Photoc hemist ry
Volume 18
A Specialist Periodical Report
Photochemistry Volume 18
A Review of the Literature published between July 1985 and June 1986 Senior Reporter D. Bryce-Smith, Department of Chemistry University of Reading Reporters N. S. Alien, Manchester Polytechnic A. Cox, University of Warwick R. 8. Cundall, MRC Radiobiology Unit, Didcot A. Gilbert, University of Reading A. Harriman, The Royal Institution W. M. Horspool, University of Dundee S. T. Reid, The University of Kent
6
+&
ROYAL SOCIETY OF CHEMISTRY
ISBN 0-85 186-165-2 ISSN 0556-3860
Copyright @ 1987 The Royal Society of Chemistry A11 Rights Reserved
N o part of this book may be reproduced or transmitted in any form or by any means-graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems-without written permission from the Royal Society of Chemistry
Published by The Royal Society of Chemistry Burlington House, London, W1V OBN Printed in Great Britain by Whitstable Litho Ltd., Whitstable, Kent
Introduction ~~~
Volume 18 i s c o n t i n u i n g w i t h o n l y o n e major change from r e c e n t p r e v i o u s Volumes, namely o m i s s i o n of t h e C h a p t e r on G a s Phase P h o t o p r o c e s s e s .
T h i s change h a s a r i s e n from a number of
c o n s i d e r a t i o n s , n o t least o u r d e s i r e t o k e e p t h e o v e r a l l l e n g t h of t h e Volume, and hence t h e p r i c e , a t a manageable and economic level.
I n t h e p a s t , we have t r i e d t o p r o v i d e broad-spectrum
c o v e r a g e of p h o t o c h e m i s t r y , a l t h o u g h w e have r e a l i s e d t h a t most p h o t o c h e m i s t s t e n d t o work i n s p e c i a l i s e d a r e a s of t h e s u b j e c t , and many whose p r i n c i p a l i n t e r e s t s l i e i n , s a y , t h e more p h y s i c a l a s p e c t s may n o t f i n d t h e t i m e t o r e a d t h o s e s e c t i o n s more c o n c e r n e d w i t h s y n t h e t i c a p p l i c a t i o n s o f p h o t o c h e m i c a l t e c h n i q u e s , f o r example.
Although w e s t i l l r e t a i n t h e o r i g i n a l
i d e a l o f c o v e r i n g most a s p e c t s of p h o t o c h e m i s t r y w i t h i n a s i n g l e volume, w e have f e l t a b l e t o withdraw t h e s e c t i o n on gas-phase photoprocesses because D r . J.E.Baggott,
who c o n t r i b u t e d t h i s
s e c t i o n i n Volumes 16 and 1 7 , h a s now j o i n e d w i t h
Dr. M.N.R.Ashfold
(who i s a l s o a p r e v i o u s c o n t r i b u t o r t o
' P h o t o c h e m i s t r y ' ) t o p r o d u c e a new i n f o r m a l series o f books, commissioned by t h e Royal S o c i e t y of C h e m i s t r y , w h i c h are d e s i g n e d t o meet t h e r e q u i r e m e n t s of t h e s c i e n t i f i c community i n t h e f i e l d s of g a s k i n e t i c s , gas-phase m o l e c u l a r s p e c t r o s c o p y and p h o t o c h e m i s t r y , and r e a c t i o n dynamics.
These new r e v i e w s w i l l t h e r e -
f o r c o n t i n u e t h e c o v e r a g e o f gas-phase more g e n e r a l p h y s i c o - c h e m i c a l c o n t e x t .
photochemistry, but i n a R e a d e r s may l i k e t o n o t e
t h a t t h e f i r s t volume e n t i t l e d "Molecular P h o t o d i s s o c i a t i o n Dynamics" i s d u e t o be p u b l i s h e d i n t h e summer o f 1987. I t i s hoped t h a t t h e a n n u a l Review of t h e Year w i l l b e resumed i n Volume 1 9 .
D . Bryce-Smith.
Contents PART I
PHYSICAL ASPECTS OF PHOTOCHEMISTRY Photophysical Processes in Condensed Phases By R.B.
3
Cundall
1
General
3
2
Singlet State Processes
8
2.1 2.2 2.3 2.4 2.5 2.6 2.7
3 4
Electron Transfer Processes and Exciplexes Dyes and Related Systems Photoisomerization and Related Processes Electronic Excitation Energy Transfer Polymeric Systems Colloidal and Heterogeneous Systems Biological Systems
11
14
16 18 19
20 24
Triplet Processes
30
Other Systems References
36
37
PART I1
PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS
Chapter 1
The Photochemistry of Transition-metal Complexes
57
B y A . Cox 1
Introduction
57
2
Titanium
57
3
Vanadium and Niobium
59
4
Chromium, Molybdenum, and Tungsten
59
5
6
Manganese Iron
63
7
Ruthenium
64
8
Osmium
72
9
Cobalt Rhodium
72
10 11
Iridium
76
12
77
13
Nickel Palladium and Platinum
14
Copper
79
63
74
77
Contents
viii 15
Lanthanides
16
Uranium
81 83
17
Actinides
84
18
Miscellaneous
84
References
88
Chapter 2
The Photochemistry of Transition-metal Organometallic Compounds By A .
105
Cox
1
Introduction
105
2
Zirconium
105
3
Vanadium,
4
Chromium, Molybdenum, a n d T u n g s t e n
105
5
Manganese a n d Rhenium
113
6
Iron
115
7
Ruthenium
121
8
Osmium
121
9 10
Cobalt
123
Rhodium and I r i d i u m
124
11
Nickel, Palladium, and Platinum
126
12
Copper
129
13
Miscellaneous
129
References
129
The Photochemistry of Compounds of the Main Group Elements
140
Chapter 3
By A .
Niobium, and Tantalum
105
Cox
Introduction
140
Anions
140
A l k a l i Metals
140
Boron
140
Silicon
140
Nitrogen
145
Oxygen a n d S u l p h u r
145
Halogens
146
Miscellaneous
147
References
147
ix
Contents PART I11
ORGANIC ASPECTS OF PHOTOCHEMISTRY
Chapter 1
Photolysis of Carbonyl Compounds B y W.M.
1 2 3
4
Chapter 2
Norrish Type I Reactions Norrish Type I1 Reactions Oxetan Formation Rearrangement and Fragmentation Reactions References Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones By W . M .
1
2
3
4
5
6
Chapter 3
155 165 168 171 172
176
Horspool
Cycloaddition Reactions Intramolecular Additions Additions to Cyclopentenones Additions to Cyclohexanones Intermolecular Additions Open Chain Systems Cyclopentenone Cyclohexenones Miscellaneous Reactions Rearrangement Reactions
176 176 176 179 179 179 184 184 190 195
a,@-Unsaturated Systems $,y-Unsaturated Systems Photoreactions o f Thymines and Related Compounds Photochemistry o f Dienones Linearly Conjugated Dienones Cross-conjugated Dienones 1,2-, 1,3-, and 1,4-Diketones 1,2-Diketones 1,3-Diketones 1,4-Diketones Phthalimides and Related Compounds Quinones References
195 199 204 208 208 208 212 212 212 215 215 222 228
Photochemistry of Albenes, Alkynes. and Related Compounds
237
B y W.M.
1
155
Horspool
Horspool
Reactions of Alkenes Group Migration Reactions cis-trans Isomerization Halogeno-alkenes Addition Reactions
237 237 237 243 243
Contents
X
2
Alkynes Reactions involving Cyclopropane Rings
243 243
3
R e a c t i o n s of D i e n e s , T r i e n e s , a n d H i g h e r P o l y e n e s
248
4
(2+2) Intramolecular Additions
255
5
Dimerization and I n t e r m o l e c u l a r Cycloadditions
259
6
Miscellaneous Reactions
263
References
267
Photochemistry of Aromatic Compounds
273
Chapter 4
By A .
Gilbert
1
Isornerization Reactions
273
2
Addition Reactions
277
3
Substitution Reactions
289
4
Intramolecular Cyclization Reactions
303
5
Dimerization Reactions
322
6
Lateral-Nuclear
327
Chapter 5
Rearrangements
References
333
Photo-reduction and -oxidation
338
By A .
Cox
338
Introduction
338
R e d u c t i o n of t h e C a r b o n y l G r o u p R e d u c t i o n of N i t r o g e n - c o n t a i n i n g
Compounds
Miscellaneous Reductions
345
S i n g l e t Oxygen
346
O x i d a t i o n of A l i p h a t i c Compounds
347
O x i d a t i o n of A r o m a t i c Compounds Oxidation of Nitrogen-containing
Chapter 6
342
350
Compounds
353
Miscellaneous Oxidations
357
References
358
Photoreactions of Compounds containing Heteroatoms other than Oxygen
368
By S.T.
Reid
1
N i t r o g e n - c o n t a i n i n g Compounds
368
2
Rearrangements Addition Reactions Miscellaneous Reactions S u l p h u r - c o n t a i n i n g Compounds
368 386 399 402
xi
Contents 3
Chapter 7
Compounds containing Other Heteroatoms References
407
Photoelimination
420
By S . T .
414
Reid
1
Elimination of Nitrogen from Azo-compounds
420
2
Elimination of Nitrogen from Diazo-compounds Elimination of Nitrogen from Azides Photoelimination of Carbon Dioxide Fragmentation of Organosulphur Compounds
428
3 4 5 6
By N.S. 1 2
3
5 6
PART V
Introduction Photopolymerization
2
457
457 457
Photoinitiated Addition Polymerization Photografting 2.3 Photocrosslinking Optical and Luminescent Properties Photodegradation and Photooxidation Processes 4.1 Polyolefins 4.2 Poly(viny1 halides) 4.3 Polyacrylates 4.4 Polyamides and Copolymers 4.5 Polystyrenes and Copolymers 4.6 Polyesters 4.7 Bisphenol A Polymers 4.8 Miscellaneous Polymers
458 469 470
Photostabilization Processes Photochemistry of Dyed and Pigmented Polymers References
501
PHOTOCHEMICAL ASPECTS OF SOLAR ENERGY
523
By A . 1
442
Allen
2.1 2.2
4
440
Miscellaneous Decomposition and Elimination Reactions 4 4 6 References 450
POLYMER PHOTOCHEMISTRY
PART I V
434
474 487 487 489 491 491 492 493 495 495 506 509
Harriman
Introduction Homogeneous Photosystems Valence Isomerism Photosensitizer s
523 525 525 526
Contents
xii H2 P h o t o p r o d u c t i o n 0 Photoproduction Ciarge Separation
527 530 531
3
Heterogeneous Photosystems
533
4
P h o t o e l e c t r o c h e m i c a l Cells
538
5
Luminescence Solar C o l l e c t o r s
540
References
541
AUTHOR INDEX
555
Part I PHYSICAL ASPECTS OF PHOTOCHEMISTRY
Photophysical Processes in Condensed Phases BY R. B. CUNDALL T h e form o f t h i s r e v i e w follows that in previous volumes although it has been decided this year t o c i t e m o r e o f t h e w o r k published o n biochemical systems.
T h e applications o f l u m i n e s c e n c e
to biological problems is t h e most active area in condensed phase
photophysics and t h i s survey attempts t o reflect this situation. 1 General
Theoretical studies in photophysics tend t o be d i v e r s e and no particular themes are evident at the present time.
A somewhat
refined paper d e a l s w i t h radiation-molecule interactions f r o m t h e viewpoint o f q u a n t u m electrodynamics'
and a m o r e c o n v e n t i o n a l
approach through t u n n e l effect theory has been used t o interpret t h e a-cleavage o f k e t o n e s 2 .
Solvent influences o n excited states
and solvatochromism have also been examined theoretically in some detail3-"
A m o d e l for t i m e dependent
fluorescence dependent
solvent shifts is timely in view o f t h e current intensity o f e x p e r i m e n t a l effort'.
Theoretical a n a l y s i s o f t h e d e t a i l s o f
quenching processes have involved consideration o f long r a n g e , t h e role o f dielectric constant and
electrostatic interactions' ionic strength',
and t h e effects o f q u e n c h e r s on luminescent
polyelectrolytes w i t h pendant probes'
.
The theories o f
fluorescence depolarization in macroscopically ordered u n i v e r s a l systems
11
and concentration d e p o l a r i z a t i o n in t h e presence o f
orientational correlation d u e t o incoherent energy transfer"
are
highly t o p i c a l i n v i e w o f many e x p e r i m e n t a l studies w h i c h a r e underway. Steady progress in i n s t r u m e n t a l d e s i g n and data processing i s f u n d a m e n t a l to research in photophysics. this area can be quoted.
Only selected papers in
Yip13 has reviewed picosecond absorption
spectroscopy in some d e t a i l and treats both methods and applications.
Hopkins and Rentzepis"
discuss biological
applications, particularly primary processes in vision, o f picosecond laser phenomena.
Three papers w h i c h d e a l w i t h
3
Photochemistry
4
m e a s u r e m e n t o f m o l e c u l a r a n i s o t r o p i e s using l a s e r t e c h n i q u e s , a l t h o u g h d e a l i n g w i t h g a s p h a s e s i t u a t i o n s a r e a l s o relevant and applicable to condensed phase
photo physic^^^.
Details o f a high
resolution picosecond transient absorption spectrometer utilising d y e e m i s s i o n and s t r e a k c a m e r a have been published16 high s e n s i t i v i t y o f picosecond
and t h e u l t r a -
pump-probe measurements of
c o n c e n t r a t i o n has been d r a m a t i c a l l y d e m o n s t r a t e d using c r e s y l violet17.
O p t i c a l m u l t i c h a n n e l a n a l y s i s i s a l s o very u s e f u l in
e x a m i n i n g s h o r t l i v e d transients".
T h e use o f a h i g h i n t e n s i t y
l a s e r t o m o d u l a t e c o n c e n t r a t i o n d i f f e r e n c e s is e x p l o i t e d t o increase sensitivity o f detection i n concentration modulated a b s o r p t i o n s p e c t r o s c o p y (COMAS)'
.
Using m i c r o c h a n n e l p l a t e
detectors with time correlated single photon counting coupled with a pico- and s u b - p i c o s e c o n d l a s e r m a k e s i n s t r u m e n t a l f u n c t i o n w i d t h s of
20 ps s e e m feasible2'.
A d e s i g n f o r a high s e n s i t i v i t y l a s e r
f l u o r i m e t e r d e t e c t i n g as f e w a s 8 0 0 0 m o l e c u l e s o f r h o d a m i n e R 6 G i s noteworthy2'
.
W e h r y 2 2 h a s published a very c o m p r e h e n s i v e c o l l e c t i o n o f references to recent work o n techniques relevant to molecular f l u o r e s c e n c e , p h o s p h o r e s c e n c e , and c h e m i l u m i n e s c e n c e .
V i ~ s e rhas ~ ~
edited t h e q u i t e e x t e n s i v e p r o c e e d i n g s o f a s y m p o s i u m o n t i m e resolved f l u o r e s c e n c e s p e c t r o s c o p y . subjects, with multifrequency
P a p e r s d e a l , amongst o t h e r
p h a s e f l ~ o r o m e t r y, ~ p~h a s e resolved
f l u o r e s c e n c e s p e c t r o s c ~ p y, ~t~i m e c o r r e l a t e d s i n g l e p h o t o n c o u n t i n g using l a s e r e x c i t a t i o n 2 6 , t h e k i n e t i c i n t e r p r e t a t i o n o f fluorescence decays27 , determination o f t i m e resolved flUOreSCenCe spectra and a n i s o t r o p y d e c a y s using s i n g l e p h o t o n c o u n t i n g and synchronously pumped d y e l a s e r excitation2',
photon t i m e o f f l i g h t
( b r o u g h t a b o u t by u s e o f e x t r e m e l y l o n g silica l i g h t p i p e s ) 29 fluorescence spectroscopy , and t h e a p p l i c a t i o n o f picosecond s p e c t r o s c o p y t o a n a l y s e t h e s t r u c t u r e and m o t i o n s o f b i o p o l y m e r s , p a r t i c u l a r l y DNA3'.
Many o t h e r p u b l i c a t i o n s h a v e d e a l t w i t h t h e
m e a s u r e m e n t o f f l u o r e s c e n c e d e c a y times.
A system describing t h e
r e p l a c e m e n t o f a m u l t i c h a n n e l a n a l y s e r by A D C and a m i c r o c o m p u t e r has c o n s i d e r a b l e f i n a n c i a l a t t r a c t i o n s
31
.
Short l i v e d f l u o r e s c e n t
t r i p h e n y l m e t h a n e d y e s m a y b e used t o c o r r e c t f o r i n s t r u m e n t a l a r t i f a c t s i n p h o t o d e t e c t o r s in l i f e t i m e
measurement^^^.
On t h e fly
d e t e r m i n a t i o n o f f l u o r e s c e n c e l i f e t i m e s c a n be obtained f r o m t w o point d e c a y measurements3'
and p h o t o t u b e t i m e s h i f t s c a n be
e l i m i n a t e d by p h a s e p l a n e m e t h o d s 3 4 .
T h e use of microchannel plate
p h o t o m u l t i p l i e r s in a l l a s p e c t s o f t i m e c o r r e l a t e d f l u o r e s c e n c e
I: Photophysical Processes in Condensed Phases
5
spectroscopy 1 s described in a very u s e f u l paper by Y a m a z a k i Bt aL3’.
A comparative study o f correction methods for t h e
wavelength d e p e n d e n c e o f instrument r e s p o n s e functions i n t i m e correlated s i n g l e photon c o u n t i n g indicates this to be o n e o f t h e A method
principle d i f f i c u l t i e s in getting good data fits36.
for
carrying out t i m e resolved multiphoton counting has a l s o been developed3’
.
P h a s e shift and modulation t e c h n i q u e s have come i n t o greater P r o m i n e n c e largely d u e to t h e feasibility o f varying t h e m o d u l a t i o n frequency o f t h e exciting light.
An authoritative d e s c r i p t i o n o f
recent developments w i t h illustrative examples of multiexponent d e c a y s , decay o f a n i s o t r o p y , and t i m e resolved emission spectra has been given by Lakowicz pt al?
A n e w approach t o the analysis o f
heterogeneous emitting systems and t i m e d o m a i n fluorescence s p e c t r o m e t r y , has been f o r m u l a t e d 3 g and four components ( a n t h r a c e n e d e r i v a t i v e s ) analysed using two modulation frequencies and t h r e e 40 . A l l f o u r parameters needed t o express e m i s s i o n wavelengths systems w i t h two lifetimes h a v e shown to be d e t e r m i n a b l e by t h e use o f modulation techniques4
’.
G l o b a l and target analysis o f complex decay phenomena and t h e examination of ground state heterogeneity, anisotropic m o t i o n s , and excited state reactions has been critically reviewed42 and a method for t h e analysis o f t h e complete decay surface for systems undergoing excited state deprotonation proposed43
.
The theory and
applications o f anisotropy decay associated fluorescence spectra and analysis o f r o t a t i o n a l heterogeneity h a v e been d i s c ~ s s e d ‘ ~and applied to t h e behaviour o f U - U 1 , 6 - d i p h e n y l - t , 3 , 5 - h e x a t r i e n e ( D P H ) in lipid bilayers4’.
Global d e c o n v o l u t i o n has been used t o
g e n e r a t e time emission spectra and applied to 1 , 2 - - ( 1 0 acetoxyanthryl) e t h a n e , intramolecular excimer f o r m a t i o n , and analysis o f a t h r e e component m i x t u r e composed o f P O P O P , a n t h r a c e n e , and diphenylanthracene
46
,
Order parameters of ground
and excited states have been measured and it has been pointed out that t h e orientational distributions are not necessarily t h e s a m e for ground and excited s t a t e s , as is t h e case for D P H 4 t .
The
significance o f 4th rank orientational o r d e r parameters for fluorophores in m e m b r a n e s and their use a s a m e a n s o f distinguishing different m o d e l s o f structure and organization has been m a d e and t h e much studied DPH s y s t e m , in particular, has been examined in detail4’.
6
Photochemistry T h e p o s s i b i l i t y that m u l t i c o m p o n e n t d e c a y s obtained by s i n g l e
photon c o u n t i n g w h i c h , a l t h o u g h a p p e a r i n g t o yield a s a t i s f a c t o r y fit t o a s m a l l n u m b e r o f e x p o n e n t i a l d e c a y s m a y c o n c e a l u n d e r l y i n g e x t e n s i v e s e t s o f l i f e t i m e s w i t h a variety o f d i s t r i b u t i o n s has been c o n s i d e r e d i n s e v e r a l p u b l i c a t i o n s .
F a u l t s i n e q u i p m e n t can
m a k e t h i s s i t u a t i o n d i f f i c u l t t o d i s t i n g ~ i s h ' ~ and a m e t h o d for t h e recovery s u c h c o m p l e x d i s t r i b u t i o n has been p r o p o s e d S o . T h e d i s t r i b u t i o n o f f l u o r e s c e n c e l i f e t i m e s o f m o l e c u l e s absorbed o n s u r f a c e s w h i c h a r e c o n s i s t e n t w i t h t w o m e a s u r e d l i f e t i m e s c a n be fitted to either a single Gaussian or bimodal distributions1 A method developed
f o r e s t i m a t i n g e x c i t e d s t a t e pK
*
.
for
f l u o r e s c e n t c o m p o u n d s f r o m r a t e s o f proton t r a n s f e r t o an a p p r o p r i a t e d o n o r o r a c c e p t o r has been a p p l i e d t o t y r o s i n e , $ - n a p h t h o l , 2 - m e t h o x y c i n n a m i c acid and B - c a r b o l i n e S 2 .
It has been
proposed t h a t 8 - c a r b o l i n e i n 1 N H Z S 0 4 i s a b e t t e r f l u o r e s c e n c e (Amax = 4 5 0 nm, *F = 0 . 6 0 ) with a em s i n g l e e x p o n e n t i a l l i f e t i m e o f 22.03 2 0.12 n s s 3 . M e a s u r e d
standard t h a n q u i n i n e b i s u l p h a t e
f l u o r e s c e n c e i n t e n s i t y and p o l a r i z a t i o n v a l u e s a r e s e v e r e l y affected by a b s o r p t i o n a n d l o r s c a t t e r i n g i n c u v e t t e s and an e x p r e s s i o n has been d e r i v e d w h i c h r e l a t e s t h e o b s e r v e d a n i s o t r o p y t o sample turbiditys4.
Retro-diffracted light in T-format
f l u o r e s c e n c e s p e c t r o m e t e r s m a y be s o u r c e o f e r r o r p a r t i c u l a r l y w h e n m o d e l o c k e d l a s e r e x c i t a t i o n s y s t e m s a r e being usedss.
Two
papers d e a l w i t h c h a r a c t e r i s a t i o n of l a t e r a l d i f f u s i o n i n a r t i f i c i a l and b i o l o g i c a l m e m b r a n e s by p h o t o b l e a c h i n g and m e a s u r e m e n t o f t h e a p p r o p r i a t e d i f f u s i o n constantss6
I s 7
.
T h e a p p l i c a t i o n o f t i m e r e s o l v e d r e s o n a n c e Raman s p e c t r o s c o p y for studying t r a n s i e n t s has b e e n reviewed and t h e p r o p e r t i e s o f b a c t e r i o r h o d o p s i n and h a e m o g l o b i n d y n a m i c s a r e s p e c i f i c a l l y discusseds8.
T h i s t e c h n i q u e a l l o w s p h o t o p h y s i c a l and p h o t o c h e m i c a l
p r o c e s s e s in t h e s u b p i c o s e c o n d r e g i m e t o b e e l u c i d a t e d and characterised.
C i r c u l a r l y polarized
luminescence spectroscopy, a
t e c h n i q u e w h i c h is l i m i t e d to a s m a l l n u m b e r o f l a b o r a t o r i e s , h a s a l s o been c o m p r e h e n s i v e l y reviewed"
.
The application of E u l 1 1 1 )
and T b ( I I 1 ) c o m p l e x e s and p h o t o n c o u n t i n g m e t h o d s d e m o n s t r a t e s a method w i t h c o n s i d e r a b l e p r o m i s e f o r t i m e r e s o l v e d l u m i n e s c e n c e probe s t u d i e s o f b i o c h e m i c a l s t r u c t u r e s . extensively reviewed t h e application
of
8 r a s l a ~ s k y has ~~ p h o t o a c o u s t i c and
p h o t o t h e r m a l m e t h o d s as m e a n s o f s t u d y i n g r a d i a t i o n l e s s deactivation processes in systems o f biological interest.
The
a p p l i c a t i o n o f 3 0 f l u o r e s c e n c e t o t h e n e e d s o f f o r e n s i c science. in
I: Photophysical Processes in Condensed Phases
7
particular t h e identification o f gasoline, have also been surveyed A n o t h e r u s e f u l r e v i e w w h i c h a s been p u b l i s h e d d e a l s
by S i e g e 1 6 1 .
w i t h bioanalytical applications o f fluorescence quenching62
.
A number o f interesting observations using luminescence s p e c t r o s c o p y f o r t h e o b s e r v a t i o n o f n e w e f f e c t s h a v e been r e p o r t e d . f l u o r e s c e n c e h a s been o b s e r v e d t o f o l l o w S n +-T 1
S,+S,,
apparently for t h e first time63.
absorption,
Shock compression of condensed
m e d i a c a n b e produced by i n t e n s e l a s e r l i g h t i l l u m i n a t i o n . s h i f t o f u p t o 800 cm-'
A red
has b e e n o b s e r v e d w i t h b a n d s i n t h e
a n t h r a c e n e f l u o r e s c e n c e s p e c t r u m at p r e s s u r e s u p t o 10 kbar6"
and
t h e c h a n g e o f v i s c o s i t y o f g l y c e r o l w i t h p r e s s u r e s u p t o 19 k b a r
.
e s t i m a t e d f r o m c r y s t a l violet f l u o r e s c e n c e polarization6'
A study
o f t h e e f f e c t s o f p H , s u b s t r a t e , heavy a t o m s , e 2 . o n use o f s o l i d s t a t e r o o m t e m p e r a t u r e f l u o r e s c e n c e and p h o s p h o r e s c e n c e f o r a n a l y s i s o f m i x t u r e s h a s a l s o been reported".
T i m e r e s o l u t i o n has
been used t o s u p p r e s s t h e e f f e c t s o f f l u o r e s c e n c e i n R a m a n spectroscopy
67
.
C o n v e r s e l y , Raman b a c k g r o u n d i n l a s e r i n d u c e d
f l u o r e s c e n c e has been r e d u c e d by d e t e c t i o n o f t h e second h a r m o n i c : i n fact t h e b a c k g r o u n d i s s o r e d u c e d t h a t a m o u n t s as l o w a s 210 f l u o r o p h o r e m o l e c u l e s c a n b e d e t e c t e d i n t h e p r o b e volume6'.
Time
r e s o l v e d d e t e r m i n a t i o n o f t e r b i u m as binary and t e r n a r y c o m p l e x e s h a s a l s o b e e n described6'.
A n i n t e r e s t i n g d e s i g n f o r an a n n u l a r
photochemical reactor shows that some o f t h e more conventional 70
photochemical techniques are still being improved also A
.
c o m p r e h e n s i v e a t l a s o f f l u o r e s c e n c e s p e c t r a and l i f e t i m e s o f
d y e s attached t o p r o t e i n s w i l l p r o v e i n v a l u a b l e t o u s e r s o f b i o l o g i c a l probes71.
F l u o r e s c e n c e i s proving t o be u s e f u l
p h e n o m e n o n in c y t o g e n e t i c s .
P e r t u r b a t i o n s o f d y e f l u o r e s c e n c e by
v a r i a t i o n s i n DNA c o m p o s i t i o n and i n t e r d y e e n e r g y t r a n s f e r c a n b e used t o study c h r o m o s o m e s t r u c t u r e , r e p l i c a t i o n and r e p a i r 7 2 . i s o b v i o u s l y o f c o n s i d e r a b l e v a l u e t o biologists.
This
Fluorescence
m i c r o s c o p y i s b e c o m i n g an e x t r e m e l y u s e f u l t o o l i n c e l l b i o l o g y e s p e c i a l l y i n v i e w o f t h e e x t e n s i v e r a n g e o f p r o b e s w h i c h have b e c o m e available.
A
very c o m p r e h e n s i v e r e v i e w o n f l U O r e S C e n C e
d i g i t a l i m a g i n g m i c r o s c o p y i n d i c a t e s t h e p o w e r and p r o m i s i n g f u t u r e 73 o f this technique . Amongst o t h e r p a p e r s p a r t i c u l a r a t t e n t i o n i s d r a w n to a d e s i g n f o r a f l u o r e s c e n c e m i c r o s c o p y s y s t e m w i t h p i c o s e c o n d t i m e r e s o l u t i o n 7 4 and t h e o b s e r v a t i o n o f f l u o r e s c e n c e microscopy in three dimensions o r microtomoscopy
75
Photochemistry
8 2 Siwalet State Processes
T h e r e i s a t r e n d away f r o m t h e s t u d y o f p a r t i c u l a r m o l e c u l e s , such as b e n z e n e , w h i c h h a v e been r e g a r d e d a s b e i n g e x a m p l e s o f specific chromophore properties which are essential for a complete u n d e r s t a n d i n g o f b e h a v i o u r in m o r e c o m p l e x s i t u a t i o n s .
Simple
m o l e c u l e s a r e h o w e v e r s t i l l i m p o r t a n t s u b j e c t s f o r research. l i f e t i m e s o f 'Ago2
The
m o l e c u l e s i n r a r e g a s m a t r i c e s h a v e been
m e a s u r e d and f o u n d t o r e l a t e t o t h e r e f r a c t i v e i n d e x o f t h e E m i s s i o n f r o m O 2 ('Eg*)
medium.76
has been detected for t h e first
t i m e by s e n s i t i z a t i o n f r o m t h e b e n z o p h e n o n e t r i p l e t at 1.93 p m w i t h a very s h o r t l i f e t i m e 7 7 .
T h e s a m e s t a t e h a s b e e n d e t e c t e d by
d e c o m p o s i t i o n o f l , 4 - d i m e t h y l n a p h t h a l e n e e n d o p e r o x i d e and by d i r e c t e x c i t a t i o n o f g r o u n d s t a t e 3 0 2 t o t h e S2 state.
The photochemistry
o f selected C2 and C3 c o m p o u n d s in l o w t e m p e r a t u r e m a t r i c e s has been r e v i e w e d by Perutz'l'
and f o u r w a v e m i x i n g h a s b e e n used t o
study i n t e r a c t i o n s and r e o r i e n t a t i o n o f c a r b o n d i s u l p h i d e i n o r g a n i c liquids7'. p h o t o l y s i s o f S8
An unusual study i s that reported on t h e in c y c l o p e n t a n e t o g i v e S3 and S4
80
.
T h e f l u o r e s c e n c e d e c a y o f a l k a n e s i s a c c e l e r a t e d by x e n o n w h i c h i n f l u e n c e s both i n t e r s y s t e m c r o s s i n g and i n t e r n a l c o n v e r s i o n 81 processes . T h e f l u o r e s c e n c e l i f e t i m e o f c y c l o h e x a n e i n solid l i q u i d , and v a p o u r phases has been m e a s u r e d by VUV s y n c h r o t r o n radiation".
S y n c h r o t r o n r a d i a t i o n h a s a l s o b e e n used t o m e a s u r e 83
.
l i f e t i m e s o f a n u m b e r o f p a r a f f i n s and a l i c y c l i c c o m p o u n d s S2
4
So
e m i s s i o n has b e e n s e e n i n u - t r a n s
-
1,3,5,7,9*11,13-
t e t r a d e c a - h e p t a e n e i n s o l u t i o n at r o o m t e m p e r a t u r e and a t 77 K i n glassese4.
In t h i s c a s e t h e S2
and t h a t f o r S 1
4
S
is 2 l A -
9
So
-+
-+
transition is l l B :
llA-. g
3
llA9
Picosecond t i m e resolved
a b s o r p t i o n s p e c t r a o f l i q u i d CC14 and a l k y l c h l o r i d e s h a s been m e a s u r e d by 266 n m m u l i p h o t o n l a s e r p h o t o l y s i s a 5 is involved.
.
Photoionisation
T h e s i n g l e t and t r i p l e t e x c i t e d s t a t e s o f
n i t r o s a m i n e s h a v e been e x t e n s i v e l y e x a m i n e d e 6 and t h e m e c h a n i s m o f photolysis o f nitromethane in ethyl ether solution studied
87
.
T r a n s i e n t s i n t h e v a p o u r and s o l u t i o n p h a s e s o f h e x a f l u o r o b e n z e n e h a v e b e e n c h a r a c t e r i s e d a s S n s t a t e s and t h e 88 L a s e r f l a s h p h o t o l y s i s h a s used precursor of t h e Dewar isomer
.
t o s t u d y n u c l e o p h i l i c s u b s t i t u t i o n o f 4-chloro- and 4 - f l u o r o a n i s o l e i n a q u e o u s s o l u t i ~ n ~ ~T h.e p h o t o p h y s i c a l b e h a v i o u r o f p h e n o l and a n i s o l e i n v a r i o u s s o l v e n t s i n v o l v e s d e a c t i v a t i o n o f S1 V J t h e triplet manifold, although t h e nature o f t h e final state is Solvent
I: Photophysical Processes in Condensed Phases dependent”.
9
S o l v e n t e f f e c t s o n Lne f l u o r e s c e n c e s p e c t r a o f
a m i n o b e n ~ e n e s ~, ’ p i c o s e c o n d s t u d i e s o n e x c i t e d s t a t e f o r m a t i o n i n
p-
d i e t h y l a n i l i n e g 2 , and t h e e f f e c t o f i n t r a m o l e c u l a r r o t a t i o n i n cyano-fl , N - d i a l k y l a n i l i n e s 3 h a v e a l s o been r e p o r t e d .
Red s h i f t s i n
t h e f l u o r e s c e n c e s p e c t r a o f t w o p y r r y l i u m i o n d e r i v a t i v e s h a v e been assigned t o f a s t s o l v e n t r e l a x a t i o n p r o c e s s e s g 4 . T h e S,
s t a t e o f b i p h e n y l i n s o l u t i o n h a s been o b s e r v e d by b o t h
a b s o r p t i o n and by Raman spectra”. s t e p w i s e t w o p h o t o n excitation.
T h e c a t i o n r a d i c a l i s f o r m e d by P u l s e r a d i o l y s i s h a s b e e n used t o
follow intramolecular excimer formation in stereoisomeric d i p h e n y l t r i d e ~ a n e s ’ ~w h i c h a r e m o d e l s y s t e m s f o r p o l y s t y r e n e . T h e S1
s t a t e o f n a p h t h a l e n e has a l s o been o b s e r v e d by t i m e r e s o l v e d
r e s o n a n c e R a m a n s p e c t r o s c o p y and has a broad a b s o r p t i o n a r o u n d 425 n m g 7 .
O t h e r s h o r t t i m e s t u d i e s o n t h e S2 s t a t e o f a z u l e n e h a v e
d e m o n s t r a t e d s i n g l e v i b r a t i o n a l l e v e l f l u o r e s c e n c e and t h i s h a s allowed t h e d y n a m i c s o f v i b r a t i o n a l e n e r g y r e l a x a t i o n t o be studied9’.
T h e same investigators have also examined t h e transient
Raman spectra o f various substituted stilbenesg9.
Fluorescence
l i f e t i m e s o f t r a n s - s t i l b e n e and i t s s t r u c t u r a l l y r i g i d d e r i v a t i v e s , t h e t e t r a h y d r o c h r y s e n e s , h a v e b e e n m e a s u r e d and compared’ O 0
.
The
effect o f m o d e r a t e l y high p r e s s u r e o n t h e a b s o r p t i o n and f l u o r e s c e n c e s p e c t r a o f D P H , 1 , 8 - d i p h e n y l o c t a t e t r e n e , and 4 , 4 ’ d i c y a n o - O P H s h o w t h e s e p a r a t e e f f e c t s on t h e e m i s s i o n f r o m b o t h t h e
’ Ag
and ’Bu states”‘.
A
detailed study o f t h e fluorescence o f a 102 S2 s t a t e
n u m b e r o f DPH d e r i v a t i v e s h a s a l s o been p u b l i s h e d
.
properties o f fixed 8-cyanoheptafulvenes, i n particular values o f B F and T~
have been measured l o 3 .
p y r i d i n e matrices’”
-
Anthracene excimers i n
and i n l i q u i d anthracene’
O5
have examined as
w e l l 8s m i x e d e x c i m e r s f o r m e d by a n t h r a c e n e and p h e n a n t h r e n e S1
Sn
and T 1 -+
T
d e r i v a t i v e s h a v e bee:
106
.
absorption spectra o f anthracene d e t e r m i n e d by l a s e r f l a s h p h o t ~ l y s i s ’ ~ ’ .
The
fluorescence anisotropy o f 1,9-dimethylanthracene has been studied o v e r a w i d e r a n g e o f t e m p e r a t u r e and v i s c o s i t y u s i n g s y n c h r o t r o n r a d i a t i o n f o r excitation’
O’
.
Solvent effects on electronically
excited s t a t e s o f 9 , 9 ‘ - b i a n t h r y l s h o w e v i d e n c e f o r s o l v e n t e x c i p l e x e s w h i c h m a y , i n s t r o n g l y p o l a r s o l v e n t , be p r e c u r s o r s o f ionsl o g E-l-(g-anthryl)-P-( 10-methyl-9-anthryllethene gives excimer emission which correlates well with predictions which can be m a d e f r o m t h e c r y s t a l structure‘”. of t r a n s - ( 9 - a n t h r y l ) e t h y l e n e s
The e x c i t e d s t a t e p r o p e r t i e s
show t h e effects o f geometric
d i s t o r t i o n about t h e s i n g l e bond”’.
The conformations o f 9 -
Photochemistry
10
cyanoanthracene excimers have studied i n t h e crystalline state as a f u n c t i o n o f pressure’
-
Torsional dynamics of 9-carbonyl
2.
substituted a n t h r a c e n e s a f t e r t h e S
*
S ( r , n 1 transition
s h o w a c h a n g e f r o m a nearly perpendPcularl t o a c o p l a n a r f o r m 1 l 3 . The fluorescence properties o f meso-substituted h a v e been e x a m i n e d also’
’‘ .
amidoanthracenes
Pyrene excimers still attract
c o n s i d e r a b l e i n t e r e s t , f o r e x a m p l e , a p i c o s e c o n d t i m e resolved study has been m a d e o f e x c i m e r f o r m a t i o n in s i n g l e c r y s t a l s 1 1 5
.
T h e c o r r e c t e m i s s i o n s p e c t r u m o f f l u o r a n t h r e n e has b e e n obtained by u s e o f purified
samples’16.
T h e e m i s s i o n at 350 n m , w h i c h has been
reported p r e v i o u s l y , is p r o b a b l y a n i m p u r i t y , a c e p h e n a n t h r e n e . Solvent e f f e c t s on t h e p u r e r a d i a t i v e l i f e t i m e o f o v a l e n e have a l s o been observed‘
’
7 .
Trace amounts o f polynuclear aromatic compounds
( P N A I can be d e t e c t e d by t h e use o f a n t h r a c e n e as sensitizer’”. T h e r o t a t i o n a l d i f f u s i o n o f p - t e r p h e n y l and fl-quarterphenyl i n s o l u t i o n has been e x a m i n e d as a f u n c t i o n o f v i s c o s i t y and t e m p e r a t u r e by t i m e r e s o l v e d f l u o r e s c e n c e depolarization”
.
The
d e t a i l s o f p r o c e s s e s i n v o l v e d h a v e been d i s t i n g u i s h e d . H e t e r o c y c l i c s y s t e m s e x a m i n e d i n c l u d e v i b r a t i o n a l and e l e c t r o n i c r e l a x a t i o n i n n a p h t h a z a r i n and i t s d e u t e r a t e d d e r i v a t e s i n Ne and Ar matrices12’, azanaphthalenes of durene’ 22.
121
r e l a x a t i o n k i n e t i c s in
, and r e a c t i o n s o f q u i n o x a l i n e i n s i n g l e c r y s t a l s
The picosecond reorientational dynamics of resorufin
has been c o r r e l a t e d w i t h l i q u i d s t r u c t u r e 1 2 3 .
It a p p e a r s that t h e
first solvent shell strongly influences t h e rotational dynamics. Work on t h e p h o t o p h y s i c s o f c a r b o n y l c o m p o u n d s i s m u c h l e s s e x t e n s i v e t h a n i n p r e v i o u s years.
S o l v e n t a f f e c t s h a v e been
i n t e r p r e t e d as i n v o l v i n g T I - r *and n-m* t r a n s i t i o n s i n c a r b o n y l s and h y d r a ~ o n e s ” ~ . T h e t - b u t y l and m e t h y l e s t e r s o f 9 - a n t h r o i c acid ( a n d also t e t r a p h e n y l b u t a d i e n e ) s h o w a d e p e n d e n c e o f t h e e m i s s i o n s p e c t r u m on e x c i t a t i o n w a v e l e n g t h d u e t o t h e p r e s e n c e o f
conformer^'^^.
CNDO/S-CI
c a l c u l a t i o n s h a v e been performed on
e l e c t r o n i c states o f s o m e c a r b o n y l c o m p o u n d s c o n t a i n i n g o r g a n i c luminophores with a stilbene chromophore
126
.
A b s o r p t i o n and f l u o r e s c e n c e s p e c t r a o f P - ( g - a m i n o p h e n y l ) benzimidazole is shown to excite in two forms arising from internal hydrogen bonding t o an e x t e n t w h i c h d e p e n d s o n s o l v e n t polarity’ 2 7 M u l t i p h o t o n i o n i s a t i o n and d i s s o c i a t i o n o f N - i s o p r o p y l d i m e t h y l o x a t i r i d i n e o c c u r s t h r o u g h an assigned Shizuka’*’
s e r i e s o f Rydberg states’ 2 8
.
has reviewed excited state proton transfer
r e a c t i o n s and proton induced q u e n c h i n g of a r o m a t i c c o m p o u n d s .
The
.
I: Photophysical Processes in Condensed Phases
11
l a t t e r i n v o l v e s i n t r a m o l e c u l a r C T s t r u c t u r e and s i m p l e a c i d - b a s e e q u i l i b r i a c a n n o t be achieved d u r i n g t h e l i f e t i m e o f e x c i t e d s t a t e s and c a r e i s needed i n d e t e r m i n i n g p,K
*
values.
Excited s t a t e
proton t r a n s f e r in m e t h y l - 5 - c h l o r o s a l i c y l a t e and m e t h y l 5 0 are examples o f systems examined equilibrium m e t h ~ x y s a l i c y l a t e3 ~
is not set u p i n t h e excited s t a t e o f 4 - ( 9 - a n t h r y l ) - N , N - d i m e t h y l a n i l i n e d u e t o t h e very slow d e p r o t o n a t i o n o f t h e e x c i t e d ' A H * F r e q u e n c y - d o m a i n f l u o r o m e t r y has been used t o e x a m i n e 132 Both r e v e r s i b l e and excited state deprotonation o f $-naphthol state131.
.
i r r e v e r s i b l e i o n i z a t i o n p r o c e s s e s i n t h e $ - n a p h t h o l s y s t e m c a n be distinguished.
P i c o s e c o n d s i n g l e p h o t o n c o u n t i n g has b e e n used t o
measure rate constants for excited state proton transfer o f c a r b a z o l e i n a l k a l i n e solution' 3 3 . hydroxyflavone
134
, 3-hydroxyxanthone
O t h e r s y s t e m s e x a m i n e d a r e 3135 , 2-hydronybenzimidazole' 3 6 ,
2- ( a m i n ~ m e t h y l ) b e n z i m i d a z o l e ' ~ and ~ , protonated
S c h i f f bases13'.
T h e p h o t o p h y s i c s o f r a d i c a l s a t t r a c t s c o n s i d e r a b l e i n t e r e s t at present.
Emission from short lived p - a m i n o p h e n y l t h i y l r a d i c a l s has
an e f f i c i e n c y o f a b o u t 1.52
139
.
A r y l m e t h y l r a d i c a l s at 7 7 K s h o w
e m i s s i o n p r o p e r t i e s w h i c h d e p e n d u p o n i n t r a m o l e c u l a r twist' 4 0 R e a c t i o n s o f 1 - n a p h t h y l m e t h y l radicals'
4'
.
, r a d i a t i v e and n o n -
radiative decay o f electronically excited ketyl radicals o f several s u b s t i t u t e d b e n z o p h e n o n e k e t y l r a d i c a l s in p o l y ( v i n y 1 a l c o h o l ) f i l m s at 7 7 K l 4 * .
intersystem crossing efficiencies in biradicals as
affected by s p i n o r b i t
and m a g n e t i c field e f f e c t s u p o n
t h e l a t t e r h a v e a l l been m e a s u r e d by nanosecond absorption'"
transient UV
.
