structure determination of the cycloadduct (22) formed by photochemical ring-closure of (23) has been reported.

'

R'

lo

l2

l3

Y. Yamashita and M. Masumura, Heterocycles, 1980, 14, 29. B. Fuchs, Isr. J. Chem., 1980, 20, 203 (Chem. Abstr., 1981, 94, 46633). T. Hamada, H. Iijima, T. Yamamoto, N . Numao, K. Hirao, and 0.Yonemitsu, J . Chem. Soc., Chem. Commun., 1980, 696. T. Hamada, H. Iijima, T. Yamamoto, N . Numao, and 0. Yonemitsu, Kokaguku Toronkai Koen Yoshishu, 1979, 2 (Chem. Abstr., 1980,93, 70445). H. D. Becker, B. W. Skelton, and A. H. White, J . Chem. SOC.,Perkin Trans. 2, 1981, 442.

Pho tockemistry

244

(20)

R'

= -Me*,R 2 = p-MeOC,H,

(21)

PhH,C M e Ph \

H , C Me

4,Ph 0 Me (22)

(23)

The unstable cycloadducts (24) and (25) are obtained from the photolysis of the enone ethers (26).14 A similar approach has been reported by Barker and Pattenden in their study of the photocyclization of enol acetates. Thus the intramolecular photocycloaddition affords the adducts (27) from the mixture of enol acetates derived from (28). An analogous regioselective cycloaddition is encountered in the irradiation of the enol acetates derived from (29) to afford the adduct (30).

(25)

R

=

Me or 6u'

(27) a; R3 = M e , R 2 = H (62%) (28) R' = H or Me (29) R = H or Me b; R 3 = H,R2 = Me (16%)

(30)

The norbornene derivatives (3 la, b) gradually disappear on irradiation without the formation of oxetan derivatives, the result of intramolecular cycloaddition. l4

Is l6

W. Oppolzer and S. C. f)urford, Helv. Chin?.Acta, 1980, 63. A. J. Barker and G. Pattenden, Tetrahedron Lett.. 1980, 3513. R. R. Sauers and D. C. Lynch, J . Org. Chem., 1980, 45, 1286.

Enone Cycloudditions und Rearrungements

245

c

0" 'kH2 (31) a; R b; R

= SCH2Ph

(32)

NEt, C; R = ON d; R = C1 e;R=H =

R = OH d; R = CI

C;

(33)

Th derivative (3 lc), however, undergoes a clea photoreaction to afford the oxetan (32c). The chloroketone (3 Id) affords, on irradiation, many products among which are the oxetan (32d) and the dechlorinated compound (31e). The homolysis of (31d) to the radical (33) is a facile process and occurs in competition with cyclization to the oxetan.16 Intermolecular.-The control of regiospecificity in photocycloadditions remains a much sought after goal. de Mayo and Syndes l 7 have found that some control can be exercised on the reaction when the cycloadditions are carried out in micellar potassium dodecanoate (KDC). The ratios of products are sufficiently different (Table 1) from those obtained in non-polar solvents to merit further study of this

Table 1 Products from the cycloaddition of olefins (34) to 3-butylcyclopentenone' Medium KDC Diethyl ether Cyclohexane KDC Acetonitrile Methanol Cyclohexane KDC Methanol Diethyl ether KDC Methanol Diethyl ether

R'

=

Olejin (34) Bu", R 2 = H

R'

=

hexyl, R2 = H

R'

=

Bu", R2 = OAC

R'

= pentyl,

R2 = OAc

Products (%) (35) (36) 78 22 57 43 51 49 88 12 63 37 62 38 53 47 70 30 0 100 0 100 70 30 0 100 0 1 00

effect. The authors believe that the regioselectivity observed is a micellar effect and not a function of the solvent polarity. The regiospecific photoaddition of the P. de Mayo and L. K. Sydnes, J . Chem. Sac., Chem. Commun., 1980, 994.

246

Photochemistry

cyclopentenone (37) to the olefins (38,39) affords the [2 + 2ladducts (40,41) shown in Scheme 3.18 When the acetylene (42) and the olefin (43) are used as the substrate for the addition, two [2+2]adducts are formed in both cases, one from head-tohead addition and the other from the head-to-tail mode (Scheme 4).The additions

&

SiMe, + MeM 'e (38)

(37)

A

&le

+

Me (40) 0

&Me ratio 5.4: 1

+ (39) R'--R2 = (CH,), R ' = OAc; R 2 = Me

(41)

Scheme 3

SiMe3

+ H,C=CHMe (43)

--+

*Me (20%)

H

'*H

(47%)

H (33%)

Scheme 4

are sometimes complicated by the formation of additional products, as shown in Scheme 3. Furthermore, care has to be taken to select the correct wavelength for the irradiation to avoid secondary photolysis of the adducts, e.g., the conversion of (40) and (44) by a Norrish Type I process. The addition of olefins to the uracil

derivative (45) was also studied (Scheme 5). In these experiments the influence of the trimethylsilyl group was seen in that only one addition mode was observed in each case." C . Shih, E. L. Fritzen, and J. S. Swenton, J . Org. Chem., 1980, 45, 4462.

Enone Cycloadditions and Rearrangements

247

0

H (45)

R 1 = R 2 = Me RI-R~

=

(CH,),

R 1= H, R2 = Me

90% 85% 87% ex0 : endo 15:85

Scheme 5

nn* Excitation (350 nm) of the enones (46a-d) in the presence of the cyclobutene (47) affords good yields (75-80%) of the cycloadducts ( 4 8 a 4 ) . 1 9 The use of enones (46e, f) gave lower yields (4&50%) of the corresponding adducts (48e, f), whereas enone (46g) gave only a trace of a photoproduct. This enone (46g) is apparently noted for its abnormal behaviour.20*2 1 The formation of (*)-adduct (48d) (73%) was also reported from the photoaddition of the olefin (47) to (-)piperitone (46d) using Corex-filtered light at 0 0C.22After desilylation and cleavage of the resultant diol the 1,Cdione (49) is obtained. A full account,23,24 originally reported in note of the photoaddition of 1-methylcyclobutene (50) at low temperature (- 78 "C)to piperitone (46d) as a route to the synthesis of shyobunone (51) and isocalmendiol (52) has been published. Blechert 26 has published a short review dealing with the photochemical synthesis of natural products.

R1QR3 R2 0 (46) a; n = 1, R' = R3 = H, RZ = Me a O SOSiMe3 iMe3 b; n = 1, R' = R2 = Me, R 3 = H c; n = 2, R' = Me, R2 = R 3 = H (47) d; n = 2, R' = Me, R2 = H, R 3 = Pr' e; n = 1 , R' = Me, R2 = R3 = H f; n = 2, R' = R2 = Me, R 3 = H g; n = 2, R' = R 3 = H, R2 = Me

(48)

?! Me

l9 2o 21

23 24 25

26

M. Van Audenhove, D. De Keukeleire, and M. Vanderwalle, Tetrahedron Lett., 1980, 1979. E. J. Corey, J. D. Bass, R. Le Mahieu, and R. B. Mitrd, J . Am. Chem. Soc., 1964, 87, 5570. E. P. Serebryakov, S. D. Kulomzina, and A. K. Margaryan, Tetrahedron, 1979, 35, 77. J. R. Williams and T. J . Caggiano, Synthesis, 1980, 1024. J. R. Williams and J . F. Callahan, J. Org. Chem., 1980, 45, 4479. J. R. Williams and J. F. Callahan, J . Org. Chem., 1980, 45, 4475. J. R. Williams and J . F. Callahan, J . Chem. SOC.,Chem. Commun., 1979, 404, 405. S. Blechert, Nachr. Chem. Tech. Lab., 1980, 28, 883 (Chem. Abstr.. 1981, 94, 64641).

248

Photochemistry

A high yield of the cycloadduct (53) is obtained from the direct irradiation of a hexane solution of tetramethylethylene and the enone (54).2 Controlled hydride

reduction and ring opening affords the keto aldehyde (55) which undergoes basecatalysed cyclization to yield the cyclohexenone derivative (56). Several examples

(54)

(53)

(56)

(55)

of this process are reported. Of importance in this reaction is the apparent regioselectivity observed when unsymmetrical olefins are employed (Scheme 6). The cycloaddition of enones to olefins is a reaction of great synthetic utility. Duc et ~ 1 have . extended ~ ~ the synthetic value in their report of the BF,-etheratecatalysed ring opening of the enone-allene adducts (e.g., 57 and 58). This chemical treatment of the adducts is a convenient method for the introduction of an isopropenyl group into unsaturated ketones (e.g., 59 and 60, respectively).

ratio 1.1.6

0

0 Scheme 6

Earlier work by Wiesner 2 9 proposed a set of empirical rules to account for the outcome of cycloaddition reactions to enones. Wiesner et a/. have now examined the photoaddition of allene to the sterically hindered system (61).30This work has

(57)

''

'' 29

''

(59)

(58)

S. W. Baldwin and J. M. Wilkinson, J . Am. Chem. Soc., 1980, 102, 3634. D. K. M. Duc, M . Fetizon, I . Hanna, and S. Lazare, Synrhesis, 1981, 139. K. Wiesner, Tetrahedron, 1975, 31, 1655. J. F. Blount, G. D. Gray, K. S. Atwal, T. Y . R. Tsai, and K. Wiesner, Tetrahedron Lett., 1980, 4413.

Enone Cycloadditions and Rearrangements

249

R' = 0, R2 = H2, R3 = b; R' = H,, R2 = 0, R3 = C8H17

(61) a;

(62)

aimed at answering the criticism of de Mayo and L o ~ t f y , ~who ' had implied that stereochemical control of the cycloaddition might depend exclusively upon steric factors. The cycloaddition to enone (61a) yielding the adduct (62) on the a-fxe is in line with Wiesner's predictions. This product was accompanied by the byproduct (63) formed by the route outlined in Scheme 7. Enone (61a) is sterically

I

H2%

HC

CH2 Scheme 7

hindered on the a-face as is enone (61b) but in addition to this, if the empirical rules are operative, then a-addition should also be inhibited. Indeed when the enone (61b) was irradiated in the presence of allene no adduct was obtained under conditions where (61a) yielded an adduct. On prolonged irradiation a trace of an adduct was obtained. The photoaddition of allene to the enone (64) yields the [2 + 21-adduct (65) in 78% yield. 32 0

H$

C0,Me (64) 31

32

(65)

R. 0. Loutfy and P. de Mayo, J . Am. Chem. Soc., 1977, 99, 3559. R. B. Kelly, M. L. Harley, and S. J. Alward, Can. J . Chem.. 1980, 58, 755.

250

Photochemistry

The single adduct (67a) is obtained by photoaddition of 1,l -dimethoxyethylene to the ester (66a). Adducts (67b) and (68) were also obtained by the photoaddition of the same olefin to the enone (66b). The molecules obtained by this process were chemically elaborated to yield compounds with the proto-illudane skeleton (69).33

Me Me& Me

HA

Me0 (67) a; R = C 0 2 M e , 67% b; R = Me, 19%

(66) a; R = C 0 2 M e b; R = Me

M eO (68) 5%

The cyclopentenones (70) do not undergo cycloaddition reactions with cyclohexene.34 The only reaction encountered in the irradiation of these molecules is the facile isomerization by a 1,3-alkyl shift to (71).35 In contrast with this, irradiation of cyclopentenone (72a) in the presence of ethylene yields (73a). The cyclopentenone (72b) yields (73b) with cyclohexene. It is clear from these results that there is some structural phenomenon within the molecules which make some, the (4,3,2)-propellanes prone to rearrange, while others, the (3,3,3)-propellanes, undergo cycloaddition.

(70)

R' = RZ = H; R' R' = R2 = Me

=

(72) a; R' = R2 = Me b; R' = Rz = H 33 34

35

R'

Me, R2 = H; (71)

(73) a; R' = R 2 = Me, R 3 = H b; R' = R 2 = H, R3-R3 = (CH,),

H. Takeshita, I. Kouno, H . Iwabuchi, and D. Nomura, Buff. Chem. SOC. Jpn., 1980, 53, 3641. R. L. Cargill, N. P. Peet, D. M . Pond, W. A. Bundy. and A. B. Sears, J . Org. Chem.. 1980,45, 3999. See later in this chapter for further examples of 1,3-alkyi migrations.

Enone Cycloadditions and Rearrangements 25 1 Two modes for the photoaddition of acetylene to the cholestenone (74) have been reported.36 Thus [2 21-cycloaddition yields the adducts (75) and (76) whereas an ene-type addition yields the ethylidene derivative (77).

+

@ ogl

0 '

;/

/

.

o@ Me

I

H (77)

(76)

(75)

(74)

The acetone-sensitized photoaddition of ethylene to the imidazolinone (78) yields the adduct (79).37Other adducts can also be obtained by the use of different I

Ac

Ac

olefins of imidazolinones. Photoaddition of olefins (e.g.,2-methylbut-2-ene)to the dienone (80a) results in the formation of the conventional adduct (81). When the thioketone (80b) is employed the reaction affords the adduct (82) where cyclization involving the sulphur has taken place.38 The adducts (83) are formed by the photoaddition of electron-rich olefins (CH,=CMe,, CH,=CHOAc, CH,=CHOMe) to the pyridone (84) in acetone. 39 When electron-deficient olefins (CH,==CHCO,Me, CH,==CHCN) were employed the photoaddition yielded the adducts (85). It seems reasonable that the formation of the adducts arises from the triplet state df the pyridone populated by acetone-sensitization. Evidence to this effect comes from the formation of the photo-pyridone (86) when irradiation is carried out in alcohol, ether, or dichloromethane. 39 Regioselective addition of 2methylpropene to the quinolones (87) affording the adducts (88a, b) is achieved when the photolysis is carried out in MeOH-Et3N. Similar addition was achieved

"$. Me

C Y R

MeM

/N Me (80) a; X = 0, R = H, Me, or Ph b; X = S, R = H 36 37

j9

d

Y /N R

\ N II

Me

Me (81)

(82)

E. P. Serebryakov, I:v. Akad. Nauk SSSR, Ser. Khim., 1979, 2313 (Chem. Abstr., 1980,92, 147037). K.-H. Scholz, J. Hinz, H.-G. Heine, and W. Hartmdnn, Chem. Ber., 1981, 114, 248. Y. Kanaoka, M. Hasebe. and E. Sato, Fukusokan Kagaku Toronkai Koen Yoshishu, 12rh, 1979, 156 (Chem. Abstr., 1980, 93, 71 679). H. Fujii, K. Shibd, and C. Kaneko, J . Chem. SOC.,Chem. Commun.. 1980, 537.

Photochemistry

252

using acrylonitrile and 1-acetoxyethylene affording (88c) and (88d), respectively. Ring opening to (89) was readily achieved using NaHCO, in boiling methanol.40 R' RZ

H

H

(83) a; R' = R2 = Me b; R' = CH,OAc, RZ = H c; R' = OMe, R2 = H

(84)

H

(85) a; R = C02Me b;R=CN

(86)

Cerfontain and van Noort 4 1 have reported a photosynthesis of 4-0x0-alkanoic acids and esters (90). The reaction is achieved by the benzophenone-sensitized addition of aldehydes (91) to a$-unsaturated esters (92). The yields obtained from

(87) a; R = H b;R=Me

H (88) a; R' = H, R2 = R3 = Me b; R 1 = R2 = R 3 = Me c; R2 = CN, R3 = H, R' = H or Me d; R2 = OAc, R 3 = H, R' = H or Me

RI-C-H-H II 0

3

~2

4

~

(90)

0

R'CHO (91)~ R' =~ Me, 5Pr", or Ph

(89)

R3 R4

X

R2 COOR5 (92) R2 = R3 = R4 = H, R5 = Me R2 = R4 = H, R3 = R5 = Me R2 = R3 = Me, R4 = H, R5 = Et

the process are varied ranging from 7 to 8 1%. This technique has also been used in the formation of the adduct (93) by acetone-induced addition of formamide to the ester (94).42 Irradiation of dimethyl acetylenedicarboxylate in the presence of propylene oxide yields the adducts (95,96).43 The products are the results of hydrogen abstraction by the excited acetylene followed by radical combination reactions. The reaction can be both quenched and triplet sensitized (benzophenone) suggesting the involvement of a triplet state. The yields on the whole are only moderate. Cyclohexene oxide behaves in a like manner and yields the two products (97).43 The dimerization of the enone (98a) in micellar and liquid-crystal systems gave dimers of both the cis- and the trans-enone. The presence of a long chain 40 41

42

43

T. Naito, and C. Kaneko, Chem. Phurm. BUN., 1980, 28, 3150 (Chern Abstr., 1981, 94, 139591). H . Cerfontain and P. C. M. van Noort, Synthesis, 1980, 490. A. Rosenthal and J. Chow, J. Curbohydr., Nucleosides, Nucleotides, 1980, 7 , 77 (Chem. Abstr., 1980, 93, 168537). H. Hasegawa, H. Saito, and K. Tsuchitani, Waseda Daigaku Rikogaku Kenkysusho Nokoku, 1979, 16 (Chern. Abstr.. 1980, 92, 214564).

Enone Cycloadditions and Rearrangements

253

H O OH (93)

(94)

(94) (4.3%)

R2 (95) a; R' = C02Me, R2 = H (27.1%) b; R' = H, R2 = C02Me (3.4%) Me0,C

R' R2

(97) a; R' = CO,Me, R2 = H (7.5%) b; R' = H, R2 = C0,Me (7.5%)

substituent on the benzene ring (98b) facilitated the dimerization of the cisThe solid-state dimerization of the cinnamic acid (99) yields the head-to-head dimer (100). When this process is carried out in the presence of hydrocarbons as a dispersant the dimer obtained contains incorporated solvent.45.46 A study of a series of crystalline compounds based on benzylidenecyclopentanone (101) has provided a basis for the assessment of topotactic and topochemical phot~reactivity.~'The topochemical photodimerization of the

R (98) a; R = H b; R = CH,(CH,),O

compound (101, Ar = Ph) has been determined.48 The crystal structure of the ester (102) has been determined and the solid-state photoreactivity of the molecule has been rationalized in terms of the molecular packing in the crystal. The main product from this photoreaction is the dimer (103).49 44

M. Nakamura and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 186 (Chem. Absfr., 1980, 92,

45

F. Nakanishi, M . Hiriakawa, and H . Nakanishi, Isr. J . Chem., 1979, 18, 295 (Chem. Abstr., 1980,93,

46

F. Nakanishi, S. Yamada, and H. Nakanishi, J . Chem. SOC.,Chem. Commun., 1977, 247. W. Jones, H. Nakanishi, C. R.Theocharis, and J. M. Thomas, J . Chem. SOC., Chem. Commun., 1980,

214 557). 94 473). 47

610. 48

49

H. Nakanishi, W. Jones, J. M. Thomas, M. B. Hursthouse, and M. Motevalli, J. Chem. SOC.,Chem. Commun., 1980, 61 1. L. Kutschabsky, G . Reck, E. Hohne, B. Voigt, and G . Adam, Tetrahedron, 1980, 36, 3421.

Ph o t oclzemist r y

254

(103)

The sensitized irradiation (acetophenone) of the coumarin (104) yields two dimers which have been identified as (105) and (106).50All four possible dimers (107, 108) are obtained from the irradiation of the thio-chromone (109) in aromatic solvents. In contrast the sulphone (1 10) is u n r e a c t i ~ e . ~ '

M e 0W

0W 0 O

O

M Me e

%

Me

(107) a; R b; R

= a-H

a-H

(108) a; R b; R

= a-H = P-H

0

J0 st

A. Z . Abyshev, Khim. Prir. Soedin., 1980, 165 (Chem. Ahstr., 1980, 93, 150082). I. W. J. Still and T. S . Leong, Tetrahedron Lett.. 1981, 1183.

Enone Cycloadditions and Rearrangements 255 2 Enone Rearrangements Agosta and Wolff 5 2 have studied the influence of substituents upon the mode of cyclization of the enones (1 1 1). The irradiation of enones (1 1la+) follows the path dictated by Srinivasan's rule of five 53 yielding the biradical (1 12) which subsequently yields the products shown in Scheme 8. Enone ( l l l b ) had to be

( 1 1 1 ) a; R' = R 2 = R3 = R4 = H b; R ' = R 2 = H, R 3 = R4 = Me

(1 12)

bc)

c; R 1 = R 2 = Me, R 3 = R4 = H

6Me 0

Scheme 8

0-

Me

0

(1 13)

p"'

0 (1 1 Id)

_____)

+k

co \

0 QM'-

(-p Me

OMe (1 14)

Scheme 9

irradiated in refluxing xylene to achieve cyclization. With enone (1 1 Id) the rate of cyclization in the 1,5-sense is diminished somewhat, and cyclization follows both the 1,6-pathway to yield (1 13, 27%) and the 1,5-path to yield (1 14, 4373, as in Scheme 9. The results are compared with earlier studies related to the cyclization of 5-hexenyl radicakS4 A full account of the photochemical behaviour of citral (1 15) at elevated temperatures has been p ~ b l i s h e d , ~supplementing ' the original note.56At 80 "C irradiation results in the formation of aldehyde (1 16) and (1 17) as well as other products (118-120). These products are not formed at 30°C. The 52 53

54

55 56

W. C. Agosta and S. Wolff, J. Org. Chem., 1980, 45, 3139. R.Srinivasan, Abstracts, 156th National Meeting of the American Chemical Society, San Francisco, April 1968, 89. A. L. J. Beckwith, 1. A. Blair, and G. Phillipon, Tetrahedron Lett., 1974, 2257. S. Wolff, F. Barany, and W. C. Agosta, J. Am. Chem. SOC., 1980, 102, 2378. F. Barany, S. Wolff, and W. C. Agosta, J. Am. Chem. SOC.,1978, 100, 1946.

256 Photochemistry temperature effect is thought to be a manifestation of the control exercised upon the biradical intermediates (121) and (122), the former being dominant at higher temperatures (Scheme 10). Other workers have observed similar effects.5 7

I

(1 16)

Scheme 10

Detailed studies of the &-trans and trans-cis isomerization of chalcone 5 8 and some of its derivatives and analogues (123) 5 9 have been reported. Perkins and his co-workers 6o have reported an irradiative method of reducing enone systems such as chalcone to the corresponding saturated compounds. The cis-trans isomerization o f chalcone has been studied in CC1, solution.61

(123) R2 = H, NO,; R' = MeO, Me, H, Br, or NO,

A solvent dependence has been reported for the photocyclization of the chalcones ( 124).62Efficient cyclization takes place yielding the flavanones (125) 57 58

59

6o 62

M. Yoshioka, K. Ishii, and H. R. Wolf, Helv. Chim. Acra, 1980,63, 571. V. G . Mitina, M. Reinhardt, and W. F. Lavrushin, Zh. Obshch. Khim., 1980,550,134 (Chern. Abstr., 1980,92, 197 665). M.Reinhardt, V. G . Mitina, N. S. Pivneko, and V. F. Lavrushin, Zh. Obshch. Khim., 1980,550,2770 (Chem. Abstr., 1981,94,120601). M.J. Perkins, B. V. Smith, and E. S. Turner, J . Ciiem. SOC.,Chem. Commun., 1980,977. M . Nowakowska and J. Kowal, Bull. Acad. Pol. Sci., 1979,27,409(Chem. Abstr., 1980,92,180344). R. Matsushima and I. Hirao, Bull. Chem. Soc. Jpn., 1980,53, 518.

Enone Cycluadditiuns and Rearrangements

257

when irradiation (A > 365 nm) is carried out in ethyl acetate or dioxan. However low efficiency of cyclization is experienced when benzene, chloroform, ether, acetonitrile, or ethanol is employed. An explanation for this observation is awaited. The photochemical ring-opening of a series of flavanones ( I 26) in benzene to yield the chalcones (127) has been reported.63

R

eR .

/

\

R

/

0

0 ( 124)

/ \

W

wR (125)

R' \

f\ l

R2 0

R

R,

\

\

OH 0

( 1 26)

'

R3

(127)

R 1 = R 2 = R 3 = R4 = H; R 1 = R2 = R3 = H, R4 = OMe or OCOMe; R' = OMe or OCOMe,. R2= R3 = R4 = H

trans-cis Isomerization of (1 28) occurs upon irradiation. Subsequent irradiation converts the cis-isomer into the coumarin (129), a process thought to involve a triplet

Me

do

aM

A study of the photochemical behaviour of the enone epoxide (130) has been published.6s Several compounds (Scheme 11) are formed upon irrlidiation (2 > 347 nm) in pentane. When the reaction is carried out in methanol these products are accompanied by the methanol addition product (131) which is proposed as good evidence for the intermediacy of the ylide (132), and the cyclopropane (133). Compounds (1 34) and (135), related to epoxy-enone (1 30), are also photoreactive and studies of these have been reported.66-68

64 65 66 6'

68

R. Matsushima, T. Kishimoto, M. Suzuki, M. Morioka, and H. Mizuno, Bull. Chem. SOC.Jpn., 1980, 53, 2938. I. R. Bellobono, D. E. Paglia, B. Marcandalli, and M. T. Cataldi, Ga::. Chim. Ital., 1979, 109, 697 (Chem. Abstr., 1980, 93, 203 633). K. Murato, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 2212. N . Nakamura, W. B. Schweizer, B. Frei, H. R. Wolf, and 0.Jeger, Helv. Chim. Acta, 1980,63, 2230. A. P. Alder, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 1833. K. Murato, B. Frei, W. B. Schweizer, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 1856.

258

Photochemistry

p*y-Jy+Q+&-J H

AC

Scheme 11

The oxiran system in (136) undergoes bond cleavage on excitation (m*) and yields the furan derivative (137) as the major product (13%). Several other minor products were also isolated and identified.69 The irradiation of the enone (1 38) has been r e p ~ r t e d . ~ '

(135) a; R = H2 b; R = CH,

(1 36)

0

(137)

(138)

Further work has been carried out on the photoconversion of enones (e.g., 139) into the cyclic ethers (140) and the enone (141). The conversion may be carried out using either i= 254 or A > 347nm.7' The results of a detailed study of the photochemical behaviour of the ionone (142) and its conversion into the pyran (143) has been published.72

(139) 69

( 140)

(141)

K . Tsutsumi and H. R. Wolf, Helv. Ckim. Acra, 1980, 63, 2370.

O '

Murato, H. R. Wolf, and 0. Jeger, Helv. Chim.Acta. 1981, 64, 215. '' K. Ishii, H . R . Wolf, and 0. Jeger, Helv. Cliim. Arta, 1980, 63, 1520. '' K. H . Cerfontain, J. A. J. Geenevasen, and P. C. M. van Noort, J. Chem. Soc., Perkin Trans. 2, 1980, 1057.

259

Enone Cycloadditions and Rearrangements M

F

o

M

b Me

Me

O

y

y

t

x

EtO NHC0,Bu'

Me

(142)

(143)

(1 45)

(144)

The pyrrolinone (144) undergoes photochemical ring contraction in Bu'OH to yield ultimately the cyclopropyl carbamate ( 145).73Formally this is a reaction akin to the Norrish Type I process in ketones in that initial fission of a C-C bond results in a biradical which recombines to yield a ring-contracted isocyanate. The irradiation of the thioisoxazolinones (146) in methanol results in the extrusion of CO, and the formation of products (147).74 The products are thought to be

(146) R

=

Me R SPh, S-P-naphthyl, SCH,CH=CH,, SCH,CH,OH, SCH,CH,OAc Me I

M e q o M e

R ( 147)

. I

A.

. Me

. SR'

(1 48)

Me\

N=r 9

0

Me R (149) R = H, C1, or OPh

formed by the intermediacy of a sulphur-stabilized carbene (e.g., 148) which is trapped by solvent and the resultant imine hydrolized by water. The presence of the sulphur is critical for the success of the reaction since the compounds (149) appear to be inert under the same conditions. Cossy and Pete 7 5 have reported the conversion of the (alky1amino)cyclohexenone (150) into the cyclized derivatives (1 5 1 and 152, Scheme 12) by irradiation in diethyl ether. The reaction superficially

Scheme 12

appears similar to a Norrish Type I1 process, but irradiation in MeOD only leads to incorporation of D at C-3 of the cyclohexenone. Thus the exact mechanism of the process is unknown although the possibility of an electron-transfer process cannot be excluded. The use of sulphonated derivatives (153) affords different The behaviour of the compounds (153) is seen to be dependent upon 73

'* l5 76

G . C. Crockett and T. H . Koch, Org. Synth., 1980, 59, 132 (Clzern. Ahstr., 1980, 93, 149837) T. Sasaki, K. Hayakawa, and S. Nishida, J . Chem. Soc., Client. Contrnun., 1980, 1054. J. Cossy and J. P. Pete, Tetrahedron Lett., 1980. 2947. J. C. Amould, J. Cossy. and J. P. Pete, Terrahetiron, 1980, 36, 1585.

260

Photochemistry

Table 2 Products from irrcrdiution of uminoenones (153) in ethanol76 (154) 30 50 40

Me Ph ally1 Pr' Pr' Pr' Pr' Pr'

-

-

__ -

Products PA) (155) (156) 25 10 35 15 30 40 -

20 40 35

the nature of the substituent on the nitrogen atom (Table 2). Pete and Portella 7 7 have studied the photoconversion of arene sulphonates into alcohols in various solvents.

R

The direct or sensitized irradiation (1, > 330nm) of the enone (157) in solution affords the [2 + 21 cycloadduct (158).78 When the irradiation is carried out using the same wavelength but with the compound in the crystalline phase the main product (75%) obtained in (159) formed by a hydrogen-abstraction path. Some of the [2 + 2ladduct (158, 25%) is also obtained. The change in the reaction from solution to crystal phase is the result of (1 57) being the preferred conformation in the crystal, a prediction which was verified by an X-ray structure. Scheffer 7 9 has reviewed the influence of crystal lattice control on the outcome of such photochemical reactions.

&;

Me

Me

Me

Me

\OH

Me

0 (157)

HO

Me OH ( 1 58)

Me (1 59)

The enone (160) undergoes a Norrish Type I fragmentation in methanol to afford the product (161).80The product is formed from the intermediate biradical (162) by fission of the 5.10-bond to give a trappable ketene. Irradiation of the -_l

'' ''

J . P. Pete and C. Portella. Bull. Soc. Chim. Fr., 1980, 275. Z . Q. J i m g .I.R. ScheKer. A. S. Secco. and J . Trotter, 7etrcrlrc4roii Lett.. 1981, 891. J. R . ScheKer. A w . C'hcw. Rcs., 1980, 13. 283. A . Canovas and J.-J. Bonet, Hrlr.. Clritii. Acto, 1980. 63, 2390.

Enone Cycloadditions and Rearrangements

Mfl

26 1

Me OAc

& O H

Me0

( I 60)

0

H

O& '0

(1611

162)

cyclic lactam (163) in t-butyl alcohol affords the lactam ether (1 64) presumably by trapping of an intermediate imine (165) formed from the biradical (166) by

g

HN 0

(163)

*

(Mb \

0

OCN

H

fyj? O

N H H

Me0 0

H OMe

kN H H

O

hydrogen abstraction. When the reaction is carried out in methanol this product (165) is accompanied by (1 67). The lactam (168) yields the isocyanate (169) when the irradiation is carried out in t-butyl alcohol but when methanol is used as solvent the ether (170) and the product (171) are formed, as well as a trace of the isocyanate (169). The lactams (172) and (173) afforded the products shown in Scheme 13 when irradiation was carried out in methanol. Irradiation in t-butyl alcohol gave only minor products which could not be separated from starting material." A review of the photocyclization of eneamides has been published.82 An ylide intermediate (174) is proposed as the key intermediate in the photocyclization of the enamino ketone (175) into the products (1 76) and ( 177).83 The photochemistry of enones has been reviewed by S c h ~ s t e r The . ~ ~ observation of orthogonal twisted triplet states has been reported from the laser flash A. Canovas, J . Fonrodona, J.-J. Bonet, M. C. Brianso, and J. L. Brianso, Helv. Chim. Acta, 1980,63, 82

83 R4

2380. I. Ninomiya and T. Naito, Kagaku No Ryoiki, Zokan, 1979, 69 (Chem. Abstr., 1980,93, 95447). D. Watson and D. R. Dillin, Tetrahedron Lett., 1980, 3969. D. I. Schuster, Org. Cliem., 1980, 42, 167.

262

Photochemistry

MeN

MeOH

&

O

hv

___)

MeOH

Me N

O b p J Me OMe

(173) Scheme 13

COMe

&Le \

m

-

+N

Me

(175)

( 174)

e

~

I Me

I Me

\

M

M I Me

(176)

( 177)

study of various en one^.^^ The lifetime of the transient is of the order of tens of nanoseconds and the degree of twist is dependent upon the rigidity of the molecule in question. The direct irradiation of the enone (178) results in a mixture of starting material and a new product (179) in a ratio of 1 : 3.2. The formation of the deconjugated product was not affected by oxygen but was suppressed when acetone was used as the solvent for the irradiation.86" Thus a singlet state is thought to be involved in the transformation. The enone (180) is formed when

( 178)

(179)

( 180)

(179) is irradiated in benzene solution. Such reactions as 1,3-migration are common in the photochemistry of b,y-unsaturated enones. 8 6 b The non-volatile fraction from the irradiation of this enone (178) contains four products identified as cyclobutane-type dimers of gross structure (18 1-1 83). Ketene and the phenol (184) are formed on irradiation of the enone epoxide (185)?' The mechanism for the formation of the phenol remains unsure even from the results of deuterium labelling experiments. The isomeric epoxide (186) is also photoreactive and yields the three products shown in Scheme 14. The formation of the cyclopentadiene (187) is due to the thermal rearrangement of tricyclic ether 85 86

*'

R. Bonneau, J . Am. Chem. SOC.,1980, 102, 3816. (a) B. Gioia, M. Ballabio, E. M. Beccalli, R. Cecchi, and A. Marchesini, J . Chem. Soc.. Perkin Trans. 2, 1981, 560. ( b ) see e.g. ref. 90. H. Hart, S.-M. Chen, S. Lee, D. L. Ward, and W.-J. H. Kung, J. Org. Chem.. 1980, 45, 2091.

Enone Cycloadditions and Rearrangements

263

M e M e Me

Me % ' Me Me 0

Me

Me Me (185)

(188). This compound is thought to arise via the ylide (189) formed on C-C bond cleavage in the epoxide ring. A study of the biradical (190) formed by the irradiation of the enone (191) has been

& Me@e Me

+

Me

Me

Me

6

+

/

Me

M e \ / Me

Me

(187)

Scheme 14 Me&Me

~k

Me

Me

Me

t 188) 0'

(190)

(191)

The irradiation of the enones (192-194) via a nn* excitation affords as the principal products (195-197), respectively, from 1,3-acyl migrations and (198200) from 1,2-acyl migrations. In contrast with this behaviour, the dieneone (201) undergoes 1,3- and 1,5-acylmigrations to yield the products (202) and (203). When nn* excitation is employed with (192 and 201) only decarbonylation occurs. The authors 8 9 suggest that the 1,3-acyl migrations occur from the excited singlet state,

**

(a) D . E. Seeger, E. F. Hilinski, and J. A. Berson, J . Am. Chem. SOC.,1981,103,720. (b)M. Rule, A. R.

89

Mathin, E. F. Hilinski, D. A. Dougherty, and J. A. Berson, J . Am. Chem. SOC..1979, 101, 5098. H. Eichenberger, K. Tsutsumi, G. de Weck, and H. R. Wolf, Helv. Chim. Acta, 1980, 63, 1499.

Photochemistry

264

priPAc al*, R

O

0

(192) R = Me or Pr'

(194)

(193)

(195) R' = Pr', R 2 = Me R' = Me, RZ = Pr'

&

0

Ac

(196)

0 0

whereas the 1,2-acyl migrations involve the triplet state: such tendencies have long been known. Interest continues in the ground-state control of photoreactions, i.e. the dependence on molecular conformation in the ground state. In cycloheptenes the more stable conformation is a chair which when photolysed will undergo a 1,3acyl migration, as exemplified in photolysis of the enone (204) to give the spiroketone (205)." In the more complex molecule (206), a similar rationale accounts for the formation of the single photoproduct (207). An X-ray crystal structure of this compound (207) proves that the conformation is as shown and

(204)

HO C=C

@ 0 (206)

*

(205)

@L

H*C (207)

J

(208)

that this will arise from the chair form (208) of the starting material." Acetonesensitized irradiation of the enones (209) leads to mixtures of the 1,3-acyl shift product (210) and the di-mmethane product (21 l), but the 1,3-acyl shift products 90

J . R. Williams and G . M. Sarkisian, J . Org. Cliem., 1980, 45, 5088.

Enone Cycloadditions and Rearrangements

265

alone are formed by direct irradiation." However when acetophenone was used as the sensitizer only the oxa-di-n-methane products were produced. It is clear from this study that the 1,3-acyl shift products formed in the sensitized experiments arise from stray light absorption by the starting material. Attempts to induce asymmetry in the product by the use of an optically active sensitizer were poor. Resolution of the starting material and acetophenone-sensitization afforded the (-)-product (212) from 1R,4S starting material (213a) and the (+)-product (214) 0

&R2

R'

'

R'

(209) R' = R2 = H R' = Me, R2 = H R' = H , R2 = Me

(212)

&o

R2y-J-y

R2

(211)

(210)

(2I3a)

(213b)

(214)

from the lS, 4 R starting material (213b). The stereospecificity of the reaction is in line with that predicted by the usual mechanism for the di-n-methane process. The sensitized irradiation (acetophenone) of the enones (215 ) brings about a regiospecific di-n-methane process to yield in each case one product identified as (216).92 R' R2 R 3 R4 R 5 R6

R4 0

(215 )

Me But But Me H H Me Me Bu'

H H 0-CH, C0,Me H H 0-CH, C02Me H H CH,-0 C0,Me M e H 0-CH, C0,Me H MeO-CH, C0,Me H M e H O Me C 0 , M e H MeO-CH, C0,Me H M e H O Me C 0 , M e H Me 0-CH,CO,Me

0

R'/ R2\

R3

(217)

R6 R6

R2 (216)

Me Me (218) R = C3H,

0 Me Me (219) R' = H, R 2 = Bu" R' = Bu", R2 = H

The enones (215) are converted into the aromatic compounds (217) by the loss of the ketene bridge. Full details 930f the use of the regiospecific di-n-methane 91

M. Demuth, P. R. Raghavan, C. Carter, K. Nakano, and K. Schaffner, Helv. Chim. Acta, 1980, 63,

92

H.-D. Becker and B. Ruge, J. Org. Chem., 1980, 45, 2189. G. Pattenden and D. Whybrow, J . Chem. Soc.. Perkin Trans. I , 1981, 1046.

2434. 93

266 Photochemistry reaction towards the synthesis of the natural product, taylorione (218) from (219) has supplemented the original note.94 Ciganek 9 5 has prepared the 9,lO-bridged ethenoanthracenes (220, 221). These compounds are photochemically reactive and on direct irradiation in THF solution are converted into the cyclo-octatetraenes (222,223). Sensitized (acetone)

(220) a; X = 0,Y = H, b;X=Y=O c; X = NMe, Y = 0

R R

b; R-R

= (CHI),

irradiation, on the other hand, brings about a di-z-methane conversion to semibullvalene derivatives e.g., (224 and 225) from (220c): see Scheme 15.

+

-

0-

(220c)

A

Scheme 15

Excitation of the ketone (226) brings about a 1,7-hydrogen transfer to afford the biradical intermediate (e.g., 227).96 Cyclization within this species yields the alkenyl-tetrahydrofurans (228) and (229) in the yields and ratios shown. The cyclization process is reasonably selective in that the geometry of the double bond is retained in the cyclized product. This was demonstrated for the enone (230) (a cis-trans mixture of ratio 1 : 3), which gave the cyclized products (231-234) (Scheme 16). Two principal products (235, 15%) and (236,60%) are obtained from irradiation of the ketone (237) in dioxan ~ o l u t i o n . ~Two ’ minor products (238) 94

95

96

’’

G . Pattenden and D. Whybrow, Tetrahedron Lett., 1979, 1885. E. Ciganek, J . Org. Chem., 1980, 45, 1505. H . A. J. Carless and D. J. Haywood, J . Chem. SOL-.,Chem. Commun., 1980, 657. J. Mattay, Tetrahedron Lett., 1980, 2309.

Enone Cycloadditions and Rearrangements

cz

R3 R' R

3

R2+

267

2

(226) a; R' = R2 = R 3 = H b; R' = R3 = H, R2 = Me

R2

(227)

R3

R2

R3

(228) (229) a; 1.4 : I (94"/,) b; 1.65:1 (85%) C; 0.6 :1 (80%) d; 1-5:l (88%)

c; R' = Me, R2 = R3 = H d; R' = R 2 = H , R3 = Me

Me OH

Mae? H

ratio 1:1.4:1.3:1

MepH

(234)

Scheme 16

and (239) were also detected. The intramolecular cycloaddition reaction affording (235) is not quenched by the addition of penta-1,3-diene, thereby suggesting that this reaction arises from the singlet manifold. The formation of the other products (236-239) is quenched and their formation is also influenced by the presence of tri-n-butyltin hydride. To account for these effects, Scheme 17 showing the formation of products (236, 238, and 239) is suggested.

(235)

(236)

(237)

(238)

(239)

Scheme 17

The enone (240) undergoes C-C bond fission in the oxiran ring to yield (241) on direct irradiation (254nm).98 This compound (241) is accompanied by the fission product (242) and by (243) and (244). 98

G . de Weck and H. R. Wolf, Helv. Chim. A c f a , 1981, 64, 224.

Photochemistry

268

3 Photoreactions of Thymines erc. A study of the photodimerization of the pyridones (245) in a micellar environment

has been reported.99The results show that there is an alignment of the molecules in the micelle. The pyrazinone derivative (246) is photochemically unreactive when it is irradiated in solution at room temperature.loOHowever when it is irradiated in the solid state at room temperature a [4 + 4l-dirner (247) is formed. R2

R' (245)

R' = CH2CH2C02H,R 2 = H, C,H,, or C,H,, R' = (CH2),C02H, R2 = H R' = (CH2),,C02H, R 2 = H

Me I

The acetone-sensitized irradiation of the bis-pyrimidine (248) yields the [2 + 21cyclized product (249). A chair-like conformation is adopted by the cycloheptane part of the molecule (249) in the solid and in solution."' The dimerization of the bichromophores (250) to yield the cycloadducts (25 1) was slow by comparison with the dimerization in analogous less heavily substituted systems. The slowness of the process is, it is thought, due to steric factors.102 99 loo lo' lo'

Y. Nakamura, T. Kato, and Y. Morita, Tetrahedron Lett., 1981, 1025. T. Nishio, N. Nakajima, and Y.Omote, Tetrahedron Lett., 1980, 2529. A. Rajchel and K. Golankiewicz, Pol. J . Chem., 1980, 54, 123 (Chem. Abstr., 1980, 93,70 500). K. Golankiewicz and L. Celewicz, Pol. J. Chem., 1979, 53, 2075 (Chem. Abstr., 1980, 93, 71 684).

Enone Cycloadditions and Rearrangements

269

v 0

0

(249)

0

de Mayo et al.lo3 have investigated the photoreactions of the aza-dienone (252a). Irradiation of (252a) at -70°C led to the formation of the bicyclic intermediate identified as (253a). Warming this intermediate to -40 "C brought about quantitative conversion into the intermediate (253b). This compound was stable in solution at 0 "C but at room temperature formed two oxazinones (252a) and (252b) in equal amounts. The irradiation of (252b) at -78°C gave the intermediate (253b). The authors l o 3 reason that (253b) is the thermodynamically stable intermediate and that the interconversion of (253a) into (253b) takes place

.o"r.h-- N N

yo

(252) a; R' = Ph, R2 = Me

b; R'

=

Me, R2 = Ph

R' (253) a; R' = Ph, R 2 = Me b; R' = Me, R2 = Ph

Me (254)

via the zwitterion (254). The bicyclic aza-compounds (255) can be prepared by the irradiation of the pyrimidones (256) in benzene solution.l o 4 The products (255) are thermally labile and can be readily converted into the quinoline derivatives (257).

(255) Ar = Ph (50%) Ar = p-tolyl (50%) Ar = p-anisyl (20%) 103

(256)

(257) R = H R = Me

R=MeO

P. de Mayo, A. C. Weedon, and R. W. Zabel, J . Chem. SOC..Chem. Commun., 1980, 881 T. Nishio, K. Katahira, and Y. Omote, Tetrahedron Lett., 1980, 2825.

27 0

Photochemistry

Irradiation of the pyrimidone (258) in methylamine+ther proceeds via ring closure to the tricyclic structure (259). Attack of methylamine on this molecule followed by ring opening (Scheme 18) affords the final product (260). Other examples of this process were reported. l o 5

(259)

Scheme 18

The regiospecific formation of the cyclobutene-type adduct (26 1) has been reported as a result of the photoaddition of diphenylacetylene to the cyanouracil (262).l o 6 The cycloaddition of 1-phenylprop-1-yne to the same substrate is reported to yield the cyclobutene (263) as the main product when Pyrex-filtered irradiation is used. The irradiation of the same compounds using 254nm light afforded the novel adduct (264), presumably formed by the secondary cyclization of the initially produced adduct (265). lo’ Indeed the sensitized irradiation of the uracil (262) and the propyne yields this adduct (265) as a 2-E-mixture as well as the cyclobutene (263). Direct irradiation of (265) affords the cyclized compound 0

0

Me

(263) ‘06

lo’

(264)

(245)

Y. Hirai, T. Yamazaki, S. Hirokami, and M. Nagata, Tetrahedron Lett., 1980, 3067. I. Saito, K. Shimozono, and M. Teruo, Fukusokan Kagaku Toronkai Koen Yoshishu, IZth, 1979, 161 (Chem. Abstr., 1980, 93, 45 547). I. Saito, K. Shimozono, S. Miyrazaki, K. Fukuyama, Y. Katsube, and T. Matsuura, Tetrahedron Lett., 1980, 2317.

Enone Cycloadditions and Rearrangements

27 1

(264). The photoreaction of the cyanouracil (262) with cyclo-octene, hex- 1-ene, and acetoxyethylene in acetonitrile yields the adducts (266a--c) and the rearranged adducts (267a-c). *'* The reaction is proposed to occur by the addition of the olefin to the excited state of the uracil yielding the biradical (268). This biradical can either ring close to yield the cycloadduct (266) or else cyclize to form

(266) a; R ' - R ~ = (CH,),, 35% b; R' = H, R2 = Bu", 40% C; R 1 = OAC, R2 = H, 60%

M e N k R ' O N R2 Me CN

O

A

(267) a; R ' - R ~ = (CHZ),, 52% b; R' = H, R2 = Bun, 42% C; R' = H, R2 = AcO, 10%

MTV

N

O

Me

(268)

N

N

Me

R2

N

(270)

(269)

a new biradical (269) and then (270) from which the cyano-migrated compounds (267) are obtained by bond cleavage. The reaction is temperature dependent as can be seen from the irradiation of cyclopentene with the uracil (262) where the cyclobutane (271, 26%) is the minor product at 20°C but becomes dominant at

M

e

N

Ph e

NL

20 "C

MeN

L

Me CN (27 1) 26% 56%

43% 15%

- 20 "C

L

Scheme 19

lower temperatures (-20 "C)(Scheme 19). When the reaction is carried out in ethanol the product formed is the imine (272) produced by trapping of the biradical [270, R'-R2 = (CH2)J. M

Ae

O

N Me

N

v NH

(272)

The adducts (273) are readily formed by the sensitized photocycloaddition of the azauracil (274) to the maleimides (275).'09 A [2 + 21-adduct is formed from I. Saito, K. Shimozono, and T. Matsuura, J . Am. Chem. SOC., 1980, 102, 3948. G. Szilagyi and H . Wamhoff, Angew. Chem. In?. Ed. Engl., 1980, 19, 1026.

212

Photochemistry M e N q

OAN" Me (273) R = Me or H

Br

(274)

(275)

the cycloaddition of thymine to 5,7-dimethoxy-coumarin. '' The cycloaddition of olefins to the diazaenone (276a) is reported to yield the cyclobutane-type adduct, e.g., (277) from 2-methylbut-2-ene. When the thioenone (276b) was used the cycloaddition yielded the adduct (278). l 1 Me

Me

Me (276) a; X = 0, R = H , Me, or Ph

b; X

=

S, R

=

(277)

H

The photoaddition of stilbene to caffeine (279) leads to the formation of six products (280-285). The first three products (280-282) can be readily accounted for by conventional [2 + 21-addition leading to (280) and (281) and a [4 + 21-addition followed by methylamine elimination giving (282). The other products are more difficult to explain, but the authors 'l 2 suggest that the biradical intermediates (286, 287) are involved in which various migrations and bond fissions occur. The fate of the missing carbon receives no comment.

''

.Ph

MeN

AN

O Me

'")

'" ' l2

Me

S. C. Shim and K. H . Chae, Photochern. Photohiol.. 1979, 30,349. Y. Kanaoka. M . Hasabe, and E. Sato. Fiikitsokm Koyciku loronkcii Koeri Yosliishu, 1979, 156 (Chem. Ahslr.. 1980. 93, 1679). G. Kaupp and H . - W . G r u u , .fiigczn. C'/ivrn. f r i t , Ed DigI., 1980. 19. 714.

Enone Cycloadditions and Rearrangements

273

A highly fluorescent uridine derivative (288a) has been prepared by the irradiation of the iodouridine (288b) in the presence of pyrene.'13 An analogous product (288c) is obtained when the irradiation is carried out in the presence of benzene. The acetone-sensitized photocoupling of 5-bromouridine (2884) with tryptophan has been studied. l4 The photochemical coupling of tryptophan (289) and 5-bromouridine (288e) in a frozen aqueous system yielded the single adduct (290)." A study of the photoreactions between bromouracil (291) and electronrich arenes (e.g., 292) has been reported.I16 0

H (288) a; R' = pyrenyl, R2-R2 = Me$ b; R ' = I , R Z - R 2 = Me,C c; R ' = phenyl, R2-R2 = Me,C d; R ' = Br, RZ-RZ = Me,C e; R ' = Br, R2 = H

(289)

OMe

The photoreaction of the flavin ( 93) with the amines (294,295) has been shown to yield a single photoproduct in each case identified as (296) and (297), respectively. When (298) is irradiated in the presence of hydrogen donors (e.g.,CH,OH) the reduced dimer (299) and the adduct (300) are formed, presumably via the intermediate radical (301).' l 8 Irradiation of the cytosine derivatives (302) in

'I5 116

'I8

I . Saito, S. Ito, T. Shiiimura, and T. Matsuura, Tetruhedron Lett., 1980, 21, 2813. S. Ito, I. Saito, and T. Matsuura, J . A m . Cheni. SOL'.,1980, 102, 7535. S. Ito, 1. Saito, H . Sugiyama, and T. Matsuura, Kokagaku Toronkai Koen YosAishu, 1979, 10 (Chem. Abstr., 1980, 93, 8476). S. Ito, I. Saito, and T. Matsuura, Tetrahedron, 1981, 37, 45. A. Krantz, B. Kokel, A. Claesson, and C. Sahlberg, J . Org. Chem., 1980, 45, 4245. Y . K d n d O k a , M . Hasebe, and Y . Hatanaka, Heterocycles, 1979, 13, 263 (Ckem. Ahstr., 1980, 93, 94474).

Photochemistry

274

propan-2-01 leads to the formation of the adducts (303). This reaction presumably involves the formation of the radical (304), by abstraction of hydrogen from the solvent followed by coupling.

(298)

(299)

(300) R

=

~

A

0 Me (302) R = NH,, NHMe,or NMe,

13 R

R N

(301)

CH,OH

N Me

Y

CMe,

(303)

H

0

N Me (304)

0 H x y i H M e P r

0

N H

(305)

The photodegradation of pentobarbital (305) in buffer solution at pH 11 has been studied.'*' The photoreactions of purines and related compounds has been reviewed.l 2 4 Photochemistry of Dienones Schaffner and Demuth lz2 have reviewed the photoreactions of conjugated cyclic dienones. 'Iy

Iz1

K . I . Ekpenyong and M. D. Shetlar, Photochem. Photobiof., 1979, 30, 455. H . Barton, J. Mokrosz, J. Bojarski, and M. Klimiczak, Pharmazie, 1980,35, 155 (Chem. Abstr., 1980, 93, 101426). M. Rafalska and G . Wenska, Wiad. Chem., 1980, 34, 9 (Chem. Abstr., 1980, 92, 215652). K. Schaffner and M. Demuth, Org. Chem., 1980, 42, 281.

Enone Cycloadditions and Rearrangements 275 Cross-conjugated Dienones.- From results obtained from the photorearrangement of the resolved dienone (306) the reaction yielding the lumiketone (307, 308) have been proved to involve the intermediacy of a zwitterion. The subsequent sigmatropic shift occurs with inversion of configuration of the migrating carbon.lz3 Details of the chemical trapping experiments relating to photorearrangement of the dienones (309), reported earlier in note have been published.’ 2 5 The zwitterion (310) in question derived from (309b) was successfully trapped with cyclopentadiene as the adducts (311) and (312). The methyl group in the adducts is endo which is proof that the carbon walk reaction takes place with inversion of configuration of the migrating carbon, in agreement with the work of Schu~ter.”~

Me

. H

(307)

(308)

Me R = Me b; R = CC13

(309) a; R

0-

6

,---.

Me CCl3

The quantum yields of the photochemical reactions of the dienone (313) have been shown to be solvent dependent with the efficiency enhanced in methanol and depressed in benzene. lZ6 The products from the reaction in methanol-benzene were the rearrangement product (3 14a) and the two methanol incorporation products (315a and b). The rearrangement product is obtained from both the sensitized and the direct irradiative conversions. It is of interest to note that the ground-state rearrangement of the zwitterion (3 16) yields the same products (3 14, 315) as are obtained in the photolytic process. From this it is reasoned that the excited-state process also arise via a zwitterionic process. In contrast with the

(313)

lz4 lz5 lz6

(314)a; R = CN b; R = OMe

(3 15a)

(3 15b)

D. I. Schuster, K. V. Prahbu, K. J. Smith, J. M. van der Veen, and H. Fujiwara, Tetrahedron, 1980, 36,3495. C. J. Samuel, J. Chem. SOC.,Chem. Commun., 1979, 275. C. J. Samuel, J. Chem. SOC.,Perkin Trans. 2, 1981, ?36. H. E. Zimmerman and R. J. Pasteris, J. Org. Chern., 1980,45,4864.

276

Photochemistry 0-

0

OMe

(317)

(3 16)

Ph Ph

(318)

(3 19)

foregoing, irradiation of the dienone (317) yields two photoenones (314b) and (3 18) as well as an unexpected product 3-methoxy-4,5-diphenylphenolderived from a phenyl migration.127There is, however, a preference for the formation of the enone (3 14b) over the enone (3 18) of 1.4 : 1 when benzene is used as the solvent. The fact that the enone (314b) is formed is proposed as evidence that not all the rearrangement reaction occurs via a zwitterion. Proof of this comes from the independent generation of the zwitterion (3 19) and the observation that this leads solely to the enone (314b). The cross-conjugated dienones (320) are readily converted by irradiation (254 nm) into lumiketones (321).lz8 Irradiation of these products (321) using Pyrex-filtered light and aqueous acetic acid gave the spirodienones (322). The lumiketone (324) can be prepared from (323) by irradiation under the same conditions as above. The subsequent irradiation of (324) in aqueous acetic acid was not as clean as the previous conversions and yielded the two products (325) and (326), as well as recovered starting material. The two dieneones (325) and (326) are formed from the lumiketone (324) however the spiroketone (325) is itself photolabile and yields starting material and the dienone (326). The rearrangements clearly involve the intermediacy of carbocation intermediates (327) which in

(320) R

=

Me or H

(323)

Me ....

(324)

Me (327)

”’ H. E. Zimmerman and R.J. Pasteris, J. Org. Chern., 1980, 45, 4876. lz8

D. Caine, C.-Y. Chu, and S. L. Graham, J. Org. Chem., 1980, 45, 3790.

Enone Cycloadditions and Rearrangements 277 some instances only rearrange in one mode or in others two possible pathways arise in competition. Direct irradiation of the steroidal dienones (328) in neutral media affords the expected lumiketones (329).12' The lumiketones (329a, b) are

0 (328) a; R' = OH,R 2 = H,R3 = COCH20H,R4 = OH b; R' = H,R2 = OH, R' = COCH20H,R4 = OH C;

R'

=

H,R2 = OH,R3 = COCH,,R4 = H

(329) a; 42% b; 78% c; 47%

(330)

themselves photolabile and are readily transformed into the cyclic ether (330). This product can be accounted for in terms of the accepted behaviour of the bicyclic ketone system and presumably involves intramolecular trapping of the zwi tterion (331) generated by fission of the cyclopropyl system in (329). When the steroidal dienones (328a, b) were irradiated in 50% acetic acid in water the products shown

yield from a; 20"," yield from b; 20'2;

a; 64"/ / O b; 50"/,

a; 16% b; 19%

Scheme 20

in Scheme 20 were isolated. The photorearrangement of betamethasone (332) affords the lumi-product (333) in good yield.'30 COCH20H

I3O

J. R. Williams, R. H . Moore, R. Li, and C. M. Weeks, J . Org. Chern., 1980, 45, 2324. T. Hidaka, S. Huruumi, S. Tamaki, M . Shimishi, and H. Minato, Yuktrgcrklc Zasshi, 1980, 100, 72 (Chern. Abstr., 1981, 94, 109 184).

27 8

Photochemistry

Irradiation of the tropolone (334a) as a complex with fj-cyclodextrin gave the isomer (335a, 64%) as the main product, accompanied by a small amount of (336a). A similar result was obtained from the photolysis of (334b) as a complex which yielded the two products (335b) and (336b). The photoisomers obtained from these reactions were optically active.

(334) a; R = O H b; R = OMe

(335) a; R b; R

(336) a; R = H b; R = Me

=H = Me

Compounds (337a, b) are formed initially from sensitized irradiation of the lactones (338a, b). 1 3 * The reaction is formally a 1,5-phenyl migration. Subsequent irradiation of (337) transforms it into the fused system (339) when the solvent used is protophilic. In other solvents the rearrangement of (338) follows a different path yielding the products (340). The use of optically active sensitizers has been

(337) a; R = H b; R = Me

(338) a; R b; R

R2 (340) R'

R'

'Ph

=H =

Me

(339)

k,,

= Ph, R2 = H, = H, R 2 = Ph,

R3 = H or Me R3 = H or Me

employed in a study of the phototransformation of racemic (337b).133 The isolation of optically active starting material indicates that enantiomer differentiation has occurred at the sensitization stage. 5 1,2-, 1,3-, and 1,4Diketones The photochemical addition of biacetyl to indene and furan affords the oxetans (341a) and (341b) as the major ~ r 0 d u c t s . lThis ~ ~ result confirms the earlier reports. 13', 36 From the kinetic study of these reactions and from the reaction of biacetyl with tetramethylethylene where ene products predominate it is clear that 13'

133

134

136

H. Takeshita, M. Kumamoto, and I. Kuono, BUN. Chem. SOC.Jpn., 1980, 53, 1006. N. Hoshi, H. Hagiwara, and H. Uda, Kokaguku Toronkui Koen Yoshishu, 1979, 14 (Chem. Abstr., 1980, 92, 214634). N. Hoshi, Y. Furukawa, H. Hagiwara, H. Uda, and K. Sato, Chem. Lett., 1980, 47 (Chem. Abstr., 1980, 93, 131 721). G. Jones, 11, M. Santhanam, and S.-H. Chiang, J . Am. Chem. Soc., 1980, 102, 6088. H.-S. Riang, K. Shima, and H. Sakurai, J. Org. Chem., 1973, 38, 2860. H.-S. Riang, K. Shimd, and H. Sakurai, Tetrahedron Lett., 1970, 1041.

Enone Cycloadditions and Rearrangements 279 the biacetyl triplet is operative. Extension of this work to include the reaction of biacetyl with cis-dimethoxyethylene as the addend has been made. This yields the four oxetans (342a-d) with the trans-pair (342a, b) predominating in a ratio of 2 : 1. The loss of stereochemistry in the olefin is further evidence that biacetyl triplets are involved in cycloaddition reactions. A new study of the photoreaction

Ac (341) a; R-R = ( C H d H ) , , X = CH2 b; R,R = H, X = 0

Me

Me

'OMe

(342a)

,&

"0Me

(342b)

,OMe

Ac (Q jo

Me M~ 'OMe (342c)

Me

3' ..

'OMe

Ac

(342d)

between biacetyl and tetramethylethylene has shown that the products from the reaction are those shown in Scheme 2 1. 3 7 A detailed kinetic study has shown that MeCOCOMe

-w++w++H+o 0

0

Scheme 21

an exciplex is involved produced by the quenching of the biacetyl triplets by the olefin. This interaction accounts for the lack of a significant deuterium isotope effect. A study of the photochemical behaviour of biacetyl in fluorocarbon solvents has been reported.138

+ Scheme 22 13' 13*

N. J. Turro, K. Shirna, C. Chung, C. Tanielian, and S. Kanfer, Tetrahedron Lett., 1980, 2775. E. J. Broomhead; K. A. McLauchlan, and J. C. Roe, J. Chem. SOC.,Perkin Trans. 2, 1980, 796.

280

Photochemistry

The dione (Scheme 22) reacts photochemically with aromatic aldehydes 139 in processes similar to the reactions between quinones and aldehydes. 140 Irradiation of the diketone (343) leads to the formation of the remarkable diol (344).141 The structure of this product was verified by X-ray analysis. The reaction, brought about by irradiation through Pyrex in various solvents, proceeds via the intermediate keto alcohol (343, a compound isolated at shorter reaction times. There is some doubt in the minds of the authors as to whether the reaction arises by hydrogen abstraction from the y- or the &-position.They propose that if the former occurs then the rearrangement by hydrogen migration to yield (1) is kinetically favoured.

(343)

(344)

Courtot 142 has reported some of the transformations encountered in the photochemistry of some chelates of P-diketones. A study of the photochemical interconversion of chelated enols of triacylmethanes has been reported. 43 The results of a study of the photochemical behaviour of the anhydrides (346) has been published. 144 The photoreactions of the thiolane-2,4-diones (347) have been studied. 145, 146 0

0 0 II II Ar CH,COCCH,Ph

14* 14'

14'

143 144

14' 146

R ' ~0 R '

K. Maruyama, Y. Narutama, A. Osuka, and H . Suzuki, Bull. Chem. SOC.Jpn.. 1980, 53, 2093. see e.g. A. Takuwa, Bull. Chem. SOC.Jpn., 1977, 50, 2973. D. W. Balogh, L. A. Paquette, P. Engel, and J. F. Blount, J . Am. Chem. SOC.,1981, 103, 226. P. Courtot, R. Pichon, and J. Le Saint, Bufl. Chim. SOC.Fr., 1980, 457. B. Couchouron, J. Le Saint, and P. Courtot, Bull. SOC.Chim. Fr., 1980, 381. A. A. M. Roof, H. F. van Woerden, and H . Cerfontain, J . Chem. SOC.,Perkin Trans. 2, 1980, 838. K. Saito and T. Sato, Bull. Chem. SOC.Jpn., 1979, 52, 3601. K. Saito and T. Sato, Chem. Lett., 1978, 307.

Enone Cycloadditions and Rearrangements

28 1

Scaiano et al.'47 have characterized two triplet states with different lifetimes in the photochemistry of o-phthalaldehyde (348). They believe that the products (349) and (350) arise from singlet state reactions although their data does not exclude the operation of a short-lived triplet state. Norrish Type I1 reactivity is shown by the formamide derivative (351a) when irradiated in t-butyl alcohol. The product formed from this reaction is the result of ring closing in the biradical intermediate (352) to afford the lactam (353).'48 When the formamide is Nmethylated (35 1b) two Norrish Type I1 hydrogen abstractions occur. One involves the abstraction of the formamide hydrogen yielding (353, R = Me), and the other proceeds by hydrogen abstraction from the N-methyl group affording (354). 0

acHo d

CHO

(348)

(349).

HN

RNKH 0 (351) a; R = H b; R = Me

o

'n'

0 (352)

0

RN*OH 0

PH

N CHO

Irradiation of the enedione (355) results in formation of the two acids (356a, b) and the lactone (357) when the reaction is carried out in benzene solution. 149 The formation of the lactone is presumed to involve the intermediacy of the biradical (358) within which a 1,2-phenyl migration occurs to yield product (357). A biradical (359) is also proposed as the key intermediate to the formation of the acids by way of the ketene intermediate (360) which is trapped by adventitious water. Further proof of the involvement of a ketene was obtained from experiments in methanol when the esters (356c, d) are obtained. Behaviour analogous to the above is also encountered with the ene diones (361). When the bridging chain is reduced as in (362) the irradiation yields only the quadricyclane (363).149An account of the photochemical cis-trans isomerization of (364) applied to an undergraduate experiment has been reported. The use of dibromo-N-methylmaleimidefor the photosubstitution of aryl compounds has been further studied. 147

"13

'*' I5O

J. C. Scaiano, M. V. Encinas, and M. V. George, J . Chem. Soc., Perkin Trans. 2. 1980, 724. H. Wehdi, Helv. Chim. Acta, 1980, 63, 1915. S. Lahiri, V. Dabrai, S. M. S. Chauhan, E. Chakachery, C. V. Kumar, J. C. Scaiano, and M. V. George, J. Org. Chem., 1980, 45, 3782. L. Poncini, Sch. Sci. Rev., 1980, 61, 520 (Chem. Absrr.. 1980, 92, 197228). K. M. Wdd, A. A. Nada, C. Szilagyi, and H. Wamhoff, Chem. Ber., 1980, 113, 2884.

282

Photochemistry

R2

(357)

(355)

(356) a; R' = C 0 2 H , R2 = H b; R' = H, R2 = C 0 2 H c; R' = C02Me, R2 = H d; R' = H, R2 = C 0 2 M e

(358)

&

C \\

0

(359)

(360)

0 Ph (361) a; n = 1 b;n=2

&::: phn (363)

0 Ph (364)

(362)

Maleimide and N-methylmaleimide both undergo dimerization yielding (365) when irradiated in carbon tetrachloride.lS2 When the irradiation is carried out in tetrahydrofuran oligomers are formed via a chain process.

(365) R = H or Me

(366) R

=H

or Me

The photoaddition of diketene to the anhydrides (366) yields the [2 + 21 adducts (367) and (368).153A study of the photocycloaddition of cyclohexene to maleic anhydride sensitized by an insoluble benzoylated polystyrene has shown that the technique is nearly as efficient as the use of free benzophenone.154 The cycloadducts (369) and (370) are obtained from the acetone-sensitized addition of 3,3-dimethylbut-l-yne to the anhydride (371). The product (372) is also found in 1the reaction mixture. This material is light sensitive and is converted by 152

153

P. Boule and J. Lemaire, J . Chim. Phys. Phys.-Chim. Biol., 1980, 77, 161 (Chem. Abstr., 1980, 93, 149 356). T. Kato, T. Chiba, and S. Tsuchiya, Chem. Pharm. Bull.. 1980, 28, 327 (Chem. Abstr., 1980, 93, 45 532).

154 155

J. L. Bourdelande, J. Font, and F. Sanchez-Ferrando. Tetrahedron Lett., 1980, 3805. W. Mayer, D. Wendisch, L. Born, and W. Hartmann, Chern. Ber., 1981, 114, 1287.

283

Enone Cycloadditions and Rearrangements

(369)

x; B u'

\

0 (372)

;F (370) MeMe 0

\\i

(371)

Se

:

Bu' Bu'

HMe 0

(373)

(374)

irradiation into the dimer (373). The [2 + 21-adduct (374) is obtained from the photoaddition of dimethylmaleic anhydride to selenophene. 5 6 Photocycloaddition of but-2-yne to the anhydride (375) yields the novel adduct (376, 36%). 157 This compound was subsequently chemically transformed into the pentaene (377). The photosynthesis of the adduct (378) obtained from the cycloaddition of acetylene to the anhydride (379) has been r e ~ 0 r t e d . I ' ~This adduct (378) was a key intermediate in the synthesis of the novel compound (380). 0

:=Meo2 Me0,C

0

0

C0,Me

The efficiency of triplet-triplet energy transfer to maleic acid has been studied with particular reference to the influence of P H . ' ~ ~ The photocyclization of the anhydride derivative (38 1) yields the naphthalene (382) after hydrolysis and esterification.I6O Irradiation of the epoxynaphthaquinone (383) leads to ring opening of the oxiran ring. When the reaction is carried out in the presence of xanthene, hydrogen abstraction leads to the formation of (384) and (385).16' Rearrangement also 156

Is'

161

C. Rivas, D. Pacheco, and F. Fargas, J. Heterocycl. Chem., 1980, 17, 11 51. R. Askani and B. Peleck, Tetrahedron Lett., 1980, 1841. T. Tsuji, Z. Komiya, and S. Nishida, Tetrahedron Lett., 1980, 3583. A. Gupta, R. Mukhtar, and S. Seltzer, J . Phys. Chem., 1980, 84, 2356. A. S. R. Anjaneyulu, P. Raghu, and K. V. R. Rao, Indian J. Chem., Sect. B, 1980, 19, 51 I (Chew. Abstr., 1980, 93, 220 132). K. Maruyama, S. Arakawa, A. Osuka, and H. Suzuki, Kokaguku Toronkai Koen Yoshishu, 1979, 24 (Chem. Abstr., 1980, 92, 197 663).

284

Photochemistry

Me0

HC OMe Ri

Me0 O M e R'

(381) (382) R' = 2,4,5-(MeO),C,H,; R2 = Br or M e 0

occurs to afford the quinone (386). In the more sterically crowded molecule (387), hydrogen abstraction from xanthene yielding (388) also takes place but rearrangement to (389), the ring-contracted product, dominates. Type I1 hydrogen abstraction reactions occur with the epoxyquinone (390) yielding (386a), the product of elimination, and (39 l), the cyclization product. Further irradiation of this

0

0

(383) R = H, Me, Et, Pr, or Pr'

(384)

%IH

0

0

0

0

(385)

H*

@ M $e 0

Me

R

(388) R = 9:xanthenyl or H

R

Ac

(389) or /I-OH

= u-

0 0

@J:

CH,CHR$

0

R2 R2

(390) R 1= Me, R2 = Ph or Me; R 1 = H, R 2 = Me

(391)

compound converted it into the products shown in Scheme 23. The photoringopening of epoxyquinones of the type (387) has previously been interpreted in

(391)

hv

R2 R2

Me Me Scheme 23

Enone Cycloadditions and Rearrangements

285

terms of the formation of the zwitterion (392).16' Intermolecular trapping of this intermediate accounts for the formation of the dimers (393) and (394) obtained from the photolysis of benzene solutions of the epoxyquinone (387). Further irradiation of the dimers (393 and 394) brings about their further transformation into the dimers, phthalides, (395) and (396).'63 Phthalides (397) are also formed from the irradiation of the adducts (398) in benzene solution. A mechanism involving Norrish Type cleavage as the first step is thought to be The adducts (398) are formed by the trapping of intermediate (392) by aldehydes. The

(392)

0

(393) 0

3 (394)

0

/ \

0

Me

(395)

0 (396)

(397)

(398) R = H,alkyl, or aryl

zwitterionic intermediate (392) is also thought to be involved in the formation of the oxygenated products (399) and (400) obtained from the irradiation (Pyrex

164

K. Maruyama and A . Osuka, Cliem. Left., 1979, 77 (Chem. Ahsfr., 1979, 90,167615). K. Maruyama and A. Osuka, J . Org. Cltem., 1980, 45, 1898. K . Maruyama, A. Osuka, and H. Suzuki, Clrem. Lett., 1979, 1477 (Ckem. Ahsfr., 1980,92, 214628).

286

Photochemistry

filter) of the epoxyquinone (387) in benzene.165 The trapping of the initially formed ylide (392) by singlet oxygen is thought to produce adduct (401). Thermal or photochemical transformation of this yields the observed products (399) and (400). Intermolecular trapping by ally1 alcohols (402) of an ylide intermediate can account for the formation of the adducts (403) from the epoxyquinone (404).'66

H ,C=CHCR:OH

(402) R 2 = H or Me

q HO

&; 0

0

R2 R 2

(404)R'

=

Me, Et, or Ph

(403)

The naphthalene- 1,3-dione derivatives (405) are photochemically transformed in benzene-t-butyl alcohol into the two products (406, 407).16' The reaction is proposed as a Norrish Type I1 process involving the biradical (408) as the key intermediate. The formation of both products can be accounted for from this intermediate either by bond formation or by the more unusual disproportionation to yield (407). A study of the dependence of product distribution with time has shown that while the olefinic product (407) can be produced from the biradical (408), there is also a secondary process in the direct reaction that cleaves the product (407) into the same biradical. The cleavage of this product is clearly dependent on the presence of the additional carbonyl function (perhaps via intramolecular energy transfer) since the acetate (409) is unreactive under the conditions of irradiation. 0

0

R4 R' R2 (405) a; R' b; R ' C;

165

''' 16'

R2 = M e H, R2 = Me R'-RZ = (CH,), =

=

(406)

(407) a; R 3 = Me, R4 = H b; R 3 = R4 = H C;

R3-R4

= (CH,),

K. Maruyama, A. Osuka, and H. Suzuki, J . Chem. SOC.,Chem. Commun., 1980, 723. K. Maruyama, A. Osuka, and H. Suzuki, Chem. Lett.. 1980, 919 (Chem. Abstr., 1981, 94, 30045). A. Osuka, M. H. Chiba, H. Shimizu, H. Suzuki, and K. Maruyama, J . Chem. SOC., Chem. Commun., 1980,919.

Enone Cycloadditions and Rearrangements

287

q R' R2 (408)

The irradiation of the dione (410) in methanol yields the epoxyketone (41 1).168 The authors suggest that an electron-transfer process is involved in the reaction which results in the formation of the methanol adduct (412), which dehydrates to yield the final product.

e M &

0 0

The photoaddition of N-ethylphthalimide (413) to cyclohexene in methanol affords the two adducts (414) and (415). The incorporation of methanol could result from trapping a radical ~ a t i 0 n . I ~Such ' a mechanism has been put forward for the formation of the products (416) and (417) from the phthalimide derivatives (418). The cyclized products (419, 420) are formed on the irradiation of the phthalimide derivatives (421a-c) in methanol.171In the case of 0

R' R2 I I

q

,

A2

R3R c, OMe l (416)

168 169

170 t7L

HO R 3 ~ 2 0 R' M e (417)

go

NCH2CH2C=C, R 0

(418)

R1 = R2 = R3 = H or Me

A. Schonberg, E. Singer, and P. Eckert, Chem. Ber., 1980, 113, 3094. H. Hayashi, S. Nagakura, Y. Kubo, and K. Maruyama, Koen Yoshishu-BunshiKozo Sogo Toronkai, 1979, 232 (Chern. Abstr., 1980, 93, 220 113). M. Machida, K. Oda, K. Maruyama, Y. Kubo, and Y. Kanaoka, Heterocycles, 1980,14,779 (Chem. Abstr., 1981, 94,3432). K. Maruyama, Y. Kubo, and T. Ogawa, Kokagaku Toronkai Koen Yoshishu, 1979, 268 (Chem. Abstr., 1980, 93, 70456).

288

& R2R '

Photochemistry Me

\

&..OMe R2,R1 @;RjR2

\

\

0

0 (419) a; 41% b; 54% c; 15%

0

(420) a; 41% b; 27% c; 54%

(421) a; R' = R2 = Me b; R' = R2 = Ph C; R' = H, R2 = Ph

(421c) the cyclized products were accompanied by the isomer (421, R 1 = Ph, R2 = H) of the starting material. When the reaction of (421c) was sensitized by benzophenone only cis-trans isomerization of the side-chain took place indicating that the cyclization process was a singlet-state reaction. The imidazoisoindolone (422) can be successfully prepared by the photocyclization of (423). 7 2 The phthalimides (424) photocyclize to yield the products (425). 7 3 The sulphur-containing phthalimides (426) yield the products (427) on irradiation.'74 Macrocyclic lactams (CZ8)are prepared in 2 6 5 7 % yield from the photocyclization of the phthalimides (428).1 7 5 Larger ring lactams, C,, and C38,

'

(422)

(423)

@:

(CH

NR R

R3

0

(425) R2 = Me, R3 = H R2-R3 = (CH,), or (CH,),

(424) n = 2 or 3 R' = R2 = Me,

R'-R2 = (CH,), or (CH,),

(426)

n = 5, 6, 8, 9, 10, or 12

(427)

112

J. D. Coyle, J. F. Challiner, E. J. Haws, and G . L. Newport, J . Heterocycl. Chem., 1980, 17, 1131.

173

M. Machida, H. Takechi, and Y. Kanaoka, Heterocycles, 1980, 14, 1255 (Chem. Abstr., 1981, 94, 47 286).

174

17s

Y. Sato, M. Wada, H. Nakai, Y. Hatanaka, and Y . Kanaoka, Fukusokan Kagaku Toronkai Koen Yoshishu, 22th, 1979, 151 (Chem. Abstr., 1980, 93, 1738). Y. Kanaoka, Y. Hatanaka, Y . Sato, M. Wada, and H . Nakai, Kokagaku Toronkai Koen Yoshishu, 1979, 266 (Chem. Abstr., 1980, 93, 70455).

Enone Cycloadditions and Rearrangements 289 were also produced from analogues of (428). Cyclization of (429) yielding macrocyclic lactones (c16, C18, C20,C,,, C25, and C27) was also r e ~ 0 r t e d . l ~ ~

(428)

(429)

Irradiation (254 nm) of the imide (430) brings about partial isomerization of the starting material to the trans-isomer (431).176This product is accompanied by the ring-contracted compounds (432) and (433). 769 7 7 Secondary irradiation of the

(433)

(434)

ring-opened compound (433) converts it into (432). From these results it is clear that the reaction proceeds by fission to the biradical (434) from which the isomerized starting material and the N-formyl derivative are derived. The scope of the reaction has been investigated. The usefulness of the cyclization process whereby N-formyl derivatives (e.g., 435) can be converted into azetidine diones R'-RZ = (CH,), or(CH2), R1 = R2 = Me R' = H, R2 = Me, Pr",Pr', Bun,or Bu' (435)

Scheme 24

was also studied (Scheme 24). The ring-expansion products (436a) are forrned on irradiation of the succinimides (437a).I These products are accompanied by the ring-contracted materials, the azetidines (438a). In some cases, as with the succinimides (437b), ring expansion did not take place and only azetidines (438b) were formed. The Norrish Type I1 fission of the N-alkyl side-chain is only important when the side-chain has a b-hydrogen. 177

17'

K. Maruyama, T. Ishitoku, and Y. Kubo, J. Org. Chem., 1981,46, 27. K. Maruyama, T. Ishitoku, Y. Koba, and T. Ogawa, Fukusokun Kaguku Toronkai Koen Yoshishu, 12th, 1979,46 (Chem. Absfr., 1980,93, 203 617). Y. Kanaoka, H. Okajima, and Y. Hatanaka, Kokuguku Toronkai Koen Yoshishu, 1979, 16 (Chem. Abstr., 1980, 93, 45 533).

290

Photochemistry

(436) a;

=

(437) a; R = Et, n = 2 or 4 b; R = Me, n = 2 or 4

Or

(438) a; n = 2 or 4, R = Et b;n=2or4,R=Me

6 Quinones An earlier report by Maruyama et al. described the formation of dimers (439) from the direct irradiation of the acetylquinone 18* In the presence of an electron-donating sensitizer (Rose Bengal) irradiation of the same quinone yields a different dimer assigned structure (441).18' A further account of the regio- and stereo-specific dimerization of the quinones (442) to yield (443) has been reported.182 The possibility of the involvement of an enol intermediate was considered. In one example, that of (444),dimerization failed and the cyclobutene derivative (455) was obtained via a Norrish Type I1 reaction.

0

" R'' C f O C H z R 3 0 (442) R 3 = H, Me, Et, Pr, or Bu, R 1 = H, Me, CI, or Br, R2 = H, or R'-RZ = (CH=CH),

R'

R2 (443) R4 = COCHzR3 OH

(pMe Me

0

OH

Photocyclization of the toluquinone (446) to (447) has been reported. The mechanism favoured by the authors 183 involves intramolecular hydrogen abstraction, proton transfer, and cyclization. 179

I8O 181 18'

183

K . Maruyama, N. Narita, and Y. Miyagi, Chem. Lett., 1979, 1033. K. Maruyama and N. Narita, J . Org. Chem., 1980, 45, 1421. Y. Miyagi, K. Kitamura, K. Maruyama, and Y. L. Chow. Chem. Lett., 1978, 33. Y. Miyagi and K. Maruyama, Kokagaku Toronkai Koen Yoshishu, 1979,26 (Chem. Abstr., 1980,92, 197841). K. Maruyama and T. Kozuka, Chem. Lett., 1980, 341 (Chem. Abstr., 1980,93, 70473).

Enone Cycloadditions and Rearrangements

29 1 The novel cage compounds (448, 449)are formed when duroquinone (450) is irradiated (Pyrex filter, benzene solution) in the presence of cycloheptatriene. 184* 185 The reaction takes place via the intermediate (451), which subsequently undergoes intramolecular cyclization to yield (448) or intermolecular addition of duroquinone followed by intramolecular cyclization to afford the

R C0,Me Me 0

OH (447)

(446) R = Me, Et, CO,Me, or (CH,), NHPh

0

Me

0 (448)

(450)

(449)

second product (449). A cage compound (452) was also obtained by irradiation of the quinone with the triene (453). The product indicates, however, that the triene undergoes photoisomerization to (454) before the addition to the quinone takes place. When cyclo-octatetraene is used as the addend, dimerization and isomerization yield (455) prior to the photoaddition to the quinone to yield (456).

(455)

(454) (456)

K . Ogino, T. Minami, S. Kozuka, and T. Kinoshita, J . Org. Chem., 1980, 45, 4694. K. Ogino, T. Minami, and S. Kozuka, J . Chem. Soc., Chrm. Commun., 1980, 480.

lB4

292

Photochemistry

A detailed study of the photochemical reaction of naphthaquinone with aldehydes has shown that the reaction occurs via an 'in cage mechanism' at low temperatures but at ambient temperatures a small part of the reaction arises from an 'out-of-cage' process. 186 Photocycloaddition of 2-methyl- and 2-ethyl-naphthoquinone to styrene yields three cyclobutane products (457,458) in which the.8-phenylisomer dominated. * 8 7 The ratio of 7-phenyl to 8-phenyl products was 1 : 6 for the methylquinone and 1 : 3.5 for the ethyl derivative. The authors l g 7 suggest that in these examples dipoledipole interactions overcome any adverse repulsions. Changes in the olefin brings about changes in the ratio of products. Thus with 2-phenylpropene the ratio

8

Ph

0

0

(457a)

0 (459)

(457b)

0 (460)a; R' = H,R 2 = AcO b; R' = AcO,R2 = H c; R' = Me,R2 = AcO

0 (458)

R2

_.

(461) a; R2 = H c; R 2 = Me

of 7: 8 isomers is 1 and with 1,l-diphenylethylene the ratio is about 2. Photoaddition of vinyl acetate to the methylquinone (459) yields the adducts (460a,b) regiospecifically.188 An analogous adduct (460c) is obtained when the olefin, isopropenyl acetate, adds to the same quinone. The adducts (460a, b) and (460c) undergo acid-catalysed conversion into the naphthofurans, (46 1a) and (46 lc), respectively. Irradiation of the quinones such as (462) with 1,l-diarylethylenes has been reported as a convenient one-pot synthesis of the benz[a]anthracene skeleton Scheme 25. This report is an extension of earlier work by the same 0

Scheme 25 lg6

K . Maruydma, A. Tdkuwa, S. Matsukiyo, and 0 . Soga, J . Chem. Soc., Perkin Trans. I, 1980, 1414. K . Maruyama and N. Naritd, Bull. Chem. SOC.Jpn., 1980, 53, 757. H. Liu and W. H. Chan, Can. J . Chem., 1980, 58, 2196.

Enone Cycloadditions and Rearrangements

293

(463)

(464)

authors.189-l g 2 A route to novel anthraquinones (e.g., 463) has been reported following the successful photoaddition of olefins (e.g., 464).l g 3 Further investigation into the reactions of quinone (462)has shown that low yields of

Me Scheme 26

products (Scheme 26) are obtained from irradiation in the presence of 1,ldicyclopropylethylene. 94 Interestingly no products were obtained from the addition reaction in which the cyclopropyl ring had opened. This fact is put forward as evidence for the operation of an ionic rather than a free-radical path. The photoaddition of the olefin (465)to the same quinone yields (466).Ig5 0

40SiMe3 R (465)

(466)

R

= Ph, 4-MeC6H,, or 2-thienyl

Phenanthraquinone (467)has been added photochemically to both alicyclic and bicyclic olefins.196 The nature of the products obtained is dependent upon the structure of the olefin. Thus with the bicyclic olefins (468470)the keto-oxetans (471473)are formed exclusively. The use of alicyclic olefins (474)as the addend I9O 191

19'

193

194

195

196

K. Maruyama, T. Otsuki, and K. Mitsui, J . Org. Chem., 1980, 45, 1424. K. Maruyama and T. Otsuki, Chem. Lett.. 1975, 87. K. Maruyama, T. Otsuki, and K. Mitsui, Bull. Chem. SOC.Jpn., 1976, 49,3361. K.Maruyama, K. Mitsui, and T. Otsuki, Chem. Lett., 1978, 323. K. Maruyama, T. Otsuki, K. Mitsui, and M. Tojo,J . Hererocycl. Chem., 1980,17,695 (Chem. Abstr., 1980, 93,239 128). K. Maruyama, M. Tojo,and T. Otsuki. Bull. Chem. SOC.Jpn.. 1980, 53, 567. K. Maruyama, M. Tojo, K. Matsumoto. and T. Otsuki, Chem. Lett.. 1980,859 (Chem. Abstr.. 1980, 93,239375). K. Maruyama, M. Muraoka, and Y. Naruta. J . Org. Chem., 1981, 46, 983.

Photochemistry

294

R3 (468) a; R' = R2 = H, n = 1 b; R' = R2 = H,n = 2 c; R'-R2 = 0, R3 = H, n = 1 d; R2-R3 = OCOCO, R' = H, n = 1

(467)

(469) a; R = H b; R-R = (CH=CH)2

(470)

(472)

(47 1)

also yields keto-oxetans (475) but these are accompanied by dioxins (476) and keto alcohols (477). In contrast, photoaddition of phenanthraquinone to the olefins

F

Y

@ (474) a; n = 1 b;n=2 c;n=3 d;n=4 e;n=8

0 W ) r . (475) a; 18% b; c; d; 20% e; -

(476) a; b; 29% c; 42% d; 56% e; 46%

\ +QIl

(477) a; 70% b; 59% c; 34% d; 6% e; 39%

(478) has been reported to yield the adducts (479).19' The photoaddition of the quinones (480) and (481) to the enzymes (482) yields the carboxamides (483), which undergo spontaneous ring closure to yield the adducts (484a) and (484b), respectively. The initial addition reaction presumably involves the formation of an oxeten which subsequently ring opens to (483). 19'

'98

P. Kertesz and J . Reisch, Arch. Pharm (Weinheim. Ger.), 1980, 313, 476 (Chem. Abstr., 1980, 93, 186 258). W. Verboom, A. V. E. George, L. Brandsma. and H. J. T. Bos, R e d . Trav. Chim. Pays-Bas, 1980.99, 29.

Enone Cycloadditions and Rearrangements

295

H p&CHZOR

H (479) R = H, 1 :5 cis :trans R = Bz, 1:lQ cis:trans

(478) R = H or Bz

8

By' R~CH =CHC=CNR:

/

(482)

R4

rONR!

CONR!

R' (483)

(484) a; R'-R3 = Rz-R4 = (CH=CH)2

b; R'

=

R2 = Bu', R 3 = R4 = H

The photocycloaddition of trans-piperylene to the quinone (485) yields the oxetan (486).199From a study of this and other dienes (e.g., cyclopentadiene and cyclohexa-l,3-diene), it was concluded that the addition involves an exciplex where both the singlet and the triplet states are involved.

& @ Ye

I

0

(485)

I

0

(486)

The study of the photochromism of a series of anthraquinone derivatives (487) has been reported.200The reaction involves the Norrish Type I1 hydrogen transfer from a neighbouring methyl group to a photoexcited carbonyl group yielding the enol(488). The photohydroxylation of anthraquinone in aqueous organic solvents has shown that both 1- and 2-hydroxyanthraquinone are produced.201- *04 A 199

'01

"' z03 '04

A. Ezaki, H. Inoue, and M. Hida, Kokagaku Toronkai Koen Yoshishu, 1979,164 (Chem. Abstr., 1980, 93, 7264). N. P. Gritsan, V. A. Rogov, N. M. Bazhin, V. V. Russkikh, and E. P. Fokin, izv. Akad. Nauk SSSR. Ser. Khim., 1980, 89 (Chem. Abstr., 1980, 93. 7382). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16,2117 (Chem. Abstr., 1981,94,83287). 0 .P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, I101 (Chem.Abstr., 1980,93, 150035). 0.P. Studzinskii, R. P. Ponomareva, and V. N. Seleznev, izv. Vys. Uchebn. Zuved., Khim. Teknol., 1980, 23, 51 1 (Chem. Abstr., 1980, 93, 168 004). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, I100 (Chem.Absrr., 1980.93, 168 005).

aR

296

Photochemistry

/

0 (487) R = H , 3 4 1 -cyclohexen-!-yl), 4-Me0, 3-cyclohexyl, 3-(2-nitro-l -cyclohexen-l-yI), or 4-CI.

0 (489) R = NH, or OH

detailed study of the photoreactions of amino- and hydroxy-anthraqwinones (e.g., 489) has been reported.205 Photoreactions of the quinones (490) have been described.206

205

K . Hamilton, J. A. Hunter, P. N. Preston, and J. 0. Morley, J . Chem. Soc., Perkin Trans. 2, 1980,

'06

Yu. E. Gerasimenko, N. T. Poteleshchenko, and V. V. Romanov, Zh. Org. Khim., 1980, 16, 1938 (Cliem. Abstr., 1981, 94, 47021).

1544.

