Photochemistry (Volume 07)

A Specialist Periodical Report

Photochemistry Volume 7

A Review of the Literature Published between July 1974 and June 1975

Senior Reporter D. Bryce-Smith, Department of Chemistry, University of Reading Reporters M. D. Archer, The Royal lnsfifufion, London H. A. J. Carless, Birkbeck College, London A. Gilbert, Universify of Reading W. M. Horspool, Universify of Dundee J. M. Kelly, Universify of Dublin, Eire D. Phillips, Universify of Soufhampfon S. 1.Reid, Universify of Kent at Canferbury K. Salisbury, Universify of Soufhampton

@ Copyright 1976

The Chemical Society Burlington House, London W I V OBN

ISBN :0 85186 065 6

ISSN : 0556-3860 Library of Congress Catalog Card No. 73-17909

Organic formulae composed by Wright's Symbolset method Printed in Great Britain by John Wright and Sons Ltd. at The Stonebridge Press, Bristol BS4 5NU

Introduction and Review of the Year

In Volume 7 we retain essentially the same layout as in Volume 6, except that the Chapter on Developments in Instrumentation and Techniques is being deferred until Volume 8 where it will form part of a biennial review of this area. This is the first Volume of ‘Photochemistry’ to suffer the general restriction on length which the Chemical Society has been obliged for economic reasons to apply to all Specialist Periodical Reports. Some Reporters have found this restriction more irksome than others. We hope, however, that the general quality has not suffered unduly; but we shall as always be grateful to receive any comments from readers which may help us to preserve or improve the quality of the presentation and the critical content without adding to the length. On the theoretical and spectroscopic side of the subject, one of the more interesting developments during the year has been the reformulation by Colpa on a strict SCF approximation of Hund’s rules for predicting the ordering of electronic states. This appears to avoid some of the difficulties recently recognized in the conventional basis of these rules. Calculations on NH and CH2 have led Colbourn to question the normal assumption that electrons in triplet species are more widely separated than in the corresponding singlets. One may also note the important survey of effects of polarization in fluorescence measurements presented by Cehelnik and his co-workers. Correction for such effects may sometimes be necessary. There has been considerably increased experimental and theoretical interest in two-photon processes during the year from a number of groups, and Swofford and McClain have given a full description of a two-photon excitation spectrometer. Birks has emphasized the precautions which are necessary to eliminate errors in the measurement of molecular fluorescence parameters of aromatic molecules, for example those due to self-quenching, and has questioned the accuracy of many published data. The growing list of molecules showing fluorescence from S2states now includes thiophosgene and various other thiocarbonyl compounds (Levine, de Mayo) and 1,2-benzanthracene (Nickel). The fluorescence from S, thiophosgene has the remarkably high quantum yield of 0.7. As with the well-known case of azulene, this phenomenon appears to be associated with a large energy gap between the Sland S, states, and the absence of any efficient radiationless transformations of the S2 state. There has been considerable interest in benzene during the year. The rearomatization of valence-isomers of benzene has been recently discussed in detail separately by Dewar and Dorko, and their co-workers. Stein and his co-workers have confirmed that benzvalene arises from vibrationally excited Sl benzene, and report that the population of non-totally symmetrical vibrational

iv

Introduction

levels plays an important role in the process. Knight, Parmenter, and Schuyler have presented an excellent study of the single vibronic level fluorescence spectra of benzene which has confirmed and established 28 absorption assignments in the So S, band. In another important study, Wunsch, Neusser, and Schlag have used a two-photon method to populate upper vibronic levels of S, benzene vapour, and have reported the surprising result that the 14; level has a nonradiative lifetime longer than that of the zero-point level. This effect may be related to the interesting observation that the frequency of the ~ 1 vibration 4 in the S1state is abnormally greater than that in the So state: the phenomenon is also observed with aniline, and may well be more general. This study is also relevant to the general consensus of opinion which is developing that the hitherto rather mysterious Channel I11 non-radiative process in S, benzene is in fact the S, So internal conversion (Heller, Freed, and their co-workers). There is, however, a considerable body of chemical evidence that S,benzene has a tendency to undergo intramolecular rneta-bonding to give the ‘prefulvene’ biradical : it was pointed out in 1966 that this process should be symmetry-allowed from S, benzene (Bryce-Smith and Longuet-Higgins). In the writer’s opinion, the energy-dissipating Channel I11 process may well involve formation of the prefulvene biradical in its electronic ground state, probably by a thermally activated route, followed by the rearomatization of this singlet biradical to Sobenzene in competition with its conversion into benzvalene and fulvene. It is interesting that internal-conversion processes of the S, -+ So type are being increasingly considered as important in other molecules, for example naphthalene and higher condensed aromatic hydrocarbons, and even in some highly halogenated ketones (Hackett and D. Phillips, Gillespie and Lim, inter alia). For some aromatic compounds, however, and p-difluorobenzene is an example, the fluorescence quantum yield is unity. The irradiation of a mixture of benzene and deuterium at 254 nm gives CGH6Dwith quantum yield 0.01. This product was not found on irradiation at shorter wavelengths, so the process may not compete effectively with Channel I11 (Hellner and Vermeil). The use of a tunable dye-laser has made possible several studies on the excitation of individual vibronic features of some simple aldehydes, e.g. formaldehyde and glyoxal. The results have provided interesting evidence concerning the mechanisms of energy transfer (Lineberger and co-workers, inter alia). The controversial question of possible effects of oxides of nitrogen and Freons on ozone levels in the upper atmosphere is stimulating numerous studies of related chain-reaction processes, especially those involving chlorine atoms (see Part I Chapter 3), and extraterrestrial photochemical phenomena. We now even have a discussion of the photochemistry of hydrocarbons in the atmosphere of Titan (Strobel)! For obvious reasons, there is also growing interest in the photochemistry of polluted urban atmospheres and the formation of ‘photochemical smog’ (Part I Chapter 3). The same Chapter also contains a description of two important applications of lasers, firstly the remote sensing of atmospheric components and pollutants, and secondly the use of a narrow spectral bandwidth for selective excitation of single components of mixtures. The latter application has been employed to give isotope separation of H 3 T l and H3’Cl: more sinisterly, ZS6Uand 238U have been separated on a laboratory scale. Any scientific --f

--f

Introduction

V

development which has the effect of making such potentially dangerous material as 2 3 6 U more readily available is strongly to be deplored in the present state of human moral achievement. Shetlar has derived non-linear relationships of the Stern-Volmer type suitable for systems in which quenching occurs by more than one mechanism. Rate constants for ‘heavy atom’ fluorescence quenching of polynuclear aromatic hydrocarbons by 1-iodopropane in benzene have been found to decrease exponentially with the energy difference between the fluorescing state and the nearest lower triplet state (Dreeskamp et al,). Bromocyclopropane has been recommended as a heavy-atom quencher of excited singlet states since it is more photostable than simple alkyl bromides (Flemming, Quina, and Hammond). Laser studies with chlorophyll a have provided evidence for the interesting radiationless intermolecular process TI S, -+ T2 So (Menzel). Davidson has provided a valuable review of the role of exciplexes in photoreactions, and has reported exciplex emission from aromatic hydrocarbons and furan. Hirayama and Lipsky have presented an important paper on photophysical processes in simple alkenes, an area rather neglected hitherto : fluorescence quantum yields are surprisingly low. Dewar and Kirschner have reported that the potential-energy surface of triplet dioxetan intersects the surface for the singlet between dioxetan and the transition state for the decomposition of dioxetan to formaldehyde. This finding suggests a reason for the previously known, but rather surprising, thermolysis of dioxetans to produce triplet ketones. The rates of physical quenching of singlet oxygen by some proteins have been found to be approximately the sum of the rates for their amino-acid constituents, notably histidine, tryptophan, and methionine (Matheson and co-workers). There is indeed a high level of continuing interest in singlet oxygen, for example as a photochemically produced air pollutant (probably more of a problem in Los Angeles than in Reading) and as a possible intermediate in enzymatic oxidation processes (although it has been ruled out for the case of lipoxidase). It is interesting that singlet oxygen has been generated by i.r. radiation (> 900 nm) using a cyanin dyestuff as sensitizer (Nathan and Adelman). There is a continuing controversy on the question whether photo-oxidation of alkenes involves a perepoxide or an ene-reaction having a cyclic transition state, but the balance of further evidence is tending towards the latter. However, there is evidence that the transition state may be largely dipolar in some cases, for example certain norbornenes (Jefford and Boschung). Schaap and co-workers have introduced a new cyclic phosphite ozonide derived from cyclohexane-l,3,5-triol as a convenient thermal source of singlet oxygen. Wasserman and Saito have reported that the conversion of diphenyl sulphide into the sulphoxide provides a useful trapping system for dioxetan intermediates formed in photo-oxidation reactions. Saito et al. have provided a possible example of 1,Zaddition of singlet oxygen to the benzene ring. Part I11 Chapter 5 reports a number of continuing studies on the mechanism of quenching of excited states of ketones by amines and hydrazines, and a general scheme involving complexation, electron-transfer, and proton-transfer can be

+

+

vi Introduction advanced with some confidence; but some uncertainty remains whether hydrogenatom transfer ever occurs in solution in a way distinguishable from successive electron- and proton-transfers. Abuin et al. have provided evidence that hydrogen-atom transfer as such may well occur from aliphatic primary and secondary amines to triplet ketones in the gas-phase. Davidson and Wilson have provided further e.s.r. evidence for Schuster and Weil’s earlier suggestion of hydrogen-atom transfer in an excimer of benzophenone formed at high concentrations in benzene. Schuster and Weil now suggest that the same process occurs in carbon tetrachloride, where the radical p-PhCOC,H,- formed by disproportionation of the excimer abstracts chlorine from the solvent to give p-chlorobenzophenone and C,Cl,. Among solvent effects in this area reported during the year, Suppan’s observation that Michler’s ketone is far more reactive to photoreduction in cyclohexane than in ethanol is of particular interest. The photochemistry of carbonyl compounds still continues to be a major general area of interest, and physical methods, especially e.s.r., CIDNP, and CIDEP (electron polarization), continue to be widely applied for detection of radical-like transient intermediates. Qwinkert and Jacobs have provided further evidence that ring expansion of cyclobutanones to oxacarbenes, and thence to tetrahydrofurans, occurs in a concerted fashion without the intermediacy of biradicals formed by Norrish Type I fission of a C-CO bond. Medary et al. report that Norrish Type I cleavage of 2-ethylcyclopentanoneis non-stereospecific, and gives the cis- and trans-hept-4-enals : previous reports (Srinivasan and Cremer, 1965) that reactions of this type are stereospecific appear to require revaluation. Wagner and Liu have reported an interesting study of 1,4-biradicals formed by Norrish Type I1 processes. It is becoming evident that conformational equilibria in excited states can critically determine quantum yields for some Norrish Type I1 processes (Alexander and Uliana; Lewis and co-workers). In some cases of this type, substituent effects have suggested that intramolecular charge-transfer complexation may be important (Kanaoka and Migita). Bicham and Winnik have applied the principle of intramolecular oxetan formation to link two substituent groups para to each other in a benzene ring. A paper by Bradshaw et al. has cast doubt on the long-standing belief that unstable intermediate oxetens are formed by photoaddition of carbonyl compounds to acetylenes; but it would in the Reporter’s opinion be premature at this stage completely to reject the idea of intermediate oxetens in all processes of this type, and the possibility of effects resulting from the presence of oxygen or peroxides needs further investigation. The use of vinylcyclopropanes as the ethylenic moieties in photoadditions to benzophenone and benzaldehyde appears to show clearly that the oxetans arise by a biradical pathway rather by concerted addition (Shimizu and co-workers). In Part I11 Chapter 2, allusion is made to several reports on bichromophoric systems in which two photoreactive components are separated by a polymethylene chain, e.g. bismaleimides. In some cases, but not all, ground-state interaction between the two components appears to be of importance in the photoprocesses. Noyori and Kato have provided evidence for the transient existence of transcyclohexenone.

vi i

Introduction

It has previously been thought that 1,3-acyl shifts occur uniquely by singlet mechanisms, the triplet processes giving 1,2-shifts : several examples of triplet 1,3-acyl shifts have now been reported (see Part I11 Chapter 2). The occurrence of photochemical Diels-Alder reactions has always seemed slightly at variance with Woodward-Hoffmann concepts, so it is interesting that Epiotis and Yates have now described a theoretical treatment of these processes. The photochemistry of aromatic systems continues to attract a good deal of interest. Photochemical ring-transposition reactions (e.g. 0- -+ rn-xylene, pyridazines += pyrazines) have previously been interpreted in terms of intermediate benzvalenes and other valence-bond isomers. Barltrop and Day have now suggested that it would be more profitable to concentrate on the numerous patterns of ring-transposition processes which are theoretically possible rather than to speculate on the chemical intermediates which may be involved. This is a stimulating new approach, but it remains to be seen whether it will prove useful in practice, for there do not appear to be any ring-transposition processes presently known which cannot be interpreted in terms of intermediate benzvalenes etc. Lutz and Stein have reported that the quantum yield for the formation of benzvalene from benzene at 254 nm is independent of temperature over the range 9-50 "C. The finding is contrary to previous work, and must be regarded as controversial. Haszeldine and his co-workers have added to their previous reports on the formation of Dewar-isomers and prismanes from polyCperfluoroalky1)benzenes. Although the photoisomerization of indenes to the non-aromatic isoindenes was originally reported by Roth in 1964, Feast and Preston have now shown that perfluoroindene also undergoes this rearrangement in a process which appeared to provide the first example of a sigmatropic 1,2fluorine-shift. Two apparently contradictory independent reports on the cycloaddition of furan to benzene have appeared (Berridge et al., Cantrell); but these are in fact less discrepant than appears at first sight, for most of the differences between the two sets of findings result from the different experimental conditions used. These reports provide the first known examples of the cycloaddition of two monocyclic aromatic systems. In one of the most interesting reports to appear during the year, Tazuke and Ozawa have provided the first example of the abiological photofixation of CO, in the formation of 9,lO-dihydrophenanthrene-Pcarboxylicacid from irradiation of phenanthrene and carbon dioxide with an amine in dimethyl sulphoxide or dimethylformamide. Naphthalene and some other polycyclic aromatic systems also seem to react similarly. A photochemical Reimer-Tiemann reaction has been reported (Hirao et al., cf. Akiyama et al.). Disciples of Woodward and Hoffmann will be intrigued by the ~4~ + ~ 2 + , ~ 2 , 7r4, ~ 2 , 7~2, cycloaddition described by Inoue, Kaneda, and Misumi. A reinvestigation of the photochemistry of diphenylacetylene by Ota has provided evidence for the intermediate formation of the isomeric 2-phenylbenzocyclobutadiene as an unstable green crystalline compound which is a precursor of the dimers 1,2,3-triphenylazulene and 1,2,3-triphenylnapht halene.

+

+

+

v iii

Introduction This remarkable isomerization provides the first known example of the intramolecular cycloaddition of an acetylenic bond to an aromatic ring. Houser and his co-workers report that the irradiation of anisole gives m-cresol, possibly via cyclohexadienone rearrangement of a keto-tautomer of p-cresol. An interesting 1H-aza[l3]annulene has been synthesized by Anastassiou and Elliott by a photochemical procedure. The 1 H parent appears to be aromatic, but the N-acetyl and N-methoxycarbonyl derivatives appear to be non-aromatic. The photo-Fries rearrangement continues to find numerous new applications, and a potentially useful rneta-photo-Fries rearrangement has been observed by Siuta and his co-workers in a suitably constrained system. Examples of the photoisomerization of pyrazoles to imidazoles have been reported by Nishiwaki et al. In the photoisomerization of perfluoroalkylpyridazines to the corresponding pyrazines, Chambers et al. have shown that an intermediate diaza Dewar-benzene is involved rather than a diazaprismane. Ogata and Takagi have observed a novel photoisomerization of 2-pyridylacetonitrile to o-aminobenzonitrile, possibly via a Dewar-intermediate. Nitrile methylides can conveniently be generated by photolysis of azirines, and are useful in 1,3-dipoIar additions to form various heterocyclic systems (Schmid, Padwa, and co-workers). There is continuing interest in the photochemistry of oxaziridines. Suginome and Takahashi have provided evidence that the photo-Beckmann rearrangement of oximes occurs in a concerted manner from an excited singlet oxaziridine intermediate. But this mechanism does not apply in all cases of oxime photolysis : for example, o-hydroxyacetophenone oxime gives the corresponding imine, possibly via an initial N-0 bond homolysis (Grellman and Tauer). An oxaziridine is also involved as an intermediate in the irradiation of 1,3,5-tri-t-butylnitrobenzene, although the initial photoproduct is an isolable 3H-indole (Dopp and Sailer). Leitis and Crosby have reported some analogous reactions of N-substituted 2,6-dinitroanilines. Certain a#l-unsaturated amides have been shown to produce p-lactams in high yields: the process seems likely to prove synthetically useful (Hasegawa ef al.). The following valence-bond isomerization has been confirmed as the first example of this process in the thiophen series (Kobayashi et a/.), and contrasts interestingly with the behaviour of furans which isomerize to cyclopropenecarboxaldehydes.

Increased interest in the photochemistry of organosilicon compounds appears to be developing. Silacyclopropanes and silahexatrienes are now being proposed as photochemical intermediates on the basis of trapping experiments: the former compounds appear to be produced by addition of silylenes R,Si to alkenes

ix

Introduction

(Nakadaira et aZ., Ishikawa and Kumada). Jouin and Fourrey have reported that di-7r-silane photochemistry differs markedly from the di-7r-methane type in that cis-trans isomerization predominates : no isomerization to silacyclopropanes appears to occur in some systems, but in others these intermediates have been suggested (Koch et aZ.). Thioketen appears to be formed as an intermediate in the photolysis of 1,2,3-thiadiazole in an argon or nitrogen matrix, but the involvement of thiiren remains uncertain (Krantz and Laureni). Flynn and Michl have obtained o-xylylene from the low-temperature photoelimination of nitrogen from 1,4-dihydrophthalazine. On the basis of trapping experiments with a secondary amine, DeGraff, Gillespie, and Sundberg have suggested that the species shown below is formed in the flash photolysis of phenyl azide: it had a lifetime of 5 ms in the absence of the amine.

In the field of inorganic photochemistry, Zink has presented an interesting molecular orbital analysis of the photochemical reactions of d 3 and d s compounds which complements his previous ligand-field approach and provides predictions in accord with experimental findings. Exceptions to Adamson’s empirical rules for photochemical ligand release continue to appear (Kirk and Kelly). Endicott et al. have provided a critical examination of models for photoredox reactions of transition-metal ammine complexes. They stress the role of the solvent in relaxation of the Franck-Condon excited state to the primary radical-pair products. A study of Cr(bipy)aa+has provided the first report of emission from the quartet state in fluid solution at room temperature (Kane-Maguire, Conway, and Langford). Burdett has reported molecular orbital calculations relating to M(CO), and M(N2), species, where x = 2-6, and has successfully predicted the geometries of Fe(CO), and Cr(CO),. There is, however, still some controversy about the initial product formed on photolysis of Cr(CO),, although the proposal of a structural photoisomer, e.g. (CO),Cr+-O=C, is probably incorrect (Kuendig and Ozin; Turner, Braterman). Two groups (Krausz, Garnier, and Dubois; Agapiou and McNelis) have independently reported that the strange olefin metathesis previously known to occur thermally in the presence of certain complexes of tungsten and related metals can be brought about by a catalyst generated by irradiation of w(C0)e in carbon tetrachloride. Various other reactions can be catalysed by photochemically generated ‘subcarbonyl’ species, for example, 1,4-addition of silanes to 1,3-dienes (Wrighton and Schroeder). Re,(CO),, produces Re(CO), on photolysis, which ‘activates’ molecular hydrogen via the reaction Re(CO), H2-+ H,Re(CO), (Byers and Brown). A species previously described as Re(CO), is now known to be Re(CO),O, (Symons et al.). Some previous reports of ‘uphill’ quenching of triplet states by ferrocene may have arisen from assignment of too high a value for the energy of TI ferrocene

+

Introduction

X

[ETput at ca. 15 000 cm-l (ca. 180 kJ mol-l) by Kikuchi et al.]. The observation that some triplet states of energy lower than this can be quenched, but with lower efficiency, has been ascribed by these workers to charge-transfer; but Gilbert, Kelly, and Koerner von Gustorf have discounted this mechanism, at least for fluorenone and anthracene triplets, preferring an energy-transfer mechanism. This latter interpretation is also supported by work by Wrighton, Pdungsap, and Morse. It may be noted that electron transfer between ferrocene and N,O requires excitation of a charge-transfer absorption of ferrocene ( h = 254 nm), and is not observed on irradiation at longer wavelengths (Powell and Logan). Wavelength effects may well prove to be of wider importance in the photochemistry of ferrocene and related compounds. Aumann has made the interesting observation that quadricyclane and some other strained hydrocarbons form 1:1 adducts and other products on irradiation with Fe(CO),. Knox and Pryde have observed the following novel photochemical rearrangement of a ruthenium complex. R

oc

0

1-

YP

\Ru

Ru

cp/ ‘s’ I

R

‘co

Jtv

>

CP \

II

F\

Ru-RU

/ \/ OC

I R

/sR

\

CP

Strohmeier, a pioneer worker in this area, has made the interesting observation that irradiation of some catalysts for homogeneous hydrogenation, e.g. IrCl(CO)(PPh3)2,can bring about a great increase in catalytic activity: the effect is attributed to photoexpulsion of a molecule of PPh, to produce a more coordinatively unsaturated species. Photoactivation effects have been noted with TiO, and other metal oxide catalysts for oxidation and dehydrogenation (Cunningham, and other workers). Interest continues in the use of transition-metal co-ordination complexes, e.g. VO(acac),CI, as photoinitiators for vinyl polymerization. Note that the patent literature relating to photopolymerization is covered in Appendix Al. It is interesting that some 1,3-allylic shifts of C1 can be photocatalysed by cupric acetate and other copper compounds (Strohmeier). Eisch et al. have generated Na+(BPh,)-, a species showing carbenoid reactivity, by irradiation of a solution of sodium tetraphenylborate in tetrahydrofuran. It has long been known that the reaction between oxygen and arylmagnesium bromides is chemiluminescent: Bolton and Kearns have now shown that the emission arises from bromobiaryls. Photoreactions in inert matrices continue to prove useful for the synthesis of novel small inorganic molecules, for example FNO, FNO,, F,CO, NF,, KrF,, XeF,, XeCI2, and alkali-metal trioxides M+03-. Considerable interest continues in the photochemistry and photophysics of metalloporphyrins and related species containing zinc and other metals. Details will be found in Part 11. The biosynthesis of haem can be partially diverted to produce a zinc protoporphyrin in iron-deficiency anaemia and lead poisoning : measurement of fluorescence emission from this species has been recommended

Introduction

xi

as the basis of a sensitive test for detecting these all-too-common conditions (Lamola et aZ.). Fong has a new theory to explain the photo-oxidation of water in the chloroplast. Photoconductivity in chlorophyll a has been induced in the microcrystalline state by Bromberg et al., and in ethereal solution after flash photolysis by Gudhov et al. Part V deals with photochemical aspects of the increasingly important area of solar energy conversion, although the goal of a cheap and efficient system suitable for large-scale applications remains to be attained. Efforts have been made to employ the photosensitized isomerization of trans- to cisisomers, e.g. of styrylpyridine, but it is highly questionable whether the amounts of energy which can be absorbed and stored in these systems are large enough to be of practical use. Various proposals have been made for the generation of molecular hydrogen by solar radiation. In particular there is continued interest in Fujishima and Honda’s cell for the photochemical electrolysis of water which is based on irradiation of an electrode composed of semiconducting TiO, at wavelengths shorter than 413 nm. The efficiency of this cell is very low, but it may be increased by application of an electrochemical bias as low as 0.25 V so as to make the TiOz electrode positive. This seems one of the more promising approaches. Photovoltaic cells based on silicon have until recently appeared to offer the greatest practical utility despite their rather high cost, so it is interesting that S. Wagner et al. have described p-InP/n-CdS cells having an efficiency even greater than that of silicon cells. The cost and growing scarcity of silver have for some years provided a spur to the search for silver-free photographic processes. The systems described by Yurre et al. may well prove important. February 1976

D. BRYCE-SMITH

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

iii

Part I Physical Aspects of Photochemistry Chapter 1 Spectroscopic and Theoretical Aspects By D. Phillips 1 Introduction 2 MO Calculations

3

3 Spectra Absorption Stark Effects Circular Dichroism and Magnetic Circular Dichroic Spectra Two-photon Spectroscopy Photoionization and Electron Detachment Photofragment Spectroscopy Singlet-Triplet Absorption Spectra Electron-impact Spectra Triplet-Triplet Absorption S, -+ S, Spectra Fluorescence Spectra Phosphorescence Spectra Double-resonance Spectroscopy E.S.R. Studies CIDNP and CIDEP Studies Scattering Phenomena

8 8 15 15 16 21 22 23 24 26 27 28 33 33 35 36 38

4 Theories of Radiative and Non-radiative Decay Radiative Processes Two-phot on Excitation Resonant Scattering Processes Vi bronic Coupling, and Franck-Condon Factor Determinations Polarization and Environmental Effects Miscellaneous

38 38 39 40 41 42 43

xiv

Contents Non-radiative Decay Vibrational Relaxation Photochemical Reactions Treatment of Data

Chapter 2 Photophysical Processes in Condensed Phases By K. Salisbury

44 46 46 49 51

1 Introduction

51

2 Excited Singlet-state Processes

51

Singlet Quenching by Energy Transfer and Exciplex Format ion Heavy-atom Quenching Fluorescence Quenching by Inorganic Species Excimer Formation and Decay Exciplexes, Electron Donor-Acceptor Complexes, and Related Charge-transfer Phenomena

67 71 72 73 75

3 Triplet-state Processes Radiative and Non-radiative Processes E.S.R. and Microwave Studies, and Related Topics Triplet Quenching and Triplet Energy Transfer

78 78

4 Physical Aspects of some Photochemical Studies Phot o-oxidations Chemiluminescence Photochromism

90 90 94 96

Chapter 3 Gas-phase Studies By D. Phillips 1 Introduction

84 86

98 98

2 Alkanes

98

3 Alkenes, Alkynes, and Polyenes

99

4 Aromatic Hydrocarbons

101

5 Carbonyl and Oxygen-containing Compounds

111

6 Nitrogen Compounds

117

7 Sulphur Compounds

120

8 Halogenated Compounds

122

9 Atom Reactions

124

10 Miscellaneous

129

11 Applications of Lasers

129

Contents

xv

134 134 135 136 139 142 144 146 147 148

12 Atmospheric Chemistry Extraterrestri a1 Phenomena Neutral and Ionic Atomic and Molecular Hydrogen Stratospheric Chemistry 0, Reactions HO, Reactions N2, NO,, and HNO, Reactions CO, Reactions SO,, H2S Reactions Photochemical Urban Atmospheric Pollution

Part I1 Photochemistry of Inorganic and metallic Compounds

Organo-

By J. M. Kelly 1 Photochemistry of Metal Ions and Co-ordination Compounds Vanadium Chromium Molybdenum and Tungsten Manganese Rhenium Iron Ruthenium and Osmium Cobalt Rhodium and Iridium Nickel Platinum Copper Silver Zinc Mercury Lanthanides Uranium 2 Transition-metal Organometallics and Low-oxidation-state Compounds

Titanium, Zirconium, and Hafnium Niobium Chromium, Molybdenum, and Tungsten Manganese and Rhenium Iron, Ruthenium, and Osmium Cobalt, Rhodium, and Iridium Nickel Copper, Silver, and Gold Zinc and Mercury

153 154 154 157 157 157 158 159 161 167 168 169 170 170 170 170 171 172 174 174 175 175 179 182 1 a9 191 191 191

xvi

Contents

3 Porphyrins and Related Molecules of Biological Importance Metalloporphyrins Chlorophylls Haem

192 192 199 200

4 Water, Hydrogen Peroxide, and Anions

201

5 Main-group Elements

204 204 204 205 206 207 207 208 208

Magnesium Boron Aluminium, Gallium, Indium, and Thallium Silicon Germanium and Tin Lead Phosphorus 0ther Elements 6 Surface Photochemistry and Miscellaneous Topics

Part / I /

209

Organic Aspects of Photochemistry

Chapter 1 Photolysis of Carbonyl Compounds By W. M. Horspool

213

1 Introduction

213

2 Norrish Type I Reactions

214

3 Norrish Type IT Reactions

221

4 Rearrangement Reactions

233

5 Oxetan Formation and Addition Reactions

237

6 Fragmentation Reactions

242

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

246

1 Cycloaddition Reactions Intramolecular Intermolecular Dimerization

246 246 248 252

2 Enone Rearrangements

254

xvii

Contents 3 Photoreactions of Thymines etc.

273

4 Photochemistry of Dienones Linearly Conjugated Dienones Cross-conjugated Dienones

279 279 283

5 1,2-, 1,3-, 1,4-, and 1,5-Diketones

286

6 Quinones

292

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

300

1 Reactions of Alkenes Addition Reactions Hydrogen-abstraction Reactions cis-trans-Isomerization Structural Isomerization Reactions

300 300 301 302 305

2 Reactions involving Cyclopropane Rings

306

3 Reactions of Dienes

316

4 Reactions of Trienes and Higher Polyenes

322

5 Reactions of Carbonium Ions

329

6 Photolysis of Insecticidal Chlorocarbons

331

7 [2

+ 21 Intramolecular Addition Reactions

333

8 Dimerization and Intermolecular Cycloaddition Reactions

337

9 Reactions of Acetylenic Compounds

343

10 Miscellaneous Reactions

Chapter 4 Photochemistry of Aromatic Compounds By A. Gilbert

345 35 1

1 Introduction

35 1

2 Isomerization Reactions

351

3 Addition Reactions

356

4 Substitution Reactions

364

5 Intramolecular Cyclization Reactions

371

6 Dimerization Reactions

385

7 Lateral-nuclear Rearrangements

387

xviii

Contents

Chapter 5 Photo-oxidation and -reduction By H. A. J. Carless 1 Conversion of C=O into C-OH

391 391

2 Reduction of Nitrogen-containing Compounds

400

3 Miscellaneous Reductions

404

4 Singlet Oxygen

407

5 Oxidation of Aliphatic Unsaturated Systems

409

6 Oxidation of Aromatic Compounds

415

7 Oxidation of Nitrogen-containing Compounds

416

8 Miscellaneous Oxidations

420

Chapter 6 Photoreactions of Compounds containing Heteroatoms other than Oxygen By S. T. Reid 1 Nitrogen-containing Compounds Rearrangement Addition Miscellaneous Reactions

422 422 422 446 454

2 Sulphur-containing Compounds

458

3 Compounds containing other Heteroatoms

466 47 1

Chapter 7 Photoelimination By S. T. Reid 1 Photodecomposition of Azo-compounds

47 1

2 Elimination of Nitrogen from Diazo-compounds

479

3 Elimination of Nitrogen from h i d e s

485

4 Photodecomposition of other Compounds having N-N

Bonds

491

5 Photoelimination of Carbon Dioxide

493

6 Fragmentation of Organosulphur Compounds

494

7 Miscellaneous Decomposition and Elimination Reactions

498

xix

Contents

Part I V Polymer Photochemistry By D. Phillips 1 Introduction

507

2 Photopolymerization Photoinitiation of Addition Polymerization Photografting Photocondensation Polymerization Photochemical Cross-linking Radiation-induced Polymerization

507 507 511 512 514 516

3 Optical Properties, including Luminescence of Polymers

519

4 Photochemical Reactions in Polymeric Materials Polyethylene Polypropylene Poly(methy1 methacrylate) and Related Polymers Polystyrene Poly(viny1 halides) and Poly(viny1 alcohol) Elastomers Polyamides Natural Fibres Miscellaneous Reactions of O,(lA,) U.V. Stabilizers Radiation-induced Degradation Photochemistry of Pigments and Dyestuffs Photodegradation of Bioactive Materials

527 528 529 530 53 1 532 532 532 533 533 534 535 535 535 537

5 Appendix: Review of the Patent Literature Photopolymerizable Systems Radiation-induced Polymerizations Table A1 : Prodegradants and U.V. Sensitizers Table A2: U.V. Absorbers and Stabilizers Table A3 : Optical Brighteners

537 537 539 541 548 554

Part V Photochemical Aspects of Solar Energy Conversion By M. D. Archer 1 Introduction

561

2 Photochemistry

561 561 563 566

Endergonic Isomerization and Substitution Reactions Photochemical Water Decomposition The Fixation of Carbon Dioxide and Nitrogen

Contents

xx

3 Photoelectrochemistry Photogalvanic cells Semiconductor-Electrolyte Systems Titanium Dioxide 0ther Semiconductors

567 567 569 569 574

4 Photochemistry in Micellar Systems

576

5 Photosynthesis

577

6 Photovoltaic cells Inorganic Semiconductors Schottky Barrier Solar Cells Organic Semiconductors

579 579 581 583

Erratum

585

Author Index

586

Part I PHYSICAL ASPECTS OF PHOTOCHEMISTRY

1 Spectroscopic and Theoretical Aspects BY D. PHILLIPS

1 Introduction The format here is the same as that used in Volume 6 of the series. Some special emphasis has been given to interesting developments in simultaneous two-photon absorption and excitation spectroscopy and photofragment spectroscopy, but otherwise reportage in this section has been kept to a minimum. 2 MO Calculations As before, this section is confined to estimates of energy levels, transition energies, and oscillator strengths obtained through calculation. Papers dealing with potential-energy surfaces in relation to photochemical reaction and nonradiative decay are found in later sections. A brief account has been given of the applications of qualitative MO theory,l and the use of a least-squares method in CI calculations has been discussed.2 A new vector method has been proposed to describe the electronic states of atoms and molecule^,^ and the use of one-electron MO theory for energy-level determination di~cussed.~ Ab initio computations of spin-orbit interactions in polyatomic molecules using gaussian orbitalss and optimal orbitals for SCF CI calculations on excited states have been considered. Polynomial expansion methods for energies and excitation strengths have been outlined.' Two new methods, the multiconfiguration electron-hole potential method and a timedependent variation perturbation a p p r o a ~ hhave , ~ been used to calculate electronic transition parameters in a variety of molecules. The generally accepted basis for the widely used Hund's rules for predicting the ordering of eIectronic states has been challenged in recent years, yet the rules appear to be valid. A reformulation of the rules in a strict SCF approximation in which many of the elements of the traditional theory are retained has been proposed, to surmount this difficulty.1° Electron repulsion in the singlet and triplet states of the helium atom, natural orbitals of several excited states of this a

' @

lo

B. M. Gimarc, Accounts Chem. Res., 1974, 7 , 384. I. Roeggen, Chem. Phys. Letters, 1975, 31, 271. R. F. Hausman, jun., S. D. Bloom, and C. F. Bender, Chern. Phys. Letters, 1975, 32, 483. A. B. Anderson, J. Chem. Phys., 1975, 62, 1187. G. I. Bendazzoli and P. Palmieri, Internat. J. Quantum Chem., 1974, 8, 941. R. McWeeny, Mot. Phys., 1974,28, 1273. J. P. Draayer and J. B. French, Phys. Letters (B), 1975,55,263; C . D. H. Chisholm and K. B. Lodge, Mol. Phys., 1974, 28, 249. S. Iwata and K. Morokuma, Theor. Chim. Acta, 1974, 33, 285. W. M. Huo, J. Chem. Phys., 1974,62,2072. J. P. Colpa, Mol. Phys., 1974, 28, 581.

3

4 Photochemistry atom,Il and the application of the SCF method to lP and 3P excited states of twoelectron atomic systems l2have been discussed recently. Among papers appearing concerned with the spectroscopy and energy levels of atomic species are included those on the subjects of Li (11),13 K+ (I),14 the Be (ls22s2-> ls22s2p) and B (ls22s22p-+ ls22s2p2)l6 transitions, the C (2s2p3) 3S0-+ IDo isoelectronic sequence,16the vacuum-u.v. lines in N (I) to N (IV),17 the Na S states,l* oscillator strengths in elements of the iron group,lg isotope shifts in the arc spectrum of xenon,20excitation energies in other atomic systems,21and van der Waals interactions for atoms in excited states.22 There have been several studies on diatomic species, ions in particular, which indicate the growing current interest in the experimental study of such molecular entities. Theoretical studies have been carried out on 23 HD+,24 HeH+,?*26 Ne2+,26N2+,27Li2+,28and other ions.29 Neutral species investigated include H2,30He2,31Ne2,26Ar2,32LiH,23,33 LiF,34 and CH4.23 N2,35NO,36OH,37BH,38MgH2,39Na2,40C2,23 Triatomic species investigated are relatively few. Several papers have investigated the excited states of the water molecule using ab initiu methods, including l1 R. L. Snow and J. L. Bills, J. Phys. Chem., 1974,78,1334;P.Winkler and R. N. Porter, J. Chem. H2+,79

la

l3 l4 l5

l8

l7 l8 l8

2o 21

22

23 a4

28

2s 80

31 3a

33 s4 35

37

38 38

40

Phys., 1975,62,257. C. R. Guerillot and R. Lissillour, Znternat. J. Quantum Chern., 1974,8, 825. H. G. Berry, E. H. Pinnington, and J. L. Subtil, Phys. Rev. (A), 1974, 10, 1065. M. W.D. Mansfield, Proc. Roy. Soc., 1974,A341,277. 0.Sinanoglu and S. L. Davis, Chem. Phys. Letters, 1975, 32, 449; 0.Sinanoglu and D. R. Herrick, J. Chem. Phys., 1975,62,886;K.E. Banyard and G. K. Taylor, Phys. Rev. (A), 1974, 10, 1014; Y. Horino and H. Takeisaki, Internat. J. Quantum Chem., 1975, 9, 287. 0.Sinanoglu and B. J. Skurnik, J. Chem. Phys., 1974, 61, 3670. P. D. Dumont, E. Biemont, and N. Grevesse, J. Quant. Spectroscopy Radiative Transfer,

1974, 14, 1127. S. D. Mahanti, T. Lee, and T. P. Das, Phys. Rev. (A), 1974, 10, 1091. E. Biemont, Solar Physics, 1974, 38, 15; 1974, 39, 304; J. Quant. Spectroscopy Radiative Transfer, 1974, 14,959. D. A. Jackson, M. C. Coulombe, and J. Bauche, Proc. Roy. SOC.,1975, A343, 443,453. T.C.Collins, A. B. Kunz, and P. W. Deutsch, Phys. Rev. (A), 1974,10,1034. I. I. Gutman and T. V. Shendrick, Ukrain.fiz. Zhur., 1975,20, 334. A. Antoci and G. Nardelli, Theor. Chim. Acta, 1974,35, 89. P. R. Bunker, Chem. Phys. Letters, 1974,27, 322. T. A. Green, H. H. Michels, J. C. Browne, and M. M. Madsen, J. Chem. Phys., 1974,61,5186; T.A. Green, J. C. Browne, H. H. Michels, and M. M. Madsen, ibid., p. 5198. J. S. Cohen and B. Schneider, J. Chem. Phys., 1974,61,3230;B. Schneider and J. S . Cohen, ibid., p. 3240. D. C. Cartwright and T. H. Dunning, jun., J. Phys. (B), 1975, 8, L100; A. L. Roche and H. Lefebvre-Brion, Chem. Phys. Letters, 1975,32, 155. D. Hasman, Chem. Phys. Letters, 1974,29, 260. J. C. Leclerc and C. Guissard-Gallory, Bull. SOC.chim. belges, 1974,83,327. C. S. Lin, J. Chem. Phys., 1974,60,4660;T.A. Miller and R. S. Freund, ibid., 1974,61,2160; L. Wolniewicz, Chem. Phys. Letters, 1975, 31, 248; E. N. Svendsen and H. F. Hameka, Internat. J. Quantum Chem., 1974, 8, 789. P. B. Foreman, P. K. Rol, and K. P. Coffin, J. Chem. Phys., 1974,61,1658. R. C. Michaelson and A. L. Smith, J. Chem. Phys., 1974, 61, 2566. M. Oppenheimer and K. K. Docken, Chem. Phys. Letters, 1974,29,349. L. R. Kahn, P. J. Hay, and I. Shavitt, J. Chem. Phys., 1974, 61,3530. M. L. Sink, H. Lefebvre-Brion, and J. A. Half, J. Chem. Phys., 1975,62, 1802. H. Hertz, H. W. Jochims, H. Schenk, and W. Sroka, Chem. Phys. Letters, 1974, 29, 572; S. P. Walch and W. A. Goddard, tert., ibid., 1975,33, 18. S. I. Chu, M. Yoshimine, and B. Liu, J . Chem. Phys., 1974,61,5389. S. A. Houlden and I. G. Csizmadia, Theor. Chim. Acta, 1974,35, 173. W.J. Balfour and €3. M. Cartwright, Chem. Phys. Letters, 1975, 32, 82. P. F. Williams and D. L. Rousseau, Phys. Rev. Letters, 1974,33, 1515.

5 the improved virtual orbital and CI treatment^.^^ Good agreement with experiment was obtained in these studies. In one case it was shown that the 9.81 eV triplet state observed in electron-impact studies corresponds to the 10.17 eV singlet (lA1[bl -+3pJ) rather than the expected 10.00 eV singlet (lB1[bl -+ 3pJ) owing to the larger splitting between the lAl and 3A1states of 0.46 eV compared with that between the 4B1and 3B1 states of only 0.08 eV which rises from the magnitudes of the corresponding exchange integrals. It is of interest to compare these results with those obtained in a photo-fluorescence excitation spectroscopic study of H 2 0 described in a later section. Rydberg states in superexcited states of H 2 0 and NH3 and H F have been The existence of a 3A" state of the HNO radical at 5485 cm-I lying between the lA" excited and lA' ground states has been predicted from an equation-ofmotion-method The usual assumption that electrons are further apart in triplet states than in singlet states has been challenged on the basis of calculations performed on the NH and CH, species,44in which it is shown that electron repulsion can be greater in the state of lowest energy for a number of systems, in accord with statements made earlier concerning Hund's rules.l0 Methylene (carbene) is a species of some photochemical interest, and has also been much studied from a theoretical standpoint. It possesses a triplet ground state, whereas difluoromethylene is reported to have a singlet ground state, with CHF having a singlet ground state if electron correlation is included in computations, but a triplet ground state within the SCF approximation. Computed triplet-singlet energy separations including electron correlation were 10, 6, - 1 1 , The and -47 kcal mol-l for CH,, CHCH3, CHF, and CF,, respecti~ely.~~ spectroscopy of CH, requires that the first excited triplet state of CH, be highly bent, 3A2 in character, and 8.75 eV above the ground state, whereas ab initio calculations show that the state will decrease in energy with decreasing angle. Recent SCF calculations 46 have shown that there are three 3A2states which are highly bent, and in the right energy region (7.5-8.9 eV), but which result from 3al -+ 3p,, 3d,,, and 3dVzexcitations rather than the l b , -+ 3al so-called valence excitation previously c o n ~ i d e r e d . ~Spin-orbit ~ contributions to the singlettriplet splitting in meth~lene,~' ab initio methods for correlated wavefunctions of the ground and excited states of m e t h ~ l e n eand , ~ ~the vertical ionization potential of CF, dB have been discussed. CI studies on ozone and 03+ have been reported.60 It has been shown recently that electronically excited states of C 0 2 which arise from the same electronic configuration can in fact have different degrees of Rydberg character; for example, together with the '2, ground state, the 3&,+, Spectroscopic and Theoretical Aspects

43 44 46

'*

47

m 4s

6o

D. Yeager, V. McKoy, and G. A. Segal, J . Chem.Phys., 1974,61,755; J.A. Smith, P. Jorgensen, and Y. Ohru, ibid., 1975,62,1285; N. W. Winter, W. A. Goddard, tert., and F. W. Bobrowicz, ibid., p. 4325; W. A. Goddard, tert., and W. J. Hunt, Chem. Phys. Letters, 1974, 24, 469; R. Buenker and S. Peyerimhoff, ibid., 1974, 29, 253. S. Nishikawa and T. Watanabe, Chem. Phys., 1975,8,201. G. R. Williams, Chem. Phys. Letters, 1975, 30, 495. E. A. Colbourn, Chem. Phys. Letters, 1975, 30, 490. V. Staemmler, Theor. Chim. Acta, 1974, 35, 309. J. F. Hamson and D. A. Wernette, J. Chem. Phys., 1975, 62, 2918. S. R. Langhoff, J . Chem. Phys., 1974, 61, 3881. D. L. Hildenbrand, Chem. Phys. Letters, 1975, 30, 32. W. R. Wadt and W. A. Goddard, tert., J. Amer. Chem. SOC.,1974,96,5996. P. Jeffrey-Hay, T. H. Dunning, jun., and W. A. Goddard, tert., J . Chem. Phys., 1975,62, 3912.

Photochemistry

6

1s3Zu-, and l#3Ausingly excited states are valence states, whereas the is of Rydberg character. Recent calculations on acetylene have reinforced this pointys1 although earlier assignments of the acetylene spectrum based upon the method used in this study have been challenged recently.62 INDO calculations on the potential curves of ethylene give very poor agreement with ab initio result^.^^ 63 Reports have appeared on the geometries of excited states of small polyenesYK4 the low-lying electronic states of the ethynyl free radical,65the vibronic structure of the 7r -+ 7r* transition in cis-stilbene,66the singlet-state geometries of diphenyla~etylene,~~ and the dissociation products of the HN2+ion in its ground and excited states.6s Formaldehyde, being the simplest aliphatic carbonyl compound, has been widely studied from a theoretical standpoint.8* These studies have been concerned variously with Rydberg transitions and the lower-lying n -+ 7r* and 7r + n* transitions, and include an excellent review by Mode and Walsh. A theoretical description has been given of the peroxyformyl radical,60 a species thought to be of importance in polluted urban atmospheres. Results indicate that the excited state of this radical may be formed by association of Oa and HCO in their ground states, and may decompose readily to give OH and COz. INDO calculations on the lA1, lA", and 3A" states of keten and diazomethane,61 the 3Aa,lE, and lAl states of methylnitreneYs2ab initio calculations on the electronic spectrum of ethaneYs3and excited electronic states of a-dicarbonyls, including b i a ~ e t y l ,have ~ ~ been reported. There have also been a number of reports concerned with the electronic excited states of radicals and radical Simple rules for an estimate of correlation effects in the low-lying states of alternant hydrocarbons have been formulated,66 and the polarizabilities of the 491

b1 ba

63

64

titi I6 67

69

6o

6a

63 64

66

66

M. Jungen, Chem. Phys. Letters, 1974, 27, 256. W. E. Kammer, Chem. Phys., 1974,5408. U. Fischbach, R. J. Buenker, and S. D. Peyerimhoff, Chem. Phys., 1974,5,265; S . Iwata and K. F. Freed, Chem. Phys. Letters, 1974,28, 176; J. Chem. Phys., 1974, 61, 1500. J. LangIet and J. P. Macrieu, Theor. Chim. Acta, 1974, 33, 307. S. P. So and W. G. Richards, J.C.S. Faraday ZZ, 1975, 71, 660. A. Warshel, J. Chem. Phys., 1975, 62, 214. L. B. Clark, Chem. Phys., 1974, 5, 484. K. Vasudevan, S. D. Peyerimhoff, and R. J. Buenker, Chem. Phys., 1974,5, 149. D. L. Yeager and V. McKoy, J. Chem. Phys., 1974,60,2714; K. J. Miller, ibid., 1975,62, 1759; J. Gayoso, A. Boucekkine, and H. Bouanani, J. Chim. phys., 1973, 70, 1643; B. J. Garrison, H. F. Schaefer, tert., and W. A. Lester, jun., J . Chem. Phys., 1974, 61, 3039; T. D. Davis, G. M. Maggiora, and R. E. Christofferson, J. Amer. Chem. SOC.,1974,96, 7878; K. Tanaka, Internat. J. Quantum Chem., 1974, 8, 981; C. R. Lessard, D. C. Moule, and S. Bell, Chem. Phys. Letters, 1974, 29, 603; S. Langhoff, S. Elbert, C. Jackels, and E. R. Davidson, ibid., 1974, 29, 247; D. C. Moule and A. D. Walsh, Chem. Rev., 1975, 75, 67; E. R. Farnworth, G. W. King, and D. C. Moule, Chem. Phys., 1973, 1, 82. N. W. Winter, W. A. Goddard, tert., and C. F. Bender, Chem. Phys. Letters, 1975, 33, 25. R. Caballol, R. Carbo, and M. Martin, Chem. Phys. Letters, 1974, 28, 422. D. R. Yarkony, H. F. Schaeffer, tert., and S. Rothenberg, J. Amer. Chem. SOC.,1974,96,5974. R. J. Buenker and S. D. Peyerimhoff, Chem. Phys., 1975, 8, 56. J. C. Brandand A. W. H. Mau, J. Amer. Chem. SOC.,1974,96,4380; J. F. Arnett, G. Newkome, W. L. Mattice, and S. P. McGlynn, ibid., p. 4385; J. F. Arnett and S. P. McGlynn, J. Phys. Chem., 1975, 79, 626. P. Carsky, J. Kuhn, and R. Zahradnik, J. Mol. Spectroscopy, 1975, 55, 120; H. M. Chang, H. H. Jaffe, and C. A. Masmanidis,J.Phys. Chem., 1975,79,1118; G. Levin and W. A. Goddard, tert., Theor. Chim. Acta, 1975, 37, 253. J. Cizek, J. Paldus, and I. Hubac, Internat. J. Quantum Chem., 1974,8,951; J. Paldus, J. Cizek, and I. Hubac, Internat. J. Quantum Chem. Symp. 8, 1974, 293.

Spectroscopic and Theoretical Aspects

7

three lowest singlet and triplet states of a number of conjugated molecules have been calculated using a perturbation theory approach,s7 which also shows that methods based upon Hiickel theory give unsatisfactory results. SCF-CI calculations on the luminescent transitions from equilibrium excited states in aromatic molecules have also been reported.68 Ab initio, PPP-type, and equationsof-motion-type calculations on benzene, and other calculations concerned with spin density, vibronic interactions, and conjugation in excited electronic states in the same m01ecule,~~ have been described. A MIND0/3 study of the singlet and triplet forms of the isomeric bisdehydrobenzenes shows that the singlet state of (1) is the more stable, but that the singlet of (2) is at least comparable in stability, and such intermediates merit consideration in benzyne reaction mechanism^.^^

HQ H

H

H

H

Calculation has shown that the lBgu,3B2u,and 3B1,states of naphthalene are as states are much more polarizable as the ground state, whereas the lBzuand 3B3u so, especially in the long-axis direction. The polarizability of the lB1, state is extremely Several studies of the pyrene crystal have been A valence-bond model for the lone-pair interactions in py~azine,'~the electronic structure and spectra of quinalene, quinolines, and benzoq~inolines,~~ and calculated spectra in other azanaphthalenes 76 and pyridine 77 have been reported, and SCF-CI calculations on the excited-state geometries of p-fluorophenol and p-fluoroaniline carried O U ~ ? Excited-state energies in p-benzoqin~ne,~~ protonated aromatic carbonyl compounds,80halogen-substituted benzaldehydes and 67 68

70

71 72

73 74

7s

76 77

78 70

8o

B. L. Burrows and A. T. Amos, Theor. Chim. Acta, 1974,36, 1. F. Fratey, G. Khibaum, and A. Gochev, J. Mol. Structure, 1974, 23, 437. J. Norbeck and G. Gallup, J. Amer. Chem. SOC.,1974, 96, 3386; J. B. Rose, T. I. Shibuya, and V . McKoy, J. Chem. Phys., 1974, 60,2700; A. Pellegatti, J. Cizek, and J. Paldus, ibid., p. 4825. V. A. Kuznetsov, A. N. Egorochkin, G. Razuvaev, S. Skoboleva, and N. Pritula, Doklady Akad. Nauk S.S.S.R.,1974,216, 812; J. Van Egniond and J. H. van der Waals, Mol. Phys., 1974,28,457; H. Joela and P. Pyykko, Chem. Phys. Letters, 1975,31,574; C . B. Duke, N. 0. Lipari, and L. Pietronero, ibid., 1975,30,415; J. S . Rosenfield, A. Moscowitz, and R. E. Linder, J. Chem. Phys., 1974,61,2427. M. J. S. Dewar and L. Wai-Kee, J. Amer. Chem. SOC.,1974, 96, 5569. H. Meyer, K. W. Schulte, and A. Schweig, Chem. Phys. Letters, 1975, 31, 187. M. D. Cohen, E. Klein, 2. Ludmer, and V. Yakhot, Chem. Phys., 1974,5, 15; M . D. Cohen and V. Yakhot, ibid., pp. 27,478; A. Warshel and E. Huler, ibid., 1974,6,463. W. R. Wadt and W. A. Goddard, tert., J. Amer. Chem. SOC.,1975, 97,2034. M. Kobayushi, Y. Tanizaki, andT. Hoshi, Canad.J. Spectroscopy, 1975,19,165; H.Yamaguchi, T. Ikeda, and H. Mametsuka, Bull. Chem. Soc. Japan, 1975, 48, 1118; H. Yamaguchi and T. Nakajima, ibid., 1975, 48, 1325. J. E. Ridley and M. C.Zerner, J. Mol. Spectroscopy, 1974, 50, 457. H. H. Jaff6, C. A. Masmanidis, H. M. Chang, and R. L. Ellis, J. Chem. Phys., 1974,60, 1696. J. S. Yadav, P. C. Mishra, and D. K. Rai, Chem. Phys. Letters, 1975, 31, 129. M. H. Wood, Theor. Chim. Acta, 1975, 36, 345. A. I. Kiss and F. Joo, Internat. J . Quantum Chem., 1975, 9, 261.

8

Photochemistry benzoyl halides,s1 and dibenzofuran,8a and the use of the CNDO method to describe triplet excited states of organic molecules83have been the subjects of recent reports. Calculations have been carried out on the spectroscopy and excited-state energies and geometries of p ~ l y e n e s the , ~ ~ 1,5-cyclo-octadiyne radical the visual chromophore, 11-cis-retinal,86 polyene ~arbaldehydes,~'aromatic hydrocarbon anions and cations,s8trimeth~lenemethane,~~ thiamine d e r i ~ a t i v e s , ~ ~ p o r p h y r i n ~ ,l ~ ~m i f l a v i nc, h~l~~ r o p h y l l nucleic ,~~ acids,94and ferrocene.n6 Many other papers have appeared concerned with the assignment of electronic transitions based upon various types of calculations, and these will be found in later sections of this chapter, in which experimental work is discussed. 3 Spectra The format here is identical with that in Volume 5.

Absorption.-The studies reported here are conventional one-photon absorption studies on ground-state molecules and atoms. The use of a rapidly tuneable CW dye laser for direct absorption spectroscopy has been d e s ~ r i b e d .Transition ~~ probabilities in the spectra of Ne (I),g7 and the classification of the 650.4 nm line of Xe 97 have been discussed. Pressure-broadening coefficients for the atomic iodine zPh-2P+ transition for C02, N2, He, Ne, Ar, Kr, and Xe have been measured as 7.4 2 0.7, 6.2 f 0.8, 3.6 rt 0.3, 4.3 rt 0.4, 5.1 rt 0.5, 4.4 k 0.4, and 3.0 k 0.3, respecti~ely.~~ Measurements of the polarizabilities of alkalimetal atoms have been described,gnand hyperfine interactions in the excited states of sodium discussed.100 Excitation parameters in the vacuum-u.v. region

8a

83 84

D. Bhaumik, Indian J. Phys., 1974, 48, 895. T. Keumi, M. Honda, M. Kondo, N. Mochinaga, and Y. Oshima, J. Chem. SOC.Japan, Ind. Chem. Sect., 1974, 11, 2075. H. M. Chang, H. H. Jaffk, and C. A. Masmanidis, J. Phys. Chem., 1975,79, 1109. R. Lemke, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 663. G. Bieri, E. Heilbronner, E. Kloster-Jensen, A. Schmelzer, and J. Wirz, Helv. Chim. Acta, 1974,57, 1265.

87

A. Warshel and M. Karplus, J. Amer. Chem. SOC.,1974,96, 5677; R. R. Birge, K. Schulten, and M. Karplus, Chem. Phys. Letters, 1975,31,451; B. Honig, A. Warshel, and M. Karplus, Accounts Chem. Res., 1975, 8, 92. K. Inuzuka and R. S . Becker, Bull. Chem. SOC.Japan, 1974,47, 88; K. Inuzuka, ibid., 1975, 48, 779.

P. Jorgensen and J. C. Poulsen, J. Phys. Chem., 1974,78, 1420; I. P.Cook and G. J. Hoytink, Theor. Chim. Acta, 1974, 36, 145. W. T. Borden, J. Amer. Chem. SOC.,1975,97,2906. F . Jordan, J. Amer. Chem. SOC.,1974,96, 3623. G. M. Maggiora and L. J. Weimann, Znternat. J. Quantum Chem., 1974, 8, 179. O2 B. Grabe, Acta Chem. Scand. (A), 1974,28, 363. O3 J. LeBrech, R. M. LeBlanc, and A. F. Antippa, Chem. Phys. Letters, 1974, 26, 37. 94 M. Kamiya and Y. Akahori, Bull. Chem. SOC. Japan. 1974,47,2871. e5 M. M. Rohmer, A. Veillard, and M. H. Wood, Chem. Phys. Letters, 1974, 29, 466. J. M. Telle and C. L. Tang, Optics Comm., 1974, 11, 251. s7 R. A. Lilly, J. Opt. SOC. Amer., 1975, 65, 389; D. A. Jackson and M. C. Coulombe, ibid., p. 464. O8 T. D. Padrick and R. E. Palmer, J. Chem. Phys., 1975, 62, 3350. 99 R. W. Molof, H. L.Schwartz, T. M. Miller, and B. Bederson, Phys. Rev. (A), 1974, 10, 1131 ; W. D. Hall and J. C. Zorn, ibid., p. 1141. l o o S. D. Mahanti, T. Lee, and T. P. Das, Phys. Rev. ( A ) , 1974, 10, 1091; G. Huber et al., Phys. Rev. Letters, 1975, 34, 1209. 88

9

Spectroscopic and Theoretical Aspects

for metal atoms, including thallium, chromium, strontium, and copper, have been reported.lol The vacuum-u.v. absorption spectrum of mercury atoms in rare-gas matrices correlates with that of mercury vapour, but is shifted from it by as much as 2000cm-l for the 'So 3 lP1 transition, and shows fine strucfure.lo2 The effect of H-Hg interactions on the line-shape of the ISo -+ 3P1253.7 nm transition in mercury has also been The fine structure of Rydberg, Lyman, and Werner bands of the H, molecule,lo4 the high-resolution spectrum of the Xe, molecule in the 115-1 30 nm region, and a comprehensive re-analysis of the 02(B3E3,+Schumann-Runge band system have been reported.los The optical absorptions in solid 0, have been discussed from a theoretical sfandpoint.lo6 High-resolution studies have been carried out on the JIX++- 8 Z + transitions of C0,1°7 the B211+ x2IIsystem in matrix-isolated N0,1°8 and the McLennan bands of I2.lo9 The dissociation energies of diatomic halogen fluorides and other molecules,111 and r-centroids and Franck-Condon factors in the J22n-+ T2CBeF system112 and in other a new band system in Si0(J1n +- 21Z),113 the absorption spectrum of diatomic phosphorus between 137 and 60 nm,l14 absorption and fluorescence of gaseous TeSe,l16 optical spectra of matrix-isolated Be and Be,,l16 and pressure effects on the vibronic transitions of NO and NH, 117have been reported. The bond length and angle of the excited 3B1state of SO, have been calculated to be 1.491 f 0.002 A and 126.1 f 0.1" from a modified Franck-Condon analysis of the absorption and emission spectra.l18 Photoabsorption of solid CO, llB and rotational analysis of the 593.3 and 800-900 nm bands of NO2120 have been reported. The application of the laser spectroscopy of supersonic molecular beams to the NO, spectrum has been discussed.121 The A%+ t X22n

z&-)

101

ioa 103 104 106 I08

107 108 100

110 111

iia iia 114 111 118 117 118 119 120 121

M. W. D. Mansfield and J. P. Connerade, Proc. Roy. SOC.,1975,A342,421;M.C. E. Huber, R. J. Sandemann, and E. F. Tubbs, ibid., p. 431 ; M. G.Kozlov and B. E. Krylov, Optika i Spektroskopiya, 1975,38,826;V. S.Vukstich, V. V. Samsonov, and A. M. Demeter, Ukrain. $2. Zhur., 1974,19, 1040;A. Bielski, J. Quant. Spectroscopy Radiative Transfer, 1975, 15, 463. S. A. Malo, J. Chem. Phys., 1974, 61, 2408. D.Perrin-Lagarde and R. Lennuier, J. Phys. (Paris), 1975,36, 357. A. N. Jette and T. A. Miller, Chem. Phys. Letters, 1974,29, 547; A. L. Ford, J. Mol. Spectroscopy, 1975,56, 251. M.-L. Castex, Chem. Phys., 1974,5, 448;D. M.Creek and W. R. Nichols, Proc. Roy. Soc., 1975,A341, 517. T. Fujiwara, J. Phys. SOC.Japan, 1974, 36, 1530. K.N. Klump and E. N. Lassettre, J. Chem. Phys., 1974,60,4830. E. Boursey and J. Roncin, J. Mol. Spectroscopy, 1975,55, 31. J. Tellinghuisen, Chem. Phys. Letters, 1974,29, 359. J. A. Coxon, Chem. Phys. Letters, 1975,33,136. M. I. P. Rao, D. V. K. Rao, and P. T. Rao, Phys. Letters (A), 1974,50, 341. V. B. Gohel and N. P. Shah, Indian J. Phys., 1974,48, 932. G.A. Capelle, H. P. Broida, and R. W. Field, J. Chem. Phys., 1975,62,3131. P. K. Carroll and P. I. Mitchell, Proc. Roy. SOC.,1975,A342,93. F. Ahmed, R. F. Barrow, and K. K. Yee, J. Phys. (B), 1975,8,649. J. M. Brom, jun., W. D. Hevett, jun., and W. Wellner, jun., J. Chem. Phys., 1975,62,3122. M. Miladi, J. Le Falher, J. Roncin, and H. Damany, J. Mol. Spectroscopy, 1975, 55, 81. J. P. Vikesland and S . J. Strickler, J. Chem. Phys., 1974,60,660. K. M. Monahan and W. C. Walker, J. Chem. Phys., 1974,61,3886. C. G. Stevens and R. N. Zare, J. Mol. Spectroscopy, 1975, 56, 167; J. C. D.Brand, W.H. Chan, and J. L. Hardwich, ibid., p. 309. R. E. Smalley, B. L. Ramakrishna, D. H. Levy, and L. Wharton, J. Chem. Phys., 1974, 61, 4363.

Photochemistry band system of NC0,122 the vacuum-u.v. absorption spectrum of OCSe,12s and excited states of the NO+ 12* and H20+126 ionic species have been discussed in recent papers. The vapour-phase absorption spectra of cyanogen, cyanoacetylene, dicyanoacetylene, and dicyanodiacetylene have been shown to be dominated by a lXU++ lXg+ system arising from the lowest T -+ T * configuration, together with several Rydberg bands.126 A moderately intense intra-valence-shell band assigned as a llIu-+ lXg+transition arising from the lowest n -+ V * configuration is also characteristic. The CN bond dissociation energy in nitrosyl cyanide has been Assignment of Rydberg transitions in the methyl halides, excluding methyl fluoride, using a method of correlation with ionization potentials, has been shown128to give results in good agreement with the Rydberg formula 10

Y ~ , ( I )= I

- R/(n +

(1)

where Yna(I) is the energy of that spectral feature which is thought to be the nth member of the ath Rydberg series which converges to the specific ionization limit I, and R is the Rydberg constant, while ,a, is an appropriately defined quantum defect. It seems likely that the method have general application. The results may be compared with assignments of transitions in alkyl halides by Raymonda et alles The vibronic structure of crystalline ethylene,12ea comparison of the vacuumU.V. absorption spectra and photo-electron (PE) spectra of propylene, cyclopropane, and ethylene U.V. spectra of non-conjugated allylcycloalkenes,191 vibrational and electronic spectra of C3, C3H, CsH2, and C3H9arising from the vacuum-u.v. photolysis of allene and methyla~etylene,~~~ and the absorption spectra of cyclohexyl and cyclohexenyl radicals 133a have been reported. A highresolution spectrum of formaldehyde has been analysed in terms of coupling of the Sl and Tl and the Rydberg states of this molecule have been The polarization of both nn* bands of glyoxal in a 2-methyltetrahydrofuran glass has been measured using the photoselection method, and the bands at 30 O00 cm-l and 43 OOO cm-l have been assigned to a lAg + lBg (nn*) molecular transition and a charge-transfer transition in a complex of glyoxal P. S. H. Bolman, A. Carrington, J. M. Brown, I. Kopp, and D. A. Ramsay, Proc. Roy. SOC., 1975, A343, 45. lZ3 E. J. Finn and G . W. King, J. Mol. Spectroscopy, 1975,56,39,52; S . Cradock, R. J. Donovan, W. Duncan, and H. M. Gillespie, Chem. Phys. Letters, 1975, 31, 344. l a c L. C. Lee and D. L. Judge, J. Phys. (B), 1974,7,626. n6 A. J. Lorquet and J. C. Lorquet, Chem. Phys., 1974,4,353. lZB R. E. Connors, J. L. Roebber, and K. Weiss, J. Chem. Phys., 1974, 60,5011. 12' B. G. Gowenlock, G. A. F. Johnson, C. M. Keary, and J. Pfab, J.C.S. Perkin 11, 1975, 351. las P. Hochmann, P. H. Templet, H.-C. Wang, and S. P. McGlynn, J. Chem. Phys., 1975, 62, 2588; J. W. Raymonda, L.-0. Edwards, and B. R. Russell, J. Amer. Chem. SOC.,1974,96, lZ2

1708. I3O lS1

Is* 133

P. Dauber, M. Brith, E. Huler, and A. Warshel, Chem. Phys., 1975, 7 , 108. R. Krassig, D. Reinke, and H. Baumgartel, Ber. Bunsengesellschaft phys. Chem., 1975, 79, 116. G. B. Butler and J. J. Van Heiningen, J . Macromol. Sci., 1974, A8, 1139. M. Jacox and D. E. Milligan, Chem. Phys., 1974,4,45. (a) R. H. Schuler and L. F. Patterson, Chem. Phys. Letters, 1974,27, 364; (b) J. C. D. Brand and D. S. Liu, J . Phys. Chem., 1974, 78, 2270; C. R. Lessard, D. C. Moule, and S. Bell, Chem. Phys. Letters, 1974, 29, 603.

Spectroscopic and Theoretical Aspects

11

and the ~01vent.~3* A reinvestigation of the absorption spectrum of crystalline biacetyl at 4-8 K confirms that there are two systems, the lA,+ lA, and 3A, + lA, bands.135 Evidence for an absorption due to a singlet-singlet transition in a cis or skew rotational isomer is also discussed. The symmetry-allowed 180 nm transition in steroidal polycyclic ketones has been shown to be polarized along the C-0 axis,1s6in accord with both v -+ v* and n -+ uc-c assignments. The blue shift of the n -+v* band of acetone in water has been An extensive review of the spectroscopy and electronic structure of linear polyenes has appeared.13* An authoritative study using single-vibronic-level fluorescence analysis, which is discussed later, has permitted confirmation and establishment of twenty-eight absorption assignments in the benzene lBZu+- lA,, Four new vibrational frequencies in the excited state were identified, these being the va’, v6’, vg’, and vl,’ at 365, 749, 1148, and 712 cm-l, respectively. The molecule occupies a place of some importance in the realm of photophysics, and the new assignments, observed in addition to the previously well-characterized 6&49, 6:1&4!), 6;1:(Ai), 6:16&4;), 6!(B3, 6!16;(B,9, and 6i(Ct) bands, are given in Table 1. The results show that a set of twelve vibrations encompassing six of the ten symmetry species are responsible for most of the structure in the lBzu+- lAl, transition, and every vibration in the six symmetry species is ‘active’. Excitonphonon coupling in crystalline benzene has been The electronic spectra of lY2,3-trimethylbenzene141 and a variety of dihalogeno-toluenes 142 have been reported. Rydberg transitions in the U.V. spectra of difluorobenzenes 143 have been investigated. The absorption cross-sections for benzene, pyridine, quinoline, and 2-ethylnaphthalene in the 2-10.6 eV region have been shown to be similar in the liquid phase to those in the vapour phase, indicating that the transitions involved are the same, although there is also evidence of collective excitations of electrons in the liquid phase, which is not seen in the ~ap0ur.l~~ The puzzle concerning the apparent red shift in polar solvents of the n --f v* absorption band of nitrosobenzene in the 25 000-33 000 cm-l region, whereas a blue shift would be expected, has been resolved in a study which shows that the apparent shift is caused by an increase in the intensity of the v -+ v* band, with a maximum at 34 750 cm-l, which underlies the n -+ v* t r a n ~ i t i 0 n . l ~Linear ~ 134

186 136

137 138 198

140 141 14a

149 144 146

J. Kelder, H. Certonfain, J. Eweg, and R. P. H. Rettschnick, Chem. Phys. Letters, 1974,26, 491. J. C. D. Brand and A. W.-H. Mau, J. Amer. Chem. SOC.,1974,96,4380. A. Yogev, J. Sagiv, and Y. Mazur, Chem. Phys. Letters, 1975,30, 215. J. E. Del Bene, J. Amer. Chem. SOC.,1974, 96, 5643. B. Hudson and B. Kohler, Ann. Rev. Phys. Chem., 1974,25,437.

A. E. W. Knight, C. S. Parmenter, and M. W. Schuyler, J. Amer. Chem. Soc., 1975,97, 1993, 2005. S. D. Colson, T. L. Netzel, and J. M. van Pruyssen, J. Chem. Phys., 1975, 62, 606. P. Mallick and S. Banjeree, Chem. Phys. Letters, 1974, 27, 503. D. R. Singh, U. S. Tripathi, R. C. Maheshwari, and D. Sharma, Current Sci., 1975,44,218; G . N. R. Tripathi, B. N. Tewari, R. M. Verma, and S. Ram, J. Chim. phys., 1974, 71, 545; C. P. D. Dwivedi and S. N. Sharma, Spectroscopy Letters, 1975,7, 324. R. Gilbert and G. Sandorfy, Chem. Phys. Letters, 1974, 27, 457. P. Hindle, S. Walker, and J. Warren, J. Chem. Phys., 1975,62, 3230; R. A. MacRae, M. W. Williams, and E. T. Arakawa, ibid., 1974, 61, 861. B. Vidal and J. N. Murrell, Chem. Phys. Letters, 1975, 31, 46.

12

Photochemistry

Table 1 Absorption assignments of benzene vapour from S VLfluorescence study. Band maxima are shown only where SVL fluorescence confirms the assignment Band maximum1 Absorption Assignment region cm-l (vac) 6;

0:

6t11; 16; 16i17; 4; 10; 6; 16; 1; 6; 16; 10i16: 6;lO: 1611; 6:162,1; 9; lo; 6;1 1; 6! 6; 10; 16; 17: 6; 16; 17; 6x4; 10; 6; 16; 6i10;

c,o

64 17; 621; 625: 6i1 lil;

37 392.5 37 392.7 38 517.2

y:

y: Y!

39 038.5

y:

G

39 082.1

G:

a

G:

IG

39 235.8 39 255.0 39 368.0

K: K:

4

E,o E,o E,o 0: B': B':

39 560.6 39 783.1 39 765.0 40 050.2 40 108.9

K:

00,

Q:

41 165.3

dichroism studies have confirmed the existence of a new transition at 265 nm in dialkylanilines which may be due to a transition to a molecular Rydberg The vapour-phase electronic absorption spectra of nitrosobenzene v a p o ~ rthe ,~~~ acidity of ground and excited states of methyl pheno1s,l4*and the visible excitation spectra of benzyl, C2H7]benzyl,and p-methylbenzyl radicals in rigid solution at 77 K have been r e p 0 ~ f e d . l ~ ~ The linear dichroism method utilizing naphthalene molecules oriented in stretched poly(ethy1ene) and poly(propy1ene) matrices at 77 K and 296 K suggests that the 245-275 nm absorption of BBupolarization is due to a B1,vibronic perturbation of the lBZustate.160 Results also showed that the orientation in poly(ethy1ene) and poly(propy1ene) was different. Absorption spectra of crystal-

148

A. Davidsson and B. Norden, Chem. Phys. Letters, 1974,28,39; H. Tsubomara and T. Sakata, ibid., 1973, 21, 511. V. V. Bhujle, C. N. R. Rao, and U. P. Wild, J. Chem. Phys., 1974,70, 1761. I. A. Abronin, S. G. Gagarin, and G. M. Zhidomirov, Izvest. Akad. Nauk S.S.S.R.,Ser. khim.,

160

D. M. Friedrich and A. C . Albrecht, Chem. Phys., 1974, 6, 366. A. Davidsson and B. Norden, Chem. Phys. Letters, 1974,28,221.

146

14?

1974,11,2627.

Spectroscopic and Theoretical Aspects

13

line naphthalene 151 and vapour-phase halogenated naphthalenes 152 have been reported. The electronic transitions of biphenyl 153 and the influence of molecular conformation upon the spectroscopic properties of 1,l-binaphthyl 154 have been discussed. Detailed polarized absorption and emission spectra of anthracene and some of its methyl and methoxy-derivativesin rigid solution at 77 K have been and it was shown that no new transitions were introduced by substitution. This important study also claims to identify the 'Lb band in substituted anthracenes which is hidden in the parent compound, although such a conclusion is not in accord with a further study 156 in which the available evidence for the 'Lb band is considered, and positive identification of the state is strongly queried. In the latter study it was shown that the substitution of methyl and fluoro-groups in the aromatic ring system does not alter significantly the polarization directions, whereas amino-substitution has a large effect in this respect. The reflection spectrum of crystalline anthracene at low temperatures has been ~ep0rted.l~' Lineshapes in the electronic absorption spectra of crystalline phenanthrene have been The 300 nm (lBz +- lAl) system of this compound in durene at 4 K illustrates an electronic transition in which vibronic perturbations occur in both the small- (sparse intermediate) and large-molecule (statistical) limits, since both broad (300cm-l) and narrow (10 cm-l) lines were observed. A model involving interaction of the initial levels with a small number of strongly coupled levels, which in turn are broadened by interaction with a near continuum of levels in the lower excited state, successfully reproduces many of the features of the lBz spectrum. The system is thus of interest in that a single electronic state thus provides both a sparse and a dense manifold of levels for coupling to the initial levels. The absorption spectra of oriented and amorphous films of naphthacene, pentacene, perylene, and ~ o r o n e n e ,the ~ ~ polarization @ of electronic transitions in coronene, pentahelicene, and hexahe1icene,l6O electronic spectra of perylene and 1,12 benzperylene crystals,lsl and the orientation of coronene, perylene, and pyrene in monocrystalline n-heptane 162 have been reported. In the last study, the orientation was evidenced by dichroic absorption, fluorescence, and phosphorescence 151

152

153

15* 155

158 15'

lS8 16*

le0 161 lea

2

F.Ochs, P. N. Prasad, and R. Kopelman, Chem. Phys. Letters,

1974, 29, 290; Chem. Phys., 1974, 6, 253; E. F. Sheka and I. P. Terenetskaya, ibid., 1975, 8, 99. S. N. Singh, 0. P. Sharma, and R. D. Singh, Spectroscopy Letters, 1975, 8, 7; R. D. Singh, Indian J. Pure Appl. Phys., 1975, 13, 48. M. Shiho, J. Phys. SOC.Japan, 1974, 36, 1636; K. R. Popov, L. V. Smirnov, V. L. Grebneva, and L. A. Nakhimovskaya, Optika i Spektroskopiya, 1974, 37, 1070. M. F. M. Post, J. Langelaar, and J. D. W. van Voorst, Chem. Phys. Letters, 1975,32, 59. D. M. Friedrich, R. Mathies, and A. C. Albrecht, J. Mol. spectroscopy, 1974, 51, 166. J. Michl, E. W. Thulstrup, and J. H. Eggers, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 575. J. M. Turlet and M. R. Philpott, J. Chem. Phys., 1975, 62, 2777. G. Fischer, Chem. Phys., 1974, 4, 6 2 ; L. A. Lissado, Chem. Phys. Letters, 1975, 33, 57. Y. Kamura, I. Shirotani, H. Inokuchi, and Y. Maruyama, Chem. Letters, 1974, 627; Y. Kamura, K. Seki, and H. Inokuchi, Chem. Phys. Letters, 1975, 30, 35. A. Yogev, L. Margulies, B. Strasberger, and Y. Mazur, J. Phys. Chem., 1974, 78, 1400. J. Tanaka, T.Kishi, and M. Tanaka, Bull. Chem. SOC.Japan, 1974,47,2376; T. B. Tamm and P. M. Saari, Chem. Phys. Letters, 1975, 30, 219. M. Lamotte, J. Joussot-Dubien, M. Mantione, and P. Claverie, Chem. Phys. Letters, 1974, 27,515; M. Lamotte and J. Joussot-Dubien, J. Chem. Phys., 1974,61, 1892.

14

Photochemistry

spectra, and it was found that aromatic molecular planes were perpendicular to the growth axis, with the largest axis oriented in the direction of the alkane chains. A simple relationship between the energy of the electronic singlet-singlet transition energy lE and half-wave reduction (Eled)and oxidation potentials in non-aqueous solvents given by (2), where k, and k, are constants, has been

(w)

tested with respect to the ,La band in benzenoid hydrocarbons,ls3 and an excellent correlation observed. Similar correlations have been noted in heterocyclic amine N-oxides and other The electronic spectra of azobenzene,ls4 p-nitrophenylhydrazine,166 N-( 1naphthyl)ethylenediamine,lsa 1-azabicyclo[3,3,3]undecane,la7 and carbazole 16* have been recorded. In the last study polarization measurements clearly indicated that the lowest singlet transition in absorption and emission, and also the phosphorescence in both carbazole and four of its nitrogen-substituted derivatives, was of a symmetry-forbidden character. Acid-base equilibria of N-phenyl-lnaphthylamine and N-phenyl-2-naphthylamine and other molecules in the ground and excited states have been determined from spectral characteristic^.^^^ The absorption spectrum of pyrazine has been measured in the vapour, pure crystal, and in crystalline solid solutions in cyclohexane and benzene, and it has permitted assignment of the vl, v60, vga,and vlOamodes in the nn* singlet It was found that the last mode (vloa) has a strongly quartic component in its potential function owing to strong perturbations between the lBQunn* state and the lBzum* state, and also that there is a large negative anharmonic coupling term between trga and vlOa. These results can be interpreted qualitatively in terms of the tendency of the carbon atoms in the nv* state to pass into a tetrahedrally hybridized geometry. Thus the combined effect of modes 10a and 6a can be understood as the tendency of the C-C-C angle to be reduced as the out-ofplane motion in 10a increases, which is the beginning of conversion into tetrahedral hybridization. These results should be compared with other recent results on the pyrazine The reported variation of the absorption spectrum of benzo[c]cinnoline in non-polar solvents with temperature has been interpreted recently in terms of hydrogen-bonding interactions which occur in all but the most rigorously dried non-polar solvents, microcrystal formation, and le3

Ie4 le5

16e

Ie7 lea

H. Miyazaki,T. Kubota, and M. Yamakawa, Bull. Chem. SOC. Japan, 1972,45,780;T.Kubota, H. Miyazaki, K. Ezumi, and M. Yamekawa, ibid., 1974, 47, 491; T. Kubota and H. Miyazaki, Bunseki Kiki, 1974,11, 9. J. Kleps and T. Prot, Roczniki Chem., 1974,48, 1525. F.Bertinolli and C. Taliani, Chem. Phys. Letters, 1974,28,231. R. J. Shirgeon and S. G. Schulman, Anulyt. Chim. Actu, 1975,74, 192. A. M. Halpern, J. Amer. Chem. Soc., 1974,96,7655. G.E. Johnson, J . Phys. Chem., 1974,78, 1512. I. Janic, P. Ristac, and A. Kawski, Bull. Acad. polon. Sci., 1974, 22, 857; R. Blume, H. Lachmann, and J. Polster, 2.Nuturforsch., 1975,30b,263. E.F.Zalewski, D. S. McClure, and D. L. Narva, J. Chem. Phys., 1974,61,2964. H.K. Hong and G. W. Robinson, J. Mol. Spectroscopy, 1974,52, 1; 1. Suzaka, N. Mikami, and M. Ito, ibid., p. 21.

Spectroscopic and Theoretical Aspects

15

photoproduct formation.172 High-resolution absorption spectra of s-tetrazine crystals have been The low-energy absorption system of dibenzofuran vapour has been measured at high resolution174 and it was shown that the origin (0) band and the prominent feature at (0 + 445) cm-I have opposite polarization, indicating strong vibronic coupling in this molecule. The absorption spectrum of 9-fluorenone is a near mirror-image to the fluorescence so Herzberg-Teller interactions are not prominently displayed in this molecule. The low-energy transition near 23 O00 cm-l is assigned to a IB2 +- lAl type, with the + lAl n -+ T* transition at 26 OOO cm-l. Four other systems between 31 OOO and 44 OOO cm-' were also assigned. The T -+ n* absorption bands of p-quinones and o-benzoquinone have been assigned,176and a comparison has been made between the absorption and fluorescence spectra of 2-methyl-l-aceanthrenoneand its cation with anthracene-9~arboxa1dehyde.l~~ Some new assignments of the electronic transitions of thiones 178 and absorption and emission spectra of several substituted benzoyl-thiophens 179 have been reported. Electronic absorption properties of ferrocene 180 and of several biomolecules lE1have also been discussed. Charge-transfer spectra between substituted diphenyl sulphides with chloranil, tetracyanoethylene, and 2,3-dichloro-5,6-dicyano-p-benzoquinone,182 and between tetracyanoethylene and a variety of substituted benzenes,lE3have been reported. Stark Efects. Stark effects in the absorption spectroscopy of benzene, naphthalene, and anthracene IE4 and in a merocyanine dye IE5 have been discussed. A potential model of dye molecules based upon measurements of the photocurrent in monolayer assemblies has been developed.ls6 Circular Dichroism and Magnetic Circular Dichroic Spectra.-There have been two papers concerned with the theory of c.d.; one concerned with vibronic coupling,lE7the other with radiationless decay.ls8 Circular dichroism detected 17* 178

17&

J. R. Honner, P. R. Nott, and B. K. Selinger, Austral. J. Chem., 1974, 27, 1613. J. H. Meyling, R. P. van der Werf, and D. A. Wiersma, Chem. Phys. Letters, 1974, 28, 364; R. M. Hochstrasser and D. S. King, Chem. Phys., 1974, 5, 439. A. Bree, A. R. Lacey, I. G . Ross, and R. Zwarich, Chem. Phys. Leiters, 1974,26,329; A. Bree, V. V. B. V. Ikos, and R. Zwarich, J. Mol. Spectroscopy, 1973, 48, 135. R. Zwarich and A. Bree, J. Mol. Spectroscopy, 1974, 52, 329. A. Kuboyama, S. Matsuzaki, H. Takagi, and H. Arano, Bull. Chem. Soc. Japan, 1974, 47, 1604.

S. Hirayama, Bull. Chem. Soc. Japan, 1975, 48, 1127. 17* J. Barrett and F. S. Deghaidy, Spectrochim. Acta, 1975, A31, 707. D. R. Arnold and B. M. Clarke, jun., Canad. J. Chem., 1975,53, 1. lSo L. V. Logansen and F. A. Uvarov, Zhur. fit. Khim., 1975,49, 587. ls1 P.-S. Song and H. Baba, Photochem. and Photobiol., 1974,20,527; T . Inagaki, R. N. Hamm, E. T. Arakawa, and L. R. Painter, J. Chem. Phys., 1974, 61,4246. laa G. G. Aloisi, S. Santini, and S. Sorriso, J.C.S. Faraday I, 1974,70, 1908. V. A. Kuznetsov, A. N. Egorochkin, G . A. Razuvaev, S. E. Skobeleva, and N. A. Pritula, Doklady Akad. Nauk S.S.S.R., Ser. khim., 1974, 216, 812. lS4 R. Mathies and A. C. Albrecht, J. Chem. Phys., 1974,60,2500. Ig6 A. P. Marchetti, Mol. Cryst. Liquid Cryst., 1974, 29, 147. U. Schoeler, K. H. Tews, and H. Kuhn, J. Chem. Phys., 1974, 61, 5009. 0. E. Weigand and E. C. Ong, Tetrahedron, 1974, 30, 1783. B. V. Bokut, A. N. Serydyukov, and V. V. Shepelevich, Optika i Spektroskopiya, 1974, 37, 17'

113.

16

Photochemistry

by a fluorescence two-photon c.d.,lgOand c.d. and 0.r.d. in diketopiperazines lgl and hexahelicene lg2 have been reported. The use of semi-empirical models for the calculation of B terms in magnetic circular dichroic (m.c.d.) spectra has been widely discussed in a series of papers lg3 recently, and other theoretical treatments of m.c.d. have appeared.ls4 Measurement of circular polarization has proved to be useful in the assignment of resonance fluorescence bands in molecular iodine,lg5and m.c.d. measurements in the absorption spectra of 12, Br,, and Clz in the 800-250nm region have resulted in the resolution of the overlapping contributions from the 3110u+and ill Considerable m.c.d. work has been carried out on benzene and its derivatives. In the lBzu+- lAlg transition two ezg modes of wavenumber 608 and 1596 cm-1 have negative m.c.d. and two e,, modes of 1178 and 3056 cm-1 have positive m.c.d.ls7 The m.c.d. spectrum of the lEluregion of the spectrum is too complex to analyse,lgSbut that of toluene shows a large A component, which permits calculation of the magnetic moment of the lElu state of benzene. This study is of interest in that it is the first use of m.c.d. in the vacuum-u.v. spectral region. The magnetic moments in the lE' states of substituted benzenes have been shown to be sensitive to the nature of the substituent, being totally absent in 1,3,5-trinitrobenzene, benzene-l,3,5-tricarboxylic acid, and benzene-l,3,5-tricarbonyl chloride.1sg The m.c.d. spectrum of azulene reveals strong vibronic interactions in the second transition,200aand an extensive study of the absorption, m.c.d. and linear dichroism, and polarized fluorescence excitation spectra of fluoranthenes has been carried out.200b M.c.d. measurements on gaseous RuO, 201 and on phthalocyanine derivatives 202 have been reported. Two-photon Spectroscopy.-Papers dealing with the theory of simultaneous twophoton absorption processes are covered in Section 4 of this chapter. Two-photon absorption processes are of great interest in that the selection rules differ from those for single-photon events, thus permitting excitation of new features in absorption spectra. There is also considerable current interest in the use of twoD. H. Turner, I. Tinoco, jun., and M. Maestre, J . Amer. Chem. SOC.,1974,96,4340. I. Tinoco, J. Chem. Phys., 1975, 62, 1006. J. Schlessinger, A. Gafni, and I. Z . Steinberg, J . Amer. Chem. SOC.,1974,96, 7396. E. Leuliette-Devin, R. Locqueneux, and J. Tillien, Chem. Phys. Letters, 1975, 30, 109. l g 3 J. Michl and J. Michl, J. Amer. Chem. SOC.,1974, 96, 7887; Tetrahedron, 1974, 30, 4215; J. Michl, J. Chem. Phys., 1974, 61, 4270; S. M. Warnick and J. Michl, J. Chem. Phys., 1974, 60, 703; J. Amer. Chem. SOC.,1974, 96, 6280. lS4 I. Z. Steinberg and B. Ehrenberg, J . Chem. Phys., 1974, 61, 3382; A. E. Hansen and E. N. Svendsen, Mol. Phys., 1974, 28, 1061. la6 R. Clark and A. J. McCaffery, J.C.S. Chem. Comm., 1974,1039; L. Seamans, A. Moscowitz, R. E. Linder, E. Bunnenberg, G . Barth, and C. Djerassi, J. Mol. Spectroscopy, 1975, 54,412. l g 6 M. Brith, 0. Schnepp, and P. Stephens, Chem. Phys. Letters, 1974,26, 549. J. S. Rosenfield, A. Moscowitz, and R. E. Linder, J . Chem. Phys., 1974, 61, 2427. S. D. Allen, M. G. Mason, 0. Schnepp, and P. J. Stephens, Chem. Phys. Letters, 1975, 30, 140. 19@ A. Kaito, A. Tajiri, and M. Hatano, Chem. Phys. Letters, 1974, 28, 197; N. Teramae, K. Yazawa, T. Matsui, and S. Tanaka, Chem. Letters, 1974, 581. (a) E. W. Thulstrup, P. L. Case, and J. Michl, Chem. Phys., 1974, 6, 410; (b) J. Kolc, E. W. Thulstrup, and J. Michl, J. Amer. Chem. SOC.,1974, 96, 7188. 201 A. Bowman, R. Evans, and A. Schreiner, Chem. Phys. Letters, 1974, 29, 140. aoa M. J. Stillman and A. J. Thomson, J.C.S. Faraday 11, 1974, 70, 805; B. Hollebone and M. Stillman, Chem. Phys. Letters, 1974, 29, 284. IeB

Spectroscopic and Theoretical Aspects

17

photon excitations to cause selective dissociation or ionization of atomic and molecular species, especially where this might prove to be a practical route to isotope separation. Studies relating to this application will be discussed in Chapter 4. It should again be noted that detection of two-photon absorption is conveniently carried out by monitoring emission, and the technique is thus a form of excitation spectroscopy. Two-photon absorption in several atoms has been In the excellent study by Harvey et al., two-photon spectroscopy has permitted measurement of the Stark effect in the 5s 2Si and 4d 2Dg and 2Dilevels of sodium. The use of the two-photon process eliminates Doppler broadening, and thus allows fine structure to be resolved, as in the case of the studies on sodium of Pritchard et al., Biraben et al., and Bloembergen et al. Clearly the method should be capable of extensive use in spectroscopy where spectral structure has been hitherto unresolved owing to Doppler broadening. The basis of the method is to arrange for excitation sources of the two photons to produce beams in opposite directions, which greatly minimizes the Doppler width. This point is discussed in Section 4. Discrete and diffuse emission following two-photon excitation of the E-state (lXOg+or 31Tn,,+)of molecular iodine has been reported 204 in a study which utilizes the second advantage of two-photon excitation of promoting transitions to states which are parity-forbidden in one-photon excitations. In the study a single rovibronic level is excited, and the resulting extremely simple fluorescence (Figure 1) has been analysed as due to the E -+ B(31T,,+) transition. The sharp structure evident to longer wavelengths than 26 000 cm-1 arises from transitions to bound levels of the state, that to shorter wavelengths resulting from transitions to dissociative &state levels. The bands observed in the latter region are broad (ca. 100cm-l) but not continuous, as might have been expected. The observed intensity variations occur because of the phase relationship between the initial and final wavefunctions, a phenomenon labelled by Condon ‘internal diffraction’. The study reported here represents perhaps the simplest observation of the ‘internal diffraction’ effect to date. A complete rotational analysis has been performed on the 2X++ 211t twophoton absorption transition in NO,205 which automatically but rather tediously permits assignment of the symmetry properties of the electronic wavefunctions of the states in the transition. It has further been shown that it is in fact a very simple exercise to achieve this assignment by measurement of the polarization of the two-photon absorption.205bThe results for a small portion of the NO absorption are shown in Figure 2, from which it can be seen that the intensity of fluorescence is 1.53 f 0.17 times greater for a circularly polarized than for a linearly polarized excitation source, in accord with the expectations for a X -+ I3 transition. 203

*06

D. Pritchard, J. Apt, and T. W. Ducas, Phys. Rev. Letters, 1974, 32, 641; F. Biraben, B. Cagnac, and G . Grynberg, ibid., p. 643; M. D. Levenson and N. Bloembergen, ibid., p. 645; K. C. Harvey, R. T. Hawkins, G . Meisel, and A. L. Schawlow, Phys. Rev. Letters, 1975, 34, 1073; E. V. Baklanov and V. P. Chebotaev, Kuant. Elektron, 1975,2,606; M. S . Pindzola and H. P. Kelly, Phys. Rev. ( A ) , 1975, 11, 1543. D. L. Rousseau and P. F. Williams, Phys. Rev. Letters, 1974, 33, 1368. (a) R. G. Bray, R. M. Hochstrasser, and J. E. Wessel, Chem. Phys. Letters, 1974, 27, 167; (b) R. G . Bray, R. M. Hochstrasser, and H. N. Sung, Chem. Phys. Letters, 1975, 33, 1.

18

Photochemistry

7

H

FREQUENCY (cm-1) Figure 1 Fluorescence spectrum from t wo-photon excitation of molecular iodine. Top spectrum obtained at ten times sensitivity of bottom. i? + 8 transition in fluorescence excited by laser at 28 5 14 cm-l (Reproduced by permission from Phys. Reo. Letters, 1974,33, 1368)

fI

I

- bronch

P,-branch

0,, -branch

A

1

S,, -t'awh 1

LINEAR POLARIZATION

I

I

I

I

4535

I

1

t

RIt- branch d

CIRCULAR POLARIZATION

I

I

I

I

1

I

LASER WAVELENGTH

1

1

'

4545

4540

(A)

Figure 2 Two-photonpolarized fluorescence excitation spectrum of NO (Reproduced by permission from Chem. Phys. Letters, 1975, 33, 1)

Spectroscopic and Theoretical Aspects

19

Several studies, reported almost simultaneously, have been concerned with the two-photon excitation spectroscopy of benzene vapour at high (ca. 80 Torr) pressures and in crystals.2o5b, 206 The results are too extensive to be reported here in detail, but the papers are in agreement that vibrations of wavenumber ca. 1570 cm-l are of great importance. The strongest bands have been assigned to both a vla(b2J and vl8(eZu)transition, with the weight of evidence supporting the former assignment. Polarization studies have assisted greatly in the assignment. It is well known that when atoms absorb circularly polarized light, A4 must change by, say, + 1 unit, and therefore in a two-photon process an S -+ S transition must have zero probability if both photons have the same sense of circular polarization, but will be allowed if the two photons have opposite circular polarization, or are plane-polarized. The same situation prevails for a molecule with tetrahedral symmetry for an A -+ A transition, but when the symmetry is reduced to axial, A -+ A transitions may occur with two circularly polarized photons in the same sense, but with reduced efficiency compared with transitions which are not A + A . It should therefore be relatively easy to tell whether or not a two-photon absorption is occurring between states of the same symmetry through the comparison of circular and plane polarization effects. It is rather surprising that the dominant lines in the two-photon excitation spectrum of benzene have circular/linear polarization ratios of almost zero and, as for an A --+ A transition, are therefore of bzucharacter, since the upper state is lBzU,and this implies that there must be Herzberg-Teller coupling of the lB2, and lAle ground state. This is, of course, of no consequence in one-photon absorption, since parity forbids it to contribute to intensity, but clearly it is of great importance in the two-photon spectrum. The results imply that a substantial contribution of the lAzu+ lAlo transition moment is involved as the intermediate in the two-photon transition. These are not T --f n* excitations, and thus significant vibronic coupling of m* with UT*, nu*, or Rydberg states is implied. Fluorescence lifetimes of two-photon excited states of benzene in the vapour ‘isolated molecule’ limit 207 are discussed in Chapter 4. The two-photon excitation spectrum of naphthalene has been reportedY2O8 and two vibronically-induced odd-parity 1B3u+ lAl, and lBzu+- lAls transitions and two even-parity allowed lB1,-+ lA,, and lA,, t- lA1, transitions have been observed. Two-photon spectra of many biphenyl derivatives have been recordedY2O9 and the assignment of states in a sample of o,o’-bridged biphenyls is given in Figure 3. In crystalline 2,2-paracyclophane two two-photon absorption bands in the 34 700-36 500 cm-1 region have been assigned to even-parity allowed lB1, + lAl, and lB2, -+ lAlg transitions.210 Two-photon excitation spectra of alloxazines and isoalloxazines211 and a full description of a two-photon excitation spectrometer 212 have been given recently. 206

*07

208

L. Wunsch, H. J. Neusser, and E. W. Schlag, Chem. Phys. Letters, 1975, 31, 433; D. M. Friedrich and W. M. McClain, ibid., 1975, 32, 541. L. Wunsch, H. J. Neusser, and E. W. Schlag, Chem. Phys. Letters, 1975, 32, 210. A. Bergman and J. Jortner, Chem. Phys. Letters, 1974, 26, 323; N. Mikami and M. Ito, ibid., 1975, 31, 472.

2os

211 21a

R. P. Drucker and W. M. McClain, J. Chem. Phys., 1974, 61, 2609, 2616. K. Fuke, S. Nagakura, and T. Kobayashi, Chem. Phys. Letters, 1975,31, 205. N. Y. C. Chu and K. Weiss, Chem. Phys. Letters, 1974, 21, 567. R. L. Swofford and W. M. McClain, Rev. Sci. Instr., 1975,46,246.

One- TwoPhoton Photon

om- TwoPhoton Photon OneTwoPhoton Photon

One- TwoPhoton Photon One- TwoPhoton Photon

Figure 3 Summary of two-photon and one-photon excited states in biphenyl and o,o'-bridged biphenyls (Reproduced by permission from J. Chem. Phys., 1974, 61, 2616)

25

7

t

OneTwoPhoton Photon

--

0

h)

21

Spectroscopic and Theoretical Aspects

Photoionization and Electron Detachment.-Photoelectron spectroscopy is not within the scope of this volume, but some papers on photoionization which may be of some interest are listed here. Several theoretical treatments of photoionization in atoms and small molecules have appeared.213 Photoionization in the rare gasesY2l4 atomic hydrogen,216alkali-metal and alkaline-earth atoms,216 magnesium group I1 atoms,21smercury atoms,21gmolecular hydrogen,220 several polyatomic and solvated electrons 222 has been discussed. Multiphoton ionization in the rare gases,223benzene,224and in molecular crystals has also been Electron photodetachment [process (3)] experiments are of interest in that they can provide information regarding the electron affinities of the A* species. For A-

hv

A.

+ e-

(3)

atomic systems, the threshold for photodetachment is a precise and direct means of estimation of the electron affinity, but for molecular anions, photodetachment cross-sections may be unusual since complications can arise. Photodetachment is a vertical process, and for a large change in structure between ion and neutral species, poor Franck-Condon factors for the adiabatic process would restrict observation to the vertical detachment energy, which could greatly exceed the adiabatic electron affinity. Photodetachment thresholds have recently been measured for alkali-metal negative ions (including Li-, Na-, and K-),226yielding results for the electron affinities of 0.61 1, 0.539, 0.497, 0.490, and 0.470 eV for Li, Na, K, Rb, and Cs 213

214

216

216

217 218

21s 220

221

222

223

224 2*6

226

T. J. Broad and W. P. Reinhardt, J. Chem.Phys., 1974,60,2182; J. W. Rabalais, T. P. Debies, J. L. Berkosky, J.-T. J. Huang, and F. 0. Ellison, ibid., 1974, 61, 516; F. M. Chapman, jun. and L. L. Lohr, jun., J. Amer. Chem. SOC.,1974,96,4731;T. E. H. Walker and J. T. Waber, J. Phys. (B), 1974, 7, 674; L. S. Cederbaum, Mol. Phys., 1974, 28, 479; M. Ya. Amus’ya, V. K. Ivanov, and N. A. Cherepkov, Zhur. eksp. teor. Fiz., 1974, 66, 1537; J.-T. J. Huang and F. 0. Ellison, J. Electron. Spectroscopy Related Phenomena, 1974, 3, 339. F. B. Dunning and R. F. Stebbings, Phys. Rev. Letters, 1974, 32, 1286; V. L. Jacobs, ibid., p. 1399; J. A. R. Samson and J. L. Gardner, ibid., 1974, 33, 671 ; F. B. Dunning and R. F. Stebbings, Phys. Rev. (A), 1974, 9, 2378; T. N. Rescigno and C. W. McCurdy, jun., ibid., p. 2409; T . L. John and D. J. Morgan, J. Quant. Spectroscopy Radiutive Transfer, 1974, 14, 777; J. J. Wendoloski and G. A. Peterson, J . Chem. Phys., 1975, 62, 1016. P. M. Dehmer, J. Berkowitz, and W. A. Chupka, J. Chem. Phys., 1974,60,2676. J. L. Carlsten, T. J. McIlrath, and W. H. Parkinson, J. Phys. (B), 1974,7, L244; R. W. Labahn and E. A. Garbaty, Phys. Rev. (A), 1974, 9, 2255; V. G. Mikhalev and S . N. Ogorodnikov, Zhur. priklad. Spektroskopii, 1974, 20, 1079. D. G. Thompson, A. Hibbert, and N. Chandra, J. Phys. (B), 1974,7, 1298. V. Zilitis, Uchen. Zap. Latv. Gosud. Univ., 1972, 171, 82. J. Berkowitz, J. L. Dehmer, Y.-K. Kim, and J. P. Desclaux, J. Chem. Phys., 1974, 61, 2556. K. E. McCulloh and J. A. Walker, Chem. Phys. Letters, 1974,25,439; P. H. S. Martin, T. N. Rescigno, V. McKoy, and W . H. Henneher, ibid., 1974,29,496; J. W. Cooper, Phys. Rev. (A), 1974, 9, 2236. F. 0. Ellison, J. Chem. Phys., 1974, 61, 507; J. Aihara and H. Inokuchi, BuZI. Chem. SOC. Japan, 1974,47,2631; H. G . Grimmeiss and L.-A. Ledebo, J. Appl. Phys., 1975,46, 2155. H. Aulich, L. Nemec, and P. Delahay, J. Chem. Phys., 1974, 61, 4235. J. Bakos, M. L. Nagaeva, and V. G. Ovchinnikov, Kratk. Soobshch. Fiz., 1973,9,3; J. A. R. Samson and G. N. Haddad, Phys. Rev. Letters, 1974, 33, 875; R. Benattar and G. Sultan, J . Appl. Phys., 1974,45,4539; N. B. DelonC, Uspekhi Fiz. Nauk, 1975, 115, 361. P. M. Johnson, J. Chem. Phys., 1975, 62, 4562. B. Kumar, V. E. D. Parkash, and T. S . Jaseja, Indian J. Pure Appl. Phys., 1974,12, 626. D. L. Moores and D. W. Norcross, Phys. Rev. (A), 1974,10, 1646; H. J. Kaiser, E. Heinicke, and R. Rackwitz, 2.Physik, 1974, 270, 259.

22

Photochemistry

respectively. Theoretical studies on photodetachment in C- and F- 227 and other negative ions228have been carried out. Electron affinities for O2 and NO have been measured as 0.44 and 0.024eV, respectively, by this method,229and the electron affinities of OH, NH2,NH, SO,, and S, have been given as 1.829, 0.779, 0.38, 1.097, and 1.663 eV, respectively.230 The onset of photodetachment of electrons from gaseous SH- ions occurs at 538.7 & 0.3 nm, giving an electron affinity of *SH of 2.301 k 0.001 eV. The method of detection in this experiment was a pulsed ion cyclotron resonance spectrometer, and full details of this potentially powerful method have been given.231 Laser photodetachment of nitrite ions has been and some estimates given for the vertical electron affinity of the ONO- species differ somewhat, being 2.36 eV in the study of Lineberger et al. and 2.8 eV in the other paper. An upper limit to the electron affinity of ethylnitrene of 1.87 eV has been given by a photodetachment measurement.233Thresholds for the photodetachment of electrons from silyl, g e r m ~ I , ~ ~ * trifluorosilyl, and trifluoromethyl 235 negative ions have been measured. In the case of the last species, thermochemical data permit the evaluation of the electron affinity of CF3-as 2.01 eV, and considerable differences in geometry between ion and neutral species are indicated, since the photodetachment threshold is measured as 2.82 k 0.01 eV. This result will be of interest to those interested in the substituent effect of CF3, which has been discussed If the reasonable assumption is made that the structures of the pyrrole radical and pyrrolate ion are similar, the electron affinity of the radical is given as 2.39 +, 0.13 eV.237 Electron affinities of benzene and pyridine have been given 238 as 1.15 and 0.62 eV, respectively. Diazines and s-triazine were shown to have positiue electron affinities, i.e. the negative ions are more stable than the parent species. Photoionization measurements have been made on the heat of formation of ally1 cations.23g Photofragment spectroscopy.-The analysis of the angular distribution and energies of fragments arising from photodissociation, using polarized light, permits evaluation of the states involved in the dissociation process and an approach towards the ‘ideal’ experiment in which microscopic reaction rates can be measured, and there has been much increased interest in this phenomenon in the past year, both from an experimental and theoretical standpoint. Papers 227

2La 229

230

231

232

203 234

236 238

237

23*

238

T. Ishihara and T. C. Foster, Phys. Rev. ( A ) , 1974,9,2350. F. H. M. Faisal, J. Phys. (B), 1974, 7, L393. M. W. Siegel, R. J. Celotta, J. L. Hall, J. Levine, and R. A. Bennett, Phys. Rev. (A), 1972, 6, 607; R. J. Celotta, R. A. Bennett, J. L. Hall, M. W. Siegel, and J. Levine, ibid., p. 631. R. J. Celotta, R. A. Bennett, and J. L. Hall, J. Chem. Phys., 1974, 60, 1740. J. R. Eyler and G. H. Atkinson, Chem. Phys. Letters, 1974, 28, 217; J. R. Eyler, Reo. Sci. Instr., 1974, 45, 1154. E. Herbst, T. A. Patterson, and W. C. Lineberger,J. Chem.Phys., 1974,61,1300; J. H. Richardson and L. M. Stephenson, Chem. Phys. Letters, 1974, 25, 318. J. H. Richardson and L. M. Stephenson, Chem. Phys. Letters, 1974,25,321. K. J. Reed and J. I. Brauman, J. Chem. Phys., 1974,61,4830. J. H. Richardson, L. M. Stephenson, and J. I. Brauman, Chem. Phys. Letters, 1975, 30, 17. S. A. Holmes and T. D. Thomas, J. Amer. Chem. SOC.,1975,97, 2337; M. R. Padhye and S. A. Agnihotry, Current Sci.,1975, 44, 264. J. H. Richardson, L. M. Stephenson, and J. I. Brauman, J. Amer. Chem. Soc., 1975,97, 1160. I. Nenner and G. J. Schulz, J . Chem. Phys., 1975, 62, 1747. S. E. Buttrill, A. D. Williamson, and P. Le Breton, J . Chem. Phys., 1975,62, 1586.

Spectroscopic and Theoretical Aspects

23

of a theoretical nature are reported in the final section of this chapter, and amongst the interesting experimental developments can be included the extensions of photofluorescence excitation spectroscopy, described for the visible region in detail in a recent paper,24oto the vacuum-u.v. spectral region.241 In this study the excitation spectrum for the photodissociation of water vapour in the 130 nm region was diffuse, but with vibrational structure of spacing 800cm-l, corresponding to the bending frequency. The OH fragment is formed in a rotationally excited level of the A2Z+ state, and analysis showed that the results were incompatible with the dissociation of the lAl state known to be populated at 130 nmY4lbut they must be due to pre-dissociation of a species of symmetry. All of the observations could be explained if the dissociating vibronic state were the lA2 electronic state with one quantum of the v3(b2)asymmetric stretching vibration excited. A brief report has appeared on the crossed-beam reaction between Ba and LiCl, using laser-induced fluorescence detection of the BaCl product, which gives a lower bound for the bond-dissociation energy of BaCl of 110 k 3 kcal m 0 1 - l . ~ ~Similar ~ studies on the reactions of alkali-metal dimers with hydrogen atoms and molecules 243 and the photodissociation of alkali-metal iodides 244 have been reported. In the photodissociation of C2N2,CN radicals are produced in both the and R2Z+states, as shown by laser-induced photoluminescence ~ p e ~ t r ~ ~ ~ ~ Since the photodissociation does not produce the maximum amount of vibrational excitation in the CN fragments, it was suggested that the excess energy appears as translational or rotational excitation of the fragments. This study can be compared with one in which HCN, CH,CN, C2N2,ClCN, and BrCN were dissociated by electron Synchrotron radiation in the extreme U.V. has been used to excite O2 and N2, and the vacuum-u.v. fluorescence from the atomic fragments was a n a l y ~ e d Both .~~~ discrete regions and continua were observed in the photodissociation spectra, the former corresponding to known Rydberg series. Photodissociation and recombination radiation in diatomic the angular dependence of the spectra of secondary luminescence in gases, 248 and photodissociation spectra and the assignment of low-lying states in butadiene and toluene cations 249 have been discussed. Singlet-Triplet Absorption Spectra.-Spin-orbit interactions and relative intensities of forbidden transitions in I2 and IX molecules (X = other halogen)

x22n

240

241 242 243

244 246

248

24R 24B

R. N. Zare and P. J. Dagdigian, Science, 1974, 185, 739. G. A. Chamberlain and J. P. Simons, Chem. Phys. Letters, 1975, 32, 355. P. J. Dagdigian and R. N. Zare, J. Chem. Phys., 1974, 61,2464.

W. S. Struve, J. R. Krenos, D. L. McFadden, and D. R. Herschbach, J. Chem. Phys., 1975, 62, 404. R. C. Ormerod, T. R. Powers, and T. L. Rose, J. Chem. Phys., 1974,60,5109. (a) W.M. Jackson and R. J. Cody, J. Chem. Phys., 1974,61,4183; (b) I. Tokue, T. Urisu, and K. Kuchitsu, J. Photochem., 1974, 3, 273. L. C. Lee, R. W. Carlson, and D. L. Judge, J. Chem. Phys., 1974, 61, 3261. A. V. Aletsky, B. M. Smirnov, and G. V. Shlyapnikov, Optika i Spektroskopiya, 1974, 36, 1075. L. M . Khayutin, Optika i Spektroskopiya, 1974,36, 1083. R. C. Dunbar, Chem. Phys. Letters, 1975,32, 508.

Photochemistry

24

have been discussed.260The 0 band in the So -+7 ' spectrum of biacetyl was shown to occur at 490 nmy136and vibrational assignments have been given. The So -+Tlabsorption spectra of several substituted benzenes in the vapour phase have been obtained by the oxygen perturbation method,261and the effect of pressure on the singlet-triplet absorption of anthracene crystals has been discussed.2S2The oxygen perturbation method has revealed that the 7" states of substituted pyridine N-oxides are of a n-n* 3L, charge-transfer nature.2s3 The (3) has also been triplet spectrum of tetramethyl-l,3-~yclobutanedione Me Me O+O Me Me

and it was shown that the lowest triplet state of 3A, character lies at 25 718 cm-l. The carbonyl carbons in the excited state adopt a pyramidal structure. Electron-impact Spectra.-A review of electron-scattering spectroscopy has appeared.266 Electron-impact spectra have been reported of helium,2S6H and C0,262 RbI and KI,263NO and N20,264 water,266 He,267Li,258Ba ,25g Hg,260H2,261 and C02.267The study on NO2 yields the ammonia and methane,265bN02y266 interesting result that the 2B2state is asymmetric, possessing different equilibrium bond lengths between the N atom and each 0 atom: this can explain the results of recent microwave-optical double-resonance experiments.268 260 251 252 253

256 255

258

257

258 259 560 281

262

265 284 265

266 287

268

V. S. Yarunin and V. A. Ganin, Optika i Spektroskopiya, 1974,37, 866. J. Metcalfe, M.G. Rockley, and D. Phillips, J.C.S. Faraday ZZ, 1974,70, 1660. S. Arnold, W.B. Whitton, and A. C. Damask, J. Chem. Phys., 1974, 61, 5162. M. Yamakawa, K. Ezumi, Y. Mizuno, and T. Kubota, Bull. Chem. SOC.Japan, 1974, 47, 2982. M. T. Vala, J. Wrobel, and R. Spafford, Mol. Phys., 1974,27, 1241. I. C.Walker, Chem. SOC.Rev., 1974,3,467. D.G.Truhlar and D. C. Cartwright, Phys. Rev. (A), 1974, 10, 1908;R. A. Bonham, Chem. Phys. Letters, 1974,27,332;R.A. Heppner and J. C. Zorn, Phys. Rev. Letters, 1974,33,1321; D.E.Lott, tert., R. E. Glick, and J. A. Llewellyn, J. Quant. Spectroscopy Radiative Transfer, 1975,15, 513. M.R. C. McDowell, L. A. Morgan, and V. P. Myersough, J. Phys. (B), 1975,8, 1053;L. A. Morgan and M. R. C. McDowell, ibid., p. 1073; A. J. Dixon, A. yon Engel, and M.F. A. Harrison, Proc. Roy. SOC.,1975,A343, 333. D. Leep and A. Gallagher, Phys. Rev. (A), 1974,10,1082. G.F. Hanne, J. Kessler, and H. Silberbach, Phys. Letters (A), 1975,51, 351. B. S. Bhakar and B. J. Choudhury, J. Phys. (B), 1974,7,1853. H. Schmoranzer, J. Phys. (B), 1975, 8, 1139. A. Chutjian, D. G. Truhlar, W. Williams, and S . Trajmar, Phys. Reu. Letters, 1974,33,1524; K.N.Klump and E. N. Lassettre, J. Chem. Phys., 1975,62, 1838. T. Huang and W. H. Hamill, J. Chem. Phys., 1974,61, 3144. A. Zecca, I. Lazzizzera, M. Krauss, and C. E. Kuyatt, J. Chem. Phys., 1974,61,4560. (a) C . I. M. Beenakker, F. J. de Heer, H. B. Krop, and G. R. Mohlmann, Chem. Phys., 1974, 6,445; (b) H.D. Morgan and J. E. Mentall, J. Chem. Phys., 1974,60, 4734. M. Krauss, R. J. Celotta, S. Mielczarek, and C. E. Kuyatt, Chem. Phys. Letters, 1974,27,285. M. Misakian, M. J. Mumma, and J. F. Faris, f. Chem. Phys., 1975,62,3442;S. Tsurubuchi and T. Iwai, J. Phys. SOC.Japan, 1974,37, 1077. R.Solarz and D. A. Levy, J. Chem. Phys., 1974,60,842.

Spectroscopic and Theoretical Aspects

25

Electron-impact studies of the following molecules have been reported : methane and simple formaldehyde 270 and other simple carbonyl corn pound^.^^^ In the case of acetone vapour, a second triplet state was identified in the 5.3-6.1 eV region, with a maximum at 5.88 eV. Acetylene, allene, ethylenes, and simple alkynes have been studied by this method,272as have methyl cyanide 273 and trans-az~methane,~~~ which shows two hitherto unreported triplet states, with maxima at 2.75 and 4.84 eV. There have been several studies on benzene and substituted benzenes.275The study of Freund et al. is of interest in that in the low-pressure region of 1 x Torr, results indicate that the lifetime of triplet benzene is at least 500 ps, an order of magnitude longer than the value at 20Torr. Studies on the fluorescence from the lBeu state of benzene produced by electron impact 278 show that, for low-energy electrons, excitation to a new species at -6.5 eV, identified as the 3Elustate, results in fluorescence, implying that intersystem crossing from the initially formed triplet to the singlet competes with internal conversion in the triplet manifold. At higher electron energies, emission from fragments is observed. Low-pressure electron impact on naphthalene and azulene yields luminescence from the S, and S2 levels, respectively, as would be Electron-impact spectra of p ~ r i d i n e , ~ ~ ~ Ar-Kr-Xe and carbon 280 have been reported, and contamination of electron-impact spectra due to negative-ion formation has been discussed.281 The vertical ionization potential of CF2 has been measured as 11.54 eV by electron-impact methods.282 269

270 271 272

273 274

276

T. Huang and W. H. Hamill, J. Phys. Chem., 1974,78,2077,2081; C. W. Duncan and I. C. Walker, J.C.S. Faraday IZ, 1974, 70, 577; F. J. de Heer, Internat. J. Radiation Phys. Chem., 1975, 7, 137; L. Walter and S. Lipsky, ibid., p. 175; C. I. M. Beenakker and F. J. de Heer, Chem. Phys., 1975,7, 130. A. Chutjian, J. Chem. Phys., 1974,61,4279; W.-C. Tam and C. E. Brion, J. Electron Spectroscopy Related Phenomena, 1974, 3, 467; 1974,4, 139, 149. W. M. St. John, tert., R. C. Estler, and J. P. Doering, J. Chem. Phys., 1974,61, 763. D. F. Dance and I. C. Walker, J.C.S. Faraday II, 1974,70,1426; M. Coggioca, 0. A. Mosher, W. Flicker, and A. Kuppermann, Chem. Phys. Letters, 1974, 27, 14; C. I. M. Beenakker and F. J. de Heer, Chem. Phys., 1974, 6, 291; C. I. M. Beenakker, P. J. F. Verbeek, G. R. Mohlmann, and F. J. de Heer, J , Quant. Spectroscopy Radiative Transfer, 1975, 15, 333; 0. A. Mosher, W. M. Flicker, and A. Kuppermann, J. Chem. Phys., 1975,62,2600; M. Tsuji, T. Ogawa, Y. Nishimura, and N. Ishibashi, Chem.Letters, 1975, 317. T. Shibata, T. Fukuyama, and K. Kuchitsu, Bull. Chem. Soc. Japan, 1974,47,2573. 0. A. Mosher, M. S. Forster, W. M. Flicker, A. Kuppermann, and J. L. Beauchamp, Chem. Phys. Letters, 1974, 29, 236; 0. A. Mosher, M. S. Forster, W. M. Flicker, J. L. Beauchamp, and A. Kuppermann, J. Chem. Phys., 1975,62,3424. H. J. Hartfuss, 2.Naturforsch., 1974, 29a, 1489; L. V. Iogansen, Z h u r . 3 ~Khim., . 1974, 48, 1345; H. P. Mehta and A. T. Peters, Appl. Spectroscopy, 1974, 28, 241; C. I. M. Beenakker and F. J. de Heer, Chem. Phys. Letters, 1974,29,89; K. C. Smyth, J. A. Schiavone, and R. S. Freund, J. Chem. Phys., 1974, 61, 1789; R. Azma and G. J. Schulz, ibid., 1975, 62, 573; T. Ogawa, T. Imasaka, M. Toyoda, M. Tsuji, and N. Ishibashi, Bull. Chem. Soc. Japan, 1975, 48, 645.

278 277

278

279 280 281

a82

K. C. Smyth, J. A. Schiavone, and R. S. Freund, J. Chem. Phys., 1974,61,1782,4747; C. I. M. Beenakker, F. J. de Heer, and L. J. Oosterhoff, Chem. Phys. Letters, 1974, 28, 320, 324. M. Tsuji, T. Ogawa, and N. Ishibashi, Chem. Phys. Letters, 1974, 26, 586; K. C. Smyth, J. A. Schiavone, and R. S. Freund, J. Chem. Phys., 1975, 62, 136. A. E. Kassem and R. S. Hickman, Phys. Fluids, 1974,17, 1976; R. G. Suchannek and J. R. Sheridan, J. Chem. Phys., 1975, 62, 3036; E. H. van Veen and F. L. Plantenga, Chem. Phys. Letters, 1975, 30, 28. E. T. Verkhovtseva, A. E. Ovechkin, and Ya. M. Fogel, Chem. Phys. Letters, 1975, 30, 120. R. Le Sage, P. Bocquillon, and J. Faucherre, Compt. rend., 1974, 279, C, 125. E. N. Lassettre and W. M. HUO,J. Chem. Phys., 1974, 61, 1703. D. L. Hildenbrand, Chem. Phys. Letters, 1975, 30, 32.

Photochemistry Triplet-Triplet Absorption.-A modulation method has been devised which permits the determination of absolute extinction coefficients for triplet-triplet Spectra for fluorenacene (4) were presented which showed two 26

Me

Me (4)

strong peaks at 21 900 and 20 800 cm-' with extinction coefficients of 55 600 and 93 500 mol-1 cm-l, respectively. Modulation spectroscopy has been further Linear dichroic measurements on the triplet-triplet absorption spectrum of phenanthrene 28Sa and naphthalene 2 8 S b have been carried out, and in the case of phenanthrene, polarization has been found in the 20 000-25 OOO cm-I region, which identifies the transition as a long-axis-polarized ,A1 +- 3B2+- ,BZ+transition in phenanthrene has been transition. The location of the discussed.28sIn the case of naphthalene the polarization results were insufficient to identify the short-axis-polarized T-T absorption in the 350-410 nm region as the 3A,- + ,BIu+transition or a vibronic band of the ,B3,- --f ,Blu+ transition promoted by a b,, vibrational mode. The effects of matrix upon the linewidth of the 3B2u++ 3B1,transition in naphthalene in durene have been There have been extensive studies on the triplet-state absorptions in nitronaphthalenes 288 and metho~y-naphthalenes,~~~ from which it was concluded that the /3-substituted compounds have T-T absorption spectra resembling closely those of the parent naphthalene, whereas a-substitution leads to dramatically different spectra which can be associated with enhancement of the 3Blp++- 3B2u+ and ,A,- +- Ball+transitions of the parent. The polarized triplet-triplet absorption spectra of biphenyl, carbazole, and phenanthrene have been compared, and phenanthrene has been found to differ considerably from the other two m01ecules.~~~ T-T Absorption spectra of cyano-substituted benzenes,291several aromatic v a p o ~ r s tetracene , ~ ~ ~ in THF,2g3 and hexachloroacetone 2g4 have been reported, and an interesting use of the triplet state of anthracene as a probe for measuring the rates of lateral diffusion of molecules of biological interest has been Absorption spectra of 283 2E4 286

286 287 288

288

2Bo 201 203

293 294

Zs6

U. B. Ranalder, H. Kanzig, and U. P. Wild, J. Photochem., 1975, 4, 97. H. H. Gunthard, Ber. Bunsengesellschaft phys. Chem., 1974, 78, 1110. (a) T. Hoshi, K. Ota, E. Shibuya, and K. Murofushi, Chem. Letters, 1975, 137; (b) H. G. Kuball and E. Ewing, Chem. Phys. Letters, 1975, 30, 457. T. G. Pavlopoulos, Chem. Phys. Letters, 1974, 27, 245. H. Haertel, F. Z. Khelladi, and R. Ostertag, Chem. Phys. Letters, 1975, 30, 472. C. Capellos and G. Porter, J.C.S. Faraday II, 1974,70,1159; J. J. Mikala, R. W. Anderson, jun., and L. E. Harris, Ado. Mol. Relaxation Processes, 1973, 5, 193. K. Hara, T. Takemura, and H. Baba, J. Mol. Spectroscopy, 1974, 50, 90. D. Lavalette and C. Tetreau, Chem. Phys. Letters, 1974, 29, 204. H. Morita, S. Matsumoto, and S. Nagakura, Bull. Chem. SOC.Japan, 1975, 48, 420. C. W. Ashpole and S . J. Formosinho, J. Mol. Spectroscopy, 1974, 53, 489. G. Levin and M.Szwarc, Chem. Phys. Letters, 1975, 30, 116. M.Koyanagi and L. Goodman, Chem. Phys., 1974,5, 107. K. Razi Naqvi, J.-P. Behr, and D. Chapman, Chem. Phys. Letters, 1974, 26, 440.

Spectroscopic and Theoretical Aspects

27

anions of aromatic ketones and other reactive free radicals have been recorded.2g6a An extensive paper has given an excellent outline of the use of T-T absorption spectra in identifying potentially useful laser S, + Sn Spectra.-A description has been given of a method for recording ultrafast absorption spectra using a passively mode-locked ruby laser with a ruby amplifier, a pulsed flashlamp probe source, and streak-camera detection for ps time resolution. Results for the dye 3,3'-diethylthiatricarbocyanine in methanol were These results can be compared with those obtained by an alternative method 287b which permits nm spectral resolution and ps time resolution over the entire visible region, and which was f i s t used on the Sl-+ Sn absorption of 3,3'-diethyloxadicarbocyanine iodide, and which has recently been used to record the S, S, absorption spectra of bis-(4-dimethylaminodithiobenzil) nickel(rI), and of SnIv, Pd", and Cu" p o r p h y r i n ~ .The ~ ~ ~use of timeresolved Sl -+ s,,T, + T, absorption and emission spectroscopy to assist in the selection of laser dyes has been illustrated with respect to anthracene and its S, -+ S, Spectra of coronene, 1:Zbenzanthracene, 1:12-benzperylene, 1,2,3,4-dibenzanthraceneYand benzo[b]chrysene in poly(methy1 methacrylate) and toluene have been reported, the method of detection being modulation spectrophotometry, for which it is claimed that species of lifetime down to 50 ns can be detected, although measurement of lifetimes below s is not possible.300 For coronene the band at 21 700 cm-l is assigned to a T, -+ T, transition, in accord with an early study by Porter and Windsor, but in disagreement with Hodgkinson and Munro's recent Transient S, -+ s,, and T, -+ T n spectra of naphthalene in 3-methylpentane at 85 K and 293 K and of anthracene in poly(methylmethacry1ate) using a solid-state laser in the pulsetransmission mode have been The large difference in the S, -+ Sn absorption spectrum and fluorescence properties of 1,1'-binaphthyl in fluid solution compared with rigid solution is related to the ability of the fluorescent S, state to change its conformation in the fluid rnedium,ls4but not in the solid. A high-resolution spectrum of the lag-+ lau system of O2 has permitted evaluation of the molecular constants for the l(DU state of oe = 1071 k 4 cm-l, x u , = 8.3 1 0.8cm-l, Be = 1.116 5 0.008cm-l, and ole = 0.014 k 0.005 c 1 ~ 1 - l . ~ ~ ~ The modulation excitation method has been used to observe the absorption spectrum of the pyrene excimer in different solvents, triplet excimer bands in lY2-benzanthracene and lY2;3,4-dibenzanthracenein high concentration, and the excited --f

28e

297

288

29s

(a) J. E. Jordan, D. W. Pratt, and D. E. Wood, J. Amer. Chem. SOC.,1974, 96, 5588; H. Hoshino, S. Arai, M. Imamura, and A. Namiki, Chem. Phys. Letters, 1974,26, 582; (b) T. G. Pavlopoulos and P. R. Hammond, J. Amer. Chem. SOC.,1974, 96, 6568. (a) A. Miiller and G. R. Willenbring, Ber. Bunsengesellschuftphys. Chem., 1974, 78, 1153; (b) H. Tashiro and T. Yajima, Chem. Phys. Letters, 1974, 25, 582. D. Magde and M. W. Windsor, Chem. Phys. Letters, 1974,27,31; D. Magde, B. A. Bushaw, and M. W. Windsor, ibid., 1974, 28, 263; D. Magde, M. W. Windsor, D. Holten, and M. Gouterman, ibid., 1974, 29, 183. J. Langelaar, Appl. Phys., 1975, 6, 61. K. H. Hodgkinson and I. H. Munro, J. Mol. Spectroscopy, 1973, 48, 57; M. A. Slifkin and A. 0. Al-Chalabi, Chem. Phys. Letters, 1974, 29, 405; G. Porter and M. Windsor, Proc. Roy. SOC.,1958, A245, 238. D. Bebelaar, Chem. Phys., 1974, 3, 205. D. H. Katayama, R. E. Huffmann, and Y. Tanaka, J. Chem. Phys., 1975,62,2939.

28

Photochemistry

states of organic charge-transfer complexes.3o3Absorption due to ion pairs and charge-transfer complexes on a ps time-scale has been monitored in some elegant experiments using anthracene and diethylaniline pairs.3o4 Fluorescence Spectra.-Broad U.V. emission from magnesium atoms in argon and krypton matrices at 4.2 and 12 K, respectively, has been observed at 297.0 and 323.6 nm, respectively. The band is due to the lP +- IS excitation of the atom, but the nature of the emitting species was not positively identified.305There have been several studies on the emission systems of helium, neon, argon, and xenon.3o6Emission intensities of OH U.V. bands 307 and U.V. spectra of CH+ and OD+,308transition moments of CH in emission,3oea re-examination of the vacuum-u.v. emission spectrum of CO in the 95-120 nm region 310 which shows that many bands assigned previously to CO arise from N,, the SO B3Z- -+ band vacuum-u.v. emission from electronically excited N2,312 fluorescence from molecular iodine log* lg5# l g 6313 ~ and diatomic halogen fluorides,l1° fluorescence from the C2Z+state of NS,314Cd, fluorescence (phosphorescence) due to the 3Cu+-+lZg+ photoluminescence from Rb, 316 and R u O , ~the ~ ~ytterbium vapour gas and laser-stimulated fluorescence of diamond 319 have been the subjects of recent papers. The fluorescence of NO, excited by the He-Cd 442 nm laser exhibits characteristics of perpendicular transitions belonging to 2B1(K’ > 0) vibronic Near4.r. emission from H 0 2 arising from both vibrational ground-state overtone transitions and vibronic 2A‘ -+ ,A” transitions has been and lAg 0,

x3X-

303 304

306

310 311 312 313

314 316 316 317

319

3ao

321

M. Slifkin and A. Al-Chalabi, Chem. Phys. Letters, 1974,29, 110; 1975, 30,227; 1975,31, 198. T.J. Chuang and K. B. Eisenthal, J. Chem. Phys., 1975,62,2213. L. B. Knight, jun., R. D. Brittain, M. A. Starr, and C. H. Joyner, J. Chem. Phys., 1974,61, 5289. H. H. Carls, 2. Naturforsch, 1974, 29a, 1435;N. G. Basov, V. A. Danilychev, and V. A. Dolgikh, Pis’ma Zhur. Eksp. Teor. Fiz.,1974, 20, 124; P. Moerman, R. Boucique, and P. Mortier, Phys. Letters (A), 1974,49,179;R. C. Michaelson and A. L. Smith, J. Chem. Phys., 1974,61,2566;A. J. T.Holmes and J. R. Cozens, J. Phys. ( D ) , 1974,7,1723;J. Dupont-Roc and M. Leduc, J. Physique-Lettres, 1974,35,L-175;E. Koch, V. Saile, N. Schwentner, and M. Skibowski, Chem. Phys. Letters, 1974, 28, 562; R. Brodmann, R. Haensel, U. Hahn, U. Nieisen, and G. Zimmerer, ibid., 1974,29, 250;E. H. Fink and F. J. Comes, ibid., 1975, 30, 267; G. Baravain, J. Bretagne, J. Godart, and G. Sultan, 2. Physik (B), 1975, 20, 255. D.H. Edwards, G. T. Davies, and D. E. Phillips, J . Phys. (D), 1974, 18, 2562. A. J. Merer, D. N. Malm, R. W. Martin, M. Honni, and J. Rostas, Canad. J. Phys., 1975,53, 251. A. D. Smirnov, L. A. Kuznetsova, and N. E. Kuz’menko, Vestnik. Moskou. Unio. Khim., 1974,No. 6,p. 673. S. G.Tilford and J. D. Simmons, J. Mol. Spectroscopy, 1974,53,436. G.R. H6bert and R. V. Hodder, J. Phys. ( B ) , 1974,7,2244. M. F. Golde, Chem. Phys. Letters, 1975, 31, 348. J. Tellinghuisen, Phys. Rev. Letters, 1975,34, 1137. S. J. Silvers and C. L. Chiu, J. Chem. Phys., 1974,61, 1475. H. Vreede, F. C. R. Claridge, and L. F. Phillips, Chem. Phys. Letters, 1974,27, 1. J. M. Brom, C. H. Durham, and W. Weltner, J. Chem. Phys., 1974, 61,982. R. Scullman and B. Thelm, J. Mol. Spectroscopy, 1975,56,64. V. M. Klimkin, Kvan. Elektron., 1975, 2, 579. D. M. Adams and S . J. Payne, Acta Phys. Polon., 1974,B5, 1959;J.C.S. Faraday 11, 1974,70, 1959. S. Butler, C. Kahler, and D. H. Levy, J. Chem. Phys., 1975,62,815. K. H. Becker, E. H. Fink, P. Langen, and U. Schurath, J. Chem. Phys., 1974,60,4623.

Spectroscopic and Theoretical Aspects 29 'dimol' emission in Nd-laser-pumped 0,in the vapour and solution phases has been seen.322Intense red fluorescence has been seen in matrix-isolated CC12, CBr,, and CCIBr,323but corresponding emission from CI, was not obtained. Blue emission from CFCl was also Of the many papers on the fluorescence spectral properties of complex polyatomic molecules published during the past year, a few may be singled out as meriting special attention. There have been several additions to the growing list of molecules exhibiting relatively easily observable fluorescence from second excited singlet states. The observations this year have been largely confined to S

sulphur-containing molecules, and include xanthione (9,which has a quantum yield of fluorescence from S, in solution of 5 x and the spectra shown in Figure 4;324a number of other aralkyl thiones with similar spectra and quantum yields,325and a simpler molecule, thiophosgene, which exhibits very strong S2 emission in the vapour phase.32s In the last study excitation spectroscopy showed that the S, fluorescence originated in the upper levels corresponding to the 0" or 3l (147 cm-l above 0') and 4' (38 cm-l above 0") levels of the S, state. Transitions to higher vibrational levels did not result in observable S, emission, indicating an efficient non-radiative decay process for these levels. Also prominent in the excitation spectrum was the 474 cm-l out-of-plane bending mode of ground-state thiophosgene, and the observation of S2fluorescence is rationalized on the basis of the distortion of the planar ground state to pyramidal configuration by this vibrational excitation, producing the pyramidal excited S, state, which under collision-free conditions lives long enough to emit. Delayed fluorescence from higher excited singlet states of 1,2-beazanthracene and fluoranthene has also been Hirayama and Lipsky have extended their observations of weak fluorescence from unlikely candidates for luminescence by examining propylene, 1-butene, cis-2-butene, trans-2-butene, l-hexene, cis-2-hexene, trans-2-hexeneY2-methylpentene, and 2,3-dimethyl-2-butene excited at 184.9 nm in the vapour and liquid phases.328 Quantum yields in general were of the order of and fluorescence observed was in the 35 000-50 000 cm-1 region of the spectrum. The authors s23 823

324

321 32e

sa7 828

I. B. C. Matheson, J. Lee, B. S. Yamanashi, and M. L. Wolbarsht, Chem. Phys. Letters, 1974, 27, 355. D. E. Tevault and L. Andrews, J. Mot. Spectroscopy, 1975,54, 54, 110; J. Amer. Chem. SOC., 1975, 97, 1707. J. R. Huber and M. Mahaney, Chem. Phys. Letters, 1975, 30, 410. M. H. Hui, P. De Mayo, R. Sau, and W. R. Ware, Chem. Phys. Letters, 1975,31,257. S . Levine, A. R. Knight, and R. P. Steer, Chem. Phys. Letters, 1974,29,73. B. Nickel, Chem. Phys. Letters, 1974,27, 84. F. Hirayama and S. Lipsky, J. Chem. Phys., 1975, 62, 576.

30

Photochemistry

identify the emission as due to transitions between Rydberg upper states and ground electronic states, and consider the insensitivity of the fluorescence spectrum compared with the absorption spectrum of environmental perturbation to be due to the possibility that the vibrationally relaxed Rydberg state has an electron distribution significantly less extended spatially than the vertically excited state.

Also worthy of comment is the survey of the single-vibronic-level fluorescence spectra of benzene published recently.lsS The study confirms that the dominant fluorescence structure from every emitting level is that arising from transitions in which the e,, mode v6 changes quantum number by k 1, while A ~ I= 0 for all other modes except vl. All other transitions are at least an order of magnitude

Spectroscopic and Theoretical Aspects

31

weaker and derive intensity from first-order Herzberg-Teller transitions involving e2, modes other than v g or more commonly from second-order effects. Readers are recommended to this excellent treatment of transitions in the molecule that has long been held to be the perfect example of Herzberg-Teller coupling theory. The emission spectra of formaldehyde have been discussed in a review article.sB Difluorodiazirine fluoresces strongly in the vapour phase with the emission assigned to the x1Bl(n7r*) + transition.32B The fluorescence of phenylacetylene,330fluorescence and phosphorescence of chlorobenzene and benzyl luminescence from the highly polar fluorobenzonitriles and cyanoan is ole^,^^^ azulene and pyrene and indane, indene, and the a-indonyl p y r a ~ i n e ,336 ~ ~ carbazole,ls8 ~, and other azo337 phenyl- and b e n z - o x a ~ o l e sbenzoquinone, ,~~~ camphorquinone, and 9-flu0renone,~~@ rigid and non-rigid phenylalkylcarboxylic acids,340retinal p01yenes,~*lproteins,342and many dyestuffs 343 have been reported. The red shift (termed ‘edge excitation red shift’, EERS) observed in the fluorescence of quinine and related compounds upon excitation at the long-wavelength edge of the first absorption band has been attributed to the result of the solvent reorientation relaxation rate being small compared with the emission rate (TP < T R ) and the Franck-Condon solvation energy being large with respect to solvent The phenomenon may thus be general. There have been many studies reported on the fluorescence of molecular species in crystalline and thin-film matrices,

zlAl

3p8 330

331

332 333

334 33s 336

337

338

339

340

341

34a

343

P. H. Hepburn, J. M. Hollas, and S. N. Thakur, J. MoL Spectroscopy, 1975,54,483. M. A. Shashidhar and K. Suryanarayana Rao, Current Sci., 1975,44, 154. T. Ichimura, T. Hikida, and Y . Mori, J. Phys. Chem., 1975,79,291. J. H. Lui and S. P. McGlynn, J. Luminescence, 1975,9,449;J. Mol. Spectroscopy, 1975, 55, 163. J. M. Friedman and R. M. Hochstrasser, Chem. Phys., 1974, 6, 145; G.Eber, F. Griineis, S. Schneider, and F. Dorr, Chem. Phys. Letters, 1974,29,397. P. Kroning, 2. Nuturforsch., 1974, 29a, 804; S. Hino, T. Hirooka, and H. Inokuchi, Bull. Chem. SOC.Japan, 1975, 48, 1133. B. Brocklehurst and D. N. Tawn, Spectrochim. Actu, 1974,30A,1807. H.-K. Hong and G. W. Robinson, J. Mol. Spectroscopy, 1974,52, 1. I. Yamazaki, K. Uchida, and H. Baba, Chem. Letters, 1974, 1505; H. Bisle and H. Rau, Chem. Phys. Letters, 1975,31, 264;J. M. P. J. Verstegen, J. L. Sommerdijk, B. Pakula, and Z. Slanina, J. Luminescence, 1975, 10,39. N.A. Borisevich, L. A. Barkova, and V. V. Gruzinsky, Actu Uniu. Szeged. Phys. Chem., 1974, 20, 251. T. M. Dunn and A. H. Francis, J. Mol. Spectroscopy, 1974,50, 14;R.Zwarich and A. Bree, ibid., 1974,52,329;D. B. Larson, J. F. Amett, A. Wahlborg, and S. P. McGlynn, J. A m r . Chem. SOC.,1974,96, 6507. J. Tournon, M. Abu-Elgheit, P. L. Avouris, M. Ashraf, and M. A. El-Bayoumi, Chem. Phys. Letters, 1974, 28, 430. R. Christensen and B. Kohler, Photochem. andPhotobiol., 1974,19,401;J. B. Birks and D. J. S . Birch, Chem. Phys. Letters, 1975,31, 608. Z.Varkonyi and L. Szalay, Acta Univ. Szeged. Phys. Chem., 1974,20, 199;A. G.Szabo and K. B. Berens, Photochem. und Photobiol., 1975,21,141. N. A. Borisevich and V. V. Gruzinskii, Acta Univ. Szeged. Phys. Chem., 1973, 19, 327; I. Ketskemety, B. Racz, Z. Bor, and L. Kozma, ibid., 1974,20,191;E. N. Kaliteevskaya and T. K. Razumova, Optiku i Spektroskopiyu, 1974,36,1118;G. A. Reynolds and K. H. Drexhage, Opt. Comm., 1975,13,222;L. A. Bykovskaya, R. I. Personov, and B. M. Kharlamov, Chem. Phys. Letters, 1974,27,80;B. S . Neporent, V. B. Shilov, G. Lukomsky, and A. G. Spiro, ibid., 1974,27,425;G. Mourou and M. M. Malley, ibid., 1975,32,476. K. Itoh and T. Azumi, Chem. Phys. Letters, 1973, 22, 395, J. Chem. Phys., 1975, 62, 3431.

32

Photochemistry

including naphthalene,345a n t h r a ~ e n e ,346 ~ ~t e~t,r a ~ e n e , ~ biphenyl,348u ~' pe~ylene,~~~~ and tetraphenyl-Group IV Excimer emission has been recorded in glassy films of some aromatic hydroc a r b o n ~ carbazole ,~~~ double m01ecules,~~~ d i n a p h t h y l p r ~ p a n e and , ~ ~ ~pyrene in poly(methy1 m e t h a ~ r y l a t e ) . In ~ ~ this ~ last study it was shown that the pyrene excimer emission seen at high concentrations does not arise from microcrystallites, but from pairs of molecules close to the excimer configuration. The yield of this emission was enhanced by aggregation caused by attraction between groundstate molecules due to van der Waals forces. These forces account also for the observed broadening and red shift in the absorption. Emission spectra of anthraquinone radical anions,354 p-xylene-type free radicals,355and of aromatic hydrocarbon mono- and di-negative ions 356 have been recorded. Fluorescence spectra of a charge-transfer complex have been preusing single-mode laser-induced resonance fluorescence to ~ e n t e d .A~ method ~~ obtain the rotational structure of large molecules has been There have been several papers concerned with the analytical uses of fluorescence. Thus the determination of lead in blood by atomic fluorescence the determination of mercury at picogram I-1 levels in the use of isocein as a fluorescent reagent for calcium,361fluorescent reactions of eriochrome red B with Be, Mg, Al, In, Ga, and Zn as a method of determinat i ~ n fluorimetric , ~ ~ ~ determination of chloroquine 363 and of anthracene in a n t h r a q u i n ~ n eand , ~ ~the ~ use of fluorescence methods in the characterization of complex mixtures 365 have been discussed. Readers with criminal tendencies 345

348

347 348

349

350 361 36a

363 364

356

366 367

358

35g

360

361

J. J. Dekkers, G. P. L. Hoornweg, C. MacLean, and N. H. Velthorst, Chem. Phys., 1974,5, 393; F. W. Ochs, P. N. Prasad, and R. Kopelman, Chem. Phys. Letters, 1974, 29, 290. L. N. Kivach, Muter. Resp. Konf. Molodykh Uch. Fiz., 1972,2,28; W. Haller, H. Stichtenoth, and H. H. Perkampus, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 1221; J. B. Birks, Mol. Cryst. Liq. Cryst., 1974,28, 117; E. Glockner and H. C. Wolf, Chem. Phys. Letters, 1974, 27, 161; A. Brillante and D. Craig, ibid., 1974, 29, 17; M. Sceats, ibid., p. 298; A. Brillante, D. P. Craig, A. W.-H. Mau, and J. Rajikan, ibid., 1975,30, 5 ; P. C. Subudhi, N. Kanamaru, and E. C. Lim, ibid., 1975, 32, 503; M. D. Cohen, Z. Ludmer, and V. Yakhot, Phys. Status Solidi (B), 1975, 67, 51 ; S. Iwashima, H. Honda, M. Kuramachi, T. Sawada, M. Takekawa, S. Fujisawa, and J. Aoki, Nippon Kagaku Kaishi, 1975, 746. H. Muller, H. Bassler, and G. Vaubel, Chem. Phys. Letters, 1974, 29, 102. (a) A. Bree, M. Edelson, and R. Zwarich, Chem. Phys., 1975, 8, 27; (b) 1. Abram, R. A. Auerbach, R. R. Birge, B. E. Kohler, and J. M. Stevenson, J. Chem. Phys., 1974, 61, 3857. T.-S. Lin, Chem. Phys., 1974, 6, 235. W. Arden, L. M. Peters, and G. Vaubel, J. Luminescence, 1974, 9, 257. G. E. Johnson, J. Chem. Phys., 1974,61, 3002. P. Avouris, J. Kordas, and M. A. El-Bayoumi, Chem. Phys. Letters, 1974,26, 373. P. Avis and G. Porter, J.C.S. Faraday 11,1974, 70, 1057. V. Y. Oginets and V. L. Rapoport, Zhur. fiz. Khim., 1974, 48, 729. Kh. I. Mamedov and M. M. Khalilov, Optika i Spektroskopiya, 1975,38, 701. G. J. Hoytink, Chem. Phys. Letters, 1974,26, 318. M. Itoh, Chem. Phys. Letters, 1974, 26, 505; E. Gaweda and J. Prochoron, Chem. Phys. Letters, 1975, 30, 155; J. Prochorow, J. Luminescence, 1974, 9, 131. S. H. Dworetsky, L. E. Brus, and R. S. Hozack, J. Chem. Phys., 1974, 61, 1581. H. G. C. Human and E. Norval, Analyt. Chim. Acta, 1974, 73, 73. R. J. Watling, Analyt. Chim. Acta, 1975, 75, 281. G. M. Huitink, Analyt. Chim. Acta, 1974, 70, 311. C. P&ez Conde, J. A. PBrez-Bustamante, and F. Burnel Marti, Analyt. Chim. Acta, 1974,73, 185.

363 364

385

R. J. Lukasiewicz and J. M. Fitzgerald, Appl. Spectroscopy, 1974, 28, 151. M. Funisawa, S. Iwasaki, and Y . Matsaura, J. Chem. Soc. Japan, 1974, 11, 2228. J. B. F. Lloyd, Analyst, 1974, 99, 729.

Spectroscopic and Theoretical Aspects

33

may wish to know that the first successful prosecution in the U.K. has been reported of a murderer based upon identication of car-tyre prints by their fluorescence spectral characteristic^.^^^ The use of fluorescent 1,3-dialkylindoles as probes for micellar systems has been PhosphorescenceSpectra.-Luminescence from a low-lying triplet state of water has been reported. It has been shown that two long-lived emission systems in the biacetyl crystal described previously by Sidman and McClure (see ref. 368) are in fact due to impurities, and a complete analysis is presented of the true 3A, -+ lA, phosphorescence. The zero-zero band in emission is found at 20 3 2 7 ~ r n - l . l ~A~ satisfactory account of the six characteristic bands in the phosphorescence spectrum of benzene has been given on the basis of pseudoJahn-Teller vibronic interactions between the lower 3Bluand 3Elustates in which two active vibrations in the pseudo-cylindrical approximation are r o~n~e n e , benzophenone ~'~~ in The phosphorescence spectra of a n t h r a ~ e n e c, ~ ~ aqueous pyrimidine porphyrins,208,373 and crystalline charge-transfer complexes 374 have been reported. Tribophosphorescence in aniline hydrochloride and coumarin 375 and recombination luminescence in benzene and L-tryptophan 376 have also been discussed, and some chemiluminescence spectra of CN, SrO, and FeO Double-resonance Spectroscopy.-A review has been given of dou ble-resonance methods in Attention will be focused here on optically (usually phosphorescence) detected magnetic resonance experiments (ODMR). Microwave-optical double-resonance experiments have been carried out on the specpermitting assignment of the rotational K = 0 - 4 trum of gaseous N02,37D side-bands of the 493 nm band. Studies have been carried out using ODMR methods on the lowest triplet state of toluene,380p - c h l o r ~ a n i l i n e and , ~ ~ ~dibromonaphthalene single 366 367

36*

369 3i0

J. Loughtan, J. Lloyd, and T. Watson, Nature, 1974,250, 762. N . E. Schore and N . J. Turro, J. Amer. Chem. SOC.,1975, 97, 2488. A. Bernas and T. B. Truong, Chem. Phys. Letters, 1974, 29, 585. J. van Egmond and J. H. Van der Waals, Mol. Phys., 1974,28, 457. (a) J. Ferguson and A. W.-H. Mau, Mol. Phys., 1974, 28, 469; A. Brillante, D. P. Craig, and A. W.-H. Mau, Chem. Phys. Letters, 1975, 30, 5 ; (6) M. Zander, 2.Naturforsch., 1974, 29a, 1520.

371 3ia 973

3i4

G. Favaro, Chem. Phys. Letters, 1975, 31, 87. J. J. Aaron, R. Fischer, and J. D. Winefordner, Talanta, 1974, 21, 1129. M. Gouterman and D. B. Howell, J. Chem. Phys., 1974, 61, 3491; M. P. Tsvirko, K. N. Solov'yov, A. T. Gradyuzhko, and S. S. Dvornikov, Optika i Spektroskopiya, 1975,38, 705. H. Mohwald and E. Sackmann, Chem. Phys. Letters, 1974,26,509; T. Amano and Y. Kanda, Bull. Chem. SOC.Japan, 1974,47,1326; A. Ponte-Goncalves and R. J. Hutton, J. Phys. Chem., 1975, 79, 71.

376

376 377

J. I. Zink, J. Amer. Chem. SOC.,1974, 96, 6775; Chem. Phys. Letters, 1975, 32, 236; J. I. Zink and W. Klint, J. Amer. Chem. SOC.,1974, 96, 4690. J. Moan, J. Chem. Phys., 1974, 60, 3859; J. L. Houben, S. Monti, C. Berti, and I. Boustead, J.C.S. Faraday ZZ, 1974,70, 1211. B. Brunetti and G. Liuti, Z . phys. Chem. (Frankfurt), 1975, 94, 19; G. A. Capelle, H. P. Broida, and R. W. Field, J. Chem. Phys., 1975, 62, 3131; J. B. West and H. P. Broida, ibid., p. 2566.

378 37D

381

382

K. Mobius, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 1116. T. Tanaka, R. W. Field, and D . 0. Harris, J. MoZ. Spectroscopy, 1975, 56, 188,. P. L. Vergragt and J. H. van der Waals, Chem. Phys. Letters, 1974,26, 305. E. Kanezaki, N . Nishi, M. Kinoshita, and K. Niimon, Chem. Phys. Letters, 1974, 29, 529. R. Schmidberger and H. C. Wolf, Chem. Phys. Letters, 1975,32,21.

34 Photochemistry In the last study it was shown that the ODMR lineshape is a sensitive detector of the mobility of triplet excitation in crystals. An extensive study has been reported on the spin-forbidden non-radiative decay of anthracene, acridine, and phenazine using delayed fluorescence detection of magnetic It was shown that, in anthracene, the spin states T, and T' (axis system is x : long axis, p -THIOMETHOXYACETOPHENONE

p -METHOXYACETOPHENONE

I N DMB

IN DMB

k = 2.90k = 20.4

K=I

k 0.727

TN

HEXANE

IN HEXANE

K-44

k 23.3

K =I

-

I( 0.952

Figure 5 Summary of kinetic data for the lowest triplet states of p-methoxyacetophenone and p-thiomethoxyacetophenone in p-dimethoxybenzene and hexane at 1.6 K . Decay rates are in s-l and populating rates k are relative (with total pumping rate = 100) (Reproduced by permission from Chem. Phys., 1974,6, 193)

y: short axis, z: perpendicular) are active in both TI + So and S1-+TI inter-

system crossings, that deuterium substitution affects the non-radiative decay rates, but not for particular spin states, and that aza-substitution decreases the k,/k, and P y / P z ratios dramatically, but that k , and k, increased by a factor of two in going from acridine to phenazine. 8as

D, A. Antheunis, J. Schmidt, and J. H. van der Waals, Mol. Phys., 1974,27, 1521.

Spectroscopic and Theoretical Aspects

35

Similar studies have been carried out on tetramethylpyra~ine,~~~ quinoxaline and 2,3-dichloroquinoxaline and other a ~ a n a p h t h a l e n e s ,2-aminopyrimidine ~~~ in p - ~ y l e n e ,and ~ ~ ~[2H,o]phenanthrenein biphenyl 387 and other polycyclic aromatic r n ~ l e ~ ~and l ein~ 1,3-diaza-az~lene.~~~ , ~ ~ ~ There have been two studies of phosphorescence microwave double resonance (PMDR) on the benzophenone molecule in which direct observation of level anticrossing and mixing effects is achieved,3B0and further studies on aromatic carbonyls have been reported.391As a good example of the amount of detail about triplet kinetics one can obtain with the method, Figure 5 is presented, which relates to intersystem-crossing rates for the triplet sub-levels in p-thiomethoxyacetophenone and p-methoxyacetophenone. Similar dynamics for tyrosine, tryptophan, and in dole^,^^^ p o r p h y r i n ~and , ~ ~chlorophylls ~ 394 have been presented. Polarization effects in double-resonance ~ p e ~ t r ~ spin-selectivity ~ ~ ~ p y , in ~ ~low-tem~ perature solid-state p h o t o ~ h e m i s t r yoptical , ~ ~ ~ and magnetic resonance spectra of linear-chain e x ~ i t o n svibrational ,~~~ lifetime measurements from optical doubleresonance experiments in matrix-isolated m01ecules,~~~ a theory of optical nuclear the lowest triplet state of a simple merocyanine dye studied by ODMR,"O and ODMR studies of molecular aggregation and triplet excimer formation in hexachlorobenzene crystals 401 have been reported.

E.S.R. Studies.-E.s.r.

studies have been carried out on the U.V. photolysis of aqueous H202,402 on the photochemical reactions of hypofluorites with SOF, and OBI

M.S. de Groot, I. A. M. Hesselmann, F. J. Reinders, and J. H. van der Waals, Mol. Phys.,

1975,29, 37; D. A. Antheunis, B. J. Botter, J. Schmidt, and J. H. van der Waals, ibid., 1975, 29, 49. OBS L. W. Dennis and D. S . Tinti, J. Chem. Phys., 1975,62,2015; P. E. Zinsli and M. A. El-Sayed, Chem. Phys. Letters, 1975, 30, 171. N. Nishi and M. Kinoshita, Chem. Phys. Letters, 1974, 27, 342. C. A. Hutchison, jun., and V. H. McCann, J. Chem. Phys., 1974,61, 820. s88 R. H. Clarke and J. M. Hayes, Chem. Phys. Letters, 1974, 27, 556. T.4. Lin, Chem. Phys. Letters, 1974, 28, 77. J. A. Mucha and D. W. Pratt, Chem. Phys. Letters, 1975,30,181; W. S . Veeman, A. L. J. van der Poel, and J. H. van der Waals, Mol. Phys., 1975,29,225. Iol E. T. Harrigan and N. Hirota, Chem. Phys. Letters, 1974,27,405; E. W. Gossett and M. A. El-Sayed, ibid., 1975,32, 51; M. A. Souto, P. J. Wagner, and M. A. El-Sayed, Chem. Phys., 1974, 6, 193; M. Sharnoff and E. W. Iturbe, J. Chem. Phys., 1975,62, 145. Oga J. Zuclich, J. U. von Schiitz, and A. H. Maki, Mol. Phys., 1974,28,33 ;T.-T. Co, R. J. Hoover, and A. H. Maki, Chem. Phys. Letters, 1974, 27, 5. H. Levanon and A. Wolberg, Chem. Phys. Letters, 1974,24,96; W. G. van Dorp, M. Soma, J. A. Kooter, and J. H. van der Waals, Mol. Phys., 1974,28, 1551;H. Levanon and S . Vega, J. Chem. Phys., 1974, 61, 2265; 1975, 62, 4245; E. R. Davidson, M. Gouterman, W. R. Leenstra, and A. L. Kwiram, ibid., 1975,62,169; G. W. Canters, M. Noort, and J. H. van der WaaIs, Chem. Phys. Letters, 1975, 30, 1. 894 J. R. Norris, H. Scheer, M. E. Druyan, and J. J. Katz, Proc. Nat. Acad. Sci. U.S.A., 1974,71, 4897; J. Kleibeuker and T. Schaafsma, Chem. Phys. Letters, 1974,29, 116; H. Levanon and A. Scherz, ibid., 1975, 31, 119; R. H. Clarke and R. H. Hofeldt, J. Chem. Phys., 1974, 61, 4582. D. S. Frankel and J. I. Steinfeld, J. Chem. Phys., 1975, 62, 3358. OS6 M. h u n g and M. A. El-Sayed, J. Amer. Chem. Soc., 1975, 97, 669. 8s7 R. M. Hochstrasser and A. Zewail, Chem. Phys., 1974, 4, 142. L. J. Allmandoca and J. W. Nibler, Chem. Phys. Letters, 1974,28, 335. D. Stehlik, A. Doehring, J. P. Colpa, E. Callaghan, and S . Kesmarky, Chem. Phys., 1975,7, 165. I o o A. P. Marchetti, J. F. Landry, and D. S . Tinti, J. Chem. Phys., 1974, 61, 1086. Iol L.T. Lin and M. A. El-Sayed, Chem. Phys., 1974,5,315. '02 J. R. Harbour, V. Chow, and J. R. Bolton, Canad. J. Chem., 1974, 52, 3549.

36

Photochemistry

S02,403 on the photoreduction of quinone~,~O~ on acetyl and acetyl peroxide radicals in gas-phase reactions,405on fluoroalkyl radicals in on the on pyridine-3,5photochemistry of 2,2-dimetho~y-2-phenylacetophenone,~~~ dicarboxylic on photolytically reduced p y r a ~ i n e on , ~ ~the ~ dimerization of 9-azabicyclo[3~,3,l]nonan-3-on-9-oxyl (6),410 on naphthalene-tetracyano-

0

benzene charge-transfer complexes,s74and on the triplet states of naphthalene,411 1 ,2,5,6-dibenzanthracene,"12quinoline and q ~ i n o x a l i n e p, ~o~r p~ h y r i n ~ choro,~~~ p h ~ l l alkylcobal~ximes,~~~ ,~~~ Rhodamine 6 G,417and thiazine-type The measurement of spin-lattice relaxation times of triplet states in fluid solution has also been CIDNP and CIDEP Studies.-Two mechanisms have been proposed to account for the observation of electron spin polarization in radical reactions (CIDEP), the first being termed the radical pair mechanism, in which the polarization results from the mixing of the singlet and triplet states of the radical pair by the magnetic interactions within the radicals, and the second the triplet mechanism, in which the polarization originates in the triplet as a result of spin-selective intersystem crossing from the photoexcited singlet state, as is known to occur in several systems from ODMR measurements (see above). It has recently been pointed out 420 that, for the latter mechanism, unequal population of the triplet sub-levels will depend upon zero-field D and E terms and Zeeman terms, but also 403 404

406 406

407 408 408 410

414 413

414

415 416

418 41B 420

J. R. Norton and K. F. Preston, J. Chem. Phys., 1973, 58, 2657. J. R. Harbour and G. Tollin, Photochem. and Photobiol., 1974, 20, 387. K. G. Gazaryan, T. A. Garibyan, and R. R. Grigoryan, Armyan. khim. Zhur., 1974,27, 363. P. J. Krusic, K. S. Chen, and P. Meakin, J. Phys. Chem., 1974,78,2036. M. R. Sandner and C. L. Osborn, Tetrahedron Letters, 1974, 415. H. Zeldes and R. Livingstone, Radiation Res., 1974, 58, 338. H. Zeldes and R. Livingstone, Mol. Phys., 1974, 27, 261. F. Genoud, M. C. Schouler, and M. Decorps, Chem. Phys. Letters, 1974, 26, 414. C. A. Hutchison, jun. and G. W. Scott, J. Chem. Phys., 1974, 61, 2240; A. S. Cullick, R. E. Gerkin, D. L. Thorsell, and A. M. Winer, ibid., p. 3450; F. B. Bramwell, M. E. Laterza, and M. L. Spinner, ibid., 1975, 62, 4184. M.-C. Chen, A. S. Cullick, and R. E. Gerkin, J. ChPm. Phys., 1975, 62, 1954. H. Blok, J. A. Kooter, and J. Schmidt, Chem. Phys. Letters, 1975, 30, 160. H. Levanon and S. Vega, J. Chem. Phys., 1974, 61, 2265; S. R. Langhoff, E. R. Davidson, M. Gouterman, W. R. Leenstra, and A. L. Kwiram, ibid., 1975, 62, 169; B. M. Hoffmann, J. Amer. Chem. SOC.,1975, 97, 1688. V. A. Kim, V. M. Voznyak, and V. B. Evstigneev, Biofizika, 1974,19,992; J. T. Warden and J. R. Bolton, Accounts Chem. Res., 1974, 7, 189. C. Giannotti and J. R. Bolton, J. Organometallic Chem., 1974, 80, 379. M. Yamashita and H. Kashiwagi, J . Phys. Chem., 1974, 78, 2006. E. Vogelmann and H. Schmidt, 2. phys. Chem. (Frankfurt), 1975, 94, 101. P. W. Atkins, A. J. Dobbs, and K. A. McLauchlan, Chem. Phys. Letters, 1974, 29, 616. F. J. Adrian, J. Chem. Phys., 1974, 61, 4875; J. B. Pedersen and J. H. Freed, ibid., 1975,62, 1706.

Spectroscopic and Theoretical Aspects

37

upon the relevant chemical reaction rates and rotational tumbling times, and moreover will be sensitive to the plane of polarization of excitation radiation with respect to the magnetic field, should plane-polarized light be employed for excitation. The extension of such studies to include the use of plane-polarized excitation is thus of some interest, and several papers recently have observed that e.s.r. signals in emission from a variety of radicals (including 1,4-benzosemiquinone and 9,lO-anthrasemiquinone radicals), 1,4-benzoquinone, and duroquinone radicals 421 are greater when the electric vector of the excitation radiation is perpendicular to the magnetic field than when these are parallel, in accord with the triplet theory. It seems, therefore, that there is considerable support for the triplet mechanism in the CIDEP case, although the parallel CIDNP observations in the photolysis of benzoquinone in 2-propanol could be explained also by the radical-pair theory. Other studies have indicated that CIDEP observations on y-irradiated alcohols may arise from the radical-pair mechanism.422 A simple model has been offered to account for CIDEP in cyclopentyl radicals produced in r a d i o l y ~ i s . ~ ~ ~ The controversy over the mechanism of CIDEP in radical reactions extends also to CIDNP. An elaboration of a theory for CIDNP based upon the radicalpair approach has been offered recently,424and a brief note has been published which questions the need for an alternative to the radical-pair approach to account for CIDNP, and further shows that the same assumptions are necessary in both the radical-pair and Overhauser mechanisms, namely, that nuclear relaxation can occur in the escaping radicals.42s It would seem that, whereas in CIDEP the experimental observations require some alternative to the radicalpair treatment for satisfactory explanation, so far, CIDNP observations can be explained on the basis of the radical-pair theory, although this does not preclude the possibility that other mechanisms are also operative. In the photolysis of several cyclic ketones the recent observation of CIDNP in I3C Fourier-transform n.m.r. is taken as good evidence for the involvement of biradical species in the reactions.42s Other reactions studied with lH n.m.r. CIDNP techniques include the photolysis of some simple a l k a n o n e ~ , ~some ~' decarboxylation in in electron-transfer reactions in aromatic ketones,430in methyl d i a z o a ~ e t a t eand , ~ ~in~ acylsilane 432 and cleavage of 421

422

423

424 426

426

02'

428

430 431

p32

B. B. Adeleke, K. Y . Choo, and J. K. S. Wan, J. Chem. Phys., 1975, 62, 3822; H. M. Vyas, S. K. Wong, and B. B. Adeleke, J . Amer. Chem. SOC., 1975,97, 1385; A. J. Dobbs and K. A. McLauchlan, Chem. Phys. Letters, 1975, 30, 257. A. D. Trifunac and E. C. Avery, Chem. Phys. Letters, 1974, 27, 141 ; 1974, 28, 294. S. K. Wong and J. K. S. Wan, Chem. Phys., 1974, 4, 289. J. B. Pedersen and J. H. Freed, J. Chem. Phys., 1974, 61, 1517. G . L. Closs, Chem. Phys. Letters, 1975, 32, 277; F. J. Adrian, ibid., 1974, 26, 437. R. Kaptein, R. Freedman, and H. Hill, Chem. Phys. Letters, 1974, 26, 104. S. P. Vaish, R. D. McAlpine, and M. Cocivera, Canad. J. Chem., 1974, 52, 2978; B. Blank, A. Henne, and H. Fischer, Helv. Chim. Acta, 1974, 57, 920. R. Schwerzel, R. Lawler, and G. Evans, Chem. Phys. Letters, 1974, 29, 106; M. Weinstein, K. A. Muszkat, and J. Dobkin, J.C.S. Chem. Comm., 1975, 68. B. Winkler-Lardelli and H. J. Rosenkranz, Helo. Chim. Acta, 1973,56,2628; G. Vermeersch, N. Febvay-Garot, and S. Caplain, Tetrahedron Letters, 1974, 3127; K. A. Muszkat and M. Weinstein, J.C.S. Chem. Comm., 1975, 143. H. D. Roth and A. A. Lamola, J. Amer. Chem. SOC.,1974, 96, 6270. H. D. Roth and M. L. Manion, J. Amer. Chem. SOC.,1975, 97, 779. N. A. Porter and P. M. Iloff, jun., J. Amer. Chem. SOC.,1974, 96, 6200.

38 Photochemistry trimethyl~tannyldiethylamine.~~~ Other CIDNP observations have been made,434 and l9F CIDNP has been used to detect fluorinated phenoxyl and anilinyl radicals.435 There have been some recent related observations on the quenching or nonquenching of radical reactions and luminescence of various species by magnetic fields.436 Scattering Phenomena.-A review has appeared of the scattering of depolarized light by simple Pre-resonance Raman spectra of NH,, CH3NH2,formamide, cis-dichloroethylene, propargyl alcohol, and pyra~ine;~,*resonance Raman scatter of I2 in solution and in inert matrices;43Qtime-resolved resonance fluorescence and resonance Raman 440 and stimulated resonance Raman scatt e r i ~ ~ pseudo-Raman g;~~~ spectra in stacked benzene and birefringence in CS2443 have been the subjects of recent reports. 4 Theories of Radiative and Non-radiative Decay Radiative Processes.-A large number of papers concerned with the various aspects of the electronic absorption and emission processes in atomic species have appeared. Of general interest is a paper which presents an expression suitable for the evaluation of the infinite sum describing absorption due to a hydrogenic series of Lorenzian lines.444 The Doppler lineshape in atomic the effect of metastable collision effects on lineshapes of atomic dimers on the radiative transition in pairs of atoms447and in donor-acceptor pairs,44s and other aspects of excitation transfer in two-atom s y ~ t e m s450 ,~~~~ 433 434 435 436

437 438

438

440 441

442 443

444

446

446

*" 448

44B

M. Lehnig, Tetrahedron Letters, 1974, 37, 3323. J. Bargon and K. L. Seifert, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 187, 1180. M. L. Kaplan and M. L. Manion, J. Phys. Chem., 1974, 78, 1837. D. M. Goodall, N. Orbach, and M. Ottolenghi, G e m . Phys. Letters, 1974, 26, 365; B. Brocklehurst, R. S. Dixon, E. M. Gardy, V. J. Lopata, M. J. Quinn, A. Singh, and F. P. Sargent, ibid., 1974, 28, 361; E. L. Frankevich, B. M. R. Rumyantsev, and V. I. Lesin, Optika i Spektroskopiya, 1974,37, 376; A. Matsuzaki and S . Nagakura, Chem. Letters, 1974, 675; H. Sakuragi, M. Sakuragi, I. Mishima, S. Watanabe, M. Hasegawa, and K. Tokamaru, ibid., 1975, 231. W. M. Gelbart, Adv. Chem. Phys., 1974, 26, 1. I. Suzuka, N. Mikami, Y. Udagawa, K. Kaya, and M. Ito, J. Chem. Phys., 1972, 57, 4500; M. Ito, I. Suzuka, Y.Udagawa, N. Mikami, and K. Kaya, Chem. Phys. Letters, 1972, 16, 211; M. Ito and I. Suzuka, ibid., 1975, 31, 467; A. Y. Hirakawa and M. Tsubio, Science, 1975, 188, 359. S. Matsuzaki and S . Maeda, Chem. Phys. Letters, 1974,28, 27; C. A. Wight, B. S. Ault, and L. Andrews, J. Mol. Spectroscopy, 1975, 56, 239. A. Szoke and E. Courtens, Phys. Rev. Letters, 1975, 34, 1053. H. J. Weighmann, M. Pfeiffer, A. Lau, and K. Lenz, Optics Comm., 1974,12, 231. N. Kollias and J. Biscar, Chem. Phys. Letters, 1974, 26, 82. A. Davidsson and B. Norden, Chem. Phys., 1975, 8, 223; J. P. Heritage, T. K. Gustafson, and C. H. Lin, Phys. Rev. Letters, 1975, 34, 1299. R. T. Brown, J. Quant. Spectroscopy, 1974, 14, 1351. J. Cooper and D. N. Stacey, J. Phys. (B), 1974, 7, 2143; Yu. S. Oseledchik, Optika i Spektroskopiya, 1974, 37, 427; G. I. Stepanova and G. M. Shoed, Fizika Atmosfery i Okeana, 1974, 10, 1056. W. Steets, A. P. Hickman, and N. F. Lane, Chem. Phys. Letters, 1974,28, 31 ;J. C. Lewis and J. A. Tjon, ibid., 1974, 29, 558; P. R. Berman, Appl. Phys., 1975, 6, 283. R. H. Callender, J. I. Gersten, R. W. Leigh, and J. L. Yang, Phys. Rev. Letters, 1974,33,1311. A. T. Vink, J. Luminescence, 1974, 9, 159. J.-C. Andre and M. Bouchy, J. Chim. phys., 1974, 71, 1541; B. Cheron, J. Phys. (Paris), 1975,36,17,29; P. W. Milonni and P. L. Knight, Phys. Rev. (A), 1974,10,1096; 1975,11,1090. L. F. Phillips, J. Photochem., 1973/4, 2, 255.

Spectroscopic and Theoretical Aspects

39

including an extensive computer simulation of phase-shift measurements of the quenching and trapping of resonance radiation at large optical have been reported, This last study will be of considerable practical value to workers in this field, and was exemplified by the case of the trapping of Cd 228.8 nm resonance radiation. The rapid development of lasers has led to the publication of increasing numbers of papers concerned this year with such subjects as superfluorescence and co-operative radiation processes,461the thermodynamics of co-operative luminescence,452saturation, collisional dephasing, and quenching of fluorescence a theoretical model for of organic vapours in intense laser excitation fluorescence in gases subjected to continuous i.r. excitation,454a quantum treatment of spontaneous emission from strongly driven two-level the development of site-selection and measurements of relaxation times 457 using laser excitation. Two-photon Excitation. Two-photon excitation spectroscopy and also the selective excitation of isotopic species leading to isotope separation have developed significantly this year, with a concomitant increase in the interest among theoreticians in the phenomenon. As stated earlier, the tremendous advantage that two-photon excitation offers over the single-photon process is that by arranging that the two photons being absorbed travel in opposite directions, the limitations of Doppler broadening are eliminated. This is an important point, that has been shown simply in two recent papers,458and it can lead both to greatly improved spectral resolution and, moreover, selective excitation in a system which has overlapping absorption bands. Consider a gas mixture of species A and B at a pressure low enough that the bandwidth of absorption lines is primarily due to the Doppler effect, which means that the particle velocities in the direction of observation are determined by the Maxwell distribution (4). W(U) = [1/4774l exP t - ( V / 4 2 1

(4)

where u = ( 2 k T/M)a ~ and the width of the observed spectral line is: AwDopp. = J(2 In 2ku)

where k = o l c = 27r/X; w and A are the frequency and wavelength of the line. However, the spectral line for an individual particle 2 r is much less than the 461

45a

4z3

464 466

456

467 468

L. A. Nefedier, V. V. Samartser, and A. J. Sirasiev, Spectroscopy Letters, 1974, 7, 285; G. Banfi and R. Bonifacio, Phys. Rev. Letters, 1974,33, 1259; R. Bonifacio and L. A. Lugiato, Phys. Rev. (A), 1975, 11, 1507. T. M. Makhviladze, I. Rez, and M. E. Saritchev, Phys. Letters (A), 1974, 49, 293; J. PastriiSk and B. Hejda, J. Luminescence, 1974, 9, 249. V. L. Bogdanov, V. P. Klochkov, and B. S. Neporent, Optika i Spektroskopiya, 1974,37,375; V. V. Danilov and Yu. T. Mazurenko, ibid., p. 1179; S. Speiser, Chem. Phys., 1974, 6,479; D.W. Vahey and A. Yariv, Phys. Rev. ( A ) , 1974,10, 1578. R. R. Parenti, J. F. Whitney, and J. 0. Artman, J. Chem. Phys., 1975, 62, 3955. H.J. Carmichael and D. F. Walls, J . Phys. (B), 1975, 8, L77. K. Cunningham, J. M. Morris, J. Fiinfschilling, and D. F. Williams, Chem. Phys. Letters, 1975, 32, 581. V. Z. Pashchenko and L. B. Rubin, Zhur. j i z . Khim., 1974,48,2367. P . L. Kelley, H. Kildal, and H. R. Schlossberg, Chem. Phys. Letters, 1974, 27, 62; V. P. Chebotayev, A. L. Golger, and V. S. Letokhov, Chern. Phys., 1975, 7, 316.

Photochemistry

40

Doppler width (Figure 6), and selective excitation of a chosen particle would be possible if the condition of equation (6) were satisfied.

Under normal one-photon excitation conditions, no selective excitation is possible. For two-photon excitation, the moving particle sees each photon of frequency w as a travelling wave of different frequencies o k ku, depending on the direction of motion of the particle. If the particle absorbs both photons from a single travelling wave, then the resonance condition is: 2(w & kv) = wo

(7)

.-p--T----z d w b p P

Figure 6 The coeficient of the two-quantum absorption as a function of standing-wave frequency (Reproduced by permission from Chem. Phys., 1975, 7, 316)

and the absorption is still Doppler-limited. If, however, the two quanta are absorbed from wave-trains travelling in opposite directions, then the resonance condition for each particle is: (w

+ ku) +

- ku)

(0

= 2w = wo

(8)

and the Doppler effect is completely compensated for. Selective excitation is thus possible in this case. Experimental results 203 using this method are discussed on p. 17. Several other papers on the theory of two-photon absorption processes have appeared.459 Resonant Scattering Processes. One of the problems which has attracted great interest this year is again due to the development of finely tunable dye lasers as light sources, and poses the question of what will be the temporal characteristics of excitation by a pulse as it is tuned through an atomic or molecular resonance, 469

F. F. Kormendi, Physica, 1974,75, 359; 0. Kafri and S. Kimel, Chem. Phys., 1974, 5, 488; A. D. Bandrauk, Mol. Phys., 1974, 28, 1259; R. G. Brewer and E. L. Hahn, Phys. Rev. (A), 1975, 11, 1641.

Spectroscopic and Theoretical Aspects

41

the processes of interest being resonance or near-resonance scattering of radiation and absorption, followed by re-emission. Several papers, using different approaches and shapes of excitation pulses, have treated this problem theoreti~ a l l y , ~and ~ O all are in essential agreement that there is a continuous transition from fast Raman scattering to resonance fluorescence, which is the only process occurring with a long characteristic lifetime on resonance provided the excitation is broad-banded. This has been observed in experimental observations on 12.204 However, in the limit of extreme narrow-banded excitation, the treatments show that all time-resolution is lost, and the usual resonance scattering intensity formulae are obtained. Clearly the time-evolution of scattered and emitted radiation following the interaction of light sources with resonance depends crucially upon the nature of the light source, as has been shown earlier,461and it is of interest that both limiting-case and intermediate-case calculations can be performed successfully. In the paper by Hilborn 460 it was shown that, provided the resonant excited state has two or more nearby levels, quantum beats may be observed even when the incident light is tuned off-resonance. The depolarization of light by atomic gases462 and the use of Raman scattering to probe exciton-phonon coupling in molecular crystals 463 have been discussed. Vibronic Coupling, and Franck-Condon Factor Determinations. Two papers have appeared which develop a systematic approach for the classification of the relative orders of approximation of such couplings as the vibronic (HerzbergTeller) and Born-Oppenheimer ones, the Condon approximation, and for studying the importance of anharmonicity in the quantitative calculation of spectral A Green’s function method has been intensities and electronic used in an excellent paper to explain the observed absorption spectrum of naphthalene in the S2 region, where strong coupling to the relatively sparse set of levels of the S1state lying 3000cm-l below S2 places the system in the ‘intermediate case’ rather than the ‘statistical’ limit.465This leads to a forest of new lines that are unassignable on the basis of known normal vibrational modes rather than a broadened spectrum that is typical of the statistical limit. The excellent agreement between calculation and experiment is illustrated in Figure 7. The computed spectrum is in excellent agreement with observation, permitting vibronic assignments to be made to within 2-3 cm-l acccuracy. A new perturbation expansion has been derived and applied to the coupling between non-adiabatic Born-Oppenheimer states in polyatomic molecules, for which previous methods are often unreliable.46s Franck-Condon computations on excited states of simple AB2 polyatomics, including SO2, CS2, and many 460

462

463

464 46b

‘88

S. Mukamel and J. Jortner, J. Chem. Phys., 1974, 61,227; 1975, 62, 3609; J. M. Friedman and R. M. Hochstrasser, Chem. Phys., 1974,6, 155; J. 0.Berg, C. A. Langhoff, and G. W. Robinson, Chem. Phys. Letters, 1974, 29, 305; R. C.Hilborn, ibid., 1975,32,76;J. Friedman and R. M. Hochstrasser, ibid., 1975, 32, 414. W.Rhodes, B. R. Henry, and M. Kasha, Proc. Nat. Acad. Sci. U.S.A., 1969,63,31;W.Rhodes, Chem. Phys., 1974, 4, 259. B. A. Baron and W. M. Gelbart, Chem. Phys., 1974,6, 140. M. G. Sceats and S. A. Rice, J. Chem. Phys., 1975,62, 1098. S. H.Lin and H. Eyring, Proc. Nat. Acad. Sci. U.S.A., 1974, 71,3415,3802. C. A. Langhoff and G . W. Robinson, Chem. Phys., 1974,6,34; Mol. Phys., 1975,29,613. A. Gregory and W. Siebrand, Chem. Phys. Letters, 1974, 29, 13.

Photochemistry

42

and methods of computation of Franck-Condon factors using PeckelTeller wavefunctions 468 and the single a-approximation 46g have been reported. A method for determination of vibrational temperature of organic molecules in solution from bandwidth and Stokes-shift measurements has been and several aspects of the structure of electronic spectra in polyatomic molecules have been

L U U L -9.60

-7.80

-5.a

-3.80

-1.80

0.X

I

I

I

1

2.20

U.20

8.20

0.20

ENERGY( LINEWIOTHS)

Figure 7 Naphthalene absorption spectra (in durene host). Numbers on observed spectrum refer to origin of lBSusystem and denote prominent bands. The weighted density of zeroth-order states which reproduces the observed spectrum is given at the bottom of the figure (Reproduced by permission from Chem. Phys., 1974,6, 34) Polarization and Environmental Efects. An important survey of the effects of

polarization in fluorescence measurements has been published, and all readers engaged in making such measurements are urged to consider this treatise, which L07

468

470 471

K. Ramaswamy and K. Ganesan, Acta Chim. Acad. Sci. Hung., 1974, 81, 71 ; 1974, 82, 57; E. V. Doktorov, I. A. Malkin, and V. I. Man'ko, J. Mol. Spectroscopy, 1975,56, 1. 0. P. Shadrin and N. I. Zhirnov, Optika i Spektroskopiya, 1975, 38, 648. C. S. Lin, Cunad. J. Phys., 1975,53, 310. A. Ringler and L. Szalay, Acta Univ. Szeged. Phys. Chem., 1974,20, 19. R. I. Personov and E. I. Al'shits, Chem. Phys. Letters, 1975, 33, 85; T. Bolotnikova and 0. El'nikova, Optika i Spectroskopiya, 1974, 36, 895; S. 0. Mirumyanto, E. A. Vandyukov, and Yu. S. Demchuk, ibid., 1975, 38, 46; E. A. Gastilovich, G. T. Kryuchkova, and D. N. Shigorin, ibid., p. 500.

Spectroscopic and Theoretical Aspects 43 gives quantitative expressions for correction of measurements for discrepancies due to polarization In particular, it is shown that the use of 90" viewing geometry, by far the most widespread in commercial spectrofluorimeters, maximizes the errors due to polarization. The paper shows that 54.75" or 125.25" viewing minimizes these effects, but the authors recommend making totally polarized or depolarized measurements to be absolutely sure of correcting for anisotropy in emission. A theoretical evaluation has also been made of the effect of photoselection on the measurement of the circular polarization of and several papers have appeared which are concerned with the concentration and collisional depolarization of luminescence.474Two papers of interest to the field of the luminescence of biological molecules in which orientation effects are important have appeared, being concerned with the anisotropy of chromophores attached to macromolecules and performing local Brownian motion and rotating between two reflecting Rotational diffusion effects in dye-laser solutions have also been There have been many papers published concerned with the emission characteristics of a dipole situated between two mirrors,477and surface effects on decay characteri~tics,~~~ and the use of laser light and a diffraction grating to accelerate electrons has been A review (in German) has appeared concerned with the effects of microenvironment upon the luminescence properties of molecular species,4s0and one in English also on solvent Temperature effects on solvent param e t e r ~ a, ~model ~ ~ for the ab initio calculation of solvent and the reorientation of hydrogen-bonded solvents around a large dipole 483 have been discussed. Miscellaneous. The systematics of molecules according to their luminescence spectral the interpretation of fluorescence a simple E. D. Cehelnik, K. D. Mielenz, and R. A. Velapoldi, J. Res. Nut. Bur. Stand. Sect. A , 1975, 79, 1. I. Z. Steinberg and B. Ehrenberg, J. Chem. Phys., 1974,61,3382; J. Snir and J. A. Schellman, ibid., 1974, 78, 387. 474 A. Kawski and J. Kaminski, 2. Naturforsch., 1974, 29a, 452; 1975, 30a, 15; C. Bojarski, J . Luminescence, 1974,9,40; R. Bourret, Opt. Acta, 1974,21,721; C . Bojarski, J. Dudkiewicz, and A. Bujko, Acta Univ. Szeged. Phys. Chem., 1974, 20, 267; C. Bojarski and J. Domsta, Acta. Phys. Acad. Sci. Hung., 1974,37, 191; V. N. Rebane, Optika i Spektroskopiya, 1974, 37, 216. Ph. Wahl, Chem. Phys., 1975, 7, 210, 220. 47@ D. N. Phillion, D. J. Kuizenga, and A. E. Siegman, J. Chem. Phys., 1974, 61, 3828. 477 K. H. Tews, J. Luminescence, 1974,9,223; R. R. Chance, A. Prock, and R. Sibley, J. Chem. Phys., 1975, 62, 771, 2245. 478 M. R. Philpott, J. Chem.Phys., 1974,61,5306; Chem.Phys.Letters, 1975,30,387; H. Morawitz and M. R. Philpott, Phys. Rev. (B), 1974, 10, 4863; K. H. Tews, 2.Naturforsch., 1974, 29a, 712; P. Beckett, P. J. Forster, V. Hutson, and R. L. Moss, J. Quant. Spectroscopy Radiative Transfer, 1974, 14, 1115. 47B K. Mizuno, S. Ono, and 0. Shimoe, Nature, 1975, 253, 184. A. Kawski, Chimia (Switz.), 1974, 28, 715. 481 M. F. Nicol, Appl. Spectroscopy Rev., 1974,8, 183; 1. Gryczynski and A. Kawski, 2.Naturforsch., 1975, 3Oa, 287. rsa J. Hylton, R. E. Christofferson, and G. G. Hall, Chem. Phys. Letters, 1974, 26, 501. 489 W. Struve and P. M. Rentzepis, Chem. Phys. Letters, 1974,29, 23. 484 D. N. Shigorin, Zhur. Vsesoyuz. Khim. obshch. im D.Z.Mendeleeva, 1975,20, 32. 486 J. B. Birks, J. Luminescence, 1974, 9, 3 11. 47a

44

Photochemistry

theoretical model for dual p h o ~ p h o r e s c e n c e , fluorescence ~~~ correlation spect r o s ~ o p y ,and ~ ~ ~photon-photon delayed coincidence methods for molecular lifetimes 488 have been the subjects of recent reports. Non-radiative Decay.-One of the assumptions in the Bixon-Jortner model of non-radiative decay in polyatomic molecules is that a single initial level is coupled to a dense manifold of final levels of equal spacing E by a coupling of strength u which is independent of level. While such an approach has been extremely useful in developing a basis for furthering the understanding of non-radiative decay processes, it does not represent the situation in most non-radiative transitions in real molecules, where the requirement of promoting mode excitations, for example, dictates that coupling strengths between the initial level and different final levels vary greatly. The simple model in the limit of high density of final states predicts irreversible intramolecular non-radiative decay and thus exponential decay of the initial state, and such behaviour is not universally observed even in complex polyatomic molecules. A recent treatment provides an exactly soluble model for non-radiative decay but uses variable coupling strength, and it is shown that intermediate-case behaviour can result even with large numbers The of coupled final states; this is a result in keeping with Bixon-Jortner model has been further generalized to allow for physically reasonable non-uniformities in the spacing of the final levels, and in particular it was shown that the condition of the Bixon-Jortner model for large-molecule behaviour that u B E is too restrictive, and that exponential relaxation can be observed in some conditions even when u d E . Thus ~ ~ it ~was illustrated that, for a case where u = ~ / 2 ,exponential decay of the initial state can result with a lifetime that is short compared with the radiative lifetime, the latter process removing the possibility of observing recurrences which would occur on a longer timescale. The intermediate case in non-radiative decay has been further disCalculations mentioned earlier 465 on the naphthalene second singlet state reveal also that in the time evolution of fluorescence from the state, picosecond or subpicosecond quantum beats should be present, although these are at intensities at least two orders of magnitude lower than the initial fluorescence intensity, and will thus be undetectable with present experimental techniques. A quantum-mechanical tunnelling model of non-radiative decay 492 has been proposed. Several papers have been concerned with the choice of basis set for treatments of non-radiative decay,493and it has been shown in the paper of Sharf that higher-order vibronic terms are comparable in magnitude with those of the first-order term. It is thus not sufficient to make the usual assumption that interactions describing non-radiative decay are independent or linearly dependent on nuclear co-ordinates. The other papers reinforce this point, and 486

487 488

48e

491

402 493

S. Y . Chu and L. Goodman, Chem. Phys. Letters, 1975, 32, 24. D. E. Koppel, Phys. Reo. ( A ) , 1974, 10, 1938. G. L. King, F. H. Read, and R. E. Imhof, J. Phys. ( B ) , 1975,8, 665. K. Morokuma and K. F. Freed, J. Chem. Phys., 1974, 61, 4342. W. M. Gelbart, D. F. Heller, and M. L. Elert, Chem. Phys., 1975,7, 116. G. W. Robinson and C. A. Langhoff, Chem. Phys., 1974, 5, 1. S. J. Formosinho, J.C.S. Faruday IZ, 1974, 70, 605. T. Azumi, Chem. Phys. Letters, 1974, 25, 135; B. Scharf, Chem. Phys., 1975, 7 , 478; E. V. Dokotorov, I. Malkin, and V. 1. Manko, J. Mol. Spectroscopy, 1975,56, 1.

45 that by Azumi predicts that the most likely route of intersystem crossing in a molecule such as pyrazine can be shown to be different for different choices of basis set, although there is no experimental evidence available to date to test which mechanism is correct, and therefore which basis functions are correct. Some years ago it was conventional wisdom to assert that for aromatic hydrocarbons Sl+ So internal conversion was an improbable process compared with S, + T, non-radiative decay. However, it has recently been demonstrated that in naphthalene and related compounds the internal conversion can be the dominant decay process, particularly for vibrationally excited species.494It is of interest to note that calculated rates for the internal-conversion process in naphthalene could only be made to fit experimental values if some redistribution of vibrational energy occurred, but not complete statistical distribution among normal modes. Inclusion of the effects of anharmonicity has been shown to cause an increase in computed 3Blu lA,, intersystem-crossing rate constant for benzene by a factor of lo3, and also to increase the effectiveness of the C-H symmetric stretching modes as energy acceptor^.*^^ The role of the promoting mode in non-radiative decay rates in large molecules has also been d i ~ c u ~ ~ eThe d.~~~ energy gap between the S1and T' levels in anthracene is known to be small, and sensitive to environmental perturbation. The fluorescence properties of the parent molecule and of substituted anthracenes have been rationalized on the basis of a calculation of the way in which Franck-Condon factors for the S, + Ta transition vary with energy gap.497 A very thorough analysis of the non-radiative decay processes in benzene, which considerably extends earlier studies, has been One of the significant features of this treatment is that it offers a possible explanation of the obscure Channel 111 process which results in total quenching of fluorescence and intersystem crossing in benzene at around 3000 cm-l excess energy in the S1state. It was shown that, because of the large C-C bond-length change and frequency change in the totally symmetric carbon skeletal breathing mode v1 between So and S1states, this vibration is a particularly good accepting mode for the S1+ So internal conversion (compare the naphthalene case above), and by the time l 4 excitation (and possibly 13) is reached, the internal conversion could be a favoured process over S, -+ T, intersystem crossing. For isoenergetic excitations which place the excess energy in poor accepting modes, however, the internal conversion should be less efficient, and the observed fluorescence from the isolated molecule supports this hypothesis. Channel I11 may thus be simply S, + Sointernal conversion. The importance of modes which undergo large frequency and equilibrium displacements as accepting modes has been further stressed, particularly with Spectroscopic and Theoretical Aspects

--f

4B4

49b 496

487 488

3

S. F. Fischer, A. L. Stanford, and E. C. Lim, J. Chem. Phys., 1974, 61, 582; C. S. Huang and E. C. Lim, ibid., 1975, 62, 3826; S. F. Fischer and E. C. Lim, Chem. Phys. Letters, 1974, 26, 312. Y.Mikami, K. Mizunoya, and T. Nakajima, Chem.Phys. Letters, 1975,30,373 ;N. Shimakura, Y.Fujimura, and T. Nakajima, Theor. Chim. Acra, 1975, 37, 77. Y.Fujimura and T. Nakajima, Bull. Chem. SOC.Japan, 1975, 48, 1186. F. Tanaka and J. Osugi, Chem. Phys. Letters, 1974, 27, 133. M. G. Prais, D. F. Heller, and K. F. Freed, Chem.Phys., 1974,6,331.

46

Photochemistry

respect to out-ot-plane bending modes in aromatic molecules with non-bonding A classical treatment of intramolecular twisting relaxations 6oo and open-shell generalized perturbation theory 601 have been discussed. Vibrational Relaxation. Stochastic processes, including vibrational relaxation in condensed media, have been considered from a theoretical standpoint in an extensive review,so2and a further review has considered measurement of such processes Models have been presented for vibrational relaxation in diatomic liquids 604 and in condensed media,606using a master-equation approach. An extensive development of quantum ergodic theory for relaxation processes has been published,606 and quantum resonance effects in electronic to vibrational energy transfer have been considered.607 A paper has also considered the coupling between vibrational relaxation and molecular electronic transitions.60s A theory has also been outlined for the time-resolved electronic absorption spectrum of a molecule undergoing collisional vibrational relaxation.609 Photochemical Reactions.-The use of correlation diagrams in chemical dynamics has been discussed in a review article,610and the problem of potential-surface crossing in diatomic sll and polyatomic molecules has been widely considered in several papers.612 A paper has appeared concerned with the quantummechanical expression to describe the relaxation processes in a chemically reacting gas under monochromatic (laser) excitati01-1.~~~ Other quantum theories of molecular photodissociation have also been published.s1* These are too extensive for detailed consideration here, but in general provide solvable models for small-molecule reactions. Experimental determinations of photofragmentation dynamics have been matched by increasing interest in models for the photodissociation process. Several papers have been concerned with the calculation of angular distribution 4Q8

boo

604

N. Kanamaru and E. C. Lim, J. Chem. Phys., 1974, 61, 1582; 1975, 62, 3252. W. Rapp, Chem. Phys. Letters, 1974, 27, 187. K. F. Freed, Chem. Phys., 1974,4, 80. S . H. Lin and H. Eyring, Ann. Rev. Phys. Chem., 1974, 25, 39. S. Ormonde, Rev. Mod. Phys., 1975, 47, 193. D. J. Diestler, Chem. Phys., 1975, 7 , 349. S. H. Lin, J. Chem. Phys., 1974, 61, 3810. K. S. J. Nordholm and S. A. Rice, J. Chem. Phys., 1974, 61, 203; K. S. J. Nordholm and S. A. Rice, ibid., p. 768. I. H. Zimmermann and T. F. George, J. Chem. Phys., 1974, 61, 2468; Chem. Phys., 1975,7, 323.

610

611

612 613 614

A, Nitzan, MoI. Phys., 1974, 28, 559. G. R. Fleming, 0. L. J. Gijzeman, and S. H. Lin, J.C.S. Faruday 11, 1974,70, 1074. B. H. Mahan, Accounts Chem. Res., 1975,8, 55. B. Garetz, M. Rubinson, and J. Steinfeld, Chem. Phys. Letters, 1974, 28, 120; M. Berrondo and D. H. Rojas, Znternat. J. Quantum Chem., 1975, 9, 119. B. R. Johnson, Chem. Phys. Letters, 1974,27, 373; T . F. George, K. Morokuma, and Y.-W. Lin, ibid., 1975, 30, 54; H. C. Longuet-Higgins, Proc. Roy. SOC.,1975, A344, 147. R. Kapral, J. Chem. Phys., 1974, 61, 1723. K. G. Kay, J. Chem. Phys., 1974, 60, 2370; E. J. Heller and S. A. Rice, ibid., 1974, 61, 936; S. Nordholm and S. A. Rice, ibid., 1975, 62, 157; S. Mukamel and J. Jortner, J. Chem. Phys., 1974,60,4760; Mol. Phys., 1974,27,1543; Chem. Phys. Letters, 1974,29, 169; F. J. McLafferty and P. Pechukas, Chem. Phys. Letters, 1974, 27, 511 ; J. C. Light and A. Altenberger-Siczek, ibid., 1975, 30, 195; F. S. M. Tsui and K. F. Freed, Chem. Phys., 1974, 5, 337.

47

Spectroscopic and Theoretical Aspects

of molecular photo fragment^.^^^ A Golden-rule approach to product populations and energy distributions in photofragmentation and related reactions has been developed 616 and applied successfully to the photodissociation of COz,HCN, and halogen cyanides, and to reaction (9). Hg*(6To)

+ CN(fZ+)

-

CN*(82X,u')

+ Hg('S,)

(9)

The treatment ignores interfragment dynamics such as vibrational-translational energy transfer, but experimental data seem to justify this, although many previous impulsive models517have included such effects by evaluation of the forced diatom oscillation caused by the repulsive interaction between recoiling fragments. In interfragment models, changes in the potential-function produce forces and torques between the fragments, whereas in intrafragment models changes within the fragment are considered. These two factors were incorporated into a single model involving only two parameters, L, a measure of the repulsion between the separating fragments, and Ar a measure of the change in potential within the fragment.618 The use of new experimental data for the populations arising in products from reaction (9) in which the effects of vibrational relaxation had been eliminated showed that a one-parameter model was sufficient to account for the observed energy distributions; but it was further shown that for the dissociation of HCN, the impulsive half-collision model could not predict any significant degree of vibrational excitation in the CN fragment with Ar = 0, and thus intra-fragment changes must be considered. The treatment by Mukamel and Jortner 619 includes evaluation of Franck-Condon factors for the overlap of initial and final diatom vibronic states together with intercontinuum coupling strengths which are parametrized to give a best fit to experimental data. The model by Band and Freed620resembles the Golden-rule approach6ls in that intercontinuum coupling is ignored and the parametric dependence of calculated distributions depends only upon intrafragment dynamics in the form of FranckCondon factors. This model was also applied successfully to the HCN photodissociation problem. When competing paths are open to activated or photoexcited molecules, the fraction of species undergoing a particular decay route, or branching ratio, is usually expressed in terms of rate-constants to provide a convenient basis for quantitative experimental measurement ; but the calculation from first principles is not usually simple. A successful model for prediction of branching ratios has been developed which is based simply upon the tenet that the branching ratio is 514s

616

616

R. Bersohn, Israel J. Chem., 1973, 11, 675; T. B. Stewart and H. S. Judeikis, Rev. Sci. Instr., 1974,45, 1542; S.-C. Yang and R. Bersohn, J. Chem. Phys., 1974,61,4400; R. C . Ormerod, W. R. Anderson, and T. L. Rose, ibid., 1975, 62, 127. A. D. Wilson and R. D. Levine, Mol. Phys., 1974,27, 1197; M. J. Berry, Chem. Phys. Letters, 1974, 27, 62; 1974, 29, 323, 329.

617

618 61a 660

K. E. Holdy, L. C. Klotz, and K. R. Wilson, J. Chem. Phys., 1970,52,4588; M . A. Gonzalez, G . Karl, and P. J. S. Watson, ibid., 1972,57,4054; M. Shapiro and R. D. Levine, Chem. Phys. Letters, 1970, 5, 499; R. D. Levine and R. B. Bernstein, ibid., 1972, 15, 1; A. D. Wilson and R. D. Levine, Mol. Phys., 1974, 27, 1197. J. P. Simons and P. W. Tasker, Mol. Phys., 1973,26, 1267; 1974,27, 1691; Ber. Bunsengesellschaft phys. Chem., 1974, 78, 176. S. Mukamel and J. Jortner, Chem. Phys. Letters, 1974, 29, 169. Y. B. Band and K. F. Freed, Chem. Phys. Letters, 1974,28, 328.

Photochemistry

48

such as always to maximize the entropy of the system, subject to known cons t r a i n t ~ Branching .~~~ ratios for superexcited states undergoing pre-dissociation and pre-ionization have been measured,622and the photofragmentation dynamics of dimethylcadmium Photoinduced recombination radiation 6z4 and the theory of dissociativerecombination and related processes 5z5 have been reported. In the extremely useful treatments above, the detailed dynamics of essentially simple (diatomic type) reactions are considered, whereas clearly the majority of photochemical reactions are studied in conditions in which product energy distributions are quickly Boltzmannized, and for which potential-energy surfaces are of such complexity, owing to the size of the reacting molecules, that such computations are impossible and irrelevant. The organic chemist nevertheless requires to rationalize results in terms of potential-energy surfaces ; albeit these are, of necessity, of a more empirical nature than for simple molecules. A recent series of papers has done much to categorize potential-surface types, including surface crossings and avoided crossings, and to provide a substantial basis for rationalizing organic photochemistry,6z6and this topic has been further widely Specific reactions studied by this method include the addition of %HZ to butadiene,628cycloaddition of ethylene to d i a ~ o m e t h a n ethe , ~ ~dimeriza~ tion of ethylene,630the photochemical isomerization of butadiene and cyclobutene and cyclobutadiene d i m e r ~ the , ~ ~photochemical ~ Diels-Alder the rearomatization of valence isomers of benzene,633the photochemical isomerization of c y c l o b ~ t a n o n eand , ~ ~the ~ formation of the triplet state in the thermolysis of d i ~ x e t a n . ~ ~ ~ 621

623 623

626

R. D. Levine and R. B. Bernstein, Chem. Phys. Letters, 1973, 22, 217; ibid., 1974, 29, 1; Accounts Chem. Res., 1974, 7, 393; R. D. Levine and R. Kosloff, Chem. Phys. Letters, 1974, 28,300; R. D. Levine, B. R. Johnson, and R. B. Bernstein, ibid., 1973,19,1; 1. Procaccia and R. D. Levine, ibid., 1975,33,5; U. Dinur, and R. D. Levine, ibid., 1975,31,410; R. D. Levine, Ber. Bunsengesellschaftphys. Chem., 1974,78, 111; A. Ben-Shaul, Chem. Phys., 1973, 1, 244; A. Ben-Shaul, R. D. Levine, and R. B. Bernstein, J. Chem. Phys., 1972, 57, 5427; ibid., 1974, 61,4937; R. B. Bernstein and R. D. Levine, ibid., p. 4926. H. Nakamura, Chem. Phys. Letters, 1974, 28, 534; 1975, 33, 151. M. Tamir, U. Halavee, and R. D. Levine, Chem. Phys. Letters, 1974, 25, 38. A. V. Eletskii and B. M. Smirnov, Optika i Spektroskopiya, 1974,36, 1075; V. A. Kuz’Mitskii and V. A. Kotlo, Zhur. priklad. Spektroskopii, 1974, 21, 636. P. W. Harland and J. L. Franklin, J. Chem. Phys., 1974, 61, 1621; C. Bottcher, Proc. Roy. SOC.,1974, A340, 301.

626

627

628

62@

L. Salem, J. Amer. Chem. SOC.,1974, 96, 3486; L. Salem, C. Leforestier, G. Segal, and R. Welmore, ibid., 1975, 97, 479; W. G. Dauben, L. Salem, and N. J. Turro, Accounts Chem. Res., 1975, 8, 41. J. P. Daudey, J. Langlet, and J. P. Malrieu, J. Amer. Chem. Sac., 1974, 96, 3393; S. Wolfe, H. Bernhara-Schegel, I. G. Csizmadia, and F. Bernard, ibid., 1975,97,2020; M. J. S. Dewar and S. Kirschner, ibid., 1974, 96, 5244; D. M. Silver and M. Karplus, ibid., 1975, 97, 2645; J. Michl, Topics Current Chem., 1974,46, 1. H. Fujimoto and R. Hoffman, J. Phys. Chem., 1974, 78, 1167. T. Minato, S. Yamabe, S. Inagaki, H. Fujimoto, and K. Fukui, Bull. Chem. SOC.Japan, 1974, 47, 1619.

630 631

63a

633

634

636

M. J. S. Dewar and S. Kirschner, J. Amer. Chem. SOC.,1974, 96, 5246. 0. Kikuchi, Bull. Chem. SOC.Japan, 1974,47, 1551; R. S. Case, M. J. S.Dewar, S. Kirschner, R. Pettit, and W. Slegeir, J. Amer. Chem. SOC.,1974, 96, 7581. N. D. Epiotis and R. L. Yates, J. Org. Chem., 1974,39,3150. M. J. S. Dewar, S. Kirschner, and H. Kollmar, J. Amer. Chem. SOC.,1974, 96, 7579; M. J. S. Dewar and S . Kirschner, ibid., 1975,97,2932; E. A. Dorko, R. Scheps, and S. A. Rice, J . Phys. Chem., 1974, 78, 568. W. D. Stohrer and G. Weich, Angew. Chem., 1974, 86, 200. M. J. S. Dewar and S . Kirschner, J. Amer. Chem. Soc., 1974, 96, 7578.

Spectroscopic and Theoretical Aspects

49

Non-empirical calculations on the following simple reactions have been the dissociation of HN2+,538 reported : the predissociation of Nz+636 and Hz0+,537 reaction (10),6aathe exchange reactions between H and Hz640and H+ and D2,641 He(llS)

+ He(1lS)

-

He(1lS)

+ He(2IP) or He(2'S)

(10)

the reaction between atomic carbon and H2,64a the reactions between methylene and Hz,643and O(3P)and ethylene,644 the photodecomposition of the peroxyformyl radical to OH and COZY and the photodissociation of formaldehyde.646 The vexed question of the mechanism of the direct and sensitized cis-trans isomerization of stilbene has been the subject of recent papers.546 The studies of the two groups differ in the favoured mechanism for the direct cis-trans isomerization, one proposing the conventional triplet-state mechanism, the other plausibly invoking the intervention of a doubly excited singlet potential surface with a deep potential minimum at a 90" configuration. RRKM calculations on triplet species in diazirine p h o t o l y ~ i s BEBO , ~ ~ ~ calculations on the activation energies for hydrogen-transfer stereochemistry as a probe for photochemical reaction mechanisms,649photochemistry with polarized light,650dimer formation,661the formation of molecular complexes,662hydrogen bonding in electronically excited and the interactions between excited-state aromatic molecules and O2654 have been the subjects of recent theoretical treatments. Treatment of Data.-Various applications of the Stern-Volmer equation 665 and the kinetic analysis of bimolecular reactions which can occur from both singlet and triplet states,666corrections for inner filter effects on rate expressions for s37 638 638 540

641 642

s43 644

b45 646

647 648

648 550 651

55a

66s

654 665

J. Tellinghuisen and D. L. Albritton, Chem. Phys. Letters, 1975, 31, 91. A. J. Lorquet and J. C. Lorquet, Chem. Phys., 1974, 4, 353; J. C. Leclerc, J. A. Horsley, and J. C. Lorquet, ibid., p. 337. K. Vasudevan, S. D. Peyerimhoff, and R. J. Buenker, Chem. Phys., 1974, 5, 149. R. E. Olson, E. J. Shipsey, and J. C. Browne, J. Phys. (B), 1975, 8, 905. J. R. Stine and R. A. Marcus, Chem. Phys. Letters, 1974, 29, 575. Y.-W. Lin, T. F. George, and K. Morokuma, Chem. Phys. Letters, 1975, 30,49. R. J. Blint and M. 0. Newton, Chem. Phys. Letters, 1975, 32, 178. P. Cremaschi and M. Simonetta, J.C.S. Faraday ZZ, 1974, 70, 1801. P. Mezey, R. E. Kari, A. S. Denes, I. G. Csizmadia, R. K. Gosavi, and 0. P. Strausz, Theor. Chim. Acta, 1975, 36, 329. R. L. Jaffe, D. M. Hayes, and K. Morokuma, J. Chem. Phys., 1974,60, 5108. F. Momicchioli, M. C. Bruni, I. Baraldi, and G. R. Corradini, J.C.S. Faraday ZI, 1974, 70, 1325; F. Momicchioli, G. R. Corradini, M. C. Bruni, and I. Baraldi, ibid., 1975, 71, 215; G. Orlandi and W. Siebrand, Chem. Phys. Letters, 1975, 30, 352. A. Cobo, J. M. Figuera, and V. Menendez, Anales de Quim., 1974, 70, 496. N. L. Arthur, K. F. Donchi, and J. A. McDonell, J. Chem. Phys., 1975, 62, 1585. H. E. Zimmerman, Tetrahedron, 1974, 30, 1617. 0. Buchardt, Angew. Chem., 1974,86,222. W. L. Schieve and H. W. Harrison, J. Chem. Phys., 1974, 61,700; J. Bertran, V. Forero, and F. Mora, Tetrahedron, 1974,30,427. S . Yomosa, J. Phys. SOC.Japan, 1973, 35, 1738; 1974, 36, 1655; W. J. Madia, J.-C. Schug, A. L. Nichols, and H. J. Ache, J. Phys. Chem., 1974, 78, 2682. S. Nagase and T. Fueno, Theor. Chim. Acta, 1974, 35, 217; P. Kollman, J. McKelvey, A. Johansson, and S . Rothenberg, J. Amer. Chem. SOC.,1975,97, 955; J. E. Del Bene, J. Chem. Phys., 1975, 62, 666. 0. L. J. Gijzeman, J.C.S. Faraday ZZ, 1974, 70, 1143. M. D. Shetlar, Mol. Photochem., 1974, 6, 143, 167, 191. C. J. Dalton and J. J. Snyder, Mol. Phatochem., 1974, 6, 291.

Photochemistry

50

photochemical the kinetics of diffusion-controlled reactions,668the effects of depletion of photochemical reactant on rate expressi0ns,6~*and the analysis of pulsed fluorescence decay data by the Laplace-transform method 660 have been discussed in recent reports. 5s7 6b8 668 660

G. Mark and F. Mark, Z . Naturforsch., 1974,29a, 610. T. L. Nemzek and W. R. Ware, J . Chem. Phys., 1975,62,477. D . R. A. Cuff, D. Price, and R. Whitehead, J. Photochem., 1974, 3, 215. M. Almgren, Chem. Scripta, 1974, 6, 193; A. Gani, R. L. Modlin, and L. Brand, Biophys. J., 1975, 15, 263.