The photochemistry o f pyrenylmethylphosphonium salts shows p h o t o i n d u c e d s o l v o l y s i s by a h e t e r o l y t i c s c i s s i o n t o g i v e t h e a l k o x y m e t h y l p y r e n e and t r i p h e n y l p h o s p h i n e c o m p o u n d s i n alcohols'
2.1
".
F l e c t r o n T r a n s f e r R e m o n s and Fx-lexes.
-
New aspects o f
the role of solvent i n photoinduced electron transfer in polar s o l u t i o n s h a v e been analsyed i n d e t a i l by K a k i t a n i and Mataga'"
.
The effect o f solvent o n the dipolar contribution t o exciplex s t a b i l i t y has b e e n s h o w n by m e a s u r e m e n t s o n a r a n g e o f u n s a t u r a t e d c o m p o u n d s o n t h e d e a c t i v a t i o n o f t h e S, n a p h t h a l e n e derivatives1".
state of several
Q u e n c h i n g o f e x c i m e r s o f p y r e n e and
9 , l O - d i c h l o r o a n t h r a c e n e by e l e c t r o n d o n o r s i n d i f f e r e n t s o l v e n t s is less e f f i c i e n t t h a n f o r t h e parent
molecule^'^^.
The
thermodynamics o f formation of t h e perylene/Ag+ exciplex shows that
12
Photochemistry
q u e n c h i n g by t h i s r o u t e i s e s s e n t i a l l y e n t r o p y driven’”. Intramolecular exciplex formation occurs i n 6-(2’,3’butenoxy ) m e t h y l - I - c y a n o n a p h t h a l e n e ’ ” . T i m e r e s o l v e d s p e c t r o s c o p i c t e c h n i q u e s a r e w e l l suited t o t h e study o f e l e c t r o n t r a n s f e r and s o l v e n t e f f e c t s . and energy r e s o l v e d d e c a y m e a s u r e m e n t s
Both f l u o r e s c e n c e
show orientational
isomerization takes place in t h e excited singlet state of electrondonor acceptor complex o f p-xylene with 1 , 2 , 4 , 5 t e t r a c y a n ~ b e n z e n e ’ ~.’ T h e d y n a m i c s o f an e x c i t e d t r a n s - s t i l b e n e o l e f i n contact pair i n v o l v e s s o l v e n t and salt e f f e c t s on back e l e c t r o n t r a n s f e r and ion pair s e p a r a t i o n l S 2
.
Subpicosecond
spectroscopy shows that relaxation processes in iron ( 1 1 1 ) t e t r a p h e n y l p o r p h i n e o c c u r o n f e m t o s e c o n d t i m e scales’ 5 3
.
The
t r a n s i e n t s o l v a t e d e l e c t r o n g e n e r a t e d by p h o t o i o n i z a t i o n o f p h e n o l shows s p e c t r a l s h i f t s i n d i f f e r e n t s o l v e n t s and e v i d e n c e i s produced f o r a l o n g l i v e d solvated e l e c t r o n - i o n p a i r l S 4 .
The
i n f l u e n c e of s o l v e n t r e l a x a t i o n o n e l e c t r o n t r a n s f e r r a t e s h a s been examined i n rigid solution’s5 and t h e r o l e o f i o n pairs i n e l e c t r o n d o n o r - a c c e p t o r s y s t e m s m a d e in a f r u i t f u l c o m p a r i s o n o f picosecond s p e c t r o s c o p y and C I O N P studies’ 5 6
.
A very
detailed investigation
has been r e p o r t e d on t h e d i s a p p e a r a n c e o f t h e t w i s t e d c h a r g e transfer state ( T I C T ) of p - d i m e t h y l a m i n o b e n z o n i t r i l e by p i c o - and nanosecond
spectrosc~py’~~ I ’
and p h a s e m o d u l a t i o n
f l u o r o m e t r y h a s a l s o been used t o study s o l v e n t c a g e r e o r i e n t a t i o n around t h e e x c i t e d s t a t e o f e t h y l a m i n o - 9 - m e t h o x y - 2 - c h l o r o - 6 - a c r i d e in g l y e r o 1 1 5 9 . A number of similar
s t u d i e s h a v e a l s o b e e n made.
These
include the dynamic Stokes shift of trans-4-dimethylamino-4’cyanostilbenel
6o
, d i f f e r e n t r e l a x a t i o n m e c h a n i s m s i n a p r o t i c and
p r o t i c s o l v e n t s o f ~-bJ,fi-dimethylamino-benzonitrileand related
-N , N_-dialkylaniline
compounds’ 6 1 , t h e d u a l f l u o r e s c e n c e o f 4 - N ,y-
d i m e t h y l a m i n o b e n z o n i t r i l e r e l a t e s t o h y d r o g e n bonding and t h e red
shift i s d u e t o t h e t w i s t e d c o n f o r m a t i o n ’ 6 2 , and s o l v a t o c h r o m i c e f f e c t s i n t h e f l u o r e s c e n c e o f 2 - a m i n o a n t h r a c e n e and tj.N_-dimethyl -2-aminoanthracene where a detailed comparison with different m o d e l s i s g i ~ e n ” ~ . T h e g i a n t d i p o l e m o m e n t d e v e l o p e d by 4 d i e t h y l a m i n o - 4 ‘ - n i t r o s t i l b e n e o n e x c i t a t i o n i n s o l u t i o n and p o l y m e r films g i v e s r i s e t o p r o p e r t i e s w h i c h h a v e i n t e r e s t i n g t e c h n o l o g i c a l p o s s i b i l i t i e s i n o p t o - e l e c t r o n i c s ’ “ . A c o m p a r i s o n of e x c i t e d s t a t e d i p o l e m o v e m e n t s and p o l a r i z a b i l i t i e s w h i c h a r e e s t i m a t e d f r o m solvent s p e c t r a l s h i f t s h a v e been c o m p a r e d w i t h t h o s e d e t e r m i n e d by
I: Photophysical Processes in Condensed Phases electro-optical measurements’ 6 5
.
13
D u e t o t h e u n c e r t a i n t i e s involved
i n t h e a p p l i c a t i o n o f t h e f o r m e r m e t h o d s u c h c o m p a r i s o n s a r e very significant.
T h e f l u o r e s c e n c e s p e c t r a o f 4 and 4 , 4 ‘ - n i t r o -
d e r i v a t i v e s o f DPH a r e r e m a r k a b l y d e p e n d e n t o n s o l v e n t polarity’“. I n d o l e d e r i v a t i v e s h a v e been studied i n s o l u t i o n and t h e v a p o u r p h a s e and t h e ’La-’Lb
l e v e l i n v e r s i o n e f f e c t s a r e used t o
account for the o b s e r ~ a t i o n s ’ ~ ~ A p a p e r by Suppan17’
16’.
draws attention t o electrostatic
interaction effects on condensed phase photoinduced electron t r a n s f e r and t h e need t o t a k e a c c o u n t o f t h e f a c t t h a t s o l v e n t i s not i n r e a l i t y a u n i f o r m d i e l e c t r i c m a t e r i a l .
Pressure effects o n
e x c i p l e x f o r m a t i o n h a s been e x e m p l i f i e d i n t h e pyrene-pc y a n o b e n z e n e system’ 7’
.
Ternary electron donor acceptor complexes
a r e f o r m e d and in t h e c a s e o f anthracene-tetracyanoethylene g i v e s rise t o (DO+ 1 dimer radical cations17*.
Laser flash photolysis
shows that perylene i n acetonitrile undergoes three distinct electron transfer processes, P:
+
( i ) g i v e s P’ + MeCN:,
(iii g i v e s
P 7 , and ( i i i ) t r i p l e t - t r i p l e t i n t e r a c t i o n y i e l d s P:
and P T 1 7 3 .
T h e d u a l f l u o r e s c e n c e o f 4 , 4 ‘ - d i m e t h y l a m i n o - and
4,4‘-diaminophenylsulphone is a consequence of d-orbital
participation in intramolecular charge separation i n polar
solvent^'^'.
E x c i p l e x promoted e l e c t r o n t r a n s f e r h a s a l s o b e e n
e x a m i n e d i n 1 - ( p h e n y l a m i n o1-3- ( 9 a n t h r y l ) propanes’ ”
.
T h e barriei
d u e t o s o l v e n t r e o r g a n i s a t i o n h a s been c o n s i d e r e d i n t h e i n t e r p r e t a t i o n o f s o l v e n t e f f e c t s o n p h o t o i n d u c e d e l e c t r o n transfei in the rigid bichromophoric systems involving methoxybenzene as d o n o r and a variety o f e l e c t r o n a c c e p t o r groups’ 7 6 .
Intramoleculal
electron transfer involving porphyrins bearing trinitroaryl a c c e p t o r g r o u p s h a s been studied’ 7 7 .
T h e p h o t o p h y s i c s o f polarizec
enones in various solvents shows that intramolecular charge t r a n s f e r a l s o o c c u r s in t h e s e m o l e c u l e s 17’. Solute-solvent exciplexes are involved i n photoinduced f o r m a t i o n o f r a d i c a l i o n s o f 4-tJ,N-dimethylaminobenzonitrile and r e l a t e d c~rnpounds’~’.
T h e c o r r e s p o n d i n g t r i p l e t s t a t e s d o not
appear t o form exciplexes.
Radical ion formation from l-anisyl-
2 , 2 - d i p h e n y l b r o m i d e i n a c e t o n i t r i l e and a c e t i c acid h a s a l s o b e e n examined i n d e t a i l l e 0
.
Photo-induced methoxy substitution i n 3 -
n i t r o a n i s o l e and 3 , 5 - d i n i t r o a n i r o l e o c c u r s via a n u c l e o p h i l e C a t o m r e a c t i o n w h i c h i s t h e r a t e d e t e r m i n i n g step’”.
+
The
d y n a m i c s o f t r a n s i e n t i o n p a i r s and r a d i c a l pairs i n a n t h r a c e n e derivative/ tetranitromethane systems have been examined a s a
rin!
Photochemistry
14 f u n c t i o n o f s o l v e n t and salt e f f e c t s by t i m e r e s o l v e d spectroscopy’82.
The effect of solvent structure on t h e hydration
d y n a m i c s o f e l e c t r o n s formed f r o m t h e f l u o r e s c e n t p r o b e 6 - p t o l u i d i n e - 2 - n a p h t h a l e n e s u l p h o n a t e has been i n v e s t i g a t e d i n H 2 0 / E t O H
mixed s o l v e n t systernsle3.
A c l u s t e r o f t h r e e or f o u r w a t e r
m o l e c u l e s is found t o b e t h e e l e c t r o n a c c e p t o r i n t h i s case. TICT states occur i n t h e intramolecular quenching o f fluorescence in a m i n o - c o u m a r i n s w h e r e s o l v e n t e f f e c t s s h o w d e v e l o p m e n t o f a large dipole in the excited s t a t e t E 4 .
R e s o r u f i n i n t h e excited
s t a t e i n t e r a c t s w i t h a n i o n s a s s h o w n by m o l e c u l a r r e o r i e n t a t i o n measurements’”.
Aggregates of ions are probably involved in
q u e n c h i n g o f t h e f l u o r e s c e n c e o f t h e pyrene-H,pt-dimethylaniline e x c i p l e x in s o l v e n t s o f l o w e l e c t r i c constant“‘.
Picosecond
dynamics of proton transfer within amine-ketone acid-base pairs, including dimethylaniline
-
a n t h r a q u i n o n e h a s been studied”’
.
P h o t o i n d u c e d i s o m e r i z a t i o n and c h a r g e t r a n s f e r i n t r a n s - 1 , 2 - b i s ( l -
-
methyl-4-pyridine)
e t h y l e n e salts’”,
dichloroanthroquinone
photoreduction o f 1,8-
by t r i e t h y l a m i n e 1 8 9 and a n t h r a q u i n o n e by all occur via exciplexes.
t r i e t h y l a m i n e i n acetonitrile’”
Switching o f p h o t o c h e m i c a l r e a c t i o n p a t h w a y s i n a s e r i e s o f b i c h r o m o p h o r i c s p e c i e s , ~ - C w - ( ~ - n i t r o p h e n o x y l ) a l k y l la n i l i n e s f r o m a photo-Smiles rearrangement to a photoredox reaction with The effects o f electron
i n c r e a s i n g c a r b o n c h a i n length’”.
transfer processes i n heterogeneous photochemistry in various systems has been r e v i e w e d t g 2 .
2.7 Dves and Related
SYS-
-
A
m a j o r r e a s o n f o r an i n t e r e s t i n
dyes is the search for continuous improvement in t h e design o f tuntable lasers.
Amplified spontaneous emission is observed from
3 - h y d r o x y f l a v o n e and a r e l a t e d l a s e r d y e d u e t o a r a p i d t a u t o m e r i s m which occurs in t h e ground stateIg3.
Quaterphenyl dyes are
s u i t a b l e as U V l a s e r d y e s p a r t i c u l a r l y s u b s t i t u t e d
p-
q ~ a t e r p h e n y l s ” ~ and ring b r i d g e d q u a t e r p h e n y l ~ ’. ~ ~A very d e t a i l e d study has been m a d e o f t h e s p e c t r a l and t e m p o r a l fluorescence o f 4-dicyanomethylene-2-methyl-6-dimethylaminostyryl4H-pyran ( D C M ) l g 6 .
A n u m b e r o f e x p l a n a t i o n s a r e put f o r w a r d t o
explain t h e d u a l f l u o r e s c e n c e i n c l u d i n g a g g r e g a t i o n and s o l v e n t exciplex formation.
Q u a n t u m c o u n t i n g by l a s e r d y e s w h i c h c o v e r a
broad s p e c t r a l r a n g e i n c l u d i n g t h e n e a r I R can be used t o extend the range for correction o f fluorescence spectra up t o 7 0 0 - 7 8 0 nm
197
. I n v e s t i g a t i o n s o f b e n z o p y r y l i u m s a l t s C Z 1 4 4 and C Z 6 8 2 i n
I: Photophysical Processes in Condensed Phases CH2C12
s h o w t h a t Of > 0 . 5 .
15
Excited state absorption d a t a i n
l a s e r d y e s at t h e X e C l w a v e l e n g t h h a v e a l s o been publi~hed'~'. A b s o r p t i o n and f l u o r e s c e n c e spectra o f 7-aminocoumarin d e r i v a t i v e s h a v e been recorded'" i n c l u s i o n c o m p l e x e s w i t h B-
and t h e photophysics o f c o u m a r i n
and y - c y c l o d e x t r i n s investigated'".
Solvent e f f e c t s on t h e p h o t o p h y s i c a l behaviour o f pyrrolocoumarin d e r i v a t i v e s a r e similar t o t h o s e o n t h e psorolens2".
Vibronic
exciton bands and t h e absorption spectra o f Eosin Y d i m e r s h a v e been analysed theoretically and compared W i t h e x p e r i m e n t a l data202
.
Picosecond spectroscopic s t u d i e s h a v e been m a d e o n t h e i o n i c
.
photodissociation d y n a m i c s o f m a l a c h i t e g r e e n l e u ~ o c y a n i d e ~ ' ~ T h e lowest s t a t e p r o d u c e s i o n s w i t h i n 0.1 t o 0.5 n s w h i l s t f o r higher s t a t e s 6 - 1 3 ps a r e sufficient for t h e development o f c h a r g e separation.
T h e photophysics of c r y s t a l violet i n a series o f n-
a l c o h o l s 2 0 4 and t h e picosecond bleaching behaviour of c r y s t a l violet in t h e ground and excited s t a t e s between 4 5 5 and 7 2 0 nm'" are l a s e r relevant studies.
Picosecond spectroscopy o f
i n t r a m o l e c u l a r hydrogen bonding o f 4 , 4 ' , 7 , 7 ' - t e t r a m e t h y l i n d i g o is an interesting s t r u c t u r a l study206
.
T h e f l u o r e s c e n c e and
absorption spectra o f t h i o f l a v i n T a r e strongly affected by freezing in w a t e r d u e t o d i m e r i z a t i o n o f d y e s t u f f i o n s 2 0 7 . F l u o r e s c e n c e a s w e l l as t r i p l e t s t a t e properties h a v e been m a d e i n
.
l I 4 - U C 2 -( 5 - p h e n y l - o x a z o l y l )I b e n ~ e n e ~ ~ ' T h e t e m p e r a t u r e d e p e n d e n c e o f t h e l i m i t i n g f l u o r e s c e n c e anisotropy of P O P O P in c e l l u l o s e a c e t a t e film has a l s o been measured'".
The influence o f
solvent o n t h e absorption spectra and excited deactivation m e c h a n i s m o f U V stabilizers o f t h e 2 - ( h y d r o x y p h e n y l ) b e n z o t r i a z o l e class i s o f c o n s i d e r a b l e t e c h n i c a l interest'".
The n a t u r e o f t h e
red f l u o r e s c e n c e f r o m t h e coloured m e r o c y a n i n e f o r m o f 1 , 3 , 3 trimethyl-6'-nitrospiro[indoline-2,2'-
12Hlbentopyranl in s o l u t i o n
and polymer f i l m s has been examined and t h e extent o f t a u t o m e r i z a t i o n t o a c o l o u r l e s s f o r m assessed2".
The decay o f t h e
excited J a g g r e g a t e of p s e u d o i s o c y a n i n e i o d i d e has been found t o occur w i t h a decay t i m e of 25 ps2l2. 2-Phenyl-3- i n d o l o c y a n i n e d y e s show d o u b l e e x p o n e n t i a l d e c a y t i m e s indicating t h e involvement o f a photoinduced cis-trans isomerization2'3
.
Excited s t a t e r e l a x a t i o n
processes of m o n o m e r i c and aggregated d i e t h y l t h i a c a r b o c y a n i n e iodide h a v e been studied by picosecond a b s o r p t i o n spectra'". Aggregated states h a v e fast and efficient r a d i a t i o n l e s s d e c a y processes w h i c h depend on very strong d i p o l e - d i p o l e interactions which a r e enhanced by t h e i n f l u e n c e o f t h e solvent d i p o l e moment.
16
Photochemistry F l u o r e s c e n c e l i f e t i m e s and e f f e c t s o f a g g r e g a t i o n o f d y e s o n
microcrystals o f silver bromide give information directly relevant to the improvement o f photographic processes215
.
P h o t o p h y s i c a l and
photochemical properties o f common dyes i n amphiphilic media like
S O S and C T A B s h o w that t h e d y e s a r e l o c a t e d at c o n s i d e r a b l y hydrated s i t e s 2 1 6 . A x i a l l i g a t i o n s i g n i f i c a n t l y a f f e c t s t h e f l u o r e s c e n c e of tetrakispheny1porphyrins2’
and f o r s o m e p o r p h y r i n s and I X
m e t a l l o p o r p h y r i n s l u m i n e s c e n c e and p h o t o d i m e r i z a t i o n h a v e been reported2”
.
Very s h o r t f l u o r e s c e n c e l i f e t i m e s h a v e been m e a s u r e d
f o r i r o n , n i c k e l and c o b a l t p h t h a l o c y a n i n e s
(
2 - 3 ps 1 2 ’
.
P h o t o r e d u c t i o n o f i n d i g o d y e s by e l e c t r o n d o n o r s s h o w s t h e involvement o f o n e or two electron transfer reactions which occur as a c o n s e q u e n c e o f e x c i t e d s t a t e q u e n c h i n g 2 2 0 .
Quenching of
f l u o r e s c e n c e h a s b e e n used t o f o l l o w s u c h p h o t o i n d u c e d e l e c t r o n t r a n s f e r r e a c t i o n s o f r h o d a m i n e B w i t h s e v e r a l r e d o x q u e n c h e r s in films o f p o l y ( N - - v i n y l p y r r o l i d o n e ) 2 2 1
.
Electron transfer efficiency
d e p e n d s o n t h e r e d o x p o t e n t i a l o f q u e n c h e r and c a n o c c u r at distances up t o 1 5 8
.
7.3 Pho-tation
and R e b t e d Processes,
-
These
rearrangements provide model systems for t h e examination of primary processes but a r e n o w s h o w i n g i n c r e a s i n g p r o m i s e f o r e x p l o i t a t i o n in the design o f various electrooptical devices.
S t a t m a n and
Robinson222 have analysed the molecular dynamics of cis-trans i s o m e r i z a t i o n and d e t a i l s o f t h e i n f l u e n c e o f s o l v e n t s t r u c t u r e . Excluded v o l u m e e f f e c t s and t h e d i f f e r e n t s i z e s o f
cis
and t r a n s
i s o m e r s h a v e b o t h been t a k e n i n t o a c c o u n t in t h i s m o d e l .
The
isomerization o f alkenylanthracenes in solution has rate constants w h i c h a r e a f f e c t e d by s o l v e n t
The alternative Grote-
H y n e s and K r a m e r s m o d e l s f o r t h i s t y p e o f p r o c e s s a r e c o m p a r e d w i t h t h e experimental data. B e c k e r and his c o w o r k e r s h a v e i n v e s t i g a t e d t h e p h o t o i s o m e r i z a t i o n o f p r o t o n a t e d and u n p r o t o n a t e d n - b u t y l a m i n e S c h i f f b a s e s o f v a r i o u s r e t i n a l ~and ~ ~ a~l s o h a v e r e p o r t e d t h e s p e c t r o s c o p y and p h o t o i s o m e r i z a t i o n o f a s e r i e s o f p o l y f e t h y l e n e g l y c o l ) p e p t i d e S c h i f f bases o f 1 1 - c i s - r e t i n a 1 2 2 s . T h e picosecond d y n a m i c s o f b a r r i e r c r o s s i n g in t h e conformational change of 1 , l ‘ - b i n a p t h y l in a series o f alcohol solvents shows excellent agreement with t h e Kramer’s model for i n t e r m e d i a t e and high f r i c t i o n regimes226
.
Deviation from t h e
I: Photophysical Processes in Condensed Phases
17
Kramer's m o d e l may b e d u e t o e f f e c t s o t h e r t h a n n o n - M a r k o v i a n friction.
The fluorescence properties o f t h e conformational isomer
mixtures of trans-2-styryl-naphthalene provides further evidence for different radiative decay properties o f t h e two rotamers o f t h i s compound227
.
T h e r e s o l u t i o n and c h a r a c t e r i s a t i o n h a s been
m a d e o f t h e r o t a m e r s o f 1-phenyl-2- ( 2 - a n t h r y l ) ethylene2"
and t h e
three conformers i n case o f trans-di(2-napthyl)ethyleneaa9
.
A
c o m b i n e d p h o t o c h e m i c a l and UV a b s o r p t i o n s t u d y c o n d u c t e d i n r i g i d media elucidates t h e role o f rotamers in a z o n a p h t h a l i n e ~ ~ ~ ~ . Dynamic solvent effects on t h e large amplitude isomeritation rates 231 , 2 - ( 2 ' - p r o p e n y l ) a n t h r a c e n e , and (=)-2-(but-
of 2-vinylanthracene 2'-en-2'yl)
anthraceneZ3'
coworkers.
T h e p h o t o i s o m e r i z a t i o n o f t h e S c h i f f b a s e o f 11-cis-
h a v e been r e p o r t e d by Barbara and h i s
r e t i n a l h a s been e x a m i n e d o v e r t h e u n u s u a l l y e x t e n s i v e ps t o 1 s
or l o n g l i v e d t r a n s i e n t s w e r e d e t e c t e d
time range233.
No t r i p l e t s
in t h i s study.
The photochemical trans-cis isomerization o f 1,2-
-
U ( h e t e r o a r y 1 ) e t h y l e n e and 1 , 2 - u ( p y r a z i n y l l e t h y l e n e s h o w s t h a t t h e q u a n t u m yield o f t r a n s
c i s conversion increases with solvent
polarity b e c a u s e o f t h e p r o x i m i t y o f ' ( n , I T * ) and states234.
'(IT, n * )
The triplet state i s involved i n t h e direct
i s o m e r i z a t i o n i n c o n t r a s t w i t h s t i l b e n e w h i c h only i n v o l v e s c h a n g e s occurring in t h e singlet manifold.
T h e fluorescence of trans-
s t i l b e n e in l i q u i d e t h a n e g i v e s b a r r i e r c r o s s i n g r a t e s a s a function
of
p r e s s u r e in t h e r a n g e 0 t o 170 atmZ3'.
r a t e o c c u r s at 1 2 0 a t m .
A peak
Femtosecond pulse excitation o f
in t h e
cis-
s t i l b e n e i n h e x a n e at 312.5 n m y i e l d s a t r a n s i e n t a b s o r p t i o n i n t h e visible with a 1.35 ps lifetime236.
The kinetics show a n evolution
which is interpreted as resulting from the intermediacy o f a s t i l b e n e 'phantom' s t a t e w i t h a l i f e t i m e o f 3 2 2 p s .
Fluorescence
and i s o m e r i z a t i o n i n 4 , C ' - d i a m i n o s t i l b e n e a r e m a r k e d l y a f f e c t e d by s o l v e n t viscosity w h i c h i n f l u e n c e s t h e e n e r g y barrier237
.
Photoinduced electron transfer competes w i t h phtoisomerization i n the quaternary salts o f 4-nitro-4'-azastilbene quinolinium analogues238.
and t h e i r
P h o t o i s o m e r i t a t i o n o f 3-styryl-2' , 4 * ,6'-
trisopropylstilbene shows t h e steric effects o n t h e location o f electronic excitation at groups within t h e molecule239. Trans
---*
c i s i s o m e r i z a t i o n o f 4 - s u b s t i t u t e d 4 - a z a s t i l b e n e s t a k e s p l a c e by a s i n g l e t m e c h a n i s m and t r i p l e t s t a t e s h a v e a l s o b e e n ~haracterised'~'. c i s isomerization
A n e w mechanism has been
o f c y a n i n e dyesz4'
.
proposed f o r t h e t r a n s -
Picosecond spectroscopic
m e t h o d s h a v e m a d e it p o s s i b l e t o o b s e r v e p h o t o i s o m e r s o f s h o r t
Photochemistry
18 chain cyanine dyes.
A l s o s o l v e n t d e p e n d e n t b a r r i e r h e i g h t s have
been e s t a b l i s h e d i n e x c i t e d s t a t e s o f d i e t h y l t e t r a m e t h y l i n d o carbocyanine iodide in n-alcohol solution242
.
S o l v e n t s t r u c t u r e and d y n a m i c s o f t h e e x c i t e d - s t a t e tautomerization o f 7-azaindole/alcohol complexes are explained as proton a r i s i n g f r o m t r a n s f e r r e a c t i o n s w h i c h r e q u i r e s o l v e n t involvement2‘
.
It has b e e n proposed t h a t c o n c e n t r a t e d s o l u t i o n s o f a z o b e n z e n e can be used f o r a ~ t i n o m e t r y ~ ~Q u~ a.n t u m y i e l d s o f t h e p h o t o i s o m e r i z a t i o n needed f o r t h i s p u r p o s e a r e f u l l y q u o t e d i n t h e paper.
. . 2.4 F l e c t r o n i c F x c i t a t i o n Enerav T r a n s f e r .
-
T h e n u m b e r o f papers
d e a l i n g w i t h t h e o r y and s i m p l e m o l e c u l e s a p p e a r t o h a v e d e c l i n e d o v e r r e c e n t years.
An e x c e p t i o n t o t h i s s t a t e m e n t i n v o l v e s
b i o l o g i c a l s y s t e m s and it i s i n b i o c h e m i s t r y t h a t m o s t s i g n i f i c a n t recent w o r k o n e l e c t r o n i c e x c i t a t i o n e n e r g y t r a n s f e r h a s been d o n e . S o m e r e c e n t e x a m p l e s w i l l be m e n t i o n e d i n a l a t e r s e c t i o n o f t h i s review. T w o very m a t h e m a t i c a l t r e a t m e n t s o f e n e r g y t r a n s f e r i n condensed m e d i a d e a l w i t h e x c i t o n s and phononsZ4’ ’ 2 4 6 . C l o s e l y related i s a p a p e r by P a r r i s and Kenkre247 w h i c h e x t e n d s e a r l i e r t h e o r y t o c o v e r l o n g r a n g e t r a p p i n g i n v o l v i n g e x c i t o n m i g r a t i o n and r e l a t e s t h i s t o t h e s t r e n g t h and r a n g e o f t h e c a p t u r e process.
A
detailed k i n e t i c a n a l y s i s h a s been m a d e o f i n t e r m o l e c u l a r m i g r a t i o n o f e x c i t a t i o n e n e r g y and q u e n c h i n g
in regular lattices248.
An
i n t e r e s t i n g i n v e s t i g a t i o n h a s been m a d e o n e n e r g y t r a n s f e r i n s y s t e m s w i t h r e s t r i c t e d g e o m e t r i e s s u c h a s e x e m p l i f i e d by m i c e l l e s , z e o l i t e s , p o l y m e r c o i l s , and p o r o u s glass249.
Deviations from
F o r s t e r t h e o r y , w h i c h a s s u m e s a n i n f i n i t e array a r e f o u n d i n t h e s e finite systems.
A
computer simulation o f t h e effects o f non-random
o r i e n t a t i o n on t i m e d e p e n d e n t e x c i t a t i o n p r o b a b i l i t y h a s a l s o been c o n ~ t r u c t e d ~ ~ ’ .Burshtein2”
h a s prepared a r e v i e w o f e n e r g y
t r a n s f e r k i n e t i c s i n d i s o r d e r e d s y s t e m s and a l s o p r o d u c e d a p a p e r w h i c h d i s c u s s e s q u a n t u m y i e l d s i n t e r m s o f M a r k o f f i a n and nonMarkoffian theories for luminescence o f solids252.
F o r fluid
s y s t e m s a k i n e t i c t h e o r y o f e x c i t a t i o n t r a n s f e r b e t w e e n d o n o r and a c c e p t o r s , w h e r e r e a c t i o n p r o b a b i l i t y i s m o d u l a t e d by t r a n s l a t i o n a l d i f f u s i o n s , h a s been submitted t o n u m e r i c a l analysis253
.
An e x p e r i m e n t a l i n v e s t i g a t i o n h a s been m a d e o f e n e r g y t r a n s f e r 254 for m e s i t y l e n e / 9 , 1 0 - d i p h e n y l a n t h r a c e n e , 2,3-
I: Photophysical Processes in Condensed Phases
19
d i m e t h y l n a p h t h a l e n e l a n t h r a c e n e in mixed
c r y s t a l s 2 5 5 , and aromatic
.
hydrocarbons t o tetra cyanoquinone anions in MeOH
Investigation of r a d i a t i v e energy transfer in t h e case o f pyrene and 9 , l O - d i p h e n y l a n t h r a c e n e has indicated that t h i s process c a n provide t h e dominant m e c h a n i s m for t r a n s f e r in many s y s t e m s 2 5 7 . Fluorescence depolarization o f r h o d a m i n e 6 6 in g l y c e r o l has been used t o test t h e theories o f t h r e e d i m e n s i o n a l excitation transport theory2”.
Transfer between r h o d a m i n e 6 6 ( d o n o r ) and m a l a c h i t e
green ( a c c e p t o r ) has been followed by picosecond t i m e resolved single photon counting and donor fluorescence decay examined by a theoretical function including t r a n s l a t i o n a l d i f f u s i o n 2 S s .
The
simple Forster equation considering diffusion is found t o over estimate t h e critical d i s t a n c e for transfer. Intramolecular electronic energy transfer in bichromophoric molecules consisting o f t w o coumarins linked by a variable number of m e t h y l e n e g r o u p s has been investigated by multi-frequency phase modulation fluorometry260
.
Picosecond fluorescence spectroscopy
shows that fast energy transfer occurs in phycocyanin 6 1 2 2 6 1
2.5 P o l v w i c S v s t e m s .
-
.
Since polymer systems are extensively
discussed elsewhere in this volume only selected examples w i l l b e quoted which indicate h o w polymeric structures c a n i n f l u e n c e photophysical phenomena.
For e x a m p l e , fluorescence polarization
has been used to monitor polymer cure in resin mixtures w h e n a f l u o r o p h o r e , k-(2-hydroxyalkyl) d e r i v a t i v e o f 4-aminonaphthalimide. is u s e d 2 6 2 .
PolyC2- ( 9 - c a r b a z o y l l e t h y l methacrylatel f i l m s s h o w
monomer fluorescence from carbazoyl chromophores but no d e t e c t a b l e excimer emission is seen even in t h e solid s t a t e 2 6 3 .
Highly
efficient sensitized photoconductivity by electron acceptor d o p i n g shows effective electronic excitation migration can occur through carbazole chromophores.
Formation o f an exciplex by pyrene and
dimethylaniline has been used t o probe end t o end cyclisation o f polystyrene in a variety o f s o l v e n t s 2 6 4 .
Solvent site
inhomogeneity i s shown in polymethyl m e t h a c r y l a t e g l a s s e s by t h e extent o f t h e formation o f TICT states o f
.
same probe shows that t h e free d i r n e t h y l a m i n o b e n ~ o n i t r i l e ~ ~The ~ volume in polyhydroxyethyl m e t h a c r y l a t e i s l e s s than t h a t in PHHA. Electronic energy transfer in p o l y ( 2 - v i n y l n a p h t h a l e n e ) and polystyrene shows energy m i g r a t i o n i s not limited t o nearest neighbour rings266.
Short r a n g e interactions other t h a n dipole-
d i p o l e interactions are involved.
F l u o r e s c e n c e and energy
Photochemistry
20
m i g r a t i o n i n a l t e r n a t i n g and r a n d o m c o p o l y m e r s o f 2-vinyln a p h t h a l e n e and m e t h y l m e t h a c r y l a t e o r m e t h a c r y l i c acid s h o w s a l t e r n a t i n g c o p o l y m e r s h a v e e s s e n t i a l l y n o e x c i m e r e m i s s i o n and 267 The random exhibit a monoexponential fluorescence decay
.
c o p o l y m e r s h o w s e x c i m e r e m i s s i o n and a t h r e e e x p o n e n t i a l d e c a y . Q u e n c h i n g o f t h e f l u o r e s c e n c e o f acrylamidomethylthionine c o p o l y m e r s by Fe2+ and Fe3+ s h o w s Fe2+ f o r m s an a d d u c t t o g i v e t h e 268 semithionine radical which subsequently disproportionates
.
Fluorescence quenching of phenanthryl groups covalently linked t o p o l y e l e c t r o l y t e s h a s a l s o b e e n studied269
.
Such examples
c o n s t i t u t e u s e f u l m o d e l s f o r c o m p l e x b i o l o g i c a l systems. of the 6 s
-+
The rate
trans photoisomerization o f polymer azoaromatic
p o l y i m i d e i n c o n c e n t r a t e d H SO d i f f e r e n t s t r u c t u r e s involv:d2+'.
shows that t h e rate depends o n the P y r e n e has been used as a
photophysical probe for intermolecular interactions o f watersoluble polymers in dilute solution271
.
P e r y l e n e a g g r e g a t e s in
PMMA polymer matrices shows that there is a distribution o f ground state pair combinations272. 2 . 6 C o l l o i d a l and H e t e r o a e n e o u s S v s t e m a
-
The study o f photophysics
in colloidal systems i s now o n e of t h e most active areas o f photochemistry.
P r o b a b l y t h e m o s t n o t a b l e a c h i e v e m e n t so f a r
has been t h e i n f o r m a t i o n p r o v i d e d o n t h e n a t u r e o f c o l l o i d s and their properties. T h e f l u o r e s c e n c e o f 6 - d o d e c y l - 2 - n a p h t h o l i n m o n o l a y e r s at air273
water interfaces is the simplest o f all heterogeneous systems
.
P y r e n e and 1 , 3 - d i - l - p y r e n y l p r o p a n e h a v e b e e n used a s f l u o r e s c e n c e probes in rapidly f r o z e n w a t e r c o n t a i n i n g 0.5 t o 5 % ( v / v ) acetone274.
The liquid acetone forms domains within t h e ice
c r y s t a l and a n o t h e r p r o b e , 1 - a n i l i n o n a p h t h a l e n e s u l p h o n a t e , s h o w s that t h e amount o f water in these domains is less a s t h e temperature decreases.
S t r u c t u r a l d o m a i n s i n lipid m e m b r a n e s h a v e
been e x a m i n e d by m e a s u r e m e n t o f d e c a y t i m e s o f DPH using p h a s e and modulation techniques275.
Only i n s p e c i a l c a s e s c a n t h e c o -
e x i s t e n c e o f g e l and fluid p h a s e s be r e s o l v e d s i n c e t h e p r e c i s i o n r e q u i r e d f o r t h e d e c a y t i m e s i s very exacting.
Biexponential
d e c a y s a r e a l s o found f o r t h e l , l t - d i a l k y 1 - 3 , 3 , 3 ' , 3 ' - t e t r a m e t h y l i n d o c a r b o c y a n i n e d y e s ( N = 1 2 , 18 and 2 2 ) in a variety o f l i p i d bilayer membranes276.
The sensitivity o f t h e fluorescence lifetime
o f l-palmitoyl-2C2-[4-(6
phenyl-trans-l,3,5-hexatrienyl)
phenyllcarbonyll- 3 - s n - p h o s p h a t i d y l c h o l i n e
(DPH-PC)
t o environment
I: Photophysical Processes in Condensed Phases
21
h a s b e e n used t o m o n i t o r l i p i d m i x i n g and p h a s e s e p a r a t i o n d u r i n g membrane fusion2??.
T h e e f f e c t s o f C a 2 + h a s a l s o been e x a m i n e d .
M o l e c u l a r r e l a x a t i o n f l u o r e s c e n c e m e t h o d s h a v e been used t o a n a l y s e t h e n a t u r e and d y n a m i c s o f a m p h i l i c m o l e c u l e s absorbed i n t h e p o l a r r e g i o n o f a p h o s p h o l i p i d b i l a ~ e r ~ ~ ’ .T h e power o f t h e m e t h o d i s demonstrated
in s h o w i n g t h a t t h e polar s u r f a c e i s h i g h l y m o b i l e and
d i p o l a r r e l a x a t i o n i s rapid. The theory of the concentration depolarization of luminescent molecules embedded in a homogeneous media with orientational c o n s t r a i n t s has been d e v e l o p e d 2 7 9 and t h e i n f l u e n c e o f m o l e c u l a r organisation on t h e photophysical properties of two a l k y l c y a n o d i p h e n y l s examined2”.
T h e l a t t e r s y s t e m s h o w s both head
t o head and t a i l t o head e x c i m e r s . F l u o r e s c e n c e d e c a y t i m e m e a s u r e m e n t s h a v e been used t o o b s e r v e c l u s t e r i n g in m i c r o e m u l s i o n s near t h e c r i t i c a l point2”.
The
d y n a m i c q u e n c h i n g o f f l u o r e s c e n c e i s used t o e s t i m a t e s i z e s o f t h e droplets.
F l u o r e s c e n c e probing h a s a l s o been used t o s t u d y
s u r f a c t a n t o x y g e n a t i o n i n a q u e o u s s o l u t i o n s o f mixed i o n i c micelles282.‘ k c r i d i n e f l u o r e s c e n c e has been used a s a p r o b e o f m i c e l l e f o r m a t i o n in S D S t o s h o w t h a t t h e p r e s e n c e of poly[N-(Whydroxyalkyll-L-glutaminesl
process2B3.
has n o s i g n i f i c a n t effect on t h i s
L a s e r probing s h o w s t h a t f a s t i n t e r m i c e l l a r e x c h a n g e
o f m i c e l l e s o l u b i l i z e d p y r e n e o r c e t y l p y r i d i n i u m ion o c c u r s o n a t i m e s c a l e o f 0.3 t o 10 v s 2 0 4 .
A model involving fragmentation
into submicellar aggregates is proposed. o f S D S h a v e been
Heptanol swollen micelles
studied u s i n g p y r e n e as c h r o m o p h o r e and
b e n z o p h e n o n e a s a quencher2”.
The aggregation numbers depend on
t h e h e p t a n o l / S D S c o n c e n t r a t i o n ratio.
Picosecond absorption o f d y e
probes o f water i n o i l microemulsions shows evidence of complexing o f d y e p r o b e s w i t h n e i g h b o u r i n g o u r f a c t a n t m o l e c u l e s and t h e r e o r i e n t a t i o n m o t i o n determined2“
.
The dynamic behaviour o f
fluorescence quenchers o f pyrene in cetyltrimethylammonium
chloride
m i c e l l e s by i m m o b i l e , m o b i l e h y d r o p h o b i c , and m o b i l e h y d r o p h i l i c q u e n c h e r s has been e x a m i n e d z 8 7 ,
The r e s u l t s a l l o w c o n c l u s i o n s t o
be d r a w n a b o u t t h e s h a p e and s i z e o f C T A C m i c e l l e s .
The quenching
o f p y r e n e f l u o r e s c e n c e by i n d o l e i n m i c e l l a r s o l u t i o n s i s i n c r e a s e d by l o c a l high c o n c e n t r a t i o n s o f i n d o l e w h i c h a c c u m u l a t e i n t h e micelle2B8.
T h e q u e n c h i n g o f p y r e n e f l u o r e s c e n c e by C s * i o n s i n
m i c e l l e s i s r e d u c e d by t h e p r e s e n c e o f s u r f a c e a c t i v e c r o w n etherszB9.
The effect o f alkali metals o n fluorescence of pyrene
on t h e m i c e l l a r p r o p e r t i e s o f c r o w n e t h e r s u r f a c t a n t and t h e
Photochemistry
22
i n f l u e n c e o f p o l a r i t y o n t h e 1 1 / 1 3 band r a t i o o f t h e p y r e n e have The evidence shows that t h e metal ions complex
been examined2".
w i t h t h e c r o w n e t h e r . T h e q u e n c h i n g o f e x c i t e d p y r e n e bound t o c e t y l t r i m e t h y l a m m o n i u m m i c e l l e s by i n o r g a n i c c a t i o n s has a l s o been r e p o r t e d by O l e a and Lissi2".
Ground and e x c i t e d s t a t e proton
t r a n s f e r s i n r e v e r s e d m i c e l l e s h a v e been e x a m i n e d i n I - h y d r o x y 1 , 3 , 6 - p y r e n e t r i s u l p h o n a t e and s h o w p o l a r i t y r e s t r i c t i o n s and isotope effects292.
S t e a d y s t a t e l u m i n e s c e n c e has been used t o
determine the polarity of ionic clusters o n t h e Nafion 293 . (perfluorosulphonate polymers) D i p y r e n y l p r o p a n e c a n be used t o m e a s u r e m i c r o v i s c o s i t y o f DMPC b i l a y e r s in t h e l i q u i d c r y s t a l p h a s e as a f u n c t i o n o f h y d r o s t a t i c pressure
294
.
Dynamic fluorescence measurements
show different
m e c h a n i s m s f o r e x c i m e r f o r m a t i o n i n l i q u i d c r y s t a l l i n e and p r e s s u r e induced g e l phases.
S u r f a c t a n t and h y d r o p h o b i c d e r i v a t i v e s o f
t r a n s - s t i l b e n e s as probes o f v e s i c l e and m i c e l l e s o l u b i l i z a t i o n sites235.
As w e l l a s fluorescence, photoisomerization
can also
g i v e i n f o r m a t i o n o n o r d e r l i m i t e d r a t h e r t h a n viscosity l i m i t e d factors.
The effect of micelles o f Triton X - 1 0 0
biexponential fluorescence decay o f inve~tigated~~'.
( U022t
on the
1 * has been
The ion penetrates into t h e core of t h e micelles
but e x c i m e r s d o not p e n e t r a t e .
Differences in spectroscopic
properties of tris(2,2'-bipyridine) ruthenium I 1 absorbed on inner and o u t e r s u r f a c e s m a y be d u e t o packing d i f f e r e n c e s and v a r i a t i o n of ionic strength297. An i m p o r t a n t a s p e c t o f p h o t o c h e m i c a l e f f e c t s i n m i c e l l e s i s t h e f o r m a t i o n and s t a b i l i z a t i o n o f c h a r g e t r a n s f e r e f f e c t s w i t h a v i e w t o a p p l i c a t i o n i n solar e n e r g y c o n v e r s i o n .
An e x a m p l e o f t h i s
i s a study o f e l e c t r o n t r a n s f e r in m i c e l l a r - m e t a l ion s y s t e m s , where k
q
and e l e c t r o n t r a n s f e r y i e l d s f r o m S 1
-N - e t h y l c a r b a z o l e ,
and t h e T,
s t a t e s o f p y r e n e and
state o f N-methylphenothiazine
by a
n u m b e r o f m e t a l i o n s i n s o d i u m t a u r o c h o l a t e and s o d i u m l a u r y l s u l p h a t e h a v e been m e a s u r e d 2 3 8
.