Photochemistry of Olefins, Acetylenes, and Related Compounds ~~~

~~~

BY W. M. HORSPOOL

1 Reactions of Alkenes

Addition Reactions.-The photochemical conversion of the optically active aniline (1) into the indoline (2), and the methanol adducts (3, 4) of (l), have been described. Irradiation of the substituted naphthoic acid ( 5 ) yields the cyclized lactone (6). This is a key step in the synthesis of the quinone (7).2

OMe

OMe

(6)

(5)

0

(7)

Photoaddition of acetaldehyde to the stereoisomers of (8) gave only two (9) of the eight possible ad duct^.^ The acetyl group apparently enters specifically at C-4 frans- to the hydroxy-group. Addition products are formed when iminium salts (10) are irradiated in ethers or alcohol^.^ The mechanism of the addition involves an electron transfer as shown

'

B. Scholl and H.-J. Hansen, Helv. Chim. Acra, 1980, 63, 1823. R. G . F. Giles, M. K. Reuben, and G . H. P. Roos, S. Afr. J . Chem., 1979,32, 127 (Chem. Abstr., 1980, 93. 204403). 3. Srogl, M. Janda. F. Liska, and I. Stibor, Collect. Czech. Chem. Commun., 1980, 45, 888. J. Stavinoha, E. Bay, A . Leone, and P. S. Mariano, Tetrahedron Lett., 1980, 21, 3455.

297

298

Photochemistry M e C O e E

CHzOH

M e 0P O M e

Me0

(8)

(9)

in Scheme 1. The results obtained from a study of the photoaddition of electron-acceptor olefins e.g. acrylonitrile, to iminium salts (1 1) indicate that the reaction occurs by initial 1,2-addition to the aromatic ring5 The intermediate

QR1

CH, In.OH'

0

~

+

CH30& 1

I R2

\

R2

-

QRl+

+OH

/\

H R2

Q IG Z O "

R2

a/ % \ 2 0 H

R2 H

Scheme 1

Table 1 Products (13) formed by cycloaddition of olefn (CH,=CHCN) iminium salts (I 1) Salt (1 la) (1 lb) (1 lc) (1 Id)

to

Product (7; yield) (13a, 18%) ( 1 3b, 20%) ( 1 3 50%) ~ (134 5%)

adduct (12) rearranges to the spirocyclic amines (13) (Table 1). The anisyl compound (lle) is an exception to this generality and yields the abnormal cycloadduct (14).

'R

ClO,

HkR NC

H N & /NC J-

(11) a; R = Me

b:R=F R = CI d; R = Br e; R = OMe C;

aCN /I- McOC,,H,

(14)

R

299

Photochemistry of OZefins, Acetylenes, and Related Compounds

Hydrogen Migrations and Abstractions.-Morrison and Giacherio have reported the acid-catalysed photoisomerization of 2-alkylindenes (e.g., 15) into the corresponding alkylidene indans (e.g., 16). The reaction involves the singlet state of the indene since the triplet state yields only dimers. However, it is obvious from the failure of HCl to affect the fluorescence of the indenes that the interaction of the acid is with a state other than the simple singlet excited state. Further study has shown that the addition of a proton occurs at C-3 of the indene. Intramolecular hydrogen transfer has been demonstrated by deuterium labelling in the photorearrangement of the rigid homoallyl alcohol (17) into the aldehyde (18).7 ~\

M

W \

(1 5 )

(17)

(18)

C c

H

,

(16)

(19)

(20)

(21)

Irradiation of the deuteriated alcohol (19) affords the aldehydes (20) and (21) each containing one deuterium atom. Such an experiment indicates that the alcoholic hydrogen is abstracted. A similar experiment with the endo-exo mixture of alcohols (22) gave an analogous result with the two aldehydes (23, 24) each containing two deuterium atoms. The cyclized products (25a) and (25b) are

&OD D

R' = CO,H or CONH,, R2 = H b; R' = H, RZ = C02H or CONH,

(25) a;

(26) R

= CO,H

or CONH,

formed by the irradiation of the chlorinated tricyclic starting material (26).8 The reaction involves abstraction of hydrogen by the photoexcited double bond and bonding within the resultant biradical.

'

H. Morrison and D. Giacherio, J . Chem. Soc.. Chem. Commun., 1980, 1080. J. Studebaker. R. Srinivasan, J . A. Ors, and T. Baum, J . Am. CIwm. Soc., 1980, 102, 6872. J. Schmitzer, K. Hustert. H. Parlar, and F. Korte, Z . Naturforsch.. Teif B. 1980,35, 502 (Chem. Abstr., 1980, 93. 220 110).

300 Photochemistry Fission Processes.-Irradiation of the deuteriated mesylate (27) with 2 = 254 nm resulted in the formation of the products shown in Scheme 2.9 The recovered (27,

(27) R'

=

a; R = NHCOMe, 41% b; R = OMS. 7% Scheme 2

D, R2 = OMS

R = OMS, 17%

35%) was shown to be identical with starting material: the absence of deuterium migration suggests that the ion (28) is not a primary product. Kitamura et al."

(28)

have reported the synthesis of the compounds (29) following the irradiation of the olefin (30) in the presence of azide ion and dimethyl fumarate. The reaction is interpreted in terms of the formation of the ion (31) produced by the photoinduced ionization of the vinyl bromide. The ion is trapped by azide which presumably, on photoexcitation, produces an azirine. Ring opening of the azirine and trapping by the diester yields the observed products. The bromide (30a) yields the oxazole (32) when irradiated in the presence of azide and acetone. -0Me

"-.

R p-MeOC,H,

R p-MeOC6H4

R

R

XBr

(30) a; R =p-MeOC,H4 b; R = Ph c; R = Me

P+ (31)

Me (32) R = p-MeOC,H, cis-trans 1somerization.-The influence of triplet energy on the photo-equilibrium position of several /I-alkylstyrenes (33) has been studied.l19 l 2 The high ratio of the S. J. Cristol and R. M. Strom, J . Am. Chem. Soc., 1980, 102, 5577. T. Kitamura, S. Kobayashi, and H. Taniguchi, Kukagaku Toronkai Koen Yoshishu, 1979, 84 (Chem. Abstr., 1980, 92, 180331). T. Arai, H. Sakuragi, and K. Tokumaru, Kokuguku Toronkai Koen Yoshishu, 1979,112 (Chem. Abstr., 1980, 93, 70 606).

T. Arai, H. Sakuragi, and K. Tokumaru, Chem. Left., 1980, 261 (Chem. Abstr., 1980, 93, 70069).

Photochemistry of Olefins, Acetylenes, and Related Compounds

30 1

cis-t-alkylstyrene at the photostationary state was attributed to a lower rate constant for energy transfer to the cis-form than to the trans. The influence of oxygen upon the triplet-induced photostationary state composition of the olefin (34) has been as~essed.’~ The ‘betweenanenes’ (e.g., 35) present a novel class of compounds in which there has been some interest over the last few years. Marshall l4 has reviewed the area recently. Marshall and Black l 5 have reported the synthetic steps to some new examples (35)’ the key step in which is a photochemical cis-trans isomerization induced by irradiation in xylene or cyclohexane of the isomers (36). The ‘betweenanenes’(37) have been synthesized by the irradiation of the olefins (38).16 PhCH=CHR

Me

(33) R = Me, Et, Me2CH, M e X , or EtCMe,

M eMe bx2-naphthyl

(‘m a”?) (34)

(CH2),o

(CHdlo

(35)

n)2H & CrC(

(36)

(37)

m = 20, 22, and 26 a

m

(38) n = 8, 10, or 20 m = 6 , 8, or 18

The rate constants for the cis-trans isomerization of stilbene have been obtained.”. l 8 A study of the trans-cis isomerization of the stilbenes (39) using proton and fluorine CIDNP has been made.” Maciejewski 2o has published an account of a laboratory experiment based on the photoisomerization of cisstilbene.

R

5

c

(39)

L

R

(

=

H

3 / R 5

Or

F

pb \

/

(40)

A kinetic analysis of the behaviour of the styrene (40) upon irradiation using oxygen and azulene as quenchers has shown that the lifetime of the triplet state is

*’T. Arai, H. Sakuragi, and K. Tokumaru, Chem. Lett., 1980, 1335 (Chem. Abstr., 1981,94, 64815). l4 lS

l6

J. A. Marshall, Acc. Chem. Res., 1980, 13, 213. J. A. Marshall and T. H. Black, J . Am. Chem. SOC.,1980, 102, 7581. J. A. Marshall, M. Constantino, and T. H. Black, Synth. Commun., 1980,10,689 (Chem.Abstr., 1981, 94, 15 263).

l7

M. Sumitani, N . Nakashima, and K. Yoshihara, Chem. Phys. Lett., 1979, 68.

’* M. Sumitani, N. Nakashima, and K. Yoshihara, Kokuguku Toronkai Koen Yoshishu, 1979,40 (Chem. l9 2o

Abstr., 1980, 92, 163 331). T. V. Leshina, S. G. Belyaeva, V. I. Mar’yasova, R. Z. Sagdeev, and Yu. N . Molin, Dokl. Akad. Nauk. SSSR, 1980, 255, 141 (Chem. Abstr., 1981, 94, 102 547). A. Maciejewski, Mech. Kinet. Procesow Fizykochem., 1979, 89 (Chem. Abstr., 1980, 93, 131 529).

302

Photochemistry

104-150ns.2' The isomerization of the styrene (40) in the presence of electron acceptors has been reported.22

R

Ph

Po>

0

Ph (41) R

=

H , OAc, or OMe

(42)

(43)

A study of the excited-state properties of the trans- and cis-dianthrylethylenes (41) has been made.23 The cis-isomer photoconverts with low quantum yield (9 x into the trans-form. The reverse transformation does not take place. Irradiation of the crown ether (42) under various conditions yields the expected phenanthrene derivatives (50--60%) together with the cis-trans-isomer (43, 0.5%).24 Inoue et aE.25have described their study of the singlet sensitized isomerization of cyclo-octene. They 2 5 report that the use of methyl benzoate or other aryl esters results in the anomalously high trans-cis ratio of 0.25. This result is only anomalous if a triplet mechanism is operative but the authors 2 5 have shown that in this instance a singlet state is the active species. The same sensitizer has been used in a study of the photochemical behaviour of the diene (44), which is converted into the isomer (45) and subsequently into (46).26

0 (2(44)

(45)

(46)

2 Reactions involving Cyclopropane Rings Kaupp 27 has published a review in which reference is made to the di-n-methane reaction, a process which continues to yield interesting results. The di-n-methane 21

22

23 24 25

26

J. Saltiel and D. W. Eaker, Chem. Phys. Lett., 1980, 75, 209. G . Gennari, G. Cauzzo, G. Galiazzo, and M. Folin, J . Photochem., 1980, 14, 1 1 (Chern. Ahstr., 1981, 94, 3517). H. D. Becker, K. Sandros, and L. Hansen, J . Org. Chem., 1981, 46,82 1. M. Eichner and A. Merz, Tetrahedron Lett., 1981, 22, 1315. Y. Inoue, S. Takamuku, Y. Kunitomi, and H. Sakurai, J. Chem. SOC.,Perkin Trans. 2, 1980, 1672. S. Goto, S. Takamuku, H. Sakurdi, Y. Inoue, and T. Hakushi, J. Chem. SOC., Perkin Trans. 2 , 1980, 1678.

'' G . Kaupp, Angew. Chem. Int. Ed. Engl., 1980, 19, 243.

Photochemistry of OleJins, Acetylenes, and Related Compounds

303

Rb

R2

R' = RZ = H or HO (48) R 3 = H or Me rearrangement of the diene (47) into the pentacyclic compound (48) has been described.28 No products of bond homolysis or bond heterolysis were observed when the compounds (49) were irradiated in acetonitrile solution. 29 The products obtained were all of the di-n-methane type (50). The same reaction was observed when (49a) was irradiated in acetic acid. However, when (49b) was irradiated in (47)

(49) a; X

= HO b; X = AcO C: X = OCOEt

(50) a; X = OH b; X = AcO C;

X

=

,

OCOEt

( 5 1 ) a;

R' = AcO, RZ = H , 32';; b; R' = H,R 2 = AcO, 4%

Scheme 3 acetic acid the products (Scheme 3) were obtained. The propionate (49c) yielded the products shown in Scheme 4. The authors2' believe that the photoreactions are influenced by acid catalysis. (49c)

-&-

( ~ O C24: , ")

+ (49c, 47" ") + (5 1a, 4"/,) + (5 1b, 4%) Scheme 4

The acetone-sensitized irradiation of the bicyclo-octadienones (52) leads to the formation of a single photoproduct (53) in each case.3oThis product is presumed to arise from a di-n-methane reaction involving the bridging intermediate (54) exclusively, despite the polar substituents in the benzene ring. In constrast, similar irradiation of the compounds ( 5 5 ) leads to products, the nature of which is dependent upon the type and position of the polar substituent. The results are 28 29

30

I. Kasahara, H . Sugiyama, and M . Nitta, Kokagaku Toronkai Koen Yoshishu, 1979. 156 (Cliem. Abstr., 1980, 93, 7385). S. J. Cristol and R. D. Daussin, J . Am. Chern. Soc., 1980, 102, 2866. M.Kuzuya, E. Mano, M . Ishikawa, T. Okuda, and H . Hart, Tc.trrihcrlrori Lrrt.. 1981, 22. 1613.

304

Photochemistry

0

0

Ph

R3 R' ( 5 2 ) a; R' = R 2 = H, R3 = CN mdiS= 0.18 b; R' = R 3 = H, R2 = CN mdis = 0.17 c; R 3 = OMe, R' = R2 = H Qdiq = 0.19 d; R' = OMe, R2 = R 3 = H Qdis = 0.16

(53)

(54)

shown beside the appropriate structures (Scheme 5). Schnaffner and his coworkers 31 have examined further the photorearrangement of the barrelene 0

n

0

R2

0

II

Scheme 5 analogue (56) into the three isomeric semibullvalene products (57-59), Scheme 6. Their original proposal 32 was that two discrete biradical intermediates were presumably involved in the rearrangement process. They now report 3 1 that irradiations at 77K lead to a matrix which yields two e.s.r. spectra assignable to radical intermediates formed in the reaction. It is evident from this set of experiments that the reaction proceeds in a stepwise fashion via biradicals of the type shown in Scheme 6 . A study of the bridging selectivity shown in the compounds (60) has been reported (Scheme 7).33 The analysis of the reaction was carried out by spectroscopic means and the results are shown in Table 2. The preference for the type of bridging shown is dependent on the stabilization of the cyclopropyl radicals (61) and (62), i.e. whether the cyclopropane is stabilized or destabilized by the type of substituent at the bridgehead. A similar study has been carried out for the benzeno-bridged Compounds. Table 2 lists the findings. 31 32

33

K. Schaffner, M. Demuth, and D. Lernrner, J. Am. Chern. Soc., 1980, 102, 5407. M. Dernuth, C. 0. Bender, S. E. Braslavsky, H. Corner, V. Burger, W. Amrein, and K. Schaffner, Helv.Chim. Acta, 1979, 62, 847. M. Iwamura, H. Tukada, and H. Iwamura, Tetrahedron L x t i . , 1980, 21, 4865.

p:

Photochemistry of Olefins, Acetylenes, and Related Compounds /D

305

D

4

p

\

.COPh

I

\

J

P \C

--+ product

Scheme 7

(57) O (57)

P

h

Photochemistry

306 Table 2

Bridging selectivity for compounds (60a) and (60b) 3 3 Subs t it uent

(R2) Me0 AcO OCOPh But

Br Ph Ac Me CHO

Ethenoanthracene (604 path i path ii 0 100 0 100 0 100 0 100 0 100 100 0 29 71 29 71 12 88

Benzenoanthracene (60b) path ii path i 100 0 100 0 100 0 0 100 100 0 0 100 100 0 21 79 100 0

Prolonged irradiation of the tricyclic olefin (63) affords the spiro-compound (64) as the sole product.34 However, on shorter exposure times this compound is accompanied by the isomeric material (65). It is clear from a separate study that the irradiation of this dihydronaphthalene results in its conversion into the starting material (63). This compound (63) is also formed on irradiation of the isomeric compound (64) and (66). Both the products (64, 65) from the initial irradiation result from the migrations of the methylene unit on a methylene indene unit. Theoretical aspects are discussed.

Direct irradiation of the resolved ester (67) gave the optically active products (68-70), and the naphthalene (72). The two products (69) and (70) formally arise by 1,5-migrations of the methylene in both possible direction^.^' That the products obtained from these migrations preserved high optical purity is proposed

Bu'

(70)

(71)

as good evidence for the migration following the postulates of conservation of orbital symmetry and that the reactions occur with inversion of the configuration 34

35

H. E. Zimmerman and R. E. Factor, J . Am. Chem. Soc., 1980, 102, 3538. M. Kato, K. Takatoku, S. Ito, M.Funakura, and T. Miwa, Bull. Chem. SOC.Jpn., 1980, 53, 3648.

Photochemistry of Olefins, A cetylenes, and Related Compounds 307 of the migrating carbon. Irradiation of the diene (72) brings about a photochemical 1,5-sigmatropic migration to afford the product (73).36 The inversion in

(73)

(72)

configuration at the migrating carbon is as expected for a Woodward-Hoffman photochemically allowed process. However, the authors 36 raise the question of the applicability of the W.H. postulates to such a system since the thermal process also yields an inverted product. They 36 argue that a biradical intermediate could be involved since closure via a least motion pathway would lead to inverted configuration.

(74) a; R = Br b;R=CN c; R = OMe

(75)

Scheme 8

A study of the migratory aptitudes of aryl groups in the indenes (74) has been reported. 37 These results show that the substituted phenyl group migrates preferentially on triplet sensitization. The results obtained (Table 3) are broadly in Table 3 Migratory aptitudes for photorearrangement of indenes (74) 3 7 Indene (in hexane)

% Reaction

Ratio of (75):(76)

59

98:2 86: 14 95: 5

88 89

line with those obtained for other systems by Zimmerman et aL3* where a radicallike transition state was proposed. However, the present authors 37 have suggested an alternative interpretation that involves the intermediacy of an internal exciplex. Sensitized irradiation of the indene derivative (77) gives a quantitative yield of the cycloadduct (78).39An analogous product (79) is obtained from the irradiation of the indene (80). This product (79) is, however, accompanied by the two rearrangement products (81) and (82a). These products are thought to be formed by a 1,2-phenyl migration to afford the isoindene (83a), which thermally undergoes 1,5-hydrogen migrations to yield either (81) or (82a). The formation of the cycloadducts (78) and (79) is explained by crossed addition of the olefin unit to 36 3’

” j9

W. T. Borden, J. G. Lee, and S. D. Young, J. Am: Chem. SOC.,1980, 102,4841. C. Manning, M. R. McClory, and J. J. McCullough, J . Org. Chem., 1981, 46,919. H. E. Zimmerman, R. D. Rieke, and J. R. Scheffer, J. Am. Chem. Soc., 1967, 89. 2033; H. E. Zimmerman, R. C. Hahn, H. Morrison, and M. C. Wani, J . Am. Chem. Soc., 1965,87, 1138. A. Padwa and M. Pulwer, J. Am. G e m . SOC.,1980, 102, 6386.

308 Photochemistry the indene double bond. This behaviour is common in the photochemistry of hexa1,5-diene~.~' This crossed mode of cycloaddition is not followed by all the systems studied. Thus irradiation of the indene (84) gave the cycloadduct (85) as well as the rearranged indenes (82b) and (83b). An analogous adduct (86) is obtained from

@ \ $?R@R

\

Me H (81)

Me (82) a; R = H b; R = Me

Me (83) a; R = H b;R=Me

irradiation of the isomeric indene (87). The cycloadduct is presumably formed via the intermediacy of the biradical(88) since in this latter case it is accompanied by the olefin (89), which is presumably formed by disproportionation within the biradical (88). The cyclopropene (90a) undergoes dimerization to (9 1) when irradiated in benzene or hexane with Pyrex-filtered light.41 When the irradiation was carried out in the presence of a triplet quencher the dimerization product is absent and a new product (92a) is formed. A bicyclohexene (92b) is also formed from the irradiation of the cyclopropene (90b). The authors 4 1 suggest that the most likely route to these products is via an intermediate carbene (93). Further evidence for the existence of the carbene was obtained by trapping experiments in methanol 40 41

see W. L. Dilling, Chem. Rev., 1966, 66, 373. A. Padwa, T. J. Blacklock, R. Loza, and R. Polniaszek, J . Org. Chem., 1980, 45, 2181.

Photochemistry of Olefins, Acetylenes, and Related Compounds

(90) a; R = H b; R = Me

(95)

(91)

(92) a; R = H b; R = Me

(93)

(97)

(96)

309

(98) a; R = H b;R=Me

Ph

when (94) and (95) were isolated from (90b). The behaviour of other cyclopropenes (96, 97) was also studied and these gave the indenes (98, 99) on direct irradiation. Under sensitized conditions the [2 21-adduct (100) was formed from (97). Direct irradiation of the cyclopropene (101) affords the two products (102) and (103): Scheme 9. The bicyclohexene (102) is likely to be formed from the

+

Ph

Ph

addition to the double bond of the carbene analogous to (93).42 A carbene mechanism is also thought to be involved in the formation of the butadiene product (104) obtained along with other products (Scheme 10) from the irradiation of (105).42 Diphenylcyclopropenes (106-108, Scheme 11) have been shown to quench the fluorescence of 9, lO-di~yanoanthracene.~~ When these compounds are irradiated in the presence of the anthracene, reaction products are obtained that are different from those obtained by either direct or triplet-sensitized irradiation. The route to products (Scheme 11) fits best with an electron-transfer process from the 42 43

A. Padwa, T. J. Blacklock, D. M. Cordova, and R. Loza, J. Am. Chem. SOC.,1980, 102, 5648. A. Padwa, C. S. Chou, and W. F. Riecker, J. Org. Chem., 1980,45, 4555.

Photochemistry

310

Ph

Me

Ph

Me Ph

Me

Scheme 10

Ph Ph +

@ph

Et

-k

&Ph

i&Ph

Ph

Me

Ph Et

Scheme 11

cyclopropene to the anthracene. The products formed are thus derived from reaction of the radical cation (e.g., 109-1 10). Sensitized irradiation of the arylcyclopropene (1 1 1) results in hydrogen abstraction to produce the intermediate biradical (1 l 2).44 This biradical can either undergo bond formation to yield (1 13), the principal product, or else undergo conversion into (1 14) which yields the minor product (1 15). The absence of dimethyl stabilization of the benzylic part of the biradical [derived from (1 16d)l affords a readily reactive species that exclusively cyclizes to (1 17) without ring opening. With the unsymmetrical cyclopropene (1 18) sensitized irradiation affords only the cyclized product ( I 19) clearly showing that hydrogen abstraction has resulted in the formation of biradical(120). The reaction is thus stereospecific with hydrogen transfer only to the methyl-bearing carbon. A similar study has been

31 1

Photochemistry of Olefins, Acetylenes, and Related Compounds

m

Ph Me

Ph /

(121) R' = Ph, R2 = Me R' = Me, R2 = Ph

(122)

carried out on the alkyl derivatives (121). In these cases hydrogen abstraction appears to follow the same path with the formation of a biradical prior to cyclization and the formation of the final product (122). The influence of deuterium substitution on the reaction has shown that deuterium ends up in the expected endo-position of the product (123-1 24).44

Ph (1 23)

( 124)

Streith and Nastasi 45 have reviewed the photoreactions of three-membered rings. A study of the photo-ring-opening reactions of the azirines (125) has been reported.46 A CIDNP study of photoelectron transfer from cis- and trans-1,Z The evidence collected diphenylcyclopropane to chloranil has been carried from this study indicates that the intermediate involved is the radical cation (126), since no polarized rearrangement product was observed. The failure to observe reaction is in marked contrast to the behaviour when the cyclopropane is irradiated in the presence of 1,4-di~yanonaphthalene.~* 44 45

46

47 48

A. Pddwa and C. S. Chou, J. Am. Chem. SOC.,1980. 102, 3619. M . Nastasi and J. Streith, Org. Chem., 1980, 42, 445. K. Dietliker, W. Stegmann, and H. Heimgartner, Heterocycles, 1980, 14,929 (Chem. Abstr., 1980,93, 238 239). H. D. Roth and M . L. M. Schilling, J . Am. Chern. SOC.,1980, 102, 7956. P. C. Wong and D. R . Arnold, Tetrahedron Lett., 1979, 2101.

Photochemistry

312

PiPh-N (125)

( 126)

Srinivasan and his co-workers 49 have continued their study of the behaviour of olefinic compounds when irradiated at 185 nm (6.7 eV photons). The irradiation of (127) under such conditions gave the diene (128) and the internal cycloaddition product (129) as the only detectable volatile products. The irradiation of the endoadduct (130) also gave the diene (128) and the same cycloadduct (129) but in addition the di-n-methane product (1 3 la) was observed. This compound had previously been shown to result from irradiation of the diene (128).” Separate direct irradiation of this diene (128) also revealed that the other di-n-methane product (131b) was also formed at high conversions. The principal product from the irradiation of the endo-olefin (1 32) was the diene (133) and the adduct (1 34).

Several minor products were also detected but not identified. The exo-isomer (135) yielded the adduct (134) with no trace of the diene (133). Again several minor products were detected. A theoretical analysis of these systems was r e p ~ r t e d . ~ ’ Fission of a cyclopropane bond also occurs following the irradiation (254nm) of the tricyclohexene (1 36) in ethanol. The products formed are shown in Scheme 12. The dependence of the amounts of product on irradiation time showed that products (1 37 and 138) are the primary photoproducts and that the others are derived by secondary phot~lysis.~ 49

R.Srinivasan, J. A. Ors, K . H. Brown, T. Baum, L. S. White, and A. R. Rossi, J . Am. Chem. SOC.,

50

1980, 102, 5297. R. R. Sauers and A. Shurpik, J . Org. Chem., 1968, 33, 799.. A. P. Kouwenhoven, P. C. M. van Noort, and H. Cerfontain, Tetrahedron Lett., 1981, 22, 1745.

51

Photochemistry of Olejins, Acetylenes, and Related Compounds

& &

+

R' = H, R2 = Me =

products 2 unidentified

+

---+

R'

313

R' = OMe, R 2 = H R' = H,R 2 = OMe

Me, R' = H

Scheme 12 Patents have been lodged dealing with the photoconversion of the dihydrofurans (139) into the cyclopropane derivatives (140).5 2 * Intramolecular cycloaddition was not encountered during the photolysis of the 1,3-divinylcyclobutane (141a). The products formed from the reaction were identified as the cyclopropanes (142). With the substituted compounds (141b) only

R 0 2 C Me Me a

M

X x ( 139)

q

c

CO,R

X = CI or Br R = H or Me

(140)

JdR g

R-

R'

R/RR2

R = H,n = 1 b; R = C02Me, n = I c; R = CO,Me, n = 2

(142) R ' = CH=CH,, R 2 = H R' = H, R2 = C H S H ,

(14)

(1 45)

(141) a;

k

(143) a; R' = R = C02Me, R 2 = H b; R' = H, R = R2 = C 0 2 M e

cis-trans isomerization results in the formation of ( 143).54Increase in the ring-size to the cyclopentane derivative (141c) brings a profound change in the photoreaction and this molecuIe yields the [2 + 21-adducts (144, 145). 52

53 54

H. G . Schmidt, Ger. Offen., 2851 957 (Chern. Abstr., 1981, 94, 3785). H. G. Schmidt, USP, 4 198341 (Chern. Abstr., 1980, 93, 71 536). W. Trautrnann and H. Musso, Chem. Ber., 1981, 114, 982.

Photochemistry

314

The direct irradiation of the anion (146) using visible light (A > 450nm) leads to the formation of the cyclized product (147) formed by protonation of (148) and the formation of a polymer of undetermined c o n ~ t i t u t i o nWhen . ~ ~ the irradiation was carried out in the presence of benzophenone, thought to act as an electrontransfer agent, a quantitative yield of the cyclopropyl derivative (147) was obtained.

3 Diene Isomerization Baldry 5 6 , 5 7 has studied the influence of aryl substituents on the photoreactions shown by arylbutadienes (149). The author 5 6 * 5 7 concludes that the formation of the products (150), (151), and (152) correlates with the ground-state CT or CT’ substituent constant rather than with the excited-state constant nex.The mechanism for the formation of the products (150-1 55) was also discussed. Product (153) A

r

w

( 149)

Ar

Ar

=

% ( 1 50)

Ph, 3-MeC,H4, 4-MeC,H4, 2,4,6-Me,C6H,, 3-C1C,H4, 4-ClC6H4, 3-MeOC,H4, 4-MeOC,H4, or 4-Me2NC,H, A

r (151)

G

A

r

d

e

(152)

presumably arises by valence-bond isomerization of the diene. This is also reported 5 8 for the formation of (1 56) from 2,3-dimethylbuta-l,3-diene. In an effort to mimic the conditions encountered in ‘in vivo’ irradiation in the epidermis, the irradiation of 7-dehydrocholesterol (157) in various ordered lipid multilayers has been studied.59The results (Table 4 and Scheme 13) clearly show ” J6 57

59

D. H. Hunter and R. A. Perry, J. Chem. SOC.,Chem. Commun., 1980, 877. P. J. Baldry, J. Chem. SOC.,Pwkin Trans. 2, 1980, 805. P. J. Baldry, J. Chem. SOC.,Perkin Trans. 2, 1980, 809. A. V. Dolidze, M. V. Kodanashvili, and Kh. I. Areshidze, Izv. Akud. Nuuk. Gruz. SSR, Ser. Khim., 1980, 6 , 88 (Chem. Absrr., 1980,93, 149839). R. M. Moriarty, R. N. Schwartz, C. Lee, and V. Curtis, J. Am. Chem. SOC.,1980, 102, 4257.

Photochemistry of Olefins, Acetylenes, and Related Compounds Table 4 Products from irradiation of (1 57) in lipid multilayers System Dilauryl-L-a-phosphatidylcholine Distearyl-L-a-phosphatidylcholine Dimyristoyl-L-a-phosphatid ylcholine Dipalmitoyl-L-a-phosphatidylcholine Thin film Hexane solution

Filter quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex

315

’’

(157)

(158)

(159)

(160)

(161)

(%I

(%I

(%I

(%I

(%)

88.1 82.8 89.2 83.3 85.2 81.9 88.5 81.9 96.4 100 27.2 46.4

8.2 6.45 7.0 6.15 9.2 6.3 7.2 6.2 2.7 0 20.7 21

0.6 0.43 0.87 0.97 1.9 1.1 1.3 1.3 0.87 0 4.9 3.3

0.95

2.1 7.9 2.0 6.7 2.7 9.1 2.2 8.5 0 0 2.1 8.5

2.4

0.9 2.8 1.0 1.6 0.6 1.9 0 0 44.9 19.9

(159)

1. i HO

HO’

the difference between the lipid reactions and the thin-film process in that conversions are lower in the thin film and the products (160) and (161) are absent. Irradiation in hexane solution shows that tachysterol(l60) is the major product, whereas in the lipid material this product is minor. The authors5’ suggest that the membrane effect discernible in these experiments is due to the influence on the opening of the starting material to the triene (1 58). Since rotation is restricted in the membrane conversion to (158) and (1 60) is disfavoured. The irradiation of the dehydrocholesterol analogues (1 62) results in the formation of the ring-opened vitamin D,

316

Photochemistry

compounds (163).60The ring-opening process and the 1,7-antarafacial hydrogenmigration path is the same as that encountered in the transformation of the parent. Further work by Moriarty and Paaren61 has included the study of the stereochemistry of the photochemical-thermal conversion of dehydrocholesterol into vitamin D,. They61 argue that the key to the stereochemical problem is the thermal 1,7-hydrogen transfer and have approached its solution by the synthesis of the deuterium-labelled dehydrocholesterol (164). Irradiation and thermal transformation affords the vitamin D, (165) with 26.4% hydrogen in the C-l9(Z) position. They argue that this transformation can only arise from a left-handed conformation of the triene (166) produced by photochemical ring-opening of the diene starting material.

&R

R '0 (162) a; R' b; R'

= R2 = Ac = Ac, R2 =

Me

Irradiation of 7,8-didehydrocholesterol (167) at 3 10-3 12 nm gave the previtamin D, (168, 20.4%),lumisterol, (169, 5.979, and vitamin D, (1 70, 69.7%).62 The position of the photoequilibrium between the cis- and the trans-isomer of vitamin D is dependent upon the energy of the triplet sensitizer employed.63 Vycor-filtered irradiation of the diene (1 67) in pentane afforded the triene (168) in a photoequilibrium of diene: triene 30: 70.64 When the diene (167) was irradiated at 270-330nm the triene was absent and the product was identified as the tricyclononene (169). Normally the diene (167) was prepared in situ by the decarbonylation of the ketone (170). This afforded a ready method for the preparation of large quantities of the diene and also permitted the successful " 61

62 63

'4

R. M. Moriarty and H. E. Paaren, J . Org. Chem., 1981,46, 970. R. M. Moriarty and H. E. Paaren, Tetrahedron Lett., 1980, 21, 2389. R. I. Yakhimovich and V. P. Vendt, Khim.-Farm. Zh., 1980, 14,93 (Chem. Abstr., 1980,93, 46993). J. W. J. Gielen, R. B. Koolstra, H. J. C . Jacobs, and E. Havinga, Red. Truv. Chim. Pays-Bus, 1980,99, 306. W. G. Dauben and M. S. Kellogg, J . Am. Chem. SOC.,1980, 102,4456.

317

Photochemistry of Olejins, Acetylenes, and Related Compounds 0

completion of preparative runs. At high conversions another product was isolated and identified as the cyclononene (171). The authors 64 endeavour to explain the wavelength dependence of the system as a result of facile closure of the triene (168) back to starting material. However, an additional feature of the system would suggest that the cyclohexadiene ring in (168) will be skew rather than planar. The temperature-dependent photochemistry of the system is in accord with this since the efficiency of ring-opening (167-1 68) increases with decreasing temperature. This is a further example of the control exercised on the photochemical reactivity of a molecule by the ground-state conformation. A reinvestigation of the photoreaction of (172) has shown that it is converted into the two products (173) and (174). The absence of (175) or (176) contrasts with the behaviour of diene (167). The reactions of the diene (172) did not show a wavelength dependence. The

&I$-J($J~(y \

H

H

H

(1 72)

( 173)

( 174)

(175)

(176)

two photoproducts formed from the irradiation of the diene (1 77) were identified as (178) and (179). The wavelength dependence of this system is not as marked as

H (177)

(1 78)

(1 79)

that seen for diene (167). However, it was seen that the irradiation at shorter wavelengths favoured the formation of the triene (178). In another study Dauben and Olsen 6 5 have further studied the question of ground-state conformation control of the photo-ring-opening of cyclohexadienes. They propose that ringopening will follow the path that involves the least motion. The ring-opening reactions of the dienes (180) and (181) are in accord with this postulate and yield the trienes (182) and (183), respectively. These trienes are very thermally labile and convert readily into (172) and (1 84). The diene (185), however, has been shown to yield the all-cis-triene (186). The authors 6 5 argue that the path followed by this diene (185) is dictated by the strain inherent in the bicyclic structure. The photochemical ring-closure of the trienes (182) and (183) afford the starting materials. However, triene (186) also yields the photoproduct (187). Dauben and 65

W. G . Dauben and E. G. Olsen, J . Org. Chem., 1980,45, 3377.

318

Photochemistry

rn

&& H

H

H

H

(1 84)

(1 85)

( 182)

QH

(1 86)

(187)

his co-workers 66 have published a review dealing with the photorearrangements of trienes. Direct irradiation at 254 nm of the acetal(l88) leads to two reaction modes, viz, valence-bond isomerization to yield (189, 3%), and bond fission to yield the Me Me

Me Me

0 1

0

Me

Me

(188)

M@Me

Me Me

(190)

(189)

biradical(l90) which ultimately affords products (191,4%E and 60x2).Acetonesensitized irradiation of (188) yields the same enones (191) as 2 - E isomers in 7% Me Me

Me

Me Me

0

(193)

(20%)

Me

254 nrn

CHz (9%)

(3%)

(10%)

(34%)

Scheme 14 66

W. G . Dauben, E. L. McInnis, and D. M. Michno, Org. Chem., 1980, 42, 91.

Photochemistry of Olefins, Acetylenes, and Related Compounds

319

and 3%, respectively, as well as a low yield (9%) of the ketone (192).67A study of the photochemical behaviour of the acetal (193) was also carried out and direct irradiation was shown to yield the products indicated in Scheme 14. Irradiation of the sultone (194) in methanol affords the ring-opened products (195) and (196).68 Subsequent irradiation of these compounds brings about elimination of the S0,Me group and formation of the fluoranthene (197). This compound is thought to be the result of cyclization within the anion (198).

4 Reactions of Trienes and Higher Polyenes Direct irradiation of the benzcycloheptene (199a) gave the two isomeric products (200) and (201) in a temperature- and solvent-independent ratio of 95 : 5.69 The influence of substituents was obvious from the fact that the irradiation of (199b) exhibited solvent dependency and the yield of the products (200) and (201) showed an increasing predominance of the endo-product. The sensitized irradiation was less efficient.

\

/

-

(199) a; R' = CH,CO,Me b; R' = CN

(200)

Arnold and his co-workers 70 have reported the electron-transfer-induced photodimerization of 1,l-diphenylethylene. This reaction is thought to proceed to the triene (202a) which, in the absence of other reaction paths, undergoes hydrogen migration to afford the product (203).70When the reaction is carried out 67 69 'O

K. Murato, B. Frei, H. R. Wolf, and 0. Jeger, ffelv. Chim. Acra, 1980, 63,2221. J. L. Charlton and G. N. Lypka, Can. J. Chem., 1980, 58, 1059. H. Kobayashi, K. &to, M. Kato, and T. Miwa, Koen Yoshishu-Hibenzenkei Hokozoku Kagaku Torunkai Kozo Yuki Kadaku Toronkai,12th, 1979, 13 (Chem. Abstr., 1980, 92, 214528). D. R. Arnold, R. M. Borg, and A. Albini, J. Chem. SOC.,Chem. Commun., 1981, 138.

320

Photochemistry

a

in the presence of acrylonitrile, for example, the triene is trapped as the ene-adduct (204a). An analogous reaction sequence affords the adduct (202b) from the crossed addition of 1,l-diphenylethylene with methylpropene.

Ph Ph

RR (202) a; R b; R

@2CH2CN

=

Ph

=

Me

R R (204) a; R = Ph b ; R = Me

(203)

A study of the photoequilibrium involving 1,5-hydrogen transfer between the isomeric cycloheptatrienes (205a) and (205b) has been r e p ~ r t e d .The ~ influence of substitution in the aryl ring, e.g. (206), has also been studied.'* Irradiation of the diazepins (207) affords the bicyclic compounds (208).73This result, valence-bond isomerization, is in contrast with the thermal treatment of this compound which yields the 1,3-diazepins (209). These compounds undergo photochemical ring-closure to yield the bicyclic compounds (210). In some instances the bicyclic compounds of similar structure to (210) are also photolabile, as with (21 I), which on irradiation (254nm) yields the acetylene (212) and the imidazole (2 13). 74 R Q - R ' /

R3 (205) a; R ' = p-NMe,C,H,, R2 = C,H,, R 3 = H b; R' = H, R 2 = C,H,, 'R3 = p-NMe2C6H,

(206) R = H, F, C1, Br, Me, MeO. MeOC,H,CH=CH

C02Et (207) R ' = Me, R2 = H; R' = H, R2 = Me; R' = OMe, R2 = H; R' = H, R2 = OMe; R' = Me, R2 = Me; R ' = NHAc,R2 = H; R' = H , R 2 = NHAc;R' = NEt,, R Z = H

(208) 71

'' 73 74

(209)

(210)

W. Paulick, W. Abraham, and D. Kreysig, J . Prakt. Chem., 1980,322, 499 (Chem. Abstr., 1980, 93, 238 404). W. Abraham, K. Buck, and D. Kreysig, Z . Chem., 1980, 20, 214 (Chem. Abstr., 1980, 93, 238394). T. Tsuchiya, J. Kurita, and H. Kojima, J . Chem. Soc., Chem. Commun., 1980, 444. Y. Kobayashi, T. Nakano, M. Nakajima, and I . Kumadaki, Tetrahedron Lett., 1981, 22, 1369.

Photochemistry of Olefns, Acetylenes, and Related Compounds

(2 12)

(21 1)

321

(213)

Irradiation of perfluorocyclo-octatetraeneat 254 nm yields the anti- and syndienes (214) and (215).75 The ions (216) can be prepared by protonation of the corresponding 2,3homotropones in fluorosulphonic Irradiation (A > 360 nm, - 70 "C) of the ions leads to their isomerization. The selectivity shown in the photoisomerizations is attributed to the circumambulatory migration of the C-8 group via intermediates such as (2 17-2 19). Photoisomerization about the C- 1 - 4 and about the C-2-C-3 bond of the ally1 cations (220-222) has been r e p ~ r t e d : 'cf ~ the earlier preliminary report. 78 Childs 79 has reviewed the photochemical reactions of protonated unsaturated compounds.

I

I(

R2

R2

OH

R'

= R2 = H (217) b; R' = R2 = Me c; R' = Me, R2 = H

(216) a;

(220)

(2 18)

(22 1)

(219)

(222)

Barltrop et a1." have reported a study of the phototranspositions of alkylsubstit uted pyrylium cations. Sugawara and Iwamura have reported the photoproduction of the nitrene

''

75

A. C. Barefoot, tert., W. D. Saunders, J. M. Buzby, M. W. Grayston, and D. M. Lemal, J. Org. Chem., 1980, 45,4292.

76 77

78

l9 8o

*'

R. F. Childs and C. V. Rogerson, J . Am. Chem. Soc., 1980, 102, 4159. R. F. Childs and M. E. Hagar, Can. J . Chem., 1980, 58, 1788. R. F. Childs and M. E. Hagar, J . Am. Chem. SOC.,1979, 101, 1052. R. F. Childs, Rev. Chem. Intermed., 1980, 3,285 (Chem. Abstr., 1980, 93,203427). J. A. Barltrop, A. W. Baxter, A. C. Day, and E. Irving, J . Chem. Soc., Chem. Commun., 1980, 606. T. Sugawara and H. Iwamura, Kokaguku Toronkai Koen Yoshishu, 1979,78 (Chem. Abstr., 1980,93, 70 605).

322

& /

Photochemistry

/ \ - ,

NC

(223) from azatriptycene (224). The nitrene yields the azepine (225) and the adduct (226) when the reaction is carried out in the presence of tetracyanoethylene. 5 12

+ 21 Intramolecular Additions

Photocyclization of the methylenenorbornadienes (227a) and (227b) yields the quadricyclanes (228), which can be converted by ozonlysis into the two quadricyclanones (229).82The thermal cyclQadduct (230), obtained from the furan (23 1) and cyclo-octyne (232), undergoes photocyclization to yield the oxa-quadricyclane derivative (233).83This compound undergoes thermal conversion to the oxepin

Pr (227) a; R'-R' b; Rl-R'

=

(CH,),, R 2 = C 0 2 M e , R3 = H R 2 = H, R3 = CO,Me

= (CH,),,

AR3

Pri

83

H . P. Figeys, M. Destrebecq, and G . Van Lommen, Tetrahedron Lerr., 1980, 21, 2369. W. Tochtermann and P. Rosner, Tetrahedron Lett.. 1980, 21, 4905.

Photochemistry of Olefins, Acetylenes, and Related Compounds

323

derivative (234). The influence of a coppper(1)-nitrogen catalyst on the conversion of norbornadiene to quadricylane has been assessed.B4A kinetic study of the behaviour of quadricyclane as an electron donor has been reported.85 Photocyclization of the alcohols (235) in the presence of ‘copper triflate’ has been reported to yield the products (236).86 The stereochemistry of the alcohols was not fully established but the results are interesting in that the stereochemistry of the hydroxy- group does not seem to play a major part in the reaction since either of the two isomers cyclize readily. The authorsB6 suggest that the coordinated copper ion is not intimately involved in the transition state leading to product. Irradiation of the dienes (237) and (238) brings about ring closure to the propellanes (239) and (240), respectively.” Irradiation of the related diene (241) gave only the isomeric compound (242) by a 1,3-hydrogen migration. The

84

K. Maruyama, K. Terada, Y. Naruta, and Y. Yamamoto, Chem. Lett., 1980, 1259 (Chem. Absfr.,

85

G. Jones, 11, S, Chiang, W. G. Becker, and D. P. Greenberg, J . Chem. SOC.,Chem. Commun., 1980,

86

J. E. McMurry and W. Choy, Tetrahedron Lett., 1980, 21, 2471. R. Bishop and A. E. Landers, Aust. J . Chem., 1979,32, 2615.

1981, 94, 64866). 681. 87

324

Photochemistry

Me Me (243A)

M;:

Me Me

Me (243B)

'Me

V

Me

Me

(243C)

1

IVY/

Me

Me

Scheme 15 X

I b*

14 (249)

eH2-

X = 0, N H , NMe, or NPh

Y = - CH,

Me

Photochemistry of Olefins, Acetylenes, and Related Compounds 325 germacrene system (243)afforded the products shown in Scheme 15.88 The type of cyclization mode adopted depends on the ground-state conformation. Thus conformation (243A)yields the adduct (244)whereas (243B) leads to the three products (245),(246),and (247),and conformation (2436)gives (247)and (248).89 Ashkenazi et al.'* have reported intramolecular cycloaddition in the cyclic structure (249) to afford the cycle of cage molecules (250).

6 Dimerization, Intermolecular Cycloaddition, and Reactions of Acetylenes The three dimers (251-253) are formed from the xylene-sensitized irradiation of cyclohexene. Regardless of the solvent used, the cis-trans-product (252) predominates. It is reasoned that the dimers are produced by a non-stereospecific

& & H H

H H

(25 1)

(252)

(253)

addition of cis- and trans-cycl~hexene.~~ Cycloheptene fails to yield dimers under the same condition. Various cyclobutane derivatives have been synthesized by the direct or sensitized irradiation of indene as shown in Scheme 16.The compounds were required for a detailed study of the electron-transfer-induced monomerization of the ad duct^.^^

Indene

I1 I'

& ' H

Illdene

h

F

13

X

Ph

H I

Scheme 16 The two adducts (254) and (255) are formed from the irradiation of trans93 The two adducts are stilbene in the presence of trans-3-phenylacrylonitrile. themselves photolabile and are converted into cis- and trans-stilbene and cis- and 88

89

90 91

92 93

P. J. M. Reijnders, R.G. van Putten, J. W. De Haan, H. N. Koning, and H. M. Buck, Red. Trav. Chim. Pays-Bas, 1980,99, 67. See also references 64-66 for other examples of conformational control. P. Ashkenazi, R.D. Macfarlane, W. A. Oertling, H. Wamhoff, K. M. Wald, and D. Ginsburg, Angew. Chem. Int. Ed. Engl., 1980, 19, 933. P. J, Kropp, J. J. Snyder, P. C. Rawlings, and H. G. Fravel, jun., J. Org. Chem., 1980, 45, 4471. T. Majima, C. Pac, and H. Sakurai, J. Am. Chem. Soc., 1980, 102, 5265. T. Kitamura, S.Toki, and H. Sakurai, Kokaguku Toronkai Koen Yo'oshishu,1979, 190 (Chem. Abstr., 1980,93,70806).

Photochemistry

326

trans-3-phenyiacrylonitrile.The authors 93 suggest that the steric interactions of the phenyl groups in (255) are greater than in (254). The regiospecific photocyclization of olefins (256) to cyanophenanthridine (257) yields the two adducts (258) and (259).94Photoaddition of 2-cyanopyridine to olefins affords the readily hydrolysable imines (260) isolated as the ketones (26 l).95

ph\dPh

ph\qPh Ph

Ph'

CN

'CN

(255)

(254)

(256) R'CH = CHR2 R' = R 2 = p-MeOC,H,, Me, PhO, or H

(257)

& NH

0

~

The benzophenone-sensitized addition of chlorofluoro-olefins (262) to indene has been The identity of the adducts (263) was established by detailed spectroscopic analysis. The mechanism of the addition is believed to involve biradicals such as (264). R'

R3

X

&jl \

y4

9s 96

*cCl, W \

L

F

2

H

S. Futamura, H. Ota, and Y. Kamiya, Chem. Letf., 1980, 655 (Chem. Ahstr., 1980, 93, 238631). I. Saito, K. Kanehira, K. Shimozono, and T. Matsuura, Tefruliedron Lett., 1980, 21, 2737. H . Kimoto, K. Takahashi, and H . Muramatsu, Bull. Chem. SOC. Jpn., 1980, 53, 764.

Photochemistry of OleJins, Acetylenes, and Related Compounds

327

Caldwell 9 7 has reported a method for the prediction of reactivity for allowed + 21 and [4 41 cycloaddition reactions. The triplet state of the alkyne (265) is involved in the photochemical reactions with di-isopropyl ether. The proof that a triplet is involved was obtained from quenching and sensitization studies. The products (266, 267) obtained from the reaction arise from hydrogen-abstraction and radical-combination reaction^.'^

+

[2

w~~

HC ECC0,Me

C0,Me

(265)

(266)

M e OMe k Me c o 2 M e (267)

The irradiation of benzisothiazole (268) in the presence of dimethyl acetylenedicarboxylate is thought to proceed by initial N-S fission to yield the biradical intermediate (269, Scheme 17). This intermediate is trapped by the acetylene to

(268) a; R ' = H , R2 = H b; R ' = H, R2 = CI C; R ' = CI, R 2 = H

(270)

CN (271 j

Scheme 17 yield the cis-trans mixture of esters (270) and the thiophen (271) as the main products of a complex reaction mixture. The details of the formation of products are shown in Scheme 1 7.99 With electron-rich-olefins, however, cycloaddition occurs with benzisothiazole (272) to yield the adduct (273), again as a result of trapping of a biradical such as (269).'0°

R'

"

,

d

R'

N

= R2 = H b; R' = Me. R2 = H C; R' = H . R 2 = C1

(272) a; R '

'9 98

99 loo

R. A. Caldwell, J . Am. Chem. SOC.,1980, 102, 4004. H. Hasegawa, A. Kimura, and M. Takayama, Wusedu Daigaku Rikoguku Kenkyusho Hokoku, 1979, 44 (Chem. Abstr., 1980, 92, 163 327). M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Left., 1981, 22, 525. M. Sindler-Kulyk and D. C. Neckers, Tetruhedron Left., 1981, 22, 529.

328

Photochemistry

7 Miscellaneous Reactions The photochemical reversion of the cage compound (274) into the diene (275) has been studied by Mukai and his co-workers."' The process can be brought about by various catalysts such as ZnO or CdS. These experiments are related to the utilization of strained cage compounds as a means of energy storing. Mukai et al. l o 2 have further reported on their detailed study of the cycloreversion reactions of cage compounds (276) involving electron-transfer processes. Another report has described work with cationic sensitizers (277).'03

The cycloreversion of the cyclobutane (278) to the olefin occurs from the singlet state on irradiation at 265 nm. '04 Triplet-state reactivity is reported for cycloreversion using A = 347 nm. The isomerization of 1,2-diphenylcyclobutaneshas been used as a means of establishing the efficiency of electron-transfer processes in the phenanthreneedicyanobenzenesystem. l o 5 Meier and Kolshorn lo6 have reported the results obtained from a study of the conversion of oxirens and thiirens to the open-chain isomers. Photochemical rearrangement of the epoxyolefins (279, 280) gives the dihydrofuran derivatives (281, 282).'07 Direct irradiation of the epoxydiene (283) is reported to yield products derived from the fission of the C--C bond of the oxiran (Scheme 18). Other systems studied in this report are the trienes (284) and (285) whose photochemical behaviour is analogous to that reported for (283). Acetonesensitized irradiation of (289, however, yields products from the fission of a C - 0 Iol lo2

lo4 lo'

lo'

K. Okada, K. Hisamitsu, and T. Mukai, J. Chem. Soc., Chem. Commun., 1980, 941. T. Mukai, K. Sato, and Y. Yamashita, J. Am. Chem. Sor., 1981, 103, 670. K. Okada, K. Hisamitsu, and T. Mukai, Tetrahedron Left., 1981, 22, 1251. S. Takamuku and W. Schnabel, Chem. Phys. Lett., 1980, 69, 399. T. Gotoh, M. Kato, M. Yamamoto, and Y. Nishijima, J. Chem. Soc., Chem. Commun., 1981, 90. H. Meier and H. Kolshorn, Z. Nafurforsch., Teil B, 1980, 35, 1040 (Chem. Abstr., 1981, 94, 3515). W. Eberbach and J. C. Carre, Chem. Ber., 1981, 114, 1027.

Photochemistry of Olejns, Acetylenes, and Related Compounds

I-naphthyl

329

"C0,Me (278)

(279) a; R = H, fi = 1 b; R = CO,Me, n = 1 c; R = CO,Me, n = 2

(280)

(282)

(281) a; R = H , n = 1 b; R = CO,Me, n = 1 c; R = CO,Me, n = 2

bond (Scheme 19).lo8 C - 4 Bond fission also accounts for the photoinduced (254nm) formation of the ketone (286) from (287).lo9

(283)

Scheme 18

The regio- and stereo-selective ring opening of the oxaziridines (288) on photolysis to yield the lactams (289) has been reported.' l o The stereo-electronic

.

(286) lo'

lo9 'lo

(287)

-.

R

(288) n = 1, 2, 3, 4,8, 9; R = H n=Ior2;R=Me

A. P. Alder, H. R. Wolff, and 0. Jeger, Helv. Chim. Acra, 1981, 64, 198. D. Avnir and J. Blum, J. Heterocycl. Chem., 1980, 17, 1349. E. Oliveros, M. Riviere, and A. Lattes, N o w . J . Chim.,1979,3,739 (Chem.Abstr., 1980,92, 163 322).

330 Photochemistry control is due to rupture of a C--C bond that lies quasi-antiperiplanar to the nitrogen lone pair. The authors l o suggest that oxaziridines are intermediates in the photo-Beckman reaction. Irradiation of the chromene (290) in benzene afforded the styrene (291) and the ketene (292) which was detected by low-temperature i.r."' The presence of a ketene intermediate was confirmed chemically by irradiation of the chromene (290) in methanol when the ester (293) was obtained. The styrene photoproduct (291) is clearly a secondary product formed by the photodecarbonylation of the ketene to yield a carbene (294) which rearranges to the styrene. The route to the primary product (292) is thought to involve the conversion of the chromene into (295), which subsequently undergoes H or D transfer to affford the ketene (292). The o-xylylene intermediate (295) could not be trapped as a Diels-Alder adduct, presumably as a result of a rapid hydrogen-transfer process. The benzopyran (296) undergoes ring cleavage to yield (297) on irradiation in ethanol.'12 The product (297) is accompanied by the novel cyclized product (298), which is derived from (297) by a second photochemical step. The acetophenone-initiated reactions of tetrahydropyrans (299) have been described. l 3

Me

Me (290) R

=

H or D

(293)

Me (294)

Irradiation of the iodoalkane (300) in the absence of oxygen and with the removal of hydrogen iodide results in the formation of the alkene (301).'14 In contrast with this result, irradiation of the iodoalkene (302) yields a product from an ionic process. The reactions of the iodides (304-306) have been studied.' l 5 'I' 'I2

'I3

J. M . Hornback and B. Vadlamani, J . Org. Chem., 1980, 45, 3524. A. Bowd, J. Turnbull, and J. D. Coyle, J. Chem. Res. ( S ) , 1980, 202. B. W. Babcock, D. R. Dimmel, D. P. Graves, jun., and R.D . McKelvey, J. Org. Chem., 1981,46,736. J . L. Charlton, G . J. Williams, and G. N. Lypka, Can. J . Chem., 1980, 58, 1271. K. M . Saplay, R. Sahni, N. P. Damodaran, and S. Dev, Tetrahedron, 1980, 36, 1455.

Photochemistry of OleJins, Acetylenes and Related Compounds

331

I (300)

(301)

Quantum yields for the photodechlorination of insecticides of the type (307) have been obtained. Discussion of the mechanism in terms of C-CI bond fission and the generation of radical pairs was made.'16 Cristol and his co-workers ' I 7 have reported the results of the photolysis of the chloro-compounds (308). The results from this work have given an insight into the stereochemistry of the photochemical reactions.

(307) R

= CH=CH(CH,),,

n

= 1

4

(309) a; R = Br (308) a; R' = H, R 2 = C1, R 3 = H b; R = C1 b; R' = C1, R2 = H, R 3 = H c; R = OMe c; R' = H, R2 = C1, R 3 = M e 0 d; R = OEt d; R ' = H, R Z = R 3 = C1 e; R = OCHMe, f:R=OH

1-Haloadamantanes (309a, b) are formed from the ethers (309c-f) when they are irradiated in haloalkanes (CC1,Br or CCI,). ' 1 8 The phospholene (3 10) undergoes photofragmentation to afford 2,3dimethylbuta- 1,3-diene and (3 1 l ) , a product derived from the intermediate 'I6

'I7

'"

H. Parlar and F. Korte, Chemosphere, 1979,8, 873 (Chem. Abstr., 1980, 93, 70444). S. J. Cristol, R. J. Opitz, T. H. Bindel, and W. A. Dickenson, J. Am. Chem. Soc., 1980, 102, 7977. R. Perkins, Chem. Ind. (London), 1980, 700 (Chem. Abstr., 1981, 94, 83665).

332

Photochemistry

(312).'l9 The product (311) is also photolabile and is converted during the photolysis into the derivative (313). Irradiation of the cyclopentadiene (314) as a liquid or in solution a'ffords an 12' intermediate species identified as the free radical (31 Two reports have described the photochemical behaviour of triarylmethyl cations. 22* 5 ) . ' 2 0 9

5

Phi=S (312)

II PhP(OMe), (313)

Me

"'

IZo

H. Tomioka, S. Takata, Y. Kato, and Y. Izawa, J. Chem. SOC.,Perkin Trans. 2, 1980, 1017. A. G. Davies and J. Lusztyk, J. Chem. SOC.,Chem. Commun., 1980, 554. A. G. Davies and J. Lusztyk, J. Chem. SOC.,Perkin Trans. 2, 1981, 692. L. M. Tolbert, J . Am. Chem. SOC.,1980, 102, 3531. L. M. Tolbert, J . Am. Chem. SOC.,1980, 102, 6806.

4 Photochemistry of Aromatic Compounds ~

~

~~

BY J. D. COYLE

1 Introduction The interest in photoreactions that involve chemical change in an aromatic ring continues at a high level. Aromatic photosubstitution reactions have assumed a greater importance than they once had, but the classification of these reactions on a mechanistic basis is not easy because one of several different mechanisms may operate, and published information may not be sufficient to distinguish between the likely possibilities. However, it is clear that straightforward photochemical electrophilic substitution is as yet of very limited importance. Various thermal and photochemical rearrangements of the benzene ring have been reviewed including valence isomerization and ring transpositions, and, fairly briefly, a range of other reactions that can be classed formally as rearrangements.

2 Isomerization Reactions Valence-bond isomers of aromatic compounds (both 6-membered and 5-membered) that are stabilized by trifluoromethyl groups are reviewed,2 and it is concluded that both steric and electronic effects contribute to the stabilizing influence of the CF, group. A fascinating example is provided of a substituted Dewar benzene (1) that is more stable thermodynamically than the isomeric

'

BU'

Bu'

'".*B tu hv

+

CO,Me

Bu'

"'Q:g:;: Bu'

Bu'

(1)

benzene; the benzene can be generated by irradiating the Dewar benzene. Gasphase photoisomerization of trifluoro- and tetrafluoro-benzenes and of a tetrafluorotoluene gives mainly Dewar isomer^.^ However, the high-temperature ( > 1000 "C) thermal ring-transposition reactions of the three difluorobenzenes D. Bryce-Smith and A. Gilbert, in 'Rearrangements in Ground and Excited States', ed. P.de Mayo, Academic Press, New York, 1980, Vol. 3, p. 349. Y. Kobayashi and I. Kumadaki, Ace. Chem. Res., 1981, 14, 16. G. Maier and K. A. Schneider, Angew. Chem., Int. Ed. Engl., 1980, 19, 1022. B. Sztuba, E. Ratajczak, M. Pieniazek, A. Grzybala, and R. Janusz, Bull. Acad. Pol. Sci., Ser. Sci. Chim., 1979, 27, 581.

333

334

Photochemistry F

Q+pJ:.Q,;.l

F

F

QF=(J F

(2)

(e.g., 2) can best be rationalized5 on the basis of a benzvalene mechanism or something equivalent to it; one source of uncertainty in these results is that defluorination and polymerization occur to a large extent as competing processes. A theoretical description (based on INDO/S calculations) of the benzene-toDewar benzene isomerization suggests that the photoreaction is more likely to occur through a singlet state (which is in keeping with an earlier report that reaction occurs via S 2 benzene), although the thermal re-aromatization of Dewar benzene may give a small yield of triplet ( 3 B 1 , )benzene. On irradiation in solution 9-t-butylanthracene, unlike other 9-substituted anthracenes, gives a Dewar isomer (3), which reverts thermally to the parent anthracene (t+at 20 "C = 6.5 h).' Although the quantum yield is low (4 0.01), the absorption properties of this system make it more suited to further study for possible use in solar energy storage than many other photoisomerizations.

-

&

A , (3)

6

- 0.01

Photocyclization of the phenalenyl carbanion (4) can also be effected by visible light (A > 450nm), and the yield of the cyclized isomer is quantitative in the presence of benzophenone,8 which acts to suppress the competing electrontransfer and polymerization process. A pentafluoro-Dewar-pyridine, tentatively assigned the structure (5), has been isolated in very low yield from the complex mixture obtained in about 400 photolyses of pentaflu~ropyridine;~ its half-life is about 5 days at room temperature. Flash photolysis studies of pentafluoropyridine provide evidence for two azafulvene isomers (6) and (7), and it is suggested9 that an aza-benzvalene is the precursor to both the fulvenes and the Dewar isomer, although this mechanistic argument is quite speculative. The first hetero-benzvalene to be isolated and

'

L. T. Scott and J. R. Highsmith, Tetrahedron Lett., 1980, 21, 4703. M. Tsuda, S. Oikawa, and K. Kimura, h t . J . Quanrum Chem., 1980, 18, 157. H. Guesten, M. Mintas, and L. Klasinc, J . Am. Chem. SOC., 1980, 102, 7936. D. H. Hunter and R. A. Perry, J . Chem. SOC.,Chem. Commun., 1980, 877. E. Ratajczak, B. Sztuba, and D. Price, J . Photochem., 1980, 13, 233,

335

Photochemistry of Aromatic Compounds

characterized is that from tetrakis(trifluoromethy1)-l74-diphosphabenzene(8), and this isomer is quite stable at room temperature. 4-Alkoxypyridin-2-ones (9) undergo efficient photoisomerization to give bicyclic compounds, which on heating give a mixture of the original 4-alkoxypyridone and an isomeric 6-alkoxypyridone. Unlike many other pyridin-2-ones, the alkoxysubstituted derivatives show no tendency to undergo efficient [4 + 41photodimerization, and this accounts for the high yields of photoisomers that can be achieved. Further papers have appeared dealing with the photochemistry of OR

H 80-92%

0 II

Me

M~NHCCH=C/ \

N =C\

Me /

OMe

Me lo

Y . Kobayashi, S. Fujino, H. Hamana, Y. Hanzawa, S . Morita, and I. Kumadaki, J . Org. Chem., 1980, 45, 4683. C. Kaneko, K. Shiba, H. Fujii, and Y . Momose, J. Chem. Soc., Chem. Commun., 1980, 1 177.

336

Photochemistry

pyrimidin-4-ones. The trimethyl derivative (10) gives a bicyclic photoisomer that cannot be separated from unreacted pyrimidinone; however, its chemistry has been investigated and products isolated that result from abstraction of the methine proton by base (MeO-) or nucleophilic addition to the imino-group by methanol or methylamine. 2 * Dimethylpyrimidinones have also been studied, l4 as has the bicyclic derivative (1 1) that eventually gives an eight-membered lactam, 1 2 - l4 and a closely related sulphur-containing bicyclic system (12). In a slightly different heterocyclic system, an oxaza-bicyclic species (13) is an intermediate in the reversible photoisomerization of oxazinones.

MeNH,

cj?

H2

H

10% Me0

Ph

NH2

(R,R' = Me, Ph) (1 3)

Phototransposition reactions of hydroxypyrylium salts have been studied extensively, and now the first report has appeared l 7 of the corresponding reactions of pyrylium salts with only alkyl substituents. The reaction is efficient only when both C-3 and C-5 bear an alkyl group, and this is interpreted in terms of either an oxoniabenzvalene primary product (14) that re-aromatizes thermally in a concerted manner, or an oxabicyclohexenyl cation (1 5) whose formation involves an activation energy that is sensitive to the stability of the cation. These results are consistent with others from the irradiation of the pyrylium salts in water, where alternative, photohydration products are formed. Photorearrangemen t s of 5-membered heterocyclic aromatics are reviewed by Padwa. * Thiophen and 2-phenylthiophen photorearrangements are the subject

''

l3 l4

l5 l6

18

Y. Hirai, T. Yamazaki. S. Hirokami. and M. Nagata, Tetrahedron Lett., 1980, 21, 3067. S. Hirokami. T. Takahashi. M. Nagata, Y. Hirai, and T. Yamazaki, J . Org. Chenr., 1981, 46, 1769. S. Hirokami, Y . Hirai, T. Takashi, M. Masanori, and T. Yamazaki, Kokuguku 7oronkui Koen Yoshishu, 1979, 12 (Chem. Ahstr., 1980. 92, 197 575). T. Kato. N. Katagiri, U. Izumi, Y . Miura, T. Yamazaki. and Y. Hirai, Heterocycles, 1981, 15, 399. P. de Mayo, A. C . Weedon, and R. W. Zabel, J . Client. Soc.. Cltenr. Commun., 1980, 881. J . A. Barltrop, A. W. Baxter, A. C. Day, and E. Irving, J . Chern. Soc., Cltem. Cnmmun.,1980, 606. A. Padwa. in 'Rearrangements in Ground and Excited States', ed. P. de Mayo, Academic Press, New Ynrk. 1980, Vol. 3, p. 501.

337

Photochemistry of Aromatic Compounds

40

+

r

I

(14)

of an ab initio MO calculation,'g and it is concluded that two singlet excited states are involved, followed by cleavage of the C-S bond or by 'flapping' of the five ring atoms. Photoreaction of thiophens with amines gives pyrroles, and in an attempt to elucidate the mechanism of this reaction N-substituted 5azabicyclo[2.1.O]pentenes (16) have been prepared 2o from the corresponding sulphur compounds (in turn derived by photoreaction of tetrakis(trifluor0methy1)thiophen) and also cyclopropenyl imines (17). Neither of these species gives pyrroles in thermal reactions, although (16) rearranges to pyrroles on irradiation. It is proposed2' that the thiophenlamine reaction goes by way of nucleophilic attack by the amine on a 5-thiabicyclo[2.1.O]pentene intermediate (18), with initial attack at the thiirane ring as shown or at the double bond.

RNH, S

n-

NHR SH

ASH

RNH

The well documented photorearrangement of isoxazoles to oxazoles has been investigated theoretically,*' 2 2 and it is suggested that excitation of the aclyazirine 9

l9 2o

22

T. Matsushita, Y. Osamura, H. Tanaka and K. Nishimoto, Kokugaku Toronkai Koen Yoshishu, 1979, 114 (Cfiem.Abstr., 1980, 92, 180 534). Y . Kobayashi, A. Ando, K. Kawada, and I. Kumadaki, J . Org. Chem., 1980, 45, 2968. H. Tanaka, T. Matsushita, Y. Osamura, and K. Nishimoto, Kokagaku Toronkai Koen Yoshishu, 1979, 176 (Chem. Abstr., 1980,92, 197664). H. Tanaka, T.Matsushita, Y. Osamura, and K . Nishimoto, Int. J . Quantum Chem., 1980, 18,463.

338

Pho tochemistry

Q

-&

N-0

a

"R,a',"3+

N

N O 35% (R = H)

(20)

(12: R

62% (R = Me)

intermediate (19) to S1 (n,n* state associated with c----O) leads to isoxazole formation, whereas excitation to S , (n, n* state associated with C=N) gives the oxazole. The previously reported reaction of the bicyclic isoxazoles (20) has now 2 3 been described as a synthetic route to bridged oxazoles and imidazoles. Interestingly, with the isoxazolo[4,5-~]pyridines (21) a different formulation is used 24 for the intermediate as an acylnitrene species rather than an acylazirine, apparently on D

.

N-N

D

H O A

'CI

\R

(22) X = 0, NBz

= NMeNHMe

37-800/,

the basis of the alternative products (triazine or pyrazole) formed by intramolecular trapping of the intermediate. The mesoionic dithioles (22) undergo a similar 1,2-phototransposition of ring atoms,25 but it is proposed that a bicyclic valence isomer is an intermediate in this process. In the case of (22; X = 0), 23 24

25

E. M . Beccalli, L. Majori, A. Marchesini, and C. Torricelli, Chem. Lett., 1980, 659. G. Adembri, A. Camparini, D. Donati, F. Ponticelli, and P. Tedeschi, Tetrahedron Lett., 1981, 22, 2121. H . Tezuka, T. Shiba, N. Aoki, K. Iijima, and H . Kato, Kokagaku Toronkai Koen Yoshisl7~4,1979, 8 (Chern. Abstr., 1980, 92, 197661).

Photochemistry of Aromatic Compounds 339 tetraphenyl-l,4-dithiin and tetraphenylthiophen are also formed by way of an initial [4 + 4lcycloaddition of the original dithiole. Two further papers in a series on the generation of nitrilimines (RC=&NR’) by irradiation of sydnones suggest that the reactive excited state is a (n,n*) triplet state,26 and demonstrate again the use of the reactive nitrilimines in the synthesis of heterocyclic compounds.*’ In continuing studies on the formation of thiirens from 1,2,3-thiadiazoles (23), the parent thiiren has been characterized 28 in a lowtemperature matrix after photolysis of (23; R = R’ = H). Product analysis in experiments with 3C-substituted substrates suggests 29 that thiiren is formed to a considerable extent thermally but to a lesser extent photochemically from (23; R = H, R’ = Ph).

(23)

Finally in this Section, the saga continues of the photolysis of sym-tetrazines, with a report 30 that complexes between a nitrile (RCN) and HCN, or between two molecules of nitrile, can be formed and studied in a low-temperature matrix by irradiation of appropriately substituted tetrazines. 3 Addition Reactions A review 3 1 of the photochemistry of alkaloids includes reactions in which addition to an aromatic compound or substitution in an aromatic ring occurs. The second part32 of a review of the thermal and photochemical addition of dienophiles to arenes and their vinyl- and hetero-analogues covers additions to styrenes, stilbenes, and related systems. There is once again little to report in the way of photoaddition reactions to aromatic compounds that involve cleavage of the aromatic ring. Benzene can be ‘photomineralized’ (i.e. converted to carbon dioxide) by photolysis on silica or similar s ~ b s t r a t e s .More ~ ~ usefully for the synthetic chemist, pyridine-N-oxide (24) or its 4-methyl analogue undergo facile ring-cleavage on irradiation in the presence of aqueous amine, to give reasonable yields of 5-aminopenta-2,4dienenitriles.34

026

’’ 28

29

30 31

32 33 34

2-30;,

(24) G. Eber, S. Schneider, and F. Doerr, Bey. Bunsmges. Phys. Chem., 1980, 84, 281. K. H. Pfoertner and J. Foricher, Helv. Chim. Actn, 1980, 63, 653. A. Krantz and J. Laureni, J. Am. Chem. Soc., 1981, 103,486. U. Timm, U. Merkle, and H. Maier, Chem. Ber., 1980, 113, 2519. J. Pacansky and H. Coufd, J. Phys. Chem., 1980, 84, 3238. S. P. Singh, V. I. Stenberg, and S. S. Parmar, Chem. Rev., 1980. 80, 269. T. Wagner-Jauregg, Synthesis, 1980, 769. J. Schmitzer, S. Gaeb, and F. Korte, Chernosphere, 1980, 9, 663. J. Becher, L. Finsen, 1. Winckelmann, R. R.Koganty, and 0. Buchardt, Tetruhedron, 1981, 37, 789.

340

6

RR'NH

6 &

&NRRl+

or

NRR'

Photochemistry +

NRR'

NRR'

(25)

,$ F

RR'NH hv

F

F

,

\

F

/

F

F

(26)

The photoreaction of fluorobenzene (25) and the difluorobenzenes (26) with tbutylamine or diethylamine gives mixtures of 1 : 1 adducts arising mainly by 1,2addition to the ring,35 although with p-difluorobenzene the major products are derived by 1,4-addition. In all cases, products are also formed by substitution of a fluorine atom, and this is the only reaction for hexafluorobenzene and diethylamine. In a subsequent paper,36 the reactions of other substituted benzenes with these amines are described, and again addition and substitution products are both formed. Addition predominates for PhR (R = Me, C1, or CF,) and for rn- or p fluorotoluene; substitution is a major reaction for PhR (R = C1 or CN) and for anisoles and fluorotoluenes. A new type of acyclic adduct (27) is isolated from the product mixture from toluene and t-butylamine, and this may be formed by ringopening of an initial 1,2-adduct with a subsequent hydrogen shift.

(28)

In aqueous solution, phenylphosphonic acid gives phosphoric acid on prolonged irradiation, and an intermediate bicyclic species (28) has been identified;3 this represents an unusual acyclic 1,3-addition to a substituted benzene, related to the photohydration reactions of benzene itself and of pyridinium salts. Photoreduction of naphthalenes (and also of phenanthrene or anthracene) by sodium borohydride can be effected in the presence of an electron-acceptor such as rn- or p-di~yanobenzene.~'The naphthalenes are reduced to 1,4-dihydro35 36 37

A. Gilbert and S. Krestonosich, J . Chem. Soc., Perkin Trans. I , 1980, 1393. A. Gilbert, S. Krestonosich, and D. L. Westover, J . Chem. Suc., Perkin Trans. I , 1981, 295. M . Takahashi, J. Migita, and S. Takano, Nippon Noyaku Gakkaishi, 1980,5407 (Chem. Abstr., 1981, 94, 93 469). M . Yasuda, C. Pac, and H. Sakurai, J . Org. Chem., 1981, 46, 788.

Photochemistry of Aromatic Compounds

34 1

compounds (29), although 1-methoxynaphthalene also gives some 1,2-dihydroproduct (30), and 2-methoxynaphthalene gives a product (3 1) that incorporates part of the sensitizer molecule. The use of substituted borohydride reducing agents has been in~estigated:~’ product distributions are affected by the choice of reagent. 1,4-Dicyanonaphthalene gives products by photoaddition with toluene;40 one adduct (32) arises by straightforward 1,2-addition to the ring, and the other (33)

apparently by a subsequent reaction between a benzyl group and an unsaturated nitrile grouping. Replacement of one cyano-group by benzyl also occurs to a 39

M. Yasuda, C. Pac, and H . Sakurai, Kokagaku Toronkai Koen Yoshishu. 1979, 262 (Chem. Abstr.,

40

1980, 93, 94 535). A. Albini, E. Fasani, and R. Oberti, J. Chem. SOC.,Chem. Commun., 1981, 50.

342

Photochemistry

rn \

/

/

C6H12 hv’ 77

&+&

’\

/

/

/

(34)

certain extent. Photoreduction of anthracene in cyclohexane at 77 K gives 9,lOdihydroanthracene and 9-cyclohexyl-9,1O-dihydroanthracene(34), as well as 9cycl~hexylanthracene.~~ Similar photoadducts arise when phenanthrene is irradiated in glassy methylcyclohexane or in microcrystalline cyclohexane dispersed in liquid n i t r ~ g e n : ~as ’ shown previously, the reaction is biphotonic and involves an upper excited triplet state of the aromatic hydrocarbon. A principal product formed by irradiating quinoline-2-carbonitrile (35) in acidified aqueous propan-2-01 has two quinoline rings linked through the 2 4 ’ positions and has lost both cyano-groups. The mechanism put forward 43 for this formal 1,2-addition reaction begins with electron transfer from propan-2-01 to an upper triplet state of protonated ( 3 9 , followed by attack on a second (groundstate) molecule of (35). A photophysical study 44 of the photoreduction of acridine hv

Pr’OH, aq. HCI

’

ONH

(35)

H (36) 36%

19% 41

42

43 44

M . Lamotte, R. Ldpouyade, J. Pereyre, and J. Joussot-Dubien, J . Chem. Soc., Chem. Commun., 1980, 725. M . L’amotte, R. Lapouyade, J . Pereyre, and J. Joussot-Dubien, C . R . Hebd, Seances Acad. Sci., Ser. C, 1980, 290, 21 I . T. Caronna, S. Morrocchi, and B. M . Vittimberga, f. Org. Chem., 1981, 46, 34. K . Okutsu and M. Kobayashi, fosai Shika Daigaku Kigo, 1979.8,215 (Chern.Absrr., 1980,93,45 404).

Photochemistry of Aromatic Compounds 343 by amines suggests that a singlet exciplex is involved that can be derived from the (n,n*) state or from the (n,n*) state depending on the solvent. Acridine also undergoes photoaddition of acetaldehyde to give an acetyldihydro-product (36),45 and phenazine (37) reacts in a similar way, although it gives a ring-substituted product as well as the photoadduct. The photoreduction of mono-protonated phenazine in aqueous solution gives the dihydrophenazine radical cation via the lowest excited singlet state,46 and water is oxidized to hydrogen peroxide. Octahydrophenazine (38) behaves like phenazine in giving the NN'-dihydroderivative on irradiation in the presence of propan-2-01, or the radical cation in water;47 this report is of interest in that it provides an example of the photoreduction of a fairly simple substituted pyrazine.

H

(39)

40%

(R = Pr)

The well known photoalkylation of N-heterocyclic aromatic compounds has been extended 48 to sym-triazolo[4,3-b]pyridazine(39); the substitution can be effected by photoaddition of an alcohol followed by heating the initially formed adduct. Photocycloaddition reactions are not observed for diphenylmethane (40) unless either a charge-transfer complex between (40)and, for example, maleic anhydride is involved, or a species such as excited N-ethylmaleimide initiates reaction by attack on an aromatic ring of (40).49 In both of these examples cycloaddition occurs in a 1,Zmanner to only one of the aromatic rings. Interaction between the two phenyl groups is thought to provide a mechanism for dissipating energy in the S , state of diphenylmethane. With benzene and an electron-deficient alkene, 1,2photocycloadducts predominate, and the same is true for electron-deficient aromatic substrates. So hexafluorobenzene gives 1,Zadducts as major products on 45 46

47 48 49

M . Takagi, S. Goto, and T. Matsudd, Bull. Chem. SOC.Jpn., 1980, 53, 1777. H. Kawata, Nihon Kaigaku Nojuigukuba Ippan Kyoyo Kenkyu K i p , 1979,15,27 (Clzem. Abstr., 1980, 93, 177 113). F. Benayache, Y. Gounelle, and J. Jullien, J . Chem. Res. ( S ) , 1981, 158. D. H . Brown and J . S. Bradshaw, J. Org. Chem., 1980,45, 2320. A. Gilbert and J. C. Lane, J . Chem. Soc., Perkin Trans. I , 1981, 142.

344

Photochemistry 0

irradiation with indene or 1,2-dihydronaphthalene, and alkoxypentafluorobenzenes (4 1) with cyclopentene give 1,2-~ycloadductsand products derived by further photochemical ring-closure. 5 0 Pentafluoropyridine (42) behaves in a similar way with cy~loalkenes,~' except that no 1 : 1 adducts are isolated, but only 2 : 1 products arising from further reaction with alkene. OR

2148% 51

B. Sket and M. Zupan, Croat. Chem. Acta, 1979, 52, 387. M. G. Barlow, D. E. Brown, R. N. Haszeldine, and J. R. Langridge, J. Chem. SOC.,Perkin Trans. I , 1980, 129.

Photochemistry of Aromatic Compounds

345

Details are now presented 5 2 of studies on the benzene-furan system, in which a + 2]cycloadduct (43) and a [4 4ladduct (44) are the major products; adduct (44)can be converted thermally or photochemically into (43). This photoaddition is the first example involving two monocyclic aromatic compounds; benzene and thiophen give products in only very low yield on irradiation.

+

[2

m0" do: & (43)

(44)

h"

\

/

,

J"\

OH-,

/

(45) 36%

\

/

76%

The 1,2-photocycloaddition of acrylonitrile to naphthols or their methyl or trimethylsilyl ethers produces cyclobutane adducts (e,g., 4 9 , and these can be cleaved with base.53 This provides a synthetic route to (1- or 2-cyanoethy1)substituted derivatives of the original naphthol. 1-Cyanonaphthalene (46) gives both 1,2-cycloadductsto the ring and a C=N cycloadduct on irradiation with 1,2dimethylcycl~pentene,~~ and the two reactions proceed by way of different singlet excited states of the aromatic nitrile. The photophysics of this system has been studied p r e v i o ~ s l y ,but ~ ~ this is the first report in which the photoproducts are characterized. An intramolecular version of the reaction starting with the the major one substituted 1-cyanonaphthalene (47) gives two 1,2-~ycloadducts,~~

CN

4 = 0.03 52 53

" "

''

J. C. Berridge, A. Gilbert, and G. N. Taylor, J . Chem. SOC.,Perkin Trans. 1, 1980, 2174. I. A. Akhtar and J. J. McCullough, J. Org. Chem., 1981, 46, 1447. F. D. Lewis and B. Holman, J . Phys. Chem., 1980, 84, 2328. D.V. O'Connor and W. R. Ware, J. Am. Chem. SOC.,1979, 101, 121. J. J. McCullough, W. F. MacInnis, C. J. L. Lock, and R. Faggiani, J . Am. Chem. SOC.,1980,102,7780.

346

Photochemistry

arising by attack at positions 1 and 2, and the minor one by reaction at positions 3 and 4. Solvent effects on the weak exciplex emission from systems containing an aromatic nitrile and furan or an alkene are reported.57 The 1,2-photocycloaddition reactions of methyl phenanthrene-9-carboxylatewith styrenes are proposed 5 8 to go by way of singlet exciplexes, partly on the basis of results from fluorescence studies of compounds such as (48). 6-Cyanophenanthridine (49) behaves like its

(49)

Ar = p-C,H,OMe

84%

16%

phenanthrene analogue on irradiation with alkenes, and by way of an exciplex intermediate provides a route to azetidines and a z ~ c i n e s .6~o ~ . p-Xylene sensitizes the cis-trans-isomerization of cyclohexene, but with cycloheptene (50) the major products are cycloadducts involving 1,3-addition to the

(58

” 58

59

ho

+ 22%)

H. Sakurai, Prepr. Div. Pet. Chem., Am. Chem. Soc.. 1979. 24, 143. H. Sakuragi, H. Itoh, T. Arai, and K. Tokumaru, Kokngrrkrc Toronkrri Koen Yoshishu, 1979, 188 (Chem. Ahsrr., 1980. 93, 70450). S Futamura, H. Ota, and Y. Kamiya, Chem. Left., 1980, 655. S. Futamura, H . Ota, and Y . Kamiya, Kokriguku Toronkai Koen Yoshishu, 1979. 272 (Chem. Abstr., 1979.93, 113518).

347

Photochemistry of Aromatic Compounds

aromatic ring.61 A detailed study 6 2 of the 1,3-photocycloaddition of cis-cyclooctene (51) to PhR (R = Pri, But, or OMe) or p-MeC,H,R (R = Pr' or OMe) suggests that both of the previously proposed mechanistic pathways are required to account for the selectivity of the reaction. The extent of participation of initial meta-bonding in the arene or of initial 1,3-addition of the alkene to the arene seems to be governed by both steric and electronic effects. An intramolecular version of this reaction has been investigated 63 for various substituted benzenes: with 5-phenylpent-1-ene (52), three 1,3-~ycloadductsare formed, but 1,4-addition

(52)

l p

=0.11

0.023

0.02

$ = 0.23

(53)

predominates for phenethyl vinyl ether (53). The balance between 1,3- and 1,4cycloaddition, and the preferred positions of attack on the ring, depend not only on the length of the linking group between the benzene ring and the alkene unit, but also on the nature of the linking group, i.e. whether or not it contains oxygen, and the position of the oxygen in the chain. An intramolecular photocycloaddition involving the substituted benzene (54) has been, employed 64 in a synthesis of acedrene.

(54)

65%

In a detailed report 6 s of the photoreactions of dienes with benzene, it is shown that with 1,4-dienes one of the double bonds generally adds 1,3-(meta-) to the benzene ring, although evidence is presented for the formation of 1,4-(para-)adducts as well. Rigid 1,3-dienes such as 1,2-dimethylenecyclohexane(55) give regioselectively meta- and para-adducts that involve both of the double bonds in the diene; flexible 1,3-dieneslead to complex mixtures of products. 1,2-Dienes such 61

63 64

65

P. J. Kropp, J. J. Snyder, P. C. Rawlings, and H. G. Fravel, J . Org. Chem., 1980, 45, 4471. M. Dadson, A. Gilbert, and P. Heath, J . Chem. Soc., Perkin Trans. 1, 1980, 1314. A. Gilbert and G . N. Taylor, J . Chem. Soc., Perkin Trans I , 1980, 1761. P. A. Wender and J . J . Howbert, J. Am. Chem. SOC.,1981, 103, 688. J. C. Berridge, J. Forrester, B. E. Foulger, and A. Gilbert, J . Chem. SOC., Perkin Trans. I , 1980,2425.

Photochemistry

348

(55)

major

as allene (56) give predominantly para-adducts, which is unusual for the reactions of benzene with simple alkenes. A brief report 6 6 of the irradiation of naphthalene with trans-cyclo-octene suggests (without evidence) that a 1,3-cycloadduct (57) is involved as an intermediate in the isomerization of the cyclo-octene.

+

Q

There are several reports this year of photocycloaddition reactions between polycyclic aromatic hydrocarbons and 1,3-dienes. Anthracene (58; R = H) or 9cyanoanthracene (58; R = CN)give [4 + 41 and [4 + 2ladducts on irradiation with buta-1 ,3-diene,67but the different product ratios and temperature effects are used to support the previously proposed biradical mechanism for the reaction. Another report from the same group deals with anthracene-hexa-2,4-dieneand 9-phenylanthracene-penta-1,3-diene or cyclohexa-1,3-diene systems; in the case of 9-phenylanthracene (59) and cyclohexa-1,3-diene, two [2 + 2]cycloadducts involving a terminal aromatic ring are isolated, as well as the more usual [4 + 21 and [4 + 4ladducts involving the central ring. Irradiation of substituted anthracenes 66 67 68

Y . Inoue, T. Hakushi, and N. J. Turro, Kokagaku Toronkai Koen Yoshishu, 1979, 152 (Chem. Abstr., 1980, 92, 214 553). G . Kaupp and H. W. Grueter, Chem. Ber., 1980, 113, 1458. G. Kaupp and E. Teufel, Chem. Ber., 1980, 113, 3669.

Photochemistry of Aromatic Compounds

349

15%

41%

17%

(R,R'

= H, Me, Ph, Br, CN)

32--63%

+

with cycloheptatriene (60) provides [4 + 21, [4 + 41, and [4 + 6]cycloadducts, as well as other products;69 the selective formation of particular product types is rationalized on the basis of orbital and steric interactions. Yang has shown '* that the initial concentration of the arene has a large effect on product ratios ([4 + 41 versus [4 + 21) in the reaction of 9,lO-difluoroanthracene with 2,5-dimethylhexa-2,4-dieneY and this effect is also found with anthracene (61) and cyclohexa-l,3-diene, which [like 9-phenylanthracene (59) and cyclohexa-1,3-diene] gives a minor product involving [2 + Zladdition to a 69

O'

H. Kondo, M . Mori, and K. Kanematsu, J . Org. Chem., 1980, 45, 5273. N. C. Yang, H . Shou, T. Wang, and J. Masnovi, J . Am. Chem. Soc., 1980, 102, 6652.

350

Photochemistry

10%

terminal ring of anthracene, as well as another minor product involving [4 + 2]cycloaddition to a terminal ring. The photoreactions of dibenzanthracenes have already been studied with cyclohexa-l,3-diene, and similar reactions are now reported 7 1 with cyclopentadiene to give mixtures of [4 + 21 and [4 + 4]cycloadducts with well defined stereochemistry. Although 9,lO-endoperoxides can be formed readily in anthracene systems, the corresponding benzene compounds are not common. Cycloaddition of hexamethylbenzene with singlet oxygen is shown to give an endoperoxide (62), although this reacts quickly with more singlet oxygen to give a hydroperoxyderi~ative.~~

* \

/

/ OOH

(62)

The photodimerization of 2-pyridones is a [4 + 4]cycloaddition process, and it is reported 7 3 that the length of the alkyl chain in N-(cu-carboxyalkyl)-2-pyridones (63) governs the ratio of cis: trans dimers when the process is carried out in micellar solution. Photocyclization that involves 1,4-addition to a styrene moiety is included in a more general review 74 of photosensitization in organic synthesis. In a trapping

’’ G . Kaupp and H. W. Crueter, Chem. Ber., 1980, 113, 1626. ’’ C. J . M. Van den Heuvel, A. Hofland, H . Steinberg. and T. J. De Boer, R e d . Trav. Chim. Pays-Bas, ”

1980, 99. 275. Y. Nakamura. T. Kato, and Y. Morita, Tetrahedron Lett., 1981, 22, 1025.

74

A. Albini, S~.nthessis,1981, 249.

Photochemistry of Aromatic Compounds

351

R (63) R =(CH,),COOH

Ph Ph

&

Ph

4-

(R

)==

=

Ph

-@

C,Ht&):

R R

Me, Ph)

ICH,=CHX

R R

dx (X= CN, C0,Me)

\

R R

experiment using acrylonitrile or methyl acrylate, the formation of products (64) is taken as evidence for the proposed triene intermediate in the electron-transfer sensitized photodimerization of 1,l -diphenylethylene or in the cross-cycloaddition between 1,l-diphenylethylene and 1-methylpropene. A related [4 + 2]cycloadduct is formed photochemically from N-methyl-2-phenyl-maleimide (65), accompanying a number of [2 + 2]cycloadducts involving only the maleimide double bond.76 The [4 2ladduct is also produced on prolonged heating of (65). A reaction that bears some resemblance to the styrene reaction is the formation of spiro-indanes

’’

+

GMe hv

d

Ph’

[2 + 21 dimers

+ 0

0

x (Y = F, Br, C1, Me, OMe) 75

76

(X

= CN,

C0,Me)

(66) 5-50%

D. R. Arnold, R . M. Borg, and A. Albini, J. Chem. Soc., Chem. Commun., 1981, 138. K. Ichimura, S. Watanabe, K . Ueno, and H. Ochi, Nippon Kagaku Kuishi, 1980, 846 (Chem. Abstr., 1980, 93, 185 480).

352

Photochemistry

(66) on irradiation of 2-aryl- I-pyrrolinium salts in the presence of electronacceptor alkenes. 77 However, the proposed mechanism starts with [2 + 2]photocycloaddition of the alkene to the aromatic ring. [2 + 2lCycloaddition to five-membered heterocyclic aromatic compounds is well documented. Examples reported this year include the formation of azetidine adducts (67) by irradiation of 3-(p-cyanophenyl)-2-isoxazolinewith furan or thiophen (and also with benzene);78 benzophenone-sensitized reaction of selenophen with dimethylmaleic anhydride (68) to give 1 : 1 and 1 : 2 ad duct^;^' and oxetan formation from benzophenone and 1-acylimidazoles (69), thiazoles, or isoxazoles.8o

COR

COR

(69)

34-41%

Closer investigation of the photoreaction between benzo[b]thiophenes and dimethyl acetylenedicarboxylate reveals 81 that the unrearranged photoadduct (70) can be isolated if longer-wavelength radiation is excluded, and that (70) shows a charge-transfer absorption band (A,,, 3 6 6 3 6 9 nm), which is responsible for the facile conversion to the previously observed rearranged photoadducts when 366 nm radiation is available (as in the output of a medium-pressure mercury arc). 3-Phenyl- 1,2-benzisothiazoIe (7 1) gives a 1,4-benzothiazepin on irradiation with ethyl vinyl ether,82 consistent with initial S-N bond cleavage rather than ”

7a

P. S. Mariano and A. Leone-Bay, Tetrahedron Lett.. 1980, 21, 4581. T. Kumagai, Y. Kawamura, K. Shimizu, and T. Mukai, Koen Yoshishu-Hibenzenkai Hokozoku Kagaku Toronkai (oyobi) Kozo Yuki Kagaku Toronkai 12th. 1979, 317 (Chem. Abstr., 1980, 92, 197 557).

79

8’

*’

C. Rivas, D. Pacheco, and F. Vargas, J . Hetercycl. Cliem., 1980, 17, 1151. T. Nakano, W. Rodriguez, S. Z. de Roche, J. M. Larrauri, C. Rivas, and C . Perez, J . Heterocycf. Chem., 1980, 17, 1777. S. R. Ditto, P. D. Davis, and D. C . Neckers, Tetrahedron Lett., 1981, 22, 521. M. Sindler-Kulyk and D. C . Neckers, Tetrahedron Lett., 1981, 22, 529.

Photochemistry of Aromatic Compounds

353 C02Me

d

R

+

Me02C-C~C-C02Me

PhCOMe. hv &C02Me

'

S R (70)

(71)

80%

cycloaddition to the C=N bond. This proposal is supported by the observation that 1,2-benzisothiazoleitself reacts with dimethyl acetylenedicarboxylate to give two isomeric ring-opened products and a cyano-substituted benzo[b]thiophen (72). Further work by the same group shows that 2-phenylbenzothiazole (73) may also undergo bond cleavage, this time of a C-S bond to give in the presence of alkenes a 1,5-benzothia~epin;~~ the reaction is stereospecific.

mf

+

MeOzC-CCrC-CO,Me 602Me (30% cis

+ 50% trans) C02Me

+

p

C

0

2

M

e

CN

4 Substitution Reactions Many examples of photosubstitution reactions in aromatic systems are reported, and it is not easy to group the reactions on a mechanistic basis (in part because 83 84

M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Lett., 1981, 22, 525. M . Sindler-Kulyk and D. C. Neckers, Tetrahedron Lett., 1981, 22, 2081.

Photochemistry

354

many papers are concerned with synthetic rather than mechanistic investigations). Reactions in which direct electrophilic substitution occurs in the excited state are very rare; however, nucleophilic substitution can take place by several mechanisms, including initial electron transfer from the aromatic compound to give an aromatic radical cation. Attack by a radical on the excited state of an aromatic compound is again a rare occurrence, but the reactions of photochemically generated radicals with ground-state aromatics are included briefly at the end of this section. Electrophilic substitution in excited-state aromatics is the subject of only one report, concerned with a photophysical investigation of hydrogen4euterium exchange in 1-metho~ynaphthalene.~~ hv (R

= F) RR’NH (R, R’ = Et or R = H:

(74)

\

R’

= Bu‘)

hv(R

7H(X)Me

= H)

(X = OEt, NHEt, NEt,)

+

Irradiation of 2-fluoropyridine (74;R = F) with t-butylamine or diethylamine gives (di)alkylaminopyridine as the sole product, formed by nucleophilic photosubstitution.86 With triethylamine a more complex mixture of products is formed. Pyridine itself (74; R = H) reacts with diethylamine, triethylamine, or diethyl ether to give 2- and 4-substituted pyridines that reflect attack on the a-methylene group in the aliphatic component; this process involves a formal hydrogenabstraction step from the activated CH, group by an excited-state aromatic. A full report has now appeared 87 of the reactions of alkenes with 3-chlorotetrafluorowhere insertion pyridine (75), and also with 3,5-dichloro-2,4,6-trifluoropyridine, F

77%

8 1-90%

(of ethylene) into the carbon-halogen bond or replacement of chlorine by cycloalkyl (cyclopentyl or cyclohexyl) is the major reaction. The chlorine in these ”

”

S. Tobita and H. Shizuka, Koen Yoshishu Bunshi Kozo Sogo Toronkai, 1979,228 (Chem. Abstr., 1980, 93, 185503). A, Gilbert and S. Krestonosich, J. Chem. SOC.,Perkin Trans. I , 1980, 2531. M . G. Barlow, R. N. Haszeldine, and J. R. Langridge, J . Chem. SOC., Perkin Trans. I , 1980, 2520.

355

Photochemistry of Aromatic Compounds

compounds is readily replaced by hydrogen on irradiation in hydrogen-donor solvents such as ethanol or diethyl ether, a reaction that is similar to the photodechlorination of (po1y)chlorobiphenyls. On irradiation, amines readily replace a hydrogen (or halogen) in a wide range of nitroindazoles (e.g., 76), and in a few cases ethanol similarly gives rise to YO2 NHMe

NHR

(77)

up to 56%

+

Q-fyJNO2 \

+

OH\ NHR up to 25%

& y o 2

\

o \ up to 28%

ethoxyindazoles by nucleophilic photosubstitution.88 However, with 2-nitrodibenzodioxin (77), attack by amine occurs at the C-0 position to give substituted diphenyl ethers or an N-alkyl-2-nitrophenoxazine(which is the sole product in non-polar solvents);89it is proposed that a triplet excited state of the dibenzodioxin forms an exciplex with the amine, which in polar solvents dissociates to give solvated radical ions. This reaction is related to the photoSmiles rearrangement, the mechanism of which is the subject of several reports.

The photorearrangement of I-anilino-o-(p-nitrophen0xy)alkanes(78) to N-(pnitropheny1)-o-anilinoalkan-1-01sis shown to proceed by way of a radical ion pair and a Meisenheimer complex, both of which are observed in flash photolysis experiment^.^^. 91 In a simpler system, the Smiles rearrangment of the " 89

92

P. Bouchet, R. Lazaro, M. Benchidmi, and J. Elguero, Tetrahedron, 1980, 36, 3523. M. A. Leoni, G. F. Bettinetti, G. Minoli, and A. Albini, J . Org. Chem., 1980, 45, 2331. K. Yokoyama, R. Nakagaki, J. Nakamura, K. Mutai, and S. Nakagura, Bull. Chem. Suc. Jpn., 1980, 53, 2472. K. Yokoyama, R. Nakagaki, J. Nakamura, S. Nakagura, and K. Mutai, Koen Yoshishu Bunshi Kozo Sogo Toronkai, 1979, 236 (Chem. Abstr., 1980, 93, 220 114). K. Mutai and K. Kobayashi, Bull. Chem. SOC.Jpn., 1981, 54, 462.

Photochemistry

356

0-, m-, or p-isomers of 2-(nitrophenoxy)ethylamine has been studied.93 The 0-and p-isomers undergo a Smiles rearrangement thermally, but photochemically this is not important; instead the o-compound gives a mixture of unidentified products, and the p-compound (79) gives two products in which the amine nitrogen has

NHCH,CH,OH OH

OCH,CH ,N H (79)

14%

aq NaOH hv

~

25%

6

OCH,CH,NH,

NHCH,CH,OH

(80)

= 0.23

become bonded to the adjacent ring atom. The m-compound (80) does not undergo the Smiles rearrangement on heating, but the rearrangement does occur photochemically. These results are thought to have a wider significance, because they suggest that in intermolecular nucleophilic photosubstitutions involving alkoxy-nitrobenzenes, electron-transfer interaction between the nitro-group and the nitrogen lone pair (of the nucleophile) may be important; this is not possible in the intramolecular reactions studied, and a more direct nucleophilic attack on the ring may occur. Photocyanation of aromatic compounds is dealt with in several papers this year. In the presence of an electron acceptor such as p-dicyanobenzene, aromatic hydrocarbons such as naphthalene (8 I), substituted naphthalenes, phenanthrene, or anthracene give mixtures of products on irradiation with sodium cyanide.94 The major products involve substitution of hydrogen by cyanide or addition of hydrogen cyanide to the aromatic hydrocarbon. When oxygen is present, the product mixture is less complex, and a good yield of cyano-substituted compound is obtained. It is proposedg4 that the aromatic radical cation is involved in the CN I

18%

(81)

44%

OMe

OMe

OMe

(82)

13%

CN 11%

93

94

G. G. Wubbels, A. M. Halverson, and J. D. Oxman, J. Am. Cheni. Suc., 1980, 102, 4848. M. Yasuda, c'. Pac, and H. Sakurai, J. Chem. Suc., Perkin Trans. I, 1981, 746.

357

Photochemistry of Aromatic Compounds

mechanism, and a similar conclusion is reached 95 in a mechanistic study of the photocyanation of naphthalene and biphenyl. The latter study is concerned more with the reaction in the absence of added electron acceptor, and it is suggested that a singlet excimer is then involved, which dissociates into radical ions before the attack by cyanide ion. An extension of work on the photosubstitution by cyanide in anisole (82) supports previous conclusions about the mechanism in the presence or in the absence ofp-di~yanobenzene,'~ and it also shows that polyethylene glycol can replace a crown ether as co-solvent (with dichloromethane) for the reaction. A mechanistic link is proposed 97 between the photoreduction of chloro-aromatics such as p-chloroanisole (83) and photosubstitution, involving aromatic radical OMe

61 (83) CN -,M

OMe

, ~

OMe

OMe 13%

79%

O

H

~

OMe

OMe

OMe

4%

OMe 5%

CN 89%

cations and anions; the anions can lead to overall photoreduction, and the cations to the replacement of chlorine by methoxy (from methanol solvent) or by cyano (from added cyanide). Replacement of cyano by hydrogen in a photosubstitution reaction is not as frequently encountered as the reverse process, but the dicyanopyrazine (84), and a related compound with a crown ether group attached to the phenyl ring, undergoes an efficient photoreaction in which first one cyano group is replaced and hv

Ar

CN

(84) (Ar.= C,H,(OMe),]

Ar

CN

79% 95 96 97

Ar

80%

9%

N. J. Bunce, J. P. Bergsma, and J. L. Schmidt, J. Chem. Soc., Perkin Trans. 2, 1981, 713. N. Suzuki, K . Shimazu, T. Ito, and Y. Izawa, J. Chem. Soc., Chem. Commun., 1980, 1253. J. P. Soumillion and B. de Wolf, J . Chem. Soc., Chem. Commun., 1981, 436.

3 58

Photochemistry

then the second The reaction is thought to proceed by way of an aromatic radical anion, which loses cyanide ion: the resulting radical then abstracts hydrogen from the solvent. Dicyanobenzenes react with amines in a different way, however; o-dicyanobenzene (85), or the p-isomer (but not the m-isomer), on irradiation with primary, secondary, or tertiary amines gives products in which one cyano-group is replaced either by the amine linked through the cx-position or by an alkyl group of the amine.99 The first product arises by initial electron transfer (in an exciplex) followed by proton transfer, combination of radicals and elimination of HCN; the alkylated product is formed by subsequent photoreaction of this initial product, again initiated by electron transfer. The analogous substitution reaction of 2-cyanoquinoline in ethanol was reported some time ago, l o o and now an investigation of the effect of a magnetic field on the reaction of 1-cyanoisoquinoline (86) suggests that a triplet radical pair is a likely reaction intermediate. O 1 The same reaction occurs with 4-cyanopyridine (87) and pent-4en-1-01 or hex-5-en-1-01 in neutral solution,'02 but in the presence of HCl attack occurs instead at the ethylenic bond of the alcohol to give products having chlorohydroxy-substituted alkyl chains. Chloroalkyl substituted pyridines (without the OH group) are formed in the reaction of (87) with alkenes in the presence of HCl. l o 2 The same research group reports l o 3 that photosubstitution products are formed from 2- or 4-cyanopyridine (88) with simple alkenes in the absence of acid, in contrast to an earlier report that showed no such allylic substitution products.

HO CN

Q

+

CH,=CH(CH,),OH (n = 3, 4)

'"*

Y

(CH,),$H=CH,

Q Q

(88) 98

99 loo

lo'

7-60%

M. Tada, H. Hamazaki, and H. Hirano, Chem. Lett., 1980, 921. M. Ohashi, K. Miyake, and K. Tsujimoto, Bull. Chem. SOC.Jpn., 1980, 53, 1683. N. Hata, I. Ono, S. Matono, and H. Hirose, BuK Chem. SOC.Jpn., 1973, 46,942. N. Hata and Y. Yamada, Chem. Lett., 1980, 989. T. Caronna, A. Clerici, D. Coggiola, and S. Morrocchi, Tetrahedron Lett., 1981, 22, 2115. R. Bernardi, T. Caronna, S. Morrocchi, and P. Traldi, Tetrahedron Lett., 1981, 22, 155.

Photochemistry of Aromatic Compounh

359

Fluorenol(89) is reduced photochemically by triethylamine to give fluorene in high yield;lo4a small amount of 9-ethylidenefluoreneis also formed. Other amines are effective, although the yields are generally lower, and 9-acetoxyfluorene also reacts to give fluorene in rather low yield. The photoreduction reaction is related formally to the photoreduction of dicyanopyrazine (84). An apparently straightforward replacement of hydrogen by nitro in the photolysis of butyl phydroxybenzoate (90) in aqueous sodium nitrite is shown to be more complex,105 and it seems possible that the initial attack is by HO' radicals, followed by reaction with N02.

84%

COOBu I

9%

YOOBu

OH

4 = 0.012 Nucleophilic photosubstitution with enolate anions continues to attract attention. p-Dihalobenzenesreact to give doubly substituted products (91),Io6 although 0

C'

+ 61

RCOCH,-

Rd 0

(91) 65%

(R = But)

there can be complications caused by the fact that the anion derived from the initial photoproduct can act as a nucleophile towards the excited state of the chloroaromatic. The use of o-iodoanisole (92) in this reaction provides a route to benzo[b]furans, and 3-amino-2-chloropyridine(93) similarly leads to azaindoles.108A detailed mechanistic investigation l o 9 of the reaction with ketone and ester enolates highlights the competition between substitution and hydrogen-atom transfer from the enolate anion to a transient phenyl radical; the same report lo4

lo6 lo'

'09

M. Ohashi, Y. Furukawa, and K. Tsujimoto, J. Chem. Soc., Perkin Trans. I , 1980, 2613. Y. Usui and H. Shimizu, Nippon Kugaku Kaishi, 1979, 1636 (Chem. Abstr., 1980,92, 180305). R. A. Alonso and R. A. Rossi, J . Org. Chem., 1980,45,4160. R. Beugelmans and H. Ginsburg, J . Chem. Soc., Chem. Commun., 1980, 508. R.Beugelmans, B. Boudet, and L. Quintero, Tetrahedron Lett., 1980, 21, 1943. M. F. Semmelhack and T. Bargar, J. Am. Chem. Soc, 1980, 102, 7765.

360

Photochemistry I hv

U O M e (92)

\

RCOCH,-'

(It ='H, Me,

40-100%

100%

Pr', But)

(93)

(R = Me, Pri, But)

23-100%

(94) 25-35%

shows that intramolecular reactions of this type can give products (e.g., 94) with new rings of up to ten atoms. Polychloromethanes can take part in photochemical electron-transfer reactions with aromatic compounds, leading (in alcohol as solvent) to products with oxygenated one-carbon substituents. It is reported that ruthenocene (95), like ferrocene, gives the corresponding ethoxycarbonyl, formyl, or ethoxymethyl compounds when irradiated with carbon tetrachloride , chloroform, or dichloromethane, respectively. Carbazole (96) behaves in a similar way with CCl,, and the

C1 (97)

major products are 1- and 3-ethoxycarbazole;l 1 in a hydrocarbon solvent the reaction is diverted to produce mainly N-(trichloroviny1)carbazole (97) by way of further reaction with trichloromethyl radical. In contrast, NN-dialkylanilines give amino-substituted diphenylmethanes as major products on irradiation in CH,Cl,, 'lo

''I

A. Sugimori, M.Matsui, T. Akiyama, and M. Kajitani, Bull. Chem. SOC.Jpn., 1980, 53, 3263. B. Zelent and G . Durocher, J . Org. Chem., 1981,46, 1496.

Photochemistry of Aromatic Compounds 361 and further examples of aromatic amine and phenol systems are reported 1 1 * to provide similar product ranges in low yield. Dialkylanilines irradiated in the presence of acrylonitrile give ring-substituted products with ortho- or para-groups

incorporating one (MeCHCN) or two (NCCH,CH,CH,&HCN) molecules of the unsaturated nitrile;' l 3 a product of intramolecular cyclization (98) is also formed.

R2

(R = Me, Et)

(98)

Pyridinecarboxylates (99) give photosubstitution products on irradiation with alcohols; the products have alkyl or alkoxy substituents, and the product ratios depend on the absence or presence of added mineral acid. A mechanistic rationalization is presented,'l4P based on the involvement of a triplet excited state located largely on W or a triplet located largely on the ring (for alkylation), and a singlet excited state (for alkoxylation). The reaction of pyridinecarboxylic acids in the presence of transition-metal ions is reported: l 6 pyridine-2-carboxylic acid gives pyridine and 2,2'-bipyridyl with iron(rn), but 2pyridone with copper(@; pyridine-3-carboxylic acid (1 00) with Fe"' gives a dehydrodimer without decarboxylation.

'

Me COOMe

(99)

COOMe

Me0 up to 88%

Irradiation of aqueous solutions of 5-methylphenazinium salts yields the 10hydro cation radical and the 1-hydroxy-derivative (101) in a stoicheiometric 2 : 1 ratio. An e.s.r. study '17 suggests that free hydroxyl radicals are not likely to be involved in the reaction. A more extensive study l a shows that addition of water 112

T. Latowski, E. Latowska, B. Poplawska, M. Przytarska, M. Walczak, and B. Zelent, Pol. J . Chem.,

113

H. Terashima, S. Toki, and H. Sakurai, Kokagaku ToronkaiKoen Yoshishu, 1979,264 (Chem.Abstr.,

114

T. Sugiyama, E. Tobita, K. Takagi, S. Akiyama, Y. Kumagai, K. Yagi, G . P. Sato, and A. Sugimori, Kokagaku Toronkai Koen Yoshishu, 1979, 114 (Chem. Abstr., 1980, 93, 70 449). T. Sugiyama, E. Tabita, K. Takagi, M. Sato, Y. Kumagai, S. P. Sato, and A. Sugimori, Chem. Letr.,

1980, 54, 1073. 1980,93, 70454). 115

1980, 131. 116

T. Takada, T. Kimura, and A. Sugimori, Kokagaku Toronkai Koen Yoshishu, 1979, 206 (Chem.

117

Abstr., 1980, 93, 70452). V. S. F. Chew and J. R. Bolton, J. Phys. Chem., 1980,84, 1903. V. S. F. Chew, J. R. Bolton, R. G. Brown, and G. Porter, J . Phys. Chem., 1980, 84, 1909.

118

362

Photochemistry

to the excited phenazinium cation gives a strongly oxidizing species that can be intercepted by added reagents. Related to this reaction, synthetic proof is presented 'I9 that the photoproduct from lumichrome in aqueous solution is 9hydroxylumichrome (I 02). Similar hydroxylation occurs on irradiation of Nsubstituted alloxazinium cations,' 2o although at lower pH some hydroxylation at C-6 also occurs.

Interest continues in the photoreactions of quinones, especially anthraquinones, in which substitution occurs in one of the aromatic rings. In the 1,4naphthoquinone series, irradiation of an aqueous solution of sodium 1,4-naphthoquinone2-sulphonate gives a mixture of products including the 5-hydroxy-compound: 12' the effects of pH, irradiation wavelength, solvents, and radical scavengers are described. Replacement of halogen by butylamino in anthraquinone (103) is NHAc

0 (103)

Br

N HAc

0

NHBu

reported 22 to proceed through a triplet charge-transfer excited-state of the substrate. Substitution of halogen in 1-chloroanthraquinone on irradiation in aqueous sulphuric acid gives the l-hydroxyq~inone,'~~ and in both of these reactions the 1-halo-isomers are inactive, possibly because they lack low-lying charge-transfer states. 22 Nitro-groups in aminonitroanthraquinones such as (104) can be replaced by hydroxyl,'24*125 although in this system the oxygen of 119 120 121

B. Te Nijenhuis, A. C. Mulder, and W. Berends, Recl. Trav. Chim. Pays-Bas, 1980, 99, 115. R. R. Dueren, R. H. Dekker, H. I. X. Mager, and W. Berends J . Phofochem., 1980,13, 133. S . Hashimoto and M. Mouri, Sci. Eng. Rev., Doshisha Univ., 1980, 21, 39 (Chem. Abstr., 1980, 93, 2 13 2 16).

122

123

124 125

M. Tajima, H. Inoue, and M. Hida, Nippon Kagaku Kuishi, 1979, 1728 (Chem. Absrr., 1980, 92, 2 14 527). K. Seguchi and H. Ikeyama, Chem. Lett., 1980, 1493. 0 . P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1979, 15, 2597 (Chem. Abstr., 1980, 93, 7885). 0. P. Studzinskii and A. V. El'tsov, Zh. Obshch. Khim., 1980, 50, 2575 (Chem. Abstr., 1981, 94, 120 526).

Photochemistry of Aromatic Compounds 0

(104)

363

NHR

0

NHR

(R = H,Me)

the OH group presumably can come from the nitro-group, since benzene can be used as a solvent for the irradition. The photohydroxylation of anthraquinone itself in 77% sulphuric acid gives largely (62%) 2-hydroxyanthraquinone, with a small amount of the 1-hydroxyisomer.126 A mechanism involving electron transfer to the (n,n*) triplet state of anthraquinone is propo~ed,'~'followed by attack of the hydroxyl radical soformed on ground-state quinone. A product investigation of the reaction in 96% H,SO, shows that the 2-hydroxyquinone is formed as its sulphate ester,128and that, in the absence of oxygen, reduction products derived from the radical (105) are obtained. In 77% acid and in the presence of boric acid, the 1,4-dihydroxyquinone (106) is formed in high yield from l-hydroxyanthraquin~ne.~~~

&&-+& /

, &OH \

96%H+, hv

/

0

O \

80%

\

a

/

\

/

OH (105)

(106) 81%

2-aminoanthraquinone can be made in a similar manner by irradiating anthraquinone with ammonia in aqueous propan-2-01 in the presence of air, 30 although the yield is only 33%. Similar reactions between 1- or 2-hydroxyanthraquinone and ammonia or methylamine give amino-substituted derivatives (e.g., 107); again an electron transfer from amine to quinone is postulated as the first

IJ1

0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, 1100 (Chem. Abstr., 1979,93, 168005). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16,2117 (Chem. Abstr., 1981,94,83 287). A. D. Broadbent and J. M. Steward, J. Chem. Soc., Chem. Commun.,1980, 676. 0.P. Studzinskiiand A. V. El'tsov, Zh. Org. Khim., 1980,16, 1101 (Chem. Abstr., 1979,93, 150035). 0.P. Studzinskii, A. V. El'tsov, and Yu. K. Levental, Zh. Obshch. Khim., 1980,50,435 (Chem.Abstr., 1980, 93, 7286). 0. P.Studzinskii, R. P. Ponomareva, and V. N. Seleznev, I n . Vyssh. Uchebn. Zuved., Khim. Khim. Techno/., 1980, 23, 511 (Chem. Abstr., 1980, 93, 168004).

364

Photochemistry

step in the reaction of the excited state. Substitution in 1-hydroxyanthraquinone with sodium sulphite gives mixture of the 2-, 4-, and 2,4-di-~ulphonates,'~~ but selectivity is greater when amino-substituents are present. 1-Aminoanthraquinone (108) gives exclusively the 2-sulphonate with Na,S03 and the 2-thiolate with

& 0

;:x,

&XNa

(X=S,SO,)

/

\

0

0

(108)

70-100%