2 Photophysical Processes in Condensed Phases BY K. SALISBURY

1 Introduction In spite of the need to keep this chapter within the size limitation set by the Chemical Society, it is hoped that the standard has been maintained. However, in order to make best use of the available space it has been decided to omit coverage of those publications which will receive some attention in other Chapters. The areas in which this change will be most noticeable are: (i) publications covering spectroscopic as well as kinetic studies (refer to Part I, Chapter 1); (ii) publications covering more synthetic aspects of organic photochemistry but with some quantitative information (refer to Part 111). 2 Excited Singlet-state Processes In an article which is critical of many generally accepted molecular fluorescence parameters of aromatic molecules (and by inference the parameters for other systems), Birks emphasizes the precautions necessary to eliminate errors due to self-absorption secondary fluorescence and/or self-quenching.' The points are made that reliable data for 7f and Q are available for only a few compounds, e.g. diphenylanthracene (DPA), perylene, quinine bisulphate, and acridone, and that these provide suitable standards. The value of @f (DPA) is now set at 0.83. The importance of solvent effects on a>f and 7f of DPA is stressed in a publication which reports Tf for DPA in cyclohexane and benzene.2 The value of 6.95 f 0.04 ns for benzene solution is in good agreement with the earlier work of Birks and Dyson and Ware and Baldwin (7.35 k 0.05 ns). The value obtained for cyclohexane solution, 7.58 & 0.04ns, although in poor agreement with earlier results, is probably the most acceptable. The absolute fluorescence quantum yield of quinine bisulphate has also been redetermined (Of= 0.56).6 A re-investigation of the fluorescence yields and fluorescence lifetimes of benzene in polar and non-polar solvents and an analysis of the quantum yields of benmalene formation under a variety of conditions has led to the conclusions that benzvalene is formed from the vibrationally excited S, state of benzene and that the population of non-totally symmetric vibrational levels plays a key role in benzvalene formation.6-8 The quenching of benzene fluorescence by dissolved a 8

4 5 6 7

J. B. Birks, J. Luminescence, 1974, 9, 311. D. J. S. Birch and R. E. Imhof, Chem. Phys. Letters, 1975, 32, 56. J. B. Birks and D. J. Dyson, Proc. Roy. Sac., 1963, A275, 135. W. R. Ware and B. A. Baldwin, J. Chem. Phys., 1964,40, 1703. B. Gelernt, A. Findelsen, A. Stein, and J. A. Poole, J.C.S. Faruduy II, 1974, 70, 939. M.Luria, M. Ofran, and G. Stein, J. Phys. Chem., 1974, 78, 1904. H.Lutz and G. Stein, J. Phys. Chem., 1974, 78, 1909. Y. Ilan and G . Stein, Chem. Phys. Letters, 1975, 31, 441.

51

52

Photochemistry

xenon and the lack of effect on the quantum yield of benmalene formation under the same conditions (excitation at 254 nm) provide convincing evidence for this mechanism. The initial quantum yield (0.18) of benzvalene formation as determined by a bromine-trapping technique is temperature independent over the range 9-50 "C, and thus it seems unlikely that benzvalene formation can account for the inverse temperature dependence of fluorescence observed by others. An analysis of the low-temperature thin-film absorption and fluorescence excitation spectra of CeHs, sym-C6H3D3,and CgDshas been carried out.' The absorption, fluorescence, and phosphorescence spectra and luminescence lifetimes of the o-, m-,and p-cyanoanisoles (Table 1) are consistent with absorption in the first band leading to the population of a single m r * state in the case of the ortho- and meta-isomers and the population of two m r * states in the case of the para-isomer.lo The isomeric fluorobenzonitriles have also been examined (Table l).ll The large value of QP/@ for thepara-isomer is the direct consequence of the forbiddenness of the lLb-lA transition of this isomer, the large value of k I s ~and , possibly also the result of a large value for the radiative rate constant (Tl So). -+

Table 1 Fluorescence and phosphorescence quantum yields and lifetimes of the isomeric cyanoanisoles (CA) and JZuorobenzonitriIes(FB) a dns O-CA m-CA p-CA

(I

5 + 2 5 + 2 7 + 2 O-FB 25.3 m-FB 24.7 p-FB 33.9 Measured in ethanol glass at 77 K.

Tp/S

+

1.4 0.2 1.8 k 0.2 1.6 jz 0.2 2.43 2.6 2.05

% 0.11 0.094 0.24 0.093 0.082 0.23

@f

0.26 0.21 0.22 0.51 0.54 0.24

A single-photon counting technique has been used in the measurement of the luminescence quantum yields of chlorobenzene and benzyl chloride at 77 K in a range of matrices [@f(C6H5C1) = (1 f 0.5) x QP(C6H8Cl)= (2 4 1) x lo-'; @f(C7H7Cl)= (1 f 0.5) x @p(C7H7Cl)= 1 It 0.5 x A comparison of these data with the gas-phase results leads to some interesting It may be that the conclusions. @f for C,&.Cl in the gas phase is only 2.7 x value of @ ~in f the vapour phase is attributable to a large value of k ~ asc compared with C6H5C1while the decrease in @(decomposition) of C,H,Cl with increasing pressure is attributed to vibrational relaxation in the triplet manifold. The larger is attributed value of @f in the vapour phase, @f(C7H,Clvapour) = 4.5 x to an increased singlet-triplet coupling of some unspecified nature. This year a number of papers on the fluorescence of benzyl and related radicals have appeared.l3-le The fluorescence lifetimes are surprisingly long (Table 2) lo I1

l2 l3 l4 l5 lo

E. Pantos, A. M. Taleb, T. D. S. Hamilton, and I. H. Munro, Mol. Physics, 1974, 28, 1139. Y . H. Lui and S. P. McGlynn, J. Mol. Spectroscopy, 1975, 55, 163. Y . H. Lui and S. P. McGlynn, J. Luminescence, 1975, 9, 449. T. Ichimura, T. Hikida, and Y . Mori, J. Phys. Chem., 1975, 79, 291. T. Okamura, K. Obi, and I. Tanaka, Chem. Phys. Letters, 1974, 26, 218. J. D. Laposa and V. Morrison, Chem. Phys. Letters, 1974, 20, 270. A. Bomberg, D. M. Friedrich, and A. C. Albrecht, Chem. Physics, 1974, 6, 353. P. M. Friedrich and A. C. Albrecht, Chern. Physics, 1974, 6, 366.

53

Photophysical Processes in Condensed Phases

Table 2 Fluorescence lifetimes of benzyl and substituted benzyl radicals at 71 K. Compiled from Refs. 13-15 Compound C6H6CH2

C6D5CD2 c6 H5 CD2

C6D6CH2

2,6-dideuterio-C6H,D,CD,

Mesityl

Glass 3MP

MeOH EtOH 3MP 3MP 3MP 3MP 3MP

isopentane Duryl

3MP

isopentane

Ttl@

1.45 1s o 1.44 3.65-3.93 1.26 (1.74) 3 26 (3.22) 3.21 0.54 0.61 0.50 0.53

but can be rationalized in terms of the forbidden character of the 2Az +- 2Bz radiative transition and the absence of efficient non-radiative relaxation routes. Since there can be no state of higher multiplicity between the emitting 2A2state and the ground state, 2B2,the problem of determining substituent effects on Tf reduces to determining variations in k, and kIc. By using equations of the type

where Bo = 7f-l(C7D7), B2 = T~-~(C,H,CD,), and Bp = ~f-l(2,6-dideuterioC6H3D2CD2)and kl, k2, and k, are the enhancements of the radiationless rates for protonation at the methylene, the ortho, and the combined mefa and para sites, respectively (compared with the perdeuteriated compound), and k12is an interaction term between methylene and ortho protons, values of the k’s may be obtained. Once this effect of deuteriation and other substituent effects on the non-radiative processes can be extracted, the benzyl system presents an attractive model for determining variations in internal conversion in the absence of competing spin-forbidden processes. The remarkable effect of the ortho deuteriation is considered to arise from a dominant role of the ortho hydrogens in the internal conversion process, possibly through both the vibronic part of the electronic matrix element coupling the two states and through the Franck-Condon factors. Fluorescence from the indanyl radical produced by photolysis of crystalline indane at 77 K has been observed and the 0-0 band (20 727 cm-l) is very close to that of the benzyl radical. An analysis of the fluorescence and phosphorescence from indane, and fluorescence (no phosphorescence could be observed, contrary to previous reports) from indene has been rep0~ted.l~ The large differences between the So-S, absorption spectrum, fluorescence spectrum, and fluorescence decay time of 1,l’-binaphthyl in fluid solutions as compared with those in rigid solutions can be related to a change in the dihedral angle, 0, between the two rings on electronic excitation. The red shift of the fluorescence spectrum demonstrates clearly that after excitation to the S1state, l7

B. Brockelhurst and D. N. Tawn, Spectrochim. Acta, 1974,30A,1807.

Photochemistry

54

conformational changes take place so as to decrease 8 and thus decrease the energy to the S1state.l* Fluorescence from upper singlet states continues to attract interest, and in particular the role of the S1-S2energy gap in controlling @&!?,-So) and @&S2-S0). It has been shown that, using appropriate substituents, the energy gaps in the singlet manifold of azulene can be varied, and the emission characteristics thus change from predominant S, -+ So to predominant S, + So.10For azulene and azulene-l-carboxylic acid, in which the S2-S1splittings are 14 000 and 1 1 500 ern-', respectively, only S2 + So fluorescence is observed, whereas with diethyl-2amino-6-bromoazulene-1,3-dicarboxylic acid (S2-S1 = 4300 cm-l) S,-So fluorescence is dominant. Perhaps the most interesting class of azulenes are those which exhibit dual S2-So and &-So fluorescence and which have S,-S, energy gaps of between 9000 and 9800 cm-1 (e.g. 1-trichloroacetylazulene). In this latter class, while the S2-Sofluorescence quantum yield is found to be temperature independent, this is not the case for the S,-So fluorescence. Polarization emission spectra of naphthalene, anthracene, and naphthacene in stretched polyethylene sheets at 90 K, and also in crystalline normal hydrocarbons at 20 K, have been obtained. While the emission polarization data for naphthalene are in agreement with earlier reports, this is not so for anthracene and naphthacene.,O The discrepancies obtained have been attributed to an oversimplified analysis of the polarization spectra by earlier workers. Thus it is suggested that the variation in the polarization spectrum at 25 500 cm-l for anthracene is the result of a lack of bands with appreciable intensity rather than important changes in the band polarizations. The stretched-film method for polarization studies does have the advantage of experimental simplicity and we may therefore expect more developments in this area. The temperature dependence of monomer and excimer emissions from a range of crystalline anthracenes has been determined and the 0-0 transition (25 096 k 6cm-l) for crystalline anthracene located.21 Further studies of the dual fluorescence from crystalline anthracene have been carried out using a lifetime determination approach. The occurrence at 4 K of emissions with different lifetimes has been interpreted as the result of a two-step mechanism. Excited and thermalized excitons (probably free excitons) have lifetimes of 1 ns, and, in addition to fluorescing, transfer energy to other crystal states to produce localized excitons (T 3.5 ns).22 In a detailed analysis of the influence of reabsorption on the fluorescence of organic crystals, Birks 23 has reviewed existing data on the fluorescence lifetimes of crystalline anthracene and derived expressions to rationalize lifetime variations in terms of guest-host exciton transfer, host crystal and defect reabsorption, and defect and impurity fluorescence. The technical fluorescence lifetime, N

.

Tmt = 18 19

20 21 22

23

l/kmt =

\

I

Tm/(l

- a m @fm

-I-

2

n

M [ 'X, 1)

(4)

M. F. M. Post, J. Langelaar, and J. D. W. van Voorst, Chem. Phys. Letters, 1975, 32, 59. G. Eber, F. Griineis, S. Schneider, and F. D o n , Chem. Phys. Letters, 1974, 29, 397. J. J. Dekkers, G. P. Hoornweg, C. Maclean, and N. H. Vethorst, Chem. Physics, 1974,5, 393. M. D. Cohen, Z . Ludmer, and V. Yakhot, Phys. Status Solidi (B), 1975, 67, 51. M. D. Galanin, Sh. D. Khan-Magometova, Z . A. Chizhikova, M. I. Demchuk, and A. F. Chernyavskii, J. Luminescence, 1975, 9, 459. J. B. Birks, Mol. Crystals Liquid Crystals, 1974, 28, 117.

55

Photophysical Processes in Condensed Phases

where subscript m refers to the molecular parameters of the host, n refers to the guest (impurities and defects) parameters, and U n M = k,,M/k, (km = total decay rate of l M * , and k n M is the rate constant for exciton transfer from lM* to lXn). It is obvious that an analysis of this kind could be improved with more knowledge of the contributions of guest and defect emissions to the total fluorescence observed. Data of this kind are difficult to obtain by the usual techniques, but further frequency-dependent lifetime studies could be most informative. A number of other emission studies of pure crystalline anthracene and anthracene in mixed crystals have been r e p ~ r t e d , and ~ ~ -a~paper ~ by Hochstrasser and Wessel deserves special mention. These workers have for the first time applied picosecond spectroscopic techniques to studies of mixed crystals at low f e m p e r a t ~ r e s ,and ~ ~ although the limitations of excitation frequencies and the time intervals between observations severely restricted the investigation, some important conclusions were reached : (i) vibrational relaxation of anthracene at 2 K in single naphthalene crystals takes place in 10-100 ps, consistent with the limits set by the optical linewidths; (ii) in the anthracene-naphthalene system several relaxation pathways compete for excitation of 4000’ lattice. The recent interesting observation that the fluorescence quantum yields of some polycyclic hydrocarbons are not affected by external heavy-atom perturbation has been attributed to a large energy gap between S, and the accepting triplet state. The negligible effect of bromination of perylene on Q and rf in the series perylene, 3-bromoperylene, and 3,9-dibromoperylene confirms this.2s Pyrene, on the other hand, is greatly affected by bromination, and this can be seen as the result of a much smaller singlet-triplet splitting (Figure 1). The trapping of polycyclic aromatic molecules in n-heptane monocrystalline matrices, prepared by slow cooling, leads to oriented molecules inside the paraffinic crystal lattice, and it appears that the trapping sites for coronene, perylene, and pyrene are similar to those observed earlier for quickly frozen solutions of coronene and designated ‘pseudo-liquid sites’ and ‘substitutional sites’.2D From the former studies it seems that aggregation does not play a dominant role. A nitrogen-pumped laser has been used to excite perylene in n-octane at 4.2 K in order to investigate non-linear dependence of fluorescence on excitation intensity in a Shpol’skii system. The approximately square dependence of one of the vibronic emission lines on the excitation intensity is consistent with super-radiant emission.3o The variations in the vibrational structures of the fluorescence spectra of coronene and triphenylene can be broadly understood in terms of increased intensities of forbidden vibronic bands with increase in solvent dielectricconstant. However, some inconsistencies exist, and a proper quantitative interpretation must await the development of a suitable theory.a1 N

+

as as 2e

ao

A. Fort and A. Coret, J. Chem. Phys., 1975, 62, 3269. E. Glockner and H. C. Wolf, Chem. Phys. Letters, 1974, 27, 161. J. Aihara and H. Inokuchi, Bull. Chem. SOC.Japan, 1974,47,2631. R. M. Hochstrasser and J. E. Wessel, Chem. Physics, 1974, 6, 19. H. Dreeskamp, E. Koch, and M. Zander, Chem. Phys. Letters, 1975, 31, 251. M. Lamotte and J. Joussot-Dubien, J. Chem. Phys., 1974, 61, 1892. J. Ibram, R. A. Auerbach, R. R. Birge, B. E. Kohler, and J. M. Stevenson, J. Chem. Phys., 1974,61, 3857.

A. Nakajima, J. Luminescence, 1974, 8, 266.

56

Photochemistry

The emission spectra of non-crystalline tetracene films have been interpreted in terms of emission from a molecular pair in a sandwich configurati~n.~~ Substitutional and surface fluorescence in pentacene-anthracene crystals s3 and the changes in luminescence of single crystals of pure anthracene, pure tetracene, and pentacene-doped tetracene as a result of electrode-induced changes in electrical charge carriers34B3K have been examined. Hot bands in the fluorescence and phosphorescence of coronene have been a n a l y ~ e d . ~ ~

'Lg-., c

La-, \

\

\

\

'1

\

3La

\

\

\

-3

'A

3-Bromopyrene

LU-

\

\

I

1

\ \

-

033

9-Bromoanthracene

\ \

La

-

3L,

'A

-

82 9

3 -Bromoperylene

Figure 1 Schematic energy level diagram for 3-bromopyrene, 9-bromoanthracene, and known, - - - - assumed) 3-bromoperylene ((Reproduced by permission from Chem. Phys. Letters, 1975, 31, 251)

Two-photon absorption spectra give some important information about the even-parity transitions of molecules and solids which are forbidden in one-photon absorption. The two-photon absorption of 2,2-paracyclophane, monitored by the intensity of fluorescence, has allowed the assignment of the two bands in the region 34 700-36 500 cm-l. (Even-parity-allowed lBlg+- lAl, and lB2,+- lAIa.) 37 A quantitative investigation of the photophysical processes in simple alkenes has in the past been restricted because of the lack of kinetic information about excited-state decay routes. However, Hirayama and Lipsky, in their observation of fluorescence from a series of alkenes, have opened up new possibilities for more quantitative studies of structure-reactivity relationships in this area.38 32 33

34 36 36 37 38

H. Muller, H. Bassler, and G. Vaubel, Chem. Phys. Letters, 1974, 29, 102. A. Brillante and D. P. Craig, Chem. Phys. Letters, 1974, 29, 17. J. Kalinowski and J. Godlewski, Acta Phys. Polon. (A), 1974, 46, 523. J. Kalinowski and J. Godlewski, Phys. Status Solidi (B), 1974, 65, 789. M. Zonder, Z . Naturforsch., 1974, 29a, 1520. K. Fuke, S. Nagakura, and T. Kobayashi, Chem. Phys. Letters, 1975, 31, 205. H. Hirayama and S. Lipsky, J. Chem. Phys., 1975,62, 576.

57

Photophysical Processes in Condensed Phases

As Table 3 shows, the values of Of are very low. A case is made that the observed emission is the result of relaxation from a Rydberg singlet state; although the evidence is not definitive. The low fluorescence yields may be the result of a rapid competitive internal conversion to the l n r * state (i.e. emission is from S,) from which emission cannot occur. This would account for the large value of @f for 2,3-dimethylbut-2-ene (DMB) since, unlike the lower members of the series, even the origin of the l r r ~ * transition may be energetically above the Rydberg state. Fluorescence lifetimes were estimated from a study of quenching by CC14, and ~t (neat DMB) ~ ( 1 . 5k 0.5) x 10-l1 s. Table 3 Fluorescence A,,

and q5f for some mono-olefins excited at 184.9 nm

Propylene But-l-ene trans-But-2-ene Hex-1-ene trans-Hex-2-ene 2-Methylpent-2-ene 2,3-Dimethylbut-2-ene

Condition a vapour vapour

vapour liquid liquid liquid liquid

225 228 235 23 1 238 246 263

38

Of x 106 0.4 0.6 1 2 4 8 150

Vapours at 1 atmosphere and liquids neat at 25 "C.

Although the photochemistry of stilbenes has been studied in considerable depth, the closely related styrenes have been largely neglected. A few recent studies have concentrated on the factors controlling the efficiencies of the nonradiative processes in the latter systems. Zimmerman, by studying a series of l-phenylcycloalkenes, has emphasized the importance of twisting about the olefinic n-bond as a means of non-radiative d e ~ a y It . ~is ~argued ~ ~ ~that the change in the singlet state non-radiative rate constant (k,) going from l-phenylcyclobutene [k, (300 K) = 6.29 x lo7s-l] to l-phenylcycloheptene [knr(300 K) = 3.57 x lo9 s-I] reflects the ring constraint to rotation about the olefinic n-bond. A parallel trend in the values of 3k,, is also observed. However, the values of 3knr are not so well defined as those for 'k,, since an indirect (biacetyl sensitization) method is used to obtain them. Pariser-Parr-Pople-type calculations for the dependence of the excited-state energy levels on 8, the angle of twist about the olefinic n-bond give a qualitative pictorial representation of the changes that occur in going from the acyclic styrene to the highly constrained phenylcyclobu t ene. Although recognizing the importance of the rotational process in the nonradiative decay of styrenes, other workers have explored the participation of nonrotational non-radiative processes in the Table 4 gives the values of km obtained from @f and Tf measurements for a series of styrenes. The importance of C-H bonds, and the olefinic rr-bond, in controlling the magnitude of lknr is apparent. The case for an efficient non-radiative process perhaps involving a state in which a hydrogen atom is shared between atoms 2 and 3 is reinforced H. E. Zimmerman, K. S. Kamm, and D. P. Werthemann, J. Amer. Chem. SOC.,1974, 96, 7821. 41

H. E. Zimmerman, K. S. Kamm, and D. P. Werthemann,J. Amer. Chem. SOC.,1975,97,3718. P. M. Crosby and K. Salisbury, J.C.S. Chem. Comm., 1975,477.

Photochemistry by a comparison of trans-l-phenylprop-1-ene and 3,3-dimethyl-1-phenylbut-l-ene. If a branching ratio of unity is assumed for both olefins, the rate constants for rotation can be calculated by k,t = 2ki,,, where kiWmis obtained in the usual way from 7f and @isom. For the butene, k,t N Cknr, while for the propene k,t 4 Ckm. One can only speculate that the inefficiency in cyclopropane formation from acyclic styrenes must be because of a preferred relaxation to the ground-state styrene from the state described above rather than complete hydrogen-atom transfer to give a 1,3-biradical. 58

Table 4 Photophysical parameters of some styrenes in cyclohexane 41 Compound Styrene Styrene Styrene

0.15 0.36

*/ns 12.5 11.4 20.3

trans-p-t-But ylst yrene trans-p-Methylstyrene cis$- Methylst yrene a-Methylstyrene E-cup-Dimethylstyrene 1 -Phenylcyclohexene

0.155 0.028 0.0045 0.028 0.014 0.018

12.6 2.4 2.7 2.7 1.9 1.8

@fa

T

k, x lO-'/s-l 1.20

-

1.80

-

1.25 1.15 0.17 1.05 0.700 1 .OO

k,, x ~O-'/S-' 6.7

-

3.2 (gas phase) 6.7 40.5 37.0 36.0 52.0 54.5

Excitation wavelength 265 nm. However, for a-methylstyrene @ f was found to be independent of excitation wavelength (250-285 nm). Excitation wavelength 254 nm. Ref. 41. See 'Fluorescence Spectra of Aromatic Molecules', ed. I. B. Berlman, Academic Press, 2nd edn., 1971, p. 174. M. H. Hui and S. A. Rice, J. Chem. Phys., 1974, 61, 883.

Acyclic dienes do not luminesce, and until recently ergosterol was the only aliphatic acyclic diene known to fluoresce. However, fluorescence from seven cholestadienes (s-trans-dienes) has now been detected, and the 0-0 bands are in the region 310-326 nm.42 Two recent theoretical studies have reached opposite conclusions as far as the mechanism of direct photochemical geometric isomerization of stilbenes is concerned. Momicchioli et al. found a potential-energy barrier of 35 kcal mol-l for rotation about the central olefinic bond in the S, state, clearly inconsistent Orlandi and Siebrand, on the with geometric isomerization from this other hand, have argued that if extensive CI calculations are carried out using a greater number of doubly excited states, then the S2 state may be seen to play a crucial role (Figure 2), as indicated by an approximate welectron calculation treating stilbene as two benzyl radicals; if this situation obtains then isomerization from S1 is clearly possible.44 Calculations of the structure of the T +- 7 ~ * transitions in trans- and cis-stilbene indicate that the description of photoisomerization by a one-dimensional torsional oscillator is an over~implification.~~ An examination of the effect of meta- andpara-bromination on the quantum yields of isomerization and the photostationary-state ratios has shown that, while a para-bonded bromine enhances S1+ T,, intersystem crossing, bromination at 42 43

44 46

J. Pusset and R. Beugleman, J.C.S. Chem. Comm., 1974, 448. F. Momicchioli, M. C. Bruni, I. Baraldi, and G. R. Corradini, J.C.S. Faruday ZZ, 1974, 70, 1325; 1975,71, 215. G. Orlandi and W. Siebrand, Chem. Phys. Letters, 1975, 30, 352. A. Warshel, J . Chem. Phys., 1975, 62, 214.

59

Photophysical Processes in Condensed Phases

the meta-positions has no effect on this process.4s Activation energies for isomerization are typical of this type of system (2-10 kcal mol-l) and the wavelength dependence of and OCDW was explained in terms of selective excitation of different conformers.

trans

0-

cis

- Q

trans

Figure 2 Potential energy diagrams (schematic) of stilbene as a function of angle of rotation about the central bond. (a) Conventional picture, (b) ref. 44 (Reproduced by permission from Chem. Phys. Letters, 1975, 30, 352)

am-Diphenylpolyenes have received more attention this ~ear,~'-~O and the interpretation of the anomalous behaviour of @ ~ and f Tf for all-trans-l,6-diphenyl61 An examination hexatriene (DPH) has been the subject of some controversy.60~ of the wavelength dependence of @f for diphenyloctatetraene, anhydrovitamin A, and all-trans-retinal showed that only the retinal fluorescence was wavelength dependent.61 The following three possible explanations for the unusual variation in @f were considered : (i) an impurity is present which is weakly fluorescent and which competes with retinal for photons within the main absorption band; to the emitting (ii) internal conversion occurs from an initially excited state (m*) state, possibly an nr* or lA, state, competing with a fast radiationless process (perhaps of a photochemical nature); (iii) there is competition between vibrational relaxation in the S, state and a fast radiationless process. Although the authors favour process (ii) their conclusion can only be a tentative one. In a review of the electronic structures and spectroscopy of linear polyenes, Hudson and Kohler have summarized the data available on the photochemical and photophysical parameters of a wide range of molecules, including aa-diphenylpolyenes, retinals, and retino1s.62 The role of an excited state lower in energy than the lBUstate in polyenes does reconcile some of the anomalies in the fluorescence parameters of polyenes. There is clearly a need for a better theoretical 40

47

J. Saltiel, D. W.-L. Chang and E. D. Megarity, J . Amer. Chem. Sac., 1974, 96, 6521. W. E. Slack, C. G. Moseley, K. A. Gould, and H. Shechter, J . Amer. Chem. Sac., 1974, 96, 7596.

4.9 4D

60

61

aa

M. Sumitani, S. Nagakura, and K. Yoshihara, Chem. Phys. Letters, 1974, 29, 410. T. Wismonski-Knittel, G. Fischer, and E. Fischer, J.C.S. Perkin IZ, 1974, 1930. E. D. Cehelnik, R. B. Cundall, J. R. Lockwood, and T. F. Palmer, Chem. Phys. Letters, 1974, 21, 586. J. B. Birks and D. J. S. Birch, Chem. Phys. Letters, 1975, 31, 608. B. Kohler, Ann. Rev. Phys. Chem., 1974, 25, 437.

60

Photochemistry

description of the electronic states of these molecules. One attempt to meet this need has been reported : a conformationally dependent ordering of the excited states of retinals has been predicted from a PPP c a l ~ u l a t i o n . ~ ~ Dichlorocarbene prepared in an argon matrix fluoresces in the region of 700 nm, and an analysis of the structure has confirmed that the observed structure is due to progressions in the ground-state stretching and bending The mechanism of photo-ionization of sodium tetracene and the energies of the lowest excited states of the mono- and di-negative ions of naphthalene, anthracene, tetracene, pentacene, and biphenyl have been obtained by an analysis of the lowfrequency regions of the absorption ~ p e c t r a . ~The ~ - ~photo-ionization ~ of the mono- and di-sodium salts of tetracene has been examined using nanosecond ruby laser pulses and has led to the conclusion that photo-ionization is a twophoton process.K8aPicosecond techniques have also been applied to an analysis of the kinetics of photo-ionization of tetracene d i a n i ~ n . ~ * ~ It has been concluded that acetone tends to undergo hydrogen bonding to only one water molecule and that the blue shift in the n --f n* absorption band in going from heptane to water reflects the additional energy required to break the hydrogen bond in the excited In a related study of the n -+n* transitions in ketones, a comparison of changes in the heats of solution in different solvents with n -+7 ~ *band blue shifts has led to the proposal that the changes in blue shifts are the result of changes in the solvation of the ground states and excited states.6o Studies of deuterium isotope effects have proved useful in the determination of the details of excited chemical and physical processes. However, some of the observed isotope effects pose as many questions as they answer. Such is the case for the formation of unsaturated ketones from certain cyclic ketones, e.g. (l).61 The observed primary isotope effect is of the same order as that observed earlier by these authors for similar systems, but is much smaller than literature values for radical disproportionations. One explanation is that the rate of hydrogen abstraction is controlled by the conformation at the starred carbon (*).

Scheme 1 63 54 55 B6

57

58 59

(lo

R. R. Birge, K. Schulten, and M. Karplus, Chem. Phys. Letters, 1975,31,451. D. E. Tevault and L. Andrews, J. Mol. Spectroscopy, 1975, 54, 110. G. J. Hoytink, Chem. Phys. Letters, 1975, 31, 21. G. J. Hoytink, Chem. Phys. Letters, 1975, 31, 201. G . J. Hoytink, Chem. Phys. Letters, 1974, 26, 318. (a) T. L. Netzel and P. M. Rentzepis, Chem. Phys. Letters, 1974, 29, 337; (b) D. K. Sharma, J. Stevenson, and G. J. Hoytink, ibid., p. 343. J. E. Del Bene, J. Amer. Chem. SOC.,1974, 96, 5643. P. Haberfield, J. Amer. Chem. SOC.,1974, 96, 6526. W. B. Hammond and T. S. Yeung, Tetrahedron Letters, 1975, 1173.

61

Photophysical Processes in Condensed Phases

Following the report last year of the measurements of intersystem crossing rates in the picosecond time domain using different harmonics of the Nd3+/glass laser to excite and to monitor triplet-triplet absorption, these studies have been Table 5 extended to benzophenone in n-heptane and 1- and 2-nitrona~hthalene.~~ shows the combined results of this and the earlier studies and clearly demonstrates that the relative spacing of the inn* and 3 7 r ~ * states in benzophenone cannot be crucial in determining k ~ s c(n-heptane would be the least favourable solvent in this respect). Another explanation is that since vibrational relaxation must be occurring on a similar time-scale to intersystem crossing, the solvent may be controlling the efficiencies of relaxing the excited benzophenone molecules to or from vibrational levels which are strongly coupled to the triplet manifold. The large value for k ~ s cfor the nitronaphthalenes, taken with low intersystemcrossing yields, indicates an unusually rapid Sl-S, process.

Table 5 Lgetimes for triplet build-up following excitation at 354.5 nm 62 Molecule 1-Nitronaphthalene 1-Nitronapht halene 2-Nitronapht halene 2-Nitronapht halene Benzophenone Benzophenone Benzophenone

Solvent ethanol benzene ethanol benzene ethanol benzene n-heptane

TISC

(= kIsc-l)/Ps

8 4 2 12 f 2 22 f 2 10 & 2 16.5 f 3 30 f 5

8f2

The temperature dependence of and the quantum yields of the products for 9-a-bromopropionylanthracene have been analysed in terms of rotation of the carbonyl group from the orthogonal geometry (with respect to the anthracene ring) enhancing intersystem crossing.63 The extent of rotation need not be large, but rotation of the corresponding -CH=CH2 in 9-vinylanthracene does not enhance intersystem crossing. The enhancement effect in the bromopropionylanthracene is examined in terms classified by Siebrand, and it is shown that the electronic matrix element coupling the lnr* and %n* states will depend upon C,, where C,is the coefficientfor the 2p atomic orbital on oxygen, i.e.

where the state coupling matrix element is proportional to (n?i* I

Hso [ i f * )a (n I hso [ ii>

C, will in turn be a function of 8, the angle of rotation of the carbonyl group, becoming larger for small values of 8. Emission studies of 2-methyl-1-aceanthrenone and its anion 64 and 9-fluorenone85 have been reported. 62

R. W. Anderson, R. M. Hochstrasser, H. Lutz, and G. W. Scott, Chem. Phys. Letters, 1974, 28, 153.

63

64

T. Matsumoto, M. Sato, and S. Hirayama, Chem. Phys. Letters, 1974, 27, 237. S. Hirayama, Bull. Chem. SOC.Japan, 1975, 48, 1127. R. Zwarich and A. Bree, J. Mol. Photochem., 1974, 52, 329.

62 Photochemistry Biacetyl, a molecule much used in energy-transfer investigations, has never had its lower excited states fully analysed. In order to rectify this situation, Brand and Man have carried out absorption and emission studies at 4-8 K in the polycrystalline state.66 In absorption all the features reported earlier by Sidman and McClureg7are confirmed. However, the earlier assignments of the longlived emissions have been shown to be in error owing to participation by an impurity. The green emission from the impurity is produced on prolonged irradiation and comes from a product of biacetyl photolysis. The somewhat confused situation as regards the assignments of the electronic transitions in a-diketones has also prompted McGlynn and co-workers to re-investigate the dependence of the excited-state energies on the CO-CO dihedral angle (0).6a The model compounds used were 3,3-dimethylindanedione (4) (0 0")and l-phenylpropane-l,2-dione( 5 ) (70" < B < 1 loo), and available data for glyoxal(0 II 1 SO") were accepted. A CNDO/S-CI method with variable 0 was used as the theoretical basis for comparison with experiment. A study of the emission efficiency from S, and Tlconfirms the importance of CO-CO rotation as an energy-dissipation mode both in the triplet and singlet manifolds. Furthermore, the blue shifts in absorption and phosphorescence of (4) and (5) on cooling from 300 to 77 K are also attributed to changes in 0, perhaps as a result of changes in solvation. In comparing the experimental data for these and other a-dicarbonyl compounds it is concluded that, within the one-electron approximation, the two observed ,T,* t %, transitions, in order of increasing energy, are best considered as v+* + n+ and r-* + n,. The importance of 0 is also seen in the emission of camphorquinone.6B The phosphorescence peaks observed at 77 K for a glass or at 300 K for the solid are 600 cm-l lower in energy than the TI state and can be ascribed to emission from a defect. This defect could be a camphorquinone molecule with a greater coplanarity of the carbonyl groups than is normal. The lTn,* + ,TI energies of the diaromatic a-dicarbonyl compounds dimesityl diketone and phenyl mesityl diketone vary over the broad range of 5400 cm-l. On the other hand, the Tn,*+- T1and 3T,,* +. lT1energies span 500 cm-l, a very narrow range. This near-constancy of emission energies indicates that the three compounds decay radiatively from similar well-defined states. From these observations and energy-transfer studies it is concluded that, while the ground states of these compounds have variable values of 0 and therefore variable excitation energies, the S1 states exhibit CO-CO ~oplanarity.'~ The fluorescence quantum yields of indole and L-tryptophan in aqueous solution at 296 K increase by 45% in going from excitation wavelength 230 nm to 260nm, whereas outside this region @f is constant. The constancy of the fluorescence to phosphorescence ratio indicates that intersystem crossing is not the competitive process, and the increase in @(photo-ionization) below 260 nm N

66

67 68

J. C. D. Brand and A. W.-H. Man, J . Amer. Chem. Soc., 1974,96,4380. J. W. Sidman and D. S. McClure, J. Amer. Chem. SOC.,1955, 77, 6461, 6471. J. F. Arnett, G. Newkome, W. L. Mattice, and S. P. McGlynn, J. Amer. Chem. SOC., 1974, 96, 4385.

68

D. B. Larson, J. F. Amett, A. Wahlborg, and S. P. McGlynn, J. Amer. Chem. Soc., 1974, 96,

6507. 70

J. F. Arnett and S. P. McGlynn, J. Phys. Chem., 1975, 79, 626.

63 Photophysical Processes in Condensed Phases suggests that photo-ionization from higher excited electronic states is competitive with internal conversion to the fluorescent state.71 The discussion of the role of a charge-transfer state as an intermediate in the formation of %, is interesting in that it rationalizes the wavelength dependence of Of at low temperatures where electron ejection is inefficient. It is argued that internal conversion to So via a charge-transfer-to-solvent(CTTS) state provides an efficient relaxation route in the glass. The possibility of CTTS participation is further supported by studies in solvents of different static dielectric permittivity. A comparison between the results of fluorescence studies and studies of the efficiencies of %, production highlights the problems of an accurate and meaningful analysis of econcentrations in systems such as this, where the following complications arise : (i) geminate recombination of radical cation and electron; (ii) direct interaction of an electron scavenger and excited states, e.g. a CTTS state. Temperature effects on and @(e,,) also tend to confirm CTTS ~ a r t i c i p a t i o n .An ~ ~ examination of the Stokes shift of 1-methylindole, 2-methylindole, and 2,3-dimethylindole in ethyl acetate at different temperatures has given the dipole moments in the S1 states .72 Photolysis of indole and tryptophan in a glass at 77 K produces cation-radicals and electrons, and subsequent absorption of visible light by the electron results in recombination of these species and the production of S1and 7'' states of the amine. An analysis of the emissions resulting from the recombinations in different glasses shows how electrostatic interactions can influence the energetics of electron-cation recombinations. Thus in an ether glass stimulated at 650 nm, 28% of the charge-transfer combination states do not have enough energy to populate the S1state whereas in ethylene glycol-water (70-30) this is increased to 80%. In addition, corrected cation spectra for stimulated emission indicate that more energy is required to release an electron from an EG-W glass than from an ether glass.73 Isothermal delayed fluorescence along with visible 6000 A photostimulated fluorescence and phosphorescence emissions have also been recorded and analysed for diphenylamine and for carbazole in rigid ether glasses.74 The large environmental dependence of the 11-(3-hexyl-l-indolyl)undecyltrimethylammonium bromide fluorescence lifetime and fluorescence spectrum has led to its continued use as a fluorescence probe for micellar systems.76 Fluorescence-detected circular dichroism, a technique which appears to have considerable potential, has been applied to the determination of the c.d. spectra of L-tryptophan and L-cystine and two macromolecular systems.76 The photo-ionization threshold for tetramethyl-p-phenylenediamine(TMPD) in polycrystalline hydrocarbons at 77 K has been shown to be lowest for the most globular hydrocarbons, and for the same solute-solvent system the values are systematically greater in the crystalline phase than in the liquid solvent by 1 eV.77

I* 74

78 77

H. B. Steen, J. Chem. Phys., 1974, 61, 3997. G. Jacyno and A. Kawsk, Bull. Acud. polon. Sci.,1974, 22, 339. D. Muller, M. Ewald, and G. Durocher, Canud. J. Chem., 1974, 52, 407. D. Muller, M. Ewald, and G. Durocher, Cunud. J. Chem., 1974, 52, 3707. N. E. Schore and N. J. TUITO,J. Amer. Chem. SOC.,1975,97,2488; D. Creed, Photochem. and Photobiol., 1974, 19, 459. D. H. Turner, I. Tinoco, and M. Maestre, J. Amer. Chem. SOC.,1974, 96, 4340. A. Bernas, J. Blais, M. Gauthier, and D. Grand, Chem. Phys. Letters, 1975, 30, 383.

Photochemistry

64

Other studies of the TMPD system have been r e p ~ r t e d7Q. ~One ~ ~ of these reports claims the observation of a new emission at A,, 430 nm attributed to a solutesolvent charge-transfer The luminescence observations do tend to indicate that impurities may be responsible for the emission, but the authors seem to have eliminated the possibility with some degree of certainty. Reports of intramolecular field effects on the absorption and fluorescence spectra of N-(1-naphthyl)ethylenediamine8o and of an analysis of the electronic spectra of pyrazine 82 have appeared. Although, in general, azo-compounds do not emit, there are certain exceptions to this rule. A new group of azo-compounds which fluoresce at 77 K but not at room temperature has been identified. These are sterically hindered azobenzene derivatives with low-lying (nn*) states. It is suggested that, as in the case of cyclic (cis) azo-compounds, steric hindrance in these azobenzenes (e.g. 2,2’,4,4‘,6,6’hexaisopropylazobenzene and 2,2’-dimethyl-4,4’,6,6’-tetra-t-butylazobenzene) prevents the molecular distortion(s) necessary for at least one path for radiationless 1 -Pyrazolines undergo photochemical nitrogen extrusion but the efficiency of extrusion is very structure-dependent. The very low quantum yield for this process in the case of 4-oxo-3,3,5,5-tetramethyl-l-pyrazoline (6) warrants further investigati~n.~~ 81p

0

Fluorescence studies of the commercially important 1,3-dipheny1-2-pyrazoline derivatives have been extended to a wide range of phenyl- and methyl-substituted derivatives. The fluorescence yields in non-polar solvents are all close to unity, with the exception of 1,3,5,5-tetraphenyl-2-pyrazoline.This is not the case in (See the section on methanol, when a large variation in yields is oxidation for other photochemical processes in these compounds.) By an examination of the fluorescence spectra and fluorescence excitation spectra of 9-aminoacridine at 4.2 K, the fine-structure fluorescence spectrum of the neutral molecule has been identified and investigated using laser excitation.8s A Meisenheimer complex (7), a model for the o-complex formed by nucleophilic attack of certain species on polynitroaromatic compounds, has been observed to fluoresce. The emission maximum is at 670nm in acetonitrile and 0.09. It has been suggested that such a compound may be useful as a fluorescent biophysical

-

78

7Q

J. Blais and M. Gauthier, J . Luminescence, 1974, 9, 143. K. S. Bagdaxir’yan, R. I. Milutinskaya, and Y. V. Kovalev, Internat. J. Radiation Phys. Chem., 1974, 6, 465.

8o

sa 83 84

ss

R. S. Sturgeon and S. G. Schulman, Analyt. Chim. Acra, 1975, 74, 192. I. Suzuka, N. Mikami, and M. Ito, J . Mol. Spectroscopy, 1974, 52, 21. H.-K. Hong and G. W. Robinson, J. Mol. Spectroscopy, 1974, 52, 1. H. Bisle and H. Rau, Chem. Phys. Letters, 1975, 31, 264. P. S. Engel and L. Shen, Canad. J. Chem., 1974, 52,4040. I. H. Leaver and D. E. Rivett, MoZ. Photochem., 1974, 6, 113. L. A. Bykovskaya, R. I. Personov, and B. M. Kharlamov, Chem. Phys. Letters, 1974, 27, 80. S. Farnham and R. Taylor, J. Org. Chem., 1974, 39, 2446.

65

Photophysical Processes in Condensed Phases

02Nt?No2 Nt

-o/

(7) R'

=

'0-

R? = H

sym-Triazine, like carbonyl compounds, reacts rapidly with hydrogen-atom donors on excitation to the nm* singlet or triplet states. Quenching of the mm* state by hydrogen donors also takes place but is much less efficient.88 Thioxanthone should be used as a triplet sensitizer only with caution, as recent work has shown that in hydrogen-bonding solvents (e.g. alcohols), the singlet lifetime is sufficiently long [q(MeOH) = 2.4 ns] for singlet energy transfer to be possible. The large variations in Ofand 7fas a function of solvent may be understood from Figure 3.s0 The isomeric sulphur compound xanthione exhibits

s,

nonpolar, poor hydrogen bonding solvent

so

polar, good hydrogen bonding solvent

Figure 3 Energy level diagram to account for solvent efects on thioxanthone fluorescence (Reproduced by permission from J. Amer. Chem. Soc., 1974, 96, 6230)

quite different photophysics in that no S, emission is observed. However, S2(lA,, m*)-+ Sofluorescence has now been observed. af(3-methylpentane) = 0.0051 k 0.001 for excitation at 298 nm.O0 In a parallel study of alkyl aryl thioketones by Hui et al., S2 + So fluorescence was observed for a range of molecules. S1fluorescence was not observed even when a krypton-ion laser was used for excitation, and therefore @&-So) was set as < 5 x On excitation in the So-Sz and So-S, bands, phosphorescence from the same, T,, state was observed. The reason for the presence of S,-So fluorescence in the thioketones, as is the case for azulenes, is almost certainly because of the large S,-& energy gap, and the resulting inefficient S2-S, internal c o n v e r s i ~ n .Another ~~ consequence of inefficient S2-S1 internal conversion is that chemical reactions from the S2 state may compete with photophysical relaxation and therefore wavelengthdependent photochemistry is observed.g2 The lumichromes and alloxazines

Ba

D. V. Bent and E. Hayon, Chem. Phys. Letters, 1975,31, 325. J. C. Dalton and F. C. Montgomery, J. Amer. Chem. SOC.,1974, 96, 6230. J. R. Huber and M. Mahaney, Chem. Phys. Letters, 1975, 30, 410. M. H. Hui, P. De Mayo, R. Suan, and W. R. Ware, Chem. Phys. Letters, 1975, 31, 257. P. De Mayo and R. Suan, J. Amer. Chem. Soc., 1974,96, 6807.

66

Photochemistry

which fluoresce at 42-80 nm and are substituted at N-1 show an additional fluorescence at 500-560 nm in dioxan-pyridine and acetic acid-ethanol which can be ascribed to fluorescence from isoalloxazines formed by tautomerization in the excited The acidity dependence of 7-hydroxy-4-methylcoumarin has been examined by gain spectros~opy.~~ Developments in sub-nanosecond techniques have led to a considerable amount of work on fast singlet-state processes in large organic molecules. Time-resolved fluorescence studies of eosin, erythrosin, and fluorescein in water and of perylene in cyclohexane reveal that, contrary to an earlier the relaxed fluorescent S, state is formed within 10 ps of excitation even when higher excited states are Halogen substitution of fluorescein results in variations of 7f over a factor of 40 owing to enhanced intersystem crossing. The singlet lifetime or ‘recovery time’ of cryptocyanine (DCI) has been measured using a number of different techniques but there is considerable variation in the reported values. A modified version of a previously reported picosecond spectroscopy technique has been used to redetermine the singlet lifetime g6 and the values obtained [la 4 3 ps (methanol); 75 +_ 15 ps (glycerol)] support two earlier 98

The anomalous dual fluorescence from p-dimethylaminobenzonitrile has been further investigated, and the effect of solvent hydrogen-bonding on the S2-+ So fluorescence has received special attention. The observation that the fluorescence rise time (S, -+So)in the weakly hydrogen-bonding solvents 2,2,2-trifluoroethanol and 2-fluoroethanol is much shorter than in methanol and ethanol (< 20 ps us. 40 ps) provides evidence that solvent reorientation retarded by hydrogen-bonding largely governs fluorescence in these The picosecond kinetics of tetracene dianions have been studied using a new extension of picosecond spectroscopy methods.loOThe rise times of the Stokesshifted fluorescence from rhodamine B, rhodamine 6G, and erythrosine B dissolved in water have been investigated using picosecond techniques. Figure 4 schematically indicates the situation following excitation. The best fit to the data corresponds to a relaxation time within the vibronic manifold of Slof < 1 ps.lol Although these fast spectroscopic techniques provide direct means of examining the behaviour of short-lived species, indirect methods are more convenient and often quite successful. Such is the case for the determination of Tffrom calculated radiative rate constants and measured @f values for a series of cyanine dyes.lo2 A series of papers describes the photophysics of 2-N-arylamino-6-naphthalenesulphonates. In glycerol the fluorescence maxima are due to emission from a naphthalene-centred excited state, and fast intersystem crossing from both P. S. Song, M. Sun, A. Koziolowa, and J. Koziol, J. Amer. Chem. SOC.,1974, 96, 4319. A. M. Trozzolo, A. Dienes, and C. V. Shank, J. Amer. Chem. SOC.,1974, 96,4699. 96 (a) R. R. Alfano and S. L. Shapiro, Optics Comm., 1972, 6 , 9 8 ; (b) G. Porter, E. S. Reid, and G. J. Tredwell, Chem. Phys. Letters, 1974, 29, 469. J, P. Fouassier, D.-J. Lougnot, and J. Faure, Chem. Phys. Letters, 1975, 30, 448. g7 M. A. Duguay and J. W. Hansem, Optics Comm., 1967,1,254. 88 K. R. Naqvi, D. K. Sharma, and G. J. Hoytink, Chem. Phys. Letters, 1973, 22, 222. W. S. Struve and P. M. Rentzepis, Chem. Phys. Letters, 1974, 29, 23. l o o T. L. Netzel and P. M. Rentzepis, Chem. Phys. Letters, 1974, 29, 337. Io1 G. Mourou and M. M. Malley, Chem. Phys. Letters, 1975, 32,476. l o p A. C. Craig, J. Phys. Chem., 1974, 78, 1154. gs O4

Photophysical Processes in Condensed Phases

67

vibrationally excited and vibrationally relaxed S, states is promoted by heavyatom substituents (halogens) at the 4-position of the N-aryl By use of the monolayer assembly technique it has been shown that the efficiencies of intersystem crossing from high and the lowest vibrational levels of the S, state of a cyanine dye are similar.1o4,lo6 A new range of coumarin derivatives with structurally rigid amino-groups show considerable potential for use in tunable dye laser systems.1o6 The lowtemperature fluorescence spectra and quantum yields of bilirubin have been reported. lo7

0 0

TF

VFLUO

Figure 4 A diagram of the four-level model of a dye molecule in solution is shown. The equilibrated ground state, 1, is surrounded by a solvent cage. Upon transition to the Franck-Condon excited state, 2, the nuclear configuration of the dye and the solvent cage remains stationary. Resonance fluorescence from the Franck-Condon state is shown. Eguilibration in the excited state of the dye molecule and the surround solvent is obtained in level 3. The major portion of fluorescence takes place between levels 3 and 4, although emission also occurs continuously from the intermediate levels (Reproduced by permission from Chem. Phys. Letters, 1975, 32,476)

Singlet Quenching by Energy Transfer and Exciplex Formation.-In a series of papers Shetlar has examined the kinetic consequences of there being more than one quenching process in a system. The non-linear Stern-Volmer type expressions derived will be useful in both luminescence studies and studies of photochemical reactions.1o8 (a) E. M. Kosower and H. Doduik, J. Amer. Chem. SOC.,1974,96,6195; (b) E. M. Kosower and H. Doduik, Chem. Phys. Letters, 1974, 26, 545; (c) E. M. Kosower, H. Doduik, K. Tanizawa, M. Ottolenghi, and N. Orbach, J. Amer. Chem. Soc., 1975, 97, 2167; ( d ) K. Kano, Tetrahedron Letters, 1974, 4323. lo' 0. hacker and H. Kuhn, Chem. Phys. Letters, 1974, 27, 471. lo6 0. hacker and H. Kuhn, Chem. Phys. Letters, 1974, 28, 15. lo( G. A. Reynolds and K. H. Drexhage, Optics Comm., 1975, 13, 222. lo' I. B. C. Matheson, G. J. Faini, and J. Lee,Photochem. and Photobiol., 1975, 21, 135. lo* F. M. D. Shetlar, Mol. Photochem., 1974,6, 143, 167, 191. lo8

Photochemistry

68

As the single-photon counting technique becomes more sophisticated and the convolution programmes more refined, it is expected that such phenomena as transient effects in fluorescence quenching may be determined with some accuracy. Furthermore, the information obtained has significance for other diffusioncontrolled processes. Ware and co-workers have continued their activities in this area with an analysis of the quenching of 1 ,Zbenzanthracene and naphthalene fluorescence by CBr,. It was possible to observe non-exponential decay which follows the decay law exp(at - 2bV-3, as predicted by the continuum model. Reasonable values for the encounter radii and pair diffusion coefficients were obtained from the decay curves. Ground-state complexing may also be taken into account with the analysis used.loB A cylindrical diffusion model has been applied to fluorescence quenching,l1° the effect of both electronic energy transfer and reabsorption on lifetime measurements has been examined,lll and a general analysis of effects produced by excitation transfer between luminescent molecules in solution previously put forward has been extended.l12 Determination of the absolute fluorescence quantum yields for solids is usually much more difficult than for solution systems. A method based on energy transfer has been employed to determine the absolute Of of thiocyanine dye molecules in monomolecular 1 a ~ e r s . l ~ ~ Bromocyclopropane has been used as a heavy-atom quencher of singlet states. The advantage of bromocyclopropane is that the C-Br cleavage reaction, which leads to alkyl radical and bromine atom formation and results in difficulties in the quantitative interpretation of the heavy-atom quenching experiment, is inefficient because cyclopropyl radicals are formed only with difficulty. This technique has been used to show that 1,8-divinyInaphthalene (8) undergoes intramolecular photocycloaddition to give (9) and (10) via the triplet sfate.ll*

(9)

The relative rate constants for the fluorescence quenching of benzene and a series of its simple derivatives by some chloro- and fluoro-methanes and CDCI, are found to follow qualitatively but not quantitatively the hypothesis that the rate-determining step in the quenching process is formation of a donor-acceptor exciplex. The study examined the kinetics following excitation to Szand S3as well as S1.115The lack of quantitative correlation with the theoretical model used may be due to a deficiency in the model for excited-state quenching or due to the lo9 110

111 lla 113

114

116

T. L. Nemzek and W. R. Ware, J. Chem. Phys., 1975, 62, 477. C. S. Owen, J. Chem. Phys., 1975, 62, 3204. J. C. Andre and M. Bouchy, J. Chim. phys., 1974,71, 1541. A. Jablonshu, Acta Phys. Chem., 1975, 20, 223. D. Mobius and G. Debuch, Chem. Phys. Letters, 1974, 28, 17. R. H. Fleming, F. H. Quina, and G. S. Hammond, J. Amer. Chem. SOC.,1974, 96, 7738. D. Saperstein and E. Levin, J. Chem. Phys., 1975, 62, 3560.

69

Photophysical Processes in Condensed Phases

presence of ground-state complexes, as previously described for anthracene quenching by CClP.ll6 The ‘critical radius’ 117 of the resonant energy transfer from the triplet state of benzophenone to the singlet state of perylene at 77 K in a mixture of chloroform and ether has been determined to be 68 .$,a value similar to those obtained for related pairs of molecules.118 A laser two-photon absorption method has been used to determine the efficiency of self-quenching of the Slstate of trans-stilbene in chloroform.11s The quenching of naphthalene fluorescence by p-ethylstyrene apparently leads to naphthalene triplets and ground-state molecules and p-ethylstyrene groundstate molecules [reaction (9) in Scheme 21. It is assumed that process (9) involves formation and decay of a singlet exciplex; although why the exciplex partitions in such a way as to exclude triplet p-ethylstyrene formation when naphthalene and /I-ethylstyrene triplets are nearly isoenergetic remains a mystery.120 The 1,4-concerted addition of Me,SnH to singlet excited penta-1,3-dienes yields cis and trans adducts having stereochemistry incompatible with an allylmethylene configuration. However, the addition products can be accounted for by addition to a doubly twisted species which can be seen as an intermediate state in the formation of bicyclobutanes.121 N lN lN

lN

+ trans-E

-

hv

1N N

(6)

+ hvl

3N

dN

(7)

(8)

+ (1 - ol)N + trans-E

(9)

Scheme 2

The production of S1(lA) and T1(3A)acetone by the decomposition of tetramethyl-1,2-dioxetan has been employed to probe the modes of energy transfer in a polystyrene matrix. The most important conclusions reached were as follows: (i) diphenylanthracene quenches l A by a long-range through-space mechanism ; (ii) the major mechanism for energy transfer to dibromoanthracene T ca. lo9 1 mol s-1.122 is the spin-forbidden triplet-singlet process ~ E = The efficiency of fluorescence quenching by oxygen has been extensively studied for a number of aromatic hydrocarbons adsorbed on Vycor glass plates immersed in liquid oxygen at 77 K.123 From a study of fluorescence and triplet quenching of a series of aromatic hydrocarbons by tetramethylpiperidine nitroxide (TEMPO) in methylcyclohexane it has been concluded that both quenching processes (10) and (1 1) are the result of ll8

11’ 118 B l

120 lz1 122 123

W. R. Ware and C. Lewis, J. Chem. Phys., 1972,57, 3546. N. Mataga, Chem. Phys. Letters, 1973, 20, 376. J. L. Laporte, Y. Rousset, P. Peretti, and P. Ranson, Chem. Phys. Letters, 1974, 29, 444. E. Heumann, W. Triebel, and B. Wilhelmi, Chem. Phys. Letters, 1975, 32, 589. A. Gupta and G. S. Hammond, J. Amer. Chem. SOC.,1975, 97, 254. M. Bigwood and S. Boue, J.C.S. Chem. Comm., 1974, 529. N. J. Turro and H.-C. Steinmetzer, J. Amer. Chem. SOC.,1974, 96, 4677, 4679. H. Ishida and H. Tsubomura, J . Photochem., 1974, 285.

70

+ TEMPO 3Ar1 + TEMPO

lArl

-

Photochemistry

+ TEMPO lAr0 + TEMPO 3Arl

(10)

(1 1)

induced intersystem c r 0 ~ s i n g . lThe ~ ~ large rate constants for singlet-state quenching may be rationalized in terms of the much smaller energy gap (lArl - 3Ar,)as compared with triplet quenching (3Arl - lAr0). The same general trend in triplet quenching is observed in the cases of quenching by NO and di-t-butyl nitroxide (Figure 5).124

-,

9.5

9.0-

8.5 -

=; . s!

-

01

0.0 -

7.5-

6.5:

1

1.5

' 1 I 2.5 3.0 TRIPLET ENERGY /eV

2.0

Figure 5 Dependence of the logarithm of the rate constant kqT on the energy of the triplet being quenched. A Tetramethylpiperidine nitroxide in methylcyclohexane; NO in n-hexane; 0 di-t-butyl nitroxide in n-hexane (Reproduced by permission from Chem. Phys. Letters, 1974, 29, 526)

Anilines having low ionization potentials quench both the excited singlet and triplet states of fluorenone, and N-alkylanilines show similar behaviour although, unlike secondary aliphatic amines, no reduction results.126 Studies of pentan-2one singlet quenching by aliphatic amines,12'jfluorescence quenching in carbazole amine energy transfer between like molecules (rhodamine By9-methylanthracene, and 5-rnethyl-2-phenylind0le),~~* and intramolecular energy transfer 12' 126

126

12' 128

A. R. Watkins, Chem. Phys. Letters, 1974, 29, 526. G. H. Parsons, L. T. Mendelson, and S. G. Cohen, J. Amer. Chem. SOC.,1974, 96, 6643. M. V. Encina, H. Sato, and E. A. Lissi, J . Photochem., 1975, 3, 467. H. Masuhara, T. Honie, and N. Mataga, Chem. Letters, 1975, 59. A. Kawaski and J. Maninski, Z . Naturforsch., 1975, 3Oa, IS.

Photophysical Processes in Condensed Phases

71

in 4R-1,2,4-triazoline-3,5-diones 120 have been reported. Transient and energytransfer studies in the photochromic bianthrone mechanisms of quenching by acids in poly(N-vinyl~arbazole),~~~ and energy transfer in dioxan scintillation solutions containing primary and secondary scintillators 132 have been studied, as have interactions between fluorescent dyes and surfactants in aqueous A number of energy-transfer studies involving dyes in rather unusual environments have been reported. Thus a pH-sensitive coumarin dye embedded in an electrically charged solid/electrolyte interface has served as an energy donor for a cyanine dye in an ordered dye-lipid-electrolyte system which is sensitive to U.V. light, acids and bases, electrical charges, and the The resonance energy transfer of rhodamine G and a coumarin dye in a range of aqueous micellar media has been demonstrated and the location of the dye molecules in the micelle deduced from the fluorescence lifetime. Energy transfer from dyes to specific singlet- or triplet-energy acceptors in monolayer assemblies has been dem~nstrafed.~~~ If a large concentration of the Tl state of a molecule is prepared using intense laser excitation and this is followed by a weaker second pulse preparing the S1 fluorescent state, the process depicted in equation (14) might well occur, and could be detected by fluorescence quenching on excitation with the second weak p ~ 1 s e . l ~Evidence ~ for the presence of such a radiationless intermolecular singlet-triplet energy transfer in chlorophyll a has been obtained. Energy transfer between densely packed photosynthetic units is suggested as the cause of non-exponential decay in the reduction of 2,6-dichlorophenolindophenolin chloroplasts.

so Sl Ti

+ S1 Sl

hv

(12)

81

TI

(13)

+ So + hv' So

T 2

(14) (15)

Energy transfer in fluorescent derivatives of uracil and thyamine13*and the quenching of fluorescence and phosphorescence in wool by the disulphide linkage have been exarnined.l3O Heauy-atom Quenching. From a study of the quenching effect on the fluorescence of 20 polynuclear hydrocarbons and heterocycles by 14odopropane in benzene solutions, it has been shown that the rate constants for fluorescence quenching decrease exponentially with AE, the energy difference between the fluorescing A. V. Pocuis, J. Chem. Phys., 1974, 61, 2779. H. H.Richtol, R. L. Strong, and L. J. Dombrowski, Israel J . Chem., 1974, 12, 791. 131 D.J. Williams, J. Phys. Chem., 1974, 78, 2009. 132 M. Bordeaux-Pontier, F. ROUX, and C. Briand, J . Chim.phys., 1974, 71, 1455. 133 I. Honura, Nippon Kuguku Kuishi, 1974, 10, 1832. 13* P. Fomherz, Chem. Phys. Letters, 1974, 26, 221. 0. hacker and H. Kuhn, Chem. Phys. Letters, 1974, 27, 317. uRE. R. Menzel, Chem. Phys. Letters, 1974, 26, 45. 13' S. Mulliken, Biophys. Chem., 1974, 2, 327. las J. G. Bur, W. A. Summers, and Y. J. Lee, J. Amer. Chem. Soc., 1975, 97, 245. K. P. Ghiggino, C. H. Nicholls, and M. T. Pailthorpe, J. Photochem., 1975, 4, 155. 12* 130

72

Photochemistry

state and the nearest lower triplet Perylene fluorescence is quenched by bromonaphthalene but not by bromobenzene. This is explained by the assumption of an intermolecular S1+ T energy transfer. Thus the T1state of bromobenzene is higher in energy than the S1state of ~ e r y 1 e n e . l ~ ~ The apparent bimolecular rate parameters k m , k m characteristic of the external heavy-atom quenching of the molecular singlet and triplet states of anthracene (A) (solvent = cyclohexane, quenchers = bromobenzene and ethyl iodide) and 9,lO-dibromoanthracene (DBA) (solvent = ethanol, quencher = KI) have been determined and used to describe the sensitivity of the external heavyatom effect acting on the non-radiative S1 + Tl and T + So processes.141uThe interesting observation that ethyl iodide and benzene increase the fluorescence efficiency from excited dibromoanthracene has been explained in terms of the formation of 'photoassociation product E' (exciplex This species then undergoes its own characteristic photophysics. The dominant processes for the ethyl iodide case are:

'DBA

+

fluorescence

(16)

3 E * 3 'MQ

(17)

Q -+ E *

Rate data have been obtained from a detailed analysis of the previously reported 142u maximum and fall off in the photodimerization of acenaphthylene with increasing concentrations of dissolved ethyl iodide.142b The heavy-atom solvent dibromomethane facilitates the cross cycloaddition of acenaphthylene to trans- and cis-penta-l,3-diene by inducing intersystem crossing to the triplet state of the aromatic hydrocarbon. The intermediacy of a biradical is proposed and the stereospecificity can be understood in terms of the maintenance of the stereochemical integrity of the allylic radical The fluorescence quenchings of anthracene by dimethyl- and diphenyl-mercury are of similar efficiency and are seen as being due to induced intersystem c~0ssing.l~~ Fluorescence Quenching by Inorganic Species. Acting on indications that neither the electron-transfer mechanism nor the heavy-atom is sufficient to explain the fluorescence-quenchingproperties of inorganic anions, Watkins has carried out kinetic studies and an investigation of short-lived intermediates in aromatic hydrocarbon-inorganic anion systems. Calculations of the free-energy change for electron transfer and the expected trend in heavy-atom perturbation efficiency by a series of hydrocarbons and ions indicate that neither of these mechanisms Furthermore, flash photolysis showed that can account for the 130a

140 141

14?

143 144

145

H. Dreeskamp, E. Koch, and M. Zander, Ber. Bunsengesellschaftphys. Chem., 1974,78,1328. M.Zander, 2. Naturforsch., 1974, 29a, 1518. (a) R.P.DeToma and D . 0. Cowan, J. Amer. Chem. Sac., 1975,97,3283; (b) R. P. De Toma and D. 0. Cowan, ibid., p. 3291. ( a ) D. 0. Cowan and J. C. Koziar, J. Amer. Chern. SOC.,1974, 96, 1229; (6) D. 0. Cowan and J. C. Koziar, ibid., 1975, 97, 249. W.I. Ferree, B. F. Plummer, and W. W. Schloman, J. Amer. Chem. SOC.,1974, 96, 7741. E. Vander Donckt, M. Lootens, and D. Swinnen, Bull. SOC.chim. belges., 1975, 84, 77. (a) A. R. Watkins, J. Phys. Chem., 1974, 78, 2555; (b) A. R. Watkins, ibid., p. 1885.

Photophysical Processes in Condensed Phases

73

the hydrocarbon radical-anions were not formed.145bIt is proposed that the interactions present in the collision complex between hydrocarbon and anion induce intersystem crossing. The triplet state of the initially excited molecule is formed, in almost every case, with almost unit efficiency. Some evidence for the mechanism of triplet-state quenching is also presented. Fluorescence quenching of styrylpyridines and their pyridinium cations by anions correlates well with the redox potentials of the anions, and since it seems that the charge-transfer complex decays through the styrylpyridines, it is possible that these results can be fitted to Watkins' mechanism. The suggestion made by these workers of 'Some sort of CT complex formation and heavy-atom enhanced intersystem crossing' may amount to the same thing.148 Heavy-atom perturbation has been invoked to account for the fluorescence quenching of aromatic hydrocarbons by CsC1,14' and an electron-transfer mechanism suggested as the mode of fluorescence quenching of indole and some indole derivatives by lanthanide ions.148 The singlet quenching of 1O-methylacridinium chloride by chromium(lr1) complexes is probably an energy-transfer process,14Qand a linear free-energy relationship between U-values and the rate constants for fluorescence quenching of substituted anthracenes by triphenylphosphine has been recognized.160 Excimer Formation and Decay. The time dependence of intramolecular excimer formation in 1,341 ,l'-dinaphthy1)propane has been examined using a singlephoton counting technique. Rate constants for association to the excimer and its dissociation were obtained and although the excimer may have a centrosymmetric geometry, the results indicate that emission may be induced by thermal excitation of torsional oscillations.161 Excimer emissions from pyrene have received considerable a t t e n t i ~ n . ~ Solvent ~ ~ - ~ ~ effects ~ have been used to determine the excimer dipole moment (2.46D),152and the absorptions of the pyrene excimer in different solvents have been obtained using a modulation An examination of the time dependence of excimer fluorescence for pyrene in poly(methylmethacry1ate) (PMM) has revealed that fluorescence does not arise from microcrystallites, as previously suggested. It is now proposed that ground-state interactions (van der Waals-London forces) cause a pairing of molecules in geometries close to the excimer geornetry.l5* A series of papers from Cohen and co-workers166 has appeared in which absorption and emission from crystalline pyrene are reported. It is argued that excitation is localized at sites containing pairs of close-spaced molecules (Frenkel excitons). By taking into account anharmonicity (vibron-vibron interactions), it is possible to explain why, in ground-state-to-excimer absorption in pyrene, IQ6 IQ7 148

14n

150

151 155

lS3 154 155

Is6

P. Bontulus, G. Bartocci, and U. Mazzucato, J. Phys. Chem., 1975, 79,21.

L. K. Patterson and S. J. Rzad, Chem. Phys. Letters, 1975, 31, 254.

R. W. Ricci, J. Phys. Chem., 1974, 78, 1953. K. K. Chattersjee and S. Chattersjee, 2. phys. Chem., 1975, 94, 107. M. E. R. Marcandes, Tetrahedron Lerters, 1974, 4053. P. Avouris, J. Kordas, and M. A. El-Bayoumi, Chem. Phys. Letters, 1974, 26, 373. A. S. Ghosh, J. Photochem., 1974, 3, 247. M. A. Slifkin and A. 0. Al-Chalabi, Chem. Phys. Letters, 1975, 31, 198. P. Aris and G. Porter, J.C.S. Faraday 11, 1974, 70, 1057. ( a ) M. D. Cohen, E. Klein, Z . Ludmer, and V. Yakhot, Chem. Physics, 1974,5, 15; (b) M. D. Cohen and V. Yakhot, ibid., p. 27; (c) M. D. Cohen and V. Yakhot, ibid., p. 478. W. Arden, L. M. Peter, and G. Vaubel, J . Luminescence, 1974, 9,257.

74

Photochemistry

the non-phonon peak can be resolved whereas the other peaks are overlapped. Finally, a model based on vibrational relaxation to a bath can be used to explain a previously estimated relaxation time of 10-13 s. This relaxation time, known radiative lifetimes, and a reasonable value for relaxation times of the isolated molecule are then used to formulate a model for excimer absorption and emission. Excimer interactions, from randomly orientated aromatic molecules formed in films by evaporation onto cooled surfaces, are found to be a common feature for planar molecules.16s The modulation technique mentioned above has been used to identify triplet excimers in 1,Zbenzanthracene and 1,2:3,4-dibenzanthracene at high solute concentrations 16’ and the differences between luminescence from naphthalene in fluid solution in the temperature range 353-173 K and naphthalene in a rigid solution at 77 K have been ascribed to phosphorescence from a triplet excimer.lS8 Excimer formation in solid poly-(2-vinylnaphthalene) and polystyrene is found to be dependent on the temperature at which the film is cast, and a statistical model based on the rotational isomeric state approximation has been used to formulate an expression for the fraction of excimer sites in the solid ~ y ~ t e m s Kinetic . ~ ~ * equations for dimer formation and decay, based on the statistical mechanics of ideal gases, have been obtained. These equations, derived from the N-atom von Neumann equation, take into account both bimolecular and termolecular equations.lBo The emission properties of some carbazole ‘double’ molecules [l ,n-bis(Ncarbazoyl)alkanes] have been examined and one compound in particular, 1,3-bis(N-carbazoy1)propane (1,3-BCP), was found to be a useful model for poly(N-vinylcarbazole). Measurements of the temperature dependence of monomer and excimer decay constants have provided useful kinetic and thermodynamic information on this system. The binding energy for the intramolecular excimer of 1,3-BCP was shown to be 2.76 kcal mol-l, a rather low value. Measurements on other carbazole ‘double’ molecules showed that Hirayama’s n = 3 rule is obeyed and that the preferred geometry of the intramolecular excimer is sandwich3ike.le1 The quenching of the photodimerization of coumarin by tetramethylethylene may be the result of quenching the excimer (precurser to cycloaddition).le2

(11)

11 =

2, 3, 5, or 9

Non-linear Stern-Volmer plots in the quenching of 7,7’-polymethylenecoumarins (11) may also be the result of excimer quenching. If a non-linear plot is taken as indicative of the quenching of two different excited states, one could be the M. A. Slifkin and A. 0. Al-Chalabi, Chem. Phys. Letters, 1974, 29, 110. T. Takemura, Chem. Letters, 1974, 1091. 16@ C. W. Frank and L. A. Harrah, J. Chem. Phys., 1974,61, 1526. le0 J. T . Lowry, J. Chem. Phys., 1974, 61, 2320. lel G. E. Johnson, J . Chem. Phys., 1974,61, 3002. le2 P. P. Wells and M. Morrison, J. Amer. Chem. SOC.,1975, 97, 152.

15’

168

Photophysical Processes in Condensed Phases

75

isolated coumarin while the other could be a short-lived singlet state (excimer) formed from ground-state molecules with favourable conformations for intramolecular c y c l o a d d i t i ~ n s .The ~ ~ ~association of some pyridyl radicals to radical pairs and the optical interconversion of these radical pairs have been examined.ls4 Exciplexes, Electron Donor-Acceptor Complexes, and Related Charge-transfer Phenomena.-A wide-ranging review of the role of exciplexes in photochemical reactions has appeared.la5 A theory of diffusion-limited recombination of donor-acceptor pairs, based on the probability of DA pair recombinations according to the relationship ooexp I - V / V B I, where oois constant, r is the separation between defects, and rB is the half Bohr radius of the more diffuse wavefunction,166has been developed. The viscosity dependence of emission from the charge-transfer complexes of tetracyanoethylene with benzene and a number of alkylbenzenes has been studied. At high viscosities the fluorescence spectra of alkylbenzenes have a double-band character and the two sub-bands change in different ways with changing viscosity. These observations and the dependence of the excitation spectrum on observation wavelength are discussed in terms of different orientational isomers of the groundstate charge-transfer complexes.1s7 The fluorescence from polycyclic aromatic hydrocarbons is quenched by fumaronitrile, and a new long-wavelength exciplex emission is observed in nonpolar or weakly polar solvents. The ionization potentials of the aromatic donors show a good correlation with the Amax of the exciplex emission. Furthermore, on direct irradiation into the charge-transfer absorption bands (high concentration), the same exciplex emission is observed.lS8 Fluorescence from exciplexes in the sym-tetracyanobenzene-p-xylenelsg and 9,lO-dicyanoanthracene and alkyl-substituted naphthalene systems 170 has been studied. Photoconductivity measurements on benzoquinone and tetramethylenephenylenediamine 171 have been carried out, and triplet-triplet absorption, phosphorescence, and e.s.r. spectra obtained for some sym-tricyanobenzenealkylbenzene systems.172 NN-Diethylamine-anthracene1730 and the model system NN-dimethyl-4[3-(9-anthryl)propyl]aniline 173b have been used in an investigation of the dynamics of inter- and intra-molecular charge-transfer interactions on the picosecond timescale. In hexane solutions, it has been determined that electron transfer occurs very rapidly (10 ps) when the free anthracene (A) and dimethylaniline (DMA) are separated by 8 A or less. In the model compound, with the A and DMA separated by only ca. 4 A, it takes 900 ps to form the charge-transfer ’

F. C. De Schryver, J. Put, L. Leenders, and H. Loos, J. Amer. Chem. SOC.,1974, 96, 6994. Y. Ikegami and S. Seto, J. Amer. Chem. SOC.,1974, 96, 78 11. R. S. Davidson, in ‘Molecular Association’, vol. 1, ed. R. Foster, Academic Press, London. lBQI. Fabrihant and E. Kotomin, J . Luminescence, 1975, 9, 502. le7 J. Prochorow, J . Luminescence, 1975, 9, 131. le8 Y. Shirota, I. Tsushi, and H. Mikaw, Bull. Chem. Soc. Japan, 1974, 47, 991. loo E. Gaweda and J. Prochorow, Chem. Phys. Letters, 1975,30, 155. 1 7 0 (a) M. Itoh, J. Amer. Chem. SOC., 1974,96,7390; (6)M. Itoh, Chem.Phys. Letters, 1974,26,505. J. Nakata, T. Imura, and K. Kawabe, Bull. Chem. SOC.Japan, 1975, 48, 701. 17* S. Matsumoto, S. Nagakura, and Y. Shimozato, Bull. Chem. SOC. Japan, 1974, 47, 604. ln (a)T. J. Chuang and K. B. Eisenthal, J. Chem. Phys., 1975, 62, 2213; (6)T. J. Chuang, R. J. Cox, and K. B. Eisenthal, J. Amer. Chem. SOC.,1974, 96, 6828. lU3

lU4

le6

76

Photochemistry

- :-I

state. It is concluded that this effect is the result of internal orientational motion to the conformation necessary for electron transfer. Scheme 3 accounts for the lAl

+ lD,

l(A-D+)

+D 7 l(A-D+D) 3A

To

lA Scheme 3

+

+D

1-

To1

temperature dependence of intersystem crossing and fluorescence yields, as well as for the lifetime of the exciplex for the anthracene-diethylamine in non-polar solvents. The exciplex l(A-D+) reacts with a second donor molecule to yield the triple complex l(A- D+D), which fluoresces around 16 000 cm-l. It is suggested that triple complex formation may be a general feature of systems of this type, although the precise nature of the complex is not known.174 A flash photolysis study of the photoreduction of naphthalene by triethylamine has been ~ep0rted.l~~ The observation of exciplex emission from mixtures of aromatic hydrocarbons and furans, thiophens, pyrroles, and indoles may have a profound effect on the mechanistic interpretation of the photochemical reactions in these systems (Table 6).176 Fluorescence quenching of fluorene, dibenzofuran, and dibenzothiophens by aromatic nitriles and aliphatic amines is the result of electron transfer with exciplex formation,177 and ion-pair formation in pyromellitic dianhydrideethylbenzene is followed by dissociation into separated ion pairs in their highly excited Photochemical iodination of aromatic hydrocarbons may proceed by way of an electronically excited 1,-aromatic charge-transfer complex.170Modulation excitation spectrophotometry has been used to analyse the nature of some complexes between polycyclic aromatic hydrocarbons and chloranil.lS0 The formation of a luminescent exciplex between fumarate and phenanthrene, recently questioned, has been confirmed.lal Quenching of the exciplex emission by electron donors without quenching of the phenanthrene monomer fluorescence and a parallel quenching of cycloadduct formation confirm the role of the exciplex in product formation. The products formed in the photolysis of the ether-0, charge-transfer complex can be understood in terms of the primary electron-transfer process (18).lS2 Et-0-Et

......0 2

hv

+.

Et-0-Et

+

02-

(18)

Triplet nitrogen (N,) reacts with non-phosphorescent aromatic and heterocyclic compounds and induces p h o ~ p h o r e ~ c e n c e . ~ ~ ~ K. H. Grellman and U. Suckow, Chem. Phys. Letters, 1975, 32, 250. H. D. Burrows, Photochem. and Photobioi., 1974, 19, 241. 176 R. S. Davidson, A. Lewis, and T. D. Whelan, J.C.S. Chem. Comm., 1975,203. 177 G. G. Aloisi, F. Masetti, and U. Mazzucato, Chem. Phys. Letters, 1974, 29, 502. M. hie, S. Irie, Y . Yamamoto, and K. Hayashi, J . Phys. Chem., 1975, 79, 699. 17@ R. F. Cozzens, J. Phys. Chem., 1975, 79, 20. I 8 O M. A. Slifkin and A. 0. Al-Chalabi, Chem. Phys. Letters, 1975, 30, 227. 181 D. Creed and R. A. Caldwell, J. Amer. Chem. SOC., 1974, 96, 7369. lS2 C. von Sonntag, K. Neuwald, H.-P. Schuchmann, F. Weeke, and E. Janssen, J.C.S. Perkin 11,

174

17&

1975, 171.

183

R. Demary and 0. Dessaux, J. Chim. phys., 1974,71, 555.

P

c

C

Thiophen 452 nm 9 x 1096 520 nm 455 nm

c

1-Cyanonaphthalene 4 x 107d 1 x 1098 414 nm 432 nm

500 nm

8 x

c

c c

c

Anthracene

spectroscopy.

437 nm

3 x 10Qd 5 x 1096 1 x 107d 1 x 1078 2 x 1OQd 6.5 x loge

Ionization poten-

515 nm 455 nm

452 nm

C

c

c

c

U.V.

(I

9-Cyanophenanthrene

k 0.5 for fluorescence quenching

9-Cyanoanthracene 1 x 107d 1 x 1076

s-l;

In none of the systems investigated could association between the hydrocarbon and heterocycle be detected by tials. a Exciplex emission not observed in these systems. Cyclohexane solvent. Acetonitrile solvent.

1,2,5-Trimethylpyrrole 1-Methylindole

430 nm

C

2-Methylfuran (8.39 eV) 2,5-Dimethylfuran (8.01 eV)

1-Methylpyrrole (8.2 eV)

C

Naphthalene

Wavelengthlnm of exciplex emission in benzene solution or rate constant11 mo1-l

Furan (8.89 eV)

Table 6

2:

8

3

3 2 b

g

3

2

2

x

"a

.c

2.

L" 2

G

2

78

Photochemistry

3 Triplet-state Processes Radiative and Non-radiative Processes.-The variation of the ratio of phosphorescence to fluorescence for C6H5, C6D6, C6H&H3, and o-C6H4(CH3),in methylcyclohexane at 77 K can be accounted for by an increase in the importance of triplet-triplet annihilation at high solute concentration. The detection of delayed fluorescence in these systems supports the triplet-triplet annihilation mechanism.ls4 This conclusion is different from that reached in earlier reports,la6 when it was suggested that an increase in concentration of the aromatic affected the efficiency of intersystem crossing (S,-+ Tl). An analysis of the triplet-triplet absorption spectra of m- andp-dicyanobenzenes and 1,3,5tricyanobenzene indicates that the T-T bands correspond to transitions from the locally (benzene ring) excited state to the intramolecular chargetransfer stafe.lB6T-T absorption spectra for some substituted naphthalenes have also been studied.la7 An attempt to provide evidence for the formation of triplet benzyne has failed.lsaa In order to settle a controversy over the effects of deuteriation on the radiative lifetimes of aromatic hydrocarbons, some systems have been examined, using two independent techniques. Table 7 shows the 7, values obtained from phosphorescence lifetimes and quantum yields. Evidence for the intramolecular nature of the deuterium isotope effect on T~ comes from the lack of sensitivity to solvent. Although no definitive evidence as to the origin of the isotope effect is put forward, it is suggested that there may be two important contributing mechanisms to the T, -+ So radiational process, an isotope-independent and an isotopesensitive one. The isotope-insensitive mechanism is almost certainly first-order spin-orbit coupling. It therefore remains to determine the nature of the other process, which will only be important when spin-orbit coupling is inefficient.lash Studies of the triplet state of biphenyl in a carbazole host crystal and of the triplet-state processes of anthracene in different environments 100-103 have been reported, and triplet diffusivity in crystalline pyrene lo4 and the multiplet structure of spectra in the S1t-) So,TI -+ So,and S2 t-) Sotransitions in 1,12-benzperylene (matrices at 4.2 K) lo5examined. Early discrepancies between the lifetime of the triplet state of trans-stilbene (“) obtained from pulse radiolysis and azulene quenching studies have been reconciled by a recognition that azulene quenches the twisted triplet (”) with R. B. Cundall and L. C. Pereira, Chem. Phys. Letters, 1974, 29, 71, 561.

lS4

(a) F. Hirayama, J. Chem. Phys., 1965, 42, 3726; (b) M. D. Lumb and L. C. Pereira, in ‘Organic Scintillators and Liquid Scintillation Counting’, ed. D. L. Horrocks and C. I. Peng, Academic Press, New York, 1971. la6 H. Morita, S. Matsumoto, and S. Nagakura, Bull. Chem. SOC. Japan, 1975, 48, 420. lS7 T. Takemura, K. Hara, and H. Baba, Bull. Chem. SOC. Japan, 1971,44, 977. la8 (a) R. T. Luibrand and R. W. Hoffmann, J. Org. Chem., 1974, 39, 3887; (b) N. Kanamaru, H. R. Bhattacharjee, and E. C. Lim, Chem. Phys. Letters, 1974, 26, 174. lR9 T. N.Misra and K. Mandal, J. Chem. Phys., 1974, 61, 292. lgO J. Ferguson and A. W.-H. Mau, Mol. Phys., 1974, 28, 469. lS S.1 Arnold, W.B. Whitten, and A. C. Damask, J. Phys. Chem., 1974, 61, 5162. lg2 M. M. Fisher, B. Veyret, and K. Weiss, Chem. Phys. Letters, 1974, 28, 60. l g 3 A. Brillante, D. P. Craig, A. W.-H. Mau, and J. Rajikan, Chem. Phys. Lefters, 1975, 30, 5. lg4 S. Arnold, J. L. Fave, and M. Scott, Chem. Phys. Letters, 1974, 28, 412. lg6 T.B. Tamm and P. M. Saari, Chem. Phys. Letters, 1975, 30, 219. lS6

(I

0.24 f 0.01 0.47 f 0.02 0.10 f 0.01 0.32 zk 0.02 0.050 f 0.005 0.20 f 0.01 0.022 f 0.002 0.088 f 0.004 0.025 +_ 0.002 0.13 & 0.01 0.021 f 0.002 0.11 f 0.01 (2.15 f 0.1) x (9.0 f 0.5) x 0.43 f 0.02 0.40 f 0.02 0.66 f 0.04 0.94 2 0.05

@pP

7pIS

3.7 f 0.2 8.9 f 0.1 63 f 4 3.6 f 0.1 65 f 4 14.7 f 0.2 55 f 1 2-35 f 0.1 56 f 1 13.4 f 0.2 2.6 f 0.1 17.0 f 0.5 2.30 i- 0.05 18.5 & 0.2 45.5 f 0.5 1.43 fr 0.05 38.5 f 0.5 8.6 f 0.2 450 f 5 0.58 4 0.02 460 f 5 3.50 +, 0.05 3-16 f 0.1 3.5 f 0.1 0.89 f 0.03 1.26 4 0.04

7flS

13 f 1 16 f 1 31 k 3 40 f 3 36 f 4 52 f 4 53 f 5 73 f 4 56 f 5 81 f 6 55 f 5 66 f 6 22 f 8 51 f 13 5.15 & 0.3 5.5 3. 0.3 1.35 f 0.07 1.40 f 0.08

rrls 7mIS

5.2 f 0.3 20 f 1 4.1 f 0.4 21.2 f 0.3 2.5 f 0.3 18 k 1 2.7 f 0.1 22 f 1 2.40 f 0.05 23.8 +_ 0.2 1.47 f 0.05 9.9 f 0.2 0.60 f 0.02 3.77 +_ 0.05 8.1 f 0.5 9.6 f 0.5 2.63 f 0.3 1.2, k 3.0

1,2,5,6-Dibenzanthracene. a Dibenzo[f,h]quinoxaline. T h e two protiums in [BHs]DBQare attached to C-7and C-10.

Compound @f Biphenyl 0.14 f 0.01 [2Hlo]Biphenyl 0.15 f 0.01 Phenanthrene 0.13 f 0.01 [2Hlo]Phenanthrene 0.12 2 0.01 Chrysene 0.23 f 0.01 [2H12]Chrysene 0.23 f 0.01 Acenaphthene 0.55 f 0.03 [eHlo]Acenaphthene 0.62 f 0.03 Naphthalene 0.39 +_ 0.02 [2H8]Naphthalene 0.43 f 0.02 DBA 0.185 f 0.01 [2H1,]DBA * 0.155 f 0.01 Pyrene 0.92 f 0.03 [2H,]Pyrene 0.87 f 0.03 Benzonitrile 0.30 f 0.02 [2H,]Benzonitrile 0.38 f 0.02 DBQ (1.47 f 0.08) x ['HHBIDBQ (1.47 f 0.09) x

Table 7 Deuterium isotope efect on triplet-state radiative lifetimes ( 7 ~ ) .All data in EPA glass at 77 K

1.04 zk 0.06

1.06 f 0.07

2.3 f 0.9

1.38 f 0.15

1-46 f 0.15

1.3 k 0.15

rrD/rrH 1.2 f 0.1

$q

f&

3

3'

?i

2

P

80

Photochemistry

formation of the trans-stilbene isomer (Scheme 4). By carrying out oxygenquenching experiments and assuming that k,, is the same as for nitrostilbene (7.0 x lo9 1 mol-1 s-l) the stilbene triplet lifetime (”) is determined to be 119 ns in air-saturated solution, in good agreement with the pulse radiolysis s t ~ d i e s . ~ ~ ~

Scheme 4

Azulene (and some other quenchers) quenches the twisted triplet state with formation of trans-stilbene whereas oxygen quenching results in the production of the cis- and trans-isomers; this suggests that, while energy transfer to 302, producing lAB oxygen (energy gap = 22 kcal mol-l), may be achieved by torsional motion from 3p to either ground-state isomer, the greater energy requirements for energy transfer to azulene can only be met by a torsional motion to the lower energy trans-stilbene. The absorption spectrum and emission spectrum from the lowest triplet state of hexachloroacetone have been examined lg7and the reactions of pentan-2-one triplets with CC14 reported.lQs The role of ground- and excited-state conformational equilibria in the photochemistry of ketones has come under scrutiny in the past few years. Evidence for the involvement of excited-state conformational equilibrium in the photochemical reactions of aryl cyclobutyl ketones (12) to give aryl bicyclo[l,l,l]pentanols has been obtained (Scheme 5).lg9 Since or-cleavage and y-hydrogen *3

Y

products

“A

0 ’ Ph

Scheme 5

abstraction in cyclohexyl phenyl ketones are more rapid than ring inversion, product compositions are controlled by ground-state conformational populations. In contrast, conformational changes in cyclopentyl phenyl ketones are more rapid than photochemical reactions.200 Measurements of Arrhenius activation lB6 Ie7

lea

lsg 2oo

J. Saltiel and B. Thomas, J. Amer. Chem. SOC.,1974, 96, 5660. M. Koyang and L. Goodman, Chem. Physics, 1974, 5, 107. E. A. Lissi, J. Photochem., 1974, 3, 237. E. C. Alexander and J. A. Uliana, J. Amer. Chem. SOC.,1974, 96, 5644. F. D. Lewis, R. W. Johnson, and D. E. Johnson, J. Amer. Chem. Soc., 1974, 96, 6090.

Photophysical Processes in Condensed Phases

81

parameters for a series of alkyl aryl ketones show that the rate enhancements in conformationally restricted molecules are entirely entropic in origin.201 The photochemistry of a variety of substituted acyclic 1,3-diene-p-quinone Diels-Alder adducts can be generally described as a @-hydrogenabstraction by the excited carbonyl oxygen followed by C-C bond formation.202Following the recent recognition of dual phosphorescence from certain alkyl aryl ketones, it has now been demonstrated that, in the case of indanone and six related ketones, the two components of the dual phosphorescence possess different excitation spectra. From an examination of these spectra it has been concluded that the most favourable intersystem crossing routes are Sl(n7r*) -+T(nr*) and S ~ , ~ ( T I T--f* ) T(TT*).~O~ Tanimoto and Nagakura have analysed the dual phosphorescence from acetophenone in non-polar solvents in terms of monomer and dimer 3rr* states. This explanation, which conflicts with earlier ones, seems to be worthy of further investigat Figure 6 summarizes the analysis of Lim and co-workers carried out on propiophenones (PM is isopentane and methylcyclohexane 1 : 1 by volume, and Hp is n-heptane). They suggest that the prerequisites for the observation of dual emissions are the proximity of the lowest energy nr* and rr* states and high viscosity of the glassy Nanosecond flash photolysis studies of the abstraction of hydrogen by benzophenone have confirmed that two successive processes are involved in photoreduction (Scheme 6). The activation parameters observed for triplet quenching of benzophenone in rigid media and the results obtained in this study indicate that

+ 3Ph,C0 Ph2kOH + RHO RH,

J

L

Ph,kOH

+ RHO

(19)

Y

Ph,CO

+ RH,

(20)

Ph,kOG+ RH*

+ Ph,CO RHO+ RH, RHO+ RH* Ph,kOH + Ph,kOH RH*

where L-v-J

indicates co-solvation

Scheme 6

transient hydrogen abstraction is an intermediate in the deactivation route, even in the absence of photoproducts. The quantum yield of photoproduct formation is dependent upon the efficiency of the above process and the efficiency of the aoa 203

206

F. D. Lewis, R. W. Johnson, and D. R. Kory, J. Amer. Chem. Soc., 1974, 96, 6100. J. R. Schepper, K. S. Bhandari, R. E. Gayler, and R. A. Wostradowski, J. Amer. Chem. SOC.,1975, 97, 2178. W. Amrein, I. M. Laarson, and K. Sheffner, Helv. Chim. Acra, 1974, 57, 2519. Y. Tanimoto, N . Hirota, and S. Nagakura, Bull. Chem. SOC.Japan, 1975, 48, 41. N. Kanamura, M. T. Long, and E. C. Lim, Chem. Phys. Letters, 1974,26, 1.

4

0

PP

€PA

< 30 m sec

-

HP

6.3 m sec

n + n*(+ n + a*)

N

-

n+ n+

PM

:75msec

-

pMPP

E PA

-

HP

76 rn sec

n + n*(+ n + n*)

n -+ n*)

< 90 m sec

II + n*(+

160 m sec 1 + n*(+ n + n*)

-

60 rn sec

I

n+ n*

~~

PM

E PA pMxPP

d

n + n*

HP

250 m sec

z

4

5

Figure 6 Correlation diagram, showing the emission characteristics of propiophenone and its derivatives. The assignments of the triplet states 2 are based on the lifetime and the polarization of phosphorescence. PP is propiophenone; pMPP is p-methylpropiophenone; pMxPP is p- 2 methoxypropiophenone 3 (Reproduced by permission from Chem. Phys. Letters, 1974, 26, 1)

PM

<10msec

/

0

-

130 m sec

-

n+ n*

n + n*(+ n + n*)

n + n*(+n+

/

25 000

5

a w

t!l

>

\

E

I

4

26 000

24 m sec

-

n+n*

Photophysical Processes in Condensed Phases

83

The pK (1.5 k 0.1) of benzophenone triplet separation of two caged in aqueous solution has been determined and is in good agreement with Forster cycle calculations based on recent revisions of the ground-state pK of benzop h e n ~ n e . ~In ~ ' a related study of the environmental effects on benzophenone phosphorescence it has been demonstrated that three species, one of which is a benzophenone-solvent complex, may give rise to phosphorescence, and the importance of each contribution depends on pH.208 The detection of diphenylhydroxymethyl radical by an e.s.r. study of irradiated concentrated solutions of benzophenone in benzene provides good evidence of hydrogen abstraction by 3Ph2C0 from the ground-state ketone. When irradiation was carried out in perdeuteriated benzene, the protonated and not the deuteriated radical was Another study of benzophenone photolysis provides supporting evidence for the abstraction of hydrogen by 3Ph2C0 from ground-state benzophenone.20sb Photoreduction of para-substituted [C02-, SO3-, and N(CH,),+] benzophenones in propan-2-01 over a wide pH range has been examined.21o Transient absorption spectra of benzophenone and several phenyl pyridyl ketones in perfluoromethylcyclohexane have been identified as being due to triplet states,211the anomalous formation of cyclopropanol on irradiation of 4-butyrylpyrimidine has been rationalized,212aand an examination of roomtemperature phosphorescence and a-cleavage of some deoxybenzoins has been carried out .212b 4-(1-Naphthylmethyl)benzophenone in benzene solution exhibits two transient absorptions. The initially populated species having a lifetime of 10 ps has been ascribed to an upper benzophenone-like triplet which decays to the lowest naphthalene-like lowest triplet Triplet quantum yields for all-trans- and 11-&retinal have been established. The fact that triplet-energy transfer to 11-cis-retinal leads to geometric isomerization with 15-1 7% efficiency, whereas triplet sensitization of the all-trans-isomer does not lead to isomerization, may be the result of an isomerization process which occurs only from vibrationally excited triplets; also, in the case of ll-cisisomer, relatively more energy is accumulated in the isomerization active torsional modes of the 11-12 bond.214 Related studies of the triplet states of retinals and their Schiff bases have been reported.21S The diverse emissive characteristics of the triplet states of amide-containing molecules (amides, ureas, oxamides, parabanic acids, acylureas etc.) have been ~ * in the lowest rationalized in terms of the amount of 3n7r and 3 ~ character 208 207 208

20*

210

211 212

213

214 215

M. R. Topp, Chem. Phys. Letters, 1975, 32, 144. D. M. Rayner and P. H. Wyatt, J.C.S. Faraday ZI, 1974, 70, 945. G. Favaro, Chem. Phys. Letters, 1975, 31, 87. (a) R. S . Davidson and R. Wilson, Mol. Photochem., 1974, 6, 231; (6) D. I. Schuster and T. M. Weil, ibid., p. 69. S. G. Cohen, G. C. Ramsay, N. M. Stein, and S. Y. Weinstein, J. Amer. Chem. SOC.,1974, 96, 5124. J.-P. Blanchi and A. R. Watkins, Mol. Photochem., 1974, 6, 133. (a) E. C . Alexander and R. J. Jackson, jun., J. Amer. Chem. SOC.,1974, 96, 5663; (b) F. D. Lewis and C. E. Hoyle, Mol. Photochem., 1974, 6, 235. R. W. Anderson, jun., R. M. Hochstrasser, H. Lutz, and G. W. Scott, Chem. Phys. Letters, 1975, 32, 204. T. Rosenfeld, A. Alchalel, and M. Ottolenghi, J . Phys. Chem., 1974, 78, 336. M. M. Fisher and K. Weiss, Photochem. and Photobiol., 1974, 20, 423.

84

Photochemistry

triplet state. A m r * triplet is non-emissive; a state of mixed nr* and nn* character is weakly or moderately emissive; an n7r* triplet is strongly emissive, with the phosphorescence spectra exhibiting a dominant C=O stretching mode. Table 8 summarizes the observations made. The consequences of the conclusions reached in this study for the Tl state of the peptide linkage are discussed.216 The effect of partial deuteriation on the phosphorescence lifetime of NNN’N‘tetramethyl-p-phenylenediamine,217 the ratio of phosphorescence to fluorescence produced by excitation of indole in glycol-water glasses using a variety of excitation sources,218biphotonic processes in some proteins,21sand the phosphorescence of pyrimidine derivatives in frozen aqueous solutions 220 have been examined. The only observable transient species in the laser flash photolysis of a-nitronaphthalene in solution at room temperature has been designated as the triplet state ( T ~ 30 ms). The change of dipole moment accompanying the transition Tl + T,,, as well as rate constants for electron and proton transfer involving the TI state, were determined, and the low reactivity of the Tl state in polar solvents was attributed to reduced n7r* and increased charge-transfer character of the triplet state.221Heavy-atom perturbation experiments have implicated the triplet state of the nitro-compound (13) in the photochemical formation of (14).222 N

Evidence has been obtained for the intermediacy of the triplet state in the direct photoisomerization of thioindigo a long-lived intermediate has been detected in the flash photolysis of 4-thiouridine in aqueous s01ution,~~~ and the pK values of the lumiflavin triplet state have been determined by flash photolysis.22s E.S.R. and Microwave Studies and Related Studies.-The recently demonstrated technique of triplet absorption detection of magnetic resonance (TADMR) has been used to determine intersystem crossing from individual spin levels of [lHlo]- and [2Hlo]-anthracene and 3,4-benzpyrene triplets.226 Optically detected magnetic resonance (ODMR) has been used to probe out-of-chain hopping of excitons in 216

D. B. Larson, J. F. Arnett, C. J. Seliskar, and S. P. McGlynn, J. Amer. Chem. Soc., 1974,

217

96, 3370. N. Yoshida and N. Ebara, Bull. Chem. Soc., Japan, 1975, 48, 709. H. B. Steen, J. Phys. Chem., 1975, 79, 426.

218 219 220

221

222

223 224 22b

2aa

M. Bazin, M. Aubailly, and R. Santus, Photochem. and Photobiol., 1974, 20, 37. J. J. Aaron, R. Fisher, and J. D. Winefordner, Talanta, 1974, 21, 1129. C. Capellos and G . Porter, J.C.S. Faraduy 11, 1974, 70, 1159. P. M. Crosby, K. Salisbury, and G . P. Wood, J.C.S. Chern. Cornrn., 1975, 312. A. D. Kirsch and G. M. Wyman, J. Phys. Chem., 1975, 79, 543. A. Favre, Photochem. and Photobiol., 1974, 19, 15. S. Schreiner, U. Steiner, and H. E. Kramer, Photochem. and Photobiol., 1975, 21, 81. R. H. Clarke and J. M. Hayes, Chem. Phys. Letters, 1974, 27, 556.

Multiply crystallized/water

Multiply vacuum distilled

Multiply recrystallized/water-NaOH

Biuret

Ethyl NN-dimethylglycinate

Lead glycinate

a

All of these emission studies refer to clear glassy solutions at 77 K.

Thiourea

Used as purchased Vacuum sublimed Used as purchased Multiply crystallized/methanol ; vacuum sublimed ; chromatographed on AI,O, column Multiply crystallized/water

Preparative methods Multiply vacuum distilled; multiply crystallized/water Multiply vacuum distilled ; gas chromatographed ; zone refined Multiply vacuum distilled Multiply crystallized/water Multiply crystallized/water

c-Caprolactam 2,5-Diketopiperazine Alanine anhydride Urea

NN-Dimethylacetamide 2-Chloroacetamide Thioacetamide

Molecule Acetamide N-Methylacetamide

Table 8 Phosphorescence of simple amides and related compounds a Emission characteristics No emission Very weak emission; very dependent on wavelength of excitation No emission No emission; dissociates in solution Freshly prepared solutions show no emission; decomposes in solid and in solution No emission No emission No emission Very weak emission ; very dependent on wavelength of excitation Very weak emission; very dependent on wavelength of excitation Very weak emission; very dependent on wavelength of excitation No emission; decomposition upon irradiation Very weak emission; very dependent on wavelength of excitation

8 2

2

g

9 3

3

2 2 2

Photochemistry

86

crystalline 1,4-dibrom0naphthalene,~~~~ and the spin-lattice relaxation of 1,4DBN has been examined by e.s.r. techniques.227bThe nature of triplet traps of indole in glassy solvents, single crystals, and Shpol'skii matrices has been probed.228 The new technique of polarized microwave spectroscopy (PMDR), applied to 1,3,5-trichlorobenzene and hexachlorobenzene molecules in a hexamethylbenzene host and as neat crystals, taken with other results, suggests that low-temperature triplet traps result from crystal-induced geometrical and orientational changes in the molecules at point defect^.^^^ Microwave-induced delayed fluorescence studies have provided information on the triplet states of toluene 230 and p - c h l o r ~ a n i l i n e . ~ Magnetic ~~ resonance saturated phosphorescence decay measurements on t y r o ~ i n e ,and ~ ~ ~CIDNP studies on but-2-enone and pentan-3-0ne,~~~ 1,4-benzoquinone in p r o p a n 0 1 , ~ ~ ~ 9-methyla~ridine,~~~ and the dye-sensitized photo-oxidation of phenols 236 have been reported. A technique for measuring triplet spin-lattice relaxation times in fluid solution, based on the observation of chemically induced electron spin polarization, in the presence of a triplet quencher, has been applied to duroquinone with triethylamine as the triplet q ~ e n c h e r . ~E.s.r. ~' studies of the triplet states of 9-aza-bicyclo[3,3,l]nonan-3-0ne-9-oxyl,~~~ oxazine, thiazine, and selenazine benzophenone and d i p h e n ~ l a r n i n eand , ~ ~ ~1,3-diaza-azulene241 have been carried out. Triplet Quenching and Triplet Energy Transfer.-A study of the diffusion of aromatic triplet states in solution by the irradiation of an array of illuminated strips and the monitoring of delayed fluorescence as a function of strip dimensions reveals that in the cases of anthracene and 9,lO-diphenylanthracene both material transfer and energy transfer contribute to the observed mobilities. Among the possible energy-transfer modes, triplet-triplet energy transfer by a mechanism approaching linear chain character or else radiative singlet transfer offer the best explanations for the A picosecond technique used to follow the build-up of the T-Tabsorption of acceptor molecules following S,excitation of donors has given direct information on triplet energy transfer. For example, the build-up (k) and decay (k,) rates

234

(a) R. Schmidberger and H. C. Wolf, Chem. Phys. Letters, 1975, 32, 21 ; (b) R. Schmidberger and H. C. Wolf, ibid., p. 18. J. Zuclich, J. U. von Schutz, and A. H. Maki, J. Amer. Chem. SOC.,1974, 96, 710. C. T. Lin and M. A. El-Sayed, Chem. Physics, 1974, 4, 161. P. J. Vergragt and J. H. Van der Waals, Chem. Phys. Letters, 1974, 26, 305. E. Kanezaki, N. Nishi, M. Kinoshita, and K. Niimori, Chem. Phys. Letters, 1974, 29, 529. T. Co, R. J. Hoover, and A. H. Maki, Chem. Phys. Letters, 1974, 27, 5 . S. P. Vaish, Canad. J. Chem., 1974, 52, 2978. H. M. Vyas, S. K. Wong, B. B. Adeleke, and J. K. S . Wan, J. Amer. Chem. SOC.,1975, 97,

236

G. Vermeersch, N. Febvay-Garat, S. Caplain, and A. Lablache-Combier, Tetrahedron, 1975,

227

228

248

231 232

233

1385.

31, 867. 236 237 238 *3v

K. A. Muszkat and M. Weinstein, J.C.S. Chem. Comm., 1975, 143. P. W. Atkins, A. J. Dobbs, and K. A. McLauchlan, Chem. Phys. Letters, 1974, 29, 616. F. Genoud, M . 4 . Schouler, and M. Decorps, Chem. Phys. Letters, 1974, 26, 414. E. Vogelman, H. Schmidt, U. Steiner, and E. A. Herst, Z. phys. Chem. (Frankfurt), 1975,94, 101.

24Q

241

242

J. H. Marshall, J. Phys. Chem., 1974, 78, 2225. T. S. Lui, Chem. Phys. Letters, 1974, 26, 77. R. D. Burkhart, J. Amer. Chem. SOC.,1974, 6276.

PhotophysicalProcesses in Condensed Phases

87

following benzophenone excitation in cis-piperylene (acceptor) have been measured (k-l = 7 ps; k,-l = 9 ps).243 Energy transfer from the T2 state of naphthalene (N) has been demonstrated using a clever adaptation of a technique used in energy transfer in solids and previously tested for anthracene. Scheme 7 outlines the system employed. The

Tl state of benzene (B) was used as an energy carrier to populate the TI level of endo-dicyclopentadiene(E). Population of the Tl state of E can be easily monitored since it undergoes an internal cycloaddition. Figure 7 shows the linear SternVolmer plot obtained as a function of benzene concentration. Intermolecular 3E) can be dismissed as a possible means intersystem crossing (lN E -+ N of accounting for the results since naphthalene fluorescence is unaffected by

+

+

Triplet-triplet annihilation of ly2-benzanthracene and fluoranthene leads to a delayed S,,-S, fluorescence from the highest accessible singlet state (n = 3 for ~~ and prompt 1,Zbenzanthracene and n = 4 for f l u ~ r a n t h e n e ) . ~Delayed fluorescence spectra and delayed fluorescence decay data for crystals of anthracene in phenanthrene show that host-dopant annihilation takes place to produce the excited singlet state of the The effect of deuteriation of aromatic hydrocarbons on the oxygen quenching of their triplet the effect of concentration and magnetic field on the radical-ion quenching of anthracene triplets in and a flash photolysis study of the quenching of tetracene triplets by tetracene radical anions 249 have been reported. ars a44

247

248

R. W. Anderson, J . Chem. Phys., 1974,61, 2500. C. C. Ladwig and R. S. H. Lui, J. Amer. Chem. SOC.,1974, 96, 6210. B. Nickel, Chem. Phys. Letters, 1974, 27, 84. S. H. Tedder and S. E. Webber, Chem. Phys. Letters, 1975, 31, 611. V. L. Ermolaev and S. S. Tibilov, Optika i Spektroskopiya, 1975, 38, 824. H. Tachikawa and A. J. Bard, Chem. Phys. Letters, 1974, 26, 10. G. Levin and H. Szwarc, Chem. Phys. Letters, 1975, 30, 116.

88

Photochemistry

The rate constant for triplet-triplet energy transfer (kt)in fluid solution depends on k d g and a: kt = akda (26) The determination of (11has often relied upon a theoretical calculation of kdif using

120

100

80

. Y 0 c(

60

40

20

I

I

I

2

4

I

I 8

6

I 10

I

t ~*nrcne]-l

Figure 7 Stern- Volmer plots of (a) the naphthalene-sensitized reaction of endodicyclopentadiene (0) and (b) the fluorescence of naphthalene in the presence of benzene (0) (Reproduced by permission from J. Amer. Chem. SOC.,1974, 96, 6210)

the Debye equation (27). The fact that both acetophenone and 1,4-dibromonaphthalene phosphoresce in fluid solution at room temperature can be used to kdg

= 8RT/30007

(27)

determine donor quenching, and acceptor (1,4-dibromonaphthalene) triplet populations make an analysis of energy transfer straightforward. From the temperature dependence of energy transfer, a and kag were independently determined.260The (11values of 0.28 at 25 "C in isopentane and 0.43 at 21 "C in iso-octane indicated that T-T energy transfer is not strictly diffusion controlled. The k a g values are very close to those predicted by the modified Debye equation (28). kdif

= 8RTJ20007

(28)

Further studies of linear free-energy relationships in the quenching of the triplet states of ketones by amines have been carried out. A plot of kk [see equation (29)] uersus o+ for a series of 11 meta- and para-substituted anilines is Ar,C=O(T,) 250

+ ArNMe,

>

[Ar2k-O-Ar&+Me,]

T. Takemura, M. Aikawa, and H. Baba, Bull. Chem. SOC.Japan, 1974,41, 2476.

(29)

89

Photophysical Processes in Condensed Phases

linear from p-OEt to p-COMe. However, rn-CF,, p-C02Et, and p-CN substituents lead to larger decreases in rate (Figure 8). Other fluorenone-amine systems were examined.261 Triplet quenchers having triplet energies well below that of naphthyl halides and halogeno-biphenyls do not quench the triplet-state reactions of these molecules in the normal way, and it has been speculated that some reactionenhancing process counterbalances energy transfer.262 A study of triplet + singlet energy transfer between benzophenone and perylene in vitreous solution

10.0 9.5 s.

m

-0 9.0 0.5

8.0

p-CN

7.5 )

1

- 0.5

0 U +

I .o

0.5 ' U

Figure 8 Rates of interaction of fluorenone triplet with meta- and para-substituted anilines; p = -0.96 (Reproduced by permission from J. Amer. Chem. Soc., 1974, 96, 6643)

has been reported,26sand the effects of solvent on quenching of biacetyl phosphorescence by indole and methionine have been examined.264 The efficient quenching of the triplet states of a range of polycyclic hydrocarbons leads to an estimate of the triplet energy level of ferrocene (15 000 f 1OOOcm-l). No transient species were observed in the quenching processes.265 The quenching of pyrazine (m*) triplet state by hydrogen-atom donors results in formation of the neutral pyrazyl radical [ks (isopropyl alcohol) = 1.3 x lo81 mol-1 s-1],266 and hydrazines efficiently quench the triplet states of ketones in water, with little p h o t o r e d u ~ t i o n . ~ ~ ~ One recent application of the equations derived in ref. 108 has been provided by Wagner and Nakahira in a study of the photolysis of a mixture of alkyl aryl ketones with similar absorbances at the excitation wavelength but with quite 261

262

26s 264 26s 260 267

(a) G. H. Parsons, L. T. Mendelson, and S. G . Cohen, J. Amer. Chem. SOC.,1974, 96, 6643; (b) G . H. Parsons and S. G . Cohen, J. Amer. Chem. SOC.,1974, 96,2948. L. 0. Ruzo and N. J. Bunce, Tetrahedron Letters, 1975, 511. J. L. Laporte, Y. Rousset, P. Peretti, and P. Ranson, Chem. Phys. Letters, 1974, 29, 444. E. Fujirnori, Mol. Photochem., 1974, 6, 91. M. Kikuchi, K. Kikuchi, and H. Kokubun, Bull. Chem. SOC.Japan, 1974,41, 1331. D. V. Bent, E. Hayon, and P. N. Moorthy, Chem. Phys. Letters, 1974, 27, 544. S. Ojanpera, A. Parola, and S. G . Cohen, J. Amer. Chem. SOC.,1974,97, 7379.

90

Photochemistry

different triplet lifetimes. Thus the quenching of the Norrish type I1 reaction by added dienes is not expected to follow a simple Stern-Volmer relationship.266 Cyclo-octatetraene quenching of the triplet state of rhodamine 6G produced by argon ion laser excitation is explained in terms of triplet-triplet energy by an electron-exchange process.26s A flash photolysis study of interaction between halide ions and triplet eosin has been carried out,26oand a laser photolysis procedure has demonstrated that the porphyrin-globin triplet state can be used to probe the diffusion of oxygen into the haemoglobin pocket in which the porphyrin is embedded.261 Energy transfer from ketone triplet states adsorbed on porous Vycor glass to but-2-enes 262 and NO 263 has been investigated. Most of the studies which have involved investigations of triplet exciplexes and triplet charge-transfer species have also been concerned with the corresponding singlet states and therefore have been discussed in an earlier section. The remaining few studies of the above species are discussed here. High concentrations of nitroaromatic and organic chloro-compounds quench triplet states of anthracene and metalloporphyrins such as zinc aetioporphyrin, and in some cases new transients are observed which are exciplexes, intermediate in the quenching process.264The nature of the triplet state of the naphthalenetetracyanobenzene complex has been shown to be critically dependent upon the environment. This observation removes the apparent contradiction between some earlier phosphorescence and e.p.r. results. In EPA glasses at least two distinctly different types of triplet state have been recognized ; locally excited triplet states (on the naphthalene moiety) and triplet states with considerable charge-transfer The degree of polarization of phosphorescence from charge-transfer complexes of tetracyanobenzene, o-, m-,and p-dicyanobenzenes, tetrachlorophthalic anhydride, and phthalic anhydride as electron acceptors and methyl-substituted benzenes as electron donors is found to be constant in all regions of the phosphorescence spectra for each complex. The degree of polarization is found to decrease as the ionization potential of the donor decreases.2ss 4 Physical Aspects of some Photochemical Studies Photo-oxidations.-Some aspects of the theoretical expression (30) developed to account for singlet oxygen quenching have been According to the simple quenching theory, no significant temperature dependence is expected.

P. J. Wagner and T. Nakahira, J. Amer. Chem. Soc., 1974, 96, 3668. M. Yamashita and H. Kashiwagi, J . Phys. Chem., 1974,78, 2006. 260 T. Akiyama, M. Kamiya, and Y. Akahori, Bull. Chem. SOC. Japan, 1975,48, 1033. 261 B. Alpert and L. Lindqvist, Science, 1975, 187, 836. K. Otsuka and A. Morikawa, Bull. Chem. SOC.Japan, 1974,47,2335. Y . Kubokawa and M. Anpo, J. Phys. Chem., 1974,78,2442. 264 J. K. Roy, F. A. Carroll, and D. G. Whitten, J. Amer. Chem. SOC.,1974, 96, 6349. 266 A. M. Ponte Goncalves and R. J. Hunton, J . Phys. Chem., 1975, 79, 71. I e O T. Amano and Y. Kanda, Bull. Chem. SOC.Japan, 1974,47, 1326. 267 C. A. Long and D. R. Kearns, J. Amer. Chem. SOC.,1975,97,2018. 268 269

91

Photophysical Processes in Condensed Phases

The observation that on going from - 20 to 25 "C the singlet oxygen lifetime only decreases by 50% has been accepted as being in agreement with theory. The apparently anomalous photo-oxidation results for benzene-CS, mixed solvent systems in which it was indicated that singlet oxygen may have an abnormally short lifetime in mixed solvents 268 as compared with the pure solvents has been resolved. Direct measurements of 710, in CS, as a function of added benzene show that 710, varies in a simple fashion with the percentage of benzene. Thus it is suggested that the anomalous behaviour observed is the result of changes in the rate of reaction of singlet oxygen with the acceptor used (anthracene). Some solvents in which singlet oxygen is particularly long-lived (Table 9) 267 have been found.

Table 9 Singlet oxygen lifetimes in various solvents 267 Solvent CHCI,

cs2 CDCl, c6F6

CCl4 Freon 11

Lifetime1ps 60 k 15 200 f 60 300 f 100 600 & 200 700 & 200 1000 f 200

The physical quenching of singlet oxygen by amino-acids and proteins in D 2 0 has been measured by their inhibition of the oxidation of bilirubin anion. Singlet oxygen was produced by the direct excitation of ground-state oxygen (lAU+ I V+- ,Xu-). The rate of quenching by most of the proteins studied is approximately the sum of the quenching rates of their amino-acids histidine (k, = 17 x lo71 mol-1 s-l), tryptophan (k, = 9 x lo71mol-1 s-l), and methionine (k, = 3 x lo71mol-1 s-l). These quenching rate constants differ from earlier values (except for methionine).268The absolute rate constants for the reaction of lo2with 1,3-diphenylisobenzofuran and physical quenching of lo2by groundstate oxygen have been and a comparison of dye-sensitized and microwave-generated lo, oxidation of amino-acids has been made.271 Near-i.r. irradiation has been used to photosensitize the production of singlet , ~been , observed oxygen.272aDim01 emission, 2O2(lAU)-+ 2O2(,Zu-) h ~ ~has from neodymium-glass-pumped oxygen in the gas phase and in 1,1,2-trichlorotrifluoroethane Foote reactivity indices (/3) have been measured for rubrene and 9,lO-dimethylanthracene undergoing autophotoperoxidation in a range of solvents for which ~ 1 0has , been measured. The variation in /3-values (about a factor of 40) is almost entirely due to the solvent dependence of PO,. Thus kM = ~ / B T ~varies O ~ by less than a factor of 2 (kM is the singlet oxygen addition rate constant). However, for

+

26Q

C. S. Foote, E. R. Peterson, and K.-W. Lee, J. Amer. Chem. SOC.,1972, 94, 1032. I. B. C. Matheson, R. D. Etheridge, N. R. Kratowich, and J. Lee, Photochem. and Photobiol.,

270

I. B. C. Matheson, J. Lee, B. S. Yamanashi, and M. L. Wolbarsht, J . Amer. Chem. SOC.,1974,

1975, 21, 165. 96, 3343. 27L 27a

J. R. Fischer and G . R. Julian, Physiol. Chem. Phys., 1974, 6, 179. (a) R. A. Nathan and A. H. Adelman, J.C.S. Chem. Comm., 1974,675; (b) I. B. C. Matheson, J. Lee, B. S. Yamanashi, and M. L. Wolbarsht, Chem. Phys. Letters, 1974, 27, 355.

92

Photochemistry

systems with k H approaching the diffusion-controlled value, or for those systems in which lo2is subject to a purely physical quenching, this may not be the case.273 The role of exciplexes in self-sensitized photo-oxidations has been further investigated by Stevens and c o - ~ o r k e r s . ~ Photoperoxidation ~~*~ of lY3-diphenylisobenzofuran in solution proceeds at a rate which is independent of acceptor concentration when this is very low, and this observation has been interpreted in terms of a re-encounter of lo2and ground-state acceptor molecules generated in the same triplet-triplet annihilation act. This interpretation accounts for the failure of tetramethylethylene to inhibit the reaction completely. Processes 1-3 in Scheme 8 account for the observations if re-encounter effects are included,

I

2; 1

Y

Scheme 8

without the introduction of the spin-forbidden addition of O2(302) to the acceptor singlets M(S1).273dAn orbital correlation diagram for the concerted addition of lAg O2to anthracene has been It has been demonstrated that the lASO2reactivity indices (16) measured for a range of aromatic hydrocarbons correlated well with the n-eIectron relocalization energy in the case of the unsubstituted acceptors. Electron-donating substituents at the site of lo2addition increase the acceptor reactivity in the order H < Ph < Me0 Me.273d N

273

(a) B. Stevens and S. R. Perez, Mol. Photochem., 1974, 6, 1 ;(b) B. Stevens, S. R. Perez, and J. A. Ors,J. Amer. Chem. SOC., 1974, 96, 6846; (c) B. Stevens, J. Photochem., 1974, 3, 393; ( d ) B. Stevens, J. A. Ors, and M. L. Pinsky, Chem. Phys. Letters, 1974, 27, 157.

Photophysical Processes in Condensed Phases

93 Directly measured rate constants for lo2quenching by a series of substituted NN-dimethylanilines indicate that a partial charge-transfer interaction may be responsible for the quenching action.274 Quenching of lAgO2 by transition-metal chelates 276 and the singlet oxygen oxidation of vinyl sulphides 276 have been investigated, and it has been shown that diphenyl sulphide, previously used to bring about the monodeoxygenation of persulphoxides, can be used to trap dioxetans formed in the reaction of singlet oxygen with certain electron-rich ethylenic and heterocyclic A singlet oxygen scavenging method has been used to determine ketone peroxide The trapping of oxetans, formed by the photoaddition of benzoquinone to olefins, can be achieved using molecular oxygen. The oxygen is seen as reacting with the 1,4-biradical to give a trioxetan (Scheme 9).278 Dioxetans from the singlet-oxygen oxidation of indenes have been isolated.280

The photo-oxidation of the commercially important 1,3-dipheny1-2-pyrazolines has been further 282 and the photo-oxidation of 6,6-diarylfulvenes Another polymer-bound singlet oxygen carrier has been used to simplify photo-oxidation and the decomposition of bis-(triphenylbromoantimonyl) peroxide provides another useful source of singlet oxygen.285 The dye-sensitized photo-oxidation of 1,3-diphenylisobenzofuran has been developed as a teaching experiment.28sa The production of singlet oxygen by thiazine dye photosensitization as measured by the rate of photo-oxidation of tryptophan has been found to be very pH sensitive. The effect was shown to be related to the pK,'s of the triplet dyes.28sbThe occurrence of lo, in the photodynamic oxidations of g u a n o ~ i n ethe , ~ ~reaction ~ rates of bilirubin with lo2in the 274 47ti

978

R. H. Young, Canad.J. Chem., 1974,52, 2889. D. J. Carlsson, T. Supruchuk, and D. M. Wiles, Canad. J. Chem., 1974, 52, 3728. R. H. Young, D. Brewer, R. Kayser, R. Martin, D. Periozi, and R. A. Kellei, Canad. J. Chem., 1974,52, 2889.

877 278 a79 ago

281 482

283 484

286

we 287

H. H. Wasserman and 1. Saito, J. Amer. Chem. SOC.,1975, 97, 905. J. R. Anderson, J . Org. Chem., 1974, 39, 3183. R. M. Wilson and S. W. Wunderly, J.C.S. Chem. Comm., 1974, 461. R. A. Burns and C. S. Foote, J . Amer. Chem. SOC.,1974,96,4339. N. A. Evans and I. H. Leaver, Austral. J. Chem., 1974, 27, 1797. N. A. Evans, D. E. Rivett, and J. F. K. Wiltshire, Austral. J . Chem., 1974, 27, 2267. N. Harada, S. Kimdo, H. Uda, and S. Utuoni, Chem. Letters, 1974, 893. 1. Rosenthal and A. J. Archer, Israel J. Chem., 1974, 12, 897. J. Hahlmann and K. Winsel, Z . Chem., 1974,14,232. (a) J. A. Bell and J. D. MacGillavry, J. Chem. Educ., 1974, 51, 677; (b) R. Bonneau, R. Pottier, 0. Bagno, and J. Joussot-Dubien, Photochem. and Photobiol., 1975, 21, 159. 1. Saito, K. Inoue, and T. Matsuura, Photochem. and Photobiol., 1975, 21, 27.

Photochemistry

94

presence of base,288and an investigation of a lo2model for an oxygenase reaction 280 have been reported. In the photocyclodehydrogenation of N-methyldiphenylamine (NMP) to N-methylcarbazole (NMC), oxygen participates in two ways. It oxidizes the intermediate N-methyl-dihydrocarbazole to NMC and it quenches ,NMD iil competition with the dihydrocarbazole formation.200 The results of an investigation of the oxidation of CD,N,CD, indicate the presence of three processes (3 1)-(33) which destroy CD302.201 2CD,02

-

___+

---+

+ O2 CD,OD + C D 2 0 + 0, CD,02CD, + O2

2CD,O

(31) (32)

(33)

The photo-oxidation of iodomethane in solid argon containing oxygen has been reported.2Q2 Chemi1uminescence.-The triplet potential-energy surface of dioxetan has been found to intersect the singlet surface between dioxetan and the transition state for dioxetan decomposition to formaldehyde. This provides support for the argument that the reason for efficient triplet ketone formation on thermolysis of dioxetans is because intersystem crossing is an integral part of the The decomposition mechanism of lY2-dioxetanshas been the subject of another theoretical investigation.2Q4 Singlet sensitization of tetramethyl-l,2-dioxetan by pyrene results in the formation of triplet acetone.20s In a theoretical study related to the one reported in ref. 293, it was concluded that the triplet surface intersects the ground-state surface between (15) or (16) and cyclo-octatetraene. Evidence for triplet product

formation was obtained from the pyrolysis of the benzo analogue, syn-benzocyclo-octene.206aPyrolysis of ‘Dewar-acetophenone’ produces the triplet state of acetophenone, but very inefficiently.206b 288

290

J. Lee, J. Amer. Chem. SOC.,1974, 96, 3348. J. Matsuura and H. J. Cahnmann, Tetrahedron Letters, 1975, 9, 641. G. Fischer, E. Fischer, K. H. Grellmann, H. Linschitz, and A. Temizer, J. Amer. Chem. SOC., 1974, 96, 6267.

291

298

ag6

J. Weaver, R. Shortridge, J. Meagher, and J. Heicklen, J. Photochem., 1975, 4, 109. J. F. Ogilvie, V. R. Salares, and M. J. Newlands, Canad. J . Chem., 1975, 53, 269. M. J. S. Dewar and S. Kirschner, J. Amer. Chem. SOC.,1974,96, 7578. G. Barnett, Canad. J. Chem., 1974, 52, 3837. W. J. Baron and N. J. Turro, Tetrahedron Letters, 1974, 3515. (a) R. S. Case, M. J. S. Dewar, S. Kirschner, R. Petit, and W. Slegeir, J. Amer. Chem. Soc., 1974, 96, 7581; (b) N. J. Turro, G. Schuster, J. Pouliquen, R. Petit, and C. Mauldin, ibid., p. 6797.

Photophysical Processes in Condensed Phases

95

A theoretical analysis of Dewar-benzene pyrolysis to give triplet benzene 287 and a report of the direct and sensitized photoreactions of benzvalene have appeared. 298 Studies of chemiluminescence from iodine-luminol,2sghypochlorite-luminol,800 and aryl Grignard-oxygen and from succinylfluorescein 302 and several xanthene dyes 303 have been reported. Oxygen-18 studies of the chemiluminescence of a firefly luciferin analogue have provided evidence which contradicts other earlier reports in that it suggests that the dioxetanone is an important intermediate in light Spinstatistical contributions in redox chemiluminescence quantum efficiency have been a n a l y ~ e d ,and ~ ~ ~a striking deuterium isotope effect in phosphorus chemiluminescence has been discovered.306 A novel sensitized chemiluminescence from thiazine dyes sensitized by singlet oxygen has been observed307 and the absolute yields of chemiluminescence from the pulse radiolysis of aqueous dye solutions have been determined.308 In a series of important papers, Bard and co-workers have presented a report of their techniques for studying electrogenerated chemiluminescence and the results they have ~ b t a i n e d . ~ O The ~ - ~effect ~ ~ of a magnetic field on a number of systems (pyrene, rubrene, l,Zbenzanthracene, pyrene-AWN”‘-tetramethyl-pphenylenediamine, and 9-methylanthracene-tri-p-tolylamine)has helped to probe the intermediates in the generation of chemiluminescence. Reports of electrogenerated chemiluminescence from liquid a n t h r a ~ e n e ,[2Hlo]phenanthrene,a1s ~~~ 5,12-dibromo-5,12-dihydro-5,6,11,12-tetraphenylnaphthacene,314 and benzoyl peroxide plus a polycyclic aromatic hydrocarbon m have appeared. A series of papers report the electrogenerated chemiluminescence in laser c a v i t i e ~ , ~and ~ ~ -electrogenerated ~~~ chemiluminescence systems with energy transfer to some rare-earth chelates have been examined.319 ee7

oIe9

aoo aol ao2

aoe

a12

s13 a14

als 31e

81B

M. J. S. Dewar, S. Kirschner, and H. W. Kollmar, J. Amer. Chem. SOC.,1974, 96, 7579. C. A. Renner, T. J. Katz, J. Pouliquen, N. J. TUTZO, and W. H. Waddell, J. Amer. Chem. SOC.,1975, 97, 2568. W. R. Seitz and D. M. Hercules, J. Amer. Chem. SOC.,1974, 96, 4094. W. R. Seitz, J. Phys. Chem., 1975, 79, 101. P. H. Bolton and D. R. Kearns, J. Amer. Chem. SOC.,1974, 96,4651. I. Kamiya and K. Aoki, Bull. Chem. SOC.Japan, 1974,47, 1744. I. Kamiya and K. Aoki, Bull. Chem. SOC.Japan, 1974,47, 1908. E. H. White, J. D. Miano, and M. Umbreit, J. Amer. Chem. SOC.,1975, 97, 198. C. P. Keszthelyi, Bull. Chem. SOC. Japan, 1975, 48, 1083. R. J. Van Zee and A. U. Khan, J. Amer. Chem. SOC.,1974,96,6805. D. E. Brabham and M. Kasha, Chem. Phys. Letters, 1974, 29, 159. W. A. Prutz and E. J. Land, J. Phys. Chem., 1974,78, 1251. H. Tachikawa and A. J. Bard, Chem. Phys. Letters, 1974, 26, 568. H. Tachikawa and A. J. Bard, Chem. Phys. Letters, 1974, 26, 246. C. P. Keszthelyi, N. E. Tokel-Takvoryan, and A. J. Bard, Analyt. Chem., 1975,47,249. K. Shinsaka and G. R. Freeman, Canad. J. Chem., 1974, 52, 3559. N. Periasamy and K. S. V. Santhanam, Canad. J. Chem., 1975,53, 76. C. P. Keszthelyi and A. J. Bard, J. Org. Chem., 1974, 39, 2936. D. L. Akins and R. L. Birke, Chem. Phys. Letters, 1974,29,428. C . P. Keszthelyi, Spectroscopy Letters, 1974, 7, 409. C. P. Keszthelyi, Acta Phys. Chem. Szeged, 1974, 20, 365. C. P. Keszthelyi, Spectroscopy Letters, 1975, 8, 25. R. E. Hemingway, Su-Moon Dark, and A. J. Bard, J. Amer. Chem. SOC.,1975,97,200.

96 Photochemistry Photochromism.-As reported last year, two publications 320, 321 on the photochromism of bianthrones present rather conflicting evidence for the mechanism of formation and decay of intermediates in this system. A study of the compounds (17), (18), and (19) has concentrated on the role of triplets in the 0

0

bianthrone photochromism. Flash photolysis and biacetyl sensitization and quenching experiments clearly show that the photochromic form B can be produced through a triplet state. However, the results do not clarify whether the triplet observed directly in rigid media or in fluid media at low temperatures is in fact the triplet being photosensitized by bia~ety1.l~~ 2-Hydroxytriphenylmethan01 (20) exhibits p hot ochromism in fluid solution and in the crystalline state: the coloured form has been deduced to be o-fuchsone (21), produced by photodehydration (Scheme 10). The reactive state of (20) has

-

+

I1 v

' dark

H,O

0

been shown to be the singlet state and the mechanism seems to be quite different from that shown by other triarylmethane 2-Hydroxy-4-methoxytriphenylmethanol has also been shown to be p h o t o c h r o m i ~ . ~ ~ ~ The interesting story of the photochromism of fulgides and fulgimides has continued with a report that the cyclization process in a series of fulgides occurs by nrr* excitation of one of the two largely independent chromophores in the m01ecule.~~* The luminescence and photochromism of some azomethines 326 and the isomeric forms of hydronaphthyl radicals 326 have been investigated, and the 380

321 322 a23 324

326

T. Bercovici and E. Fischer, Helv. Chim. Acra, 1973, 56, 1114. K. H. Gschwind and U. P. Wild, Helv. Chim. Acta, 1973, 56, 809. S. Hamai and H. Kokubun, Bull. Chem. SOC.Japan, 1975, 48, 798. S. Hamai and H. Kokubun, Bull. Chem. SOC.Japan, 1974, 47, 2085. H. G. Heller and M. Szewczyk, J.C.S. Perkin I, 1974, 1487. Yu. V. Revinskii and M. I. Knyazhanskii, Zhur.fiz. Khim., 1974,48,993. V. A. Smirnov, 0. M. Andreev, and M. V. Alfimov, Chem. Phys. Letters, 1974,28, 84.

Photophysical Processes in Condensed Phases

97

photochromic behaviour of some copolymers of indolino-spirobenzopyran has been Two useful publications outlining methods for calculating the absorption spectra of the components of photochromic systems have a p p e a ~ e d328 .~~~~ a27 828 928

J. Verborgt and G. Smets, J. Polymer Sci., Polymer Chem., 1974, 12, 2511. D. G. Starenga, Photochem. and Photobiol., 1975, 21, 105. G. M. Wyman, Mol. Photochem., 1974, 6, 81.

3 Gas-phase Studies BY

D. PHILLIPS

1 Introduction The format is as before, with the addition of one small section on the use of lasers in isotope separation and remote sensing of atmospheric pollutants. Emphasis is again placed upon the physical fates of excited molecules, and in particular on studies of isolated molecules. 2 Alkanes

The photolysis of n-[2Hlo]butanehas been investigated with 8.4 eV and 10.0 eV photons, using HI as a radical scavenger.' The major conclusions in the study are that although the quantum yield of process (1) decreases from 0.70 to 0.37 upon increase in photon energy from 8.4 to 10.0eV, the relative importance of direct C - C bond-cleavage processes, alkane elimination processes, and D-atom elimination processes is insensitive to photon energy. Of the possible C-C bond-cleavage processes, those involving breakage of the 2,3 C-C bond predominate over the 1,2 cleavages.

Hydrogen elimination has been found to be an unimportant process in the photolysis of neopentane at 7.6, 8.4, and 10.00 eV photon energies, the important primary processes being (2) and (3)., Reaction (3) increases in importance over (2) with increase in photon energy. In the photolysis of isobutane,, processes hv hv

+ neo-C,H,, + iso-C,Hlo

-

+ iso-C,H, CH,* + t-C,H,* CH, + G H ,

CH,

iso-C4Ha + H,

(2)

(3) (4) (5)

(4) and ( 5 ) were the predominant chemical fates of the molecule excited at 7.6 and 8.4 eV. Two pathways for these reactions are possible, that of lower energy, involving direct olefin formation, being of greater importance at 7.6eV: the other higher-energy channel involving carbene formation is operative at 8.4 eV. The radiative lifetime of the L2Astate of CH has been measured as 460 k 70 ns, using a molecular ion beam m e t h ~ d . ~ a a

J. A. Jackson and S. G. Lias, J . Photochem., 1974, 3, 151. R. E. Rebbert, S. G. Lias, and P. Ausloos, J. Phorochem., 1975,4, 121. S. W. Jorgensen and G. Sorensen, J . Chem. Phys., 1975, 62, 2550.

98

99 The CH4+ ion has been observed to dissociate to the methyl cation and a hydrogen atom [reaction (6)] upon irradiation with white light from a 2.5 kW Gas-phase Studies

CH4+

+ hv

CH3+ + H*

(6)

xenon arc lamp, with a maximum photodissociation cross-section of 3 x 10-19 cm2 at 335 nm.4 Isotopic scrambling in the reactions of CH3+ with deuteriated methane has been discussed.6 Vibrational relaxation in highly excited butyl radicals and photochemical reactions of fluoro-oxyperfluoroalkaneswith perfluorocyclo-olefins ' have been reported. 3 Alkenes, Alkynes, and Polyenes The photolysis of ethylene has been studied at 147, 163.4, and 184.9 nm.8 The relative quantum yields for reactions (7)-(9), expressed as percentages, are as follows : C2H4

+ hv

-

+ H2 C2H2+ 2H*

C2H2

C2H3*

+ H*

(7)

147 nm 45

163.4 nm 47

184.9 nm 53

(8)

54

48

5

(9)

1

5

14

The reactions of the energized vinyl radical, summarized by reactions (10) and (1 l), were also studied. Fluorescence from propylene and several other monoolefins has been observed with quantum yields of 10-s.8a CZH4

+ hv

H*

+ C2H3***

-

C2H2

+ H* + H*

(10)

The vacuum-u.v. photolysis of the difluoroethylenes in low-temperature matrices has been compared with vapour-phase s t u d i e ~ . ~ A Garton-type flash lamp with significant output in the vacuum-u.v. has been used to flash photolyse propylene.1° End-product analysis showed that the system differed from the results of continuous photolysis, owing to radicalradical reactions between the CH3*,CzH3*, and C3H5*and H* species that are produced in large concentrations under flash conditions. The vacuum-u.v. photolysis at 8.4 and 10.0 eV of 3-methylbut-l-ene l1 gives molecular product M. Riggin and R. C. Dunbar, Chem. Phys. Letters, 1975, 31, 539. J. M. S. Henis and M. K. Tripodi, J. Chem. Phys., 1974, 61, 4863. R. C. Ireton and B. S. Rabinovitch, J. Phys. Chem., 1974,78,1979; R. C . Ireton, A.-A. KO,and B. S. Rabinovitch, ibid., p. 1984. M. S. Toy and R. S. Stringham, J. Fluorine Chem., 1974, 5, 481. H. Hara and I. Tanaka, Bull. Chem. SOC.Japan, 1974, 47, 1543; H. Hara, K. Kodama, and I. Tanaka, ibid., 1974, 48, 711. 8a F. Hirayama and S. Lipsky, J. Chem. Phys., 1975, 62, 576. W. A. Guillory and G. H. Andrews, J. Chem. Phys., 1975,62, 3208. l o D. R. A. Cuff, G. R. Johnston, and D. Price, J. Photochem., 1974, 3, 107. l1 G. J. Collin and C. Bertrand, J. Photochern., 1974, 3, 123. ti

Photochemistry

100

quantum yields, at 8.4 eV, of buta-lY3-diene(0.55); propyne (0.15), ethylene (0. lo), acetylene (0.09), isoprene (0.05), buta-1 ,Zdiene (0.04), and cyclobutene (0.13), iso-C,H, (0.04), with radical product yields of CH, (1.35), H (0.62), CBHD (0.04), and C2Hs (0.03). At 8.4 eV there is no isomerization. At 10.0 eV ionization occurs to the extent of 0.165, giving rise to 2-methylbut-2-ene and 2-methylbut-1-ene as products. The reactions of vibrationally excited 3,3-dimethylbut1-ene and the 2,2-dimethylbuta-l,3-diylbiradical arising from the Hg(3P,) photosensitization of the olefin,12and the formation of carbene intermediates in the photochemistry of alkenes,13have been discussed. In the vapour-phase photolysis of cyclopentene, photoionization occurs at an excitation wavelength of 123.6nm with an efficiency of 0.16, and leads to the formation of cyclopentane through ion-molecule rea~ti0ns.l~At 147 and 123.6 nm the decomposition of the molecule could be accounted for the reactions (12)-(18), with the quantum yields shown. The photodissociation of C2H2and

+ hv

c-C~HB

____+

CdHd

+ CH2 + H2

(12)

C2H2

+ GHt?

(13)

147 nm 123.6 nm 0.04 0.03

+

C2H2 G H 4 + H, (14) C2H4 + GH3* + H* (15) c2H4

CsH, C3H3.

+ GH4

+ 2H*

(16)

0.03

0.03

0.05

0.08

0.25

0.20

0.02

-

(17)

0.23

0.13

+ GH,. + H2 (18)

0.10

0.11

C2HBr in the vacuum-u.v. produces emission in the 400-550nm region that has been identified as due to electronically excited C2H*.lS The measured lifetime of this species is 6 ps, and corresponds to the dissociation lifetime of excited acetylene rather than the actual fluorescence lifetime of the C2H* species. The results could be rationalized on the basis of reactions (19)-(25). The dissociation C2H2

+ hv

C2H2*

C2H2** CBH2**

GH2** + M C2H2**+ C2H2

____+

C2H2*

(19)

C2H2**

(20)

C2H**+ H*

+ H2 C2H*+ H* C2H2+ M

C2

Predissociation

products

(21) (22) (23) (24) (25)

of C2HBr also produced the C2 Swan bands in emission. These were also seen in a recent study of the electron-impact dissociation of C2H2,18and emission from CH, H, and C was also observed. In both studies, threshold energies and la l3

l4 l6

D. C. Montague, J.C.S. Faraday I, 1975, 71, 398. T. R. Fields and P. J. Kropp, J . Amer. Chem. SOC.,1974,96,7559. C.-K. Tu and R. D. Doepker, J. Photochem., 1974/5,3, 13. H. Okabe, J. Chem. Phys., 1975,62,2782. C . I. M. Beenakker and F. J. De Heer, Chem. Phys., 1974,6,291.

101

Gas-phase Studies

other thermochemical data relating to the appearance of emission and dissociation to various fragments are given. The radiative lifetimes of some excited states of methylidyne CH have been reported," and photoionization studies of acetylene with emphasis on C2H2+ion reactions with HZhave been discussed.18 The temperature dependence of collisional energy transfer in the photoisomerization of cycloheptatriene has been discussed.1s The reactions of singlet methylene with butadieneY2Othe excitation of charge-transfer complexes of C2H,-02-Ar mixtures at low temperatures,21 and the photodissociation of the perfluoroallyl cationzzhave been reported. The product of the last reaction is the CF3+ion, and the threshold wavelength for its production is 295 nm. 4 Aromatic Hydrocarbons The two-photon-absorption method has been used to populate vibronic levels of the lBaU state of benzene vapour under isolated-molecule conditions at ca. 0.1 T ~ r r These . ~ ~ important data are shown in Figure 1, compared with corresponding one-photon data in the form of non-radiative lifetimes as a function

EXCESS ENERGY [crn-l]

Figure 1 The non-radiative lifetimes of vibrational levels of benzene in the collisionless region as a function of excess energy. The lifetimes of the two-photon-excited states (triangles) are measured at 0.6 Torr and 0.1 Torr, respectively. The lifetimes of onephoton-excited states (circles) at 0.1 Torr are taken from J. Chem. Phys., 1971,55, 5561 (Reproduced by permission from Chem. Phys. Letters, 1975, 32, 210) la lD 2o 21 2p

23

J. Hinze, G. C. Lie, and B. Liu, Astrophys. J., 1975, 196, 621. S. E. Buttrill, jun., and J. K. Kim, J. Chem. Phys., 1974, 61, 2122. S. H. Luu and J. Troe, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 766. P. M. Crane and T. L. Rose, J. Phys. Chem., 1975,79,403. H. W.Buschmann, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 1344. B. S. Freiser and J. L. Beauchamp, J. Amer. Chem. Soc., 1974, 96, 6260. L. Wunsch, H. J. Neusser, and E. W. Schlag, Chem. Phys. Letters, 1975, 32, 210.

102

Photochemistry

of excess energy. Actual lifetimes (and therefore fluorescence quantum yields) can be obtained from the original reference. There are several features in the study worthy of note. Firstly, the slopes of the values of ~ N Rfor the progressions involving v18 are much less than those for ~14,being similar to the one-photon slopes for v g , for which decay is accepted to be by intersystem crossing to the triplet manifold. Secondly, and surprisingly, the 14; level has a non-radiative lifetime longer than that of the zero-point level, similar to the situation seen in aniline.24 Both of these observations are explicable in terms of the abnormal increase in wavenumber of the ~ 1 vibration 4 from 1309 cm-1 in the lAln ground state to 1566cm-l in the lBZustate, and assuming that the vibrational wavenumbers of the triplet and ground states are similar. Thus simple calculation shows the ratio of lifetimes 0 : 14: on this basis to be 0.89, in excellent agreement with the observed ratio of 128 : 154 = 0.83. It may be a general phenomenon that excitation of an upper-state vibrational mode having a frequency greater than that in the ground state leads to a longer non-radiative decay lifetime. The third important feature of this study on two-photon-excited levels is that at 3300 cm-l the non-radiative lifetime becomes very small, in accord with one-photon results, the threshold corresponding to the channel I11 process. For the one-photon case this process has been identified on the basis of calculations as the S1-+ Sointernal c o n v e r ~ i o n ,which ~ ~ requires excitation of a good accepting mode (such as vl) to be competitive with the intersystem-crossing process. Although the authors of the two-photon paper state that their results show that total excess energy, irrespective of vibrational make-up, seems to be the only criterion for the onset of channel 111, it should be noted that the shortest-lived state observed in their study, the 14i1: level, does have two quanta of vl, and may thus satisfy the requirements for the S1-+ So process to be competitive with S1+ Tl. It would be of interest, if possible, to obtain data on levels excited around this excess energy mark with a lesser content of mode v1 excitation to see if the lifetime is lengthened correspondingly. Finally, and significantly, for excitation of the 14; and 1461; transitions, lifetimes have been measured at points within the vibrational envelope corresponding to different amounts of rotational excitation, and variations noted, indicating that rotational effects on the lifetime are of importance, as has been seen in naphthalene (see below). One-photon excitation studies on the fluorescence decay properties of isolated aniline,Z4 deuteriated 26 and difluoro- benzene^,^' and other simply substituted benzenes 28 have been carried out. In the case of aniline, the results quoted by different groups of workers differ markedly. As an example, results for excitation of four transitions populating two levels are given in Table 1. As can be seen from Table 1, the vast difference in results makes discussion of the trends difficult. N

24

26

26

O7

28

W. R. Ware and A. M. Garcia, J. Chem. Phys., 1974, 61, 187; R. Scheps, D. Florida, and S. A. Rice, ibid., p. 1730; H. von Weyssenhoff and F. Kraus, ibid., 1971, 58,2387; R. LopezDelgado, A. Tramer, and I. Munro, Chem. Phys., 1974, 5, 72. M. G. Prais, D. F. Heller, and K. F. Freed, Chem. Phys., 1974, 6, 331; D. F. Heller, K. F. Freed, and W. M. Gelbert, J. Chem. Phys., 1972, 56, 2309. C. Guttmann and S. A. Rice, J. Chem. Phys., 1974, 61, 651; W. H. Waddell and C. Renner, Mol. Photochem., 1974, 6, 321. C. Guttmann and S. A. Rice, J . Chem. Phys., 1974,61,661; M. D. Swords, M.Sc. dissertation, University of Southampton, 1974. M. G. Rockley and D. Phillips, J. Photochem., 1975, 3, 365.

103

Gas-phase Studies Table 1 Decay characteristics of isolated aniline Excess energy/cm-l 0 0 0 0 492 492 492

Transition

1: 1: 0-0 0-0 6ak 1: 6a; 6ah a Ware et al., ref. 24;

kR

70bfhS

QF

x 10-7/s-1

~ N R

x lO-?/s-l

7.45 5.62 0.57 7.65 0.095 1.15 10.97 8.25 0.61 8.26 5.28 7.38 0.30 3.52 8.23 8.51 7.06 0.47 6.66 7.51 6.20 0.55 7.58 7.26 0.21 2.66 12.83 7.89 Rice et al., ref. 24; I refers to NH2 inversion mode.

Refi a b a b a a

b

It is noted that the lifetimes measured are reasonably similar, given the different excitation bandpass used in the two studies, but that there are enormous disparities in the quantum yields quoted. Moreover, for the results of Rice et al. the decay characteristics and quantum yields quoted for the same level, e.g. the zero-point level, pumped by two different transitions are again vastly different, the quantum yields quoted differing by a factor of three, whereas clearly these results ought to be identical unless one of the transitions being pumped is contaminated by other transitions, a point discussed by these authors. It could be that the method used by one group to evaluate quantum yields is in error. This point is reinforced by the studies on difluorobenzenes27 discussed below in which some differences exist between results of two groups, and between results of Rice et al. for the same level pumped by different transitions. In the case of aniline the results of Ware et al. are self-consistent, as shown in Table 1, and lifetimes agree with those obtained using excitation radiation from a synchrotron storage ring by Lopez-Delgado et al.24 Despite reservations about the accuracy of results quoted, both groups are in agreement that population of excited levels of the I inversion mode in the NH2 group does not promote non-radiative decay of the state. Since this mode is abnormal in the sense that the frequency increases in the excited state, the results are qualitatively in agreement with those discussed above for two-photon excitation of the ~ 1 mode 4 of benzene. Because of the uncertainty of the absolute magnitude of rate-constants for radiative and nonradiative decay arising from the differences in experimental measurements, detailed discussion of the successful fitting of results to the theory of Freed et a1.26by Rice et al. will not be included here. As stated above, similar but smaller differences exist between values of T and OF measured by Rice et al. and other workers for difluor~benzenes,~~ as evidenced in Table 2. Again, the more serious difficulty concerns the self-consistency, Table 2 a7

Decay characteristics of isolated p-difuorobenzene AE/cm-l @p Tp/nS k ~ / 1 S0-' ~ k ~ ~ / 1 S-'0 '

Transition 0-248 0-0

0 0 0-0 0 (1;)O 2(819) 1638 (1i)O 2(819) 1638 a Guttman and Rice; Swords.

+ +

0.76 1.00 1.0 0.69 0.50

9.9 11.3 11.4 0.6 7.6

7.7 8.9 8.8 8.0 6.6

2.4 0 0 3.6 6.6

Ref. a

a b a b

104

Photochemistry of the one set of results, since it can again be seen that both quantum yields and decay times for the same level reached by different transitions differ markedly. This is not commented upon by the authors, but could again be due to sequence congestion. p-Difluorobenzene is remarkable in that the fluorescence quantum yield of the zero-point level is unity. Non-radiative decay characteristics again qualitatively fit the model of Freed et aZ.26 In all cases the dominant non-radiative decay process is assumed to be intersystem crossing to the triplet manifold, which may be true for small excess energies, but, as has been shown for a variety of molecules, may not be universally the case, since Sl-+ So internal conversion rapidly increases in importance with excess energy.2BThe energy dependence of the radiative process has been considered,28and it was shown that consideration of frequency changes between vibrational modes in ground and excited states is insufficient to account for the observed variation in k~ with excess energy for a variety of substituted benzenes. It thus appears that other factors may be of importance, such as displacements and anharmonicities and the assumption of the Born-Oppenheimer approximation excluded in the simple treatment to account for variations in k ~ . Among collisional processes in benzenes in the vapour phase are included a study of collisional vibrational relaxation in p-fluorotoluene (PFT),30 using a model developed by Freed et aL31 and modified by Beddard et aZ.31 In this the molecule is represented as an N-fold degenerate oscillator for which collisions induce transitions to adjacent levels only, the decay rate of levels is assumed to increase linearly with quantum number, and the two variables used are the collision efficiencyand spacing of levels of the degenerate oscillator, the degeneracy being included to mimic the density-of-states function of the molecule. Detailed description of the model will not be included here, but the results of fitting the model to ‘lifetimes’ obtained from non-exponential decay characteristics for the PFT molecule are illustrated in Figure 2, from which the best-fit oscillator characteristics obtained are a six-fold degenerate oscillator of wavenumber 500cm-l with a collision efficiency of 90%. Vibrational relaxation is thus very efficient, and reasons for this were discussed in this and a similar study by the same group on difluor~benzenes.~~ The model has also been used very successfully in a similar, earlier study by Beddard et aZ. on other aromatic molecule^,^^ discussed below. The magnitude of the exchange and dipole-dipole contributions to energy transfer in the vapour phase between p-difluorobenzene and a variety of substituted acetones and between a variety of substituted benzenes and pentan-Zone and biacetyl has been In both studies it was concluded that longrange contributions are significant, and in the thorough treatment of Lee et aZ. it was shown that steric effects can be of importance in the exchange mechanism 29

30

31 32

J. C. Hsieh, C.4. Huang, and E. C. Lim, J . Chem. Phys., 1974,60,4345; J. C. Hsieh and E. C. Lim, ibid., 1974, 61, 736; S. F. Fischer, A. L. Stanford, and E. C. Lim, ibid., p. 582; C . 4 . Huang and E. C. Lim, ibid., 1975, 62, 3826. R. G. Brown, M. G. Rockley, and D. Phillips, Chem. Phys., 1975, 7 , 41; K. F. Freed and D. F. Heller, J . Chem. Phys., 1974, 61, 3942. G. S. Beddard, G. R. Fleming, 0. L. J. Gijzeman, and G. Porter, Proc. Roy. SOC.,1974, A340, 519. G. L. Loper and E. K. C. Lee, J. Chem. Phys., 1975, 63, 264; R. G. Brown, D. Phillips, and G. Das Gupta, J . Phys. Chem., 1974,78,2407.

105 but not in the dipole-dipole interaction. The quenching of singlet states of many substituted benzenes by a variety of additives in the vapour phase has been 34 and consideration given to excited-state charge-transfer complex formation as a quenching mechanism. In most cases indirect means, such as linear free-energy correlations, are used to substantiate the mechanism ; but in Gas-phase Studies

22

zo 18

4‘

F

A 2

6

4

8

10

12

14

16

11

Pressure of PFT ( t o r r )

Figure 2 Plots of inverse ‘lifetime’ obtained from the non-exponential decay of PFT against PFT pressure. Data points: (0) excitation at 271.2 nm, (@) 265.4 nm, ( x ) 262.6 nm, ( 0 )259.9 nm, (A) 249.6 nm, (0)244.7 nm. Solid lines represent best fit to stochastic model (Reproduced by permission from Chem. Phys., 1975, 7 , 41)

the case of quenching by NO,33thought initially to be similar to that by 0, in involving initial complex formation and resulting finally in the formation of the triplet state of the aromatic and ground state of O2 Lprocess (26)] or NO (27) in a

+ 30, + 2N0

lA lA

-

+ 30,

(26)

3A + 2 N 0

(27)

3A

spin-allowed process, the operation of a charge-transfer mechanism is now questionable, since recent values of the electron affinity of NO cast doubt on the correlation originally In the case of p-fluorotoluene plus transpiperylene (P), complex formation has been demonstrated more directly by the observation of significant non-exponentiality in the decay characteristics of the fluorescence of the aromatic molecule, although care has to be taken that this is ss s4

R. G. Brown and D. Phillips, J.C.S. Faraday ZZ, 1974,70, 1435; J. Phofochem., 1975,3,337. R. S. Davidson, A. Lewis, and T. S. Whelan, J.C.S. Chern. Comm., 1975, 203; M. E. Sime, Kh, Al-Ani, and D. Phillips, Mol. Photochem., 1976, 7, in press.

106 Photochemistry not due to vibrational relaxation. Assuming complex formation to occur, individual rate constants k- and k, were evaluated for this pair as 4 x lo7s-l, respectively, taking k , to be 2 x loll 1 mol-1 s-1.33 The same type of complex formation has been observed in the extremely efficient quenching of singlet states lA

+P

<

k+

-

8-k

kq

>[‘....PI

>

quenching

k-

of trifluoromethylbenzenes by heterocyclic molecules, although no exciplex emission was observed with these pairs as was observed by Davidson et al. in solution with other aromatics plus heterocyclic^,^^ and is also invoked, with charge transfer in the opposite sense, for quenching of benzenes in solution by halogenated the results of which confirm an earlier gas-phase The quenching of the triplet state of benzene by NO has been studied by the indirect means of the observation of growth of biacetyl phosphorescence upon flash photolysis of benzene-biacetyl The value for the quenching rate-constant obtained was 6.5 x 1081mol-1s-1, about half that for oxygen quenching, and larger than expected when considering that oxygen may quench both by electronic energy transfer and a charge-transfer process analogous to (29). The biacetyl method has been used in an investigation of the triplet state a~

+

NO

7

2 ( 3 ~ - 2 ~ 0 )

-

A

+

NO

(29)

of benzene in the vapour phase, using pulse r a d i ~ l y s i s ,in~ ~which it was shown that the rate-constants for processes (30)-(32) are, respectively, 5.2 f 3.0 x lo3 s-l, 6.6 f 2.4 x lo71mol-l s-l, and 9.6 f 4.2 x 1O1O 1 mol-1 s-l. The benzene triplet lifetime at 40 Torr pressure was found to be 6.7 f 3.2 ps. 3A 3A

+A

-

A

(30)

quenching

(31)

3A+B3B+A (where A is benzene, B is biacetyl)

An elegant molecular-beam study of the photofragmentation of aryl halides and methyl iodide has permitted extraction of excited-state lifetimes from a measured anisotropy parameter which depends upon the lifetime of excited state, the rotational correlation time of the molecule, and the orientation of the electronic transition dipole with respect to the C-X bond.38 The lifetimes obtained were methyl iodide 0.07 ps, iodobenzene 0.5 ps, a-iodonaphthalene 0.9 ps, and 4-iodobiphenyl 0.6 ps, from which it was concluded that, whereas methyl iodide dissociates directly, the aryl halides predissociate. A crossed-beam experiment using electron-beam excitation has yielded the results for the Sl-Tl intersystem-crossingrelaxation time in benzene, [2H,]benzene, fluorobenzene, and 36 38 s7

38

D. Saperstein and E. Levin, J. Chem. Phys., 1975, 62, 3560; G. Das Gupta and D. Phillips, J.C.S. Faraday II, 1972, 68, 2003. M. Schuh, H. Sporborg, and K. E. Williams, Chem. Phys. Letters, 1974,26, 541. Y. Hatano, S. Takao, and T. Ueno, Chem. Phys. Letters, 1975, 30,429; Y. Hatano, personal communication. M. Dzvonik, S. Yang, and R. Bersohn, J. Chem. Phys., 1974, 61, 4408.

107 Gas-phase Studies chlorobenzene of 110 ns, 160 ns, 48 ns, and 240 ns, respecti~ely.~~ The same method was used upon excited fragments resulting from the impact, yielding lifetimes for the J 2 A state of CH and CD of 443 ns.3g In the vapour-phase irradiation of C,H, and D2at 253.7 nm, C6H5Dis observed, with a quantum yield of formation of 0.01.40 The product is not observed at higher photon energies, and it thus seems that the exchange reaction is entirely unconnected with the channel I11 decay route, in accord with the assignment of this process to S1 So internal c o n v e r ~ i o n . ~ ~ Reactions involving excited states of benzene include the photoaddition of benzene to f ~ r a n , to ~ l ole fin^,^^ and to a m i n e ~the , ~ ~photochemical chlorination of benzenes,44the photo-oxidation of benzene,46 and the photo-reactions of tetrafluoroiodobenzene.4s These papers will be discussed in detail in Part I11 of this volume. The gas-phase structures of benzvalene and hexamethylprismane and hexamethylbenzene have been e~aluated.~' Hui and Rice4* have reported an analysis of the non-radiative relaxation of styrene, tran~-/?-[~H,]styrene, and [2H8]styrene. Their analysis depends upon the ~S values for styrene assumption that the difference between ~ N R (deactivation) and phenylacetylene is the result of a rotational (isomerization) relaxation, which is of course not possible in the acetylene. This, however, seems to be a rather gross assumption, which, given the difficulties involved in estimating ~ N R for complex molecules, may, however, be considered acceptable. The predominance of the rotational non-radiative decay is tested using the GelbartRice-FreedZ5 prediction that for small G values (where G is the difference in energy between the minimum for S1and maximum for So in the P.E. curve), relative to the energy of excitation, the excess energy is taken up predominantly in the torsional modes. It is assumed that the torsional motion of the methylene becomes a quasi-free rotation and that the isotope effect on TLm(kmbtion) must be proportional to the densities of states for the different groups. The argument is necessarily crude and the method of estimating G is questionable but, nevertheless, the ratio of densities of the free-rotor states calculated, 1.00 : 1.225 : 1.415 for CH, : CHD : CD2, is of the same magnitude as the observed ratios of kmbtion(styrene) : kmtation([2Hl]~tyrene) : kmtation([2Hs]~tyrene). The implication of the above analysis is that isomerization is a singlet-state process. However, this conclusion cannot be accepted because in the analysis of the data it is assumed that a fraction of the total non-radiative decay is represented by an intersystemcrossing process to the triplet manifold, from which all the evidence from other --f

40

H. J. Hartfuss, 2.Nafurforsch., 1974, 29a, 1431; 1489. L. Hellner and C. Vermeil, J. Chim. phys., 1974,71, 1269.

46

J. Berridge, D. Bryce-Smith, and A. Gilbert, J.C.S. Chem. Comm., 1974, 964; T. S. Cantrell, Tetrahedron Letters, 1974, 3959. J. Cornelisse, V. Y. Merrit, and R. Srinivasan, J . Amer. Chem. SOC.,1973,95, 6197; D. BryceSmith, A. Gilbert, and B. Orger, J.C.S. Chem. Comm., 1974, 334. D. Bryce-Smith, A. Gilbert, and C. Manning, Angew. Chem., 1974, 86, 350. A. A. Ushakov, G. V. Motsarev, and V. R. Rozenberg, Zhzcr. org. Khim., 1974, 10, 2183. P. S. Gukasyan, A. S. Saakyan, and A. A. Mantashyan, Armyan. khim. Zhur., 1974, 27, 83. M. Ya. Turkina, V. V. Orda, and 1. P. Gragerov, Doklady Akad. Nauk S.S.S.R., 1974, 216,

47

R. B. Kan, jun., and S. H. Bauer, J. Mol. Structure,

48

and S. H. Bauer, ibid., p. 17. M. H. Hui and S. A. Rice, J. Chem. Phys., 1974, 61, 833.

42

43

46

113.

1975,25, 1 ; R. B. Kan, jun., Y. C. Wang,

108 Photochemistry studies would indicate that isomerization would occur, this being the most efficient relaxation route for the triplet state. Thus the very assumption of comparability of intersystem-crossing rates in the styrenes and phenylacetylene leads necessarily to the conclusion that some triplet isomerization will occur in the styrenes, which thus negates the authors’ contention that isomerization is solely a singlet-state process. Recent solution-phase studies indicate that the intersystem-crossing efficiency in acyclic styrene derivatives may in fact be very low. Readers may consult ref. 49 and Chapter 2 of this volume for a further discussion of developments in this area. trans-cis Isomerization in trans-1 phenyl-2-(2-naphthyl)ethylene has been studied by laser photolysis.60 The flash photolysis of toluene cations has been shown to yield two forms of C,H,+ ions, one of which can react to give C8HB+[reaction (33)].61 The reactive form was shown to be the benzylium form, the non-reactive one the tropylium ion.

-

A high-resolution study has been carried out on the fluorescence yields and decay characteristics of naphthalene vapour in the isolated-molecule limit, using excitation bandwidths of 0.05 A.62 The results are of great interest in that they show considerable variation of the fluorescence decay time in scanning through vibronic bands, showing that rotational excitation may be an important factor in determining lifetime. The lifetime of the zero-point level was measured as 310 ns, and this probably represents the best measure of this quantity to date. The variation in decay rate with excess energy is shown in Figure 3, from which it can be seen that individual sequence bands have been resolved in this study. Only the 55 cm-l sequence bands [3(b,,) symmetry] show strong energy dependence of the decay rate, and since vibrations of this symmetry are likely to couple the S, state to nro*/an* intermediate states, they can be considered to be promoting modes for the intersystem-crossing process, although the evidence suggests that there must be other promoting modes, and that the Franck-Condon factors play as important a role in determining decay rates as do the electronic matrix elements and their vibronic enhancement. In direct contrast with the structured nature of Figure 3, the ratio of decay rates for individually selected states of perhydro- and perdeuterio-naphthalenes,k ~ / kplotted ~ , as a function of excess energy, gives a smooth curve for all vibrations except the 10cm-l sequence, irrespective of symmetry.62 Since the initial states are the same for each isomer, the smoothness of the ratio of rates as a function of excess energy suggests that 49

s1 62

M. G . Rockley and K. Salisbury, J.C.S. Perkin 11,1973,1582; H. E. Zimmerman, K. S. Kamm, and D. Wenthemann, J. Amer. Chem. SOC.,1974,96, 7821 ; ibid., 1975,97, 3718. M. Sumitani, S. Nagakura, and K. Yoshihara, Chem. Phys. Letters, 1974, 29, 410. J. M. Kramer and R. C. Dunbar, J. Chem. Phys., 1974, 60, 5122; R. C. Dunbar, J. Amer. Chem. SOC.,1975,97, 1382. U. Boesl, H. I. Neusser, and E. W. Schlag, Chem. Phys. Letters, 1975, 31, 1, 7.

Gas-phase Studies

109

Figure 3 Decay rates of vibronic leveIs in S, of [2H8]naphthaleneas a function of the excess energy. Different sequences are marked by different lines beginning at the principal bands. The notation of all vibrations under investigation is given in the scheme at the bottom of the figure (Reproduced by permission from Chem. Phys. Letters, 1975, 33, 1)

the identity of the final (triplet) vibronic state is immaterial to the overall rate, since a strong influence on the Franck-Condon factors as a result of the symmetry of the final state would give non-systematic variations of k ~ / kThe ~ . study thus implies that there is no retention of vibrational make-up in passing from singlet to triplet manifold, i.e. that rapid communication (vibrational redistribution) between final triplet states occurs, even though this is known to be absent 5

Photochemistry

110

in the singlet manifold.20 The strong inverse isotope effect noted for singlet levels excited up to 400 cm-l above the zero-point level is taken as evidence that the T, state of naphthalene is involved in the ISC process. For excess energies in naphthalene above 5000 cm-l, it has recently been shown that the Sl-+ So internal conversion becomes the dominant non-radiative decay process over the S, -f T , intersystem crossing (cf. the proposals for channel I11 in benzene).20s31 The model for vibrational relaxation mentioned earlier with respect to relaxation in a substituted benzene was first applied to the problem of relaxation in naphthalene, and the study showed conclusively that Boltzmann equilibrium was being approached from below as well as from above. The results for argon as the colliding gas gave best fits with an effective oscillator of energy 300 cm-l and a collision efficiency of 2%. These are considerably smaller than the corresponding values for the relaxation of excited singlet PFT by its ground but in the latter case some resonant processes are possible which are not available to the naphthalene-argon pairs. Fluorescence arising from naphthalene and products due to electron-impact excitation has been recorded.s3 Values of rate constants for reactions (30) and (31) for naphthalene and other aromatic molecules have been measured using flash photolysis in the vapour phase, and are given in Table 3.64 Table 3 Rate constants for decay of aromatic triplets Molecule

Naphthalene Anthracene Pyrene Acridine

T/"C

1,2;5,6-Dibenz-

20 110 110 110 200

anthracene Tetracene Chrysene

290 340

k,,/103 s-1 1.3 i-0.5 0.65 _+ 0.20 0.80 & 0.40 1.6 k 0.8 1.3 1 0.6

k3,/10101 mol-l s-l 6.0 _+ 1.0 15 k 5 8.6 k 1.5 9.7 2.0

*

-

6.0 & 3.0 10.0 k 5.0

The fluorescence decay time of anthracene vapour does not vary greatly for excess energies up to 6000 crn-l,,ls 66 but then shortens considerably. The initial invariance has been discussed in terms of displacements AQ for the symmetric carbon-skeletal vibrations in the Sl and Tl states of anthracene, which are much smaller in this molecule than in the case of other aromatic molecules, with consequent lack of sensitivity of the ISC rate constant upon excess energy in this The decrease in 7 at higher excess energies in this and 9,l O-dimethylanthracene, phenanthrene, and fluorene is discussed in terms of the onset of the S, -f Sointernal-conversion process.55 A series of papers concerned with the fluorescence of pyrene vapour has been published.6e It was shown in a temperature study that sequence congestion in the absorption process produces a distribution of emitting upper-state levels which 63 64

6s

6e

K. C. Smyth, J. A. Schiavone, and R. S. Freund, J. Chem. Phys., 1975,62, 136. C. W. Ashpole, S. J. Formosinho, and M. A. West, J.C.S. Furuduy 11, 1975,71, 615. S. F. Fischer and E. C. Lim, Chem. Phys. Letters, 1974, 26, 312; C.-S. Huang, J. C. Hsieh, and E. C. Lim, ibid., 1974, 28, 130. T. Deinum, C. J. Werkhoven, J. Langelaar, R. P. H. Rettschnick, and J. D. W. van Voorst, Chem.Phys.Letters, 1974,27,206,210,552; 28,51; C. J. Werkhoven, T. Deinum, J. Langelaar, R. P. H. Rettschnick, and J. D. W. van Voorst, ibid., 1975, 30, 504; 32, 328.

Gas-phase Studies

111

contributes to the shortening of the decay time for Sa emission compared with that for S1, although weak coupling between S2and S, states may also contribute an effect. The effect of collisions with inert gases upon the fluorescence of pyrene excited to the S3level has been studied, yielding approximate vibrational relaxation parameters. For the S1excitation process, a component having a short decay time in the fluorescence has been ascribed to a redistribution of vibrational energy from the promoting mode into other vibrational modes, and the effects of this upon the energy dependence of the rates of radiative and nonradiative decay of the molecules have also been discussed. The marked excess-energy dependence of the fluorescence-decay characteristics of tetracene vapour has again been interpreted in terms of the S, --+ Sointernalconversion process being enhanced by population of higher vibrational levels of the S1 The process has been observed directly in the case of pentacene by the recognition of transient absorption bands ascribed to hot Solevels produced in the internal conversion.68 Non-linear absorption in the laser photolysis of a n t h r a ~ e n ethe , ~ ~intramolecular photocycloaddition reaction of 1-(9-anthryl)-3(l-naphthyl)propane,60 and the quenching of fluorescence of aromatic hydrocarbons by caesium chloride 61 have been reported. 5 Carbonyl and Oxygen-containing Compounds A study has been reported in which the fluorescence decay characteristics of formaldehyde vapour excited to selected vibrational levels were Values obtained for lifetimes were up to a factor of four shorter than those reported in an earlier study by Moore et aLezbbut appear to be in agreement with the study of Sakurai et aZ.62cThe study shows that the stronger promoting mode for radiative decay is the asymmetric C-H stretch mode (v,’) rather than the expected C-C out-of-plane bending mode (Y~’)(Figure 4). Excitation of the latter appears to promote non-radiative decay, which is identified, on the basis of triplet sensitization studies with benzene, as an intersystem crossing to T1rather than the internal conversion supposed earlier, although it should be noted that ISC does not occur in isolated glyoxal, for example. The lifetimes of triplet formaldehyde have also been reported.6S The spectrophone technique has shown that a transient chemical species formed in the photolysis of acetaldehyde vapour, previously identified as an oxetan, is in fact the acetyl radical formed by the sensitized decomposition of trace amounts of bia~etyl,~* and the involvement of biacetyl in the photodecomposition of other simple aliphatic carbonyl compounds may be much more important than has been realized hitherto.

6s u4

G. R. Fleming, C. Lewis, and G. Porter, Chem. Phys. Letters, 1975, 31, 33. B. Soep, Chem. Phys. Letters, 1975, 33, 108. M. M. Fisher, B. Veyret, and K. Weiss, Chem. Phys. Letters, 1974,243, 60. J. Ferguson, A. W. H. Mau, and M. Puza, Mol. Phys., 1974, 28, 1457. L. K. Patterson and S. J. Rzad, Chem. Phys. Letters, 1975, 31, 254. (a) R. G. Miller and E. K. C. Lee, Chem. Phys. Letters, 1974, 27, 475; ibid., 1975, 33, 104; (b) E. S. Yeang and C. B. Moore, J . Chem. Phys., 1973,58, 3988; (c) K. Sakurai, G. Capelle, and H. P. Broida, ibid., 1971,54, 1412. A. C. Luntz and V. T. Maxson, Chem. Phys. Letters, 1974,26, 553. C. A. Emeis, E. Drent, E. Farenhorst, I. A. M. Hesselmann, and M. S. de Groot, Chem. Phys. Letters, 1974, 27, 17.

112

Photochemistry

Because of the lack of structure in the absorption spectra of many simple carbonyl compounds, excitation of individual vibronic features is rarely possible. However, in simple aldehydes such as glyoxal and methylglyoxal (pyruvaldehyde)66 and propynal,B6 as indeed for formaldehyde (discussed above), such studies are possible and have recently been reported. In the very thorough study by Lineberger et al. using tunable dye-laser excitation, collision-free lifetimes for 26 single vibronic levels (svl) of the lA, state of glyoxal in the 10-6-10-1 Torr range have been reported.66 Evidence was presented for very rapid rotational and vibrational collisional energy transfer, and, by monitoring emission from an entire vibronic band, the effects of the former transfer could be eliminated. Svl collisional loss-rates thus measured (for collision with

-

I

'

/

r - ' I

5'-

/

0.51

L-__L'IIIL_I---'-'--

1000

2000

3000

4000

5000

6000

E M,b(crn-')

Figure 4 Observed radiative lifetimes at 1.0 Torr versus vibrational energy of H2C0 (lA2): v i = C - 0 stretch; vq' = out-of-plane bending; v6' = asymmetric C-H stretch (Reproduced by permission from Chem. Phys. Letters, 1975, 33, 104)

ground-state glyoxal) for the 26 vibronic levels varied between gas-kinetic to seven times greater than gas-kinetic, the most efficient loss mechanism being vibrational relaxation, but with intersystem crossing also contributing. Similar studies were carried out with 24 other collision partners, and cross-sections varied between 1 and 22 x 10-l6 cm2. Correlations between results and various expressions resulting from consideration of the polarizability of the quencher, dispersion forces, and dipoledipole interactions were investigated. Good correlations were found for several of these parameters, but Lineberger et al. stress that this does not of necessity establish the mechanism as correct. For the low-lying levels of the lA, state of glyoxal, the principal quenching mechanism is a 66

e6

R. A. Coveleskie and J. T. Yardley, J. Amer. Chem. SOC.,1975,97, 1667; R. A. Berger, P. F. Zittel, and W. C. Lineberger, J. Chem. Phys., 1975, 62, 4016; R. A. Berger and W. C. Lineberger, ibid., p. 4024. C. A. Thayer and J. T. Yardley, J. Chem. Phys., 1974, 61,2487; C. A. Thayer, A. V. Pocius, and J. T. Yardley, ibid., 1975, 62, 3712.

113

Gas-phase Studies

collision-induced intersystem crossing to the 3A, state, in contrast to the fate of higher vibrational levels discussed above. In the study on methylglyoxal by Yardley et al. the absorption is shown to be due to the lA"(lA,') transition, and the 0-0 band was determined to be either at 22260 or 22090cm-l. Emission spectra show that the 3A"(3A,T) state lies approximately 2400 cm-l lower than the corresponding singlet state. The phosphorescent triplet state was found to decay exponentially, with a pressuredependent lifetime, indicating self-quenching of the triplet state, the extrapolated zero-pressure lifetime being 1.92 ms. The fluorescence decayed exponentially only at pressures above 2 Torr, with a collision-free lifetime of 20.4 ns, and a quenching cross-section of eO.08 x l0ls cm2 for added argon, that for methylglyoxal being approximately twice as large, but in both cases the effects of pressure on the singlet state are small. The results were explained on the basis of a simplified scheme which assumed irreversible non-radiative decay from singlet to triplet above 2 Torr pressure. The breakdown of this assumption is held to be responsible for the observed non-exponential decay in the singlet state at pressures < 2 Torr. In the study on propynal vapour,g6 the observed behaviour was explicable in terms of a simple model [(34)-(42)], for which individual rate-constants were N

P

+ hv lP 1P 'P

+P lP + P lP

3P 3P 3P

+P

____+

Absorption

1P

P

+h

v ~ Fluorescence

(34)

(35)

P

Collision-free IC

(36)

3Pn

Collision-free ISC

(3 7)

3Pn + So Collision-induced ISC

+P + hvp

(38)

Pn

Collision-induced IC

(39)

P

Phosphorescence

(40)

Collision-free ISC

(41)

Collision-induced ISC

(42)

Pn P,

+P

evaluated in a thorough study and, moreover, the energy dependence of the decay rates was evaluated and compared with golden-rule calculations. Vibrational energy transfer in some XzCO type molecules on collision with argon has been studied.67 The luminescence decay characteristics of biacetyl vapour have also been studied at low pressures as a function of excess energy.68 Kommandeur et al. showed that at very low pressures the decay of the optically excited lA; states into isoenergetic 3Au1states is reversible, giving rise to two components in the fluorescence decay, viz. a short (nanosecond) component and a longer component which is sensitive to pressure and excitation wavelength, extrapolating to a rate of 4.5 x lo4 s-' at zero pressure, hex = 420 nm, and 2 x lo7s-l for hex = 370 nm. 67

Y. Yonezawa and T. Fueno, Bull. Chem. SOC.Japan, 1974,47, 1894. R. Van der Werf, D. Zevenhuijzen, and J. Kommandeur, Chem. Phys. Letters, 1974,27,325; A. Z . Moss and J. T. Yardley, J. Chem. Phys., 1974,61,2883; K. Kaya, W. R. Harshbarger, and M. B. Robin, ibid., 1974, 60,4231.

114

Photochemistry

This group of workers ignore the possible fate in the vibrationally hot triplet state of intersystem crossing to the gound state, but the data have been reconsidered in the paper by Yardley ei aZ.68to include this possibility, which seems to be plausible on both experimental and theoretical grounds, and the authors show the interpretation to be consistent also with the spectrophone measure-

Figure 5 Collated data from ref. 68 for log of non-radiative decay rate of glyoxal and biacetyl relative to vibrational relaxation rate-constant a as a function of excess triplet vibrational energy. Right-hand scale assumes a = 0.96 x lo7s-l Torr-l for all triplet levels. Theoretical curves shown are -- - - retention model; - * - communicating-states model (Reproduced by permission from J. Chem. Phys., 1974, 61, 2883)

ments of Kaya et aLB8The excess-energy dependence of the intersystem-crossing process [analogous to process (41) for propynal] is illustrated in Figure 5, compared with calculations based upon the total retention of vibronic make-up in the ISC process, and those in which vibrational redistribution (communicating

Gas-phase Studies

115

states) occurs. As can be seen, neither model is particularly good at high excess energies, but the retention model is significantly better at low excess energies. The intra- and inter-molecular decay characteristics of the J1A’(lB1) state of 4-methyl-l,2,4-triazoline-3,5-diones [TAD, (l)] have been considered in a further

.

.

N=N

(I) TAD

thorough A simple model was developed to account for the observed vibrational relaxation, giving vibrational relaxation rates for the collision partners helium, argon, CCL, 02,and cyclohexane of 1.17 x 1O1O, 1.30 x lolo, 4.65 x lo@, 2.79 x lolo, and 1.4 x 101llmol-ls-l, respectively (compare glyoxal results above 66). The model used makes the assumptions that the decay rate of a vibronic state changes with and depends only upon its excess vibrational energy, but in a weak fashion; that collisional electronic quenching is negligible; and that the average vibrational energy returns to its equilibrium value according to a first-order decay. Within these assumptions, unique values of relaxation rat e-const ant s are obtained . Radiative and non-radiative rate-constants for a series of symmetrically substituted methylated 70 acetones in the vapour phase have been reported. The rate-constants for radiative decay are found to be much larger than those obtained from integration of the area under absorption profiles, and an empirical expression is derived which permits evaluation of k~ from a knowledge of the integrated absorption data and a geometry-sensitive correction factor. Non-radiative rates are found to be drastically reduced by the a,&’substitution of methyl groups, and this is ascribed to steric crowding, which suppresses the vibrational motion of the promoting mode for the Sl-+ Tl non-radiative decay. A recent paper has, on the basis of simple calculations, ascribed the increase in rate-constant for nonradiative decay of excited singlet states of 1,3-dichlorotetrafluoroacetoneand chloropentafluoroacetone with excess energy to the onset of an S, -+ Sointernalconversion process, which in the case of the more heavily fluorinated molecule is already as fast as the S1-+ Tlprocess at an excess energy of 5000 cm-1.71 Clearly, if the internal-conversion process does occur as the model suggests, there are significant implications for the interpretation of kinetic data for the photochemistry of simple aliphatic ketones, much of which in the past has concentrated exclusively on triplet-state decomposition processes. The kinetics of the formation of ethane from methyl radicals in the flash photolysis of acetone v a p ~ u r the , ~ ~interaction of nr* states of alkanones with EB ‘O ‘I1

A. V. Pocius and J. T. Yardley, J. Chem. Phys., 1974, 61,2779, 3587. D. A. Hansen and E. K. C. Lee, J. Chem. Phys., 1975, 62, 183. P. A. Hackett and D. Phillips, J. Phys. Chem., 1974,78, 665; G. D. Gillespie and E. C. Lim, Chem. Phys. Letters, 1975, 34, 513. M. L. Pohjonen, L. Leinonen, H. Lemmetyinen, and J. Koskikallio, Finn. Chem. Letters, 1974,207.

116

Photochemistry

electron-rich e t h y l e n e ~ ,and ~ ~ various aspects of the chemistry of the excited states of pentan-2-one have been A recent study on the rate of formation of products from excited hexafluoroacetone in the presence of a vibrational relaxer and azoalkanes as triplet quenchers has produced data which the authors use to support the notion that vibrational relaxation in the singlet manifold is a multistep collisional process.76 The reaction between excited perfluoroacetone and ethane 76 and the photochemistry of hexafluorobiacetyl vapour 77 have also been discussed. Processes (43) and (44) were found to predominate in the photolysis of cyclobutanone at 147 and 123.6 nrn,'* with aa3/Od4= 0.95 at 147nm and 0.45 at

do+ hv U

-

CH,CO + CH2=CH2 'CH2CH2CH2*-1- CO

(43) (44)

123.6 nm, at the limiting high pressure. No electronically excited CO was observed, although this is thermochemically possible, and the authors discuss the possibility that an excited CO species is formed but quenched before observation because of the long radiative lifetime and high pressures pertaining in these experiments. The photochemistry of perfluorocyclobutanone (PFCB) has been reinvestigated and conclusions have been reached which are irreconcilable with those in an earlier In the earlier report the two decomposition routes (45) and (46) were proposed as excited singlet-state reactions, with the relative importance being dependent upon excess energy. However, the recent study PCFB

+ h~

-

+ CO C2F4 + CFZCO

C-GF6

(45) (46)

at lower pressures has revealed unequivocally that process (45) is a triplet-state decomposition process, since it can be sensitized by the 3Blustate of benzene, and that (46) arises from a hot Sostate of the ketone, produced by internal conversion from S1.Furthermore, the C F 2 C 0 product in (46), which was observed experimentally in neither system, can reasonably be shown to dissociate further to give CF2 and CO, the CF2 then recombining to form C2F4 [processes (47), (48)]. CF2CO CF2

+ CF,

-

CF2 C2F4

+ CO

(47) (48)

The failure in the earlier study to observe the production of large quantities of C2F4 was due to the quenching out of the hot ground-state reaction because of 73

74

76

78

N . E. Schore and N. J. Turro, J. Amer. Chem. SOC.,1975,97, 2482. H. E. O'Neal, R. G. Miller, and E. Gunderson, J . Amer. Chem. SOC.,1974, 96, 3351; E. B. Abuin, M. V. Encina, and E. A. Lissi, J. Photochem., 1974, 3, 143; M. V. Encina, H. Soto, and E. A. Lissi, ibid., 1975, 3, 467; M. V. Encina, A. Nogales, and E. A. Lissi, ibid., 1975, 4, 75. F. M. Servedio and G . 0. Pritchard, Internat. J. Chem. Kinetics, 1975, 7 , 195. A. S. Gordon, W. P. Norris, R. H. Knipe, and J. H. Johnson, Internat. J. Chem. Kinetics, 1975, 7, 15.

77 78

79

G. B. Porter and W. J. Reid, J. Photochem., 1974, 3, 27. B. G. Gowenlock, P. John, and C. A. F. Johnson, J. Photochem., 1974, 3, 45. D. Phillips, J. Phys. Chem., 1966, 70, 1235; R. S. Lewis and E. K. C. Lee, ibid., 1975, 79, 187; J. Chem. Phys., 1974, 61, 3434.

Gus-phase Studies

117

the high pressures used in the study, and the quantum yields of CO production in the former study are also too high. The photochemistry of this ketone has thus been shown to resemble closely that of its perhydro-analogue. The fluorescence decay time of the ketone was determined as 110 ns under isolatedmolecule conditions for excitation near the zero-point level at 410 nm. A brief study has been carried out on the photophysics of benzaldehyde vapour excited to the S1and S, states.8o Excitation spectra for S1fluorescence were recorded for excitation to the Sl, Sz,and S, levels, from which the variation in fluorescence quantum yield was extracted as a function of excess energy, and the results were compared to those from photochemical studies. A recent study on the emission of benzophenone vapour has cast doubts on previous interpretations of observed behaviour.81 The sharp decrease in lifetime observed in one of the earlier studies with increase in pressure, and attributed to an efficient selfquenching, is in fact an experimental artefact due to the use of change in temperature to produce change in pressure. The self-quenching rate-constant for the long-lived emission component is in fact small, being 9 x lo6 1mol-l s-l at 25 "C and 1.2 x lo7 1mo1-1 s-l at 170 "C, but at increased temperatures the lifetime decreases because of the onset of efficient temperature-dependent non-radiative physical and chemical decay paths. It was further shown that the short-lived emission from benzophenone may have a 'lifetime' which is dictated by wall collisions under the conditions of earlier experiments, thus accounting for the lack of agreement between the two sets of workers. The measurement of ISC kinetics using picosecond pulses as probes has been carried out for benzophenone and nitronaphthalenes.82 the vacuumThe photochemistry of 7-ketonorbornane in the vapour U.V. photochemistry of diethyl ether,84the flash photolysis of methyl f ~ r m a t e , ~ ~ and the far4.r. laser action in optically pumped CD,OD 86 have been reported. N

6 Nitrogen Compounds Simple oxides of nitrogen are covered in the final section of this chapter. The lifetimes of various levels of the J2Z-, J2h,and c2E+states of NH+ (and OH+ and SH+) have been determined and found to lie between 1.09 ps and 390 13s.~' Emission from the JzAl, @E, and states of the neutral NH species produced in the photolysis of ammonia in the vacuum-u.v. has been observed.8s Threshold energies for various products were determined as shown in Table 4.

clII

8o

82

J. Metcalfe, R. G. Brown, and D. Phillips, J.C.S. Faraday ZZ, 1975, 71, 409. G. E. Busch, P. M. Rentzepis, and J. Jortner, J. Chem. Phys., 1972, 56, 361; R. M. Hochstrasser and J. E. Wessel, Chem. Phys. Letters, 1974, 19, 156; J. A. Bell, M. Berger, and C. Steel, ibid., 1974, 28, 205. R. W. Anderson, R. M. Hochstrasser. H. Lutz, and G. W. Scott, Chem. Phys. Letters, 1974, 28, 153.

83 84

T. F. Thomas and B. Matuszewski, J. Phys. Chem., 1974,78,2637. C . A. F. Johnson and W. M. C. Lawson, J.C.S. Perkin ZZ, 1974, 353. S. L. N. G. Krishnamachari, Photochem. and Photobiol., 1974,20, 33. S . Kon, E. Hagiwara, T. Yano, and H. Hirose, Japan. J. Appl. Phys., 1975, 14, 731. J. Brzozowski, N. Elander, P. Erman, and M. Lyyra, Physica Scripta, 1974, 10, 241. M. Kawasaki and I. Tanaka, J. Phys. Chem., 1974, 78, 1784; C. Vermeil, J. Masanet, and A. Gilles, Znternat. J. Radiation Phys. Chem., 1975,7, 275; J. Masanet, A. Gilles, and C. Vermeil, J. Photochem., 1975, 3, 417.

Photochemistry

118

-

Table 4 Threshold energies in ammonia decomposition NH,

Reaction NH(Z3C-)

+ HZ(lXu+) NH,(f2B,) + H(V) NH(6lA) + H,(lCI,+) NH,(32A,) + H(,S) NH(hlC+) + Hz(lZU+) NH(J3n) + H2(lCg+) NH(Z3C-) + H(2S) + H(%) NH(2lII) + HZ(lXu+) HN(6lA) + H(2S) + H(2S) NH3+ + e NH(h%+) + H(%) + H ( V ) NH(A"SII) + H(%) + H(2S)

EIeV 3.9 rf: 0.1

No. (49)

4.4 f 0.1

(50)

5.5 & 0.1

(51)

5.7 zk 0.1

(52)

6.6 rf: 0.1

(53)

7.6 rf: 0.1

(54)

8.4 & 0.1

(55)

9.3

(56)

* 0.1

9.9 rf: 0.1 10.14

(57) (58)

11.1 rf: 0.1

(59)

12.1

(60)

_+

0.1

The NH2 produced in reaction (50) has been studied by laser-excited fluore s c e n ~ e and , ~ ~ the rate of the reaction between ground-state NH2 and NO was determined as 1.26 x 1O1O 1mol-l s-l at 298 K. Laser excitation has allowed evaluation of radiative lifetimes of individual rotational levels in CN B2Z+,that of the unperturbed levels being 65.6 & 1.0 ns, but that for the K' = 4 level being longer, 72 i- 1 ~ S . ~ OThe quenching crosssection of the state was found to be 41 rt 20 x 10-l8cm2, independent of rotational energy. The CN observed in this study was produced by the photolysis of C2N2. Laser emission from various levels in the CN + Z2X+and groundstate vibrational transitions has been observed upon photolysing HCN, CCN, BrCN, ICN, CaN2,CH3NC, CF,CN, and C2FbCN.91Vibronic populations and angular distributions of products arising from such molecules in photofragment spectroscopic studies D2 have been discussed more fully in Chapter 1. The bonddissociation energy of NCNO has been determined as 28.8 & 2.5 kcalmol-', the weakest yet measured for a C-nitroso-compound.e3 The photoionization yields of trimethylamine, dipropylamine, di-isopropylamine, and tetramethylene sulphide at 147 nm have been determined as 0.38, 0.46, 0.096, 0.15, and 0.10 respectively, and their use as actinometers at this wavelength has been Photoionization and ion-molecule reactions in propyl-, ethyl-, diethyl-, and triethyl-amines have also been and striking differences between the vapour-phase and solution-phase photochemical 89

go

92

83 g4

85

G . Hancock, W. Lange, M. Lenzi, and K. H. Welge, Chem. Phys. Letters, 1975, 33, 168. W. M. Jackson, J. Chem. Phys., 1974, 61, 4177. G. A. West and M. J. Berry, J . Chem. Phys., 1974, 61, 4700. M. J. Berry, Chem. Phys. Letters, 1974,27,73; 29,323, 329; Y.B. Band and K. F. Freed, ibid., 28, 328; J. P. Simons and P. W. Tasker, Mol. Phys., 1974,27, 1691. B. G. Gowenlock, C. A. F. Johnson, C. M. Keary, and J. Pfab, J.C.S. Perkin 11, 1975, 351. D. Salomon and A. A. Scala, J. Chem. Phys., 1975,62, 1469. J. M. Brupbacher, C. J. Eagle, and E. Tschuikow-Roux, J. Phys. Chem., 1975,79, 671.

Gas-phase Studies 119 reactivity of dimethylamine The mechanism of quenching of singlet and triplet states by amines has also been commented upon.e7 The radiative properties of the two related saturated amines ABCO (2) and ABCU (3) have been measured in the vapour phase.gs For ABCO, measured

(2)ABCO

(3) ABCU

values of kR agreed well with values from integrated absorption calculations, but this was not so for ABCU, the calculated value being only 0.6 of the measured value, indicating vibronic activity in the radiative processes of the latter compound. Measured ka, r , and OF values at zero pressure were 1.1 x lo7, 91 ns, and 1.0 for ABCU; 2.75 x lo6, 363 ns, and 1.0 for ABCO. The compounds are thus strongly fluorescent. At higher concentrations, ABCO was shown to give rise to vapour-phase excimer emission, with a quantum yield of about 0.2, and formed by the head-on approach of two ABCO molecules. The excimer formation could be enhanced by addition of up to 90 Torr of n-hexane. The photo-oxidation of CDsNzCD3,eethe photolysis of azocyclohexane alone and in the presence of Oz,looand the photolysis of l,l,l-trifluoromethylazomethane as a source of CF3 and CH;, radicalslO1 have been reported. Other studies of interest are concerned with the flash photolysis of hydrazine,loZthe photolysis of H,O,-p-nitrosodirnethylanilin~O, mixtures,103 temperaturedependent relaxation processes in electronically excited n i t r o ~ a m i d e the , ~ ~flash ~ photolysis of difluoramine lo5 and the difluoroamino radical,lo6and the lifetime of the #I'I state of PN.lo7 The photophysics of aniline has been discussed in Section 4 of this chapter. The fluorescence decay time of b-naphthylamine vapour has been shown to decrease from 14.0 to 0.50 ns for excitation wavelengths of from 347 to 215 nm.2g The shortening is ascribed to the onset of a new non-radiative decay mode (internal conversion to So) in the upper Sllevels of the molecule, and a discontinuity is observed at the onset of Szexcitation. Intramolecular vibrational redistribution is shown to be slow compared with electronic relaxation. The K. G. Hancock and D. A. Dickinson, J. Org. Chem., 1975,40, 969. R. H. Young, D. Brewer, R. Kayser, R. Martin, D. Feriozi, and R. A. Keller, Cunad.J. Chem., 1974, 52, 2889; H. T. Masuhara, Y. Tohgo, and N. Y. Mataga, Chem. Letters, 1975, 59. A. M. Halpern, J. Amer. Chem. SOC.,1974, 96, 4392, 7655. J. Weaver, R. Shortridge, J. Meagher, and J. Heicklen, J . Photochem., 1975, 4, 109. l o o J. C. Currie, H. W. Sidebottom, and J. M. Tedder, J.C.S. Faruday I, 1974, 70, 1851. lol N. L. Craig and D. W. Setser, Internat. J. Chem. Kinetics, 1974, 6, 517. loa M. Arvis, C. Devillers, M. Gillois, and M. Curtat, J. Phys. Chem., 1974, 78, 1356. lo3 M. Hatada, I. Kraljic, and A. El-Samahy, J . Phys. Chem., 1974, 78, 888. lo* R. S. Lowe, J. N. S. Tam, K. Hanaya, and Y. L. Chow, J. Amer. Chem. SOC.,1975,97,215. lo5 V. M. Zamanskii, E. N. Moskvitina, and Yu. Ya. Kuzyakov, Bull. Moscow Univ., Chem., O7

1974, 544.

'06

lo'

R. J. Collins and D. Husain, J. Photochem., 1974, 2, 459. M. B. Moeller, M. R. McKeever, and S. J. Silvers, Chem. Phys. Letters, 1975, 31, 398.

120

Photochemistry

extremely short fluorescence decay time of pyrazine has been roughly measured, using synchrotron radiation, as 0.5 k 0.2 ns.24 The radiationless decay in the aza-benzenes has also been investigated directly, using the spectrophone technique.lo8 Two classes of behaviour were observed. In pyridine, pyridazine, sym-tetrazine, and sym-triazine, relaxation rates from nn* and ~ n excited * states were equally fast (implying k > lo6s-l), but in the presence of biacetyl the inn* relaxation in pyridine and sym-triazine was noticeably slowed, although this was not observed in pyridazine or sym-tetrazine. The inn* relaxation rates were unaffected by biacetyl. By contrast, in pyrazine, pyrimidine, and 2,6-dimethylpyrazine the inn* relaxation rate was significantly lower than from the lmr* state, and even lower when biacetyl was added. The results indicated that an Sl(m*)-+T3relaxation opened up within the S1envelope, and that relaxation of the S2(n7r*)levels to the ground state avoided S,, T,, and Tl levels. Diazanaphthalenes have also been investigated in the vapour phase.lo9 With respect to the 1,4-isorner quinoxaline, the two studies differ somewhat in reported rate parameters for wavelength dependence of lifetime of the long-lived fluorescence and quantum yield, but the studies agree on the fact that fluorescence decay in this compound for excitation into the nn*SZlevel is non-exponential owing to anharmonic coupling between triplet levels both strongly and weakly coupled to the singlet state (intermediate-case behaviour). Excitation of quinoxaline and quinazoline into the nn*(S1) state produces statistical-limit intersystem crossing (exponential fluorescence decay), and the degree of nonexponentiality observed for S, excitation is dependent on wavelength, intermediate-case behaviour giving way to statistical behaviour at high excitation energies. The fact that the 3B2triplet lifetime, when extrapolated to zero pressures, it close in value to the low-temperature condensed-phase value seems to argue against rotational degrees of freedom playing an important part in determining non-radiative decay rates, as proposed by Hunter et aZ.losa Luminescence from phenyloxazole and benzoxazole derivatives in the vapour phase has been reported.109b 7 Sulphur Compounds

SO, is discussed in the last section of this chapter. The dye-laser photodetachment of electrons from SH- has a threshold at 538.7 nm, indicating an electron affinity for *SH of 2.301 eV.l1° The reaction rate between CS and Oa (61)

cs + oa

__I_,

ocs + 0 co + so

1

between 300 and 670 K in a flow tube has been shown to be very small, with a rate constant < lo41 mol-1 s-l.ll1 The fluorescence of the lA2 state of CS, has lo8

K. Kaya, C. L. Chatelain, M. B. Robin, and N. A. Kuebler, J. Amer. Chem. Soc., 1975, 97, 2153.

log

110

ll1

J. R. McDonald and L. E. Brus, J. Chem. Phys., 1974, 61, 3895; B. Soep and A. Tramer, Chem. Phys., 1975, 7 , 52; (b) N. A. Borisevich and L. A. Barkova, Actu Phys. Chem., 1974, 20,251. J. R. Eyler and G . H. Atkinson, Chem. Phys. Letters, 1974, 28, 217. W. H. Breckenridge, W. S. Kolln, and D. S. Moore, Chem. Phys. Letters, 1975, 32, 290.

(a) T. F. Hunter and M. G. Stock, Chem. Phys. Letters, 1973,22, 308;

121

Gas-phase Studies

been shown to be quenched by a factor of two by a magnetic field of strength 12.6 kG,l12 presumably through enhancement of intersystem crossing from the singlet state. Aspects of the C 0 2chemical laser from the photochemical CS2-Oz reaction have been discussed.l13 The rate-constant for reaction (62) has been found to be of Arrhenius form, k,, = [(1.52 k 0.20) x 10-l2exp (- 3.63 k 0.12) kcal m0l-~/RT1 cm3 moleS(3P) +

ocs

-

co + S,(32)

(62)

cule-l s-l.ll* Quantum yields for the production of S(lS) from the photolysis of OCS have been shown by Black et al. to range from -0.8 in the 142-160 nm region to less than 0.1 below 140 nm,ll5 CO laser emission has been observed in this system by Lin,l16and shown to be due entirely to reaction (63), (64) being

ocs + hv S(1D) + ocs

-

___j

cot + S(1D) s2* + co

(63)

(64)

unimportant. The abstraction of sulphur atoms from OCS by H atoms has been discussed.lls Strong fluorescence (quantum yield from zero-point level = 0.7 k 0.3) has been observed from the lower-lying levels of the second excited singlet state of thiophosgene vapour.l17 The energy-level spacings of this relatively small molecule are such as to favour fluorescence from low-lying levels. Excitation to levels higher than the 3l state (147 cm-1 above Oo) or 4' (38 cm-l above Oo) does not result in observable fluorescence, presumably because excitation of two quanta of the out-of-plane bending mode is sufficient to overcome the inversion barrier and promote rapid non-radiative decay. The photolyses of H2Se,l18dimethyl sulphide, dibutyl sulphide, and methyl vinyl sulphide,ll@and dimethyl sulphoxide,120the role of concerted and hot biradical reactions in the photolysis of thietan and thietan-cyclopentadiene mixtures,121 and the photolysis of aromatic sulphur compounds 122 have been reported. 112 119

11* 116

A. Matsuzaki and S. Nagakura, Chem. Letters, 1974, 675. A. B. Petersen and C. Wittig, Chem. Phys. Letters, 1974, 27,

442; M. P. Popovich and Yu. N . Zhitnev, Vestnik Moskov. Univ., Khim., 1974, 15, 537. R. B. Klemm and D. D. Davis, J . Phys. Chem., 1974,78, 1137. M. C. Lin, Chem. Phys., 1975, 7, 442, 443; G. Black, R. L. Sharpless, T. G. Slanger, and D . C. Lorents, J. Chem. Phys., 1975,62, 4274. S . Tsunashima, T. Yokota, I. Safarik, H. E. Gunning, and 0. P. Strausz, J . Phys. Chem., 1975, 79, 775.

11'

11*

S. Z.Levine, A. R. Knight, and R. P. Steer, Chem. Phys. Letters, 1974, 29, 73; R. P. Steer, personal communication. D. C. Dobson, F. C. James, J. Safarik, H. E. Gunning, and 0. P. Strausz, J. Phys. Chem., 1975, 79, 771.

llD

M. Casagrande and G. Gennari, Gazzetta, 1974, 104, 1251; R. A. Cox and F. J. Sandalls, Atmos. Environment, 1974, 8, 1269; G. Leduc and Y. Rousseau, Canad. J. Chem., 1975, 53, 483.

lZo lal

A. M. Koulkes-Pujo, F. Barat, and J. C. Mialocq, J. Photochem., 1974, 2, 439. D. R. Dice and R. P. Steer, J. Amer. Chem. SOC.,1974,96,7361; Canad. J . Chem., 1974,52,

122

3518. F. C. Thyrion, J. Phys. Chem., 1974,78, 1442; A. Granzow, ibid., p. 1441.

122

Photochemistry

8 Halogenated Compounds Halogenated ketones and cyano-compounds have been covered in Sections 5 and 6, respectively, and the photofragment spectroscopy of the latter has been covered in more detail in Chapter 1. Photoionization of I2123 and CHJ 124 and photodissociation of the diatomic negative ions of halogens 12s have been discussed. The photolysis of alkyl iodides and the reactions of excited iodine atoms continue to excite interest owing to their importance in the iodine photochemical laser system. The quantum efficiency for the production of I(2P&from the photolysis of I2 near 500nm has been reported,126and the rate-constants for total quenching [reactions (65) and (66)] of this species by 12,CH31, CD31, CFJ, and CzFshave been given as 12' 2.16 k 0.2 x lolo, 1.56 k 0.36 x lolo, 2.76 k 0.48

+ CX31 I(2Pt)

+ CX,I

-

I(2Pt)

I2

+ CHJ

+ cx3

(65)

(66)

x lo6, 2.4 x lo5, and 2.58 x lo5lmol-ls-l, respectively. In the case of quenching by CH31, the physical quenching dominates, whereas for CDsI the chemical route is preferred. Donovan et al. have rationalized the greater quenching efficiency of CH31 compared with CDJ by considering conditions necessary for resonant energy transfer of electronic energy to vibrational and rotational energy in the iodide. For matching, CH31requires the excitation of three quanta, whereas CDsI requires four quanta, and consequently has lower probability. The reactions of I(2P*)with NOC1,12*the photolyses of propyl and isopropyl iodide,12e and various processes in the CF31photochemical laser 130 and in the heptafluoroiodopropane laser 131 have been reported. The yield of excited iodine atoms from the photolysis of simple alkyl iodides 132 and the kinetics of reaction (67) in the vacuum-u.v. photolysis of alkyl iodides 133 have been discussed. Support has recently been given by the information-theoretic approach to electronically nonadiabatic processes discussed in Chapter 1, that the two greatly different energy 123

lZ4 lZ6 lZ6

12'

lZ8 lZg

IS1 Isa ls3

G. Petty, C. Tai, and F. W. Dalby, Phys. Rev. Letters, 1975,34, 1207. V. S. Ivanov and F. I. Vilesov, Optika i Spektroskopiya, 1974.36, 1023. R. Rackwitz, D. Feldmann, E. Heinicke, and H. J. Kaiser, Z . Naturforsch., 1974,29a, 1797. D.H.Burde, R. A. McFarlane, and J. R. Wiesenfeld, Phys. Rev. (A), 1974,10,1917. K. Hohla and K. L. Kompa, 2. Naturforsch., 1972,27a, 938;D. Haafland and R. Meyer, Internat. J . Chem. Kinetics, 1974, 6, 297; R. J. Donovan and C. Fotakis, J. Chem. Phys., 1974, 61, 2159; R. J. Butcher, R. J. Donovan, C. Fotakis, D. Fernie, and A. G. A. Rae, Chem. Phys. Letters, 1975,30, 398;D. H.Burde, A. McFarlane, and J. R. Wiesenfeld, ibid., 1975,32, 296. L. G. Karpov, A. M. Pravilov, and F. I. Vilesov, Khim. vysok. Energii, 1974,8,483. S. V. Kuznetsova and A. I. Maslov, Kuantovaya Elektron (Moscow), 1973, 31; L. G. Karpov, A. M. Pravilov, and F. I. Vilesov, Khim. vysok. Energii, 1974,8,489;V. G . Seleznev and G. A. Skorobogatev, Zhur. obshchei Khim., 1974,44,2260. S . V. Kuznetsova and A. I. Maslov, Kratk. Soobshch. Fiz., 1973, 10, 18; R. E. Palmer and M. A. Gusinow, J. Quantum Electron, 1974, 10,615;J. Appl. Phys., 1974, 45,2174; M. A. Gusinow and J. R. Freeman, ibid., 1975,46,796;R. Srinivasan and J. R. Lankard, J. Phys. Chem., 1974,78,951;V. G. Seleznev and G. A. Skorobogatev, Zhur. obshchei Khim., 1974, 44, 1293;G. A. Skorobogatev and V. M. Tret'yak, Zhur. Tekh. Fiz., 1974, 44, 784; H.J. Baker and T. A. King, J. Phys. ( D ) , 1975,8,L31. W. T. Silfvast, L. H. Szeto, and 0. R. Wood, Appl. Phys. Letters, 1974,25, 593. G. A. Skorobogatev, V. S. Komarov, and V. G. Seleznev, Doklady Akad. Nauk. S.S.S.R., 1974,218, 886;T. Donohue and J. R. Wiesenfeld, Chem. Phys. Letters, 1975,33, 176. M. R. Levy and J. P. Simons, J.C.S. Faraday 11, 1975,71,561.

Gas-phase Studies He

+ CH31 + ClI

H*

__I,

+ CH,. + I(2P+) HCl + I('P*) HI

HCI

distributions found in the reaction of hydrogen atoms with ICI and Iz do in fact correspond to two different reactions (68) and (69), one of which produces I(2Pt).134H-atom abstraction reactions of CF, and CDs have also been disand papers reporting the photolyses of HI and DI in 3-methylpentane between 20 and 300K,13s the quenching of electronically excited Iz,137and the quenching of I(2P&by slow electrons 13* have appeared. The question of the mechanism of recombination of ground-state halogen atoms, including iodine atoms, has again attracted some interest.139 In the presence of NO and helium, Troe et al. established the mechanism as (70) and (71). The bond-energy of I N 0 was established as 21 f 3 kcalmol-l. The I+NO+He I+INO

_I__+

INO+He

(70)

_____+

I,+NO

(71)

overall rate of recombination of I atoms in the presence of NO was reported by Meyer to be 2.4 f 1.4 x 1013l2 mo1-2 s-l. The absolute rate constant for the combination of the CsF7radical with ground-state iodine atoms has been obtained 140 and electronic to vibrational energy-transfer reactions of the type (72)

X* + CO

-

X

+ Cot

(X = 0,I, or Br)

(72)

have been studied.141 The effect of halide atoms on the photochemistry of aromatic diazoketones has been reported.lQ2 The photolyses of methyl chloride 143 and its positive ion, ethyl chloride,lq4 and carbon tetrachloride145have been described. In the last study an increase in photon energy was shown to favour molecular fragmentation processes. The electron affinity of the CF3 radical has been shown from electron-detachment J. B. Anderson and R. T. V. Kung, J. Chem. Phys.,

1974, 60, 2202; M. A. Nazar, J. C. Polanyi, and W. J. Skrlac, Chem. Phys. Letters, 1974, 29, 473; U. Dinur and R. D. Levine, ibid., 1975, 31, 410. 136 T. N. Bell, P. Slade, and A. G. Sherwood, Canad. J . Chem., 1974, 52, 1662. 130 L. Perkey and J. E. Willard, J. Chem. Phys., 1974, 60, 2732. lY7 E. D. Bugrim, S. N . Makrenko, and I. L. Tsikora, Optika i Spektroskopiya, 1974, 37, 1065. 13* Yu. A. Tolmachev, Optika i Spektroskopiya, 1975,38, 814. 130 B. P. Dumov and G. A. Skorobogatev, Kinetics and Catalysis (U.S.S.R.), 1974, 15, 940; A. A. Filyukov and V. B. Mitrofanov, Doklady Akad. Nauk. S.S.S.R., 1974, 219, 403; W. K. Hackmann and A. Mann, Chem. Phys. Letters, 1974,28, 72; K. Luther and J. Troe, ibid., 1974, 24, 85; H. van den Bergh and J. Troe, ibid., 1975, 31, 351; H. W. Chang and G. Bums, J. Chem. Phys., 1975,62, 2426. 140 G.A. Skorobogatev, V. S. Komarov, and V. G. Seleznev, Zhur. tekhn. Fiz., 1974,44, 1996. 141 M. Lin and R. Shortridge, Chem. Phys. Letters, 1974, 29, 42. 14!d A. P. Martynenko and V. S. Korsakov, Zhur. fit. Khim., 1974,48, 1826. A. K. Basak, J . Indian Chem. SOC.,1973,50,767; M. Vestal and J. Futrell, Chem.Phys. Letters, 1974,28, 559; T. Baer, A. S. Werner, and B. P. Tsai, J. Chem. Phys., 1974, 61, 5468. 144 L. Cremieux and J. A. Herman, Canad. J. Chem., 1974, 52, 3098. 146 D.D. Davis, J. F. Schmidt, C. M. Neeley, and R. J. Hanrahan, J. Phys. Chem., 1975,79, 11.