Photosensitized charge transfer
and r e c o m b i n a t i o n o f t h e i o n i c p r o d u c t s i n m i c e l l a r s o l u t i o n s h a v e been e x a m i n e d i n m e s o - t e t r a - m e t a - N - m e t h y l p y r i d y l p o r p h i n e i n a q u e o u s s o l u t i o n and m i c e l l e s 2 9 9 . f r o m t h e t r i p l e t state.
In this case electron transfer occurs Photoionization thresholds o f chlorophyll
a and N . ~ , l j ' , ~ ' - t e t r a m e t h y l b e n z i d i n ei n v e s i c l e and m i c e l l e f r o z e n s o l u t i o n s has been studied by esr3".
Differences are d u e t o the
i o n i c n a t u r e and d e g r e e o f p e n e t r a t i o n i n t o t h e m i c e l l e s and vesicles.
A full survey o f t h e influence o f micelles
on
I: Photophysical Processes in Condensed Phases
23
p h o t o c h e m i c a l reactivity by c a g e and microviscosity e f f e c t s , l o c a l i s a t i o n and c o m p a r t m e n t a l i z a t i o n , p r e - o r i e n t a t i o n a l , p o l a r i t y , and counter ion e f f e c t s is extremely u s e f u l 3 0 1 -
The e f f e c t s o f
c e t y l t r i m e t h y l a m m o n i u m bromide m i c e l l e s on complex stability and photoinduced electron t r a n s f e r on t h e c o m p l e x formation w h i c h o c c u r s between a n t h r a q u i n o n e - 2 , 6 - d i s u l p h o n a t e and n e u t r a l z i n c 302
porphyrin c o n s t i t u t e a d e t a i l e d e x a m i n a t i o n of such a s y s t e m
.
P h o t o l y s i s o f 2-phenylbenzoin i n m i c e l l a r s y s t e m s g e n e r a t e s a rearranged r a d i c a l pair w h i c h c a n suosequently c o m b i n e t o g i v e s t a b l e product303.
T h e d y n a m i c s of r a d i c a l pair r e a c t i o n s i n
m i c e l l e s h a v e been t i m e resolved by t h e application o f pulsed l a s e r f l a s h p h ~ t o l y s i s ~ ' ~ . G e m i n a t e r a d i c a l pairs decay i n 20-2000 x 10%
w h e r e a s e n c o u n t e r s o c c u r at t i m e separations of l o n g e r t h a n In reversed m i c e l l e s o f
2000 x 1 O-'s.
Bin- (2-ethylhexyll-
s u l p h o s u c c i n a t e in h e p t a n e t h r e e fluorescent acid probes u n d e r g o photolysis in t h e m i c e l l e c o r e w h i c h c o n t a i n s water3''.
Phase
fluorometry w a s used i n t h i s investigation. S t u d i e s have been m a d e o n t h e m i c r o e n v i r o n m e n t a l effects o f cyclodextrins: t h e s e i n c l u d e excimer f o r m a t i o n in p o l y m e t h y l e n e bis-$-naphthoates3"
and t h e f l u o r e s c e n c e o f p y r e n e and n a p h t h a l e n e
in c y c l o d e x t r i n - a m p h i p h i l e c o m p l e x systems w h i c h provide a very h y d r o p h o b i c environment for pyrene307
.
Absorption and f l u o r e s c e n c e
s t u d i e s o f t h e i n t e r a c t i o n of pyrene w i t h fl-cyclodextrin i n a q u e o u s surfactant solutions have a l s o been examined
308
.
T h e f l u o r e s c e n c e decay of pyrene i n t h e presence o f n o n i o n i c surfactants at solid-liquid interface is influenced by t h e polar c h a i n length3".
T h e f l u o r e s c e n c e o f t h e bifunctional p r o b e 1 , 3 -
d i p y r e n y l p r o p a n e absorbed o n silica and reversed phase silica surfaces31
'
and t h e d u a l f l u o r e s c e n c e o f l - ( Y , N - d i m e t h y l a m i n o ) - 4 -
benzonitrile absorbed on silica surfaces c a n be used as a probe o f s u r f a c e polarity3''.
T h e effect of t e m p e r a t u r e on t h e singlet
q u e n c h i n g o f pyrene absorbed o n silica g e l by 2-bromonaphthalene i n d i c a t e s t h a t d i f f u s i o n of t h e s e m o l e c u l e s i s rapid w h e n t h e s u r f a c e i s uniform3''.
Dye t o s u r f a c e n o n r a d i a t i v e e x c i t a t i o n
t r a n s f e r is a n important decay m o d e for t h e S1
state of c r e s y l
violet separated f r o m Ti02 s u r f a c e s by d i s t a n c e s between 8 0 and 5098 3 1 3 .
T h i s paper e x a m i n e s t h e t h e o r y of energy t r a n s f e r f r o m
an excited s t a t e t o a d i e l e c t r i c surface.
T h e cis-trans
iiomerization o f six s t y r e n e d e r i v a t i v e s has been observed on c a d m i u m s u l p h i d e particles and a kinetic a n a l y s i s o f t h e data attempted3 l 4
.
Photochemistry
24
An e n h a n c e m e n t o f m o l e c u l a r f l u o r e s c n e c e and p h o t o c h e m i c a l r a t e s i s brought about by s m a l l m e t a l p a r t i c l e s c a p a b l e o f sustaining e l e c t r o m a g n e t i c r e s o n a n c e s
315
.
Picosecond resonance
Raman s c a t t e r i n g o f m e t h y l v i o l o g e n r e d u c t i o n on s u r f a c e o f phtoexcited C d S s h o w s that a f t e r o p t i c a l e x c i t a t i o n t h e M V * s p e c t r u m w h i c h is observed
i n d i c a t e s t h a t t h e n a s c e n t MV+ may be
complexed w i t h o t h e r species3’
.
2.7 B i o l o a i c a l S v s t e m s - T h e s e n s i t i v i t y
o f luminescence techniques
and t h e u s e o f e x t r i n s i c and i n t r i n s i c f l u o r e s c e n c e p r o b e s have Only a
found c o n s i d e r a b l e a p p l i c a t i o n s in b i o l o g i c a l r e s e a r c h .
s e l e c t i o n o f s u c h s t u d i e s h a v e been s e l e c t e d f o r c i t a t i o n . F l u o r e s c e n c e and p h o s p h o r e s c e n c e o f a r o m a t i c 8 - c a r b o l i n e s , n o r h a r m a n , h a r m a n , and h a r m i n e , as d i s p e r s e d s o l i d s at 7 7 K and absorbed o n c e l l u l o s e at r o o m temperature3’? tautomeric equilibria o f the S been r e p o r t e d .
T h e photophysi:s
ergostatetraen-3$-01
and S
and a c i d - b a s e and
s t a t e s o f h a r m 0 1 ~ ~ ’have
of e:go~terol~’~,
I9
‘ 2 2-
(”
in micelles as w e l l as with sterol-carrier
p r o t e i n c o m p l e x e s and i n i n t e r a c t i o n w i t h plasma m e m b r a n e s 3 2 0 , and excited s t a t e p r o t o n t r a n s f e r o f e q u i l e n i n and d i h y d r o e q u i l e n i n i n i n t e r a c t i o n w i t h b i l a y e r v e s i c l e s 3 2 1 h a v e a l l been i n v e s t i g a t e d i n considerable detail.
F l u o r e s c e n c e and p h o s p h o r e s c e n c e o f
p h y o s t i g m i n e , r u b r e s e r i n e , and a d r e n o ~ h r o m e and ~ ~ ~t h e p h o t o i o n i z a t i o n o f NADH i n a q u e o u s s o l u t i o n c o n s e q u e n t upon t w o photon e x c i t a t i o n 3 2 3 a r e o t h e r i n t e r e s t i n g i n v e s t i g a t i o n s w h i c h have reported. Indole derivatives including tryptophan compounds still c o n t i n u e t o g e n e r a t e p r o b l e m s and r e s e a r c h o f p h o t o p h y s i c a l P o l a r i z e d 2 p h o t o n f l u o r e s c e n c e s p e c t r a of i n d o l e i n a
interest.
number o f s o l v e n t s has been e x c i t e d i n t h e r e g i o n o f L The multiexponential
bands322.
and L b
fluorescence decay o f indole-3-
a l k a n o i c a c i d s as a f u n c t i o n o f pH s h o w s t h e d y n a m i c i n t e r a c t i o n o f t h e side chain with t h e indole moiety is probably occurring during t h e lifetime o f t h e excited state32S,
308 n m X e C l l a s e r l i g h t
e x c i t e s t h e red e d g e o f t h e 1st e x c i t a t i o n band and S1 and
T
-+
T
-+
Sn
t r a n s i t i o n s i n N - m e t h y l i n d o l e and t h e f o r m a t i o n
of i o n pair s p e c i e s c h a r a c t e r i z e d .
A
very i n t e r e s t i n g s t u d y h a s
been a study o f t r y p t o p h a n i n t h e g a s p h a s e using a cold s u p e r s o n i c jet327.
C o n f o r m e r s i n g r o u n d and e x c i t e d s t a t e s h a v e b e e n
i d e n t i f i e d and r o t a m e r m o d e l s c o n f i r m e d 3 2 7 .
The results o f t h e
study h a v e c o n s i d e r a b l e v a l u e f o r r e s o l v i n g m a n y a s p e c t s o f t h e
I: Photophysical Processes in Condensed Phases
25
results arising from investigations i n solution.
The
n o n e x p o n e n t i a l f l u o r e s c e n c e d e c a y o f t r y p t o p h a n has been e x p l a i n e d by a m o d e l c o n s i s t i n g o f t w o c o n f o r m e r s e a c h c o n s i s t i n g o f d i s t r i b u t i o n s o f o t h e r very s i m i l a r c o n f o r m e r s 3 2 8
.
Homotryptophan,
an a n a l o g u e o f t r y p t o p h a n w i t h a CH2 g r o u p s e p a r a t i n g t h e i n d o l e ring f r o m t h e a m i n o acid m o i e t y , is very s i m i l a r in i t s fluorescence properties t o tryptophan32g
.
Its b e h a v i o u r i s a l s o
e x p l a i n e d by t h e i n v o l v e m e n t o f t w o r o t a m e r s ( o r c o n f o r m e r s ) e a c h with a distribution o f lifetimes which analyses a s only involving two apparent lifetimes. Complex formation with solvent also occurs. Intramolecular exciplex formation occurs with N-2-acetyl-1-pyrenyl-
.
alanyl- 1 -methyltryptophan methyl ester330
The evaluation o f
charge effects on quenching o f tryptophan fluorescence i n peptides by I- and C1- i o n s has been e x a m i n e d i n t e r m s o f s e p a r a t e d y n a m i c and s t a t i c q u e n c h i n g e f f e c t s as w e l l a s a s i n g l e p r o c e s s
mechanism^^^'.
T h e e f f e c t o f pH o n t h e a e r o b i c and a n a e r o b i c
p h o t o l y s e s o f t r y p t o p h a n and s o m e t r y p t o p h a n d i p e p t i d e s h a s been 332 studied using f l u o r e s c e n c e s p e c t r o s c o p y
.
T y r o s i n e i s t h e o t h e r s i g n i f i c a n t f l u o r e s c e n t a m i n o acid residue.
T i m e r e s o l v e d f l u o r e s c e n c e and p r o t o n NMR s t u d i e s h a v e
been r e p o r t e d f o r t y r o s i n e and t y r o s i n e a n a l o g u e s i n d i c a t i n g m o r e This w o r k h a s been
c o m p l e x i t y t h a n has been e x p e c t e d h i t h e r t o 3 3 3 . e x t e n d e d t o t h e o x y t o c i n and o t h e r s m a l l
pep tide^^^^.
Tyrosyl
fluorescence spectra o f proteins lacking tryptophan shows that t y r o s i n e e m i s s i o n i s affected by c o n f o r m a t i o n a l c h a n g e s t h o u g h t t o be d u e t o f o r m a t i o n o f h y d r o g e n b o n d s b e t w e e n t h e h y d r o x y l o f t y r o s y l r e s i d u e s and p r o t o n a c c e p t o r g r o u p s 3 3 S
.
P r o t e i n s p r o v i d e m a n y p r o b l e m s s u i t a b l e f o r s t u d y by photophysical techniques.
The fluorescence behaviour o f sequential
t y r o s y l p o l y p e p t i d e s has been studied in a l k a l i n e solution336
and
q u e n c h i n g by e n e r g y t r a n s f e r t o t r y p t o p h a n - 1 9 i n m e l i t t i n has been used i n c o n f o r m a t i o n a l s t u d i e s
337
.
The environment o f tryptophan
r e s i d u e s in a z u r i n h a s been e x a m i n e d by o b s e r v i n g e l e c t r o n i c e n e r g y t r a n s f e r w i t h and w i t h o u t t h e p r e s e n c e o f c o p p e r i o n s 3 3 8 . F l u o r e s c e n c e l i f t i m e q u e n c h i n g and a n i s o t r o p y s t u d i e s h a v e been m a d e w i t h r i b o n u c l e a s e T1 w h i c h a s a l o n e t r y p t o p h a n 3 3 9 .
The
s i n g l e t r y p t o p h a n r e s i d u e i n cod p a r v a l b u m i n i s l o c a t e d i n a p o l a r r e g i o n and q u e n c h i n g by O2 and a c r y l a m i d e s h o w s t h a t d y n a m i c p e n e t r a t i o n by a c r y l a m i d e i s r e q u i r e d 3 4 0 .
I o d i d e ion and
a c r y l a m i d e q u e n c h i n g o f t r y p t o p h a n f l u o r e s c e n c e has b e e n used t o probe t h e a c t i v e s i t e i n r e n i n
341
, creatine k i n a ~ e ~ ~ * ,
Photochemistry
26
.
u r ~ c a n a s e, ~and ~ ~ t e r m i n a l d e o x y n u c l e o t i d y l t r a n ~ f e r a s e ~ ~P r~ o b e m o e i t i e s g i v e i n f o r m a t i o n on both s t r u c t u r e and c o n f o r m a t i o n a l changes.
Energy transfer takes place between tryptophan residues
i n t u b u l i n and bound brig-(8-anilionaphthalene-l-sulphonate)
which
i s an i n h i b i t o r o f m i c r o t u b u l e a s s e m b l y t h a t binds t o a f l e x i b l e region in t h e enzyme345.
Excimer formation in N - a c e t y l - U ( l -
pyrenylalanine) methyl ester allows the dynamics o f peptide chain m o t i o n t o be s t u d i e d 3 4 6 .
Q u e n c h i n g c a n be used t o study protein
d y n a m i c s by t h e s e p a r a t i o n o f s o l v e n t exposed and s o l v e n t masked f l u o r ~ p h o r s. ~ ~F r~ e q u e n c y d o m a i n s p e c t r o s c o p y m a k e s it possible t o o b s e r v e s u b n a n o s e c o n d a n i s o t r o p y d e c a y s ; m e l i t t i n , m o n e l l i n and straphylococcal nuclease are systems examined with time resolution d o w n t o 50 ps3“. T h e s a m e t e c h n i q u e has b e e n used t o s t u d y d a n s y l c h r o m o p h o r e s in m o d e l c o m p o u n d s and e n z y m e s
349
.
A t t e n t i o n i s d r a w n t o t h e need
for f l u o r o p h o r e s w i t h better p r o p e r t i e s t h a n t h o s e a v a i l a b l e s o f a r f o r t h i s purpose.
I n t r a m o l e c u l a r e x c i t a t i o n energy t r a n s f e r
b e t w e e n p h e n y l a l a n i n e and t y r o s i n e i n t h e p e p t i d e d e m o r p h i n e and i t s a n a l o g u e s is i n good a g r e e m e n t w i t h t h e o r y 3 5 0 .
The association
of a c r y l a m i d e w i t h p r o t e i n s i s i m p o r t a n t i n v i e w o f i t s r e l e v a n c e
.
t o f h e i n t e r p r e t a t i o n o f f l u o r e s c e n c e q u e n c h i n g experiments3”
R a d i a t i o n l e s s e n e r g y t r a n s f e r h a s been used t o s t u d y t h e effect o f a n i o n s on t h e a c t i v i t y o f c a r b o x y p e p t i d a ~ e - A ~ ~The ~ . dimeric form o f ANS i s a b e t t e r p r o b e t h a n A N S i t s e l f and has been used f o r and ~ ~ tubulin3” structural studies o n b o v i n e - 2 - l a ~ t a l b u r n i n ~
.
ANS
has been used a s an e x t r i n s i c p r o b e f o r c o n f o r m a t i o n c h a n g e s i n c i l i a r y d y n e i n w h i c h p r o v i d e s t h e o r i g i n f o r m e c h a n i c a l t h r u s t in cell motility355.
T h e f l e x i b i l i t y o f m o l e c u l a r f o r m s of
a c e t y l c h o l i n e e s t e r a s e h a s been m e a s u r e d by steady s t a t e and t i m e c o r r e l a t e d f l u o r e s c e n c e p o l a r i z a t i o n s p e c t r o s c o p y using c o v a l e n t l y bound probes3”.
F l u o r e s c e n c e e n e r g y t r a n s f e r has been used t o
o b s e r v e c o n f o r m a t i o n a l c h a n g e s o f c y t o c h r o m e P - C S O .~ ~A ~ r e m a r k a b l e s t u d y has been m a d e o n t h e p r o t e i n b r e v i n w h i c h has 1 0 t r y p t o p h a n and 2 7 t y r o s i n e r e s i d u e s and t h e e f f e c t s o f Ca2* ions on t h e c o n f o r m a t i o n investigated3”.
Binding o f C a 2 * , L n 3 * , Eu”
Tb3+ t o p a r v a l b u m i n h a v e a l s o b e e n quantified3”.
and
Oistances
between a c t i v e s i t e p r o b e s i n g l u t a m i n e s y n t h e t a s e i n f r e e and stacked c o n d i t i o n s h a v e a l s o been m e a s u r e d by f l u o r e s c e n c e energy transfer360.
I n t r i n s i c t y r o s i n e f l u o r e s c e n c e o f h i s t o n e H 1 c a n be
used t o study t h e e f f e c t s o f f o l d i n g and u n f o l d i n g w h i c h i s i n d u c e d by salt and e f f e c t s excited s t a t e p r o t o n transfer36’.
The
I: Photophysical Processes in Condensed Phases
27
i n h i b i t i o n o f b o v i n e p a n c r e a t i c t r y p s i n has been studied by t h e
.
l a b e l l i n g o f t h e 2 - a m i n o g r o u p w i t h 2 - n a p h t h o x y a c e t i c acid362
Interactions between subunits o f skeletal muscle troponin have been i n v e s t i g a t e d by f l u o r e s c e n c e q u e n c h i n g , p h o t o c h e m i c a l c r o s s l i n k i n g , and e n e r g y t r a n s f e r 3 6 3 .
Calcium binding t o troponin has
been s h o w n by l a b e l l i n g w i t h t h e p r o b e 5 - ( i o d o a c e t a m i d o e t h y l ) a m i n o n a p h t h a l e n e - 1 s u l p h o n i c acid
[1
, 5 -IAEDANS1364
.
Haem protein
fluorescence detects conformational changes a s small as a f e w t e n t h s o f an
8
d u e t o pressure induced folding365.
T h e plant
protein pinellin has tryptophan residues whose intrinsic f l u o r e s c e n c e and C D t h a t h a v e been used t o f o l l o w c o n f o r m a t i o n a l changes366.
P i c o s e c o n d t i m e - r e s o l v e d R a m a n s t u d i e s h a v e been used
t o e x a m i n e t h e p h o t o d i s socia t i o n o f c a r b o ~ y m y o g l o b i n ~ (Ca2+
+
.
M g 2 + ) - A T P a s e o f s a r c o p l a s m i d r e t i c u l u m i s an
e x t e n s i v e l y studied system.
Distances between functional sites
h a v e been m e a s u r e d by using l u m i n e s c e n t i o n s a s d o n o r s and acceptors368.
T h e q u e n c h i n g o f t r y p t o p h a n y l r e s i d u e s by a c r y l a m i d e
i n t h i s e n z y m e h a s been e x a m i n e d i n r e c o n s t i t u t e d s y n t h e t i c p h o s p h o l i p i d membranesJ6’.
T h e i n t e r a c t i o n w i t h v a l i n o m y c i n and
m o n o v a l e n t c a t i o n s w i t h t h e A T P a s e h a s been m e a s u r e d by u s e o f a f l u o r e s c e n t ATP a n a l o g u e a s probe370
and t h e o p e n i n g u p o f t h e
e n z y m e by Ca2* i o n s has been s h o w n by p y r e n e g r o u p l a b e l l i n g o f thiol residues3?’
.
I n t e r a c t i o n b e t w e e n A T P a s e m o l e c u l e s has b e e n
e x a m i n e d by p y r e n e e x c i m e r f o r m a t i o n 3 7 2 and a g g r e g a t i o n e x a m i n e d by energy t r a n s f e r b e t w e e n l a b e l l e d p r o t e i n m o l e c u l e s 3 7 3
.
I n t r a m o l e c u l a r d i s t a n c e d i s t r i b u t i o n s h a v e been m e a s u r e d by e x c i t a t i o n energy t r a n s f e r m e a s u r e m e n t s i n b o v i n e p a n c r e a t i c The effects of ionic strength o n t h e protein
trypsin inhibitor374.
c o n f o r m a t i o n and f l u i d i t y o f t h e p o r c i n e b r u s h b o r d e r m e m b r a n e h a s been m a d e using t h e p r o b e s ~ - [ 7 - d i m e t h y l a m i n o - 4 - c o u m a r i n y l l m a l e i m i d e and pyrene3 7 5
.
Calcium release from sacroplasmic
r e t i c u l u m c a n a l s o be f o l l o w e d by t h e u s e o f s u c h p r o b e s
376
.
P i c o s e c o n d and f e m t o s e c o n d f l u o r e s c e n c e s p e c t r o s c o p y h a s been used t o s t u d y b o v i n e r h ~ d o p s i n ~ and ~ ’ bacteriorhodopsin
378
.
In
t h i s l a s t c a s e i n t e r m e d i a t e s w i t h d e c a y t i m e s o f 4 3 0 2 5 0 fs h a v e been d e t e c t e d and a n u p p e r l i m i t o f 5 0 f s d e t e r m i n e d f o r t r a n s f e r o f excitation energy
from an electronically coupled trimer t o a
s i n g l e r e t i n a l unit. A t h e o r e t i c a l r e v i e w o f t h e a b s o r p t i o n o f l i g h t by V i s u a l p i g m e n t s i n v i t r o , i n s i t u and i n v i v o u n d e r d i f f e r e n t c o n d i t i o n s of i l l u m i n a t i o n has b e e n e x t e n s i v e l y r e v i e w e d ( 1 4 2
reference^)^'^.
Photochemistry
28
T h e f l u o r e s c e n c e q u e n c h i n g o f c h l o r o p h y l l a i n a c e t o n e has been examined by s i n g l e b e a m p h o t o a c o u s t i c s p e ~ t r o m e t e r ~ ~. ' A L a n g m i u r f i l m has been used t o o b s e r v e t h e effect o f m o l e c u l a r o r g a n i s a t i o n on t h e l i f e t i m e and s t e a d y s t a t e f l u o r e s c e n c e o f c h l o r o p h y l l a in monolayers of dioleophosphatidylcholine at an N2-water interface3a'.
The kinetics of fluorescence decay i n a small finite
v o l u m e has been a p p l i e d t o t h e $-subunit o f t h e p h y c o e r y t h r i n a g g r e g a t e w h e r e t h e r e i s ground s t a t e d e p l e t i o n and u p p e r excited state a b s o r p t i o n 3 8 2 . T h e m o n o m e r i z a t i o n o f t h y m i n e by i r r a d i a t i o n o f a c o m p l e x o f t h y m i n e d i m e r w i t h Hg2* i n v o l v e s b r e a k i n g o f t h e c y c l o b u t a n e ring of t h e d i m e r 3 8 3 .
T h e h y p o c h r o m i c e f f e c t and e l e c t r o n i c energy
t r a n s f e r in Y t - ( C H 1 - a d e n i n e s y s t e m s , w h e r e Y t i s a p u r i n e 2 n d e r i v a t i v e has been m e a s u r e d a s a f u n c t i o n o f n 3 a 4 . T h e effect o f interaction is strongest when n = 3 .
Energy t r a n s f e r i n n u c l e i c
a c i d s and p o l y n u c l e o t i d e s c a n be studied using c o m p l e x t e r b i u m a s T h e p h o t o p h y s i c s o f r u t h e n i u m c o m p l e x e s w i t h DNA
an acceptor3".
has been used t o e x a m i n e t h e n a t u r e o f t h e i n t e r a c t i o n and i t s environment386
.
The interactions of polycyclic aromatic
h y d r o c a r b o n s w i t h DNA by a b s o r p t i o n and f l u r o r e s c e n c e q u e n c h i n g involve moderately strong 1 : l
charge transfer states which
correlate with solvent reorganisation energies better than the Marcus model of electron transfer307
.
Nanosecond fluorescence
s t u d i e s o f DNA i n t e r c a l a t o r s , w h i c h a r e potent m u t a g e n s i n m o n o m e r i c and d i m e r i c s t a t e s , h a v e a l s o been made3".
Transition
m e t a l i o n s q u e n c h t h e f l u o r e s c e n c e o f DNA i n t e r c a l a t e d e t h i d i u m and a t i m e r e s o l v e d study h a s b e e n m a d e o f p h e n y l i n d o l e h y d r o c h l o r i d e binding t o p o l y n u c l e ~ t i d e s.~ ~T~h e l a t t e r r e a g e n t i s used a s a p r o b e o f n u c l e i c acid s t r u c t u r e w i t h a p p l i c a t i o n s t o cytology. F l u o r e s c e n c e d e t e c t e d C D o f e t h i d i u m i o n s bound t o DNA i n v i v o and i n v i t r p i n d i c a t e s t h a t t h e e t h i d i u m i o n binds t o n u c l e i c acid i n E.coli, c e l l s by i n t e r c a l a t i ~ n ~ ~ ' . T h e m e t h o d i s highly s e n s i t i v e and c o m b i n e s t h e s p e c i f i c i t y o f f l u o r e s c e n c e w i t h t h e c o n f o r m a t i o n a l s e n s i t i v i t y o f C D and c a n a l s o be used w i t h s c a t t e r i n g and o p t i c a l l y d e n s e samples. A n o t h e r very s i g n i f i c a n t study i s c o n c e r n e d w i t h e n e r g y t r a n s f e r i n p o l y n u c l e o t i d e s a f t e r t w o s t e p picosecond
excitation392
.
The distances measured under
d i f f e r e n t c o n d i t i o n s a r e r e l e v a n t t o both r a d i o b i o l o g y and photobiology.
T h e b i n d i n g o f 9 - a m i n o a c r i d i n e t o c a l f t h y m u s DNA i s
c o n s i s t e n t w i t h c u r r e n t binding m o d e l s and e x c i t o n i n t e r a c t i o n 3 3 3 T h e i n t e r a c t i o n s o f n o n - h i s t o n e c h r o m o s o m a l p r o t e i n H M G I w i t h DNA
.
I: Photophysical Processes in Condensed Phases
29
h a v e been e x a m i n e d using t r y p t o p h a n as probe394.
Diffusion
e n h a n c e d energy t r a n s f e r s t u d y o f DNA bound C o ( I I 1 ) b l e o m y c i n s using e x c i t e d L n ( I 1 1 ) has been used t o c o m p a r e t h i s c o m p l e x w i t h e t h i d i u m and a c r i d i n e o r a n g e s y s t e m s 3 9 5
.
F l u o r e s c e n c e e m i s s i o n and
p o l a r i z a t i o n h a s been used t o s t u d y t h e c o n f o r m a t i o n s o f c o r e nucleosomes with histone H 4 3 9 6 .
An e x t r e m e l y s o p h i s t i c a t e d
a p p l i c a t i o n o f f l u o r e s c e n c e i s t h e o b s e r v a t i o n o f t-RNA t o p o g r a p h y d u r i n g t r a n s l o c a t i o n by t h e u s e o f w y b u t i n e as d o n o r and p r o f l a v i n e as acceptor397. T h e use o f diphenylhexatriene
(DPH)
as a p r o b e i s very
e x t e n s i v e . The t r a n s v e r s e l o c a t i o n o f OPH in m o d e l b i l a y e r m e m b r a n e s y s t e m s has been studied by r e s o n a n c e e x c i t a t i o n energy t r a n s f e r t o a fluorescein acceptor398.
Lipid s o l v a t i o n o f t h e a q u e o u s f o r m o f
m y e l i n p r o t e o l i p i d a p o p r o t e i n l e a d s t o t w o lipid p o p u l a t i o n s w h i c h c a n be c h a r a c t e r i z e d by t h e f l u o r e s c e n c e p o l a r i z a t i o n o f DPH3"
.
T h e r e l a t i o n s h i p b e t w e e n l i p i d f l u i d i t y and w a t e r p e r m e a b i l i t y o f b o v i n e t r a c h a e l e p i t h e l i a l c e l l a p i c a l m e m b r a n e s has been e x a m i n e d by f l u o r e s c e n c e p o l a r i z a t i o n o f OPH4"
.
Chronic ethanol increases
l i v e r plasma m e m b r a n e f l u i d i t y a s s h o w n by d e c r e a s e d p o l a r i z a t i o n o f O P H w h e r e a s t h e s u r f a c e probe t r i m e t h y l a m m o n i u m D P H 1 s unaffected4"
.
I n t r a c e l l u l a r pH c a n be m e a s u r e d by a n a l y s i n g t h e e m i s s i o n s p e c t r a o f 1 , 4 - d i h y d r o x y p h t h a l o n i t r i l e s i n c e both t h e a c i d and b a s e f o r m s f l u o r e s c e differently4".
T h i s p r o b e has t h e a d v a n t a g e t h a t
it i s a p p a r e n t l y not t o x i c t o cells.
Fluorimetric detection of
p h o s p h o l i p i d v e s i c l e s bound t o p l a n e r p h o s p h o l i p i d m e m b r a n e s and detection o f multilamellar vesicles (liposomes) can be m a d e with 6 - c a r b o x y f l u o r e ~ c e i n.~ ~ L~o c a l i z a t i o n o f t h e v i g i n i a m y c i n S b i n d i n g s i t e o n b a c t e r i a l r i b o s o m e by energy t r a n s f e r has b e e n a c h i e v e d by using t h e h y d r o x y p i c o l i n y l m o i e t y a s d o n o r and c o u m a r i n y l d e r i v a t i v e s o f r i b o s o m a l p r o t e i n s as a c c e p t o r s 4 0 4 .
The
theory o f t i m e resolved fluorescence polarization from ordered b i o l o g i c a l a s s e m b l i e s has been applied t o f l u o r e s c e n t l a b e l l e d m y o s i n c r o s s b r i d g e s i n r e l a x e d m u s c l e fibres405
.
Fluorescence
e n e r g y t r a n s f e r h a s b e e n used t o c h a r a c t e r i s e m y o s i n i n t h i c k f i l m a s s e m b l i e s , a m e t h o d w h i c h has been s h o w n t o be s e n s i t i v e and r e p r o d ~ c i b l e ~ ~. ' Rapid c h a n g e s i n t h e m e m b r a n e p o t e n t i a l o f heart m u s c l e c a n b e m a d e by f l u o r e s c e n c e m o n i t o r i n g o f t h e v o l t a g e s e n s i t i v e d y e f?H23T407
.
F l u o r e s c e n t i n d i c a t o r s f o r Ca2+ a r e e x t r e m e l y useful.
T h e r e l a t i o n s h i p b e t w e e n t h e c o n c e n t r a t i o n o f c y t o s o l i c f r e e Ca2+
Photochemistry
30
and s e c r e t i o n o f p a r a t h y r o i d h o r m o n e has b e e n i n v e s t i g a t e d i n b o v i n e p a r a t h y r o i d c e l l s u s i n g t h e C a 2 + i n d i c a t o r Q~in-2.'~'.
The
i d e n t i f i c a t i o n o f b a c t e r i a l p a t h o g e n s by l a s e r i l l u m i n a t i o n c a n be m a d e by t h e h y d r o l y s i s o f n o n f l u o r e s c e n t L - a m i n o acid-8naphthylamides.'"
.
Diffusion of dichlorofluorescein,
c a r b o x y f l u o r e s c e i n , and l u c i f e r y e l l o w w i t h i n s e p t a t e m e d i u m g i a n t axon o f t h e e a r t h w o r m h a s been m o n i t o r e d and a m o d e l Translational movements of mitochondria i n cultured rat liver cells a r e c h a r a c t e r i s e d by u s i n g a v i d e o c a m e r a and v i d e o - d i g i t i z e r computer system t o analyse fluorescent images o f mitochondria stained w i t h r h o d a m i n e - 1 2 3 4 1 1 .
The motion of myosin cross bridges
in s k e l e t a l m u s c l e f i b r e s h a s been studied b y t i m e r e s o l v e d f l u o r e s c e n c e d e c a y using 1 , 5 - 1 A E D A N S a s p r o b a 4 1 2 . P h o t o s e n s i t i z a t i o n i s o f both b i o l o g i c a l and c l i n i c a l importance.
The n a t u r a l l y o c c u r r i n g h y p e r c i n and i t s p h o t o d y n a m i c
a c t i o n has been c o m p r e h e n s i v e l y reviewed4'
.
P h t h a l o c y a n i n e s and
t h e i r use f o r t h e p h o t o d y n a m i c t h e r a p y o f t u m o u r s has been r e v i e w e d a p p a r e n t l y f o r t h e f i r s t t i m e , by S p i k e s 4 1 4 .
P h t h a l o c y a n i n e s could
have advantages over haematoporphyrin derivatives as clinical p h o t o s e n s i t i z e r s i n t h a t they a b s o r b m o r e strongly in t h e red and a l s o may b e t a k e n u p s e l e c t i v e l y by t u m o u r cells.
Moan4"
has also
produced a very c o m p r e h e n s i v e r e v i e w o f r e c e n t w o r k o n p o r p h y r i n p h o t o s e n s i t i z a t i o n and p h o t o t h e r a p y .
The nature of t h e active
c o m p o n e n t i n t h e t u m o u r l o c a l i s i n g h a e m a t o p o r p h y r i n s e n s i t i z e r has been considered in a n o t h e r r e v i e w by Kessel.""
The a b s o r p t i o n and
f l u o r e s c e n c e s p e c t r a o f h a e m a t o p o r p h y r i n I X , P h o t o f r i n , and P h o t o f r i n I 1 h a v e been m e a s u r e d as a f u n c t i o n o f pH. c o n c e n t r a t i o n , and t e m p e r a t u r e t o i s o l a t e i o n i c e q u i l i b r i a f r o m m o n o m e r f d i m e r / a g g r e g a t e f orma tion4
'
.
I n t e r e s t i n t h e t r i p l e t s t a t e i s not a s a c t i v e nor a r e t h e r e as m a n y d i v e r s e d e v e l o p m e n t s as i s t h e c a s e f o r e x c i t e d s i n g l e t states.
T h e r e i s l e s s d e t a i l e d s p e c t r o s c o p i c w o r k on t r i p l e t s t a t e
p r o p e r t i e s and b i o l o g i c a l i n v o l v e m e n t i s not e x t e n s i v e a l t h o u g h t h e photosensitizer systems mentioned in t h e previous section operate largely through triplet state intermediates. E v i d e n c e has been o b t a i n e d f o r a l i n e a r excited t r i p l e t s t a t e
(3E:)
o f a c e t y l e n e i n a rigid m a t r i x
( N e , Ar and X e ) at 4 . 8 K w h i c h
I: Photophysical Processes in Condensed Phases e m i t s b e t w e e n 190 and 2 4 0 n m 4 l 8 .
31
The phototoxic polyacetylene,
phenylheptatriyne shows strong triplet state absorption with a l i f e t i m e o f a b o u t 28
$JS
in methano1419.
1 , 3 - o c t a d i e n e and by O2 t o g i v e
lo2.
T h e t r i p l e t i s q u e n c h e d by
The triplet state of
c y c l o h e p t a t r i e n e has b e e n p r o d u c e d by p u l s e r a d i o l y s i s i n t o l u e n e w i t h a l i f e t i m e o f 6 2 1 ~ 1 s ~ ~ ' . T h e l o w e s t excited t r i p l e t s t a t e s o f a l l t r a n s - o c t a t r i e n e , a l l o c i m e n e , and n e o - a l l o c i m e n e h a v e been studied by t i m e resolved r e s o n a n c e Raman s p e c t r o ~ c o p y ~ ~ ' .It i s not p o s s i b l e t o d e c i d e w h e t h e r t h e t r i p l e t s t a t e s o f t h e s e t h r e e molecules are identical. A m a g n e t i c r e s o n a n c e study has been m a d e o f t h e t r i p l e t s t a t e o f p y r i d i n e present a s a g u e s t in a b e n z e n e s i n g l e c r y s t a l 4 2 2 . Evidence is produced for a pseudo Jahn-Teller deformation of the t r i p l e t state.
L a s e r f l a s h p h o t o l y s i s o f c h l o r o b e n z e n e in polar
s o l v e n t s a l l o w s t h e t r i p l e t s t a t e t o be c h a r a ~ t e r i s e d ~ ~Triplet ~. state properties of meas'ured
2-,
rn-
and e - d i c h l o r o b e n z e n e s and y i e l d s
by t r a n s f e r t o a n t h r a ~ e n e ~ ~T h~e. e f f e c t o f t h e
e n v i r o n m e n t o n t h e p h o s p h o r e s c e n c e p r o p e r t i e s o f _p-aminoa c e t o p h e n o n e ( P A A P ) under a w i d e r a n g e o f c o n d i t i o n s h a s been studied and it i s a p p a r e n t t h a t c h a r g e t r a n s f e r i s s i g n i f i c a n t i n t h e o b s e r v e d r o o m t e m p e r a t u r e p h o s p h o r e s c e n c e o f PAAP425
.
Interactions responsible for inducing the room temperature phosphorescence
o f p - a m i n o b e n z o i c acid absorbed o n N a A c - N a C 1
m i x t u r e s h a v e been e l u c i d a t e d and at l e a s t t w o m e c h a n i s m s identified426.
L a s e r f l a s h p h o t o l y s i s o f a c y l p h o s p h o r i c acid
e s t e r s g e n e r a t e s t r i p l e t s t a t e s w h o s e k e t o and e n o l s t a t e s h a v e been c h a r a c t e r i z e d 4 2 7
.
T h e c i s - t r a n s i s o m e r i z a t i o n o f 1 , 3 - p e n t a d i e n e and s e n s i t i z e d p h o s p h o r e s c e n c e o f b i a c e t y l h a v e been used t o m e a s u r e t h e e f f e c t o f t e m p e r a t u r e o n t h e t r i p l e t y i e l d s o f m e t h y l and p h e n y l - s u b s t i t u t e d biphenyl molecules428.
The phosphorescence o f trans-stilbene i n
t h e c r y s t a l l i n e s t a t e at 4 . 2 K h a s a l i f e t i m e o f 100 published
esr spectrum of t h e T,
The
state of trans-stilbene i n a glass
at 7 7 K i s t h e f i r s t r e p o r t o f t h e e s r s p e c t r u m o f a t r i p l e t 430 Triplet-triplet absorption spectra o f trans-stilbene,
polyene
.
6,4'-dehydroxystilbene, 4 , 6 ' - d i a m i n o - 2 , 2 ' - s t i l b e n e
disodium
d i s u l p h a t e , and 4 , & ' - d i p h e n y l s t i l b e n e w h i c h h a v e s h o r t t r i p l e t l i f e t i m e s have been m e a s u r e d 4 3 1 . C2,23
(1,C)
The phosphorescence properties o f
naphthaleno-paracyclophane
and C 2 , 2 1 ( 1 , 4 ) -
c h r y s e n o p a r a c y c l o p h a n e and t h e g r o u n d s t a t e c o m p l e x e s o f t h e s e hydrocarbons with silver perchlorate have also been
32
Photochemistry
published432 ' 4 3 3
.
T h e d e l a y e d f l u o r e s c e n c e and 7 - T a b s o r p t i o n
f o r a n t h r a c e n e , t e t r a c e n e , and m e s o d i p h e n y l h e l i a n t h r e n e
has been
used t o d e t e r m i n e t h e k i n e t i c s and e f f i c i e n c y o f s i n g l e t s t a t e Photoacoustic measurements o f triplet yields for a n t h r a c e n e , a c r i d i n e , p h t h a l a z i n e , and q u i n o x a l i n e a r e in good agreement with literature values435.
The lifetimes of the triplet
states i n v o l v e d m u s t be g r e a t e r t h a n 1 p s f o r t h e s u c c e s s f u l application of this technique.
T-T
t r a n s i e n t a b s o r p t i o n spectra
for a n t h r a c e n e , and i t s 2- and 9 - m e t h y l d e r i v a t i v e s i n d i f f e r e n t s o l v e n t s u n d e r t h e i n f l u e n c e o f p r e s s u r e s h o w s an e f f e c t upon intersystem crossing which is d u e t o a change to t h e Franck-Cordon factors brought about by v a r i a t i o n o f t h e S ,-TZ e n e r g y g a p
436
.
P h o s p h o r e s c e n c e l i n e n a r r o w i n g o f c o r o n e n e and p h e n a t h r e n e absorbed on c e l l u l o s e b e t w e e n 4 and 3 0 0 K has been o b s e r v e d f o r t h e f i r s t time437.
Intersystem crossing from singlet states o f molecular
d i m e r s o f p e n t a c e n e in m i x e d m o l e c u l a r c r y s t a l s (_p-terphenyl) has been studied by picosecond
s t i m u l a t e d p h o t o n e c h o experimentsi3'
.
T r a n s i e n t Raman s p e c t r a p r o v i d e e v i d e n c e f o r a " o n e w a y " c i s t o t r a n s i s o m e r i z a t i o n in t h e l o w e s t e x c i t e d t r i p l e t s t a t e o f 2 styrylanthracenei3'.
T h e d e c a y of p h o s p h o r e s c e n c e o f p h e n a n t h r e n e
in b i p h e n y l p o l y c r y s t a l s d e p e n d s o n t h e d u r a t i o n of t h e e x c i t a t i o n pulse due t o distance dependent interaction of quest molecules in t h e l o w e s t t r i p l e t state'". A time resolved
e s r s t u d y o f t h e m a g n e t i c and d e c a y p r o p e r t i e s
of t h e short l i v e d n o n p h o s p h o r e s c e n t
( n , n * ) state of pyridazine
shows t h e very l a r g e n o n r a d i a t i v e d e c a y constantb".
T h e yield t h e
triplet s t a t e o f 1 , 3 - d i a z a a z u l e n e in b e n z e n e has been m e a s u r e d t o be 0 . 6 3 4 4 2 .
The role o f triplet states in t h e trans
-+
cis
photoisomerization of quaternary salts o f 4-nitro-4'-azastilbene and t h e i r q u i n o l i n i u m s a l t s h a v e been c h a r a c t e r i s e d by l a s e r f l a s h p h o t ~ l y s i s ~ ~In ~ .c o n t r a s t w i t h s t i l b e n e t h e i s o m e r i z a t i o n o f 1 , Z - U - p y r a z y l e t h y l e n e p r o c e e d s t h r o u g h t h e t r i p l e t state. Nanosecond l a s e r f l a s h p h o t o l y s i s s h o w s e f f i c i e n t i n t e r s y s t e m crossing on direct excitation44i.
T h e e n e r g y l e v e l s o f t h e c i s and
t r a n s - t r i p l e t s h a v e b e e n d e t e r m i n e d and a c h a n g e o f '(IT,
TI*)
c h a r a c t e r o c c u r s w i t h s o l v e n t polarity.
( n , n * ) and
The triplet state
o f N , N - d i m e t h y l a n i l i n e d e c a y s by 2nd o r d e r k i n e t i c s i n c y c l o h e x a n e
and l e a d s t o d e l a y e d f l u o r e s c e n c e but d e c a y s f i r s t o r d e r i n methanoli4'.
The line pattern of t h e phosphorescence excitation
spectra o f b e n z o C a 3 p h e n a z i n e at b K i s s t r o n g l y s i t e d e p e n d e n t d u e t o t h e s m a l l e n e r g y s e p a r a t i o n o f t h e S,(n, n * ) and
S2(w,
a*)
I: Photophysical Processes in Condensed Phases states446.
33
The deactivation mechanism o f photoexcited phenazine in
s h o w s i n t e r s y s t e m c r o s s i n g and r a d i c a l f o r m a t i o n d e p e n d s
C F C H OH 3 2
o n t h e p r o x i m i t y o f S 2 ( n , n * ) , S1 ( n , n * ) , and T 2 ( n , n * ) states447. T h e r e l a t i v e s u b l e v e l populating r a t e s via t h e z e r o f i e l d s u b l e v e l s o f p h t h a l a z i n e i n 2 - o c t a n o l h a s been d e t e r m i n e d by OOMR'". Time resolved phosphorescence spectra of vitreous benzophenone at d i f f e r e n t t e m p e r a t u r e s h a v e been i n t e r p r e t e d a s d u e t o e n e r g e t i c relaxation o f triplet excitons44g
.