Na,S; 2-aminoanthraquinone with sulphite gives only the 3-sulphonate. The lower selectivity with hydroxyquinones is attributed 32 to partial ionization of the OH group in the reaction medium. A homolytic cleavage mechanism with aryl radicals as intermediates is generally accepted for the photodehalogenation reactions of haloaromatics, and this type of reaction is included in a review 133 of modern methods of aryl-aryl bond formation. An example of such bond formation is seen in the photolysis of 0-or p (but not rn-) chlorobenzonitrile, or of tetrachloro- or tetrafluoro-phthalonitrile (109), in the presence of methoxybenzenes; this leads to the formation of biaryls, in

6 Ncm F

+

F \ F (109)

CN

h v ,

F OMe

\ /

\ /

\

OMe

CN F

OMe 36%

some cases in reasonable yield.134 At 193nm, the photolysis of simple halobenzenes occurs from a state derived from S, (PhC1) or from S , , S,, or S , (PhBr).135 In the benzene, naphthalene, and biphenyl series in solution the preferred reaction pathway for aromatic carbon-halogen bond homolysis involves the aromatic triplet state, provided that the triplet energy is close to the required bond-dissociation energy; 36 this is not so for 1-chloronaphthalene, and an 132

K . Hamilton, J. A. Hunter, P. N. Preston, and J. 0. Morley, J . Chem. SOC.,Perkin Trans. 2, 1980, 1544.

13' 134

135 136

M. Sainsbury, Tetrahedron, 1980, 36, 3327. K. A. K. Al-Fakhri, A. C. Mowatt, and A. C. Pratt, J . Chem. Sot., Chem. Commun., 1980, 566. A. Freedman, S. C. Yang, M. Kawasaki, and R. Bersohn, Kokagaku Toronkai Koen Yoshishu, 1979, 232 (Chem. Abstr., 1980, 92, 180338). N.J . Bunce, J. P. Bergsma, M. D. Bergsma, W. De Graef, Y. Kumar, and L. Ravandl, J . Org. Chem., 1980,45, 3708.

Photochemistry of Aromatic Compounds 365 inefficient singlet-state reaction occurs in this case. A triplet state reaction is also proposed for the photodehalogenation reaction of the chlorotoluenes in the presence of ethane,13' and an initial quantum yield of 0.7-1.0 is estimated for this system. p-Dichlorobenzene on irradiation in benzene gives 4-chlorobiphenyl, and on further photolysis this gives p-terphenyl.' 38 p-Dibromobenzene (110) behaves in a similar way,139and flash photolysis studies reveal the cyclohexadienyl radical intermediates, and quenching studies point once again to a triplet mechanism. Br

x (1 1 I )

15--81%

(X= C1, Br; n = 2-10)

A mechanistic study 140 of the photoreactions of (p-ha1ophenoxy)alkyl bromides (1 11) yields some surprising results. First, despite the commonly encountered triplet nature of many aryl-halogen homolytic cleavage reactions, these compounds appear to react by way of an excited singlet state. Secondly, cleavage of the much weaker aliphatic carbon-bromine bond is seen in only one case, although intermolecular sensitization of such cleavage is possible using benzene as sensitizer. Photodehalogenation of a wide range of substituted dichlorobenzenes in methanol is reported to give the corresponding monochlorobenzenes.I4' 142 There is little that is new this year on the photochemistry of polychlorobiphenyls, except that the differing selectivity towards chlorine loss in neutral or alkaline solution (reported previously for polychlorobenzenes) is confirmed for b i p h e n ~ 1 s . lThe ~ ~ major difference is that the preference for loss of ortho-C1 in neutral solution becomes a competition between ortho- and para-C1 loss in the presence of alkali. Polychlorobiphenyls are used as examples in a paper 144 that gives equations to determine quantum yields in solution for situations where products act as inner filters in competing for light absorption. 1

13'

'" 140 14' 142 143

144

Y.Koso, T. Ichimura, T. Hikida, and Y. Mori, Kokakagu Toronkai Koen Yoshishu, 1979,170 ( C h m . Absir., 1980,92, 197 578). K. Chikasawa and M. Uyeta, Chem. Pharm. Bull., 1980, 28, 57. C. L. Pederson and C. Lohse, Acta Chem. Scand., Ser. B, 1979, 33, 649. R. S. Davidson, J. W. Goodin, and G. Kemp, Tetrahedron Lett., 1980, 21, 291 1. M. Mansour, H. Parlar, and F. Korte, Chemosphere, 1980, 9, 59. M . Mansour, S. Wawrik, H. Parlar, and F. Korte, Chem.-Ztg., 1980, 104, 339. T. Nishiwaki, M.Usui, and K. Anda, Tokyo-toritsu Kog-vo Gijutsu Senta Kenkvu Hokoku, 1980, 133 (Chem. Abstr., 1980, 93, 113 514). N.J. Bunce, J. Phorochem., 1981, 15, 1.

Photochemistry

366

Irradiation of thyroxine (1 12) liberates iodine prior to more extensive photodegradation. 14’ Polyhaloheteroaromatic compounds are shown 146 to undergo dehalogenation on irradiation, and in some cases a product (e.g., 113) of attack on

68%

(114)

the solvent is also identified. Tetrachloro-4-(phenylthio)pyridine (1 14) and similar (ary1thio)pyridines give benzothienopyridines on irradiation, by attack of the photogenerated aryl radical on the phenyl group of the substituent. Aromatic hydrocarbons can be readily substituted by radicals that are generated photochemically. A typical example is the reaction of N-methyldibromomaleimide and 4,4‘-bipyridyl,which gives a 3,8-phenanthroline-5,6-dicarboximide (1 15). This example is from a report 14’ that deals with many similar reactions

Q’

hv

d

Br’ QMe0

#;Me

N’

(115) 42%

between cyclic derivatives of dibromomaleic acid and aromatic compounds. 5Bromo-I ,3-dimethyluracil{116)reacts with electron-rich aromatics to give 5-aryl1,3-dimethyluracilsin a similar way,148although here a charge-transfer mechanism is proposed rather than a simple homolytic cleavage of a carbon-halogen bond in the uracil, Similar substitutions occur with indole derivatives,14’ and ‘4b

’*’ 14’

S. Koya, Kirakanta Igaku, 1979, 29, 341 (Chem. Absfr., 1980, 93. 131 762). J . Bratt, B. Iddon, A. G. Mack, H. Suschitzky, J. A. Taylor, and B. J. Wakefield, J . Chem. SOC., Perkin Trans. I , 1980, 648. K. M. Wald, A. A. Nada, G. Szilagyi, and H. Wamhoff, Chem. Ber., 1980, 113, 2884. S. Ito, I. Saito, and T. Matsuura, Tetrahedron, 1981, 37, 45. S. Ito, I. Saito, and T. Matsuura, J . Am. Chem. SOC.,1980, 102, 7235.

Photochemistry of Aromatic Compounds

:$Br+

0 (1 16)

aRq‘ -%

367

NMe

(R = Me,OMe)

NAO Me

4M5%

between 5-iodo-1,3-dimethyluraciland pyrene or phenanthrene. 5-Iodo- or 5bromo-uridine can also be coupled in this way to benzene, pyrene,’” or tryptophan;”’ in the last example the product (117) is formed only in a frozen aqueous solution. These reactions feature in a general review l S 2of the photochemistry of 5-bromo- and 5-iodo-uracil.

(R = ribosyl)

[R’= CH2CH(NH,)C0,H]

(1 17)

Me

Reports of the substitution of aromatic hydrocarbons by radicals derived by photolysis of peroxides include the photoreaction of peracetic acid and xylenes,’ 5 3 which gives products of ring and side-chain substitution by methyl or hydroxyl radicals; mechanistic studies of the photodecomposition of dibenzoyl peroxide in toluene to give, amongst other products, dimethylbiphenyls through the dimerization of (benzy1oxy)methylcyclohexadienyl radicals (1 18); s4 the reaction of toluene with phenyl or methyl radicals generated photochemically from dibenzoyl or diacetyl peroxide;155and the formation of naphthyl benzoates and phenylnaphthalenes in the naphthalene-sensitized photolysis of dibenzoyl peroxide.’56 The photolysis of the a-azohydroperoxide (1 19) in substituted benzenes (PhR; R = MeO, C1, NO,, or Me) gives hydroxylated products RC,H40H in isomer

’

lS1

lS2 154

’”

I. Saito, S. Ito, T. Shinmura, and T. Matsuura, Tetrahedron Lett., 1980, 21, 2813. S. Ito, I. Saito, H. Sugiyama, and T. Matsuura, Kokaguku Toronkai Koen Yoshishu, 1979, 10 (Chem. Absrr., 1980, 93, 8476). F. Hutchinson and W. Kohnlein, Prog. Mol. Sub-cell. Biol., 1980, 7 , 1. K. Tomizawa and Y. Ogata, To-yodaKenkyu Hokoku, 1980, 1 (Chem. Abstr., 1980, 93, 185 648). Y. Sakaguchi, H. Hayashi, and S. Nakagura, Bull. Chem. SOC.Jpn., 1980,53, 3059. Y. Ogata, K. Tomizawa, K. Furata, and H. Kato, J . Chem. Soc., Petkin Trans. 2, 1981, 110. A. Kitamura, H. Sakuragi, M. Yoshida, and K. Tokumaru, Bull. Chem. SOC. Jpn., 1980, 53, 2413.

Photochemistry

368

6

N-CH,

,OOH Ph

COOH

0

hv

HZOZ

’

FH \

(120)

Br (1 19)

ratios that are consistent with the formation of hydroxyl radicals as intermediates. s’ Hydroxylation also occurs on irradiating benzoic acid in the presence of hydrogen peroxide; salicyclic acid (120) is a major product at low conversion.l S 8 Other photohydroxylations are the formation of 2,5-dichloro-6nitrophenol (121) as the major product on photolysis of p-dichlorobenzene with nitric oxide in air,’” and the related formation ofp-nitrophenol, along with other

’

(122)

Cl

c1

c1

61

20%

phenols, from bromobenzene and nitrogen oxides in air.’60 In the absence of nitrogen oxides, the main products from bromobenzene are phenol and pbromophenol. 16* ortho-Hydroxylation occurs when the quinoxalin-2-one (1 22) is irradiated in sunlight.161 When the charge-transfer complex between hexamethylbenzene (123) and oxygen is irradiated (313 nm) in methanol, a methoxymethyl derivative and pentamethylanisole are formed. 16’ These are not the products obtained when singlet oxygen attacks (123): see structure (62). Finally in this section, an example of substitution in benzene by a phosphorus-centred radical is seen in the formation of 0-ethyl diphenylphosphinate(124) y s one of the products of photolysis of 0ethyl S-propyl phenylphosphonothibilte in benzene. 63 15’

16’ 16’ 16’

N . Narita, T. Tezuka, and W. Ando, Kokagaku Toronkai Koen Yoshishu, 1979, 198 (Chem. Abstr., 1980, 93, 25 562). Y. Ogata, K. Tomizawa, Y. Yamashita, and K. Takagi, Kokagaku Toronkai Koen Yoshishu, 1979, 120 (Chem. Absrr., 1980, 92, 180334). K . Nojima and S. Kanno, Chemosphere, 1980, 6, 437. K. Nojima, T. Ikarigawa, and S. Kanno, Chemosphere, 1980, 9, 421. M. J. Haddadin, J. Makhluf, and A. A. Howi, Heterocj&s, 1980, 14, 457. K. Onodera, H. Sakuragi, and K. Tokumaru, Tetrahedron Lett., 1980, 21, 2831. H. P. Benschop, C. A. G . Konings, D. H. J. M. Platenburg, and R. D e n , J . Chem. SOC.,Perkin Trans. 2, 1980, 198.

369

Photochemistry of Aromatic Compounds ,OMe

(123)

Eta,P/p 'hP

?Me

24% hv

+

'SPr

5 Intramolecular Cyclization Reactions A good review of the 4a,4b-dihydrophenanthrenesformed by photocyclization of

stilbenes has appeared,'64 which includes details of evidence for the stereochemistry at the ring junctions. A stilbene (1 25) substituted with a long-chain

carboxyalkyl group has been used as a probe for investigating conditions in vesicle solution^,'^^ the variables measured being the fluorescence and photoisomerization (trans + cis) quantum yields; a phenanthrene is also formed in the irradiation. Stilbene units incorporated into crown ethers (1 26) provide a substrate for the formation of new crown ethers with one or two phenanthrene rings.'66

(

+ <0.5% trans)

lhv

164

16' 166

K. A. Muszkat, Top. Curr. Chern., 1980, 88, 89. J. C. Russell, S. B. Costa, R.P. Seiders, and D. G. Whitten, J. A m . Chem. Soc., 1980. 102, 5678. M. Eichner and A. Merz, Tetrahedron Lett., 1981, 22, 1315.

370

Photochemistry

Five-membered ring systems with two adjacent phenyl groups can often be cyclized photochemically to give fused phenanthrene products. This type of reaction is reported 16' for 2,3-diphenylbenzo[b]thiophens (127); if a primary

-

(127) (R,R' = H,Me)

85%

1

PrNH, hv

-

R &R\ I

-

+

R' (1 28)

( 20%)

-

75%

amine is also present, a second product (128) is formed in which one of the aromatic rings is partially reduced. It seems likely from the results of deuteriumlabelling studies that the amine is involved in a subsequent photoreduction of the 1-oxide aromatic product. The photocyclization of 1,3,4-tripheny1-3-phospholene (1 29) leads to a phenanthrene that can be cleaved by ozonolysis to give a large-ring

hv 12. 0 2

4\

0 Ph

+

0 w o P

4\

0 Ph

phosphorus heterocyclic system.16* The reaction of diphenylmaleimides (130) gives both phenanthrenedicarboximides and their 9,1O-dihydro-derivatives,16' lb7

16* 169

A . Buquet. A. Couture, A. Lablache-Combier, and A. Polfet. Tetrahedron, 1981, 37, 75. E. D. Middiemas and L. D. Quin, J . Am. Chem. SOC.,1980, 102, 4838. K. Ichimura, S. Wdtanabe, K. Kusakawa, and H. Ochi, Nippon Kagaku Kaishi, 1980, 837 (Chem. Absfr., 1980, 93, 185 380).

Photochemistry of Aromatic Compoundr 37 1 and a study of the effect of acid shows that the relative yield of the dihydrocompound increases with decreasing pH. Stilbene-type photocyclizations provide a good route to condensed polycyclic aromatic hydrocarbons, and a study 170 of distyrylbenzenes and styryl- and distyryl-naphthalenes provides syntheses of a range of such hydrocarbons, including benzo[ghiJperylene(I 3 1) and fulminene (I 32). Two studies relating to

(132)

asymmetric photochemical synthesis of hexahelicene are reported. Starting from 1-(2-naphthyl)-2-(3-phenanthryl)ethylene (1 33) in a chiral mesophase, laevorotatory hexahelicene is obtained in very low optical yield.171With the alkene (134)as substrate optical yields are also and this report suggests that the asymmetric induction arises from both pitch and solute-solvent interactions. 1,4Dimethylhexahelicene, made by photocyclization on a dimethylstyryl alkene

( 134)

17'

172

T. S. Skorokhodova, G. N. Ivanov, V. I. Luk'yanov, Yu. G. Yur'ev, V. F. Kam'yanov, and E. B. Merkushev, Neftekhimiya, 1979, 19, 839 (Chem. Absrr., 1980,92, 215 131). A. Okami, H. Sakuragi, K. Tokumaru, and T. Tachibana, Kokugaku ToronkuiKoen Yoshishu, 1979, 184 (Chem. Abstr., 1980, 92, 197 579). M. Hibert and G . Solladie, J . Org. Chem., 1980, 45, 5393.

372

Photochemistry

(1 35) 64% (1 35), has been resolved and used as a starting point for a synthesis of an optically active [2.2]paracyclophanohexahelicene. All isomers of the parent phenanthro[b]thiophenes (e.g., 136) have been made, four of them by the photocyclization of appropriately oriented naphthyl thienyl

’

p

hv 12

’ (136)

32%

ethylenes. 74 In a related process, styrylimidazoles (1 37) react to give naphthoimidazoles,l although a p-nitro-substituent inhibits the cyclization. Several examples of azaphenanthrene (or more complex azapolycyclic aromatic hydrocarbon) formation by photocyclization are reported. In one study,’ 7 6 2-(parylviny1)pyrazines are the substrates, and a typical product is the pyridoquinoxaline (1 38). 1,4,5,8-Tetra-azaphenanthrene (1 39) is formed from 1,Zbis(pyrazy1)ethylene: 7 7 * interestingly, oxygen is used to oxidize the dihydrointermediate; iodine is not suitable because it complexes strongly with the starting material and enhances intersystem crossing, which deactivates the reactive (n,n*) singlet state.

’’

’*

(138) 173 174

177

M . Nakazdki, K. Yamamoto, and M. Maeda, J . Org. Chem., 1980,45, 1985. M. Iwao, M. L. Lee, and R. N. Castle, J . Heterocycl. Chem.. 1980, 17, 1259. K. Lindgren, K.-E. Stensio, and K. Wahlberg, J . Heterocycl. Chem., 1980, 17, 679. A. Ohta, K. Hasegawa, K. Amano, C. Mori, A. Ohsawa, K. Ikeda, and T. Watanabe, Chern. Pharm. Bull., 1979, 27, 2596. S. C. Shim and S. K. Lee, Synthesis, 1980, 116. S. C. Shim and S. K. Lee, Bull. Korean Chem. Soc., 1980, 1, 68.

Photochemistry of Aromatic Compounds

373

(139) 90%

The double photocyclization of 1,2-diphenylpyridiniumsalts has been reported previously, 79 and extensions of this reaction to many other polyaryl pyridinium compounds are now given;IE0amongst the examples are pyridylpyridinium salts (140).

Related to the stilbene cyclization is the photoreaction of 2-vinylbiphenyls to give 9,IO-dihydrophenanthrenes.The photocyclization of (141) and its Z-isomer is shown to be highly stereoselective on direct irradiation, but totally unselective when sensitized with benzophenone or xanthene. These results support the proposal that the singlet state undergoes conrotatory ring-closure followed by a suprafacial 1,5-shift of hydrogen, whereas the triplet-state reaction proceeds through a common intermediate, possibly a ‘perpendicular’ triplet state. Work on photochromic fulgides continues. The fury1 compound (142) gives a 2 ring-closed product in near quantitative yield on irradiation or on heating: I Ethe reaction can be reversed using visible (‘white’) light. This report also describes the

*e0 * :*

0

\

0

A. R. Katritzky, Z. Zakaria, E. Lunt, P. G. Jones, and 0. Kennard, J . Chem. SOC.,Chem. Commun.,

1979,268. A. R. Katritzky, Z . Zakaria, and E. Lunt, J. Chem. Soc., Perkin Trans. 1. 1980, 1879.

R. Lapouyade, R. Koussini, A. Nourmamode, and C. Courseille, J . Chem. Soc., Chem. Commun., 1980, 740.

H. G. Heller and S. Oliver, J . Chem. Soc., Perkin Trans. 1 , 1981, 197.

lBZ

Photochemistry of Aromatic Compounds

375

0 (146)

(R = H,Me)

693%

related reaction of 2-(pyridylviny1)chromones (146),'88 and in the formation of benzo[c]phenanthridines (147) from styryl-substituted isoquinolones. With these examples the interest has been mainly synthetic, but the reversible formation

'

OMe

7" hv

W

N

M

e

I'

fl::e \

NMe

'

0

0 (147) 16

+ 19%

+ 20

+ 21%

(R = aryl) of photocyclized products from 2-vinyl-3H-indolium salts (148), and their subsequent irreversible oxidation, is thought to provide a basis for explaining the fading of hemicyanine dyes. ''O Further mechanistic studies of the photoAash photolysis evidence for three cyclization of 1,Miarylbutenynes provide transient species: a non-participating triplet, an intermediate common to photocyclization and photo-oxidation, and a radical formed by hydrogen abstraction from the solvent. (148)

"'

'" 's9x

19'

I. Yokoe, K. Miguchi, Y. Shirataki, and M.Momatsu, J . Chem. SOC.,Chem. Commun., 1981,442. Y. Harigaya, T. Seiko, Y. Hiroko, T. Kusano, and M. Onda, Chem. Pharm. Bull., 1980, 28,2029. K. B. Soroka and J. A. Soroka, Tetrahedron Lurt., 1980, 21,4631. P. Fournier de Violet, R. Van Arendonk, W. Laarhoven, and J. Joussot-Dubien, C. R. Hebd. Seances Acad. Sci., Ser. C, 1980, 291, 9.

376 Photochemistry The formation of fused anthraquinone systems in a two-stage photoreaction between 2-bromo-3-methoxy-1,4-naphthoquinone and 1,l-diarylethylenes is well established, and the reaction has been extended to include 1-(heteroary1)-1phenylethylenes (e.g., 149). In general the preferred mode of ring-closure follows

0 hv

d

0

w 0

\

0

0

31%

-

the order 5-membered heterocycle > phenyl >> pyridyl, though the origin of this preference is not known. The same reaction type is used to prepare regioselectively the 8-, 9-, lo-, and 1 1-isomers of methoxy-5-phenylbenz[a]anthracene-7,1Zdione ( 150).

Me0

(151)

(R = H, Me)

A cyclization that involves a 1,Zdiarylethane system is the intramolecular reaction of the bridged azulene-benzene compounds (15 l), which gives, after dehydrogenation, azuleno[1,2,3-cd]phenalenes.Ig4 The initial product is said to be a tetrahydroazulenophenalene,although this would require an oxidative formation process.

'94

K . Maruyama, T. Otsuki, K. Mitsui, and M. Tojo, J . Hereroc.ycf. Chem., 1980, 17, 695. K. Maruyama, M. Tojo, H. Iwamoto, and T. Otsuki, Chem. Letr., 1980., 827. Y. Nesumi, T. Nakazawa, and I. Murata, Koen Yoshishu-Hibenzenkei Hokozoku Kagaku Toronkai (oyobii K o x Yuki Kagaku Toronkai. I l t l i , 1979, 145 (Cliem. Abstr., 1980, 92, 198 157).

377 Applications of enamide photocyclization in the synthesis of heterocyclic 19' by one of the most active groups in the field, and compounds are reviewed a further example of the reaction to give an azaberberine derivative (152) is Photochemistry of Aromatic Compounds 1959

hv

MeCN

(153)

66%

reported. 19' A related reaction occurs with N-aryl amides of a$-unsaturated acids, such as the amide (153) derived from benzo[b]furan-2-carboxylicacid or the corresponding indole and benzothiophene acids. The reaction of the isomeric amide (1 54) from benzo[b]furan-3-carboxylic acid gives the expected cyclization 0 bNMe

0

LNMe

product in aprotic solvents, but in protic solvents (or by subsequent treatment of the photoproduct with aqueous base) opening of the furan ring occurs, and it is suggested that a spirocyclohexa-2,4-dienone might be an intermediate in the reaction. 19* Heteroatom analogues of the stilbene-typeof photocyclization are known, such as that involving N-arylimines (1 5 5 ) of fluoro-substituted benzophenones,lg9 where cyclization takes place with elimination of HF to give phenanthridines. 196

19'

19* 199

I. Ninomiya, Heterocycles, 1980, 14, 1567. I. Ninomiya and T. Naito, Kaguku N o Ryoiki. Zokan. 1979, 69 (Chem. Abstr., 1980, 93, 95447). T. Naito and I. Ninomiya, Heteroc.vcles. 1980, 14, 959. Y. Kanaoka and K. pan-nohe, Tetrahedron Lett., 1980, 21, 3893. N. I. Danilenko, T. V. Fomenko, I. K. Korobeinichevd, T. N . Gerasimova, and E. P. Fokin, Izv. Akud. Nauk. SSSR, Ser. Khirn., 1980, 1606 (Chem. Abstr., 1981,94, 3905).

Photochemistry

378

F (155)

F

(R = F, CF,, MeO; R1= H, Me, MeO, F)

F 27--85%

Anilinoarylboranes undergo a similar reaction, and with the anilinodimesitylboranes (156) there is the possibility of forming products with elimination or with migration of methyl group. It is shown 2oo that the concentration of added iodine alters the ratio of elimination to migration significantly, and the suggestion is that iodine can assist (at low concentrations) or quench (at high concentrations) the formation of a radical cation, as well as assisting in the formation of another reactive species. N-Methylcarbazole is formed photochemically by cyclization in N-methyldiphenylamine, and a mechanistic study 201 shows that the effect of oxygen on triplet intermediates is not altered by a change from non-polar to aqueous or micellar solution, whereas the dehydrogenation of the 4a,4b-dihydrocarbazole is enhanced in polar media. Benzo[a]carbazole cannot be made by direct photocyclization of N-phenyl- 1-naphthylamine, but an indirect route by way of the tetrahydroThe related photocyclization of some naphthylamine (1 57) is substituted anilinoethylenes with electron-withdrawing groups on the alkene is reported203 as a route to indoline systems in high yield. In the case of 4-(Nmethylanilino)pent-3-en-Zone (158), an indole is formed in the presence of oxygen; but in the absence of oxygen the product is a different indole formed by J. L. R. Williams, J. Organomet. Chem., 1980, 195, 123. N. Roessler and T. Wolff, Photochem. Photobioi., 1980, 31, 547. R. J. Olsen and 0. W. Cummings, J. Heterocycl. Chem., 1981, 18, 439. A. G. Schultz and C.-K. Sha, Tetrahedron,1980, 36, 1757.

2oo M. E. Glogowski and '01

202 203

Photochemistry of Aromatic Compounds

/o

8 379

5

chloranil,

/

(1 57)

65 94

41%

35%

35%

elimination of acetaldehyde.204 Hydride shifts in a zwitterionic intermediate are proposed to account for the loss of the acetyl group. A mechanistic investigation ' 0 5 of the photocyclization of 1-(N-methylani1ino)3,4-dihydronaphthalene and other systems, both by flash photolysis and with steady-state irradiation, provides evidence for the importance of back reactions in the overall process. A similar flash photolysis study ' 0 6 of aryl vinyl ethers (closely related to the aryl enamines just described) confirms that the mechanism of cyclization is similar to that of the nitrogen analogues, going through an excited triplet state and a zwitterionic intermediate. Further studyzo7 of the photoreactions of l,l-dicyano-2-methyl-4-phenylbut1-ene (1 59) suggests that the 1,3sigmatropic shift (which is solvent- and wavelength-dependent) occurs via an

+ CN excited state with a staggered arrangement of groups, but the cyclization to an indane goes through a charge-transfer excited state with an eclipsed conformation; a charge-transfer absorption band is seen in the absorption spectrum of (1 59). 204 205 '06

'07

D. Watson and D. R. Dillin, Tetrahedron Lett., 1980, 21, 3969. T. Wolff and R. Waffenschmidt, J . Am. Chem. Soc., 1980, 102,6098. T. Wolff, J . Org. Chem., 1981,46, 978. R. C. Cookson, D. E. Sadler, and K. Salisbury, J . Chem. SOC.,Perkin Trans. 2, 1981, 774.

Photochemistry

380

Irradiation of anilides of o-bromo- or o-iodo-benzoic acids provides a route to phenanthridones, and with compounds such as (160) better yields are obtained when the iodo-derivative is used than with the bromo-acid, and the best solvent is The acetone (which may also act as a photosensitizer for the reaction).

Meoq! 2 Me0

Ho

Ly

\

hv

d

0

L 6

(162) 26%

photocyclization of 1-(o-bromobenzy1)-1,2,3,4-tetrahydroisoquinolines continues to be employed in the synthesis of aporphine alkaloids such as domesticine (161) 209 or oliveroline (162).210 An extension of this reaction to halogen derivatives of N-(benzy1)phenylethylamines such as (163) gives products that are apogalanthamine analogues. A full paper has appeared 213 dealing with the mechanism of photocyclization of 5-(o-halophenyl)-1,3-diphenyfpyrazoles (164), proposing that the reaction occurs by assisted homolysis of the carbon-halogen bond. The reasons for this

' ' 3

208 209

B. R. Pai, H. Suguna, B. Geetha, and K. Sardda, Indian J. Chem., Sect. B, 1979, 17, 503. B. R. Pai, H. Suguna, S. Natarajan, P. K. Vanaja, and R. Meenakumari, Indian J . Chern., Sect. B,

210

S. V. Kessar, Y. P. Gupta, V. S. Yadav, M. Narula, and T. Mohdmmad, Tetrahedron Lett., 1980,21,

211

S. Kobayashi, M. Kihata, Y. Ishida, and T. Shingu, Fukusokan Kagaku Toronkai Koen Yoshishu,

1979, 17, 525. 3307. 212

213

IZth, 1979, 196 (Chem. Abstr., 1980, 93, 72043). S. Kobayshi, M. Kihara, and T.Shingu, Yakugaku Zasshi, 1980, 100, 302 (Chem. Abstr., 1980,93, 1 50 429). J . Grimshdw and A. P. de Silva, Can. J . Chem., 1980, 58, 1880.

Photochemistry of Aromatic Compountis

R'

38 1

R'

hv

fi3

(163)

R3

(X or Y = halogen; R-R3

= H,MeO, OCH,O)

Ph

(164)

(X = CI, Br, I)

Ph

8&84%

proposal are that the quantum yields of product formation do not correlate with carbon-halogen bond energies [which are much higher than the energies of the lowest triplet states of (164)], and that they are unaffected by air, triplet quenchers, wavelength of irradiation, or concentration; they do, however, depend on solvent viscosity. The same group suggests 214 that in 5-(o-halophenyl)-1,3-diphenyl-4,5dihydropyrazoles (165) a homolytic cleavage occurs if X = I and Y = H,but an electron-transfer mechanism operates if X = Br and Y = COOMe.

Photocyclization of N-chloroacetyl amines has been used previously in the synthesis of nitrogen heterocycles, and the reaction of the substituted amine (1 66) leads to a benzazepinone that can be elaborated to give pseudoprotopine alkaloids.2 N-Chloroacetyl derivatives of the seven isomeric indolylethylamines give azepinoindoles and azocinoindoles by photocyclization. Quantum yields for the reaction are correlated with calculated (CND0/2 and INDO) electron densities, and on this basis mechanisms are suggested; the conclusion is that both indole radical cations and indolyl radicals (for the 1-substituted compounds) are

'

'I4 'lS 216

J. Grimshaw and A. P. de Silva, J . Chem. Soc., Chem. Commun., 1980, 1236. K. Orito, S. Kudoh, K. Yamada, and M. Itoh, Heterocycles, 1980, 14, 11. S. Naruto and 0. Yonemitsu, Chem. Pharm. Bull., 1980, 28, 900.

Photochemistry

382

involved. In a more complex system, a similar cyclization of an N-chloroacetylindolylethylamine (167) is a key stage in the construction of the catharanthine alkaloid skeleton.21 There are numerous reports of cyclizations to an aromatic ring that involve reactive centres generated ,photochemically. The elimination of nitrogen from Nphenyltriazolopyrimidines (1 68) gives an intermediate that leads on to pyrimidino[4,5:b]indoles in high yield. 218 A similar reaction involving a more

R

c1

2;". 'N

hv

C1

(169) (R = H, Me)

35%

highly substituted N-(6-isoquinolyl)triazolopyridine (169) provides a route to the 9-azaellipticine system,21 and substitution of the reactive chloro group is possible with nucleophiles such as R,N(CH,),NH,. Cyclization of arylnitrenes to give ring-expanded products in the presence of a secondary amine is a well known '17 218

R. J. Sundberg and J. D. Bloom, J . Org. Chem., 1980,45, 3382. T. Higashino, H . Eisaku, H. Matsuda, and T. Katori, Heterocycles, 1981, 15, 483. C. Rivalle, C. Ducrocq, J.-M. Lhoste, and E. Bisagni, J . Org. Chem., 1980, 45, 2176.

Photochemistry of Aromatic Compounds 383 process, and an example reported this year is derived from 6-azidobenzothiazoles.’” Irradiation of the 2,2’-bisazidobipheny1 (170) gives a dimethylphenazine as an unusual minor product, together with the major product, a 9,lOphenanthroline:22 the phenazine is thought to arise from aziridine intermediates.

hv

via

,

O

R

Irradiation of the substituted I-azido-2-phenoxyanthraquinones(1 71) gives products of nitrogen insertion into an aromatic C-H bond.222The reaction is not one of direct insertion of a nitrene intermediate, however: isoxazoles are shown to be involved, and can be isolated in the thermal reaction. The photocyclization of the (0-azidopheny1)benzimjdazoles (1 72) leads to products in which a new

(172) (R = Me,Pr‘,But)

1546%

nitrogen-nitrogen bond is formed, and the reaction can go through a triplet excited state of the azide, and not through a nitrene.223 In the presence of strong base, irradiation or azatriptycene gives a rearranged product (1 73) by way of 2-(9-fluorenyl)phenylnitrene and an a~anorcaradiene.~’~ The azanorcaradiene can be trapped by added tetracyanoethylene, and further proof of the intermediacy of the nitrene comes from the production of the same 220 221 222

P. T. Gallagher, B. Iddon, and H. Suschitzky, J . Chem. SOC.,Perkin Trans. J , 1980, 2362. A. Y a k , Bull. Chem. SOC.Jpn., 1980, 53, 2933. M. L. Gornostaev and V. A. Levdanskii, Zh. Org. Khim., 1980, 16, 2209 (Chem. Abstr., 1981, 94, 83 359).

223

D. Hawkins, J. M. Lindley, I. M. McRobbie, and 0. Meth-Cohn, J . Chem. Soc., Perkin Trans. J ,

224

T. Sugawara and H. Iwamura, J. Am. Chem. SOC.,1980, 102, 7134.

1980, 2387.

Photochemistry

384

4 \

/

\ /

\

\

I

(173) 69%

product mixture when 9-(o-azidophenyl)fluoreneis irradiated.225A carbene and its insertion product are proposed as intermediates in the photoreaction of substituted triptycenes (174),226 which is a mechanism directly analogous to that just described for the azatriptycenes.

(174)

(X = O,CPh, SMe, OPh)

( 175)

up to 70%

20%

Formation of a new carbon-oxygen bond in aromatic photocyclization is seen in the reaction of phenanthrene-4-carboxylic acid (175) in the presence of t-butyl h y p ~ i o d i t e , ~which ~ ’ involves radical attack on the ring system. Attack by an oxyradical is also evident in the formation of a heterocyclic oxygen compound in the 225

T. Sugawara and H. Iwamura, Kokagaku Toronkai Koen Yoshishu, 1979,78 (Chem. Abstr., 1980,93, 70 605).

226

227

Y. Kawada, H. Tukada, and H. Iwamura, Tetrahedron Lett., 1980, 21, 181. S. A. Glover, S. L. Golding, A. Goosen, and C. W. McCleland, J. Chem. SOC.,Perkin Trans. 1, 1981, 842.

Photochemistry of Aromatic Compounds 385 photolysis of the oxazoline (176),228and in the generation (in very low yield) of the naphthofuran (1 77) when ethyl 3-(2-naphthyl)-2-nitroacrylate is irradiated in acetone.*”

NOH

+

II

CloH,CCCO&t ll 0

(177) 3%

There are two unusual reports of reactions in which attack on a benzene ring by an excited-state ketone appears to give rise to products. Irradiation of 2(phenylthio)thiolan-3-one in acetonitrile gives (1 78), which could arise by a

(178) 45%

hydrogen-abstractionxyclization process that is typical of ketones when the site of attack is an aliphatic C-H position.230A more likely mechanism, however, involves the enol tautomer of the ketone and photocyclization of this phenyl vinyl sulphide system. The formation of (179) from 2,3-dibenzoylbicyclo[2.2.2]octa-2,5diene is rationalized 2 3 1 by a mechanism that involves initial attack by oxygen on a phenyl group. A new carbon-carbon bond is formed when the sultone (180) is irradiated;232 initially a ring-opened sulphonate ester is produced, and in a second photochemical stage ring-closure occurs after a-cleavage of the sulphonate. Carbon-carbon bond formation to an aromatic system is also apparent in the formation of the major product in the photolysis of (181) in the presence of diphen~lacetylene.~~~

”* 229

230 231

232

233

P. Zalupsky, T. Kamagai, and T. Mukai, Kokagaku Toronkai Koen Yoshishu, 1979, 158 (Chem. Abstr., 1980, 92, 214554). S. Hirotani and S. Zen, Kokagaku Toronkai Koen Yoshishu, 1979, 200, (Chem. Abstr., 1980, 93, 45 537). T. Sasaki, K. Hayakawa, and S. Nishida, Tetrahedron Lett., 1980, 21, 3903. S. Lahiri, V. Dabral, S. M. S. Chauhan, E. Chakachery, C. V. Kumar, J. C. Scaiano, and M. V. George, J. Org. Chem., 1980, 45, 3782. J. L. Charlton and G. N . Lypka, Can.J . Chem., 1980,58, 1059. N. E. Kolobova and L. V. Goncharenko, Khim. Geterotsikl. Soedin., 1979, 1461 (Chem. Abstr., 1980, 92, 198 198).

Photochemistry

386

\

COPh

Ph

(R = H, Me; X = O,S,CH = CH)

6 Dimerization Reactions Photodimerization reactions involving aromatic rings of two naphthalene units are not as frequently encountered as those involving anthracene. A study234 of the effect of high pressure on the photodimerization of methyl 3-methoxynaphthalene-2-carboxylateshows that the rate can be doubled (at 2000 bars), but this represents a much lower activation volume than for similar thermal reactions. An intramolecular dimer is formed when the anti-[3.3]-( 1,4)naphthalenophane (182) is irradiated;235the cycloadduct reverts to (182) on heating or on further irradiation. The syn isomer of (1 82) does not undergo this reaction. Anthracene photodimers have been investigated extensively. A study 2 3 6 of the photodissociation of the dimer of 9-methylanthracene, under both steady-state and flash conditions, suggests that the process occurs through an excited singlet 234

235 236

S. D. Hamann, M. Linton, and W. H. F. Sasse, Aust. J. Chem., 1980, 33, 1419. M.Yoshindga, T. Otsubo, Y. Sakata, and S. Misumi, Bull. Chem. SOC.Jpn., 1979, 52, 3759. S. Yamamolo, K. H. Grellmann, and A. Weller, Chem. Phys. Lerr., 1980, 70, 241.

Photochemistry of Aromatic Compounh

387

hv

c-hv

state at temperatures above 220 K, whereas below 200 K an exciplex is formed as an intermediate, and at 77K the excited triplet state is involved. Naphthacene (183) gives two isomeric dimers on i r r a d i a t i ~ n , ~not ~ ’ one as reported previously, and 1,2,3,4tetrahydronaphthacenebehaves in the same way. In each case nonfluorescent excimers are proposed as intermediates. The benzoquinoline (1 84) and the corresponding N-methylbenzoquinoliniumsalt both give head-to-tail photodimers that are dissociated to the monomers with radiation of a different wavelength.238

237 238

R. Lapouyade, A. Nourmamode, and H. Bouas-Laurent, Tetrahedron,l980,36, 231 1. J. Bendig, J. Fischer, and D. Kreysig, Tetrahedron, 1981, 37, 1397.

Photochemistry

388

A group of papers dealing with the intramolecular photodimerization reaction of a,mbis(9-anthryl)alkanes (185; n = 2-10) fails to produce agreement about the detailed mechanism of the reaction. Measurements of quantum yields for fluorescence, photoreaction, and intramolecular deactivation as a function of temperature are said to provide no support for a biradical intermediate,239 but rather to support a concerted mechanism. In reply, the proposers of the biradical mechanism reinterpret these data and find them consistent with their mechanism.24oA third research group reports results in fluid solution at room temperat ~ r e ; ~their ~ ’ concern is more with the question of excimer involvement in the mechanism, and they report that in many of the systems unidentified photoproducts are formed via excimers that do not lead to the ‘normal’ 9,9’-linked photodimer. The internal photodimer from (185; n = 3) has been studied in a matrix at 10K,242 and photodissociation is shown to lead to two different modifications of (185; n = 3) with different reactivities. A geometrical constraint on the intramolecular photoreactions of 9,9’-linked bisanthracenes is demonstrated243 by the failure of the di-substituted ethylenes (186) to give internal dimers.

(186; cis or trans)

(187; n = 3-45)

Anthracenes linked by a much longer chain also give internal photodimers, and this is demonstrated 244 by the formation (with reasonably high quantum yield) of photoproducts from bis(9-anthry1)polyoxa-alkanes (187) with linking chain lengths of up to 19 atoms. Kinetic parameters for this reaction have also been reported.245An elaboration of this system to the cyclophane (188), which has one 239 240

14’ 242 243

244 245

J. Ferguson, Chem. Phys. Lett., 1980, 76, 398. G. Jones, W. R. Bergmark, and A. M. Halpern, Chem. Phys. LRtt., 1980,76,403. A. Castellan, J. P. Desvergne, and H. Bouas-Laurent, Chem. Phys. Lett., 1980, 76, 390. A. Dunand, J. Ferguson, and G. B. Robertson, Chem. Phys., 1980, 53, 215. H.-D. Becker, K. Sandros, and L. Hansen, J . Org. Chem., 1981,46, 821. J . P. Desvergne, and H. Bouas-Laurent. Isr. J . Chem., 1979, 18, 220. J. P. Desvergne, A. Castellan, and R. Lesclaux, Chem. Phys. Lett., 1980, 71, 228.

Photochemistry of Aromatic Compounds

389

-

(188)

100%

short bridge and one long polyoxa-alkane bridge, provides a crown ether capable of complexing with alkali-metal cations and capable of changing its internal cavity size on irradiation.246- 248 The photocyclized complexes have different half-lives for thermal reversion according to the metal ion involved.

7 Lateral-Nuclear Rearrangements The archetypal photochemical lateral-nuclear rearrangement in aromatic compounds is the photo-Fries rearrangement, and a relatively simple example is reported 249 in which pchlorophenyl salicylate (189) gives 5-chloro-2,2'dihydroxybenzophenone. Use is made of the photo-Fries rearrangerhent of 1naphthyl esters (190) in the regioselective synthesis of tricyclic analogues of

CI ( 189)

q.JJ OCOR

~

\

R' (190)

(R = Me, C6HI1;R'

R@ \

/

/

R' = H,OMe)

33-7

1%

adriamy~inone;~~' in this, as in other examples, the photochemical version of the rearrangement is a 'cleaner' reaction than the corresponding thermal process. It is 246

247

248 249 250

I. Yamashita, T. Kaneda, T. Otsubo, and S. Misumi, Koen Yoshishu-Hibenzenkei Hokozoku Kagaku Toronkai (oyobi) Kozo Yuki Kagaku Toronkai, I2th, 1979, 181 (Chem. Absrr., 1980,92, 181 150). I. Yamashita, M. Fujii, T. Kaneda, T. Otsubo, Y. Sakata, and S. Misumi, Kokagaku Toronkai Koen Yoshishu, 1979, 64 (Chem. Abstr., 1980, 93, 70447). I. Yamashita, M. Fujii, T. Kaneda, S. Misumi, and T. Otsubo, Tetrahedron Lett., 1980, 21, 541. H.-C. Chiang and C.-H. Chi'en, Hua Hsueh, 1979, 7 (Chem. Abstr., 1981,94, 46445). D. J. Crouse, S. L. Hurlbut, and D. M. S. Wheeler, J . Org. Chem., 1981, 46, 374.

390

Photochemistry

reported 2 5 1 that l-acyl-l,2,4-triazoles and N-acyltetrazoles do not undergo photo-Fries reaction, unlike the related 1-acylimidazoles that have been shown to give photo-Fries products. The nitrogen analogue of the photo-Fries rearrangement is the photo-anilide reaction, in which irradiation of acetanilide, for example, gives a mixture of 0-and p-aminoacetophenones. If acetanilide is treated with singlet oxygen, however, paminoacetophenone is formed with very little of the ~ r t h o - i s o m e r an ; ~ ~energy~ transfer mechanism is proposed, though without conclusive evidence. The mechanism of the photorearrangement of ethyl N-arylcarbamates (191) has been R1QR2N HC0,R

RQC02R NH,

\

RQR2NH2

+

\

R3

R3

+

R 1 NHZ 0 R 2

\

\

CO,R

R3

(191)

investigated,”’ and the suggested pathway involves a (n,n*) triplet state, homolytic cleavage of the nitrogen-carbon bond, and reaction of the radical pair within a solvent cage. The in-cage radical pair mechanism is analogous to that generally accepted for the photo-Fries reaction. N-(p-Chloropheny1)butanamide (192) is a model compound for a series of herbicides, and its photochemistry in cyclohexane gives products of a photoanilide rearrangement and of substitution of the ring chlorine atom;254no Norrish type 2 product (p-chloroacetanilide) is found. A modification of the photoanilide reaction is applied in an approach to the synthesis of iboga alkaloids; the relevant photochemical stage involves the indole NHCOPr

c1 (192)

I$

= 0.006

n

(193)

derivative (193), which on irradiation gives a rearranged tetracyclic lactam, apparently formed by cleavage of the aromatic nitrogen-acyl bond followed by attack of the acyl fragment on the secondary amine in the ~ i d e - c h a i n . ~ ~ ~ 251 252

253 254 255

K. Murato, T. Yatsunami, and S. Iwasaki, Helv. Chim. Acta, 1980, 63, 588. H. M. Chawla, A. Mittal, K. Chakrabarty, and S. S. Chibber, Curr. Sci., 1980, 49, 497. J. E. Herweh and C. E. Hoyle, J . Org. Chem., 1980, 45, 2195. V. A d a , H. E. Gsponer, and C. M. Previtali, Rev.Latinoam. Quim., 1980, 11, 145. Y. Ban, K. Yoshida, K. Kobayashi, J. Goto, E. Ishigamori, and T. Oishi, Koen Yoshishu-Tennen Yuki Kagobutsu Toronkai, 22n4 1979, 548 (Chem. Abstr., 1980, 92, 198606; 1981,93, 168461).

Photochemistry of Aromatic Compounds

39 1

The photorearrangement of sulphur, selenium, and tellurium analogues of phenyl carboxylates has been reported in a series of papers over the past few years. Some of the reactions are reviewed in a more general account256 of the photochemistry of organic selenium and tellurium compounds. Typical examples of the process are seen in the reactions 2 5 7 of thiol esters (194) and (195), and those 0

Br hv

+

( 195)

of the corresponding selenol esters.258Note that with (194) subsequent oxidative

cyclization of the thiophenol occurs, whereas in the case of bromine-containing systems such as (195) elimination of HBr takes place in the second stage of the reaction. The same reaction type is also described259for a pyridine derivative (196). In a paper concerned mainly with the cyclization of radicals generated by cleavage of an acyl-sulphur bond in aromatic thiol esters, the disulphide (197) is reported to give a thioxanthone in a process that must involve a photochemical lateral-nuclear rearrangement at some stage.260

0

37% (197) 256

’” 258 259

’

J. Martens and K. Praefcke, J. Organomet. Chem., 1980, 198, 321. K. Beelitz and K. Praefcke, Liebigs Ann. Chem.. 1980, 1597. K. Beelitz, K. Praefcke, and S. Gronowitz, J . Organomet. Chem., 1980, 194, 167. K. Praefcke and U. Schulze, J. Organornet. Chem., 1980, 184, 189. B. Kohne, K. Praefcke, and C. Weichsel. Phosphorus Sulfur, 1979, 7 , 21 1 .

Photochemistry

392

(1 98)

13-35%

635%

N-Phenylsulphonamides ( 198) undergo a rearrangement on irradiation to give amino-substituted diaryl sulphones,261 and this may be a significant factor in light-induced dermatoses or photosensitization with these compounds. The photolysis of aryldisilanes gives products that include those of a lateral-nuclear rearrangement, and it is now shown 2 6 2 that the reaction involves homolytic cleavage of the silicon-silicon bond; the silicon radicals can undergo various incage reactions, or they can escape from the solvent cage and be trapped by added 1,l-di-t-butylethylene. Finally there are a number of papers dealing with photoreactions of diarylcyclopropenes and arylindenes, which formally involve migration of a carbon group from the ‘side-chain’ to the ortho-position of an aromatic ring. An example of the basic reaction is the formation of indenes when 1,3-diphenylcyclopropenes (199) are irradiated directly. Now it is shown 263 that isomeric indenes are formed when the reaction is carried out in the presence of 9,10-dicyanoanthracene, and an electron-transfer mechanism is invoked to account for the change of product. In a separate paper 264 concerned largely with intramolecular photocycloaddition reactions, cyclopropenes (199; R = allyl) are reported to give both types of indene on direct irradiation, via the normally postulated vinylcarbene intermediate. The

R

Ph

261

262

263 264

B. Weiss, H. Durr, and H. J. Hass, Angew. Chem., Int. Ed. Engl., 1980, 19, 648. H. Sakurai, Y. Nakadaira, M. Kira, H. Sugiyama, K. Yoshida, and T. Takiguchi, J . Organomet. Chem., 1980, 184, C36. A. Padwa, C. S. Chou, and W. F. Rieker, J. Org. Chem., 1980 45, 4555. A. Padwa, T. J. Blacklock, R. Loza,and R. Polniaszek, J. Org. Chem., 1980, 45, 2181.

Photochemistry of Aromatic Compounds

393

preference for phenyl migration in the photorearrangement of 1-aryl-1phenylindenes (200) contrasts with the unselective nature of the thermal rearrangement.265 Reactions of this type are included in a review266 of isoindenes as intermediates in both thermal and photochemical reactions.

"' C. Manning, M. R.McClory, and J. J. McCullough, J. Org. Chem., 1981, 46, 919. 266

J. J. McCullough, Acc. Chem. Res., 1980, 13, 270.

5 Photo-reduction and -oxidation ~~

BY A. COX

1 Reduction of the Carbonyl Group Detailed information has been made available on the kinetics of some transient processes from a study of the photochemistry of various aliphatic ketones using laser flash photolysis and other techniques.' Excitation of pentan-2-one in water leads to a triplet state of lifetime 62ns, which proceeds to Type I1 fragmentation with a quantum yield of 0.43. All of the triplet-derived biradicals lead to products. In the case of 5-methylhexan-2-one, there is evidence to suggest that the species detected is a Type I1 biradical. The photoreduction of benzophenone by benzhydrol has been further studied.2 Following H-abstraction from benzhydrol by the yln* uncomplexed triplet state of benzophenone, a radical pair is formed. This fails to couple measurably within the solvent cage and after escape of the radicals from the cage, there ensues a series of H-transfer reactions with the ground-state ketone. The mechanisms normally written for the overall process imply that the pairs of radicals, initially generated by hydrogen-abstraction, couple to give pinacol, but such mechanisms are now untenable. Solvent effects have been shown to play an important role in the photochemistry of xanthone. Values of the bimolecular rate constant obtained for the reaction of the triplet state with Me,CHOH are found to be highly sensitive to the hydrogen-bonding properties of the medium and the results are taken to imply an unusually large inversion of the nn* and m*triplet states. The photoreduction of benzophenone by triethylamine has been studied by ps absorption spectroscopy and this has revealed that a CT complex (A,, 610nm) is formed within lops of photolysis. This is quenched within 15ps by 545 nm). Laser proton transfer generating benzhydrol and amine radicals (A, flash photolysis studies have shown5 that the primary photoreaction of the benzophenone triplet in benzene solution containing low concentrations of aliphatic amines is to give the benzophenone ketyl radical. The quantum yield of this process is 0.9-1.0 and implies that the initial exciplex does not play a significant role. Overall quantum yields for the reduction of benzophenone by neat t-butylamine are low, suggesting that the starting materials are regenerated by disproportionation of ketyl and aminyl radicals. In some related work,6 the same authors report that quenching of excited benzophenone by amines normally occurs by hydrogen abstraction from N or C,, with radical formation. However this is not the case with DABCO, which leads to formation of the triplet amine CT complex or radical ion pair. The radical anion generated in the photoreduction of

'

V. Encinas, E. A. Lissi, and J. C. Scaiano, J. Phys. Chem., 1980,84, ' M. Schuster and P. B. Karp, J. Photorhem., 1980, 12, 333. ' J.D.C.I. Scaiano, J. Am. Chem. SOC.,1980, 102,1141.

948.

G. Schaefer and K. S. Peters, J. Am. Chcm. SOC.,1980, 102, 7566. ' C Inbar, H. Linschitz, and S. G. Cohen, J. Am. Chem. SOC.,1980, 102, 1419. ' S.S. Inbar. H. Linschitz, and S. G . Cohen. J. Am. Chem. SOC.,1981, 103, 1048.

394

Photo-reduction and -oxidation 395 benzophenone by DABCO has been shown to form within 20ps and to be stable on the ps time scale. By contrast, the radical anion of fluorenone also forms in 20ps but is unstable and decays in 6Ops. Aliphatic thiols are reported * to retard the photoreduction of benzophenone by tertiary amines and to accelerate reductions that are retarded by Me,CNH,. This catalytic effect is interpreted in terms of a sequence of H-atom transfers, which are normally involved in the retardation process. The N-centred aminyl radicals from primary and secondary amines and from Me,CNH, abstract H from the sulphur atom of the thiol, and this is then followed by abstraction by the thiyl radical of the H from the a-carbon atom of the amine. Efficient reduction depends upon the participation of Ccentred radicals. A new process for the sensitization of ketone photoreduction depends on the use of low-lying metal-to-ketone charge-transfer excited states.' Thus quenching of the optical emission of fac-[XRe(CO),L,] o( = C1, L = 4-benzoylpyridine; X = I, L = 4acetylpyridine) by triethylamine initiates a sequence of reactions which ultimately gives Re-bound methyl- or phenyl-4pyridylmethanol and oxidation products of the amine. This is the first reported example of a photoredox process involving MLCT in which L is a ligand undergoing the redox reactions. Hydrogen selenide has proved to be an effective trap for radicals generated in Norrish Type I reactions, and also for short-lived excited carbonyls." The rate constant for the photoreduction of acetophenone with H,Se in THF has been determined as 4.7 x 1 0 8 ~ - ' s - ' . The reduction of various other ketones and aldehydes by hydrogen selenide has also been described.' Investigation of the temperature dependence of the photochemistry of omethylacetophenone has revealed', that the rate of decay of the biradical generated in the photoenolization is associated with a low A factor. An explanation for the effect lies in the requirement for spin inversion in the process. The key step in a newly developed synthesisof ( +)-oestrone is the photoinduced cyclization (1) + (2). Excitation of (1) induces photoenolization to the kinetically

'

0& HO

i.> 340 nm

Me0 \

Me (1)

H

Me0 \ (2)

unstable o-quinodimethane, which undergoes intramolecular [4 + 2]Cycloaddition to (2). This can be readily converted to (+)-oestrone. In a flash photolysis study of the photoreduction of chloranil to tetrachlorohydroquinone,solvent and isotope effects have been interpreted in terms of

' a lo

l2 l3

K. S. Peters, S. C. Freilich, and C. G. Schaeffer, J. Am. Chem. SOC.,1980, 102, 5701. P. G. Stone and S. Cohen, J. Am. Chem. SOC.,1980, 102, 5685. S. M. Fredericks and M. S. Wrighton, J . Am. Chem. SOC.,1980, 102, 6166. N. Kambe, K. Kondo, and N. Sonoda, Chem. Lett., 1980, 1629. N. Kambe, K. Kondo, S. Murai, and N. Sonoda,Angew. Chem., Int. Ed. Engl., 1980, 19, 1008. J. C. Scaiano, Chern. Phys. Lett., 1980, 73, 319. G. Quinkert, W. D. Weber, U. Schwartz, and G.Duerner, Angew. Chem., Int. Ed. Engf., 1980, 19, 1027.

Photochemistry

396

a charge-transfer mechanism.l4 E.s.r. data obtained from measurements on the photoreduction of frozen solutions of some diphenoquinones by amines suggest the existence of radical pairs in liquid solution." Photoreduction of 1,Znaphthoquinone by acetaldehyde proceeds by a mechanism involving the initial radical pair, as shown l 6 by measurements of 'H CIDNP and of the change of product distribution with temperature. However, at 20 "C at least 6.7% occurs by addition of a free acyl radical to the quinone in its ground state. In some related work,17 strong evidence has been obtained for secondary polarization of 1,4-naphthosemiquinone radicals during photoreduction. The temperature dependence of the chemical decay rate constant showed that the termination process is diffusion controlled. The photoinduced reduction of some quinones by zinc porphyrin and also by its tetraphenyl derivative has been studied in micellar systems. The mean time for intramicellar electron transfer has been established as 0.2 p,and for duroquinone the rates of entry and exit from the micelle have been found to be 5 x 10" M - sand 6 x lo5 M - s- ', respectively. Quinones possessing long chains are less mobile and partial charge separation could be achieved. Irradiation of anthraquinone in aqueous sodium dodecyl sulphate leads to anthraquinol and the surfactantanthrahydroquinone ether as major products via the triplet state of the anthraquinone. CHMeR

I F'h%N,CHMeR 0

HS Me

ha

MeOH

(3) R = Me, Et

Ph 0 e < H M e R

On irradiation in MeOH, (3; R = Me or Et) undergoes 7-hydrogen abstraction followed by intramolecular radical reaction to give a B-lactam. However, excitation in the nn* region of the thiocarbonyl group does not induce this transformation, suggesting that photocyclization of the thioxoacetamides proceeds from upper excited states as in the case of thiones.20

2 Reduction of Nitrogen-containing Compounds The first results have been reported 2 1 of the synthesis of 1,l'-bis[3(trimethoxysilyl)propyl]-4,4'-bipyridinium bromide and of its use in the derivatization of Pt or p-type Si electrodes. In the dark, p-type Si is blocking to reduction but illumination with light of greater energy than the band gap results in reduction of the surface-confined reagent. This surface will reduce a variety of species such as Fe(y5-C5Hs)2+in MeCN, or [Ru(NH&I3+ in water, and is l4 l5

l7 l9

'' *'

T. Nanun, T. Iwata, H. Kobayashi, and T. Morita, Koen YoshishuBunshi Kozo Sogo Toronkai, 1979, 230. G. G. Lazarev, 0. B. Lantratova, Yu. A. Ivanov, I. E. Pokrovskaya, and M. V. Serdobou, tzv. Akad. Nauk SSSR, Ser. Khim., 1980, 942. K. Maruyama, A. Takuwa, S. Matsukiyo, and 0. Soga, J. Chem. Soc., Perkin Trans. I , 1980, 1414. S. Frydkjaer and L. T. Muus, Chem. Phys., 1980, 51, 335. M. P. Pileni and M. Graetzel, J . Phys. Chem., 1980, 84, 1822. V. Swayambunathan and N. Periasamy, J, Photochem., 1980, 13, 325. H. Aoyama, S. Suzuki, T. Hasegawa, and Y. Omote, J. Chem. Soc., Chem. Commun., 1979, 899. D. C. Bookbinder and M. S . Wrighton, J. Am. Chem. Soc., 1980, 102, 5123.

397 capable of undergoing many thousands of redox cycles without significant deterioration. The mechanism of the CdS-sensitized photoreduction of heptylviologen has been investigated and is thought to occur by transfer of a photoexcited electron from the conduction band of the CdS to the absorbed heptylviologen.22Addition of surfactants was observed to enhance the reaction rate. The methylviologen dimer (4) undergoes a photoinduced two-electron Photo-reduction and -oxidation

[

M e N x C H 2 ] C2 H 2 4C10, (4)

reduction by propan-2-01, a process which leads exclusively to the stable radical cation dimer.23 An intramolecular process seems to be involved. Methylviologen itself has also been photoreduced in an alcoholic medium 24 as well as in the solid phase adsorbed on cellulose paper.25 Other polysaccharides such as starch and cotton wool were found to be similarly effective. The kinetics and mechanism of the photoreduction of water to hydrogen have been investigated26 in a system containing methylviologen and haematoporphyrin as sensitizer in an aqueous micellar solution together with a reducing agent such as (HOCH,CH,),N or HSCH2CH20H. Hydrogen was found to be evolved if the system contained hydrogenase or colloidal Pt as catalyst. Irradiation of solutions of methylviologen containing cysteine and cationic micelles into which Zn" tetrasulphophthalocyanine had been incorporated leads 2 7 to irreversible reduction of the viologen. The non-sulphonated phthalocyanine was found to be a more efficient photosensitizer for this reaction. Kinetic studies have shown a strong dependence of the initial rate on cysteine concentration and on pH, and the reaction probably involves reductive quenching of the cysteine to give the radical anion of the zinc complex, together with the cysteine radical cation. A study has been made of the kinetics of the photoreduction of methylviologen by zinc tetraphenylporphyrin triplets in mixed micelles containing the functional surfactant N-dodecyl-Nmethylviologen ( 5 ) and cetyltrimethylammonium chloride.28It was found that the back electron-transfer from reduced (5) to oxidized zinc tetraphenylporphyrin could be intercepted if a donor such as NADH was cosolubilized in the micelle, and in fact irreversible reduction of ( 5 ) and production of hydrogen has been successfully achieved. Sensitized irradiation of the amphiphatic viologens (6; n = 10, 12, 14, or 16) using a Ru" trisbipyridine-type complex in the presence of edta brings about its photoreduction. Bilayer systems give the best yields and

(6)

*' 23 24

'' 26 27

F. D. Saeva, G. R. O h , and J. R. Harbour, J . Chem. SOC., Chem. Commun., 1980,401. M. Furve and S. Nozakura, Chem. Lett., 1980, 821. M. Kaneko, H. Araki, and A. Yamada, Sci. Pap. Inst. Phys. Chem. Res. (Jpn). 1979, 73, 67. M . Kaneko, J. Motoyoshi, and A. Yamada, Noture (London), 1980, 285, 468. I. Okura and K. T. Nguyen, J . Chem. Soc., Faraday Trans. I , 1980, 76, 2209. J. R. Darwent, J. Chem. SOC.,Chem. Commun., 1980, 805. M. P. Pileni, A. M. Braun, and M. Raetzel, Photochem. Photobiol., 1980, 31, 423.

398 Photochemistry examination of electron transport across the lipid bilayer using several electron carriers revealed that dialkylalloxazines were the most satisfactory.29 Aliphatic amines have been found'O to quench the fluorescence of acridine efficiently and a linear relationship has been demonstrated between the logarithms of the Stern-Volmer quenching constants and the ionization potentials of the amines. The photoreduction of the acridine occurs in 20% Me,COH-MeCN via an exciplex formed between the ground state of the amine and the acridine '(n,n*) state and in 20% Me,COH-C,H, via the '(n,n*) state of the acridine. A quantitative study has been reported 31 of the photoreactivity of 2-nitrophenazine with tertiary amines. Excitation to the '(n,n*) state leads via a non-emitting complex (7) to abstraction of hydrogen from the a-carbon atom of the amine to

(7)

give the 2-nitrophenazinyl radical. Photoreductive acylation of phenazine has been observed 3 2 on irradiation of the parent heterocycle in the presence of aldehydes, and leads to N-acylated 5,lO-dihydrophenazineas product. The mechanism of the transformation has not yet been investigated but it is suggested that it may be related to the reductive photoalkylation of acridine by aliphatic carboxylic acids, and its analogy to pyruvate dehydrogenase activity is discussed. Deoxygenation reactions have been recorded for same methoxyquinoline and methoxyisoquinoline N-oxides.3 3

3 Miscellaneous Reductions Irradiation of aromatic hydrocarbons such as phenanthrene, anthracene, naphthalene, and certain substituted naphthalenes in the presence of NaBH, and rn- or p-(NC),C,H, promotes a Birch-type photoreduction.34* 3 5 The reaction seems to occur by electron transfer from the excited singlet state of the arene to the electron acceptor giving the arene radical cations, which are then reduced by the borohydride. Other reducing agents such as NaBH,, NaBH,CN, and NaBH(OMe), have been found to be effective and all lead to different isomer ratios. In a mechanistically related reaction, both fluoren-9-01and the corresponding acetate are reported 36 to be photoreduced to the parent hydrocarbon in the presence of aliphatic amines. The products arise by photoinduced electron transfer followed by proton transfer from the amine. The yield depends on the structure of the amine and increases in the order primary < secondary < tertiary amine. In 29

30 31

32 33 34

35 36

T. Matsuo, K . Takuma, K. Itoh, and K. Sakura, Kokagaku Toronkai Koen Yoshishu, 1979, 244 K. Okutsu and M. Kobayashi, Josai Shika Daigaku Kiyo, 1979, 8, 215. A. Albini, G. F. Bettinetti, and G. Minoli, J. Chem. SOC.,Perkin Trans. I , 1980, 191. M. Takagi, S. Goto, and T. Matsuda, Bull. Chem. SOC. Jpn., 1980, 53, 1777. A. Albini, E. Fasani, and L. M. Dacrema, J. Chem. Soc., Perkin Trans. 1, 1980, 2738. M. Yasuda, C. Pac, and H. Sakurai, Kokagaku Toronkai Koen Yoshishu, 1979, 262. M. Yasuda, C. Pac, and H. Sakurai, J . Org. Chem., 1981,46, 788. M. Ohashi, Y. Furukawa, and K. Tsujimoto, J . Chem. Soc., Perkin Trans. I , 1980, 2613.

399 pyrene-amine systems, a study has been made of H-atom transfer via the heteroexcimer state.37Using flash phatolysis, the transient exciplexes originating from 2,7-di-t-butylpyrene with 3,4,6-(Me,C),C,H,NH,, and from pyrene and PhNHEt have been observed. In all cases, steric hindrance to electron transfer appears to be less important than steric hindrance to atomic hydrogen transfer. Photo-oxidation and photoreduction of the zinc tetraphenylporphyrin radical cation have been described.38 The disproportionation equilibrium [equation (l)] Photo-reduction and -oxidation

2ZnTPPt, C10,-

ZnTPP2', 2C10,-

+ ZnTPP

(1)

was investigated by flash photolysis and the values obtained for the forward and backward rate constants are 1.2 x 1 0 5 ~ - ' s - ' and 1.4 x l o l o M u I - ' S - ' , respectively. Metalloporphyrinshave been used 39 to catalyse the photoreduction of water in a system consisting of Zn" porphyrins, and colloidal Pt together with methylviologen, edta, or N-phenylglycine. The efficiencies far exceed those obtained for the [Ru(bipy),12+ system. Cetyltrimethylammonium bromide, SDS, and Tween 20 micelles have been used4* to solubilize alkylanthraquinones in the photoreduction of electron acceptors such as (8) and ferricyanide in an aqueous medium. Irradiation of

M e a M Mee Me

I

optically active 2,3-trans-3-hydroxyflavanones in anhydrous ethyl acetate is reported 41 to give free phenolic flavanone analogues. This is a photochemical equivalent of a Clemmensen reduction and is important as it constitutes a general method of direct access to optically pure flavanones in moderate yield. A comparison has been published 42 of the photodechlorinations of chloroderivatives of benzene, naphthalene, and biphenyl. Numerous mechanisms are possible for reductive dechlorinationsin general, but for chloroacenes the reaction seems to occur by triplet-state homolysis of the A r 4 1 bond provided that the triplet energy is close to the bond-dissociation energy. This is not the case for 1chloronaphthalene, however, and an inefficient reaction occurs from the singlet state. In a quantitative study of the photoreduction of 0-ethyl S-n-propyl phenylphosphonothioate (9),irradiation at 254nm has been shown to lead to a mixture of 0-ethyl phenylphosphinate, propanethiol, 0-ethyl phenyl37

I. Karaki, T. Okada, N. Mataga, Y. Sakata, and S. Misumi, Kokagaku Torondai Koen Yoshishu, 1979,

38

W. Potter, R. N. Young, and G . Levin, J . Am. Chem. SOC., 1980, 102, 2471. G. McLendon and D. S. Miller, J. Chem. SOC.,Chem. Commun., 1980, 533. G . V. Fomin, M. M. Shabarchina, and Yu. Sh. Moshkovskii, Zh. Fiz. Khim., 1980,54, 2400. J. H. Van der Westhuizen, D. Ferreira, and D. G. Roux, J . Chem. SOC.,Perkin Trans. I , 1980, 1003. N. J. Bunce, J. P. Bergsma, M. D. krgsma, W. De Graaf, Y. Kumar, and L. Ravanal, J . Org. Chem.,

34. 39 40 41

42

1980,45, 3708.

400

Photochemistry

phosphonothioic acid, and propane.43 These compounds are formed by photoreductive cleavage of the P-S or S--C bond (+ = 0.14 or 0.05, respectively). The rate of these photoreductions is not influenced by the H-donor capacity of the solvent, suggesting that the reaction proceeds without prior H-abstraction, but rather by direct homolysis of the excited state of (9). The intermediate radical [EtO(Ph)P(O)]’ has been detected by e.s.r. in support of this conclusion. Several new photochemical hydrogen-abstraction reactions of epoxynaphthoquinones have been described 44 (Scheme 1) and various other transformations of a broadly similar nature are also reported. 0

R

=

H, Me, Et, Pr, or Me,CH

a,R 0

+

+

9, 9’-bixanthenyl

OH

0 Scheme 1

4 Singlet Oxygen Reviews have appeared on photo-oxidation and toxi~ity,~’ and on the involvement of singlet oxygen in the photofading of dyes.46 A study of solvent deuterium isotope effects on the lifetime of singlet moleqular oxygen has found that on going from MeCN and CHC1, to the corresponding perdeuteriated analogues, the lifetime increases by at least an order of magn i t ~ d e . ~These ’ results suggest that an earlier treatment of the quenching of singlet oxygen by solvent interactions may need revision.48The lifetime of singlet oxygen has been measured 49 in different solvents by monitoring the luminescence decay time at 1270nm using palladium mesoporphyrin as sensitizer. Deactivation occurs by exchange of electronic energy to overtones of vibrations of CC, CH, and OH groups of solvent molecules. In some related works0 the same authors report lifetime studies that suggest that the 1588nm luminescence is a result of the electron-vibrational transition IAg(vl = 0) -+ 3Z,-(v = 1). Quenching of singlet oxygen luminescence by chlorophylls, porphyrins, carotenoids, and lipids has been 43

44

” 46

47

48 49

H . P. Benschop, C. A. G . Konings, D. H. J. M. Platenburg, and R. Deen, J . Chem. SOC.,Perkin Trans. 2, 1980, 198. K. Maruyama, S. Arakawa, A. Osuka, and H. Suzuki, Kokagaku Toronkai Koen Yoshishu, 1979,24. C . S. Foote, Mol. Basis Environ. Toxic., 1980, 37. T. Kitao, Kagaku Kogyo, 1980, 31, 1035. P. R. Ogilby and C. S. Foote, J . Am. Chem. SOC.,1981, 103, 1219. D. R. Kearns and P. B. Merkel, J . Am. Chem. SOC.,1972, 94,7244. I. M. Byteva and K. I. Salokhiddinov, Biqfizika, 1980, 25, 358. K. I. Salokhiddinov, B. M. Dzhagarov, I. M. Byteva, and G . P. Gurinovich, Chem. Phys. Letr., 1980, 76, 85.

Photo-reduction and -oxidation

401

examined51 in H,O and in D20, and the results suggest that the lifetime is independent of the nature of the solvents and is about 500s. Complexes of porphyrins, e.g. tetraphenylporphine (TPP), with highly charged metal ions such as FeII', Mn"' , Sn'" , and AlI", the synthetic dimer of TPP (p-0x0-bis-FeTPP), and Fen'-mesoporphyrin IX dimethyl ester have been used 5 2 to quench the luminescence of singlet molecular oxygen. Stern-Volmer kinetics are obeyed, and with the monomeric iron and manganese porphyrins, quenching is probably by energy transfer from singlet oxygen to the 7t-d levels of the quenchers. An attempt has been made to establish the efficiency of energy transfer from singlet oxygen by use of steady-state yield data. 5 3 Triplet-sensitized reactions of singlet oxygen with 2,5di-butylfuran were investigated for benzophenone, acridine, and anthracene. In no case was unit efficiency observed and the ketone was established as being a significantly poorer sensitizer for singlet-oxygen production than either of the other compounds. Excited states of porphyrins and metalloporphyrins are quenched by 0, in protic and aprotic solvents. E.s.r. studies suggest54 that superoxide ion and singlet oxygen are formed in quenching processes of nett electron and excitation energy-transfer, respectively. The partitioning ratio is quite different from that obtained with Rose Bengal, and singlet oxygen is the major product. The yield of singlet oxygen in the quenching of triplet states of aromatic compounds by molecular oxygen has been reported. This was found to decrease along the series 9,lO-diphenylanthracene > fluorene > 9-methylanthracene > phenanthrene > acenaphthene > p-terphenyl > anthracene > fluorenone > Ph,CO > Ph,N, and confirmed the importance of CT states in triplet quenching by 02. The reactions of oxygen (2l0,) and oxygen (Z3PJ)with halomethanes have been examined,s6 and for O(2'0,) with CF,Cl, CF,Br, CF31, and CHF,Cl, the dominant channel is abstraction yielding a halogen oxide. Reactions of O(2'0,) closely parallel those of singlet methylene and an efficient mechanism appears to exist for the quenching of O(2l0,) to the ground state. A kinetic study of the reactions of singlet molecular oxygen with organic compounds has established that the second-order rate constants are in the order olefins and monomers > carbonyl compounds > saturated hydrocarbons. For the olefins examined, agreement is found with the data obtained in this study and the known agreement between electron density at the unsaturated centre and the quantum yield for oxidation. An equation has been derived for the quantum yield of photoperoxidation of unsaturated organic molecules, and has been applied to lipoic acid inhibition of the self-sensitized photoperoxidation of 1,3-diphenylisobenzofuranin acetonitrile.58 Evidence has been presenteds9 to suggest that in benzene solution photoperoxidation of 1,3-diphenylisobenzofuran proceeds with formation of 51 52

53 54

55 56

"

59

A. A. Krasnovskii, Zh. Prikl. Spektrosk., 1980, 32, 852. E. A. Venediktov and A, A. Krasnovskii, Biojizika, 1980, 25, 336. A. A. Gorman, I. R. Could, and I. Hamblett, Tetrahedron Lett., 1980, 21, 1087. G. S. Cox, D. G. Whitten, and C. Giannotti, Chem. Phys. L e f f . ,1979, 67, 511. V. B. Ivanov, B. G. Kuprashvili, and 1. L.Edilashvili, Khim. Vys. Energ., 1980, 14, 280. M. C. Addison, R. J. Donovan, and I. Garraway, Faraday Discuss. Chem. SOC.,1979, No. 67, 286. R. K. Datta and K. N. Rao, Indian J. Chem., Secf. A , 1979, 18, 102. B. Stevens and K. L. Marsh, J. Chem. Res., (S), 1980, 290. B. Stevens, J. A. Ors, and C. N. Christy, J. Phys. Chem., 1981, 85, 210.

402

Photochemistry

endoperoxide as primary product. This, however, further reacts with the triplet state of 1,3-diphenylisobenzofuranto give a secondary product, which is hitherto unidentified. However, it is concluded that at moderate concentrations this diene exhibits normal stoicheiometic behaviour as an O,( 'Ag) acceptor. The stereochemistry of singlet-oxygen capture by cyclopentadiene rings fused to norbornyl and norbornenyl frameworks has been investigated 6o and shown to proceed only with moderate endo-stereoselectivity. Energetic factors arising from the ionization potential of lo2( 16.12eV) appear to be responsible, since this value differs considerably from that of the nl(S)energies of normal dienophiles (10.5-1 1.5 eV) and the n,(S) energies of the diene substrates (9.6-10.0eV). The disparate nature of the singlet molecular oxygen energy is the cause of the inability of the reagent to distinguish between the advantages of endo-attack relative to exo-bonding. A design has been described 6 1 for an inexpensive apparatus for the measures) exponential processes, and its use has ment of the lifetimes of long-lived (> been illustrated by an example in the study of photo-oxidation.

5 Oxidation of Aliphatic Compounds Kinetic data have been published 6 2 for the photo-oxidation of air-saturated cyclohexane, and a radical mechanism has been described to explain the results. The photosensitized oxidation of the 19-norsteroid 1 1P-chloro-17a-19norpregn-4-en-20-yn-17-01 has been shown 6 3 to lead to the mixture of products in Scheme 2, but a satisfactory rationalization of the stereoselectivity has not yet

&+HO

@ HO

oH

Scheme 2

been made. Evidence has also been presented by the same authors to suggest that in the photosensitized oxidation of a related 19-norsteroid, a pseudoaxial tertiary hydrogen atom is less readily abstracted than a pseudoaxial secondary hydrogen atom.64Even though the substrate is an unactivated alkene, the structure of one of the products implies that some of the singlet oxygen reacts via the dioxetan pathway. An interesting example of remote oxidation has a ~ p e a r e d . ~ 6o 61 62

63

64

L. A. Paquette, R. V. C. Carr, E. Arnold, and J. Clardy, J. Org. Chem., 1980, 45, 4907. S. Joly, J. C. Andre, F. Baronnet, and R. L. Lyke, Oxid. Commun., 1980, 1, 175. L. G. Galimova, S. 1. Maslennikov, and A. I. Nikolaev, Izv. Akad. Nuuk SSSR,Ser. Khim., 1980, 2464. K. H. Schonemann, N. P.Van Vliet, and F. J. Zeelen, Reel. Truv. Chim. Pays-Bas, 1980, 99, 91. J. A. M. Peters, K. H. Schonemann, N. P. Van Vliet, and F. J. Zeelen, J. Chem. Res., ( S ) , 1979,402. D. Wolner, Tetrahedron Lett., 1979, 4613.

Photo-reduction and -oxidation

403

I

b (10) Z = CH,O, CONH, or SO,

Photoinitiated free-radical chlorination of ( 10) using phenyliodine dichloride is directed exclusively to the C(9) position, probably as a result of the conformation of the steroid placing the C(l) complexed to the template iodine atom close to the C(9) hydrogen. Dehydrochlorination then places a double bond in the C(9)-C( 1) position.

CH2CH2CH2CH0

H

H

CH,CH,CH,CHO

The singlet oxygenation of trans-cyclo-octene has been investigated and leads to the products shown (Scheme 3). Treatment of this mixture with Ph,P is found to increase the (1 2) :(13) ratio suggesting the stereospecific formation of (1 1) as the initial product of the reaction.66*" This is the first example of dioxetan formation in a molecule which carries sterically accessible and abstractable allylic hydrogen atoms, and does not have electron-donating substituents. In protic media, the singlet oxygenation of cr-pinene has been examined and has been found to be partially deviated towards the formation of bifunctional compounds such as hydroperoxymenthene (14; R = OH) and acetamidohydroperoxymenthene (14; R = NHAc). These observations support a zwitterionic mechanism.68 Photooxidation of bicyclopropylidene in CDC1, using tetraphenylporphyrin has been reported to give the spiro-compounds (15) and (16). It is suggested that the reaction proceeds initially to form the intermediate 1,4-zwitterion (17), which is in equilibrium with the perepoxide (18), and, which can undergo a cyclopropylcarbinyl-to-cyclobutylring enlargement.69 Oxidation of the strained olefins (19) has been examined 'O and found to lead to a wide range of different

'' Y. Inoue T. Hakushi, and N. J. Turro, Kokuguku Toronkai Koen Yoshishu, 1979, 150. 67

'* 69 'O

Y. Inou and N. J. Turro, Tetrahedron Lett., 1980, 21, 4327. P. Capdevielle and M. Maumy, Tetrahedron Lett., 1980, 21, 2417. A. De Meijere, G . Rousseau, and J. M. Conia, Tetrahedron Lett.. 1980, 21, 2501. A. A. Frimer and A. Antebi, J . Org. Chem., 1980,45, 2334.

Photochemistry

404 Me

(14)

(1 5 )

(16)

(17)

(18)

(19) R = C02Et, COMe, or H

products, which seem to have been derived by secondary rearrangements of an initially formed hydroperoxide and epoxide. However, singlet oxygen does not appear to be involved, and the products are thought to have arisen from a freeradical process. The failure of singlet oxygen to react may be due to the relatively high ionization potential of cyclopropenes. In this connection it may be significant that cyclopropenes epoxidize only slowly and that the rates of both epoxidation and singlet-oxygen photo-oxygenation are known to decrease with ionization potential. The stereoselective addition of singlet oxygen to the 8-isopropylidenetricyclo[3.2.1.02~4]octanes(20) and (21) has been discussed in terms of Walsh and n

/31)

R' = R2 = H R = R' = bond, R2 = H R = R' = bond, R2 = cyclopropyl

(20) R

=

\L'i

orbital interactions. 7 1 Following irradiation in acetone and reduction with Me$, mixtures of alcohols are obtained whose ratios seem to imply that the endocyclopropane ring of (20)has a similar effect on the selectivity as does the double bond of (21). lt is also suggested that the Walsh orbital interacts with the orbital of the exocyclic double bond more strongly than the orbital of the endocyclic double bond of (21). The singlet-oxygen oxidation of the vinylcyclopropane (22) in the presence of diphenyl sulphide has been reported to give a cis-glycol on cleavage of the dioxetan intermediate.72 This observation has necessitated revision to (23) of the structure of the azido-alcohol formed during the photosensitized oxygenation of (22)in the presence of N3-. No peroxidic products have been detected from contact of singlet oxygen and anti- 1,2,3,4,5,6,7,8-octahydro-1,4,5,8-dimethanonaphthalene (sesquinorbornene) (24). However, (24) does react with mchloroperbenzoic acid and with the oxygen photosensitized by biacetyl gives (25). It appears, therefore, although the presence of the bridge atoms in (24)still permit reaction at one end of the double bond, they seem to inhibit concerted reaction.73 71 72

73

K. Okada and T. Mukai, Tetrahedron Lett., 1979, 3429. T. Hatsui and H. Takeshita, Bull. Chem. SOC.Jpn., 1980, 53, 2027. P. D. Bartlett, A. J. Blakeney, M. Kimura, and W. H. Watson, J . Am. Chem. SOC.,1980, 102, 1383.

Photo-reduction and -oxidation

(24)

405

(25)

The formation of 1,2-dioxolanes has been reported74 to occur by photooxidation of (Z,Z)-octadeca-9,12-dienoicacid methyl ester (methyl linoleate). These compounds are predominantly of &configuration and arise from an alkenylperoxy radical cyclization. It is suggested that b,y-unsaturated lipid hydroperoxides in general may cyclize stereoselectively in this way, and that this may be significant in the enzymatic formation of prostaglandin hydroperoxides. The reduction products of the hydroperoxides resulting from singlet-oxygen oxidation of methyl linoleate have been characterized.7 5 Methyl 1O-hydroxytrans-8-cis-12-octadecadienoate was detected among the products and was proposed as a test to probe the involvement of singlet oxygen in biological oxidations. Certain fatty acids have been shown to act as sensitizers for the oxidation of methyl linoleate, and the initiation is induced by those fatty acids having a conjpgated oxodiene system which produce start radicals.76 This is supported by the observation that fatty acids having a conjugated triene system, which absorbs in the same region as the oxodiene, are ineffectivesensitizers. A study has also been made of modes of hydroperoxidation in the photo-oxygenation of unsaturated fatty acid esters such as methyl oleate and methyl arachidonate.” (2,E)-Tetradeca-9,ll-dienyl acetate is the main component of the sex pheromone of the female Egyptian cotton leaf worm and on photo-oxidation this has been found7* to undergo cyclization of the furan (26); Scheme 4. Singlet oxygenation of cis&-cyclo-octa- 1,5-diene produces 6-hydroperoxycyclo-octa-1,4-diene and on further oxidation 5,8-dihydroperoxycyclo-octa-1,3diene. Since reduction of this hydroperoxide with Ph,P leads to cis-5,8-dihydroxycyclo-octa-1,3-diene, the whole sequence represents a convenient synthetic entry into 5,8-difunctionalized oxygen derivatives of cyclo-octa-1,3-diene. A highly stereoselective method has been developed for the cis-oxygenation of cycloheptyl systems.80 This involves irradiation of methanolic solutions of 1-acetoxycyclohepta-3,5-diene in the presence of haematoporphyrin as sensitizer to give

’’

74 75 76

l7 78 79 *O

E. D. Mihelich, J . Am. Chem. SOC.,1980, 102, 7141. M.J. Thomas and W. A. Pryor, Lipidr, 1980, 15, 544. U. Semmler, R. Radtke, and W. Grosch, Fette, SeiJen, Ansrrichm., 1979, 81, 390. N. A. Khan, J . Bangladesh. Acad. Sci., 1978, 2, 77. A. Shani and J. T. Klug, Tetrahedron Lert., 1980, 21, 1563. W. Adam and B. H. Bakker, Tetrahedron Lett., 1979, 4171. D. M. Floyd and C. M. Cimarusti, Tetrahedron Lett., 1979, 4129.

406

Photochemistry

(z.E)-EtCH=CHCH=CH(CH,),OAc 4

(E. E)-EtCH=CHCH=CH(CH,),OAc

1

kr. 0,

Scheme 4 0

OAc

H OAc

(27)

AcO H

(29)

(28)

(27) as the major product arising from attack syn to the acetoxy-substituent, together with (28) and (29). Triplet-sensitized irradiation of cis- or trans-vitamin D is known to establish a photostationary state between the two isomers and it is now reported " that in the presence of oxygen highly selective photo-oxygenation of the trans-isomer occurs. The difference in reactivity between these geometric isomers is paralleled in their behaviour towards maleic anhydride and may have applications in the synthesis of hydroxylated vitamin D metabolites. Several 6,19-epidioxy vitamin D derivatives (30) have also been prepared by dye-sensitized photo-oxygenation. The biological activity of these compounds has been examined and a significant degree of Ca transport found.82A study has also been made of the photosensitized oxidation of abietic Oxygen functionalization of some norcaradienes or cycloheptatrienes has been communicated. Thus the endoperoxides (31) and (32) have been obtained from the corresponding h y d r ~ a r b o n s . ' ~An investigation has also been made of the photosensitized oxidation of 7-methoxycycloheptatriene. The product, a [4 + 2]cycloadduct (33), could be thermally isomerized to 4-methoxytropone. 8L

82

83 84

J. W, J. Gielen, R. B. Koolstra, H. J. C. Jacobs, and E. Havinga, Red. Trav. Chim. Pays-Bas, 1980,99,

306. S. Yamada, K. Nakayama, H. Takayama, A. Itai, Y. litaka, S. Moriuchi, F. Tsuruki, and Y. Otawara, Tennen Yuki Kagobutsu Toronkai Koen Yoshishu, 22nd. 1979, 25. A. Fukuchi, H. Negishi, and H. Kanno, Tokyo Gakugei Daigaku Kiyo, Dai-Cbumon, 1979,31, 127. W. Adam, M . Balci, B. Pietrzak, and H. Rebollo, Synthesis, 1980, 820.

407

Photo-reduction and -oxidation

..u-..,,

R'O.

Mc

Similar photo-oxidation procedures can be used to prepare 4-hydroxytropone and 3-methoxytropone. Sensitized photo-oxidation of the vinylallenes CH,=C=CRCR'=CH, [R = Bu, R' = H; R = (CH,),Me, R' = Me] and 3-(cyclohex-1-en- 1-yl)penta-1,Zdiene have been found 86 to lead to the tetrahydropyranones (34) and (35). 1,2-Dioxetans are reported to be products of the OMe

(31) R

=

Me, Et, or CHMe,

Rb

(33)

(32) Et

R'

(34)

(35)

singlet oxygenation of ketene silyl acetals and are formed together with the expected or-peroxy esters RO,CCH(CMe,)OOSiMe,. The dioxetan undergoes a chemiluminescent thermolysis and rearranges to Me,CCHO and the Mperoxyester. Formation of this product is interesting in that it represents the first example of a thermal transformation of 1,2-dioxetans in which the peroxide bond is p r e ~ e r v e d . ~ ~ Two papers have appeared on the singlet photo-oxygenation of enol ethers. In the first of these,88the (+)-methoxymethylenefenchanes (36) were found to give 85 86 87

88

M. Yagihara, Y. Kitahara, and T. Asao, Bull. Chem. SOC.Jpn., 1980, 53, 236. M. Malacria and J. Gore, Tetrahedron Lett., 1979, 5067. W. Adam, J. Del Fierro, F. Quiroz. and F. Yany, J . Am. Chem. SOC.,1980, 102, 2127. E. W. Meijer and H. Wynberg, Tetrahedron Lett., 1979, 3997.

408

Photochemistry

two pairs of isomeric 1,2-dioxetans. Methoxymethyleneadamantane has similarly been converted to a dioxetan. Examination of the chemiluminescence produced on thermal decomposition of these dioxetans has enabled a comparison to be made of light- and chemically-induced circular polarization of luminescence. Sensitized photo-oxidation of silyl enol ethers of cyclic ketones has also been i n ~ e s t i g a t e d . ~ ~ Following a prototropic ene-reaction and subsequent reduction and solvolysis, or,B-unsaturated (37) and a-hydoxyketones (38; R = H) were produced. A competing silatropic ene-reaction leads to the formation of or-silyloxy ketones (38; R = Me$) and the partition between these different pathways was found to be dependent on such considerations as ring size, configuration, and substitution pattern.

= H, R' = OMe; (37) (38) R = H or Me$ R = OMe, R' = H Although simple acetylenes do not react with singlet oxygen that has been generated using methylene blue or Rose Bengal in MeOH, photosensitized oxygenation of aryl acetylenes is reported" to occur in the presence of some cyanoaromatics and yields benzils (Scheme 5). Diphenylacetylene (39) also

(36) R

+

Rvo RAO '

t I

1

I

hP, 0,

RCOzH Sheme 5

undergoes efficient photo-oxidation using dicyanoanthracene as sensitizer but does so only inefficiently if tetracyanoanthracene (40) is used.g1 This is because the oxidation occurs largely by reaction of (39 ?) with 0, :, and in the second case no 0, is formed. In the presence of acids and bases, the reaction is catalysed because protonation of the radical anion (40') suppresses back-electron transfer to (39 ?) as does nucleophilic addition of pyridine to (39?). Irradiation of cis- and transdiphenylcyclopropane in the presence of electron acceptors such as chloranil, 1,489 90 91

E. Friedrich and W. Lutz, Chem. Ber., 1980, 113, 1245. N. Berenjian, P. De Mayo, F. H . Phoenix, and A. C. Weedon, Tetrahedron Lett., 1979,4179. S. L. Mattes and S. Farid, J . Chem. SOC.,Chem. Commun., 1980, 457.

Photo-reduction and -oxidation 409 dicyanonaphthalene,or 9-cyanophenanthrene have been reported 9 2 to lead to the formation of radical ion pairs. The structures of the triplet state and radical ions are somewhat uncertain and the available evidence is unable to distinguish between the ‘closed’ and ‘open’ structures for the cyclopropane bond. However, substantial spin density does appear to be present at the benzylic position in the radical cations suggesting that one of the ring bonds may be very weak. The photolysis, and photo-oxidation of normal saturated aldehydes has been examined. In the range 10-’-10-*~ it has been shown that the triplet states deactivate principally by self-quenching, and that self-quenching of the singlet state represents a more efficient initiation process than triplet ~elf-quenching.~~ The same authors also find that self-quenchingis the only important deactivation path of the triplet state of branched aldehyde^.^^ The photolysis of aldehydes adsorbed on porous Vycor glass has been observed to decrease in the order Me,CHCHO > > PrCHO > EtCHO > > MeCHO and this is unaffected by oxygen. However, under these conditions photo-oxidation occurs at a rate which is dependent on the oxygen pressure. The species 0, and 0, derived by glass photosensitization, are considered as possible photo-oxidation intermediate^.^' Reports have also appeared of ketone photo-oxidation.96 Photolysis of menaquinone (41; R = CH,CH=CMe,) gives a mixture of the hydroperoxide (41; R = CH=CHCMe,OOH) and the trioxane (42) in a reaction that may involve 0

trapping of oxygen by a quinone-olefin exciplex or a 1,4-preoxetane biradical species. Irradiation of b-ionone in an oxygen atmosphere but in the absence of sensitizers has been shown97 to lead to a mixture consisting of unreacted pionone, 2,3-epoxy-/?-ionone (4573, 2,6,6-trimethyl-2,3-epoxycyclohexylideneacetaldehyde (2%) and dihydroactinidiolide (3%). Rate constants have also been determined 98 for the reaction of chalcone with singlet oxygen, and the dyesensitized photo-oxygenation of chalcones into aurones has been de~cribed.’~ Irradiation of 3a,5-cyclo-5a-cholestan-7-onein methanol gives a 7-oxasteroid.* O0 This phototransformation of an oxosteroid into an oxasteroid in the presence of oxygen appears to be a new type of reaction of excited cyclic ketones. 92 93 94

95 96

97 90

99

loo

H. D. Roth and M. L. M. Schilling, J . Am. Chem. SOC.,1980, 102, 7956. L. M. Coulangeon, G . Guyot, and J. Lemaire, J. Chim. Phys., Phys.-Chim. Biol., 1980, 77, 497. L. M. Coulangeon, G . Guyot, and J. Lemaire, J. Chim. Phys., Phys.-Chim. Biol., 1980, 77, 217. M. Anpo, Y. Ueda, A. Kanno, and Y. Kubokawa, Kokagaku Toronkai Koen Yoshishu, 1979, 60. R. M. Wilson, T. F. Walsh, and S. K. Gee, Tetrahedron Lett., 1980, 21, 3459. H. Etoh and K. h a , Agric. Biol. Chem., 1979,43, 2593. M. Nowakowska and J. Kowal, Bull. Acad. Pol. Sci. Ser. Sci. Chim., 1979, 27, 409. A. Sharma, S. S. Chibber, and H. M. Chawla, Indian J . Chem., Sect. B., 1980, 19, 905. H. Suginome and C.-M. Shea, Bull. Chem. SOC.Jpn., 1980, 53, 3387.

Photochemistry

410

In the presence of FeCl,, photo-oxidation of trisubstituted cyclic olefins in pyridine-benzene has been reported lo' to give gem-dichloroketones from which methyl ketones possessing a terminal triple bond can be obtained by dehydrochlorination. For example, under these conditions 1-methylcyclohexene has been converted l o 2 into (43), an important intermediate in the preparation of brevicomin (44). These reactions have been interpreted in terms of a long-range

(43)

electron-transfer mechanism. At present, no experimental evidence is available concerning the nature of the light-absorbing species, but it seems quite probable that this might be FeC1, modified by olefin co-ordination and s o l ~ a t i o n . The '~~ reaction could, therefore, be visualized as proceeding according to Scheme 6. C

~

F

e

~

~

h

O

,

Scheme 6

Irradiation of certain hydroxyacids, e.g. lactic, glycolic, or 2-hydroxybutanoic acids in the presence of Cu" ions, brings about oxidation of the hydroxyl function with formation of Cu'. At pH > 1, the dominant photoprocess is oxidative decarboxylation, and the presence of free-radical scavengers is found to suppress formation of the a-keto acids. O4 The photoassisted dehydrogenation and dehydration of aliphatic alcohols on ZnO and TiO, surfaces at room temperature has been studied.lo5 The former process occurs via co-ordinatively unsaturated O2- sites, and evidence has been found for photoassistance in the cleavage of the C,-C, bond. An examination of the photocatalytic oxidation of isobutene and butane on these same metal oxides at temperatures between 100-300 "Chas shown l o 6 that local interactions in the catalysts are more important than collective interactions. Heterogeneous photooxidation of alkanes has been reported l o 7 to lead to alcohols and olefins, which are further oxidized into ketones and aldehydes in a process in which the oxidizing agent appears to be surface-lattice, u.v.-activated oxygen. Products of a more intense oxidation are sometimes formed, and it is suggested that in these cases adsorbed and u.v.-activated oxygen is participating. A mechanism has been proposed l o * to explain the heterogeneous photocatalytic oxidation of hydrocarbons in oxygen-containing solutions at platinized TiO,. This is based on the photogeneration of hydroxyl radicals at the TiO, surface [equations (2>--(4), where h + = hole]. However, another paper suggests that the lo'

Io4 lo'

lo' lo'

A. Kohda and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 194. E. Murayama, K. Nagayoshi, and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 196. A. Kohda, K. Ueda, and T. Sato, J . Org. Chem., 1981, 46, 509. R . Matsushima, Y. Ichikawa, and K. Kuwabara, Bull. Chem. SOCJpn., 1980, 53, 1902. J . Cunningham, K. Hodnett, and D . J. Morrissey, Rev. Port. Quim., 1977, 19, 158. L. V. Lyashenko, Katal. Katal., 1979, 17, 6 . N . Djeghri and S. J. Teichner, J . Catal., 1980, 62, 99. I. Izumi, W. W. Dunn, K. 0.Wilbourn, F.-R. F. Fan, and A. J. Bard, J. Phys. Chern., 1980,84,3207.

Photo-reduction and -oxidation TiO,

H,O

+ h+

RH + H O

hv

-H'

41 1

+ h+

e-

HO

+ H+

ROH

(2)

(3) (4)

fundamental step in the activation process is the creation of a neutral atomic oxygen activated species.'0g This may arise from neutralization of an adsorbed 0-ion by a photoproduced hole, h'. The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed.' l o A study has appeared of the effect of pcarotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between p-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer.' l 2 At 400 nm and using eosine and methylene blue as sensitizers, the results show that up to 13% incorporation of abietic acid, uniform photo-oxidation occurs along the matrix, but that above 13%, oxygen diffusion is hindered by oxidation products.

''

6 Oxidation of Aromatics Hexamethylbenzene has been photo-oxidized by singlet oxygen in a two-step process and each step consumes one molecule of oxygen. Step one is a [4 + 2lcycloaddition and this is followed by an ene-reaction to give (45); 0 /I

Me

OOH (45)

''

pentamethylbenzene behaves similarly. A recent paper l4 on the irradiation of the hexamethylbenzene-oxygen charge-transfer complex reported results that were in conflict with earlier work of Wasserman. These discrepancies have now been investigated and accounted for in terms of the wavelength of the incident light leading to production of different excited species. Singlet oxygen has also been found to react with all possible isomers of mono- and di-methylnaphthalenes

''

'lo 'I1

"*

'I3

' l4 'I5

J. M. Herrmann and P. Pichat, Geterog. Katal., 1979, 4th, Pt. 1, 21. D. J. Carlsson, K. H. Chan, A. Garton, and D. M. Wiles, Pure Appl. Chem., 1980, 52, 389.

M. Nowakowska, Makromol. Chem., 1980, 181, 1013. L. Ya. Tantsyura and N . G . Kuvshinskii, Fund. Om.Opt. Pamyati Sredy, 1978, 9, 132. C. J. M . Van den Heuvel, A. Hofland, H. Steinberg, and T. J. De Boer, Recl. Trav. Chim. Pays-Bas, 1980, 99, 275. C. J. M. Van den Heuvel, H. Steinberg, and Th. J. de Boer, Recl. J . R . Neth. Chem. SOC.,1977, %, 157. H. H.Wasserman, P. S. Mariano, and P. M. Keehan, J. Org. Chem., 1971, 36, 1765. K. Onodera, H. Sakuragi, and K. Tokumaru, Tetrahedron Lett., 1980, 21, 2831.

412

Photochemistry

’

with the exception of 2-methylnaphthalene. l 1 Endoperoxides are formed by 1,4or 5,8-attack. Dioxetans are also intermediates in the photosensitized oxygenation of indene and of acenaphthylene, and their reduction leads to substantial amounts of the expected cis-glycols.l Irradiation of Ph,C==CHOMe produces a complex mixture whose constituents all arise from decomposition of the initial endoperoxide.’lg Photoaddition of oxygen to (46) has been reported to give (47). 0

0

Interestingly, further photolysis of (47) involves an irreversible decomposition of low quantum yield, which occurs via S,(n,n*) or T , (n,n*), together with a photoreversible reaction to give ground-state (46) via S , (n,n*). This strongly supports the state-correlation diagram predictions of the concerted photocleavage of endoperoxides.12’ The INDO method has been used to study the lightstimulated interaction of anthracene and oxygen in various geometries, and interactions in the ground and first excited states are classified according to the principle of orbital-symmetry conservation. ” Calculations on the anthracene-Ni model catalyst show that the photo-oxidation is catalysed by transition metals. Photo-oxygenation of alkylbenzenes can be initiated by electron transfer. Thus irradiation of p-xylene in the presence of 9,lO-dicyanoanthracene gives ptolualdehyde and p-toluic acid in a radical chain process 1 2 2 (Scheme 7). Irradiation of (48) in the presence ofp-dicyanobenzene and an aromatic hydrocarbon such as phenanthrene has been found123to lead to ring cleavage. This process is induced by n-complex formation between (48) and the aromatic hydrocarbon radical cation generated by electron transfer to the p-dicycanobenzene. Photoredox reactions can thus provide another route for ring cleavage of cyclobutanes. In MeCN the products of photocoxidation of Ph,G=--H,, cis- and transPhCH=CHPh, and Ph,C=CPh, using 9,lO-dicyanoanthracene and 9-cyanoanthracene as sensitizers include benzophenone, benzaldehyde, epoxides, and products of cis-trans-isomerization. 24 A correlation is established between the rate constants for electron-transfer processes and those determined from the acceptor concentration-dependence of product formation. These observatiqns appear to implicate a sensitizer radical anion that subsequently reduces 0, to 0,.

‘I9 120 12‘

”*

lZ3 124

C. J. M. Van den Heuvel, H. Steinberg, and T. J. D e Boer, R e d . Trav. Chim. Pays-Bas, 1980,99, 109. T. Hatsui and H. Takeshita, Bull. Chem. Sor. Jpn., 1980, 53, 2655. D. S. Steichen and C. S. Foote, Tetrahedron Lett., 1979, 4363. R . Schmidt, W. Drews, and H . D. Brauer, J . Am. Chem. SOC.,1980, 102, 2791. M . Ceppan, L. Lapcik, M . Liska, and P. Pelikan, Eur. Polym. J., 1980, 16, 607. I. Saito, K. Tamoto, and T. Matsuura, Tetrahedron Lett., 1979, 2889. T. Majima, C. Pac, and H. Sukurai, J . .4m. Chem. SOC.,1980, 102, 5265. J . Ericksen and C. S. Foote, J . Am. Chem. SOC.,1980, 102, 6083.

-

Photo-reduction and -oxidation - DCA

I)"

413

'DCA*

X DCA:

+

+

(exciplex)

R D C H 2 0 0 '-_.'

termination

1

Products

Scheme 7

Evidence has been presented

25

that suggests that the oxidation of trans-stilbene

to benzaldehyde using methylene blue as sensitizer does not involve singlet oxygen,

but rather proceeds by the mechanism shown (Scheme 8). Dye-sensitized photooxygenation of 1-phenylcyclobuteneto 3-benzoylpropanal and 2-phenyl-3-hydroperoxycyclobutene has been reported to occur via singlet oxygen. A third product l-(2-hydroxyphenyl)cyclopropanecarboxaldehyde may arise from superoxide anion. MB+

4 * M B& OMB* +

TS+

ISC(

c

2PhCHO

'MB*

TS

lo2 --+

-N.R.

Scheme 8

Oxidative photocyclization of 1-(2-naphthyl)-2-(3-phenanthryl)ethylene has been carried out in a chiral liquid crystal and an optically active helicene obtained. 27 A synthetically useful conversion of 2-(/3-arylvinyl)pyrazines to azaphenanthrenes has also been described using the same oxidative procedure. The position at which ring closure occurs is dependent on the structure of the aryl group.

'

L. E. Manring, J. Ericksen, and C. S. Foote, J. Am. Chem. SOC., 1980, 102, 4275. M. Sakuragi and H. Sakuragi, Chem. Lett., 1980, 1017. "' A. Okami, H. Sakuragi, and K. Tokumaru, Kokugaku Toronkai Koen Yoshishu, 1979, 184. 12* A. Ohta, K. Hasegawa, K. Amano, C. Mori, A. Ohsawa, K. Ikeda, and T. Watanabe, Chem. Pharm. Bull., 1979, 27, 2596.

414 Photochemistry Irradiation of o-nitrobenzaldehyde in benzene gives o-nitrosobenzoic acid (4 0.5) in a process that occurs via a triplet state having a lifetime of 0.6 ns, and the transient enol(49). A mechanism is proposed 12' and this is outlined in Scheme 9. The kinetics of the photo-oxidation of benzaldehyde have been studied in the liquid phase and the rate constants extracted found to be in close agreement with those obtained from the photodecomposition of PhC0,OH. 13*

-

N=O

I -0 Scheme 9

Benzoic acid has been reported 1 3 1 * 32 to be photo-oxidized in the presence of H 2 0 2 ,but if [H,O,]/[PhCO,H] c 10 complete reaction is suppressed by the inner filtering effect of polyhydroxylated aromatics, and complete decomposition is only achieved for ratios >25. In the early stages of the reaction, the products are salicylicacid together with some phenol and benzene, and at longer reaction times, lower aliphatic diacids such as CH,(C0,H)2 appear. The photo-oxidation of a-benzoylbenzyl ethers has been found to occur in the solid phase as well as in solution, and takes place by mechanistically distinct routes. Scheme 10 has been suggested to account for the crystalline-phase PhCOCH(0R)Ph -.!!-L [ PhC ( =0) C H (0R)Ph] SOlld

PhC0,R

+

PhC0,H

+-

[PhC(=O)-OO-CH(OR)Ph]

Scheme 10

processes. Photo-oxidation of various methoxynaphthalenes in the presence of lead tetra-acetate gives a wide range of products including acetoxy derivatives, dimers, 0- and p-quinones, and polysubstituted derivatives. 34 A substratereagent complex seems to be involved and the site of the initial attack appears to be influenced by the location of the methoxy-group. 129

130 lJ1 132

133 134

M. V. George and J. C. Scaiano, J. Phys. Chem., 1980, 84,492. T. Shirotsuka, M. Sudoh, and H. Fukawa, Kagaku Kogaku Ronbunshu, 1980, 6, 53. Y. Ogata, K. Tomizawa, and Y. Yamashita, J. Chem. Soc., Perkin Trans. 2, 1980, 616. Y. Ogata, K. Tomizawa, and Y. Yamashita, Kokagaku Toronkai Koen Yoshishu, 1979, 120. H. Tomioka and Y. Izawa, J. Chem. SOC.,Chem. Commun., 1980,445. E. R. Cole, G. Crank, and B. J. Stapleton, Aust. J . Chem., 1979, 32, 1749.

Photo-reduction and -oxidation 415 Irradiation of anthraquinone in aqueous organic solvents leads to 2-hydroxyanthraquinone together with some of the corresponding 1-hydroxy-isomer. The transformation seems to involve electron transfer from HO- or H,O to the anthraquinone in its 3(n.n*) excited state followed by attack of HO' on unexcited starting material. 35 Photohydroxylation of hydroxyanthraquinones in 75% ~ ~study has been made of the variations of H,SO, has also been d e ~ c r i b e d . 'A fluorescenceand photo-oxidation quantum yields of o-phenylphenolat differential pH. Oxygen inhibits the recombination of the solvated electron and PhO and electron scavengers, such as Cd2+ and NO3-, also increase the quantum yield for disappearance of irradiated o-phenylphenol. 37 Examination of the sensitized photo-oxygenation of a group of coumarins has shown 138 that those bearing a 4hydroxyl group undergo cleavage of the heterocyclic ring; absence of the hydroxyl group suppresses this reaction. It has been suggested that these reactions may

'

HO

Scheme 11

involve a dioxetan intermediate (Scheme 1 1). Photo-oxygenation of epoxynaphthoquinone (50) has been described and may occur by a mechanism involving addition of singlet oxygen to a transient carbonyl ylide. 13' The mechanism of the photoinitiated oxidation of alkylbenzenesulphonates in aqueous media has been discussed.140 Results have been presented that show that furan endoperoxides such as (51)

13'

139

14*

0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980, 16, 2117. 0. P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980, 16, 1101. L. M. Coulangeon, G. Perbet, P. Boule, and J. Lemaire, Can. J. Chem., 1980,58, 2230. S . S. Chibber and R. P. Sharma, Indian J. Chem., Sect. B, 1979, 18, 538. K. Maruyama, A. Osuka, and H. Suzuki, J. Chem. SOC.,Chem. Commun., 1980, 723. V. Chekulaev and M. Gubergrits, Eesri NSV T e d . Akad. Toim. Keem., 1980,29, 157. M. L. Graziano, M. R. Iesce, and R. Scarpati, J . Chem. SOC..Perkin Trans. I , 1980, 1955.

416

Photochemistry

can be obtained in quantitative yield by dye-sensitized photo-oxidation of 3methoxycarbonylfurans at - 15 "C. Studies have been reported of the photooxidation of furans in aprotic solvents 4 2 and of a fluorescein-photosensitized oxidation of furan derivatives in methanolic and reversed micellar solutions. Aniline seems to enhance the photo-oxidation of 1,3-diphenylisobenzofuranin methanol and to inhibit the reaction in dodecylammonium propionate reversed micelles. The predominant pathway appears to be a Type I1 oxidation involving singlet oxygen, but addition of aniline promotes oxidation by introducing a competitive radical mechanism (Type I). However, in the reversed micelle, aniline quenched the singlet oxygen leading to inhibition. 143 - 145 7 Oxidation of Nitrogen-containing Compounds The selectivity of tertiary amine oxidations using singlet trans-stilbene has been investigated 146 in the cases of Et,NMe, Me,NEt, and Me,NCHMe,. A relatively non-selective deprotonation of the aminium radical is shown by the stilbene radical anion and the selectivity of the oxidation appears to be due to a stereoelectronic effect, which is most evident when two or three alkyl groups are highly branched. In the photosensitized oxidation of 3-diazocamphor in either MeCN or PhCN as solvent the amide (52) is produced. The formation of this amide strongly supports the intermediacy of a carbonyl oxide intermediate. 14' Me Me

(52) R = Me or Ph

Oxidation of benzophenone N-alkylimine in propan-2-01 is reported to occur on irradiation in a stream of oxygen and gives PhCH,OH, PhCH,NHCHPh,, Ph,CO, and PhCH,NH,. It is suggested that the reaction proceeds through an initial light-induced 1,3-H transfer (Scheme 12). Phenyl-substituted 1,3oxazepins (53) undergo photosensitized oxygenation in CCI, to form various products, all of which can be derived from the peroxides (54) and (55).149 Ph

CH2Ph

>=.'

Ph

h I' 2-PrOH

PhCH=NCHPhz

Scheme 12 142 143 144 145 146

14' 14' 149

W. Grimminger and W. Kraus, Liebigs Ann. Chem., 1979, 1571. N. Miyoshi and G. Tomita, Z. Natuforsch., Teil. B., 1979, 34, 1552. N . Miyoshi and G. Tomita, Kokagaku Toronkai Koen Yoshishu, 1979, 146. N. Miyoshi and G. Tomita, Z. Naturjorsch., Teil. B., 1980, 35, 107. F. D. Lewis and T.-I. Ho, J . Am. Chern. SOC.,1980, 102, 1751. K. Okada and T. Mukai, Teirahedron Lett., 1980, 21, 359. K. N. Mehrotra and G. P. Pandey, hdian J. Chem., Sect. B., 1979, 18, 475. A . Tokida, K. Okada, and T. Mukai, Fukusokan Kagaku Toronkai Koen Yoshishu, IZrh, 1979, 221.

Photo-reduction and -oxidation

417

R'

R'

Ph

R'

Ph

Ph

(53)

(55)

(54)

The photocyclization of diphenylamine shows a pH dependence and gives carbazole, or if the solution is degassed, carbazole and tetrahydrocarbazole. 5 0 Similar behaviour is also observed for p-Me,CHNHC,H,NHPh. The mechanism of the oxidative photocyclization of N-methyldiphenylamine to N-methylcarbazole has been examined in the presence of surfactants and the bimolecular found to dehydrogenation of the intermediate 4a,4b-dihydro-N-methylcarbazole be enhanced. This appears to be the result of the difference in oxygen solubility between the organic and aqueous solutions. In contrast to an earlier published result, 152 diphenylamine is now reported 53 to undergo photo-oxidation using chlorophyll as sensitizer to give N-phenyl-p-benzoquinonimineas primary product. m-Hydroxydiphenylaminebehaves similarly, 54 and singlet oxygen has been confirmed to participate in this system. Irradiation of dibenzylaniline and CBr, in a poly(viny1 chloride) matrix has been found to lead to the formation of a triplet exciplex between the two compounds. This then dissociates to give final products which themselves sensitize the photo-oxidation of the dibenzylaniline. 5 5 A review on the dye-sensitized photo-oxygenation of indole derivatives has appeared.'', At low temperature, dioxetan (56) has been obtained 157 from the dye-sensitized oxygenation of indole (57) (Scheme 13) and zwitterionic intermediates have been trapped 1 5 8 using nucleophiles such as MeOH, EtOH, and

'

''

'

'

'

Me

Me

(57)

(56)

Scheme 13

Pr'OH. Hydroperoxyindolineshave been trapped by reduction with KBH,.' 59 In the photo-oxidation of aqueous indole-3-acetic acid and of its methyl ester using various sensitizers at different pHs, cleavage by singlet oxygen appears to compete with hydroperoxidation of the CH, group. 160 The mechanism of photo-oxidation of bacteriochlorophyll C derivatives has also been examined.16' D. Lopez, P. Boule, and J. Lemaire, Nouv. J. Chem., 1980, 4, 615. N. Roessler and T. Wolff, Photochem. Photobiol., 1980, 31, 547. M.S. Ashkinazi, V. E. Karpitskaya, and B. Ya. Dain, Russ. J . Phys. Chem., 1964, 38, 1571. R. Kumar, W. R. Bansai, and K. S. Sidhu, Indian J. Chem., Sect. B., 1980, 19, 373. N. Ram and K. S. Sidhu, Can. J . Chem., 1980,58, 2073. A. D. Grishina and G. M. Chernov, Khim. Vys. Energ., 1980, 14, 28. T. Hino and M. Nakagawa, Kagaku No Ryoiki Zokan, 1980, 177. I J 7S. Matsugo, I. Saito, and T. Matsuura, Kokagaku Toronkai Koen Yoshishu, 1979, 202. 15' 1. Saito, Prepr., Div. Pet. Chem., Am. Chem. SOC.,1979, 24, 95. 1 5 9 C. Amsterdamsky and J. Rigaudy, Tetrahedron Lett., 1980, 21, 3187. F. Guerri and R. Martinez-Utrilkd, Rev. R. Acad. Cienc. Exactas, Fis. Nat. Madrid, 1979, 73, 596. 161 R. F. Troxler, K. M. Smith, and S. B. Brown, Tetrahedron Lett., 1980, 21, 491.

418

Photochemistry

Regiospecific oxidation of substituted 1-benzyl-3,4-dihydroisoquinolines to give the corresponding 1-benzoyl compounds has been achieved using singlet oxygen.16* Solvent trapping experiments failed to provide evidence for a zwitterionic peroxide intermediate and it is concluded that either the reaction occurs via a dioxetan or that, if formed, the zwitterionic intermediate is too short lived to be trapped. The photo-oxidation of 2-(Zquinolyl)indan- 1,3-dione (58) to phthalic acid, quinoline-2-carboxaldehyde,and quinoline-2-carboxylicacid has been found to be both self- and Rose Bengal-sensitized. A mechanism has been suggested involving attack of singlet oxygen on the central double bond.163 lO-Methyl-9methylene-9,lO-acridane undergoes methylene blue-sensitized oxygenation at - 78 “C with the formation of three chemiluminescent compounds, the most stable