Ia4

124 Photochemistry measurements on CF,- to be 2 eV.las Reactions of CBr, with H2 and D214' and the reactions of radicals produced from photoexcited bromoform, bromodichloromethane, and CBr, with olefins have been described.la8 Detailed studies of the chlorine-atom-sensitized oxidation of chloromethane, dichloromethane, 1,1,2-trichloroethane, CH2CC12,and C2C1, 148 have been reported. Reports on the photolysis of Freons of interest to upper-atmosphere chemistry are discussed in the last section of this Report, and laser enhancement of some halogen-containing molecular reactions is discussed in Section 11. A paper concerned with the mechanism of photodissociation of alkyl and aryl halides was discussed earlier.s8 The photochemical chlorination of 1,Zdichloroethane laDand fluorination of carbonyl fluoride,lS0reactions of C102 radicals,lS1and the photochemical decomposition of F20 at elevated temperatures 152 have been reported. 1.r. lasers based upon photochemically excited chloroethylene~,~~~ yielding vibrationally excited HCl, have been discussed in great detail, and a simple model has been developed to explain vibronic state distributions. There is insufficient space here to do credit to the arguments outlined in this extensive article, but interested readers are recommended to study it. The reactions of vibrationally excited HC1 with 0 and H atoms have also been reported.lS4 Absolute rate-constants for reactions of chlorine atoms with HX (where X = Br or I) [reaction (73)] have been determined as 4.56 x lo@and 5.76 x l o l l 1 N

C1

+ HX

-

HCl(v 2 0)

+X

(73)

mol-1 s-l for X = Br and I, respectively. The rate-constant for the deactivation process C1 HCI (u = 1) was also measured as 4.56 x lo* 1mol-l s-1.165 Various reports relevant to the H2-Fa photochemical laser system have also appeared,16*and reactions of F atoms with several species 16' have been discussed.

+

9 Atom Reactions This year, reactions of noble gases are covered in this section, but, as before, reactions of 0, H, and N atoms are covered in the atmospheric section (Section 146

14'

149

I6O

161 162

Is3 lS4 16*

J. H. Richardson, L. M. Stephensen, and J. I. Brauman, Chem. Phys. Letters, 1975, 30, 17. S. Hautecloque, T. Minh, and N. Nguyen, Compt. rend., 1975, 280, C, 609. K. Shinoda and S. Anzai, Nippon Kagaku Kaishi, 1974, 1584; G. Mathias, E. Sanhueza, I. C. Hisatsune, and J. Heicklen, Canad. J. Chem., 1974, 52, 3852; J. C. Gibb, J. M. Tedder, and J. C. Walton, J.C.S. Perkin II, 1974, 807; D. S. Ashton, D. J. Shand, J. M. Tedder, and J. C. Walton, ibid., 1975, 320; E. Sanhueza and J. Heicklen, J. Photochem., 1975, 4, 17; J. Phys. Chem., 1975, 79, 7. A. S. Bratolyubov and G. S. Goncharenko, Zhur. priklad. Khim., 1974, 47, 708. M. I. Lopez, E. Castellano, and H. J. Schumacher, J. Photochem., 1974, 3, 97. M. A. A. Clyne and D. J. McKenney, J.C.S. Faraday II, 1975,71, 322. D . Soria and 0. Salinovich, J. Fluorine Chem., 1974, 4, 437; E. Ghibaudi, J. E. Sicre, and H. J. Schumacher, 2.phys. Chem. (Frankfurt), 1974, 90,95. M. J. Berry, J. Chem. Phys., 1974, 61, 3114. D. Arnoldi and J. Wolfrum, Chem. Phys. Letters, 1974, 24, 234. F. Wodarczyk and C. B. Moore, Chem. Phys. Letters, 1974, 26, 484. R. D. Levine and 0. Kafri, Chem. Phys. Letters, 1974, 27, 175; J. F. Bott, J. Chem. Phys., 1974, 61, 3414; L. M. Peterson, G. H. Lindquist, and C. B. Arnold, ibid., 1974, 61, 3480; G. P. Quigley and G. J. Wolga, ibid., 1975, 62, 4560; D. B. Nickols, K. H. Wrolstad, and J. D. McLure, J . Appl. Phys., 1974,45, 5360; 0 . M. Batovskii and V. I. Gur'ev, Kvantovaya Elektron, 1974, 1446. J. G. Moehlmann, J. T. Gleaves, J. W. Hudgens, and J. D. McDonald, J. Chem. Phys., 1974, 60,4790; J. G. Moehlmann and J. D. McDonald, ibid., 1975,62, 3061; J . H. Parker, Chem. Kinetics, 1975, 7, 433.

125

Gas-phase Studies

12). Many halogen-atom reactions have been discussed in the previous section and will not be repeated here. Chlorine-atom reactions of possible stratospheric importance are also to be found in Section 12. Lifetime measurements on the following states of noble gases have been reported: He(23P), 125 & 7 ns;158 Ne+(2Df), 8.0 ns;15DAr(4S3, 7.2 ns; Ar(2F&, 8.8 ns; Ar(,F+), 8.0 ns;lSo Ar+(T&),8.8 ns; Ar+(2Pa), 8.7 ns; Ar+(,Pt), 9.4 ns; Ar+(,Dt), 9.8 ns; Ar+(,Dt), 9.1 ns;15Band the Kr+(Sp) levels and Xe (I) and Xe (11) and Xe+(6p) ~ t a t e s . ~ The ~ ~ ~excitation of low-lying excited states of Ne (I) and He (I) by He+ + Ne collisionsls2 and the measurement of the fluorescence yields of Ar and C by electron impact have been discussed.ls3 Rate-constants for several reactions of Ar(3P) and Ar(lP) atoms and Xe atoms have been measured.ls3 Rate-constants are given in Table 5. Excitation of Table 5 Rate-constants for noble-gas reactions lS3

+ O(3P) O*(3P)+ Ar(lS0) Ar(lPl) + C2H4 Ar(3P2)+ C2H4 Ar(3P,) + N#&+) Xe(Vl) + Ares,) AI-(~P,)

Reaction

----+

+ Ar('S0) O*CP) + Ar(lS0) Ar(lS0) + C2H4* Ar(lS0) + C,H4* O*(3P)

Ar(lS,)

Rate-const.J 1 mol-l s-l 1.38 x 1O1O

Piper

1.68 x loD

Piper

6.18 x loll

Hurst et al.

Authors 163

3.36 x lo1'

Hurst et al.

+ N2*(31&J

(a2 = 11.8 A)

Winicur et al.

+ Ar(lS,)

1.02 x lo7

Jortner et al.

Xe(3P2)

N,(B3TZ,; u1 4 5 ) levels has been shown to involve Xe(",) atoms and not Xe(3P1) Chemiluminescence from ArO and ArCl arising from reactions of metastable Ar atoms has been reported.ls6 Several papers have reported on molecular emission in noble-gas discharges,lssand laser action in the vacuum-u.v. using noble gases has been reporfed.ls7 R. T. Thompson, J. Quant. Spectroscopy Radiative Transfer, 1974,14, 1179. K. E. Donnelly, P. J. Kindlmann, and W. R. Bennett, jun., I.E.E.E. J. Quant. Electronics, 1974,10, 848. lB0 N. V. Afanas'ev and P. F. Gruzdev, Optika i Spektroskopiya, 1975,38,794; C. Camhy-Val, A. M. Dumont, M. Drew, L. Perret, and C. Vanderriest, J. Quant. Spectroscopy Radiative Transfer, 1975, 15, 527. E. Jimenez, J. Campos, and C. Sanchez del Rio, J. Opt. SOC.Amer., 1974, 64, 1009. IEa R. C. Isler, Phys. Rev. (A), 1974, 10, 2093. L. G. Piper, Chem. Phys. Letters, 1974,28, 276; R. Atzman, 0.Cheshnovsky, B. Raz, and J. Jortner, ibid., 1974,29,310;D. H. Winicur and J. L. Fraites, J. Chem.Phys., 1974,61,1548; G . S. Hurst, E. B. Wagner, and M. G. Payne, ibid., p. 3680;Th. P. Hoogkamer, F. W. Saris, and F. J. de Heer, J. Phys. (B), 1975, 8, L105. la* T. Nguyen, N. Sadeghi, and J. Pebay-Peyroula, Chem. Phys. Letters, 1974,29, 242. M. F. Golde and B. A. Thrush, Chem. Phys. Letters, 1974,29, 486. J. W. Keto, R. E. Gleason, jun., and G. K. Walters, Phys. Rev. Letters, 1974, 33, 1365; P. Moerman, R. Boucique, and P. Mortier, Phys. Letters, 1974,49a, 179; T.Okay K. U. S. Rama Rao, J. L. Redpath, and P. F. Firestone, J. Chem. Phys., 1974, 61,4740;J. DupontRoc and M. Leduc, J. de Physique, 1974,35,L175;E. H. Fink and F. J. Comes, Chem. Phys. Letters, 1975,30, 267. 16' W.A. Johnson and J. B. Gerardo, J. Appl. Phys., 1974,45,867; D. J. Bradley, D. R. Hull, M. H. R. Hutchinson, and M.W. McGeoch, Chem. Phys. Letters, 1974,11,335; F. Lagarde and M. Novaro, Onde Electr., 1974,54, 463. 168

lSD

126

Photochemistry

The powerful technique of two-photon absorption, which permits limitations of Doppler broadening to be overcome (see Chapter l), has been used in a study on sodium atoms in which the Stark effect in the 5s 2S* and 4d 2Dt and 2 D f levels was observed.lB8The radiative lifetimes of the S and D Rydberg levels of Na,lBethe use of laser-induced resonance fluorescence for the measurement of small concentrations of Na v a p ~ u r the , ~ quenching ~~ of Na(32P) and K(42P) by N2, 02,H,, and H20,171the chemi-ionization reactions of photoexcited K atoms,172and excitation of the K(42Pj) level in collisions with rare-gas atoms 173 have been the subjects of recent reports. Transfer of electronic excitation between the 62P4 and 62P4 states of rubidium and the 72P4and 72P*states of caesium has cross-sections of the order of 100250 x 10-ls cm2.174Reactions of M (M = Ca, Ba, or Sr) with X, (X = F, C1, or Br) give rise to visible chemiluminescence from the MX* species in the $TI and B2Z+states and from electronically excited MX2* complexes.176 Detailed product state analysis of the reactions of Ba with CO, and O2 [reactions (74), (75)] has been achieved, using the technique of monitoring laser-

+ 0, Ba + C02 -. Ba

____+

+0 BaO + CO

BaO

(74) (75)

induced Photon yields and the spectra resulting from reactions of Ca with oxidants have also been ~ e p 0 r t e d . l ~ ~ An electron-photon delayed coincidence method has been used to measure the lifetime of a 63P state of mercury as 120 ns, but since the identity of the state is not made clear (i.e. 3P0, 3P1, or 3P2),the report seems of limited v a 1 ~ e . l ~ ~ Population transfers between the 6s and 6d configuration levels of Hg induced by collisions with N2 have been and a theoretical study of the longrange interaction between Hg(lp3P1) and noble-gas atoms has appeared.lso Selected cross-sections for the quenching of Hg(3P1) atoms by a variety of molecules, from two studies, are summarized in Table 6.181 Cross-sections for many other molecules are also given in these studies, as are the cross-sections for the quenching process Hg(3&, -+6'So) by some seventeen simple molecular species, cross-sections varying from 50 x 10-l6 cm2 for propylene to cm2 16*

K. C. Harvey, R. T. Hawkins, G. Meisel, and A. L. Schawlow, Phys. Rev. Letters ( A ) , 1975, 34, 1073.

lBB

170 171 172

173

17'

T. F. Gallagher, S. A. Edelstein, and R. M. Hill, Phys. Rev. (A), 1975, 11, 1504. W. M. Fairbank, jun. and T. W. Haenisch, J. Opt. SOC.Amer., 1975, 65, 199. P. L. Lijnse and J. C. Hornman, J. Quant. Spectroscopy Radiative Transfer, 1974, 14, 1079; P. L. Lijnse, ibid., p. 1143. A. Fontijin, P. F. Fennelly, and R. Ellison, Chem. Phys. Letters, 1975, 31, 172. H. Alber, V. Kempter, and W. Mecklenbranck, J. Phys. (I?), 1975, 8, 913. M. Menzinger, Chem. Phys., 1974, 5, 350; P. W. Pace and J. B. Atkinson, Canad. J. Phys., 1974, 52, 1635, 1641.

M. Menzinger, Canad. J. Chem., 1974,52, 1688; D. J. Wren and M. Menzinger, Chem. Phys. Letters, 1974, 27, 572. 170 P. J. Dagdigian, H. W. Cruse, A. Schultz, and R. N. Zare, J. Chem. Phys., 1974, 61, 4450. G. A. Capelle, C. R. Jones, and J. Zorskie, J. Chem. Phys., 1974, 61, 4777. 178 G . L. King and A. Adams, J. Phys. (B), 1974,7, 1712. 170 B. Laniepce, J. de Physique, 1974, 35, 953. la0 H. A. Hyman, Chem. Phys. Letters, 1975, 31, 593. 181 H. Horiguchi and S . Tsuchiya, Bull. Chem. SOC. Japan, 1974,47,2768; J. V. Michael and G. N. Suess, J. Phys. Chem., 1974, 78, 482; S. D. Gleditsch and J. V. Michael, ibid., 1975, 79, 409. 17&

127

Gas-phase Studies

Table 6 Selected cross-sections x 1O16/cmaf o r quenching of HgCP1) MoIecule H2 0 2

co NO NaO

Process cross-section a ti3P1-+ 63P0 7.8 c 0.1 17-19 <2 3.0 3.9 30 5 20-22 <2

63P1-61S0

43-48

c2H4 a

Ref. 181,Horiguchi et ul.;

<5

Total cross-section 11.1 23.9 7.4 28.3 21.2 39.6

ref. 181, Michael et ul.

for methane, The cross-section for this process for ammonia, reported by Horiguchi et aZ.,lS1of 0.016 x 10-l6 cm8compares favourably with that reported earlier by Callear,lSabwith that of Freeman et aZ.,182band with recent evaluations by Callear.18aa Rate coefficients for the processes (76)-(79) in the recent study HgeP1)

+ NHS

Hg(3Po) + NH3 Hg(3Po) + NH3 + M

HgNH3*

____+

+ NH3 + NH3 + hv HgNH3* + M Hg + NHS + hv Hg('P0)

Hg(lS0)

(76) (77) (78) (79)

by Callear were also in good agreement with earlier reports. At low pressures (0.08 Torr) an emission observed in the above system could not be explained on the basis of reactions (76)-(79), and it was tentatively ascribed to an Hg(T'&NHs complex.1s3 The lifetimes of Hg(3P0)complexes with ammonia, methanol, and HzO have been further investigated.lS4 For the ammonia complex, lifetimes were obtained that were in good agreement with the studies reported above, but for the methanol and water complexes, the lifetimes measured in this study (1.4 x and s) are much shorter than those reported earlier. The actual experi<8 x mental data of this group and of previous workers are in good agreement, but the interpretation of the phase-shift results is different, yielding the different decay constants. The formation of the methanol complex was shown to be consistent with the analogous reaction to (78). This study can be compared with the recent publication on the Hg('P&H,O complex by Callear et a1.,lsa in which the rate-constant for relaxation of Hg(3P,) by H 2 0 is smaller than that quoted by Phillips et al.lsa No clustering around the Hg(3P,) atom was observed for H20, in contrast to the case of NH3,and the termolecular quenching reaction analogous to (78) was absent. Excitement of the 63S1level of Cd atoms by collision with Hg(6lP1) atoms has been described,la6and with Hg(63P3 atoms, the Cd(5'&) level is excited with a ( u ) A . B. Callear, J. H. Connor, and J. Koskikallio, J.C.S. Furuduy 11, 1974, 70, 1542; (b) A. B. Callear and J. C. McGurk, ibid., 1973, 69, 97; C. G. Freeman, M. J. McEwan, R. F. C. Claridge, and L. F. Phillips, Trans. Furuduy SOC.,1971,67,2004. laS T.Hikida, T. Ichimura, and Y. Mori, Chem. Phys. Letters, 1974,27, 548. la' K.Luther, H. R. Wendt, and H. E. Hunziker, Chem. Phys. Letters, 1975,33,146;C.G.Freeman, M. J. McEwan, R. F. C. Claridge, and L. F. Phillips, Trans. Furuduy Sac., 1971,67,3247. A. B. Callear and J. H. Connor, J.C.S. Furuduy ZZ, 1974,70,1767. lad B. Cheron, G. Cremer, D. Lecler, and L. Saintout, J. de Physique, 1974,35,L247. la2

Photochemistry

128

cross-section of 0.05 x 10-l6 cm2.1e7 This process has been shown by Baker et aI.la7to be sensitive to the presence of a rotating magnetic field, but theoretical models proposed to account for the observation were unsuccessful. Excitation transfer between mercury atoms in the 63P0and 6lS, levels has been studied,la8 and rates of collisional deactivation of the Hg(3P0)state [5.46 eV above Hg(lS,)] by chlorine and chlorinated methanes, N2,and CO have been reported.leO In the case of quenching of this state by the halogenated molecules, large cross-sections were observed for the reaction (80), which occurs via an electron-transfer ‘harpooning’ mechanism.

+

H S ( ~ ~ P ~RCI )

-

HgCl(B21:+)

+ R*

(80)

The Hg(63Pl)-sensitized photolyses in the vapour phase of C2C14,180cycloheptene,lol triethylborane,lg2and perfluorocyclobutane lg3and the U.V. photolysis of bis(trichloromethy1)mercury vapour lo* have been reported. Other Hgsensitized reactions will be found in appropriate sections of Part I1 of this volume. The determination of Hg by atomic absorption and fluorescence spectrometry has been reviewed.les The quenching of the Cd(lP1) state with the resonance line at 228.8 nm has been studied by a method using radiation trapping.lo6 Typical trapping times in the absence of quencher were 1.4 ps, and quenching rate-constants varied from 1.12 x lo0 to 9.0 x 10l11 mol-1 s-l for He and propylene, respectively. Cross-sections for the quenching of the Cd(53P0)and Cd(53P1) states by a variety of molecules, including ammonia, noble gases, methane, N2,H2,SF6,and ethylene, have been given.lg7 The photochemical reactions of Cd with CH3Cl have been described.lO*Second-order rate constants for the removal of Sn(S1D2)atoms have been shown to vary from < 1.2 x lo6for He to 1.2 x loll mol-1 s-l for SnMe, in a study in which resonance radiation was monitored in absorption.lo8 A similar study has been carried out on Sn(53P2)and Sn(53P1),100 Sb(52D8, 2Dt),200Pb(3f?2 and 3P1),201 and A s ( ~ ~ D ~ , ~ , ~ P ~ , ~ ) . ~ ~ ~ N

M. Czajkowski and L. Krause, Canad. J. Phys., 1974,53,2228; R. S . Baker and W. Gough, J. Phys. (B), 1975, 8, 552. lea D. Vienne-Casalta and J. P. Barrat, J . de Physique, 1975, 36, 367. R. Burnham and N. Djeu, J. Chem. Phys., 1974, 61, 5158; E. Jacobson, J . Phys.(B), 1975,8, 869; H. F. Krause, S. G. Johnson, S. Datz, and F. K. Schmidt-Bleek, Chem. Phys. Letters, 1975, 31, 577.

E. Sanhueza and J. Heicklen, Canad. J . Chem., 1974,52, 3863. Ig1 Y. Inoue and M. Kadohira, Tetrahedron Letters, 1974, 459. lS2 E. A. Lissi and L. Larrondo, J. Photochem., 1974, 2, 429. l g 3 R. L. Cate and T. C. Hinkson, J . Phys. Chem., 1974,78,2071. l g 4 N. D. Kagramanov and A. K. Mal’tsev, Izvest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 2146. lo5 A. M. Ure, Analyt. Chim. Acta, 1975, 76, 1. lo6 P. D. Morten, C. G. Freeman, R. F. C. Claridge, and L. F. Phillips, J. Photochem., 1974,3,285. lg7 W. H. Breckenridge and T. W. Broadbent, Chem. Phys. Letters, 1974, 29, 421 ; P. Young, E. Hardwidge, and S. Tsunashima, J. Amer. Chem. SOC.,1974, 96, 1946; S. Tudorache, Rev. Roumaine Phys., 1974, 19, 541; S. Yamamoto, S. Tsunashima, and S. Sato, Bull. Chem. Sac. Japan, 1975, 48, 1172. l e a M. Freiberg, D. Meyerstein, and S. Weiss, J. Inorg. Nuclear Chem., 1974, 36, 1902; A. Brown and D. Husain, J. Photochem., 197415, 3, 37. lag P. D. Foo, J. R. Wiesenfeld, and D. Husain, Chem. Phys. Letters, 1975, 32, 443. 2 o o M. J. Bevan and D. Husain, J. Photochem., 1975, 4, 51. 201 J. J. Ewing, D. W. Trainor, and S. Yatsiu, J. Chem. Phys., 1974, 61, 4433; J. Ewing, Chem. Phys. Letters, 1974,29,50; D. Husain and J. G . F.Littler, Internat. J. Chem. Kinetics, 1974,6,61. z o a M. J. Bevan and D. Husain, J. Photochem., 1974, 3, 1. lgO

Gas-phase Studies

129

10 Miscellaneous Chemiluminescence and photoluminescence in diatomic iron oxide, Rbz, and alkali-metal dimers with halogen atoms and metal vapour-oxidant lifetime measurements of selectively excited states of diatomic h y d r i d e ~ photo,~~~ dissociation of alkali-metal halide vapours,20sspin-orbit relaxation of the HTe (TzrI4) the photodecomposition of metal carbonyl anions such as [Mn(CO,)]- in the vapour phase,207and the fluorescence of Rhodamine 6G in the vapour phasezo8have been studied in recent reports. In the last study it was concluded that an insufficient concentration of the fluorescing dye could be maintained in the vapour phase to permit laser action to occur.

11 Applications of Lasers In many of the sophisticated experimental techniques applied to photophysical problems, the rapid development of the laser has enabled results to be obtained which were unheard of only a few years ago. These developments have been described adequately in previous and current volumes, but there are two applied uses of the laser which have not yet received significant attention, and to which readers’ attention is drawn by this short extra section this year. The first is concerned with the remote sensing of atmospheric pollutants. The methods available to achieve this object can be classified as passive, for example the heterodyne detection of thermal emission,2o9or active, involving some radiation source. The means of attenuating the intensity of such a source are listed below. (a) Mie scattering (particulates, aerosols). (b) Rayleigh scattering. (c) Resonance Rayleigh scattering. ( d ) Raman scattering. (e) Resonance Raman scattering. (f)Electronic fluorescence. (9)1.r. (vibrational) fluorescence. (h) Absorption. (i) Scattering due to temperature and pressure fluctuations. Category (h) is unique in that a reflector is required, and ranging is impossible, as shown in Figure 6(~).~lO Nevertheless, the differential absorption method using lasers that is summarized in Figure 7211has been used successfully to 2os

204

205

2oe 207 208 208

210 211

J. M.Brom, jun., and H. P. Broida, J. Chem. Phys., 1974,61,982; S . E. Johnson, P. B. Scott, and G. Watson, ibid., p. 2834; W. S. Struve, J. R. Krenos, D. L. McFadden, and D. R. Herschbach, ibid., 1975, 62, 404; J. B. West and H. P. Broida, ibid., p. 2566. K. H. Becker, G. Capelle, D. Haaks, and T. Tatarczyk, Bet. Bunsengesellschaft phys. Chem., 1974,78, 1157. B. L. Earl and R. R. Hem, J. Chem. Phys., 1974, 60, 4568; R. C. Ormerod, T. R. Powers, and T. L. Rose, ibid., p. 1509. D. J. Little, R. J. Donovan, and R. J. Butcher, J. Phorochem., 1974, 2, 451. R. C. Dunbar and B. B. Hutchinson, J. Amer. Chem. Suc., 1974, 96, 3816. T. Sakurai and H. G. de Winter, J. Appl. Phys., 1975,46, 875. E. Huppi, J. Rogers, and A. Stair, Appl. Optics, 1974, 13, 1466. J. W. Robinson and J. D. Dake, Analyt. Chim. Acta, 1974, 71, 277. J.-C. Fontanella, A. Girard, L. Gramont, and N. Louisnard, Appl. Optics, 1975, 14, 825; D. C. O’Shea and L. G. Dodge, ibid., 1974, 13, 1481.

Photochemistry

130

3.

Figure 6 (a) Absorption remote sensing apparatus. (1) Tunable laser, (2) polluted region, (3) remote retroreflector, (4) telescope, ( 5 ) detector. (b) Backscatter remote sensing apparatus. (1) Laser, (2) polluted region, (3) telescope, (4) spectrometer and detector (Reproduced by permission from Analyt. Chim. Acta, 1974, 71, 277) c-

PULSE I -.GENERATOR 1

4

47 +TO RETROREFLECTOR

-

Gnza-@-.; LIGHT

-~: ,

/

SINE F I N G J

FRESNEL LENS

Gas-phase Studies

131

monitor 03,213, NH3, and CzHp 214 and has also been water vapourY2l2 advocated for sensing of pollutants from aircraft 21s and satellites.216 The other methods listed above involve no reflector, being ‘backscattering’ methods, and with a suitable gating or time-resolution and pulsed sources (Lidar) both the concentration and range of the pollutant can be obtained. Mie scattering is particularly useful for but laser-induced i.r. fluorescence has recently been shown to be a feasible means of monitoring such species as Electronic fluorescence (using, however, Zn 213.8 nm resonance radiation rather than laser radiation) has been employed to monitor SO, levels,a10and dye-laser excitation of formaldehyde fluorescence has been used to sample this pollutant.220a Laser depolarization from melting snowflakes has also been reported.220b The methods may be compared with the widely used chemiluminescent method for NO in which the luminescence arising from reaction (81) is monitored,2a1

The second recent interesting application of lasers is concerned with the use of the narrow spectral bandwidth of the laser as a means of selectively exciting single components in mixtures, particularly in isotopic mixtures, thus achieving selective reaction and ultimately isotope separation. In order to obtain high selectivity, in general a two-step excitation process is required, but one-photon radiation of several species with i.r. lasers has been shown to lead to enhancement of reaction rates. Thus C0,-laser-induced vibrationaz excitation of 0,leads to enhancement of reaction rates with SO (85), NO (86), and SF4-02 mixtures.222 212

R. S. Eng, P. L. Kelley, A. R. Lalawa, T. C. Harman, and K. W. Nill, Mol. Phys., 1974,28, 653.

21s 214

215

216 217

C. Young and R. H. Bunner, Appl. Optics, 1974,13, 1438. R. R. Patty, G. M. Russwurm, W. A. McClenny, and D. R. Morgan, Appl. Optics, 1974,13, 2850; W. A. McClenny, R. E. Baumgardner, jun., F. W. Baity, jun., and R. A. Gray, J. Air Pollution Control ASSOC.,1974, 24, 1044. R. T. Menzies and M. T. Chahine, Appl. Optics, 1974,13,2840. C . Ludwig, M. Griggs, W. Malkmus, and E. R. Bartle, Appl. Optics, 1974, 13, 1494. R. W. Weeks and W. W. Duley, J. Chem. Phys., 1974,45,4661; R. A. Reck, Science, 1974, 186, 1034.

218

218 220

211

zaa

J. W. Robinson and N. Katayama, Spectroscopy Letters, 1974, 7, 581 ; N. Katayama and J. W. Robinson, ibid., 1975, 8, 61. F. P. Schwarz, H. Okabe, and J. Whittaker, Analyt. Chem., 1974, 46, 1024. (a) K. H. Becker, U.Schurath, and T. Tatarczyk, AppI. Optics, 1975, 14, 310; (b) K.Sassen, Nature, 1975, 255, 316. B. A. Ridley and L. Howlett, Rev. Sci. Instr., 1974, 45, 742; J. 0. Jackson, D. H. Stedman, R. G. Smith, L. H. Hecker, and P. 0. Warner, ibid., 1975, 46, 376; F. P. Schwartz and H. Okabe, Analyt. Chem., 1975,47,703; C. H. Wu and H. Niki, Environ. Sci. Technol., 1975,9, 46; P. Bourbon, J. Alary, J. Esclassan, and J. C. Lepert, Analysis, 1975, 3, 217. W. Braun, M. J. Kurylo, A. Kaldor, and R. P. Wayne, J. Chem. Phys., 1974, 61, 461; A. Kaldor, W. Braun, and M. J. Kurylo, ibid., p. 2496; M. J. Kurylo, W. Braun, C. N. Yuan, and A. Kaldor, ibid., 1975, 62, 2065; M. J. Kurylo, W. Braun, and A. Kaldor, Chem. Phys. Letters, 1974, 27, 249; W. Braun, M. J. Kurylo, and A. Kaldor, ibid., 1974, 28, 440; M. J. Kurylo, W. Braun, A. Kaldor, S. M. Freund, and R. P. Wayne, J. Photochem., 1974/5, 3, 71.

132

The CO, laser has been used to promote reactions in SF6-C2H6 mixtures223 [(87)-(91)], the results being equivalent to heating the system, but this has been

shown not to be the case with CF2C12-SF, mixtures,224since only excitation with a frequency corresponding to an i.r. absorption in CF2C1, (935 cm-l) resulted in significant dissociation of the CF2C12,excitation of SF, (at 949 cm-l) producing no reaction at all. This result is significant since it implies that selectivity can be achieved in a one-step excitation process, as discussed and this selectivity in reaction has also been observed, again with C 0 2 laser excitation, in the reaction of diborane to give icosaborane, BzoH16.226 More significantly, when mixtures of BC13 and H2S were irradiated with 10.55 pm radiation (C02 laser) it was found that the loB : llB ratio of recovered material was 50% greater (29.2%) than before irradiation (19.5%),227whereas for irradiation with 10.18 pm radiation, the loB concentration was lowered to 14.4%.227 Clearly, the method has applications for isotope separation. Selectivity can be greatly enhanced by utilizing one of the two-step excitation processes illustrated in Figure 8, and this method has been widely discussed.22s In particular, Kelley et al. have given the values of absorption coefficient, nonlinear coefficient, and power required for efficient two-photon events (ranging from vibrational two-photon absorption to vibronic two-photon absorption), and Letokhov has illustrated the vibrational-electronic two-photon excitation process with respect to NH, and HCl, leading in the latter case to chlorine isotope separation [reactions (92), (93)], through processes illustrated in Figure 8(a), ~

3

6

+~ ~1 3

hvi, hvs

7

%C1*+NO

~

1

H-

+ 3 5 ~ 1 .+

NOV1

~

3

7

~

1

(92)

(93)

where hv, is a 1.04 eV photon from a Raman-shifted Nd-in-glass laser and hv, is a 4.7eV photon from the quadrupled Nd laser. One-step chlorine isotope a28

aar

227 2a8

F. Lempereur, C. Marsal, and M. J. Tardieu de Maleissye, Compt. rend., 1974, 279, C, 433. R. N. Zitter, R. A. Lau, and K. S. Wills, J. Amer. Chem. SOC.,1975, 96, 2578. A. Yogev, R. M. J. Loewenstein, and D. Amar, J. Amer. Chem. Suc., 1973, 95, 1091. H. R. Bachmann, H. Noth, R. Rinck, and K. L. Kompa, Chem. Phys. Letters, 1974,29,627. S. M. Freund and J. J. Ritter, Chem. Phys. Letters, 1975, 32, 255. V. S. Letokhov, Science, 1973, 180, 451; P. L. Kelley, H. Kildal, and H. R. Schlossberg, Chem. Phys. Letters, 1974,27,62; V. S . Letokhov and A. A. Makarov, J. Photochem., 1974, 2, 421; 3, 249; Y. S. Liu, Appl. Optics, 1974, 13, 2505; J. I. Brauman and T. J. O'Leary, Optics Comm., 1974, 12, 223; Yu. G. Basov, R. U. Utirov, and V. K. Korovkin, 2 h u r . F ~ . Khim., 1974,48, 342; Yu. G. Basov and V. N. Makarov, Atomnaya Energiya, 1974,36, 522.

Gas-phase Studies

133

Figure 8 A schematic diagram of two-photon selective photodissociation and photopredissociation of a molecule (Reproduced by permission from Applied Optics, 1974, 13, 2505)

Figure 9 Ca energy levels involved in the two-step photoionization (Reproduced by permission from Applied Physics, 1974, 5, 109)

Photochemistry

134

separation has been achieved using highly selective electronic excitation of thiophosgene22Band ICl.230 In the first case the isotopically pure species is trapped by reaction with diethyloxyethylene, in the second with halogenated ethylenes. In both cases the 35Cl: 37Clratio could be made to change from 3 initially to 2 or 4, depending upon which isotope was excited initially. Isotopically selective excitation of bromine 231 and calcium 232 has been achieved, the latter involving the novel double electronic excitation of the selected Ca isotope first to a metastable state, followed by ionization, which provides a convenient collection mechanism (Figure 9). This technique has of course excited much interest in that 23sUand 23aUhave been separated by the same means on a laboratory scale, which is a process of considerable commercial and military potential to which one cannot necessarily offer an unreserved welcome. 12 Atmospheric Chemistry

The format here is as before, with the addition of a short section emphasizing potential ozone-loss mechanisms in the stratosphere. Extraterrestrial Phenomena.-The photochemistry of the growing number of molecular species found upon other celestial bodies and in interstellar space is of prime importance in understanding the means of synthesis and destruction of such species, and the spectroscopic search for new species is also of interest. At least 26 molecular species, ranging from diatomics to those containing seven atoms, have been observed in interstellar space : even polymers of formaldehyde A recent search for 14 diatomic species has employed have been satellite U.V.measurements upon, and models for, U.V. stars have also been The microwave search for molecules, including OH, in comets, including the recently observed comet Kohoutek, has been The cosmic far-u.v. background radiation 237 and various aspects of solar U.V. radiation 238 have been discussed. Solar helium particle events 23B and the observation of CO, and HCN in sunspots240have been reported, and the U.V. measurement of helium distribution has been described.241 228 230

231 232 233 234

236

236

237

238

239 240 241

M. Lamotte, H. J. Dewey, R. A. Keller, and J. J. Ritter, Chem. Phys. Letters, 1975,30, 165. D. D . 4 . Liu, S. Datta, and R. N. Zare, J. Amer. Chem. SOC.,1975, 97,2557. S. R. Leone and C. B. Moore, Phys. Rev. Letters, 1974,33,269. U. Brinkmann, W. Hartig, H. Telle, and H. Walther, Appl. Phys., 1974,5, 109. N. C.Wickrarnasinghe, Nature, 1974,252,462. J. Drake, Proc. Roy. SOC.,1974,A340, 457. J. C. Pecker, Astrojizika, 1973, 9, 525; E. T. Verkhovtseva and V. I. Yaremenko, Kosm. Issled. Ukr., 1973,3,66;D. S. Leckrone and J. W. Fowler, Astron. Astrophys., 1974,32,237; J. I. Katz, R. C. Malone, and E. E. Salpeter, Asfrophys. J., 1974, 190, 359. F. H.Mies, Asfrophys.J., 1974,191,L145;G. A. Harvey, Publ. Astron. SOC.Pac., 1974,86, 552; M.N. Simon and T. 0. M. Simon, Nature, 1974,252,666. A. Webster, Scientific American, 1974,231, 26; A. Davidson, S. Bowyer, and M. Lampton, Nature, 1974,247, 513. A. T. Wood, jun., R. W. Noyes, and E. M. Reeves, Progr. Astronaut. Aeronaut., 1972,30, 117;S. Suzuki, Solar Phys., 1974,38, 3; 0.A. Avaste and G. M. Vainikko, Fiz. Armosfery i Okeana, 1974,10, 1054;S. S. Prasad and D. R. Furman, J. Geophys. Res., 1974, 79, 2463; R. D. Chapman and W. M. Neupert, ibid., 1974,79,4138;U. Feldrnan and E. W. Behring, Astrophys. J., 1974, 189,L45; M. Ackerman, Canad. J . Chem., 1974,52, 1505. V. K. Balasubrahmanyan and A. T. Serlernibos, Nature, 1974,252,460. M. C.Pande and V. P. Gaur, Nature, 1975,253, 104. R. R. Meier and C. S. Weller, J. Geophys. Res., 1974,79, 1575.

Gas-phase Studies

135

hydrocarbon abundances U.V. measurement of the Saturnine on and the photochemistry of hydrocarbons in the atmosphere of Titan 244 have been discussed. Recent satellite observations have resulted in a new look to the Martian and recent studies have been concerned with U.V. hydrogen emission from this photodissociation of CO, in the upper Martian the use of an emission spectrometer for detection of C0,247and photoinduced reactions in a simulated Martian comprising silica gel with an atmosphere of CO, with trace amounts of CO, O,, and H,O. In the last study the production of C0,H radicals was demonstrated. The products of NH3 photolysis in the presence of C0249have been investigated in an attempt to understand the lack of nitrogen compounds on Mars. The main products were ammonium cyanate and other water-soluble compounds, including urea, which suggests that nitrogeneous materials may exist on Mars, trapped in the surface. The absence of atomic hydrogen in the Lunar atmosphere has been demonstrated with a u.v.-emission probe.260 Neutral and Ionic Atomic and Molecular Hydrogen.-Hydrogen is the most abundantly distributed cosmic material, and the photochemistry and physics of these species are thus of astrophysical importance as well as of importance in the Earth's atmosphere. excited The fluorescence intensity of the H2 Lyman bands (@Xu+ -+ T4&+), by 106.6 nm radiation, was shown to be linearly dependent upon H, pressure for pressures < Torr, as is the case for naturally abundant HD.261 Fluorescence may thus be used as a monitor for these species, and the emission has been observed arising from solar excitation of exhaust gases from H, fuel cells in the Apollo 17 spacecraft.262The lifetime of the 3Xu+state of H, has been measured as 10.5 ns.263The photoionization and dissociative photoionization of H,, Dz,and H D have been The flash photolysis of H,-F,-He mixtures,266the H, vacuum-u.v. laser,266and the yield of atomic hydrogen in the combustion of CH,-air and H,-air mixtures 267 have been reported. 242 243 244 246

246 247 248 249

250 261 251 253 254 266 268

25 7

V. G. Teifel, Astron. Vestn., 1974,8, 3. D. F. Strobel, Astrophys. J., 1974,192, L47. D.F. Strobel, Zcarus, 1974,21, 466. G. E. Hunt, Proc. Roy. Soc., 1974, A341, 317; H. W.Moos, J. Geophys. Rev., 1974, 79, 2887. C.A. Barth, 2. Nuturforsch., 1974,29a, 185. A. W.Mantz and J. P. Maillard, J. Mol. Spectroscopy, 1974,53, 466. S . 4 . Tseng and S. Chang, Origins Life, 1975,6,61 ; Nature, 1974,248,575. J. P. Ferris, E. A. Williams, D. E. Nicodem, J. S. Hubbard, and G. E. Voecks, Nature, 1974, 249, 437. W.G. Fastie and P. D. Feldman, Science, 1973, 182, 710. E. C. Y. Inn and W. L. Starr, J. Opt. SOC.Amer., 1975,65, 320. P. D. Feldman and W. G. Fastie, Astrophys. J., 1973,185, L101. G.C. King, F. H. Read, and R. E. Imhof, J. Phys. (B), 1975,8, 665. A. L. Ford, K. K. Docken, and A. Dalgardno, Asfruphys.J., 1975,195, 819. S. N.Suchard and D. G. Sutton, Z.E.E.E.J. Quantum Electron., 1974,10, 490. M. Gallardo, C. A. Massone, and M. Garavaglia, I.E.E.E.J. Quantum Electron., 1974, 10, 525. L. A. Gussak, 0. B. Ryabikov, and G. G. Politenkova, Zzuest. Akad. Nauk S.S.S.R.,Ser. khim., 1974,479.

136

Photochemistry

The photodissociation of H2+and Dz+ions has been In the studies of van Asselt et al. a crossed-beam experiment was carried out, and the momentum of the resulting H+ or D+ fragment recorded, as well as the angular distribution, indicating that the polarization of the primary ion beam is perpendicular to its direction. This type of spectroscopy represents a powerful new advance, and will no doubt be used increasingly to investigate ionic species of astrophysical importance, such as the CH4+ ion discussed ear lie^.^ The crosssections for the production of H(3s) and H(4s) states in the collision between H+ and D+ on H2, Nz, and O2 have been and excitation of electronically excited H atom states in collisions between H atoms has also been observed.260 Kinetic measurements of a large number of H-atom reactions have been made. Papers are too numerous to be discussed in detail, but include reactions with carbon,261molecular oxygen,262C0,263N02,264 NH3,265HBr, HI, and DBr,26s vibrationally excited HCl,154 ethane and other and many olefins.268 Stratospheric Chemistry.-Interest in the past year has centred again upon the possibility of man’s activities depleting the protective ozone u.v.-barrier in the stratosphere, with Freons providing the latest potential hazard. In the cases of the reaction of 0,with NO produced from S.S.T. aircraft or thermonuclear explosions, or with Freons, laboratory rate constants are usually available, and results of recent measurements are included below. The most controversial aspects of this vital subject revolve around transport processes in the troposphere/ stratosphere and unknown loss and regeneration processes, leading to extreme differences in opinion concerning potential dangers. Unfortunately, differences in 0,concentration resulting from the relatively few S.S.T. aircraft currently flying and the amount of Freon calculated to have reached the upper atmosphere to date appear to be smaller than the error in such determinations, and less than the natural fluctuations that may possibly be associated with solar activity. Several papers have been concerned with the measurement of the vertical distrithe bution in concentration of 0,and oxides of nitrogen in the 258

259 260 261 262

263 264

2e6 266

267

N. P. F. B. van Asselt, J. G. Maas, and J. Los, Chem. Phys., 1974,5,429; Chem. Phys. Letters, 1974,24, 5 5 5 ; J. D . Argyros, J. Phys. (B), 1974, 7 , 2025. D. H. Loyd and H. R. Dawson, Phys. Rev. ( A ) , 1975, 11, 140. T. J. Morgan, J. Geddes, and H. B. Gilbody, J. Phys. (B), 1974, 7, 142. M. Coulon and L. Bonnetain, J. Chim. phys., 1974, 71,717, 725. A. Agkpo and L. Sochet, Combustion and Flame, 1974,23,47; W. Wong and D. D. Davis, Intern. J. Chem. Kinetics, 1974, 6, 401 ; J. Giachardi, G. W. Harris, and R. P. Wayne, Chem. Phys. Letters, 1975, 32, 586. V. V. Azatyan, N. E. Andreeva, and E. I. Interzarova, Armyan. Khim. Zhur., 1973,26, 959. A. McKenzie and M. F. R. Mulcahy, J.C.S. Faraday I, 1974, 70, 549; J. H.Brophy, J. A. Silver, and J. L. Kinsey, J. Chem. Phys., 1975, 62, 3820. J. E. Dove and W. S. Nip, Canad. J. Chem., 1974, 52, 1171. A. Persky and A. Kuppermann, J. Chem. Phys., 1974, 61,5035; H.Y.Su, J. M. White, and L. M. Raff, ibid., 1975, 62, 1435. P. Camilleri and R. M. Marshall, J.C.S. Faraday I, 1974, 70, 1434; L. E. Compton, G. D. Beverley, and R. M. Martin, J. Phys. Chem., 1974, 78, 559; G. K. Winter and D. S. Urch, Chem. Phys. Letters, 1975, 32, 527. J. H. Purnell, Acta Cient. Venez. Supl., 1973, 24, 40; J. P. Kilcoyne and K. R. Jennings, J.C.S. Faraday I, 1974,70, 379; Yu. P. Yampol’skii, Kinetics and Catalysis (U.S.S.R.), 1974, 15,938; A. M. Dubinskaya and N. N . Yusubov, Izuest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 1484; K. Furukawa, D. G . L. James, and M. M. Papic, Internat. J . Chem. Kinetics, 1974,6,337. A. Pittock, Nature, 1974,249, 641 ; J. Harries, D. Moss, and N. Swann, ibid., 1974, 250, 475; J.-C. Fontanella, A. Girard, L. Gramont, and N. Louisnard, Appl. Optics, 1975, 14, 825.

Gas-phase Studies

137

variation and effect of U.V. radiation reaching the earth’s surface,27othe radiative heating of the atmosphere and its relation to ozone p h o t o ~ h e m i s t r y ,energy~~~ transfer processes in the and models for stratospheric and atmospheric boundary-layer photochemical reactions.273 As stated above, interest is centred upon the complex reaction sequence in the stratosphere involving many of the 34 chemically different diatomic and polyatomic species which maintain the ozone concentration in this atmospheric region, and in particular upon whether or not man-made species introduced into the stratosphere, directly or indirectly, can influence the concentration of O3 maintained. Hampson has stressed the possible dangers of thermonuclear war producing stratospheric NO which could deplete the O3 level through reaction (94),274but most other reports O3

+ NO

-

NO,

+ O2

(94)

are more directly concerned with the effect of NO from aircraft engines.275 Estimates seem to agree that, with the cancellation of the large Boeing 2707 S.S.T. aircraft, danger from this quarter has receded, since the smaller Anglo-French Concorde and Soviet TU 144 will operate in small numbers at less harmful altitudes. Potentially more hazardous, and certainly as controversial, is the contention that the annual 0.5 million tons of Freon gases used as aerosol propellants and refrigerant fluids and released into the trophosphere may ultimately significantly reduce the stratospheric O3 concentration through U.V. photolysis producing chlorine atoms [reaction (95)], which destroy ozone in a chain reaction (96), (97),27salthough Lovelock believes that the release of Freons may be insignificant

+ hv C1 + O3 c10 + 0

CF2CI2

____j

CF,CI*

+ C1*

+ O2 c1 + 0, C10

(95)

(96)

(97)

compared with halogens occurring naturally in marine environments. Concentrations of tropospheric fluorocarbons 277 and the photochemistry of halogenated compounds in marine atmospheres 278 are the subjects of reports relevant to this particular problem. As stressed above, the controversy surrounding the potential hazard of 0, destruction is usually associated with the simplicity of the model 270

271

2i2 273

274

a7e

277 278

R. Schulze, Radiation Environ. Biophys., 1974, 11, 21; A. E. S. Green, T. Sawada, and E. P. Shettle, Photochem. and Photobiol., 1974, 19, 251; P. Cutchis, Science, 1974, 184, 13. P. Rigaud, Ann. Geophys., 1974, 30, 319; J. H. Park and J. London, J. Atmos. Sci., 1974,31, 1898; K. Fukuyama, J. Atmos. Terr.Phys., 1974,36, 1321; J. J. Barnett, J. T. Houghton, and J. A. Pyle, Quart. J. Roy. Met. SOC.,1975, 101, 428. R. L. Tayler, Canad. J . Chem., 1974, 52, 1436. J. London and J. H. Park, Canad. J . Chem., 1974, 52, 1599; M. I. Hoffen, W. G. Hoydysh, S. Hameed, A. Sergey, and A. S. Lebedeff, Atmos. Environ., 1975, 9, 33. J. Hampson, Nature, 1974, 250, 189. E. Hesstvedt, Canad. J. Chem., 1974, 52, 1592; H. S. Johnson, Acta Astronaut., 1974, 1, 135; F. N. Alyea, D. M. Cunnold, and R. G . Prinn, Science, 1975, 188, 117; J. L. Goldberg, Search, 1975, 6, 112. R. S . Stolarski and R. J. Cicerone, Canad. J. Chem., 1974, 52, 1610; M. J. Molina and F. S. Rowland, Nature, 1974, 249, 810; J. E. Lovelock, ibid., 1974, 252, 292; 1975, 256, 193; J. P. Chesick, ibid., 1975,254,275; P. A. Lacey, Science, 1975,187, 1181 ; R. S. Rowland and M. J. Molina, Rev. Geophys. Space Phys., 1975, 13, 1. N. E. Hester and E. R. Stephens, J . Air. Pollution Contr. ASSOC., 1974, 24, 591. 0. C. Zafiriou, J. Geophys. Res., 1974, 79, 2730.

138

Photochemistry

assumed for stratospheric transport of materials, and the number of reactants involved. All participants must agree, however, that more meaningful estimates of the magnitude of the problem will result from laboratory experiments in which rate-constants for reactions of prime aeronomic interest are measured. Several reviews of such important stratospheric reactions involving 0,, HO,, SO,, NO,, and CIO, have been published recently,27gto which readers are recommended. The rate-constant of reaction (94) is clearly of critical importance, and this has recently been measured as kg4

= (9.44 f 2.46) x 1O1O exp [(-2509 f 76) KJT]cm3mol-l s-1

over the temperature range 259-362 K.280Finer details of the reaction have also been probed. Thus it has been shown in a molecular-beam study that NO(,n#) reacts differently (98) from N0(21Ti)(99),,*l and it was further shown that the

rate of reaction (loo), producing primarily the 2B1state of NO,, giving rise to chemiluminescence,was enhanced by a factor of 5.6 k 1 .O upon vibrational excitaThe rate-constants for reactions (100)-(103) were measured tion of the 03.222

+ NO 03t + NO O3 + NO 03t + NO O3

+

___c,

+ O2 N0,*(2B1) + 0, NO,*(,B,)

(1Oo)

(101)

+ 0, (102) N02t(2A1)+ 0, (103) (k,,, + + klo2)= 16.2 k NO,t(,A1)

as klol k103 = 1.62 x lo8 1mo1-1 s-l; k103)/(klOO 4.0; klO1/klOO = 4.1 f 2.0; and k103/k102 = 17.1 f 4.3, where the vibrational excitation of the O3exclusively in the v, bending mode promotes reaction.222The vibrational chemiluminescence from reaction (102) has also been studied,282and rate-constants for quenching of NO2+ by Ar and NO, are quoted as 3.6 x lo7 and 1.8 x log I mol-1 s-l, respectively. The quantum yield of removal by photolysis of the Freon CF,Cl, in oxygen at 184.9 nm has been shown to be 1.12 0.09, with CO, being a major product, with quantum yield 1.11 f 0.05.283Reactions (104)--(106) and the reactions of

+ NO C1 + CH, OH + HCI ClO

279

280

281

28s

-

C1* + NO,

(104)

+ CH3 H,O + C1

(105)

HCl

(106)

M. Nicolet, Canad. J . Chem., 1974, 52, 1381; K. H. Welge, ibid., 1974, 52, 1424; R. J. Cvetanovic, ibid., p. 1452; P. Crutzen, ibid., p. 1569; S. C. Wofsy and M. B. McElroy, ibid., p. 1582. R. E. Huie and J. T. Herron, Chem. Phys. Letters, 1974, 27, 411. A. E. Redpath and M. Menzinger, J . Chem. Phys., 1975, 62, 1987. M. F. Golde and F. Kaufman, Chem. Phys. Letters, 1974, 29, 480. R. Milstein and F. S. Rowland, J. Phys. Chem., 1975, 79, 669.

139

Gas-phase Studies

C1 atoms with H,, HO,, H202, and HN03 could all be of importance in the stratospheric destruction of C1- and rates of removal of C1* by these reactions have been given.284 Rate-constants for reactions of O(l0) with CHF,CI, CF2CI2,CFC13, CF2ClCF2CI,CF2C1CFCl2,CF,, and neopentane relative to that with N20 were found to be 286 1.6, 2.4, 2.65, 1.5, 2.5, < 0.1, and 8.4, respectively, which means that, with the exception of that for CF4,they are close to the diffusioncontrolled rate, in contrast to reactions of O(3P) with fluorocarbons. Major products of the reactions with methanes were COF, and COFCI. Stratospheric aerosols corresponding to a volcanic eruption,286the formation of the ionosphere 287 and the U.V. airglow from 121.6 to 30.4 nm,288aand 0 atom concentrations in the lower ionosphere 288b have been discussed. Many of the reactions of 0,, HO,, NO,, CO,, and SO, discussed below are also of relevance to stratospheric chemistry.

0, Reactions.-The cross-section for charge transfer between 0- ions and 02(3&-) has a maximum value of 7.8 x 10-l6 cm2 at an energy of 5 keV of the incident whereas that for 0-and 02(lAg) was less than 1 x 10-16cm2. Reaction rate-constants for reactions of 0-,OH-, 02-,C1-, C 0 3 - ,and OH-(H20) with H,O have been measured, and association rate-constants for several ions The rate of formation of NO+ by the reaction of with CO, and SO, O+ with N, has been commented upon.201 The formation of H02+and Os+by the reaction of O2+(li4nu)with H2and O2has been reported,202and 02+-O,, NO+-NO interactions have been Rate-constants for reactions of 02+(a"*rIu) with N2, Ar, CI, CO,, Ha, and 0,have been and electron-transfer transitions during the collision of O,, N,, NO, and CO with their respective ions discussed.206The nearly resonant process (107) has been shown not to occur with high efficiency.206The lifetime of the X3n, state of OH+ has been shown to be 900 ns.87 N

He+(ls2S)

+ 02(23Zg-;u = 0)

-

He(ls21S)

+ 02+(E4X,-;

u = 0)

(107)

The reaction of O(l0) with N20 has been found to be independent of excess energy in the atomic species.207Absolute values for quenching O(l0) by several 285

286

zs8 289

2no 281

283

2n3

284

28b 2g6

297

M. J. Molina and F. S. Rowland, J. Phys. Chem., 1975, 79, 667. J. N. Pitts, jun., H. Sandonal, and R. Atkinson, Chem.Phys.Letters, 1974,29,31; H. Sandonal, R. Atkinson, and J. N. Pitts, jun., J. Photochem., 1974/5, 3, 325. A. B. Meinel and M. P. Meinel, Science, 1975, 188, 477. B. Landmark, Cosmical Geophys., 1973, 73. (a) R. R. Meier, Ann. Geophys., 1974, 30, 91 ; (b)P. G . Dickinson, R. C. Bolden, and R. A. Young, Nature, 1974, 252, 289. R. F. Mathis and W. R. Snow, J. Chem. Phys., 1974, 61,4274. F. C. Fehsenfeld and E. E. Ferguson, J . Chem. Phys., 1974, 61, 3181. R. B. Cohen, Chem. Phys. Letters, 1975, 30, 284. J. M. Ajello, K. D. Pang, and K. M. Monahan, J. Chem. Phys., 1974, 61, 3152; J. M. Ajello, W. T. Huntress, and A. L. Lane, ibid., 1974, 60, 1211. T. F. Moran, M. R. Flannery, and P. C. Crosby, J. Chem. Phys., 1974, 61, 1261. W. Lindinger, D. L. Albritton, M. McFarland, F. C. Fehsenfeld, A. L. Schmeltekopf, and E. E. Ferguson, J. Chem. Phys., 1974, 62, 4101. Y. N. Chiu and Y. K. Pan, Chem. Phys. Letters, 1975, 32, 67. H. H. Harris, M. G . Crowley, and J. J. Leventhal, Chem. Phys. Letters, 1974, 29, 540. H. A. Wiebe and G . Paraskevopoulos, Canad. J. Chem., 1974,52,2165; J. C. Tully, J. Chem. Phys., 1975, 62, 1893.

140

Photochemistry

Table 7 a Rate-constants for quenching of O(lD) Quencher k/l mol-l s-l He <4.2 x 105

Ref. b

He Ne Ar Ar Ar Kr Xe

<3.0 x 107 6.6 x lo7 4.26 x lo8 4.8 x lo8 4.8 x lo8 9.30 x los 6.6 x 1Olo

H 2 H 2

1.5 x 10l1 1.8 x loll

C

b b C

d b b C

d

For more relative rate constants for O ( l D ) deactivation see ref. 325; et al.; Ref. 298, Stief et al.; From ref. 325.

Ref. 298, Husain

species are given in Table 7.2s8The production of 0,(41&+; u = 0, 1, 2) by the reaction of O(lD) with 0,has been discussed.2s0 The rate of collision-induced emission from O(lS) has been shown to depend linearly upon argon or xenon concentration in the gas Reactions of O(l0) with CO to give O(3P) and CO (u < 7) have been reported.l*l Absolute rate-constants for the reactions of O(3P) with a variety of substrates from modulation techniques are given in Table 8.301 CH3Br and Various aspects of reactions of O(3P)with ammonia and C02,302 CHaC1,303 C2C14and CH2CC12,304 H202,306 formaldehyde, crotonaldehyde, and dimethyl s ~ l p h i d eand , ~ ~with ~ H, N, and NO 308 have been reported. Crosssections for the reaction of O(3P) with H+, Of, N+, 0-, and 0,- have been Reaction (108) has been found to have a rate constant of 1.08 x loB 1, mol-, s-l when M = 0, or N,.310 O + 0 2 + M

-

03t+M

(108)

Energy partitioning in the photoionization of NO and 02,311the extreme-u.v. photodissociation of 02,312 and predissociation in the Schumann-Runge bands of 02313 have been discussed. 298

2ss 300 301

302 303 304 Sob 306

308

310

311 312

R. F. Heidner, tert., and D. Husain, Internat. J. Chem. Kinetics, 1974, 6, 77; L. J. Stief, W. A. Payne, and R. B. Klemm, J. Chem. Phys., 1975,62,4000. M. J. E. Gauthier and D. R. Snelling, Canad. J. Chem., 1974, 52, 4007. D. L. Cunningham and K. C. Clark, J. Chem. Phys., 1974, 61, 1118. R. Atkinson and J. N. Pitts, jun., Chem. Phys. Letters, 1974, 27, 467; ibid., 1974, 29, 28; J. Phys. Chem., 1975, 79, 295; I. R. Slagle, R. E. Graham, J. R. Gilbert, and D. Gutman, Chem. Phys. Letters, 1975, 32, 184; S. Furuyama, R. Atkinson, A. J. Colussi, and R. J. Cvetanovic, Internat. J. Chem. Kinetics, 1974, 6, 741. J. N. Bass, J. Chem. Phys., 1974, 60, 2913. A. A. Westenberg and N. de Hass, J. Chem. Phys., 1975, 62, 4477. G. Sanhueza and J. Heicklen, Canad. J. Chem., 1974, 52, 3870; J. Photochem., 1975, 4, 1. J. H. Birely, J. V. V. Kasper, F. Hai, and L. A. Damten, Chem. Phys. Letters, 1975, 31, 220. D. D. Davis, W. Wong, and R. Schiff, J. Phys. Chem., 1974, 78, 463. R. D. Cadle, H. H. Wickham, and C. B. Hall, Chemosphere, 1974, 3, 115. B. Brunetti and G. Liuti, Z. phys. Chem. (Frankfurt), 1975, 94, 19; T. Ibaraki, K. Kodera, and I. Kusunoki, J. Phys. Chem., 1975,79, 95. J. A. Rutherford and D. A. Vroom, J. Chem. Phys., 1974, 61, 2514. C. W. von Rosenberg, jun., and D. W. Trainor, J. Chem. Phys., 1974, 61,2442. G. M. Lawrence, Chem. Phys. Letters, 1975, 31, 419. R. W. Carlson, J . Chem. Phys., 1974, 60, 2350. P. S. Julienne and M. Krauss, J. Mol. Spectroscopy, 1975, 56, 270.

Gas-phase Studies

141

Table 8 Rate-constants for O(3P)reactions Substrate

cs Ethylene Propylene But-1-ene Isobutene cis-But-2-ene Trimethylethylene Tetramet hylethylene NO(+M = NzO) NO(+M = N,O) SO,(+M = N,O) Benzene Toluene o-Xylene m-Xylene p-Xylene 1,2,3-Trimethylbenzene 1,2,4-Trirnethylbenzene 1,3,5-Trimethylbenzene a

Temperature range/K 305 300a 300-392 300 a 300-392 300 a 300 a 300 a 300 a 300 a 300 a 300-392 299-392 300-392 300-392 300-392 300-392 300-392 300-392 300-392 300-392

k/l mol-l s1 [or (12 moP2 s-l)*] 1.24 x 1O1O 4.3 x 108 3.37 x logexp [(- 1270 & 200)/RT] 2.0 x 109 2.08 x lo9exp [-(0 f 300)/RT] 2.4 x 109 9.85 x 109 9.00 x 109 3.11 x 1O1O 4.44 x 1010 5.78 x 1O1O 9.6 x log exp [-(go0 k 200)/RT] 3.32 x loloexp [-(2000 & 400)/RT] 1.11 x 1OlOexp [-(3980 k 400)/RT] 8.2 x log exp [-(3100 & 300)/RT] 6.25 x logexp [-(2430 k 300)/RT] 7.7 x lo9 exp [-(2150 k 300)/RT] 7.9 x log exp [-(2540 i-300)/RT] 1.03 x 1O1O exp [ -(16OO f 300)/RT] 9.35 x 10gexp [-(1650 f 300)/RT] 6.05 x log exp [-(770 k 300)/RT]

Ref. 301, Cvetanovic et al., others Pitts et al.

The quenching efficiency kq of Oz(l&,+) by a variety of molecules has been shown to correlate inversely with the maximum vibrational frequency of the quencher according to relation (log), where q is the quenching rate divided by the

K logq = -

AE’ vvib(maX)

+c

collision number and AE’ is the energy difference between 0-0 levels of the 02(1C,+) and O,(lA,) Thus the closer vvib(max) approaches AE‘, the more efficient the quenching becomes. Chemiluminescence from HNO* has been observed in the reaction system 0(3P)-C3H,-NO-0,(1~,)-0, from reactions (1 10) and (111) 316 and in the reacHNO(lA’) HNOCA”)

+ 02(lA,> + O,(lA,)

-

+ + 02(3C,-)

H N 0 ( 3 ~ ” ) 02(3Cg-)

(1 10)

HNO*(lA”)

(111)

tion of O,(lA,) with ethyl vinyl ether.31s The production of O,(lA,) with neari.r.,317 the vibrational relaxation of 02(1Ag),318and the observation of ‘dimol’ 314

316 s16

317

s18

6

J. A. Davidson and E. A. Ogryzolo, Canad. J. Chem., 1974, 52, 240; K. Kear and E. W. Abrahamson, J . Photochem., 1975, 3, 409; R. G. 0. Thomas and B. A. Thrush, J.C.S. Faraday ZZ, 1975, 71, 664. T. Ishiwata, H. Akimoto, and I. Tanaka, Chem. Phys. Letters, 1974, 27, 260. D. J. Began, R. S. Sheinson, R. G. Gamm, and F. W. Williams, J. Amer. Chem. Soc., 1975, 97, 2560. R. A. Nathan and A. H. Adelman, J.C.S. Chem. Comm., 1974, 674. J. G. Parker and D. N. Ritke, J . Chem. Phys., 1974, 61, 3408; J. G. Parker, ibid., 1975, 62, 2235.

142

Photochemistry

emission at 633 nm in the gas phase319 have been reported. Arrhenius parameters for some reactions of O,(lA,) with simple olefins were found to have preexponential factors of 8.2, and activation energies between 3.2 and 7.5 kcal m01-1.320 The role of O#&) in organic peroxide chemistry has been reviewed.321 Several aspects of oxidation reactions have been reported e x t e n s i ~ e l y . ~ ~322~ ~ The far4.r. rotational spectrum of 03323 and the mechanism of O3 formation in an 0, glow discharge324have been discussed. The rate constants for O(lD) deactivation and O,(lC,+) deactivation relative to those for 0, and 03,respectively, were found to be (l.O), 0.72, 8.0, 5.0, 5.1, 3.3, 2.7, 4.0, 1.0, 10.8, 14.0, 3.0, and 4.1 for O(lD) and 0, 0, (l.O), 0.22, 0.004, 0.002, 0.010, 0.04, <0.001, 0.015, 0.018, 0.003, and 0.0024 for O,(l&+) for the following gases, respectively: 02,N2,03,HzO, CH4, NzO, CO,, H2, Cl,, C3Hs, neo-C,Hl,, HCl, and OCS,326 in a study of U.V. photolysis of ozone at 253.7 nm. and enhancement of reaction rates of O3 by Vibrational relaxation in 03326 vibrational excitation 222 have been discussed. Reactions of ozone with saturated ~ l e f i n s H2S,32B , ~ ~ ~ metal alkyl~,~~O a c e t a l ~ carbon ,~~~ and CH3*, CH30*, and CH302*radicals3s3 have been reported. These last studies are, of course, of great importance in polluted urban atmospheres, but lack of space forbids detailed discussion of these papers. lBo9

HO, Reactions.-The lifetime for the K' levels 0, 1, 2, and 4 of the J2x+ state of OH has been found to be of the order of 688 ns, which when corrected for quenching, by extrapolation, leads to an average value of 765 ns.334 The rateconstants for reactions (112) and (113) have been measured as 1.26 x lo8 318

I. B. C. Matheson, J. Lee, B. S. Yamanashi, and M. L. Wolbarsht, Chem. Phys. Letters,

320

R. D. Ashford and E. A. Ogryzlo, Canad. J. Chem., 1974, 52, 3544; J . Amer. Chem. SOC.,

1974, 27, 355. 1975,97, 3604.

321

322

323 524

326

3f6

327

328

3as

3s0

331

332 339 334

W. Adam, Chem. Z., 1975, 99, 142. P. Jones, K. Selby, M. Tidball, and D. Waddington, Combustion and Flame, 1974, 22, 209; C. Jachimowski, ibid., 1974, 23, 233; W. G. Alcock and B. Mile, ibid., 1975, 24, 125; E. A. Dorko, D. M. Bass, R. W. Crossley, and K. Scheller, ibid., 1975, 24, 173; D. F. Cooke and A. Williams, ibid., 1975, 24, 245. J. W. Fleming and R. P. Wayne, Chem. Phys. Letters, 1975, 32, 135. L. E. Khvorostovskaya and V. A. Yankovsky, Optika i Spektroskopiya, 1974, 37, 26. M. J. E. Gauthier and D. R . Snelling, J. Photochem., 1975, 4, 27. K. K. Hui, D. I. Rosen, and T. A. Cool, Chem. Phys. Letters, 1975,32, 141; D. I. Rosen and T. A. Cool, J. Chem. Phys., 1975, 62,477. H. Varkony, S. Pass, and Y. Mazur, J.C.S. Chem. Comm., 1974, 437. K. H. Becker, U. Schurath, and H. Seitz, Internat. J. Chem. Kinetics, 1974,6,725; J. T. Herron and R. E. Huie, J. Phys. Chem., 1974, 78, 2085; S. M. Japar, C. H. Wu and H. Niki, ibid., p. 2318. S. Glavas and S . Toby, J. Phys. Chem., 1975, 79, 779. H. U. Lee and R. N. Zare, Combustion and Flame, 1975, 24, 27. P. Deslongchamps, P. Atlani, D. Frehel, A. Malaval, and C. Moreau, Canad. J. Chem., 1974, 52, 3651; P. Deslongchamps, C. Moreau, D. Frehel, and R. Chehevert, ibid., 1975, 53, 1204. P. S. Bailey, J. W. Ward, T. P. Carter, E. Nieh, C. M. Fischer, and A. Y. Khashab, J . Amer. Chem. SOC.,1974, 96, 6136. R. Simonaitis and J. Heicklen, J. Phys. Chem., 1975, 79, 298. K. H. Becker and D. Haaks, 2. Naturforsch., 1973, 28a, 249; J. H. Brophy, J. A. Silver, and J. L. Kingsey, Chem. Phys. Letters, 1974, 28, 418; R. K. Lengel and D. R . Crosley, ibid., 1975,32,261; P. Hogan and D. D. Davis, ibid., 1974,29, 5 5 5 ; J. Chem. Phys., 1975,62,4574; K. R. German, ibid., p. 2584.

Gas-phase Studies

-

OH+OH OH

+ OH + N,

1 mo1-1 s-l and 9.0 x

143 H,O+O

H,O,

(1 12)

+ N,

(113)

1 O 1 O 1, m o P s-l, respectively.336Recent evaluations of the temperature dependence of the important reaction (1 14) have shown peculiarities, non-Arrhenius behaviour being The complete collated data for this reaction fit the empirical expression (115). An analysis of the vibrational

C O + OH

C02+ H

logk,,, = 10.83

+ 3.94 x

(1 14)

low4T/K

(1 15)

energy content in the products revealed no i.r. emission from any of the fundamental or strong combination bands in C02, and the implications of this for the energetics of the reaction were considered. The reactions of OH radicals with a variety of substrates have been investigated, including ammonia,337 H2S,338DMS0,339 aromatic NO and N02,343 and some olefins and hydrocarbons.344 Results from the last two papers are shown in Table 9.3a4The chemiluminescence from OH in lean H,-0, flames has been

Table 9 344 Rate-constants for OH reactions with substrates Substrate c2H4

GH6

GH6

But-l-ene trans-But-2-ene Propane n-Butane Cyclobut ane Cyclohexane a

Rate-constantllmol-l s-l 1.38x 109 3 x 109 8.04 x 109 9 x 109 7.2 x 109 1.32 x 109 1.74 x 109 1.42x 109 7.2 x 109 4.0 x 109

Ref. 344, Carr et al. ; a Ref. 344, Volman et al. ;

Ref. a a b a a b

b C

b b

From ref. 350.

Studies on the photolysis of water vapour at 147 nm, producing H, (a) in a primary process at 174 nm, (b) by two-photon absorption, and (c) in a photo335

336

337

338

339 340

y41

349

344

346

D. W. Trainor and C. W. von Rosenberg, jun., J. Chem. Phys., 1974, 61, 1010. D. Baulch and D. Drysdale, Combustion and Flame, 1974, 23, 215; D. Trainor and C. W. von Rosenberg, Chem. Phys. Letters, 1974, 29, 35; D. D. Davis, S. Fischer, and R. Schiff, J. Chem. Phys., 1974, 61,2213. M. J. Kurylo, Chem. Phys. Letters, 1973,23,467; W. Hack, K. Hoyermann, and H. G.Wagner, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 386. F. Stuhl, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 230. B. C. Gilbert, R. 0. C. Norman, and R. C. Sealy, J.C.S. Perkin 11, 1975, 303, 308. M.F. R. Mulcahy and B. C. Young, Carbon, 1975,13, 115. D. D. Davis, W. Bollinger, and S . Fischer, J. Phys. Chem., 1975, 79, 293. W. B. DeMore and E. Tschuikow-Roux, J. Phys. Chem., 1975,78, 1447. J. G. Anderson, J. J. Margitan, and F. Kaufman, J. Chem. Phys., 1974, 60, 3310; G. W. Harris and R. P. Wayne, J.C.S. Faraday I, 1975, 71, 610. R. A. Gorse and D. N. Volman, J. Photochcm., 1974, 3, 115; A. V. Pastrana and R. W. Can, jun., J. Phys. Chem., 1975,79, 765. M. G. Davis, W. K. McGregor, and A. A. Mason, J. Chem. Phys., 1974, 61, 1352.

Photochemistry

144

fluorescence excitation experiment, have been Near-i.r. emission bands of HO, 347 and the reactions of this species with NO and NO, [reactions (116)-( 118)] 348 have been discussed, rate-constants for (1 16)-( 118) being measured at 296K as 7.2 x lo8, 8.4 x lo7, and 7.2 x lo7lmol-ls-l, respectively. HO,+NO HO,

+ NO (+ M) HO,+NO,

___+

N02+OH

(116)

HONO, (+ M)

(117)

H O N O + 0,

(1 18)

Rate-constants for the reactions of hydrogen atoms with H 2 0 zobtained in a photolysis experiment in two studies differ slightly, the results of Volman et aLsr4 for reactions (119) and (120) being 3.42 x lo6 and 1.86 x lo6 lmol-ls-l, H

-

+ H,O, ---+

+ OH + HO2

H,O H2

report a ratio kl19/k120= 1.3. The thermally induced whereas Heicklen et chain reaction in the gas phase between H202, NO,, and CO has been reported.350 N,, NO,, and HNO, Reactions.-There have been several studies on the atmospherically important ion N2+.351 Dufayard et al. have shown that the lifetimes of selected rotational bands in the B2Zu++ system increase from 60 to 90 ns when perturbed by the interacting A2111,state. The reaction of N2+with N, to give N3+,studied by Bowers et al., seems to indicate that two excited states of N2+are of importance, and the quenching of CO,+, N,O+, and N2+produced by 58.4 nm excitation by a variety of atmospheric gases was reported by Freeman and Phillips. Charge-transfer cross-sections for quenching of metastable N+(lD) by krypton and CO have been and the formation of NO+ in the reaction between O+ and N, was A kinetic study of the reactions of electronically excited N(,Dj and ") atoms has been reported which uses vacuum-u.v. resonance radiation as a and such radiation has also been observed in studies in the photodissociation Various aspects of N2(A3Zu+)in N, afterglows have fragments of N, and 0,.355 been NO(f211 + emission in the radiative recombination of

z2&+

x2Z+)

346

347

348 349 350

351

A. Y. M. Ung, Chem. Phys. Letters, 1974,28, 603; G. A. Chamberlain and J. P. Simons, ibid., 1975, 32, 355; C. C. Wang and L. I. Davies, jun., J. Chem. Phys., 1975,62, 5 3 ; C . C. Chou, J. G. Lo, and F. S. Fowland, ibid., 1974, 60, 1208. K. H. Becker, E. H. Fink, P. Langen, and U. Schurath, J. Chem. Phys., 1974, 60,4623. R. A. Cox and R. G . Derwent, J. Photochem., 1975, 4, 139. J. F. Meagher and J. Heicklen, 3. Photochem., 1975, 3, 455. I. M. Campbell, B. J. Handy, and R. M. Kirby, J.C.S. Faraday Z, 1975,71, 867. J. Tellinghuisen and D. L. Albritton, Chem. Phys. Letters, 1975, 31,91; C . G. Freeman and L. F. Phillips, Cunud. J. Chem., 1974, 52, 426; J. Dufayard, J. M. Negre, and 0. Nedelec, J . Chem. Phys., 1974, 61, 3614; M. T. Bowers, P. R. Kemper, and J. B. Laudenslager, ibid., 1974, 61,4394.

352

363 364 356 358

J. A. Rutherford and D. A. Vroom, J. Chem. Phys., 1975, 62, 1460. R. B. Cohen, Chem. Phys. Letters, 1975, 30, 284. D. Husain, S. K. Mitra, and A. N. Young, J.C.S. Faraday IZ, 1974, 70, 1721. L. C. Lee, R. W. Carlson, D. L. Judge, and M. Ogawa, J. Chem. Phys., 1974, 61, 3261. W. Brennen, R. V. Gutowski, and E. Shane, Chem. Phys. Letters, 1974, 27, 138; A. Y. M. Ung, ibid., 1975, 32, 193; F. Faure, F. Valadier, and J. Janin, J. dePhysique, 1975, 36, 117.

145

Gas-phase Studies

N and 0 atoms, and in photodissociation and excitation lasers,357and vibrational excitation and relaxation in the NO(T2n~) ground state have been The reactions of NO(,IIl) and N0(2nt) with ozone 281 and NH28D were discussed earlier,281the rate-constant for the latter process being 1.26 x 1Olo 1 mol-1 s-l. Continuous emission from NO, 35D and single vibronic level fluorescence from NO,360 have been reported. The lifetimes of the 2B1(K’ > 0) states were measured, and the interesting result was obtained that the lifetime of the K’ = 4, N’ = 16 f 1 level was 36 ps, substantially greater than that of the K’ = 0 levels. The increase in lifetime is attributed to Renner interaction of the ,B1 and 2Al components of the linear 211ustate. Rotational excitation has been shown to assist in the dissociation of NO, in the 249.1 nm system, but this is minor in extent compared with that observed in the 397.9 nm system. Yields of O(l0) were In the report by The photolysis of NOz has been further Harteck et al., a two-photon excitation process was observed when a pulsed ruby laser was used for excitation. Thermal and photochemical reactions of NO, with b u t ~ r a l d e h y d e ,other ~ ~ ~ aldehyde-NO, and methylperoxyl radicalNO, reactions 365 have been discussed. The vacuum-u.v. photolysis of N 2 0 has been reported in several For ,A, > 185 nm, reaction (121) occurs with unit quantum yield, but at shorter wavelengths reactions (122) and (123) become of importance, the quantum yield N20

+ hv

___j

N,

+ O(l0)

(121)

I__,

N,

+ O(lS)

(1 22)

-

N2(X3aC,+) + O(3P)

(123)

of O(lS) atoms approaching unity at 129 nm. Most of these atoms are deactivated to the O(l0) state. Simons et al. showed that, at ,A, = 140-155 nm, N O is formed through O(l0) and Nz(x3C,+),with N,O (see also ref. 297) with O(lS) reactions perhaps also contributing. The production of N,(s311g)with a threshold at 9.025 eV (137.4 nm) was shown by McEwan et al. to require two different processes, one direct, the other indirect, involving a precursor with a lifetime of 27 ps. Vacuum-u.v. fluorescence from photodissociation fragments of N20367 and the formation of N,0+(x2C+)in the photoionization of N20368 have been 367

358

359 3G0

361 362

363 364 356 3G6

367

3G8

C. K. K. Yeung and C. R. Phillips, Atmos. Enoiron., 1974, 8, 493; M. C. Lin, I.E.E.E. J . Quantum Electron., 1974, 10, 516; T. W.Dingle, P. A. Freedman, B. Gelernt, W. J. Jones, and I. W. M. Smith, Chem. Phys., 1975,8, 171. Y. Nachshon and P. D. Coleman, J . Chem. Phys., 1974,61, 2520; M.Tronc, A. Huetz, M . Landau, F. Pichon, and J. Reinhardt, J. Phys. (B), 1975,8, 1160. S. Butler, C. Kahler, and D. H. Levy, J. Chem. Phys., 1975,62, 815. S. E. Schwartz and G. I. Senum, Chem. Phys. Letters, 1975,32, 569. W.M.Uselman and E. K. C. Lee, Chem. Phys. Letters, 1975,30, 212. D. Hakala, P. Harteck, and R. R. Reeves, J . Phys. Chem., 1974,78, 1583; H.Gaedtke and J. Troe, Ber. Bunsengesellschaftphys. Chem., 1975,79, 184. S. Jaffe and E. Wan, Enoiron. Sci. Technol., 1974,8, 1024. S. L. Kopczynski and A. P. Altschuller, Enoiron. Sci. Technol., 1974,8, 909. R. Simonaitis and J. Heicklen, J. Phys. Chem., 1974,78, 2417. M. J. McEwan, G. M. Lawrence, and H. M. Poland, J . Chem. Phys., 1974, 61,2857; G. Black, R. L. Sharpless, T. G. Slanger, and D. C. Lorents, ibid., 1975,62,4266;G. A.Chamberlain and J. P. Simons, J.C.S. Faraday ZI, 1975,71,402. L. C.Lee, R. W. Carlson, D. L. Judge, and M. Ogawa, J . Phys., 1975, 8, 977. H. Hertz, H. W. Jochims, and W. Sroka, J . Phys. (B), 1974,7, L548.

146

Photochemistry

reported. Microwave discharge of N20-N2 mixtures as a source of 0 chemiluminescence in N,O-metal and vibrational excitation and relaxation in COS, N20, CS2,and C,N, 371 have been discussed. The photochemistry of N205with adamantanes has been The photolysis of nitrous acid (HN02) has been investigated.373 The predominant reaction at 330-380 nm is (124a), with reaction (124b) accounting for H N O , + hv H N O , + hv OH

+ HNOZ

-

O H + NO

(1 24a)

H+NO2

(125b)

HZO

+ NO,

(1 25)

not more than 10% of reaction at A,, = 366 nm. The rate-constant for reaction (125) was estimated as 1 . 1 x lo@1 mol-l s-1 by Cox, and rate-constants were also given by him for reactions of OH radicals with NO, HN02, and SO, [reactions (126)-(128)] of 3.66 x lo@,1.32 x lo@,and 3.6 x 1081mol-1s-1,respectively (see also refs. 337-344, and Table 9).

-

+ NO + M HN02 + M + HNO, H,O + NO, OH + SO, + M HS03 + M (M = N, + 02,1 atmosphere) OH

OH

CO, Reactions.-The

(126) (127) (128)

lifetimes of the v' = 0, u' = 1, and v' = 2 levels of the

B2C+ states of CO+ have been shown to be 54 k 5, 50 +_ 5, and 52 f 6 n s , re~pectively.~The lifetime of the B2Z+ state of CO,+ was also shown to be 112 k 12 n ~ The . ~ kinetics of reactions of CO+ and HCO+ with C0,37pthe

photoionization of C0,-CO-0, mixtures,37sand the reactions of ion c l u ~ f e r ~ , ~ ~ ~ and the cross-sections for the production of CO+(BzC+)in the photoionization of CO 377 have been discussed. The rate-constants for the quenching of CO(C3n) by H,, D,, O,, CHo, C2H2, and C,H, have been measured at 300 K and (77 K) as 1.2 (0.6), 1.08 (0.72), 1.38 (0.96), 0.78 (0.45), 2.16 (1.08), 10.8 (4.08), and 4.02 (1.62), respectively, in units of 10" 1 mol-1 s - ~ . ~ ~ ~ The photodissociation of CO, at wavelengths between 106.7 (Phillips and Sethi) and 150 nm (Slanger et al.) has been The quantum yield of CO production was reported as 0.57 (121.6 nm), 0.21 (130 nm), 0.46 (139 nm), and 0.58 (149 nm). At 106.7 nm, 0 atoms were lost in the system, and it was 369

370

A. Y. M. Ung, Chem. Phys. Letters, 1975, 32, 351. S. A. Edelstein, D. J. Eckstrom, N . E. Perry, and S. W. Benson, J . Chem. Phys., 1974, 61, 4932.

371

372 3i3 374 3i6

3i6 377

378

379

J. K. Hancock, D. F. Starr, and W. H. Green, J. Chem. Phys., 1974, 61, 3017. I. Tabushi, S. Kojo, and Z. Yoshida, Chem. Letters, 1974, 1431. R. A. Cox, J. Photochem., 1974, 3, 175, 291 ; T. Nash, Tellus, 1974, 26, 175. M. Meot-Ner and F. H. Field, J . Chem. Phys., 1974, 61, 3742. L. W. Sieck and R. Gorden, jun., J . Res. Nut. Bur. Stand., Ser. A., 1974, 78, 315. M. Meot-Ner and F. H. Field, J . Chern. Phys., 1974, 61, 3742. L. C. Lee, R. W. Carlson, and D. L. Judge, J . Geophys. Res., 1974, 79, 5286. W. G. Clark and D. W. Setser, Chem. Phys. Letters, 1975, 33, 71. T. G. Slanger, R. L. Sharpless, G. Black, and S. V. Filseth, J . Chem. Phys., 1974, 61, 5 0 2 2 ; R. F. Phillips and D. S. Sethi, ibid., 1974, 61, 5473.

Gas-phase Studies

147

suggested that these might react with window material. The results all suggest that current estimates of photodissociation rates in the atmospheres of Mars and Venus may be too great by a factor of 2.2463246s 248 Vibrational relaxation in CO and C02,380 and various aspects of the CO, 113*381 371* 116 lasers, have been reported. The oxidation of CO 383 and the and CO effect of CO on the photo-oxidation of NO-hydrocarbon mixtures 384 have been discussed. SO,, H2SReactions.-The photolysis of SO, in H, at 147 nrn and 116-123.6 nm has been and emission from O H ( 2 -+ z),S,(B -+ and SO(8 +- 2) was observed in addition to SO, fluorescence. The quantum yield of SO, formation was found to be GO.4 at 123.6 nm. A fuller paper has appeared on single vibronic level fluorescence from the lB1 state of SO, vapour. This confirms that there are two different groups of rovibronic states, one of which is very longlived (80-600 p), the other being short (-50 ps) and with a bimolecular quenching rate-constant that is an order of magnitude greater than the gaskinetic rate.386 The extensive implications of this important observation were discussed in Volume 5,387and will not be repeated here. The photochemistry of SO, excited to the and lB1 states has been reported in an extensive paper.388 Apparently contradictory reports of quantum yields in earlier studies were reconciled in terms of the occurrence of reactions (129) and (130) in experiments of long residence time: the rate-constants were 1.2 x lo6 and 5 x lo5 1 mol-l s-l, respectively. For excitation to the ,B1state, this was the sole precursor to SO3 formation, and if this is again the precursor on 313 nm

x),

so + so, 2SO

-

2s02

SO,

+ S [or (SO),]

(129)

(1 30)

(lB,) excitation, the observations demand either that the 3B1 state is produced collisionally with higher efficiency from the lB1state than previous results indicate, or that another triplet, such as the or S02(3B2)state, is as efficient a reactant with SO, and NO as S02(3B1).Vibrational relaxation in the lB1 and 3B1states has been followed spectrosc~pically,~~~ and it was shown that phosphorescence persisted even at the lowest pressures used (0.6 mTorr) for excitation at 302.0 or 313.1 nm, and that the mechanism of production of the 3B1state was consistent with the evidence for two fluorescing species presented earlier.386~ 387 380

381

383 384

386 a86

988

3s0

D. F. Starr, J. K. Hancock, and W. H. Green, J. Chem. Phys., 1974,61,5421; R . C. Sepucha, Chem. Phys. Letters, 1975, 31, 75. E. P. Velikhov, E. A. Muratov, and V. D. Pis’mennyi, Pis’ma Zhur. Eksp. Teor. Fiz., 1974, 20, 108; C. Young and R. E. Chapman, J. Quant. Spectroscopy Radiative Transfer, 1974, 14, 679; J, Schwartz and E. Margalith, J. Appl. Phys., 1974, 45, 4469; 0. P. Judd, ibid., p. 4572; R . W. Weeks and W. W. Duley, ibid., p. 4661; I. Kitazima, ibid., p. 4961; R. C. Lind, J. Y. Wada, and G. J. Dunning, I.E.E.E. J . Quantum Electron., 1974, 10, 818. D. B. Cohn, I.E.E.E. J . Quantum Electron., 1974, 10, 459. C. H. Yang, Combustion and Flame, 1974, 23, 97. W.A. Glasson, Environ. Sci. Technol., 1975, 9, 343. C. Lalo and C. Vermeil, J . Photochem., 1975, 3, 441. L. E. Brus and J. R. McDonald, J . Chem. Phys., 1974, 61, 97. L. E. Brus and J. R. McDonald, Chem. Phys. Letters, 1973, 21, 283; J. G. Calvert, ibid., 1973, 20, 484. K.Chung, J. G. Calvert, and J. W. Bottenheim, Internat. J. Chem. Kinetics, 1975,7, 161. R. B. Caton and A. R. Gangadharan, Canad. J . Chem., 1974,52, 2389.

148

Photochemistry

Vibration-vibration energy transfer in SO, has also been The SO,-sensitized cis-trans isomerization of but-2-ene is a complex reaction, which at low pressures can be explained as involving only the 3B1 state of SO,, but which at higher pressures requires the intervention of some triplet state other than the phosphorescent 3B1 The photolysis of SO, in the presence of acetylene and allene also involves these non-phosphorescent triplet states, yielding CO as product, and giving rise to aerosol formation.3Q2Aerosol formation in SO,-N,-O, mixtures has been experimentally investigated,393and the effects of NO,, proInteractions between pylene, and water on SO, reactions have been SO, and atmospheric particulate matter,3Q5photochemical removal of SO, from the lower the use of SO, to trap 1,4-biradicals generated photochemically,3Q7 and the photochlorination of SO, s98 have all been discussed in recent publications. The photo-oxidation of H,S and dimethyl sulphide has been mentioned ea~1ier.l~~ SO, was a product from H2S, but not from Me,S: the latter was proposed to dissociate through the formation of an energy-rich dimethyl sulphoxide formed from O-atom attack [reactions (131), (132)]. 0

+ Me,S

[ ::

Me-S-Me

]*

+

[

?

---+

CH,.

+

Me-S-Me

]*

t-86.6 K cal mol-l

(131)

CH3SO’

Photochemical Urban Atmospheric Pollution.-Many of the reactions discussed in the headings above are of importance in an understanding of photochemically induced atmospheric pollution in urban situations, and are also important in stratospheric aeronomy. The remote sensing of airborne pollutants has been covered in Section 11, but we present here briefly the subject of some papers of general interest to atmospheric pollution. Many papers have been concerned with the mechanism of photochemical air pollution and its modelling,39Qand reports on ‘photochemical smog’ from 380 381

382

393

38p 885 388 397

3R8

D. Siebert and G. Flynn, J. Chem. Phys., 1975, 62, 1212. R. D. Penzhorn and W. G. Filby, J. Photochem., 1975, 4, 91; K. L. Demerjian and J. G. Calvert, Internat. J. Chem. Kinetics, 1975, 7, 45. M. Luria and J. Heicklen, Canad. J. Chem., 1974, 52, 3451; M. Luria and K. J. Olszyna, J. Aerosol. Sci., 1974, 5, 435. R. A. Cox, J. Aerosol. Sci., 1973, 4, 473; M. Takahashi and M. Kasahara, Kyoto Daigaku Genshi Enerugi Kenkyusha Iho, 1974, 45, 40. J. P. Smith and P. Urone, Enuiron. Sci. Technol., 1974, 8, 742. M. Vacatello, Ann. Chim. (Italy), 1974, 64, 27. R. D. Penzhorn, W. G. Filby, and H. Gusten, 2. Nuturforsch., 1974, 29a, 1449. M. R. Wilson and S. W. Wunderly, J. Amer. Chem. SOC.,1974, 96, 7350. G. J. Quarderer and R. H. Kadlec, Amer. Inst. Chem. Engineers J., 1974, 20, 141. B. J. Huebert, J. Chem. Educ., 1974, 51, 644; T. A. Hecht and J. H. Seinfeld, Environ. Scr. Technol., 1974,8,327; R. J. O’Brien, ibid., p. 579; H. Guesten and R. D. Penzhorn, Naturwiss. Rundschau, 1974,27, 5 6 ; P. J. Crutzen, Tellus, 1974,26,47;P. M . Roth and P. J. W. Roberts, Atmos. Enoiron., 1974, 8, 97; R. G. Lamb and J. H. Seinfeld, ibid., p. 527; M . Benarie, ibid., 1975,9, 552; P. Fabian, J. Geophys. Res., 1974,79,4124; W. Chameides and J. C. G. Walker, ibid., p. 4126; M. Munemori, Bunseki Kaguku, 1974,23,215; M. K. Liu, S . D. Reynolds, and P. M. Roth, Proc. Heat Transfer Fluid Mech. Inst., 1974, 287; B. E. Salzmann and J. E. Cuddeback, Analyt. Chem., 1975,47,1R; J. N. Pitts, jun., and B. J. Finlayson, Angew. Chem. Internat. Edn., 1975, 14, 1; R. S. Scorer, Naturwiss., 1975, 62, 46.

Gas-phase Studies

149

centres as far apart as Sydney, N.S. W.,400Southern England,401Japan,4o2MilanY4O3 and North America404 have been published. The detection and analysis of pollutant levels,4osthe reactivity of 0, and OaY4O6 the loss of SO, and Oafrom the and the effects of pollutants upon children and plants 408 have been discussed. Many papers have been concerned with tropospheric aerosol formation and their effects,40gand, finally, the inhibition of formation of photochemical smog by free-radical scavengers, phenol, benzaldehyde, aniline, and other aromatic molecules and amines 410 has been reported. ‘0°

(01

G. S. Hawke and D. Iverach, Atmos. Environ., 1974, 8, 597; G. Robinson, D. Iverach, and G. S . Hawke, ibid., 1975, 9, 272. E. R. Stephens, S. A. Penkett, F. J. Sandalls, and J. E. Lovelock, Atmos. Environ., 1975, 9, 461.

(Oa

(03

4n4

(06

loe *07

*08

(OB

L1o

Y. Ogata, Kagaku No Jikken, 1974, 25, 21. G. Ziglio, A. Pagano, and G. M. Fara, Minerva Med., 1973, 65, 4489. D. 1. Hammer and V. Hasselblad, Arch. Environ. Health, 1974, 28, 255; L. Varfalvy and Z . Jegier, Chemosphere, 1974, 3, 35; W. S. Cleveland, Science, 1974, 186, 1037; G. C. Tiao, G. E. P. Box, and W. J. Hamming, J. Air Pollution Control ASSOC.,1975, 25, 260; J. S. Jacobson and G. D. Salottolo, Atmos. Environ., 1975, 9, 321. R. L. Grob and J. J. Schuster, Environ. Letters, 1974, 6, 303; H. Uehara and Y . Ijuuin, Chem. Phys. Letters, 1974, 28, 597; D. D. Davis, G. Smith, and G. Klauber, Science, 1974, 186, 733; B. Haynes and N. Kirov, Combustion and Flame, 1974, 23, 277; J. D. Allen, ibid., 1975,24, 133; T. Sebayashi, Kogai To Taisaku, 1974,10,493; F. Chisaka and S . Yanagihara, Kikai Gijutsu Kenkyushu Shoho, 1974, 28, 213. R. Criegee, Chem. Z., 1975, 99, 138. N. Turner, P. Waggoner, and S . Rich, Nature, 1974, 250, 486; A. Eliassen and J. Saltbones, Atmos. Environ., 1975, 9, 425. J. Bull and T. Mansfield, Nature, 1974, 250, 443; J. Kagawa and T. Toyama, Arch. Envion. Health, 1975, 30, 117. A. Angstrom, Appl. Optics, 1974, 13, 1477; B. A. Reck, Atmos. Environ., 1975, 9, 89; K. J. Chu and J. H. Seinfeld, ibid., p. 375; K. T. Whitby, W. E. Clark, V. A. Marple, G. M. Sverdnip, G. J. Sem, K. Willeke, B. Y. H. Liu, and D. Y. H. Pui, ibid., p. 463 ;G. M. Sverdnip, K. T. Whitby, and W. E. Clark, ibid., p. 483; R. D. Cess, J. Quant. Spectroscopy Radiative Transfer, 1974, 14, 861; K. M. Shotkin, H. Ludewig, and J. F. Thompson, jun., J . Appl. Meteorology, 1975, 14, 189. A. Gitchell, R. Simonaitis, and J. Heicklen, J. Air Pollution Control ASSOC., 1974, 24, 357, 772; R. K. M. Jayanty and R. Simonaitis, Atmos. Enoiron., 1974, 8, 1283; C. W. Spicer and D. F. Miller, Environ. Sci. Technol., 1974, 8, 1028.

Part 11 PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS By J. M. KELLY

1 Photochemistry of Metal Ions and Co-ordination Compounds Two recent reviews consider quenching and sensitization processes involving co-ordination compounds and energy transfer between organic molecules and transition-metal ions.?- The photochemistry of hexaco-ordinate compounds of second- and third-row transition metals (principally Rh'lI, I P , PtIV, and Ru") has been re~iewed.~ Briefer surveys of transition-metal complex photochemisand of flash photolysis of co-ordination compounds have been published. try Other authors have discussed relaxation processes for excited states of transitionmetal c ~ m p o u n d svibronic ,~ spectra of co-ordination compounds,8 and the use of two-dimensional potential energy surface cross-sections in analysing such ~pectra.A ~ collection of Russian publications on the photochemistry of coordination compounds has appeared.1° Zink, who has previously developed a ligand field theory to explain the pattern of the photochemical reactions of d3 and de compounds,ll has now presented an MO approach to the problem.12 In particular he has calculated the increase in antibonding character along the labilized axis for the vertical ligand field excited state. This was performed first for a linear model system and then for CrI" and Col" ammine complexes. These calculations showed that labilization is greater the larger the metal-ligand overlap and the smaller the ligand orbital ionization energy. MO theory has also been used to explain the reactions of co-ordinated azide Incorvia and Zink l4 have used ligand field theory to interpret the photosolvation quantum yields for da complexes of C,, and Dra symmetry. The theory 49

V. Balzani, L. Moggi, M. F. Manfrin, F. Bolletta, and G. S . Laurence, Coordination Chem. Reo., 1975, 15, 321. a

' a @

lo

l1 la l8

lP

V. L. Ermolaev, E. B. Sveshnikova, and T. A. Shakhverdov, Uspekhi Khim.,

1975,44, 75.

P. C. Ford, J. D. Petersen, and R. E. Hintze, Coordination Chem. Rev., 1974, 14, 67. V. Balzani, Guzzetta, 1974, 104, 55. T. Yoshida and S . Otsuka, Kugaku, 1974, 29, 445. G. Semerano, Coordination Chem. Rev., 1974, 16, 185. M. K. DeArmond, Accounts Chem. Res., 1974, 7 , 309. C. D. Flint, Coordination Chem. Rev., 1974, 14, 47. P. E. Hoggard and H. H. Schmidtke, Chem. Phys. Letters, 1974,25,274. 'Prevrashch. Kompleks. Soedin Deistviem Sveta, Radiats. Temp.', ed. G. A. Lazerko, Izd. Beloruss. Gos. Univ., 1973. J. I. Zink, J. Amer. Chem. SOC.,1972, 94, 8039; Mol. Photochem., 1973, 5, 151. J. I. Zink, J. Amer. Chem. Soc., 1974, 96, 4464. J. I. Zink, Znorg. Chem., 1975, 14, 446. M. J. Incorvia and J. I. Zink, Inorg. Chem., 1974, 13,2489.

153

Photochemistry assumes that a greater concentration of excitation energy along a particular axis will lead to a higher quantum yield for loss of the ligands along that axis, and this has been calculated using crystal field parameters. Certain aspects of this theory have been criticized by Ford.16 Models for photoredox reactions of transition-metal ammine complexes have been critically examined.18 The role of the solvent is stressed; in particular it will participate in the processes involved in the relaxation of the Franck-Condon excited state to the primary radical pair products. As in last year's Report, the photochemistry of each transition metal is treated systematically. Transition-metal organometallics, low oxidation-state compounds, and porphyrins are considered in later sections. 154

Vanadium.-VO(acac),Cl (acac = acetylacetone) is a photo-initiator for methylmethacrylate polymerization both in the absence1'" and in the presence17bof electron donors D, such as dimethyl sulphoxide or pyridine. Reactions (1) and (2) have been proposed as the initial photochemical steps. VVO(acac),Cl [VO(acac),D]+Cl-

hv

hv

_____+

V1vO(acac)z+ C1*

(1)

[V'VO(acac),Dt]C1-

(2)_

Photolysis of Vv in perchloric acid solution leads to VIV and oxygen.le Photoreduction of VOC& proceeds efficiently in ethanol Chromium.-The photochemical behaviour of trans- and cis-[Cr(en),(NCS)CI]+ 21 The reactions observed for the trans-complex 2o are (3)has been (3,while for the cis-complex the principal reaction is (6), but NCS- and C1trans-[Cr(en),(NCS)Cl]+

,$+ >

+

trans-[Cr(en),( NCS)Cl]+

cis-[Cr(en),( NCS)(Ha0)l2+ C1-

trans-[Cr(en),(NCS)Cl]+

h v R rO

cis-[Cr(en)2(NCS)Cl]

gL

+

[Cr(en)(enH)(H,0)(NCS)C1]2+

+

+

(3) (4)

cis-[Cr(en),(H2O)C1I2+ SCN-

(5)

[Cr(en)(enH)(H,O)(NCS)Cll2+

(6)

aquation also occur. The spectra and quantum yields for the reactions are shown in Figure 1. For the trans-complex, SCN- and C1- release originates from the lowest 4E state, while the 4B,state is responsible for reaction (3). For the ciscomplex reaction (6) also occurs from the 4T,,state (splitting into the 4B2and 4E components is not observed in this case), but in contrast to the trans-complex, SCN- and C1- aquation appear to originate from a charge-transfer excited state. l5 l6 l7 la

l9

P. C. Ford, Znorg. Chem., 1975, 14, 1440. J. F. Endicott, G. J. Ferraudi, and J. R. Barber, J . Phys. Chem., 79, 630. (a) S. M. Aliwi and C. H. Bamford, J . C. S. Furuduy I, 1974, 70, 2092; (b) S. M. Aliwi and C. H. Bamford, ibid., 1975, 71, 52. B. G. Jeliazkowa, S. Nakamura, and H. Fukutomi, Bull. Chem. Soc. Japan, 1975,48, 347. A. I. Kryukov, 2.A. Trachenko, and S. Y. Kuchmii, Dokludy Akad. Nuuk S.S.S.R., 1974, 216, 592.

2o

M. T. Gandolfi, M. F. Manfrin, A. Juris, L. Moggi, and V. Balzani, Znorg. Chem., 1974,13,

I1

M. F. Manfrin, M. T. Gandolfi, L. Moggi, and V. Balzani, Gazzetta, 1973, 103, 1189.

1342.

155

Photochemistry of Inorganic and Organometallic Compounds

[Cr(en),(NH3)NCSI2+provides another exception to Adamson's empirical rules.22 These predict that excitation of the ligand field states of the complex should lead mainly to NH, separation, whereas NH3 made up only 40% of the base released on photolysis, just double that which would be predicted on a purely statistical basis.

-

0.1

-

0.01

I

1 250

300

400

500nm

9 , 290

360

400

560nm

Figure 1 Electronic absorption spectra of trans- and cis-[Cr(en),(NCS)Cl]+ and quantum yields for the observed photoreactions (Reproduced by permission from Inorg. Chem., 1974, 13, 1342)

The photosolvation reactions of [Cr(NH,R),C1I2+ (R = H, Me, Et, PP, or Bun) in acidic media have been examined for both aqueous solution and wateracetone mixtures.23 Estimation of the relative efficiencies of the processes (7) and (8) is hampered by the occurrence of thermal processes corresponding to (8) and (9). When these complications were minimized, however, the quantum yield (at

+ H,O [Cr(NH,R),C1I2+ + H,O+ A [Cr(NH,R)4(H,0)C1]2+ + H 2 0 [Cr(NH,R)6C1]2+

____+

+ C1(7) [Cr(NH,R)4(H,0)C1]2++ RNH,+ (8)

[Cr(NH2R)6(H,0)]3+

[Cr(NH2R),(H,O),I3+

+ Cl-

(9)

565 nm) for C1- formation from [Cr(NH3),C1I2+in water was found to be <0.001, an order of magnitude smaller than that reported previously. While reaction (8) is unaffected by change of the solvent from water to 33% acetone,

C1- photosubstitution (7) increases substantially. From this and other observations, the authors conclude that the excited state causing reaction (8) is a quartet ligand field state and that responsible for reaction (7) has some charge-transfer character. a2 2s

A. D. Kirk and T. L. Kelly, Inorg. Chem., 1974, 13, 1613. (a) C. F. C. Wong and A. D. Kirk, Canad. J. Chem., 1974,52, 3384; (b) C. F. C. Wong and A. D,Kirk, ibid., 1975, 53, 419.

156

Photochemistry

The photoaquation quantum yield for [Cr(CN)(H20)s]2+ increases with wavelength in the range 500-650 nm.24 By assuming no conversion between the states, the authors deduce that the quantum yields for aquation of the 4E and 4B2states are 0.20 and 0.55 respectively. Possible mechanisms normally considered for isomerization of tris-chelate complexes require either intramolecular twisting or bond rupture. Irradiation of Cr(tfa), (tfa = 1,l ,l-trifluoropentane-2,4-dionate)with circularly polarized light shows that both pathways are Although in solution [Cr(ox),13(ox = oxalate) also undergoes isomerization, irradiation (A > 250nm) of [Cr(ox),13- in K3Al(ox),,3H20 crystals at 100 and 250 K produced no detectable phot oreactions .26 Energy transfer from [Cr(en),13+ to [Cr(CN),I3- in [Cr(en),][Cr(CN),],2H20 has been observed by monitoring the rise time (6.2 ns) of the [Cr(CN)J3emission.27aThe same authors have reported evidence for energy transfer from [Co(CN),I3- to [Cr(CN),I3- in their non-stoicheiometric mixed The quenching of the fluorescence of 10-methylacridinium chloride by CrlI1 complexes in aqueous solution proceeds with rate constants in the range 1.3 x lo0 --f 7.7 x lo0 dm3mol-1 s-1.28 Emissions from [Cr(MIDA)2]- and [Cr(IDA),]- [(M)IDA = (methy1)iminodiacetate] have been reported 20 to exhibit pronounced ‘pseudo Stokes shifts’, attributed to a displacement of the potential energy surface of the 2E,, state relative to the ground state. A reassignment of the spectra indicates that this is incorrect.30 The emission spectra of [Cr(phen),I3+ and [ C r ( b i ~ y ) ~ in ] ~ aqueous + solution at room temperature contain not only 2E -+ 4A2 emission bands but also others assigned to 2Tl -+ 4A2.31 As the 2Tl emission becomes stronger at higher temperatures, it is suggested that the 2T, emission takes place after repopulation from the 2E state. On addition of dimethyl sulphoxide to the [Cr(bipy)J3+ solution, emission assigned to the 4T2 *A2 transition was recorded - apparently the first report of emission from the quartet state in fluid solution at room temperature. Other reports consider the luminescence properties of [Cr(py),F2]+,32a [cr(Ncs)6]3-,32b[Cr(en)2F2]+,32c [Cr(CN)6]3-,33oxygen-co-ordinated Cr”’ comand plexes at 5 K,34 Cr(CH2NH2C02)3,H20and Cr2(OH)2(CH2NH2C02)0,3s Crlll ions in MgO 36 and Al(Urea)&.37 --f

er 2b

27

28

29

30

31 s2

33 34

s5 36

s7

W. Coleman and W. Schaap, J.C.S. Chem. Comm., 1975,225. K. L. Stevenson and T. P. van den Driesche, J. Amer. Chem. Soc., 1974, 96, 7964. D. C. Doetschman, J. Chem. Phys., 1974, 60,2647. (a) F. Castelli and L. S. Forster, Chem. Phys. Letters, 1975, 30, 465; (b) F. Castelli and L. S. Forster, J. Phys. Chem., 1974, 78, 2122. K. K. Chatterjee and S. Chatterjee, 2.phys. Chem. (Frankfurt), 1975, 94, 107. P. E. Hoggard and H. H. Schmidtke, Ber. Bunsengesellschuft phys. Chem., 1972, 76, 1013. C. D. Flint and A. P. Matthews, J.C.S. Furuduy ZZ, 1975, 71, 379. N. A. P. Kane-Maguire, J. Conway, and C. H. Langford, J.C.S. Chem. Comm., 1975, 801. (a) C. D. Flint and A. P. Matthews, Znorg. Chem., 1975,14, 1008; (b) C. D. Flint and A. P. Matthews, J.C.S. Furuduy ZZ, 1974, 70, 1301; (c) C. D. Flint and A. P. Matthews, ibid., p. 1307. C. D . Flint and P. Greenhough, J.C.S. Furuduy ZZ, 1974,70, 815. H. Otto, H. Yersin, and G. Gliemann, 2.phys. Chem. (Frankfurt), 1974, 92, 193. A. Ranade, E. Koglin, and W. Krasser, 2.unalyt. Chem., 1975,273,463. F. Castelli and L. S. Forster, Phys. Reo. (B)., 1975, 11, 920. E. Koglin, W. Krasser, G. Wolff, and H. W. Nuernberg, Z . Nuturforsch., 1974, 29a, 211.

Photochemistry of Inorganic and Organometallic Compounds

157

Quantum yields for production of D, on photolysis of Cr2+in D 2 0 solution are lower than those for H, liberation from H,0.S8 From pulse radiolysis experiments Cohen and Meyerstein 39 have determined the rate constant for reaction (10) (1.5 x logdm3mol-l s-l) and they have compared their results with those obtained in earlier photochemical studies of CP+. Molybdenum and Tungsten.-Flash photolysis and e.s.r. studies 40 have been carried out on [MO(CN)8]3- in solutions of varying pH, concentration, and solvent. The results are consistent with (11) as the primary reaction following excitation of the complex to an LMCT state, [MO(CN),l3-

hv

[Mo(CN),I3-

+ eCN

(1 1)

Aspects of the photochemistry of [M(CN)8I4- (M = Mo or W) recently reported include an e.s.r. study of irradiated crystalline M1,[M(CN)8],xH20 and [M1(en),],[M(cN),] (M1 = c u or ZII),~' photolysis of [Mo(CN),]~- in liquid a ammonia,42 the photosubstitution of [MO(CN)8]4- in alkaline modified preparation of the blue K,[MoO(OH)(CN),],~H,O,~~ and the photoaquation chemistry of [MO(CN)8]*-.45 Efficient photoreduction of nitrate to nitrite by riboflavin can be effected using molybdate in glacial acetic acid.46 From a study of a large number of amine molybdates it has been shown that only secondary amines and tri- or di-molybdates give strongly photochromic Reaction (12) is proposed as the initial photoprocess followed by reduction of the m ~ l y b d a t e . ~ ' ~ R2NH,+

hv

He

+ R2NH+

(12)

Manganese.-The quantum yield for photochemical decomposition of K3[Mn(ox),],3H,0 has been determined for reactions both in thin powdered layers 48 and bulk The photochemical redox reaction of K,Mn(edta) in the solid state has been in~estigated.~~ Rhenium.-The photochemical cleavage of the Re-Re quadruple bond in [Re,Cl8I2- has been rep~rted.~'After irradiation in acetonitrile solution, (2) and 38 38 4O

41 43

44 46

46 47

48

4* 6o

6L

M. W. Rophael and M. A. Malati, J. Inorg. Nuclear Chem., 1975, 37, 1326. H. Cohen and D. Meyerstein, J.C.S. Dalton, 1974, 2559. Z. Stasicka and H. Bulska, Rocznicki Chem., 1974, 48, 389. E. Nagorsnik, D. Rehorek, and P. Thomas, 2. Chem., 1974, 14, 366. R. D. Archer and D . A. Drum, J. Inorg. Nuclear Chem., 1974, 36, 1979. E. Nagorsnik, P. Thomas, and E. Hoyer, Inorg. Nuclear Chem. Letters, 1974, 10, 353. R. L. Marks and S. E. Popielski, Inorg. Nuclear Chem. Letters, 1974, 10, 885. R. P. Mitra and H. Mohan, J. Inorg. Nuclear Chem., 1974, 36, 3739. P. W. Moors, J. Inorg. Nuclear Chem., 1975, 37, 1089. (a) F. Arnaud-Neu and J. Schwing-Weill, J . Less Common Metals, 1974,36,71; (b) F. ArnaudNeu and J. Schwing-Weill, 'Chemistry and Uses of Molybdenum', ed. P. C. H. Mitchell, Climax Molybdenum Co. Ltd., London, 1974, p. 35; (c) T. Yamase, H. Hayashi, and T. Ikawa, Chem. Letters, 1974, 1055. E. L. Simmons, J. Phys. Chem., 1974, 78, 1265. E. L. Simmons and W. W. Wendlandt, J . Phys. Chem., 1975,79, 1158. T. Takeuchi and A. Ouchi, Nippon Kagaku Kaishi, 1974, 1486. G. L. Geoffroy, H. B. Gray, and G. S. Hammond, J. Amer. Chem. SOC.,1974,96, 5565.

158

-

Photochemistry

a smalI amount of (1) were isolated. A two-step mechanism was proposed for [Re2C1,I2[ReCl,(MeCN),]-

hv

hv

2[ReCl,(MeCN),]-

(13)

(1)

ReC13(MeCN)s (2)

(14)

radiation between 300 and 366 nm. Excitation at longer wavelengths corresponding to the 6-S* band did not produce any photoreaction. Nevertheless the facile photochemical cleavage is not consistent with previous estimates for the Re-Re bond strength of 120&--1700 kJ mol-l. The electronic structure of [Re2C1,I2-has recently been discussed.62 Iron.-E.s.r. spectra taken after U.V. irradiation of [Fe(CN),l3- in aqueous methanol at 77 K indicated the presence of CH,OH, HCO, and an FeIII species assigned to [Fe(CN),(MeOH)]2-.63 It is postulated that the reactions proceed via an LMCT process followed by extraction of an electron from the solvent by the electron-deficient ligand, as in reaction (15).

nn

[(CN),FeCN---HOMeI3-

___+

[Fe(CN),14-

.+

MeOH'

(1 5 )

Previous workers 64, 66 have suggested that the primary step on photolysis of [Fe(CN),(N0)I2- is (16) and this mechanism has been favoured by Stoeri and

West from studies of the reaction of the photoproducts with SCN-66a and Wolfe and Swinehart 67 have proposed, however, that the principal reaction after irradiation at 366 nm (a = 0.35) and 436 nm (0= 0.18) is (17), and that previously reported effects on varying the pH and oxygen concentration may be rationalized by secondary reactions of NO. [Fe(CN),NOI2-

hv

[Fe(CN),I2- -1- NO

The OH. radical formed on photolysis of Fe3+ may be effectively scavenged by low concentrations of alcohols.68 At higher concentrations (0.1-5 moll-l) an additional quenching effect for methanol and propan-2-01, but not for t-butyl alcohol, was observed. This was attributed to reaction of the alcohol either with a vibrationally equilibrated charge-transfer state of Fe3+ or with the geminate pair [Fe", *OH]. Ia 68 K4

s6 MI O7 68

A. P. Mortola, J. W. Moskowitz, N. Roesch, C. D. Cowman, and H. B. Gray, Chem. Phys. Letters, 1975, 32, 283. M. C. R. Symons, D. X. West, and J. G. Wilkinson, J. Phys. Chem., 1974,78, 1335. R. P. Mitra, B. K. Sharma, and S. P. Mittal, J. Znorg. Nuclear Chem., 1972, 34, 3919. A. Lodzinska and R. Gogolin, Roczniki Chem., 1973, 47, 497, 881, 1101. (a) P . A. Stoeri and D. X. West, J. Znorg. Nuclear Chem., 1974, 36, 2347; (b) P. A. Stoeri and D. X. West, ibid., p. 3883. S. K. Wolfe and J. H. Swinehart, Inorg. Chem., 1975, 14, 1049. J. H. Carey and C. H. Langford, Znorg. Nuclear Chem. Letters, 1974, 20, 591.

Photochemistry of Inorganic and Organometallic Compounds

159

Photochemical decomposition of [Fe(ox),13- may be induced by a Q-switched ruby laser pulse (A = 694.3 nm).6QIntensity studies showed that a two-photon absorption process was involved. The photochemical decomposition of K3Fe(ox),,3H20 has been discussed in a series of publication^.^^-^^ Other reports consider the light-induced decomposition of Fe"'(dibenzoy1methanate), in the presence of 02,64 the photoreactions of FeCl, with toluene and the photoredox reactions of Fe"'(tartrate) 88 and FelI1substituted (citrate) 87 complex ions, the [Fe(CN)J3- and UOz2+sensitized photochemical cleavage of pyrimidine dimeq8*and e.s.r. studies of the photo-oxidation of aminoacids and dipeptides 6 Q and of wool 70 in the presence of Fe"'. Photo-oxidation of Fe2+in HzS04and HCIOl glasses at 77 K has been investigated:?' the primary process appears to be (18) rather than (19).

Ruthenium and Osmium.-The quenching of the luminescent excited state of [Ru(bipy),I2+ has continued to receive a t t e n t i ~ n . ~As ~ -discussed ~~ in last year's Report, controversy exists as to whether this process for Co"' complexes proceeds via electron-transfer (20) or energy-transfer (21). Navon and Sutin 72 have obtained

+ 3[Ru(bipy),]2+ + Co"'

3[R~(bipy)3]2+ Co"'

-

+ [Ru(bipy),12+ + 3C~111 [ R ~ ( b i p y ) ~ ] ~ +Co2+

(20) (21)

the Stern-Volmer constants for quenching of [R~(bipy),]~+ phosphorescence by [CO~'~(NH,),X]~+ (X = NH,, H20, Br-, or C1-) and also by [RU'''(NH~)~X]~+ (X = Cl- or NHs). From consideration of the Co"' excited state which would be formed and of the effect of propan-2-01 on the Stern-Volmer constant, it was concluded that an electron-transfer mechanism is operative for the CorlI 6o

62

O.5 Oa

67

6u 70

'l 73

75

76

H. Zipin and S. Speiser, Chem. Phys. Letters, 1975, 31, 102. G . G. Savelev, A. A. Medvinskii, V. L. Shcherinskii, L. P. Gevlich, N. I. Gavryusheva, Y. T. Pavlyukhin, and L. I. Stepanova, J. Solid State Chem., 1975, 12, 92. G. G. Savelev, A. A. Medvinskii, V. L. Shcherinskii, L. P. Gevlich, N. I. Gavryusheva and Y . V. Mitrenin, Khim. vysok. Energii, 1974, 8, 458. G . N. Belozerskii, 0. I. Bogdanov, A. N. Murin, Y.T. Pavlyukhin, and V. V. Sviridov, Zhur. fir. Khim., 1974,48, 2785. A. A. Medvinskii, G. N. Belozerskii, Y. T. Pavlyukhin, V. N. Stolpovskaya, V. V. Sviridov, A. N. Murin, and V. V. Boldyrev, Teor i eksp. Khim., 1974, 10, 411. C. Parkanyi and J. H. Richards, J . Coordination Chem., 1974,4, 41. H. Inoue, M. Izumi, and E. Imoto, Bull. Chem. SOC.Japan, 1974,47, 1712. N. A. Kostromina, N. V. Beloshitskii, and V. F. Romanov, Doklady Akad. Nauk S.S.S.R., 1974,215, 373. S. 1. Arzhankov and A. L. Poznyak, Zhur. priklad. Spektroskopii, 1974,21, 745. I. Rosenthal, M. M. Rao, and J. Salomon, Biochim. Biophys. Acta, 1975, 378, 165. A. L. Poznyak, S. I. Arzhankov, and G. A. Shagisultanova, Biofizika, 1974, 19, 233. G. J. Smith, New Zealand J. Sci., 1974, 17, 349. V. V. Korolev and N. M. Bazhin, Khim. vysok. Energii, 1974, 8, 506. G. Navon and N. Sutin, Inorg. Chem., 1974, 13, 2159. C. R. Bock, T. J. Meyer, and D. G. Whitten, J. Amer. Chem. SOC.,1974, 96, 4710. C. R. Bock, T. J. Meyer, and D. G. Whitten, J. Amer. Chem. SOC.,1975, 97,2909. G. S. Laurence and V. Balzani, Znorg. Chem., 1974, 13, 2976. C. Lin and N. Sutin, J. Amer. Chem. SOC.,1975, 97,3543.

160

Photochemistry

complexes. For Ru"' quenchers, which in general react more efficiently than the Co"' complexes, the electron-transfer pathway is also favoured. Other workers 73 have unambiguously shown by luminescence quenching and flash photolysis studies that for the weak organic oxidants (3) and (4) and for

(3)

(4)

-

[Fe(Hzo)6]3+and [Ru(NH~)~],+ the initial step is electron transfer (22), followed by a thermal recombination (23). For example, energy transfer to (3) would

+ ox. 3[R~(bipy)3]2+ [Ru(bipy),P+

+ red.

[ R ~ ( b i p y ) ~+ ] ~red. +

+

[ R ~ ( b i p y ) ~ ] ~ox. +

(22) (23)

produce its triplet state which would then undergo transcis isomerization; however, the yield of this reaction was small indicating that energy transfer is responsible for < 1% of the quenching. In another study 74 substituted nitrobenzenes were used as quenchers. The quenching rate constants (k,) were calculated and values are given in Table 1. From these results a value for

Table 1 Comparison of the quenching rate constants for 3[R~(bipy),]2+ by substituted nitrobenzenes with their reduction potentials 7 4 Quench er k,/dm3 mol-l s-l -4 p-Ni tronitrosobenzene 9.18 x 109 0.525 p-Dinitrobenzene 6.56 x 109 0.69 3.10 x 109 o-Dinitrobenzene 0.81 1.96 x 109 p-Nitrobenzaldehyde 0.863 1.56 x 109 m-Dinitrobenzene 0.898 6.56 x lo8 Methyl-4-nitrobenzoate 0.947 cis-4,4'-Dinitrostilbene 1.83 x lo8 1 .oo 4,4'-Dini trobiphenyl 1.18 x 108 1.004 4.89 x 107 3-Nitrobenzaldehyde 1.016 1.66 x 107 Methyl-3-nitrobenzoate 1.044 8.04 x 108 4-Chloronitrobenzene 1.063 8.32 x 105 4-Fluoronitrobenzene 1.128 < 2 x 105 1.147 Nitro benzene < 3 x 105 4-Methylnitrobenzene 1.203

E~([R~(bipy),]~+/~[Ru(bipy),]~+) of - 0.8 1 f 0.02 V was obtained, Electron transfer from 3[Ru(bipy),]2+ to T13+,75and to [Fe(H20)6]3+76 has been demonstrated. Two reports of a static contribution to the quenching of emission from Ru"' complexes have been published. Measurement of both phosphorescence lifetimes and intensities allowed Bolletta et aZ.77to observe static quenching (through ion-pair formation) of 3[R~(bipy)3]2+ by [Mo(CN),14- and [PtCl4I2- in DMF. For [IrC1J3- only dynamic quenching was found. Demas and Addington 78 77

F. Bolletta, M. Maestri, L. Moggi, and V. Balzani, J. Phys. Chem., 1974, 78, 1374.

78

J. N. Demas and J. W. Addington, J. Amer. Chem. SOC.,1974, 96, 3663.

161

Photochemistry of Inorganic and Organometallic Compounds

found that Cu2+caused static quenching of [Ru(phen),(CN),] emission. In this case ground-state association of the Cuz+, probably through the CN group, is postulated. Deuteriation of the ligand in [Ru(bipy),12+causes only a 20% increase in the lifetime of the emitting state, whereas change of the solvent from HzO to D,O produces a doubling of the lifetime.7e This is surprising in view of the usual assignment of the excited state as MLCT, and the authors suggest that some CTTS character must be present. Other reports on [ R ~ ( b i p y ) ~ ]include ~+ a review (in Japanese) of energy transfer and a report on the effect of magnetic field on the low-temperature emission spectrum.s1

The quantum yield for pyridine photo-aquation (24) from [ R U ( N H ~ ) ~ ( ~ ~ ) ] ~ + varies only slightly with wavelength in the range 436-254nm, and photooxidation to give Ru"' is only important at < 334 nm.s2a Similarly, only photo-aquation of [Ru(NH,)~(M~CN)]~+ is found on irradiation at 366 nm while photoredox reactions are very important at shorter wavelengths (Q = 0.51 at 214 nm).82b For both complexes a CTTS state is implicated in the photoredox reactions. As H2 is a significant product for [RU(NH,),(M~CN)]~+ photolysis at 254 nm, particularly in the presence of propan-2-01, steps (25) and (26) are probably important. [Ru(NH,),(MeCN)lZ+ eaq-

+ H+

-

[Ru(NH,),(MeCN)l3+

-

Co2+

hv

+ q,-

H*

(25)

(26)

In contrast to results obtained at X > 200 nm, irradiation at 185 nm of [Ru"'(NH,),X]~+ (X = HzO, NH,, or Cl-), in the presence of propan-2-01, leads to photoreducti~n.~~ C~S-[RU(NH~)~X,]+ (X = Br or I) undergo photoaquation of X- in acidic Several luminescent 0 s " and Ir"' complexes, including [0s(bipy),l2+, have been used as singlet oxygen sensitizers.86 Cobalt.-It has previously been suggested 86 that only solvent viscosity is responsible for the change in the relative yields of the photoreactions (27) and (28) on [CO(NH~),NO,]~+ [CO(NH,),NO,]~+ 7B

82

hv

hv

+ 5NH3+ NO,

[Co(NH,),(0NO)l2+

(27)

(28)

J. Van Houten and R. J. Watts, J. Amer. Chem. SOC.,1975, 97, 3843. Y.Kaizu and H. Kobayashi, Kagaku, 1975, 30, 67. D. C. Baker and G. A. Crosby, Chem. Phys., 1974,4,428. (a) R. E. Hintze and P. C. Ford, Inorg. Chem., 1975,14,1211; (6) R. E. Hintze and P. C. Ford,

86

J. Amer. Chem. SOC.,1975, 97, 2664. J. Siege1 and J. N. Armor, J. Amer. Chem. SOC.,1974, 96, 4102. A. Ohyoshi, N. Takebayashi, Y. Hiroshima, K. Yoshikuni, and K. Tsuji, Bull. Chem. SOC. Japan, 1974,47, 1414. J. N. Demas, E. W. Harris, C. M. Flynn, and D. Diemente, J. Amer. Chem. Soc., 1975, 97,

86

F. Scandola, C. Bartocci, and M. A. Scandola, J. Amer. Chem. SOC.,1973,95, 7898.

84

3838.

162

Photochemistry

adding amounts of glycerol to aqueous solutions of [CO(NH~),(NO,)]~++. This interpretation has been questioned by NatarajanYE7 as a result of experiments on the photolysis of this complex in aqueous solutions containing 1-10% of poly(acry1amide) or poly(vinylpyrro1idine) (viscosity of the resulting solution up to 100 times greater than that of water). It was found that varying the viscosity in this manner did not affect the relative yields of reactions (27) or (28), and the quantum yield for redox decomposition of [Co(NH&N3]*+ was similarly unaffected. On irradiation of solid [Co(NH&N02]C1, at 77 K a species forms which is stable at low temperatures but which converts into the nitrito-isomer on warming.88 On the basis of its i.r. spectrum this has been assigned the structure (5). 2+

Endicott and co-workers have published an interesting series of papers on the influence of the solvent on the photoreactivity of LMCT excited states of Col*' complexes.le#8Q-Q1 The f i s t steps in the reaction may be described by reactions (29)--(31), where lCT* represents the Franck-Condon excited state and "CT CoIIIX

lCT* "CT

hv

___j

1CT* "CT

(30)

(CO"(NH~)~,-X}

(31)

(29)

may have different spin multiplicity or thermal equilibration. Qualitatively it might be expected that increase in solvent viscosity would lead to more recombination or isomerization within the solvent cage, and therefore a lower quantum yield for photoreduction would be observed. As previously noted, this interpretation had been given to the effect of glycerol on reactions (27) and (28).86 However for [CO(NH&NCS]~+a more complex reaction pattern has emerged.8B For A > 280 nm, is indeed lower in 50% glycerol-water than in aqueous solution; but for 280 2 )I > 214nm, is greater in the more viscous medium. Further, substantial activation energy is found for the reaction at long (e.g. 350 nm) but not at short (e.g. 254 nm) wavelengths. Dramatic medium effects are also found for the photoredox reactions of [Co(NH3),BrI2+(Figure QgO Thus whereas in water or 87% phosphoric acid a constant value of @'redox is reached as the excitation energy is increased, behaviour in 80% acetonitrile, 75%- and 50%-glycerol is strikingly different. This effect clearly demonstrates the importance of the immediate solvent environment for reactions of LMCT states. Further, the authors point out that this phenomenon 88

P. Natarajan, J.C.S. Chem. Comm., 1975, 26. D. A. Johnson and K. A. Pashman, Inorg. Nuclear Chem. Letters, 1975, 11, 23. J. F. Endicott and G. J. Ferraudi, J. Amer. Chem. SOC.,1974, 96, 3681. J. F. Endicott, G. J. Ferraudi, and J. R. Barber, J. Amer. Chem. SOC.,1975, W,219. J. F. Endicott, Znorg. Chem., 1975, 13, 448.

163

Photochemistry of Inorganic and Organornetallic Compounds

will have important consequences for sensitization reactions of Co”’ complexes. The nature of the solvent environment of the complex will be strongly affected by the energy donor, particularly if it is ionic, and thus the authors see ‘no clear way to relate intermolecular energy transfer studies to intrinsic processes within “molecular” CT states of co-ordination complexes’.

kgL

?0.6

-

0,s.

a.

0.5

~

f

1.

Exitation

Enorgy , kK

Figure 2 Absorption spectrum in water (upper curve) and variations in quantum yields of Co2+ (lower curves) with excitation energy and solvent medium on irradiation of [Co(NH,),BrI2+. Aqueous solvent media employed: H,O, W; 80% MeCN, A ; 50% glycerol, A; 75% glycerol, a; 87% H,P04, 0 (Reproduced by permission from J . Amer. Chem. SOC.,1975, 97, 219)

Consideration of the nature of the LMCT transitions, redox energetics, and photoredox behaviour of transition-metal ammine complexes has allowed Endicott and co-workersls to propose new models for the potential energy surfaces describing their photoredox reactions. These models have been used to discuss the differences in photoreactivity of [Co(NH,),Brl2+ and [Co(NH,),NOp]P+.alThese differences are ascribed to (i) more Co-radical bonding in the

1 64

Photochemistry

LMCT excited state of the bromo-complex and to (ii) the vibrational relaxation being faster than solvent dielectric relaxation for [Co(NH3),BrI2+but proceeding with similar rates for [CO(NH,),NO,]~+. Using MO calculations of the type outlined earlier,12 Zink has predicted the expected reaction modes of the various types of excited state of [M(NH3)5N3]2+ (M = Co, Rh, or Ir) (Table 2).13 Generally good agreement with experiment 92 is observed. Table 2 Predictions of the photoreactivity of [M(NH3),N,I2+ (M = Co, Rh, or Ir) l3 Excited state LMCT MLCT LL

a

Trend in bonding state Cobalt to Iridium no N-N labilization weakly labilize N’-N” form IrN N, all N-N labilized strongly labilize N”-N“ CON, + N more form IrN, N probable strongly labilize N’-N” all N-N labilized CON, + N more form IrN + N, only probable

+ +

LL = ligand localized; M-N’-N”-N”’.

Two reports on the flash photolysis of [Co(ox),13- in aqueous solution have been g4 Hoffman and co-workers 93 assigned the intermediate species observed in solution at pH = 6.0 to (6) in equilibrium with small amounts of (7) (Scheme 1). In the presence of excess oxalate, another species (8) could be detected. For [Cr(ox),13- in the presence of 3 x 10-3M oxalic acid, Cordemans

-

0 0

I:.(

#)

- 5-

I

0-c-c-0:

/ (OX),COII

\

0-c-c-0:

L

II II 0 0

(8) Scheme 1 ma OS

J. L. Reed, H. D. Gafney, and F. Basolo, J. Amer. Chem. SOC.,1974, 96, 1363. N. S. Rowan, M. Z. Hoffman, and R. M. Milburn, J . Amer. Chem. SOC.,1974, 96, 6060. L. Cordemans, J. D’Olieslager, J. Hendrix, and S. De Jaegere, J. Phys. Chem., 1974,78, 1361.

Photochemistry of Inorganic and Organometallic Compounds

165

et aLo4also recorded a transient absorption spectrum similar to that reported for (8). At high flash intensities this species further photolysed to yield another transient species ascribed to [CO(OX)(C~O~-)~]~---. Photolysis of [CO(NH,),O,CR]~+(R = Me or Et) in the presence of Co"(N4) complexes (N4 = cyclic tetra-amine or cyclic di-imine-diamine) provides the first preparative route to Co'II-alkyl compounds with a saturated equatorial ligand The reactivity of CO,;, generated by photolysis of [Co(NHJ4C03]+,towards tryptophan and derivatives has been investigated.BsFree radicals formed by photolysis of various Co'I' complexes in NaCIO, and H2S04glasses at low temperatures have been studied by e.~.r.~'Sensitization of [Co(NH,),Brl2+ by the excited singlet state of acridinium or quinolinium ions can be most readily explained in terms of electron transfer.gS Sheridan and Adamson Dg have reported the photochemistry of ligand-field band excitation of ci~-a-[Co~~'(trien)CIX]~+, ~is-/3-[Co'~~(trien)CIX]~+, and [ C ~ ~ ~ ~ ( t r e n ) C(X l X= ] ~ C1+ or H20) [trien = (NHzCH2CH2NHCH2)2; tren = (NH2CH2CH2),N]. In no case was photoredox behaviour observed (@ < Further, the photochemical reactions are very different from those induced thermally; for example, no light-induced C1- exchange was observed for the aquo-chloro-complexes although they readily undergo aquation in the dark. A striking difference was observed between the geometric isomers cis-a- and cis-/3[Co(trien)Cl,]+. The cis-a-compound (9) is photostable, whereas the cis-/3compound (10) reacts to form tran~-[Co(trien)CI(H,O)]~+ (1 1) = 0.01 1; also photoaquates (@,,, = 0.015). These and a 5 1 4 = 0.0080). [C~(tren)CI~]~+ other observations with Co"' complexes of uni-, bi-, and quadri-dentate ligands can be rationalized using rules similar to those applied to Cr"' complexes: (i) octahedral axis having average weakest crystal field will be labilized; (ii) on the labilized axis, the ligand with greatest ligand field is activated; (iii) for ColI1 complexes heterolytic bond cleavage, possibly solvent assisted, is stereoretentive. Scheme 2 shows how this applies for various ammine complexes (labilized ligand marked with an asterisk). ColI1derivatives of the type (13) undergo predominantly photo-aquation of the ligand X, even after irradiation in charge-transfer bands of the complex, a quite different photochemistry from that of CoI1' ammine complexes.loo It is proposed, however, that at shorter wavelengths, homolysis (32) does occur, but that a reverse

hv

CO"'-X (CO",*X}

___,

{Co",*X}

(32)

(Co"',X-}

(33)

electron transfer takes place within the solvent cage (33) and that the ColI1species then rapidly aquates. Photoredox reactions following irradiation in LF bands of CorlI complexes are unusual. Recently reported examples are those due to [Co(phen),ox]+ and T. S. Roche and J. F. Endicott, Inorg. Chem., 1974, 13, 1575. S. N . Chen and M. Z . Hoffman, J. Phys. Chem., 1974,78, 2099. 8 7 A. L. Poznyak and S. I. Arzhankov, Doklady Akad. Beloruss. S.S.R., 1974, 18, 523. R8 H. Gafney and A. W. Adamson, Coordination Chem. Rev., 1975, 16, 171. Q9 P. S. Sheridan and A. W. Adamson, Znorg. Chem., 1974, 13, 2482. l o o F. Diomedi-Camassei, E. Nocchi, G. Sartori, and A. W. Adamson, Znorg. Chem., 1975,14,25. O5

Photochemistry

166

(c)

x+

--+ no reaction

X

(10)

('1

*qx

-

&xh X

X

(1 1)

no

w +reaction X

(cr) n . m s - [ ~ o ( e n ) , ~ ~;, (b) ] ci.s-[~o(en),~~,l+ ; cis-a-[Co(trien)CI,]+; (d) c*is-P-[Co(trien)CI,] ; (e) [Co(tren)Cl,]+ Scheme 2 +

(c)

+

C/c\c

I

I

0-H-0

(13) X

=

NJ or NO,

167

Photochemistry of Inorganic and Organometallic Compounds

[C~(bipy)~ox]+. [ C ~ ( @ h e n ) ~also ] ~ +undergoes photoreduction in the presence of oxalate, illustrating that the oxalate may function as either an inner- or an outersphere reducing agent.lol Irradiation of [ C O ( N H ~ ) ~in] ~its+LF lAl, + lTZ,band with light ( h = 337 nm) from a pulsed nitrogen laser causes photoreduction of the complex.10a A two-photon mechanism is presented in which a ligand field state *LF absorbs a further photon to give the reactive CT state (steps 34-37). lAl,

lTZ, *LF *CT

hv

hv

____+

(34) *LF

(35)

*CT

(3 6)

products

(37)

A detailed analysis of the spectrum and temperature dependent lifetime of the emission of crystalline K&o(CN), and comparison with a computer-generated fit have given information about the geometry and energy of the E(3T,) state.103 The effect of the counter-ions K+, Cd2+,and Ir3+on the low-temperature emission of M(CN),3- (M = Co, Rh, or Ir) has been discussed.lo4 Two groups have reported photoreactions of cobalt-containing bridged dinuclear ions. Vogler and Kunkely lo6have studied the ions [(CN)&ol''NCM1'(CN),l6- (M = Ru or Fe). These compounds exhibit an absorption band assigned to an M -+ Co intervalence CT band. Irradiation in this band causes reaction (38). In the case of M = Fe, in the absence of oxygen, the reaction is thermally reversible. Other workers lo6have investigated reaction (39), where L = 02C(CHz),CH=CHR or NH2(CH2).CH=CHR. Irradiation in the

+

[(NH~)~CO"'LCU']~+6H+

hv

CO'+

+ CU'+ + 5NH4+ + LH+

(39)

Cu(d)-olefin(n*) band causes efficient reaction (0= 0.34-0.65), but the process is also observed following population of the Co"' ligand-field bands. The photoreactions of alkyl-cobaloximes are discussed in the Organometallic Compounds section. Rhodium and Iridium.-Ford l6 has discussed the deficiencies of the ligand-field model for de systems when applied to Rh"' photochemistry. In particular he criticizes (i) the neglect of possible variations in the efficiency of radiationless processes in estimating the relative quantum yields for the reactions of the photoexcited states and (ii) the use of crystal-field parameters derived from the groundstate configuration. C. H. Langford, C. P. J. Vuik, and N. A. P. Kane-Maguire, Inorg. Nuclear Chem. Letters, 1975, 11, 377. loa K. M. Cunningham and J. F. Endicott, J.C.S. Chem. Comrn., 1974, 1024. l o 3 K. W. Hipps and G. A. Crosby, Inorg. Chern., 1974, 13, 1543. lo4 A. Woelpl and D. Oelkrug, Ber. Bunsengesellschaftphys. Chem., 1975, 79, 394. lo5 A. Vogler and H. Kunkely, Ber. Bunsengesellschaft phys. Chem., 1975, 79, 83, 301. lo6 J. K. Farr, L. G. Hulett, R. H. Lane, and J. K. Hurst, J . Arner. Chem. Soc., 1975, 97, 2654. lol

168

Photochemistry

Photo-exchange of water from [Rh(NH,)5H,0]3+ in oxygen-18 enriched water proceeds efficiently on ligand-field excitation of the complex.1o7 In the presence of Cl- photo-anation (40) takes place.

The first report of luminescence from a transition-metal exciplex has been published.lo8 In D M F solution the emission of cis-[Tr(phen),CI,]+ is quenched by naphthalene and replaced by a new structureless emission band at longer wavelengths. In aqueous solution cis-[Ir(phen),CI,]+ undergoes C1- aquation (reaction 41) with a quantum yield of 0.05 independent of A in the range 25-04 nm.log On flash photolysis a transient species, which is not an intermediate in reaction (41), [Ir(phen)CI,]+

+ H,O hv

[Ir(phen),C1(H,0)]2+

+ C1-

(41)

was observed. This was assigned to a species of the type [Cl,(phen)Xr'"(phen-)I+ arising from the MLCT excited state. rner-[Rh'''(py)3(ox)C1] produces Rh'(py),CI on photolysis.l1° Investigation by e.s.r. reveals that Rh3+ acts as an efficient electron-trapping centre when present in irradiated AgBr single crystals.111 The emission of the complex [IrCI2Cphen)(5,6-Me,phen)]+C1- in ethanolmethanol glasses at 77 K originates from at least two non-thermally equilibrated states.112 The longer-lived component is assigned to a T-T* transition localized on the 5,6-Me2phen ligand, while the other is ascribed to a d-T* transition involving the metal and the phen ligand. The emission spectra of substituted 1,lo-phenanthroline complexes of RhlI1 and Ir111,113and of phosphine complexes of Rh' and Ir*,l14have been discussed. Nickel.-Studies of the time-resolved absorption spectra of (14) following modelocked laser photolysis have been reported.l16 Spectra could be recorded down

P. C. Ford and J. D. Petersen, Inorg. Chem., 1975, 14, 1404. R. Ballardini, G. Varani, L. Moggi, and V. Balzani, J. Amer. Chem. SOC.,1974, 96, 7123. l o o R. Ballardini, G. Varani, L. Moggi, V. Balzani, K. R. Olson, F. Scandola, and M. Z. Hoffman, J. Amer. Chem. SOC.,1975, 97, 728. 1 1 0 A. W. Addison, R. D. Gillard, P. S. Sheridan, and L. R. H. Tipping, J.C.S. Dalton, 1974,709. R. S . Eachus and R. E. Graves, J. Chem. Phys., 1974, 61, 2860. R. J. Watts, J. Amer. Chem. SOC.,1974, 96, 6186. 113 R. J. Watts and J. Van Houten, J. Amer. Chem. SOC., 1974, 96, 4334. 114 G. L. Geoffroy, M. S. Wrighton, G . S. Hammond, and H. B. Gray, J. Amer. Chem. SOC.,1974, lU7

lo8

96, 3105. 115

D. Magde, B. A. Bushaw, and M. W. Windsor, Chem. Phys. Letters, 1974, 28, 263.

Photochemistry of Inorganic and Organometallic Compounds

169

to within 10 ps of the excitation pulse, illustrating the application of this technique to the study of very short-lived, non-emitting excited states. For (14), the excited state observed is formed within 10 ps and its decay is accelerated in a heavyatom solvent (9 ns in benzene; 0.22 ns in iodoethane). However, an unambiguous assignment of the state was not possible. Photochemical perturbation of equilibrium (42) using a pulsed neodymium laser has been reported 116 [dpp = Ph,P(CH,),PPh,]. Irradiation at 1060 nm, Ni(dpp)CI,

Ni(dpp)Cl,

planar

tetrahedral

where the tetrahedral species absorbs, causes formation of the planar isomer, while pulsing at 530 nm produces the tetrahedral species from the planar. Laser-induced photochemical interconversions of NiLCI, (L = 1,1,7,7-tetramethyl-diethylenetriamine) have been compared to those caused by electricfield jump rnethods.ll7 The quenching of singlet oxygen 11*$ 119 and triplet carbonyls 119 by Ni" chelates has been investigated. cis-trans photo-isomerization and photoreduction reactions of Platinum.-The ci~-[Pt(pn),CI,]~+ (pn = propylenediamine) have been studied.120 The isomerization proceeds more rapidly in acidic solution, suggesting that protonation of propylenediamine plays an important role. Isomerization of tr~zns-[Pt(pn),Cl~]~+ could not be observed. The photo-aquation of [Pt(SCN)JZ- has been investigated in acetonitrilewater solvent mixtures.121 The mechanism appears to be different from that for [PtBr,l2- as the reaction quantum yield is dependent on both wavelength and solvent. The intermediacy of Pt"' is suggested. The photoredox reactions of [PtIV(NH3),(NO,)(OH),X] (X = CI, Br, or SCN),122a[Pt1V(NH3)2(N02)X3] (X = C1 or Br),122band of [Pt(en)(CN),X,] have been reported. On irradiation (A = 313 nm) in the presence of Br- (reaction 43) or in alkaline solution (pH = 12) (reaction 44), the ion [Pt(dien)I]+(dien = diethylenetriamine) [Pt(dien)I]+ [Pt(dien)I]+

+ Br-

+ OH-

___+

+ I[Pt(dien)OH]+ + I[Pt(dien)Br]+

(43) (44)

undergoes ligand As the quantum yield for reaction (43) is sensitive to Br- concentration, a geminate pair [Pt(dien)(H20),2+,I-]+is proposed as an intermediate. The quantum yield for the analogous reaction of [Pt(dien)(py)I2+ is independent of [Br-] (up to 2 x 10-2moll-1), and in this case 116

11'

118 120 121

lZ2

J. J. McGarvey and J. Wilson, J. Amer. Chem. SOC.,1975, 97, 2531. H. Hirohara, K.J. Ivin, J. J. McGarvey, and J. Wilson, J, Amer. Chem. SOC.,1974, 96,4435. D. J. Carlsson, T. Suprunchuk, and D. M. Wiles, Canad. J. Chem., 1974, 52, 3728. P. Hrdlovic, J. Danecek, M. Karvas, and J. Durmis, Chem. Zuesti, 1974, 28, 792. G. A. Shagisultanova, A. V. Loginov, and S. V. Krupitskii, Khim. uysok. Energii, 1974,8,467. V. S. Sastri and C. H. Langford, J. Inorg. Nuclear Chem., 1974, 36, 2616. (a) A. G. Samatov, N. N. Zheligovskaya, and V. I. Spitsyn, Zzuest. Akad. Nauk S.S.S.R., Ser. khim., 1974,274; (b) A. G. Samatov, N. N. Zheligovskaya, and V. 1. Spitsyn, ibid., 1974, 1467.

N.N.Zheligovskaya, N. Kamalov, and V. 1. Spitsyn, Zzuest. Akad. Nauk S.S.S.R., Ser. khim.,

lZ3

1975,264. 184

C . Bartocci, F. Scandola, and V. Carassiti, J . Phys. Chem., 1974, 7 8 , 2349.

170

Photochemistry [Pt(dien)(H20)l2+is the intermediate. The different behaviour of the two complexes is attributed to greater residual electrostatic attraction within the geminate pair of the iodo-complex. Calculations have been carried out on the electronic structures of [Pt(CN)4]2-,125[PtC1J2- and [PdC14]2-,126 and [Pt(C,H4)C13]-.127The allowed U.V. transitions of [PtCl4I2-and [PdCI4l2-have been assigned.128 Copper.-The labile complexes [Cu(mal),12- and Cu(ma1) (ma1 = malonate) undergo photolysis in solution to give acetate and carbon dioxide but Cur[ is not permanently reduced.12Q On flash photolysis, however, transient species assigned to Cu' compounds were observed. Cu" derivatives of carboxylic acids have been used in the preparation of photosensitive ~ 1 a t e s . l ~ ~ Light has been found to inhibit the oxidation of peptides by molecular oxygen in Cu" peptide complexes.131 A possible explanation is that light causes the decomposition of the Cu"-peptide-O, complex required for the dark reaction. Other reports consider the fluorescence thermochromism of Cul-base comp l e ~ e s the , ~ ~fluorescence ~ of Cu' complexes of pyridine carboxylic acids,133the light-induced darkening of CuCl and the quenching of flavosemiquinone radicals by Cu2+and Ni2+.136 Silver.-In a 1 : 1 complex, Ag+ quenches the fluorescence of tryptophan and induces a three-fold increase in the phosphorescence quantum yield.lS6 This observation is attributed to an intramolecular heavy-atom effect in the complex. Zinc.-Changes in the fluorescence and phosphorescence yields of /3-diketone chelates of 2n2+,Be2+,and A13+have been attributed to interligand Other authors have studied the luminescence properties of salicylalaniline chelates of Zn2+, Hg2+,Cd2+,and Be2+,138and of a dinuclear complex of ZnC1, with zinc salicylidene-toluidinate.139 The photolysis of Zn(N,), in the solid state has been Mercury.-Two mechanisms are possible to explain the formation of 12y following flash photolysis of HgI,. Following laser flash photolysis, it was possible both to observe HgI and to follow the formation of 1,- (reaction 46).141 This shows that 125

lZe

L.V. lnterrante and R. P. Messmer, Chem. Phys. Letters, 1974, 26, 225. R. P. Messmer, L. V. Interrante, and K. H. Johnson, J. Amer. Chem. SOC.,1974, 96, 3847.

N. Roesch, R. P. Messmer, and K. H. Johnson, J . Amer. Chem. SOC.,1974, 96, 3855. B. G. Anex and N. Takeuchi, J . Amer. Chem. Soc., 1974,96,4411.

le7 128

lZ8 13* 131

lS2 lS3 13*

J. Y. Morimoto and B. A. Degraff, J. Phys. Chem., 1975,79, 326. K. Sugita, H. Ide, K. Tamura, and S. Suzuki, Bull. Soc. Photogr. Sci. Technol.Japan, 1973/4,6. G . L. Burke, E. B. Paniago, and D . W. Margerum, J.C.S. Chem. Comm., 1975,261. H. D. Hardt, Naturwiss., 1974, 61, 107. M. A. S. Goher and M. Dratovsky, Naturwiss., 1975, 62, 96. Y.V. Karyakin and A. V. Zaval'skaya, Zhur.$z. Khim., 1974,48, 346. I. V. Khudyakov, A. V. Popkov, and V. A. Kuzmin, Izvest. Akad. Nauk S.S.S.R.,Ser. khim., 1974, 2208.

R. F. Chen, Arch. Biochem. Biophys., 1975, 166,584. 13' T. Ohno and S. Kato, Bull. Chem. SOC.Japan, 1974, 47, 1901. ld* M. I. Knyazhanskii, P. V. Gilyanovskii, 0. A. Shchipakina, 0. A. Osipov, V. V. Litvinov, and V. A. Kogan, Zhur. priklad. Spektroskopii, 1974, 21, 183. lag V. V. Litvinov, M. I. Knyazhanskii, 0. A. Osipov, V. A. Kogan, A. S. Rakov, P. V. Gilyanovskii, 0. T. Asmaev, and A. S. Burlov, Zhur. priklad. Spektroskopii, 1974, 20, 426. 140 S. R. Yoganarasimhan and R. K. Sood, J. Solid State Chem., 1974, 10,323. 141 P. Fornier de Violet, R. Bonneau, and S. R. Logan, J. Phys. Chem., 1975, 78, 1698. 13k

Photochemistry of Inorganic and OrganometaIZic Compo~nds

171

process (47) cannot be operative and the mechanism is presumed to involve steps (45) and (46). I* + I HgI,

- -

____+

hv

(46)

1,;

[Hg+I,-]

127

+ products

(47) Akagi et aZ.142have considered the effect of sulphur and mercuric sulphide on the photolysis of Hg(OAc), to give methylmercury compounds. Lanthanides.-The quenching of CeI'I fluorescence in aqueous solution by [S,O,]e- involves irreversible electron transfer and results in overall photooxidation (48).lP3 It was also shown that quenching of CelI1* by H,O+ does not result in the production of hydrogen atoms. Cell1* + S,0e2- ___r+ CeIv + SOP2- + SO,: (48) Energy transfer between an exciplex and a Eu"' chelate has been 0 b ~ e r v e d . l ~ ~ The exciplex was generated by the reaction of tri-p-tolylamine radical cation (Dt) and the radical anion (AT) of either dibenzoylmethane or benzophenone. In the presence of Eu"', quenching of the exciplex luminescence and appearance of Eu"' emission was detected.

+ AT + Eu"'

Dt (D+A-)*

-

(49)

(D+A-)* D

+ A + Eul"*

(50)

Quenching of the singlet state of indole and its derivatives appears to proceed via electron transfer from the indole to the lanthanide ion, as the order of quenching efficiency (Eu"' > Yb"' > Sm"' > Tb"' > Gd"' > Ho"' Dy"') parallels the reduction PO tent ial. Study of energy transfer from o-benzoylacetate to Eu"' in aqueous ethanol solutions shows that this occurs only when the species are c ~ m p l e x e d Assuming .~~~ this, the stability constant for the complex was calculated, and good agreement found with the value determined potentiometrically. Although in crystalline ~u1''(CF3C0CHCOCF3),]-[ButNH3]+ energy transfer from the /3-diketone ligand to the Eu'" occurs via the triplet in [EU"~(P~COCHCOCF~)~]-[pipH]+ (pip = piperidine) direct ligand singlet to Eu"' transfer takes place.147b Other authors have reported on the luminescence properties of Eu'" complexes of ,&diketones 148-151 and Schiff bases,152and on the quenching of Eu(RC0CHN

142 143

144 146

146

148

14D

lS1

16a

H. Akagi, Y . Fujita, and E. Takabatake, Chem. Letters, 1975, 171; Nippon Kuguku Kaishi, 1974, 1180; H. Akagi, E. Takabatake, and Y . Fujita, Chem. Letters, 1974, 761. R. W. Matthews and T. J. Sworski, J. Phys. Chem., 1975,79, 681. R. E. IIemingway, S.-M. Park, and A. J. Bard, J. Amer. Chem. SOC.,1975, 97, 200. R. W. Ricci and K. B. Kilichowski, J . Phys. Chem., 1974,78, 1953. S. P. Tanner and D. L. Thomas, J. Amer. Chem. SOC.,1974,96, 706. (a) C. R. S. Dean and T. M. Shepherd, J.C.S. Furuday ZZ, 1975,71, 146; (b) C. R. S. Dean and T. M. Shepherd, Chem. Phys. Letters, 1975, 32, 480. G. D. R. Napier, J. D. Neilson, and T. M. Shepherd, Chem. Phys. Letters, 1975, 31, 328. B. A. Knyazev and E. P. Fokin, Zhur. priklad. Spektroskopii, 1974, 20, 818. G. A. Cotton, F. A. Hart, and G. P. Moss, J.C.S. Dalton, 1975, 221. R. A. Puko, N. N. Mitkina, V. V. Kuznetzova, V. N . Kotlo, and V. S. Khomenko, Zhur. priklad. Spektroskopii, 1974, 21, 736. V. F. Zolin, V. A. Kudryashova, V. V. Kuznetsova, and T. I. Razvina, Zhur. priklad. Spektroskopii, 1974,21, 831.

172

Photochemistry

COR), (R = Me or Ph) phosphorescence by anthracene and cu-naphthylamine.153 The rate constant for Tb3+(5D04) to Nd3+ energy transfer is dependent on the extent of complexation of the ions, increasing markedly with the number of anion (AcO-) groups present between donor and a ~ c e p t 0 r . lBy ~ ~determining the rate of transfer as a function of [OAc-] it was possible to estimate the stability constants for the various complex ions present. Stein and Wuerzberg 155a have reported results on the fluorescence yields and lifetimes for Tb3+,Dy3+,Sm3+,Pr3+,and Tm3+in H 2 0and D20solutions. From consideration of these and earlier results, it was shown that solvent isotope effects on the rates of radiationless decay are expected to be high when (E/Aw) = 2-5 ( E is the energy gap between the emitting excited state and the ground state and Ew the vibrational quantum energy of the O-H or O-D bond). Within this range the energy-gap law applies, whereas for larger energy gaps other deactivating pathways are more efficient. The same authors 155b have shown that the quantum yield for Eu3+ emission is dependent on the excitation wavelength and they discuss critically the methods to be used in measuring emission quantum yields for rare earth ions. Other authors have discussed the fluorescence of Tb3+156 and Nd3+9'51 158 in POCI,,SnC14. Uranium.-The mechanism for photoreduction of UOz2+(Uvl) by many organic Chibisov and cocompounds (Q) may be represented by reactions (51)-(55). workers 159 have followed the decay of the Uv species formed after flash photolysis

Uv

+ Qt

Qt + Qt

-

+Q

(54)

products

(55)

Uvl

of UOZz+in the presence of ethanol, ascorbic acid, and hydroquinone. For hydroquinone (54) is the only process involved in consumption of Uv, whereas for ethanol, at these flash intensities, step (52) is most important. Quantum yields for the photoreduction of UOZ2+by ethanol using light from an argon ion laser (A = 476 and 514 nm) and a neon laser (633 nm) have been reported.160a At 633 nm, the authors assume that the light is absorbed by water bonded to the UOz2+. The variation of quantum yield with temperature in the 153

B. D. Joshi, A. G . Page, and B. M. PateI, 2.phys. Chem. (Leipzig), 1974, 255, 103. V. P. Gruzdev and V. L. Ermolaev, Optika i Spektroskopiya, 1974,37, 1097. (a) G. Stein and E. Wuerzberg, J . Chem. Phys., 1975,62,208; (b) G . Stein and E. Wuerzberg, Chem. Phys. Letters, 1974, 29, 21. P. Tokousbalides and J. Chrysochoos, Chem. Phys. Letters, 1974, 29, 226. T. K. Andreeva, M. E. Zhabotinskii, L. V. Levkin, and V. I. Ralchenko, Optika i Spektroskopiya, 1974, 37, 927. 0. V. Yanush, G. 0. Karapetyan, V. I. Mosichev, and S. V. Chinyakov, Zhur. priklad. Spektroskopii, 1974, 20, 43 1. G. I. Sergeeva, A. K. Chibisov, L. V. Levshin, A. V. Karyakin, B. F. Myasoedov, and A. A. Nemodruk, Khim. vysolc. Energii, 1974, 8, 358. (a)J. T. Bell and S. R. Buxton, J. Inorg. Nuclear Chem., 1974,36,1575; (b)J. T. Bell and S. R. Buxton, ibid., 1975, 37, 1469.

lb4 156

156

15* 16D

160

Photochemistry of Inorganic and Organometallic Compounds

173

range 25-87 "C has also been studied.leob The photoreduction of UOzz+by citric acid gives UIV, acetone, and carbon dioxide as products.lG1 Quantum yields are pH dependent, and it is proposed that intramolecular decomposition of UOZ2+-citratecomplexes is involved. On irradiation into a band corresponding to co-ordinated pyridine, U02(py),(NO,), undergoes photosolvation [reaction (56)].1e2 Pyridine photoproducts are

also formed but it was shown that these arise as a result of a secondary photoreaction of the liberated pyridine. Irradiation of UOz(py)2C12in dry ethanol gave (pyH),UVOC16and U(OEt)6.1e3 The photochemical processes following excitation of [UIvC1J2- and [Uv102C1,]2-in their (Cl- to metal) CT bands have been discussed.lG4 Quenching of UOz2+emission by inorganic ions has been investigated.le6 For anions, the order of quenching (I> SCN- > Br- =- C1- > F- > CN-) suggests strongly that an electron transfer mechanism is operative. For metal aquo-ions no single correlation was possible, probably indicating that several types of deactivating process are involved. The authors also showed that energy transfer from UOz2+results in sensitization of Eul" emission and in the sensitized photo-aquation of [Co(CN),I3- and [Cr(en)J3+. Other authors leehave reported the quenching by T1+ of UOZ2+emission and of its photoreduction by lactic acid (k, = 5.2 x log dm3mol-1 s-I at 22 "C). The spectrum of the triboluminescence (i.e. emission caused by mechanical stress) of UOz(N03)2,6Hz0is similar to that for photo-induced l u m i n e ~ c e n c e . ~ ~ ~ Possible causes for this effect are electrical excitation (i.e. pressure-induced electrochemiluminescence), intermolecular interactions, and intramolecular deformations. Arguments are presented to show that the third mechanism is not important in this case. Other relevant publications are concerned with electrochemiluminescence of U022+in perchloric acid,lG8absorption and luminescence spectra of U022+in and detailed analyses of the emission spectrum of crystalline UOaZ+salts at low temperature^.^^^-^^^ lel

lea leS leP

166 16e

16' 16*

170

173 17(

A. Ohyoshi and K. Uneo, J. Znorg. Nuclear Chem., 1974, 36, 379. 0. Traverso, V. Carassiti, R. Portanova, and P. A. Vigato, Znorg. Chim. Acta, 1974, 9, 227. 0. Traverso, R. Portanova, and V. Carassiti, Znorg. Nuclear Chem. Letters, 1974, 10, 771. G. Condorelli, L. L. Costanzo, S. Pistara, and E. Tondello, Inorg. Chim. Acta, 1974, 10, 115. R. Matsushima, H. Fujimori, and S. Sakuraba, J.C.S. Faraday Z, 1974, 70, 1702. Y. Yokoyama, M. Moriyasu, and S. Ikeda, J. Inorg. Nuclear Chem., 1974, 36, 385. J. I. Zink, Znorg. Chem., 1975, 14, 555.

R. G. Bulgakov, V. P. Kazakov, G. S. Parshin, and G. L. Sharipov, Izoest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 1916. D. D. Pant and H. B. Tripathi, J. Luminescence, 1974, 8, 492. L. V. Volod'ko, A. I. Komyak, G. P. Vitkovskii, and S. E. Sleptsov, Zhur. priklad. Spektroskopii, 1974, 20, 634. V. 1. Belomestnykh, V. 1. Burkov, V. A. Kizel, Y.I. Krasilov, V. A. Madii, and R. N. Shchelokov, Zhur. priklad. Spektroskopii, 1974, 20, 8 14. L. V. Volod'ko, A. N. Sevchenko, A. I. Komyak, and D. S. Umreiko, Doklady Akad. Nauk Beloruss. S.S.R.,1974, 18, 601. A. P. Abramov and N. A. Tolstoi, Optika i Spektroskopiya, 1974, 37, 360. A. P. Abramov and I. K. Razumova, Optika i Spektroskopiya, 1975,38, 565.

7

174

Photochemistry 2 Transition-metal Organometallics and Low-oxidation-state Compounds The photochemistry of metal carbonyl compounds has been reviewed.176 The relationship between photochemistry in low-temperature matrices and atom synthesis methods has been discussed with special reference to metal ca~bony1s.l~~ Both of these types of study have been useful in allowing the determination of spectroscopic properties, and hence of the structures, of species such as Cr(CO), and Fe(CO),, which at room temperature are highly reactive. One particular problem has been whether the structures observed for these compounds in rare-gas matrices might differ from those in the gas phase because of constraints in the matrices. Recent articles by Burdett have described MO calculations of the structures of M(CO), and M(N,), species ( x = 2-6) 177a and a method for predicting the geometry of these and other binary transition-metal complexes.177bThe results of these calculations are in good agreement with the observed structures of Fe(CO), 178 and Cr(C0)5 179 in rare-gas matrices. Recent examples of preparative applications of photosubstitution reactions of metal carbonyls are collected in Table 5 (see p. 193). Others, less suited to tabular presentation, are discussed below in the section dealing with the particular element. In general, synthetic methods involving initial photochemical formation of the metal carbonyl-THF complex, followed by thermal reaction of this complex with an added substituent, have not been included. Titanium, Zirconium, and Hafnium.-Several reports on the photochemistry of titanocene derivatives have appeared this year. Harrigan et aZ.lS0observed that the photolysis (A > 480nm) of Cp,TiCI, in chlorinated hydrocarbons gave CpTiCl,, and they proposed that light-induced cleavage of the Ti-Cp bond occurs, as in reactions (57) and (58). In support of this mechanism, photoCp,TiCI, CpTiC1,

+ CHCI,

hv

+ Cp CpTiC1, + -CHC12

CpTiC1,

(57)

(58)

decomposition in neat benzene is inefficient, leading to CpTiC1, in low yield. Similarly no evidence for Ti-Br bond rupture was found on photoIysis ( A > 580nm) of Cp,TiBr, in chloroform. [With Cp,TiMe, (A > 300nm), however, cleavage of the Ti-Me bond was observed.] Under somewhat different irradiation conditions ( A = 313 nm), Vitz and Brubaker observed the exchange reaction (59), while in the presence of methanol Cp(OMe)TiCl, was formed.

hv

Cp,TiCl, 4- ( 7 ~ - C ~ D ~ ) ~ T i c l ,

2(v-C6D,)CpTiCI,

(59)

These findings are consistent with a recent report of the photoelectron spectra of CpzMClz(M = Ti, Zr, or Hf), which shows that transitions involving electron 176

176

M. Wrighton, Chem. Rev., 1974, 74,401. J. J. Turner, Angew. Chem., 1975,87, 326; Angew. Chem. Internat. Edn., 1975,14, 304. (a) J. K. Burdett, J.C.S. Faraday ZI, 1974, 70,1599; (b)J. K. Burdett, Inorg. Chem., 1975,14, 375.

M. Poliakoff and J. J. Turner, J.C.S. Dalton, 1974, 2276. R. N. Perutz and J. J. Turner, Znorg. Chem., 1975, 14, 262. l E o R. W. Harrigan, G. S. Hammond, and H. B. Gray, J. Organometallic Chem., 1974,81, 79. lS1 E. Vitz and C. H. Brubaker, J . Organometallic Chem., 1974, 82, C16. 17*

17*

175 Photochemistry of Inorganic and Organometallic Compounds transfer from the cyclopentadienyl ring to the empty d-orbitals of the metal occur at lower energy than those arising from the CI ligands.le2 Photolysis of Cp,MMe2 (M = Ti, Zr, or Hf) leads to the corresponding metallocenes, which may be isolated if the solvent is inert.le3 Irradiation in the presence of diphenylacetylene yields the metallocycle (1 5 ) .

Cp,MMe2

hv

Ph

Cp2M + 2Me-

(60)

Ph

P h Q P h

CP, (15)

Niobium.-The reactions of Cp2NbH2, generated photolytically from t-butylperoxide and Cp,NbH,, have been studied by e.s.r.le4~ le5 Chromium, Molybdenum, and Tungsten.-The debate about the structure of Cr(CO), has continued this year. Perutz and Turner 1 7 0 have analysed the i.r. spectra of M(C0)5 (M = Cr, Mo, or W) formed by photolysis of 13CO-enriched M(CO)6 in argon or methane matrices at 20 K. In all cases the spectrum of the isotopically substituted M(CO)6 agrees with that calculated for a squarepyramidal (C4J structure and is inconsistent with that for the trigonalbipyramidal ( D 3 J isomer. Evidence is also presented that the matrix material is weakly co-ordinated to the complex. On the other hand, Kuendig and Ozin le6 have interpreted spectra recorded on condensing Cr atoms in CO matrices at 10 K as indicating that Cr(CO), exists as the Dsnform. They have also suggested that the species produced by photolysis of Cr(CO), is an isomeric compound (16) (CO>,Cr+ OrC

0 (CO),Cr + 111 C

or (1 7). However, both Turner 17*and Braterman have convincingly argued that both these proposals are incorrect. In a later publication Ozin et aZ.le8 agree that the species formed photochemically is the C,,isomer and report that the fragment they assign to the D 3 h is converted into the C40structure on annealing the matrix at 40-45 K. Cr(CO),

+ CO

hv (visible)

Cr(CO),

(41)

It has previously been shown that recombination of the fragments formed on photolysis of Cr(CO), in methane matrices may be induced by irradiation in the G. Condorelli, I. Fragala, A. Centineo, and E. Tondello, J. OrganomefallicChem., 1975, 87, 311.

H. Alt and M. D. Rausch, J. Amer. Chem. SOC.,1974, 96, 5936. I. H. Elson, J. K. Kochi, U. Klabunde, L. E. Manzer, G. W. Parshall, and F. N. Tebbe, J. Amer. Chem. SOC.,1974, 96, 7374. l a b I. H. Elson and J. K. Kochi, J . Amer. Chem. SOC.,1975, 97, 1263. E. P. Kuendig and G. A. Ozin, J. Amer. Chem. Soc., 1974, 96, 3820. J. D. Black and P. S. Braterman, J. Amer. Chem. SOC.,1975, 97, 2908. Iaa H. Huber, E. P. Kuendig, G. A. Ozin, and A. J. Poe, J. Amer. Chem. SOC.,1975, 97, 308.

176

Photochemistry

absorption band (Amx = 489 nm) of Cr(CO),. This reaction has now been stimulated using plane-polarized light .IE9 Figure 3 illustrates the polarized i.r. and visible spectra of Cr(CO), after 15 min of such irradiation. Two effects may be observed. Firstly, as the absorption band corresponds to a lAl --+ lE transition

o’2

0.6

1

T

----7P 550 nm

Figure 3 Polarized absorption spectra of Cr(CO),. Al C - 0 stretching vibration (i.r. = 1932 cm-l) and electronic transition (Amx = 489 nm). -, polarizer 11; , pofarizer 1. Spectra taken after (a) 15 min I;(b) 15 min 11 photolysis with h > 375nm (Reproduced from J.C.S. Chem. Comm., 1975, 157)

------

of Cr(CO),, only correctly oriented Cr(CO)5 molecules may be excited. Secondly, as the intensities of the absorption bands of the other orientation actually increase, photo-orientation of the Cr(CO), must be taking place. It is suggested that this may involve an excited state of Cr(CO), having Dghsymmetry, as has been predicted by recent MO calculations.177a Flash photolysis of Cr(CO)6, Mo(CO),, w(co)6, or Fe(CO), in the gas phase produced the respective metal atoms and also species assigned as Cr, and MO~.~@O In the presence of O2 the corresponding monoxides were detected, and CrH and CrD were formed on photolysis of Cr(CO), in a hydrogen or deuterium atmosphere. J. K. Burdett, R. N. Perutz, M. Poliakoff, and J. J. Turner, J C.S.Chem. Comm.,1975, 157. A. N. Samoilova, Y. M. Efremov, D. A. Zhuravlev, and L. V. Gurvich, Khim. oysok. Energii, 1974, 8, 229.

Photochemistry of Inorganic and Organometallic Compounds

177

In a study of the light-induced exchange of CO from (norbornadiene)M(CO), (M = Cr, Mo, or W) using 13C0, it was found that the axial ligand is preferentially displaced (equation 62).lg1 Secondary reactions then cause scrambling 0

0

of the CO ligands. The authors suggest that a mechanism involving initial photodissociation of one of the metal-olefin bonds would be inconsistent with the experimental observations. In contrast to the thermal reaction, where the norbornadiene is readily displaced, photochemical reaction of (norbornadiene)Cr(CO)4 with PPh3 gives (norb~rnadiene)Cr(CO),(PPh,).~~~ Photo-induced transformations of (benzonorbornadiene)Cr(CO), derivatives are shown in Scheme 3.1a3

Irv

5

>

'lrv

-L

L = PPh,, PF,, MeC(CH,O),P, or Bu'NC Scheme 3

On photolysis (21), which is itself prepared photochemically, forms (22) and (23).lg4 Recent publications dealing with (arene)chromium compounds include an investigation of the photodecomposition of (benzene)Cr(CO), in cyclohexane

lS1 Iya

D. J. Darensbourg and H. H. Nelson, J. Amer. Chem. SOC.,1974,96,6511. G. Platbrood and L. Wilputte-Steinert, J. Organometallic Chem., 1975, 85, 199. B. A. Howell and W. S. Trahanovsky, J . Arner. Chem. SOC.,1975,97,2136. M. Herberhold and W. Golla, Chem. Ber., 1974, 107, 3199.

178

Photochemistry

the photochemical preparation of compounds of the type (arene)Cr(CO)LL', in which the Cr atom is a ~ y m m e t r i c , ~ ~a ~report - ~ ~ * on the photostability of (benzene),Cr in cyclohexane ~ o l u t i o n ,and ~ ~ ~two studies of the photoelectron spectra of various (arene)chromium compounds.200~ 201 Photochemical substitution of a homoleptic isocyanide complex has been reported [equation (63); R = Ph or MePh; L = dimethylfumarate or fumaronitrile].202 (RNC),Cr

+L

hv

(RNC),CrL

+ RNC

(63)

Previously reported photo-induced M(CO),-catalysed reactions of olefins and dienes include isomerizations, hydrogenations, and polymerizations. Recently two groups have reported that irradiation of W(CO), in CCll causes the metathesis of olefins, e.g. of pent-2-ene (reaction 64).203v204 Me 2

Et

4

-

Me

/ J + Me

Et

4 Et

(64)

Another novel photo-initiated reaction is the Cr(CO),-catalysed addition of silanes to 1,3-dienes (e.g. reaction 65).205 The reactions of photochemically generated Mo(CO),(mma) (mma = methylmethacrylate) with chlorinated hydrocarbons have been studied.206

+

HSiMe,

+

m S i M e 3

Photolysis of Cp2WH2in methanol produces the insertion products Cp,WH(OMe) and Cp,W(Me)(OMe).207 In mesitylene solution compound (24) is formed.208 As in the analogous insertion into benzene,20Dit is proposed that tungstenocene WCp, is the reactive intermediate. This species can also be

208

V. N. Trembovler, B. M. Yavorskii, V. N. Setkina, N. V. Fok,N. K. Baranetskaya, and G. B. Zaslavskaya, Doklady Akad. Nauk S.S.S.R., 1974,218, 1153. G. Jaouen and R. Dabard, J. Organometallic Chem., 1974,72, 377. J. Nasielski and 0. Denisoff, J. Organometallic Chem., 1974, 81, 385. G. Simmoneau, A. Meyer, and G. Jaouen, J.C.S. Chem. Comm., 1975,69. P. Borrell and E. Henderson, Inorg. Chim. Acra, 1975, 12, 215. J. A. Connor, L. M. R. Derrick, and I. H. Hillier, J.C.S. Faraday 11, 1974, 70, 941. M. F. Guest, 1. H. Hillier, B. R. Higghson, and D. R. Lloyd, Mul. Phys., 1975, 29, 113. K. Iuchi, S. Asada, and A. Sugimori, Chem. Letters, 1974, 801. P. Krausz, F. Gamier, and J. E. Dubois, J. Amer. Chem. Soc., 1975, 97, 437. A. Agapiou and E. McNelis, J.C.S. Chem. Comm., 1975, 187. M. S. Wrighton and M. A. Schroeder, J. Amer. Chem. SOC.,1974,96, 6235. C. H. Bamford and I. Sakamoto, J.C.S. Faraday I, 1974,70, 344. L. Farrugia and M. L. H. Green, J.C.S. Chem. Comm., 1975,416. K. Elmitt, M.L. H. Green, R. A. Forder, I. Jefferson, and K. Prout, J.C.S. Chem. Comm.,

2og

C . Giannotti and M. L. H. Green, J.C.S. Chem. Comm., 1972, 1114.

lPS lee

lg7 lea lee

2n1 203

zn4 2os 208

207

1974, 747.

Photochemistry of Inorganic and Organometallic Compounds

179

generated efficiently by photo-decarbonylation of Cp,W(CO) and this method has been employed as a route to various alkyne and alkene derivatives.210 Attempts to develop the photochemically induced and thermally reversible reaction (66) as a photochromic system have been Photolysis of [C~MO(CO)~], + Br-

hv

CpMo(CO),Br

+ [C~MO(CO)~]-(66)

[(Me,Cp)Mo(CO),], gives [(Me6Cp)M~(C0)2]2 probably via cleavage of the Mo-Mo bond.212 Some remarkable reactions of M(N,),(dpe), [M = W or Mo; dpe = 1,2bis(diphenylphosphino)ethane] have been reported. Addition of an alkyl group to the dinitrogen ligand takes place during photolysis in the presence of RBr in benzene solution (reaction 67) (R = Me, Et, or In THF solution compounds of type (25), in which the ligating N, has apparently displaced the oxygen from THF, are also formed.214 M(N,),(dP42

hv

+ RBr

MBr(N,R)(dpe),

(67)

(25)

Manganese and Rhenium.-Wrighton and Ginley have shown that photolysis of compounds X1(C0)4M1-M2(CO)4X2 [i.e. Mn,(CO),,, Rez(CO)lo, MnRe(CO),,, Mn2(C0)9(PPh3),and Mn2(CO)8(PPh3)z] causes homolysis of the metalmetal bonds with high quantum efficiency (equation 68). The fragments have been X1(C0)4M1-M2(C0)4X2

M1(C0)4X1 + M2(CO)4X2

hv

(68)

trapped with CC14, PhCH,CI, Ph3CCI, and 1,. It is also suggested these species are thermally labile undergoing either dissociation (69) or association with a ligand present in solution (70). M(C0)5 M(CO)5 + L

M(CO),

[M(CO),L]

+ CO

e. M(CO),L + CO

(69)

(70)

Byers and Brown 216 have also presented evidence for the lability of Re(CO),, although they propose that a dissociative process (69) is most important. They have also demonstrated that on photolysis Re2(CO)lo activates molecular hydrogen, the important step being (71).216aOn irradiation, Re,(CO),, acts as a 210 211 212 213

K. L. T. Wong, J. L. Thomas, and H. H. Britzinger, J. Amer. Chem. SOC.,1974, 96, 3694. J. L. Hughey and T. J. Meyer, Znorg. Chem., 1975,14, 946. D. S. Ginley and M. S. Wrighton, J. Amer. Chem. SOC.,1975, 97, 3534. A. A. Diamantis, J. Chatt, G. J. Leigh, and G. A. Heath, J . Organometallic Chem., 1975, 84, c11.

211

216 216

A. A. Diamantis, J. Chatt, G. A. Heath, and G. J. Leigh, J.C.S. Chem. Comm., 1975, 27. M. S. Wrighton and D. S. Ginley, J. Amer. Chem. SOC.,1975, 97, 2065. (a) B. H. Byers and T. L. Brown, J. Amer. Chem. SOC.,1975,97, 3260; (b) B. H. Byers and T. L. Brown, ibid., p. 947.

180 Re(CO),

+ H,

-

Photochemistry H,Re(CO),

catalyst for substitution reactions of HRe(CO), by phosphines.21eb Further details of the free-radical polymerization of methyl methacrylate on irradiation of Re2(CO)lohave been 1.r. spectral data have been recorded for Re(CO)521eand for Mn(CO),lsa prepared by metal atom reactions in CO matrices at 10 K. Symons and coworkers 21g have demonstrated that a species previously assigned 220 to Re(CO), is in fact Re(CO),O,. Evidence for the homolysis of the metal-carbon bond in R-Mn(CO), (R = Me or PhCH2) on irradiation has been provided by spin-trapping the radical species with nitrosodurene.221 Similar results were obtained on irradiating the acyl compounds RICOMn(CO), when the radical R1 but not R'CO was trapped. On photolysis of Mn,(CO),, in low concentration Mn(CO), was trapped, but at higher concentrations other unidentified species were also observed. RMn(CO),

R* + Mn(CO),

+ 2ArNO

hv

+ Mn(CO), Ar-N-R + Ar-N-Mn(CO), R-

I

I

0.

(72) (73)

0.

Photolysis of XRe(CO),L, (X = C1 or Br; L = trans-3- or trans-4-styrylpyridine) causes trans -+ cis isomerization of co-ordinated L with quantum yields and resulting photostationary states similar to those of the free ligand (Table 3).222As the lowest excited state is assigned to an intra-ligand excited state localized on the styrylpyridine, these results suggest that the perturbing effect upon co-ordination is small. The photochemical disproportionation of TI[Mn(CO),], to give TlMn(CO), and Mn,(CO),, has been The photoconversion of the carbene complex (26) to the keten complex (27) proceeds only in low yield because of the light-sensitive nature of the 0 Cp(C0)2Mn-C,

II ,C-Ph Ph

Ph Ph

I/

CP(C0)2Mn>f

Photodecarbonylation of Mn(C0),(B,H8) leads to Mn(C0)3(B3Hs) in which the [B,H,]- acts as a terdentate ligand.225

219

C. H. Bamford and S. U. Mullik, J.C.S. Faraday I, 1975, 71, 625. H. Huber, E. P. Kuendig, and G. A. Ozin,J. Amer. Chem. Sac., 1974, 96, 5585. S. A. Fieldhouse, B. W. Fullam, G. W. Neilson, and M. C. R. Symons, J.C.S. Dalton, 1974,

220

567. E. 0. Fischer, E. Offhaus, J. Muller, and D. Nothe, Chem. Ber., 1972, 105, 1027.

217 218

221

322 223 224

225

A. Hudson, M. F. Lappert, P. W. Lednor, and B. K. Nicholson, J.C.S. Chem. Comm., 1974,

966. M. S. Wrighton, D. L. Morse, and L. Pdungsap, J. Amer. Chem. SOC.,1975,97, 2073. J. M. Burlitch and T. W. Theyson, J.C.S. Dalton, 1974, 828. W. A. Herrmann, Chem. Ber., 1975, 108, 486. D. F. Gaines and S. J. Hildebrandt, J. Amer. Chem. Sac., 1974, 96, 5574.

C1Re(CO)3(trans-4-styrylpyridine)2 BrRe(CO),(trans-4-styrylpyridine), CIRe(CO),( trans-3-styrylpyridine),

trans-3-St yrylp yridine trans-4-St yrylp yridine

Compound

222

0.48 0.38 0.49 0.64 0.60

(t-c) (313 nm)

Table 3 Photoisomerization of co-ordinated styrylpyridines

(t-c)

0.54 0.51 0.51

-

(366nm)

313nm 90 88 84 99 93

90 98 90

-

-

366nm

% cis at photostationary

99 > 99 99

2

g

-- $ s

0

5 436nm g

state

182

Photochemistry

Iron, Ruthenium, and Osmium.-Although ferrocene has been extensively used as a quencher for triplet states of organic molecules, the mechanism for the quenching processes is by no means clear. Thus the observation 228 that anthracene triplet (ET = 176 kJ mol-l, 14 700 cm-l) is efficiently quenched by ferrocene (ET = 223 kJ mol-l, 18 600 cm-l from visible spectroscopy assignment a27) appears to be incompatible with an energy-transfer mechanism. A flash photolysis study by Kikuchi et al. of the quenching of the triplet states of several organic molecules by ferrocene has led these authors to propose that ET for ferrocene is ca. 15 O00 cm-l. As shown in Table 4, triplet states having ET lower Table 4 Rate constants for the quenching of triplet states by ferrocene in ethanol solution 228 ET/Cm-' 23 800 21 300 20 700

Compound

Triphenylene Naphthalene p-Acetonaphthone 1,2,5,6-Dibenzanthracene

18 300

Pyrene Phenazine Eosin Anthracene Perylene Tetracene Pentacene a

16 800

15 250 14 800 14 700 12 6OO 10 250 8000

Quenching rate constant1 dm3 mol-l s-l 6.5 x lo0 7.0 x 109 6.0 x 109

5.0 x 109

6.0 x lo0 4.6 x 109 3.5 x 109 3.5 x 109 1.3 x 109 4.6 x 107 < 107

In benzene solution.

than this value are still quenched but with reduced efficiency, and in these cases quenching uia charge transfer is suggested.a28 However, even in acetonitrile no ionic species were detected. The possibility that charge-transfer processes (74) DT + A

- (D--A+)

D

+A

(74)

might be responsible for the quenching reactions of dibenzenechromium, ferrocene, and other iron organometallic compounds has been investigated and discounted at least for fluorenone and anthracene triplet states.220 In these cases an energy-transfer mechanism is preferred. Rate constants for quenching of benzil and [ R u ( b i ~ y ) ~ ]emission ~+ by ferrocene, ruthenocene, and various substituted metallocenes have been determined.230 The quenching efficiencies observed again suggest that neither charge transfer nor heavy-atom quenching pathways are important, and the results are consistent with energy transfer. The quenching of biacetyl phosphorescence by ferrocene in cyclohexane, chloroform, and carbon tetrachloride is diffusion controlled and therefore independent of the complexation of the ferrocene to the chlorinated a26 227 228 229

230 231

A. S. Fry, R. S. H. Liu, and G. S. Hammond, J. Amer. Chem. SOC.,1966, 88,4781. Y. S. Sohn, D. N. Hendrickson, and H. B. Gray, J. Amer. Chem. Soc., 1971,93,3603. M. Kikuchi, K. Kikuchi, and H. Kokubun, Bull. Chem. SOC.Japan, 1974,47, 1331. A. Gilbert, J. M. Kelly, and E. Koerner von Gustorf, Mol. Photochem., 1974, 6, 225. M. S. Wrighton, L. Pdungsap, and D. L. Morse, J. Phys. Chem., 1975, 79, 66. F. Scandola, Ann. Univ. Ferrara, Sez. 5, 1974, 3, 135.

Photochemistry of Inorganic and Organometallic Compounds

183

All these quenching studies are therefore best explained by energy transfer to the triplet state of ferrocene. While no reproducible emission from ferrocene has been reported, luminescence from ruthenocene 230s 233 and from 1,1'-diacetylruthenocene 230 has recently been observed. The lifetime and quantum yield for emission of ruthenocene is markedly temperature dependent and this is attributed to thermal equilibration of the levels arising from spin-orbit coupling within the 3E1 A large Stokes' shift is observed indicating that the excited state of ruthenocene is substantially and symmetrically expanded. This distortion is certain to have important consequences on the quenching efficiencies of the metallocenes. Other reports deal with the electronic absorption spectra of ferrocene at 77 K,23aand ab initio calculations on excited states of f e r r ~ c e n e . ~ ~ ~ Quantum yields for photochemical decomposition of Cp2M (M = Fe, Ru, Ni, The 18-electron or Co), (benzene),Cr, and their cations have been compounds were found to be photostable. Electron transfer between ferrocene and nitrous oxide (reaction 75) takes place after excitation of a CT state of ferrocene (h = 254 nm). No reaction is observed Cp,Fe

+ N20

hv ___+

+

[Cp2Fe]+ N2

+ 0-

(75)

for longer wavelength irradiation.23s Traverso et al. have reported on the photosensitivity of ferrocene-LiCl a d d u ~ t s and , ~ ~improved ~ methods for the photochemical preparation of [Cp,Fe]+ from Cp,Fe and cc14.237, 2s8 In a similar fashion to Cp,Fe, Cp,Ru forms complexes with CC14 and other halogenocarbons. On irradiation of this complex [Cp,Ru]+ is f ~ r m e d . ~ ~ @ - ~ ~ With light corresponding to the maximum of the CTTS band of the complex (A = 280 nm), the reaction is reported to proceed with = l.240 Other studies of the direct photolysis (h = 313 or 365 nm), the naphthalene-sensitized reaction, and the quenching of the process by SmCI, or oxygen suggest that both singlet and triplet states of the complex are involved in reaction (76).23B Cp,Ru,CC14

hv

[Cp,Ru]+

+ C1- + CCI,*

(76)

Benzophenone-photosensitized hydrolysis of CpFe(Cp-CR1=NRz) leads to the corresponding ketone or aldehyde CpFe(Cp-COR1).242 Photodecomposition of ferrocenyl and photochemical oxidation of ferrocene carboxylic acids on 254 nm irradiation have been G. A. Crosby, G. D. Hager, K. W. Hipps, and M. L. Stone, Chem. Phys. Letters, 1974,28, 497. A. N . Nesmeyanov, B. M. Yavorskii, N . S. Kochetkova, E. 1. Mrina, and N. S. Voroshilova, Doklady Akad. Nauk S.S.S.R., 1974,219, 123. m4 R. M. Rohmer, A. Veillard, and M. H. Wood, Chem. Phys. Letters, 1974, 29, 466. J. A. Powell and S. R. Logan, J. Photochem., 1974, 3, 189. E. Horvath, S. Sostero, 0. Traverso, and V. Carassiti, Gazzetta, 1974, 104, 1003. 0. Traverso, R. Rossi, and V. Carassiti, Synth. React. Inorg. Metal-Org. Chem., 1974,4, 309. S . Sostero, 0. Traverso, and R. Rossii, Ann. Univ. Ferrara, Sez. 5, 1974, 3, 183. P. Borrell and E. Henderson, J.C.S. Dalton, 1975, 432. r40 0. Traverso, S. Sostero, and G. A. Mazzocchin, Inorg. Chim. Acta, 1974, 11, 237. 241 0. Traverso and S. Sostero, Ann. Univ. Ferrara, Set. 5, 1974, 3, 91. a42 J. H. J. Peet and B. W. Rocket, J. Organometallic Chem., 1975, 88, C1. C. Baker and W. M. Horspool, Tetrahedron Letters, 1974, 3533. a44 0. Traverso, R. Rossi, and V. Carassiti, Ann. Univ. Ferrara, Sez. 5 , 1974, 3, 103. ma

184

Photochemistry

A full report on the photochemistry of matrix-isolated Fe(CO), at 20 K has ap~eared."~The photochemical reactions characterized are shown in Scheme 4. Some of the observed properties of Fe(CO), may well be relevant to its reactivity

Fe atoms Reagents: i, U.V.photolysis; ii, 'Nernst-glower' photolysis (A > 320 nm); iii, annealing matrix; ivy A > 375 nm

Scheme 4

in solution. Fe(CO), has a C,,structure and probably exists as a ground-state triplet. While it has been found to complex with CH, and N2, it is certainly less reactive in this respect than Cr(CO),. However, as the authors point out, this weaker co-ordination to hydrocarbons may well mean that Fe(CO), is more reactive in solution than is Cr(CO),. Irradiation of Fe(CO), in hydrocarbon glasses containing 1M methyltetrahydrofuran gives Fe(CO),(MeTHF) and both the bis(axia1) and axial-equatorial isomers of Fe(C0)3(MeTHF),.246 The photodecompositions of [Fe(CO),]-, to give [Fe(CO)3]-,244"and of [M(CO),]- (n = 3-5; M = V, Cr, Mn, Fey Co, or Ni) 247 have been examined in the gas phase using an ion cyclotron resonance technique. The stereochemical course of the photochemical decarbonylation reaction of iron-acyl compounds is a subject of much current i n t e r e ~ t . ~By ~ ~labelling -~~~ 245 246

2b7 200 24s

2s1

263

J. D. Black and P. S. Braterman, J. Organometallic Chem., 1975,85, C7. J. H.Richardson, L. M. Stephenson, and J. I. Brauman, J. Amer. Chem. SOC.,1974,96,3671. R. C. Dunbar and B. R. Hutchinson, J. Amer. Chem. SOC., 1974,96, 3816. J. J. Alexander, J . Amer. Chem. SOC.,1975,97, 1729. P. Reich-Rohrwig and A. Wojcicki, Znorg. Chem., 1974,13, 2457. T. G. Attig and A. Wojcicki, J . Organometallic Chem., 1974,82, 397. A. Davison and N. Martinez, J. Organometallic Chem., 1974,74, C17. H. Brunner and J. Strutz, 2.Naturforsch., 1974,29b, 446.

Photochemistry of Inorganic and Organornetallic Compounds

185

studies, Alexander 248 has shown that for CpFe(CO),COMe the reaction proceeds by loss of a terminal CO group (Scheme 5). Species (28) may be trapped by PPh3, suggesting that the methyl migration is not synchronous with termhaLC0

co 0 / lI* CpFe-C-Me \

co

'I"

>

/

0 11 *

CpFe-C-Me

co

+

/

CO + CpFe-Mc

\*

co

co

(28) Scheme 5

expulsion. The photodecarbonylation of each pair of enantiomers of CpFe(C0)(PPh,)(C(O)CH,CHMePh} proceeds with high stereospecificity at both the Fe and C asymmetric It is not clear however whether the reaction proceeds with retention or inversion of configuration at the Fe atom. Similar high stereospecificity has been obtained for the decarbonylation reaction of (1-Me-3-Phcyclopentadienyl)Fe(CO)(PPh3)(COMe),250 and of CpFe(CO)(PPh3)(COEt).2s1 However, decarbonylation of CpFe(CO)(PPh,)(COMe) leads only to low optical activity in the Photolyses of (cyclobutadiene)Fe(CO), 253 and (1,2-diphenyl-3,4-di-t-butylcyclobutadiene)Fe(CO), 264 yield the products (29) and (30), respectively. By 0

F\ Fe =Fe

OC\

0

,co

I

I

analogy with compound (29) it is suggested that (31) may be an important intermediate in reactions of Fe(CO), in Irradiation of (32) and subsequent reaction with CelVgives (33).255 The photo-induced reactions of Fe(CO), with strained hydrocarbons lead to a series of interesting compounds. Quadricyclane (34) reacts to give (35a), (36), and

264

266

I. Fischler, K. Hildenbrand, and E. Koerner von Gustorf, Angew. Chem., 1975, 87, 3 5 ; Angew. Chem. Internat. Edn., 1975, 14, 54. S. I. Murahashi, T. Mizoguchi, T. Hosokawa, I. Moritani, Y. Kai, M. Kohara, N. Yasuoka, and N. Kasai, J.C.S. Chem. Comm., 1974, 563. R. H. Grubbs, T. A. Pancoast, and R. A. Grey, Tetrahedron Letters, 1974, 2425.

186

Photochemistry

(34) (35) a; R1= R2= H b; R', R2 = 0

(37).26eu With quadricyclanone the major product is (35b). Reaction of homosemibullvalene gives (38) and (39) as well as the simple Fe(CO), complex.266b The Fe(CO), complex (40) was isolated after photolysis of mixtures of Fe(CO),

u-p and vinylcyclopropane at - 50 oC.esecWhile the dispirane compound (41) gives (42) as the main product on irradiation with Fe(CO),, the monospiranes (43) form the conjugated enones (44).257 The photoreaction of (45) and Fe(CO), leads to a number of isomeric Fe2(CO)6(C8H8)complexes.268 Light-induced reaction of dimethyldiacetylene with Fe(CO), yields (46).260 ma

(a) R. Aumann, J. Organometallic Chem., 1974, 76, C32; (b) R. Aumann, ibid., 1974,77, C33; R. Aumann, J. Amer. Chem. SOC.,1974,96, 2631. S. Sarel, A. Felzenstein, R. Victor, and J. Yovell, J.C.S. Chem. Comm., 1974, 1025. R. Victor and R. Ben-Shoshan, J. Organometallic Chem., 1974, 80, C1. R. C. Pettersen, J. L. Cihonski, F. R. Young, and R. A. Levenson, J.C.S. Chem. Comm.,

(c) a67

268

1975, 370.

187

Photochemistry of Inorganic and Organometallic Compounds

b;n=2 c; 2H

in place of (CH,),

0

II

/-GN-c-oMe (49)

(51)

(50)

(52)

Lactone derivatives (47) are the product of photochemical addition of Fe(CO), to (48).eso Under similar conditions, (49) gives the analogous lactam compounds. Irradiation of (50) with Fe(CO), produces (51) via (52), which may be isolated at low temperatures.2s1 Excitation of LFe(CO), (L = cis- or trans-dihalogenoethylene) causes both CO and L dissociation.262 Typically irradiation of complex (53) leads to (54) (Scheme 6). Br

Br

l~

KC/ Br (CO),Fe

- -ICI

H’

(CO),Fe.-Fe / Bi

(CO),

a.

‘Br

(53)

(54)

Scheme 6 2eo

261 2a2

R. Aumann, K. Froehlich, and H. Ring, Angew. Chem., 1974, 86, 309; Angew. Chcm. Znternat. Edn., 1974, 13, 275. R. Aumann and H. Averbeck, J. Organometallic Chem., 1975, 85, C4. F. W. Grevels and E. Koerner von Gustorf, Annalen, 1975, 547.

188 Photochemistry Low-temperature (- 30 "C) photolysis of LFe(CO), (L = CH,=CHCO,Me) in the presence of L yields L,Fe(CO), in two isomeric forms, in both of which L is co-ordinated to the metal by the olefinic double bond.2e3 On warming the solution to 0 "C the ligand L is expelled and (55) is formed. At room temperature, however, the isomeric metallocycles (56a) and (56b) are the principal products from the photolysis reaction of LFe(CO), and L.

R'

Me0,C (56) a; R1= H; R2= C0,Me b; R1= C0,Me; R2 = H

The cycloaddition of MeO,CC=CCO,Me to (57)lgiving (58) has been discussed in terms of the Woodward-Hoffmann although these Rules may not be strictly applicable to polyenes bearing transition-metal ligands. The light-induced addition of PhCECPh to (59) gives (60).266

RR

(57) a ;

R R

R =H

I'=

b; 2R

' 0

Ph

Q.aMe Me

P

/ \

Ph Et

CpFe(CO),(CH,SiMe,SiMe,) photoisomerizes to CpFe(CO),(SiMe,CH,SiMe3).266The isocyanate complex CpFe(CO),(NCO) is formed in low yield by photolysis of CpFe(CO),(N3).267Photochemical syntheses of LFe(C0)3 (L = 863

264

26s 2a6 287

F. W. Grevels, D. Schulz, and E. Koerner von Gustorf, Angew. Chem., 1974,86,558; Angew. Chem. Internat. Edn., 1974, 13, 534. R. E. Davis, T. A. Dodds, T. H. Hseu, J. C. Wagnon, T. Devon, J. Tandrede, J. S. McKennis, and R. Pettit, J. Amer. Chem. SOC.,1974, 96, 7562. C. Krueger and H. Kisch, J.C.S. Chem. Comm., 1975, 65. K. H. Pannell and J. R. Rice, J . Organometallic Chem., 1974, 78, C35. A. Rosan and M. Rosenblum, J. Organometallic Chem., 1974, 80, 103.

189

Photochemistry of Inorganic and Organometailk Compounds

1,2-dimethyl-l,2-dihydropyridazine-3,6-di0ne),~~* and [Fe(CO)(dienyl)(diene)]+26g have been described. Photo-induced replacement of the aromatic ligand in (61) by dimethylb ~ t a d i e n e , ,and ~ ~ of the arene in (arene)RuCl,(PR,) by other arenes 271 has been observed. CpRu(CO),SR (R = C,F,) is more photoreactive than its iron analogue and, on photolysis, compounds (62)-(64) are produced.a72 The rearrangement of (62)

R I

0 II

/ \ ,cp ,Ru Ru CP \ ‘co

oc,

S

RO

C

S

CP,

sc

/ \ ,SR

k\

Cp-Ru-Ru-Cp

OC/RU--RU,

1

\s/

I

R

I R

(62)

(63)

CP

\S/ R

(64)

to (63), which is light-induced, is of a type not previously observed in the chemistry of organometallic compounds. Cobalt, Rhodium, and Iridium.-Irradiation of vitamin B,, coenzyme or ethylcobalamin in the presence of a spin-trap (ButNO or nitrosodurene) has allowed the trapping of the radicals formed by cleavage of the Co-C bond.273 Alkylcobaloximes (65)are of interest as models for vitamin B12. Giannotti and co-workers have previously shown that insertion of oxygen into the Co-C

R

(65) a; R = M e

b; R = P r i C; R = Bu* d; R = n-pentyl e; R = cyclohexyl f; R = benzyl

bond, forming alkylperoxycobaloximes takes place, when alkylcobaloximes are photolysed in the presence of 0,. It has been proposed in a recent publication that the initial step is photolysis of the Co-X bond, followed by photocatalysed insertion of oxygen and recombination of the base X2’*However, e.s.r. spectra R[Co]X

268

aeB

271

27a 273

A

R[Co]

+X

hvlOi

+ RO,[Co]X (77) A. N. Nesmeyanov, M. I. Rybinskaya, L. V. Rybin, A. V. Arutyunyan, L. G. Kuzmina, and Y. T. Struchkov, J. Organometallic Chem., 1974, 73, 365. J. Ashley-Smith, D. V. Howe, B. F. G. Johnson, J. Lewis, and I. E. Ryder, J. Organometallic Chem., 1974,82,257. I. Fischler and E. Koerner von Gustorf, 2.Naturforsch., 1975, 30b, 291. M. A. Bennett and A. K. Smith, J.C.S. Dalton, 1974, 233. G. R. Knox and A. Pryde, J. Organometallic Chem., 1974, 74, 105. K. N. Joblin, A. W. Johnson, M. F. Lappert, and B. K. Nicholson, J.C.S. Chem. Comm., 1975, 441. C. Giannotti, C. Fontaine, and B. Septe, J . Organometallic Chem., 1974, 71, 107.

Photochemistry

190

taken during low-temperature (1 13-273 K) photolysis of (65a-f) (X = py) show that for all compounds except (65a) and (65f), fragments due to the radical R*and a Co" complex are formed.27s This suggests that for these compounds, homolysis of the Co-C bond is an important reaction, and it was further found that this is often followed by rupture of the Co-X bond. The results for (65a) and (65f) are quite different: the e.s.r. spectra indicate that a Co" species with intact Co-C bond is generated on irradiation. In these cases it is proposed that electron transfer from the solvent or the dimethylglyoxime ligand is occurring. Further evidence for electron transfer from the equatorial ligand has been provided by irradiation of (65a) in the presence of spin-trap (66).276This experi-

Q I

ment showed that hydrogen atoms are ejected from the photo-excited complex, and selective deuteriation of the ligands and of the solvent indicated that these atoms originate from the dimethylglyoxime ligands. Further investigation of the primary processes of the photochemistry of these compounds should prove especially interesting in the light of recent work on macrocyclic ligand complexes of C O ' ~e.g. ~ , ref. 100. Another paper on the insertion of oxygen into the Co-R bond of alkylcobaloximes confirms that this reaction proceeds non-stere~specifically.~~~ Other reports contain brief discussions of Co-C bond homolysis in cobaloximes 278 and related Strohmeier has reported on the effect of U.V. irradiation on catalytic hydrogenation by Co', Rh', and Ir' corn pound^.^^^-^^^ It has been shown, for example, that the activity of IrCI(CO)(PPh,), as a catalyst for the hydrogenation of dimethylmaleate is increased by up to 40 times on irradiation.2E0bThis is attributed to the reaction (78) which produces the catalytically reactive species IrCI(C0)(PPh3). IrCl(CO)(PPh,),

hv

IrCl(CO)(PPh,)

+ PPh,

Light-induced CO dissociation from CpCo(CO), in solution at 5 "C leads to (67), which on standing is converted partially into (68).a8a 276

27a 277 278

279 280

281

28a 285 284

C. Giannotti and J. R. Bolton, J . Organometallic Chem., 1974, 80, 379. C. Giannotti, G. Merle, C. Fontaine, and J. R. Bolton, J. Organometallic Chem., 1975,91,357. H. Shinozaki and M. Tada, Chem. and Ind., 1975, 178. K. L. Brown and L. L. Ingraham, J. Amer. Chem. SOC.,1974,96,7681. R. M. McAllister and J. H. Weber, J. Organometallic Chem., 1974, 77, 91. (a) W. Strohmeier and G. Csontos, J . Organometallic Chem., 1974,67, C27; (b)W. Strohmeier and G. Csontos, ibid., 1974, 72, 277. W. Strohmeier and K. Gruenter, J. Organometallic Chem., 1975, 90, C48. W. Strohmeier and L. Weigelt, J. Organometallic Chem., 1974, 82, 417. W. Strohmeier and E. Hitzel, J. Organometallic Chem., 1975, 87, 353. K. P. C. Vollhardt, J. E. Bercaw, and R. G. Bergman, J. Amer. Chem. SOC.,1974,96, 4998.

Photochemistry of Inorganic and Organometallic Compounds

0 CII

O

cIp /co-co A/

L-co--c

oc\ / / ,co-co\

,CP

191

/p

CP (67)

II

0

(68)

Compounds of the type [Rh(phen)(CO),]+X- (X = CI or ClOJ are phototropic. 286 Nickel.-On irradiation in chlorocarbon solvents, nickelocene undergoes reaction (79).286 The photodecomposition of [Ni(allyl)Cl], compounds has been disCp,Ni

+ RCl

hv ___+

[Cp,Ni]+

+ C1- + R-

(79)

During the photo-induced transformation of (69) into (70) the carbonyl insertion into the cyclopropane and co-ordination of the incipient double bond appear to take place synchronously.288

/"'.-a

C

&/

Copper, Silver, and Gold.-The photoisomerization reaction (80) is catalysed by Cu(OAc),, Cu(acac),, or C U C I ~Cu(ClOJ, . ~ ~ ~ promotes the photocyclodimerization of N-vinylcarbazole (VCZ).290The process involves initial electron-transfer from the singlet or triplet state of VCZ to Cu", giving VCZ+ and Cul. In contrast to its thermal decomposition, irradiation of Ag(Bun)(PBun,) causes cleavage of the Ag-C bond and the liberation of butyl radicals.291 ClCHMeCH=CH,

MeCH=CHCH,CI

(80)

Zinc and Mercury.-Photolysis of diphenylzinc in either CHCl, or CC14produces PhZnC1.292 Homolysis of one of the Hg-C bonds is the primary process on irradiation of 286 288

ae7 2E8

28s 2@0 281

2Ba

R. D. Gillard, K. Harrison, and I. H. Mather, J.C.S. Dalton, 1975, 133. 0.Traverso and R. Rossi, Ann. Univ. Ferrara, Sez. 5, 1974,3, 167. V. A. Kormer, L. F. Shelokhneva, and N. A. Kartsivadze,Zhur. obshchei Khim., 1974,44,710. J. M.Brown, J. A. Conneely, and K. Mertis, J.C.S. Perkin II, 1974,905. W.Strohmeier, 2.Naturforsch., 1974,29b,282. M. Asai, H. Matsui, and S. Tazuke, Bull. Chem. SOC.Japan, 1974,47, 864. G.M. Whitesides, D. E. Bergbreiter, and P. E. Kendall, J. Amer. Chem. SOC.,1974.96,2806. R. F.Galiullina, G . G. Petukhov, V. I. Khruleva, and Y. N. Krasnov, Zhur. obshchei Khim., 1974,44,1978.

192

Photochemistry

Hg(CCl,), in the solid,293solution, or gas phase.294 Similarly, Hg(OAc){CH(COBU~)~} undergoes photolysis of the Hg-C bond.295 C0,R radicals formed from PhHgCO,Me, Hg(CO,Me),, and PhHgC0,Et have been trapped by nitrones and 2,4,6-tri-t-butylnitro~obenzene.~~~ The carbyne species formed on irradiation of (71) reacts with Mn(CO),Br to give (72).207

v F-

CO,Et

I

CO,Ef

I"\ \/

(CO),Mn Mn(C%

Hg \C- CO,Et

C

II

I

C0,Et

N2

(71)

(72)

A study of R1,CHgMRZ3(M = Si or Sn) showed that on irradiation, preferential cleavage of the Hg-C bond occurs.208 p-Hg(OAc)(N-nitroso-Nmethylaniline) undergoes light-induced intramolecular rearrangement to N-methyl-p-nitrosoaniline.20DThe quenching of anthracene fluorescence by HgPhz is a consequence of increased intersystem crossing.3oo 3 Porphyrins and Related Molecules of Biological Importance As in previous years this section consists of a short account of recent developments in metalloporphyrin photochemistry and photophysics and a selective survey of the in vitro photochemistry of chlorophyll and haem. Metal1oporphyrins.-Phot olysis in pyridine converts (OEP)M(CO)(py) into (OEP)M(py), (OEP = octaethylporphyrin) both for M = Ru325 and for M = Photo-oxygenation of (0EP)Mg gives (73).327 The analogous Et CHO

Et

Et

29a

A. K. Mal'tsev, N . D. Kagramanov, and 0. M. Nefedov, Zzvest. Akad. Nauk S.S.S.R., 1974, 1993.

N. D. Kagramanov, A. K. Mal'tsev, and 0. M. Nefedov, Zzvest. Akad. Nauk S.S.S.R., 1974, 2146. 295 2B6 297 298 299

R. H. Fish, R. E. Lundin, and C. G . Salentine, J. Organometallic Chem., 1975, 84, 281. A. L. Bluhm and J. Weinstein, Spectroscopy Letters, 1975, 8, 43. W. A. Herrmann, Angew. Chem., 1974, 86, 8 9 5 ; Angew. Chem. Znternat. Edn., 1974,13, 812. T. N . Mitchell, J. Organometallic Chem., 1974, 71, 21. E. Y.Belyaev, N. I. Rtischchev, S. V. Demko, B. B. Kochetkov, and A. V. El'tsov, Zhur. org. Khim., 1974, 10, 887. E. Vander Donckt, M. Lootens, D. Swinnen, and C. Haquin, Bull. Soc. chim. belges, 1975,84, 77.

310

30Q

307

306

304

303

Ar(C0)2L

T. Kruck and H. Breuer, Chem. Ber., 1974, 107, 263. T. Kruck and H. U. Hempel, Angew. Chem., 1974, 86, 233; Angew. Chem. Internat. Edn., 1974,13,201. M. Schneider and E. Weiss, J. Organometallic Chem., 1974, 73, C7. F. Cristiani, D. De Filippo, P. Deplano, F. Devillanova, A. Diaz, E. F. Trogu, and G . Verani, Znorg. Chim. Acta, 1975, 12, 119. T. Kruck, F. J. Becker, H. Breuer, K. Ehlert, and W. Rother, 2. anorg. Chem., 1974,405,95. S . S. Sandhu and A. K. Mehta, J. Organometallic Chem., 1974, 77,45. A. B. Cornwell, P. G . Harrison, and J. A. Richards, J. Organometallic Chem., 1974,76, C26. J. A. Connor, G. K. McEwen, and C. J. Rix, J. Less-common Metals, 1974, 36, 207. G. Schmid, R. Boese, and E. Welz, Chem. Ber., 1975, 108, 260. M. Herberhold, K. Leonhard, and C. G . Kreiter, Chem. Ber., 1974, 107, 3222.

ArCr(CO), Ar = subst. benzene

M = W

M = Mo

M = Cr or W M = Cr M = Mo

Reactant L SnC1,PF3 CH2=CH- CH2Cl CH2=CH- CR=CH2

Table 5 Photochemical substitution reactions of metal carbonyl compounds

309

w \o

CI

D

.sr

23

3

2

307 8 307 Q 308 0

-

[Cp(CO),FeS(Et)Fe(CO),Cp]+

CpFe(CO)&= CPhC(CF3),0CH2 Fe(NO),(CO),

-

1

CpFe(CO)(L)C=CPhC(CF,),OCH, [Fe(N0),L2l2-

~~

PPh, SnC1,-

I

Cp(CO),MnAsMe,Mn(CO), Fe( CO)&

320 321

318 319

317

315 316

312 313 313 314

[(MeCp)MnLPCpMn(C0)L Cp Mn(CS)L Mn(CO),(NO)L and Mn(CO)L,

m

Ref. 31 1

Products CpMn(CO),L or (MeCp)Mn(CO),L

(CO),FeSi Me,CH,CH,Si Me, cis-Fe(CO),(SiMq), and Hg [Fe(CO), SiMe, l2

COOMe

O

COMe,

HMe,SiCH,CH,SiMe,H Hg(SiMq),

P

R1N=CR2- CR2=NR1

-

Reactant L H,C=CH-COMe, PhC=CHor 2-cyclohexenone CN(Ph2PCH,CH2),PPh (Ph,PCH,CH,),PPh CH,=CH-CH=CH,

*I3

312

321

s20

319

s18

317

s16

816

314

313

31a

311

PPha cycloheptatriene SnC1,-

CpFe(CO)L[Si(Ph)(Me)( 1-Np)] Ru(CO),L tCo(No)(Co),(snC1,)1-

M.Gifford and P. Dixneuf, J. Organometallic Chem., 1975, 85, C26. J. A. Dineen and P. L. Pauson, J. Organometallic Chem., 1974, 71, 91. I. S. Butler and N. J. Coville, J. Organometallic Chem., 1974, 80, 235. M. Herberhold and A. Razavi, Angew. Chem., 1975, 87, 351; Angew. Chem. Internat. Edn., 1975,14351. H. Vahrenkamp, Chem. Ber., 1974,107, 3867. H. tom Dieck and A. Orlopp, Angew. Chem., 1975,87, 246; Angew. Chem. Itnernat. Edn., 1975,14,251. J. Agar, F. Kaplan, and B. W. Roberts, J. Org. Chem., 1974, 39, 3451. L. Vancea and W. A. G. Graham, Inorg. Chem., 1974,13,511. W. Jetz and W.A. G. Graham, J. Organometallic Chem., 1974, 69, 383. D. W. Lichtenberg and A. Wojcicki, Inorg. Chem., 1975, 14, 1295. T. Kruck and W. Molls, 2.anorg. Chem., 1975,411, 54. R. B. English, R. J. Haines, and C. R. Nolte, J.C.S. Dalton, 1975, 1030. G. Cerveau, E. Colomer, R. Comu, and W. E. Douglas, J.C.S. Chem. Comm., 1975,410. J. C . Burt, S. A. R. &ox, and F. G. A. Stone, J.C.S. Dalton, 1975, 731.