A l o w temperature emission
s t u d y o f d i m e t h y l b e n z o p h e n o n e and n a p h t h a l e n e - d i m e t h y l b e n z o p h e n o n e crystals shows that t h e mechanism o f phosphorescence quenching is d i f f e r e n t t o t h a t o f b e n z o p h e n o n e and i n v o l v e s e l e c t r o n - p h o n o n c o u p l i n g i n f l u e n c e d by c r y s t a l s t r u c t u r e i S 0
.
Triplet states of ring substituted $-phenylpropiophenones have been c h a r a c t e r i z e d by l a s e r f l a s h p h o t o l y s i s and p h o s p h o r e s c e n c e at
.
- 7 0 O c ~ ~ '
S p i n r e l a x a t i o n o f t h e b e n z i l t r i p l e t has b e e n s t u d i e d
by n a n o s e c o n d s i n g l e p h o t o n counting"
*
and p h o s p h o r e s c e n c e l i n e
narrowing reported for several 1-indanone derivatives
153
.
S o l v a t o c h r o m i c e f f e c t s i n t h e f l u o r e s c e n c e and T-T a b s o r p t i o n s p e c t r a o f x a n t h o n e , t h i o x a n t h o n e , and N - m e t h y l a c r i d i n e p r o d u c e red shifts with increasing solvent polarity ( p * increase) whereas T-T i s strongly blue shifted
(p*
decrease)454.
Laser flash photolysis
has been used t o study t h e t r i p l e t s t a t e s o f c y c l o b u t a n e t h i o n e s and the transfer of triplet excitation from them to D P H 4 5 5 . t h e r m a l d e a c t i v a t i o n o f S, and T,
The
states o f acridine dyes i n
p o l y ( v i n y 1 a l c o h o l ) f i l m s h a s been used t o m e a s u r e t r i p l e t y i e l d s by Parker's m e t h o d 4 s 6 . Hydrogen atom transfer from triplet 1-naphthol t o ground benzophenonei5
and q u e n c h i n g o f t r i p l e t b e n z o p h e n o n e by a V a r i e t y
of biological antioxidants, some o f which involve charge-transfer e f f e c t s 4 5 0 , a r e c h e m i c a l r e a c t i o n s w h i c h h a v e been s t u d i e d .
2-
Phenoxyacetophenone undergoes intramolecular triplet deactivation by q u e n c h i n g d u e t o p h e n y l r i n g , a p r o c e s s m u c h f a s t e r t h a n f o r 8 phenoxyacetophenone (n,
T*)
459
.
T h e photochemical reactions between t h e
t r i p l e t s t a t e o f b e n z o p h e n o n e and N , g - d i e t h y l a n i l i n e h a v e
been studied by a C I D E P m e t h o d i n p o l a r and n o n p o l a r media'". Direct h y d r o g e n a t o m t r a n s f e r o r t h e f o r m a t i o n o f an i o n pair a r e a l t e r n a t i v e p r o c e s s e s w h i c h d e p e n d u p o n t h e polarity o f t h e solvent.
T h e d e c a y k i n e t i c s and q u e n c h i n g o f w a t e r s o l u b l e i o n i c
b e n z o p h e n o n e s c o n t a i n i n g q u a r t e r n i s e d a m i n e and s u l p h o n a t e g r o u p h a v e been i n v e s t i g a t e d by l a s e r f l a s h p h o t ~ l y s i s. ~ ~W a~t e r s o l u b l e b e n z o p h e n o n e s i n m i c e l l a r s o l u t i o n a r e q u e n c h e d by m o n o m e r s and
Photochemistry
34
a m i n e ~ ~ ~and ' t h e i s o m e r i c a n t h r a c e n e sulphona t e s , 1 - A S , 1 , 5 - A S , and 1 , 8 - A S
2-AS
a l l p r o d u c e high y i e l d s of t r i p l e t s 4 6 3 .
D i f f u s e r e f l e c t a n c e l a s e r f l a s h p h o t o l y s i s o f a n u m b e r of k e t o n e s on silica and z e o l i t e s s h o w that t r i p l e t d e c a y k i n e t i c s a r e complex464
.
e4"
T h e effect o f t e m p e r a t u r e o n t h e l u m i n e s c e n c e
and l i f e t i m e o f b i s ( C - c h l o r o t h i o p h e n o l ) - ( l , 1 0 p h e n a n t h r o l i n e ) z i n c ( 1 1 ) has been
the
(n, **I
interpreted as d u e t o a barrier for t h e conversion of l e v e l t o l o w l y i n g CT l e v e l s 4 6 6 .
o f m e t h y l e n e blue i s q u e n c h e d by t h e ground
The
(n,
TT*)
state
state of phenazine
t h r o u g h a c h a r g e t r a n s f e r e x c i p l e x w h i c h p r e v e n t s b l e a c h i n g of t h e dye467.
T h e p h o t o p h y s i c s and r e a c t i o n s ot z i n c p r o t o p o r p h y r i n s
h a v e been characterized4"
and t h e r e s o n a n c e Raman s p e c t r a o f M g ,
Z n and P d t e t r a p h e n y l p o r p h i n e s annihilation o f metal
(71,
reported469
.
The triplet-triplet
m * ) p o r p h y r i n s and 3 ( a , r * )
phthalocyanines involves dimerization t h a n d i f f u s i o n controlled470
.
into excimers at a rate less
Contrary to earlier reports triplet
e x c i p l e x e s h a v e not b e e n d e t e c t e d i n t h e q u e n c h i n g o f t r i p l e t p o r p h y r i n s , c h l o r o p h y l l a , and a n t h r a c e n e by n i t r o c o m p o u n d s , q u i n o n e s , and c h l o r o c o m p o u n d s 4 7 1
.
Some triplet exciplexes have
been d e t e c t e d in o t h e r s y s t e m s h o w e v e r 4 7 2 .
Triplet state
p h o t o p h y s i c s and t r a n s i e n t p h o t o c h e m i s t r y o f c y c l i c e n e t h i o n e s , i n c l u d i n g t h i o c o u m a r i n , have a l s o b e e n r e p o r t e d 4 7 3 Q u e n c h i n g o f s t i l b e n e t r i p l e t by O2
.
in benzene gives
' O2
with
a n e f f i c i e n c y o f 18 f. 5 2 so q u e n c h i n g i s not e x c l u s i v e l y o n e s i n g l e 474 . Biphenyl enhances t h e rate of 9.10-dicyanoanthracene
process
sensitized p h o t o x i d a t i o n r e a c t i o n s by i n c r e a s i n g t h e
'
O2
yield475
.
S u b s t i t u e n t e f f e c t s i n t h e q u e n c h i n g o f a c e t o p h e n o n e and b e n z o p h e n o n e t r i p l e t s by 0 r a d i c a l s o n ' 0 2 generation'has
and t h e i n f l u e n c e d i - t e r t - b u t y l n i t r o x y been m e a s u r e d and t h e m e c h a n i s m
a n a l y ~ e d ' .~ ~ S i n g l e t O 2 g e n e r a t i o n by f u r o c o u m a r i n t r i p l e t s t a t e s varies f r o m 0 . 1 3 t o unity w i t h o u t g e n e r a t i o n o f 02 .
The use of cyanine
lo2 g e n e r a t i o n in o r g a n i c A b s o l u t e q u a n t u m y i e l d s o f lo2
dyes as alternatives to rose bengal for s o l v e n t s has been proposedi7'.
p r o d u c t i o n h a s b e e n d e t e r m i n e d by t h e r m a l l e n s i n g using s e v e r a l sensitizers including tetraphenylporphyrin, zinc 479 . Time resolved thermal
t e t r a p h e n y l p o r p h y n i n . and a n t h r a c e n e
l e n s i n g c a n a l s o b e used t o d e t e r m i n e q u a n t u m y i e l d s f o r p r o d u c t i o n o f t r a n s i e n t s w i t h l i f e t i m e s o f t h e o r d e r o f 1 t o 100 u s ie. s p e c i e s w i t h a l o n g e r l i f e t i m e t h a n t h e t r a n s i t t i m e o f a sound wave. Direct t i m e r e s o l v e d d e t e c t i o n o f l u m i n e s c e n c e at 1 2 7 0 nm
I: Photophysical Processes in Condensed Phases
35
f r o m ' 0 2 has been used t o estimate sensitized singlet oxygen yields f r o m a series o f related p o r p h y r i n ~ ~ " .
Incorporation o f the
s e n s i t i z e r , dihaematoporphyrin ester ( D H E I into cetyltrimethylammonium bromide in 0 0 increases the yield of from 0 0 alone. DHE.
O2
This is attributed t o s t r u c t u r a l alteration o f t h e
i l e c t r o n transfer and ' 0 2 formation c o m p e t e in t h e 9 , l O -
d i c y a n o a n t h r a c e n e sensitized photooxygenation o f olefins4"
.
Microheterogeneous photooxidation can i n v o l v e enhancement of oxidation by covalently binding a sensitizer to a ligand complexing t h e acceptor
482
, for example r o s e bengal tethered t o $-cyclodextrin
enhances t h e photooxidation o f 1,2-diphenyl-p-dioxene. T i m e resolved studies have been m a d e o f t h e dynamics o f triplet state spectral d i f f u s i o n in the presence o f o r i e n t a t i o n a l and substitutional disorder in binary solutions4a3 .
For 1 -bromo-
4-chloronaphthlene and 1 , S - d i b r o m o n a p h t h a l e n e the spectral d i f f u s i o n is very concentration dependent and consistent with 2-dimensional excitation exchange interaction.
Steric e f f e c t s on
triplet energy transfer is not so m u c h d u e to limits on closeness of
m o l e c u l a r approach as limitation o n t h e twisting H systems w h i c h
m i n i m i s e s overlap for electron exchange according t o the findings o f S c a i a n o s t i ~ l . ~ Triplet-triplet ~ ~ . energy transfer between t h e s a m e species has been measured using deuterated a n a l o g u e s 4 a 5 .
The
c r i t i c a l transfer d i s t a n c e i s usually smaller for similar m o l e c u l e s than that for different molecules.
The quenching o f triplet
excited sensitizers by d i a r o y l peroxides apparently involves exchange energy transfer to the conjugated electronic systems o f peroxides486.
T h e fluorescence o f t h e furanoxy r a d i c a l can be used
to m o n i t o r triplet state energy t o t h i s s p e c i e s b a 7 .
OOMR
has been
used t o i n v e s t i g a t e t h e donor-acceptor pair orientation f r o m triplet-triplet transfer in frozen SDS micelles containing benzophenone and naphthalene-hg at 1 . 2 K 4 "
.
Quenching o f
anthracene and sodium anthracene-2-sulphonate triplets by s e v e r a l nitroxyl radicals in the presence of i o n i c surfactants g i v e s information on micelle-surfactant interaction on the p s t o ms t i m e scale4e9.
Triplet energy transfer involving $-ionone as acceptor
or donor i s another system ~tudied'~'.
Phosphorescence f r o m
biacetyl and benzophenone at surfaces has been induced by collision with the triplet state o f benzene produced by electron impact
491
.
The behaviour of g e m i n a t e triplet benzyl r a d i c a l pairs in anionic micelles has been investigated as a function o f added L n 3 + ions in the presence and a b s e n c e o f m a g n e t i c fields492. G e r m i n a t e
36
Photochemistry
r a d i c a l c o u p l i n g i s field s e n s i t i v e in t h e p r e s e n c e o f Ln3+ i o n s but u n a f f e c t e d by d i a m a g n e t i c ions.
A d e t a i l e d study o f t h e
m e c h a n i s m o f t h e p h o t o s e n s i t i z e d r e d u c t i o n o f m e t h y l e n e b l u e in a q u e o u s S D S m i c e l l a r s o l u t i o n s , u s i n g 1 0 - d o d e c y l a c r i d i n e o r a n g e has been r e p ~ r t e d " ~ . involved.
Both t r i p l e t e n e r g y and e l e c t r o n t r a n s f e r a r e
Excited t r i p l e t a c e t o n e i s g e n e r a t e d by t h e r m o l y s i s of
tetramethyldioxetane excites S2 xanthione4".
-+
So
e m i s s i o n f r o m a z u l e n e and
Only t h e t r i p l e t s t a t e t r a n s f e r s energy t o t h e S 2
state of the acceptor. A c t i v a t i o n o f u r o c a n a s e by e l e c t r o n i c a l l y excited t r i p l e t species occurs generated
495
.
For e x a m p l e , t r i p l e t i n d o l e - 3 - a l d e h y d e
by p e r o x i d a s e c a t a l y s e d o x i d a t i o n o f i n d o l e - 3 - a c e t i c acid
i s such an a c t i v a t o r .
T r i p l e t s i n g l e t energy t r a n s f e r o c c u r s in
the complex of auramine 0 with horse liver alcohol d e h y d r ~ g e n a s e ~ ~Many ~ . of t h e mechanistic details of peroxidase catalysed f o r m a t i o n o f t r i p l e t a c e t o n e and c h e m i l u m i n e s c e n c e f r o m i s o b u t y r a l d e h y d e and m o l e c u l a r o x y g e n h a v e a l s o been w o r k e d OU?.
A number of photochemical papers use physicochemical techniques which m a k e them relevant to this review.
These include
a study o f i n t e r m o l e c u l a r r e a c t i v i t y o f e x c i t e d d i p h e n y l m e t h y l radicals498, biradicals derived from the photodecomposition 499
2.2,6,6-tetraphenylcyclohexane
of
, and c h a r a c t e r i z a t i o n o f
transient i n t e r m e d i a t e s in t h e l a s e r e x c i t a t i o n o f c y c l o h e x e n o n e s in t h e p r e s e n c e o f a m i n e s S o 0 .
A comprehensive
examination o f the
picosecond d y n a m i c s o f P a t e r n o - B u c h i r e a c t i o n shows t h a t a 1 , 4 b i r a d i c a l u n d e r g o e s h e t e r o l y s i s t o a c o n t a c t i o n pairs0' A
.
very u s e f u l r e v i e w o f t i m e r e s o l v e d CIDNP and i t s
a p p l i c a t i o n t o r a d i c a l and b i r a d i c a l c h e m i s t r y has been prepared by c l o s s et .lSo2. C h e m i l u m i n e s c e n c e i s observed f r o m t h e t h e r m o l y s i s of trans-alkyl hyponitritesSo3.
of
a number
Excited s t a t e p r o d u c t i o n o c c u r s
via d i s p r o p o r t i o n a t i o n o f a l k o x y l r a d i c a l s w i t h i n t h e solvent c a g e f o l l o w e d by r e a c t i o n s o f t h e t r i p l e t state.
The mechanism o f
a q u a l u m i n e s c e n c e in a l k a l i n e l u m i n o l s t i m u l a t e d in v a r i o u s w a y s has been a n a l y s e d S o 4 .
S i n g l e t o x y g e n i s produced by S o y b e a n
l i p o x y g e n a s e i s o e n z y m e s in t h e o x i d a t i o n o f l i n o l e i c acid and i d e n t i f i e d by l u m i n e s c e n c e at 1 2 6 8 nrnSos. T r i b o l u m i n e s c e n c e o f E - a l k y l and E - a l k y l - 3 s u b s t i t u t e d
I: Photophysical Processes in Condensed Phases
37
carbazole crystals has been related t o t h e crystal structureso6
.
Microsecond and nanosecond flash photolyses has been used t o study photochromic reactions o f spiropyrans o f the indoline seriesso7.
The photophysics, photochemistry, kinetics and
mechanism o f t h e photochromism o f 6‘-nitroindolinospiropyran h a v e New transients in the
b e e n i n v e s t i g a t e d by L e n o b l e a n d B e c k e r s o 8 .
1-10 ns time regimes have been detected and t h e triplet state gives t h e c i s o i d o p e n f o r m a l s o i n t h e t r i p l e t s t a t e w i t h i n 10 n s .
The
same authors have reported a n extensive study on photochromic 510 . Steric requirements
fulgidesSo9 and 2H-pyrans and chromenes
f o r p h o t o c h r o r n i s m a n d t h e r m o c h r o m i s m o f tj,lj’-bis(salicylidene) d i a m i n e s h a v e a l s o b e e n defined’”
.
References D.P.Craig and T.Thirunamachandran, Acc. Q&.m.
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L.G.Arnout and S.J.Formosinho, J. Photochem,.
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2.Smedartchina and F.Dietz, J. Photochem., 1985,
x,315.
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8.J.McClelland and A.Modinos, J. Chem. S O C . . Faradav Trans. 2 , 1985, 81, 673. 5
P.Suppan, Bectrochlm, Acta , 1985, 0 ,1353.
6
J.E.8rady and P.W.Carr, J. Phvs. CQ~QL, 1985, 89, 5759.
7
G.van der Zwan and J.T.Hynes, J. Phvs. C m , 1985,
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R.I.Cukier,
9 10
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a,5457. R.I.Cukier, J.Am. Chem. S O C . , 1985, m , 4115. R.E.Sassoon, Chem. Phvs. Lett., 1986, m , 74. J. Chem. Phvs., 1985,
11
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Part 11 PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS
1
The Photochemistry of Transition-metal Complexes BY A. COB 1.
Introduction
Reviews have solids,
appeared
on
the
of
luminescence
inorganic
photophysics of metal complexes,2'3 pressure effects on
photochemical react ions, compounds,
photoredox react ions of mixed-valence
photochemical
electron
transfer
react ions,
dipole-forbidden energy transfer processes in solution, and
of
mechanisms
hydrogen photogeneration photo-excited
react ions,8
me tallopor phyr in
metalloporphyr in-photosens it ized
format ion
of
from water ,lo exciplex
copper complexes,
' kinetics
hydrogen, quenching
of
photochemistry of transit ion
metal-organic systems,l2 photochemistry of metal-metal bonds, l3
-
photogeneration of cobalt ( I ) complexes,l4 photoisomer isation of
,
rhodium( I I I ) m i n e complexes
and cataly?is and photoelectro
chemistry on ruthenium disulphide surfaces .I6 The photodeposition of metallic catalysts on supports has also been discussed. l7
2.
.
.
Titanium
Intermed iates in colloidal t itania-catalysed photoreact ions have
been detected,18 and
a study of
the heterogeneous
and
homogeneous photoox idat ion of var ious organic cornpounda in both gas and liquid phases has associated the photocatalytic centre of the catalyst with the Ti-0 bond. During light absorption the Ti ion change8
its
oxidation
state
photocatalytic oxidation of
and
coordination
ethane has been
number.
studied
The
at room
temperature, and in particular the effect on the rate of ethane oxidation of the partial pressure of reactants, the W 57
light
58
Photochemistry
intensity, the amount of catalyst, and the residence time have all been evaluated.20
tracer study on the Ti0,-sensitized
An 0 '
photooxidation of aromatic compounds has shown that hydroxylation proceeds through two different reaction pathways depending on pH. At higher pH benzenes are attacked mainly by Hb formed by one-electron reduction of molecular oxygen with excited TiO,, and at low pH attack is by Hb formed from the h+ oxidation of water.21 4-Chlorophenol
has
been
catalytically photodegraded
in
the
presence of TiO, particles to give CO, and HCl quantitatively.22 The preparation of TiO, for use as a photocatalyst in the decomposition of water, acetic acid and isopropanol has been described23 and a simple method has appeared for the preparation of M/TiO, photocatalysts (M-metal or metal oxide).
This latter
method modifies not only the surface but also the internal electronic structure of the catalyst. 24 A complex formed by direct reaction between polymerised n-butyl orthotitanate and MeOH in benzene solution will catalyse the photodecomposition of water, and results involving the use of this catalyst alone and with added FeS0;7HZO presence of
or catalase have been compared.25 In the
plat inum/titania
photodehydrogenated
to
give
catalysts isopropanol has acetone
and
hydrogen
in
been equal
amounts26 and methanol has been photooxidised us ing a MoOJTiO, catalyst
comprising
a
molybdate
monolayer.
Although
the
photo-efficiency is about one fifth of the photoefficiency of pure TiO,, the selectivity for suppressing secondary oxidation is greater. 27
Dilute
aqueous
solutions
of
H,SO,
have
been
photooxidised by 0, in the presence of irradiated TiO, and the rate of oxidation is observed to be greatly enhanced when noble metals
are
deposited
on
the
TiO,
(Ru
The
ZIIl: The Photochemistry of Transition-metal Complexes electrochemical
behaviour
of
platinized electrochemically
TiO,
59
s ingle
crystal electrodes,
photocatalytically, and that of
OK
electrochemically platinized TiO, polycrystalline electrodes has been disc~ssed.~’Light distribution in a diffusing medium of TiO, and water can, to a reasonably good approximation, be represented by
a
phenomenological
Beer-Lambert
Law.3o
expression
Pressure
of
the
dependence
same of
type the
as
the
rate
and
stoichiometry of water photolys is over platinised TiO, has been measured31 and the effect of added alkali metal cations (Li’, Na’, Rb’)
on Pt-, Rh-, or Pd-loaded TiO,
catalysts with respect to
changes in selectivity of the photoreduction of MeOH with H,O
has
been reported. 32 An investigation of the structure of NiO-SrTiO, powder, a photocatalyst for the decomposition of H,O
into H, and O,,
has shown that the Ni metal exists at the interface of NiO and During the photoreaction in water the surface of NiO
SrTiO,.
changes further into Ni(0H) L. 33 Cyclic photocleavage of water with the intermediate redox couple Hg,O/Hg
and using TiO, as sensitizer
has been described. 34 Views of MUKaki3’
on the photocatalytic
oxidation of water to hydrogen peroxide have been disputed.36 3.
Vanadium and Niobium
The possibility
of
photosplitting
irradiation of aqueous V,O,
water
by visible
light
or V,O, dispersions loaded with RuO, and
Pt has been studied,37 and a method of producing concentrated V( IV) on V,O,/silica photoepoxidised
gel has with
been
described. 38 Olef ins
molecular
oxygen
using
the
have
been
porphyr in
tri-p-oxobis( (5,10,15,20-tetra(p-tolylporphinato)niobium(V)]
in
benzene using visible light. 39
4. Plash
C h r o m a Molvbdenphotolysis
of
a
number
of
representative
Cr(II1)
Photochemistry
60 coordination
complexes
has
established
that
the
transient
absorption appears in s l p s in all cases. It is suggested that these findings may be true generally for Cr(II1) complexes having a lowest
excited
doublet
state.*'
Optically
detected
magnetic
resonance (ODMR) of the lowest doublet excited state of Cr(acac), has
been
reported4'
and
the
influence
hydroxylic
of
and
nonhydroxylic glassy solvents on the emitting states of quadrate Cr ( I I I ) complexes of the type CrN,XY (X or Y
=
F- or HO-) have been
determined. 4 2 Theoretical studies on the photoreact ion paths of monocyanopentaminechromium( I I I )
show that l o s s of equator ial
m i n e gives a pentacoordinated square pyramidal structure with a Following bending of the
CN- ligand in an equatorial position.
N-CK-CN group to give a trigonal bipyramidal intermediate having an equatorial CN-,
association with the solvent occurs by lateral
attack on one edge of the equatorial triangle.43 A ~ e - e x a m i n a t i o n ~ ~
'+
phosphorescence yields
has revealed discrepancies with earlier
reported values. 45 46
of the wavelength dependence of [ Cr (en)
[~r(sar)l~+ (sar-3,6,10,13,16,19-hexaazabicyclo[6.6.61eicosane)
and
[Cr (diamsar)1''
(d iamsar-1,8-d iamino-3,6,10,13,16, 19-hexazabicyclo[6.6.6]eicosane) strongly
at
77
K.47
chromium(II1)-sulphur
have been prepared, and emit
Photoselection
and
for
the
D,
Cr (ethylxanthanato),,
complexes
Cr(dimethyldithiocarbamato),
data
Cr(acetylacetonato),
are
consistent with an intensity mechanism for emission involving a pure spin-orbit mixing of quartet and doublet manifold.48 Simple angular overlap coneiderations indicate that several dissociative and
associative
species
intermediate
in
photosubstitution
IIII: The Photochemistry of Transition-metal Complexes
61
reactions of transition metal complexes are likely to have energies comparable to or less than the vibrationally equilibrated LF excited states, and a model has been proposed for estimating nuclear barr iers to formation of tr igonal bipyramidal Cr ( I I I ) intermediates.49 Ligand field photosolvolysis of [Cr (CN),]'MeCN at 366 nm gives (Cr(CN),(MeCN)]f-.50
[Cr,O(AcO),]C1-6H,O low
-p-cyano-PJ,N-dimethylaniline
Oxygen
chain
;-oxide
a
transfer probably
react ion
tetraphenylporphinatochromium(V) undergo
Luminescence spectra of
at 6 K confirm a static nature o f distortions at
temperatures.5 1
photo initiated
in
0x0
disproport ionat ion
tetraphenylporphinatochromium(II1)
to
involves generate
species
reaction
from a a
which
may
with
unchanged
to
then
yield
two
tettaphenylporphinatochromium( IV) 0x0 species. 52 Excitation of
HCr0,-
in polyacrylamide at 365 run induces an sp transition and
quantitative reduct ion of Cr (VI) to Cr ( I I I )
.
Complexat ion of the
excited state results in primary formation of Cr(V) and an organic radical.53 The same group has irradiated [HCrO,]
in its charge
transfer band
induced redox
in the presence of glycine, and
decomposition of Cr (VI) to Cr ( I I I ) .
ESR signals have been detected
.
and ass igned to Cr (V) 54 Three types of Cr (V) compound are formed on irradiation of ethanolic solutions of KzCr20,. products
These are primary
arising from electron-transfer between
alcohol and
chromium hydroxyanion, a complex of Cr(V) and ethanol, and a free Cr (V) hydroxyanion.55 An analysis of the temperature dependence of the emission
spectrum and emission lifetime of trens-(N,)2M(Ph,PCH,CH2PPh,)2 (M=Mo,W) in a homogeneous medium has been carried out in terms of a manifold of thermally equilibrated emitting levels.
A 'B,"
(W+P)
Photochemistry
62
CT term is lowest in energy followed by a 'BZg cm-'
200
above.
Orbital
schemes
are
Lp
term lying about €or
proposed
both
compounds. 56 The temperature dependence of the luminescence of the hexanuclear
Mo( I I )
chloride cluster
[MO,C~,,]~- has
been
investigated over the range 1.4-300 K and analysed in terms of the emission from several Boltzmann populated triplet sublevels. The lowest triplet state was identified as 'T," and is due to the t,
to t,, orbital e~citation.'~ A flash photolysis study of the
quenching of [MO,C~,,]~- by [IrCl,,]'-
shows it to occur by a one
electron transfer process from the cluster; medium and pressure effects
have
been
noted.58
An
photosubstitution reactions of K,M(CN),
investigation
yields
of
formation
were
the
(M-Mo,W) in the presence
of 1,lO-phenanthroline and 2,2'-bipyridine
Quantum
of
has been reported.
recorded
for
the
final
photoproducts [ M o ( O H ) , ( C N ) ( p h e n ) , l ' 2 H , O ,
IMo(oH),(~N)(biPY),l-3Hzo, [W(OH),(CN) (bipy),]-H,O, solid
state. 59
Ligand
solutions of K+[M(CN),] 6o and photolysis
CW(oH),(~N)(Phen),l.2Hzo,
all of which were
f ield
photolys is
of
and
isolated
in their
aqueous
alkaline
(M=Mo,W) containing KCN gives [Mo(CN),l3-
of H,[Mo(CN),]
in DMSO at 300-450 nm gives
[MO(CN),(DMSO)]~-.~~Photolysis of HC10,
solutions of dimeric
complexes of Mo(V1) in the preeence of EtOH leads to reduction of the central atom and format ion of coordination compounds of Mo (V) in
a
dimeric
form,62
and
octahedrally
coordinated
Mo(V1)
supported on silica has been observed by W spectroscopy and the effect of surf ace hydration character ised. 63 Polytungstate anions [MW,,O,,l"-
(M-I?, Si, Fe, Co, H,;
n-3,4,5,6 and 6 respectively)
have been studied as sensitizers for the photoreduction of H,o and 0, by alcohols.
Optimisation was achieved using [SiW,z0,,]4-,
I I i l : The Photochemistry of Transition-metal Complexes
63
alternative polyanions with more negative reduct ion potentials being less efficient due to the lower yields of [ XW, zO,,]
("')-.
64
Photocatalyt ic mult ielectron photoreduct ion
of 18-tungstodiphosphate ( P,W,,0,2]6compounds has been described
in the presence of organic
and leads to the production of
hydrogen. 65 5 . Manaanese
Salts of the type [Mn(saltm)X] ( H,saltm-l,3
-y ,N' -propyleneb is (salicylideneamine); X=F , C1, Br ,
I , NCS, C N , OAc) have been isolated and characterised. none undergo
photolysis
Mn( acac) (OCOCF,)
form
in aqueous solution.66 reactive
ligand
However,
Mn(acac),
radicals
and
during
irradiation, the yield being greater for the heteroligand complex than for the single ligand complex.67 The central metal atoms in Mn(III)(tpp)X
(tpp=5,10,15,20-tetraphenylporphinato;
C1, OAc, NCS), Fe(III)(tpp)Cl, (X=Br, C1, P, N C S , N,)
X=I,
Br,
Co(III)(tpp)Cl, and Mo(V)O(tpp)X
in 2-methyltetrahydrofuran are reported to
be photoreduced with visible light at room temperature. 68 6 . Iron
Lifetimes
of
emitting
states
of
Fe,
Co,
and Ni
isolated in Ar and Rr matrices lie in the range 150-1250 ps.
atoms The
role of the matrix and the possibilities of magnetic dipole or vibrationally induced electric dipole mechanisms for emission have been discussed.69 Ligand field excitation of [Pe(CNCH,),,lZ+ in acetonitrile solution induces consecutive photoaubstitution processes involving formation of the monosolvated intermediate IFe(CNCH,) ,(NCCH,) lL+, [Fe(CNCH,),(NCCH,),]zt.70
which
subsequently
g ivee
Irradiation of horse heart cytochrome c
at 300 nm causes reduction of Fe(I1I) to Fe(I1) and involves as
Photochemistry
64
primary photochemical event electron transfer from the S atom of methionine-80 to Fe.71 Theoretical studies of charge transfer interactions and the photochemical reactivity of d6 transition metal
complexes
with
n-acceptor
ligands
have
been
described
together with the in€h e n c e of inductive, mesomer ic, and ster ic effects on the n-acceptor ability of the isolated ligand and on the
electronic
structure
[Pe(CN)sL]3-
of
(L-pyr idine-type
ligand) .72 Solvent complexes of the type [Fe(CN) sL]"' EtOH, ethylene glycol, HC(0)NRR' been
prepared
by
photolysing
, pyridine, CH,CN,
(L=MeOH,
DMSO) have
in L.73 The
[Fe(CN),NOIr-
same
authors also report that in these solvents the photodegradation
of [Pe(CN),NO]Z- is similar to that in aqueous aolution, namely that oxidation is accompanied by an exchange of NO by the solvent molecule. 74 ,7 5 Photod isproport ionat ion has been demonstrated for
w-oxo-bis(tetraphenylporphinato)iron(IIf), continuous
and
flash
photolysis
directly from the excited state.
A
[FeTPP),O],
con€ irm
and both
disproportionation
strong one-electron oxidant,
the ferry1 complex FeOTPP, is produced, and catalytic oxidation of olefins can be performed
by photolysing
(FeTPP),O
in the
presence of both dioxygen and olef in.76 Oxygen is produced from water containing a Pe,O,
colloid on visible
light. irradiat-ion
(@-025). 77
2Lwaw&m The photophys ical propert Fes of Ru ( I I ) polypyr idyl complexes of the type [Ru(A?i),(BB),,,IZ+, Ru(AA),(D,)
[Ru(AAA),lzt,
[Ru(AAA) (BC)D]+, and
(n-0,1,2, or 3, AA and BB are bidentate and AAA
tridentate polypyridine type aromatic ligands, and D=CN- or C1-) have been atudied,7 8 as well as [Ru(bpy) s,,(taphen),]L+ taphen
-
(11-0-3 and
dipyr ido[ 3,2-C: 2 ' ,3 '-el pyr idaz ine)79 and [Ru(dmb) 5] ",
I l l l : The Photochemistry of Transition-metal Complexes [Ru(dmb),(decb)Izf, [Ru(decb),(dmb) 4,4 '-dimethyl-2, 2 '-pyr idine, decb
Izt,
= 4,4'
65
and [Ru(decb),I2'
(dmb
=
-bis (ethylcarboxy)-2,2 ' -
bipyridine) .80 Emission properties of [Ru(bpy),]X2-nH,081 and the circular dichroism spectrum of the excited state absorption of (A)-[Ru(bpy),]'+
have both been reported.82 The luminescence of
Ru(1I) and Os(I1) polypyridyla has been measured
in MeCN as a
function of pressure and temperature, and it has been found that at high pressures
the radiative and non-radiative
transition
rates between the luminescent CT level and the ground state are generally
increased
by
5-10%. 83
Temperature
dependence
luminescence studies on [Ru(bpy),L]'+ (L-4,5-diazafluorene, (py),) have also been carried out and these show large decreases in the emission intensity and lifetime near
170 K.
This is ascribed to population of a LF state lying only The same group
2000 cm-' above the lowest MLCT excited
has examined the temperature dependence of photosubstitution of several Ru( I I) polypyridine complexes85 and has made a study of the quenching [Ru(bpy),J'+
of by
the
luminescence and
ferrocene
and
photosubstitution of
oxygen.86
Identical
Stern-Volmer plots were obtained for both processes.
linear Solution
and solid phase measurements of the excited-state resonance Raman spectra of
[ R ~ ( b p y ) ~ ] ~and + of the corresponding complex with
blpyr idine-5,s' -dicarboxylic
acid
suggest
that
charge
localiaation occurs rapidly in solution but is inhibited in rigid media.87 and that
Resonance Raman spectra obtained for [Ru(bpy),(DMB) 1''
[ Ru ( bpy ) (DMB)
,J
2+
(DMB-4,4' -d imethyl- 2,2 ' -b i pyr id ine )
show
in the W C T state, the optical electron preferentially
resides on a bpy ligand rather than on a DMB ligand, on the vibrational time scale.88 The emission maxima of structures in
Photochemistry
66
Me
Me
Ph CI
\
IIIl: The Photochemistry of Transition-metal Complexes which [Ru(bpy), 1''
67
is intercalated between layers of a-Zr (HPO,),
.
have been reported 89 Problems
associated
electron-transfer
with
back
sensitization have
electron
transfer
been discussed
with particular reference to the coulombic effect, of
the
electron
quenching
of
generally
and studies
(R~(bpy),]~+
and by (Co(sepu1chrate) 1''
(X-Cl, Br)"
[Pt(NH,),X] (CLO,), been described.
transfer
in
by
92 have
Kinetic parameters have been reported fer the
electron transfer quenching of the luminescent excited state of [Ru (bPy)
I '+,
CRu (bpy12 (biq 1 I "t
(biq=2,2'-biquinoline, DMCH
-
IRu (bpy)2 ( M C H 1 I "
and
a 2,2*-bipyridine derivative) by a
series of aromatic amines in MeCN.93 Solution medium control of the
[ Ru (bpy),] L+/methylv iologen/EDTA
been examined.
photochemical system
has
The pairing of cations with EDTA in alkaline
solution and the formation of larger aggregates at high substrate concentrations is found to affect the yields of redox products from the excited-state oxygen
has
[Ru(bpy),]'+
been
electron transfer
quantitatively
reaction. 94 Singlet
generated
reaction
of
with superoxide in aqueous solutiong5 and by using a
photocatalyst obtained by exchanging [Ru(bpy)
Y. 96 The
covalently
complexes
(1) (n-2
[RuL',L'
by
linked (L),
,12+
on to zeolite
photosensit izer/electron
acceptor
(L')), [R~(bpy),L~]~' (Lz=L,L'),
3
(L3-4,4 ' -dimethyl-2,2 ' -bipyr id ine,
1',
4 , 4 ' , 5, S*-tetramethyl-2,2'-bipyridine, 4,4'-bis(carboxyethy1)-2,
2 ' -bipyr idine) , electrochemical, properties
and
[RuL: ]
''
have
been
prepared
spectroelectrochemical,
compared. g7 98 Quenching of
and
[Ru (bpy),]
and
their
luminescent
'+
has been
studied using a series of electron-acceptor quenchers in order to reveal the effects of charge type on the yield of photoinduced
68
Photochemistry
electron transfer
involving the Ru( 1 1 )
luminescent
state as
electron donor.99 This Ru( I I) (2,2'-bLpyridine-4,4'-dicarboxylic acid)
is a redox sensitizer
containing catalyst"'
capable of
oxidising H,O
to oxygen in the absence of a heterogeneous
S,O,z-
and the kinetics of the oxidation reaction of oxalate induced by visible light irradiation of an aqueous
ion by S,O,'-
solution containing [Ru(bpy) ,Izt
of reversible
have been reported.lol The use
redox reagents such as Fe(II1)
electron acceptors
in place of S,O,'-
and
Hg(I1)
has been described
as and
enables the formation of oxygen to be observed in non-sacr if icial systems. lo2 A kinetic analys is of the intramolecular electron ion pair has
transfer within the *[Ru(bpy),]2+-[CoSiW,,0,,H,0]eappeared. lo3 Chemiluminescence
has
been
observed
dur ing
dissolution of y-irradiated sodium chloride in aqueous solution containing [Ru(bpy),I"
lo4 and
[Ru(bpy),]'+ together
with
EDTA, and [Ru(bpy),IZ+ with to
be
shown
Quenching [Co(en),]'+,
in
the
of excited
also
Et,N,
in
N(C,H,OH)
the
,,
and 2n.l"
S,0,2-
Belousov-Zhabotinskii states of
and [Co(NH,),Cl]'+
[Ru(bpy),]'+
five
systems
CH,=CHCONH,,
and
Interest continues reaction. Io6, by
[CO(NH,),]~+,
has been reported to proceed by
both energy and electron transfer pathways.
Rate constants
have been evaluated for the quenching of different
(polypyridine)ruthenium( 11) complexes by [CoLJZt and [CoL,Izt as a function of L, and the dominant quenching mechanism,
i>.
reductive, oxidative, or energy transfer is determined by the particular sensitizer-quencher combination. log The partitioning of quenching between energy and electron transfer channels has
also been studied for [Ru(bpy) ,I2+ Rate
patterns
for
quenching
and Co( I I I ) cage complexes. 110 of
excited
states
of
Ru(I1)
IIlI: The Photochemistry of Transition-metal Complexes
69
polypyr idyl complexes by a series of Cr ( I I I ) amine and cyanoamine complexes suggest that the net energy transfer process is best described as vibronic tunnelling between nearly nested reactant and product P.E.
surfaces.'"
A
study of excited state lifetimes
and quenching by Cu( I I ) of the luminescence of several a-diimine Ru(I1) photosensitizers with Triton X-100 and X-114 has shown that the binding of the photosensitizer to the micelle exerts a considerable
shielding
effect.
Quenching
suppression
is
attributed to binding of the sensitizer to the surface of the dry hydrocarbon core and blocking of penetration of the hydrophilic quencher 1 2 micelle. '
Cu(I1)
by
the
polyethylene
oxide
sheath
of
the
The hydrophobic complex
t r is (4,4' -di-tr idecyl-2,2 ' -bipyr idyl)ruthenium( I I ) associates in SDS micelles at high ionic strength and a concomitant enhancement of
light-induced
Ru[ (C,,H,,),bpy]
charge
separation
,Zt/MVz'/EDTA/SDS
is
system.l13
retard reverae electron transfer
observed
Colloidal SiO,
the can
in the photochemical system
H,O/[Ru(bpy) ,IZ+/TEOA/zwitter ionic viologen, the
in
and a study of
reactions
has been
*[Ru(bpy),IZ+
+ MVzt
[Ru(bpy),]"
+ MVt
initiated
9 .)
[Ru(bpy),]" [R~(bpy),]~'
t
MVt
+ MVz+
in cellophane under which conditions the
possibility of translation is eliminated. Quenching occurs by electron tunnelling transf er with a rate constant which depends exponentially on the reacting distance. The back reaction is slower by about three Order8 of magnitude and this has been ascribed to Franck-Condon factors.
The same authors have also
studied the diffusion controlled quenching of *[Ru(bpy),l'+
by
Cu(I1) in cellophane film in 50% water-glycerol mixtures. Energy
Photochemistry
70
transfer quenching is more efficient over large distances while electron transfer is more efficient over short distances. effect
of
the
polyelectrolyte
poly(viny1
sulphate)
The on
photosensitized electron-transfer reactions of (Ru(bpy),Izt
the with
a dipolar zwitterionic viologen is reported to be acceleration of the forward reaction and retardation of the reverse process. '17 The same authors have extended this work to include various polyviologen
polyelectrolytes
and
photoexcited
states
[ R ~ ( b p y ) ~ ] ~and +
Hydrophobic
of
interact ions
both
always
their
appear
reactions
to
be
with
the
Ru(bpy),(CN),. important
in
determining the kinetics of the system and in some cases may completely dominate the electrostatic forces present. 'l8,
''' The
quenching rate constant of excited copolymer-pendant [Ru( bpy) ,]
'+
containing acrylic acid by MVrt shows a novel pH effect in water which depends on the dissociation of acrylic acid to acrylalo. This
is
caused
by
the
dissociated
acrylic
acid
forming
a
microdomain around the pendant ruthenium complex which attracts the positively charged MVz+ and so enhances the apparent rate of quenching
by
10-30 times.120
poly(methacry1ic
The
effect
of
conformation of
acid) on the photophysical and photochemical
processes of Ru[ (bpy),Irt
has also been studied. 121 Photolysis of
[Ru(bpy),Izt
on
absorbed
disproportionation.
porous
This seems to
Vycor
glass
leads
to
between a fixed array of
OCCUK
absorbate ions and only arises when the mean separation between rcucling
absorbate
distance. 122
The
ions
is
within
the
electron
Ligand-aubst itut ion
[COC~(NH,),]~+ and EDTA has been induced by aqueous solutions containing [ Ru (bpy),]
'+
react ion
migration between
irradiating their
as photocatalyst.
The
transformation constituted a chain reaction containing a cycle of
IIIl: The Photochemistry of Trunsition-metal Complexes
71
[Ru(bpy),IZt and [Ru(bpy),I3+ in which the reaction is initiated by
reaction
between
photoexcited
[CoCl(NH,) s]2+.123
Carbon
f ormate, 124
C,H,
and
[Ru(bpy),]'+/N[ C,H,
and
has
reduct ively
(CH,),OH],.
dinitrogen
dioxide
[Ru(bpy),]'' been
photoreduced
cleaved
bonds,
this
, 4-C,H4CN, 4-CaH,C0,Me, RZ=R'=Ph,
latter
R' -RZ=Ph,
RZ=R'=H,
R'-H;
l-benzyl-l,4-dihydronicotinamide
[Ru(bpy),]'+
by
In view of the similarities between process
R' =R'=Ph,
in
the
have The
(R-CO,Me,
R' =RZ=Ph, R'-H;
R-COMe , (2)
may
to NH,.
photosens it ized reduct ion of C-C bonds of R' CR'=CRR'
R' =HI
to
CH,125
to
implications for the photochemical fixation of N,
R' -CO,Me
and
R-CN,
R2=H)
by
presence
of
is reported to be cakalysed by MgLt ions by
a
mechanism involving retardation of electron transfer from (2) to excited
[R~(bpy),]".~~~ Studies have
Ru( I I )
complexes
2,2'-bipyridine.
po lyaz ine
examined12'
128 12' 511
been
ligands
reported other
on
than
Tris-chelated Ru( I I ) complexes having various
b identate
c Ru ( m y ) "
incorporating
also
1
1igands and
the
or
(n-1
have
been
luminescence 2,
prepared behaviour
and of
LL-2,2 ' -biquinoline,
2,2 ' -bi isoquinoline or a 2,2 ' -biquinoline der ivat ive) has been studied in the temperature range 84-250 K, and marked changes are evident in the r igid-f h i d transition region.
These have been
interpreted in terms of the dependence of radiationless processes
on viecosity. 130 Luminescence quenching studies on [Ru(bpz) 'I2+ (bpz-2,2 ' -bipyrazine) carried
out
using
and
its monoprotonated
organic
compounds
such
form as
have
been
amines
and
methoxybenzenes and a range of metal ions and complexes.