(58)

(59)

of which is 3,3,7,7-bis( 1O-methyl-9’,9’-acridanyl)-1,2,5,6-tetraoxocane,a dioxetan dimer.164A paper has appeared which describes a general photo-oxygenation procedure for the regiospecific introduction of an oxygen function at position 13 of the photoberberine alkaloids.1658-Azapurines are reported 166 to be photooxidized to the 6-0x0-derivative(59) probably via a hydrate intermediate, and some triazapentalenes undergo 16’ self-sensitized photo-oxidative ring cleavage to the epoxyketone (60) (Scheme 14). By contrast if Me = H, use of Rose Bengal as sensitizer leads to (61). ,COMe

. I

OHC--CH=CH, N-N

(61) Scheme 14 162 163 164 165

166 16’

N. H. Martin, S. L. Champion, and P. B. Belt, Tetrahedron Lett., 1980, 21, 2613. N. Kuramoto and T. Kitao, J. Chem. Soc., Perkin Trans. 2, 1980, 1569. E. H. White, N. Suzuki, and W. H. Hendrickson, Chem. Lett., 1979, 1491. Y.Kondo, J. Imai, and H. Inoue, J. Chem. SOC.Trans. I , 1980, 91 1. F. Kazmierczak, Pol. J . Chem., 1980, 54, 1333. A. Albini, G. F. Bettinetti, G. Minoli, and S. Pietra, J . Chem. SOC.,Perkin Trans. I , 1980, 2904.

419

Photo-reduction and -oxidation

8 Miscellaneous Oxidations The photo-oxidation of sulphur compounds appears to be a field in which there is increasing interest. Tamagaki 16' has presented evidence to refute an earlier claim 16' that singlet oxygen is solely responsible for the photo-oxidation of di-tbutylthioketone. This new work suggests two distinct paths for the transformation namely singlet-oxygenoxidation to give a sulphine, and oxidation to a ketone via a biradical intermediate. Di-t-butyl thioketone is also reported to undergo photooxidation to (Me,C),C=S=O and (Me,C),CO on irradiation in various aerated solvents.170*171 In the case of thione (62, R = S), irradiation in CH,Cl,-MeOH containing 1% crosslinked polystyrene-anchored Rose Bengal under an atmosphere of oxygen gave a mixture from which the sulphine (62, R = S=O) (4.5%)

R

together with 3% of the corresponding ketone could be is01ated.l~~ This mechanism is, however, not claimed to be general. Rate comparisons have been made for the singlet-oxygen oxidation of the C=S function in various thione compounds, e.g. thioamines, thioureas, and thiocarbonates. Again, steric effects and other evidence strongly suggest that photo-oxidation to the ketones proceeds via a sulphine intermediate. 73 The nature of the intermediates produced by the photosensitized oxygenation of organic sulphides has also been investigated. Competitive studies have been made 174 of the oxidation of pairs of compounds of structure (4-RC6H,),S, R = H, 02N, C1, Me, or MeO, using intermediates formed by photosensitized oxidation of Et,S and PhCN2COPh. A Hammett correlation established that the oxidizing intermediates were electrophilic and most probably were a persulphoxide and a carbonyl oxide, respectively. Dibutyl sulphide has been found 75 to undergo photo-oxidation to BuzSO on sensitization by chrysene. A peroxide intermediate is involved, which reacts further with either a sulphoxide product or with the starting sulphide. Photosensitized oxygenation of a-ketoketene mercaptals has been described 76 and these give dioxetanols, which subsequently collapse to carboxylic acids. Photo-oxidation of the mesoionic compounds (63) and (64)gives ring-cleavage products via endoperoxides 177 and irradiation of tetrathiatetracene and of its selenium analogue in halocarbon solvents leads to radical cation salts. 17'

I7O

17' 17' 174

17' 17'

178

S. Tamagaki, R. Akatsuka, M. Nakamura, and S. Kozuka, Tetrahedron Lett., 1979, 3665. R. Rajee and V. Ramamurthy, Tetrahedron Lett., 1978, 5127. V. J. Rao and V. Ramamurthy, Indian J . Chem., Sect. B., 1980, 19, 143. V. J. Rao and V. Ramamurthy, Curr. Sci., 1980,49, 199. S. Tamagaki and K. Hotta, J . Chem. Soc., Chem. Commun., 1980, 598. S. Tamagaki, R. Akatsuka and S. Kozuka, Mem. Fac. Eng., Osaka City Univ., 1979, 20, 97. W. Ando, Y. Kabe, and H. Miyazaki, Photochem. Photobiol., 1980, 31, 191. G. Cauzzo, G. Gennari, F. Da Re, and R. Curci, Gazz. Chim. Ital., 1979, 109, 541. W. Ando, S. Kohmoto, Y. Nakata, and Y. Haniyu, Kokagaku Toronkai Koen Yoshishu, 1979, 22. H. Kato, K. Tani, H. Kurumisawa, and Y. Tamura, Chem. Lett., 1980, 717. M. Masson, P. Delhaes, and S. Flandrois, Chem. Phys. Lett., 1980, 76, 92.

420

Photochemistry

phpph

Ph

.-/

-0

-0

"Ph

Chloride ions have been photo-oxidized to gaseous chlorine using anthraquinonesulphonic acid and anthraquinonemethanesulphonic acid in aqueous solution. 7 9 The reaction involves transfer of an electron from the halide to the triplet state of the quinone (4 = 0.1--0.13), and in the presence of oxygen the semiquinone radical can be oxidized to ground-state anthraquinone and the whole cycle repeated. In this way partial storage of radiation energy as chemical energy can be achieved. The photosensitized oxidation of I - by anthracenesulphonates appears to proceed by two pathways,'80 sensitizer-peroxide formation which appears to be important for low values of [I-], and direct attack by singlet oxygen which dominates at high values of [I-]. Flash photolysis at 380 nm reveals the presence of a sensitizer-peroxy radical, which is most likely to be of the type AOO, and, which could be an intermediate in the reaction of A0, with I - . By monitoring at 450nm, 10,- is shown to be an intermediate in the photo-oxidation reaction. Several papers have appeared on the photo-oxidation of porphyrins and related compounds. Irradiation of the two water-soluble derivatives of zinc porphyrin, 5,10,15,20-tetra-p-sulphonatophenyl-and 5,10,15,2O-tetra-p-N-methylpyridiniochloride, gives their triplet states, which in the presence of electron donors such as edta are quenched reductively, and in the presence of acceptors such as methylviologen are quenched oxidatively.' The cationic porphyrin will sensitize the photoreduction of water to hydrogen and this offers an attractive alternative to the use of inorganic complexes such as [Ru(bipy)J2+. Photolysis of chlorophyll a or b acting as excited donor together with an electron acceptor such as p-benzoquinone in solvents of low or medium polarity give rise to a triplet exciplex. This decays with formation of solvated radical ions and the effect of solvent polarity has been examined over the range E = 3-20. Unsensitized photo-oxygenation of magnesium tetraphenylporphyrin has been reported to lead to oxidative ring cleavage yielding a bilitriene.18, The transformation is suppressed in the presence of 8carotene or a-tocopherol, which suggests that singlet oxygen is involved. However, although the mechanism of formation of the bilitriene is unclear, it seems reasonable to assume that a zwitterionic peroxide is initially formed and that this reacts with MgTPP to give an epoxide. The photo-oxygenation of oxodipyrromethene is reported to be self-sensitized and to involve singlet oxygen. l g 4 A group of substituted p-benzophenones of the form CH,kEt,Br-, cH2k(C8Hl.,)$r-, p-RC+,H,COPh (R = CH,kEt,q-, CH,NMe,(C,,H,,)Br-, OCl,H,,NMe,Br-) have been shown 185 to be more

'

18*

lS5

H. D. Scharf and R. Weitz, Tetrahedron, 1979, 35, 2255. K . K. Mukherjee and A. K. Gupta, Indian J. Chem., Sect. A., 1979, 17A,332. K. Kalyanasundarum and M. Graetzel, Helv. Chim. Actu, 1980, 63, 478. N. E. Andreeva and A. K. Chibisov, Teor. Eksp. Khim., 1979, 15, 668. T. Matsuura, K. Inoue, A. C. Ranade, and 1. Saito, Photochem. Photobiol., 1980, 31, 23. Y.-T. Park, Taehan Hwahakhoe Chi., 1980, 24, 146. S. Tazuke, Y. Kawasaki, N. Kitamura, and T. Inoue, Chem. Left., 1980, 251.

Photo-reduction and -oxidation 42 1 efficient sensitizers than benzophenone as measured by their ability to photooxidize leuco crystal violet to crystal violet in MeCN. This property is ascribed to the ease of the primary electron transfer from the dye to the triplet excited state of benzophenone. The effect of oxygen on the photodecomposition of rhodamine dyes in ethanol solution has been investigated, and found to increase the stability of the dye solutions.186 A review has appeared on the current status of chemiluminescence. 87

V. A. Mostovnikov, G. R. Grinevich, and A. L. Shalimo, Dokl. Akad. Nauk BSSR, 1980,24, 596. K. D. Gundermann, Proc.-Int. Symp. Anal. Appl. Biolumin. Chemilumin., ed. E. Schram and P. Stanley, State Print. and Publ. Inc., Westlake Village, Ca, 1978, 37.

6 Photoreactions of Compounds containing Heteroatoms other than Oxygen BY S.

T. REID

1 Nitrogen-containingCompounds

Useful reviews on the photochemistry of imides, the photoreactions of alkaloids,2 and selected aspects of photochemically induced preparative heterocyclic chemistry have been published.

'

Rearrangements.-Z,E-Photoisomerization about the carbon-nitrogen double bond has been the subject of further investigations, and the role of both inversion and rotation in this process has been demonstrated the~retically.~E -+ Zphotoisomerization has been observed in (E)-2-hydroxyiminocyclododecanone,5 whereas in singlet excited (E)-/?-ionone oxime ethyl ether (l), isomerization competes with 1,Shydrogen migration to give the 2-isomer (2) and (2)-retro-yionone oxime ethyl ether (3), respectively.6 The results obtained from a study of the E % Z-photoisomerization of the 0-methyl ether of 2-acetylnaphthalene oxime in various microemulsions illustrate the importance of interfacial processes in colloidal systems. Me (yJ/f Me LNPEt

___* /IF

Mp I

Me

OEt

(2)

(1)

+-

PN/

Me Me

(:v

Both direct and triplet-sensitized photoisomerization of pyridylhydrazones has been reported, and a syn-anti-photoisomerization of the carbon-nitrogen double bond has been shown to be responsible for the photochromism observed

'

'

P. H. Mazzocchi, Org. Photochem., 1981, 5, 421. S. P. Singh, V. I. Stenberg, and S . S. Parmar, Chem. Rev., 1980, 80, 269. H. Wamhoff, L. Farkas, H. J. Hupe, A. A. Nada, P. Sohar, G. Szilagyi, H. C. Theis, and K. M. Wald, Kern. Kozl., 1979, 52, 393. P. Russegger, Chem. Phys. Lett., 1980, 69, 362. S. McLean, J. Wong, and P. Yates, J. Chem. SOC.,Chem. Commun., 1980, 746. P. Baas, H. Cerfontain, and P. C. M. Van Noort, Tetrahedron, 1981, 37, 1583. I. Rico, M. T. Maurette, E. Oliveros, M. Riviere, and A. Lattes, Tetrahedron, 1980, 36, 1779. L. L. Costanzo, U. Chiacchio, S. Giuffrida, and G. Condorelli, J . Photochem., 1980, 13, 83. L. L. Costanzo, U. Chiacchio, S. Giutfrida, and G. Condorelii, J. Photochem., 1980, 14, 125.

422

Photoreactions of Compounds containing Heteroatoms other than Oxygen

423

in the 2-arylhydrazones of certain 2-substituted 1,2-diketones.l o Syn-antiphotoisomerization has been confirmed in the 2-phenylhydrazones of some 1,2,3triketones. l 1 Irradiation of 3or-acetoxy-5a-androstan- 17-one acetylhydrazone (4) leads to the formation of the corresponding 2-isomer ( 5 ) and in the presence of -NH Ac

oxygen to the lactams (6) and (7). Pathways accounting for the formation of these lactams have been proposed but not substantiated. The methylthiomethyl nitrone (8) undergoes reversible E Z-photoisomerization on irradiation in deuteriochloroform.l 3 Prolonged irradiation of the E-isomer affords the oxazole (9); the proposed pathway is outlined in Scheme 1. Other photoproducts arising by SMe I

HO

SMe

N-0-

H+ Ph

Ph

?Me

H SMe

4

x H Ph Ph

0

N-OH

-Hzo~

HPh

Ph

(9)

Scheme 1

carbon-sulphur bond homolysis have been described. The photochromism of certain aryl-substituted acyclic azines is also the result of an analogous E + Zphotoisomerization,14 and the process has been shown to be singlet derived.15 The Z-Ziminodiazene 1-oxides (10) are converted on irradiation (A > 300 nm) into the corresponding E-isomers (1 1); irradiation (A < 300 nm), however, results in cleavage and the formation of phthalimidonitrene (12) and nitroso-compounds (13). l6 1-Amino-2-phthalimido-diazene1-oxides are reported to undergo similar transformations.

’

lo l1 l2 l3

l4

l6

”

R. Pichon, J. Le Saint, and P. Courtot, Terrahedron, 1981, 37, 1517. P. Courtot, T. Pichon, and J. Le Saint, J. Chem. SOC.,Perkin Trans. 2, 1981, 219. H. Suginome and T. Uchida, J. Chem. SOC.,Perkin Trans. 1, 1980, 1356. N. S. Ooi and D. A. Wilson, J. Chem. Res. ( S ) , 1980,366. K. Appenroth, M. Reichenbkher, and R. Paetzold, J. Photochem., 1980, 14, 39. K. Appenroth, M. ReichenbEher, and R.Paetzold, J . Phorochem., 1980, 14, 51. L. Hoesch and B. Koppel, Helv. Chim. Acra, 1981, 64, 864. L. Hoesch, Helv. Chim. Acta, 1981,64, 890.

424

Photochemistry

N=N '0-

Me,C

N-N

+

R-NO (13)

0 (12)

The photoisomerization of azo-compounds continues to attract attention. Evidence that photoisomerizationof certain steroidal-substitutedazo-compounds proceeds by way of an inversion mechanism has been described.18 Full details have now been reported of the photorearrangement of 1,2-diaza-(Z)-cyclo-oct-1ene (14) to the E-isomer (15), and analogous transformations have been observed

(14)

(15)

in cis- and trans-3,8-dimethyl-1,2-diaza-cyclo-oct-1-ene. Photoisomerization has also been reported in trans- 1-(3,5-di-t-butyl-4-hydroxyphenyl)-2-phenyldiazene, and transient species, detected on flash photolysis in viscous solution of several trans-4-nitro-4-(dialkylamino)azobenzenes,are believed to be lowest trans-(n, n*) triplet states.21Other examples of E -+ 2-photoisomerization have been reported in azobenzene derivatives.22.23 E-Azobenzene is virtually planar, whereas in Z-azobenzene one of the phenyl groups occupies a plane at an angle of 56" to the plane of the second phenyl group and the azo-nitrogen atoms. Irradiation of complex molecules to which an azobenzene function has been added can therefore be accompanied by profound conformational changes. This approach has been employed to study several biochemically-related problems. Artificial photoresponsive membranes have been constructed by incorporating amphiphatic alkylammonium salts containing azobenzene chromophores into dipalmitoylphosphatidylcholine l i p ~ s o r n e s2.5~ ~ ~ Photocontrol of micellar catalysis has been effected in a similar fashion using the photoresponsive surfactant (1 and the hydrolysis of p-nitrophenyl acetate l9 2o 21 22

23

f4 " 26

U. Kolle, H. Schatzle, and H. Rau, Photochem. Photobiol., 1980, 32, 305. C. G. Overberger and M . 4 . Chi, J . Org. Chem., 1981,46, 303. E. Hofer, Z . Naturforsch., Teil B. 1980, 35, 233. H. Gtkmer, H. Gruen, and D. Schulte-Frohlinde, J . Phys. Chem., 1980,84, 3031. U.-W. Grummt and H. Langbein, J . Photochem., 1981, 15, 329. H. J. Timpe, U. Mueller, and J. Franze, Z . Chem., 1980, 20, 440. K. Kano, Y. Tanaka, T. Ogawa, M. Shimomura, Y. Okahata, and T. Kunitake, Chem. Lett., 1980, 421. T. Kunitake, N. Nakashima, M. Shimornura, Y. Okahata, K. Kano, and T. Ogawa, J. Am. Chem. SOC.,1980, 102, 6642. S. Shinkai, K. Matsuo, M. Sato, T. Sone, and 0. Manabe, Tetrahedron Lett., 1981, 22, 1409.

Photoreactions of Compoundr containing Heteroatorns other than Oxygen 425 catalysed by /3-cyclodextrin can be photoregulated in the presence of an azobenzene moiety.27.2 8 The conformational changes induced by light in the and azobenzene-containingply@-glutamic acid) ( 17) are completely re~ersible,~' similar photoisomerizations in crown ethers have been employed in the control of ion extraction and ion t r a n ~ p o r t . ~ ' - ~ ~ -NH-CH-CO-

CH, I

C=O NH

I Ph (17)

New examples of well established photo-induced rearrangements arising by electrocyclic pathways have been reported. A classification for such processes in systems containing heteroatoms has been proposed.33 1H-1-Benzazepines are readily converted on irradiation in tetrahydrofuran into dihydrocyclob~t[b]indoles,~~ whereas the 4,6a-dihydro[1,2]diazeto[1,4-a]pyrroles (18) are formed preferentially on irradiation of the 3H- 1,Zdiazepines (19).35A high yield

(19)

R' = Rz = Me; R 1= H,RZ = Me or Ph

(18)

preparation of 5-alkoxy- and 5-acetoxy-3-oxo-2-azabicyclo[2.2.0]hex-5-enes (20), without any competing [,4 + ,4] photodimerization, has been achieved by irradiation of the corresponding 2-pyridones (21),j6 and several 1-aryl-4,6diphenyl-2(1H)-pyrimidin-2-ones (22) have been similarly converted in benzene into the bicyclic photoisomers (23).37In contrast, the imines (24) are obtained on 27

29 'O

'' " 33 34

"

'' ''

A. Ueno, K. Takahashi, and T. Osa, J . Chem. SOC.,Chem. Commun., 1980, 837. A. Ueno, K. Takahashi, and T. Osa, J. Chem. SOC.,Chem. Commun., 1981, 94. 0.Pieroni, J. L. Houben, A. Fissi, P. Costantino, and F. Ciardelli, J . Am. Chem. SOC.,1980,102,5913. S. Shinkai, T. Nakaji, Y. Nishida, T. Ogawa, and 0. Manabe, J . Am. Chem. Soc., 1980, 102, 5860. S. Shinkai, T. Nakaji, T. Ogawa, K. Shigematsu, and 0. Manabe, J. Am. Chem. SOC.,1981,103, 11 1. M. Ship, M. Takagi, and K. Ueno, Chem. Leu., 1980, 1021. 0. Kikuchi, Tetrahedron Lett., 1981, 22, 859. M. Ikeda, K. Ohno, T. Uno, and Y. Tamura, Tetrahedron Lptf., 1980, 21, 3403. C. D. Anderson and J. T. Sharp, J. Chem. SOC..Perkin Trans. I , 1980, 1230. C. Kaneko, K. Shiba, H. Fujii, and Y. Momose, J . Chem. SOC.,Chem. Commun., 1980, 1177. T. Nishio, K. Katahira, and Y. Omote,Tetrahedron Lett., 1980, 21, 2825.

Photochemistry

426

R3

-Et,O

R4

(22) Ar

=

Ph, p-MeC,H4, or p-M&C,H,

(23)

irradiation of unsubstituted 1-arylpyrimidin-2(lH)-ones (25) in benzenemethan01;~'evidence supporting the pathway outlined in Scheme 2, in preference

(25) Ar = Ph, p-MeC,H,, or p-MeOC6H4

+ N

MC

lAr

o c N'H (24)

Scheme 2

to an alternative one involving bicyclic isomers, has been described. A bicyclic intermediate (26) has previously been proposed to account for the photoinduced transformation of 2,3,6-trimethylpyrimidin-4-one(27) to the /3-methoxy-p-lactam

(28) in methanol. The intermediacy of (26) has now been verified by irradiation in liquid ammonia-ether solution at -40 0C,39 and application of this reaction sequence to the ring-fused pyrimidin-4-one (29) affords a novel route to the azocine (30) as shown in Scheme 3.40 38 39 40

T. Nishio, K. Katahira, and Y. Omote, J . Chem. Soc., Perkin Trans. 1 , 1981, 943. S. Hirokami, T. Takahashi, M. Nagata, Y. Hirai, and T. Yamazaki, J . Org. Chem., 1981,46, 1769. Y. Hirdi, T. Yamazaki, S. Hirokami, and M. Nagata, Tetrahedron Lett.. 1980, 21, 3067.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

427

Gi2 - s:i2 0 Me

H 0 Me Scheme 3

Bicyclic valence isomers (31) and ring-opened ketens (32), characterized spectroscopically, have been obtained by low-temperature irradiation of the oxazinones (33),41 and analogous oxa-azabicyclo[2.2.0]hexenones have been shown to be intermediates in the photoinduced ring-scrambling of other oxa~inones.~~ R'

(33) R' = H, R2 = R3 = H or Me R' = R2 = Me, R 3 = H or Me R1 = But, R2 = Me, R3 = H

R'

R'

(31)

Examples of nitrogen-containing analogues of the stilbene-to-dihydrophenanthrene electro-cyclization and related transformations have been reported. Thus, photocyclization of 1-(2-pyridy1)-2-arylpyridiniumsalts affords benzo[c]pyridi[ I ,2-a]-1,8-naphthyridinyliumcations;43similar cyclizations have been observed in ind~lylpyridylethylenes,~~ in 4-(5)arylethenylimidazoles,4s and in 2(pyridylvinyl)chromen-4-ones,which, on irradiation in benzene in the presence of oxygen, yield 12H-[l]benzopyrano[1,2-f or h]-isoquinolin-12-ones and -quinolin12-0nes.~~ Related transformations include the photodehydrocyclization of the perchlorate salt (34) to give the 7H-indolo[l ,2-a]quinoliniumsalt (35),47the synthesis 41

42 O3 O4

45

" "

G . Maier and U. Schafer, Liebigs Ann. Chem., 1980, 798. P. de Mayo, A. C. Weedon, and R. W. Zabel, J . Chem. SOC.,Chem. Commun., 1980, 881. A. R. Katritzky, Z. Zakaria, and E. Lunt, J . Chem. Soc., Perkin Trans. 1, 1980, 1879. D. Pelaprat, R. Oberlin, I. L. Guen, J. B. Le Pecq, and B. P. Roques, J . Med. Chem., 1980,23, 1330. G . Lindgren, K. E. Stensio, and K. Wahlberg, J . Heterocycl. Chem., 1980, 17, 679. I. Yokoe, K. Higuchi, Y. Shirataki, and M. Komatsu, J . Chem. SOC.,Chem. Commun., 1981, 442. K. B. Soroka and J. A. Soroka, Tetrahedron Lett., 1980, 21,4631.

428 Photochemistry of 12-acetoxybenzo[c]phenanthridines from substituted styryli~ocarbostyrils,~~ and the rather surprising conversion in high yield of the enamines (36) into the 11methoxyindoloquinolizidines(37).49

M e ’Me (34)

Me0

(35)

JqJQ,

(36) R’ = R2 = H R’ = C1, R2 = H R’ = H, R2 = OMe

(37)

The application of enamide photocyclization to the synthesis of heterocycles has again been reviewed.” The key step in the total synthesis of the photoberberine alkaloid, xylopinine, is the conversion by photocyclization and [1,5]hydrogen migration of the enamide (38) into 8-oxoprotoberberine (39) in 73% yield.’l Enamides of the N-aroylenamine type, which contain an electron-withdrawing substituent in the aromatic ring, undergo both photochemical and thermal cyclization,5 2 whereas the benzofuran derivative (40) is converted on irradiation in an aprotic solvent into the trans-fused product (41) by a pathway involving conrotatory cyclization and [1,5]suprafacial hydrogen migration. s3

Me0

___,

OMe (38)

OMe (39)

Diarylamines are known to undergo analogous photoinduced electrocyclizations; N-phenyl-1,2,3,4-tetrahydro-S-naphthylamine, for example, is con48

Y. Harigayd,

s. Takamatsu, H. Yamaguchi, T. Kusano, and M . Onda, Chem. Pharm. Bull., 1980,

28, 2029. 49

A. Rahman and M. Ghazala, Heterocycles, 1981, 16, 261.

’’ I. Ninomiya and T. Naito, Heterocycles, 1981, 15, 1433. T. Kametani, N. Takagi, M. Toyota, T. Honda, and K. Fukumoto, Heterocycles, 1981, 16, 591. ’’ ’’ T. Naito and 1. Ninomiya, Heterocycles, 1980, 14, 959. 51

Y.Kanaoka and K. San-nohe, Tetrahedron Lett., 1980, 21, 3893.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

429

verted in this way into 1,2,3,4tetrahydro-1 1H-benzo[a]carbazole.54 The photocyclization of N-aryl enamines has similarly been employed in the synthesis of 2,3dihydroindoles. A detailed study of the reaction mechanism has revealed that in acyclic enamines such as (42), cis-trans-isomerization competes with cyclization.

The zwitterion (43) has been detected by flash photolysis. Reverse reactions have also been observed, but these are suppressed at lower temperatures. This cyclization has been used in the synthesis of substituted indolines as shown, for example, for enamine (44)in Scheme 4.56Analogous photocyclizations have been

H

Scheme 4

observed in N-aryl enamino ketone^;^'. ” thus, on irradiation, the 2-anilinocyclohex-Zenone (45) is converted into the tetrahydrocarbazoles(46)and (47) by the pathway outlined in Scheme 5.” 54

55 56

” 58

R. J. Olsen and 0. W. Cummings, J. Hetermycl. Chem.. 1981, 18, 439. T. Wolff and R. Waffenschmidt, J . Am. Chem. Soc., 1980, 102,6098. A. G. Shultz and C.-K. Sha, Tetrahedron, 1980,36, 1757. J. C. Amould, J. Cossy, and J. P. Pete, Tetrahedron, 1980, 36, 1585. D. Watson and D. R. Dillin, Tetrahedron Lerr., 1980, 21, 3969.

Photochemistry

430

(47) Scheme 5

An unusual 1,7-electrocyclic ring closure has been observed in the diazoalkane

(48) to give the diazepine (49).59 In contrast, irradiation of the isomeric N-

+gp

(49)

(48)

(50)

diazoalkane (50) affords products derived only from an intermediate photochemically generated carbene. Photorearrangement of 3-(N-methylanilino)-2Hazirine (51) leads to the formation of the nitrile ylide (52), which has been trapped as the oxazoline (53) and as the 1,2+triazoline (54) by reaction with the appropriate dipolarophiles.60 Photorearrangements of heterohexa- 1,3,5-trienesto five-membered heterocycles have been reviewed.6 Me I Me P h ” k + N

A

Me\

+

N-CEN-C,,

Ph’

Me

-/

Me (52)

Me

(53)

Further studies of the photorearrangement of five-membered heterocycles have been described. The isoxazole-oxazole rearrangement has previously been shown

’’ D. P. Munro and J. T. Sharp, J. Chent. Soc., Perkin Trans. 1, 1980, 1718. 6o 61

K. Dietliker, W. Stegmann, and H. Heimgartner, Heterocycles. 1980, 14, 929. M. V. George, A. Mitra, and K. B. Sukumaran, Angew. Chem., Int. Ed. Engl., 1980, 29, 973.

431 to involve 2H-azirine intermediates. Indeed, Pyrex-filtered irradiation of the isoxazolophanes (55) affords the corresponding 2H-azirines (56).62 3-Methylisoxazolo[4,5-clpyridines are similarly converted on irradiation into 2rnethyloxazol0[4,5-c]pyridines.~~The 4-hydrazino-derivative (57), however, has

Photoreactions of Compounds containing Heteroatoms other than Oxygen

(55)

R

=H

Me

or Me

(56)

NHMe hv

Me (58)

(57)

been reported to undergo a different photorearrangement to give the 1,2dihydropyrido[3,2-e]-1,2,4-triazine (58); a common intermediate is probably involved. Results of a molecular orbital study of isoxazole-oxazole photoisomerization have been published.64 Not surprisingly the allyloxazolinone (59) Ph

Ph

co, hv

Me&Me

r

‘Me p

M

e

Me (61)

(59)

I”.

FMe

Ph

0

N

&Me

(60)

hv

(62) R = Ph, p-M&&, 62

c4

or p-M& C&

Ph (63)

E. M. Beccalli, L. Majori, A. Marchesini, and C. Torricelli, Chem. Lett., 1980, 659. G. Adembri, A. Camparini, D. Donati, F. Ponticelli, and P. Tedeschi, Tetrahedron Lett., 1981, 22, 2121. H. Tanaka, T. Matsushita, Y. Osamura, and K. Nishimoto, Int. J . Quantum Chem., 1980, 18, 463.

432

Photochemistry

behaves differently on irradiation and is converted via a symmetry-allowed 1,3sigmatropic rearrangement into the isomer (60)."' The oxazolinone (59) was itself prepared by addition of carbon dioxide to the nitrile ylide, generated in turn by irradiation of the 2H-azirine (61). A 1,5-sigmatropicrearrangement is preferred on irradiation of the photolabile pyrrolines (62) and results in the formation of ringexpanded products (63),66 whereas competing photochemically induced benzyl migrations have been observed in N-substituted 3-pyrazolin-5-0nes.~' Two pathways appear to be implicated in the transposition reactions of 3cyano-1-methylpyrazole (64)."* The first, which leads to the imidazole (65), is believed to involve 2,5-bonding followed by a nitrogen 'walk', whereas the second proceeds by way of the azirine (66) and yields the isomeric imidazole (67); both processes are illustrated in Scheme 6. Sensitization and quenching experiments CN

p N N' I Me

hv

6'"-

CN

M e - N N e

N I Me

I

+N I

Me (65)

Me (67)

%heme 6

suggest that the reactive excited state of the pyrazole has the singlet z,z* configuration. The possible role of 'Dewar' pyrroles or cyclopropenyl imines as intermediates in the photorearrangement of tetrakis(trifluoromethy1)pyrroleshas also been inve~tigated;~' the valence-bond isomer (68), for example, does seem to be involved as an intermediate in the conversion of the N-phenylpyrrole (69) into the cyclobutindole (70).

65

" 68 69

A. Padwa, M. Akiba, L. A. Cohen, and J. G. MacDonald, Tetrahedron Lett., 1981, 22, 2435. T. Debaerdemaeker, W.-D. Schroer, and W. Friedrichsen, Liebigs Ann. Chem., 1981, 502. G. Singh, D. Singh, and R. N. Ram, Tetrahedron Lett., 1981, 22, 2213. J. A. Baritrop, A. C. Day, A. G . Mack, A Shahrisa, and S. Wakamatsu, J . Chem. SOC.,Chem. Commun.. 1981, 604. Y . Kobayashi, A. Ando, K. Kawada, and I. Kumadaki, J . Org. Chem., 1980,45, 2968.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

433

A novel photorearrangement has been observed in the 3-amino-4-(phenylthio)sydnones (7 1) and yields the isomeric 2-aza- 1,3-diazoniacyclopentadiene-1,4diolates (72); the proposed route is outlined in Scheme 7.70

I

I NR2

NR 2

'*\

RhC'

1 11u

N=O

R

Few new examples of photorearrangement in six-membered heterocycles have been reported. Irradiation of pentafluoropyridine in the gas phase affords the 'Dewar' isomer with a half-life of 5 days at room temperature." Two transients, thought to be isomers of azafulvene, were detected on flash photolysis. The conversion of the lactam (73) into the seco-steroid (74) on irradiation in t-butyl alcohol is viewed as arising via an electrocyclic ring-opening process, followed by addition of solvent, as shown in Scheme 8.72 Spectroscopic evidence for the

-0

(73)

Ha}

MeJCO

-0 HyJ}

'

0

(74)

Scheme 8

intermediacy of the 2,4-diazabicyclo[3.1.O]hex-2-(3)ene (75) in the photoisornerization of the I ,4-(3,4)-dihydropyrimidine (76) has been published.73 The

'* 71

72

73

H. Gotthardt and F. Reiter, Chem. Ber., 1981, 114, 1737. E. Ratajczak, B. Sztuba, and D. Price, J . Phofochem.. 1980, 13, 233. A. Canovas, J. Fonrodona, J.-J. Bonet, M. C. Brianso, and J. L. Brianso, Helv. Chim.Acta, 1980,63, 2380. R. E. van der Stoel, H. C. van der Plas, and G. Geurtsen, J . Heferocycl., 1980, 17, 1617.

Photochemistry effect of substituents on the regioselectivity of di-z-methane rearrangement in 5,6benzo-2-azabicyclo[2.2.2]octadienones has been examined,74 and 1,2,4,6,7pentakis(trifluoromethyl)-3,5-diazatricyc10[4.1 .0.02*7]hept-J-ene(77)is converted, on irradiation in ether, into the isomer (78); various mechanisms have been considered for this transformation. 7 5 On further irradiation, the bicycle (78) undergoes cleavage to the imidazole (79)and hexafluorobut-2-yne.

434

(76) R

= p-CF,C,H,

(75)

R R

'C~FR hv R

N

R H (77) R

=

CF,

-

R

I ) - R

hv

R

R E (78)

R

+

R-CEC-R

H (79)

Oxaziridines are of interest in their own right and as intermediates in various photorearrangements. It has been shown that the nature of the nitrogen substituent does not affect the regioselectivity of lactam formation on irradiation of spiroo~aziridines.'~ The oxaziridine (80) has been proposed without any real evidence as an intermediate in the photoinduced transformation of trans-canadine N-oxide

(81) to the lactam (82) and the formamide (83).77 The photorearrangements of heteroaromatic N-oxides have, in general, been rationalized in terms of intermediate oxaziridines, although in most cases, definite evidence for the existence of 74

75

76 77

M. Kuzuya, E. Mano, M. Ishikawa, T. Okuda, and H. Hart, Tetrahedron Lett., 1981, 22, 1613, Y. Kobayashi, T. Nakano, M. Nakajima, and 1. Kumadaki, Tetrahedron Lett., 1981, 22, 1369. E. Oliveros, M. Riviere, and A. Lattes, J . Heterocycl. Chem., 1980, 17, 1025. P. Chinnasamy, R. D. Minard, and M. Sh,amma, Tetrahedron, 1980, 36, 1515.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

435

such species is lacking. The previously reported ring opening of pyridine N-oxide (84) in aqueous solution in the presence of secondary amines to give the 5-amino2,4-pentadienenitriles(85) and (86) has been developed as a preparative method.78

(86)

(85)

(84)

A two-step synthesis of Chydroxyindole derivatives (87) has also been reported and involves photorearrangement of isoquinoline N-oxides (88) via oxaziridines (89) to the benzoxazepines (go), followed by treatment with acid, as shown in Scheme 9.'' In a separate study, 3,l-benzoxazepines have been shown to undergo THCO,R

(88) R

=

rHC02R

Et or CH,Ph

(89)

?H

N HC02R

C02R (87)

(90)

Scheme 9

a novel photoinduced ring-contraction to yield 3-formylindoles. An oxaziridine (9 1) has been detected on irradiation of 6-cyanophenanthridone5-oxide (92) in an ethanol or 2-methyltetrahydrofuran matrix at 77K and is an intermediate in the formation of 5-ethoxyphenanthridone (93) and 6-cyanophenanthridine (94), respectively.'l 6-Cyano-3,1-dibenzoxazepine (95) was also obtained, presumably via an axygen 'walk' process involving oxaziridine (96). 1- and CAzaphenanthrene N-oxides undergo solvent-dependent photorearrangement, yielding naphtho- 1,3oxazepines in aprotic solvents and benzoquinolin-1(2H)-ones in aqueous solution.** A biphotonic process via an oxaziridine has been observed in pyrazine NN-di~xide;'~the likely product is 2,s-dihydroxypyrazine. Oxaziridines are also reported to be intermediates in the photodecomposition of chlordiazepoxide 78

79 80

81

82

83

J. Becher, L. Finsen, I. Winckelmann, R. R. Koganty, and 0. Buchardt, Tetrahedron, 1981,37, 789. C . Kaneko, W. Okuda, Y. Karasawa, and M. Somei,Chem. Left., 1980, 547. C. Kaneko, H. Fuji, S. Kawai, A. Yamamoto, K. Hashiba, T. Kimata, R. Hayashi, and M. Somei, Chem. Pharm. Bull., 1980, 28, 1157. K. Tokumura, H. Goto, H. Kashiwabara, C. Kaneko, and M. Itoh, J . Am. Chem. SOC.,1980, 102, 5643. A. Albini, G. F. Rettinetti, and G. Minoli, J. Chem. SOC.,Perkin Trans. 2, 1980, 1159. H. Kawata, S. Niizuma, and H. Kokubun, J . Photochem., 1980, 13, 261.

436

Photochemistry

I OEt (93)

(94)

C1

Ph (97)

0-

I 0. (98)

(97) 84 and the nitroxyl radical (98).85 Examples of oxygen-atom transfer have been observed on irradiation of heteroaromatic N-oxides.86- 8 8 Azomethane imines undergo an analogous photoinduced cyclization to give diaziridines. The dihydroisoquinoline derivative (99), for example, is converted on irradiation in cyclohexane or benzene into the diaziridine the transformation is thermally reversible. In contrast, the pyrazolidinone azomethine imines (101) undergo photoreversible conversion into the diaziridines (102), providing in this way a useful reversible photochromic system.g0The analogous photoisomerization of a pyrene-substituted pyrazolidinone azomethinimine has 84

86

89

P. J. G. Cornelissen and G. M. J. Beijersbergen van Henegouwen, Pharm. Weekbl. Sci.Ed., 1980, 2, 547. G. I. Shchukin, I. A. Grigor’ev, and L. B. Volodarskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 1421. Y.Ogawa, S. Iwasaki, and S. Okuda, Tetrahedron Lett., 1981, 22, 2277. A. G. Rowley and J. R. F. Steedman, Chem. Ind. (London), 1981, 365. M . N. Akhtar, D. R. Boyd, J. D. Neill, and D. M. Jerina, J. Chem. Sot:., Perkin Trans. I , 1980, 1693. G. Tomaschewski, U. Klein, and G. Geissler, Tetrahedron Lett., 1980, 21, 4877. G. Tomaschewski, G. Geissler, and G . Schauer, . I Prakt. . Chem., 1980, 322,623.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

431

(99)

R3 R3

hv

hv

also been described.” The first authenticated example of a triaziridine, 1ethoxycarbonyl-trans-2,3-di-isopropyltriaziridine(103), has been prepared in a similar fashion;92 irradiation of isomeric acylazimines (104) gave a species with a half-life of 3.5 days at room temperature to which the triaziridine structure (103) has been assigned. Pyridine and quinoline N-imides undergo related ring-expansion reactions via diaziridines to afford diazepines. The regiospecific synthesis of 3-methoxy-1,2diazepines (105) has been achieved in this way by irradiation of ylides (106).93

OY”-

Such ring-expansion reactions have previously been limited to ylides possessing an electron-withdrawing substituent on nitrogen. Now, the tricyclic Niminopyridinium ylides (107) have been reported to give the tricyclic 1H-1,2diazepines (108) by the pathway outlined in Scheme Quinoline N-imides (109) having an electron-donating substituent in the 6- or 8-position are converted on irradiation into the 3H-l,3-benzodiazepines (1 intermediates (1 11) and 91

92

93 94

”

A. Klirnakova, M. V. Koz’menko, G. Tomashewskii,and M. G. Kuzmin, Khim. Vys. Energ., 1980,14, 149. C. Leuenberger, L. Hoesch, and A. S. Dreiding, J . Chem. Sor., Chem. Commun., 1980, 1197. T. Kiguchi, J.-L. Schuppiser, J.-C. Schwailer, and J. Streith, J. Org. Chem., 1980, 45, 5095. Y. Yamashita and M. Masumura, Chem. Lett., 1980, 621. T. Tsuchiya, S. Okajima, M. Enkaku, and J. Kurita, J. Chem. Soc., Chem. Commun., 1981. 211.

Photochemistry

438

R'

MeOH

Me

'

Ph

Ph

R2F +N

R3

R'

hv

R

2

W

R3

-N

R N,N

1

\

CO,Et

k02Et (111)

(109) R' = Me, R3 = H, RZ = OMe, NMe,, or Me R' = R3 = Me, R2 = H R' = R3 = H, R2 = O M e

N-CO Et

R3

R'

R3

(1 12) are believed to be involved. Analogous quinoline N-imides having an electron-donating group in other positions or having an electron-withdrawing group are not converted into diazepines, whereas 1H-l,3-benzodiazepines are formed in a novel two-step photorearrangement from isoquinoline N-acylirnide~.'~ The photoinduced formation of pyrazole derivatives from pyrazine and pyrimidine N-imides and of pyrrole derivatives from pyridazine N-imides is thought to involve cyclization to a diaziridine, followed by ring expansion, photoisomerization to the triazabicyclo[3.2.0]heptadiene system, and elimina t i ~ n . The ~ ' photocyclization of the phenol betaine (1 13) to the 8,lkycloberbine (1 14) has been employed in a novel synthesis of (+)-f~maricine.~*

Me0

hv ____,

'' T. Tsuchiya, M. Enkaku, and S. Okajima, Chern. Phum. Bull., 1980,28,2602. 97

98

T. Tsuchiya, J. Kurita, and K. Takayama, Chem. Phum. Bull., 1980,28,2676. M. Hanaoka, S. Yasuda. Y. Hirai, K. Nagami, and T. Imanshi, Herertwycles, 1980, 14, 1455.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

439

Oxaziridines are accepted as intermediates in the photorearrangements of oximes to amides and lactams. The formation of host-guest complexes in acetophenone oxime derivatives that incorporate a crown ether moiety has been shown to stimulate triplet-derived 2-E-isomerization and to depress singletderived oxaziridine formation.99 Low yields of lactams (1 15)--(117) have been obtained on irradiation of ~-nor-5a-androstan-16-one oxime (118) in methano1.'O0 The unusual formation of lactam (1 17), in which the chirality of the

H

(115)

(1 18)

+

~

(1 16)

C

E

(117)

+ N G

\

C

q \

N

\ (1 19)

+

-

L

(120)

N

+

g E i 2 0 H

\H

H (121)

(122)

migrating carbon centre is not retained, supports the intervention of a ring-opened intermediate. The major products of this photoreaction are the seco-nitriles (1 19)--(122) arising, it is suggested, by competing ionic carbon-carbon bond cleavages. a-Fission is not observed, however, on irradiation of 3a,5cyclo-5acholestan-7-one oxime (123) in methanol, the major products being the parent ketone (124) and the isomeric lactams (125) and (126);'" these results are in

(125) 99

loo lo*

M. Tada, H. Hirano, and A. Suzuki, Bull. C k . SOC.Jpn.. 1980,53,2304. H. Suginome and T. Uchida, Bull. Chem. Soc. J p . . 1980,53,2292. H. Suginome and C.-M.Shea, J. Chem. SOC.,Perkin Trans. I , 1980, 2268.

(126)

Photochemistry

440

agreement with the suggested mechanism for the 'normal' photo-Beckmann rearrangement. Lactam formation also predominates on irradiation of steroidal p,y-unsaturated ketone oximes. The photorearrangement of o-nitrobenzaldehyde (127) to o-nitrosoknzoic acid (128) has been re-examined. l o 3 the mechanism of this conversion remains uncertain, but a transient species has been detected and tentatively assigned the

a'"" -

H,O

hv

,

a'''" N- OH I

NO2

( 127)

I 0-

OH

I

Scheme 11

structure (129); the proposed pathway is outlined in Scheme 11. This transformation has been used as the basis for a photolabile protecting group. Irradiation of the o-nitrobenzylidene acetal-containing disaccharide (1 30), for example, followed by mild oxidation with trifluoroperacetic acid (to effect OMe

i, hv ii, CF,CO,H

H',"

I c=o

6"".

oxidation of the nitroso-group), gave the partially protected disaccharide (1 3 1) with a free hydroxy-group at C(3).'04 Other similar applications have been described. l o 6 The photocyclization of certain o-nitrophenyl alkyl ethers (1 32) to give benzoxazoles (133) is also thought to involve intramolecular hydrogen abstraction by the nitro-group as shown in Scheme 12.''' Other miscellaneous photorearrangements reported include the isomerization of l o 5 7

Io3

lo4 Io5 lo6 lo'

H. Suginome, N. Maeda, Y. Takahashi, and N. Miyata, Bull. Chem. SOC.Jpn., 1981, 54, 846. M. V. George and J. C. Scaiano, J . Phys. Chem., 1980, 84, 492. P. M . Collins and V. R. N . Munasinghe, J . Chem. Soc., Chem. Commun.. 1981, 362. E. Ohtsuka, S. Tanaka, and M. Ikehara. Nucleic Acid Chem., 1978, 1, 401. A. D. Broom and D. G . Bartholomew, ivucleic Acid Chem., 1978, 2, 771. S. Oguchi and H. Torizuka, Bull. Chem. SOC.Jpn., 1980,53, 2425.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

(132) R = H, Me, or Ph

441

OH

-0

0-

(133) Scheme 12

aryl isocyanides to aryl cyanides,"* examples of photo-Smiles rearrangement, log*loo and photo-Fries rearrangement of N-arylcarbamates. Rearrangements in nitrogen-containing compounds originating from excitation of a carbonyl group merit brief discussion in this Section as well as in Part 111, Chapter 1. Norrish Type I cleavage is responsible for the conversion of 2aminopyrrolin-5-ones (134) into aminocyclopropylisocyanates (135);' the products are isolated as the dimethylurea derivatives (136) by reaction with dimethylamine. The bis(2-aminopyrrolin-5-ones)(137) undergo a similar photorearrangement to form bis(isocyanates) (1 38). The azetidine-2,4-dione (1 39) has been

'''

''

6

NMe

hv

I

R (134) R = Me or Ph 0

0

J)<:rN II

r>(ziz=o I

R (135)

Me NH 2

I

R

(1 34)

(137)

prepared by irradiation of N-methylcyclohexane-1,Zdicarboximide( 140) in acetonitrile;' N-formyl-N-methylcyclohexene-1-carboxamide(141) has been shown to be an intermediate in this transformation and the proposed mechanism is shown in Scheme 13. l4 Competitive Type I and Type I1 processes have been observed in N-acylpyrrolidones.

'

lo'

Io9 'Io

'I2

'I5

''

J. H. Boyer, V. T. Ramakrishnan, K. G. Srinivasan, and A. J. Spak, Chern. Left., 1981, 43. K. Mutai and K. Kobayashi, Bull. Chern. SOC.Jpn., 1981, 54, 462. G. G. Wubbels, A. M. Halverson, and J. D. Oxman, J. Am. Chem. Soc., 1980,102,4848. J. E. Herweh and C. E. Hoyle, J. Org. Chern., 1980, 45, 2195. B. J. Swanson, G. C. Crockett, and T. H. Koch, J . Org. Chem., 1981, 46, 1082. K. Maruyama, T. Ishitoku, and Y. Kubo, J. Org. Chem., 1981,46, 27. K. Mayuyama, T. Ishitoku, and Y. Kubo, Chem. Left., 1980, 265. M. Machida, H. Takechi, A. Sakushima, and Y . Kanaoka, Heterocycles. 1981, 15, 479.

Photochemistry

442

-

hv

L

hv

0

Scheme 13

2-(N-Methylanilino)acetophenones undergo Type I1 cyclization on irradiation in diethyl ether to give 1,3-diarylazetidin-3-01~. Analogous cyclizations were observed in 2-(N-methylanilino)-2'-acetonaphthone and 2-(N-methylanilino)-ltetralone. Likewise, the heteroaryl N-methylanilinomethyl ketones (142) are converted on irradiation in diethyl ether, into isomeric 3-heteroaryl- 1phenylazetidin-3-01s (143),' and N-benzyl-a-aminoacetophenonesgave cis-2,3diarylazetidin-3-01s on n -+ n* excitation.' l 8 OH Ph,

hv

N- CH2-C-R ------+ I II Me 0 (142) R = 2-fury1, benzo[b]furan-2-yl, 2-thienyl, 1 -methylpyrrol-2-yl, or 2,4-dimethylthiazol-5-y1

Ph' (1 43)

RZ

or

R'

GR3 0

(144) R' = R3 = Ph,(145) R' = R2 = R3 = Me (146) R' = R2 = R3 = Me R2=H ' R' = Ph, R 2 = R3 = Me R' = Ph, R2 = R 3 = Me R' = R3 = Ph, R2 = H

Competing pathways to p-lactams (144) and oxazolidin-4-ones (145) were observed on irradiation of N-alkyl-a-oxoamides (146). Similar photoreactions have previously been reported for NN-dialkyl-a-oxoamides, but in the present case the reactions are less clean with many unidentified by-products. A novel intramolecular hydrogen abstraction from a formyl group is apparently responsible for the photorearrangement of N-phenacylformamide (147) to the /?-lactam (148). 120 &Hydrogen.abstraction, followed by cyclization of the biradical thus formed, has

''

K. L. Allworth, A. A. El-Hamamy, M. M . Hesabi, and J. Hill, J . Chem. Soc., Perkin Trans. I , 1980, 'I'

'I8

'I9

1671. M . M . Hesabi, J. Hill, and A. A. El-Hamamy, J . Chem. SOC., Perkin Trans. I , 1980, 2371. H. G. Henning, J. Fuhrmann, and U. Krippendorf, Z . Chem., 1981, 21, 36. H. Aoyama, M. Sakamoto, and Y. Omote, J . Chem. SOC., Perkins Truns. 1, 1981, 1357. H. Wehrli, Helv. Chim. Acfa, 1980, 63, 1915.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

443

been observed to occur readily in the Mannich base (149) to give the imidazoline (150), whereas E- and t-hydrogen abstractions are preferred in N-aminoalkylphthalimides yielding hexahydropyrazines and hexahydro- 1,$-diazepines, respectively.122A mechanism involving a radical ion has been proposed to account for the latter transformation.

N

0 ( 149)

(150)

2-Dialkylaminocyclohex-2-enonesalso undergo intramolecular hydrogen abstraction on irradiation, but the delocalized biradical thus formed cyclizes in a different sense to afford a-ketoazetidines as shown, for example, in Scheme 14 for

Scheme 14

diethylaminocyclohex-2-enone(15 l).' 23 For reasons that are not entirely clear, 2benzylaminocyclohex-2-enone (1 52) is unexpectedly converted on irradiation in diethyl ether into a mixture of isomeric a-ketoaziridines (153) and (1 54). 124 NNDibenzyl- and NN-diallyl-P,y-unsaturatedamides (1 55) undergo photocyclization to give the corresponding pyrrolidin-2-ones (1 56) and (1 57); 25 intermediate lZ1

''' lZ3 lZ4 If5

J. D. Coyle, J. F. Challiner, E. J. Haws, and G. L. Newport, J . Heterocycl. Chem., 1980, 17, 1 131. M. Machida, H. Takechi, and Y. Kanaoka, Heterocycles, 1980, 14, 1255. J. C. Amould, J. Cossy, and J. P. Pete, Tetrahedron, 1981, 37, 1921. J. Cossy and J. P. Pete, Tetrahedron Lett., 1980, 21, 2947. H . Aoyama, Y. Inoue, and Y. Omote, J . Urg. Chem., 1981, 46, 1965.

Photochemistry

444 O

H

O

H

___)

R

R

I

I H ZC\ ,CHzR

.CH

\ ,CH,R

--,h

Me

I'

PhG O Me Me

P

N

h V O Me Me

( I 55) R = Ph or CH=CH,

( 1 58)

Me Me

Me Ph

CH2R

CH2R

( 156)

(157)

biradicals (158), formed in this case by an unprecedented 1,6-intrarnolecular hydrogen transfer to the alkene, appear to be implicated. An initial cyclization to the oxazoline (159) is involved in the photodecomposition of 'propyzamide' (160),'26 and the conversion of dialdehyde (161) into ( )-cis-alpinigenine (162) is the result of photoinduced enolization followed by thermal [,4 + ,2] cycloaddition. 127 R-C-NH-C-CECH 0 II Me I

hv

___+

I Me ( 1 60) R

p,.

Me

-N

Me

= 3,4-C1,C,H3

(1 59)

Me0 M e o r N h 4 e hv ___*

Me0

OMe

Meo

'H dM e 0 - OMe (162)

Addition.-Examples of photodimerization arising by [,2 + ,2] cycloaddition have been reported in unsaturated nitro-compounds 12' and the effect of solvent lZ6 12'

128

P. Meallier, B. Pouyet, J. Badin, J. Bastide, and C. Coste, Chemosphere, 1980, 9, 105. S. Prabhakar, A. M. Lobo, M. R. Tavares, and I. M. C. Oliveira, J . Chem. SOC.,Perkin Trans. I , 1981, 1273. Y. Slavcheva, V. V. Perekalin, E. S. Lipina, and 2. F. Pavlova, Zh. Org. Khim., 1980, 16, 2413.

Photoreactions of Compounds containing Heteroatoms other than Oxygen 445 on such dimerizations in maleimide and N-methylmaleimide has been investigated.12’ An intramolecular equivalent process has been observed in the 1,l’trimethylbisuracil (163), which on irradiation is converted into the cyclobutane derivative (164).130

H

O

O

H

FN N -(CH 2)3-N

O% ( 163)

HI;,-. &

do’” O

(164) D

1,3-Diacetylimidazolin-2-0ne(165) undergoes [z2 + .2] cycloaddition to ethylene on irradiation in acetone to give the cis-fused adduct (166).13’ In a separate study, good yields of cyclobutane derivatives were obtained by photoaddition of 1,3-diacetylimidazolin-2-oneto cyclopentene, dihydropyran, and 2metho~y-3,4-dihydropyran.~~~ Irradiation of N-benzoylindole (167) in the Ac

Ac

Ac ( 165)

CH ,==CHCO,Me

COPh ( 167)

presence of methyl acrylate gave a stereoisomeric mixture of dihydrocyclobut[b]indoles (168),133whereas photoaddition of N-isobutenylpyrrolidine to dimethyl fumarate takes place only in non-polar solvents.134 The preferred stereochemistry of the photoadducts, (169) and (170), of 3-ethoxycarbonyl-2phenyl-2-pyrroline4,5-dione(1 71) with substituted alkenes has now been firmly established by chemical and spectroscopic means;13’ styrene and butadiene principally form 7-excpisomers, whereas ethyl vinyl ether and vinyl aetate afford 7-endo-adducts. P. Bouk and J. Lemaire, J. Chim. Phys.. Phys. Chim. Biol., 1980, 77, 161. K. Golankiewicz and L. Celewicz, Pol. J . Chem., 1979, 53, 2075. K.-H. Scholz, J. Him, H.-G. Heine, and W. Hartmann, Liebigs Ann. Chem., 1981, 248. R. A. Whitney, Tetrahedron Lett., 1981, 22, 2063. lJ3 M. ikeda, K. Ohno, T. Uno, and Y . Tamura, Tetrahedron Lett., 1980, 3403. IJ4 F. D. Lewis, T.-I. Ho, and R. J. DeVoe, J . Org. Chem.,1980, 45, 5283. 13’ T. Sano, Y. Horiguchi, and Y. Tsuda, Heterocycles, 1981, 16, 359.

”’

IJo

Photochemistry

446

The 5-trimethylsilyl group has been shown to have a profound effect on uracil photocycloaddition reactions. 36 Irradiation of the uracil (172), for example, in SiMe,

hv

AN O

AN

O

R’ = R2 = Me or -(CH2)5R’ = H, R2 = Me

(172)

R2

H H R’ (1 73)

propene, isobutylene, or methylenecyclohexane gave only the head-to-tail adduct (173). Photocycloaddition of 6-cyanouracil (174) to alkenes gave, in addition to normal cyclobutane derivatives, products arising by migration of the cyanogroup. 37 The proposed mechanism for this transformation is illustrated in Scheme 15 for cyclopentene;adducts (175) and (176) were obtained on irradiation

’

-

M e . 5

0A

N Me ( 1 74)

hv

cyclopentene

CN

M e . 5 7 0 N’O CN Me

I

__+

M e N 5 - 0 Me

CN

(175)

in acetonitrile, whereas the imine (I 77) was the major product on irradiation in ethanol. Adducts (178) and (179), arising by [,2 + %2]process, and the pyridine (180), formed by [,4 + ,2] cycloaddition followed by methylamine elimination, have been obtained on irradiation of caffeine (181) in the presence of stilbene (182).138The competing but unprecedented formation of photoproducts (183)(185) has also been observed. The photocycloaddition of 5-fluorouracil to 5,7dimethoxycoumarin has been described,’39 and five nucleoside4’13‘

13’ 13’ 139

C. Shih, E. L. Fritzen, and J. S. Swenton, J . Org. Cliem.. 1980, 45. 4462. 1. Saito, K. Shimozono, and T. Matsuuri. J. Am. Chem. Soc., 1980, 102, 3948 G. Kaupp and H.-W. Griiter, Angew. Cheni.. Int. Ed. Engl., 1980. 19. 714. S. C. Shim. C. S. Ra. and K. H. Chae, Bull. Korean Chem. Soc.,-1980,, 1, 121.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

0

0

+

+

O

N Me

447

MTk:>R O

N Me (184) R (185) R

Ph

(183)

= Ph = CH,Ph

hydroxymethyl-4,5’,8-trimethylpsoralencycloadducts have been obtained on irradiation of psoralen with native double-stranded DNA. 140 Intermolecular hydrogen-bonding in alkenyl-substituted 2-pyridones brings carbon-carbon double bonds into close proximity and thus facilitates [,2 + ,2] cycloaddition.14’ Contrasting photocycloadditions have been reported in 4methoxy-Zpyridone (1 86);14* irradiation in acetone in the presence of electronrich alkenes affords the 3-azabicyclo[4.2.0]ot4en-2-ones( 187), whereas with R

“ . O d H

hv

f---

@R

N

H

O

(187) R = Me,, CH,OAc,

or OMe

hv

, ( 186)

(1 88) R = C0,Me or C N

electron-deficient alkenes the 2-azabicyclo[4.2.0]oct-4-en-3-ones(188) are obtained. An analogous [,2 + ,2] photoaddition of 4-methoxyquinol-2-one to ethylene 143 and further examples of the photoaddition of 4-hydroxyquinol-2-one to alkenes 144 have been published. In a molecular orbital study of the photocycloaddition of quinol-Zone to alkenes, the calculated regioselectivity has been I4O 14’ 14’ 143

K. Straub. D. Kanne, J. E. Hearst, and H. Rapport, J. Am. Chem. SOC.,1981,103, 2347. P. Beak and J. M. Zeigler, J. Org. Chem., 1981,46,619. H. Fuji, K. Shiba, a 4 C. Kaneko, J. Chem. Sm., Chem. Commun., 1980, 537. C. Kaneko, T. Naito, and N. Nakayama, Chem. Pharm. Bull., 1981,29, 593. T. Naito and C. Kaneko, Chem. Pharm. Bull., 1980,uI, 3150.

Photochemistry

448

+

found to correlate with experimental results.145 [ ~ 2 ,2] Cycloadditions of isoquinol-1(2H)-ones to alkenes have also been accomplishedphotochemically;14‘ reaction of 4-acetoxy isoquinol-l(2H)-one (189) with acrylonitrile, vinyl acetate, and methylenecyclohexane, for example, proceeds in high yield to give a mixture of diasterioisomeric adducts (190).

Examples of intramolecular [,2 + ,2] cycloaddition are common and frequently occur more efficiently than related intermolecular cycloadditions. N-Methylmethacrylimide (191) undergoes reaction of this type on irradiation in acetonitrile to give cis- 1,3,5-trimethyl-3-azabicyclo[3.2.O]heptane-2,4-dione( 192) in 66% yield. 14’ An acetone-sensitized intramolecular cycloaddition in the ester (193)

hv

Me

Me 0

‘

0

-Ac

Me 0
I .

‘a

P

has been employed as the key-step in two separate syntheses of 2,4methanoproline.14** 14’ Intramolecular addition has also been observed in bis[5-alkyluracils] linked through the l,l’-positions.l Although the number of successful photoinduced [,2 ff2]cycloadditions to the azomethine bond remains few, new examples have been described during the period covered by this Report. Particularly notable is the addition of 6cyanophenanthridine(194) to electron-donor alkenes (195) to give azetidines (196) and azocines (197), l 5 the latter almost certainly arising by further irradiation of the azetidinesin ethanol. The addition takes place regiospecificallyfrom the lowest excited singlet state via an exciplex intermediate. An analogous photoaddition has been observed between 1,3-dimethy1-6-azauraciland dibromomaleimide, 5 2 but

+

14’ 146

14’

149

R. Chadha and N. K. Ray, Proc. Indian Acad. Sci.,(Ser.): Chem. Sci.,1980, 89, 539. T. Naito and C. Kanebo, Tetrahedron Lett., 1981, 22, 2671. K. Maruyama and T. Ishitoku, Chem. Lett., 1980, 359. M. C. Pirrung, Tetrahedron Lett., 1980, 21, 4511. P. Hughes, M. Martin, and J. Clardy, Tetrahedron Lett., 1980, 21, 4579. A. Rajchel and K. Golankiewicz, Pol. J . Chem., 1980, 54, 123. S. Futamura, H. Ohta, and Y. Kamiya, Chem. Lett., 1980, 655. G . Sazilagyi and H. Wamhoff, Angew. Chem., Int. Ed. Engl., 1980, 19, 1026.

Photoreactions of Compounds containing Heteroatorns other than Oxygen

+

449

hv

R' (195) = Me, R2 = MeOC,H, = H, R2 = PhO

(197)

attempts to add 1,3-dimethyluracil (198) to the 2,5-diaryl-l,3,4-oxadiazoles(199) led to ring cleavage and the formation of benzoylhydrazones (200). 5 3 Addition of electron-acceptor afkenes to 2-aryl-1-pyrrolinium perchlorates has been found to proceed by initial [,2 + ,2] cycloaddition to the aromatic ring. 5 4 An exception to

hv ___, e C N

c10,-

OMe

eoM CN

this behaviour has been found in 2-anisyl- 1-pyrrolinium perchlorate (20 1) which, on irradiation in methanol in the presence of acrylonitrile, is converted into the azetidine (202). Further studies of the photoreaction of N-ethylphthalimide with alkenes have shown that the lowest triplet state of N-ethylphthalimide is involved. 5 5 Benzophenone undergoes photoinduced cycloaddition to 1-acetyl- and 1-benzoylimidazole (but not imidazole itself) to give the corresponding oxetans. 56 2-Cyanopyridine (203) is reported to undergo photoaddition to cyclopentene in acetonitrile to give the ketone (204);15' a pathway involving the diradical (205) followed by imine (206) formation and subsequent hydrolysis is outlined in Scheme 16. Similar results were obtained with 2-methylbut-2-ene. On reinvestigation by other workers, this reaction gave only a low yield of ketone (204); the major product in this case proved to be 2-(2-~yclopentenyl)pyridine(207). 5 8 lS3 lS4 155

lS7 lS 8

L. Farkas, J. Keuler, and H. Wamhoff, Chem. Ber., 1980, 113, 2566. P. S. Mariano and A. Leone-Bay, Tetrahedron Lett., 1980, 21, 4581. H. Hayashi, S. Nagakura, Y . Kubo, and K. Maruyama, Chern. Phys. Lett., 1980,72, 291. T. Nakano, N. Rodriguez, S. 2.de Roche, J. M.Larrauri, C. Rivds, and C. Perez, J . Heterocycl. Chem., 1980, 17, 1777. I. Saito, K. Kanehira, K. Shimozono, and T. Matsuura, Tetrahedron Lett., 1980, 21, 2737. R. Bernardi, T. Caronna, S. Morrocchi, and P. Traldi, Tetrahedron Lett., 1981, 22, 155.

Photochemistry

450 hv

cyclopentene

CN (203)

N.

I

I

hs cyclopentene

cqp

Photosubstitution by the cyclopentenyl group was also observed in 4-cyanopyridine. The reason for this difference in behaviour is not clear and warrants further investigation. Examples of cycloaddition arising by a [,4 + .4] pathway are, as usual, relatively rare. Pyrid-2-one has recently been shown to yield four [,4 .4] stereoisomeric dimers on irradiation in aqueous solution. A micellar alignment effect has been observed in related N-o-carboxyalkylpyrid-Zones; 5 9 on irradiation in micellar and reversed-micellar systems, the ratio of cis :trans dimers has been found to increase with decreasing length of the alkyl chain. In the corresponding 4-alkyl derivatives, only cis-dimers were obtained. The reversible formation of [,4 + ,4] photodimers of benzo[g]quinoline and N-methylbenzo[g']quinolinium has been reported. 6 o Various examples of the addition of simple solvent molecules to nitrogencontaining systems have been reported. Special attention has been devoted in a review to the photoreactions of purines in the presence of alcohols, ethers, amines, and amino-acids.161 A radical pathway is obviously implicated in the photoaddition of ethanol to 1,3-dimethylthyrnine to give 1,3-dimethyl-6-(1-hydroxy-1ethyl)thymine, 1,3-dimethy1-5-(2-hydroxy-1-propyl)uracil, and cis- and truns-5,6dihydro-l,3-dimethyl-6-(1-hydroxy-1-eth~l)thymine.'~~ Irradiation of symtriazolo[4,3-b]pyridazine(208) in butan- 1-01 similarly leads to the photoalkylation products (209) and (210). 163 Photoadditions of propan-2-01 to pyrid-4-one 164 and water to 1,3-dirnethylthymine165 have also been reported. An electron-transfer mechanism appears to be implicated in the photoaddition of alcohols and ethers to 2-phenyl- and 2-isobutenyl-1-pyrrolinium salts. 66 Irradiation of 2-phenyl-1pyrrolinium perchlorate (2 1 1) in tetrahydrofuran, for example, gave a mixture of the diastereoisomeric adducts (2 12). Photoaddition of formamide to the unsaturated ester (2 13), followed by cyclization and deprotection, gave dihydroshowdo-

+

'

159 160

16t 162 163 164

Y. Nakamura, T. Kato, and Y. Morita, Tetrahedron Lett., 1981, 22, 1025. J. Bendig, J. Fischer, and D. Kreysig, Tetrahedron, 1981, 37, 1397. M. Rafalska and G. Wenska, Wiad. Chem., 1980, 34, 9. M. D. Shetlar, Photochem. Photobiol., 1980, 32, 587. D. H. Brown and J. S. Bradshaw, J . Org. Chem., 1980,45, 2320. M.Yamazaki, J. Koshitani, Y. Ueno, and T. Yoshida, Aromatikkusu, 1980,32, 241 (Chem. Abstr., 1981, 94, 174823).

165 166

E. Fahr and P. Fecher, Z . Naturforsch., Ted B, 1981, 36, 226. J. Stavinoha, E. Bay, A. Leone, and P. S. Mariano, Tetrahedron Lett., 1980, 21, 3455.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

hv THF

QPh H

BzocF hv

____)

HOCH, ~

Z

HCONH,

0

45 1

0

0

X

H

HO OH

Me Me (2 13)

(2 14)

mycin (214). lci7 Irradiation of 1,3-dimethy1-4-thiouracil(215) in aqueous solution in the presence of L-lysine led to the formation of two products, one of which was shown to be the adduct (216).16* This is thought to arise by nucleophilic addition S

M e N 5

hr

A

L-lysine

OAN

Me

(215)

M e N y

A

O

N Me

CO,H NkNH, H (216)

rather than via a radical pathway. An analogous photoaddition appears to be responsible for the formation of the N-1-substituted thymine (217)from thymidine (218) and L-lysine (219) on irradiation in aqueous solution:'69 a likely mechanism is outlined in Scheme 17. The same photoproduct was obtained from the photoreaction of DNA with L-lysine, and it has therefore been suggested that this transformation could be implicated in u.v.-induced damage to cellular nucleic acids. Tertiary amines have been reported to undergo addition to singlet transstilbene; product selectivity appears to be determined by the orientation of deprotonation of the aminium radical intermediate by the stilbene radical anion. 170 Intramolecular addition has been observed in S-2-(1'-methylalky1)aniline (220) on irradiation in methanol to give the 2S,3R-2,3-dimethylindoline 16' 169

""

A. Rosenthal and J. Chow, J . Carbohydr., Nucleosides, Nucleotides, 1980, 7 , 77. S. Ito, I. Saito, A. Nakata, and T. Matsuura, Photochem. Photobiol., 1980, 32, 683. 1. Saito, H. Sugiyama, S. Ito, N. Furukawa, and T. Matsuura, J . Am. Chem. SOC.,1981, 103, 1598. F. D. Lewis, T.4. Ho, and J. T. Simpson, J. Org. Chem., 1981,46, 1077.

Photochemistry

452

HNjy .Me

A

H N y M e

0

N I

NHR2

R'

0

0

3

I

R'

82

OH

Scheme 17 H Me @M ;e

___, MeOH ,

&e

H

\

\

(221). 1 7 1 Methanol addition products have also been obtained and are believed to arise by stereospecific methanol-induced ring opening of intermediate cisspiro[2.S]octa-4,6-dien-8-imines.An unusually selective addition takes place on irradiation of 3-methyl-lumiflavin (222) with N-buta-2,3-dienyl-N-benzylmethylamines (223) to give the flavocyanines (224);' 7 2 attack at both C(4a) and N(5) in the isoalloxazine ring is normally observed in the photoreactions of unsaturated amines with flavins. N-Acylated 5,lO-dihydrophenazines are obtained on irradiation of phenazine in acetaldehyde or propionaldehyde,' 73 and direct alkylamination of 1-benzamidoanthraquinone 74 and various transformations initiated by photoinduced hydrogen abstraction from amines 7 7 have been described.

'

17' 172

173 174

17' '71 17'

B. Scholl and H.-J. Hansen, Helv. Chem. Acfa, 1980, 63, 1823. A. Krantz, B. Kokel, A. Claesson, and C. Sahlberg, J . Org. Chem., 1980, 45, 4245. M. Takagi, S. Goto, and T. Matsuda, Bull. Chem. SOC.Jpn., 1980, 53, 1777. K. Yoshida, T. Okugawa, and Y. Yamashita, Chem. Letl., 1981, 335. A. Gilbert and S. Krestonosich, J . Chem. SOC.,Perkin Trans. I, 1980, 2531. K. N. Mehrotra and G . P. Pandey, Bull. Chem. SOC.Jpn., 1980, 53, 1081. T. Tokumitsu and T. Hayashi, Bull. Chem. SOC.Jpn., 1980, 53, 1183.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

Me I

453

-

The principal product from irradiation of quinoline-Zcarbonitrilein propan-2ol-aqueous HCl is the radical-derived dimer (225).17*The factors influencing the photoaddition of N-haloamides to alkenes have been examined,'79 and full details of the photoaddition of 3-chlorotetrafluoropyridine to ethylene to give 3-(2ch1oroethyl)tetrafluoropyridine have been reported. 8o Irradiation of thiazyl fluoride (226) in hexafluoropropene (227) affords the sulphenylaziridines (228) and (229). *

F NSF

17* 179 16'

+

CF,-CF=CF,

hv

__+

F3c$N-SNSF, F

T. Caronna, S. Morrocchi, and B. M. Vittimberga, J. Org. Chem., 1981, 46, 34. J. Lessard, M. Mondon, and D. Touchard, Can. J . Chem., 1981, 59, 431. M. G. Barlow, R. N. Haszeldine, and J. R. Langridge, J . Chem. SOC.,Perkin Trans. I , 1980, 2520. W. Bludssus and R. Mews, Chem. Ber., 1981, 114, 1539.

Photochemistry Miscellaneous Reactions.-Little interest has been shown this year in the photochemistry of alkyl nitrites. Irradiation of the acetylenic nitrite (230) led to the formation in poor yield of y-butyrokctone (23l).' 82 A mechanism involving cyclization of the alkoxy-radical, followed by formation of the spiro-intermediate (232), is shown in Scheme 18. The intramolecular addition of thiiyl radical to

454

hv

R-CEC-(CH,)3-O-N0

R-C~C-(CH2)3-O*

+

NO

1

(230)

n

ON R

R

I scbeme 18

alkynes is known to be much more efficient. Several ll/?-hydroxy steroids have been specifically labelled with deuterium on the angular C(13) methyl group by photolysis of the 11b-nitrite ester, followed by reaction of the resulting C(18) radical with PhSD.lB3Nitrite photolysis has also been employed in the synthesis of 17,18-cyclo-steroids.184 Oxidative photoaddition of N-nitroso- or N-nitrodimethylamine to trans,trans,trans-cyclododeca1,5,9-triene in acidified methanol affords a mixture of cis- and trans-1-nitrato-2-dimethylamino-trans,transcyclodeca-5,9-diene (233). 8 5

(233)

A study of the primary photoprocesses in gaseous 1-nitropropane has been undertaken.ls6 The major product, ethylene, is believed to arise via a pathway analogous to that responsible for the Norrish Type I1 reaction. At higher temperatures, carbon-nitrogen bond homolysis is also observed. A curious series of transformations has been reported for 2-nitrodibenzo[b7e][ 1,4]dioxin (234) on

"* lS3 lS4

'W

C. Dupuy and J. M. Surzur, Bull. SOC.Chim. Fr., 1980, 314. M. J. Green, H. Shue, P. Bartner, J. B. Morton, R. E. Youngstrom, and J. Meinwaid, J. Ldelled Comp. Radiopharm., 1980, 17, 91 1 . P. Bogan and R. E. Gall, A w t . J . Chem., 1979, 32, 2323. Y. L. Chow, H. Richard, and Y. Sakano, Synthesis, 1980, 818. K. A. Khan, Radiat. E f l , 1980, 46, 221.

Photoreactiom of Compounds containing Heteroatoms other than Oxygen

455

R

OH

NHR

OH

NHR

irradiation in the presence of primary amines leading to the phenoxazine (235)and the two isomeric diphenyl ethers (236) and (237).'*' The reaction proceeds by way of a triplet state and an exciplex which, provided the medium is sufficiently polar, dissociates to solvated radical ions. The synthesis of amino- and alkoxy-indazoles has been effected by nucleophilicaromatic photosubstitution in the corresponding nitroindazoles,'88 and the photodecomposition of 5-nitrofuran antibacterials has been the subject of two separate communi~ations.'~~~ The photoinduced substitution of 14soquinolinecarbonitrile (238) by ethanol to give 1-(1-hydroxyethy1)isoquinoline (239) has been found to be subject to a magnetic field effect.191This suggests that the reaction proceeds predominantly via a triplet radical pair, followed by hydrogen abstraction from the solvent as shown

/N CN

MeCH,OH

W \

N H CN

+

MecHOH

I

(238)

W

N

+ -HCN ---

W

A Me

N NC. CHMe I OH

HO

(239)

Scheme 19

in Scheme 19. In contrast, 4'-(5,6-dicyanopyrazin-2-yl)benzo- 15-crown-5 is converted on irradiation in acetonitrile in the presence of triethylamine into the monodecyano- and the bisdecyano-derivatives.192 The reaction is facilitated by sodium ions, an observation which supports an electron-transfer mechanism. la'

190 192

M. Alessandra, G. F. Bettinetti, G. Minoli, and A. Albini, J. Org. Chem., 1980, 45, 2331. P. Bouchet, R. Lazaro, M.Benchidmi, and J. Elquero, Tetrahedron, 1980, 36, 3523. A. B. Narbutt-Mering and W. Weglowska, Acta Pol. Pharm., 1980,37, 301. M. Shahjahan and R. P. Enever, J. Banglaksh A c d . Sci., 1979,3, 65. W. Hata and Y. Yamada, Chem. LAW., 1980,989. M. Tada, H. Hamazaki, and H. Hirano, Chem. LRtt., 1980, 921.

Photochemistry

456 Ph

Ph

Ph

Ph H

Ph

Carbon-nitrogen bond homolysis is preferred. to intramolecular hydrogen abstraction in the tertiary 0-benzoylbenzamides (240); these are converted on irradiation into phenylphthalide (241) and bisphthalide (242).193The first synthesis of thermally unstable aziridine-2,Zdiones (243) has been accomplished by irradiation at low temperature of the ozonides (244)of diphenylmaleylimides;194 at room temperature, the reaction products are benzoic anhydride (245), methyl 0

O T f O

QCR Ph

0

0

PhKoAph

4-

4 $-“ 0

(24)

(243)

isocyanate (246), and carbon monoxide, and the intermediacy of the biradical (247) has been proposed. Irradiation of the hydrazones of benzophenone, 4methylbenzophenone, and 4methoxybenzophenone in carbon tetrachloride in the presence of oxygen gave the corresponding azines via initial nitrogen-nitrogen bond h o r n o l y ~ i s ,and ~ ~ ~the products of photodecomposition of ~-nor-Saandrostan-16-one acetylhydrazone also in the presence of oxygen have been described. 4,5-Diaryl-4-oxazolin-2-ones surprisingly appear to undergo photoinduced cleavage only in the presence of oxygen.”’ The conversion of the azocompound (248)into photoproducts (249)and (250)in benzene has been explained in terms of a pathway involving addition of water and oxidation, but the details remain uncertain.I9’ 193 19* 195 196

19’ 198

J. C. Gramain and M. F. Lhomme, Bull. SOC.Chim. Fr., 1981, 141. H. Aoyama, M. Sakamoto, and Y. Omote, J . Am. Chem. Soc., 1980, 102, 6902. H . Suginome and T. Uchida, Bull. Chem. SOC.Jpn., 1980, 53, 3225. H. Suginome, T. Uchida, K. Kizuka, and T. Masamune, Bull. Chem. SOC.Jpn., 1980, 53, 2285. F. S. Guziec and E. T. Tewes, J . HererocyJ. Chem., 1980, 17, 1807. A. Mitra, S. M. S. Chauhan, and M. V. George, J . Org. Chem., 1980,45, 3182.

Photoreactions of Cornpoundr containing Heteroatoms other than Oxygen

+

hv ____, benzene

Ph

457

(249)

(248)

Other transformations worthy of note are those concerned with the photodegradation of barbiturates, 2oo are photohydrolysis of pyridostigmine bromide,20’ and the intermediate formation of aminyl radicals in the photoreactions of 2,2,4-trimethyl- 1,2,3+tetrahydroquinolines. 202 ‘’’9

2 Sulphur-containing Compounds

Z-1‘,2’-Dithiol-3’:4-ylidene-2-cyanobut-2-ene nitriles (251) undergo photoisomerization to the less stable E-isomers on irradiation in ethanol.203 Matrixisolated monothioacetylacetone has been shown to exist in two photochemically interconvertible forms, namely chelated (2)-4-mercaptopent-3-en-2-one (252)and its less stable s-trans-conformer (253).204

Me

__

Me

H-

Me

The 1,3-thiazine (254) undergoes a novel photorearrangement on irradiation in toluene, dioxan, or methanol to give the cyclopropathiazolidine (255).205This transformation can most simply be rationalized in terms of an initial carbon-sulphur bond homolysis as shown in Scheme 20; the reaction can alternatively be viewed as a heterocyclic analogue of the di-7r-methane rearrangement. The thiazine (256)undergoes a photoreaction, which is typical of pyrimid-4ones, to afford the azetidinone (257), presumably via 47r electrocyclization to the azetine (258).206 The stereospecific photocyclization of the a-bisulphenylated ketone (259) to the ci~-dihydrobenzo[6]thiophen (260) in acetonitrile solution has been r e p ~ r t e d . ~cis-Dihydrothiophens ” obtained in this way are easily dehydrated to the corresponding benzo[6]thiophens. The most persuasive mechanism is one involving conrotatory photocyclization of the enol (261)as shown in Scheme 21. 199 200

201 202

203 204 205

206 207

H. Barton, J. Mokrosz, J. Bojarski, and M. Kfimczak, Pharmazie, 1980, 35, 155. J. Mokrosz, M. Klimczak, H. Barton, and J. Bojarski, Pharmazie, 1980, 35, 205. C. Patel, J. B. Stanford, and J. K. Sugdcn, Phann. Acra Helv., 1980, 55, 138. P. P. Levin, I. V. Khudyakov, V. A. Kuz’min, and Y. A. Ivanov, Izv. Akad. Nauk SSSR, Ser. Khim., 1980,421. C . T. Pedersen, C. Lohse, Y. Mollitr, and .I.-M. Catcl, Acta Chem. Scand., Ser. B, 1980, 34,493. J. Gebicki and A. Krantz, J. Chem. SOP., Chem. Commun., 1981,486. P. B. Hitchcock, R. W. McCabe, D. W. Young, and G . M. Davies, J . Chem. SOC.,Chem. Commun., 1981, 608. T. Kato, N. Katagiri, U. Izumi, Y. Miurd, T. Yamazaki, and Y. Hirai, Heterocycles, 1981, 15, 399. T. Sasaki, K. Hayakawa, and S. Nishida, Tetrahedron Lptt., 1980, 21, 3903.

Photochemistry

458 0

0

0

hv

%>Me

oT&H+

COZEt

Me COzEt

1

(254)

t--

Me CO,Et (255) Scheme 20

hv ___, MeOH

Me

cqoMeOH

N-

Me

Several novel photocycloaddition processes together with further examples of known additions have been reported in sulphur-containing systems. [,2 + .2]Dimerization is the principal photoreaction observed in 2- and 3arylbenzo[b]thi~phens,~~~ and a mixture of all four [=2 + .2] photodimers was

1

hv MeCN

scheme 21

obtained on irradiation of thiochromone in aromatic solvents.209Photoaddition of 2-phenylbenzothiazole(262) to alkenes is reported to give 1,Sbenzothiazepines in a regiospecificand stereospecificmanner.'l* Irradiation in ethyl vinyl ether, for example, gave 3-ethoxy-4-phenyl-2,3-dihydro1,5-bemothiazepine (263). Two 208 '09

'lo

A. Buquet, A. Couture, A. Lablache-Combier,and A. Pollet, Tetrahedron, 1981, 37,75. I. W. J. Still and T. S. Leong, Tetrahedron Lett., 1981,22, 1183. M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Lea., 1981, 22, 2081.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

459

+

mechanisms are in theory possible, one involving [z2 z2] cycloaddition to the carbon-nitrogen double bond followed by thermal ring opening of the resulting azetidine, and a second involving carbon-sulphur bond homolysis and subsequent radical addition to the alkene. The second pathway has also been proposed to account for the photoaddition of 3-phenyi- 1,2-benzisothiazole (264) to ethyl vinyl

ether to give 3-ethoxy-5-phenyl-2,3-dihydro1,4-benzothiazepine (265) in high yield.2 1,2-Benzisothiazole (266) itself undergoes photoaddition to dimethylacetylenedicarboxylate, leading to the formation of the isomeric phenylthioalkenes (267) and 7-cyano-2,3-dicarboxybenzo[b]thiophen(268).2' The proposed pathway is outlined in Scheme 22. This behaviour is different from that previously hv

MeO,CCdCO,Me

K' s-c

,,C-CO,

Me

I C0,Me

CN (268)

Scheme 22

observed in benzo[b]thiophen and indole. Product formation in the addition of benzo[b]thiophen to dimethylacetylenedicarboxylate has recently been shown to be wavelength-dependent.213This is a direct result of the existence of a photoequilibrium between the two cycloadducts (269) and (270) and of their differing ultraviolet absorptions. The allylic biradical (271) is assumed to be an intermediate in this interconversion. Further examples of [x2 ,2] photoaddition of thiones to alkenes to afford thietans have been reported. Irradiation of thioxanthenethione (272) and the pentatetraene (273) in dichloromethane, for example, is accompanied by the

+

211 212 213

M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Lett., 1981, 22, 529. M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Lert., 1981, 22, 525. S. R. Ditto, P. D. Davis, and D. C. Neckers, Tetrahedron Leu., 1981, 22, 521.

Photochemistry

460 C0,Me

$ZO,Me hY

m

C

0

,

M

e

(249)

C02Me CO,Me

formation of the isomeric thietans (274)--(276).214 The known photoaddition of indoline-2-thiones to methyl acrylate has been employed in a new synthesis of desethylcatharanthine. 2 1 A 1:2-adduct (277) is formed on irradiation of 1,3-dimethy1-2-thioparabanic acid (278) in the presence of dimethylacetylenedicarboxylate. With diphenylacetylene, however, the spirothiet 1:1-adduct (279) can be isolated and is formed along with the 1,2-dithiole (280). The probable mechanism for these transformations is briefly outlined in Scheme 23. It has previously been shown that aralkyl thiones, on n + n* excitation, undergo intramolecular hydrogen abstraction from the b-carbon atom yielding cyclopentane thiols. In the oxygen-containing aralkyl thione (28 l), where such a pathway is impossible, S , excitation leads to the formation of the alternative thiols (282) and (283). &-Hydrogenabstraction has been shown to occur only from the l(n,n*) state, whereas y-hydrogen abstraction occurs from both '(71, n*) and 3(n,n*) states. The first example of Type I a-cleavage in thiones has now been reported. Irradiation of the dithiolactone (284), for example, in cyclohexane or benzene gave tetramethylcyclobutane-1,3-dithione(285) and in methanol the ether (28Q218The proposed pathway is shown in Scheme 24. Irradiation of N-acyl derivatives (287) of 2-thionothiazolidine in the presence of

'

'I4

'I6 217

'I8

R. G . Visser, E. A. Oostveen, and H. J. T. Boz, Tetrahedron Lett., 1981, 22, 1139. C. Marazano, J.-L. Fourrey, and B. C. Das, J . Chem. SOC., Chem. Commun., 1981, 37. H. Gotthardt, S. Nieberl, and J. Donecke, Liebigs Ann. Chem., 1980, 873. S . Basu, A. Couture, K. W. Ho, M. Hoshino, P. de Mayo, and R. Suau, Can. J . Chem., 1981,59,246. V. Muthuramu and V. Ramamurthy, J . Org. Chem., 1980, 45, 4532.

Photoreactions of Compounh containing Heteroatoms other than Oxygen Me

46 1

Me CO,Me

4

0 Me CO,Me hv

C0,Me

TDMA

(277)

Me 0

scheme 23

Me Me

ethanol affords the corresponding ethyl esters (288).219A mechanism involving yhydrogen abstraction has been proposed and is outlined in Scheme 25. It appears, therefore, that these N-acyl-2-thionothiazolidinescan serve as latent activators of the carboxyl group.

L. P. J. Burton and J. D. White, Tetrahedron Lett.,

1980, 21, 3147.

Photochemistry

462

Direct excitation (A > 240 nm) of thiiran is followed by intersystem crossing to the lowest excited state. This species is capable of undergoing reversible addition to alkenes, thereby inducing Z,E-isomerization;220inefficient irreversible addition ,has been proposed as has also been observed. The carbonyl sulphide, Ph2&S a possible intermediate in the photodecomposition of diphenyloxathiiran, which is itself formed by irradiation of thiobenzophenone S-oxide at 77 K.22' An unexpected photoinduced fragmentation and solvent incorporation was observed on irradiation of N-(6,7-dimethoxy-2-methyl-3-quinazolinio)ethoxythioformamidate (289) in ethanol to give photoproducts (290)--(292). 2 2 2 The photoreactions of some N-isoquinolinio(thioamidates)have been compared with those M

e

Me0

O

~

~

--

' NA

Me

(289)

Ns\ I

OEt

C

~

R

& MeO

H,N-C-OEt

(290) R = AC (291) R = MeCHOH

II

s (292)

of the corresponding a r n i d a t e ~ .6-Alkylthio~~~ and 6-phenylthio-5H-benzo[a]phenoxazin-5-ones (293) have been synthesized by the photoreaction of 5Hbenzo[a]phenoxazin-5-one (294) with the appropriate alkylthiols and thioThe mechanism for this conversion is at present unknown. Finally in this Section, irradiation of pent-4-yne-1-thiol (295) has been reported to lead, via

''O

E. M. Lown, K. S. Sidhu, A. Jodhan, M. Green, and 0. P. Strausz, J . Phys. Chem., 1981,85, 1089. 1257. M. Lempert-Sreter, K. Lempert, and J. Moeller, Chem. Scr., 1979, 13, 195. M. Lempert-Sreter, K. Lempert, J. Tamas, and K. Vekey, Actu Chim. Acad. Sci. Hung., 1980, 103, 259. Y. Ueno, Y.Takeuchi, J. Koshitani, and T. Yoshida, J. Heterocycl. Chem., 1981, 18, 259.

'" L. Carlsen, J. P. Snyder, A. Holm, and E. Pedersen, Tetrahedron, 1981,37, 222

223 224

Photoreactions of Compounh containing Heteroatoms other than Oxygen

463 intramolecular addition of a thiiyl radical, to thiacyclohex-Zene (296), 2methylenethiacyclopentane (297), and 2-methylthiacyclopent-2-ene(298).2 2 5

3 Compounds Containing Other Heteroatoms Once again, the emphasis in this section is placed on the photoreactions of organosilicon compounds. A review of the photochemistry of organopolysilanes, with particular attention being paid to the formation of silicon-containingreactive intermediates, has been published.226Six primary processes have been proposed to explain the formation of hydrogen, methane, ethane, dimethylsilane, methyldisilane, dimethyldisilane, and polymer on irradiation (A = 147nm) of methylsilane.2 2 Two primary processes, involving respectively carbon-silicon bond homolysis and elimination of methane, have been observed on photolysis of tetramethylsilane in the gas and liquid phases.228 Pentasilanes undergo disproportionation on irradiation in 2,3dimethylbutane at room temperature, npentasilane for example being converted into 3-silylhexasilane and 4-silylhepta~ i l a n e . ~Alternatively, ~’ on irradiation in acetone, tri-, n-tetra-, i-tetra-, and npenta-silane are converted into mono- and poly-isopropoxysilanes.230 The photoinduced generation and reactions of dimethylsilylene, Me2Si, continue to attract attention. The insertion of dimethylsilylene, prepared by irradiation of dodecamethylcyclohexasilane, into the oxygen-hydrogen bond of alcohols to yield alkoxydimethylsilanes has been used to probe the effect of solvent on dimethylsilylenereactivity.23 Dimethylsilylene is more selectivein diethyl ether or tetrahydrofuran than in hydrocarbon solvents and this has been attributed to the formation of complexes between dimethylsilylene and donor solvents. Kinetic studies of the insertion reactions of dimethylsilylene have been undertaken.232* 233 Previous investigations have resulted in the isolation of dimethylsilylene in an argon matrix at 10 K. Further irradiation of dimethylsilylene (299) under the same conditions gave 2-silapropene (300), which in turn is converted into the dimer (301) at 50 K.234

-

Me

Me,Si: (299)

hv, 1 = 450nm Ar, 10K

\

Si=CH,

/

H

(300)

Ar, 50K

H

Me \SiASi’

H

/ v \Me (301)

Methylphenylsilylene (302), generated photochemically from 2-phenylheptamethyftrisilane (303), undergoes addition and insertion to 2,3-dimethylbutadiene to give the alkene (304) and the diene (305), re~pectively,~~’ whereas dimesityl225 226 227

229

230 231

232 233 234

”’

C. Dupuy, M. P. Crozet, and J. M. Surzur, Bull. SOC.Chim. Fr., 1980, 361. M. Kumada, Kem. Kozl., 1979, 52, 341. P. A. Pongeway and F. W. Lampe, J. Phorochem., 1981, 14, 31 1. E. Bastian, P.Potzinger, A. Ritter, H. P. Schumann, C. Von Sonntag, and G. Weddle, Ber. Bunsenges Phys. Chem., 1980,84, 56. F. Feher and I. Fischer, Z. Anorg. Allg. Chem.,1980,466, 23. F. Feher, I. Fischer, and D. Skrodzki, Z. Anorg. Allg. Chem., 1980,466, 29. K. P. Steele and W. P. Weber, J . Am. Chem., Soc., 1980, 102, 6095. 1. M. T. Davidson, F. T. Lawrence, and N. A. Ostah, J . Chem. SOC.,Chem. Commurt., 1980, 859. I. M. T. Davidson and N. A. Ostah, J. Organornet. Chem., 1981, 206, 149. T. J. Drahnak, J. Michl, and R. West, J. Am. Chem. SOC.,1981, 103, 1845. M. Ishikawa, K.Nakagawa, R. Enokida, and M. Kumada, J. Organornet. Chem., 1980,201, 151.

Photochemistry

464 Me\

Me3SiSiMe(Ph)SiMe3 (303)

Si:

+

Me3SiSiMe3

Ph! (302)

Me Me

M+ Si

r

Me -Si-

/ \

Me

Me

I

H

Ph

(304)

(305)

silylene, generated by photolysis of 2,2-dimesitylhexamethyltrisilane, reacts with epoxides to give the adducts (306);236a pathway is suggested in Scheme 26.

R'

= mesityl

I

R' R' \ /

Si

,Si=O

R'

+

R2CH=CH2

R2 (306) Scheme 26

Compounds containing C=Si bonds have again been prepared photochemically. Species of this type have been proposed as intermediates (307) in the phototransformation of some di- and tri-substituted silacyclobutanes (308) in

R2 I R'-Si-OMe I

Me (309) 236

W. Ando, M. Ikeno, and Y. Hamada, J . Chem. SOC.,Chem. Commun., 1981, 621

465 methanol to the ethers (309).237The major products of the photolysis of 1,ldimethylsilacyclobutanein the gas phase are ethylene and 1,1,3,3-tetramethyl-l,3disilacyclobutane, the latter arising presumably by dimerization of Me2Si==CH2.238Preliminary results suggest that intermediates with .n-bond character are formed on irradiation of octamethyl-l,2-disilacyclobutane.239 Irradiation of 1-(trimethylsilylethynyl)-1,l-diphenyl-2,2,2-trimethyldisilane (310) in the absence of trapping agents led to the formation of the 1,2disilacyclobutane (31 1) via the reactive intermediate (312).240 The unstable silacyclopropene(3 13) was also obtained by an alternative rearrangement, and, in Photoreactions of Compoundr containing Heteroatoms other than Oxygen

-

Ph I Me,SiC=CSiSiMe, I Ph

Me,Si

Me, SiwSi \

hv

C=C=SiPh2

/

+

Si

MeJSi

/ \

Ph Ph

(3 12)

(3 10)

Me3

/

(3 13)

Ph-Si-S,i -Ph I

I

Ph Ph

/ \

Ph

Ph

(31 1)

fact, in a separate investigation two stable silacyclopropenes have been similarly prepared.24’ Further irradiation of 1,Zdisilacyclobutane (3 11) gave the isomer (314)by way of a 1,3-shift of the disilanyl group. The 1,3-sigmatropic shifts of disilanyl and silyl groups, observed in recently reported experiments, have been explained in terms of F ~ k u i - t h e o r y . ~ ~ ~ Irradiation of tris(trimethylsily1)phenylsilane in the presence of hex- 1-yne and other alkynes affords the corresponding silacyclopropenes.243Those silacyclopropenes formed from monosubstituted acetylenes undergo further photoisomerization to disilanylacetylenes via a 1,Zhydrogen shift. Two competing pathways have been observed on irradiation of the disilabicyclo[2.2.2]octa-2,5-diene (315) in n-hexane, the first leading via a novel 1,241~1migration to the cyclopropane (316) and the second providing clear evidence for the formation of tetramethyldisilene (3 17);244 this highly reactive species has been effectively trapped as the [,4 + %2]adduct of cyclopentadiene. Analogous 1,Zsilyl migrations in other 1,4-silylated dihydronaphthalenes have been reported.245 z37

238 239 240 241 242

z43 244

245

P. Jutzi and P. Langer, J. Organomet. Chem., 1980,202,401. H. C. Low and P. John, J . Organomet. Chem., 1980, 201, 363. I. M. T. Davidson, N. A. Ostah, D. Seyferth,,and D. P. Duncan, J . Organomet. Chem., 1980,187, 297. M. Ishikawa, D. Kovar, T. Fuchikami, K. Nishimura, M. Kumada, T. Higuchi, and S. Miyamoto, J. Am. Chem. SOC.,1981, 103, 2324. M. Ishikawa, K. Nishimura, H. Sugisawa, and M. Kumada, J. Organomet. Chem., 1980, 194, 147. L. Fabry and P. Csaszar, J . Organomet. Chem., 1980, 195, 155. M. Ishikawa, K. Nakagawa, and M. Kumada, J . Organomet., 1980, 190, 117. Y. Nakadaira, T. Otsuka, and H. Sakurai, Tetrahedron Lett., 1981, 22, 2417. Y. Nakadaira, T. Otsuka, and H. Sakurai, Tetrahedron Lett., 1981, 22, 2421.

466

Photochemistry

i"l'" Me2 Si

%Me2

hv ___,

(31 5 )

"'I [Me$ =SiMe2] t (3 17)

Attack by triplet-excited carbonyl compounds on the benzosilacyclobutenes (318) leads to the formation of the benzoxasilacyclohexenes (319) and (320) as shown in Scheme 27.246The photoreactions of acylsilanes have been the subject

RZ

(319)

m 7 i R ' + R3 )=O R1 (318) R'

=

Me or Ph

Scheme 27

of detailed investigations. The formation of the acetal (321) on irradiation of acetyltrimethylsilane (322) in propan-2-01 results from rearrangement to the siloxycarbene (323) by way of the TI The photoaddition of acylsilanes to electron-deficient alkenes does not, however, appear to involve s i l o ~ y c a r b e n e s . ~ ~ ~ 0 hr. I1 -+ Me-C-OOSiMe, Me -C-Si Me3

Me CHOH

OCHMe,

I I

M=-C-OSiMe

(323)

The [1[.2+ ,2] photocycloaddition of I ,4-naphthoquinone to allyltrimethylsilane has been described,249 and irradiation of 1,2-bis[trirnethylsilyloxy]246 247

248 249

R. Okazaki, K.-T. Kang, and N. Inamoto, Tetrahedron Lett., 1981, 22, 235. R . A. Bourque. P. D. Davis, and J. C. Dalton, J . Am. Chem. Soc., 1981, 103, 697. J. C. Dalton and R. A. Bourque, J . Am. Chem. Soc., 1981, 103, 699. M. Ochiai, M. Arimoto, and E. Fujita, J . Cham. Soc.. Chem. Commun.. 1981, 460.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

467

cyclobutene (324) in the presence of (-)-piperitone (325) affords the adduct (326).250 (a-Alk- 1-enylsilanes can be readily prepared by photoinduced isomerization of the corresponding ( Z ) - i s o m e r ~ ,and ~ ~ ~cationic as well as freeradical organosilicon intermediates appear to be implicated in the photoreactions of i o d ~ s i l a n e s . ~ ~ ~

aosi OSiMe3 Me

(324)

+

hP

.-pri 0

(325)

. ,

(327)

0

(329)

Pr’

(330)

The photochemistry of organo-selenium and -tellurium compounds has been reviewed.2 5 3 Benzophenone-sensitized addition of 2,3-dimethylmaleic anhydride (327) to selenophen (328) affords the 1:l-adduct (329) and the 2:l-adduct (330).254 Benzo- and pyrido-selenothiopyrans (331) have been prepared, as shown in

(331) X = CH, Y = CMe X=N,Y=CH X=CH,Y=N

Scheme 28

Scheme 28, by application of the known thiol ester-thiopyrone phototransformation to selenium-containing 5H-[ l]Benzoselenino[2,3-b]and 9H-seleno[3,2-b][l]benzo~ y r i d i n e ,4H-selenolo[2,3-b][l]benzoselenine, ~~~ selenine 5 7 have similarly been obtained by the corresponding selenol ester-seleninone conversion. Phenyl areneselenosulphonates undergo facile photoinduced homolysis of the selenium-sulphur bond; in the presence of alkenes, a free-radical chain reaction leads to the formation o f fl-phenylselenosulphones.2 5 * J. R. Williams and T. J. Caggiano, Synthesis, 1980, 1024. 2s1

Zweifel and H. P. On, Synthesis, 1980, 803. ’” GC .. Faborn, K. D. Safa, A. Ritter, and W. Binder, J. Chem. SOC.,Chem. Commun., 1981, 175.

2s3 2s4 2ss

’” ’” 2s7

J. Martens and K. Praefcke, J . Organomet. Chem., 1980, 198, 321. C. Rivas, D. Pacheo, and F. Vargas, J. Heterocycl. Chem., 1980, 17, 1151. K. Beelitz, K. Praefcke, and S. Gronowitz, Liebigs Ann. Chem., 1980, 1597. K. Praefcke and U. Schulze, J. Organomet. Chem., 1980, 184, 189. K. Reelitz, K. Praefcke, and S. Gronowitz, J. Organomer. Chem., 1980, 194, 167. R. A. Gancaa and J. L. Kice, Tetrahedron k t t . , 1980,21.4155.

Photochemistry

468

The photoreduction of carbon4arbon and carbon-nitrogen double bonds has been effected by irradiation with added ben~eneselenol.~ 59

u

Ph

Ph

4\

hv, quartz

benzene

0 Ph

0 Ph

(333)

(332)

The dibenzophosphonin (332) has been synthesized by the oxidative photocyclization of 1,3,4-triphenyl-3-phospholeneoxide (333).260 Photofragmentation is observed, however, on irradiation in methanol of 3,4-dimethyl-3-phospholene sulphide (334) to give the diene (335) and 0-methyl phenylphosphinothioate (336) Me Me

1

(334)

S II Ph- 7-OMe

S hv

e-MeOH

OMe

II

Ph-7-H OMe

(337)

(336)

Scheme 29

as shown in Scheme 29.261 Further irradiation of (336) gave CO-dimethyl phenylphosphonothioate (337) Irradiation of di-isobutyl, dipropyl, and diethyl (trichloromethy1)phosphonates(338) in acetonitrile resulted in Type I1 elimination H

R2

CI3C/=;O’ OR (338)

(339)

and the formation of the monoesters (339) and the alkenes (340).262 In the case of di-isobutyl (trichloromethyl)phosphonate, products arising by Type I elimination were also obtained. The ratio of methyl group migration to methyl group loss in the photocyclization of anilinodimesitylborane has been shown to be dependent upon the concentration of iodine present.263 259 260

261 262

263

M. J. Perkins, B. V. Smith, and E. S. Turner, J . Chem. SOC.,Chem. Commun., 1980, 977. E. D. Middlemas and L. D. Quin, J. Am. Chem. SOC.,1980, 102, 4838. H. Tomioka, S. Takata, Y. Kato, and Y. Izawa, J . Chem. SOC.,Perkin Trans. 2, 1980, 1017. N. Suzuki, T. Kawai, S. Inoue, N. Sano, and Y. Izawa, Bull. Chem. SOC.Jpn., 1980,53, 1421. M. E. Glogowski and J. L. R. Williams, J . Organomet. Chem., 1980, 195, 123.

7 Photoelimination BY S. T. REID

1 Introduction This Chapter is principally concerned with the photochemically induced fragmentation of organic compounds accompanied by the formation of small molecules such as nitrogen, carbon dioxide, and sulphur dioxide. Photodecompositions resulting in the formation of two or more sizable fragments are reviewed in the final Section. Fragmentations arising by Norrish Type I and Type I1 reactions of carbonyl-containing compounds are considered in Part 111, Chapter 1. The photoextrusion of small molecules has been reviewed in detail elsewhere.'

2 Elimination of Nitrogen from Am-compounds The mechansim of the thermal and photochemical decomposition of azo-alkanes has been the subject of a comprehensive review,2 and the synthesis of unusual organic molecules by photoelimination of nitrogen from azoalkanes has been surveyed. The photodecomposition of azoalkanes provides a convenient route to alkyl radicals. A detailed mechanism has been proposed to account for the formation of methane, ethane, and nitrogen on irradiation of azomethane in p r ~ p a n e .In~ contrast, the major products of irradiation of azobenzene in cyclohexane are N cyclohexylaniline, phenylazocyclohexane, and 1-phenyl-2-cyclohexylhydrazine; pathways involving carbon-nitrogen homolysis and hydrogen abstraction are thought to be involved. Examples of the photoelimination of nitrogen from tetrazenes have also been reported. 1,4-Diaryl-1,4-dialky1-2-tetrazenesundergo photodecomposition via a radical pathway, the formation of hydrazines being the result of recombination of methylarylamino radicals.6 Evidence that photoelimination of nitrogen from 2-tetrazenes is a two-step process is to be found in the isolation of the triazole (1) from the tetrazene (2);' the aza-ally1 radical (3) is an intermediate in the formation of this and other products arising by loss of nitrogen. The formation of a trifluoromethyl radical-recombination product (4) on irradiation of the carbonium ion ( 5 ) has been taken as evidence for the existence of an intermediate cage-radical cation.*

' '

' '

R. S. Givens, Org. Photorhem.. 1981, 5, 221. P. S. Engel, Clieni. Rev., 1980, 80, 99. W. Adam and 0. De Lucchi. Angew. Client.. Int. Ed. Engl., 1980, 19, 162. P. C. Durban and R. M . Marshall, Int. J. Cheni. Kinet., 1980. 12. 1031. A. M. J. Ali and Z. Y.Al-Saigh, J. CIiem. Terhnol. Biotechnol.. 1980. 30,440. D.-H. Bae and H.J. Shine, J. Org. Cheni., 1980. 45, 4448. F. Lubbe, K.-P. Grosz. W. Hillebrand, and W. Sucrow. Tetrtilte(1ron Len.. 1981, 22, 221. P. Golitz and A. de Meijere, Angeir. Client., Inr. Ed. Engl.. 1981, 20. 298.

469

470

Photocliemistry

CH2Ph

CH2Ph

(2)

The photodecompositions of 3,3-bis(I , 1 -difluorohexyl)diazirine and 34 I , I difluoro-octyl)-3H-diazirine have been examined.' On irradiation in cyclohexane or methanol, competing photoisomerization to linear diazo-compounds and photofragmentation ticl carbene intermediates to cyclopropanes and alkenes has been observed and is illustrated for 3,3-bis( I , 1-difluorohexyl)diazirine (6) in Scheme 1. The majority of investigations of nitrogen photoelimination in cyclic N=N

x

C,H, , F , d CF,C,H,

,

(A = 410nm)

C,H, ,CF,-C-CF2CSH,

,

/

/ir(A=410nm)

Scheme I

azoalkanes have again, however, been concerned with pyrazolines. Examples of cyclopropane formation have been reported. 7-Methyl- and 7-aryltetracyclo[4.1.0.02-403. 'Iheptanes (7)have been prepared in this way by irradiation of 7,8-diazdtetrdcyc~o[4.3.0.~2-403-s]non-7-enes (8), l o and the syntheses of dicy-

"'

B. Erni and H. G. Khorana. J. AIII. C'liiwt. Sw.. 1980. 102. 3888. M . Christ1 and E. Brunn. Aitgiw. CItiwi.. hit. Ed. Engl.. 1981. 20. 468.

47 1

Photoelimination

R' R2

eM

f

(10)

topterene B (9) and dicytopterene D (10) have been accomplished by lowtemperature photolysis of the pyrazoline (1 I).' The first example of the synthesis of a propellane by this route has also been described. Thus, irradiation of the pyrazoline (12) in diethyl ether gave the tetracyclic photoproduct (13) and the alkene (14), the latter arising, as shown in Scheme 2, via the diazoalkene (1 9.''An

'

V (12)

independent examination has clearly established that two pathways are similarly involved in photoelimination of nitrogen from ( + )- and (-)-truns-3,5-diphenyl- Ipyrazoline, the first involving a biradical intermediate and the second proceeding by way of cycloreversion to phenyldiazomethane and styrene followed by carbene generation and subsequent addition to the alkene. 1 3 * l 4 Photoelimination of I' 'I

M. P. SEhneider and M . Goldbach. J . Am. Chctn. SK.. 1980, 102, 61 14. J. W. Wilt and R. Niinemae, J . Org. Clicni., 1980, 45. 5402. M. P. Schneider. H. Bippi. H. Rau. D. Ufermann. and M. Homann. J . Clietn. Soc., Clicni. Cotiitiiiin..

'4

M . P. Schneider and H. Bippi. J.

1980.957. Ant. Clwttt. Suc.. 1980, 102.

7363.

412

Photochemistry

nitrogen from the azoalkane (16) provides a convenient entry to the biradical(l7) proposed as an intermediate in the di-n-methane rearrangement of 7,7-dimethylenebenzonorbornadiene ( 1 8): direct irradiation (;I = 350 or 254 nm) does, in fact, afford the same photoproduct (19) as obtained in the rearrangement, whereas

a "\

N

benzophenone-sensitized irradiation yields the novel diaza-system (20). Variable amounts of bicyclo[4.2.2]decatetraene and bullvalene have been obtained on irradiation of azo-compounds (21) and (22); attempts to formulate a common mechanism of decomposition have been unsuccessful. The regioselectivity of cycloaddition of singlet 2-methylenecyclopenta- 1,3-diyl (23), generated by photoelimination of nitrogen from 7-methylene-2,3diazabicyclo[2.2.l]hept-2-ene (24), to alkenes has been explained in terms of

orbital symmetry. The major products obtained from addition to cyclopentadiene are the fused 1,2- and syn-bridged 1,4-cycloadducts and their formation is in agreement with these predictions." Irradiation of the diazene (25) in the presence I5 l6

W. Adam and 0. De Lucchi, Angcw. Chent., liit. Ed. Engl., 1981, 20, 400 R . Jose1 and G . Schroder, Chent. Ber., 1980, 113. 1428. R . K. Siemionko and J. A. Berson, J . Ant. Clten?.Soc.. 1980, 102, 3870.

Photoelimination

473

(26)

M

i

c

+A CN

N

(27)

(28)

of acrylonitrile affords the hydrocarbon (26) and the adducts (27) and (28).18 Evidence has been advanced supporting the formation of a discrete singlet biradical as an intermediate in this transformation. Short-wavelength irradiation (1, = 185nm) has proved to be effective in promoting photoelimination of nitrogen in 3,3,5,5-tetramethylpyrazolin-4-one (29),19 a compound which has previously been reported to undergo inefficient photodecomposition (4313nm = 0.012). The products of irradiation in n-pentane are the ketone (30), 2,3-dimethylbut-2-ene (31), and the azine (32): the proposed pathway is outlined in Scheme 3. Loss of nitrogen is favoured in polar solvents and 0

Me h - - N * Me

Me

Me

Me

Me

(32)

Me

XMe (31)

Scheme 3

at lower temperatures.20 The analogous thioketone (33) is converted exclusively on irradiation into the thiiran (34).

(33) 19

2o

(34)

M. R. Mazur and J. A. Berson, J . A m . Client. Soc., 1981, 103. 684. W. Adam. A. Fuss, F. P. Mazenod, and H. Quast. J . A m . Clic.ni. Sot,., 1981, 103, 998. H. Quast and A. Fuss, Angcw. CIicm., lnt. Ed. Engl., 1981. 20, 291.

Photochemistry

474

Six-membered azocycloalkanes, previously reported to be 'reluctant' to undergo photoelimination of nitrogen, have also been shown to lose nitrogen efficiently on irradiation at i = 18511m.~' Under these conditions, the azoalkane (35) is converted into isobutylene (36) and 1,1,2,2-tetramethylcyclobutane(37) with a quantum yield of 0.22, whereas on irradiation at 350nm, 4 = 0.0083. A 1,8naphthoquinodimethane biradical, generated in a similar fashion by photoelimination of nitrogen, has been characterized by electron paramagnetic resonance spectroscopy,22 and the biradical (38) is claimed to be an intermediate in the conversion of the indazole (39) into the hydroxyaceanthrylene (40).23 0

0 hY

d

-N*

(39)

OH

Photoelimination of nitrogen from triazolines can similarly be employed in the synthesis of aziridines. Thus, the triazolines (41) have been converted in this way

(41) z1 22

23

R

=

Ph, C,H,,, Bu', or H

(42)

W. Adam and F. Mazenod, J . Am. Chem. SOC.,1980. 102. 7131. W. P. Chisholm, S. I. Weissman, M. N. Burnett, and R. M. Pagni, J. Am. Cliem. SOC.,1980,102,7103. K. Hirakawa, T. Toki, K. Yamazdki, and S. Nakazawa, J . Cliem. SOC..Perkin Trans. 1, 1980, 1944.

Pho toelimination

475

.0.02.5]hexanes (42) in n-pentane solution.24 A into the 2-thia-5-azatricyclo[3.1 more complex reaction sequence has been proposed to account for the formation of the pyrrole ester (43) from the triazoline (44)on irradiation in methanol; details are shown in Scheme 4.25 2H-Azirines have been prepared in high yield by photoelimination of nitrogen from 4 H - t r i a ~ o l e s . ~ ~

"d do

N

"'Et

"-Et

hv

\

Ph -N

Ph- N I C0,Me

//i$ ''Et

--+

\

Ph -N I C0,Me

I C0,Me

I

(44)

cNaEt C0,Me

Ph -N

I

C0,Me

0

MeOH

Ph-N

ZN-+t

I C0,Me

/i

(43) Scheme 4

The major product of irradiation of the N-aryltriazolo[4,5-b]pyridine(45) in ethanol is the pyrido[2,3-b]indole (46);27the imino-ether (47) is also formed, and

both products are regarded as arising via the intermediate biradical (48). The conversions of 3-phenyl-3H- 1,2,3-triazol0[4,5-d]pyrimidines into 9Hpyrimido[4,5-b]indoles and 1-(1-chloroisoquinolin-6-yl)-1H-triazolo[4,5-c]pyridines into lO-chlor0-5H-pyrido[3',4': 4,5]pyrrolo[2,3-g]isoquinolines2 9 are 24 25 26 27

28 29

Y.Kobayashi, A. Ando, K. Kawada, and I. Kumadaki, J . Org. Chew., 1980, 45, 2966. A. G. Schultz and C.-K. Sha, J . Org. Chem., 1980, 45, 2040. C. Bernard and L. Ghosez, J . Chem. SOC.,Chem. Commun., 1980, 940. C. Rivalle, C. Ducrocq, J.-M. Lhoste, F. Wendling, E. Bisagni, and J.-C. Chermann, Tetrahedron, 1981, 37, 2097. T. Higashino, E. Hayashi, H. Matsuda, and T. Katori, Heterocycles. 1981, 15,483. C. Rivdlle, C. Ducrocq, J.-M. Lhoste, and E. Bisagni, J. Org. Chem., 1980, 45, 2176.

476

Photochemistry

believed to proceed in a like manner. Biradicals formed on irradiation of 1cycloalkyloxy-5-chloro- 1,2,3-benzotriazoles (49) undergo fragmentation, as shown in Scheme 5, to give the azobenzene (50) and cycloalkanones (51),30 and an

1

(49) n = 4, 5 , or 6

Scheme 5

Ph

/

Ph

(54)

EtO )=N-NH-Ph Ph (55)

analogous transformation has been observed in 1 -benzyloxy- 1,2,3benzotriazole.3 ' 3C-Labelling studies have shown that the biradical, formed on photoelimination of nitrogen from 5-phenyl- I ,2,3-thiazole, is reversibly converted into 2-phenylthia~ole;~~ no such conversion has been observed in 4-phenyl- 1,2,3thiazole. "

''

W. A. Feld and M . P. Serve, J. Hi>reroc,ji!. Clicwr.. 1980, 17, 825. W . A . Feld. R . Paessum. and M . P. Serw. J . H c t i v w j d . Cliim.. 1980. 17. 1309. U . Iiniin. U . Merkle, and H. Meier. Clwrn. Bar.. 1980. 113. 2519.

477

Photoelimination

Photoelimination of nitrogen from 2,5-diphenyltetrazole (52) in an ether-pentane-ethanol glass at 77 K gave a product identified spectroscopically as diphenylnitrilimine (53).33 Dimerization of this species was observed on heating to 160-175K to give the alkene (54). Diphenylnitrilimine, generated in the same fashion, has also been trapped by ethanol as the adduct (55),34 and intramolecular addition of a nitrilimine to an alkene was observed on irradiation of the oallyloxyphenyltetrazole (56) as shown in Scheme 6. Ph I

+ -

C=N-N-Ph -

N2

0

I

I

Ph

Scheme 6

3 Elimination of Nitrogen from Diazo-compounds

The photoelimination of nitrogen from diazo-compounds provides a simple and versatile route for the generation of carbenes. The reactions of such carbenes are easily studied under various conditions. The relative amounts of carbene-derived products arising by 1,2-hydrogen migration, ( 5 7 ) and (58), and 1.2-phenyl migration, (59), on irradiation of 1,2-diphenyl-I-diazopropane (60), have been Ph

Me

+ -+Phxph

XPh N2

H

Me

(57)

(60)

(61)

Ph#Me H Ph

+

Ph

Me

Ph

H

+( (59)

(58)

(62)

found to vary with t e m p e r a t ~ r eIrradiation .~~ of the diazocycloalkene (61) affords the cyclohexadiene (62) and products arising by carbene addition to a l k e n e ~ . ~ ~ This decomposition, like those of other diazoalkanes, evidently involves the S , 33

34 3s 3h

H. Meier. W. Heinzelmann, and H. Heimgartner. Chiiwiu. 1980, 34. 504. H. Meier. W. Heinzelmann. and H. Heimpartner. Chhiu. 1980. 34, 506. H. Tomioka, H. Ueda, S. Kondo. and Y. Izawa, J . Aiu. C/tiw. Snc.. 1980. 102, 7817. G. R. Chambers and M. Jones, J. Aiii. Clierw. Sol... 1980, 102. 4516.

Photochemistry

478

state. The oxidation products obtained by irradiation of 3-n-butyl-3-phenyldiazirine in the presence of m-chloroperbenzoic acid are derived mainly from the intermediate 1-diazo- 1- ~ h e n y l p e n t a n e , ~and ~ products arising by singlet methylene insertion into the sulphur-hydrogen bond are formed on irradiation of diazomethane-hydrogen sulphide mixtures. 38 Particular interest has been shown in the reactions of photochemically generated arylcarbenes. A study of the photodecomposition of phenyldiazomethane in 2-chloropropane has revealed that carbon-chlorine bond insertion of singlet phenylcarbene predominates at low temperature in solution, whereas carbon-hydrogen bond insertion is preferred in a rigid matrix.39 The principal products of irradiation of diazoalkane (63) are phenylacetylene (64)and the cyclobutene (65), even in the presence of alkene~.~'At lower temperatures, however, carbene addition predominates as shown, for example, with isobutene as shown in Scheme 7.

\

Nz

-Nz hv

'

Ph

4:-

PhCzCH

+

"0

Ph

(63)

(64)

(65)

Me Scheme 7

The interconversion of photochemically generated singlet and triplet diphenylmethylene' has been investigated using methanol and isoprene as selective trapping agent^.^' Supporting evidence for a carbene singlet-triplet equilibrium is provided by a study of the addition of diphenylmethylene to cis- and truns-1,2di~hloroethylene.~~ Singlet addition affords the corresponding cyclopropane with greater than 90% stereospecificity, whereas triplet addition is accompanied by rearrangement and affords the alkene (66) as shown in Scheme 8. It has also been reported that pulsed excimer laser-induced excitation of diphenyldiazomethane affords certain photoproducts, namely 9,10-diphenylanthracene,9,lO-diphenylphenanthrene, and tetraphenylethylene, which have not been detected in conventional lamp-induced i r r a d i a t i ~ n .The ~ ~ rate of reaction of photochemically generated triplet phenylmethylene, diphenylmethylene, and fluorenylidene in isobutene has been monitored using e.s.r. s p e c t r o ~ c o p y . ~ ~ 37 38 j9

40 41

42

43

M . T. H. Liu. G. E. Palmer, and N. H . Chishti, J . Cliem. Snc.. Perkin Trms. -7. 1981, 53. C. W. Whang. H. L. Kao. and S. Y. Ho, J . Chin. Cliem. Sac. ( TciipciJ, 1980, 27. 137. H. Tomioka, S. Suzuki. and Y. Izawa, Ciieni. Lett., 1980. 293. R. A. Moss and W. P. Wetter. Tetraliedron Lett., 1981. 22, 997. K. B. Eisenthal. N. J. Turro. M. Aikawa. J. A. Butcher, C. DuPuy, G . Hefferon. W. Hetherington, G . M. Korenowski. and M. J. McAuliffe, J . Am. Clieni. Soc.. 1980. 102, 6563. P. P. Gaspar, B. L. Whitsel. M. Jones, and J. B. Lambert, J . Am. Cheni. Soc., 1980, 102. 6108. N. J. Turro, M. Aikawa, J. A. Butcher, and G. W. Griffin. J . Am. Client. Soc., 1980, 102, 5127. C.-T. Lin and P. P. Gaspar. Tetrahedron Lett.. 1980, 21, 3553.

Pho toeIimination Ph

Ph

):

)=N2 Ph

’

Ph

-

-

479

CI

Ph >: Ph

ci

+Cl

Ph Ph

>7

PhZC* CI

Ph

PI

)= CHCHCI,

c1

Ph (66) Scheme 8

Singlet and triplet fluorenylidenes have been generated and observed spectroscopically as transient products of irradiation of diazofluorene in a~etonitrile.~’ As a result, it has proved possible to calculate the rate of intersystem crossing and the rate constants for reaction of both carbenes with alkenes and alcohols. Reaction of singlet fluorenylidene (67) with alkenes affords cyclopropanes as the major product, as shown for methyl methacrylate in Scheme 9.46 Surprisingly,

Me

Scheme 9

such cyclopropanations have been shown to be non-stereo~elective,~~ and further studies are obviously necessary to elucidate fully the nature of the reaction intermediates. 1-Phosphoryl-substituted2-vinylcyclopropanes have been prepared by the addition of photochemically generated carbenes to 2,3-dimethylbuta~iiene.~~ Similarly, benzophenone-sensitized photodecomposition of the dimethyl ( r diazoalky1)phosphonates (68) in the presence of diketen (69) affords E- and Z-1substituted 1 -(dimethylphosphono)-5-oxaspiro[2.3]hexanes (70) and (7 1).49 Rearrangement of the carbene (72), leading to the formation of short-lived 45

46 47 48

49

J. J. Zupancic and G. B. Schuster, J. Am. Clicvii. Sot., 1980. 102, 5958. J . J. Zupancic and G. B. Schuster. J . din. Clicwi. Soc.. 1981. 103. 944. J . J . Zupancic. P. B. Grasse, and G . B. Schuster, J . Am. C l i m . Sol... 1981. 103, 2423. G. Mans and R. Hoge, Liebigs Ann. Cheni.. 1980, 1028. T. Kato. N. Katagiri, and R. Sdto, J . Org. Clicwi., 1980, 45, 2587.

480

(68) R = H, Me. Ph, p-MeOC,H,, or p-NO,C,H,

(69)

1

PhCHO

Ph (75)

(diphenylmethy1ene)phenylphosphane oxide (73), has been observed on photoelimination of nitrogen from (diazobenzy1)diphenylphosphane oxide (74): s the oxide (73) can be trapped as the adduct (75) with benzaldehyde. 4E- and 4Z-ethyl diazoethylidenecyanoacetates (76), on irradiation in benzene, are converted viu loss of nitrogen into the cyclopropene (77) and the furan (78), respectively.s2 2,5Diazocyclopentadienylidene (759, generated by irradiation of 2-diazo-2Hit imidazole (go), is biradical in character in contrast with ~yciopentadienylidene;~~ readily undergoes reaction with benzene derivatives to give 0-, rn-, and psubstituted 2-phenylimidazoles (8 1). CN