CpFe(CO),[Si(Ph)( Me)(1-Np)] RudCO),, Co(NO)(CO),

196

Photochemistry

reaction is not observed for (OEP)Zn, probably because of its higher oxidation potential ; however, (octaethylch1orin)Zn is oxidized. Photo-oxygenation of other porphyrins has been Whitten et al. have made a flash photolysis study of the quenching of the triplet states of (aetio I)Zn, (OEP)Zn, and (aetio 1)Mg (aetio I = aetioporphyrin I) by aromatic nitro-compounds and by organic chloro-compounds in benzene.32e At low concentrations of Q to 5 x mol I-l) only quenching of the triplet states was observed, but at higher concentrations the absorption spectra of new species were recorded. These species, which may be quenched by other substances having very low-lying triplet states, have been ascribed to exciplexes P0r.Q and Por.Q,. Ternary exciplexes also appear to be involved in the aminestimulated reversible photoreduction of TPPH2 and (TPP)Zn by quinones and n i t r o - c ~ m p o u n d s . ~Other ~ ~ authors have used e.s.r. techniques to study the photo-oxidation of Mg- and Z n - p ~ r p h y r i n s and ,~~~ the electron-transfer reactions of aetioporphyrin I1 and b e n z o q ~ i n o n e . ~ ~ ~ It has been found that OEP derivatives of S C ~ ~ TitV, ' , Zrtv, HfIV,NbV, and TaV emit both fluorescence and phosphorescence - a behaviour which parallels that normally observed with other closed-shell metall~porphyrins.~~~ Values of Q, QP, and T~ indicate greater spin-orbit coupling for the heavier elements, i.e. Zr, Hf, Nb, and Ta, although the extent of this effect is lessened if the metal atom is out of the porphyrin plane. The Mg and A1 derivatives of aetioporphyrin I also emit both fluorescence and phosphore~cence.~~~ The absorption spectra of the paramagnetic complexes, (TPP)CrttlCI and phenol-phenoxo-(TPP)Cr"', show bands additional to the Soret and red bands of the p ~ r p h y r i n .The ~~~ long-wavelength bands may be attributed to transitions to porphyrin tripquartet states (i.e. states formed by coupling of the porphyrin triplet to the CrlI1 d3 system). Emission from these compounds is markedly temperature dependent, displaying two bands at low temperatures (at 81 1 nm and 847 nm; at 4 K, Isll/Is4, = 0.12) but only one band (at 815 nm) at T > 160 K. These bands are assigned to *T1-+ 4S0and T1+= ",-, transitions, where the 4T1and T-,states arise by the coupling mentioned earlier. For Yb"'-TBP complexes (TBP = tetrabenzoporphyrin) emission occurs from the Yb centre following transfer of energy from the p ~ r p h y r i n .It~ has ~ ~ been shown that an impurity was responsible for 325

F. R. Hopf, T. P. O'Brien, W. R. Scheidt, and D. G. Whitten, J. Amer. Chem. SOC.,1975,97, 277.

326

J. W. Buchler and P. D. Smith, Angew. Chem., 1974, 86, 378; Angew. Chem. Znternat. Edn.,

327

J. H. Fuhrhop, P. K. W. Wasser, J. Subramanian, and U. Schrader, Annalen, 1974, 1450. I. M. Byteva, G. P. Gurinovich, and 0. M. Petsol'd, Biofizika, 1975, 20, 51. J. K. Roy, F. A. Carroll, and D. G. Whitten, J. Amer. Chem. SOC.,1974, 96, 6349. I. N. Ivnitskaya and I. 1. Dilung, Biofizika, 1974, 19, 636. V. A. Umrikhin and 2.P. Gribova, Biofizika, 1974, 19, 640. Y. V. Glazkov and N. I. Zotov, Zhur. priklad. Spektroskopii, 1974,20, 921. M. Gouterman, L. K. Hanson, G. E. Khalil, J. W. Buchler, K. Rohbock, and D. Dolphin, J. Amer. Chem. SOC.,1975, 97, 3142. M. P. Tsvirko, K. N. Solovev, A. T. Gradyushko, and S. S. Dvornikov, Zhur. priklad. Spektroskopii, 1974,20, 528. M. Gouterman, L. K. Hanson, G. E. Khalil, W. R. Leenstra, and J. W. Buchler, J. Chem. Phys., 62, 2343. T. F. Kachura, A. N. Sevchenko, K. N. Solovev, and M. P. Tsvirko, Doklady Akad. Nauk S.S.S.R., 1974, 217, 1121.

1974, 13, 341. 328 329 350

331 3 32 333

334

336

336

Photochemistry of Inorganic and Organometallic Compounds

197 the previously reported 337 anomalous phosphorescence of (TPP)SnC12.338 Studies on the polarization of fluorescence from upper excited states of TBPHa and (TBP)Zn have been carried The effect of heavy atoms on the relative yields of fluorescence and phosphorescence has been investigated both by inserting Br and I substituents in the ring of deuterioporphyrin IX and its Zn derivative,340and by adding ethyl iodide to the solution of a number of free base p o r ~ h y r i n s .Other ~ ~ ~ authors discuss the luminescence of protoporphyrin IX dimethylester after pulse radiolysis in benzene,342 and from monomeric and dimeric ethylenediamine-substituted protoporphyrin IX and some metal Several reports consider the emission from porphyrins in Shpolskii matrices and other crystalline organic h o ~ t ~ . ~ ~ ~ - ~ ~ ~ Electrochemiluminescence of (TPP)Pd and (TPP)Pt originates from their triplet states formed after recombination of the cation and anion.347 [(TPP)Pd]+

+ [(TPP)Pd]-

-

(TPP)Pd*

+ (TPP)Pd

(81)

Gardiner and Thomson have published an interesting paper on the luminescence properties of metallocorrins (74).348 Many parallels exist with the

CN

(74)

analogous porphyrins. Thus fluorescence is observed for the free corrin and for its Li', Be", Mg", Zn", and Cd" derivatives, phosphorescence (perturbed by the ion present) for the Pt", Pd", and Rh"' complexes, and no emission at all for the C O ~ ~CuII, ' , and Ni" compounds. The absence of luminescence from these latter species is consistent with their lack of reactivity in the photoisomerization of A/D secocorrin to corrin.

344

M. Gouterman, F. P. Schwarz, P. D. Smith, and D. Dolphin, J. Chem. Phys., 1973, 59, 676. M. Gouterman and H. B. Howell, J. Chem. Phys., 1974, 61, 3491. I. E. Zalesskii, V. N. Kotlo, A. N. Sevchenko, K. N. Solovev, and S. F. Shkirman, Doklady Akad. Nauk S.S.S.R., 1974, 210, 324. A. T. Gradyushko, D. T. Kozhich, K. N. Solovev, and M. P. Tsvirko, Optika i Spektroskopiya, 1974, 37, 892. M. Gouterman and G . E. Khalil, J. Mol. Spectroscopy, 1974, 53, 88. S. J. Chantrell, C. A. McAuliffe, R. W. Munn, A. C. Pratt, and E. J. Land, J.C.S. Chem. Comm., 1975,470. R. R. Das, J. Znorg. Nuclear Chem., 1975, 37, 153. A. T. Gradyushko, K. N. Solovev, and S. G. Khokhlova, Zhur. priklad. Spektroskopii, 1974,

345

21, 252. V. N. Kotlo, K. N. Solovev,

337 33R 330

340 341

342

343

346

347

348

S. F. Shkirman, and I. E. Zalesskii, Vestsi Akad. Navuk Belarus. S.S.R., Ser.fiz.-mat. Navuk, 1974, 99. B. F. Kim, J. Bohandy, and C. K. Jen, Spectrochim. Acta, 1974, 30A, 2031. N. E. Tokel-Takvoryan and A. J. Bard, Chem. Phys. Letters, 1975, 25, 235. M. Gardiner and A. J. Thomson, J.C.S. Dalton, 1974, 820.

198

Photochemistry

It is clear from the first report of the application of picosecond flash photolysis to the study of porphyrin photophysics that this technique will become increasingly Thus it has been found possible to record the absorption spectra of both the singlet state (T 500ps) and triplet states of (OEP)SnCl,. Further, (DISC could be measured, and the value differed from that found by previous workers. For (0EP)Pd both singlet and triplet states could be observed, whereas only one species was found for the paramagnetic (0EP)Cu and (TPP)Cu complexes. Nanosecond laser flash photolysis has been used in the study of the transients formed from Cu" and Pb" p o r p h y r i n ~ .No ~ ~observable ~ intermediates were detected for the Ag", Ni", and Co"' derivatives. Triplet-triplet absorption spectra of a series of porphyrins and their Zn complexes have been The rate constants for radiationless decay of the triplet state of mesoporphyrin IX dimethyl ester at 77 K are 26 s-l in EtOD and 57 s-l in EtOH.352 The most probable cause is a decrease in the rate of tautomerism in the porphyrin due to deuteriation of the N-H hydrogen. However, for TPPH, triplet state in n-octane matrices363such tautomerism does not appear to be an important mechanism for radiationless deactivation. Several recent reports deal with the low-temperature e.s.r. spectra of triplet states of p ~ r p h y r i n s . ~The ~ ~ -zero ~~~ field splittings and depopulation rates of the various spin sub-levels of the triplet state of Zn-chlorophyll-a have been determined by an optically detected magnetic resonance method.359 Subjects of recent publications on the spectroscopic properties and electronic structure of porphyrins include the photochemically induced dichroism of [ ( a e t i ~ ) Z n ] - ,the ~ ~ ~absorption spectra of metallo-TPP compounds in SF6, Ar, and n-octane matrices,361the Zeeman effect in the absorption spectra of Pdporphin in n-octane single the electronic spectra of Cu"- and Nil'corrin derivatives,363m.c.d. studies on p ~ r p h y r i n s366 , ~photoelectron ~~~ spectra of porphyrins and p y r r o l e ~ ,and ~ ~ ~quantum mechanical calculations on porp h y r i n ~368 .~~~~ E J

34g 350

D. Magde, M. W. Windsor, D. Holten, and M. Gouterman, Chem.Phys. Letters, 1974,29, 183. B. M. Dzhagarov, G. P. Gurinovich, and A. M. Simonov, Optika i Spektroskopiya, 1974,37, 254.

351 352

363 364 356

366

357 358 358

360 361 302 363 364

86s

366 3R7

36*

V. V. Sapunov, K. N. Solovev, and M. P. Tsvirko, Zhur. priklad. Spektroskopii, 1974,21,667. R. P. Burgner and A. M. Ponte Goncalves, J. Chem. Phys., 1974,60, 2942. R. H. Clarke and R. E. Connors, J. Chem. Phys., 1975,62, 1600. H. Levanon and S. Vega, J . Chem. Phys., 1974,61,2265. A. M. Ponte Goncalves and R. P. Burgner, J. Chem. Phys., 1974,61, 2975. S. R. Langhoff, E. R. Davidson, M. Gouterman, W. R. Leenstra, and A. L. Kwiram, J. Chem. Phys., 1975, 62, 169. W. G. van Dorp, M. Soma, J. A. Kooter, and J. H. Van der Waals, Mol. Phys., 1974,28, 1551. B. M. Hoffman, J. Amer. Chem. SOC.,1975, 97, 1688. R. H. Clarke and R. E. Connors, Chem. Phys. Letters, 1975, 33, 365. V. G. Maslov, Optika i Spektroskopiya, 1974, 37, 1010. J. J. Leonard and F. R. Longo, J. Phys. Chem., 1975,79, 62. G. W. Canters, M. Noort, and J. H. Van der Waals, Chem. Phys. Letters, 1975, 30, 1. N. S. Hush, J. M. Dyke, M. L. Williams, and I. S . Woolsey, J.C.S. Dalton, 1974, 395. G. Barth, R. E. Lindner, E. Bunnenberg, C. Djerassi, L. Seamans, and A. Moscowitz, J.C.S. Perkin ZI, 1974, 1706. R. E. Lindner, G. Barth, E. Bunnenberg, C. Djerassi, L. Seamans, and A. Moscowitz, J.C.S. Perkin 11, 1974, 1712. H. Falk, 0. Hofer, and H. Lehner, Munatsh., 1974, 105, 366. J. Almlof, Internat. J. Quantum Chem., 1974, 8, 915. G. M. Maggiora and L. J. Weimann, Internat. J. Quantum Chem., Quantum Biol., Symp., 1974, 1, 179.

Photochemistry of Inorganic and Organometallic Compounds

199

The photosubstitution reaction (82) of the phthalocyanine (Pc) complex (Pc)Fe(RNC)L (L = py, piperidine, or methylimidazole) proceeds efficiently, (Pc)Fe(RNC)L

+L

hv

(Pc)FeL,

+ RNC

(82)

whereas the back reaction is favoured in the dark.380 The system displays useful photochromic properties as the system may be cycled several hundred times without loss in reversibility. Other publications concerned with phthalocyanine photophysics discuss the determination of @ISC for 4-t-butylphthalocyanine and its metal the phosphorescence of Pt-phthalocyanine single crystals at 4 K,371the line spectra of Mg-and Zn-phthalocyanines in n-decane at 4 K,372 m.c.d. of p h t h a l o ~ y a n i n e s ,and ~ ~ ~the fluorescence and absorption spectra of Zn- and P d - a z a p ~ r p h y r i n s . ~ ~ ~ Ch1orophylls.-Aspects of the primary processes of photosynthesis which have recently been reviewed include excitation energy transfer in p h o t o ~ y n t h e s i s , ~ ~ ~ primary photochemical reactions in chloroplast p h o t o s y n t h e ~ i s light-induced ,~~~ paramagnetism in photosynthetic and photosynthetic reaction centres and primary photochemical Fong370has presented a new theory to explain the function of light in the photo-oxidation of water in the chloroplast. The reaction centre is assumed to be the dimeric species (Chl.H,O),. It is further predicted that the triplet state of this complex will have an anomalously long lifetime. Transfer of energy from the singlet state of the ‘antenna’ chlorophyll to this state will produce a triplet CT state, in which the photo-oxidation of water may occur. It has recently been proposed that the ‘antenna’ chlorophyll-a molecules in the chloroplast have an oligomeric form similar to that observed for chlorophyll-a in nonpolar solvents such as hexane, i.e. (Ch12)n.380l H N.m.r. has been used to obtain structural information about the dimers of chlorophyll-a formed in CC14 and benzene and 13Cand lSNn.m.r. spectra of chlorophyll-a have been assigned.382 Photoconductivity has been induced both in microcrystalline chlorophyll-a on laser and in ether solutions after flash p h o t o l y s i ~ .In ~ ~a~publication which was incorrectly abstracted in last year’s Report, it has been shown 368

370

371 372 3i3

374

376 3i6

377 378 379

380

s81 382 383

3R4

D. V. Stynes, J. Amer. Chem. SOC.,1974, 96, 5942. A. V. Butenin, B. Y . Kogan, E. A. Luk’yanets, and L. I. Molchanova, Optika i Sepktroskopiya, 1974, 37, 696. K. Kaneto, K. Yoshino, and Y . Inuishi, J. Phys. SOC.Japan, 1974, 37, 1297. 0. N. Korotaev and R. I. Personov, Optika i Sepktroskopiya, 1974, 37, 886. (a)M. J. Stillman and A. J. Thomson, J.C.S. Faraday 11, 1974,70,790; (b) M. J. Stillman and A. J. Thomson, ibid,, p. 805. V. A. Mashenkov, K. N. Solovev, A. E. Turkova, and N. A. Yushkevich, Zhur. priklad. Spektroskopii, 1974, 21, 73. A. Y . Borisov and V. 1. Gokid, Biochim. Biophys. Acta, 1973, 301, 227. A. J. Bearden and R. Malkin, Quart. Rev. Biophys., 1974, 7, 131. J. T. Warden and J. R. Bolton, Accounts Chem. Res., 1974, 7, 189. B. Ke, Photochem. and Photobiol., 1974, 20, 542. (a) F. K. Fong, J. Theor. Biol., 1974, 46,407; (b) F. K. Fong, Proc. Nut. Acad. Sci. U.S.A., 1974,71, 3692; (c) F. K. Fong, Appl. Phys., 1975, 6, 151. T. M. Cotton, A. D. Trifunac, K. Ballschmiter, and J. J. Katz, Biochim. Biophys. Acta, 1974, 368, 181. A. D. Trifunac and J. J. Katz, J. Amer. Chem. SOC.,1974, 96, 5233. S. G. Boxer, G. L. Closs, and J. J. Katz, J. Amer. Chem. Soc., 1974, 96, 7058. A. Bromberg, C. W. Tang, and A. C. Albrecht, J. Chem. Phys., 1974, 60,4058. N. D. Gudkov, Y. M. Stolovitskii, and V. B. Evstigneev, Biofzzika, 1973, 18, 807.

200 Photochemistry that photolysis of chlorophyll-a in ethanol at low temperatures produces Chlt ~ ~photochemical ~ interaction of chlorophylls and in the absence of q u i n ~ n e .The related compounds with quinones has been studied by e.s.r. technique^,^^^-^^^ and by measurement of pH 391 and electrode potential 392 changes during irradiation. Electron transfer has also been observed between chlorophyll and quinones in lecithin Photo-oxidation of chlorophyll-a by oxygen 3 8 4 ~385 and the photoreduction of chlorophylls and related compounds by various reagents 396-398 have been discussed. Chlorophyll-a in monomolecular layers or adsorbed on nylon 400 or other polymers 401 photosensitizes the reduction of methyl red. Other chlorophyll-sensitized reactions include the photoreduction of ferredoxin 402 and of cytochrome c.403 Reports on chlorophyll f l u ~ r e s c e n c e , ~phosphores~ence,~~~ ~~-~~~ and photochemiluminescence 411 have been published. The properties of the triplet state of chlorophyll have been studied by e,s.r.412-416and by optically detected magnetic resonance.416,417 Haem.-The photodissociation of carbonylhaem (83) and its subsequent reformation have been studied in 80% ethylene glycol: water and in glycerol solutions 4108

(C0)haem

hv

haem

+ CO

(83)

J. R. Harbour and G. Tollin, Photochem. and Photobiol., 1974, 19, 69. 388 V. M.Voznyak, I. I. Proskuryakov, and V. B. Evstigneev, Biofizika, 1974, 19,815. 387 A. P. Kostikov, N. A. Sanovnikova, V. B. Evstigneev, and L. P. Kayushin, Biofizika, 1974, 19,244. 388 A.P. Kostikov, L. P. Kayushin, L. N. Chekulaeva, N. A. Sadovnikova, and V. B. Evstigneev, F.E.B.S. Letters, 1974, 48, 149. 3 R 8 V. A. Kim, V. M. Voznyak, and V. B. Evstigneev, Biofizika, 1974, 19, 992. 300 (a) J. R. Harbour and G. Tollin, Photochem. and Photobiol., 1974,19,163;(b) J. R. Harbour and G. Tollin, ibid., 1974,20, 271. 381 V. B. Evstigneev and V. S . Chudar, Biofizika, 1974, 19, 425; 1974, 19, 997. 302 V. B. Evstigneev, A. A. Kazakova, and B. A. Kiselev, Biofizika, 1974, 19, 810. 393 G. S. Beddard, G. Porter, and G. M. Weese, Proc. Roy. SOC.(A), 1974,342,317. 304 A. A. Krasnovskii, M. G. Shaposhnikova, and F. F. Litvin, Biofizika, 1974,19, 650. 305 J. P. Chauvet, R. Journeaux, R. Viovy, and F. Villain, J. Chim. phys., 1974,71,879. 308 H.Scheer and J. J. Katz, Proc. Nut. Acad. Sci. U.S.A., 1974,71, 1626. 307 E. V. Pakshina and A. A. Krasnovskii, Biofizika, 1974, 19, 238. 3g8 V. P. Suboch, A. P. Losev, and G. P. Gurinovich, Photochem. and Photobiol., 1974,20,183. 390 S. M. de B. Costa and G. Porter, Proc. Roy. SOC.,1974,A341, 167. 4 0 ° N. I. Loboda, L. I. Nekrasov, and N. A. Shchegoleva,2hur.fiz. Khim., 1974,48,338. I. G. Nazarova and V. B. Evstigneev, Biofizika, 1974,19, 178. 402 E.N. Mukhin, N. F. Neznaiko, A. Y. Shkuropatov, Y.M. Stolovitskii, and V. B. Evstigneev, Doklady Akad. Nauk S.S.S.R., 1975,220,978. 403 A. A. Krasnovskii and E. S . Mikhailova, Doklady Akad. Nauk S.S.S.R., 1974, 215,727. 404 M. Kaplanova and K. Vacek, Photochem. and Photobiol., 1974,20,371. 405 K.Vacek, E. Vavrinec, V. Cerna, 0. Vinduskova, J. Naus, and P. Lokaj, Stud. Biophys., 1974, 44, 155. 408 R. M. Leblanc, G. Galinier, A. Tessier, and L. Lemieux, Canad. J. Chem., 1974,52, 3723. 407 L. V. Levshin, T. D. Slavnova, and V. 1. Yuzhakov, Biofizika, 1975, 20, 150. E. R. Menzel and J. S. Polles, Chem. Phys. Letters, 1974,24, 545. 40° A. A.Krasnovskii, N. N. Lebedev, and F. F. Litvin, Doklady Akad. Nauk S.S.S.R., 1974,216, 1406. 410 A. A. Krasnovskii and F. F. Litvin, Photochem. and Photobiol., 1974, 20, 133. 411 A. A. Krasnovskii and M. G. Shaposhnikova, Mol. Biol. (Moscow), 1974, 8, 666. 412 J. F. Kleibeuker and T. J. Schaafsma, Chem. Phys. Letters, 1974,29, 116. *I3 H.Levanon and A. Scherz, Chem. Phys. Letters, 1975,31, 119. 414 J. R. Norris, R. A. Uphaus, and J. J. Katz, Chem. Phys. Letters, 1975,31, 157. 415 R. A. Uphaus, J. R. Norris, and J. J. Katz, Biochem. Biophys. Res. Comm., 1974,61, 1057. 418 R. H. Clarke and R. H. Hofeldt, J. Chem. Phys., 1974,61,4582. 417 R. H.Clarke and R. H. Hofeldt, J. Amer. Chem. SOC.,1974, 96, 3005. 385

Photochemistry of Inorganic and OrganometaIIic Compounds

201

over a range of pressures (1-2760 bar) using a laser flash photolysis apparatus.418 For gIycerol the viscosity is markedly pressure dependent, and in this way it has been possible to show that the quantum yield for the photodissociation reaction falls off markedly with increasing viscosity. The same apparatus has been employed in a study of the binding of O2 and CO to haemoglobin and myog l ~ b i n . Investigation ~~~ of the processes following photodissociation of CO from carbonylhaemoglobin and related compounds has provided useful information for the formulation of theories of the reactivity of these species.420-429 Similarly the dissociation of CO and O2 from their complexes with cobalt431 and of NO from nitrosyl-manganesemyoglobin and -haemoglobin haemoglobin 432 have been described. The photoreduction of cytochrome c 433 and a comparison of the photoactivity of low-spin myoglobins with that of the high-spin species 434 have been the subjects of recent reports. 430t

4 Water, Hydrogen Peroxide, and Anions The relative importance of the processes (84) and (85) in the gas phase has been determined directly using a flash photolysis-resonance fluorescence method.435 It was established that at 105 < h < 145 nm, the relative efficiencesfor reactions h 185 nm reaction (85) is (84) and (85) are 0.89 and 0.11, whereas for 145 of negligible importance (< 1%). H,O

hv

-= -=

H

+ OH

(84)

In another study it has been shown that 23% of the hydrogen formed on irradiation of water at 147 nm is produced via step (85).436The new technique of polarized photofluorescence excitation spectroscopy has been applied to the OH radicals produced by reaction (86) on irradiation at h N” 130nm.437 The H,O 41* 418 420

4’11

422

423

424

42b 426 427

hv

H

+ OH(A2+)

(86)

E. F. Caldin and B. B. Hasinoff, J.C.S. Faraday I, 1975, 71, 515. B. B. Hasinoff, Biochemistry, 1974, 13, 31 11. M. Brunori, B. Giardina, and E. E. Di Iorio, F.E.B.S. Letters, 1974, 46, 312. P. H. Fang, Phys. Rev. Letters, 1974, 33, 1515. R. H. Austin, K. Beeson, L. Eisenstein, H. Frauenfelder, and I. C. Gunsalus, Phys. Rev. Letters, 1975, 34, 845. E. Chiancone, N. M. Anderson, E. Antonini, J. Bonaventura, C. Bonaventura, M. Brunori, and C. Spagnuolo, J . Biol. Chem., 1974, 249, 5689. Y.A. Ermakov, V. I. Pasechnik, and S. V. Tulskii, Biofizika, 1975, 20, 153. R. D. Gray, J . Biol. Chem., 1975, 250, 790. E. Whitehead, Biophys. Chem., 1974, 2, 377. V. N. Kulakov, A. L. Lyubarskii, E. E. Fesenko, and M. V. Vol’kenshtein, Stud. Biophys., 1974, 42, 55.

428 408 430 431 432

43s 434

4~ 436

437

T. Iizuka, H. Yamamoto, M. Kotani, and T. Yonetani, Biochim. Biophys. Acta, 1974,371,126. P. Debey and P. Douzou, F.E.B.S. Letters, 1974, 39, 271. T. Yonetani, H. Yamamoto, and T. Iizuka, J. Biol. Chem., 1974, 249, 2168. T. Iizuka, H. Yamamoto, M. Kotani, and T. Yonetani, Biochim. Riophys. A m , 1974,351,182. Q. H. Gibson, B. M. Hoffman, R. H. Crepeau, S. J. Edelstein, and C. Bull, Biochem. Biophys. Res. Comm., 1974, 59, 146. W. P. Vorkink and M. A. Cusanovich, Photochem. and Photobiol., 1974, 19, 205. M. Folin, G. Gennari, and G. Jori, Photochem. and Photobiol., 1974, 20, 357. L. J. Stief, W. A. Payne, and R. B. Klemm, J. Chem. Phys., 1975, 62, 4000. A. Y. M. Ung, Chem. Phys. Letters, 1974, 28, 603. G. A. Chamberlain and J. P. Simons, Chem. Phys. Letters, 1975, 32, 355.

202 Photochemistry results are consistent with the excited OH radical being formed by the predissociation of a vibronic *B1state, probably the lAz electronic state carrying one quantum of the antisymmetric stretching frequency ~3(bZ). The quantum yield for the mercury-sensitized emission of water vapour (Amax = 283 nm), produced by the bimolecular process (87), is 0.28 at 293 K.438

+ H,O

Hg(SSPu)

-

Hg(6'SO)

+ H,O + hv

(87)

Emission (Arnx = 380 nm), assigned to that from the lowest triplet state of water, has been observed following either y-irradiation or mercury sensitization of crystalline H,O or D,0.438For the mercury sensitization a triplet energytransfer mechanism appears to be operative, while for the y-irradiation the excited state is formed via reaction (88). Photolysis of water adsorbed on various organic materials is observed with short-wavelength U.V. light ( A < 250 nm).440

The results of electron impact studies with water are consistent with a vertical excitation energy of 7.4 eV for the 3B1state of and this has been confirmed by recent calculations on H20.442-44s It is well established that photolysis of H20zin aqueous solution leads to OH* and HO,. radicals via steps (89) and (90). The adducts of both these radicals HZO, OH.

+ HZO,

hV

20H*

HZO

+ HO2*

(89) (90)

with spin-traps, 5,5-dimethyl-l-pyrroline-l-oxide(66) and phenyl-t-butylnitrone, have now been identified by e . ~ . r . " ~In neutral solution HO,. rapidly deprotonates yielding 0 2 T . The rate constant for the reaction of this ionic species with HzOzhas recently been redetermined.447Studies of the photolysis of H,O, in the presence of p-nitro~odimethylaniline,~~~ /3-ammonioalcohols,449 and propan-2-01 4s0 have been reported. HO2*

0,:

+ H,Oz

__I+

+ 0,' OH* + OH- + 0, H+

(91) (92)

The absorption spectra of iodine-solvent complexes have been recorded following nanosecond laser flash photolysis of I- in MeCN, EtCN, PPCN, A. B. Callear and J. H. Connor, J.C.S. Furuduy ZI, 1974, 70, 1767. A. Bernas and T. B. Truong, Chem. Phys. Letters, 1974, 29, 585. 440 L. L. Basov, Y.P. Efimov, and Y. P. Solonitsyn, Uspekhi Fotoniki, 1974, 4, 12. 441 E. N. Lassettre and A. Skerbele, J . Chem. Phys., 1974, 60, 2464. 442 D. Yeager, V. McKoy, and G. A. Segal, J. Chem. Phys., 1974,61, 755. 443 R. J. Buenker and S. D. Peyerimhoff, Chem. Phys. Letters, 1974, 29, 253. 444 N. W. Winter, W. A. Goddard, and F. W. Bobrowicz, J. Chem. Phys., 1975, 62, 4325. 446 C. Peterson and G. V. Pfeiffer, Theor. Chim. Actu, 1974, 33, 115. u6 J. R. Harbour, V. Chow, and J. R. Bolton, Cunad. J. Chem., 1974,52, 3549. 447 V. D. Maiboroda, E. P. Petryaev, V. M. Byakov, and L. F. Ivashkevich, Khim. uysok. Energii,

43n 439

1974, 8, 284.

M. Hatada, I. Kraljic, A. El Samahy, and C. N. Trumbore, J. Phys. Chem., 1974, 78, 888. 448 T. Foster and P. R. West, Canad. J . Chem., 1974, 52, 3589. u0 S. Paszyc and H. Zalecka, Bull. Acud. polon. Sci., Ser. Sci. chim., 1974, 22, 695. d46

Photochemistry of Inorganic and Organometallic Compounds

203

MeOH, Pr*OH, or MeO(CH2)20Me.451aSimilarly, the corresponding Br-H20 and Cl-H20 complexes have been observed on laser photolysis of Bra and C1, in The primary photoprocess following nitrogen-laser irradiation of I,' is (93).462 However, for solutions in various alcohols it has been shown that 1,- is produced on laser flash photolysis of Iz/IThis species is formed by reaction of iodine atoms, formed on photolysis of I,, with Is-. 14T has also been observed following y-irradiation of Iz in methyltetrahydrof~ran.4~4 hv

____*

+I

1,-

(93)

Exchange of hydrogen between benzene and acidified water has been induced by photolysis of the mixture in the presence of I-.4s6 The active species involved are hydrogen atoms formed from the hydrated electrons liberated by I-. The reaction of hydrated electrons, formed by photolysis of I-, with alkyl halides has also been The photochemical behaviour of Br04- differs from that of other oxyhaloanions X0n-.467 Thus photolysis in NaOH glasses at 77 K and flash photolysis in aqueous solution provided evidence for participation of reactions (94) and (95) but not for 0;or O(sP) production. The absence of 0;is attributed to the low stability of BrO,. The photolysis of powdered samples of NaC103, both with and without previous y-irradiation, has been investigated.458 BrO,-

hV

Br0,-

+ OPD)

(94)

The mechanism for the quenching of singlet states of aromatic hydrocarbons by inorganic anions has been investigated both by fluorescence studies 4s90 and by flash p h o t o l y s i ~ .It~ ~has ~ ~ been shown that although the quenching rate constant parallels the ease of oxidation of the anion, in most cases electrontransfer processes (96) are not important. Further the flash photolysis experilM*

+ A-

1_1+

M-

+ A-

(96)

ments indicate that the triplet state is formed in high yield after the quenching process, and it is proposed that the singlet state deactivation involves an efficient radiationless conversion into the triplet state, induced by coupling of higher-lying electron-transfer states within the collision complex (lM* A-). Evidence has also been reported for enhanced intersystem crossing from the singlet state of azastilbenes in the presence of inorganic anions.46o 9..

461

462 463

454 466

4G6

4~

45D 460

(a) A. Treinin and E. Hayon, Internat. J. Radiation Phys. Chem., 1975,7, 387; (6) A. Treinin and E. Hayon, J . Amer. Chem. SOC.,1975, 97, 1716. A. Barkatt and M. Ottolenghi, Mol. Photochem., 1974, 6,253. P. Fornier de Violet, R. Bonneau, and J. Joussot-Dubien, Chem. Phys. Letters, 1974, 28,569. T. Shida, Y. Takahashi, H. Hatano, and M. Imamura, Chem. Phys. Letters, 1975, 33, 491. V. Gold, M. A. Major, and M. J. Gregory, J.C.S. Faraday I, 1974, 70, 965. S. R. Logan and P. B. Wilmot, Internat. J. Radiation Phys. Chem., 1974, 6, 1. U. K. Klaening, K. J. Olsen, and E. H. Appelman, J.C.S. Faraday I, 1975, 71, 473. P. J. Herley and P. W. Levy, J. Chem. Phys., 1975, 62, 177. (a) A. R. Watkins, J. Phys. Chem., 1974, 78, 2555; (b) A. R. Watkins, ibid., p. 1885. P. Bortolus, G. Bartocci, and U. Mazzucato, J . Phys. Chem., 1975, 79, 21.

Photochemistry

204

Other reports consider the gas-phase photodecomposition of co3T,461 the photoformation of C0,2- from COST and K atoms in argon matrices at 14 K,462 and the catalysis of the photo-initiated autoxidation of SO,,- by Fe3+.463 5 Main-group Elements Magnesium-Excitation of the Grignard reagents (75; R1 = PhCH,, R2 = H; R1 = Ph, R2 = Me) in bands assigned to the C-Mg chromophore causes the p-elimination reaction represented in equation (97).464 HMgX subsequently disproportionates to yield MgX2 and MgH,. R1CH,CHR2MgX (75)

hv

R1CH=CHR2 3- HMgX

(97)

Chemiluminescence is observed during the reactions of aryl Grignard reagents with oxygen 465a or with aryl peroxides.4ssbAnalysis of the luminescence spectrum and e.s.r. data indicates that for the oxygen-induced reaction brominated biphenyls are the emitters, whereas in the peroxide case triphenylmethane is the luminescent species. Boron.-The principal reaction on photolysis of Na+[BPh,]- in tetrahydrofuran or dimethoxyethane solution is formation of biphenyl and Na+[BPhz]-.466This latter species exhibits carbenoid-like activity and reacts with diphenylacetylene to give an equilibrating mixture of (76) and (77). Radical formation on irradiation of MPh3 (M = B, Al, or Ga) at 77 K has been Ph

Ph

\

,c=c

/ \

Ph

Ph

/

/

c,=/c f

R1 R6-B’

R54,

I N‘B-R2 ,A--R3

B I

(77) (78) a; R 1 = M e ; R 2 - R 6 = H b; R‘ = H ; R2= OCH(CFJ2;R3-R6 = H C; R1 = H ; R2= OC(CF3)3;R3-RG =H d; R’, R3,R” = Me; R2,R4, R6 = H

R4 Photolysis (at 1849 nm) of N-methylborazine (78a) produces H,, CH,, and borazanaphthalene derivative^.*^* The initial reaction appears to be decomposition of the excited borazine into H, or CH, and the corresponding borazyne compound. This benzyne analogue then reacts with another borazine molecule 461

aa 4s4 466

46e

487

4e8

J. T. Moseley, R. A. Bennett, and J. R. Peterson, Chem. Phys. Letters, 1974, 26, 288. M. E. Jacox and D. E. Milligan, J . Mol. Spectroscopy, 1974, 52, 363. J. Veprek-Siska, S. Lunak, and A. El-Wakil, 2. Naturforsch., 1974, 29b, 812. B. 0. Wagner and G . S. Hammond, J. Organometallic Chem., 1975, 85, 1. (a) P. H. Bolton and D. R. Kearns, J. Amer. Chern. SOC.,1974, 96, 4651; (6) P. H. Bolton and D. R. Kearns, J. Phys. Chem., 1974,78, 1896. J. J. Eisch, K. Tamao, and R. J. Wilcsek, J. Amer. Chem. Sac., 1975, 97, 895. K. L. Rogozhin, A. N. Rodionov, D. N. Shigorin, N. I. Sheverdina, and K. A. Kocheshkov, Izuest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 2740. L. J. Turbini and R. F. Porter, Znorg. Chem., 1975, 14, 1252.

205

Photochemistry of Inorganic and Organometallic Compounds

to yield the borazanaphthalene. Irradiation of hexafluoroacetone and borazine, under conditions where the hexafluoroacetone absorbs the light, gives (78b) and ( 7 8 ~ ) . ~ ~Compound O (79) has been isolated following the mercury-sensitized photolysis of H2 in the presence of (78d).470

(80) The emission properties of anilinodimesitylboranes (80) have been investigated.*?’ These compounds show very large Stokes’ shifts (148-258 kJ mol-l) and the position of the fluorescence band is markedly solvent dependent. From these observations it $as been concluded that the lowest excited singlet state has very pronounced B=N character. By contrast, other aminoboranes exhibit only slight Stokes’ shifts (ca. 34 kJ mol-l), and in this case the emission has been characterized as that from a polar m* excited The anomalously large Stokes’ shifts for the anilinodimesitylboranes is attributed to steric hindrance which causes the ground-state to adopt sp3 hybridization around the N atom. Several i.r. laser-induced reactions of boron compounds have been o b ~ e r v e d . ~Thus ~ ~ - B2oH16 ~ ~ ~ is formed as the main product on irradiation of B2Hg using a C 0 2 Excitation of BCl, in the presence of H2S causes enrichment of loB (log: llB from 0.242 to 0.413) for 10.55 pm radiation, while photolysis at 10.18 pm leads to a decrease of the loB : llB ratio to 0.169.474The decomposition of H3BPF3 to B2H6 and PF, has also been stimulated by C 0 2 laser irradiation but in this case no isotope effect was Visible luminescence of BCI, has been induced using a C 0 2laser.476The absorption and emission spectra of BI have been recorded following flash photolysis of B13.477 Aluminium, Gallium, Indium, and Thallium.-The phosphorescence spectra of the acetylacetonates of Mg, Al, Ga, and In in EPA at 77 K have been The oxidation of Mn2+or Fe2+and the reduction of Co3+by T12+have been studied following the generation of T12+ by flash photolysis of T13+.470U.V. 471

L. J. Turbini, G. M. Golenwsky, and R. F. Porter, Inorg. Chem., 1975, 14, 691. L. J. Turbini, T. J. Mazanec, and R. F. Porter, J. Inorg. Nuclear Chem., 1975, 37, 1129. M. E. Glogowski, P. J. Grisdale, J. L. R. Williams, and L. Costa, J. Organometallic Chem.,

47a

K. G. Hancock, Y. KO, D. A. Dickinson, and J. D. Kramer, J. Organometallic Chem., 1975,

460

070

1974, 74, 175. 90, 23. 47s

47b 476

07’ 478

‘7D

8

H. R. Bachmann, H. Noeth, R. Rinck, and K. L. Kompa, Chem. Phys. Letters, 1974,29,627. S. M. Freund and J. J. fitter, Chem. Phys. Letters, 1975, 32, 255. E. R. Lory, S. H. Bauer, and T. Manuccia, J . Phys. Chem., 1975,79, 545. R. V. Ambartzumian, N. V. Chekalin, V. S. Doljikov, V. S. Letokhov, and E. A. Ryabov, Chem. Phys. Letters, 1974, 25, 515. J. Lebreton, J. Ferran, A. Chatalic, D. Iacocca, and L. Marsigny,J. Chim.phys., 1974,71,587. R. H. Clarke and R. E. Connors, Spectrochim. Acta, 1974, 3QA,2063. B. Falcinella, P. D. Felgate, and G. S. Laurence, J.C.S. Dalton, 1975, 1.

206

Photochemistry

irradiation of Tl(OAc), in 10% sulphuric acid at 77 K produces methyl radicals.480 The effect of chloride ion on the luminescence of T1' in solution has been d i s ~ u s s e d482 .~~~~ Silicon.-Organic aspects of the photochemistry of silicon-containing compounds are discussed in Part 111, Chapter 6, Section 3. A review of the photochemistry of polysilanes has been The luminescence properties of Group IV metal tetraphenyl compounds have been 485 Other authors have considered the assignment of electronic transitions in p o l y ~ i l a n e s , the ~ ~ ~nature of the long-wavelength U.V. transitions in a c y l ~ i l a n e s ,the ~ ~ ~extent of (p-d)?r-bonding in PhMMe, (M = Si, Ge, or Sn),48eand the assignment of the photoelectron spectra of M(CHaSiMe3), (M = Ti, Zr, Hf, Ge, or Sn).48g The photochemical decomposition of Ph,SiN=NPh is presumed to proceed via process (98).490 However, although Ph- could be spin-trapped by arN-diphenylnitrone, the corresponding adduct could not be observed for the Ph3Si* species. Ph3SiN=NPh

A

[Ph,Si.*.N,.-Ph] Ph3Si* Na Ph*

+

+

(98)

Reaction (99) proceeds in high yield, but low conversion, following the photolysis of the Si-H bond in HSiMeX, (X = Me or Cl).4g1 Addition of Sic],, formed on photolysis of HSiCl,, to halogenated ~ l e f i n s and , ~ ~formation ~ of (MeO),(Me)Si-Si(Me)(OMe), from (MeO),(Me)SiH,4g3have been reported. [(CF,),N],C=CH,

+ HSiMeX, A

[(CF,),N],C=CHSiMeX,

+ H,

(99)

Insertion of the carbene Me,SiCH: into C-H and Si-H bonds has been investigated following p hot olysis of Me,SiCHN,. 4g4 0ther photochemically induced reactions include the addition of H2Sto dimethyldiallylsilane,4g6 and the chlorination of alkyltrichlorosilanes.4gg 480

461 482 483

484

486 486 487

C. T. Cazianis and D. R. Eaton, Canad. J . Chem., 1974,52, 2471. M. U.Belyi, N . G. Musienko, and B. A. Okhnmenko, Ukrainfiz. Zhur., 1974,19, 1460. P. J. Mayne and G. P. Kirkbright, J. Inorg. Nuclear Chem., 1975,37, 1527. M. Kumada, M. Ishikawa, H. Okinoshima, and K. Yamamoto, Ann. New York Acad. Sci., 1974,239, 32. M. Gouterman and P. Sayer, J. Mol. Spectroscopy, 1974,53, 319. T.S. Lin, Chem. Phys., 1974,6, 235. B. G. Ramsey, J . Organometallic Chem., 1974,67,C67. B. G. Ramsey, A. Brook, A. R. Bassindale, and H. Bock, J. Organometallic Chem., 1974,74, C41. P. K.Bischof, M. J. S. Dewar, D. W. Goodman, and T. B. Jones, J. Organometallic Chem., 1974,82, 89. M. F. Lappert, J. B. Pedley, and G. Sharp, J. Organometallic Chem., 1974, 66, 271. H.Watanabe, Y. Cho, Y. Ide, M.Matsumoto, and Y. Nagai, J . Organometallic Chem., 1974, 78, C4.

491

482 483

494

4s6

D. H. Coy, F. Fitton, R. N. Haszeldine, M. J. Newlands, and A. E. Tipping, J.C.S. Dalton, 1974, 1852. W.I. Bevan, R. N. Haszeldine, J. Middleton, and A. E. Tipping, J.C.S. Dalton, 1974,2305. M. E.Childs and W. P. Weber, J. Organometallic Chem., 1975,86, 169. R. N. Haszeldine, D. Scott, and A. E. Tipping, J.C.S. Perkin Z, 1974, 1440. K. E. Koenig, R. A. Felix, and W. P. Weber, J. Org. Chem., 1974,39, 1539. (a) T.Burton and A. Bruylants, J. Organometallic Chem., 1974, 69, 397; (b) T. Burton and A. Bruylants, Bull. SOC.chim. belges, 1973,82, 737.

Photochemistry of Inorganic and Organometallic Compounds

207

Germanium and Tin.-A general photochemical method for the preparation of metal-centred radicals (R2CH),M1 and (R2N),M2 (R = SiMe,; M1 = Si, Ge, or Sn; M2 = Ge or Sn) from the corresponding (R2CH)2M1or (R2N)2M2has been described.4B7The radical species, which have been characterized by e.s.r., have lifetimes at room temperature of from 10 min [for (R2CH),Si] to 5 months [for (R,N),Ge]. R1,Ge radicals (R1 = Ph, Me, Et, Prn, Pri, or Bun) have been identified by e.s.r. following reactions of photochemically generated Me,CO* radicals with GeR13H.4B81.r. spectra have been recorded for the free-radical species formed from GeH,Cl,-, (n = H), GeH,Br, and GeH,Br, on photolysis in argon and carbon monoxide matrices at 4 and 24 K 4 0 9 The photochemical decomposition of [Ge*V(ox),]2-,500 and the light-induced reactions of Et,MC=CH (M = Ge or Sn) with BunSH601have been discussed. In contrast with their behaviour on heating, cis- and trans-penta-l,3-dienes produce the 1,4-addition products cis- and trans-Me,SnCH,C= CHEt on photolysis in Me,SnH.602 No products arising from Sn-C bond rupture could be observed after irradiation of 2-trimethylstannylbuta-1,3-diene,and the main products found were the isomers (8 1)--(83).603

=-

Evidence for the photochemical cleavage of the Sn-N step in reaction (100) has been adduced from CIDNP 2M%Sn-NEt2

hv

Me,Sn-SnMe,

bond as the primary The reactions

+ Et,NH + MeCH=NEt

(100)

of alkyl halides with R,Sn (R = Ph or Bun), produced on photolysis of Sn2Ra,606 and the light-induced free-radical reactions of organotin alkoxides with polyhalogenomethanes have been investigated.606 Lead.-Recent reports on solid-state photoprocesses of Pb" compounds include investigations in the far- and near-i.r.608of the effect of photodecomposition of Pb(N,),, the low-temperature photoluminescence of Pb(N3)2,60B photoproduction of disorder in Pb(N,), and Tl(N3),610studies of the photolysis of PbCl, J. D. Cotton, C. S. Cundy, D. H. Harris, A. Hudson, M. F. Lappert, and P. W. Lednor, J.C.S. Chem. Comm., 1974,651. H. Sakurai, K. Mochida, and M. Kira, J. Amer. Chem. SOC.,1975, 97, 929. 4D9 W. A. Guillory, R. J. Isabel, and G. R. Smith, J. Mol. Structure, 1973, 19, 473. 6 o o E. L. J. Breet and R. van Eldik, Inorg. Chim. Acta, 1974, 9, 177, 183. 601 M. G. Voronkov, R. G. Mirskov, and V. I. Rakhlin, Zhur. obshchei Khim., 1974,44, 954. lio2 M. Bigwood and S. Boue, J.C.S. Chem. Comm., 1974,529. lies P. Vanderlinden and S. Boue, J. Organometallic Chem., 1975, 87, 183. b04 M. Lehnig, Tetrahedron Letters, 1974, 3323. lio6H. G. Kuivila and C. C. H. Pian, J.C.S. Chem. Comm., 1974, 369. lio0J.-C. Pommier and D. Chevolleau, J. Organometallic Chem., 1974, 74, 405. lio7S. P. Varma, F. Williams, and K. D. Moeller, J. Chem. Phys., 1974, 60, 4950. S. P. Varma and F. Williams, J. Chem. Phys., 1974, 60, 4955. lio9 J. Schanda, B. Baron, and F. Williams, J. Luminescence, 1974, 9, 338. HO D. A. Wiegand, Phys. Reu. (B), 1974,10, 1241.

208 Photochemistry crystal surfaces,611 photolysis of PbBr2,612s 613 and photoluminescence of PbIa at 4.2 K.614 Phosphorus.-E.s.r. data have been presented as evidence for formation of PPh2- on U.V. irradiation of crystalline PPh3 616 or PPh2H.61s Other publications discuss the fluorescence spectra of triarylph~sphines,~~~ and the correlation with Hammett (T values of the rate constants for quenching of the singlet states of substituted anthracenes by PPh3.61* U.V. irradiation of PF2Cl yields PF2*,610whereas photolysis of PF3 in the presence of F20 or ROOR produces PF4- and PF30R- respectively.620 The photoaddition of P2F4to olefins has preparative applications.621 Other Elements.-The photochemical transformations of the organoselenium compounds (84) and (85) have been described.622Photo-induced rupture of the PhCH,SeSeCH,Ph (84)

PhCH,SeSeCH,Ph

+ O2

PhCH,SeC(Se)SeCH,Ph (85)

hv

-

-__+

hv

hv

+ Se

PhCH2SeCH2Ph 2PhCHO

+ 2Se

Ph2CH,SeSeCH2Ph

(101) (102)

+ [CSe]

(1 03)

rings leads to the polymerization of Photochemical preparations of S03F2,S206F2,and S206F2,624 and of SF40R*626 have been reported. Photo-induced reactions in inert matrices continue to be very useful techniques for the synthesis of novel small molecules. Thus photolysis ( h < 240nm) of FsNO in argon matrices at 8 K produces FN0,626and similarly the main primary product on irradiation of CF30F or CF30Cl is F2C0.627NF2* is formed on photolysis of NF3 in argon or carbon monoxide matrices.628Irradiation of mixtures of F2 and NO2 in nitrogen matrices at 8 K gives FNOa.62goOn warming s 8

611 612

513 614

515 61%

617

618 619

J. F. Reber and R. Steiger, Surface Sci., 1975, 49, 236. M. T. Kostyshin and E. V. Mikhailovskaya, Ukrain.jiz. Zhur., 1974, 19, 507. M. T. Kostyshin, E. V. Mikhailovskaya, and V. M. Sharyi, Ukrain.fiz.Zhur., 1974,19,1327. (a) F. Levy, A. Mercier, and J. P. Voitchovsky, Helv. Phys. Acta, 1974, 47, 440; (b) F. Levy, A. Mercier, and J. P. Voitchovsky, Solid State Comm., 1974, 15, 819. W. T. Cook, J. S.Vincent, I. Bernal, and F. Ramirez, J. Chem. Phys., 1974,61,3479. M. Geoffroy, E. A. C.Lucken, and C. Mazeline, Mol. Phys., 1974,28, 839. N. A. Rozanel'skaya, A. I. Bokanov, B. M. Uzhinov, and B. I. Stepanov, Zhur. obshchei Khim., 1975, 45, 277. M. E. R. Marcondes, V. G. Toseano, and R. G. Weiss, Tetrahedron Letters, 1974, 4053. A. J. Colussi, J. R. Morton, K. F. Preston, and R. W. Fessenden, J. Chem. Phys., 1974, 61, 1247.

520 621 522 523 624 62.5

A. J. Colussi, J. R. Morton, and K. F. Preston, J. Phys. Chem., 1975, 79, 651. J. G. Morse and K. W. Morse, Inorg. Chem., 1975, 14, 565. W. Stanley, M. R. Van De Mark, and P. L. Kumler, J.C.S. Chem. Comm., 1974, 700. T. Nakayama, T. Nose, H. Kokada, and E. Inoue, Chem. Letters, 1974,287. M. Gambaruto, J. E. Sicre, and H. J. Schumacher, J. Fluorine Chem., 1975, 5, 175. A. R. Gregory, S. E. Karavelas, J. R. Morton, and K. F. Preston, J. Amer. Chern. SOC.,1975, 97, 2206.

62%

127 628

629

R. R. Smardzewski and W. B. Fox, J. Chem. Phys., 1974, 60, 2193. R. R. Smardzewski and W. B. Fox, J. Phys. Chem., 1975,79, 219. M. E. Jacox, D. E. Milligan, W. A. Guillory, and J. J. Smith, J. Mol. Spectroscopy, 1974,52, 322. (a) R. R. Smardzewski and W. B. Fox, J. Chem. Phys., 1974,60, 2980; (b) R. R. Smardzewski and W. B. Fox, ibid., 1974, 61, 4933.

Photochemistry of Inorganic and Organometallic Compounds

209

the matrix to 20 K further fluorine atoms diffuse through the matrix and react with NO2 to give ONOF. This compound on further irradiation isomerizes to the more stable FNO,. Small amounts of OF are also found during this matrix reaction and it is suggested that these arise from combination of 0 and F atoms formed respectively from NO, and F2.629b Noble gas dihalides have been synthesized on photolysis of mixtures of Kr and F2, or Xe and F2, Cl, or ClF in low-temperature matrices,630and of Xe and F2at 77 K.631 It is proposed that the production of M+03- on photolysis of alkali-metal atoms M, O,,and NaO in argon matrices involves reaction (104).632 Similarly, nitrites are formed by process (105) when NO is substituted for 02. The M+O,-.-ON, M+NO---ON2

hv hv

+ N, M+NO,- + N, M+03-

(104)

(105)

fluorescence spectra of C102633and of IC1534in noble-gas matrices have been reported.

6 Surface Photochemistry and Miscellaneous Topics A review (in Japanese) of the photochemistry of Ti02 has been Irradiation of high-purity ZnO in aqueous solution produces e.s.r. signals which have been assigned to unpaired electrons both in the conduction band of the bulk ZnO and in partially ionized donors (e.g. Zn+) near the surface.636 Illumination of the TiOa plate in a TiO, electrolyte Pt cell induces photocurrents with low efficiency (0= 10-3).637The photoreduction of methyl viologen in the presence of Ti02has been Other studies deal with the photoreduction of TiOa in organic media,639and the photocatalytic deposition of Pd on Ti02.640 The photo-oxidation of SO, to SO3- in the presence of H 2 0 and O2or N20has been monitored by e . ~ . r . ~The ~ l photo-oxidation of carbon monoxide by oxygen may be catalysed by illumination of a number of inorganic and in another study it has been shown that the catalytic activity of ZnO for this reaction depends on the contact time of the catalyst with the gases prior to irradiation.643 Flash illumination of Ti02 initiates the dehydrogenation of methanol or ethanol to formaldehyde and acetaldehyde, The oxidation of paraffins and olefins to ketones takes place on irradiation of Ti02 in the presence of these 630 6a1

W. F. Howard and L. Andrews, J. Amer. Chem. Soc., 1974, 96, 7864. A. I. Malkova, V. I. Tupikov, I. V. Isakov, and V. Y . Dudarev, Zhur. neorg. Khim., 1974,19, 1729.

543

L. Andrews and T. E. Tevault, J. Mol. Spectroscopy, 1975, 55, 452. F. K. Chi and L. Andrews, J. Mol. Spectroscopy, 1974, 52, 82. V. E. Bondybey and L. E. Brusk, J. Chem. Phys., 1975, 62, 620. H. Mimuro, Shikizai Kyokaishi, 1974,47, 605. J. Cunningham and S. Corkery, J. Phys. Chem., 1975, 79, 933. T. Ohnishi, Y. Nakato, and H. Tsubomura, Ber. Bunsengesellschaftphys. Chem., 1975,79,523. A. A. Krasnovskii and G. P. Brin, Doklady Akad. Nauk S.S.S.R., 1973, 213, 1431. V. S. Il’enko and A. V. Uvarov, Kinetika i Kataliz, 1974, 15, 543. F. Moellers, H. J. Tolle, and R. Memming, J. Electrochem. Soc., 1974, 121, 1160. M. J. Lin and J. H. Lunsford, J. Phys. Chem., 1975, 79, 892. L. V. Lyashenko and Y . B. Gorokhovatskii, Teor. i eksp. Khim., 1974,10, 186. V. S. Zakharenko, A. E. Cherkashin, and N. P. Keier, React. Kinet. Catal. Letters, 1974, 1,

544

J. Cunningham, E. Finn, and A. L. Penny, Chemica Scripta, 1974, 6, 87.

632 533 634

635

637

538 63D s40 641 64a

381.

210

Photochemistry

substrates and oxygen,646and in the case of isobutane it has been shown that excited atomic oxygen is the active species.646From e.s.r. measurements it has been demonstrated that photolysis of water on silica gel at - 170 “Cyields OH., while *CHO is formed from carbon monoxide or carbon A theory for the photocatalysed exchange reaction of deuterium and hydrogen In the photocatalysed over semiconductors such as ZnO has been and 1802 over TiO, it has been shown that 03-is the important exchange of le02 intermediate,64eand other authors have recorded the e.s.r. signal of this species on irradiating TiOa applied on silica gel in the presence of molecular o ~ y g e n661 .~~~~ The binding of methyl radicals to silica gel has been examined for species produced both by y-irradiation and by photolysis of methyl iodide.652It has been found that the subsequent rates of decay of these radicals depend on the energy with which the species is ‘born’ and on the specific site on which the methyl iodide is absorbed. Photolysis of butyl methacrylate over AI2O3or Ga,O, gives radical species bonded to the surface, which may then be used to initiate polymerization Other subjects recently discussed include the photocoabsorption of carbon monoxide and oxygen on Zn0,654the relative photoabsorption of oxygen and methane over Zn0,666the photocatalytic properties of ZnO and Mg0,666the effect of irradiation on the dielectric properties of Ti02,667 the photoluminescence of an oxide layer on aluminium,668the singlet-triplet splitting of the free A-exciton in Zn0,669the properties of the photosensitive film of copper in iodine solution,S6o and the photosensitivity of layers of CuCl, and [ F e ( o ~ ) ~ ] ~ - . ~ ~ l 645

647

548

650 551

M. Formenti, F. Juillet, P. Meriaudeau, and S. J. Teichner, in ‘Catalysis, Proc. International Congress, 5th’, ed. J. W. Hightower, North Holland, Amsterdam, 1973, p. 1011. S. Bourasseau, J. R. Martin, F. Juillet, and S. J. Teichner, J . Chim. phys., 1974, 71, 1025. S. S. Tseng and S. Chang, Origins Life, 1975, 6, 61. F. F. Vol’kenshtein and V. B. Nagaev, Kinetika i Kataliz, 1974, 15, 373. K. Tanaka, J. Phys. Chem., 1974,78, 555. V. V. Nikisha, B. N . Shelimov, and V. B. Kazanskii, Kinetika i Kafaliz, 1974, 15, 676. V. V. Nikisha, S. A. Surin, B. N. Shelimov, and V. B. Kazanskii, React. Kinet. Catal. Letters, 1974, 1, 141.

652 653

654 665 666

657

G. R. Joppien and J. E. Willard, J. Phys. Chem., 1974,78, 1391. V. P. Galkin, V. B. Golubev, and E. V. Lunina, Z h u r . 3 ~Khim., . 1974,48, 777. J. M. Balois, M. Guelton, and J. P. Bonnelle, J . Chirn. phys., 1974, 71, 431. G. N. Kuz’min and Y. P. Solonitsyn, Kinetika i Kataliz, 1974, 15, 700. A. A. Lisachenko and F. I. Vilesov, Uspekhi Fotoniki, 1974, 4, 18. V. 1. Kovalevskii, V. V. Sviridov, and M. S. Mironov, Izvest. Vyssh. Ucheb. Zaved., Fiz., 1974, 17, 156.

M. I. Eidel’berg and I. I. Petrenko, Izvest. Vyssh. Ucheb. Zaved., Fiz., 1974, 17, 135. E. Tomzig and R. Helbig, Solid State Comm., 1974, 15, 1513. 6 8 0 J. Franco and N . K. Patel, J. Chem. Phys., 1975, 61, 2169. 561 L. I. Stepanova and V. V. Sviridov, Vestsi Akad. Navuk Belarus. S.S.R., Ser. khim. Navuk, 568

558

1974, 38.

Part III ORGANIC ASPECTS OF PHOTOCHEMISTRY

I Photolysis of Carbonyl Compounds BY W. M. HORSPOOL*

1 Introduction As in past years this chapter describes the photochemistry of those carbonyl compounds where the reaction type is dictated by the carbonyl function. Thus Norrish Type I and I1 reactions, rearrangements, and cycloadditions are dealt with in this chapter, but reductions and reactions of enones will be covered in later chapters in Part 111. The shift in emphasis away from the study of simple carbonyl compounds which was pointed out in Volume 6 has been noticeable throughout this year. Some review articles reported during the past year focus attention on material which is pertinent to this chapter. Dalton and Snyder have compiled a selective review of the 1972 literature, and Schaffner and Jeger have reviewed their own contribution in the area of carbonyl photochemistry. A review dealing with chemical methods for the generation of electronically excited states has also been published. It is interesting to note that the development of photochemical reactions for the undergraduate laboratory has continued, and Haas4 has reported one such experiment dealing with the photochemistry of cyclic ketones. Salem has reported detailed calculations analysing several photochemical reactions with special reference to the way by which the excited state of the molecule decays back to the ground state. Another publication has dealt with the classification of photochemical reactions* and is in part an elaboration of an earlier paper.' Further attention has been directed at the Stern-Volmer analysis of photochemical reactions dealing with non-linearity when two excited states are reactive and one or both are quenched.*# A generalized treatment of the equation has resulted.lo 1

J. C. Dalton and J. J. Snyder, Mol. Photochem., 1973, 5, 471. K. Schaffner and 0. Jeger, Tetrahedron, 1974, 30, 1891. E. H. White, J. D. Miano, C. J. Watkins, and E. J. Breaux, Angew. Chem. Internat. Edn., 1974, 13, 229.

' J. W. Haas, jun., J. Chem. Educ., 1974, 51, 346.

L. Salem, J. Amer. Chem. Soc., 1974, 96, 3486. W. G. Dauben, L. Salem, and N. J. Turro, Accounts Chem. Res., 1975, 8,41. L. Salem, W. G. Dauben, and N. J. Turro, J . Chim. phys., 1973,70,243. M. D. Shetlar, Mol. Photochem., 1974, 6, 143. M. D. Shetlar, Mol. Photochem., 1974, 6, 167. l o M. D. Shetlar, Mol. Photochem., 1974, 6, 191. * This chapter, and the two folIowing, were written while the author was on leave at the Department of Chemistry, The University of Wisconsin, Madison, Wisconsin. The author expresses his sincere thanks to the University of Wisconsin for hospitality received.

213

Photochemistry The interest in the kinetic analysis of bichromophoric systems and of mixtures of aryl ketones having similar triplet excitation energies has continued. Wagner and Nakahirall have shown, in this context, that in the study of the kinetics of the nonaphenone-p-methoxynonaphenone system, curved Stern-Volmer plots are obtained. They have observed that the presence of the second ketone drastically affects the quenching behaviour. 214

(2) R (3) R

(1) R-R = H R-R = (CH,),

= =

p-H a-H

(4)

The phosphorescence of the ketones (1)-(4) has been studied.12 The methylated benzoylthiophens ( 5 ) have been synthesized and their photochemistry has been studied.13 Their phosphorescence shows a great similarity to that of benzoylthiophen, although the position of the 0-0 band depends on the position of the methyl groups on the thiophen ring. The spectral studies indicate that the ketones ( 5 ) have low-lying m* triplet states although the lowest singlet state is nn*. However, the ketones (5a) and (5b) both undergo cycloaddition with isobutene affording unstable oxetans which eliminate formaldehyde to yield the olefins (6). The n7r* state usually involved in such additions is not involved in

0

R1 = Me,R2 = R? = R4 = H b; R2 = Me, R1 = R? = R4 = H c ; R3 = Me, R1 = R2 = R4 = H d; R4 = Me, R1 = R2 = R3 = H

(5) a ;

A (6) a; R1 = Me, R2 = H b; R’ = H, R2 = Me

these reactions. Iwata and Morokuma’s observations l4 on the formaldehydewater system have led them to suggest that the blue shift in the nr* band in acetonewater is the result of the formation of an acetonewater trimer in solution, with one acetone molecule hydrogen-bonded to two water molecules. A more recent treatment of the subject has interpreted the results in terms of an acetone-water dimer.15 2 Norrish Type I Reactions A study of the results of photolysis of methyl t-butyl ketone, di-t-butyl ketone, pivalaldehyde, and isobutyraldehyde by CIDNPhas been reported.ls Other workers l1 l2 l3

l4 l6

l6

P. J. Wagner and T. Nakahira, J. Amer. Chem. Soc., 1974,96, 3668. W. Amrein, I.-M. Larsson, and K. Schaffner, U e h . Chim. Acta, 1974, 57, 2519. D. R. Arnold and B. M. Clarke, jun., Canad. J . Chem., 1975,53, 1. S. Iwata and K. Morokuma, J. Amer. Chem. SOC.,1973, 95, 7563. J. E. Del Bene, J. Amer. Chem. SOC.,1974, 96, 5643. B. Blank, A. Henne, and H. Fischer, Helv. Chim. Acta, 1974, 57, 920.

215 have studied the photolysis of butan-2-one and pentan-3-one by the same technique." A CIDNP study of the photo-chemistry of the acylsilanes (7) has shown that the primary process may not be the fission of the Si-CO bond1* as was originally proposed.l@From analysis of the products formed in the reaction and from a careful study of the CIDNP spectra, Scheme 1 is proposed for the decomposition in CC14. Clearly some caution must be exercised in the interpretation

Photolysis of Carbonyl Compounds

MeCOSi(Me),Ph (7)

1

Itv CCI,

[MeCOSi(Me),Ph.CCI,]

--+

CISi(Me),Ph Scheme 1

+ MekO + &I3

of such photolyses. An e.s.r. study of the photochemistry of hydroxyacetone and 1,3-dihydroxyacetone in aqueous solution has shown that the chemistry is dominated by Norrish Type I C-C fission.20 In contrast, 1,3-dicarboxyacetone exhibits hydrogen abstraction reactions in the presence of hydrogen donors. An e.s.r. study of the photochemistry of di-t-butyl ketone at 77 K has been reported.21 This showed that fission of the ketone yielded ButCO radicals, Acetyl chloride undergoes the expected fission into radicals (MeeO and C1) when irradiated (254 nm) in ethereal The major product (8) (72% at 18 "C) is formed by hydrogen abstraction and radical combination within the solvent cage. The other product (9) (28% at 18 "C) is formed by combination of two MeeHOEt radicals, presumably as a result of escape of this radical from the solvent cage in which it is formed. The proportion of (9) diminishes with decreasing temperature (21 % at - 45 "C). Propionyl chloride behaved similarly. Irradiation of the thioacetates (10) results in both S-alkyl and S-acyl bond cleavage.23 MeCOCH(Me)OEt

[Me(EtO)CHh

(8)

(9)

(Me),Si(CH,),SCOMe (10) n = 3 or 2

A report of the photochemistry of benzoin alkyl ethers in solution has been published.24 The photochemistry (n -+ T* excitation) of these ethers has been studied with particular attention to the influence of the a-substituent, ether group, solvent, and temperature on the quantum yields for product f o r m a t i ~ n .Photo~~ cleavage in oxygen-saturated methanol leads to benzoyl and a-alkoxybenzyl

2o

S. P. Vaish, R. D. McAlpine, and M. Cocivera, Canad. J . Chem., 1974, 52, 2978. N. A. Porter and P. M. Iloff, jun., J . Amer. Chem. SOC.,1974, 96, 6200. A. G. Brook and J. M. Duff, J. Amer. Chem. SOC.,1969,91, 2118. S. Steenken, W. Jaenicke-Zauner, and D. Schulte-Frohlinde, Photochem. and Photobiol.,

21

M. Y. Mel'nikov and N. V. Fok, Khim. Vysok Energii, 1974, 8, 468 (Chem. Abs., 1975, 82,

l7 l8 lo

1975, 21, 21.

37 237). 21

23 24

A. Nikiforov and U. Schmidt, Monatsh., 1974, 105, 1044. T. I. Ito and W. P. Weber, J. Org. Chem., 1974, 39, 1691. S. Adam, Nuclear Sci. Abs., 1974,29, 15147 (Chem. Abs., 1974,81,44005). S . Adam, H. Giisten, S. Steenken, and D. Schulte-Frohlinde, Annalen, 1974, 1831.

216

Photochemistry

radicals.26 Further study on the photochemistry of benzoin derivatives has been published. One paper 27 reports the predominance of a-cleavage in benzoin, benzoin ethers, and benzoin acetate. Other workers report evidence for different reaction pathways, e.g. benzoin phenyl ether affords some phenol derived from B-cleavage, and benzoin acetate undergoes cyclization to 2-phenylbenzof~ran.~~ Further work on the photochemical reactions of deoxybenzoin (11) has sought to PhCOCH,Ar (1 1) Ar = Ph, p-anisyl, p-tolyl, p-fluorophenyl,

mfluorophenyl, p-chlorophenyl, nt-chlorophenyl, m-trichloromethylphenyl

evaluate the influence of aryl substituents which are not conjugated with the carbonyl function.2n Kinetic analysis of the reaction has shown that the primary process of a-fission arises from the triplet state of the ketone. Electron-donating substituents in the aryl ring give a modest increase in the quantum yield for bibenzyl formation whereas electron-withdrawing groups have little effect. Several of the deoxybenzoins exhibit phosphorescence at room t e m p e r a t ~ r e . ~ ~ Values for the triplet lifetimes and a-fission rates were computed. A review of cyclobutanone photochemistry has been published by Quinkert and his c o - w o r k e r ~ .One ~ ~ of the intriguing problems associated with the photochemical ring-expansion of cyclobutanones to oxacarbenes (12) and thence

tetrahydrofuran derivatives is whether a stepwise biradical mechanism is followed as a result of Norrish Type I fission of the C-CO bond (see Vol. 6, p. 318),32 but Quinkert and Jacobs 33 have published further more detailed results on this reaction (Scheme 2) which again demonstrate that the tetrahydrofuran derivatives (13)-(15) are formed without loss of the configuration of the migrating carbon. It can therefore be concluded that the reaction takes place, at least in these examples, in a concerted fashion without the intermediacy of a biradical. Miller et aZ.34have examined the photochemistry of the cyclobutanones (16)-(21) 26 27

28

29

30

31

a2

33 34

S. Adam, H. Giisten, and D . Schulte-Frohlinde, Tetrahedron, 1974, 30, 4249. F. D. Lewis, R. T. Lauterbach, H.-G. Heine, W. Hartmann, and H. Rudolph, J. Amer. Chem. SOC.,1975, 97, 1519. J. C. Sheehan and R. M. Wilson, J. Amer. Chem. SOC.,1964,86, 5277; J. C. Sheehan, R. M. Wilson, and A. W. Oxford, ibid., 1971, 93, 7222. F. D. Lewis, C. E. Hoyle, J. G. Magyar, H.-G. Heine, and W. Hartmann, J . Org. Chem., 1975, 40, 488. F. D. Lewis and C. E. Hoyle, Mol. Photochem., 1974, 6, 235. W. D. Stohrer, P. Jacobs, K. H. Kaiser, G. Weich, and G. Quinkert, Topics Current Chem., 1974,46, 181 (Chem. Abs., 1975,82, 15748). G. Quinkert, P. Jacobs, and W.-D. Stohrer, Angew. Chem. Internat. Edn., 1974, 13, 197; G. Quinkert, K. H. Kaiser, and W.-D. Stohrer, ibid., p. 198; G. Wiech, W.-D. Stohrer, and G . Quinkert, ibid., p. 199; W.-D. Stohrer, G. Wiech, and G . Quinkert, ibid., p. 200. G . Quinkert and P. Jacobs, Chem. Ber., 1974, 107, 2473. R. D. Miller, D. L. Dolce, and V. Y. Merritt, Tetrahedron Letters, 1974, 3347.

217

PhotoZysis of CarbonyZ Compounds

eih

hv N

Me-Ph

M e s Ph,Me t M e

Ph (14)

Scheme 2

--OMe

H

Go OMe

(24) 510,;

(23) 13%

in anhydrous methanol and have found that the single unifying feature of the process is the low stereospecificity, e.g. (16) yields products (22)-(24). Their results show that when the bicyclic ketone has even moderate strain the cycloelimination of keten is depressed. The authors 34 suggest that there is a similarity between this ring-expansion and the Baeyer-Villiger process because of the involvement of alkyl-group migration to an electron-deficient oxygen atom, the consequence of nrt* excitation. This similarity is echoed by the observation that similar specificities are obtained from the Baeyer-Villiger oxidation of, for example, (16) which affords the two lactones (25) and (26).

& O

H

&o H

o

218 Photochemistry Ring-expansion of the 1,3-dione (27a) at - 70 "C gives the acetal (28) in low yield, probably via an oxacarbene intermediate.36 The main product, the ketoester (29) (5573, is formed by the Norrish Type I reaction and is photolabile, forming the ester (30) as well as methyl cyclopentanecarboxylate. The ringexpansion is dependent upon the ring size of the substituent groups and does not occur when the dione (27b) is used.

(

a

)?l

0

(27) a ; n

1 b:n=2 =

0 (28)

0

A review of some reactions of organosilicon compounds has been published.36 This article contains information dealing with the ring-expansion of some silyl ketones, e.g. (31).37 The Norrish Type I photocleavage of some cyclic 2-alkylketones has been suggested to give stereoselective formation of the unsaturated aldehydes.38 Medary et ~ 1 1have . ~ ~ reinvestigated the photoreaction of 2-ethylcyclopentanone and observed that formation of both cis- and trans-hept-4-enal is efficient (@ = 0.45). The ratio of the two aldehydes remained steady (1.6-2.2) throughout the irradiation. The authors point out that even at low conversions an appreciable amount of the cis-aldehyde is formed, clearly showing that the original work is in error. The photochemical reactivity of the cyclohexanones The bulk of the C-5 substituent in the 5-substituted(32) has been 2-methylcyclohexanones (33) influences the aldehyde :ester ratio when the ketones are irradiated in benzene-methan~l,~~ in agreement with the prediction that a large group at C-5 should influence the proportion of the conformation (34) present in the reacting biradical formed by the Type I cleavage. Thus as the size R is increased from H to t-butyl the ratio of the aldehyde : ester quantum yields changes from 2.3 to 9.1. s6

37

40

'l

K. Kimura, M. Takamura, A. Kunai, and Y. Odaira, J.C.S. Chem. Comm., 1974,685. A. G . Brook, Accounts Chem. Res., 1974, 7 , 77. A. G. Brook and J. M. Duff, J. Amer. Chem. SOC.,1967, 89, 454; A. G. Brook, H. W. Kucera, and R. Pearce, Canad. J. Chem., 1971, 49, 1618; A. G. Brook, R. Pearce, and J. B. Pierce, ibid., 1971, 49, 1622. R. Srinivasan and S. E. Cremer, J . Phys. Chem., 1965, 69, 3145; J. Amer. Chem. SOC.,1965, 87, 1647. R. T. Medary, J. E. Gano, and C. E. Griffin, Mof. Photochem., 1974, 6, 107. B. Guiard, B. Furth, and J. Kossanyi, Bull. SOC.chim. France, 1974, 3021. W. B. Hammond and T. S. Yeung, Tetrahedron Letters, 1975, 1169.

219

Photolysis of Carbonyl Compounds

(32) a ; R1 = R2 = H b ; R1 = R2 = Me c; R1 = H, R2 = Me d ; R' = H, R2 = Et e ; R1 = H, R2 = Pri f; R1 = H, R2 = Prn g; R1 = H, R2 = Bu'

@)ald./@efker

(33) a; R = H b; R = trans-Me c; R = cis-Me d ; R = tr.cms-Pri e; R = But

2.3

2.2 2.2 5.4 9.1

(35) a ; n = 1 b;n=2

(34)

Chip and Lynch, who previously 42 reported the photochemical ring enlargements of the cyanoalkanones (35), have now described the work in detail.4s The Norrish Type I photocleavage of the 2-(2-cyclopropylcyclopropyl)alkanones (36) has been described.44 The many products from the reaction were reduced in number by catalytic hydrogenation to afford (37a; 61%) and (38a; 20%) from (36a), and (37b; 51%) and (38b; 24%) from (36b). Studies at low conversion of (36a) indicated that the six-atom ring-expansion was a primary photoprocess involving one photon.

(36) a ; n = 1 b;n=2

(37) a ; b;

11 = 11 =

(38) a; b;

1 2

iz =

N =

1 2

Valeranone (39) undergoes a-cleavage upon irradiation (high pressure Hg arc).46~4~This affords a keten which is trapped as the acid (40a) in aqueous acetic acid or as the amide (40b) when the reaction is carried out in tetrahydrofuran-cyclohexylamine. Similar a-cleavage has been reported in the

0 (39)

46

46

(40) a ; R b; R

= =

OH NHCCH,,

G. K. Chip and T. R. Lynch, J.C.S. Chem. Comm., 1973,641. G . K. Chip and T. R. Lynch, Canad. J . Chem., 1974,52,2249. R. G . Carlson and W. S. Mardis, J. Org. Chem., 1975, 40, 817. S. C. Gupta, M. L. Maheshwari, and S. K. Mukerjee, Indian J. Chem., 1973, 11, 1202. J. Krepinsky, M. Romanuk,V.Herout, and F. Sorm, COILCzech. Chem. Comm.,1962,27,2638.

220

Photochemistry

irradiation of lupan-3-one (41a) in n-hexane solution, which yields five products (42)-(46).47 The formation of the isopropenyl group in the unsaturated aldehyde (42) is unusual but may reflect conformational difficulties in the abstraction of the hydrogen on C-5. The compound (41b) was also photoreactive."

(42)

(41) a; R b; R

=

=

(43)

2-propyl 2-propenyl

The conformational effects operative in the photochemistry of bicyclooctanones (47) have been The authors argue that several products should be possible if conformational effects control the fate of the biradicals formed by the Norrish Type I fission. However, if hydrogen abstraction is faster than conformational relaxation, the products must be derived from that conformation, e.g. (48),present immediately after bond fission. The results obtained

(47)

( A > 280 nm, benzene-methanol, 30 "C) show that there is good correlation between conformational effects present in the six-membered rings and the products formed. Thus the ketones (47a and b) afford the products (49a and b) respectively, from the stable conformation (48). However, with ketones (47c-e) the inverted conformer (50) is preferred and the products formed are the aldehydes (51c-e). The final ketone (47f) hardly discriminates between the two I7

H. Hirota, T. Tsuyuki, Y. Tanahashi, and T. Takahashi, Bull. Chem. SOC.Japan, 1974, 41, 2283.

W. C. Agosta and S. Wolff, J . Amer. Chem. SOC.,1975, 97, 456.

22 1

Photolysis of Carbonyl Compounds

Rf = But, R2 = H ; 96% b; R1 = R2 = Me; 75% f; R1 = Me, R2 = H ; 51%

(49) a;

(51)

R' = R2 = H; 93% d; R1 = R2 = Me; 85% e; R1 = H, R2 = OMe; 85% f; R' = Me, R2 = H; 44% C;

possible conformers and affords (49f) and (51f). The ratio of the products (52) and (53) (@bt= 0.62) from the irradiation (313 nm, benzene) of (54) was 1.07 : l ( k ~ / k ~the ) ;authors 4B point out that this is small and suggest that the acyl radical abstracts the first H or D which it encounters. A slightly larger isotope effect ( k ~ / = k ~ 1.24) was observed for the photolysis of the cyclohexanone ( 5 9 , which gave (56) and (57) as aldehyde products. The authors49 argue that the conformers (58) and (59) must interchange on a time-scale comparable with that required for disproportionation.

3 Norrish Type II Reactions

Wagner and Liuso have studied the reaction of the ketone (60) in an endeavour to obtain more accurate values for the lifetime of 1,4-biradicals produced by the Norrish Type I1 process. In this example the biradical produced, (61), can follow several reaction paths, i.e. oxetan formation, fission, reversion to ground state by disproportionation, and formation of norbornanol (62). The products obtained are illustrated in Scheme 3. From the analysis of the system the authors concluded that cyclization and cleavage of the biradical (61) each occur with a rate constant of 6 x los s-l. Coyle and Kingstons1 have reported a study of Norrish Type I1 cleavage in a series of 2-(dimethylamino)ethylbenzoates (63). Since neither penta-l,3-diene nor biacetyl quenches the reaction, although both 40

6o

61

W. B. Hammond and T. S . Yeung, Tetrahedron Letters, 1975, 1173. P. J. Wagner and K.-C. Liu, J. Amer. Chem. SOC.,1974, 96, 5952. J. D. Coyle and D. H. Kingston, Tetrahedron Letters, 1975, 1021.

222

Photochemistry

Scheme 3

quench the elimination in alkyl benzoates, e.g. (63c), an electron transfer mechanism is considered to operate. This postulate is also borne out by the influence of nitrogen protonation (63d) which leads to products with a quantum yield similar to that for the alkyl benzoate (63c). ArCO2CH,CH2X (63) a; Ar = Ph, X = b; Ar = p-FC,H,, c ; Ar = Ph, X = d; Ar = Ph, X =

NMe,; OArCOplI = 0.24 X = NMe,; @ArC0211 = 0.19 Me; @ArCOoH = 0.0057 = 0.018 H&Me,CI-;

A full report of the Type I1 elimination reactions of organic esters, carbonates, 63 has been p~blished.~* and thiocarbonates, reported in note 1,4-Dibenzoylbutane undergoes Norrish Type I1 fragmentation to yield acetophenone and 1-phenylbut-3-en-l -one.6s

(64) a; X b; X

X d; X C;

62

69

64

= = = =

H C1 or Br But CN

(65) e ; X = H f; = c1

x

A. A. Scala and G. E. Hussey, J. Org. Chem., 1971, 36, 598. A. A. Scala and J. P. Colangelo, Chem. Comm., 1971, 1425. A. A. Scala, J. P. Colangelo, G. E. Hussey, and W. T. Stolle, J. Amer. Chem. Soc., 1974, 96, 4069.

66

Y. Okamura, K. Fuke, and S. Furukawa, Rep. Fac. Sci. Shizuoka Univ., 1973, 8, 37 (Chem. Abs., 1974, 81, 84 350).

223

Photolysis of Carbonyl Compounds

Study of the bichromophoric systems (64)-(67) has shown that the Type I1 reactions which all the ketones undergo arise from the singlet manifold.66 In contrast, ordinary alkyl ketones undergo this reaction from both the singlet and the triplet manifolds. The results (Table 1) show that the introduction of para Table 1 Rate constants for the photoreactions of aryl ketones (64)-(67) Ketone

kf, x

lO-?/s-l

0.4

160 47 57 0.01 0.1 0.4 0.4

ET/kJ mol-l 326.4 341.5 336.5 326.0 357.4 350.3 331.0 -

kIsc x 10-7/s-1 3.3 130 190 110 0.89 19 0.1 30

66

k$ x 10-7/s-1 18 820 712 170 5.4 180 2.7 36

substituents into the aryl ring greatly influences the rate of reaction. Although a homoconjugative stabilization of the biradical intermediate was considered to account for this effect it was discarded in favour of an interchromophoric interaction through space. The triplet states of all the ketones studied were unreactive although intersystem crossing did take place. The triplet energies of the ketones were obtained from their phosphorescence at 77 K. The failure of the triplet state to undergo hydrogen abstraction could be due to the fact that the lower triplet state is an aromatic m* state, although the authorss6 suggest that this is not compelling evidence in every case. There is evidence from other systems that there must be interchromophoric coupling even in the triplet state. The Norrish Type I1 reaction of the peptide (68) at room temperature leads to the formation of acetophenone and oligomers of the thioaldehyde (69) (shown as its enoQ6? The thio-enol (69) (characteristic U.V. absorptions at 335 nm were

-IfPh 0 PhCH,CONH

0

\

, N 4 C02R1

SH PhCH,CONH$

,

OAN-4CO,R1

detected) was prepared by the low-temperature photolysis of the peptide in pyridine. The enol could be trapped by the addition of sodium methoxide and 1-chloro-2,4-dinitrobenzeneto give the thio-ether (70a). Photolysis of (68) in sodium methoxide-methanol and the addition of benzyl bromide gave the thioether (70b). This is reasonable evidence for the formation of the enol tautomer of the thioaldehyde (69). Study of the photochemical decomposition of the keto-peroxide (71) has shown that both unimolecular and higher order reactions account for the formation of

67

G. L. B. Carlson, F. H. Quina, B. M. Zarnegar, and D. G. Whitten, J. Amer. Chem. SOC., 1975, 97, 347. J. Cheney, C. J. Moore, J. A. Raleigh, A. I. Scott, and D. W. Young, J.C.S. Perkin I, 1974, 986.

224

Photochemistry

CO,R1 (70) a ; R 2 = O

N

O

,

NO2

b; R2 = CH2Ph

the products, benzoic acid and acetophenone.6E The quantum yield was concentration dependent, uiz. 0.47 at 0.025 moll-1 and 1.44 at 0.48 moll-’. The proposed pathway is shown in Scheme 4. More conventional Norrish

Products

HO h w 0-0 Scheme 4

t

P

6 P h w P h 0-0

Type I1 fragmentations have been reported in the photochemistry of the alkoxycyclohexanones (72), where the principal product from the irradiation is cyclohexanone. Only in the case of 2-methoxycyclohexanone is the oxetanol (73) formed by bond formation in the biradical intermediate. Elimination of the side-chain is also encountered in (74) and (79, although in the latter case formation of the oxetanol (76) is a competing process. A similar fragmentation path is found in the case of 2-methoxycyclopentanone,although Norrish Type I fission yielding 5-methoxypent-4-en-1-a1 is competitive.6a s8

W. H. Richardson, G. Ranney, and F. C. Montgomery, J. Amer. Chem. SOC.,1974,96,4688. J. C. Arnould and J. P. Pete, Tetrahedron, 1975, 31, 815.

Photolysis of Carbonyl Compounds

(72) R = Me, Et, Pri, PhCH,

225

(73) (74)

The photochemistry of the pyrimidyl ketones (77)-(79) has been studied by Alexander and Jackson.go The 2- and 5-ketones, (77) and (78) respectively, follow the path shown in Scheme 5 whereby excitation (300nm in benzene)

(78) Scheme 5

produces reactivity at the carbonyl group with resultant Norrish Type I1 reaction to give chain fission and cyclobutanol formation. These reactions are typical of those encountered in other systems where 1,4-biradical intermediates are known to be formed (cf. ref. 50). Irradiation of the 4-derivative (79) leads to anomalous reactivity and affords the product of chain fission (80) and the cyclopropanol(81) in the ratio 40 : 60. It is likely that the former arises by conventional Norrish Type I1 reactivity; the cyclopropanol is thought to be formed by the route shown in Scheme 6. This involves the abstraction of hydrogen by the 3-nitrogen. Thus in this instance two excited states are operative, one located on the carbonyl function and the other associated with the pyrimidyl ring. The evidence obtained from these experiments does not permit differentiation between a mechanism Oo

E. C. Alexander and R. J. Jackson, jun., J. Amer. Chem. SOC.,1974,96, 5663.

Photochemistry

226

Q 0 - 4 (80) Scheme 6

involving a vibronically mixed triplet state and a partitioning between two triplet states in a thermal equilibrium. The pyrimidones (82a-c) undergo elimination of the N-side-chain when irradiated ( A > 290nm) in benzene solution under an atmosphere of nitrogen.'jl The elimination is reminiscent of the Norrish Type I1 reaction, e.g. (77), encountered in many ketonic systems. The reaction in this instance affords the pyridone (82e) and the side-chain yields an aldehyde, e.g. acetaldehyde, benzaldehyde, or decanal. All of the above examples involve the fission of an N-0 bond in the elimination of the sidechain. An example of N-N bond rupture has been reported in the irradiation of the piperidine derivative (82d), which also yields the pyridone (82e). A rearrangement product (83) is also found in this reaction and could arise from a radical mechanism involving fission and recombination.

R (82) a; X = O,R = b; X = 0, R = C; X = 0, R = d ; X = N, R = e ; X R = H2

Me PhCH2 CloH2, (CHJ,

(83)

lY5-Hydrogentransfer, of which the foregoing are examples, is also important in the photoenolization of suitably substituted phenyl aldehydes and ketones. Thus Horii et aLBahave reported formation of the enols (84), which could be H. Furrer, Tetrahedron Letters, 1974, 2953. 2. Horii, Y. Hori, F. Kanazawa, and C. Iwata, Chem. and Pharm. Bull. (Japan), 1974, 22, 736 (Chem. Abs., 1974, 81, 12 793).

227 trapped by dienophiles, from the irradiation of the aldehydes (85). Findlay and Tchir 63 have also shown that the enol (84a) can be trapped by oxygen as the cyclic peroxide (86). The enol (84a) was also detected by flash spectroscopy.

Photolysis of Carbonyl Compounds

H

(84) a; R b; R

= =

H Ph

(85) a; R b; R

= =

H Ph

zi".:o / Me

/

(86)

\

I

(87)

At higher concentration (0.2 the rate of disappearance of the enol is more rapid as a result of formation of a dimeric hemi-acetal(87) in the absence of oxygen. This behaviour differentiates the enol of the aldehyde from that obtained from o-methylbenzophenone. Oxygen has also been used as a trap for

H

(89)

(91)

(90) n

=

2 or 3

(92)

the enols (88), yielding (89), obtained by irradiation at 253 nm of the cyclobutenols (90).64 In the absence of oxygen the ketones (91) and the alcohols (92) were formed. The ketones (93) were also photolabile and gave the mixture shown in Scheme 7. The excited state in this reaction was shown to be a triplet

& (93) a; n = 3 b;n=4

63

+ &In \

A @In

+ pinacol

H

a; 44% b; 44% Scheme 7

a; 17%

D. M.Findlay and M.F. Tchir, J.C.S. Chem. Comm., 1974, 514. M. L. Viriot-Villaume, C. Carre, and P. Caubere, Tetrahedron Letters, 1974, 3301.

228 Photochemistry by quenching with piperylene. Ring-size is important in the photoreactions shown by the cyclic ketones, as was demonstrated by the irradiation of a series of o-methyl derivatives (94) which exclusively undergo hydrogen abstraction from the methyl group when the ring contains 7-9 carbons. At larger ring sizes (CloyCI2,and CIJ transannular hydrogen abstraction becomes important (Scheme 8).

mln

+

n I & ?+ (

(94) a; n = 1 b;n=2 c;n=3 d;n=4 e;n=6 f;n=8

H

a;

-

b; c; d ; 35% \

a; 55% b; 55%

c; -

c; 78% d; 12% e; f; -

b;

-

H

-

a;

-

d; 20% /

e; 49% f ; 33% Scheme 8

The photoreduction of the diones (95a-c) has been The irradiation of (95a) has been examined by Bishop and Hamer 66 and Ogata and TakagLB7 The latter authors 67 favour the formation of the enol(96), which can be trapped by dienophiles. x&Me M -e

(95) a; X = H b; X = p-OMe C ; X = o-OMe d ; X = o-Me

OH (96)

The biradical intermediate in the Norrish Type I1 reaction can also lead to formation of cyclobutanols (see also refs. 50, 59, 60, and 64). In a steroidal system, e.g. the conversion of the ketone (97) into the cyclobutanol (98),68 this is often the only reaction detected since the biradical cannot adopt the transition state necessary for fragmentation ; thus ring-closure results. On n7

Y. Ogata and K. Takagi, Bull. Chem. SOC.Japan, 1974, 47, 2255. R. Bishop and N. K. Hamer, Chem. Comm., 1969, 804; J. Chem. SOC.( C ) , 1970, 1193. Y. Ogata and K. Takagi, J. Org. Chem., 1974,39, 1385. P. Gull, Y. Saito, H. Wehrli, and 0. Jeger, Helu. Chirn. Acta, 1974, 57, 863.

229

Photolysis of Carbonyl Compounds

Padwa and Eisenberg 69 have previously reported the photochemistry of the cyclobutyl aryl ketone (99a). In this system there is an inefficient conversion of the starting material into the bicyclic alcohol (100). The inefficiency of this process was interpreted by them in terms of a preference for the cyclobutane ring to exist in a quasi-equatorial conformer in which the carbonyl group cannot abstract the necessary hydrogen. Alexander and Uliana 7 0 have re-examined the problem and have substantiated the earlier proposal. They examined the reactivity of the substituted ketones (99b-e) and found that the quantum efficiencies for the reactions are enhanced as the reactivity of the ketonic triplet state is enhanced. These data are in agreement with an analysis of the system which places the onus for the inefficiency upon the excited-state conformational equilibrium. The kinetic analysis of these effects suggests that the reactivity of 0

(99) a; X

b; X C; X d; X e; X f; X

=

H

p-Me = p-F = p-CF, = o-CF, = p-OMe =

the p-anisyl ketone (99f) should be zero. This is borne out by experiment. A full report (the original reports were in note form 72) of the photochemical behaviour of the ketones shown in Scheme 9, with particular reference to the 718

R = MeorH

R

=

MeorH

Scheme 9

degree of conformational control on the reaction, has been p ~ b l i s h e d .Other ~~

work has examined the entropic control of the Norrish Type I1 process. This study considered the reactivity of several ketones (Scheme 10) and observed that there was a rate enhancement as the flexibility, in conformational terms, increa~ed.~~ Meinwald and Mioduski 76 have studied the photochemistry of the bicyclic ketones (101) which are prepared by addition of enones to cyclobutadiene iron A. Padwa and W. Eisenberg, J. Amer. Chem. SOC.,1972, 94, 5859. E. C. Alexander and J. A. Uliana, J. Amer. Chem. SOC.,1974,96,5644. F. D. Lewis and R. W. Johnson, J. Amer. Chem. SOC.,1972,94, 8914. F. D. Lewis and R. W. Johnson, Tetrahedron Letters, 1973, 2557. F. D. Lewis, R. W. Johnson, and D. E. Johnson, J. Amer. Chem. SOC.,1974,96,6090. F. D. Lewis, R. W. Johnson, and D. R. Kory, J. Amer. Chern. Soc., 1974,96,6100. J. Meinwald and J. Mioduski, Tetrahedron Letters, 1974, 4137.

IJ~

70

71

73 7p 75

230

Photochemistry

Ph

L 0

Scheme 10

oAPh

tricarbonyl. The ketone (lola), when irradiated (Pyrex filter, benzene solution), affords the Norrish Type I1 fission product (102) presumably via the biradical (103). The introduction of an exo-methyl group as in (101b) suppresses the fission process, and the products (104) result from cyclization of the biradical. This is a further example of the controlling influence of an exo-methyl Other workers77 have also observed the same effect in the Pyrex-filtered U.V. irradiation of the bicyclic ketones (105) and (106) in benzene which affords the alcohols (107) and (108), respectively. The reactions described above involve the more usual 1,5-hydrogen transfer. However, other hydrogen transfer pathways can become available in suitably designed systems. Thus Roth et aZ.78have reported the cyclization of the aminoketones (109) into the aminocyclopropanols (1 10) by a 8- or 1,4-hydrogen transfer pathway. 6- or 1,6-Hydrogen abstraction has been reported to arise from the n.rr*-tripletstate of some p-aminovinyl ketones, e.g. (1 1l).78 The reaction affords the pyrroles (112) in low to moderate yields by two sequential photochemical steps. Thus initial excitation produces the biradical (1 13), which ring77 78

F. D. Lewis and R. A. Ruden, Tetrahedron Letters, 1971, 715. C. L. Perrin and M.-T. Hsia, Tetrahedron Letters, 1975, 751. H. J. Roth, M. H. El Raie, and T. Schrauth, Arch. Pharm., 1974,307, 584 (Chem. Abs., 1974, 81, 135 596).

H. Aoyama, T. Nishio, Y.Hirabayashi, T. Hasegawa, H. Noda, and N. Sugiyama, J.C.S. Perkin I, 1975, 298.

231

Photolysis of Carbonyl Compounds

6

C' CO,Me

@

hPh

HO Ph

0 (105) a; R = OMe b; R-R = 0

R1

(109) R1 = R2 = H, Ph, Me, Et

Me I R3 = R4 = Me, (CH,),, or (CHJ,CH(CHJ, R2c)Ph Ph (111)

NR;

CH2R2

R1 = Me, Et, Prn.,or Bun

( 1 14)

CHR2 HO QCH2R2 Ph

(112)

--

(113)

R2 = H, Me, Et, or Pr"

closes to the phenyl cyclopropyl ketones (1 14). These products are not isolated but undergo secondary photolysis to yield the pyrroles. Low yields of the tetrahydrofuran derivatives (115) were obtained as a result of &hydrogen abstraction and cyclization when the 3,3-dialkoxyketones (1 16) were irradiated (Pyrex filter) in benzene solution.6o The major products were the ketones (117) and (118), but the exact mechanism of their formation is not known. 80

T.Nishio and H. Aoyama, Bull. Chem. SOC.Japan,

1974,47, 2615.

232

Photochemistry

(116) a; R

=

(117) a; 6% b; 15%

H

b;R=Me

Ph (118) a; 35% b; 15%

Further interest in the photochemical reactions of N-substituted phthalimides has been reported where it has been shown that irradiation of the phthalimides (119a and b) fails to yield a product. With a four-methylene chain (119~) cyclization gives (120c), but in low yield.81 The success of this reaction was a surprise since this product is the result of &-hydrogentransfer. The order of reactivity in these systems is such that y- and &abstraction normally occur in

2,X = H 3,X = H C ; 11 = 4, X = H d; n = 4, X = 2, 3, or 4-Me; 3,4-di-Me ; 2,3-di-MeO; or 3,4-di-MeO e; n = 3, X = 2,4-di-MeO or 3,4-di-MeO

(119) a; n b; n

=

=

(120)

preference to &-abstraction. The yield of product (120d) was enhanced when the aryl group bore an electron-donating substituent (1 19d). The introduction of such substituents also overcame the effects which originally brought about failure. The authors 81 suggest that a charge-transfer relationship (121) exists 0

CH

W/

0

O

(CH, ),Me

(122) n = 0, 2, 8, 9, 10, 1 1 , 13, 15 ,17, 19, or 21

x Y.Kanaoka and Y . Migita, TetrahedronLetters, 1974,3693.

Photolysis of Carbonyl Compounds

233

between the aryl group on the side-chain and the aryl group of the phthalimide system. This results in the carbonyl group of the imide being held close to the benzylic methylene group, thus permitting the hydrogen abstraction (cf. refs. 70-74). Several reports during the past few years have dealt with the application of excited benzophenone moieties to the functionalization of remote methylene groups. A computer simulation of this process has sought to establish the role played by the flexibility of the hydrocarbon chain in determining the specificity of the reaction.82 Winnik et aLs3have examined the conformation of the hydrocarbon chains in molecules of type (122) using the benzophenone hydrogenabstracting moiety as the probe, as in the earlier study by Breslow and Winnik.84 In this later report the quantum yields for the processes are recorded for irradiation at 366 nm. The results obtained suggest that there is no evidence for ‘hairpin’ or micellar aggregation. The chains are thus highly flexible and can adopt all possible conformations. 4 Rearrangement Reactions A study of the photochemical reactions of the isomeric steroidal epoxides (123) has shown that the main reaction is fission of the C-0 bond to produce the 1,3-diketones (124);8sthe other product is the 1,4-diketone (125). Of the epoxyketones (126), only the ketones (126c) and (126d) proved to be photoreactive. The epoxyketone (127a) yields the spiro-diketone (128a) as a result of a 1,2-

H Ph

Ph H ( I 23a)

(1 23b)

Ph H (I 23c)

H Ph (123d)

.H<-y-J) ;yy)tJ/-J-H Ph

Ph H

; y o n ] 0 ( 1 26a) Ba

8s

R4

(126b)

( I 26c)

(1 26d)

M. A. Winnik, R. E. Trueman, G. Jackowski, D. S. Saunders, and S. G. Wittington, J. Amer. Chem. Soc., 1974,96,4843. M . A. Winnik, C. K. Lee, S. Basu, and D. S. Saunders, J. Amer. Chem. Soc., 1974,96,6182. R. Breslow and M.A. Winnik, J. Amer. Chem. Soc., 1969, 91, 3083. J. Muzart and J. P. Pete, Tetrahedron Letters, 1974, 3919.

234

Photochemistry

migration.86 This migration also occurs in the acetone-sensitized irradiation of (127b). The reactions can be accommodated within a scheme whereby excitation is followed by C , - 0 bond fission. This simple representation is complicated by

(127) a ; n = 1

(128)

b;n=2

0

the results of quantum yield measurements with optically active epoxide which show that a common biradical intermediate such as (129) cannot be formed for all the reaction paths. The kinetic data reveal that the rearrangement is faster than rotation about the C,-Cp bond. Attempts to trap such a biradical intermediate by irradiation of epoxyketones in the presence of tri-n-butylstannane gave the enones (130) in high yield. Verbenone epoxide (131), in common with

(133) a; R1 = H, R2 = Me b; R1 = Me, R2 = H

other arp-epoxyketones, yields a ring-contracted lY3-diketone(132); the lactones (133) were also isolated.87 No trace of the expected 1,3-diketone (134) was detected in this instance. It is highly likely that the lactones are formed by secondary photolysis of the ketone (134) as outlined in Scheme 11. One other

( 134)

Scheme 11 J. R. Williams, G. M. Sarkisian, J. Quigley, A. Hasiuk, and R. Vandervennen, J. Org. Chem., 1974,39, 1028.

T. Gibson, J. Org. Chem., 1974,39, 845.

235

Photolysis of Carbonyl Compounds

feature of this study is the formation of two ring-contracted ketones, (132) being an inseparable mixture. Ring-contraction in epoxides is usually stereospecific. However, epimerization may be a photochemical process (a Norrish Type I react ion). The photochemistry of py-epoxyketones is dominated by Norrish Type I fission to yield biradicals. However, the fate of the biradicals formed depends to a great extent on the substitution pattern or the presence of specific constraints on the paths by which the biradicals can react. Thus the normal pattern for reaction will be as shown in Scheme 12. The epoxyketone (135a) gives two

Scheme 12

products (136a) and (137a).88189 This pattern of reactivity is not affected either by ring size, as is shown by formation of the two products (1 36c) and (137b) from the irradiation of (135c), or by additional methyl substitution as in (135b) which affords (136b).g0

(135) a; R1 = Me, R2 = H,n = 1 (136) a; R1 = Me, R2 = H, ir = 1 b; R1 = R2 = Me,n = 1 b; R1 = R2 = Me,n = 1 c; R1 = R2 = H,n = 2 c; R1 = R2 = H, n = 2

(137) a; R b; R

= =

Me, n = 1 H,n = 2

R. K. Murray, jun. and D. L. Goff, J.C.S. Chem. Comm., 1973, 881. R. K. Murray, jun., T. K. Morgan, jun., H. Hart, and V. J. Hull, J. Org. Chem., 1973, 38, 3805. 90

R. K. Murray, jun., T. K. Morgan, jun., J. A. S. Polley, C. A. Andruskiewicz, jun., and D. L.

Goff, J. Amer. Chem. Soc., 1975, 97, 938.

236 Photochemistry Previous study of the photoreactions of the dihydrocoumarin (138) has shown that the reaction path is determined by the presence of the enol form which is present in low concentration in alcoholic But in benzene or acetonitrile the enol concentration is at a minimum and irradiation under these conditions (Pyrex filter) yields a new product (139) which is formed by the route shown in Scheme 13.Q2 A detailed report of the photochemistry of 3-phenylisocoumarin (140), originally reported in note form,Q3 has been published.94

0

0 Ph

Ph

Ph

J

(138)

Ph

(139)

Scheme 13

The irradiation of (141a) in non-degassed t-butyl alcohol solution affords a good yield of the rearrangement product (142a).Q6Acylation of the nitrogen was unimportant since the compound (141b) gives the product (142b). Prolonged irradiation of (141a) in methanol affords a mixture of products by radical fission and recombination pathways. The ring-contraction, for which an intramolecular electron transfer process is has obvious applications to the synthesis of penicillins. HN-NR

Qo \

Ph H

-0

R = COCHzPh b;R=H

(141) a;

(140)

H

RNFo (142)

Direct (313 nm) or sensitized (l-methylnaphthalene) irradiation of the dihydropyran (143) yields the single product (144: 0 = 0.11; 900/,).Q7Irradiation at 253.7 nm also yields this product (144; 5%) and several others (Scheme 14).

O2

9s Or 96 Be O7

A. Padwa and G. A. Lee, J. Amer. Chem. SOC.,1974,96, 1634. A. Padwa and A. Au, J.C.S. Chem. Comm., 1975, 58. A. Padwa and G. A. Lee, J. Amer. Chem. Sue., 1973,95, 6147. A. Padwa, D. Dehm, T. Oiyne, and G. A. Lee, J . Amer. Chem. SOC.,1975,97, 1837. C. E. Hatch and P. Y. Johnson, Tetrahedron Letters, 1974, 2719. P. Y. Johnson and C. E. Hatch, J. Org. Chem., 1975,40, 909. P. Chaquin, B. Furth, and J. Kossanyi, Compt. rend., 1974, 279, C, 359.

237

Photolysis of Carbonyl Compounds

32%

(144) 5%

25%

0

3%

+

1 20% 0

Scheme 14

5 Oxetan Formation and Addition Reactions A previous study on the photochemical reactions of benzofuran with sensitizers suggested that dimers were obtained when high-energy sensitizers were used, whereas oxetans were formed from those of lower energy (benzophenone and ben~aldehyde).~~ Reinvestigation has shown that the high-energy sensitizers (propiophenone and acetophenone) yield both oxetans (145a and b) and d i r n e r ~ , ~ ~ and that the ratio of products is sensitive to the ratio of the reactants. The latter observation has been rationalized in terms of a reversible energy-transfer step which competes with oxetan formation. The results suggest that the triplet energies of propiophenone and acetophenone are closer than was previously indicated by low-temperature phosphorescence measurements. The authors gg indeed suggest that the triplets of propiophenone and acetophenone are isoenergetic in benzene solution at room temperature. Kawase et aZ.loO have described the addition of benzophenone and benzaldehyde to derivatives of benzofuran, yielding oxetans (14%-f).

(145) a; R1 = Me, R2 = R3 = H b; R' = Et, R2 = R3 = H C; R ' = H or Ph, R2 = H, R3 = Me d ; R' = H or Ph, R2 = R3 = M L e ; R' = H or Ph, R2 = R3 = (CH,),

f; R'

0.9

*D

100

9

=

Ph, R2 = H, R3 = CH,OH

C. H. Krauch, W. Metzner, and G. 0. Schenck, Chem. Ber., 1966,99, 1723. S. Farid, S. E. Hartman, and C. D. DeBoer, J . Amer. Chem. SOC.,1975,97, 808. Y. Kawase, S. Yamaguchi, H. Ochiai, and H. Horita, Bull. Chem. SOC.Japan, 1974,47,2660.

238

Photochemistry A full report of the addition of 2,3-dimethylbut-2-ene to 2-acetylthiophen has appeared.101s102The products from this reaction are shown in Scheme 15.

H

'

a; R = Me b;R=H

a; R1 = R2 = Me b; R1 = Me, R2 = H c ; R1 = H , R2 = Me Scheme 15

Cantrelllo2suggests that the triplet excited state of the acetylthiophen may be predominantly 7rn* in character, rather than nv*. This proposal is backed up by the observation that the long-lived phosphorescence at 77 K is VT* in character. Similar products are isolated from the reaction of the same ketone with isobutene. 2-Benzoylthiophen gave the oxetan (146a) when it was irradiated with 2,3dimethylbut-2-ene. Unstable oxetans (146b-d) are also obtained from the

(146) a ; R1 = Ph, R2 = Me b ; R' = Ph, R2 = H c ; R1 = p-anisyl, R2 = H d ; RL = p-CNCGH,, R2 = H

irradiation of 2-benzoylthiophen, 2-p-anisoylthiophen, and 2-p-cyanobenzoylthiophen in the presence of isobutene (see also ref. 13 this chapter). N o evidence for the formation of [2 21 cyclobutane adducts was obtained.lO3 3-Aroylthiophens behave similarly. The oxetans were identified by n.m.r. spectroscopy but could not be isolated since they all lost formaldehyde to yield methylene derivatives. Surprisingly, although all the ketones give good yields of oxetans, only the 3-benzoylthiophen exhibits a lowest excited state of nn* character from which oxetans are usually formed. The 2-benzoylthiophens exhibit lowest excited states with mr* character, a conclusion which was also reached for 2-acetylt hiophen.lo2 Oxetans (147) have been reported to be produced from photochemical addition of 1-naphthaldehyde, 2-, 3-, and 4-benzoylpyridine, and 2-benzoylthiophen to 2,3-dimethylthiophen.lo4Other carbonyl compounds, 2-naphthaldehyde, benzaldehyde, 1-benzoylpyrrole, and acetophenone were not reactive under these

+

T. S. Cantrell, J.C.S. Chem. Comm., 1972, 155. T. S. Cantrell, J . Org. Chem., 1974, 39, 2242. l o 3 D. R. Arnold, R. J. Birtwell, and B. M. Clarke, jun., Cunud. J. Chem., 1974, 52, 1681. lo* C. Rivas and R. A. Bolivar, J . Hererocyclic Chem., 1973, 10, 967.

lol

lo2

PhotoIysis of Carbonyl Compounds

239

conditions. An interesting oxetan (148; 83%) was obtained from the irradiation of non-10'-enyl 4-benzoylbenzoate in CCl, This oxetan is readily transformed into (149).

(147) a; b; c; d; e;

R1 = H, R2 =. 1-naphthyl

R1 = R1 = R' = R' = f; R1 =

1-naphthyl, R2 = H Ph, R2 = 2-, 3-, or 4-pyridyl 2-, 3-, or 4-pyridyl, R2= Ph 2-thienyl, R2 = Ph Ph,R2 = 2-thienyl

Dioxen has been used as the substrate for the photochemical addition of 1,l-diphenylethylene, benzophenone, and acetone.lo6 The products from the reactions were (150a-c). An approach to the synthesis of long-chain enals has been described whereby the oxetans (15Od,e) obtained from the photochemical addition of benzaldehyde to cyclohexene or propionaldehyde to cyclohexadiene (followed by catalytic reduction) are ring-opened under a variety of conditions to yield (151a) and (151b), respe~tive1y.l~~

(yj-q.Rl (150) a; X = b; X =

y H R2 CH,,R1 = R2 = Ph, Y Y = 0,R' = R2 = Ph

=

0

x = y = 0,R1 = R2 = Me d; X = 0,Y = CH2, R' = Ph, R2 = H e; X = 0, Y = CH,, R' = H, R3 = Et C;

OHC(CH,),CH=CHR (151) a; R = Ph b; R = Et

The spiroketone (152) undergoes oxetan formation (153) when irradiated (Pyrex filter) in degassed benzene so1ution.lo8 This type of addition has been reported previously for endo-acylnorbornene~.~~~ The exo-compound (154), as a result of the inaccessibility of the double bond, undergoes Norrish Type I fission to yield five products two of which were identified as the endo-ketone (152) and the oxetan (153). The aldehyde (155) is also photolabile and yields the oxetan (156). A study of the photoreaction of benzaldehyde with hex-l-yne has shown that the several products obtained arise by a free radical path.l1° No evidence was obtained for the oxeten intermediates which had previously been claimed by D. Bichan and M. A. Winnik, Tetrahedron Letters, 1974, 3857. N. R. Lazear and J. H. Schauble, J. Org. Chem., 1974,39,2669. 1°7 G . Jones, M. A. Acquardo, and M. A. Carmody, J.C.S. Chem. Comm., 1975, 206. R. R. Sauers and T. R. Henderson, J. Org. Chem., 1974, 39, 1850. l o @R. R. Sauers and A. Shurpik, J . Org. Chem., 1967, 32, 3120. ll0 J. S. Bradshaw, R. D. Knudsen, and W. W. Parish, J. Org. Chem., 1975,40, 529. 106

106

Photochemistry Buchi et al. in the photoreaction of benzaldehyde with dec-5-yne.lll An unstable imino-oxiran has been suggested as an intermediate in the formation of (157) from the irradiation of a mixture of benzaldehyde and t-butylisocyanate.l12 240

Carless 113,114 has reported in detail his reinvestigation of the photochemical reactions of acetone and [2H6]acetone with 2,3-dimethylbut-2-ene. Several products (Scheme 16) are obtained as a result of the primary process. Extended

(1 59)

Scheme 16

irradiation affords another oxetan (158) as a result of addition of acetone to the olefinic product (159). Carless 114 has also carried out a kinetic study of the system and has reached the conclusion that both singlet and triplet states are involved. An investigation of addition of photochemically excited benzophenone and benzaldehyde to the vinylcyclopropanes (1 60) has been reported.l16 Two principal products (161) and (162) are formed (Table 2). The results are interpreted in

(160) a; RL = cyclopropyl, R2 = H b; R1 = Me, R2 = H C;

112

113 114

116

R‘ =

R2 z=

H

G. Buchi, J. T. Kofron, E. Koller, and D. Rosenthal, J. Amer. Chem. Soc., 1956, 78, 876. R. P. Widera, L. A. Singer, R. Easton, and F. A. L. Anet, J.C.S. Chem. Comm., 1974, 784. H. A. J. Carless, J.C.S. Chem. Comm., 1973, 316. H. A. J. Carless, J.C.S. Perkin 11, 1974, 834. N. Shimizu, M. Ishikawa, K. Ishikura, and S. Nishida, J. Amer. Chem. SOC.,1974, 96, 6456.

241

Photolysis of Carbonyl Compounds

a ; RL = cyclopropyl, R2 -- H, R3 = Ph b; R1 = Me, R2 = H,R3 = Ph e; R1 = cyclopropyl, R2 == R3 = H f; R1 = Me, R2 = R3 = H 6 ; RL = RZ = R3 = H

Table 2 Products from the reaction of benzophenone and benzaldehyde with vinyl cyclopropanes (160)116 Ketone

Olefin

Temp/"C

Ph,CO

(160a) (I 60a) (160a) (160b) (160b) (160b) (160b) (160b) (160b) (160c) (1604 (16oc)

rt 130 160 rt 130 160 rt 70 130 25 75 100

Ph,CO

PhCHO PhCHO

Oxetan (161) a, 86 a, 36

a, 29.4 b, 86.5 b, 43.1 b, 21 e, 65 f, 49.6 f, 32.2 g, 17.3 g, 14.8 g, 5.9

Products/% Oxepin (162) a, 55 a, 64.5 b, 3 b, 31.2 b, 45

1- Cyclopropyl2-phenyiethylene

f, 2.3 f, 10.1 g, g, 4.2 g, 2.9

f, 0.7 f, 4.3 f, 0.5

terms of a biradical intermediate (163) which undergoes ring-closure to the oxetan (1 61) or cyclopropylcarbinyl-ally1 radical rearrangement prior to rebonding. This step is enhanced as the temperature is increased (Table 2) and tetrahydro-oxepin (1 62) formation is dominant at higher temperatures. The authors suggest that the evidence obtained shows conclusively that a biradical intermediate is involved in the oxetan-forming reaction. PhCSOR (164) R = Et R = Me

Excitation of the O-alkylthiobenzoates (164) in the m* (290 nm) or nn* (420 nm) bands leads to their reaction, via a triplet state, with olefins.lls Various products are obtained, some of which are shown in Scheme 17. Their formation is attributable to addition to the olefin of the thio-end of the biradical formed upon excitation, followed by radical recombination and thermal reaction. 110

A. Ohno, T.Koizumi, and Y.Akasaki, Bull. Chem. SOC.Japan, 1974, 47, 319.

242

Photochemistry r

S I1 PhCOEt

+

PhCH,CH=CH,

”’

PhCH2CH2COPh CH2Ph

+

4

\ +

PhCH,CH=CMe,

PhCH2CH2COPh +

’la’

’”’

MeCH,CH,CH=CH,

Pr”CH,COPh

Rgt

+ PhCOMe

Scheme 17

6 Fragmentation Reactions Photodecarboxylation is the major reaction path encountered when the aminoesters (165) are irradiated in non-polar s01vents.l~’A full account of the photochemical transformations of the naphthylmethyl phenylacetates (1 66) and (1 67) R2NCH2C02CH2Ph (165) R = Et

R-R

= (CH,),, (CH,),, or CH2CH20CH2CH2

has been published.l18 This report is complementary to an earlier publication.lle The decarboxylation reaction of both esters affords products of radical combination as shown in Scheme 18. The failure of sensitization studies is Ph

0

\

/

300 n m , c6&

, ,

/

+ Ph-ph \

/

ratio 1 : 10 : 1

0

+ Ph-Ph ratio 1 : 10 : 1

Scheme 18

considered to suggest a singlet mechanism. A study of the photochemistry of the anhydrides (168) shows that only (168a) is photoreactive (at 254 nm) yielding bibenzyl as the major product.120 The activity of this anhydride compared with the others is thought to arise as a result of the close proximity of the two 117

llS 110

lZo

K. Kimoto, K. Tanabe, S. Saito, Y. Umeda, and Y. Takimoto, Chem. Letters, 1974, 859. R. S. Givens, B. Matuszewski, and C. V. Neywick, J. Amer. Chem. SOC.,1974, 96, 5547. B. Matuszewski, R. S. Givens, and C. V. Neywick, J. Amer. Chem. SOC.,1973, 95, 595. A. A. M. Roof, H. F. van Woerden, and H. Cerfontain, Tetrahedron Letters, 1975, 815.

Photolysis of Carbonyl Compounds

243

aryl chromophores. Triphenylacetic anhydride also undergoes photochemical decomposition. [Ph(CH2),CO12O (168) a; n = 1

b;n=2 c ; n = 3 d;n=O

Photodecarboxylation of the adducts (1 69) in benzene solution yields the unstable quinomethides (170a-c) which are sensitive to air exposure and further irradiation.121 Thus the phenyl adduct (169; R = Ph) gave the cyclobutane (171 ; 28%) as well as the dihydronaphthalene (172; 23%), and the cyclopropane (173 ; 3.5%) which could arise by an oxa-di-x-methane process.

(169)

R

=

H, Me, or Ph

of-&. \

Ph

R1 = R2 = H , X = Me R1 = X = Me, R2 = H C ; R1 = Ph, R2 = H, X = Me d ; R1 = R2 = Ph, X-X = (CH,), e; R1 = R2 = Ph, X = Me

(170) a; b;

9 0

\

0

(171)

0

NMe

@:e \ 0

(173)

(1 72)

The related stable o-quinomethide (170d) is prepared by photodecarbonylation (irradiation through quartz with benzene as solvent) of the adduct (174a).122 The dimethyl adduct (170e) also affords a stable methide (174b) when irradiated under the same conditions. The presence of steric crowding in the quinomethides is an important feature in determining their stability. Irradiation of the ketone

(174) a ; X b; X l*l 131

= =

(CH,), Me,

D.W.Jones and G . Kneen, J.C.S. Perkin I, 1975, 175. D. W.Jones and G.Kneen, J.C.S. Perkin I, 1975, 171.

244

Photochemistry

(175) in benzene solution results in decarbonylation and loss of ethylene to yield the fluoranthene (176a).123 Loss of ethylene is also encountered when the hydrocarbons (177) are irradiated ; the fluoranthenes (1 76) are again produced.

(176) a ; R = Pri b;R=Mc C; R = Et d ; R = Prn

(177)

A full report on the synthesis of a-dithiones by the photochemical decarbonylation of vinylenecarbonates has been pub1i~hed.l~~ The Norrish Type I fragmentation of the cyclic ketone (178) has been used in a synthesis of grandisol (179), a major component of the male boll weevil pheromone.126 The cleavage reaction gave the aldehyde (180) which was subsequently decarbonylated to give the desired product.

The thietanone (181) shows an nr* transition at 302.5 nm in acetonitrile. The compound also shows weak fluorescence with a maximum at 350 nm and triplet emission at 405 nm (293 kJ mol-l) at 77 K. Irradiation of (181) in acetonitrilealcohol mixtures yields the products shown in Scheme 19.126 These products

hv

0

310nm ROH

CH2 II

CH,

+ co I1 so,

-

MeC02R

+ MeS0,R

Scheme 19

arise from the keten and the sulphene (182) formed by the cycloreversion of the thietanone. Irradiation (280 nm) of the thietanone in a pentane matrix at 77 K gave evidence for the formation of the sulphene by the appearance of characteristic i.r. absorptions. Kinetic analysis of the photolysis showed that the reaction occurred by two excited states only one of which could be quenched. Intersystem crossing efficiency measurements show that @ISC = 0.28. 123 la5 12E

K. Matsumoto, T. Uchida, and K. Maruyama, G e m . Letters, 1974, 877. W. Kiisters and P. de Mayo, J. Amer. Chem. SOC.,1974, 96, 3502. P. D. Hobbs and P. D. Magnus, J.C.S. Chem. Comm., 1974, 856. R. Langendries, F. C. De Schryver, P. de Mayo, R. A. Marty, and J. Schutyser, J. Arner. Chem. SOC., 1974, 96,2964.

Photolysis of Carbonyl Compounds 245 The irradiation of the acetate (183) in t-butyl alcohol under nitrogen gave the product (184).lZ7 The ring-contraction in this exampIe can be interpreted in terms of Norrish Type I fission followed by elimination of isobutene and

AcO (184)

(185)

a;R=H b;R = OSO,

rebonding in the new biradical. The pyranosidulose (185a) is formed in 38% yield, along with an unidentified product, when the tosylate (185b) is irradiated (Vycor filter) in acetatewater-triethylamine.128 12’

lZ8

P. Y. Johnson and M. Berman, J.C.S. Chern. Comm., 1974, 779. W. A. Szarek and A. Dmytraczenko, Synthesis, 1974, 579.

2 Enone Cycloadditions and Rearrangements: Phot0reactio ns of Cyclo hexad ieno nes and Q uinones BY W. M. HORSPOOL

1 Cycloaddition Reactions Intramolecular.-Irradiation of the enone (1) yields a mixture of the crossaddition products (2) and (3).l The isomer (3) was converted into the tricyclic ketone (4) by treatment with KOBd in ether. De Schryver and his co-workers a

(2)

(3)

have continued their investigation of bichromophoric systems and have reported that irradiation of the polymethylenedioxycoumarins ( 5 ) in methylene chloride solution using 334nm light affords two adducts, (6) and (7), the amounts of which are shown in Table 1. Quenching studies show that there are at least two excited states, and the Stern-Volmer plots obtained are non-linear. There is

( 5 ) a; b; c; d;

a

11

2 3 = 5

ia

=9

it

=

0

ri =

C.-Y. Ho and F. T. Bond, J. Amer. Chem. SOC.,1974,96, 7355. F. C. De Schryver, J. Put, L. Leenders, and H. Loos, J. Arner. Chem. Suc., 1974,96,6994.

246

247

Enone Cycloadditions and Rearrangements

Table 1

Yields of the isomers from the irradiation of the biscoumarins (5) Head-to-head Head-to-tail dimer (7)/% a) Coumarin dimer (6)/% (5a)

(5b) (5c) (5d)

85 41 40 33

15 59 60 67

0.0024 0.0125 0.0142 0.0044

evidence from the U.V. spectra that there is some ground-state interaction between the bichromophoric units. This interaction is more dominant in (5c) than in (5a). The existence of interaction is borne out by irradiation of (5c) at different wavelengths when it is observed that at longer wavelength the reaction becomes more regiospecific(3 13 nm; h :h-h :t = 0.77; 334 nm, h :h-h :t = 0.67; 360 nm, h : h-h : t = 0.6). An enhancement of regiospecificitywas also observed in the quenching studies. A full report of the approaches to the synthesis of (CH), carbocations has been p ~ b l i s h e d . ~The ~ carbocations were synthesized to study the suggestion that the most stable structure for such species was the pyramidal structure (8).6 Hart and KuzuyaS approached the problem by the synthesis of the tetracyclic alcohols H

(10) a ; R1 = CD,, R2 = H b; R1 = Me, R2 = D C; R1 = CD,, R2 = D

(9), which were made by the photochemical ring-closure of the enones (10) and reduction of the carbonyl group. The ions were then produced by treatment of the alcohols with FS03H-S02CIF. The cage compounds (1 1) can be obtained in reasonable yield by U.V. irradiation (Pyrex filter) of the Diels-Alder dimers (12) in ethanol solution.s The cage compound (1 la) also undergoes photochemical rearrangement to afford an enol by the ring-opening of one of the oxiran rings. An intramolecular photochemical cycloaddition suggested for inclusion in the undergraduate laboratory curriculum couples a ground-state Diels-Alder reaction with the sunlight-induced cage formation of (13a) from the crystals of the thermal adduct (14a),' as depicted in Scheme 1. Marchand and Allen * have reported an improved synthesis of the pentacycloundecane (15) using the photochemical intramolecular cycloaddition of the dienedione (14b), which was achieved in 86% yield by acetone-sensitized irradiation.

' *

H. Hart and M. Kuzuya, J. Amer. Chem. SOC.,1974,96, 6436. H. Hart and M. Kuzuya, J . Amer. Chem. SOC.,1972, 94, 8958; H. Hart and M. Kuzuya, Tetrahedron Letters, 1973, 4123. W.-D. Stohrer and R. Hoffmann, J. Amer. Chem. Soc., 1972, 94, 1661. H.-D. Becker, B. Ruge, and T. Westlof, Tetrahedron Letters, 1975, 253. E. G. Nash, J. Chem. Educ., 1974, 51, 619. A. P. Marchand and R. W. Allen, J. Org. Chem., 1974,39, 1596.

248

Photochemistry

.R’ 0 R2’

+;&

0

2I@:

x@ x

+

0

X H 0

Y

(14) a; X = C1

b;X=H

\

Y

(13) a; X = Cj, Y = 0 b; X = H, Y = 0 (15) X = H , Y = H,

Scheme 1

Intermolecular.-Methyl acetopyruvate, as its enol, has been added photochemically to cyclopentadieneg and cycloheptatriene.l*#l1 In the reaction with cyclopentadiene, [2 21 addition affords the products (16) and (17) via an unisolated cyclobutanol. Diels-Alder type addition also occurs giving (1 8) and (19). In the cycloheptatriene reaction, [4 + 21 and [6 + 21 addition occur.

+

0 H &

lo

l1

“C0,Me

0 @02Me “OH

H. Takeshita, A. Mori, and Y. Toyonaga, Bull. Chem. SOC.Japan, 1975,48, 307. H. Takeshita, A. Mori, and S . Ito, Bull. Chem. SOC.Japan, 1974, 47, 1767. H. Takeshita and A. Mori, Bull. Chem. SOC.Japan, 1974,47,2901.

Enone Cycloadditions and Rearrangements

249

However, the main product (20) is thought to arise by hydrogen abstraction and radical combination. The bichromophoric systems (21a and b) do not show evidence for important intramolecular interactions in the ground state. They do, however, undergo [2 21 addition to afford polymeric material. The cyclobutane rings in the polymeric material were shown, by spectral analysis, to have the cis,trans,cisgeometry. From quenching studies and a kinetic analysis the polymerization reaction is suggested to arise from the triplet state. The reaction is multistep with each step requiring the absorption of a photon.12 Other bismaleimides (21c and d) also photopolymerize from the triplet state.13 Dibromomaleimide undergoes photoaddition to trans-1,2-dichioroethylene affording the products (22).14 The formation of (22c) suggests that a biradical, perhaps a triplet,

+

R2

R3

Br

(21) a; X = (CH,),, R = Me (22) a; R1 = b; X = (CH2)ll, R = Me b; R1 = C ; X = (CH,),, R = Cl C; R1 =

d; X

=

R4 = H, R2 = R3 = C1 R4 = C1, R2 = R3 = H R 3 = H, R2 = R4 = C1

(23)

(CH2ll1,R = Br

mechanism is involved. A triplet mechanism is involved in the benzophenonesensitized addition of maleic anhydride to 2,5-dimethoxy-2,5-dihydrofuran yielding the single adduct (23; 400/,).1s Maleic anhydride has also been used in the photochemical addition to ethyl /3-aminocrotonate giving the pyrroline (24 ; 28%).l6 Other enamino-esters (25) undergo benzophenone-sensitized addition to dihalogenomaleimides (26) to yield the alkylation products (27).17 A similar reaction is encountered for the enamino-ketone (28) which gives (29) with 2,3-dibromo-N-methylmaleimide.17 Exclusive oxetan (30a-e) formation has been observed in the photochemical addition of olefins to the cyclopentene-1,3-diones (31a,b).le The regioselectivity of the addition was established as 4.26 : 1 for the formation of the oxetans (30b) and (3Oc) by the addition of isobutene to dione (31a) and 3.55 : 1 for the formation of (30d) and (3Oe) from the addition of the same olefin to dione (31b). This addition follows the now well-established path in oxetan formation involving addition of the nn* excited state of the ketone to the olefin to afford preferentially the more stable biradical intermediate. The fact that a triplet state was involved in the addition was demonstrated by the stereochemical scrambling encountered in the addition of either cis- or trans-but-2-ene, when four oxetans were obtained. la l3

l4

F. C. De Schryver, N. Boens, and G. Smets, J. Amer. Ciiem. Soc., 1974, 96, 6463. F. C. De Schryver, N. Boens, and G. Smets, Macromolecules, 1974, 7, 399. E. K. G. Schmidt, Chem. Ber., 1974,107,2440. J. C . Hinshaw, J . Org. Chem., 1974, 39, 3951. G. Szilhgyi and H. Wamhoff, Acad. Chim. Acad. Sci. Hung., 1974,82, 375 (Chem. Abs., 1975, 82, 16 645).

l7 l8

G. Szilhgyi, H. Wamhoff, and P. Sohar, Chem. Ber., 1975,108, 464. Z. Yoshida, M. Kimura, and S. Yoneda, Tetrahedron Letters, 1974, 2519.

Photochemistry

250 Et0,C

CH,CO,H

0 H

xco2Et

Me

0

(24)

(25) R'

X + ? .

NHRl

=

0 H, Et, Ph, AC (26) R2 = H,X = C1 R2 = Me, X = C1 K2 = H, X = Br R2 = Me, X = Br R 2 =H , X = 1 R2 = Me, X = I

In contrast to this the cyclopentenones (31c and d), when irradiated (A > 300 nm) in tetramethylethylene, afforded both oxetan (30f and g) and cyclobutane (32) products.l0 As the polarity of the solvent increases the amount of oxetan product decreases. The authors suggest (following several precedents) that an nn* triplet is responsible for oxetan formation whereas a m* triplet state is involved in cyclobutane formation. A full account of the photochemical addition of dienes to cyclohexenone and cyclopentenone has been reported.20n21The addition process affords [2 21

+

R1R'

= H or Me, R1 = R3 = Me, X-X = 0 b; R1 = R2 = H, R3 = Me, X-X = 0 C; R' = R3 = H, R2 = Me, X-X = 0 d ; R' = R3 = Me, R2 = H,X-X = 0 e ; R' = R2 = Me, R3 = H, X-X = 0 f ; R' = H,R2 = R3 = Me, X-X = OCH,CH,O g; R1 = H, R2 = R3 = X = Me

(30) a; R'

R R

(31) a; R

=

b; R

=

H,X-X = 0 (32) a ; R-R = OCH,CH,O Me, X-X = 0 b; R = Me C; R = H, X-X = OCH2CH20 d ; R = H , X = Me

l9 2o

21

Z. Yoshida, M. Kimura, and S. Yoneda, Tetrahedron Letters, 1975, 1001. T. S. Cantrell, Chern. Cornm., 1970, 1656. T. S. Cantrell, J. Org. Chern., 1974, 39, 3063.

Enone Cycloadditions and Rearrangements

25 1

Scheme 2

adducts (see Scheme 2). Cyclopentadiene, cyclohexadiene, cycloheptatriene, and furan were among the dienes used in the addition reactions. The fact that dienes which are known triplet quenchers add to the enones could account for the erratic results reported previously for such systems. The addition of allene to the cyclohexenone (33) gave the adduct (34).22

A reinvestigation of the photoaddition of tetramethylethylene to coumarin 23 has confirmed that the photoproduct is the cyclobutane (35).24 Kinetic study of the reaction has shown that both the triplet and the singlet states of the coumarin are involved in the addition process. Thus cis-piperylene was only capable of quenching ca. 20% of the reaction. The surprising result is that tetramethylethylene completely suppresses the dimerization of singlet coumarin. Previous work has shown that the dimerization of coumarin in its singlet state arises from an excimer. To account for the suppression of the dimerization the authors2* suggest that the mechanism involves the interception of the singlet excimer by the olefin. The photochemical (360 nm) addition of tropone to 1,l-diethoxy- and 1,l-dimethoxyethylene yields the adducts (36a and b) in ca. 40% yield.25 This mode of addition is in direct contrast with the thermal addition which affords both the adduct (36c) and the normal [4 21 adduct. This complete reversal of behaviour is also seen in the photochemical addition of 1,l-diethoxyethylene to cyclohexenone which yields (37a) whereas the thermal reaction affords a low

+

22

23 z4

D. K. M. DUC, M. Fetizon, and S. Lazare, J.C.S. Chem. Comm., 1975, 282. J. W. Hanifin and E. Cohen, Tetrahedron Letters, 1966, 1419. P. P. Wells and H. Morrison, J. Amer. Chem. Soc., 1975, 97, 154. T. S. Cantrell, Tetrahedron Letters, 1975, 907.

252

Photochemistry

(39) a ; R1 = R2 = H b; R'-R2 = (CH2)S C; R1-R3 = (CH,),

yield of (37b). The cycloaddition of olefins and acetylenes to the enone (38) affords good yields of the cycloadducts, e.g. (39).26 The study of the photoreactions of oxaenones has been receiving attention in the past few years. In particular a rationale for such reactions has been sought. Recent work (Scheme 3) by MargarethaZ7has shown that electronic factors are

a ; TI = 0, R = H b; n = I , R = H

ratio a; 1 : 1 b; 1 : 2 c; 2 : 3

c; n = I, R = Me

Scheme 3

important in the control of regiospecificity. The influence of alkyl substituents in the photoreaction of the enones (40) has been studied.2B Cycloaddition reactions (at 366 nm) with cyclopentene as the addend occur with all four enones. Only one product (41a) is obtained fron enone (40a), but the unsubstituted enone (40d) yields both cis- and trans-adducts. Enones (40b and d) add to 2,3-dimethylbut-2-ene but enones (40a and c) do not, a fact which is attributed to steric hindrance.

6 H R20

(40) a; b; c; d;

R1-R2 = (CHJ4 R' = H, R2 = Pri R' = H, R2 = Me R' = R2 = H

(41) a; RI-R2 = (CH,), b; RL = H, R2 = Me C ; R' = H, R2 = Pri d ; R' = RZ = H

Dimerization.-The dihydropyrones (40a and b) do not photodimerize, whereas the photodimerization of (40c) shows an interesting solvent dependence.28 Thus in hexane the head-to-head and head-to-tail dimers are obtained in a 65 : 35 ratio, whereas in acetonitrile only the former is produced. In contrast, (40d) shows no solvent dependence in its dimerization reaction and yields only the 28

27 28

A. Kunai, T. Omori, K. Kimura, and Y. Odaira, Tetrahedron Letters, 1974, 2517. P. Margaretha, Helv. Chim. Acta, 1974, 57, 1866. P. Margaretha, Helu. Chim. Acta, 1974, 57, 2237.

Enone Cycloadditions and Rearrangements

253

cis,anti,cis-head-to-headdimer. Margaretha 28 suggests that the electrondonating effect of the alkyl group on the C, reduces the charge density on the double bond and that ground-state dipoledipole interactions become important in non-polar solvents. The solution-phase photolysis of the pyrone (42) at 254nm leads to four products (43)-(46) : the most abundant is the head-to-head dimer (44),although

JFi-JWM 0

0

0

0

so 0

(43)

0

this shows a tendency to photodissociate at 254 nm.29 The head-to-tail dimer (43) yields the cage compound (45) upon irradiation. The same dimer (43) is also the precursor of the cage compound (46) formed when crystals of the monomer are exposed to sunlight. Formation of the dimer (47) is the major reaction when 2-pyridone (1 moll-l) is irradiated ( A > 295 nm).30 At lower concentrations (10-3-10-2 moll-l) the valence isomer (48) becomes an important product.

Both products arise from the singlet state of the pyridone since the reaction could not be quenched by oxygen or hexa-2,4-dienol. Similar behaviour was observed for 5-chloropyridone in ethanol. However, 3- and 4-chloropyridone only yield the [4 + 41 dimers on irradiation in methanol or ethanol. It appears that concentration is the factor which controls whether dimerization or valence bond isomerization occurs. The furocoumarins (49) yield cis,anti,cis-dimers when irradiated directly or upon Michler's ketone-sensitized irradiati~n.~'However, the dihydrofurocoumarins (50) are not so selective and yield both the cis,anti,cis-head-to-head and the cis,syn,cis-head-to-taiIdimers on direct irradiation but only the former 29

91

D. J. MacGregor, Mol. Photochem., 1974, 6, 101. W. L. Dilling, N. B. Tefertiller, and A. B. Mitchell, Mol. Photochem., 1973, 5, 371. J. Gervais and F. C. De Schryver, Photochem. and Photobiol., 1975,21, 71.

254

mo a.

Photochemistry

R

(49) a; R b;

R

cwao R

=

OMe

= Ac

(50) a; R b; R

=

=

OMe AC

L0WoJ

0

0

0

0

O H H O

+

on sensitization. The bisfurocoumarin (5 1) also undergoes [2 21 cycloaddition yielding (52). The furan ethylene bond can also react under certain conditions. 2 Enone Rearrangements The photochemical isomerization of the E-isomers (53) to the corresponding Z-isomers 32 and of the furylacrylic acids (54) has been reported.33 The conjugated ester, methyl cyclopent-1-en-1-carboxylate, undergoes complete deconjugation forming methyl cyclopent-1-en-3-carboxylateupon irradiation in methan01.~~ An intermolecular path is suggested since deconjugation reactions of this type are not likely to occur easily in cyclic systems. The photochemistry of (55) has been d e ~ c r i b e d . ~ ~

w". R

\

0

(53) R

=

Ph, p-NOzCsHa,p-MeOC,H,, or Me

& 2>R (5 5 )

92 99

36

(54)

C02H

R1 = R2 = H R1 =

Ph

Me, R2 = H

0

Ph 0 Ph (57)

E. Wachsen and K. Hartke, Chem. Ber., 1975, 108, 683. G. Karminski-Zamola and K. Jakopcic, Croat. Chem. Actu, 1974, 46, 71 (Chem. A h , 1974, 81, 151 873).

34

(56) R = Ph or Me

Q JR

B. M. Trost and P. J. Whitman, J. Amer. Chem. Soc., 1974, 96, 7421. T. D. R. Manning, Tefrahedron Letters, 1974, 2669.

Enone Cycloadditions and Rearrangements

255

The principal product from irradiation of the enones (56) in propan-2-01, The authors propose cyclohexane, or benzene is 1,1,4,4-tetraphenylb~tadiene.~* that this product arises from the singlet state by addition of an excited-state molecule to a ground-state molecule to afford a biradical (57) which fragments to product and acyl radicals. A reduction product (e.g. 1,3,3-triphenylpropanl-one) is also formed, but only from irradiations in propan-2-01, The E-ionone (58) undergoes reversible cis-trans-isomerization to the 2-isomer The 2-isomer (59) is photolabile and, (59) when irradiated in pentane as well as undergoing cis-trans-isomerization, affords the product (60) which is converted by further photolysis into (61). Related to this work is the report of the irradiation (acetone filter) of the epoxy enone (62).3e This affords two primary products (63) and (64), which could arise by C-C bond fission yielding an intermediate carbonyl ylide (65). The two primary products can be converted into (66) and (67) by further irradiation.

(62)

(63) (64)

R1 = Ac, R2 = H R1 = H, R2 = AC

9 fi

COMe

The enones (68) can be induced to cyclize to (69) using Pyrex-filtered light when BF3-Et20 is added to the An attractive mechanistic rationalization would involve a Cope process but this was excluded by the failure of the enol ether (70)to cyclize. This system undergoes cis-trans-isomerization,which is an efficient method of excited-state relaxation in these systems since the enone 37

K. Maeda, I. Moritani, and A. Sonoda, Bull. Chem. SOC.Japan, 1974,47, 1018. J. Becker, J. Ehrenfreund, 0. Jeger, G. Ohloff, and H. R. Wolf, Helu. Chim. Acta, 1974, 57,

3D

2679. J. Ehrenfreund, Y.Gaoni, and 0. Jeger, Helv. Chim. Acta, 1974, 57, 2704. M. Tada, H. Saiki, K. Miura, and H. Shinozaki, J.C.S. Chem. Comm.,1975, 55.

98

256

Photochemistry

(68)

11 =

1, 2, 3, or 4

(68d) does not cyclize but presumably cis-trans-isomerizes. The authors 3g suggest from spectroscopic evidence that excitation involves a BF,-Et,O-enone charge-transfer complex. The enamino-ketones (71) and (72) also undergo photocyclization to yield (73) and (74).40s41

= CAc, Y = N b; X = N, Y = CAC

(73) a; X

Several examples of the work of Agosta and his co-workers have appeared in the past few years describing the hydrogen-abstraction reactions of cyclopentenones and related systems. The recent publication42 in this series has sought to examine the effect of hydrogen abstraction in 3-substituted cyclopentenyl systems (75). The results of these experiments are shown in Scheme 4. The side-chain olefins arise by hydrogen abstraction by the /%site of the enone system giving the biradical (76). This biradical can either undergo a second hydrogen-transfer step, as illustrated in Scheme 5, or cyclize to bicyclic products. Isomerization of the double bond within the cyclopentene ring also arises viu the biradical (76). The hydrogen transfer in this case is by the alkyl radical. This pathway was identified conclusively by irradiation of the deuteriated materials (77) and (78) (see Scheme 6). do

‘l

I. Ninomiya and T . Naito, Heterocycles, 1974, 2, 607 (Chem. Abs., 1975, 82, 31 429). R. Lenz,J. Org. Chem., 1974,39,2839,2846. A. B. Smith and W. C . Agosta, J, Amer. Chem. SOC.,1974,96, 3289. G.

257

Enone Cycloadditions and Rearrangements

k

k"

15%

(75)

AMe

< 0

I

0,

44%

L

13% Scheme 4

45%

+

52';/,

'0

OK (76) a; b;

X X

= =

CH,, R1 = Me, R2 = H R2 = Me

0, R1 = H,

Scheme 5

The photoaddition of ethers to cyclopentenone affords products of the type (79).48 The mechanism involves the excitation of the enone followed by hydrogen

abstraction from the substrate by the a-carbon of the enone system. Benzophenone can sensitize the reaction. The authors 4s discount the intervention of a ketyl radical, chemical sensitization, mechanism. A full report of the photochemistry of the aryl-substituted cyclopentenones (go), originally published in note form,44has appeared.4s The results show that Is 46

Z. Yoshida and M. Kimura, Tetrahedron, 1975, 31, 221. H. E. Zimmerman and R. D. Little, J.C.S. Chem. Comm., 1972, 698. H. E. Zimmerman and R. D. Little, J. Amer. Chem. SOC.,1974,96,4623.

pLy

258

Photochemistry

H... D

H...

D

p-p 0

H’

H

okD2H Scheme 6

(79)

irradiation leads to phenyl group migration and ring-opening giving the keten (8 1). Acetophenone sensitization and cyclohexadiene quenching were held to demonstrate (not very conclusively) that the unsensitized process involves triplet intermediates, as in Scheme 7. A similarity to cyclohexenone photochemistry 0

Ph H

Ph

(80) a; R b;

R

= =

0 II

Me Ph

(81) Scheme 7

was suggested by formation of the bicyclic intermediate (82) when the irradiations were carried out at low temperature. This intermediate is converted into the keten by both thermal and photochemical routes. The conversion of the enone (83) into the products shown in Scheme 8 upon irradiation in t-butyl alcohol is quite inefficient (0= 0.017).46 This study was aimed to solve one of the problems which has bedevilled the study of cyclohexenone photochemistry, namely that of the concertedness or non-concertedness of the rearrangement to the lumiketone products. When optically active starting material (83) was used all the products were optically active. The formation of 46

D.I. Schuster and B. M. Resnick, J. Amer. Chem. SOC.,1974, 96, 6223.

259

Enone Cycloadditions and Rearrangements H

0 I1

f

(84)

Scheme 8 (84) from (83) therefore occurs in a stereospecific manner by the movement of the C-4 upwards to place the bulkier substituent in the pseudo-equatorial position.

The authors46 conclude that the conversion of the cyclohexenone into the lumiketone is a concerted process despite the fact that the reaction arises from the triplet state, and is inefficient in terms of the utilization of light energy.

@

R2 H&f? R'

0

R1 = R2 = H; 90% R1 = H, R2 = Me; 60% c; R1 = R2 = Me; 65% d; R1 = H, R2 = Ph; 70%

(85) a; b;

m

R1

(86) a; 10% b; 15% c; 30%

0

RY R2

(88) a; R = But b; R = Me

(87)

Hydrogen abstraction by the enone carbonyl groups is also encountered. Thus the oxetans (85) and (86) are formed from the photolysis of the enones (87) at 366 nm in Hydrogen abstraction is also encountered in the photochemistry of the imino-lactone (88a) which undergoes side-chain fragmentation to (88b) in t-butyl alcohol. This process is reminiscent of the Norrish Type I1 reaction. However, if such a mechanism involving intramolecular hydrogen abstraction were operative the quantum yield for product formation would be concentration independent. This is not the case and CD increases with concentration (0,0011 at 0.0255 and 0.0023 at 0.204 moll-'). Thus the authors 48 suggest that a more complex mechanism is operative possibly involving chemical sensitization, as has been proposed for the photoreduction of other imines.49 Gloor and SchaffnerS0 have reported a study of the photoreactions of some 47 48

50

A. Enger, A. Feigenbaum, J. P. Pete, and J. L. Wolfhugel, Tetrahedron Letters, 1975, 959. T. H. Koch, 1. 0. Olesen, and J. DeNiro, J . Org. Chem., 1975, 40, 14. A. Padwa, W. Bergmark, and D. N. Pashayan, J. Amer. Chem. SOC.,1969,91, 2653. J. Gloor and K. Schaffner, Helv. Chim. Acta, 1974, 57, 1815.

260 Photochemistry cyclohexenones induced by irradiation into the nn*(S2)band of the molecules. The reactions reported do not arise from the singlet nn*(SI) state, but could arise from a thermally equilibrated nr*(S2)state. Several reactions occur, e.g. elimination of a 4-substituentY1,3-rearrangement, and a cyclization path involving hydrogen abstraction at C , of the enone. The reactions encountered and probable mechanisms which were checked by deuterium labelling are recorded in Scheme 9.

0

The crystal structure of the product (89) has been determined by X-ray diffraction methods.61 Similar cyclization reactions have been reported for the steroid derivatives which yield the products shown in Scheme 61

6a

G. Bernardinelli and R. Gerdil, Helv. Chim. Acru, 1974, 57, 1846. H. Karvas, F. Mark, H. Wehrli, K. Schaffner, and 0.Jeger, Helv. Chim. Actu, 1974,57, 1851.

261

Enone Cycloadditions and Rearrangements

65% Scheme 10

A novel method for the introduction of a 3-aryl substituent into a cyclohexanone has been reported.SS This route uses the photocyclization of the thioaryl compounds (90) to the cyclic products (91), which can be desulphurized by Raney nickel. This treatment partiaIly reduces the carbonyl function but oxidation of the crude product affords high yields of the ketones (92). The nr* triplet excited state is responsible for the transformation of 3-anilino-6-methylcyclohex-2-en- 1-one into 3,4-dihydro-5-hydroxy-4-methyl1-benza~ocine.~~

The use of benzophenone as a hydrogen-abstracting agent for the free-radical addition of alcohols or dioxolanes to delicate enones has been reported.66 Some examples of this are given in Scheme 11.

63 64

55

A. G. Schultz, J. Org. Chem., 1974, 39, 3185. K. Yamada, M. Kamei, Y. Nakano, and H. Iida, Chiba Daigaku Kogakubu Kenkyu Hokoku, 1974, 25, 73 (Chem. A h . , 1975,82, 15 994). B. Fraser-Reid, D. R. Hicks, D. L. Walker, D. E. Iley, M. B. Junker, S. Y.-K. Tam, R. c. Anderson, and J. Saunders, Tetrahedron Letters, 1975, 297.

262 Photochemistry A full report of the behaviour of irradiated cycloalkenones (93) towards protic solvents has been published.66 Earlier reports of this work have also appeared.57, The study has demonstrated that cis-trans-isomerization of the cycloalkenone double bond precedes the addition to form the adducts (94). Thus irradiation of (93a) in methanol permits the isolation of the trans-isomer

(95a). The thermal stability of this compound is remarkable but nevertheless the thermal addition of methanol does take place at 100 "C.With increasing strain the enone affords more reactive species. Thus the enone (93b) yields the unstable trans-isomer (95b) when irradiated at 195 K. The thermal reaction of methanol takes place at room temperature. The trans-cycloheptenone (95c) can only be obtained at 77 K, and at higher temperatures the addition of methanol is extremely rapid. The authors 68 suggest that although cyclohexenone undergoes dimerization when irradiated in methanol, the formation of the adduct (94; n = 1) indicates that trans-cyclohexenone may have a transient existence. Further work has been reported on the photochemical isomerization of the bicyclohexenones (96).

Irradiation of the verbenone derivatives (97a) leads to the two products (98a) and (98b) in the ratio 1 : l.60 This evidence suggests that the isomerization of verbenone (97b) to isochrysanthenone (98c) takes place with loss of the stereochemistry of the migrating group. A biradical intermediate (99) is considered likely. This result is also borne out by the results of the photolysis of the acetoxy derivative (97c). However, although this compound showed complete scrambling when irradiated neat at room temperature, the ratio of products (98d) and (98c) is strongly dependent upon the solvent in which the reaction is carried out. Thus by careful selection of the conditions it is possible to obtain either one or the other product. These results are shown in Table 2. 67

R. Noyori and M. Kato, Bull. Chem. Sac. Japan, 1974,47, 1460. R. Noyori, A. Watanabe, and M. Kato, Tetrahedron Letters, 1968, 5543. H. Nozaki, M. Kurita, and R. Noyori, Tetrahedron Letters, 1968, 2025. W. Dannenberg, D. Lemmer, and H. Perst, Tetrahedron Letters, 1974, 2133. G . W. Shatter and M. Pesaro, J. Org. Chem., 1974, 39, 2489.

263

Enone Cycloadditions and Rearrangements

0

(97) a; R = CD, b;R=Me C; R ='AcO

(98) a; R1 = H, R2 = CD, b; R'.= CD,, R2 = H c; R1 = R2 = Me d; R1 = H, R2 = OAC e; R1 = OAc, R2= H

(99)

Table 2 Ratio of products obtained from the irradiation of (9lc) 6o Solvent Ratio of(98d) to (98c) 1.9 Cyclohexane 1.2 Neat (room temp.) 1.o Acetic acid 0.9 Cyclohexane-silica gel 0.9 Methanol 0.3 Neat (- 65 "C) Good yields of the cyclopentenes are obtained from the photodecarbonylation of the cyclopentene aldehydes Kinetic analysis of the reaction indicates that decarbonylation arises mainly from the singlet state, although the triplet state does show some reactivity.

R:g2 R1 = R2 =

R1 CHO

Ph

R1 = Ph, R2= p-MeOC,H4 R1 = Ph, R2 = p-CICGH, R1 = Et, R2 = Ph

The ring-size effect upon the photochemical reactions of &unsaturated ketones (Scheme 12) has been studied.6a It is clear from the results that the triplet-state reactions achieved by acetone sensitization are sensitive to the ring size. The four-membered ring system is more efficient in its rearrangement than the five system. With larger rings the rearrangement reaction is very inefficient. The authors 62 suggest that as the ring size increases, the radiationless deactivation of the excited state by twisting of the double bond becomes increasingly important. Surprisingly, products of 1,3-acyl migration (101) and (102) were also obtained in the sensitized studies; usually only 1,2-acyl shifts are encountered in sensitized reactions. However, careful study has shown that these 1,3-acyl shifts are the result of authentic triplet-state reactions. It is argued that intersystem crossing must be extremely inefficient since no triplet products (1,2-acyl shift) are obtained in the direct irradiations. It was also observed that there is an efficiency decrease as the ring size increases in much the same way as was observed for the triplet reactions. The authors 62 suggest, as a result of the photoelectron spectroscopy studies, that the decrease in the efficiency is a result of the increasing electron density in the double bond. Norrish Type I cleavage of the enones is only found 61

63

H. Diirr, P. Herbst, P. HeitkLmper, and H. Leismann, Chem. Ber., 1974, 107, 1835. P. S. Engel and M.A. Schexnayder, J. Amer. Chem. SOC.,1975,97, 145.

<

4

264

t h(D v, acetone =0.45 -

(101)Q = 0.22

6

(103) @

=

= -

+

+ dimers 0

0.15

0

0.09

Q> = 0.28

i v , acetone 4 = 0.25

+

-i-

___,

0 liv,=direct 0.58

+

0

(102)Q (lC,

&

Photochemistry

fl

hv, direct

_____f

+

@ = 0.31

(D = 0.02

0

4) = 0.03

".&I

'
0

0.04 u.u4

07

direct 0 = 0.24

OH

@ = 0.1

direct

___j

@ = 0.18

do

+

Q, =

0.02

a+ OH

(D = 0.03

@ = 0.02

(y%%O$+r OH

Q, =

0.007

Q, =

0.05

Scheme 12

for the cyclobutene (103). A full account of the related photochemical transformations of some 2-(cycloalk-1-enyl)cycloalkanones (104a) has been publ i ~ h e d .The ~ ~ work has shown that the reactivity of the ketones often depends upon the ring size. Thus the ketone (104a) is unreactive to both direct and sensitized irradiation. The ketone (104b) and its isomer (105a) gave a mixtuIe of cyclobutanols (106) as a result of hydrogen abstraction (Norrish Type 11) and rebonding. The reaction of the conjugated ketone also gave the cyclobutanols and it is likely that this reaction involves initial deconjugation to the &-isomer, again by a hydrogen-abstraction path. The authors 63 suggest that the deconjugation arises from the triplet state while the cyclobutanol formation is a singlet-state process. Deconjugation arises in the larger ring ketones (104c and d). The &isomers (105b and c) undergo a [2 + 21 cycloaddition reaction to yield the oxetans (107). The photoreactions of the enone (108) have been reported previously.64a Quantitative details of its transformations have now been published and the 63 64

R. C. Cookson and N. R. Rogers, J.C.S. Perkin I, 1974, 1037. (a) R. G. Carlson, R. L. Coffin, W. W. Cox, and R. S. Givens, J.C.S. Chem. Comm., 1973, 501; (b) R. L. Coffin, R. S. Givens, and R. G. Carlson, J. Amer. Chern. Sac., 1974, 96, 7554.

265

Enone Cycloadditions and Rearrangements 0

(104) a;

71 =

1

b;n=2 c ; 71 = 3

(105) a; b; c;

TI =

1

71 =

2

=

3

ll

(107) a; n = 1 b;n=2

direct irradiation to the isomeric compound (109) occurs with 0 = 0.054. The sensitized reaction (0= 0.25) yields the compound (110).64bThe main part of this communication deals with a study of the stereospecificity of the reaction of the optically active acids (111). Irradiation of the enone (111; 011) = - 130") yields the isomeric enone (1 12; (YD = 147"). At low conversions there is no evidence of racemization of the starting material. However, at longer irradiation

+

0

R '*08)

(109) R = Me

(112) R = CH,C02H

0

(JyJ

CH,C02H

0 (1 13)

times (70 h), when the photoequilibrium has been reached, 72% racemization of both the starting material and the photoproduct has taken place. This means that the racemization results from reversal of the initial reaction, perhaps by a non-stereospecific path. Acetone-sensitized irradiation of the enone (111 ; OLD= + 131") gives the rearrangement product (1 13; (YD = 52") in high yield. In this instance the photoproduct was stable to further irradiation. Analysis of the configuration of this product and of (1 14) leads to the reaction path shown in Scheme 13, whereby the 1,2-migration essential for the formation of photoproduct (1 14) arises with inversion at C-2.

+

266

Photochemistry

Scheme 13

The reactions of the Py-enones (1 15) and (1 16) have provided a useful route for the synthesis of 1,4-diketone~.~~ The irradiation of (1 15) in degassed benzene affords hexane-2,5-dione (35%) by a 1,3-acyl shift, probably from the singlet state (the reaction could not be sensitized or quenched). However, rearrangement of the enone (116) to 3-acetylcyclohexanone (22%) under the same conditions 0

could be sensitized by xanthone and quenched by cyclohexadiene. Thus it is likely that this rearrangement affords an example, albeit a rare one, of a 1,3-acyl shift arising from the triplet state (see also ref. 62). 2-Acetylmethylenecyclohexane does not undergo the 1,3-acyl shifts normally associated with r63/unsaturated enones.66 The reactions of this enone and some substituted derivatives are all of the Norrish Type I1 class and the reaction products depend on the conformation adopted by the biradical intermediate. 1,3- and 1,5-Acyl shifts have been reported to occur on irradiation (300nm) of the E- and Z-retroionones (1 17).67 Considerable differences are found in the ratios of 1,3 : 1,5-acyl shift products. Compounds (1 17a-d) favour 1,3-shift (1 18) whereas (1 17-g) favour 1,Sshift (1 19). The reaction arises from the singlet excited state since sensitization leads only to Z-E-isomerization, as does irradiation at 254 nm. The authors 67 rationalize their observations in terms of the Houk and Northington 68 proposals for such enone photochemistry. The 65 66

68

K. G. Hancock, J. T. Lau, and P. L. Wylie, Tetrahedron Letters, 1974, 4149. J. C. Dalton and H.-F. Chan, Tetrahedron Letters, 1974, 3351. A. van Wageningen, P. C. M. van Noort, and H. Cerfontain, J.C.S. Perkin 11, 1974, 1662. K. N. Houk and D. J. Northington, J . Amer. G e m . SOC.,1972,94, 1387; K. N. Houk, D. J. Northington, and R. E. Duke, jun., J. Amer. Chem. SOC.,1972,94, 6233.

267 Enone CycIoadditions and Rearrangements 1,3-acyl shift products are stable to further photolysis whereas the 1,5-products (119e and f ) afford 1,3-products (118e and f). The 1,5-product (119g) is photostable.

Ph

Hassner and his co-workers69 have reported an example of 1,3-benzoyl migration in the rearrangement of the triene (120) to (121). A reinvestigation 70 of the photochemistry of the norbornenone (122) has shown that this compound undergoes a 1,3-acyl shift to (123) under sensitized (acetone) conditi~ns.'~This is a further example 73 of such triplet-sensitized reactions (see also refs. 62 and 65). The failure to observe this reaction in the earlier report 70 could be due to analytical problems and also to the fact that the product (123) also undergoes 1,2-acyl shifts to the tricyclic ketone (124).71 The reaction of the ketone (122) can be sensitized by acetone, acetophenone, or benzophenone. However, the efficiency of the reaction falls off dramatically in the case of the last two sensitizers. It is particularly surprising that acetophenone should be so inefficient, since it has been reported74 that the triplet energy of (122) is 291.2 kJ mol-l. This value was based upon the phosphorescence studies but the 72p

6B 70

71 72

73

D. J. Anderson, A. Hassner, and D. Y. Tang, J. Org. Chem., 1974, 39, 3076. J. Ipaktschi, Tetrahedron Letters, 1969, 2153; Chem. Ber., 1972, 105, 1840. M. A. Schexnayder and P. S. Engel, Tetrahedron Letters, 1975, 1153. P. S. Engel and M. A. Schexnayder, J . Amer. Chem. SOC.,1972,94,9295. R. K. Murray, jun. and K. A. Babiak, Tetrahedron Letters, 1974, 319. K . G. Hancock and R. 0. Grider, J.C.S. Chem. Comm., 1972, 580.

268

Photochemistry

present paper points out that the enone (122) has no phosphorescence when it is pure. Thus the previous value is gravely in error. Kinetic studies have shown that triplet sensitizers (benzophenone and acetophenone) can form an excited-state complex with the enone which competes favourably with energy transfer. The problem of the interaction of acetophenone with another enone (125) has also been observed 75 and the reaction fails to yield an isolable product. This failure to populate the triplet state of the enone (125), which is reported 76 to yield (126) on

direct irradiation and upon acetone sensitization, suggests that the energy of the enone is greater than that of acetophenone but less than that of acetone, i.e. between 310 and 326.8 kJ mo1-l. Murray and Babiak 73 previously reported the acetone-sensitized conversion of 2-protoadamantanone (127a) into the dehydroadamantanone (128a). A full

(127) a; n

=

1

(128) a ; n = 1

report of this work has now been published.?? The conversion fits into the scheme whereby triplet-excited py-enones rearrange by a 1,2-acyl shift. Another study 78 has shown that (127b) is converted into (128b) upon sensitization. Direct irradiation of (127b) affords the product (129) of 1,3-acyl migration. Acetone sensitization of the enone (130) yields the isomer (131) as a result of a 1,2-acyl migrati~n.?~ This reaction is to be contrasted with the direct irradiation of the ketone (130) which yielded the cage compound (132) by 1,3-acyl shift and [2 + 21 addition.*O 76

P. S.Engel, M. A. Schexnayder, W.V. Phillips, H. Ziffer, and J. I. Seeman, Tetrahedron Letters, 1975, 1157.

m 77

8o

J. R. Williams and H. Ziffer, Chem. Comm., 1967, 194, 469; Tetrahedron, 1968, 24, 6725. R. K. Murray, jun., T. K. Morgan, jun., and K. A. Babiak, J . Org. Chem., 1975, 40, 1079. R. K. Murray, jun., D. L. Goff, and R. E. Raytch, Tetrahedron Letters, 1975, 763. K. Yano, Tetrahedron Letters, 1974, 1861. R. L. Cargill, T. Y. King, and A. B. Sears, J. Urg. Chem., 1971,36, 1423.

269

Enone Cycloadditions mid Rearrangements

P 0

( I 32)

@ 0

b; R

=

Me

(1 35)

(134)

The enones (133) add methanol to afford the addition products (134),81 believed to arise by a protonation of the twisted double bond. This supports the argument that one of the deactivation paths for the triplet r r ~ * state is twisting about the double bond. Other products are also formed, e.g. the 1,3-acyl migration product (135) from (133b). Compound (136) is formed from the hydroxysantonenes (137), presumably by a 1,2-acyl shift as outlined in Scheme 14.82 Other products (138) are also formed

'0 (136)

Scheme 14

but these are photolabile and are converted into the pentanolides (139) presumably by a Norrish Type I pathway (Scheme 15). The initial products (138) are most likely formed by a type of di-rr-methane process. A similar reaction is 81

82

J. Pusset, M.-T. LeGoff, and R. Beugelmans, Tetrahedron, 1975, 31, 643. D. Stuart, R. East, T. B. H. McMurry, and R. R. Talekar, J.C.S. Chem. Comm., 1974, 450. 10

270

Photochemistry

fi

0

0

0

0

(139)

Scheme 15

encountered in the conversion of the enone (140) into the tetracyclic ketone (141 ; Odir = 0.02; = 0.3).83 As a follow-up to their worka4 on the photorearrangements of the dioxides (142), Mukai and his co-workers 85 have examined the mechanism of the reaction in more detail. The diphenyl dioxide (142; R1 = R2 = Ph) was shown to

Q 0

Q

0

ph$o

(143)

rearrange from an excited state which, since it could not be sensitized or quenched, was probably a singlet. The product from the reaction was the lactone (143). When the irradiation was carried out in a KBr disc at 77 K the formation of a keten band at 2100 cm-I in the i.r. suggested the presence of the keten (144) as an intermediate in the conversion. When the KBr matrix was allowed to warm up, the keten band was replaced by a band characteristic of the lactone (143) showing this latter step to be thermal. Other evidence has been collected which clearly shows that the rearrangement from the keten to the lactone takes place via an ionic intermediate (145). The mechanistic path suggested is proposed as Z. Goldschmidt and U. Gutman, Tetrahedron, 1974, 30, 3327. T. Tezuka, R. Miyamoto, T. Mukai, C. Kabuto, and Y . Kitahara, J. Amer. Chem. SOC.,1972, 94, 9280.

T. Tezuka, R. Miyamoto, M. Nagayama, and T. Mukai, Tetrahedron Letters, 1975, 327.

27 1

Enone Cycloadditions and Rearrangements

good evidence for the interaction of the enone-r system and not for enone-lone pair overlap. Sasaki et aLa6previously reported the singlet-state (induced by direct irradiation) rearrangement of the enone (146a). Goldschmidt and Bakal have reinvestigated the reaction and have reported that the acetone-sensitized process of the same enone affords two products (147a) and (148). The influence of the carbonyl function in this reaction appears to be profound since the irradiation of the diene (146b) affords products dependent upon whether the reaction is singlet or triplet. Thus the acetone-sensitized reaction yields the diazabarbaralane derivative (149b) whereas direct irradiation gives the semibullvalene (147b). In contrast with these results the triplet-state reactions of the dienes (146c and d) afford the semibullvalenes (147c and d).

(146) a; X b; X

= =

X d; X

= =

C;

(147) a; X 0 b; X CH, C; X OCH2CH20 d; X HO, H

= = =

=

0 CH, OCH,CH,O OH, H

( 1.18)

The bicyclic enones (150) have been synthesized and irradiated under both direct and sensitized conditions.Ba Direct irradiation of (150a) gave a single product (151a) whereas (150b) gave four products. The major photoproduct was identified as (151b), again a product of 1,3-acyl migration. Another ketoalcohol (152) was also identified from this reaction and this product could arise by a 1,3-acyl shift from (150b) or in the photoproduct (15lb). Interestingly (151b) is not photostable and affords an equilibrium mixture of itself and starting material. The excited state responsible for photoisomerization of (150b) was established as a triplet having substantial nr* character. This could well be yet another example of a 1,3-acyl shift from the triplet state. The photoelectron spectrum of the trienone (153) shows that there is no conjugation between all the isolated There is, however, a strong interaction between the non-bonded electron pair and the highest filled level of the

89

T. Sasaki, K. Kanematsu, and K. Hayakawa, J. Chem. SOC.(C), 1971, 2142. Z. Goldschmidt and Y. Bakal, Tetrahedron Letters, 1974, 2809. C . Lam and J. M. Mellor, J.C.S. Perkin ZI, 1975, 412. W. SchBffer, H. Schmidt, and A. Schweig, Tetrahedron Letters, 1974, 1953.

272

Photochemistry

R = Ph b;R=H

(150) a;

(151) a; R

= Ph b ; R = H

(152)

(153)

butadiene moiety, but it is not known whether this has a bearing on the photochemistry of the molecule. Irradiation of the dienone (154) at 196 K results in the formation of CO, cyclo-octatriene (@ = 0.68) and the tricyclic compound (155; CD = 0.14).B0 Both these reactions arise from the singlet state. The tricyclic product (155) was synthesized independently by the reaction shown in Scheme 16. Michler's

@ Q $ & /--

H

ketone-sensitized irradiation of the dienone takes a different path and affords the dihydrobarbaralone (156) from the triplet state with a quantum yield of 0.89. Previously Paquette et aLQ1had shown that the dienone (157) rearranged to the bicyclic ketone (158). Schuster and KimQ0have now shown that this reaction arises from the triplet state (a = 0.81) and that any reaction arising from the direct irradiation even with a quencher present does so from a barely quenchable triplet state. Thus this reaction and that of (154) involve triplet 1,2-acylmigrations. M e 0 OMe h v ,

& M

H+,

(155)

Scheme 16 O0

D. I. Schuster and C. W. Kim, J. Amer. Chem. SOC., 1974, 96, 7437. L. A. Paquette, R. F. Eizember, and 0. Cox, J . Amer. Chem. SOC., 1968, 90, 5153.

273

Enone Cycloadditions and Rearrangements

The cis-enone (159) undergoes cis-trans-isomerization by irradiation of a degassed solution in benzene using Pyrex-filtered light.g2

3 Photoreactions of Thymines etc. The addition of the thio-radical derived from cysteine (160), produced by its irradiation in acetone-water, to cytosine (161) results in the formation of 5-Scysteinyl-5,6-dihydrouraci1(162;24%).93 An analogous product is obtained when

0

(163) a; R1 = R2 = K3 = H b; R1 = R2 = Me, R3 = H c; R1 = R2 = H, R3 = Me

d ; R1 = R2 = H, e ; R1 = R3 = H, f ; R1 = H, R2 = g; R1 = R3 = H,

R3 = Br R2 = ribosyl ribosyl, R3 = hexyl R2 = Me

the irradiation is carried out using butanethiol. Two other products, dihydrouracil (72%) and uracil (163a; 273, are also formed.e3 Another study has shown that the photoreaction of uracil (163a) and thymine (163c) with cysteine (160) yields several addition products together with dimers of the pyrimidine bases.04 The mechanism suggested for the formation of the adducts and the dimers involves population of the triplet state of the pyrimidine base. This either collides with a ground-state molecule of base to yield the dimers or else abstracts hydrogen from the cysteine to afford a radical pair from which the addition products are formed. Elad and co-workersV6have shown that the photochemistry of dimethyluracil (163b) in propan-2-01 solution leads to the alcohol O2

G. L. Lange and T.-W. Hall, J. Org. Chem., 1974, 39, 3819.

OS

N. C. Yang, R. Okazaki, and F. Liu, J.C.S. Chem. Comm., 1974,462.

*'

G . J. Fisher, A. J. Varghese, and H. E. Johns, Photochem. and Photobiol., 1974, 20, 109. D. J. Leonov, J. Soloman, S. Sasson, and D. Elad, Photochem. and Photobiol., 1973, 17, 465.

274

Photochemistry

adduct (1 64a), probably via hydrogen abstraction. Shetlar Be has examined the photochemical behaviour of dimethyluracil in primary alcohols and has observed that similar products (163b and c) are formed. Shetlar's study was carried out at X > 260nm and at concentration of 7 x 10-smoll-l. In more dilute solutions mol I-l) of dimethyluracil in ethanol or propan-2-01 there is evidence that another product, perhaps (165), is formed. This is more in agreement with an earlier report of this rea~tion.~'It is clear that the concentration at which the reaction is carried out is critical to the type of product. Adducts (166) and (167) are formed in the irradiation (sensitized and direct) of thymine (163c) in the presence of g l ~ t a t h i o n e . ~ ~

(164) a; R1 = R2 = Me b; R1 = Me, R2 = H C;

R' = Et, R2 = H

66) R

=

kf ,CON HC H,CO ,H CH,CH, NHCO CH, CH, CH (N H ,)CO ,H

,CON HCH,CO,H 67) R = SCH,CH,

N HCOCH,CH,CH(N H,)CO,H 5-Bromouracil(l63d) undergoes rapid reaction when irradiated in the presence of cysteine (160) to yield the products (168a and b) and a saturated adduct of unknown ~ t r u c t u r e .The ~ ~ photochemical disappearance of (163d) in the presence of an H-donor, e.g. H 2 0 ,as radical scavenger has a quantum yield of 1.8 x Campbell et d 1 O 0 have observed that the quantum yield for disappearance can be enhanced from this value by changes in the dielectric constant of the H-donor and in THF @ = 45 x (in methanol @ = 25 x However, there is no linear correlation between the reactivity and solvent polarity. The authors loo suggest that the increase in reactivity is a result of enhanced H-abstraction from the solvent cage which prevents cage recombination to starting material. The irradiation of (163d) in 0,-H,O has also been studied.lo1 M. D. Shetlar, Tetrahedron Letters, 1975, 477. S. Y. Wang, Nature, 1961, 190, 690. A. J. Varghese, Photochem. and Photobiol., 1974, 20, 339. A. J. Varghese, Photochem. and Photobiol., 1974, 20, 461. l o o J. M. Campbell, D. Schdte-Frohlinde, and C. Von Sonntag, Phorochem. and Photobiol., 1974, 20, 465. lol E. Gilbert and C. Cristallini, Z . Naturforsch., 1973, 28b, 615. 97

Enone Cycloadditions and Rearrangements

275

0

(168) a ; R 1 = SCH,CH(NH,)CO,H, R2 = H b; R1 = H, Rz = SCH2CH(NH2)COzH

Uridine (163e) is formed by the U.V. irradiation (254 or 265 nm) of 5-hexyluridine (163f) in neutral so1ution.lo2 The dealkylation proceeds by an intramolecular reaction (Scheme 17) forming a cyclobutane derivative (169). This

Hyc4Hg 0

(163f)

I? v

HN

__j

OAN

R2

0

(1634 R2 = ribosyl

Scheme 17

undergoes photodecomposition to uridine and hex-1-ene. A similar cyclobutane (170) was formed as a mixture of diastereoisomers by photoaddition of hex-l-ene to l-methyluracil (163g).lo2 The uracil derivative (171) photocyclizes to (172).lo3 A full report of the photoaddition of olefins to the imine linkage of the azathymine (173b) and the azauracil (173a) has appeared,loq following initial 0

loa E.

Sztumpf-Kulikowska and D. Shugar, Acfa Biochim. Polon., 1974, 21, 73 (Chem. Abs.,

1974, 81, 100 904). loa lo4

F. Yoneda and T. Nagamatsu, Hererocycles, 1974,2, 153 (Chem. Abs., 1974,80, 146 104). J. S. Swenton and J. A. Hyatt, J. Amer. Chem. SOC.,1974, 96, 4879.

276

Photochemistry 0

+ R

=

b; R

=

(173) a ;

Mf2

H Mc

Scheme 18

(173b)

--+ Me Scheme 19

publication in note form.lo5 Typical of this process is the acetone-sensitized addition of isobutene to the uracil (173a) (Scheme 18) and of 2,3-dimethylbut2-ene to the thymine (173b) (Scheme 19). Swenton et al.lo6have also examined the photochemical addition of 1,3-dirnethyluracil to keten diethylacetal yielding (174) and (175), to t-butyl vinyl ether yielding (176a) and (177a), and to vinyl

(174)

(175)

(176) a; R = OBut b; R = OAC

R = OBut b; R = OAC

(177) a;

acetate yielding (176b) and (177b). The structures of the adducts were established by chemical and spectral studies. Further work by Swenton and B a l c h ~ n i s , ~ ~ ~ using the photochemical addition of vinyl acetates (178) to 6-azauracil to yield azetidines, has revealed a versatile high-yield synthesis of 5-substituted 6-azauracils (179). The reaction path is shown in Scheme 20.

(178) a ; R2 = H, R3 = Me b; R2-RS = (CH,),

1 79)

Scheme 20 J. A. Hyatt and J. S. Swenton, J.C.S. Chem. Comm., 1972, 1145. J. S. Swenton, J. A. Hyatt, J. M. Lisy, and J. Clardy, J. Amer. Chem. SOC., 1974, 96, 4885. J. S. Swenton and R. J. Balchunis, J. Heterocyclic Chem., 1974, 11, 453.

lob '06

lo'

277

Enone Cycloadditions and Rearrangements

Irradiation (A > 280 nm) of aqueous acetone solutions of uracil (163a) affords the oxetan (18O).lo8 The photoreaction of 3-methyl-4-thiouracil (181) with 2-methacrylonitrile in CH,CI, at 0 "C affords two products (182) and (183).108,110 The indications are that the thietan (184) is formed initially, and then ring-opens to an intermediate which can be trapped as (185) when the irradiation is carried out in methanol at room temperature. At - 10 "C in methanol (183) is the sole product. In CH,Cl, the ring-opened thietan-derived intermediate dimerizes to afford the thermally unstable intermediate (186) which yields the two photoproducts (182) and (183). Other thiouracil derivatives have been reported to yield thietans (187)-( 189) when irradiated in the presence of 2-metha~rylonitrile.~~~

H

lo8 log l10 111

A. J. Varghese, Photochem. and Photobiol., 1975, 21, 147. C. Fombert, J. L. Fourrey, P. Jouin, and J. Moron, Tetrahedron Letters, 1974, 3007. P. Jouin and J. L. Fourrey, Tetrahedron Letters, 1975, 1329. J. L. Fourrey, P. Jouin, and J. Moron, Tetrahedron Letters, 1974, 3005.

278 Photochemistry The influence of micellar (sodium dodecyl sulphate) effects upon the photochemical (255 nm) dimerization of uracil (163a) has been studied.l12 The best yields of products (190) are obtained in degassed aqeuous solutions where the 2.3%), (190b; 0 = 4.1 x 3.1%), yields are (190a; 0 = 3.1 x 18.9%) and (190d; @ = 1.0 x 75.6%). In the (19Oc; CD = 2.5 x micellar solutions (degassed) the greatest effect is shown in the decrease in dimer (19Oc; Q, = 5.0 x 6.0%) and the increase in the dimers (19Oa) and (19Ob).

(190a)

(190b)

(190c)

(190d)

Leonard and Cundall 113 have continued their study of intramolecular photoaddition of variously linked thymine units. The 3,3'-molecule (191) undergoes a very slow photoreaction upon direct irradiation to give cyclobutanes. A much

0

I

0

cx

(H2C),

0 (193) lx2 lr9

?I =

0

H

2, 3, or 4

J. H. FendIer and G. Bogan, Photochem. and Photobiol., 1974,20, 323. N. J. Leonard and R. L. Cundall, J . Amer. Chem. Soc., 1974,96, 5904.

279

Enone Cycloadditions and Rearrangements 0

0

O

N

(195)

(197)

better yield is obtained on irradiation in acetone: the cis-syn-compounds (192) are produced. Direct irradiation also gives slow reaction with the 1,5’-linked units (193) and triplet-sensitized irradiation is again more efficient in yielding products (194), which have the trans-anti geometry. The cis-anti-compounds (195) are encountered in the sensitized irradiation of (196). Golankiewicz and Skalski 114 have reported the u.v.-induced intramolecular cycloaddition of the 1,l’-dithymine (197) to yield (198).

4 Photochemistry of Dienones Linearly Conjugated Dienones.-2-E-Isomerization of the 7 : 3 dodecadienoate mixture (199a and b) was achieved by sensitized (ET 3 222 kJmol-’)

(199a) (1 99b)

irradiation.l15 This procedure gave a photostationary state mixture of 1 : 1. It is argued that the triplet energy of the dienoate must be ca. 193-201 kJ mol-l. Liu and his co-workers116have continued their study of the photochemistry of

116

K. Golankiewicz and B. Skalski, Bull. Acad. polon. Sci., Ser. Sci. chim., 1974, 22, 393 (Chem. A h . , 1974, 81, 120 569). C. A. Henrick, W. E. Willy, D. R. McKean, E. Baggiolini, and J. B. Siddall, J. Org. Chem.,

116

V. Ramamurthy and R. S. H. Liu, J. Amer. Chem. SOC.,1974, 96, 5625.

l1’

1975, 40, 8 .

280

Photochemistry

ionyl and ionylidene derivatives. In a previous report 117 the isomerization of the compounds (200a-c) was shown to go only one way and produce the corresponding 7-cis-isomers. However, when the study was extended to the aldehyde (200d), which is an important intermediate in the synthesis of Vitamin A, the

(200) a; Y = H b ; Y = CO,R

Y d; Y

C;

= =

CN CHO

photochemical isomerization to the 7-cis-isomer failed. The authors 116 suggest that this failure to isomerize is an intrinsic property of the ionylidene triplet state. There is definite evidence that triplet energy is transferred from the sensitizer, in this instance 9,10-dimethyl-l,2-benzanthracene (ET = 185.6 kJmol-l), to the compound (200d). This phenomenon was manifested in isomerization around the 9,lO-double bond affording the transtrans-isomer and the trans-cis-isomer in the ratio 6 : 4. This ratio was confirmed as a real photostationary state. Liu et aZ.l16 report that there is an obvious trend in the series of compounds studied which shows that geometric isomerization around the 7,8-double bond shows a decay ratio prohibitively towards the trans-isomer when the conjugation within the molecule involves four or more bonds. Photochemical ring-opening in benzene solution to the allenic keten (201) explains the conversion of the cyclobutenone (202) into the lactone (203; 8O%).ll8 A similar route explains the formation of (204) from (205). Such ring-opening

I

Ph

117

11*

V. Ramamurthy, Y. Butt, C. Yang, P. Yang, and R. S. H. Liu, J. Org. Chem., 1973, 38, 1247. F. Toda and S. Todo, Chem. Letters, 1974, 1279.

28 1

Enone Cycloadditions and Rearrangements

of a cyclobutenone has been reported previously.'lU Krantz 120 has reported a laser flash study of the ring-opening of benzocyclobutenone (206) to the keten (207). The thermal reversal is slow in this instance. However, the keten (208), formed by the photolysis of the a-pyrone (209a), reverts rapidly to starting material (lifetime of the keten is 2.4 ps at 26.5 "C). The photochemical reaction of a-pyrone (209b) in methanol affords the two products (210) and (211).121

R'

0

R1 = R2 = R3 = H b; R1 = R3 = Me, R2 = OH c ; R1 = R2 = H, R3 = C0,Me

(209) a;

(210)

The synthesis of the iron carbonyl adduct of cyclobutadiene carboxylic acid (212) has been reported.lz2 This synthesis involved photolysis of the pyrone (209c) in THF solution to yield the bicyclic lactone (213) in the presence of an excess of iron pentacarbonyl. The ester (212a) obtained from this process is lightsensitive, but hydrolysis yields a more stable acid (212b) in a maximum yield of 21%.

flCo2R I

(212) a; R = Me b: R = H

C0,Me (2 1 3)

Irradiation of the steroidal enones (214) at 350 nm in pyridine-trifluoromethyl iodide yields the trifluoromethylated dienones (215).123The pyrrolines (216) are the products of irradiation of the pyridazone (217) in methan01.l~~ The photochemistry of linearly conjugated cyclic dienones has provided many interesting results over the past few years. A further study has uncovered yet another facet of this chemistry. This deals with the dimerization of the dienone J. E. Baldwin and M. C. McDaniel, J. Amer. Chem. SOC.,1968, 90, 6118. A. Krantz, J . Amer. Chem. SOC.,1974, 96, 4992. lZ1 M. Muto, T. Nyui, Y. Butsugan, and T. Bito, Nagoya Kogyo Daigaku Gakuho, 1972,24, 117 (Chem. A h . , 1974, 80, 120 692). l Z 2J. Agar, F. Kaplan, and B. W. Roberts, J. Org. Chem., 1974, 39, 3451. la% G. H. Rasmusson, R. D. Brown, and G . E. Arth, J . Org. Chem., 1975, 40, 672. 15* T. Tsuchiya, M. Hasebe, H. Arai, and H. Igeta, Chern. and Pharm. Bull. (Japan), 1974, 22, 2276 (Chem. A h . , 1974,81, 179 813). 11*

lZo

282

Photochemistry

R

&

0 (214) a; R b; R C; R

d; R

= = = =

CF,

p-OAc, (Y-H P-Ac, a-OAc

(2 15 )

fl-OCH2CH2CHz-n: /3-CH(CH3)(CH2)3CH(CH3)-,~

H (216) a; R = H b; R-R = CH2

(217)

(218) 125 which yields products from a nr* triplet state when irradiated in cyclo-

hexane. Surprisingly no monomeric products were isolated. The products were identified as the dimers (219) and (220) on the basis of their spectral properties and X-ray structural analysis.126It is proposed that a concerted [4 + 21 photoallowed process is followed by 1,3-acyl migrations to afford the isolated products (Scheme 21).

_j_

0

lZ6 lZ6

Y

H. Hart, T. Miyashi, D. N. Buchanan, and S. Sasson, J. Amer. Chem. SOC.,1974,96,4857. C. G. Biefeld and B. L. Barnett, Acfa Crysf., 1974, 30B, 2411.

Enone Cycloadditions and Rearrangements

283

Cross-conjugated Dienones.-Irradiation of the vinylcyclohexadienone (221) in methanol results in formation of the dienone (222).lZ7Careful analysis of the photolysate failed to show the presence of an intermediate between the starting material and the final product. A route to the product (222) was suggested by the irradiation of the labelled starting material (221b) which gave the product (222b) with the labels as shown. This path (Scheme 22) rules out a di-r-methane

(221) a; R = Me b; R = CD,

route, involving instead bicyclohexenone formation, in common with the rearrangement of other cyclohexadienones, followed by a thermal transformation of the resultant vinylcyclopropane intermediate. A full account of the photochemical transformations of the cyclohexadienone (223), originally published in note form,128has appeared.120 Several products are formed from the dienone which rearranges from the triplet state with high efficiency (0= 0.95). The products are shown in Scheme 23. Kinetic studies have shown that there are two

0

OBut c1

+

clQ c13c

Scheme 23 la*

lZs

H. Hart and M. Nitta, Tetrahedron Letters, 1974, 2113. D. I. Schuster, K. V. Prabhu, S. Adcock, J. van der Veen, and H. Fujiwara, J. Amer. Chem. Soc., 1971, 93, 1557. D. I. Schuster and K. V. Prabhu, J . Amer. Chem. Soc., 1974,96, 3511.

284

Photochemistry

distinguishable triplet states, one which gives rise to the lumiketones (224) and (225), and the other which yields a phenol. The specificity of the formation of the lumiketones was also examined in the light of earlier investigations into such stereospecificity. Schuster and Prabhu 129 reason that electronic effects are dominant in the disrotatory closure of the excited-state dienone and are more powerful than steric factors which originally were thought to be important in the cases considered by Rodgers and Hart.130 Extension of cyclohexadienone studies to molecules containing silicon has been re~0rted.l~’ The silacyclohexadienones (226) have nm* bands in the 350400 nm region and undergo conversion into the cyclopentenones (227) when

& R2/ \R1 (226) a ; R1 b; R‘ C;

= =

R* =

R2 = M e R2 = Ph Ph, R2 = Me

,R1

Si. I “OBut

R2

(227)

p, Si

/ \

R2 R’

&Rl ‘R2

(229)

(228)

irradiated at 350nm in t-butyl alcohol. The reaction is thought to follow the same path as that for the more conventional cyclohexadienones, to involve the intermediacy of a zwitterion (228), and to stop at this stage with the products being formed by nucleophilic attack of the solvent on the silacyclopropane moiety. This route is preferred, according to the since if the rearrangement followed the path to intermediate (229) then attack by solvent would give rise to both 2- and 3-substituted cyclopentenones. The photorearrangement of the cross-conjugated dienone (230) in 45% aqueous acetic acid gave a 50% yield of the hydroxy-ketone (231).132 This material was converted, by a series of reactions, into 4-epiglobulol (232). A cyclohexadienone

rearrangement has been proposed133 to account for the formation of rn-cresol from the irradiation of methoxybenzene. The authors 133 reason that rn-cresol is formed by photochemical isomerization of the p-tautomer (233) of p-cresol into a bicyclohexenoiie which subsequently ring-opens. Isomerization of this type is well established in cyclohexadienone photochemistry. An analogous rearrangement has been proposed to account for the formation of the isocoumarin la0 131 132 laS

T. R. Rodgers and H. Hart, Tetrahedron Letters, 1969, 4485. T. H. Koch, J. A. Sonderquist, and T. H. Kinstle, J. Amer. Chem. SOC.,1974, 96, 5576. D. Caine and J. T. Gupton, J. Org. Chem., 1975, 40, 809. J. J. Houser, M.-C. Chen, and S. S. Wang, J . Org. Chem., 1974, 39, 1387.

285

Enone Cycloadditions and Rearrangements 0

0 (234) a ; R = Me

(235)

b;R=H

(234) from irradiation of the isoflavone (235) in Previous studies on the irradiation of the aroylchromenes had shown that they did not afford an enol when the methyl group was attached to the chromophore (236a).135 However, when the methyl group is attached to the aroyl group (236b) an enol is formed. The picture is further complicated by the fact that when the dimethyl derivative (236c) is irradiated an enol is also formed, and in this instance the enol (237)

(236) a; R1 = H, R2 = Me b ; R' = Me, R2 = H C; R1 = RZ = Me

(237)

involves the ~ h r o m o n e .This ~ ~ ~enol can be trapped by suitable dienophiles, and deuteriation studies have show that it is formed by a thermal 1,7-hydrogen shift from the photochemically produced enol(238). The latter is formed by hydrogen abstraction using the aroyl carbonyl group. However, hydrogen abstraction by the dienone chromophore has been reported 13' in the photochemical conversion

oer

,CH,R

I1v

0

0

(239) a; R b; R

= =

H

CH=CH,

0

Q? N. Ishibe, S. Yutaka, J. Masui, and Y. Ishida, J.C.S. Chem Comm., 1975, 241. W. A. Henderson and E. F. Ullman, J. Amer. Chem. SOC.,1965, 87, 5424. l a 6 P. G. Sammes and T. W. Wallace, J.C.S. Chenr. Comm., 1974, 562. S. C. Gupta and S. K. Mukerjee, Indian J . Chem., 1973, 11, 1263.

194

ls6

286

Photochemistry

of karanjin (239) into photokaranjin (240). A study of the photochemical processes in the naphthoquinone methide (241) has been pub1i~hed.l~~ 5 1,Z-, 1,3-, 1,4-, and 1,5-Diketones The photochemistry of 1,2-diketones is discussed in a review of halogenovinylene carbonate chemistry.139 The emission characteristics of camphorquinone 140 and a CIDNP study of camphorquinone photochemistry with aldehydes 141 have been reported. Deltic acid (242a) has been prepared via the photochemical decarbonylation of the squaric acid derivative (243) in hexane soIution using a Vycor filter to

(242) a; R b; R

=

=

H SiMe,

(243)

yield (242b). The silyl groups were removed by treatment with n-butan01.l~~ Double decarbonylation of the diketone (244) affords the thio-ozonide (245).143 The irradiation (light filtered through naphthalene in n-hexane) of methyl pyruvate in the presence of methyl-substituted olefins affords ethers, oxetans (from a quenchable triplet state), or hydroxyolefins from a singlet state, depending upon the nature of the olefin used (Scheme 24).144 Bos and his co-workers146 have reported further additions of 1,2-dicarbonyl compounds to acetylenes. These reactions involve photochemical addition of benzil, biacetyl, 1-phenylpropane-lY2-dione,and phenylglyoxal to the propynes (246), and afford the diones (247), presumably via the oxeten, e.g. (248). The photoenolization of the dione (249) has been Maier has reviewed the synthesis of cyclobutadienes, including the photochemical syntheses by decarbonylation and decarboxylation of anhydrides.14' The diones (250a-c) yield the olefins (251) by double decarbonylation on irradiation in methylene ch10ride.l~~ Formation of the olefins suggests that the 138

lS9 140

J. Wirz, Helv. Chim. Acta, 1974, 57, 1283. H.-D. Scharf, Angew. Chem. Internat. Edn., 1974, 13, 520. D. B. Larson, J. F. Arnett, A. Wahlborg, and S. P. McGlynn, J. Amer. Chem. SOC.,1974,96, 6507.

141 lPa 143 144

146 146

14'

148

K. Maruyama and T. Takahashi, Chem. Letters, 1974,467. D. Eggerding and R. West, J. Amer. Chem. SOC.,1975, 97, 207. H.-J. Kyi and K. Praefcke, Tetrahedron Letters, 1975, 555. K. Shima, T. Kawamura, and K. Tanabe, Bull. Chem. SOC. Japan, 1974, 41, 2347. A. Mosterd, H. J. Matser, and H. J. T. Bos, Tetrahedron Letters, 1974, 4179. Y. Ogata and K. Takagi, J. Org. Chem., 1974, 39, 1385. G. Maier, Angew. Chem. Znternat. Edn., 1974, 13, 425. A. P. Krapcho and B. Abegaz, J. Org. Chem., 1974,39, 2251.

Enone Cycloadditions and Rearrangements

1 Phz=

RR = R'

-

287

=

H, R? = Ph; 50, 27;i

-

Scheme 24

MeC

SR

(246) R = Me, Et, But, or Ph

w R3

(247)

Me &Me

Ph

0 (249)

cyclopropanone (252), the result of monodecarbonylation, is an intermediate. The dione (250d) behaves differently and yields the lactone (253) under the same reaction conditions. The photochemistry of dihydro- and methyl dihydrousmic acids has been

149

K. Takahashi, M. Takani, and A. Fukomoto, Chem. and Pharm. Bull. (Japan), 1974, 22, 115 (Chem. Abs., 1974, 80, 107 642).

Photochemistry

288

An attempt to prepare triplet benzyne by the triplet-sensitized (benzophenone) decomposition of the peroxide (254) has shown that a singlet benzyne is This conclusion was reached even though a kinetic study showed that the decomposition occurred from the triplet state of the peroxide. The two products (255), obtained in the ratio 82 : 18 by trapping the benzyne with transcyclo-octene, could be produced in identical yield using benzyne formed by a variety of paths. The absence of other products which might have arisen from a biradical such as (256) is thought to be conclusive evidence for the absence of triplet benzyne in these experiments.

QMe

OCH,R

HO

0

R

(257) a ; R-R = CH,CH, (258) a ; Rl = R2 = Me b ; R-R = CHzOCHz b; R1 = Me, R? = Ph c ; R = R = Me c; R1-R2 = (CH,),, (CH,),, (CH,),, or (CH,),

q0

HO

R1 R2

Further work on the phthalimide system has shown that N-methylphthalimide undergoes intramolecular hydrogen abstraction when irradiated in ethers (THF, dioxan, and diethyl ether) to yield the adducts (257).151 Hydrogen abstraction also occurs in the presence of cyclopentene or cyclohexene. Intramolecular hydrogen abstraction in the phthalimides (258) gives the oxazoloisoindoles (259).152 Similar hydrogen abstraction and cyclization in the phthalimides (260) affords a route to the multi-cyclic benzazepines (261) (Scheme 25).153 The lK0

lSa

lS9

R. T. Luibrand and R. W. Hoffmann, J. Org. Chem., 1974, 39, 3887. Y . Kanaoka and Y . Hatanaka, Chem. and Pharm. BUN.(Japan), 1974, 22,2205 (Chem. Abs., 1974, 81, 179 809). H. Nakai, Y . Sato, H. Ogiwara, T. Mizoguchi, and Y. Kanaoka, Heterocycles, 1974, 2, 621 (Chem. A h . , 1975, 82, 43 230). Y . Kanaoka, K. Koyama, J. L. Flippen, I. L. Karle, and B. Witkop, J. Amer. Chem. SOC., 1974,96,4719.

Enone Cycloadditions and Rearrangements

289 0

0

0 (260) a; tz = 3 b; c;

d;

IZ = t1 = II =

4 5 6

hv

0 (261) a ; n

= 1 b;n=2

Scheme 25

structure of (261b) has been determined by X-ray methods.153 Irradiation of the dihydrophthalimide (262) yields five products (Scheme 26).15* The authors rationalize the products via cleavage to a biradical (262a), the intermediacy of which can explain all the products.

0

(25%)

0

(262 a)

, f C W

+

dNH \

0

H H O 3% Scheme 26 164

G . Scharf and B. Fuchs, J.C.S. Chem. Comm., 1975, 244.

2%

290

Photochemistry

I

hv A > 340 n m

Y R

R

'

Scheme 27

A full account of the reactions encountered in the photochemical investigation of the quinone-diene thermal adducts (e.g. Scheme 27) has been p u b l i ~ h e dlS6 .~~~~ Irradiation of cyclo-octa-l-ene-3,8-dioneresults in cis-trans-isomerization affording (263).lK7The trans-isomer reacts in the usual fashion dependent upon

.c

0

the solvents, forming a dimer in ether and an adduct in methanol. The existence of the trans-isomer was further proved by its Diels-Alder reactivity. 2,2-Dimethylcyclo-octa-l,6dione undergoes Norrish Type I fission (in n-hexane at 300 nm) to afford the enal (264) as the major product.lK8The minor product (265) arises by a 1,3-acyl shift. A 1,3-acyl shift is also encountered in the formation of (266) following photodecarbonylation of the truxone (267) (Scheme 28).lSe The photochemical rearrangements of the dienediones (268) to the asteranes (269) by 1,2-acyl migrations and to the diones (270) by 1,3-acyl shifts have been shown to arise from the triplet state.lso Although the nature of the excited state is not known in every case, the emission from (268a) suggests that an nn* state is involved. Mukai and his co-workerslel have reported the isomerization of (271) to (272) by a 1,3-sulphur migration. The reaction was brought about by lS6

J. R. Scheffer, K. S. Bhandari, R. E. Gayler, and R. A. Wostradowski, J. Amer. Chem. Soc., 1975,97, 2178.

J. R. Scheffer et al., Tetrahedron Letters, 1973, 2871; J. Amer. Chem. SOC.,1971, 93, 3813; 1972, 94, 285; Tetrahedron Letters, 1972, 677. lS7 Y. Kayama, M. Oda, and Y. Kitahara, Chem. Letters, 1974, 345. lS8 R. G. Carlson and A. V. Prabhu, J. Org. Chem., 1974, 39, 1753. lS9 G . Jammaer, H. Martens, and G. Hoornaert, J. Org. Chem., 1974, 39, 1325. loo C. Lam and J. M. Mellor, J.C.S. Perkin ZZ, 1974, 865. H. Tsuruta, M. Ogasawara, and T. Mukai, Chem. Letters, 1974, 887.

Enone Cycloadditions and Rearrangements

291

0

1

Meo%

,,"+ M e 0 0 /

OMe

\

H@OMe

H R

0

0

(267) a; R = Me b; R = CH2C02Et

fp 0

0

(268) a; R = C,H, b ; R = p-MeOC,H, C ; R = IIZ-NO~CGHJ d ; R = ~I-CIC,H, e; R = p-BrC,H,

a

R1

@

0

@ 0

R 2

0

HO

Photochemistry irradiation at 350 nm in benzene. A similar migration has been reported to occur when the hydroxy-ketone (273) is irradiated under the same conditions. The product (274) was isolated as its hemi-acetal (275). 292

6 Quinones 3,6-Di-t-butyl-1,2-benzoquinoneundergoes photodecarbonylation when irradiated at 380 nm to produce 2,5-di-t-butylcyclopentadienonewhich can be trapped as the adduct (276) when maleic anhydride is added to the photolysate.ls2 A

comparison of the photochemical and thermal additions of o-chloroanil and o-bromoanil with olefins yielding adducts (277) has been reported.ls3 o-Chloroanil yields monoesters of tetrachlorocatechol (278) when irradiated in benzene solution with aldehydes,ls4presumably by a hydrogen abstraction path similar to that observed in the photoreactions of p-quinones and aldehydes.lsSa In two cases, i.e. the reactions with isobutyraldehyde and 2-ethylbutyraIdehyde, a different path was followed. This gave the products (279), which could be formed by hydrogen abstraction from the tertiary centre of the aldehyde [radical pair (280)] followed by recombination and cyclization. A CIDNP study confirmed that

c1 (278) R = Et, Pr", CH, = CH,, MeCH = CH, Ph, p-ClC&, ni-NOzCsHa,I-naphthyl

(279) a ; R1 = R2 = Me

b; R1 = R2 = Et Isa lE3

Ie6

V. B. Vol'eva, V. V. Ershov, I. S. Belostotskaya, and N. L. Komissaraova, Zzoest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 739 (Chem. Abs., 1974,81,44025). H. Bann and W. Schroth, Z . Chem., 1974, 14,239. K. Maruyama, T. Miyazawa, and Y . Kishi, Chem. Letters, 1974, 721. (a) J. M. Bruce and K. Dawes, J. Chem. Soc. ( C ) , 1970,645; (6) K. Maruyama and Y . Miyagi, Bull. Chem. SOC.Japan, 1974,47, 1303.

Enone Cycloadditions and Rearrangements

293

the products are formed by a radical-pair mechanism.165b Maruyama and Takuwa lBBhave reported the irradiation of 1,2-naphthoquinones (281) with aldehydes. The products from this procedure were the esters (282) and (283) and the C-acylated product (284). Although an obvious mechanism for the formation of C-acylation products is by a photo-Fries reaction of the esters, the esters were found to be photostable under the reaction conditions.

(281) R'

= R2 = H R1 = H,R2 = BI. R1 = H,R2 = Me R' = CN, R2 = H

(282)

OCOR

OH

R1

R1

R2

-

(283)

(284)

The photochemical addition of 9,10-phenanthraquinone, tetrachloro-l,2benzoquinone (and benzil) to alkenynes (285) has been re~0rted.l~'The addition of the quinones takes place to the ethylenic bond of the alkenyne to yield alkynyl dioxins (286) and (287). The reaction is not stereospecific and a biradica1 intermediate is proposed to account for the loss of the stereochemical integrity of the olefin. Ishibe et af.ls8have published the results of an investigation of the photoaddition of p-benzoquinone, 1,4-naphthoquinone, 2-methyl-l,4-benzoquinone,

R2 R'

XN

H (285) a ; b; c; d; e;

lee le7

R' = R2 = H R'-R2 = (CHZ), R' = Me, R2 = H R' = H,R2 = Me R1 = H, R2 = M e 0

(286)

K. Maruyama and A. Takuwa, Chem. Letters, 1974, 471. R. J. C. Koster, D. G . Streefkerk, J. Oudshoorn van Veen, and H. J. T. Bos, Rev. Trav. chim., 1974, 93, 157.

(a) N. Ishibe, K. Hashimoto, and Y. Yamaguchi, J.C.S. Perkin I , 1975, 318; (6) N. Ishibe and I. Tanigushi, Tetrahedron, 1971, 27, 4883.

294

Photochemistry

Scheme 29

and tetrachloro-l,6benzoquinoneto allenes. The outline of the reaction is typified by the process in Scheme 29. Kinetic studies indicate that triplet quinone adds to allene to afford an oxetan which undergoes secondary photolysis to give the isolated products. The reaction is reminiscent of that described in the earlier 1iterat~re.l~~ A full account of the argon-laser-induced photoaddition of p-benzoquinone to cyclo-octatetraene yielding (288) in anaerobic conditions has been publi~hed.170~ 171 Under aerobic conditions irradiation of the quinone in the presence of 1,l-diphenylethylene, styrene, and t-butylethylene yields the trioxans (289) 172 (see also ref. 173). The trioxans are accompanied by the anticipated oxetans but formation of these products is suppressed in favour of the trioxans when the reaction is carried out under oxygen (1 1 atm). The absence of oxygen scrambling and the formation of only one trioxan in each case indicate that the products are formed by trapping of the biradical (290) formed by the addition of the excited quinone to the olefin. The biradicals can also be trapped by 0

0

(288)

(289) R'

=

R'

=

R2 = Ph H . R2 = PI1

The triplet states of some ubiquinone analogues (291) have been studied by laser flash p h o t o l y s i ~ .The ~ ~ ~electron-transport quinones such as Plastoquinone-9 have been the subject of several studies during the past few years. The interest in these systems arises from their implication in many in vivo processes such as heart disease, muscular dystrophy, and cancer. The in vitro studies are therefore 170

H. Gotthardt, R. Steinmetz, and G. S. Hammond, J. Org. Chem., 1968, 33, 2774. R. M. Wilson, E. J. Gardner, R. C. Elder, R. H. Squire, and L. R. Florian, J. Amer. Chem.

171

SOC.,1974, 96, 2955. E. J. Gardner, R. H. Squire, R. C. Elder, and R. M. Wilson, J. Amer. Chem. SOC.,1973, 95,

loo

1693.

17a

17' 17s

R. M. Wilson and S. W. Wunderly, J.C.S. Chem. Comm., 1974, 461. D. Creed, H. Werbin, and E. T. Strom, J . Amer. Chem. SOC.,1971, 93, 502. R. M. Wilson and S. W. Wunderly, J. Amer. Chem. SOC.,1974, 96, 7350. E. Amouyal, R. Bensasson, and E. J. Land, Photochem. and Photobiol., 1974, 20, 415.

295

Enone Cycloadditions and Rearrangements 0

0

R1 = Me, R2 = M e 0 R1 = H , R2 = M e 0 c; R1 = MeO, R2 = H

(291) a ; b;

essential for a better understanding of the transformations which are possible by both thermal and photochemical processes. Plastoquinone-9 (292) yields one main product (293) when irradiated in mixtures of ben~ene-methanol.~~~ Several other minor products are also formed.

OH

0

2

0

(294) a; R1 = Me,R2 = R3 = H b; R1 = R2 = Me, R3 = H c; R1 = R3 = Me, R2 = H d ; R1 = R2 = R3 = H e; R1 = CI,R2 = R3 = H f ; R' = R2 = C1,R3 = H g ; R 1 ,= Br, R2 = R3 = H h ; R1 = R2 = Br, R3 = H

\ / (295)

Intermolecular hydrogen abstraction in the 1,4-naphthoquinone-xanthone system has been studied.17' When the quinones (294a-c) were employed only the corresponding quinol and bixanthyl (295) were isolated. However, when quinones (294d-h) were used a more complex reaction mixture was obtained. The reaction was further complicated by the fact that cooling from room temperature to 0 "C had a marked effect, for example the reaction of (294e) at the two temperatures gave the products and the yields shown in Scheme 30. Intramolecular hydrogen abstraction in 2-alkoxynaphtho-1,4-quinonesin the presence of olefins (hex-I -ene, hept- 1-ene, oct-1-ene, cyclohexene, cyclo-octene, 176

17'

D. Creed, H. Werbin, and E. T. Strom, Tetrahedron, 1974, 30, 2037. K. Maruyama and S. Arakawa, Bull. Chem. SOC.Japan, 1974,47, 1960.

296

Photochemistry

(294 e)

+

hv

OH /

& \

I

dcl

I

\

+

0°C; 48% RT; 28%

+

(29 5)

0°C; 23%

RT; 5%

+

0 0 "C; 0.5%

RT; 2.1% 0°C; 4:4 RT; 8.6%

0

0°C;

-%

RT; 14:;

Scheme 30

1,4-cyclo-octadiene, bicyclo [2,2,1]hept-2-ene, bicyclo [2,2,1]hepta-2,5-diene, styrene, and indene) gave the adducts (296).17*317@ The products were obtained in reasonable yields and only the 2-isopropoxynaphthoquinonefailed to give a good

(296) a; b; C;

d; e; f; g; h; i; 178

170

R1 = Bu", R2 = R3 = H R1 = n-pentyl, R2 = R3 = H R1 = n-hexyl, R2 = R3 = H R'

= H, R1 = H, R1 = H, R' = H,

R2-R3 = (CH,), R2-R3 = (CHZ), R2-R3 = (CH,)Z-CH=CH-(CH2)2 R2-RS = 1,3-cyclopentyl R' = H, R2-RS = 1,3-cyclopentenyl R1 = Ph, R2 = R3 = H

T. Otsuki, BUN. Chem. SOC.Japan, 1974, 47, 3089. K. Maruyama and T. Otsuki, Chem. Letters, 1974, 129.

297

Enone Cycloadditions and Rearrangements

0

0 Scheme 31

yield of adduct. The formation of e.g. adduct (296i) from styrene is thought to involve a biradical intermediate (Scheme 31). The formation of such an intermediate is reminiscent of the structural rearrangement of side-chains encountered with t-butylbenzoquinones.lS0 Irradiation of 2-methoxy- and 2-ethoxy-l,4-naphthoquinonein acetic anhydride solution gave the dimers (297).la1 The formation of dimer (297b) was best brought about at 436 nm when a 90% yield was obtained. Irradiation of this dimer (29%) at 365 nm converted it into the bisoxetanol(298b) by a Norrish Type I1 hydrogen abstraction path. A similar reaction has been described for the dimer of 3-metho~ychromone.~~~ The oxetanol (298a) was obtained, along with dimer

(297) a ; R b; R

= =

Me Et

(298) a; b;

R R

=H = Me

(297a), when 2-methoxynaphthoquinone was irradiated at 365 nm. 2-Ethoxy3-methylnaphthoquinone failed to dimerize under these conditions. No dimer was formed on irradiation of 2-isopropoxynaphthoquinone. Instead the quinone undergoes Norrish Type I1 reaction resulting in the formation of the dioxole (299). There is some similarity in this cyclization to others involving t-butylquinones.180 A mechanism similar to this cyclization might be operational here (Scheme 32), rather than one involving free radicals exclusively. Interest in naphthoquinone epoxides (300) has been reported by three research groups in the past year. Kato et aZ.lS3have shown that the epoxide (300a) undergoes ring-opening when irradiated (benzene solution, Pyrex filter). This unstable la0 lB1

C. M. Orlando, H. Mark, A. K. Bose, and M. S. Mankas, J . Org. Chem., 1968, 33, 2512. J. V. Ellis and J. E. Jones, J. Org. Chem., 1975, 40, 485. S. C. Gupta and S. K. Mukerjee, Tetrahedron Letters, 1973, 5073. H. Kato, K. Yamaguchi, and H. Tezuka, Chem. Letters, 1974, 1089.