Rate
constants have been obtained for both oxidative and reductive quenching and in general are faster than for the corresponding
Photochemistry
72
(Ru(bpy),JZt excited state.131 The quantum yield of formation of methylv iologen radical cat ion from photolys is of the [Ru(bpz),I2+
/MVZ+/EDTA
and the radiation stability of
the hydroxytetranitroruthenates M(Ru(N0,) ,OH],H,O
(M-Sr,
Ba, Zn,
Pb, Na, Ag) have been described.133 8.
Osmium
Non-chromophor ic ligand var iations have been carr ied out in
'+
the series of osmium complexes (0s(phen)L,] phosphine,
(L-pyr idine, MeCN,
arsine) and emiasion energies, excited-state
redox
potentials, and radiative and non-radiative rate constants found
to vary systematically with the potential of the ground-state Os( I I I / I I )
couple.134 Phosphorescence from (Os(TTP)(CO)MeOH] and
(Os(TTP)(CO)pyridine] acceptors
by
a
is
quenched
reversible
Irradiation at 300 nm
in CCl,,
iKKeVetSlbh3
and
reaction
(Os(IV) (TTP)Cl,]
by
electron
electron
donors
transfer
CHCl,,
or
CH,Cl,
formation
of
what
and
mechanism. promotes an is
probably
Optimum condftions have been reported for
determination of osmium by measurement of the lumhescence of its 1:3-complex with 1,lO-phenanthroline-
A catalyst, prepared by
reducing the product of grafting 080, on to the C-C bond of sepiolite, has been found to mediate the photooxidation of water but to do so less efficiently than RuO,.
This is the first
example of a dispersed water oxidation catalyst grafted on to a solid support.137
9 . Cobalt The
dioxygen
adduct
of
Co(I1)
tetraphenylporphyrin
is
reported to undergo facile photoinduced dissociation of 0.13* Biacetyl-sensitized CCo (!?hen)zp Ic 1
photodecomposition of aqueous solutions of
-
trans (0) [ Co (pic).phen]+,
and
trans ( N )
IIIl: The Photochemistry of Transition-metal Complexes
73
-[Co(pic),phenJt (Hpic-picolinic acid) have been described139 and some reported magnetic
circular dichroism spectra of several
acidoamine complexes of Co( I I I ) show that the quintet atate lies at relatively high energy.14'
Cobalt cage complexes derived from
3,6,10,13,16,19-hexaazabicyclo[6.6.6 J icosane, 1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]icoaane,
and
3,6,10,13,15,18-hexaazabicyclo[6.6.5 J nonadecane are reported to
quench
the luminescence of
polypyridyls. complexes
and
as
stable
electron-transfer
photoreduction of water.141
ruthenium
with either I - or oxillate'-
electron donor,
photoreduct ion
of
H,O.
tetraacetatocobaltate ( I I I )
agents
Excitation of the
H,
has
the
IPCT bands o€
Using oxalate ion as
been
Photolys is in
in
as anion causes primary
electron transfer from anion to cation. sacrificial
other
In the presence of EDTA and Pt(PVA) these cage
act
[Co(sep) 1''
[Ru(bpy)' ' 1
obtained of
neutral
from
the
ethylened iamine solut ion
gives
(ethylenediaminetriacetato)aquacobaltate(III) together with 25%
of
Co( I I )
complexes.
Micellar-promoted
atereoselect ive
photoreduction of this complex has been achieved by a long-chain chiral ruthenium complex. for
(t)-Coy'
investigated
and the
Different rate constants were found and
micelle-accelerated
the
same
electron
authors
have
transfer
from
photoact ivated l-benzyl-l,4-d ihydronicot inamide to a hydrophi 1ic metal complex of potassium
.
ethylenediaminetetraacetatocobaltate ( I I I ) 14s The quantum yield of photolyais of (Co(glycine),(glycine
methyl ester)Cl]Cl, at 254
n m ha5 been observed to increase slightly with temperature and
the photochemistry of this complex correlated with theoretical predictions based on electronic absorption upectra of Co(II1)
Photochemistry
74 glycine
[ (en).Co (p-OH, 02'-)Co ( en) J
complexes. 146
ester
'+
undergoes deoxygenation on irradiation in aqueous basic solution, probably via a ligand and
photolysis
5-coordinated
of
(OZz-)
-to-metal charge-transfer state147
aqueous
alcoholic
complexes
Co( I I I )
solutions
(RCoSalen]
of
the
(R-C,-,alkyl;
Salen=bis(salicylaldehydediethylenediamine)) leads to evolution
of hydrogen; the effect of pH and excitation wavelength were investigated. [ Co (CN)
The
'- at
charge
transfer
absorption
band
50,6OOcm--' has been assigned to a a( CN)M a * (Co)
transition149 and the photochemical reactivity of [Co(CN),]'reported
to be
macrocyclic possible
controlled
receptors.
to
of
protect
by
association with
Published
data
coordination
suggest
compounds
is
polyammonium that
against
it
is
ligand
photodissociation by using appropriate receptors
10. Rhodium Variation
1-2
(TMB
41
of
'+
the
Arrhenius
parameters
obtained
(TMB-2,5-dimethyl-2,5-diisocyanohexane)
for in
different solvents has been studied and an analysis using the Barclay-But ler
correlation
suggests
that
the
activated
non-radiative decay from the triplet occurs by the same mechanism KegaKdleSS of the environment.lS1 The same authors also report that dinuclear rhodium( I ) (b=l,3-diisocyanopropane) ( 'AZu+'Alg)
isocyanides of the form [Rh,b, display
a
short-lived
J2+
fluorescence
and a longer lived phosphorescence ( SA2u+'A,g).
The
intensity of the fluorescence excitation spectrum falls off at higher energies and this implies that intersystem crossing from
an upper excited state can compete kinetically with internal conversion.152 some
mono-
The low-temperature lumineecence propert ies of
and
dinuclear
tetraamine
Eth(1II)
complexes are
1111: The Photochemistry of Transition-metal Complexes
(tetramine-A,- (NH,) +,
r epor ted
75
(en)2
(tn),;
OK
tn-propan-l,3-diamine). Of the dihalo complexes [Rh(tn),X,]ClO, (X=C1 or Br), the trans complexes showed smaller Stokes shifts as well as longer excited-state lifetimes than do the analogous cis complexes,
and
this
is
interpreted
in
terms
mechanisms
and
of
possible
effects . 153
nonradiative
deactivation
media
"N-labelling
studies have been used to show that the NH, ligand
that is photoaquated in aqueous HC10, solution at 1 3 O as a result of ligand field excitation of
originates to an
(Rh(NH,),C1]Z+
equal extent from axial and equatorial positions.
This implies
that the axial NH, is labilised four times as efficiently as the equatorial
NH,
ligands. 154
[cis-Rh(en),(OH)X]"+
(X-OH,
of
Irradiation H,O)
at
313
optically
act ive
induce8
ligand
nm
labilisation, rearrangement of an excited state, 5-coordinate fragment relaxation, and solvent addition. to
show
that
in
both
systems
the
Evidence is presented
rearranging
species
is
[Rh(en),(OH) Jz+.155 Di-and trimethoxybenzenes and aromatic m i n e s such as diphenylamine, phenylenediamine reported
to
reduce
the
w,n*
triplet
[Rh(4,7-diphenyl-l, 10-phenanthroline),]", [Rh(phen),lS+, (RhCl,(dp-phen),]' bimolecular
and
the
and
ligand
field
[RhCl,(phen),]'
electron transfer.
and benzidine are all excited
state
(Rh(dp-phen) ,Is+, excited highly
of and
states
of
efficiently
by
The rates of
spin-inverted
backward electron tranflfers within the geminate radical pair were der ived from the efficiencies of the electron transfer product formation in the quenching process. lS7 Electronic and temperature effects
on
photocatalytic
the
[Rh(bpy) ,] '+/dextrose/TiO,-Pt/buf
system have been investigated,
and
f er
temperature
A~~ found to have little effect on hydrogen p h o t o e v ~ l u t i o n . ~
Photochemistry
76
quantitative investigation of the photosubst itut ion react ions of [Rh(CN),]’has
and (Ir(CN),]’-
been
descr ibed;
lifetimes
of
(M(CN),(H,O)
1‘-
in acidic aqueous solutions at 25OC
low
these
temperature
species
and
emission
of
have also appeared.15’
the
spectra
and
photoproducts,
Reduction of Rh( 1II)TPPS
(TPPS-tetrakis(4-sulphonatophenyl)porphyrin) photochemically
in
alkaline aqueous solution gives Rh( I I )TPPS which dimer ises to (Rh(II)TPPS), reduced by Via ible
by a Rh-Rh bond.
the solvated
light of
solutions various
bridged
This can be further
electron to the n-radical anion.160
irradiat ion
of
propan-2-01
or
cyclohexanol
chloro(tetraphenylporphinato)rhodium(III)
experimental
conditions
gives
H,
and
under
or
Me,CO
cyclohexanone. 161
. .
11. Irldlum The intense luminescence of (Ir(2 = phos),]ClO, CIS
12
= phos
=
-1,2-bis(diphenylphosphino)ethylene in a rigid glass matrix at
9.5 K has been monitored while external magnetic fields were applied.
Radiative coupling to the ground state from a forbidden
component was induced by the f ield.162 Decay curves of emission CIS- ( IrCl, (bpy),I C1,
from
,
cl8- 1 IrC1, ( 4 , 7-Me2phen) ] C1
and
cls- ( I rC1, ( 5,6-Me,phen) ,] C1
non-exponential behaviour in DMF/H,O thought to
correspond
cls- [ IrCl,(phen),]Cl,
show
at 77 K and 298 K and are
to two kinds
of
solvated
complex. 163
Iridium s o l s prepared by radiation induced reduction of iridium ions have been used as catalysts to convert H,O to H via electron transfer from MV’ [Ir(O,)(dppe),]+ [M(X,)
(L-L),]’
dmpe).165
164
and photochromiam has been observed
in
at 77K and also in the S2 and Se, analogues,
(M-Rh,
Ir;
X,-chelating
S,,
Se,;
L-L-dppe,
Bromfde la photooxfdised to bromine by oxygen In the
1111: The Photochemistry of Transition-metal Complexes
presence of (Ir(C”, N‘-bpy) (bpy),I2+. pulsed
laser
exciplexes
experiments and
photoreactions
the
suggest
involving
the
Steady-state emission and mechanism
a
Br,T
transients
77
sane
and
complex
involving
H0,.166 have
two
Other
also
been
deacr ibed - 167 12. Nickel AKOmdtiC ketones having a high triplet energy such as Ph,CO and xanthen-9-one sensitize the photoreduction of Ni[CH(COMe),], to give
transient Ni(1)
complexes which
decompose to Ni(0)
complexes in the dark.lb8 UV irradiation of diazido(meso-S,7,7,1
2,14,14-hexanethyl-l,4,8,ll-tetraazacyclotetradecane)nickel(II) leads to n + n* excitation of the azido group to give a singlet nitrene intermediate.
This intermediate can scavenge NH, to give
hydrazine.169 The Ni( I I) bis-2-chlorodithiobenzil (3) is reported to be capable of functioning as a photosensitizer-catalyst for the photochemical cleavage of water
in a system consisting of
EDTA as sacrificial reagent and methylviologen as relay.17*
13.
Palladium and P W i n u m
Photolysis of [PdCl(tert-BuNC),],
,J
frans- [PdCl, (ferf-BuNC)
bond.
indicating
in CH,Cl,
gives
cleavage of the metal-metal
Complexes of the type (Pd (bpy)(XX)] (H,XX
4-fert-butylcatechol, 3 4-dimercaptotoluene)
=
catechol
have been prepared
and show intense LLCT transitions in the visible region. also photosensitize the formation of
resolved
spectroscopy
phosphorescence sub-levels.
spectra
has of
been
They
singlet oxygen. 172 Time used
K,[ Pt,(P,O,H,)
to
J
aeparate into
the
individual
The upper degenerate component ia well-structured
and has a progression due to the Pt-Pt atretching vibration; by contrast the lower is broad, structureless and shifted to the red
Photochemistry
78
by
- 300
The delayed fluorescence from this complex is an
emission from the singlet excited state and is created by the annihilation observed
of
from
Pt(Phpy),,
two triplet states.174 the
ortho-metallated
Luminescence has been platinum(I1)
complexes,
Pt(Thpy), and Pt(Bhq), (Phpy-, Thpy-, and Bhq- are the
or tho
C-deprotonated
forms
of
2-phenylpyridine,
2-(2-thienyl)pyridine, and benzo(h)quinoline) between 500 and 600
nm and occurs from two MLCT excited states.175 Magnetooptical evidence
for
two-level
phosphorescence
cis -bis (2-phenylpyr idine)platinum( I I )
Energy-
and
triplet
excited
together
with
solvents.
electron-transf er state its
has
processes
[ Pt, (POP) J
of
~
luminescence
in
originating been
published.
involving
'-
have
the
been
aqueous
from
and
lowest
examined nonaqueous
The inveatigation suggests that this complex is an
excellent candidate for use as an "energy" sensitizer of triplet states
for
organic
and
inorganic
systems
in
homogeneous
solution. 177 8-Quinolinol metal complexes M(Qo)n (M-Pt", Bi",
IT";
n-2,3) are efficient sensitizers
€OK
Pb2+,
visible light
induced hydrogen generation in aqueous TiO, dispersions178 and the
first
example
[Pt(II)]'+[Pt(II)]2reduction of water particular
of as
the
particulate
Xa
[Pt(bpy),[Pt(CN),]
method
has
been
Magnus-type
double
photosensitizers
EDTA has been
containing
and
(MHB-4-methyl-4'-heptyl-2,2'-bipyr The
of
use
salts
for
the
reported."'
In
[Pt(bpy)(MHB)][Pt(CN),]
idine) were studied.
used
as
a
tool
for
structure
elucidation of some short lived transients such as [PtC1,JS-, [PtC1,12-, and [PtCl,]-,
generated by pulse radiolyais or flash
photolys is. I8O Mea13UKementS of the I R luminescence and absorption spectra of [Pt(en),] [Pt(en),Cl,] [ C l O , ] ,
using polariaed light at 2
IIIl: The Photochemistry of Transition-metal Complexes
79
K and room temperature has shown the presence of a resonance peak at
the
CT
absorption
edge
for
Cl-Pt(IV)-Cl.
This
explained by a two-band model in a one-dimensional Photolysis of [Pt(NOZ),-,~]'-
system,181
involving format ion of the
Pt ( IV) as primary
isomer of
be
(X-C1, Br, x=O-2) gives a nitrite
complex of Pt( I I ) v i a a mechanism nitrite
can
photoproduct
which then
'' is
decomposes thermally. 182 Photoaquat ion of trans- [ Pt (NH,) 4C12] reported to proceed
states and to
from two electron-excited
involve homolysis of a Pt-C1 bond, but by contrast photoaquation of trens-[Pt(NH,),Br2]'+ excited
occurs from the lower LF-type electron
state and
leads to Pt-Br
bond homolysis.
photolysis of both Pt( IV) complexes using
Sensitized
[Ru(bpy),]'+
gives
Pt ( I I I ) intermed Fates. 183 The pressure dependence of the quantum
€or
yield
the
reductive
elimination
of
azide
from
[tfens-Pt(~),(N,),]'-
to give [Pt(CN),]'-
results interpreted
in terms of formation of a caged radical
has been examined and the
species via simultaneous scission of both Pt-N, charge-transf er excited state.184
bonds in the
Alcohols have been oxidised in
a two electron process at room temperature by 0, in the presence of
a H,PtCl,/CuCl,catalyst
.
A cyclic process
incorporating a
Pt(II1) species which undergoes a redox reaction with Cu(I1) t o regenerate
the
Pt( IV)
catalyst
appears
to
be
inv01ved.l~~
3 4 . CoDDer [ Cu (L)(PPh,) J
'
(L-2,9-d imethyl-1, 10-phenanthroline
4 , 4 ' ,6,6'-tetramethyl-2,2'-bipyridine)
reduce
ethanollc
[CoC1(NH,),]L+,
solutions
[CoL2]'
(H,L2
of =
will the
or
photocatalytically Co( I I I)
EDTA), and Co(acac),
acetylacetone) on excitation o€ the MLCT band
of
complexes (Hacac
-
the Cu(1)
complex186 and an examination of the decay o f t.he long lived
Photochemistry
80 intermediate eormed
in the photooxidat ion of
complexes has
reinforced the view
Cu( I ) -Cu( I I )
chloro
complexes
chlorocuprate( I )
that dimeric or are
produced
polymeric
during
the
photooxidation. 18’ The
luminescence
and
photochemistry
of
ML,
(HI,
=
4-salicylideneamino-l,2,4-triazole; M-Cu, Ni, Co, Zn, Cd, Hg, Be)
have been examined and the phosphorescent lifetimes found to be dependent on M and to follow a decay curve which suggests only monomolecular processes. biacetyl,
pyrene, and
Triplet acceptors such as naphthalene, anthracene were
used
to study triplet
states. 188 The photorespons ive crown ethers ( t r a n s - ( 4); Z=CH,, CO) have been synthesised and the rrans-(4)-2Cu(I)
complex formed.
This is irreversibly oxidised by oxygen to the Cu(I1) complex in contrast to the cis-(4)-2Cu( I ) partly reversible manner.
complex which binds oxygen in a
Consequently the stability of the 0
complex is determined by photoinduced changes in the Cu(1)-Cu(1) interatomic distance. 18’ A detailed investigation has appeared o € the dependence of +z as
Air,,
format ion on exper imental conditions such
temperature, and ionic strength, following photolysis of
Cu( I ) bromo and chloro compounds.
Pulse laser photolysis of
Cu(I1) chloride complexes at 308 nm in frozen ethanol produces transient complexes of Cu( I ) with a matrix radical (CH,CHOH) ,lgl and quantitative aspects of the photoredox chemistry of chloro and bromo complexes of Cu(I1) have also been examined in fluid methanolic
solution.lg2
[Cu(bpy)zC1]+,
and
The
[Cu(bpy) ,I7+
Cu( I I) have
complexes been
[Cu(bpy),]’+,
phototeduced
irradiation in MeOH and H,O solutions to give [Cu(bpy),]+
as products. lg3An alkyl-copper
by
and HCHO
intermediate produced on laser
f l a s h photolysis of Cu( I I ) -polyacrylic acid complexegl is reported
81
IIII: The Photochemistry of Transition-metal Complexes to undergo secondary photolys is at high f lash intens it ies with the formation of solvated electrons. lg4 Following radiationless
excitation
in
deactivation
isopropanol,
and
[AuCl,-]
undergoes
chemical transformation which
proceed as one-step, one-photon reaction with participation of a higher
electronically
excited
state having
a charge-transf er
nature - 195 'd s Luminescence data have been reported for sandwich complexes between various lanthanide ions and 15-crown-5 ether (L) of the form LnX,L, involving
(Ln-La, Nd, Eu; X,-PF,, other
crown
ethers
C10,).196 have
Similar complexes
also
been
studied.lg7
Application of an internal magnetic field between 0.1 and IT to the photochemical reaction of naphthoquinone in a micelle and in the presence of lanthanide ions leads to a decrease in the yield of escaping semiquinone radicals with increasing concentration of paramagnetic
lanthanide
This is thought to be due to
relaxation of the electron spins in the triplet radical pair caused by the electron spins of the ions.
Measurements of the
concentration dependence of energy transfer between Cr ( I I I ) and Nd(II1) in Li-La phosphate glasses have shown that it is possible to increase the luminescence obtained from the Nd(II1).
However,
even under the optimum conditions of 0.05 mole$ of Cr(I1I) and 2 mole%
of
Nd(III),
the
increase
is no more
than
An
emission intensity enhancement has been observed from the Eu(I1) ion
following
reaction
derivatives in methanol.
of
anhydrous
EuC1,
and
18-crown-6
This may be due to insulation of the
Eu(1I) ion from close approach of solvent molecules so preventing nonradiative energy losses .2oo Fluorescence quenching of crown
82
Photochemistry
ether complexes of Eu(I1) by 5-substituted-1,3-dimethyluracils has
been
investigated
electron-transfer
and
the
results
lend
support
mechanism
for
the Eu(III)/Eu(II)
to
the
photoredox
system. 201 The pH dependence of the fluorescence band intens it ies
of lanthanide ions such as Eu(III), G d ( I I I ) ,
Tb(III), and Dy(111)
with EDTA and NTA in aqueous solution has been reported,202 and luminescence data obtained cryogenic temperatures. 203
on Eu(IE1)
activated
In this latter WOKk,
transitions could be interpreted by assuming a for
Eu(II1).
Laser-induced
niobates
C,
at
all spectral site symmetry
fluorescence techniques have been
used to study the complexation of various anions to Eu( I I I ) in aqueous solutions.204 From this work the use of the magnitudes of ETFP/MT.FP
(ETFP = electric dipole trans it ion f luoresence peak,
MTFP = magnetic dipole transition fluorescence peak) emerged as a
criterion for comparing symmetry
of
the
the abilities of anions to vary the
ligand field
acting
on Eu(II1).
Circularly
polarised luminescence studies of adducts formed by Eu(DK),(CDK) and Eu(DK)(CDK),
(DK
=
achiral p-diketone ligand; CDK
-
chiral
p-diketone ligand) with DMSO and DMF have been reported. contrast
to
earlier
stereoelectronic effects
studies
methyl
Eu(CDK),
in these mixed-ligand
found to be much smaller.205 ternary complexes
involving
adducts,
compounds were
The same group has studied the
formed by Eu ( I I I )
_p-tolyl sulphoxide. 206
In
p-d iketone complexes
Evidence
has
been
and
presented
supporting the formation of an inner sphere coordination exciplex between ('D, )Eu'+aq
and Br- in aqueous solution.207
The emission intensity of Tb( I I I ) complexea with picolinic ac id, squar ic ac id, and 2,3 -pyraz id ined icarboxyl ic ac id in water and aqueous ethanol has been observed to increase with increases
IIII: The Photochemistry of Transition-metal Complexes
83
in the ethanol content.208 Luminescence lifetime measurements have
been
used
to determine the
formation constant of
the
monoacetato complex of Tb(III)209 and also to show that the format ion of Tb-EDTA-ligand complexes is essent ially complete at 1:1:1
molar
ratios.210
The
sensitivity
of
lanthanide
ion
photophysics to detai Is of the metal coord inat ive env ironments represents a powerful method for investigating the coordination sphere.
Complexat ion phenomena associated with the interact ion
of simple amino acids and chelated Tb( I I I ) (EDTA) complexes have also
been
studied
spectroscopy.211
by
Ternary
circularly complexes
(2,s) -ethylenediamine-Y,g'-disuccinic achiral
carboxylate
polar ised formed acid
ligands,212
lqminescence Tb( I I I )
by and
and
a
with
series
with
of
chiral
aminopolycarboxylates and achiral substrate ligands213 have been investigated.
Yb( I I I)
determined
luminescence measurements
by
in
tetraligand
complexes in
the
has
been
presence of
Rhodamine B. 214 16. Uranium
A study of the photoluminescence spectra of hydrated and anhydrous u r m y l sulphates at cryogenic temperatures has been found to show nonequivalent spectra. energies
varied
with
frequencies exhibited reflecting a groups.215 AI
the
system
E1eCtKOniC and vibronic and
certain
vibrational
a dependence on environment, probably
linking of
bridging
sulphate
investigation of the effect of Triton IOOX
micelles
UOZz+
on the biexponential decay of
centres by
* (UO,z+)
has given further support
to the solvent mechanism for reversible processes between the states U* and X*.216 Luminescent properties of solids derived by intercalation of some Cr(I1I) Werner complexes into the lamellar
Photochemistry
84
so 1 id HUO,PO,
- 4H,O
have been character ised . Emiss ion is observed
from the host lattice and guest complex.217 The luminescence of solid solutions of caesium uranyl nitrate with rubidium uranyl nitrate (Cs,Rb,,UO,(NO,),
x
< 0.04) has also been reported.218
The effect of perchlor ic acid concentration on the quantum yield of the photoinduced 0 exchange between
and H,O
UOZzt
has
been invest igated21gas has that of the concentrat ion of HCO,H, HCO';, HNO,, NO,,
and UOzz+ on the quantum yield of
in the photoreduction
U(
IV) formation
of UOZz+ by a formic acid/nitric
acid
mixture. 220 Cyclohexene has been photocatalytically oxidised by UO,"
using visible light in the presence of
polymolybdate(VI)221
and
irradiation
aqueous solution containing H,SO,
of
UOZzt at
313
nm
in
and HMPT leads to formation of
U(IV) by a mechanism which probably involves 0 atom transfer from UOZz+
to the amide molecule.222 U(IV)
photochemical
reduction
of
IJOzLt
is also produced in the by
f~ r m a l d e h y d e ~and ~~
photoreduction of U(V1) in MeOH can be more effectively achieved using a high peak power KrF laser rather than a low power Hg lamp. 224 Photodissociation yields of UP,
have been measured
ae a
function of incidient light intensity in the presence of various additives,225 and multiphoton ionisation of UF,
as a probe of
laser-induced dissociation of UP, has been investigated using an
-
ionisation chamber 226
J7.
Actinides
Photolysis of Np(1V) in HNO, gives Np(V), the concentration of which is found to increase with time due to reaction of NO6 photolysis products with Np( IV) .227 18. M i s c e U e o u a
1111: The Photochemistry of Transition-metal Complexes
a5
Luminescence and decay lifetimes have been measured €or some
metalloporphyr ins,
emisa ion
S,
observed
from
ZnPn
(H,Pn=porphine) as well as from AlClTPP
( H,TPP=5,
10,15,20-tetraphenylporphine),
CaClTPP,
and
InClTPP,228 and the effect of temperature on the luminescence intensity and excited state lifetimes o€ interpreted in terms
bis(4-chlorothiophenol)(l,lO-phen)zinc(II)
of a barrier to the transfer of energy from the lowest
level
'mr*
to lower-lying CT levels.229 Charge separation and photoreduction of
2 inc
tetrakia (sulphonatophenyl)porphyr in by nitrobenzene and
methylviologen in aqueous solution,230 and the quenching rate constant,
back
electron
transfer
rate
constant
and
charge
separation efficiencies in some related processes have been investigated,231, 232 Studies have been made of the photoredox propert ies presence
of of
some
tetra-2,3-pyr idinoporphyrazines and
EDTA
methylviologen,233
and
in of
the the
photoreactivity of the zinc derivative of the related complex meso- tetr a-m-N-methylpyr idylporphine
solutions.234 The effect of
in
aqueous
and
micellar
ionic polymer environment on the
photoinduced electron transfer from metal porphyr in to viologen has
been
investigated
for
aqueous nylon
containing pendant
viologen and quaternised amino groups. 235 Fluorescence quenching of
Zn,
Mg,
and
Co
phthalocyanines
together
with
the
photosensitized reduction of viologen have also been studied236 and zinc tetracarboxylphthalocyanine has been used as sensitizer
in a new photocatalytic aystem f o r producing hydrogen.237 ,238 In aqueous
solutions
containing
cationic
surf actants,
the
concentration of dimers is reduced and the charge separation improved, so increasing the efficiency of the photocatalytic
Photochemistry
86
'y '-O
\
Me
O '\
Me
r
1
IIII : The Photochemistry of Transition-metal Complexes system.
87
n-Cation-radical format ion has been reported following
via ible light photolys is of porphyr ins in frozen solution using alkyl chlorides or quinones as electron acceptors,239 and the stability of Zn porphyr in n-radical cations in aqueous solution found to depend on the nature of the periphery groups on the pOKphyKin and on pH.240
Quinone-capped porphyrins are a useful
model for photosynthetic systems and an NMEt study of (5) (X-H,, Zn, Mg; n-2,3) has showed that highly efficient fluorescence quenching occurs when the quinone and porphyrin chromophores are effectively parallel, whereas intramolecular metal coordination forces
the
quinone
to
be
perpendicular
and
reduces
the
fluorescence quenching. 241 A n examinat ion of the bis (d ithiolene) complexes of Zn, Cd, and Hg suggests that although all of the compounds studied fluoresce and phosphoresce at 77 K in ethanol and 2-methyltetrahydrof ufan,
room temperature emiss ion occurs
only in compounds having aromatic ligands. Photoionisation to give the corresponding metal dithiolene radical and the solvated electron
is also observed.242
photoinduced
electron
Studies have also appeared
transf er
processes
dithiolenes (6) (M-Zn, Ni, Cd, Hg; G-K', aqueous
ethanol and
of
the
Na',
photocatalytic
involving
of
metal
NBuf) in water and isomer isation
of
butenes over ZnO and Sn0,.244 Irradiation of Hg(CN), of
in aqueoue solution in the presence
phenyl 4-tert-butylnitrone as spin trap gives spin adducts
corresponding to the hydroxyl and aminof ormyl radicals245 and irradiation of the thymine dimer-mercury(I1)
complex leads to
monomer isat ion?46 Rad icale capable of reduc ing Mn( I I I ) porphyr ins
to Mn(I1) with high efficiency have been generated in aqueoue solution using diamagnetic metalloporphyr ins such as [SnCl,L] "
Photochemistry
88 ( L-meso
as
- 5,lO ,15,20-tetr ak is (E-methy1-4-pyr id ino ) por phyr in( 2t ) )
photosensitizers.
In
negatively
charged
micelles,
the
efficiency is lower but reduction still occurs.247 R e p o r t s of mechanistic investigations of the role of axial ligands on the tin metalloporphyrins
photoreactivity of
in
redox
reactions
between Ph,P and methylviologen and of quantum efficiencies for a number of different axially ligated porphyr in complexes248 have appeared.
Quasiharmonic self-oscillations of chemiluminescence
have been observed in the system S-Cr,0,7--U077+
in concentrated
H2SO+; the emissions are due to HS,6,.249
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3
The Photochemistry of Transition-metal Organometallic Compounds
-
BY A. COX
Reviews have appeared of photochemical disproport ionat ion of metal-metal bonded carbonyl dimers,
transition metal
cluster carbonyls
photof ragmentation of
in the gas
phase,2
and
f -element photochemistry.
Photolysis of (1) at low temperature is reported to yield (2,3-Bit3 (methylene)bicycle[ 2.2. 21octane)z i r conocene
( 2 ) .4
been
obtained
by
photolysis
of
2,3-bis(methylene)bicyclo[2.2.2]octane
diphenylzirconocene
has and
in toluene at -2SoC, and
NMR spectroscopy indicates a rapid alternation of diene faces co-ordinated to z i r c ~ n i u m . ~ Parallel thermolysis (at 75OC solution)
and
[ ( q5-C5H4Me)&H(
dimers
(3)
photolys is p-H) 3
,
and
studiee of
the
( 2OoC)
in
of
s ilylbie (cyclopentadienyl)
(R-Me, Et, Pr) have shown that these dinuclear
zirconocene hydr ide complexea reductively eliminate H,.
Photodissociation of the transition-metal cluster ion We' provides an indirect measure of the absorption spectrum of the
ion.'
Matrix photolysis of M(q5-C,H,),(H)C0
(M-Nb,
Ta) yields the monohydrides M(qs-C,H,)H,8
of (q5-C,H,),V(CH,),
The
amount of
and M(vI~-C,H~),H, and irradiation
results in formation of methane and ethane. ethane
formed
is dependent on the
concentration of substrate, time and temperature.
4. Chromium. netsanuTt-oM 105
solvent,
106
Photochemistry Collisional quenching of Cr'
and
its
chemical
in a metastable excited state
reactions with
Cr(CO),
and
CH,
have
been
discussed. lo Time resolved IR laser absorption spectroscopy has been used to show that following photoactivation of Cr(CO), 249 nm, there is rapid decay to Cr(CO), translationally
and
vibrationally
and CO.
excited
and
at
The CO the
is
Cr(CO),
possesses sufficient energy to decay further to Cr (CO), and CO. l1 Formation of uncomplexed Cr(CO), reported
by
other
workers
who
in the gas phase has also been have
measured
its
visible
absorption spectrum and have monitored subsequent reactions with itself and various ligands.12 Photolysis of Cr(CO),
in matrices
doped with H, gives three adducts of molecular hydrogen, Cr(CO),H, Cr (CO),(H, 1,,
and
Cr (CO),Hz
-
The
hydrogen
seems
to
be
coordinated to the metal as a simple ligand and the evidence is that Cr(CO),(H,), molecules
of
is formed from reaction of Cr(CO), [Cr(CO)rr(H,)3
hydrogen. l3
has
and two
also
been
characterised in liquid Xe doped with H, at 200 K, the coordinated
H, being reported to have
v E at ~
3030 cm-' ,14 and observed as a
relatively stable transient (kx2.5 s-' at room temperature) on flash
photolysis
s01ution.l~ The
of
Cr (CO)
in
H-saturated
chromium carbonyl catalysed
water
cyclohexane gas
shift
reaction has been shown to occur by a dissociation mechanism in which the rate determining step is substitution of Cr(CO),
by
formate to give [cr(co),(formate) ]--I6 Photolysis of
(q4-diene)Cr (CO),
(diene
=
butadiene, trans,
frans-hexa-2,4-diene, 2,3-dimethylbutadiene) in a N, matrix leads to l o s s of CO and reaction of the resulting complex with N, to give
(q'-diene)Cr(CO),(N,).
In a CO matrix there is stepwise
displacement of the diene ligand to give ($-diene)Cr(CO),
and
IIl2: The Photochemistry of Transition-metal Organometallic Compounds
q5-L
107
Photochemistry
108 ultimately Cr (CO),,I7. M(CO),L
The photophys ics and photochemistry of
(M-Cr, Mo; L- pyridine or substituted pyridine) have been
described. l8 Two short-lived
intermediates have been observed
following
M(CO),
photolysis
of
1,4-di-terf-butyl-1,4-diazabutadiene
(M-Cr,
Mo,
with
W)
(l,4-dab) and identified as
M( CO)I( 1,4-dab) and M( CO) (solvent impur ity) . Abaorpt ion spectra and kinetic data have been obtained. 19' 2o Complexes of the type Cr(CO),(DMPE)(q4-diene) been
synthesised
(DMPE-bis(dimethy1phosphino)ethane) have
photochemically
from
Cr(CO),(DMPE)
and
the
corresponding dienes and show temperature-dependent NMR s ignals due to hindered
ligand movements
the formally octahedral
of
bischelate complexes. 21 Metallacyclic alkenyl ketone complexes such as (4) are formed on photolysia of q'-ArM(CO),R C,H,Me,
Cp,,
C,H,;
(qs-Ar =
C,H,,
M=Cr, Mo, W; R-Me, Et, n-Pr, n-Bu) with
alkynea, R'CICR2(R', RZ = H, Me, Ph).22 Photolysis of M(CO),(M=Cr,
Mo, W) with Ph,PCSNRR' (L) in THF leads to substitution of CO to give P-coordinated M(CO),F
(R=H, R'=Ph)
(R-H, R'=Me, Ph; R-R'=Me;
R=Me,Si,
M(CO),L,
presence
R'=Ph)
(R-H, R'=Me) .23,24 Sunlight
carbene complexes auch a8 of
azirines
, P,S-cordinated M(CO),L irradiation of
(OC),Cr:C(OMe)R
(5, R'=H,
and P,P-coordinated
Rz=Me,
chromium
(R-Me, Ph)
Ph;
in the
R'=Rr=Me)
gives
N-vinylimidates .25 Tricarbonyl(1-6-~-(8,8-dimethylhepta€ulvene)]chromium(O)
is
reported to undergo [4+6] cycloaddition with conjugated dienea to give
from
(6)
buta-l,3-diene
and
(7)
from
2,3-dimethylbuta-lr3-diene. 26 A study of the quenching of the phosphorescence of PhCaCR (R-H, Me) by C r (CO),(q*-L) EtO,CPh,
PhC1,
M(CO),(q'-PhEt)
PhF,
C,H,,
PhMe
(M=Cr, Mo, W) in CH,Cl,
Me,C,H,-,;
(L=MeO,CPh, n=2-6)
and
matrices at 77 K has shown
lIJ2: The Photochemistry of Transition-metal Organometallic Compounds
Me Me
(CO,,
(6 1
Me
/
Me
109
Photochemistry
110 that
donor-acceptor
complexes
are
formed
in
which
the
organometallic compound acts as the electron acceptor. 27 In the stereoselective homogeneous hydrogenation of methyl sorbate and of trans,rrans conjugated fatty esters using Cr(CO),
as catalyst,
the activity is significantly increased by exposing the catalyst to 350 nm radiation in cyclohexane/MeCN. of
1,4-hydrogen
add it ion. 28
E+Z_
The products are those
photo isomer isat ion
has
been
observed for the system (8) and is the first example of such a
( E )-diphosphenes .29
process in
Temperature programmed desorpt ion exper iments have been used to examine the photochemical properties of Mo(CO), Si(100).
150 K, KrP
At
laser
decomposes the adsorbed Mo (CO)
radiation
(248
adsorbed on
nm) partially
releasing gas-phase CO. 30 MoL,
(HL-monothiodibenzoylmethane) has been synthesised by W induced in the presence of HL in
oxidative decarbonylation of Mo(C0). THF
.
S imi lar ly
,, and
M( CO),Sn [N (SiMe,) J (M-Mo, W)
M(CO),(Sn[N(SiMe,),J,),
(L) and M(CO),L,
Sn[N(SiMe,),],
are
formed
from M(CO),
and
represents the first examples in
which both cis and trans isomers are observed upon substitution of bulky divalent main Group IV l i g a n d ~ .The ~ ~ bridged Mo complex Mo,L,(CO),(phen),
(H,L
=
pyrocatechol and
its -p-C1,
_p-Br,
and
tetrabromo derivatives) in which two Mo atoms are bridged by two catecholato ligands and one CO ligand have been produced by irradiation
of
Mo(CO),
with
1,lO-phenanthroline
and
.
pyrocatechols 33 Mo(CO).(dppe)
[dppe-lf2-bis(dipheny1phosphino)ethaneJ
undergoes
photosubstitution reactions to give tac-(Mo(C0) ,(dppe)L] (L=PF,, Me,NPF,,
MeN(PF,),
and P(0Me) ,)
the mer configuration.
which subsequently isomerises to
Further reaction with exce8s L is also
1112: The Photochemistry of Transition-metal Organometallic Compounds
descr ibed.3 4
Charge-transf er
excitation
of
111
[ ( q5-CsH,) rMXr]nC
(M=Mo, W; X-C1, BY, I) in the presence of a variety of liganda (L)
gives ( (q5-C5H,),MXL]+
and [ (qs-C,H,),ML,]z+
for both n-0 and n=1.
EHMO calculations show that the reactive transition is LMCT and
suggest that excitation leads to dissociation of the halogen and radical pair formation.35 Dihydrogen is reported to react with photolytically generated HMo(q’-C,H,)
(CO), to form cis and trans
dihydrogen adducts in argon matrices.
In addition to adduct
formation, hydrogen exchanges for deuterium during photolysis in the parent molecule, presumably via the intermediacy of the D, adduct. 36 Photolys is of solut ion
(qs-C,H,) ,MoH,
and Pe (CO)
in benzene
c ~ ~ 5 - ~ , ~ , ~ , ~ ~,HI~ ~ ~ and ~ ~ 1 + ~
g ives
-.
[ ( qs-C5H5),Mo (CO ) H ] + [ ( q5-CsHs)Mo(CO)3]
3 ide-on coord inat ion of
vinylidene (9) has been reported at a dimolybdenum centre when [Moz(CO),(q5-C,Me,),] The
product
is irradiated in the presence of acetylene.
is
[Mo,(CO),(p-q‘
,qZ-CCH,) (qs-C,Me5),]
and
the
reactivity of vinylidene in this situation is markedly different
ftom (qS-C ,H
(10).38
A
,1 ( CO 1 ,Mo -MO ( CO 1
( q5-C,H
photochemical
study
of
1
and
(qs-C,H,)(C0)2Mo~o(CO),(q5-C~H5) in the presence of nitrite and
nitrate ions has shown that the Mo-Mo single bond is selective towards one-electron reduction, whereas the Mod40 triple bond is active for both one- and three-electron reductions. 39 Irradiation of [Mo[CCH(cMe,)COcMeJ [P(OMe),],(q’-C,H,)
q’-allyl
is reported to give the
complex (11) in a process that is apparently without
precedent.
It
is
suggested
that
photoreaction involves a singlet
(n
the
+
n*)
initial
in
the
transition to a linear
excited atate followed by relaxation to a more dipolar form.
step
stable bent
The 168 Mo centre so generated would then be
Photochemistry
112
capable of reacting with a C-H bond of the t-BuCO group.40 Polarised low temperature luminescence of pyridine-W(CO), has been examined with particular reference to vibrational fine structure and magnetic phys isorbed
field
Photolysis of W(CO),
onto porous Vycor
glass
gives
the corresponding
pentacarbonyl and the properties of this material have been described. W(CO),-PVG
In particular, activation parameters suggest that the interaction energy is < 29 kJ mol-1.42
benzene solutions of W(CO),(AP) disproportionation
to
W(CO),
(AP
=
and
Irradiation of
4-acylpyridine) leads to
W(CO),(AP),
in
a
process
initiated by loss of AP, and followed by subsequent attack of W(CO), on ground state W(CO),(AP) Photolysis of acetylene
hydrocarbon
leads
involving
solutions of W(CO),
alkyne
coordination
rearrangement
polymerisation
of
the
to a vinylidene
polymerisation suggested
to
to give W(CO), and W(CO),(Ap).43
by
that
the
"carbene"
photosubstitution
through
alkyne
complex
a
process
followed
by
its
(CO),W=C=CFW
and
then
has
been
mechanism.44 of
and PhCaCH or
CO
It
in W(CO),(a-diimine)
occurs by an associative mechanism and that the photosubstitution quantum yield depends on steric and electronic effects of both the
substituting
luminescent
a-diimine
organometall ic
metal-alkylidene [XW(CO),L,(CPh)J
and
linkage
and
ligand.45
A
complexes general
of
new
class
contain Fng
of a
stoichiometry
(X-Hal, L-ligand donor) has been described.
The
luminescent state is associated with the alkylidene l i g ~ d . * ~ Irradiation of q5-CSH,W(CO) ,Me in inert solvents in the presence of
PPh,
gives
[PPh,CH,]+[q5-C,H5W(CO),
1-
by a mechanism which
involves the intermediate format ion of phosphoranyl radicals, ;Ph,Me.
This mechanism is isolobal with that proposed for the
lIl2: The Photochemistry of Transition-metal Organometallic Compounds
113
photochemical dlsproportionation of metal-metal bonded dimergl involving
19-valence-electron
intermediates.47
The
dihydr ide
(12) has been prepared which on photolysis gives sequentially the
.
tucked- in compounds ( 13 ) and ( 14) 48 5. Manganese and Rhen iuq The photochemical react ions of Mn, (CO),
in hydrocarbon
solution have been described, including the importance of the CO dissociation process. involvement
of
Preliminary views on Re,(CO),,
homolysis
and
similar
showing the
processes
are
also
pre~ented.~’The same authors report a laser flash photolyais study of M,(CO),,(M=Mn,
Re) in which they discuss two primary
photoprocesaea, metal-bond
cleavage to give M(CO),,
dissociation without metal-metal
bond
cleavage to
coordinatively unsaturated dimetallic species M,(CO) time measurement
of
the
branching
and
ratio
give
CO the
50 A real
between
these
two
processes has been made at different excitation wavelengths,51 and the photodissociation of Mn,(CO),,
in the gas phase has been
investigated using frequency- and time-resolved IR fluorescence
,
techniques.52 Photochemical react ion of Mn, (CO) 248
K
gives
a
mixture
of
E-
and
with dienes at
Z-q3-dienyl
manganese
complexes.53 A report has appeared
on the photo-induced degradation of a
, (R=Me, Et ,
ser ies of organomanganese carbonyls , RMn( CO)
CH,Ph,
Ph) as well as on similar reactions of (q’-C,HS)M(CO),CH,Ph
(M-Mo,
W) and (q’-C,H,)W(CO)
series, Mn,(CO),,, were
produced
CO, and the hydrocarbons corresponding to R while
( (q5-C,H,)Mo(CO),],.S4
(q’-CH,C,H,)
,Ph in hydrocarbon solvents. From the former
the
latter
Hydrido-silyl
(CO)(PR,)Mn(H)SiHR:
gave
compounds
complexes
(R’=Ph;PR,-PMe,,
of
such the
PBu,,
as type PH,,
Photochemistry
114 P (p-ClC,H,) containing
,,
,,
P (p-MeC,H,)
R' =Et ;
PMe,Ph;
thr ee-centr e bonds
Mn-H-S i
PR,=PBu,,
have
been
PPh,]
prepared
by
irradiation of a mixture of diphenylsilane or diethylailane with ( Q~-CH,C,H,)
( CO)
Mn, (w-PPh,) ,(CO)
(PR,)Mn. 55
has
been a
photochemically decarbonylated to form Mn,(p-PPh,),(~-CO)(CO)6,
compound having a Mn-Mn single bond and a semibridging carbonyl group.56
At
temperatures in
(CO),MM'(CO),(a-diimine) [MI
above
K
200
2-MeTHF
of
[M(CO),]-
and
gives
and M'=Mn,
(CO),(a-diimine) (2-MeTHF) ] + M=Mn
photolysis
Re.