M . Regitz and H. Eckes. Chrnt. Bcv-., 1980, 113, 3303. ’ M. Regitz and H. Eckes, Tetrulirdron, 198 1, 37. 1039. ’’ C . Guiborel, R. Danion-Bougot, R . Danion. and R. Carrie, Terrcrlterlron LLJrt., 1981, 22, 441.

50

s3

N . Rru and J . Vilarrasa, C/imi. Lett., 1980. 1489.

Photoelimination 48 1 The study of the mechanism and synthetic applications of photodecomposition of diazoketones has continued to attract attention. There is already much indirect evidence for the existence of an r-0x0-carbene interconversion on photoelimination of nitrogen. A study of unsymmetrically substituted r-diazoketones (82) and (83) has now established that not only are singlet x-0x0-carbenes (84) and Ph-C-S-R II 0

Ph-C-C-R II II 0 N2

(84)

(85) in equilibrium, but that these rearranged carbenes can be trapped with a l k e n e ~The . ~ ~observation that irradiation of azibenzil-' 3 C 0 in methanol yields partially scrambled methyl diphenylacetate and unscrambled azibenzil adds further support to the intermediacy of an oxiren and virtually eliminates the possibility of any involvement of the bicyclic intermediate (86).55The carbene generated by irradiation of azibenzil (87) has been intercepted with diphenylmethanimine leading to the formation of the cyano ether (88);56 the proposed pathway is shown in Scheme 10. The amido-ether (89) is also formed, presumably Ph-C-C-Ph II II 0 Nz (87)

Ph-C-c-Ph II 0

-

Ph Ph'

'C=C=O

Ph

Ph

Ph

\ /

Ph

Ph

Ph

0 Ph II CH-C- NHf Ph / OMe Ph

Ph

\

(89)

Scheme 10

by way of a photo-WoIff rearrangement, followed by successive additions of imine and methanol. Numerous examples of photochemically induced Wolff rearrangements have been described. In a detailed study of several a-diazoketones, it has 54

"

H. Tomioka, H . Okuno, S. Kondo, and Y. izawa, J . Ant. Cheni. Soc., 1980, 102, 7123 M . A. Blaustein and J. A. Berson, Terrnlierlron Lett., 1981, 22. 1081. K. N. Mehrotra and G. Prasad, Bull. Ciiem. Sou. Jpn., 1981, 54, 604.

482

Pho t ockemist ry

been reported that Wolff rearrangement to form ketens takes place directly viu the excited singlet state of the sym-2 c ~ n f o r m e r . ~The ' sym-Econformer, however, on excitation undergoes photoelimination of nitrogen and yields products characteristic of singlet carbenes. Ring contraction has been observed on irradiation of 3diazothiochroman-4-one (90) in methanol to give the dihydrobenzo[b]thiophen ester (91) and the spiro-compound (92),'* and various unusual products have been obtained on photoelimination of nitrogen from the z-diazoketone of 2,2,5,5tetramethylthiolane-3,4-dione (93).59In particular, diazoketone (93) is converted 0

M e v MM e Me (93)

on irradiation in benzene into the dihydrothiophen (94). A Wolff rearrangement has also been observed on irradiation in methanol of the diazoketone (95) to give esters (96) and (97) of tricyclo[4.2.0.0' .4]octane.60 The effect of substituents on the temperature dependence of z-carbonyl-carbene reactivity has been examined using carbenes generated by low-temperature photolysis of methyl diazophenylacetate.6 A correction to the literature on the photoreaction of isopropylidene diazomalonate (98) with 1,3,3-trimethyIcyclohexane (99) has been reported.62The photoproduct, originally thought to be a cyclopropane derivative, has now been shown to be the cyclobutanone (1OO), the formation of which presumably involves a photo-Wolff rearrangement as illustrated in Scheme 11. Substituent effects observed in the product distribution of diazo-amide photochemistry have been ascribed to conformational factors;63 the b-lactam, oxindole, and Wolff rearrangement products appear to arise directly from the excited singlet state of the sym-2 form of the diazo-amide itself.

'' 5y 60

" b2 63

H . Tomioka. H. Okuno, and Y. Izawa. J . Org. Cltcwt., 1980, 45, 5278. Y. Tamurd, H . Ikeda, C. Mukai. S. M. M. Bayomi, and M. Ikeda, C h m . Pltmv. Bull., 1980,28. 3430. J . Bolster and R. M . Kellogg, J . Org. CIteni., 1980, 45, 4804. S. Wolff and W. C. Agosta, J . Clieni. Soc., Clicwi. Conintun.. 1981, 1 18. H . Tomioka, H . Okuno, and Y. Izawa, J . Cltcwi. Soc.. Perkin Truns. 2, 1980. 1636. R. V . Stevens. G. S. Bisacchi, L. Goldsmith, and C. E. Strouse. J . Org. Cltmi., 1980, 45. 2708. H . Tomioka. M . Kondo, and Y . Izawa, J . Org. Chcw., 1981, 46, 1090.

483

Photoelimination

hv. MeOH

Me (95)

(96)

(97)

Scheme I I

Irradiation of the pyrazoline diazo-amide (101) in methanol affords a mixture of isomeric methyl 3-phenylazobut-2-enoates ( 1 0 2 y 4 Details of the precise mechanism implicated in this transformation are uncertain, but the process must presumably involve ring opening of the intermediate carbene (1 03). A carbeneinsertion reaction is observed on irradiation of the diazo-amide (104) to give the novel p-lactam (105).65

Me

Me N=N

Ph

Ph

)=CHCO,Me Me

(105) 64

65

S. N. Ege, E. J. Gess. A. Thomas. P. Umrigar. G. W. Griffin. P. K. Das, A. M. Trozzolo, and T. M. Leslie, J. Clieni. Soc., Clwn. Commun.. 1981. 1263. G . M. Bright, M. F. Dee, and M. S . Kellogg, Heterocycles, 1980, 14, 1251.

484

Photochemistry

2-0x0-carbenes are formed on irradiation of o-naphthoquinonediazides in alcohols;66 the singlet species undergoes ring contraction yielding indenecarboxylates, whereas triplet carbenes are converted into naphthols. The photoreactions of o-quinonediazides have been r e ~ i e w e d . ~ ' Esters and thioesters of (dansy1diazomethyl)methylphosphinic acid undergo carbene insertion reactions in high yield on irradiation;68 their fluorescent properties make them suitable reagents for photoaffinity labelling studies. 4 Elimination of Nitrogen from Azides The photoreactions of azides can in most cases be rationalized in terms of intermediate nitrenes. Irradiation of t-butyl azide (106) in nitrogen matrices at 12K gave the imine (107), but no evidence was obtained for a nitrene intermediate.69 Photoelimination of nitrogen from 4-azido-2-pyrolinones provides a new synthetic route in high yield to 3-cyano-2-azetidines, as shown, for example, for the pyrrolinone (108) in Scheme 12.70 Zwitterionic intermediates have been Me I .Me-C-N3

Me, ,Me ,C=N Me

h1'

I

Me

proposed. A thermally unstable azacyclobutadiene is thought to be implicated in the conversion of tri-t-butylcyclopropenyl azide (109) into the acetylene (1 10) and the nitrile (1 11) on irradiation in an argon matrix.71

(109)

(1 10)

(1 11)

Further examples of the preparation of 2H-azirines by irradiation of a$unsaturated azides have been r e p ~ r t e d . 'The ~ azirine (112) has been proposed as an intermediate in the photoreaction of 6-azido- 1,3-dimethyluracil (1 13) with 66 67

68 69

70

R.P. Ponomareva, A. M.Komagorov, and N. A. Andronova, Zh. Org. Khim.,1980, 16, 146. R.P. Ponomareva, A. M. Komagorov, and 0. P. Studzinskii. Izv. Vvssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1980, 23, 812. J. Stackhouse and F. H. Westheimer, J. Org. Chem., 1981, 46, 1891. I. R. Dunkin and P.C. P. Thomson, Tetrahedron Lett., 1980, 21, 3813. H. W. Moore, L. Hernandez, D. M. Kunert, F. Mercer, and A. Sing, J . Am. Chem. Soc., 1981, 103,

11

1769. G. Maier and U. Schafer, Liebigs Ann. Chem., 1980, 798.

71

K . Isomura, S. Noguchi, M. Saruwatari, S. Hatano, and H. Taniguchi, Tetrahedron Lett., 1980, 21, 3879.

Photoelimination

485

I

Me

I

(’ 12)

(114)

R = Ph, 3-MeC6H,, 4-MeC6H,, PhCH,, or MeS

0

Me Scheme 13

tetrazoles (1 14) to give the 6-tetrazolyluracils (1 15): 7 3 further irradiation gave the 3-substituted fervenulins (1 16) as shown in Scheme 13. Many photoreactions of aryl azides can be interpreted as arising v i a unstable ring-fused azirines. The formation of the 6,7-diaminobenzothiazoles(1 17) and the 6-amino-8H-thiazolo[5,4-c]azepines (1 18) on irradiation of the corresponding 6azidobenzothiazoles (1 19) in diethylamine can be explained in this way, as shown in Scheme 14.74An alternative explanation for the photodecomposition of phenyl azide (120) at low temperatures has recently been advanced and involves the formation of an intermediate 1-azacyclohepta-1,2,4,6-tetraene (121). Further evidence for this pathway is to be found in a study of the photodecomposition of phenyl azide in acetic acid:75the azepin-Zone (122) is believed to arise in this way, as shown in Scheme 15. The formation of the same azepin-Zone on irradiation of phenyl azide in the presence of ‘naked’ acetate anion has been reported;76 the nature of the intermediate in this transformation is still open to question, but both benzazirine and 1-azacyclohepta- 1,2,4,6-tetraene intermediates are considered possible. In contrast, irradiation of the azide (123) in an argon matrix at 10K affords, on the basis of spectral evidence, the cyclic carbodi-imide (124).77 273 74

” 76

”

K. Hirota, K. Maruhashi, T. Asao, and S. Senda, Heterocycles, 1981, 15, 285. P. T. Gallagher, B. Iddon, and H. Suschitzky, J. Chem. Soc.. Perkin Trans. 1, 1980, 2362. H. Takeuchi and K. Koyama, J. Chem. Soc., Chem. Commun., 1981, 202. R . Colman, E. F. V. Scriven, H. Suschitzky, and D. R. Thomas, Chem. Ind. ( L o n h n ) , 1981, 249. H.-W. Winter and H. P. Reisenauer, Angen,. Chem., Inr. Ed. Engl., 1980, 19, 566.

!A2' N3

(1 19)

..a-R ElR Photochemistry

486

R

= H,

!!

N

Me, SMe, SPh, or CI

1

Et,NH

Scheme 14

Azidophenazine is converted, on irradiation in acetonitrile in the presence of amines, into 2-alkylamino-1 -aminophenazines and 2-aminophenazine. Singlet nitrene, formed by direct irradiation of the pyrazole (1 25), undergoes cyclization in high yield to give the 5H-pyrazolo[1,2-a]benzotriazol-4-iuminner salt ( 126).79 An alternative reaction pathway is preferred on triplet-sensitized

hi-. sens

(1 27) 78 79

( 125)

( 126)

G. F. Bettinetti, E. Fasani, G. Minoli, and S. Pietra, Gazz. Chim. ital., 1980, 110, 135. A. Albini, G. F. Bettinetti, and G. Minoli, Chem. LRtt., 1981, 331.

487 photodecomposition leading, presumably via a radical mechanism, to the dihydropyrazine (1 27). 1,3-Dimethyl-SH-pyrazolo[ 1‘,2’: 1,2]triazol0[3,2-a]phenazin-4-ium inner salt is similarly formed from the corresponding azide via either singlet or and the indazolo[3,2-b]triplet l-(3,5-dimethylpyrazolyl)phenazinyl-2-nitrene,80 benzothiazole (128) is a product of irradiation of the azide (129).*’ Photoelimination

(129)

(1 28)

The phenazine (130) was unexpectedly formed in low yield in addition to the benzo[c]cinnoline (13 1) on irradiation of the 2,2’-diazidobiphenyl (1 32).82 The proposal of intermediate (133), arising presumably by two successive nitrene additions to the phenyl nuclei, lacks conviction. Triazinylnitrene, generated by photoelimination of nitrogen from 2-azido-4,6-dimethoxy- 1,3,5-triazine ( 134),

(133) Me0

Me0

‘7kN3

N

F N

Me0

( 1 34)

f

O

R

NF“ Y N F N D R

Me0 (135)

has, however, been shown to add intermolecularly to alkylbenzenes to give the corresponding N-triazinylazepines (1 35).83 The nitrene (1 36), formed either by irradiation of the azide (137) or by photofragmentation of 1-azatriptycene ( 1 38), undergoes analogous conversion into the indenoacridine (139) by the route shown in Scheme 16;84in the presence of acetic acid, the acridine is further converted into A . Albini, G. F. Bettinetti, and G. Minoli, J . Chem. Soc.. Perkin Trcins. 1 , 1981, 4. D. Hawkins, J. M. Lindley, I. M. McRobbie, and 0. Meth-Cohn, J . Cliem. Soc., Perkin Trms. I , 1980, 2387. ” 83 84

A. Y a k , Bull. Chem. SOC.Jpn., 1980, 53, 2933. S. Tamura, H. Imaizumi, Y. Hashida, and K. Matsui, Bull. G e m . So<. Jpn., 1981, 54, 301. T. Sugawara and H. Iwamura, J . Am. Chem. Soc., 1980, 102, 7134.

488

Photochemistry

(1 37)

I

Scheme 16

the 12b-rnethyl-5,12b-dihydro-derivative(140), whereas in dilute methanolic sodium methoxide, the stable azepine (141) is obtained. Irradiation of the 2-azidopyridine 1-oxides (142) in benzene affords the 6-cyano1,2-oxazines (143)? A pathway involving photoelimination of nitrogen and ring

0(142) R' = R 2 = R 3 = H R' = Me, R 2 = R3 = H R' = R 3 = H , RZ = Me R' = R 2 = H , R3 = Me

CN

C=N

-N2

II

0

(143)

(144)

opening to give the nitroso-nitriles (144), following by electrocyclization, has been proposed. The use of 3-azido-9-[{4-(diethylamino)-1-methylbutyl)amino]-7methoxyacridine as a photoaffinity label at quinacrine binding sites has been R5

R. A. Abramovitch and C. Dupuy, J . CIwni. Soc., Cltem. Coninrim.. 1981. 36.

Photoelimination 489 suggested,86and the stereochemistry of the addition of photochemically generated nitrenes to cyclic vinyl ethers has been described.87 Di-t-butylphosphinic azide (143, on irradiation in methanol, undergoes rearrangement with loss of nitrogen to give NP-di-t-butylphosphonamidate ( 1 46) in 40 P / \ Me3C N3 (145)

I,,! -*z

Me,C, Me,C’

P

/p N ‘

-

0

Me3C-P

// \

N-CMe,

( 147)

high yield, presumably by way of a monomeric metaphosphonimidate (147) which is trapped by solvent. 88 Di-isopropylphosphinic azide behaves in a similar fashion, but the less-hindered diethylphosphinic azide suffers extensive solvolysis in methanol to give methyl diethylphosphinate. Evidence for the formation of a transient metaphosphonimidate in the photodecomposition of the oxide of diphenylphosphine azide has also been reported.89 Novel silacarbodi-imides have been obtained on irradiation of diazidosilanes and can be trapped with tbutan01,~Oand evidence for the formation of transient germa-imines on irradiation of germanium azides has been described.”

5 Photodecomposition of Other Compounds having N-N Bonds A novel photoelimination of nitrogen from the 1,l-diazene (148) has been reported giving the hydrocarbons (149)-( 152).’* A competing process leading to the tetrazene (1 53) has also been observed, and both types of reaction product appear to be singlet- and triplet-derived. New examples of the photodecomposition of sodium and lithium salts of p toluenesulphonylhydrazones to give carbenes, by way of unstable diazo intermediates, have again been reported. Benzocyclobuten- 1 -ylcarbene, 2-methylbenzocyclobutenylidene, and o-styrylcarbene have been prepared in this way from the sodium salts of the tosylhydrazones of benzocyclobutene- 1-carboxaldehyde, 2methylbenzocyclobutenone, and o-formylstyrene, r e ~ p e c t i v e l y .Similarly, ~~ 5norbornen-2-one tosylhydrazone (1 54) is converted on irradiation in aqueous sodium hydroxide solution into 5-norbornen-2-01 ( 1 5 5 ) and nortricyclanol 86

89

” ” 93

D. M. Mueller, R. A. Hudson. and C . Lee, J. Ani. Cliiwi. Sot., 1981, 103. 1860. E. Kozlowska-Gramsz and G. Descotes, Tetnrlic~clroriLett.. 1981. 22, 563. M . J. P. Harger and M. A. Stephen. J. C‘lieni. Soc.. Pcrkiii Trtnis. I, 1981. 736. G. Bertrand, J.-P. Majordl, and A. Baceiredo, Tcirtrh~~rlroti Lcir., 1980, 5015 . W. Ando. H. Tsumaki, and M. [keno, J. Cherii. So(,..Cherii. Cotwiiwi.. 1981. 597. A. Baceiredo, G. Bertrand, and P. Mazerolles, Tctrhclroii LCII.,I98 I , 22, 2553. P. G. Schultz and P. B. Dervan. J . Atit. Ctierii. Soc.., 1981. 103. 1563. M . A. O’Leary and D. Wege, Tctrcthetlrorr. 1981. 37,801.

Photochemistry

490

hv -78 C

Me

Me

Me

+

czE Me

Me

+

Q--N-N-N>

Me Me

152)

Me Me (1 53)

(1 56).94 The alcohol (1 57) was also obtained and is formed via the 5-norbornene-2endo-diazonium ion. 3-, 5, 6-, and 7-Methylnorbornane-2-diazonium ions have been generated as exo-endo-mixtures by photodecomposition of the corresponding methyl-2-norbornanone tosylhydrazones under similar condition^.^^

&

L& NdOH +HOp.J+Q,

N-NHTs

OH

OH

( 154)

(1 55)

( 1 56)

( 1 57)

Few studies of p-toluenesulphonylhydrazonesthemselves have been reported. The major products of p-tosylhydrazone derivatives of aryl and r,B-unsaturated carbonyl compounds have now been shown to be azines and sulphones, the formation of the former being preferred in benzene and the latter in methanol.96 Interest continues to be shown in the photodecomposition of diazonium salts,97*98 and aryldiazonium tetrafluoroborates have been recommended as potential photoaffinity labelling reagents for protein^.^' The key step in a recent synthesis of pyrazofurin involves the photodecomposition of the diazopyrazole (1 58) to give the hydroxypyrazole ( 1 59). l o o 2-Azahypoxanthine (160) is the major

AcO OAc (1 58) 44

" "" " <> H

" ''')

AcO OAc ( 159)

W. Kirmse. N . Knopfel, K. Loosen, R . Siegfried.and H . -J. Wroblowsky, C h ~ i i iBcr., . 1981. 114, 1187. W. Kirmse, M . Hartmann, R. Siegfried. H.-J. Wroblowsky. B. Zarig, and V. Zellmer, C / i f ~ 7B.w . , 1981. 114, 1793.. F. Bellesia. R. Grand]. U . M . Pagnoni. and R. Trave. J . Clriw. Res. / S ) . 1981. 112. D. Rehorek. F. Walkow. and J. Marx. Z . C h m ~ . 1980, , 20. 416. D. Isac, M . Mracec. N . Prosteanu, and Z. Simon. R i v . Roitnr. C/rim., 1981, 26, 29. B. L. Kieffer, M. P. Goeldner. and C. G. Hirth, J . Cl7cw. SOC.,Cltcw. Coninitin., 1981, 398. J . G. Buchanan, A. Stobie, and R . H . Wightman. J . Clicwr. Soi..,C/ri.ni. Coiirnrun., 1980, 916.

49 1

Photoelimination CONH,

N 2+

'-'

H

0-

(161)

(160)

( 1 62)

product of irradiation of 5-diazoimidazole-4-carboxamide( 161) in aqueous solution at pH 1 or pH 7.4-1 2. l o ' 4-Carbamoylimidazolium-5-olate (1 62) is formed, presumably via a carbene, at intervening pH values. 6 Photoelimination of Carbon Dioxide N-Alkyl-N-nitroso a-amino-acids (163), on irradiation in solution or in the solid state, are converted into amidoximes (164) with eliminatipn of carbon dioxide. l o 2 r-0x0-carboxylic acids undergo oxidative photodecarboxylation via a pathway thought to involve electron transfer. O 3 Photoelimination of carbon dioxide from esters has also been observed. Hindered biphenyls have been prepared'in this way

'

R-N-CH,CO,H , I -co, ' NO (163) R = Me, Et, CHMe,, or (CH,),Ph

HNR OH \ / /C=N

H (164)

0

hV ___)

- co,

(1 65) R = OMe or C0,Me

from substituted methyl benzoates. ' 0 4 Similarly, the dilactones (1 65) are converted on irradiation into the [2.2]paracyclophanes (166);"' the nature of the substituent has a profound effect on the efficiency of these transformations: electron-donating groups strongly enhance the formation of paracyclophanes. Photodecomposition of maleic anhydride in the gas phase has been reported to give ethylene, carbon dioxide, and carbon monoxide. O6 The fragmentation is believed to proceed via internal conversion to a vibrationally excited ground state. Photoelimination of carbon dioxide has also been observed in perfluoro-nbutanoic anhydride O 7 and in perfluorosuccinic anhydride to give tetralo' lo'

Io3 lo4

lo' '06 lo'

J. K. Horton and M. F. G. Stevens, J. Clicwi. Soc.. Perkin Truns. I , 1981. 1433. Y. L. Chow, D. P. Horning, and J. Polo, C m . J . Chem.. 1980, 58, 2477. R. S. Davidson, D. Goodwin, and G. Turnock, Tetrrilierlron Lett., 1980, 21 4943 R. Luedersdorf. J. Mai, and K. Praefcke, Z. Nrrturfimdi.. Ted. B, 1980, 35. 1420 M. Hibert and G. Solladie, J. Org. Clieni., 1980. 45, 4496. R. A. Back and J. M. Parsons, Cm. J. Chem.. 1981, 59, 1342. C. J. Stock and E. Whittle, J. Cheiii. Soc.. Frircrdiiy Trims. 1. 1980. 76, 496.

Pho tochemistry

492

fluoroethylene. l o 8 Carbon dioxide is formed together with other radical-derived products on irradiation of various acyl peroxides. Irradiation of the 4-sulphenylated 2,3-dimethylisoxazolin-5-ones ( 167) is accompanied by the loss of carbon dioxide and leads to the formation of the sulphurstabilized iminocarbenes (1 68), which can be intercepted by methanol as shown in Scheme 17.' l 2 Evidence for the formation of an organic fulminate has, at last,

''

(167) R

=

Ph, 2-naphthyl, CH,CH=CH,, CH,CH,OH, or CH,CH,OAc

(168)

SR

SR Scheme 17

'

been described. I 3 Irradiation of the 4-oximinoisoxazol-5(4H)-one (169) in an argon matrix as 1 0 K gave a species identified spectroscopically as phenyl fulminate ( 1 70).

7 Fragmentation in Organosulphur Compounds Photoreactions arising by carbon-sulphur bond homolysis have again been described. Thus, irradiation of 2-methylthio-5-alkyluracils in aqueous solution affords the corresponding 4-0x0-5-alkylpyrimidines. I4 Multilayered paracyclophanes have similarly been synthesized from the corresponding cyclic sulphides by photochemically induced removal of sulphur in the presence of triethyl phosphite.' I 5 An oxidative step must be involved in the photodecomposition of the fungicide, quinomethionate (171), in benzene to give, with loss of sulphur and carbon monoxide, the quinoxalinedione (1 72) and the methylquinoxalines ( 1 73) and ( 1 74). '

''

P. E. Watkins and E. Whittle, J . C h i . Soc., Fiirirtliij. Trrins. I. 1980, 76,503. J . Y. Nedelec and D. Lefort. Tetrrrhethon, 1980. 36. 3199. A. Kitamura. H . Sakuragi, M . Yoshida. and K. Tokumaru. Bull. C h i . Soc. Jpn., 1980. 53, 1393. 111 A . K 'itainura. H . Sakuragi, M . Yoshida. and K. Tokumaru. Bull. Chcwi. Soc. Jpn., 1980. 53. 2413. l'' T. Sasaki, K . Hayakawa, and S. Nishida, J . C / i o i ) i . Soc., Clicwt. C o t i i n i u t ~ . .1980, 1054. 'IJ C . Wentrup, B. Gerecht, D. Lagua, H , Briehl. H.-W. Winter, H. P. Reisenauer, a n d M . Winnewisser, J . Org. Chwi., 198 1, 46,1046. ''-I K . Golankiewicz, M . Szajda. a n d E. Wyrzykiewicz, Pol. J . C%ern.,1980, 54,363. 115 H. Machida. H. Tatemitsu, T. Otsubo, Y. Sakata, and S. Misumi, Bull. Clicw. SOC.J p . , 1980, 53.

lo'

'(Iy

'lo

IIh

2943. T. Clark and R. S. T. LoeRler. Prstic Sci.. 1980, 11, 45 1.

493

Pho toelimination

H

(173) R’ = H , R2 = Me (174) R’ = Me, R2 = H

( 172)

Carbon-sulphur bond homolysis has been shown to be, in addition to sulphur-sulphur bond homolysis, a primary process in the photolysis of disulphides in solution. Sulphur-sulphur bond homolysis is, however, responsible for the establishment of an equilibrium between various alkyl disulphides on irradiation. Other liquid-phase studies of the photodecomposition of acyclic alkyl disulphides have been reported,’ 1 9 * I 2 O and the quantum yield for the formation of methyl ethyl disulphide from methyl disulphide and ethyl disulphide has been determined. The disulphide ( I 75), obtained by photo-oxidation of 6-mercapto- 1,3-dimethyllumazine, undergoes photorearrangement to the dithiin derivatives (1 76) and ( 1 77) by way of initial sulphur-sulphur bond homolysis. 2 2 The photodecomposition of 2.2’-dithiodibenzoic acid derivatives has also been examined. Irradiation of

’

’’

’*

’

mi

MeCHO’ il I’

OC”” S-C-Me II

‘I7

I”

I2O I22

123

G . H. Morine and R. R. Kuntz, Pliotoclieni. Photohiol.. 1981, 33, 1. D. Gupta and A. R. Knight, Ccrtt. J . Clieiti., 1980, 58. 1350. D. Gupta, Inctirm J . Clieni., Sect. B, 1980, 19, 206. D. Gupta, lntlicrn J . CIieni., Sect. B, 1980, 19, 328. D. Gupta, Indim .I. Clieni., Sect. B, 1980. 19, 371. A. Heckel and W. Pfleiderer, Tetrcrhedron Lett., 1981. 22. 2161. B. Kohne, K. Praefcke, and C. Weichsel. Plio.sp1ioru.s Sulfitr, 1979, 7 . 21 I .

494

Photochemistry

organic disulphides in aldehydes resulted in reductive fission of the sulphur-sulphur bond and leads to the formation of an equimolecular mixture of the corresponding thiol and the thiol ester.'24 The cyclic disulphide (178) is converted in this way on irradiation in acetaldehyde into the S-acetylated dithiol (179). A photoinitiated radical chain mechanism has been proposed.

Dihydrothiadiazole 1,l -dioxides ( 180) undergo photoelimination of sulphur dioxide on irradiation to give the azines (181),'25 and the conversion of 2-ptoluenesulphonyloxycyclopent-2-enone( 182) in to 2-hydroxy-3p-tolylcyclopent-2enone ( 1 83) on irradiation is believed to proceed viu photoelimination of sulphur dioxide from an intermediate diketosulphone. ' 2 6 Singlet-state photodecomposition of alkyl arenesulphones in various solvents affords alkanols, aromatic hydrocarbons, and sulphur dioxide. 12' Further irradiation of the methyl sulphonates (184) and (185), obtained by photoinduced ring opening of the sultone

12* 125

12'

M. Takagi, S. Goto, M. Tazaki, and T. Matsuda, Bull. Cliem. Sot.. Jpn., 1980, 53, 1982. H . Quast and F. Kees, Chem. Ber., 1981, 114, 787. K. Tomari, K. Machiya, I. Ichimoto, and H . Ueda, Agric. B i d . Chem., 1980, 44, 2135. J. P. Pete and C. Portella, Bull. Sot.. Chim. Fr., 1980, 11, 275.

495

Pho toeliminution

(1 86), yields 12-hydroxy-1 l-phenylbenzolj]fluoranthene ( 1 87), ' 2 8 and the conversion of unsaturated sultones into furan derivatives by formal elimination of sulphur dioxide has been described. 29 Competing photodecomposition pathways have been observed in sulphonamides and sulphonylureas, 30 and the photohydrolysis of sulphonamides, viu the formation of donor-acceptor ion pairs with electron-donating aromatic compounds, has been reported. l 3 Irradiation of N-tosylmethylphenethylamine (188) in the presence of veratrol (189) in ethanol, for example, gave methylphenethylamine (190) in 66% yield. This procedure has also been employed in the selective detosylation of lysine peptides. Elimination of COS is effected on irradiation of o-phenylene thioxocarbonate (191) in an argon matrix, leading to the formation of cyclopentadienylidene keten (192);' 3 2 no transient species corresponding to an intermediate benzoxiren was detected.

'

'

0

CH ,CH2-N -Me Ts I

+

8 Miscellaneous Decomposition and Elimination Reactions Fragmentation and elimination reactions that cannot be included in any of the above categories are briefly reviewed in this Section. It has not proved possible to classify these processes, but analogous reactions are grouped together. Products arising by carbon-nitrogen bond homolysis have been obtained on irradiation of N-benzyldiphenylamine, 3 3 dimers of 2,4,5-triphenylimidazolyl,3 4 and N-aIkyl-4-(carboalkoxy)pyridinylradicals. ' The pyrazoline carbonyl ylides (193) are formed on irradiation of the oxirans (194),'36 and substituted 3,4epoxycycloalkenes have been converted photochemically into the corresponding 2,3-dihydrofurans. 3 7 The major products, in order of decreasing amounts, of the photolysis (A = 147 nm) of 1,l-dimethylcyclopropanehave been shown to be isobutene, ethylene, hydrogen, buta- 1,3-diene, 2-methylbuta- 1,3-diene, propylene, allene,

'

'

'

J. L. Charlton and G . N. Lypka, Can. J . Cliem., 1980, 58, 1059. H. Itokawa, T. Tazaki, and S. Mihashi, Heferocycles, 1981. 15, 1105. B. Weiss, H.Diirr, and H. J. Haas, Angew. Cltem.. Inr. Ed. Engl., 1980, 19, 648. ''I T. Hamada, A. Nishida, Y . Matsumoto, and 0. Yonemitsu, J . Am. Cltem. Soc., 1980, 102, 3978. ''' M . Torres, A. Clement, and 0. P. Strausz, J . Org. Cliem.. 1980, 45, 2271. M. Z. A. Badr, M. M. Aly. and A. M. Fahmy, Can. J . Chem., 1980, 58, 1229. T. Goto, H. Tanino, and T. Kondo, Cltem. Lett., 1980, 431. 13' K. Takagi and Y. Ogata, J . Otg. Chem., 1981, 46, 989. 13' S. N. Ege, E. J. Gess, A. Thomas, P. Umrigar, G . W. Griffin, P. K. Das, A. M. Trozzolo, and T. M. Leslie, J . Chem. Soc., Chem. Commun., 1980, 1263. *''W. Eberbach and J. C. Carrt, Chem. Ber., 1981, 114, 1027. 129

"'

Plio tocheniist ry

496

I

I

Ph

Ph (193)

( 194)

methylacetylene, and acetylene;’ 3 8 up to ten primary processes have been postulated. Irradiation (3. = 185 nm) of cis- or rruns-bicyclo[6.1 .O]nonane gave nona-l,8-diene together with small amounts of cis- and trans-cyclononenes.’ 3 9 Examples of [2 + 2]photocycloreversions of cyclobutane derivatives have been reported. 140-142 Transformations arising by photoinduced nitrogen-chlorine bond homolysis have again been observed. The Hofmann-Loftler-Freytag reaction of N-chloro-Lamino-acids, for example, affords &chlorinated intermediates which can be cyclized to proli lines,'^^ and the N-chloroamine (195) is converted on irradiation

Me” “CI

into the iminocholestane (1 96). 144 Irradiation of N-chloroammonium perchlorate and hexane in trifluoroacetic acid gave monochlorohexanes in high yield with a striking preference for the 2-isomer; 145 a free-radical chain reaction with hydrogenatom abstraction by the tertiary aminium radical has been proposed. Intramolecular photoelimination of HCI, HBr, and HI, often initiated by carbon-halogen bond homolysis, has again been widely used in the synthesis of heterocycles and alkaloids. 6-Acetyl- 1,2-dimethoxy-4H-5,6,6a,7-tetrahydrobenzo[&]thieno[2,3-g]quinoline (l97), for example, has been obtained in this way by irradiation of the bromothiophen ( 198). 46 Analogous photocyclizations have been employed in the synthesis of ( )-oliveroline, 14’( +)-domesticine, 14*

+

13H 13Y

I40 141

I 4’

143 144

155

J . B. BinkewicL. M. Kaplan. and R. D. Doepker. Cm. J. C/rcw~..1981. 59. 537. R. Srinivasan. J. A. Ors. and T. Baum. J. Org. Chcwr.. 1981. 46. 1950. K. Okada. K . Hisamitsu. and T. Mukai. J. C % c w . Sot.., C/riw. C01711171111.. 1980. 941. K. Okada. K. Hisamitsu. and T. Mukai. Tcvrtrhc,tirori Lc,/t., 1981, 22. 1251. S. Takunuku and W. Schnabel. CIICIJI. P h ~ x f*i,//.. . 1980. 69. 399. S. L. Titouani. J.-P. Lavergnr. Ph. Viallefont. and R. Jacquier. T m w h l h m . 1980. 36. 2961. A . X1. Farid. .I.McKenna. and J. M. McKennn. J . Chcw~.Soc. Ptrk.. 1979. 1. I3 I. S. E. Fuller, J. R. L. Smith, R.0. C. Norman, and R. Higgins, J . Chem. Soc.. Perkin Truns. 2. 1981,

545. I46 14-

148

S. Jeganathan and M. Srinivasan, //tt/io/r J. Clrcwr.. See./. B, 1980. 19. 1028. S. V. Kessar. Y. P.Gupta. V. S. Yadac. M. Nwrula. and T. Mohammad. Tc~/rci/ictiri~ri LCV/..1980. 21. 3307. B. R. Pai, H . Suguna, S. Natarajan, P. K. Vanaja, and R. Meenakumari, Indian J . Chem., Sect. B, 1979. 17. 525.

497

Pho toeliminat ion

I1 I'

MeOH-H,O

'

a:1,R2fJlL1' 3

I

0-JI2

-2.L

I

R' (199) R ' = Me, R 2 = H. Bu", or Ph R' = H, R 2 = H, Me, or Ph R ' = CH2Ph, R 2 = H

I

R'

R'

(200)

(201)

'

apogalanthamine analogues, 49 and certain phenanthridones. 5 0 Treatment of N alkyl-N-acyl-o-chloroanilines( 199) with excess lithium di-isopropylamide and irradiation of the resulting carbanions (200) provides a general and efficient route to oxindoles (201), 5 1 and a mechanism involving homolytic fission assisted by radical complexation has been proposed to account for the photocyclization of 5(2-halogenopheny1)- 1,3-diphenylpyrazoIes. 5 2 Intramolecular photoelimination of HCI from N-chloroacetamide derivatives is also a useful and versatile approach to the synthesis of aza-heterocycles. The Nalkyl-N-chloroacetyl derivatives (202), for example, undergo photocyclization to (203),'53 and the conversion of the N the I ,2,3,4-tetrahydroisoquinolin-3-ones chloroacetamide (204) into the lactam (205) is the key step in a synthesis of 20-deethylcatharanthine. 5 4 Intermolecular photoeliminations of HX of potential

'

OMe

OMe

7m+ Me0 (202) R

Me0 =

Me, CMe,, or CH,Ph

(203)

*o T& H

144

50

15'

Is' Is'

Is4

C02Me

C0,Me

S. Kobiyashi. M . Kihara, and T. Shingu. Ydugcrh-ir Zasslii. 1980, 100. 302. B. R . Pal, H. Suguna, B. Geetha. and K. Sardda, Inclitrri J . Clr~wi.,S c ~ r B. . 1979, 17, 503. J . F. Wolfe, M. C. Sleevi, and R . R. Goehring. J . Aiii. Clwrn. Soc.. 1980. 102, 3646. J . Grimshaw and A. P. de Silva, Can. J . Cliewi., 1980, 58. 1880. T. Hamada. Y. Okuno. M . Ohniori, T. Nishi, and 0. Yonemitsu, Clicvir. P h ~ r r i i i Bu//., . 1981, 29. 128. R . J . Sundberg and J . D. Bloom. J . Org. Clicw., 1980, 45. 3382.

498 Pho todiemistrjt synthetic value have also been described.' 55-' 6 1 Nb-Acetyltryptophan methyl (207), for example, unester (206) and 2',3'-O-isopropylidene-5-bromouridine dergo reaction on acetone-sensitized irradiation to give the substituted uridine (208). 6 2

Hop I1 I'

- HBr

X0

Me Me

(207)

Many other photochemically induced decomposition reactions arising by carbon-halogen bond homolysis have been reported, but these are essentially radical processes having no special photochemical significance and so are not reviewed in detail in this report. Attention should be drawn, however, to the accumulating evidence for both radical and ionic intermediates in such transformations. 6 3 - 1 6 5

'' 15H

lho Ihl

I" Ih3

lh4

Ih5

K. M. Wald, A. A. Nada, G. Szildgyi. and H. Wamhoff. Clicvii. Bc~r..1980. 113, 2884. K. Maruyama, M. Tojo. H. Iwamoto. and T. Otsuki, Clicwi. Leu.. 1980. 827. K. Maruyama. M. Tojo. K. Matsumoto. and T. Otsuki. Clicw. Lptt., 1980, 859. I. Saito. S. Ito. T. Shinmura. and T. Matsuura, Tktnrlidron Lcrt.. 1980, 21. 2813. S. Ito. I. Sdito. and T. Matsuura. Tc~trcrhirlrori,1981. 37. 45. K. Maruyama, T. Otsuki. K. Mitsui. and M. Tojo, J. H c w r o q d . Cliciii.. 1980. 17, 695. M. Terashima, K. Seki. C. Yoshidd. and Y. Kanaoka. Hc~fcwc,sclc~s. 1981. 15. 1075. S. Ito. 1. Saito, and T. Matsuura. J. An?. Clicw. Sol... 1980. 102. 7535. P.C. Purohit and H. R. Sonawane. T~~trcrhc.tlrort. 1981. 37. 873. B. J. Swdnson. J. C. Kutzer. and T. H. Koch, J. h i . Clicwr. Soc.. 1981. 103. 1274. J. L. Charlton. G. J. Williams. and G. N. Lypka. C w . J . Chcwi.. 19x0, 58. 1271.

Part IV POLYMER PHOTOCHEMISTRY By N. S. Allen

1 Introduction The format of this year’s report is unchanged. The past twelve years’ growth in the field of polymer photochemistry has continued, not least because of the industrial applications in such fields as photopolymerization. In fact, a new journal specifically devoted to polymer photochemistry is now available (see later references). Modern techniques such as laser flash photolysis, time-resolved emission, and derivative spectroscopy are being used to unravel the complex photophysical and photochemical processes involved in polymers. 2 Photopolymerization Photopolymerization is now a well established and highly efficient industrial process. Since the last report, some twenty-four review articles have appeared. Arthur has compiled two excellent reviews on the photoinitiated grafting of monomers onto cellulose and vinyl polmers.2 Mechanisms and commercial applications of photografting are discussed. Crivello, an international authority on cationic photopolymerization, has reviewed recent developments in photoinitiation by sulphonium salts.3 Hayashi on the other hand has reviewed both cationic and anionic photopolymerization initiated by charge-transfer complexe~.~ Several review articles have appeared on the commercial aspects of photopolymerization in coatings technology. These include discussions on the present status and f ~ t u r e applications,6,~ * and a comparison of the energy requirements between ultraviolet and electron-beam ~ u r i n g .Marechal ~ l o has reviewed his own work on the use of dyes in accelerating U.V. curing, whereas Hasegawa has reviewed four-centre-type photopolymerizations in the solid state. Interest continues in the u.v.-initiated curing of epoxy-resins 1 2 - l4 and inks.15.l6 Several general articles on U.V.curing have appeared,”-” and Bayer has given an overview of the subject.” Other review articles of interest include

’ lo I’

l3 l4

“ l9

2o

”

J. C. Arthur, jun., in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 3, p. 69. J. C. Arthur, jun., in ‘Developments in Polymer Photochemistry’, ed.N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 2, p. 39. J. V. Crivello, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. I , p. 1. K. Hayashi, J. Radiat. Curing, 1980, 7 , 11. T. Sugimoto, Toso To Toryo, 1980,32445. C. Loucheux, Double Liaison-Chim. Paint, 1980,27, 263. K. Inomata, Shikizai Kyokaishi, 1980, 53, 530. G. E. Green and B. P. Stark, Chem. Br., 1981, 17, 228. Y. Hishino, Shikizai Kyokaishi, 1980, 53, 537. E. Marechal, Pure Appl. Chem., 1980, 52, 1923. M. Hasegawa, PoljJm.Prepr., Am. Chem. Soc., Div. Polvm. Chem., 1979, 20, 430. I. A. Provina, T. S. Yushchenko, and A. V. Uvarov, Lakokras. Mater. Ikh. Primen., 1980, 2, 313. B. Passalenti, S. Vargiu, and S. Bollani, Ind. Vernice. 1979, 33, 3. W. R. Watt, Am. Chem. Soc., 1979, 114, 17. K. Hashimoto and S. Saraiya, Am. Inkmuker, 1981,59, 20. A. Van Neerbos, Adhesion, 1980, 24,413. J. W. Prane, Polvm News, 1980, 6, 265. N. Fukumara, Kumi To Purasuchikku, 1979, 7 , 8 . K. K. Kogyo and A. Denka, Kumi To Parasuchikku, 1977, 5 , 30. H.Akiyama, Kumi To Parasuchikku, 1979, 7 , 24. W. G. Bayer, Tech. Pup. Assoc. Finish. Proc., S.M.E., (Ser) F.C., 1979, F.C. 79-203.

50I

502

Photochemistry

flash xenon curing,22 photosensitized c r ~ s s l i n k i n g , and ~ ~ photoinitiators for paint. 24 On a more commercial note, articles have appeared on photocurable pressuresensitive adhesives,25.26 trigger curing of epo~y-resins,~'and development of a photocolorimeter for monitoring cure rates.28 role of carbonyl compounds in Photoinitiated Addition Polymerization.-The initiating photopolymerization continues to be an area of prolific research. Laser flash photolysis has provided a valuable insight into both the photophysical and photochemical processes involved in carbonyl-initiated photopolymerizations. For example,,Fouassier and co-workers 29- 3 3 have found that carbonyl-initiated vinyl polymerization proceeds faster in a micellar system2' and an example of this interesting effect is shown in Table 1. Laser flash photolysis3' has shown that Table 1 Activity of photoinitiators with methyl acrylate 4 2 Photoinitiator"

Benzophenone Benzophenone + (triethylamine)b Fluorenone Benzoin Benzoin methyl ether Benzoin isopropyl ether Benzil 4,4'-Bis(dimethylamino)benzophenone Benzil diethyl ketal "1.57 & O . O I m ~ l d r n - x~ 10'.

Conversion at 10 min (%) 0.1 62.7 0.2 15.8 59.8 33.5 0.2 3.9 80.3

b4.64moldm-3 x lo2.

the presence of the micelle enhances the initiation step. The rate of propagation was found to be unaffected by the micelle. The workers have also studied the photoinitiating behaviour of various aromatic carbonyl compounds in THF solution.3'* 32 Using laser flash photolysis they determined the rate constants of several processes. For example, for benzoin the substituted benzyl radical was found to interact more strongly with THF than the unsubstituted benzyl radical, as shown in Scheme 1. The triplet lifetimes of the aromatic carbonyls were also found to be reduced at very low THF concentration^.^^ In another study the same group of workers33 have also studied vinyl polymerization by the well known 22

23

'' " 26

''

'' 29 30

31

32 33

E. Blank, J . Radiat. Curing, 1980, 7 , 15. M. Sierocka, J. Paczkowski, A. Wrzyszczynski, and A. Zakrzewski, Pr. Wydz. Nauk. Tech.,Bvdgoskie TOM', Nauk. Ser. A , 1980, 14, 67. R. Kirchmayr, G. Berner, and G . Rist, Farbe Lack, 1980, 86, 224. W. C. Perkins, J . Radiat. Curing, 1980, 7 , 4. J. Schields, Adhesion, 1977, 1, 165. R. A. Gardiner, Tech, Pap. SOC.Mnnuf. Eng., ( S e r ) Ad., 1979, AD79-917. R . W. Bush, A. D. Ketty, C. R. Morgan, and D. G . Whitt, J . Radiat. Curing, 1980, 7 , 20. A. Merlin and J. P. Fouassier, Polymer, 1980, 21, 1363. D. J . Longnot, A. Merlin, P. Jacques, and J. P. Fouassier, Makromol. Chem., Rapid Commun:, 1980, 1, 687. A. Merlin and J. P. Fouassier, Mukromol. Chemie, 1980, 181, 1307. A. Merlin, D. J. Longnot, and J. P. Fouassier, Polym. Bull., 1980, 2, 847. A. Merlin, D. J. Longnot, and J. P. Fouassier, Pofym. Buff.,1980, 3, 1 .

- -

Polymer Photochemistry 'DMPA ,DMPA

'MPA

'DMPA OCH,

+ *{*

&*

6)

0

kq

@:H3

I

THF

~

OCH,

503

k, > 10'os-l

OCH,

OCH, L + THH F * k, = 2 . 5 ~1041 mol-1s-1 I OCH, Scheme 1

benzophenone-amine system. In contrast to a previous theory 34 these workers find no evidence for an excited charge-transfer complex. Instead they propose the following mechanism involving an amine free radical as the initiating radical (Scheme 2).

Ketyl' +THF' MMA* f BP

\MMA

J

MMA' BP +Amine

Ketyl' + Amine' Scheme 2

MM A'

-1

8

Decker and Fizet3j have developed a novel laser nephelometry method for monitoring continuously by the kinetics of facile photopolymerizations. Figure 1 A

Lamp HPK 125

U.V.

Photodiode BPY 13

Figure 1 Laser-nephelometry device for investigation of photopolymerizations (Reproduced by permission from Makromol. Chem., Rapid Commun.,1980, 1, 637) 34

35

J. B. Guttenplan and S . G. Cohen, Tetrahedron Lett.. 1972, 2163. C. Decker and M. Fizet, Makromol. Chem., Rapid Commun., 1980, 1, 637

Photochemistry

504

shows the device used. The helium-neon laser analysing source emits light that is not absorbed by the monomer or photoinitiator. The laser beam passes through the quartz reaction cell and into a photodiode detector. The U.V. mercury lamp induces polymerization in the cell resulting in a translucent white gel. As the turbidity grows, the analysing laser beam is increasingly absorbed and the transmitted light decreases rapidly. The curves of percent transmittance against time then reflect the kinetics of polymerization, an example of which is shown in Figure 2 for the polymerization of trimethylolpropane triacrylate in propan-2-01.

Time in seconds

Figure 2 Transmission of the laser beam as a function of the irradiation lime in the photopolymerization of trimethylolpropane in propan-2-01 (20g 1 - ') (Reproduced by permission from Makromol. Chem., Rapid Commun., 1980, 1, 637)

Schnabel and co-workers 36 have examined the behaviour of aromatic carbonyl compounds in laser flash photolysis. For l-pheny1-2-hydroxy-2-methyl-propan1one (1) in the absence of a hydrogen-atom donating solvent, or-cleavage to give (2) and (3) was the dominant initiating step. CH,

I HO-C-C-Ph I II H,C

0

(1)

:'" -% HO-C.

I C'H,

(2)

+

C-Ph II 0 (3)

Naito et af.37 have examined the photopolymerization of methyl methacrylate initiated by poly(3-methyl-3-buten-2-one).Again or-cleavage was found to be the dominant initiating step. The photoinitiated polymerization of methyl methacrylate by benzophenone derivatives has been found to depend upon the nature of the substituent, which in turn influences the activity of the sernipinacol 39 36

37

j9

J. Eichler, C. P. Herz, 1. Naito, and W. Schnabel, J . Photochem., 1980, 12, 225. I. Naito, IS. Koga, H. Hashiuchi, and A. Kinoshita, Kobunshi Ronbumhu, 1979, 36, 777. I. 1. Dilung, V. M. Granchak, and V. P. Sherstyok, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim, 12th. 1977, 212. V. M . Granchak, P. A. Kondratenko, V. P. Sherstyok, and I. I. Dilung, Vvsokomol. Soedin., Ser. A . 1980, 22, 1865.

Polymer Photochemistry 505 Essentially electron-donor substituents retarded polymerization, whereas electron-acceptor substituents accelerated the process. In fact, these workers obtained a good correlation between the Hammett cr values of the substituents and the polymerization rate. Remaining with benzophenone, the photopolymerization of 1,3,5-trithianehas been found to be inhibited by amines and also the absence of oxygen," whereas in the hydrogen peroxide-initiated photopolymerization of methyl methacrylate-benzophenone has been found to be a powerful accelera t ~ r .In ~ the l latter study different solvents were found to have different effects on initiation. In solvents giving low conversions, degradative initiator transfer was found to be a dominant process. The search for more efficient carbonyl photoinitiators continues to be an active area of research. Clarke and Shanks 42 have compared the photoinitiating efficiencies of several carbonyl systems using methyl acrylate as monomer, and it is found that benzil diethyl ketal is the most efficient system. Pappas and Lam43 have shown that methylsulphonate derivatives of benzophenone are more efficient photoinitiators of the polymerization of diethylene glycol divinyl ether than benzophenone itself, whereas Gupta et aZ.44 have found that 4,4'-divinylbenzophenone polymer is a better photosensitizer than benzophenone for the cycloaddition of benzo[b]thiophene with ethylene dichloride. Turro and co-workers 4 5 have found that the emulsion polymerization of styrene proceeds faster and to higher conversions when initiated by light in the presence of aromatic carbonyl compounds. Clearly, this work emphasizes the importance of U.V. methods in improving the efficiency of industrial processes. Other workers have examined the influenceof light intensity, temperature, and reaction time on the benzoin methyl ether photoinitiated polymerization of ~tyrene.'~High conversion without a sacrifice in the molecular weight was obtained by operating the reactor at a metastable state. Interestingly, the curing of polyesters by benzil-amine mixtures has been found to be hardly affected by the concentration of the benzil." This work would tend to confirm the mechanism of Fouassier et al.," where the amine radical was found to be the main initiating species. In the photodimerization of omono- and a,o-di-anthrylpolystyrenes, both inter- and intra-molecular excimer formation was found to be important.48 Other studies of intert include the photopolymerization of NN-methylenediacrylamide by anthraquinone-/.?sulphonates in the presence of bisdiazo methyl acrylate by alkoxysubstituted benzophen~nes,~~ and methyl methacrylate by pyromellitic dianhydride and anthracene. O0

41

42 43

44

" 46 47 48

S. Andrzcjewska and A. Zuk, Mater. Kauf. Ogolnopol. Symp. Polim. Siarkowsych, Ist, 1978, 38. P. Gosh, G. Mukhopadhyay, and R. Gosh, Eur. Polym. J., 1980, 16,457. S. R. Clarke and R. A. Shanks, J . Macromol. Sci., Chem., 1980, 14, 69. S. P. Pappas and C. W. Lam, J. Radiat. Curing, 1980, 7 , 2. S. N. Gupta, L. Thijs, and D. C. Neckers, Macromolecules, 1980, 13, 1037. N . J. Turro, M. F. Chow, C. J. Chung, and C. H. Tung, J. Am. Chem. Soc.. 1980, 102, 7391. H. T. Chen, C. N. Kuan, S. Settachayanon, and P. A. Chartier, AIChEJ. 1980, 26, 672. J. Mleziva and V. Cennak, Congr. FATIPEC, 1980, 15th, (1) 360. I. Mita, H. Ushiki, A, Okamoto, and K. Horie, Polym. Prepr.. Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 1045.

49

G. V. Formin and P. I. Mordvintsev, Zh, Fiz. Khim., 1980, 54, 1877. A. Borer, R. Kirchmayr, and G . H. Rist, Magn. Reson. Relat. Phenom., Proc. Congr. AMPERE, 20th. 1979, 167.

E. G. Varisova and N . S. Vshiutseva, Issled. Obl. Khim. Vysokomol. Soedin. Neftekhim, 1977, 73.

506

Photochemistry

Transition-metal carbonyls have been found to exhibit some unusual behaviour with various systems.52.53 In one study 53 the presence of a halogen-donating solvent was found to be essential in the photopolymerization of phenylacetylene. The results of this work are shown in Table 2 where it can be seen that the tungsten carbonyl is particularly effective in carbon tetrachloride. Table 2 Polymerization of phenylacetylene by Group VZA metal carbonyls” No. 1 2 3 4 5 6 7

Catalyst W(CO), Mo(CO), Cr(CO), W(CO), W(CO), W(CO), W(CO),

Solvent CCl, CC1, CCl, Toluene CCl, CCl, CCI,

Zrradn. time, h 1 1 1 1 0 1/2 2

Convn.

%

R”

92.9 7.9 0.0 0.0 0.0 90.7 96.4

76900

78800 76600

“Polymerized at 30°C for 24h after catalyst solutions were irradiated at 30°C: [MI, [Cat] = 1OmM.

=

1.0~,

Clarke and Shanks 54 have examined the influence of sample thickness on the benzoin photoinitiated polymerization of butyl acrylate. They found that as the photoinitiator concentration increases so the extent of polymerization become less susceptible to changes in sample thickness. Grauchak et al. have successfully photopolymerized acrylic monomers in polyamide matrices with aromatic carbony1 compounds. In the photocycloaddition of olefins to poly(4,-vinylbenzophenone) and its copolymers with styrene, the rate of addition was found to be independent of the glass transition temperature suggesting that large-scale molecular motion is unimportant in this photoreaction. 56 The photopolymerization of methyl methacrylate using a quinoline-chlorine charge-transfer complex has been investigated. Bulk polymerization was found to follow normal free-radical kinetics, whereas in solution variable monomer exponents were observed depending on the nature of the solvent. The kinetic nonideality in solution was attributed to retardation and initiator termination via degradative chain-transfer involving solvent-modified initiating complexes and chain radicals. Similar observations were made in the photopolymerization of methyl methacrylate by a dimethylaniline-nitrobenzene complex.5 8 Remaining with methyl methacrylate photopolymerization by N-benzylpyridinium chloride in methylene dichloride is believed to be initiated by a chlorine atom formed from the decomposition of a charge-transfer complex.5 9 The presence of the halogen-

’’ V. A. Padgorodetskaya, Issled 061. Khim. Vysokomol. Soedin. Nefrekhim, 1911, 12. 53 54

55

T. Masuda, Y. Kuwane, K. Yamamoto, and T. Higashimura, Polym. Bull., 1980, 2, 823. S. Clarke and R. A. Shanks, Polym. Photochem., 1981, 1, 103. V. M. Grauchak, V. P. Sherstynk, T. 1. Viktorova, and I. I. Dilung, Tezisy. Dokl. Ukr. Resp. Kauf. Fiz. Khim, 12th. 1971, 212.

56

” 5E

s9

D. A. Holden and J. E. Guillet, J . Polym. Sci.,Polvm. Chem. Ed., 1780, 18, 565. P. Gosh and S. Chakraborty, Makromol. Chem., 1980, 181, 2597. P. Gosh and N. Mukherji, Eur. Pol-vm. J., 1981, 17, 541. K. Tabuchi, H. Okazaki, K. Inoue, T. Okubo, and T. Tanigaki, Niihama Kogyo Koto Semmon Gakko Ciyo, Rikogaku Hen, 1980, 16, 80.

Polymer Photochemistry 507 containing solvent was found to be essential for polymerization. Two independent groups of workers 60*6 1 have postulated the involvement of a charge-transfer complex in the photoinitiated copolymerization of styrene with maleic anhydride. Conversion was found to be a maximum at 405 nm in tetrahydrofuran.60 Complex formation was believed to occur between the maleic anhydride and the solvent in both investigations. Other workers have identified the free-radical species (4)---(6) in the photopolymerization of styrene-maleic anhydride.62 H,C-CH

\ oc,I ,co

0

HOCH~-HC--CH

oc,I ,c'\o 0

HC-CH

I t,.2\ \ ()-C.(-)C-O 0

The photopolymerization of N-vinylcarbazole by perylene-l,4-dicyanobenzene is believed to involve electron transfer.63 Quantum yields were found to be higher in electron-transfer sensitization than in other systems. One study of interest is the photopolymerization of acrylonitrile by nickel chloride-dimethyl formamide and hydrochloric acid. Unfortunately, the role of the acid could not be explained. The role of sulphur-containing compounds in photopolymerization appears to have attracted some interest. Bis(~-methylpyridazinyl)-3,3'-disulphide has been found to initiate the photopolymerization of styrene but inhibits the thermal p ~ l y me r iz atio n .~~ The role of thiyl radicals (PhS -) in photoinitiated polymerization of vinyl monomers by aromatic thio-compounds has been postulated by several workers.65*66 In one study,66 flash photolysis was used to identify the nature of the radical. Sulphur-containing monomers such as 4-methyl-2(viny1thio)thiazole67 and thiocyclanes 6 8 have been photopolymerized and copolymerized with other vinyl monomers. Luca et have devised a mathematical model for the photopolymerization of 2,3-dimethylbutadiene and thiourea. In the cyclic acetal-photosensitized polymerization of styrene and methyl methacrylate, the conversion was found to increase with an increase in the number of cyclic acetal groups in the initiating Asakura et al.71have described in detail the homo- and co-polymerization of P-allyloxypropionaldehydeby direct photoexcitation. Although no mechanism was postulated it was certainly free radical in nature. Triallylidene sorbital (7) has also been found to polymerize by direct photoexcitation by the radical mechanism shown in Scheme 3.72 6o 61

63 64

'' 67 68 69 'O

71

72

M. Raetzsch and G. Schicht, Acta Pol?/m..1980, 31, 419. E. Borsig, D. Hlubocka, and A. Romanov, Acta Pol.vm., 1980, 31, 407. J. Barton, I. Capek, and J. Tino. Makromol. Chem., 1980, 181, 255. N. Kitamura and S. Tazuke, Bull. Chem. Soc., Jpn., 1980, 53. 2594. T. Eda, C. Y. Huang, Y. Matsubara, M. Yoshihara, and T. Maeshima, J . Macromol. Sci., Chem., 1980, 14, 1035. S. Hayama, M. Ikehata, M. Takeishi, and S. Niino Kobunshi Ronbunshu, 1980, 37, 255. 0. Ito and M. Matsuda, Polym. Prepr.. Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 562. H. Ohnishi and T. Otsu, J . Macromol. Sci., Chem., 1980, 14, 1015. A. A. Mochalov, Issled. Obi. Khim. Vysokomol. Soedin. Neftekhirn, 1977, 72. C. h c a , A. Popa, and F. Vitan, Bull. Inst. Politech. Iasi, Sect. 2, Chim. Ing. Chim., 1980, 25, 5 5 . T. Ouchi, N. So, and Y. Kornatsu, J . Macromol. Sci., Chem., 1980, 14, 277. J. I. Asakura, Y. Matsubara, M. Yoshihara, and T. Maeshima, . I Macrornol. . Sci.,Chem., 1980, 14, 803. T. Ouchi and M. Imoto, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20, 670.

Photochemistry

508 H,C-CH-HC-CH-HC-CH, I I I I 0, ,o 0, o , CH CH I I CH=CH, CH=CH (7)

HlC-

I

0,

CH-HC-

o, CH

I

I CH=CH,

I

0,

I 0,

I

/o

CH I CH=CH,

CH-HC-7H2 I I 0,dO

o, CH

I CHLCH,

C I CH=CH,

k i n g - o pcnmg

H,C-CH-HC-CH-HC-CH,’ I I I I I 0, /O 0, / O 0, 40 CH CH C I I I CH=CH, CH=CH, CH=CH,

‘(7)

, Polymer

Scheme 3

At high light intensities, the photopolymerization of methyl methacrylate has been found to deviate from the square-root law.73Radical termination at high light intensities was believed to be dominant. The photopolymerization of propylene oxide by arenediazonium salts has been found to depend markedly on the pretreatment of the monomer. 74 Several workers have observed the production of long-lived radicals in the photoinitiated polymerization of N-methylacrylamides 7 5 and propane- 1,3-diol bis(methacrylogloxyethy1carbonate). 76 In the former study, post-polymerization was observed in dioxan but not in benzene. Other studies of interest include the photoinitiated polymerization of polyionenes bearing pendant (9-anthry1)methyl groups,77 water-soluble polyesters based on sulphonimide oligourethane acrylates with methyl metha~rylate,~’unsaturated groups, polyesters,80and the telomerization of ethylene and dimethylformamide.81 In the photopolymerization of allylic and acrylic monomers, the presence of polythiols was found to enhance the process in the presence of oxygen.82 On a more commercial note, Ohtsuka et aLE3have developed light focusing plastic rods prepared from the photocopolymerization of methyl methacrylate with vinyl

’*

’3 74

T. Y . Yu, L. H . Wang, H. S. Bu, H. S. Li, and Y. L. Zhao, Kao Fen. Tzu Tung Hsun, 1980, 1, 10. T. S. Bal, A. Cox, T. J. Kemp, and J. P. Murphy, Pliotogr. Sci., 1978, 26, 49. H. Tanaka, T. Sato, and T.Otsu, Mcrkromol. Chem., 1980, 181,2421. T. E. Rudnitskaya, 0. Ya. Grinberg, A. A, Dubinskii, A. P. Shvedchikov, B. G . Dzantiev, and Ya. S. Lebedev., Khim. Vw. Energ., 1980, 14, 126. Y. Suzuki and S. Tazuke, Mncromolecules. 1980, 13, 25. J . M . Novnan and R. C. McCorkey, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1978,19,407. A. P. Karnaukh, R. I. Dryagileva, I. A, Pronina, and Yu. I. Spirin, Vvsokomol. Soedin, Ser. B, 1980,

l5

76

’’ ” 79

22, 570. ‘O

81

83

A. V. Shevchuk, V. G . Matyushova, and N. A. Luneva, Plrst. Massey, 1980, 11,46. T. Gascard, B. Dederichs, and A. Sam, Tenside Deterg., 1981, 18, 17. C. R. Morgan and A. D. Ketley, J . Radicrt. Curing, 1980, 7, 10. V. Ohtsuka, Y. Koike, and H. Yamazaki, Appl. Opt., 1981, 20, 280.

Polymer Photochemistry

509

benzoate, whereas Chartier and Chen 84 have developed a system for controlling the initiation and polymerization of vinyl monomers, and Kolek and Hammill 8 5 have prepared u.v.-curable polyesters with good electrical properties. Photopolymerization in the solid state at ambient and cryogenic temperatures has attracted considerable interest. The amphilic diacetylene derivative pentacosa10,12-olignoic acid in the form on multilayers has been investigated by Fouassier et aLE6Interestingly, 3,3-distearyl thiocarboxyamine iodide was found to act as a sensitizer only if it was included into the multilayers by a co-spreading technique. was found The lattice packing of cyclo-octatriaconta-l,3,9,11,17,19,25,27-0ctayne to have a marked effect upon its solid-state photop~lymerization,~~ and a diacetylene derivative has been polymerized as rigid monolayers at a gas-water interface.88 There has been active interest in the low-temperature photopolymerization of diacetylene crystals such as hexa-2,4-diyne- 1,6-diol di-p-toluenesulphonate. These include, e.~.r.~’* optical and kinetic ~tudies.’~From e.s.r. work the structures of the diradical dimer and trimer initiators were established as shown in Scheme 4.’l The photopolymerization of 2,4-heptadecadiynoic acid and phenazine has been studied and monitored by p h o t o c o n d u ~ t i o nElectron .~~ transfer was believed to be important in initiation. Using molecular-orbital structures the photopolymerization of alkadiynes was shown to be allowed and a [2+2]-photocycloaddition process has been used to describe the topochemical polymerization of chiral 9 5 The solid-state polymerization of acrylonitrile has been inpolyrner~.’~. vestigated at cryogenic temperatures using NNN’ZV-tetramethyl-p-phenylenediamine as initiat~r.’~, 97 Surprisingly, efficient polymerization occurred owing to an electron-transfer process. Also of interest is the observation that formaldehyde undergoes photopolymerization at cryogenic temperatures to give polyoxymeth~lene.’~Other studies of interest include a discussion on crystalline-lattice control in photopolymerization,gg polymerization of surfactant polystyrene derivatives in monolayers,”’ copolymerization of 4-(methacryloyloxy)chalcone with NN-dimethylaminoethyl methyacrylate for use as a reverse osmosis membrane,lO’ and the curing of resins onto solid alumina surfaces.lo2

’’

84 85

86 87

88

P. A. Chartier and H. T. Chen, Polym. Eng. Sci., 1980, 20, 1197. R. L. Kolek and J. L. Hammill, J . Radiat. Curing, 1980, 7, 3 . J. P. Fouassier, B. Ticke, and G. Wegner, Isr. J . Chem., 1979, 18, 227. K. C. Yee, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1978, 19, 165. D. R. Day, H. Ringsdorf, and J. B. Lando, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1978, 19, 16.

89

90 91

92 93 94 95

96

” 98

99 loo lo’ lo’

R. Huber and M. Schmoerer, Chem. Phys. Lert., 1980, 72, 10. C. Bubeck, H. Sixl, and W. Neumann, Chem. Phyx., 1980, 48, 269. C. Bubeck, W. Hersel, W. Neumann, H. 5x1, and J. Waldmann, Chem. Phys., 1980, 51, 1 . H. Niederwald, H. Eichele, and M. Schwoerer, Chem. Phys. Lett., 1980, 72, 242. F. Braunschweig and H. Baessler, Ber. Bunsenges. Phys. Chem., 1980,84, 177. J. K. Burdett, J . Am. Chem. SOC.,1980, 102, 5458. L. Addadi, C. D. Cohen, and M. Lahav, Charged React. Polym., 1979, 5, 183. G. N . Gerasimov, S. M . Dolotov, and A. D. Abkin, Radial. Phys. Chem., 1980, 15, 405. S. M. Dolotov, G. N. Gerasimov, and A. D . Abkin, Dokl. Akad. Nauk. SSSR, 1980, 250, 384. S. M. Dolotov, 0. A. Yuzhakov, G. N . Gerasimov, and A. D. Abkin, Vysokomol. Soedin.. Ser. B, 1980, 22, 575. M. Hasegawa, Kobunshi N o Kin0 Sekkei To Sono Oyo Shinpojumi, 1980, 1 . 0. G. Whitten and P. R. Worsham, Org. Coat. PIasr. Chem., 1978,38, 572. W. Karwai, Kobunshi Ronbunshu, 1980, 37, 157. K . Nate and T. Kobayashi, J . Coat. Technol., 1980, 52, 57.

510

Photochemistry

R

-.’ R

* ’

R’

.& .

R

/c.

I R

d R

R R

RNL

R

Schematic representation of the structure of the intermediates. n is the number of monomer units. (a) DR ( 2 d n < 5) e.g. dimer, (b) AC (2 < n < 6) e.g. trimer, (c) MO ( 3 d n < 7) e.g. trimer, (d) DC ( 3 < n < 10) e.g. trimer, (e) C (10 < n < 30) e.g. short pol-vmer, (f) SP (30 < n < 50) e.g. polymer. Scheme 4

Smets and c o - w o r k e r ~ ’have ~ ~ examined in depth direct and radical-induced cationic photopolymerizations. The latter mechanism is interesting and the authors quote as an example the cationic polymerization of butyl vinyl ether in the presence of phenylazotriphenylmethane and a silver salt with a non-nucleophilic anion, such as silver hexafluorophosphate. Scheme 5 shows initial radical production to give a triphenylmethane radical followed by electron transfer with the silver salt to give a complex. Unfortunately, such a free-radical process *03

G. Smets, A. Aerts, and J. Van Erum, P o l p i . J . , 1980, 12, 539.

Polymer Photochemistry

51 1

2 6h + N1 +

Ph-N=N-CPh3

Ph,C

+

Ag+PF,-

+ AgPF,

-CH,-eH

I

Ph,C+PF,-

_+

Ph,k

+

Ag

+ ........ ...... +

-CH,-CH-OC4H9

OC4H9

+

Ag

PF,Scheme 5

although quite efficient, is sensitive to oxygen and therefore commercially unattractive. Crivello and Lam continue to be highly active in the search for new cationic photoinitiators. Some of the most recent include dialkylphenacylsulphonium salts lo4** O 5 and triarylsulphonium salts bearing a thiophenoxysubstituent lo6, lo' with the general structures (8) and (9,' MX, = BF,-, PF,-,

AsF,-, SbF,-, ClO,-, etc.), respectively. In the case of the latter photoinitiators their efficiencies were found to be very much dependent upon the position of substitution of the thiophenoxy-group. This effect is shown in Figure 3 for the polymerization of cyclohexene oxide. lo' The para-substituted derivative gave the highest conversion probably owing to the absence of steric hindrance. In another study lo* the same workers have found that the reactivity of triphenyl sulphonium salts decrease in the order Ph,S+SbF,- 2 Ph,S+AsF,- 2 Ph3S+PF6- 2 Ph,S+BF,- for the photopolymerization of cyclohexene oxide. Ledwith and coworkers t O9 have reported ion-pair dissociation equilibria for iodonium and sulphonium, which are believed to be important for gaining an understanding of their photoinitiation behaviour. Ledwith ' l o has also reported on the use of p,pdimethoxy-#I-phenylactophenoneand di-p-tolyliodonium hexafluorophosphate as an effective initiator for the photopolymerization of THF. Several objections have been raised regarding two earlier papers published by Kennedy and Diem on the photopolymerization of isobutylene by TiCl,. Here an olefin-TiCl, complex was postulated as the initiator. According to Gandini et ai. the paper contains

'' ''

loo lo5

lo'

lo'

'I1 '13

'

J. V. Crivello and J. H. W. Lam, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979,20, 415. J. V. Crivello and J. H. W. Lam, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1021. J. V. Crivello and J. H. W. Lam, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 2677. J. V. Crivello and J. H. W. Lam, J . Polym. Sci.,Polym. Chem. Ed., 1980, 18, 2697. J. V. Crivello and J. H. W. Lam, Org. Coat. Plast. Chem., 1978, 39, 31. A. Ledwith, S. Al-Kass, D. C. Sherrington, and P. Bonner, Polymer, 1981, 22, 143. A. Ledwith, Makromol. Chem., Suppl., 1979, 3, 348. J. P. Kennedy and T. Diem, Polym. Bull., 1978, 1, 29. T. Diem and J. P. Kennedy, J. Macromol. Sci. Chem., 1978, 12, 1359. A. Gandini, H. Cheradame, and P. Sigwalt, Polym. Bull.. 1980, 2, 731.

512

Photochemistry

-i

80

-

70

-

60

0

2

4 0 kred-Tm(mh.)

8

10

Figure 3 Photopolymerization of cyclohexene oxide at 20 "C using 0.021 M diflerent sulphonium salt photoinitiators (Reproduced by permission from J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 2697)

three major discrepancies: (ij the mechanism of TiC1, photolysis was partly inferred; (iij the reaction scheme of the photogenerated cocatalyst is in total conflict with known experience; and (iiij the explanation of photopolymerization in terms of a condensation mechanism is highly questionable. Apparently there has been no rebuttal in the literature from Kennedy and Diem and consequently the reporter can only assume at this juncture that Gandini et al. are correct in their criticisms. Tabata and co-workers have investigated the photodimerization of Nvinylcarbazole in benzonitrile and nitrobenzene solvents. In aerobic benzonitrile the mechanism of initiation was essentially cationic, whereas in anaerobic solution it was a radical process. Using picosecond laser photolysis it was shown that cyclodimerization occurs through a diffusion-controlled encounter collision of the excited singlet state of the vinylcarbazole with an oxygen molecule, producing a vinylcarbazole radical cation and an oxygen radical anion as shown in Scheme 6. The oxygen radical anion is believed to be the initiator. In nitrobenzene, only 'I4

K. Hamanoue, H. Teranishi, M. Okamoto, Y . Furakawa, S. Tagawa, and Y . Tabata, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 91. S. Tagawa and Y . Tabata, Polym. Prepr., Am. Chem. Soc., Div.Polym. Chem., 1979,20, 411.

Polymer Photochemistry

4 ISC

VCZ hv (VCZ*)singlet

513

-

(VCZ*):riplct

(VCZt)solv+ (0,;)solv Scheme 6

radical polyherization

-

dimerization

cationic polymerization took place and was independent of oxygen. In this case a contact charge-transfer complex is believed to be important, giving rise to the charged radical ions shown in Scheme 7. VCZ +PhNO,

-

CT complex -% (VCZ f - - -PhNO, ) Scheme 7

-

(VCZ:

)solv

+ (PhNO,

)solv

Hayashi has investigated in some detail the ionic photopolymerization of styrene monomers. Free ion lifetimes measured by pulse electrical conductivity measurements were found to agree with those calculated from steady-state conductance measurements. Other studies of interest on radical addition polymerization include the photodimerization of polymers containing thymine bases, l 7 diene polymerization by terbium complexes,' l8 polymerization of vinyl acetate, l9 and preparation of light-sensitive polyacrylates.120

'

Photografting.-Photografting of monomers onto cellulose continues to be a topic of considerable activity and industrial importance. Reinhardt and Arthur 21 have produced wrinkle-resistant cotton fabric by photografting N-methylolacrylamide monomer from an aqueous solution onto the fabric (see also reference 147). The efficiency of the process was apparently greater when the cotton-monomer solution was irradiated wet than when it was dry. Herold and Fouassier 122 have grafted methyl methacrylate onto cotton using aromatic carbonyl photoinitiators. These workers found that the presence of THF enhances the percentage photograft through its hydrogen-atom donating properties (Scheme 8).

'

R'+M R"+M R'+THF

---

RM' R'M' RH+THF' R"+THF R'H+THFr THF-M' THF'+M R'+Cell RH +Cell' Cell' +'DMPA 3DMPA i-Cell Cell'+M Cell-M' Scheme 8 'I6

''.' 120

'" 122

K. Hayashi, Polym. J., 1980, 12, 583. Y. Kita, Y. Inaki, and K. Takemoto, J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 427. S. R. Rafikov, G. A. Tolstikov, B. Yu. Monakov, N. A. Vakhrnsheva, D. D. Afonichev, and V. P. Kazakov, Dokl. Akad. Nauk, SSSR, 1980,251,919. C . Simionescu and M. Bezdadea, Bul. Inst. Politech. Iasi., Sect. 2, Chim. Ing. Chim., 1980, 25, 93. Z. K, Brzozonski, B. Jozwik, and J. Kielkiewiez, J. Appl. Polym. Sci., Appl. Pofyrn. Syrnp., 1979, 35, 377.

R. M. Reinhardt and J. C. Arthur, Tex. Res. J.,1980,50,261; R.M. Reinhardt and J. A. Harris, Tex. Res. J., 1980, 50, 139. R. Herold and J. P. Fouassier, Angew. Makromol. Chem., 1980,86, 123.

Photochemistry

514

Guthrie and co-workers 123 have used an anthraquinone dye to photosensitize the grafting of N-vinyl-2-pyrrolidone onto cotton. The dye (10) sensitizes in two

ways depending upon the pH of the system. At low pH, where protonation would occur, hydrogen-atom abstraction would occur through the quinone group of the dye, whereas at high pH hydrogen abstraction would occur through the vinyl group resulting not only in grafting but also homopolymerization. Takahashi et a1.'24-126have reported on the photografting of vinyl monomers onto preoxidized cellulose. In one study'26 the rate of grafting decreased in the order methyl acrylate > methyl methacrylate > vinyl acetate > acrylonitrile > styrene. Flame-resistant textiles have been made by a continuous photografting process using a vinyl phosphonate.' 27 The photografting of methyl methacrylate onto nylon-6 has been found to occur only in the presence of fructose.'28 Other sugars do not appear to have been investigated and no mechanism was proposed. Also, the thermal stability of the polymer was considerably reduced by the grafting process. Other studies of interest include the photografting of vinyl acetate onto poly(methy1 methacrylate), 29 methacrylic acid onto high-density polyethylene,' 30 vinyl monomers onto polypropylene, l 3 and acrylic acid onto poly(viny1 alcohol) and starches. 3 2 Bellobono et al. have successfully photografted acrylated azo dyes onto polyamide and polypropylene fibres, whereas Guthrie and co-workers 34 have developed a novel water-soluble grafting photosensitizer, 4-(sulphomethy1)benzil sodium salt.

'

'

'

'

Photocrosslinking.-A considerable number of research papers have appeared in this area. One article of special interest by Damen and Neckers 1 3 5 describes a series of styrene-divinylbenzene copolymers, which not only recognize their origins, but which are also capable of guiding a subsequent photochemical 123 124

125

126 12' 12* 129

130

131 13* 133

134

F. I. Abdel-Hay, P. Barker, and J. T. Guthrie, Makromof. Chem., 1980, 181, 2063. A. Takahashi, Y. Sugahara, and S. Takahashi, Kogakuin, Daigaku Kenkyu Hokoku, 1980,48,46. A. Takahashi and S. Takahashi, Seni, Gakkaishi, 1980,36, T397. A. Takahashi and S. Takahashi, Kobunshi Ronbunshu, 1980, 37, 151. J. A. Harris, E. J. Keating, and W. R. Goynes, J . Appl. Polym. Sci., 1980, 25, 2295. A. K. Mukherjee and H. R. God, Man-Made Text., India, 1980, 23, 301. Y. P. Shim, J. S. Kim, and J. K. Lee, Polfimo, 1980, 4, 138. M. Mikhailov and I. Ibeva, God. Vissh. Khim-Tekhnol. Inst. Burgas. Bulg., 1979, 13, 47. C. H. Ang, J. L. Garnett, R. Levot, A. M. Long, andT. N. Yen, J . Polym. Sci., Polym. Lett. Ed, 1980, 18, 47 1 . D. Trimnell and E. I. Stout, J . Appf. Polym. Sci., 1980, 25, 2431. I. R. Bellobono, T. Tolusso, E. Selli, and A. Berlin, J . Appl. Polym. Sci., 1981, 26, 619. P. Barker, J. T. Guthrie, A. Godfrey, and P. N. Green, J. Appl. Polym. Sci.. 1981, 26, 521. J. Damen and D. C. Neckers, J . Am. Chem. Soc., 1980, 102, 3265.

Polymer Photochemistry

515

reaction in a stereochemicaldirection. This is believed to be the first ever example of a 'photochemical template effect'. These authors have converted stereoisomeric a-truxillic (1 l), fl-truxinic (12), and 6-truxinic acids (13) into polymerizable monomers. These were than copolymerized with an excess of styrene and divinylbenzene to form highly crosslinked polymers. Removal of the truxillate or truxinate esters by acidic hydrolysis in methanol leaves two benzyl alcohol groups in the cavity (Table 3). Treatment of the hydrolysed polymers (14) with an excess of trans-cinnamoyl chloride yielded the polymer (15) as shown in Scheme 9. Table 3 Synthesis of memory-containing viny2 polymers 35 Monomer composition in mol % Polymer @ a-(14) @ $-( 14) @ - (1 4)

X

Template monomer, X bis(vinylbenzy1)-a-truxillate

5.0 5.0 4.8

bis(vinylbenzyl)-B-truxin~te bis(vinylbenzyl)-d-truxinate

Styrene 29.8 30.0 45.1

DVB

ZHydrolysis 30 50

65.2

65.0 50.1

30

Hydrolysis of the template molecule to completion. No additional truxillate or truxinate ester could be subsequently removed.

+

$'""

phxH H

H

p x 02CHH

COCl

= a$, or 6)

H

x =a

- 7 z

4\ 0 0

Ph

b3o=ct5

0 0

A0

\ /

0

+

I

db

b

Ph

0 0

0 0

I

Ph

4

\

HCI-CH,OH

HOOC

[Jj + COOH (1 1)

\\

COOH COOH

Ph

0 Ph

Ph

IHCI-CH,OH

6" + (11)

H O W Ph Ph

Ph

(12)

(13)

Scheme 9

4

516

Photochemistry

Irradiation of these polymers in degassed benzene produced mixtures of photodimers that would be released from the polymer by acid hydrolysis. Decout et a/. 36 - 38 have prepared a wide range of photocrosslinkable vinyl polymers containing pyridine N-oxide and aromatic N-oxide groups. The actual mechanism is not clear, but is believed to involve coupling of radicals, supposedly formed by hydrogen abstraction by the atomic oxygen or oxygen radical anion generated in the film by photochemical cleavage of the N-oxide bond. In another article,13' the same workers found the order of photosensitivity of the N-oxide polymers decreases in the order 4-vinylpyridine N-oxide > 4-vinylquinoline Noxide > p-NN-dimethylaminostyrene N-oxide > 2-methyl-5-vinylpyridine Noxide. Other photocrosslinkable polymers developed by these workers include copolymers of methyl methacrylate with cyanocinnamylydene-pyridinium groups '40 and pyridinium dicyanomethylide groups. 41 Photocrosslinkable elastomers have been developed by previously grafting photosensitizer molecules onto the polymer backbone. 142 Modification was performed by a Friedel-Crafts reaction and the subsequent crosslinking reaction was found to be extremely efficient even at low concentrations of grafting. In the preparation of photocrosslinkable polymers bearing propargyl and ally1 groups the presence of a hydroxygroup in the para-position of styrene was found to be essential for stabilizing the polymer towards oxidation. 143, 144 The photocrosslinking of poly(4-bromoacetylstyrene) in the solid phase has been found to be enhanced by the presence of divinylbenzene, ethylene glycol diacrylate, and trimethylolpropane tria ~ r y 1 a t e . l14'~ ~Wrinkle-resistant . cotton has been made by Reinhardt et al.14' by polymerizing with poly(glycidy1 methacrylate) followed by crosslinking (see also reference 121). Poly(viny1 alcohol) has been photocrosslinked with terephthalic aldehyde according to Scheme 10.148 The photocrosslinking of poly(viny1 alcohol) cinnamate has been associated with cycloaddition between polymer-bound cinnamoyl groups.'49 Only half of the reactive sites, however, undergo this reaction; the rest remain intact. Apparently site geometry is believed to control reactivity. In a study of the photosensitized polymerization of cyclic acetals,' 5 0 a terpolymer of vinyl formal-vinyl acetate-vinyl alcohol underwent decomposition, while poly(Zviny1-1,3-dioxolane) and poly(2-vinyl-4-hydroxy methyl- 1,3dioxolane) were crosslinked (Scheme 1 1).

'

'

136

13' 13' '39

140 141

143 144

145

14' 14'

150

.I.L. Decout, A. L. Combier, and C. Loucheux, J . Pol-vm. Sci., Polym. Chem. Ed., 1980, 18, 2371. J . L. Decout, A. L. Combier, and C. Loucheux, J . Pol-vm. Sci., Pol-vm. Chem. Ed., 1980, 18, 2391. J . L. Decout, A. L. Combier, and C. Loucheux, Photogr. Sci. Eng., 1980, 24, 255.

J. L. Decout, A. L. Combier, and C. Loucheux, Photogr. Sci.Eng., 1979, 23, 309. C. Roucoux, C. Loucheux, and A. L. Combier, J. Appl. Polym. Sci., 1981, 26, 1221. J. J. Cottart, C. Loucheux, and A. L. Combier, J . Appl. Polym. Sci.,1981, 26, 1233. J. A. Bouquet, J. B. Donnet, J. Faure, J. P. Foudssier, B. Haidar, and A. Vidal, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 765. M . Kato and Y. Yoneshige, Kobunshi Ronbunshu, 1980, 37, 243. M. Kato and Y. Yoneshige, J . Radial. Curing, 1980, 7 , 23. M. Tsunooka, H. Sasaki, and M. Tanaka, Kobunshi Ronbunshu, 1980,37, 249. M . Tsunooka, H. Sasaki, and M. Tanaka, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 407. R. M . Reinhardt, J. C. Arthur, and L. L. Muller, J. Appl. Polym. Sci.,1980, 25, 933. J. Poldvka, M. Uker, L. Lapcik, M. Ceppan, J. Valasck, and B. Havlinova, Chem. Zvesti, 1980, 34, 780. P. L. Egerton, E. Pitts, and A. Reiser, Macromolecules, 1981, 14, 95. T. Ouchi, C. Sato, and T. Yamamoto, J . Macromol. Sci., Chem., 1980, 14, 265.

Polymer Photochemistry

bI

H-C-0'

6+

I 6/.o,

H"

I

I

CH2-CH-CH2-CH-

I

CH2-CH-CH2-CHI

Scheme 10

-CH2-CHI

-CH2-CHI

o/ceo I I H2C-CHR

___, -hv H-

O O L O

I I H2C-CHR

-CH2-CHI 4% 0 OCH,CHR

-CH2-CHI C /\ *CH2CHR0 0 k i n g

Network Polymer

Scheme 11

H

Photochemistry

518

Several studies have appeared on the photocrosslinking of polymers by diazides. l 5 - 5 3 These include polyphenylenes and poly(phenylquinoxoa1ines).5 2 In the former case photocrosslinking occurred in the absence of oxygen, whereas in the second case photocrosslinking was inhibited by oxygen owing to the formation of nitrenes, which underwent reaction with oxygen to form peroxyradicals. These peroxy-radicals apparently inhibited the crosslinking. Benzophene has been found to be ineffective in the photocrosslinking of certain types of polyester resins, 5 4 whereas an oligo-carbonate methacrylate of xylitol has been found to be highly suitable for the preparation of resins of high photosensitivity.lSs Pan and Morawetz lS6 have examined the rate constants for the acylation of aromatic amine groups in polymers dispersed by crosslinking, whereas Negishi et ~ 1 . ' ~have ' studied the influence of molecular motion on the photocrosslinking of poly(alky1 methacrylate)-aromatic bisazide systems. In the photocrosslinking of a copolymer of tri-n-butylstannyl methacrylate with maleic anhydride a supermolecular transformation involving anhydride and organotin segments was observed,' 5 8 whereas photodimerization has been observed in the photopolymerization of butadiene monolayers.'59 Crivello and Lam and Watt 161 have studied the photocrosslinking of epoxy-resin systems. In the former study cationic photoinitiators were found to be very effective. Many studies have appeared dealing with the properties of crosslinked polymer systems. These include adhesion of epoxy-acrylates onto tin-plate, 6 2 adhesion of isocyanate and epoxy-resin coatings,163adhesion of butadiene-acrylate rubbers onto metals, glass, and ceramics,164 adhesion of acrylic, thiol, and polyester resins to aluminium bodies,'65 and the mechanical and physical properties of photocrosslinkable poly(viny1 cinnamate), vinyl-divinyl copolymers,168 polythiols,' 6 9 acrylates, epoxies, and thiols,' 7 0 epoxy resins,"' polyesters on wood,' 7 2

''

'

151

15'

.

153

154 155

15' Is'

159

I6l 162 164

l'' I"

16' 169

V. M. Trenshnikov, N. V. Frolova, A. V. Oleinik, and Yn. D. Semehikov, Fiz.-Khim. Osnovy. Sinteza Pererab. Polim. (Gorkii). 1979, 4, 76. V. M . Trenshnikov, T. V. Kudoyavtseva, A. V. Oleinik, V. A. Sergaev, and Yn. A. Chernomordik, Vysokomol. Soedin., Ser. A , 1980, 22, 830. V. M. Trenshnikov, N. V. Frolova, N. V. Karayakin, and A. V. Oleinik, Vysokomol. Soedin., Ser. A , 1980. 22, 1443. V. Cermak and J. Mleziva, Poiimerz, 1979, 24, 401. E. Keitners, R. Pernikis, N. Veinberg, I. Zaks, and V. P. Karlivans, Latv. PSR Zinat. Akad. Vestis. Khim. Ser., 1979, 5 , 553. S. S. Pen and H. Morawetz, Macromolecules, 1980, 13, 1157. N. Negishi, T. Suzuki, M. Momiyama, and I. Shinohara, Kobunshi Ronbunshu, 1980, 37, 549. Z. M. Rzaev, A. T. Aliev, S. Z. Rizaeva, S. G. Mamedova, M. R. Kiselev, and U. Kh. Agaew, Vysokomol. Soedin., Ser. B, 1980, 22, 831. A. Barraud, C. Rosilio, and A. Ruaudel-Teixier, Polym. Prepr., Am. Chem. SOC.,Div.Polym. Chem., 1978, 19, 179. J. V. Crivello and J. H. W. Lam, Am. Chem. SOC., Symp. Ser., 1979, 114, 1. W. R. Watt, Am. Chem. SOC.,Symp. Ser., 1979, 114, 17. A. Neerbes, C. A. M. Hoefs, and E. A. Giezen, Congn. FATIPEC, 1980, 15th (I), 1-319. A. Noomen, Congn. FATIPEC, 1980, 15th (I), 1-346. V. V. Kadykov and D. A. Kochkin, Kuuch Rezinu, 1980, 11, 59. G. M. Lucas, A. Patsis, and D. A. Bolon, J. Radiat. Curing, 1980, 7, 4. M. Koshiba, T. Yamaoka, and T. Tsunoda, Kobunshi Ronbunshu, 1980, 37, 227. T. Yamaoka, J. Rudiat. Curing, 1980, 7, 4. M. M. Micko and L. Paszner, J . Rudiat. Curing, 1980, 7, 1. H. Kanehiro and T. Hanyuda, Shikizai Kyokaishi, 1980, 53, 140. D. A. Bolon, G. M. Lucas, D. R. Olson, and K. K. Webb, J. Appl. Polym. Sci., 1980, 25, 543. Y. Suzuki, T. Fujimoto, S.Tsunoda, and K. Shibayama, J. Macromol. Sci.,Phys., 1980, 17, 187. E. M. Garyachaya and V. F. Kashan, Izv. Vyssh. Uchebn. Zuved. Lesn. Zh., 1980, 4, 71.

Polymer Photochemistry

519

and acrylourethanes.173Barrett 174 has described the use of a number of methods for measuring the degree of cure of photopolymers. Other studies of interest include the photocrosslinking of urea resins,175polyesters,176paint films,’ 77 epoxy resins,’ 78 i~ocyanates,”~ooligoester rnaleates,l8O and substituted methacrylates. 81 3 Optical and Luminescence Properties Several interesting review articles have appeared by authorities in the field. de Schryver 8 2 has discussed general photophysical processes in polymers including photopolymerization, and Schnabel 8 3 has reviewed energy-migration processes. Ciardelli et have reviewed optically active polymers and Prabhakarran 18’ has discussed model materials for photo-orthotropic-elasticity.Stress analysis of composites through photo-anisotropic elasticity has been examined by Jacob. 186 Several research papers have appeared on optically active polymers. 18’- lg2 Chiellini et ul.187i18* have prepared optically active copolymers of N-vinylcarbazole with menthyl acrylate-methacrylate and menthyl acrylate-methacrylate with spaced carbazole monomers. Farina has also prepared optically active polymers by inclusion polymerization. Other optically active polymers that have been prepared include polyethylenimine containing L-proline and thymine 191 and copolymers of 9-vinylcarbaxole and menthyl vinyl ether.’ 9 2 Labsky et al.lg3have studied the photochromic behaviour of spiropyrans. For example, 1’,3‘,3’-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2’-indoline) undergoes the configurational change shown in Scheme 12.

’

Scheme 12 173 174 17s

176 177 178 179

180

181

182

183 184

185

186 187 188 1 UY

I 90 191

192 I93

J. R. McDowell, Radiat. Phys. Chem., 1979, 14, 883. J. L. Barrettt, J. Radiat. Curing, 1979, 6, 20. V. V. Panov, Zb. Ref. Semin. Prokroky Vyrobe Ponziti Lepide Drevopriem, 1979, 4, 83. R. L. Kolek and J. L. Hammill, Plast. Compd., 1979, 2, 52. A. C. J. Van Oosterhaut, Double Liaison-Chim. Paint, 1980, 21, 135. W. R. Watt, Org. Coat. Plast. Chem., 1978, 39, 36. V. G. Matyushova, A. V. Shevehuk, P. V. Datsenko, and S . L. Melnikova, Vysokomol. Soedin., Ser. A , 1980, 22, 1233. A. S. Rat, A. E. Chermyan, and V. D. Gerber, h k o k r a s . Mater. Ikh. Primen, 1980, 3, 27. J. C. Dubois and A. Eranian, Plast. Electron Microelectron (J. Etud. Group. Primot. Connaiss Plast.) , 1978, 187. F. C. de Schryver, Makromol. Chem., Suppl., 1979, 3, 85. W. Schnabel, Pure Appl. Chem., 1979,51, 2373. F. Ciardelli, E. Chiellini, and C. Carlini, in ‘Optically Active Polymers’, Vol. 5 of Charged and Reactive Polymers, ed. E. Selegny, D. Reidel, Boston, 1979, p. 83. R. Prabhakaran, Fibre Sci. Technol., 1980, 13, 1. K. A. Jacob, J. Ind. Inst. Sci., 1980, 62, 129. E. Chiellini, R. Solaro, G. Galli, and A. Ledwith, Macromolecules, 1980, 13, 1654. E. Chiellini, R. Solaro, F. Ciardelli, G. Galli, and A. Ledwith, Polym. Bull., 1980, 2, 577. C. G . Overberger and Y . Morishima, J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 1433. M. Farina, G. D. Silvestro, and P’. Sozzani, Makromol. Chem., Rapid Commun., 1981, 2, 51. C. G. Overberger and Y . Morishima, J. Polym. Sci.,Polym. Chem. Ed., 1980, 18, 1433. E. Chiellini, R. Solaro, A. Ledwith, and G. Cali, Eur. Polym. J., 1980, 16, 875. J. Labsky, F. Mikes, and J. Kalal, Polym. Bull., 1980, 2, 785.

520

Photochemistry

Photoelectron spectra of molecularly doped polyacetylenes have been examined,194and the thermal degradation of PTFE has been studied by the same technique. The spectroscopic properties of poly( 1,6-di-p-toluene sulphonyloxy2,6hexadiyne) have been examined in the solid state and solution.196The polymer chains were found to exist in two forms; a quasicrystalline form with properties close to those of a single crystal and a chain-extended-form occurring in solution and colloidal suspension. Chapoy and co-workers 19' have examined the spatial disposition of a probe molecule in uniaxially orientated poly(N-vinylcarbazole) by dichroic absorption. They found that the visible dichroic absorption of the probe was related only to the amorphous regions of the polymer. Surprisingly, the probe was found to align itself perpendicularly to the stretching direction. Of particular interest are a few articles by Nuyken and Talskylg8 and Allen and coworkers 99-2oo on the use of u.v.-visible derivative spectroscopy for analysing polymer films. This technique has been shown to have several advantages over normal zero-order spectroscopy, particularly for resolving the absorptions due to mixtures of impurities or additives. An example of this outstanding effect is shown in Figure 4 for polyethylene made using an aromatic peroxide. All the impurity chromophores are seen to be clearly resolved. The conformation of polypeptides Absorbance (----I

2nd Derivative (-)

2.0

1.o

0.5

0.0 Wavelength (nm)

u.v.-visible absorption Figure 4 Normal (zero) (- -- -) and second-order derivative (-) spectra of low-density polyethylene film made using an aromatic peroxide (100 pm thick) (Reproduced by permission from Chem. Ind. (London), 198 1, 28 1) H. R . Thomas, W. R. Salaneck, C. B. Duke, E. W. Plummer, A. J. Heeger, and A. G. MacDiarmid, Polymer, 1980, 21, 1238. 195 D. Betteridge, N. R. Shoko, M. E. A. Cudby. and D . G. M. Wood, Polymer, 1980, 21, 1309. ' 9 6 D. Bloor, D . N. Batchelder, J. Ando, R. T. Read, and R. J. Young, J. Poivm. Sci., Polvm. Phys. Ed., 1981, 19, 321. IY7 L. L. Chapoy, R. K. Sethi, P. R. Sorensen, and K. H. Rasmussen, Polym. Photochem., 1981, 1, 131. 19' 0. Nuyken and G. Talsky, Poldvm.Bull., 1980, 2, 719. 19' N . S. Allen, Polq'm. Pliotocltem., 1981. 1, 43. N. S. Allen, K. 0.Fatinikun, and T. J. Henman, Chem. fnd. (London), 1981, 119. 19'

Polymer Photochemistry

52 1

has been studied by circular dichroism,201 and photochromism in polymers has been related to the free-volume theory.202 The luminescence properties of polymers continue to be widely used for investigating degradation processes. Stuckey and Roberts 203 have examined the luminescence and photo-oxidation properties of copolymers of poly(ethy1ene terephthalate+V-sulphonyl dibenzoate) yarns. They found that the presence of the sulphonyl linkages sensitize photo-oxidation of the polyester. The luminescence studies ruled out an energy-transfer process. Dellinger and Roberts '04 report a similar study on copolymers of butylene terephthalate and oxytetramethylene terephthalate; but in this case they concluded that singlet oxygen generation could be important owing to the long-lived nature of the triplet terephthalate chromophores. However, the mechanism was highly speculative and completely lacked any experimental evidence. Davidson and Roberts 2 0 5 have classified the luminescence characteristics of a wide range of bromine-containing fire-retardants, and Selwyn and Scaiano '06 have characterized the triplet state of pol y @-methoxyacry lophenone). The chemi- and thermo-luminescence of polymers have also been widely investigated as an analytical probe for degradative and oxidative processes. The chemiluminescence of poly(viny1 methyl ether) in the absence of oxygen has been associated with the decomposition of surface hydroperoxide groups. 2 0 7 Oxyluminescence has been used to study polymer composition.208 It was found that the spectra of the block copolymers of styrene, polybutadiene, and their copolymers resembled that of the polybutadiene phase (Figure 5). It was suggested that the surface composition of the copolymer resembles that of polybutadiene. The oxyluminescence of nylon-6,6 has been associated with non-stationary alkyl peroxy radicals in the polymer '09 whereas the thermoluminescence of irradiated aliphatic oligesters has been associated with two phenomena, viz, recombination of acyl radicals and recombination of an ester cation with trapped electrons.210 There appears to be some conflict in the literature regarding the origin of thermally stimulated current in anionic polystyrene. Neumann and Macknight 2 1 have associated it with a simple viscosity effect unlike other workers who have associated it with some molecular origin. 2 1 The activation energy of polymer mobility has been measured using radio-thermoluminescence and a correlation has been found between radio-thermoluminescence intensity and gel fraction in low density polyethylene.2l4 The chemiluminescence of stressed polymers has

'O'

'03 '04 '05

'06 '07

'08 '09 'lo

'I1 'I' '13

A. Ueno, J. Anzai, K. Takahashi, and T. Osa, Kobunshi Ronbunshu, 1980,37, 281. C. D. Eisenbach, Ber. Bunsenges. Phys. Chem., 1980,84, 680. W. C. Stuckey and C. W. Roberts, J . Appl. Polym. Sci., 1981,26, 701. J. A. Dellinger and C. W. Roberts, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 3129. T. E. Davidson and C. W. Roberts, J. Appl. Polym. Sci., 1980, 25, 2439. J. C. Selwyn and J. C. Scaiano, Polymer, 1980, 21, 1365. K. Naito and T. W. Kwei, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1635. K. Naito and T. W. Kwei, Macromolecules, 1980, 13, 1018. G. A. George and S. Z. Riddell, J . Macromol. Sci., Chem., 1980, 14, 161. M. Tsumura, S. Takahashi, N . Omi, and Y. Hama, Radiat. Phys. Chem., 1980, 16, 67. R. M. Neumann and W. J. MacKnight, J . Polym. Sci., Pol-vm. Phys. Ed., 1981, 19, 369. G. Lacabanne, P. Goyand, and R. F. Boyer, J. Polym. Sci., Pol.vm. Phys. Ed., 1981, 19, 369. V. A. Aulov and N. F. Bakeev, Dokl. Akad. Nauk. SSR, 1980,255, 1400. I. Mikhaleevd and S. Jipa, Radiochem. Radioanal. Lett., 1980, 43, 19.

522

Photochemistry I 06 0

POLYBUTADIENE

105

104

In V

Io3

102

Figure 5 Oxyluminescence of polystyrene, polybutadiene, and their copolymers. Ordinate, counts per second (Reproduced by permission from Macromolecules, 1980, 13, 1018).

’

been used to elucidate the mechanochemical contribution to polymer ageing,2 whereas other studies have dealt with carrier traps in crystalline polymers,216 effect of environment on thermoluminescence,2l 7 electroluminescence of poly(viny1 chloride),21 and triboluminescence of poly(methy1 methacrylate) in laser irradiati~n.~”The photoconductivity of dyed nylon films has been investigated using a transverse field The peak photocurrent was found to be proportional to the actual power of the light quanta absorbed. Polymer photochemistry has now moved into the solar energy field involving water photolysis. Japanese workers 2 2 1 - 2 2 4 have discovered that certain ruthenium trisbipyridyl complexes with viologen-containing polymers have the ability to generate molecular hydrogen. Electron migration along the polymer chain is believed to be an important process in the mechanism. The photophysics and photochemistry of polymers and doped polymers continue to be widely investigated by luminescence spectroscopy. Intermolecular energy-transfer processes and their importance in various photochemical applications such as a photopolymerization, polymer mobility, and photostabilization D. L. Fanter and R. L. Levy, Org. Coat. Plast. Chem., 1978, 39, 599. M . Ieda, Y. Suzuoki, and T. Mizutani, Conf. Rec. IEEE Int. Symp. Elect. Insul., 1980, 158. ’I7 D. L. Fanter, R. L. Levy, and K. 0. Lippold, Org. Coat. Plast. Chem., 1978, 39, 6 0 3 . ‘IU P. Cracium. An. Univ., Timisoara,. Ser. Stiite Fiz. Chem., 1979, 17, 15. ’Iy N. P. Norikov, Ukr. Fiz. Zh., 1980, 25, 1956. 2 2 0 D. B. Freeston. C. H. Nicholls, and M. T. Pailthorpe, Polym. Photochem., 1981, 1, 85. 2 2 1 T. Nishyima, T. Nagamura, and T. Matsuo, J . Polym. Sci.. Polym. Lett. Ed., 1981, 19, 65. 22’ H. Kamogawa, T.Rui, and M. Navasawd, Chem. Lett., 1980, 9, 1145. 2 2 3 T. Matsuo, T. Sakamoto, and T. Nishyima, Kokagaku Toronkai Koen Yoshishu, 1979, 98. 224 T. Shimizu and K. Fukni. Koenshu-Kvoro Daigaku Nippon, Kagaku Seni Kenkvrusho, 1979,36, 101. 215

’’‘

Polymer Photochemistry

523

have been reviewed by Owen.225Holden and Guillet 226 have reviewed the use of luminescence for studying polymer structure and mobility. Excimer formation in polymers continues to be an important area of study. Ledwith and co-workers 2 2 7 have made an important observation that carbazole-containing polymers do not exhibit excimer formation unless the carbazole units are linked to the molecular backbone. The migration of singlet and triplet excitons in vinylcarbazole polymers has been shown to have a strong influence on both their luminescence properties and photochemical reactions.228 In copolymers of N-vinylcarbazole and 1vinylnapthalene, monomer, excimer, and exciplex emissions were observed. 229 Ledwith and co-workers 230 have studied in some depth the emission properties of a range of different poly(N-ethyl-vinylcarbazole) polymers. Interestingly, poly(Nethyl-3-vinylcarbazole) was found to exhibit a much higher excimer-to-monomer fluorescence than the 2- and 4-substituted isomers owing to its higher isotactic content. A similar observation was made by G ~ i l l e tand ~ ~co-workers on naphthyl ester polymers and copolymers with methyl acrylate and methacrylate. In this case, intramolecular excimer fluorescence was found to be greater in the more flexible polyacrylates. In butyl-substituted vinylnapthalene polymers it is interesting to note that excimer formation was significantly suppressed by the steric effect of the butyl According to de Schryver and c o - w ~ r k e r sa, simple ~~~ kinetic scheme based on intermolecular excimer formation is not sufficient to describe the kinetics of excimer formation of polymers in solution. Using poly(2vinylnapthalene) the decay of the excimer fluorescence suggests the presence of more than one stabilized excited-state complex. Liao and Morawetz 234 have examined excimer formation from dichromophoric residues situated in poly(ethy1ene oxide). Apparently the activation energy for excimer formation was found to be the same in the polymer as in low molecular weight analogues. Thus, crankshaft-type motions in the polymer would appear to offer no hindrance to excimer formation. Excimer formation in poly(wmethy1styrene)has been found to be higher than in polystyrene,235but differences in excimer formation in isotactic and atactic polystyrenes were found to be variable.236In the latter study, excimer formation was found to be intimately related to the exciton diffusion length in the polymer chain. Temperature effects on excimer formation in polystyrenes and polysiloxanes have Seen studied. 2 3 7 Although low temperatures favour excimer formation, high temperatures favour their dissociation. Steric effects were found E. D. Owen, in ‘Developments in Polymer Photochemistry’, ed. N . S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1 , Chap. 1, p. 1. 2 2 6 D. A. Holden and J. E. Guillet, in ‘Developments in Polymer Photochemistry’, ed. N . S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 2, p. 27. 2 2 7 A. Ledwith, N . J. Rowley, and S. M. Walker, Polymer, 1981, 22, 435. 2 2 8 A. N. Faidysh, V. V. Slobodyanik, and V. N. Yashuk, J . Lumin., 1979, 21, 85. 2 2 9 W. R. Cabaness, Y. K. Cheng, and R. Ganzalez, Pol-vm. Prepr., Am. Chem. Soc., Div. Po17vm.Chem., 1978, 19, 561. 230 M. Keyanpour-Rad, A. Ledwith, and G . E. Johnson, Macromolecules, 1980, 13, 222. 231 L. M. Aubry, D. A. Holden, Y. Merle, and J. E. Guillet, Macromolecules, 1980, 13, 1138. 2 3 2 T. Nakahira, T. Sakuma, S. Iwabuchi, and K. Kojima, Makromol. Chem., Rapid Commun., 1980,1, 413. 2 3 3 K. Demeyer, M. Van Der Auwerner, L. Aerts, and F. C. de Schryver, J . Chim. Phys., 1980, 77, 6. ”’T. P. Liao and H. Morawetz, Macromolecules, 1980, 13, 1338. 23’ L. Bokobza and L. Monnerie, Polvmer, 1981, 22, 235. 236 T. Ishii, T. Handa, and S. Matsunago, J . Polym. Sci., Polym. Phys. Ed., 1979, 17, 811. 237 S. K. Wu, Y. C. Jiang, and J. F. Rabek, Pol.vm. Bull., 1980, 3, 319. 225

Photochemistry

524

to be important in phenyl-substituted methacrylate polymers. 238*239 Increasing the number of phenyl groups in the side chain was found to induce excimer formation. The results were interpreted in terms of excimer formation between non-nearest neighbours. Pyrene-excimer formation has been used as a probe to study terminally-substituted p ~ l y s t y r e n e . ~The ~ ' corrected value for the rate constant for end-to-end cyclization was found to depend upon the degree of polymerization of the polymer. Excimer formation in poly(2-vinylnaphthalene) Both has also been found to depend upon the molecular weight of the p01ymer.~~' singlet and triplet excimers were formed with increasing molecular weight. Polymers containing pendant 3-pyrenylmethyl groups also give excimer emision,^^^ and Nishijima and Yamamoto 243 discuss excimer formation in various polymerxopolymer systems. Polymer-blend compatibility has been investigated using excimer emission for polystyrenes and poly(alky1 phenyl ethers) 244 and aromatic vinyl polymers with poly(alky1 met ha cry late^).^^' Time-resolved emission spectroscopy has provided valuable information on the nature of excited states in polymers. Two distinct types of excimers have been observed in pol y(N-vinylcarbazole) using picosecond time-resolved fluore ~ c e n c eThe . ~ ~sandwich-type ~ excimer emitting at 420 nm was formed in several nanoseconds, whereas a second excimer emitting at 375nm was formed immediately after a 10ps electron pulse. (Scheme 13). Similar observations were also

\i

(-M-M-)

'I,

J\

(375nm)

(-M-M-)+ hv,, (-M-M-) (420nm) Scheme 13 +Main pathway, -- -+ minor pathway, JIMF) other energy-loss processes, (-M-M-): polyvinylcarbazole (PVCZ),-M-M-*: excited singlet state of PVCZ before relaxation, (-M-M-*): relaxed excited singlet state of PVCZ, D,: sandwich-type excimer of PVCZ, D,: so-called second excimer of PVCZ 238

239 240 241

242

243 244 245

246

E. A. Abuin, E. A. Lissi. L. Gargallo, and D. Radic, Eur. Polym. J., 1980, 16, 1023. E. A. Abuin, E. A. Lissi, L. Gargallo, and D. Radic, Eur. Polvm. J . , 1980, 16, 793. M. A. Winnik, T. Redpath, and D. H. Richards, Macromolecules, 1980, 13, 328. N . Kim and S. E. Webber, Macromolecules, 1980, 13, 1233. H. Ooki, K. Sato, and S. Tazuki, Kokagaku Toronkai Koen Yoshrshu, 1979, 30. Y. Nishijima and M. Yamamoto, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979,20, 391. F. Mikes, H. Morawetz, and K. S. Dennis, Macromolecules, 1980, 13, 969. C. W. Frank, M. A. Gashgari, P. Chutikamontham, and V. J. Haverly, Stud. Phys. Theor. Chem., 1980, 10, 187. S. Tagawa, M. Washio, and Y. Tabata, Chem. Phys. Lett., 1979, 68,276.

525 made by Ghiggino et ~ 1 . ’ ~ and ’ Phillips et In the latter study, however, a third excimer site was observed at 370nm which does not interconvert to the normal sandwich excimer. Scheme 14 was proposed for comparison with that of Tagawa et al. above. Several fluorescent states were also observed in poly(Nvinylcarbazole) using laser flash photolysis.249

Polymer Photochemistry

main pathway minor pathway Scheme 14 D, is identiJiedas the low-energy sandwich-type excimer, D, as the high-energy dimer, and (MM)* as “re1axed”monomer. D, and (MM)* are populated rapidly ( < 10 ps) by an exciton diflusion mechanismfrom the initially excited monomer M*, and D, isformed from (MM)* (but not from D2*) with a rise time of about 2ns

Time-resolved emission studies on copolymers of 1-vinylnaphthalene and methyl methacrylate indicate a third emitting species other than the expected monomeric or excimer forms.’” Similar observations were made for copolymers of 1-vinylnaphthalene and methyl acrylate,’ and copolymers of acenaphthalene and methyl methacrylate.2s2 Similar studies on homopolymers of vinylnaphthalene and naphthyl methacrylate found that dual exponential functions were unable to account for the decays of monomeric and excimeric erni~sions.~’~ Fluorescence decay curves for poly(acenaphtha1ene) are shown in Figure 6 as an e~arnple.’’~ Decay curves recorded in the region of monomer emission and in the region of excimer emission are displayed along with the excitation pulse. Comparison of curves (b) and (c) clearly demonstrates that the lifetime of the monomer is considerably less than that of the excimer. Consequently, the monomer and excimer species are capable of differentiation by means of timeresolved emission spectroscopy. Two emitting singlet states have also been observed in p~ly(phenylacetylene).~~~ In some naphthalene-containing polymers, long-lived monomer emission was observed.’ s6 The emission was not associated, however, with thermal dissociation of the polymeric excimer, but results from singlet naphthalene being unable to form an excimer within the excited state

’

24’

248

249

K. P. Ghiggino, D. A. Archibald, and P. J. Thistlethwaite, J . Polym. Sci., Polym. Lett. Ed., 1980, 18, 673. A. J. Roberts, C. G . Cureton, and D. Phillips, Chem. Phys. Lett., 1980, 72, 554. H. Masuhara, S. Ohwada, N. Mataga, A. Itaya, K. Okamoto, and S. Kusabayashi, J. Phys. Chem., 1980,84,2363.

Phillips, A. J. Roberts, and I. Soutar, J . Polym. Sci.. Polym. Phys. Ed., 1980, 18, 2401. ’” D. D. Phillips, A. J. Roberts, and I. Soutar, Polymer, 1981, 22, 293. 252

2s3 254

255 256

D. Phillips, A. J. Roberts, and I. Soutar, Eur. Polym. J., 1981, 17, 101. D. Phillips, A. J. Roberts, and I. Soutar, Polymer, 1981,22,427; R. D. Burkhart, R. G . Aoiles, and K. Magoini, Macromolecules, 1981, 14, 91. D. Phillips, A. J. Roberts, and I. Soutar, J . Polym. Sci., Polym. Lett. Ed., 1980, 18. 123. J. R. MacCallum, C. E. Hoyle, and J. E. Guillet, Macromolecules, 1980, 13, 1647. D. A. Holden, P. Y. K. Wang, and J. E. Guillet, Macromolecules, 1980, 13, 295.

526

Photochemistry

I

T IME

Figure 6 Fluorescence decay curves for undegassed poly (acenaphthylenr) solution (THF, 298 K): (a) excitation pulse, (b) monomer decay (analysed at 325 nm), ( c ) excimer decay (analysed at 450 nm) (Reproduced by permission from J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 123)

lifetime. Singlet electronic-energy transfer has been found to be very efficient in poly( 1-naphthylmethyl methacrylate) 2 5 7 and poly[2-(-naphthyl)ethyl methacrylate] containing anthracene end 2 5 9 A Forster mechanism is believed to be involved. Exciplex formation in polymers has also attracted some interest. The effect of chain binding on the reactivity of naphthyl groups towards intermolecular exciplex formation with triethylamine has been investigated in p ~ l y a m i d e s5.9~The intermolecular exciplex interaction involving a chain-bound reactive group was found to be sensitive to the flexibility of the intervening chain. Exciplex dissociation in the poly(N-vinyl carbazole)-dimethyl terephthalate system has been foundSo occur through the carbazole triplet state,260and other workers have observed the quenching of the same exciplex by an applied electric field.261The same system has also been characterized by nano- and pico-second flash photolysis.262The latter technique indicates that molecular complexation is absent prior to excitation and occurs by a diffusional process following excitation of the polymer. Exciplex formation in a copolymer of p-NN-dimethy1-aminostyrene-pcyano-styrene was found to be significantly higher than in a model system.263* 264 Fluorescence polarization studies have also provided valuable information on excimer formation, energy migration, and molecular mobility in polymers. The role of hydrophobicity was analysed for mixtures of poly(methacry1ic acid) and poly(N-vinyl-2-pyrrolidone) in solution,265 and the motion of 8-anilino-lnaphthalenesulphonic acid covalently bound to poly(methacry1ic acid) has been 257 258 259 2hD 261

262

263 2h4

D. A. Holden and J. E. Guillet, Macromolecules, 1980, 13, 289. J . E. Guillet, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 395. J . A. Ibemesi, J. B. Kinsinger, and M. A. El-Bayoumi, J . Macromol. Sci., Chem., 1980, 14, 813. U . Lachish and D. J. Williams. Macromolecules, 1980, 1322. M. Yokoyama, Y. Endo, A. Matsubura, and H. Mikawa, Pol-vm. Prepr., Am. Chem. Soc., Div. Pol~~m Chem., . 20, 399. U . Lachish, R. W. Anderson, and D. J. Williams, Macromolecules, 1980, 13, 1143. K . Iwai, M . Furne, S. Nazakura, Y . Shirota, and H. Mikawa, Polym. J . , 1980, 12, 97. M. Furue, Y. Ito, S. Nozakura, K. Iwai, and F. Takemura, Kokagaku Toronkai Koen Yoshishu, 1979, 32.

265

H . Ohno and E. Tsnuchida, Makromol. Chem., Rapid Commun.. 1980, 1, 591.

Polymer Photochemistry

527

investigated by the same workers.266 Soutar and co-workers 267 have examined intramolecular excimer formation in acenaphthalene-methyl acrylate copolymers. Excimer formation was found to be enhanced by an increase in the degree of substitution in the comonomer. Energy migration was found to be less in acenaphthy lene-me thacrylat e than in acen aph th ylene-met hy 1 methacrylate as detected by fluorescence polarization. Phosphorescence depolarization has been found to be valuable for investigating relaxation phenomena in labelled poly(methy1 methacrylate).268 Ester group motion, for example, was found to occur at temperatures in the vicinity of the @-relaxationof the polymer. David et al.269 have also examined acenapthylene-methyl methacrylate copolymers by fluorescence polarization. Fluorescence polarization has been used to measure segmental orientation in stretched p o l y i ~ o p r e n e .Two ~ ~ ~ deviations from the classical theory of rubber elasticity were observed. The first involves an extra orientation of dry networks owing to the existence of weak nematic-like interactions between segments and the second is a saturation of orientation at high elongations that is associated with local conformational changes in the polymer. Mobility in hydroxyethyl cellulose and poly(ethy1ene oxide) tagged with fluorescein has been investigated and found to be much greater in the latter sy~tern.’~’ Relaxation phenomena in styrene and 9-vinyl anthracene polymers,’ 7 2 9-methylanthracene solubilized in poly(methacry1ic acid),273 polystyrene,274 formyl styrene-methyl methacrylate copolymer,’ poly(methacry1ic acid) containing spirobenzopyranindan side groups,’76 polystyrene and poly(methy1 methacrylate) with anthracenoid groups,277 copolymers of phenylazo-substituted aspartic and oligester-acrylates 279 have been studied using luminescence and optical methods. The photoreduction of a fluorescent probe auramine 0 in poly(methy1methacrylate) has been found to be very dependent upon the physical state of the polymer.280The rate of photoreduction was found to be reduced at temperatures higher than the Tgof the polymer owing to enhanced radiationless deactivation processes of both the excited singlet and triplet states of the probe. Triplet-energy migration and transfer processes have been studied to some extent. The efficiency of the decay of the triplet-triplet of excited poly(2vinylnaphthalene) by an added quencher, piperylene, has been found to decrease with an increase in the molecular weight of the polymer.281 An increase in the 266 267

268

269 270 271

272 ’13 274

’15 276 277

’” 279 280

H. Ohno and E. Tsnuchida, Makromol. Chem., Rapid. Commun., 1980, 1, 585. R. A. Anderson, R. F. Reid, and I. Soutar, Eur. Polym. J . , 1980, 16, 945. H . Rutherford and I. Soutar, J . Polym. Sci.,Polyrn. Phys. Ed., 1980, 18, 1021. C. David, D . Baeyens-Volant, and M. Piens, Eur. Polym. J . , 1980, 16, 431. J. P. Jarry and L. Monnerie, J . Polym. Sci., Polym. Phys. Ed., 1980, 18, 1879. H. Elmgren, J . Polym. Sci., Polym. Lett. Ed., 1980, 18, 351. J. Fuhrmann and R. Leicht, Colloid Polym. Sci.. 1980, 258, 631. K. L. Tan and F. E. Treloar, Chem. Phys. Lett., 1980, 73, 234. A. E. C. Redpath and M. A. Winnik, J . Am. Chem. SOC.,1980, 102, 6869. I. P. Zydt’kov and V. V. Mogil’nyi, Zh. Prikl. Spektrosk., 1980, 32, 49. M. Irie, A. Menju, Y. Hirano, and K. Hayashi, Kokagaku Toronkai Koen Yoshishu, 1979, 56. M. G . Krakovyak, E. B. Milovskaya, G . D. Rudkovskaya, L. V. Zamoiskaya, V. B. Lushchik, and G . D. Anan’eva, Vysokomol. Soedin., Ser. A , 1980, 22, 143. A. Ueno, K. Takahashi, J. Anzai, and T. Osa, Macromol. Chem. Phys., 1981, 182, 693. Yu. V. Zelenev and Yu. M. Sivergin, Acta Polym., 1981, 32, 75. G. J. Kettle and I. Soutar, Polym. Photochem.. 1981, 1, 123. J. F. Pratte, W. A. Noyes, jun., and S. E. Webber, Polym. Phorochem., 1981, 1, 3; J. F. Pratte and S. E. Webber, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20, 927.