298

Photochemistry

& %

f

OAc Scheme 32

(300) a; R1 = R2 = Ph b; R1 = Me,R2 = Ac c; R1 = H,R2 = Me d; R1 = R2 = Me . e ; R1 = H,R2 = Et

3 0

\

(303)

0

/

/

0

0

(304)

Enone Cycloadditions and Rearrangements

299

species (301) produced by the irradiation can be trapped as adducts of N-phenylmaleimide or norbornadiene. However, Maruyama and Arakawa lS4in a study of epoxide (300b) have shown that the lactone (302) is formed exclusively by a Norrish Type I fission. In this molecule there are two discrete Norrish Type I pathways which would be equally feasible. Jimenez et aZ.la5have studied the photoreaction of (300c-e). Reviews of the photochemistry of anthraquinone derivatives la6 (in Japanese) and of the photoreduction of anthraquinone lS7 have been published. Photoreduction of the p-quinone (3O3)la8 and of the pentacene diquinone (304) laQhas been studied. The cage compound (305) is formed in high yield (90%) when the benzoquinophane (306) is irradiated in the solid phase.lgo lS6 18(

K. Maruyama and S. Arakawa, Chem. Letters, 1974, 719. M. Jimenez, L. Rodriguez-Hahn, and J. Romo, Rev. Latinoamer. Quim., 1974,5, 184 (Chem. Abs., 1975, 82, 42 611). H. Inoue and M. Hida, Yuki Gosei Kagaku Kyokai Shi, 1974,32, 348 (Chem. Abs., 1974,81, 129 756).

D. M. Hercules, US. Nut. Tech. Inform. Ser. A.D. Rep., 1973, No. 77547018GA (Chem. Abs., 1974, 81, 56227). lS8 S. Tsuruya and T. Yonezawa, J. Org. Chem., 1974, 39,2438. lSB G. A. Val'Kova, D. N. Shigorin, V. M. Gebel, N. S. Dokunikhim, N. N. Artmonova, and L. N. Gaeva, 2hur.fiz. Khirn., 1974, 48, 1259 (Chem. A h . , 1974, 81, 84 319). l D o H. Irngartinger, R.-D. Acker, W. Rebafka, and H. A. Staab, Angew. Chem. Internat. Edn., la'

1974, 13, 674.

3 Photochemistry of Olefins, Acetylenes, and Related Compounds BY W. M. HORSPOOL

1 Reactions of Alkenes Addition Reactions.-Methanol has been shown to quench the fluorescence of 1,2-diphenylcyclobutene. This is good evidence that the photo-reaction of methanol with the cyclobutene to afford (1) and (2) arises from the singlet state.l The mechanism of the addition is thought to involve the cation (3) which either is

(3)

(1)

attacked by methanol or rearranges prior to formation of the ether (2) A similar reaction has been found with acetic acid, which yields the corresponding acetates. A reinvestigation of the photochemical hydration (sensitized with o-xylene) of cholest-5-ene (4) has been r e p ~ r t e d . This ~ work (Scheme 1) has examined the deuteriation as well as the protonation and is complementary to the earlier work. The deuterium oxide studies showed that all the products had

& + OH (4) 17% recovery

( 5 ) 33%

32%

6%

Scheme 1 a

a

M. Sakuragi and M. Hasegawa, Chem. Letters, 1974, 29. H. Compaignon and R. Beugelmans, Tetrahedron Lerters, 1969, 1901. J. A. Waters, Steroids, 1974, 23, 259.

300

Photochemistry of Olefins, Acetylenes, and Related Compounds

30 1

undergone multiple incorporation of deuterium. Thus isomerization by addition and elimination is the more important reaction of the two olefins (4) and (5) and nucleophilic attack by water is of secondary importance. The u.v.-induced addition of dibutyl phosphite to NN-dibutyloleamide gave a high yield of NN-dibutyl-9-dibu tylphosphono-octadecanamide.4 Hydrogen-abstraction Reactions.-The main product from the irradiation of the ene-ol (6) in hexane or benzene is the tetrahydrofuran (7).6 This arises from the singlet state of the olefin, probably by intramolecular protonation and cyclization. In benzene the tetrahydrofuran is accompanied by 2-phenylpropene and acetophenone. These products arise from the triplet state (their formation is suppressed by the addition of cyclohexa-l,3-diene as quencher). The mechanism for the formation of the fission products is shown in Scheme 2 and is analogous

P

h u P h R/l'Rl (6) a; R1 = R2 = H b; RL = D, R2 = H C; R1 = H, R2 = D

(6a)

A

P

h g P R' R1

h

H

Me

R2 OH

-

P h y y Ph (7)

R2-)=(R1 Ph R1

+

PhCOMe

Scheme 2

to the Norrish Type I1 reactions of ketones involving the transfer of hydrogen from the y-carbon to the ethylene. Proof of this mechanism was obtained from the use of the deuterium-labelled species (6b, c). Intramolecular hydrogen abstraction is also encountered in the photochemistry of the enone (8), which yields the tetracyclic isomer (9).6 The most likely mechanism for the formation of the products is shown in Scheme 3 where the dominant reaction is that of the

(9)

Scheme 3 J. C. Arthur, jun., R. Mod, and J. A. Harris, J. Amer. Oil Chemists' SOC.,1974, 51, 35 (Chem. A h . , 1974, 80, 133 557). J. M. Hornback, J. Amer. Chem. SOC.,1974, 96, 6773. R. R. Sauers and T. R. Henderson, J. Org. Chem., 1974,39, 1850. 11

302 Photochemistry ethylene unit of the norbornene. The triplet state of norbornene, populated by energy transfer from excited-state acetophenone, also undergoes hydrogenabstraction reactions. Thus the adducts (10) can be obtained by irradiation of the olefin in the presence of nitriles or esters.'

R = CH2CN, CHMeCN, CMe2CN,CH,CO,Et, CH2C0,H, COEt, CH,COMe

cis-trans-1somerization.-Coyle has published a short general review of the photochemistry of olefinic compounds.8 A study of the decay of excited states as a function of the degree of twist possible in a double bond has been published for the molecules ( l l ) . g The total decay rate (kdt singlet) of the excited states was

(11) a; n = 1 b;n=2 c;n=3 d;n=4

e;n=5

measured by the previously reported method for ultra-fast rates.lO9 l1 By the dissection of the original kdt singlet according to the equation kdt singlet = kf + kisc + ki,, the rates of the other decay processes were obtained. The details of the computation are given in Table 1. It should be noted that ki, increases with

Table 1 Rate constants for the decay processes in olefins (1 1 ) singlet/ 107 s-1 4.26 6.29 5.75 7.14 6.31 69.4 10.7 357

kdt

T/K

T/ns

77 300 77 300

23.45 15.89 17.38 14.01 15.84 1.44 9.33 0.28

77 300 77 300

a+ 0.62 0.27 0.72 0.43 0.4 0.03 0.42 0.016

kfl

107 s-1 2.64 1.7 4.14 3.07 2.52 2.08 4.49 5.71

i

kiscl k d t

~

~ 107,

0.004

25

-

0.11 0.0008 0.0016

79

5

57

triplet/ S-1

280 1700 6300 30000

kit/

107 s-1 1.6 4.6 0.98 3.3

3.8 67 6.2 351

increasing ring flexibility. Thus it is obvious that the twisting about the double bond in the excited state is an important energy-dissipation pathway. Ground-state and lowest excited-state energy surfaces for stilbene have been calculated by a semiempirical procedure.12 Calculations show that in the first

@

lo lr la

S. H. Schroeter, Annalen, 1974, 1890. J. D. Coyle, Chem. SOC.Rev., 1974, 3, 329. H. E. Zimmerman, K. S. Kamm, and D. P. Werthemann, J. Amer. Chem. Suc., 1974,96,7821. H. E. Zimmerman, D. P. Werthemann, and K. S. Kamm, J. Amer. Chem. Suc., 1973,95,5094. H. E. Zimmerman, D. P. Werthemann, and K. S. Kamm, J. Amer. Chem. Suc., 1974,96,439. F. Momiccioli, C. M. Bruni, I. Baraldi, and G. R. Corradini, J.C.S. Faraday 11, 1974, 1325.

Photochemistry of Olefins, Acetylenes, and Related Compounds

303

excited state the trans-cis-conversion is hindered by an energy barrier of 146.7 kJ mol-l. The authors l2 suggest that in the direct irradiation experiments a triplet excited state is favoured as the precursor for trans-cis-isomerization of stilbene. Dainton et al.13 previously reported the existence of a transient species (absorbing at 360 nm) following pulse radiolysis of trans-stilbene. This transient was identified as a stilbene triplet. The lifetime of 110 ns is, however, much longer than the 10ns estimated for the same species by the azulene quenching technique. Saltiel and Thomas I4 have reinvestigated their results and have proposed a modified mechanism for the decay of stilbene triplets (Scheme 4). trans

L3,

Scheme 4

This new scheme takes into account the fact that all stilbene triplets must be twisted, and that the azulene quenches the twisted triplet and not the linear triplet as was thought originally. This new kinetic scheme permits the calculation of the stilbene triplet lifetime as 119 and 129 ns for air- and oxygen-saturated experiments, respectively, in good agreement with the pulse radiolysis experiment. Saltiel and his co-workers15 have also examined the influence of halogen substituents upon the trans-cis isomerization. They have observed that there is a strong positional influence. The bromine markedly influences the radiationless spin-orbit coupling. Thus with the para-isomer the bromine enhances the intersystem crossing, whereas with the meta-isomer no effect is detectable. Bortolus and Galiazzo l6 have studied the photochemical trans-cis-isomerization of the styrylnaphthalenes (12) and (13), by both direct and anthraquinonesensitized irradiation. The influence of oxygen upon the irradiation has shown

R (13) a; R = H b; R = Cl c; R = Br l3 l4

l6

F. S. Dainton, E. A. Robinson, and G. A. Salmon, J . Phys. Chem., 1972,76, 3897. J. Saltiel and B. Thomas, J. Amer. Chem. Suc., 1974, 96, 5660. J. Saltiel, D. W.-L. Chang, and E. D. Megarity, J. Amer. Chem. Suc., 1974, 96, 6521. P. Bortolus and G . Galiazzo, J. Photochem., 1974, 2, 36 1.

304 Photochemistry (Table 2) that oxygen assists in the intersystem crossing of S,-T, in the naphthalene. This phenomenon has previousIy been reported for other aromatic hydrocarbon^.^' In the present work the authors l6 interpret the oxygen effect as due to a direct intermolecular exchange reaction rather than to a charge-transfer interaction. Enhanced intersystem crossing efficiency was also observed when Table 2

Unsensitized trans-cis photoisonierization of styrylnaphthalenes (1 2) and (13) l6 De-aerated

A ir-saturated

Styrylnaphthalene

a,-,

@f

@t-c

(12) (13a) (1 3b) (13c)

0.13 0.16 0.13 0.21

0.74 0.69 0.76 0.47

0.27 0.23 0.19 0.23

@f

0.25 0.60 0.69 0.44

air-equilibrated solutions of stilbenes (14) and (1 5) were irradiated.'* The quantum yield was raised to 0.4, compared with values of 0.13 and 0.01 for cis-transisomerization on direct irradiation in degassed acetonitrile solutions. Population

of the triplet state was demonstrated by heavy-atom solvents in degassed acetonitrile when the fluorescence of the stilbene (14) was quenched and cis-transisomerization became more efficient (Table 3). A heavy-atom effect was also Table 3 Induced trans-cis isomerization and fluorescence quenching of (14) Quencher Benzene Chlorobenzene Bromobenzene Iodobenzene 2-Bromoethanol Bromoe t hane 1,ZDibromoethane Ethanol

kq7fluor)

19 23 39 70 7.8 33 2.6 14

kq7(react)

0 29 38

104 6.1 36 3.1 0

l8

@t-C

0.33 0.32 0.29 0.30

0.48

-

detected for the stilbene (15). However the result in this case was not as straightforward. Although the fluorescence quenching (by bromoethane and 1,2-dibromoethane) followed a linear Stern-Volmer plot the trans-cis-isomerization varied sharply, and at low concentration of quencher where no fluorescence quenching could be detected, the quantum yield for isomerization was in the range 0 . 2 4 . 4 ; no change from these values was detected as the concentration of l7

C. R. Goldschmidt, R. Potashnik, and M. Ottolenghi, J. Phys. Chem., 1971, 75, 1025. A. D. Gutierrez and D. G. Whitten, J. Amer. Chem. SOC.,1974, 96, 7128.

Photochemistry of Olefins, Acetylenes, and Related Compounds

305

the quencher was increased. These results were interpreted in terms of a longlived exciplex between the stilbene (15) and the solvent acetonitrile. Structural Isomerization Reactions.-In earlier work Kropp and his co-workers lD suggested that the unsaturated and cyclopropane products formed by the irradiation of olefins in solvents of low nucleophilicity were produced by initial rearrangement to carbenes. In a later study Kropp and Fields20 have demonstrated that carbene intermediates are indeed formed in the irradiation of olefins (16) and (17) in pentane solution. The products and the yields are detailed (TabIe 4). The products obtained can all be accommodated in a scheme which Table 4 Products from the irradiation of the olefins (16) and (17) 2o Products (%) Olefin (% recouery) (18) (19) (20) (21) (22) (23) (16) (25 %) 4 1 8 9 5 13 6 2 30 9 4 5 (17) (21 %) Carbene (24) 7 3 83 - - Carbene (25) 51 27 22 c

involves the formation of the two carbenes (24) and (25) from each olefin. Indeed the carbenes, when generated by more conventional means, produce the same products in the same ratio as the photochemical experiments. Thus carbene (24) yields products (18)-(20) and carbene (25) yields (21)-(23). Kropp 2o suggests that the formation of the carbenes by irradiation of the olefins must arise from a Rydberg state. Other carbene-derived products are obtained in the photolysis of the olefin (26) (see Scheme 5). A carbene intermediate (27) has also been

(26)

Scheme 5 P.J. Kropp, E. J. Reardon, jun., Z. L. F. Gaibel, K. F. Williard, and J. H. Hattaway, J. Amer. 2o

Chem. Sac., 1973,95,7058. T. R. Fields and P. J. Kropp, J . Amer. Chem. Sac., 1974,96, 7559.

Photochemistry

306

implicated in the irradiation (Vycor filter) of a cyclohexane solution of 1,ldiphenyl-3,3-dimethylbut-l-enewhich affords products [(28), 36%] and [(29), 6%].21 The feasibility of the carbene pathway to products was demonstrated by deuterium-labelling studies. After the formation of the carbene by hydrogen migration, insertion into a methyl C-H bond affords the major product while phenyl migration would yield 1,2-dipheny1-3,3-dimethylbut-l -ene. This olefin was not isolated since it undergoes oxidative photodehydrocyclization to the minor product (29).

Cristol and Micheli 22 have reported a study of the photochemistry of a series of ally1 chlorides. On acetone-sensitized irradiation in acetonitrile these compounds (30)undergo rapid transcis-isomerization to set up a photostationary mixture. The photoallylic rearrangement yielding products of group migration (3 1) accompanied the E-Z-isomerization but at a slower rate. Kinetic studies indicate that both the singlet and the triplet states are involved since direct irradiation also brings about rearrangement. Direct irradiation apparently affords a singlet state which does not undergo intersystem crossing, in accord with normal behaviour in olefin photochemistry.

R2 R3 (30) a; R1 = Ph, R2 = H, R3 = CI b; R1 = Me, R2 = H, R3 = C1 C; R1 = H, R2 = R3 = Ph d; R1 = Me, R2 = H, R3 = Pli R2

I

R1CHClC =CH, (31) a; R1 = Ph, R2 = C1 = 0.016; OD,,,, = 0.024) b; R1 = Me, R2 = C1 (O,,,,, = 0.073) C ; R1 = R2 = Ph (@,Ilr = 0.025; CD,,,,, d ; R1 = Me, R2 = Ph (asen5 = 0.042)

=

0.086)

2 Reactions involving Cyclopropane Rings The naphthalene-sensitized isomerization of 1,2-diarylcyclopropanes has been the subject of several investigations during the past few years. The most recent study has examined the isomerization of cis-l,2-diphenylcyclopropanesensitized 2'

S. S . Hixson, J. Amer. Chem. SOC.,1975, 97, 1981. S. J. Cristol and R. P. Micheli, J. Org. Chem., 1975, 40, 667.

Photochemistry of Olefins, Acetylenes, and Related Compounds

307

by substituted naphthalene^.^^ The experiments carried out indicate that the isomerization is sensitized from the singlet state of the naphthalene and it is likely that there is charge transfer from the cyclopropane to the naphthalene in the formation of an exciplex. cis-trans-Isomerization of cis-l,2-diphenylcyclopropane has also been studied using energy transfer from poly-(y-l-naphthylmethylL- and D-gl~tamafe).~‘ A full report of the studies of the photochemical addition of amines to cyclopropanes, originally published in note form,25 has been made.26 A typical example of this reaction is shown in Scheme 6. The stereochemistry of the

+m+

Ph-fph HNW

Ph

Scheme 6

addition process was followed by an examination of the addition of cyclohexylamine to the semibullvalene (Scheme 7). Here it can be seen that there is a preference for the formation of the more hindered isomer. The mechanism of the

reaction was shown to involve the singlet state of the semibullvalene since there was no evidence for sensitization with the usual triplet sensitizers. The author 26 suggests that the most likely mechanism for the addition process is excitation to a singlet state which then relaxes to a lower energy state in which the C-C bond is stretched. This stretched bond is susceptible to both polar and radical reactions. It is impossible to be categorical concerning the pathway involved in this instance, but it is suggested that an exciplex leading to bond fission and formation of products is most likely. The photochemical addition of alcohols to cyclopropanes appears to follow a path exactly analogous to that outlined for the addition of 23 24

zb

S. S. Hixson, J. Boyer, and C. Gallucci, J.C.S. Chem. Comm., 1974, 540. A. Ueno, F. Toda, and Y . Iwakura, J. Polymer Sci., Polymer Chem., 1974, 12, 1841. S . S . Hixson, J.C.S. Chem. Comrn., 1972, 1170. S . S. Hixson, J. Amer. Chem. SOC.,1974, 96, 4866.

308 Photochemistry amines to the same substrates. Hixson and Garrett 27 have also examined the influence of substituents upon this addition and some examples of the reaction are shown in Scheme 8.

A

P h q A r

hv

Ar Ph a ; Ar = p-anisyl

a; 60%

b ; Ar = nz-anisyl = p-CNC6H,

b ; 46% c ; 100%

OMe

c ; Ar

Ph

Ph-Ar OMe a; 40% b; 54%

rnCN

Scheme 8

The discovery of a real photochemical homoallylic rearrangement of 2-arylcyclopropylcarbinyl acetates (32) and (33) has been reported.28 In cyclohexane the products formed [from (32a)l are the corresponding cis-cyclopropane and the homoallyl product [(34), 25x1 (minor amounts of benzylcyclohexane and l-phenylbutadiene were also detected). Acetone sensitization shows that the RCO

A/ phwoAc phL phk

xc6H4/@fo2cR

(32)

Ph

XC6H4

(34)

(33)

OMe

ph

Ph

(35)

(36)

homoallyl product arises from the singlet state with
Table 5 Substituent effect on @ for product formation from irradiation of (32) in cyclohexane 2g Substituents (32) a; X = H, R = Me (32) a; X = H, R = Me (32) b; X = OMe, R = Me (32) c; X = CI, R = Me (32) d; X = H, R = CMe, a8

@'re1

1 .o 1.1 (in acetonitrile) 0.12 0.055 0.86

S. S. Hixson and D. W. Garrett, J . Amer. Chem. SOC.,1974, 96, 4872. S.S. Hixson, J.C.S. Chem. Comm., 1974, 681.

309

Photochemistry of Olefins, Acetylenes, and Related Compounds

Direct irradiation ( A = 250nm) of the allylcyclopropane (37) yielded five products, viz. 1,l-diphenylethylene; 1,l-diphenyl-2 2-dimethylethylene; 1,l-diphenyl-4-methylpenta-1,3-diene ; 1,l-diphenylbuta-1,3-diene; and the vinylcyclobutane (38). Independent photolysis of the vinylcyclobutane (38) shows that it photochemically fragments into 1,l-diphenyl-2,2-dimethylethyleneand l,i-diphenylbuta-l,3-diene exclusively. Although other routes, e.g. via a carbene, were considered for the formation of the other irradiation products, the authors 2Q favour a single path as outlined in Scheme 9.

+

Ph

X

Ph

hv

ph3p (38)

Scheme 9

The text of a lecture dealing with the di-n-methane reaction has been publi~hed.~OZimmerman 31 has discussed the use of stereochemical changes as probes for the mechanism of photochemical reactions. Di-n-methane reactions have been reported for the aryl olefins (39).32 In all cases studied the product was the arylcyclopropane (40). The formation of the products was sensitive to the nature and position of the substituent on the aryl ring. These results, and the fact that the quantum yield for product formation is higher in cyclohexane than in acetonitrile, suggest that the biradical intermediate (41) might be important in the transformation. An excited singlet-state mechanism is proposed. 2o

30

3a

H. E. Zimmerman and C. J. Samuel, J . Amer. Chem. SOC.,1975,97,448. H. E. Zimmerman, Preprittts Diu. Petroleum Chem., Amer. Chem. Soc., 1973. 18, 292 (Chem. Abs., 1975, 82, 567878). H. E. Zimmerman, Tetrahedron, 1974, 30, 1617. R. C. Cookson, A. B. Ferreira, and K. Salisbury, J.C.S. Chem. Comm., 1974, 665.

310

Photochemistry

(39) R = H, p-Me, p-CN, nz-Me

(40)

(41)

Further examples of the conversion of allylanisoles (42) into cyclopropylanisoles [e.g. (43)] have been reported to arise upon the irradiation of the allylanisoles in 34 Successful formation of cyclopropylaminobenzene, acetone, or benzenes (44) was also reported 33 upon irradiation of the aminoallylbenzenes (45). A report of the photochemical transformation of phenyl ally1 ethers has been published.36 The conversion of substituted o-allylphenols into cyclic ethers does not show a correlation with the pK, of the excited states of the phenols.36

(42) a; R1 = CH2CH=CH2, R2 = R4 = H, R3 = Me b; R1 = CD2CH=CH2, R2 = R4 = H, R3 = Me c; R1 = 3’-but-l’-enyl, R2 = R4 = H, R3 = Me d ; R1 = R4 = Me, R2 = H, R3 = CH2CH=CH2 e; R1 = R3 = R4 = H, R2 = CH2CH=CH2

(43) a; R1 = R2 = H b; R‘ = R2 = D c; R1 = H or Me, R2 = Me or H

R’N R2

(43) d ; R1 = R4 = Me, R2 = H, R3 = cyclopropyl (44) R3 = cyclopropyl R’, R2 = Mc or Et e ; RL = R3 = R4 = H, R2 = cyclopropyl (45) R3 = ally1

)

of studies on the stereoA full account, following the preliminary chemistry of the C-3 in the di-n-methane reaction has been published.38 The effect of substituents on the di-n-methane reaction has been examined. The

84

s6 36

U. Koch-Pomeranz, H.-J. Hansen, and H. Schmid, Helv. Chim. Acta, 1975, 58, 178. T. C. Clark and D. A. M. Watkins, J.C.S. Perkin I, 1974, 2124. G . S. Hamrnond, U.S. Nut. Tech. Inform. Serv. A D Rep., 1973, No. 77105717GA (Chem. Abs., 1974, 81, 49 040). S. Houry, S. Geresh, and A. Shani, Israel J. Chem., 1973, 11, 805. H. E. Zimrnerman, J. D. Robbins, R. D. McKelvey, C. J. Samuel, and L. R. Sousa, J. Amer. Chem. SOC.,1974,96, 1974. H. E. Zirnmerman, J. D. Robbins, R. D. McKelvey, C. J. Samuel, and L. R. Sousa, J. Amer. Chem. SOC.,1974, 96, 4630.

Photochemistry of Olefins, Acetylenes, and Related Compounds

311

results show that the two dienes (46a) and (46b) both undergo the rearrangement to [(47a), CD = 0.1641 and [(48b), CD = 0.0951 respectively from the singlet Although energy transfer to produce triplet excited states of each diene did take place the triplets were almost completely unreactive. The reaction is highly regiospecific and the biradical intermediate (49), which is implicated in the

(46) a; Arl = p-CNC,H4, Ar2 = Ph b; Arl = Ar2 = p-CNC,H, c; Arl = Ar2 = Ph

(47) Arl = Ph, Ar2 = p-CNC,H4 (48) Arl = Ar2 = p-CNC,H, V

(49)

reaction, opens in one direction only to afford the observed product. Interestingly, the rate of singlet reactivity increases with increasing cyano-substitution. The rates obtained are 2.2 x loll s-l for diene (46a) and 3.3 x 10'l s-l for diene (46b). These results should be compared with the diene (46c) where the rate is 1.4 x loll s-l. Zimmerman and Little 41 have reported in detail the work on the di-.rr-methane reaction designed to establish the role of the second doublebond in the rearrangement. The mono-olefin (50) was very inefficient in its reactions (a = 0.001) compared with the diene (46c) (a = 0.08). The products

Ph (50)

(51)

Ph

(52)

from the reaction are the phenyl-migrated product (51) and the cyclopentane (52), both of which arise from the excited singlet state. The triplet state, populated by sensitization, failed to react. The absence of the di-n-methane products in the reaction of the mono-olefin clearly shows that both double bonds are necessary for that process. The problem of the free-rotor effect and the efficient dissipation of triplet energy is still of interest. Hixson and Tausta42have found that the excited singlet state of the naphthyl olefin (53a), a typical substrate for a di-n-methane reaction, undergoes cis-trans-isomerization to (53b) and conversion into the cyclopropane (54). Continued irradiation leads to the formation of cyclopropane at the expense of cis-olefin (53b). Sensitized irradiation gave very efficient ge

pa

H. E. Zimmerman and B. R. Cotter, J. Amer. Chem. SOC.,1974, 96, 7445. H. E. Zimmerman and R. D. Little, J. Amer. Chem. SOC., 1974, 96, 5143. H. E. Zimmerman and R. D. Little, J. Amer. Chem. SOC.,1972, 94, 8256. S. S. Hixson and J. C. Tausta, Tetrahedron Letters, 1974, 2007.

Photochemistry

312

formation of the cyclopropane (54), with only inefficient formation of the cisester: the efficient formation of the cyclopropane from the triplet state is in direct contrast to the failure of the triplet state of the phenyl analogue to produce a cyclopropane The authors 4 2 suggest that the absence of the free-rotor effect in the naphthyl case is a result of the localization of excitation energy in the naphthyl moiety, and that the reaction occurs solely by naphthyl migration.

. ,

(53) a; R1 = CO,Et, R2 = H b; R' = H, R' = C0,Et

The irradiation of (55a) in [2H,]acetone at -70 "C gave (56a) and (57a).44 This latter product, which presumably arises by a di-a-methane rearrangement, is thermally unstable and forms (56a) on warming. At room temperature the irradiation of (55a) gives only (56a). The chloro-compound (55b) gives (56b) and

(55) a; X b; X

=

Br

=

C1

(56) a; X = Br b; X = C1

(57) a ; X = Bt b; X = C1

the di-=-methane product (57b), as the primary product, upon direct or acetonesensitized irradiation. Acetone-sensitized irradiation of the azanorbornadiene (59a) yields (58).45 However, the reaction is susceptible to the substitution pattern. Thus the dimethyl analogue (59b) yields the fulvene (60) on acetone sensitization. NCO But

m C 0 2 B u t (58)

'I

R =H b;R=Me

(59) a;

D. Keukeleire, E. C. Sanford, and G . S. Hammond, J . Amer. Chem. SOC.,1973,95,7904. S. J. Cristol, T. D. Ziebarth, N. J. Turro, P. Stone, and P. Scribe, J . Amer. Chem. SOC.,1974, 96, 3016.

J. S. Swenton, J. Oberdier, and P. D. ROSSO, J. Org. Chem., 1974,39, 1038.

Photochemistry of Olefins, Acetylenes, and Related Compounds

313

This divergence of the reaction path in the rearrangement of azanorbornadienes has already been commented upon by Prinzbach and his c o - w ~ r k e r s .The ~ ~ direct irradiation of (59a) gave the benzazepine [(61), CD = 0.051. Both direct and sensitized irradiation of the alcohol (62) and the diene (63) gave the di-r-methane

(66)

(65)

products [(64), @ = 0.061 and [(65), QSim = 0.11; @)trip = 0.021 respe~tively.~~ These products arise by benzovinyl bridging. The authors 47 discuss the relative reactivity of the compounds particularly with respect to the lower reactivity of the triplet than the excited-singlet state of the diene (63). A similar decrease in reactivity is seen in the conversion of (66) into (67), (Q8b = 0.11 ; @)trip = 0.0141. Surprisingly there is no evidence for a free-rotor effect in diene (63). However the authors 47 point out that there is structural flexibility in these bicyclic species which might provide a route for triplet deactivation by twisting (30") about the double bond. Direct irradiation of the cyanobarrelene (68a) affords three products (Scheme Triplet sensitization, using acetophenone, of the barrelene (68a) gave the

mLN*m+a \

(68) a; R = H b;R=D

-

/

-

CN+

&\

CN

17%

54%

29 %

Scheme 10

semibullvalene as the sole product. By use of the deuterium-labelled material (68b) it was shown that the 7-cyanocyclo-octatetraenewas formed by vinylvinyl bridging. This is to be contrasted with earlier workqgwhere benzo-vinyl bridging was important in benzobarrelene photochemistry. This is a case where the introduction of a polar group modifies the reaction pathways. Di-n-methane photochemistry has been extended to the study of the dibenzbarrelene (69).60 This compound is converted into one product (70) by direct irradiation (254 nm) 'I 40

49

sg

G. Kaupp, J. Perreten, R. Leute, and H. Prinzbach, Chem. Ber., 1970, 103,2288. Z . Goldschmidt and U. Gutman, Tetrahedron, 1974, 30, 3327. C. 0. Bender and S. S. Shugarman, J.C.S. Chem. Comm., 1974,934. H. E. Zimmerman, R. S. Givens, and R. M. Pagni, J. Amer. Chem. SOC.,1969,90, 6096. K. G. Srinivasan and J. H. Boyer, J.C.S. Chem. Comm., 1974, 1028.

314

Photochemistry

in furan solution. The absence of the other possible product from vinyl-benzobridging is thought to be the result of steric factors. The surprisingly exclusive benzo-vinyl bridging is to be contrasted with equal amounts of benzo-vinyl and naphtho-vinyl bridging reported 61 for the irradiation of /3-naphthobenzbarrelene. The photochemical conversion of triptycene (71a) into the product (72) has

R2

(71) a; R1 = R2 = H b; R1 = COMe, R2 = H C; R1 = H, R2 = OMe

& Meo /

(73) a; R = H b; R = COMe

s1

z

Me

(74) a; R2 = H b ; R2 = OMe

H. E. Zimmerman and M.-L. Viriot-Villaume, J. Amer. Chem. Soc., 1973,95, 1274.

Photochemistry of Olefins, Acetylenes, and Related Compounds

315

been interpreted in terms of the di-n-methane process.62 An alternative interpretation of this is one involving a carbene intermediate. Iwamura and coworkers 5 3 s 64 have reported trapping experiments in which carbene (73a), formed from the photolysis of triptycene, is trapped by methanol as the ether [(74a), 75x1. The reaction is efficient in terms of both the yield and the light utilization (0= 0.3). They 63, 64 have established that although the product (72) is also not stable to light in methanol, the product from its irradiation is a dihydrobenz(a)aceanthrylene. Further evidence for the carbene mechanism was obtained from the irradiation of the substituted triptycene (71b) whereby the carbene (73b), formed by the irradiation, is converted by Wolff rearrangement into a keten which is trapped as the ester (75). It is thus likely that the formation of the photoisomer (72) in inert solvents arises by a carbene mechanism and not by the di-v-methane path. The generality of the carbene mechanism has been questioned by Wheeler and co-workers 55 who have reported the photochemical conversion of dimethoxytriptycene (71c) into the aceanthrylene (76) in benzene or methanol solution. In this experiment there was no evidence for the formation of (74b), a product which would be expected if the mechanism proposed by Iwamura and Yoshimura 64 were general. The absence of the carbene-derived product could cast doubt upon the mechanism, but rigorous control experiments should be carried out. Direct irradiation of the diene (77a) in cyclohexane solution using 254 nm light afforded many minor products. However acetone-sensitizedirradiation gave a single product, identified as (78).66 Two mechanisms were considered for the 639

1

(77) a ; R = H

b;R=D

hv, sensitized

n

Scheme 11 68

6s

64 66

T. D. Walsh, J. Amer. Chem. SOC.,1969, 91, 515; N. J. Turro, M. Tobin, L. Friedman, and J. B. Hamilton, ibid., 1969, 91, 516. H. Iwamura and K. Yoshimura, J. Amer. Chem. Soc., 1974,96, 2652. H. Iwamura, Chem. Letters, 1974, 5. R. 0. Day, V. W. Day, S. J. Fuerniss, and D. M. S. Wheeler, J.C.S. Chem. Comm., 1975,296. R. K. Russell, R. E. Wingard, jun., and L. A. Paquette, J. Amer. Chem. SOC.,1974, 96, 7483.

316 Photochemistry formation of this product, both of which involve a di-r-methane path. Deuterium labelling of (77b) demonstrated that the product was formed predominantly by the route shown in Scheme 11. The di-77-methane reaction of diene (79) afforded the tricyclic product (80).67

3 Reactions of Dienes A theoretical treatment of the photochemical Diels-Alder reaction has been p u b l i ~ h e d .Pusset ~ ~ and Beugelmans have measured the fluorescence spectra and singlet energies of several conjugated dienes (81).59

(81) a ; b; c; d;

(81) e; R f; R

R' = R' = R3 = H ; E. = 383.4 kJ1110Ik~ R1 = Me. R 2 = R3 = H ; €. = 381.3 kJmol-I R' = R 3 = H , R' = M e ; E, = 381.3 kJmol-1 R'

=

=

H : E,

=

Me; E,

R2

=

=

H , R:'

=

Me; €,

379.2 kJmol 368.7 kJmol

=

381.3 kJniol-'

(81) g ; E,

=

387.6 kJmol-I

=

The text of a lecture on the benzophenone-sensitized cis-trans-photochemistry of penta-l,3-diene and hexa-2,4-diene has been published.s0 A quantum-chain process is described. Wrighton and Schroeder 61 have reported the photochemical hydrosilylation of dienes by irradiation in the presence of Cr(CO), and a silane. The following example is typical:

>-I +

Cr(CO)6

+

HSiMe,

-%-

SiMe, +Me, Si 40 %

m 68 69

6o

h

60 %

G. W. Klumpp, G. Ellen, and J. J. Vrielink, Tetrahedron Letters, 1974, 2991. N. D. Epiotis and R. L. Yates, J. Org. Chem., 1974, 39, 3150. J. Pusset and R. Beugelmans, J.C.S. Chem. Comm., 1974, 448. J. Saltiel, D. E. Townsend, and A. Sykes, Preprints Div. Petroleum Chem., Amer. Chem. SOC., 1973, 18,277 (Chem. Abs., 1975,82, 30 647). M. S. Wrighton and M.A. Schroeder, J. Amer. Chem. SOC.,1974, 96, 6235.

317

Photochemistry of Olefins, Acetylenes, and Related Compounds

Bigwood and Boue 6 2 have examined the reaction of penta-1,3-dienes with trimethyltin hydride and have found that the irradiation not only yields cyclobutene but also gives the two addition products (82) and (83). The absence of 1,2-addition products suggests that the addition is concerted. The authors 6 2 therefore suggest that a doubly twisted excited state (84) is preferred to the allylmethylene state which had been suggested at an earlier date for the conformation of the relaxed S1 state of d i e n e ~ .The ~ ~ divinylsilanes ( 8 5 ) have been

R

R

Ph H

H

fix \ /

SnMes

%

Sn Me

%-< (8 3)

(84)

Ph

(85) a ; R = Me b; R = Ph

investigated with particular emphasis on their di-n-methane r e a ~ t i v i t y .How~~ ever, analysis of the system shows that there is no evidence for the C-2-C-4 bonding which would be necessary for rearrangement. Indeed the only reactivity encountered either under direct or benzophenone-sensitized irradiation conditions was trans-cis-isomerization. The acetophenone-sensitized photochemical reactions of allene have been interpreted in terms of non-vertical energy transfer to produce the planar allene triplet.85 Several products are formed in the reaction, among which are allene dimers and trimers. Two ketones are also obtained, one (86) of which arises by attack of the central carbon of the allene triplet on the ortho-position of the acetophenone.

& A0

(86)

;;bPh

R1CH,Ph

CH,Ph

(87) a; R1 = Ph, R2 = H b ; R1 = p-MeC,H,, R2 C;

R'

=

p-ClCsHd,

= H R 3= H

(88)

The 4H-pyrans (87a-c) undergo photoisomerization into the 2H-pyrans (88) when irradiated through a quartz filter in cyclohexane solution.66 This reaction is formally a 1,3-sigmatropic migration. Accompanying this reaction when R1 = Ph in (87a) is a photo-oxidative dehydrocyclization affording a phenanthrene. A 1,5-migration of a hydroxy group is encountered in the photoconversion of the cyclopentadienol(89) into its isomer a 03

Ob

M. Bigwood and S. Boue, J.C.S. Chem. Comm., 1974, 529. E. M. Evleth, Chem. Phys. Letters, 1969,3, 122; N. C. Baird and R. M. West, J. Amer. Chem. Soc., 1971,93,4427; K. Inuzuka and R. S. Becker, Bull. Chem. SOC.Japan, 1971, 44, 3323; W. G. Dauben and J. S. Ritscher, J. Amer. Chem. SOC.,1970, 92, 2925. E. KrochmaI, jun., D. H. O'Brien, and P. S. Mariano, J. Org. Chem., 1975,40, 1137. H. Gotthardt and G. S. Hammond, Chem. Ber., 1975, 108, 657. N. K. Cuong, F. Pournier, and J.-J. Basselier, Bull. SOC.chim.France, 1974, 2117. J.-J. Basselier, F. Caumartin, J.-P. Le ROUX,and J.-C. Cherton, Bull. SOC.chim. France, 1974, 2935.

318

Photochemistry

a (91)

\

(92)

Valence bond isomerization of 2-trimethylstannylbuta-1,3-dieneto 1-trimethylstannylcyclobutene occurs when the diene is irradiated at 253.7 nm or 228.8 nm.se Other valence-bond isomers, 2-trimethylstannyl-1-methylenecyclopropaneand 3-trimethylstannylbuta-1,2-dieneYare also formed. The diene (91), formed in glassy solution at - 196 "C from the phthalazine (92), isomerizes into benzocyclobutene upon irradiation at h > 345 nm.6B An improved synthesis of methyl photolevopimarate (93) from the diene (94), originally reported by Dauben and C o a t e ~ , 'has ~ been de~cribed.~'The synthesis of the cyclobutene derivative (95) has been achieved by the irradiation of the

(95)

diene (96).72+ 73 The influence of the solvent in the photoisomerization of cycloocta-l,3-diene into bicyclo[4,2,0]oct-7-enehas been The homoazepine (97) undergoes valence-bond isomerization upon irradiation to yield the isomeric compound (98).75 A valence-bond isomer (99) is formed along with

'I0

'Is

P. Vanderlinden and S. Boue, J. Organometallic Chem., 1975, 87, 183. C. R. Flynn and J. Michl, J. Amer. Chem. SOC.,1974, 96, 3280. W. G. Dauben and R. M. Coates, J. Amer. Chem. SOC.,1964, 86, 2490. W. Herz, M. G. Nair, and D. Prakash, J. Org. Chem., 1975, 40, 1017. D. H. Aue and R. N. Reynolds, J . Org. Chem., 1974, 39, 2315. D. H. Aue and R. N. Reynolds, J. Amer. Chem. SOC.,1973,95, 2027. A. Kisaichi and M. Ogawa, Technol. Report Kansai Univ., 1973, 14, 57 (Chem. Abs., 1974, 80, 145 502).

7b

K. Shudo and T. Okamoto, Chem. and Pharm. Bull. Japan, 1974,22, 1204 (Chem. Abs. 1974, 81, 63 468).

Photochemistry of Olefns, Acetylenes, and Related Compounds

319

hepta-2,4,6-trienal (the main product, obtained as a mixture of isomers) and cyclohepta-3,5-dienone when 8-oxabicyclo[5,1,O]octa-2,4-diene is irradiated at 254 nm in ether.76

The influence of chloro-substituents on the exo-endo ratio for the ring closure in the irradiation of the bicyclononadienes (100) has been studied.77 Direct irradiation of the parent compound (100a) is likely to be a singlet reaction and yields a product ratio biased towards the endo-isomer. The increase in heavy atom (chlorine) content might be expected to influence the intersystem crossing and in accord with this reasoning the exo-isomer has been found to assume

(100) a ; R1 = R2 = R3 = H b; R’ = R3 = H,R2 = CI

c; R1 = d ; R1 = e ; RL = f;

RI

=

Cx’U

30 53 H,R2 = R3 = Cl 60 R2 = C1, R3 = H 61 R3 = CI, R2 = H 71 R2 = R? = C1 75 Scheme 12 a; b; c; d; e; f;

: 70 direct

: 47 direct : 40direct : 39 direct : 29 direct : 25 direct

enrib 68 : 30 sens. 70 : 30 sens. 71 : 29 sens. -

74 : 26 sens. 70 : 30 sens.

major importance. The acetophenone- or acetone-sensitized cyclization, presumably via a triplet state, gives a ratio of ca. 70 : 30 favouring the exo-isomer (Scheme 12). A study of the influence of substituents and multiplicity on the rearrangement pathways of the bicyclononatrienes (101) has been published.78 The results are shown in Table 6. The results show that the di-rr-methane route Table 6 Product yield (%)from irradiation of bicyclononatrienes (101)

Products (%) Bicyclononatriene

Irradiation mode

(101a)

direct sens. direct sens. direct sens. direct sens.

(101b) (101c)

(101d)

78

77 78

(102) 23 48 68 64 61 70

-

(105) 60 100

(103) 17

(104)

52 32 36 39 20

-

-

-

P. Schiess and M. Wisson, Helv. Chim. Acta, 1974, 57, 1692. C. W. JeRord and F. Delay, J . Amer. Chem. SOC.,1975,97,2272. R. C. Hahn and R. P. Johnson, J. Amer. Chem. SOC.,1975,97,212.

-

7.8 21

-

-

2.2 79

320

Photochemistry

to products is only followed by the unsubstituted or methyl-substituted derivatives of starting material. The presence of the heavy atoms in derivatives (101b) and (101c) completely inhibits the rearrangement, and cyclobutene formation results.

c; X = Br d ; X = l

The irradiation at 254 nm of hexane solutions of the 1 ,Zdimethylenecyclobutane (106) indicates that a singlet state is involved in bond cleavage to the biradical (107) which is the main pathway for i s o m e r i ~ a t i o n . ~A~ biradical intermediate (Scheme 13) is also involved in the formation of (108) from the

Scheme 13

irradiation of 4-methylverbenene The same product is formed on direct irradiation, but it is also accompanied by several unidentified minor products. Bond fission to a biradical followed by rebonding accounts for product formation in the irradiation of [(llo), Scheme 14].81Similar studies have been reported by P. A. Kelso, A. Yeshurun, C. N. Shih, and J. J. Gajewski, J. Amer. Chem. SOC.,1975,97, 1513. P. S. Mariano and D. Watson, J . Org. Chem., 1974, 39, 2774. Y. Kobayashi, I. Kumadaki, A. Ohsawa, and Y. Sekine, Tetrahedron Letters, 1974, 2841.

32 1

Photochemistry of Olefins, Acetylenes, and Related Compounds

(110) R = Hor Me

Scheme 14

Eberbach 82 who observed that the 1,s-dienes (1 11) photochemically isomerized to (112) via biradical (113). The products from this reaction are photochemically labile and can be converted into the bicyclic compounds (114) by acetone sensitization.

(1 11) a ; X b; X

spiro-C,H4, R1 = R2 = C0,Me = R3 = R4 CH,, R1 = R2 = R3 = R4 = CQMe c ; X = CH,, R1 = R2 = CO,Me, R3 = R4 = H d; X = CH,, R1 = CO,Me, R2 = R3 = R4 = H = =

(112)

(1 13)

The 7-silanorbornadiene (1 15) was converted in 88% yield into diniethyl . ~~ silabicyclo3,4,5,6-tetraphenylpht hala te by irradiation in benzene s o ht i ~ n The anhydride (116) gave the silapentadiene (117) in good yield. The diene (118),

Ph Ph (1 15) Ba 8a

s1

R2 (116) a; R = Me b; R = Ph

(117)

W. Eberbach, Chem. Ber., 1974, 107, 3287. R. Balasubramanian and M. V. George, J. Organometallic Chem., 1975,85, 131.

322

Photochemistry

formed by decarbonylation of (1 19), undergoes photochemical fragmentation into 1,4-dimethy1-2,3-diphenylbenzeneand the highly unstable azetinone (120).84

4 Reactions of Trienes and Higher Polyenes The photochemistry of natural products, especially those with polyene and carbonyl chromophores 85 and of C9Hlo hydrocarbons,86 has been reviewed. The sunlight photochemistry of retinyl acetate has been reported.87 Irradiation of 1,3,6-triphenylhexa-l,3,54riene in the presence of iodine in benzene or cyclohexane solution affords a good yield of 1,2,4-triphenylbenzene. This result is surprising, all the more so since the product is also formed in a thermal reaction of the triene with iodine.88 However, attempts by the authors to isolate an intermediate in the photochemical reaction were not successful and it is assumed that the cyclization follows a Cope-type path rather than the more t c S i M e 2

H

:fiiMe,

RcsiMeroMe

R -*

(121)

Ph (122) a ; R b; R

= =

H Ph

Ph (123) a ; R b; R

=

=

H Ph

/

Ph (124) a; R b; R

=

=

H Ph

Ph

Ph

( I 29)

87

G. Kretschmer and R. N. Warrener, Tetrahedron Letters, 1975, 1335. E. P. Serebryakov and V. F. Kucherov, Zhur. Vsesuyuz. Khim. obshch. im. D . I. Mendeleeva, 1974, 19, 403 (Chem. Abs., 1974, 81, 162 004). H. Tsuruta, T. Kumagai, and T. Mukai, Yuki Gosei Kagaku Kyokai Shi, 1974,32,496 (Chem. Abs., 1975, 82, 42 419). K. K. Das, Indian J. Chem., 1974, 12, 1216. W. Carruthers, N. Evans, and D. Whitmarsh, J.C.S. Chem. Conm., 1974, 526.

323

Photochemistry of Olefns, Acetylenes, and Related Compounds

common cyclization of aryl-substituted trienes which have been reported by Cyclization to the bicyclic compound (121) occurs with the silatriene (122a) formed by ring-opening of the diene (123a) when irradiation is carried out in an inert solvent. In methanol, however, the triene (122a) is trapped as the adduct (124a).0° The photochemistry of hexatrienes is often dominated by steric factors which dictate whether the triene yields the bicyclic structure (121) or forms a cyclobutene. This latter type of reactivity is followed by the tetraphenyl derivative (123b) which yields the triene (122b) on photochemical excitation. No spectral evidence for the intermediacy of the triene was obtained, but this is the most likely precursor of the single photoproduct (125). The trapping experiment with methanol also suggests the presence of the triene since two adducts (124b) from the triene and (126) from the cyclobutene are formed. Nakadaira et aLgl have also studied the photoreactivity of the disila-derivative (127). Irradiation of this in C,D, solution gave the air- and moisture-sensitive isomer (128). This product is also thermally unstable and can be converted into the product (129). c8H17

,,& /

Me

HO'

(131)

(133) R1 = Me, R2 = OEt (134) R1 = OEt, R2 = Me

(135)

Further products have been identified from the irradiation of 7-dehydrocholesterol [(130), provitamin DJ. In ether or alcohol the main component of the photolysate was assigned structure (131) which results from the photochemical cyclization of the trans-Z-cis-conformationof the triene (132) formed by ringopening of the cholester01.~~From reaction in ethanol two alcohol-addition products (133) and (134) have been identified. Two other products of the toxisterol type have been assigned structures (1 3 3 , the difference between them O0

Oa

A. Padwa, L. Brodsky, and S. Clough, J. Amer. Chem. SOC.,1972, 94, 6767. Y.Nakadaira, S. Kanouchi, and H. Sakurai, J. Amer. Chem. SOC.,1974,96,5621. Y. Nakadaira, S. Kanouchi, and H. Sakurai, J. Amer. Chem. SOC.,1974, 96, 5623. F. Boosma, H. J. C. Jacobs, E. Havinga, and A. van der Gen, Tetrahedron Letters, 1975,427.

324

Photochemistry

depending only upon the configuration at C-8. Finally, a hydrogen-transfer product (136) was also isolated. Toxisterols (137) have also been obtained in low yields from irradiation of ergosterol (138) in degassed ethanol-water containing citric The complete structure of (137a) was determined by X-ray diffraction analysis. The formation of the products arises by a hydrogen-transfer step, e.g. in biradical (139) to yield (140) which bonds to afford the isolated products. Fragmentation products (141) were also

(137a)

(137b)

p7 71@

R1 (141) a; R’ b ; R‘ C;

R2 = =

R1 =

R2 = H OEt, R2 = H H, R2 = OEt

(137c)

C9Hlf

R

(141) d ; R = H o r Me

@ (141e)

An oxa-analogue of the hexatriene-bicycl0[3,1,O]hex-2-ene conversion has been reported from the study of the photolysis of the isochromenes (142).95 Irradiation (Pyrex filter) in methanol gave two products (143) and (144), the second of which arises by secondary photolysis of the oxabicyclohexene (143). This product most likely arises by [4 + 2lphotoaddition of the quinone methide intermediate (145). The formation of products is inefficient [@ = 0.02 for the formation of (143, R = Ph)] but this is to be expected for two sequential photoprocesses. Padwa and co-workers 96 have previously reported the photoreactions of the O3

84

O6

O6

A. G . M. Barrett, D. H. R. Barton, M. H. Pendlebury, L. Phillips, R. A. Russell, D. A. Widdowson, C. H. Carlisle, and P. F. Lindley, J.C.S. Chem. Comm., 1975, 101. A. G. M. Barrett, D. H. R. Barton, R. A. Russell, and D. A. Widdowson, J.C.S. Chem. Comm., 1975, 102. A. Padwa, A. Au, and W. Owens, J.C.S. Chem. Comm., 1974, 675. A. Padwa and G. Lee, J.C.S. Chem. Comm., 1972, 795; A. Padwa, A. Au, and W. Owens, ibid., 1974, 675.

325

Photochemistry of Olefins, Acetylenes, and Related Compounds HO Ph

a / Ph

\ =

p

@Me

h

\

R (142) R

0

R

\

R

Ph, Me, or H

(143)

a \

'

PI1

R (145)

chromenes (146). A full account of this work has now been p~blished.~'The photochemistry of the enols (146f, g) has also been studied.gs A 1,5-hydrogen transfer is encountered in the conversion of the triene (147) into (148).99 This product is also photolabile.

(147)

(1 48)

A detailed reinvestigation looof the photoproduct produced by irradiation of the diene (149) has shown that the structure is (15O).lo1 This product presumably arises by thermal ring-closure of the triene (151) formed by photochemical ring P

P hh H

Ph \ Ph H (149)

p

a IP h ' h O Ph Pi(1 50)

Ph

l

1

-

b

Ph

(151)

opening of (149) in a conrotatory fashion. The monocyclic lH-aza[l3]annulene (152a) is obtained by acetone-sensitized irradiation at 0" C of the bicyclic pentaene (153).lo2 The structural information obtained from the compound was not sufficiently detailed to eliminate the possibility of a trans-double bond in the molecule. The aza-annulene (1 52b) does, however, exhibit aromatic character. A. Padwa, A. Au, G. A. Lee, and W. Owens, J . Org. Chem., 1975, 40, 1142. A. Padwa and A. Au, J. Amer. Chem. SOC.,1975, 97, 242. V. Ramamurthy and R. S. H. Liu, J. Org. Chem., 1974, 39, 3435. l o o R. C. Cookson and D. W. Jones, J, Chem. SOC., 1965, 1881. lol R. C. Cookson and D. W. Jones, J.C.S. Perkin I, 1974, 1767. lo2 A. G. Anastassiou and R. L. Elliot, J . Amer. Chem. SOC.,1974, 96, 5257. s7

326

Photochemistry

b;R=H (153) A few years ago the conversion of (154) into the isomeric material (155) was reported by Paquette et a1.1°3 to result from a photochemical 1,3-shift. A reexamination of this process has shown that the reaction is considerably more complex and the photochemical step is the formation of the thermally labile

(155)

Scheme 15

(CH),, derivative (156) which is thermally converted into (155) by the route shown in Scheme 15.1°4 The photochemical decomposition of the azafulvenes (157) has been described.lo6 Prinzbach and Sauter lo8have reported the conversion of the polyenes

(157) R

=

Ph or p-ClC,H4

(158) into the fulvalenes (159) by irradiation (either direct or ketone-sensitized) in acetonitrile solution. The transformation is thought to follow the path outlined in Scheme 16 whereby the polyene isomerizes into a norcaradiene by a 1,3-shift followed by ring opening to the observed products. A 1,3-shift accounts for the minor product (160) formed in the photolysis of the 3,4-benzotropilidenes (161).lo7 The main product (162) is the result of 1,7-migration. Both of these L. A. Paquette, M.J. Kukla, and J. C. Stowell, J. Amer. Chem. SOC.,1972,94,4902. E. Vedejs, R. P. Steiner, and E. S. C. Wu, J . Amer. Chem. SOC.,1974, 95, 4040. lo5 E. M. Burgess and J. P. Sanchez, J. Org. Chem., 1974, 39,940. lor, H. Prinzbach and H. Sauter, Tetrahedron Letters, 1974, 3049. 10' K. A. Burdett, F. L. Shenton, D. H. Yates, and J. S. Swenton,Tetrahedron, 1974,30,2057.

los

lo'

327

Photochemistry of Olefins, Acetylenes, and Related Compounds

IIV

(158)

(159)

R1 = R2 = Ph, R3 = C0,Me R1 = Ph, R2 = H, R3 = C02Me R1

=

R2

=

R3

=

H

Scheme 16

processes are photochemically ‘allowed’. The results have permitted the assessment of migrational aptitudes; thus hydrogen migrates a thousand times more readily than the methyl group. Whereas these results for migratory aptitudes are similar to results for thermal processes, the authorslo7suggest that it would be unwise to extrapolate their results to other photochemical systems. Finally, the formation of the norcaradiene products occurs with high quantum efficiency and it is likely that group migration serves as a major path for excited-state decay.

R1 = R 2 . = H b; R1 = Me, R2 = H

(160) a; C;

R1

= R2 =

(162) a; b; C;

d;

(161) a; R1 = R2 = H b; R1 = Me, R A = H c ; R1 = R2 = Me d; R1 = R2 = C02Me

Me

R1 = R2 = H; cf, = 0.87 R1 = Me, R2 = H; 0 = 0.93 R1

=

R2

=

Me; @

=

R1 = R2 = C0,Me;

0.34

CD = 0.78

The reactions of the cycloheptatriene moiety dominates the photochemistry of the spiro-compound (163) which shows U.V. absorptions at 263 and 350 nm.lo8 Irradiation into the long-wavelength band, or benzophenone sensitization led to a

(163) lo*

( 16 9

(1 65)

K. Saito, T.Toda, and T. Mukai, Bull. Chem. SOC.Japan, 1974, 47, 331

328

Photochemistry

quantitative recovery of the starting material. However, irradiation into the 263 nm band resulted in the formation of the valence bond isomers (164) and (165). The bis-norcaradiene (1 66) was produced in solution (CDC1,-Frigen 11) when the mixture of valence bond isomers (167) was irradiated (A = 360 nm) at -70 "C. The presence of the norcaradiene (166) was established by n.m.r. ~pectro~copy.~~~

(167a)

(167b)

Hart and Kuzuya 110 have described reactions involving [2 + 2ladditions which do not arise by a concerted pathway. These observations arise from the report ll1 that the dienes (168) do not undergo cycloaddition reactions whereas &1R

RZ (168) a; b;

R1 = Ph, RZ = H R1 = H,R" = Ph

the triene (169) does so. The difference between the two classes is that the latter can be accommodated within the di-n-methane framework. Indeed this triene is converted upon irradiation in ether into the [2 21product (170). The mechanism by which this conversion arises is as shown in Scheme 17. [2 21Addition, also by a two-step process, is encountered in the trienes (171) which

+

+

(170) Scheme 17 109

l10 111

H. Diirr, M. Kausch, and H. Kober, Angew. Chem. Internat. Edn., 1974, 13, 670. H. Hart and M. Kuzuya, J. Amer. Chem. SOC.,1974, 96, 3709. G. Kaupp and K. Krieger, Angew. Chem. Internat. Edn., 1972, 11, 719.

329

Photochemistry of Olefins, Acetylenes, and Related Compounds

(171) R1 = R2 = Me R1 = Me, R2 = H R1 = H, R2 = Me

(1 72)

are converted into the isomers (172). Again a di-rr-methane path is proposed. Quartz-filtered irradiation of the triene (173) in pentane at -40 "C yielded at least eight products, seven of which have been identified and are shown in Scheme 18.112

IIV

49%

26%

trace

(173)

9%

5%

3%

6% Scheme 18

5 Reactions of Carbonium Ions

A report of an unidentified single product from the irradiation of protonated cyclo-octatetraene (174) has been made re~ent1y.l~~ A re-examination of the problem has identified the ion as (175).l14 This ion can be produced by the protonation of the dihydropentalene (176). The formation of the ion (175) photochemically probably arises by an allowed disrotatory closure between C-1 and C-5. This is followed by a double-hydride migration. These reactions are pictured in Scheme 19. A review of such processes has been published.l16 The

Scheme 19 11*

114

D. Borse and A. de Meijere, Angew. Chem. Internat. Edn., 1974, 13, 663. H. Hogeveen and C. J. Gassbeck, Rec. Trav. chim., 1970, 89, 1079. P. A. Christenson, Y.Y.Huang, A. Meesten, and T. S. Sorensen, Canad. J. Chem., 1974,52, 3424.

116

P. W. Cabell-Whiting and H. Hogeveen, Ado. Phys. Org. Chem., 1973, 10, 129.

330

Photochemistry

thermal transformation of the cation (177a) into the ion (178a) is a forbidden process. Conversely the photochemical transformation should be allowed. have examined this problem and have demonstrated that the ion Childs et (177a) is photochemically converted into (178a) upon irradiation in FS0,H at -78 "C. A similar transformation was also found for the tetramethyl analogue (177b). This report gives in detail work which was reported earlier in note

R (177) a ; R = Me b; R = . H

R (178)

form.117 Another full report,lls giving greater detail than the original note,ll9 has been published on the photochemical ring closure of ion (179) to (180). The thermal transformations of these ions have also been studied in great detail. The cyclohexadienyl cations (181) can be conveniently prepared by the dissolution of

the corresponding cyclohexadienones in 96% sulphuric acid. Irradiation of the resultant solutions using quartz-filtered irradiation transformed the cations into the bicyclic cations (182) and (183). N.m.r. analysis of the solutions indicated that two cations (182a) and (183a) are formed from the cation (181a) in a ratio of 1.4 : 1.120 A ratio of 1.1 : 1 was obtained for the two ions, (182b) and (183b), which were formed from the ion (181b). In both these examples the smaller group predominantly occupied the endu-position in the new ion. The study of the steric effects was made using the ion (181c) which gave the rearranged ions (182c) and (183c) in the ratio of 1.4 : 1. An enhanced ratio of 2 : 1 was obtained for the two ions (182d) and (183d) formed from the cation (181d). Again there is a remarkable preference for the formation of the endu-methyl bicyclic cation. The authors 120 argue that the observed results fit into the proposals put forward by Hart and Rodgers121 that as the second group on C-4 is increased in size 116

R. F. Childs, M. Sakai, B. D. Parrington, and S. Winstein, J. Amer. Chem. SOC.,1974, 96, 6403.

11'

R. F. Childs, M. Sakai, and S. Winstein, J. Amer. Chem. SOC.,1968, 90, 7144; R. F. Childs

11*

R. F. Childs and S. Winstein, J. Amer. Chem. SOC.,1974, 96, 6409.

and B. D. Parrington, Chem. Comm., 1970, 1540.

R. F. Childs and S. Winstein, J . Amer. Chem. SOC.,1968, 90, 7146.

J. M.Pavlik and R. J. Pasteris, J. Amer. Chem. SOC.,1974, 96, 6107. 121 T.R. Rodgers and H. Hart, Tetrahedron Letters, 1969, 4845.

120

Photochemistry of Olefins, Acetylenes, and Related Compounds

331

the smaller group will pass through the C-3,C-5 plane more easily. This is certainly the case when C-3 has a methyl substituent. One other steric factor seems to be important and that is the interaction of the C-1 hydroxyl with R1on C-4. This interaction is more important than the interactions between the substituents on C-4 and C-5. Photochemical cyclization of the ions (184) and (185) in 98% sulphuric acid yields the ions shown in Scheme 20.122 Disrotatory cyclization of the two ions (184) and (185) affords the intermediate ions (186) and (187) which undergo a stereospecific 1,4-hydride transfer to yield the observed products (188) and (189). The electrocyclic process which leads to the ring closure is photochemically allowed. However, the 1,4-hydride migration is a forbidden process yet it occurs with stereospecificity which the authors 121, rationalize in terms of interaction of the hydrogen 1s orbital with the secondhighest molecular orbital of the dienic unit thus stabilizing the transition state for the transfer. The other products of the reactions (190) and (191) must arise by 21 mode but the details of this are unknown. another [2

+

R

OH

+

H

(190)

Scheme 20

6 Photolysis of Insecticidal Chlorocarbons A review of the photochemistry of chlorocarbon insecticides has been published.12S The photochemical decomposition of the insecticides resmethrin and of some pyrethroids has been described.124 The rate of photoisomerization of endrin (192) in sunlight has been The u.v.-irradiation ( A > 230 nm) of photoDieldrin (193) spread on glass gave two products (194).12* The irradialaa la*

R. Noyori, Y.Ohnishi, and M. Kato, J. Amer. Chem. SOC.,1975, 97, 928. J. R. Plimmer, Pesticide Chem., Proc. Internat. Conf., 1972, 5, 413 (Chem. Abs., 1974, 80, 23 385).

lz4

les

K. Ueda, L. C. Gaughan, and J. E. Casida, J. Agric. and Food Chem., 1974,22,212 (Chem. Abs., 1974, 80, 146 364). W. B. Burton and G. E. Pollard, Bull. Environ. Contam. Toxicol., 1974, 12, 113 (Chem. Abs., 1975, 82, 27 186).

S. Glib, H. Parlar, and F. Korte, Chemosphere, 1974,3, 187 (Chem. Abs., 1975, 82, 52 596).

332

Photochemistry CI,

&cl

*'

c1

CI

(195) a; R b; R

= =

C0,Me CO,H

(196)

(197)

(199) a; R1 = H, R2

= C1; 30% b; R1 = CI,R2 = H ; 20%

tion (A > 300 nm) of the diester (195a) in acetone affords two photodechlorination products (196) and (197).127 Photodechlorination of (198) has also been reported and yields (199).128 Under the same conditions the irradiation of the diacid (195b) was much more complicated and gave, after esterification, the products shown in Scheme 2l.lZ7 le7 la*

S. Gab, H. Parlar, and F. Korte, Tetrahedron, 1974, 30, 1145. J. B. Bremner, Y. Hwa, and C. P. Whittle, Austral. J. Chem., 1974,27, 1597.

333

Photochemistry of OIeJins, Acetylenes, and Related Compounds

+

R

=

C0,Me in products

R ' Reagents: i, hv; ii, esterification

Scheme 21

+

7 [2 2]Intramolecular Addition Reactions The cage compound (200a) has been synthesized by the photochemical cyclization of the chlorodiene (2O1).l2O The photochemical ring closure of cyclopentadiene dimer (201b) to the bis-homocubane (200b) was originally reported by Schenck and stein met^.^^^ A recent reinvestigation has claimed that the reaction, which is

R (200) a; R = C1 b;R=H

(201) a; R = C1

b;R=H

achieved by irradiation of an acetone solution of the diene, can be capricious unless the dimer is purified carefully by chromatography prior to the photo1 ~ s i s . lThe ~ ~ cage compound (202) is formed in quantitative yield when the phosphoIe oxide dimer (203) is irradiated in benzene-acetone solution in a lZ8

lal

W. L. Dilling, R. A. Plepys, and J. A Alford, J. Org. Chem., 1974, 39, 2856. G. 0. Schenck and R. Steinmetz, Chem. Ber., 1963, 96, 520. J. Blum, C. Zlotogorski, and A. Zoran, Tetrahedron Letters, 1975, 1117.

12

334

Photochemistry 0

-\

ph-P4 O’/p‘Ph

OH

‘Ph

quartz reactor.lge Direct irradiation in methanol brings about fragmentation to yield methyl phenylphosphonate as the sole product. Homocubanone (204) has been efficiently synthesized in a six-step procedure, one stage of which involved the acetone-sensitized photocyclization (75%yield) of (205) to (206).133The cage compound (207) is readily prepared by irradiation of the diene (208).13*Previous reports have dealt with the synthesis of the corresponding ethyl

$gOM OMe

(2 10)

+

An ethereal solution of the triene (209) affords the [2 Illadduct (210) when irradiated.138 Spectral evidence permitted the assignment of this structure rather than the alternative which might have been produced by the di-7r-methane pathway. Cage compounds (21 1) are also formed in the irradiation of the trienes lsa 133

136

lS6

H. Tomioka, Y. Hirano, and Y. Izawa, Tetrahedron Letters, 1974, 4477. W. G. Dauben and L. N. Reitman, J. Org. Chem., 1975,40, 835. R. Askani, I. Gurang, and W. Schwertfeger, Tetrahedron Letters, 1975, 1315. R. Askani, Chem. Ber., 1969, 102, 3304; Tetrahedron Letters, 1970, 3349. H. Hart and M. Kuzuya, J. Amer. Chem. Soc., 1974,96,6436.

335 (2l2).l3'~13* However, these compounds are not formed by direct [2 + 2laddition but undergo prior isomerization to the allenes (213). Ring closure to (211) is only exclusive when the allene (213) is disubstituted. With mono-substitution (2130 two other products are formed by a di-n-methane reaction.

Photochemistry of Olefns, Acetylenes, and Related Compounds

a;

R2 = R3 = R4 = RS = Me R3 = R4 = R5 = Me, R2 = H R1 = R2 = R4 = R 5 = Me, R3 = H R1 = R2 = Ph,R3 = R4 = R5 = Me R1 = R2 = R3 = Me, R4 = R5 = ph R1 = H, R2 = R3 = R4 = R5 = Me R' = R3 = R4 = R = Me, R2 = H R1

=

b; R1

=

c; d; e; f;

g;

The pentacyclic hydrocarbon (214) was obtained in high yield by direct irradiation of an ethereal solution of (215).lS9 The [2a 2n] reaction type is also encountered in the conversion of the bishomobarrelene (216) into (217).140

+

(216)

(217)

Polovsky and Franck 141 have re-examined the irradiation of the endo-oxide (218). Previously Hammond and Ziegler 142 had shown that irradiation in ethanol or ether solution gave the benzoxepin (219) in a low yield. In the re-examination of the photochemistry naphthalene and the reduced compound (220) were also H. Hart and M. Kuzuya, Tetrahedron Letters, 1974, 1909. H. Hart and M. Kuzuya, Tetrahedron Letters, 1974, 1913. lS9 T. Sasaki, S. Eguchi, F. Hibi, and 0. Hiroaki, J . Org. Chem., 1975, 40,845. loo V. A. de Meijere, D. Kaufmann, and 0. Schallner, Tetrahedron Letters, 1974, 3835. S. B. Polovsky and R. W. Franck, J . Org. Chem., 1974, 39, 3010. G. R. Ziegler, J. Amer. Chem. SOC.,1969, 91, 446; G. S. Hammond and G. R. Ziegler, J. Amer. Chem. Soc., 1968, 90, 513. Is7 lS8

Photochemistry

336

detected. The yield of these products was greatly enhanced when the reaction was carried out in triethylamine as solvent. The having excluded several other mechanistic routes, suggest that the naphthalene arises by an extrusion of the oxygen atom. Further study on the isomerization of, e.g., oxanorbornadiene (221) has shown that it can be converted into the fulvene [(222b), 75x1 by action of iodine atoms produced photochemically (visible light). The oxaquadricyclanes (223) also undergo isomerization (A = 254 nm) into the fulvenes (222).143

C0,Me (22 1)

(222) a; R.= H b;R=Me

R2 (223) a; R1 = H, R2 = Me b; R1 = R2 = Me

Hammond et aZ.la4have described experiments on the photochemistry of 1,s-divinylnaphthalene using bromocyclopropane, a heavy-atom solvent, as an aid to intersystem crossing ((Disc = 0.25) from the singlet to the triplet manifold of the naphthalene. The products (0= 0.16) obtained were (224) and (225)

which had been previously reported by Meinwald et aZ.146 The bromocyclopropane quenches the fluorescence of the 1,s-divinylnaphthalene (0= 0.71) and from these data a fluorescent lifetime of 1.4 ns was calculated. The effect of the quencher was to enhance the disappearance of starting material, increase the quantum yield for product formation, and decrease the fluorescence. These results are shown in Table 7. 143

R. K Bausal, A. W. McCulloch, P. W. Rasmussen, and A. G. McInnes, Canad. J . Chem., 1975, 53, 138.

114 l45

R. H. Fleming, F. H. Quina, and G. S. Hammond, J . Amer. Chem. SOC.,1974, 96, 7738. J. Meinwald and J. W. Young, J . Amer. Chem. SOC.,1971, 93, 725; J. Meinwald and J. A. Kapecki, ibid., 1972, 94, 6235; J. Meinwald, J. W. Young, E. J. Walsh, and A. Courtin, Pure Appl. Chem., 1970,24, 509.

337 Table 7 Influence of heavy-atom solvent on fluorescence and product formation from 1 ,g-diuinylnaphthalene 144

Photochemistry of Olefns, Acetylenes, and Related Compounds

Brornocyclopropane

@fO1@f

@prod/@prodo

0.00

1.oo 1.08 1.18 1.28 1.38 1.46

1.oo 1.25 1.52 1.65 1.81 1.95

0.50 0.99 1.49 1.99 2.48

8 Dimerization and Intermolecular Cycloaddition Reactions Kricka and Ledwith 146 have reviewed the photochemical synthesis of cyclobutanes by dimerization of mono-olefins. Routes which involve radical cations, species of recent interest, are discussed. Yamamoto et al.14' have shown that p-methoxystyrene undergoes photodimerization in acetonitrile solution with p-cyanobenzene as an electron acceptor. These conditions (Pyrex filter) yield the trans-head-to-head-dimer [(226a), 13%]. Dimerization does not occur in non-polar solvents. A study of the emission characteristics of the styrene-cyanobenzene system shows that the fluorescence of the styrene is quenched and a broad exciplex emission is observed at 440nm. The likely path for dimerization involves electron transfer as shown in Scheme 22. p-NN-Dimethylaminostyrene Me0

Me0

Me0

CN

CN

iiii

1

Me0

(226a)

f---

t

\

M eO Reagents: i, hv; ii, p-dicyanobenzene; iii, p-methoxystyrene

Scheme 22 148

147

L. J. Kricka and A. Ledwith, Synthesis,

1974, 539. M. Yamamoto, T. Asanuma, and Y . Nishijima, J.C.S. Cliem. Comm., 1975, 5 3 .

338

Photochemistry

also affords a trans-head-to-head-dimer (226b) when irradiated in polar However, in this case electron acceptors are not required. It is argued, however, that the lower ionization potential of this styrene permits the formation of the radical cation. In non-polar solvents (benzene or hexane) the cis-head-to-head-dimer is produced. A cis-head-to-head-dimer (227) is obtained from the solid-phase photolysis of (228).148 U.V. irradiation (366nm) of the

R

xPh Ph R (226) a ; R b; R

= =

OMe MezN

(227)

(228) a; X

-

CIC,H4S0, b; X = Br C; X = BF4 =

azastilbenes (228) in acetonitrile solution results in rapid trans-cis isomerization The photodimerization of and the establishment of a photostationary benzo[b]thiophen 1,l-dioxide at 313 nm has been shown to be solvent dependent.lso Thus in benzene solution the quantum yield for dimerization is 0.17 while in bromoethane it is 0.043. The other feature of this solvent dependency is the increase in the intersystem crossing efficiency from 0.18 in benzene to 1.O in bromoethane. The kd/k, ratio also increases from benzene to bromoethane. The results obtained can be rationalized in terms of an intermolecular heavyatom effect. A full report of the influence of heavy-atom solvents on the photodimerization of acenaphthylene has been reported.lS1 As in the initial account lS2 of this work, ethyl iodide was found to be an effective heavy-atom solvent but there is a practical limit to which one can push the effect after which no benefit can be obtained. The principal effect of the ethyl iodide is to influence the Sl-Tl crossing efficiency. This happens up to 10 mol % of ethyl iodide. After that value a decrease in the dimerization efficiency is encountered as a result of competition by deactivation from the triplet to the ground-state singlet. The products formed from the dimerization are the cis- and the trans-dimers (229) and

118

lSo 161 lSa

T. Asanuma, M. Yamamoto, and Y. Nishijima, J.C.S. Chem. Comm., 1975, 56. F. H. Quina and D. G. Whitten, J. Amer. Chem. SOC.,1975, 97, 1602. W. W. Schloman, jun. and B. J. Plummer, J.C.S. Chem. Comm., 1974, 705. D. 0. Cowan and J. C. Koziar, J. Amer. Chem. SOC.,1975, 97, 249. D. 0. Cowan and J. C. Koziar, J. Amer. Chem. SOC.,1974,96, 1229.

339 Photochemistry of Olefins, Acetylenes, and Related Compounds (230), the ratio of which is independent of the concentration of acenaphthylene, or added triplet quenchers. There is a small effect on the dimer ratio as the amount of ethyl iodide is increased. It is proposed that this effect arises from a change in the dielectric permittivity of the solution. It is thought that this solvent effect is due to increased stabilization of the transition state leading to the cisdimer relative to that leading to the trans-dimer. Labrum et aZ.153have synthesized the compound (23 1) by the photochemical addition of acenaphthylene to 1,2-dibromoacenaphthylene to afford (232) which was subsequently debrominated. This compound (231) was irradiated in an EPA glass at - 196 "C with monochromatic light of 277 nm and longer wavelength with no detectable reaction. Simultaneous irradiation with visible light also had no effect. However, irradiation at 254 nm brought about conversion into (233).

A review of the influence of substituent effects on photochemical cycloaddition reactions has been p~b1ished.l~~ Another short review on photocycloaddition reactions has also appeared.lS5 Two studies of the addition of olefins to 9-cyanophenanthrene have been reported.16s~ Mizuno et aZ. have examined the addition of the olefins (234a-e)

R1

R2

(234) b; a; R1 = R2 = RR3 R3 3R ' 4 = H, R4 = OMe OEt c; R1 = H, R2 = R3 = R4 = Me d; R1 = R2 = R3 = R4 = Me e ; R1 = H, R2 = CH=CMe,, RE = R4 = Me f; R1 = R4 = H, R2 = Me, R3 = p-MeOC,H4 g; R1 = Me; R2 = R4 = H, R3 = p-MeOC,H4

$$:; (235)

to yield the cyclobutane adducts (235a-e) and have shown that the additions are highly stereoselective. Contradictory results were obtained regarding the excited state involved in the reaction. Thus the olefins (234a-c) added via a triplet-state mechanism while the addition of olefin (234d) could not be sensitized. A singlet lS8

Is' lS6 lS7

J. M. Labrum, J. Kolc, and J. Michl, J. Amer. Chem. SOC.,1974, 96, 2636. W. C. Herndon, Topics Current Chem., 1974, 46, 141 (Chem. Abs., 1975, 82, 15 745). R. P. Ghandi, S. Garg, and S. M. Mukherji, J. Indian Chem. SOC.,1974,51,324. K. Mizuno, C. Pac, and H. Sakurai, J. Amer. Chem. Sac., 1974,96, 2993. R. A. Caldwell and L. Smith, J. Amer. Chem. Soc., 1974,96,2994.

340 Photochemistry state is likely in this case and also with the olefin (234e) where a singlet state was definitelyproven. Fluorescence of the phenanthrene could be quenched by olefin (234e) and evidence for a singlet exciplex mechanism was obtained. Further evidence for an exciplex mechanism was obtained by the isolation of a product which had incorporated methanol (the solvent). It is therefore clear that the mechanism of addition depends to a large extent on the ionization potentials of the olefins used in the addition. Singlet-state addition has also been reported for olefins (234f, g). The authors of this study report that a singlet exciplex mechanism is most likely in these cases since photoaddition occurs simultaneously with exciplex emission. Considerable speculation about the mechanism for the photo-reaction of phenanthrene with dimethyl fumarate and maleate has appeared. Farid et nZ.1s8originally proposed that a singlet or triplet exciplex might be involved in the addition but Kaupp questioned the intermediacy of such an exciplex. Creed and Caldwell 160 have re-examined the process and have published good evidence for the involvement of a singlet exciplex. The irradiation (347 nm) of phenanthrene in the presence of dimethyl fumarate gave the products outlined in Scheme 23. The evidence for the formation of an exciplex comes

/

Reagents: i, hv, dimethyl fumarate; ii, H+

Scheme 23

from the observation that the fluorescence of phenanthrene is quenched by fumarate and a new emission appears at 452 nm. This new emission is very weak. That the emission is from an exciplex is evidenced by the fact that the fluorescence can be quenched by the addition of electron donors. The quenching efficiency follows the ionization potentials of the quenchers (Table 8). The quencher also quenches the formation of the products and the authors160 believe that the exciplex is a viable precursor for the formation of the three p hot opr oducts. S. Farid, J. C. Doty, and J. L. R. Williams, J.C.S. Chem. Comm., 1972, 711. G . Kaupp, Angew. Chem. Internat. Edn., 1973, 12, 765. D. Creed and R. A. Caldwell, J. Amer. Chem. Soc., 1974, 96, 7369.

lB8

15@

160

341

Photochemistry of Olefins, Acetylenes, and Related Compounds

Table 8 Influence of quenchers of diflerent ionization potential on exciplex emission form the phenanthrene-fumarate system 160 Quencher 2-Methyl but-2-ene Ethyl vinyl ether 2,3-Di methylbut-2-ene Dihydropyran Phenanthrene Triethylamine

IPIeV 8.89 8.49 8.30 8.34

kqTtfluor)/l mol-l

kqT(react)/lmol-1

0.1 0.7 2.4 3.9 5.0 9.4

-

8.10 7.50

2.3 4.2 8.7

Ferree et have studied the reaction of acenaphthylene with cis- and trans-piperylene. The reaction has been shown to be regiospecific as outlined in Scheme 24; the total yields of the products (236) are atso shown. The authors

(236) a ; R1 = cis-CH=CHMe, R2 = H b; R1 = H, R2 = cis-CH=CHMe

(236) e; R1 = H , R 2 = CH=CH2 f ; R' = CH=CH,, R2 = H

(236) c; R' = CH=CH2, R2 = H d ; R' = H, R2 = CH=CH2

(236) g ; R1 = H, R2 = Me. h; R' = Me, R2 = H

(236a) 51"& direct + (236b) 41% direct + (236d, f, h) traces and sensitized 4206 sensitized

+

(236c, e , g) traces (236a) 49% direct + (236b) 42:: direct 50% sensitized 4374 sensitized

Scheme 24

were particularly interested in the influence of heavy-atom solvents on the process, an area to which considerable attention has been paid in the past few years. The results show that the same products are obtained and in the same lel

W. I. Ferree, jun., B. J. Plummer, and 7741.

W.W. Schoman, jun., J . Amer. Chern. Soc., 1974, 96,

Photochemistry

342

ratio regardless of whether the reaction is brought about by sensitization, using dicyc1ohexy1-18-crown-6-ether complex of the disodio-salt of Rose Bengal and excitation at 589 nm, or by direct irradiation, using 360 nm light in dibromoethane as the heavy-atom solvent. Thus, in view of these results and from the fact that the direct reaction is adversely affected by the presence of oxygen, both reactions are thought to arise from the triplet excited state. Although the authorslsl cannot exclude a triplet exciplex as the intermediate in the formation of products the evidence available suggests that the products are formed by way of biradicals (237a) and (237b). It is likely at the low temperatures at which the reactions are carried out that the allylic radicals formed would retain the stereochemistry of the original olefin.

(237a)

(237 b)

A previous publication of the attempted photoaddition of fumaric acid to stilbene reported the failure of the reaction.la2 Green and Retjole3 have reexamined the reaction and have found that a 46% yield oft the diester (238) of p-truxinic acid is obtained when trans-stilbene is irradiated (Pyrex) in benzene solution with dimethyl fumarate. Trace amounts of dimethyl 8-truxinate (239) and dimethyl neo-truxinate (240) are also formed.

CO,Me PQC02Me Ph

(238)

C02Me @C02Me

C02Me C0,Me

k

Ph Ph

Ph (239)

(240)

A full report of the photochemical addition of 1,3-diphenylisobenzofuran to cycloheptatriene has been made.la4,ls6 The p-acetonaphthone-sensitizedaddition of cis- and trans-1-chloropropene to cyclopentadiene has been reported in detail.lss, ls7 The isomer distribution was shown to be temperature dependent. F. A. Ode, Scientia (Valparaiso), 1953, 20, 169 (Chem. Abs., 1955, 49, 3031). B. S. Green and M. Retjo, J . Org. Chem., 1974, 39, 3284. le4 T. Sasaki, K. Kanematsu, K. Hayakawa, and M. Sugiura, J. Amer. Chem. SOC.,1975,97,355. 166 T. Sasaki, K. Kanematsu, and K. Hayakawa, J . Amer. Chem. SOC.,1973, 95, 5632; Tetrahedron Letters, 1974, 343. lee L. A. Hull and P. D. Bartlett, J. Org. Chern., 1975, 40,824. lB7 P. D. Bartlett and L. A. Hull, J. Org. Chem., 1975, 40,831. lea

Photochemistry of Olefns, Acetylenes, and Related Compounds

343

9 Reactions of Acetylenic Compounds The u.v.-induced addition of propan-2-01 to acetylene has been studied with and without acetone as sensitizer.lss The acetylene (241) undergoes photoaddition of isopropylamine and isopropyl ether to yield (242) and (243a) r e s p e c t i ~ e l y .The ~~~ same acetylene also reacts with ethyl 2-methylpropionate giving trans-(243b) and the cyclic product (244).

(244)

A reinvestigation of the photochemistry of diphenylacetylene has suggested that the primary photochemical process is the formation of 2-phenylbenzocyc10butadiene.l~~This is reported to be an unstable pale-green crystalline

(245) a; R b; R

Q

= =

H Ph

(247)

is-

R (246) a; R = H

b; R = Ph Ph

lo* la0

170

1. B. Afanas'ev, M. B. Levinskii, and G. I. Samokhvalov, Zhur. org. Khim., 1974, 10, 1375 (Chem. A h . , 1975, 82, 15 964). L. M. Kostochka, E. P. Serebryakov, and V. F. Kucherov, Zhur. org. Khim., 1974,10, 1822 (Chem. Abs., 1974,81, 151 454). K. Ota, K. Murofushi, T. Hoshi, and H. Inoue, Tetrahedron Letters, 1974, 1431.

344

Photochemistry

compound which is thermally transformed into 1,2,34riphenylnaphthalene and 1,2,3-triphenylazulene, the usual products of the reaction. Irradiation (lowpressure Hg arc) of a cyclohexane solution of the dialkynyl benzene derivatives (245) led, from (245a), to the unstable azulenes [(246a), 1%] and [(247), 0.273 and, from (245b), to the azulene [(246b), 2x1 and the naphthalene [(248), 3%].171 Bichromophoric molecules and their photochemistry still are the subject of considerable interest. One particularly interesting example which has been published in the last year deals with the photochemistry of 6-phenylhex-2-yne which is transformed via a singlet state into the cyclo-octatetraene [(249), CD = 3.3 x 10-3],172possibly by way of a n intermediate (249a).

(249a)

(249)

Foote et aZ.173have examined the photochemical addition of dimethyl acetylenedicarboxylate to cis- and trans-but-2-ene. Theoretically in this reaction there are seven possible [2 + 2ladducts of the general type (250). However only four (251) were isolated together with an open-chain adduct (252). It is likely that the triplet ester adds to the olefin affording biradicals (253) and (254). Diphenylacetylene also undergoes double [2 + 2laddition of cyclopentadiene giving the adducts [(255), 32x1 and [(256), 11x1 when irradiated (Pyrex) at - 30 0C.174

C0,Me

C0,Me

Me

Me

Me C0,Me

(253)

(254)

(252) 171 172 173

G. Klauss and W. Ried, Chem. Ber., 1975, 108, 528. W. Lippke, W. Ferree, jun., and H. Morrison, J. Amer. Chem. SOC.,1974, 96, 2134. S. Majeti, V. A. Majeti, and C. S. Foote, Tetrahedron Letters, 1975, 1177. G . Kaupp, C. Kuchel, and I. Zimmermann, Angew. Chern. Internat. Edn., 1974, 13, 816.

Photochemistry of Olefins, Acetylenes, and Related Compounds

345

Presumably the adducts are formed by singlet addition yielding (257) followed by a second addition. [2 4lAddition is also encountered yielding the photochemically labile 2,3-diphenylnorbornadiene. The irradiation (206 nm, pentane solution, degassed) of cyclo-octa-1J-diyne at room temperature rapidly gave butatriene as the only

+

10 Miscellaneous Reactions

A review of the use of cyclic peroxides in organic synthesis including photochemical decomposition has been p ~ b 1 i s h e d . l ~Photochemical ~ reactions of carbohydrate molecules have been the subject of another review.17' have re-examined the photoreactions of the benzene oxideChapman et benzoxepin rearrangement and at 235.7 nm obtained evidence that the deuterioisomer (258a) isomerizes into (258b) by an oxygen-walk reaction. At low temperature (77 K) a keten [(259), vmax 2112 cm-l] is obtained which is converted

R2

(258) a; R1 = H, R2 b; R1 = D, R2

(259) = =

D H

into phenol upon continued irradiation or warming. Pyrene oxide (260), an important molecule in cancer research, is very reactive when exposed to U.V. light. The oxepin [(261), 36x1 was the major product isolated from the r e a ~ f i 0 n . l ~ ~

176

170

177 178

178

E. Kloster-Jensen and J. Wirz, Helo. Chim. Acta, 1975, 58, 167. W. Adam, Angew. Chem. Internat. Edn., 1974, 13, 619. K. Matsuura and Y . Araki, Kagaku No Ryoiki, 1973,27,1099(Chem. Abs., 1974,80, 133 706). D . M. Jerina, B. Witkop, C. L. McIntosh, and 0. L. Chapman, J. Amer. Chem. SOC.,1974, 96,5578. B. L. Van Duuren, G. Witz, and S. C. Agarwal, J. Org. Chem., 1974, 39, 1032.

346 Photochemistry Kaupp laoahas rationalized the orientational selectivity observed in the ringopening of phenylcyclobutanes in terms of relief of steric strain present in the molecules as a result of phenyl-phenyl crowding. In accord with this, in a study of stilbene dimers it was shown that the cis-anti-cis-dimer (262) decomposed Ph

Ph

Ph

Ph

(262)

(263)

(jy H

'Ph

H

three times faster than the all-trans-dimer (263) into trans-stilbene. Similarly stilbene was liberated from (264) on irradiation (254 nm; - 190 "C)since this process eliminates the cis-interaction of the phenyl and the cyclopentenyl ring. On the other hand, with cis-phenyl groups (265) the reaction follows an alternative path to yield trans-trans-l,7-diphenylhepta-l,6-diene. Several other examples were also discussed. Phenyl-phenyl interaction is also relieved in the conversion (254 nm) of cis-l,2-diphenylcyclobutane into the trans-isomer.181 Styrene is also formed in this process. The photochemical reaction gave low quantum yields and could not be sensitized efficiently with benzophenone or acetophenone but occurred efficiently in acetone solution. The results suggest that there may be a significant concerted component in the reaction. Ringopening to (266) results when the silane (267) is irradiated in MeOD.ls2 H P hPDs /i < OMe

Qi<

Ph

Interest in the photochemistry of small ring compounds has been maintained. Study of the rearrangement of oxazirines (268) has shown that the substituent on nitrogen and the ring-size have little effect on the reaction path. Thus the oxazirines (268a-d) all ring expand to the lactams (269) in excellent yield (8595%).lg3* 18* When there is only one a-substituent (270) some selectivity is seen in the rearrangement pathway yielding either (271) or (272) in a ratio of 15 : 1. The reaction path shows some dependence on the solvent. Thus, in cyclohexane (a) G. Kaupp, Angew. Chern. Internat. Edn., 1974, 13, 817; (b) G. Kaupp, 'Houben-Weyl', Thieme, Stuttgart, Vol. IV/S. G. Jones, tert. and V. L. Chow, J. Org. Chern., 1974, 39, 1447. lS2 P. B. Valkovich, T. I. Ito, and W. P. Weber, J. Org. Chem., 1974,39,3543. us E. Oliveros-Desherces, M. Riviere, J. Parello, and A. Lattes, Tetrahedron Letters, 1975, 851. la4 E. Oliveros-Desherces, M. Riviere, J. Parello, and A. Lattes, Compt. rend., 1972, 275, 581. la0

Photochemistry of Olefins, Acetylenes, and Related Compounds

347

the routes discussed above are preferred, whereas in propan-2-01 there is evidence for the formation of ring-opened lactams. R2

(268) a; b; c; d;

R2 0; R1 = PhCH,, R2 = H = 1 ; R1 = PhCH,, R2 = H or Me = 2,3, or 7; R1 = PhCH2, R2 = H = I ; R1 = C,H,, or Pr', R? = H

R2

71 =

71 II 11

(269)

RJ - - f ( (270) a; b;

12

1; R = PhCH2 l ; R = Me

= 0 or

11 =

0

(272)

n-n* Excitation of phenyl azirines (273) leads to their ring-opening and the formation of a nitrile-ylide (274). The use of this ylide for the synthesis of a variety of novel compounds has been reported in detail over the past few years by Padwa and Schmid. These ylides (273a-c) react e.g. with CO, to yield oxazolinones (275) and (276) in high yield.186 Addition to CS, has also been observed and yields the adduct (277). Irradiation of the oxazolinones also yields the ylide (274) by

N R1

"$ R1R2

R2 PhCr&--(-\ R1

(273) a; R1 = R2 = Me b; R1 = H, R2 = Me C; R1= H, R2 = Ph d; R1 = R2 = H

0 0

(275) a; R1 = R2 = Me b; R1 = H, R2 = Me C; R1 = H, R2= Ph

(274)

MeMeN PhffR

ph
0 (276) b; R = Me C; R = Ph

N

Me

(277)

Ph

Ph N ANC02Et ~iSbfCO2Et

R2 (278)

Ph

Me (279) lab

(280)

A. Padwa and S. I. Wetmore, jun., J. Amer. Chem. SOC.,1974, 96, 2412.

348 Photochemistry extrusion of CO,. The ylide can be trapped by suitable dipolarophiles. A kinetic analysis of the extrusion process has shown that the CO, elimination arises from the singlet manifold (quenchers and triplet sensitizers had n o effect). The ylide (274) also adds to ketones, acyl cyanides, and kefo-esters.lE6 The ylides (274b, d) undergo addition to diethyl azodicarboxylate to yield the triazolines (278LlE7 The ylides also undergo addition to acid chlorides affording (279) from ylide (274b) lE8 and to triphenyl vinylphosphonium bromide yielding (280) from ylide (274b).lE9Addition of the ylide (274c) to benzo- and naphtho-quinones gives (281) and (282).lQoThe ylide (283) is also reactive in addition reactions,lgl as are dialkyl ylides obtained from the ring-opening of the azirines (284) and (285).lQ2 0

WNH \

v

--.

n

Ph

H Prn

Y

N- Prn

A further study of the photochemical transformations of diaminomaleonitrile and diaminofumaronitrile has been p ~ b 1 i s h e d . lg4 l~~~ Kropp and his co-workers lB5have continued their studies on the photochemical reactions of alkyl halides. The compounds studied in this report were the halonorbornanes (286). The iodonorbornane (286a) forms the ether (287) when P. Clauss, P. Gilgen, H.-J. Hansen, H. Heimgartner, B. Jackson, and H. Schmid, Helu. Chim. Acra, 1974, 57, 2173. lS7 P. Gilgen, H. Heimgartner, and H. Schmid, Helu. Chim. Acta, 1974, 57, 1382. lS8 U. Schmid, P. Gilgen, H. Heimgartner, H.-J. Hansen, and H. Schmid, Helo. Chim. Acra, 1974, 57, 1393. lB9 N. Gakis, H. Heimgartner, and H. Schmid, Helv. Chim. Acra, 1974, 57, 1403. l D 0 P. Gilgen, B. Jackson, H.-J. Hansen, H. Heimgartner, and H. Schmid, Helu. Chim. Acra, 1974, 57,2634. lol A. Padwa and S. I. Wetmore, jun., J. Org. Chem., 1974, 39, 1396. lo2 A. Orahovats, H. Heimgartner, H. Schmid, and W. Heinzelmann, Helu. Chim. A d a , 1974, 57, 2626. lu3 T. H. Koch and R. M. Rodenhorst, J . Amer. Chem. SOC.,1974, 96, 6707. R. S. Becker, J. Kolc, and W. Rothman, J. Amer. Chem. SOC.,1973, 95, 1296. le6 G. S. Poindexter and P. J. Kropp, J. Amer. Chem. SOC.,1974, 96, 7142. lS6

Photochemistry of Olefns, Acetylenes, and Related Compounds

349

the irradiation (250nm) is carried out in methanol under an atmosphere of nitrogen. This product is also accompanied by the reduction product, norbornane. This material is the predominant product when the bromo-derivative (286b) is irradiated under the same conditions. In this experiment the minor product was the ether (287). It is likely that the ethers are formed by the trapping

(286) a ; X b; X

= =

1 BI.

(287) R (290) R

= =

Me H

(288)

of the carbonium ion (288) whereas the reduced products are formed by a radical path. An alternative path to reduction was also uncovered when irradiation in MeOD led to incorporation of deuterium at the bridgehead position. The likely path for this reaction is shown in Scheme 25. Further evidence for the formation

R-03 I

H Scheme 25

of a carbanion (289) and a radical was obtained from the irradiation of the iodide (286a) in methanol saturated with 02,under which conditions the alcohol (290), formed from the hydroperoxide by reductive work-up, was obtained. Surprisingly the amount of ether (287) also diminished under these conditions although the disappearance of the starting material was not affected. These results were interpreted in terms of fission of the C-I bond to afford a radical pair which subsequently undergoes electron transfer to yield an ion pair, and in the presence of oxygen trapping competes with the electron transfer process. Electron transfer in the bromide case is obviously not a high-yield process since the reduction product predominates. However, it was argued that if the departing bromine atom was held for a longer time in the proximity of the norbornyl radical, electron transfer might become efficient. This is found to be the case when a viscous solvent (ethylene glycol) is used. The photochemistry of haloadamantanes has also been studiedlgs and shows products of both radical and carbonium-ion processes. These yield adamantane (28% from bromo- and 5% from iodo-adamantane) and the l-methoxy derivative (72% from bromo- and 95% from iodo-adamantane). Photoreactions of the dihalides (291) also followed lg8

R. R. Perkins and R. E. Pincock, Tetrahedron Letters, 1975, 943.

Photochemistry

350

(291) a; R1 = Br, R2 = H b;R1=T,R2=H c ; R1 = Br, R2 = Me d; 'R1= I, R2 = Me

+ a; 11% b; 4% c ; 9% d; 5%

+ a; 50% b; 0% c ; 53% d; 0%

a ; 39% b; 96% c ; 38% d; 95%

Scheme 26

radical and carbonium-ion reaction pathways (Scheme 26) but in all cases the reactions of each halogen atom was independent of the other and no bond formation leading to propellane derivatives was detected. The authors lB6 of this article suggest that the greater stability of the bridgehead adamantyl carbonium ion than that in the norbornyl system results in a greater ionic contribution to the reaction.

4 Photoc hemistry of Aromatic Compounds BY A. GILBERT

1 Introduction

The format of this Chapter follows that used previously in this series with the exception that the current literature concerning the photochemistry of furan, thiophen, and pyrrole is now considered by reaction type in the appropriate section. Interest in aromatic chemistry continues at the same high level as in recent years. Substitution and cyclization processes are two areas which have attracted considerable attention over the past year. Pertinent here, as elsewhere in this volume, are the reviews on photochemistry with circularly polarized light by Buchardt,l and the photochemistry of carbonium ions by Cabell-Whiting and Hogeveen.2 Current literature describing light-induced reactions of pyrroles has also been briefly reviewed.s 2 Isomerization Reactions One of the potentially more controversial publications which appeared during the year was that by Barltrop and Day,4 who question the widely held opinion that, in general, photo-transposition reactions of six-membered aromatic compounds (e.g. o- -+ rn-xylene) proceed via benzvalene or Dewar benzene and prismane intermediates. The literature cited in support of this point of view is the transformation of 3,6-difluoro-4,5-dichloropyridazine into 2,5-difluoro-3,6-dichloropyrazine,6 and a photosequence which has been noted for some pyrylium salts;6 they assert that neither process fits into the accepted mechanistic framework involving intermediate valence-bond isomers. These examples appear to have been unfortunately chosen; for in 1971 Chambers and co-workers isolated a parabonded ‘conventional’ isomer from a very similar pyridazine-pyrazine rearrangement and showed this to be an intermediate in the con~ersion;~ i.e. the transformation can be achieved by isomerization of an intermediate diaza-Dewar benzene. In addition, plausible precursors suggested for the cited pyrylium conversion are either the ‘oxoniabenzvalene’ or 2,6-bonded ‘prefu1vene’-type cations (see Scheme 1). Barltrop and Day consider that analysis can be simplified if attention is fixed on the pattern of transposition rather than ‘speculating 0. Buchardt, Angew. Chem., 1974, 86, 222. P. W. Cabell-Whiting and H. Hogeveen, Adu. Phys. Org. Chem., 1973, 10, 129. a D. A. Lightner, Photochem. and Photobiol., 1974, 19,457. ‘ J. A. Barltrop and A. C. Day, J.C.S. Chem. Comm., 1975, 177. D. W. Johnson, V. Austel, R. S. Feld, and D. M. Lemal, J. Amer. Chem. SOC.,1970, 92,7505. J. W.Pavlik and E. L. Cleannan, J. Amer. Chem. SOC.,1973,95, 1697. R. D. Chambers, W. K. R. Musgrave, and K. C. Srivastava, J.C.S. Chem. Comm., 1971,264.

’

351

Photochemistry

352 OH <---.

d

‘Prefulvene’ cation

+

.

‘Oxoniabenzvalene’ cation Scheme 1

upon the innumerable intermediates that are conceivable’. The 120 permutations for transposing the six ring atoms can be reduced to twelve distinct permutation patterns, and the authors emphasize correctly that there is no case in which it has been definitely established which of these 12 permutations is actually involved in the photo-transposition of any six-membered aromatic ring - i.e., in no case has the movement of all six ring atoms been followed throughout a reaction. Thus the authors are considering that photoisomerizations of aromatic rings might in principle occur by more numerous patterns of redistribution of ring atoms than have hitherto been considered - a valid point but, as yet, there are no experimental results known to the reporters which require explanation by such alternative pathways. The approach of permutation patterns has the advantage that when the pattern is defined, the range of possible intermediates and conceivable mechanisms is greatly restricted. The paper is stimulating and doubtless will provoke much discussion.* The formation of benzvalene from the irradiation of benzene was first reported in 1967,* but the process continues to receive further study. The quantum yield (0.18) for formation of this valence-bond isomer from 254 nm radiation of oxygen-free solutions of benzene in hexane is reported to be independent of temperature within the range 9-50 OC.@ The benzvalene is estimated as 5,6-dibromobicyclo[2,1,l]hex-2-eneand the results are discussed in terms of a kinetic model which incorporates the known step of triplet-benzene-sensitized disappearance of the benzvalene. Light-induced transposition of ring substituents in K. E. Wilzbach, J. S. Ritscher, and L. Kaplan, J. Amer. Chem. SOC.,1967, 89, 1031. H. Lutz and G . Stein, J. Phys. Chem., 1974, 78, 1909. * After this manuscript had been completed two communications very relevant to the present discussion were published (J. Barltrop, R. Carder, A. C. Day, J. R. Harding, and C. Samuel, J.C.S. Chem. Comm., 1975, 729, and R. D. Chambers, R. Middleton and R. P. Corbally, ibid., p. 731). Comment on these reports must await next year’s review but it is pertinent to note here that the former report describes an example involving pyrylium cations in which the fate of all the ring carbons is defined while the latter describes transposition of perfluoroalkyl-pyridazines and -pyridines.

3 53

Photochemistry of Aromatic Compounds

xylenes is well knownlO and has been extended to the case of the m-CH,C6H4CH2- radical which is formed in paraffin matrices at 77 K.ll Irradiation of this species with 313 nm light causes isomerization via transfer of the *CH2group to the o- and p-positions. Haszeldine and co-workers have previously described the remarkable thermal conversion of perfluorohexaethylbenzene into its para-bonded isomer.12 The same school have extended these studies with an investigation of the lightinduced and thermal formation of such valence bond isomers from perfluoropen taethylmethylbenzene and perfluoro-1,2,3 5-tetraethyl-4,6-dimethylbenzene.13 With light of 270 nm wavelength or when heated in the dark at 425-600 "C, the former compound yields a mixture of the bicyclo[2,2,0]hexadienes (1) and possibly (2) and at shorter wavelength (>ZOO nm) the prismane isomer (3).

Similar results are reported for the perfluorodimethyl compound. The introduction of fluoro-substituents and particularly perfluoroalkyl groups thus imparts a notable increase in the ease of formation and stability of valence bond isomers of aromatic compounds, and the physical properties of those involved in the lightinduced interconversion of perfluoro-ly3,5- and -1,2,4-trimethylbenzeneshave also been discussed by the Manchester g1-0up.l~The energetics of the back reaction (i.e. valence-bond isomer to benzenoid compound) have been studied, and it is interesting to note that in the conversion of Dewar acetophenone into acetophenone, the location of the excitation starts off m*-like but ends as m*-like.l5 Another example from the current literature of photoisomerization of an aromatic perfluoro-compound is the formation of perfluoroisoindene (4) from the indene (5);l6 the novelty here is that although the light-induced indene-

'WFi~

F

hv

F

lo

l1 l2 l3

l4 l6 l6

F F

~

F

--.F

F

See Volumes 1 to 6 in this Series for pertinent references. K. I. Mamedov and M. M. Khalilov, Zzuest. V.U.Z. Fit., 1974, 17, 155. E. D. Clifton, W. T. Flowers, and R. N. Haszeldine, J.C.S. Chem. Comm., 1969, 1216. M. G. Barlow, R. N. Haszeldine, and M. J. Kershaw, Tetrahedron, 1975,31, 1649. M. G. Barlow, R. N. Haszeldine, and M. J. Kershaw, J.C.S. Perkin Z, 1974, 1736. N. J. Turro, G . Schuster, J. Pouliquen, R. Petit, and C. Mauldin, J. Amer. Chem. Soc., 1974, 96, 6797. W. J. Feast and W. E. Preston, J.C.S. Chem. Comm., 1974, 985.

354 Photochemistry isoindene conversion is known,17 this isomerization provides the first unambiguous example of a sigmatropic fluorine shift. Full details of the first light-induced valence bond isomerization of the naphthalene nucleus have now been published.l* The irradiation of the naphthalene (6) yields a photostationary state containing 95% of the hemi-Dewar isomer (7). The only Dewar isomer detected from irradiation of the tri-t-butylderivative (8) was (9), and this emphasizes the importance of proximate bulky But

(8)

R

But

=

But

But

(7) R = But (9) R = H

H

groups in the stabilization of such valence bond isomers. Singlet states of the aromatic compounds are apparently involved in these transformations, as in the benzene series. The light-induced valence bond isomerization of six-membered heteroaromatic compounds has been observed with a number of systems.1° In 1970 the formation of Dewar pyridine from pyridine was reported,lg and this type of intermediate is tentatively suggested to be formed in the intriguing photoisomerization of 2-pyridylacetonitrile to anthranilonitrile (see Scheme 2).20 The quantum yield

1

3,3-migration

pJCN

t--

NH,

NH

Scheme 2

for the process is 0.02, which compares with 0.05 for the pyridine isomerization. Singlet intermediates are suggested and it would appear that for the transformation to occur an electron-withdrawing substituent on the pyridine nucleus is necessary. Thus methyl 2-aminobenzoate is formed from methyl 2-pyridylacetate, whereas a-picoline simply yields y-picoline, and no aniline is detected. 1'

W. R. Roth, Tetrahedron Letters, 1964, 1009; L. L. Miller and R. F. Boyer, J. Amer. Chem. SOC.,1971, 93, 650.

2o

R. W. Franck, W. L. Mandella, and K. J. Falci, J. Org. Chem., 1975,40, 327. K . E. Wilzbach and D. J. Rausch, f. Amer. Chem. SOC.,1970, 92,2178. Y.Ogata and K. Takagi, J Amer. Chem. SOC.,1974, 96, 5933.

355

Photochemistry of Aromatic Compounds

Some aspects of the pyridazine-to-pyrazine isomerization have already been mentioned in this review. The work described in ref. 7 concerning isolation of the intermediate diaza-Dewar isomers in this conversion has been extended, and the 1,3-shifts that are observed on irradiation of tetrafluoropyridazine and some (10)

R1 =

R1

=

R2 = F

CF(CF3)2,Ra = F

R1 = R2 = cF(CF3), R1 = CzF5,R2 = F R' = R2 = CzF,

R2 Rj$ F

R1 =

CF(CF3)CF2CF3,R2 = F

R1 = R2= CF(CF3)CFZCF3

perfluoroalkyl derivatives (10) in the vapour phase have been reported in some detail.21 It had earlier been tentatively suggested that the conversion occurred via a diaza-prismane intermediate (Scheme 3),22but such a proposal conflicts

Scheme 3

with the later observation that the relative positions of the original 4,5-substituents change in the course of the conversion. Isolation of the intermediates (1 1) and (12) completely establishes the reaction pathway for such conversions. It is

pertinent here to remember that valence isomers of fluorinated pyridines had been isolated p r e v i o u ~ l y .The ~ ~ present rearrangement is not general for pyridazines, and the reaction with some derivatives is slow, whereas others, e.g. perfluoro-3,4,6-tri-isopropylpyridazine and perfluorotetraethylpyridazine, are photochemically inerta1 The same report also describes the slow light-induced interconversion of perfluoro-2,5-di-isopropylpyrazineto the 2,6-isomer in the liquid phase : this process is explained by the intermediacy of diazabenzvalenes, although these were not detected. Photolysis of pyridazine itself in the gas phase at 10(&160 "C yielded nitrogen and vinylacetylene from the nn* singlet ~tate.~4 The acetylene is suggested to arise from the CpHodiradical by a 1,3-hydrogen migration. a1

az pa

R. D. Chambers, J. A. H. MacBride, J. R. Maslakiewicz, and K. C. Srivastava, J.C.S. Perkin I, 1975, 396. C. G. Allison, R. D. Chambers,Yu. A. Cheburkov, J. A. H. MacBride, and W. K. R. Musgrave, Chem. Comm., 1969, 1200. M.G. Barlow, R. N. Haszeldine, and J. G. Dingwall, J.C.S. Perkin I, 1973, 1542. J. R. Fraser, L. H. Low, and N. A. Weir, Cunud. J. Chem., 1975,53, 1456.

Photochemistry

356

3 Addition Reactions The photoaddition of maleic anhydride to benzene to yield the 2:l adduct (13) was first reported 15 years but the mechanism of the process has remained uncertain despite a considerable amount of work.I0 Last year Hartmann and co-workers synthesized the originally postulated bicyclic intermediate (1 4),26cr and found it to have surprisingly low reactivity towards tetracyanoethylene (tcne) which explains the previous failures to intercept the intermediate with tcne. They have now clearly demonstrated that (14) is the intermediate in the formation of (13) from both the sensitized and unsensitized reactions.2eb Other workers have found that N-phenylmaleimide is more effective than tcne for the trapping of intermediate (14), and have reported that it can totally suppress the formation of (13) and produce instead the corresponding 1:l:l adduct (15).27 In order to account for the previous observation concerning the effect of proton donors on the unsensitized reaction,28 the species immediately prior to (14), and resulting from excitation within the maleic anhydride-benzene charge-transfer absorption band, is postulated to be the zwitterion (16).27 In complete agreement with this and the earlier work, it was observed that the use of a heavy-atom solvent (CH,Br,) facilitates intersystem crossing in the excited complex, and the reaction, as in the case of the benzophenone-sensitized process, is now less sensitive to a proton The suggested mechanism is outlined in Scheme 4, from which

iv

S, Complex --+

I

-t-

’Phenylsuccinic anhydride

-0

Complex of benzene inaleic anhydride

\;,

(16)

...

111

ii

TI Complex

I

+ 8+

1

8-01

(13) R-R = CO.O.CO (15) R-R = CO-NPhCO Reagents: i, hv; ii, Ph,CO; iii, CH,Br,; iv, H+

Scheme 4 2a

28

H. J. F. Angus and D. Bryce-Smith, Proc. Chem. SOC.,1959, 326; J . Chem. SOC., 1960, 4791. (a) W. Hartmann, H. G. Heine, and L. Schrader, Tetrahedron Letters, 1974, 883; (b) ibid., p. 3101. D. Bryce-Smith, R. R. Deshpande, and A. Gilbert, Tetrahedron Letters, 1975, 1627. D. Bryce-Smith, R. R. Deshpande, A. Gilbert, and J. Grzonka, J.C.S. Chem. Comm., 1970, 561.

Photochemistry of Aromatic Compounds

357

it is seen that the unsensitized process is considered to occur via singlet intermediates. Descriptions of the formation of derivatives of (13) have continued to appear, and the addition of maleimide to biphenyl, giving (17), has been reported to occur in 40% yield ;20 maleic anhydride gives a similar 2: 1 adduct with biphenyl.30

0 (1 7) Last year the factors affecting the relative proportions of 1,2- and 1,3-cycloadducts from irradiation of ethylenic compounds in benzene were described.31 It was noted that whereas both exo- and endo-1,3-adduct isomers were normally formed, the 1,2-~ycloadditionprocess was remarkably specific, giving only one isomer; it was also noted, from the relatively few examples with known stereochemistry, that the pattern seemed to be emerging that donor ethylenes add to give endo-1,2-cycloadducts whereas only the exo-isomer is formed from acceptor ethylenes. Accordingly, formation of the 1,2cycloadduct from cis-cyclo-octene and benzene, although a minor process, would be expected to give a product with endo-stereochemistry, despite the obvious steric problems. It has now been s h o m that maleimide reacts quantitatively with this 1,Zcycloadduct, and from X-ray crystallographic studies of the resulting Diels-Alder product, the cyclobutane has been deduced to have endo-stereo~hemistry.~~ It is satisfying that the n.m.r. evidence for stereospecificground-state interactions between ethylenes and benzene matches precisely the stereospecificities observed in these 1,2-~ycloadditions.~~ Thus donor ethylenes have a preferred tendency for endo-associations (downfield shift of vinyl protons), whereas with acceptor ethylenes there is a marked upfield shift of the vinyl protons, which indicates a strongly preferred exo-orientation. The 1,3-cycloaddition of ethylenes to benzene and its derivatives, giving rise to dihydrosemibullvalenes, has been known for a number of years and the reaction has recently been reviewed.34 The reaction with cyclopentene as olefin has been the subject of several earlier reports.lO Its light-induced addition to anisole can be used as a stereospecificsynthesis of perhydroazulenes;3Jthe adduct (18) is formed in 85% yield. Its consumption of only one mole of hydrogen on catalytic hydrogenation and its failure to undergo photosensitized decomposition have been

so *l

sa as s4 s5

S. H. Shaikhrazieva. E. V. Talvinskii, and G. A. Tolstikov, Zhur. org. Khim., 1974,10, 3,663 (Chem. A h . , 1974, 81, I . 3456). D. Bryce-Smith and A. Gilbert, J. Chem. SOC.,1965, 918. D. Bryce-Smith, A. Gilbert, B. H. Orger, and H. M. Tyrrell, J.C.S. Chem. Comm., 1974, 334. H. M. Tyrrell and A. P. Wolters, Tetrahedron Letters, 1974. 4193. D. Bryce-Smith. A. Gilbert. and H. M. Tyrrell, J.C.S. Chem. Comm., 1974, 699. R. Srinivasan, Preprints Diu. Petrol. Chem., Amer. Chem. SOC.,1973, 18, 2, 286. R. Srinivasan, V. Y. Merritt, and G. Subrahmanyam, Tetrahedron Letters, 1974, 2715.

358

Photochemistry

attributed to the bulk of the methoxy-group on the cyclopropane ring. Like all 1,3-adductsY(18) undergoes ring fission in aqueous acid but in this case yields the ketone (19). Treatment of (19) with potassium t-butoxide yields the perhydroazulenes (20) and (21).36 Compound (19) may also be obtained by Cr0,oxidation of the acid-cleavage product (22) of the cyclopentene-benzene adduct

[the assigned structure of (22) has been corrected recently 36]. It is interesting to note here that (19) is also reported to be formed directly, albeit in low yield, from the irradiation of phenol and cyclopentene. Details of how the product from this latter reaction was identified as (19) were, of course, not given in the preliminary communicationYS6 and thus, as yet, it is not possible to say whether the authors have discounted the formation of the likely isomeric adduct (19a) resulting from Diels-Alder cycloaddition of the ethylene to the keto-tautomer of phenol. The 1,3-~ycloadditionof 3,4-dichlorocyclobutene to benzene has been previously r e p ~ r t e d , ~and ' the alcohol obtained by its treatment with acid has now been found (from X-ray crystallographic studies of the p-nitrobenzoate racemate) to have the cis-exo-structure (23).38 The thermal rearrangement of lY3-adductsto bicyclo[3,3,0]dienes has been used both in synthesis sg and as a means of assigning the stereochemistry of such photo product^.^^ The reaction has been investigated in the case of the two lY3-adductsresulting from irradiation of methylenecyclobutane in benzene.41 At 300 "C, isomer (24) yields (25) whereas (26) is stable at this temperature for 20 h. An explanation for this stability may be that no allowed concerted 1$hydrogen shift is possible and that a 2'-vinyl cyclopropyl-cyclobutane rearrangement would give an impossibly strained compound. At higher tempera36

sa 3B

dl

V. Y. Merritt, J. Cornelisse, and R. Srinivasan, J. Amer. Chem. Sac., 1975, 97, 1987. E. L. Allred and B. R. Beck, J . Amer. Chem. SOC.,1973,95, 2393. G. Subrahmanyam, R. Srinivasan, S. J. Laplaca, and J. E. Weidenborner, J.C.S. Chern. Comm., 1975,231. R. Srinivasan, Tetrahedron Letters, 1972, 4537. R. Srinivasan, Tetraliedrun Letters, 1971, 4551. R. Srinivasan, Tetrahedron Letters, 1974, 2725.

359

Photochemistry of Aromatic Compounds

tures, as with other systems, a vinyl-cyclopropane rearrangement of (26) yielded (24) and thence (25), which subsequently eliminated C,H, to form (27).

(22) (23)

R-R R-R

= =

CH,CH,CH2 CHCI-CHCl

(24)

Cantrell has reported the photoaddition reactions of tetramethylethylene and isobutene to 2-acyl-thiophensY -furam, and - p y ~ r o l e s . ~Products ~ of both [4 + 21- and [2 + 21-addition to the ring and oxetan formation are observed in amounts dependent upon the olefin, the particular five-membered heteroaromatic compound, and its acyl substituent, e.g. 2-acetylthiophen with tetramethylethylene yields the [4 + 2lDiels-Alder adduct as the major product, with minor amounts of the [2 + 2lcyclobutane adduct and the oxetan, whereas isobutene gives the two isomers of the [4 + 21product and the oxetan. All the previously reported examples of photoaddition of acetylenes to benzene involve 1,2-~ycloadditionand subsequent formation of cyclo-octatetraenes lo (but see ref. 43 for a discussion of the addition of perfluorobut-2-yne to benzene). The report of 1,3-~ycloadditionof diphenylacetylene to the trimethyl ester of trimesic acid, is, therefore, of interest as this leads directly to the semibullvalene The reaction apparently requires 6 days, the yield of the product is low, and the adduct (28) is not isolable in the pure state. The triethyl ester and the acetylene also yield (29) via a stilbene-phenanthrene cyclization of the primary lY3-photoadduct. This work is all the more interesting in the light of the previous

E E

E Ph (28) E = ester (29) I*

I4

T. S. Cantrell, J. Org. Chem., 1974, 39, 2242. See R. S. H. Liu and C. G. Krespan, J . Org. Chem., 1969,34, 1271, and Vol. 3 of this Series, p. 500, for pertinent discussion. T. Teitei and D. Wells, TetrahedronLetters, 1975, 2299.

360

Photochemistry

studies with the trimesic acid trimethyl ester-cyclo-octene system, when 1,3addition was not observed but the product was deduced to comprise three isomers of the tetracycl0[6,6,0,0,~~~0~~~]tetradec-4-ene system and thus reflect 1,2-additi0n.‘~ It may well also be that in this case the efficiency of the two processes is determined by the donor-acceptor properties of the addends.31 It has been suggested that the ground-state conformation of 1,3-dienes could determine the structure of their photoadducts with benzene and also that the sym-cisoid conformation would be more reactive than the ~ y m - t r a n s o i d .Some ~~ evidence for this was obtained using 2,3-dimethylbuta-l,3-dieneand symcisoid 2,4-dimethylpenta-1,3-diene.48 Other workers have considered that the interpretation of these studies can be complicated by the use of acyclic dienes which are conformationally flexible, and have used the conformationally fixed Irradiation dienes 1,2-dimethylenecyclohexane and 3-methylenecy~lohexene.~~ of the fixed cis-diene in benzene yielded only the two products (30) and (31),

reflecting 1,3-, 1’,4‘- and 1,4-, 1’,4’-cycloadditions, respectively. In contrast, the reaction of 3-methylenecyclohexene in benzene gave only low yields of a complex mixture containing a diene dimer, traces of aromatic products, and at least four 1:l adducts; evidence was obtained for 1,2-cycloaddition to the benzene ring, and the =CH, group was present in at least one of the adducts. These results are entirely in accord with the earlier predictions for factors which affect diene additions.46 There appeared this year two independent and apparently conflicting descriptions of the photoaddition of furan to benzene.‘** Gilbert and co-workers 48 reported that the major primary product from this system is the 2,5-, 1’4’cycloadduct (32); this is thermally and photochemically labile, and gives the Cope-rearranged isomer (33), which is also present in the original mixture of reaction products. Three minor adducts were also observed, and preliminary work suggested that they were 173-cycloadductsof furan and benzene. Sensitized irradiation (benzene or acetone) of both (32) and (33) caused their reversion to starting materials. Cant~e11,*~ however, assigned structures (34), (39, and (36) to the products. Although the presence of (32) was inferred as the intermediate in the formation of (35), the former 1:l adduct was not isolated in this study. Both groups have carried out further experiments and consulted each other. The apparent discrepancies arise principally from the differing experimental conditions 46

Y.Katsuhara, T. Nakamura, A. Shimizu, Y. Shigemitsu, and Y. Odaira, Chem. Letters, 1972, 1215.

48

N. C. Yang and J. Libman, Tetrahedron Letters, 1973, 1409. J. C. Berridge, D. Bryce-Smith, and A. Gilbert, Tetrahedron Letters, 1975, 2325. J. C . Berridge, D. Bryce-Smith, and A. Gilbert, J.C.S. Chem. Cornm., 1974,964. T. S. Cantrell, Tetrahedron Letters, 1974, 3959.

Photochemistry of Aromatic Compounds

361

used in the two studies, and these differences are aggravated by the photo- and thermal labilities of adducts (32) and (33).* These reports are also noteworthy as they describe the first examples of the cycloaddition of two monocyclic aromatic

(34)

(35 )

systems. It is pertinent to note here that furans, thiophens, pyrroles, and indoles have recently been reported to form fluorescent exciplexes with aromatic hydroc a r b o n ~ . Cantrell ~~ has also described the 1,3-, 1’4’-cycloaddition of cyclopentadiene to xylene;4gthis product and (30) (ref. 47) provide the first examples of a type of concerted cycloaddition (predicted in 196962)between a cis-buta1,3-diene and benzene involving either S1diene or S,benzene. Although the light-induced chlorination of benzenoid compounds has been known for years, the process still receives occasional comment. Within the year, Russian workers have described the control of a reactor for the chlorination of benzene 53 and benzotrifluoride 54 Photochlorination of 1-chloronaphthalene has also been described.55 The initial product is a mixture of dichlorides which on further reaction yields several new 1-chloronaphthalene tetrachlorides. The irradiation of aliphatic amines in the presence of aromatic compounds is known to yield products of acyclic 1,2- and lY4-additionand reduction of the aromatic compound.1o The reaction has now been examined with pyridinium and pyridine derivatives and diethylamine.66 The former heterocyclic compounds undergo a thermal reaction with the amine whereas the pyridine derivatives give the reduction products (37) and (38) but no adducts. Light-induced reduction of K1

Is

J. C. Berridge, D. Bryce-Smith, A. Gilbert, andT. S. Cantrell, J.C.S. Chem. Comm., 1975,611 R. S. Davidson, A. Lewis, and T. D. Whelan, J.C.S. Chem. Comm., 1975, 203. D. Bryce-Smith, Chem. Comm., 1969, 806. Y.D. Govdya and A. S. Fedorov, Otkrytiya, Zzobret, Prom. Obruztsy, Tovarnye, Znaki, 1973, 50, 19.

A. A. Ushakov, G. V. Motsarev, V. R. Rozenberg, V. I. Kolbasov, L. V. Belova, and I. N. Chuvaeva, Zhur. org. Khim., 1974, 10,2183. Ks J. W. Barnett, K. R. Bedford, G. W. Burton, P. B. D. de la Mare, and S. Nicolson, J.C.S. Perkin ZI, 1974, 1908. K. Kano and T. Matsuo, Tetrahedron Letters, 1975, 1389. * Detailed comment on these differences must await next year’s Volume, however, as the joint paper which largely reconciles the two reports was still in the press at the time of writing. K’

362

Photochemistry H

Me

N

Me

H

I

H

naphthalene by triethylamine has been studied by flash p h o t ~ l y s i s and , ~ ~ evidence has been provided in support of the earlier proposed mechanism for this process.68 It was also demonstrated that the reduction of the triplet state is markedly less efficient than that of the singlet.67 Acyclic addition products are among those from the irradiation of l-methoxynaphthalene in the presence of phenylacetic acids.6BThe study was undertaken as there is some controversy in the literature over the pathway for light-induced hydrogen-isotope exchange in aromatic compounds by acids,60and the present system allowed an examination of the way in which structural variations of the acid might affect its different modes of interaction with the photoexcited naphthalene derivative. Irradiation of 1-methoxynaphthalene and p-methoxyphenylacetic acid yields the alkylation adduct (39) as the major product, along with decomposition products of the acid. With [carboxy-2Hlp-methoxyphenylacetic acid the deuterium in the product is in the 5-position; from a range of acids and their deuterio-derivatives, it was noted that the quantum yield for disappearance of the naphthalene correlates well with Hammett u constants of the respective phenylacetic acids. The results suggest that the rate-determining step is proton transfer from the acid to the naphthalene followed by combination of the protonated naphthalene with the benzyl residue to yield (39) and carbon dioxide (see Scheme 5). A competing process is deprotonation and formation of the starting materials. Addition of simple ethylenes to polynuclear aromatic compounds has been reported for a variety of systems in recent years.lo The light-induced lY2-addition of acrylonitrile to naphthalene has been intensively studied by McCullough and co-workers.61 It is, however, now interesting to read that polymerization of the ethylene can occur under such conditions.62 Pac and his group have carried out several studies in this area and they have now described the stereospecific 1,2photocycloaddition of l-naphthonitrile with cis- and trans-l-phenoxypr~penes.~~ b7 68

b8 60

61

6a

@3

H. D. Burrows, Photochem. and Photobiol., 1974, 19,241. J. A. Barltrop and R. J. Owers, Chem. Comm., 1970, 1462. J. Libman, Tetrahedron Letters, 1975, 2507. C. G. Stevens and S. J. Strickler, J. Amer. Chem. Soc., 1973,95, 3922; G. F. Vesley and B. D. Olafson, J. Phys. Chem., 1973, 77, 1345; G. Lodder and E. Havinga, Tetrahedron, 1972, 28, 5583. R. M. Bowman, C. Calvo, J. J. McCullough, R. C. Miller, and I. Singh, Canad. J. Chem., 1973, 51, 1060 and references therein. I. Capek and J. Barton, J. Polymer Sci., Part B, Polymer Letters, 1974,12, 6, 327. K. Mizuno, C. Pac, and H. Sakurai, J.C.S.Chem. Comm., 1974,648.

363

Photochemistry of Aromatic Coinpounds HAr

RCH2C0,D

'Iv

HAr*
OMe CH,R

co, +

+-

I

+ RMe + C 0 2 + RCH2CH2R (HArD+**.-O,CCH,R) -+ ArD + RCH2C02H HAr

(H)

H D(H) (39) Scheme 5

Yields are good and endo-location of the phenoxy-group [i.e. (40)] is favoured (8:l from the cis-olefin and 17:l from the trans) although it is sterically more hindered. This high selectivity is accounted for by assuming the formation of exciplexes which have a fairly rigid configuration. Both singlet 84 and triplet 64* 86 exciplexes have been suggested as intermediates in the photoadditions of dimethyl fumarate and maleate to phenenthrene, which yield adducts of type (41). The

involvement of such intermediates has, however, recently been questioned by Kaupp and an alternative singlet biradical pathway has been proposed.88 Further work has been carried out on this system and it is now reported that a broad weak emission ( A 452nm) is observed in the fluorescence quenching of phenanthrene by the f~rnarate.~'The emission is both red-shifted and decreased in intensity by methanol addition, and the authors confirm the earlier proposal of the involvement of a singlet exciplex: the weakness of the emission is suggested to explain the failure 8u to observe it. The quenching of the emission by electron donors parallels their ionization potentials and an exciplex lifetime of about 1 ns can be inferred from oxygen quenching of this emission.68 Photoproduct formation is also attenuated by electron donors and the exciplex is thus considered to be 'a viable precursor' of the adducts. Further, the authors also support the suggestion in ref. 64 that intersystem crossing in the excited complex can account for the absence of stereospecificity. Full details of the photoaddition of furan and its methyl derivatives to 9-cyanoanthracene to yield (42) B4

13' O8

S. Farid, J. C. Doty, and J. L. R. Williams, J.C.S. Chem. Comm., 1972, 71 1. R. A. Caldwell, J. Amer. Chem. Soc., 1973, 95, 1690. G. Kaupp, Angew. Chem. Internal. Edn., 1973, 12, 765. D. Creed and R. A. Caldwell, J . Amer. Chem. SOC.,1974, 96,7369. R. A. Caldwell and L. Smith, J. Amer. Chem. Soc., 1974, 96, 2994.

364

Photochemistry

(42) R

=

H o r Mt.

have been published, and again on the basis of fluorescence measurements and kinetics of the process, an exciplex between the singlet excited anthracene and ground-state furan is considered to be involved;sg head-to-tail dimers of the anthracene are formed in these cases. Neither thiophen nor 1-methylpyrrole reacts in this system. The exciplex fluorescence and fluorescence of the chargetransfer complex in the polynuclear aromatic hydrocarbon-fumaronitrile system have been described, and it is suggested that the electronic structure of the fluorescent state of the exciplex and the excited complex is the same.7o The first example has been reported of the photofixation of COz in a nonbiological system ; this involves the formation of g,lO-dihydrophenanthrene-9carboxylic acid from irradiation of the phenanthrene-amine-C02 system in DMSO or DMF.71 Both aliphatic and aromatic amines are effective, but the polarity of the solvent is important and the reaction does not occur in THF, dioxan, or n-hexane. Yields of carboxylic acids (up to 46%) have been reported and seemingly anthracene, pyrene, naphthalene, and biphenyl also undergo this reductive car boxylation.

4 Substitution Reactions Numerous publications have appeared within the year which formally describe light-induced substitution of an aromatic compound. As in previous years, the current account is restricted mainly to reactions in which the light-absorbing species is the aromatic compound and the aromatic ring is directly involved. Reactions in which the substituent undergoes chemical change are only briefly mentioned, and accounts of attack of photo-generated free radicals on the aromatic species are not included. Reviews relevant to this section which have been published within the year describe general photo-substitution reactions,72 and the mechanism of photoaddit ion-su bstitution reactions of six-membered aza-aroma tic compounds, but both of these are in Russian. The reactions of aromatic nitro-compounds via their triplet states have received a very comprehensive review treatment ;hydrogen abstraction, reduction, incorporation of solvent fragments, and addition and substitution processes have been described for a wide variety of s y s t e m ~ .In ~ ~view 70 71 72

7a 74

K. Mizuno, C. Pac, and H. Sakurai, J.C.S. Perkin I, 1974, 2360. Y. Shirota, I. Tsushi, and H. Mikawa, Bull. Chem. SOC.Japan., 1974, 47, 991. S. Tazuke and H. Ozawa, J.C.S. Chem. Comm., 1975, 237. V. L. Ivanov, Zhur. Vsesoyuz. Khim. 0-Va., 1974, 19, 4, 385. A. Castellano, J. P. Catteau, A. Lablache-Combier, B. Planckaert, and G. Allan, Khim. geterotsikl. Soedinenii, 1974, 7 , 867. D. Dopp, Fortschr. Chem. Forsch., 1975, 55, 51.

Photochemistry of Aromatic Compounds

365

of the increasing interest in aryl nitro-compounds, this review is timely and will be a useful reference source. The reactions of nitrobenzene and a range of its monosubstituted derivatives in concentrated aqueous hydrochloric acid have been studied by Wubbels and Let~inger.'~The principal reaction in most cases is conversion of the NO2 group into NH, and substitution of three aryl hydrogens by chlorine; e.g. nitrobenzene yields 2,4,6-trichloroaniline. 4-Chloronitrosobenzene is implicated as the intermediate in this case as it yields the photoproducts when placed in the photolysis media in the dark. Nitrobenzene in methanolic hydrogen chloride yields N-(4-~hlorophenyl)hydroxylarnine as the major product. In 12 mol 1-1 aqueous acid the quantum yields of the reactions are little influenced by electronwithdrawing substituents, but the presence of electron-donor groups markedly decreases the efficiency. The results have been interpreted in terms of a mechanism involving electron transfer from the chloride ion to the electronically excited nitro-aromatic compound as the primary process. Further work on the light-induced hydrogen isotope exchange of simple benzenoid compounds has been published7s (see also ref. 59). In the present study the photoelectrophilic substitution in deuteriated and tritiated toluene and anisole has been examined. It is observed that the relative reactivities in toluene of the o-, m-, and p-positions are 2 : 1 : 1.4 and thus differ from those of the and 30% ground state. Exchange up to 51% was observed for [~-~H]toluene for [~-~H]anisole but extensive decomposition occurred under all conditions, although such side-reactions were slower with toluene. Comparison of excitedstate electron distributions with experimental results points to the involvement of the aromatic S, or T' states in this exchange process; as yet, however, experiments to substantiate this have not been performed. Photodeuteriation of aryl methyl groups has been noted; this occurs in o-methyl-N-(diphenylmethy1ene)acetamide in MeOD and involves the light-induced formation of the o-quinonoid system, N-H-N-D exchange, and rearomatization with migration of the N-D deuterium onto the resulting methyl group.77 Photo-excited benzenoid compounds substituted with electron-donor groups 70 In the former case react with both chloroform 78 and carbon tetra~hloride.'~~ the reaction is carried out in the presence of diethylamine, and salicylaldehydeand 4-hydroxybenzaldehyde result from phenol via a photo-Reimer-Tiemann reacti01-1.~~ Dihydroxy-compounds, in the absence of base, yield the corresponding aldehydes and the cyclohexadienone (43). Replacement of chloroform by carbon

6

HO CHCI, (43) 76

77 la

lB

G . G . Wubbels and R. L. Letsinger, J. Amer. Chem. SOC.,1974,96, 6698. W. J. Spillane, Tetrahedron, 1975, 31, 495. M. Saeki, N. Toshima, and H. Hirai, Bull. Chem. SOC.Japan, 1975,48,476. K. Hirao, M. Ikegame, and 0. Yonemitsu, Tetrahedron, 1974,30,2301. T. Akiyama, 0. Ikarashi, K. Iwasaki, and A. Sugimori, Bull. Chem. SOC.Japan, 1975,48,914

13

366 Photochemistry tetrachloride and in alcoholic solutions gives a similar type of reaction and the formation of esters 79 e.g. ethyl o-, m-,and p-methoxybenzoates, p-chloroanisole, and ethyl salicylate result from the irradiation of anisole in carbon tetrachloride-ethanol ~ 0 1 ~ t i o nIt~ is . ~reported ~ that in general this photoethoxycarbonylation proceeds effectively when the exciting radiation is within the charge-transfer absorption band of the aromatic and CCl,, but attack by -CC& radicals formed by sensitized decomposition of CCll occurs in parallel with this charge-transfer mechanism. Esters are also formed from the irradiation of benzaldehyde in alcohols in the presence of catalytic amounts of hydrogen chloride and in an oxygen atmosphere.*O Full details have been published of the substitution reactions which result from irradiation of the charge-transfer complexes of 1,2,4,5-tetracyanobenzene and toluene and of 7,7,8,8-tetracyanoquinodimethaneand toluene.82 The former reaction yields l-benzyl-2,4,5-tricyanobenzene(44)via, it is suggested, the intermediate 1,4-acyclic adduct (49,and this reaction is quenched by trifluoroacetic acid. In contrast, the formation of aa-dicyano-4-dicyanomethylbibenzyl (46)from irradiation of the latter system is markedly accelerated by both methanol ;78p

Ncn::ph NC

CN W

C

N

and trifluoroacetic acid. These acid effects have been accounted for by the suggestion that an important step in the formation of (46)is proton transfer followed by radical combination, whereas in the former reaction it is considered that the acid protonates the anion radical of the charge-transfer species, and backtransfer of an electron from the resulting radical to give the cation radical, followed by deprotonation, yields the starting materials. The light-induced reactions of fluoro-, chloro-, and bromo-naphthalenes have been studied in the nucleophilic solvents methanol and dieth~lamine.~~ The fluoro-derivative yields substituted products from the naphthalene singlet state, but the other halogenonaphthalenes react from the TI state to give mainly the radical products naphthalene and binaphthyl, although some substitution is observed. Attempts to quench the reactions led to anomalous behaviour in that the quantum yields were actually increased in the presence of several potential triplet q u e n ~ h e r s . Aryl ~ ~ iodides have been reported to react rapidly with potassium dialkyl phosphates in liquid ammonia when irradiated with 350 nm wavelength light.85 Dialkyl arylphosphonates are formed in 87-96% yield 8o

82

83 84

H. Sakuragi and K. Tokumaru, Chem. Letters, 1974,5,475. A. Yoshino, K. Yamasaki, T. Yonezawa, and M. Ohashi, J.C.S. Perkin I, 1975, 735. K. Yamasaki, T. Yonezawa, and M. Ohashi, J.C.S. Perkin I, 1975,93. L. 0. RUZO,N. J. Bunce, and S. Safe, Canad. J. Chem., 1975,53,688. L. 0. Ruzo and N. J. Bunce, Tetrahedron Letters, 1975, 51 1. J. F. Bunnett and X. Creary, J , Org. Chem., 1974, 39, 3612.

367

Photochemistry of Aromatic Compounds

(Scheme 6). An 2 7 ~ ~mechanism 1 is suggested for both this substitution and for the facile light-induced condensation of aryl halides with thiolate and carbanion nu~leophiles.~~ 0 II At1 (R0)2PO- K+ Iry > Ar-P-OR KT I

+

+

OR

Scheme 6

Dehalogenation of aromatic compounds, and in particular polychlorinated biphenyls which are environmental pollutants, appears to be an area of widespread concern involving much research effort. Thus the photodechlorination and degradation of chlorinated biphenyls has been studied in neutrals8 and alkalines8, isopropyl alcohol solution, in ~y~lohe~ane,~~methanol,~~~ O1 solid-phase and hydrocarbon so1utionYo1and under natural and simulated natural conditions.02 Dependent upon the particular conditions, a number of side-reactions are observed, but sodium hydroxide appears to increase the dechlorination rate considerably.88 As one group points out, it does appear that in the absence of adequate degradative pathways of polychlorobiphenyls by organisms, the chemical stability of these compounds means in practice that the only possible agent for their removal from the environment is the U.V. radiation from the sun. Light-induced dehalogenation has also been observed with 2,4-dichlorophenoxyacefates,O3di- and octa-chlorodibenzofurans,O*and 9,lO-dibromo- and -dichloroa n t h r a c e n e ~ . Reaction ~~ with the latter compounds occurs in the presence of diethylamine and is a singlet-state process. Examples of photosubstitution reactions of parent aromatic hydrocarbons are rare. Methylated anthracenes and dihydroanthracenes are, however, afforded by the irradiation of anthracene in the presence of methyl-lithium.06 The isomer distribution of methyl-anthracenes thus produced is very different from that observed from the thermal reaction, and the process appears to be only successful with higher methyl-lithium concentrations than were previously The reaction is also reported to occur with naphthalene and phenanthrene.Og The efficiency of light-induced substitution reactions of methoxyanthraquinones with nucleophiles has been shown to be very dependent upon the position of the methoxy-group and the particular nucleophile.O* In general, the 1-methoxyderivative is more reactive than the 2-isomer, and whereas reaction was observed 80 87 88 88 90

91 82

93 94

86 86 97

88

J. F. Bunnett and X. Creary, J. Org. Chem., 1974,39, 3173, 3611. J. F. Bunnett and B. F. Gloor, J. Org. Chem., 1974, 39, 382. T. Nishiwaki, A. Ninomiya, S. Yamanaka, and K. Anda, Nippon Kagaku Kaishi, 1973,12,2326. S . Arai, M. Matsui, and M. Imamura, Japan Kokai, 74 45 027. L. 0. Ruzo, M. J. Zabik, and R. D. Schuetz, J. Amer. Chem. Soc., 1974,96, 3809. K. Hustert and F. Korte, Chemosphere, 1974, 3, 153. 0. Hutzinger, W. D. Jamieson, S. Safe, and V. Zitko, Preprints Papers Nut. Meet. Div. Water Air Waste Chem., Amer. Chem. SOC.,1972, 12, 74. R. W. Binkley and T. R. Oakes, Chemosphere, 1974, 3, 3. 0. Hutzinger, S. Safe, B. R. Wentzell, and V. Zitko, Environ. Health Perspectives, 1973,5,267. 0.M . Soloveichik and V. L. Ivanov, Zhur. org. Khim., 1974,10,2404. S . S . Hixson, J.C.S. Chem. Comm., 1974, 574. H. J. S. Winkler, R. Bollinger, and H. Winkler, J. Org. Chem., 1967, 32, 1700; Intra-Sci. Chem. Reports, 1969, 3, 261. J. Griffiths and C. Hawkins, J.C.S. Perkin I, 1974, 2283.

368

Photochemistry

with ammonia and primary aliphatic amines to give 1-amino- and l-alkylaminoanthraquinones, respectively, from the 1-isomer, no reaction was observed with secondary amines or primary arylamines. Both OH- and C1- yield substitution products in this system although the latter gives 1-methoxy-4-chloroanthraquinone. Oxygen has an accelerating effect on these processes. Accounts have appeared within the year describing the irradiation of anthracenesulphonic acids in aqueous acid anthrahydroquinone sulphonates in aqueous alkaline solution,100and of 9,1O-anthraquinone-2-sulphonatein neutral and basic solution.lol The former two reactions afford desulphonated products although the 2-isomers appear to be inert. Hydroxylation occurs in the latter system, and the rates of this process have been measured and their dependence upon the reaction conditions noted. An intriguing intramolecular substitution has been observed with the formation of 5-methoxybenz[alaceanthrylene (47) from 1,4-dimethoxytripty cene (48).lo2 The reaction is carried out in methanol or benzene solution and is suggested to

R (48) R (50) R

(47)

OMe = Me =

OMe

(49)

(51) R

=

H or OMe

involve the intermediate (49). On the other hand, irradiation of dimethyltriptycene (50) is reported to provide a one-step synthesis for 1,4-dimethyl-9arylfluorenes (5 1).Io3 Again this year there have been a number of reports which describe reactions of heteroaromatic compounds in alcoholic solvents; many of these reactions are dependent upon the acidity of the media and the structure of the alcohol. The reactivity of nicotinic acid and its derivatives in such systems demonstrates this 0. P. Studzinskii, N. I. Rtishchev, N. N. Kravchenko, and A. V. Eltsov, Zhur. org. Khim., 1975, 11, 386. looL. M. Gurdzhiyan, A. V. Devekki, 0. P. Studzinskii, G. V. Fomin, and A. V. Eltsov, Zhur. org. Khim., 1973, 10, 2730. lol A. D. Broadbent, H. B. Matheson, and R. P. Newton, Cunud. J. Chem., 1975, 53, 826. lo2 R. 0. Day, V. W. Day, S. J. Fuerniss, and D. M. S. Wheeler, J.C.S. Chem. Comm., 1975,296. lo3 H. Iwamura, Chem. Letters, 1974, 10, 1205. gg

Photochemistry of Aromatic Compounds

369

acidity dependence.lo4 Generally, the cationic form in aqueous solution undergoes photo-hydroxylation and -ethylation in ethanol, but the anionic form is inert to irradiation in strongly alkaline aqueous solution although photodecarboxylation does occur in alkaline ethanol. The same report also describes the photosubstitution of the neutral forms of 3-cyanopyridine and ethyl nicotinate in ethanol solution by the l-hydroxyethyl group. 2-Cyanopyridinium ions also react photochemically with ethanol to yield both the 2-cyano-6-ethoxy- and 2-(1-hydroxyethyl)-pyridinium ions.lo5 It is suggested that in this case the former product arises by a mechanism involving an excimer, whereas the latter results from a radical process. The excimer is also postulated from kinetic evidence to be involved in the similar photoreaction of methyl pyridine-2-carboxylate On the other in alcohol solvents to give 6-alkoxy-pyridine-2-carboxylates.106 hand, irradiation of neutral or slightly basic solutions of 3- and 4-pyridineboronic acids causes a light-induced deboronation and the formation of pyridine and borate.lo7 The photonucleophilic substitution of five-membered heteroaromatic nitrocompounds has been investigated with the nucleophiles CN-, CNO-, OMe-, and water.lo8 Both 2-nitrofuran and the thiophen undergo smooth substitution of the nitro-group, but 2-nitropyrrole is stable to light. Such substitution reactions may be of synthetic importance as the 2-nitro-compounds are readily available. Light-induced nitro-group replacement has also been observed for 8-nitroquinoline, which in the presence of a hydrogen donor yields 8-hydroxyquinoline.10g In carbon tetrachloride solution the keto-oxime (52) is reported to be formed.

The photoreplacement reactions of both quinoline -2- and -4-carbonitriles, 111 With the 2-isomer the cyanoagain in alcohol solvents, have been group is substituted to yield 2-(1-hydroxyalkyl)quin~lines.~~~ It is considered that the reaction is initiated by hydrogen abstraction from the alcohol by the quinoline nucleus. Radical combination is followed by elimination of HCN to afford the product. In this study an interesting relationship between fluorescence intensity and photo-reactivity was observed, and the addition of water to the system increases both. It has been suggested that the hydrogen-abstraction step is markedly facilitated by hydrogen-bond formation of the nitrogen lone pair F. Takeuchi, T. Sugiyama, T. Fujimori, K. Seki, Y. Harada, and A. Sugimori, Bull. Chem. SOC. Japan, 1974,41, 1245. lo5 T. Furihata and A. Sugimori, J.C.S. Chem. Comm., 1975, 241. lo6 T. Sugiyama, T. Fwihata, Y. Edamoto, R. Hasegawa, G. P. Sato, and A. Sugimori, Tetrahedron Letters, 1974, 4339. lo' F. C. Fischer and E. Havinga, Rec. Trau. chim., 1974, 93,21. lo8 M. B. Groen and E. Havinga, Mol. Photochem., 1974, 6, 9. lo* A. N. Frolov, A. V. Eltsov, N. A. Kuznetsova, L. L. Pushkina, and L. P. Ignateva, Zhur. org. Khim., 1974, 10, 1551. N. Hata and T. Saito, Bull. Chem. SOC.Japan, 1974, 47, 942. 111 N. Hata, I. Ono, and H. Suzuki, Bull. Chem. SOC. Japan, 1974, 47, 2609.

lop

370

Photochemistry

with water. Irradiation of the 4-cyano-isomer in alcohols affords substitution by the 1- and/or 2-hydroxyalkyl group at the quinoline 2-position.lll The photochemical cyanoethylation of indoles has been the subject of two reports from the same group within the year. Irradiation of the heterocyclic compounds in the presence of acrylonitrile yields various substituted isomers, dependent upon the substitution pattern in the indole starting material.l12 Indole and acrylonitrile in acetonitrile as solvent give 8% of 1-(l-cyanoethy1)indole and 12% 3-(1-cyanoethyl)indole.l13 Reaction of indoles unsubstituted at the nitrogen occurs in both methanol or acetonitrile as solvent, but N-methylindoles are only labile in methanol: thus proton transfer is suggested to be an important step.112 The intermediacy of an exciplex is proposed and the observed high reactivities of the 3- and 4-positions of the indoles correlate with the calculated spin densities of the indole cation-radical. Phthalazine (53) and quinoxaline (54) both react photochemically in acidified alcohols to give 1-alkyl and 2-alkyl derivatives The quantum yields in the former case are very dependent upon the alcohol, and increase in the order methanol, ethanol, 2-propanol. It is suggested that these photoalkylations

(53)

(54)

0

(5 5 ) (56)

proceed via electron transfer from the solvents to the excited states of the protonated diazines. The behaviour of phenazine (55) in acidified hydroxylic solvents varies with the acid c o n c e n t r a t i ~ n .In ~ ~the ~ presence of phosphoric acid, hydroxylation in the 1-position is observed, but the 1-alkoxyphenazine or 1-acetoxyphenazine is formed with hydrochloric acid, acetic acid, or toluenep-sulphonic acid in alcohols. In strongly acidified alcoholic solution the mechanism is considered to be one of electron transfer, as above, from the solvent to the excited singlet di-cation, whereas in moderately concentrated acidified media, the reaction proceeds by solvent addition to the excited monocation. Photohydroxylation has been reported for flavine derivatives [c.g. (56)], resulting in corresponding 6- and 9-hydroxy-derivatives.ll8 ll2

114 116

lle

K. Yamasaki, T. Matsuura, and I. Saito, J.C.S. Chem. Comm., 1974, 944. K. Yamasaki, I. Saito, and T. Matsuura, Tetrahedron Letters, 1975, 313. S. Wake, Y. Takayama, Y. Otsuji, and E. Imoto, Bull. Chem. SOC.Japan, 1974,47, 1257. S. Wake, Y. Otsuji, and E. Imoto, Bull. Chem. SOC.Japan, 1974,47, 1251. G. Schoellnhammer and P. Hemmerich, European J. Biochem., 1974, 44, 561.

371

Photochemistry of Aromatic Compounds

5 Intramolecular Cyclization Reactions Interest in light-induced intramolecular cyclization processes of aromatic systems has continued at a high level and, as in previous years, the reports have ranged from fundamental examples of the well-known stilbene-to-phenanthreneconversion to the use of such reactions in the synthesis of helicenes and natural products. The synthesis of 1-, 2-, 3-, and 4-phenylphenanthrenes by the cyclization of isomeric phenylstilbenes in the presence of air and iodine has been described,l17 and Giles and Sargent have published full details of the formation of phenanthrenes from 2-metho~ystilbenes.~~~ The latter conversion is a non-oxidative reaction and the elimination of methanol in the process is a general feature of intramolecular cyclization reactions where the preferred site of attack is blocked by a methoxy-substituent. It would seem that the cyclization process is not greatly affected by substituents in non-reacting positions, for stilbene-4,4’dicarboxaldehyde yields the phenanthrene, albeit in low yield and after 2 days’ irradiation llQ(see also ref. 140 for further examples of this). 9-t-Butylphenanthrene is reported to be one of the products from irradiation of 2-t-butyl-1,ldiphenylethylene, and is suggested to arise via the appropriate stilbene, which results from intramolecular phenyl migration within the carbene (57) (Scheme 7).120 MC

Ph2C=CHC(CH3)3 -% Ph,C-e-h--Me I I H Me

-+ PhzCH

Me

(57)

Ms,/

Me

Scheme 7

The photochemistry of styrylbenzenes has received regular comment over the past six years or soyloand this year is again the subject of two publications. In 1972 Laarhoven and Cuppen, who are well known for their researches into stilbene-phenanthrene-type cyclizations, reported that from 2,2’-distyrylbiphenyl (58) the olefin dimer (59) is the kinetically controlled product and that 4,5,9,10tetrahydr0-4~9-diphenylpyrene (60) results from thermodynamic 7-Phenylbenzo[c]chrysene was formed from (58) in the presence of iodine. These findings have been substantiated by Padwa and Mazzu, who have also examined the reactions of the other derivatives (61a, by and c).122 It was found that no S. C. Dickerman and I. Zimmerman, J. Org. Chem., 1974,39,3429. R. G. F. Giles and M. V. Sargent, J.C.S. Perkin I, 1974,2447. 119 J. Y. Wong and C. Manning, Angew. Chem., 1974,86,743. la0 S. S. Hixon, J . Amer. Chem. Soc., 1975,97, 1981. lal W. H. Laarhoven and T. J. H. M. Cuppen, J.C.S. Perkin I, 1972, 2074. laa A. Padwa and A. Mazzu, Tetrahedron Letters, 1974, 4471. 11’

118

3 72 Photochemistry analogue of the olefin dimer (59) was produced from any of these derivatives but all gave the cyclization products (62a, by and c). Cyclization of (63) also yields (60). Laarhoven and Cuppen have further examined this reaction with (58) and (61a, d, e, and f), and report that the nature of the major reaction product depends not only on the experimental conditions but also on the choice of substituents R1and R2in (61).123Again no cyclobutane compounds were formed from (61a

(58) R' (61) a ;

=

R2 = Ph

K1 = R2

= =

(59)

H

b ; R1

=

R'

c ; R'

=

R' = CO,Me H, R' = Ph R2 = P-naphthyl

d ; R' = e ; R1 = f; Rl =

R2 =

CN

(60) R' = R2 = Ph (62) a ; R1 = R2 = H h ; R1 = R? = CN c ; R1 = R2 = C0,Me d ; R1 = H, R' = Ph

Z-benzo[c.]phenanthryl

(63)

(64)

and d) under any conditions. Instead under anaerobic conditions cyclization occurred to (62a and d) and also (64) from (61d). In the presence of iodine, (61a) gave 4,5-dihydropyrene via the same type of ring closure as under the anaerobic conditions and as a result of dehydrogenation steps. In contrast, (61d) produced results similar to those from ( 5 8 ) in the presence of iodine, and benzo[c]chrysene was the sole product. Derivatives of (61) with large aryl residues [i.e. (61e and f)] only yielded cyclobutanes, irrespective of the exciting wavelength. The effect of temperature on this type of cyclization reaction with 1-naphthyl-2-phenyl- and 1,2-dinaphthyl-ethyleneshas been described in a most comprehensive paper by Fischer and c o - w o r k e r ~ .The ~ ~ ~relative contributions of deactivation processes which can occur from the photoexcited diarylethylenes vary sharply with the particular compound and temperature ;e.g., the cyclization of the cis-isomer into the dihydrophenanthrene is slowed at low temperatures whereas the reverse process is attenuated only on cooling with the 2-naphthyl derivatives. Also with the three 2-naphthyl compounds, the ratio of the trans-isomer to the dihydrophenanthrene resulting from deactivation of the excited cis-isomer varies with the exciting wavelength. This effect is explained by selective excitation of the lZ3

P. H. G . Op Het Veld, J. C. Langendam, and W. H. Laarhoven, Tetrahedron Letters, 1975,

12*

T . Wismonski-Knittel, G . Fischer, and E. Fischer, J.C.S. Perkin ZZ, 1974, 1930.

231.

Photochemistry of Aromatic Compounds

373

various isoenergetic conformers which exist in solution. Indeed some of these conformers are observed to give hitherto unknown dihydrophenanthrenes, and this aspect has been discussed further in another report from the same research scho01.l~~ It is observed that photocyclization of 1,2-di(2-naphthyI)ethylene gives the two isomeric 4a,4b-dihydrophenanthrenes(65) and (66) derived from two of the three possible conformers of the starting materials. Compound (65) has a thermal stability 1Olo times greater than that of the isomer (66). Cyclizations of the present type are currently used as a convenient route to helicenes, and this aspect has again received comment. 1-Phenylpentahelicene

125

T. Wismonski-Knittel, T. Bercovici, and E. Fischer, J.C.S. Ckem. Comm., 1974, 716.

3 74 Photochemistry (67) is the product from photodehydrocyclization of 8’-phenyl di-p-naphthylethylene (68).12s The helicene undergoes a further light-induced transformation to benzocoronene (69), and to explain this cyclization the authors have outlined a mechanism which involves a 1,2-phenyl radical shift to 7-phenylbenzo[g,h,i]perylene, which then undergoes rapid dehydrocyclization to (69). The generality of this 1,2-shift is shown by the cyclization of derivatives of (68) to substituted benzocoronenes. Synthesis of the new double helicene diphenanthro[4,3-a;3‘,4’olpicene (70) by photocyclodehydrogenation of (71) is the subject of two publications this year.127,12* It is deduced from n.m.r. spectra that, of the two possible diastereoisomers of the cyclization product, only one, (70), is obtained as the racemate. Naturally, rigidly held stilbene moieties yield phenanthrene derivatives on irradiation, and the cyclization of 9-benzylidenexanthenes and 9-benzylidenethioxanthenes yields compounds of type (72) from both sunlight and U.V.

(72) R = H or Ph, X

=

0 or S

irradiation.12* Not surprisingly, 2,3-diphenyl-indoles and -benzofuran are also photolabile. The former compounds, however, display both light-induced dehydrocyclization to dibenzocarbazoles (73) and oxidation to benzophenone derivatives(74).130 Substituents greatly affect the course of these reactions, and in

+ I Ph

I

/

Ph

most examples given in the report only one product is formed. The cyclization of 2,3-diphenylbenzofuran leading to benzo[b]phenanthro[9,lO-d]furan was reported earlier,131 but the effects of solvents on the process have now been Cyclization occurs smoothly in chloroform or ethanol but in the presence of n-propylamine 12.5% of the reduced phenanthrene derivative (75) was obtained; deuteriation studies showed that hydrogens from the amine alkyl las lap

la8 128

I3O 131

132

A. H. A. Tinnemans and W. H. Laarhoven, J. Amer. Chem. SOC.,1974,96,4611. R. H. Martin, C. Eyndels, and N . Defay, Tetrahedron, 1974, 30, 3339. W. H. Laarhoven, T. J. H. M. Cuppen, and R. J. F. Nivard, Tetrahedron, 1974,30,3343. A. Schoenberg and M. M. Sidky, Chem. Ber., 1974,107, 1207. C. A. Mudry and A. R. Frasca, Tetrahedron, 1974, 30, 2983. G. R. Lappin and J. S. Zanucci, J . Org. Chem., 1971, 36, 1808. A. Couture, A. Lablache-Combier, and H. Ofenberg, Tetrahedron Letters, 1974,2497.

375

Photochemistry of Aromatic Compounds

L7rph

(75)

Ph

0 "

chain are incorporated into (75). Phenanthrene derivatives are also reported to be formed from the prolonged irradiation of the 2-isoxazoline (76).133The same report also describes the light-induced formation of 2-phenylquinoline from (77). Studies continue into the photo-aryI coupling of the two phenyl groups in [2,2]metacyclophanes. From 254 nm irradiation of the dimethyldiene derivative (78), a 35% yield of 2,7-dimethylpyrene (79) is obtained;134from other routes the

I1 v

0,

Me

M e

yields were < 5%. The photointerconversion of the system [2,2]metacyclophan1-ene (80) and 4,5,15,16-tetrahydropyrene(81) has been examined over a range of temperatures and exciting wa~e1engths.l~~ Compounds (80a and b) yield 43dihydropyrene with iodine even at - 30 "C.The quantum yields in each direction do not vary significantly with temperature down to - 190 "C,and this is the first

(80) a; b;

R1 = K' = H R1 = H, R? = Me

(8 1)

Y.Ito and T. Matsuura, Tefruhedron, 1975, 31, 1373. 13' 136

R. H. Mitchell and R. J. Carruthers, Cunud. J. Chem., 1974, 52, 3054. R. Naef and E. Fischer, Helu. Chim. Acru, 1974, 57, 2224.

376

Photochemistry

example in which the cyclization of stilbene compounds is not attenuated on cooling; the authors consider that this reflects the special character of highly constrained structures. The cyclization of [2,2]metacyclophane to 4,5,9,10tetrahydropyrene in the presence of iodine is proposed to occur via the chargetransfer complex of the cyclophane with the ha10gen.l~~ The reaction has now been reported to occur in both aerated and degassed solutions although the quantum yield in the former system is greater than that in the latter.137 The quantum yield for this cyclization increases with temperature but the radiationless deactivation is considered to be very efficient as the value is less than 0.01, and no fluorescence or phosphorescence is apparently observed. Cyclization also occurs when the ethylene is substituted with heteroaromatic groups (see also refs. 147 and 148 later), but whereas reaction of l-(l-benzothien-3-yl)-2-(l-naphthyl)ethylene (82) yields the expected product (83), the

~ ~ irradiation behaviour of the isomeric 2-naphthylethylene (84) is u n ~ s u a 1 . lThus of (84) in the presence of iodine yields (85) as a result of cyclization at the P'-position of the naphthalene nucleus ; this contrasts with all previously known examples of /3-styrylnaphthalene cyclizations which normally occur at the a-position even when this is already substituted. At present this result is not explained, but the authors discount the effect arising from steric factors. Observations of reactions of the present type with compounds in which the aryl groups are separated by conjugated polyenes date back to 1962.13g There have been several further reports of the process, and Leznoff and co-workers have described the reaction of l-formylphenyl-4-phenylbuta-1 ,3-dienes.l4"~ 141 The reaction does not occur with acetyl or nitro-substituents on such compounds since the lowest transition is m*, but from l-(p-formylphenyl)-4-phenylbuta-1,3diene, for example, 1-(p-formylpheny1)naphthalene and 8-phenyl-2-naphthaldehyde are formed : similar results have been reported for the rn-formylphenyl S. Hayashi and T. Sato, Bull. Chem. SOC.Japan, 1972, 45, 2360. K. Sorimachi, T. Morita, and H. Shizuka, Bull. Chem. SOC.Japan, 1974,47,987. 13* A. Croisy, P. Jacquignon, and F. Perin, J.C.S. Chem. Comm., 1975, 106. G . J. Fonken, Chem. and Ind., 1962, 1327. li10 C. Manning and C. C. Leznoff, Canad. J . Chem., 1975,53, 805. J. Y.Wong, C. Manning, and C. C. Leznoff, Angew. Chem. Internut. Edn., 1974,13, 666.

la@ Ia7

Photochemistry of Aromatic Compounds

377

derivative. The 1,4-diphenylbuta-1,3-dienesystem in overcrowded molecules based on dibenzylidenesuccinic anhydrides and imides (86) is very photolabile and results in photochromism of these compounds.1o The process has been further studied, e.g. with the yellow (E)-benzylidene-(E)-(a-phenylethy1idene)-succinic

R’

(86) a; X = 0, R1 = H, R3 = Me

anhydride (86a), which on irradiation reversibly forms the red compound (87).142The dependence of product composition on temperature in this reaction is attributed to thermal disrotatory ring-opening and 1&hydrogen shift in (87). Irradiation of 1,6-diarylhexa-1,3,5-trienesis known to yield substituted chrysenes,1° and such a reaction has been observed with lY6-dimethyl-and 3-methyl-l,6-diphenylhexa-l,3,5-trienes : in the latter case the chrysene is formed following methyl e j e ~ t i 0 n . lIn ~ ~contrast, the reaction with the 1,3,6-triphenylhexatriene gave neither 6-phenylchrysene nor 2-phenyl-1-styrylnaphthalene, as may have been expected, but 1,2,4-triphenylbenzene was formed via (it is suggested) either the triphenylcyclohexa-l,3-diene(88) or the triphenylbicyclo[3,1,O]hex-2-ene (89).

Cyclization of azobenzene and its derivatives tends only to occur under acid conditions. The reaction of the conjugate acids of azobenzene with anhydrous aluminium chloride, stannic chloride, and ferric chloride in 1,2-dichloroethane has now been reported in detail.lq4 Benzo[c]cinnoline is formed, but the production of benzidine suggests that the reaction involves photodisproportionation. Similar cyclization is observed with the conjugate acids of azobenzenedicarboxylic With these compounds the reaction also occurs in 98% sulphuric acid to yield, from the 2,2’-isomer, benzo[c]cinnoline-4,7-dicarboxylic acid (90) and indazolo[2,1-a]indazole-6,12-dione(91) in equal amounts: the 3,3’and 4,4’-dicarboxylic acids of azobenzene likewise give the corresponding cinn01ines.l~~It is important to note here that benzo[c]cinnoline is light-labile in 142 143

144

145

H. G. Heller and M. Szewczyk, J.C.S. Perkin I, 1974, 1487. W. Carruthers, N. Evans, and D. Whitmarsh, J.C.S. Chem. Comm., 1974,526; W. Carruthers, N. Evans, and R. Pooranamoorthy, J.C.S. Perkin I, 1975, 76. C. P. Joshua and V. N. R. Pillai, Tetrahedron, 1974, 30, 3333. C. P. Joshua and V. N. R. Pillai, Indian J. Chem., 1974, 12, 60.

378

Photochemistry

+

hv

0-g 0

(91)

acidified alcohols and undergoes photoreduction; depending upon the wavelength of exciting light and the media, either 2,2'-diaminobiphenyl or carbazole and ammonia are also formed.146 The photocyclodehydrogenation of phenylazopyridine has been investigated as a possible step in the synthesis of a~obipheny1enes.l~'Indeed photolysis of (92) in concentrated sulphuric acid does yield the appropriate azobenzocinnolines

(93) Ji v

>

+

(93) and (94), which pyrolyse to the two azobiphenylenes (95) and (96); this provides the first example of photocyclization of a heteroaromatic azo-compound. Diazophenanthrenes are afforded by cyclization of benzylidenaminopyridines (97) and pyridinalanilines (98), again in concentrated sulphuric acid.14* Ph-CH=N (97) 146 147 148

(98)

H. Inoue, T. Sakurai, and F. Tanaka, Bull. Chem. SOC.Japan, 1975,48,924. J. W. Barton and R. B. Walker, Tetrahedron Letters, 1975, 569. H. H. Perkampus and B. Behjati, J. Heterocyclic Chem., 1974, 11, 51 1.

Photochemistry of Aromatic Compounds

379

The non-cyclization of these compounds in organic solvents is explained by a fast cis-trans-isomerization and the non-planar geometry of these Schiffs bases. Cyclization of proximate phenyl groups separated by moieties other than ethylenic systems is a general reaction and has again been noted with a number of diverse systems (see also refs. 126 and 137). Both 4,5-diphenyltriphenyleneand 4,5-diphenylphenanthene undergo this cyclization process and, as with the reaction of 1-phenylpentahelicene,126 1,Zphenyl shifts occur to give, e.g. from the triphenylene, l-phenyldibenzo[e,rJpyrene (99, tribenzo[e,g,h,i,k]perylene (loo),

and benzo[e]naphtho[l,2,3,4-g,hYi]perylene (101).149 It is suggested that (101) arises by a sigmatropic rearrangement in the same intermediate radical which undergoes the phenyl shift. The well-known cyclization of diphenylamine to carbazole has been intensively studied with the N-methyl derivative.160 Conversion into the N-methylcarbazole proceeds via the successive intermediates, the triplet diphenylamine, and N-methyl-4a,4b-dihydrocarbazole. Oxygen takes part in this reaction in two ways, firstly by dehydrogenation of the dihydrocarbazole in competition with reversion of this to the diphenplamine, and secondly by quenching of the triplet species in competition with its ring closure to the dihydrocarbazole. The values of the quantum yield calculated for formation of the carbazole as a function of oxygen concentration, using rate constants determined by flash photolysis techniques, are reported to be in satisfactory agreement with those determined experimentally. Photochemical format ion of carbazoles has been reported from azidobiphenyls but here the intermediates are biphenyl nitrenes.161 Utilization of the present cyclization with heterocyclic 14@

A. H. A. Tinnemans and W. H. Laarhoven, J . Amer. Chem. Soc., 1974,96,4617. G. Fischer, E. Fischer, K. H. Grellmann, H. Linschitz, and A. Temizer, J. Amer. Chem. Soc., 1974,96, 6267.

lS1

R. J. Sundberg and R. W. Heintzelman, J. Org. Chem., 1974, 39, 2546; A. Yabe and K. Honda, TetrahedronLetters, 1975, 1079.

380

Photocheniistry

triarenes as a synthesis of new ring systems is exemplified by the formation of (102) from (103).152 Cyclization of aryl and/or heteroaryl groups by the light-induced elimination of halogen acids is a facile and widely applicable process, and has been used as a step in the synthesis of nitidine and avicine salts (104).153Thus irradiation of (105)

(104)

0

0-CH,-0, R2 = H R' = OMe. R2-R2 = 0-CH,-0 R1-R' R2- R' = O-C14,-0

(105) R'-R'

= ~

provides a highly effective route to (106) which by two further steps can be converted into the required salts (104). The interest in such compounds as(104) stems from their cytotoxic and antileukaemic properties. Light-induced migration of the aryl group in 1-arylindoles to the 3-position has been previously re-

ported,I5* and an analogous process has now been observed with the benzoyl With 1- and 3-o-iodobenzoylindoles, however, cyclodehalogenation occurs, and the 1-isomer yields a mixture of (107) and (108), whereas only (108) is formed from the 3-is0rner.l~~Significantly, no (109) is formed from l-o-iodobenzoylindole, but small yields are obtained by a similar photolysis of l-o-iodobenzoylindoline. Dehydrohalogenation and cyclization are reported to occur both on 254 nm radiation and electro-reduction of 5-(2-~hlorophenyl)-l-phenyl162

Is'

A. Mitschker, U. Brandl, and T. Kauffmann, Tetrahedron Letters, 1974, 2343. S . V. Kessar, G . Singh, and P. Balakrishnan, Tetrahedron Letters, 1974, 2269. M. Somei and M. Natsume, Tetrahedron Letters, 1973, 2451. W. Carruthers and N. Evans, J.C.S. Perkin I, 1974, 1523.

381

Photochemistry of Aromatic Compounds

pyrazole (1 The same product, pyrazolo[l,5-f]phenanthridine (1 1l), is formed from both reactions, but the work-up procedure from the photolysis is much simpler. Ethylene-aryl intramolecular interaction in the excited state leading to cyclization products is known for a number of diverse systems.1° The formation of benzocyclobutenes from styrenes is the simplest reaction of this type and it has recently been observed in the irradiation of polyfluorinated styrenes (1 12) 15' C,F,CR1=C, (112)

R1 = R2 R'

R1

=

/R2

R

R3 = H or F R2 = R3 = H

= F or Me, = R2 = H,

R3

=

Me

(cf. ref. 158 for the formation of phenylbenzocyclobutadiene from diphenylacetylene). But the authors also report that allylpentafluorobenzene gives 2-allyl-1,3,4,5,6-pentafluorobicyclo[2,2,0]hexa-2,5-diene on irradiation and no olefin-phenyl cyclization products. Formation of dibenzofurans from diphenyl A similar reaction has now been observed ethers was reported two years on irradiation of aryloxyenones.lGoIn this case the cyclization product (113) is photolabile and undergoes rearrangement to form the 2-hydroxystyrene derivative (114): the mechanism of this cleavage with rearrangement is reported to be under investigation. The authors also note that this cyclization could have potential as a synthetic approach towards morphine alkaloids (1 15).

lS6 16' 168

lSB

W. J. Begley, J. Grimshaw, and J. Trocha-Grimshaw, J.C.S. Perkin I, 1974, 2633. V. V. Brovro, V. A. Sokolenko, and G. G. Yakobson, Zhur. org. Khim., 1974,10,2385. K. Ota, K. Murofushi, T. Hoshi, and H. Inoue, Tetrahedron Letters, 1974, 1431. J. A. Elix, D. P. H. Murphy, and M. V. Sargent, Synthetic Comm., 1972,2,427. A. G. Schultz and R. D. Lucci, J. Org. Chem., 1975, 40, 1371.

3 82

Photochemistry

Reports of light-induced cyclization of N-arylenamines, N-benzoylenamines, and ap-unsaturated anilides continue to appear and, as in the pastylothese reactions have been used as a step in the synthesis of some natural products.lsl Fundamental systems such as (1 16) have also been studied, and further details have been published of the mechanism for the methylene elimination and the

8

OH

. Phy

intramolecular ring-opening to yield 3,4-dihydro-5-hydroxy-4-methyl-l-benzazocine (117) from (116).lS2 Sensitizer studies indicate that the excited species in this transformation may be the nn* triplet. Examples of the cyclization reaction with N-benzoylenamines have been reported by two groups. Lenz has studied (118) as a the process with 2-aroyl-l-methylene-1,2,3,4-tetrahydroisoquinolines

(118) R = H (120) R = OMe

PhNH

Me0 OMe

OMe (122)

(123) (121) R = OMe (125) R = H

(124)

(126) R

=

H or R-R

=

OCH,O

H. Ishii, K. Harada, T. Ishida, E. Ueda, K. Nakajima, I. Ninomiya, T. Naito, and T. Kiguchi, m

Tetrahedron Letters, 1975, 319. K. Yamada, M. Kamei, Y. Nakano, and H. Iida, Chiba Daigaku Kogakubu Henkyu Hokoku, 1974, 25, 73.

Photochemistry of Aromatic Compounds 383 route to 8-oxoberbines (1 19).163 The cyclization is apparently not affected by substituents in the rn- andp-positions of the phenyl group, but with an o-methoxy substituent, as in (120), elimination preferentially occurs, as so frequently observed in the past, to yield (l2I).la4 Non-oxidative cyclization and elimination of the methoxy-group were also observed in the formation of phenanthridones (122) from 2-methoxybenzanilides (123), although not all derivatives of (123) reacted. The generality of cyclization reactions in the formation of such compounds as (121) was examined by the photolysis of (124), when indeed (125) was formed as the major product, although those from formal addition of water to the ethylenic bond in (124) and the expected stilbene-phenanthrene cyclization were also observed. A Japanese group has used this reaction with enamido-ketones (126) and have thereby developed a new synthetic route to lycorine-type alka10ids.l~~ Further to their earlier studies and those of other workers on the general cyclization of ap-unsaturated anilides,1° Ninomiya and co-workers have now reported on the stereochemical aspects of this process.166 Both (127) and (128)

(129)

R

= Me or CH,Ph

R

(127)

are formed from (129), but the ratios are solvent-dependent. In protic solvents, the cis-isomer (128) predominates, whereas in aprotic solvents the trans-isomer (127) is favoured. From such studies, and experiments with deuteriated solvents, the authors propose a mechanism of electrocyclic cyclization of the 6wenamide system to give an intermediate which undergoes a thermal hydrogen shift in either a stepwise or concerted manner to yield (127) and (128). In aprotic solvents the shift is considered to be concerted but in protic media, stepwise, involving protonation and deprotonation ; the preponderance of cis-products has not as yet been explained. The authors also demonstrate the usefulness of this reaction for the synthesis of phenanthridines (cf. ref. 164). An interesting new rearrangement-cyclization has been reported and involves the formation of 2-methylthiaxanthone (130) from 4'-tolyl-2-methylsulphanothiobenzoate (l31).la7 The keten derivative (132) is suggested as the reaction intermediate. In contrast, neither the 3-methylsulphano thiobenzoate nor 4'-t olyl2-methyl sulphanobenzoate undergoes this reaction. The former compound undergoes cleavage of the S-benzoyl bond and the resultant thiyl and benzoyl radicals yield the dimerization and hydrogen-abstraction products, bis4'-tolyl disulphide and 3-methylsulphanobenzaldehyde. In the latter case, a normal 1txi

166

G. R. Lenz, J. Org. Chem., 1974, 39, 2846. G. R. Lenz, J. Org. Chem., 1974, 39, 2839. H. Iida, S. Aoyagi, and C. Kibayashi, J.C.S. Chem. Comm., 1974,499. I. Ninomiya, S. Yamauchi, T. Kiguchi, A. Shinohara, and T. Naito, J.C.S. Perkin I, 1974, 1747.

la7

J. Martens and K. Praefcke, Tetrahedron, 1974, 30, 2565.

384

Photochemistry

0

Me

OH

Me

photo-Fries reaction of the benzoate occurs, and the benzophenone derivative (133) is formed. Again this year several accounts have appeared which describe the cyclization of o-substituents. As these do not involve the aromatic ring directly, only a few examples will be mentioned, Dopp has continued his studies on the photochemistry of aryl nitro-compounds and has further commented upon the cyclization of o-substituents, particularly t-butyl, with the nitro function;16*this and a variety of other light-induced processes of aryl nitro-compounds are the subject of an excellent review by the same The two nitro-groups in 2,2’dinitrodiphenylmethane undergo light-induced cyclization and the process is reported to provide a new route to the dibenzo[c,f][l,2]diazepine system (134).le9 Two groups report on the intramolecular cyclization of ethylene moieties with phenolic hydroxy-groups. Irradiation of simple o-allylphenols is reported

OH

R2 0 0 (1 34)

(135) R1

=

,R2= OMe (136) R1= ~

Me (137) R1 = Ph, R2 = H

M

~ = OMe ,

0

(138)

R1= &ph,R2

=H

to yield both benzodihydrofuran and benzodihydropyran derivatives.170 The mechanism is presumed to be ionic and the reaction showed no correlation with the pKa values of the excited state of the phenols in aqueous solution. The second report describes the photosynthesis of chromanones (1 35) from sorbophenones (136):l’l this process has been extended to a synthesis of flavanones (137) from le8 leQ 170 171

D. Dopp and K. H. Sailer, Tetrahedron Letters, 1975, 1129. C. P. Joshua and P. K. Ramdas, Synthesis, 1974, 12, 873. S. Houry, S. Geresh, and A. Shani, Israel J. Chem., 1973, 11, 805. F. R. Stermitz, J. A. Admovics, and J. Geigert, Tetrahedron, 1975,31, 1593.

R

Photochemistry of Aromatic Compounds

385

chalcones (138). It is relevant to note here that light-induced cleavage of certain benzoheterocycles can occur to yield o-disubstituted benzenes.172 6 Dimerization Reactions Interest continues in the intramolecular photodimerization reactions of polynuclear aromatic moieties joined by an alkane chain. The absorption and exciplex emission spectra of the naphthalene-anthracene sandwich pair have been previously studied : this species was generated by the light-induced (254 nm) cleavage of the intramolecular photo‘dimer’ (1 39) of 1-(9-anthryl)-3-(1-naphthyl)propane at low temperatures in a rigid The generation and properties of the sandwich pair have been examined by other workers, using single crystals of the intramolecular cycloadduct (1 39).17* The exciplex fluorescence is broad and

at 77 K the decay time is of the order of 80 ns. As the temperature is increased the emission is quenched by a process involving photocycloaddition of the pair to form (139). The earlier reports 173 have prompted Cristol and Perry to describe their work with the related compound 1,2-bis(lO’-methy1-9’-anthryl)ethane (140).176The formation of the intramolecular dimer (141) is found to occur in

Me

IrV

+

( 140)

(141)

ordinary laboratory light (at least, as the authors point out, that experienced in Boulder, Colorado!); this extreme photolability was not mentioned in an earlier description of the synthesis of (140).176The retro-reaction occurs readily at temperatures just below the decomposition point of (141)but in contrast to (139), (140) is formed with only low efficiency when (141) is irradiated with 254nm light. 172

17s 174

17i5

W. Heinzelmann and M. Marry, Helv. Chim. Acta, 1974, 57, 376. E. A. Chandross and A. H. Schiebel, J. Amer. Chem. SOC.,1973,95, 611, 1671. J. Ferguson, A. W. H. Mau, and M. Puzu, Mol. Phys., 1974,28, 1457. S. J. Cristol and J. S . Perry, Tetrahedron Letters, 1974, 1921. A. L. J. Beckwith and W. A. Waters, J. Chem. Sac., 1956, 1108.

386

Photochemistry

It has been observed that piperylene catalyses the photodimerization of 9-pheny1anthra~ene.l~' The process appears to be an example of a general phenomenon, for the reaction can be catalysed by other dienes, and improvement of dimer yields has been noted with other anthracenes, including those which undergo dimerization in the absence of dienes. From kinetic data, a scheme is proposed which involves the excimer as the reactive intermediate. The role of crystal imperfections in the dimerization of substituted anthracenes Similar has been described in the case of 1,8-dichlor0-9-methylanthracene.~~~ studies have now been conducted for the 10-methyl isomer.179 In order to explain how the topochemically forbidden trans-dimer (head to tail) is produced from irradiation in the solid phase, optical and electron microscopic examinations of the (010) faces of the orthorhombic crystals of the monomer have been carried out, together with differential-enthalpic and dielectric measurements. Again it is shown that the dimer nuclei appear at emergent dislocations. It is well established that mono-meso-substituted anthracenes yield head-to-tail dimers as a result of steric and/or electrostatic repulsions between the substituents.lso The first head-to-head mixed dimers have now, however, been reported, and control of the selectivity of this addition is considered to result from charge-transfer and dipole-dipole interactions.l*l Thus irradiation of a mixture of 9-methoxy- and 9-cyano-anthracenes in ether yields solely the head-to-head dimer (142), with no trace of the head-to-tail isomer. At room temperature (142) is thermally converted into the starting materials. Irradiation of the mixture of anthracenes in a polar solvent, such as acetonitrile, which is able to stabilize the

(142) (143)

R1 .== R2 = H R1 = OMe, R2 = CN

radical ions dramatically decreases the mixed to true dimer ratio. In contrast, solutions of 9,lO-dimethoxy- and 9,lO-dicyano-anthracenesdo not yield a mixed dimer, and 9-methoxy-10-cyanoanthraceneaffords the unstable head-to-tail dimer (143), which has the same cis-arrangement of the cyano- and methoxygroups as in (142). 177 178

R. 0. Campbell and R. S. H. Liu, Mol. Photochem., 1974, 6, 207. J.-P. Desvergne, J. M. Thomas, J. 0. Williams, and H. Bouas-Laurent, J.C.S. Perkin 11, 1974, 363.

178

180

181

J. M. Thomas, J. 0. Williams, J.-P. Desvergne, G. Guarini, and H. Bouas-Laurent, J.C.S. Perkin II, 1975, 84. J.-P. Desvergne, H. Bouas-Laurent, R. Lapouyade, J. Gaultier, C. Hauw, and F. Duphy, Mol. Cryst. and Liq. Cryst., 1972, 19, 23 and references therein. A. Castellan, R. Lapouyade, H. Bouas-Laurent, and J. Y.Lallemand, Tetrahedron Letters, 1975,2467.

Photochemistry of Aromatic Compounds

387

Novel photochemical multicycloaddition reactions have been reported for the diyne (144),182 which on irradiation in benzene solution by sunlight gives the unconventional dimer (145) as a result of intramolecular alkyne additions to the 9,lO-positions of the anthracene and dimerization of the resulting species. The

(146)

authors point out that this is a ‘photochemically symmetry-allowed [,4# + ,2, + ,2, + ,,4, + ,2, ,,2,]’ cycloaddition. Irradiation of (144) in the presence of cyclic dienes allows trapping of the highly strained 1,2,3-triene intermediate to form 1:l adducts of type (146).

+

7 Lateral-nuclear Rearrangements The mechanism of the photo-Fries reaction, both in the vapour and condensed phases, has been thoroughly established, and the many reported examples of the process with a wide variety of systems indicate the generality of the reaction.1° Although o- and p-migration products normally result from irradiation of aryl esters, structural constraints can lead to rneta-rearrangement products, and the first useful meta-Fries reaction has now been described.183 Thus irradiation of the amino-lactone (147) in THF leads to 57% of the red crystalline isomer (148) via,

NH2

Me0 0

’ OH

0

N

Me0

’N OH

(147) (149) laa lS8

T. Inoue, T. Kaneda, and S. Misumi, Tetrahedron Letters, 1974,2969. G . J. Siuta, R. W. Franck, and A. A. Ozorio, J.C.S. Chem. Comm., 1974,910.

388 Photochemistry it is suggested, the radical (149). The authors note that such easy access to these highly substituted tricyclic structures is potentially useful for syntheses in the mit omycin synthesis. The migration reaction has been reported for both heteroaromatic acid phenyl esters la* and hydroxypyridine esters.ls5 The former report describes the process for both 3- and 4-isomers of (150) and for the 5-ring heteroaromatic compounds

QCWh

(151). Both series of compounds lead to o- and prearrangement Beugelmans and Le Goff have previously described the photo-Fries reactions of a- and /3-benzoyl esters of pyridine,las and now report on the rearrangement of such compounds variously substituted on the acyl and heterocyclic moieties.la5 The light-induced reaction yields 2- and 4-acylpyridinols, pyridinols, substituted benzoic acids, and diary1 a-diketones. In contrast, no photo-Fries reaction is observed with 3-acetylindole, but indigo and biacetyl are formed instead; irradiation in the presence of benzophenone yieIds 2-diphenylmethylene indolin3-one (152) as the major product (cf. reaction of l-substituted indoles laB).The rearrangement of heteroaromatic amides previously observed with such simple compounds as (153) laghas now been extended to the benzoylaminopyridines (154a, b, and c).lgo The photo-Fries reaction is observed with both the a- and /%isomers (154a and b), and although the cyclization product (155) is formed

8" \

H

(153)

(152)

& N '

(154) a; R1 = NHCOPh, R = R3 = H b ; R' = NHCOPh, R1 = R3 = H C; R3 = NHCOPh, R1 = R = H 0

0 H

Y. Kanaoka and Y. Hatanaka, Heterocycles, 1974, 2, 423. M. T. Le Goff and R. Beugelmans, Bull. SOC.chim. France, 1974,9, 2047. lS6 R. Beugelmans and M. T. Le Goff, Bull. SOC.chim. France, 1972, 1106. la7 K. Oe, M. Tashiro, and 0. Tsuge, Heterocycles, 1974,2, 663. 188 M. Somei and M. Natsume, Tetrahedron Letters, 1973, 2451. la9 J. T. Edward and L. Y . S. Mo, J. Heterocyclic Chem., 1973, 6, 1047. lgo K. Itoh and Y . Kanaoka, Chem. and Pharm. Bull. (Japan), 1974, 22, 1431. la4

lB6

Photochemistry of Aromatic Compounds

389

from (154a), the equivalent compound (156) is the sole product from the y-isomer (154~). The influence of hydrogen bonding on the photo-Fries reaction of N-phenylurethane has been the subject of two reports from Noack and S c h w e t l i ~ k The . ~ ~ formation ~ of ethyl 2-aminobenzoate, the 4-isomer, and aniline has been monitored with time, concentration, presence of quenchers, temperature, and solvent. The quantum yield for formation of the rearrangement products decreases in polar solvents and at high concentrations of the urethane. This decrease is dependent upon the hydrogen-bonding acceptor strength of the polar aprotic solvents with the urethane. The reaction has been investigated in dibutyl ether, THF, 2-propanol, ethanol, and biacetyl; the singlet rr* state is involved. Irradiation of 3,5-dimethoxybenzyl acetate in hexane leads to 1,3-dimethoxy-5methylene-6-acetoxycyclohexa-1,3-diene(157) as one of the major Compound (157) may be regarded as a precursor of the rearrangement product (158) and indeed is readily converted into this. Other reaction products are

3,5-dimethoxytoluene, 3,5-dimethoxyethylbenzene, 3,5-dimethoxyheptylbenzene, and 3,5,3’,5’-tetramethoxybibenzyl. The first step in the reaction which leads to all these products is reasonably considered to be benzyl-OCOMe bond fission. Irradiation of the labelled compound (159) leads to carboxyl oxygen equilibration. The absence of the ‘crossed’ product from irradiation of (159) in the presence of 3,5-dimethoxy[l,l-2H,]benzyl acetate clearly indicates that the equilibration reaction is i n t r a m ~ l e c u l a r . ~ ~ ~ The lateral-nuclear rearrangement of aryloxy-l,3,5-triazines had previously received the attention of Shizuka and c o - ~ o r k e r s .The ~ ~ ~same research school now reports the effect of irradiation on a large number of aryloxy-sym-triazines (160).le5 In general o- and/or p-hydroxy-derivatives of aryl-sym-triazines (161) NqR1

N+R’

A r q J

AriqN

R2 (160)

R2

(161)

are formed. p-Methyl, -chloro and -methoxy substituents in the phenoxy-group do not affect the reaction, but p-CHO, -COMe, -C02Et,and -nitro groups inhibit formation of the products (161). The effect of substitution in the sym-triazine R. Noack and K. Schwetlick, Tetrahedron, 1974,30, 3799; 2.Chem., 1974,14,99. D. A. Jaeger, J. Amer. Chem. SOC.,1974, 96, 6216. lU3 D. A. Jaeger, J. Amer. Chem. SOC.,1975, 97, 902. le4 H. Shizuka, N. Maeno, and K. Matsui, Mol. Photochem., 1972,4, 335. Y. Ohto, H. Shizuka, S. Sekiguchi, and K. Matsui, Bull. Chem. SOC.Japan, 1974,47, 1209. lel le2

390 Photochemistry moiety has also been examined and whereas chloro-, methoxy-, phenoxy-, and methyl groups did not prevent reaction, the migration is inhibited by phenyl and amino-groups. In contrast with the reaction of (160),arylamino- and arylthiosym-triazine did not rearrange. Further studies on the photobenzidine rearrangement of NN’-dimethylhydrazoaromatics [e.g. (162)] have revealed that isomerization to the orrho-semidines (1 63) involves singlet intermediates, and appears to be i n t r a r n o l e c ~ l a r . ~ ~ ~

(162)

Me (1 63)

J. D,Cheng and H. J. Shine, J. Org. Chem., 1974, 39, 2835.

3 Photo-oxidati o n and -red uction BY

H. A. J. CARLESS

1 Conversion of C=O into C-OH Hydrogen abstraction by photoexcited benzophenone (1) continues to be a topic of interest. Schuster and Weill had reported previously that, at high concentrations of (1) in benzene, a ketone excimer is formed which may subsequently lead to the hydrogen abstraction process shown in reactions (1)-(4). Ph2C0 kv, 'Ph2CO* --+ 3Ph2CO* 3Ph2CO* 4- PhzCO + excimer excimer + 2Ph2C0 excinier + PhzeOH

+ Ph-C'Q.

(2)

(1) (2)

(3) (4)

(3)

Davidson and Wilson2 have now provided further proof for such selfabstraction at relatively high (0.1 moll-l) concentrations of (1) in benzene, by e.s.r. detection of the ketyl radical, diphenylhydroxymethyl(2). On irradiation in deuteriated benzene, the protonated, not the deuteriated, radical was observed. This provides strong evidence for hydrogen abstraction from benzophenone itself, rather than from solvent. Schuster and Wei13 have now extended their study to benzophenone in purified carbon tetrachloride solvent, and again have found the results interpretable in terms of self-abstraction of hydrogen (reaction 4). The major reaction products are benzpinacol (quantum yield, @, 0.14 x 10-3-1.6 x and hexachloroethane, with a smaller amount of 4-chlorobenzophenone, and reactions (5)-(8) are postulated. The ratio of excimer in CC14, somewhat less than the ratio reaction to decay, k4/k3,is 2.8 x

(3)

+

PhzCO +dimers, polymers, elc.

2(2) --+

a

Ph,C(OH)C(OH)Ph,

D. I. Schuster and T. M. Weil, J. Amer. Chem. SOC.,1973, 95, 4091. R. S. Davidson and R. Wilson, Mot. Photochem., 1974, 6, 231. D. I. Schuster and T. M. Weil, Mol. Photochem., 1974, 6, 69.

391

(6)

(7)

392

Photochemistry

(lo-,) in benzene.l Related to the above reaction, flash photolysis of phenyl 2-pyridyl ketone at high concentrations in perfluoromethylcyclohexane(PFMCH) solvent shows the absorption of the corresponding ketyl radical, which must be formed by hydrogen abstraction of excited ketone from another ground-state m01ecule.~ However, in general the species produced on photolysis of several phenyl pyridyl ketones in PFMCH were thought to be the triplet states of the ketones, although their absorption spectra closely resemble those of the corresponding ketyl radicals. Phot oreduct ion of pentafluoro benzophenone (4) by pent afluorobenzhydrol(5) to decafluorobenzpinacol (6) on irradiation at 254nm in hexane has been 0

II

OH

C6Fs-CC-C6Hs (4)

+

I

’”

C~FS-C-C~H~ I H

OH OH

I

5

C6F5-CI H5C6

I

C-Cs F5 I C6H5

(6)

(5)

r e p ~ r t e d .The ~ pinacol(6) was not formed in neat propan-2-01, but was produced (in 65% yield) by 350 nm light in a propan-2-ol-hexane (1 : 40) solvent. Presumably, this is because the disproportionation of fluorinated pinacols such as (6) to (4) and ( 5 ) is rapid in alcohols, as has been found for the corresponding eicosafluorobenzpinacol from perfluorobenzophenone.6 Cohen et al. have studied the question of pinacol stability in the photoreduction of substituted benzophenones (7a-d) in aqueous propan-2-01 over the

(7) a; X = H b; X = C 0 2 -

c; x d; X

= =

so,-

NMe,b

pH range 6.5-1 2.5. The presence of electron-donating or electron-withdrawing substituents, or a more alkaline solution, all make decomposition of the pinacol to ketone and hydro1 more rapid. The ketones (7b-d) are photoreduced to pinacols in acidic media, but in alkaline solutions some hydrols are directly produced, even at pH 8-9 in which the pinacols are stable. The hydrols arise by disproportionation reactions of the ketyl radical anions with ketyl radicals [reaction (9)], which compete favourably in alkaline solutions with ketyl radical combinations [reaction (lo)]. Ar,C%

+ Ar,COH

-

ROH

Ar,kOH 4

(I

+ Ar,COH

Ar,CO

+ Ar,COH + RO-

Ar,CHOH

Ar,C(OH)C(OH)Ar,

(9) (10)

J.-P. Blanchi and A. R. Watkins, Mol. Photochem., 1974, 6, 133. R. Filler and H. H. Kang, J. Org. Chem., 1975,40, 1173. J. Dedinas, J . Amer. Chem. Soc., 1973, 95, 7172. S. G. Cohen, G . C. Ramsay, N. M. Stein, and S. Y. Weinstein, J . Amer. Chem. SOC.,1974,96, 5124.

393

Photo-oxidation and -reduction

The intramolecular photoreduction of long-chain alkyl esters of p-benzophenone carboxylates (8) has previously been used as a means of introducing a functional group at a saturated position in the attached alkyl chain. Winnik et aL8 have now carried out Monte Carlo calculations on such intramolecular hydrogen abstractions. Measurements of the phosphorescence quantum yield

(9)

(8)

and lifetime of (8) as a function of alkyl chain length provide a guide to the rate constants for intramolecular reaction, and the results obtained in CCll provide evidence for a randomly oriented hydrocarbon chain in this solvent.Q Suppan lo has re-investigated the photoreactivity of Michler's ketone (9) (MK) in solution. In cyclohexane at low concentrations of MK mol 1-l), efficient photoreduction (0= 0.36) takes place on irradiation at 365, 313, or 265 nm. At higher concentrations (> mol F), irradiation leads to long wavelength U.V. absorption, and it is possible that a bimolecular reaction to give dimers is involved. Both reduction and dimerization can be completely quenched by added naphthalene, and presumably occur from the lowest triplet excited state of (9). In on 365 or 313 nm irradiation, although ethanol, (9) is very unreactive (Q, < there is some variable reactivity, thought to be due to traces of benzophenone impurity, at 265 and 254 nm. Perfluoroketones are able to abstract hydrogen on irradiation in solution, producing the corresponding ketyl radicals which are detected by e.s.r. spectro~ c o p y .Abstraction ~~ occurs from trifluoroacetaldehyde [reaction (1 I)] and from cyclopropane as hydrogen donors. E.s.r. studies also show that photoexcited (CF3),C0

+ CF3CH0

hv

(CF,)$OH

+ CF$O

(11)

173-dicarboxyacetone can abstract from hydrogen donors, a process which effectively competes with a-cleavage (Scheme 1).12 0

0 ti

I1 -0,CCH2C* 4- kH,CO,

-02CCH2CCH2C02-02CCH2qCH2C02Scheme 1

+

R

A full report of the factors governing the stereoselectivity of photoreduction of some substituted cyclohexanones has now appeared.13 Irradiation of 3,3,5trimethylcyclohexanone (lo), for example, in hydrogen-donating solvents leads

lo l1 la

M. A. Winnik, R. E. Trueman, G. Jackowski, D. S. Saunders, and S. G. Whittington, J. Amer. Chem. Soc., 1974,96, 4843. M. A. Winnik, C. K. Lee, S. Basu, and D. S. Saunders, J. Amer. Chem. SOC.,1974,96,6182. P. Suppan, J.C.S. Faraday I, 1975,71, 539. P. J. Krusic, K. S. Chen, P. Meakin, and J. K. Kochi, J. Phys. Chem., 1974, 78, 2036. S. Steenken, W. Jaenicke-Zauner, and D. Schulte-Frohlinde, Photochem. and Photobiol., 1975, 21, 21.

J. C. Micheau, N. Paillous, and A. Lattes, Tetrahedron, 1975, 31, 441.

394

Photochemistry

(1 1)

(10)

(12)

to a mixture of alcohols, (11) and (12). The ratio (11) : (11) + (12) varies from 0.27 to 0.67 with ketone : hydrogen-donor ratios, solvents, and light intensities. The origins of such selectivity are still unclear, and may be due to either preferential solvation of the planar hydroxycyclohexyl radical intermediate or preferential approach to a pyramidal radical centre. Photoexcited acetone has been used previously to generate aromatic compounds from dihydroaromatic compounds by hydrogen abstraction. Further studies l4 have revealed the limitations of this procedure, and shown that other products are often formed from ketyl and hydroaromatic radical coupling. Only the conversion of indoline into indole occurs in reasonable yield (46%). Hydrogen abstraction by excited acetone also appears to be responsible for an unusual reaction on irradiation of friedelin (1 3) in ether-acefone.ls The known intramolecular reaction which occurs in the cyclohexanone ring gives a keten (Scheme 2), but this is followed by addition of a ketyl radical and subsequent reduction to produce an hydroxycarbonyl compound (14).

$}

0

(13) Scheme 2

Irradiation of acetophenone and acetaldehyde in THF or diethyl ether gives diastereoisomeric alcohols (15 ) or (1 6), formed by hydrogen abstraction of the carbony1 compound from the ether, followed by combination of the radicals Me Me I I R-C -CH- OCH,Me 0 OT -AH R OH I (15)

R

=

PhorH

(16) R = Ph or H

produced.le Cyclohexyl phenyl ketone and trans-4-t-butylcyclohexylphenyl ketone give the corresponding cyclohexylphenylcarbinols amongst the products on irradiation in benzene A transition-state theoretical model has been proposed for the photoreduction of aromatic ketones by propan-2-01.l~ l4 l6 l6 l7

T. Matsuura and Y . Jto, Bull. Chem. SOC.Japan, 1974,47, 1724. H. Shirasaki, T. Tsuyuki, and T. Takahashi, Tetrahedron Letters, 1975, 2271. M. Tokuda, M. Hasegawa, A. Suzuki, and M. Itoh, Bull. Chem. SOC.Japan, 1974,41,2619. F. D. Lewis, R. W. Johnson, and D. E. Johnson, J. Amer. Chem. SOC.,1974,96, 6090. J.-P. Blanchi, J. Chim. phys., 1973,70,905.

395 Further chemically induced dynamic nuclear polarization (CIDNP) studies have appeared concerning the photoreduction of acetone by propan-2-01, includThe enol of acetone has ing the use of a variety of deuteriated been detected by such methods,,O and Bargon and Seifert 21 have now observed by CIDNP spectroscopy the enols from acetaldehyde (giving vinyl alcohol) and several aliphatic aldehydes. Vinyl alcohol, for example, is generated in a spinpolarized state by photoreduction of [2H6]acetone with ethanol in D20 (Scheme 3).

Photo-oxidation and -reduction

(CD,),CO

+ CH,CH20H

hv

[(CD3),kOH HOkHCH,]

(CDJ2CHOH Scheme 3

+ HO-CH=CH,

E.s.r. spectroscopy has provided the rate constants and Arrhenius parameters for the reduction of triplet (nr*) pyruvic acid by various alcohols.22 The rate constants for abstraction from selected alcohols at 298 K are shown in Table 1. Table 1 Rate constants for reaction of triplet (nr*) pyruvic acid and biacetyl acid and biacetyl with various hydrogen donors at 298 K Donor BU~OH MeOH EtOH Pr'OH PhCH20H PhMeCHOH

Rate constantll mol-l s-l 3(nr*) Biacetyl

3(nr*) Pyruvic acid 1.7 k 0.2 x 105 4.5 k 0.5 x 106 3.5 & 0.4 x lo6 4.2 k 0.5 x TO6 1.4 k 0.15 x lo7 1.7 0.2 x 107

-

3.5 _+ 1.1 _+ 2.8 f 6.5 -t

0.6 x 0.2 x 0.4 x 1.5 x

103 104 104 104

Rate constants for reaction of triplet (n,r*) biacetyl with the same hydrogen donors are also included, being generally two or three orders of magnitude less. CIDNP studies on the photoreduction of pyruvic acid by propan-2-01 show the occurrence of abstraction [reaction (12)], followed by the transfer of a hydrogen atom from the polarized ketyl radical to ground-state pyruvic acid [reaction (1 3)],23 exactly as for the corresponding photoreduction of benzophenone.

+ Me,CHOH MeCOC0,H + Me,kOH

MeCOC0,H

hv

[Mek(OH)CO,H Me,kOH] Mek(OH)CO,H

+ Me,CO

(12) (13)

The photolysis of 1,dbenzoquinone in propan-2-01 has been studied by both CIDNP and CIDEP (electron polarization) methods, with a view to correlating *O

22 e3

K.-G. Seifert, Chem. Bet., 1974,107, 3749. G. P. Laroff and H. Fischer, Helv. Chim. Acra, 1973, 56, 2011. J. Bargon and K.-G. Seifert, Chem. Ber., 1975,108,2073. P. B. Ayscough and R. C. Sealy, J.C.S.Perkin IZ, 1974, 1402. K.-G. Seifert, Chem. Ber., 1974, 107, 2412.

396

Photochemistry

the two methods on the same chemical An e.s.r. study of the radicals formed on photoreduction of benzoquinone (BQ) in alcohols or acetone suggests the mechanism for reduction by an alcohol is as shown in reactions (14)-(18).25 Electron transfer from solvent to photoexcited quinone to form a complex [reaction (15)] is an important step. Below about - 115 "C, the complex reverts to ground-state reactants [reaction (16)], but above this temperature it dissociates to quinone radical anion and alcohol radical cation [reaction (17)]. Additionally, about 10% of reaction occurs by the separate pathway of hydrogen atom abstraction [reaction (18)]. BQ 3BQ*

+ EtOH

-

[BQYEtOHt] -----+ [BQ-EtOHt] 3BQ*

+ EtOH

hv

lBQ*

3BQ*

(14)

[BQYEtOHt]

(15)

+ EtOH BQ- + EtOHt BQH- + CH3kHOH

(16)

BQ

(17) (18)

The products from photoreaction of 1,4-naphthoquinone and its methyl and halogeno-derivatives, with xanthene as a hydrogen donor, have been reported.2s A study has been made of the photoreduction of chloranil in acetone in the presence of aromatic hydrocarbons as electron and of the photoreduction in ethanol of pentacene-5,7,12,14-diquinoneand some derivatives.28 Photoreduction of 3,3',5,5'-tetramethyldiphenoquinone (17) occurs in benzene, leading

to the corresponding dihydroxybiphenyl and biphenyl ;2e this supplements results reported by Bruce 30 last year. Irradiation of sodium anthraquinone sulphonates in micelles leads to photoreduction to the corresponding radical anions, whose lifetimes are much lengthened compared with those obtained in the absence of s ~ r f a c t a n t s .It~ ~is reported that photoreduction of anthraquinone sulphonates in basic wateralcohol solutions can lead on to desulphonation of the 9,lO-dihydroxyanthracenes which are Photoreduction of sodium 1,2-naphthoquinone-4In this reaction, sulphonate in water gives the 1,2-dihydroxy-c0mpound.~~ 24

H. M. Vyas, S. K. Wong, B. B. Adeleke, and J. K. S. Wan, J. Amer. Chem. SOC.,1975, 97, 1385.

zK 2e

27 28

2g

s1 s2

J. R. Harbour and G . Tollin, Photochem. and Photobiol., 1974, 20, 387. K. Maruyama and S. Arakawa, Bull. Chem. SOC.Japan, 1974, 47, 1960. A. 1. Kryukov and V. A. Krasnova, Teor. i eksp. Khim., 1974,10, 820. G . A. Val'kova, D. N. Shigorin, V. M. Gebel, N. S. Dokunikhin, N. N. Artamonova, and L. N. Gaeva, Zhur.fiz. Khim., 1974,48, 1259. S. Tsuruya and T. Yonezawa, J. Org. Chem., 1974,39,2438. J. M. Bruce and A. Chaudhry, J.C.S. Perkin I , 1974, 295. K. Kano and T. Matsuo, Bull. Chem. SOC.Japan, 1974,47, 2836. A. V. El'tsov, 0. P. Studzinskii, N. I. Rtishchev, A. V. Devekki, and M. V. Sendyurev, Zhur. org. Khim., 1974, 10, 2567. K. Kano and T. Matsuo, Tetrahedron Letters, 1974, 4323.

Photo-oxidation and -reduction

397

hydroxide ion is thought to give electron transfer to the quinone, producing an hydroxyl radical and the semiquinone radical anion. Protonation and disproyortionation of the radical anion then complete the reaction sequence. A subsequent reaction with hydroxyl radicals could lead to hydroxylated products ; such may be the case in the formation of 1- and 2-hydroxy-9,10-anthraquinone-2sulphonates (18) on irradiation of neutral or alkaline solutions of 9,lO-anthraq~inone-2-sulphonate.~~ The quantum yield of monohydroxylation varies with concentration of (18), reaching 0.20 in alkaline solutions, or a maximum constant value of 0.08 in neutral solutions. Dihydroxylated products appear to arise from reaction of oxygen with an intermediate. However, the overall reaction mechanisms of hydroxylation remain far from settled. The photoreduction of the naphthoquinone methide (19) has been investigated,35in connection with Barton's use of photocyclization of derivatives of (19) in tetracycline synthesis.3e Hydrogen abstraction by the triplet of (19) from

propan-2-01 gives the semiquinone radical (20), which dimerizes to (21). The lowest ( m r * ) triplet state is the intermediate responsible for the photoreduction of (19). Hydrogen abstraction by (m*)excited states is likely to be less rapid than for (n.rr*) states, and in fact the rate of abstraction from propan-2-01 by triplet (19) is about five orders of magnitude less than that of triplet (n.rr*) benzophenone. Nevertheless, the long triplet lifetime of the former compound allows photoreduction to be reasonably efficient (a = 0.05 at 25 "C). Acyl hydrazides generally undergo fission of the N-N bond on irradiation in a solvent such as acetonitrile, but on irradiation in a good hydrogen donor such as propan-2-01 it is suggested that the excited carbonyl group may abstract hydrogen from the solvent, and the radical so produced may then fragment, as shown in Scheme 4.37

+ PhCH2CONH2

84

36 3a

s7

PhCH,C(OH)=NH Scheme 4

+ Ph,6

RH

Ph,NH

A. D. Broadbent, H. B. Matheson, and R. P. Newton, Canad. J. Chem., 1975,53, 826. J. Wirz, Helv. Chim. Acta, 1974, 57, 1283. D. H. R. Barton, D. L. J. Clive, P. D. Magnus, and G . Smith, J. Chem. Soc. (0,1971, 2193. R. S. Davidson and A. Lewis, Tetrahedron Letters, 1973, 4679. 14

398 Photochemistry It is well known that amines quench the triplet excited state of ketones, with or without resulting photoreduction of the ketone. Quenching may occur by complexation, electron transfer, or hydrogen transfer. For example, Scheme 5

Ar,&

+

AqeOH

R12&H2R2

+ Rl2NtHR2

Scheme 5

summarizes some of the proposed pathways for deactivation of a triplet aromatic ketone by a tertiary amine. Photolysis of 4,4’-disubstituted benzophenones in the presence of ‘dabco’ (1,4-diazabicyclo[2,2,2]octane) has been investigated using CIDNP technique^.^^ The nuclear spin polarizations observed for the ketones provide evidence for electron transfer from amine to triplet ketones as the quenching step in the photoreaction. However, the production of ketone radical anions and amine radical cations in this manner does not exclude the possibility of an excited complex 3Q as an intermediate in the electron-transfer reaction. U.V. irradiation of benzene solutions of benzophenone and diphenylamine leads to detection by e.s.r. spectroscopy of the diphenylamino-radical (Ph,N*), possibly formed by hydrogen atom abstraction of ketone from amine, with a measured rate constant of 2.3 x loQ1 mol-1 s-’.~* The expected benzophenone ketyl radical (Ph&OH) could not be observed, perhaps owing to a rapid subsequent reaction, although Davidson et al.41have detected this species by flash photolysis of similar solutions. Various rn- and p-substituted anilines and mono-N-alkylanilines have been used to quench the fluorenone photoreduction of NN-dimethylaniline and triethylamine in benzene.42Rates of complexation so derived between triplet ketone and anilines are correlated in a linear free-energy relationship. A small isotope effect on the quenching by aniline ( k ~ / = k ~1.3 for PhNH, and PhND,) shows partial hydrogen transfer in the transition state for quenching, so that both charge- and hydrogen-transfer are implicated. Cohen and co-workers 43 have reported the photoreduction of aromatic ketones by hydrazines and hydrazinium ions, and some of their results are shown in Table 2. Thus, hydrazine and methylhydrazine at pH 12 are efficient quenchers of the excited 4-benzoylbenzoate anion in water, but they are not good photoreducing agents. However, at pH 7, when mainly monoprotonated, they become effective reducing agents. Tetramethylhydrazine on protonation shows little increase in photoreduction quantum yield, hardly s* 3B 40 41

4a

H. D. Roth and A. A. Lamola, J. Amer. Chem. SOC.,1974, 96, 6270. S. G. Cohen, A. Parola, and G. H. Parsons, Chem. Rev., 1973, 73, 141. J. H. Marshall, J. Phys. Chem., 1974, 78, 2225. R. S. Davidson, P. F. Lambeth, and M. Santhanam, J.C.S. Perkin 11, 1972, 2351. G. H. Parsons, L. T. Mendelson, and S. G. Cohen, J. Amer. Chem. SOC.,1974,96, 6643. S. Ojanpera, A. Parola, and S. G. Cohen, J. Amer. Chem. SOC.,1974,96,7379.