These ions
are not formed by direct heterolysis of the metal-metal bond but rather
by
product
thermal disproport ionat ion of
the photosubst ituted
at
(CO),MnRe(CO),(a-diimine)
K
133
of
Photolyais
(CO),MM' (CO),(a-diimine) (2-MeTHF) . induces
cleavage
of
the
metal-N bond.57 The same authors have also shown that photolysis
(M, M'=Mn, Re) in the presence of PBu,
of (CO),MM'(CO),(a-diimine) using
2-MeTHF
or
THF
[ (Mn(CO),(a-diimine)
as
solvent
at
room
temperature gives
(P(~-Bu),)]+[M(CO),I-.~~
Evidence has now appeared for dissociative loss of CO as a
,o.
second pr imary process in the solution photolys is of Re, (CO) This
reaction
corresponding
is
more
reaction
important
in
Mn,(CO)
in
Re,(CO),, A
FTIR
than
the
photoacoustic
investigation of the surface species resulting from photochemical reaction
of
Re,(CO),,
with
silica and alumina has shown the
formation of tricarbonyl species on the surface of both An ESR study of the photolysis of a Re,(CO)lo-Et,SiH
system has
been described and the rate constant for abstraction of H from Et,SiH
by k e ( C 0 )
group
in Re,(CO)
products.
The
measured.61
Photosubstitution of a carbonyl
with P(OPh), observed
pattern
gives four well-characterised of
disubstituted and
triply
IIi2: The Photochemistry of Transition-metal Organometallic Compounds
115
substituted dirhenium compounds can be accounted for in terms of ster ic replusion between the phosphites and electronic effects. 62 The cluster compounds H,Re,(CO),,,
HRe,(CO),,
and Re,(CO),z(OH),
have been isolated from photochemical reaction of Re,(CO),, thiophene.63 Products arising 1,2-Re,(CO),L,,
from
photolysia of
Re,(CO),L,
A
and
with
Re,(CO),(p-LL)(L=PMe,
PPh,
;
A
LL,=bis(dimethylphosphino)methane, bia(diphenylphosphino)ethane,
and bis (dimethylphosphino)ethane) with alkenes provide evidence for metal-metal bond cleavage64 and a mechanistic investigation
of the ReBr(CO),(bpy)/TEOA//CO,
system has shown that CO, is
efficiently and specifically photoreduced to CO, and that the initial
photostep
is
reductive
ReBr (CO),(bpy) by TEOA?’
quenching
of
photoexcited
(qs-CsMe5),ReH has been prepared by
cocondensation of Re vapour with 1,2,3,4,5-pentamethylcyclopentadiene at 77 K66 and catalytic H/D
exchange between benzene, THF, and a variety of alkanes occurs upon photochemical activation of ( q5-CsHs)Re (PPh,)H. 67 6. Iron
Zeolite
supported
Fe
systems
have
photolysis and thermolysis of Fe(C0) ,/”a-Y
been
obtained
adducts.
by
Prolonged
photolysis at 290 K under a fluidised shallow bed does not result in formation of naked F e ( 0 ) clusters but gives a limited fraction of magnetically coupled Fe,(CO),
entities.68
Fe(C0)
has been
irradiated in LDPE (low density polyethylene) or PTFE, and IR evidence advanced to suggest that the main photof ragment reacts with
unchanged
Fe(CO),
to
form
Fe,(C0),.69
However,
the
assignment of some of these IR bands has been que~tioned.’~ Mossbauer spectroscopy has been used to study the W photolysis of Fe(CO),
in a low temperature N, matrix.
In addition to the
Photochemistry
116 Me
,M -& $ e
W
W-H
/H 'H Me% 'Me
Me
Me
Me
Me (1 3)
(12)
Me
I
(15 )
W
Me% ' Me Me (1 4)
(16)
III2: The Photochemistry of Transition-metal Organometallic Compounds stable compounds Fe,(CO),
and Pe,(CO)
117
the unstable species
,z,
Fe(CO), and Fe(CO), were produced, and these were found to react with the nitrogen matrix to give Fe(CO),N,.71
Low-temperature
photolysis of pentane aolut ions of Pe (CO), under high pressur es of H, gives a complex mixture of hydrides.72 A flash photolysis study of the behaviour of Fe(CO),
in C,D,
evidence for the formation of Pe(CO);C,D,. to give Fe(CO), and with Fe(CO),
has provided clear This can react with CO
to give Fe,(CO),
(n=8 or 9).73
Photocatalyaed isomer isat ion of allylbenzenes with Fe (CO), has
-
been r ecorded 74 Fe(CO),
Irradiation of
d i lute pentane solutions of
and tetramethylethylene produces (15) as shown by ESR
measurements.
However,
on
s imilar
2,3-dimethylbut-l-ene gives (16) at -130'
and (15) at -80°C.75
frttns-Deca-l,4,9-tr ienetr icarbonyliron has photochemical Fe(C0),76
react ion
between
treatment
been
synthesised by
trans-deca-l,4,9-tr iene
and
and the same authors also report that photolysis of
trans,trans,cis-cyclododeca-1,5 ,9-tr iene (L) with Fe (CO) g ives ( 17) together
with
LFe(CO),
and
L'Pe(C0),.77
Transition
metal
carbonyls such as Pe(CO), and W(CO), mediate the photochemical
r eact ions
cycloadd it ion
of
1,2-d is i lacyclobutene
with
cyclohexadiene. Some intermediates have been isolated and their structures deter~nined.~~ Irradiation of Fe,(CO)
,2
in ethylene or
propene gives (alkene)Pe(CO), via the intermediacy of Pe(CO),. the
case
of
terminal to
higher
alkenes
internal alkenes
nonsequential is promoted.7g
isomerisation of As
part
investigation of the dependence of the M(CO),-butadiene interactions on
stereochemistry, gas-phase
In
W
of
an
(M-Fe,Ru)
photoelectron
spectra have been recorded for a series of mono- and bi-metallic M(CO), (M-Fe, Ru) derivatives of
Photochemistry
118 5,6,7,8-tetramethylenebicyclo[2.2.2]0ct-2-ene. spectral differences were observed
Surprising
between
8x0,
and
exo-
endo,
ero-isomers, and on the basis of ab initio calculations these were ascribed to long range electrostatic effects from the Fe(CO), moiety.80 The same approach has also been used in respect of the bonding
in
Pe,(p-CO)(CO),(C,R,)
and
Fe,(p-CO),(CO),(C,R,),
enabling the role played by the carbonyl groups to be clarified and
ascribing
the
metallacyclopentadienyl
very
high
stability
of
the
ring to the presence of a strong M-C
interaction of a-character - 81 Iron atoms and dimers have been shown to interact with ethylene to give a hydrogen-bonded trans it ion metal ethylene complex as well as the classical n-complex in cryogenic matrices. Photoactivation
of
the
hydrogen-bonded
complex
induces
rearrangement to the vinyl iron hydride.82 It has been reported that the ferrocene derivative bis(q5-indenyl)iron(II) can act as a photocatalyst. for the reduct ion of methylviologen in methanol. The
results
suggest
that
this
complex
may
be
capable
of
functioning as a catalyst suitable for the product ion of hydrogen from water. 83 Dif errocenylbenzenes will also serve as catalysts for photochemical cleavage of water, and
in the case of the
p-diferrocenylbenzene/MVZ+/TEOA/ colloidal Pt system,
efficiencies of hydrogen evolution comparable to that from the analogous system Complexes
of
naphthalene,
involving [Ru(bpy) ,]
the
type
benzene,
'+
have been recorded. 84
[ (qs-C,H,)Fe(qe-arene)
_p-xylene, durene; X=PP,-
]+X-
(arene
or BF,-)
=
are
reported to serve as photocatalysts for the isomerisation of hexamethyl(Dewar
benzene)(HMDB)
to
hexamethylbenzene.
Two
possible mechanisms have been suggested, namely dissociation of a
IIl2: The Photochemistry of Transition-metal Organometallic Compounds HMDB/photocatalyst
exciplex
giving
rise
to
an
119
ionic
chain
reaction, and a photoinduced internal electron transfer within
1’
this same e~ciplex.~’ Irradiation of [q’-C,H,)Pe(q’-arene)
or
analogous complexes in which q5-C5H5 is substituted with P(OR), (R-Me,
Et,
Ph)
induces
ligand
Two
[ (q5-C,H,)Fe[qb-[P(OR),l,]
procesaes, 1088 of CO and irradiation of
( qs-C,R,)
1088
reaction8
primary
to
give
photochemical
of a benzyl radical, occur during
Fe (CO) ( q ’-CH,Ph)
(R-H, Me)
in alkane
However, at 77 K in a rigid alkane matrix CO-loss is
solvents. the
exchange
only
detectable
reaction.87
investigation
An
the
of
energetics of the photocatalytic hydrogenation of ethylene by has shown that the rate determining step is C,H,
Fe(CO),(C,H,)
insertion into an Fe-H bond,88 and a radical mechanism has been proposed for the photochemical Fe(CO), catalysed hydrogenation of octenea. H,Fe(CO), active
The primary photolysis product Pe(CO), to give HFe(CO), hydrogenation
reacts with
radicals which are thought to be the
promoters. 89
Irradiation
of
the
iron
cyclopropylacyl complex (18) is reported to undergo photochemical decarbonylat ion subsequent
to
the
rearrangement
complex (20).
cyclopropyliron to
the
u-complex
and
(19)
ferracyclopentenone
carbene
The transformation is suggested to proceed via a
f erracyclobutene intermediate which undergoes CO insertion.
A
ferracyclopentene carbene complex is formed on photorearrangement
of
W e ( qs-C,H,)
(qs-C,Me,),Pe,(CO), hydrocarbon highly
(R-methoxycyclobutyl) .91
(CO),,
or (q5-C,Me,)Fe(CO),H
solutions
synanetrical
gives
molecule
at 355 nm in Ar-purged
(qs-C,Me,),Fe,(~-CO)., in
of
Photolys is
which
the
This C,
rings
is
a
are
perpendicular to and centred upon the Fe-Fe bond.92 The allene complex (q5-C,H,),Fe,(CO),(~-CH2=C=CH2)
can be synthesised in good
120
Photochemistry
I
Me
(19)
x
OC-Fe-Fe-CO
Ph
NKHMezIz
I EC0
C H I‘Fe-P-M-CO
oc’
I H
(23)
IIi2: The Photochemistry of Transition-metal Organometallic Compounds
121
yield from (21) by photoinduced rearrangementg3 and irradiation of the br idg ing ethenylidene complex [ (qS-C,Hs) (CO)P~],(~L-CO) (p-C=CH,)
.’*
presence of CO gives (22) (q”-CsHs)Fe(CO),Co(CO)4
with diphenylacetylene in the
In argon matrices, photolyais of
can
occur
by
two
reversible CO loss to form (q’-C,H,)FeCo(CO),
namely
and heterophotolysis
to form [(qs-CsH,)Pe(CO),J+
and
[Co(CO),]-
N,-doped
the
main
matrices,
pathways,
ions.
However, in
product
is
(qs-CsH,)FeCo(CO)a(NZ)(w-CO),. 95 The synthesis of heterobimetallic complexea
from
metal
carbony1
bis(diisopropy1amino)phosphine photolysis
of
(23) in
has
been
pentane gives
complexes
of
described;
thus
(24).96
Perrocene and
ruthenocene have been photosubstituted with CO,R, alkyl;, aryl, CF,,
and COCF,.
CHO, CH,OR,
The reaction proceeds via a CT
complex of metallocene and halogenated compound. 97 7. -R
The IR spectra of isotopically enriched Ru( “CO) nr( “CO),(x= 1 to 5) have been measured in liquid Xe both before and after W photolya is. Ru,(CO),
These latter
spectra indicate the formation of
with a single bridging CO group.98 An investigation of
organotr iruthenium
clueter
photodehydrogenation of
shows
that
(25) gives (26) and (27) and that on
-
prolonged irradiation H,Ru,(CO) products.
compounds
,5
and hexane are formed as final
Photodehydrogenation of HRu,( CO)*( CsCCMe,)
has also
been studied. 99
A
study
of
electron
transfer
subetitution reactions of Os,(CO) photochemically
generated
catalysed
and Fe(CO),
(,
19-electron
species
phosphine
initiated by has
been
Photochemistry
122
0
5
(9-C5"4,
oc'
/c\I,co
Fe
(MetCH),N
co M,
Et&Me0
- p
co R G R " 'it'
H
(25)
(24)
(26)
(27)
Scheme 1
IIi2: The Photochemistry of Transition-metal Organometallic Compounds
123
described.loO These processes, which fail with M(CO),(M=Cr,
Mo,
W), may occur by a mechanism similar to one already reported for Ru, (CO),2.
Dual
luminescence involving two components and
corresponding to emission from each of the localised MLCT states
of both chromophores has been observed from the unsymmetrical ligand- bridged dime18 [ (bpy),(CO)OsL.Os(phen) (dppe)C1J3t.102
9. Cobalt Ab
initio CI
calculations of
ground and
excited state
potential energy surfaces of HCo(CO), have been reported and the two electronic states 'A,
and ' E found to be close in energy. The
molecule reaches E'
intersystem crossing, and
by
dissociation to products occurs along the E ' Irradiation of
P.E. surface.lo3
the stable complex CoH[PhP(OEt),],
unsaturated active complex CoH[PhP(OEt),], of
subsequent
catalysing
intramolecular
cyclohex-2-en-1-01
to
produce
gives the
(28) which is capable
transfer
of
cyclohexanone.
H
from
When
the
irradiation is interrupted (28) recombines with photodissociated phosphonite to give the starting complex.1o4 ESR evidence shows that photolys is of Co, (CO), (PBu,) , in the presence of pquinones leads to the spin adduct of Co(CO),PBu, chelation Photolysis
to
of
both
carbonyl oxygen
,
Co, (CO) ( PBu,)
and
to the quinone via Co
atoms
of
the
phenothiazine
quinones. gives
the
phenothiazine radical.105 Near W irradiation of (Q~-C~H~)~M,(CO), (M-Co, Rh) in low temperature hydrocarbon matrices results in
rapid
and
clean
loss
of
CO
to
produce
the
metal-metal
double-bonded, doubly CO bridged product [ ( Q ~ - C ~ H ~ ) M ( ~ -Iz. C OIo6 ) PhOtOi801119ri8atiOn of a cobalt buta-113-diene complex has been described together with stereochemical evidence which clearly links simultaneous double exo-endo exchange with a switch of the
Photochemistry
124
metal from one n-face of the ligand to the other (scheme 1).
The
observations provide strong evidence for the occurrence of the envelope inversion mechanism
in the
fluxional behaviour
of
q4-diene complexes.lo’ Factors
determining
the
photohomolys is
rate
of
metal-carbon bond in the alkylcobaloximes Co(dmg).(H,O)R Et, Pr, CHMe,, Bu, CH,CHMe,, maximum
quantum yield
temperature
ef fects
a
(R=Me,
hexyl), have been investigated and a
obtained
showed
at
Solvent and
436
discrepancies
with
the
Adamson
radical-pair model. The same authors also describe the effect of temperature and solvent on parameters of the ESR spectra of the photolysis
products
of
RCoL
(R=Me,
.
Bu,
Me,CHCH,;
f re8
Some
L=bis (acetylacetone)ethylenediamine) log rearrangements of
Pr,
organocobaloxime(II1) complexes
radical
have
been
.
descr ibed 110 Isomer isat ion of
(~-substituted-ethyl)bls(disubstituted glyoximato)(L)cobalt(III) or
(L-pyridine
primary
amine)
to
the
a-substituted
ethyl
complexes occurs on visible light irradiation of the sample in the solid
state; the reverse
however, proceed. formed when
CCL,
isomerisation
(*@)
does not,
Exc itat ion of the donor -acceptor complexes
or
CHC1,
is
added
to CH,CN
solution8 of
bls(fulva1ene)dlcobalt monocation leads to oxidation to the dication.
Similarly, replacing the chlorocarbon by Ph,B-
and
using the dication of the organometallic gives the monocation. These
processes
illustrate
principle participate as
a
that
[ (C,,,Ha) ,Co,
photocatalyst
1‘+jl +
in the net
reaction which oxidises Ph,B- and reduces CC1, or CHC1,.ll2 10. Rhodium and Iridium
Photolysis of
can
in
redox
125
IIl2: The Photochemistry of Transition-metal Organometallic Compounds
(p-tetraphenylporphyrinato)bis[dicarbonylrhodium(I) ] mixture
of
5: 1
Cl(TPP)Rh( 111) (CO)
benzene-CC1,
promotes
Laser
(30)
(29) in a
oxidation
photolysis
to
examination
suggests that homolysis of the Rh(1)-N bond occurs in the higher excited singlet states of
(29) to give TPP[Rh(II)(CO),]
as
transient and the assumption is that (29) abstracts a chlorine atom from CC1, [LM ( CO ) C 1]
,
to give
(30).
The four binuclear systems M=Rh ,
( Ph,As ) ,CH, ;
( L=( Ph,P ) ,CH,,
Ir )
exh ib it
temperature-dependent low- and high-energy luminescence which can be interpreted as the phosphorescence and fluorescence arising from the metal-centred np, + (n-l)dZ2 transition (n-6 for Ir and 5 for ~ h.I14 ) u s e r phOtOly8i8 of
chloro(tetraphenylporphinato)carbonylrhodium(III) solution
shows
that
tr iplet
format ion,
in
benzene
photo induced
decarbonylation and isomer f ormat ion occur within 20 ns following the
laser
pulse115 and
photocleavage of
(OEP-octaethylporphyrin)
CH,Rh(III)OEP
the C-Rh bond
proceeds
in
in
benzene
solution by a wavelength-dependent process to give Rh(I1I)OEP which dimer ises elucidated. AgClO,
.
The primary photochemical process has been
(OEP)Rh(III)Cl reacts with arenes in the presence of
or AgBF.
to give phenyl-rhodium( 111)
complexes which
undergo photochemical homolysis of the C-Rh bond as well as its halogen-induced heterolys is
.
Photolys is
in benzene leads to
4-substituted biphenyls and the halOgenOly8i8 gives _p-haloarenes with better than 99% r e g i o ~ e l e c t i v i t y . ~Methanol ~~ has been photodehydrogenated in the liquid phase using c/s-Rh,Cl,(CO),(dpm),
and Pd,Cl,(dpm),
to give a gas-phase product
which is almost pure hydrogen118 and the nature of the mechanism8 has been discussed.
Photochemistry
126
Carbonylat ion of benzene to benzaldehyde has been achieved with
IrBr(CO)(dppe)
(dppe=Ph,PCH,CH,PPh,)
IrH(Co),(dppp)(dppp-Ph,P(CH,),PPh,)
or
IrH,(CO)(dppe)
catalyst120 and photolysis of (31) (R-CH,CMe,,
, as
R‘=Me) leads to a-H
elimination and formation of the new iridium methylidene complex (32)
Flash
trans-IrCl(C0)(PPh,),
photolysis
of
Ir( I)
the
complexes
and its dihydrogen adduct H,IrCl(CO) (PPh,),
shows that both complexes give the same transient intermediate
I
Results of the study suggest that CO labilisation from Ir(1) and Ir(II1) is an especially facile photochemical pathway and that photoreductive elimination of H, is more complex than previously thought. 122
31. Nickel. Pall&ium
and
Platinum
Photolysis of Kr matrices containing HI and Ni(CO),
at 4 K
leads to a new product which on the basis of its ESR spectrum is thought to be the radical HNi(CO),. and a ‘A, ground state of
This has a trigonal geometry
C,, symmetry.123
The f irst examples of
d‘O metal phosphine and phosphite complexes of Ni, Pd, and Pt which
possess
long-lived
emissive
excited
states
in
fluid
solution at room temperature have been described; these complexes are photochemically reactive towards organic substrates.124 The primary photoprocess in the homo- and heteronuclear palladium(1) and platinum(1) hexakis(methy1 iaocyanide) dimers [MM’(CNMe),Jr+ (M-MI-Pd, Pt; M-Pd, MI-Pt),
is metal-metal bond
homolysis to give the 15-valence electron radicals [M(CNMe), I + . These radicals are reactive towards halogen atom abstraction from CX,
(X=Cl, Br) to give mononuclear pseudo-square planar
[MX(CNMe),]+
(b¶=Pd, Pt)
Photolyais of ~ ~ ~ ~ S - [ P ~ ( P P ~ ” , , . ( N C S ) ~ ]
In MeOH or MeCN leads by a stepwise process to
IIf2: The Photochemistry of Transition-metal Organometallic Compounds
R
R'
R
PdBrL N=N
I
Q R'
127
Photochemistry
128
1. 126
[Pr,P(SCN-S),Pd(p-NC)Pd(PPr,),(SCN-N)
Comparison
the
of
react ivit ies of quadr icyclane, 2-carbomethoxyquadr icyclane,
2,3-dicarbomethoxyquadricyclane, and 4-carbomethoxyhomocubane in the presence of PdClZ(q4-NBD) (33 ,NBD-norbornadiene) reveals a correlation beteween the quantum efficiency of isomerisation and the
ease
oxidation
of
of
the
organic
compound.
These
observations are consistent with a redox-chain mechanism in which electron transfer from the organic substrate to photoexcited (33)
role. 127 Reg ioselect ive ox idat ion of the
plays a a prominent
ally1 sulphone (34) can be catalysed by Pd(O,CCF,),
and light, and
occur s at the allylic posit ion to give RCOCR' :CR2S0,C,H,Me-p
and
HOCHRCR' :CR2S0,C,H4Me-p.
and
Intramolecular
sen8 it izat ion
other excited-state pathway6 involving orthometalated azobenzene complexes of Pd(I1) (35) have been studied and although the free ligand does not luminesce in fluid solution at room temperature, upon metalation by Pd, intraligand fluorescence is observed.129 diplatinurn( I I I)
Disubstituted
complexes
of
the
type
(X-Br, I ) are formed from oxidative addition
[Pt,(p-P,0,H,),ArX]4-
of the excited state of [Ptz(p-PZO,Hz),]*-
to aryl bromides and
iodides (ArX) in a process which is inhibited by quenchers such as
hydroquinone,
SO,,
(LIL'IPEt,,
Pt(Ca04)LL' L'=P(CHMe,) of C,O,
,,
PR,;
and
acrylonitr ile.130
PPh,,
SEt,,
PMe,,
Irradiation PBu,;
of
L=SEtz,
R=cyclohexyl) leads to reductive elimination
as 2 C 0 , and formation of PtLL'
Photochemical formation
of a a-methyl complex of Pt(IV),
[MePtCl,]'-
complex of Pt( 11), [ (CHz-CH,)PtC1,],
(36) occurs on irradiation of
[PtC1,I2-
in the presence of methyl and ethyl derivatives of tin
and germanium. S,l
and a n-ethylene
The mechanism of electrophilic substitution is
and involves electron transfer f tom t.he t.st.raa1 kylmetal to
IIi2: The Photochemistry of Transition-metal Organometallic Compounds
129
Pt(IV), whereas (36) is formed by @-hydrogen elimination from [EtPtC1,]z-.132
Kinetics
and
mechanisms
of
thermal,
photochemical, and y-induced reactions of [PtCl,]- with arsnes as well as alkylmercury compounds have also been reported. 133 12. coStudies of the photochemistry of [Cu(cis,cis-cycloocta-1,s-diene)2 3 +
[Cu(C,H,)]+
and
have shown the participation
of several u-bound Cu-alkyl intermediates with lif etimes in the ns time d01nain.l~~A very high efficiency has been reported for the norbornadiene to quadr icyclane (Ph,P) ,CuX
(X-Cl,
Br ,
I) ,
phOtOi8Omeri8atiOn using
(MePPh,) ,CuX
(X=same) ,
or
CuCl as sen8 it izer , and the react ion occurs by
(Ph,PCH,CH,PPh,)
conventional bimolecular energy transfer from the triplet excited state of the sensitizer to norbornadiene.13'
The pO88ibility that
cyclic enone photodimeriaation might be effected by coordination of Cu(1) to either the nonbonded pair on 0, or to the C-C n-bond
to
leading
regiocontrol
investigated.
However,
in no
(2t2) clear
cycloadditions synthetic
has
been
advantage
observed.136 CO adducts of stable monomeric Cu( I )
was
complexes
derived from some newly synthesised tripod ligands are reported to luminesce in the range 480-550 nm; this is the first reported example of emission f rom Cu carbonyls. J3. Miscellaneous
Room temperature emission from (qs-Me,C,)2Eu-OEt, quenching
by
(qs-Me5C5) .Yb-OEt,
through
an
energy
and its transfer
and spin trapping of the photolysis products of ethyl( tetr aphenylporphyrinato)aluminium139 have been descr ibed.
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3 The Photochemistry of Compounds of the Main GrouD Elements
-
BY A. COX
1. Introduction The photochemistry of
8
ilanes has been reviewed.
'
Measurements of the photodissociation dynamics of CO; show that in the energy range 1.95-2.2 eV fragmentation to CO, and 0occurs by two distinct mechanisms and involves three electronic states, the 'B, repulsive
LB,
ground state, a 'A,
weakly bound state and a
state . z
3 - AlkU Metals
-
The formation and dissociation of Kf, R b f , and Cs:
by ruby
laser radiation has been reported.
The photostability of boron-containing organic complexes has
discussed,*
been
properties
of
and
a
p-diketonates
study made of
of
disubstituted
the
luminescent
boron
and
of
bie-~-diketonatoboron. A novel photochemical alkyl migration from B to C in the dialkylboryl acetylacetonate complexes (1) ( R-cyclohexyl, Bu, isopinocampheyl, R'mH; R-cyclohexyl, Bur
R1=Me ) has appeared. Crossover experiments show that the alkyl migration is essentially intramolecular.6
5. Silicon A
report has appeared of the chemiluminescent gas-phaae
ailane-ozone system which incorporates a MO study supporting the conclusion that
the
important emitting
Reaction of atomic oxygen with Me,SiH 140
apecies
is
H,SiO.'
has been inveatigated by
IIl3: Compounds of the Main Group Elements
141
Me
S iM ezCMe3
\
Q’
(4)
OSiMej
142
Photochemistry
the discharge flow technique as well as by stationary photolysis exper iments
.
The pallad ium-catalysed ox idat ion of allyls ilanes
~ a novel with W and molecular oxygen has been d e s ~ r i b e d ,and photosubstitution reaction of dicyanobenzenes by allylic and benzylic silanes which occurs in homogeneous solution is reported to involve photoelectron transfer fromthe ailanes to the excited singlet state of the aromatic compound. lo Photolysis of SiH,-GeH, mixtures
has
been
studied
and
following
photodecomposition of SiH, to SiH, and H,,
primary
SiH, seems to insert
into an Si-H bond of SiH, or a Ge-H bond of GeH, to form Si,H, H,SiGeH,
respectively.
report
A
of
the
or
methylene-methyl
exchange in the reaction of triplet state methylene-d,
with
methylfluorosilanes has appeared12 and dimethyldiazidosilane is reported
to
be
matr ix-isolated
of
Irradiation
a
superior
photochemical
dimethylsilylene
MeN=CMeCH=C(OH)SiMe,,
(R=N,)
and for R=SO,Ph,
to
-
and
Me,CRCH,COSiMe,
precursor
l-methylsilene l3 in
hexane
gives
NCS, the product is the
.
pyrrolidine der ivat ive (2) l4 Evidence has been described for the primary formation of a benzyl-silyl radical pair and also for the mechanism
of
f ree-radical
+
1,2-(carbon
silicon)-acyloxy
migration following irradiation of acyloxymethyl(benzy1)silanes15. (R-9-anthryl) In benzene intramolecular
Photolysis
gives
9,lO:I' ,2'
(3)16 and
anthracene
bis( 9-anthry1)dimethylsilane
has
been
a
of
R,S iMe,
silicon guided
photodimerisation descr ibedl'.
An
in ESR
investigation of the photochemical reaction of aroylsilanes with phosphorus compound8 has appeared.
Two mechanisms have been
suggested, one involving fragmentation of an aroyl-Si bond and a second proceeding through a
siloxycarbene; the
experimental
IIN: Compounds of the Main Group Elements evidence
favours
the
Me,C(Me,Si)zSiCOQ
former
mechanism18.
(Q=l-adamantyl) which
Me,C(Me,Si)Si=C(OSIMe,)Q
Me(Me,SiO)Si=C[SiMe,CMe,]Q
an argon matrix
which
at
10
at
K
gives
the
of
silene
the
silene
spontaneously gives
the
n-Bonded silaacrylate has been isolated following photolysis of
10 K
Brief
pentamethyldisilanyldiazoacetate.
compound
Photolysis
photoisomer ises to
and
head-to-tail dimer (4). in
143
using
irradiation of
nm
240
ethyl
radiation
this
leads
to
(ethoxydimethylsilyl)(trimethylsilyl)ketone. 2o trans-l,2-Bis ( (trimethylsilyl)amino]-1,2-dimeaityldisilene and trans-l,2-di-tert-butyl-l,
2-dimes ityldis ilene
undergo photoisomerisations at 254 and 350 nm to give products having cis-enr ichment. mixtures
of
trens-and
25'C,
At
these revert to equilibrium
cis-disilenes. 21
TCNE
decomposition of the oxas ilacyclopropane (5) (R the carbene (6) and R,SiO, direct photolysis of
photosensitized
-
mesityl) gives
but by contrast DCA sensitized or
(5) gives R,Si
and
It has been
(7).
suggested that the first process involves an exciplex and that the
second
may
Photocleavage of
involve
a
rapid
back-electron
transfer.22
hexa-tert-butylcyclotr isilane catalysed by Pd
salts is reported to give (Me,C),Si:
and (Me,C)zSi=Si(CMe,),.23
Singlet methylene has been inserted into l-methylsilacyclobutane to produce an activated 1,l-dimethylsilacyclobutane (8). decays
to
products
whose
distribution
is
This
virtually
indistinguishable from that obtained by activating (8) with 254
nm photons.24
A
study has
been made
of
the photolysis of
1,1,3-tr imethylsilacycl~butane~~ and of 3-phenyl-Q-[phenyl(trimethylsilyl)methylene]-l,l,2-tris(tri-
Photochemistry
144 Me
Me
Me
Me
Me Me
IIl3: Compounds of the Main Group Elements
145
methyls ilyl)-1-8ilacyclobut-2-ene .26
Photoreaction
peralkylcyclotetraailanes, (R'R'Si),
CH,SiMe,)
in
hydrocarbon
(R' = RL
solvents
gives
-
CH,CHMe,,
the
of CHMeEt,
corresponding
cyclotrisilanes and the disilenes (R1R2Si:SiR'R2),27 and in the presence of CC1,
or CHCl,,
photolysis of
dodecaaxnethylcyclohexasi lane abstraction from
the
r esu Its
leads to
chloroalkanes by
Photolysis of the cyclotrigermane (R,Ge),
suggest ing
C1
dimethylsilanediyl.28 (R = 2,6-Et,CeH,)
gives
.
bis (2,6-diethylphenyl)germium ( I I ) 29
L-uhaml Meaeurements of the quenching rate constant between N,(ASC, u'=O)
and SO (x'f)
at room temperature suggest that the SO t N,(A)
excitation transfer process appears to be an efficient system for utilising the electronic
energy
quenching,
of
the metastable N,(A)
rotational
relaxation,
The and
radiative
u'-0 N ' ) have been measured31 and
lifetime of imidogen (NH)(A%,
vibrationally excited NOCl* has been observed via its strong cont inuous absorpt ion in the 230-280 nm reg ion following partial flash photodissociat ion of gaseous NOCl mixtures.
Format ion of
NOCl* is attributed to a vibrational energy transfer from C1,* which
itself
arises
by
reaction
of
C1
with
N O C L ~ ~
Photodissociation of methyl nitrite at 248 and 350 nm has been examined in a molecular beam and average translational energies compared with the results of a recent investigation of the NO internal state distr ibutions.33 7.
ow-
Reaction of oxygen (O('D)) with NO has been shown to be primarily an energy transfer process.34 and results of the L I P monitoring of ground state NH,
kinetics after pulsed laser 0,
Photochemistry
146
photolysis in the presence of NH, have been recorded.35, 36 Photolysis of a complex formed by codeposition of Me1 and 0, in an argon
matr ix
gives
iodosomethane
which
following
further
photorearrangement leads to a HCHO-HI molecular complex. The IR 37 spectra of this complex and of iodosomethane are reported. Sulphur
atoms
produced by
photolysis of
an Ar
matrix
containing OCS at 20 K have been found to react with PX,(X=P C1) and with the hydrocarbons CH,,
CzH,,
and C,Hz,38
or
and liquid
sulphur has been photochemically oxidised by Pe( I I I) at 150*5°.39 Calculations have been performed on species relevant to the photoionisation of the Van der Waals molecule (H,S),40
and the
photochemical reaction between SF, and F, at 365 nm and within the range 213-214 K is a chain process which gives SP, and SzF,, aa the only products.' *
Sulphur dioxide has been photoox id ised at
365 nm by 0, and proceeds via formation of the excited triplet state of ~0,.42 8. HalOaen8
Quantum yields of luminescence of iod ine chlor ide, xenon chloride, and xenon iodide have been measured in the presence of var ious
buffer
gases43
and
chlor ine
monof luor ide
has
been
synthesised by pulse phOtOly818 of stoichfometric mixtures of
.
gaseous chlor ine and f luor ine 44 SF,-sen8 it ized decompos it Ion of CH,I and cDsI
proceeds faster with the latter compound as a result
of a different distribution of energy levels in the Visible
radiation
photolysing CF,f
(A-450 nm)
is
reported to be
capable of
molecule8 which have been subject to strong IRMP
exc itat ion,46 and the distr ibut ion of photof ragmentat ion products of CH,I
resulting from irradiation at 249 nm i n ~ e s t i g a t e d .ESR ~~
studies of the photolysis of halogenated compounds in glassy and
1113: Compounds of the Main Group Elements
polycrystalline matrices results
of
a
have
study of
the
147
been
descr ibed48’
photooxidation of
and
49
CF,ClBr
the have
appeared.50 Photodissociation of the matrix isolated molecular complex CF,I-0,
at wavelengths greater than 470 nm gives CF,IO
whereas within the range 240-220 nm irradiation leads to CF,OI and
two CF,O-IF
homolytic
molecular complexes.51 The kinetics of
the
Pr, Me,CH,)
by
substitution of
R,SnI
(R-Me, Et,
photochemically generated iodine atoms have been measured52 and gas phase photolysis of a mixture of CC1, and silicon-containing compounds such as Me,SiH
or Me,ClSiH
gives products resulting
from abstraction of a hydrogen atom from the o ~ g a n o s i l a n e . ~ ~ 9. Miscellaneoua Photo induced react ions of benzyltr imethylt in with methylt in chlor ides54 and of tr iphenylgermane and l-naphthylphenylmethylgermane
have
been
.
descr ibed 55
Some
results obtained by flash and modulated photolysia experiments on several related gas phase reactions between fluorooxygenated compounds and CO have appeared,56 and chemiluminescence has been observed during oxidation of XeF, MO(CO)~,W(CO),,
by metal carbonyla such as
Fe(CO), and some of their de~ivatives.~’
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A.
Khan,
and
Iqbal,
R.
Int. J. Enerav Res., 1985, 9, 171. 40.
F.
P.
Fernandez,
J.
J. Chem. Phys., 1986, 41.
V.
Ortiz,
E.
and
A.
Walters,
a,1653.
P. F. Aramendia and H. J. Schumacher, J. Photochew., 1985,
a,491. 42.
L. G. Kop'eva, V. G. Sirota, S. N. Khvorostovskii, and V. P. Chelibanov, Zh. Prikl. Kh im. (Leninarad), 1985,
43.
a,2347.
N. K. Bibinov and I. P. Vinogradov, PDt.. SDeMrosk., 1985,
2,317. 44.
45.
A.
P. Kharitonov and A. P. Suetinov, Zh. Neora
30,
2703.
J.
Rejnek,
P.
Engst,
M.
Jakoubkova,
. Khim.,
and
M.
1985,
Horak,
Collect. Czech. Chem. Commug., 1985, 50, 215. 46.
V. PJ. Bagratshvili, S. I . Ionov, G. V. Mishakov, and V. A, Semchishen, Chem. Phvs. Lett., 1985,
115, 144. 1985, A , 211.
47.
Q. Zhu and S. Huang, Yuli Huaxue XUebaQ
48.
R. Stoesser, B.Pritze, W. Abraham? B. Dreher, D. Krey8ig, J. P r a M
49.
R.
. Chem.,
1985, 327, 310.
Stoesser, B. Pxitze,
W.
Abraham, B. Dreher, and D.
Kreysig, J. P a . Chem., 1985,
m, 317.
50 *
R. T. Tuckerman and E. Whittle? J. Photochm., 1985, X,7.
51.
L.
Andrews,
M.
Hawkins,
and
R.
Withnall,
Inora. Chem., 1985, 24, 4234. 52.
P. H. De Ryck, L. Verdonck, and G. P. Van der Kelen,
III3: Compounds of the Main Group Elements I n t . J. Chem. 53.
J.
A.
w.,1985,
Rice,
J.
J.
151
JJ, 9 5 .
Treacy,
and
H.
W.
Sidebottom,
I n t . J. Chem. K i n e t . , 1984, J.6, 1505. 54.
S. C. Su, A. V. Podoplelov, V- M. Moralev, and R . 2 .
Sagdeev,
Ezv. Akad. Nauk . SSSR. 55.
Hayaahi,
H.
1984,
and
R.
Mochida,
K.
6 , 90.
P. F. Aramendia and E . San Roman, An. Aaoc 1985,
57 *
Sakaguchi,
Y.
Peza Kaaaku Ken-, 56.
S e x . Kh im., 1984, 2406.
. Ouim.
Arae n t . ,
u , 189.
G. Bulgakov,
Tolstikov,
S.
and V .
P.
Kuleshov,
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P.
Kazakov,
Izv.
Sex. K h b . , 1985, 1215.
N. Yakovlev, G . Akad.
Nauk
A.
SSSE ,
Part 111 ORGANIC ASPECTS OF PHOTOCHEMISTRY
1
Photolysis of Carbonyl Compounds BY W. M. HORSPOOL
The interest in the photochemical behaviour of simple carbonyl compounds continues t o wane, a trend which has been detectable for a number of years. Several reviews which are of general interest to photochemists have been published during the period covered by this survey. Thus Scharf and his coworkers have published an account dealing with the energy storage of light and the synthetic uses of light in organic systems.' Coyle2 has reviewed some aspects of organic photochemistry and Horspool has reported on matrix isolation techniques and electron transfer reactions applied to organic photochemi~try.~Ramamurthy4 has published a review of the photochemistry of thiocarbonyl compounds and Xu and Wu have reported on some aspects of the Zimmerman-Mobius-Huckel approach to the interpretation of concerted react ions.5
1
Norrish Type I Reactions
There has been considerable interest on the influence of zeolites on several aspects of the photochemical behaviour of ketones. Turro et al. have carried out further work on the influence of zeolites on the photochemical activity of dibenzyl ketones. In this study pentasil zeolites were used.6 In other work Turro has reported the use of triplet-triplet energy transfer as a probe of surface diffusion rates.' The luminescent properties of some aromatic ketones in the presence of the hydrophobic zeolite Silicalite have been examined' and a spectral study of transients formed by the irradiation of aryl ketones in zeolites has been reported.' An examination" of the behaviour in the solid state of guest molecules such as aliphatic ketones ( acetone and ethyl methyl ketone) and aromatic ketones (acetophenone and mC1-acetophenone) in deoxycholic and apocholic acids has identified stereospecific addition of the guest molecules to the host by a hydrogen abstraction radical combination path." A flash photolytic study of fluorenone has shown that the triplet state reacts with electron rich alkenes in an electron transfer process.12 Norrish type I cleavage of benzyl ketones has been studied in detail using the CDNIP te~hnique.'~Excited state cleavage of the RT* state of the enone (1) in
155
156
Photochemistry
methanol/methyl hbutyl ether results in the formation of the radical pair (2) which recombines affording the ketene (3). This is trapped by methanol as the ester (4). 1,1,2,2-Tetraphenylethane is also formed as a minor product by combination of diphenylmethyl radicals. Other minor products such as methyl diphenylacrylate and the indanone (5) were also identified. The presence of the ketene (3) was demonstrated in the i.r. following photolysis of (1) in benzene.14 The substituted cyclopentanones (6) undergo normal Norrish Type I fission to yield the more stable biradical where fission has occurred between the carbonyl carbon and the substituted ring carbon. Disproportionation then follows to afford the E and 2 alkenes (7).15 Norrish type I reactivity is also observed on irradiation of the ketone (8a). In this example rebonding within the biradical brings about epimerization at C-13 to yield the product (Sb)." The steroidal ketone (9) is photochemically reactive and undergoes Norrish Type I fission in alcohol solution to afford the products (10) and (11). These products are the result of fission of the two a-bonds of the carbonyl group. This results in the formation of the appropriate ketenes which are subsequently trapped by solvent as the esters." Fetizon et aL" reported that irradiation of a mixture of the ketones (12) and (13) gave the enone (14) by a Norrish type I1 path. A reinvestigation of the photoreactions of the individual ketones has shown that the enone (14) is not formed. In this new study the transketone (12) yields the aldehyde (15) by Norrish type I fission and the cisketone (13) undergoes slow reduction yielding (16). Ring size appears to have Borne influence on reactivity as seen in the ring opening of the cicketone(l7) by the Norrish Type I route giving the aldehyde (18).19 Norrish Type I photoreactivity of the ketone (19)yields the aldehyde (20) which was used as an intermediate in the synthesis of (-)seco longifolenediol.20 The irradiation of the hydroxy ketones (21) in benzene yields the lactones (22) and (23) in a ratio of 96:4. The formation of these products is the result of Norrish type I fission followed by the formation of a ketene which is trapped intramolecularly. The loss of stereochemistry of the site next to the carbonyl group means that the alkyl radical centre does not retain its configuration during the hydrogen abstraction process. This is different behaviour to that exhibited by the steroidal analogues.21 An example in the steroidal system has been reported by Scharf and his coworkers who have observed that the irradiation of the steroid (24) results in the formation of the lactone (25) again by intramolecular trapping of the ketene (26). The presence of the ketene was demonstrated by trapping in methanol to yield the ester (27).22 In related work Stiver and Yates have studied the photochemical behaviour of the steroidal ketone (28). This ketone (28) undergoes Norrish type I fission to afford the biradical (29) which disproportionates to afford the ketoaldehdye (30). This compound is also photoreactive and is converted by Norrish type I1 reactivity into the fragmentation product (31). The path followed in this reaction, and which differentiates it from the previous
157
ZIIIl: Photofysis of Carbonyl Compounds
'h
Ph
Ph
Ph
) I
Ph
Ph
(1)
eM( , .Ph +}
Ph
Ph
Ph
Ph //C/'O
Ph
(3)
@
&
R2
Ph
(41
0 (5)
(6)
R' = H, Me,Et, Pr, MezCHCH2
R2= CN, COzMe
( 7 ) R' =H,Me, Et, Pr,Me,CHCH,
R2 =CN, C%Me
( 8 ) a; R = p - M e b; R = a - M e
LfPCSCH
0
H
Photochemistry
158
Q Qo m H
Ho 0
0
H
0
IIIIl: Photolysis of Carbonyl Compounds
159
0
Q-j?