528 Photochemistry density of the polymer coil in solution was associated with this effect. Alkyl substitution in poly(2-naphthylalkyl methacrylate) was found to have a favourable effect on triplet energy migration in the polymer.282Triplet energy migration has been shown to control the photochemistry of polymers containing phenyl vinyl ketone and o-tolyl vinyl ketone The average ‘residence time’ of the triplet exciton in any chromophore was found to be about 30 ps. Photoenolization of the o-tolyl vinyl ketone moieties provided an energy sink, thereby reducing the degree of photodegradation. Triplet-state photosensitizers based on polyb-(trifluoroviny1)benzophenonel and polyb-(trifluoroviny1)-acetophenone] have been described284 and triplet energy transfer in styrene-methyl methacrq late copolymers has been studied using triphenylene and coronene as triplet ~ I i m e r s . ~ ~ ~ Diffusion-controlled intramolecular reactions in polymers have been described by Cuniberti and Perico.286 Singlet energy transfer has been studied in polycarbonate resins using laser flash photolysis and phenyl salicylate as a q ~ e n c h e rThe . ~ ~quenching ~ results suggest that facile migration of singlet energy occurs in the polymer. Both singlet and triplet states were observed in picosecond laser flash photolysis of 2-hydroxy-3allyl-4,4’-dimethoxybenzophenone copolymerized with methyl methacrylate.288 Laser flash photolysis of polymers containing pendant 1-pyrenyl groups resulted in the production of dense populations of fluorescent most of which decayed by S-S annihilation. A similar study was carried out on poly(Nvinylcarbazole) 2-( 1-pyrenylmethyl)-propene-1,3-diol d i a ~ e t a t e . ~ ~ ~ Isomerization has been studied in polymers containing aromatic azo-groups. For example, E i ~ e n b a c h ~has ~ ’ investigated isomerization of azo-groups in poly(ethy1 acrylate) and found the process to be very dependent on the crosslinking density. Photoinduced reversible pH changes in poly(carboxy1ic acid)-azo dye complexes were found to be very dependent upon the composition of the 293 Cis-trans isomerization of azobenzene has been used as a tool to enforce conformational changes in crown ethers and polymers.294 Conformational changes in poly(L-glutamic acid) containing photochromic side groups have been investigated.2 9 282

T. Nakahira, S. Ishizuka, S. Iwabuchi, and K. Kojima, Makromol. Chem., Rapid Commun., 1980, 1, 759.

283 284 285

286

”’

J. P. Bays, M. V. Encinas, and J. C. Scaiano, Macromolecules, 1980, 13, 815. N . Asai and D. C. Neckers, J . Org. Chem., 1980, 45, 2903. A . N. Jassim, J. R. MacCallum, and T. M. Shepherd, Eur. Polym. J . , 1981, 17, 125. C. Cuniberti and A. Perico, Conv. Ital. Sci. Macromol. ( A t t i ) , 1979, 182. A. Gupta, R. Liang, J. Moacanin, R. Goldbeck, and D. Kilger, Macromolecules, 1980, 13, 262. A. Gupta, A. Yavronian, S. di Stefano, C. D. Merritt, and G . W. Scott, Macromolecules, 1980, 13, 821.

290 291 292

293

294 295

H. Masuhara, S. Ohwada, Y . Seki, N. Mataga, K. Sato, and S. Tazuki, Photochem. Photobiol., 1980, 32, 9. H. Masuhara, S. Ohwada, Y. Seki, N . Mataga, A. Itaya, K. Okamoto, S. Kusaabayashi, K. Sato, and S. Taguke, Kobunshi Ronbunshu, 1979, 36, 281. C . D. Eisenbach, PoIymer, 1980, 21, 1175. N . Negishi, K. Tsunemitsu, T. Suzuki, and I. Shinohara, Kobunshi Ronbunshu, 1980,37, 293. N . Negishi, T. Matsuo, K. Tsunemitsu, and I. Shinohara, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 1017. S. Shinkai, T. Nakaji, Y . Nishida, T. Ogawa, and 0. Manabi, J. Am. Chem. Soc., 1980, 102, 5860. 0. Pieroni, J. L. Houben, A. Fissi, P. Costantino, and F. Ciardelli, J . Am. Chem. Soc., 1980, 102, 5913.

529

Polymer Photochemistry

Fluorescence spectroscopy has also been widely used for investigating microviscosity in carbohydrate^,^^^ deformation of poly(viny1 composition of rare-earth metal-containing polymers,298 crystallinity in polyolefins 300 and p o l y c a r b o n a t e ~ ,hydrophobicity ~~~ in crosslinked polystyrene gels,3o2polymerization of methyl methacrylate doped with pyrene, 303 lubricants in fibres,304and photocrosslinking of tris(bipyridine)ruthenium complexes doped in polymers. 305 Other luminescence studies of interest include diffusion in labelled polystyrene,306 tunnelling in polyethylene,307and aggregation of eosin in polyvinyl acetate. 308 Hamanoue et aL309have studied photoreactions of nitroanthracene derivatives in poly(methy1 methacrylate). In the presence of triethylamine, anthryloxy anions were formed, whereas in its absence only the anthryloxy radical was formed. However, in the monomer only the anthryloxy radical was formed even in the presence of the amine. The microscopic medium polarity of the methyl methacrylate by the polymerization process was believed to be responsible for this effect. Finally, photoinduced charge separations have been observed in polymers containing pendant tris(bipyridy1)ruthenium chlorine complexes. l o 2999

4 Photodegradation and Photo-oxidation Processes The photodegradation and photo-oxidation of polymer systems is still a subject of considerable scientific and technological activity. A number of general review articles have appeared on the subject. Allen and McKellar 311 have reviewed the interactions of light with polymers, and Shalaby 312 has written a comprehensive review on all the chemical, physical, and environmental aspects of polymer photodegradation. Three other reviews of interest have also a ~ p e a r e d . ~ ' ~ - ~ ' ~

Polyo1efins.-Polyolefin oxidation continues to be a subject of considerable controversy. Wiles and co-workers * have written a comprehensive review of polyolefin photo-oxidation mechanisms with particular emphasis on the role of 296 29'

298 299

300

H. Elmgren, J. Polym. Sci.,Polym. Lett. Ed., 1980, 18, 815. Yu. V. Brestkin, E. S. Edilyan, N. G. Bel'nikevich, G. Mann, and S. Ja. Frankel, Actu Polym., 1980, 31, 646. Y. Ueba, E. Banks, and Y. Okamoto, J. Appf. Polym. Sci., 1980,25, 2007. J. Fuhrmann and M. Hennecke, Mukromol. Chem., 1980, 181, 1685. M. Hennecke and J. Fuhrmann, Colloid Polym. Sci., 1980, 258, 219.

L. S . Bogdan, Zh. Prikl. Spektrosk., 1980, 32, 937. K. Horie, I. Mita, J. Kawabata, S.Nakahama, A. Hirdo, and N. Yamazaki, Pofym. J., 1980,12.319. 303 I. I. Kalechits, M. G. Kuz'min, V. P. Zubov, and V. A. Kabdnov, Dokl. Akud. Nauk. SSSR, 1981, 256, 407. 304 N. P. Chekrii, Khim Volokna, 1980, 4, 31. j o 5W. Kawai, Kobunshi Ronbunshu, 1980, 37, 303. 306 I. Mita, K. Hone, and M. Masuda, Polym. Bull., 1981, 4. 369. 307 V. A. Aulov, Dokl. Akud. Nauk. SSSR. 1980, 254,910. 308 I. P.Zharkov, P. A. Kondratenko, and M. V. Kurik, Opt. Spektrosk. 1980, 49, 523. '09 K. Hamanoue, S. Hirayama, T. Hidaka, H. Ohya, T. Nakayama, and H. Teranishi, Pofym. Photochem., 1981, 1, 57. 310 M. Kaneko, A. Yamada, and Y. Kurimura, Inorg. Chim. Acta, 1980, 45, 73. 311 N. S. Allen and J. F. McKellar, Chem. Br., 1980, 16, 480. S. W. Shalaby, J. Polym. Sci.,Macromol. Rev., 1979, 14, 419. 3 1 3 L. Gansel, Tekstif, 1979, 28, 804. 314 S. C. Shim and S. K. Chang, Pollimo. 1979, 3, 342. 315 D. M. Wiles, J. Appl. Pol-vm. Sci., Pol-vm. Symp., 1979, 35, 235. 316 A. Garton, D. J. Carlsson, and D. M.Wiles, in 'Developments in Polymer Photochemistry', ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 4. p. 93. jol

jo2

530

Photochemistry

the solid-state environment in controlling radical reactivity. Slobadetskaya 3 1 has also reviewed polyolefin photo-oxidation processes with particular emphasis on the prediction of their service life. Wiles and co-workers 318 have examined the role of peroxy-radicals in polyolefin photo-oxidation. They suggest that radical recombination processes have a high probability even if they escape the primary polymer cage. The occurrence of secondary cage-recombination processes was considered. Vasilenko et aL3 have also studied the role of free radicals in polyethylene photo-oxidation. They found that the quantum yield for C-H bond rupture was 10-100-fold higher than for C-C bond rupture. In the photo-oxidation of radiation-modified polyethylene, the formation of carbonyl groups was associated with diene formation in the Frank321 has reported on the lifetimes of free radicals during the intermittent exposure of polypropylene. The initiation mechanism of polyolefin photo-oxidation is still unsettled. According to Karpukhin et al,322the rate of photo-oxidation of polyethylene is controlled more by hydroperoxide than carbonyl groups. G ~ i l l e ton , ~the ~ ~other hand, has produced evidence to show that carbonyl groups photosensitize the breakdown of hydroperoxides in polyolefin photo-oxidation. But both Allen 324 and Verdu325 have produced evidence to show that polymer oxygen or unsaturation-oxygen charge-transfer complexes are important precursors of hydroperoxide formation in the photo-oxidation of polyolefins. For example, prior destruction of photoactive carbonyl and hydroperoxide groups in polyolefins by pre-irradiation in an inert atmosphere was found to have‘no effect on the subsequent rate of p h o t o - ~ x i d a t i o n . ~ ~ ~ Vink 3 2 6 has produced evidence in total conflict with previous experience which is suggested to show that the photo-oxidation of polypropylene is a bulk reaction rather than a surface phenomenon. ESCA studies, however, have shown that the photo-oxidation of polypropylene is clearly a surface phenomenon.327In a recent study by Kollmann and Wood 328 the photo-oxidation of polypropylene was found to be dependent upon the intensity of the light source. Thus, for unstabilized polymer the rate was proportional to 1°-5,whereas for stabilized polymer the rate was proportional to I0.*-O.’ . There appears to be some conflict in the literature as to whether chemical changes during the photo-oxidation of polyolefins correlate with the changes in mechanical properties.329,330 This has always been a difficult

’” E. Slobodetskaya, Usp. Khirn., 1980, 49, 1594.

318

319

320 321

322

323

324 325 326 327

328 329 330

A. Garten, D. J. Carlsson, and D. M. Wiles, Macrornol. Chern., 1980, 181, 1841. V. V. Vasilenko, E. R. Klinshpont, V. K. Milinchuk, and L. I. Iskakov, Vysokomol. Soedin., Ser. A , 1980, 22, 1770. V. P. Pleshanov, V. V. Vasilenko. S. M. Berylant, E. R. Klinshpont, and V. K . Milinchuk, Vjsokomol. Soedin., Ser. A , 1980, 22, 1622. H. P. Frank, Kunstst. Fortschrittsber., 1979, 5, 5 3 . 0.N. Karpukhin, E. M. Slobodetskaya, and T. V. Magamedova. Vykomol. Soedin..Ser. B, 1980,22, 595. J. E. Guillet, Pure Appl. Chem., 1980, 52, 285. N. S. Allen, Polym. Deg. Stab., 1980, 2, 155. J. Verdu, Eur. Polym. J . , 1980, 16, 565. P. Vink, J . Appl. Polym. Sci., Appl. Polyrn. Symp.. 1979, 35, 265. J . Peeling and D. T. Clark, Polym. Deg. Stab., 1981, 3, 177. T. M. Kollmann and D. G . M. Wood, Polym. Eng. Sci.,1980, 20, 684. G. Akay, T. Tincer, and H. E. Ergoz, Eur. Pol-vm. J . , 1980, 16, 601. S. Orban, Kunstst. Fortschrittsber., 1979, 5, 119.

Polymer Photochemistry

53 1

problem, and in the author's experience it should be assumed that no correlation exists. Only the particular property changes desired should be monitored for a particular application. Reprocessing effects have been studied by Sadrmohaghegh and S ~ o t t . ~ They ~ ' found that alternating processing and ultraviolet-exposure cycles have a more severe effect on photo-oxidation than repeated reprocessing. This effect is believed to be due to the formation of vinyl unsaturation in the polymer by Norrish Type I1 photolysis (Scheme 15), which considerably decreases

TH2

-CH2C-CH-CH2I -CH2C-CH-CHz-

-CH~C-~H-CH, II CHZ

< 0,-RH

II

Crosslinking

OOH CHzI -CH2C-CH-CH2II CH2

CH2C-CHO II

+ *CHzChain-scission

Scheme 15

the thermal oxidative stability of the polymer. Mathur et have found that the thermal stability of polypropylene is inversely proportional to the concentration of photo-oxidized groups, which would tend to confirm the work on re~ycling.~ Other studies of interest on polyolefins include determination of supramolecular structure,333 influence of rotational moulding,334 comparison of natural and accelerated weathering,335 and measurement of gel formation on photocrosslinking.336

'

Poly(viny1 halides).-Vink and Van Bloois 337 have reviewed the general mechanism of photo-oxidation of PVC. Boyd-Cooray and Scott 3 3 8 have shown that hydroperoxides are primary initiators in the photo-oxidation of poly(viny1 chloride). At low processing temperatures, hydroperoxides are believed to be 33'

332 ' j 3

334 335

336 337 338

C. Sadrmohaghegh and G. Scott, Eur. Polym. J., 1980, 16, 1037. A. B. Mathur, V. Kumar, and G. N. Mathur, Ind. Polym. Radiat., Proc. Symp., 1979, 143. D. A. Akhemedzade, E. I. Markova, and N. F. Ozhavibekov, Sb. Tr. Inst. Nefekhim. Protsessov, im Yu. G. Mamedalieva, Akad. Nauk Ar. SSR, 1980, 11, 104. B. A. Golender, V. P. Shein, and S . Ya. Kleinman, Plust Massy. 1980, 11, 36. S. Khadzhidocheva, L. Peeva, and V. Tsveteva, Kunstst. Fortschrittsber., 1980, 279. Yu. I. Dorofeev and V. E. Skurat, Dokl. Akad. Nauk. SSSR, 1979, 249, 1142. P. Vink and F. I. Van Bloois, Overdruk Wit Plastica, 1975, 5, 167. B. Boyd-Cooray and G. Scott, Polym. Deg. Stab., 1981, 3, 127.

532 Photochemistry formed, whereas at higher temperatures carbonyl and unsaturation predominates and tend to control the subsequent photoinitiated oxidation of the polymer. Verdu et aZ.339have studied the photosensitized oxidation of PVC and propose the involvement of unsaturated sites as initiators. The unsaturated groups are believed to originate from thermolabile groups such as a-chloroperoxides or #l-chloroketones. Rabek and co-workers 340 have examined the photosensitized oxidation of PVC. They also believe unsaturation plays a vital role in photoinitiated oxidation and have proposed the following detailed mechanistic scheme to account for both radical formation and the observed carbonylic products (Scheme 16). According to the same group of polyene sequences may also

+ -CH2-CH-I

-CH-(CH=CH),,-l-CH-

-

c1

+

-cH,-(cH=cH),-,-~H-

-~H-cH-

I

CI

b

I 0 -CH2-eH-CH2-CH-

I CI

+ 0,

I

-CH2-CH-CH2-CH-

+

I CI

H

I

6

0 I 0

I 0

I

-CH2-CH-CH2-CH-

I

I + RH + -CH2-CH-CH2-CH-

+ R.

CI H

I

0 I 0 I -CH2-CH-CH2-CH-

6 I

% -CH2-CH-CH2-CH-

I CI

I

+ HOB

c1 OH

I

b

-CH2-CH-CH2-CH-

+ Rm

I -CH2-CH-CH2C1 H

C1

Scheme 16

339 340

341

J . Verdu, A. Michel, and D. Sonderhof, Eur. Polym. J., 1980, 16, 689. J . F. Rabek, G . Canaback, and B. Ranby, J . Appl. Polym. Sci., Appl. Polym. Symp., 1979,35, 299. J. F. Rabek, B. Ranby, B. Ostensson, and P. Flodin, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 299.

Polymer Photochemistry 533 photosensitize the formation of singlet oxygen in the polymer (Scheme 17). Owen et 343 have made some dramatic observations which indicate unequivocally ~

1

.

~

~

~

3

fCH=CHj-

+

'0,___* -CH-CH=CHI OOH Scheme 17

that polyene sequences play a key role in the photoinitiated oxidation of PVC. Polyenes in degraded PVC samples were found to exhibit some astonishing spectral changes in solution which have been associated with the prototropic equilibrium shown in Scheme 18. In one experiment the absorption spectrum of chemically

aCH2CHCICH=CH-CH=CHCH2CHCl* -H+/

/+H+

~CH~CHCICH-CH-CH-CH~CH~CHCIO

+ +H+T

l-H+

-CH2CCl=CH-CH=CH-CH2CH2CHCl@ The overall result would be

-(CH=CH)r(CH=CH)r

__*

-(CH=CH)oy

Scheme 18

degraded PVC showed a dramatic increase in the visible region in dichloromethane on standing. This effect was illustrated in Volume 12. Subsequent photo-oxidation experiments showed that these strongly absorbing species are extremely photosensitive. The photobehaviour of these species in the presence of aromatic carbonyls was also studied in solution. Benzophenone, for example, was a powerful sensitizer in dichloromethane, whereas in THF there was an induction period in the presence of oxygen. The induction period was associated with the build-up in solvent THF radicals, which inhibited photoreaction of the polyenes by reaction with oxygen. Polyene structures have also been invoked in the photodegradation of various other poly(viny1 halides), such as poly(viny1 bromide) and poly(viny1 iodide).344Polyenyl radicals have also been observed at room temperature during the photo-oxidation of Pvc.345

"' E. D. Owen, I. Pasha, and F. Moayyedi, J . Appl. Polym. Sci., 1980, 25, 2331. 343 344

345

E. D. Owen and 1. Pasha, J . Appl. Polym. Sci., 1980, 25, 2417. M. Yamamoto, M. Yano, and Y. Nishijima, Kobunshi Ronbunshu, 1980, 37, 319. N. L. Yang, J. Liutkus, and H. Haubenstack, Am. Chem. SOC.. Symp. Ser., 1980, 142, 35.

534

Photochemistry

Other studies of interest on PVC photo-oxidation include the influence of light intensity,346 chlorination,347 solvent and inhibition of dehydrochlorination at the surface layers.349 The chlorination process destabilized the PVC. Polystyrenes.4euskens and Davis 3 5 0 * 3 5 1 have reviewed their work on the mechanism of the photo-oxidation of polystyrene. It would appear that carbonyl groups are responsible for the sensitized photolysis of hydroperoxide groups, as with polyolefins. Quantum yields of hydroperoxide photolysis were found to be significantly higher in the presence of aromatic ketones. Ranby and Lucki 3 5 2 have discussed in some depth their work on the photo-oxidation of polystyrene and present some novel evidence for the formation of hydroxylated products (Scheme 19). Ring-opening reaction schemes were also proposed to account for photoyellowing: see earlier Volumes. have also used model compounds such as 3-phenylpentane for Ranby et investigating the mechanisms of photo-oxidation of polystyrene. The photooxidation of polystyrene has been investigated in solution by a number of workers. Woolinski 3 5 4 has observed the development of unsaturation and implicated the involvement of singlet oxygen in the mechanism of photo-oxidation, whereas Easton and M a ~ C a l l u m ~invoke ~ ~ " the involvement of polymer-solvent complexes in initiation. The photo-oxidation of polystyrene has been found to have a kinetic chain length of 103-104.355b ESCA has provided valuable and novel information in the surface changes during the photo-oxidation of polystyrene. 3 5 6 Initially C--O groups are formed followed by carbonyl, carboxyl, and carbonate groups. Ring-opening reactions were also observed, but the bulk of the polymer remains virtually unaffected. Light scattering 3 5 7 a and laser flash photolysis 3 5 7 b techniques have also been applied to the study of polystyrene photo-oxidation. The photo-oxidation of polystyrene has also been investigated using gel permeation chromatography 3 5 8 and dielectric techniques.359The former indicated initial high rates of chain scission followed by crosslinking, whereas in the latter the presence of oxygen caused a dramatic increase in the dielectric constant of the polymer. Waligora et al.360have studied the sensitized photo-oxidation of polystyrene by a,b-enones. These chromophores introduced an induction period due to D. Braun and S. Kull, Angew. Makromol. Chem.. 1980, 85, 79. C. Decker and M. Balandier, Makromol. Chem., Rapid Commun., 1980, 1, 389. 34a J. Polanka, L. Lapcik, and J. Valasek, Chem. Zvesti, 1980, 34, 63. 349 T. G. Fedoseevn, L. D. Strelkova, E. 0.Krats, V. P. Lebedev, and K. S. Minsker, Plast. Massv, 1980. 7, 28. G. Geuskens and C. David, Pure Appl. Chem., 1979, 51, 2385. 3s1 G. Geuskens, J . Chim. Phys., 1980, 77, 487. 352 B. Ranby and J. Lucki, Pure Appl. Chem., 1980, 52, 295. 353 J. Lucki, J. F. Rabek, and B. Ranby, J . Appl. Polym. Sci., Appl. Polym. Sci., 1979, 35, 275. 3 5 4 L. Wolinski, Makromol. Chem.. 1980, 18, 2335. 3 5 5 ( a ) M. J. Easton and J. R. MacCallum, Polym. Deg. Stab.. 1981, 3, 229; (b) S. I. Kingina and A. I. Mikhailov, Dokl. Akad. Nauk. SSR, 1980, 253, 1150. 3 s b J. Peeling and D. T. Clark, Polym. Deg. Stab., 1981, 3, 97. 3 5 7 ( a ) W. Schnabel, Po[ym. Eng. Sci., 1980,20,688; (b)S . Tagawd and W. Schnabel, Makromol. Chem., Rapid Commun., 1980, 1, 345. 35R B. Wandelt, J. Brzezinski, and M. Kryszenski, Eur. Polym. J., 1980, 16, 583. '" N. A. Weir and T. Milkie, J . Appl. Polym. Sci., Appl. Pol.vm. Sci., 1979, 35, 289. 360 B. Waligora, M. Nowakowska, and J. Kowal, Polym. J . , 1980, 12, 767. 346 34'

Polymer Photochemistry

535

I". MeCH,CMe

+

'H

H I

b

0

I 0

I

0

b

OH

I

ONo' H

I

I

C'

Me-C,

,CH2

I

J.

1 Me I MeCH,-C-0-OH

H

b

I O H I I Me -C -CkH,

6"

k

0.

I

MeCH,-C-Me

I". b

I Me-C-CH=CH,

8I.

+ H,O 4tHd

0 II MeCH,C

RH

OH I Me-y-CH=CH,

+'R

6""

0 II

Me-C

(yoH

Scheme 19

trans cis isomerization followed by rapid oxidation. The photo-oxidation of polystyrene blended with poly(2,6-dimethyl-1,Cphenylene oxide) 361, 3 6 2 and N--+

36'

362

J. P. Tovborg Jenson and J. Kops, J . Polym. Sci., Polvm. Chem. Ed., 1980, 18, 2737. B. Wandelt and M.Kryszewski, J . Appl. Pol-vm. Sci., Appl. Pol-vm. Svmp., 1979, 35, 361.

536

Photochemistry

ethylmaleimide 363 has also been studied. In the former studies there is an increase in the rate of photo-oxidation of the poly(2,6-dimethyl-1,4-phenylene oxide) due to energy transfer from the polystyrene. The photo-oxidation of poly(p-methylstyrene) has been studied initiated by azobis-is~butyronitrile.~~~ The effects of polymer concentration, light intensity, initiator concentration, and oxygen pressure were related by the following expression:

-!!?!

~ ( 0 2 ) '

(Polymer)0.6 (AlBN)0.95 (]o)l.os

dt

High-impact polystyrene has also been studied by a number of workers. Ghaemy and have correlated changes in infrared with impact strength during photo-oxidation. Thermal treatment has a deleterious effect on the photo-oxidation of ABS 366 and DSC 367a has been found useful for determining the amount of unoxidized polybutadiene in the terpolymer. Another study includes the measurement of hardness. 3 6 7 b Polyacry1ics.-Gupta et al.368 have investigated in some detail the mechanism of photodegradation of poly(methy1 methacrylate) using various spectroscopic techniques and they have confirmed, for example, the presence of the radical species shown in Scheme 20 during photodegradation. These workers found that bond scission occurs as a result of direct excitation of the ester carbonyl group absorbing at 254nm. Panke and Wunderlich 369 have examined the molecular weight changes during the photo-oxidation of poly(methy1 methacrylate) and found that the kinetic chain length is limited by termination reactions between the depolymerizing radicals and other small mobile radicals. Grassie and Davidson 3 7 1 have found that whereas copolymerization of maleic anhydride decreases the rate of chain scission of methyl methacrylate during exposure to 254 nm light, copolymerization of vinyl ketones accelerates the rate. In the latter case the rate of chain scission passes through a maximum at 2 0 30% ketone content. Copolymers of methyl methacrylate and a-chloroacrylonitrile are also photolysed rapidly by 254nm light.372 Scission at the C-C1 bond is primarily responsible for photodegradation. Defects in poly(methy1 methacrylate) 374 The introduction of 4induced by laser photolysis have also been chromanone groups into poly(methy1methacrylate) imparts some improvement in 3703

363

364 36s 366

367

368 369

370 371

372 373

374

I . K. Chernova, S. S. Leshchenko, V. P. Golikov, and V. L. Karpov, Vysokomol. Soedin., Ser. A , 1980, 22, 2175. N. Weir and T. H. Milkie, Polym. Deg. Stub., 1980, 2, 225. M. Ghaemy and G. Scott, Polym. Deg. Stub., 1981, 3, 233. W. Y. Chiang, Ta T'ung Hsuch Pav, 1979, 9, 129. (a) H . E. Blair, D. J. Boyle, and P. G. Kellcher, Polym. Eng. Sci., 1980, 20, 995; ( b ) H. H. Racke, Kunststoffe, 1980, 70, 76. A. Gupta, R. Liang, F. D. Tsay, and J . Moncanin, Macromolecules, 1980, 13, 1696. D. Panke and W. Wunderlich, J . Appl. Pol.vm. Sci., Appl. Polym. Symp., 1979, 35, 321. N. Grdssie and A. J. Davidson, Pof-vm.Deg. Stab., 1981, 3, 25. N. Grassie and A. J. Davidson, Pofym. Deg. Stab., 1981, 3, 45. N. Grassie and A. S. Holmes, Polym. Deg. Stab., 1981, 3, 145. A. A. Manenkov, V. S. Nechitailo, and A. S. Tsapvilov, Izv. Akad. Nauk. SSSR, Ser. Fiz., 1980, 44, 1770. N. P. Novikov and L. N. Trukhanova, Fiz.-Khim. MekA. Muter., 1980, 16, 31.

537

Polymer Photochemistry y

3

y

-CHz-CI C ‘0-CH,

h,, __+

8

3

tCHZ-C$ I f-

k,

k2 V

I

C*

d

-CH,-C-

+ bCH,

s

I

+ eOOCH, 1

HCOOCH,

1

k41 y

-CH,-c-

c, d + e0H3

CH,OH

CH4

k.1

y-43

3

-CH2-c-

7H3

t‘H3

743 -CHz-C-

+CO

-CH2-c-

+ co, y

-CH2-C-

3

k6

7H-I -CH,-C* I COOCH,

7H3 CH2=C-

7H3

+

k,

y

-7’

(PR. RAD.) COOCH, 2

CH2=C + (PR. RAD.) I COOCH,

Scheme 20

light stability.375 In copolymers of poly(ester-urethanes) with poly(methy1methacrylate) the presence of the urethane links and ester groups were found to be unimportant in determining the rate of p h o t o - ~ x i d a t i o nAn . ~ ~e.s.r. ~ study 377 on the photo-oxidation of poly(acry1amide) has identified the formation of propionamide radicals, and the photolysis of sodium acrylate has been studied by vi~cornetry.~~~ Polyamides-Copolyamides derived from truxillic acid are highly photosensitive by the mechanism shown in Scheme 21.379*380 The effect of pH on the photodegradation rate indicates that protonation in the first excited singlet state accelerates ring cleavage. 375

3’6 3’’ 378 37q

380

H. Matsuda, A. Ninagawa, and Y. Tokunaga, Kenkyu Hokoku-Asahi Garasu Kogyo Giiutsu Shoreikai, 1979, 34, 47. J. A. Simms, Polym. Sci. Technol., 1980, 11, 137. U. Ramelow and B. M. Baysal, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 329. T. Saito, Jpn, J. Appl. Phys., 1980, 19, 2501. G. G. Aloisi, U. Mazzucato, P. Maravigna, G . Montaudo, A. Recca, and M. Scarnporrino, Chim. Ind., 1979, 61, 800. P. Maravigna, G . Montaudo, A. Recca, E. Scamporrino, G. G. Aloisi, and U. Mazzucato, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 5 .

Photochemistry

538

hv

+H'-

Scheme 21

Infrared has been used for investigating the photodegradation of polyamide whereas several other workers have studied mechanical changes.382- 384 A comprehensive review has appeared on polyamide photoageing.

Poly(Z,6-dimethyl-l,4phenylene oxide) (PPO).-The photo-oxidation of this polymer has attracted some interest. Wandelt 386 has found that the photoinitiated oxidation of PPO depends upon the mobility of one more unit in the polymer chain. A marked increase in the rate of photo-oxidation of the polymer occurs in the temperature range 45-40 "C, which corresponds with the p-relaxation phenomena. Chain mobility markedly controls the diffusion of oxygen. From detailed analysis of the products of PPO photo-oxidation the following reaction 388 hydroperoxide photolysis schemes have been proposed to account for (Scheme 22) and quinone photoreaction with aromatic aldehydes to give aromatic esters, for example (1 6) (Scheme 23). The three chromophores are formed during 3879

PCH,COC

-

[PCH,O"OHI-

PCHO

\ PCH,O' +

+

H20

'OH

Scheme 22

processing of the polymer. Direct absorption of light by the phenylene oxide units also occurs. Zinc isopropylxanthate has been found to be a photostabilizer in PPO, whereas the cobalt form was a p h o t o s e n s i t i ~ e r . ~ ~ ~ Polyurethanes.-Rek and Bravar 390- 392 have proposed the following mechanism to account for the photo-oxidation of polyurethanes (Scheme 24). Direct photolysis of N-C and C - 0 bonds are believed to be the primary photochemical steps

"' 3g3 384

385

386 388

389 390

392

I. S. Polikarpov, Zaved Teknol. Legk. Prom. Sti., 1979, 22, 21. S. Yano and M . Murayama, Nippon Reoraji Gakkaishi, 1980, 8, 84. Y . W. Mai, D. R. Head, B. Cotterell, and R. W. Roberts, J. Muter. Sci., 1980, 15, 3057. S. Yano and M. Murayama, J. Appl. Polym. Sci., 1980, 25, 433. A. L. Margoiin and L. M. Postnikov, Usp. Khim., 1980, 49, 1106. B. Wandelt, Polym. Bull., 1981, 4, 199. Z. Slama, E. Svejdova, and J. Majer, Makromol. Chem., 1980, 181, 2449. J . Petrij and Z. Slama, Makromol. Chem., 1980, 181, 2461. R. Chandra, B. P. Singh, S. Singh, and S. P. Handa, Polymer, 1981, 22, 523. V. Rek and M. Bravar, Cell. Noncello Polyurethanes, Inst. Conf., 1980, 845. V. Rek and M. Bravar, Kunstst. Fortschrittsber., 1980, 5, 107. V. Rek and M. Bravar, J. Elast. Plast., 1980, 12, 245.

539

Polymer Photochemistry

0

+

0

0

followed by the formation of aromatic amino, azo, and carbonyl structures. Lipskerova and Mel’nikov 393 have proposed a similar mechanism. Aromatic urethanes have been stabilized by complexation of peroxides in the polymer394 and the effect of prior y-irradiation has been investigated, on polyurethane^.^^^ The ageing of polyurethane coatings has been investigated,396 and light-stable integral skin foams have been developed for polyurethanes. 3 9 7 Creep behaviour of polyurethanes on ultraviolet exposure has also been investigated.398 Rubbers.-Golub and Rosenburg 399 have proposed the following general mechanism to account for the loss of unsaturation during the photodegradation of 1,2poly(cis- and trans-hexa-1,4-dienes). The reaction (Scheme 25) is believed to occur through cyclization of the double bond. Chandra and co-workers 400, 401 have investigated aldehyde production during the photo-oxidation of butyl rubber. Diphenyl ally1 mercury was an effective stabilizer for the polymer but it did not inhibit aldehyde formation. Clearly, the aldehyde production must be a side product and has little importance in the 393

394 395

396

397 398 399 400 401

E. M. Lipskerova and M. Ya. Mel’nikov, Dokl. Akad. Nauk. SSSR, 1980, 253, 1154. V. A, Kosobutskii, M. N. Kurganera, 0. G. Tarakanov, and V. K. Belyakov, Vysokomol. Soedin., Ser. A , 1980, 22, 1264. E . M. Lipskerova and M. Ya. Mel’nikov, Khim. Vys. Energ., 1980, 14, 143. M. V. Karyakina, V. V. Luk’yanova, N. V. Mairova, and A. Kalnavais, Mod$ Polim. Muter., 1979, 8, 102. H. Horacek and 0. Volkert, Angew. Mukromol. Chem., 1980, 90, 109. A. K. Aleksandvova, V. F. Stepanov, and S. E. Vaisberg, Kuuch. Rezina, 1980, 11, 30. M. A. Golub and M. L. Rosenberg, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 2543. R. Chandra, B. P. Singh, and S. Singh, Indian J. Chem., Sect. A , 1980, 19, 527. R. Chandra, J . Indian Chem. Soc., 1981, 58, 49.

Photochemistry

540 O-CH2-CH2-R-

H

i

1.1

I -R'-N'

+

L+"RI-

+ -R~NH-NH-R~-

*CH2-CH2-R-

+

L + 2RO'+ TH2-CH2-R-

+

-R'-

CO,

-R'N=NR'NH,

+

+ 2ROH

CH,=CH-R-

0 I1

li

-R'-N-C' I H

1 -R'-N'

I H R' R

4-

+ CO

*O-CH2-CH2-R-

'

C H 2 0 +*CH2-R-

L + 0, = =

+

O O C H -R-

aromatic part from di-isocyanate aliphatic part from polyglycol Scheme 24

If,

-RCHO

+ 'OH

-m

Scheme 25

photodegradation mechanism. Lala and Rabek 402 have proposed that hydroperoxides are the key initiators in the photo-oxidation of poly(buta-l,4-diene). Ranby and co-workers403 have studied the effect of various active oxygen species on poly(buta- 1,2-diene). Interestingly all the species attacked the polymer causing marked crosslinking. In the photosensitized oxidation of polyisoprene it has been found that the presence of an OH group in an allylic position to a double bond causes considerable deactivation of the group towards singlet-oxygen attack.404 *02

*03 404

D. Lala and J. F. Robek, Eur. Polym. J . , 1981, 17, 7. J. Lucki, B. Ranby, and J. F. Rabek, Eur. Polym. J., 1979, 15, 1101 C. Tanielian and J. Chaineaux, Eur. Polym. J . , 1980, 16, 619.

Polvmer Photochemistry

54 1

Other studies of interest on rubbers include weathering 405 and photolysis in the far ~ l t r a v i o l e t . ~The ’ ~ resistance of rubbers to ultraviolet attack has been found to decrease in the order neoprene > polybutadiene > p o l y c h l ~ r o p r e n e . ~ ~ ~

Natural Polymers-Two comprehensive review articles have appeared on wool 408 and cellulose 409 photodegradation. Holt and Milligan 410* 4 1 have examined the photo-oxidation of serine, threomine, and cystine side chains in wool. Serine is converted into a-carboxyglycine, cystine to a-formylglycine, and threomine to r-acetylglycine. Waters et have shown that the ph’otodegradation of wool is due to disulphide bond scission and main-chain cleavage. Polikarpov and Kottyar 413 have used polarography for studying the photooxidation of wool. Aqueous polysaccharide gels have been investigated by Phillips and cow o r k e r ~ These . ~ ~ ~workers found that the photochemical processes in gels were the same as in solution suggesting that the gel structure is fluid. Nickel and copper ions have been found to inhibit the photodegradation of silk, whereas zinc and chromium ions accelerate the process.415 Other studies of interest include surface photoreactions on the fibre stalk of e.s.r. studies on polypeptide p h o t o l y s i ~ , ~photoyellowing ~’ of silk studied by ATR,418 and the photodiscoloration of w001.4’9-421 Miscellaneous Polymers.-Buchanan and McGill 42 have investigated in detail the photodegradation of poly(viny1 esters). First results indicated that there is a close relationship between the photodegradation of poly(viny1 esters) and model ester compounds. The following mechanisms were proposed to account for carboxylic acid formation (Scheme 26), ketone formation (Scheme 27), and aldehyde formation (Scheme 28). It is seen that two mechansims, one involving hydrogen abstraction by the acyl radical formed in a Norrish Type I cleavage process (Scheme 29), and the other involving an intramolecular hydrogen abstraction by an excited carbonyl group followed by fragmentation have been proposed to account for aldehyde formation. 405 406

407 408

409

410 411

R. Vesely and 2.Prauseova, Kunstst. Fortschritfsber., 1980, 5, 27. Yu. I. Dorofeev and V. E. Skurat, Khim. Vys. Energ., 1980, 14, 431. E. M. Abdd-Bary and E. A. Abdel-Razik, Proc. Int. Rubber Conf.,1979, 970. C. H. Nicholls, in ‘Developments in Polymer Photochemistry’. ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 5, p. 125. P. J. Baugh, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 5 , p. 165. L. A. Holt and B. Milligan, Text. Res. J., 1980, 50, 387. B. Milligan and L. A. Holt, Fibrous Proreins, Sci. Ind. Med. Asp. Proc. Inr. Conf. 4th. 1979, 1980, 2, 203.

412

413

415 416 417

418 419 420 421

422

P. J. Waters, N. A. Evans, L. A. Holt, and B. Milligan, Quinquenn. Int. Wool. Test. Res. Conf. (Pup.) 6rh, 1980, Fiche, 13, D, 7. L.S. Polikarpov and G. I. Kottyar, Tekst. Prom-Sti (Moscon), 1980, 12, 26. D. J. Wedlock, G. 0. Phillips, and J. K. Thomas, Polymer J., 1979, 11, 671. F. Shimiza, Zoku Kenshi No Kozo, 1980, 485. H. Banmann, Quinquenn. Int. Wool Text. Res. Conf. (Pap.) 6th, 1980, Fiche, 14, F, 5. F. Y. Lion, M. Kuwabara, and P. Riesz, J. Phys. Chem., 1980, 84, 3378. A. Watanabe, M. Tagawa, and R. Osawa, Kaseiguku Zasshi, 1979, 30,706. K. Umchara and N. Minemura, Rinsan Shikenjo Geppo (Hokkaido), 1979, 331, 15. K. Umchara, N. Minemura, and T. Suganuma, Rinsan Shikenjo Geppo (Hokkaido), 1979, 327, 15. L. L. Lamparski, R. H. Stehl, and R. L. Johnson, Environ. Sci. Techno(., 1980, 14, 196. K. J. Buchanan and W. J. McGill, Eur. Polvm. J.. 1980. 16, 309. 313, and 319.

542

Photochemistry -CH H4‘YHe

-CH2-CH0 I

P -

*

/Ill

*.

> o, C

___+

0.0,

I

R

4

eCH H QCHI I :o<.(0 C I R

Scheme 26

R-C-H Scheme 27

Scheme 28

Scheme 29

543

Polymer Photochemistry

Laser flash photolysis of o-tolyl vinyl ketone-methyl vinyl ketone copolymers [e,.g.,(17)] has produced some interesting observations.423The triplet state of the aromatic carbonyl decays to give 1,4-biradicalsthat are capable of transferring an electron to an acceptor such as paraquat. In the absence of an acceptor the macroradicals decay to yield photoenols, which then tautomerize to regenerate the original polymer (Scheme 30).

F";

IT

/

Scheme 30

Other studies on ketone containing polymers include copolymers of unsaturated ketones with styrene and methyl methacrylate 424 and poly(methylisopreny1 ketones)42s for use as photoresists. A review has appeared on the laser flash photolysis of vinyl ketones.426 In the photoageing of polycarbonates, photo-oxidation has been shown to be a more important process than the photo-Fries reaction.427The photo-oxidation of epoxy-resins has been found to depend on the type of hardener and its c ~ n c e n t r a t i o n .A~ ~correlation ~ has been observed between the changes in chemical structure and thermally stimulated current of poly(viny1 alcohol) during p h o t o - o ~ i d a t i o n Other . ~ ~ ~ studies of interest include the weathering of polymers 433 on polymers, effect of drawing,434effect o ~ t d o o r s , ~ ~effect ' - ~of ~ ozonation ~ of b i ~ d e g r a d a t i o n and , ~ ~ changes ~ in mechanical properties of thermoplastic^.^^^ 423 424

425 426

42' 428 429 430 03'

432

433 434

43s

436

J. P. Bays, M. V. Encinas, and J. C. Scaiano, Polymer, 1980, 21, 283. I. Naito, K. Koga, and A. Kinoshita, Kobunshi Ronbunshu, 1980,37, 77; G. Nenksv, T. Georgieva, A. Stoyov, and V. Kabaivanov, Angew. Makromol. Chem., 1980,91, 69. Y. Namdrijama, Nippon Shashin Gakkashi. 1980, 43, 298. A. Kineshita and I. Naito, Nippon Insatsu Gakkai Ronbunshu, 1980, 19, 29. A. Factor and M. L. Chu, Polym. Deg. Stab., 1980, 2, 208. V. Bellenger, C. Bouchard, P. Claveirolle, and J. Verdu, Polym. Photochem., 1981, 1, 69. H . Aoki, M. Uehara, T. Suzuki, and A. Yoshida, Eur. Polym. J., 1980, 16, 571. M. C. Gough, J . Appl. Polym. Sci., Appl. Polym. Sci., 1979, 35, 387. A. Davis, Polym. Deg. Stab.. 1981, 3, 187. G . Lubin and P. Donohue, Poliplasti. Plast. RinJ, 1980, 28,49. S. Imamura, M. Teramoto, Y. Ogawa, and H. Teranishi, J. Appl. Polym. Sci., 1980, 25, 997. G. Akay, T. Tincer, and E. Aydin, Eur. Polym. J.. 1980, 16, 597. S. J. Huang, C. Byrne, and J. A. Pavlisko, Am. Chem. SOC.,Symp. Ser., 1980,121, 299. J. Pabiot and J. Verdu, Polym. Eng. Sci., 1981, 21, 32.

544

Photochemistry

The photodegradation and photo-oxidation of poly(organ~siloxanes),~~ 7 ? 438 poly(N-~inylcarbazole),~~~ poly(alkoxyphosphazones),440 thymine-containing polymers,441 cellulose t r i a ~ e t a t e ,cellulose ~~~ acetophthalate complexes with poly(viny1 acrylonitrile-butyl acrylate-vinylene chloride terpolymer,444 446 polyethylene and poly(o-nitrobenzyl acrylate) 448 have been studied.

5 Photosensitized Degradation Ranby and Rabek449 have reviewed in depth the mechanisms by which various species sensitize the photodegradation of polymers. Photosensitive Polymers.-Li and Guillet 4 5 0 have prepared photosensitive polymers of ethylene copolymerized with carbon monoxide, methyl vinyl ketone, and methyl isopropenyl ketone. Infrared studies showed the presence of a number of unexpected ketone structures in all the copolymers formed as a result of a 1,5hydrogen transfer or ‘back-biting’ during the polymerization. Scheme 3 1 was proposed on the basis of analysis of the gaseous off-products for the photooxidation of the CO-containing copolymer and its minor ketone-containing side structures. The abundance of propene as a photoproduct is due to the Norrish Type I process giving rise to two macroalkyl radicals. Hrdlovic et al.45 have prepared photosensitive polystyrene by copolymerizing with benzalacetophenone, whereas Nakahira et af.452have prepared photosensitive methyl methacrylate by copolymerizing with an anthraquinone derivative. In the latter study the incorporation of hydroxyethyl groups was found to desensitize the polymer to light exposure through intramolecular chemical quenching of the anthraquinone triplet. Highly photosensitive poly(viny1 alcohol) has been synthesized by copolymerizing with stilbazolium 4 5 4 Films of this copolymer were used for immobilizing enzymes. Azuma et a1.455, 4 5 6 have I

03’

439

440 44 I

442

443

‘04 445 446

447 04’

449 45” OS1

45L 453

OSs

A. Gupta, J. Moacanin, T. Smith, and D. H. Kaelble, Polym. Prepr., Am. Chem. Soc., Div. Pol-vm. Chem., 1978, 19, 702. L. N. Pankratova, M. V. Zheleznikova, A. N. Goryachev, V. V. Severnyi, N. V. Varlamova, and E. A. Rogal, Vestn. Mosk. Univ.. Ser. 2 Khim., 1980, 21, 79. 0. V. Kolninov, K. V. Milinchuk, E. G. Strukov, and V. V. Kolesnikova, Vvsokomol. Soedin., Ser. A . , 1980, 22, 2042. W. T. Farran, J. P. O’Brien, and H. R. Allcock, Polym. Prep., Am. Chem. SOC.,Div. Poivm. Chem.. 1978, 19, 557. Y. Kita, T. Uno, Y. Inaki, and K. Takemoto, Nucleic Acids. Symp. Ser., 1979, 6, 563. T. M. Muinov, G. A. Gedrovich, V. A. Ustinov, and S. N. Isaev, Dokl. Akad. Nauk. Tadzh. SSSR, 1980, 23, 438. G. N. Sevastenko, I. N. Ermolenko, and E. G. Lomonosova, Vesti Akud. Navuk, USSR, Ser. Khim. Nuvuk, 1981, 1, 60. 1. Demetrescu and M. Tomescu, Rev. Roum. Chim., 1980, 25, 729. E. E. Said-Galiev, V~sokomol.Soedin., Ser. B , 1980, 22, 20. A. Toirov and T. M. Muinov, Dokl. Akad. Nuuk. Tudzh. S S R , 1979, 22, 538. U. Grollmann and W. Schnabel, Makromol. Chem., 1980, 181, 1215. H. Barzynski and D. Sanger, Angew. Makromol. Chem., 1981,93, 131. B. Ranby and J. F. Rabek, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 243. S. K. L. Li and J. E. Guillet, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 221. P. Hrdlovic, I. Lukac, I. Zvava, M. Kulickova, and D. Bereck, Eur. Pol-vm. J., 1980, 16, 651. T. Nakahira, H. Maruyama, S. Iwabuchi, and K. Kojima, J. Mucromof. Sci., Chem., 1980, 14, 779. K. lchimura and S. Watanabe, J . Pol.vm. Sci.. Polvm. Lett. Ed., 1980, 18, 613. K. Ichimura and S. Watanabe, J. Polym. Sci.,Polym. Chem. Ed., 1980, 18, 891. C. Azuma, T. Mitsuboshi, K. Sanui, and N. Ogata, J. Polvm. Sci.,Pol-vm. Chem. Ed., 1980, 18, 781. C. Azuma, K. Sanui, and N. Ogata, J. Appl. Polym. Sci., 1980, 25, 1273.

Polymer Photochemistry

545

Major component

JuCH~-CH,-CH,-C-CH,-CH~-

4

..-

p:E,!y

+

*CH,-CH,*

.C-CH,-CH,*

II

0

pnmaryltypc I t

k y l a t i o n

+ CH3-C-CH2-CH2*

-CH=CH,

co +

II

y2

0 secondary t),w/

H-CH,-CH,* CH,-C-CH, II 0

0 1 I CH,C*

-tCH,=CH*

vinyl

0 I1 CH,C-H

.~H,-cH,-

RY v + CH,=CH,

+ *CH,CH,-

*CH,CH,-

I . 5 radical /transfer

I. +

CH

,-( CH

2)j-

k H -C H ,*

I I

H-CH2CH2-

+

C3H,.

CH,*

CIH, Minor component H

I ~CHz-CHz-C-CHz-CH2m

type I

I

H I

I CH2

YH2

/E

I

H

*CH~--CH~-~-CH,-CH,I CJH,

if,,

11

CI H 11 CH,

('0+ H'

I. 4 radical transfer

c=o

*CHz-CH2-C-CHz-CH2-

HCO

1

I

?HZ fHZ

vinyl double bond

+

* *CH,-CH,-C-CH,-CH,-

+

CH,CHO

b-scission

*CH

C H 2- C-C H Z-CH

2-

II

2-

+

C 2H 5 *

CH2

py; 3 i - b C,H,

Minor component

m C H ,-CHZ-

H I C - C H ,-CH z* I CH2

c=o

H

I

m C H ,-C H -C=CH -C H disubstituted double bond

,* + C H ,COC ,H

I C2H5

Scheme 31

prepared photosensitive polymers based on hydroxymethylated polydienes and copolymers of polydienes with cqhnsaturated carboxylic acids. Other photosensitive polymers include polyamides copolymerized with 4,4'-bis(chloroformy1)benzil 4 5 7 and pol yo xi mu re thane^.^^^ 4s7

4s8

K. Nagakubo, M.Miura, and F. Akutsu, Kankyo Kagaku Kenkya Hooku (Chiba Daigaku), 1978,3, 37. E. M. Lipskerova and M. Ya. Melnikov, Pol-vm. Bull., 1980, 2, 653.

546

Photochemistry

Photoactive Additives.-Ferric compounds, in particular, the chloride, continue to attract much interest as photosensitizers for thermoplastic^.^^^-^^^ From e.s.r. work the mechanism appears to involve a redox reaction resulting in the formation of active hydroxy-radicals. Photodegradable polyethylene film has been developed by doping it with radiation-modified atactic polypropylene 463 and hydroxyethylf e r ~ o c e n eSeveral . ~ ~ ~ workers have studied the dye-sensitized photo-oxidation of polyisoprene 465 and di-n-butyl sulphide embedded in PVC 466 Augustyniak and Wojtczak 467 have found that the photosensitized degradation of polyethylene glycols decreases in the order triethylene glycol > polyethylene glycol 400 mol. wt. > polyethylene glycol 4000 mol. wt. Sastre and Gonzalez 468 have shown that bromoalkanes are powerful sensitizers for the photo-oxidation of polystyrene, and Rabek and Ranby 469 have found that polynuclear aromatics are photosensitizers for polybutadiene. Aromatic carbonyls have been shown to induce free-radical formation in cellulosic materials.470 6 Photostabiliza tion The photostabilization of polymers continues to be a rapidly advancing area of scientific and technological interest. Carlsson and Wiles 471 - 4 7 4 have written several reviews on photostabilizing mechanisms in polymers, while Swasey 4 7 5 has given an updated guide to stabilization, and Reid476has discussed the effects of stabilizers in vinyl polymers. Nemzek and Mayo 477 have predicted the service life of polypropylene, and Bredereck 478 has reviewed the photostabilization of PVC. Several comprehensive review articles have appeared. Pospisil 479 has reviewed in considerable depth the photo-oxidation mechanisms of phenolic anti-oxidants, Shlyapintokh 480 has reviewed the kinetics of stabilizer distribution, Vink 48 has 459

460 46 I 462

463 464

06’

*“ 467

4hu 46y

*” 471 472

473 4’4

475 476

477 47u 479

480 481

Z. Joffe and B. Ranby, J. Appl. Polym. Sci., Appl. Polym. Svmp., 1979, 35, 307. J. F. Rabek, G. Canback, and B. Ranby, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 299. A. Negishi and Y. Ogiwara, J. Appl. Pol-vm. Sci., 1980, 25. 1095. T. V. Pokholok, N. I. Zaitseva, G. B. Pariiskii, and D. Ya. Toptygin, Vysokomol. Soedin., Ser. A , 1980, 22, 196. H. Omichi and M. Hagiwara, Polym. Photochem., 1981, 1, 15. M. Z. Borodulina, M. S. Kurzhenkova, T. E. Pashchenko, T. N. Zelenkova, and T. M. Yanishihikova, Plenoch Polim. Muter. Ikh Primen. Muter. Kratkosrochnogo Semin, 1977, 43. J. Chaineaux and C. Tanielian, J. Appl. Polym. Sci., Appl. Polvm. Symp., 1979, 35, 337. R. A. Kenley, N. A. Kirshen, and T. Mill, Macromolecules, 1980, 13, 808. W. Augustyniak and J. Wojtczak, J. Polym. Sci., Pol.vm. Chem. Ed., 1980, 18, 1339. R. Sastre and F. Gonzalez, Pol-vm. Photochem., 1981, 1, 153. J. F. Rabek and B. Ranby, Rev. Roum. Chim.. 1980, 25, 1045. A. Merlin and J. P. Fouassier, Angew. Makromol. Chem., 1980, 86, 109. D. M. Wiles and D. J. Carlsson, Chemtech, 1981, 11, 158. D. J. Carlsson and D. M. Wiles, Pol-vm. Prepr.. Am. Chem. SOC.,Div. Pol.vm. Chem., 1979, 20, 387. D. M. Wiles and D. J. Carlsson, Pol.vm. Deg. Stab., 1980, 3, 61. D. J. Carlsson and D. M. Wiles, Polym. News, 1980, 6 , 152. C. C. Swasey, Plast. Eng., 1980, 36, 33. W. J. Reid, J. Vinyl Technol., 1979, 1, 76. T. L. Nemzek and F. R. Mayo, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1978, 19, 679. P. Bredereck, J. Vinyl Technol., 1979, 1, 218. J. Pospisil, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 3, p. 53. V. Ya. Shlyapintokh, in ‘Developments in Polymer Photochemistry’, ed. N. S.Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 6, p. 215. P. Vink, in ‘Developments in Polymer Stabilisation’, ed. G. Scott, Applied Science Publishers Ltd., London, 1981, Vol. 3, Chap. 4, p. 117.

547

Polymer Photochemistry

discussed the processes of stabilizer loss, and Allen482has reviewed in depth the mechanisms of photostabilization by hindered piperidine compounds. Carlsson et al.483have also reviewed the mechanisms of stabilization by hindered piperidines, and several workers 484* 485 have discussed synergism in polymers. The photostability of synthetic fibres has also been examined.486 Of all the photostabilizers now in commercial use, those based on the hindered piperidine structure have attracted the most interest. On the commercial front, several workers have shown how effectively photostabilizers operate in a 488 and in one article Karrer 489 has described in considerable detail methods of their preparation. On the scientific front there has been considerable activity into their mode of operation. It is now well established that these hindered-piperidine stabilizers operate through a radical scavenging mechanism to produce a substituted hydroxyalmine, as in Scheme 32.

Scheme 32

Recent e.s.r. work by Hodgeman4" has shown that a high percentage of the nitroxyl radicals produced from the amine above are linked to the macromolecular backbone. In fact, work by Allen and McKellar 491 has shown that the nitroxyl radical can inhibit the initial photoisomerism of photoactive ct,j?-unsaturated carbonyl impurity groups in polypropylene by linking onto the y-carbon radical site in the polymer chain. The radical scavenging behaviour of these hinderedpiperidine compounds has been confirmed by the detailed work of Son 4 9 2 and it is interesting to note that in this work the stability of the nitroxyl radical appeared to be a vital factor in controlling stabilizing performance. According to Chakraborty and Scott 493 the hydroxylamine acts as a reservoir for the regeneration of nitroxyl radicals by reaction with peroxy radicals [equation (l)]. It is this regeneration process that is responsible for their exceptional light-stabilizing performance. In fact it is believed that this regeneration process can occur up to ten times for each \

/

N-0-P

+ \

POz*

AH*+ ,N-0. 482

483 484 485 486

48'

488

489

490 491 492

493

-

\

+

,N-O. A

+

\

,N-O-H

P0,P

(1)

(2)

N. S. Allen, in 'Developments in Polymer Photochemistry', ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 7, p. 239. D. J. Carlsson, D . M. Wiles, and D. W. Grattan, Org. Couf. Plasr. Chem., 1978, 39, 628. I. Tincul, C. Variu, M. Laiber, M. Cotovanu, and C. Boboradea, Muter. Plust., 1979, 16, 229. N. A. Rozenborn, L. G. Angert, V. B. Ivanov, and V. Ya. Shlyapintokh, Kuuch. Rezina. 1980. 31. P. Ts. Lioniskii and A. F. Chudakov, Soversh. Tekhnol. Pererab Khim. Volokon, 1980, 3, 36. G . P. Balint, T. Kelen, F. Tudos, and A. Rehak, Magy, Kern. Foly, 1980, 86, 366. V. P. Biryakov, V. A. Gerasimovich, V. G . Kalashnikov, G . M. Trasaran, and L. A. Skriplev, KozhObaun, Prom-sti, 1979, 21, 31. F. E. Karrer, Makromol. Chem., 1980, 181, 595. D. K. Hogeman, J . PoZvm. Sci., Po1.vm. Chem. Ed., 1981, 19. 807. N. S. Allen and J. F. McKellar, Eur. Polym. J., 1980, 16, 553. P. N. Son, Polym. Deg. Stab., 1980, 2, 295. K. B. Chakraborty and G . Scott, Polymer, 1980, 21, 252.

548

Photochemistry

radical. Such a regeneration process was demonstrated by Allen 495 using flash photolysis. In this work the nitroxyl radical was found to completely inhibit the formation of the semiquinone radical (AH .) on flash photolysis of anthraquinone in n-hexane by the regeneration process: shown in equation (2). It is seen that this mechanism results in regeneration of the original quinone. The hindered piperidine had no effect on transient absorption indicating the nitroxyl radical is the active species. The hindered piperidines, however, were effective in inhibiting the photosensitized oxidation of polypropylene by aromatic carbonyl compounds, including anthraq~inone.~'~ One other problem with these hindered-piperidine compounds is the first step in Scheme 32, which is the conversion of the amine to a nitroxyl radical. Allen 495 has produced evidence to show that the amine group is converted quantitatively by thermally-generated hydroperoxides in polypropylene to the nitroxyl radical. However, Sedlar et a1.497*498 have shown that such an oxidation process does not occur, at least for photogenerated hydroperoxides. They do, however, provide evidence to show that the hindered amine and nitroxyl radical are capable of forming associated complexes with hydroperoxides. This confirms earlier work by Wiles and ~ o - w o r k e r s where , ~ ~ ~ they found that the solubility of nitroxyl radicals in polypropylene increased with an increase in irradiation time (Table 4). This association process is highly important since the nitroxyl radical will be in a position ready for immediate reaction with the radicals produced on photolysis of the hydroperoxides. 4949

Table 4 Solubility of nitroxide Z in photo-oxidized P P j l m s Photo-oxidation" (h) 0

40 57 70 57 (+ SF, or SO,)

[ - OOH]" M X lo2 ~ 0 . 5 3.2 14 30 t0.5

[I3'

M x 104

1.5 6.6 14 26 0.5

Irradiation in an Atlas xenon arc Weather-Ometer. * Hydroperoxide concentration after irradiation, estimated from the 3400cm-' i.r. absorption (extinction coefficient = 70111-lcm-'). 'After 8 h immersion in 3.3 x lop2M solution of I in iso-octane.

The interactions of these hindered-piperidine compounds with other conventional stabilizers has also attracted widespread interest. Allen et al. 500 have clearly shown that the presence of phenolic anti-oxidants antagonize the stabilizing performance of hindered-piperidine compounds. Furthermore, their performance is drastically reduced by processing and this effect is demonstrated in Table 5 for bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (known commercially as Tinuvin 770) and a commercial phenolic anti-oxidant, Irganox 1010. With U.V. absorbers such as the 2-hydroxybenzophenones the hindered piperidines seem to 494 495 496

497

498

N. S. Allen, Polym. Deg. Stab., 1980, 2, 269. N. S. Allen, Makromol. Chem., 1980, 181, 2413. N. S. Allen, Polym. Deg. Slab., 1980, 2, 179. .I. Sedlar, J . Petruj, J. Pac, and A. Zahradnichova, Eur. Polym. J., 1980, 16, 659. J. Sedlar, J. Petruj, J. Pac, and A. Zahradnichova, Eur. Polym. J . , 1980, 16, 663. K. H. Chan, D. J. Carlsson, and D. M. Wiles, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 607, N. S. Allen, J. Luc-Gardette, and J. Lemaire, Polym. Photochem., 1981, 1, 111.

'""

499

Polymer Photochemistry

549

Table 5 Efect of processing history (190 "C)on the light stability of polypropylene films (300 pm) containing Irganox 1010 and hindered-piperidine additivies (0.1% each). Exposure unit: microscal-1000 Additive

Irganox 1010 Nitroxyl radical Tinuvin 770 Tinuvin 144 Nitroxyl radical + Irganox 1010 Tinuvin 770 + Irganox 1010

W

Embrittlement times (h) Solvent blended 10 min 20 min 125 75 60 260 250 260 1100 540 440 950 450 400 240 210 150 lo00 560 575

30 min 80 260 550 500 220 590

perform very well. In fact, Allen et aLSo1have shown that both the hinderedpiperidine compounds and its nitroxyl radical inhibit the photolysis of 2hydroxylbenzophenonesin polypropylene. The inhibition process was found to be more effective with the amine derivative owing to its ability to destroy hydroperoxides. The 2-hydroxybenzophenones are known to be destroyed by active hydroxyl radicals produced in the photolysis of hydroperoxides, and recent work by Scott and YusoffSo2 has shown this. The nitroxyl radicals will, of course, protect the 2-hydroxybenzophenone stabilizer by trapping the active hydroxyradicals. B a h t et aLSo3have shown that the presence of a 2-hydroxybenzophenone absorber inhibits the build-up of nitroxyl radicals from these hinderedpiperidine compounds during photo-oxidation, but the mechanism involved was uncertain. Hindered-piperidine compounds have been found to be highly effective in protecting recycled pigmented polypropylene in a relatively dry atmosphere, but in a humid atmosphere their efficiency is reduced. Whitefield et al. have developed some novel 2,2'- and 4,4'-dinitrobiphenyl compounds that also give rise to highly effective nitroxyl radicals in the photo-oxidation of polybutadiene. The role of U.V. absorbers such as the 2-hydroxybenzophenones and 2hydroxybenzotriazoleshave also attracted some interest. Ivanov and Anisimov 5 0 7 believe that the former type stabilize by quenching photoactive excited species in polymers, whereas the latter type have been shown by Hodgeman and Gellert to be converted by hydroperoxides into active dienones. This latter effect is believed to account for the poor stabilizing action of these additives in processed polymers. Several workers have examined the effect of grafting stabilizing molecules onto For example, Burchill polymers and the results appear to be conflicting. l o 501 502

503 504

505 506

'lo 511

N. S. Allen, J. Luc-Gardette, and J. Lemaire, Polym. Deg. Stab., 1981, 3, 199. G. Scott and M. F. Yusoff, Polym. Deg. Stab., 1980, 2, 309. G . Baht, A. Rockenbauer, T. Kelen, F. Tudos, and L. Jokay, Polym. Photochem., 1981, 1, 139. N. S. Allen and J. F. McKellar, Plast. Rubb., Mat. Appl., 1980, 5, 67. N. S. Allen and J. F. McKellar, Eur. Polym. J., 1980, 16, 544. R. H. Whitfield, D. I. Davies, and M. J. Perkins, Chem. Ind., 1980, 418. V. B. Ivanov and 0. M . Anisimov, Dokl. Akad. Nauk, SSSR., 1980, 253, 1401. D. K. C. Hodgeman, J . Macromol. Sci., Chem.. 1980, 14, 173. D. K. C. Hodgeman and E. P. Gellert, J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 1105. P. J. Burchill and D. M. Pinkerton, Polym. Deg. Stab., 1980, 2, 239. H. Watamoto and H. Tonami, Nippon Kaguku Kakhi, 1980,7, 1163. B. D. Saidov and U. G. Gafurov, Uzb. Khim. Zh., 1980, 5, 57. D. Adams and D. Braun, J . Polym. Sci., Polym. Lett. Ed., 1980, 18, 629.

550

Photochemistry

and Pinkerton 510 have shown that y-ray-induced grafting of a 2-hydroxybenzophenone absorber into polypropylene is less efficient than the simpler addition process, whereas Watamoto and Tonami 5 1 have shown that pad-curing of alkyl benzoxazole stabilizers into cellulose give much improved resistance to U.V.light Clearly, the method of application could be vitally important here. The use of yrays for grafting could have a deleterious effect in the polymer itself and this was not accounted for. Chandra et al. 14- 5 1 ha ve studied in depth the photostabilization of poly(but-1ene). Hydroxyphenyltriazine-N-oxideswere found to be highly efficient stabilizers. Carotenoids have been found to be effective photostabilizers in cispoly(buta-l,4-diene) owing to their singlet oxygen quenching ability,518but their commercial application was not apparent. Al-Malaika and Scott l 9 have found that nickel dialkyldithiophosphates and xanthates are effective photostabilizers for polyethylene. Their activity is believed to be due to their inherent stability to U.V. light, which enables them to act as light-stable reservoirs for active species in the polymer. Fernando and Scott 5 2 0 have found that binding an anti-oxidant ( 3 3 di-t-butyl-4-hydroxybenzyl mercaptan) and a U.V.stabilizer (4-benzoyl-3-hydroxyphenyl-0-ethylthioglycollate)to acrylonitrile-butadiene-styrene terpolymer improves its thermal and light stability, in contrast with the results of other workers.5 1 Dioctyltin bis(iso-octylthioglycollate) has been found to be an effective stabilizer for PVC,521while in the same polymer the efficiency of lead stabilizers has been examined,522as has the performance of stabilizers in a 1 :4 blend of PVC with polyurethane^.^^^ Other articles of interest on photostabilization include oligomeric azomethanes 5 2 5 and carbazolesulphonanilates 5 2 6 in cellulose acetate, phosphonates 5 2 7 in impact resistant polystyrene, manganese 5 2 8 and heterocyclic 5 2 9 compounds in polyamides, transition-metal compounds in u.v.-curable resins,53o oxanilides in paints,531 phosphites in styrene-acrylonitrile copolymer,532copper 5243

514 515 516 '17

'"

519 520 521

s22 523 524

525

s26 527

528 529

'jO

531

532

R. R. R. R.

Chandra and R. P. Singh, Indian J. Technol., 1980, 18, 250. Chandra, R. P. Singh, and A. Syamal, Indian J. Chem., 1980, 19, 20. Chandra and R. P . Singh, Makrornol. Chem., 1980, 181, 1637. Chandra, Eur. Pol-vm. J., 1980, 16, 1207. J. F. Rabek and D. Lala, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 427. S. Al-Malaika and G. Scott, Eur. Polvm. J., 1980, 16, 709. W. S. E. Fernando and G. Scott, Eur. Polym. J . , 1980, 16,971. D. Braun and S. Kull, Angeiv. Makromol. Chem., 1980, 87, 165. J . Imhof, W. Schdmshula, and R. Haberleitner, J. Vinyl Technol., 1979, 1, 47. Z. Zamorsky, Plasty Kauc., 1980, 17, 110. 0. A. In, K. M. Makhkamov, I. Ya. Kolontarov, and Yu. N. Polyakov, Vopr. Khim. Ekol Tekst. Prve, L . 1979, 110. 0. A. In, 1. Ya. Kolontarov, K. M . Makhkamov, M. R. Marupov, A. Usmanov, Yu. N. Polyakov, and V. I. Sobolev, Izv. Akad. Nauk Tadzh. SSR Otd. Fi-..-Mat. Geo1.-Khim. Nauk. 1979, 3, 92. N. E. Maksimova, V. I. Shishkina, I. Ya. Kakdntarov, F. F. Niyazi, and A. Abadirazakov, Dokl. Akad. Nauk Tadzh. SSSR, 1980, 23, 713. L. A. Zhidkova, G. M . Baranov, V. G. Kutimova, A. A. Efimov, and A. F. Tyutereva, Plast. Mass),, 1980. 10, 42. R. Gurau, Matrr. Plast. (Bucharest), 1980, 17, 98, E. V. Vichutinskaya, E. V. Merkur'eva, L. M. Postnikov, and L. N. Smirnov, Plast. Massv, 1980,6, 54. M. J . Malin, J. Appl. Polym. Sci.. 1980, 25, 26, 13. L. Wlhan, Polsm. Paint. Colour J., 1980, 170, 696. M. Panaiotova, Z. Nikolova, K. Kovacheva, and M. Petkova. Sb. Dok1.-Nats. Konf. Mladite Nanchni Rah. Spets. "eft. Khim', lst, 1976. 154.

Polymer Photochemistry 55 1 and nickel salts in silk,533 anti-oxidants in p o l y ~ h l o r o p r e n e ,stabilizers ~~~ for elastomers 535 and poly(benzoxazoles),536and the influence of crosslinking on p~lyethylene.~~’ The luminescence properties of 2-hydroxyphenylbenzotriazole stabilizers 5 3 8 and the photochemistry of sterically-hindered phenols 539 have also been studied.

7 Photochemistry of Dyed and Pigmented Polymers This Section deals only with research papers directly or indirectly concerned with the photochemistry of dyes and pigments in polymers. An excellent book has appeared in the photochemical properties of dyes and pigments in polymer systems.540In this book, Owen has reviewed absorption and emission properties of dyes, Giles and Forrester the physical factors influencing the fading of dyes, Leaver has discussed reduction and oxidation processes, Evans has discussed structural effects on light stability, and Allen and McKellar have reviewed photosensitized oxidation processes. In another book, Griffiths 541 has reviewed the photochemical fading of azo-dyes, while Allen and McKellar 542 have reviewed their work on the influence of structure on the photofading of anthraquinone dyes. Sinclair 543 has reviewed photodegradation reactions of dyes, and Kitao 544 has reviewed the involvement of singlet oxygen in the photofading of dyes. Arnaud and Lemaire 5 4 5 have reviewed in depth the photocatalytic oxidation of polyolefins and polyamides by TiO, and ZnO pigments. McKellar and Phillips546have discussed the phototendering properties of anthraquinone dyes. A number of articles have appeared on pigments, in particular titanium dioxide. Colling and Dunderdale 547 have reviewed the durability of titanium dioxidecontaining paint films, and Hauffe and Viswanath 548 have developed a model for the photochemical behaviour of rutile, and Voelz et aLS4’ have developed a new exposure device for monitoring the weathering of pigmented polymers. Some pigments have been found to impair the photostabilizing performance of hindered 533 534

535

F. Shinizn, S. Iwasaki, and I. Sakaguchi, Nippon Sanshiguku Zusshi, 1979, 48, 473. R. A. Petrosyan, S. A. Kazaryan, and R.V. Bdgdasargan, Vwokornol. Soedin., Ser. A , 1980,22,277. Yu. S. Korshov, V. V. Moiseev, T. P.Zharkikh, and V. P. Safinova, Promorsti, Sin(, Kauch, 1980,12, 17.

536 537 538 539 540

541

542 543 544 545

546

54’ 548

549

B. Desparx, N. Paillons, A. Lattes, and A. Paillous, J. Polym. Sci.,Polym. Chem. Ed., 1980, 18, 593. M. Narkis, Mod. Plust., 1980, 57, 68. A. A. Efimov and V. S. Sivokhin, Dokl. Akad. Nauk. SSSR, 1980,250, 387. L. V. Samsonova, V. Ya. Shlyapintokh, and V. V. Ershov, Vysokomol. Soedin., Ser. A , 1980,22,209. E. 0. Owen, Chap. 1; C. H. Giles and S. D. Forrester, Chap. 2; N. A. Evans, Chap. 3; I. Leaver, Chap. 4; and N. S. Allen and J. F. McKellar, Chap. 5; in ‘Photochemistry of Dyed and Pigmented Polymers’, ed. N. S. Allen and J. F. McKellar, Applied Science Publishers Ltd., London, 1980. J. Griffiths, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 6, p. 145. N. S. Allen and J. F. McKellar, in ‘Developments in Polymer Photochemistry’, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 7, 191. R. S. Sinclair, Photochem. Photobiol., 1980, 31, 627. T. Kitao, Kuguku Kogyo, 1980,31, 1035. R. Arnaud and J. Lemaire, ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 1, Chap. 4, p. 135. J. F. McKellar and G. 0. Phillips, fnd. Eng. Chem. Prod. Res. Dev., 1980, 19, 23. J. H. Colling and J. Dunderdale, Prog. Org. Coat., 1981, 9, 47. K. Hauffe and R . P. Viswanath, Chem.-Ztg., 1980, 704, 295. H. G . Voedz, G. Kaempf, and A. Klaere, Furbe Lucke. 1980, 86, 1047.

552

Photochemistry

’

piperidine compounds in polypropylene fibre^,^ and Schwindt 5 1 has developed a new method for characterizing the durability of Ti0,-pigmented coatings. The role of TiO, pigments in the weathering of paints has also been examined by many other workers.552*5 5 3 Davidson and Meek 554 have observed that TiO, pigments considerably suppress the formation of hydroperoxides during the photooxidation of polyolefins. They believe that the pigment is catalytically inducing the decomposition of the hydroperoxides to carbonyl groups. Rasti and Scott have observed that although verdigris (basic copper acetate) effectively inhibits the photo-oxidation of paints it can induce some yellowing.555.5 5 6 The photofading of dyes continues to attract much interest. Shakra and coworkers 5 5 7 , 5 5 8 have observed that hydrogen bonding has an important influence on the light stability of azo-dyes, and Hida and Yabe 5 5 9 have proposed a kinetic model for the photofading of bis(alkylbenzoxazoly1)dyes based on a simultaneous trans-cis isomerization and photodimerization process. Sorokina et al.5 6 0 have observed a relationship between the concentration of stable paramagnetic centres, measured by e.p.r. and the light stability of dyes. The y-ray induced grafting of acid dyes on nylon was found to much improve their light stability, whereas on acrylonitrile no improvement was observed.56 Crease-proofing agents, on the other hand, have been found to accelerate the photofading of dyes.562Allen and co-workers 563* 564 have investigated the mechanism of the photofading of basic triphenylmethane dyes. They observed a correlation between transient absorption due to the triphenylmethyl radical on flash photolysis of the dyes in isopropanol and their poor light stability in cellulose. These workers also found that the presence of a triplet donor, benzophenone, and a hydrogen-atom donor, benzhydrol, considerably accelerate the fading of basic dyes in non-reductive environments like polyacrylonitrile. According to the following mechanism, basic cationic triphenylmethane dyes fade through an electron-transfer step to give the dye radical (Do) (Scheme 33). Confirmation of the electron transfer step is shown by the results in Table 6 where it is seen that three electron traps, namely tetracyanoethylene, acetone, and nitrous oxide, reduce or inhibit completely the production of the dye radical on flash photolysis of Malachite Green. The mechanism of the catalytic photofading of yellow azo-dyes by blue anthraquinone dyes has attracted much interest. Two independent groups of 550 551

552 553

554 555 556

55’ 558 559 560

561 562

563 564

F. Steinlin and W. Saar, Melliand Testilber. h t . , Text. Rep. (Germ), 1980, 61, 941. R. Schwindt, ind. Vernice, 1979, 33, 19. R. R. Blakey, Congr. FATIPEC, 1980, 15th, I , 1-244. H. G. Voelz, G . Kaempf, and A. Klaeren, Congr. FATiPEC, 1980, 15th, 1 1 1-41. R. S. Ddvidson and R. R. Meek, Eur. Polym. J . , 1981, 17, 163. F. Rasti and G. Scott, Eur. Pofym. J . , 1980, 16, 1153. F. Rasti and G. Scott, Stud. Conserv., 1980, 25, 145. S. Shakra and A. A. G . Ghattas, Kolorisztikai Ertesito. 1979, 21, 287. S. Shakra, H. L. Hanna, and A. Hebish, Angew. Makromol. Citem., 1981, 93, 7 5 . M. Hider and Y. Yabi, Seni Gakkaishi, 1980, 36, T85. L. S. Sorokina, G. E. Krishevskii, 0. Ya. Grinberg, and A. I. Dubinskii, I n . Vyssh. Uchebn, Zaved. Tecknol. Tekst. Prom.-Sti., 1979, 2, 42. W. B. Achwal and M. R. Nagar, Ind. J . Text. Res., 1979, 4, 49. I. I. Shiiko, B. D. Semak, and G. D. Korodenko, Izv. Vyssh. Uchebn. Zaved. Technol. Legk. Prom-sti., 1979, 22, 9. N . S. Allen, J. F. McKellar, and B. Mohajerani. Dyes Pigments. 1980, 1, 49. N. S. Allen, B. Mohajerani, and J. T. Richards, Dyes Pigments, 1981, 2, 31.

Polymer Photochemistry DyeD+

A

+

553

'D+ + 3D+

3D+ substrate or solvent D + + + e' (solvated) D. + solvent D + + e' (solvated) DH + D + + O H 2D. + H 2 0 and/or 02' + solvent e' (solvated) + O2 02;-+ H 2 0 H 0 2 ' + OH2HO; H 2 0 2 + 0, D+ + H202 oxidation products

- -

Scheme 33

Table 6 Eflect of additives on the transient absorption produced onflash photolysis of Malachite Green and Para Rosaniline in nitrogen saturatedpropan-2-01 (Pyrex cell) Additive Control N-oxy radical Tetracyanoethylene Acetone Nitrous oxide a&,ax

=

450nm. 'Amnx

=

Transient absorption (log, Io/I,) Malachite Green" Para Rosanilineb 4.2 x 8 x 2.2 x 4.1 x 2.9 x 10-3 4.8 x 1 0 - 3 None None None None

440nm.

workers565,566appear to confirm the involvement of singlet oxygen in the catalytic fading mechanism. However, both studies were carried out in solution and as yet the degree of involvement of singlet oxygen remains obscure. Singlet oxygen is also believed to be important in the photosensitized oxidation of cellulose by vat Certain azo-dyes were found to undergo both photoreductive and oxidative fading in alcohol solution, but in acetone only oxidation was In another study, ultraviolet absorbers were found to inhibit the photofading of a basic cationic dye.569 In acetic acid, rhodamine B has been shown to fade by d e a l k y l a t i ~ n , ~and ' ~ certain fluorescent brightening agents have been shown to induce photoyellowing in silk. 7 1 The luminescence properties of xanthene and 573 acridine dyes have been quantified.572*

565 566 s67

s69 570

5"

572

s73

N. Kuramoto and T. Kitao, J. Chem. Technol. Biotechnof., 1980.30, 129. M . W. Rembold and H. E. A. Kramer, JSDC, 1980, %, 122. B. Garston, JSDC, 1980, 96, 535. N. Kuramoto and T. Kitao, JSDC, 1980,%, 529. H. Suzuki, Y. Tanaka, and Y. Ishii, Seni Gakkaishi, 1980, 36. T535. T. Yamakawa, J. Koshitani, Y. Ueno, and T.Yoshida, Aromatikkusu, 1979, 31, 290. M. Minagawa and Y. Yoshida, Osaka Shiritsu Daigaku Seikutsukagakubn Kuyo, 1979, 27, 91 I. Hamori, E. Farkas, and L. Kozma, Acta Phys. Chem., 1979. 25, 97. R. T. Kuznetsova, R . M. Fofonova, and V. I. Danilovd, Zh. Fiz. Khim., 1980, 54, 1475.

554

Photochemistry

8 Appendix: Review of Patent Literature Photopolymerizable Systems.-The following patents have appeared on photopolymerizable systems for UK, Europe, West Germany, Japan, and USA. European (other than U K and W. Germany) 7265 6777 17 555 17 364 12 652 10 355 6370 8246 14 785

8837 12 079

7059 7468

13939 18672

UK 2015003 2027921

2037550 1550811

1 560 822 I 570 992

2 019 398

1 564 543

2017723

1564542

W. Germuny 2 325 955 2 923 602 2 934 929 2 842 641 2951 763 3 006 960 3 010 534 2917837

2 9 19 094 3014581 2917861 3 009 928 3018 891 2 828 453 2 829 259 2 937 266

2944817 3 002 922 3 007 572 2 909 379 2917833 2915011 3014722

3013 170 2 906 193 3 027 574 2 829 256 2830928 2842004 2949349

3000305 3 006 167 3 009 942 2 948 127 2913853 2948 127 3007212

2928512 3 029 247 2 829 258 2831 159 2842935 2 938 292 2 807 933

2930224 3 909 993 2 842 938 2909993 2917847 3 008 657 3 023 696

USA 4229514 4 192 794 4 198465 4202742

4203919 4209 371 4218392 4 181 752

4 194955 4 199648 4210691 4207 155

4214026 4227980 4 167464 4 191 622

4 197 173 4 199420 4201 842 4218295

4233425 4189366 4 188455 4203723

4201 640 4208471 4221 892 4238619

79,153 890 79,154 447 79,160 49 1 80,09 004 79,152 075 80,03 44 I 79,133 527 79,139 943 79,144469 79,132 633 79,153 855 79.144 437 79,143 493 79,162 734 80,27 2 14 80,25 441 80,34 2 1 1 80,38 809 80,45 748 80,52 353

80,60 526 80,137 117 80,102 604 80,99 9 17 80,112 276 80,12 1 057 80,108 4 12 80,142 070 80,80 476 80,71241 80,75 459 80,80433 80,46 750 80,94 9 19 80,112 21 1 80,123 659 80,134 673 80,98 742 80,140 551 80.133 468

80,139 883 80,142 07 1 80,09 465 80,45 753 80,45 747 80,42 246 80,lO 303 80,59 965 80,89 365 80,99 9 I0 80,110 121 80,108 479 80,104 3 18 80,116 725 80,154 I58 80,92 637 80,92 635 80,OO 97 1 80,125 117 80.54 362

80,82 167 80,102652 80,108 47 1 80,27 337 80,139 216 8I ,00 8 14 80,144 342 80,155 0 12 80,09 644 80,45 749 80,09 624 80,36 226 80,62 975 80,65 264 80,99 9 19 80,94 938 80,125 123 80,106 567 80,112219 80,137 127

80,65 2 17 8032 3 10 80,65 21 1 80,71 704 80,73 61 8 80,71 705 80,65 2 19 80,127 097 80,127 467 80,108 663 80,127 468 80,145 717 80,142003 80,149 3 13 80,25 404 80,23 139 80,36 240 80,40 732 80,04 770 80,116 763

80,79 07 1 80,86 844 80,104 347 80,112219 80,99 922 80,142072 80,58 2 13 80,75 403 80,78 027 80,82 113 80,69 678 80,45 75 1 80,80 414 80,86 848 80,33 944 80,108 664 80,33 441 80,133 999 80,152 573 80,90 506

Japan 79,162 798 79,130 633 79.128 482 80,OO 735 79,148 094 79,143 776 79,155 268 79,155244 80,16 083 79,127 444 79,146 834 79,138037 79,153 889 79,130693 79,12403 1 79,95 69 1 80,Ol 846 80,18 463 79,162 784 79,116388 79,118 499

578

576 577

575

574

For polyethylene

-

578

577

For polyethylene 25%

575

574

-

= Ph, pyridyl, or Bz; R2 = Me, Ph, or pyridyl

Canadian Titanium Pigments Ltd., Can. P, 1073 581, 1980. Owen-Illinois Inc., US P, 4 191 320, 1980. I. Lukac, I. Zvara, P. Hrdlovic, and Z. Manasek, Czech. P, 2 179304, 1979. Chevran Research Corp., US P, 4 197 375, 1980. Societe Chimique des Charbonnages, Can. P, I 072 803, 1980.

Polyisobutylene Iron carboxylates

for polypropylene

polyethylene

3-7.5%

Application

576

R'

Unsaturated ketones R iC H d H C O R 2

Specification

For styrenes polymers

-

Benzophenone 2-ethylanthraquinone

+

-

Anatase

Class and general formula

Table A1 Prodegradant and U.V.sensitizers

Photochemistry

0

00 IA

c

a

4

;2

N

r-4

c

599

598

597

596

595

594

593

592

591

590

589

5B8

587

584

583

582

580

579

R = Ph,H2C=CH,Me,C, octyl,3,5-di-t-butyl4-hydroxyphenyl, PhCH =CH, cyclohexy1 R' = Me,Me,C, cyclohexyl, or 1-methylcyclohexyl R2 = Me or Et; R3 = H,Me,CH, or Me,CHCH,CMe,CH, For PVC, polyolefins, polyesters, etc.

Institute of Physical-Organic Chemistry, Academy of Sciences, Belorussian SSR; Polimir Industrial Enterprises, USSR P, 740 787, 1980. American Cyanamid Corp., US P, 4 192796, 1980. Kyodo-Chemical Corp., Jap. P, 80,89 344, 1980. Borg-Warner Corp., G P, 2914312, 1980. Eastman Kodak Corp., US P, 4 194989, 1980. Adeka Argus Chem. Co. Ltd., Jap. P, 80,13762, 1980. Ciba-Geigy AG, Jap. P, 79,141 753, 1979. Kyodo Chemical Co Ltd., Jap. P, 80,129437, 1980. Adeka Argus Chemical Co Ltd., Jap. P, 80,05927, 1980. Adeka Argus Chemical Co Ltd., Jap. P, 79,154442, 1979. American Cyanamid Corp., Eur. P, 10 346, 1980. Institute of Physical-Organic Chemistry, Belorussian SSR, USSR P, 744 001, 198 1. Ciba-Geigy Corp., US P, 4233 207, 1980. Ciba-Geigy AG, G P, 3 010 749, 1980. GAF Corp., US P, 4233442, 1980. Mobil Oil Corp., Eur. P, 5345, 1980. Asahi Chemical Ind. Co. Ltd., G P, 2984468, 1980. L. A. Skiyiko, Z. G. Lapova, T. A. Pankova, V. M. Levin, E. N. Lerkureva, and E. I. Kirillova, USSR P, 732257, 980. Ciba-Geigy AG, Eur. P, 6564, 1981. Asaki Chemical Ind. Co. Ltd., Jap. P, 80,106258, 1980. E. I. Kinllova, A. T. Emelyanova, E. S. Lenina, A. F. Nikolaev, V. S. Kuznetsova, L. V. Glushkova. S. Yu. Belova, F M. Egidis, G. V. Kutimova, and A. A. Efimov, USSR P. 757565, 1980.

Other hindered phenols of interes,t

Stericd?y hindered phenols OH OH

Other organosulphur compounds of interest

596-599

Photochemistry

558

4

-

0 r m -4

\o 0

\o N

0

u

d

x

m

v

)

! i 3 & d

0

a

a

0

I

I

a

-& 0

a

i

z z 3:

u, z u

T Z

I N N \o

634

632 633

631

629

628

627

626

62s

624

623

622

620 621

619

617 618

616

614

613

612

610 611

609

608

607

606

6os

604

'03

601 602

Ciba-Geigy AG, Eur. P, 93665, 1980. Ciba-Geigy AG, US P, 4202 836, 1980. Ciba-Geigy AG, Eur. P, 13682, 1980. Eastman Kodak Co., US P, 4 187213, 1980. Ciba-Geigy AG, Eur. P, 17617, 1980. Ciba-Geigy AG, Jap. P, 8 112278, 1980. Chimosa Chimica Organica Sp.A., Eur. P, 19 578, 1980. Chimosa Chimica Organica Sp.A., Belg. P, 877916, 1980. Haccks b AG, G P, 2839711, 1980. Ciba-Geigy AG, US P, 4 191 682, 1980. Ciba-Geigy AG, Eur. P, 14683, 1980. Ciba-Geigy AG, Eur. P, 7059, 1980.

732 324, 1980.

continued

Leningrad Technological Institute, USSR P, 737401, 1980. Anic Sp A., G P, 2 945 130, 1980. S. A. Argus Chemicals N.V., Br. P, 2037778, 1980. Academy of Sciences, USSRP, 732 322, 1980. Kanelo Ltd., Jap. P, 80,54329, 1980. D. Pone and L. Irgen, USSR P, 732 320, 1980. American Cyanamid Corp., US P, 4248 594, 1981. Leningrad Inst. of Text. and Light Ind., USSR P, 763386, 1980. Nippon Oils and Fats Co., Jap. P, 80,82 167, 1980. Ciba-Geigy AG, Eur. P, 15 230, 1980. K. Yamamoto, Belg. P, 882 562, 1980. Unitika Ltd., Jap. P, 80,13766, 1980. GEC Corp., Can. P, 1079287, 1980. Ciba-Geigy AG, Jap. P, 80,49 355, 1980. Fujikura Rubber Works Ltd., Jap. P, 80,79 149, 1980. GEC Corp., G P, 2 917 836, 1980. Bayer AG, G P, 2829257, 1981. Taoka Chemical Co. Ltd., Jap. P, 80,149359, 1980. GEC Corp., US P, 4 197392, 1980. Toray Ind. Inc., Jap. P, 80,64055, 1980. Ciba-Geigy AG, Eur. P., 13 665, 1980. Eastman Kodak Co. Ltd. US P, 4 182703, 1980. Ciba-Geigy AG, Eur. P, 17617, 1980. Argus Chemical Corp., US P, 4219463, 1980. E. I. Kivillova, E. N. Matreeva, G. P. Fratkina, E. P. Mezhivikina, A. B. Shapivo, E. G. Rosantsev, and A. A. Usvyatsov, USSR P,

648

641

646

ti45

644

643

642

h4 1

640

ti39

638

637

Specijication

= =

=

0,1,2)

H,alkyl,aryl; ary1,Zhydroxyaryl

R1,R2 = alkyl,aryl(n

R' R2

R = alkyl, alkenyl, alkynyl, aralkyl, alkoxyalkyl, or similar group

Mitsubishi Rayon Co. Ltd., Jap. P, 80,69 670, 1980. Argus Chemical Corporation, US P, 4219463, 1980. Adeka Argus Chemical Co. Ltd., Jap. P, 80,78 033, 1980. Ciba-Geigy AG, Eur. P, 15237, 1980. Sankyo Co. Ltd., Eur. P, 6536, 1980. Ciba-Geigy AG, Eur. P, 6213, 1980. Hoechst AG, G P, 2 849444, 1980. Hoechst AG, G P, 2834455, 1980. Labaz S.A., Fr. P, 2437422, 1980. Labaz S.A., Fr. P, 2439215, 1980. Wyzoza Sz Kola Pedagagiczna, Pol. P, 107448. 1980. Showa Chemical Ind., Jap. P, 80,144049, 1980.

HCH R 1 (CH )" c H (0H )RZ Other miscellaneous stabilizers of interest

A

I N HCHR R,

Other hydropyridines of interest Carbazole derivatives

H

1,4-dihydr0-2,6-dimethylpyridine

Class and general formula Miscellaneous compounds

Table A2 (cont.)

Polyethylene

For PVC

Application

648496

647

646

645

Ref.

Ul Q\ 0

649

684 685

683

682

679 680

678

b77

676

b75

674

673

672

671

670

668 669

667

666

664

663

662

661

660

659

656

655

654

653

652

651

650

continued

Vistron Corp., Can. P, 1082 393, 1980. Institute of Organic Chemistry, Ukranian SSR, USSR P, 732 247, 1980. Eastman Kodak Co., G P, 3007797, 1980. Ciba-Geigy AG, Eur. P, 10518, 1980. Mitsubishi Petroleum Co. Ltd., Jap. P, 80,78 058, 1980. Dainoppon Toryo Co. Ltd., Jap. P, 80,164254, 1980. Zaklady Wlokien Chemicznych ‘Chemistex-Stilon’, Pol. P, 108 178, 1980. Sankyo Organic Chemical Co. Ltd., Jap. P, 80,165936, 1980. Nitto Kasei Co. Ltd., Jap. P, 80,142041, 1980. Showd Chemical Industries Ltd., Jap. P, 80,144049, 1980. Ciba-Geigy AG, Jap. P, 80,112 278, 1980. GAF Corp., US P, 4202 836, 1980. GAF Corp., US P,4202 834, 1980. Hoechst AG, G P,2912 170. 1980. Standard Oil Co., US P, 4 175071, 1979. H. Matsuda and A. Ninagawa, Jap. P, 79,130648, 1979. Hoechst AG, G P, 2828464, 1979. Matsushita Electric Works Ltd., Jap. P. 79,162 145, 1980. Kiev Technological Institute of Light Industries, Tambor Scientific Research Institute of Chemistry and Polymer Materials, USSR P, 712422, 1980. Damichi Nippon Cables, Jap. P, 79,130655, 1979. Hoechst AG, G P, 2 828 552, 1980. Hoechst AG, G P, 2828463, 1979. Asahi Chemical Ind. Co. Ltd. and Kyodo Chem. Co. Ltd., Jap. P, 79,145 736, 1979. TDK Electronics Co. Ltd., Jap. P, 79,152055, 1979. Yashitomi Pharmaceutical Ind. Ltd., Jap. P, 80,27 330, 1980. Katsuta Kako Co. Ltd., Jap. P, 80,45765, 1980. Mitsui Toatsu Chem. Inc., Jap. P, 80,75459, 1980. Eastman Kodak Co., G P, 3007979, 1980. Mitsubishi Plastics Ind. Ltd., Jap. P, 80,84331, 1980. Borg-Warner Corp., G P, 3 001 114, 1980. Ciba-Geigy Corp., US P, 4233 412, 1980. Labaz S.A., Fr. P, 2435496, 1980. GAF Corp., Jap. P, 80,100 351, 1980. GAF Corp.. US P,4238442, 1980. Ciba-Geigy AG, Jap. P, 80,112278, 1980. Teijin Ltd., Jap. P, 80,09641, 1980. Kohkoka Chem. Ind. Co. Ltd., Jap. P, 80,09656, 1980.

h9h

695

694

693

692

"'

6y9

'''

Eastman Kodak Co., U S P. 4 192, 794, 1980. B. F. Goodrich, Jap. P, 79,153850, 1980. Labaz S.A., Br. P, 78,07675, 1980. Tyoto Co. Ltd.. Jap. P, 80,127457, 1980. GEC Corp., Neth. P, 79.03331. 1980. E, I. DuPont de Nemours Co. Inc., US P, 4208465. 1980. Tyoto Rubber Ind. Co. Ltd., G P, 2945 855, 1980. Tyoto Central Res. and Dev. Labs, Inc., Jap. P, 80,45 760, 1980. 0. Svoba, Czech. P, 182875, 1980. GEC Corp., G P, 3014581, 1980. GEC Corp., G P, 3014772, 1980.

Table A2 (cont.)

686

711

710

709

708

701

106

105

104

703

702

701

100

699

698

697

NH2

NYN R3

Shin Nisso Kako Co. Ltd., Jap. P, 79,36239, 1979. Hoechst AG, G P, 2 820 322, 1979. Ciba-Geigy AG, G P, 2 921 641, 1979. Ciba-Geigy AG, Swiss P, 612817, 1980. Hoechst AG, Eur. P, 6171, 1980. Ciba-Geigy AG, G P, 2 921 641, 1979. Mitsuitoatsu Chem. Inc., Jap. P, 80,75 452, 1980. Bayer AG, G P, 2901 480, 1980. Bayer AG, G P, 2841 519, 1980. Hoechst AG, Eur. P. 6176, 1980. Hoechst AG, Eur. P, 8123, 1980. Ciba-Geigy AG, Br. P, 79,04 505, 1980. Cibd-Geigy AG, Eur. P.,14 177, 1980. Ciba-Geigy AG, Jap. P, 80,143940, 1980. Hoechst AG, G P, 2 835 540, 1980.

Triaziny1-stilbenes

Other stilbenes of interest

NYN

R y * ; y N H Q C H = C " p H y N y ' S0,Na SO,Na R'

Class and general formula St ilbenes

Table A3 Optical brightening agents

R = subst. 1,3,4-oxadiazol-2-y1, 1,3,4-thiadiazol-2-~1, 1,2,Coxadiazol3-yl, or 1,2,4-oxadiazol-5-y1. Rings A and B can be additionally substituted by non-chromorphoric substituents

R,R' = C1, OH, NH, subst. amino-groups, alkoxy, phenoxy, morpholino, piperidine; R2,R3 = NH, subst. amino, alkoxy, phenoxy, morpholino, piperidine

Specijication

For polyamides and polyesters

For polyamides

Application

71 1

698-710

697

Ref.

2

%

<

"0 s-

2

3

.1"

Other oxadiazoles of interest

Oxadiazoles

Other coumarins of interest

Coumarins

Other triazinyl stilbenes of interest

Class and general formula

Table A3 (cont.)

R = a functionally modified carboxy-group, an optionally substituted Ph group or an optionally substituted 5-membered heterocyclic ring; R' = H, an alkyl group or an optionally subst. Ph group, n = 0 or 1 and A or B may contain non-chromophoric substituents

R = amino, OH, alkoxy; R' = CN, carboxamide, aryl, heteroaryl (bonded directly or through a CO or SOz group); RZ = H, CN, halogen; R3 = functionally converted carboxyl group

Specijicat ion

For polyesters

For polyester

Application

726, 727

725

723, 724

722

7 12-72 1

Ref.

*

2

3

R5

' ~ 7

733

732

131

730

729

728

727

726

725

724

723

722

721

720

719

718

717

116

715

714

713

712

Ciba-Geigy AG, UKP, 2026054, 1980. Hoechst AG, G P, 2 850 382, 1980. Hoechst AG, Swiss P, 615 164, 1980. Bayer AG, G P, 2917619, 1980. J. Pirkl, Czech P, 183350, 1980. Shin Nisso Kako Co. Ltd., Jap. P, 80,62967, 1980. Hoechst AG, G P, 2839936, 1980. J. Pirkl, Czech. P, 179 165, 1980. M. J. R. Sevil, Sp. P, 468365, 1979. J. Prikl and C. Fisar, Czech. P, 180341, 1979. Ciba-Geigy India, Indian P, 145954, 1979. Hodogaya Chem. Co. Ltd., Jap. P, 79,145735, 1979. Bayer AG, G P, 2 902 470, 1980. Hoechst AG, G P, 2 833 470, 1980. Ciba-Geigy AG, Swiss P, 610478, 1980. Hoechst AG, G P, 2 844 394, 1980. Bayer AG, G P, 2 853 765, 1980. Bayer AG, G P, 2904829, 1980. Bayer AG, G P, 2852 531, 1980. Bayer AG, G P, 2 920 948, 1980. Bayer AG, G P, 2821 116, 1979. Bayer AG, G P, 2918965, 1980.

Other benzimidazolylbenzofurans of interest

R

R R' 2 & - 7 J $

Benzimidazolylbenzofurans

Miscellaneous

alkylsulphonyl, phenylsulphonyl, CN, CF,, carbalkoxy, sulphonate ester, carbamoyl, or sulphamoyl

=

H, alkyl, alkoxy, or halogen, R' = H, halogen, alkyl, alkoxy, aryl, or 1,2,3-triazol-2-yl, R4,R' (independently) = H or hydrocarbyl, and R6 = H, halogen, alkyl, alkoxy,

R, R2, R3,and R' (independently)

Not given

729-733

741

740

739

738

737

735 736

734

R. C. Bertelson, US P, 4 200 752, 1980. J. Krompa, Czech. P, 181 872, 1980. Ciba-Geigy AG, G P, 3 001 424, 1980. K. Ga. A. Henkel, G P, 2 844463, 1980. Ciba-Geigy AG, G P, 2 946 48 I , 1980. Instytut Przemyslu Organiaznego, Pol. P, 103 437, 1979. BASF AG, G P, 2 560051, 1980. Bayer AG, G P, 2 842 686, 1980.

Other miscellaneous optical brightening agents of interest

v- Triazolo /4,5-d)pyrimidines

Other naphthalimides of interest

Naph thalimides

Class and general formula

Table A3 (cont.)

R' = H, C1-12alkyl, C 2 - 6 hydroxyalkyl, R R ' N = 5- or 6-membered ring which can be further substituted; R2 = C, - 1 2 alkyl, C, - 8 alkoxyalkyl, optionally substituted C , - alkenyl, R3 = H, C, - alkyl, or alkoxy-deriv.; R4 = H, C l - 4 alkyl, or alkoxy, halogen; RJR4 = methylenedioxy, ethylenedioxy, methylenoxy = methyleneoxy

R = alkyl, subst. alkyl, phenylalkyl, or 5- or 6-membered alicyclic group, R' and R2 = alkyl, phenylalkyl, alicyclic group, or tetrahydrofuranylmethyl, or NR'R' = heterocyclic group, and the total no. of C atoms in R R 1 R 2 > 9 and in RR'3 4

Specijicat ion

film

For polyesters, acetates , acrylics, and PVC polyamides,

Liquid penetrant agents for defective surfaces

Application

737-741

736

735

734

Ref:

Part V PHOTOCHEMICAL ASPECTS OF SOLAR ENERGY CONVERSION By L.

M. Peter

1 Introduction The impressive number of recent meetings’-5 devoted to various aspects of photochemical solar energy conversion bears witness to the sustained growth of interest in the search for practical conversion systems. The recent Faraday Discussion on Photoelectrochemistry was strongly oriented towards semiconductor-based devices, and it provides an excellent perspective of current research effort. In his introduction to the Faraday Discussion, Nozik has shown how apparently different approaches to the problem of solar energy conversion are, in fact, closely inter-related. The systems discussed at the meeting have much in common with photosynthesis, and it is useful to record at this point the features which Nozik singles out to make this clear: in each case some kind of interface is involved, i.e. the systems are heterogeneous; the essential function of the interface is to separate or in some way stabilize the electron-hole pair created by the absorption of a photon; successful charge separation allows redox reactions to occur. Nozik’s useful classification of the different systems is shown in Table 1. Table 1 Comparison of routes to solar energy conversion’ System Photoelectrosynthesis

Light absorption Semiconductor

Interface Semiconductorelectrolyte

output Chemical

Electrochemical photovoltaic cells

Semiconductor

Semiconductorelectrolyte

Electrical

Photogalvanic cells

Molecular pigment in solution

Metal (or degenerate semiconductor)electrolyte

Electrical

Microheterogeneous redox chemistry

Molecular pigments in solution

Micelles-liquidmetal-liquid semiconductor-liquid

Chemical

Synthetic chloroplasts

Molecular pigments on membranes

Membranes-liquid

Chemical

There is now an increasing awareness of the essential similarities between different approaches to photoinduced charge-transfer, and it is significant that the period under review has produced several examples of cross-fertilization of concepts and methods between photochemical and photoelectrochemical research. It is difficult to maintain a broad and coherent view when one is confronted with the flood of papers concerned with photochemical and photoelectrochemical 3rd International Conference on Photochemical Conversion and Storage of Solar Energy. Boulder, Colorado, August, 1980. NATO Advanced Summer Institute, University of Gent, Belgium, August, 1980. ‘Photoeffects at Semiconductor-Electrolyte Interfaces’, ACS Symposium, Houston, Texas. March, 1980. Am. Chem. Soc., Symp. Ser., 1981, 146. ‘Physico-chemical processes for conversion and storage of solar energy’. Papers presented at the 79th Meeting of the Deutsche Bunsengesellschaft. Ber. Bunsenges., Phys. Chem., 1980, 84, 941. Faraday Discussion of the Royal Society of Chemistry, 1980, No. 70 ‘Photoelectrochemistry’.

569

570

Photochemistry

systems. Luckily, this task is made easier by excellent general reviews prepared by Gerischer and by Nozik.'. * Gerischer's discussion covers photosynthesis and familiar topics, such as photogalvanic cells and photoelectrolysis cells, before going on to consider novel systems with asymmetric membranes. Gerischer concludes that the photovoltaic mode of cell operation is more likely to be practical and successful since photoelectrolysis must always compete with the alternative hybrid arrangement of a photovoltaic cell in tandem with an optimized electrolysis cell. It will be interesting to see how the new cells developed at Bell Laboratories stand up to this stringent criterion of success. Photoelectrochemical cells are being developed in many laboratories, and several reviews have appeared that treat fundamental aspects of their design and operation.l0-l3 Bard has given a useful summary of basic priniciples as well as a brief survey of photovoltaic systems, photoelectrolysis, and heterogeneous photocatalysis with particulate systems." In case we should think that photoelectrochemistry is merely the product of the present energy crisis, Bard speculates on the possibility that the synthesis of amino-acids on TiO, dispersions may have been significant in the context of evolution (in the absence of platinum catalysts, one may assume that the time scale of the photosynthetic process was longer than is currently fashionable). It is difficult, of course, to keep abreast of the developments in photoelectrochemical cells when progress is so rapid. The group at Bell Laboratories appears to have lost none of its impetus; it has always been at the forefront of efforts to develop practical and efficient photoelectrochemical devices. For this reason, the review by Heller is particularly welcome at this time. The astonishingly rapid advance in conversion efficiency and the improvements in photoelectrode stability can be appreciated within the framework of a research programme which began at Bell Laboratories as recently as 1975. During the intervening six years, the performance of semiconductor photoanode systems has been pushed close to an upper limit by surface treatment procedures, and the group has now turned its attention to p-type semiconductor photocathodes. Early work with p-GaP was not encouraging (conversion efficiencies were less than 3%) but a breakthrough came with the discovery that the p-InP appears to be much better behaved than p-Gap. A 9.3% solar to electrical conversion efficiency was obtained with a p-InP/VCl,, VCI,, HCl/C cell, and a subsequent oxidative treatment of the semiconductor surface increased this efficiency to 1 1.5%. These high conversion efficiencies are complemented by the superior resistance of the p-type semiconductor to photocorrosion.

'

H. Gerischer. Pure Appl. C h e i . . 1980. 52. 2649. A. J. Nozik, 'Photoelectrochemical Devices for Solar Energy Conversion'. Presented at the NATO Advanced Summer Institute (ref. 2). ' A. J . Nozik, 'Photoelectrosynthesis at Semiconductor Electrodes'. Presented at the 3rd International Conference on Photochemical Conversion and Storage of Solar Energy (ref. 1). ' A. Heller, Acc. Chem. Res., 1981, 14, 154. '" A. J. Bard. Science, 1980, 207, 139. 'I A. Heller and B. Miller, 'Energy Storage, Trans. Int. Assem. 1980 Ist', ed. J. Silvermann, Pergamon, Oxford, 1979, p. 405. '' G . Horowitz and A. Bourrasse, Rev. Phys. Appl., 1980, 15. 463. l3 A. J. Bard, Proc. Electrochem. Soc., 1980, NO-83, 136.

'

Photochemical Aspects of Solar Energy Conversion

57 1 The more gloomy prognoses for efficient photoelectrolysis appear to have been unjustified in view of the development at Bell Laboratories of p-InP photocathodes coated with thin ( - 10 nm) islands of Pt, Rh, or Ru.’ These electrocatalyticdeposits increase the efficiency for photoassisted electrolysis at p-InP by four orders of magnitude, and the 12% ‘engineering efficiency’ quoted by Heller far exceeds any value reported previously for photoelectrolysis cells. Since the cells also operate successfully at high levels of insolation, the way may be open to the production of hydrogen at practical generation densities. Although photoelectrochemical systems are able to offer respectable conversion efficiencies, the refinement of other solution-based processes continues. Gratzel 14+ l 5 has reviewed photoredox processes, paying particular attention to the use of organized assemblies such as micelles and vesicles. He emphasizes the central role of efficient colloidal metal catalysts in these schemes and also describes the recent development of bifunctional redox catalysts that allow the combination of cycles for the generation of hydrogen and oxygen. Photobiological systems, although less efficient than photovoltaic or photoelectrochemical cells, are still very much under discussion. Weaver et al.,I6 in a comprehensive review, attempt to assess the potential of a number of bacterial and algal systems for in vivo and in vitro hydrogen generation. Hall l 7 has also given a realistic evaluation of the possibility that solar energy conversion by biological methods could contribute significantly to energy needs before the turn of the century. 2 Biological Systems It is clear that much can be learned from biological systems, and although, strictly speaking, they fall outside the scope of this review, some key references may be of interest. Lehninger l 8 has outlined in considerable detail the primary energytransformation steps in biological systems, and Seibert and Janzen l 9 have demonstrated that photoactive biological membrane components can be used in photoelectrochemical cells. The systems have small power outputs, but the isolation of the bacterial photosynthetic reaction centre from Rhodopseudomonas splzaeroides, and its subsequent direct attachment to a tin oxide electrode gave measurable effects which may assist the elucidation of the fundamental process of charge separation in such centres. In related research, Ochiai et 2 1 have shown that the living blue-green alga Mastigocladus laminosus can be immobilized on tin oxide electrodes with calcium alginate to form a ‘living electrode’ which can function as a photoanode for considerable periods of time. Groby and Hall22 have also used alginate-immobilized chloroplasts and enzymes for biophotolytic hydrogen generation. ~

’’ l5

’‘

l7

l9 ’O

” 22

1

.

~

M. Gritzel, Ber. Bunsenges.. Phys. Chem., 1980, 84, 981. M. Gritzel, J . Chim. Phys., Phys.-Chim. Biol., 1981, 78, 1 . P. F. Weaver, S. Lien, and M . Seibert, Sol. Energy, 1980, 24, 3 . D. 0. Hall, Fuel, 1978, 57, 322. A. Lehninger, Ber. Bunsenges., Phys. Chem., 1980,84, 943. M . Siebert and A. F. Janzen, Sol. Energy Res. Inst. Tech. Rep., 1979, SERI/TP-322-476. For a short description see New Scientist, 14th August, 1980. H. Ochiai, H. Shibata, Y. Sawa, and T. Katoh, Proc. Natl. Acad. Sci. U S A , 1980, 77, 2442. D. E. Groby and D. 0. Hall, Nufure (London), 1980, 287, 5779.

~

3

572 Photochemistry Hall continues to put the case for large-scale biological solar energy conversion,23*24 but isolated systems have also received considerable attention in the laboratory. Bhardwaj et al.2 have described a chloroplast photoelectrochemical cell in which chloroplasts were placed between an electron acceptor, such as anthraquinone-2-sulphonate and an electron donor, dichlorophenol or indophenol. The authors claim a 1% monochromatic power conversion efficiency for their most successful cells. Adams et a1.,26 by contrast, have used isolated chloroplasts for the generation of hydrogen. Methylviologen was used as an electron relay, and colloidal platinum replaced hydrogenase as the catalyst for hydrogen evolution. Cuendet and Gratzel 27 have also compared the hydrogen evolution rates produced by hydrogenase and by ultrafine platinum dispersions, and they have shown that the efficiency of hydrogen production can be improved by the use of substituted viologens having more negative standard potentials as electron relays. Figure 1 illustrates this effect. It appears that the catalytic behaviour of the colloidal platinum particles parallels the features observed in photochemical model systems; for example, a clear trend to higher activity is apparent as the catalyst particle size decreases. Calvin2* and Willner et ~ 1 . ~have ’ discussed in detail the simulation of photosynthesis, Calvin paying particular attention to the role of manganese

30 T L 20 L

-

‘m .

0

10

E

%

Figure 1 Hydrogen evolution rate at pH 7 from chloroplast-Pt-Carbowax system as a function of the redox potential of the viologen mediator (Data taken from ref. 27). 23 24 25

26

’’ 28

29

D. 0. Hall, Nature (London), 1979, 278, 114. D. 0.Hall, M . Adams, P. Giby, and K . Rao, New Scientist, 10th April, 1980. R. Bhardwaj, R. L. Pan, and E. L. Gross, Nature (London), 1981, 289, 396. M. W. W. Adams, K. K. Rao, and D. 0. Hall, Photobiochem. Photobiophys., 1979, 1, 33. P. Cuendet and M. Grltzel, Photobiochem. Photobiophys., 1981, 2, 93. M. Calvin, in ref. 5 , p. 383. I. Willner, W. E. Ford, J. W. Otvos, and M . Calvin, Bioelectrochemistry (Proc. U.S. Australian Joint Seminar), ed. H. Keyser and F. Gutmann, Plenum, NY, 1980.

573

Photochemical Aspects of Solar Energy Con version

porphyrin natural catalysts in the oxygen evolution reaction. The importance of the membrane structure in photosynthesis is well known, and not surprisingly the application of membranes to photochemical solar energy conversion continues to receive attention.30.

3 Homogeneous and Microheterogeneous Photochemical Systems The photochemical cleavage of water can be achieved by coupling a sensitizer to an electron relay system as shown in Figure 2. A critical feature of cyclic reaction

\n

S+

R-

Figure 2 General scheme for the cyclic photodecomposition of water. S is a sensitizer and R is an electron relay system

schemes is the need for effective catalysts which will accelerate the production of hydrogen and oxygen as well as the regeneration of the sensitizer from its oxidized state, and recently considerable progress has been made by Gratzel’s group in Lausanne with the development of bifunctional redox catalysts 32 - 34 for cyclic water photodecomposition. The catalyst was prepared by deposition of platinum and ruthenium dioxide on a dispersion of the anatase modification of TiO, (particle size -45nm). With light of sufficiently high energy, direct excitation of the semiconductor was found to give appreciable amounts of hydrogen and oxygen, but, more importantly, the catalyst particles appear to be able to fulfil a dual role as catalyst for both oxygen and hydrogen evolution in the presence of a suitable sensitizer and electron relay. The sensitizer is a [R~(bpy)~],derivative and the electron relay is methylviologen, although in this case the scheme also appears to work without the electron relay if a long alkyl chain is introduced into the [ R ~ ( b p y ) ~complex. J~+ The best hydrogen yields were obtained with an ndodecyl derivative, probably because the sensitizer adsorbs on the catalyst particles. The reactions taking place at the bifunctional catalyst particle are shown schematically in Figure 3, although the use of the conventional band description is open to criticism for such small particles, where surface effects are dominant. +

30

31 32 33

T. Sugimoto, J. Miyazaki, T. Kokubo, S. Tanimoto, M. Okano, and M. Matsumoto, Tetrahedron Lett., 1981, 22, 1119. K. Singh, H. Lebedera, and S. R. Caplan, in ref. 5, p. 375. M. Gratzel, in ref. 5, p. 359. J. Kiwi, E. Borgarello, E. Pelizzetti, M. Visca, and M. Grltzel, Angew. Chem., Int. Ed. Engl., 1980,19, 646.

34

E. Borgarello, J. Kiwi, E. Pelizzetti, M. Visca, and M. Gritzel, Nature (London), 1981, 289, 158.

Photochemistry

574 ENERGY

H20

0,

Figure 3 The reaction scheme for the bifunctional redox catalyst. RuO,/Pt on TiO,. The conduction und valence hand energies are compared with the standard hydrogen and oxygen potentials

Several other reports of studies on the [Ru(bpy),12+/MV2+ scheme have appeared in which either platinum or hydrogenase catalysts were used. - 40 Giro et managed to obtain hydrogen directly by using Ti3+to quench the excited [Ru(bpy),12+; the reaction of Ti2+ with protons is very rapid and competes favourably with the thermal back-reaction. The work of Miller and McLendon 39 is particularly interesting. They used a series of [Ru(bpy),12 derivatives of the type (1) and (2) and were able to establish a linear relationship between electrode +

R

R'

u

2Br-

RmR' u

( I ) R = Me, R '

-N+

=

Me; R

=

H. R '

=

1-I

+N-

2Br-

(2) R = Me, R ' = Me; R = Ph. R' = Ph; R = Me, R ' = H ; R = H . R ' = H ; R = C 1 , R ' = tI

potential and hydrogen yield, providing additional support for the 'microelectrode' model 41,42 of the catalytic function of the dispersed platinum. The 35 36

3' 38

39 40 41

42

G . Giro, G . Casalbore, and P. G . Di Marco, Chem. Phys. Lett., 1981, 71, 476. A. I . Krasna, Phorochem. Phorohiol., 1980, 31, 75. I. Okura, N. Kim-Thuan, and M. Takeuchi, Inorg. Chim. Acra, 1981, 53, L149. 1. Okura and N. Kim-Thuan, Chem. Left., 1980, 151I . D. Miller and G . McLendon, Inorg. Chem.. 1981, 20, 950. T . Nijishima, T. Nagamura, and T. Matsuo, J . Polym. Sci.,Polym. Lett. Ed., 1981, 19, 65. L. M . Peter, 'Photochemistry', ed. D. Bryce-Smith (Specialist Periodical Reports), Royal Society of Chemstry, London, 1981, Vol. 12, p. 537. See discussion of M. Griitzel's paper in ref. 5.

Photochemical Aspects of Solar Energy Conversion

575

interpretation of the effect of catalyst particle size on the hydrogen evolution rates and efficiencies is, however, controversial. Keller and Moradpour 4 3 deny that particle size effects are important at all in the [Ru(bpy)J2 +/MV2+/e.d.t.a. system. Using widely polydispersed colloidal hydrosols and samples with narrower size distributions obtained by centrifugation, they found that the optimum values for the rates and yields of hydrogen formation were very similar for all the catalysts studied; this was true for polydispersed or selected small (- 10 nm) as well as for large (- 100nm) particles. These results appear to conflict sharply with the observations of Kiwi and G r a t ~ e lwho , ~ ~found a marked particle size dependence of the rate of MV’ oxidation at colloidal PV. If the reaction of MV+ at the platinum catalyst occurs under diffusion-controlled conditions, a specific size effect is expected since each particle will develop a spherical diffusion field.41*44 If, on the other hand, pure kinetic control is established under the reaction conditions, the specific size effect should no longer be significant when the surface area has been properly accounted for. The differences in the observations made by the two groups may therefore originate in different experimental conditions or catalyst surface activity. The reversible potential of the viologen derivative must exert a strong influence on the rate of the electron-transfer reactions at the metalcatalyst particle, and it is clear that more work is needed before an unambiguous distinction can be made between kinetic and mass transfer effects on the one hand, and surface area and surface activity effects on the other. Some of the problems encountered in the use of catalyst hydrosols have been discussed by Brugger et ~ l . , who ~ ’ have examined platinum particles only 3.2 nm in diameter. The stability of the hydrosol against floculation by salts depends critically on the nature of the polymeric protecting agent used; simple poly(ethy1ene glycols) were found to be very poor protective agents, whereas Carbowax-20M, which is a block copolymer containing two poly(ethy1ene glycol) chains linked by a short hydrophobic epoxide chain, gave excellent results. The [Ru(bpy)J2+ complexes are not the only sensitizers that can be used for cyclic water photodecomposition, indeed metal p o r p h y r i n ~-, 48 ~ ~metal phthalo5 0 pr~flavin,~’, 5 2 and other compounds 53 have been investigated as ~yanines,~’. possible sensitizers. Although sensitizer/relay/catalystschemes have become very popular, alternative approaches exploiting homogeneous photochemistry are being studied. Reactions in which radical ions 54 or carbanions 5 5 are generated by illumination have been discussed, and the interesting properties of polynuclear rhodium 43

44 45

46 47

49 50

51

52

”

’’

”

P. Keiler and A. Moradpour, J . Am. Chem. SOC.,1980, 102, 7193. J. Kiwi and M. Gratzel, J. Am. Chem. SOC.,1979, 101, 7214. P.-A. Brugger, P. Cuendet, and M. Gratzel, J . Am. Chem. SOC.,1981, 103, 2923. N. Neumann-Spallart and K. Kalyanasundaram, 2. NaiurSorsch., Teil A 1981, 365, 596. K. Kalyanasundaram and M. Gratzel, Helv. Chim. Acta, 1980, 63, 478. N. Carreiri and A. Harriman, J. Phorochem., 1981, 15, 341. A. Harriman and M. C. Richoux, J . Photochem., 1980, 14, 253. M. De Backer, M. C. Richoux, F. Leclerq, and G. Lepoutre, Rev. Phys. Appl., 1980, 15, 529. K. Kalyanasundaram and D. Dung, J . Phys. Chern., 1980, 84, 2551. M.-P. Pileni and M . Grltzel, J . Am. Chem. SOC.,1980, 84, 2402. I. Okura and N . Kim-Thuan, Chem. Leti., 1980, 1569. K. Chandrasekaran and D. G. Whitten, J . Am. Chem. SOC.,1980, 102, 51 19. M . A. Fox, Kabir-ud-Din, and N. J. Singletary, Sun 2 Proc. Int. Solar Energy SOC.Silver Jubilee Congress 1, 102, ed. K. W. Boeer and B. H. Glenn, Pergamon, NY, 1979.

Photochemistry

576