399

Photo-oxidation and -reduction

Table 2 Eflect of pH on quantum yield in the photoreduction of 4benzoylbenzoate anion (0.003 mol I-l) by hydrazines (0.04 mol I-l) in water Compound HZNNH, H,NNH, H,NNH, MeNHNH, MeNHNH, MeNHNH, M%NNMe, Me2NNMe,

PH 12 9 7 12 9 7 12 7

\

TNH+PW

a)

0

0.01 1 0.16 0.29 0.011 0.12 0.21 0.011 0.026

9 91 0 7 88 0 17

Monoprotonated hydrazine.

more than expected from the change in reduction product from hydro1 at pH 12 to pinacol at pH 7.' These results are understandable in terms of the mechanism outlined in Scheme 5. The free hydrazines thus appear to form charge-transfer complexes by electron transfer; the complexes decay to reactants with little overall reaction, apart from quenching. In the monoprotonated hydrazines, interaction occurs at the non-protonated n-electron pair. The complex is then well placed to give proton transfer from the protonated nitrogen, leading to reduction as shown in Scheme 6. It may be that the conformation of mono-

Scheme 6

protonated tetramethylhydrazine is unfavourable for this subsequent proton transfer, and so reduction remains inefficient even for the protonated form. Attempts have been made to compare the reactivity of triplet ketones towards aliphatic amines in the gas phase with their reactivity in Rate constants for reaction with amines are less in the gas phase than in solution, and depend on the presence of N-H or a-C-H bonds in the amine. It is concluded that quenching of triplet ketone in the gas phase involves a radical-like hydrogen abstraction. The quenching of pentan-2-one singlets by aliphatic amines is even more rapid than triplet quenching (e.g. ksblet = 2.2 x lo01 mol-1 s-l for triethylamine in h e ~ a n ecf. , ~ktriplet ~ = 3.2 x lo* 1 mol-1 s - ~ ) . ~Surprisingly, ~ the singlet quenching rate appears constant for several amines of differing ionization potential.4s A quantum yield of ketone disappearance of 0.2 in the presence of triethylamine suggests that a significant proportion of quenching leads on to photoreduction. Benzophenone photosensitizes the tautomerization of a cyclic amidine

I

I

(-N=C-NH,) to the imino-isomer (-NH-C=NH), abstraction reaction and its reversal.4s

perhaps by a hydrogen-

E. B. Abuin, M. V. Encina, E. A. Lissi, and J. C. Scaiano, J.C.S. Faraday I, 1975,71, 1221.

4= 4e

M. V. Encina, H. Soto, and E. A. Lissi, J. Photochem., 1975, 3,467. K.-H. Pfoertner, Helv. Chim. Acta, 1975, 58, 861.

Photochemistry

400

2 Reduction of Nitrogen-containing Compounds Further reports have described the photoreduction of aromatic nitro-compounds in hydrochloric acid solutions. Wubbels, who had examined previously the photoreduction of nitrobenzene in aqueous propan-2-01 solutions containing HCl," has gone on to investigate in detail the photoreduction of nitrobenzene and monosubstituted nitrobenzenes in the absence of propan-2-01.~~Again, photoreduction and chlorination appear to be quite general reactions ; e.g. irradiation of nitrobenzene in 12M aqueous HCl gave the product distribution shown in Scheme 7. In general, electron-withdrawing substituents on the aro-

Cl

c1

62 %

16%

2.7 yo

Scheme 7

matic ring have little effect on the quantum efficiency of reaction, but electrondonating substituents cause marked decreases in efficiency. The limited solubility of many nitro-aromatics in aqueous HCl made acetic acid useful as an inert co-solvent. A more efficient photoreduction does occur in the presence of alcohols, for which a reaction mechanism has previously been This involves electron-transfer from chloride ion to excited nitrobenzene, followed by protonation of the radical pair and hydrogen abstraction, leading eventually to nitrosobenzene [the essential steps are outlined in reactions (1 9)-(22)]. Dark reactions of the nitrosobenzene in acidic propan-2-01 then give the observed products. PhN02* + C1[PhfiO,kl] [PhfiO,Hkl]

+ H+

+ Me,CHOH 2Phfi02H

-

[Phfio,kl]

(19)

[PhfiO,Hkl]

(20)

+ HCl + Me,kOH + PhNO + H 2 0

Phfi0,H

3 PhNO,

(21) (22)

In the absence of alcohol, the pathway in reaction (21) is not available. To explain reduction, Wubbels therefore proposes that the protonated ion pair [PhfiO,Hd] couples at the para-position of the aromatic ring forming (22), followed by elimination to yield 4-chloronitrosobenzene (23),48 as shown in [PhNO,H

47

'*

dl1

-++

G. G. Wubbels, J. W. Jordan, and N. S . Mills, J . Amer. Chem. SOC.,1973, 95, 1281. G. G. Wubbels and R. L. Letsinger, J. Amer. Chem. SOC.,1974, 96,6698.

401

Photo-oxidation and -reduction

Scheme 8. In fact, when placed in the reaction medium in the dark, (23) gives a product distribution similar to that observed in the photochemical reaction. In contrast with reduction in alcohols, the quantum yield in aqueous HCI drops rapidly with decreasing HC1 concentration (
Me,CHOH-H,O HCI

H (24)

' dl (25)

photoreduction increases with HC1 concentration, reaching an upper limit of 5.4 x when [HCl] 2 1 moll-'. These results have been interpreted in terms of a previously proposed mechanism 47 of electron transfer from chloride ion to the triplet state of the nitro-compound, although Cu and Testa49 prefer an hydroxylamino- rather than a nitroso-intermediate. A full account of the photoreduction of the sterically hindered 2,4,6-tri-tbutylnitrobenzene (26) in diethylamine and triethylamine shows that the main photoproducts result simply from reduction of the nitro-group to the corresponding hydroxylamino- or amino-group.60 In contrast, irradiation of (26) in a variety of other solvents leads to intramolecular hydrogen abstraction by the excited nitro-group from the neighbouring t-butyl group. Photoreduction to give 4-t-butyl-2-nitro-6-nitrosoaniline is reported to be the main process involved in the U.V. irradiation of the herbicide N-~-butyl-4-t-butyl-2,6-dinitroaniline.~~ An isotope effect ( k ~ / zk 2.6) ~ has been found for the quantum yield of photoreduction of rn- and p-dinitrobenzene in aqueous alcoholic Intramolecular hydrogen abstraction by excited nitrobenzene derivatives may lead to the introduction of an oxidized functional group in a remote part of the molecule, as previously reported by Scholl and Van De Mark.63 Japanese workers have now extended this reaction to the preparation of some oxidized derivatives of the triterpene d a m m a r a n e d i ~ l . ~ ~ Reduction of nitrogen-containing heterocyclic compounds continues to receive attention. Hoshino and Koizumi 6s have postulated two mechanisms, one 40 60 61 6a

63 64

66

A. Cu and A. C. Testa, J. Phys. Chem., 1975,79, 644. D . Dopp and K.-H. Sailer, Chem. Ber., 1975, 108, 301. J. R. Plimmer and U. I. Klingebiel, J. Agric. Food Chem., 1974, 22, 689. N. A. Kuznetsova, A. V. El'tsov, G. V. Fomin, and A. N. Frolov, Zhur. fiz. Khim., 1975, 49, 115. P. C. Scholl and M. R. Van De Mark, J. Org. Chem., 1973,38,2376. R. Kasai, K. Shinzo, 0. Tanaka, and K. Kawai, Chem. and Pharm. Bull. (Japan), 1974, 22 1213. M. Hoshino and M. Koizumi, Bull. Chem. SOC.Japan, 1973, 46, 745.

PhotochCmistry

402

molecular and the other radical, in the photoreduction of acridine (27) in alcohols. French workers 67 have now studied by CIDNP spectroscopy the radical contribution in the photoreaction of (27) and 9-methylacridine with alcohols and ethers. A singlet radical pair (28), formed by hydrogen abstraction from the 669

hydrogen donor by excited (27), is implicated. Relatedly, pyrazine and quinoxaline abstract hydrogen on irradiation in cyclohexane The observed reaction products derive from combinations of cyclohexyl radicals with pyrazinyl or quinoxalinyl radicals, or from reactions of the radicals with added oxygen. state is the hydrogen-abstracting species.6Q In the case of pyrazine, the triplet (m*) Likewise, the U.V. irradiation of pyrimidine (Py) or 4- or 5-methylpyrimidine in methanol at 113 K gives the corresponding pyrimidinyl radical (WHO),derived via the (nn*)triplet state of the pyrimidine.80 Irradiation of the diazines phthalazine and quinoxaline in acidified alcohols is thought to result in electron transfer from solvent to the excited state of the diazinium cation.61 In strongly acidic methanol, reduction of phenazine may involve electron transfer from solvent to the excited singlet phenazinium dication.62 N-Methylphenazine undergoes photoreduction, often accompanied by dealkylation to phenazine, on irradiation in alcohols.8s Photoreduction of the herbicide paraquat dichloride in aqueous propan-2-01 is more efficient in the presence of a sensitizer such as benzophenone than on direct i r r a d i a t i ~ n . ~Hyde ~ and Ledwith 64 propose that the paraquat cation radical is formed by electron transfer from ketyl radicals, in turn produced during the conventional photoreduction of the sensitizer ketone, The suggested mechanism is given in reactions (23)-(25), where PQ2+is the paraquat dication. The reduction process therefore involves chemical sensitization, rather than electronic energy transfer.

+ Me,CHOH Ph,kOH + PQ2+ -

SPh,CO

Me,kOH

_I_+

+ PQ2+

-

+ Me,kOH Ph,CO + PQ: + H+ Me,CO + PQt + H+ Ph,kOH

(23) (24) (25)

G. Vermeersch, N.Febvay-Garot, S. Caplain, and A. Lablache-Combier,Tetrahedron Letters, 67

6B

6o

63

64

1974, 3127. G. Vermeersch, N. Febvay-Garot, S. Caplain, and A. Lablache-Combier, Tetrahedron, 1975, 31, 867. A. Lablache-Combier and B. Planckaert, Bull. SOC.Chim. France, 1974, 225. D. V. Bent, E. Hayon, and P. N. Moorthy, Chem. Phys. Letters, 1974,27, 544. A. Castellano, J. P. Catteau, and A. Lablache-Combier,Photochem. and Photobiol., 1974,20, 27. S . Wake, Y.Takayama, Y. Otsuji, and E. Imoto, Bull. Chem. SOC.Jupan, 1974, 47, 1257. S. Wake, Y. Otsuji, and E. Imoto, Bull. Chem. SOC.Japan, 1974, 47, 1251. W. Rubaszewska and Z. R. Grabowski, J.C.S. Perkin ZI, 1975, 417. P. Hyde and A. Ledwith, J.C.S. Perkin II, 1974, 1768.

Photo-oxidation and -reduction

403

The photoreduction of some Nl-substituted nicotinamides has been studied, as a model of pyridine nucleotide reductions.6sBonneau and his group 67 have continued their investigations on the pH dependence of the photoreduction of thiazine dyes in aqueous solutions, using edta as an electron donor. Reductive ring cleavage of 3,5-dimethylisoxazole (29) to (30) occurs on irradiation in 66p

(29)

(30)

acetonitrile in the presence of triethylamine.6s Reduction product (30) is not observed on irradiation in propan-2-01, so that a straightforward hydrogenabstraction mechanism of (29) following N-0 bond fission is unlikely. The photoreduction of imines is not as well understood as that of carbonyl compounds. Padwa et aLSe have suggested that the low reactivity of imines towards hydrogen abstraction may be a result of twisting about the C=N bond, which leads to rapid radiationless decay of excited imine. Such a process cannot be the only factor involved, because the cyclic imine (31),'O where syn-anti isomerization is prohibited, only shows reactivity comparable with that of the acyclic imine N-benzylidenecyclohexylamine.6gIt is also reported that the cyclic imines (33) and (34) undergo photoreduction in propan-2-01 to

(36)

(37) a; R = Me b; R = PhCH, C:

66

m

68

a 70

=

Ph

H. Hanschmann, Stud. Biophys., 1974, 45, 183. R. Bonneau, P. Fornier de Violet, and J. Joussot-Dubien, Photochem. and Photobiof., 1974, 19, 129.

67

R

R. Bonneau and J. Pereyre, Photochem. andPhotobiol., 1975,21, 173. T. Sat0 and K. Saito, J.C.S. Chem. Comm., 1974, 781. A. Padwa, W. Bergmark, and D. Pashayan, J. Amer. Chem. SOC.,1969,91,2653. J. M. Homback, G. S. Proehl, and I. J. Stamer, J. Org. Chem., 1975,40, 1077.

Photochemistry

404

give the corresponding saturated amines; this process is sensitized by traces of acetone present as an impurity in propan-2-01 or produced as reaction progresses. Photoreduction of 4,6-dimethylpyrimidin-2-01(35) in propan-2-01 produces a C-4 linked d i h y d r ~ d i m e r ,analogously ~~ to the conversion of (31) into (32). Likewise, irradiation of the iminolactone (36) in propan-2-01 gives a mixture of the meso- and &isomers of the reduced C-C bonded dimer.72 The lactone carbonyl group may well act as an internal sensitizer for hydrogen abstraction in this reaction. In contrast, the cyclic aromatic imines (37) are unreactive on irradiation in propan-2-01.~~ Photochemical deoxygenation of N-oxides leads to reduced products, and has been noted under a variety of conditions. Photolysis of azanaphthalene N-oxides in benzene containing boron trifluoride e t h e ~ a t eand , ~ ~of isoalloxazine N-oxides in the presence of cyclohe~a-1,4-diene,~~ leads to deoxygenation. It is also a major reaction in the photochemistry of 6-methyl- and 6,9-dimethylpurine-lStenberg and Schiller 77 have suggested that oxygen in such reactions is lost as the oxygen radical anion (0;) or as its conjugate acid, the hydroxyl radical. 3 Miscellaneous Reductions The interesting results reported last year (Vol. 6, p. 529) on the photo-assisted hydrogenation of dienes by Cr(CO)6 have been extended by mechanistic studies;78p7g e.g. norbornadiene (38) gives nortricyclene (39) and norbornene (40)

(39)

in the ratio 2.8 : la7*There is evidence that the first catalytic species formed is a stable complex of Cr(C0)4 with (38). Irradiation of this complex leads to a species which probably has one Cr-diene bond broken, and which subsequently reacts with hydrogen. Collapse to products bonded to Cr(CO), then occurs. Photo-induced hydrogenation of hexa-2,4-diene has also been observed : the trans,trans-isomer produces 100% cis-hex-3-ene, and is reduced much faster than the cis,trans-isomer which produces 89% cis-hex-3-ene and 11% cis-hex-2ene.79 Ability to adopt a syn-cis planar conformation of the diene is apparently an essential pre-requisite for reaction. Cyclohexa-l,3-diene gives cyclohexene by photochemical hydrogenation using the iridium catalyst, IrCl(CO)(PPh3)2.80 72

73 74 76

76

77 78 7D

K.-H. Pfoertner, Helu. Chim. Acta, 1975,58, 865. T. H. Koch, J. A. Olesen, and J. DeNiro, J . Org. Chem., 1975,40, 14. H.Ohta and K. Tokumaru, Tetrahedron Letters, 1974,2965. N. Hata, I. Ono, and M. Kawasaki, Chem. Letters, 1975,25. M.Gladys and W.-R. Knappe, 2.Naturforsch., 1974,29b, 549. F. L.Lam and J. C. Parham, J. Amer. Chem. SOC.,1975,97,2839. V. I. Stenberg and J. E. Schiller, J. Amer. Chem. SOC.,1975,97,424. G. Platbrood and L. Wilputte-Steinert, J. Organometallic Chem., 1974, 70, 393. G. Platbrood and L. Wilputte-Steinert, J. Organometallic Chem., 1974,70, 407. W. Strohmeier and L. Weigelt, J. Organometallic Chem., 1974, 82, 417.

Photo-oxidation and -reduction

405

The photoreactions of simple chloro- and bromo-naphthalenes in cyclohexane or methanol solution involve mainly photoreduction to naphthalenes (@ = 0.005-0.012) and production of binaphthyls.81 Reduction appears to progress via the triplet state of the halogenonaphthalene, which makes homolytic fission of the aryl-halogen bond an unlikely mechanism on energetic grounds. Instead, the authors advance an electron-transfer mechanism, exemplified for chloronaphthalene (NpC1) in reactions (26)-(28), in which a chloronaphthalene molecule (also represented as ArH) acts as an electron donor towards another molecule of excited chloronaphthalene [reaction (26)]. The electron-transfer complex involved may be related to the r-chlorobenzene recently invoked to explain the photoreduction of chlorobenzene in cyclohexane.82 Interestingly, experiments using conjugated dienes or biacetyl as potential triplet quenchers of the halogenonaphthalenes appear to enhance both product formation and halogenonaphthalene disappearance, though reaction can be quenched by oxygen.81p83 It may be that the quenchers are also acting as electron donors [reaction (29)], and thus facilitate reduction.

+ ArH Np* + RH

NpCl*

+ ArH NpCl* + Q

Np.

-

____+

+ Cl- + ArHt NpH + Re Np.

Np-Ar Np* + C1-

(26)

(27) (28)

+ Qt

(29)

U.V.photolysis of 5-bromouracil in the presence of hydrogen donors such as which is independent alcohols leads to uracil, with a quantum yield (1.8 x of donor and its concentration over a wide range.84 Alkyl halides undergo photoreduction on irradiation in methanol or diethyl ether (in competition with nucleophilic substitution), but the mechanism of reduction is not simple homolytic fission of the carbon-halogen bond, followed by hydrogen abstraction.86 Thus, irradiation of (41a) or (41b) in MeOD gives

(41) a; X = Br

b;X=I

norbornane with substantial incorporation of deuterium (1 8 or 30%, respectively) at the bridgehead position. It is therefore proposed that the radical mechanism competes with heterolytic processes involving nucleophilic attack by solvent on the (nu*) excited state of (41) to generate the bridgehead carbanion, *a

L. 0. RUZO,N. J. Bunce, and S. Safe, Canad. J. Chem., 1975,53, 688. M.-A. Fox, W. C. Nichols, and D. M. Lemal, J. Amer. Chem. SOC.,1973, 95, 8164. L. 0. Ruzo and N. J. Bunce, Tetrahedron Letters, 1975, 51 1. J. M. Campbell, D. Schulte-Frohlinde, and C. von Sonntag, Photochem. and Photobiol., 1974, 20, 465. G. S. Poindexter and P. J. Kropp, J . Amer. Chem. SOC.,1974, 96, 7142.

406

Photochemistry

which becomes pro t onated. The insecticide M irex (dodecachloropent acycl o[5,3,0,02~e,03~a,04~s]decane) undergoes dechlorination on irradiation in aliphatic arninesss Reaction occurs by charge-transfer absorption in a complex of amine with halogenocarbon, and gives products different from those which arise by direct irradiation in hydrocarbon An important high-yield method for the conversion of alcohols into alkanes involves 254 nm photolysis of the ester of the alcohol in wet hexamethylphosphoric triamide (H20 : HMPA = 5 : 9 9 , when reaction (30) O C C ~ S . The ~ ~ major product is the alkane, in yields of around 70% from acetates. Reaction (30) R1C02Ra

hg

RlOH

+ R2H

seems applicable to a variety of esters (formates, acetates, and benzoates), and to acetates derived from primary, secondary, and tertiary alcohols. The mechanism of reaction remains unexplored, although water obviously plays a role, since little decomposition of the esters occurs in dry HMPA.aQ Deoxygenation of 1,4-epoxy-1,4-dihydronaphthalene (42) to naphthalene occurs in low yield on direct irradiation at 254 nm in ethanol, and is enhanced

14-fold on irradiation in trieth~lamine.~~ Concomitantly formed are the known benzoxepin (43) and the reduced product (44). de MayoB1has extended his studies on thione photochemistry to the photoreduction of adamantanethione (45). Excitation of (45) in the long wavelength (nn*) band at 470-500 nm in the presence of the thiol (46) gives the disulphide (47)

(45)

as essentially the only product. In contrast to carbonyl photochemistry, where abstraction from C-H rather than O-H bonds occurs (see Section 1 of this Chapter), thiocarbonyl abstraction from weak S-H bonds will predominate [reaction (3 l), where Ad = the adamantyl residue]. Subsequently, either radical E. G. Alley, B. R. Layton, and J. P. Minyard, J. Agric. Food Chem., 1974,22, 727. E. G. Alley, B. R. Layton, and J. P. Minyard, J. Agric. Food Chem., 1974,22,442. H. Deshayes, J.-P. Pete, C. Portella, and D. Scholler, J.C.S. Chem. Comm., 1975, 439. R. Beugelmans, M. T. Le Goff,and H. Compaignon de Marchville, Compt. rend., 1969,269, C, 1309. S. B. Polovsky and R. W. Franck, J. Org. Chem., 1974,39, 3010. J. R. Bolton, K. S. Chen, A. H. Lawrence, and P. de Mayo, J. Amer. Chem. SOC.,1975, 97, 1832.

Photo-oxidation and -reduction

407

combination [reaction (32)] or a chain process [reactions (33)-(34)] could lead to the disulphide. There are two pieces of evidence which clearly argue against any

+ AdCHSH AdCHi + AdCHi AdCHi + AdC=S AdCHSSCAd + AdCHSH AdC=S*

-

____+

AdCSH

+ AdCHi

(31)

AdCHSSCHAd

(32)

AdCHSSkAd

(33)

AdCHSSCHAd

+ AdCHi

(34)

major involvement of reaction (32) and for the existence of a chain process leading to photoreduction. Firstly, quantum yields of photoreduction of (45) in benzene solutions of (46) are 1 . 8 4 . 0 . Secondly, [2-2H]-2-adamantylthiol gives (47) with >98% incorporation of a single deuterium atom per molecule. Using this deuteriated thiol, additional e.s.r. spin trapping experiments with nitroso-tbutane implicate the radical AdCDSSCAd, as might be expected from reaction (33). Photoreduction of 4-thiouracil(48) to the compound (49) has been reported on U.V. irradiation in the presence of sodium borohydride, whereas 2-thiouracil (50) is reduced under these conditions to the ring-opened compound (51).92

Various reports of the photoreduction of organic dyes have appeared. The photoreduction of methylene blue in the presence of several electron thionine in the presence of allylthi~urea,~~ f l ~ o r e s c e i nRhodamine ,~~ B, and other xanthene dyes 96 have all been investigated by spectrophotometric or e.s.r. techniques. 4 Singlet Oxygen As usual, this Section serves to review only those papers concerning singlet molecular oxygen (lo2, la,) which have general or organic significance. The possible participation of loain the mechanisms of photochemical air pollution has been reviewed by Pitts and F i n l a y s ~ n ,and ~ ~ the photochemical reactions of lo, have been reviewed (in Japanese).Ds Nilsson and Kearns gg have investigated the part played by singlet oxygen in some chemiluminescence and Oa

n4

E. Sato and Y. Kanaska, Chem. and Pharm. Bull. (Japan), 1974, 22, 799. M. K. Pal and K. K. Mazumdar, Histochemistry, 1974,40,267. U. Steiner, M. Hafner, S. Schreiner, and H. E. A. Kramer, Photochem. and Photobiol., 1974, 19, 119.

O6

O7

U. Kriiger and R. Memming, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 670. U. Kriiger and R. Memming, Ber. Bunsengesellschaftphys. Chem., 1974, 78, 679. J. N . Pitts and B. J. Finlayson, Angew. Chem. Internat. Edn., 1975, 14, 1. T. Abe, M. Sukigara, and K. Honda, Seisan-Kenkyu, 1974,26,71. R. Nilsson and D. R. Kearns, J. Phys. Chem., 1974,78,1681.

408

Photochemistry

enzymic oxidation reactions. Whereas lo2is involved in the H,O,-NaOCIinduced fluorescence of fluorescein, there is no evidence for its involvement in the decomposition of superoxide radical ion (029by hydroxylic solvents or in the oxidation of linoleic acid by lipoxidase. New sources of singlet oxygen continue to be developed. Near i.r. radiation (A > 900 nm), in the presence of a cyanine dye as sensitizer, has been used to Thermal decomposition of the ozonide (52) produces lo2and the generate 102.100

(53)

phosphate (53).lo1 This may provide a more convenient reagent than the triphenyl phosphite ozonide previously reported by Murray and Kaplan,lo2because (52) decomposes sufficiently slowly to be used at room temperature, and may even be dissolved in aqueous solutions. In the photo-oxidation of rubrene and g,lO-diphenylanthracene,change of solvent affects the lifetime of lo2, rather than the rate constant for addition.lo3 However, Long and Kearns lo4have shown that the lifetime of lo2is little altered by change in temperature, varying by only ca. 50% over a 100 "C temperature range in chloroform. The reactivity of aromatics such as anthracene towards lo2 has been related to orbital and state correlation diagrams,lo59log and Arrhenius parameters for the gas-phase cycloaddition reactions of lo2to conjugated dienes and furans have been reported.lo7 For thiazine dyes such as methylene blue, the efficiency of lo2production depends on the pH of the solution, being greater in basic rather than acidic media.loS The variation in efficiency by a factor of five over the pH range 5-9 shows the importance of exact pH control for quantitative measurements using methylene blue. Controversy still surrounds the measurement of the rate constant for reaction between 1,3-diphenylisobenzofuran (54) and lo2. Matheson et aZ.loa had suggested that the measured rate constant for interaction primarily reflected physical quenching rather than reactive quenching, and thus was an order of magnitude too high. In a recent communication Merkel and Kearns argue for the original loo

lol loa lo3 lo4 loti lo6 lo' loB

R. A. Nathan and A. H. Adelman, J.C.S. Chem. Comm., 1974, 674. Org. Chem., 1975, 40, 1185. R. W. Murray and M. L. Kaplan, J. Amer. Chem. Soc., 1969, 91, 5358. B. Stevens and S. R. Perez, Mol. Photochem., 1974, 6, 1. C. A. Long and D. R. Kearns, J . Amer. Chem. SOC.,1975, 97, 2018. B. Stevens, S. R. Perez, and J. A. Ors, J . Amer. Chem. SOC.,1974, 96, 6846. B. Stevens, J. Photochem., 1975, 3, 393. R. D. Ashford and E. A. Ogryzlo, Cunud. J. Chem., 1974,52, 3544. R. Bonneau, R. Pottier, 0. Bagno, and J. Joussot-Dubien, Photochem. and Photobiol., 1975,

A. P. Schaap, K. Kees, and A. L. Thayer, J.

21, 159. lo9

110

I. B. C. Matheson, J. Lee, B. S. Yamanashi, and M. L. Wolbarsht, J. Amer. Chem. SOC.,1974, 96,3343. P. B. Merkel and D. R. Kearns, J. Amer. Chem. Soc., 1975,97,462.

409

Photo-oxidation and -reduction

value, producing some strong supporting evidence which would rule out physical decay as the major reaction. The self-sensitized photo-oxidation of (54) proceeds at a rate independent of (54) concentration at < 10-6mol 1-l.ll1 To explain this independence, Stevens et aZ.l12 have suggested the formation of a re-encounter complex between lo2 and ground-state molecules of (54) (probability, 0.61), generated as shown in reaction ( 3 9 , where M represents (54). 3M

+ 02(3C,-)

-

M

+ O,(lAJ

(3 5 )

Three separate accounts have measured the quenching of lo, by the natural anti-oxidant, a-tocopherol (vitamin E).l13-l15 All conclude that the major process for quenching is a physical mechanism, rather than a chemical mechanism, which occurs in only ca. 1% of the molecules quenched. Values for the quenching rate constant (in 1mo1-1 s-l) vary from 0.9 x lo8 in cyclohexane and 1.7 x lo8 in benzene,l13 to 2.5 x lo8 in pyridine114and 6.7 x lo8 in methan01.l~~ Full details have appeared of the quenching of lo2 by transition-metal chelates,lls and a comparison of their quenching properties towards lo2and triplet carbonyl compounds has been p~b1ished.l~~ The azomethine dyes, of general formula ( 5 3 , form a class of lo2quenchers which, unusually, do not X

Y

photosensitize formation of 102.118 The importance of charge-transfer interactions in the quenching of lo, by amines has been reiterated in a study of the Singlet quenching of lo2 by a series of substituted NN-dimethylaniline~.~~~ oxygen is also quenched by amino-acids and proteins, as shown by a study using directly laser-generated 1 0 2 . 1 2 0 Rates of quenching (/1mo1-1 s-l) of lo2by alanine (0.2 x lo7), methionine (3 x lo7), tryptophan (9 x lo7), and histidine (17 x lo7) have been reported. It seems that the quenching rate for proteins is approximately the sum of the quenching rates for their individual amino-acids, so the inference is that all the amino-acid residues of the protein are about equally accessible to the lo2.

5 Oxidation of Aliphatic Unsaturated Systems A matter of much dispute has been whether the photo-oxidation of olefins to allylic hydroperoxides involves an ene-reaction or a perepoxide intermediate (see 111

iia iia 114 116 116 117 118 118

J. Olmsted and T. Akashah, J. Amer. Chem. SOC.,1973,95, 6211. B. Stevens, J. A. Ors, and M. L. Pinsky, Chem. Phys. Letters, 1974, 27, 157. B. Stevens, R. D. Small, and S. R. Perez, Photochem. and Photobiol., 1974, 20, 515. S. R, Fahrenholtz and F. H. Doleiden, Photochem. and Photobiol., 1974,20, 505. C. S. Foote, T.-Y. Ching, and G. G. Geller, Photochem. and Photobiol., 1974, 20, 511. D. J. Carlsson, T. Suprunchuk, and D. M. Wiles, Canad. J. Chem., 1974, 52, 3728. P. Hrdlovic, J. Danecek, M. Karvas, and J. Durmis, Chem. Zvesti, 1974, 28, 792. W. F. Smith, W. G. Herkstroeter, and K. L. Eddy, J. Amer. Chem. Soc., 1975, 97, 2764. R. H. Young, D. Brewer, R. Kayser, R. Martin, D. Feriozi, and R. A. Keller, Canad.J. Chem., 1974, 52, 2889.

120

I. B. C. Matheson, R. D. Etheridge, N. R. Kratowich, and J. Lee, Photochem. and Photobiol., 1975, 21, 165.

Photochemistry

410

Vol. 6, p. 535). In the past year no more evidence has been produced which strongly supports a perepoxide as an intermediate in this reaction. Jefford and Boschung 121report interesting results on the mechanism of lo2attack on olefins from a study of the methylene blue-sensitized photo-oxidation of the norbornenes (56) and (57). The products are generally the expected allylic hydroperoxides,

R=H b;R=Me

(57) a; R = H b; R = Me

(56) a;

with the exo : endo ratios for attack being 66 from (56a), and 0.19 from (56b). The use of deuteriated derivatives of (57a) and (57b) allows calculation of the exo : endo attack ratios as 28 and 0.67 respectively. Together with relative rates of reactivity, these values allow the authors to calculate the relative rates for exo-attack on (56a) to (56b) as 250 : 1. This ratio is somewhat lower than those obtained for other bona fide one-step cyclic processes occurring at the norbornene system, but nevertheless suggests that the rate-determining step is of similar nature. The authors further conclude (from other evidence) that the transition state for reaction with lo2is largely dipolar, and that a discrete perepoxide is not formed as an intermediate. Jefford and Boschung122 also report that norbornene (58) is not inert to singlet oxygen, as previously supposed. Photo-oxygenation of (58) in acetonitrile,

(58)

(59)

(60)

using methylene blue as sensitizer, slowly leads to the formation of the dialdehyde (59) and the epoxide (60). The ration of (59) : (60) is solvent dependent, varying from 61 : 39 in acetonitrile to 35 :65 in acetone. The formation of dialdehyde (59) is considered to involve the formation and decomposition of a dioxetan (see below), but the steps leading to the epoxide (60) are not well underformation of an epoxide by lo2 stood. For adamant~lidene-adarnantane,~~~ attack on olefin has been taken as evidence for a perepoxide intermediate. Deoxygenation of the perepoxide would be especially favourable in the presence of pinacolone as a trapping agent, and leads to the epoxide and t-butyl acetate. However, oxidation of (58) in pinacolone as solvent does not lead to increased amounts of epoxide (60), nor to t-butyl acetate.122Thus, the results do not favour the existence of a perepoxide intermediate in olefin photo-oxidation. lZ1 lZz lZ3

C. W. Jefford and A. F. Boschung, Helv. Chim. Acta, 1974,57,2242. C. W. Jefford and A. F. Boschung, Helv. Chim. A d a , 1974, 57, 2257. A. P. Schaap and G. R. Faler, J. Amer. Chem. SOC.,1973,95,3381.

41 1 Methylene blue-sensitized oxidation of quadricyclane (61) in methanol leads to a complex mixture, and reduction of hydroperoxides to alcohols gives the major products shown in Scheme 9.124 The methoxynortricyclyl alcohols (62) and

Photo-oxidation and -reduction

(63) predominate, and (62) is also the main product from the much slower photo-sensitized oxidation of norbornadiene. Chung and Scott 126 have claimed that sensitized photo-oxidation of the cyclodecadiene(64) leads exclusively to the hydroperoxide (65). No products of a

transannular reaction were found. The highly regioselective attack at the more substituted double bond could be interpreted as a consequence of the preferred conformation of (64) preventing suitable geometry for abstraction of hydrogen from the allylic methylene groups in an ene-reaction. The importance of stereochemistry in determining the pathway of the reaction with lo2is also shown by the photosensitized oxidation of the steroidal olefin 3p-acetoxycholest-7-ene, where two consecutive attacks by lo2give various ene bis-hydroperoxides.12u Other photo-sensitized oxidations to be reported are those of the sex pheromone (ZYE)-tetradeca-9,12-dienyl-l-acetate,which gives the expected allylic hydroperoxides,12' and of several unsaturated-ring c aromatic diterpenoids.128Japanese workers 12@ have claimed that the Pyunsaturated ketone, 5-methylhex-4-en-2-one9 gives only a single photo-oxidation product, the y-hydroperoxy-ap-unsaturated ketone, but some doubt has been thrown on these results by Thomas and Dubini,130who have now shown that the closely related sesquiterpene davanone (66) on photo-oxidation gives two products (in the ratio ca. 6 : 4), to which they assign the structures (67) and (68) (Scheme 10). Electron-donor (nucleophilic) olefins react with lo2 to give dioxetans in competition with, or to the exclusion of, formation of allylic hydroperoxides. Foote and co-workers have reported that photo-oxidation of indenes apparently T. Kobayashi, M. Kodama, and S. Ito, Tetrahedron Letters, 1975, 655. S. K. Chung and A. I. Scott, J. Org. Chem., 1975,40, 1652. n6 G. 0. Schenck, W. Eisfeld, and 0. A. Neumiiller, Annalen, 1975, 701. la' G. Oto, Y.Masuoka, and K. Hiraga, Chem. Letters, 1974, 1275. 12* R. C. Cambie and R. C. Hayward, Austral. J. Chem., 1974,27,2001. lZ9 N . Furutachi, Y.Nakadaira, and K. Nakanishi, J.C.S. Chem. Comm., 1968, 1625. 130 A. F. Thomas and R. Dubini, Helu. Chim. Acta, 1974, 57, 2076. lZ4 lZ6

412

Photochemistry

Scheme 10

involves dioxetan infermediates,l3l and this group has now gone on to isolate by low temperature (- 78 "C) photodioxetans (70) in good yield (31-55%) sensitized oxidation of indenes (69) in methan01.l~~ The dioxetans, which can be

R3 (69) (70) a ; R' = b ; R 1= c; R 1= d ; R1 =

RZ = Ph; R3 = H Me; R2 = Ph; R3 = H Pr'; R 2 = R 3 = H Me; RZ = H . R3 = But

chromatographed on silica gel and crystallized, are cleaved to dicarbonyl compounds on thermolysis. Curiously, dioxetan formation is much more rapid in methanol than in aprotic solvents. This point is taken up by other who have compared the rates for attack by lo2in the ene mode and in the dioxetan mode as a function of solvent and temperature. Rose Bengal-sensitized photooxidation of the vinyl sulphide (71) in methanol, for example, leads to the dioxetan-derived products (72) and (73) in 65% and 26% yield respectively; whereas, in acetone, (72) and (73) are produced in respective yields of 49% and 12% together with a 19% yield of the aldehydes (74) and (75) derived from an ene-reaction (see Scheme 11). At low temperatures (-78 "C) in acetone or methylene chloride, only the products arising from the dioxetan mode are produced. The solvent effect is even more noticeable in the photo-oxidation of the analogous vinyl ether, l-ethoxy-2-ethylhex-l-ene(76). In methanol, the dioxetan mode products [(72) and (73)] from (76) amount to 37% and the ene products [(74) and (75)] form 38%, yet in acetone the respective yields of dioxetan and ene products are 4% and 70%. Diphenyl sulphide appears to be a good trapping agent for dioxetans, and may provide evidence in photo-oxidations for dioxetan intermediates when these are not is01able.l~~Thus, oxidation of the imidazole (77) to (79) is thought to 13%

lS3 134

C. S. Foote, S. Mazur, P. A. Burns, and D. Lerdal, J . Amer. Chem. SOC.,1973, 95, 586. P.A. Burns and C. S. Foote, J . Amer. Chem. SOC.,1974, 96, 4339. W. Ando, K. Watanabe, J. Suzuki, and T. Migita, J. Amer. Chem. SOC.,1974, 96, 6766. H.H.Wasserman and I. Saito, J. Amer. Chem. SOC.,1975, 97, 905.

41 3

Photo-oxidation and -reduction Et

0 [““)~-Bu] 0-0

di an ”*V oxet

EtS

+

EtCBu I1

(72)

Bu-C-CHO I OH I

Et

w

(73)

Bu 0 II

+ HCC=CHMe HOO

’

I Bu

Bu

]

Et’<

HOO

(74) __f

0 HCC=CHPr II I Et

Pr

(75)

Scheme 11

proceed via the unisolated dioxetan (78).136 Photo-oxidation in the presence of diphenyl sulphide leads to the usual product [(79), 1 2 7 3 , together with the rearrangement product [(8l), 3 3 x 1 and diphenyl sulphoxide (41%). Formation of (81) could easily be rationalized by nucleophilic attack of diphenyl sulphide on the dioxetan, which leads to the zwitterion (80), followed by its rearrangement to (81) and Ph2S0, as shown in Scheme 12.

ph)@ph

Ph

2‘’

-

> Ph I

I Ph

0

It

PhC-N 0 ,bh

II

PhC-N

I Ph

(79)

-t

Ph

’&fiI,N

Ph A

(80) Scheme 12

N

(8 1)

tias-pnase reaction or W2 witn ethyl vinyl ether leads to observation of the high-resolution chemiluminescence spectrum of formaldehyde, arising from thermal decomposition of the dioxetan (82) shown in Scheme 13.136 la6

lS6

H. H. Wasserman, K. Stiller, and M. B. Floyd, Tetrahedron Letters, 1968, 3277. D. J. Bogan, R. S. Sheinson, R. G. Gann, and F. W. Williams, J. Amer. Chem. Suc., 1975, 97, 2560.

414

Photochemistry

+ CH2=CHOEt

'0,

0-0

--+

OEt

CH,O*

+

HCOzEt

(82) Scheme 13

Sensitized photo-oxidation of cyclic, conjugated dienes usually gives 1,4-endoperoxides, or products derived from them. Thus, in the oxidation of 6,6-disubstituted fulvenes such as (83; Ar = Ph), the observed products arise from subsequent thermal reactions of the unstable peroxides (84) produced by 1,4addition of lo, to the fulvenelS7 (see, e.g., Vol. 4, p. 744). However, in the

(85)

(86)

photo-oxidation of di-p-anisylfulvene (83; Ar = p-MeOC,H,) at -70 "C in methylene chloride, the presence of the ketol (86) as a minor product suggests the unusual possibility that a competing 1,Zaddition of lo2occurs to give the dioxetan (85), followed by its rearrangement to (86). The photo-oxidation of some annulenes has been For example, the bridged [lOIannulene (87) produces the 1,4-endo-peroxide (89), possibly by

a-.[a]-a /

(87)

/

(88)

(89)

way of valence isomerization of the unisolated adduct (88). Some of the stereochemical features of photosensitized oxidation are provided by a study of the s-trans steroidal diene The two s-cis diene hydroperoxides (91) which are produced can undergo further [4 + 21 reaction with lo2to give four possible 1,l l-epidioxy-5-hydroperoxides. Reactions involving lo2attack on conjugated dienes continue to be used in synthesis. Kaneko et c 1 1 . l ~have ~ described a procedure for the synthesis of lS7

la8

13@ 140

N. Harada, S. Kudo, H. Uda, and S. Utsumi, Chem. Letters, 1974, 893. E. Vogel, A. Alscher, and K. Wilms, Angew. Chem. Internat. Edn., 1974, 13, 398. M. Maumy and J. Rigaudy, Bull. SOC.chim. France, 1974, 1487. C.Kaneko, A. Sugimoto, and S. Tanaka, Synthesis, 1974, 876.

415

Photo-oxidation and -reduction

(91) a; Sa-OOH b; 5jS-00H

cyclic cis-l,4-diols from the corresponding cyclic 1,3-dienes by photosensitized oxidation in methanol in the presence of thiourea at room temperature. This procedure intercepts the cyclic lY4-peroxide,which otherwise decomposes above - 30 "C. Singlet oxygen reaction with dienes has also provided a photochemical synthesis of p-tropoquinone (cyclohepta-3,6-diene-l,2,5-trione),141and forms an essential step in the synthesis of the unknown cyclo-octa-3,5-diene-1,2-dione from 2,3-hom0tropone.l~~Rose Bengal-sensitized oxidation of the insect juvenile hormone analogue ethyl 3,7,11-trimethyldodeca-2E-4E-dienoateproduces an unstable cyclic peroxide,143as does photo-oxygenation of the steroid Sa-androsta14,16-diene144 and of the diterpene palustric 6 Oxidation of Aromatic Compounds Judging by the few papers published, there has been little activity over the past year in this field of photo-oxidations. Some mention has been made in Section 4 of the rate of quenching of '0,by 1,3-diphenylisobenzofuran(54). Rio and Scholl 146 have isolated the unstable peroxide intermediate (92) (Scheme 14)

produced on sensitized photolysis of (54) in ether at - 50 "C,and they have studied its chemistry. Methylene blue-photosensitized oxidation of (54) to the diketone (93) in methanol forms the basis of a recently described teaching experiment in p h o t o - ~ x i d a t i o n . ~Some ~ ~ reactions of aromatic amines which appear to involve 1,2- and 1,4-addition of oxygen to the aromatic ring are discussed in the next Section. 141

S. Ito, Y. Shoji, H. Takeshita, M. Hirama, and K. Takahashi, Tetrahedron Letters, 1975,

142 ldS

Y.Ito, M.Oda, and Y. Kitahara, Tetrahedron Letters, 1975, 239. C. A. Henrick, W. E. Willy, D. R. McKean, E. Baggiolini, and J. B. Siddall, J. Org. Chem.,

1075.

144 14b 14(

1975,40, 8. J.-C. Beloeil and M. Fetizon, Compt. rend., 1974, 279, C , 347. A. Enoki and K. Kitao, Mokuzai Gakkaishi, 1974, 20, 342. G. Rio and M.-J. Scholl, J.C.S. Chem. Comm., 1975, 474. J. A. Bell and J. D. Macgillivray, J. Chem. Educ., 1974, 51, 677.

416

Photochemistry

The dye-sensitized photo-oxidation of phenols has been examined using CIDNP It is concluded from the observed polarizations of nuclear spin that sensitization by xanthene dyes (such as Rose Bengal) is the result of reversible hydrogen abstraction by the triplet dye molecule from the phenolic hydroxyl group. Any resulting photochemical reactions (e.g. with oxygen) arise from irreversible reactions of the phenoxy-radicals produced, rather than from direct reactions of the phenols with lo2.Dye-sensitized photo-oxidation of p-hydroxyphenylpyruvic acid (94) in solution at pH 7 (conditions under which

(94)

(95)

(97)

(96)

the keto-form predominates) gives the dienone [(95), 18x1, p-hydroxybenzaldehyde [(96), 1273, and p-hydroxyphenylacetic acid [(97), 15%].14QSimilar oxidation of (94) in its enol form gives high yields of [(96), 70x1 and oxalic acid.

7 Oxidation of Nitrogen-containing Compounds Photo-oxidation of amines remains a subject of interest. The photosensitized oxidation of methyl-substituted tertiary amines leads to NN-disubstituted formamides.160 The mechanism of this reaction has been studied, and Scheme 15 has been proposed.151 Charge-transfer complexation of amine with sensitizer, R,NCH,

sensitizer

R,NdH,

- e ,

+

R, N =CH, (98) 1H.F

0 II RZNCH

f--

R2NCHZOOH

(99)

Scheme 15

followed by hydrogen abstraction and further electron loss to sensitizer, leads to the iminium ion, (98). Evidence is put forward which suggests that hydrogen peroxide (produced during photo-oxidation) reacts with (98) to give an unstable hydroperoxyamine, followed by loss of water to produce the formamide derivative (99). 118 148

lS0

K. A. Muszkat and M. Weinstein, J.C.S. Chem. Comm.,1975, 143. I. Saito, M. Yamane, H. Shimazu, and T. Matsuura, Tetrahedron Letters, 1975, 641. D. Herlem, Y. Hubert-Brierre, F. Khuong-Huu, and R. Goutarel, Tetrahedron, 1973, 29, 2195.

lS1

F. Khuong-Huu, D. Herlem, and Y. Hubert-Brierre, Tetrahedron Letters, 1975, 359.

Photo-oxidation and -reduction

417

Conflicting accounts of the dye-sensitized photo-oxidation of diphenylamine in alcohols have been published, with one group of workers 152 reporting diphenylnitroxide as the product, and another group 163 repeating their claim (see Vol. 6, p. 545) that N-phenyl-p-benzoquinonimineis formed. The photo-oxidation of 2,4,6-triphenylpyridine N-phenylimine may involve ozone production.16* The mechanism of formation of (99) in Scheme 15 may also apply to the production of the aldehyde (101) on Rose Bengal-photosensitized oxidation of the dimethylamino-substituted benzenes (100) in methanol, during experiments Me

RxxNMe2 hv. 0,

R

NMe,

(100) a; R

=

sensitizer

I

’

(101) a; R = H b;R=Me

H

b;R=Me

which have yielded some interesting The amine (100a) gives the aldehyde (101a) in low yield, whereas (1OOb) produces the analogous compound (101b) as well as the epoxyenone (102) in 17% isolated yield (Scheme 16). Forma0

tion of (101) does not involve lo2,but the epoxyenone (102) is thought to arise by 1,4-attack of lo2on the aromatic ring, followed by rearrangements. The conversion of the amine (103) into ring-cleaved product (105) in 60% yield is thought to involve the dioxetan (104), and to represent the first example of 1,Zaddition of lo, to the benzene ring. Enamines behave as electron-donor olefins (see Section 5 ) and are attacked by lo2to yield dioxetans, which are stable only at low temperatures. Foote et aZ.lb6

cfMe lsensitizer

’

NMe,

+

@,Me /

hv’02

OMe

( 103)

lSa

lSa ls4 ls5 166

OMe

OMe

(104)

(105)

N. R. K. Raju, M. Santhanam, B. Sethuram, and T. N. Rao, Indian J. Chem., 1974, 12,422. W. R. Bansal, S. Puri, and K. S. Sidhu, Bull. Chem. SOC.Japan, 1974, 47, 2319. C. W. Bird and M. A. Sheikh, Tetrahedron Letters, 1975, 1333. I. Saito, S. Abe, Y.Takahashi, and T. Matsuura, Tetrahedron Letters, 1974, 4001. C. S. Foote, A. A. Dzakpasu, and J. W.-P. Lin, Tetrahedron Letters, 1975, 1247.

Photochemistry have now extended their investigation 16' to the characterization at low temperatures of the dioxetans from NN-dimethylisobutenylamine and 1,2-diphenyl-lmorpholinoethylene. At room temperature, photo-oxidation gives carbonyl and amide fragments from thermal decomposition of the dioxetan. Photo-oxygenation of a series of enamides from cyclic ketones at -78 "C in methanol gives isolable dioxetans, but at room temperature cyclic a-diketones are the main reaction products.16B In an attempt to mimic an enzymatic demethylation process, nitroxide photolysis has been used as a method for oxidizing the C-4 j?-methyl group of 4,4dimethylcholestanone.16u Further applications have been published of the photolysis of N-nitrosoamides in the presence of oxygen to the synthesis of nitrate esters having functionalized methyl and methylene groups.160 It has now been shown that an azoxy-compound (107) can be formed (albeit in low quantum yield, Q, < loA4)by reaction of an azo-compound (106) with light and oxygen.lS1 41 8

(106)

(107)

The photo-oxidation of nitrogen-containing heterocyclic compounds continues to attract research. 1,3-Diaryl-Zpyrazolines such as (108) are used as fluorescent whitening agents for fibres, but are not totally stable to light. Direct irradiation of the pyrazoline (108) gives the pyrazole (109) in good yield. Dye-sensitized photo-oxidation of (108) in methanol gives the propiophenone (1 10) additionally (Scheme 17).le2The authors show that lo2is certainly involved in the production

LN,N

O,, MeOH '

0 II PhCCH2CH(OMe)2

Hph + qN,'N

(1 10)

Scheme 17

of (log), and that the pyrazoline (108) interacts with the dye triplet, but the mechanism of formation of (110) is left unclear. Methylene blue-sensitized oxidation of the thiazole (1 11) occurs in methylene chloride to give the product (112) in 67% yield.lss Singlet oxygen is thought to C. S. Foote and J. W.-P. Lin, Tetrahedron Letters, 1968, 3267. H. H. Wasserman and S. Terao, Tetrahedron Letters, 1975, 1735. nS J. A. Nelson, S. Chou, and T. A. Spencer, J. Amer. Chem. SOC.,1975,97, 648. l o o J. N. S. Tam, T. Mojelsky, K. Hanaya, and Y . L. Chow, Tetrahedron, 1975, 31, 1123. lG1 H. Gruen and D. Schulte-Frohlinde, J.C.S. Chem. Comm., 1974,923. m N. A. Evans and I. H. Leaver, Austral. J. Chem., 1974, 27, 1797. le8 H. H. Wasserman and G. R. Lenz, Tetrahedron Letters, 1974, 3947.

15'

16*

Photo-oxidation and -reduction

419 '0

-4 QNHCOMe S

attack the thiazole ring by 2,5-addition, followed by rearrangement of the adduct. Photosensitized oxidation of (1H)-1,Zdiazepines also involves [2 + 41 addition of lo2to the diazepine to give a relatively stable cyclic peroxide.la4 Conversely, a [2 + 21 addition product, the dioxetan, may be involved in the reactions of 3-hydroxypyridinium derivatives with 10,.1s6 Reports have appeared of the photo-oxidation by direct irradiation of some 2,3-diphenylindole~,~~~ and of carbaz01e.l~~Methyl-substituted tryptamines have been oxidized by irradiation at 254 nm in the presence of aromatic N-oxides.lse The role of singlet oxygen in the dye-sensitized photo-oxidation of guanosine has been investigated.lsO Neonatal jaundice is associated with high levels of bilirubin in the serum and tissues; the pigment can be broken down on exposure to light, and phototherapy is now a widely used treatment. This has made the photo-oxidation of bilirubin a subject of importance (see Vol. 4, p. 755). Bonnett and Stewart 170 have now published a full account of the photo-oxidation of bilirubin in hydroxylic solvents. All the observed products can be understood in terms of lo2attack, with 1,4-addition to the pyrrole rings competing with 1,2-addition (i.e. dioxetan formation) to the enamino-groups of the pyrrole-methine bonds. Dyesensitized photo-oxidation of hemopyrrole (2,3-dirnethyl-4-ethyIpyrr0le)~~~ gives products very similar to those previously reported for the isomer kryptopyrrole.172 The photosensitized oxidation of certain amino-acids in proteins plays an important part in photodynamic action. A study has been made of the oxidation of amino-acids by microwave-generated 102.173 The photo-oxidation of tryptophan-containing peptides 174 and of histidine (sensitized by flavin) 176 have been noted. It is reported that the crystal violet-sensitized photo-oxidation of cysteine to cysteic acid does not involve lo2 Photo-oxidation of enzymes is often a very specific process, and continues to give useful evidence of their tertiary structure. Destruction of a single histidyl residue is observed for the photo-oxidation of the & subunit of tryptophan Ie4

T. Tsuchiya, H. Arai, H. Hasegawa, and H. Igeta, Tetrahedron Letters, 1974, 4103.

m H. Takeshita, A. Mori, and S. Ohta, Bull. Chem. SOC.Japan, 1974, 47, 2437. le6

Ie7

C. A, Mudry and A. R. Frasca, Tetrahedron, 1974, 30, 2983. G. N. Ivanov and V. Y. Tolmacheva, Izvest. Tomsk. Politekhn. Inst., 1973, 257, 101. M. Nakagawa, T. Kaneko, H. Yamaguchi, T. Kawashima, and T. Hino, Tetrahedron, 1974, 30, 2591.

170 171 172

173 174 176

I. Saito, K. Inoue, and T. Matsuura, Photochem. and Photobiol., 1975, 21, 27. R. Bonnett and J. C. M. Stewart, J.C.S. Perkin I, 1975, 224. D. A. Lightner, R. D. Norris, D. I. Kirk, and R. M. Key, Experientia, 1974, 30, 587. D. A. Lightner and D. C. Crandall, Experientia, 1973, 29, 262. J. R. Fischer, G. R. Julian, and S. J. Rogers, Physiol. Chem. Phys., 1974, 6, 179. I. I. Sapezhinskii and E. G. Dontsova, Biofzika, 1974, 19, 616. P. G. Johnson, A. P. Bell, and D. B. McCormick, Photochem. and Photobiol., 1975,21,205. G. Gennari, G. Cauzzo, and G. Jori, Photochem. and Photobiol., 1974,20, 497.

420

Photochemistry

synthetase,17’ for the protoporphyrin-apoperoxidase complex 178 and for yeast imidazoleglycerolphosphate d e h y d r a t a ~ e . ~ Photo-oxidation ~~ studies of horse and sperm-whale myoglobin sensitized by the haem group,180 of lysozyme at different wavelengths,lS1of pineapple stem bromelain,182and of bovine carbonic anhydrase le3all show specific oxidations of histidyl, tryptophanyl, or methionyl residues. 8 Miscellaneous Oxidations Large quantities of dichlorodifluoromethane and other chlorofluorocarbons (‘Freons’) are used as aerosol propellants, and it has been calculated that there is a danger of reducing the earth’s protective ozone layer following photolysis to produce chlorine atoms in the upper afmosphere.ls4 Milstein and Rowland lE5 have now measured quantum yields of unity for CF,Cl, dissociation [reaction (36)] and for appearance of photo-oxidation products in oxygen. Studies of the CFzClz

hv

kF,C1

+ el

(36)

photo-oxidation of other halocarbons include iodomethane in solid argon,lSs 1,l ,2-trichloroethane,ls7 and tetrachloroethylene.188 As a study relevant to ecology, the photo-degradation of aldrin and dieldrin as solids under the influence of U.V. light in a current of oxygen has been i n v e ~ t i g a t e d . ~ ~ ~ Papers on the photo-oxidation of sulphur-containing molecules have been published. a-Lipoic acid has been oxidized by a variety of reagents, including 102.190 The complex mixture of products contains the four possible thiolsulphinates and two possible thiolsulphonates. Stevens et aZ.lgl have calculated the rate constant for interaction of a-lipoic acid with lo2. The photo-oxidation of dimethyl sulphide in the gas phase,lQ2of dibutyl sulphide in ethanolic and of the drugs thioridazine lQ4and chlorpromazine lQ5has been explored. Irradiation of benzaldehyde in methanol under oxygen gives methyl benzoate and, in the presence of a catalytic amount of hydrochloric acid, its yield is up to 90% of the aldehyde c o n ~ u r n e d .Oxygen ~ ~ ~ is essential for reaction, but the mechanism is unknown. E. W. Miles and H. Kumagai, J. Biol. Chem., 1974, 249, 2843. M. R. Mauk and A. W. Girotti, Biochemistry, 1974, 13, 1757. 17g R. D.Glaser and L. L. Houston, Biochemistry, 1974,13, 5145. 1 8 0 M. Folin, G.Gennari, and G. Jori, Photochem. and Photobiol., 1974, 20, 357. lalE. Silva, S. Risi, and K. Dose, Radiation and Environ. Biophys., 1974, 11, 111. la2 T. Murachi, T. Tsudzuki, and K. Okumura, Biochemistry, 1975, 14, 249. lS3 P. Walrant and R. Santus, Photochem. and Photobiol., 1974, 20, 455. la* S.C.Wofsy, M. B. McElroy, and N. D. Sze, Science, 1975,187,535; see also A. L. Hammond, ibid., p. 1181. R. Milstein and F. S. Rowland, J. Phys. Chem., 1975, 79, 669. la6 J. F. Ogilvie, V. R. Salares, and M. J. Newlands, Canad. J. Chem., 1975, 53, 269. K. Shinoda and S . Anzai, Nippon Kagaku Kaishi, 1974, 1584. la8 E. Sanhueza and J. Heicklen, Canad. J. Chem., 1974, 52, 3863. lag S. Gaeb, H.Parlar, S. Nitz, K. Hustert, and F. Korte, Chemosphere, 1974, 3, 183. lgO F.E.Stary, S. L. Jindal, and R. W. Murray, J. Org. Chem., 1975, 40, 58. Ig1 B. Stevens, S. R. Perez, and R. D. Small, Photochem. and Photobiol., 1974, 19, 315. lea R.A.Cox and F. J. Sandalls, Atmos. Enuiron., 1974, 8, 1269. lg3 M. Casagrande, G. Gennari, and G. Cauzzo, Gazzetta, 1974, 104, 1251. lg4 E. Pawelczyk and B. Marciniec, Pharmazie, 1974, 29, 585. lg5 T. Iwaoka and M. Kondo, Bull. Chem. SOC.Japan, 1974, 47, 980. lg6 H. Sakuragi and K. Tokumaru, Chem. Letters, 1974, 475. 177

Photo-oxidation and -reduction

421

Irradiation at 254nm in the charge-transfer band of the complex between diethyl ether and oxygen leads to several products (with the quantum yields given): H202(0.24), 1-ethoxyethyl hydroperoxide (0.04), ethyl acetate (0.26), acetaldehyde (0.1 S), ethanol (O.lS), ethyl formate (0.04), methanol (0.035), formaldehyde (0.005), and ethyl vinyl ether (O.013).ls7 The primary process appears to be electron transfer from ether to oxygen, as shown in reaction (37). Reaction with [EtOEt*-02]

hv

EtOgt

+ 0,'

(3 7)

other C-H bonds is involved in the photo-oxidation of the triterpene lupan2 8 - 0 1 , ~rotenone,1ag ~~ and in the synthesis of l*O-xanthone from xanthene.200 Singlet oxygen has been shown to be capable of oxidizing organic phosphites to phosphates,201and of giving a photo-oxidative cleavage of epoxides.202 lS7

C. von Sonntag, K. Neuwald, H.-P. Schuchmann, F. Weeke, and E. Janssen, J.C.S. Perkin 11, 1975, 171.

and J. Protiva, CON.Czech. Chem. Comm., 1974, 39, 1382. M. Chubachi and M. Hamada, Chem. Letters, 1974, 397. H. J. Pownall, J . Labelled Compounds, 1974, 10, 413. P. R. Bolduc and G. L. Goe, J. Org. Chem., 1974,39, 3178. M. R. Parthasarathy and D. K. Sharma, Indian J. Chern., 1974, 12, 1009.

lB8 A. VystrCil lns

2oo *01

202

6 Photo reactions of Co mp o unds contai ning Heteroatoms other than Oxygen BY S. T. REID

1 Nitrogen-containing Compounds Rearrangement.-The photochromism exhibited by A 2~2’-bi-(2H1&benzothiazine) in solution is the result of the reversible conversion of the yellow stable trans-isomer (1) into the thermally unstable cis-isomer (2).l The colour changes known to occur in structurally related pigments are presumably analogous. The trans -+ cis-isomerization in thioindigo and 6,6‘-diethoxythioindigo has been reported to take place through a relatively long-lived transoid triplet intermediate,

(5)

(3)

(4)

whereas the reverse process either follows a singlet pathway or involves a shortlived twisted triplet.* A detailed quantitative study of the photorearrangement of diaminomaleonitrile (3) to 4-amino-5-cyanoimidazole(4) indicates that the trans-isomer (5), formed from the cis-isomer with a quantum yield of 0.045, is an intermediate in this p r o ~ e s s . ~ Photochemical isomerization about the carbon-nitrogen double bond continues to be the subject of numerous investigations, although whether the excitedstate isomerization proceeds by way of rotation or linear inversion remains to be clarified. The greater configurational stability of oxime ethers compared with N-aryl- or N-alkyl-imines makes them an attractive subject for detailed study. The O-methyl oxime ether of acetophenone undergoes facile syn -+ anti isomerization on direct irradiation ( A 254 nm) in pentane, the photostationary state ratio (syn : anti) being 2.20 k 0.03.4 The photoreaction is not quenched by high 1

4

G. Prota, E. Ponsiglione, and R. Ruggerio, Tetrahedron, 1974, 30, 2781. A. D. Kirsch and G. M. Wyman, J . Phys. Chem., 1975,79, 543. T . H. Koch and R. M. Rodehorst, J. Amer. Chem. SOC.,1974,96,6707. A. Padwa and F. Albrecht, J. Amer. Chem. SOC.,1974, %, 4849.

422

Photoreactions of Compounds containing Heteroatoms other than Oxygen

423 concentrations (ca. 3 mol 1-l) of piperylene. Photoisomerization can also be induced by triplet excitation; a plot of the photostationary state concentration versus the triplet energy of the sensitizer can arbitrarily be divided into three distinct regions, (i) a high-energy region in which the stationary state ratio is ca. 1.5, (ii) a region (ET = 72-59 kcal mol-l) in which there is a gradual increase in the syn : anti ratio, and (iii) a region (ET = 59-54 kcal mol-l) in which there is a sharp decrease in the photostationary state ratio. The behaviour in regions (ii) and (iii) has been ascribed to non-vertical excitation of the acceptor. The O-methyl oxime ether of 2-acetonaphthone has also been reported to undergo facile syn -+ anti photoisomerization.6 The composition of the photostationary state appears to be concentration-dependent with the syn-isomer predominating at low concentrations. Evidence supporting the involvement of the singlet state was obtained from fluorescence-quenching studies and from photosensitization experiments. Quantum yields for the direct and 9-fluorenone-sensitized syn -+ anti photoisomerization of 2-naphthaldehyde phenylhydrazone have been determined,g and the photoisomerization of a series of 2-benzothiazoylhydrazones has been described.' Photocyclization of the azocine (6) in methanol to give the cyclobuta[c]pyridine (7) has been reported, and is presumably the result of a concerted disrotatory process.8 Attempts to reverse this reaction thermally were unsuccessful.

-N

Ph

(7)

(6)

(8)

R' R' R' R'

=

= = =

Ac, R2 = H R2 = Ac C02Et, R2 = H CO,Et, Ra = AC

Analogous cyclizations have been described for a number of 2,3-dihydro1,2(1H)-diazepines (8) and for 3,4-dihydro-l,2(2H)-dia~epine.~The n.m.r. spectrum of the photoproduct obtained from Wet hoxycarbonyl-2,3-homoazepine (9) is incompatible with the stereochemistry previously assigned. The product 6

A. Padwa and F. Albrecht, J. Org. Chem., 1974, 39, 2361. G. Condorelli, L. L. Costanzo, S. Pistara, and S. Giuffrida, 2.phys. Chem. (Frankfurt), 1974, 90, 58. S. Kwon and K. Isagawa, Nippon Kagaku Kaishi, 1974, 524; S . Kwon, M. Tanaka, and K. Isagawa, ibid., p. 1526. R. M. Acheson, G. Paglietti, and P. A. Tasker, J.C.S. Perkin I, 1974, 2496. T. Tsuchiya and V. Snieckus, Canad. J. Chem., 1975,53, 519.

424

Photochemistry Ilv

>

I

I

"H

C0,Et

COzEt (9)

(10)

which is obtained in over 90%yield by irradiation in methanol is now believed to have the cis,anti,cis stereochemistry (lO).lO A report of the photochemical preparation of the azaphosphabicycloheptene oxide (1 1) from the azaphosphacycloheptadiene (12) has appeared in the patent 1iterature.ll

H (17) lo

l1

K. Shudo and T. Okamoto, Chem. and Pharm. Bull. (Japan), 1974,22, 1204. F. Mathey and J. P. Lampin, Fr. P. 2 171 596 (Chem. A h . , 1974, 81, 25 805).

Photoreactions of Compounds containing Heteroatoms other than Oxygen

425

Numerous examples of heterocyclic analogues of the stilbene to dihydrophenanthrene cyclization (usually accompanied by oxidation) have again been reported. Details of the photocyclodehydrogenation of certain 3-(2-aryl and 2-pyridy1)vinylindoles have been published,12and the reaction has subsequently been used in the synthesis of 5-ethyl-11H-pyrid0[3,4-a]carbazole.~~ 2,3-Diphenylindole was similarly converted into the corresponding dibenzocarbazole by irradiation in acetic acid in the presence of oxygen.14 The synthesis of the novel ring system (13) was accomplished in like manner.15 Ring-opening of the azacyclohexadiene system (14) has been proposed to account for the formation of products (15)-( 18) from the furopyridin-2-one (19) by irradiation in methanol.le Further studies and numerous synthetic applications of the photocyclization of enamides have been reported. Irradiation of N-methyl- and N-benzylcyclohex-l-enecarboxanilide(20) affords a mixture of cis- (21) and trans-phenanthridones (22).17 N-Methyl-3,4-dihydronaphthalene-l-carboxanilide is analogously converted into the corresponding benzophenanthridones. Formation of

(20) R = Me or PhCH, (21) (22) cis-isomers is favoured in protic solvents such as methanol, whereas the transisomers are the major products in the aprotic solvents benzene, ether, and even dimethyl sulphoxide. No thermal or photochemical interconversion of cis- and trans-isomers could be detected. These results can be rationalized in terms of competing stepwise and concerted hydrogen shifts in the intermediate arising by electrocyclic ring-closure. In a similar fashion, 2-aroyl-l-methylene-l,2,3,4-tetrahydroisoquinoline enamides yield on irradiation the corresponding 8-oxoberberines.l* Cyclization of analogous enamides containing ortho-substituents in the aryl residue is followed by elimination of the substituent leading to formation of the unsaturated oxyprotoberberine~.~~ Thus, for example, the enamide (23) is converted on irradiation in benzene into the oxyprotoberberine (24), presumably via the intermediate (25). An alternative pathway involving methoxyl migration has been observed by other workers.20 Related cyclizations have been employed in the syntheses of ( k )-angustoline 21 and of lycorine-type alkaloids.22 la l3

I7

Is *O

a1 aa

S. 0. De Silva and V. Snieckus, Canad. J. Chem., 1974,52, 1294. D. Cohylakis, G. J. Hignett, K. V. Lichman, and J. A. Joule, J.C.S. Perkin I, 1974, 1518. C. A. Mudry and A. R. Frasca, Tetrahedron, 1974,30, 2983. A. Mitschker, U. Brandl, and T. Kauffmann, Tetrahedron Letters, 1974, 2343. G . Jones and J. R. Phipps, J.C.S. Perkin I, 1975, 458. I. Ninomiya, S. Yamauchi, T. Kiguchi, A. Shinohara, and T. Naito, J.C.S. Perkin I, 1974, 1747. G. R. Lenz, J. Org. Chem., 1974,39,2846. G. R. Lenz, J. Org. Chem., 1974,39,2839. H. Ishii, K. Harada, T. Ishida, E. Ueda, K. Nakajima, I. Ninomiya, T. Naito, and T. Kiguchi, Tetrahedron Letters, 1975, 3 19. I. Ninomiya and T. Naito, Heterocycles, 1974, 2, 607. H. Iida, S. Aoyagi, and C. Kibayashi, J.C.S. Chem. Comm., 1974,499.

426

Photochemistry Me0 Me0

IIV

(23)

I

- MeOH

(24)

Further studies of the photochemically induced conversion of N-methyldiphenylamine into N-methylcarbazole have been Two successive intermediates have been detected, namely the amine triplet and N-methyl-4ay4bdihydrocarbazole. Oxygen appears to participate in the overall reaction in two ways, uiz. by dehydrogenation of the dihydrocarbazole intermediate to carbazole and by quenching the amine triplet. Non-oxidative cyclization of 5-(N-methylani1ino)- and 5-(N-acetylanilino)-1,3-dimethyluracil (26) similarly gives the transdihydropyrimido[5,4-b]indoles(27) in high yield.24 Orbital symmetry arguments

(26)

(28)

(27)

support the view that the cyclization should occur in a conrotatory manner leading to formation of a dipolar intermediate (28), analogous to that observed in the cyclization of diphenylamine. Evidence that the trans-isomer (27) arises from this intermediate (28) by a suprafacial [1,4] hydrogen shift comes from deuterium labelling studies. Oxidative cyclization of uracil derivatives having a phenylthiogroup at C-5 or C-6 affords the corresponding benzothien~pyrimidines.~~ Other cyclizations resulting in the exclusive formation of trans-isomers have been described.25 Irradiation of the enamine (29), however, gives the diastereoisomeric OS

a4

G. Fischer, E. Fischer, K. H. Grellmann, H. Linschitz, and A. Temizer, J. Amer. Chem. Soc., 1974,96, 6267. S. Senda, K. Hirota, and M. Takahashi, J.C.S. Perkin I, 1975, 503. J. G. Berger, S. R. Teller, C. D. Adams, and L. J. Guggenberger, Tetrahedron Letters, 1975, 1807.

421

Photoreactions of Compounds containing Heteroatoms other than Oxygen

QLNA Me

11"+

QTl

+

Q-J

Me

N

Me

Q,A Me

(29)

indolines (30) and (31);26 in this case, a rapidly developing photostationary equilibrium between the E- and 2-isomers of (29) prevents any mechanistic interpretation based on considerations of orbital symmetry. Diazaphenanthrenes are obtained by irradiation of benzylidenaminopyridines in concentrated sulphuric acid;27the failure of this cyclization to occur in organic solvents is attributed to a rapid photochemical cis -+ trans isomerization. Cyclization of 3-phenylazopyridine to give 2,9,lO-triaza- and 4,9,10-triazaphenanthrene has also been observed in sulphuric acidYa8 whereas irradiation of azobenzene-2,2'-dicarboxylic acid (32) under the same conditions yields equal quantities of the expected benzo[c]cinnoline (33) and the indazolo[2,1-a]indazole

=(J2H \

N=N

Q

3:GI'""+

N

\

k

"

C02H

(32)

C02H

(33)

0

(34)

(34).29 In the presence of Lewis acids such as anhydrous AlC13, anhydrous

SnCII, and anhydrous FeCl,, azobenzene itself is also converted into benzo[c]c i n n ~ l i n e .The ~ ~ additional isolation of benzidine provides evidence for overall disproportionation. The lH-aza[l3]annulene (35) has been generated from the bicyclic precursor (36) by irradiation in acetone;31the product is believed to have the stereochemistry represented in (36). lH-Aza[l3]annulene itself appears from n.m.r. studies to be endowed with significant aromatic character, whereas the N-acetyl and N-methoxycarbonyl derivatives are not. The first 2H-quinolizine derivative (37) has been described and is obtained along with other products by irradiation of the benzo[c]quinolizine (38) in benzene.32 The precise mechanism of this reaction ae

OD

M. Riviere, N. Paillous, and A. Lattes, Bull. SOC.chim. France, 1974, 1911. H. H. Perkampus and B. Behjati, J. Heterocyclic Chem., 1974, 11, 511. J. W. Barton and R. B. Walker, Tetrahedron Letters, 1975, 569. C. P. Joshua and V. N. R. Pillai, Indian J. Chem., 1974, 12, 60. C. P. Joshua and V. N. R. Pillai, Tetrahedron, 1974, 30, 3333. A. G. Anastassiou and R. L. Elliott, J. Amer. Chem. Soc., 1974, 96, 5257. A. 0. Plunkett, Tetrahedron Letters, 1974, 4181.

428

"s H"

Photochemistry

IIV

>

, C02Me

MeO& +CO2 C0,Me

hv

m

C

0

2Me

Me C02Me

(38) R = H or D

(3 7)

has not been ascertained, but a simple [1,31 shift of hydrogen has been eliminated by deuterium labelling studies. A photochemically controlled tautomeric equilibrium has been observed in both alloxazines 33 and in cyclic amidines.34 Numerous rearrangements of the photo-Fries type have again been reported in systems containing nitrogen atoms. A detailed study of the photorearrangement of N-phenylurethane has been reported.36 The quantum yields for formation of ethyl 2-aminobenzoate and ethyl 4-aminobenzoate in cyclohexane and 5.7 x respectively, but these values were solution are 8.1 x found to decrease in polar solvents and at high concentrations. This decrease appears to depend linearly on the hydrogen-bonding acceptor strength of the polar aprotic solvent with N-phenylurethane. Rearrangement of 0- and p-methoxyacetanilides to the corresponding aminoacetophenones has been and optical activity has been reported to be retained in products derived by photorearrangement of chiral anilides containing an amino-acid residue (glycine, alanine, valine, proline, etc.) in the acyl portion of the molecule.37 A meta-orientated photo-Fries reaction (Scheme 1) has been observed and is potentially useful in mitomycin synthesis.3B

0

Scheme 1 P A . Song, M. Sun, A. Koziolowa, and J. Koziol, J. Amer. Chem. SOC., 1974, 96, 4319. 34

3h

sa

*'

38

K.-H. Pfoertner, Helv. Chim. Acta, 1975, 58, 861. R. Noack and K. Schwetlick, Tetrahedron, 1974, 30, 3799. J. Reisch and W. Koebberling, Arch. Pharm., 1974, 307, 197. H. Keroulas, C. Ouannes, and R. Beugelmans, Bull. SOC.chim. France, 1975, 793. G. J. Siuta, R. W. Franck, and A. A. Ozorio, J.C.S. Chem. Comm., 1974, 910.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

429

Other heterocyclic systems readily undergoing photo-Fries or related rearrangements include O-benzoyl- and N-benzoyl derivatives of hydroxypyridines 39 and amin~pyridines,~~ respectively, the phenyl esters of a variety of heteroaromatic acids,41certain aryloxy-l,3,5-triazine~,~~ and l-ben~oylindole.~~ The 3H-azepine (39) is readily converted by 1,3-benzoyl transfer into the isomer (40),"" and,

somewhat more surprisingly in view of the other pathways available, the pyridone (41) affords the photoproduct (42) in low yield together with the parent pyridone (43).46 Isomeric nitrile methylides are the primary products of irradiation of 3-phenyl2H-azirines. These ylides continue to be of interest as synthetic intermediates because of the ease with which they undergo 1,3-dipolar addition to a variety of unsaturated species. Irradiation in benzene of 2,2-dimethyl-3-phenyl- or 2,3-diphenyl-2H-azirine(44) in the presence of diethyl azodicarboxylate gave the 1,2,4-triazolines (45).46 In a similar fashion, oxazoles 47 and 2H-pyrroles 48 were obtained by addition of the photochemically generated ylides to acid chlorides and to triphenylvinyl phosphonium bromide, respectively. Analogous nitrile ylides can be obtained from /3-naphthyl-substituted azirines, and these are readily trapped by electrondeficient alkenes to produce 1- p y r r ~ l i n e s . ~2-@-Naphthyl)azirine ~ (46), for example, affords the l-pyrroline (47) on addition to acrylonitrile. The ringopening of the azirine appears to proceed from the excited singlet state, and the rate of ring-opening was found to decrease with increasing methyl substitution. M. T. Le Goff and R. Beugelmans, Bull. SOC.chim. France, 1974,2047, 2056. K. Itoh and Y . Kanaoka, Chem. and Pharm. Bull. (Japan), 1974,22, 1431. 41 Y.Kanaoka and Y . Hatanaka, Heterocycles, 1974, 2, 423. 4a Y . Ohto, H. Shizuka, S. Sekiguchi, and K. Matsui, Bull. Chem. SOC. Japan, 1974, 47, 1209. 48 W. Carruthers and N. Evans, J.C.S. Perkin I, 1974, 1523. 44 D. J. Anderson, A. Hassner, and D. Y. Tang, J. Org. Chem., 1974,39, 3076. H. Furrer, Tetrahedron Letters, 1974, 2953. l6P. Gilgen, H. Heimgartner, and H. Schmid, Helv. Chim. Acta, 1974, 57, 1382. U. Schmid, P. Gilgen, H. Heimgartner, H.-J. Hansen, and H. Schmid, Helv. Chim. Acta,

40

1974,57, 1393. a N. Gakis, H. Heimgartner, and H. Schmid, Helv. Chim. Acta, 1974, 57, 1403.

a A. Padwa and S. I. Wetmore, J. Org. Chem., 1974, 39, 1396.

15

430

Photochemistry

R'

Ph R1 \+R2 N

-t.

-/

N I1

+

Ph-CEN-C /R2

,C02 Et

Et02CY N

(44) R1 = R2 = Me R' = H, RS .= Ph

'X' N,

CO,Et

R1R2 Evidence for the existence of aliphatic nitrile ylides, stable at 77 K, has now been presented ;60 irradiation of 2,3-dipropyl-2H-azirine or 9-azabicycl0[6,1,O]non-l(9)-ene (48) in acetone or methyl trifluoroacetate yields the corresponding 3-oxazolines (49).

/IV

N (48)

>

RICOR'

(49)

d)R1 R2

R1 = R2 = Me R1 = CF3, RY = OMe

The indano[ 1,241aziridine (50) also undergoes ring-opening on irradiation and is converted into the red isoquinolinium imine (51).61 This reactive 1,3-dipole can be trapped with, for example, dimethyl acetylenedicarboxylate to give the adduct (52) which, on further irradiation, is converted into the benzazocine (53). Ring-opening rather than elimination of nitrogen, which is characteristic of most pyrazolines, is observed in the bicyclic pyrazoline (54) on irradiation through Pyrex.62 Aziridines (55) are formed together with the corresponding imines by direct but not by ketone-sensitized irradiation of the aliphatic allylamines (56).63 The cyclization is believed to proceed via a zwitterion, analogous to the intermolecular ci0 I1 63

A. Orahovats, H. Heimgartner, and H. Schmid, Helv. Chim. Acta, 1974, 57, 2626. A. Padwa and E. Vega, J. Org. Chem., 1975,40, 175. L. E. Friedrich, N. L. de Vera, W. P. HOSS,and J. T. Warren, TetrahedronLetters, 1974,3139. S . J. Cristol, T. D. Ziebarth, and G. A. Lee, J. Amer. Chem. SOC.,1974, 96, 7844.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

43 1

Ph

aMe C0,Me

NI

C6Hll

C6HI

IlV

1

(53)

CH,=CC

H

CHzNHR

hv

>N h 1

R

exciplexes derived from photo-excited arenes and amines ; similar exciplexes have been proposed as intermediates in the photoaddition of amines to alkenes and benzene. Examples of the photorearrangement of five-membered heterocycles have again been described. 3-Arylisothiazoles are obtained by irradiation of 2-arylt h i a z o l e ~ ,and ~ ~ 3-hydroxy-5-phenyl- and 3-hydroxy-5-methyl-isoxazoleundergo rearrangement on irradiation in methanol to 5-phenyl- and 5-methyl-4-oxazolin2-one, respectively.66 Ring transposition is observed, in addition to reduction, in the conversion of the pyrazoles (57) into the 1,2-bis-(l-arylimidazol-4-yl)ethane-1,Zdioles (58),66 Transposition products were not obtained from benzoisothiazoles;irradiation of benzo[d]isothiazole(59) gave the disulphide (60), whereas irradiation of benzo[c]isothiazole (61) gave the benzophenone (62), presumably via the corresponding thione, and the dibenzodiazocine (63).67 64 65 68

67

H. J. M. DOU,G. Vernin, and J. Metzger, Chim. Acta Turc., 1974, 2, 82. M. Nakagawa, T. Nakamura, and K. Tomita, Agric. and Biol. Chem. (Jupun), 1974,38,2205. T . Nishiwaki, F. Fujiyama, and E. Minamisono, J.C.S. Perkin I, 1974, 1871. M. Ohashi, A. Ezaki, and T. Yonezawa, J.C.S. Chem. Comm., 1974,617.

432

Photochemistry 0 ll C-R1

HO OH I

I

I

R2 (57) R’ =

R2 = Ph R‘ = p-MeOC,H4, R? = Ph

(58)

CN

. .

(63)

Surprisingly, ring transposition is not observed when 3,5-dimethylisoxazole is irradiated in acetonitrile in the presence of triethylamine.s8 The major product arises by reductive cleavage of the isoxazole ring and involves initial formation of an encounter complex between the isoxazole and triethylamine. 2-Alkyl-2-thiazolines (64)have been reported to undergo rearrangement to the alkenylthioamides (65) and (66) on irradiation.6g Evidence for the irreversible

&XR (64)

IW

’

4%~F

(67)

Y S

R +H2c
formation of a thioacylaziridinium intermediate (67), for which there is ample precedent, is provided by a detailed study of variously substituted thiazolines. Phenylbutazone (68) also undergoes ring-contraction on irradiation to yield the unstable aziridinone (69) which, in the presence of methanol or dimethylamine, is readily converted into the corresponding adducts (70) and (71).g0 Full details of the rearrangement of perfluoroalkylpyridazines (72) to the related pyrazines (73) have now been described.s1 The possibility of a diazaprismane intermediate has been eliminated by a study of suitably substituted pyridazines, and the only pathway compatible with these results is that outlined in Scheme 2. The isolation of such intermediates has been reported elsewhere and provides support for this proposal. A bicyclo[2,2,0]-intermediatehas also 68 60

T. Sat0 and K. Saito, J.C.S. Chem. Comm., 1974,781. T. Matsuura and Y. Ito, Tetrahedron, 1975, 31, 1245. J. Reisch, K. G. Weidmann, and J. Triebe, Experientia, 1974,30, 451. R. D. Chambers, J. A. H. MacBride, J. R. Maslakiewicz, and K. C. Srivastava, J.C.S. Perkin r, 1975,396.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

/-OH

433

(69) \:NH

7%

FH9

PhNHCO- C-CONHPh

PhNHCO-C-CONHPh 1 NMe, (71)

I

OMe (70)

been proposed to account for the novel photoisomerization of 2-pyridylacetonitrile to o-aminobenzonitrile.e2 Di-T-methane rearrangements have been observed on direct irradiation of benzoquinoxalinobicyclo[2,2,2]octatriene,65 and

6

Scheme 2

on direct and triplet-sensitized irradiation of the diazabicyclo[3,2,2]nona-3,8diene (74), the latter providing a synthetic entry into the diazabarbaralane system (75).64 0

Ph\NAN hv, sens

O%

1

OYN)-”

CH, (74)

sa sa 64

Y. Ogata and K. Takagi, J. Amer. Chem. Sac., 1974, 96, 5933. K. G. Srinivasan and J. H. Boyer, J.C.S. Chem. Comm., 1974, 1026. Z. Goldschmidt and Y . Bakal, Tetrahedron Letters, 1974, 2809.

434

Photochemistry

Although further examples of photochemically induced rearrangement of nitrones and N-oxides have been described this year, little novelty can be attached to most of these reports. The N-oxide (76), on irradiation in the presence of a proton source such as persulphate or dilute sulphuric acid, is converted into the corresponding 4-aryl-2H-1,4-benzoxazin-3(4H)-one (77) ;ss evidence for the pathway outlined in Scheme 3 involving the oxaziridine (78) as an intermediate is presented. 0-

I

CH=N, +

Ph

hv

~

OCH,C02H

OCH, CO,H

OCH,CO,H

0CH, CO, H

(77) Scheme 3

Heterocyclic N-oxides are well known to undergo a variety of rearrangements, ring-expansions, and ring-contractions on irradiation. These are usually interpreted as occurring via an unstable oxaziridine intermediate, although recently conflicting evidence has been advanced on this point. New evidence for the role of the oxaziridine has been described.66 In contrast to the large solvent effects on product composition observed in the irradiation of quinoline N-oxide and its 2-alkylated derivatives, the photochemistry of the 2-(trifluoromethyl)quinoline N-oxides (79) shows no such effect; 3,l-benzoxazepines (80) are the major

(79) R

=

H, Me, OMe, or CN

products in a wide variety of solvents. An oxazepine is also formed by irradiation of 2-styrylquinoline N-~xide.~'In the presence of BF,-etherate, however, analogous N-oxides appear to undergo only deoxygenation, leading to formation of the parent amine.68 An intermediate was identified spectroscopically in the 66

67

O8

A. R. Forrester, J. Skilling, and R. H. Thomson, J.C.S. Perkin Z, 1974, 2161. C. Kaneko, S. Hayashi, and Y. Kobayashi, Chem. and Pharm. Bull. (Japan), 1974, 22, 2147. I. Yokoe, M. Ishikawa, and C. Kaneko, Zyo Kizai Kenkyusho Hokoku, Tokyo Ika Shika Daigaku, 1972, 6, 18 (Chem. Abs., 1974, 81, 105233). N. Hata, I. Ono, and M. Kawasaki, Chem. Letters, 1975, 25.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

435

photorearrangement of 2,4,6-trimethylpyrimidine 1-oxide (81) to the imidazole (82) and the pyrimidone (83);6Bthis intermediate, which reverts to the N-oxide at room temperature, but not below, is believed to be the oxaziridine (84). Two oxaziridine intermediates are, however, possible in the rearrangement of pyrimidine l-oxides and various attempts have been made to predict the preferred direction of cyclization. Recent results with 2-methoxy- and 5-methoxypyrimidine 1-oxide appear to be in conflict with these earlier prediction^.^^ Irradiation of the 2-methoxy 1-oxide (85) in acetonitrile affords the enaminonitrile (86) and the imidazole (87) in approximately equal yields. The predicted regiospecificity therefore does not appear to prevail as formation of these products is best explained in terms of the two oxaziridine intermediates (88) and (89), as outIined in Scheme 4. The reported photoisomerization of l-hydroxy- to

3-hydroxy-xanthine may involve rearrangement of an intermediate n i t r ~ n e . ~ ~ The pyridazinone l-oxides (90) are converted on irradiation into the products (91)--(93), the formation of which can also, although somewhat tentatively, be rationalized in terms of an intermediate oxaziridine (Scheme 5).72 Direct deoxygenation to the parent pyridazinone is also observed. Other deoxygenations have been reported.78 Five-membered heterocyclic N-oxides undergo analogous ring-expansions. Thus, the nitrone (94) is converted into the oxazine (95).74 Support for the 6s

'O

'l

7s 74

F. Roeterdink, H. C. van der Plas, and A. Koudijs, Rec. Trau. chim., 1975,94, 16. F. Bellamy, P. Martz, and J. Streith, Tetrahedron Letters, 1974,3189. F. L. Lam, G. B. Brown, and J. C. Parham, J. Org. Chem., 1974,39,1391. T.Tsuchiya, H. Arai, M. Hasebe, and H. Igeta, Chem. and Pharm. Bull. (Japan), 1974, 22,

2301. M. Gladys and W. R. Knappe, Z. Naturforsch., 1974, 29b, 549; M. Nakagawa, T.Kaneko, H. Yamaguchi, T. Kawashima, and T. Hino, Tetrahedron, 1974,30,2591. M.Colonna and M. Poloni, Ann. Chim. (ZtaZy), 1973,63,287.

436

"no"00 Photochemistry

hv

=

-0 OMe I NHMe

0-N-N Me

Me

(90) R

MeOH>

H or Me R = 1-1

EII

N-N H Me (9 1)

O

O

/N Me

MeNH

(92)

(93)

Scheme 5

intermediacy of an oxaziridine in the previously reported photorearrangement of 5,7-di-t-butyl-3,3-methyl-3H-indole 1-oxide comes from the observation that the same products are obtained by peracid oxidation of the corresponding 3H-ind0le.'~ 2,1,3-Benzoselenadiazole N-oxide (96), however, behaves quite differently on irradiation and yields only benzofurazan (97).76

0(94)

0-

(97)

(96)

R

IlV

(99) 76 76

D. Dopp and H. Weiler, Tetrahedron Letters, 1974, 2445. C. L. Pedersen, J.C.S. Chem. Comm.,1974, 704.

(98)

Photoreactions of Compounds containing Heteroatoms other than Oyxgen

437

The results of separate photochemical studies of oxaziridines have been published. The azahomoadamantanes (98) can be prepared in 85-95% yield by irradiation of the spiroadamantane-oxaziridines (99).77 The photorearrangement of substituted spiro-oxaziridines and the effect of solvent on these rearrangements have also been exarnined.?8 Pyridinium and quinolinium ylides undergo many of the reactions associated with N-oxides. N-Iminopyridinium ylides, for example, are readily converted into 1H-1,Zdiazepines, whereas until recently N-iminoquinolinium ylides and analogous isoquinolinium ylides had given only 2-aminoquinolines and 1-aminoisoquinolines, respectively. Irradiation of the N-iminoquinolinium ylide dimers (100) has now been reported to give the 1H-1,2-benzodiazepines (101), presumably via the diaziridine (102).79 Whether the diaziridine is formed directly from the dimer (100) or from the monomer (103) is uncertain. Rearrangement without

R

. I

-NH

R

(104

(101)

ring-expansion has also been observed in certain 3-ethoxycarbonylimino-l-alkylbenzimidazolium ylides and in the quinoxalinium ylide (104)? Nitrogennitrogen bond cleavage leading to the formation of the parent heterocycle is the preferred pathway in a series of 3-benzoylimino-1-alkylbenzimidazoliumylides 8o and in benzo[c]cinnoline N-imide.82 A diaziridine may be an intermediate in the novel photorearrangement of the mesoionic pyridazines (105) into the pyrimidones (1 O 6 y 3 77

ID

8a

E. Oliveros-Desherces, M. Riviere, J. Parello, and A. Lattes, Synthesis, 1974, 812. E. Oliveros-Desherces, M. Rieiere, J. Parello, and A. Lattes, Tetrahedron Letters, 1975, 851. T. Tsuchiya, J. Kurita, H. Igeta, and V. Snieckus, J.C.S. Chem. Comm., 1974, 640. Y. Tamura, H. Hayashi, J. Minamikawa, and M. Ikeda, J. Heterocyclic Chem., 1974,11, 781. B. Agai, K. Lempert, and J. Mprller, Acta Chim. Acad. Sci. Hung., 1974, 80, 465. S. F. Gait, M. E. Peek, C. W. Rees, and R. S. Storr, J.C.S. Perkin I, 1975, 19. Y. Maki, M. Suzuki, T. Furuta, T. Hiramitsu, and M. Kuzuya, Tetrahedron Letters, 1974, 4 107.

Photochemistry

438

a>

hv, Pyrex

MeCN

’ 0

(105)

R

=

Me, Ph, p-C\C,H,, or p-MeC,H,

(106)

Further study of the photo-Beckmann rearrangement of oximes suggests that the reaction occurs by way of a concerted pathway from an excited singlet oxaziridine intermediate.8* Thus, in the rearrangement of syn- or anti-5Pcholestan-6-one oximes (107), which are photochemically interconvertible, the original configuration at C-5 is retained in both lactam products (108) and (109).

(1071

Analogous steroidal oxime acetates, on the other hand, are reported to give the oxime, the parent ketone, and products derived therefrom.8s Photochemically induced Beckmann rearrangements have also been observed in the oximes of pyridoxal and pyridoxal S - p h o ~ p h a t e .Other ~ ~ workers have isolated an unstable intermediate in the photorearrangement of pyridoxal oxime (1 10) which they suggest could be the oxaziridine (1 1l), although conclusive evidence is still lacking.*’ In the oximes of ap-unsaturated ketones, conversion into the corresponding ketone is known to be the major or even the exclusive reaction. Further 84 86

88

H. Suginome and H. Takahashi, Bull. SOC.Chem. Japan, 1975,48, 577. M. Onda and K.Takeuchi, Chem. and Pharm. Bull. (Japan), 1975,23,677. N.P. Bazhulina and M. P. Kirpicknikov, Mol. Photochem., 1974, 6,43. A. C. Ghosh and W. Korytnyk, Tetrahedron Letters, 1974, 4049.

Ho6cH Hofi=:&

Photoreactions of Compounds containing Heteroatoms other than Oxygen

439

O-NH \ /

Av

( 1 10)

(111)

studies have clarified certain aspects of the mechanism of this reaction.8s Irradiation ( A 254 nm) of diastereoisomeric mixtures of 4,4- and 5,5-dimethylcyclohex-Zenone oximes in iso-octane gave the corresponding ketones and hydrazine. The quantum yields for the disappearance of oxime increased markedly with concentration, suggesting a bimolecular reaction step either of the excited oxime or of a primary photoproduct such as an oxaziridine with ground-state oxime. A different and somewhat unexpected pathway is apparently preferred in o-hydroxyacetophenone oxime, which on irradiation in a wide variety of solvents is converted into the corresponding imine, presumably via an initial nitrogen-oxygen bond cleavage.8e Further examples of rearrangements resulting from intramolecular hydrogen abstraction by the excited aromatic nitro-group, typified by the well-known conversion of o-nitrobenzaldehyde into o-nitrosobenzoic acid, have been reported. In this connection, the o-nitrobenzyl group has again been widely used as a photolabile protecting group. Attached to the imidazole ring of histidine derivatives, for example, it can subsequently be removed under mild, highly specific conditions, by irradiation (Scheme 6).Q0The o-nitrobenzyl group is stable under

J. CH,-CHC0,H

7N0 Scheme 6

most of the conditions used in peptide synthesis, and is therefore widely used in this context. Two new resins, a 4-bromomethyl-3-nitrobenzoyl amide resin Q1and a 4-aminomethyl-3-nitrobenzoyl have been prepared and have proved suitable for the solid-phase synthesis of t-butoxycarbonyl-protected peptides *g

ga

P. Margaretha, Tetrahedron Letters, 1974, 4205. K. H. Grellman and E. Tauer, Tetrahedron Letters, 1974, 3707. S . M. Kalbag and R. W. Roeske, J. Amer. Chem. Soc., 1975,97,440. D. H. Rich and S. K. Gurwara, J. Amer. Chem. SOC.,1975,97, 1575. D.H. Rich and S. K. Gurwara, Tetrahedron Letters, 1975, 301.

Photochemistry

440

possessing a free C-terminal carboxy-group. The protected peptide acid is removed from the resin by irradiation at 350nm. Ribonucleosides bearing a photolabile o-nitrobenzyl protecting group may be regenerated without affecting either the purine or pyrimidine basesyn3and the o-nitrobenzyl group has been used for protecting the phosphate function in certain mononucleotide systems (Scheme 7).n4 0

\ t

hv (h > 305 nm)

AcO

Scheme 7

Two successive hydrogen abstractions are necessary to account for the reported conversion of 2,2‘-dinitrodiphenylmethane (1 12) into the diazepine (113); the dinitroso-compound (114) is a likely intermediate.n6 In contrast, irradiation of the same diphenylmethane (112) in the presence of sulphuric acid leads to

formation of the benzisoxazole (1 15);n6this may well be the result of irreversible acid-catalysed elimination of water from the intermediate (116), which in the absence of acid undergoes ring-cleavage to afford the mononitroso-compound. O3 94 g6 O6

D. C.Bartholomew and A. D. Broom, J.C.S. Chern. Comm., 1975, 38. M. Rubinstein, B. Amit, and A. Patchornik, Tetrahedron Letters, 1975, 1445. C. P. Joshua and P. K. Ramdas, Synthesis, 1974,12, 873. C. P. Joshua and P. K. Ramdas, Tetrahedron Letters, 1974,4359.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

441

Irradiation of the 3-epi-p-nitrophenyl acetate has been similarly employed to effect remote oxidation in dammarenediol ILQ7 A detailed account of the photochemistry of 1,3,5-tri-t-buty1-2-nitrobenzene (117) has now been published;98irradiation in a wide range of solvents or in the crystalline form leads to formation of the 3H-indole (1 18), which may be isolated. In Further irradiation gives, via the oxaziridine (1 19), the products (120)-(122).

be,, I

J.

di- or tri-ethylamine solution, photoreduction of the nitro-group takes place without any participation by the o-t-butyl group. Analogous reactions have been and more surprisingly in certain reported in other o-t-butylnitrobenzene~,~~ N-substituted 2,6-dinitroaniline~,~~~ the latter affording benzimidazolines, benzimidazoles, and benzimidazole N-oxides. The photochemistry of other o-nitroaniline derivatives has recently been investigated.l0lPlo2 Unlike other aryl-2-nitroprop-l-enes, which undergo rearrangement on irradiation, E-l-(9-phenanthryl)-2-nitroprop-l-ene (123) is converted into phenanthrene-9-carboxaldehyde (1 24), a process for which there is some precedent, and the furan (125).lo3 The reaction, which takes place on direct or camphorquinone-sensitized irradiation, appears to proceed via the Z-isomer, and R. Kasai, K. Shinzo, 0.Tanaka, and K.-I. Kawai, Chem. and Pharm. Bull. (Japan), 1974, 22, 1213.

D. Dopp and K.-H. Sailer, Chem. Ber., 1975, 108, 301. D. Dopp and K.-H. Sailer, Tetrahedron Letters, 1975, 1129. l o o E. Leitis and D. G . Crosby, J . Agric. Food. Chem., 1974, 22, 842. lol J. R. Plimmer and U. I. Klingebiel, J. Agric. Food Chem., 1974, 22, 689. loa G. A. M. Butchart, M. F. G. Stevens, and B. C. Gunn, J.C.S. Perkin I, 1975, 956. lo9 P. M. Crosby, K. Salisbury, and G. P. Wood, J.C.S. Chem. Comm., 1975, 312. n8

442

Photochemistry

I

the proposed pathway is outlined in Scheme 8. Rearrangement is observed in low yield on irradiation of 3-methyl-1-nitropyrazole.lo4 The conversion of the nitrouracil (126) into the triazole N-oxide (127) is best explained in terms of initial formation of the unstable isomer (128).106 Although NN'-dimethyl-p-hydrazotoluene (129; R = Me) readily undergoes rearrangement on irradiation, little is known of the mechanism of this reaction. Evidence for the involvement of an excited singlet state in formation of the o-semidine (130; R = Me) has now been advanced;lo6the quantum yield for formation of the o-semidine was not affected by the presence of a triplet quencher, cyclohexa-l,3-diene, nor was any o-semidine obtained on irradiation in the presence of a triplet sensitizer. Furthermore, irradiation of a mixture of the toluene derivative (129; R = Me) with the corresponding biphenyl derivative (129; R = Ph), under conditions (A 350nm) in which only the biphenyl compound would rearrange, led to formation of the expected products (130;R = Ph) and (131; R = Ph), together with a new hydrazo-compound (132). 'Crossed' J. W. A. M. Janssen, P. Cohen-Fernandes, and R. Louw, J. Org. Chem., 1975,40, 915. Y . Maki, M. Suzuki, K. Izuta, and S. Iwai, Chem. and Pharm. Bull. (Japan), 1974, 22, 1269. loo J.-D. Cheng and H. J. Shine, J. Ore. Chem., 1974, 39, 2835.

104

loL

Photoreactions of Compounds containing Heteroatoms other than Oxygen

443

Me Me

+

rearrangement products did not appear to be formed, and the authors therefore propose that the hydrazo-compound (132) is formed by a non-radical route, probably involving a four-centre process. In view of the lack of positive evidence, this suggestion must be treated with caution.

Rearrangements arising by carbonyl hydrogen abstraction are frequently of value in the synthesis of nitrogen-containing heterocycles. The NN-disubstituted /3-keto-amides (133), on irradiation in benzene, are converted into the 4-hydroxy2-pyrrolidinones (1 34), presumably by &hydrogen abstraction, in yields of up to 88%.lo7 Further reports of the cyclization of N-substituted phthalimides have been published. Irradiation of a series of N-alicyclic phthalimides (1 35) provides a route to the benzazepines (136) via the cyclobutanols (137);lo8 the cis-ring junction in the final product was confirmed by independent synthesis, The 107

lo8

T. Hasegawa and H. Aoyama, J.C.S. Chem. Comm., 1974, 743. Y.Kanaoka, K. Koyama, J. L. Flippen, I. L. Karle, and B. Witcop, J. Amer. G e m . Soc., 1974,96,4719.

444

Photochemistry 0

0

R 1-N-CCH2R2

hv,

I

I CH, R3 (1 34)

0

corresponding cyclization of N-o-arylalkylphthalimideshas been found to be dependent on alkyl chain length and on the nature of substituents present in the aromatic nucleus.1og Synthesis of the oxazolo[4,3-a]isoindole system can be similarly achieved by irradiation of N-alkyloxymethylphthalimides.lloConversion of the /3-aminovinyl phenyl ketones (138) into the pyrroles (139) is thought to involve an initial hydrogen abstraction and the intermediacy of the aziridine (140) as outlined in Scheme 9.ll1 The zwitterion (141) is similar to that proposed as an intermediate in the photoreaction of 2-aroylazetidine. The isomeric a/3-unsaturated amides (142) behave quite differently on irradiation in benzene and are converted in yields of up to 84% into the p-lactams (143).l12 This transformation is best explained in terms of an unprecedented hydrogen abstraction by the p-carbon atom as illustrated in Scheme 10. The anomalous type I1 photoreaction observed in butyrylpyrimidines leading to cyclopropanol rather than cyclobutanol formation has tentatively been accounted for in terms of y-hydrogen abstraction by a pyrimidine nitrogen atom.113 Y. Kanaoka and Y. Migita, Tetrahedron Letters, 1974, 3693. H. Nakai, Y. Sato, H. Ogiwara, T. Mizoguchi, and Y. Kanaoka, Heterocycles, 1974,2,621, ll1H.Aoyama, T.Nishio, Y. Hirabayashi, H. Noda, and N. Sugiyama, J.C.S. Perkin I, 1975.

log

298. 11*

113

T.Hasegawa, H.Aoyama, and Y. Omote, Tetrahedron Letters, 1975, 1901. E. C. Alexander and R. J. Jackson, J. Amer. Chem. SOC.,1974, 96, 5663.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

CH, R2 I N-CH2R3

0

2

445

CH2R3

~ H R Z 1

/1v

Ph'k&1

Ph

Ph

(138)

R1 R2

R'

0-+,CH2R3

-h;.H N

R2

1

.-4

2~ " '

Ph

R'

I CH,R3

CH2R3

(14!)

(139)

Scheme 9

,CH, Ph

R 2 ~0; c H 2 P h I1v

R1

Ph

H \

Ph

= H R' = Me, RP = H R1 = H, R2 = Me

(142) R1 = R2

CHzPh R1H2C R:.-;h (143)

Scheme 10

Intramolecular hydrogen abstraction has also been proposed to account for the specific deuteriation occurring on irradiation of the imine (144) in deuteriomethan01.l'~ The failure of imines in general to undergo hydrogen abstraction is usually attributed to facile radiationless deactivation accompanied by syn anti isomerization. Results of a recent study of cyclic imines in which syn + anti isomerization is not possible are in conflict with this expIanation.ll6 1,3-TriphenyIisoindolenineand l-methyl-, l-benzyl-, and l-phenyl-3,4-dihydroisoquinoline were found to be stable to irradiation in propan-2-01, methanol, --f

&A=

&NAc IIV

CH,

\ CH,D

(1.44) 11'

11i5

M. Saeki, N. Toshima, and H. Hirai, Bull. Chem. SOC.Japan, 1975, 48, 476. H. Ohta and K. Tokumaru, Tetrahedron Letters, 1974, 2965.

446

Photochemistry ether, or toluene. This lack of reactivity appears to be due to the high 7~n* character of their triplet states. 2-Methylindolines (145) are the major products of irradiation in cyclohexane but not in methanol of N-alkyl-2-allylanilines (146).ll6 The cyclization is thought to involve electron transfer from the excited aniline chromophore to the carboncarbon double bond followed by proton transfer to give the intermediate biradical (147). The ring-contraction of 2-acylpyrazolidin-3-ones(1 48) has also been

(148) R

=

( 149)

Me, Et, Pri, But, or CH,Ph

N COR IH

tTO

I

0

N--NKR f---

*o-

(1 50)

explained by intramolecular electron transfer leading to formation of the radicalanion radical-cation species (149).l17 The final products are /I-lactams (1 50) and are formed in yields of 2(t-65%.

+

[,2 m2] cycloadditions in nitrogen-containing Addition.-Intermolecular heterocycles continue to arouse interest, particularly in systems which are related to constituents of nucleic acids. Cyclobutane dimers are readily obtained on direct irradiation of furo[3,2-b]pyridin-2(4H)-ones and the pyrrolo[3,2-b]pyridin-2-one (151), although it is not possible on the basis of the evidence available to distinguish between the head-to-head (152) and the head-to-tail (153) structures.118 Cyclobutane dimers have also been obtained from alkyl4-stilbazole salts on irradiation in solution and in the solid state.l1° Examples of analogous ,2] cycloadditions have also been reported.lz09lZ1 The intramolecular [,2 [,2 + ,2] cycloaddition of quinol-2-one to furan has been described,122but

+

ll8 117

11*

121 12a

U. Koch-Pomeranz, H.-J. Hansen, and H. Schmid, Helv. Chim. Acta, 1975, 58, 178. P. Y. Johnson and C. E. Hatch, J. Org. Chem., 1975,40,909. G . Jones and J. R. Phipps, J.C.S. Perkin I, 1975, 458. F. H. Quina and D. G. Whitten, J. Amer. Chem. SOC.,1975, 97, 1602. R. Askani, I. Gurang, and W. Schwertfeger, Tetrahedron Letters, 1975, 1315. L. A. Paquette, D. R. James, and G. H. Birnberg, J. Amer. Chem. SOC.,1974, 96, 7454. T. S. Cantrell, J. Org. Chem., 1974, 39, 3063.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

447

R'

0 X X X

= = =

0,R1 = Ac, R2 = H NH, R = Ac, R2 = Br 0, R = Me, R" = H

"'

R1 (153)

+

although 9-cyanoanthracene forms a [*4 w4] adduct with furan, no adduct was obtained with l-methylpyrrole or with t h i 0 ~ h e n . l ~ ~ Further evidence has been advanced supporting the cis,syn stereochemistry proposed for the cyclobutane dimer of d(T,T) - dinucleoside m o n o p h ~ s p h a t e . ~ ~ ~ Isotope effects observed in the photosensitized dimerization of uracil suggest that an intermediate complex may be No deuterium isotope effect was, however, evident on the rate of photodimerization of thymine.128 Polymethylene bridges have again been employed to study intramolecular interactions between nucleic acid bases. 1,l '-Polymethylenebisthymineshave previously been studied in this connection, and, more recently, 1,1'-pentamethylenebisthyrnine (154) has been reported to undergo intramolecular dimerization of the thymine residues to give the photoproduct (155) in 20% ~ie1d.l~'This study has now been

hv

extended to 3,3'-, 1,3'-, and 1,5'-linked bisthymines, which on acetone-sensitized irradiation (A 300nm) are converted into the cis,syn-, the cis,anti-, and the trans,anti-cyclobutane derivatives, respectively.128 From the examples cited, it K. Mizuno, C. Pac, and H. Sakurai, J.C.S. Perkin I, 1974, 2360. F. E. Hruska, D. J. Wood, K. K. Ogilvie, and J. L. Charlton, Canad.J. Chem., 1975,53, 1193. las A. Kornhauser, J. B. Burnett, and G. Szabo, Croat. Chem. Acta, 1974, 46, 193. 126 R. F. Borkman and B. S. Yamanashi, Photochem. and Photobiol., 1974,19, 173. 127 K. Golankiewicz and B. Skalski, Bull. Acad. polon. Sci., Skr. Sci. chim., 1974, 22, 393. laa N. J. Leonard and R. L. Cundall, J. Amer. Chem. SOC.,1974,96, 5904.

12a

la'

Photochemistry

448

would appear that product structure is controlled by the positions of attachment of the linking polymethylene chains. Thus, for example, the 1,5’-polymethylene bridge (n = 2, 3, or 4) favours head-to-head addition and formation of the adduct (156). The structure and stereochemistry of the products of acetone-sensitized photoaddition of 1,3-dimethyIuracil to keten diethyl acetal, t-butyl vinyl ether, and vinyl acetate have been elucidated;12gcis- and trans-fused 8,8-diethoxy-2,4diazabicyclo[4,2,0]octane-3,5-diones(157) and (158) are obtained in the ratio M e N 5

AN

O

JIV, Me,CO CH2=C(OEt),

MeN%

~

OEt

OAN Me

Me (159)

OEt

(157)

+

MT% *

OEt #eH

OEt

(158)

84 : 16 and in an overall yield of 85% on irradiation of 1,3-dimethyluracil (159) with keten diethyl acetal, whereas only cis-fused photoproducts were obtained from the other two alkenes. The precise requirements for the successful cycloaddition of alkenes to the carbon-nitrogen double bond remain uncertain, although various explanations have been advanced to account for the observed lack of 1,3-Dimethyl-6-azauracil and 1,3-dimethyl-6-azathymine, however, undergo high-yield cycloaddition to a variety of alkenes including ethylene, tetramethylethylene, isobutylene, ethyl vinyl ether, vinyl acetate, and isopropenyl acetate. With ethyl vinyl ether and 1,3-dimethy1-6-azauracil(1 60), for example, epimeric azetidines MJ ,e N 5

0

E~OCH=CH,Z M IIV

N” Me (160.)

e

N

&NHN Me (161)

s

:6 (162)

(161) and (162) were obtained in comparable yields. The corresponding addition of 6-azauracils to isopropenyl acetate or cyclohexenyl acetate forms the basis of a versatile high-yield synthesis of 5-substituted 6 - a ~ a u r a c i l s . ~ Somewhat ~~ surprisingly, three analogous imino-lactones, namely 5,6-dihydro-3,5,5-trimethyl-, 5,6-dihydro-5,5-dimethyl-3-phenyl-, and 3- butyl-5,6-dihydro-5,5-dimet hyl- 1,4oxazin-2-one, are unreactive in this respect.132 This lack of reactivity is attributed to the fact that, at least in the singlet excited state, these molecules have lowenergy nn* states, whereas low-energy n7r* states are thought to be involved in cycloaddition. 21 cycloaddition of sym-triazoIo[4,3-b]pyridazine (163) to The unusual [3 alkenes has been extended to cis- and tr~ns-hex-3-ene;l~~ in each case, six products

+

lag 130 131

132

lS3

J. S. Swenton, J. A. Hyatt, J. M. Lisy, and J. Clardy, J. Amer. Chem. SOC.,1974, 96, 4885. J. S. Swenton and J. A. Hyatt, J. Amer. Chem. SOC.,1974, 96, 4879. J. S. Swenton and R. J. Balchunis, J. Heterocyclic Chem., 1974, 11, 453. T. H. Koch, J. A. Olesen, and J. DeNiro, J. Org. Chem., 1975,40, 14. J. T. Carlock, J. S. Bradshaw, and W. Zmolek, Tetrahedron Letters, 1975, 2049.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

G:' (163)

449

CH2CN I1v

> E t f i )

+

E*t

N-N

N-N

hex-3-ene

Et

Et (1 65)

(164)

were obtained, the cis- and trans-5H-pyrrolo[l ,Zb]sym-triazoles (164) and the four isomeric cyano-sym-triazoles (165). A 1,l-adduct, the pyridazine-3,5-dione (166), was obtained by irradiation of azobenzene (167) in chloroform in the presence of diketen (168).134 The addition arises via the more reactive cisazobenzene and may involve the spiro-intermediate (169), although there is no real evidence to support this postulate.

(147)

(166)

Cycloaddition is not observed on irradiation of indole or substituted indoles in the presence of acrylonitrile. The corresponding 3-(2-cyanoethyl) derivatives (170) are obtained from indole (171; R1 = R2 = H), 2-methylindole (171; R1 = Me, R2 = H), and 1,2-dimethylindole (171; R1 = R2 = Me), and a

mechanism involving exiplex formation has been proposed to account for these t r a n ~ f o r m a t i o n s .Proton ~ ~ ~ transfer to the acrylonitrile group appears to be an important step in the decay of the exiplex. A more recent report describes the preferred N-cyanoethylation of indole, benzimidazole, and carbazole on irradiation with acrylonitrile in a~efonitri1e.l~~ Exiplex formation is again implicated. lS4 lS5 lS6

T. Kato, M. Sato, and K. Tabei, J. Org. Chem., 1974, 39, 3205. K. Yamasaki, T. Matsuura, and I. Saito, J.C.S. Chem. Comm., 1974,944. K. Yamasaki, I. Saito, and T. Matsuura, Tetrahedron Letters, 1975, 313.

Photochemistry

450

Examples of the addition of solvent molecules to nitrogen-containing heterocycles, arising uia initial hydrogen abstraction from the solvent, have again been described. The mechanism of this reaction with reference to six-membered aza-aromatic compounds has been the subject of a recent review,137and in the reaction of acridine with alcohols and ethers, a radical-pair intermediate has been detected.13* Hydrogen abstraction is also implicated in the conversion of 4-quinolinecarbonitrile (172) into the alcohol (173) on irradiation in the

dihydroquinoline intermediate (174) was not isolated in this case, presumably owing to its rapid oxidation to the heteroaromatic quinoline. 2-Quinolinecarbonitrile is converted into the corresponding 2-hydroxyalkylquinoline on irradiation in ethanol or t-butyl alcohol by what is, at least formally, a substitution r e a ~ t i 0 n . lIn ~ ~fact, an analogous pathway initiated by hydrogen abstraction and followed by elimination of HCN rather than oxidation of the dihydroquinoline is almost certainly involved. Results using a variety of solvents indicate that hydrogen abstraction by the nitrogen atom is facilitated by hydrogen-bond formation. Photoaddition of methanol to the purine (175) to afford the 1,6-dihydropurine (176) is a vital step in the synthesis of c ~ f o r m y c i nthe ; ~ ~addition, ~ which takes

AcoH2wAcoH2d 11v

'

M~OH

AcO OAc (175)

place in 96% yield, is surprisingly stereospecific. Direct irradiation ( A > 260 nm) of caffeine, adenine, or guanosine with tetrahydrofuran, tetrahydropyran, dioxan, tetrahydrofurfuryl alcohol, or dioxolan led to formation of the appropriately 13'

138

A. Castellano, J. P. Catteau, A. Lablache-Combier, B. Planckaert, and G. Allan, Khim. geterotsikl. Soedinenii, 1974, 7, 867. G. Vermeersch, N. Febvay-Garot, S. Caplain, and A. Lablache-Combier, Tetrahedron, 1975, 31, 867.

139

140 141

N. Hata, I. Ono, and H. Suzuki, Bull. Chem. SOC.Japan, 1974, 47, 2609. N. Hata and T. Saito, Bull. Chem. SOC.Japan, 1974, 47, 942. M. Ohno, N. Yagisawa, S. Shibahara, S. Kondo, K. Maeda, and H. Umezawa, J. Amer. Chem. SOC.,1974,96, 4326.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

45 1

8-substituted purine, again via a dihydr~-intermediate.l*~Yields of up to 90% of the same products were obtained on irradiation ( A > 290 nm) in the presence of peroxides as photoinitiators. The well-documented photoaddition of alcohols to pyrimidines is suppressed in the presence of purines.143 Irradiation in propan2-01 with peroxide as initiator of a mixture of uracil and thymine in the presence of purines gave only the corresponding 8a-hydroxyalkylpurine adducts ; the failure of uracil and thymine to undergo photoaddition is attributed to base association in solution. Direct m* excitation of 4,6-dimethylpyrimidinol (177) in methanol gave the adduct (178), whereas in propan-2-01 the major product is the dihydro-dimer (179).144 In contrast to earlier reports, the photoaddition of HOHJ,

ethanol to NN-1,3-dimethyluracil (180) occurs in an analogous fashion to yield the adduct (181).lP6 Similarly, U.V. irradiation of DNA in the presence of propan2-01 and di-t-butyl peroxide led, after liberation of the purine bases with mild acid, to the selective production of 8a-hydroxyisopropyladenineand 8a-hydroxyis~propylguanine.~~~ The influence of acid on these additions is considerable. In ethanol, for example, ethyl nicotinate is converted into the corresponding 6a-hydroxyethylpyridineY whereas in acidified solution the 6-ethylpyridine derivative is The function of the acid may, of course, simply be to promote dehydration of the intermediate 6a-hydroxyethyldihydropyridine. Phthalazine and quinoxaline are converted by irradiation in acidified methanol into 1-methylphthalazine and 2-methylquinoxaline, respecti~e1y.l~~ In this case, however, there is evidence to suggest that the alkylations proceed by way of electron transfer from the solvent to an excited state of the protonated diazines; in neutral solution, a hydrogen D. Leonov and D. Elad, J. Org. Chem., 1974,39, 1470. D. Leonov and D. Elad, J. Amer. Chem. SOC.,1974,96, 5635. 144 K.-H. Pfoertner, Helv. Chim. Acta, 1975, 58, 865. M. D. ShetIar, Tetrahedron Letters, 1975, 477. la6 J. Salomon and D. Elad, Biochem. Biophys. Res. Comm., 1974, 58, 890. F. Takeuchi, T. Sugiyama, T. Fujimori, K. Seki, Y. Harada, and A. Sugimori, Bull. Chem. SOC.Japan, 1974, 47, 1245. ld8 S. Wake, Y. Takayama, Y. Otsuji, and E. Imoto, Bull. Chem. SOC. Japan, 1974,47, 1257.

laa 143

452

Photochemistry

abstraction pathway is again proposed. Competitive reaction pathways, namely photo-hydroxyethylation and photo-ethoxylation, have been observed with 2-cyanopyridine (182).149 The alcohol (183) is believed to arise by a radical mechanism involving initial hydrogen abstraction, whereas the ether (1 84) is I1v

EtO

CN

H

EtOH-HI-

EtOH-H-

H (183)

( 1 82)

(184)

formed via an excimer. Support for the role of an excimer in the photochemical alkoxylation of methyl pyridine-2-carboxylatehas also been described.lS0 The isolation of two diastereoisomeric photohydrates of 2’-deoxyuridine has been achieved.lS1 The quantum yields for the photohydration of the dansylpyrimidones (185) are much lower than those for the parent pyrimidones.ls2 This difference is ascribed to intramolecular energy transfer from the absorbing uracil chromophore to the fluorescent dansyl component ;intermolecular quenching of the photohydration of uracil is unknown. 0

CH,CH,CH,NH 70,

NMe, (185)

R

=

H or Me

CONHCH,C02H H&S,-CH2(H \

0%)

H

NHCOCH,CH,CH(NH,)CO,H

(1 86)

Glutathione enhances the photochemical reactivity of pyrimidines in aqueous solution. With thymine, the major products of this reaction are the sulphide (186; It = 1) and the disulphide (186; n = 2), higher concentrations of glutathione favouring formation of the latter.ls3 Triplet-sensitized irradiation (A > 290 nm) led to increased yields of the adducts. The photoaddition of cysteine to T. Furihata and A. Sugimori, J.C.S. Chem. Comm., 1975, 241. T. Sugiyarna, T. Furihata, Y. Edamoto, R. Hasegawa, G. P. Sato, and A. Sugimori, Tetrahedron Letters, 1974, 4339. lK1 I. Pietrzykowska and D. Shugar, Acfa Biochem. Polon., 1974, 21, 187. lLa J. G. Burr, W. A. Summers, and Y. J. Lee, J. Amer. Chem. SOC.,1975,97, 245. lKa A. J. Varghese, Photochem. and Photobiol., 1974, 20, 339.

140

lK0

Photoreactions of Compounds containing Heteroatoms other than Oxygen

453

uracil has also been described.lb* Three photoproducts, (1 87)-(189), have been identified, and there is indirect evidence for formation of a fourth (190). Uracils (187) and (188) are the principal products of irradiation ( A > 290 nm) in acetone and presumably arise from triplet uracil. Uracils (189) and (190), on the other

(1 87)

(1 88)

R

=

( 190)

(1 89) -CH,CH(NH,)CO,H

hand, are the major products of irradiation ( h > 240 nm) in aerated solution and are thought to result from the addition of the thiyl radical to ground-state uracil. Other miscellaneous reactions arising at least in part by photoaddition have been reported. The photoaddition of primary and secondary amines to 1,2-diphenylcyclopropane(191) has been described in detai1.ls6 Irradiation in

n-butylamine, for example, gave a 57% yield of the adduct (192). The corresponding addition of cyclohexylamine to dibenzosemibullvalene proceeded stereoselectively, there being a pronounced preference for the formation of the more hindered syn-isomer. Mechanistic details are not yet clear although an exciplex may be involved. Photoaddition of isopropylamine to alkynes has been reporfed.lss Irradiation of nitrogen(v) oxide, NzOs, with adamantane leads to formation of 1-adamantyl nitrate, 1-nitroadamantane, adamantanone, and 2-nitroadamantane in the ratio 5.5 :4.4: 2.2: l.15' Reaction occurs via the triplet state of NaOs, quantum yield measurements indicating a typical chain character; NOs is shown to be the chain carrier. A dimeric adduct (193) was obtained by irradiation of benzaldehyde and t-butyl isocyanide in benzene or acetonitrile.ls8 Little is known of the mechanism of this unusual reaction, although the intermediacy of 0 Ph - //

cXNBut 6 - C N

B u t N H C-Ph

d

(195)

MeOH It,,

~

SH (194)

(193) lS4

lSa lS7

lS8

A. J. Varghese, Biochim. Biophys. Acta, 1974, 374, 109. S. S. Hixson, J . Amer. Chem. SOC.,1974, 96, 4866. L. M. Kostochka, E. P. Serebryakov, andV. F. Kucherov, Zhur. org. Khim., 1974, 10, 1822. I. Tabushi, S. Kojo, and Z . Yoshida, Chem. Letters, 1974, 1431. R. P. Widera, L. A. Singer, R. Easton, and F. A. L. Anet, J.C.S. Chem. Comm., 1974, 784.

Photochemistry a reactive imino-oxiran, which rapidly dimerizes, has been proposed. The formation in low yield of the imino-ether (194) from the a-cyano-ketone (195) can be rationalized in terms of ring-cleavage and subsequent radical addition to the c y a n o - g r o ~ p .The ~ ~ ~3(2-H)-pyridazinones (1 96) undergo a novel ring-contraction accompanied by addition of methanol to yield the two pyrrolin-Zones (197) and (198).lao The most plausible explanation for this transformation is outlined in Scheme 11, involving a reactive diaziridine intermediate. 454

(196)

I

R1 K2 Rd II H H MeH H H MeH H H Me H 'H H OMe Ph

MeOH.

R'

R 2

R Me0

3

n0

i HCHO --

N I

4

N%ir,

N H, (197)

(198)

Scheme 11

Miscellaneous Reactions.-A recentIy reported simple synthesis of ( 2 )-perhydrohistrionicotoxin is based on nitrite photolysis.lsl Irradiation of the nitrite (199) results in functionalization of the cyclopentane ring and formation of the oxime (200) via a typical Barton reaction pathway; the isomeric oxime arising by functionalization of the t-butyl group is also formed. 12-Hydroxyimino-derivatives are similarly obtained by photolysis of certain (20S)-20-nitrosyloxy-30norlupanes, although surprisingly the corresponding 20R-nitrates do not undergo this reaction.ls2 The direct photo-oximation of saturated hydrocarbons by

Me

Me

"

C

/ \

Me

Me

(20 1)

IfV+

Me

Me

Me

CH=N-OH

\C/ / \

(202)

G. K. Chip and T. R. Lynch, Canad. J. Chem., 1974,52,2249. l o o T. Tsuchiya, M. Hasebe, H. Arai, and H. Igeta, Chem. and Pharm. Bull. (Japan), 1974, 22,

lsS

2276. laa

E. J. Corey, J. F. Amett, and G. N. Widiger, J . Amer. Chem. SOL, 1975,97,430. A. Vystrcil and V. Pouzar, Coll. Czech. Chem. Comm., 1974, 39, 2961.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

455

photolysis in the presence of nitrosyl chloride has been further investigated. By using a new method of anhydrous work-up, methyl groups can now be converted into the corresponding aldoximes;ls3 thus, 2,2-dimethylpropane (201) affords the oxime (202). Photolysis of a N-nitrosamide under an inert atmosphere and in the presence of oxygen has previously been demonstrated to functionalize specifically the &position with respect to the amide nitrogen atom, leading to the formation of the corresponding C-nitroso- and C-nitrato-derivatives respectively. Two nitrosamides, N-nitroso-N-acetyldehydroabietylamineand N-nitroso-N-methylo-toluamide (203), have been used to illustrate applications of this reaction.ls4 In the latter case, the two expected products, namely the oxime (204) and the

II I 0 NO (203)

CH=N-OH

CHZONOZ

C-NHMe

C-NHMc

0

0

(204)

(205)

II

/I

nitrate ester (209, are themselves subject to further photochemical or thermal reaction. The mechanism of N-nitroso-N-methylacetamidephotolysis has been the subject of detailed investigations using flash excitation methods and steadystate quantum yield determinations.lsa The acetamido-radical is apparently generated from lowest singlet excited N-nitroso-N-methylacetamide.Spectra observed in a more recent study at 123 K (A 405 nm) have been assigned to the unstable rotamer of the nitrosamide.lss Arninium radicals are readily generated by photolysis of N-nitrosodialkylamines in dilute acid solution. A study of the relative reactivities of m- and p-substituted styrenes towards piperidinium radical addition has been described.ls7 There exists good evidence that the aminium radical is an electrophilic species, and the polar effects observed in this addition are thought to be the result of ground-state electrostatic attraction between the positive charge of the aminium radical and the welectrons of the styrene. The intramolecular addition of photochemically generated aminium radicals has been employed in the synthesis of the 2-azatricyclo[4,3,1,04,e]decane(206).lSs Formation of a pyrrolidine is also preferred in the irradiation in benzene of the unsaturated N-chloro-amide (207).laa The reaction, which is initiated by photolysis of the nitrogen-chlorine bond has been employed in the synthesis of y-lactam (208). Photochemically initiated HofmannLoeffler-Freytag cyclizations, for example in the synthesis of ( 5 )-dihydrodeoxyepiallocernuine (209), have again been described.l7O8171 163

lS4 16(

lB6 Is' 16*

E. Muller and A. E. Bottcher, Chem. Ber., 1975, 108, 1475. J. N. S. Tam, T. Mojelsky, K. Hanaya, and Y. L. Chow, Tetrahedron, 1975, 31, 1123. J. N. S. Tam, R. W. Yip, and Y. L. Chow, J. Amer. Chem. SOC.,1974,96,4543. R. S. Lowe, J. N. S. Tam, K. Hanaya, and Y. L. Chow, J. Amer. Chem. SOC.,1975,97,215. T. Mojelsky and Y. L. Chow, J. Amer. Chem. SOC.,1974, 96, 4549. R. W. Lockhart, K. Hanaya, F. W. B. Einstein, and Y. L. Chow, J.C.S. Chem. Comm., 1975, 344.

ld0

*'l

M. E. Kuehne and D. A. Home, J. Org. Chem., 1975,40, 1287. Y. Ban, M. Kimura, and T. Oishi, Heterocycles, 1974, 2, 323. R. Tadayoni, J. Lacrampe, A. Heumann, R. Furstoss, and B. Waegell, Tetrahedron Letters, 1975, 735.

456

Photochemistry

COMe

The light-induced degradation of pyrazolinone drugs has been reviewed.17a Decomposition is initiated in all cases by homolysis of the nitrogen-nitrogen bond and is frequently accompanied by formation of aziridinones. The 4-amino3-pyrazolin-3-one (21 0), on irradiation in aqueous solution, is converted into the products (211) and (212), expected by analogy with the behaviour of other NH2

MeN>o

0 (2 10)

0

I1

5

0

C-NHPh Me-C-OH /

+

\

C-NHMe II

I

COzH

(212)

0 (21 1)

+

17a

II

Me-CH-C-NPh I

J. Reisch, Deut. Apoth.-Ztg., 1974, 114, 2028.

0 COMe II I PhNH-C-C-N=C,

0 II C-NHPh

/

Photoreactions of Compounds containing Heteroatoms other than Oxygen

457

pyrazinones, together with the unusual adduct (213).173 Competitive nitrogennitrogen and carbon-nitrogen bond cleavage resulting in formation of amides and amines, and aldehydes and acids, respectively, was observed in a series of benzoic and acetic acid h y d r a ~ i d e s . ~ ~ ~ Photochemically induced ring-expansion of the spiro-/?-carboline (214) provides a valuable route to the decadehydroyohimban-21-one(215).176 The

synthesis of the alkaloid oxogambirtannine has been achieved in a similar fa~hi0n.l’~lY2-Dihydrophthalimide(216 ) undergoes a variety of transformations Formation of benzene, benzamide, on irradiation (A 257 nm) in a~etonitri1e.l~~ and the isomer (217) are thought to arise by initial a-cleavage as outlined in Scheme 12, a 1,2-acyl shift being responsible for formation of (217). Other

E\

Z 0H

I”

>

0

NH

(217) Scheme 12 173

17‘ 176

17* 177

J. Reisch and A. Fitzek, Arch. Pharm., 1974,307, 21 1. A. C. Watterson and S. A. Shama, J. Org. Chem., 1975, 40, 19. T. Kametani, H. Takeda, Y. Hirai, F. Satoh, and K. Fukumoto, J.C.S. Perkin I, 1974,2141. H. Irie, J. Fukudome, T. Ohmori, and J. Tanaka, J.C.S. Chem. Comm., 1975, 63. G. Scharf and B. Fuchs, J.C.S. Chem. Comm., 1975,244.

458 Photochemistry minor photoproducts are phthalimide and the bicyclo[2,2,0]hexene(218). Results of the direct and sensitized irradiation of 0-acetylindoxyl have been p~b1ished.l~~ 2 Sulphur-containing Compounds A wide variety of rearrangement reactions have again been reported in sulphurcontaining compounds. cis -+ trans-Isomerization is observed on irradiation of a series of higher polysulphur analogues (219) of 1,2-dithio1-3-ylidene ketones in ethanol containing a catalytic amount of hydrogen chloride;17* the trunsphotoproduct (220) rapidly reverts to the cis-isomer by a dark process which

s-s

s-s , A A

RlJzyy+ (220)

(219)

obeys first-order kinetics. A 1,3-sigmatropic shift has been proposed to account for the photochemical conversion of 8-thiabicyclo[3,2,1]oct-3-en-2-one(221) into the bridged 3-thietanone (222),lS0whereas the rearrangement of several N-vinylsulphonamides to the corresponding /3-sulphonylvinylaminesis thought to involve a chain reaction.lsl

Not surprisingly, the thianaphthalene (223) is easily isomerized on irradiation to the thiopyran (224),la2 and exo-2,3-epithio-5-norbornene(225) has been reported to undergo ring-cleavage on irradiation in acetonitrile to give the isomer

Ph (223)

17*

180 lal

lsa

(224)

K. Oe, M. Tashiro, and 0. Tsuge, Heterocycles, 1974, 2, 663. C. T. Pedersen, C. Lohse, and M. Stavaux, J.C.S. Perkin I, 1974, 2722. H. Tsuruta, M. Ogasawara, and T. Mukai, Chem. Letters, 1974, 887. W. R. Hertler, J . Org. Chem., 1974, 39, 3219. M. Hori, T. Kataoka, and H. Shimizu, Chem. and Pharm. Bull. (Japan), 1974,22, 2485.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

Ii

(226).lS3 cis- and trans-Dibenzoylstilbenesare known to be the products of photodecomposition of a compound to which the 2,3-diphenylthiiran structure (227) was originally assigned. Recent work supports the viewpoint that this compound is, in fact, a lY3-oxathiole(228) which undergoes a thermally reversible rearrangement to the thiiran (227) on irradiation.ls4 Similarly, a series of 2,5dialkyl-2,5-dihydrothiophensundergoes ring-contraction on irradiation, producing

vinylthiirans which on desulphurization are converted into dienes.les Irradiation of the dihydrothiophen (229), for example, yields the two unstable thiirans (230) and (231), which are readily converted into the corresponding dienes. Convincing evidence for a biradical intermediate arising by initial carbon-sulphur bond cleavage in the dihydrothiophen has been presented. Related sulphoxides and sulphones undergo essentially the same photoreactions. The Dewar thiophen structure (232) of the photoproduct of tetrakis(trifluor0methy1)thiophen (233) has been confirmed.186 The possible intermediacy of a

valence-bond isomer of this structure or of a thiocarbonyl derivative in the photoreaction of thiophens with n-propylamine to give the corresponding pyrroles has been A symmetry-allowed disrotatory cyclization has been reported for the benzo[b]thiepin (234; R = N-piperidino) to give the cyclobutene (235).lsa The analogous hydroxybenzo[b]thiepin (234; R = OH) undergoes a secondary photoreaction to give the isomer (236), presumably via the stabilized biradical (237). The sulphene (238), arising by photochemical ring-cleavage, is lqs

IH6

T. Fujisawa and T. Kobori, Japan Kokai, 74/42 677 (Chem. A h . , 1974, 81, 135 999). U. Jacobsson, T. Kempe. and T. Norin, J . Org. Chem., 1974.39, 2722. R. M. Kellog and W. L. Pins, J. Org. Chem., 1974,39, 2366. Y. Kobayashi, I. Kumadaki, A. Ohsawa, and Y. Sekine, Tetrahedron Letters, 1974, 2841. A. Couture, A. Delevallee, A. Lablache-Combier, and C. Parkanyi, Tetrahedron, 1975, 31, 785.

D. N. Reinhoudt and C. G. Kouwenhoven, Tetrahedron, 1974, 30, 2431.

460

Photochemistry

(234)

Photoreactions of Compounds containing Heteroatoms other than Oxygen

461

proposed as an intermediate in the conversion of 2H-1-benzothiopyran 1,l-dioxide (239) into the sulphinate esters (24O)-(242).lsQ Surprisingly, it did not prove possible to trap the sulphene with methanol or with reactive dienophiles. The major product of irradiation of the isomer (243) in methanol is the adduct (244), although a low yield of sulphinate ester (245) was also obtained. The reason for the differing behaviour of these isomers is not clear. A new synthesis of 3-arylcycloalkanones is based on the photocyclization of 2-thioaryloxyenones (246) to the corresponding dihydrothiophens (247), followed by desulphurization.lQoConrotatory cyclization to give an intermediate thiocarbonyl ylide (248), and subsequent 1,4-hydrogen migration, are presumably involved in the formation of the dihydrothiophen. Photochemical cyclodehydrogenation of 1-(benzothien-3-~1)-2-( 1-naphthyl)ethylene gave the expected pentacyclic product on irradiation in cyclohexane in the presence of iodine, whereas the isomer (249) was converted into the product (25O).lo1 The latter result contrasts with known examples of /3-styrylnaphthalene

(249)

photocyclization, all of which take place at the a-position. Thiobenzoates normally undergo photochemically induced carbon-sulphur bond cleavage leading to fragmentation and formation of a variety of products. Two exceptions to this behaviour have been reported ; the 2-azathioxanthone (251) has been obtained by irradiation of the S-aryl thionicotinate (252),lo2and a photo-Fries rearrangement, albeit in low yield, has been described.los &Hydrogen abstraction is preferred in the photochemistry of aralkyl thiones (253) and leads to formation of cyclopentanethiols (254).lQ4In sharp contrast, the thione (255), lacking a %hydrogen atom but having activated y- and &-hydrogen atoms, is converted into products (256)-(258). Unlike ketones, aralkyl thiones show photochemical behaviour which is dependent on excitation wavelength, and from such studies 6- and c-cyclizations have been shown to be essentially a consequence of excitation to a higher excited state. Photorearrangement of an aryl thione has been used in a synthesis of ( k ) - c ~ p a r e n e . ~ ~ ~ C. R. Hall and D. J. H. Smith, Tetrahedron Letters, 1974, 3633. A. G. Schultz, J. Org. Chem., 1974, 39, 3185. lg1 A. Croisy, P. Jacquignon, and F. Perin, J.C.S. Chem. Comm., 1975, 106. lea G. Buchholz, J. Martens, and K. Praefcke, Angew. Chem., 1974, 86, 562. lS3 D. Rungwerth and K. Schwetlick, Z . Chem., 1974, 14, 17. lS4 P. de Mayo and R. Suau, J . Amer. Chem. SOC.,1974,96, 6807. lB5 P. de Mayo and R. Suau, J.C.S. Perkin I, 1974, 2559. l*@

loo

16

462

Photochemistry

(255)

(256)

(257)

The quantum yield for photodimerization of thianaphthene 1,l -dioxide is enhanced in the presence of bromoethane.1g6 The increase is not due to solvent polarity; it does, in fact, appear to be the result of enhanced intersystem crossing to the reactive triplet. Cycloaddition reactions of the thione group have also attracted attention, particularly those occurring in pyrimidine thiones. The isolation of thietans, previously proposed as intermediates in the photoaddition of electron-deficient alkenes to thiouracil derivatives, has now been realized ;le7 in this way, for example, the dihydrouracil (259) is converted into the adduct

Mb O

N Me

+

/Me CH2=C, CN (26 1)

IIV

~

Me

R1

(264)

(260) by reaction with methacrylonitrile (261). A necessary condition to stabilize

these thietans is substitution at N-3 in the uracil. In the absence of such substituents, as in 4-thiouridine triacetate (262; R1 = ribosyl triacetate, Rt = H) and 4-thiothymidine diacetate (262; R1 = deoxyribosyl diacetate, Rg = Me), lD8

W. W. Schloman and B. F. Plummer, J.C.S. Chem. Comm., 1974, 705. J. L. Fourrey, P. Jouin, and J. Moron, Tetrahedron Letters, 1974, 3005.

Photoreactions of Compounds containing Heteroatoms other than Oyxgen

463

reaction with acrylonitrile and with methacrylonitrile affords the adducts (263) and (264), respectively.lQ8The formation of these adducts can best be explained through the intermediacy of an unstable thietan. Intermediates in the decomposition of the thietan (265), obtained from 3-methyl-4-thiouraciland methacrylonitrile, have been detected.lQQOn irradiation in dichloromethane, products (266) and (267) were obtained, whereas in methanol there is good evidence for intermediates (268) and (269). The pathway proposed is outlined in Scheme 13.

MeN

H

Cycloaddition of thioparabanates to a variety of electron-donor and electronacceptor alkenes, giving the appropriate thietans in high yield, has been reported.2oo With ethoxyethylene, for example, the adduct (270) is obtained in 88% yield. The use of light with A > 400 nm is essential as it provides selective excitation to the nn* state on which the success of the addition depends. The formation of thietans by the addition of thiophosgene 201 and aromatic thionecarbonates 202 to alkenes has also been described. An unusual photodimerization of l-hydroxypyridine-2-thione (271) has been reported;e03the dimer (272) is further converted into 1,6-diazathianthrene (273) on heating at 100 "C. lD* lee

*01

aoz 203

C. Fombert, J. L. Fourrey, P. Jouin, and J. Moron, Tetrahedron Letters, 1974, 3007. P. Jouin and J. L. Fourrey, Tetrahedron Letters, 1975, 1329. H. Gotthardt and S. Nieberl, Tetrahedron Letters, 1974, 3397. H. Gotthardt, Chem. Ber., 1974, 107, 2544. H . Gotthardt and M. Listl, Chem. Ber., 1974, 107, 2552. M. Edrissi, H. Kooshkabadi, and I. Lalezari, Microchem. J., 1974, 19, 282.

464

Photochemistry

?-

Photoaddition of the dithiazole-3-thione (274; X = N) and of the dithiole-3thiones (274; X = CH or CPh) to alkenes leading to formation of the 1,3dithiolans (275) has been described.204The reactions are non-stereospecific, the same mixture of isomers being obtained with cis- and trans-but-2-ene, and a radical pathway (Scheme 14) has therefore been proposed. Two separate reports

3

(275)

Scheme 14

of photoaddition of 4,5-benzo-l,2-dithiole-3-thione (276) to alkenes 206 and cycloalkenes 206s 208 have been published, leading in both cases to formation of deep-blue o-thioquinomethides (277) which are in thermal equilibrium with the colourless dimers formed by [4 + 41 dimerization. Evidence favours the head-tohead structure (278) for these dimers. Irradiation of 2-acetylthiophen with tetramethylethylene or isobutene results in [,/+ I *2] addition of thiophen to the alkene; oxetan formation is a minor pathway in this Examples of the 204 206 208

ao7

R. Okazaki, F. Ishii, K. Okawa, K. Ozawa, and N. Inamoto, J.C.S. Perkin I, 1975, 270. P. de Mayo and H. Y. Ng, J.C.S. Chem. Comm., 1974, 877. R. Okazaki and N. Inamoto, Chem. Letters, 1974, 1439. T. S. Cantrell, J. Org. Chem., 1974, 39, 2242.

Photoreactions of Compounds containing Heteroatoms other than Oxygen R

465

R

R

(278)

addition of alkylthioacetylenes to phenanthraquinone,208to 1 , 2 - d i k e t o n e ~and ,~~~ to phenylglyoxal 209 have been described. The final step in the synthesis of 4-thia-5j3-cholestane (279) involves stereospecific intramolecular addition of the photochemically generated thio-radical to the double bond.21o An analogous cyclization must be responsible for the formation of 1,l-dimethyl-l-sila-5-thiacyclo-octane (280) from hydrogen sulphide

2\ HS

Me,

F

MeNS< (281)

H

hV

HzS

Me, ,Si

fl

Me k

S

(282)

hv

H

Me,

M

n e

O

U

(280)

and dimethyldiallylsilane (281);211 the thiol (282) is also converted photochemically into the cyclo-octane (280) and is presumably an intermediate in the addition of hydrogen sulphide. This is a remarkable cyclization in view of the problems associated with the synthesis of medium-ring compounds from alicyclic precursors. Excitation of adamantanethione in the nr* band in the presence of the corresponding thiol yields exclusively diadamant-2-yl disulphide ; evidence for a chain process has been presented.212 Irradiation of 4-thiouracil in the presence of sodium borohydride leads to formation of 2-oxohexahydropyrimidine.213 No dimerization or addition of solvent is observed. Alkanethiols are reported to undergo photoaddition with trialkylethynylgermanes and with trialkylethynyl~tannanes.~~~ The cyclic sulphite 4-ethyl-S-methyl-1,3,2-dioxathiolan 2-oxide has been prepared by the photosulphoxidation of trans-pentao8 210 211

A. Mosterd, R. E. L. J. Lecluijze, and H. J. T. Bos, Rec. Trav. chim., 1974,94, 72. A. Mosterd, H. J. Matser, and H. J. T. Pos, Tetrahedron Letters, 1974, 4179. D. N. Jones, D. A. Lewton, J. D. Msonthi, and R. J. K. Taylor, J.C.S. Perkin I, 1974, 2637. K. E. Koenig, R. A. Felix, and W. P. Weber, J. Org. Chem., 1974, 39, 1539. J. R. Bolton, K. S. Chen, A. H. Lawrence, and P. de Mayo, J. Amer. Chem. Sac., 1975, 97, 1832.

als 214

E. Sat0 and Y . Kanaoka, Chem. and Pharm. Bull. (Japan), 1974,22,799. M. G. Voronkov, R. G. Mirskov, and V. I. Rakhlin, Zhur. obshchei Khim., 1974, 44, 954.

466 Photochemistry 2-ene using sulphur dioxide in the presence of oxygen.216The proposed mechanism involves formation of a charge-transfer complex between sulphur dioxide and the alkene and is consistent with the participation of the triplet state of the former. Sulphur dioxide has also found use in the trapping of photochemically generated 1,4-biradical~.~l~ 3 Compounds containing other Heteroatoms

The photochemistry of silicon-containing compounds has attracted increased attention with the publication of some interesting results. In particular, studies of the effect of the inclusion of silicon in organic molecules which undergo wellknown photochemical reactions have been initiated. The photochemical isornerization of 1-silacyclohexa-2,4-dienesshould be of interest because the proposed intermediates and products are the elusive silahexatrienes and silacyclopropanes. In fact, irradiation through Pyrex of the diphenyl derivative (283) affords the bicyclic product (284) via the silahexatriene (285);217convincing

0iMe3 Ph

Ph (283)

Ph ,hv

.L

~

Ph (285; not isolated)

GM.; Ph

Csim

Ph (284)

Y Ph

Ph (287)

Ph (289; not isolated)

evidence for the intermediacy of the (285)comes from the isolation of the adduct (286) in the presence of methanol. In contrast, the tetraphenyl derivative (287) gave the cyclobutene (288), although again there was evidence for the intermediacy of the corresponding hexatriene (289). 1,6-Disilahexa-l,3,5-trienehas alb 21(1 217

P. W. Jones and A. H. Adelman, Tetrahedron, 1974, 30, 2053. R. M. Wilson and S. W. Wunderly, J. Amer. Chem. Soc., 1974, 96, 7350. Y. Nakadaira, S. Kanouchi, and H. Sakurai, J. Amer. Chem. Soc., 1974, 96, 5621.

Photoreactions of Compounds containing Heteroatoms other than Oxygen

467

similarly been proposed as an intermediate in the photorearrangement of 1,2-disilacyclohexa-3,5-dienes.218 Di-wsilane photochemistry is apparently different from di-wmethane photochemistry.a1g No isomerization to silacyclopropanes was observed on irradiation of the di-?.r-silanes(290), the sole products being the cispans-isomers (291) and (292). Rearrangement together with solvent incorporation was observed,

however, on irradiation ( A 350 nm) of the 4,4-disubstituted 4-silacyclohexa-2,5dienones (293) in t-butyl an intermediate zwitterionic species (294) is proposed by analogy with the corresponding carbocyclic systems. Further evidence for the existence of a silacyclopropane has been reported in the reaction of the photochemically generated silylene species (295) with cyclohexene.221The initially formed silacyclopropane (296) reacts readily with methanol to give the cyclohexylmethoxysilane (297) and undergoes rearrangement on further irradiation to 3-silylcyclohexene (298). 1,1-Dimethyl-2-phenyl-l-silacyclobutanealso

218 218 220

221

Y.Nakadaira, S. Kanouchi, and H. Sakurai, J. Amer. Chem. SOC.,1974, 96, 5623.

E. Krochmal, D. H. O’Brien, and P. S. Mariano, J. Org. Chem., 1975, 40, 1137. T. M. Koch, J. A. Soderquist, and T. H. Kinstle, J. Amer. Chem. SOC.,1974,96, 5576. M. Ishikawa and M. Kumada, J . Organometallic Chem., 1974, 81, C3.

Photochemistry

468

undergoes photochemical ring-cleavage in methanol to give 3-phenylpropyldimethylmethoxysilane, the product expected of simple nucleophilic attack.222 This behaviour is in contrast with that of 1,1-diphenyl-1-silacyclobutane. The photolysis of 2-phenylheptamethyltrisilane (299) in the presence of 2,3-dimethylbutadiene leads to formation of products (300)-(302).223 The diene Me I Me,Si-Si-SiMe, I Ph

I”

+

Me,SiSiMe,

Ph’

Me

> Me?3: Ph/

I“ Me3Si-Si-CH I I Ph SiMe,

?’

/ \

Me Ph

H

J.

,Si/ Me \

(300) and the silacyclopentene (301) are believed to arise via the unstable silacyclopropane (303), whereas a novel pathway involving a 1,l-addition of the silicon-silicon bond has been proposed to account for formation of (302). Analogous reactions have been observed for the photodecomposition of 2-phenylheptamethyltrisilane in the presence of alkenyltrimethyl~ilanes.~~~ A useful synthesis of allylsilanes has been described using a photocatalysed 1,dhydrosilation of 1 , 3 - d i e n e ~ Addition .~~~ of trichlorosilane and trimethylsilane to tetrafluoropropyne has been reported and a radical pathway proposed.226 Triethylsiloxy nitroxide radicals have been generated by photolysis of 2-nitroand 3-nitro-thiophen in triethyl~ilane.~~~ Irradiation of the 7-silabicyclo[2,2,1]hepta-2,5-diene (304) in benzene gives dimethyl tetraphenylphthalate (305) in 88% yield.2Z8As there is no evidence for

aa7

P. B. Valkovich, T. I. Ito, and W. P. Weber, J. Org. Chem., 1974, 39, 3543. M. Ishikawa, F. Ohi, and M. Kumada, J. Organometallic Chem., 1975, 86, C23. M. Ishikawa, F. Ohi, and M. Kumada, Tetrahedron Letters, 1975, 645. M. S. Wrighton and M. A. Schroeder, J. Amer. Chem. SOC.,1974, 96, 6235. R. N. Haszeldine, C. R. Pool, and A. E. Tipping, J.C.S. Perkin Z, 1974, 2293. C. M. Camaggi, L. Lunazzi, G. F. Pedulli, G. Placucci, and M. Tiecco, J.C.S. Perkin IZ, 1974,

228

R. Balasubramanian and M. V. George, J. Organometallic Chem., 1975, 85, 131.

aab a2L

1226.

Photoreactions of Compounds containing Heteroatoms other than Oxygen M: ,Me

469

I1v -SiMe2’

Ph

C0,Me

(304)

(305)

M\e ,Me Ph hv

Ph

~

0

/ \

Me Mc (306)

0

radical intermediates in this decomposition, a symmetry-allowed loss of the dimethylsilylene moiety may be implicated. A different pathway is observed in the analogous anhydride (306). Photodecarbonylation is a vital step in a synthesis of dihydroxycyclopropenone.22Q The photochemistry of acylsilanes has been reviewed.230The application of CIDNP to the study of acylsilane photolysis in carbon tetrachloride casts doubt on the accepted mechanism (a Norrish type I cleavage yielding an acyl-silyl radical pair) and provides support for the initial formation of an acylsilane-carbon tetrachloride exciplex followed by selective Ph 0

\4

0

OMe Ph 0

II

(309)

0

(307) Me,CO-benzene

Ph I

aso

D.Eggerding and R. West, J . Amer. Chem. SOC.,1975, 97, 207. A. G . Brook, Intra-Sci. Chem. Reports, 1973, 7 , 131.

470

Photochemistry

collapse of this to an acetyltrichloromethyl singlet radical pair and silyl Little of significant interest has been reported concerning the photochemistry of organophosphorus compounds. The successful photoaddition of 3-phenyl2H-azirine to diethyl benzoylphosphonate has been described,2a2and details of the photodecomposition of disodium a-D-glucose 6-phosphate 233 and phosphorus ylides 234 have been published. Singlet and triplet states of l-phenylphosphole oxide dimer (307) are chemically reactive, but lead to entirely different Direct irradiation in methanol gave methyl phenylphosphinate (308) as the only isolable product ; the expected dihydrophosphindole (309) could be neither detected nor trapped. Sensitized irradiation, on the other hand, in 1 : 3 acetone-benzene solution gave the cage product (310). The first study of the solution-phase photochemistry of organoselenium compounds has been reported.23e In the absence of oxygen, irradiation of dibenzyl diselenide affords dibenzyl monoselenide as the major product (60%) together with other unidentified products and a trace of elemental selenium. a31 a3a

a33 a34

Ba6 a36

N. A. Porter and P. M. Iloff, J. Amer. Chem. SOC.,1974, 96, 6200. N. Gakis, H. Heimgartner, and H. Schmid, Helu. Chim. Actu, 1975, 58, 748. C. Triantaphylides and M. Halmann, J.C.S. Perkin ZZ, 1975, 34. H. Diirr, D. Barth, and M. Schlosser, Tetrahedron Letters, 1974, 3045. H. Tomioka, Y. Hirano, and Y. Isawa, Tetrahedron Letters, 1974, 4477. W. Stanley, M. R. Van De Mark, and P. L. Kumler, J.C.S. Chem. Comm., 1974,700.

7 Photoelimination BY S. T. REID

This chapter is principally concerned with the photochemically induced fragmentation of organic molecules accompanied by the formation of small molecules such as nitrogen, carbon dioxide, and sulphur dioxide. Photodecompositions resulting in the formation of two or more sizeable fragments are reviewed in the final section. Fragmentations arising by Norrish type I and I1 reactions of carbonyl-containing compounds are considered in Part 111, Chapter 1. 1 Photodecomposition of Azo-compounds The photolysis of azoalkanes is an attractive route for the generation of alkyl radicals ; studies of this photodecomposition leading to formation of benzyl radicals,l cyclohexyl radicalsY2and methyl and trifluoromethyl radicals have been reported. Photodecomposition of phenylazotriphenylsilane, Ph,SiN=NPh, in carbon tetrachloride has been shown to be the result of initial silicon-nitrogen and carbon-nitrogen homolytic bond cleavage^.^ Both isomerization and elimination of nitrogen are observed on irradiation of a series of alkyl aryl diazosulphides (1).5 Irradiation (A > 400 nm) leads to interconversion of

6 -

+ x o s - R

hv

N=N

/

S-R

(2)

+

(3)

R-S-S-R (4)

a

+

R-SH

(5)

(1) K. J. Skinner, H. S. Hochster, and J. M. McBride, J. Amer. Chem. Sac., 1974, 96, 4301. J. L. Currie, H. W. Sidebottom, and J. M. Tedder, J.C.S. Faraduy I, 1974, 70, 1851. N. L. Craig and D. W. Setser, J. Chem. Kinetics, 1974, 6, 517. H. Watanabe, Y. Cho, Y. Ido, M. Matsumoto, and Y. Nagai, J. Organometallic Chem., 1974, 78, C4. J. Brokken-Zijp, TetrahedronLetters, 1974, 2673.

47 1

472

Photochemistry

Z- and E-isomers, whereas photodecomposition (A > 365 nm) occurs only from the 2-isomer and yields products (2)--(5). As in previous years, much time and effort have been devoted to the study of the photochemistry of cyclic azo-compounds. Photoreactions of this type offer a unique opportunity to examine the mechanism of this decomposition, and also provide a useful synthetic route to cyclopropane derivatives. Irradiation of several steroidal 4’/?,5-dihydro[17a,16-~]pyrazolesleads exclusively by elimination of nitrogen to cyclopropa[l 6aY17a]compounds.6 The penicillin derivatives (6) are similarly converted into the cyclopropanes (7).’ Complete retention of

(6) R = OMe, OAc, or OH

H

k

(7)

H

(9)

configuration is observed in the direct photolysis of l-pyrazolines (8) and (9) in benzene solution, whereas in the corresponding benzophenone-sensitized irradiation, mixtures of isomers are obtained.8 Singlet and triplet excited states, respectively, are believed to be implicated. Quantum yields for the elimination of nitrogen from a series of substituted l-pyrazolines have been determined and range from 0.12 to 0.88.O 4-Oxo-l-pyrazoline is, however, comparatively stable under identical conditions, being 0.012. l-Acetyl-5,5-dimethylbicyclo[2,lYO]pentane and 1-acetyl- and 1-acetyl-6,6-dirnethyl-bicyclo[3,1,O]hexane have been successfully prepared by triplet-sensitized elimination of nitrogen from the appropriate pyrazolines.1° The direct and sensitized photolysis of the homopyrazoline (10) and its possible role as an intermediate in the decomposition of bis-l-pyrazolines have been

O

lo

P. Bladon, D. R. Rae, and A. D. Tait, J.C.S. Perkin I, 1974, 1468. R. J. Stoodley and N. S. Watson, J.C.S. Perkin I, 1974, 1633. C. Benezra and N. D. Tho, Tetrahedron Letters, 1974, 4437. P. S. Engel and L. Shen, Canad. J. Chem., 1974,52,4040. P. S. Engel and M. A. Schexnayder, J. Amer. Chem. SOC.,1975,97, 145.

473

Photoelimination

examined.ll Direct irradiation of pyrazoline (10) leads to formation of the bicyclobutane (ll), the isomeric dienes (12) and (13), and the cyclopropene (14). Products (1 1)-(13) are also obtained, although in significantly different

R

relative yields, on irradiation of the diazoalkene (15), a possible intermediate in the decomposition of the pyrazoline (10). Benzophenone-sensitized irradiation of the bispyrazolines (16; R = C0,Me) and (16; R = CN) l2 affords the dienes (17; R = C02Me or CN) in virtually quantitative yield. The major product of

photolysis of the azo-compound (18) is not the cyclopropane (19) but the triene (20);13formation of both products as well as two other minor products (21) and (22) can easily be rationalized in terms of a biradical intermediate arising from elimination of nitrogen. The photochemistry of mono- and bi-cyclic pyrazolines in which the postulated biradical intermediate is allylic in character has been studied in some detail. Direct or sensitized irradiation of the diazabicyclooctadiene (23) yields predominantly the cyclopropane (24a; R1 = H, R2 = Me) together with the isomer (24b; R1 = Me, R2 = H):14 the photoreaction therefore proceeds with retention of configuration whereas inversion is observed in the corresponding thermal reaction. Similar observations are recorded for other l1

M. Franck-Neumann, D. Martha, and C. Dietrich-Buchecker, Tetrahedron Letters, 1975, 1763.

la la la

M. Franck-Neumann and D. Martha, Tetrahedron Letters, 1975, 1767. M. J. Wyvratt and L. A. Paquette, TetrahedronLetters, 1974, 2433. M. Schneider, Z . Naturforsch., 1974, 29b,290.

474

Photochemistry

hv

-N,

R1 R2

(24) a; R1 = H, R2 = Me b; R1 = Me, R2 = H

bicyclic vinyl-1-pyrazolines l6 and for exo-4-methyl-2,3-diazabicyclo[4,3,0]nona2,8-diene.le A diallylic lY3-biradicalhas been proposed as an intermediate in the photodecomposition of a mixture of cis- and trans-3,5-divinyl-l-pyrazolines(25) and (26) which gives trans-l,2-divinylcyclopropane(27) and cyclohepta-lY4-diene (28), the latter derived either from the thermally unstable cis-isomer (29) or

directly from the biradica1.l' Further study of this photolysis at low temperatures led to the detection of the cis-isomer and confirmation of its role as a precursor of cyclohepta-1,4-diene.le Photoelimination of nitrogen from the azo-compound (30) to give octamethylsemibullvalene (31) proceeds at a rate comparable with that for 3,3'-a~oprop-l-ene.~~ The failure to prepare the isomeric azo-compound (32), however, is believed to be a consequence of orbital symmetry considerations; the concerted elimination of nitrogen is forbidden in the case of azocompound (30) but allowed in (32). l6

l6 l1

M. Schneider, A. Erben, and I. Merz, Chem. Ber., 1975,108, 1271. M. Schneider and A. Erben, 2.Naturforsch., 1974,29b,228. M. Schneider and G. Mossinger, Tetrahedron Letters, 1974, 3081. M. P. Schneider and J. Rebell, J.C.S. Chem. Comm., 1975,283. Y . C. Toong, W. T. Borden, and A. Gold, Tetrahedron Letters, 1975, 1549.

475

Photoelimination

N=N

(30)

Examples of the photoelimination of nitrogen from triazolines and the sub21 In particular, triazoline sequent formation of aziridines have been ring-contraction has been investigated as a possible synthetic route to mitomycins.22 Irradiation of the triazolines (33), in the presence of a triplet quencher

0

(33) R

=

H, CH,OMe, or CH,OCH,Ph

0 (34)

(piperylene) to suppress further reaction, produced the aziridines (34). Reversible ring-opening of the aziridines (35), obtained by irradiation of the aryltriazolines (36), gave deeply coloured solutions of the isoquinolinium betaine (37).23 Under the same conditions, the corresponding alkyltriazolines were recovered unchanged.

3H-PyrazolesYon irradiation, are analogously converted into cyclopropenes or products derived therefrom. Much discussion has centred around the mechanism of this photoelimination, and evidence both for biradical intermediates and for vinyl azo intermediates has been reported. The dibenzo[2,4]spirenes (38) are obtained in good yield by irradiation of the spiropyrazoles (39);24 pathways involving vinylcarbene and biradical intermediates have been proposed and are outlined in Scheme 1. The effect of substituents on the photofragmentation of other spiropyrazoles has been d o ~ u r n e n t e d . Irradiation ~~ of the 3H-pyrazoles (40) results in formation of the isomeric vinyl diazo-compounds (41); these are stable for hours at room temperature in benzene Further irradiation ao s1

sa 34 16

L. H. Zalkow and R. H. Hill, Tetrahedron, 1975, 31, 831. D. M. Stout, T. Takaya, and A. I. Meyers, J. Ore. Chem., 1975,40, 563. 0.J. Siuta, R. W. Franck, and R. J. Kempton, J. Org. Chem., 1974, 39, 3739. P. E. Hansen and K. Undheim, J.C.S. Perkin I, 1975, 305. H. Diirr, W. Schmidt, and R. Sergio, Annalen, 1974, 1132. H. Diirr, A. C. Ranade, and I. Halberstadt, Tetrahedron Letters, 1974, 3041. G. E. Palmer, J. R. Bolton, and D. R. Arnold, J. Amer. Chem. SOC.,1974, 96, 3708.

476

Photochemistry

hv ___+

-N2

\

R

f j q R R

\ / (39) R

=

C0,Me

___, -Na

& \ /R

Scheme 1

of (41) at room temperature gave the cyclopropenes (42) in good yield. Strong e.s.r. signals, assigned to vinylmethylene triplets, were detected on irradiation of the pyrazoles at 5 K. Other examples of cyclopropene formation from pyrazoles have been rep~rfed.~'

R' (40)

RL = R2 = Ph R' = Ph, R2 = COMe R1 = C02Me, R2 = Ph

(41)

R'

1 (42)

The major product of photolysis of l-methoxy-l,2,3-benzotriazole(43) in benzene, methanol, and acetonitrile (but not cyclohexane) is azobenzene (44), although 1,2,3-benzotriazole (45) is also formed.26 The formation of these two 27

M. I. Komendantov and R. R. Bekmukhametov, Khim. geterotsikl. Soedinenii, 1975, 79. M. P. Serve, J. Org. Chem., 1974, 39, 3788.

477

Photoelimination

Scheme 2

products can be rationalized in terms of competing loss of nitrogen and nitrogenoxygen bond cleavage as shown in Scheme 2. Elimination of nitrogen followed by intramolecular hydrogen transfer is implicated in the conversion of l-hydroxy1,2,3-benzotriazole (46) into nitrosobenzene (47).29 The matrix photolysis of

1,2,3-thiadiazole (48) has been examined with a view to obtaining evidence for the involvement of thiiren.sO Previously, both thiirens and thioketens have been proposed as intermediates in this decomposition. Spectral evidence for the thioketen (49)has now been obtained on irradiation ( A > 220 nm) in an argon or nitrogen matrix, but the most likely precursor of the other photoproduct, ethynethiol (SO), is thiiren (51). Ethynethiol is not formed from the thioketen (49).

M. P. Serve. J. Heterocyclic Chem., 1974, 11, 245. A. Krantz and J. Laureni, J. Amer. Chem. SOC.,1974, 96, 6768.

Photochemistry Photoelimination of nitrogen from six-membered cyclic azo-compounds also occurs readily. Irradiation of the thermally unstable 1,4-dihydrophthalazine (52) at 77 K in a matrix led to formation of a species having the spectral properties of o-xylylene (53).31 On further irradiation, (53) is converted into benzocydobutene

478

(54). o-Xylylene is stable indefinitely in the matrix but dimerizes rapidly at higher temperatures to give the spiro dimer (55). On irradiation, the azo-compound (56) is converted into the cyclobutane (57) and the diene (58); e.s.r. evidence for

the intermediacy, at least in part, of a triplet 1,s-naphthoquinodirnethane is

presented.32 Elimination of nitrogen and formation of vinylacetylene have been reported in the gas-phase photolysis of p y r i d a ~ i n e .kradiation ~~ of the 3H-1,2benzodiazepine (59; R = H) in dichloromethane gave 3-vinylindazole (60) and indene (61; R = H) in 90 and 2% yield, respectively, whereas irradiation of the corresponding 5-methyldiazepine (59; R = Me) gave only the indene (61; 81

sa 8s

C. R. Flynn and J. Michl, J. Amer. Chem. Soc., 1974, 96, 3280. R. M. Pagni, C. R. Watson, J. E. Bloor, and J. R. Dodd, J . Amer. Chem. Soc., 1974,96,4064. J. R. Fraser, L. H. Low, and N. A. Weir, Canad. J. Chem., 1975,53, 1456.

479

Photoelimination

H

R = Me).3* These results suggest that (60) and (61) are formed from the key intermediate (62) by competing 1,3-hydrogen migration and elimination of nitrogen. The photolysis of a number of 3-aryl-3H-diazirines has been inve~tigated.3~ Two pathways were observed, photoelimination of nitrogen, resulting in formation of the arylcarbene, and photorearrangement to the aryldiazomethane, which itself undergoes further photoreaction. A second intermediate, which on irradiation is converted into the aryldiazomethane, has been tentatively identified as the 7aH-indazole. The photolyses of 3-halogeno-3-phenyldiazirines have been re-investigated and are now claimed to yield ‘free’ phenylhalogenocarbene~.~~ A novel synthesis of a benzimidazo[l,2-c]benzopyrimidine(63) has been achieved

by photoelimination of nitrogen from 4-(benzotriazol-l-yl)-2-phenylquinazoline (64).37 2 Elimination of Nitrogen from Diazo-compounds Photoelimination of nitrogen from diazo-compounds is a simple and versatile process for the generation of carbenes. The diazoadamantane (65) is a surprisingly stable compound which on irradiation yields the hydrocarbon (66), the azine (67), and the alcohol (68) via the ~ a r b e n e .The ~ ~ origin of the oxygen atom 84

86

J. Kurita and T. Tsuchiya, J.C.S. Chem. Comm.,1974,936. R. A. G. Smith and J. R. Knowles, J.C.S. Perkin 11, 1975, 686. R. A. Moss and F. G. Pilkiewicz, J. Amer. Chem. SOC.,1974, 96, 5632. A. J. Hubert, J. Heterocyclic Chem., 1974, 11, 737. J. H. Wieringa, H. Wynberg, and J. Strating, Tetrahedron, 1974, 30, 3053.

480 l-Ad\ ,C=Nz l-Ad (65)

Photochemistry hv ]-Ad\ + CH2

l-Ad’

+

l-Ad\ 1-Ad l - A d , ~ = ~ ~ = ~ ’ \l-Ad

(66)

+

l-Ad\ l-Ad’

(67)

CHOH

(68)

in the alcohol (68) is uncertain as attempts were made to exclude oxygen and water from the reaction. An explanation involving formation of vibrationally excited propylene as an intermediate has been advanced to account for the gas-phase photodecomposition of d i a z ~ p r o p a n e .The ~ ~ 2-pyridyldiazomethane l-oxides (69), on irradiation in benzene or methanol, are converted into the

(69) (70) 2-acylpyridines (70).40 AIternative mechanisms have been considered for this novel elimination, and although there is no direct evidence for the formation of a free carbene, such a species may well be involved. Spectroscopic evidence for the carbene cyclopentadienylidene (71) has been observed in the photodecomposition of diazocyclopentadiene (72) in a lowtemperature Dimerization of the carbene to afford fulvalene (73) occurs

(74)

on raising the temperature to 30 K, and in the presence of carbon monoxide the carbene is converted into the keten (74). Photolysis of substituted diazocyclopentadienes in the presence of alkynes has been reported to afford the corresponding spiro[2,4]heptatrienes in moderate yield, although 1,3-dipolar addition of the diazo-compound to the alkyne is a competing reaction.42 Electron-donor alkynes give a higher yield of spiro[2,4]heptatriene, thereby demonstrating the electrophilic character of cyclopentadienylidene. Other evidence for the electrophilicity of this species has been published.4s Adducts (75) and (76) are obtained 89 40

41 42

J. M. Figuera and E. Fernandez, J. Phys. Chem., 1974,78, 1348. R. A. Abramovitch, C. S. Menon, M. Murata, and E. M. Smith, J.C.S. Chem. Comm., 1974, 693. M. S. Baird, I. R. Dunkin, and M. Poliakoff, J.C.S. Chem. Comm., 1974, 904. H. Diirr, B. Ruge, and B. Weib, Annalen, 1974, 1150. H. Diirr and F. Werndorff, Angew. Chem. Internat. Edn., 1974, 13, 483.

Photoelimination

481

by reaction of the carbene obtained from photodecomposition of 9-diazofluorene (77) with 1,l-dicyclopropylethylene (78).44 The ratio of (75) to (76) is much higher in the photodecomposition than in the analogous thermolysis.

The photolyses of diethyl mercurybisdiazoacetate and ethyl diazoacetate in chloroalkanes have been compared, the former yielding mainly carbon-chlorine insertion products and the latter products derived by free-radical pathway.46 A new class of radicals, the organosilicon iminamino radicals, were detected in the irradiation of diphenyldiazomethane in the presence of silanes, the radicals Photobeing formed by the addition of silyl radicals to diphenyldia~omethane.~~ elimination of +trogen from diazomethyltrimethylsilane yields trimethylsilylcarbene (Me,SiCH), which reacts with diazomethyltrimethylsilane,trans-but-2ene, and ethylene to give trans-2,2,5,5-tetramethyl-2,5-disilahex-3-ene, trans-l,2dimethyl-3-trimethylsilylcyclopropane,and trimethylsilylcyclopropane, respecti~ely.~’ Direct irradiation of methyl diazoacetate is known to result in reactions characteristic of singlet methoxycarbonylcarbene. In the presence of benzaldehyde, evidence for energy transfer leading to triplet methoxycarbonylcarbene Triplet methoxycarbonylcarbene has been obtained from CIDNP readily abstracts hydrogen atoms from hydrocarbons, whereas singlet methoxycarbonylcarbene did not show any evidence of hydrogen abstraction. Oxazoles are the major products of photoelimination of nitrogen from l-phenyl-2,2dimethoxy-2-(alkoxycarbonylamino)diazoethanes and are believed to arise by intramolecular addition of the photochemically generated carbene to the carbonyl gr0up.49 The photoelimination of nitrogen from diazoketones and the fate of the resulting species are still subjects of major interest. A successfulphotochemically induced Wolff rearrangement of an acyclic /3y-wnsaturated diazo-ketone in aqueous dioxan has been reported.6o In the photodecomposition of the diazo-ketone (79), formation of the keten (80) by elimination of nitrogen and rearrangement is followed by intramolecular photoaddition to give the cyclobutane (8 1).61 Two reports of the photochemistry of a/3-epoxydiazo-ketones have been published. Irradiation of l-diaza-3,4-epoxy-4-phenylbutan-2-one (82) in methanol 44 ‘6 46

47

4a

6o

61

N . Shimizu and S. Nishida, J. Amer. Chem. SOC.,1974, 96, 6451. T. B. Patrick and G . H. Kovitch, J. Org. Chem., 1975, 40, 1527. P. P. Gaspar, C.-T. Ho, and H. Y. Choo, J. Amer. Chem. SOC.,1974, 96, 7818. R. N. Haszeldine, D. L. Scott, and A. E. Tipping, J.C.S. Perkin I, 1974, 1440. H. D. Roth and M. L. Manion, J. Amer. Chem. SOC.,1975,97, 779. M. L. Graziano, R. Scarpati, and E. Fattorusso, J. Heterocyclic Chem., 1974, 11, 529. J. P. Lokensgard, J. O’Dea, and E. A. Hill, J . Org. Chem., 1974,39, 3355. D. Becker, Z. Harel, and D. Birnbaum, J.C.S. Chem. Comm., 1975, 377.

482

Photochemistry

gave the ester (83) in 62% yield;62the most likely pathway for this conversion would appear to involve nucleophilic addition of methanol to the keten accompanied by ring-cleavage, as illustrated in Scheme 3. On irradiation in benzene

Ph

Ph

PhY

O

M

e

OH (83)

Scheme 3

of a series of such diazo-ketones (84), the intermediate ketens (85) undergo spontaneous ring-expansion to give the butenolides (86).63 Photolysis of a series of unsymmetrical 2-diazo-l,3-diketones was studied with a view to comparing

the migration capability of various substituents in the Wolff rearrangement ;64 this was found to decrease in the order Me > Et > Ph > But. The phosphorus analogue (87) undergoes a remarkable series of transformations on irradiation in benzene in the presence of unsaturated ketones to give the dienes (88).66 The proposed pathway is outlined in Scheme 4. 62

63 64

b6

N. F. Woolsey and M. H. Khalil, Tetrahedron Letters, 1974, 4309. P. M. M. van Haard, L. Thijs, and B. Zwanenburg, Tetrahedron Letters, 1975, 803. V. A. Nikolaev, S. D. Kotok, and 1. K. Korobitsyna, Zhur. org. Khim., 1974, 10, 1334. H. Eckes and M. Regitz, Tetrahedron Letters, 1975, 447.

483

Photoelimination

R3

c=c/\

R2

R4

Scheme 4

Rearrangement of the carbenes generated by photoelimination of nitrogen from cyclic diazo-ketones is frequently accompanied by ring-contraction. This process has found extensive use in synthesis; recent examples include the synthesis of the [7]paracyclophane ring systemYs64,8-dihydrodibenzo[cdYgh]~entalene,~' 2,2,4,4-tetramethylcyclobutanecarboxylicacid,s8 and the carboxy-/Ilactams (89).s9 Ring-contraction was not observed on irradiation of the unstable

a-diazo-y-butyrolactone (go), the major products being the bis-y-lactone (91) and the a/3-butenolide (92) derived respectively from the carbene by dimerization and hydrogen shift.60 a-Oxocarbenes, generated by photolysis of certain aliphatic and aromatic a-diazo-ketones, have been shown to undergo isomerization to the oxiren. No such isomerization appears to be implicated in the photodecomposition of the labelled diazo-ketone (93), which on irradiation in aqueous dioxan is converted 67

tiB

O0

N . L. Allinger, T. J. Walter, and M. G. Newton, J . Amer. Chem. SOC.,1974, 96, 4588. B. M. Trost and P. L. Kinson, J . Amer. Chem. SOC.,1975, 97,2438. L. L. Rodina, V. V. Bulusheva, and I. K. Korobitsyna, Zhur. org. Khim., 1974, 10, 1937. G. Stork and R. P. Szajewski, J. Amer. Chem. SOC.,1974, 96, 5787. A. Schmitz, U. Kraatz, and F. Korte, Chem. Ber., 1975,108, 1010.

484

Photochemistry 0

II

hv (93)

0

0 (96)

MeOH

(99)

HO

485

Photoelimination

exclusively into the acid (94).61 The diazo-ketones (95) and (96) both give high yields of the same ring-contracted product (97) on irradiation in water or Surprisingly, the isomeric diazo-ketone (98) did not undergo an analogous ring-contraction. The parent diazo-ketone (99) on irradiation in methanol was reported to give products (100)-(103) in yields of 50, 2, 30, and 15%, respe~tively.~~ On irradiation, 2,6-bis(diazo)cyclohexanone (1 04) also undergoes elimination of nitrogen accompanied by ring c o n t r a ~ t i o n .A ~ ~cyclopropenone (105) rather

a

C02Me

OMe

than keten has been propos d as the intermediate in this and relat d transformat ions. 3 Elimination of Nitrogen from h i d e s Photoelimination of nitrogen is an efficient and mild method for the generation of nitrenes. Irradiation of the azide (106) results in formation of the N-acylimine

82

63 84

K.-P. Zeller, J.C.S. Chem. Comm., 1975, 317. J. Griffiths and M. Lockwood, Tetrahedron Letters, 1975, 683. M. Yagihara, Y. Kitahara, and T. Asao, Chem. Letters, 1974, 1015. B. M. Trost and P. J. Whitman, J. Amer. Chem. SOC., 1974, 96, 7421.

486 Photochemistry (107) and the methanol adduct (108).66 A nitrene has been proposed as an intermediate in this transformation, a primary cleavage of the Norrish type I being possible but unlikely. The conversion of 4-a~ido-A~~~-3-keto-steroids such as (109) into the corresponding 5~-cyano-~-nor-~~-3-keto-steroids (110) by photoelimination of nitrogen has been reported.se Various mechanistic pathways have

been proposed for this photoreaction, the most plausible being that implicating a nitrene and/or an azirine. Direct irradiation of 2,2'-diazidobiphenyl (1 11) in n-hexane gave the carbazole (1 12), benzo[c]cinnoline (1 13), and the adduct (1 14), whereas in the benzophenone-sensitized photolysis, the adduct (1 14) was the major p r o d ~ c t . ~Irradiation ' in a glassy matrix led to formation of benzo[c]cinnoline (1 13) in quantitative yield.

Photoelimination of nitrogen from 2-alkyl-substituted 3-azidocyclohex-2en-1-ones (1 15) and cyclopent-Zen-1-ones in methanol gave mainly the a-aminoketal derivatives (116) resulting from ring-opening of the intermediate azirines by methanol.68 The corresponding 2-unsubstituted compounds also gave products (1 17) arising by a Curtius-type rearrangement of the nitrene. An analogous 66

W. A. Court, 0. E. Edwards, C. Grieco, W. Rank, and T. Sano, Canad. J. Chem., 1975,53,

O7

E. M. Smith, E. L. Shapiro, G. Teutsch, L. Weber, H. L. Herzog, A. T. McPhail, P . 4 . W. Tschang, and J. Meinwald, Tetrahedron Letters, 1974, 3519. A. Yabe and K. Honda, Tetrahedron Letters, 1975, 1079. Y . Tamura, S. Kato, Y. Yoshimura, T. Nishimura, and Y. Kita, Chem. and Pharm. Bull. (Japan), 1974, 22, 1291.

463.

487

Pho toelimination

ring-expansion has been employed in the synthesis of some 2-alkoxy-3-alkoxycarbonyl-3H-azepines.6e The nucleophilic trapping of azirines with secondary amines is a welldocumented approach to the study of the photochemistry of aryl azides. The major product of irradiation of phenyl azide (118) in the presence of di-nbutylamine is the 3H-azepine (119). A flash photolytic study has shown that

N,,NBu,

0.di-n-butylamine reacts not with a nitrene but with a species derived from a nitrene, probably the azirine (12O).'O This intermediate does not absorb strongly above 300 nm and has a lifetime of ca. 5 ms in the absence of an amine. The 3H-azepine is formed via the 1H-tautomer (121). Irradiation of 4-azidoindane (122) in diethylamine gave the aza-azulenes (123)-( 12 3 , derived presumably from the two possible a ~ i r i n e s .Competition ~~ between carbazole formation and 2-diethylamino-3-aryl-3H-azepineformation has been reported in the photodecomposition of 2-azidobiphenyls in the presence of dieth~lamine.~~ Photolysis 'O 71 72

R. K. Smalley, W. A. Strachan, and H. Suschitzky, Synthesis, 1974, 503. B. A. DeGraff, D. W. Gillespie, and R. J. Sundberg, J. Amer. Chem. SOC.,1974, 96, 7491. R. N. Carde and G. Jones, J.C.S. Perkin I, 1975, 519. R. J. Sundberg and R. W. Heintzelman, J. Org. Chem., 1974, 39, 2546.

488

Photochemistry

T3

y 3 2

( 126)

(1 27)

of #3-naphthyl azide (126) gave the naphthalene derivative (127), the yield being increased in the presence of pyrene, a singlet ~ e n s i t i z e r . The ~ ~ diamine (127) arises presumably by nucleophilic attack by diethylamine on an azirine intermediate which is in equilibrium with singlet nitrene. 6-Azido[b]thiophens have been reported to undergo analogous decompositions to give 7-amino-6-diethylaminobenzo[b]thiophens together with low yields of 6-diethylamino-8H-thieno[2,3-~]azepines.~~ The yields of azepines are increased in the presence of pyrene, suggesting that in this case singlet nitrene participates in their formation, Evidence for a common intermediate, the azirine, in formation of 2-diethylamino3H-azepines from azides and from nitro-compounds by reduction with tervalent phosphorus reagents has been published.75 Photolysis of 8-azidocaffeine (128) in ethanol leads somewhat unexpectedly to the amino-ether (129);7sa diazetidine may be involved in this transformation. The addition of singlet nitrene derived photochemically from the azido-l,3,5triazine (130) to nitriles (131) has been The adducts (132) are further converted thermally into the triazine-diones (133). Interest in the photochemical generation and fate of acyl nitrenes has again been expressed. In benzoyl, p-methoxybenzoyl, and m-fluorobenzoyl azides, Curtius rearrangement of the photochemically generated acyl nitrenes to the corresponding isocyanates competes with formation of insertion products in halogen-free In halogenomethanes, the yields of isocyanates are 73 74

75 76

77

S. E. Hilton, E. F. V. Scriven, and H. Suschitzky, J.C.S. Chem. Comm., 1974, 853. B. Iddon, M. W. Pickering, and H. Suschitzky, J.C.S. Chem. Comm., 1974, 759. T. de Boer, J. I. G. Cadogan, H. M. McWilliam, and A. G . Rowley, J.C.S. Perkin ZI, 1975,554. D. R. Sutherland and J. Pickard, J . Heterocyclic Chem., 1974, 11, 457, H. Yamada, H. Shizuka, and K. Matsui, J. Org. Chem., 1975, 40, 1351. E. Eibler and J. Sauer, Tetrahedron Letters, 1974, 2569.

=N Me0

R-C=N (131) R =Me,Et, or Ph

OMe

increased. Irradiation of benzoyl azide (1 34) and the five-membered heterocycles (135) and (136) in Me,CHEt, Me&, or cyclohexane gave the same insertion products via the common nitrene (137);'@ isocyanates and amides were also

formed by rearrangement. Cyclization of the acyl nitrenes generated photochemically from alkyl azidoformates is not apparantly a particularly facile process. The analogous thermal reactions are more successful, but the azidoformate (138) has been converted into the 1,3-oxazin-2-one (139) by irradiation in dichloromet hane.80

*O

E. Eibler and J. Sauer, Tetrahedron Letters, 1974, 2565. P. F. Alewood, M. Benn, and R. Reinfried, Canad. J. Chem., 1974, 52, 4083.

490 Photochemistry The addition of photochemically generated ethoxycarbonylnitrene to 16-dehydropregnenolone acetate to give three aziridines has been described.s1 The corresponding addition of ethyl azidoformate to norbornene to give the aziridine (140) as the major product has been reported.82 The possible intervention of the triazoline (141) as an intermediate in the photoreaction has been excluded; photoelimination of nitrogen from the triazoline (141) gave not only the aziridine (140) but also the imine (142) in a yield of 25%.

The highly reactive nitrenes derived from phosphoryl azides do not readily undergo rearrangement. They also appear to have a low selectivity with respect to C-H insertion reactions. Thus, irradiation of diethylphosphoryl azide (143 ; R = Et) in cyclohexane, for example, led to formation of diethyl cyclohexylphosphoramidate (144; R = Et) in 88% yield.83 A lower yield (67%) of insertion product, diphenyl cyclophosphoramidate (144; R = Ph), was obtained on (RO),PON3 -----+ hv (RO),POG:

- N2

cyclohexane

(143)

irradiation of diphenylphosphoryl azide in cyclohexane, but this was still much higher than that reported for phenyl azidoformate (19%), where rearrangement is preferred. Rearrangement is observed, however, in the phosphinyl nitrene (145) obtained on irradiation of l-azid0-2,2,4,4-tetramethylphosphetan l-oxide (146);84 the 1,2-azaphosphoIidine 2-oxide (147) is presumably formed via a Curtius-type rearrangement involving the metaphosphonimidate (148) as an intermediate. The second product, the phosphonamidate (149), is believed to be formed directly from the nitrene as shown in Scheme 5. Stereochemical evidence for the intermediacy of metaphosphorimidates in the ring-expansion of l-azido2,2,3,4,4-pentamethylphosphetanhas been described.86 Separate irradiation of 8a

n4

nb

R. P. Gandhi, M. Singh, and T. D. Sharma, Indian J. Chem., 1974, 12, 117. 0. E. Edwards, J. W. Elder, M. Lesage, and R. W. Retallack, Canad. J. Chem., 1975,53,1019. R. Breslow, A. Feiring, and F. Herman, J . Amer. Chem. Soc., 1974,96, 5937. M. J. P. Marger, J.C.S. Perkin I, 1974,2604. J. Wiseman and F. H. Westheimer, J. Amer. Chem. Soc., 1974, 96,4262.

49 1

Photoelimination

(145)

Scheme 5

the cis- and trans-isomers in methanol led to formation of an identical mixture of cis- and trans-2-methoxy-3,3,4,5,5-pentamethyl-l,2-azaphospholidene2-oxides. o-Dialkylaminobenzenesulphonylazides were converted into the corresponding benzothiadiazines on irradiation in dimethyl sulphoxide.8e 4 Photodecomposition of other Compounds having N-N Bonds Photodecomposition of sodium salts of toluene-p-sulphonylhydrazonesis a wellestablished route for the generation of carbenes. Irradiation of the lithium salt of the hydrazone (150) or the diazoalkenyl ether (151) derived from it afforded l-methoxy-3,3-dimethyl-2-phenylcyclopropene (152).*' This provides a much

improved route to the enol ethers of cyclopropanone. Evidence has been presented for the existence of a cyclopropene intermediate (153) in the rearrangement of the carbene (154) generated from the hydrazone salt (155) into phenanthryl carbene (156); the final product of irradiation in benzene is the phenanthrene (157).88 The carbene (158) generated by photodecomposition of the hydrazone salt (159) undergoes rearrangement to the alkenes (160) and (161).89 The failure J. Martin, 0. Meth-Cohn, and H. Suschitzky, J.C.S. Perkin I, 1974, 2451. D. P. G. Hamon and K. M. Pullen, J.C.S. Chem. Comm., 1975,459. T . T . Coburn and W. M. Jones, J. Amer. Chem. SOC.,1974,96. 5218. A. Viola, S. Madhavan, and R. J. Proberb, J. Org. Chem., 1974, 39, 3154.

492

Photochemistry

to produce the tricycle (162) is attributed to the fact that neither the singlet nor the triplet can assume the requisite geometry for intramolecular cycloaddition. The 1H-cyclobuta[de]naphthalene (163) has been prepared by the photodecomposition of the hydrazone salt (164).90 The photodecompositions of a number of diazonium salts 91s 92 and of benzenediazonium o-carboxylate 83 have also been studied.

so s1 O2

s3

R. J. Bailey and H. Shechter, J. Amer. Chem. SOC.,1974, 96, 8116. H. Boettcher and H. G. 0. Becker, 2. Chem., 1974,14, 100. P. E. MacraeandT. R. Wright, J.C.S. Chem. Comm., 1974, 898. M. Kato, T. Tamano, and T. Miwa, Bull. Chem. SOC.Japan, 1975,48,291.

493

Photoelimination ~ = N - N Nat - T s

hv ___,

Photoelimination of nitrogen from the hydrazine (165) is reported to yield the ketone (166),94and both singlet and triplet nitrenes are obtained on irradiation of trimethylammonio-p-chlorobenzamidate.gs 5 Photoelimination of Carbon Dioxide Carboxylic acids of general formula R-X-CH2COBH (X = 0, NH, or S) are known to undergo photosensitized decarboxylation to yield R-X-CHs. The participation of the radicals (167) and (168) in the sensitized photodecarboxylation of phenylthioacetic acid is now supported by the results of a CIDNP Ph-S -eHz

Ph-S-kH(168)

(167)

0

CO,H

0

II II Ph-CH2-C-0-C-CH2-Ph (16’)

-co,,It’ -co+ Ph- CH2-CH2--Ph (170)

hv(254nrn)

-c& Ph-CHZ-

II Jg-0 C-CHZ-Ph (171)

Irradiation (254 nm) of phenylacetic anhydride (169) in acetonitrile results in elimination of CO, and CO and formation of bibenzyl (170) and 1,3-diphenylpropanone (171).97 The ketone is known to eliminate CO rather efficiently via a short-lived triplet, and at least part of the bibenzyl may therefore originate in this way. Many esters readily undergo photoelimination of carbon dioxide, the products being derived by reaction of the radicals thus formed. Examples reported B4

u6

C. V. Juelke, D. W. Boykin, J. I. Dale, and R. E. Lutz, J. Org. Chem., 1975,40, 545. V. P. Semenov, A. K. Khusainova, A. N. Studenikov, and K. A. Ogloblin, Zhur. org. Khim., 1975, 11, 218.

O7

M. Weinstein, K. A. Muszkat, and J. Dobkin, J.C.S. Chem. Comm., 1975, 68. A. A. M. Roof, H. F. van Woerden, and H. Cerfontain, Tetrahedron Letters, 1975,815. 17

494

Photochemistry

(172) R

=

H, Me, or Ph (1 73)

include a-and 8-naphthylenemethyl phenylacetate~,~~ benzyl aminoacetate~,~~ and 3,5-dimethoxybenzyl acetate.loO The adducts of 2-benzopyran-3-ones and trimethylmaleimide (1 72) are converted into the unstable o-quinodimethanes (1 73) on irradiation by elimination of carbon dioxide.lol Photodecarboxylation of a p-lactone has been employed in a simple synthesis of the tricarbonyliron complex of cyclobutadienecarboxylic acid (Scheme 6).lo2

COzMe

Scheme 6

In an attempt to generate benzyne in its triplet state, the benzophenonesensitized decomposition of phthaloyl peroxide (174) was studied.lo3 Reaction of the benzyne with trans-cyclo-octene gave isomericcycloadducts in a ratio indicative of reaction of singlet benzyne. These results suggest that the rate of triplet-singlet

A&

phryC*z

\

Q)$-~co~>

0 1

0

0 (174)

(175)

interconversion in one of the intermediate species is faster than loss of two carbon dioxide molecules; spin inversion is thought to occur in the intermediate (175). 6 Fragmentation of Organosulphur Compounds Photolysis (23G270 nm) of methyl vinyl sulphide yields products explicable in terms of the two homolytic cleavages

MeSCH=CH, MeSCH=CH2

hv

hv

+ .SC=CH2 Me& + *CH=CHI

Me.

R. S. Givens, B. Matuszewski, and C. V. Neywick, J. Amer. Chem. SOC.,1974, 96, 5547. K. Kimoto, K. Tanabe, S. Saito, Y. Umeda, and Y. Takimoto, Chem. Letters, 1974, 859. l o o D. A. Jaeger, J. Amer. Chem. SOC.,1974, 96, 6216. lol D. W. Jones and G. Kneen, J.C.S. Perkin I, 1975, 175. lol J. Agar, F. Kaplan, and B. W. Roberts, J. Org. Chem., 1974, 39, 3451. lo3 R. T. Luibrand and R. W. Hoffmann, J. Org. Chem., 1974,39, 3887.

495

Photoelimination

At short reaction times, the sum of the quantum yields for formation of methane and ethylene is near unity.lo4 Irradiation of thietan (176) has previously been reported to yield ethylene, propene, and, by inference, thioformaldehyde. Monomeric thioformaldehyde has now been trapped as the adduct (177) by

irradiation of thietan in the presence of cyclopentadiene.lo6 Evidence for formation of ‘hot’ triplet biradicals which decompose stereospecifically on decomposition of 3-ethyl-2-propylthietan vapour has been described.lo8 The photosensitized decomposition of tetrahydrothiophen 1,l-dioxide in the vapour phase has also been examined and yields sulphur dioxide, ethylene, acetylene, and cyc10butane.l~~ Irradiation of the adduct (178) obtained from benzyne and a mesoionic thiazol-4-one in benzenemethanol solution resulted in extrusion of sulphur and formation of the isoquinolone (179).lo8 This is in complete contrast with the Ph

I

Ph

Ph

(178)

(1 79)

corresponding thermal decomposition, which affords diphenylbenzo[c]t hiophen and phenyl isocyanate. A novel ring-contraction of the acetate (180) to give the thiolactone (1 81) has been described.loQ OAc hv M~OH’

( 1 80)

Irradiation of a series of tolyl esters (182) is accompanied by S-aroyl bond cleavage and formation of aroyl and thiyl radicals; the major products, the aldehydes (183), disulphide (184), and the benzils (185), are derived from these radicals.l10 The thiobenzoate (186) undergoes a different type of photoreaction G. Leduc and Y.Rousseau, Canad. J. Chem., 1975,53,483. D. R. Dice and R. P. Steer, Canad. J. Chem., 1974, 52, 3518. lo6 D. R. Dice and R. P. Steer, J. Amer. Chem. SOC.,1974,96, 7361. lo’ K. Hondo, H. Mikuni, M. Takahashi, and Y. Morii, J. Phofochem., 1974,3, 199. lo* S. Nakazawa, T. Kiyosawa, K. Hirakawa, and H. Kato, J.C.S. Chein. Comm., 1974, 621. l o g P. Y.Johnson and M. Berman, J.C.S. Chem. Comm., 1974, 779. 110 J. Martens and K. Praefcke, Chem. Ber., 1974,107, 2319.

10‘

lo6

Photochemistry

leading to formation of the thiaxanthone (l87).l1l Details of the mechanism of this cyclization are not clear, although the keten (188) may be an intermediate. There is no evidence for products arising directly from any of these thiobenzoates by a thia-photo-Fries rearrangement. Thiaxanthones are also obtained by irradiation of 2-halogenothiobenzoic acid S-aryl esters,112and the effect of an adjacent trimethylsilyl group on the photochemical fragmentation pathways of S-alkyl thioacetates has been studied.ll3

ll1 11* 11*

J. Martens and K. Praefcke, Tetrahedron, 1974,30, 2565. G. Buchholz, J. Martens, and K. Praefcke, Synthesis, 1974, 666. T. I. Ito and W. P. Weber, J. Org. Chem., 1974, 39, 1691.

497

Photoelimination Ph Ph

Ph

Ph

Organic thiocarbonates have been reported to undergo type I1 elimination^.^^^ Attempts to prepare diphenyldithiet (189) by photodecomposition of diphenylThe dithiet was vinylene dithiocarbonate (190) were not altogether too reactive to allow isolation, and underwent further decomposition to tetraphenyldithiin (191) and diphenylacetylene. The p-dimethylamino-analogue of (189) exists in the solid state as the corresponding a-dithione. The ditholan (192) undergoes fragmentation also with elimination of CO on irradiation to give the trithiolan (193).ll6

(192)

(193)

Homolysis of the S-acyl bond is responsible for formation of phenylthiocyclohexane and 3-phenylthiocyclohexene from SS'-diphenyl dithiocarbonate by irradiation in c y ~ l o h e x e n e .A ~ ~cyclic ~ mechanism, however, has been proposed to account for the photodecomposition of certain carbohydrate dithiobisthioformates.ll* On irradiation, O-ethyl thioacetate is converted into cis- and trans-2,3-diethoxybut-2-eneYtogether with small amounts of 2,3-diethoxybut-lene, 2,3-diethoxybuta-1,3-diene, and l-ethoxyethane-l-thiol.llg Free sulphur was trapped by reaction with 1,2-dimethylenecyclohexane. Details of the photoelimination of sulphur dioxide from D-glucofuranosyl phenyl sulphone acetates have been published.120 An efficientsynthesis of another 1&bridged naphthalene (194) has been achieved by photoelimination of sulphur dioxide from naphtho[1,8-cd]-1,2-dithiol 1,l-dioxide (195).121 Photodecomposition of 3,5-diphenyl-l114

A. A. Scala, J. P. Colnagelo, G. E. Hussey, and W. T. Stolle, J. Amer. Chem. SOC.,1974,96, 4069.

11° 11' lln llD lao 121

W. Kusters and P. de Mayo, J. Amer. Chem. SOC., 1974, 96, 3502. H.-J. Kyi and K. Praefcke, Tetrahedron Letters, 1975, 555. K. Kosegaki, S. Kondo, and K. Tsuda, Nippon Kagaku Kaishi, 1975, 171. E. I. Stout, W. M. Doane, C. R. Russell, and L. B. Jones, J. Org. Chem., 1975,40, 1331. R. Jahn and U. Schmidt, Chem. Ber., 1975,108, 630. P. M.Collins and B. R. Whitton, Carbohydrate Res., 1974,36, 293. J. Meinwald and S. Knapp, J. Arner. Chem. SOC., 1974, 96, 6532.

498

Photochemistry

phenylsulphonylpyrazole and related 1-phenylsulphonylpyrazolinesis principally the result of nitrogen-sulphur bond cleavage.122 Increasing interest has been shown in the photodecomposition of biologically important compounds such as drugs, insecticides, and herbicides which are subject to exposure to light. Sulphur-containing compounds are widely used in this context, and a number of studies of their photodecomposition have been undertaken .123-126 7 Miscellaneous Decomposition and Elimination Reactions Fragmentation and elimination reactions which cannot be included in any of the above categories are briefly reviewed in this section. It has not proved feasible to classify these processes, although analogous reactions are grouped together. The major product of irradiation of dimethylamine (196) in a hydrocarbon solvent (n-nonane) is the diamine (197), arising via a primary photochemical /I V

Me,NH

+

Me,NCH,NMe,

MeNH,

(197)

+

Me,NCH,NHMe

+

Me,N-NMe,

(200)

(1 99)

cleavage of the nitrogen-hydrogen bond.I2’ Products (1 98)-(200) are also obtained in low yield. The observed N-3 dealkylation of NN-1,3-diethyluracil (201) is probably an example of a Norrish type I1 photoelimination rather than a direct carbon-nitrogen bond Further evidence for nitrogen-nitrogen 0

cx Et

laa 123

Izr

0

cx Et

M. Lempert-Sreter, J. Tamas, and K. Lempert, Acfa Chim. (Budapest), 1974,30, 455.

J. Pawlaczyk, W. Turowska, and Z . Baranska, Acfa Polon. Pharm., 1974,31, 71. R. A. Okerholm, F. J. Keeley, and A. J. Glazko, US.Nut. Tech. Inform. Serv. A D Reports, 1973,No.771 108/8GA(Chern. A h . , 1974,81, 056 562).

W.P. Dejonckheere and R. H. Kips, J. Agric. Food Chem., 1974,22, 959. L. Molnar and M. Sivak, Pharmazie, 1974,29, 417. lz7

128

K. G. Hancock and D. A. Dickinson, J. Org. Chem., 1975,40,969. M. D. Shetlar and P. J. S. Koo, Tetrahedron Letters, 1975,2015.

Photaelimination

499

bond cleavage in the photolysis of dimethylnitrosamine has been reported,12* but a different pathway is observed in the photodecomposition of N-nitroso4-aza-1 ,Zdioxolans (202).lS0 NO

(203)

(204)

The photosensitized dealkylation of 8a-hydroxyalkylpurines (203) on irradiation ( A > 290 nm) leads to regeneration of the original purines (204) in yields of up to Sensitizers used include carbazole and NN-dimethylaniline, and a mechanism involving electron transfer from the sensitizer to the purine has been proposed. The well-known L2 -+,2] photocleavage of cyclobutane derivatives has been further studied. Orientation effects have been revealed in phenyl-substituted cyclobutanes.182 cis-Diphenylcyclobutane (205) undergoes only one cleavage to

Ph

-- 4

Ph

hv

hV

7Ph

hv

Ph

yield styrene, this being preferred presumably for steric reasons, whereas competing cleavages to styrene and stilbene are observed in trans-diphenylcyclobutane (206). A radical recombination mechanism is involved, at least in part, in the photodecomposition of perfluorocyclobutane.133 A cyclobutane cleavage has also been employed in an attempted synthesis of the unsaturated /%lactam la@ lao 131 lSa

133

B. B. Adeleke and J. K. S. Wan, Mol. Photochem., 1974, 6, 329. N. Durhn, J. Org. Chem., 1974, 39, 1791. J. Salomon and D. Elad, J. Amer. Chem. Soc., 1974, 96, 3295. G . Kaupp, Angew. Chem. Internat. Edn., 1974, 13, 817. R. L. Cate and T. C. Hinkson, J. Phys. Chem., 1974,78,2071.

500

Photochemistry

'NHMe Co2Me

MeNH JCo2Me +

501

Photoelimination

(207).134 Irradiation of the cyclobutane (208) led to elimination of carbon monoxide and formation of the diene (209), which on further irradiation gave products (210) and (211) via the unstable #l-lactam (207). The photodecomposition of the adduct (212) to 2-benzoylnorborn-2-ene (213) has been shown not to involve initial rearrangement to the cyclobutane (214), but to arise via a biradical pathway.136 Photochemically induced cleavage of the cyclobutanols (215 ) takes place in a different sense to give the ring-enlarged ketones (216) and unsaturated 0 OH

(21 5 )

iz

=

- L

OH

2 or 3

alcohols (217).136 The photochemically induced cleavage of the glycoside linkage in sap on in^,^^' the photofragmentation of and the photodecomposition of the peroxide (218) to mixtures containing the anhydride (219) laQ have also been reported. 10-Alkyl and 10-cycloalkyl-isoalloxazines(220) have been reported to undergo photodealkylation to alloxazine (221) and the appropriate alkene.140 This photodealkylation proceeds aerobically via the first excited singlet state, and anaerobically via singlet and triplet states in a ratio of 1 : 8. A six-membered transition state (222) is implicated, and the results are compared with those for the photodecomposition of riboflavin. Irradiation of 5-hexyluridine in neutral aqueous solution also resulted in dealkylation and formation of uridine and hex-1-ene.l4l A novel example of the cleavage of an imine to a nitrile has been ~ e p 0 r t e d . l ~ ~ Irradiation of N-( 1-phenyl-2-propylidene)benzylamine (223) affords acetonitrile, toluene, and bibenzyl, by a process which is at least formally analogous to the Norrish type I cleavage of ketones. On irradiation, the amine (224) is converted into the quinofine (225) by an unprecedented photoelimination of water.143 G. Kretschmer and R. N. Warrener, Tetrahedron Letters, 1975, 1335. P. S. Ventataramani, S. Chandrasekaran, and S. Swaminathan, J.C.S. Perkin I, 1975, 730. 136 M. L. Viriot-Villaume, C. Carre, and P. Caubere, Tetrahedron Letters, 1974, 3301. 13' I. Kitagawa, M. Yoshikawa, Y. Imakura, and I. Yoshioka, Chem. and Pharm. Bull. (Japan), 1974,22, 1339. laa A. G. M. Barrett, D. H. R. Barton, R. A. Russell, and D. A. Widdowson, J.C.S. Chem. Comm., 1975, 102. 13* E. G. E. Hawkins and R. Large, J.C.S. Perkin I, 1974, 2561. 140 M. Gladys and W.-R.Knappe, Chem. Ber., 1974, 107, 3658. 141 E. Sztumpf-Kulikowska and D. Shugar, Acta Biochim. Polon., 1974, 21, 73. l t a H. Ohta and K. Tckumaru, Chem. Letters, 1974, 1403. l P 8 T. Kametani, F. F. Ebetino, and K. Fukumoto, Tetrahedron, 1974, 30, 2713. 134

136

Photochemistry

502

Me,

,CHzPh

II NN

PhCHz

(223)

1 Iv _I_,

MeC=N

+

PhMe

+

PhCHzCHzPh

Photoelimination

503

Other low-yield photodecomposition reactions involving elimination of small molecules have been r e p ~ r t e d . ~ ~ + ~ ~ ~ Photochemical intra- and inter-molecular elimination of HCl, HBr, and HI, arising in most cases by initial carbon-halogen bond cleavage, has again been widely described. The syntheses of various alkaloids l4',148 and of pyrazolo[1,5-.]phenanthridine149 have been achieved in this way. Irradiation of the chloroacetamide (226) gave the tetracyclic lactam (227).lb0The alkylation of the enamino-esters (228) has been accomplished by sensitized irradiation with

dihalogenomaleimides (229),lb1and irradiation of 3-o~o-A~~*-steroids (230) in the presence of trifluoromethyl iodide affords 3-oxo-A-trifluoromethyl-A4~6-steroids (231) as the sole Numerous other examples of intermolecular ~ ~ - other ~ ~ ~ decompositions and elimination of HX have been r e p ~ r t e d . ~Many

J. Reisch and W. Koebberling, Pharmazie, 1974, 29, 144. W. A. Szarek and A. Dmytraczenko, Synthesis, 1974, 579. H. Deshayes, J.-P. Pete, C.PorteIla, and D. Scholler, J.C.S. Chem. Comm., 1975, 439. 147 M. Shamma and D.-Y. Hwang, Tetrahedron, 1974,30, 2279. 148 K. Ito and H. Tanaka, Chem. and Pharm. Bull. (Japan), 1974, 22,2108. 140 W. J. Begley, J. Grimshaw, and J. Trocha-Grimshaw, J.C.S. Perkin I, 1974, 2633. lL0A. Wu and V. Snieckus, Tetrahedron Letters, 1975, 2057. lL1G. Sziligyi, H. Wamhoff, and P. Sohir, Chem. Ber., 1975, 108, 464. lsa G. H. Rasmusson, R. D. Brown, and G. E. Arth, J. Org. Chem., 1975,40, 672. 153 R. D. Youssefyeh and L. Lichtenberg, J.C.S. Perkin I, 1974, 2649. T. Akiyama, 0.Ikarashi, K. Iwasaki, and A. Sugimori, Bull. Chem. SOC.Japan, 1975, 84, 914. 1s6 A. J. Varghese, Photochem. and Photobiol., 1974, 20, 461. lL6 E. Gilbert, Z. Naturforsch., 1973, 28b, 805. J. M. Birchall, G. P. Irvin, and R. A. Boyson, J.C.S. Perkin ZZ, 1975, 435. 144

146

504

Photochemistry

rearrangements arising by carbon-halogen homolytic bond cleavage have been described, but these are essentially radical processes and will not be included in this Report. As mentioned in Section 6, attention is now being directed to the study of the photodecomposition of technically useful compounds which are subject to exposure to light, and in particular to the class of compounds known as ‘agrochemicals’. Publications not previously considered in this Report are listed in references 158-1 67. D. A. M. Watkins, Chem. and Ind., 1974, 185. M. Nakagawa and H. Tamari, Nippon Nogei Kagaku Kaishi, 1974,48, 651. 160 C. Galvez, J. Albala, and J. Mesa, Anales de Quim., 1973, 69, 1319. H. Mueller, S. Gaeb, and F. Korte, Chemosphere, 1974, 3, 157. le8 J. B. Addison, P. J. Silk, and I. Unger, Bull. Enuiron. Contam. Toxicol., 1974,11, 250. 16s P. J. Silk and I. Unger, Internat. J . Enuiron. Analyt. Chem., 1973, 2, 213. 164 L. L. Miller, G . D. Nordblom, and G. A. Yost, J. Agric. Food Chem., 1974, 22, 853. 16) M. Nakagawa and D. G. Crosby, J . Agric. Food. Chem., 1974,22, 849. L. 0. Ruzo, M. J. Zabik, and R. D. Schuetz, J. Agric. Food Chem., 1974,22, 1106. 16’ D. A. M. Watkins, Chemosphere, 1974, 3, 239.

Part IV POLYMER PHOTOCHEMISTRY By D. PHILLIPS

1 Introduction The format is as followed previously, but owing to the extremely limited space permitted for coverage of the growing number of papers in this field, detailed comment is restricted to relatively few papers. 2 Photopolymerization Photoinitiation of Addition Polymerization.-Much of the research reported in this section has arisen from commercial and environmental needs for surface coatings which do not rely on polymerization in solvent media. One approach to this problem has been to initiate the addition polymerization of monomer/ oligomer/pigment formulations with U.V. light and suitable photoinitiators. The initiators most commonly used are benzophenone, Michler’s ketone (l), and benzoin ethers, but the search for other efficient photoinitiators continues.

0

Many applications of metal salts as photoinitiators have been described. These include (i) vinyl monomer polymerization using iron(m) salt-saccharide systems ;l (ii) mixtures of tetraphenylporphineiron(m), amine, and CCl, ;2 (iii) tetrafluoroethylene with rhenium carbonyls;3 (iv) stannic chloride-catalysed copolymerization of methyl methacrylate (MMA) and ~ t y r e n e (v) ; ~ acrylamide with sodium chloroaurate,6 and isobutene * and methyl methacrylate with vanadium complexes. In the case of isobutene-VC1, mixtures, a spectroscopic study revealed that the initiator was a coloured complex of VC14 and the monomer, photoinitiation accounting for all of the polymerization at 253 K, but thermal initiation becoming a 8

6

T. Okimoto and Y. Inake, J. Macromol. Sci., Chem., 1974,7, 1537. T. Okimoto and M. Takahashi, J. Polymer Sci.,Polymer Letters, 1974, 12, 121. C. H. Bamford and S. V. Muilik, J.C.S. Faraday I, 1975, 71, 625. H. Hirai and M. Komiyama, J. Polymer Sci., Polymer Letters, 1974, 12, 673. K. Imamura and M. Asai, Makromol. Chem., 1973, 174,91. L. Toman, M. Marek, and J. Jokl, J. Polymer Sci.,Polymer Chem., 1974, 12, 1897. S. M. Aliwi and C. H. Bamford, J.C.S. Faraday I, 1974,70,2092; 1975,71,52.