‘
(30)
0
H
OHC) (31 1
Ph Ph
Ph Ph Ph
Ph
Ph
l l e h p h
(33)
(34)
(35) a ; n = 2 b;n = 1
160
Photochemistry
examples, is dictated by conformational factors.23 Photo-decarbonylation of the cyclohexanone (32a) is efficient with a quantum yield of 0.9. The reaction yields the two products (33) and (34) in a ratio of 1:2. The cyclopentanone (32b) also decarbonylates photochemically but is less efficient with a quantum yield of 0.5. A laser flash study has been carried out on these systems and has identified the biradicals produced by the Norrish type I process. The lifetime of the biradicals (35a) and (35b) are 0 . 9 ~ sand 0 . 5 ~ sr e ~ p e c t i v e l y . ~In~ a related study the photodecarbonylation of cis and trms2,6-diphenylcyclo-hexanone has been shown to yield a mixture of cis and tran41,2-diphenyl-cyclopentane and cis and trans1,5-diphenyl-pent-l-ene. The product yields did not depend upon the configuration of the starting ketone. The reaction is a standard Norrish type I process leading to was less stereospecific than decarbony lation. Interestingly recombination disprop~rtionation.~~ Johnston and Scaiano have studied the photochemical behaviour of the biradicals (35a) formed by the decarbonylation of the ketone (32a). The laser excitation of the biradical (35a) affords the new product. (36). This is formed by the path outlined in Scheme 1 involving cyclization and hydrogen migration.26 The irradiation of the cyclanone (37) in a variety of solvents leads to products, enals, of Norrish type I fission and disproportionation within the biradical. No evidence for the formation of cyclophanes (38) was obtained. In contrast, the larger ring cyclophanes (39) gave good to excellent yields of the cyclophane products with little of the more conventional products being detected. The formation of the cyclophane products is presumed to arise by pa-coupling of the biradical followed by rearomatization by hydrogen migration. The study was extended to examine the behaviour of the cyclanones (39) encapsulated in a zeolite.27 The ketocyclopropane (40) photochemically rearranges into the cyclo-octadiene (41) which itself is photoconverted into the isomeric compound (42). The formation of the cyclo-octadiene involves the ring opening of the cyclohexenone and the cyclopropane moieties t o afford the ketene (43),28 Another mode of reaction for small ring cyclic ketones involves Norrish Type I fission and rebonding to afford the ring expanded carbene. Pirrung has reported the use of this photo-ring expansion of cyclo butanones via the oxacarbene path in the synthesis of bicyclic acetals. The results of this are shown in Scheme 2.29 The optically active ketone (44a) follows the same photochemical path giving a carbene which is trapped intramolecularly as the ketal (45). An additional reaction mode, that of retro (2+2) addition, also occurs yielding the intermediate ketene (46) again trapped intramolecularly as the optically active lactone (47). These products are formed in a ratio of about 1:l. The irradiation of the isomeric ketone (44b) undergoes primarily retro (2+2) fragmentation to afford the lactone (48). The ketone (49) is also photoreactive giving
161
IIIi1: Photolysis of Carbonyl Compounds
(36) Scheme 1
(37)
(38)
H (40)
(39)n = 5,6,7 or 10
(41)
Photochemistry
162
Me
M
aC 0 2 M e (42 1
(43)
R'
MeO ~
o
'
R'
R2
H d; R ' = H, n = 2 , R 2 = H b; R 1 = Me, n = 1 , R2 = H C ; R' = H, R 2 = CN, /I = 1
Me0
+
Htf
Scheme 2
A
CO 2M e
Me
Me
Me H
Ri
@Me
R2
(45 1
( 4 4 ) a; R' = OH, R 2 = H b; R' = H, R 2 = OH
0
kMe Me
bH
Me
(46)
(47 1
~
IIZII: Photolysis of Carbonyl Compounds
163
H
HO’’ (50)
(49)
Me-‘
Me
151)
(53) R’ = H,Me E t ; R 2 = H
0
( 5 7 ) n = 1, 2,3
0
%
OR*
Ph
Ot
4
\
OH
Photochemistry
164
fiAr 0
(61) a; R' =OH, R 2 = Ar b; R' = A r , R2 = O H
( 6 0 ) Ar = p - MeOC6H5
,KN U R:f
(62) a;
R' = R 2 = H
b ; R' = R 2 = M e C ; R ' = R2 = P h d ; R' = MeO, R 2 = H e;
R' =EtO,
R2=
H
(63) a; 48% b ; 59"/0 c ; 11 V
O
d ; l6V0 e ; 26'10
0 ( 6 4 ) a; 0% b; c; d; e;
Oe/* 51Ye 31 *I* 56%
0 ( 6 5 ) C; 66'10 d ; 57% e ; 65%
%
Ph
(66) a; n = 1
b ; n= 2
(67)
I I I / l : Photolysis of Carbonyl Compounds
165
the ketal (50) and the lactone (51).30 The crystal structure of phototetrahydrozexbrevin (52) has been determined.31
2 Norrish Type 11 Reactions A study of the photochemical behaviour of a variety of ketones (e.g. 53) in Dianin’s compound (54) has been carried out. The conclusion is reached that the environment of the ketone included in the clathrate is non polar in character. The ratio of acetophenone to cyclobutanols obtained from the irradiations is not any different from those obtained from irradiation in Fragmentation is also observed on irradiation (at 254 nm) of the bile acid derivative (55). This brings about side chain degradation by a Norrish type I1 process to yield (56).33 A study of the photochemical Norrish type I1 process in the ketones (57) has shown that hydrogen abstraction follows the reactivity pattern of cycloheptane > cyclopentane = cyclohexane > cyclobutane. The hydrogen abstraction rate constants in solution do .not correlate with abstraction geometries determined by X-ray methods. The authors suggest that the hydrogen abstraction occurs from non-minimum energy conformations of the reactant.34 y-Hydrogen abstraction dominates the photochemistry of the ketone (58) affording the cyclobutanol (59) as the principal product.35 A comparison of the photochemical behaviour of the ketone (60) in benzene or acetonitrile with its behaviour in the solid In benzene solution the irradiation affords the two state has been carried out. cyclobutanols (61a) and (6lb) in a ratio of 2.6:l. The formation of the more hindered cyclobutanol (61b) predominates when the reaction is carried out in the solid state. The ratio of products in this instance is 051. The authors suggest that in solution conformational isomerism in the biradical is faster than bond closure while in the solid state the biradical is restricted to the conformation which gives rise to the more hindered product .36 The synthesis of p-lactams continues to be of interest. Sakamoto et a1 have studied the reaction of the thiazines (62) towards this end. On irradiation of (62) in benzene at temperatures > 4OoC elimination of the side chain affords (63) while cyclization yields (64) in reactions dependent on the substitutions pattern. At lower temperatures a different process occurs affording an unstable lactam which could be isolated as the
derivative (65).37 The Norrish Type I1 behaviour of the ketoaldehyde (%a) has been described by Ounsworth and Scheffer. The irradiation of the compound in benzene or moist acetonitrile through a Pyrex filter results in the formation of acetophenone and the ketobutanol (67). Under optimum conditions the yield of the cyclic product is 70%. The quantum yield for the formation of this product is 0.3 in benzene and 0.4 in
Photochemistry
166
A' (72) R' = M e or H
R3
R2
0
0 PhuNARf
+
+
Ph'.S.
(R1
It;' I
CH,R~
a; 29 ' l ~
R3
(73) a; R' = R 2 = R3 = H b ; R' = Me, c ; R1 = Ph, d ; R1 = Ph, e ; R' = Ph,
R2 = R3 = H
R2 = R3 =Me R 2 = Me, R 3 = H
b ; 27 ' l o
a ; 57 ' l a
c ; 86'10 d ; 71 '1. e ; 20 ' l o
b ; 66 ' l a c ; 11 'I'
R2 = R3 = H
d ; 28 '10
e ; 72 ' l o Scheme 3
RZCHC02R3
I
R2
kNk2,.' I H o d : '
Ph
R1 H
R
Ph"
Ph R = tosyl or benzyl ; R' = H, Me, Ph ; R 2 = H, Me, Ph;
(75)
(76)
R3 = Me, Et
(77)
Mil: Photolysis of Carbonyl Compounds
167
(78) R' = E t , R 2 = M e
R' = R2 = Me R' = Me, R2 =Et
R3 R 2 J 5 y M e
(81)
R' = R 2 = H , R3= H or Me (82) R' = MeO, R 2 = H, R 3 = Me R' = MeO, R2 =Ph, R 3 = PhCH, Me
I
Me
Me
Scheme 4 Me
Me
0
Me
0
168
Photochemistry
acetonitrile. The keto aldehyde (66b) also shows the same behaviour and on excitation undergoes abstraction of the aldehydo hydrogen to afford (68) as the product of cyclization!' The irradiation of ortho-kbutylbenzophenone affords the indanol (69) by way of &hydrogen abstraction from one of the kbutyl methyl groups. The quantum yield for the process varies from 0.04 in hexane to unity in methanol. Cyclization is also reported for (70) which yields (71) with a quantum yield of 0.35 in benzene. Details of a laser flash study of the transients involved were also reported.3g This recent work supplements the account originally reported in note f0rm.l' Hasegawa et al. have studied the photochemical behaviour of a series of alkyl oxamides (72, 73). The compounds are reactive from the triplet state and undergo hydrogen abstraction of the Norrish Type I1 type. y-Hydrogen abstraction is the only reaction of the oxamides (72) yielding the fragmentation product (74). Changes in substitution brings about competition between y- and &abstraction as shown in Scheme 3 resulting in Henning and his coworkers have fragmentation or the formation of pyrr~lidinones.~~ continued their study of the photo behaviour of amino ketones (75). In these examples irradiation brings about the formation of the cyclopropanols (76) and the In benzene and cyclohexane the hydroxyprolies (77) in non-polar solvents. hydroxyprolines (77) are f a v 0 ~ r e d . l ~ Photeenoliiation Reactions.- Pete et af. have reported that the photodeconjugation of the esters (78) in the presence of (-)-ephedrine leads to a product (79) where there is a small enantiomeric exce~s.4~ Photoenolization of the acetophenone derivative (80) has been studied. The structure of the product formed, after methylation of the react ion mixture, was identified as 4-benzy1-6-hydroxy-2-methyl-5-phenyla~etophenone~~ Bolivar et a/. have made use of the Diels-Alder trapping of the dienes (81), produced by the photo enolization of the ketones (82), in the synthesis of naphthalene derivative^.^^ The predominant product formed from the irradiation of the ketone (83) in methanol is the indanone (84). This ketone is accompanied by the three products shown in Scheme 4. The formation of the indanone and the dechlorinated product arise from a photoenolization path. The other two products are thought to be the result of expulsion of chlorine either as an atom or as chloride. The products of the latter type are suppressed with chloroketone (85). In this instance the only products formed are those resulting from the hydrogen abstraction path.lG The ability of polyketones, e.g. (86) to undergo cyclobutene formation by Norrish type I1 hydrogen abstraction/recombinanationhas been studied.17
3 Oxetan Formation The mixture of products (87) and (88) is formed on irradiation of furan and benzophenone in benzene at OOC. The structures of the products were established by X-ray and by chemical and spectral studies.18 Biacetyl adds photochemically to the
169
IIIII: Photolysis of Carbonyi Compounds
Bu"0
0
68""
(91)
(90)
BffO
X0+ 0
(94)
(93)
CO 2R
Ph
b; R
(97)
( 96)
(95) a; R = H
R = (-) 0- phenyI mnthyl
= Me
0 Q C\
( 98)
>:
C1 CL
0
y:
CI
CI
COzR
(99)
(100)
(101)
Photochemistry
170
Ph
t 102)
(103)
(106) Scheme 5
a;xPh 0
0
ph&
Ph Ph
O K N
0
(110)
.
N
'R2
.
R' = Ph, Et, Pr',Bu' ; R2= H R' = R2 = Ph
(111)
0
(112)
(113)
OPh
IIIIl: Photolysis of Carbonyl Compounds vinyl ether (89) to yield the oxetan (90) as the major product.
171 The cycloaddition
occurs with reversal of the regioselectivity normally expected for oxetan formation. Minor products of the addition were identified as the vinyl ether (91) and the ally1 ethers (92), products which presumably arise by 1,Shydrogen transfer within the alternative biradical (93). A 3-alkoxyoxetan (94) is formed using the vinyl ether (95a) while a 2-isomer (96) arises in the photoaddition of biacetyl to the vinyl ether (95b). The authors suggest that an exciplex between the vinyl ether moiety and the triplet biacetyl directs photoaddition to that site!' Photochemical addition of fiRJR,4S)(-)-&phenylmethyl phenyi glyoxalate (97) to the dioxole (98) affords the oxetan (99). This has been used as a building block in the synthesis of an L-apio f~ranoside.~'
4 Rearrangement and Fragmentation Reactions Abdul et a/. have reported the remarkable isomerization of the ketone (100) into the compound (101).51 Direct and sensitized irradiation of the cyclopropylketone (102) leads to the formation of the cisisomer (103) and the two rearrangement products (104) and (105). The transcis isomerization is a normal event by ring opening of the cyclopropane ring followed by rebonding. The formation of the rearrangement products is thought to arise via the biradical (106) as illustrated in Scheme 5.52 The benzoxazinone (107) decarbonylates to yield (108) on i r r a d i a t i ~ n . ~ ~ The photochemical Photodecarboxylation of (109) provides a route to e~aftoljde.~~ decarboxylation of the lactones (110) provides a convenient method for the synthesis of l-azabicyclobutanes (111). The reaction is, however, restricted to those compounds with two aryl groups on C-2.55 The norbornadienone (112) has been produced in a matrix by the irradiation of the azo compound (113). These authors point out that the outcome of the irradiation is dependent to a large extent on the material of which the matrix is composed.56
Acknowledgements.- I would like to express my sincere thanks to Dr. Stephen Bell and to Mr. Mike Whitehead of the Department of Chemistry and the Computing Centre respectively of the University of Dundee for invaluable assistance with the computer compiling programs used in these reviews.
Photochemistry
172
5 References 1. H. D. Scharf, H. Leismann, and H. Koch, Photochem. Convex, (symp. 1, 1983, 133 (Chem. Abstr., 1985, 102, 203351). 2. J . D. Coyle, Annu. Rep Pmg Chem., Sect. B, 1984, 80 (B),141. 3. W. M. Horspool, Annu. Rep. Pro& Chem., Sect. C, 1985, 80 ( C ) , 87. 4. V. Ramamurthy, Org. Photochem., 1985, 7, 231. 5. J. X u and G. Wu, Youj Huaxue, 1985, 113 (Chem. Abstf., 1985, 103, 159800). 6. N. J. Turro, X. Lei, C. Cheng, D. R. Corbin, and L. Abrams, J. Am. Chem. Soc.,1985, 107, 5824. 7. N. J. Turro, M. B. Zimmt, I. R. Gould, and W. Mahler, J. Am. Chem. Soc.,1985, 107, 5826. 8. H. L. Casal and J. C. Scaiano, Can. J. Chem., 1985, 63, 1308. 9. F. Wilkinson, C. J. Willsher, H. L. Casal, L. J. Johnston, and J. C. Scaiano, Can. J. Chem., 1986, 64, 539. 10. R. Popovitz-Biro, C. P. Tang, H. C. Chang, M. Lahav, and L. Leiserowitz, J. Am. Chem. Soc.,1985, 107, 4043. 11. C. P. Tang, H. C. Chang, R. Popovitz-Biro, F. Frolow, M. Lahav, L. Leiserowitz, and R. K. McMullan, J. Am. Chem. Soc.,1985, 107, 4058. 12. J. Gersdorf and J. Mattay, J. Photochem., 1985, 28, 405 (Chem. Abstr., 1985, 103, 177904). 13. M. Laeufer and H. Dreeskamp, J. Mag. Reson., 1984, 60,357 (Chem. Abstr., 1985, 103, 36967). 14. W. Adam, A. Berkessel, E.-M. Peters, K. Peteres, and H. G. von Schnering, J. Org. Chem., 1985, 50, 2811. 15. J. Totrajada, B. Van Hemelryck, and J. P. Morizur, Bull. Soc. Chim. Fr., 1985, 243.
IIIIl: Photolysis of Carbonyl Compounds 16. G. Neef, G. Sauer, R. Wiechert, S. Beier, W. Elger,
D. Henderson, and R. Rohde, Eur. Pat. A p - . EP 129,499 (Chem. Abs.fr., 1985, 103, 6617). 17. J. R. Williams, P. L. Mattei, A. Abdel-Magid, and J. F. Blount, J. Org. Chem. 1986, 51, 769. 18. D. D. H. Manh, J. Ecoto, M. Fetizon, H. Colin, and J.-C. Diez-Masa, J. Chem. Sm., Chem. Commun., 1981, 953. 19. R. J. Batten and H. A. J. Carless, J. Chem. Sac., Chem. Commun., 1985, 1146. 20. N. Satyanarayana and U. R. Nayak, Swth. Commun., 1985, 15, 331 (Chem. Abstr., 1985, 103, 160713). 21. S. Stiver and P. Yates, Tetrahedron Lett., 1985, 26, 5501.
H.-D. Scharf, J. Photochem., 1985, 28, 443. 23. S. Stiver and P. Yates, Tetrahedron Lett., 1986, 27, 2215. 24. D. H. R. Barton, B. Charpiot, K. U. Ingold, L. J. Johnston, W. B. Motherwell, J. C. Scaiano, and S. Stanforth, J. Am. Chem. Soc.,1985, 107, 3607. 25. V. F. Tarasov, B. B. Klimenko, D.' B. Askerov, and A. L. Buchachenko, Izv, Akad. Nauk SSSR, Ser. Khim., 1985, 361 (Chem. Abstr., 1985, 103, 53559). 26. L. J. Johnston and J. C. Scaiano, J. Am. Chem. Soc.,1986, 108, 2349. 27. X. Lei, C. E. Doubleday, jun., M. B. Zimmt, and N. J. Turro, J. Am. Chem. Sac., 1986, 108, 2444. 28. A. G. Schultz, K. K. Eng, and R. K. Kullnig, Tetrahedron Lett., 1986, 27, 2331. 29. M. Pirrung, Angew. Chem. ht. Ed. End.,1985, 24, 1043. 30. H. G. Davies, S. M. Roberts, B. J. Wakefield, and J. A. Winders, J . Chem. Soc., Chem. Commun., 1985, 1166. 31. M. Soriano-Garcia, R. A. Toscano, E. Dim, and L. R. Hahn, Rev. Latinoam. Quim., 1985, 16, 112 (Chem. Abstr,, 1986, 104, 149187).
22. G. Hilgers, G. Beyer, and
173
174
Photochemistry
32. P. C. Goswami, P. de Mayo, N. Ramnath, G. Bernard,
N. Omkaram, J. R. Scheffer, and Y.-F. Wong, Can. J. Chem., 1985, 63, 2719. 33. G. Hilgers and H.-D. Scharf, Liebig Ann. Chem., 1985, 1498. 34. A. Ariel, S. Evas, N. Omkaram, J. R. Scheffer, and
J. Trotter, J. Chem. Soc.,Chem. Commun., 1986, 375. 35. R. Phaff, N. Bischofberger, P. Mathies, W. Petter,
B. Frei, and 0.Jeger, Helve Chim. Acta, 1985, 68, 1204. 36. S. Evans, N. Omkaram, J. R. Scheffer, and
J. Trotter, Tetrahedron Lett., 1985, 26, 5903. 37, M. Sakamoto, H. Aoyama, and Y. Omote, Tetrahedron Lett., 1986, 27, 1335. 38. J. Ounsworth and J. R. Scheffer, J. Chem. Soc., Chem. Commun., 1986, 232. 39. P. J. Wagner, B. P. Giri, J. C. Scaiano. D. L. Ward, E. Gabe, and F. L. Lee, J. Am. Chem. Soc., 1985, 107, 5483. 40. P. J. Wagner, M. A. Meador, B. P. Giri, and
J. C. Scaiano, J. Am. Chem. Soc., 1985, 107, 1087. 41. T. Hasegawa, Y. Arata, K. Mizuno, K. Masuda, and N. Yoshihara, J. Chem. Soc., Perkin Trans. 4 1986, 541.
42. H. Haber, H. Buchholz, R. Sukale, and
H. G. Henning, J. Prakt. Chem., 1985, 327, 51 (Chem. Abstr., 1986, 104, 130228). 43. R. Mortezaei, F. Henin, J. Muzart, and J.-P. Pete, Tetrahedron Lett., 1985, 26, 6079. 44. R. A. Bolivar and R. Machado, Acta Cient. Venez., 1984, 35, 208 (Chem. Abstr., 1985, 103, 53632). 45. R. A. Bolivar, R. Machado, and C. Rivas, Acta Stzd. Am. Quim., 1984, 4, 29 (Chem. Abstr., 1985, 103, 160190). 46. W. R. Bergmark, C. Barnes, J. Clark, S. Paparian,
and S. Marynovski, J. Org: Chem., 1985, 50, 5612. 47. Y. Ito, N. Kawatsuki, B. P. Giri, M. Yoshida, and T. Matsuura, J . Org. Chem., 1985, 50, 2893.
IIIII: Photolysis of Carbonyl Compounds
175
T. Oshima, S. Mihashi, and Y. Iitaka, Yakugaku Zasshi 1985, 105, 19 (Chem. Abstr., 1985,
48. H. Itokawa,
103, 71213). 49. 50. 51. 52.
53.
H. A. J. Carless and G . K . Fekarurhobo, Tetrahedron Lett., 1985, 26, 4407. A. Nehrings, H.-D. Scharf, and J. Runsink, Angvw. Chem. h t . Ed. Engl., 1986, 24, 877. M. H. Abdul, L. Huelskaemper, and P. Weyerstahl, Chem. Ber., 1985, 110, 840. H. E. Zimmerman and R. W. Binkley, Tetrahedron Lett., 1985, 26, 5859. E. Tauer and K.-H. Grellmann, Chem. Ber., 1986, 119, 215.
54. G. B. V. Subramanian, A. Mehrotra, and K. Mehrotra,
Chem. hd. Fondon), 1985, 379 (Chem. Abstr., 1985, 103, 160267). 55. R. Bartnik, 2. Cebulska, A. Laurent, and
B.
Orlowska, J. Chem. Research (S), 1986, 5. 56. B. F. LeBlanc and R. S. Sheridan, J. Am. Chem.
Soc.,1985, 107, 4554.
3
L
Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones BY W. M. HORSPOOL
1 Cycloaddition Reactions Intramolecular Additions.- A comparison of the influence of a trimethylsilyl group with alkyl groups on photo-cyclization reactions has been carried out using two sets of compounds (1) and (2). The irradiation of the enones (1) gave the bicyclic compounds (3), a l,!kyclization, shown in Scheme 1 accompanied by the esters (4). The esters are formed by 1,6-closure to the biradical ( 5 ) which then ring opens to a ketene and is trapped by solvent. In contrast, irradiation of the enone (2a) gave only the 1,5-cyclization products (6). Enone (2b) failed to yield products of this type but was photoreactive yielding the cyclopropyl ketone (7). The influence of the trimethylsilyl group on the reaction is not understood.'
Additions to Cyclopentenones. Considerable use is being made of intramolecular cycloadditions to cyclopentene systems to provide key intermediates for the synthesis of natural products or highly strained compounds. Several examples of this have been published this year. Thus the enone (8) undergoes intramolecular (2+2)-addition to afford the tricyclic ketone (9) which was used as the starting material in a synthesis of (4.4.5.51-fenestrane (10).' Intramolecular cycloaddition of the allene unit t o the cyclopentenone in the compounds (11) affords two products (12) and (13) the result of straight (2+2)-additi0n.~ The enone (14) undergoes efficient intramolecular cycloaddition using a uranium glass filter to afford the products shown in Scheme 2. At shorter wavelengths several unidentified products are formed. The cyclobutane ring in the cycloadducts (Scheme 2) can be ring opened to afford the spiro compounds (15) which can be used in the synthesis of pentalene derivatives! Photo-cycloaddition in the enone (16) yields the adduct (17) which was used as a key step in a new synthesis of stoe~hospermol.~ Adduct (18) is formed in high yield on irradiation of enone (19) in a variety of solvents.'
A detailed report of the reactions of bishomocubane and homocubane systems has been reported. The key step in the synthetic sequence is the photochemical ring closure of the enone (20) to yield the cage compound (21).7 The major compound from 176
11112 Enone Cycloadditions and Rearrangements
177 SiMe,
0 (1)
a; R b;
0 I
H
R =Me
( 2 ) a; R = H b; R = Me
( 4 ) a; 6% b; 87'10 Scheme 1 H
(3) a; 94% b ; 13 '/e
Photochemistry
178
H
Me
(14) Scheme 2
#
Me (17)
(16)
(1 5 )
(18)
4 Br 0
(1 9)
(20)
ZZZl2 Enone Cycloadditions and Rearrangements
179
the irradiation of the enone (22) is the (2+2)-cycloaddition product (23). Accompanying this is a minor product which has been identified as the cage structure (24). The authors discuss the formation of this compound that it is formed via a 3,5-allyl shift. They suggest that the intra molecular arene-alkene complex which gives a biradical yields an intermediate (26) which subsequently undergoes a yield the final product (24).8
and reject the possibility product (24) arises via an (25). Bonding within this photochemical 1,3-shift to
Additions to Cyclohexenones. Intramolecular additions in cyclohexene systems also provide access to natural products. Thus the photocyclization of enone (27) affords the adduct (28) which is suggested as a route to the nortaxane or taxane ~ k e l e t o n . ~ Intramolecular reaction of the enone (29) affords two products (30,70%) and (31, 14%). The identity of the major products was determined by X-ray crystallography and is the result of hemiacetalisation of the original (2+2)-adduct (32). The minor product (31) is formed from the major by a retmAldol reaction." Cycloaddition occurs on irradiation of the alkenyltropone (33) in acidic methanol not in aprotic solvents. The products from the addition are the (6+2)- (34) and and (8+2)-adducts (35). The reaction is complicated in terms of the re+ sterwchemical outcome as shown in Scheme 3. To account for the products authors propose that two conformers (36, 37) of the tropylium species are involved."
but the the the
Intermolecular Additions.- Open Chain Systems. The involvement of a singlet exciplex is proposed in the selective photoaddition of 2,3-dimethylbut-2-ene to the transnitrile (38) yielding the (2+2)-adducts (39).12 The photodimerization of (40) affords the cyclobutane derivative (41).13 The de Mayo addition reaction continues to be of considerable value for the formation of precursors for further synthesis. One example of this is the formation of the photoadducts (42, 43), prepared by photoaddition of isoprene to the enol of the dione ester (44), and have been used in a general synthesis of cyclopentenes. The photoadducts (42, 43) are produced in the standard fashion by the formation of a labile cyclobutane which subsequently ring open^.^^^^^ Takeshita et al. have reported the photochemical addition of myrcene (44A)to the enolate ester (45). The normal mode of addition is accompanied by a minor product which has been identified as (46). This product is formed via a proton transfer step within the initial photoadduct (46A). The yield of the adduct (42) is 28% when the reaction is carried out at -35OC but is only formed in 20 % yield at 0 to 50C.16 Photoaddition of the ynone (47) to 1,l-diethoxyethene gave the oxetan (48) (so%), by a conventional (2+2)-cycloaddition route, as well as the furan derivative (49) (18%). The formation of this latter product arises by way of the carbene (50), itself a product of (3+2)-addition of the ynone to the alkene. Intramolecular trapping of the carbene
180
Photochemistry
Me
Br
&
(24)
( 2 5)
(26)
fi OH
(29)
(30)
181
IIIi2 Enone Cycloadditions and Rearrangements
+
+
f
Scheme 3
Ar
/J?*
% Ar
A r = m - Br, m - C I , p - C I , m - O M e , p - O M e , m - N O z and p - N O z C 6 H ,
(38)
(39)
COPh COPh
\
RO, C
rco X Ar
Ar
Photochemistry
182
COzMe
(44A)
(46)
(45)
OEt
Ph
OEt OEt
(49)
(50)
(51) R'
= OEt, R Z = H
R ' = H, R Z = OEt
11112 Enone Cycloadditions and Rearrangements
183
BU'
But
(52)
(53)
H
HO
0
Me
-
(+I (63)
'Me
Photochemistry
184
affords the isolated product. The ynone also adds to ethoxyethene yielding the isomeric oxetans (51) and the corresponding (3+2)-adduct (52). In both these examples there is a preference for the (2+2)-cycloaddition mode. However, when but-2-yne is used as the olefin component in the cycloaddition, the (3+2)-adduct (53) was obtained in 60% yield.17
+
Cyclopentenones. Phot- (2 2) -cycloaddit ion of 1,l-die t hoxyet hene to cyclopentenone yields the adduct (54). Subsequent involved chemical transformations were used to complete a total synthesis of racemic Ag(12)-capneffene.’8 The cyclopentenone (55) photochemically ( a laser source) adds hex-l-yne to yield the cycloadduct (56) in good yield. By using a Pyrex-filtered Hg arc lamp the same starting materials yield the tropovalene (57) (25%) and the bicyclic product (56) (38%). Independent irradiation of the tropovalene (57) yields the tropone (58) (83%). The cycloadduct (56) can also be converted into the tropone (58) by A120, catalyzed elimination of acetic acid followed by irradiation of the enone (59).” Meyers and Fleming have reported a synthesis of (-)-Grandisof (60) commencing with photochemical (2+2)-addition of ethene to the chiral enone (61). This yields the adduct (62) in 93% yield contaminated with 7 4 % of the endoisomer. Ring opening of the adduct (62) affords the two keto esters (63) and (64) in 45 and 55% respectively. The former is taken on to complete the synthesis of GrandisoL20 A study of the influence of silica gel surfaces on the photochemical addition of allene to a series of cyclic enones has been carried out. Using this technique cycloaddition occurs to the more hindered face of the enone.21 A typical example of allene addition, where addition takes place to the less hindered face, is reported by Piers et af. in the photoaddition to the enone (65) which affords the four isomeric products (66) in ratios of 40:51:6:3. The two major products (66a) and (66b) were used as starting materials for total syntheses of naturally occurring compounds of the stemodane type.22 (2+2)-Cycloaddition of 1,2-dichloroethene to the enone (67) affords, after elimination of chlorine, the adduct (68).23 Cyclohexenones. A short review has been published dealing with the cycloaddition reactions leading to the formation of (+)-fongrblene and Corey’s lact0ne.2~ Phot-addition of ethene to 3-methylcyclohex-2-en-l-onegives the (2+2)-adduct (69).25 Lange and Lee have described a route to Germacranolides starting from the photoaddition of cyclobutene carboxylic acid to the enone (70) to give the adduct (71) in an overall yield of 58%. This was elaborated to afford the Germacranofides.2G Photocycloaddition of the cyclobutene (72) to cyclohex-Zenones provides adducts (73) which are useful in the synthesis of decalins. The functionalisation of these decalins makes them useful precursors for the synthesis of some natural products.27
185
HI12 Enone Cycloadditions and Rearrangements
I
Me
0
(69)
(68) Me
Me
*Me COOH 0 (70)
COOMe
(71)
OSiMe3 OSiMe,
R (73)
Photochemistry
186 Asymmetric
induction
in synthesis continues to receive attention as in the
photoaddition of cyclopentene to the optically active enone esters (74). The (2+2)-cycloadducts obtained are claimed to have substantial enantiomeric excesses. The adducts are diastereoisomeric and two types are obtained, the cisanticis (75) and the c i s s p c i s (76). Analysis of the results shows that the yield of the cisaaticis isomers diminishes as the size of the ester group increases due to steric interactions.28 The photochemical addition of ethene at O°C in methylene chloride to the enedione (77) affords a high yield of the adduct (78). This was converted to the monochloro derivative (79) which also undergoes photoaddition of ethene to yield the bisadduct (80). This on elimination of HC1 yielded the quinol (81) which can be oxidised to the quinone (82).29 Cycloaddition of alkenes (cyclopentene, cyclohexene, and cycloheptene) has been carried out to the same enedione (77) to yield the adducts (83).30 Iyoda et al. have also described a convenient synthesis of the bicyclo-octanediones(84) by a photochemical addition of alkenes to the enedione (77). The adducts (84) can be reduced by zinc in acetic acid to the desired products. Cycloaddition of ethyne to the same enedione followed by reduction affords the bicyclooctanes (85). The photoaddition of alkenes to the dibromo-enedione (86) is also effective and yields, after reduction, the adducts (87). 31 The de Mayo reaction with cyclohexa-l,3-diones is a method which still attracts interest as a synthetic approach to natural products. Typical of this is the short route to hirsutene (88). This involves photoaddition of the cyclohexanedione (89) to 2-methylcyclopent-Zen01 to yield the adducts (90,91) following ring expansion of the initial (2+2)-adduct. Adduct (90) is used as the precursor to (88).32 Photo-addition of the enone (92) to the alkene (93) gives the ring opened cycloadduct (94). This compound was used as a starting material for the synthesis of bicyclo~ndecenes.~~ Harwood et al. have reported a variant of the photochemical addition of alkenes to the enols of lY3-diketones. By using the enol ethers (95) as the alkene component reasonable yields of the 2-alkylated products (96) are obtained by the route shown in Scheme 4. Apparently there is little evidence for the formation of cyclobutane products and the usual cyclization path is diverted by the intramolecular hydrogen abstraction route shown. The reaction is prone to the influence of substituents and fails with heavily substituted enol ethem3* Several approaches to the taxane skeleton (97) have been published recently (see also reference 9). All have involved (2+2)- cycloaddition of the type reported by Berkowitz et a/. who have added cyclopentene and cyclohexene to the enone (98) to yield the cycloadducts (99). Successful addition of the alkene (100) to the same enone yields the ring-opened adduct (101). In a similar fashion the intramolecular addition of the enone (102) affords a (2+2)-adduct which can be treated with base to provide a route to the skeleton of the same natural product.35
11112 Enone Cycloadditions and Rearrangements
187
R’ = Ph or H
+ + 0
OH
OH
0
(80)
(81)
“fp”
0
Cl”
0
(83) n
-
0
1,Z or 3
II
(84) R ’ = H, Me, But, Ph, COMe, CH,=CH, M e OH
RZ= H R’ = R Z = S C H ~ +cH,+, ~ ~ ,
CHZ-CH
=C H-CHZ
+ c H ~ + ~ or .
Photochemistry
188
0
AOH Q?" (89)
@" AOAc Me
0
(93)
(94)
11112 Enone Cycloadditions and Rearrangements
= H or Me, R 2 = Et, Bun, R 3 = H R' = H or Me, RZ = Me, R3 I Me R'
189
(95)
Scheme 4
(97)
(98)
(99)
n
= I, R '
t
p-~-
n =z, R ' = ~ - H and a - H
0
0
190
Photochemistry
Acetone-sensitized addition of ethyne to the enone (103) gives the adduct (104) in 50% yield. This adduct was subsequently elaborated to provide a route to optically active tri~hothecenes.~’The photoaddition of the enone (105) to a-terphed (106) gives a mixture of (2+2)-cycloadducts (107) containing both the head to head and head to tcu‘l isomers. The bead to head mixture was used as the starting material for a total synthesis of (+)-Elemol (108).37 Qu’mtitative yields of the adducts (109) are obtained by low temperature, -20 to -4OoC, irradiation of the enamine carbaldehyde (110) with the alkenes (lll).38The enamide (112) also undergoes photoaddition of acrylonitrile. The adduct from this, on catalytic hydrogenation, provides a synthetic route to the carboxamides (113).39 (2+2)-Adducts (114) are formed on irradiation of the quinolone (115) with cyclopentene, cyclohexene, and 2,3-dimethylb~t-%ene.~~ Kaneko et a/. have studied the addition of diketene to the quinolinone (116) to yield the adduct (117)?l The rearrangement of the cyclobutanol (118) can be brought about by irradiation in the presence of H ~ o / I , . ~ ~ Successful dimerization of the coumarin derivatives (119) in the solid state has been reported.43 The photobasicity of several coumarin derivatives (120) has been e~a1uated.l~A series of twenty eight coumarins have been studied in the solid state. This has shown that only twelve of these, as shown in (121), actually photodimerize. X-Ray crystal data indicates that double bonds can interact in (2+2)-dimerizations even if the bonds are more than 420 pm apart.45 Calculations relating to the reactivity of the double bond in the psoralen (122) have been made?‘ Other work on furocoumarins has been reviewed by Bensasson4’ and Dall-Acqua et .d8 Photochemical addition of alcohols and acetic acid to the enone double bond of Decomptin (123) affords the adducts (124) in high yield when the irradiations are carried out in benzene solution.49 Dimethyl acetylenedicarboxylate photoadds to the pyrone (125) under sensitized conditions to yield the benzene derivative (126) presumably by decarboxylation of the (4+2)-adduct (127). Adducts of this type (128) are obtained by the sensitized addition of acrylonitrile to the same substrate. The (2+2)-adduct (129) is formed also but in low yield.50
A detailed study of the photo-ring closure of the hydroxychalcones (130) to yield the flavanones (131) has been made51 and proton transfer reactions in 3-hydroxyflavones have also been carried out.52 Miscellaneous Reactions.- The syn-trans dimer (132) is obtained on irradiation of the pyrazinone (133) in the solid state. The structure, a (4+4)-dimer, was fully identified by X-ray crystallographic analysis.53 This report corrects an earlier account of the
11112 Enone Cycloadditions and Rearrangements
191
O & iy PH
Me M e
(107b)
(107~)
(107d)
(108)
(109)
(110)
R1 = e g r o R AcO
OAc
Rz = R 3 = C02Me RZ = COZMe, R3 = H or vice versa R 2 = C02But, R3 = H or vice versa RZ = R3 = H or Me
(111)
Photochemistry
192
$ 8' NH,
RZ
I
H
Ph
'Ph
(113) a; R' = CN, RZ = H b; R ' = H, RZ = CN
(112)
(114) R-R = (CH2& or R = R =Me
(CtiZl4
Me Me
OAc
&; 0
H (115)
Me
Me
(117) R
Me
a.
(119)
(116)
R
= CI or Me0
R'
Rz
R3
R4
R5
Me0
AcO
H Me0 H H
H H Me0 H
H H H H
H H H H
H
AcO
H H H
Cl
H Me CI H H Me Me H
H H H
CL
AcO H H
H H H H H H H H
~~
H H (1 20)
R5
R4
Cl
H
H H
Cl Me
H H H
H H
193
11112 Enone Cycloadditions and Rearrangements
& -(
*
OAc
OMe
(122)
$O,Me MeOzC
D
-
0
OAc
(124)
i
R = H, Me, Pr or Ac
(126)
(125)
CN C0,Me
II
\
Meo2c*
QK”o-.
qA 0
OH
(131)
(130) Me
Ph
Photochemistry
194
R (&
H
(135) a; n = 1
( 1 3 4 ) a; n = 1, 8lol0 ( R = Me) b; n = 2, 76% (R = Me) c; n = 1, 67%(R = H )
b;n=2
0
cp
(1 35c)
(135d)
(137)
(140)
(138)
( 1 39)
11112 Enone Cycloadditions and Rearrangements
195
dimerization of (133) by the same authors.54 Cyclopentanols (134) are formed by the photo-reductive cyclisation of the enones (135). Reactions are carried out in HMPA and irradiation of the enones (135) in this medium effects electron transfer to yield the radical anion of the carbonyl group. Cyclization follows the "Rule of Five" and yields the cycl~pentanols.~~
2
Rearrangement Reactions
a,P-Unsaturated Systems.- A reinvestigation of the photochemistry of the epoxy enone (136) has been carried out. The W I T * excitation of this compound yields several products which were reported previ~usly.~' The present work has shown that the compounds (137-139) are also formed. This result adds to the already known complexity of the reaction system." Muller has reported that the epimino derivatives of these systems are also reactive. Thus the irradiation of the derivative (140) affords the two products (141) and (142) by reactions which are similar to the reactions of the epoxy ana~ogues.~' A detailed study of the photoenolization of the ketones (143) and their reketonization has been rep~rted.~'The enone (144) undergoes deconjugation when subjected to u. v. irradiation.m White et a/. have observed that the photochemical deconjugation reaction Deconjugation, of the triene (145) yields (146) as a mixture of E and $isomers. yielding (147) as a 51:59 mixture of isomers, was reported to occur for either triene (148)6' Photo-deconjugation of the lactones (149) in the presence of (-)- ephedrine rapidly yields the deconjugated lactones (150) with a slight enantiomeric excess. To some extent the reactions were both solvent and temperature dependent62 George et al. have reported a study of electron transfer reactions of the furanones (151)."3 The triplet state of the ecdpone (152) is reactive and affords the products shown in Scheme 5. The formation of the reduction products (153) and (154) is presumed to follow a path where loss of a hydroxyl radical yields the ally1 radical (155) which then gives the products (153) and (154) by hydrogen abstraction. The ketone (156) is formed by a 1,2-bond migration and the cyclobutanol (157) arises by secondary irradiation of the diketone (156).0Q The enone (158) shows solvent dependent photochemistry. Thus in ethyl acetate the deconjugated product (159) is formed while in methanol the reduced ketone (160) is pr0d~ced.g~ Irradiation of the thiolactone (161) in alcohols produces the esters (162). The ester (162, R = Me) is itself photochemically reactive and on prolonged irradiation in methanol is converted into the acetal (163).% The enones (164) all undergo photoisomerisation into the lactones (165). The mechanism suggested for this isomerization involves the intermediacy of the cyclopropyl ketone (e.g. 166). However
196
Photochemistry R4
R2 R* (1 4 3 )
R'
RZ
R3
R4
Me H H H Me H
Me Et ally1
H H H H
Me Me
R ' Me Me Ph Me
Me H Me Ph
&
C02Me
Me
i)SiMe3
(145)
(144)
%
COzMe RZ OAc
OSiMe, (147)
(146)
OAc (148) a; R' b; R '
= C02Me, R2 = H = H, R2 = COLMe
(149)
Ph
n n n n
= 2, R ' = R 2 = H =l, R'=R2=H = 1, R' = Me, RZ = H = 1, R ' = R 2 = Me
0
197
11112 Enone Cycloadditions and Rearrangements
OH
OH
'
O --H -
hv
0 R
{flj
+
0
OH (157)
(156)
(1 55)
Scheme 5
& M3 0
0
/
(159)
(1581 R ' = H, R Z = Me, R 3 = d-H, P-OH R' o H, R2 = Et, R 3 = cl-CfCH, P-OH
R'
P
R2
=
Me, R 3
= a-H, P-OH
&
0
H
(160)
OMe
JYcozR (161)
(162)
R = Me, C,H5, Pr', But
(163)
Photochemistry
198
(164)
(166)
R3 R'
R 3 = Ph, R' = Me or Ph, R 2 = Me or Et
(169)
0 Ph
Ph
COOPh
Ph
Me
Ph
ii
Me (172)
(171)
ph%
(173)
R'
(174)
(170)
11112 Enone Cycloadditions and Rearrangements
199
no direct evidence for this was obtained. The irradiation of enone (164e) did show divergence from the general path and gave the enone (167) as the principal photoproduct. This is proposed as reasonable evidence for the intermediacy of (168) which in this instance undergoes decarbonylation rather than cy~1ization.b~ The allenic esters (169) yield the the cyclobuteneones (170) on irradiation. In these is the major product and is accompanied by examples , this 1,1,4,4-ktraphenylbuta-1,3-diene. The cyclobutenones are photochemically unstable and can be completely destroyed by irradiation for 4-6 h. When the phenyl ester (171) was irradiated no cyclization occurred and the only compound obtained was the photo-Fries product (172). One interpretation of the cyclization process is that the ester undergoes Cyclization and fission of the carbonyl-ester 0 bond yielding a radical pair. recombination would afford the product. However, attempts to trap intermediates such as (173) were unsuccessful.08
transcis Isomerisation of the oxime (174) can be brought about photochemi~ally.6~ Irradiation of a mixture of E,Zisomers (175) induces cyclization and loss of methanol to yield the fused quinoline derivatives (176).70 The cinnamates (177) are photochemically reactive in micelles. Irradiation brings about G O bond fission and recombination within the radical pair affords the chalcones (178).71 The E Z isomerization of the enone (179) is followed by the photochemical isomerization into the cyclopentenone derivative (180). This occurs by amide bond fission followed by recombination within the biradi~al.~'
P,y-Unsaturated Systems.- The direct irradiation of the cyclohexenone (181) affords the three products shown in Scheme 6. The quantum yield for the direct irradiation are shown below each product. The influence of triplet sensitizers and quenchers on the reaction was studied and a triplet state was shown to be involved. A detailed interpretation of the mechanism of the reaction was g i ~ e n . ' ~The enone (182a) undergoes triplet excited state rearrangement into the two products (183) and (184). It is of considerable interest that the bicyclehexanone (183) is formed to the exclusion of the cisisomer. The reaction is remarkably efficient and the quantum yields are shown below the appropriate structures. Again a detailed analysis of the mechanism is reported. Interestingly the P-naphthyl enone (185b) is also photoreactive and yields the products shown in Scheme 7. In this instance both the trans and the cisbicyclic isomers were formed.74 Details of the photochemical behaviour of the p,y- unsaturated enones (186) has been reported. This supplements the report made earlier in note form.75 The reaction described involves the photoconversion of the enones (186) into the imines (187) and (188) by a path which is thought to involve a 1,Sbenzoyl migration. The terminus for this is a pendant phenyl group. Such a process has not previously been described. An
Photochemistry
200
R’ = R Z = (CH=CHIZ R’ = H, RZ = But
(176)
R4
R4
OH
(177)
0 (180)
( 1 79)
+
oih--Ar + t? - -Ar
At
Ar
Ar A T
0
Scheme 6
= 0.024
0
H
= 0.020
201
IIIJ2 Enone Cycloadditions and Rearrangements
4 Ar
H- J%+o
Ar
a; Ar = a-naphthyl b;Ar = 0-naphthyt
(182)
(&
Ar I I
(183) d
Ar
5
0.46
(184) 0
Ar 0
Ar
0.54
Ar
= 0.38
0 = 0.02
Scheme 7
(186) A t
=
C,H,
or p-ClC6H,
( 1 88)
(187)
Art L
p
h
A r ’ A k P Ph h Me
ArCO
H
OCOAr (189 1
( 1 SO)
(192 A )
(191) a; R’ = Me, R 2 L: H b; R’ = H , R Z = Me
(192 8 )
Photochemistry
202
1193) a; R'
COMe, COPh, R 2 = H
(194) a; R = COMe
b; R' = H, R Z = COMe, COPh
& R3
b; R
= COPh
a; R' = R Z = R 3 = H
b; R' = Me or OMe, R 2 = R3 = H R' = OMe, R Z = M e or H, R 3 = H or Me d; R ' = OMe, R Z = R 3 = Me c;
R2
( 1 96)
O
a
HM
(195)
e
CH=C=O
R'
(197)
m %
0
0
a
02"
(261)
( 202 1
(203)
P > O (204)
(205)
(206)
11112 Enone Cycloadditions and Rearrangements
203
electron transfer mechanism is thought to be ~ p e r a t i v e . ~A~ full account of the photochemical conversion of the azadiene esters (189) into the dihydrwxazole derivatives (190) has also been reported. The reaction is interpreted in terms of a l,%benzoyl migration in the enol ester followed by cyclization within the resultant biradical. The rearrangement is proposed as the first example of a 1,2-acyl migratioxi in an enol ester.77 This paper expanda the material originally published in note The photodecarbonylation of the dienones (191a) and (191b) has been examined and shown to be a concerted process. The cisisomer (191a) yields initially the triene (192A) while the trwisorner (191b) affords the triene (192B). These experiments prove conclusively that the decarbonylation is a concerted process?' 1,SAcyl migrations occur on the irradiation of the lactones (193, R1 = COMe). This treatment yields (193b, R' = COMe) which is also photoreactive and is transformed into the valence bond isomers (194). Irradiation of the lactone (193a, R' = COPh) under acetone-sensitized conditions also brings about the 1,Smigration yielding (193b) which is not isolated since it undergoes oxetan formation yielding (195).8* A full account of the photochemical reactivity of the enones (196) and their photoconversion into (197) by a 1,bacyl migration has been reported!' This supplements the material already published in note form.82 In contrast acetone-sensitized irradiation of (196b, R1 = Me) brings about an oxa-di-n-methane reaction affording the tricyclic product (198). With a methoxy substituent at the bridgehead only the 1,3-acyl migration is observed. The derivative (196b, R' = MeO), on both direct and acetone sensitized irradiation, affords a mixture of the isomeric ketones (199). The carene skeleton can be synthesized using the ready rearrangement of bicyclic systems of the type illustrated in structure (200). Irradiation of these molecules has been shown to proceed by Norrish type I bond fission with rebonding within the resultant biradical to yield ketenes (201). This route has been applied by Uyehara et d as part of a total synthesis of sesqicarene and sirenin and involves the specific rearrangement described above with trapping of the ketene as the acid (202). Subsequent chemical transformation of the acid provides a route to the natural products.83 Mehta and Subrahmanyam have reported the oxa-di-n-methane photoconvenion of the enone (203) into (204) as a route to (3,3,3)- propellanes and specifically to racemic modhephene (205).84 Uyehara et a/. have described the photochemical conversion of the enone (206) into (207) by a 1,bacyl migration. The compound (207) was used as the starting material for a synthesis of racemic @i/ocauiin (208)8 5 Adam and his coworkers have studied the oxa-di-n-methane rearrangement of the norbornenone (209). They approached the problem by the synthesis of precursors of the putative biradicals such as (210).86 The oxa-di-n-methane rearrangement of the P,y-unsaturated enones (211, 212) has been reported by Schultz and his coworkers.