isocyanide complexes may also find application. 5 7 Other transition-metal complexes with excited states of possible interest for photochemical solar energy conversion are the dithiolenes 5 8 and the molybdenum(r1) cluster M O , C ~ , , -~. 5 9 One of the key problems in the reaction scheme shown in Figure 2 is that the products of the charge-transfer reaction between the sensitizer and electron relay quencher can undergo a back reaction, reducing the overall quantum yield. The kinetic constraints for successful photochemical energy conversion in the homogeneous phase are therefore severe. The most promising approaches to this problem involve the design of an appropriate microenvironment to assist rapid separation of the products before they are able to react in the reverse direction. This can be done at the molecular level by using micelles, vesicles, and microemulsions, and Gratzel has reviewed these organized assemblies in the Faraday Discussion on Photoelectrochemistry.60 Recent progress in the application of amphiphilic viologen redox relays in micellar assemblies has been summarized by Brugger et a1.61 In this case the sensitizer was zinc tetrakis(Nmethylpyridy1)porphyrin (Zntmpyp4+) and the best results were achieved using dichloride as electron relay. The forward C,, N-alkyl-N-methyl-4,4'-dipyridinium electron transfer occurs with the viologen present in the aqueous phase, but after reduction, the compound becomes hydrophobic and is rapidly solubilized into the cetyltrimethylammonium chloride cationic micelles. The electrostatic surface repulsion reduces the rate constant for the thermal back reaction by a factor of at least 500, and more than 90% of the excitation energy of the triplet state of the porphyrin is converted into the chemical potential of the redox products. One of the disadvantages of using micelles to facilitate charge separation is that rather high surfactant concentrations are required. Vesicles are formed at lower concentrations, and several reports of their use in photoredox systems have appeared.62Monserrat and Gratzel 6 2 have used dioctadecyldimethylammonium chloride (DODAC) as a vesicle-forming agent with an amphiphilic viologen derivative in combination with either [Ru(bpy)J2 or a porphyrin as sensitizer. The reduced form of the C14 viologen derivative is then trapped in the interior of the DODAC vesicles, resulting in a retardation of the back reaction with the oxidized sensitizer by a factor of 50 or more. In this work the watersplitting cycle was not completed; e.d.t.a. was used instead to regenerate the sensitizer. Monserrat and Gratzel observed that the reduced viologen molecules form multimer units in the vesicles, giving rise to a characteristically broadened 567

+

''

I . S. Sigal, K. R. Mann, and H. B. Gray, J . Am. Chem. Soc., 1980, 102, 7252. H . B. Gray, V. M. Miskowski, S. J. Milder, T. P. Smith, A. W. Maverick, J. D. Buhr, W. L. Gladfelter, I. S. Sigal, and K. R. Mann, Fundam. Res. Homog. Catal., 1979, 3, 819. R. Henning, W. Schlamann, and K. Horst, Angew. Chem., 1980, 92, 664. 5 y A. W. Maverick and H. B. Gray, J . Am. Chem. SOC.,1981, 103, 1298. '' M. Gdtzel, in ref. 5, p. 359. '*P.-A. Brugger, P. P. Infelta, A. M. Braun, and M. Gratzel, J . Am. Chem. SOC.,1981, 103, 320. " K. Monserrat and M. GrTtzel, J . Chem. Soc., Chem. Commun., 1981, 183. 63 M . S. Tunuli and J. H. Fendler, J . Am. Chem. Soc., 1981, 103, 2507. 64 S. S. Atik and .1. K. Thomas, J . Am. Chem. SOC.,1981, 103, 3543. '' S. S. Atik and .I.K. Thomas, J . Am. Cheni. Soc., 1981, 103, 3869. 6 b T. Takayanagi, T. Nagamutd, and T. Matsuo, Ber. Bunsenges., Phys. Chem., 1980, 84, 1125. '7 R. Humphrey-Baker, Y. Moroi, M. GrTtzel, E. Pelizzetti, and P. Tundo, J. Am. Chem. Soc., 1980,102. 3689. K. Monserrat, M. Grltzel, and P. Tundo, J . Am. Chrm. SOC.,1980, 102, 5527. 57

''

577

Photochemical Aspects of Solar Energy Conversion

absorption spectrum. Unfortunately the multimers appear to be more stable than the monomer units formed in micelles, reacting only slowly with water to produce hydrogen in the presence of a finely dispersed platinum catalyst. Tunuli and Fendler,63 in a study of the properties of dihexadecyl phosphate (DHP) vesicles, have gone to great lengths to specify the micro-organization of reactants at the vesicle interface. Four different DHP vesicle systems were prepared by ionexchange methods with the sensitizer and electron relay distributed as shown in ~ + MV2+ on the same side of the Figure 4. The localization of [ R u ( b ~ y ) ~ ]and

System I

System II

System 111

System IV

Figure 4 The four kinds of distribution of methylviologen (MV") vesicles discussed by Tunuli and Fendler

and [ R ~ ( b p y ) ~ ] in ~'

vesicle interface leads to an enormous increase in the apparent rate constant for the quenching of the excited state of the ruthenium complex; Stern-Volmer quenching constants are 2-3 orders of magnitude greater than those found for simple aqueous systems. At the same time, however, the close proximity of the reactants on the same side of the membrane greatly enhances the rate of the back reaction. Under these circumstances the back electron-transfer reaction probably takes place on a two-dimensional surface without the intervention of a slow threedimensional diffusion process, and little is gained, since the end result is a rapid quenching of the excited [Ru(bpy),12-t species, without effectivecharge separation. The most important aspect of Tunuli and Fendler's work is their elegant demonstration of efficient electron transfer ucross the vesicle bilayers. In the most favourable arrangement, the sensitizer is localized on the outer surface and MV2 in the interior of the vesicles (see Figure 4).In the presence of e.d.t.a. in the aqueous phase, the MV+ concentration increased linearly with time under illumination up to 75% conversion, with a quantum efficiency of 2.4%. This result provides convincing evidence that electrons can pass from the excited sensitizer across the +

578 Photochemistry 5nm bilayer to the MV2+ in the interior of the vesicle. The potential gradient across the vesicle shifts the energy levels of the donor and acceptor states so as to greatly reduce the rate of the reverse electron transfer. The MV+ generated within the vesicle can be regenerated by incorporating small amounts of colloidal platinum in the interior of the vesicles, and efficient hydrogen generation is then possible with a system which requires unusually low concentrations of sensitizer relay and catalyst. Several other reports of photoinduced electron-transfer reactions in organized assemblies have appeared re~ently,’~. 64 and the special properties of the crown ethers appear particularly promi~ing.~’. 6 8 Humphry-Baker et ~ 1 have . in~ ~ vestigated the ability of the Cu2+ crown-ether complex (3) to participate in photoredox processes. The crown-ether complex aggregates to form micelles into which a hydrophobic donor can be incorporated, i.e. (4)in Figure 5. Photoexcitation of the donor species then leads to charge transfer to the Cu2+ion in the crown ether. Charge transfer is evidently sufficiently rapid that it competes effectively with

A

Figure 5 Micelle formation with crown ether complex of Cu2+.The lower part of the figure shows the photoinduced reduction of Cu2+6 7

Photochemical Aspects of Solar Energy Conversion

579

intersystem crossing in the deactivation of the excited singlet state of the donor molecule (N-methylphenothiazine, m.p.t.). The back reaction between Cu+ and m.p.t.+ is only partly successful since the m.p.t.+ cation is ejected rapidly into the aqueous phase, so that at least half of the electrons transferred originally to the Cu2+ ions in the micelle remain as stored charge. This electron-storage effect appears to be unique to macrocyclic micelles, and the crown-ether complexes show considerable promise as electron relays for light energy conversion. Monserrat et al.6 8 have discussed the properties of surfactant aza-crown ethers complexed with silver. Photoinduced electron transfer from a surfactant Ru complex was found to lead to the formation of zerovalent silver stabilized by the microenvironment of the vesicles and again the electron-transfer reaction was extraordinarily rapid, competing efficiently with other pathways for the deactivation of the excited singlet state. The design of sophisticated sensitizer/relay systems has been reported. Nijishima et aL4' have managed to build 'pendant' MV2+ groups into a polysoap that was then used with a platinum catalyst to give an electron-relay system in which the electron relay is attached directly to the catalyst centre. Although the idea looks promising, the efficiency of the viologen relay appears to be lower in this arrangement, possibly because the chance of encounter between the photosensitizer and electron-relay molecules is reduced. Matsuo et aL6' have gone further and linked [ R ~ ( b p y ) ~ and ] ~ viologen units covalently to form photoreaction centres which are used with the viologen polysoap, but it is clear from their results that, although the rates of electron transfer may be increased by using an aligned relay system, the overall efficiency is low unless the reverse reaction can be prevented. This essential prerequisite for efficient cyclic photoredox systems requires manipulation of the microenvironment in a way that favours the equilibrium as well as the kinetic properties. This can often be achieved quite simply; for example, the photoinitiated electron-transfer reaction from Ru(bpy),(CN), to Fe(CN,)3- has a quantum yield of at least 0.9 when a positive polyelectrolyte is added to the solution to assist charge ~eparation.~' +

4 Photogalvanic Cells The systems discussed in the previous Section are designed to store energy in a chemical fuel such as hydrogen. Alternatively the products of electron-transfer quenching of the excited dye can be used to set up an electrochemical concentration cell. This is the strategy behind the photogalvanic cell. Albery et al.7137 2 have given a detailed treatment of the influence of the kinetics and characteristic dimensions on the performance of photogalvanic cells. One of the major problems with simple electron-transfer quenching is that the rate of the back reaction is often the most important factor which limits efficiency. One promising way of preventing the reverse reaction is to use a dye that can be effectively removed after the initial electron-transfer quenching step by a disproportionation reaction. The best known example is of course the iron-thionine system, and the reaction scheme 69

70 71

72

T. Matsuo, T. Sakamoto, K. Takuma K. Sakura, and T. Ohsako, J . Phy. Chem., 1981,85, 1277. R. E. Sassoon and J. Rabani, J . Phys. Chem., 1980,84, 1319. W. J. Albery, W. R. Bowen, and M. D. Archer, J . Photochem., 1979, 11, 15. W. J. Albery, W. R. Bowen, and M. D. Archer, J. Photochem., 1979, 11, 27.

580

Photochemistry

is summarized in Scheme 1, where Th is thionine, S is semithionine, and L is leucothionine. hv

Th -----+ Th*

Th* photoexcitation elect ron-transfer quenching

k + Fe" + H + 1 S' + Fe"' P

k- 1

2s'

+ H+

L FeIII

+

k3

, Th + L

Th

+

disproportionation

3H+

+

regeneration at the 2e illuminated electrode

, FeI, regeneration at the dark electrode

Scheme 1

In spite of the comprehensive theoretical treatments of the iron-thionine cell, progress towards the development of practical cells has slowed noticeably in the last year. Some aspects of the theoretical treatment have been discussed by 74 who have reported that the decay of leucothionine after Brokken-Zijp et al.739 irradiation is not pseudo-first order, so that it may be necessary to include the synproportionation reaction (1) as an alternative route for the disappearance of L

+ Th

2s'

+ H+

(1)

leucothionine. Dung et aL7' have also considered the application of the reaction scheme to the iron-thionine cell, and their analysis stresses the importance of coupled non-linear reaction-diffusion systems. Depending on the magnitude of the concentration and intensity variables, the model predicts behaviour ranging from overshoot and oscillations to 'chemical chaos'. No experimental evidence for non-linear behaviour of photostationary states in this, or indeed any other, photogalvanic system, exists and it will be interesting to see whether the theoretical prediction that the cell can be driven into oscillation can be verified experimentally. The non-stationary response of photogalvanic cells has also been considered by Dual et al.76.77who provide computer solutions for the case of the a.c. photogalvanic' cell. Further experimental work on the iron-thionine cell has been discussed by Archer et al.78 and by Kirsch-De Mesmaeker et 73 74

7s 16

J. C. M. Brokken-Zijp and M. S. De Groot, Chem. Phys. Lett., 1980, 76, 1 . J. C. M . Brokken-Zijp, M. S. De Groot, and P. A. J. M. Hendriks, Chem. Phys. Lett., 1981,81, 129. M. H. Dung and J. J. Kozak, J. Photochem., 1980, 14, 205.

C. Daul, 0. Haas, A. von Zelewsky, and H.-R.Zumbrunnen, J . Elrctroanal. Chem., Interfac. Electrochem., 1981, 125, 307. C. Daul, 0. Haas, A. von Zelewsky, and H.-R. Zumbrunnen, J . Electroanal. Chem. Interjac. Electrochem., 1980, f07, 49. l a M. D. Archer, M . I. C. Ferreira, W. J. Albery, and A. R. Hillman, J . Electround. Chem. Interfac. Electrochem., 1980, 111, 295. 79 A. Kirsch-De Mesmaeker, M. Wyart-Remy, and J. Nasielski, Sol. Energy, 1980, 25, 117. 11

Photochemical Aspects of Solar Energy Conversion 58 1 The disproportionation of the semithionine in the iron-thionine system provides a successful escape route from the severe limitations imposed by the reverse reaction between the products of the electron-transfer quenching reaction, but an alternative way of tackling the problem is to remove the metal ion as rapidly as possible. De Graff et a1." have shown that the Hg2 ion opens such an alternative route for harvesting excited-state energies. By using [Ru(bpy)J2' with Hg2 instead of Fe3+, the thermal back-reaction rate was reduced by five orders of magnitude because the Hg+ ion, formed by electron transfer from the excited state of [Ru(bpy)J2+, dimerizes rapidly. The performance of the cell is promising, although of course it is still subject to the other restrictions analysed explicitly by Albery et al.7197 2 A practical restriction on the conversion efficiency of photogalvanic cells results from the limited solubility of the photoactive dye, and Albery et aLal have made a systematic attack on this problem by synthesizing a range of new modified thiazine dyes. Although the dyes are more soluble, several other problems arise, for example new methylene blue NN forms dimers at high concentration, and these do not contribute to the photocurrent. Sulphonation of thionine leads to a shift in the standard electrode potential of the dye redox system, which unfortunately increases the rate of the reverse reaction. In a realistic analysis of the photogalvanic cell, Albery et al. conclude that the 'best possible' upper limit of efficiency is 574, which would effectively exclude the cells from serious consideration for solar energy conversion. Nevertheless, interest in other dye-based photogalvanic systems is likely to continue, and the collection of data given by Chan and Bolton 8 2 for over sixty synthetic water-soluble dyes will be useful for future work on photogalvanic as well as on homogeneous and microheterogeneous systems. Several studies of other dye photogalvanic cells have a ~ p e a r e d , and ~ ~ these -~~ may be of general interest since they give kinetic data for the photochemical reactions of dyes such as methylene blue.83,84 The important influence of adsorbed thionine layers on the selectivity of the electrodes in the iron-thionine photogalvanic cells was first identified clearly by Albery et a1.,88v89and Quickenden et al.90991have reported similar effects for rhodamine B layers deposited on gold. Bowen92 has measured the rates of electron transfer at electrodes modified with thionine and rhodamine B, and has shown that the thionine-coated electrode could be useful in a wide range of photogalvanic systems, whereas the adsorption of rhodamine B appears to be disadvantageous. +

+

B. A. De Graff and J. N . Demas, J . Am. Chem. Soc., 1980, 102, 6169. W. J. Albery, P. N. Bartlett, J. P. Davies, A. W. Foulds, A. R. Hillman, and F. S. Bachiller, in ref. 5, 82

83 84

85

86

" 88

89 91

92

p. 341. M. S. Chan and J. R. Bolton, Sol. Energy, 1980, 24, 561. D. E. Nicodern and S. M. C. De Menezes, Sol. Energy, 1981, 26, 365. D. W. Hay, S. A. Martin, S. Ray, and N. N. Lichtin, J . Phys. Chem., 1981, 85, 1474. A. Bhardwaj, R. L. Pan, and E. L. Gross, Photochem. Photobiol., 1981, 34, 215. M. F. Perrone, M. Zaninelli, and I. R. Bellobono, Gazz. Chim. Ital., 1981, 111, 9. T. Yamase, Photochem. Photobiol., 1981, 34, 11 1 . W. J . Albery, W. R. Bowen, F. S. Fisher, A. W. Foulds, K. J. Hail, A. R. Hillman, R. G. Edgell, and A. F. Orchard, J. Electroanal. Chem. Intetjac. Chem., 1980, 107, 34. W. J. Albery, A. W. Foulds, K. J. Hall, and A. R. Hillman, J. Efectrochem. Soc., 1980, 127, 654. T. I. Quickenden, D . P. Herring, and G. K. Yim, Electrochim. Acta, 1980, 25, 1397. T . I. Quickenden and R. L. Bassett, J . Phys. Chem., 1981, 85, 2232. W. R. Bowen, Acta. Chem. Scand., Ser. A , 1980, 34, 437.

582

Photochemistry

Several rather more exotic photogalvanic cells have been proposed, Goldstein et a1.93have described a cell containing rubidium crown-ether complexes in t.h.f. for which quite large photovoltages were observed. Stevenson and Erbelding 94 have based a photogalvanic cell on the photodissociation of iodine, but this appears to be an example where rapid back reaction reduces the efficiency to very low levels (the monochromatic efficiency is less than 0.03%!).The photochemical properties of the molybdates are unusual, and Yamase and Ikawa 96 have shown that it is possible to generate hydrogen in a photogalvanic cell containing molybdate complexes. Finally, Neumann-Spallart et aL9' and Rillema et al.98have discussed systems in which photoelectrolysis is carried out in a photogalvanic cell. NeumannSpallart et al. coupled the light-induced reduction of peroxydisulphate by [Ru(bpy),12+ to oxygen evolution at a ruthenium dioxide anode (the low overpotentials associated with electrode reactions at Ru0,-coated anodes are exploited commercially in industrial electrolysis), and illumination of the [ R ~ ( b p y ) , l ~ + / S , O , half ~ - cell was found to lead to oxygen evolution at the RuO, anode [equations (2)+5)]. Photovoltages of 0.5 V and photocurrents of the order 957

+ S20,2-

[Ru(bpy)312+* SO,'

+ + SO,' [Ru(bpy)J3+ + SO,2-

4 [ R ~ ( b p y ) ~ ] ~ SO,2+

+ [ R u ( b ~ y ) ~ ] ~--+-+

(2) (3)

At the Pt electrode:

At the RuO, electrode: 2H20

0,

+ 4H' + 4e

(5)

of 300--400 pA were observed with this arrangement, but the cell suffers from the practical disadvantage that it is irreversible since peroxydisulphate is consumed. A similar type of cell reported by Rillema et al.98 uses C O ( C , O , ) ~ ~rather than S,OS2- to quench [ R ~ ( b p y ) ~ ] , +and * , oxygen is evolved at the anode.

5 Photoelectrolysis with Semiconductor Electrodes Goodenough et al.993'00 have discussed approaches to the design of suitable catalytic electrodes for photoelectrolysis, and they have taken care to distinguish between localized and delocalized states introduced by doping TiO, or SrTiO,. The improvements in spectral response reported for doped oxide systems must be examined critically with this distinction in mind because, in principle at least, only delocalized photoexcited states should give rise to a true d.c. photocurrent response. In practice, some d.c. response can be obtained from localized states if y3 y4 y5

'' "

S. Golstein, S. Jaenicke, and H. Levanon, Chem. Phys. Lett., 1980, 71, 490. K. L. Stevenson and W. F. Erbelding, Sol. Energy, 1981, 27, 139. T. Yamase and T. Ikawa. Inorg. Chim. Acta, 1979, 37, L529. T. Yamase and T. Ikawa, Inorg. Chim. Acta, 1980, 45, L.55. M. Neumann-Spallart. K. Kalyanasundaram,C. Grltzel, and M. Grltzel, Hcdv. Chim. Acta, 1980.63,

1111. '' D. P. Rillema, W. J . Dressick, and T. J. Meyer, J . Chem. Soc., Chem. Commun., 1980, 5, 247. y9 lo"

J. B. Goodenough, A. Hamnett, M. P. Dare-Edwards, and G. Campet, Surf: Sci., 1980, 101, 531. G . Campet, M . P. Dare-Edwards, A. Hamnet, and J . B. Goodenough, Nouv. J . Chim., 1980, 4, 501.

Photochemical Aspects of Solar Energy Con version

583

electrons can tunnel to band states by field or thermal emission. The dangers of relying on experiments with chopped illumination are clearly demonstrated in the case of Cr-doped SrTiO,, where only a transient photoresponse is obtained (at low overpotentials at least), because the photoexcited state is localized. The pressing need for a detailed description of the semiconductor-electrolyte interface is becoming increasingly apparent: Gerischer 'O' has given an excellent and timely general account of photoassisted interfacial electron transfer, in which particular attention is paid to the role of surface states at the semiconductor-electrolyte interface. Kowalski et al. O 2 have used the SCF-X-scattered wave method to calculate the position and character of surface states at various characteristic interfaces, and then used these results to develop a model of photoelectrolysis at TiO, surfaces. Other experimental studies of surface states on TiO, and on similar oxides have appeared recently,lo3- l o 6 and the participation of these states in the mechanism of photoelectrolysis is now generally recognized. At the same time, it is clear that the search for new materials for photoelectrolysis must aim to combine optimum band gap and low electron affinity, and Scaife lo' has examined a wide range of oxides with these limitations in mind. Scaife shows that oxides which do not contain partly-filled d-levels exhibit a linear relationship between flat-band potential and band-gap, given by equation (6). The nature of this relationship

'

effectively limits the chances of finding oxides suitable for efficient photoelectrolysis without external bias. The predicted maximum efficiency for unbiased photoelectrolysis with this type of oxide is 3.4% for Eg = 3eV, and for voltagebiased electrolysis 6.3% for Eg = 2.4eV. The prospects of obtaining satisfactory efficiencies with oxides containing partly-filled d-levels are not encouraging either since they are limited by the simultaneous requirements of stability, flat-band potential, and band-gap. Figure 6 demonstrates how closely the majority of oxides follows the linear relationship between flat-band potential and band gap. In spite of the fact that it is unsuitable for efficient photoelectrolysis, titanium dioxide continues to attract considerable attention as a model oxide system. Attempts to dope the oxide with transition metals have met with little and it is clear that care must be taken to distinguish between the introduction of localized and delocalized states (see references 99 and 100). The electrochemical properties of single-crystal rutile are still being characterized in lo'

lo' Io3 Io4 105

lo'

'lo

I"

H . Gerischer, S u ~ fSci., 1980, 101, 518. J . M . Kowalski, K . H . Johnson, and H. L. Tuller, J . Electrochem. Soc., 1980, 127, 1969. M . Tomkiewicz, J . Elecfrochem. Soc., 1980, 127, 1518. R . H. Wilson, J . Electrochem. Soc., 1980, 127, 228. P. Braun, W. Weissmann, F. P. Viehboeck, and I . Balberg, Contrih. Symp. At. Surf. Phys., 1980, 52. M. A . Butler, M. Abramovich, F. Decker, and J. F. Juliao, J . Electrochem. Soc., 1981, 128, 200. D. E. Scaife, Sol. Energy, 1980, 25, 41. G. Campet, J . Verniolle, J. P. Doumerc, and J. Clavene, Mnter. Res. Bull., 1980, 15, 1135. Y . Matsumoto, J . Kunimoto, Y. Amagasaki, and E. Suto, J . Electrochem. Soc., 1980, 127, 2148. A. Monnier and J. Augustynski, J . Electrochem Soc., 1980, 127, 1576. H.-R. Spriicken, R. Schumacher, and R. N. Schindler, Ber. Bunsenges., Phys. Chem., 1980,84, 1040.

10-

\ Fn4 ?4 " 3 4

I

W-

FeTaO,

-

0

-2 -02 c

a C

F n

3

-04-

CrNbq A

LL

-0 6

-

-06

-

-I

0I

I

2 0

25

30 Band gap.

35

40

Eg (eV)

Figure 6 Flut-hand potential vs. hand gap for oxide semiconductors (Reproduced by permission from, Sol. Energy, 1980, 25, 41).

detail, 1 1 1 - 114. and some aspects are still controversial (see discussions in ref. 5). CVD films of TiO, and oxide films formed on titanium metal have also been investigated. 1 6 , Similarly, SrTiO, still has its afficionados,l' 8 , l 9 and the identity of surface species involved in photoelectrolysis at pure and Pt-doped SrTiO, surfaces has recently been established by photoemission studies.' l 9 Other oxides for which data have been presented include BaTiO, 1 2 0 and Cd2Sn0,,l2' although neither oxide is suitable for photoeleotrolysis. Jarrett et u1.122,1 2 3 on the other hand have drawn attention to the rare-earth rhodates (which have the distorted perovskite structure) as materials suitable for photoelectrolysis. Lutetium rhodate, for example, has a band gap of 2.2eV and as prepared is p-type, although it can be made n-type by doping with Th4+. The n-Tio,/p-LuRhO, photoelectrolysis cell constructed by Jarrett et ul. produces hydrogen and oxygen

''

'Iz 113

I15

I18

12'

H.-R. Spriinken, R. Schumacher, and R. N. Schindler, in ref. 5, p. 5 5 . P. Gautron, P. Lemasson, and J. F. Marucco, in ref. 5, p. 81. T. Kobayashi, H. Yoneyama, and H. Tamura, J . Efectroanaf.Chem., 1981, 124, 179. Y. Takahashi, K. Tsuda, K. Sugiyama, H . Minoura, D. Makino, and M. Tsuiki, J . Chem. Sor., Furuduy Trans. I , 1981, 77, 1051. J. F. McAleer and L. M. Peter, in ref. 5, p. 67. W.-T. Kim, C.-H. Choe, and Q. W. Choi, Appl. PIi.vs. Left., 1981, 39, 61. F. T. Wagner and G. A. Somorjai, J . h i . Cltem. Soc., 1980, 102, 5494. F. T. Wagner, S. Ferrer, and G. A. Somorjai, Surf. Sci., 1980, 101, 462. J . M . Kowalski and H . L . Tuller, Mazer. Sci. Monogr., 1980, 6, 1027. F. P. Kaffyberg and F. A. Benko, Appl. Phvs. Lett., 1980, 37, 320. H. S. Jarrett, A. W. Sleight, H. H. Kung, and J. L. Gilson, Surf Sci., 1980, 101, 205. H. S. Jarrett, A. W. Sleight, H. H . Kung, and J. L. Gilson. J. Appl. Phys., 1980, 51, 3916.

Photochemical Aspects of' Solur Energy Con version

585

without external bias, in fact the cell has sufficient excess power for a small load. The behaviour of the material is evidently complex since it has deep lying donor states and exhibits Fermi-level pinning. Guruswamy et al. 124 have characterized the lanthanides of Cr, Rh, V, and Au prepared by heating pastes of the mixed oxides on a titanium substrate, and with an n-TiO,/p-LaCrO,/TiO, cell they obtained a solar efficiency of 2% for photoelectrolysis, a considerable advance on the figures for the TiO,/GaP cell. The poor performance of p-GaP for hydrogen evolution has already been mentioned, and Dare-Edwards et ~ 1 . ' ~have ' attributed this to the re-oxidation of hydrogen adatoms by holes tunneling to the surface from the valence band. The efficiency improves drastically when Ru"' is 'adsorbed' on the electrode surface, although p-GaP is by no means as promising as p-InP, which is discussed below. Dispersed semiconductor systems are an attractive alternative to conventional two-electrode photoelectrolysis cells. Commercial interest in 'semiconductor diodes' continues, l Z 4 and the photoelectrochemical properties of a number of semiconductor powder systems have been investigated. 27 - 134 Platinized TiO, to produce chlorine, bromine, powders have been used by Reichman and Byvik and iodine from solutions of the corresponding halide ions. The reaction occurs in oxygen-saturated solutions, the photoproduced electron reducing oxygen at the and Kalyanasundaram et have gone a step platinum sites. Kiwi et further and designed bifunctional redox catalysts which combine catalytic centres for hydrogen and oxygen evolution on a single semiconductor (further details have been given by Borgarello et ~ 1 . l ~ ~ ) Interesting . results have been obtained by with CdS dispersions loaded with Pt and RuO,, and Kalyanasundaram et Darwent and Porter 13' have obtained similar results with Pt-treated CdS in a sacrificial e.d.t.a. system. CdS is thermodynamically unstable under illumination since holes in the valence band are sufficientlyenergetic to oxidize the crystal lattice to form sulphur. However, Kalyanasundaram et al. show that the deposition of finely dispersed RuO, and Pt on CdS particles effectively retards photodecomposition, a fine example of the kinetic stabilization of a semiconductor against photodecomposition. One of the surprising features of these bifunctional systems is that the oxidation and reduction reactions appear to be sufficiently independent that no short-circuit reaction between intermediates occurs. It is very unlikely that the simple semiconductor model proposed by Kalyanasundaram et al.' 3 3 (and also discussed by Gratzel 32) is adequate, since the close proximity of the catalytic sites on the semiconductor surface would simply lead to an effective quenching of

-

'

124

126

12'

129

130 131

132

133 134

V. Guruswamy, P. Keillor, G. L. Campbell, and J. O M Bockris, Sol. Energy Mater., 1980, 4, 1 1 . M . P. Dare-Edwards, A. Hamnett, and J. B. Goodenough, J . Electroanal. Chem. Interfac. Electrochem., 1981, 119, 109. R. M. Hooper and R . 4 . Russell, US P, 1981, 4263 1 1 1. S. Sat0 and J. M. White, J . Phys. Chem., 1981, 85, 336. S. Sat0 and J. M. White, J . Phys. Chem., 1981, 85, 592. W. W. Dunn, Y. Aikawa, and A. J. Bard, J . Electrochem. Soc., 1981, 128, 222. I. Izumi, F.-F. Fan, and A. J. Bard, J. Phys. Chem., 1981, 85, 218. B. Reichman and C. E. Byvik, J . Phys. Chem., 1981, 85, 2255. J. Kiwi, E. Borgdrello, E. Pelizzetti, M. Visca, and M . Grltzel, Angew. Chem.,Int. Ed. Engl., 1980,19, 646. K. Kalyanasundaram, E. Borgarello, and M. Gritzel, Helv. Chim. Acta, 1981, 64, 362. E. Borgarello, J. Kiwi, E. Pelizzetti, M. Visca, and M. Grltzel, Nature (London), 1981, 289, 158. J. R. Darwent and G . Porter, J . Chem. Soc., Chem. Commun., 1981, 145.

586

Photochemistry

photoexcited electrons and holes if these were mobile species in the bands. It seems more likely that localized hole and electron states are involved, since in most cases the semiconductors involved (TiO, and CdS) are likely to contain a high density of surface and bulk-trapping states. In the case of the CdS dispersions, the efficiency for photoelectrolysis is evidently and this underlines the importance of recombination processes which may even be accelerated by the deposition of catalytic centres. Clearly much work remains to be done on these systems, although they have been investigated extensively as photocatalysts in a more general context. (At the time this review was being written, a report appeared in the scientific press of efficient splitting of H,S with bifunctional CdS dispersions by Gratzel's group,'36 and it appears that the H,S system works best with RuO, alone. The quantum efficiency of 35% for the splitting of H,S to hydrogen and sulphur makes the process attractive to the oil industry, which produces large quantities of H,S during hydrosulphurization of crude oil. At present most of the H,S is converted into calcium sulphate and water, but an alternative route which leads to hydrogen fuel is obviously attractive.) 6 Liquid-junction Solar Cells

Cadmium Chalcogenides-Numerous papers and patents in the past year have been concerned with the preparation of photoelectrochemical cells based on cadmium chalcogenides, but they have not been included in this review since no fundamentally new aspects are involved. Many of the published experimental papers deal with the influence of the surface properties on the photoelectrochemical performance of cadmium chalcogenide photoanodes. Cahen et al. 3 7 have investigated the surface changes that occur when CdS or CdSe electrodes are used in polysulphide electrolytes, and results obtained by low angle X-ray diffraction, reflection electron diffraction, and scanning electron microscopy show that extensive restructuring of the surface layer occurs. In the case of CdSe electrodes, a layer of CdS forms on the surface, and De Silva and Haneman 1 3 * have used XPS to follow its growth during cell operation. The layer appears to be of low crystallinity, forming essentially a physical barrier rather than a semiconductor heterojunction. The addition of Se to the polysulphide electrolyte limits the growth of the layer sufficiently that cell performance is not degraded. Tenne 1 3 9 , 140 has discussed the effect of some surface treatments on the characteristics of the cadmium chalcogenide/polysulphide Schottky barrier, and has concluded that the most successful method involves photoelectrochemical etching. that stable cell This agrees well with the conclusion reached by Cahen et performance can be achieved by deliberate photocorrosion of CdS and CdSe photoanodes. Tenne et al. 142 have shown that the photoetching of CdSe results in the formation of small pits around lOOnm in diameter, but it is clear that the

'

13' 13'

'

39

14() 14' 14'

N c w Sc%w/i.sf. 1981, 8 October, p. 100. D. Cahen. B. Vainas, and J. M. Vandenberg. J . Elcc~troc~l~cwi. Soc... 1981, 128, 1484. K. T. L. De Silva and D. Haneman. J . Etctroc~heiir.So(,., 1980, 127, 1554. R . Tenne, Brr. Bun.smgc~s..PIiys. Clicwi.. 1981, 85, 41 3. R. Tenne, A p p l . PIij*,s., 1981, 25, 13. D. Cahen, G. Hodes, J . Manassen, and R. Tenne, A m . Chem. So(.., Symp. Ser., 1981, 146 (Photoeffects at Semiconductor Electrolyte Interfaces), 369. R. Tenne, Appl. Phj-.s. L e f t . , 1980, 37, 428.

Photochemical Aspects of Solar Energy Conversion

587

decrease in reflectance losses alone cannot account for the improved cell performance; it is more likely that surface recombination centres are selectively eliminated by photoelectrochemcial dissolution. Similar results have been obtained by Liu et a1.’43 who suggest that the method may be suitable for large-scale application. Hodes et al.14’ have shown that the output stability of Cd(Se, Te)/ polysulphide photoelectrochemical cells depends on the crystal structure of the photoanode material; the cubic lattice is considerably less stable than the hexagonal. The origin of these differences is not readily identified since the surface layer is present in polysulphide and lattice mismatch to the substrate may be involved. Several other papers concerned with fundamental aspects of cadmium chalcogenide cells have been published,’44- l 5 but they do not greatly change the current view of these systems, although the need to look for Fermi-level pinning effects is underlined by the work of Aruchamy and Wrighton on CdTe. Gallium Arsenide.-Nominated as ‘material of the year’ in last year’s review, GaAs is still the subject of fundamental and applied research in photoelectrochemistry. The n-type material which was used with such success by the group at Bell Laboratories has been used in such exotic solvents as liquid ammonia l S 4 and ambient temperature molten salts. lS6 The photocorrosion of n-GaAs has been studied in detail by several workers. 5 7 - l S 9 Tench et al. 5 7 have managed to reduce photocorrosion in a ferricyanide system by photodepositing a polypyrrole film on GaAs, a promising approach which has been applied by Skotheim et al. to the stabilization of n-type Si.l6’ Decker and Parkinson l S 8 have used watersoluble sulphonated anthraquinones in an attempt to achieve kinetic stabilization of n-GaAs. This approach requires very effective hole scavenging by the reduced partner of the redox couple, and Frese et a1.lS9have given a detailed kinetic analysis of a corrosion-competition reaction on n-GaAs, which makes this clear (see also ref. 161, and Section 7).

’”

155i

’

’

’

Gallium Phosphide.-Nakato et al. 62 in a series of papers, have discussed the complicated surface properties of n-Gap. The main problem encountered with 144 145 146

14’ 14’ 149

I5O 151

Is’

156

Iho

Ibl

164

Ib6

C.-H. Liu, J. Olsen, D. R. Sdunders, and J. H. Wang, J. Electrochem. Soc., 1981, 128, 1224. K. Colbow, D. J. Harrison. and B. L. Funt, J. Electrochem. Soc., 1981, 128, 547. G. Hodes, J. Manassen, and D. Cahen, J. Am. Chem. Soc., 1980, 102, 5962. Z. Harzion, N. Croituru, and S. Gottesfeld, J. Electrochem. Soc., 1981, 128, 551. R. Noufi, D. Tench. and L. F. Warren, J. Electrochem. Soc., 1980, 127, 2709. J. L. Sculfort and A. M. Baticle, Rev. Phys. Appl., 1980, 15, 1209. Y. Nashimoto, S. Fuyuki, T. Akutagawa, and S. Hayakawa, Jpn. J. Appl. Phys., 1981, 20, 565. J. S. Curran, J. Electrochem. Soc., 1980, 127, 2063. D. Vainas. G. Hodes, J. Manassen, and D. Cahen, Appl. Phys. Lett., 1981, 38,458. A. Aruchamy and M. S. Wrighton, J. Phys. Chem., 1980, 84, 2848. See ref. 41, p. 545 and 546 for references to Bell Laboratories’ work on GaAs. R. E. Malpas, I. Kingo, and A. J. Bard. J. Am. Chem. Soc., 1981, 103, 1622. P. Singh, R. Singh, K. Rajeshwar, and J. Du Bow, J. Electrochem. Soc., 1981, 128, 1145. P. Singh, K. Rajeshwar, J. Du Bow, and R. Job, J. Am. Chem. Soc., 1980, 102, 4676. R. Noufi, D. Tench, and L. F. Warren, J. Electrochem. Soc., 1980, 127, 2310. F. Decker and B. A. Parkinson, J. Electrochem. Soc., 1980, 127, 370. K. W. Frese, jun., M. J. Modou, and S. R . Morrison, J. Electrochem. Soc., 1981, 128, 1527. T. Skotheim, I. Lundstrom, and J. Prejza, J . Electrochem. SOL.., 1981, 128, 1625. K. W. Frese, jun., M. J. Madou, and S. R. Morrison, J. Phvs. Chem., 1980, 84, 3172. Y.Nakato, A. Tsumura, and H. Tsubomura, J. Electrochem. Soc., 1980, 127, 1502. Y. Nakato, A. Tsumurd, and H. Tsubomura. J. Electrochem. Soc., 1981, 128, 1300. Y. Nakato, A. Tsumura, and H. Tsubomura, in ref. 3, p. 145. Y. Nakato, A. Tsumura, and H.Tsubomura, Chem. Lett., 1981, 127. Y. Nakato, A. Tsumura, and H.Tsubomura, Chem. Lett., 1981, 383.

588

Photochemistry

this material is that the energy levels appear to shift when surface intermediates accumulate under illumination. Little is known about the detailed surface chemistry of Group 111-V metal semiconductors in an electrochemical environment, but the shifts in flat-band potential that result from illumination show that the chemical composition of the interface changes considerably in the absence of an efficient hole scavenger in solution. Nakato et al. use the term 'surface-trapped hole' to describe the relatively stable intermediates formed when n-GaP is illuminated in the pH range 5-10. Accumulation of surface-trapped holes modifies the energy barrier at the semiconductor
'''

'

Indium Phosphide.-Exciting developments in photoelectrochemical cells have come from the Bell Laboratories' group, and the 'material of the year' is without doubt p-InP.' Heller et ~ 1 . have ' ~ ~ given details of the first efficient p-type photoelectrochemical cell, p-InP/VCl,-VCl,-HCl/C, with a 9.4% solar conversion efficiency. The success of this cell came as a surprise, since previous studies of InP '74 has suggested that it was rather unstable in aqueous solution. Subsequently Heller et a1.'75 announced an 11.5% solar efficiency for the same cell after treatment of the InP photocathode with alkaline peroxide and cyanide. The p-type semiconductor appears to be completely stable in acid in the reducing environment provided by the V(II)/V(III) couple, whereas it is rapidly etched in air-saturated HC1. One of the main problems encountered with p-type semiconductors is that their interfacial photoelectrochemistry is often dominated by a high density of

'" 170 17'

173 174

17'

A. Etcheberry, J. L. Sculfort, and A. Marbeuf, Sol. Energy Mater., 1980, 3, 347. M. A. Butler and D. S. Ginley, J . Electrochem. Soc., 1980, 127, 1273. M. A. Butler and D. S. Ginley, J . Electrochem. SOC.,1981, 128, 712. A. M. Redon. J. Vigneron, and J. Chevallier, J. Electrochem. Soc., 1980, 127, 613. A. M . Redon and J. Vigneron, J . Electrochem. SOC.,1980, 127, 2347. W. E. Pinson, Surf. Sci., 1980, 101, 251. A. Heller, B. Miller, H . J. Lewerenz, and K. J. Bachmann, J . Am. Chem. Soc., 1980, 102, 6555. A. B. Ellis, J. M. Bolts, and M. S. Wrighton, J . Electrochem. Soc., 1977, 124, 1603. A. Heller, B. Miller, and F. A. Thiel, Appl. Phys. Lett., 1981, 38, 282.

Photochemical Aspects of Solar Energy Con version

589

surface states near the valence band; these states lower the fill-factor and output photovoltage of photoelectrochemical cells, and their effective and permanent removal is essential if an efficient cell is to be made. Heller et al. chose to follow up recent work 17' on the p-InP-gas interface that showed that the chemisorption of oxygen greatly reduces the surface recombination rate. Oxidation of the p-InP surface in alkaline hydrogen peroxide followed by immersion in a 1% KCN solution gave an interface which behaved almost ideally; the open-circuit voltage tracking the solution redox potential over at least 0.5 V. This observation contrasts with the evidence presented by Dominey et ~ 1 . for l Fermi-level ~ ~ pinning at p-InP in acetonitrile. These authors found a nearly constant shift of 0.8V in the reduction potentials for redox systems spanning a range of standard potentials greater than the band-gap of InP itself. Clearly surface preparation is important, and more work is needed to estabish the chemical composition of the InP surface under different conditions. Menezes et a1.I7*believe that the p-InP/electrolyte contact is best described as an electrolyte-oxide-semiconductor junction, the oxide layer consisting of indium oxide, possibly in a hydrated form. Electrons can evidently tunnel through the thin (- 2 nm) oxide layer, allowing efficient minority carrier collection by V(II1) species in solution. Heller et al. 17' in their most recent report of progress with p-InP cells, describe the preparation of photocathodes with islands of noble metals (Ru,Rh, or Pt) on their surface. Although photoelectrolysis at such electrodes still requires an external bias voltage, the 12% conversion efficiency for hydrogen production is very high. The cells also operate successfully at extraordinarily high levels of irradiance. Figure 7 shows how the solar-to-hydrogen conversion efficiency depends on the current density under typical solar conditions, and Figure 8 illustrates the photocurrent-voltage characteristics of the same cell under very high levels of monochromatic illumination. Photoelectrolysis should be possible with the cell in solar concentrators at up to losuns, provided, of course, that stability can be maintained. Heller ef a/. discuss in the same paper alternative ways of reducing surface recombination in p-InP photoelectrochemical cells. The best method involves the 'adsorption' of Ag from Ag(CN), - solutions; a surface coverage of 10--20% appears sufficient to bring about a considerable improvement of the fill factor in the V(IT)/V(III) cell. Attempts to replace the vanadium couple with Eu(II)/Eu(III) were not entirely successful; the cells were less stable, and the loss of silver from the surface appeared to be more rapid. Impressive results were obtained with polycrystalline CVD p-InP films; after silver treatment, the best cells had efficiencies of around 7%. Layer-type Dicha1cogenides.-The unique photoelectrochemical properties of the layer-type dichalcogenideswere first pointed out by Tributsch, and in the Faraday Discussion I8O he reviews this group of compounds. Table 2 lists some of the 17' 17' 179

'*O

W. E. Spicer, I . Lindau, P. Skeath, C. Y. Yiu, and P. Chye, Phys. Rev. Lett., 1980, 44, 420. R. N. Dominey, N. S. Lewis, and M. S. Wrighton, J. Am. Chem. SOC.,1981, 103, 1261. S. Menezes, H. J. Lewerenz, F. A. Thiel, and K. J. Bachmann, A p p f . Phys. Lett., 1981, 38, 710. A. Heller, R . G . Vadimsky, W. D. Johnston, jun., K. E. Strege, H. J. Leamy, and B. Miller, Proc. 15th IEEE Photovoltaic Specialist Conference, 198 1. H. Tributsch, in ref. 5, p. 189.

Photochemistry

590 1

SUNLIGHT,84.7mW/cm2

1 ' 1

/

/

p-InPf Ruf

/ ,5

VOLTS vs SCE

1

10

mA/cm2

15

20

0 30

25

PHOTOCURRENT DENSITY mA/cm2

Figure 7 Dependence of the solar to hydrogen conversion eficiency on current density in the cell p-InP(Ru)/3M-HCI/Pt under 84.7 mW cm- solar irradiance. The insert shows the current voltage characteristics of the platinum cathode and of the p-InP( Ru) photocathode under 84.7 mW cmP2sunlight (Reproduced by permission from Ace. Chem. Res., 1981, 14, 154).

properties of a range of layer-type materials, and it is clear from the Table that many are attractive for solar energy conversion, particularly since both n- and phave also considered the type samples can be prepared. Kautek et application of layered materials for electrochemical solar energy conversion, and they have demonstrated the important influence of surface morphology on the conversion efficiency of cells. The p-type materials may be interesting for photoelectrolysis cells, and Kautek et af. report that hydrogen is generated under illumination at p-type WSe, electrodes with catalytic Pt deposits on their surfaces. Tributsch has speculated 8 2 that the ability of the layer-type dichalcogenides to form intercalation compounds could be exploited in photoelectrochemical energy storage devices. Theoretical considerations and preliminary results obtained with ZnSe, suggest that light can be used to drive an electrochemcial intercalation reaction which effectively stores chemical energy. The idea of combining energy conversion and storage in one material is novel, and further studies of the photoelectrochemical properties of intercalation compounds of this type will be very interesting. Although the layer-type dichalcogenides are stable even under the most aggressive conditions, their performance as photoelectrodes is limited by surface recombination at steps in the crystal surface. Lewerenz et uf.' 84 have discussed the relationship between the surface morphology and solar conversion efficiency of 8 3 3

181

IgL IS3

W. Kautek, J. Gobrecht, and H. Gerischer, Bet-. Bunsenges., Phys. Chem., 1980, 84, 1034. H. Tributsch, Appf. Phys., 1980, 23, 61. H. J. Lewerenz, A. Heller, H. J. Leamy, and S. D. Ferris, in ref. 3, p. 17. H. J . Lewerenz, A. Heller, and F. J. Di Salvo, J . Am. Chmni. SOC.,1980, 102, 1877.

Photochemical Aspects of Solar Energy Conversion

59 1

V vs SCE

0'

-50

-100

- 150 -200

-25a mA/cm2

7

Figure 8 Current voltage characteristics of the p-InP(Ru)/3 M-HCI/Pt cell at high levels of irradiance (argon laser) (Reproduced by permission from, 15th IEEE Photovoltaic Specialist Conference, 198 1).

WSe, and n-MoSe, photoanodes. The deleterious effect of steps is explained by the deflection of minority carriers towards recombination sites at the edges of steps by an electric field component parallel to the layers. The preparation of crystals entirely free of such steps is difficult, if not impossible, and Parkinson at al.18s3 la6 have investigated ways in which the effect of the recombination centres can be minimized. These workers reason that the chemisorption of suitable compounds at metal sites in the steps should shift the surface-state energy levels out of the band gap and in this way decrease the rate of carrier recombination. Direct binding of ligands such as phosphines to the metals atoms was tried, but the ligand itself was found to be unstable to oxidation by photoexcited holes, so that the initial improvement in electrode performance was soon lost. Intercalation at edge sites using pyridine derivatives was more successful; although the initial improvement in cell performance was lost during extended operation, renewed treatment with the pyridine derivative restored the original characteristics. If compounds can be found which remain in a stable intercalation configuration at edge sites, the 185

la6

D. Canfield and B. A. Parkinson, J. Am. Chem. Soc., 1981, 103, 1279. B. A. Parkinson, T. E. Furtak, D. Canfield, K. Kam, and G. Kline, in ref. 5, p. 233.

1.96 (ind.)

1.13 (ind.)

0.83 (ind.)

1.13-1.6 (?) (ind.)

1.09- 1.35 (ind.)

3 1.02 (ind.)

HfSe,"

HfS,"

TiS,"

MoS,

MoSe,

MoTe,

+

1.03 (ind.)

d+d

d+d

P+d

P+d

P+d

P+d

Electron transition

So,HfIV

n-type SC p-type SC (?)

sc

n-type SC

n-type P-tYPe

degen. SC n z lo2'

Se, Zr"

n-type SC p-type SC

Mo"

Wv'

0,; complexes of platinum (small amounts)

SeO,'-,

so,2- wvl

TeO,'-,

SO,,-, MoV1

SO,, MoV1 0,( small amounts)

So, TiIV

Se, HPv

s,, Zr"

Anodic (photo) reaction products

n-type SC p-type SC (?)

Conduction type

H2

H,Se

H2

H2 H,S

H ,Te

1

Lower oxidation states of W

of Mo

oxidation

H,S, H2 intercal. products H,Se, H, intercal. products H,S, H2 intercal. products H2Se, H2 intercal. products Intercal. products

Cathodic (photo) react ion products

d

C

C

C

b

b

Reaction of redox systems

O.U.8

0.6-0.8

0.6-0.8

0.6-0.8

O.M.8

< 10-5

5 0.05

5 0.05

50.1

0.1-0.2

Photocurrent ejiciencies reached

h

5s

.L g

f

f

e

e

e

e

Possible application

a

Measurements with crystals of moderate photoelectrical quality; non-specific reaction with holes; specific photoreaction (e.g. with I-); photocurrents shift characteristically with redox potential; 'photointercalation: solar energy conversion and storage; regenerative electrochemical solar cells; photodecomposition of HI into )H2 *I2; *photoelectroanalyticalprobe.

PtS,

WSe,

~1.2--1.6 (?) (ind.) 1.16-1.4 (?) (ind.)

1.05-i.22 (ind.)

ZrSe,"

ws2

1.68 (ind.)

ZrS,"

Compounds

Energy gap le v

<

5

r;r

s

s-

m

s

2

Photochemical Aspects of Solar Energy Conversion

593 performance of even rather inferior crystals could be improved to a level suitable for a conversion device. Several reports have appeared of efficient and stable photoelectrochemical cells based on n-MoSe, and n-WSe, photoanodes,'87- l E 9 and solar to electrical conversion efficiencies as high as 10% have been obtained with selected crystals in an 13-/1- electrolyte.'87 The extraordinary stability of MoSe, is demonstrated by the cell described by Schneemeyer et a1.IE9in which the redox couple is Cl,/Cl- in acetonitrile. In fact, chlorine and bromine can be generated at MoSe, and MoS, I9O without damaging the semiconductor electrodes. Further details of the properties of n-MoSe, and of n- and p-WSe, can be found in papers by Fan and Bard,'" and Fan et al.192The classification of WSe, crystals as simply n- or ptype may need closer examination since Menezes et al.193have shown that macroscopic n- and p-type domains can exist in nominally smooth single crystals of WSe,. Menezes et al. demonstrated the existence of these regions by rotatingdisc measurements and scanning laser spot-carrier collection analysis; and careful control of the growth conditions is clearly needed if maximum solar conversion efficiencies are to be obtained with crystals of this type. Menezes et a1.'94 have also considered the competition between the photo-oxidation of solution species and photocorrosion at n-WSe, and n-MoSe, photoanodes. The great resolving power of the hydrodynamically modulated rotating ring-disc electrode is elegantly demonstrated in this work. The importance of indirect optical transitions in the layer-type dichalcogenides is evident in the work of Kautek et al.,'95 who have shown that charge carriers generated outside the space-charge region by weakly absorbed light contribute appreciably to the measured photocurrent. Carrier diffusion lengths as high as 5 x 10-4cm were observed for MoSe, for example. Analysis of the photocurrent spectra values of the band-gap of 1.17 eV (MoS,), 1.06eV (MoSe,), and 1.16eV (WSe,). Meanwhile, Tributsch continues to set the pace for work on the layer-type compounds, and his most recent contributions concern the properties of ZnS, 19' and R u S , . ' ~ ZnS,, ~ which has a band-gap of 1.68 eV, is able to form energystoring intercalation compounds (see also ref. 182), and RuS,, which has a bandgap in the range 1.3-1.5eV, shows some promise as a material for photoelectrolysis. White et a l l 9 * and Nagasubramanian and Bard 1 9 9 have interpreted measurements on n- and p-type WSe, as evidence for Fermi-level pinning or inversion effects. The problem of distinguishing between Fermi-level pinning and inversion Kline, K. Kam, D . Canfield, and B. A. Parkinson, Sol. Energy Muter., 1981, 4, 301. "' G. F.-R. F . Fan, H. S. White, B. Wheeler, and A. J. Bard, J . Electrochem. SOC.,1980, 127, 518. 190 19'

19' 193 194

19' 196

19'

19'

199

L. F. Schneemeyer, M. S. Wrighton, A. Stacy, and M. J. Sienko, Appl. Phys. Lett., 1980, 36, 701. C. P. Kubiak, F. Schneemeyer, and M. S. Wrighton, J. Am. Chem. Soc., 1980, 102, 6898. F.-R. F . Fan and A. J. Bard, J . Electrochem. SOC.,1981, 128, 945. F.-R. F. Fan, H. S. White, R. L. Wheeler, and A. J. Bard, J . Am. Chem. SOC.,1980, 102, 5142. S. Menezes, L. F. Schneemeyer, and H. J. Lewerenz, Appl. Phys. Lett., 1981, 38, 949. S. Menezes, F. J. Di Salvo, and B. Miller, J . Electrochem. SOC.,1980, 127, 1751. W. Kautek, H. Gerischer, and H. Tributsch, J . Electrochem. SOC.,1980, 127, 2471. H . Tributsch, J . Electrochem. SOC.,1981, 128, 1261. R. Guittard, R. Heindl, R. Parsons, A. M. Redon, and H . Tributsch, J . Electroanal. Chem. Inter&. Electrochem., 1980, 111, 401. H. S. White, F.-R. F. Fan, and A. J. Bard, J . Electrochem. Sac., 1981, 128, 1045. G. Nagasubramanian and A. J. Bard, J . Electrochem. SOC.,1981, 128, 1055.

594

Photochemistry

for narrow band-gap semiconductors has been discussed by Gerischer and Bard.200Kautek and Gerischer 2 0 1 have studied inversion effects at n-type MoS,, MoSe,, and WSe,, and they suggest that the maximum photovoltage can be obtained under inversion conditions, provided of course that the semiconductor is stable to decomposition by minority carriers. Schneemeyer and Wrighton 202 provide convincing evidence that Fermi-level pinning occurs at n-type MoSe, in acetonitrile, so that a maximum output voltage of -0.4V is obtained once the redox potential of the solution species is sufficiently positive. These results appear to contradict the observations made by Kautek and Gerischer,,O1 and the resolution of these discrepancies may have to wait until appropriate methods of surface analysis are used to characterize the crystal surfaces. Interest in the layertype dichalcogenides is likely to persist, and we may hope in the next few years to see the practical realization of some of the speculations made by Tributsch 1 8 2 in his stimulating discussions of the chemistry of these materials. Silicon.-The poor chemical stability of silicon might appear to exclude its use in semiconductor liquid-junction cells, but recent work has shown that it is possible to stabilize silicon with different surface coatings. Bocarsly et aL203 have used ferrocene-derivatized n-type Si in aqueous media, and Hinckley and Haneman ,04 have determined surface barrier hieghts for Ge and Si with adsorbed ferrocenes. Further characterization of textures derivatized n-Si surfaces has been achieved by Bruce and Wrighton using electron microscopy and Auger spectroscopy. An alternative method of stabilization, which has met with some success, involves the deposition of a conducting organic polymer, such as polypyrrole, on the electrode surface.160. Phthalocyanine coatings have also been used, but with less success ,07 and temporary stabilization of n-Si has been obtained under conditions where a thin oxide film is formed on the surface.208 The outlook for Si photoanodes does not appear to be promising and attention has turned to the ptype material. Heller et al.209have reported a 2.8% light-to-electrical conversion efficiency with p-type Si photocathodes in a p-Si/VCl,-VCI,-HCl/C cell. In common with p-InP, the p-Si photocathode does not appear to suffer from Fermilevel pinning problems, and Calabrese and Wrighton l o have reported efficient platinum-catalysed hydrogen generation with p-Si 'derivatized with surface viologen units. Several other reports of studies on Si photoelectrodes have appeared. 'O0 '01

'O'

'03 204 205 206

'07 '08 '09

'lo

''I 212

'13

'I4 *I5

See discussion in ref. 5. W. Kautek and H. Gerischer, Ber. Bunsenges., Phys. Chem., 1980, 84, 645. L. F. Schneemeyer and M. S. Wrighton, J . Am. Chem. Soc., 1980, 102, 6964. A. B. Bocarsly, E. G . Walton, and M. S. Wrighton, J . Am. Chem. Soc., 1980, 102, 3390. S. Hinckley and D. Haneman, Surf. Sci., 1980, 101, 180. J . A. Bruce and M . S. Wrighton, J . Electroanal. Chem. Interfar. Electrochem., 1981, 122, 93. R. Noufi, A. J. Franck, and A. J. Nozik, J . A m . Chem. SOC.,1981, 103, 1849. Y. Nakato, M. Shioji, and H. Tsubomura, J . Phys. Chem., 1981, 85, 1670. R. S. Morrison, M. J. Madou, and K. W. Frese, in ref. 3, p. 178. A. Heller, H. J. Lewerenz, and B. Miller, .I. Am. Chem. SOC.,1981, 103. 200. D. C. Bookbinder, J. A. Bruce, R. N . Dominey, N . S. Lewis, and M. S. Wrighton, Proc. Natl. Acad. Sci. U S A , 1980, 77, 6280. G . S. Calabrese and M . S. Wrighton, J . Electrochem. Soc., 1981, 128, 1014. J. A. Turner, J. Manassen, and A. J. Nozik, Appl. Phys. Lett., 1980, 37, 488. J . Chardhiel, J . Electrochem. Soc., 1980, 127, 1822. Y . Avigal, D. Cahen, G. Hodes, J. Manassen, and B. Vainas, J . Electrochem. Soc., 1980, 127, 1209. N . S. Lewis and M. S . Wrighton, in ref. 3, p. 146.

Photochemical Aspects of Solar Energy Conversion

595

Other Semiconductors.-Kennedy et aL2' have continued to study Fe,O, photoelectrodes, and their most recent work shows that high efficiencies are obtained with Si-doped sintered electrodes. Dare-Edwards et aL21 have characterized lithium-doped NiO in some detail but, as expected, the very low carrier mobility in this material makes it quite unsuitable for solar energy conversion. Gissler 2 1 * has investigated trigonal Se films, and Davidson and Willsher have given further details of the properties of HgS powder photo anode^.^ 1 9 * 220 Derivatized tin-oxide electrodes have been prepared by Fox et a1.,221and Janzen et a/. have successfully attached the photosynthetic reaction centre molecule isolated from Rhodopseudomones sphaeroides to tin oxide 2 2 2 (see also Section 2).

'

Photosensitization.-The photosensitization of semiconductor electrodes is still the subject of a number of papers every year. Although the chance is small that single-crystal systems will benefit appreciably from photosensitization, the possibilities for high surface area systems, such as dispersions, are more exciting. Key references on photosensitization have been included in this review,223- 2 3 7 although they do little to change the currently accepted view of the mechanism or efficiency of photosensitization. 7 Advances in Theory and Techniques of Semiconductor Electrochemistry

The simple models of electron transfer at semiconductor interfaces, which have been used until recently, are now being extended and improved, and Wilson 2 3 8 has provided an authoritative review of the theory, which includes some discussion of solar photoelectrochemical cells. Albery et have explored the transport and kinetics of minority carriers at illuminated semiconductor electrodes. The exact analytical solution of the problem is obtained in terms of confluent 216

'I7

'I9 220 221 222

223 224

225 226 227 228

229

230 231 232 233 234 235

236 237

'" 239

J. H. Kennedy, R. Shinar, and J. P . Ziegler, J . Elecrrochem. SOC.,1980, 127, 2307. M . P. Dare-Edwards, J. B. Goodenough, A. Hamnett, and N. D. Nicholson, J. Chem. SOC.,Faraday Trans. 2, 1981, 77, 643. W. Gissler, J. Electrochem. Soc., 1980, 127, 1713. R. S. Davidson and C. J. Willsher, J. Chem. Soc., Faraday Trans. 1, 1980, 76, 2587. R. S. Davidson and C. J. Willsher, in ref. 5, p. 177. M. A. Fox, F. J. Nobs, and T. A. Voynick, J, Am. Chem. Soc., 1980, 102, 4029. A. F. Janzen and M. Seibert, Nature (London), 1980, 286, 584. H. Hada, Y.Yonezawa, and H. Inaba, Ber. Bunsenges., Ph.w Chem., 1981,85, 425. M. A. Fox, F. J. Nobs, and T. A. Voynick, J. Am. Chem. SOC.,1980, 102,4036. A. Giradeau, F.-R. F. Fan, and A. J. Bard, J . Am. Chem. SOC.,1980,. 102, 5137. C. D. Jager, F.-R. F. Fan, and A. J. Bard, J. Am. Chem. SOC.,1980, 102, 2592. P. Fromherz and W. Arden, J. Am. Chem. Soc., 1980, 102, 6211. W. Arden and P. Fromherz, J. Electrochem. Soc., 1980, 127, 370. V. N. Alonso, M. Beley, P. Chartier, and V. Ern, Rev. Ph-vs. Appl., 1981, 16, 5 . M. P.Dare-Edwards, J. B. Goodenough, A. Hamnett, K. R. Seedon, and R. D. Wright, in ref. 5, p. 285. M. Matsdmuri, K. Mitsuda, N. Yoshizawa, and H. Tsubomura, Bull. Chem. SOL..Jpn., 1981,54, 692. R. Memming, Surf. Sci., 1980, 101, 551. R. Schumacher, R. H. Wilson, and L. A. Harris, J . Electrochem. SOC.,1980, 127, 96. T. Tennekone and W. M. R. Divigalpitiya, Jpn. J. Appl. Phys., 1981, 20, 299. T. Watianabe, T. Takizawa, and K. Honda, Ber. Bunsenges., Phys. Chem., 1981,85, 430. T. Watdndbe, M. Nakao, A. Fujishima, and K. Honda, Ber. Bunsenges., Phys. Chem., 1980,&1, 74. I. Willner, J. M. Otvos, and M. Colvin, J. Am. Chem. Soc., 1981, 103, 3203. R. H. Wilson, CRC Crit. Rev. Solid-State Muter. Sci., 1980, 10, 1. W. J. Albery, P. N. Bartlett, A. Hamnett, and M. P.Dare-Edwards, J. Electrochem. Soc., 1981, 128, 1492.

596

Photochemistry

hypergeometric functions, but their simpler expressions (accurate to better than 5%) will find widespread application. Earlier theoretical treatments, for example by Butler 240 and Gartner 241 have assumed that the rate of electron transfer at the interface is rapid, but Albery et al. demonstrate, for reasonable values of the diffusion coefficient and diffusion length of minority carriers, that the ratedetermining step may be electrochemical charge transfer. Under these conditions, recombination within the space-charge region becomes important. The importance of kinetic factors in the photocorrosion of semiconductors has become increasingly clear during the past year. Of course, the thermodynamic calculation of decomposition potentials serves as a useful guide to the equilibrium situation, but detailed kinetic and mechanistic considerations are more immediately relevant to the problem of long-term photoelectrode stabilization. Gerischer 242 has reviewed thermodynamics and kinetics of photodecomposition, and Cardon et a1.243-245have developed a detailed kinetic treatment. Similar kinetic equations have been discussed by Frese et af.*'51 16' who, like Cardon et al. have used the rotating ringdisc electrode to follow the competition between redox reactions and photocorrosion. Frese et al. consider the following mechanism [equations (7)-(1 O)] for the corrosion-competition reaction for a binary semiconductor such as GaAs. The >A'Bc species is comparable to the 'surface >A:B<

+ h+

-

1

+

- =

S

1

k,

>A'B<

(7)

kAJ3

k- lk32C,2

trapped hole' proposed by Nakato et (see Section 6 ) . The reciprocal stabilization ratio can be defined as shown in equation (1 l), wherej, is the rate of hole capture by the reducing agent R., and C , is the combination of R. Since S and j , are readily available from ringaisc measurements, the kinetic parameter k ,k,/k - lk,2 can be determined. Figure 9 shows examples of the stabilizing effect of Fe" at different pH values. The improved stability evident at low pH values is consistent with the energy levels of the reduced species lying predominantly below 240 24 1 242 243

2 44

245

M. A. Butler, J. Appl. Phys., 1977, 48, 1914. W. W. Gartner, Phys. Rev., 1959, 116, 84. H. Gerischer, in ref. 5, p. 137. F. Cardon, W. P. Gomes, F. Vanden Kerchove, D. Vanmaekelbergh, and F. Van Overmeire, in ref. 5, p. 153. F. Van Overmeire, F. Vanden Kerchove, W. P. Gomes, and F. Cardon, Bull. SOC.Chim. Belg., 1980, 89, 181. W. P. Gomes, F. Van Overmeire, D. Vanmaekelbergh, P. Vanden Kerchove, and F. Cardon, in ref. 3, p. 119.

597

Photochemical Aspects of Solar Energy Conversion I

I

1

I

(7.65)

6

5

4

11s

3

2

1

I

I

I

I

I

0

0.2

0.4

0.6

0.0

j3 rm/cm2

Figure 9 Reciprocal stabilization eQiciency vs. redox stabilization current for n-GaAs at various pH values. Stabilizing agents 0.02 M-Fe" e.d.t.a. (0.1 M-e.d.t.a.), open symbols; 0.02 M Fe" d.t.p.a. (0.1 M d.t.p.a.), closed symbols (Reproduced by permission from, J. Electrochem. Soc., 1981, 128, 1527).

the valence band, and Frese et al. have used the Marcus theory of electron transfer to treat their experimental results in more detail. The importance of surface states in semiconductor photoelectrochemical cells has become increasingly apparent as materials with narrow band-gaps have been 247 have discussed Fermi-level pinning by surface investigated. Bard et al.246* states, and Wilson248 has considered the role of interface states in electrontransfer processes at semiconductor electrodes. The surface-state concept is evidently flexible enough to include specifically adsorbed ions, and Wilson ~ ~ ' considers that case of S2- adsorption on CdS in detail. Mavroides et ~ 1 . have discussed interfacial energy states for several kinds of composite electrodes (e.g. CdSe-SrTiO,) that have been used in photoelectrochemical cells. Surface recombination is one of the most important limitations on photoelectrochemical cell performance, and Heller 2 5 0 has shown that the density and energy of surface states can be controlled by chemisorption. This is particularly necessary in the case of polycrystalline electrode materials where the surface states at grain boundaries seriously reduce cell efficiency. In the case of wide-band-gap semiconductors, on the other hand, surface states are necessary to promote efficient charge transfer to

246 247

248

249 250

A. J. Bard, F.-R. F. Fan, A. S. Gioda, G. Nagasubramanian, and H. S. White, in ref. 5 , p. 19. A. J. Bard, A. B. BOCdrSly, F.-R. F. Fan, E. G . Walton, and M. S. Wrighton, J . Am. Chem. SOC., 1980, 102, 3671.

R. H. Wilson, in ref. 3, p. 103. J. G . Mavroides, J. C. Fan, and H. G. Zeiger, in ref. 3, p, 217. A. Heller, in ref. 3, p. 57.

598

Photochemistry

solution species at energies located in the band-gap. Kowalski et aL2” have stressed the role of these surface states in the photoelectrolytic decomposition of water at semiconductor electrodes, and they have made theoretical calculations to determine the position and nature of surface states for oxide systems. A high density of surface states can lead to Fermi-level pinning, but it is important to distinguish between Fermi-level pinning and inversion effects (see the discussion of ref. 246 by Gerischer in ref. 5). Turner et al.252have chosen to use the term ‘band edge unpinning’ to describe the way in which the surface energy levels change under inversion conditions, although the need for such a term is not clear (under accumulation or inversion Conditions, the potential drop in the Helmholtz layer becomes potential dependent since the capacity of the space-charge capacitance becomes comparable to the double-layer capacity). Time-resolved measurements in photoelectrochemistry are relatively new, and Perone et a l . 2 5 3 - 2 5have 5 followed the changes in charge distribution after pulsed laser excitation of photoelectrodes. The interpretation of the potential changes, which follow flash excitation under coulostatic conditions, must take into account the distribution of charge between the semiconductor and the solution, and it is not clear how a distinction can be made between a net redistribution of charge in the solid on the one hand and interfacial charge-transfer on the other (a discussion of this point can be found in ref. 5). Karas et al. and others 2 5 6 - 2 6 1 have published several papers which deal with the use of luminescence from Te-doped CdS photoelectrodes to probe excited-state deactivation processes in photoelectrochemical cells, and Fu-jishima et al. 2 6 2 have applied photothermal spectroscopy to the simultaneous determination of quantum efficiency and energy efficiency of CdS and TiO, photoelectrodes. As more sophisticated models are developed to describe interfacial photoelectrochemistry, measurements of this kind will be needed to separate the different routes for the deactivation of excited charge carriers. 8 Organic Solid-state Systems The problems with organic solid-state photovoltaic devices are well known; the localized nature of the optical excitations in most cases and the high density of charge-carrier traps in polycrystalline dye films limit the efficiency of chargecarrier generation and separation. Nevertheless, Chamberlain et al. 2 6 3 have 25f 252

253

254 255

256

”’ 258 259

260 261

263

J. M. Kowalski, K. H. Johnson, and H. L. Teller, J. Electrochem. Soc., 1980, 127, 1969. J. A. Turner, J. Manassen, and A. J. Nozik, in ref. 3, p. 253. S. P. Perone, J. H. Richardson, S. B. Deutscher, J. Rosenthal, and J. N. Ziemer, J. Elecfrochem. Soc., 1980, 127, 2580. J. H. Richardson, S. P. Perone, and S. 8 . Deutscher, J . Phys. Chem., 1981, 85, 341. S. B. Deutscher, J. H. Richardson, S. Perone, J. Rosenthal, and J. Ziemer, in ref. 5, p. 33, B. R. Karas, H. H. Streckert, R. Schreiner. and A. B. Ellis, J . Am. Chem. SOC.,1981, 103, 1648. H. Streckert, B. R. Karas, D. J. Mordno, and A. B. Ellis, J. Phys. Chem., 1980, 84, 3232. A. B. Ellis and B. R. Karas, in ref. 3, p. 295. B. R. Karas, D. J. Mordno, D. K. Bilich, and A. B. Ellis, J . Electrochem. Soc., 1980, 127, 1144. A. B. Ellis, B. R. Karas, and H. H. Streckert, in ref. 5, p. 165. B. R. Karas, J. Electrochem. Soc., 1980, 127, 314C. A. Fujishima, Y. Maeda, K. Honda, G. H. Rrilmyer, and A. J. Bard, J . Electrochem. Soc., 1980,127, 840. G. A. Chamberlain, P. J. Cooney, and S. Dennison, Nature (London), 1981, 289, 45.

Photochemical Aspects of Solar Energy Conversion

599

reported a 2.1 % power conversion efficiency for merocyanine solid-state photocells, and Triyama et aE.264obtained an open-circuit voltage of 1.5V for one of a series of merocyanine dyes which they used in Al/dye/Ag sandwich cells. Moriizumi and Kudo 2 6 5 have prepared flexible photovoltaic cells by depositing a merocyanine dye layer on a transparent polyester film coated with an indium-tin oxide layer. Musser and Dahberg 266 have used pulsed laser excitation to examine Al/merocyanine/Ag sandwich cells, and it appears from their work that the photovoltage spectrum is dominated by the forbidden SOT,transition in the neari.r. The most likely explanation for this is that the photovoltage is a bulk effect that results from the release of trapped carriers by triplet excitons. The importance of distinguishing photoinjection currents from photodetrapping currents has not been generally appreciated, and more work is needed to characterize the nature of the metal dye contacts in these systems. The phthalocyanines are still of some interest, and Ayers 2 6 7 has interpreted the photoelectrochemistry of copper phthalocyanine in terms of the band-model for semiconductors. Menzel et a1.268 have studied the photoconductivity and electrical field-induced fluorescence quenching in metal-free phthalocyanine films. Doping of the film increases charge-carrier photogeneration, and it seems likely that the mechanism is extrinsic, involving field-assisted exciplex dissociation. These are complicated materials, which are difficult to purify, and the mechanisms of carrier generation in polycrystalline and amorphous films are still obscure. The porphyrins 2 6 9 - 2 7 1 and monolayer assemblies of chlorophyll on SnO, elec273 have also been studied. trodes Polyacetylene and other organic polymer semiconductors have been in the news recently, and MacDiarmid and Heeger 74 have used polyacetylene photoanodes in a polysulphide solar cell. Polyacetylene and other organic polymers have also been used in solid-state photovoltaic - 277 but conversion efficiencies are still very low. 2729

K. Irlyamd, M. Shivaki, K. Tsuda, A. Okada, M. Sugi, S . lizima, K. Kudo, S. Shiokawa,T. Moriizumi, and T. Yasuda, Jpn. J . Appf. Phvs., 1980, 19, (Suppl. 19-2), 173. 2 6 5 T. Moriizumi and K. Kudo, Appf. Phys. Lett., 1981, 38, 85. 266 M. E. Musser and S. C. Dahlberg, J . Chem. Phys., 1980, 72, 4084. 267 W. M. Ayers, in ref. 5, p. 247. 268 E. R. Menzel and R. 0. Loutfy, Chem. Phys. Lett., 1980, 72, 522. 269 H. T. Tien and J. Higgins, J . Electrochem. SOC.,1980, 127, 1475. 2 7 0 C. H. Langford, B. R. Hollebone, and D. Nadezhdin, Can. J . Chem., 1981, 59, 652. 2 7 1 F. J. Kampas, K. Yamashita, and J. Fajer, Nature (London), 1980, 284, 40. 272 T. Miyasaka and K. Honda, Surf Sci., 1980, 101, 541. 273 R. Jones, R. H. Tredgold, and J . E. O'Mullare, Photochem. Photobiol., 1980, 32, 223. "'A. G. MacDiarmid and A. J. Heeger, Proc. 30th Electronic Components Conference, 1980, 201. 2 7 5 P. J . Reucroft and H. Ullal, Sol. Energy Mater., 1980, 2, 217. 2 7 6 J. Tsukamoto, H. Ohigashi, K. Matsamura, and A. Takahashi, Jpn. J . Appl. Phys., 1981, 20, L127. 277 B. R. Weinberger, S. C. Gau, and Z . Kiss, Appf. Phys. Left., 1981, 38, 555. 26J

Author Index Aakermark, B., 177 Abadirazakov, A,, 550 Abado, S.. 27 Abakerli. R. B., 99 Abdd-Bary, E. M., 541 Abdel-Hay, F. I.. 514 Abdel-Razik, E. A., 541 Abdukadirov, A,, 56 Abdullah, A. H., 25 Abkin, A. D., 509 Abraham, W., 320 Abrahamson, H. B., 199. 201 Abramovich, M., 583 Abrdmovitch, R. A., 488 Abreu, V. J., 21 Abuin, E. A,, 524 Abyshev, A. Z., 254 Achwal, W. B., 552 Acuna. A. U., 65, 125 Adachi, G., 192 Adachi. Y.. 8 Adam, F., 232 Adam, G., 230, 253 Adam, W., 29, 405, 406, 407, 469,472, 473, 474 Adams, D., 549 Adams, H. M., 145 Adams, M. J., 22, 40 Adams, M. W. W., 572 Adams, N., 137 Adamson, A. W., 171, 172, 174, 180, 185, 187, 199 Addadi, L., 509 Addison, M. C., 126, 401 Adembri, G., 338. 431 Aegerter, M. A., 26 Aerts. A,, 510 Aerts, F., 163 Aerts, L.. 86, 523 Afonichev, D. D., 513 Agaew, U. Kh., 518 Agarwal, B., 186 Agarwala, B. V., 186 Agosta. W. C., 242, 255, 482 Agrdnat, I., 48 Ahiman, V., 147 Ahmad, A,, 79 Aikawa, M., 36, 84, 102, 478 Aikawa, Y., 585 Akatsuka, R., 419 Akay, G.. 530, 543 Akhemedzade, D. A., 531 Akhtar, I. A,, 345 Akhtar. M. N., 436 Akiba, M., 432

Akimoto H., 124, 151, 154, 157 Akiyama, H., 501 Akiyama. S., 361 Akiyama. T., 203, 360 Akutagawa, T., 587 Akutsu, F.. 545 Albanov, A. I., 216 Alberding, N., 89 Albery, W. J.. 579, 580, 581. 595 Albini, A,, 223, 319, 341, 350, 351, 355. 398, 418, 435, 455, 486, 487 Alcock, A. J., 7 Alcock, N. W., 189, 195, 209 Alder, A. P., 257, 329 Aleksandvova, A. K., 539 Alessandra, M., 455 AI-Fakhri. K A. K., 364 Alfano, R. R.. 6, 14, 35, 73 Alfimov, M. V., 32, 56, 113 Al-Hassan, K. A,, 68 Ali, A. M. J.. 469 Aliev. A. T., 518 Alimarin, I. P., 176 Alimonti. A., 3 Al-Kass, S., 51 1 A k a , D. L., 25 Allcock, G., 4 Allcock, H. R., 544 Allen, C. S., 25 Allen, N S., 520. 529, 530, 547, 548, 549, 55 I , 552 Allen, P. J., 162 Allinger, K., 81 Allison. S. A,, 91 Allsopp, S. R., 173 Allworth, K. L., 231 Al-Malalka, S., 550 Almgren. M., 84, 1 1 1 Aloisi, C . G., 56, 66, 77, 537 Alonso, R. A,, 359 Alonso, V. N., 595 Alpert, R., 89 Al-Saigh, Z. Y., 469 Alt, H. G . , 200 Altman, T. E., 105 Altmann, J., 15, 18, 19 Altwegg, L., 47 Alvarez, D. C., 38 Alward, S. J., 249 Aly. M . M., 495 Alyea, F. N., 149 Amagasaki, Y., 583

600

Amano, K., 372,413 Ambartzumian, R. V., 23, 140 Arner, N. A., 13 Arner, S., 200 Amimoto, S. T., 150 Aminoff, C. G.. 8 Amirav, A., 117 Arnouyal, E., 31, 102, 181 Arnrein, W., 304 Amsterdamsky, C . , 417 Anan’eva, G. D., 527 Anda, K., 365 Anderson, C. D., 425 Anderson, D., 145 Anderson, D. L., 14 Anderson, J. A., 163 Anderson, L. G., 157 Anderson, L. W., 165 Anderson, P. C., 156 Anderson, R. A., 86, 527 Anderson, R. R., 210 Anderson, R. W., 47, 256 Anderson, S. L., 159 Anderson, W. R., 132 Andersson, K., 48 Ando, A., 337,432. 475 Ando, J., 520 Ando, W., 419, 464, 489 Andre, J. C., 75, 80. 89, 230, 402 Andreeva, N. E., 420 Andrejevic, V., 2 17 Andreoni. A,, 13, 36, 68 Andresen, P., 155 Andrews, I., 219 Andrews, L. J., 172 Andronova, N. A., 484 Andrzcjewska, S., 505 Ang. C. H., 514 Angelos, G. H., 237 Angelova, G., 186 Angert, L. G., 547 Angus, R., 14 Anisimov, 0. M., 549 Aiijaneyulu, A. S. R., 283, 374 Anpo, M., 409 Antebi, A., 403 Antonov, V. S., 24, 167 Anunuso, C. I., I16 Anzdi, J., 521, 527 Aoiles, R. G., 525 Aoki, H., 543 Aoki, N., 338 Aoydma, H . , 396, 442, 443, 456

A ut hor Index Aoyama, Y ., 209 Appellof, C . J., 91 Appenroth, K., 115, 423 Arai, S., 37, 148, 165 Arai. T., 300, 301, 346 Arakawa. S., 283, 400 Araki, H., 191, 397 Arbeloa, 1. L., 27, 40 Arce, R., 30 Archer, L. J., 176 Archer, M. D.. 579, 580 Archibald, D. A., 86, 525 Arden, W., 595 Areshidze, Kh. I., 314 Argyrakis, P., 80 Arimoto, M., 466 Arnaud, R., 551 Arnold, D. R.,31 1, 319, 351 Arnold, E., 402 Arnold, F., 152 Arnold, G. S., 154 Arnould, J. C., 259, 429, 443 Aron, K., 159 Arots-Avotins, P., 101 Arrowsmith, P., 166 Arthur, J. C., jun., 501, 513, 5 I6 Aruchamy, A., 587 Asai, K., 27, 28, 156. 161 Asai, N., 528 Asakura, J. I., 507 Asano, M., 35, 175 Asao, T., 407,485 Asbury, R. P.,191 Ashfold, M. N.R., 23, 119, 126, 129, 132, 141, 142 Ashkenazi, P., 325 Ashkinazi, M. S., 417 Ashworth, H. A., 40 Asinovskii, E. I., 159 Askani, R.,283 Aspler, J. S., 86 Assher, M., 130 Atanov, A. N., 192 Atik, S. S.. 576 Atkins, C. G., 23 Atkinson, J. B., 137 Atreya, S. K., 152 Atwal, K. S., 248 Atwood, J. L., 197 Aubailly, M., 73 Aubry, J. M., 37, 523 Auerbach, R.A., 25 Augustsson, T. R.,152 Augustyniak, W., 230, 546 Augustynski, J., 583 Aulov, V. A., 521, 529 Ault, B. S., 207 Austin, D. H., 13 Austin, R.G., 206 Austin, R. H., 89 Authier-Martin, M., 212 AuYeung, J., 6 Avigal, Y., 594 Avila, V., 390

60 1 Aviles, R. G . . 34, 157 Avnir, D., 329 Avouris, P.. 30, 146 Aydin, E., 543 Ayers, W. M.. 599 Azuma, C., 544 Azumi, T.. 94, 96, 216 Baas. P., 422 Baba, H.. 25. 125. 128 Babcock. B. W., 330 Babu. S. V., 27 Baceiredo, A.. 489 Bachiller, F. S., 581 Bachmann, K. J.. 588. 589 Bacis, R.,163 Back, R. A., 491 Bacyens-Volant, D., 527 Badin, J., 444 Badr, M. Z. A., 495 Bae, D.-H., 469 Baeckstroem, P., 177 Baer, M., 154 Baessler, H., 509 Baev, V. M., 17 Baeyens-Volant, D., 65 Bagdasargan, R. V., 551 Bagger, S., 186 Baggott, J. E., 179 Baha, F. C . , 152 Baier, H., 232 Bailkowski, S. E., 147 Bakeev, N. F., 521 Baker, M. D., 20 Baker, W. R., 241 Bakker, B. H., 405 Bakurdzhieva, D., 186 Bal, T. S., 508 Balakhin, V. P., 155 Balandier, M., 534 Balbach, B., 198, 206 Balberg, I., 583 Balci, M., 406 Baldachini, G., 19 Baldry, P. J., 314 Baldwin, A. C., 145, 147 Baldwin, S. W., 248 Balint, G. P., 547, 549 Balk, M. W., 18 Balk, R. W., 200, 202 Ballabio, M., 262 Baller, T., 132, 133, 135 Balling, L. C., 137 Balogh, D. W., 233, 280 Balter, A., 34 Balzani, V., 80, 98, 99, 175 Bamberg, W., 3 Bamford, D. J., 121 Ban, Y., 390 Banaba, Y., 15 Bandrauk, A. D., 158, 167 Banks, E., 192, 529 Banmann, H., 541 Bansal, W. R.,417 Bantegnie, J. G., 19

Baraldi, I., 45 Baranov, G. M., 550 Barany, F., 255 Barbara, P. F., 35, 61, 68 Barbe, A., 20, 150 Barber, J., 92 Bard, A. J., 22, 180, 410, 570, 585, 587, 593, 595, 597 Barefoot, A. C., tert., 321 Barg, G. D., 154 Bargar, T., 359 Barigelleti, E., 56, 99 Barker, A. J., 244 Barker, J. R.,27, 120, 147 Barker, P., 514 Barlow, M. G., 234, 344, 354, 453 Barltrop, J. A., 321, 336, 432 Barnes, I., 157 Barnes, W. T., 13 Baronavski, A. P., 129, 149 Baronnet. F., 402 Barraud, A., 518 Barrett, J. L., 519 Barrett, J. W., 149 Bartholemew, D. G., 440 Bartlett, D. F., 15 Bartlett, P. D., 404 Bartlett, P. N., 581, 595 Bartner, P., 454 Bartocci, G., 56, 65, 66, 77 Bartolo, B. D., 30 Barton, H., 274,457 Barton, J., 507 Bartoszek, F. E., 166 Barwise, A. G., 235 Baryshok, V. P.. 216 Barzynski, H., 544 BdSlaS, R. K., 227 Bass. J. D., 247 Bassanelli, R.,188 Basset, R. L., 581 Basso, H. C., 26 Bastian, E., 212, 463 Bastide, J., 444 Bastow, S. J., 12 Basu, S., 460 Batchelder, D. N., 520 Bates, D. R., 153 Baticle, A. M., 587 Batsanov, A. S.. 206 Batt. L., 130 Battaglia, R.,204 Bauer, D., 225 Bauer, R. K., 34 Bauer, S. H., 29, 165, 205 Baugh, P. J., 541 Baughcum, S. L., 131 Baugher, J. F., 96 Baum, T., 299, 312,496 Bauman, D., 92 Baumgart, R.,18 Bause, D. E., 29 Baxendak, J . H., 183 Baxter, A. W., 321, 336

A u t h or Index

602 Bay, E., 236, 297,450 Bayer, W. G., 501 Bayes, K. D., 155 Bayomi, S. M. M . , 482 Bayraceken, F., 30, 56 Bays, J . P., 528, 543 Baysal, B. M., 537 Bazhin, N. M., 121, 178, 190, 192, 295 Bazin, M., 31, 73, 87 Beak, P., 447 Beauchamp, J . L.. 146, 147, 148 Beaudet, R. A,, 164 Beccalli, E. M., 262, 338, 431 Becher, J . , 339, 435 Bechthold, P. S., 22 Beck, S. M., 28, 120 Becker, H.-D., 48, 56, 243, 265, 302, 388 Becker, J . C., 182 Becker, K . H., 152 Becker, R. S., 22, 40, 59, 103 Becker, W. G., 323 Beckwith, A. L. J., 255 Beddard, G. S., 32, 33, 88 Beebelaar, D.. 6 Beecham, A. F., 58 Beecroft, R. A,, 81 Beelitz, K . , 218, 391, 467 Behrens, U . , 200 Beigang, R., 5 Beijersbergen van Henegouwen, G. M. J., 436 Belanger, L. J., 22 Belanger, P. A., 5 Beley, M., 595 Bell, J. T., 171 Bell, T. N., 212 Bellenger, V., 543 Bellesia, F., 490 Bellobono, I. R.,257, 514, 581 Bel’nikevich, N. G . , 529 Belova, S. Yu., 557 Belt, P. B., 418 Bel’tyukova, S. V., 192, 193 Belyaeva, S. G . , 301 Belyakov, V. K., 539 Belyi, M. U., 212 Bemschop, H. P., 400 Benard, D. J., 137, 163 Benayache, F., 343 Benchidmi, M., 355, 455 Bender, C. O., 304 Bendig, J . , 26, 66, 387, 450 Benedix. R., 185 Benetti, P., 139 Benioff, P. A., 158 Benko, F. A., 584 Benn, R., 198 Bennett, C. A., 22 Bennett, J. A., 23, 27 Benschop, H. P., 368 Ben-Shaul, A,, 145 Benson, R.,164, 218

Benson, S W., 153 Bera, S. C., 63 Bereck. D., 544 Berends. W., 362 Berenjkan, N., 408 Berg, W. W.. 150 Bergeman, T., 158 Bergkamp, M. A,. 186, 187 Bergman, J . G . , 25 Bergman, R. G., 146 Bergmann, E. E., 12 Bergmark, W. R., 388 Bergsma. J . P., 357, 364, 399 Bergsma, M. D., 364, 399 Berigang, R., 5 Berlin, A,, 514 Berlman, I.B., 48 Berlyant, S. M . , 530 Berman, M . R., 146 Bernage, P., 12, 20 Bernal, I., 204 Bernard, C . , 475 Bernard, 0.. 15 Bernard, P.. 5 Bernardi, R., 358, 449 Bernasconi, C., 238 Berndt, K . , 10 Berner, G., 502 Bernstein, E. R., 23, 133 Bernstein, R. B., 127, 146 Berovic. Ci. E., 34 Berridge, .J. C., 345, 347 Berry, M. J., 148 Bersohn. R.,32, 91, 126, 131, 364 Berson, J. A,, 263, 472, 473, 48 1 Bertels, P., 24 Bertelson, R. C., 566 Bertrand, G . , 489 Beswick, J. A,, 167 Beswick, J . E., 134 Bethea, C. G., 25 Bethune, D. S., 7, 30, 146 Betteridge, D., 520 Bettinetti, G. F., 355, 398, 418, 435, 455, 486, 487 Beugelmans, R., 359 Bezdadea, M., 513 Bhardwaj. A,, 572, 581 Bhattacharyya, D. K., 167 Bhattacharyya, K., 63, 192 Bhattacharyya, S. N., 30 Bielling, K., 157 Biersack, H., 197, 198 Bilich, D. K., 598 Billups, W. E., 206 Bindel, T. H., 331 Binder, W.. 467 Binkewicz, J. B., I 1 8, 496 Bippi, H., 471 Bird, T. Ci. C., 242 Birge, R. R., 23, 39, 56, 58, 91, I13 Birks, J. B., 56

Birks, J. W., IS, 152 Birot, A,, 165 Biryakov, V. P., 547 Bisacchi, G . S., 482 Bisagni, E., 382, 475 Bishop, R., 323 Bjorklund, G. C., 38, 110 Black. G., 36, 150 Black, G. M., 15 Black, J. D., 198, 202 Black, J . G., 122 Black, R. A,, 16 Black, T. D., 16 Black, T. H., 301 Blacklock, T. J., 308, 309, 392 Blair, H . E., 536 Blair, 1. A., 255 Blakeney, A. J . , 404 Blakey, R. R.,552 Blank, E., 502 Blaskie, M . W., 190 Blase, G., 176, 190 Blattocharyya, S. N., 106 Blau, W., 13 Blaustein, M. A,, 481 Blechert, S., 247 Bleijenberg, K . C.. 195 Blint, R. J., 154 Bloembergen, N., 21, 140 Blok, P., I8 Bloom, J. D., 382, 497 Bloor, D., 520 Blount, J. F., 200, 233, 248, 280 Bludsus. W., 453 Blum, J., 329 Blumen, A., 80, 81 Bly, S. H. P., 166 Boboradea, C., 547 Bobulescu, R. C., 17 Bocarsly, A. B., 594, 597 Bockris, J. O’M., 585 Boczar, B. P., 35 Boeer, K . W., 575 Bohringer, H., 152 Boesl, U., 24 Boettcher, W., 179 Bogan, P., 454 Bogdan, L. S., 529 Bohlander, R. A,, 19 Bohling, D. A,, 201 Bojarski, C., 82 Bojarski, J., 274, 457 Bokobza, L., 523 Bokor, J., 133 Bollani, S., 501 Bolletta, F., 80, 175, 178 Bolon, D. A., 518 Bolshakova, S. A., 216 Bolster, J., 482 Bolton, J . R., 104, 361, 581 Bolts, J. M., 588 Bombach, R., 121 Bonise, D. S., 117, 147, 148 Bori, M., 16

Author Index Bonchev. P., 175. 176 Bondybey. V. E., 28, 59, 159 Bonet, J.-J., 260, 261, 433 Boni, R., 1 1 Bonnedu, R.,75, 110, 262 Bonner, P., 51 1 Bonomo, R. P., 192 Bookbinder, D. C., 396, 594 Borden, W. T., 307 Borders, J. A., 15 Borders, R. A,, 15 Borejdo, J., 91 Borer, A,, 505 Boresov, A. Y., 91 Borg, R. M., 319, 351 Borgdreilo, E., 181, 573, 575, 585 Borkowski, R. P., 157 Bormans, B. J. M . , 5 Born, L., 282 Borodulina, M. Z., 546 Borrell, P. M., 157 Borsella. E., 133, 148 Borsig, E., 507 Bortolus, P., 31, 102 Bos. F., 9 Bos, H. J. T., 294 Bossard, A., 152 Bouanich, J.-P., 18 Bouas-Laurent, H., 49, 387, 388 Bouchard, C., 543 Bouchet, P., 355,455 Bouchy, M., 75, 80, 230 Boudet, B., 359 Boule, P., 37, 282, 415, 417, 445 Bouley, A. C., 15 Bourdelande, J. L., 282 Bourque, R. A., 215, 227, 228, 466 Bourrasse, A,, 570 Bousquet, J. A., 516 Boveris, A.. 115 Bowd, A., 330 Bowen, W. R., 579, 581 Bowerman, B. A., 186 Bowman, J. M., 155 Bown, D. H., 450 Boxhoorn, G., 199 Boyd, D. R., 436 Boyd, R. W., 3 Boyd-Cooray, B., 531 Boyer, J. H., 441 Boyer, R. F., 521 Boylan, M. J., 198, 202 Boyle, D. J., 536 Boz, H . J. T., 460 Brabiner, F. R., 146 Bracken, C., 236 Brackmann, U., 12 Bradley, D. J., 6, I 1 Bradley, M. G., 203 Bradshaw, J. S., 343, 450 Brandsma, L., 294

603 Brannon, J . H., 74 Brar. A. S., 194, 195 Brashears, H. C., 134 Braslavsky, S. E., 304 Brasunas, J. C., 150 Braterman, P. S., 198, 202 Bratt, J., 366 Brauchle, C., 38, 105, 110 Brauer, H. D., 108, 412 Brauman, J. I., 124, 147, 206 Braun, A. M.. 85, 183. 397. 576 Braun, D., 534, 549, 550 Braun, P., 583 Braun, W., 37, 146, 149 Braund, D. B., 18 Braunschweig, F., 509 Bravar, M., 538 Brayman, H. C., 139 Breckenridge, W. H., 137, 138 Bredereck, P., 546 Bree, A,, 46 Breford, E. J., 163 Breiland, W. G., 105 Breitenbach, L. P., 20, 158 Brenner, D. M., 140, 141 Breslow, R., 234 Brestkin, Yu.V., 529 Brewer, R. M., 33 Brerinsky, K., 141 Brianso, J. L., 261 Brianso, M. C., 261, 433 Brice, K. A., 149 Bridge, N. J., 81 Briehl, H., 492 Bright, G. M., 483 Brilmyer, G. H.,598 Brink, G., 137 Brinkmann, U., 137 Britov, A. D., 19 Brits, A. G., 194 Brittain, H. G., 193 Broadbent, A. D., 363 Brock, J. C., 150 Brodbeck, C., 18 Brody, S. S., 92 Broglia, M.. 139 Brokken-Zijp, J. C. M., 580 Brook, A. G., 228 Brookes, C., 4 Brooks, P. R., 159, 165 Broom, A. D., 440 Broomhead, E. J., 279 Brophy, J. H., 126, 154 Browell, E. V., 21 Brower, D. L., 5 Browett, R. J., 155 Brown, C., 39 Brown, D. E., 344 Brown, D. H., 343 Brown, K. H., 312 Brown, R. G., 361 Brown, R. T., 133 Brown, S. B., 417 Bru, N., 480

Bruce, J . A.. 594 Brueck, S. R. J.. 22 Briihlmann, U., 37, 123, 130 Brugger, P.-A., 85, 183, 575, 576 Brunet, J. E., 46 Brunet, H., 165 Bruni, M. C., 45 Brunn, E., 470 Brunne, M., 4 Brunner, T. A., 162 Bruno, J. W., 210 Brunschwig, B. S., 181 Brus, L. E., 35, 40, 61, 68 Bruyn, P. J. M., 66 Bryce-Smith, D., 333 Brzezinski, J., 534, 535 Brzozonski, Z. K., 513 Bu, H. S., 508 Bubeck, C., 509 Buchanan, J. G., 490 Buchanan, K. J., 541 Buchardt, 0.. 339,435 Buck, H. M., 325 Buck, K., 320 Buduls, I., I19 Buechele, J. L., 145 Buelow, S. J., 25 Buenzli, J. C. G., 192 Buffett, C. E., 24 Bufton, J. L., 21 Buhr, J. D., 187, 576 Bukow, H. H., 157 Bulatov, V. P., 30 Bulayan, A. A., 30 Bunce, N. J., 38, 39, 357, 364, 365, 399 Bunden, M., 104 Bundy, W. A,, 250 Buquet, A., 370, 458 Burdk, I., 122, 146 Burchill, B. J., 549 Burdett, J. K., 509 Bureiko, S. F., 146 Burford, S. C., 244 Burger, V., 304 Burgess, M. D. J., 8 Burghardt, B., 139 Buric, I., 177 Burkhard, P., 11, 133 Burkhardt, C. E., 136 Burkhardt, E. W., 207 Burkhardt, R. D., 525 Burland, D. M., 38, 110 Burnett, M. N., 474 Burnham, R. K., 23, 133 Burnstein, R. B., 25 Burrows, H. D., 54 Burrus, C. A,, 6 Burshaw, T. H., 13 Burshtein, A. I., 80 Burstyn, H. C., 15 Burtin, B., 164, 217 Burton, L. P. J., 461 Burtsev, A. P., 146

Author Index

604 Bush, R. W., 502 Bush, T. E., 56 Buss, R. J., 156 Busse, G.. 217 Butcher, J. A., 36, 478 Butler, J. E., 18, 118, 126, 130, 156 Butler, M. A,, 583, 588, 596 Buzby, J. M., 321 Byrne, C., 543 Byteva, I. M., 400 Byvik, C. E., 585 Cabaness. W. R., 523 Cadenas, E., I15 Caggiano, T. J., 247, 467 Cahen, D.. 22, 40, 586, 587, 594 Caine. D., 276 Caird, J . A., 26 Cais, M., 200 Calabrese. G . S., 594 Caldwell, R. A., 327 Caledonia, G . E., 159 Callahan, J. F., 247 C a k d r , A. B., 165 Callender, R. H . , 103 Calloway, A. R., 22 Calvin, M., 572, 595 Calzaferri, G . , 35 Cameron, D. G., 20 Campagna, M., 22 Caniparini, A., 338, 431 Campbell, B. F., 32 Campbell, G. L., 585 Campet, G . , 582, 583 Campo, P. A,, 24 Camy-Peyret, C., 20 Canback, G., 532, 546 Canfield, D., 591, 593 Cannon, B. D., 124 Canosa, C. E., 153 Cinovas, A.. 260, 261, 433 Canters, G. W., 93 C ~ OW.-L., . 6 Capdevielle, P., 403 Capek. I., 507 Caplan, S. R., 573 Capps, R. N., 72 Cardilla, C., 29 Cardin, C. J.. 180 Cardon. F.. 596 Cargallo, L., 524 Cargill, R. L., 250 Carleer, M.. 164, 2 I7 Carless, H. A . J., 236, 266 Carlini. C.. 519 Carlsen. L.. 462 Carlsen, W., 91 Carlson. E. R., 149 Carlsson. D. J . . 41 I , 529. 530. 546, 547, 548 Carman. T. W.. 14 Carnall. W. T., 26 Caroli. S., 3

Caronna, T., 239, 342, 358, 449, 453 Carr, R. V. C., 402 Carrasco, C., 178 Carre, J. C., 328, 495 Carre, M., 157 Carreiri, N., 575 Carrie, R., 480 Carrington, T., 118, 166 Carter, A. F., 21 Carter, C., 265 Carter, J. G., 64 Carter, S., 13 1 Caruso, A. J., 14 Casaibore, G., 181, 574 Casassa, M. P., 117, 148 Casavecchia, P., 156 Casleton, K . , 132 Caspar, J. V., 184, 204 Cassard, P., 7 Casson, L. M., 146 Castaneda, F.. 58 Castano, F.. 132 Castellan, A,, 49, 86, 388 Castellani, A,, 4 Castex, M . C., 165 Castle, R. N., 372 Castleden.. S. L., 21 Catalan, J., 125 Catalano, I . M., 23 Cataldi, hl. T., 257 Catani, F . , 133 Catel, J.-M., 457 Caulton, K. G . , 197, 203 Cauzzo, G . , 77. 179, 302, 419 Cecchi, R., 262 Celewicz, L., 268, 445 Ceppan, M., 412, 516 Cerfontain, H.. 252, 258, 280, 312. 42% Cermak, K., 92 Cermak, V., 238, 505, 518 Cerveau, G., 204 Ceulemans, A., 173, 187 Chadha, R., 448 Chae, K. H . , 272,446 Chahidi, C., 73 Chaikin, A. M . , 148 Chaikcn, J . . 122 Chaineaux, J., 540, 546 Chakachery, E.. 281. 385 Chakrabarty, K., 390 Chakraborty, K. B., 547 Chakraborty, S.. 506 Challener, W. A., 20 Challiner, J . F.. 288, 443 Chamberlain, G . A., 598 Chambers, G . R.. 477 Champagne. L. F.. 134 Champion. S. L.. 418 Chan, C . . 158 Chan, K . H . , 41 I , 548 Chan, M . S., 581 Chan, S.-F., 182 Chan, W. H.. 292

Chance, B., 115 Chance, K . V., 150 Chander, R., 194 Chandra, A. K., 47, 79 Chandra, B.-P., 116 Chandra, R.,538, 539, 550 Chandrasekaran, K., 179, 575 Chang, C. A., 29 Chang, H . , 163 Chang, R. K., 25 Chang, R. S. F., 134, 139 Chang, S. K . , 529 Chang, T., 8 Chantepie, M., 138 Chapelan, R., 61 Chapman, s., 159 Chapoy, L. L., 520 Chaquin, P., 75, 230, 236 Charlton, J. L., 319, 330, 385, 495, 498 Charters, P. E., 166 Chartier, P. A., 505, 509, 595 Chase, D. B., 205 Chatzipetros, J., 22 Chauhan. S. M . S., 281, 385, 456 Chauviere, G., 204 Chawla, H . M., 390, 409 Chayanov, B. A., 140 Chazalviel, J., 594 Cheah, C. T., 153 Chekrii, N. P., 529 Chekulaev, V.. 415 Chen, C. H.. 160 Chen, C. W., 13 Chen. H . T., 505, 509 Chen, K . - H . , 53 Chen, K . S., 104 Chen, S.-M., 262 Chen, T. M., 104 Cheng, Y . K., 523 Chentsov. S. F., 192 Cheradame, H . , 51 1 Cherek, H., 82, 89 Chermann, J.-C., 475 Chermyan, A. E., 519 ChernoK D. A . , 76, 127 Chernomordik, Yu. A., 518 Chernov. G . M . , 417 Chernova, I . K . , 536 Cheron, B., 138 Cherry, W. R., 83 Cheshnovsky, O., 25 Cheskis, S. C . , 30 Cheung, H . C., 53 Cheung, N. H.. 133 Cheung. S.-T., 63 Chevallier, J., 588 Chew, V. S. F.. 104, 361. 362 Chi. M.-S., 424 Chiacchio, U., 422 Chiang, H.-C., 389 Chiang. S., 323 Chiang, S.-H., 278 Chiang, W. Y., 536

605

Author Index Chiba, M. H., 286 Chiba, T., 282 Chibber, S. S . , 390, 409, 415 Chibisov, A. K., 194, 420 Chiellini. E.. 519 Chi’en, C.-H., 389 Chien, D. H.-T., 230 Chien, J. C. W., 197 Chihara, K., 59 Chikasawa, K., 364 Child, M. S., 135 Childs, R. F., 321 Chinn, S. R., 6 Chinnasdmy, P., 434 Chio, C. L., 163 Chisholm, W. P., 474 Chishti, N. H., 478 Chodkowska, A., 176 Choe. C.-H., 584 Choi, B. H., 154 Choi, H. K. J., 212 Choi, J. D., 72 Choi, K.-J., 7, 35 Choi, Q . W., 584 Chou, C. S., 309, 31 I, 392 Chou, J. J., 147, 148 Chou, M., 182 Chou, M.-S., 10 Chow, J., 252, 451 Chow, M. F., 11 I , 115, 505 Chow, Y. L., 290, 454.491 Chowdhury, M., 63, 178, 192 Choy, W., 323 Christensen, C. P., I I Christensen, R. L., 25 Christian, G. D., 41 Christl, M.. 470 Christmann, D. R.,26, 40 Christophorou, L. G.. 64 Christy, C. N., 401 Chu. C.-Y., 276 Chu, M. L.. 543 Chuang, T. J., 149, 219 Chudakov, A. F., 545 Chung, C. J., 279, 505 Chutikamontham, P., 524 Chye, P., 589 Ciardelli, F., 425, 519, 528 Cicerone, R. J., 151 Ciganek, E., 266 Cimarusti, C. M., 405 Cimolino, M . C., 173 Cingolani, A., 23 Cirjak, L. M.. 200 Claesson, A., 273, 452 Clardy, J.. 402, 448 Clark. D. T., 530, 534 Clark, D. W.. 160 Clark, R. J., 205 Clark, S. F.. 184, 187 Clark, T., 492 Clark, W. G., 159 Clarke, S. R.,505, 506 Clarke. W. L., 19 Clarkson, J. E., 41

Clary, D. C., 155 Claveirolle, P., 543 Clavene, J., 583 Clear, J. M., 180 Clement, A., 495 Clerici, A., 358 Cliento, G., 29 Cline Love, L. J., 33, 40, 75, 94 Clonts, G . M., 172 Clouthier, D. J., 126 Cluff, C. L., 149 Clutterbuck, F. W. J., 4 Clyne, M. A. A., 135, 153, 154, 158, 164 Coates, J. P., 18 Coates, R. M., 241 Cocin. R.,164 Codee, H. D. F., 75 Coe, D. S., 120 Coggiola, D., 358 Coggiola, M . J., 131 Cohen, C. D., 509 Cohen, L. A., 432 Cohen, S. G., 31, 63, 77, 157, 394, 395, 503 Cohn, D. B., 4 Cojan, J. L., 138 Colbow, K . , 587 Cole, A. R. H., 18 Cole, E. R.,414 Cole-Hamilton, D. J., 180, 184, 208 Coleman, G. N., 21 Coleman, W. F., 174 Coles. B., 234 Colin, J. M., 41 Colin, R., 217 Colling, J . H., 551 Collins, C. B., 17, 163 Collins, G. J., 10, 36, 118, 133 Collins, P. M., 440 Colman, R.,485 Colorner, E., 204 Colson, S. D., 127 Combier, A. L., 516 Combourieu, J., 152, 153 Comes, F. J., 37, 131, 151, 156 Comita, P. B., 146 Compton, M., IS7 Compton, R. N., 110, 127 Condirston, D. A., 101 Condorelli, G., 209. 422 Conia, J . M., 403 Conley, C., 130 Connell. P. S.. 150 Connor, J. N. L., 154, 155 Constantino. M., 301 Constantino. P., 528 Cook, J. L., 152 Cookson, R. C., 379 Cool, T. A., 133, 139 Cooley, J . M., 177 Coombe, R. D., 137, 138 Cooney, P. J., 598

Cooper, C. D., 127 Cooper, J . N., 185 Corderman, R. R.,119 Cordova, D. M., 309 Corey, E. J., 247 Corfield, M. M., 27, 93 Corin, A., 32 Corkum, P. B., 6, 7, 145 Cornelissen, P. J. G . , 436 Corr, J., 150 Corrin, A., 91 Corriu, R. J. P., 204 Cosby, P. C., 131, 157 Cossy, J., 259, 429, 443 Costa, S. B., 369 Costa, S. M . de B., 77 Costa, S. R.,180 Costantino, P., 425 Costanzo, L. L., 189. 209, 422 Coste, C., 444 Cotovanu, M., 547 Cottart, J. J., 516 Cotter, D., 8, 12 Cotterell, B., 538 Cottier, L., 238 Couchouron, B., 280 Coufal, H., 339 Coulangeon, L. M . , 409, 415 Coulter, D. R.,146 Courseille, C., 373 Courtot, P., 209, 280, 423 Couture, A., 370, 458, 460 Cova, s., 13 Coveleski, R.A., 28, 132 Cox, A., 173, 193, 508 Cox, A. J., 82 Cox, D. M., 148 Cox, G. S., 75, 401 Cox, M . F., 21 Cox, R. A., 130 Coyle, J. D., 288, 330, 443 Cracium, P., 522 Craig, D. P., 80 Crance, M., 165 Crank, G., 414 Crawford, M. K., 35, 76 Craxton, R. S., 11 Creber, K. A. M., 201 Cremers, T. L., 188 Crerar, D. A . , 16 Creswick, M., 204 Creutz, C., 178, 182 Crim, F. F.. 124 Cristol, S. J., 300, 303, 331 Crivello, J . V., 501, 511, 518 Crockett, G. C., 259, 441 Crocombe, R. A,, 20 Croituru, N., 587 Crosby, G. A., 184, 186, 188 Cross, A. J., 32, 73 Cross, L. A., 10 Crosskand, N. M., 226 Crouch, S. R..26, 40 Crouse, D. J., 389 Crozet, M . P., 463

Author Index

606 Cruickshank, J. M., 5 Crutchley, R. J., 182 Crutzen, P. J., I50 Cruz, M., 27 Csaszar, P., 465 Cubeddu, R.,8, 36, 68, 195 Cudby, M. E. A., 520 Cuendet, P., 572 Cueto, O., 29 Cugley, J . A., 18 Cummings, J. C . , 19 Cummings, 0. W., 378,429 Cuniberti, C . , 528 Cunningham. J., 410 Cunnold, D. M., 149 Cuong. N . K . , 37 Curci, R., 419 Cureton, C. G., 127, 525 Curl, R. F., 19, 166 Curran, J. S., 587 Curtis, P. M., 141 Curtis, V., 314 Curtois, D., 5 Cusamano, M., 189 Czakis-Sulikowska, D. M., 192 Dabral, V., 281, 385 Daccord, G., 75, 230, 236 Dacrema. L. M., 398 Dadson, M., 347 DHhne, S., 63, 76 Dagdigian, P. J., 137 Dahl, L. F.. 200 Dahlberg, S. C . , 599 Dahler, P., 204 Dahlgren, R. M., 200 Dai, H. L., 141 Daily, J. W., 158 Dain, B. Ya.. 417 Dalgarno, A., 163 Dalhoeven, G. A. M., 176 Dallinger, R. F.. 208 Dalton, J. C . . 215. 227, 228, 466 Dalton, W. S.. 18 Daltrosso, E., 59 Damany, H., 16 Damen, J.. 514 Damen, T. C., 6 Damodaran, N. P., 330 Danilenko, N . I., 377 Danilov, I . L., 146 Danilova, V. I., 553 Danion, R., 480 Danion-Bougot, R., 480 Dankowski, M., 229 Dannacher, J., 118, 121 Dannenberg, J. J., 93 Darby, M. I.. 33 Darcy, P. J . , 374 Da Re, F., 419 Dare-Edwards, M. P., 582, 585, 595 Darensbourg, D. J., 199 Darwent, J. R., 397, 585

Das, B. C . , 460 Das, G . , 158 Das, P. K , 30, 59, 86, 102. 106, 483, 495 Das, P. P. 19 Das, S., 191 Datsenko, P. V., 519 Datta, A . K., 216 Ddtta, R. K., 401 Datta-Ghosh, S., 24 Dauben, W. G., 316, 317, 318 Daul, C., 580 Daussin, R. D., 303 David, C.. 65, 527, 534 Davidson, A. J., 536 Davidson, E. R., 41. 119 Davidson, I. M. T., 213, 463, 465 Ddvidson, R. S., 75, 81, 96, 365, 49 I , 552, 595 Davidson. T. E., 521 Davies, A G., 332 Davies, D. I., 549 Davies, G , M . , 457 Davies, J . P., 581 Davis, A., 543 Davis, C. R., 191 Davis, D. D., 27. 28, 150, 151, 156, 161, 191 Davis, D. M., 23 Davis, P. D., 215, 227, 352, 459. 466 Davis. S. .I., 10, 135 Dawson, D. R., 26 Day. A. C., 321, 336, 432 Day, D. R., 509 De Backer. M., 575 Debaerdernaeker, T., 432 De Boer. T. J., 350, 41 1. 412 Decker, C., 503, 534 Decker, F., 583, 587 Decout, J . L., 516 Dederen, I . C . , 83 Dederichs, B., 508 Dee, M . F.. 483 Deen, R., 368, 400 Degani, J.. 13 De Graaf, w., 364. 399 De Grdff, B. A,, 581 De Groot, M. S.. 580 de Groot, R. L., 18 De Haan, J. W., 325 de Haas, N., 153 de Haseth, J. A., 20 de Hemptinne, X., 146 Deka, B. K., 5 De Kenkeleire, D., 247 de Keuster, D., 146 Dekker. R. H., 362 Delahaigue, A., 5, 1 I DeLaive, P.J., 171, 179 de Leng, H . C., 75 Del Fierro, J., 407 Delgardo-Barrio, G., 134 Delhaes, P..419

Dellinger, €3.. 39 Dellinger, J. A., 521 Dellonte, S., 56 del Marmol, P.,148 Deloupy, C., 15 De Lucchi, O., 469, 472 DeLuisi, J. J., 151 DeMaeyer, L., 34, 73 Demaray, R. E., 159 debfartino, A,, 12 Dernas, J. N., 26, 73, 179, 581 de Mayo, P., 85, 245, 249, 269, 333, 336, 408, 427,460 de Meijere, A., 469 De Menezes, S. M. C . , 581 Demetrescu, I., 544 Derneyer, K., 86, 523 Demin, A. I., 4 Demuth, M . , 265, 274, 304 Denka, A., 501 Dennis, E., 201 Dennis, K. S., 524 Dennis, P. N. J., 15 Dennison, S., 598 De Oliveira, S. M., 206 Depannemaecker, J. C . , 19 De Paoli, M . A., 206 Depoorter, G. L., 171 de Roche, S. Z., 352,449 Deronzier, A., 180 Dervan, P. B.. 489 Derwent, R. G., 130, 149. 150 Deschaux, M., 193 Deschtnes, J.. 118 de Schryver, F. C . , 76, 79, 83, 86, 519, 523 Descotes, G., 238, 489 DeSerio, R.,14 de Silva, A. P.. 8, 41, 380, 381, 497 de Silva. J . A. F., 27 De Silva, K. T. L.. 586 desilvestri, S., 8, 36, 68 Deslauriers, H., 36, 118 Desparx, B., 551 Destrebecq, M., 322 Desvergne, J. P., 49, 86, 388 Deutsch, E. A., 185 Deutscher, S. R.,598 Dev, S., 330 de Vente, J., 66 Devi, V. M., 19 de Violet, P. F., 96 de Vlieger, G.. 135 DeVoe, R. J.. 445 de Vries, A. E., 132. 133, 135 de Vries. M . S.. 132, 133. 135 de Weck, G., 263, 267 Dewey. T. G., 81 Dewhurst, R. J . , 7 Dewinter. J. C., 13 de Wolf, B., 357 Dey, A. K., 186 de Young, R. J., 135 de Zafra, R. L.. 149

Author Index Diadiuk, V., 13 Dickenson, W. A., 331 Diegelmann, M., 10 Diem, T., 51 1 Dietel, W., 10 Dietliker, K., 31 1, 430 Dietrich, W., 197 Dietz, T. G., 119 Dignam, M. J., 20 Dijols, H., 165 Dilella, D. P., 25 Dillin, D. R., 261, 379, 429 Dilling, W. L., 308 Dilung, I. I., 504, 506 Di Marco, P. G., 181. 574 Dimmel, D. R., 330 Dimpfl, W. L., 154 Dinev, S. G., 8 Dinur, V., 58, 91 Diodati, F. P., 6 Dirscherl, R., 139 Di Salvo, F. J., 590, 593 Dissado, L. A., 80 Di Stefano, G., 219 di Stefano, S., 528 Ditto, S. R., 352, 459 Divigalpitiya, W. M . R.,595 Divisia, B., 188 Dixon, B. G., 66 Dixon, R. N., 131 Dixon, R. W., 6 Djeghri, N., 410 Djeu, N., 133 Dlabal, M. L., 10, 31, 135 Doany, F. E., 32 Dobkowski, J., 63 Dobrowolski, J. A., 15 Doepker, R. D., 118,496 Doerr, F., 339 Doetschman, D. C., 106 Dodin, E. I., 176 Dohrmann, J. K., 22 Doi, Y., 171 Dolidze, A. V., 314 Dolotov, S. M., 509 Dolson, D. A., 132 Dominey, R. N., 589, 594 Donahue, T. M., 152 Donati, D., 338, 431 Donecke, J., 460 Dong, D . C., 63 Donnelly, V. M., 161, 162 Donnet, J. B., 516 Donohue, P., 543 Donovan, R. J., 11, 126, 134, 40 1 Dopel, E., 10 Doras, P.J., 114 Dorer, F. H., 125, 218 Dorofeev, Yu. I., 531. 541 Dorozhkin, L. M., 140 Dorr, F., 59 Dors, B., 63 Dougherty, D. A., 263 Douglas, A. E.. 16

607 Doumerc, J. P., 583 Dows, D. A,, 164 Doyle, W. M., 19 Dozov, I. N., 41 Drahnak, T. J., 213, 214, 463 Dreiding, A. S., 437 Dreiling, T. D., 159 Dressick, W. J., 184, 582 Dreus, W., 108 Drews, W., 412 Drexhage, K. H., 9 Drkze, C., 164, 217 Drickamer, H. G., 43, 74 Drouin, M., 142 Drozdoski, W. S., 126 Druetta, M., 157 Drummond, J. R., 150 Dryagileva, R. I., 508 Duarte, F. J., 8 Dubac, J., 215 Duheny, J. M., 40 Dubinskii, A. A., 508, 552 Dubois, J. C., 519 Du Bow, J., 587 Duc, D. K. M., 248 Ducrocq, C., 328, 475 Duddell, D . A., 89 Dueren, R. R., 362 Duerner, G., 395 Diirr, H., 239, 392, 495 Duff, J. M. J., 228 Duffy, J. C., 110 Duguay, M. A., 6 Duke, C. B., 520 Dulcey, C. S., 27, 160 Dunand, A,, 388 Dunbar, R. C., 35, 147 Duncan, A. L., 15 Duncan, D. F., 465 Duncan, D. P., 213 Duncan, I. A., 91 Duncan, M. A,, 119 Duncan, W. M., 200 Dunderdale. J., 551 Dung, D., 575 Dung, M. H., 580 Dunkin, I. R., 484 Dunlop, R. B., 28 Dunn, M. J., 12 Dunn, W. W., 410, 585 Duperrex. R., 144 Dupuy, C.. 35, 454, 463, 478, 488 Duran, N.. 29 Durand, A,, 48 Durban, P. c.,469 Duren, R.. 163 Durkee, S., 157 Durner, G., 232 Durocher, G., 79, 360 Dutuit, O., 165 Dyadkin, A. P., 141 Dyer, P. E., 4. 5, 14 Dykstra, C. E., I15 Dzantiev, B. G., 508

Dzhabiev, T. S., 171 Dzhagarov, B. M., 400 Dzyvbenko, M. I., 10 Eaborn, C., 467 Eaker, D . W., 56, 302 Easterlang, R. G., 20 Easton, M . J., 534 Eastwood, D. L., 27 Ebara, N., 105 Ebata, T., 30 Eber, G., 339 Eberhach, W., 328, 495 Ebrey, T. G., 58 Eckert, P., 287 Eckes, H., 480 Eda, T., 507 Edelmann, F., 200 Eden, J. G., 10, 31, 135 Edgell, R. G., 581 Edgell, W. F., 18 Edilashvili, I. L.. 401 Edilyan, E. S., 529 Edwards, A. J., 180 Edwards, B. H., 200 Edwards, C. B., 11, 134 Edwards, J. G., 12, 14 Efiniov, A. A., 550, 551, 557 Efremov, Y. M., 30 Egbert, W. G . , 8 Ege, S. N., 483, 495 Egerton, P. L., 516 Egidis, F. M., 557 Egger, H., 155 Eggleton, A. E. J., 149 Egorov, V. I., 155 Eichelberger, T. S., 124 Eichele, H., 509 Eichenberger, H., 263 Eichler, H. J., 10 Eichler, J., 504 Eichmann, R., 150 Eichner, M. E., 200, 302, 369 Eilbracht, P., 204 Eilenberger, D. J., 6 Eisaku, H., 382 Eisele, F. L., 152 Eisenbach, C. D., 521, 528 Eisenthal, K. B., 35, 76, 77, 478 Eitel, E., 190 Eklund-Westlin, U., 177 Ekpenyong, K. I., 274 Ekstrom, A., 16 Ekwenchi, M. M., 153 El-Bayoumi. M. A,, 68, 526 Elert. M. L.. 120 Elgersma, H., 158 Elguero, J., 355 El-Hamamy, A. A., 231 Elieh, E. R., 8 Ellenson, W. D., 189 Ellerhorst, G., 204 Elliot. D . A,, 33 Elliot, J. R., 15

608 Ellis, A. B., 588, 598 Ellison, G. B., I19 Elmgren, H., 527, 529 El Mohsni, S., 89 Elquero, J., 455 El-Sayed, L., 180 El-Sayed, M. A., 91, 119 El-Sayed, T. M., 157 El’tsov, A.V., 295, 362, 363,4 15 Emelyanova, A. T., 557 Encinas, M . V., 58, 86, 230, 281, 394, 528, 543 Endicott, J. F., 175 Endo, Y., 526 Enever, R. P., 455 Enkaku, M., 437, 438 Eng, R. S., 18 Engel, K . , 197 Engel, P., 280, 469 Engelke, F., 163 Engelking, P. C., 119, 165 English, J. H., 59 Ennis, C. A., 152 Enokida, R., 213, 463 Ensminger, M. D., 37 Era. K., 9 Eranian, A,, 519 Erbelding, W. F., 582 Ergoz, H . E., 530 Ericksen, J., 412, 413 Erker, G., 197 Erlandson, A. C.. 133 Erman, P., 158 Ermolenko, I. N., 544 Ern, V., 93, 595 Erni, B., 470 Ershov, V. V., 551 Etcheberry, A., 588 Etoh, H., 409 Ettinger, K. V., 116 Evans, D. K . , 140, 145 Evans, N. A,, 541, 551 Evans, W., 207, 210 Even, U., 117, 165 Evett, I . W., 40 Exton, R. J., 163 Eyring, E. M., 23 Ezaki, A,, 295 Ezell, M. J., 154 Fabeni, P., 212 Fabes, L., 16 Fabry, L., 465 Fabrycy, A., 171 Factor, A., 543 Factor, R. E., 306 Paggiani, R., 345 Fahmy, A. M., 495 Fahr, E., 450 Faidyxh, A. N., 523 Fairchild, P. W., 17, 121 Fajer, J., 599 Faltynek, R. A., 202, 208 Fan, F.-R. F., 410, 585, 593, 595, 597

Author Index Fan, J. C., 597 Fanter, D. L., 522 Fantoni, R., 148 Fardntos, s. c., 154 Fargas, F., 283 Farid, A. M., 496 Farid, S., 408 Farina, M., 519 Farkas, E., 553 Farkas, L.., 422, 449 Farmer, J . W., 14 Farquharson, G . K., 157 Farran, W. T., 544 Farrell, J . , 210 Farrington, G . L., 235 Farrow, M . M.. 23 Fasani, E., 341, 398, 486 Fassel, V. A., 8, 41 Fatinikun, K. O., 520 Faure, J., 516 Favaro, G., 66, 77, 95 Faxvog, I:. R., 22 Fayer, M. D., 32, 51 Fecher, P., 450 Fedoseevn, T. G., 534 Fedosejeves, R., 6, 8 Feher, F., 212, 463 Feld, W. A., 476 Felker, P. M., 17 Fell, B., 159 Feller, D., I19 Fendler, J. H., 83, 89, 576 Feng, D., 11 Ferguson, J., 48, 49, 388 Fernando, W. S. E., 550 Ferraudi, G . , 174, 175, 178, 180, 210 Ferreira, D., 232, 399 Ferreira, M. I . C., 580 Ferrer, S., 584 Ferris, J . P., 164, 218 Ferris, S. D., 590 Fetizon, M., 248 Field, R. W., 21, 163 Fields, R., 216 Figeys, H . P., 322 Figuiere, P., 18 Fiksinski, K., 43 Filho, E. D. V., 116 Filkin, D. L., 150 Fill, E. E., 11 Filseth, S. V., 118 Finch, F. T., 148 Finch, P. S. H., 28 Fink, E. H . , 21, 157 Finlayson-Pitts, B. J., 154 Finn, T. G., 134 Finsen, L., 339, 435 Firsov, V. V., 162 Fisanick, G. J., 124 Fisar, C., 565 Fischell, D. R., 139 Fischer, E., 56 Fischer, I., 212, 463 Fischer, J . , 198, 387, 450

Fischer, R. D., 210 Fischer. S. D.. 151 Fischer, T. A., 5 Fischler, I., 206 Fish, J. L., 106 Fisher, F. S., 581 Fishman, V. A., 22 Fisk, G. A,, 157 Fissi, A,, 425, 528 Fitch, P. S. H., 131 Fite, J. D., 159 Fitzgerald, B. J., 201 Fitzsimmons, W. A., 165 Fix, G. L., 16 Fizet, M., 503 Flamme, J. P., 118 Flandrois, S., 419 Flaud, J . - M . , 20 Fleming, G. R., 9, 32, 33, 73, 88 Fleming, J . W., 118, 161 Flodin, P., 532 Floyd, D. M., 405 Flynn, G. W., 145, 146, 162 Fofonova, R. M., 553 Fogarty, M. P., 26 Fokin, E. P., 295, 377 Folcher, G., 210 Foley, M. B., 122 Folin, M., 77, 302 Fomenko, T. V., 377 Foniin, G . V., 399 Fonrodona, J., 261, 433 Font, J., 282 Foote, C. S., 400, 411, 412 For, I. L., 43 Force, A. P., 150, 153, 156 Ford, C. D., 41 Ford, D., 61 Ford, P. C., 186, 187, 188 Ford, T. M., 227 Ford, W. E., 572 Fordyce, W. A., 186 Foreman, T. K . , 171, 179 Foren, J., 40 Foricher, J., 339 Fork, R. L., 9 Formin, G. V., 505 Formosinho, S. J., 84 Forrester, J., 347 Forrester, S. D., 551 Forseman, T. C., 16 Forster, A. R., 14 Fort, A., 93 Foster, T., 104 Fotakis, C . , 11, 126, 134 Fotr, S., 15 Fouassier, J.-P., 63, 110, 502, 509, 513, 516, 546 Foulds, A. W., 581 Foulger, B. E., 347 Fountoulakis, M., 209 Fournier de Violet, P., 375 Fourrey, J.-L., 218, 460 Foust, D. F., 197

609

Author Index Fox, K., 18 Fox, M. A,, 575, 595 Frackowiak, D., 43 Franck, A. J., 594 Frank, C. W., 86, 524 Frank, H. P., 530 Franke, U., 198 Frankel, S. Ja., 529 Franze, J., 424 Fratkina, G. P., 559 Fravel, H. G., jun., 325, 347 Frazier, C. C., 200 Freddi, G., 133 Frederick, L. A., 173, 174 Fredericks, S. M., 202, 395 Freed, K. F., 91, 130, 164, 167 Freedlander, R. S., 28 Freedman, A., 126, 364 Freeman, G. H. C., 16 Freeman, J. J., 25 Freeman, R. R., 165 Freeston, D. B., 522 Frei, B., 257, 319 Freidlina, R. Kh., 199 Freilich, S. C., 395 Frese, K. W., jun., 587, 594 Frey, R., 12 Freyer, W., 63, 76 Friedman, H. A,, 171, 195 Friedman, N., 45 Friedmann, H., 147 Friedrich, E., 408 Friedrichsen, W., 432 Frigo, N., 9, 35 Frijns, J. H. G., 196 Frimer, A. A., 403 Fripiat, J. J., 27 Fritzen, E. L., 246, 446 Froelich, P., 41 Frolova, N. V., 518 Fromherz, P., 595 Fronina, I. A., 508 Frueholz, R. P., 139 Frydkjaer, S., 396 Fu-Cheng, L., 10 Fuchikami, T., 214, 465 Fuchs, B., 243 Fueki, K., 81 Fueno, T., 153 Fugate, R. D., 72 Fuhrmann, J., 527, 529 Fujii, H., 242, 251, 335, 425, 435,447 Fujii, M., 389 Fujimoto, G. T., 155 Fujimoto, T., 518 Fujino, S., 335 Fujisdwa, A., 4, 595, 598 Fujita, E., 466 Fujita, M., 25, 128 Fujiwara, H.,275 Fujiwara, I., 28 Fujiwara, M., 21 Fukawa, H., 414 Fukuchi, A., 406