507

Photochemistry

508

of additional importance at temperatures above 283 K. In the work by Aliwi and B a m f ~ r d , two ~ complexes, chloro-oxobis(pentane-2,4-dionato)vanadium [VO(acac),Cl], and VOQ,OMe (2) (Q = 8-quinolyloxo), were shown to photoinitiate the polymerization of methyl methacrylate at 365 nm. For the former

complex the quantum yield of initiation was low, being 2 x and the mechanism involved free chlorine atoms arising from reaction (1). For the VvO(acac),C1 + hv

V1vO(acac), + C1-

____+

(1)

second complex, no initiation was observed at excitation wavelengths 436 or 570 nm, and thermal initiation was absent up to 353 K. The quantum yield of The initiating species were shown to be initiation was again low (2 x -CH20Hand MeO. arising from the photolysis of (2) according to reaction (2). VOQ20Me

+

+

hv

-+

[VOQ,OCH,]*

II, VOQz

+

MeO* (2)

I

The results also showed that the isomerization of MeO- to -CH20H may be catalysed by a vanadium species, and that chelates of the type considered can be incorporated into polymers by two methods to give photosensitive products which undergo grafting and cross-linking reactions on irradiation. MMA has also been polymerized by photoinitiation with iodine,* iodinemonoethanolamine mixture^,^ quinoline-bromine charge-transfer complexes,1o and quinoxaline derivatives.l1 The initiation with iodine was not attributed to simple dissociation of molecular iodine, but rather to absorption by an iodinemonomer (M) complex [reaction (3)]. A 1 : 1 complex between I2 and monoI,

+

2M

7[M***I--I-*.M] +

hv

__+

latent radicals

-1.

(3)

initiating radicals R* ethanolamine, absorbing at 245 nm, was proposed as the initiating species for this ~ y s t e m . ~ Vinyl monomer polymerization has been photoinitiated with quaternary ammonium salts, an example of the mechanism of which is given in reaction (4), the benzoyl radical being the initiating species.l*

* lo

l1 la

P. Ghosh and A. N. Banerjee, J. Polymer Sci., Polymer Chem., 1974, 12, 375. S. Sakai, K. Takahashi, and N. Sakota, Polymer J., 1974, 6, 341. P. Ghosh and P. S. Mitra, J. Polymer Sci., Polymer Chem., 1975, 13, 921. D.Braun and G. Quarg, Angew. Makromol. Chem., 1975,43, 125. M. KO,T. Sato, and T. Otsu, J. Polymer Sci., Polymer Chem., 1974, 12, 2943.

Polymer Photochemistry

509 BF,-

-%- PhC* + II

0

Oximes such as MeCOCMe=NOCONHPh and related compounds upon photolysis yield radicals such as MeCO,., PhCO,*, and EtOC02*, which are capable of initiating polymerization of MMA, and are also useful for grafting.ls The polymerization of styrene can be photoinitiated by 1,3-dioxolan-type compounds (3) through reactions of type (5).14 Vinyl polymerization has also been photosensitized by 1,4-bis(pentamethylene)-2-tetra~ine.~~

(3)

Sulphur dioxide with but-1-ene and acrylonitrile, and maleic anhydride with the same monomers, can yield terpolymers upon 250-300 nm u.v.-irradiation,l6 the initiating species being complexes between but-l-ene and the SO, or maleic anhydride. Phenyl vinyl sulphide polymerizes easily through reaction (6).17 PhSCH=CH,

hv

PhSCH=CH2*

-

PhS*

+ *CH=CH,

(6)

SS'-Diphenyl dithiocarbonate, PhSC(O)SPh, also photodecomposes to PhS* radicals, and these can initiate addition po1ymerization.ls Photopolymerization of acrylonitrile in the presence of naphthalene and its d e r i ~ a t i v e s ,of ~ ~ 9-vinylanthracenesYz0and of sulphonyl activators for dyephotosensitized polymerization,21 and the polymerization of MMA photoinitiated by anthraquinone (AQ) and 2-t-butylanthraquinone 22 have been reported. Some of the important steps in this latter process are shown in reactions (7)-( 10).

AQ

+ hv --+

-

'AQ*'+ THF (solvent)

'AQ*+

'AQ*

(7)

?' /

/

OH

(THF*)

(AQH.1 l4

S. I1 Hong, T. Kurosaki, and M. Okawara, J. Polymer Sci., Polymer Chem., 1974, 12, 2553. T. Ouchi, S. Nakamura, M. Hamada, and M. Oiwa, J. Polymer Sci.,Polymer Chem., 1975, 13, 455.

l6

K. Sugiyama, T. Nakaya, and M. Imoto, Makromol. Chem., 1974,175, 1497. J. Furukawa, E. Kobayashi, and M. Nakamura, J. Polymer Sci.,Polymer Chem., 1974, 12,

l7

185 1,2789. S. Kondo and K. Tsuda, Nippon Kagaku Kaishi, 1975, 174.

l8

K.Kosegaki, S. Kondo, and K. Tsuda, Kobunshi Ronbunshu, 1974, 31,

l6

lo 2o

Ba

541; Nippon Kagaku Kaishi, 1975, 171. I. Capek and J. Barton, J. Polymer Sci., Polymer Letters, 1974, 12, 327. M. G. Krakovyak and E. V. Anufrieva, Poiymer J., 1974, 10, 685. G. A. Delzenne, H. K. Peeters, and V. L. Laridon, J. Photogr. Sci., 1974,22, 23. A. Ledwith, G. Ndaalio, and A. R. Taylor, Macromolecules, 1975, 8, 1.

510

+ THF. THF- + MMA AQH.

-

Photochemistry

adduct MMA.

_ ~ _ f

(9) ____+

polymer

(10)

Hydrogen peroxide has been used as a photosensitizer in the emulsion polymerization of tetraflu~roethylene.~~ Phot oinduced copolymerization of methacrolyl-L-proline and D- and L-valine methyl esters with maleic anh~dride,~' N-Z-menthylmaleimide with styrene and MMA,26 and charge-transfer interactions in the copolymerization of phenyl methacrylates have been discussed.26 The effect of the cyanoethyl group in the photopolymerization of NN-bis(2-cyanoethy1)acrylamide [CH2= CHCON(EtCN),] has been studied.27 Other recent reports have been concerned with the photoinduced polymerization of maleic anhydride,2athe cationic photopolymerization of vinyloxyethyl acrylate,28 the photosensitizing ability of poly[(p-benzoylbenzyl)-1-glutamate],30 new trends in radical-induced copolymerization,s1 and the mechanism of photochemical initiation in polar vinyl monomer-complexing agent Several papers have reported on the charge-transfer cationic and radical photopolymerization of N-vinylcarbazole (VCZ).33 In the study by Asai et al., the initiator was a sodium chloroaurate solution. In the work by Tada et al. and Crellin and Ledwith, formation of the photodimer (4) was shown to be in

competition with radical polymerization of VCZ. Ionic polymerization in Ledwith's work was prevented by using ethanol as solvent, and the photoinitiator was Rhodamine 6G, reacting via exciplex formation with VCZ to give the photodimer, and inefficiently via the triplet dye to initiate polymerization. 23

24

25 28

28 29 80

81 82

33

N. Suzuki and J. Okamoto, J. Polymer Sci., Polymer Letters, 1974, 12, 95, 143; N. Suzuki, 0. Matsuda, and J. Okamoto, J . Polymer Sci., Polymer Chem., 1974, 12, 911. K. Nishihara and N . Sakota, J. Polymer Sci., Polymer Chem., 1973, 11, 3171; N. Sakota, 1. Nagahiro, and H. Nishihara, J. Polymer Sci., Polymer Letters, 1974, 12, 503. N. Sakota, K. Kishine, and S. Shimada, J. Polymer Sci., Polymer Chem., 1974, 12, 1787. Y. Kadoma, K. Takeda, K. Uno, and Y. Iwakura, Kobunshi Ronbunshu, 1975,32, 218. C. Azuma and N . Ogata, J. Polymer Sci., Polymer Chem., 1975, 13, 741. I. Nagahiro, K. Nishihara, and N. Sakota, J. Polymer Sci., Polymer Chem., 1974, 12, 785. T. Nishikubo and M. Kishida, Makromol. Chem., 1974, 175, 3357. A. Ueno, F. Toda, and Y. Iwakura, J. Polymer Sci., Polymer Letters, 1974, 12, 287. V. A. Kabanov, Acta Chim. Acad. Sci. Hung., 1974, 81, 129. G. S. Georgiev, V. I. Pergushov, and V. B. Golubev, Vysokomol. Soedineniya (A), 1973, 15, 2008. R. A, Crellin and A. Ledwith, Macromolecules, 1975, 8, 93; K. Tada, Y. Shirota, and H. Mikawa, ibid., 1974, 7, 549; M. Asai, S. Tazuke, and S. Okamura, J. Polymer Sci., Polymer Chem., 1974, 12, 45; Y.Shirota, T. Tomikawa, T. Nogami, K. Tada, N. Yamamoto, H. Tsubomara, and H. Mikawa, Bull. Chem. SOC.Japan, 1974, 47, 2099; 0. F. Olaj, J. W. Breitenback, and H. F. Kauffmann, Angew. Chem. Internat Edn., 1973,12, 433.

Polymer Photochemistry

51 1

Tada et al. showed that increase in solvent basicity favoured the polymerization process over dimerization, apparently influencing the course of the reaction at the VCZ dimer radical-cation intermediate stage (Scheme 1).

(>N-CH=CH, VCZ radical-cation

*

+ I

=N-cH-cH2 \

,N-$H-CH2

VCZ dimer radical-cation polymer A c z (radical A' (or VCZ) polymerization)

I

polymer (cat ionic poiymerization)

(A

=

(5) 3A (cyclodimer) (or VCZ-+)

electron acceptor)

Scheme 1

Photopolymerization in the vapour phase has been observed on surfaces exposed to U.V. radiation in the presence of six fluorocarbon monomers.34 Ionic polymerization of vinyl halides in the vapour phase has been initiated by photoionization using photons with energies near the ionization threshold,35and the photochemical initiation of polymerization of gaseous ethyl acrylate 36 and MMA, butyl acrylate, and methacrylates under high pressures 37 has been reported. The last study utilized 1,l '-azocyclohexane carbonitrile as photosensitizer. A review of the use of aromatic carbonyl compounds as photoinitiators of vinyl polymerization has appeared.38 Several papers have described aspects of the u.v.-curing of surface coatings, notably photopolymerization of oligourethane a c r y l a t e ~ ,u.v.-curing ~~ to give vinyl coatings on fabrics,40free-radical homopolymerization induced by U.V. in liquid thermal sensitization effects in photop~lymerization,~~ the kinetics of u.v.-~uring,~~ and u.v.-curing Photografting.-Graft copolymerization of maleimide onto polyethylene and ethyl cellulose by photochemical techniques has been and other 34

36

9e 37

38 39 40

4z 43

44

46

M. M. Millard, J. Appl. Polymer Sci., 1974, 18, 3219. L. W. Sieck, R. Corden, S. G . Lias, and P. Ausloos, Internat. J. Mass. Spectrometry Ion Phys., 1974, 15, 181. G. D. Dixon, J. Polymer Sci., Polymer Chem., 1974, 12, 1717. M. Yokawa, Y. Ogo, and T. Imoto, Makromol. Chem., 1974, 175, 179, 2903, 2913. J. Hutchison and A. Ledwith, Fortschr. Hochpolym. Forschung, 1974, 14, 49. A. K. Chaiko, Y. L. Spirin, and V. V. Magdinets, Vjvokomol. Soedineniya (A), 1975, 17, 96. S. D. Koch and J. M. Price, J. Coated Fabrics, 1975, 4, 166. J. F. Kinstle, J . Radiation Curing, 1974, 1, 2. L. J. Miller, J. D. Margerum, and J. B. Rust, Macromolecules, 1974, 7, 179. V. D. McGinniss and D. M. Dusek, J. Paint Technol., 1974, 46, 23; M. Ibarra and J. M. Smith, Amer. Inst. Chem. Engineers J., 1974, 20, 404. C. B. Rybny and C. A. Defazio, J . Paint Technol., 1974, 46, 60; V. Cermak and J. Mleziva, Farbe Lack, 1974, 80, 125; N. Kishi and J. Kobayashi, Kobunshi, 1974, 23, 130. K. Hayakawa, K. Kawase, and H. Yamakita, J. Polymer Sci., Polymer Chem., 1974, 12,2603.

512

Photochemistry

aspects of grafting onto cellulose by photoirradiation have been The photograft polymerization of methyl methacrylate onto polymers bearing pendant thiosulphate groups, sodium poly(viny1 benzyl thiosulphate), and the sodium salt of poly(viny1 hydrothiosulphatoacetate) has been shown to proceed via the sensitizing action of the thiosulphate group through formation of the thiyl radical.47 This could be accelerated by the addition of FeCI, to the system through reactions (11)-(13). RSS0,Na RSS0,Na RS-

-

+ Fe*+ hv + Fez+ A + Fe3+

RS*

RS-

+ -SO,Na + Fe3+ + 4 0 , N a + Fe3+

RS* + Fe2+

(1 1)

(1 2) (13)

The photoinduced graft polymerization of acrylic acid and n-butyl acrylate on poly(viny1 chloride) or carbon monoxide-vinyl chloride copolymer using benzophenone as a sensitizer has been described.48 Some of the oxime copolymers discussed earlier l3 are also useful as sensitizers of graft copolymerization. Benzophenone has also been used as a photosensitizer for the grafting of vinyl monomers onto Dyes have been used for the purpose of grafting MMA onto collagen, using sunlight as the light source.6o Photocondensation Polymerization.-This term is used in the sense that the polymerization requires the absorption of a photon for every propagation step, as distinct from the photoinitiation of the free-radical chain addition polymerization discussed above. The photodimerization reaction (14) of maleimides in

the solid state has recently been extended by the synthesis of compounds such as ( 5 ) , which form a highly crystalline insoluble solid polymer upon U.V. irradiation.61

d6

47 48

49

N. A. Portnoy and M. C. Nelson, Textile Res. J., 1974,44,449; H. Kubota, Y. Ogiwara, and K. Matsuzuki, J. Polymer Sci., Polymer Chem., 1974, 12, 2809; Y. Ogiwara, H. Kubota, and Y. Murata, J. Appl. Polymer Sci., 1974, 18, 3455; H. Kubota and Y. Ogiwara, ibid., p. 887; Y. Ogiwara and H. Kubota, ibid., 1974, 19, 887; A. H. Reine and 0. Hinojosa, J. Appl. Polymer Sci., 1973, 17, 3337. M. Tsunooka, N. Ando, and M. Tanaka, J. Appl. Polymer Sci., 1974,18, 1197. W. Kawai and T. Ichihashi, J. Macromol. Sci., Chem., 1974, 8, 805. T. Nagabhushanam, K. T. Joseph, and M. Santappa, J. Polymer Sci., Polymer Chem., 1974, 12, 2953.

61

T. Nagabhushanam, K. J. Joseph, and M. Santappa, Leather Sci. (Madras), 1973,20, 403. F. C. De Schryver, N. Boens, and G. Smets, J. Amer. Chem. SOC.,1974, 96, 6463; Macromolecules, 1974,7, 399; N. Boens, F. C. De Schryver, and G. Smets, J. Polymer Sci., Polymer Chem., 1975,13,201.

Polymer Photochemistry 513 Not all such compounds can be polymerized, however, and the authors reasonably argue that the monomer crystal structure dictates the fate of the molecule upon U.V. irradiation in the solid state. The topological control of such polymerization reactions has been the subject of recent extensive reviewsysZand the same phenomenon in 2,5-distyrylpyrazine has been further The true photopolymerization process discussed here is typified by the u.v.-induced polymerization of NN'-polymethylenebis(maleimides) discussed aboveYs1and a complete study of the kinetics of the process is included in this series of papers. The conclusion is reached that the triplet state of the chromophore is the reactive species: this can be quenched by the addition of ferrocene or 3,3,4,4-tetramethyl-1,2-diazetine lY2-dioxide. The kinetics of a further example of true photopolymerization, the reductive photocopolymerization of diaryl ketones, have been compared with those of the photoreduction of the model compound benzophenone and found to be The photoreductive poly-recombination of the diaryl ketones shown in Schemes 2 and 3 has been studied exten~ively.~~ The photocycloaddition reactions (Scheme 4) of further non-conjugated bichromophoric systems, the biscoumarins, have been investigated.66 A luminescence study of the solid-state photopolymerization of p-diethynylthe photopolymerization of epoxidesYb7other photochemical poly-

PhC-Ar-CPh II 0 " 0

/ \

6a

64

IJ.S

/ \

* OH

OH

/ \ ,

G. Wegner, Chimia (Switz.), 1974, 28, 475; Adu. Chem. Ser., 1973, No. 129, 255. M. Hasegawa and H. Nakanishi, J. Polymer Sci., Polymer Letters, 1974, 12, 57; Y. Suzuki, T. Tamaki, and M. Hasegawa, Bull. Chem. SOC.Japan, 1974, 47, 210; F. C. De Schryver, T. Van Thien, and G. Smets, J . Polymer Sci., Polymer Chem., 1975, 13, 215. F. C. De Schryver, T. Van Thien, S. Toppet, and G. Smets, J. Polymer Sci., Polymer Chem., 1975, 13, 227.

st.

4- MezCHOH

F. C. De Schryver, J. Put, L. Leenders, and H. Loos, J. Amer. Chem. SOC.,1974, 96, 6994. A. A. Petrus, Khim. vysok. Energii, 1974, 8, 280. S. I. Schlesinger, Photogr. Sci. Eng., 1974, 18, 387.

514

Photochemistry

PhC-Ar’-CPh

II

0

I1

+

0

P

Y

PhC-Ar2-&Ph I I OH OH

+ MeOH

Y. HO

HO

HO

HO V

PhC-Arl-CPh I1 II 0 0

+

E

+

PhC-Ar3-CPh MeOH II I1 0 0 Scheme 3

Scheme 4

condensat ion react and the solid-state phot opolymerization of amorphous sulphur 6D have been reported. Photochemical Cross-linking.-Much of the motivation of these studies is to render polymeric materials insoluble with U.V. or visible radiation, so that with spatial control of the irradiating light, image-formation results. These processes are of course of great importance in the printing industry (photolithography) and in the electronics industry (photoresists). Cross-linkable species based upon vinylcinnamic acid derivatives are widely used for this purpose, and studies on such systems continue to appear.6o In the study by Tanaka and Otomegawa, the reverse dissociation of the model cross-linked materials (6) and (7) on irradiation at 254 nm (Scheme 5 ) could have useful applications. 58 69

6o

J. F. Kinstle and G. Sivils, J. Radiation Curing, 1974, 1, 11. T. Nakayama, T. Nose, H. Kokada, and E. Inoue, Chem. Letters, 1974, 3, 287. H. Tanaka and E. Otomegawa, J. Polymer Sci.,Polymer Chem., 1974,12, 1125; T. Nishikubo, T. Ichijo, and T. Takaoka, J. Appl. Polymer Sci., 1974,18, 2009; T. Nishikubo and T. Ichijo, Nippon Kagaku Kaishi, 1974, 45.

Polymer Photochemistry

515

\

J

hv (254 nm)

hv (254 nm)

PhCH=CH-CH=CH-CO,

\ y 2 ) 4

PhCH=CH- CH=CH-CO, Scheme 5

A new cross-linking chromophore has been investigated, based upon the 4(or 4'-)substituted benzylideneacetophenone (chalcone) molecule.61 The photocross-linking of epoxyacrylates has recently been studied quantitatively.g2 A novel kind of polymer containing the diazofluorene moiety (8), synthesized from -CH2-

?He

X

(8) X = N, (9) = 0

x

poly-(2-~inylfluorenone)(9),63 becomes insoluble very rapidly upon irradiation at 365 nm owing to loss of molecular nitrogen and subsequent carbene reactions. The thermal instability of the material would seem, however, to preclude its commercial use. For photographic uses, cross-linking must be initiated by light throughout the visible range, and the energy levels of sensitizers for this purpose have been given.sa An interesting report on silver-free photographic materials has appeared.86 Other photosensitive polymers have been described.68 Photopolymers for the recording of hologramsYB7and optical limitations in finepattern photolithography 68 have been discussed. The photochemical cross-linking of polyethylene has been described.6s 6a

6a 6p

O6

EE

O7 68

S. P. Panda, J. Appl. Polymer Sci., 1974,18,2317; Chem. and Ind., 1974, 17, 706; S. P. Panda and D. S. Sadafule, J. Polymer Sci., Polymer Chem., 1975, 13, 259. T. Nishikubo, M. Imaura, T. Mizuko, and T. Takaoka, J. Appl. Polymer Sci., 1974,18, 3445. J. F. Yanus and J. M. Pearson, Macromolecules, 1974, 7, 716, 951. P. Nielsen, Photogr. Sci. Eng., 1974, 18, 186. T. A. Yurre, V. V. Shaburov, and A. V. Eltsov, Zhur. Vsesoyuz. Khim. obshch. im D.I. Mendeleeva, 1974, 19, 412. A. V. Ryabov, Vysokomol. Soedineniya (B), 1975, 17, 195; H. Kamogawa, Progr. Polymer Sci. Japan, 1974, 7, 1. B. L. Booth, Appl. Optics, 1975, 14, 593. M. Wada and K. Uehara, Japan J. Appl. Phys., 1974, 13,2014. L. S. Bogdan, A. A. Kachan, and L. F. Polikanova, Sint. Fiz.-Khim. Polimery, 1974,14, 148; V. P. Solomko and V. A. Shrubovich, Plast. Massy., 1974, 6, 42.

516

Photochemistry

The patents literature relating to photopolymerization is reviewed in the Appendix. Radiation-induced Polymerization.-The references listed here relate to radiationinduced polymerization. Readers should note that these references have been taken directly from the Chemical Society ‘Chemscan’ Profile ‘Radiation Chemistry’, which frequently omits authors’ names from references. Apologies are offered to those authors inadvertently omitted here. The patents literature relating to this area is reviewed in the Appendix. The subjects of reports on radiation-induced polymerization have included the following monomers: efhyleney7O tetraflu~roethylene,~~ a~rylonitrile,~~ acrylic and metha~rylonitrile,~~ alkyl acrylates and rnetha~rylates,~~ other vinyl monomers,77* 78 a ~ r y l a m i d evinylcarbazoleYE0 ,~~ maleimideYE1 pentenes,8zaminoalkyl isobutyl vinyl etherYE4 and buta-1,3-diene.8S 70

72

73 74

76

76

77

78

7B

8a 83

84

S. Senrui, T. Suwa, and M. Takehisa, J. Polymer Sci., Polymer Chem., 1974, 12, 93, 105; S. Senrui, T. Suwa, and K. Konishi, ibid., p. 83; S . Senrui and M. Takehisa, ibid., p. 535; S . Senrui, A. Kodama, and M. Takehisa, ibid., p. 2403;T. Wada, T.Watanabe, M. Takehisa, and S . Machi, ibid., p. 1585;T. Watanabe, T. Wada, M. Takehisa, and S . Machi, ibid., p. 1609; Y . Nakase, H.Arai, and I. Kuriyama, J. Macromol. Sci., Phys., 1974, 10, 41. T. Seguchi, T. Suwa, N. Tamura, and M. Takehisa, J. Polymer Sci., Polymer Phys., 1974,12, 2567; T. Suwa, M. Takehisa, and S. Machi, J. Appl. Polymer Sci., 1974, 18, 2249; N. F. Shamonina and A. G. Kotov, Vysokomol. Soedineniya (B), 1974,16,342;M. A. Bruk, A. D. Abkin, and V. V. Demidovich, ibid. (A), 1975, 17, 3; M. A. Bruk, A. D. Abkin, and V. I. Muromtsev, Radiats. Khim., 1972,2, 241. T. Maekawa and S . Okamura, J. Macromol. Sci., Chem., 1975,A9, 257,265; T. O’Neill and V. Stannett, ibid., 1974,8, 949;V. V. Polikarpov, V. I. Lukhovitskii, R. M. Pozdeeva, and V. I. Karpov, Vysokomol. Soedineniya (A), 1974, 16, 2207; D. A. Kritskaya and A. N. Ponomarev, ibid., p. 2020; A. M. Kaplan, D. P. Kiryukhin, and I. M. Barkalov, Radiats. Khim., 1972,2, 258;T. Wada and M. Takehisa, Polymer J., 1973,5, 255; S. Iiyama, S . Abe, and K. Namba, Nippon Kagaku Kaishi, 1974, 12,2428. A. Chapiro, L. Perec, and S . Russo, European Polymer J., 1974, 10,71. G. Ayrey, B. C. Head, and D. J. D. Wong, European Polymer J., 1974, 10, 85. T. Wada, M. Takehisa, and S . Machi, J. Polymer Sci., Polymer Chem., 1974, 12, 1629; G. Ayrey, B. C. Head, and R. C. Poller, ibid., 1975,13,69;G. Ayrey and A. C. Haynes, European Polymer J., 1973,9,1029;A. Chapiro and R. Gouloubandi, ibid., 1974,10,1159;C . C.Allen, W. Oraby, and T. M. A. Hossain, J. Appl. Polymer Sci., 1974,18,709;M. Hatada, M. Nishii, and K. Hirota, Macromolecules, 1975,8, 19. A. C. Thomas, Polymer J., 1974, 6, 329;A. C. Thomas and T. A. Du Plessis, ibid., p. 329; V. I. Lukhovitskii, A. M. Lebedeva, and V. L. Karpov, Vysokomol. Soedineniya (A), 1973, 15,2465; M.Katayama and S . Ushimaru, Chem. Letters, 1974, 4,769. M. Tavan, G. Palma, M. Carenza, and S. Brugnaro, J. Polymer Sci., Polymer Chem., 1974, 12,411;M.Carenza, G. Palma, and M. Tavan, ibid., Polymer Symposia, 1973,No.42, 1031; A. M. Smirnov and V. I. Lukhovitskii, Vysokomol. Soedineniya (B), 1973, 15, 907; V. V. Kolesnikova, 0. V. Kolninov, V. K. Milinchuk, and S . Y . Pshezhetskii, ibid. (A), 1974, 16, 2474;A. Chapiro, Makromol. Chem., 1974,1181;N.K. Henderson, S. Yamakawa, and V. T. Stannett, J. Macromol. Sci., Chem., 1975,A9,415;T. S.Sirlibaev, L. L. Gubareva, and Kh. U. Usmanov, Uzbek. khim. Zhur., 1974,18,55. J. C. Bray and E. W. Merrill, J. Appl. Polymer Sci., 1973,17,3781. V. F. Gromov and A. P. Sheinker, Vysokomol. Soedineniya (A), 1974,16,365;A. E.Chalykh, V. W. Goryaev, G. W. Plavnik, G. G. Ryabchikova, and V. I. Spitsyn, ibid., p. 2554;G. P. Korneeva, D. M. Margolin, and E. B. Mamin, Radiats. Khim., 1973,2, 275. S. Tagawa, S. Arai, M. Imamura, and Y . Tabata, Macromolecules, 1974,7 , 262; S.Tagawa, Y. Tabata, S. Arai, and M. Imamura, J. Polymer Sci., Polymer Letters, 1974, 12, 545. L. A. Petrukhno and V. S . Ivanov, Vysokomol. Soedineniya (A), 1974, 16, 1469. I. M. Kolesnikov and G. M. Panchenokov, Radiats. Khim., 1972,2, 211. U. N.Musaev, A. N. Karmiov, R. S. Tillaev, and Kh. U. Usmanov, Vysokomol. Soedineniya (A), 1974,16, 1931. T. A. Du Plessis and V. T. Stannett, J. Polymer Sci.,Polymer Chem., 1974,12,2457. T. Shiga and S . Okamura, Polymer J., 1974,6, 1.

Polymer Photochemistry 517 Radiation-induced curing of plastic coatings has been discussed,86 and radiation-induced polymerization in the solid state r e p ~ r t e d . ~The ? radiation chemistry of epoxy-containing electron resists 88 and polycondensation induced by ionizing radiation in the urea-formaldehyde system 80 have been described. Radiation-induced copolymerization of the following pairs of monomers has been achieved; ethylene-hexafluoropropylene,Oo tetrafluoroethylenep r ~ p y l e n e , ~tetrafluoroethylene-hexa~uoropropylene,92 ~ hexafluoroacetonea-olefins,O3 MMA-di- and tri-methacrylates,04styrene-acrylonitrile,05 buta-1,3diene-acrylonitrile,O8 and acenaphthylene-vinylcarbazole.07 There have been many studies of graft copolymer formation initiated by ionizing radiation, and methods have been Among the systems studied are styrene onto p~lyethylene,~~ styrene onto polypropylene,loOstyrene onto Ny10n-6,~~~ styrene onto ethylene-vinyl acetate styrene and MMA onto natural rubber,lo3 pentafluorostyrene onto Nylon and polyethylene,lo4acrylamide onto Nylon-6,1°5acrylamide onto starch,logvinyl monomers

Oa

I. Kaetsu, A. Ito, and Y. Maeda, Plast. Znd. News, 1974,20,81; N. D. Rozenblyum and L. V. Chepel, Radiats. Khim., 1972, 2, 505. D. P. Kiryukhin and I. M. Barkalov, European Polymer J., 1974, 10, 309; V. S. Ivanov, I. I. Migunova, and L. A. Petrukhno, Radiats. Khim., 1972, 2, 269; M. K.Yakovleva, V. G. Nekhoroshev, A. P. Sheinker, and A. D. Abkin, Vysokomol. Soedineniya (B), 1975, 17, 212; I. Suguwara, E. Marchal, H. Kadoi, Y.Tubata, and K. Oshima, J. Macromol. Sci., Chem., 1974, A8, 995. L. F. Thompson, E. D. Feit, and R. D. Heidenreich, Polymer Eng. Sci., 1974, 14, 529. K. Hayasahi, S. Munari, and C. Rossi, Chimica e Industria, 1974, 56, 264. S. Senrui, M. Ito, and M. Takehisa, J. Polymer Sci., Polymer Chem., 1974, 12, 627; A. D. Sorokin and E. V. Volkova, Radiats. Khim., 1972, 2,295; R. A. Naberezhnykh and A. D. Sorokin, Zzvest. Akad. Nauk S.S.S.R., Ser. khim., 1974, 232. 0 . Matsuda, J. Okamoto, N. Suzuki, M. Ito, and Y. Tabata, J. Macromol. Sci., Chem., 1974, AS, 775; N. Suzuki, 0. Matsuda, and J. Okamoto, ibid., p. 793; N. Suzuki, 0. Matsuda, and J. Okamoto, J. Polymer Sci., Polymer Chem., 1974, 12, 2045; 0. Matsuda, J. Okamoto, N. Suzuki, M. Ito, and A. Danno, ibid., p. 1871; N. Suzuki, 0. Matsuda, and J. Okamoto, J. Appl. Polymer Sci., 1974, 18, 2457; N. Suzuki and J. Okamoto, J. Polymer Sci., Polymer Chem., 1974, 12,2693; J. Macromol. Sci., Chem., 1975, A9, 285. R. A. Naberezhnykh and A. D. Sorokin, Doklady Akad. Nauk S.S.S.R., (Phys. Chem.), 1974, 214, 149.

Y.Tabata, W. Ito, and K. Oshima, ACS Ado. Chem. Series, 1973, No. 129, 190. O4 O6 O6

O8

C. C. Allen, W. Oraby, D. R. Squire, E. P. Stahel, and V. T. Stannett, J. Macromol. Sci., Chem., 1974, AS, 965. S. Teramachi and H. Uchiyama, Polymer J., 1973, 5, 243. K. Ishiyre and V. T. Stannett, J. Macromol. Sci., Chem., 1974, 8, 337. A. Chapiro and P. Lesaulnier, European Polymer J., 1974, 10, 171. V. Ya. Kabanov, L. P. Sidorova, and V. I. Spitsyn, European Polymer J., 1974, 10, 1153; B. L. Tsetlin, Radiats. Khim., 1972, 2,297; V. S. Os’kin, A. I. Ponomarev, and A. V. Vlasov, ibid., p. 496; L. P. Yanova, G. S. Blyskosh, and A. B. Taubman, ibid., p. 330; B. L.Tsetlin, A. V. Vlasov, and I. Yu. Babkin, Radiats. Khim. Polimery, 1973, 108. M. Imai and S . Shimizu, J. Polymer Sci., Polymer Chem., 1973, 11, 3181; 1974, 12, 2729.

loo

lol

K. Nunome, B. Eda, and M. Iwasaki, J. Appl. Polymer Sci., 1974, 18, 2711, 2719. M. A. El-Azmirly, A. H. Zahran, and M. F. Barakat, European Polymer J., 1975, 11, 19.

D. Pilz, Plaste Kautsch., 1975, 22, 18. W. Dzierza, Polimery, 1973, 18, 588. lo4 J. E. Wilson, J. Macromol. Sci., Chem., 1974, 8, 307. l o s I. M. Trivedi, P. C. Mehta, and K. N. Rao, J. Appl. Polymer Sci., 1975, 19, 1; W. M. Dziedziela, M. B. Huglin, and R. W. Richards, European Polymer J., 1975, 11, 53. loe G.F. Fanta, R. C. Burr, and W. M. Doane, J. Appl. Polymer Sci., 1974, 18, 2205.

loa

lo8

518

Photochemistry onto cellulose lo’ and polyolefins,lo8acrolein onto poly(styrene),lo9 acrylonitrile and silicone onto rayon,11o butadiene 111 and vinyl fluoride 112 onto poIy(viny1 chloride), 4-vinylpyridine onto polytetrafl~oroethylene,~~~ ethylenediamine onto poly(ethylene terepht halate) ,11* acenapht hylene onto polyethyleneY1l6 and suiphonated monomers onto polyamide fibres.ll* Mechanisms of irradiationinduced grafting onto polyethylene have been Many grafts of vinyl monomers, principally styrene, onto wood have been achieved with y-irradiation,l18and the grafting of MMA onto glass has been reported.ll@ The radiation cross-linking of polyethylene,120poly(viny1 chloride),121 poly(vinylidene) fluoride,122poly(tetrafl~oroethylene),~~~ and several elastomers 124 U. Azizov, M. U. Sadykov, and Kh. U. Usmanov, Radiats. Khim., 1972, 2, 302; B. V. Drachev, N. G. Kon’kov, and V. V. Korneeva, Radiats. Tekh., 1972, 8, 16; S. R. Agarwal and A. Sreenivasan, Indian J. Technol., 1974,12,456;Y. Ogiwara, N.-S. Hon, and H. Kubota, J. Appl. Polymer Sci., 1974, 18, 2057. lo8 J. L. Garnett and N. T. Yen, J. Polymer Sci., Polymer Letters, 1974, 12,225;J. E. Wilson, J. Macromol. Sci., Chem., 1974, 8, 733. Ins S. Miyanchi and S . Ohnishi, Kobunshi Ronbunshu, 1974,31, 659. 110 L. L. Staroverova and Yu. V. Granovskii, Doklady Akad. Nauk S.S.S.R. (Phys. Chem.), 1974,215, 1168;S. Nishide and H. Shimizu, Textile Res. J., 1974,44,900. ll1 K. Hamanoue, M. Shimizu, and H. Higaki, J. Polymer Sci., Polymer Phys., 1974, 12, 1189. 112 S. M. Musakhanova and Kh. U. Usmanov, Doklady Akad. Nauk Uzbek. S.S.R., 1973, 30, 41;S. Yamakawa and V. Stannett, J. Appl. Polymer Sci., 1974, 18,2177. 113 A. Chapiro and E. Gordon, European Polymer J., 1973, 9, 975;V. Ya. Kabanov and R. E. Aliev, Vysokomol. Soedineniya (B), 1975, 17,29. 114 C.Simionescu and C. Vasiliu-Perea, European Polymer J., 1974,10, 61. 115 Z.G. Zagorskaya and N. S . Tikhomirova, Plast. Massy, 1974,9. 116 S. Munari, G.C. Tealdo, and P. Canepa, Chimica e Industria,1974,56, 358. 11’ T.Segachi and N. Tamura, J. Polymer Sci., Polymer Chem., 1974, 12, 1671, 1953;T. Sasuga, Y. Shimizu, and T. Sasaki, Kobunshi Kagaku, 1973, 30, 761; R. V. Dolgova and Z . F. Il’icheva, Vysokomol. Soedineniya (B), 1974, 16, 220. 118 M. Piatrik and S . Varga, Radiochem. Radioanalyt. Letters, 1974,18, 61, 77;ibid., 1974, 19, 11, 191; S. Varga and M. Piatrik, ibid., 1974, 18, 69, 191; 1974, 19, 135, 255; L. Paszner, Wood Sci. Technol., 1974,8, 106. llB H.Yoshioka and F. Higashide, J. Appl. Polymer Sci., 1974, 18,939. lz0 G. N. Patel and A. KeIIer, J. Polymer Sci., Polymer Phys., 1975, 13, 303,333; G.N. Patel, ibid., pp. 351, 361; T. Besmann and R. Greer, ibid., p. 527; K. Singer, M. Joshi, and J. Silverman, J. Polymer Sci., Polymer Letters, 1974,12,387;V. L. Kornov and E. E. Finkel, Radiats. Khim., 1972,365;E.E. Finkel and R. P. Braginskii, Radiats. Khim. Polimery, 1973, 186; A. M. Kabakchi, G. N. P’yankov, and E. G. Yarmilko, Radiats. Khim., 1972, 373; B. G.Fedotov, M. P. Eidel’nant, and A. G. Sirota, Plast. Massy, 1973, 18; I. V. Palei and A. I. Krivonosov, ibid., 1974, 16;G . N. Patel, L. D’Ilario, and A. Keller, Makromol. Chem., 1974, 175, 983;W.X. Wen, D. R. Johnson, and M. Dole, Macromolecdes, 1974, 7 , 199; H.Mitsui and F. Hosoi, J. Appl. Polymer Sci., 1975,19,361;G . D.Korodenko, S.N. Karimov, and A. Sultanov, Vysokomol. Soedineniya (A), 1974, 16, 2651; H. Mitsui, F. Hosoi, and T. Kagiya, Polymer J., 1974,6,20;D. Stanko, I. Slavchev, and E. Kashtieva, Angew. Makromol. Chem., 1974, 35, 1; M. Hagiwara, T. Tagawa, and E. Tsuchida, J. Macromol. Sci., Chem., 1973,7 , 1591 ; J. Loboda-Cackovic, H. Cackovic, and R. Hosemann, Colloid and Polymer Sci., 1974,252, 738. 121 K. Mori, Y. Nakamura, and H. Harada, Nippon Kagaku Kaishi, 1974,11,2235. lZ2 T. Seguchi, K. Makuuchi, and T. Suwa, Nippon Kagaku Kaishi, 1972,7,1309; K.Makuuchi, T. Seguchi, and T. Suwa, ibid., 1973,8, 1574. 193 M.Tutiya, Polymer J., 1974,6, 39; E. L. Gal’perin, Vysokomol. Soedineniya (A), 1974, 16, 1265;N. I. Bol’shakova and N. S . Tikhomirova, ibid., 1974,16, 1913. lZ4 V. G.Nikol’skii and L. Yu. Zlatkevich, J. Polymer Sci., Polymer Phys., 1974,12,1259;D.S . Pearson and B. J. Skutnik, ibid., p. 925;V. T. Kozlov, A. G. Euseev, and G. G. Gubanov, Radiats. Khim., 1972,358;I. Ya. Poddubnyi and S . V. Aver’yanov, ibid., p. 350;F . A. Makhlis, L. Ya. Nikitin, and S . N. Arkina, Khim. vysok. Energii, 1974,8, 183; R. J. Eldred, Rubber Chem. Technol., 1974,47,924;R. L. PrzybyIa, ibid., p. 285; A. S . Kuz’minskii, Ada. Radiation Res. Phys. Chem.. 1973, 2, 571. lo7

Polymer Photochemistry

519

has been reported. The fixation of dyes on natural silk 12s and the chlorination of polyethylene 126 by y-irradiation have been discussed. 3 Optical Properties, including Luminescence of Polymers A MIND0/3 method has been used to calculate the electronic structure of and comparison has been made with the photoelectron spectrum. Extended Huckel calculations on six fluorinated compounds derived from linear polyethylene have been carried out with the same objective.12* The circular dichroism of unordered polymers has been treated on the basis of timedependent Hartree and high-resolution inelastic tunnelling spectroscopy of macromolecules has been A series of papers has appeared on the molecular motions in polymer networks revealed by Rayleigh light-scattering linewidth measurements using photon The method has a resolution of one part in lo4, correlation and measures fluctuations in local dielectric permittivity in the scattering system, which in a binary system such as polymer and solvent are caused mainly by concentration fluctuations resulting from Brownian motion. The method thus provides a means of investigating motions occurring over 100 nm + 1 pm in polymer-solvent systems. The method has been used to evaluate the relaxation time T~ of the first mode in the Rouse-Zimm132 analysis of intramolecular motion in polymers, and in the case of linear polystyrene in the molecular weight ( M ) range 5 x los to 20 x los this was shown to depend upon Luminescence in polymers continues to attract interest, and one aspect of this phenomenon concerns the use of luminescence measurements to study interchromophoric distances, segmental motion, and polymer conformation. A review of relaxation processes in polymers, including electronic energy migration, has appeared.133 A novel technique has been reported for monitoring the magnetic-field-modulated delayed fluorescence in poly-(Zvinylnaphthalene) at 77 K, which yields information concerning the local ordering of the naphthalene c h r o r n o p h o r e ~ .In ~ ~the ~ case of this polymer, the normal axes of the chromophores are aligned approximately parallel to one another. An analysis of polarized fluorescence from polystyrene polymers containing an anthracene chromophore has been made,135and polarization measurements have also been M 1 a 5 .

126

lZ6

130

la2 133 134

136

M. P. Tkhomolova and V. A. Ledneva, Zhur. priklad. Khim., 1974,47, 1826. B. M. Korolev, V. I. Kosorotov, G. N. Kirillov, A. V. Egunov, A. V. Chertorizhskii, and R. V. Dzhagatspariyan, Vysokomol. Soedineniya (A), 1974, 16, 2725. M. S. Dewar, S. H. Suck, and P. K. Weiner, Chern. Phys. Letters, 1974, 29, 220. J. Del Halle, Chem. Phys., 1974, 5, 306; J. Del Halle, S. Del Halle, and J. Andre, Bull. SOC. chim. belges, 1974, 83, 107. D. A. Rabenold, J. Chem. Phys., 1975, 62, 376. M. G. Simonsen, R. D. Coleman, and P. K. Hansma, J. Chem. Phys., 1974, 61, 3789. J. D. G. McAdam, T. A. King, and A. Knox, Chem. Phys. Letters, 1974, 26, 64; J. D. G. McAdam and T. A. King, ibid., 1974,28,90; Chem. Phys., 1974,6,109; T . A. King, A. Knox, and J. D. G. McAdam, J. Polymer Sci., Polymer Symposia, 1974,44, 195; J. C. Brown, P. N. Pusey, and R. Dietz, J. Chem. Phys., 1975, 62, 1136. R. E. Rouse, J. Chem. Phys., 1953, 21, 1272; B. H. Zimm, ibid., 1956, 24, 269. A. M. North, Pure Appl. Chem., 1974, 39, 265. P. Avakian, R. P. Groff, A. Sung, and H. N. Cripps, Chem. Phys. Letters, 1975, 32, 466. B. Valeur and L. Monnerie, Compr. rend., 1975, 280, C, 57; B. Valeur, P. Rempp, and L. Monnerie, ibid., 1974, 279, C, 1009.

Photochemistry

520

used to determine the orientation of polymer Fluorescence quenching and polarization measurements have been used to study segmental motion in polystyrene 13’ dissolved in toluene, anthracene units being incorporated into the chain and on terminal sites. The results showed that the rotational relaxation time for the terminal anthracene was 0.86ns, that for an anthracene molecule incorporated within the chain being 4.7 ns. The actual physical orientation of macromolecular suspensions through the application of an electrical force in the form of the electric field from an intense pulsed laser has been reported.13* Excimer formation has been studied in polystyrene and poly(wa1kylstyrenes) 139 (PS), poly(vinylcarbazole),13g~lC0 poly-(2-vinylnaphthalene), and poly-(4-vinylbiphenyl).141 For polystyrene films, David et aZ.139showed that the fluorescence yield increased with increasing crystallinity, at both ambient temperature and 77 K. The contribution of excimer fluorescence yield increased in the sequence atactic (0.7) < atactic oriented (0.60) < isotactic amorphous (0.28) < isotactic crystallized (0.01), with normal yields relative to excimer given in parentheses. Similar results were obtained for poly(vinylcarbazole), PVCZ, although the contribution of excimer fluorescence at 77 K was independent of crystallinity. The results can be interpreted in terms of electronic energy migration to lowenergy defect sites from which excimer emission can occur. In PVCZ copolymers with fumaronitrile (lo), diethyl fumarate (1 l), and diethyl maleate (12) (Scheme 6), CH=CH, \

/ \

H

vcz

CN I

H

CN

(10) Et0,C

H

\

vcz +

/

,c=c, H

CO,Et (1 1)

H

vcz

+

H

‘

/c=c\ Et0,C

I

4

CH-CH2-CH-CH

COZEt

(12)

Scheme 6 136

13’

lS8 139

140

Yu. V. Brestkin, E. S. Edilyan, and S. Ya. Frenkel, Vysokomof.Soedineniya (A), 1975,17,451. K. Brown and I. Soutar, European Polymer J., 1974, 10, 433. B. Jennings and H. Coles, Nature, 1974, 252, 33. C. David, N. Putman de Lavareille, and G. Gueskens, European PoZymer J., 1974, 10, 617; C. David, M. Lempereur, and G. Gueskens, ibid., p. 1181; T. Ishii, H. Matsushita, and T. Handa, Kobunshi Ronbunshu, 1975, 32, 211; Yu. N. Demikhov, A. N. Faidysh, and V. N. Yashchuk, Optika i Spektroskopiya, 1974, 37, 686. M. Yokoyama, T. Tamamura, M. Atsumi, M. Yoshimura, Y. Shirota, and H. Mikawa, Macromolecules, 1975, 8, 101. C. W. Frank and K. A. Harrah, J . Chem. Phys., 1974, 61, 1526; C. W. Frank, ibid., p. 2015.

521

Polymer Photochemistry

the 1 : 1 alternating copolymers with (10) and (11) exhibit no excimer fluorescence, whereas the PVCZ homopolymer and VCZ-rich copolymer with (12) exhibit this type of luminescence. These observations suggest that for polymers with carbazole rings as pendant groups, excimer formation is possible only between two adjacent chromophores separated by a main-chain segment of three carbon atoms. Similar absence of excimer luminescence in copolymers of ol-methylstyrene of the general structure (13) has been noted 130 at room temperature in Me

Me

I

-C -CH,-CH,I

Ph (13)

~1 =

I C -(CH,) n-

I Ph

3-6

solution, whereas p oly(or-met hylstyrene), P MS, exhibits excimer fluorescence under these conditions. In films, PMS exhibits only excimer emission at ambient temperature, and both normal and excimer emission at 77 K. Copolymer films did not give excimer emission at 330 nm. An emission at 310 nm was assigned to an unidentified energy trap different from the excimer site in PS and PMS. These studies have been reinforced by a report on emission from films and solutions of alternating copolymers of styrene-MMA, 2-vinyl naphthalene-MMA, styrene-2naphthyl methacrylate, and ~tyrene-co-2-vinylnaphthalene-MMA.~~~ No excimer emission was observed from these alternating copolymers, and thus non-nearest neighbours and interchain interactions are absent in these systems. Migration of electronic energy was shown to occur, however, by the provision of triplet energy traps, although sequences of a few MMA units were sufficient to inhibit triplet migrations through aromatic groups on the same chain. This does not prevent interchain migration from occurring. A few adventitious low-energy impurities are sufficient to give rise to delayed exciplex and excimer emission under conditions where excimers themselves are not readily formed. In poly(4-vinylbiphenyl) PVBP films and solutions, excimer formation is temperature dependent ;lalthe results in rigid solutions were interpreted in terms of activated exciton migration to a preformed excimer site of conformational energy 800 cal. The mechanism for this migration was proposed to involve modulation of interchromophoric separation by the longitudinal acoustical vibrations of the polymer chain of frequency 150 -t. 30 cm-l. Energy migration in dilute solutions of poly(phenylacety1ene) has been and shown to be significantly faster in fluid media than in rigid solution. It was suggested that segmental rotation in the fluid brings neighbouring chain units into conformations suitable for resonant energy transfer and prevents conjugated sequences from functioning as excitation traps. Energy transfer in polymers containing conjugated bonds has been further and the phenomenon in vinyl polymers la6and in wool keratin 146 has also been studied. 149

148 144

146

R. B. Fox, T. R. Price, R. F. Cozens, and W. A. Echols, Macromolecules, 1974, 7, 937. A. M. North, D. A. Ross, and M. F. Treadaway, European Polymer J., 1974, 10, 411. T. G. Samedova and B. E. Davydov, J. Polymer Sci.,Polymer Symposia, 1973, 42, 913. K. Okamoto, Kubunshi, 1974,23, 514. K. P. Ghiggino, C. H. Nicholls, and M. T. Pailthorpe, J . Phurochem., 1975, 4, 155.

522

Photochemistry

In this last study it was shown that the luminescence emission from wool keratin is very similar to that from tryptophan in a solid poly(viny1 alcohol) film, which thus provides a useful model system. In both cases the triplet state could be readily studied both at 77 K and ambient temperatures by emission and absorption spectroscopy. Energy migration in a polypeptide has been studied by observing the sensitization of the cis-trans isomerization of trans-~tilbene.~~ In the studies above, the polymeric material itself contained the absorbing chromophore, but there have been several studies of energy migration in polymeric materials doped with additives. Thus transfer between like molecules (homotransfer) including Rhodamine B, 9-methylanthracene, and 5-methyl-2phenylindole in thin rigid cellulose films has been studied.14' It was shown that the critical distance R at which the probability of excitation transfer was equal to that of emission from these substances is dependent on excitation wavelength, showing that thermal relaxation does not occur prior to transfer. Energy migration in a system of dyes sorbed on a polymer has also been described.148 Energy transfer from excited species created by chemiluminescent reactions within polymers has been studied recently,149in extension of previous work.lS0 The species formed in the more recent work are the acetone singlet and triplet states from oxetan thermal dissociation, and possible processes occurring with 9,lO-diphenylanthracene (DPA), 9,lO-dibromoanthracene (DBA), 1,4-dibromonaphthalene (DBN), and camphorquinone (CQ) are illustrated in Figures 1 and 2. The study concludes that the major mechanism of quenching of triplet acetone by DBA is a long-range triplet-singlet interaction, in keeping with an earlier report on transfer from triplet cyclohexanone to DBA.lS0 The amplification of chemiluminescence by energy transfer of this nature in a polystyrene matrix is triplet-singlet to DBA, followed by singlet-singlet transfer from DBA (@ N 0.1) to DPA (@ N l.0).149 Energy-transfer processes in poly(4-vinylpyridine) 151 and poly(adeny1ic acid) 152 have been discussed. Several papers have appeared recently concerned with the luminescence arising from degraded polypropylene and other p o I y o l e f i n ~p, ~o~l y~ ~ t y r e n e16* ,~~~~ and polyamides, including nylon^.^^^^ 156 The chromophores in these cases are carbonyl and aromatic impurities introduced during processing, and pigments, l47

149

150

lS1

152

153

lS4 155

A. Kawski and J. Kaminski, 2.Naturforsch., 1975, 30a, 15. I. M. Gulis, B. N. Kas'kov, and M. A. Katibnikov, Zhur. priklad Spektroskopii, 1974, 20, 127. N. J. Turro and H. Steinmetzer, J. Amer. Chem. SOC.,1974, 96, 4677, 4679. D. Phillips, V. I. Anissimov, 0. N. Karpukhin, and V. Ya. Shlyapintokh, Nature, 1967, 215, 1163; Photochem. and Photobiol., 1969, 9, 183; Izuest. Akad. Nauk S.S.S.R. Ser. khim., 1970, 1529. Yu. E. Kirsch, N. R. Pavlova, and V. A. Kabanov, Doklady Akad. Nauk S.S.S.R. (Phys. Chem.), 1974, 218, 863. P. Szerenyi and H. H. Dearman, J. Chem. Phys., 1973, 58, 2467. N. S. Allen, J. F. McKellar, and G. 0. Phillips, J. Polymer Sci., Polymer Letters, 1974, 12, 253; ibid., Polymer Chem., 1974, 12, 2647; Chem. and Ind., 1974, 300; N . S. Allen, J. Homer, J. F. McKellar, and G. 0. Phillips, British Polymer J., 1975,7, 1 1 ;N. S. Allen, J. F. McKellar, G. 0. Phillips, and D. M. Wood, J . Polymer Sci., Polymer Letters, 1974, 12, 241. W. Klopffer, European Polymer J., 1975,11, 203; G. A. George, J . Appl. Polymer Sci., 1974, 18, 419. N. S. Allen, J. F. McKellar, and G . 0. Phillips, J. Polymer Sci., Polymer Chem., 1974, 12, 1233, 2623.

Polymer Photochemistry

:

/

523

acceptors

’0 ICQ

Figure 1 Path 1 is the long-range, through-space singlet-singlet energy transfer from IA to DPA. Path 2 is the singlet excitation of a phenyl group in the polymer followed by energy migration along the polymer chain(s). Path 3 is the singlet-singlet excitation of CQ by difusion of ‘A to CQ followed by collision, exchange energy transfer. Path 4 is the excitation of DPA or CQ after the migration of singlet excitation along the polymer chain. Only path 1 operates with detectable efficiency under the reported conditions (Reproduced by permission from J. Amer. Chem. SOC.,1974, 96, 4677)

catalyst residues, and oxygen-polymer charge-transfer complexes. The studies show that relatively long-lived species (2.3 s + 150 ms) exist in polyethylene, and polypropylene ( ~ s)1 which emit phosphorescence in the blue region of the spectrum 445-495 nm, and that these may be of importance in initiating photooxidation of the polymer. The anatase form of TiO, was found to quench strongly the polypropylene long-lived emission, resulting in emission from the

BR

3DBN

Figure 2 Path 1 is the long-range, through-space triplet-singlet energy transfer from ,A to lDBA. Path 2 is the trllplet-triplet excitation of a phenyl group in the polymer, followed by path 3, the migration of triplet energy along the polymer chain, and then by either path 4, triplet-singlet energy transfer to IDBA, or path 5, triplet-triplet energy transfer to 3DBN. Path 6 is the difusion of ,A through the medium and collisionalexchange triplet-triplet energy transfer to 3DBN (Reproduced by permission from J. Amer. Chem. SOC.,1974, 96, 4677)

Photochemistry anatase itself as the only observable luminescence. The rutile form of TiOa had no effect on the long-lived emission from the polymer. The quenching by anatase was attributed to a chemical interaction which accelerated the photodegradation of the polymer, but since the chromophore responsible for the initial light 524

A/nm

Figure 3 The corrected excitation spectrum of polystyrene phosphorescence compared with the action spectrum of photodegradation. The extent of degradation is given by AO.D., the change in sample optical density at 400 nm (Reproduced by permission from J. Appl. Polymer Sci., 1974, 18, 419)

absorption was not identified, the exact mechanism of this interaction remains obscure. Since the chromophores alluded to above all absorb solar radiation, they can be considered to be of importance in the oxidative degeneration of polymeric materials by sunlight. This has been illustrated by George164for the case of polystyrene, in which part of the emission from the polymer was shown to originate in phenyl alkyl ketone end-groups, with two decay times of 3 and 100ms. These ketones were held to be responsible for the u.v.-degradation of the polymer, and a comparison of the emission excitation spectrum and photodegradation action spectrum was given (Figure 3). The phosphorescence arising from Nylon-6, -66, and -11 has been attributed to nr* carbonyl emission.lS6 In the case of Nylon-66, two distinct bands were seen at 425 and 465 nm (Figure 4), which varied with thermal treatment. Upon photochemical excitation the two bands disappeared and were replaced by a single maximum at 455 nm. The loss of the 425 nm band can be accounted for in terms of reactions such as (15).

525 Model compounds were shown to behave in an entirely analogous manner. These studies demonstrate the usefulness of emission as a probe for photochemical oxidative reactions in polymeric materials.

Polymer Photochemistry

Figure 4 Phosphorescence emission spectra for Nylon-66 chip exciting at 300 nm : (-) before heating and (- - -) after heating for 1 h at 180 "C. Inserts: Phosphorescence decays from Nylon-66 chip. (a) excitation h = 280 nm, emission h = 420 nm, mean lifetime = 2.06 s ; (b) excitation h = 320 nm, emission h = 475 nm, mean lifetime = 0.29 s. Time scale = 0.50 s cm-l (Reproduced by permission from J. Polymer Sci., Polymer Chem., 1974, 12, 1233)

Photovoltaic effects in polymers have continued to attract interest. Polyethylene films sandwiched between parallel transparent electrodes exhibit photocurrent pulses on illumination after being subjected to d.c. fields of up to lo5V mm-l; the effect is attributed to a hopping motion of detrapped electrons in the field of an injected space-charge.166Similar studies have been carried out on poly(ethy1ene terephtha1ate),ls7 other organic polymers,168 and polymerB. Andress, Colloid and Polymer Sci., 1974, 252, 650. Y. Takai, T. Osawa, K. C. Kao, T. Mizutani, and M. Ieda, Jap. J. Appl. Phys., 1975,14,413. lS8 V. S. Mylnikov, Uspekhi Khim., 1974, 43, 1821. 18 lS8

lS7

Photochemistry

526

charge-transfer complex systems,16nbut most attention is focused upon PVCZbased systems.16o Photo-oxidation or ageing has been shown to affect the yields for carrier generation in PVCZ, and photo-oxidation mechanisms have been discussed by Pfister and Williams.lao Addition of trichloroacetic acid was shown by these authors to reduce the field dependence of carrier generation, and to sensitize it at low fields and quench it at high fields; a kinetic model was developed to account for the results. Fleming 160 has proposed an explanation of the shape of photoconductivity current-time traces in thin films of such markedly different materials as anthracene, selenium, and PVCZ ; Okamura 160 has also considered this phenomenon. The use of PVCZ for erasable image-formation by the spatial deformation of a metallized elastomer deposited on top of a photoconductor (a device termed a ‘y-Ruticon’) is reported in the paper by Lakatos.lso Photochromic polymers have been produced based upon the NN’-dialkyl4,4’-dipyridinium (‘viologen’) systerp,lsl indolinospirobenzopyrans, and aromatic azo-units 182 and other systems;las these could have important applications for information storage. Examples are given below of the chromophore responsible for the viologen (14), spiro-benzopyran (15), and azo (16) types of photochrome. The dependence of the absorption spectrum of photolysed polycarbonate upon the spectral composition of U.V. radiation has been discussed.ls4 N C H 2 C H 2 C H & ~ - C H 2 C H 2 C 0H 2 N H 0 8 ~ ~OH f 1

Br-

L

-

Br

(14) ‘viologen’‘photochromic polymer

J,

Mf ,Me

H,C

‘O-C-C=CH, II I

0 Me (15 ) monomer for indolinospirobenzopyran photochromic polymer M. Kryszewski, P. Wojcieckowski, S. Sapietia, M. Zielinski, and J. Tyczkowski, J. Polymer Sci., Polymer Chem., 1975, 13, 141. loo G. Pfister and D. J. Williams, J. Chem. Phys., 1974, 61, 2416; K. Okamura, J. Appl. Phys., 1974, 45, 5317; A. I. Lakatos, ibid., p. 4857; R. J. Fleming, ibid., p. 4944; H. Sato, S. Ono, and E. Ando, ibid., p. 1675; P. K. C. Pillai and R. C. Ahuja, J. Polymer Sci., Polymer Phys., 1974, 12, 2465; T. Minegishi, E. Kondo, T. Yamanruchi, and K. Kinjo, 2.phys. Chem. (Frankfurt), 1974, 91, 1. M. J. Simon and P. T. Moore, J. Polymer Sci., Polymer Chem., 1975, 13, 1. J. Verborgt and G. Smets, J. Polymer Sci., Polymer Chem., 1974, 12, 2511; G. Smets and F. De Blauwe, Pure Appl. Chem., 1974, 39, 225. 163 M. Kikuchi, T. Kakurai, and T. Noguchi, Kobunshi Ronbunshu, 1974,31, 551. 1. A. Mikheev, V. P. Pustoshnyi, and D. J. Toptygin, Doklady Akad. Nauk S.S.S.R.,1974,219,

lsg

389.

Polymer Photochemistry

527

L

(16) -aromatic azo photochromic polymer

The synthesis of fluorescent polymers by interfacial polymerization reactions has been achieved,lss and thermoluminescence in u.v.-irradiated polyethylene ls6 and polyurethane ls7 has been reported. The determination of refractive index changes in photosensitive polymer films by an optical waveguide technique has been described.lss The photomechanical (contraction upon irradiation) behaviour of the aromatic azo type of photochromic unit (16) when copolymerized with poly(ethy1 acrylates) has been discussed.ls2 Studies on the dimensions of oligopeptides using singlet-singlet energy transfer have been carried out .16@

4 Photochemical Reactions in Polymeric Materials Most of the papers in this section are concerned with photo-oxidation reactions, but a few papers refer to photochemical reactions in polymer matrices. Thus the kinetics of the photo-oxidation of anthracene and naphthacene in solid polystyrene (PS),17* the photoionization of aromatic hydrocarbons dissolved in PMMA and PS,171 the photoreactions of naphthalene in cellulose t r i a ~ e t a t e , ~ ? ~ the cis-trans isomerization of stilbene residues in the side-chains of polymers,173 intrachain photodimerization in photoisomerization of 1,2-diphenylcyclopropane by peptides containing naphthalene in a ~ i d e - c h a i n and , ~ ~ ~photochemical transformations of poly(viny1p-azidobenzoate) 1 7 have ~ been reported. Among reviews published are included the subjects of polymer photochemistry (in Russian),17' the photochemical oxidation of polymers (in Spanish),178and lE6

Io6

A. Uno and T. Kondo, Polymer J,, 1974, 6, 267. H. J. Wintle, Polymer, 1974,15,425; K. Araki, M. Endo, and K. Yahagi, Jap. J. Appl. Phys., 1974,13, 1787.

le7

160

V. N. Korobeinikova, V. P. Kazakov, R. S. Aleev, and Yu. N. Chuvilla, Vysokomol. Soedineniya (A), 1974, 16, 2717. H. A. Weakliem, D. H. Channin, and A. Bloom, Appl. Optics, 1975, 14, 560. R. Guillard, M. Leclerc, A. Loffet, J. Leonis, B. Wilmet, and A. Englert, Macromolecules, 1975, 8, 134.

170 171 179

173

lTQ 176

176

V. M. Anissimov, 0. N. Karpukhin, and A. M. Mattucci, Doklady Akad. Nauk S.S.S.R., (Phys. Chem.), 1974,214, 828. D. A. Sukhov and F. I. Vilesov, Khim. vysuk. Energii, 1974, 8, 162. L. N. Guseva, Yu. A. Mikheev, and D. Ya. Toptygin, Izuest. Akad. Nauk S.S.S.R., Ser. Khim., 1974, 9, 1988. F. Mikes, P. Strop, and J. Kalal, Makromol. Chem., 1974, 175, 2375; Chem. and Ind., 1973, 1164. G. I. Lashkov, M. G. Krakovyak, and N. S. Shelekhov, Doklady Akad. Nauk S.S.S.R.(Phys. Chem.), 1974, 214, 850. A. Ueno, F. Toda, and Y. Iwakura, J. Polymer Sci., Polymer Phys., 1974,12, 1841. A. G. Filimoshkin, Yu. A. Ershov, and R. M. Livshits, Vysokomol. Soedineniya (A), 1974, 16, 1078.

177

V. Y. Shlyapintokh, Zhur. Vsesoyuz Khim. obsch. im D . I. Mendeleeua, 1974, 19, 433. N. Uri, Chem. and Ind., 1975, 199; B. Ranby, Kern-Kemi, 1974,1,477; R. Sastre, J. L. Acosta, and J. Fontan, Rev. Plast. Mod., 1974, 28, 393.

Photochemistry

528

photochemistry in the solid phase.179 Photoreactions, and in particular photooxidation in specific polymers, are considered in the sub-sections below. Polyethylene WE).-A recent paper has outlined how hydroperoxides may be responsible for the initial photo-oxidation of polyethylene; the carbonyls produced then undergo Norrish type I1 photolysis as the main mechanism of degradation (Scheme 7).180 In many commercial polyethylenes, however, the OOH I R1CH2CH2CH2CH~=CH,

’”

ow I

R1CH2CH,CH2CHC=CH, I

R 2

+ OH*

kz(0~3)

I

CH*C=CHp

0

-

R1CH2CH2CH2 CC=CH2 I

I

R2 0 II

hv (Nouish 11)

R1CH=CH2

+ CH3COC=CH2 I

CH2CH- CH20R3 I R2P H

+

cross-link -6HC=CH2

RZ

I

.R2 chain scission

Scheme 7

fact that carbonyl luminescence is observable in untreated samples 163 would seem to indicate that hydroperoxides may be of less importance than is indicated by Scheme 7. Three different kinds of U.V. oxidative behaviour of polyethylene have been observed in the presence of substituted benzophenones, transitionmetal ions, and sulphur-containing metal complexes.181 In the first case, the rate of an initial rapid oxidation increases with ketone concentration and then auto-retards. In the second an auto-acceleration of oxidation occurs with increase in concentration. In the final case, an initial concentration-dependent induction period is followed by auto-acceleration to the stage of physical disintegration. The sensitization of degradation of polyethylene by aromatically substituted dienes, such as 1,lY4,4-tetraphenylbutadiene,has been studied,182 and found to involve production of 02(lAg). The introduction of carbonyl groups into polyethylene by oximation of the aliphatic chain by photolysis of NOCl (Scheme 8 ) has been shown to give rise to an easily photodegradable 17@

J. E. Guillet, Polymer Eng. Sci., 1974, 14, 482. M. U. Amin, G. Scott, and L. M.K. Tillekeratne, European Polymer J., 1975,11, 85. M. U. Amin, B. W. Evans, and G. Scott, Chem. and Ind., 1974, 206; M. U. Amin and G. Scott, European Polymer J., 1974, 10, 1019. E. Cernia, E. Mantovani, W.Marconi, M. Mazzei, N. Palladino, and A. Zanobi, J. Appl. Polymer Sci., 1975, 19, 15. V. Pozzi, A. E. Silvers, L. Giuffre, and E. Cernia, J. Appl. Polymer Sci., 1975, 19, 923.

lB0

la

lS2 lS3

529

Polymer Photochemistry NOCl -t hv (k640nm)

C1-+ R H + Re R*

+

OH

I I -c+ + -c- - - c I NHzO

1

+

+

C1*

HCI

NO + RNO

NO I -CH2-CH-CHa-

OH

NO

_3

NOH

H+

'?Ha I -NOR

II -CH2-C-CH2-

NOH,2HC1 II mCHZ-C-CH2-

0

II

-C-

+

NHzOH

Scheme 8

The effects of some fillers on the photodegradation of PE,184 the photodegradation of polyolefins,186photochemical reactions in irradiated PE,lS8 and the effect of photodegradation on the adhesion of PE to metal surfacesle7have been studied. Other reports of interest are concerned with the synthesis and photodegradation of PE bearing side-chain keto-ether groups,188 the photooxidation of poly(ethy1ene glycols),lSQthe formation of 2,4-dinitrophenylhydrazones and regeneration of carbonyl groups in u.v.-irradiated PE fdms,lQo and biodegradation of waste PE.lQ1 Polypropylene (PP).-The effects of stereoregularity in u.v.-irradiated PP upon the behaviour of the free radicals so produced have been investigated.ls2 The radicals formed at low temperatures were largely -CH2CH(CH2)CH2- and methyl, and were produced in large yield in samples of poor tacticity. On warming, acyl radicals were observed, especially in atactic and stereoblock PP. G. I. Belokoneva and S. S. Demochenko, Plast. Massy, 1975, 57. D. Baum and R. A. White, Polymer Sci. Technol., 1973, 3, 45. V. V. Vasilenko and E. R. Klinshpont, Khim. vysok. Energii, 1974, 8, 273. V. L. Vakula and E. B. Orlov, Vysokomol. Soedineniya (A), 1973,15,2698; G . I. Belokoneva and S. S. Demchenko, Plast. Massy, 1974, 37. lS8 E. Cernia, W. Marconi, and N. Palladino, J. Appl. Polymer Sci., 1974, 18, 2085. I a 8 I. Reimann, G. Hollatz, and Th. Eckert, Arch. Pharm., 1974, 307, 321, 328. lWo K. Kato, J. Appl. Polymer Sci., 1974, 18, 2449. lS1 B. Brown, J. Mills, and J. Hulse, Nature, 1974, 250, 161. lsa Y.Hama, T. Ooi,M. Shiotsubo, and K. Shinohara, Polymer, 1974, 15, 787. lE4 lS6

530 Photochemistry The kinetics of the photo-oxidation of PP sensitized by benzophenone have been studied.lg3 Effective U.V. stabilizers for PP may act as U.V. absorbers, chromophore quenchers, and 02(lAg)deactivators, and may in addition function as hydroperoxide decomposers and free-radical scavengers. Additives may (and usually do) owe their utility to a combination of these functions, the relative importance of each being determined by the nature of the additive and the type and concentration of chromophoric impurities present in the polymer, but they do not apparently prevent the primary photolytic cleavage of hydroperoxides,lS4 acting instead as scavengers of hydroxyl and macroalkoxyl radical products arising from hydroperoxide photocleavage. Nickel chelate compounds, e.g. nickel dibutyldithiocarbamate (BTN), commercially the most effective PP stabilizers, have been shown to be efficient quenchers of PP carbonyl chromophores ls4,lB5 only in solution, being much less effective in the polymer. Nevertheless, Carlsson and Wiles have shown that a nickel chelate can inhibit the formation of Norrish I and I1 products from macroketones in the polymer, and that other stabilizers retard the PP oxidation photosensitized by these macroketones, probably through a collisional quenching process. However, these authors report that macroketone phosphorescence at 77 K is not quenched by any of these stabilizers, which is at odds with a brief note stating that the PP phosphorescence lifetime was shortened by a diamagnetic chelate stabilizer, although not by a hydroxybenzophenone type of additive.lg5 Guillory and Becker lgShave also reported that excited carbonyl groups in outgassed PP films are not quenched by BTN, but that this chelate may be an effective O,(lA,) scavenger. This viewpoint has been challenged briefly and the effectiveness of BTN attributed to peroxide decomposition, quenching of O,(lA,) being completely dismissed in this paper.lg7 It is evident that the situation remains confused concerning the effectiveness of certain stabilizers, and may remain so since the many different mechanisms may operate simultaneously, thus providing some evidence to support the many hypotheses. The photoinitiation of reactions of PP peroxy radicals with MMA has been described.ls8 Poly(methy1 methacrylate) (PMMA) and Related Polymers.-The photolysis of PMMA in methyl acetate, chloroform, CH2CI2,and benzene solution has been shown to be consistent with scission resulting from random absorption directly by the polymer without participation of the The photolysis of thin films of PMMA in 0, has been shown to produce methanol, formaldehyde, methyl acetate, methyl formate, water, formic acid, carbon dioxide, and methane.200The reactions caused by light in PMMA in the presence of atomic lS3 lS4

lB6

lg6 lg7 lg8 lee

0. N. Karpukhin and E. M. Slobodetskaya, Vysokomol. Soedineniya (A), 1974, 16, 1624. D.J. Carlsson and D. M. Wiles, J . Polymer Sci., Polymer Chem., 1974, 12, 2217. D. J. Carlsson and D. M. Wiles, Macromolecules, 1974, 7, 259; J. P. Guillory and R. S. Becker, J. Polymer Sci., Polymer Chem., 1974, 12, 993; J. S. Zannucci and G. R. tappin, Macromolecules, 1974,1, 393. D. J. Harper, J. F. McKellar, and P. H. Turner, J . Appl. Polymer Sci., 1975, 18,2805. R. P. R. Ranaweera and G. Scott, J. Polymer Sci., Polymer Letters, 1975, 13,71. E. R. Klinshpont and V. K. Milinchuk, Vysokomol. Soedineniya (B), 1974, 16, 35. N.Grassie and T. I. Davis, Makromol. Chem., 1974, 175,2657. L. Ackerman and W. J. McGill, J. S. African Chem. Inst., 1974, 27, 105.

Polymer Photochemistry 53 1 chlorine have been discussed,201the phototransformations of PMMA induced by some antioxidants 202 described, and photoinitiated phenomena in y-irradiated PMMA Benzotriazole-, salicylate-, and hydroxybenzophenone-type stabilizers have been shown to act only as u.v.-absorbers in the photoscission of PMMA films irradiated at 253.7 nm,204and conversion of PMMA was shown to be sensitized by the addition of monomer or some antioxidants, owing to their higher U.V. absorptivity compared with the polymer. The kinetics of the degradation of PMMA in acetone solution produced by pulses of 15 MeV electrons have been investigated.20s The products of photolysis of poly(ethy1 acrylate) and poly(n-butyl acrylate) in D ~ C U Oand in oxygen have been reported.206 The photolysis of copolymers of MMA and methyl acrylate 207 and of MMA and p-methoxyacrylophenone 208 has been described.

Polystyrene (PS).-The initiation of PS photo-oxidation by solar radiation has been discussed 209 and shown to be due to end-chain phenyl alkyl ketone groups. A detailed study of the photo-oxidation of PS,210including the sensitizing action of quinones, has been reported which can be compared with a more brief study along the same lines.211 Results implicate 02(lAg) in the degradation process. The chemical and physical changes occurring on u.v.-irradiation of high-impact PS (styrene-butadiene copolymer) indicate that the polybutadiene fraction is selectively attacked, as has been reported for ABS (acrylonitrile-styrenebutadiene block copo1ymer).212 Paramagnetic centres in PS during lowtemperature U.V. p h o t o l y ~ i sthe , ~ ~kinetics ~ of oxidation of atactic PS in s01ution,~f4 and the effect of photodegradation of PS on its permeability characteristics 21s have been discussed. A chemiluminescence study of the kinetics of radical reactions and oxidation in solid PS and the effects of antioxidants on these processes has been the subject of an extensive report.216 The ‘dark’ initiation of the photosensitized degradation of a styrenemethyl isopropenyl ketone copolymer by thermally generated T1(3n~*) acetone using the tetramethyl-1,Zdioxetan dissociation reaction has been The reaction 201

Yu. A. Mikheev, T. S. Popravko, and L. L. Yasina, Vysokomol. Soedineniya (A), 1973, 15, 2470.

202

203

I. N. Morozova and L. N. Samsonova, Vysokomol. Soedineniya (A), 1974,16, 1820. A. Tomkai, T. Asai, T. Suzuki, and Z. Kuri, J. Polymer Sci., Polymer Chem., 1975, 13, 797.

204 205 206

207 208

2on 210

212

213 214 216

216

217

V. Ya. Shlyapintokh and V. I. Gol’denberg, European Polymer J., 1974, 10, 679. G. Beck, J. Kiwi, D. Lindenau, and W. Schnabel, European Polymer J., 1974,10, 1069. W. J. McGill and L. Ackerman, J. Polymer Sci., Polymer Chem., 1974, 12, 1541, 2697. N. Grassie, A. Scotney, and T. I. Davis, Makromol. Chem., 1975, 176, 963. I. Lukac, M. Moravcik, and P. Hrdlovic, J. Polymer Sci., Polymer Chem., 1974, 12, 1913. P. J. Burchill and G. A. George, J. Polymer Sci., Polymer Letters, 1974, 12, 497. J. F. Rabek and B. Ranby, J. Polymer Sci., Polymer Chem., 1974, 12, 273, 295. K. Nakamura and K. Honda, Kobunshi Ronbunshu, 1974,31,373; 1975,32, 79. A. Ghaffar, A. Scott, and G. Scott, European Polymer J., 1975, 11, 271. I. K. Chernova, V. P. Golikov, and S. S. Leshchenko, Khim. vysok. Energil, 1974, 8, 265. J. B. Lawrence and N. A. Weir, J. Appl. Polymer Sci., 1974, 18, 1821. R. Greenwood and N. A. Weir, J. Appl. Polymer Sci., 1975,19, 1409. T. V. Pokholok, 0.N. Karpukhin, and V. Ya. Shlyapintokh, J. Polymer Sci., Polymer Chem., 1975, 13, 525. J. E. Guillet, B. Houvenaghel-Defoort, T. Kilp, N. J. Turro, H . 4 . Steinmetmr, and G. Schuster, Macromolecules, 1974, 7, 942.

532

Photochemistry

could be completely quenched out by the triplet quencher cis,cis-cyclo-octa1,3-diene, from which the rate constant for energy transfer from triplet acetone to macrocarbonyls was estimated as 5 x lo61 mol-1 s-l. The biodegradability of photodegraded PS has been investigated.21e Poly(viny1 halides) (PVC etc.) and Poly(viny1 alcohol) (PVA).-A series of papers has appeared concerned with the photo-dehydrochlorination, discoloration, and sensitized photolysis of model compounds of PVC,21Dand its copo1ymers.220 The photolysis of poly(viny1 bromide) 221 and a trifluorochloroethylenevinylidene fluoride copolymer 222 has been described. The photo-oxidative destruction of PVA has been reported in a series of papers.223 Elastomers.-It has been shown that unsaturated polymers containing polybutadiene (PBD), polyisoprene, etc. are highly susceptible to attack by 02(1Ag),224 producing carbonyls and hydroperoxides, the secondary photoreactions of which have been discussed in Many transition-metal chelates were shown to be quenchers of 02(lAg),but that this was not the sole stabilizer mechanism was illustrated by the fact that nickel chelates of thiobisphenolamine complex type are quantitatively more efficient than other additives which are better quenchers of O,(lA,) in stabilizing such polymers (such as ABS),226and quenching of excited states was also invoked as a stabilizer mechanism.226,226 The photodegradation of high-impact PS was reported earlier to occur selectively in the polybutadiene fraction.212 Other workers have discussed the structure of PBD by I3C n.m.r. analysis,227the photochemical modification of natural rubber,228and the effect of U.V. radiation 22D and ozone 22D* 230 on rubber in commercial use. The effects of antioxidant-light stabilizer mixtures on the photo-oxidative degradation of polychloroprene have been Po1yamides.-Luminescence in nylon has been discussed earlier,16*~ lC6and a recent study has confirmed that phosphorescing carbonyl species in thermally J. E. Guillet and T. W. Regulski, Environment. Sci. Technol., 1974, 8, 923. G. Y. Ocskay, J. Levai, Z. S. Nyitrai, E. Szabados, and F. Varfalvi, European Polymer J., 1974,10,1121; G. Y.Ocskay and J. Levai, ibid., p. 1127; W. H. Gibb and J. R. MacCallum, ibid., pp. 529, 533; K. Mori, H. Harada, and Y . Nakamura, J. Polymer Sci., Polymer Chem., 1974,12,2497; E. D. Owen and J. I. Williams, ibid., p. 1933; A. Harriman, B. Rockett, and W. Poyner, J.C.S. Perkin ZI, 1974,485; K. G. Martin, British Polymer J., 1973,5,443; Y . Oki and F. Mori, Kobunshi Kagaku, 1973, 30, 737. 220 W. Kawai and T. Ichihashi, J. Polymer Sci., Polymer Chem., 1974, 12, 201, 1041; M. Kryszewski and M. Mucha, Plaste Kaut, 1974, 21, 172; 0. Sh. Khalikova, Nauch. Tr. Tashkent Gosud. Univ,. 1970, 379, 86. aal S. U. Mullik and R. G. W. Norrish, Proc. Roy. Soc., 1975, A344, 1. 222 L. A. Butomo and E. K. Kondrashov, Plast. Massy, 1974, 78. 223 G. D. Korodenko, A. Sultanov, and A. V. Zakharchuk, Doklady Akad. Nauk Tadzh. S.S.R., 1974, 17, 18; G. D. Korodenko and A. V. Zakharchuk, ibid., p. 27; H. Aoki, H. Ohashi, and T. Sumki, Zairyo, 1975, 24, 129; I. Y. Kalontarov, N. Kostina, and N. Kiseleva, J. Polymer Sci., Polymer Chem., 1974, 12, 939. 2a4 A. Zweig and W. A. Henderson, jun., J. Polymer Sci., Polymer Chem., 1975, 13, 717. 2Zb S. W. Beavan and D. Phillips, J. Photochem., 1975, 3, 349. 226 A. Zweig and W. A. Henderson, jun., J. Polymer Sci., Polymer Chem., 1975,13,993; A. Davis and D. Gordon, J. Appl. Polymer Sci., 1974, 18, 1159. K.-F. Elgert, G. Quack, and B. Stutzel, Polymer, 1975, 16, 154. 22s E. Cutts, Chem. and Ind., 1974, 7, 280. aBg Y. Iyengar, J. Appl. Polymer Sci., 1975, 19, 855. J. Andries and H. E. Diem, J. Polymer Sci., PolymerLetters, 1974,12,281; H. M. Wenghoefel, Rubber Chem. Technol., 1974,47, 1066. 2 8 0 ~R. A. Petrosyan and R. V. Bagdasaryan, Armyan. khim. Zhur., 1974,27, 635.

21s

al9

Polymer Photochemistry

533

degraded Nylon-66 are consumed upon photolysis, clearly implicating such A review of photodegradation carbonyls in the photodegradation in this polymer has appeared.232 The quenching effect of manganese ions upon the luminescence of the anatase form of TiOa has been tentatively linked to the u.v.-stabilizing effect of such species for pigmented N y l 0 n - 6 6 . ~The ~ ~photohydrolysis of aromatic p o l y a m i d e ~ , ~ ~ ~ stabilization to U.V. of aromatic p o l y a m i d e ~the , ~ ~change ~ in surface morphology of Nylon-6 fibres on U.V. irradiation,236the photolysis of polycaprolactam 237 and kapron 238 fibres, the photolysis of the poly(ester) from 9,9-bis-(4-hydroxyphenyl)10-anthrone and terephthalic and photodegradation of heterochain polymers 240 have been reported. Natural Fibres.-The photolysis of cellulose and related compounds at 253.7 nm,241 e.s.r. studies on photoirradiated cellulose,242the effects of U.V. irradiation on the structure of cotton and the stabilization of cotton against U.V. degradation by grafting with phenyl methacrylate have been A paper has appeared concerned with the stabilization of viscose silk during photomechanical degradation,245and several papers on different aspects of photo-yellowing and degradation of wool have been published 246 In one of these papers (by Leaver), it was shown that reduction of the disulphide groups in wool increased the e.s.r. signal due to the tryptophyl triplet residue by a factor of three. Miscellaneous.-Recent papers have reported the photodegradation of urethanes, 247 the p hot olysis of organopol ~(silanes),248 and the p hot odegradat ion of bisphenol-A-polycarbonate.249 The degradation in the last study was shown to involve chain scission, cross-linking, and the photo-Fries rearrangement. 231 234 233

234

236 236 237

238

23Q 240

241 24a

243

24r

248

247 24a

240

N. S. Allen, J. F. McKellar, and G. 0. Phillips, J. Polymer Sci., Polymer Letters, 1974, 12, 477. B. S. Stowe, R. E. Fornes, and R. D. Gilbert, Polymer Plastics Technol. Eng., 1974, 3, 159. N. S. Allen, J. F. McKellar, and G. 0. Phillips, J. Polymer Sci., Polymer Letters, 1974, 12, 723. E. E. Said-Galiev, S. A. Pavlova, and V. V. Korshak, Doklady Akad. Nauk S.S.S.R.,1973, 213, 1338. B. Kuester and H. Herlinger, Angew. Makromol. Chem., 1974, 265. Y. Fujiwara and S. Kobayashi, Sen’i Gakkaishi, 1974, 30, T434. A. L. Margolin and L. M. Postnikov, Vysokomol. Soedineniya (B), 1975, 17, 59; A. L. Margolin, L. M. Postnikov, and I. V. Semenova, ibid. (A), 1974, 16, 1037; G. B. Pariiski and L. M. Postnikov, ibid., p. 482. M. Kh. Kholov and G. G. Samoilov, Doklady Akad. Nauk Tadzh S.S.R., 1974,17,27; L. E. Nikulina and V. R. Koroleva, Izuest V.U.Z., Khim. i Khim. Tekhnol., 1974, 17, 778. V. V. Korshak and E. E. Said-Galiev, Vysokomol. Soedineniya (A), 1974, 16, 2002. V. V. Gur’yanova and A. B. Blyumenfel’d, Vysokomol. Soedineniya (A), 1974, 16,909. A. Bos, J. Polymer Sci., Polymer Chem., 1974, 12, 2283. N.-S. Hon, J. Polymer Sci., Polymer Chem., 1975, 13, 955; Y . Ogiwara, N . 4 . Hon, and H. Kubota, J. Appl. Polymer Sci., 1974, 18, 2057. N. Saltanov, S. Nizamidino, and Sh. Tuichiev, Mekh. Polimery, 1974, 6, 1113. H. Tonami and H. Watamoto, Nippon Kagaku Kaishi, 1974, 4, 789. T. B. Boboev and K. M. Makhkamov, Mekh. Polimery, 1974,5,920. I. H. Leaver, Photochem. and Photobiol., 1975, 21, 197; L. A. Holt and B. Milligan, Textile Res. J., 1974, 44, 452; H. Baumann, J. SOC.Dyers and Colourists, 1974, 90, 125, 326. P. L. Nielsen and Z. W. Wicks, Nuoua Chim., 1974, 50, 7 5 . M. Ishikawa and M. Kumada, J. Organometallic Chem., 1974, 81, C3; M. Ishikawa, F. Ohi, and M. Kumada, ibid., 1975,86, C23; B. G . Ramsey, ibid., 1974,67, C67; K. Kumada and M. Ishikawa, Ann. New York Acad. Sci., 1974, 239, 32. K. Tsubakiyama, Y. Sasahi, S. Hiraki, and C. Kujirai, Jap. Polymer Sci. Technol., 1974,31,629.

534

Photochemistry On irradiation at wavelengths > 220 nm in vacuo the polymer cross-linked to form a gel without much weight loss, whereas in the presence of air considerable weight loss and less cross-linking were observed. An apparatus for measuring the time dependence in the ps range of lightscattering intensity has been used to investigate the degradation of poly(pheny1 vinyl ketone) (PVK) in ~ o l u t i o n250 . ~ ~The ~ ~ PVK was irradiated with 25 ns pulses at 347.1 nm, and butyrophenone was also investigated in the same way. In both cases a transient absorption, identified by sensitization measurements as the PVK and butyrophenone triplet state, was shown to have a fist-order decay rate-constant of 1.0 4 0.2 x lo7s-l. The quantum yield of triplet state formation in PVK was estimated to be between 0.1 and 0.3, whereas the quantum yield of main-chain scission was found to be 0.4-0.6, insensitive to the presence of 0 2 . The photodegradation of the polymer poly-[2,2’-(rn-phenylene)-5,5’-bibenzimidazole] (PBI) (17) has been shown to be associated with the intense absorption

(17)

PBI

in the region of solar emission reaching the earth’s surface,251and the mechanism is one of photo-oxidation. PBI has outstanding properties such as low flammability, good abrasion resistance, and high moisture regain, and means of overcoming its susceptibility to photo-oxidative attack were considered, including protective coating. The photochemistry of the fibre-forming acrylonitrile the benzene-photosensitized depolymerization of a-truxillic and the photostability of coloured polymeric materials 2s4 have been discussed.

Reactions of 02(1b,).-Attack by 02(lA,) can be of great importance in the initial stages of photoinduced degradation in polymers, and this aspect of o2(lAu) reactions has been discussed in several papers r e ~ e n t l y 256 . ~ ~The ~~ quenching of 02(lAg) by transition-metal chelates and other light stabilizers, 256 clearly an important process for stabilization, has also been Quenching rate-constants for O,(lA,) by some sixty transition-metal chelates have been given,224and found to vary from 3 x 1O1O I mol-1 s-l for nickel(@ a50

261 262

253 264 266

268

G . Beck, G. Dobrowolski, J. Kiwi, and W. Schnabel, Macromolecules, 1975, 8, 9. J. R. Brown, P. J. Burchill, G . A. George, and A. J. Power, J. Polymer Sci., Polymer Symposia, 1975, 49, 239. L. Alexandru and J. E. Guillet, J. Polymer Sci., Polymer Chem., 1975, 13, 483. J. Rennert and D. Grossman, J. Photochem., 1974, 3, 171. Yu. A. Ershov and G . E. Krichevskii, Uspekhi Khim., 1974, 43, 537. J. F. Rabek and B. Ranby, Polymer Eng. Sci.,1975,15,40; J. A. Bell and J. D. MacGillivray, J. Chem. Educ., 1974, 51, 677; A. K. Breck, C. L. Taylor, K. E. Russell, and J. K. S. Wan, J. Polymer Sci., Polymer Chem., 1974, 12, 1505; J. R. MacCallum and C. T. Rankin, Makromol. Chem., 1974,175,2477. D. J. Carlsson, T. Suprunchuk, and D. M. Wiles, Canad.J. Chem., 1974,52, 3728; P. Hrdlovic, J. Danecek, M. Karvas, and J. Durmis, Chem. Zuesti, 1974, 28, 792; I. B. C. Matheson, R. D. Etheridge, N. R. Kratowich, and J. Lee,Photochem. and Photobiol., 1975, 21, 165.

Polymer Photochemistry

535

dithiobiacetyl to 3 x lo71mol-1 s-l for cobalt@) 3,5-di-isopropylsalicylate.22” Rate constants for quenching of O,(lA,) by a variety of amino-acids and proteins have been reportedYzs6 and the results found to be approximated by the sum of the quenching rates of the amino-acids histidine, tryptophan, and methionine, implying approximately equal quenching rates for these species. The use of a polymer-based photosensitizer to generate singlet oxygen 257 and other polymerbased photosensitizers 258 has been advocated. U.V. Stabilizers.-Many of the papers discussed in preceding sections contain discussion of the nature and mechanism of U.V. stabilizers. A brief survey of antioxidants and stabilizers used in the plastics industry has appearedyzsBand some new photostabilizers, including a polymeric U.V. absorber and a surfacegrafted antioxidant, have been proposed.260 The mechanism of nickel chelate stabilizers has been further discussedYzB1 and the diffusion of and loss of light stabilizers in poly(o1efins) described.262As part of an attempt to understand the transformations of stabilizers during the ageing of polymers, the photooxidation of 2,6-di-t-butyl-4-methylphenol sensitized by Methylene Blue has been studied.es3 U.V. light protection by sunscreens, with mechanisms of interest to the polymer field, has been Stabilizers from the patents literature are found in the Appendix, Table A2. Guillet and Scott, the two principal investigators, have presented two further papers on the accelerated degradation of polymers.266 The patents literature relating to prodegradants is reviewed in the Appendix, Table Al. Radiation-induced Degradation.-There have been several reports on radiation effects in including single fluoropolymers,268polyamides,26Q polysiloxanes,270polyethylene and its copolymers,271polypr0pylene,~7~ p ~ l y o l e f i n spolystyrene ,~~~ and its poly(viny1 chloride) and related polysulphones and other sulphur-containing p ~ l y c a r b o n a t enylon,27Q , ~ ~ ~ poly(vinylpyridines),280and Photochemistry of Pigments and Dyestuffs.-Subjects 267 268 268 260

261

26a

a64

a66 26E

268

269

of recent papers include

I. Rosenthal and A. J. Archer, Israel J. Chem., 1974, 12, 897. E. C. Blossey and D. C. Neckers, Tetrahedron Letters, 1974, 323. T. Weir and G. Ocshay, Kem. Kozlem., 1974, 42, 139. Y. Mizutani and K. Kusumoto, J. Appl. Polymer Sci., 1975, 19, 713; K. Murayama, Farumashia, 1974, 10, 573; B. W. Evans and G. Scott, European Polymer J., 1974, 10,453. R. P. R. Ranaweera and G. Scott, J. Polymer Sci., Polymer Letters, 1975, 13, 71 ; Chem. and Ind., 1974, 19, 774. J. F. Westlake and M. Johnson, J. Appl. Polymer Sci., 1975, 19, 319; J. Durmis, M. Karvas, P. Caucik, and J. Holcik, European Polymer J., 1975, 11, 219. L. Taimr and J. Pospisil, Angew. Makromol. Chem., 1974, 39, 189. G. Kahn and M. C. Curry, Arch. Dermatol., 1974,109,510; C. D. M. Ten Berge and C. H. P. Bruins, J, Soc. Cosmetic Chemists, 1974, 25, 263. J. E. Guillet, Polymer Sci. Technol., 1973, 3, 1; G. Scott, Kobunshi, 1974, 23, 323. J. H. O’Donnell, Proc. Roy. Austral. Chem. Inst., 1974, 41, 68. R. Salovey, Radiat. Chem. Macromol., 1973, 2, 307. M. Dole, Radiat. Chem. Macromol., 1973,2, 167; V . T. Kozlov, S. N. Lanin, N. G. Kashevskaya, A. A. Khan, and A. T. Soldatenko, Vysokomol. Soedineniya (B), 1975, 17, 3. J. Zimmerman, Radiat. Chem. Macromol., 1973, 2, 121. A. A. Miller, Radiat. Chem. Macromol., 1973, 2, 179. R. M. Sellers, K. M. Bansal, and E. Janata, Ber. Bunsengesellschaftphys. Chem., 1974, 48, 1085; A. G. Sirota, N. K. Zaitseva, and G. F. Karkozova, Plast. Massy, 1974, 22; M. S. Kozyreva and L. V. Konovalov, Vysokomol. Soedineniya (B), 1974,16,548; R. A. Terteryan

536

Photochemistry

the photochemistry of dyes on synthetic fibres.282Other workers have described the photobleaching of Rhodamine 6G in p~lyacrylonitrile,~~~ the determination of the photoactivity of Ti02 pigments,284and the photoreduction of dyes catalysed by organic molecules and biological materials.285The effects of optical brightening agents (OBA’s) on the photofading of azo-blue acid dyes,288and the use287and effect on wool288 of stilbene-type OBA’s have been discussed. Instrumentation for colour testing 289 and light-fastness testing 290 has been the photooutlined. Other workers have discussed the photofading of

272 a73

a74

27b

277

278 279 280

asl 282

283 284

28s 286

288

aso 291

and S. S . Leshchenko, ibid., p. 181 ; M. E. Borisova, V. E. Korsukov, S.N. Koikov, and s. N. Rubtson, ibid., (B) 1974, 16, 697; A. Basinski and W. Czerwinski, Polimery, 1973, 18, 586; D. T. Turner, Radiat. Chem. Macromol., 1973, 2, 137; M. Dole, ibid., p. 187; S . Shimada and H. Kashiwabara, Polymer J., 1974,6,448; F. Szocs, 0. Rostasova, J. Tino, and J. Placek, European Polymer J., 1974, 10, 725; C. Decker and J. Marchal, Makromol. Chem., 1974, 175, 3531 ; I. Varsanyi, Acta Almient, 1972, 1, 297; J. Petermann and H. Gleiter, Kolloid-Z., 1973, 251, 850; A. G. Sirota, E. I. Nalivaiko, and E. P. Ryabikov, Khim. vysok. Energii, 1974,8,281; F. Hosoi and H. Mitsui, Kobunshi Ronbunshu, 1974,31,94; C. Decker and F. R. Mayo, J. Polymer Sci., Polymer Chem., 1973, 11, 2879; J. A. Slivinskas and J. E. Guillet, ibid., 1974, 12, 1469; G. N. Patel and A. Keller, J. Polymer Sci., Polymer Phys., 1975, 13, 333,339; G. N. Patel, ibid., pp. 351,361 ;S. Morisaki, Thermochim.Acta, 1974,9,157; G . R. A. Johnson and A. Willson, J.C.S. Chem. Comm., 1974, 577. D. 0. Geymer, Radiat. Chem. Macromol., 1973, 2, 3. V. G. Yurkevich, V. L. Karpov, and B. I. Zverev, J. Polymer Sci., Polymer Symposia, 1973, 42, 859. C. S. Herrick, J. Polymer Sci., Polymer Phys., 1974, 12, 1849; J. A. Slivinskas and J. E. Guillet, J. Polymer Sci., Polymer Chem., 1973, 11, 3043, 3057; T. C. Chau and A. Rudin, Canad. J. Chem. Eng., 1974,52,79; W. W. Parkinson and R. M. Keyser, Radiat. Chem. Macromol., 1973, 2, 57; T. M. Muinov, A. M. Mavlyanov, and S . Kh. Kapkaeva, Doklady Akad. Nauk Tadzh. S.S.R., 1974, 17, 21; I. K. Chernova, V. P. Golikov, and S . S . Leshchenko, Khim. vysok. Energii, 1974, 8, 342; Y. Huh, G. W. Donaldson, and F. J. Johnston, Radiation Res., 1974, 60, 42. Y.J. Chung, S. Yamakawa, and V. T. Stannett, Macromolecules, 1974,7,204; F. Szocs and 0. Rostacova, J. Appl. Polymer Sci., 1974, 18, 2529; R. Salovey, Radiat. Chem. Macromol., 1973, 2, 37; K. Makuchi, M. Asano, and T. Abe, Nippon Kagaku Kaishi, 1975, 728; S . Bogdansky and P. J. Lehn, J. Pharm. Sci., 1974, 63, 802. A. Von Raven and H. Heusinger, J. Polymer Sci., Polymer Chem., 1974, 12, 2255; B. K. Pasal’skii and Ya. I. Lavrentovich, Khim. vysok. Energii, 1974, 8, 451; B. K. Pasal’skii, V. A. Vonsyatskii, Ya. I. Lavrentovich, and A. M. Kabakchi, Vysokomol. Soedineniya (A), 1974,16,2762; F. A. Makhlis and L. Ya. Nikitin, ibid., 1975,17, 170; K. Wundrich, European Polymer J., 1974, 10, 341 ; T. Kusano, Y. Sutoh, and K. Murakami, Nippon Kagaku Kaishi, 1974, 6, 1128. M. J. Bowden, J. Polymer Sci., Polymer Chem., 1974, 12, 499; H. Moenig and H. Ringsdorf, Makromol. Chem., 1974, 175, 8 1 1 . Y. Hama, K. Nishi, and K. Watanabe, J. Polymer Sci., Polymer Phys., 1974, 12, 1109. A. N. Shaitanova and K. D. Pismannik, Vysokomol. Soedineniya (B), 1974, 16, 783. J. C. Ronfard Haret and A. Lablache Combier, J. Phys. Chem., 1974, 78, 899. R. B. Beevers and K. G. McLaren, Textile Res. J., 1974, 44, 986. G. hick, jun. and E. G. Boyd, Textile Res. J., 1974, 44, 558. S. Reich and G. Neumann, Appl. Phys. Letters, 1974, 25, 119. M. Nedorost and M. Pokorny, Farbe Lack, 1974, 80, 1117. M. K. Pal and K. K. Mazumdar, Histochemistry, 1974, 40, 267. K. Yamada and H. Shosenyi, Nippon Kagaku Kaishi, 1974, 563. L. A. Holt and B. Milligan, Textile Res. J., 1974,44, 181 ; B. Milligan and L. A. Holt, Austral. J. Chem., 1974, 27, 195. H. L. Needles and R. P. Seiber, Textile Res. J., 1974, 44, 315. A. S. Von Stenuis, J. Opt. SOC.Amer., 1975, 65, 213; F. W. Billmeyer, E. Campbell, and R. Marcus, Appl. Optics, 1974,13, 1510; R. Marcus and F. Billmeyer, ibid., p. 1519; J. B. Schutt, J. F. Arens, C. M. Shai, and E. Stromberg, ibid., p. 2218. J. Park and D. J. Smith, J. SOC.Dyers Colourists, 1974, 90, 431. H. C. A. Van Beek and P. M. Heerjes, J. SOC.Dyers and Colourists, 1973, 89, 389; T. Kitao, Y. Watada, and M. Matsuoka, Nippon Kagaku Kaishi, 1974, 939; M. I. Snegov and A. S . Cherkasov, Zhur. $2. Khim., 1974,48,462.

Polymer Photochemistry 537 reduction of several the photodegradation of dyes in the photochemistry of pigments,294 and the photoinduced luminescence of 9,1O-anthraq~inone.~~~ Photodegradation of Bioactive Materials.-The photochemistry of pesticides,20s herbicides 297 and specifically polychlorinated aromatic phenothiazine aldrin-type and various other related materials301 has been discussed, with ecological emphasis. The use of U.V. irradiation for waste-water treatment has again attracted much interest.s02 5 Appendix: Review of Patent Literature Photopolymerizable Systems.-Patents of interest concerning photopolymerizable and photocurable systems can be found in references 303-388 and under the following British patent numbers :

2B4 aQ6

206

297

V. Rehak, F. Novak, and I. Cepciansky, Coll. Czech. Chem. Comm., 1973,38,697; U. Steiner, M. Hafner, and S . Schreiner, Photochem. and Photobiol., 1974, 19, 119; R. Bonneau and P. Fornier de Violet, ibid., p. 129. I. Bridgeman and A. T. Peters, Textile Res. J., 1974, 44, 639, 645; J. J. Porter, ibid., 1973, 43, 735. N. D. Fargo, J. Paint Technol., 1974, 46, 65. D. M. Hercules and S . A. Carlson, Analyt. Chem., 1974, 46, 674. R. D. Baker and H. G. Applegate, Texas J. Sci., 1974,25, 53; D. A. M. Watkins, Chem. and Ind., 1964, 5, 185; J. D. Rosen, Environment. Toxicol. Pesticide Proceedings, 1972, 435; L. Lykken, ibid., p. 449; M. A. Klisenko and M. V. Pis’mennaya, Khim. Sel. Khoz., 1973, 11, 916. J. R. Baur and R. W. Bovey, Arch. Environment. Contamination Toxicol., 1973,1,289; 1974, 2, 275. K. Hustert and F. Korte, Chemosphere, 1974, 3, 153; L. Vollner and F. Korte, ibid., p. 275; L. 0. Ruzo and M. J. Zabik, J. Amer. Chem. Soc., 1974, 96, 3809; J. Agric. Food Chem., 1974, 22, 1106; M. P. Gulan and D. D. Bills, Bull. Environ. Contamination Toxicol., 1974, 11,438; T . Sawai and T. Shimokawa, Bull. Chem. SOC.Japan, 1974,47, 1889; S . Gab, W. P. Cochrane, H. Parlar, and F. Korte, 2. Naturforsch., 1975, 30b, 239; T. Nishikawa and A. Ninomiya, Nippon Kagaku Kaishi, 1973, 2326. K. Thoma and E. Vasters, Pharm. Ztg., 1974, 119, 1430, 1591; T. Iwaoka and M. Kondo, Bull. Chem. SOC.Japan, 1974,47, 950; F. W. Grant, Adv. Biochem. Psychopharmacol., 1974, 9, 539; L. Molnar and M. Sivak, Pharmazie, 1974, 29, 417. L. Vollner and F. Korte, Chemosphere, 1974, 3, 271 ; S. Gaeb, H. Parlar, S. Nitz, and K. Hustert, ibid., p. 183; S . Gaeb, H. Parlar and F. Korte, ibid., p. 187; Tetrahedron, 1974, 30, 1145; E. Leitis and D. G. Crosby, J. Agric. Food. Chem., 1974,22,842; M. Nakagawa and D. G. Crosby, ibid., p. 849; D. G. Crosby and K. W. Moilanen, Arch. Environment Contamination. Toxicol., 1974, 2, 62; W. B. Burton and G. E. Poliard, Bull. Environment. Contamination Toxicol., 1974, 12, 113; R. Aoyagi, T. Suzuki, M. Takai, and T. Takahashi, Tetrahedron, 1973, 29, 433 1. J. Pawlaczyk and T. Turowska, Actu Polon. Pharm., 1974,31,65,71; L. L. Miller and G. D. Nordblom, J. Agric. Food. Chem., 1974, 22, 853; G. P. Nilles and M. J. Zabik, ibid., 1975, 23, 410; K. W. Moilanen and D. G. Crosby, Arch. Environment. Contamination Toxicol., 1974,2, 3; E. Pawelczyk and B. Marciniec, Pharmazie, 1974,29,585; R. L. Joiner and K. P. Baetcke, J. Assoc. Ofic. Analyt. Chemists, 1974,57,408; S . C . Gupta, M. L. Maheshwari, and S . K. Mukerjee, Indian J. Chem., 1973, 11, 1202; N. C. Joshi, H. V. Sahni, and S . K. Batra, Indian J. Pharm., 1974, 36, 12. F. A. J. Armstrong and D. P. Scott, J. Fisheries Research Board Canada, 1974, 31, 1881; E. Gilbert and H. Guesten, Kernforschungszentrum Karlsruhe (Ber.), 1974, 104; Y . Kojima, Kagaku Sochi, 1974,16, 103; M. Hirose, T. Endoh, and K. Mima, Kagaku Kogaku, 1974,38, 479. Japan Kansai Paint Co. Ltd., 9 Feb. 1973, JA 49 106 537. Nippon Oil Seal Ind. Co. Ltd., 7 March 1973, JA 49 114 690. Nippon Oil Seal Ind. Co. Ltd., 24 Jan. 1973, JA 49 099 592. Mitsubishi Rayon Co. Ltd., 16 June 1969, JA 49 010 526. Nippon Oils and Fats Co. Ltd., 17 June 1972, JA 49 030 466.

Photochemistry

538 1 365 280 1 369 210 1 372 374 1 375 594 1377737 1 378 997 1 381 002 1 386 324 1390006 1 400 504 308 308

310 311 312 313

'I4 318 317 318 310

320 321 y22

323 324 325

326

328 328 330 331 332

333 334 3p5

396

337 338

339 340

341 342

343 844

84s 346 347

348

349 350

351 352 358 354 35b 3G6 367

358 359 a60

1 365 730 1369216 1 373 146 1 375 661 1 377 740 1 379 088 1 382 472 1 386 583 1392 236 1 400 798

1 366 328 1 369 881 1 373 458 1 376 450 1 377 747 1 379 228 1 382 484 1 387 800 1 395 509 1 400 979

1 366 760 1 370 050 1 373 498 1 376 840 1 377 816 1 379 229 1 383 239 1 388 038 1 395 822 1 400 988

1 366 769 1370315 1 374 607 1 377 512 1 377 829 1 379 259 1384 343 1 388 492 1 398 032 1401 768

1 367 830 1 370 316 1375 177 1 377 535 1 378 535 1 379 968 1 384 898 1 388 946 1 398 104 1401 985

Toa Gosei Chem. Ind. Co. Ltd., 17 April 1973, JA 49 130481. Mitsubishi Rayon Co. Ltd., 19 May 1970, JA 49 035 073. Nippon Oil Seal Ind. Co. Ltd., 13 Oct. 1972, JA 49 092 175. Nippon Oil Seal Ind. Co. Ltd., 25 Sept. 1972, JA 49 053 638. Nippon Oil Seal Ind. Co. Ltd., 25 Sept. 1972, JA 74 053 640. Dainippon Ink and Chemicals Inc., 9 July 1970, JA 49 019 163. Mitsubishi Rayon Co. Ltd., 15 May 1970, JA 49 026 300. Nippon Oil Seal Ind. Co. Ltd., 23 Dec. 1972, JA 49 086 490. Nippon Zeon Co. Ltd., 26 Sept. 1972, JA 49 053 684. Sumitomo Chem. Co. Ltd., 14 March 1972, JA 48 093 677. Toa Gosei Chern. Ind. Co. Ltd., 30 Oct. 1971, JA 48 051 035. Kansai Paint Co. Ltd., 5 Nov. 1970, JA 48 032 772. Nippon Oil Seal Ind. Co. Ltd., 3 June 1972, JA 49 016 788. Nippon Oil Seal Ind. Co. Ltd., 3 June 1972, JA 49 016 789. Nippon Synthetic Chem. Ind. Co. Ltd., 5 Feb. 1973, JA 49 104989. Nippon Oil Seal Ind. Co. Ltd., 16 June 1972, JA 49 020 292. Nippon Oil Seal Ind. Co. Ltd., 25 Dec. 1972, JA 49 087 789. Japan Fugi, 7 Feb. 1973, JA 49 108 192. Japan Fuji Photo. Film Co. Ltd., 3 April 1973, JA 49 125 458. Dainippon Printing Co. Ltd., 19 Oct. 1970, JA 49 039 200. Wako Pure Chemical Inds. Ltd., 28 Dec. 1972, JA 49 097 881. Dainippon Ink and Chemicals Inc., 29 May 1970, JA 48 041 706. Asahi Chem. Ind. Co. Ltd., 14 Dec. 1970, JA 49 013 225. Kansai Paint Co. Ltd., 7 Dec. 1970, JA 49 017 414. Nippon Oil Seal Ind. Co. Ltd., 29 Sept. 1972, JA 49 054 487. Kuraray Co. Ltd., 25 Oct. 1969, JA 48 017 667. Dainippon Ink and Chem. Inc., 28 Dec. 1970, JA 49 019 098. Unitika Ltd., 7 Feb. 1973, JA 49 105 888. Kansai Paint Co. Ltd., 1 Dec. 1969, JA 49 013 870. Dainippon Printing Co. Ltd., 9 July 1971, JA 48 016 991. Reichold-Albert-Chemie AG., 13 July 1973, D T 2 426 602. Reichold-Albert-Chemie AG., 13 July 1973, D T 2 426 603. Akzo G.m.b.H., 20 June 1972, DT 2 325 179. Bayer AG., 20 Oct. 1972, DT 2 251 469. I.C.I. Ltd., 9 Oct. 1972, D T 2 350 646. BASF Farben und Fasern AG., 24 Dec. 1969, D T 1 966 796. E. I. Du Pont de Nemours and Co., 9 June 1972, DT 2 243 182. Loctite (Ireland) Ltd., 16 May 1972, DT 2 324 822. Sun Chem. Corp., 31 Jan. 1973, DT 2 404 156. Agency of Ind. Sci. and Technol., 19 Dec. 1969, DT 2 065 547. W. R. Grace and Co., 19 April 1973, DT 2 319 848. Reichold-Albert-Chemie AG., 5 Jan. 1971, DT 2 166 601. Kalle AG., 1 March 1973, DT 2 310 307. Ball Corp., 14 June 1973, DT 2 422 365. Sun Chem. Corp., 11 June 1973, DT 2 426 449. A. Uhlemato et al., 19 Oct. 1972, DT 2 264 790. Fuji Photo. Film Co. Ltd., 23 Aug. 1972, DT 2 342 687. Ciba-Geigy AG., 28 July 1972, DT 2 337 813. Sumitomo Chem. Co. Ltd., 18 Dec. 1972, DT 2 361 632. I.C.I. America Inc., 16 March 1973, DT 2 41 1 000. American Can Co. Ltd., 9 Feb. 1973, DT 2 361 141. I.C.I. America Inc., 16 March 1973, DT 2 410 220.

1 367 946 1 372 225 1375 461 1 377 664 1 378 867 1 380 909 1 386 122 1 389 388 1 398 261

Polymer Photochemistry

539

Radiation-induced Polymerizations.-Patents of interest concerning radiationpolymerizable and -curable systems can be found in references 389477 and under the following British patent numbers: 1 366 150 1 372 499 1 378 971 1 385 842 1 3 9 9 105

1 367 644 1 373 218 1 378 978 1 385 982 1 399 135

1 369 808 1 374 633 1 381 471 1 386 665

1 370 403 1 374 893 1 382 485 1 388 432

1 370 556 1 375 178 1 382 794 1 389 061

1 371 398 1 377 207 1 382 795 1 390 711

Union Carbide Corp., 26 June 1972, DT 2 332 142. Ciba-Geigy AG., 5 Dec. 1972, DT 2 360 360. 38s Minnesota Mining and Manufacturing Co., 29 May 1968, US 3 769 019. 384 Armstrong Cork Co., 22 June 1972, US 3 864 143. W. R. Grace and Co., 31 July 1972, US 3 835 085. s68 J. F. Wrzesinski, 31 July 1972, US 3 853 728. s67 Inmont Corp., 16 Nov. 1971, US 3 772 062. 368 W. R. Grace and Co., 31 July 1972, US 3 853 727. 38g American Can Co., 18 May 1971, US 3 816278. s70 American Can Co., 18 May 1971, US 3 816280. 371 Bridgestone Tire Co. Ltd., 14 Oct. 1969, US 3 795 598. s72 American Can Co., 20 Aug. 1968, US 3 835 003. 373 S.C.M. Corp., 12 Jan. 1973, US 3 827 959. 374 American Can Co., 20 Aug. 1968, US 3 816279. 376 S.C.M. Corp., 12 Jan. 1973, US 3 827960. s76 A. H. Reine and J. C. Arthur, jun., 16 March 1973, US 342 133 (applied). s77 S.C.M. Corp., 8 Nov. 1973, US 3 857 769. s78 Gaf Corp., 28 July 1969, US 3 801 638. 379 E. I. Du Pont de Nemours and Co., 7 Aug. 1972, US 3 814607. s80 E. I. Du Pont de Nemours and Co., 18 Aug. 1972, US 3 795 520. 381 General Electric Co., 19 Jan. 1970, US 3 787 382. s82 American Can Co., 18 Jan. 1971, US 3 817 850. American Can Co., 18 May 1971, US 3 817 845. s84 Ukrainian Printing Institute, 15 Feb. 1972, USSR 440 952. s85 Ukrainian Printing Institute, 13 July 1970, USSR 400 874. s86 V. Yu. Gordinskii and E. G. Akoeva, 19 Jan. 1972, USSR 428 347. 387 Ukrainian Academy of Sci., 13 April 1972, USSR 412 590. 388 General Electric Co., 19 Jan. 1970, CAN 943 942. Toray Inds. Inc., 10 April 1972, JA 8 102 839. sgO Toray Inds. Inc., 6 July 1972, JA 49 026 337. 881 Toray Inds. Inc., 20 Dec. 1967, JA 47 036 163. sg2 Japan Atomic Energy Research Institute, 7 Dec. 1971, JA 48 062 891. 9g3 Japan Atomic Energy Research Institute, 23 May 1972, JA 49 008 576. a84 Japan Atomic Energy Research Institute, 7 Nov. 1969, JA 48 014 793. sgs Japan Atomic Energy Research Institute, 13 Dec. 1971, JA 48 066 186. Mitsubishi Rayon Co. Ltd., 17 April 1972, JA 49 OOO 327. m 7 Sumitomo Chem. Co. Ltd., 30 Oct. 1969, JA 48 030 465. Japan Eidai Co. Ltd., 3 Feb. 1973, JA 49 104971. Nippon Paint Co. Ltd., 9 Jan. 1970, JA 49 026 060. 4 0 0 Mitsubishi Rayon Co. Ltd., 23 Oct. 1972, JA 49 092 152. 401 Nitto Electric Industrial Co.Ltd., 25 May 1972, JA 49 010 221. r o 2 Shinto Paint Co. Ltd., 20 Dec. 1972, JA 49 097 049. 4oa Toray Ind. Inc., 10 June 1969, JA 49 024 132. 404 Japan Atomic Energy Research Institute, 11 Aug. 1970, JA 49 023 581. 406 Nippon Oils and Fats Co. Ltd., 30 May 1972, JA 49 010 999. 406 J. Fujikawa and Y.Tabata, 10 May 1970, JA 48 044 678. Hitachi Cable Ltd., 13 Jan. 1973, JA 49 098 855. 408 Nippon Paint Co. Ltd., 9 Jan. 1970, JA 49 026 059. Japan Atomic Energy Research Institute, 2 May 1973, JA 50 OOO 085. 410 Asahi Glass Co. Ltd., 30 Dec. 1970, JA 49 043 384. 111 Mitsubishi Rayon Co. Ltd., 29 Dec. 1973, JA 49 101414. 41a Mitsubishi Rayon Co. Ltd., 10 April 1973, JA 49 128 039. Asahi Glass Co. Ltd., 28 Dec. 1970, JA 49 011 745.

s81

1 372 305 1 377 978 1 385 132 1 391 997

540

Photochemistry

Japan Atomic Energy Research Institute, 8 May 1970, JA 49 01 1 271. Nippon Oils and Fats Co. Ltd., 8 Sept. 1972, JA 49 048 730. Showa Electric Wire and Cable Co. Ltd., 28 Aug. 1972, JA 49 040 340. Toray Inds. Inc., 14 Aug. 1970, JA 48 043 369. 418 Dainippon Toryo Co. Ltd., 17 Sept. 1970, JA 49 016 111. 41D Japan Atomic Energy Research Institute, 22 Aug. 1970, JA 49 023 586. a0 Japan Atomic Energy Research Institute, 12 Aug. 1970, JA 49 023 582. a1 Mitsubishi Rayon Co. Ltd., 28 Dec. 1971, JA 48 080 517. 42a Mitsubishi Rayon Co. Ltd., 4 April 1968, JA 49 005 727. ras Dainippon Ink and Chemicals Inc., 3 Feb. 1969, JA 49 005 889. 424 Mitsubishi Rayon Co. Ltd., 4 April 1968, JA 49 005 726. 4a6 Kansai Paint Co. Ltd., 19 June 1968, JA 49 005 888. 42e Mitsubishi Rayon Co. Ltd., 4 April 1968, JA 49 005 887. 427 Chisso Corp., 24 Aug. 1972, JA 49 039 637. ae Nippon Telegraph and Telephone Public Corp., 14 Sept. 1972, JA 49 051 355. 429 H. Sakurai and Y . Okamoto, 11 May 1970, JA 49 001 949. 430 Asahi Chemical Ind. Co. Ltd., 18 Dec. 1970, JA 49 003 479. 431 Showa Electric Wire and Cable Co. Ltd., 30 Aug. 1972, JA 49 042 754. rsa Nippon Steel Chemical Ind. Co. Ltd., 30 Jan. 1969, JA 48 041 267. lS8 Japan Atomic Energy Research Institute, 1 May 1972, JA 49 005 149. 434 Dainippon Ink and Chemicals Inc., 31 March 1969, JA 48 004 444. 4s6 Asahi Glass Co. Ltd., 30 Dec. 1970, JA 48 038 219. ae Asahi Glass Co. Ltd., 30 Dec. 1970, JA 48 038 218. 437 Asahi Glass Co. Ltd., 30 Dec. 1970, JA 48 038 465. 438 Kansai Paint Co. Ltd., 20 Sept. 1968, JA 48 033 033. 439 Sumitomo Chem. Co. Ltd., 1 Sept. 1969, JA48 030464. 440 Japan Atomic Energy Research Institute, 23 Jan. 1969, JA 48 030 353. 441 Toray Inds. Inc., 13 April 1972, JA 48 103 630. rra Mitsubishi Rayon Co. Ltd., 24 Nov. 1971, JA 48 058 092. Japan Atomic Energy Research Institute, 1 May 1972, JA 49 005 148. 444 Dainippon Toryo Co. Ltd., 10 March 1970, JA 49 040 149. 446 Nippon Oil and Fats Co., 10 June 1972, JA 49 018 190. 446 Nippon Oil and Fats Co., 30 June 1972, JA 49 024 233. 447 Nippon Paint Co. Ltd., 9 Jan. 1970, JA 49 047 254. Nippon Oil and Fats Co., 19 May 1972, JA 49 014 536. 449 Hitachi Chem. Co. Ltd., 25 Aug. 1972, JA 49 040 364. 450 Mitsubishi Rayon Co. Ltd., 29 Dec. 1970, JA 49 048 585. 461 Mitsui Petrochem. Ind. Ltd., 12 April 1972, JA 48 103 627. psa Toray Inds. Inc., 13 April 1972, JA 48 103 630. 4s3 Nippon Electrocure Co., 16 Feb. 1972, JA 48 084 841. 46p Nitto Boseki Co., 4 Aug. 1972, DT 2 339 509. 466 BASF Farben und Fasern AG., 9 Oct. 1972, DT 2 249 446. 46e Mitsubishi Rayon Co. Ltd., 7 Nov. 1972, DT 2 355 657. 467 K. Tsukamoto, Y.Matsumura, T. Takahashi, and S. Simada, 7 Dec. 1972, DT 2 361 157. 468 Ford-Werke AG., 6 Oct. 1972, DT 2 350 126. 46s I.C.I. America Inc., 6 Nov. 1972, DT 2 348 400. 460 Sun Chemical Corp., 6 Dec. 1972, DT 2 357 866. 461 Desoto Inc., 18 Sept. 1972, DT 2 346424. Vianova Kunstharz AG., 24 April 1973, DT 2 41 1 506. 4es Fuji Photo Film Co. Ltd., 10 Aug. 1973, DT 2 358 133. 4ep Unisearch Ltd., 11 April 1972, DT 2 217 346. 466 PPG Ind. Inc., 9 June 1972, DT 2 328 418. Dow Chem. Co., 13 May 1971, US 3 810 825. 413~ Raychem. Corp., 24 March 1969, US 3 816 335. Japan Atomic Energy Research Inst., 22 Aug. 1970, US 3 816 284. 46v General Cable Corp., 29 Nov. 1973, US 3 852 518. 070 PPG Industries Inc., 15 Nov. 1968, US 3 770 602. 471 J. P. Stevens and Co. Inc., 7 Oct. 1971, US 3 814 676. J. E. Guillet, 30 Sept. 1971, US 3 812 025. 473 Unisearch Ltd., 11 April 1972, FR 2 179 540. 474 Institut Francais du PBtrole, 15 Dec. 1972, FR 2 210 648. 476 Institut Francais du PBtrole, 16 Nov. 1972, FR 2 206 317. 476 Unisearch Ltd., 5 April 1972, FR 2 178 758. 477 Unisearch Ltd., 29 Feb. 1972, CA 943 491. 414

0

R'

479

Used in conjunction with metal carboxylic acid salts and 2-3carbon polyolefins in the preparation of degradable compositions Compounds as shown are used in poly-a-olefin compositions, especially polyethylene and polystyrene

R1-6 are H, halogen, alkyl, alkoxy, aryloxy, benzoyl, or aryl groups and R6is (ar)alkyl, aryl, pyridyl, or these groups substituted by alkyl, aryl, alkoxy, or aryloxy R1-4 are each H, halogen, alkyl, or alkoxy-groups; R6 and R6are each H, OH, alkoxy-, or alkyl groups; R7 is a H, halogen, alkyl, or alkoxy-group and X is a carbonyl or CHR8 group (where Rs is a H, alkyl, or alkoxy-group)

478

480

478

0.02-5% by weight used as a pro-oxidant in polyolefin systems

R1 is an acyclic or cyclic hydrocarbon radical and each R2 independently represents a halogen or cyclic or acyclic hydrocarbon radical; y = 0-4

Ref.

Application

Specifications

Phillips Petroleum Co., 6 Sept. 1972, US 3 839 31 1. Princeton Polymer Lab., 6 July 1972, US 3 830 764. a0 Bio-Degradable Plastics, 20 June 1974, BE 816 594.

/

6.

Ra R1

Class and general formula Aromatic carbonyls

Table A1 Prudegradants and U.U. sensitizers

q2-

2

s

2 2 2

3

3

li"

Organometallics

m

Other aliphatic carbonyls of interest

R1- C-CH-C-R3 II II I 0 R2 0

R2

I

c=o

C=CH, I

I

R1

CH2=C-C-R1 II 0

R2 I

Aliphatic carbonyls

Class and general formula Other aromatic carbonyls of interest

Table A1 (cont.)

alkyl, OH, alkoxy, or carboxyalkyl groups; M is Fe, Co, Ni, Mn, Cr, Zn, Ca, Ba, Al, or Cu; m is an integer equal to or lower than the valence number of M, and n is an integer equal to or lower than (rn - l), where (m + n) is equal to the valence of M

X1,X2,and X3 are H, halogen, Cz-zo

506

4947 505

Prodegradants

0.01-5% by weight of this compound is used to render plastics such as polyethylene and polystyrene light-degradable

493

492

491

Ref. 481490

Used in conjunction with certain metal chelate compounds in rendering polyolefin compositions degradable

Used in the preparation of poly mer coatings

R1is a Cl-lo (cyclo)alkyl, aryl, alkenyl, or alkaryl group and R2is a H, (cyclo)alkyl, aryl, or alkaryl group having no more than 7 carbon atoms R1 is a (cyc1o)alkyl group, R3 is a (cyclo)alkyl, aryl, alkaryl, or aralkyl group-optional1 y substituted with a halogen, e.g. halophenyl, and R2is a H or organic group (but if R2 is H then R1 or R3 cannot be methyl groups). Preferably R1and/or R3 is aromatic

Employed as a prodegradant in met hacrylonitrile compositions. The resulting material is claimed to be biodegradable

Application Prodegradants

R1is a C1--galkyl, alkaryl, alkenyl, or aryl group; R2is a H or a C,-s alkyl group

Specijications

3

$E’

r:

0

CL

VI

a

Each (cyc1o)alkyl group being q-18, each keto-group having a C1-ll alkyl group bonded to the ferrocene nucleus via the carbonyl group

a1 Bio-Degradable Plastics Inc., 22 Feb. 1972, GB 1 385 497. ua Bureau of Industrial Tech. Japan, 20 Oct. 1972, JA 49 062 581. 4B8 Arc0 Polymers Iuc., 12 March 1973, US 3 832 312. 484 Mitsui Petrochemical Ind. Ltd., 30 May 1972, JA 49 010 945. Farbwerke Hoechst AG, 14 Sept. 1972, US 3 835 097. Sekisui Chemical Co. Ltd., 8 Dec. 1971, JA 48 064 134. Dow Chemical Co., 6 July 1971, US 3 825 626. Farbwerke Hoechst AG., 14 Sept. 1972, US 3 835 096. 4BD J.C.I. Ltd., 26 Oct. 1971, US 3 846 395. I.C.I. Ltd., 11 Oct. 1971, GB 1371 043. 491 I.C.I. Ltd., 26 July 1974, BE 818 168. 4ga Ecoplastics Ltd., 14 Feb. 1972, GB 1381 294. 493 I.C.I. Ltd., 23 Dec. 1971, GB 1371 192. 494 Sumitomo Chemical Co. Ltd., 28 March 1972, JA 48 097 951. 496 I.C.I. Ltd., 8 Nov. 1971, GB 1362 177. 486 Ecoplastics Ltd., 14 Feb. 1972, GB 1381 294. 497 University of Toronto, 27 April 1971, GB 1 372 182. 488 J. E. Guillet, 27 April 1971, GB 1 372 830. 4gs Agency of Industrial Sciences, 31 March 1972, JA 48 100 440. 6 o o BASF AG., 1 August 1974, BE 818 373. J. E. Guillet, 23 April 1973, US 3 853 814. Ruhrchemie AG., 2 Jan. 1974, N L 7 400 028. Ecoplastics Ltd., 7 Feb. 1972, US 3 811 931. .504 T. Kagiya, 17 March 1972, JA 48 094 742. 6os J. E. Guillet, 9 April 1973, US 3 860 538. 606 Harima Kasei Kogy Co. Ltd., 26 Oct. 1972, GB 1373 707. Harima Kasei Kogy Co. Ltd., 14 March 1972, JA 48 093 641. 608 I.C.I. Ltd., 16 May 1972, GB 1382061.

Ferrocene, or (cyc1o)alkylferrocene or a ketoferrocene

+

X is a C02 or SO3 group; R1,R2, and R3are H, halogen, alkyl, OH, alkoxy, carboxy, or carboxyalkyl groups and M is Fe, Co, Ni, Mn, Cr, Zn, Ca,Ba, Al, Cu, or Zr; (rn n) is equal to the valence of M by weight of these compounds is employed in the preparation of photodegradable polyolefin articles

0.01-2%

Used typically at a concentration of 0.5% by weight in various polymer systems

508

507

h. rc

P if G

0,

2

3

b

6 3

Miscellaneous

Other organometallics of interest

Metal salt of an organic carboxylic acid

Class and general formula Bis(cyclopentadienylferrodicarbony1)

Table A1 (cont.)

The photodegradable resin comprises a styrene-diene copolymer containing 0.1-10% by weight of butadiene or isoprene and 2=Oo.001% by weight of 2 1 of the transition-metal salts together with a brominated aliphatic hydrocarbon

Metal being selected from Fe, Co, Mn, or Cu

n is from 2 to 120 and R is 1,3-phenylene, 1,4-phenylene, diphenyl ketone-2,4-diyl, diphenylketone2,6-diyl, diphenyl ketone-2,2’-diyl, diphenylketone-2,3’-diyl,alkylphenylketone-2,5-diyl, alkylphenylketone-2,4-diyl, alkylphenylketone2,6-diyl, 2,7-naphthylene, 2,6-naphthylene, or a 2,4-naphthylene group

I

These polymeric compounds are inherently light-sensitive

Prodegradants

Application The composition patented here comprises a highly polymerized thermoplastic polyolefin and 0.01-3% by weight of the prodegradant shown

-

Specifications

528

511527

510

Ref. 509

690

aae

628

627

620

has

aa4

623

622

621

620

619

618

617

610

616

614

618

613

611

610

609

Many substituting groups discussed in patent

BASF AG., 20 June 1974, BE 816647. Sekisui Kagaku Kogyo KK., 24 Aug. 1971, US 3 864 293. Akerlund and Rausing, 4 Aug. 1972, GB 1 373 704. Ethylene-Plastique S.A., 20 Sept. 1973, GB 1 396 238. Akerlund and Rausing AG., 16 April 1973, GB 1 396 451. I.C.I. Ltd., 12 Nov. 1973, GB 1400 570. Debell and Richardson Inc., 12 Oct. 1972, GB 1 385 759. Akerlund and Rausing AG., 11 Sept. 1972, GB 1 366 207. I.C.I. Ltd., 23 Dec. 1971, GB 1371 192. Union Carbide Corp., 19 Dec. 1972, GB 1 365 989. I.C.I. Ltd., 19 May 1972, GB 1382062. BASF AG., 22 June 1973, DT 2 331 773. Nisseki Plastic Chem. Co., 31 May 1972, JA 49 010 946. Lion Fat and Oil Co. Ltd., 16 May 1972, JA 49 013 246. Debell and Richardson Inc., 23 August 1972, US 3 847 852. Lion Fat and Oil Co. Ltd., 2 March 1974, DT 2 409 966. I.C.I. Ltd., 9 Nov. 1972, US 3 840 512. Ethylene-Plastique S.A., 9 July 1973, BE 817 403. Dow Chem. Co., 30 May 1972, US 3 325 627. Mullard Ltd., 31 July 1973, GB 1386906. Showa Denko KK, 27 March 1973, US 3 856 758. Mitsubishi Chem. Inds. Co., 3 Oct. 1972, JA 49 057 051.

sym-Triazine derivatives

z

W, X,Y,and Z are each H, C+,, alkenyl, C,-,, aryl, C1--20(ar)alkyl, at least one radical being a nitrilecontaining group

Employed as photodegradation accelerators for polyolefins and polystyrene

shown

Photodegradable polymers are prepared by the ring-opening polymerization of the cyanosubstit uted nor bornene derivatives

wl

R

Others

655

662

551

560

6 40

648

647

546

646

644

543

542

541

640

639

638

637

696

635

634

533

532

531

Prodegradants

Specifications Application R1,R2are both H or C,, alkyl groups; Photodegradable resins are R3,R5are aryl or alkyl groups; R4, R6, prepared from a mixture of a and R7are arylene groups; R8is an copolymer of an unsaturated alkyl group and X is a polymerizable ketone-group-containing comorganic group pound with a radical polymerizing monomer and a copolymer of 2 1 compound of formula shown

Agency of Ind. Sci. and Tech., 11 Oct. 1972, JA 49 059 848. I.C.I. Ltd., 23 Aug. 1972, GB 1396313. I.C.I. Ltd., 8 Nov. 1971, GB 1370783. Princeton Chem. Res., 26 Oct. 1971, GB 1 364902. Agency of Ind. Sciences, 13 Oct. 1972, JA 49 059 849. Asahi-Dow Ltd., 16 Dec. 1970, JA 74 035 356. Arc0 Polymers Inc., 16 Nov. 1972, US 3 833 401. Daicell Co. Ltd., 29 March 1972, JA 48 099 243. Kureha Kagaku Kogyo KK, 28 Dec. 1973, DT 2 364 875. Sumitomo Chem. Co. Ltd., 23 Aug. 1972, JA 49 039 692. Sumitomo Chem. Co. Ltd., 24 Aug. 1972, JA 49 040 339. Nisseki Plastic Chem. Co., 23 June 1972, JA 49 022 446. Sumitomo Chem. Co., 14 Sept. 1972, JA 49 051 341. Mobil Oil Corp., 7 Aug. 1972, US 3 856 747. Mitsubishi Petrochem. Co., 2 Sept. 1972, JA 49 044 093. Canon KK., 2 June 1972, JA 49 016 766. Arc0 Polymers Inc., 18 Dec. 1973, DT 2 362 851. Mitsui Petrochem. Ind., 16 Sept. 1971, JA 48 037 445. Mitsubishi Petrochem. Co., 21 Feb. 1972, JA 48 096 683. S. Nagai, 9 June 1972, JA 49 017 895. Sekisui Kagaku Kogyo KK, 15 July 1971, CH 552 024. Sumitomo Chem. Co. Ltd., 4 April 1972, JA 48 101437. Sumitomo Chem. Co. Ltd., 4 April 1972, JA 48 101 438.

R3NH R4X R5NHR6NHR'X R'SX

Class and general formula

Table A1 (cont.)

575

532-

Ref. 531

a!

P

ch

676

674

671

670

s6v

688

667

666

565

m4

668

m1

669

55B

657

566

555

354

Mitsubishi Chem. Ind., 22 Sept. 1972, JA 49 053 232. Sumitomo Chem. Co. Ltd., 28 March 1972, JA 48 097 950. Mitsui Petrochem. Ind. Ltd., 14 April 1972, JA 48 103 643. Sumitomo Chem. Co. Ltd., 29 Dec. 1970, JA 49 004 821. Mitsubishi Chem. Inds. Co. Ltd., 16 Oct. 1972, JA 49 060 338. Mitsubishi Petrochem. Co. Ltd., 9 Nov. 1970, JA 49 013 207. Mitsubishi Petrochem. Co. Ltd., 9 Nov. 1970, JA 49 013 208. Daiichi Kogyo Seiyaku Co. Ltd., 14 July 1972, JA 49 029 294. Japan Kureha Chem. Ind. Co. Ltd., 22 March 1973, JA 49 110 739. T. Kagiya and K. Takemoto, 17 May 1972, JA 49 008 580. T. Kagiya and K. Takemoto, 5 April 1973, JA 49 126 783. M. Nakamura and H. Takeuchi, 21 July 1972, JA 49 031 782. Asahi Dow Ltd., 16 Dec. 1970, JA 49 037 591. Japan Kureha Chem. Ind. Co. Ltd., 29 Dec. 1972, JA 49 090 737. Japan Asahi Chem. Ind. Co. Ltd., 25 Jan. 1973, JA 49 099 547. Mitsubishi Rayon Co. Ltd., 2 March 1973, JA 49 112 992. Mitsubishi Rayon Co. Ltd., 28 Aug. 1969, JA 48 014 137. Agency of Ind. Sci. and Technol., 21 Aug. 1972, JA 49 039 687. Sekisui Chem. Co. Ltd., 22 June 1971, US 3 798 187. AB Akerlund Och Rausing, 20 Sept. 1972, DT 2 347 318. Debell and Richardson Inc., 23 Aug. 1972, DT 2 250 885. Ethylene-Plastique S.A., 20 Sept. 1972, DT 2 346 930.

U.V. absorbers and stabilizers

M

Organophosphorus compounds

0 0 Other organometallics of interest

f-

Class and general formula Organometallics

Table A2

X is an oxygen or sulphur atom; Y is oxygen, sulphur, or an imino-, Cl,, alkylimino-, or C,, cycloalkyliminogroup; each R is a hydrocarbon group having up to 25 carbon atoms and consisting of one or more aromatic units containing C,,,, and/or one or more saturated aliphatic and/or saturated alicyclic units containing in total up to 18 carbon atoms, in which hydrocarbon radical one or more C-C bonds may be replaced by C-0-C bonds. Each of the rings A and B may alkyl substituent; n is have a C1-12 1 or 2

R is a C1-22 alkyl group, M is Zn, Cry Ni, Co, Mn,Cu, Al, Ti, or Fe, and n is 1 or 2 such as to satisfy the valency of M

R is a C1+ alkyl group

Specification

Employed as a U.V. stabilizer in many polymer systems

Light stabilizers

Used as a U.V. stabilizer in such polymers as polyethylene, polypropylene, ABS, and Nylon-66

Used at a concentration of by weight in the U.V. stabilization of polyolefins 0.2-1.0%

Application

58 1

578580

577

576

Ref.

680

68s

688

687

686

686

684

688

682

681

680

670

678

677

676

R2is a t-butyl group, R1is a G,.alkyl group provided that one or more is a methyl group; x is 1 or 2

American Cyanamid Co., 23 Oct. 1973, US 3 843 597. Ciba-Geigy AG., 22 Aug. 1972, GB 1 399 368. Phillips Petroleum Co., 31 Oct. 1973, US 3 856 750. American Cyanamid Co., 13 Feb. 1973, GB 1 378 097. Exxon Research and Eng. Co., 3 April 1972, US 3 849 516. Sandoz Ltd., 29 March 1972, GB 1394 574. Buckman Laboratories Inc., 3 Aug. 1972, GB 1 399 106. Ciba-Geigy AG., 21 June 1972, GB 1 378 940. Adeka Argus Chem. Co. Ltd., 7 Sept. 1972, JA 49 045 884. Borg-Warner Corp., 15 March 1973, US 3 839 507. Sandoz Ltd., 28 Sept. 1971, GB 1372042. Sandoz Ltd., 15 Oct. 1971, GB 1372 528. Cincinnati Milacron Chem. Inc., 5 Aug. 1971, GB 1368 331. Bayer AG., 10 Aug. 1972, GB 1 382 525. Ashland Oil Inc., 8 May 1972, US 3 843 600.

Sterically hindered phenols and benzoic esters

Other organophosphorus compounds of interest

saturated aliphatic hydrocarbon radical which may be halogen-substituted, or a uni-, bi-, or ter-valent metal, e.g. an alkali metal, an alkaline-earth metal, Zn, Cd, Sn, Al, or Ni; n is an integer from 1 to 3 corresponding to the valency of R2,and X is H, Br, or a group of the formula -CH,P(0)(OR1), where R1 is as mentioned above

R1is a Cl-,B alkyl or haloalkyl group; R2is a uni-, bi-, or ter-valent Cl-u-

Used especially in the stabilization of ethylene and propylene polymers

U.V.stabilizers

Can be used to stabilize many polymer systems

590

589

583-

582

G

3

n

s

*a a-

/

Class and general formula

(cont.)

OMe

R2

Cyclic amines R3yHCH,0H

Other benzotriazoles of interest

HO

Benzotriazoles

Other phenols and benzoic esters of interest

Ho\

5 R 0 c 6 2 0 + + ( 2 0 c # R

Table A2

R1and R2are the same or different and each is a G-12 alkyl residue, or R1 and R2together with the carbon atom to which they are bound form a C5-1, cycloalkyl residue. Y is 0, H, a straight or branched C1-20 alkyl residue, a C&12

or R1

R1is a Cl-12 alkyl group and R2is H

groups. R3and R4are H or alkyl groups and R6is an alkyl, cycloalkyl, aralkyl, heterocyclic aromatic, or phenyl group optionally substituted by 1 or 2 alkyl groups. M is H or a bivalent cation and y is 0 or 1

Specification R1is a c4-14 t-alkyl group; R2is H, alkyl, alkoxy-, cycloalkyl, or aralkyl aryl group group optionally by 1 orsubstituted 2 alkyl or in halogen the

593596

Ref. 591, 592

Employed in the U.V. stabilization of many polymers, especially polypropylene

U.V.stabilizers

602

598601

Polyvinyl butyral interlayers are 597 stabilized using a synergistic mixture of the triazole shown and octadecylcresol at concentrations of 0.1-0.5 and 0.07-0.8% by weight, respectively

U.V.stabilizers

Application Used particularly for the U.V. stabilization of polyethylene and polypropylene

5 G

3

9

s

2 s

8

wl

012

010

Oo9

OoR

Oo7

606

Oo5

Oo4

Oo3

Oo2

Ool

Oo0

rig*

697

686

m5

693 6n4

692

691

-

Chimosa Chim. Organica, 7 June 1974, BE 816064. Sandoz S.A., 17 June 1974, BE 816453. Argus Chemical Corp., 26 April 1971, US 3 856 728. E. I. Xirilova, 21 Feb. 1972, SU 403 699. Bayer AG., 28 June 1973, GB 1 392 167. Ube Industries Ltd., 28 Oct. 1972, JA 49 062 544. Monsanto Co., 27 Oct. 1972, US 3 823 413. Hercules Inc., 18 June 1972, GB 1372963. Bayer AG., 12 March 1973, GB 1 372 826. Idemitsu Kasan Co. Ltd., 23 Jan. 1974, GB 1 397 919. E. I. Du Pont de Nemours Co., 17 May 1972, US 3 849 373. Ciba-Geigy AG., 31 Dec. 1973, GB 1402 889. Sankyo Co. Ltd., 23 July 1973, GB 1384039. Ciba-Geigy AG., 30 Nov. 1972, GB 1 395 159. Ciba-Geigy AG., 18 April 1974, BE 813 882. Ciba-Geigy AG., 30 Nov. 1972, GB 1 395 160. Sankyo Co. Ltd., 3 July 1972, GB 1 393 616. Sankyo Co. Ltd., 3 July 1972, GB 1 393 617. Sankyo Co. Ltd., 5 June 1972, GB 1 393 281. Ciba-Geigy AG., 27 Sept. 1973, GB 1 399 240. Ciba-Geigy AG., 30 Nov. 1972, GB 1 399 239. Ciba-Geigy AG., 21 June 1974, BE 816 695.

Other cyclic amines of interest

alkenyl or alkynyl residue, a C,--12 aralkyl residue, or a group having the formula -CH,CH(R)OH wherein R is H, Me, or Ph; R3is H or a C1-12 straight- or branched-chain alkyl residue

U.V.stabilizers

2 G 3 3

OH

b CH, CH, Si(OR2) 1

I

I

II

I

NOH WOH

II

QC-CJJ

(R1)a

I

R3-€-OCH2&HSi(OR2 I

R3f O

CIass and general formula Miscellaneous

Table A2 (cont.) Application

Photodegradation-resistant polyolefins such as polypropylene films employ 0.001-5% by weight of one or more of the degradation retardants shown

R1 denotes a bivalent hydrocarbon These novel silanes are used to residue or oxygen-interrupted hydrostabilize coating compositions to U.V. carbon radical of up to 10 carbon atoms; R2denotes a C,, aliphatic hydrocarbon or acyl radical, or a radical of formula (CH,CH,O),Z, where n is 1-8 and Z is a C1--4aliphatic hydrocarbon radical; R3 denotes a stable uni- or bi-valent hydroxyaromatic radical containing up to 4 aromatic rings and joined to oxygen through an aromatic carbon. a is 0 or 1 and b is 1 or 2

Specification

614

613

Re5

t 4

cn cn

640

630

638

637

636

63s

634

b33

63a

630 631

62B

628

627

626

625

624

623

622

621

620

61B

617

616

613 614

-

E. I. Du Pont de Nemours and Co., 14 Sept. 1973, GB 1 393 488. Ube Industries Ltd., 12 Oct. 1972, JA 49 059 851. Ciba-Geigy AG., 29 Dec. 1972, GB 1 373 030. Bayer AG., 28 June 1973, GB 1392 166. Sumitomo Chem. Co., 27 Sept. 1972, JA 49 053 936. Nippon Steel Chem. Co. Ltd., 7 Dec. 1970, JA 49 021 307. I.C.I. Ltd., 3 July 1974, DT 2 432 027. National Research Council, Canada, 2 July 1971, CA 939 569. Sandoz Ltd., 14 July 1972, DT 2 335 444. J. Gunis, Z. Manasek, and J. Luston, 9 June 1972, CZ 154 514. Reichhold-Albert-Chemie AG., 31 July 1972, DT 2 332 820. Ajinomoto Co. Inc., 1 Nov. 1972, DT 2 354 635. M. V. Rakhimova and M. M. Tulyaganov, 2 July 1968, USSR 443 949. N. N. Petukhova, V. P. Litvinov, L. N. Smirnov, and N. D. Zelinskii, 31 Jan. 1972, USSR 413 165. A. Paulauskas, I. Degutis, and A. Vaidakavicius, 24 Dec. 1971, USSR 423 808. United States National Aeronautics and Space Research Admin., 5 Jan. 1973, US 3 803 090. Phillips Petroleum Co., 6 Sept. 1972, US 3 843 595. Itek Corp., 25 Sept. 1972, US 3 829 318. Monsanto Co., 11 Aug. 1969, US 3 817 924. Nippon Soda Co. Ltd., 25 Sept. 1972, JA 49 052 786. Sankyo Co. Ltd., 6 March 1969, JA 49 040 557. Sumitomo Chem. Co. Ltd., 12 March 1970, JA 49 043 110. Teijin Ltd., 10 June 1972, JA 49 018 171. Mitsubishi Chem. Ind. Co. Ltd., 12 July 1972, JA 49 028 589. Otsuka Chem. Drugs Co. Ltd., 29 July 1970, JA 49 011 310. K. Murayama, S. Morimura, and H. Horiuchi, 4 Oct. 1972, JA 49 057 047. Pola Chem. Ind. Co. Ltd., 17 April 1972, JA 49 000 450. Sumitomo Chem. Co. Ltd., 16 Oct. 1972, JA 49 061 068. Mitsubishi Chem. Ind. Co. Ltd., 22 March 1972, JA 48 097 865.

Other miscellaneous U.V. stabilizers 615641

2 3

3

Other triazoles of interest

Class and general formula Benzotriazoles

Table A3 Optical brighteners

Optical brighteners

643

Employed as a polyester optical brightener

R1represents a phenyl, phenyloxy, or benzyloxy radical (which is optionally substituted by alkyl, alkoxy-, halogen, C02H, or alkoxycarbonyl groups) or stands for a cycloalkyl radical. R2is H, or together with R1forms a (CH,), or -CH=CHCH= CH- radical. Ra is an alkyl, cycloalkyl, or phenyl radical which is optionally substituted by alkyl, alkoxy-, phenyl, halogen, or cycloalkyl groups. R4is a halogen atom or an alkoxy, CN, CO,H, alkoxycarbonyl, or methyl radical, and X is =CH- or =N-. n is 0, 1, or 2

Ref.

Used for optical brightening of PVC, 642 polypropylene, polystyrene, and poly(methyl met hacrylate)

AppIicat ion

R1and R2are each C1-12 aliphatic alkyl, cycloaliphatic, araliphatic, or monocyclic aryl radicals and are optionally substituted. Hal is a halogen atom

Speci’cation

Stilbenes

648

647

646

645

644

643

eia

Bayer AG., 30 May 1973, GB 1402 371. Bayer AG., 8 Dec. 1972, GB 1 385 347. Ciba-Geigy AG., 15 Dec. 1972, GB 1 393 267. Ciba-Geigy AG., 2 March 1973, GB 1 400 963. I.C.I. Ltd., 4 Nov. 1970, GB 1373 210. Sandoz Ltd., 31 Dec. 1970, CH 554 890. Sandoz Ltd., 24 Nov. 1970, CH 551 987.

Used to brighten polyamides, polyesters, polyacrylonitrile, polystyrene, and PVC

R1,and R2,may be the same or different and each denotes an optionally substituted sulphonic acid group, a sulphone, cyano-, or modified carboxylic acid group. R2, can also denote an alkyl or alkoxy-group or a H or C1 atom. RlVand R2,,which may be the same or different, each denote a sulphonic acid group or a salt thereof, a H or C1 atom or an alkyl or alkoxy-

648

Used for optical brightening of PVC, 647 polyamides, and polyesters

R is a CIA alkyl, phenyl, or benzyl group or phenyl or benzyl substituted by Cl or Me

wl

wl

wl

3.

b

2

3

'p

s

Miscellaneous

Other stilbenes

R2

R 1 o c * =I y

(1)

Class and general formula

Table A3 (cont.)

A is a dihydrophenanthrene group bonded in the 2,7 positions to the oxazole groups, optionally substituted by a G4 alkyl or alkoxy-group or a halogen atom. Al and A, are independently benzene or naphthalene groups optionally substituted by nonchromophoric groups and which are condensed in the indicated manner with the oxazole ring

Specification A is a bivalent radical selected from (l), (2), and (3) and R1and R3 are the same or different and each is a substituent selected from H, C1, G4 alkyl, methoxy, ethoxy, and sulphonic acid radical or a salt thereof, sulphonamide radical, and G4 alkylsubstituted sulphonamide radical. R2and R4are the same or different and each is a substituent selected from H, CI, G-,-alkylsulphonic acid radical or the salts thereof, sulphonamide, or G,-alkyl-substituted sulphonamide radical

Used for brightening polyesters at a concentration of 0.0010.002% by weight

Optical brighteners

Application Used for brightening polystyrene and polyamides

653

650652

Ref. 649

\o

CI

654672

1 368 651

1 372 963

1 377 785

1 378 880

1 382 459

660

649

Ciba-Geigy AG., 20 Oct. 1972, GB 1 382 364. Ciba-Geigy AG., 29 June 1973, GB 1391 882. 661 Nippon Kayaku, 14 May 1973, GB 1 389 996. Sandoz Ltd., 13 June 1969, CH 555 847. 663 Ciba-Geigy AG., 20 Aug. 1968, CH 554 821. 664 Ciba-Geigy AG., 30 March 1973, DT 2 315 955. 666 Ciba-Geigy AG., 6 Sept. 1973, GB 1 395 469. 666 Nippon Kayaku Co. Ltd., 17 Jan. 1972, JA 48 076 927. 657 Ciba-Geigy AG., 14 April 1972, GB 1 377 247. Hoechst AG., 11 Aug. 1972, GB 1 399 509. 66g Ciba-Geigy AG., 30 Jan. 1973, GB 1 402 803. 660 Chisso Corp., 30 Sept. 1972, JA 49 055 743. Jury C. W., 29 Feb. 1972, US 3 822 214. 662 Mitsui Toatsu Chem. Inc., 28 Nov. 1970, JA 49 017 404. 669 Farbwerke-Hoechst AG., 9 Feb. 1973, DT 2 405 063. 664 Farbwerke-Hoechst AG., 9 Feb. 1973, DT 2 405 056. w6 Ciba-Geigy AG., 2 Feb. 1973, DT 2 403 455. 666 Sandoz Ltd., 29 Jan. 1973, FR 2 215 421. 667 Mitsui Toatsu Chem. Inc., 19 Dec. 1972, JA 49 085 378. 668 Japan Kanebo Ltd., 16 Jan. 1973, JA 49093 677. 06@ T. Jaskewycz, 27 Oct. 1970, US 3 780 029. 670 Henkel und Cie. GmbH., 28 April 1973, DT 2 321 693. 671 Henkel und Cie. GmbH., 1 Feb. 1973, DT 2 304 887. Albright and Wilson (Australia) Ltd., 28 Oct. 1969, AU 455 187.

1 368 482

1 384 112 1 384 821

1 398 326

Other references concerning optical brighteners and fluorescent dyes can be found under the following British Patent numbers :

Other miscellaneous optical brighteners

.=i

35

$

2 oh

2

+$ 'FI

Part V PHOTOCHEMICAL ASPECTS OF SOLAR ENERGY CONVERSION By M.

D. ARCHER

1 Introduction The work reported in this chapter is presented in an order slightly different from that used last year: as before, purely photochemical work is followed by photoelectrochemistry, but what may broadly be termed photobiological considerations now precede discussion of photovoltaics. Some papers which neither mention nor imply radiant energy conversion, yet nevertheless seem relevant, are included. A few older papers, overlooked in last year’s introductory chapter, are reported for the sake of completeness. Two interesting books l, of some relevance to photochemical solar energy conversion have appeared this year, as have the proceedings3 of the workshop sponsored by the U.S. National Science Foundation on photochemical fuel formation, mentioned last year. The range of this conference was wider than its title suggests, and the proceedings, particularly the introductory review paper by Calvin, are a useful discussion of much the same subject matter as this chapter, except that photovoltaics were excluded from consideration. It must be admitted, however, that some of the contributors have suffered by being quoted verbatim. 2 Photochemistry Endergonic Isomerhation and Substitution Reactions.-Several contributors 4-6 to the N.S.F. conference discussed energy storage by means of photochemical valence isomerization reactions such as the norbornadiene-quadricyclene conver~ion,~ which was reported as early as 1954 to be driven by sunlight, and is endothermic by ca. 40 kJmol-l. The reverse reaction can be catalysed by palladium on carbon. The valence isomers of benzene, although they store much potential energy in their highly strained structures, are moderately stable at room temperature. As benzene does not absorb light above 300 nm these are not likely to be useful in a practical sense, but they do give some feeling for the 1 2

3

*

K. L. Coulson, ‘Solar and Terrestrial Radiation’, Academic Press, New York, 1975. ‘Photosynthesis and Productivity in Different Environments’, ed. J. P. Cooper, Cambridge University Press, 1975. ‘The Current State of Knowledge of Photochemical Formation of Fuel’, Report of N.S.F. Sponsored Workshop, Osgood Hill, Mass., U.S.A., September 23-24, 1974. (Report available from Prof. N . N. Lichtin, Dept. of Chemistry, Boston University, 685 Commonwealth Ave., Boston, Mass. 02215, U.S.A.) G. Jones, ref. 3, pp. 149-161. 0. L. Chapman, ref. 3, pp. 168-171. R. Srinivasan, ref. 3, pp. 171-172.

561

Photochemistry

562

amount of energy storage achievable. The formation of benmalene from benzene is endothermic by ca. 290 kJ mol-l.' Methods of forming it, and the other two valence isomers of benzene, have been summarized in a paper * on the photochemistry of benzvalene itself, which exhibits a number of unusual features. On the whole, trans-cis-isomerizations store less energy than valence isomerizations, but may be easier to sensitize to visible light: 436 nm light, for example, absorbed by XRe(CO),(trans-3- or 4-~tyrylpyridine)~, where X = C1, Br, or I, photoassists the trans-cis-isomerization of excess styrylpyridine, which does not itself absorb at that wa~elength.~ The mechanism is as shown in Scheme 1, CIRe(CO)a(trans)a CIRe(CO),( trans)(cis)

A A

ClRe(CO)3(cz's)(trans) CIRe(CO)a(CiS)g

A

+ trans t CIRe(CO),(trans)a ,+ cis A CIRe(CO)a(trans)(cis) + (cis) CIRe(CO)g(cis)a+ trans 7

ClRe(CO),(trans)(cis)

trans = trans-styrylpyridine cis = cis-styrylpyridine Scheme 1

and the quantum yields and the percentage of the cis-isomer formed in the photostationary state are given in Table 1. The lowest excited state in these rhenium Table 1 trans-cis-Isomerizations of free and co-ordinated styrylpyridines in CHBClpat 298 K % cis in photocD(s c) a?(t -f c) stationary state 313nm 366nm 313nm 366nm 436nm Compound 9Obio d d 0.48 d trans-3-Styrylpyridine 0.38 ** * d 88 d d trans-4-Styrylpyridine 0.54 84 90 99 CIRe(CO),(trans-4-styrylpyridine), 0.49 99 98 >99 0.64 0.51 BrRe(CO),(trans-4-styrylpyridine), -f

b9

ClRe(CO)&rans-3-styrylpyridine),

0.60

0.51

93

90

99

G. Bartocci, a D. G. Whitten and M. T. McCall, J. Amer. Chem. Soc., 1969, 91, 5097. G. Favaro, U. Mazzucato, P. Bortolus, and U. Mazzucato, J. Phys. Chem., 1973, 77, 607. No absorption at these wavelengths. and F. Masetti, ibid., p. 601.

complexes is an intraligand state associated with the styrylpyridine chromophore, and this is somewhat red-shifted compared with the free ligand. The (slow) thermal substitution reactions in Scheme 1 thus allow the photochemical formation of the energy-rich cis-isomer at longer wavelengths (though in much the same proportion) as in the complex-free system. 'I

* *

N. J. Turro, ref. 3, pp. 164-167. C. A. Renner, T. J. Katz, J. Pouliquen, N. J. Turro, and W. H. Waddell, J. Amer. Chem. Soc., 1975,97,2569. M. S. Wrighton, ref. 3, pp. 63-83.

Photochemical Aspects of Solar Energy Conversion

563

The photosubstitution of complexes of alkylisocyanide (RNC) with ferrous phthalocyanine (FePc) : LFePc(RNC) (blue)

+L

Light

..r Dark

LBFePc+ RNC (green)

(1)

where L = piperidine, has also been proposed1° as a solar energy storage system. As the forward reaction is endothermic by only ca. 20 kJmol-l and no means of harnessing the energy of the unstable products spring to mind, this does not appear to be a promising candidate. The difficulties in the way of this approach to solar energy storage are formidable : highly strained molecules are generally produced only by U.V. light, and moreover cannot be cycled back to the starting material without some degradation. Slightly endergonic reactions, such as trans -+cis isomerizations, may be achieved with visible light, but may still be difficult to recycle, and store insufficient energy to be interesting anyway. Photochemical Water Decomposition.-Three methods of achieving this (using Ce3+-Ce4+, TiO,, or hydrogenase enzymes) have been briefly and uncritically reviewed.ll CI

X + H,O X + + iH20 dH,O

c2

Y + H,O Y- + HZO HZ0

c3

Z

+ HZ0 zo

hv

hv

+ 402

> H

hv

A hv

or

Y-

Y

+ H+ + OH + OH- + +Ha

+ OH 20 + HZ *Ha

z

+ 40,

(i) (ii) (iii)

c4

la

X + + H + OHX + H + + H&.

D. V. Stynes, J. Amer. Chem. SOC.,1974, 96, 5942. S. N. Paleocrassas, Solar Energy, 1974,16,45.

Photochemistry Three methods for hydrogen production from solar energy have been analysed in terms of efficiency and economics.12 Direct photochemical production from water was not considered, and the use of solar energy to decompose water in a thermochemical cycle was identified as the best approach. The others considered involved production of hydrogen by the electrolysis of water, using electric power generated either by solar cells or by a solar-powered vapour cycle engine coupled to a conventional generator. Stein13 has discussed the production of hydrogen by irradiation of aqueous solutions of I-, Fez+, Fe(CN),4-, and Eu2+in their CTTS bands. This approach was reviewed last year [when the photo-oxidation of water by U.V. excitation of the CTTM band of tris-(1,lo-phenanthroline)iron(m) l4 was overlooked by mistake] and there is little progress since then to report. Cyclic reactions, involving transition-metal complexes, which result in the photochemical formation of hydrogen from water have been divided by Balzanil5 into four categories, Cl-C4, summarized in Scheme 2, and their minimum energy requirements (per photon of absorbed light) are shown in Figure 1. C1 requires an X+-X couple having Eo > 1.23 V (e.g. Ce4+-Ce3+),and has a thermodynamic threshold energy requirement of 330 nm. C2 requires a Y--Y couple having Eo < O V (e.g. Eu2+-Eu3+)and has a threshold of 370 nm. These two cycles suffer from the disadvantages mentioned last year, namely that the CTTS and CTTM bands involved tend to lie in the u.v., and that overall quantum yields are low because of geminate recombination of the first-formed species. They have lower threshold energies than the decomposition H,O -+ H + OH because only one radical is formed in either case. By contrast, no radicals are produced in C3 and C4, and this is energetically advantageous. The first formulation of C3 involves a rather implausible simultaneous transfer of two electrons from the 'catalyst' Z to water, though this might possibly be achieved by use of a dinuclear complex in which the metal ions remain bound together on reaction (so that further steps can lead back to the original structure). The second formulation of C3 involves a dihydro transition-metal complex, some of which do decompose on irradiation as shown in equation (i) of Scheme 2 to yield molecular hydrogen. In this case, L represents an electron-donating ligand such as 1,lo-phenanthroline, and the reactions are actually slightly exergonic. There are other complexes of the type ML4a+which are known to react spontaneously with water to yield dihydro-complexes, as in equations (ii) and (iii). In this case, L is an electron-withdrawing ligand such as a phosphine. If a single ligand or readily interchangeable combination of ligands could be used to run reactions (i)-(iii) consecutively, reaction (i) being endergonic, then water would be photodecomposed without the energetically wasteful production of intermediate H or OH. The threshold energy requirement for C3 is 420 nm. C4 involves the photochemical formation of a monohydrido metal complex, followed by dimer formation and reductive cleavage. In this and the previous 564

12

l3 14

l5

M. M. Eisenstadt and K. E. Cox, Solar Energy, 1975, 17, 59. G. Stein, ref. 3, pp. 59-63. E. L. Wehry and R. A. Ward, Inorg. Chem., 1971,10, 2660. V. Balzani, ref. 3, pp. 46-58.

565

Photochemical Aspects of Solar Energy Conversion

cases, it is possible, and would be advantageous, for more than one of the reactions to be photochemical. The HTr(PF,), complex has been shownIs to undergo reaction (v) on irradiation, and reaction (vi) has been observed1' for

H

900

.(

t2-

+ H+O

- - - - - - - - onset of absorption of water

-300

,-4OC

250

-

- 500

-600

-

I

H

14-"

+ &02 +OH

2 "2+ 1%

pI 2

+ go,

Figure 1 Threshold energies for water photodissociation by cycles Cl-C4 (Reproduced by permission from ref. 3, p. 51)

several complexes. Two photons are used to split one water molecule in cycle C4, and that is the reason why the threshold energy is so low (840 nm). In order to have a cycle of this type, two photons must be absorbed simultaneously by the catalyst (and this is impossible for a low-density photon source such as solar radiation), or intermediate compounds must be formed which are l6 l7

T. Kruck, G . Sylvester, and I. P. Kunau, Angew. Chem. Internat. Edn., 1971, 10, 725. M. S. Wrighton, Plenary Lecture at the V IUPAC Symposium on Photochemistry, Enschede, Holland, July 1974.

566

Photochemistry

sufficiently stable to react with each other, as in equations (iv)-(vi), or two coupled consecutive reactions must be driven by light against a gradient of chemical potential, as in green plant photosynthesis. The Fixation of Carbon Dioxide and Nitrogen.-As reduced carbon compounds are convenient fuels, the possibility of achieving the reductive fixation of COB in vitro is appealing, if remote. There are very few data on photochemical reactions involving carbon dioxide, for it has no low-lying excited states and has not historically been of much interest to the photochemist. However, what appears to be the first example of photofixation of CO, in a non-biological system has been briefly reported.ls Photoirradiation (with a high-pressure mercury lamp) of phenanthrene in the presence of an amine and CO, in a polar solvent (Me2S0 or HCONMe,) yielded 9,1O-dihydrophenanthrene-9-carboxylic acid, in unspecified quantum yield. The mechanism appears to involve formation of COZYby electron transfer from the photoexcited amine, followed by attack of C02- on position 9 of phenanthrene. Similar reductive carboxylation of anthracene, pyrene, naphthalene, and biphenyl was observed. Interest is growing in the behaviour of CO, as a transition-metal ligand: CO, generally reacts with metal complexes to give either insertion or substitution products. For example, some transition-metal dimethylamides react with CO, reversibly to give dimethylcarbamato compounds.l@ C 0 2 displaces nitrogen from cis-[Mo(N2),(PMe,Ph),] to give [MO(CO,)~(PM~,P~),].~~ An apparently new mode of C0,-metal complex association has also been reported.21 Crystalline trans-[M(OH)(CO)(Ph,P),] (M = Rh or Ir) reacts with C 0 2 under mild conditions to form an addition compound [(C0,)M(0H)(C0)(Ph3P),] which, on pumping, releases CO, and reverts to the starting material. The addition compound was tentatively concluded to contain a bent CO, molecule hydrogenbonded to the hydroxyl ligand. The interest in these complexes, as far as this chapter is concerned, is that lowering the symmetry and bond order of CO, might make it more susceptible to photoreduction. Chapman6 has pointed out that bivalent carbon can fix both CO, and N2 according to reactions (2) and (3).

R,C:

+ N2

4__f

R,C-N=N

(3)

The fixation of molecular nitrogen has been discussed by Fischler and Koerner von Gustorf,22 who point out that Mn+-*N=N has a CTTL transition; this lS la

21

2a

S. Tazuke and H. Ozawa, J.C.S. Chem. Comm., 1975,237. M.H. Chisholm and M. Extine, J.C.S. Chem. Comm., 1975, 438. J. Chatt, M. Kubota, G. J. Leigh, F. C. March, R. Mason, and D. J. Yarrow, J.C.S. Chem. Comm., 1974, 1933. B. R. Flynn and L. Vaska, J.C.S. Chem. Comm., 1974, 703. I. Fischler and E.Koerner von Gustorf, Naturwiss., 1975, 62, 63.

Photochemical Aspects of Solar Energy Conversion

567

falls at 263 nm for [ R U , ( N H ~ ) ~ ~ NThe ~ ] ~electron +. is transferred to an orbital that is predominantly N,T* in character : however, reduction products of nitrogen have not been obtained by irradiation of any such complex. 3 Photoelectrochemistry This section is divided into two parts, the first dealing with photogalvanic cells, in which a homogeneous photochemical reaction in solution forms one or more products which diffuse to and react at the electrodes. The second part deals with cells containing semiconductor-electrolyte interfaces. A review 23 which covers the literature on these topics up to mid-1974 in a more or less comprehensive way is available.

Photogalvanic Cells.-Gomer 24 has carried out an analysis of photogalvanic cells, with particular reference to the iron-thionine system. The principal difficulties that lie in the way of developing an efficient cell are identified: firstly, diffusion to the electrodes and reaction there must be sufficiently rapid to make bulk reactions unimportant, and secondly, a means of keeping at least one active species from reaching one electrode must be found. These problems are discussed in terms of absorbed photon flux, cell-size parameters, chemical rate constants, and electrode kinetics: it is concluded that the rate constant of the (bimolecular) homogeneous back-reaction of the products must be small, preferably less than lo2 cmamol-1 s-I, unless electrode spacings of cm or less prove feasible. Standard exchange current densities of the order of lozlo3A cm mol-1 are required, which implies highly reversible electrode kinetics. These conclusions are not, however, as general as they might be as the expression used for the cell voltage, equation (4)of ref. 24, is a limiting, not a general, case. The form of this equation implies that one electrode is reversible to only one redox couple (e.g. thionine-leucothionine) while the other is reversible only to the other couple (e.g. Fe3+-Fez+). A semipermeable membrane has been introduced to achieve the second condition, but the first is simply assumed. The iron-thionine photogalvanic cell was also discussed at the N.S.F. ~ o r k s h o p . ~ American ~-~~ workers 27 have concluded that semithionine, rather than leucothionine, is the electroactive species which produces an anodic photocurrent at the illuminated electrode, though this remains to be conclusively demonstrated. They have therefore aimed to increase the lifetime of semithionine and its concentration in the photostationary state by using mixed aqueous-organic solvents, containing NN-dimethylacetamide, 1,Zdimethoxyethane, acetonitrile, or ethanol. The dependence of the semithione disproportionation rate on solvent correlated quite well with Kosower’s 2 parameter, which is a measure of solvent polarity. The use of an aqueous-organic solvent should also increase the solubility of the dye and suppress its tendency to aggregate. Data for a thin-layer sandwich cell with one platinum electrode and one NESA (SnO,) transparent electrode are given in Table 2. This cell works 25v

23 24 25 26

27

M. D. Archer, J. Appl. Electrochem., 1975, 5, 17. R. Gomer, Electrochim. Actn, 1975, 20, 13. M. Z. Hoffman, ref. 3, pp. 86-95. M. D. Archer, ref. 3, pp. 110-120. W. D. K. Clark and J. A. Eckert, ref. 3, pp. 121-130.

568

Photochemistry

despite the electrodes being uniformly illuminated, a finding which indicates that the electrode kinetics of one or possibly both redox couples must be different at these two electrodes. The very low value of the sunlight engineering efficiency in Table 2 arises mainly because only ca. 0.1% of the incident light is absorbed by the cell. Table 2 Iron-thionine thin-layer cell performance characteristics

27

lo-, M Fez+, ca. M thionine pH 1-3, aqueous solution Cell illuminated through SnO, electrode

Cell composition: Pt sputtered on glass

- Voltage at maximum power

Voltage efficiency

absorbed light energy

= 0.024

Monochromatic electrons flowing at maximum power point quantum efficiency = = 0.62 absorbed photon flux at 578 nm, 185 W m-, Monochromatic power efficiency at 578 nm

- i V at maximum power point absorbed light power

Sunlight engineering efficiency

- maximum power in sunlight incident sunlight power

= 0.015 = 10-5

A concentration cell has been described which is based upon the ionic photodissociation of the leucocyanides of the triphenylmethane dyes crystal violet or malachite green in acetonitrile or alcohol, as in reaction (4).,* This reaction is Ar3CCN

A<340 n m

Ar3C+

+ CN-

(4)

slowly reversed in the dark. Two Ag,AgCN electrodes, which are reversible to CN-, are employed in a cell of which one half is illuminated and the other dark. The exposed half cell should therefore develop a negative potential, E, with respect to the dark one, in accordance with equation (5) (which is wrongly

M quoted in ref. 28). The maximum value of I E I observed was 340 mV for crystal violet leucocyanide in alcohol, but the photopotentials were generally slow, biphasic, and irreversible, and this is ascribed to the slow removal of CNfrom solution by complexation with AgCN. An Ag,Ag(CN),- electrode gave more stable results. It should be mentioned that a series of papers2s on photogalvanic cells in which alkaline solutions of various phenazine and thiazine dyes are photochemically reduced, with the concomitant oxidation of an amine, were overlooked in last year’s report. As amine is steadily consumed, and apparently 28

2s

Yu. S. Lebedev and G. A. Korsunovskii, Rum. J. Phys. Chem., 1975,49, 527. N. Kamiya and M. Okawara, Denki Kagaku, 1968, 36, 506; 1970, 38, 273; Kogyo Kagaku Zasshi, 1969, 72, 96 and 2639; J . Electrochem. Soc. Japan (overseas edn.), 1969, 37, 81.

569

Photochemical Aspects of Solar Energy Conversion

not regenerated, by the operation of these cells, they do not appear to meet the requirement that a photogalvanic cell should operate in an overall cyclic fashion. Semiconductor-Electrolyte Systems.-Titanium Dioxide. Interest continues in the cell devised by Fujishima and Honda30 for the electrochemical photolysis of water : n-TiO, I aqueous solution 1

I I aqueous solution 2 I Pt

In this cell, irradiation of the semiconducting TiO, with light of wavelength (413 nm results in the anodic evolution of oxygen at this electrode, coupled V

YS

SCE

Pt Figure 2 Relations between the equilibrium redox levels and the energy levels of the electrodes in the cell: single crystal n-TiO, I OSM-K,SO,, 0.05M-MeCO,H, 0.05MMeC0,Na I Pt. Solid lines are for a dark, equilibrium state, and dashed lines are for a steady state under illumination. EF = Fermi level, Ev and Ec = energy of valence and conduction band edges (Reproduced by permission from Ber. Bunsengesellschaftphys. Chem., 1975, 79,523)

with the cathodic production of hydrogen at the platinum electrode, provided there are no species more readily reducible than H+ present in Solution 2, from which dissolved oxygen must therefore be removed. The relative positions of the relevant electronic levels, calculated from various sources,31are shown in Figure 2 for a cell containing pH 4.7 electrolyte throughout. The Fermi level of the TiO, electrode in the dark is at 0.17V us. SCE and a depletion layer is formed under the TiO, surface in the dark, short-circuited cell. On illumination of the surface of the TiO, electrode, hole-electron pairs are formed. Some of the holes migrate to the surface, where water is oxidized to molecular oxygen, in an overall fourquantum process. The space charge layer of the TiO, electrode causes electrons to migrate to the interior of the semiconductor, before they all recombine with holes. The Fermi levels of both electrodes are thereby shifted upwards in Figure 2. I1

A. Fujishima and K. Honda, Narure, 1972, 238, 37. T. Ohnishi, Y. Nakato, and H. Tsubomura, Ber. Bunsengesellschaftphys.Chem., 1975,79,523.

570

Photochemistry

If EF,TiO, reaches the height of the equilibrium potential of H+-H2 then hydrogen is evolved at the Pt electrode. However, irradiation cannot cause EF,TiO, to rise above the flat-band potential, which is at -0.5 V us. SCE at pH = 4.7.31(This value is in reasonable agreement with the value of -0.55 V us. SCE interpolated from Honda's data.32) When this potential is reached, the equilibrium potential of the H+-H2 couple is only just reached and there is no space charge layer remaining to separate the hole-electron pairs. Consequently, the efficiencies shown in Table 3 are very low. The energy conversion efficiency, 7, in Table 3,

Table 3 Quantum yields and eficiencies of energy conversion for the cell: n-Ti02 I aqueous electrolyte (pH = 4.7)I Pt 31 Incident light energy O/W m-2 0.00 1.05

10.4 32.0

Short-circuit Potential of Ti02 (us. SCE) current/104A m-2 0.166 1.1 - 0.265 18.9 - 0.341 20.4 - 0.372 30.4

+

771

-

6.11 x 10-3 6.70 x 10-4 3.23 x 10-4

772

-

2.68 x 10-3 2.91 x 10-4 1.41 x 10-4

The wavelength of the light is 365 nm. vl is the number of electrons flowing into the TiOs electrode per incident photon. T~ is the efficiency of energy conversion defined by equation (6).

is defined by equation (6), where i is the photocurrent, R the circuit resistance, QH,the heat of combustion of hydrogen, and Wph the irradiance.

Hydrogen can be produced more efficiently if a small electrochemical bias is applied to the cell, in such a way as to make the TiO, electrode positive with respect to the Pt electrode. This leads to an enhancement of the efficiency with which the space charge layer separates hole-electron pairs, or put another way, it moves the potential of the galvanic Ti02 electrode from near the foot of the anodic photocurrent wave to a point nearer the plateau region. The required electrochemical bias can be applied either by using strong alkali as Solution 1 and strong acid as Solution 2, or by use of a polarizing circuit. Honda and co-workers 34 have used the first method. Figure 3 shows the relation between their cell voltage and current for various Solutions 1 and 2, and the power output from the optimal cell. The difference in pH between Solutions 1 and 2 is about 13 units, leading to an electrochemical bias of ca. 0.77 V. Under such a bias, the current efficiency is of course higher, but this mode of operation involves consumption of alkali at the TiOz electrode and acid at the Pt electrode. Wrighton et al.36 also worked with single-crystal Ti02, irradiated by the 351 and 364 nm emission of an argon ion laser (1.3 x lo-' E s-l). By mass spectrometric methods and by the use of very small TiO, crystals, they established that oxygen is evolved entirely from the aqueous phase, and does not come from the decomposition of the TiO, itself. Using a two-compartment chemically biased 339

sa T. Watanabe, A. Fujishima, and K. ss K. Honda, ref. 3, pp. 105-109. s4

s6

Honda, Chem. Letters, 1974, 8 , 897.

A. Fujishima, K. Kohayakawa, and K. Honda, BUN. Chem. SOC.Japan, 1975,48, 1041. M. S. Wrighton, D. S. Grinley, P. T. Wolczanski, A. B. Ellis, D. L. Morse, and A. Linz, Proc. Nat. Acad. Sci. U.S.A., 1975, 72, 4.

Photochemical Aspects of Solar Energy Conversion 571 cell, they obtained the yields of hydrogen and oxygen shown in Table 4. The data show that these gases are evolved in the expected 2 : 1 ratio although the current efficiency is variable. Using a one-compartment electrically biased cell (Solution 1 = Solution 2) and four different single-crystal TiO, electrodes, they

Cu r rent /A m-*

B

C u rr Q n t /A

Figure 3 Cell characteristics for the cell: single crystal n-TiO, I solution 1 11 solution 2 I Pt black. Incident white light ca. 2 x lo1' quanta s-l. (above) Cell voltage vs. current density Solution 1 Solution 2 1. 1M-NaOH 1M-NaOH 2. 1M-NaOH 1M-Na,SO, 3. 1M-NaOH 0.005M-Hp304 4. 1M-NaOH 0.05 M-HZSO4 5. 1M-NaOH 0.5M-HZS04 (below) Power vs. current density Solution 1 = 1M-NaOH, Solution 2 = OSM-H,SO, (Reproduced by permission from Bull. Chem. SOC.Japan, 1975, 48, 1041)

Table 4 Photoassisted electrolysis of HzO in a two-compartment cell 3B Irradiation pmol pmol pmol Solution 1 Solution 2 timelmin of H, of 0, of electrons $I 1M-NaOH O.SM-H,SOd 426 160 80 410 0.04, 1M-NaClO, 1M-NaClO, 0.1 M-NaOH 0.05M-H,S04 572 150 76 420 0.031 1M-NaOH 0.5M-HZS04 1280 480 240 840 0.04, 4 is defined as the number of moles of HI produced per mole of photons striking the electrode.

+

+

Photochemistry

572

Table 5 Photoassisted electrolysis of H,O in a one-compartment cell 35 Electrolyte 1.OM-NaOH 1 .OM-NaClO, 1.OM-NaClO, O.1M-NaOH O.1M-NaOH O.1M-NaOH 4M-NaC10,c O.SM-H,SO, O.SM-H,SOI 0.05M-HzS04 O.1M-NaOH 1.OM-NaOH 1 .OM-NaOH 1.OM-NaClO, 2.0M-NaOH 2.0M-NaOH f

+

Applied uoltagelV 2.0 2.0 2.0 2.0 2.0

Current ejiciency a 2.2 2.6 2.1 1.9 2.6

2.0 2.0 2.0 2.0 0.5 0.5 0.5 2.0 0.25 2.0

1.9 2.2 2.4 2.2 3.1 2.8 1.9 2.0 2.1 1.9

4b 0.11 0.05, o.ogO 0.11 0.047

0.13 0.07,

0.01, 0.04, 0.01, 0.02, 0.02, 0.051

0.010 0.039

li Moles of electrons flowing per mole H, produced. r, Moles of H, produced per mole of photons striking the electrode. Electrode C. Electrode A. Electrode D. f Electrode E.

found ‘photoassisted electrolysis’ of water at applied potentials as low as 0.25 V, as shown in Table 5. These data seem slightly erratic, possibly because the optical properties of the electrodes differed. The energy storage efficiency of these electrically biased cells, defined as energy stored as Ha - energy in from power supply x 100 radiant energy stored was found to be 0.5-1% which, although small, is at least positive. Some H202 was detected after prolonged electrolysis, which is to be expected, as O H is a probable intermediate on the TiO, electrode. An n-TiO, single-crystal anode has been combined with a zinc-doped p-GaP cathode38 to make a photoelectrochemical cell in which both electrodes are light-sensitive. The potential of the GaP electrode is shifted anodically by illumination, in a manner typical of p-type semiconductors, and hydrogen evolution occurs at a higher positive potential than in the dark, owing to the reduction of H,O by photoexcited electrons in the GaP conduction band. The current-voltage curves for irradiated p-GaP and n-TiO, electrodes in acid and alkali are given in Figure 4. The saturation photocurrent region is not approached in any of these. The spectral response of the two electrodes is shown in Figure 5. The indirect band gap of GaP is at 2.38 eV (520 nm). The performance of this cell deteriorates with time, because GaP dissolves anodically, as do most small-band-gap semiconductors. The use of polycrystalline TiOz, produced either by chemical vapour ~ ~ in a somewhat deposition (CVD) 37 or by sheet titanium a n ~ d i z a t i o n38, ~results 37 38

H. Yoneyama, H. Sakamoto, and H. Tamura, Electrochim. Acru, 1975,20, 341. K. L. Hardee and A. J. Bard, J. Electrochem. Soc., 1975, 122, 739. J. Keeney, D. H. Weinstein, and G. M. Haas, Nature, 1975, 253, 719.

573

Photochemical Aspects of Solar Energy Conversion

smaller saturation photocurrent than for single-crystal rutile, though the pH and wavelength dependences of the photocurrent are the same. The reduced efficiency is probably because of the large number of charge-carrier traps in the polycrystalline electrode. Very thin TiO, films can be prepared by anodization, and 80

lot

/

c;vE

Vvs SCE

0.2

/

i

0.4

a

\

.Z

-40

p-

GaP

-80

-20-

Figure 4 Current-voltage curves for irradiated n-TiO, and p-GaP electrodes in (left ) 0.5M-H,S04, (right) 1M-NaOH. Negative currents are cathodic. Illumination (of unspecified intensity) by 500 W mercury lamp (Reproduced by permission from Electrochim. Acta, 1975, 20, 341)

I 350

1

400

1

I

450

I

500

I \

550 A /nm

Figure 5 Spectral responses of p-GaP electrode (- 1 .O V vs. SCE) and n-TiO, electrode (+ 1 .O V vs. SCE). The vertical lines mark the semiconductor band gaps (Reproduced by permission from Electrochim. Acta, 1975, 20, 34 1 )

these have a saturation photocurrent thirty to forty times smaller than that of a CVD film, probably because the semiconductor film is too thin to allow the full space charge layer to develop.37 The thickness of the anodically deposited film varies linearly with the anodic 39

L. Arsov, M. Froelicher, M. Froment, and A. Hugot-le-Goff, Compt. rend., 1974, 279, 485.

574

Photochemistry

Photoeffects at polycrystalline SnO, electrodes 40 are broadly similar to those at TiO,, though as the band gap of SnO, is 3.7eV, the threshold wavelength is too low to be of any use in connection with solar energy conversion. Other Semiconductors. G e r i ~ c h e r ,in ~ ~a very helpful paper on electrochemical photo and solar cells, has explained the mode of action of the semiconductorelectrolyte interface (when the semiconductor is in its depletion mode) as a Schottky barrier, and how this can lead to separation of hole-electron pairs

16*

10-l

I

lrradiance / Wm-* Figure 6 Variation with light intensity of (left) short-circuit photocurrent in the cell

Semiconductor

0.5-1 mm layer 0.2M-&Fe(CN)6, 0.OlM-K,Fe(CN),, OSM-KCI, pH = 11

The white light used has spectral distribution resembling that of sunlight (Reproduced by permission from J. Electroanalyt. Chem. Interfacial Electrochem., 1975, 58, 263)

produced by irradiation of the semiconductor. The behaviour of photoelectrochemical cells of the type semiconductor

I

electrolyte containing electrode reversible redox couple A-B to redox couple A-B

is discussed, and the energy losses in the circular path of the electrons are enumerated. Some preliminary results obtained with thin-layer sandwich cells CdS(CdSe,GaP) I Fe(CN),S-, Fe(CN),'-

I SnOB

are shown in Figure 6. The SnO, electrode is so highly doped that it is quasimetallic and is reversible to ferrocyanideferricyanide. The results show the 40 41

H. Kim and H. A. Laitinen, J. Electrochem. SOC.,1975,122, 53. H. Gerischer, J. Electroanalyt. Chem. Interfacial Electrochem., 1975, 58, 263.

Photochemical Aspects of Solar Energy Conversion

575

usual characteristics of diode photocells : the short-circuit current is approximately proportional to the light intensity, while the open-circuit photovoltage increases logarithmically with the light intensity and shows an approach to saturation at the highest intensities which were used. The abnormal intensity I. 25

I .oc

0.7:

U

E

.-

%

0.5c

0.25

\ \

In dar,,

0

I

l o 0

-

400

200

VImV Figure 7 Current vs. cell voltage for the cell Si [ 0.025M-Na2HP0, I Pt. The Si electrode is irradiated with 2.4 mW white light from a tungsten lamp. Cell area = 0.5 cm2 (Reproduced by permission from Appl. Phys. Letters, 1974, 25, 399)

dependence for GaP is ascribed to some corrosion reaction of the semiconductor. This is, as Gerischer points out, a general and most critical obstacle to the application of semiconductors in electrochemical cells for light-energy conversion. The CdS cell also showed evidence of corrosion: the photocurrent decayed continuously with time, because of the deposition of sulphur on the surface (reaction 7). This competes with the desired process at this electrode CdS

+ 2hf

Fe(CN)64-

+ h+

-

Cd2+(insolution) Fe(CNIes-

+S

(h = hole)

(7) (8)

576

Photochemistry

(reaction 8). The suppression of such corrosion processes is essential for the future development of these cells. Anodic photocurrents characteristic of n-type semiconductors have been observed for CdSe in the presence of f e r r ~ c y a n i d e ,and ~ ~ for CdS sensitized by rhodamine B or quinocyanine, in the presence of hydroquinone as a supersensit i ~ e r . ~ ~ Jayadevaiah 44 has also discussed the use of semiconductor-electrolyte interfaces for solar energy conversion, and Figure 7 gives the cell characteristic for his cell, which contains a silicon electrode. It is clear from the form of this that the internal resistance of the cell is rather high. The power conversion efficiency at the maximum power point is 2.7%. The stability of the Si is not discussed, but is almost certainly poor. 4 Photochemistry in Micellar Systems There may be quite a sizeable gradient of electric potential across the interface of an aqueous electrolyte solution and an organic liquid. Photoinduced charge transfer across such an interface is basically a photoelectrochemical effect, although no electrodes or continuous current flow are involved. In a recent series of elegant e ~ p e r i m e n f s , ~ Henglein, ~-~* Gratzel, and co-workers have investigated photoelectrochemical effects across the aqueous-lipoid interfaces of positively and negatively charged micelles. Electron transfer from the first excited singlet state of a phenothiazine molecule, solubilized in a negatively charged micelle, to water (forming an aquated electron) has been Ionization was also achieved in cationic micelles in the presence of the electron scavenger naphthoquinone sulphonate at the periphery of the micelles. The reverse process, transfer of an electron from the aqueous phase to an acceptor (9-nitroanthracene or pyrene) in the interior of the micelle, has also been The rate of reaction with acceptors in cationic micelles was considerably faster than with those in anionic micelles. These reactions are regarded as electron tunnelling processes, and the results are interpreted in terms of the estimated distributions of occupied and unoccupied electronic levels in the redox systems aq-e,, D-D+, and A-A- involved. If the overlap of the occupied levels of the donor with the unoccupied levels of the acceptor is not good, transfer is slow, irrespective of how thermodynamically favourable it may be. These levels are shifted, relative to one another, by the charge on the micellar head-group, which determines the direction of the electrical double layer at the interface. Reaction rates are therefore influenced both by the charge on the micelle and the concentration of electrolyte in the aqueous 48 The lifetime of normally unstable intermediates may be enormously enhanced by working in a micellar 4a 43

p6 45 48 47

** 49

R. A. L. Vanden Berghe, W. P. Gomes, and F. Carden, Z. phys. Chem., 1974,92,91. A Fujishima, T. Watanabe, 0.Tatsuoki, and K. Honda, Chem. Letters, 1975, 13. T. S . Jayadevaiah, Appl. Phys. Letters, 1974, 25, 399. S. A. Alkaitis, M. GrMzel, and A. Henglein, Ber. Bunsengesellschaftphys. Chem., 1975,79,541. M. Gratzel, A. Henglein, and E. Janata, Ber. Bunsengesellschaft phys. Chem., 1975, 79, 415. M. Gratzel, J. K. Thomas, and L. K. Patterson, Chem. Phys. Letters, 1974, 29, 393. M. Gratzel, J. J. Kozak, and J. K. Thomas, J. Chem. Phys., 1975, 62, 1632. K. Kano and T. Matsuo, Bull. Chem. SOC.Japan, 1974,47,2836.

Photochemical Aspects of Solar Energy Conversion

577

The possibility of effecting the decomposition of water in a heterogeneous micellar system by a suitable series of electron transfers offers certain advantages compared with homogeneous systems.4s Not only may the rate of geminate recombination of the products of electron transfer be lowered by the double layer, but organic sensitizers which are water insoluble, but lipid soluble, can be used. Moreover, the photon energy required to initiate the tunnelling process from the donor to the acceptor is much lower than that required for photoionization. It might not be necessary or desirable to keep the sensitizer concentration down to one molecule per micelle, and much higher concentrations are possible. Chlorophyll a in Triton X-100micelles, for example, can reach the in vivo concentration of 0.1 moll-l. Energy transfer in this system has been studied by fluorescencedepolarization, and found to follow the Forster mechanism with a calculated Ro = 5.6 nm.60 5 Photosynthesis A great deal of research continues into the elucidation of the structure and function of photosynthetic membranes, the better understanding of which might possibly lead to more efficient man-made photochemical systems for harnessing solar energy. Only some of the most recent work will be outlined here, as several reviews have appeared during the year. A recent book61 on the bioenergetics of photosynthesis provides an extremely valuable compilation of authoritative contributions. Bacterial photosynthesis 62 and primary processes in bacterial photosynthesis 63 have been comprehensively reviewed, and a concise summary of work published July 1973-June 1974 on photosynthetic reaction centres and primary photochemical processes is also Photosynthetic membranes consist mainly of lipids, pigments (chiefly chlorophylls), and proteins, some of which (the intrinsic proteins) are embedded in the membrane, possibly spanning it, and others of which (the extrinsic proteins) are adsorbed on the surface. Most of the chlorophylls and other pigments in the membranes are not involved in any photochemistry, but act as light-harvesting antennae which transfer absorbed energy to a special part of the photosynthetic unit called the reaction centre, at which electron transfer then occurs. Each photosynthetic unit in green plants contains about 300 chlorophyll molecules : smaller units are involved in bacterial photosynthesis, each containing about 50 bacteriochlorophyll molecules. The oxidized donor, D+, and the reduced acceptor, A-, formed by the primary electron-transfer reaction, are converted back into their original forms by a series of further electron transfers, which culminate in an oxidation reaction (the evolution of oxygen from water in the case of green plant photosynthesis) on the D+ side and the reduction of carbon dioxide to carbohydrate on the A- side. The location of the chlorophyll molecules in photosynthetic membranes is still something of an open question and is of prime importance in view of the 6o

61 6a

63 ti4

K. Csatorday, E. Lehoczki, and L. Szalay, Biochim. Biophys. Acta, 1975, 316, 268. ‘Bioenergetics of Photosynthesis’, ed. Govindjee, Academic Press, New York, 1975. W. W. Parson, Ann. Rev. Microbiol., 1974, 28, 41. W. W. Parson and R. J. Cogdell, Biochim. Biophys. Acta, 1975, 416, 105. B. Ke, Photochem. and Photobiol., 1974, 20, 542.

578

Photochemistry

role of chlorophyll in capturing and transferring light energy. Anderson 66 has postulated that the bulk of the antenna chlorophyll in chloroplasts is in the fixed, boundary lipids that form a monomolecular layer attached to the hydrophobic shells of the intrinsic proteins: the suggested arrangement is shown in Figure 8. The necessary aggregations of the chlorin rings, indicated by spectral data and required for maximum energy migration, would be possible in this model. The orientation of the chlorin rings, almost buried in the folds of the protein, is more securely locked in position than if the chlorophyll were in the rather fluid bulk lipid domain of the membrane.

Figure 8 Schematic cross-section of a chloroplast membrane showing an intrinsic protein spanning the membrane, with hydrophilic regions located at the membrane surfaces and a hydrophobic portion (shaded) embedded within the non-polar interior of the lipid bilayer. Anderson 56 postulates that the chlorophyll molecules (represented above with the hydrophobic portion of the chlorin ring shaded) are located as part of the boundary lipid of a chlorophyll-protein complex (Reproduced by permission from Nature, 1975,253, 536)

One of the intriguing aspects of the primary processes of photosynthesis is the high efficiency with which energy migrates from the light-harvesting antennae of pigment molecules to the trap, for this process has not as yet been achieved at anything like the same efficiency in uitro. KnoxS6 has considered excitation energy transfer and migration in photosynthetic systems and has drawn attention to the large spread (of a factor of over 100) in the estimated rates of pairwise excitation transfer between chlorophyll a molecules :considerable further analysis of the experimental data will be necessary, as the pairwise transfer rate is required to construct any model of more extensive energy migration. The estimated fluorescence lifetime of chlorophyll in v i m , and its variation with the redox 55 56

J. M. Anderson, Nature, 1975, 253, 536. R. S . Knox, ref. 51, pp. 183-221.

Photochemical Aspects of Solar Energy Conversion

579 state of the reaction centre, has also been a matter of some controversy: picosecond techniques now enable direct measurements to be made, and the first report, on the fluorescent kinetics of chlorophyll a in photosystem I and I1 enriched fractions of spinach, has a~peared.~' Another component of the photosynthetic membrane, whose structure is doubtless the key to its successful function, is the reaction centre; electronic excitation migrating from the antenna is trapped here, and an electron transfer from a donor, D, to an acceptor, A, ensues. Knowledge of the primary photochemistry of reaction centres, particularly in bacterial photosynthesis, is advancing rapidly, owing to the development of techniques for isolating them from the rest of the membrane of purple bacteria by use of detergent^,^^ and to the application of picosecond techniques to the study of their p h o t o p r o ~ e s s e s . ~ ~ - ~ ~ Each reaction centre in purple bacteria contains three different polypeptides, four bacteriochlorophyll molecules, two bacteriopheophytins, one ubiquinone, and one non-haem iron. Two of the BChl molecules are strongly exciton-coupled to form a dimer usually known as P870, whose photoinduced one-electron oxidation (which shows a maximal absorbance change at ca. 870 nm) is well established to occur in the primary photochemical process. In chloroplasts two similar dimers of chlorophyll a, P700 and P680, are known to act analogously. The nature of the primary electron acceptor, A, both in bacterial and green plant reaction centres, has been less clear, and a variety of candidates have been proposed over the past 15 years. Much recent e.s.r. evidence has indicated that A, in bacterial photosynthesis, is a 1 : 1 complex of ubiquinone and the non-haem iron molecule, (Fe-UQ). However, recent picosecond and nanosecond spectroscopic work 68-80 on the reaction centres of the purple bacterium Rhodopseudomonasspheroides has shown that a transient state, PF, which is not simply the excited singlet of P870, forms even at redox potentials at which (Fe-UQ) is chemically reduced, and so cannot act as an electron acceptor. The changes of absorbance in the region 3 0 0 900nm accompanying the formation of state PF have been measured in some detai168-60but firm conclusions as to the nature of PF have not been reached: it seems, however, very probable that state PF is the true primary product of electron transfer. 6 Photovoltaic Cells

The following section is not intended to be a comprehensive review, and only work with a chemical bias is included. Silicon cells therefore receive scant attention, as they are already well-developed devices. Inorganic Semiconductors.-Silicon cells are usually fabricated by doping and controlled diffusion to produce a p-n junction 1-2 pm below the surface of a disc or plate of single crystal which is cut as thinly as possible, 200-300 pm 67

W. Yu, P. P. Ho, R. R. Alfano, and M. Seibert, Biochim. Biophys. Acta, 1975, 387, 159. M. G. Rockley, M. W. Windsor, R. J. Cogdell, and W. W. Parson, Proc. Nut. Acad. Sci. U.S.A., 1975, 72, 2251. W. W. Parson, R. K. Clayton, and R. J. Cogdell, Biochim. Biophys. Acta, 1975,387,268. K. J. Kaufmann, P. L. Dutton, T. L. Netzel, J. S. Leigh, and P. M. Rentzepis, Science, 1975, 188, 1301.

580

Photochemistry

thick. A new design for silicon cells employing epitaxial deposition has been described,*l and preliminary experiments are reported which show the feasibility of making near-ideal abrupt junctions instead of the rather gradual junctions characteristic of diffused solar cells). A multiple-pass thin-film silicon cell has been suggested 6 2 v 63 as a means of reducing the thickness of silicon required. The design, which might be applicable to other types of cell, is shown in Figure 9. The angles at the base of the substrate are chosen to give total internal reflection for near-vertical incidence. The substrate therefore traps incident light and allows the use of a thinner layer of semiconductor than can be employed in a single-pass cell. In the case of silicon, ca. 2 pm would suffice, because it is an intensely absorbing material ( a > lO*cm-l for X < 500nm). Such a thin film of a less intense absorber would not absorb incident light efficiently unless the number of passes were rather large. The use of a thin film has the further advantage that the quality

Figure 9 Multigle-pass thin-filmsilicon solar cell (Reproduced by permission from Appl. Phys. Letters, 1975, 25, 647)

of the semiconductor can be poorer because the carrier diffusion length is required to be only ca. 2 pm instead of ca. 250 pm. Higher doping levels and polycrystalline material might therefore be usable. However, demands are made on the back and front surface charge-carrier recombination velocitie~.~~ There have been a few reports of II-VI and III-V heterojunction devices which have approached or even surpassed the performance of silicon cells. p-InP/n-CdS cells with a solar conversion efficiency of 12.5% have been f a b r i ~ a t e d .This ~ ~ good efficiency arises firstly because of the nature of InP: the band gap is at 1.34eV, which is optimal for the solar spectrum, and the transition is direct, so the absorption edge is steep. Secondly, there is an excellent crystal lattice match between InP and CdS, which means that almost fault-free junctions can be grown. p-CuInSe,/n-CdS cells which display current efficiencies (defined as electrons flowing in the short-circuit current per photon absorbed) of up to 70% between 550 and 1250nm, and solar conversion efficiencies of ca. 5% have been made.65 p-CdTeln-CdS cells of rather similar performance (current efficiency 85%, solar conversion efficiency 4.0%) have been produced without detailed attention to optimization of cell design, and it has been calculated that p-CdTe/n-Zn,Cd,-,S cells should be capable of a 82 83 64

e6

V. L. Dalal, H. Kressel, and P. H. Robinson, J . Appl. Phys., 1975, 46, 1283. D. Redfield, Appl. Phys. Letters, 1975, 25, 647. J. S. Escher and D. Redfield, Appl. Phys. Letters, 1974,25, 702. S. Wagner, J. L. Shay, K. J. Bachmann, and E. Buehler, Appl. Phys. Letters, 1975, 26, 229. S. Wagner, J. L. Shay, and P. Migliorato, Appl. Phys. Letters, 1974, 25, 434.

Photochemical Aspects of Solar Energy Conversion 58 1 conversion efficiency of 23%.ss An analysis of the performance limits of p-Al,Ga,-&/n-GaAs cells has been carried out :67 these cells show the expected increase in cell voltage and output current when operated at very high flux densities ( x 1000 suns).68 Large photovoltaic effects have been observed in the ceramic materials BaTiO, 5 wt% CaTiO,; Pb(Zro.53Tio.47)03 + 1 wt% Nb; and Pb0.93La0.07(Zr0.65Ti0.35)03.69 These large photovoltages (up to 1500 V cm-l) result from the addition of small photovoltages across individual grains of the ferroelectric crystals. The short-circuit photocurrents are, however, small : < 0.02%of incident band gap light is converted into electric energy, owing at least in part to the high internal resistance. Schottky Barrier Solar Cells.-Certain types of metal-semiconductor junction are blocking, i.e. they show rectifying, non-ohmic properties (in the dark). On irradiation, such a junction acts to separate hole-electron pairs and can therefore be made the basis of a photovoltaic device. Unlike p-n junction cells, Schottky barrier photovoltaic cells are majority carrier devices and are therefore relatively less susceptible to impurities. Figure 10 shows that a Schottky barrier is generally formed between p-type semiconductors and metals of fairly low work function, and between n-type semiconductors and metals of fairly high work function. Superficial oxide layers can, of course, greatly affect the work function of a metal, so these ‘rules’ must be cautiously applied. A Schottky barrier solar cell (SBSC) consists of a thin layer of semiconductor sandwiched between two metals, with an ohmic contact on one side, generally deposited as a finger grid so that the semiconductor can be irradiated through it, and a Schottky barrier contact on the other side. Two papers on the theory of SBSCs have appeared. The magnitude of the voltage attainable across metal-semiconductor interfaces in thermodynamic disequilibrium has been formulated in terms of electrochemical affinities, using the method of irreversible thermodynamic^.^^ The role of the interfacial layer, which may act to increase the open-circuit voltage and the fill factor, has also been

+

The fabrication of the first efficient ‘large area’ (ca. 1 cm2) SBSC has been 73 It consists of a Schottky barrier of 5 nm Cr overlaid with 5-7 nm Cu on 2 Ll cm p-type silicon, with a top (ohmic) contact of A1 fingers covered with 69 nm of antireflective silicon oxide coating. The sunlight conversion efficiency of the cell is 9.5%. SBSCs containing organic semiconductors are extremely inefficient, mainly because of high resistivity and low charge-carrier mobility. Fang 74 has analysed 66

67

68

6B 70

7s 74

A. L. Fahrenbuch, V. Vasilchenko, F. Buch, K. Mitchell, and R. H. Bube, Appl. Phys. Letters, 1974, 25, 605. V. M. Andreev, M. B. Kagan, T. L. Lyubashevskaya, T. A. Nuller, and D. N. Tret’yakov, Sou. Phys. Semicond., 1975, 8, 860. R. Davis and J. R. Knight, Solar Energy, 1975, 17, 145. P. S. Brody, J. Solid State Chem., 1975, 12, 193. P. Viktorovitch and G. Kamarinos, J. Chem. Phys., 1975, 62, 1532. S. J. Fonash, J . Appl. Phys., 1975, 46, 1286. W. A. Anderson, A. E. Delahay, and R. A. Milano, J. Appl. Phys., 1974,45, 3913. W. A. Anderson and R. A. Milano, Proc. I.E.E.E., 1975, 63, 206. P. H. Fang, J. Appl. Phys., 1974,454672

582

Photochemistry

the loss processes in organic semiconductor solar cells, and points out that the low efficiency of cells MI I organic SC 1 M, may additionally be due to Schottky barriers of opposing polarity at the two electrodes: an improvement in efficiency LOW WORK FUNCTION METAL

Before contact

After c o n t a c t

Electron energy

Evac-- - -

1

[V

n-type S C

metal

p-type S C Ohmic contact

Blocking contact f o r holes i n valence band

HIGH WORK FUNCTION METAL

n-type

After contact

Before contact

Electron

sc

metal

p-type SC

t Blocking contact f o r electrons in conduction band

t Ohmic contact

Figure 10 Schematic diagram showing the formation of ohmic and blocking junctions between metals and semiconductors. +ny +myc $ ~ = work functions of n-type semiconductor, metal and p-type semiconductor, respectively. Eva,, = vacuum level, Ec = conduction band edge, E, = valence band edge, Ep = Fermi level

of some two orders of magnitude could be expected if the organic semiconductor had an ohmic contact on one surface. Reucroft et al.76 have evaluated the efficiency of SBSCs containing poly-N-vinylcarbazole(PVK) and the 1 : lcomplex 'r,

P. J. Reucroft, K. Takahashi, and H. Ullal, Appl. Phys. Letters, 1975, 25, 664.

Photochemical Aspects of Solar Energy Conversion

583

between PVK and 2,4,7-trinitro-9-fluorenene(TNF), for a likely range of carrier photogeneration efficiencies and Schottky barrier heights. PVK absorbs strongly above 3.5 eV, PVK-TNF above 2.0 eV, and the latter could achieve a conversion efficiency of 1-2% with Schottky barriers in the range 1-3 eV. This calculation ignores losses due to carrier trapping and recombination, and is therefore highly idealized. Quite pronounced photovoltaic effects have been observed in M1 I 150 nm p-chlorophyll a I M2 sandwich cells, where M1 = A1 or Cr and Mz = Hg or A u . ~77~ ,These are ascribed to a Schottky barrier at the junction with metal M1 which has a lower work function than M2. If the M1 junction is the front (illuminated) electrode then the photovoltaic action spectrum is identical with the absorption spectrum of the chlorophyll. If it is at the rear, the action spectrum shows an inner filter effect, because only light absorbed in the region of the barrier is effective. Figure 11 shows the performance of a typical cell, which has a power conversion efficiency of ca. at 745 nm. The best efficiency, 5 x was achieved by a Crlchlorophyll a1 Hg cell. Photovoltaic properties have also been reported in the cell A1 I Mg phthalocyanine I Ag, which has a Schottky barrier of height ca. 0.6 eV at the A1 junction.78 At 690 nm, the power conversion efficiency was ca. It has been shown that oxidized A1 contacts to Cu phthalocyanine are blocking.70 Organic Semiconductors.-The development of better quality organic semiconductors would be of interest in connection with a variety of applications, particularly in electrophotography. A fair number of papers have appeared, most of which deal with semiconductors of resistivity too high to have any possible application to solar cells. Work up to mid-1973 is reviewed in the proceedings of a joint U.S.-Japan conference on energy and charge transfer in organic semiconductors.8o Myl’nikov 81 has reviewed the mechanisms of photoconduction in organic polymers: in many cases, small r-conjugated segments of the polymer molecules are highly conducting, but are interspersed with disordered dielectric regions. The estimation of meaningful electronic parameters is therefore difficult. Very highly conducting charge-transfer compounds based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) continue to attract much attention. Some of the recent work has been summarized by Holmes-Siedle.82 The theory of wmolecular charge-transfer crystals, of which the TCNQ salts form the most important category, has been thoroughly reviewed.83 The study of monolayer assemblies containing periodically arranged dye molecules may assist in the understanding of photoconduction mechanisms in organic matrices, Cells containing several layers of arachidate and incorporating 76

77 la

81

83

C. W. Tang and A. C. Albrecht, J. Chem. Phys., 1975, 62, 2139. C. W. Tang and A. C. Albrecht, Nature, 1975, 254, 507. A. K. Ghosh, D. L. Morel, T. Feng, R. F. Shaw, and C. A. Rowe, J. Appl. Phys., 1974,45,230. C. Tantzscher and C. Hamann, Phys. Stat. Solidii (A), 1974, 26, 443. ‘Energy and Charge Transfer in Organic Semiconductors’, ed. K. Masuda and M. Silver, Plenum Press, New York, 1974. V. S. Myl’nikov, Russ. Chem. Rev., 1974, 43, 862. A. Holmes-Siedle, Nature, 1975, 255, 13. Z. G. Soos, Ann. Rev. Phys. Chem., 1974,25, 121.

584 Photochemistry one layer of the dye quinquethienyl, sandwiched between A1 and Hg electrodes, exhibit photoconduction, whose variation with monolayer organization may be used to probe the shape of the potential profile across the cell.84 High-field

Photovoltage /mv

' 0 1 -

Light Intensity (arbitary units)

Figure 11 Performance of an A1 I chlorophyll a I Hg photovoltaic cell (Anegative). Cell area 0.25 cm2. (above) Photocurrent-voltage curve for incident light power 6 x W at 745 nm. (below) Light intensity dependence of open-circuit voltage and short-circuit current (Reproduced by permission from J. Chem. Phys., 1975, 62, 2143)

photoconduction in multilayered merocyanine dyelarachidate organizates has been shown85 to occur by two mechanisms, (i) quantum mechanical electron hopping, and (ii) thermionic emission of electrons from the chromophores into the conduction band. 84

86

U. Schoeler, K. H. Tews, and H. Kuhn, J. Chem. Phys., 1974, 61, 5009. M. Sugi, K. Nembach, and D. Mobius, Thin Solid Films, 1975, 27, 205.

Erratum

Volume 5, 1974 Pages 47,48 These pages are concerned with the discussion of dual fluorescence in p-(NN-dimethylamino)benzonitrile and NN-dimethyl-p-cyanoaniline. The text does not make clear that these are the same compound and the explanations offered by the two studies are in fact in conflict. Readers therefore are requested to consult the original references for a fuller discussion of the fluorescence of this compound. K. Rotkiewicz, K. H. Grellmann, and Z . R. Grabowski, Chem. Phys. Letters, 1973, 19, 315. 0. S . Khalil, R. H. Hofeldt, and S. P. McGlynn, Chem. Phys. Letters, 1972, 17, 479.

Author Index

Aaron J, J, 33, 84 Abe, S., 417, 516 Abe, T., 407, 536 Abegaz, B., 286 Abkin, A. D., 516, 517 Abrahamson, E. W., 141 Abramov, A. P., 173 Abramovitch, R. A., 480 Abronin, I. A., 12 Abu-Elgheit, M., 31 Abuin, E. B., 116, 379 Ache, H. J., 49 Acheson, R. M., 423 Acker, R.-D., 299 Ackerman, L., 530, 531 Ackerman, M., 134 Acosta, J. L., 527 Acquardo, M. A., 239 Adam, S., 215 Adam, W., 142, 345 Adams, A., 126 Adams, C. D., 426 Adams, D. M., 28 Adamson, A. W., 165 Adcock, S., 283 Addington, J. W., 160, 504 Addison, A. W., 168 Adeleke, B. B., 37,86,396,499 Adelman, A. H., 91, 141, 408, 466

Admovics, J. A., 384 Adrian, F. J., 36, 37 Afanas’ev, I. B., 343 Afanas’ev, N. V., 125 Afrina, E. I., 181 Agai, B., 437 Agapiou, A., 178 Agar, J., 195, 281, 494 Agarwal, S. C., 345 Agarwal, S. R., 518 Agkpo, A., 136 Agnihotry, S. A., 22 Agosta, W. C., 220, 256 Ahmed, F., 9 Ahuja, R. C., 526 Aihara, J., 21, 55 Aikawa, M., 88 Ajello, J. M., 139 Akagi, H., 171 Akahori, Y., 8, 90 Akasaki, Y., 241 Akashah, T., 409 Akimoto, H., 141 Akins, D. L., 95 Akiyama, T., 90, 365, 501 Al-Ani, Kh., 105 Alary, J., 131 Albala, J., 504 Alber, H., 126 Albrecht, A. C., 12, 13, 15, 52, 199, 583

Albrecht, F., 422, 423 Albritton, D. L., 49, 139, 144 Al-Chalabi, A. O., 27, 28, 73, 74,76

Alchalel, A., 83 Alcock, W. G., 142 Aleev, R. S., 527 Aletsky, A. V., 23 Alewood, P. F., 489 Alexander, E. C., 80, 83, 225, 229,444

Alexander, J. J., 184 Alexandru, L., 534 Alfano, R. R., 66, 579 Alfimov, M. V., 96 Alford, J. A., 333 Aliev, R. E., 518 Aliwi, S. M., 154, 507 Alkaitis, S. A., 576 Allen, C. C., 516, 517 Allen, J. D., 149, 364, 450 Allen, N. S., 522, 533 Allen, R. W., 247 Allen, S. D., 16 Alley, E. G., 406 Allinger, N. L., 483 Allison, C. G., 355 Allmandoca, L. J., 35 Allred, E. L., 358 Almgren, M., 50 Almlof, J., 198 Aloisi, G. G., 15, 76 Alpert, B., 90 Alscher A 414 Al’shits: E.”I., 42 Alt, H., 175 Altenberger-Siczek, A., 46 Altschuller, A. P., 145 Alyea, F. N., 137 Amano, T., 33, 90 Amar, D., 132 Ambartzumian, R. V., 205 Amin, M. U., 528 Amit, B., 440 Amos, A. T., 7 Amouyal E., 294 Amrein, W., 81, 214 Amus’ya, M. Ya., 21 Anastassiou, A. G., 325, 427 Anda, K., 367 Anderson, A. B., 3 Anderson D. J., 267, 429 Anderson: J. B., 123 Anderson, J. G., 143 Anderson, J. M., 578 Anderson, J. R., 93 Anderson, N. M., 201 Anderson, R. C., 261 Anderson, R. W., jun., 26, 61, 83, 87, 117

Anderson, W. A., 581

586

Anderson, W. R., 47 Ando, E., 526 Ando, N., 512 Ando, W., 412 Andre, J.-C., 38, 68, 519 Andreev, 0. M., 96 Andreev, V. M., 581 Andreeva, N. E., 134 Andreeva, T. K., 172 Andress, B., 525 Andrews, G. H., 99 Andrews, L., 29, 38, 60,209 Andries, J., 532 Andruskiewicz, C. A., jun., 235

Anet, F. A. L., 240,453 Anex, B. G., 170 Angstrom, A., 149 Angus, H. J. F., 356 Anissimov, V. I., 522, 527 Anpo, M., 90 Antheunis, D. A., 34, 35 Antippa, A. F., 8 Antoci, A., 4 Antonini, E., 201 Anufrieva, E. V., 509 Anzai, S., 124, 420 Aoki, H., 532 Aoki, J., 32 Aoki, K., 95 Aoyagi, R.,537 Aoyagi, S., 383, 425 Aoyama, H., 230, 231, 443, 444

Appelman, E. H., 203 Applegate, H. G., 537 Apt, J., 17 Arai, H., 281, 419, 435, 454, 516

Arai, S., 27, 367, 516 Arakawa, E. T., 11, 15 Arakawa, S., 295, 299, 396 Araki, K., 527 Araki. Y..345 Arano, H;,15 Archer, A. J., 93, 535 Archer, M. D., 567 Archer. R. D.. 157 Arden,.W., 32, 73 Arens, J. F., 536 Argyros, J. D., 136 Aris, P., 73 Armor, J. N., 161 Armstrong, F. A. J., 537 Amaud-Neu, F., 157 Amett, J. F., 6,31,62,84,286, 454

Arnold, C. B., 124 Arnold, D. R., 15, 214, 238, 475

Arnold, S., 24, 78

Author Index Arnoldi, D., 124 Arnould, J. C., 224 Arsov, L., 573 Artamonova, N. N., 396 Arth, G. E., 281, 501 Arthur, J. C., jun., 301 Arthur, N. L., 49 Artman, J. O., 39 Artmonova, N. N., 299 Arutyunyan, A. V., 189 Arvis, M., 119 Arzhankov, S, I., 159, 165 Asada, S., 178 Asai, M.,191, 507, 510 Asai, T., 531 Asano. M.,536 Asanuha, T., 337, 338 Asao, T., 485 Ashford, R. D., 142,408 Ashley-Smith, J., 189 AshDole. C . W.. 26. 110 Ashraf, M.,31 ' Ashton, D. S., 124 Askani, R., 334,446 Asmaev, 0. T., 170 Atkins, P. W., 36, 86 Atkinson, G. H. A., 22, 120 Atkinson, J. B., 126 Atkinson, R., 139, 140 Atlani, P., 142 Atsumi, M., 520 Attig, T. G., 184 Atzman, R., 125 Au, A., 236,324, 325 Aubailly, M. 84 Aue, D. H., $18 Auerbach, R. A,, 32, 55 Aulich, H., 21 Ault, B. S., 38 Aumann, R., 186, 187 Ausloos, P., 98, 511 Austel, V., 351 Austin, R. H., 201 Avakian, P., 519 Avaste, 0. A., 134 Averbeck, H., 187 Avery, E. C., 37 Aver'yanov, S. V., 518 Avis, P., 32 Avouris, P. L., 31, 32, 73 Ayrey, G., 516 Ayscough, P. B., 395 Azatyan, V. V., 136 Azizov, U., 518 Azma, R., 25 Azuma, C., 510 Azumi, T., 31,44 Baba, H., 15, 26, 31, 78, 88 Babiak, K. A., 267, 268 Babkm, I. Yu., 517 Bachmann, H. R., 132,205 Bachmann, K. J., 580 Baer, T., 123 Bgssler, H., 56 Baetcke, K. P., 537 Bagdasaryan, R. V., 532 Bagdaxir'yan, K. S., 64 Baggiolini, E., 279, 415 B a p o , O., 93, 408 Bailey, P. S., 142 Bailey, R. J., 492 Baird, M. S., 480 Baud, N. C., 317

587 Basov, Yu. G., 132 Bass, D. M., 142 Bass, J. N., 140 Basselier, J.-J., 317 Bassindale, A. R., 206 Bassler, H., 32 Basu, S.,233, 393 Batovskii, 0. M., 124 Batra, S. K., 537 Bauche, J., 4 K., Bauer, S. H., 107, 205 134 Baulch, D., 143 Balasubramanian, R., 321,468 Baum, D., 529 Balchunis, R. J., 276, 448 Baumann, H., 533 Baldwin, B. A., 51 Baumgardner, R. E., jun., 13 1 Baldwin, J. E., 281 Baumgartel, H., 10 Balfour, W.J., 4 Baur, J. R., 537 Ballardini, R., 168 Bausal, R. K., 336 Ballschmiter, K., 199 Bazhin, N. M., 159 Balois, J. M., 210 Bazhulina, N. P., 438 Balzani, V., 153,154, 159, 160, Bazin, M., 84 168, 564 Bearden, A. J., 199 Bamford, C. H., 154, 178, 180, Beauchamp, J. L., 25, 101 5117 Beavan, S. W., 532 Ban, k., 455 Bebelaar, D., 27 Band, Y. B., 47, 118 Beck, B. A., 149 Beck, B. R., 358 Bandrauk, A. D., 40 Banerjee, A. N., 508 Beck, G., 53 1, 534 Baneriee. S.. 11 Becker, D., 481 Becker, F. J., 193 Becker, H.-D., 247 Becker, H. G. O., 492 Becker, J., 255 Becker, K. H., 28, 129, 131, Baity, F. W., jun., 131 Bakal, Y., 271, 433 Baker. C.. 181 Baker; D.' C., 161 Baker, H. J., 122 Baker, R. D., 537 Baker, R. S., 128 Baklanov, E. V., 17 Bakos, J., 21 Balakrishnan, P., 380 Balasubrahmanyan, U.

142, 144

Becker, R. S., 8, 317, 348, 536 Beckett, P., 43 Beckwith, A. L. J., 385 Beddard, G. S., 104, 200 Bederson, B., 8 Bedford, K. R., 361 Beenakker, C. I. M., 24, 25, 100

Bargon, J., 38, 395 Barkalov, I. M., 516, 517 Barkatt, A., 203 Barkova, L. A., 31, 120 Barlow M. G., 353 355 Barltro;, J. A,, 351,' 362 3arnett, B. L., 282

3artocci, C., 161, 169 3artocci, G., 73, 203 %arton,D. H. R., 324,397,501 %arton,J., 362, 378, 427, 509 %asak.A. K.. 123 $asinski,A., -536 %asolo,F., 164 #asov, L. L., 202 #asov,N. G., 28

Beeson, K., 201 Beevers, R. B., 536 Began, D. J., 141 Begley, W. J., 381, 503 Behjati, B., 378, 427 Behr, J.-P., 26 Behring, U. E., 134 Bekmukhametov, R. R., 476 Bell, A. P., 419 Bell, J. A., 93, 117, 415, 534 Bell, J. T., 172 Bell, S., 6, 10 Bell, T. N., 123 Bellamy, F., 435 Beloeil, J.-C., 415 Belokoneva, G. I., 529 Belomestnykh, V. I., 173 Beloshitskii, N. V., 159 Belostotskaya, I. S., 292 Belova, L. V., 361 Belozerskii, G. N., 159 Belyaev, E. Y., 192 Belyi, M. U., 206 Benarie, M., 148 Benattar, R., 21 Bendazzoli, G. I., 3 Bender, C. F., 3, 6 Bender, C. O., 313 Benezra, C., 472 Benn, M., 489 3ennett, M. A,, 189

Author Index

588 Bennett, R. A., 22, 204 Bennett, W. R., jun., 125 Bensasson, R., 294 Ben-Shaul, A., 48 Ben-Shoshan, R., 186 Benson, S. W., 146 Bent, D. V., 65, 89,402 Bercaw, J. E., 190 Bercovici, T., 96, 373 Berens, K. B., 31 Berg, J. O., 41 Bergbreiter, D. E., 191 Berger, J. G., 426 Berger, M., 117 Berger, R. A., 112 Bergman, A., 19 Bergman, R. G., 190 Bergmark, W., 259, 403 Berkosky, J. L., 21 Berkowitz, J., 21 Berman, M., 245, 495 Berrnan, P. R., 38 Bernal, I., 208 Bernard, F., 48 Bernardinelli, G., 260 Bernas, A., 33, 43, 202 Bernhara-Schegel, H., 48 Bernstein, R. B., 47, 48 Berridge, J., 107, 360, 361 Berrondo. M.. 406 Berry, H.-G., 4 Berry, M. J., 47, 118, 124 Bersohn, R., 47, 106 Bertrand, C., 99 Berti, C., 33 Bertinolli, F., 14 Bertran. J.. 49 Besmann, J., 518 Beugleman, R., 58, 269, 316, 300, 388,406,428,429

Bevan, M. J., 128 Bevan, W. I., 206 Beverley, G. D., 134 Bhakar, B. S., 24 Bhandari, K. S., 81, 290 Bhattacharjee, H. R., 78 Bhaumik, D., 8 Bhujle, V. V., 12 Bichan D., 239 Biefeld: C. G., 282 Bielski, A., 9 Biemont, E., 4 Bieri, G., 8 Bigwood, M., 69, 207, 317 Billmeyer, F. W., 536 Bills. D. D., 537 Bills; J. L., 4 Binkley, R. W., 367 Biraben, F., 17 Birch D. J. S., 31, 51, 59 Birchhl, J. M., 501 Bird, C. W., 417 Birely, J. H., 140 Birge, R. R., 8, 32, 55, 60 Birke, R. L., 95 Birks, J. B., 31, 32, 43, 51, 54 59

Bi&baum, D., 481 Birnberg, G. H., 446 Birtwell, R. J., 238 Biscar, J., 38 Bischof, P. K., 206 Bishop, R., 228 Bisle, H., 31, 64

Bito, T., 281 Black, G., 121, 145, 146 Black, J. D., 175, 184 Bladon, P., 472 Blais, J., 63, 64 Blanchi, J.-P., 83, 392, 3 Blank, B., 37, 214 Blint, R. J., 49 Bloemberger, N., 17 Blok, H., 36 Bloom. A.. 527 Bloom; S. b.,3 Bloor, J. E., 478 Blossey, E. C., 535 Bluhm, A. L., 192 Blum, J., 333 Blume, R., 14 Blyskosh, G. S., 517 Blyumenfel'd, A. B., 533 Boboev, T. B., 533 Bobrowicz, F. W., 5, 202 Bock, C. R., 159 Bock, H., 206 Bocquillon, P., 25 Boens, N., 249, 512 Boese, R., 193 Boesl, U., 108 Boettcher, H., 492 Bogan, D. J., 413 Bogan, G., 278 Bogdan, L. S., 515 Bogdanov, 0. I., 159 Bogdanov, V. L., 39 Bogdansky, S., 536 Bohandy, J., 197 Bojarski, C., 43 Bokanov, A. I., 208 Bokut, B. V., 16 Bolden, R. C., 139 Bolduc, P. R., 421 Boletta, F., 153, 160 Bolivar, R. A., 238 Bollinger, R., 367 Bollinger, W., 143 Bolman, P. S. H., 10 Bolotnikova, T., 42 Bol'shakova, N. I., 518 Bolton, J. R., 35, 36, 189, 190, 199, 202, 406, 465, 475

Bolton, P. H., 95, 204 Bomberg, A., 52 Bonaventura, C., 201 Bonaventura, J., 201 Bond, F. T., 246 Bondybey, V. E., 209 Bonham, R. A., 24 Bonifacio, R., 39 Bonneau, R., 93,170,203,537, 403

Bonnelle, J. P., 210 Bonnetain, L., 136 Bonnett, R., 419 Bontulus, P., 73 Boosma, F., 323 Booth. B. L.. 515 Bor, Z., 31 . Bordeaux-Pontier, M., 71 Borden, W. T., 8, 474 Borisevich, N. A., 31, 120 Borisov. A. Y.. 199 Borisova, M. E., 536 Borkman, R. F., 447 Borrell, P., 178, 181 Borse, D., 329

Bortolus, P., 203, 303 Bos, A,, 533 Bos, H. J. T., 286, 293, 465 Boschung, A. F., 410 Bose. A. K.. 297 Bott,- J. F., 124 Bottcher, A. E., 455 Bottcher, C., 48 Bottenheim, J. W., 147 Botter, B. J., 35 Bouanani, H., 6 Bouas-Laurent, H., 386 Boucekkine, A., 6 Bouchy, M., 38, 68 Boucique, R., 28, 125 Boue, S., 69, 317, 318, 207 Bourasseau, S., 210 Bourbon, P., 131 Bourret, R., 43 Boursey, E., 9 Boustead, I., 33 Bovey, R. W., 537 Bowden, M. J., 536 Bowers, M. T., 144 Bowman, A., 16 Bowman, R. M., 362 Bowyer, S., 134 Box, G. E. P., 149 Boxer. S. G.. 199 Boyd,-E. G.; 536 Boyer, J., 307, 313, 43 3 Boyer, R. F., 354 Boykm, D. W., 493 Boyson, R. A., 501 Brabham. D. E.. 95 Bradley, D.J., 125 Bradshaw, J. S., 239, 448 Braginskii, R. P., 518 Bramwell, F. B., 36 Brand, J. C., 6, 9, 10, 11, 50, 62, 425

Brandl, U., 380 Braterman, P. S., 175, 184 Bratolyubov, A. S., 124 Brauman, J. I., 22, 124, 132, 184

Braun. D.. 508 Braun; W , 131 Bray, J. C., 516 Bray, R, G., 17 Breaux, E. J., 213 Breck, A., 534 Breckenridge, W. H., 120, 128 Bree, A., 15, 31, 32, 61 Breet, E. L. J., 207 Breitenback, J. W., 510 Bremner, J. B., 332 Brennen. W.. 144 Breslow,' R., -233, 490 Brestkin, Yu. V., 520 Bretagne, J., 28 Breuer, H., 193 Brewer, D., 93, 119, 409 Brewer. R. G.. 40 Briand; C., 71Bridgeman, I., 537 Brillante, A., 32, 33, 56, 7'8 Brin. G. P.. 209 Brinkmann; U., 134 Brion, C. E., 25 Brith, M.,10, 16 Brittain, R. D., 28 Britzinger, H. H., 179 Broad, T. J., 21

Author Index Broadbent, A. D., 368, 397 Broadbent, T. W., 128 Brocklehurst, B., 31, 38, 53 Brodmann, R., 28 Brodsky, L., 323 Brody, P. S., 581 Broida, H. P., 9, 33, 111, 129

Brokken-Zijp, J., 471 Brom, J. M., jun., 9, 28, 129 Bromberg, A., 199 Brook, A., 206,215, 218, 469 Broom, A. D., 440 Brophy, J. H., 134, 142 Brovro, V. V., 381 Brown, A., 128 Brown, B., 529 Brown, G. B., 435 B rown, J. M., 10, 191 Brown, J. R., 534 Brown, K., 520 Brown, K. L., 190 Brown, R. D., 281, 501 Brown, R. G., 104, 105, 117 Brown, R. T., 38 Brown, T. L., 179 Browne, J. C., 4, 49, 519 Brubaker, C. H., 174 Bruce, J. M., 292, 396 B,rugnaro, S., 516 Bruins, C. H. P., 535 B ruk, M. A., 516 Brunetti, B., 33, 140 Bruni, M. C., 58, 149, 302 Brunner, H., 184 Brunori, M., 201 Brupbaacher, J. M., 118 Brus, L.E., 32, 120, 147, 209 Bruylants, A., 206 Bryce-Smith, D., 107, 356, 357, 360, 361

Brzozowski, J., 117 Buch, F., 581 Buchanan, D. N., 282 Buchardt, O., 49, 351 Buchholz, G., 461, 496 Buchler, J. W., 196 Bube, R. H., 581 Buchi, G., 240 Buehler, E., 580 Buenker, R., 5, 6, 49, 202 Bugrim, E. D., 123 Bujko, A., 43 Bulgakov, R. G., 173 Bull, c., 201 Bull, J., 149 Bulska, H., 157 Bulusheva, V. V., 483 3unce, N. J., 89, 366, 405 Bunker, P. R., 4 Bunnenberg, E., 16, 198 Bunner, R. H., 131 Bunnett, J. F., 366, 367 Bur. J. G.. 71 Burchill, P. J., 531, 534 Burde, D. H., 122 Burdett, J. K., 174, 176 Burdett, K. A., 326 Burgess, E. M., 326 Burgner, R. P., 198 Burke, G. L., 170 Burkhart, R. D., 86 Burkov, V. I., 173 Burlitch, J. M., 180

20

589 Burlov, A. S., 170 Burnel Marti, F., 32 Burnett, J. B., 447 Burnham, R., 128 Burns, G., 123 Burns, P. A., 412 Burns, R. A., 93 Burr, J. G., 452 Burr, R. C., 517 Burrows, B. L., 7 Burrows, H. D., 76, 362 Burt, J. C., 195 Burton, G. W., 361 Burton, T., 206 Burton, W. B., 331, 537 Busch, G. E., 117 Buschmann, H. W., 101 Bushaw, B. A., 27, 168 Butchart, G. A. M., 441 Butcher, R. J., 122, 129 Butenin, A. V., 199 Butler, G. B., 10 Butler, I. S., 195 Butler, S., 28, 145 Butomo, L. A., 532 Butsugan, Y.,281 Butt, Y., 280 Buttrill, S. E., 22, 101 Buxton, S. R., 172 Byakov, V. M., 202 Byers, B. H., 179 Bykovskaya, L. A., 31, 64 Byteva, I. M., 196 Caballol, R., 6 Cabell-Whiting, P. W., 329, 351

Cackovic, H., 518 Cadle, R. D., 140 Cadogan, J. I. G., 488 Cagnac, B., 17 Cahnmann, H. J., 94 Caine, D., 284 Caldin, E. F., 201 Caldwell, R. A., 76, 339, 340, 363

Callaghan, E., 35 Callear, A. B., 127, 202 Callender, R. H., 38 Calvert, J. G., 147, 148 Calvo, C., 362 Camaggi, C. M., 468 Cambie, R. C., 411 Camhy-Val, C., 125 Camilleri, P., 134 Campbell, E., 536 Campbell, I. M., 144 Campbell, J. M., 274, 405 Campbell, R. O., 386 Campos, J., 125 Canepa, P., 518 Canters, G. W., 35, 198 Cantrell, T. S., 107, 238, 250,

251, 359, 360, 361, 446, 464

Capek, I., 362, 509 Capelle, G. A., 9, 33, 111, 126, 129

CaFellos, C., 26, 84 Caplain, S.,37, 86, 402, 450 Carassiti, V., 169, 173, 181 Carbo, R., 6 Carde, R. N., 487 Carden, F., 576 Carenza, M.,516

Carey, J. H., 158 Carless, H. A. J., 240 Carlisle, C. H., 324 Carlock, J. T., 448 Carls, H. H., 28 Carlson, G. L. B., 223 Carlson, R. G., 219, 264, 290 Carlson, R. W., 23, 140, 144, 145, 146

Carlson, S. A., 537 Carlsson, D. J., 93, 169, 409, 530, 534

Carlsten, J. L., 21 Carmichael, H. J., 39 Carmody, M. A., 239 Carr, R. W., jun., 143 Carre, C., 227, 501 Carrington, A., 10 Carroll, F. A., 90, 196 Carroll, P. K., 9 Carruthers, R. J., 375 Carruthers, W., 322, 377, 380, 429

Carsky, P., 6 Carter, T. P., 142 Cartwright, D. C., 4, 24 Cartwright. H. M.. 4 CasagrGde, M., 121,420 Case, P. L., 16 Case, R. S., 48, 94 Casida, J. E., 331 Castellano, A., 364, 386, 402, 450

Castellano, E., 124 Castelli, F., 156 Castex, M.-L., 9 Cate, R. L., 128, 499 Caton, R. B., 147 Catteau, J. P., 364, 402, 450 Caubere, P., 227, 501 Caucik, P., 535 Caumartin, F., 317 Cauzzo, G., 419, 420 Cazianis, C. T., 206 Cederbaum, L. S., 21 Cehelnik, E. D., 43, 59 Celotta, R. J., 22, 24 Centineo, A., 175 Cepciansky, I., 537 Cerfontain, H., 11, 242, 266, 493

CeGa, V., 200, 51 I Cernia, E., 528, 529 Cerveau, G., 195 Cess, R. D., 149 Chahine, M. T., 131 Chaiko, A. K., 511 Chalykh, A. E., 516 Chamberlain, G. A. 9 23, 144, 145, 201

Chambers, R. D., 351, 355, 432

Chameides, W., 148 Chan, H.-F., 266 Chan, W. H., 9 Chance, R. R., 43 Chandra, N., 21 Chandrasekaran, S., 501 Chandross, E. A., 385 Chang, D. W.-L., 59, 303 Chang, H. M., 6,78 Chang, H. W., 123 Chang, S., 135, 210 Channin, D. H., 527

590 Chantrell, S. J., 197 Chapiro, A., 516, 517, 518 Chapman, D., 26 Chapman, F. M., jun., 21 Chapman, 0. L., 345, 561 Chapman, R. D., 134 Chapman, R. E., 147 Cha uin, P 236 Chalton, J:’L., 447 Chatalic, A 205 Chatelain, %. L., 120 Chatt, J., 179, 566 Chattersjee K. K., 73, 156 Chattersjee: S., 73, 156 Chau, T. C., 536 Chaudhry, A., 396 Chauvet, J. P., 200 Chebotaev, V. P., 17, 39 Chekalin, N. V., 205 Chekulaeva, L. N., 200 Chen, K. S., 36, 393, 406, 465 Chen, M X . , 36, 284 Chen, R. F., 170 Chen, S. N.. 165 Chenevert, R., 142 Cheney, J., 223 Cheng, J.-D., 442 Chepel, L. V., 517 Cherburkov, Y.A., 355 Cherepkov, N. A., 21 Cherkashin, A. E., 209 Cherkasov, A. S., 536 Chernova, 1. K., 531, 536 Chernyavskii, A. F., 54 Cheron. B.. 38. 127 Cherton, J k , ’ 317 Chertorizhskii, A. V., 519 Cheshnovsky, O., 125 Chesick, J. P., 137 Chevolleau, D., 207 Chi, F. K., 209 Chiancone, E., 201 Chibisov, A. K., 172 Childs, M. E 206 Childs, R. F.y330 Ching, T.-Y., 409 Chinyakov, S.V., 172 Chip, G. K., 219, 454 Chisaka, F., 149 Chisholm, C. D. H., 3 Chisholm, M. H., 566 Chm, C. L., 28 Chiu, Y. N., 139 Chizhikova, 2. A., 54 Cho, Y.,206,471 Choo, K. Y.,37, 481 Chou, C. C., 144 Chou, S., 418 Choudhury, B. J., 24 Chow. V.. 35. 202 Chow; Y.‘L., i 19,346,418,455 Christensen, R., 31 Chrjstenson, P. A., 329 Christofferson, R. E., 6,43 Chrysochoos, J., 172 Chu, K. J., 149 Chu. N. Y. C.. 19 Chu; S. I., 4 ‘ Chu, S. Y., 44 Chuang, T. J., 28, 75 Chudar, V. S., 200 Chunn. K.. 147 Chung; S. K.,41 1 Chung, Y.J., 536

Author Index Chupka, W. A., 21 Chutjian, A., 24, 25 Chuvaeva, I. N., 361 Chuvilla, Yu. N., 527 Cicerone. R. J.. 137 Cihonski; J. L.; 186 Cizek, J., 6, 7 Clardy, J., 276, 448 Claridge, R. F. C., 28, 127, 128 Clark, K. L., 140 Clark. L. B.. 6 Clark; R., 16 Clark, T. C., 310 Clark, W. D. K.,567 Clark, W. E., 149 Clark. W. G.. 146 Clarke, B. hi., jun., 15, 214, 238 Clarke, R. H., 35,84,198,200, 205 Clauss, P., 348 Claverie, P., 13 Clayton, R. K., 579 Cleannan, E. L., 351 Cleveland, W. S., 149 Clifton, E. D., 353 Clive, D. L. J., 397 Closs, G. L., 37, 199 Clough, S., 322 Clyne, M. A. A., 124 CO, T.-T., 35, 86 Coates, R. M.,318 Cobo, A., 49 Coburn, T. T., 491 Cochrane, W.P., 537 Cocivera, M., 37, 215 Cody, R. J., 23 Coffin, K. P., 4 Coffin, R. L., 264 Cogdell, R. J., 577, 579 Coggioca, M., 25 Cohen. E.. 251 Cohen; H , 157 Cohen, J. S., 4 Cohen, M. D., 7, 32, 54, 73 Cohen, R. B., 139, 144 Cohen, S. G., 70, 83, 89, 392, 398 Cohen-Fernandes, P.,442 Cohn, D. B., 147 Cohylakis, D., 425 Colangelo, J. P., 222 Colbourn, E. A., 5 Coleman, P. D., 145 Coleman, R. D., 519 Coleman, W., 156 Coles, H., 520 Collin, G. J., 99 Collins, P. M., 497 Collins, R. J., 117 Collins, T. C., 4 Colnagelo, J. P., 497 Colomer, E., 195 Colonna, M., 435 Colpa, J. P., 3, 35 Colson, S. D., 11 Colussi, A. J., 140, 208 Comes, F. J., 28, 125 Compaignon, H., 300,406 Com ton L. E 134 Concforelii, G.,’i73, 175, 423 Conneely, J. A., 191 Connerade, J. P., 9

Connor, J. H., 127, 178, 193, 202 Connors, R. E., 10, 198, 205 Conway, J., 156 Cook, I. P., 8 Cook, W. T., 208 Cooke, D. F., 142 Cookson, R. C., 264, 309,325 Cool, T. A., 142 Cooper, J. W., 21, 38 Cordemans, L., 164 Corden, R., 511 Coret, A,, 55 Corey, E. J., 454 Corkery, S., 209 Cornelisse, J., 107, 358 Cornwell, A. B., 193 Corradini, G. R., 49, 58, 302 Corriu, R., 195 Costa, L., 205 Costanzo, L. L., 173,423 Cotter, B. R., 311 Cotton, G. A., 171 Cotton, J. D., 207 Cotton, T. M., 199 Coulombe, M. C., 4, 8 Coulon, M., 136 Coulson, K. L., 561 Court, W. A., 486 Courtens, E., 38 Courtin, A., 336 Couture, A., 374, 459 Coveleskie R. A., 112 Coville, N.1J., 195 Cowan, D. O., 72, 338 Cowman, C. D., 158 Cox, K. E., 564 Cox, O., 272 Cox, R. A., 121,144,146,148, 420 Cox, R. J., 75 cox. w. w.. 264

Craig, A: Ci, 66 Craig, D., 32, 33, 56, 78 Craig, N. L., 119, 471 Crandall, D. C., 419 Crane, P. M.,101 Creary, X.,366, 367 Creed, D., 63, 76, 294, 295, 340, 363 Creek, D. M., 9 Crellin, R. A., 510 Cremaschi, P., 49 Cremer, G., 127 Cremer, S. E., 218 Cremieux, L., 123 Crepeau, R. H., 201 Criegee, R., 149 Cripps,.H. N., 519 Cnstallini. C.. 274 Cristiani, P., i93 Cristol S. J., 306,312,385,430 Croisy,’ A., 376, 461 Crosby, G. A., 161, 166 Crosby, D. G., 441, 504, 537 Crosby, P. M.,57,84, 139,441 Crosley, D. R., 142 Crossley, R. W.,142

Author Index Crowley, M. G., 139 Cruse, H. W., 126 Crutzen, P., 138, 148 Csatorday, K., 577 Csizmadia, I. G., 4, 48, 49 Csontos, G., 190 Cu, A., 401 Cuddeback, J. E., 148 Cuff, D. R. A., 50, 99 Cullick, A. S., 36 Cundall, R. B., 59, 78 Cundall, R. L., 278, 447 Cundy, C. S., 207 Cunningham, D. L., 140 Cunningham, J., 209 Cunningham, K., 39, 166 Cunnold, D. M., 137 Cuong, N. K., 317 Cuppen, T. J. H. M., 371, 374 Currie, J. L., 119, 471 Curry, M. C., 535 Curtat, M., 119 Cusanovich, M. A., 201 Cutchis, P., 137 Cutts, E., 532 Cvetanovic, R. J., 138, 140 Czajkowski, M., 128 Czerwinski, W., 536 Dabard, R., 178 Dagdigian, P. J., 23, 126 Dainton. F. S.. 303 Dake, J.-D., 129 Dalal, V. L., 580 Dalby, F. W., 122 Dale, J. I., 493 Dalgardno, A., 135 Dalton, J. C., 49, 65, 213, 266 Damany, H., 9 Damask, A. C., 24, 78 Damten, L. A., 140 Dance, D. F., 25 Danecek, J., 169, 409, 534 Danilov, V. V., 39 Danilychev, V. A., 28 Dannenberg, W., 262 Danno, A., 517 Darensbourg, D. J., 177 Das. K. K.. 322 Das; R. R.,‘197 Das, T. P., 4, 8 Das Gupta, G., 104, 106 Datta, S., 134 Datz, S., 128 Dauben, W. G., 48, 213, 317, 318, 334 Dauber, P., 10 Daudey, J. P., 48 David, C., 520 Davidson, A., 134 Davidson, E. R., 6, 35, 36, 198 Davidson, J. A., 141 Davidson, R. S., 75, 76, 83, 105, 361, 391, 397, 398 Davidsson, A., 12, 38 Davies. G. T.. 28 Davis, A., 532 Davis, D. D., 121, 123, 136, 140, 142, 143, 149 Days, L. I., jun., 144 Davys, M. G., 143 Davis, R., 581

591 Davis, R. E., 188 Davis, S. L., 4 Davis, T. D., 6 Davis, T. I., 530, 531 Davison, A., 184 Davydov, B. E., 520 Dawes, K., 292 Dawson, H. R., 136 Day, A. C., 351 Day, R. O., 315, 368 Day, V. W., 3 15, 368 Dean, C. R. S., 171 Dearrnan, H. H., 522 DeArmond, M. K., 153 de B. Costa, S. H., 200 Debey, P., 201 Debies, T. P., 21 De Blauwe, F., 526 De Boer, C. D., 237 de Boer, T., 488 Debuch, G., 68 Decker, C., 536 Decorps, M., 36, 86 Dedinas. J., 392 Defay, N., 374 Defazio, C. A., 511 De Filippo, D., 193 Deghaidy, F. S., 15 Degraff, B. A., 170, 487 de Groot, M. S., 35, 111 de Hass, N., 140 de Heer, F. J., 24, 25, 100, 125 Dehm, D., 236 Dehmer, J. L., 21 Dehmer, P. M., 21 Deinum, T., 110 De Jaegere, S., 164 Dejonckheere, W.P., 498 Dekkers, J. J., 32, 54 Delahay, A. E., 581 Delahay, P., 21 de la Mare, P. B. D., 361 Delay, F.,319 Del Bene, J. E., 11, 49, 60, 214 Delavallee, A,, 459 Del Halle, J., 519 Del Halle, S., 519 Delonb, N. B., 21 Delzenne, G. A., 509 Demary, R., 76 Demas, J. N., 160, 161 de Mayo, P., 29, 65, 406, 461, 464, 465, 497 Demchuk, M. T., 54 Demchuk, S., 42 de Meijere, A., 329, 335 Demerjian, K. L., 148 Demeter, A. M., 9 Demidovich, V. V., 5 16 Demikhov, Yu. N., 520 Demko, S. V., 192 Demochenko, S. S., 529 De More, W. B., 143 Denes, A. S., 49 De Niro, J., 259, 404, 448 Denisoff, O., 178 Dennis, L. W., 35 Deplano, P., 193 Derrick, L. M. R., 178 Derwent, R. G., 144 De Schryver, F. C., 75, 244, 246,249,253, 512, 513 Desclaux, J. P., 21

Deshayes, H.,406, 503 Deshpande, R. R., 356 De Silva, S. O., 425 Deslongchamps, P., 142 Dessaux, O., 76 Desvergne, J.-P., 386 De Torna, R. P., 72 Deutsch, P. W., 4 Devekki, A. V., 368, 396 de Vera, N. L., 430 Devillanova, F., 193 Devillers, C., 119 Devon, T., 188 Dewar, M. J. S., 7, 48, 94, 95, 206, 519 Dewey, H. J., 134 de Winter, H. G., 129 Diamantis, A. A., 179 Diaz, A., 193 Dice, D. R., 121, 495 Dickerman, S. C., 371 Dickinson, D. A., 119, 205, 498 Dickinson, P. G., 139 Diem, H. E., 532 Diemente, D., 161 Dienes, A., 66 Diestler, D. J., 46 Dietrich-Buchecker, C., 473 Dietz, R., 519 DIllari.o, L., 518 31Iorio, E. E., 201 Dilling, W. L., 253, 333 lilung, I. I., 196 Dineen, J. A., 195 Dingle, T. W., 145 Dingwall, J. G., 355 Dinur, U., 48, 128. Diomedi-Camassel, F., 165 Dixneuf, P., 195 Dixon, A. J., 24 Dixon, G. D., 51 1 Dixon, R. S., 38 Djerassi, C., 16, 198 Djeu, N., 128 Dmytraczenko, A., 245, 503 loane, W. M., 497, 517 Dobbs, A. J., 36, 37, 86 lobkin, J., 37, 493 Dobrowolski, G., 534 lobson, D. C., 121 Docken, K. K., 4, 135 Dodd, J. R., 478 Dodds, T. A., 188 lodge, L. G., 129 Doduik, H., 67 Doehring, A., 35 Doepker, R. D., 100 Dopp, D. O., 364, 384, 401, 436,441 Doering, J. P., 25 DOrr, I., 54 Dorr, F., 31 Doetschman, D. C., 156 Doktorov, E. V., 42, 44 Dokunikhim, N. S., 299, 396 lolce, D. L., 216 )ole, M., 518, 535, 536 loleiden, F. H., 409 Dolgikh, V. A., 28 Dolgova, R. V., 518 l’olieslager, J., I 6 4 Doljikov, V. S., 205 Dolphin, D., 196, 197

Author Index

592 Eachus, R. S., 168 Eagle, C. J., 118 Earl, B. L., 129 East, R., 269 Easton, R., 240, 453 Eaton, D. R., 206 Ebara, N., 84 Eber, G., 31, 54 Eberbach, W., 321 Ebetino, F. F., 501 Echols, W. A., 520 Eckert, J. A., 567 Eckert, Th., 529 Eckes, H., 482 Eckstrom. D. J.. 146 Eda, B., 517 Edamoto, Y., 369,452 Eddy, K. L., 409 Edelson. M.. 32 Edelstein. S.’A.. 126. 146. 201 Edil-yan,E. S., 520 ’ Edrissi, M., 463 Edward, J. T., 388 Edwards, D. H., 28 Edwards. L.-0.. 10 Edwards; 0. E.; 486,490 Efimov, Y. P., 202 Efremov, Y. M., 176 Eggerding, D., 286, 469 Eggers, J. H., 13 Egorochkin, A. N., 7, 15 Eguchi, S., 335 Egunov, A. V., 519 Ehlert, K., 193 Ehrenberg, B., 16, 43 A811 Ehrenfreund, J., 255 Eibler, E., 488, 489 Dufa>ard, J., 144 Eidel’berg, M. I., 210 Duff, J. M., 215, 218 Eidel’nant, M. P., 518 Duguay, M. A., 66 Einstein, F. W. B., 455 Duke. C. B.. 7 Eisch, J. J., 204 Duke; R. E.; jun., 266 Eisenberg, W., 229 Duley, W. W., 131, 147 Eisenstadt, M. M., 564 Dumont, A. M., 125 Eisenstein, L., 201 Dumont, P. D., 4 Eisenthal. K. B., 28, 75 Dumov, B. P., 123 Dunbar, R. C., 23, 99, 108, Eisfeld, W., 41 1 Eizember, R. F., 272 129, 184 Elad, D., 273, 451, 499 Duncan, C. W., 25 Elander, N., 117 Duncan, W., 10 El-Azmirly, M. A., 517 Dunkin, I. R., 480 El-Bayoumi, M. A., 31, 32,73 Dunn, T. M., 31 Elbert, S., 6 Dunning, F. B., 21 Elder, J. W., 490 Dunning, G. J., 147 Elder, R. C., 294 Dunning, T. H., jun., 4, 5 Elert, M. L., 44 Duphy, F., 386 Eletskii, A. V., 48 Du Plessis, T. A., 516 Elgert, K.-F., 532 Dupont-Roc, J., 28, 125 Eliassen. A., 149 Durhn, N., 499 Elix, J. A., 381 Durham C. H., 28 Durmis,’J., 169, 409, 534, 535 Ellen, G., 316 Elliot, R. L., 325, 427 Durocher, G., 63 Ellis. A. B.. 570 Dusek, D. M., 511 Ellis; J. V.,’297 Dutton, P. L., 579 Ellis, R. L., 7 Dvornikov, S. S., 33, 196 Ellison, F. O., 21 Dwivedi, C. P. D., 11 Ellison, R., 126 Dworetsky, S. H., 32 Elmitt, K., 178 Dyke, J. M., 198 El’nikova, O., 42 Dyson, D. J., 51 El Raie, M. H., 230 Dzakpasu, A. A., 417 El-Samahy, A., 119, 202 Dzhagarov, B. M.,198 El Sayed, M. A., 35, 86 Dzhagatspariyan, R. V.,5 18 Elson I. H., 175 Dziedziela, W. M., 517 El’tsiv, A. V., 192, 368, 369, Dzierza, W., 517 396, 401, 515 Dzvonik, M., 106

Dombrowski, L. J., 71 Domsta, J., 43 Donaldson, G. W., 536 Donchi, K. F., 49 Donnelly, K. E., 125 Donohue, T., 122 Donovan, R. J., 10, 122, 129 Dontsova, E. G., 419 Dorko, E. A., 42, 48 Dose, K., 420 Doty, J. C., 340, 363 Dou, H. J. M., 431 Douglas, W. E., 195 Douzou, P., 201 Dove, J. E., 134 Draayer, J. P., 3 Drachev, B. V., 518 Drake, J., 134 Dratovsky, M., 170 Dreeskamp, H., 55, 72 Drent. E.. 111 Dreux, M.,125 Drexhage, K. H., 31, 67 Drucker, R. P., 19 Drum, D. A., 157 Druyan, M. E., 35 Drysdale, D., 143 Dubini, R., 411 Dubinskaya, A. M., 134 Dubois, J. E., 178 DUC,D. K. M., 251 Ducas, T. W., 17 Dudarev, V. Y., 209 Dudkiewicz, J., 43 Diirr, H., 263, 328, 470, 475,

I

Emeis, C.A., 111 Encina, M. V., 70, 116, 399 Endicott, J. F., 154, 162, 165, 166 Endo, M., 527 Endoh, T., 537 Eng, R. S., 131 Engel, P. S., 64, 263, 267, 268, 472 Enger, A,, 259 Englert, A., 527 English, R. B., 195 Enoki, A., 415 Epiotis, N. D., 48, 316 Erben, A., 474 Ermakov, Y. A., 201 Erman, P., 117 Ermolaev, V. L., 87, 153, 172 Ershov, V. V., 292 Ershov, Yu. A., 527, 534 Escher, J. S., 580 Esclassan, J., 131 Estler, R. C., 25 Etheridge, R. D., 91, 409, 534 Euseev, A. G., 518 Evans, B. W.. 528. 535 Evans; G., 37 . Evans, N., 322, 377, 380, 429 Evans, N. A., 93, 418 Evans, R., 16 Evleth. E. M.. 317 Evstigneev, V: B., 36, 199, 200 Ewald, M., 63 Eweg, J., 11, 128 Ewing, E., 26 Extine, M., 566 Eyler, J. R., 22, 120 Eyndels, C., 374 Eyring, H., 41, 46 Ezaki, A., 431 Ezumi, E., 14 Ezumi, K., 24 Fabian, P., 148 Fabrihant, I., 75 Fahrenbuch, A. L., 581 Fahrenholtz, S. R., 409 Faidysh, A. N., 520 Faini, G. J., 67 Fairbank, W. M., jun., 126 Faisal, F. H. M., 22 Falci, K. J., 354 Falcinella, B., 205 Faler, G. R., 410 Falk, H., 198 Fang, P. H., 201, 581 Fanta, G. F., 517 Fara, G. M., 149 Farenhorst, E., 111 Fargo, N. D., 537 Farid, S., 237, 340, 363 Faris, J. F., 24 Farnham, S., 64 Farnworth, E. R., 6 Farr, J. K., 166 Farrugia, L.,178 Fastie, W. G., 135 Fattorusso, E., 481 Faucherre, J., 25 Faure, F., 144 Faure, J., 66 Favaro, G., 33, 83 Fave, J. L., 78 Favre, A., 84

Author Index Feast, W. J., 353 Febvay-Garot, N., 37,86,402, 450 Fedorov, A. S., 361 Fedotov, B. G., 518 Fehsenfeld, F. C., 139 Feigenbaum, A,, 259 Feiring, A., 490 Feit, E. D., 517 Feld, R. S., 351 Feldman, P. D., 135 Feldman, U., 134 Feldmann, D., 122 Felgate, P. D., 205 Felix, R. A., 206, 465 Felzenstein, A., 186 Fendler, J. H., 278 Feng, T., 583 Fennelly, P. F., 126 Ferguson, E. E., 139 Ferguson, J., 33, 78, 111, 385 Feriozi, D., 119, 409 Fernandez, E., 480 Fernie, D., 122 Ferran, J., 205 Ferraudi, G. J., 154, 162 Ferree, W. I., jun., 72,341,344 Ferreira, A. B., 309 Ferris, J. P., 135 Fesenko, E. E., 201 Fessenden, R. W., 208 Fetizon M., 251, 415 Field, $. H., 146 Field, R. W., 9, 33 Fieldhouse, S. A., 180 Fields, T. R., 100, 305 Figuera, J. M., 49, 480 Filby, W. G., 148 Filimoskkin, A. G., 527 Filler, R., 392 Filseth, S. V., 146 Filyukov, A. A., 123 Findelsen, A., 51 Findlay, D. M., 227 Fink, E. H., 28, 125, 144 Finkel, E. E., 518 Finlayson, B. J., 148, 407 Finn, E., 10, 209 Firestone. P. F.. 125 Fischbach, U., 6 Fischer, C. M., 142 Fischer, E., 59, 94, 96, 372, 373, 374, 375, 379, 426 Fischer, E. O., 180 Fischer. F. C., 369 Fischer; G., 13, 59, 94, 372, 379, 4.26 Fischer, H., 37, 214, 395 Fischer, J. R., 91, 419 Fischer, R., 33 Fischer. S.. 143 Fischer; S.’F., 45, 104, 110 Fischler, I., 185, 189, 566 Fish, R. H., 192 Fisher, G. J., 273 Fisher, M. M., 78, 83, 111 Fisher, R., 84 Fitton, F., 206 Fitzek, A., 457 Fitzgerald, J. M., 32 Flannery, M. R., 139 Fleming, J. W., 142 Fleming, G. R., 104, 111,406 Fleming, R. H., 68, 336

593 Fleming, R. J., 526 Flicker, W., 25 Flint, C. D., 153, 156 Flippen, J. L., 288, 443 Florian, L. R., 294 Florida, D., 102 Flowers, W. T., 353 Floyd M. B., 413 Flynn: B. R., 566 Flynn, C. M., 161 Flynn, C. R., 318, 478 Flynn, G., 148 Fogel, Ya. M., 25 Fok, N. V., 178, 215 Fokin, E. P., 171 Folin, M., 201, 420 Fombert, C., 277, 463 Fomherz, P., 71 Fomin, G. V., 368, 401 Fonash, S. J., 581 Fong, F. K., 199 Fonken, G. J., 376 Fontaine, C., 189, 190 Fontan, J., 527 Fontanella, J.-C., 129, 134 Fontijin, A., 26 Foo, P. D., 128 Foote, C. S., 91, 93, 344, 409, 412, 417,418 Ford, A. L., 9, 135 Ford, P. C., 153, 154, 161, 168 Forder, R. A., 178 Foreman, P. B., 4 Forero, V., 49 Formenti, M., 210 Formosinho, S. J., 26, 44, 110 Fornes, R. E., 533 Fornier de Violet, P., 170,203 403, 537 Forrester, A. R., 434 Forster, L. S., 156 Forster, P. J., 43 Forster, M. S., 25 Fort, A., 55 Foster, T. C., 22, 202 Fotakis, C., 122 Fouassier, J. P., 66 Fourrey, J. L., 277, 462,463 Fowland, F. S., 144 Fowler, J. W., 134 FOX,M.-A., 405 Fox, R. B., 521 Fox, W. B., 208 Fragala, I., 175 Fraites, J. L., 125 Francis, A. H., 31 Franck, R. W., 335, 354, 387, 406, 428, 475, 520 Franck-Neumann, M., 473 Franco, J., 210 Frank, C. W., 74 Frankel. D. S.. 35 Frankevich, E.‘ L., 38 Franklin, J. L., 48 Frasca, A. R., 374,419, 425 Fraser. J. R.. 355. 478 FraserLReid. ‘B.. 26 1 Fratey, F., 7 . Frauenfelder, H., 201 Freed, J. H., 36, 37 Freed, K. F., 6, 44,45, 46, 47, 102. 104. 118 Freedman,’P. A., 145 Freedman, R., 37

Freeman, C. G., 127, 128 Freeman, G. R., 95, 144 Freeman, J. R., 122 Frehel, D., 142 Freiberg, M., 128 Freiser, B. S., 101 French, J. B., 3 Frenkel, S. Ya., 520 Freund, R. S., 4, 25, 110 Freund, S. M., 131, 132, 205 Friedman, J. M., 31, 41 Friedman, L., 315 Frjedrjch, D. M., 12, 13, 19, 52 Friedrich, L. E., 430 Froehlich, K., 187 Froehlicher, M., 573 Frolov, A. N., 369, 401 Froment, M., 573 Fry, A. S., 182 Fuchs, B., 289,457 Fiinfschilling, J., 39 Fueno, T., 49, 113 Fuerniss, S. J., 315, 368 Fuhrhop, J. H., 196 Fujimori, E., 89 Fujimori, H., 173 Fujimori, T., 369, 451 Fujimoto, H., 48 Fujimura, Y.,45 Fujisawa, S., 32 Fujisawa, T., 459 Fujishima, A., 569, 570, 576 Fujita, Y., 171 Fujiwara, H., 283 Fujiwara, T., 9 Fujiwara, Y.,533 Fujiyama, F., 431 Fuke, K., 19, 56,222 Fukomoto, A., 287 Fukudome, J., 457 Fukui, K., 48 Fukumoto, K., 457, 501 Fukutomi, H., 154 Fukuyama, K., 137 Fukuyama, T., 25 Fullam, B. W., 180 Funisawa, M., 32 Furihata, T., 369, 452 Furman, D. R., 134 Furrer, H., 226, 429 Furstoss, A., 455 Furth, B., 218, 236 Furukawa, J., 509 Furukawa, K., 134 Furukawa, S., 222 Furuta, T., 437 Furutachi, N., 41 1 Furuyama, S., 140 Futrell, J., 123 Gaeb, S., 331, 332, 420, 504, 537 Gaedtke, H., 145 Gaeva, L. N., 299, 396 Gafney, H. D., 164, 165 Gafni, A., 16 Gagarin, S. G., 12 Gaibel, Z. L. F., 305 Gaines, D. F., 180 Gait, S. F., 437 Gajewski, J. J., 320 Gakis, N., 348, 429, 470 Galanin, M. D., 54 Galiazzo, G., 303

594 Galinier, G., 200 Galiullina, R. F., 191 Galkin, V. P.,210 Gallagher, A., 24 Gallagher, T. F., 126 Gallardo, M., 135 Gallucci, C.,307 Gallup, G., 7 Gal’perin, E. L 518 Galvez, C.,504” Gambaruto, M.,208 Gamm, R. G., 141 Gandhi, R. P., 490 Gandolfi, M.T.,154 Ganesan, K.,42 Gangadharan, A. R., 147 Gani, A., 50 Ganin, V. A., 24 Gann, R. G., 413 Gano, J. E.,218 Gaoni, Y.,254 Garavaglia, M.,135 Garbaty, E.A., 21 Garcia, A. M.,102 Gardiner, M.,197 Gardner, E. J., 294 Gardner, J. L.,21 Gardy, E. M.,38 Garetz, B., 406 Garg, S., 339 Gargill, R. L.,268 Garibyan, T.A., 36 Garnett, J. L.,518 Gamier, F.,178 Garrett, D.W.,308 Garrison, B. J., 6 Gaspar, P. P., 481 Gassbeck, C.J., 329 Gastilovich, E.A.,42 Gaughan, L. C.,331 Gaultier, J., 386 Gaur, V. P., 134 Gauthier, M.J. E., 63,64, 139,

Author Index

Gold, V.,203 Goldberg, J. L.,137 Golde, M.F.,28 125 138 Gol’denberg, V. i., 5il Goldschmidt, C.R.,304 Goldschmidt, Z., 270, 271, 313, 433 Golenwsky, G. M.. 205 Golger, A: i., 39 Golikov, V. P., 531, 536 Golla. W..177 Golubev, Vi B., 210, 510 Gomer, R.,567 Gomes, W.P., 576 Goncharenko, G. S., 124 Gonzalez, M.A.,47 Goodall, D. M.,38 Goodman, D. W.,206 360. 361 Goodman, L., 26,44,80 Gijzeman, 0. L. J., 49, 104, Gorden, R.,jun., 146 406 Gordon, A. S., 116 Gilbert, B. C., 143 Gordon, D.,532 Gilbert, E.,274, 501 Gordon, E., 518 Gilbert. J. R..140 Gorokhovatskii, Y.B., 209 Gilbert; R., 1 1 Gorse, R.A.,143 Gilbert, R. D., 533 Goryaev, V. W.,516 Gilbody, H.B., 136 Gosavi, R.K..,49 Giles, R. G. F., 371 Gossett, E. W.,35 Gilgen, P.,348,429 Gotthardt, H.,294, 317,463 Gillard, R. D.,168, 191 Gough, W.,128 Gilles, A., 117 Could, K.A., 59 Gillespie, D.W.,487 Gouloubandi, R.,5 16 Gillespie, G. D.,115 Goutarel, R.,416 Gillespie, H.M.,10 Gouterman, M.,27,33,35,36, Gillois, M 119 196, 197, 198,206 GilyanovsGii, P. V., 170 Govdya, Y.D.,361 Gimarc, B. M.,3 Gowenlock, B. G., 10,116,118 Ginley, D. S., 179 Grabe, B.,8 Girard, A., 129, 134 Grabowski, Z. R., 402 Girotti, A. W.,420 Gradyuzhko, A. T., 33, 196, Gitchell, A., 149 197 Giuffre, L.,528 Gratzel, M., 578 Gragerov, I., P.,107 Giuffrida, S., 423 140 Givens, R. S., 242, 264, 313, Graham, R.E.,140 Gavryusheva, N. I., 159 494 Graham, W.A. G., 195 Gaweda, E.,32, 75 Gramont, L., 129, 136 Gladys, M., 404,435,501 Gayler, R. E.,81,290 Glaser, R. D.,420 Grand, D.,63 Gayoso, J., 6 Glasson, W.A., 147 Granovskii, Yu.V., 518 Gazaryan, K. G., 36 Glavas, S., 142 Grant, F. W.,537 Gebel, V. M.,299, 396 Glazko, A. J., 498 Granzow, A., 121 Geddes, J., 136 Glazkov, Y. V., 196 Grassie, N.,530,531 Geigert, J., 384 Graves, R. E., 168 Gleason, R. E.,jun., 125 Gelbart, W.M.,38,41,44,102 Gleaves, J. T.,124 Gray, H. B., 157, 158, 168, 174, 180 Gelernt, B., 51, 145 Gleditsch, S. D.,126 Geller, G. G., 409 Gray, R. A., 131 Gleiter, H.,536 Gennari, G., 121,201,419,420 Glick, R. E.,24 Gray, R. D.,201 Genoud, F., 36, 86 Gliemann, G., 156 Graziano, M.L.,481 Geoffroy, G. L., 157, 168 Grebneva, V. L., 13 Glockner, E., 32, 55 Geoffroy, M.,208 Glogowski, M.E.,205 Green, A. E. S., 137 George, G. A., 531, 534 Gloor, J., 259 Green. B. S.. 342 George, M.V., 321,468 Gloor. B. F.,367 Green; M. L. H., 178 George, T.F.,49,406 Gochev, A,, -7 Green, T.A.,4 Green, W.H.,146, 147 Georgiev, G. S., 510 Godart, J., 28 Gerardo, J. B., 125 Goddard, W.A.,tert., 4, 5, 6, Greenhough, P.,156 7.202 Greer. R..518 Gerdil, R.,260 Gregory, A., 41,208 Geresh, S., 310, 384 Godik, V. I., 199 Gregory, M. J., 203 Gerischer, H.,574 Godlewski, J., 56 Grellman, K. H.,76, 94, 379, Goe, G. L . , 421 Gerkin, R. E.,36 426. 439 Goff, D.L.,235,268 German, K.R., 142 Greiels,-F. W., 187, 188 Gersten, J. I., 38 Gogolin, R., 158 Gohel, V. B.,9 Grevesse, N.,4 Gervais, J., 253 Goher, M.A. S.,170 Grey, R.A., 185 Gevlich, L. P., 159 Golankiewicz, K.,279,447 Gribova, 2.P., 196 Geymer, D.O.,536 Grider, R. O.,267 Gold, A., 474 Ghaffar, A., 531 Ghandi, R. P., 339 Ghibaudi, E.,124 Ghiggino, K. P 71, 520 Ghosh, A. C.,458 Ghosh, A. K.,583 Ghosh, A. S.,73 Ghosh, P., 508 Giachardi, J., 136 Giannotti, C.,36, 189, 190 Giannotti, G., 178 Giardina, B., 201 Gibb, J. C.,124 Gibb, W.H.,532 Gibert, E.,537 Gibson, Q.H.,201 Gibson, T.,234 Gifford, M.,195 Gilbert, A.,107,180,356,357,

~

Author Index Grieco, C., 486 Griffin, C. E., 218 Griffiths, J., 367, 485 Griggs, M., 131 Grigoryan, P. R., 36 Grimmeiss, H. G., 21 Grimshaw, J., 381, 503 Grinley, D. S., 570 Grisdale, P. J., 205 Grob, R. L., 149 Groen, M. B., 369 Groff, R. P., 519 Gromov, V. F., 516 Grosby, G. A., 181 Grossman, D., 534 Grubbs, R. H., 185 Gruen, H., 418 Griineis, F., 31, 54 Gruenter, K., 190 Gruzdev, P. F., 125 Gruzdev, V. P., 172 Gruzinsky, V. V., 31 Gryczynski, I., 43 Grynberg, G., 17 Gschwind, K. H., 96 Guarini, G., 386 Gubanov, G. G., 518 Gubareva, L. L., 516 Gudkov, N. D., 199 Guelton, M., 210 Guerillot, C. R.,4 Gueskens, G., 520 Guest, M. F.,178 Giisten, H., 215, 537 Guggenberger, L. J., 426 Guiard, B., 218 Guillard, R., 527 Guillet, J. E., 528, 531, 532, 534, 535, 536 Guillory, J. P., 530 Guillory, W. A., 99, 207, 208 Guissard-Gallory, C., 4 Gukasyan, P. S., 107 Gulan, M. P., 537 Gulis, I. M., 522 Gull, P., 228 Gunderson, E., 116 Gunn, B. C.,441 Gunning, H. E., 121 Gunsalus, I. C., 201 Gunthard, H. H., 26 Gupta, A., 69 Gupta, S. C., 219, 285, 297, 537 Gupton, J. T., 284 Gurang, I., 334, 446 Gurdzhiyan, L. M., 368 Gur’ev, V. I., 124 Gurinovich, G. P., 196, 198, 2oq Gurvich, L. V., 176 Gurwara, S. K., 439 Gur’yanova, V. V., 533 Guseva, L. N., 527 Gusinow, M. A., 122 Gussak, L. A., 135 Gustafson, T.K., 38 Gusten, H., 148 Gutierrez, A. D., 304 Gutman, D., 140 Gutman, I. I., 4 Gutman, U., 270, 313 Gutowski, R. V., 144 Guttmann, C., 102

595 H aaffland, D., 122 H aaks, D., 129, 142

Hansen, P. E., 475 Hansma, P. K., 519 H aas, G. M.,.572 Hanson, L. K., 196 Haas, J. W., jun., 213 Haquin, C., 192 H aberfield, P., 60 Hara, H., 99 H ack, W., 143 Hara, K., 26, 78 H ackett, P. A., 115 Harada, H., 518, 532 H ackmann, W. K., 123 Harada, K., 382,425 H addad, G. N., 21 Harada, N., 93,414 H aenisch, T. W., 126 Harada, Y., 369,451 H aensel, R., 28 Harbour, J. R., 35, 36, 200, 202, 396 H aertel, H., 26 H afner, M., 407, 537 Hardee, K. L., 572 H ager, G. D., 181 Hardt, H. D., 170 H agiwara, E., 117 Hardwich, J. L., 9 H agiwara, M., 518 Hardwidge, E., 128 H ahlmann, J., 93 Harel, Z., 481 Hahn, E. L., 40 Harland, P. W., 48 H ahn, R. C., 319 Harman, T. C., 131 Hahn, U., 28 Harper, D. J., 530 Hai, F., 140 Harrah, L. A., 74, 520 H aines, R. J., 195 Harries, J., 134 Hakala, D., 145 Harrigan, E. T., 35 H alavee, U., 48 Harrigan, R. W., 174 Halberstadt, I., 475 Harriman, A., 532 Hall, C. B., 140 Harris, D. H., 207 Hall, C. R., 461 Harris, D. O., 33 Hall, G. G., 43 Harris, E. W., 161 Hall, J. A., 4 Harris, G. W., 136, 143 Hall, J. L., 22 Harris, H. H., 139 Hall, T.-W., 273 Harris, J. A., 301 Hall, W. D., 8 Harris, L. E., 26 Haller, W., 32 Harrison, H. W., 49 Halmann, M., 470 Harrison, K., 191 Halpern, A. M., 14, 119 Harrison, M. F. A., 24 Hama, Y.,529, 536 Harrison, P. G., 193 Hamada, M., 421, 509 Harshbarger, W. R., 113 Hamai, S., 96 Hart, F. A., 171 Hamann, C., 583 Hart, H., 235, 247, 282, 283, Hamanoue, K., 518 284, 328, 330, 334, 335 Hameed, S., 137 Harteck, P., 145 Hameka, H. F., 4 Hartfuss, H. J., 25, 107 Hamer, N. K., 228 Hartig, W., 134 Hamill, W. H., 24, 25 Hartke, K., 254 I [amilton, J. B., 315 Hartman, S. E., 237 I [amilton, T. D. S., 52 Hartmann, W., 216, 356 I [amm, R. N., 15 Harvey, G. A,, 134 I [ammer, D. I., 149 Harvey, K. C., 17, 126 I [amming, W. J., 149 Hasebe, M.,281, 435, 454 I [ammond, A. L., 420 Hasegawa, H., 419 I [ammond, G. S., 68, 69, 157, Hasegawa, M., 38, 300, 394, 168, 174, 182,204,294, 310, 513 312, 317, 335, 336 Hasegawa, R., 369, 452 I [ammond, P. R., 27 Hasegawa, T., 230,443,444 f ‘ammond, W. B., 60,218,221 Hashimoto, K., 293 I [amon, D. P. G., 491 Hasinoff, B. B., 201 t [ampson, J., 137 Hasiuk, A., 234 t [amson, J. F., 5 Hasman, D., 4 t ‘anaya, K., 119,418,455 Hasselblad, V., 149 t ancock, G., 118 Hassner, A., 267, 429 t ancock, J. K., 146, 147 Haszeldine, R. N., 206, 353, t ancock, K. G., 119,205,266, 355, 468,481 267,498 Hata N., 369 404 434,450 E ’anda, T., 520 Hataha, M., i19, i02, 516 t andy, B. J., 144 Hatanaka, Y., 288, 388, 429 t ‘anifin, J. W., 251 Hatano, H., 203 t anne, G. F.,24 Hatano, M., 16 t anrahan, R. J., 123 Hatano, Y., 106 E anschmann, H.. 403 Hatch, C. E., 236, 446 E ansen, A. E., 16 Hattaway, J. H., 305 E ansen, D. A., 115 Hausman, R. F.,jun., 3 E ansen, H.-J., 310, 348, 429, Hautecloque, S., 124 446 Hauw, C., 386 E ansen, J. W., 66 Havinga, E., 323, 362, 369

Author Index

596 Hawke, G. S., 149 Hawkins, C., 367 Hawkins, E. G. E., 501 Hawkins, R. T., 17, 126 Hay, P. J., 4 Hayakawa, K., 271, 342, 511 Hayashi, H., 157, 437 Hayashi, K., 76, 517 Hayashi, S., 376, 434 Hayes, D. M., 49 Hayes, J. M., 35, 84 Haynes, A. C., 516 Haynes, B., 149 Hayon, E., 65, 89, 203, 402 Hayward, R. C., 411 Head, B. C., 516 Heath, G. A., 179 Htbert, G. R., 28 Hecht, T. A., 148 Hecker, L. H., 13-1 Heerjes P. M., 536 Heicklen, J., 94, 119, 124, 128, 140, 142, 144, 145, 148, 149, 420 Heidenreich, R. D., 517 Heidner, R. F.,tert., 140 Heilbronner, E., 8 Heimgartner. H.. 348. 429.

Heintzelman, R. W., - .. , . Heinzelmann. W.. 348. 385 H eitklmper, P., 263 ' H ejda, B., 39 H elbig, R., 210 Heller, D. F., 44, 45, 102, 104 Heller, E. J., 406 Heller, H. G., 96, 377 Hellner, L., 107 Hemingway, R. E., 95, 171 Hemmerich, P., 370 Hempel, H. U., 193 Henderson, E., 178, 181 Henderson, T. R., 239, 301 Henderson, W. A., 285 Hendrickson, D. N., 180 Hendrix, J., 164 Henerson, N. K., 516 Henerson, W. A., jun., 532 Henglein, A., 578 Henis, J. M. S., 99 Henne, A., 37, 214 H enneher, W. H., 21 H enrick, C. A., 279, 415 H enry, B. R., 41 H epburn, P. H., 31 Heppner, R. A., 24 Herberhold, M., 177, 193, 195 Herbst, E., 22 Herbst, P., 263 H ercules, D. M., 95, 299, 537 Heritage, J. P., 38 H erkstroeter, W. G., 409 Herlem, D., 416 Herley, P. J., 203 Herlinger, H., 533 Herm, R. R., 129 H erman, F., 490 H erman, J. A., 123 H erndon, W. C., 339 H erout, V., 219 Herrick, C. S., 536 H errick, D. R., 4

derrmann, W. A., 180, 192 Herron, J. T., 138, 142 gerschbach, D. R., 23, 129 lerst, E. A., 86 lertler, W. R., 458 lertz, H., 4, 145 gerz, W., 318 gerzog, H. L., 486 lesselmann, I. A. M., 35, 111 gesstvedt, E., 137 gester, N. E., 137 geumann, A., 455 geumann, E., 69 geusinger, H., 536 levett, W. D., jun., 9 qibbert, A., 21 3ibi, F., 335 liborn, R. C., 41 dickman, A. P., 38 lickman R. S., 25 licks, D: R., 261 lida, M., 299 digaki, H., 518 ligashide, F., 518 ligginson, B. R., 178 lignett, G. J., 425 3ikida, T., 31, 52, 127 qildenbrand, D. L., 5, 25 lildenbrand, K., 185 lildebrandt, S. J., 180 lill, E. A., 481 lill, H., 37 lill R. H 475 gill: R. M'.',126 lillier, I. H., 178 -Iilton, S. E., 488 gindle, P., 11 linkson, T. C., 128, 499 iino, S., 31 lino, T., 419, 435 linojosa, O., 512 linshaw, J. C., 249 lintze, R. E., 153, 161 3inze J., 101 lipps: K. W., 166, 181 girabayashi, Y., 230, 444 3iraga, K., 41 1 jirai, H., 365, 445, 507 girai, Y., 457 lirakawa, A. Y., 38 girakawa, K., 495 liraki, S., 533 3irama, M., 415 liramitsu, T., 437 lirano, Y., 334, 470 qirao, K., 365 lirayama, F., 29, 78, 99 lirayama, H., 56 lirayama, S., 15, 61 ljroaki, O., 335 girohara, H., 169 ljrooka, T., 31 lirose, H., 117 -Iirose. M.. 537 Hiroshima,'Y., 161 Hirota, H., 220 Hirota, K., 426, 516 Hirota, N., 35, 81 Hisatsune, I. C., 124 Hitzel, E., 190 Hixson, S. S., 306, 307, 308, 367, 371, 453

Ho, C.-T., 481 Ho, C.-Y., 246

Ho, P. P., 579 Hobbs, P. D., 244 Hochmann, P., 10 Hochster, H. S., 471 Hochstrasser, R. M., 15, 17, 31, 35, 41, 55, 61, 83, 117

Hodder, R. V., 28 Hodgkinson, K. H., 27 Hofeldt, R. H., 35, 200 Hofer, O., 198 Hoffen, M. I., 137 Hoffman, M. Z., 164,165,168, 567

Hoffman, R., 48, 247 Hoffmann, B. M., 36, 198,201 Hoffmann, R. W., 78, 288, 494

Hogan, P., 142 Hogeveen, H., 329, 351 Hoggard, P. E., 153, 156 Hohla, K., 122 Holcik, J., 535 Holdy, K. E., 47 Hollas, J. M., 31 Hollatz, G., 529 Hollebone, B., 16 Holmes. A. J. T.. 28 olmes; S. A., 22 'olmes-Siedle, A., 583 [olt, L. A., 533, 536 ,olten, D., 27, 198 jomer, J., 522 on, N.-S., 518, 533 qonda, H., 32 londa, K., 379,407,486, 495, 531, 569, 570, 576

londa, M., 8 3ong, H. K., 14, 31, 64 3onie. T.. 70 [ o n i i B.; 8 ,onner, J. R., 15 lonni, M., 28 onura, I., 71 Loogkamer,Th. P., 125 loornaert, G., 290 I oornweg, G . P. L., 32, 54 [oover, R. J., 35, 86 'opf, F. R., 196 iori, M., 458 ori, Y., 226 origuchi, H., 126 I [orii. Z.. 226 Horino, Y . , 4 Horita, H., 237 Hornback, J. M., 301, 403 Horne, D. A., 455 Hornman. J. C.. 126 [orsley,J. A., 49 [orspool, W. M., 181 lorvath, E., 181 losemann, R., 518 ioshi, T., 7, 26, 343, 381, 401 loshino, H., 27 [osoi, F., 518, 536 losokawa, T., 185 [oss W. P., 430 [osskin,T. M. A., 516 iouben, J. L., 33 [oughton, J. T., 137 [oulden, S. A., 4 Loury, S., 310, 384 iouser, J. J., 284 !ouston, L. L., 420 .ouvenaghel-Defoort, B., 53 1

597

Author Index Howard, W. F., 209 Howe, D. V., 189 Howell, B. A., 177 Howell, D. B., 33 Howell, H. B., 197 Howlett, L., 131 Hoydysh, W. G., 137 Hoyer, E., 157 Hoyermann, K., 143 Hoyle, C. E., 83, 216 Hoytink, G. J., 8, 32, 60, 66 Hozack, R. S., 32 Hrdlovic, P., 169,409,531,534 Hruska, F. E., 447 Hseu, T. H., 188 Hsia, M.-T., 230 Hsieh, J. C., 104, 110 Huang, C. S., 45, 104, 110 Huang, J.-T. J., 21 Huang, T., 24 25 Huang, Y. Y.,’ 329 Hubac, I., 6 Hubbard, J. S., 135 Huber, G., 8 Huber, H., 175, 180 Huber, J. R., 29, 65 Huber, M. C. E., 9 Hubert, A. J., 479 Hubert-Brierre, Y., 416 Hudgens, J. W., 124 Hudson, A., 180, 207 Hudson, B., 11 Huebert, B. J., 148 Huetz, A., 145 Huffrnann. R. E.. 27 Hughey, J: L., 179 Huglin, M. B., 517 Hugot-le-Goff, A., 573 Huh, Y., 536 Hui, K. K., 142 Hui. M. H.. 29. 65. 107 Huie, R. E.; 138, 142 Huitink, G. M.,32 Huler, E., 7, 10 Hulett, L. G., 166 Hull, D. R., 125 Hull. L. A.. 342 Hull; V. J.,’235 Hulse, J., 529 Human, H. G. C., 32 Hunt, G. E., 135 Hunt. W. J.. 5 H[unter, T. F., 120 H[unton, R. J., 90 H,untress, W. T., 139 H,unziker, H. E., 127 H uo, W. M., 3, 25 H uppi, E., 129 H urst, G. S., 125 H urst. J. K.. 166 R usain, D., -117, 128, 140, 144 H ush, N. S., 198 H ussey, G. E., 222, 497 H ustert. K.. 367. 420. 537 H utchinson; B. B., 129 H utchinson, B. R., 184 H utchinson, M. H. R., 125 H utchison, C. A., jun., 35, 36 Hutchison, J., 51 1 H utson, V., 43 Hutton, R. J., 33 Hutzinger, O., 367 H wa, Y., 332 Hwang, D.-Y., 503

Hyatt, J. A., 275, 276, 448 Hyde, P., 402 Hylton, J., 43 Hyman, H. A., 126 Jacocca, D., 205 Jbaraki, T., 140 Ibarra, M., 511 Ibram, I., 32 Ibram, J., 55 Ichihashi, T., 512, 532 Ichijo, T.,514 Ichimura, T., 31, 52, 127 Iddon, B., 488 Ide, H., 170 Ide, Y., 206 Jdo, Y., 471 Ieda, M., 525 Igeta, H., 281, 419, 435, 437, 454

Ignateva, L. P., 369 Iida, H., 261, 382, 383, 425 Iivama. S.. 516 Iikka,-T.,’ 201 Ijuuin, Y., 149 Ikarashi, O., 365, 501 Ikawa, T., 157 Ikeda. S.. 173 1[keda; T.; 7 1tkegame, M., 365 1 kegami, Y., 75 1Ikoda, M., 437 1 kos, V. V. B. V., 15 1lan, Y., 51 1l’enko, V. S., 209 1[ley, D. E., 261 11 Hong, S., 509 I l’icheva, Z. F., 518 I]off! P. M., jun., 37, 215, 470 1ma], M., 517 Imakura, Y., 501 Imamura. K.. 507 Imarnura; M-., 27, 203, 367, 515, 516 lmasaka, T., 25 Imhof, R. E., 44, 51, 135 Imoto, E., 159, 370, 402, 451 Imoto. M.. 509 Imoto; T.,-511 Imura, T., 75 hacker, O., 67, 71 Inagaki, S., 48 Inagaki. T.. 15 InaEe, Y., 507 Inamoto, N., 464 Incorvia, M. J., 153 Ingraham, L. L., 190 [nn, E. C. Y., 135 [nokuchi, H., 13, 21, 31, 55 [noue, E., 208, 514 [noue, H., 159, 299, 343, 378, 381 [noue, K., 93, 419 [noue, T., 387 [noue, Y., 128 Interrante, L. V., 170 [nterzarova, E. I., 134 [nuishi, Y., 199 Inuzuka, K., 8, 317 [ogansen, L. V., 25 ipaktschi, J., 267 [reton, R. C., 99 :rick, jun., G., 536 kie, H., 457

Irie, M., 76 hie, S., 76 Jrngartinger, H., 299 Irvin, G. P., 501 Isabel, R. J., 207 Jsagawa, K., 423 Isakov, I. V., 209 Isawa, Y., 470 Ishibashi, N., 25 Ishibe. N.. 285. 293 Ishid& H.; 69 Ishida, Y., 285 Ishida, T., 382, 425 Ishigure, K., 517 Ishihara. T.. 22 Ishii, F.; 464 Ishii, H., 382, 425 Ishii, T., 520 Ishikawa, M., 206, 240, 434, 467,468, 533 Ishikura, K., 240 Ishiwata, T., 141 Isler. R. C.. 125 Ito, A., 517 rto, K., 503 Ito, M., 14, 19, 38, 64, 517 Ito, S., 248, 411, 415 Ito, T. I., 215, 346, 468, 496 Ito, Y., 375, 394, 432 Itoh, K., 31, 388, 429 Itoh, M.,32, 75, 394 Iturbe, E. W., 35 Iuchi. K.. 178 Ivanov, G.N., 419 Ivanov, V. K., 21 Ivanov, V. L., 364, 367 Ivanov, V. S., 122, 516, 517 Ivashkevich, L. F., 202 Iverach, D., 149 Ivin, K. J., 169 Ivnitskaya, 1. N., 196 Iwai, S.. 442 wai; T.; 24 Iwakura, Y.,307, 510, 527 Iwamura, H., 315, 368 [waoka. T.. 420. 537 Iwasaki, K:, 365, 501 Iwasaki, M., 517 Iwasaki, S., 32 Iwashima, S., 32 [wata, C., 226 [wata, S., 3, 6, 214 [yengar, Y., 532 [zawa, Y., 334 [zumi, M., 159 Izuta, K., 442 lablonski, A., 68 lachimowski, C., 142 lackels, C., 6 lackowski, G., 233, 393 lackson, B., 348 lackson, D. A., 4, 8 lackson, J. A., 98 lackson, J. O., 131 lackson, R. J., jun., 83, 225, 444 lackson, W. M., 23, 118 lacobs, H. J. C., 323 lacobs, P., 216 lacobs, V. L., 21 lacobson, E., 128 lacobson, J. S., 149 lacobsson, U., 459

Author Index

598 Jacox, M. E., 10, 204, 208 Jacquignon, P., 376, 461 Jacyno, G., 63 Jaeger, D. A., 389, 494 Jaenicke-Zauner, W., 215, 393 Jaffe, H. H., 6, 7, 8 Jaffe, R. L., 49 Jaffe, S., 145 Jahn, R., 497 Jakopcic, K., 254 James, D. G. L., 134 James, D. R., 446 James, F. C., 117 Jamieson, W. D., 367 Jammaer, G., 290 Janata, E., 535, 576 Janic, I., 14 Janin, J., 144 Janssen, E., 76, 421 Janssen, J. W. A. M., 442 Jaouen, G., 178 Japar, S. M., 142 Jaseja, T. S., 21 Jayadevaiah, T. S., 576 Jayanty, R. K. M., 149 Jefferson, I., 178 Jefford, C. W., 319,410 Jeffrey-Hay, P., 5 Jeger, O., 213, 228, 255, 260 Jegier, Z., 149 Jeliazkowa, B. G., 154 Jen, C. K., 197 Jennings, B., 520 Jennings, K. R., 134 Jerina, D. M., 345 Jette, A. N., 9 Jetz, W., 195 Jimenez, E., 125 Jimenez, M., 299 Jindal, S . L., 420 Joblin, K. N., 189 Jochims, H. W., 4, 145 Joela. H.. 7 Johansson, A., 49 John, P., 116 John, T. L., 21 Johns. H. E.. 273 Johnson, A. 'W., 189 Johnson, B. F. G., 189 Johnson, B. R., 48,406 Johnson, C. A. F., 116, 117, 118 Johnson, D. A., 162 Johnson, D. E., 80,229, 394 Johnson, D. R., 518 Johnson, D. W., 351 Johnson, G. A. F., 10 Johnson, G. E., 14, 32, 74 Johnson, G . R. A., 536 Johnson, H. S., 137 Johnson, J. H., 116 Johnson, K. H., 170 Johnson, M., 535 Johnson, P. G., 419 Johnson, P. M., 21 Johnson, P. Y., 236, 245, 446, A9 5

Johkion, R. P., 319 Johnson, R. W., 80, 81, 229, 394 Johnson, S. E., 129 Johnson, S. G., 128 Johnson, W. A., 125 Johnston, F. J., 536

Kakimoto, Y., 242 Kakurai, T., 526 Kalal, J., 527 Kalbag, S. M., 439 Kaldor, A., 131 Kalinowski, J., 56 Kaliteevskaya, E. N., 31 Kalontarov, I. Y.,532 Kamalov, N., 169 Kamarinos, G., 581 Kamei, M., 261, 382 Kametani, T., 457, 501 Kaminski, J., 43, 522 Kamiya, I., 95 Kamiya, M., 8, 90, 568 Kamm, K. S., 57, 108, 302 Kammer, W. E., 6 Kamogawa, H., 515 Kamura, Y.,13 Kan, R. B., jun., 107 Kanamaru, N., 32, 46, 78, 81 Kanaoka, Y., 232, 288, 388, 429, 444, 465 Kanaska, Y.,407 Kanazawa, F., 226 Kanda, Y.,33, 90 Kaneda, T., 387 Kaneko, C., 414,434 Kaneko, T., 419, 435 Kane-Maguire, N. A. P., 156, 166 Kanematsu, K., 271, 342 Kaneto, K., 199 Kanezaki, E., 33, 86 Kang, H. H., 392 Kano, K., 67,361, 396, 576 Kanouchi, S., 322, 466, 467 Kanzig, H., 26 Kao, K. C., 521 Kapecki, J. A., 336 Kapkaeva, S. Kh., 536 Kaplan, A. M., 516 146 Kaplan, F., 195, 281, 494 Juelke, C.V., 493 Kaplan, L., 352 Juillet, F., 210 Kaplan, M. L., 38, 408 Julian, G. R., 91, 419 Kaplanova, M., 200 Julienne, P. S., 140 Kapral, R., 406 Jungen, M., 6 Kaptein, R., 37 Junker, M. B., 261 Karapetyan, G. O., 172 Juris, A., 154 Karavelas, S. E., 208 Kari, R. E., 49 Kabakchi, A. M., 518, 536 Kariinov, S. N., 518 Kabanov, V. A., 510, 522 Karkozova, G. F., 535 Kabanov, V. Ya., 517, 518 Karl, G., 47 Kabuto, C., 270 Karle, I. L., 288, 443 Kachan, A. A., 515 Karminski-Zamola, G., 254 Kachura, T. F., 196 Karmiov, A. N., 516 Kadlec, R. H., 148 Karplus, M., 8, 48, 60 Kadohira, M., 128 Karpov, L. G., 122 Kadoi, H., 517 Karpov, V. L., 516, 536 Kadoma, Y., 510 Karpukhin, 0. N., 522, 527, Kaetsu, I., 517 530, 531 Kafri, O., 40, 124 Kartsivadze. N. A.. 191 Kagan, M. B., 581 Karvas, H.,'260 Kagawa, J., 149 Karvas, M., 169,409,534, 535 Kagiya, T., 518 Ka amanov, N. D., 128, 192 Karyakin, A. V., 170, 172 Kasahara, M., 148 KaKfer, C., 28, 145 Kasai, N., 185 Kahn. G.. 535 Kasai, R., 401, 441 Kahn; L. -R., 4 Kasha, M., 41, 95 Kai, Y.,185 Kashevskaya, N. G., 535 Kaiser, H. J., 21, 122 Kashiwabara, H., 536 Kaiser. K. H.. 216 Kashiwagi, H., 36, 90 Kaito,'A., 16 ' Kashtieva, E., 518 Kaizu, Y.,161

Johnston, G.R., 99 Joiner, R. L., 537 Jokl, J., 507 Joo, F., 7 Joppien, G. R., 210 Jones, C. R., 126 Jones, D. N., 465 Jones, D. W., 243, 325. 494 Jones, G., 239, 425, 446, 487, 561 Jones, G., tert., 346 Jones, J. E., 297 Jones, L. B., 497 Jones, P., 142 Jones, P. W., 466 Jones, T. B., 206 Jones, W. J., 145 Jones, W. M., 491 Jordan, F., 8 Jordan, J. E., 27 Jordan, J. W., 400 Jorgensen, P., 5, 8 Jorgensen, S. W., 98 Jori, G., 201, 419, 420 Jortner, J., 19, 41, 46, 47, 117, 125 Joseph, K. T., 512 Joshi, B. D., 172 Joshi, M., 518 Joshi, N. C., 537 Joshua, C. P., 377, 384, 427, 440 Jouin, P., 277, 462, 463 Joule, J. A., 425 Journeaux, R., 200 Joussot-Dubien, J., 13, 55, 93, 203, 403,408 Jovner. C. H.. 28 Jubd, 0. P., 147 Judeikis, H. S., 47 Judge, D. L., 10,23, 144, 145,

599

Author Index Kas'kov, B. N.,522 Kasper, J. V. V., 140 Kassem, A. E.,25 Kataoka, T.,458 Katayama, D.H.,27 Katayama, M.,516 Katayama, N.,131 Katibnikov, M.A., 522 Kato, H., 297,495 Kato, K., 529 Kato, M., 262, 331, 492 Kato, S., 170,486 Kato, T.,449 Katsuhara, Y.,360 Katz, J. J., 35, 134, 199,

Keszthelyi, C. P., 95 Keto, J. W., 125 Ketskemetv. I.. 31 Keukeleirg b.; 312 Keumi, T.,8 Key, R. M., 419 Keyser, R. M., 536 Khalikova, 0. Sh., 532 Khalil, G. E., 196, 197 Khalil, M. H., 482 Khalilov, M. M.,32, 353 Khan, A. A., 535 Khan, A. U.,95 Khan-Magometova, Sh. D.,54 Kharlamov, B. M.,31, 64 200 Khashab, A. Y., 142 Katz, T. J., 95, 562 Khayutin, L. M.,23 Kauffmann, H. F.,510 Khelladi, F. Z.,26 Kauffmann, T.,380,425 Khibaum, G.,7 Kaufmann, D.,335 Kholov, M.Kh., 533 Kaufman, F., 143 Khomenko, V. S., 171 Kaufman, K., 138 Khruleva, V. I., 191 Kaufmann, K. J., 579 Khudyakov, I. V., 170 Kaupp, G.,313,328,340,344, Khuong-Huu, F., 416 346, 363,499 Khusainova, A. K., 493 Kausch, M.,328 Khvorostovskaya, L. E., 142 Kawabe, K., 75 Kibayashi, C.,383, 425 Kawai, K., 401,441 Kiguchi, T.,382,383,425 Kawai, W., 512, 532 Kjkuchi, K., 89, 180 Kawamura, T.,286 K!kuchi, M.,89, 180,526 Kawasaki, M.,117,404, 434 Kikuchi, O.,48 Kawase, K., 511 Kilcoyne, J. P., 134 Kawase, Y., 237 Kildal, H., 39, 132 Kawashima, T., 419,435 Kilichowski. K.B.. 171 Kawaski, A., 70 Kilp, T.,531 Kawski, A., 14,43, 63, 522 Kim, B. F., 197 Kay, K. G.,406 Kim, C.W., 272 Kaya, K., 38, 113, 120 Kjm, H., 574 Kayama, Y.,290 Kim. J. K.. 101 Kayser, R.,93, 119,409 Kim; V. A:, 36,200 Kayushin, L. P., 200 Kim, Y.-K., 21 Kazakov, V. P., 173, 527 Kimdo, S.,93 Kazakova, A. A., 200 Kimel, S., 40 Kazanskii. V. B.. 210 Kimoto, K., 242,494 Key B., 199,577' Kimura. K.. 218 Kear, K., 141 Kimura; M'., 249, 250, 252, Kearns, D. R., 90, 95, 204, 257,455 407. 408 Kindlmann, P. J., 125 KeaG, C.-M., 10, 118 King, D. S., 15 Keeley, F. J., 498 King, G.L.,44, 126, 135 Keeney, J., 572 King, G.W.,6, 10 Kees, K., 408 King, T. A., 122,519 Keier, N. P.,209 King, T.Y.,268 Kelder, J., I 1 Kingsey, J. L., 142 Keller, A., 518,536 Kingston, D.H., 221 Keller, R. A., 93, 119, 134, Kinjo, K., 526 409 Kinoshita. M.. 33. 35. 86 Kelley, P. L., 39, 131, 132 Kinsey, J.'L., 134. . Kellog, R. M.,459 Kinson, P. L., 483 Kelly, H.P., 17 Kinstle, J. F., 511, 514 Kelly, J. M., 180 Kinstle, T. H., 284,467 Kelly, T. L., 155 Kim. R. H.. 498 Kelso, P.A., 320 KGa; M., 207 Kempe, T.,459 Kirby, R. M., 144 Kemper, P. R., 144 Kirillov, G. N.,519 Kempter, V., 126 Kirk, A. D.,155 Kempton, R. J., 475 Kirk, D.I., 419 Kendall, P. E., 191 Kirkbright, G. P., 206 Kerenetskaya, I. P.,13 Kirov, N.,149 Keroulas, H.,428 Kirpicknikov, M.P.,438 Kershaw, M. J., 353 Kirsch, A. D.,84,422 Kesmarky, S., 35 Kirsch, Yu. E., 522 Kessar, S. V., 380 Kirschner, S., 48, 94,95 Kessler, J., 24 Kiryukhin, D. P., 516, 517

Kisaichi, A., 318 Kisch, H.,188 Kiselev, B. A.,200 Kiseleva, N.,532 Kishi, N.,511 Kishi, T.,13 Kishi, Y.,292 Kishida M.,510 Kishine: K., 510 Kiss, A. I., 7 Kita, Y., 486 Kita awa I., 501 Kitaiarat Y.,270, 290, 415,

485

Kitao, K., 415 Kitao, T.,536 Kitazima, I., 147 Kivach, L. N.,32 Kiwi, J., 531, 534 Kiyosawa, T.,495 Kizel, V. A., 173 Klabunde, U.,175 Klaening, U. K., 203 Klauber, G., 149 Klauss, G.,344 Kleibeuker, J., 35, 200 Klein, E.,7, 73 Klemm, R. B., 121, 140,201 Kleps, J., 14 Klimkin, V. M.,28 Klingebiel, U. I., 401,441 Klinshpont, E. R., 529, 530 Klint, W.,33 Klisenko, M.A., 537 Klochkov, V. P., 39 Klopffer, W., 522 Kloster-Jensen, E., 8,345 Klotz, L. c.,47 Klump, K. N.,9, 24 Klumpp, G.W.,316 Knapp, S.,497 Knappe, W.-R., 404, 435, 501 Kneen, G.,243,494 Knight, A. E. W., 1 1 Knight, A. R., 29, 121 Knight, J. R., 581 Knight, L. B.,jun., 28 Knight, P. L., 38 Knipe, R. H., 116 Knowles, J. R., 479 Knox, A., 519 Knox, G. R., 189 Knox, R. S., 578 Knox, S. A. R., 195 Knudsen, R. D.,239 Knyazev, B. A.,171 Knyazhanskii, M. I., 96, 170 KO, A.-A., 99 KO, M., 508 KO, Y.,205 Kobayashi, E.,509 Kobayashi, H., 161 Kobayashi, J., 511 Kobayashi, M.,7 Kobayashi, S., 533 Kobayashi, T.,19, 56,411 Kobayashi, Y.,320,434,459 Kober, H., 328 Kobori, T., 459 Koch, E.,28, 55, 72 Koch, S. D.,511 Koch, T. H.,259, 284, 348,

404,422,448

Koch, T. M.,467

Author Index

600 Kocheshkov, K. A., 204 Kochetkov. B. B.. 192 Kochetkova, N. S., 81 Kochi, J. K., 393 Koch-Pomeranz, U 310, 446 Kodama, A,, 516 Kodama, K., 99 Kodama. M.. 411 Kodera, ’K., 140 Koebberling, W., 428, 503 Koenig, K. E., 206, 465 Koerner von Gustorf, E., 180, 185, 187, 188, 189, 566

Kofron, J. T., 240 Kogan, B. Y., 199 Kogan, V. A., 170 Koglin, E., 156 Kohara, M., 185 Kohayakawa, K., 570 Kohler, B., 11, 31, 32, 55, 59 Koikov, S. N., 536 Koizumi, M., 401 Koizumi, T., 241 Kojima, Y., 537 Kojo, S., 146, 453 Kokada, H., 208, 514 Kokubun, H., 89, 96, 180 Kolbasov, V. I., 361 Kolc, J., 16, 339, 348 Kolesnikov, I. M., 516 Kolesnikova, V. V., 516 Koller, E., 240 Kollias, N., 38 Kollman, P., 49 Kollmar, H., 48, 95 Kolln W. S., 120 Kolnihov, 0. V., 516 Komarov, V. S., 122, 123 Komendantov, M. I., 476 Komissaraova, N. L., 292 Komiyama, M., 507 Kommandeur, J., 113 Komov, V. L., 518 Kompa, K. L., 122, 123, 205 Komyak, A. I., 173 Kon, S., 117 Kondo, E., 526 Kondo, M., 8,420,537 Kondo, S., 450, 497, 509 Kondo, T., 527 Kondrashov, E. K., 532 Konishi, K., 516 Kon’kov, N. G., 518 Konovalov, L. V., 535 Koo, P. J. S., 498 Kooshkabadi, H., 463 Kooter, J. A., 35, 36, 198 Kopczynski, S. L., 145 Kopelman, R., 13, 32 Kopp, I., 10 Koppel, D. E., 44 Kordas, J., 32, 73 Kormendi, F. F., 40 Kormer, V. A., 191 Kornhauser, A.. 447 Korneeva, G. P;, 516 Korneeva, V. V., 518 Korobeinikova, V. N., 5;27 Korobitsyna, I. K., 482, 483 Korodenko, G. D., 518, 532 Korolev, B. M., 519 Korolev, V. V., 159 Koroleva, V. R., 533 Korotaev, 0. N., 199

Korovkin, V. K., 132 Korsakov, V. S., 123 Korshak, V. V., 533 Korsukov, V. E., 536 Korsunovskii, G. A,, 568 Korte, F., 331, 332, 367, 420, 483, 504, 537

Kory, D. R., 81, 229 Korytnyk, W., 438 Kosegaki, K., 497, 509 Koskikallio, J., 115, 127 Kosloff, R., 48 Kosorotov, V. I., 519 Kosower, E. M., 67 Kossanyi, J., 218, 236 Koster. R. J. C.. 293 Kostikov, A. P.,- 200 Kostina, N., 532 Kostochka, L. M., 343, 453 Kostromina. N. A.. 159 Kostyshin, M.T., 208 Kotani, M., 201 Kotlo, V. N., 48, 171, 197 Kotok, S. D., 482 Kotomin, E., 75 Kotov, A. G., 516 Koudijs, A., 435 Koulkes-Pujo, A. M., 121 Kouwenhoven, C. G., 449 Kovalev, Y.V., 64 Kovalevskii, V. I., 210 Kovitch, G. H., 481 Koyama, K., 288, 443 Koyanagi, M., 26 Koyang, M., 80 Kozak, J. J., 576 Kozhich, D. T., 197 Koziar, J. C., 72, 338 Koziol, J., 66, 428 Koziolowa, A., 66, 428 Kozlov, M. E., 9 Kozlov, V. T., 518, 535 Kozma, L., 31 Kozyreva, M. S., 535 Kraatz, U., 483 Krakovyak, M. G., 509, 527 Kraljic, I., 119, 202 Kramer, H. E., 84, 407 Kramer, J. D., 205 Kramer, J. M., 108 Krantz, A., 281, 477 Krapcho, A. P.,286 Krasilov, Y. I., 173 Krasnov, Y.N., 191 Krasnova, V. A., 396 Krasnovskii, A. A., 200, 209 Krasser. W.. 156 Krassig; R.,’ 10 Kratowich, N. R., 91,409, 534 Krauch, C. H., 237 Kraus, F., 102 Krause, H. F., 128 Krause. L.. 128 Krauss; M:, 24, 140 Krausz, P., 178 Kravchenko, N. N., 368 Kreiter G. G., 193 Krenos: J. R., 23, 129 Krepinsky, J., 219 Krespan, C. G., 359 Kressel, H., 580 Kretschmer, G., 322, 501 Krichevskii, G. E., 534 Kricka, L. J., 337

Krieger, K., 328 Krishnamachari, S. L. N. G., 117

Kritskaya, D. A., 516 Krivonosov, A. I., 518 Krochmal, E., jun., 317, 467 Kroning, P., 31 Krop, H. B., 24 Kropp, P. J., 100,305,348,’405 Kruck. T.. 193. 195. 565 Krueger, C., 188 ‘ Kriiger, U., 407 Krupitskii, S. V., 169 Krusic, P. J., 36, 393 Krylov, B. E., 9 Kryszewski, M., 526, 532 Kryuchkova, G. T., 42 Kryukov, A. I., 154, 396 Kuball, H. G., 26 Kubokawa. Y..90 Kubota, HI, 512. 518, 533 Kubota, M., 566 Kubota, T., 14, 24 Kuboyama, A., 15 Kucera, H. W., 218 Kucherov, V. F., 322,343, 453 Kuchitsu, K., 23, 25 Kuchmii, S. Y., 154 Kudo, S., 414 Kudryashova, V. A., 171 Kuebler, N. A., 120 Kuchel, C., 344 Kuehne, M. E., 455 Kuendig, E. P., 175, 180 Kuester, W., 533 Kusters E 244 Kuhn, H.,’i6, 67, 71, 584 Kuhn, J., 6 Kuivila, H. G., 207 Kuizenga, D. J., 43 Kujirai, C., 533 Kukla, M. J., 326 Kulakov, V. N., 201 Kumada, M., 206, 467, 468, 533

Kumadaki, I., 320, 459 Kumagai, H., 420 Kumagai, T., 322 Kumar, B., 21 Kumler, P. L., 208, 470 Kunai, A., 218, 252 Kunau, I. P., 565 Kung, R. T. V., 123 Kunkely, H., 166 Kunz, A. B., 4 Kuppermann, A., 25, 134 Kuramachi, M., 32 Kuri, Z., 531 Kurita, J., 437, 479 Kurita, M., 262 Kuriyama, I., 516 Kurosaki, T., 509 Kurylo, M. J., 131, 143 Kusano, T., 536 Kusters, W., 497 Kusumoto, K., 535 Kusunoki, I., 140 Kuyatt, C. E., 24 Kuz’menko, N. E., 28 Kuz’min, G. N., 210 Kuzmin, V. A., 170 Kuzmina, L. G., 189 Kuz’minskii, A. S., 518 Kuz’Mitskii, V. A., 48

Author Index Kuznetsov, V. A., 7, 15 Kumetsova, L. A,, 28, 369,

Lashkov, G. I., 527 Lassettre, E. N., 9, 24, 25, 202 mi Laterza, M. E., 36 Kuiietsova, S. V., 122 Lattes, A., 346, 393, 427, 437 Kuznetzova, V. V., 171 Lau, A., 38 Kuzuya, M., 247, 328, 334, Lau, J. T., 266 335.437 Lau, R. A., 132 Kuziakov. Yu Ya.. 117 Laudenslager, J. B., 144 Kwiiam, A. L., 35,. 36, 198 Laurence, G. S., 153, 159, 205 Kwon, S., 423 Laureni, J., 477 Kyi, H.-J., 286, 497 Lauterbach, R. T., 216 Lavalette, D., 26 Laarhoven, W. H., 371, 372, Lavrentovich, Ya. I., 536 379 Lawler, R., 37 Laarson, I. M., 81 Lawrence, A. H., 406,465 Labahn, R. W., 21 Lawrence, G. M., 140, 145 Lablache-Combier, A., 86,364, Lawrence, J. B., 531 374, 402, 450, 459, 536 Lawson, W. M. C., 117 Labrum. J. M.. 339 Layton, B. R., 406 Lacey, A. R., 15 Lazare, S., 251 Lacey, P. A., 137 Lazear, N. R., 239 Lachmann, H., 14 Lazzizzera, I.,- 24 Lacrampe, J., 455 Leaver, I. H., 64, 93, 418, 533 Ladwig, C. C., 87 Lebedeff, A., S. 137 Lagarde, F., 125 Lebedev, N. N., 200 Laitinen, H. A., 574 Lebedev. Yu. S.. 568 Lakatos, A. I., 526 Lebedeva, A. M:, 516 Lalawa, A. R., 131 Le Blanc, R. M., 8, 200 Lalezari, I., 463 Le Brech, J., 8 Lallemand, J. Y.,386 Le Breton, P., 22 Lalo, C., 147 Lebreton, J., 205 Lam, C., 271, 290 Leckrone, D. S., 134 Lam, F. L., 404, 435 Lecler, D., 127 Lamb, R. G., 148 Leclerc, J. C., 4, 49 Lambeth, P. F., 398 Leclerc, M., 527 Lamola, A. A., 37, 398 Lecluijze, R. E. L. J., 465 Lamotte. M.. 13. 55. 134 Ledebo, L.-A., 21 Lampin,-J. P:, 424 * Ledneva, V. A., 519 Lam ton M 134 Lednor, P. W., 180, 207 Landj E.?., $5, 197, 294 Leduc, G., 121,495 Landau, M., 145 Leduc, M., 28, 125 Landmark, B., 139 Ledwith, A., 337, 402, 509, Landrv. J. F.. 35 510, 511 Lane, A. L., i39 Lee, C. K., 233, 393 Lane, N. F., 38 Lee, E. K. C., 104, 111, 114, Lane, R. H., 166 116, 145 Lange, G. L., 273 Lee, G. A., 236, 324,430 Lange, W., 118 Lee, H. U., 142 Langelaar, J., 13, 27, 54, 110 Lee, J., 29,67,91,94, 142,408, Langen, P., 28, 144 409. 534 Langendam, J. C., 372 91 Lee, Lw., Langendries, R., 244 Lee, L. C., 10,23,144, 145,146 Langford, C. H., 156, 158, Lee, T., 4, 8 166, 169 Lee, Y. J., 71, 452 Langhoff, C. A., 41, 44 Leenders, L., 75, 246, 513 Langhoff, S. R., 5, 6, 36, 198 Leenstra, W. R., 35, 36, 196, Langlet, J., 6, 48 198 Laniepce, B., 126 Leep, D., 24 Lanin, S. N., 535 Le Falher, J., 9 Lankard, J. R., 122 Lefebvre-Brion, H., 4 Laplaca, S. J., 358 Leforestier, C., 48 Laporte, J. L., 69, 89 Le Goff,M.-T., 269, 388, 406, Laposa, J. D., 52 429 Lapouyade, R., 386 Lehn, P. J., 536 La?pnp7ert, M. F., 180, 189, 206, Lehner, H., 198 L.v I Lehnig, M., 38, 207 Lappin, G. R., 374, 530 Lehoczki, E., 577 Large, R., 501 Leigh, G. J., 179, 566 Laridon, V. L., 509 Leigh, J. S., 579 Laroff, G. P., 395 Leigh, P. W., 38 Larrondo. L.. 128 Leinonen, L., 115 Larson, D. B., 31, 69, 84, Leismann, H., 263 286 Leitis, E., 441, 537 Larsson, L M . , 214 Lemal, D. M., 351,405

601 Lemieux, L., 200 Lemke, J. R., 8 Lemmer, D., 262 Lemmetyinen, H., 115 Lempereur, F., 132 Lempereur, M., 520 Lempert, K., 437, 498 Lempert-Sreter, M., 498 Lengel, R. K., 142 Lennuier, R., 9 Lenz, G. R., 256, 383, 418, 425 Lenz, K., 38 Lenzi, M., 118 Leonard, J. J., 198 Leonard, N. J.. 278, 447 Leone, S. R., 134 Leonhard, K., 193 Leonis, J., 527 Leonov, D. J., 273,451 Lepert, J. C., 131 LerdaI, D., 412 Le ROUX, J.-P., 317 Lesage, M., 490 Le Sage, R., 25 Lesaulnier, P., 517 Leshchenko, S. S., 531, 536 Lesin, V. I., 38 Lessard, C. R., 6, 10 Lester, W. A., jun., 6 Letokhov, V. S., 39, 132, 205 Letsinger, R. L., 365, 400 Leung, M., 35 Leutiette-Devin, E., 16 Leute, R., 313 Levai, J., 532 Levanon, H., 35, 36, 198, 200 Levenson, M. D., 17 Levenson, R. A., 186 Leventhal, J. J., 139 Levin, E., 68, 106 Levin, G., 6, 26, 87 Levine, J., 22 Levine, R. D., 47,48, 123, 124 Levine, S., 29, 121 Levinskii M. B 343 Levkin, V., I'j2 Levshin, L. V., 172, 200 Levy, D. H., 9, 24, 28, 145 Levy, F., 208 Levy, M. R., 122 Levy, P. W., 203 Lewis, A., 76, 105, 361, 397 Lewis, C., 69, 111 Lewis, F. D., 80, 81, 83, 216, 229,230, 394 Lewis, J., 189 Lewis, J. C., 38 Lewis, R. S., 116 Lewton, D. A., 465 Leznoff, C. C., 376 Lias, S. G., 98, 511 Libman, J., 360, 362 Lichman, K. V., 425 Lichtenberg, D. W., 195 Lichtenberg, L 501 Lie, G. c., 101" Light, J. M., 46 Lightner, D. A., 351, 419 Lijnse, P. L., 126 Lilly, R. A., 8 Lim, E. C., 32, 45, 46, 78, 81, 104, 110, 115 Lin, C., 159

i.

Author Index

602 Lin, C. H., 38 Lin, C.S., 4,42 Lin. C.T.. 86 Lin; J. W.:P., 417,418 Lin, L. T.,35 Lin, M. C.,121, 123, 145 Lin, M. J., 209 Lin, S. H.,41,46 Lin. T.-S.. 32. 35. 206 Lin; Y.-W., 49,406 Lind, R. C.,147 Lindenau, D.,531 Linder, R. E.,7, 16 Lindinger, W., 139 Lindley, P. F., 324 Lindner, R. E., 198 Lindquist, G. H.,124 Lindqvist, L., 90 Lineberger, W. C.,22, 112 Linschitz, H.,94,379, 426 Linz, A., 570 Lipari, N. O.,7 Lippke W., 344 Lipsky,’S., 25, 29, 56, 99 Lisachenko, A. A., 210 Lissado, L. A., 13 Lissi, E. A.,70, 80, 116, 1 399 Lissillour, R., 4 Listl, M., 463 Lisy, J. M., 276,448 Little, D. J., 129 Little, R. D., 257,311 Littler. J. G. F.. 128 Litvin; F. F., 2dO Litvinov, V. V.,170 Liu B 101 Liu: B:’Y. H.,149 Liu, D.S., 10, 134 Liu, F.,273 Liu, K.-C., 221 Liu M. K., 148 Liu: R. S. H., 182, 279, 280, 325,359, 386 Liu, Y. S., 132 Liuti. G.. 33. 140 Livinptone, ‘R., 36 Livshits, R. M., 527 Llewellyn, J. A., 24 Lloyd, D. R., 178 Lloyd, J. B. F., 32, 33 Lo, J. G.,144 Loboda, N.I., 200 Loboda-Cackovic, J., 5 18 Lockhart, R. W., 455 Lockwood, J. R., 59 Lockwood, M., 485 LOC ueneux R., 16 Lod%er. G..’362 Lodge, ‘K. B., 3 Lodzinska, A., 158 Loewenstein, R. M. J., 132 Loffet, A,, 527 Logan, S. R., 170, 181,203 Logansen, L.V.,15 Loginov, A. V.,169 Lohr, L. L.,jun., 21 Lohse, C., 458 Lokaj, P., 200 Lokensgard, J. P., 481 London, J., 137 Long, C. A., 90,408 Long, M. T.,81 Longo, F. R., 198

,onguet-Higgins, H. C., 406 does, H.,75,246, 513 ,ootens. M.. 72. 192 -opata,’V. J., 38 ,oper, G.L., 104 ,opez, M. I., 124 ,opez-Delgado, R., 102 4orents, D. C.,121, 145 ,orquet, A. J., 10,49 ,orquet, J. C.,10 -.ow, E. R., 205 ,os, J., 136 dosev, A. P., 200 ,ott, D. E.,tert., 24 -oughtan, J., 33 uougnot, D.-J., 66 Louisnard, N., 129, 136 Louw, R.,442 Lovelock, J. E., 137, 149 Low, L.H.,355,478 Lowe, R. S., 119,455 Lowry, J. T.,74 Loyd, D. H.,136 Lucci, R. D.,381 Lucken, E.A. C., 208 Ludewig, H., 149 Ludmer, Z.,7, 32, 54, 73 Ludwig, C.,131 Lugiato, L. A., 39 Lui, J. H., 31 Lui, R. S. H., 87 Lui, T.S., 86 Lui, Y.H.,52 Luibrand, R. T., 78, 288, 494

,ukac, I., 531 ,ukasiewicz, R. J., 32 ,ukhovitskii, V. I., 516 akomsky, G., 31 Ac’yanets, E. A.,199 -urnbyM. D., 78 ,unak, S., 204 dunazzi, L.,468 ,undin. R. E.. 192 ,unina; E. V.,’ 210 ,unsford, J. H., 209 ,untz, A; C.,111 m i a , M., 51, 148 ,uther, K., 123, 127 dutz, H.,51, 61,83, 117, 352 ,utz. R. E..493 -uu.’S. H..’101 Lyashenko; L. V., 209 Lykken, L., 537 Lynch, T. R., 219,454 Lyubarskii, A. L., 201 Lyubashevskaya, T. L., 581 Lyyra, M., 117 Maas, J. G., 136 McAdam, J. D. G., 519 McAllister, R. M., 190 McAlpine, R. D., 37, 215 McAuliffe, C. A., 197 MacBride, J. A. H., 355, 432 McBride, J. M., 471 McCaffery, A. J., 16 MacCallum, J. R.,534 McCann, V. A., 35 McClain, W. M., 19 McClenny, W. A., 131 McClure, D.S., 14, 62 McCormick, D.B., 419 McCulloch, A. W.,336

Mcculloh, K. E., 21

M cCullough, J. J., 362 M acCullum, J. R., 532 M cCurdy, C. W.,jun., 21 McDaniel, M. C.,281 McDonald, J. D., 124 M cDonald, J. R., 120, 147 M cDonell, J. A., 49 M cDowell, M. R. C., 24 McElroy, M. B., 138,420 McEwan, M. J., 127, 145 McEwen, G. K.,193

M cFadden, D.L., 23, 129 M cFarland, M., 139 McFarlane, R. A., 122 M cGarvey, J. J., 169 M cGeoch, M. W.,125 M cGill, W. J., 530,531 M ’acGillivray, J. D.,93, 415, 534 McGinniss. V. D.. 511 McGlynn, 8. P., 6, 10, 31, 52, 62,84,286 MacGregor, D. J., 253 McGre or, W. K., 143 McGurf. J. C.. 127 Machi, S., 516Mcllrath, T. J., 21 McInnes, A. G.,336 McIntosh, C. L., 345 McKean, D. R., 279,415 McKeever, M. R., 1 1 7 McKellar, J. F., 522, 530, 533 McKelvery, R. D., 310 McKelvey, J., 49 McKenney, D. J., 124 McKennjs, J. S., 188 McKenzie. A.. 134 McKoy, J:, 5 McKoy, V., 6,7, 21,202 McLafferty, F. J., 46 McLaren, K. G.,536 McLaughlan, K. A., 36, 37, 86 MacLean, C., 32, 54 McLure, J. D., 124 McMurry, T. B. H., 269 McNelis. E.. 178 McPhail; A.‘T., 486 Macrae, P. E., 492 MacRae, R. A., 1 1 Macrieu, J. P.,6 McWeeny, R., 3 McWilliam, H. M.,488 Madhavan, S., 491 Madia, W. J., 49 Madii, V. A., 173 Madsen, M. M., 4 Maeda, K., 255 Maeda, M., 450 Maeda, S., 38 Maeda, Y.,517 Maekawa, T.,516 Maeno, N.,389 Mihy, M., 385 Maestre M., 16,63, 160 Magde, b.,27, 168, 198 Magdinets, V. V., 51 1 Maggiora, G. M., 6, 8, 198 Magnus, P. D., 244, 397 Magyar, J. G., 216 Mahan, B. H.,406 Mahaney, M.,29, 65

Author Index Mahanti, S. D., 4, 8 Maheshwari, M. L., 219, 537 Maheshwari, R. C., 11 Maiboroda, V. D., 202 Maier, G., 286 Maillard, J. P., 135 Majeti S.,344 Majeti: V. A., 344 Major, M. A., 203 Makarov, A. A., 132 Makhkamov, K. M., 533 Makhlis, F. A., 518, 536 Makhuiladze, T. M., 39 Maki, A. H., 35, 86 Maki, Y.,437, 442 Makrenko, S. N., 123 Makuuchi, K., 518, 536 Malati, M. A., 157 Malaval, A., 142 Malkin, I. A., 42, 44 Malkin, R., 199 Malkmus, W., 131 Malkova, A. I., 209 Malley, M. M., 31, 66 Mallick, P., 11 Malm, D. N., 28 Malo, S. A., 9 Malone, R. D., 134 Malrieu, J. P., 48 Mal’tsev, A. K., 128, 192 Mamedov, Kh. I., 32, 353 Mametsuka, H., 7 Mamin, E. B., 516 Man, W.-H., 62 Mandal, K., 78 Mandella, W. L., 354 Manfrin, M. F., 153, 154 Maninski, J., 70 Manion, M. L., 37, 38, 481 Mankas, M. S., 297 Man’ko, V. I., 41 Mann, A., 123 Manning, C., 107, 371, 376 Manning, T. D. R., 254 Mansfield, M. W., 4, 9 Mansfield, T., 149 Mantashyan, A. A., 107 Mantione, M., 13 Mantovani, E., 528 Mantz, A. W., 135 Manuccia, T.,205 Manzer, L. E., 175 Marcandes, M. E. R., 73 March, F. C., 566 Marchal, E., 517 Marchal, J., 536 Marchand, A. P., 247 Marchetti, A. P., 15, 35 Marciniec, B., 420, 537 Marcondes, M. E. R., 208 Marconi, W., 528, 529 Marcus, R. A., 49, 536 Mardis, W. S., 219 Marek, M., 507 Margalith, E., 147 Margaretha, P., 252, 439 Marger, M. J. P., 490 Margerum, D. W., 170 Margerum, J. D., 511 Margitan, J. J., 143 Margolin, A. L., 533 Margolin, D. M., 516 Margulies, L., 13 Mariano, P. S., 317, 320, 407

603 M arlyanov, A. M., 536 M Lark,F., 50, 260 M Lark,G., 50 M ark, H., 297 M arks, R. L., 157 M arnko, V. I., 44 M arple, V. A., 149 M arsai, C., 132 M arshall, J. H., 86, 398 M arshall, R. M., 134 M arsigny, L., 205 M artens, H., 290 M artens, J., 383, 461, 495, 496

M artin, J., 491 M artin, J. R., 210 M artin, K. G., 532 M artin, M.,6

M artin, P. H. S., 21 M artin, R., 93, 119, 409 M artin, R. H., 374 Martin, R. M., 134 M artin, R. W., 28 Martina, D., 473 Martinez, N., 184 Marty, R. A., 244 Martynenko, A. P., 123 Martz, P., 435 Maruyama, K., 244, 286, 292, 293,295, 296, 299, 396 Maruyama, Y., 13 Masanet. J.. 117 Masetti, -F.,’76 Mashenkov, V. A., 199 Maslakiewicz, J. R., 355, 432 Maslov, A. I., 122 Maslov. V. G.. 198 Masmanidis, C. A., 6, 78 Mason, A. A., 143 Mason, M. G., 16 Mason, R., 566 Massone, C. A., 135 Masuhara, H., 70, 119 Masui, J., 285 Masuoka. Y.. 411 Masur, Y., 13 Mataga, N., 69, 70, 119 Mather, I. H., 191 Matheson, H. B., 368, 397 Matheson. I. B. C.. 29. 67. 91, 142,408,409, 534 ‘ ‘ Mathey, F., 424 Mathias, G., 124 Mathies, R., 13, 15 Mathis. R. F.. 139 M [atsa&a, Y.,* 32 M [atser, H. J., 286, 465 M [atsuda, O., 510, 517 M [atsui, H., 191 M [atsui, K., 389, 429, 488 M [atsui, M., 367 M [atsui, T., 16 M [atsumoto, K., 244 M [atsumoto, M., 206, 471 M iatsumoto, S., 26, 75, 78 M atsumoto, T., 61 M ‘atsuo, T., 361, 396, 576 M atsuoka, M., 536 M atsushima, R., 173 M atsushita, H., 520 M atsuura, J., 94 M atsuura, K., 345 M atsuura, T., 93, 370, 375, 394, 416, 417, 419, 432, 449

Matsuzaki, A., 38, 121 Matsuzaki, K., 512 Matsuzaki, S., 15, 38 Matthews, A. P., 156 Matthews, R. W., 171 Mattice, W. L., 6, 62 Mattucci, A. M., 527 Matuszewski, B., 117, 242, 494

MaU,-A. W.-H., 6, 11, 32, 33, 78, 111, 385 Mauk, M. R., 420 Mauldin. C.. 94. 353 Maumy,’M.,- 414 Maxson, V. T., 111 Mayne, P. J., 206 Mayo, F. R., 536 Mazanec, T. J., 205 Mazeline, C., 208 Mazumdar, K. K., 407, 536 Mazur, S., 412 Mazur, Y., 11, 142 Mazurenko, Yu. T., 39 Mazzei, M., 528 Mazzocchin, G. A., 181 Mazzu, A., 371 Mazzucato, U., 73, 76, 203 Meagher, J., 94, 119, 144 Meakin, P., 36, 393 Mecklenbranck, W., 125 Medary, R. T., 218 Medvinskii, A. A., 159 Meesten, A., 329 Megarity, E. D., 59, 303 Mehta, A. K., 193 Mehta, H. P., 25 Mehta, P. C., 517 Meier, R. R., 134 Meinel, A. B., 139 Meinel, M. P., 139 Meinwald, J., 229, 336, 486, 497 M [eisel, G., 17, 126 M [ellor, J. M., 271, 290 M lel’nikov, M. Y., 215 M lemming, R., 209, 407 M [endelson, L. T., 70, 89 M enendez, V., 49 M ‘enon, C. S., 480 M (entall, J. E., 24 M [eot-Ner, M., 146 M enzel, E. R., 71, 200 M enzies, R. T., 131 M enzinger, M., 126, 138 M ercier, A., 208 M erer, A. J., 28 M eriaudeau, P., 210 M erkel, P. B., 408 M erle, G., 190 M errill, E. W., 516 M errit, V. Y.,107, 216, 357, 358 Mertis. K.. 191 Merz, I., 474 Mesa, J., 504 Messmer, R. P., 170 Metcalfe, J., 24, 117 Meth-Cohn. 0.. 491 Metzger, J.,‘ 43 1 Metzner, W.,237 Meyer, A., 178 Meyer, H., 7 Meyer, R., 122 Meyer, T. J., 159, 179 ~

~

604 Meyers, A. I., 475 Meyerstein, D., 128, 157 Meyling, J. H., 15 Mezey, P., 49 Mialocq, J. C., 121 Miano, J. D., 95, 213 Michael, J., 126 Michaelson, R. C., 4, 28 Micheau, J. C., 393 Micheli, R. P., 306 Mlchels, H. H., 4 Michl, J., 13, 16, 48, 318, 339, 478 Middleton, J., 206 Mielczarek, S., 24 Mielenz, K. D., 43 Mies, F. H 134 Migita, T.,’&12 Migita, Y., 232, 444 Migliorato, P., 580 Migunova, I. I., 517 Mikala, J. J., 26 Mikami, N., 14, 19, 38, 64 Mikami. Y.. 45 Mikawa, H., 75, 364, 510, 520 Mikes, F., 527 Mikhalev, V. G., 21 Mikheev, Yu. A,, 526, 527, c2 I

JJ 1

Mikhailova, E. S., 200 Mikhailovskaya, E. V., 208 Mikuni, H., 495 Miladi, M., 9 Milano, R. A., 581 Milburn. R. M.. 164 Mile, B.; 142 ’ Miles, E. W., 420 Milinchuk, V. K., 516, 530 Millard, M. M., 511 Miller, A. A., 535 Miller. D. F.. 149 Miller; K. J.,‘6 Miller, L. J., 511 Miller, L. L., 354, 504, 537 Mjller, R. C., 362 Miller, R. D., 216 Miller. R. G.. 111. 116 Miller; T. A.,*4, 9’ Miller, T. M., 8 Milligan, B., 533, 536 Milligan, D. E., 10, 204, 208 Mjlls, J., 529 Mills. N. S.. 400 Milonni, P.‘W., 38 Mjlstein, R., 138, 420 M!lutinskaya, R. I., 64 Mima, K., 537 Mimuro, H., 209 Minamikawa, J., 437 Minamisono, E., 431 Minato, T., 48 Minegishi, T., 526 Minh, T., 124 Minyard, J. P., 406 Mioduski, J., 229 Mironov, M. S., 210 Mirskov, R. G., 207, 465 Mirumyanto, S. O., 42 Misakian, M., 24 Mishrma, I., 38 Mishra, P. S., 7 Misra, T. N., 78 Misumi, S., 387

M[itchell, A. B., 253 M[itchell, K., 581 M [itchell, P. I., 9 M[itchell, R. H 375 M[itchell, T. N.: 192 M!itkina, N. N., 171 M itra, P. S., 508 M‘itra, R. P., 157, 158 M itra, S. K., 144 M itrenin, Y. V., 159 M itrofanov, V. B., 123 M itschker, A., 380, 425 M itsui, H., 518, 536 M ittal, S. P., 158 M iura, K., 254 M iwa, T., 492 M iyagi, Y., 292 M iyamoto, R., 270 M iyanchi, S., 518 M iyashi, T., 282 M iyazaki, H., 14 M iyazawa, T., 292 M izoguchi, T., 185, 288 M jzuko, T., 515 M izuno, K., 43, 339, 362, 364, 447 M izuno, Y., 24 M izunoya, K., 45 M izutani, T., 525 M izutani, Y., 535 Mleziva, J., 5 11 M 0. L. Y. S.. 388 Moan, J., 33. M obius, D., 68, 584 Mobius, K., 33 M ochida. K.. 207 Mochinaga, N., 8 M od, R., 301 Modlin, R. L., 50 M ohlmann, G. R., 24, 25 Moehlmann, J. G., 124 M ohwald, H., 33 M oller, J., 437 M oeller, K. D., 207 M oeller, M. B., 117 M oellers, F., 209 M oenig, H., 536 M oerman, P., 28, 125 M ossinger, G., 474 M oggi, L., 153, 154, 160, 168 M oilanen, K. W., 537 M ojelsky, T., 418, 455 M olchanova, L. I., 199 M olina, M. J., 137, 139 M olls, W., 195 M olnar, L., 498, 537 M olof, R. W., 8 M omicchioli, F., 49, 58, 302 M onahan, K. M., 9, 139 Monnerie, L., 519 M ontague, D. C., 100 M ontgomery, F. C., 65, 224 M onti, S., 33 M oore, B. C., 134 M oore, C. B., 111, 124 M oore, C. J., 223 M oore, D. S., 120 M oore, P. T., 526 M oores, D. L., 21 M oors, P. W., 157 M oorthy, P. N., 89, 402 M oos, H. W., 135 M‘ora, F., 49 Mioran, H., 157

Author Index M loran, T. F., 139

M[oravcik, M., 531 M orawitz, H., 43 Mloreau, C., 142 M orel, D. L., 583 M.organ, D. J., 21 M organ, D. R., 131 M organ, H. D., 24 M organ, L. A., 24 M organ, T. J., 136 M organ, T. K., jun., 235, 268 Mori, A., 248, 419 M ori, F., 532 Mori, K., 518, 532 M ori, Y., 31, 52, 127, 495 Morikawa, A., 90 M orimoto, J. Y.,170 Morisaki, S., 536 M orita, H., 26, 78 M orita, T., 376 M oritani, I., 185, 255 M oriyasu, M., 173 M orokuma, K., 3, 44, 49, 214, 406 M oron, J., 277, 462, 463 Morozova, I. N., 531 M orris, J. M., 39 M orrison, H., 251, 344 M orrison, M., 74 Morrison, V., 52 M orse, D. L., 180, 570 M orse, J. G., 208 M orse, K. W., 208 M orten, P. D., 128 M ortier, P., 28, 125 M ortola, A. P., 158 M orton, J. R., 208 M oscowitz, A., 7, 16, 198 M oseley, C. G., 59 M oseley, J. T., 204 M osher, 0. A., 25 M osichev, V. I., 172 M oskowitz, J. W., 158 M oskvitina, E. N., 117 Moss, A. Z., 113 Moss, D., 134 M oss, G. P., 171 Moss, R. A., 479 M oss, R. L., 43 M osterd, A., 286, 465 Motsarev, G. V., 107, 361 Moule, D. C., 6, 10 M ourou, G., 31, 66 M sonthi, J. D., 465 Mucha, J. A., 35 Mucha, M., 532 M udry, C. A., 374, 419, 425 M uller, A., 27 Mueller, H., 504 Muinov, T. M., 536 Mukai, T., 270, 290, 322, 327, 458 Mukamel, S., 41, 46, 47 M ukerjee, S. K., 219, 285, 297, 537 Mukherji, S. M., 339 Mukhin, E. N., 200 M uller, D., 63 M uller, E., 455 M uller, H., 32, 56 M uller, J., 180 M ulcahy, M. F. R., 134, 143 M ullik, S. U., 180, 507, 532 M ulliken, S., 71

605

Author Index Mumma, M. J., 24 Namba, K., 516 Munari. S.. 517. 518 Namiki, A., 27 Munemori,* M.,. 148 Napier, G. D. R., 171 Munn, R. W., 197 Naqvi, K. R., 26, 66 Nardelli, G., 4 Munro, I. H.,27, 52, 102 Murachi, T., 420 Narva, D. L., 14 Murahashi. S. I.. 185 Nash, E. G., 247 Murakami,. K., 536 Nash, T., 146 Murata, M., 480 Nasielski, J., 178 Murata, Y., 512 Natarajan, P., 162 Muratov, E. A., 147 Nathan, R. A., 91, 141, 408 Murayama, K., 535 Natsume, M., 380, 388 Murin, A. N., 159 Naus, J., 200 Murofushi, K., 26, 343, 381 Navon, G., 159 Muromtsev, V. I., 516 Nazar, M. A., 123 Murphy, D. P. H., 381 Nazarova, I. G., 200 Murray, R. K., jun., 235, 267, Ndaalio, G., 509 268 Neckers, D. C., 535 Murray, R. W., 408, 420 Nedelec, O., 144 Murrell, J. N., 11 Nedorost, M., 536 Musaev, U. N., 516 Needles, H. L., 536 Musakhanova, S. M., 518 Neeley, C. M., 123 Musgrave, W. K. R., 351, 355 Nefediev, L. A,, 39 Musienko, N. G., 206 Nefedov, 0. M., 192 Muszkat, K. A., 37, 86, 416, Negre, J. M., 144 493 Neilson, G. W., 180 Muto, M., 281 Neilson, J. D., 171 Muzart, J., 233 Nekhoroshev, V. G., 517 Myasoedov, B. F., 172 Nekrasov, L. I., 200 Myersough, V. P., 24 Nelson, H. H., 177 Mylnikov, V. S., 521, 583 Nelson, J. A., 418 Nelson, M. C., 512 Naberezhnykh, R. A., 517 Nembach, K., 584 Nachshon, Y., 145 Nemel, L., 21 Naef, R., 375 Nemodruk, A. A., 172 Nagabhushanam, T., 512 Nemzek, T. L., 50, 68 Nagaev, V. B., 210 Nenner, I., 22 Nagaeva, M. L., 21 Neporent, B. S., 31, 39 Nagahiro, I., 510 Nesmeyanov, A. N., 181, 189 Nagai, Y., 206, 471 Netzel, T. L., 11, 60, 66, 579 Nagakura, S., 19, 26, 38, 56, Neumann, G., 536 59, 75, 78, 81, 108, 121 Neumuller, 0. A., 411 Nagamatsu, T., 275 Neupert, W. M., 134 Nagase, S., 49 Neusser, H. J., 19, 101, 108 Nagayama, M., 270 Neuwald, K., 76, 421 Nagorsnik, E., 157 Newkome, G., 6, 62 Nahhimovskaya, L. A., 13 Newlands, M. J., 94, 206, 420 Nair, M. G., 318 Newton, M. G., 483 Naito, T., 256, 382, 383, 425 Newton, M. O., 49 Nakadaira, Y., 322, 411, 466, Newton, R. P., 368, 397 467 Neywick, C. V., 242, 494 Nakagawa, M., 419, 431, 435, Neznaiko, N. F., 200 504,537 Ng, H. Y., 464 Nakahira, T., 90, 214 Nguyen, N., 124 Nakai, H., 288, 444 Nguyen, T., 125 Nakajima, A., 55 Nibler, J. W., 35 Nakajima, K., 382, 425 Nicholls. C. H.. 71. 520 Nakajima, T., 7, 45 Nichols,'A. L., '49 ' Nakamura, H., 48 Nichols, R. W., 9 Nakamura, K., 531 Nichols, W. C., 405 Nakamura, M., 509 Nicholson, B. K., 180, 189 Nakamura, S., 154, 509 Nickel. B.. 29. 87 Nakamura, T., 360, 431 Nickols, D. B:, 124 Nakamura, Y.,518, 532 Nicodem, D. E., 135 Nakanishi, H., 513 NIcol, M. F., 43 Nakanishi, K., 411 Nicolet, M., 138 Nakano, Y., 261, 382 Nicolson, S., 361 Nakase, Y.,516 Nieberl, S., 463 Nakata, J., 75 Nieh, E., 142 Nakato, Y., 209, 569 Nielsen, P., 515, 533 Nakaya, T., 509 Nielsen, U., 28 Nakayama, T., 208, 514 Niimon, K., 33, 86 Nakazawa, S., 495 Niki, H., 131, 142 Nalivaiko, E. I., 536 Nikiforov, A., 215

Nikisha, V. V., 210 Nikitin, L. Ya., 518, 536 Nikolaev, V. A., 482 Nikol'skii, V. G., 518 Nikulina, L. E., 533 Nill, K. W., 131 Nilles, G. P., 537 Nilsson, R., 407 Ninomiya, A., 367, 537 Ninomiya, I., 256, 382, 383, 425 N i E W . S., 134 Nishi, K., 536 Nishi, N., 33, 35, 86 Nishida, S., 240, 481, 518 Nishihara, R., 510 Nishii, M., 516 Nishijima, Y., 337, 338 Nishikawa, S., 5 Nishikawa, T., 537 Nishikubo, T., 510, 514, 5 15 Nishimura, T., 486 Nishimura, Y;, 25 Nishio, T., 230, 231, 444 Nishiwaki, T., 367, 431 Nitta, M. 283 Nitz, S., 420, 537 Nitzan, A., 406 Njvard, R. J. F., 374 Nizamidino, S., 533 Noack, R., 389, 428 Nocchi, E., 165 Noda, H., 230,444 Noth, H., 132, 205 Nogales, A., 116 Nogami, T., 510 Noguchi, T., 526 Nolte, C. R., 195 Noort. M.. 35. 198 Norbeck, J., 7. Norcross, D. W., 21 Nordblom, G. D., 504, 537 Norden, B., 12, 38 Nordholm. J.. 46 Norin, T.,'459 Norman, R. 0. C., 143 Norris, J. R., 35, 200 Norris, R. D., 419 Norris, W. P., 116 Norrish, R. G. W., 532 North, A. M., 519, 520 Northington, D. J., 266 Norton, J. R., 36 Norval, E., 32 Nose, T., 208, 514 Nothe, D., 180 Nott, P. R., 15 Nouk, K. N., 266 Novak, F., 537 Novaro, M., 125 Noyes, R. W., 134 Noyori, R., 262, 331 Nozaki, H., 262 Nuernberg, H. W., 156 Nuller, T. A., 581 Nunome, K., 517 Nyitrai, 2. S., 532 Nyui, T., 281 Oakes, T. R., 367 Oberdier, J., 312 Obi, K., 52 O'Brien, D. H., 317, 467 O'Brien, R. J., 148

Author Index

606 O’Brien, T. P., 196 Ochiai, H., 237 Ochs, F., 13, 32 Ocskay, G., 532, 535 Oda, M., 290, 415 Odaira, Y., 218, 252, 360 Ode, F. A., 342 O’Dea, J., 481 O’Donnell, J. H., 535 Oe, K., 388,458 Oelkrug, D., 166 Ofenberg, H., 374 Offhaus, E., 180 Ofran, M., 51 Ogasawara, M., 290, 458 Ogata, N., 510 Ogata, Y., 149, 228, 286, 354, 433 Ogawa, M., 144, 145, 318 Ogawa, T., 25 Ogilvie, J. F., 94, 420 Ogilvie, K. K., 447 Oginets, V. Y.,‘ 32 Ogiwara, H., 288, 444 Ogiwara, Y., 512, 518, 533 Ogloblin, K. A., 493 Ogo, Y., 511 Ogorodnikov, S. N., 21 Ogryzlo, E. A., 141, 142, 408

Ohashi, H., 532 Ohashi, M., 366, 431 Ohi. F.. 468. 533 Ohfoff,‘G., 2 5 5 Ohmori, T., 457 Ohnishi, S., 518 Ohnishi, T., 209, 569 Ohnishi, Y., 331 Ohno, A., 241 Ohno, M., 450 Ohno, T., 170 Ohru, Y., 5 Ohsawa, A., 320, 459 Ohta H 404 419, 445, 501 Ohto: Y:: 389: 429 Ohyoshi, A., 161, 173 Oishi, T., 455 Oiwa, M., 509 Oiyne, T., 236 Ojanpera, S., 89, 398 Oka, T., 166 Okabe, H., 100, 131 Okamoto, J., 510, 517 Okamoto, K., 520 Okamoto, T., 318,424 Okamura, K., 526 Okamura, S., 510, 516 Okamura, T., 52 Okamura, Y., 222 Okawa, K., 464 Okawara, M., 509, 568 Okazaki, R.,273, 464 Okerholm, R. A., 498 Okhrimenko, B. A., 206 Oki, Y., 532 Okimoto, T., 507 Okinoshima, H., 206 Okumura, K., 420 Olafson. B. D.. 362 Olaj, O.’F., 510 O’Leary, T. J., 132 Oleson, J. A., 259, 404, 448 Oliveros-Descherces, E., 346, 437

Page, A. G., 172 Paglietti, G., 423 Pagni, R. M., 313, 478 Paillous, N., 393, 427 Pailthorpe, M. T., 71, 520 Painter, L. R., 15 Pakshina, E. V., 200 Pakula, B., 31 Pal, M. K., 407, 536 Paldus, J., 6, 7 Palei, I. V., 158 Paleocrassas, S. N., 563 Palladino, N., 528, 529 Palma, G., 516 Palmer, G. E., 475 Palmer, R. E., 8, 122 Palmer, T. F., 59 Palmieri, P., 3 Pan, Y. K., 139 Panchenokov, G. M., 516 Pancoast, T. A., 185 Panda, S. P., 515 Pande, M. C., 134 Pang, K. D., 139 Paniago, E. B., 170 Pannell, K. H., 188 Pant, D. D., 173 Pantos, E., 52 Papic, M. M., 134 Paquette, L. A., 272, 315, 326, 446,473 Paraskevopoulos, G., 139 Parello, J., 346, 437 Parenti, R. R., 39 Parham, J. C., 404,435 Pariiski, G. B., 533 Parish, W. W.. 239 Park, J., 536 . Park, J. H., 137 Park, S.-M., 171 Parkanyi, C., 159,459 Parkash. V. E. D.. 21 Parker, J. G., 141. Parker, J. H., 124 Parkinson, W. H., 21 Parkinson, W. W., 536 Parlar, H., 331, 332, 420, 537 Parmenter, C. S., 11 Parola, A,, 89, 398 Parrington, B. D., 330 Parshall, G. W., 175 Parshin, G. S., 173 Parson, G. H., 70 Parson, W. W., 577, 579 Parsons, G. H., 89, 398 Parthasarathy, M. R., 421 Pasal’skii, B. K., 536 Pasechnik, V. I., 201 Pasha an D. N., 259,403 Pashcgenko, V. Z., 39 Pashman, K. A., 162 Pass, S., 142 Pasteris, R. J., 330 Pastrana, A. V., 143 PastmBk, J., 39 Paszner, L., 518 Paszyc, S., 202 Pac, C., 339, 362, 364, 447 Patchornik, A., 440 Pace. P. W.. 126 Patel, B. M., 172 Padhye, M..R., 22 Patel, G. N., 518, 536 Padrick T. D., 8 Padwa, 229,236,259, 323, Patel. N. K.. 210 324. 325. 347. 348. 371. 403. Patrick, T. B., 481 422; 423; 429; 430 ‘ . Patterson, L. F., 10 Patterson, L. K., 73, 111, 576 Pagano, A., 149

Olmsted, J., 409 Olsen, K. J., 203 Olson, K. R.,168 Olson, R. E., 49 Olszyna, K. J., 148 Omori, T., 252 Omote, Y., 444 Onda, M., 438 O’Neal, H. E., 116 O’Neill, T., 516 Ong, E. L., 16 Ono, I., 369,404,434,450 Ono, S.,43, 526 Ooi, T., 529 Oosterhoff, L. J., 25 Op Het Veld, P. H. G., 372 Oppenheimer, M., 4 Oraby, W., 516, 517 Orahovats, A., 348, 430 Orbach, N., 38, 67 Orda, V. V., 107 Orger, B., 107, 357 Orlandi, G., 49, 58 Orlando, C. M., 297 Orloff, A., 195 Orlov, E. B., 529 Ormerod, R. C., 23,47, 129 Ormond, S., 46 Ors, J. A., 92, 408, 409 Osawa, T., 525 Osborn, C. L., 36 Oseledchik, Yu. S., 38 O’Shea, D. C., 129 Oshima, K., 517 Oshima, Y., 8 Osipov, 0. A,, 170 Os’kin, V. S., 517 Ostertag, R.,26 Osugi, J., 45 Ota, K., 26, 343, 381 Oto, G., 41 1 Otomegawa, E., 514 Otsu, T., 508 Otsuji, Y., 370, 402, 451 Otsuka, K., 90 Otsuka, S., 153 Otsuki, T., 296 Otto, H., 156 Ottolenghi, M., 38, 67, 83, 203, 304 Ouannes, C., 428 Ouchi. A.. 157 Ouchi; T.,-509 Oudshoorn van Veen, J., 293 Ovchinnikov, V. G., 21 Ovechkin. A. E.. 25 Owen, C.’S., 68 ’ Owen, E. D., 532 Owens, W., 324, 325 Owers, R. J., 362 Oxford, A. W., 216 Ozawa, H., 364, 566 Ozawa, K., 464 Ozin, G. A., 175, 180 Ozorio, A. A., 387, 428

k.,

607

Author Index Patterson, T. A., 22 Patty, R. R., 131 Pauson, P. L., 195 Pavlik, J. M., 330 Pavlik, J. W., 351 Pavlopoulos, T. G., 26, 27 Pavlova, N. R., 522 Pavlova, S. A., 533 Pavlyukhin, Y. T., 159 Pawelczyk, E., 420, 537 Pawlaczyk, J., 498, 537 Payne, M. G., 125 Payne, S. J., 28 Payne, W. A., 140,201 Pdungsap, L., 180, 182 Pearce, R., 218 Pearson, D. S., 518 Pearson, J. M., 515 Pebay-Peyroula, J., 125 Pechukas, P., 46 Pecker, J. C., 134 Pedersen, C. L., 436 Pedersen, C. T., 458 Pedersen, J. B., 36, 37 Pedley J. B., 206 Pedull;, G. F., 468 Peek, M. E., 437 Peet, J. H. J., 181 Peeters, H. K., 509 Pellegatti, A., 7 Pendlebury, M. H., 324 Penkett, S. A., 149 Penny, A. L., 209 Penzhorn, R. D., 148 Perec, L., 516 Pereira, L. C., 78 Peretti, P., 69 Pereyre, J., 403 Perez, S. R., 92, 408, 409, 420 PCrez-Bustamante, J. A., 32 Pkrez Conde, C., 32 Perpshov, V. I., 510 Penasamy, N., 95 Perin, F., 376, 461 Periozi, D., 93 Perkampus, H. H., 32, 378, 427 Perkey, L., 123 Perkins, R. R., 349 Perret, L., 125 Perreten, J., 313 Perretti, P., 89 Perrin, C. L., 230 Perrin-Lagarde, D., 9 Perry, B. E., 146 Perry, J. S 385 Persky, A.;’134 Personov, R. I., 31,42,64, 199 Perst, H., 262 Perutz, R. N., 176 Pesaro M 262 Pete, JI-P.,”224, 233, 259, 406, 503 Peter, L. M., 73 Petennann, J., 536 Peters, A. T., 25, 537 Peters, L. M., 32 Petersen, A. B., 121 Petersen, J. D., 153, 168 Peterson, C., 202 Peterson, E. R.,91 Peterson, 3. R., 204 Peterson, L. M., 124

Petersson, G. A., 21 Petit, R., 94, 353 Petrenko, I. I., 210 Petrosyan, R. A., 532 Petrukhno, L. A., 516, 517 Petrus, A. A., 513 Petryaev, E. P., 202 Petsol’d, 0. M., 196 Pettersen, R. C., 186 Pettit, R., 48, 188 Petty, G., 122 Petukhov, G. G., 191 Peyerimhoff, S. D., 5, 6, 49, 3n1

LUL

Pfab, J., 10, 118 Pfeiffer, G. V., 202 Pfeiffer, M., 38 Pfister, G., 526 Pfoertner, K.-H., 399, 404, 428.451 Phillion, D. N., 43 Phillips, C. R., 145 Phillips, D., 24, 102, 104, 105, 106, 115, 117, 522, 532 Phillips, D. E., 28 Phillips, G. O., 522, 533 Phillips, L., 324 Phillips, L. F., 28, 38, 127, 128 144 PhilliGs, R. F., 146 Phillips, W. V., 268 Philpott, M. R., 13, 43 Phipps, J. R., 425, 446 Pian, C. C. H., 207 Piatrik, M., 518 Pichon, F., 145 Pickard, D. R.,488 Pickering, M. W., 488 Pierce, J. B., 218 Pietronero, L., 7 Pietrzykowska, I., 452 Pilkiewicz, F. G., 479 Pillai, P. K. C., 526 Pjllai, V. N. R., 377, 427 Pilz, D., 517 Pincock, R. E.,349 Pindzola, M. S.,17 Pinnington, E. H., 4 Pinsky, M. L., 92, 409 Piper, L. G., 125 Pismannik, K. D., 536 Pis’mennaya, M. V., 537 Pis’mennyi, V. D., 147 Pistara, S., 173, 423 Pittock, A., 134 Pitts, J. N., jun., 139, 140, 148,407 Placek. J.. 536 Placucci, G., 468 Planckaert, B., 364,402,450 Plantenga, F. L., 25 Platbrood, G., 177, 404 Plaunik, G. W., 516 Plepys, R. A., 333 Plimmer, J. R., 331, 401, 441 Plummer, B. F., 72, 462 Plummer, B. J., 338, 341 Plunkett. A. 0.. 427 Pocuis. A. V.. 7 1 . 112. I15 Poddubnyi, 1.- Ya., 518 Poe, A. J., 175 Pohjonen,. Pohjonen, M. L., 115 Poindexter, G. S., 348, 405 Pokholok, T. V., 531

Pokorny, M., 536 Poland, H. M., 145 Polanyi, 3. C., 123 Poliakoff, M., 174, 176, 480 Polikanova, L. F., 515 Polikarpov, V. V., 516 Politenkova, G. G.., 134 Pollard, G. E., 331, 537 Poller, R. C., 516 Polles, J. S., 200 Polley, J. A. S.,235 Poloni, M.,435 Polovsky, S. B., 335, 406 Polster, J., 14 Pommier, J.-C., 207 Ponomarev, A. I., 517 Ponomarev, A. N., 5 16 Ponsiglione, E., 422 Ponte-Goncalves, A., 33, 90, 198 Pool, C. R., 468 Poole, J. A., 51 Pooranamoorthy, R.,377 Popielski, S. E., 157 Popkov, A. V., 170 Popov, K. R., 13 Popovich, M. P., 121 Popravko, T. S., 531 Portanova, R., 173 Portella, C., 406, 503 Porter, G., 26, 21, 32, 66, 73, 84. 104. 111. 200 Porter, G: B., ’116 Porter, J. J., 537 Porter, N. A., 37, 215, 470 Porter, R. F., 204,205 Porter, R. N., 4 Portnoy, N. A., 512 Pos. H. J. T.. 465 Pospisil, J., 535 Post, M.F. M., 13, 54 Postnikov, L. M., 533 Potashnik, R., 304 Pottier, R., 93, 408 Pouliquen, J., 94, 95, 353, CL3

JVA

Poulsen, J. C., 8 Pournier, F., 317 Pouzar, V., 454 Powell. J. A.. 181 Power,. A. J.,’ 534 Powers, T. R., 23, 129 Pownall, H. J., 421 Poyner, W., 532 Pozdeeva, R. M.,516 Poznyak, A. L., 159, 165 Pozzi. V.. 528 Prabhu, A. V., 290 Prabhu, K. V 283 Praefcke, K.,”286, 383, 461, 495.496.491 Prais,’M. -G.y 45, 102 Prakash, D.. 318 Prasad, P., 13 Prasad, P. N., 32 Prasad, S. S., 134 Pratt, A. C., 197 Pratt. D. W.. 27. 35 Fravdov, A. ’M.,’ 122 Preston, K. F., 36, 208 Preston, W. E., 353 Prjce, D., 50, 99 Prtce, J. M.,511 Price, T., 520

608 1Ranade, A., 156,475 1Ranalder, U. B., 26 1Ranaweera, R. P. R., 530, 535 1Ranby, B., 527, 531, 534 1hank, W., 486 1Rankin, C. T., 534 1Ranney, G., 224 1Ranson, P., 69, 89 1Rao, C. N. R., 12 1Rao, D. V. K., 9 1Rao, K. N., 517 1Rao, M. I. P., 9 1Rao, M. M., 159 1Rao, P. T., 9 1Rao, T. N., 417 Rapoport, V. L., 32 Rapp, W., 46 Rasmussen, P. W., 336 Rasmusson, G. H., 281, 501 Rau. H.. 31. 64 1iausch,’D. J., 354 1Rausch, M. D., 175 1Paymonda, J. W., 10 1Rayner, D. M., 83 1haytch, R. E., 268 1haz, B., 125 1Razavi, A., 195 1Razi Naqvi, K., 26, 66 1Razumova, I. K., 173 1Razumova, T. K., 31 1Razuvaev, G. A., 15 1Razvina, T. I., 171 1Read, F. H., 44,.135 1Reardon, E. J., jun., 305 1Rebafka, W., 299 1Rebane, V. N., 43 1Rebbert, R. E., 98 1Rebell, J., 474 Quack, G., 532 1Reber. J. F.. 208 Ouarderer. G. J.. 148 Reck, -R. A.; 131 Quarg, G.; 508 . Redfield, D., 580 Quigley, G. P., 124 A. E., 138 Redpath, Quigley, J., 234 Quina,F.H., 68,223,336,338, Redpath, J. L.,125 Reed. J. L.. 164 446 Reed; K. J‘, 22 Quinkert, G., 216 Rees, C. W., 437 Quinn, M. J., 38 Reeves, E. M., 134 Reeves, R. R., 145 Rabalais, J. W., 21 Regitz, M., 482 Rabek, J. F., 531, 534 Regulski, T. W., 532 Rabenold, D. A., 519 Rehak. V.. 537 Rabinovitch, B. S., 99 Rehorek, D., 157 Rackwitz. R.. 21. 122 Reich, S., 536 Racz, B.,‘31 . . Rejch-Rohrwig, P., 184 Rae, A. G. A., 122 Reid, E. S., 66 Rae, D. R., 472 Reid. W. J.. 116 Raff, L. M., 134 Reimann, I:, 529 Rai. D. K.. 7 Reinders, F. J., 35 Rajikan, J.; 32, 78 Reine, A. H., 512 Raju, N. R. K., 417 Reinfried, R., 489 Rakhlin, V. I., 207, 465 Reinhardt, J., 145 Rakov, A. S., 170 Reinhardt. W. P.. 21 Ralchenko, V. I., 172 Reinhoudt, D. N:, 449 Raleigh. J. A,. 223 Reinke, D., 10 Ram,-$, 11 ’ Reisch, J., 428, 432, 456, 457, Ramakrishna, B. L., 9 503 Ramamurthy, V., 279, 280, Reitman, L. N., 334 325 Rempp, P., 519 Rama Rao, K. U. S., 125 Renner, C. A., 95, 102, 562 Ramaswamy, K., 42 Rennert, J., 534 Ramdas. P. K., 384,440 Rentzepis, P., 43, 60, 117, 579 Ramirez, F., 208 Rescigno, T. N., 21 Ramsay, D. A., 10 Resnick, B. M., 258 Ramsay, G. C., 83, 392 Retallack, R. W., 490 Ramsey, B. G., 206, 533

Prinn, R. G., 137 Prins, W. L., 459 Prinzbach, H., 313, 326 Pritchard, D., 17 Pritchard, G. O., 116 Pritula, N., 7, 15 Proberb, R. J., 491 Procaccia, I., 48 Prochorow, J., 32, 75 Prock, A., 43 Proehl, G. S., 403 Proskuryakov, I. I., 200 Prot, T., 14 Prota, G., 422 Protiva, J., 421 Prout, K., 178 Prutz, W. A., 95 Pryde, A., 189 Przybyla, R. L., 518 Pshezhetskii, S. Y.,516 Pui, D. Y. H., 149 Puko, R. A., 171 Pullen, K. M., 491 Puri, S., 417 Purnell, J. H., 134 Pusey, P. N., 519 Pushkina, L. L., 369 Pusset, J., 58, 269, 316 Pustoshnyi, V. P., 526 Put, J., 75, 246, 513 Putman de Lavareille, N., 520 Puza, M., 111,385 P’yankov, G. N., 518 Pyle, J. A., 137 Pyykko, P., 7

Author Index Retio, M., 342 ReGschnick, R. P. H., 11, 110 Reucroft, P. J., 582 Reynolds, G. A., 31, 67 Reynolds, R. N., 318 Reynolds, S. D., 148 Revinskii. Yu. V.. 96 Rez, I., 39 Rhodes, W., 41 Ricci, R. W., 73, 171 Rice, J. R., 188 Rice, S. A,, 41, 48, 102, 107, 506 1Xich. D. H.. 439 1Xich; S., 149 1Xichards, J. A., 193 1Xichards, J. H., 159 1iichards, R. W., 517 1iichards. W. G.. 6 1iichardson, J. H:, 22, 124, 184 1iichardson, W. H., 224 1Xichtol, H. H., 71 1Xidley, B. A., 131 1iidley, J. E., 7 Iiied, W., 344 1Xigaud, P., 137 1iigaudy, J., 414 1higgin, M., 99 1Xinck, R., 132, 205 1Xing, H., 187 1Xingler, A., 42 1Xingsdorf, H., 536 1Rio, G., 415 1hisi, S., 420 1Ristac P., 14 1Ritke,’D. N., 141 1Ritscher, J. S., 317, 352 1Ritter, J. J., 132, 134, 205 1Rivas C., 238 1Riveti, D. E., 64, 93 1Riviere, M., 346, 427, 437 1Rix, C. J., 193 1Robbins J. D., 310 1Roberts,’B. W., 195, 281, 494 1Roberts, P. J. W., 148 1Robin, M. B., 113, 120 1Robinson, E. A., 303 1Robinson, G., 149 1Robinson, G. W.,14, 31, 41, 44, 64 1Robinson, J. W., 129, 131 1Robinson, P. H., 580 1Roche, A. L., 4 1Roche, T. S., 165 1Rockett B. W., 181, 532 1Rockle;, M. G., 24, 103, 104, 108, 579 1Rodenhorst, R. M., 348,422 1Rodgers, T. R., 330 1Rodina, L. L., 483 1Rodionov, A. N., 204 1Rodriguez-Hahn, L., 299 1Roebber, J. L., 10 1Roeggen, I., 3 1Roesch, N., 158, 170 1Roeske. R. W.. 439 1Roeterdink. F.;435 Rogers, J., -129Rogers, N. R., 264 Rogers, S. J., 419 Rogozhin, K. L.,204 Rohbock, K., 196 Rohmer, M. M., 8, 181 Rojas, D. H., 406

609

Author Index Rol, P. K., 4 Romanov, V. F., 159 Romanuk, M., 219 Romo, J., 299 Roncin, J., 9 Ronfard-Haret, J. C., 536 Roof, A. A. M., 242, 493 Rophael, M. W., 157 Rosan, A., 188 Rose, J. B., 7 Rose, T. L.,23, 47, 101, 129 Rosen, D. I., 142 Rosen, J. D., 537 Rosenblum, M., 188 Rosenfeld, T., 83 Rosenfield, J. S., 7, 16 Rosenkrantz, H. J., 37 Rosenthal, D., 240 Rosenthal, I., 93, 159, 535 Ross, D. A., 520 Ross, I. G., 15 Rossi, C., 517 Rossi, R., 181, 191 ROSSO, P. D., 312 Rostas, J., 28 Rostasova, O., 536 Roth, H. D., 37, 230, 398, 48 1 Roth, P. M., 148 Roth, W. R., 354 Rothenberg, S., 6, 49 Rother, W., 193 Rothman, W., 348 Rouse, R. E., 519 Rousseau, D. L., 4, 17 Rousseau, Y., 121, 495 Rousset, Y., 69, 89 ROUX,F., 71 Rowan, N. S., 164 Rowe, C. A., 583 Rowland, F. S., 137, 138, 139, 420 Rowley, A. G., 488 Roy, J. K., 90, 196 Rozanel'skaya, N. A., 208 Rozenberg, V. R., 107, 361 Rozenblyum, N. D., 517 Rtischchev, N. I., 192, 368, 396 Rubaszewska, W., 402 Rubin, L. B., 39 Rubinson, M., 406 Rubinstein, M., 440 Rubtson, S. N., 536 Ruden, R. A., 230 Rudin, A., 536 Rudolph, H., 216 Ruge, B., 247, 480 Ruggerio, R., 422 Rumyantsen, 3. M. R., 38 Rungwerth, D., 461 Russell, B. R., 10 Russell, C. R., 497 Russell, K. E., 534 Russell, R. A., 324, 501 Russell, R. K., 315 RUSSO,S., 516 Russwurm, G. M., 131 Rust, J. B., 511 Rutherford, J. A., 140, 144 Ruzo, L. O., 89, 366, 367, 405, 504, 537 Ryabchikova, G. G., 516 Ryabikov, E. P., 536

Ryabikov, 0. B., 135 Ryabov, A. V., 515 Ryabov, E. A., 205 Rvbin. L. V.. 189 Rybinskaya, 'M. I., 189 Rybny, C. B. 511 Ryder, I. E., 189 Rzad, S. J., 73, 111 Saakyan, A. S., 107 Saari, P. M., 13, 78 Sackmann, E., 33 Sadafule, D. S., 515 Sadeghi, N., 125 Sadovnikova, N. A., 200 Sadykov, M. U., 518 Saeki, M., 365, 445 Safarik, I., 121 Safe, S., 366, 367, 405 Sagiv, J., 11 Sahni, H. V., 537 Said-Galiev, E. E., 533 Saiki. H.. 254 Saile,' V.,*28 Sailer, K.-H., 384, 401, 441 St. John, W. M., tert., 25 Saintout, L., 127 Saito, I., 93, 370, 412, 416, 417. 419. 449 Saito,'K., 327, 403, 432 Saito, S., 242, 494 Saito, T., 369, 450 Saito, Y., 228 Sakai, M., 330 Sakai, S., 508 Sakamoto, H., 572 Sakamoto, I., 178 Sakata, T., 12 Sakota, N., 508, 510 Sakuraba, S., 173 Sakuragi, H., 38, 366, 420 Sakuragi, M., 38, 300 Sakurai, H., 207, 322, 339, 362, 364, 447, 466, 467 Sakurai, K., 111 Sakurai, T., 129, 378 Salares, V. R., 94, 420 Salem, L.,48, 213 Salentine, C. G., 192 Salinovich, O., 124 Salisbury, K., 57, 84, 108, 309,441 Salmon, G. A., 303 Salomon, D., 118 Salomon, J., 159, 451, 499 Salottolo, G. D., 149 Salovey, R., 535, 536 Salpeter, E. E.,134 Saltanov, N., 533 Saltbones, J., 149 Saltiel, J., 59, 80, 303, 316 Salzmann, B. E., 148 Samartsev, V. V., 39 Samatov, A. G., 169 Samedova, T. G., 520 Samitani, M., 108 Sammes, P. G., 285 Samoilov, G. G., 533 Samoilova, A. N., 176 Samokhvalov, G. I., 343 Samson, J. A. R., 21 Samsonov, V. V., 9 Samsonova, L. N., 531 Samuel, C. J., 309, 310

Sanchez, J. P., 326 Sanchez del Rio, C., 125 Sandalls, F. J., 121, 149, 420 Sandemann, R. J., 9 Sandhu, S. S., 193 Sandner, M. R., 36 Sandonal, H., 139 Sandorfy, G., 11 Sanford, E. C., 312 Sanhueza, E., 124, 128, 140, A?O

Sari;: T., 486

Sanovnikova, N. A., 200 Santappa, M., 512 Santhanam. K. S. V.. 95 Santhanam; M., 398,.417 Santini, S., 15 Santus, R., 84, 420 Saperstein, D., 68, 106 Sapezhinski, 1. I., 419 Sapietia, S., 526 Sapunov, V. V., 198 Sarel, S., 186 Sargent, F. P., 38 Sargent, M. V., 371, 381 Saris, F. W., 125 Saritchev, M. E., 39 Sarkisian, G. M., 234 Sartori. G.. 165 Sasahi,'Y.,'533 Sasaki, T., 271, 335, 342, 518 Sassen, K., 131 Sasson, S., 273, 282 Sastre. R.. 527 Sastri,' V. S., 169 Sasuga, T., 518 Sato, E., 407, 465 Sato, G. P., 369, 452 Sato, H., 70, 526 Sato, M., 61, 449 Sato, S., 128 Sato, T., 376, 403, 432, 508 Sato, Y.,288, 444 Satoh, F., 457 Sau, R., 29 Sauer, J., 488, 489 Sauers, R. R., 239, 301 Saunders, D. S., 233, 393 Saunders, J., 261 Sauter, H., 326 Savelev, G. G., 159 Sawada, T., 32, 137 Sawai, T., 537 Sayer, P., 206 Scaiano, J. C., 399 Scala, A. A., 118, 222, 497 Scandola, F., 161, 168, 169, 180 Scandola, M. A., 161 Scarpati, R., 481 Sceats, M., 32, 41 Schaafsma, T., 35, 200 Schaap, A. P., 408,410 Schaap, W., 156 Schaeffer, H. F., tert.. 6 Schaffer, W., 271 Schaffner, K., 213, 214, 259, 260 Schallner, O., 335 Schanda, J., 207 Scharf, B., 44 Scharf, G., 289, 457 Scharf, H.-D., 286 Schauble, J. H., 239

Author Index

610 Schawlow, A. L., 17, 126 Schecter, H., 59 Scheer, H., 35, 200 Scheffer, J. R., 290 Scheidt, W. R., 196 Scheller, K., 142 Schellman, J. A., 43 Schenck, G. O., 237, 333, 41 1 Schenk, H., 4 Schepper, J. R., 81 Scheps, R., 48, 102 Scherz, A., 35, 200 Schexnayder, M. A., 263,267, 268,472 Schiavone, J. A., 25, 110 Schiebel, A. H., 385 Schiess, P., 319 Schieve, W. L., 49 Schiff, R., 140, 143 Schiller, J. E., 404 Schlag, E. W., 19, 101, 108 Schlesinger, S. I., 513 Schlessinger, J., 16 Schloman, W. W., 72, 338, 431,462 Schlossberg, H. R., 39, 132 Schlosser, M., 470 Schmeltekopf, A. L., 139 Schmelzer, A,, 8 Schmid, G., 193 Schmid, H., 310, 348, 429, 430, 446,470 Schmid, U., 348,429 Schmidberger, R., 33, 86 Schmidt, E. K. G., 249 Schmidt, H., 36, 86, 271 Schmidt, J., 34, 35, 36 Schmidt, J. F., 123 Schmidt, U., 215, 497 Schmidt, W., 475 Schmidt-Bleek, F. K., 128 Schmidtke, H. H., 153, 156 Schmitz, A,, 483 Schmoranzer, H., 24 Schnabel. W., 531, 534 Schneider, B.; 4 Schneider, M., 193, 473, 4.74 Schneider, S., 31, 54 Schnepp, O., 16 Schoeler, U., 15, 584 Schoellnhammer, G., 370 Schoenberg, A., 374Scholl, M.-J., 415 Scholl, P. C., 401 Scholler, D., 406, 503 Schore, N. E., 33, 63, 116 Schouler, M. C., 36, 86 Schrader, L., 356 Schrader, U., 196 Schrauth, T., 230 Schreiner, A., 16 Schreiner, S., 84, 407, 537 Schroeder, M. A., 178, 316, 468 Schroeter, S. H., 302 Schroth, W., 292 Schuchmann, H.-P., 76,421 Schuetz, R. D., 367, 504 Schug, J.-C., 49 Schuh, M., 106 Schuler, R. H., 10 Schulman, S. G., 14, 64 Schulte, K. W., 7

Schulte-Frohlinde, D., 393, 215, 274, 405, 418 Schulten, K., 8, 60 Schultz, A., 126 Schultz, A. G., 261, 381, 461 Schulz, D., 188 Schulz, G. J., 22, 25 Schulze, R., 137 Schumacher, H.J., 124, 208 Schurath, U., 28,131, 142,144 Schuster, D. I., 83, 258, 272, 283, 391 Schuster, G., 94, 353, 531 Schuster, J. J., 149 Schutt, J. B., 536 Schutyser, J., 244 Schuyler, M.W., 11 Schwarz, F. P., 131, 197 Schwartz, H. L., 8 Schwartz, J., 147 Schwartz, S. E., 145 Schweig, A., 7, 271 Schwentner, N., 28 Schwertfeger, W., 334, 446 Schwerzel, R., 37 Schwetlick, K., 389, 428, 461 Schwing-Weill, J., 157 Scorer, R. S.. 148 Scotney, A., 531 Scott, A. I., 223, 411, 531 Scott, D., 206, 481, 537 Scott, G., 528, 530, 531, 535 Scott. G. W.. 36. 61. 83. 117 Scott; M., 78 . . ‘ Scott, P. B.. 129 Scribe, P., 312 Scriven, E. F. V., 488 Scullman, R., 28 Sealy, R. C., 143, 395 Seamans. L.. 16. 198 Sears, A: B.; 268 Sebayashi, T., 149 Seeman, J. I., 268 Segal, G. A., 5 , 48, 202 Seguchi, T., 516, 518 Seiber, R. P., 536 Seibert, M., 579 Seifert, K.-G., 395 Seifert, K. L., 38 Seinfeld, J. H., 148, 149 Seitz, H., 142 Seitz, W. R., 95 Seki, K., 13, 369, 451 Sekiguchi, S., 389, 429 Sekine, Y.,320, 459 Selby, K., 142 Seleznev, V. G., 122, 123 Selinger, B. K., 15 Seliskar, C. J., 84 Sellers, R. M., 535 Sem, G. J., 149 Semenov, V. P., 493 Semenova, I. V., 533 Semerano, G., 153 Senda, S., 426 Sendyurev, M. V., 396 Senrui, S., 516, 517 Senum. G. I.. 145 Septe B., 189 Sepuiha, R. C., 147 Serebryakov, E. P., 322, 343, 45 3

Sergeeva, G. I., 172 Sergey, A., 137

Sergio, R., 475 Serlemibos, A. T., 134 Serve, M. P., 476,477 Servedio, F. M., 116 Serydyukov, A. N., 16 Sethi, D. S., 146 Sethuram, B., 417 Setkina. V. N.. 178 Seto, s.; 75 ’ Setser, D. W., 119, 146, 471 Sevchenko, A. N., 173, 196, 197 Shaburov, V. V., 515 Shadrin, 0.P., 41 Shagisultanova, G. A., 159,169 Shah, N. P., 9 Shai, C. M., 556 Shaikhrazieva, S. H., 357 Shaitanova, A. N., 536 Shakhverdov, T. A., 153 Shama, S. A., 457 Shamma, M., 503 Shamonina, N. F., 516 Shand, D. J., 124 Shane, E., 144 Shani, A., 310, 384 Shank, C. V., 66 Shapiro, E. L., 486 Shapiro, M., 47 Shapiro, S . L., 66 Shaposhnikova, M. G., 200 Sharipov, G. L., 173 Sharma, B. K., 158 Sharma; D., 11 Sharma, D. K., 60, 66,421 Sharma, 0.P., 13 Sharma, S. N., I 1 Sharma. T. D.. 490 Sharnoff, M., 35 Sharp, G., 206 Sharp!ess, R. L., 121, 145, 146 Sharyi, V. M., 208 Shashidhar. M. A.. 31 Shatter, G.’W.. 262 Shavitt; I., 4 Shaw, R. F., 583 Shay, J. L., 580 Shchegoleva, N. A., 200 Shchelov. R. N.. 173 Shcherinskii, V. ‘L., 159 Shchipakina, 0.A., 170 Shechter, H., 492 Sheehan, J. C., 216 Sheffner, K., 81 Sheikh, M. A., 417 Sheinker, A. P., 516, 517 Sheinson, R. S., 141, 413 Sheka, E. F., 13 Shelekhov, N. S., 527 Shelimov, B. N., 210 Shelokneva, L. F., 191 Shen L., 64, 472 Shenhrick, T. V., 4 Shenton, F. L., 326 Shepelevich, V. V., 16 Shepherd, T. M., 171 Sheridan, J. R., 25 Sheridan, P. S., 165, 168 Sherwood, A. G., 123 Shetlar, M. D.,49,67,213,274, 451,498 Shettle, E. P., 137 Sheverdina, N. I., 204 Shibahara, S., 450

Author Index Shibata, T., 25 Shibuya, E.,26 Shibuya, T. I., 7 Shida, T., 203 Shiga, T., 516 Shigemitsu, Y., 360 Shigorin C. N., 43 Shigorin: D. N., 42, 204, 299, 396 Shih, C. N., 320 Shiho, M., 13 Shilov, V. B., 31 Shima, K., 286 Shimada. S.. 510 Shimakuia. N.. 45 Shimazu H 4-16 Shimizu ’A.1’360 Shimizu: H., 458, 518 Shimizu. M.. 518 Shimizuj N.,’240, 481 Shimizu, S., 517 Shimizu, Y., 518 Shimoe, O., 43 Shimokawa, T., 537 Shimozato, Y.,75 Shine, H. J., 390, 442 Shinoda, K., 124, 420 Shinohara, A., 383, 425 Shinohara, K., 529 Shinozaki, H., 190, 254 Shinsaka, K., 95 Shinzo, K., 401 Shiotsubo, M., 529 Shipsey, E. J., 49 Shirasaki, H., 394 Shirgeon, R. J., 14 Shirmada, S., 536 Shirota, Y., 364, 510, 520 Shirota. Y. T.. 75 Shirotani, I., 13 Shizuka, H., 376,389,429,488 Shkirman, S. F., 197 Shkuropatov, A. Y.,200 Shlyapintokh, V. Ya., 522, 527. 531 Shlyapnikov, G. V., 23 Shoed, G. M., 38 Shoji, Y.,415 Shortridge, R., 94, 119, 123 Shosenyi, H., 536 Shotkin, K. M., 149 Shrubovich, V. A., 515 Shudo, K., 318,424 Shugar, D., 275,452, 501 Shugarman, S. S., 313 Shurpik, A., 239 Sibley, R.,43 Sicre, J. E., 124, 208 Siddall, J. B., 279, 415 Sidebottom, H. W., 119, 471 Sidhu, K. S., 417 Sidky, M. M., 374 Sidman, J. W., 62 Sidorova, L. P., 517 Siebert, D., 148 Siebrand, W., 41, 49, 58 Sjeck, L. W., 146, 511 Siegel, J., 161 Siegel, M.W., 22 Siegman, A. E., 43 Silberbach, H., 24 Silfvast, W. T., 122 Silk, P. J., 504 Silva, E., 420

61 1 Silver, D. M., 48 Silver, J. A.. 134, 142 Silverman, J., 518 Silvers, A. E., 528 Silvers, S. J., 28, 117 Sime, M. E., 105 Simionescu. C.. 518 Simmoneai, G:, 178 Simmons, E. L., 157 Simmons, T. D., 28 Simon, M. J., 526 Simon, M. N., 134 Simon, T. 0. M., 134 Simonaitis, R., 142, 145, 149 Simonetta, M., 49 Simonov, A. M.,198 Simons, J. P., 23, 47, 118, 122, 144, 145, 201 Simonsen, M. G., 519 Sinanoglu, O., 4 Singer, K., 518 Singer, L. A., 240, 453 Singh, A., 38 Singh, D. R., 11 Singh, G., 380 Singh, I., 362 Singh, M., 490 Singh, R. D., 13 Singh, S. N., 13 Sink, M. L., 4 Sirasiev, A. J., 39 Sirlibaev, T. S., 516 Sirota, A. G., 518, 535, 536 Siuta. G. J.. 387. 428. 475 Sivak, M., 498, 537 . Sivils, G., 514 Skalski, B., 279, 447 Skerbele, A., 202 Skibowski. M.. 28 Skilling, J:, 434 Skinner, K. J., 471 Skoboleva, S., 7, 15 Skorobogatov, G. A., 122,123 Skrlac, W. J., 123 Skutnik, B. J., 4, 518 Slack, W. E., 59 Slade. P.. 123 Slagle, L‘R.,140 Slanger, T. G., 121, 145, 146 Slanrna, Z., 31 Slavchev, I., 518 Slavnova. T. D.. 200 Slegeir, W., 48, 94 Sleptsov, S. E., 173 Slifkin, M. A., 27, 28, 73, 74, 76 Slivinskas, J. A., 536 Slobodetskaya, E. M., 536 Small, R. D., 409, 420 Smalley, R. E., 9 Smalley, R. K., 487 Smardzewski, R. R., 208 Smets, G., 97, 249, 512, 513, 526 Smirnov, A. D., 28 Smirnov, A. M., 516 Smirnov, B. M., 23, 48 Smirnov, L. V., 13 Smirnov, V. A., 96 Smith, A. B., 256 Smith, A. K., 189 Smith, A. L., 4, 28 Smith, D. J. H., 461, 536 Smith, E. M., 480,486

Smith, G., 149, 397 Smith, G. J., 159 Smith, G. R.,207 Smith, J. A., 5 Smith, J. J., 208 Smith, J. M., 511 Smith, J. P., 148 Smith, J. W. M., 145 Smith, L., 339, 363 Smith, P. D., 196, 197 Smith, R. A. G., 479 Smith, R. G., 131 Smith, W. F., 409 Smyth, K. C., 25, 110 Snegov, M. I., 536 Snelling, D. R., 140, 142 Snieckus,V., 423,425,437,503 Snir, J., 43 Snow, R. L.. 4 Snows, W. R., 139 Snyder, J. J., 49, 213 So, S. P., 6 Sochet, L., 136 Soderquist, J. A., 467 Soep, B., 111, 120 Sohar, P., 249, 501 Sohn, Y. S., 182 Sokolenko, V. A., 381 Solarz, R., 24 Soldatenko, A. T., 535 Soloman, J., 273 Solomko, V. P., 515 Solonitsyn, Y. P., 202, 210 Soloveichik, 0. M., 367 Solovev, K. N., 196, 197, 198, 199 Solov’yov, K. N., 33 Soma, M., 35, 198 Somei, M., 380, 388 Sommerdijk, J. L., 31 Sonderquist, J. A., 284 Song, P.-S., 15, 66, 428 Sonoda, A., 255 Sood, R. K 170 Soos, Z. G.1’583 Sorensen, G., 98 Sorensen, T. S., 329 Soria, D., 124 Sorimachi, K., 376 Sorm, F., 219 Sorokin, A. D., 517 Sorriso, S., 15 Sostero, S., 181 Soto, H., 116, 399 Sousa, L. R., 310 Soutar, I., 520 Souto, M. A., 35 Spafford, R., 24 Spagnuolo, C., 201 Speiser, S., 39, 159 Spencer, T. A., 418 Spicer, C. W., 149 Spillane, W. J., 365 3uinner. M. L.. 36 Spirin, Y . L., 311 Spiro, A. G., 31 Spitsyn, V. I., 169, 516, 517 Sporborg, H., 106 Sauire. D. R.. 517 Squire; R. H.; 294 Sreenivasan, A., 518 Srinivasan, K. G., 313, 433 Srinivasan, R., 107, 122, 218, 357, 358, 561

Author Index

612 Srivastava, K. C., 351 355,432 Sroka, W., 4, 145 Staab, H. A., 299 Stacey, D. N., 38 Staemmler, V., 5 Stahel, E. P., 517 Stair, A., 129 Stanford, A. L., 45, 104 Stanko, D., 518 Stanlev. W.. 208. 470 Stanniit, V.; 516; 517,518,s 36 Starenga, D. G., 97 Starner, I. J., 403 Staroverova, L. L., 518 Starr, D. F., 146, 147 Starr, M. A., 28 Starr, W. L., 135 Stary, F. E., 420 Stasicka, Z., 157 Stavaux, M., 458 Stebbings, R. F., 21 Stedman, D. H., 131 Steel, C., 117 Steen, H. B., 63, 84 Steenken, S., 215, 393 Steer, R. P., 29, 121, 495 Steets, W., 38 Stehlik, D., 35 Steiger. R.. 208 Steiii, A., 51 Stein, G., 51, 172, 352, 564 Stein, N. M., 83, 392 Steinberg, I. Z., 16, 43 Steiner R. P., 326 Steiner: U.. 84. 86. 407. 537 Steinfeld, J. 1.,'35,'406. Steinmetz, R., 294, 333 Steinmetzer, C., 53 1 Steinmetzer, H., 69, 522 Stenberg, V. I., 404 Stepanov, B. I., 208 Stepanova, L. I., 38, 159, 210 Stephens, E. R., 137, 149 Stephens, P., 16 Stephenson, L. M., 22, 124, 184 Stermitz, F. R., 384 Stevens, B., 92, 408, 409, 420 Stevens, C. G., 9, 362 Stevens, M. F. G., 441 Stevenson, J. M., 32, 5 5 60 Stevenson, K. L., 156 Stewart, J. C. M., 419 Stewart, T. B., 47 Stichtenoth. H.. 32 Stief, L. J.,'140; 201 Stiller, K., 413 Stillman, M. J., 16, 199 Stine, J. R., 49 Stock, M. G., 120 Stoeri. P. A.. 158 Stohrer, W. D., 48, 216, 247 Stolarski, R. S., 137 Stolle, W. T., 222, 497 Stolovitskii, Y.M., 199, 200 Stohovskava. V. N.. 59 Ston'el F. G. A.. 195 Stone; M. L., 181 Stone, P., 312 Stoodley, R. J., 472 Stork. G.. 483 Storr,' R. s., 437 Stout, D. M., 475 Stout, E. I., 497

Stowe, B. S., 533 Stowell, J. C., 326 Strachan, W. A., 487 Strasberger, B., 13 Strating, J., 479 Strausz, 0. P., 49, 121 Streefkerk, D. G., 293 Streith, J., 435 Strickler, S. J., 9, 362 Stringham, R. S., 99 Strobel, D. F., 135 Strohmeier, W., 190, 191, 404 Strom, E. T., 295 Stromberg, E., 536 Strong, R. L., 71 Strop, P., 527 Struchkov. Y. T.. 189 Strutz, J., -184 ' Struve, W. S., 23, 43, 66, 129 Stuart, D., 269 Studenikov, A. N., 493 Studzinskii. 0.P.. 368. 396 Stuhl, F., 143 Sturgeon, R. S., 64 Stutzel, B., 532 Stynes, D. V., 199, 563 Su, H. Y., 134 Suau, R., 65, 461 Suboch, V. P., 200 Subrahmanyam, G., 357, 358 Subramanian, J., 196 Subtil, J. L., 4 Subudhi, P. C., 32 Suchannek, R. G., 25 Suchard, S. N., 135 Suck, S. H., 519 Suckow, U., 76 Suess, G. N., 126 Sugawara, I., 517 Sugi, M., 584 Sugimori, A., 178, 365, 369, 451, 452, 501 Sugimoto, A., 414 Suginome, H., 438 Sugita, K., 170 Sugiura, M., 342 Sugiyama, K., 509 Sugiyama, N., 230, 444 Sugiyama, T., 369, 451, 452 Sukhov, D. A., 527 Sukigara, M., 407 Sultan, G., 21, 28 Sultanov, A., 518, 532 Sumitani, M., 59 Su-Moon Dark. 95 Summers, W. A., 71, 452 Sun, M., 66, 428 Sundberg, R. J., 379, 487 Sung, A., 519 Suna. H. N.. 17 Suppan, P., 393 Suprunchuk, T., 93, 169, 409, 534 Surin, S. A., 210 Suryanarayana Rao, K., 31 Suschitzky, H., 487, 488, 491 Sutherland, D. R., 488 Sutin, N., 159 Sutoh, Y.,536 Sutton, D. G., 135 Suyuki, T., 537 Suwa, T., 516, 518 Suzuka, I., 14, 38, 64 Suzuki, A., 394 I

,

Suzuki, H., 369,450 Suzuki, J., 412 Suzuki, M., 437, 442 Suzuki, N., 510, 517 Suzuki, S., 134, 170 Suzuki, T., 531, 532 Suzuki, Y., 513 Svendsen, E. N., 4, 16 Sverdnip, G. M., 149 Sveshnikova, E. B., 153 Sviridov, V. V., 159, 210 Swaminathan, S., 501 Swann, N., 134 Swenton, J. S., 275, 276, 312, 326, 448 Swinehart, J. H., 158 Swinnen, D., 72, 192 Swofford, R. L., 19 Swords, M. D., 102 Sworski, T. J., 171 Sykes, A., 316 Sylvester, G., 565 Symons, M. C. R., 158, 180 Szabados, E., 532 Szabo, A. G., 31 Szabo, G., 447 Szajewski, R. P., 483 Szalay, L., 31, 42, 577 Szarek, W. A., 245, 503 Sze, N. D., 420 Szerenyi, P., 522 Szeto, L. H., 122 Szewczyk, M., 96, 377 SzilQgyi,G., 249, 503 Szocs, F., 536 Szoke, A., 38 Sztumpf-Kulikowska, E., 275, 501 Szwarc, H., 87 Szwarc, M., 26 Tabata, Y.,517 Tabei, K., 449 Tabushi, I., 146, 453 Tachikawa, H., 87, 95 Tada. K.. 510 Tada; M.', 190, 254 Tadayoni, R., 455 Tagawa, S., 516 Tagawa, T., 518 Tai, C., 122 Taimr, L., 535 Tait. A. D.. 472 Tajiri, A., 16 Takabatake, E., 171 Takagi, H., 15 Takagi, K., 228, 286, 354, 433 Takahashi. H.. 438 Takahashi; K.; 287, 415, 508, 582 Takahashi, M., 148, 426, 495, 507 TaEiashi, T., 220, 286, 394, -I3 I

Takahashi, Y., 203, 417 Takai, M., 537 Takai, Y., 525 Takamura, M., 218 Takani. M.. 287 Takao,'S., 106 Takaoka, T., 514, 515 Takaya, T., 475 Takayama, Y., 370 402, 451 Takebayashi, N., 161

Author Index Takeda, H., 457 Takeda, K., 510 Takehisa, M., 516, 517 Takeisaki, H., 4 Takekawa, M., 32 Takemura, T., 26, 74, 78, 88 Takeshita, H., 248, 415, 419 Takeuchi, F., 369, 451 Takeuchi, K., 438 Takeuchi, N., 170 Takeuchi, T., 157 Takimoto, Y., 494 Takuwa, A., 293 Taleb, A. M., 52 Talekar, R. R., 269 Taliani, C., 14 Talvinskii, E. V., 357 Tam, J. N. S., 119,418,455 Tam, S. Y.-K., 261 Tam, W.-C., 25 Tamaki, T., 513 Tamamura, T., 520 Tamano, T., 492 Tamao, K., 204 Tamari, H., 504 Tamas, J., 498 Tamir, M., 48 Tamm, T. B., 78 Tamura, H., 572 Tamura, K., 170 Tamura, N., 516, 518 Tamura, Y., 437, 486 Tanabe, K., 242, 286,494 Tanahashi. Y.. 220 Tanaka, F:, 45, 378 Tanaka, H., 503, 514 Tanaka, I., 52, 99, 117, 141 Tanaka, J., 13, 457 Tanaka. K.. 6.210 Tanaka; M.', 13, 423, 512 Tanaka, O., 401,441 Tanaka, S., 16, 414 Tanaka, T., 33 Tanaka, Y., 27 Tandrede, J., 188 Tang, C. L., 8 Tang, C. W., 199, 583 Tang, D. Y., 267,429 Tanigushi, I., 293 Tanimoto, Y., 8 1 Tanizahi, Y., 7 Tanizawa, K., 67 Tanner, S. P., 171 Tantzscher, C., 583 Tardieu de Maleissye, M. J., 132

Tashiro, H., 27 Tashiro, M., 388, 458 Tasker, P. W., 47, 118, 423 Tatarczyk, T., 129, 131 Tatsuoki, O., 576 Taubman, A. B., 517 Tauer, E., 439 Tausta, J. C., 311 Tavan. M.. 516 Tawn,'D. N., 31, 53 Tayler, R. L., 137 Taylor, A. R., 509 Taylor, C. L., 534 Tavlor. G. K.. 4 Tailor; R., 6 4 Taylor, R. J. K., 465 Tazuke, S., 191, 364, 510, 566 Tchir, M. F., 227

613 Tealdo, G. C., 518 Tebbe. F. N.. 175 Tedder, J. M:, 119, 124,471 Tedder, S. H., 87 Tefertiller, N. B., 253 Teichner, S. J., 210 Teifel. V. G.. 135 Teitei; T., 359 Telle, H.. 134 Telle; J. M.,8 Teller, S. R., 426 Tellinghuisen, J., 9, 28,49, 144 Temizer, A., 94, 379, 426 Temdet. P. H.. 10 Ten Berge, C. D. M., 535 Teramachi. S.. 517 Teramae, N., 16 Terao, S., 418 Terteryan, R. A., 535 Tessier, A., 200 Testa, A. C., 401 Tetreau, C., 26 Teutsch, G., 486 Tevau!t, D. E., 29, 60, 209 Tewari, B. N., 11 Tews. K. H.. 16. 43. 584 Tezuka, H., 297' ' Tezuka, T., 270 Thakur, S. N., 31 Thayer, A. L., 408 Thayer, C. A., 112 Thelm, B., 28 Theyson, T. W., 180 Thijs, L., 482 Tho, N. D., 472 Thoma, K., 537 Thomas, A. C., 516 Thomas, A. F., 411 Thomas, B., 80, 303 Thomas, D. L., 171 Thomas, J. K., 576 Thomas, J. L., 179 Thomas, J. M., 386 Thomas, P., 157 Thomas, R. G. O., 141 Thomas, T. D., 22 Thomas, T. F., 117 Thompson, D. G., 21 Thompson, J. F., jun., 149 Thompson, L. F., 517 Thompson, R. T., 125 Thomson, A. J., 16, 197, 199 Thomson, R. H.,434 Thorsell, D. L., 36 Thrush, B. A., 125, 141 Thulstrup, E. W., 13, 16 Thyrion, F. C., 121 Tiao, G. C., 149 Tibilov, S. S., 87 Tidball, M., 142 Tiecco, M., 468 Tikhomirova, N. S., 518 Tilford, S. G., 28 Tillaev, R. S., 516 Tjllekeratne, L. M. K., 528 Tillien, J., 16 Tinnemans, A. H. A., 374, 379 Tino, J., 536 Tinoco, I., 16, 63 Tinti, D. S., 35 Tjppjng, A. E., 206, 468, 481 Tlpping, L. R. H., 168 Tjon, J. A., 38 rkhomolova, M. P., 519

Tobin, M., 315 Toby, S., 142 Toda, F., 280, 307, 510, 527 Toda, T., 327 Todo, S., 280 Tokamaru, K., 38 Tokel-Takvoryan, N. E., 95, 197

Tokousbalides, P., 172 Tokuda, M., 394 Tokue, I., 23 Tokumaru, K., 366, 404, 420, 445, 501

Tolle, H. J., 209 Tollin, G., 36, 200, 396 Tolmachev, Yu. A., 123 Tolmacheva, V. Y., 419 Tolstikov, G. A., 357 Tolstoi, N. A., 133 Toman, L., 507 tom Dieck, H., 195 Tomikawa, T., 510 Tomioka, H., 334, 470 Tomita, K., 431 Tomkai, A., 531 Tomzig, E., 210 Tonami, H., 533 Tondello, E., 173, 175 Toong, Y. C., 474 Topp, M. R., 83 Toppet, S., 513 Toptygin, D. Ya., 526, 527 Toseano, V. G., 208 Toshima, N., 365,445 Tournon, J., 31 Townsend, D. E., 316 Toy, M. S., 99 Toyama, T., 149 Toyoda, M., 25 Toyonaga, Y.,248 Trachenko, Z. A., 154 Trahanovsky, W. S., 177 Trainor, D. W., 128, 140, 143 Trajmar, S., 24 Tramer, A., 102, 120 Traverso, O., 173, 181, 191 Treadaway, M. F., 520 Tredwell, G. J., 66 Treinin, A., 203 Trembovler, V. N., 178 Tret'yak, V. M., 122 Tret'yakov, D. N., 581 Triantaphylides, C., 470 Triebe, J., 432 Triebel, W., 69 Trifunac, A. D., 37, 199 Tripathi, H. B., 173 Tripathi, U. S., 11 Tripodi, M. K., 99 Trivedi, I. M., 517 rrocha-Grimshaw, J., 381,503 rroe, J., 101, 123, 145 rrogu, E. F., 193 rronc, M., 145 rrost, B. M., 254,483,485 rrozzolo, A. M.,66 rrueman, R. E., 233, 393 rruhlar, D. G., 24 rrumbore, C. N., 202 Truong, T. B., 33, 202 rsai, B. P., 123 rschang, P A . W., 486 rschuikow-Roux, E., 118, 143 rseng, S.-S., 135, 210

Author Index

614

Varsanyi, I., 536 Vasilchenko, V., 581 Vasilenko, V. V., 529 Vasiliu-Perea, C., 518 Vaska, L., 566 Vasters, E., 537 Vasudevan, K., 6, 49 Vaubel, G., 32, 56, 73 Vavrinec, E., 200 Vedejs, E., 326 Veeman, W. S., 35 Vega, E., 430 Vega, S., 35, 36, 198 Veillard, A., 8, 181 Velapoldi, R. A,, 43 Velikhov, E. P., 147 Velthorst, N. H., 32 Ventataramani, P. S., 501 Veprek-Siska, J., 204 Vacatello, M., 148 Verani, G., 193 Vacek, K., 200 Verbeek, P. J. F., 25 Vahey, D. W., 39 Verborgt, J., 97, 526 Vahrenkamp, H., 195 Vergragt, P. L., 33, 86 Vainikko, G. M., 134 198 Verkhovtseva, E. T., 25, 134 Vaish, S. P., 37, 86, 215 Verma, R. M., 11 Vakula, V. L., 529 T~,C.-K., 100 G., 37, 86, 402, Vermeersch, Vala, M. T., 24 Tubata, Y., 517 450 Valadier, F., 144 Tubbs, E. F., 9 Vermeil, C., 107, 117, 147 Valeur, B., 519 Tudorache. S.. 128 Vernin, G., 431 Val'kova, G. A., 299, 396 Tuichiev, Sh.,'533 Verstegen, J. M. P. J., 31 Valkovich, P. B., 346, 468 Tully, J. C., 139 Vesley, G. F., 362 Van Aselt, N. P. F. B., 136 Tulskii, S. V., 201 Vestal, M., 123 Van Beek, H. C. A., 536 Tupikov V. I., 209 Vethorst, N. H.,54 Vancea, L., 195 Turbini, 'L.J., 204, 205 Van De Mark, M. R., 208,401, Veyret, B., 78, 111 Turkina, M. Ya., 107 Victor, R., 186 470 Turkova, A. E., 199 Vidal B., 11 van den Bergh, H., 123 Turlet, J. M., 13 Vienie-Casalta, D., 128 Vanden Berghe, R. A. L., 576 Turner, D. H., 16, 63 Vigato, P. A., 173 van den Driesche, T. P., 156 Turner, D. T., 536 Vikesland, J. P., 9 Vander Donckt, E., 72, 192 Turner, J. J., 174, 176 Viktorovitch, P., 581 vander Gen, A., 323 Turner, N., 149 Vilesov, F. I., 122, 210, 527 Vanderlinden, P., 207, 318 Turner. P. H.. 530 V!llain, F., 200 van der Plas, H. C., 435 Turowska, T.; 537 Vincent, J. S., 208 van der Poel, A. L. J., 35 Turowska, W., 498 Vjnduskova, O., 200 Turro, N. J., 33.48, 63, 69,94, Vanderriest, C., 125 Vink. A. T., 38 95, 116, 213, 312, 315, 353, van der Veen, J., 283 Viola, A., 491 Vandervennen, R., 234 522. 531. 562 van der Waals. J. H.._7.33. TUcya,-M.; 518 . . 34.. Viovy, R., 200 Viriot-Villaume, M. L., 227, 35, 86, 198 . Tyczkowski, J., 526 314, 501 van der Werf, R. P., 15, 113 Tyrrell, H. M., 357 Vitkovskii. G. P.. 173 van Dorp, W. G., 35, 198 Vitz, E., 174 Van Duuren. B. L.. 345 Uchida, K., 31 Vlasov, A. V., 517 Vandvukov. 'E. A..'42 Uchida, T., 244 Voecks, G. E., 135 J., 7, 33 Van Egmond, Uchiyama, H., 517 Vogel, E., 414 van Eldik, R., 207 Uda, H., 93, 414 Vogelmann, E., 36, 86 van Haard, P. M. M., 482 Udagawa, Y.,38 Vogler A,, 166 Van Heiningen, J. J., 10 Ueda, E., 382,425 Voitchbvsky, J. P., 208 Van Houten. J.. 161. 168 Ueda, K., 331 Vol'eva, V. B., 292 van Noort, P. C. M , 266 Uehara, H., 149 Vol'kenshtein, F. F., 210 van Pruyssen, J. M., 11 Uehara, K., 515 Vol'kenshtein, M. V.,201 Van Thien, T., 513 Ueno, A., 307, 510, 527 Volkova E. V., 517 van Veen, E. H., 25 Ueno, T., 106 Vollhardt, K. P. C., 190 van Voorst, J. D. W., 13, 54 Uliana, J. A., 80, 229 Vollner, L., 537 van Wageningen, A., 266 Ullal, H., 582 van Woerden, H. F., 242, 493 Volman, D. H., 143 Ullman, E. F., 285 Volod'ko, L. V., 173 Van Zee, R. J., 95 Umbreit, M., 95 von Engel, A., 24 Varani, G., 168 Umeda, Y., 242, 494 Von Raven, A., 536 Varfalvi, F., 532 Umezawa, H., 450 von Rosenberg, C. W.,jun., Varfalw. L.. 149 Umreiko, D. S., 173 140, 143 Varga, S:, 518 Umrikhin, V. A., 196 Varghese, A. J., 273, 274, 277, von Schutz, J. U., 35, 86 Undheim, K., 475 von Sonntag, C., 76,274,405, 452,453, 501 Uneo K.; 173 42 1 Ung, 'A. Y. M., 144, 146, 201 Varkony, H., 142 Von Stenius, A. S., 536 Varkonyi, Z., 31 Unger, I., 504 Vonsyatskii, V. A., 536 Varma, S. P., 207 Uno, A., 527

Tsetlin, B. L., 517 Tsikora, I. L., 123 Tsubakiyama, K., 533 Tsuboi, M., 38 Tsubomura, H., 12, 169, 209, 510, 569 Tsuchiya, S., 126 Tsuchiya, T., 281, 419, 423, 435,437, 479, 454 Tsuda, K., 497, 509 Tsudzuki, T., 420 Tsuge, O., 388, 458 Tsui, F. S. M., 46 Tsuji, K., 161 Tsuji, M., 25 Tsunashima. S.. 121, 128 Tsunooka, M.,-512 . Tsurubuchi, S., 24 Tsuruta, H., 290, 322, 458 Tsuruya, S., 299, 396 Tsushi. I.. 75. 364 Tsuyuki, T., 220, 394 Tsvirko, M. P., 33, 196, 197,

Uno, K., 510 Uphaus, R. A., 200 Urch, D. S., 134 Ure, A. M., 128 Uri, N., 527 Uriusu, T., 23 Urone, P. 148, Uselman, W. M., 145 Ushakov, A. A., 107, 361 Ushimaru, S., 516 Usmanov, Kh. U., 516, 518 Utirov, R. U., 132 Utsumi, S., 414 Utuoni, S., 93 Uvarov, A. V., 209 Uvarov, F. A., 15 Uzhinov, B. M., 208

Author Index

615

Wenghoefel, H. M., 532 Wenthemann, D., 108 Wentzell, B. R., 367 Werbin, H., 294, 295 Werkhoven, C. J., 110 WerndorfF, F., 480 Werner, A. S., 123 Wernette, D. A., 5 Werthemann, D. P., 57, 302 Wessel, J. E., 17, 55, 117 West, D. X.,158 West, G. A., 118 West, J. B., 33, 129 Waber, J. T., 21 West, M. A., 110 Wachsen, E., 254 West, P. R., 202 Wada, J. Y., 147 West, R., 286, 469 Wada. M.. 515 West, R. M., 317 Wada; T.,-516 Westenberg, A. A,, 140 Waddell, W. H., 95, 102, 562 Westheimer, F. H., 490 Waddington, D., 142 Westlake, J. F., 535 Westlof, T., 247 Wadt, W. R., 5, 7 Waegell, B., 455 Wetmore, S. I., jun., 347, 348, Waggoner, P., 149 429 Wagner, B. O., 204 Wharton, L., 9 Wheeler, D. M. S., 315, 3868 Wagner, E. B., 125 Whelan, T. D., 76, 361 Wagner, H. G., 143 Whelan, T. S., 105 WziEer, P. J., 35, 90, 214, Whitby, K. T., 149 LL 1 Wagner, S., 580 White, E. H., 95, 213 Wagnon, J. C., 188 White, J. M., 134 Wahl, Ph., 43 White, R. A., 529 Whitehead, E., 201 Wahlborg, A., 31, 62, 286 Wai-Kee, L., 7 Whitehead, R., 50 Wake, S., 370, 402, 451 Whitesides, G. M., 191 Walch, S. P., 4 Whitman, P. J., 254, 485 Whitmarsh, D., 322, 377 Walker, D. L., 261 Walker, I. C., 24, 25 Whitney, J. F., 39 Walker, J. A., 21 Whittaker, J., 131 Walker, J. C. G., 148 Whitten, D. G., 90, 159, 196, Walker, R. B., 378, 427 223,304,338,446 Walker. S.. 11 Whitten. W. B.. 78 Walker; T,E. H., 21 Whittington, S.’G., 393 Walker, W.C., 9 Whittle, C. P., 332 Whitton, B. R., 497 Wallace, T. W., 285 Walls, D. F., 39 Whitton, W. B., 24 Walrant, P., 420 Wickham. H. H.. 140 Walsh, A. D., 6 Wjckramasinghe,‘ N. C., 134 Walsh, E. J., 336 Wicks, Z. W., 533 Walsh, T. D., 315 Widdowson, D. A., 324, 501 Walter, L., 25 Widera, R. P., 240, 453 Walter, T. J., 483 Widrger. G. N., 454 Walters, G. K., 125 Wiebe, H. A., 139 Walther. H.. 134 Wiegand, D. A., 207 Walton,’J. C., 124 Wieringa, J. H., 479 Wamhoff, H., 249, 501 Wiersma, D. A., 15 497 Wan, E., 145 Wiesenfeld, J. R., 122, 128 Wan, J. K. S.,37, 86,396,499, Weinstein, S. Y.,83, 392 Wight, C. A., 38 Weir, N. A., 355, 478, 531 534 Wilcsek, R. J., 204 Wang, C. C., 144 Weir. T.. 535 Wild. U. P.. 12. 26. 96 Wang, H.-C., 10 Weiss, E:, 193 Wiles, -D. M.,’93,’ 169, 409, Wang, S. S., 284 Weiss, K., 10, 19, 78, 83, 111 530, 534 Wang, S. Y.,274 Wejss, R. G., 208 Wilhelmi, B., 69 Wang, Y.C., 107 Weiss, S., 128 Wilkinson, J. G., 158 Ward, J. W., 142 Welge, K. H., 118, 138 Willard. J. E.. 123. 210 Ward, R. A., 564 Weller. C. S.. 134 Willeke; K., 149 ’ Warden, J., 36, 199 Wells, b.,359 Willenbring, G. R., 27 Ware, W. R., 29, 50, 51, 65, Wells, P. P., 74, 251 Williams, A., 142 68, 69, 102 Welmore, R., 48 Williams, D. F., 39 Warner, P. O., 131 Weltner, W., 9, 28 Williams, D. J., 71, 526 Warnick, S. M., 16 Welz. E.. 193 Williams, E. A., 135 Warren, J., 11, 430 Wen,’ W: X.,518 Williams, F., 207 Warrener, R. N., 322, 501 Wendlandt, W. W., 157 Williams, F. W., 141, 413 Warshel, A., 6, 7, 8, 10, 58 Wendoloski, J. J., 21 Williams, G. R., 5 Wasser, P. K. W., 196 Wendt, H. R., 127 Williams, J. I., 532 von Weyssenhoff, H., 102 Vorkink, W. P., 201 Voronkov, M. G., 207,465 Voroshilova, N. S., 181 Voznyak, V. M., 36,200 Vreede, H., 28 Vrielink, J. J., 316 Vroom, D. A., 140, 144 Vuik, C. P. J., 166 Vukstich, V. S., 9 Vyas, H. M., 37, 86, 396 VystrEil, A., 421, 454

Wasserman, H. H., 93, 412, 413,418 Watada, Y.,536 Watamoto, H., 533 Watanabe, A., 262 Watanabe, H., 206, 471 Watanabe, K., 412, 536 Watanabe, S., 38 Watanabe, T., 5, 516, 570, 576 Waters, J. A., 300 Waters, W. A., 385 Watkins, A. R., 70, 72, 83, 203, 392 Watkins, C. J., 213 Watkins, D. A. M., 310, 504, 537 Watling, R. J., 32 Watson, C. R., 478 Watson, D., 320 Watson, G., 129 Watson, N. S., 472 Watson, P. J. S., 47 Watson, T., 33 Watterson, A. C., 457 Watts, R. J., 161, 168 Wayne, R. P., 131, 136, 142, 143 Weakliem, H. A,, 527 Weaver. J.. 94. 119 Webber, S: E.,‘ 87 Weber, J. H., 190 Weber, W. P., 206, 215, 346, 465, 468,486, 496 Webster, A., 134 Weeke. F.. 76. 421 Weeks; R.’W.; 131, 147 Weese, G. M., 200 Wegner, G., 513 Wehrli, H., 228, 260 Wehry, E. L., 564 Weib, B., 480 Weich, G., 48, 216 Weidenborner, J. E., 358 Weidmann, K. G., 432 Weigand, 0. E., 16 Weigelt, L., 190, 404 Weighmann, H. J., 38 Weil, T. M., 83, 391 Weiler, H., 436 Weimann, L. J., 198 Weiner, P. K., 519 Weinmann, L. J., 8 Weinstein, D. H., 572 Weinstein, J., 192 Weinstein, M., 37, 86, 416,

Author Index

616 Williams, J. L. R., 205, 340, 363

Williams, J. O., 386 Williams, J. R., 234, 268 Williams, K. E., 106 Williams, M. L., 198 Williams, M. W., 11 Williams, P. F., 4, 17 Williams, W., 24 Williamson, A. D., 22 Williard, K. F., 305 Wills, K. S., 132 Willson, A., 536 Willy, W. E., 279, 415 Wilmet, B., 527 Wilmot, P. B., 203 Wilms, K., 414 Wilputte-Steinert, L., 177,404 Wilson, A. D., 47 Wilson, J., 169 Wilson, J. E., 517, 518 Wilson. K. R.. 47 Wilson; M. R.', 148 Wilson, R., 83, 391 Wilson, R. M., 93, 216, 294, 466

Wiltshire, J. F. K., 93 Wilzbach, K. E., 352, 354 W&$or, M. W., 27, 168,198, -r 1

7

Winefordner, J. D., 33, 84 Winer, A. M., 36 Wjngard, R. E., jun., 315 Winicur. D. H.. 125 Winkler: H. J. S.. 367 Winkler; P., 4 ' Winkler-Lardelli, B., 37 Winnik, M. A., 233, 239, 393 Winsel, K., 93 Winstein. S.. 330 Winter, G. K.,134 Winter, N. W., 5, 6, 202 Wintle, H. J., 527 Wirz, J., 8, 286, 345, 397 Wiseman, J., 490 Wismonski-Knittel, T., 59, 372, 373

Wisson, M., 319 Witkop, B., 288, 345, 443 Wittig, C., 121 Wittington, S. G., 233 Witz, G., 345 Wodarczyk, F., 124 Woelpl, A., 166 Wofsy, S. C., 138, 420 Wojcicki, A., 184, 195 Wojcieckowski, P., 526 Wolbarsht, M. L., 29, 91, 142, A118

Wiiierg, A., 35 Wolczanski, P. T., 570 Wolf, H. C., 32, 33, 55, 86 Wolf. H. R.. 255 Wolfe, s., 48 Wolfe, S. K., 158 Wolff, G., 156 Wolff, s., 220 Wolfhugel, J. L., 259 Wolfrum, J., 124 Wolga, G. J., 124 Wolniewicz, L., 4 Wolters, A. P., 357 Wong, C. F. C., 155 Wong, D. J. D., 516

Wong, J. Y., 371, 376 Nong, K. L. T., 179 Wong, S. K., 37, 86, 396 Wong W., 136, 140 Wood: A. T., jun., 134 Wood, D. E., 27 Wood, D. J., 447 Nood, D. M., 522 Wood, G. P., 84, 441 Wood, M. H., 7, 8, 181 Wood, 0. R., 122 Woolsey, I. S., 198 Woolsey, N. F., 482 Wostradowski, R. A., 81, 290 Wren, D. J., 126 Wright, T. R., 492 Wrighton, M. S., 168,174,178, 179, 180, 3 16, 468, 562, 565, 570

Wrobel, J., 24 Wrolstad, K. H., 124 Wu, A., 503 Wu, C. H., 131, 142 Wu, E. S. C., 326 Wubbels, G. G., 365, 400 Wuerzberg, E., 172 Wunderly, S. W., 93, 148, 294, 466

Wundrich, K., 536 Wunsch, L., 19, 101 Wyatt, P. H., 83 Wylie, P. L., 266 Wyman, G. M., 84,97,422 Wynberg, H., 479 Wyvratt, M. J., 473 Yabe, A., 379, 486 Yadav, J. S., 7 Yagihara, M., 485 Yagisawa, N., 450 Yahagi, K., 527 Yajima, T., 27 Yakhot, V., 7, 32, 54, 73 Yakobson, G. G., 381 Yakovleva, M. K., 517 Yamabe, S., 48 Yamada, H., 488 Yamada, K., 261, 382, 536 Yamaguchi, H., 7,419,435 Yamaguchi, K., 297 Yamaguchi, S., 237 Yamaguchi, Y., 293 Yamakawa, M., 14, 24 Yamakawa, S., 516, 518, 536 Yamakita, H., 51 1 Yamamoto, H., 201 Yamamoto, K., 206 Yamamoto, M., 337, 338 Yamamoto, N., 510 Yamamoto, Y., 76 Yamanaka, S., 367 Yamanashi, B. S., 29, 91, 142, 408, 447

Yamane, M., 416 Yamanruchi, T., 526 Yamasaki, K., 366, 370, 449 Yamase, T., 157 Yamashita, M., 36, 90 Yamauchi, S., 383, 425 Yamazaki, I., 3 1 Yampolskii, Yu. P., 134 Yanagihara, S., 149 Yang, C., 280 Yang, C. H., 147

Yang, J. L., 38 Yang, N. C.,273, 360 Yang, S.-C., 47, 106 Yankovsky, V. A., 142 Yano, K., 268 Yano, T., 117 Yanova, L. P., 517 Yanus. J. F.. 515 Yanush, 0.V., 172 Yardley, J. T., 112, 113, 115 Yaremenko, V. I., 134 Yariv, A., 39 Yarkony, D. R., 6 Yarmilko, E. G., 518 Yarrow, D. J., 566 Yarunin, V. S., 24 Yashchuk, V. N., 520 Yasina, L. L., 531 Yasuoka, N., 185 Yates, D. H., 326 Yates, R. L., 48, 316 Yatsiu, S., 128 Yavorskii, B. M., 178, 181 Yazawa, K., 16 Yeager, D., 5, 6, 202 Yeang, E. S., 111 Yee, K. K., 9 Yen, N. T., 518 Yersin, H., 156 Yeshurun, A., 320 Yeung, C. K. K., 145 Yeung, T. S.,60, 218, 221 Yip, R. W., 455 Yoganarasimhan, S. R., 170 Yogev, A., 11, 13, 132 Yokawa, M., 511 Yokoe, I., 434 Yokota, T., 121 Yokoyama, M., 520 Yokovama. Y.. 173 Yomdsa, s;,49; Yoneda, F., 275 Yoneda, S., 249, 250 Yonemitsu, O., 365 Yonetani. T.. 201 Yoneyama, H., 572 Yonezawa, T., 299, 366, 396, 43 1

Yonezawa, Y., 113 Yoshida, N., 84 Yoshida, T., 153 Yoshida, Z., 146, 249, 250, 257, 453

Yoshihara, K., 59, 108 Yoshikawa, M., 501 Yoshikuni, K., 161 Yoshimine, M., 4 Yoshimura, K., 315 Yoshimura, M., 520 Yoshimura, Y., 486 Yoshino, K., 199 Yoshioka, H., 518 Yodioka, I., 501 Yost, G. A., 504 Young, A. N., 144 Young, B. C.,143 Young, C., 131, 147 Young, D. W., 223 Young, F. R., 186 Young, J. W., 336 Young, P., 128 Young, R. A., 139 Young, R. H., 93, 119,409 Youssefyeh, R. D., 503

617

Author Index Yovell, J., 186 Yu, w.,579 Yuan, C. N., 131 Yurkevich, V. G., 536 Yurre, T. A., 515 Yushkevich, N. A., 199 Yusubov, N. M., 134 Yutaka, S., 285 Yuzhakov, V. I., 200 Zabik, M. J., 367, 504, 537 Zafiriou, 0.C., 137 Zagorskaya, Z. G., 518 Zahradnik, R., 6 Zahran, A. H., 517 Zaitseva, N. K., 535 Zakharchuk, A. V., 532 Zakharenko, V. S., 209 Zalecka, H., 202 Zalesskii, I. E., 197 Zalewski, E. F., 14 Zalkow, L. H., 475 Zamanskii, V. M., 117 Zander, M., 33, 55, 72 Zannusi, J. S., 374, 530 Zanobi, A., 528

Zare, R. N., 9, 23, 126, 134,

Zimmerman, H. E., 49, 57,

Zarnegar, B. M., 223 Zaslavskaya, G. B., 178 Zaval'skaya, A. V., 170 Zecca, A., 24 Zeldes, H., 36 Zeller, K.-P., 485 Zerner, M. C., 7 Zevenhuiizen. D.. 113 Zewail, A., 35 ' Zhabotinskii, M. E., 172 Zheligovskaya, N. N., 169 Zhidomirov, G. M., 12--Zhirnov, N. I., 42 Zhitnev, Yu. N., 121 Zhuravlev, D. A., 176 Ziebarth, T. D., 312, 430 Ziegler, .G. R., 335 Zielinski, M., 526 Ziffer. H.. 268 Ziglio, G',149 Zilitis, V., 21 Zimm, B. H., 519 Zimmerer, G., 28

Zimmermann, I., 344,371,406 Zimmerman, J., 535 Zink, J. I., 33, 153, 173 Zinsli, P. E., 35 Zipin, H., 159 Zitko, V., 367 Zittel, P. F., 112 Zitter, R. N., 132 Zlatkevich, L. Yu., 518 Zlotogorski, C., 333 Zmolek, W., 448 Zolin, V. F., 171 Zonder, M., 56 Zoran, A., 333 Zorn, J. C., 8, 24 Zorskie, J., 126 Zotov, N. I., 196 Zuclich, J., 35, 86 Zverev, B. I.. 536 Zwanenburg, B., 482 ZwaFich, R., 15, 31, 32, 61 Zweig, A., 532

142

108, 257, 302, 309, 310, 311, 313, 314