Fukuda, R., 172 Fukui, K., 148, 522 Fukumara, N., 501 Fukumi, T., 148 Fukumoto, J. M., 91 Fukumoto, K., 428 Fukuyama, K., 270 Fukuzumi, S., 188 Fullarton, A., 198 Fuller, S. E., 496 Fullstone, M. A., 119 Funakura, M., 306 Funayama, H., 177 Funt, B. L., 587 Furakawa, Y., 512 Furata, K., 367 Furrer, R., 105 Furtak, T. E., 25, 591 Furth, B., 75, 226, 230, 236 Furue, M., 86, 526 Furukawa, N., 451 Furukawa, Y., 237, 278, 359, 377 Furumoto, H. W., 7 Furusawa, M., 48 Furve, M., 397 Fuss, A., 473 Futamura, S.. 326, 346, 448 Fuyuki, S., 587 Gabar, G., 83 Gabel, C. W., 7 Gaeb, S., 339 Glrtner, W. W., 596 Gaffney, S. T., 32 Gafurov, U. G., 549 Gaillard, M. L., 157 Galbraith, H. W., 140 Galembeck, F., 206 Galiazzo, G., 65, 77, 179, 302 Galimova, L. G., 402 Gall, R. E., 454 Gallagher, A., 165 Gallagher, J. J., 19 Gallagher, P. T., 383, 485 Galli, G., 519 Gallup, G. A., 138 Galochkin, V. T., 141 Galy, J., 165 Gammage, R. B., 28, 29 Gancarz, R. A., 467 Gandini, A,, 51 1 Gandolfi, M. T., 174 Gano, J. E., 230 Gansel, L., 529 Ganzalez, R., 523 Garcia, D., 31, 145 Garcia, H., 225, 229 Garcia Prieto, J., 210 Gardiner, R. A,, 502 Gardini, E., 31, 102 Gardner, C. E., 157 Garecht, B., 492 Garland, N. L., 17 Garnett, J. L., 514

Gamier, F., 199 Garraway, J., 401 Garrett, A. W., 162 Garrett, B. C., 154 Garrison, A. A., 20 Garston. B., 553 Gartner, W., 113 Garton, A., 41 1, 529, 530 Garty, H., 22, 40 Carver, W. P., 35 Garvin, H. L., 20 Garyachaya, E. M., 518 Gasanov, R.G., 199 Gascard, T., 508 Gascoin, P., 14 Gashgari, M. A., 524 Gaspar, P. P., 478 Gatenby, P. V., 5 Gau. s. c.,599 Gaude, D., 110 Gauthier, M., 145 Gautron, P.,584 Gautron, R., 110 Gawlowski, J., 36 Gazo, J., 177, 190 Gebicki, J., 457 Gedrovich, F. A,, 544 Gee, S. K., 409 Geenevasen, J. A. J., 258 Geetha. B., 380, 497 Geiger, G., 37, 130 Geiger, L. C., 139 Geilhaupt, M., 161 Geissler, G., 436 Gelade, E., 83 Gelbart, W. M., 120 Gelbwachs, J. A., 22, 139 Gellert, E. P., 549 Genier, R., 140 Gennari, G.. 77, 179, 302, 419 Gentry, S. J., 18 Genzel, L., 19 Geoffroy, G. L., 203, 207 George, A. V. E., 294 George, G. A., 521 George, M. V.. 281, 385, 414, 430, 440,456 George, T. A., 176 George, T. F., 165 George, T. S., 167 Georghiou, S., 46 Georgiew, T., 543 Georgiou, A. S., 129 Gerard, D., 51 Gerard, J. C., 153 Gerasimenko, Yu. E., 296 Gerasimov, G. N., 509 Gerasimova, T. N., 377 Gerasimovich, V. A., 547 Gerber, T., 11, 133 Gerber, V. D., 519 Gerhartz, W., 204 Gericke, K. H., 151, 156 Gerischer, H., 570, 583, 590, 593, 594, 596

610 Gerrity, D. P., 24, 165 Gershuni, S., 48 Gerstenberger, D. C., 10 Gess, E. J . , 483, 495 Getoff, N., 59. 79 Getterman, W., 5 Getz, D., 81 Geurtsen, G., 433 Geuskens, G., 534 Gex. J. P., 13 Ghaemy, M., 536 Ghattas, A. A. G.. 552 Ghazala, M., 428 Ghiggino, K. P., 34, 5 5 , 86, 525 Ghosez, L., 475 Giacherio, D., 299 Cianotti, C., 75, 85, 171, 179, 208. 210, 401 Giardini-Guidoni, A., 148 Gibson. E. P., 45, 92, 199 Gibson, J. J., 158 Giby, P., 572 Gielen. J . W. J., 316, 406 Giezen, E. A., 518 Gilbert, A., 79, 333, 340, 343, 345, 347, 354,452 Gilbert, R. G., 147 Gilbro, T., 9 Giles. C. H.. 551 Giles. R. G . F., 297 Gill, T. P., 201, 203 Gilson, J. L., 584 Gimeno, J., 206 Ginley, D. S., 588 Ginsburg, D., 325 Ginsburg, H., 359 Gioda, A. S., 597 Gioia, B., 262 Girddeau, A.. 595 Giro, G., 181, 574 Giroud, M., 163 Gissler, W., 595 Gitlin, B., 37, 165, 205 Gitlin, S. N., 150 Giuffrida, A.. 209 Giuffrida, S., 189, 209, 422 Givens, R. S., 469 Gladfelter, W. L.. 187, 576 Glassman, A., 137 Glatt, I., 21, 145 Glenn, B. H., 575 Glodz, M., 137 Glogowski, M. E., 211, 378, 468 Gloor, J., 144 Glover, S. A,, 384 Glover, S. G., 173 Glownia, J. H., 127, 128 Glushkova, L. V., 557 Gnadig, K., 10, 77 Ciobrecht, J . , 590 God, H. R., 514 Goddard, R., 198 Godfrey, A., 514

A uthor Index Godfrey. L. A., 8 Godik, V. J., 91 Goehring, R. R., 497 Goeldner. M. P., 490 Golitz, P., 469 Corner, H., 304 Corner, H., 56, 106, 424 Gokay, M . C., 10 Golankiewicz, K., 268, 445, 448, 492 Goldbach, M . , 471 Goldbeck, R., 86, 187. 208, 528 Golden, D. E., 162 Gol’dfarb, E. I.. 218 Golding, S . L., 384 Goldman, A,, 20 Goldman, T. D., 81, 223 Goldsmith, L., 482 Goldstein, S., 582 Cole, J . L., 132, 139 Golender. B. A,, 531 Golikov, V. P., 536 Golub, M . A., 539 Golubev, N. S., 146 Comes, W. P., 596 Goncharenko, L. V., 385 Gonzalez, F., 546 Goodenongh, J. B., 582, 585, 595 Goodin, J . W., 365 Goodman, L., 46 Goodman, M . F., 145, 147 Goodwin, D., 96,491 Goosen, A., 384 Gorban, N. I . , 155 Gordon, M. S., 130 Gore. J . , 407 Gorman, ‘4. A,, 235, 401 Gornostaev, M. L., 383 Gorrichon. L., 242 Gorry, P. A., 155 Gorse, R., 157 Goryachev, A. N., 544 Gosh, P., 505, 506 Gosh, R., 505 Goss, L. P., 118 Goto, H . , 435 Goto, J., 396 Goto, S., 302, 343, 398, 452, 494 Goto, T., 495 Gotoh, T., 328 Gotscho, K.A., 21, 163 Gottesfeld, S., 587 Gotthardt, H., 433, 460 Gotzmer, C., 203 Cough, D. S., 3 Cough, M . C., 543 Goujon, P , 59 Gould, I. R.,401 Gould, L. P., 153 Gounelle, Y., 343 Govidanunny. T., 10 GOWdd, G , 242

Cower, M . C., 164 Goyand, P., 521 Goynes, W. R., 514 Gozel, P.. 144 Grabner, G., 59 Grabowska. E., 82 Grabowski, Z. R., 63 Graener. H., 6 Graetzel, M . , 84, 85, 181, 396, 420, 571, 572, 573, 575, 576, 582, 585 Graff, J. L., 196, 203 Graffe, M. M . , 157 Graham, S. L., 276 Grahek, F. E., 150 Gramain, J.-C., 37, 456 Granchak, V. M., 504, 506 Grande, H. J., 89 Grandi, R., 490 Graness. A., 66 Grant, E. R., 147, 148, 218 Grant, K. R., 157 Granville, M . F., 25 Grasse, P. B., 479 Grassie, N., 536 Grasyuk, A. Z., 141 Grattan, D. W., 547 Grattan, K. T. V., 110 Gratzel, C., 582 Gratzel, M., 183 Graves, D. P., jun., 336 Gray, G. D., 248 Gray, H . B., 176, 187, 200, 207, 208, 576 Grayston, M. W., 321 Graziano, M. L., 415 Grdina, M. J., 112 Grebel, V., 105 Greek, F. M. B., 7 Green, B. I., 31 Green, G. E., 501 Green, M . , 96, 125, 203, 454, 462 Green, P. N., 514 Greenberg, D. P., 323 Greene, B. I., 9, 32, 53 Grellmann, K . H., 386 Grenier, M. F., 238 Cress, M. E., 126 Grev, R. S., 154 Grevels, F. W., 198, 206 Grice, R., 155 Grieble, D. L., 19 Grieneisen, H . P., 10 Grieser, F., 34, 83, 84, 95, 108 Griesser, H . J., 53 Gritfin, G. W., 36, 478, 483, 495 Griffiths, J . , 551 Griffiths, P. R., 19 Grigor’ev, I. A,, 436 Grillo, A,, 155 Grimley, A. J., 142 Grimminger, W., 416 Grinishaw, J., 380, 381, 497

61 1

Author Index Grinberg, 0. Ya., 508,552 Grinevich, G. R.,421 Grishina, A. D., 417 Gritsan, N.P., 295 Groby, D. E., 571 Grollmann, U., 544 Gronowitz, S., 218,391,467 Groover, C.H., 29 Grosch, W., 405 Gross, E. L., 572,581 Gross, M.E., 208 Grosz, K.-P., 469 Grotheer, H. H., 155 Groves, S. H., 13 Gruen, H., 106,424 Grueter, H. W., 272,348,350,

446 Grugel, C., 216 Grummit, U. W., 106,113,

424 Grunwald, E., 21,31, 141,145 Gruter, H., 13 Grzybala, A., 333 Gsponer, H. E., 390 Gu, T. Y., 213 Guarino, A., 188 Gubergrits, M., 415 Guckel, F., 105 Gudgin, E.,33,87 Guelachvili, G . , 20 Guen, 1. L., 427 Guerri, F., 417 Guesten, H., 334 Gugger, H., 35 Guglielmo, G., 189,209 Guiborel, C.,480 Guillet,J. E., 81,86,506,523,

525,526,530,544 Guittard, R., 593 Gundermann, K. D., 421 Gupta, A., 74,86,99,137,192,

283,420,528,536,544 Gupta, D., 493 GUptd, P. K., 5 Gupta, R., 137 Gupta, S. N.,505 Gupta, Y. P., 380,496 Gurau, R.,550 Gurinovich, G. P., 400 Gurman, V. S . , 174 Gurnick, M., 122 Guruswamy, V., 585 Gurvich, L. V., 30 Gusev, Y . M., 121 Gustafson, T. K., 13 Gustafson, T. L., 13 Gustav, K., 47,65 Gusten, H., 76 Guthrie, J. T., 514 Gutierrez, A. R.,174 Gutmann, F., 572 Guttenplan, J. B., 503 Guyot, G., 409 Guziec, F. S., 456 Guzzo, A. V., 98

Haaland, D. M . , 20 Haas. H. J . , 239,392,495 Haas. J. L., 16 Haas, 0.180. 580 Haas, Y.,130, 145,167 Habarta, J. G.. 94 Habercom, M.S., 53 Haberleitner, R..550 Hack, W., 152 Hackett, P.A., 142,145 Hada, H., 595 Haddadin, M . J., 368 Haeuster, C., 14 Hagar, M.E., 321 Hagiwara, H., 278 Hagiwara. K., 000 Hagiwara, M., 546 Hahn, J., 150 Hahn, R.C., 307 Hahn, T.-R., 91 Haidar, B., 516 Haim, A,, 179 Hakushi, T., 302,348,403 Hall, D. O., 571,572 Hall, D. R.,4 Hall, G . E., 13 Hall, K. J., 581 Hall, R.B., 148 Halpern, A. M., 33,59,81, 96,

98,388 Halpern, J. B., 130 Halsey, G. W., 18 Halverson, A. M.,356,441 Hama. Y . , 521 Hamada, T., 243,495,497 Hamada, Y., 132, 164,464 Hamamoto, K., 85 Hamana, H., 335 Hamann, H.-J., 76, I15 Hamann, S. D., 386 Hamanoue, K.,65,110, 512,

528 Hamazaki, H., 358,455 Hamblett, I., 401 Hamilton, K., 296,364 Hammes, G . G., 81 Hammill. J. L., 509,519 Hammond, G . S., 191 Hammond, P. R.,73 Hamnett, A., 582,585,595 Hamori, I., 553 Hamza, M., 21 Hanaoka, M., 438 Hanazaki, I., 127,146 Hancock, G., 23, 119, 132,

141,142 Handa, S. P., 538 Handa, T., 523 Handy, N.C . , 119 Haneman, D., 586,594 Haniyu, Y., 419 Hanko, L., 10, 135 Hann, R.A., 26 Hanna, H. L., 552 Hanna, I., 248

Hannaford, P., 139 Hannah, R.W., 18 Hansen, H.-J., 297,452 Hansen, J . C., IS7 Hansen, L., 56, 302, 388 Hantschmann, A., 176 Hanyuda, T., 518 Hanzawa, Y., 335 Hara, H., 4 Hara, K., 51 Hara, Y., 47 Harada, T., 14,115 Harang, 0 . E., 153 Harbour, J . R.,397 Hardaker, M.L., 142 Harding, L. B., 156 Hardt, H. D., 190 Harel, Y., 112 Harger, M.J. P., 489 Harigaya, Y.,375,428 Harley, M.L., 249 Harper, P.G., 147 Harriman, A., 68,91,575 Harris, C. M., 63 Harris, J. A., 513,514 Harris, J. M.,13,40 Harris, L. A., 595 Harris, S. E., 11 Harris, S. J., 17 Harris, T. D., 17 Harrison, D. J., 587 Harrison, R.G., 5 Harrison, R.P., 162 Hart, H., 262,303,434 Harter, D. J., 3 Hartman, H., 66 Hartmann, M., 490 Hartmann, W., 251,282,445 Harva, D. L., 66 Harvey, G. T., 7 Harvey, K . C., 23 Harzer, R.,139 Harzion, Z . , 587 Hase, W.L., 154 Hasebe, M., 251, 272,273 Hasegawa, H., 252,327 Hasegawa, K., 194,372,413 Hasegawa, M., 501,509 Hasegawa, T., 396 Hashiba, K., 435 Hashida, Y., 487 Hashimoto, K., 122,501 Hashimoto, S . , 362 Hashiuchi, H., SO4 Hasinoft, B. B., 1 1 1 Hassner, A., 215 Hastie, D. R., 29,151 Haszeldine, R.N., 216,234,

344,354,453 Hata, N., 358 Hata, W., 455 Hatanaka, Y., 273,288,289 Hatano, S., 484 Hatano, Y., 96 Hatsui, T., 404,412

Author Index

612 Haub, J. G., 121 Haubenstock, H., 533 Hauck. J . P., 4 Hauffe, K., 551 Hauge, R. H., 206, 211 Haugen, G. R., 35. 41 Hausen, K. B., 102 Hauser, M., 83 Haushalter, J. P., 24 Hautala, R. R., 171 Hautecloque, S., 131 Haverly, V . J., 524 Havinga. E.. 316, 406 Havlinova, B., 516 Hawkins, D., 383, 487 Hawkins, H. L., 27, 93 Hawkins. K . C., 5 Hawkins, R. T.. 155 Hawkins, W. G., 37, 126 Hawley, J. G., 21 Haws, E. J.. 288, 443 Hay, D. W., 581 Hayakawa, K . , 239, 259, 385, 457, 492 Hayakawa, S., 587 Hayama, S., 507 Hayashi. E.. 475 Hayashi. H., 15, 26, 89, 224, 287, 367.449 Hayashi, K., 501, 513, 527 Hayashi. R., 435 Hayashi, T., 452 Hayes, J. K., 149 Haynam, C . A., 28, 131 Hays, G. N., 157 Hays. J. D., 147 Hays, T. R., 28, 122 Hayward, G., 91 Haywood, D. J., 236, 266 Head. D. R., 538 Heaps. W. S., 151 Hearst. J . E., 447 Heath, B. A.. 124 Heath. P., 347 Heaven, M. C., 135, 164 Heaviside, J., 25 Hebish, A., 552 Heckel, A,, 493 Hedges. R . E. M., 37 Heeger, A. J.. 520, 599 Hefferon, G., 478 Hegemann, B., 164 Heicklen, J . , 157 Heidner, R. F., 157 Heimgartner, H., 31 1, 430, 477 Heindl, R., 593 Heine, H.-G.. 251, 445 Heinriches, R. M., 12 Heinzelmann, W.. 477 Helander, P., 22 Heller. A.. 570. 588, 589, 590, 594, 597 Heller, D. F., 120 Heller, H . G., 114, 373, 374 Helm, H., 157

Helvajian, H., 133 Hemenway, C. P., 9, 35 Hemley, R. J., 28 Hemmati, H., 133 Henderson, R. S., 207 Hendra, P. J., 25 Hendrick, M. S., 27 Hendricks, L. J., 12 Hendrickson, D. N., 201 Hendrickson, W. H., 418 Hendriks, P. A. J. M., 580 Henke, W., 28, 122 Henman, T. J., 520 Hennecke, M., 529 Hennessy, R. J., 138 Hennig, H . , 175, 176, 185 Hennig. R., 189, 576 Henry. G., 218 Hepp, A. F., 201 Herbelin, J. M., 10 Hering, F’., I66 Heritage, J. P., 13, 25 Herlemont. F., 19 Herman, I . P., 148 Hermanns, H. D., 155 Hernandez, L., 484 Herold, R., 513 Herring, D. P., 581 Herrmann, J. M . , 41 1 Herrmann, W. A,, 197, 198, 204, 206 Herron, J . T., 149 Herschbach, D. R., 25 Hersel, W . , 509 Hershberger, J., 210 Hershberger, M. V., 89 Herweh, .I. E., 390. 441 Herz, C. P., 504 Herzberg, G., 155 Hesabi, M . M., 231 Hesselink, W. H., 32 Hessler, J. P., 26 Hetherington, W . M., 35, 478 Heumann, E., 63 Heytis, K., 236 Hibert, M., 371, 491 Hida, M., 295, 362 Hidaka, T., 277, 529 Hider, M., 552 Hieftje, G . M.. 9, 35 Higashi. K., 41 Higashimura, T., 199. 506 Higashino. T., 382. 475 Higgins, J . , 599 Higgins. R., 496 Highfield, J . G., 22, 40 Highsmith, J. R., 334 Higuchi, J.. 104 Higuchi, K., 427 Higuchi, T., 214, 465 Hikida. T.. 138. 159, 365 Hilbert, M.. 73 Hildebrandt, J., 10 Hilinski, E. F.. 263 Hill, J . , 231

Hill, K. O,, 11 Hrllard, M. E., 163 Hillebrand, W., 469 Hiller, W., 190 Hillman, A. R., 581 Himme, B., 156 Hinckley, S., 594 Hindley, T. W., 22 Hino, T., 417 Hino, Y., 80 Hinz, J . , 251, 445 Hipps, K. W., 178 Hirai, Y., 270, 336, 426, 438, 457 Hirakawa, K., 474 Hiraki, K., 193 Hiramatsu, T., 115 Hirano, H., 358, 439, 455 Hirano, Y., 527 Hirao, A,, 529 Hirao, I . , 256 Hirao, K., 121, 243 Hirata, Y . , 28, 124, 125, 126 Hiraya, A,, 28 Hirayama, S., 65, 110, 131, 529 Hiriakawa, M., 253 Hirlmann, C., 14 Hirokami, S., 270, 336, 426 Hiroko, Y., 375 Hirono, M., 21 Hirose, H., 358 Hirota, E., 19 Hirota, K.. 485 Hirotani, S., 385 Hirsch. K. R., 25 Hirsch, R. E., 89 Hirth, A., 7 Hirth, C. G . , 490 Hirzel, T. K . , 81, 223 Hisamitsu, K., 328, 496 Hishino, Y . , 501 Hitchcock, P. B., 457 Hlubocka, D., 507 Ho, C.-N., 41 Ho. K . W., 460 Ho, P., 37 Ho, S. Y., 478 Ho, T.-I., 416, 445, 451 Hobson, J. H., 155 Hochanadel, C. J., 158 Hochstrasser, R. M., 32, 53, I29 Hodes, G., 586, 587, 595 Hodgeman, D. K. C., 549 Hodnett, K.. 410 Hoefs, C . A. M., 518 Hoell, J. M., 152 Hormann. M., 66 Hoesch, L., 423, 437 Holer. E., 424 HolRand, L. D., 26, 130 HotTman, B. M . , 98 HofTman, M. Z., 175 Hofland, A., 350,411 Hofmann, H., 144

613

Author Index Hoge, R., 479 Hogeman, D. K., 547 Hogervorst, W., 8 Hoggard, P. E., 180 Hohla, K., 10 Hohne, E., 253 Holbrook, K. A., 155 Holbrook, M. B., 6 Holden, D. A., 81, 506, 523, 525, 526 Holder, C. H., 13 Holland, R.,83 Hollebone, B. R., 599 Holm, A., 462 Holman, B., 64, 65, 345 Holmes, A. S., 536 Holroyd, R. A., 58 Holt, L. A., 541 Holtermann, D. L., 162 119 Hokzckaw, K. w., Holzapfel, W. B., 25 Honda, K., 22, 595, 598, 599 Honda, T., 428 Honey, F. R., 18 Hong, J.-F., 1 I Honig, B., 58, 91 Honnick, W. D., 206 Honovich, J. P., 147 Hooper, R. M., 585 Hopewell, W. D., 91 Hopf, H., 113 Hopkins, J. B., 28, I 1 9, 120, 127 Horacek, H., 539 Horani, M., 157 Hordis, G. E., 116 Horie, K., 505, 529 Horiguchi, H., 139 Horiguchi, Y., 445 Hormann, M., 471 Hornback, J. M., 330 Horne, R. K., 137, 138 Homing, D. P., 491 Horowitz, G., 570 Horowitz. J., 86 Horsley, J. A., 148 Horst, K., 576 Horton, J. K., 491 Horvath, E., 190 Horwitz, A. B., 145 Hoshi, N., 278 Hoshino, M.. 460 Hosie, R. J., 91 Hossain, Q. N., 178 Hotta, K., 419 Hotten, D., 92 Houben, J. L., 425, 528 Houdart, R., 12 Houlding, V., 185 Houston, P. L., 31, 34, 37, 126, 130, 148, 157 Howard, C. J., 150, 152 Howard, W. E., 17 Howbert, J. J., 347 Howells, M. R.,4

Howi, A. A., 368 Hoyermann, K., 152 Hoyle, C. E., 86, 390, 441, 525 Hrdlovic, P., 544, 555 Hsi, S. C., 20 Hsu, D. S. Y., 37, 136, 148 Hsu, Y. C., 164 Hu, X.-J., 10 Huang, C. Y., 507 Huang, H. G., 193 Huang, J.-S., 200 Huang, S. J., 543 Hubbard, L. M., 91, 113 Huber, D. L., 80 Huber, J. R., 37, 123, 130 Huber, R., 104, 509 Hudgens, J. W., 145 Hudson, R. A., 489 Huestis, D. L., 157 Huffman, E. H., 4 Huffman, J. C., 203 Hug, G. L., 59 Hughes, P., 448 Huguenin, D., 150 Huie, R. E., 149 Hull, W. E., 113 Hulsman, H., 163 Humbert, P., 147 Hummel, A., 75 Humphry-Baker, R., 576 Huneke, J. T., 23 Hunter, D. H., 314, 334 Hunter, G., 20 Hunter, J. A., 296, 364 Hunter, T. F., 135 Hunter, W. R., 15 Hupe, H. J., 422 Hurlbut, S. L., 389 Hurley, A. C., 58 Hurst, H. J., 16 Hursthouse, M. B., 253 Hurtubise, R. J., 41, 96 Huruumi, S., 277 Hurwitz, C. E., 13 Husain, D., 158 Hustert, K., 299 Huston, A. L., 74 Hutchinson, C. A,, 104 Hutchinson, F., 367 Hutchinson, M. R. H., 10, 15, 135 Hutchinson, S. B., 10, 135 Hyman, H. A,, 12, 127 Hynes, A. J., 126 Iannozzi, M. P., 159 Ibemisi, J. A., 526 Ibeva, I., 514 Ichikawa, Y., 410 Ichirnoto, I., 494 Ichirnura, K., 351, 370, 544 Ichimura, T., 365 Iddon, B., 366, 383, 485 Ieda, M., 522 Iesce. M. R., 415

Iijima, H., 243 Iijima, K., 338 Iitaka, Y., 406 Ikarigawa, T., 368 Ikawa, T., 582 Iked, N., 79 Ikeda, H., 482 Ikeda, K., 372, 413 Ikeda, M., 425, 445, 482 Ikehara, M., 440 Ikehata, M., 507 Ikeno, M., 464,489 Ikenoue, M., 235 Ikeyamd, H., 362 Iles, M. K., 8 Il’yushenok, V. A., 172 Imai, J., 418 Imaizumi, H., 487 Imamura, M., 165 Imamura, S., 543 Imamura, T., 194 Imanshi, T., 438 Imasaka, T., 27 Imbert, C., 12 Imhof, J., 550 Imoto, M., 507 In, 0. A., 550 Ina, K., 409 Inaba, H., 21, 595 Inaki, T., 104 Inaki, Y., 513, 544 Inarnoto, N., 240, 466 Inbar, S., 31, 63, 394 Indelli, M. T., 98 Infelta, P. P., 85, 183, 576 Ingersol, K. A,, 14 Ingle, J. D., 27 Inomata, K., 501 Inoue, A., 105 Inoue, G., 124 Inoue, H., 31, 119, 295, 362, 418 Inoue, K., 420, 506 Inoue, S., 229, 468 Inoue, T., 420 Inoue, Y., 302, 348, 403, 443 Ioebenstein, H. M . , 7 Ippen, E. P., 6, 32, 43, 91 Irgen, L., 559 Irie, M., 527 Iriyama, K., 599 Iro, O., 194 Irvin, J. A,, 36, 137 Irving, E.. 321, 336 Irwin, R. S., 158 Isac, D., 490 Isaev, S. N., 544 Ishibashi, N., 27 Ishida, Y., 380 Ishigamori, E., 390 Ishiguro, T., 132 Ishii, K., 256, 258 Ishii, T., 523 Ishii, Y., 553

Author Index

614 Ishikawa, M., 79, 213, 214, 215, 303, 434,463, 465 Ishikawa, S., 110 Ishikawa, Y., 37, 148, 159 Ishioku, T., 289 Ishitoku, T., 289, 441, 448 Ishizuka, S., 86, 528 Iskakov, L. I., 530 Isobe, K., 91 Isomura, K., 484 Itai. A., 406 Itaya, A,, 86, 525, 528 Ito, M . , 23, 28, 242 Ito, O., 110, 507 Ito, S., 47, 273, 306, 366, 367, 451, 498 Ito, T., 104, 357 Ito, Y., 115, 232. 526 Itoh, H., 346 Itoh, K., 183, 398 Itoh. M., 381, 435 Itoh. T.. 125 Itokawa, H . , 495 Itzkan, I., 12 Ivanov, G. N., 371 Ivanov. T. N., 192 Ivanov, V. B., 401, 547, 549 Ivanov, V. S., 132 Ivanov, Y . A,, 457 Ivanov, Yu. A., 396 Iverson, D. J., 200 Iwabuchi. H., 250 Iwabuchi, S., 86, 523, 528, 544 Iwagami, N., 150 Iwai, K., 86, 526 Iwamoto, H., 92, 376, 498 Iwamoto, K., 92 Iwamura, H., 304, 321, 383, 384,487 Iwamura, M., 304 Iwao, M.. 372 Iwasaki. N., 105 Iwasaki, S., 390, 436, 551 Iwasaki, T., 22 Iwata, s., 122 Iwata, T., 396 Iyer, R.S., 151 Izawa, Y., 229, 332, 357, 414, 468, 477, 478, 481, 482 Izumi, I., 410, 585 Izumi, T.. 16 Izumi, U., 336, 457 Jaanimagi, P. A,, 8 Jackel, S., 7 Jackson, A . W., 96, 125 Jackson, W . M., 130 Jacob, K . A., 519 Jacobs, H . J. C., 316, 406 Jacobs. M . , 11 I Jacobs, S. D., 1 1 Jacobson, A. G . , 8 Jacques, P., 502 Jacquier, R., 496 Jaeger, D. A., 237

Jaenicke, R., 150 Jaenicke, S., 582 Jager, C. D., 595 Jaffe, S., 154 Jaing, Y . C., 523 Jaitner, P., 201 Jalenak, W. A., 142 James, F. C., 212 Jameson, A. K., 33, 128 Jameson, D. M., 33, 88 Jamieson, M. A,, 175 Janda, K. C., 117, 148 Janda, M., 297 Janecka-Sturcz, K., 33 Janusz, R., 333 Janzen, A. F., 571, 595 Jaraudis, J., 68 Jarnot, R. J., 150 Jarosz, J.., 138 Jarowski, A,, 68 Jarrett, H . S., 584 Jarrett, S. M., 8 Jarry. J. I>., 527 Jasinski, J. M., 124, 147 Jasny, J., 8, 30 Jassim, A. N., 528 Jeandrau, J.-P., 37 Jefferies, R., 14 Jeffers, P. M., 29 Jeganathan. S., 496 Jeger, O., 257, 258, 319, 329 Jennings, D. E., 18 Jensen, J. D., 15 Jensen, N. H., 102, 103 Jensen, R. J., 148, 149 Jerina, D. M., 436 Jesson, J. P., 150 Jessop, P. E., 9 Jewell, S. P., 155 Jiang, Z. Q., 260 Jianwen, C., 11 Jimenez, L. A., 30 Jipa, S., 521 Job. R., 587 Jodhan, A., 96, 125, 153,462 Josel, R., 472 Joffe, Z . , 546 Johansen. 0.. 181 Johansson, L. B.-A., 41 John, P., 27, 40, 93, 213, 465 Johnson, A . M., 13 Johnson, C. A. F., 130 Johnson, C . H . J., 58 Johnson, D. C., 11, 41 Johnson, G. E., 79, 523 Johnson, G. L., 219 Johnson, G . R. A,, 191 Johnson, K . E., 134 Johnson. K. H . , 583, 598 Johnson, L. F., 14 Johnson, P. M., 24, 159 Johnson, R. L., 541 Johnston, H . S., 157, 162 Johnston, W . D., jun., 589 Jokay. L., 549

Jolma, K., 20 Joly, S., 402 Jones, A., I8 Jones, A. C., 33 Jones, G . , jun., 278, 323, 388 Jones, M., 477, 478 Jones, M. R. O., 15 Jones, K. B., 131 Jones, P. G., 373 Jones, R., 599 Jones, R. F., 180, 208 Jones, R. G . , 180 Jones, T. A,, 18 Jones, W., 253 Jortner, J., 117, 165 Joshi, C., 6 Joshi, N. B., 65 Jost, P., 236 Jouin, P., 218 Jourdain, J. L., 153 Joussot-Dubien, J., 41, 75, 342. 575 Jouve, P., 5, 11, 20, 150 Jouvet, C., 122 Jozwik, B., 513 Judson, R. S., 166 Jugelt, W., 115 Juliao, J. F., 583 Julien, C., 14 Julienne, P. S., 163 Jullien, J., 343 Jung, K. H., 131 Junge, C., 150 Jungmann, H., 209 Jurdeczka, K., 185 Juris, A., 174 Juris, J., 178 Just, Th., 155 Jutzi, P., 213, 465 Kabaivanov, V., 543 Kabdnov, V. A., 529 Kabe, Y., 419 Kabir-ud-Din, 575 Kabze, H . , 106 Kadykov, V. V., 518 Kaelble, D. H., 544 Kacmpf, G., 551, 552 Kaffyberg, F. P., 584 Kagawa, S., 15 Kahler, C. C., 29 Kaiser, W., 5, 9 Kaivola, M., 8 Kajimoto, 0.. 153 Kajitani, M., 203, 360 Kakitani, T., 39 Kalal, J., 519 Kalashnikov, V. G., 547 Kaldor, A., 148 Kalechits, I. I., 529 Kalnavais, A., 539 Kalyanasundaram, K., 420, 515, 582, 585 Kam, K., 591, 593 Kamagai, T., 385

A u t hor index Kamat, P. V., 31, 101 Kambe, N., 218, 395 Kamei, K., 235 Kametani, T., 428 Kamigauchi, T., 227 Kamiya, I . , 115 Kamiya, Y., 326, 346, 448 Kamiyama, Y., 237 Kamogawa, H., 522 Kampa, K. L., 10 Kampas, F. J., 599 Kam'yanov, V. F., 371 Kanaoka, Y.,251, 272, 273, 287, 288, 289, 377, 428, 441, 443, 498 Kanda, Y ., 47, 94 Kaneda, N., 92 Kaneda, T., 15, 389 Kanehira, K., 326, 449 Kanehiro, H., 518 Kaneko, C., 251, 335,425, 435, 447,448 Kaneko, M . , 183, 191, 397, 529 Kane-Maguire, N. A. P., 172, 175 Kanematsu, K.. 349 Kaneoka, C., 242, 252 Kanfer, S., 279 Kang, K.-T., 240,466 Kanne, D., 447 Kanno, A,, 409 Kanno, H., 406 Kanno, S., 368 Kano, K., 27, 84, 92, 182, 424 Kanstad, S. O., 17 Kao, H . L., 478 Kaplan, L., 157 Kaplan, M., 118, 496 Kaplanova, N., 92 Kapoor, R. N., 201 Kapralova, G . A,, 148 Kar, A., 5 Karachunskaya, L. M., 176 Karaki, I., 399 Karas, B. R., 598 Karasawa, Y., 435 Karasev, V. E., 193 Karayakin, N. V., 518 Karlivans, V. P., 518 Karnaukh, A. P., 508 Karp, A. W., 162 Karp, P. B., 394 Karpitskaya, V. E., 417 Karpov, V. L., 536 Karpukhin, 0. N., 530 Karrer, F. E., 547 Karstens, T., 26, 73 Karu, T . 1.. 36 Karvaly, B., 91 Karve, R. S., 37, 146, I95 Karwai, W., 509 Karyakina, M . V., 539 Kasahara, I., 303 Kasatani, K., 23, 29, 84, 126, 127, 146

615 Kasha, M., 39, 70 Kashan, V. F., 518 Kashiwabara, H., 435 Kaska, W. C . , 116 Kasper, J. V. V., 19, 157 Kasuya, T., 8 Katagiri, N., 336, 457, 479 Katahira, K., 269, 425, 426 Katayama, D. H.,159 Katayama, M., 145 Kato, H . , 8, 163, 338, 367, 419 Kato, K., 1 1 KdtO, M., 306, 319, 328, 516 Kato, S., 121 Kato, T., 268, 282, 336, 350, 450, 457, 479 Kato, Y., 6, 173, 332, 468 Katoh, T., 571 Katori, T., 382, 475 Katritzky, A. R.,373, 427 Katsube, Y., 270 Katsumura, Y., 108 Kaufer, S., I 1 1 Kauffman, J. M., 9 Kauffman, J. W., 21 1 Kaufman, F., 157, 159, 161 Kaufmann, G., 86 Kaupp, G., 272, 302, 348, 350, 446 Kauppinen, J., 20 Kautek, W., 590, 593, 594 Kawabata, J., 529 Kawada, K., 475 Kawai, S., 435 Kawai, T., 468 Kawai, W., 529 Kawada. K., 331, 432 Kawada, Y., 384 Kawaguchi, K., 19 Kawai, T., 80, 82, 229 Kawajira, T., 153 Kawamura, Y.,352 Kawasaki, B. S., 1 I Kawasaki, M., 23, 29, 84, 126, 127, 131, 364 Kawasaki, Y., 420 Kawata, H., 343, 435 Kawazumi, H., 84 Kawenoki, I . , 226 Kaya, K., 28 Kazakov, V. P., 513 Kazanskii. V. B., 176 Kazaryan, S. A., 551 Kazitsyna, L. A., 178 Kazmierczak, F., 418 Kearns, D. R., 400 Kearsey, S. V., 130 Keating, E. J., 514 Keehn, P. M., 41 1 Kees, F., 494 Keil, D. G., 161 Keillor, P., 585 Keitners, E., 518 Kelen. T., 547, 549 Kellcher, P. G.. 536

Keller, P., 181, 575 Kellogg, M. S., 316, 483 Kellogg, R. M., 482 Kelly, C. K., 79 Kelly, D. R., 226 Kelly, J. M., 180 Kelly, R. B., 249 Kemp, G., 365 Kemp, T. J., 171, 173, 189, 193, 195, 209, 508 Kempka, U., 47, 65 Kemple, M. D., 104 Kendall, D. R., 165 Kendall, D. J. W., 150 Kenley, R. A., 546 Kenkre, V. M., 80 Kennard, O., 373 Kennedy, J. P., 159 Kennedy, J. H., 595 Kennedy, J . P., 511 Kennedy, P. M., 23, 133 Kenner, R. D., 157 Kenney-Wallace, G . A., 13, 210 Kenny, J. E., 134 Kent, J. E., 28 Kerkhoff, H., 135 Kerr, C. M. L., 126 Kerr, R. C., 172 Kertesz, P., 294 Kessar, S. V., 380, 496 Ketkar, S. N., 13 Ketley, A. D., 508 Ketley, G . W., 119, 132 Keto, J. W., 13 Ketseridis, G., 150 Kettle, G. J., 527 Ketty, A. D., 502 Keular, J., 449 Key, P. J., 4 Keyanpour-Rad, M., 523 Keyser, H . , 572 Keyser, L. F., 157 Khadzhidocheva, S., 531 Khalil, M. A. K., 149 Khan, A. U., 1 1 1 Khan, K. A., 454 Khan, N. A,, 405 Khangazheev, S. Kh., 216 Khannanov. N . K., 181 Khare. V., 154 Kharlamov, B. M., 19 Kharlamov, I . P., 176 Khorana, H. G . , 470 Khudyakov, I. V., 31, 457 Kibkalo, A . A,, 217 Kice, J. L., 467 Kido, N., 92 Kieffer, B. L., 490 Kielkiewiez, J . , 513 Kiguchi, T., 437 Kihara, M., 380, 497 Kijima, I.. 171 Kikuchi, K., 101, 102 Kikuchi. O., 425

Author Index

616 Kildal, H., 22 Kilger, D. S., 187 Killeen, T. J., 27 Killinger, D. K., 21 Kim, J. H., 184 Kim, J . S.. 514 Kim, K. C., 19, 133 Kim, N.. 524 Kim, W.-T., 584 Kim-Thuan, N.. 574, 575 Kimata, T., 435 Kimoto. H., 326 Kimura. A,, 327 Kimura, K.. 334 Kimura, M., 404 Kimura, T., 177, 361 Kineshita, A,, 543 King, B. R., 171 King, D. S., 145, 147 King, K. D., 147 Kingina, S. I., 534 Kingo, I., 587 Kinoshita, A,, 504, 543 Kinoshita, M., 105 Kinoshita, S., 33 Kinoshita, T.. 291 Kinsey, J. L., 154 Kinsinger, J. B., 526 Kira, M., 215, 392 Kirchmayr, R.,502, 505 Kirk, A. D.. 172, 173, 174, 179 Kirkbright, G. F., 21, 22, 40 Kirkovskii, L. I., 186 Kirksey, S. T., 191 Kinnse, W.. 490 Kirsch-Dc Mesmaeker, A,, 580 Kirshen. N. A., 546 Kiryukhin. Y. I.. 31 Kisch, H., 189, 204 Kiselev. M . R.. 518 Kiseleva, 0. B., 190 Kishimoto, T., 257 Kiss. Z., 599 Kita, T.. 14 Kita, Y., 513, 544 Kitagawa, I., 227 Kitahara, Y., 407 Kitamura, A,, 110, 367, 492 Kitamura, K., 290 Kitamura, N., 420, 507 Kitamura, T., 300, 325 Kitao, T., 400, 418, 551, 553 Kite, M. S., 193 Kivillova, E. I . , 557, 559 Kiwi, J., 84, 181, 573, 575, 585 Kizuka, K., 456 Klaere, A . , 551, 552 Klafter, J., 80 Klahne, E., 210 Klais, O., 151, 156 Klasinc. L., 334 Klein, U. K. A,, 83, 436 Klein, R., 31, 87 Kleindienst, T. E.. 154 Kleinermanns, C . , I45

Kleinman, S. Ya., 531 Kleinschmiett, J., 66 Kliger. D., 86, 208, 528 Klimakova, A,, 437 Klimcak, C. M., 24 Klimiczak, M., 274. 457 Kline, G., 591, 593 Klinshpont, E. R., 530 Klopffer, W., 86, 144 Klose, E., 10 Klug. J. T., 405 Knight, A. E. W., 119, 147 Knight, A. R . , 493 Knight, R . C . . 7 Knopfel, N., 490 Knorr, F. J., 40 Knox, W.. 34 Knyazev, 1. N., 142 KO, M. K. W., 152 Kobayashi, H., 319, 396 Kobayashi, K., 355, 390, 441 Kobayashi, M., 342, 398 Kobayashi, S., 300, 380, 497 Kobayashi, T., 32, 43, 509, 584 Kobayashi, T., 21 Kobayashi, Y., 320, 333, 335, 337, 432. 434, 475 Kober. E. M., 184 Kobovitch, J.. 139, 205 Kobs, K.. 26, 73, 113 Kobu, Y . , 441 10 Koch, H.., Koch, K. P., 5 Koch, T. H., 259, 441, 498 Kochi, J. K., 188 Kochkin. D. A., 518 Koda, S.. 142 Kodanashvili, M. V., 314 Kohler, G., 59. 79 Kolle, U . . 424 Koeneke. A , , 7 Koppel. B., 423 Koffend, J. B., 133 Koga, K., 504, 543 Kogan, G., 59 Koganty, R. R.,339, 435 Kogoma, M., 165 Kogyo. K. K., 501 Kohda. A., 194, 410 Kohnlein. W., 367 Kohler, B. E., 25 Kohler. S., 15 Kohmoto, S., 419 Kohn, D. H., 200 Kohne, B., 391, 493 Koike, Y., 508 Kojima, H., 148, 320 Kojima, K . , 86, 523, 528, 544 Kokel. B., 273, 452 Kokubo, T., 92, 573 Kokubun, H., 101, 102, 435 Kolb, C. E., 136, 157 Kolek, R. L., 509, 519 Kolesniknva, V. V., 544 Kollman, T. M., 530

Kolninov, 0. V., 544 Kolobova, N. E., 385 Kolontarov, I . Ya., 550 Koloshinikov, V. G., 19 Kolshorn, H., 328 Kolts, J. H., 139 Kom, G., 8 Komagorov, A. M . , 484 Komatsu, M., 427 Komatsu. Y., 507 Komiya, Z . , 283 Kommandeur, J., 128 Komotskii, V. A,, 16 Kompa, K. L., 165, 205 Konarski, M . M., 206 Kondo, H., 92, 349 Kondo, K., 218, 395 Kondo, S., 477, 481, 482 Kondo, T., 495 Kondo, Y., 418 Kondow, T., 16, 138 Kondratenko, P. A,, 504, 529 Kondratyev, A. I . , 15 Konefal, Z., 7 Konenko, L. I., 193 Koning, H. N., 325 Konings, C . A. G., 368, 400 Koningstein, J. A,, 24, 35. 175 Konishi, N., 8 Kononenko, L. I., 192 Konowalow, D. D., 163 Koolstra, R. B., 316, 406 Kooter, J. A., 93 Kopelman, R., 80 Kopownski, B., 9 Koprinkov, I . G., 8 Kops, J., 535 Koput, J.. 58 Korenowski, G. M., 35, 478 Korngor, M., 25 Korobeinicheva, I. K., 377 Korodenko, G. D., 552 Korolev, V. V., 192 Korshov, Yu. S.. 551 Korswagen, R., 201 Korte, F., 299, 331, 339, 365 Koryakin, B. V., 171 Korzhak, A. V., 172 Kosanetzky, J . , 21 Kosanic, M. M., 74 Koshiba, M., 518 Koshitani, J., 450, 462, 553 Kosinov, V. N., 141 Koskelo, A. C.. 9, 23 Kosloff, R., 80 Koso, Y., 365 Kosobutskii, V. A., 539 Kossanyi, J., 75, 226, 230, 236 Kostenko, M. I . , 15 Koster, D. F., 146 Kostuk, R. K., 4 Kottyar, G. I., 541 Kouno, I., 250, 278 Kouri, D. J., 154 Kourouklis, G., 64

617

Author Index Koussini, R., 373 Kouwenhoven, A. P., 312 Kovacheva, K., 550 Kovalenko, N. P., 56 Kovalevskii, V. A,, 141 Kovar, D., 214, 465 Kowal, J.. 256. 409, 534 Kowalski, A., 137 Kowalski, J. M., 583, 584, 598 Koya, S., 366 Koyama, K., 485 Koyava, V. T., 33 Kozak, J. J., 580 Kozliner, M. Z., 30 Kozlov, A. S., 132 Kozlowska-Gramsz, E., 489 Kozma, L., 73, 553 Koz’menko, M. V., 437 Kozuka, S., 291,419 Kozuka, T., 290 Kraeutler, B., 1 1 1, 224 Krakovyak, M. G., 527 Kramer, G. M., 148 Kramer, H. E. A., 553 Kramer, S. D., 160 Kranitzky, W., 9 Krantz, A., 273, 339, 452, 457 Krasinski, J., 10, 165, 205 Krasna, A. I., 574 Krdsnova, v. A,, 173 Krasnovskii, A. A., 401 Kratochvil, B., 177 Krats, E. O., 534 Kraus, W., 416 Krause, L., 137 Krause, U., 163 Krausz, P., 199 Kravchenko, T. B., 192, 193 Kray, H. J., 94 Krech, R. H., 28, 131, 217 Krenos, J., 139, 205 Krenske, D., 27 Krestonosich, S,, 340, 354, 452 Kreutter, N. M., 151 Kreysig, D., 26, 320, 387, 450 Kriens, M., 180 Krings, A. M., 207 Krishevskii, G. E., 552 Kristjansson, K. S., 135 Krogh-Jesperson, K., 46 Krol, D. M., 195 Krompa, J., 566 Kropp, P. J., 325, 347 Krot, N. N., 195 Krueger, C., 197, 198 Krusic, P. J., 205 Krysanov, S. A., 32, 113 Kryszenski, M., 534, 535 Kryukov, A. I., 172, 173, 176 Kryukov, P. G., 36 Kuan, C. N., 505 Kubiak, C. P., 593 Kubo, Y.. 287, 289, 593 Kuboyama, A,, 59, 66, 409 Kubota, T., 235

Kuchitsu. K., 16, 138 Kuchmii, S. Ya., 172, 176 Kudo, K.. 599 Kudoh, S., 381 Kudoyavtseva. T. V., 518 Kudriavtsev. E. M., 4 Kudriavtsev, Y. A,, 31, 141 Kuebler, N. A,, 21 Kueh, J. S. H., 241 Kuehn, K., 173 Kiihnle, W., 53 Kuhl, J., 19 Kuhlke, D., 10 Kuhn, H., 82 Kuhn, W. R.,152 Kuizenga, D. J., 7 Kulander, K. C., 162 Kuiickova, M., 544 Kull, S., 534, 550 Kulomzina, S. D., 247 Kumada, M., 79, 213, 214, 215, 463, 465 Kumadaki. I., 320, 333, 335, 337, 432. 434. 475 Kumafugi, H., 172 Kumagai, T., 352 Kumagai, Y., 361 Kumamoto, M., 278 Kumar, C. V., 281, 385 Kumar, K. A., 374 Kumar, R., 417 Kumar, V., 531 Kumar, Y., 399 Kunert, D. M., 484 Kung, A. H., 141 Kung, H. H., 584 Kung, W.-J. H., 262 Kunimoto, J . , 583 Kunitake, M., 27 Kunitake, T., 424 Kunitomi, Y., 302 Kunkely, H., I89 Kuntz, R. R., 493 Kupka, H., 173 Kupletskaya, N. B., 178 Kuprashvih, B. G . , 401 Kuramoto, N., 418, 553 Kurganera, M. N., 539 Kurihara, O., 37, 148, 21 I Kurik, M. V., 529 Kurimura, K., 182 Kurimura, Y., 181, 183, 529 Kurita, J., 320, 437, 438 Kuritsyn, Y.A,, 19 Kuroda, J . , 6 Kuroki, T., 234 Kurtz, J. L., 191 Kurumisawa, H., 419 Kurylo, M. J., 151, 156 Kurzhenkova, M. S., 546 Kusabayashi, S., 86, 525, 528 Kusakawa, K., 370 KUSdnO, T., 375, 428 Kushawaha, V. S., 136 Kushida, T., 33

Kusumato, Y., 82, 84 Kutal, C., 171, 174 Kutimova, G. V., 550, 557 Kutschabsky, L., 253 Kutzer, J. C., 498 Kuvshinskii, N. G . , 41 I Kuwabara, K., 410 Kuwabara, M., 541 Kuwane, Y., 199, 506 Kuwata, K., 146 Kuzmin, M. G., 437, 529 Kuzmin, M. V., 147 Kuz’min, V. A., 457 Kuz’min, V. E., 193 Kuzmina, N. P., 142 Kuznetsova, R. T., 553 Kuznetsova, V. S., 557 Kuzuya, M., 303,434 Kyogoku, T., 138 Kyono. K., 115 Kwei. G. H., 153 Kwei, T. W., 521 Laachach, A., 226 Laarhoven, W., 375 Labereau, A., 6 Labinger. J . A,, 203 Lablache-Combier, A., 370, 458 Labsky, J . , 519 Lacabanne, G . , 521 Lachish, U., 79, 526 Lacky, D. E., 184 Ladvishchenko, Y. M., 146 Lagua, D., 492 Lahav, M., 509 Lahiri, S., 40, 281, 385 Lahmani, F., 33, 36, 130 Lahmann, W., 15 Laiber, M., 547 Lakowicz, J . R., 89 Lala, D., 540, 550 Lam, C. W., 505 Lam, H. M. H., 101, 223 Lam, J. W. H., 511, 518 Lam, K. S., 167 Lam, L., 29, 151 Lamaire, J., 37 Lambert, J. B., 478 Lambert, W. R., 17 Lambropoulos, P., 23 Lamola, A. A., 91 Lamotte, M., 41, 342 Lamparski, L. L., 541 Lampe, F. W., 36, 164, 212, 463 Landais, J., 138 Landers, A. E., 323 Lando, J . B., 509 Lane, J. C., 343 Langan, J. R., 114, 374 Langbein, H., 106, 424 Langelaar, J., 122 Langer, P., 213, 465 Langford. C. H., 175, 599

Author Index

618 Langhoff, C. A., 77 Langridge, J. R., 344, 354,453 Langsam, Y., 165, 198 Laniepce, B., 138 Lankard, J . R., 30, 146 Lantratova, 0. B., 396 Lapcik, L., 412, 516, 534 Laporte. P., 16, 36, 68 Laporterie, A,, 215 Lapouyade, R., 342, 373, 387 Lapova, Z. G., 557 Lardeux, C., 33, 36, 130 Larrauri, J . M . , 352, 449 Larson, K. M.. 41 Larson, M. T., 187 Larsson, M., 158 Larvor. M . , 14 Laskowski, B. C. F. M., 165 Lasser, T., 7 Latowska, E., 361 Latowski, T., 361 Lattes, A., 329, 422, 434. 551 Laube, B. L.. 25 Laude. J . P., 14 Laudenslager, J. B.. 1 1 Laufer, A. H., 29, 151 Laufer, G . . 23 Launikonis, A., 181 Laureni, J . , 339 Lavalette, D., 94 Lavergne. J.-P., 496 Lavollee, M., 36, 130, 165 Lavrik, N. L., 121 Lavrushin, V. F., 256 Law, K . Y., 64 Lawrance, W . D., 147 Lawrence, F. T., 463 Lazare, S., 61, 125, ?48 Lazarev, G. G., 396 Lazaro, R., 355, 455 Leamy, H. J., 589, 590 Leaver, I., 551 Lebedera, H., 573 Lebedev, V. P., 534 Lebedev. Ya. S., 508 Le Bras, G., 152, 153 Le Calve, J., 165 Lechtken, P., 106 Leek, T. J . , 152 Leclaux, R., 86 Leclerq, F., 575 Le Doucen, R., 14 Ledwith, A . , 51 I , 519, 523 Lee. C., 314, 489 Lee. C. H., 6 Lee. E. K . C., 17, 121, 162, 218 Lee, H . U., 139 Lee. H . W. H., 32, 51 Lee. I. W., 4 Lee. J. G., 307 Lee, J. H., 153, 155 Lee. J. K., 514 Lee, J.-S., 229 Lee. K . , 64, 85

Lee. L. A., 10 Lee, L. C., 36, 130, 150 Lee. M . L.. 372 Lee, N. B., 147 Lee, P. C. C., 83 Lee, P. H. P., 191 Lee, S., 262 Lee, S. K . , 327 Lee, S. S., 4 Lee. Y. T., 28, 29, 156, 218 Lees, A. J . , 199 Leeuwen. P. W. N. M., 196 Lefebvre, R., 158 Lefort, D , 492 Leheny, R. F., 13 Lehnig, M., 216 Lehninger, A., 571 Leicht, R., 527 Lemaire,, J., 19, 282, 409, 415, 417, 445, 548. 549, 551 Lemal, D. M., 321 Lemasson, P., 584 Lemire, A,, 63 Letnmer, D., 304 Lempert, K . , 462 Lempert-Sreter, M . , 462 Lempicki, A,, 172 Lenina, E. S., 557 Lenzi. M . , 219 Leonard, D. A,, 21 Leone, A., 297, 450 Leone, S. R., 131, 135, 137 Leone-Bay. A,, 298, 352, 449 Leong. T. S., 251, 458 Leoni, M . A., 355 Leopold, D. G., 28 Le Pecq, J . B., 427 Lepere, D., 14 Lepoutre, G., 575 Lerchner. J . , 185 Lerkureva, E. N., 557 Lerner, D A., 85, 208 Le Saint, J., 280, 423 Lesclaux, R:, 388 Leshchenko, S. S., 536 Leshina. T. V., 301 Leslie, T. M., 483, 495 Lessard, J . , 453 Letokhov, V. S., 24, 31, 36. 141, 142, 167 Leuenberger, C., 437 Leutwyler, S., 165 Levanon, H., 104, 105, 582 Levdanskii, V. A , , 383 Levendis, D., 45 Levental, Y u . K., 363 Leventhal, J . J . , 136 Lever, A. B. P., 182 Levin, G . , 399 Levin, P. P., 457 Levin, V. M . , 557 Levin, Y . A,, 218 Levine, B. F., 25 Levine, J . S., 152 Levine, R. D.. 147, 167

Levot, R., 514 Levy, D. H . , 28, 131, 134 Levy, H . , 152 Levy. M . R.. 145 Levy, R. L., 522 Lew. H., 155 Lewerenz, H. J., 588, 589, 590, 593, 594 Lewis, F. D., 64, 65, 145, 210. 345, 416, 445, 451 Lewis, L. N., 197 Lewis, N . S., 589, 594 Lewis, R. S., 155 Leyland, R. B., 235 Lhomme, M . F., 456 Lhoste, J.-M., 382, 475 Li, F. Y . , 8 Li, H. S., 508 Li, R., 277 Li, S. K . L., 544 Liang, R., 86, 528, 536 Lianos, P., 51, 83 Liao, T. P., 523 Libuijs, H . , 150 Lichtin, D. A., 24, 127 Lichtin, N. N . , 31, 79, 98, 101. 177, 581 Liddy, J. P., 135 Lien, S., 571 Light, G. C., 155 Light, J . C., 162 Lignou, F., 177 Lilie, J., 173 Lim, B. T., 79, 96 Lim, E. C., 28, 33, 79, 96, 124, 125, 126, 128 Lin, C. C., 165 Lin. C.-T., 478 Lin, M. C., 118, 136, 155, 156, 161 Lin, S. H., 28, 122 Linck, R. G., 173, 174 Lindau, I., 589 Lindblom, G., 41 Lindemann, M., 198 Linden, K. J., 18 Lindgren, K., 372, 427 Lindig, B. A., 31, 82, 108, 11 1 Lindley, J. M., 383, 487 Lindqvist, L., 89 Lineburger, W. C., 119 Linn, S. H., 126 Linschitz, H., 31, 63, 394 Linton, M., 386 Lion, F. Y., 541 Lioniskii, P. Ts., 547 Lipina, E. S., 444 Lippert, E., 72 Lippold, K. A., 522 Lipskerova, E. M.,539, 545 Lipsky, S., 64 Lischewski, M., 230 Liska, F., 297 Liska, M., 412 Lissi, E. A., 58, 230, 394, 524

Author Index List, U., 21 Litfin, G., 19 Little, D. D., 150 Liu, C.-H., 587 Liu, H., 292 Liu. M. T. H., 478 Liutkus, J., 533 Liverman, M. G., 119 Lloyd, J. B. F., 40 Lloyd, L. B., 23 Lo, v . w. s.,J53 Lobko, V. V., 142 Lobo, A. M., 444 Lochmuller, C. H., 22 Lock, C. J. L., 345 Loef, R., 177 Loeffler, R. S. T., 492 Loeh, H., 16 Logan, L. M., 119 Loge, G. W., 121, 122, 134 Lohr, R., 155 Lohse, C., 365, 457 Lombardi, J. R., 132 Lomonosova, E. G., 544 Long, A. M., 514 Longeway, P. A., 36, 212 Longnot, D. J., 110, 502 Longoni, A., 13 Look, D. C., 14 Loosen, K., 490 Loper, G. L., 22 Lopez, D., 417 Lopez-Delgado, R., 33, 61, 87, I25 Loucheux, C., 501, 516 Loutfy, R. O., 76, 80, 226, 249, 599 Lovas, F. J., 19 Lovelette, D., 89 Lovell, M. W., 40 Low, H. C., 2 13,465 Low, M. J. D., 21, 22 Lowe, R. M., 139 Lowe, R. S., 165 Lown, E. M., 96, 125,462 Loy, M. M. T., 5 Loza, R., 308, 309, 392 Lubin, G., 543 Luca, C., 507 Lucas, G. M., 518 Lucatoro, T. B., 7 Luc-Gardette, J., 548, 549 Lucki, J., 534, 540 Ludlow, D. M., 154 Ludmer, Z., 34 Lue, J. T., 16 Lubbe, F., 469 Luedersdorf, R., 491 Luthy, W., 133 Luhmann, N. C., 5 Lui, J.-M., 84 Lui, M., 53 Lukac, I., 544, 555 Luk'yanov, V. I., 371 Luk'yanova, V. V., 539

619 Luniry, R., 89 Lundstrom, I.. 22, 587 Luneva, N. A., 508 Lunt, E., 373, 427 Luntz, A. C., 155, 156 Luong, J. C., 202 Lurie. J. B.. I19 Lushchik, V. B., 527 Lusztyk, J., 332 Luther, K., 117, 219 Luthgens, L. H., 75 Luthy, W.. I 1 Luty, F., 5 Lutz, W., 408 Lux, B., 51 Luypaert, R., 135 Lyashenko, L. V., 410 Lyke, R. L., 402 Lynch, D. C., 243 Lynch, M. W., 201 Lypka, G. N., 319, 330, 385, 495, 498 Lyszyk, M., 19 Lytle, F. E., 13 Lyutskanov, V. L., 12 Maas, E. T., jun., 148 Maas, G., 479 McAleer, J. F., 584 McAlpine, R. D., 140, 145 Macanita, A. L., 77 McAuliffe,, M. J., 35, 478 McCabe, R. W., 457 McCaffery, A. J., 163 MacCallum, J. R., 525, 528, 534 McClain, W. M., 28, 126 McCleland, C. W., 384 McClenny, W. A,, 22 McClory, M. R., 307, 393 McClure, D. S., 66 McClusky, F. K., 140 McCollum, B. C., 172 McCorkey, R. C., 508 McCormack, J., 163 McCreary, T. W., 21 McCrumb, J. L., 151 McCue, M., 20 McCullough, J. J., 307, 345, 393 McDade, I. C., 150 MacDiarmid, A. G . , 520, 599 McDonald, D. B., 9, 28, 32, 73, 76, 128 McDonald, J. D., 15, 37, 122, 145 MacDonald, J. G., 432 McDonald, J. R., 126, 130, 149, 156, 162 McDowell, J. R., 519 Mace, P. N., 10 McFadden, D. L., 159 Macfarlane, R. D., 325 McGarvey, J. A., jun., 133 McGee, T. J., 27, 160

McGeoch, M. W., 165 McGill, W. J., 541 McGrath, W. D., 150 Machen, R. C., 153 Machida, H., 492 Machida, M., 287, 288, 441. 443 Machiya, K., 494 McHugh, T. M., 202 Maciejewski, A., 301 Mcllrath, T. J., 7, 21, 27, 160 Mclnnes, E. L., 318 MacInnis, W. F., 345 Mclntosh, B. C., 19 McIntosh, D . F., 210 McIntosh, S., 164 Mack, A. G., 366,432 McKay, J. A., 10 McKeever, M. R., 133 McKellar, J. F., 529, 547, 549, 551, 552 McKelvey, R. D., 330 McKenna, J. M., 496 Mackie, I., 147 MacKnight, W. J., 521 McLaren, I. A., 15 McLauchlan, K. A., 279 MacLean, L., 146, 21 1 McLean, S., 422 McLellan, E. J., 12, 13 McLendon, G., 399, 574 McMahon, B. B., 150 McMikan, D. R., 190 McMurry, J. E., 323 McMurry, T. B. H., 242 McNesby, J. R., 37, 146 Macovei, V., 46 McQueen, D., 22 McRobbie, I. M., 383, 487 McVie, J., 108 Madan, S. K., 174 Madvaliev, U., 22 Miicke, H., 172, 185 Maeda, M., 21, 372 Maeda, N., 440 Maeda, Y., 598 Maeno, K., 82 Maeshima, T., 507 Maestri, M., 98, 178 Magamedova, T. V., 530 Magde, D., 32, 74 Mager, H. 1. X., 362 Magnotta, F., 162 Magnuson, A. W., 154 Magoini, K., 525 Mah, S. I., 189 Maharaj, U., 63 Mahieu, R., 247 Mahlman, J. D., 152 Mahmood, A. J., 178 Mahr, H., 9, 35 Mai, J., 491 Mai, Y. W., 538 Maier, G., 333, 427, 484 Maier, H., 339

Author Index

620 Maier, J . P., 35, 118, 126 Maier. M., 111 Mairova, N. V., 539 Majer, J., 538 Majima, T., 325, 412 Majoral, J.-P., 489 Majori, L., 338, 431 Makarov, A. A., 145 Makarov, G. N., 23, 140, 145 Makarov, V. I . , 121 Maker, P. D., 20, 158 Makharinskii, L. E., 148 Makhkamov, K. M., 550 Makhluf, J., 368 Maki, A. G., 19 Maki, A. H., 210 Makino, D., 584 Maksimova, N. E.. 550 Malacria, M., 407 Malatesta, V., 145 Malin, J. M., 179, 550 Malinovski, A., 175, 176 Malinowski, E . R., 20 Malins, R. J., 137, 153, 154 Mallard, J. R., 116 Malmin, 0. K . , 137 Malpas, R. E., 587 Mamantov, G., 20, 41 Mamedova, S. G., 518 Manabe, O., 424, 425. 528 Manasek, Z., 555 Manassen, J., 112, 586, 587, 594, 598 Mandal, K., 26, 73. 179 Mandl, A.. 127 Manenkov, A. A,, 536 Manfrin, M. F., 174 Mangir, M., 145, 149 Mann, G . , 529 Mann, K. R., 187, 201, 203, 208, 576 Mannero, E. E., 8 Manning, C., 307, 393 Mano, E., 303, 434 Manring, L. E., 413 Mansour. M., 365 Mantsch, H. H., 20 Manuccia, T. J., 37, 148 Manz, J., 80 Maple, J . R., 41 Mar, A,, 63, 102 Marason, E. G., 9 Maravigna, P., 537 Marazano. C., 460 Marbeuf, A., 588 Marcandalli, B., 257 Marcantonatos, M. D., 193 Marchal, E., SO1 Marche, P., 150 Marchesini. A.. 262, 338, 431 Marchetti, S., 19 Marciniak, B., 58 Marconi, G., 65 Marconi, M. C . , 6 Marcus, R. A.. 147

Marek, J., 137 Margani, A., 219 Margaryan, A. K., 247 Margerum, D. W., 191 Margolin, A. L., 538 Margrave, J . L., 206, 21 1 Margulies, L., 45 Margulis, W., 8 Mariano, P. S., 236, 297, 298, 352, 41 I , 449, 450 Marinelli, W. J., 157 Marinero, E. E., 43, 135 Mark, F., 92 Markova, E. I . , 531 Marks, T. J., 210 Marling, J. B., 148 Marowsky, G . , 1 I , 31, 68, 134 Marquet-Ellis, H., 210 Marsden, B., 18 Marsh, K . L., 112, 401 Marshall, 11. B., 22 Marshall, J. A,, 301 Marshall, R. M., 153, 469 Martens, J , 391, 467 Martin, E., 75 Martin, J . P., 212 Martin, M., 448 Martin, N. H., 418 Martin, S. A,, 581 Martinez, E., 135 Martinez, 0.E., 6 Martinez, P. R., 28, 29 Martinez. R. I., 149 Martinez-Utrilla, R., 225, 229, 417 Marucco, J. F., 584 Maruhashi, K., 485 Marupov, M. R., 550 Maruyama. H.. 544 Maruyama. I., 86 Maruyama. K., 280, 283, 285, 286, 289, 290, 292, 293, 323, 376, 396. 400, 415. 441, 448, 449,498 Maruyama. Y., 51 Marx, J., 490 Mar'yasova, V. I., 301 Masanori, M., 336 Masda, Y ., 79 Masetti, F , 65. 98 Maslennikov, S. I . , 402 Maslov, V. V., 10 Masnovi, J., 349 Masson, M., 419 Mastrangelo, C. J., 74 Mastropasqua. P., 204 Masuda, M., 529 Masuda, T., 199, 506 Masuhara, H., 79, 86, 525, 528 Masui, T., 522 Masumura, M., 243. 437 Mataga, N., 32, 65, 76, 79, 85, 86, 399, 525, 528 Matano, S., 358 Mathey, F., 198

Mathiasch, B., 216 Mathieu, P., 5 Mathin, A. R., 263 Mathur, A. B., 531 Mathur, G. N., 531 Matise, B. K., 82 Matreeva, E. N., 559 Matsamura, K., 599 Matsamura, M., 595 Matsubara, T., 182 Matsubara, Y., 507 Matsubura, A,, 526 Matsuda, H . , 382, 475, 537, 56 1 Matsuda, M., 85, 110, 180, 507 Matsuda, T., 343, 398. 452, 494 Matsugo, S., 417 Matsui, K., 105, 487 Matsui, M., 203, 360 Matsukiyo, S., 292. 396 Matsumi, Y . , 127 Matsumoto, A,, 172 Matsumoto, J . H., 155 Matsumoto, K., 293, 498 Matsumoto, M., 92, 573 Matsumoto, Y., 495, 583 Matsumura, M., 74 Matsunago, S., 523 Matsuo, K., 424 Matsuo, T., 182, 183, 398, 522, 528, 574, 576, 579 Matsuchima, R., 256, 257, 410 Matsushita, T., 337, 431 Matsuura, T., 115, 232, 270, 271, 326, 366, 367,412, 417, 421, 446, 449, 451 498 Matray, J . , 224, 266 Mattes, S. L., 408 Matveetz, Y. A,, 36 Matyushova, V. ti., 508, 519 Mau, A. W. H., 181 Maumy, M., 403 Maurette, M. T., 422 Maverick, A. W., 176, 187, 576 Mavroides, J . G., 597 Mayer, L. M., 29 Mayer. W., 282 Mayne, H. R.. 154 Mayo, F. R., 546 Mayo. S., 7 Mayster, D., 14 Mazenod, F. P., 473, 474 Mazerolles, P.. 2 15, 489 Mazur, L. E., 176 Mazur, M. R.. 473 Mazur, Y., 45 Mazrocchi, P. H . , 422 Mazmcato, U., 65, 77, 537 Meallier, P., 444 Meanes, C. F., 81 Medina, F. D., 18 Medvedeva. A. M., 176 Meech, S. R., 34, 40 Meek, R. R., 552

62 1

Author Index Meenakumari, R., 380,496 Meeus, F., 76 Mehrotra, K. N., 239, 416, 452, 481 Meier, H., 328, 476, 477 Meier, K., 161 Meijer, E. W., 407 Meijere, A. De., 403 Meinwaid, J., 454 Meisel, G . , 139 Meisner, R., 76 Mela, E. C. C., 77 Mellor, M., 241 Mel'nikov, M. Ya., 539, 545 Meltzer, R. S., 8 Melzig, M., 59 Memming, R., 113, 595 Mendelsohn, A. J., 1 1 Menezes, S., 589, 593 Menju, A., 527 Menoux, V., 14 Menyuk, N., 21 Menzel, E. R., 79, 599 Menzinger, M., 137 Mercer, F., 484 Mercer-Smith, J. A., 171 Merer, A. J., 164 Merienne, E., 5 Merkel, P. B., 400 Merkle, V., 339, 476 Merkur'eva, E. V., 550 Merkushev, E. B., 371 Merle, Y., 523 Merlin, A., 63, 110, 502, 546 Merritt, C. D., 74, 528 Merrow, C. N., 145 Mertes, K. B., 180 Merz, A., 302, 369 Mesamune, T., 456 Messing, I., 118 Meth-Cohn, 0.. 383, 487 Metras, F., 238 Meunier, H., 132 Mews, R., 453 Meyer, R., 7 Meyer, T. J., 180, 184, 204, 582 Meyer, V., 226 Meyer, Y. H., 8 Mezhivikina, E. P., 559 Mialocq, J. C., 59 Miano, J . D., 116 Miaohang, L., I 1 Michael, J. V., 157, 158 Michel, A., 532 Michel, C., 26, 122 Michels, H. H., 163 Michielsen, S., 164 Michl, J., 43, 213. 214, 463 Michno, D. M.. 318 Micic, 0. I., 74 Micko, M. M., 518 Middlemas, E. D., 370, 468 Mie, H., 216 Migita, J., 340

Migita, M., 65 Miguchi, K., 375 Migus, A., 43 Mihailovic, M. Lj., 217 Mihaleen, I.. 521 Mihashi, S., 495 Mihelich, E. D., 405 Mikarni, N., 23, 28 Mikami, O., 15 Mikawa, H., 86, 526 Mikawa, T., 15 Mikes, F., 519, 524 Mikhailov, A. I., 534 Mikhailov, M., 514 Milder, S. J., 187, 208, 576 Milewski, J., 4 Milinchuk, K . V., 544 Milinchuk, V. K., 530 Miljanic, S. S., 27 Milkie, T., 534, 536 Mill, T., 546 Miller, B.. 570, 588, 589, 593 Miller, C. M., 142, 150 Miller, D., 574 Miller, D. J., 83 Miller, D. S., 399 Miller, J. A,, 154 Miller, J. C., 127 Miller, J. H., 45 Miller, J . N., 63 Miller, T. A., 28, 59, 159, 165 Miller, W. H., 165, 167 Millet, P., 165 Miiligan, B., 541 Mills, A., 68 Milnikova, S. L., 519 Milovskaya, E. B., 527 Mil'shtein, S., 14 Minagawa, M., 553 Minami, F., 9 Minami, T., 291 Minard, R. D., 434 Minato, H., 277 Minemura, N., 541 Ming, N.-B., 1 I Minoli, G., 355, 398, 418, 435. 455, 486, 487 Minoura, H., 584 Minsker, K. S., 534 Mintas, M., 334 Miranda, M. A., 225, 229 Mirbach, M. F., 98, 207 Mirbach, M. J., 98, 207 Mirskov, R. G., 216 Misev, L., 118 Miskowski. V. M., 86, 187, 208, 576 Mislow, K., 200 Misumi, S., 65, 79, 386, 389, 399, 492 Mita, I., 505, 529 Mitchel, J. W., 17 Mitchell, A. D., 108 Mitchell, D. N., 162 Mitchell, S. A,, 210

Mitchener, J . C., 205 Mitewa, M., 175, 176 Mitina, V. G., 256 Mitschler, A., 198 Mitsuboshi, T., 544 Mitsuda, K., 74, 595 Mitsui, K., 293, 376, 498 Mittal, A., 390 Mittal, J. P., 37, 146, 195 Mittleman, J. P., 185 Mitra, A., 430, 456 Mitra, R. B., 247 Miura, M., 545 Miura, Y . , 336, 457 Miwa, T., 306, 319 Miyagi, Y.,94, 290 Miyahara, M., 194 Miyaishi, K., 27 Miyake, K., 358 Miyake, T., 110 Miyamoto, S., 214, 465 Miyanaga, A,, 178 Miyasaka, T., 599 Miyashita, T., 85, 180 Miyata, N., 440 Miyazaki, H., 419 Miyazaki, J., 92, 573 Miyazaki, T., 81 Miyoshi, F., 27 Miyoshi, N., 416 Miyrazaki, S., 270 Miziolek, A. W., 164 Mizoguchi, I., 124 Mizuno, H., 257 Mizutani, T., 522 Mleziva, J., 505, 518 Mo, Y.-A., 10 Moacanin, J., 86, 528, 544 Moayyedi, F., 533 Mobius, D., 82 Mochalov, A. A., 507 Mochizuki, Y., 28 Modou, M. J., 587, 594 Moellar, J., 462 Mogil'nyi, V. V., 527 Mohajerani, B., 552 Mohammad, T., 380, 496 Moiseev, V. V., 551 Mokrosz, J., 274, 457 Molin, Yu. N., 121, 301 Mollier, Y . , 457 Momatsu, M., 375 Momicchioli, F., 45 Momiyama, M ., 5 18 Momose. Y, 335, 425 Momzikoff, A ,, 73 Monakov. B. Yu., 513 Moncanin, J., 536 Mondon. M., 453 Monita, T., 77 Monk, P., 14 Monkhouse, P. B., 158 Monnerie, L., 523, 527 Monnier, A,, 583 Monserrat, K., 576

622 Montagne, J. P., 165 Montaudo, G., 537 Montelatici, V., 19 Monti, S., 31, 99, 102 Moore, C . B., 27, 37, 121, 141, 146 Moore, H. W., 484 Moore, R. H., 277 Moradpour, A,, 181, 575 Moragon, F. R., 75 Morales, M. F., 91 Morand, P., 239 Morano, D. J., 598 Morawetz, H., 518, 523, 524 Mordowicz, D., 14 Mordvintsev, P. I., 505 Moreels, G., 151 Morgan, C. R., 502, 508 Mori, C., 372, 413 Mori, M., 349 Mori, Y., 138, 159, 364 Moriarty, R. M., 314, 316 Moriizumi, T., 599 Morine, G. H., 493 Morioka, M., 257 Morishima, Y . , 519 Morita. H., 105 Morita, M., 173 Morita, S., 335 Morita, T., 396 Morita, Y., 268, 350, 450 Moriuchi, S., 406 Morizur, J. P., 226 Morland, R., 116 Morley, J. O., 296, 364 Moroi, Y . , 576 Morokuma. K., 113, 121 Morris, M. D.. 24 Morris, R. J., 89 Morrison, B. M., jun., 157 Morrison, H.. 299, 307 Morrison, S. R., 587, 594 Morrissey, D. J., 410 Morrocchi, S., 239, 342, 358, 449,453 Morrow, T.. I10 Morse, D. L., 199 Morse, M. D., 130 Morton, D. R., 226 Morton, J. B., 454 Mory. S., 8 Moseley, J. T., 157 Moshkovskii. Yu. Sh., 399 Moskovits. M., 25 Moss, M. G., 37 Moss, R. A,. 478 Mostovnikov. V. A., 421 Motevalli, M., 253 Motoyoshi. J., 397 Mount, G . H . . 14 Mouri, M., 362 Mourou, G . , 7 , 34 Mowatt. A . C., 364 Moxim, W. J., 152 Mraccc, M., 490

Author Index Mueller, D. M., 489 Mueller, U., 424 Munster, P., 137 Muetterties, E. L., 201 Muinov, T. M., 544 Mukai, C . , 482 Mukai, T., 328, 352, 385, 404, 416,496 Mukamel, S., 167 Mukherjee, A. K., 514 Mukherjee, K. K., 420 Mukherji, N.. 506 Mukhopadhyay, G., 46, 505 Mukhtar, R., 99, 283 Mulder, A. C . , 362 Muller, C . H., 111, 136 Muller, D. F., 31, 34, 157 Muller, L. L., 516 Munasinghe, V. R. N., 440 Munro, D. P., 430 Murad, E., 153 Murai, H., 94 Murai, S., 395 Murakami, Y., 209 Muraki, Y., 183 Muralidharan, S., 190, 210 Muramatsu, H., 326 Muraoka, M., 293 Murasawa, Y., 23. 127 Murata, I., 376 Murata, S., 77 Murato, K.. 257, 258, 319, 390 Murayama, E., 194, 410 Murayama, M., 538 Murphy, E. J.. 154 Murphy, J. P.. 508 Murray, D. G., 20 Murray, J. E., 7 Murray, R. K., jun., 227 Murrell, J. N., 154 Murtly, M. V. R. K.. 15 Musser, M. E., 599 Musso, H . , 313 Musumeci. .4., 192 Muszkat, K . A.. 369 Mutai, K.. 355, 441 Muthuramu, V., 460 Muus. L. T., 396 Muzart, J., 209 Myers, A. B., 39 Naaman. R., 25 Nada, A. A,, 281. 366. 422, 498 Nadezhdin, D., 599 Nadler, I., 159 Niiumann. F.. 197 Nafoar, J.. 93 Nagakubo, K., 545 Nagakura, S.. 32, 105, 110. 122, 224, 287, 449 Nagai, K . , 19, 145 Nagami, K . , 110, 438 Nagamura, T., 182, 183, 522, 574, 576

Nagar, M. R., 552 Nagasubramanian, G . , 593, 597 Nagata, M., 270, 336, 426 Nagayoshi, K., 410 Nagel, R. L., 89 Nahomy, R. E., 13 Nahor, G. S., 95 Nail, M., 13 Naito, I., 504, 543 Naito, K., 148, 521 Naito, T., 76, 242, 252, 261, 377, 428,447, 448 Najbar, J., 47 Nakadaira, Y., 215, 392, 465 Nakagaki, R., 355 Nakagawa, K., 213,463 Nakagawa, M., 417 Nakagura, S., 355, 367 Nakahama, S., 529 Nakahira, T., 86, 523, 528, 544 Nakai, H., 288 Nakaji, T., 425, 528 Nakajima, M., 320, 434 Nakajima, N., 268 Nakajo, H.. 79 Nakamura. H., 73 Nakamura, J., 110, 122, 355 Nakamura, K . , 16, 182 Nakamura, M., 77, 124, 253, 419 Nakamura, N., 257 Nakamura, S., 182 Nakamura, Y., 268, 350, 450 Nakane, R., 37, 148, 21 1 Nakanishi, F., 253 Nakanishi, H., 253 Nakano, K., 265, 320, 352, 434,449 Nakao, M., 595 Nakashima, N., 31, 46, 55, 65, 73, 82, 84. 119, 301, 424 Nakata. A., 451 Nakata, Y., 419 Nakato, Y., 587, 594 Nakayama. K., 406 Nakayama, N., 447 Nakayama, T., 65, 110, 529 Nakazaki, M., 372 Nakazawa, S., 474 Nakazawa, T., 376 Namarijama, Y ., 543 Namnath, J., 180 Nancs, R., 162 Nanun, T., 396 Naqvi. K . R.,41, 43. 92 Narayanaswamy, R., 199 Narbutt-Mering, A. B., 455 Narita, N., 290, 292, 368 Narkis, M., 551 Narula, M., 380, 496 Naruta. Y., 293, 323 Narutama, Y.. 280 Naruto, S., 381 Nasielski, J., 580

623

A u t hor Index Nashimoto, Y., 587 Nastasi, M., 311 Nataga, T., 16 Natarajan, P., 179, 184 Natarajan, s., 380, 496 Nate, K., 509 Nathanson, G., 37, 165, 205 Naudet, J. P., 150 Naumenko, I. G., 10 Nava, D. F., 153, 157 Navasawa, M., 522 Nayazi, F. F., 550 Nazakura, S., 526 Ndikumana, T., 164, 217 Nechitailo, V. S., 536 Neckers, D. C., 327, 352, 353, 458, 459, 505, 514, 528 Nedelec, J. Y., 492 Nedelec, O., 163 Neerbes, A., 5 18 Negishi, A., 546 Negishi, H., 406 Negishi, N.. 518, 528 Negus, D., 106 Neill, J. D., 436 Neitzert, V., 150 Nelson, H. H., 157 Nelson, R., 73 Nemet, N., 73 Nemoto. S., 183 Nemzek, T. L., 546 Nenadovic, M . T., 74 Nenchev, M. N., 8 Nenkov, G., 543 Neoh, S. B., 76 Nesbitt, D. J., 135 Nesbitt, R. S., 139 Neste, H.-R., 236 Nester. J . R., 24 Nesumi, Y., 376 Nettleton, D . H., 14 Neubecker, T. A., 191 Neudorful, P. S., 16 Neumann, D. K., 163 Neumann, R. M., 521 Neumann, W. P., 216, 509 Neumann-Spallart, N., 575, 582 Neuschafter, D., 29 Neusser, H. J., 24 Neve de Mevergnies, M., 148 Newport. G. L., 288,443 Newton, K. R., 24, 127 Newton, R. F., 226 Ng, C. Y., 126 Nguyen, K. T., 182, 397 Nguyen, 0. V., 159 Niay, P., 12, 20 Nichol, M . F., 47 Nicholls, C. H., 522, 541 Nicholson, N. D., 595 Nickel, B., 51, 94, 101 Nicodern, D. E., 581 Nicol, M., 33 Nicollin, D., 24, 175

Nieberl, S., 460 Niederberger, W., 84 Niederwald, H., 509 Niedzielski, J.. 36 Nieman, G. C., 127 Niemitz, K. J., 218 Nighan, W. L., 133 Niinamae, R., 471 Niino, S., 507 Niizuma, S., 435 Nijishima, T., 574 Niki, H., 20. 158 Nikolaev, A. F., 557 Nikolaev, A . I . , 402 Nikolai, W. L., 137 Nikolic, K., 177 Nikolova, Z., 550 Nikol’skii, A. B., 184 Ninagawa, A., 537, 561 Ninomiya, I., 261, 377, 428 Nip, W. S., 29, 145, 157 Nishazawa, M., 186 Nishi, N., 105, 127 Nishi, T., 497 Nishida, A., 495 Nishida, S., 239, 259, 283, 385, 457,492 Nishida, Y . , 102, 425, 528 Nishijima, T., 183 Nishijima, Y.,47, 96, 328, 524, 533 Nishikawa, Y . , 193 Nishimoto, K., 337, 431 Nishimura, K., 214, 215, 465 Nishimura, Y., 138 Nishio, T., 268, 269, 425, 426 Nishiwaki, T., 365 Nishyima, T., 522 Nitta, M., 234, 303 Nitzan, A., 40, 167 Nixon, D. E., 3 Noble, M., 131 Nobs. F. J., 595 Noda. C., 163 Nogar, N. S., 142, 145 Noguchi. S., 484 Nojima, K . , 368 Nokokavouras, J., 1 15 Nomura, D., 250 Nomura. T., 92 Noomen, A,, 518 Nordal, P. E., 17 Norikov, N. P., 522 Norman, R. 0. C . , 496 Normandin, R., I 1 Noufi, R., 587, 594 Nourmamode, A,, 373, 387 Novak, F. A., 122, 164 Novikov, N . P., 536 Novnan, J. M., 508 Nowakowska, M., 256,409, 41 I , 534 Nowikow, C. V., 155 Noyes. W. A., jun., 527 Nozaki, K., 182

Nozakura, s.,86, 397 Nozik, A. J . , 570, 594, 598 Nubbermeyer, H., 14 Numao, N., 243 Nurtdinova, G. V., 206 Nutt, G. F., 121 Nuyken, O., 520 Ny, L.-K., 76 Nyburg, S. C., 229 Oba, D., 138 Obase, H . , 138 Ober, G., 200 Oberlin, R., 427 Oberti, R., 341 Obi, K., 23, 30, 127 OBrien, J. P., 544 Obuchi, H., 79 Ochi, H., 351, 370 Ochiai, H . , 571 Ochiai, M., 466 O’Concheanainn, C., 122 O’Connell, C . M., 180 O’Connor, D. V., 34, 36, 40, 127, 345 Oda, K., 287 Oda, S., 22 O’Dwyer, M. F., 28 Oelkrug, D., 190 Oertling, W. A., 325 Oestehelt, D., 113 Offen, H. W., 26, 74 Ohashi, H., 177 Ohashi, M., 237, 358, 359, 398 Ohashi, N., 19 Ogdta, N., 544 Ogdta, Y., 367, 368, 414, 495 Ogawa, T., 27, 84, 92, 150, 2a7,289,424,425, 528 Ogawa, Y., 436, 543 Ogilby, P. R., 400 Ogino, K., 291 Ogiwara, K., 177 Ogiwara, Y ., 546 Ogren, P. J . , 158 Ogryzlo, E. A., 157 Oguchi, S., 440 Ohi, F., 213 Ohigashi, H . , 599 Ohkawa, T., 142 Ohmine, I., 46, 113 Ohmori, M., 497 Ohnishi, H., 507 Ohno, H . , 526, 527 Ohno, K., 425, 445 Ohno, T., 98 Ohno, T., 31, 79, 177 Ohnuma, Y ., 142 Ohsako, T., 579 Ohsawa, A., 372, 413 Ohta, A,, 372, 413 Ohta, H., 33, 448 Ohta, T., 124 Ohtani, H., 32 Ohtsuka, E., 440

624 Ohtsuka, V., 508 Ohwada, S., 86, 525, 528 Ohya, H., 529 Oikawa, S., 334 Oishi, S., 182 Oishi, T., 390 Ojha, P. C., 153 Oka. T., 165 Okabe, H.. 131 Okada, K., 328, 404, 416, 496 Okada, T., 32, 65, 76, 79, 399 Okahata, Y., 424 Okajima, H . , 289 Okajima, S., 79, 437, 438 Okami, A., 371, 413 Okamoto, A., 505 Okamoto, H., 92 Okamoto, K., 86, 525, 528 Okamoto, M., 512 Okamoto, Y., 192, 529 Okano, M., 92, 573 Okazaki, H., 506 Okazaki, K., 153, 155 Okazaki, R.. 240, 466 Okhrimenko, B. A., 212 Okubo, T., 506 Okuda, M., 124, 151, 154, 157 Okuda, S., 436 Okuda, T., 303, 434 Okuda, W., 435 Okugawa, T., 452 Okuno, H . , 481, 482 Okuno, T., 181 Okuno, Y.. 497 Okura, I., 182, 397, 574, 575 Okutsu, K., 342, 398 Olbertz, A. H. M., 5 Oldershaw, G. A., 154, 155 Oldenborg, R. C., 34, 133 Olea, F. A., 58, 230 OLeary, M. A,. 489 Oleinik, A. V., 518 Olin, G. R., 397 Oliveira, I. M. C., 444 Oliver, R. W. A., I8 Oliver, S., 373 Oliveros, E., 329, 422, 434 Olsen, E. G., 317 Olsen, G. H., 5 Olsen, J., 587 Olsen. M. L., 19 Olsen, R. J . , 378, 429 Olson, D. R., 518 Olson, R. W., 32, 51 Omi, N., 521 Omichi, H., 546 Omote, Y., 268, 269, 396, 425, 426, 442, 443, 456 O’Mullare, J. E., 599 On, H . P., 467 Onda, M.. 375,428 O’Neil, S. V., 119 O’Neill, F., 11, 134 Onimura, R., 181 Onishi, S.. 91

Author Index Ono, Y., 126, 138, 358 Onodera, K., 368, 41 1

Ooi. N . S., 423 Ooki, H., 524 Oomen, G. L., 1 1 Oostveen, E. A,, 460 Opitz, J., 123 Opitz, R. J., 331 Oppolzer, W., 242, 244 Oraevskii, A. N., 141 Orban, S., 530 Orchard. .4.F., 581 Orchin, M. J., 207 Orel, A. E., 165 Orfanopoulos, M., 112 Orita, K . , 381 Orlandi, C . , 65, 99 Orlov, M. S., 191 Ormerod. R. C., 132 Orr. B. J., 121 Ors, J. A , , 30, 146, 299, 312, 401, 49h Ortgies, G . , 151 Osa, T., 80, 425, 521, 527 Osamura, Y., 337, 431 Osawa, R., 541 Osif, T. L., 98 Oskam, A,, 199, 200, 202 Ostah, N. A., 213, 463, 465 Ostensson, B., 532 Osuka, A,, 280, 283, 285, 286. 400, 415 Ota, H., 326, 346 Otawara, Y., 406 Otis, C., 159 Oton, J., 65 Otsu, T., 507, 508 Otsubo. T., 386, 389,492 Otsuka, T , 465 Otsuki, T., 293, 376, 498 Ottinger, C . , 29, 162 Otto, A., 47 Otvos, J. W., 572, 595 Ouchi, T., 507, 516 Ouglielmetti, R., I10 Ourisson, G., 236 Overberger, C . G., 424, 519 Owen, E. D., 523, 533 Owen, E. O., 551 Oxman, J. O . , 356, 441 Oyama-Cannon, K., 212 Ozaki, Y., 16, 138 Ozenne, J. B., 157 Ozhavibekov, N. F., 531 Ozin, G. A , , 210 Paaren, H. E., 316 Pabiot, J., 543 Pac. C., 325, 340, 341, 356, 398, 412 Pac, J . , 548 Pacala, T. L., I I Pacanski, J . , 339 Pace, P. W., 5 Pace, S. A., 139

Pacheco, D., 283, 352, 467 Paczkowski, J., 502 Paczkowski, M., 129 Padgorodetskaya, V. A., 506 Padma Malar, E. J., 47 Padwa, A., 307, 308, 309, 336, 392, 401,432 Paessum, R., 476 Paetzold, R., 423 Paglia, D. E., 257 Pagni, R. M., 474 Pagnoni, U. M., 490 Pagsberg, P. B., 102, 103 Pai, B. R., 380, 496, 497 Paillons, N., 551 Paillous, A,, 551 Pailthorpe, M. T., 522 Paine, R. T., 193 Pak, I . , 19 Paladini, A. A. J., 43 Palmer, G. E., 478 Palpacuer. M., 15 Palumbo, L. J . , 134 Pan, R. L., 572, 581 Panaiotova, M., 550 Pande, u., 65 Pandey, G. P., 239, 416, 452 Panicker, M . M., 75 Panke, D., 536 Pankova, T. A,, 557 Pankratova, L. N., 544 Pankuch, B. J., 184 Pannell. K. H., 201, 204 Panock, R., 165 Panov, V. V . , 519 Panova, A., 186 Pansevich, V. V., 185 Papineau, N., 20 Papp, s., 177 Pappas. S. P., 505 Papsun, D. M., 203 Paquette. L. A., 233, 280, 402 Paraskevopoulos, G., 29, 157, I58 Pardo, A,, 75 Parekh, C. T., 235 Pariiskii, G . B., 546 Parisot, J. P.. 151 Park, Y.-T., 420 Parker, J. W., 165 Parker, R. T., 28 Parkinson, B. A., 587, 591, 593 Parks, K. D., 24 Parlar, H . , 299, 331, 365 Parmar, S. S., 339, 422 Parinenter, C. S., 28, 121, 122, 132

Parodi, G. A,, 21, 22 Parola, A. H., 77 Parrish, A,, 149 Parsons, J. M., 139, 491 Parsons, M. L., 14 Parsons, R., 593 Pasha, I., 533 Pashchenko. T. E., 546

625

Author Index Paske, w. c., 162 Passalenti. B., 501 Pasteris, R. J., 275, 276 Pasternack, L. R., 130. 149 Paszner, L., 518 Paszyc, S.. 58 Patel, C., 457 Patel, R. I., 132 Patrick, K. G., 130 Patsis, A., 518 Pattenden, G., 241, 244, 265, 266 Pattersen, H. H., 29 Patterson, F. G., 32, 51 Patterson, H. H., I89 Paulick, W., 320 Pavlisko, J. A., 543 Pavlova, A. M., 176 PdVlOVa, z. F., 444 Pavlovich, V. S., 33 Pavlovskii, V. I., 184, 185 Pawa, M. F. J. R.,84 Payen de la Garanderie, H., 177 Payne, M. G., 160 Payne, W. A., 157 Pazzi, G. P., 212 Pearsall, T. P., 15 Pearson, T. D. L., 26, 73, 179 Pecen, P., 238 Pederson, C. T., 457 Pederson, C. L., 365 Pedersen, E., 462 Peebles, W. A., 5 Peeling, J., 530, 534 Peet, N. P., 250 Peeva, L., 531 Pelaprat, D., 427 Peleck, B., 283 Pelikan, P., 412 Pelipenko, V. P., 10 Pelizzetti, E., 181, 573, 576, 585 Pellegrino, F., 35, 73 Pen, S. S., 518 Pence, W. H., 137 Penchev, I. I., 41 Penkett, S. A., 149 Penselin, S., 139 Penzkofer, A,, 13, 32 Pepin, H., 7 Perales, J., 226 Perbet, G., 415 Perera, I. K., 5 Perekalin, V. V., 444 Pereyre, J., 342 Perez, C., 352, 449 Periasamy, N., 85, 396 Perichet, G., 61 Perico, A., 528 Perkins, G. G. A., 164 Perkins, M. J., 256, 468, 549 Perkins, R., 331 Perkins, W. C., 502 Perkowitz, S., 19

Pernikis, R., 518 Perone, S., 598 Perrone, M. F., 581 Perry, A., I15 Perry, D. S., 137 Perry, R. A,, 150, 314, 334 Pershin, A. N., 176 Persico, M., 45 Person, J. A., 263 Person, W. B., 19 Pete, J. P., 209, 259, 260, 429, 443,494 Peter, L. M., 574, 584 Peters, J. A. M., 402 Peters, K . S., 394, 395 Peters, P. J. M., 4 Petersen, J. D., 184, 186, 187 Peterson, J. R., 131 Peterson, D. A., 126 Petkova, M., 550 Petrij, J., 538 Petrosyan, R. A., 551 Petruj, J., 548 Petrylak, D. P., 198 Pettinger, B., 25 Pfleiderer, W., 493 Pfoertner, K. H., 339 Phaneuf, R. A., 137 Phillip, J. D., 41 Phillips, D., 34, 36, 40, 86, 127, 131, 525 Phillips, G. O., 541, 551 Phillips, P., I19 Phillipon, G., 255 Philpot, M. R., 47 Phoenix, F. H., 408 Pichat, P., 41 I Pichler, G., 163 Pichon, R., 280, 423 Pieniazek, M., 333 Pienkowska, H., 43 Piens, M., 527 Pierce, R., 129 Pieroni, O., 425, 528 Pierpont, C. G., 201 Pierre, A., 190 Pietra. S., 418, 486 Pietrzak, B., 406 Pietrzycki, W., 65 Pikulik, L. G., 33 Pileni, M.-P., 85, 1 I I , 396, 397, 575 Pilling, M. J., 179 Pinkerton. D. M., 549 Pinson, W. E., 588 Piper, J. A., 8 Piper, L. G., 28, 131, 158, 159, 217 Pirkl, J., 565 Pirrung, M. C., 449 Pittman, C. U., jun., 206 Pitts, E., 516 Pitts, W. M., 129, 149, 162 Pivneko, N. S., 256 Plank, J., 204

Platenburg, D. H. J. M., 368, 400 Pleshanov, V. P., 530 Plum, C. N., 148 Plummer. E. W., 520 Pluth, J. J., 210 Plyusnin, V. F., 178, 190 Poe, R. T., 154 Poggi, G., 65 Pogonin, V. I., 194 Pogrebnyak, A. A., 206 Pokholok, T. V., 546 Pokrovskaya, I. E., 396 Pokrowsky, P., 19 Polak-Dingels, P., I36 Polanka, J., 534 Polanyi, J. C., 166 Polavka, J., 516 Poliakoff, M., 196 Polikarpov, I. S., 538, 541 Politis, T. G., 74 Pollack, J . D., 16 Pollack, M. A., 13 Pollett, A,, 370, 458 Pollmann, P., 43 Pollock, C. R., 19 Polniaszek, R., 308, 392 Poluektov, N. S., 192 Polyakov, Yu. N., 550 Polze, S., 8 Polo, J., 491 Poncini, L., 281 Pond, D. M., 250 Pone, D., 559 Pongeway, P. A,, 463 Ponomareva, R. P., 295, 363, 484 Pont, D. D., 65 Ponterini, G., 45 Ponticelli, F., 338, 431 Popa, A., 507 Popechits, V. I., 33 Popescu, D., 17, 163 Popescu, I., 17, 163 Poplawska, B., 361 Popov, A. M., 184 Poppe, D., 147 Portella, C., 260, 494 Porter, G., 91, 92, 361, 585 Porter, G. B., 172, 175, 178, 179, 180 Pospisil, J., 546 Possagno, E., 188 Post, B. H., 8 Postnikov, L. M., 538, 550 Poteleshchenko, N. T., 296 Potapov, I. A., 171 Potter, W., 399 Potzinger, P., 212, 463 Poulos, A. T., 191 Pouyet, B., 61, 444 Powell, H. T., I64 Powers, D. E., 28, 119, 120, 127 Poznyak, A. L., 177, 184, 185

Author Index

626 Prabhakar, S., 444 Prabhakaran, R., 519 Pradere, F., 12 Praefcke, K . , 218, 229. 391, 467, 49 I , 493 Pragst. F., 76, 94, 115 Prahbu, K. V., 275 Prane, J . W., 501 Prasad, G., 481 Prasad, S. S., 151, 153 Pratt. A. C., 364 Pratt, D. W., 128 Pratte, J. F., 527 Prauseova, Z., 541 Pravilov, A . M., 132 Prejza, J., 587 Preses, J . M . , 145 Prest, H. F., 126 Preston, P. N., 296, 364 Preston, R. C . , 414 Preuss, A. W., 152 Previtali. C . M., 390 Price, D., 128, 334, 433 Priestley, E. B., 148 Prieto, M. J., 77 Prinn. R. G., 149 Prior, J., 25 Priou, J. P., 14 Pritchard, D. E., 162 Proniewicz, L. M., 93 Prosser. N. J. D., 149 Prosteanu, N., 490 Protz, R., 11 1 Provina, I. A,, 501 Pruett, J. G., 164 Pryor, W. A , , 405 Przytarska, M., 361 Puchalski, A. E., 223 Pudovik, E. A,, 191 Pulet. G., 152 Pulfrey, R. E., 18 Pulos, A. T., 79 Pulwer. M., 307 Pummer, H . . 155 Purchalski, A. E., 99 Purcell, K. F., 184 Purdy, J. R., 132 Puretzky, A . A., 23, 140, 145 Purohit. P. C., 239,498 Putman, S.. 91 Puza. M., 48 Pykc, S. C . , 174 Pyle. J . A., 150 Pyper, N . C., I19 Quack. M., 147 Quan, N . N., 98 Quast. H.. 473, 494 Quercia, I. F.. 4 Quick, C . R., jun., 126, 145 Quickenden. T. I., 36, 581 Quin, L. D., 370, 468 Quinkert, G., 232, 395 Quinn. S., 204 Quintero, L., 359

Quinton, A . M., 126, 129 Quiroz, F., 407 Ra, C. S., 446 Rabani, J.. 95, 194, 579 Rabek, J. F., 523, 532, 534, 540, 544, 546, 550 Rabinovitz, M., 48 Racke, H. H., 536 Radhakrishnan, A., 184 Radic, D., 524 Radtke, R., 405 Radwanska-Daczekalska, J., 192 Raetzel, M., 397 Raetzsch, M., 507 Rafalska, M., 274, 450 Rafikov, S. R., 513 Raghavan, P. R., 265 Raghu, P., 283, 374 Rahbee. A., 158 Rahman, A., 428 Rajchel, A., 268, 448 Rajee, R., 419 Rajeshwar, K., 587 Rakhlin, V. I . , 216 Ram, N., 417 Ram, R. N., 432 Ramakrishnan, V., 75, 76, 441 Ramamurthy. V., 98, 225, 419, 460 Rama Rao, K . V. S., 37, 146 Ramaswamy, R., 147 Ramelow, U., 537 Ramsay. D. A., 126 Ramsden, S. A., 7 Ramsey, J. M., 17 Ranade, A. C., 420 Ranby, B., 532, 534, 540, 544, 546 Rand, S. D., 35 Randall, C . H., 16 Ranfagni. A., 212 Rao. K . K . , 572 Rao. K. N., 19, 401 Rao. K. V. R., 195, 283, 374 Rao. P. R., 27 Rao. V. J.. 419 Rao. V. S . , 27 Rao, Y. V. C . , 27 Rapoport. H . , 447 Rasburn, E. J., 84 Rasmussen, K. H., 520 Rasmusson, R. A., 149 Rasti, F.. 552 Rat, A. S.. 519 Ratajczak. E., 128, 333, 334, 433 Ratzlaff, K . L.. 17 Rau. H., 66, 186,424, 471 Rausch, M . D., 197, 200 Rava, R. F’., 46 Ravanal, I.., 399 Ravishankara, A. R.. 152, 156, 157, 218

Ravishankara, A. V., 151 Ravishankara, R., 151 Rawlings, P. C., 325, 347 Ray, N. K., 448 Ray, S., 581 Rayez, J. C . , 93 Rayner, D. M., 87 Read, R. T., 520 Rebhan, U., 10 Rebollo, H., 406 Recca, A,, 537 Reek, G., 253 Reddy, K. V., 17, 148 Redon, A. M., 588, 593 Redpath, A. E. C., 527 Redpath, T., 86, 524 Reece, G. D., 18 Reed, W. J., 173, 193 Regan, C . , I16 Regitz, M., 480 Rehak, A., 547 Rehder, D., 197 Rehorek, D., 175, 176, 178, 185, 490 Rehm, D., 181 Reichel, C. L., 196, 208 Reichenbicher, M., 115, 423 Reichman, B., 585 Reid, E. S., 25 Reid, R. F., 86, 527 Reid, W. J., 546 Reijnders, P. J. M., 325 Reimann, B., 157 Reinhardt, M., 256 Reinhardt, R. M., 513, 516 Reintjes, J., 11 Reisch, J., 294 Reisenauer, H. P., 485, 492 Reiser, A., 516 Reiser, C., 140 Reisfeld, M., 133 Reisler, H., 142, 149 Reiter, F.. 433 Rek. V., 538 Reksten, G., 1 1 Renibold, M. W., 553 Renlund, A. M., 142 Rennert, A. R., 125 Renrzepis, P. M., 35, 61, 68 Requena, A,, 167 Rerek, M . E., 180 Rest, A. J., 45, 178, 199, 202 Retey, J . , 209 Rettschnick, R. P. M., 122 Reuben, M. K., 297 Reucroft, P. J., 599 Reynolds, D. P., 226 Reynolds, G . A,, 6, 9 Rhodes, C. K., 133, 155 Riang, H.-S.. 278 Riant, Y.. 19 Ricchiero, F., 85, 208 Riccieri, P., 174 Rice, J. K . , 164

627

A uthor Index Rice, S. A., 28, 80, 122, 127, 128, 134, 164 Rice, S. F., 208 Rice, W. W., 26, 34, 36, 132, 133, 141 Ricevuto, V., 189 Rich, E. S., 29 Rich, J. D., 214 Richard, H., 454 Richards, D. H., 86, 524 Richards, J. T., 89, 552 Richards, P. G., 153 Richards, P. L., 20 Richardson, H. H., 23 Richardson, J. H., 41, 598 Richardson, M. C., 6, 8 Richmond, R., 22 Richoux, M. C., 575 Ricka, J., 36 Rico, I., 422 Riddell, S. Z., 521 Ridgen, J. D., 14 Ridley, B. A., 29, 151 Riecker, W. F., 309, 392 Rieke, R. D., 307 Riesz, P., 541 Rigaud, P., 150 Rigaudy, J., 37, 417 Riley, C., 146, 21 1 Riley, S. J., 127, 128, 132 Rillema, D. P., 582 Ringsdorf, H., 509 Ripoche, G., 13 Rippen, G., 86 Riseman, S. M., 23 Rist, G., 502, 505 Ritter, A., 40, 212, 463, 467 Rivalie, C., 382, 475 Rivas, C., 283, 352, 449, 467 Rivas, I. V., 159 Rivera, V., 30 Riviere, M., 329, 422, 434 Rizaeva, S. Z., 518 Rizzo, J. E., 1 1 Robb., R. A,, 10 Robbins, J. L., 201 Robbins, R. J., 33, 88 Roberts, A. J., 34, 36, 40, 86, 525 Roberts, C. W.,. 521 Roberts, D. A., 203 Roberts, R. W., 538 Roberts, S. M., 226 Robertshaw, J. S., 155 Robertson, G. B., 48, 388 Robin, M. B., 21, 124 Robinson, G. W., 33, 88 Roche, A. L., 157 Rockenbauer, A,, 549 Rockley, M. G., 23 Roden, G., 51, 101 Rodgers, M. A. J., 31, 82, 84, 108, 1 1 1 , 182, 183 Rodgers, M. O., 27, 28, 151, 156, 161

Rodriguez, L. O., 29 Rodriguez, N., 449 Rodriguez, W., 352 Roe, J. C., 279 Roebber, J. L., 28 Roellig, M. P., 130 Roessler, D. M., 22 Roessler, N., 1 1 1, 378, 417 Rofer-Depoorter, C. K., I7 1 Rogal, E. A., 544 Rogers, R. D., 197 Rogerson, C. V., 321 Rogov, V. A., 295 Rohl, R., 22 Rohly, W. G., 190 Roland, P. A., 5 Rollinson, A. M., 74 Rolt, S., 164 Romanov, A., 507 Romanov, V. V., 296 Romanovskayd, G. I., 194 Romeo, R., 189 Ron, A., 81 Ronn, A. M., 165, 198 Roobeek, C. F., 196 Roof, A. A. M., 280 Roos, G. H. P., 297 Roosen, G., 12 Roques, B. P., 427 Rordorf, B. F., 121 Rosdn, A. M., 37, 165, 205 Rosdntsev, E. G., 559 Roscoe, H. K., 150 Rose, T. L., 132, 236 Rosenberg, M. L., 539 Rosencwaig, A,, 22 Rosenfeld, A., 8 Rosenfeld, R. N., 147 Rosenfeld-Gruenwald, T., 194 Rosenfeldt, F., 197 Rosenthal, A,, 252, 451 Rosenthal, J., 598 Rosenwaks, S., 159 Rosilio, C., 518 Rosner, P., 322 Ross, I. G., 119 Rossi, A., 175 Rossi, R. A., 312, 359 Roth, H. D., 3 11, 409 Roth. P., 155 Rothberg, L. J., 24, 165 Rothe, E. W., 163 Rothschild, M., 155 Rottke, H., 162 Roucoux, C., 516 Rousseau, G., 403 Roux, D. G., 232, 399 Rowland, F. S., 151 Rowley, A. G., 436 Rowley, N. J., 523 Roxlo, C. B., 6 Roy, D. S., 63, 192 Royce, B. S. H., 23 Royt, T. R., 6 Rozenborn, N. A,, 547

Rozenkevich, M. B., 171, 186 Ruaudel-Teixier, A., 518 Rubin, M. B., 81 Rubinstein, I., 180 Rudkovskaya, G . D., 527 Rudnitskaya, T. E., 508 Ruge, B., 265 Rule, M., 263 Rumfeldt, R. C., 187 Rumin, R., 209 Ruminski, R. R., 174 Runge, S., 12 Rusev, P., 175 Russegger, P., 123, 422 Russell, G. A,, 210 Russell, J. C., 369 Russell, R.-G., 585 Russell, T. D., 134 Russkikh, V. V., 295 Russo, R. E., 9 Russwurm, G. M., 22 Rutherford, H., 527 Rutt, H. N., 5 Ryan, M. A., 27 Rybin, L. V., 206 Rybinskaya, M. I., 206 Rybka, J. S., 191 Rynard, C. M., 206 Rzdev, Z. M., 518 Rzeszotarskd, J., 68 Saar, W., 552 Sabbah, S., 75, 230 Sachok, V. V., 173 Sadeghi, N., 159 Sadler, D. E., 379 Sadowski, C. M., 118 Sadrmohaghegh, C., 531 Saeva, F. D., 397 S d d , K. D., 467 Safarzadeh-Amiri, A., 101 Safinova, V. P., 551 Sagalovich, V. P., 178 Sagan, A. G., 35 Sagdeev, R. Z., 301 Sahlberg, C., 273, 452 Sahni, R., 330 Said-Galiev, E. E., 544 Saidov, B. D., 549 Saigusa, H., 94, 96 Sainsbury, M., 364 Saito, H., 252 Saito, I., 270, 271, 273, 326, 366, 367, 412, 417, 420, 446, 449, 451, 498 Saito, K., 280 Saito, T., 537 Saito, Y., 26, 89 Sakaguchi, I., 551 Sakaguchi, U., 178 Sakaguchi, Y., 224, 367 Sakai, H., 18 Sakamoto, M., 442, 456 Sakamoto, T., 183, 522, 579 Sakano, Y., 454

628 Sakata, T., 80, 82 Sakata, Y., 65, 79, 386, 389, 399, 492 Sakharovskii, Yu. A., 171, 186 Sakisyan, A. A., 142 Sakuma, T., 523 Sakura, K., 183, 398, 579 Sakuragi, H., 110, 300, 301, 346, 367, 368, 371, 411, 413, 492 Sakuragi, M., 413 Sakurai, H., 215, 216, 235, 278, 302, 325, 340, 341. 346, 356, 361, 392, 398, 412, 465 Sakushima, A,, 441 Sala. K. L., 13 Salamero, Y., 165 Salaneck, W. R., 520 Saliby, M. J., 174 Salin, M . L., 116 Salisbury, K . , 379 Salk. J., 10 Salokhiddinov, K. I., 400 Salomon, K. E., 125, 218 Salour, M. M . , 6 Saltiel, J., 56, 99, 302 Saltiel, S. M., 12 Salvetter, J., 176 Samad, S. A,, 239 Samoiiova, A. N., 30 Samotus, A,, 176 Sams, R. L., 19 Samsonova, L. V., 551 Samuel, C. J., 275 Samuel, E., 197 Sanchez-Ferrando, F., 282 Sander, S. P., 30 Sander. U.. 22 Sanders, M . J., 23 Sanders, N. D., 130, 156 Sandhu, S. S., 194, 195 Sandrini, D., 98, 174, 178 Sandros, K., 48, 56, 302, 388 Sanger, D., 544 Sangster. D. F., 36 Sanna, G., 148 Sanner, R. D., 196, 206 San-nohe, K., 377, 428 Sano, N., 229, 468 Sano, T., 445 Santhanam, M., 278 Santin, C . C., 198 Santoku, M., 138 Santus, R., 31, 73, 87 Sanui. K.. 544 Saperstein, D. D., 20 Saplay, K . M., 330 Sarada. K., 380, 497 Sarai. A., 39 Saraiya, S., 501 Sardyukova, T. I., 176 Sarkar, S. K.. 37, 146, 195 Sarkisian, G. M., 264 Sarkisov, 0. M., 30 Sarpal, A. S., 195

Author Index Saruwatari, M., 484 Sarzhevskii, A. M., 33 Sdsaki, H., 516 Sasaki, T., 239, 259, 385, 457, 492 Sasse, W. H. F., 181, 386 Sasseville, R . L. P., 175 Sassoon, R. E., 579 Sastre, R., 546 Sathianandan, K., 9 Sato, C., 516 Sato, E., 251, 272 Sato, G. P., 361 Sato, H., 23, 29, 82, 84, 126, 127 Sato, K., 278, 328, 329, 524, 528 Sato, M., 361, 424 Sato, R., 479 Sato, S., 138, 153, 155, 159, 585 Sato, S. P.. 361 Sato, T., 194, 203, 253, 280, 410, 508 Sato, Y.. 288 Saunders, D. R., 587 Saunders, M . J., 9 Saunders, W. D., 321 Sauer, J., 216 Sauers, R. R., 244, 312 Saus, A., 207, 508 Sawa, Y., 571 Sawada, T., 22 Savage, C. M., 20, 158 Savov, s. D., 12 Saxe, P., 119 Scaife, D. E., 583 Scaiano, J. C., 30, 31, 86, 99, 100, 102, 231, 281, 385, 394, 440, 521, 528, 543 Scamporrino, E., 537 Scamporrino, M., 537 Scandola, F., 80, 98, 171 Scarpati, R., 415 Schaap, A. P.. 108 Schaefer, C. G., 394 Schlfer, F. P., 43 Schaefer, H. F., 111, 119 Schlfer, H. J., 63 Schlfer, U., 427, 484 Schltzle. H.. 424 Schafer, F. P., 8 Schafer, G., 144 Schaffner, K . , 68, 265, 274, 304 Schamshula, W., 550 Scharf, H. D., 420 Schatz, G. C., 25, 155, 158 Schauer. G., 436 Schebeske, G., 150 Scheffer, J. R., 260, 307 Scheibler. P., 175 Scherer, 0. J., 209 Schetter, K . , 7 Scheutzow, D., 113 Schicht, G., 507

Schields, J., 502 Schiff, H . I., 29, 151 Schrller, N. H., 6. 14 Schilling, M. L. M., 311, 409 Schindler, R. N., 583, 584 Schlag, E. W., 24. 28, 122 Schhmdnn, w., 189, 576 Schleicher, B. R., 164 Schlick, T., 154 Schlie, L. A., 126 Schlosser, D., 47 Schrnehl, R. H., 171 Schmid, U., 105 Schmidlin, E., 18 Schmidt, H. G., 313 Schmidt, J., 104, 357 Schmidt, M., 138 Schmidt, R., 108, 412 Schmidt, S. P., 66, 81, 115, 223 Schmidt, V. H., 137 Schmidt, W. E., 7 Schmitt, G., 37, 131 Schmitzer, J., 299, 339 Schnioerer, M., 509 Schnabel, W., 106, 328, 496, 504, 519, 534, 544 Schneemeyer, L. F., 593, 594 Schneider, K. A., 333 Schneider. M. P., 66, 471 Schneider, S.. 59, 339 Schoef, S., 76 Schoemaker, G. C.. 199 Schofield, K., 136 Scholl, B., 297, 452 Scholz, K.-H., 251, 445 Schomburg, H., 31, 68 Schonberg, A,, 287 Schoneich, R., 26 Schonemann, K . H., 402 Schoolar, R. B., 15 Schott, H. N., 223 Schram, E., 421 Schreiner, A. F., 200 Schreiner, R., 598 Schroder, H., 17 Schroder, G., 472 Schroeder, J., 219 Schroder, M., 162 Schroer, W.-D., 432 Schuchman, H. P., 108, 110, 2 12, 463 Schuh, M. D., 119 Schulman, S. G., 40 Schulte-Frohlinde, D., 106, 424 Schultz, A., 137, 378, 429, 475 Schultz, P. G., 489 Schulz, P. A., 218 Schulze, U., 391, 467 Schumacher, R., 583, 584, 595 Schumann, L., 165 Schuppiser. J.-L., 437 Schurath, U., 152 Schurman, J., 23 Schurr, J. M., 91 Schuster, D. I.. 261, 275, 394

Author Index Schuster, G. B., 66, 115, 479 Schutten, K., 91 Schwager, L., 236 Schwailer, J.-C., 437 Schwartz, R. N., 314 Schwartz, U., 232, 395 Schwarz, H . , 72 Schweig, A,, 39 Schweizer, W. B., 257 Schwenz, R. W., I39 Schwindt, R., 552 Schwoerer, M . , 104 Scott, G., 531, 536, 547, 549, 550, 552 Scott, G. W., 56, 74,-528 Scott, L. T., 334 Scriven, E. F. V., 485 Sculfort, J. L., 587, 588 Sears, A. B., 250 Sears, T. J., 28 Seaver, M., 121 Sebastian, P. J., 9 Secco, A. S., 260 Secroun, C., 20, 150 Seddon, K. R.,595 Sedlacek, W. A., 150 Sedlar, J., 548 Seeger, D. E., 263 Segal, G. I., 157 Segev, E., 158 Seguchi, K., 362 Seibert, M., 571, 595 Seiders, R. P., 369 Seiko, T., 375 Seiler, W., 150 Seilnieir, A., 5 Seitz, D., 133 Seka, W., 1 1 Seki, K., 498 Seki, Y., 528 Sekuler, P., 73 Selamoglu, N., 142 Seleznev, V. N., 295, 363 Selinger, B. K., 63 Selli, E., 514 Seltzer, S., 99, 283 Selvarajan, N., 75, 76 Selwyn, J. C . , 102, 521 Selzle, H. L., 28, 122 Semak, B. D., 552 Semchishen, V. A,, 36 Semehikov, Yu. D., 518 Semerak, S. N., 86 Seminara, A., 192 Semmelhack, M. F., 359 Semmler, U., 405 Sen, D., 65 Senda, S., 485 Sengupta, P. K., 70 Senofonte, O., 3 Senter, P. D., 241 Sepaniak, M . J., 41 Sepiol, J., 30 Serdobou, M . V., 396 Serdyukova, T. I., 172

629 Serebryakov, E. P., 247, 251 Sergaev, V. A,, 518 Serpone, N., 175 Serve, M . P., 476 Sethi, R. K., 520 Seto. K., 319 Setser, D. W . , 134, 138, 139. 153, 154, 159 Settachayanon, S., 505 Sevastenko, G. N., 544 Severnyi, V. V.,544 Sevil, M . J. R., 565 Seyferth, D., 207, 213, 465 Sha, C.-K., 378,429, 475 Shabarchina, M . M . , 399 Shafirovich, V. Ya., 181 Shah, R. C . , 151 Shahjahan, M., 455 Shahrisa, A., 432 Shakra, S., 552 Shalaby, S. W., 529 Shalimo, A. L., 421 Shamma, M., 434 Shani, A., 405 Shank, C . V., 9 , 4 3 , 9 1 Shanks, R. A., 505, 506 Shannon, P. T., 99 Shapiro, M., 131, 158 Shapiro, S. L., 34, 68 Shapivov, A. B., 559 Shappard, A., 153 Shaps, R. H., 18 Sharfin, W., 134 Sharma, A,, 409 Sharma, R. P., 415 Sharp, J. T., 425, 430 Sharp, R. C., 21, 140 Sharp, W. E., 150 Sharpless, R. L., 36, 150 Shaver, A,, 204 Shaw, M. J., 11, 134, 164 Shaw, R. J., 28 Shaw, S.-Y., 16 Shchegoleva, I . S., 172 Shchelokov, R. N., 193 Shcherbakov, V. D., 191 Shchukin, G . I., 436 Shea, C.-M., 409, 439 Shein, V. P., 531 Shekk, Y. B., 56 Shelimov, B. N., 176 Shelton, R. N., 26 Shen, S. C., 19 Shen, Y. R., 28, 218 Shepherd, T. M . , 528 Sheridan, P. S., 174, 180 Sherman, W. F., 25 Sherrington, D. C., 51 1 Sherstyok, V. P., 176, 504, 506 Sherz, A., 104 Shetlar, M . D., 274, 450 Shevchenko, Yu. N., 17!3 Shevchuk, A. V., 508, 519 Sheves, M., 45

Shiba, K., 242, 251, 335, 425, 447 Shiba, T., 338 Shibata, H., 571 Shibata, T., 21 Shibayama, K., 518 Shibuya, K.. 23 Shichida. Y., 32 Shiga, M., 425 Shigematsu, K., 425 Shigeta, I., 81 Shih, C., 246, 446 Shiiko, I. I., 552 Shikhlinskaya, R. E., 22 Shilov, V. P., 195 Shim, S. C., 184, 272, 372, 446, 529 Shim, Y. P., 514 Shima, K., 235, 278, 279 Shimiza, F., 541 Shimizu, H., 286, 359 Shimizu, K., 352, 357 Shimizu, T., 522 Shimomura, M., 424 Shimozono, K., 270, 271, 326, 446, 449 Shinar, R.,595 Shindo, Y., 128 Shine, H. J., 469 Shingu, T., 380, 497 Shinizn, F., 551 Shinkai, S., 424, 425, 528 Shinmura, T., 273, 367, 498 Shinohara, H., 127, 518, 528 Shioji, M., 597 Shiokawa, J., 172, 192 Shipley, N. J., 173 Shiraishi, M., 277 Shirataki, Y., 375, 427 Shirk, J . S., 17 Shirota, Y., 86. 526 Shirotsuka, T., 414 Shishkina, V. I., 550 Shiruka, H., 77, 79, 354 Shlyapintokh, V. Ya., 546, 547, 551 Shoko, N. R.,520 Shotov, A. P., 19 Shou, H., 349 Shternberg, B. Z., 216 Shue, H . , 454 Shufen, F., 11 Shugar, D., 65 Shukla, R. P., 15 Shurpik, A,, 312 Shvedchikov, A. P., 508 Sibbett, W., 8, 12, 34 Sibener, S. J., 156 Sidebottom, H. W., 122 Siders, P., 147 Sidhu, K. S., 96, 125, 417, 462 Siegel, A., 137 Siegel, R.,197 Siegfried, R., 490 Siegman, A., 91

630 Siegmund, M., 66 Sieklucka, B., 176 Siemionko, R. K., 472 Sienko, M. J., 593 Sierocka, M., 502 Sigal, I . S., 187, 208, 576 Sigwalt. P., 51 1 Sikora, D. J., 197 Silbey, R., 80 Sillesen, A. H., 102 Silver, D. M., 153 Silver. J. A., 157 Silvers, S. J., 163 Silvestro, G. D., 519 Sima, J . , 177, 190 Simionescu, C . , 513 Simkin, D. J., 212 Simmons, E. L., 150 Simms, J. A , , 537 Simon, Z . , 490 Simons, J. P.. 126, 129, 137, 138 Simpson, J. T.. 451 Simpson, 0. A., 19 Sinclair, R. S., 66, 108, 551 Sindler-Kulyk, M . , 327, 352, 353, 458, 459 Sing. A., 484 Singer, E., 287 Singer, R. C . , 3 Singh, B. P., 538, 539 Singh, D., 432 Singh, G . , 432 Singh, K., 573 Singh, P., 587 Singh, R., 587 Singh, R. P., 550 Singh, S. P.. 339, 422, 538, 539 Singletary, N. J., 575 Singleton, D. L., 158 Sink, M . L., 158, 167 Siomos, K., 64 Sivaram, B. M., 10 Sivergin, Yu. M.. 527 Sivokhin, V. S., 551 Sixl, H., 509 Skeath, P.. 589 Skelton, B. W., 243 Sket, B., 344 Skibsted, L. H., 186 Skidmore, A. F., 3 Skiyiko, L. A., 557 Skokheim, T., 587 Skoop. ti., 10 Skorokhodova, T. S.. 371 Skrilec, M., 94 Skripley, L. A,, 547 Skrlac, W., 1 I Skrobol, C . , 10 Skrodzki, D., 212, 463 Skubnevskaya, G. I., 121 Skurat, V. E., 531, 541 Slack, M., 155 Slama, Z., 538 Slanger, T. G., 36, 150

Author Index Slater, N. K. H., 158 Slater, S., 201 Slavcheva, Y., 444 Sleat, W. I!., 6 Sleevi, M. C., 497 Sleight, A. W., 584 Slifkin, M. A,, 33 Sloan, J. J , 155 Slobodetskaya, E., 530 Slobodyanik, V. V., 523 Smalley, R. E., 28, 119, 120, 127, 167 Smayling, M., 11, 134 Smets, G., 510 Smirnov, E. P., 132 Smirnov, L. N., 550 Smith, A. B., 129, 154 Smith, B. V., 256, 468 Smith, G. P., 27, 120 Smith, G. K., 156 Smith, I. W. M., 155 Smith, J. R. L., 496 Smith, K. J., 275 Smith, K. M., 417 Smith, N., 162 Smith, P. G.,235 Smith, P. R., 13 Smith, R. H., 157 Smith. S. D., 14, 147 Smith, T. P., 187, 544, 576 Snoeck, T.. 200 Snow, W. L., 163 Snyder, J. .I., 325, 347 Snyder, J. P., 462 So, N., 507 Sobolev, V. I., 550 Sodeau, J. R., 218 Soderquist, J. A.. 215 Soep, B., 122 SOgd, o.,292, 396 Sohar, P., 422 Sokol, J. D., 132 Solanki, R., 10 Solar, S., 79 Solaro, R., 519 Solgadi, D., 33, 130 Solladie. G., 371, 491 Solomans, D. P., 81 Solomon, P. M., 149 Somei, M., 242, 435 Somorjai, (2. A., 584 Son, P. N., 547 Sonawane, H. R., 239,498 Sonderhof, D., 532 Sone, T., 424 Song, P.-S.. 72, 91 Sonnenschein, R., 47 Sonoda, N., 218, 395 Sorensen, P. R., 520 Sorita, K., 192 Soroka, J., 171, 375, 427 Soroka. K. B., 375. 427 Sorokin, N. I . , 121 Sorokin, P. P., 30, 146 Sorokina, L.. S., 552

Sostero, S., 173, 189, 195 Soumillion, J. P., 357 Soutar, I., 27, 40, 86, 93, 525 Sowada, U., 58 Sozzani, P., 519 Spak, A. J . , 441 Sparks, R. H., 180 Spears, K . G., 26, 130 Specht, E., 121 Speiser, S., 21, 81, 141 Spicer, W. E., 589 Spirin, Yu. I., 508 Springer, G. S., 150 Sprouse, J. F., 18 Spriinken, H.-R., 583, 584 Sridharan, U. C., 157 Sriniannarayana, G., 374 Srinivasan, K. G., 441 Srinivasan, M., 496 Srinivasan, R., 255, 299, 312, 496 Sriram, R., 175 Srirath, S., 116 Srogl, J., 297 Stackhouse, J., 484 Stacy, A., 593 Stadelmann, J . P., 118, 121 Stahist, H., 37, 123, 130 Stallcop, J . R., 165 Staminov, K. V., 8, 12 Stamps, M . A,, 22 Stanciulescu, C., 17 Stanco, J., 4 Stanford, J . B., 457 Stankov, K. A., 8 Stanley, P., 421 Stanron, A. C., 136 Stapleton, B. J., 414 Stark, B. P.. 501 Stark., H . , 232 Starodubtsev, N. F., 141 Starov, V., 142 Stasicka, Z., I76 Stavinoha. J., 297, 450 Stavola, M . , 34 Steblevskaya, N. I., 193 Stedman, D. H., 150 Steed, J. M., 150 Steedman, J . R. F., 436 Steel. C . , 125, 142 Steele, K. P.. 463 Steer, R. P., 101 Stegemeyer, H . , 43 Stegmann, W., 31 1, 430 Stehl., R. H., 541 Steichen, D. S., 412 Steinberg, H . , 350, 41 I , 412 Steinberg, M., 136 Steiner, U.. 96, 105 Steinfeld, J . I., 120, 140 Steinlin, F., 552 Steinmetz, M. G.. 116 Stel'mashok, V. E., 177, 184 Stenberg, V. I., 339, 422 Stenholm, S., 165

63 1

A uthor Index Stensio, K.-E., 372, 427 Stepanov, V. F., 539 Stepanova, E. S., 195 Stephen, M. A., 489 Stephens, R., 16 Stephenson, J. C., 142, 145, 147 Stephenson, L. M., 112 Steudle, W., 105 Stevens, B., 112, 401 Stevens, C. M., 157 Stevens, M. F. G . , 491 Stevens, R. V., 482 Stevenson, K. L., 191, 582 Steward, J. L., 121 Steward, J. M., 363 Stewart, G . W., 132 Stewart, J., 137 Stewart, R. W.,21 Stibor, I., 297 Stief, L. J., 153, 157 Still, I. W. J., 254, 458 Stille, W., 43 Stobie, A,, 490 Stock, C . J., 491 Stolov, A. L., 19 1 Stolte, S., 159 Stone, J., 6, 145, 147 Stone, M. L., 186 Stone, P. G . , 395 Storz, R. H., 165 Stotlar, S. C . , 13 Stout, E. I., 514 Stoyov, A., 543 Straehle, J., 190 Straub, K., 447 Strausz, 0. P., 94, 96, 125, 153, 212, 462,495 Streckert, H . H., 598 Strege, K. E., 589 Strehlow, H., 22, 217 Streith, J . , 31 1, 437 Strelets, V. V., 181 Strelkova, L. D., 534 Stroganov, V. I., 15 Strojny, N., 27 Strom, R. M., 300 Strouse, C. E., 482 Struchkov, Yu. T., 206 Strukov, E. G., 544 Strydom, P. J., 114, 374 Stryer. L., 81, 91 Stuckey, W. C., 521 Studebaker, J., 299 Studzinskii, 0. P., 295, 362, 363, 415, 484 Stufkens, D. J., 199, 200, 202 Stuke, M., 135 Su, T. M. R., 132 Suau, R., 460 Subdo, A. S., 5 Subtil, J . L., 16 Sucharda-Sobczyk. A., 65 Sucrow, W., 469

Sudboe, A. S., 218 Sudoh, M., 414 Siihnel, J., 47, 65 Sugdhara, Y., 514 Suganuma, T., 541 SUgdWard, K . , 153, 155, 159 Sugawara, T., 177, 321, 383, 384, 487 Sugden, J . K., 457 Sugimori, A,, 177, 203, 360, 361 Sugimoto, T., 92, 115, 501, 573 Suginome, H., 409, 423, 439, 440, 456 Sugisawa, H., 215, 465 Sugiyama, H . , 216, 234, 273, 303, 367, 392,451 Sugiyama, K., 584 Sugiyama, T., 361 Suguna, H., 380,496,497 Sukhanov, A. N., 141 Sukumaran, K . B., 430 Sulkes, M., 127, 134 Sullivan, B. P., 184 Sullivan, J. A,, 148 Sullivan, J . V., 3 Sumane, R., 79 Sumitani, M., 31, 46, 55, 94, 119, 301 Sun, J . C., 154 Sun, J . N.-P., 19 Sunamoto, J., 84, 92 Sundberg, R. J., 382, 497 Sundstrom, V., 9 Suprinovich, E. S., 193 Surmeian, A., 17 Surzur, J. M., 454, 463 Susak, N. J., 16 Suschitzky, H., 366, 383, 485 Sutin, N., 178, 181, 182 Suto, E., 583 Sutoh, M., 124 Sutton, J., 59 Suzuki, A,, 439 Suzuki, H., 280, 283, 285, 286, 400, 415, 553 Suzuki, K., 32 Suzuki, M., 257 Suzuki, N., 128, 229, 357, 418, 468 Suzuki, S., 396, 478 Suzuki, T., 8, 103, 518, 528, 543 Suzuki, Y., 508, 518 Suzuoki, Y . , 522 Svejdova, E., 538 Svelto. O., 8 Svezhentsova, A. A., 173 Svoba, O., 562 Swaddle, T. W., 16 Swanson, B. J., 441, 498 Swartz, G . L., 205 Swasey, C. C., 546 Swayambunathan, V., 85. 396 Sweany, R. L., 206, 207

Sweger, D. M., 19 Swenton, J. S.. 246, 446 Swider, W., 153 Sworski, T . J., 158 Syamal, A,, 550 Syassen, K., 47 Sydnes, L. K., 245 Sykora, J., 190 Szabo, A., 9, 43, 87 Szajda, M., 492 Szcepanski, J., 7 Szczesniak, M., 65 Sze, N. D., 152 Szilagyi, G . , 271, 281, 366, 422, 448, 498 Sztuba, B., 128, 333, 334 Szues, K., 73 Szwarc, H., 18 Tabata, Y., 108, 512, 524 Tabita, E., 361 Tabuchi, K., 506 Tachibana, H., 15, 26, 89 Tachibana, M., 48 Tachibana, T., 371 Tada, M., 358, 439, 455 Tagdwa, M., 541 Tagawa, S., 106, 108, 512, 524, 534 Taghizadeh, M. R., 5 Taguke S., 528 Tait, B. L., 4 Tajima, M., 362 Takada, K., 177 Takada, T., 361 Takagi, K., 361, 368, 495 Takagi, M., 343, 398, 425, 452, 493,494 Takagi, N., 428 Takahashi, A., 514, 599 Takahashi, K., 80, 326, 425, 52 I . 527 Takahashi, M., 340 Takahashi, S., 514, 521 Takahashi, T., 336, 426 Takahashi, Y., 440, 584 Takamatsu, S., 428 Takamiya-Ichikawo, K., 51 Takamuku, S., 328, 496 Takano, S., 340 Takao, S., 165 Takashi, T., 336 Takata, S., 332, 468 Takatoku, K., 306 Takayama, H., 406 Takayama, K., 438 Takayama, M . , 327 Takayanagi, T., 183, 576 Takatsuka, K., 130 Takechi, H., 288, 441, 443 Takeishi, M., 507 Tdkemoto, K., 513, 544 Takemuku, S., 302 Takemura, F., 526 Takemura, T., 59. 128

632 Takeshita, H., 250, 278, 404, 412 Takeuchi, H., 485 Takeuchi, K., 37, 148, 21 1 Takeuchi, M., 574 Takeuchi, Y . , 462 Taki, T., 474 Takiguchi, T., 392 Takizdwa, T., 595 Takumd, K., 183, 398, 579 Takuwa, A., 280, 292, 396 Talebinasab-Sarvari, M., 188 Taliani, C., 46 Talley, L. D., 156 Talsky, G . , 520 Tamagaki, K., 139 Tamagaki, S., 419 Tamaki, S., 277 Tamas, J., 462 Tamoto, K . , 412 Tamura, H.. 584 Tamura, S., 101, 487 Tamura, Y . , 419, 425, 445, 482 Tan, K. L., 51, 527 Tanaka, F., 92 Tanaka, H., 337, 431, 508 Tdnaka, I., 23, 127 Tdnaka, M., 516 Tanaka. S., 440 Tanaka, Y . , 23, 131, 165, 424, 553

Tang. I. N., 155 Tang, K. T., 154 Tani, K . , 419 Tanielian, C., 279, 540, 546 Tanigaki, K., 104, 506 Taniguchi, H . , 300, 484 Tanimoto, S., 92, 573 Tanimoto, Y., 83 Tanimura, K., 82 Tanimura, T., 80 Tanino, H., 495 Tantsyurd, L. Ya., 41 1 Tarakanov, 0. G., 539 Tdshita, N., 32, 76 Tassell, C., 15 Tatarsky, D., 200 Tatemitsu, H., 79, 492 Tatischeff, I., 31, 87 Tausch-Treml, R., 34, 83 Tavares, M. R., 444 Taylor, C . , 16 Taylor, D. J., 202 Taylor, Ci. N., 343, 347 Taylor, J . A., 366 Taylor, J. R., 8, 12, 34 Taylor, R. L., 28, 131, 217 Tazaki, M., 494 Tazaki, T., 495 Tazuke, S., 420, 507, 508 Tazuki, S., 524, 528 Tedeschi, P., 338, 431 Teichner, S. J., 410 Telle, H., 137 Teller, H . L., 598

Author Index Tellinghuisen, J., 133, 163 Temchin, S. M., 155 Temps, F., 152 Tenaka, I., 30 Tenbrink, H. M., 122 Tench, D., 587 Teng, Y. C., 23 Te Nijenhuis, B., 362 Tenne, R., 586 Tennekone, T., 595 Teodorovic, A. V., 217 Teppner, U., 138 Terada, K.. 323 Terada, T., 47, 94 Teramoto, M., 543 Teranishi, H., 65, 110, 512, 529, 543 Terashima, H., 361 Terashima, M., 498 ter Horst, G., 128 Teruo, M., 270 Testa, A. C., 79 Tetreau, C., 94 Teuchner, K., 63, 76 Teufel, E., 348 Tewes, E. T., 456 Tezuka, H., 338 Tezuka, T., 368 Tfibel, F., 89 Thakrar, H . , 63 Thamburdj, R. K., 191 Theis, H . C., 422 Theocharis, C. R., 253 Thiebeaux, C., 5, 11 Thiel, F. A., 588, 589 Thiel, W., 39 Thiele, E., 145, 147 Thiem, J., 236 Thijs, L., 505 Thirunamachandran, T., 46 Thistlethwaite, P. J., 33, 61, 86, 88, 525 Thomas, A., 483, 495 Thomas, D. R., 485 Thomas, H . R., 520 Thomas, J.-C., 91 Thomas, J. K., 84, 108, 11 1, 203, 541, 576 Thomas, J. M., 253 Thomas, M. J., 63, 223, 405 Thomas, S. J., 148 Thommen, F., 35, 118, 126 Thomson, P. C. P., 484 Thorne, J. M., 149 Thorne, L. R., 147 Threthwey, K. R., 75 Thrush, B. A,, 132 Thulstrup, E. W., 43 Thurnaver, M . C., 105 Ticke, B., 509 Tiee, J. J., 5, 34, 36, 132, 133, 141 Tien, H. T., 599 Tikhonov, G. P., 176 Tikhonova, T. N., 178

Timm, U., 339, 476 Timnick, A,, 26, 40 Timpe, H. J., 424 Tincer, T., 530, 543 Tincul, I., 547 Tino, J . , 507 Titouani, S. L., 496 Tittel, F. K., 11, 19, 134 Tkachenko, Z. A., 172 Tobita, E., 361 Tobita, H., 215 Tobita, S., 354 Tochtermann, W., 322 Toennies, J. P., 154 Toirov, A., 544 Tojo, M., 293, 376, 498 Toki, S., 325, 361 Tokida, A., 416 Tokumaru, K., 110, 300, 301, 346, 367, 368, 371, 41 1, 413, 43:5, 492 Tokumitsu, T., 452 Tokunagd, K., 209 Tokunagd, Y., 537 Tokunov, Y. M., 159 Tolbert, L. M., 332 Tolstikov, G. A,, 513 Tolusso, T., 514 Tomari, K., 494 Tomaschewskii, G., 436, 437 Tomasik, P., 65 Toniescu, M., 544 Tomioka, H., 332, 414, 468, 417, 478, 481, 482 Toniita, G., 416 Toniita, K., 79 Toniizawa, K., 367, 368, 414 Toniliiewicz, M . , 583 Tomokiyo, K., 192 Tomov, I. V., 12 Tonaka, J., 73 Tonami, H., 549 Toomey, D. W., 154 Topp., M. R.,7, 35 Toptygin, D. Ya., 546 Toribio, F., 125 Torizuka, H., 440 Torr, D. G . , 153 Torr, M. R., 153 Torres, C., 30 Torres, M., 94, 495 Torricelli, C., 338, 431 Toscano, V. G . , 99 Toschak, P. E., 17 Toshida, K., 452 Toth, L. M., 171, 195 Touchard, D., 453 Toupance, G . , 152 Tovborg Jenson, J. P., 535 Toyania, Y., 15 Toyota, M., 428 Trainor, D. W., 12 Traldi, P., 358, 449 Tran, C. D., 89 Trasaran, G . M., 547

Author Index Traub, W. A., 150 Trautmann, W., 3 13 Trave, R., 490 Traverso, G . , 46 Traverso, O., 173, 189, 193, 196, 209 Tredgold, R. H., 599 Tredwell, C. J., 92 Tree, J. J., 26 Treloar, F. E., 51, 527 Tremblay, G . , 150 Trenshnikov, V. M., 518 Tretoba, A. R., 25 Tributsch, H., 589, 590, 593 Tric, C., 26, 122 Tricot, Y., 84 Trimnell, D., 514 Troe, J., 147, 219 Trofimova, E. M., 148 Trogler, W. C., 208 Trostin, A. I., 30 Trott, G . R., 25 Trott, W. M., 164 Trotter, J., 260 Troxler, R. F., 417 Trozzolo, A. M., 483, 495 Truhlar, D. G., 154 Trukhanova, L. N., 536 Truong, T. B., 88 Truscott, T. G, 108 Trzcinska, B. M., 93 Tsai, T. Y. R., 248 Tsao, J. Y., 122, 146 Tsapvilov, A. S., 536 Tsay, F. D., 536 Tschuikow-Roux, E., 131 Tsuboi, M., 132 Tsubomura, H., 74, 587, 594, 595 Tsuchida, E., 182, 526, 527 Tsuchinya, S., 142 Tsuchitani, K., 252 Tsuchiya, S., 282 Tsuchiya, T., 48, 320, 427, 438 Tsuda, M., 334 Tsuda, K., 584 Tsuda, Y., 445 Tsuiki, M., 584 Tsuji, M., 138 Tsuji, T., 283 Tsujimoto, K., 237, 358, 359, 398 Tsukamoto, J., 599 Tsumaki, H., 489 Tsumura, A,, 587 Tsumura, M., 521 Tsunashima, S., 138 Tsunemitsu, K., 528 Tsunoda, S., 518 Tsunoda, T., 518 Tsunooka, M . , 516 Tsuruki, F., 406 Tsutsumi, K., 258, 263 Tsutsui, M., 171 Tsutsui, Y . , 183

633 Tsveteva, V., 531 Tucker, G . , 19 Tuckett, R. C., 28 Tudos, F., 547, 549 Tukada, H., 304, 384 Tuller, H. L., 583, 584 Tully, F. P., 157, 21 8 Tundo, P., 576 Tung, C.-H., 224, 505 Tunuli, M. S., 576 Turchaninov, A. M., 172 Turek, A. M., 47, 93 Turnbull, J. H., 92, 330 Turner, D. W., 35 Turner, E. S., 256, 468 Turner, J. A., 594, 598 Turner, J. J . , 196 Turnock, G . , 491 Turro, N. J., 36, 83, 84, 98, 102, 111, 115, 224, 225, 226, 235, 279, 348, 403,478, 505 Tusa, J., 127, 134 Tway, P. C., 40 Twin, R. J., 162 Twist, J. R., 162 Tyakht, V. V., 145 Tyler, D. R., 198, 207 Tyutereva, A. F., 550 Uchida, K., 25, 128 Uchida, T., 423, 439, 456 Uchino, O., 21 Uda, H., 278 Ueba, Y., 192, 529 Ueda, H., 477,494 Ueda, K., 410 Ueda, Y., 409 Uehara, M., 543 Ueno, A., 425, 521, 527 Ueno, K . , 351, 425 Ueno, Y., 450,462, 553 Ufermann, D., 66, 471 Uker, M., 516 Ulitskiy, N. I., 19 Ullal, H., 599 Umchara, K., 541 Umehara, Y., 232 Umemoto, H., 138 Umemura, J., 20 Umino, H., 216 Umrigar, P., 483, 495 Umstadter, D., 5 Umstead, M. E., 155, 161 Uneberg, G . O., 24 Uno, T., 425, 445, 544 Unterberg, U., 219 Upton, L. M., 33, 75 Urban, W., 21 Urbanek, Z. H., 93 Urbanova, M., 91 Uriotte, A. K., 99 Ushi, Y., 359 Ushiki, H . , 505 Usmanov, A., 550 Usov, 0. M . , 190

Ustinov, V. A., 544 Usui, M., 365 USVydtSOV, A. A., 559 Uvarov, A. V., 501 Uyeta, M., 365 Uzer, T., 163 Vacek, K., 91 Vadimsky, R. G., 589 Vadlamani, B., 330 Vaida, V., 24, 28, 165 Vaidyanathan, S., 75 Vail, G . L., 150 Vainas, B., 586, 587, 594 Vaisberg, S. E., 539 Vakhrnsheva, N. A,, 513 Vala, M . , 68 Valasek, J., 516, 534 Valat, P., 13 Valigura, D., 190 Vanaja, P. K., 380, 496 Van Arendonk, R., 375 Van Audenhove, M., 247 van Blovis, F. I., 531 Vance, R. L., 138 van Craen, J., 135 van Damme, H., 27 Van den Berg, J. A., 194 Vandenberg, J. M., 586 van den Bergh, H., 134, 144, 145, 147 van den Ende, D., 159 Van den Heuvel, C. J. M., 350, 41 1. 412 Vanden Kerchove, F., 596 Van der Auweraer, M., 76, 79, 83, 86, 523 Van der Heijden, H., 196 van der Plas, H. C., 433 Vandersall, M., 127 van der Stoel, R. E., 433 van der Veen, J. M., 275 Vanderwalle, M., 247 van der Westhuizen, J . H., 232, 399 van Duyne, R. P., 24, 25 Van Eldik, R., 194 Van Erum, J., 510 van Houten, J., 175 Van Kooten, J. F. C., 104 van Leeuwen, K. A. H., 8 Van Lommen, G . , 322 Vanmaekelbergh, D., 596 Van Neerbos, A., 501 van Noort, 0. C. M., 252, 258 van Noort, P. C. M., 312,422 Van Oosterhaut, A. C. J., 519 Van Overmeire, F., 596 van Putten, R. G., 325 Vanquickenborne, L. G., 173, 187 Vansteenkiste, T. H., 22 Van Strient, A. J., 104 Van Tassel, K. D., 186 van Veenendaal, H . J., 18

634 Van Vliet, N. P.. 402 van Veen, N. J. A., 132, 133, I35 van Woerden, H . F., 280 van Woerkom, P. C. M . , 18 Vargas, F., 352, 467 Varghese. T.. I 1 Vargiu, S.. 501 Varisova, E. G . , 505 Variu, C., 547 Varlamova, N. V., 544 Vasilenko, V. V.. 530 Vasilev, B. I., 141 Vasilyak. L. M., 159 Vassilopoulos, G., 115 Vasudev, R., 28, 126 Vaucher. A. M.. 6 Vaughn, C., 130 Vedeneev, A . A., 4 Vedeneev. V. I., 217 Veeger, C., 89 Veinberg, N., 518 Vekey, K., 462 Velghe, M . , 157 Vendt. V. P., 316 Venediktov, E. A., 401 Veno, A., 80 Verboom, W., 294 Verdeyen, J. T., 10, 135 Verdu, J., 530, 532, 543 Verniolle, J., 583 Verrall, R., 89, 101 Vervisch, P., 138 Vesely, R., 541 Vetesnik, P., 238 Viallefont, Ph., 496 Vichutinskaya, E. V., 550 Vidal, A., 516 Vidal, C. R.. 1 1 Viehboeck, F. P., 583 Vigneron, J., 588 Viktorova, T. I., 506 Vilarrasa, J., 480 Vincent, M . A,, I15 Vincze, L., 177 Vink, P., 530, 531, 546 Vinogradov, I. P., 162 Vior, G., 41 Viriot, M. L., 80 Visca, M., 181, 573, 585 Vishnyakov. N. A., 141 Visser. A. J. W. G., 89 Visser, R. G., 460 Viswanath, A. K., 189 Viswanath, R. P., 551 Vitan, F., 507 Vittimberga, B. M . , 239, 342, 453 Vo-dinh, T., 28, 29 Voedz, H . G., 551, 552 Vogel, P., 236 Vogler, A., 180, 189 Vogt, B. S., 40 Vogt, J., 118, 121 Voigt. B., 253

Author Index Voitlander, J., 105 Volkert, O., 539 Volkov, A. Yu., 4 Volodarskii, L. B., 436 von Raben, K., 25 Von Schutz, J. U., 105 Von Sonntag, C., 108, 110, 212, 463 von Zelewsky, A., 580 Voris, J. S., 105 Vorkunova, E. I., 218 Vormann, H., 21 Vorob’ev, A. Kh., 174 Voronkov, M . G., 216 Voronkov, N. N., 216 Vos, J. G., 180 Voynick, T . A., 595 vozzo, o., 121 Vshiutseva, N. S., 505 Vuckovic, M., 192 Wada, A,, 26, 89 Wada, M., 288 Waffenschmidt, R., 379, 429 Wagener, R., 175 Wagner, A. F., 155 Wagner, F.-T., 584 Wagner, G . , 156 Wagner, H. Gg., 145, 152, 157, 218 Wagner, I., 217 Wagner, P. J., 63, 98, 99, 101, 223, 230 Wagner-Jauregg, T., 339 Wahlberg, K., 372, 427 Wahlen, M . , 19 Waite, B. A,, 167 Waka, Y., 85 Wakamatsu, S., 432 Wakefield, B. J., 366 Walch, S . P., 155 Walczak, M . , 361 Wald, K. M., 281, 325, 366, 422,498 Walda, A., I5 Waldeck, D., 9, 32, 73 Walden, G . L., 28, 34, 43, 92 Waldmann, J., 509 Waldorf, A,, 15 Walfbeis, 0. S., 68, 72 Waligora, B., 534 Walker, R. B., 154 Walker, S. M . , 523 Walker, W. C . , 165 Walkow, F., 490 Wallace, J. S., 150 Wallace, W. M., 180 Wallenstein, F. R., 9 Walmsley, S. H., 80 Walsh, P. T., 18 Walsh, T. F., 409 Walters, R. T., 172, 173 Walton, E. C . , 594, 597 Waltz, w. L., 173

Wamhoff, H., 271, 281, 325, 366, 422, 448, 449, 498 Wainpler, F. B., 26, 34, 36, 132, 133, 141 Wampler, J. E., 29 Wan, J. K. S., 104. 201 Wandelt, B., 534, 535, 538 Wang, J. H . . 587 Wang, L. H., 508 Wang, P. Y. K., 525 Waiig, T., 349 Waiig, Y., 35.76 Wang, Y.-N., I 1 Wani, M. C . , 307 Wantuck, P. J., 34, 133 Ward, J. L., 28, 92, 262 Ware, W. R., 33, 51, 80, 87, 345 Warneck, P., 150 Warner, I. M., 26 Warren, F., 225 Warren, L. F., 587 Warrener, R. W., 224 Wasgestian, F., 173 Washida, N., 124, 151, 154, 155, 157 Washio, M., 524 Wassam, W. A., 128 Wasserman, H. H., 41 1 Watamoto, H., 549 Wdtdnabe, A., 541 Watanabe, S., 351, 370, 544 Watanabe, T., 372, 413, 595 Waters, P. J., 541 Watkins. A. R., 56, 75, 100 Watkins, P. E., 492 Watson, D., 261, 379, 429 Watson, D. G., 236 Watson, J. K. C., 155 Watson, R. T., 30, 150, 155 Watson, T. A,, 145 Watson, W. H., 404 Watt, W. R., 501, 518, 519 Watts, R. J., 186, 187, 188 Wawrik, s., 365 Wayne, R. P., 15, 162 Weaver, P. F., 571 Webb, J. A,, 12 Webb, K. K., 518 Webber, S. E., 101, 524, 527 Weber, G., 33, 43, 88 Weber, W.-D., 232, 395 Weber, W. P., 213, 463 Websler, C. R., 12, 37, 138 Websrer, D , 96 Weddle. G., 212, 463 Wedlock, D. J., 541 Weedon, A. C . , 269, 336, 408, 42 7 Weeks, C. M., 277 Wegdam, G. H., 23 Wege, D., 489 Weglowska, W., 455 Wegner, G., 509 Wehrlr, H . , 281, 442

Author Index Wehry, E. L., 41 Weichmann, J., 206 Weichsel, C., 391, 493 Weidenhammer, K., 197 Weigert, F. J., 205 Weinberg, E., 142 Weinberger, B. R., 599 Weiner, A. M., 17 Weiner, J., 136, 165. 167 Weir, N. A., 534, 536 Weiss, B., 239, 392, 495 Weiss, E., 198 Weiss, P. S., 21 Weisshaar, J. C., 121 Weissman, S. I., 474 Weissmann, W., 583 Weitkamp, C., 18 Weitz, E., 145 Weitz, R., 420 Welford, D., 12, 34 Welge, K. H . , 161, 162 Welker, T., 19 Weller, A., 53, 101, 181, 386 Welling, H., 5 Wells, C. H. J., 65 Wells, J. S., 19 Wende, B., 14 Wender, P. A., 347 Wendisch, D., 282 Wendling, F., 475 Wendoloski, J . J., 119 Wenning, U., 25 Wenska, G., 274,450 Wentrup, C., 492 Wermer, P., 207 Wessel, J. E., 24 West, M. L., 45 West, R., 213, 214, 463 Westby, M. J., 32 Westheimer, F. H., 484 Weston, R. E., 126, 145, 162 Westover, D. L., 340 Wetter, W. P., 478 Wetzel, H., 25 Weulersse, J. M., 140 Whang, C. W., 478 Wheeler, B., 593 Wheeler, D. M. S., 389 Whitbeck, M. R., 18 White, A. H . , 243 White, E. H . , 116, 418 White, H . S . , 593, 597 White, J . D., 461 White, J . M . , 585 White, L. S., 312 Whitfield, R. H., 549 Whitney, R. A., 445 Whitsel, B. L., 478 Whitt, D. G., 502 Whittall, J., 114, 374 Whitten, D. G., 75, 171, 179, 369, 401, 509, 575 Whitten, W. B., 17 Whittle, E., 491, 492 Whybrow, D., 265

635 Wicher, J . , 197 Wieckowski, A,, 36, 118 Wieldmann, J . , 32 Wierzechowski. J., 65 Wiersma, D. A,, 32 Wiesenfeld, J . R., 31, 134, 150, 153, 156, 157 Wiesner, K., 248 Wiessenfeld. J . M., 6, 32, 91 Wieters, W., I17 Wight, C. A., 146 Wightman, R. H., 490 Wihan, L., 550 Wijnaendts van Resandt, R. W.. 34, 73 Wilbourn, K . O., 410 Wilbrandt, R., 102, 103 Wilcomb, B. E., 133 Wild, V. P., 53 Wilder, D. R., 22 Wildes, P. D., 116 Wildman, D., 165 Wildt, J., I57 Wiles, D. M., 41 I , 529, 530, 546, 548 Wilkerson, T. D., 21 Wilkinson, J. M., 248 William, J. O., 33 Williams, C. W., 26 Williams, D. J., 79, 526 Williams, G. J., 330, 498 Williams, J . L. R.,211, 378, 468 Williams, J. R., 247, 264, 277, 467 Williamson, A. D., 127 Willig, F., 82 Willis, C., 142, 145 Willis. J. B., 22 Willner, I., 572, 595 Willsher, C. J., 595 Wilson, B. M., 132 Wilson, D. A., 423 Wilson, R. M., 409 Wilson, R. H., 583, 595, 597 Wilson, T., 33, 96, 98 Wilson, W. L., 1 1 , 134 Wilt. J . W., 471 Wimmer, F. L., 189, 209 Winckelmann, I., 339, 435 Windsor, M. W., 92 Wine, P. H . , 151, 152, 156 Winefordner, J. D., 28, 34, 43, 92 Winn, J. S., 209 Winn, K. R., 34, 68 Winnewisser, M., 492 Winnik, M. A., 63, 86, 102, 524, 527 Winter, G. C., 96 Winter, H.-W., 485, 492 Winter, R., 157 Wirth, M . J., 9, 23 Withnell, R., 9 Witte, K.-J., 1 1

Witterman, W. J . , 4, I 1 Wittig, C., 5, 133, 142, 145, 149 Wodarczyk, F. J., 138 Wohlers, H. D., 186 Wojtczak, J . , 546 Wolf, H. C., 105 Wolf, H. R., 256, 257, 258, 263, 267, 319 Wolf, R. J., 154 Wolfe, J . F., 497 Wolff, G., 236 Wolff, H. R., 329 Wolff, S., 242, 255, 482 Wolff, T., 83, 92, 11 I , 378, 379, 417, 429 Wolinski, L., 534 Wolk, G. L., 162 Wolleben, J., 79 Wolner, D., 402 Wong, D., 30, 35 Wong, J., 422 Wong, J. K., 116 Wong, P. C . , 311 Wong, S. K., 104 Wong, Y . M., 80 Wood, C. P., 119 Wood, D. G. M., 520, 530 Wood, E. M., 7 Wood, J . , 130 Woodgate, B. E., 14 Woodruff, W. H., 208 Woods, R. J., 173 Woodworth, J . R., 164 Wooffer, N., 12 Woolfe, G. J., 33, 61, 88 Wormsbaecher, D., 200 Worsham, P. R., 509 Woste, L., 12 Wren, D. J., 26, 138 Wright, H . J., 130 Wright, J. J., 137 Wright, R. D., 595 Wrighton, M. S., 196, 199, 201, 202, 203, 205, 206, 208, 395, 396, 587, 588, 589, 593, 594, 597 Wrobel, D., 92 Wroblowsky, H.-J., 490 Wryzykowska, K., 59, 81 Wrzyszczynski, A., 502 w u . C.-z., 10 Wu. D., 30 WU. J.-C., 197 Wu, S. K., 523 Wu, T., 138 Wubbels, G. G., 99, 356, 44 1 Wunderlich, W., 536 Wyart-Remy, M., 580 Wyatt, R., 8, 12 Wynberg, H., 407 Wyrzykiewicr, E., 492 Xuan, C. N., 219

636 Yabe, A., 383, 487 Yabi, Y., 552 Yablonovitch, E., 21, 122, 140 Yadav, V. S., 380, 496 Yagi, K., 92, 361 Yagi, M., 104 Yagi, S., 159 Yagihara, M., 407 Yahiro, S.. 82 Yakhimovich, R. I., 316 Yamada, A,, 183. 191, 397, 529 Yamada, C., 19 Yamada, K., 381 Yamada, S., 27, 253, 406 Yamada, Y.. 115, 232, 358,455 Yamafi, T., 115 Yamaguchi, H . , 428 Yamaguchi, Y., 85 Yamakawa, T., 553 Yamamoto, A., 435 Yamamoto, K., 199, 372, 506, 559 Yamamoto, M., 47, 96, 328, 524, 533 Yamamoto, S., 386 Yamamoto, T., 243, 516 Yamamoto, Y., 323 Yamamura, S., 115, 194 Yamanaka, C., 6 Yamaoka, T., 518 Yamase, T., 581, 582 Yamashita, I., 389 Yamashita. K., 599 Yamashita, Y., 243, 328, 368, 414, 437, 452 Yamauchi, S., 96 Yamazaki, H . . 508 Yamazaki, K., 474 Yamazaki, M., 450 Yamazaki, N., 529 Yamazdki, T.. 270, 336, 426, 475 Yang, D. B., 174 Yang, N., 76 Yang. N. C., 349 Yang, N. L., 533 Yang, S. C., 126. 364 Yang, Y., 10. 41 Yang, Y.-S., 1 I Yang. Z., 11 Yanishihikova. T. M., 546 Yano, M . , 533 Yano, S., 538 Yano, T., 131 Yany, F., 407 Yardly, J . T., 37, 165, 205 Yasa. Z. A., 13 Yashchuk, V. P., 212 Yashuk, V. N., 523 Yasmenko. A. I., 31 Yasuda, M., 340, 341, 356, 398 Yasuda, S., 438 Yates, P.. 226, 422 Yatsunami. T., 390 Yavronian. A,, 528

Author Index Yee, K. C., 509 Yeh, S. M., 81 Yekta, A., 84 Yen, T. N., 514 Yencha, A. J., 138 Yersin. J . R., 192 Yesaka, H . , 32 Yeung, E. S., 41 Yim, G. K., 581 Yiu. C. Y., 589 Yogev, A., 21, 145 Yokoe, I., 375, 427 Yokota, H., 183 Yokota, M., 203 Yokoya, H., 115 Yokoyama, K., 355 Yokoyama, M., 183, 526 Yoneda, H., 178 Yonemitsu, O., 181, 243, 381, 495, 497 Yoneshige. Y., 516 Yonetmi, K., 227 Yoneyama, H., 584 Yonezawa. Y., 595 Yoshida, A,, 543 Yoshida, C., 498 Yoshida, K., 6, 390, 392 Yoshida, M . , 110, 367, 492 Yoshida, T., 450, 462,.553 Yoshida, Y., 553 Yoshihara, K., 31, 46, 55, 65, 73, 82, 94, 119, 301 Yoshihara, M., 227, 507 Yoshiie, S., 194 Yoshinaga. M., 386 Yoshioka, M., 256 Yoshizawa, N., 74. 595 Yoshizawa, T., 32 Young, D. W., 457 Young, E. F., 14 Young, J . F., I I Young, R. H . , 31, 150, 157 Young, R . J., 520 Young, R. N., 399 Young, S. D., 307 Youngstrong, R. E., 454 Yu, T. Y., 508 Yu, Y. C . , 134 Yur’ev. V. P., 206 Yur’ev, Yu. G., 371 Yusoff, M. F., 549 Yushchenko, T. S., 501 Yuzhakov, 0. A,, 509 Zaagsma, J., 66 Zabel, F., 157 Zabel, R. W., 269, 336, 427 Zacharias, H . , 9, 161, 162 Zachariasse. K. A., 53 Zafiriou, 0. C., 99 Zahniser. M . S., 152 Zahradnichova, A,, 548 Zaitseva, N. I., 546 Zakaria, Z., 373, 427 Zakrzewski, A,, 502

Zaks, I., 518 Zdlupsky, P., 385 Zamir, E., 147, 167 Zanioiskaya, L. V., 527 Zaniorsky, Z., 550 Zanipetti, P., 139 Zana, R., 83 Zanella, A. W., 188 Zang, B., 490 Zaninelli, M., 581 Zapka, W., 12 Zare, R. N., 12, 37, 137, 138, 142 Zasavitsky, I. I., 19 Zauadzkas, G. A,, 10 Zechner, J., 59 Zeelen, F. J., 402 Zegarski, B. R., 28 Zeiger, H . G., 597 Zeigler, J. M . , 447 Zeiri, L., 34 Zelenev, Yu. V., 527 Zelenkova, T. N., 546 Zelenskii, S. E., 212 Zelent, B., 360, 361 Zellmer, V., 490 Zellner, R., 156, 157, 218 Zellweger, J. M., 134 Zemel, H., 98 Zen, S., 385 Zewail, A. H., 17, 43 Zhao, Y. L., 508 Zharkikh. T. P., 551 Zharkov, I. P., 529 Zheleznikova, M . V., 544 Zheng, S.-D., 10 Zhidkova. L. A., 550 Zhu, J.-S., 11 Zhu, Z.-H., 200 Zhugalkin, A. K., 141 Zidler, B., 181 Ziebig, R., 94, 115 Ziegler, J. P., 595 Ziegler, M. L., 197, 198, 201, 206 Ziemer, J. N., 598 Ziemiecki, H . W., 83 Zigler. A,, 7 Zilinskas, B . A,, 35 Zilio, S. C., 20 Zinirnerman. H. E., 81, 223, 275, 276, 306, 307 Zimmerman, I. H., 165 Zimmermann, P., 138 Zimmermann, S., 29 Zinalo, E., 174 Zinc, J. I., 116 Zink. J., 200, 207 Zinnen, H. A,, 210 Zinner, K., 29 Zinth. W., 24 Zipf. E. C., 153 Zittel, P. F., 150 Zitter, R. N., 146 Zliechovcova. H., I77

A uthor Index Zmora, H., 7 Zois, J., 115 Zschokke-Griinacher, I., 47 Zubov, V. P,,529 Zuidema, R. J., 4

637 Zuk, A., 505 Zunibrunnen, H.-R., 580 Zumofen, G., 80 Zupan, M., 344 Zupancic, J . J., 479

Zvava, I., 544, 555 Zweifel, G., 467 Zweigenbaum, S., 7 Zwicker, W. K., 6 Zyat’kov, I. P., 527