2 04
Photochemistry
Acetone- or acetophenone-sensitized irradiation of the enones yields the rearranged ketones (213, 214) which are described as useful substrates for the synthesis of polyquinane natural products.87 The enones (215) can be converted by photosensitized irradiation into the diquinanediones (216). Irradiation of (215) in acetone gives a low yield of the tricyclic ketone (217). This ketone, while stable in the dark, is photochemically converted into the diquinanedione (215). The authors present evidence that this conversion results from fission of the cyclopropyl bond to yield the biradical (218).88 Demuth and Hinsken have reported the use of the oxa-di-.rr-methane rearrangement in the synthesis of annelated triquinanes. Thus the photo conversion of the enone (219) affords the tetracyclic ketone (220,72%). In an analogous reaction the enone (221) is converted into the isomeric ketone (222,7O%)ag
3 Photoreactions of Thymines and Related Compounds A review has outlined some chemical aspects of the photo-induced cross-linking of proteins to nucleic acidsg0 The irradiation of the bromouracil (223) in the presence of the electron rich aromatic compound (224) affords the &substituted uracil (225) exclusively. With other aromatic compounds both the 5- and the 6- substituted uracil derivatives (226) and (227) were obtained. The formation of the 5-substituted uracil was not unexpected but the &isomer had not previously been reported from such reactions. The mechanism by which this latter type of product is formed is not knownqgl A study on the photochemical isomerization of 4-pyrimidones (228) has provided a synthetic approach to the Dewar pyrimidones (229). These are prone to hydration and under the conditions of the irradiation are converted into the hydrates (230, 231). An examination of the behaviour of the hydrates has shown that they readily undergo reversal to starting materialg2 Photoisomerization to (232) and dimerisation yielding (233) of the pyridones (234) occurs on irradiation in ethyl acetate solution.93 A study of the photochemical behaviour of the uracil derivative (235) has been carried out. Details regarding the triplet energy of the Eisomer and the singlet-triplet crossing efficiency have been The fluorescence of l,3-dimethyluracil is quenched by water. The yield of photohydrates of pyrimidines in general is sensitive to the water c~ncentration?~A spectroscopic study of the triplet behaviour of the thiouracils (236) has been reported.% Irradiation of 5-ethylorotic acid (237) leads to the formation of the ethylidene analogue (238) and the dimer (239). The continued irradiation of the analogue (238) yielded 5-ethyluracilg7 The adducts (240) can be prepared by the irradiation of thymidine in the presence of 8-methoxypsoralen?8 The photocycloaddition of the thymidine derivative (241) results in the formation of six cyclobutane isomers.99
11112 Enone Cjlcloadditions and Rearrangements
205
Mpo (207)
b
0
(209)
(208)
9 @O : zMe
MeOzCH
(211) R = H or Br, n = 1 RrH, n r 2 R = H , n = 3
’\
--C02Me a
\’H
0
(212)
R@:~e (213) R = H or Br, n = 1
R=H, n=Z R = H, n = 3
“2cp&* C0,Me
OMe
(215) R = CHzCHzOMe or CH,CH(OMe),
(214)
OMe
(217)
&0 =O
(216)
Photochemistry
206 OR
8
OR
&
&
0
0
0
(219)
( 2 2 1 ) R = CH,OCH,CH,OMe
(220)
o&joR
O / \ O M eO M
Me
MeN
OMc
Me
Me (225)
0
MeN
( 2 2 6 ) R = Me, OMe or 1,4-di-Me
207
11112 Enone Cycloadditions and Rearrangements
.'ao R1
Et
dN$
A
0
RZ
OH
(240)
(239)
Me$Ko I
"
O 0I-i Y (242)
Photochemistry
208 The irradiation, using 350 nm light, of a dry film of
dimethoxycoumarin (242) and adenosine (243) affords the adduct (244). No evidence for the formation of cyclobutane products was obtained.lm A study of several psoralena has shown that only compound (245) undergoes intercalation with DNA. Photoinduction of interstrand crosslinks in calf thymus DNA was also efficient."'
4 Photochemistry of Dienones Linearly-conjugated Dienonee.- The only observed reaction of the dienones (246) from either the triplet or the singlet state was transcis isomerization around the C-7,C-8 bond The isomeric compound (247) also undergoes this isomerization as well as transcis isomerism of the C-9,C-10 bond. The diene (248) is also photo-reactive giving the product (249) by a 1,Shydrogen transfer. Irradiation of (249) yields (250) by a Norrish type I1 process.lo2
A detailed study of the photochemical reactivity axid synthetic usefulness of the o-quinolacetates (251) has been reported.lo3 Quinkert and his coworkers have lodged a patent dealing with the formation of macrolides from the photochemical ring opening of the cyclohexadienones (252).lo* The steroidal dienone (253) has been studied by laser flash excitation. The triplet state energy of this system is 42-43 k.cal. mol.-' and is slightly lower than expected from the estimates made from the spectroscopic triplet. The lower energy is thought to be due to molecular re1axati0n.l~~ Croes-conjugated Dienones.- The isomers (254) and (255) are obtained from the direct irradiation of the cyclohexadienone (256) in benzene. Prolonged irradiation of the mixture results in the photoisomerization of (254) into (255). The irradiation of (255), however, does not bring about isomerization. The study of enantiomerically pure (256) was also carried out and from this it was found that the starting material isomerized into a mixture of enantiomers.lW The photochemical rearrangement of the cyclohexadienone (257) in methanol occurs in a stereospecific fashion and yields the adduct (258) whose structure was proven by X-ray crystallographic analysis.107 Cyclohexadienone (259) is photochemically reactive and can be converted in two steps This process represents the into the adduct (260) as shown in Scheme 8. intramolecular trapping of the zwitterionic intermediate (261).'08 The photochemical reactions of a series of proaporphines have been studied. Thus the irradiation of orientahnone (262a) in sunlight affords the two isomeric products isobo/dine (263a) as the major and isothebaine (262a) as the minor. Roemeridinone (262b) is also photoreactive and is converted into methyl isothebaine (26413) as the major product and N-methyl/aurotetanine (263a) as the minor.
The stereochemical
209
11112 Enone Cycloadditions and Rearrangements
HO OH
(244)
Coke
(246)
(247)
(248)
(249)
--OAc
RZ R+
(250)
R3
(251)
R4 (252) R = H or C1 to C4 alkyl n = 2-16
210
Me0
Me0
COzMe
o,, cot Me
H
H
Photochemistry
Me0
Me
Me’
0
M eQCC13 (257)
(258)
p.
(259)
(260)
(261) Scheme 8
J$ C0,Me
11112 Enone Cycloadditions and Rearrangements
MROe
o
F
N
l
Me0 OMe
Me0
\
Me
/
0
( 2 6 4 ) a; minor b, major
b; minor
J&-& \
OH
OMe NMez
*- H
HO
.H
OH ( 2 6 3 ) a; major
( 2 6 2 ) a; R = H m
IIvMe
e 'l;@lMe
b, R
211
Me0
* -
OH
(270)
(269)
OMe
OMe
212
Photochemistry
implications of the rearrangements were discussed in some detail.'@' Photochemical rearrangement of the cyclohexadienone (265) yields the lumiproduct (266).110 The cyclohexadienone derivative (267) undergoes photochemical isomerization into the four products (268-271). The latter three of these result from ring contraction of the cyclohexadienone moiety.'"
A new approach to bklactams has been described and involves the photochemical cyclization of the pyrimidinium enolates (272). Typically irradiation of (272) in acetonitrile affords a high yield (96%) of the bicyclic lactam (273).'12 Photo-cistmmisomerization of the dienones (274) affords the transisomers (275) which can be trapped by dienes such as cyclopentadiene and isoprene yielding e.g. (276).l13 Kazama et a/. have studied the influence of conformation on the photocyclization and photoreduc t ion react ions of lo-(SH-xanthenylidene)-g ( 10H)-anthracenone. l4
'
5 1,2-) 1)3-, and 1,CDiketones 1,Z-Diketon=.- Rubin has reviewed the recent photochemistry of l,Z-diket~nes."~ Studies of the gas phase photo-decomposition of glyoxylic acid"' and of pyruvic acid have been carried out."' Hamer has reported a synthesis of cyclopentane-l,3-diones (277) using silver ion catalysed ring expansion of the cyclobutanones (278) formed on irradiation of the 172-diones (279).'18 Birney and Berson have described the photochemical double decarbonylation of the triketone (280). At room temperature in CD,CI, tri-decarbonylation gives benzene but at low temperature in a matrix the norbornadienone (281) is formed.'" 1,S-Diketones.- Intramolecular electron transfer has been used to explain the photo-degradation of gi!yy/&cine (282).120 The dione (283) undergoes Norrish Type I1 hydrogen abstraction to afford the biradical (284) as the reactive intermediate. In the presence of oxygen this biradical is trapped and the furanone (285) is the product formed.121 A detailed study of the photochemical behaviour of the ketoesters (286) has revealed that they undergo Norrish type I1 hydrogen abstraction, The products from this reaction are shown in Scheme 9. Interestingly the authors suggest that back hydrogen transfer is suppressed because of intramolecular H-bonding within the 174-biradical formed in the Norrish type I1 step. The H-bonding controls the stereochemistry of the cyclization to the cyclobutanols.122
Unstable p-lactams (287), benzoylation affords stable products, are formed by the photochemical cyclization of thioamides (288). The authors believe that a Norrish type
IIIt2 Enone Cycloadditions and Rearrangements
213
I
R2
( 2 7 2 ) a; R’ = R3
=
(273) a; 96.10 b; 91’10 C; 83’10 d; 61% e; 92’10
Ph, R Z = H
b; R’ = Ph, R 2 = Me, R 3 = H c; R’ = Ph, R 2 = R3 = M e d; R’ = R 3 = Ph, R Z = Me
e; R’ = Me,
( 2 7 4 ) R’
I
RZ = H
R’ R’
= =
OMe, R 2 = t i H, R Z = M e
RZ = SEt, R3 = Ph
(276) a; R 3 = H
(275)
b;
RA h0 R
e
B
(277)
=CH2
0 (279)
(278)
a; R = Mel, R’ = H b; R = Ph, R’ = H
&2l
0
3
R*
r
R’
R’
R 3 -R
1
R-R = +CH,+, d; R = R’ = Me C;
H H 3 2 y N +
0
co
-
Photochemistry
214
+ R Scheme 9 R2
R3
0 dN ''
Ph
(287)
t Ph, R 2 = R 3 = M e 2 9 '1. 16 % = Me, R2 = R3= Me 35% c ; R' = Me, R 2 = H , R3= Ph d; R' = Me R 2 = H, R 3 = OMe 76% 1 2 e; R = Ph ,R = H , R 3 = OMe 90%
a; R'
(287)
(288)
(288)
b; R'
11112 Enone Cycloadditions and Rearrangements
215
I1 process is involved and that a zwitterion is produced following the hydrogen transfer step.123 1,4-Diketones.- A detailed study, by product analysis and by laser flash photolysis, of the photochemical reactivity of the barrelenes (289) has been reported.la4
An n.m.r. study of phenyl fulgides has been p ~ b 1 i s h e d . l ~Heller ~ and his coworkers have continued their study of photochromic systems. In the present report the photochromism of succinic anhydride derivatives ( e.g. 290) has been Carbonyl compound-sensitized dimerization of maleic anhydride affords the dimer (291) in good ~ie1d.l~' The two dimers (292) and (293), obtained from the photodimerization of the anhydride (294), have been used as a starting material for the synthesis of some propellanes.'28 Wirz and his coworkers have developed a method for the study of the dienone (295)/ phenol equilibrium. The dienone (295) is obtained by irradiation of dione (296) which undergoes photochemical elimination of ketene. Ketene formation can be confirmed at low temperature but under these conditions very little of the dienone (295) is observed since it readily undergoes photochemical ring opening to ketene (297).12' P-Lactams (298) can be formed in low yield by the photochemical ring contraction of the diones (299). This involves N-0 bond fission followed by loss of CO, and rebonding in the resultant 1,4-biradi~al.'~' Scheffer has made use of the intramolecular hydrogen abstraction reactions in the diketones (300) to synthesize the cage compound (301). This compound was shown to have no anti viral activity.13' The cage compound (302) is formed easily on irradiation the dione adduct (303). The synthesis of the cage (302) confirms the endoarrangement in the a d d ~ c t . ' ~ ~
of
The photochemical isomerization of the muconic acid anhydride (304) to the bicyclic compound (305) has been reported to occur in high yield.'33 Phthalimides and Related Compounds.- The piperazinetetrones (306) are photochemically reactive. Irradiation of the derivative (306a) affords the cyclized product (307a) by a path involving Norrish type I1 hydrogen abstraction, 1,4-hydrogen migration within the biradical, and bond formation. The same path is followed for the derivatives (306 b, c) yielding the cyclized products (307 b, c). In these examples a 1,Shydrogen migration path also competes and yields the products (308).134
Photochemical reactions of phthalimides and related systems continues to produce new and interesting results. N-Ethylsuccinimide is converted into the azepinedione (309) in 64% yield on irradiation with a low pressure Hg lamp.135 N-Methylglutarimide adds photochemically to Zmethylpropene to yield the oxetan (310).136
Photochemistry
216
d'
'0 (292)
(293)
(294)
0
6
( 2 95)
0
(2981 R = Ph or PhCHMe (299)
(300)
(301)
0
(302)
(303)
0
217
11112 Enone Cycloadditions and Rearrangements
I R'
(307)
(3 08)
NO@
Me
0 0 (311)
(310)
(309)
RO
Me
2&NMe '
Me
0 (312) R ' = R Z = H
(313)
2
R'= M e , R = H R ' = H , R 2 = Me
R'e( 0
F?
0
218
Photochemistry
A detailed account of the photobehaviour of the phthalimide (311) with alkenes has supplemented earlier reports. The reactions encountered are either a 27r+21~addition yielding benzazepinediones or electron transfer from the alkene to the phthalimide followed by intermolecular t r a ~ p i n g . l ~ ~ - l ~In' another study N-methylphthalimide derivatives (312) undergo electron transfer reactions on irradiation in alcoholic solution. Reaction between the radical anion and radical cation yields adducts e.g. (313) a8 well as the more conventional products of addition to the carbonyl group. The identity of these new structures was verified by X-ray c r y ~ t a l l o g r a p h y . ~ ~ ~ Coyle and his coworkers have reported an approach to the alkaloids of the protoberberine type by the photochemical cyclization of the Mannich bases (314). This cyclization step yields the products (315) in moderate to good yields.14' The phthalimides (316) and (317) also undergo photochemical cyclization to afford products of the type represented by (318) and (319) respectively.142 Intramolecular photocyclization of the phthalimide derivatives (320) yields the ring expanded compounds (321) as the predominant products. Alternative modes of reaction are also encountered such as hydrogen abstraction and cyclization followed by Norrish type I1 chain elimination as shown in Scheme 10. Phthalimide (320d) also shows a solvent dependency when the isomers (322) are formed on irradiation in methanol (or ethanol).lU In another example Maruyama et a/. have reported the cyclization of the phthalimide derivative (323) to give a high yield of the benzazepinedione (324).'44 As can be seen from the foregoing, phthalimide photocyclizations have provided useful synthetic routes to a variety of heterocyclic products. Machida et al. have used the reaction to yield the spiro compounds (325) from the irradiation (in methanol) of the phthalimide derivatives (326). The products are presumed to be formed via bond formation in the biradical produced by the addition of methanol to the radical cationlradical anion pair.145 The indoles (327) undergo photochemical (2+2)-addition with N-methyl phthalimide to afford the oxetan adducts (328).'4G This work has also been the subject of a patent app1i~ation.l~' The photochemical reaction of N-methylphthalimide with 1,l-diphenyl ethene affords the phthalimide adduct (329) and the ether (330) in 44 and 12 % yield respectively. With imide (331) the byproducts are the ring opened adduct (332) and the ether (330) in yields of 31 and 44% yield respectively. The authors suggest that the formation of the ether is the result of a second electron transfer as illustrated in Scheme ll.'48 Photochemical addition of N-methylthiophthalimide to diphenylketene and the corresponding tolylketenimine affords the (2+2)-adducts (333) and (334) respectively. The ketene adduct (333) is itself photochemically reactive and undergoes loss of COS to yield (335).14' The thiophthalimide (336) undergoes hydrogen abstraction and cyclization affording (337) on irradiation using visible light.15* Norrish type I1
219
11112 Enone Cycloadditions and Rearrangements
@:
(C HtIn S R
0
0
(316) R = Me, Et,PhCH,, But , e t c . n =1-4
q, HO
(317) R = Me or E t
m - 1 or2
0
S
R (31 8)
(319)
(320)
CJy (3211
HO
(320b)
hv
*" 0
0
0
Scheme 10
NH
Photochemistry
220
(322) R =
p-
0 CHzOMe or ol- CHzOMe
0
(323)
(3 2 4)
m = 2 , n - 1 m = n = 2
m t 3 , n - l
= 3,n = 2
m
(326)
(325)
d
R
R'=
2
R'
=
R'
A c , R2 =
R3= Me, H
Ac , R2=
R3= (CH213,
0
(CH2)&, (CH,),
(328)
(327)
e
O
M
e Ph
0 (329)
Ph
(330)
22 1
11112 Enone Cycloadditions and Rearrangements
NH Me
(33 2 1
1331)
ph)+&
Ph
MeOH H+
phh
~
Ph
OMe
electron transfer
-
(330)
Ph
Scheme 11
Ph Ph
X
(333)
x=
0
(335)
(334) X = N-tolyl
(33 7)
(336)
Ph
( 3 3 8 ) n - 3 or 4 Scheme 12
Photochemistry
222
cyclization has been reported to occur on irradiation of the cyclic thioimides (338). Both 13- or E- hydrogen abstraction can arise and yield the products shown in Scheme 12. The cyclization within the Norrish type I1 biradical is followed by elimination of hydrogen sulphide. Interestingly cyclization also occurs with the thioimides (339) but excitation and hydrogen abstraction arises only at the thio carbonyl group.15' The xanthate (340) undergoes decarbonylation to afford the alkyl xanthate (341) when irradiated in benzene s01ution.l~~ Phot-addition of alkenes to N-methylnaphthalene dicarboxamides in benzene has been studied. The structure of the arene moiety in the imide was important in determining the reaction path. Mainly cyclobutane and oxetan formation occurred.lM The dicarboximide (342) undergoes photochemical cyclization with incorporation of methanol to yield the two products (343) and (344) in 55 and 16% respectively. This type of cyclization appears to be quite general for such systems and is also reported for the h i d e s (345) and (346).15* A variety of products resulting from aminolysis, reduction, and radical coupling is produced on irradiation of the phthalimide (347) in diethy lamine.155 The benzophthalimide (348) undergoes photochemical reaction with alkenes e.g. In some cisbut-2-ene to afford the isomeric addition products (349) and (350). instances, with 2,3-dimethylbut-2-ene and stilbene, the addition reaction afforded the oxetans (351, 352) or oxetan fragmentation products with no evidence for the formation of the ring expansion products encountered with the other alkenes. The oxetan products were also accompanied by products formed by hydrogen abstraction and radical combination. An electron transfer path is thought to be involved in these latter cases.15' A detailed study of the photochemical reactivity of the N-methyl carboxamide (353) with alkenes and dienes has been carried out. Typical reactions for the two addends are shown in the Schemes 13 and 14 respectively. A tentative mechanistic rationalization of the process has suggested the involvement of two exciplexes generated from the singlet state of the carboxamide and the unsaturated compounds The nature of the product is to some extent dependent on the substitution on the unsaturated moiety. Thus stilbene (both cis and trans) in addition to yielding the (2+2)-cyclobutane product also affords products (354) from the fragmentation of an oxetan product (355).I5'
6 Quinones The photochemical reaction of phosphorous derivatives with p -benzoquinones has been studied.15' The Argon matrix isolation of cyclopentadienone has been achieved using a variety of photo -precursors such as o - and p - b e z o q u i n ~ n e s . l ~ ~ pBenzoquinone and 1,Cnaphthoquinone add to cycloheptatriene to afford spirocyclic
11112 Enone Cycloadditions and Rearrangements
223
0
( 3 4 0 ) R = E t , P r , C H M e , , B u , Me,CHCH,
&-ph
&--OM. \
(341)
/
0
0
Ph
0 ( 3 4 41
(3 4 5 )
Photochemistry
224
0 (352)
(353)
(353)
Scheme 13
+ 1
Scheme 14
225
IIIl2 Enone Cycloadditions and Rearrangements
( 3 5 4 ) a; R'=
H , R'=
Ph
'0 (355)
OEt
0
Me
-Q^ OH
Me
(357)
(356)
"'WA HO
Me
0 OH
(359)
0
0
(360)
(3611
0
@? \
R2
R'
OH (362)
(363)
R'= R 2 t H R'=
M e , R2= H
R 1 = R2= Me
OH (364)
Me
226
Photochemistry
*x
Br
0 (365)
(366)
Qod 0 0(367)
(368)
@:x /
WoM OCOR 0
NwAr
Ph Ph
0 (3 69)
(370)
WoMe 0
0 (371)
OCOR
OPh 0
(372)
11112 Enone Cycloadditions and Rearrangements
227
ethers.leO The irradiation of the quinone (356) in alcohols has been studied. The authors suggest that the products formed are the result of protonation and cyclization of the excited state molecule to afford (357). Trapping by solvent yields (358) and (359) while ring expansion gives the isomeric chromones (360) and (361).16' The quinone derivatives (362) are also photochemically reactive and yield the cyclized products (363) on irradiation under nitrogen. The formation of this product arises by a Norrish type I1 hydrogen abstraction reaction affording the biradical (364) which cyclizes to the observed product.16' Maruyama et a/. have reported the use of irradiation in the conversion of the quinone (365) into the adduct (366).'63 An e.s.r. study of the photochemical reactivity of the quinone (367) has shown that the radical (368) is formed.'64 Photoaddition of triarylketenimines to phenanthraquinone affords adducts of the type illustrated in (369).165 The results of a study of structural factors on the photochemical reactions of amino anthraquinone derivatives have been published.lM Migration of the acetyl group arises on the irradiation of the anthraquinone analogues (370) yielding (371).16' The photochromic behaviour of the quinone analogue (372) has been studied.'08
228
Photochemistry
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1581. 161. K. Maruyama, H. Iwamoto, 0. Soga, A. Takuwa, and
A. Osuka, Chem. Lett., 1985, 595. 162. K. Maruyama, H. Iwamoto, 0. Soga, A. Takuwa, and A. Osuka, Chem. Lett., 1985, 1675. 163. K. Maruyama, T. Otsuki, and H. Tamiaka, Bull Chem. Soc.
Jm., 1985,
58, 3049.
164. M. C. Depew, B. B. Adeleke, A. Rutter, and J. K. S. Wan, Can.
J. Chem., 1985, 63, 2281. 165. J. P. B. Baaij, J. Kamphuis, and H. J. T. Bos, Red. Trav.
C h h . PapBas, 1985, 104, 37 (Chem. Abstr., 1985, 103, 36919). 166. V. Ya. Denisov and N. A. Pirogova, Sovrem. Tekhnol Protessy
i Oburud. Pisch. i Khim. Prom.-sti Kuzbassa, M, 1983, 54 ( Chem. Abstr., 1985, 103, 5994). 167. L. S. Klimenko, N. P. Gritsan, A. V. Konstantinova, and E. P. Fokin, lzv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1984, 84 ( Chem. Abstr., 1985, 102, 184529). 168. Yu. E. Gerasimenko, N. T. Sokolyuk, and L. P. Pisulina, Zh. Or& K h h . , 1985, 21, 453 (Chem. Abstr., 1985, 102, 203837).
3 Photochemistry of Alkenes, Alkynes and Related Compounds BY W. M. HORSPOOL 1 Reactions of Alkenes Group Migration Reactions.- Direct irradiation of cyclooctene (la) in pentane brings about cis -trans isomerization as well as the formation of the bicyclic products (28) and (3). These are formed via the carbene intermediates (4) and ( 5 ) . The latter carbene (5) also affords methylenecycloheptene. cis -trans -Isomerization also arises with the cycloalkenes (lb) and (lc). Product (2b) is formed from cyclodecene (lb) and cyclododecene (lc) yields (6) both by carbene paths.' A group migration is also reported by Hannaby and Warren. The 1,3-PhS migration results on the irradiation of the alkene (7) affording the isomer (8).2 The alkenes (9) undergo photoreaction from the singlet state. The key intermediates are thought to be the biradicals (10) and (11) arrived at via the intermediacy of electron transfer processes. The biradicals (10) and (11) are formed by 1,6 and 1,7-hydrogen transfer steps. The products obtained by the resultant cyclization are shown in Scheme l.3 Brook et al. have reported that the irradiation of the silene (12) brings about a complex rearrangement to yield the isomeric silene (13). Although the details of the mechanistic steps are not yet known the authors propose that silene to silylene steps are i m p ~ r t a n t . ~ cis -trans -Isomerieation.- Geometric isomerization, 1,bhydrogen shift, and structural isomerization results on the 184.9 nm irradiation of acyclic alkenes in the gas phase.5 The gas phase irradiation (at 184.9 nm) of cis -pent-Z-ene produces the trans -isomer. Some isomerization affording 2-methyl- but-l-ene and pent-l-ene also occurs6 A study of the cis -trans -isomerization of but-2-ene in the gas phase has shown that the photostationary state composition is independent of the pressure of butene? Irradiation (at 185 nm) of the alkenes (14-16) brings about isomerization of the double bond.8
A detailed study of the photochemical formation of the cyclobutene (17) by irradiation of 1,l'-bicyclohexenyl has been carried out. The photo- reaction also affords 1,2- and 1,4- addition products involving the incorporation of methanol. Steady state and transient methods have shown that the intermediate involved in the formation of these products is a highly strained ground state cis - trans -compound (18). This compound is the only precursor to the cyclobutene (17) following triplet sensitization of 237
Photochemistry
238
( 1 ) a; n = 1 b;n =3
H ( 2 ) a; n = 1 b; n = 2
c; n = 5
c;n= 5
0 (3)
H (61
(7)
&;
L N P Pv h
Ph
L P h
%
I
(10)
Ph R1 = Me, R2 = Ph
R1 =Ph, R2 =Me
Ph \-Ph
( 9 ) a; n = 1 b;n=2 Ph
Ph
(11)
Scheme 1
e3S
i,si 4c10H15
/
Me Si-Bu'
Me
OSiMe3
But
(12)
(13)
IIIf3: Photochemistry of Alkenes, Alkynes and Related Compounds
239
the bicyclohexenylg The trans -crown ethers (19) have been prepared by the irradiation of the corresponding cis -isomers (20). Resolution of the racemates was also carried out." cis -trans -Isomerization of isosafrole (21), by direct and sensitized irradiation, has been studied and the photo stationary photo state composition determined. Under these conditions the concentration of the cis - isomer is increased. Under electron transfer conditions the situation is reversed and the trans -isomer becomes predominant." trans -c,k Photeisomerization of the alkene (22) depends on the nature of the solvent and on the wavelength of excitation.12 Photoelectron transfer processes between styrenes and Cu(I1) and Fe (111) species have been studied. The reactions encountered include the addition of methanol to the double bond of the styrene.13 Some styrene derivatives have been irradiated in the presence of CdS. The trans -cis isomerization still occurs but the authors suggest that electron transfer is involved forming a radical-cation.14 Interest is shown still in the isomerization of stilbene and its derivatives. A study of the pathways for the cis -trans isomerization of 4-nitro, 4,4'-dinitro, and li-nitrd'-rnethoxy stilbenes has been reported.15 The dynamics of the photoisomerization of stilbenes in hydrocarbon solution has been studied" and a comparison of the trans -cis isomerization of stilbene in low viscosity liquid alkanes arid in the gas phase has been carried 0ut.l' The photoisomerization of stilbene in straight chain alcohols has provided evidence for the existence of rotational relaxation in the excited and the ground states.18 An analysis of the isomerization rates of photoexcited stilbene has been madelg and the photobehaviour of poly deuteriated stilbene has been studied.20 De Mayo and Hasegawa have studied the cis -trans -isomerization of stilbenes (23) mediated by a CdS semiconductor." Whitten and his coworkers have continued their study of photochemical processes in organized assemblies. The present work deals with the photochemistry of the stilbenes (24),22 and on photobehaviour of surfactant ~tilbenes.'~ Pic0 second spectroscopic investigations of cis -trans -isomerization of stilbene and the derivative (25) have demonstrated the presence of an intermediate which is involved in the is~merization.'~ cis -trans -Lsomerization of several pyridinium analogues of stilbene have been studied.25 The salts (26) also undergo singlet state trms 4 s -isomerization on irradiation. A detailed mechanistic examination of these systems has been carried out26 and a physical study of the influence of solvent and quencher on the decay of the excited singlet state of the stilbene derivatives (27) has been rep~rted.~'The cis trans isomerization of bis -heteroaryl ethenes has been reported in detail.28 The direct irradiation 'of the stilbene derivative (28) brings about trans
-
cis
240
Photochemistry
n= 1 or 2
Ar
Ar
ph%
R ( 2 2 ) Ar =4-N02%H4
(23) R
=H,NO2, COZMe, CI,Me, MeO, NMez
24 1
IIIi3: Photochemistry of Alkenes, Alkynes and Related Compounds
f
l/ R
% R'
3
N
0
+NR*X-
R'
R2
(?6 1
&Clc
CI
(30) a; R = C I b; R = H
( 2 7 ) R ' = Me,N, R,N, X'= 1-or Cl0,-
R Z = Me or Et,
Photochemistry
242
Jijp)
CI
2
CI
I;
(321
&CIc
CI
(36)
YcPh
Ph
(43)
OH
Cl
(33)
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds -isomerization
of
the
hindered
olefinic
double
bond.
243
Surprisingly benzophenone
sensitization effects isomerization of the less hindered double bond. The origin of the steric control is not known.2Q A report has suggested that the isomerization of the cyclophene (29) yielding the all trans -isomer occurs from the triplet state and is a direct six-fold process with no intervention of ground state intermediate^.^' Halogenc4kenes.- The photochemical behaviour of Afdrin (30a) is complex. A reinvestigation of the irradiation of this cyclodiene insecticide in hexane has isolated two new photo products (30b) and (31). Irradiation in acetone also provides surprises and the two new adducts (32) and (33) have been identifiede31 The influence of triethylamine on photodehalogenation of cyclodiene insecticides has also been evaluated. Irradiation appears to bring about selective dehalogenation at C-11 in (30a) yielding a 9:l mixture of the products (34a) and (34b). This stereoselective loss of chlorine is also seen with Dje/drin (35) and Endrin (36).32 Photoreduction products are obtained on the irradiation of the bromocamphene derivative (37) in non polar media. A vinyl radical is thought to be involved. In polar media, however, ether derivatives are produced via a carbocation intermediate and trapping by
Addition Reactions.- The photoelectron transfer process of the iminium salt (38) with the 3-butenoate anion results in the formation of the allylated product (39). The reaction involves decarboxylation of the 3-butenoate followed by a radical coupling reaction.34 The photoaddition of halogenated alkenes to the tetraiaza phenanthrene (40) yields products (41) of (2+2)-additi0n.~' The Eu(III)/Eu(II) photoredox system has been studied with regards to its reactivity towards a-methylstyrene. Irradiation of the system at A > 280 nm in methanol yielded the products (42) and(43).36 Alkynes.- Coyle has reviewed the photochemical reactions of e t h ~ n e . ~ The ~ photodissociation of acetylene has been studied at 193.5 nm.38 The alkyne (44) is photochemically reactive and has been studied in a variety of solvents.3Q
2 Reactions involving Cyclopropane Rings Zimmerman and Schissel have reported on the photochemical reactions of the highly crowded dienes (45-48). Within this series only the diene (45) was unreactive. All of the others undergo the di-n-methane rearrangement by both direct and sensitized irradiation as shown in Scheme A full account of the photochemical aza-di-n-methane rearrangement of the' azapentadienes (49) has been reported. The reaction provides a route to the cyclopropyl aldehyde (50). This rearrangement is of considerable interest since the parent aldehyde (51) from which the imines (49) are prepared does not undergo the corresponding oxaidi-n-methane rearrangement. The reaction reported in
244
Photochemistry
the paper is the first example of an aza-di- n-methane process in an acyclic imine.41142 Adam and his coworkers have described the synthesis and photochemistry of the divinyl ether (52). The direct irradiation of this compound gave several products which are thought t o arise from radical combination paths of the vinyl/vinyloxy radical pair. The 3-oxa-di-n-methane reactivity of this compound was not observed.43 The dicyanobicycloheptene (53) undergoes photorearrangement to yield three products. Tne first two products, (54) and (55), are the result of 1,3-carbon migrations. The third product, (56), is proposed to arise by a di-n- methane rearrangement to the nonisolated intermediate (57) which transforms into the isolated product (56). The introduction of the cyan0 groups appears to alter radically the photochemistry which such systems undergo but the authors suggest that a charge transfer mechanism is not 0perative.4~ The irradiation of the analogue (58) of the above using 254 nm light results in the formation of the isomeric product (59). Several routes were considered for the formation of this product and the authors suggest that the most likely mechanism involves photoconversion to the thermally unstable intermediate (60) followed by its rearrangement to the isolated product (59).45
A synthesis of substituted phenanthrenes has been reported using the bicyclooctadienes (61) as starting material. The process makes use of the nucleofugal group on C-8 and follows the path outlined in Scheme 3. This involves a di-.rr-methane bridging process followed by the collapse of the intermediate biradical (62).4G Normal di-n-methane behaviour is reported in the acetophenone-sensitized irradiation of the isoquinolinone derivative (63a). This yields the two products (64) and (65) as a 3:l mixture in a total yield of 75%. An N-oxide derivative gave a brown polymer with little evidence for the formation of di-Tr-methane products. The influence of ring substituents was also studied for the derivatives (63b, d) and the results of this are shown in Scheme 4. The authors conclude that the cyclization process is under LUMO control!’ Irradiation of the dihydropyridine (66) affords the oxidised pyridine (67) as the major product. A minor product (68) is also formed by a di-n- methane process.** Irradiation of the benzoazanorbornadiene (69) does not follow the conventional route for such photochemically active systems. The reaction, affords l-chloronaphthalene, by deamination, as well as two thermally labile indole derivatives (70, 71) by the route shown in Scheme 5. These are formed by 1,Snitrogen migrations within the a~anorbornadiene.~’ A detailed study of the rearrangement of the cyclopropanonaphthalene (72) has identified the products shown in Scheme 6. The reaction is solvent dependent and is more rapid in non polar solvents, such as benzene, than in polar solvents. The isomeric cyclopropanonaphthalene (73), a product of the rearrangement shown in Scheme 6, yields l-cyanonaphthalene as the principal product on irradiati~n.~’
245
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
Ph Ph Ph Ph
(45 1
848
Ph
h Ph Ph
Ph
Ph
(46)
& Ph Ph Ph Ph
MeS
ph&Ph
v
Ph
+& .'Ph
Ph
Ph
Ph
SMePh Ph
(48)
MeS
SMe
Scheme 2
ph45
Ph
Ph CHO
(49) R
= PhCH2, Ph, PhCHMe PhCH,CH,
( 50)
or Pr' CN
p Ph
o Ph
(51)
Photochemistry
246
CN
i
CN
(56)
(58)
(57)
CN
HgOAc
HgOAc
Me
Me
1
F y (61)
-
(62)
several steps
Me
AcOH
0
Mk Scheme 3
0;
R~=R*=H
b; R' = MeO, R2 = H C ; R' = CI, R L = H d ; R' = H, R 2 = OMe
a; ratio
3 : 1
b ; ratio 85 : 15 c ; ratio d ; ratio
79 : 21
0 : 100
75% 92.6% 55% 73%
247
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
(66)
CI
Me
Me
Me
(71 1 Scheme 5
H
CN
H
(72)
1
( 7 3 ) 2%
+
35 *I*
11*/*
&+&+ N
\
15 'lo
18%
Scheme 6
0 */*
248
Photochemistry
Several reports have focussed attention on the photochemical behaviour of methylene bicyclohexene derivatives. Thus the photoisomerization of the ex0 - or endo -isomers of (74) affords the methylenecy~lohexadienes(75)~~ with similar behaviour exhibited by the ethyl and is0 -propyl derivatives (76).52 Triplet sensitized irradiation of the methylene bicyclohexene (77) also brings about isomerization. The authors report that there is evidence for steric effects in the energy transfer step.53 Both the ex0 - and the endo isomers of the bicyclohex-2-ene (78) undergo excited singlet state rearrangement.54 Changes in substitution do seem to have an effect and Brune and his coworkers have examined the photobehaviour of the isomeric trifluoromethyl substituted bicyclohexenes (79). Irradiation of either of these follows a different path to the foregoing examples yielding a mixture of (80a) and (80b).55
A reinvestigation of the photobehaviour of the triene (81) at 254 nm has identified two new products (82) and (83). The authors suggest that a carbene species is involved in the formation of the cyclopropene (83).56 A detailed report, supplementing preliminary accounts, of the photo chemical behaviour of cyclonona-1,2-diene has been published. The reactivity encountered is outlined in Scheme 7.57558 Detailed studies of the behaviour of allenes (84) on irradiation have demonstrated that rearrangement to indenes occur. Thus the tetraphenyl derivative (84a) slowly affords the indene (85a) as the sole primary photo product while allene (84b), where both phenyl and hydrogen migration are possible, rearranges into indene (85b), 1,3,3-triphenylcyclopropene, and the alkyne (86). The authors have demonstrated congruence of product identities in the irradiation of allenes and cyclopropenes and also with carbenes generated thermally. From this it is clear that vinyl carbenes are implicated in allene photochemistry as outlined in Scheme 8.59 Full details of the rearrangement of the vinylcyclopropene (87) have been published.B0 This supplements a previous note.'l Electron transfer from 3,3'-dimethylbicyclopropenyl (88) to chloranil or fluoranil results in the formation of o and m -xylene in a ratio of 4:1.62 The photochemical ring opening of cyclopropyl anions has been studied and found to be substitution dependent. Thus irradiation of (89a) fails to bring about ring opening while irradiation of (89b) affords the anion (90).O3
3 Reactions of Dienes, Trienes, and Higher Polyenes Reviews have dealt with the selective isomerization of alkenes, dienes, and trienes with i n h r e d lasers,64 and with the photochemical reactivity of c u m u l e n e ~ . ~ ~ The formation of 3-anilinoalkenes (91) results on irradiation of acetonitrile solutions of cyclohexa-1,3-diene and aniline or N-methyl aniline. Similar addition occurs with the
IIIJ3: Photochemistry of Alkenes, Alkynes and Related Compounds
Me@MeMe
M e , & Me. ; Me
Me
Me M
Me
R'
'
hie
Me
e
e
i
i
Me
Me
Me
H (77) a; R' =Me, E!, Pr', R 2 = H b; R' '= H, R 2 = M e , Et, Pri
..
V
(78)
H (79)
Me
(80) a;
R' =CF3, R 2 = H ( D )
b;
R' =H(O), R2 =CF3
@+ H
H
H
hu
v 254 nm
C6H6
Me
( 7 6 ) R = Et or Pr'
(75 1
(74)
e
Meg
Me
Me@--R2
249
el + & ti
Scheme 7
H
250
Photochemistry Ph Ph
Ph Ph-
Ph
= -Qh Ph
Ph
( 8 4 ) a; R = Ph
b; R = H
(86 1
Ph ( 8 5 ) a; R = Ph
b ; R = H
Ph Scheme 8
Me
the
Ar
(87)
RL
(88)
Ph
(89) a; R' = CH=CH,, R 2 = Me, H b; R' = Ph, R z = H
Ph
H
H
I
R ( 90)
= H , Me
(91) R
(92)
Ph
Ar
OCOPh
(93) R = H Me
( 94)
0
(95)
11113: Photochemistry ofAlkenes, Alkynes and Related Compounds
251
same amines and 2,5-dimethyI hexa-2,4-diene. Alkyl amines and tertiary aniline derivatives do not undergo addition. An electron transfer mechanism is thought to be operative.? Reynolds and Bauld have studied the electron transfer reaction of the cyclohexa-l,3-diene / 1,Cdicyanobenzene system. The back electron transfer from the dicyanobenzene radical-anion to the diene radical- cation results in the formation of the diene triplet state. The outcome of the reaction was studied by product analysis."l The wavelength (185-254 nm) dependent photochemistry of cyclo-octa- and cycl-hepta-l,3-dienes has been studied68 cis,cis -Cyclohepta-1,3-diene is converted to the trans -cis -isomer (92) when irradiated in a matrix at low temperature. On warming this intermediate ring closes to afford to temperatures above -78OC bicyclo(3,2,0)hept-6ene, the same product obtained by irradiation at room temperature.6' The ionone series of compounds has been fruitful for Jeger and his coworkers. The area is clearly not exhausted and they have studied the behaviour of the epoxy dienes (93) under acetone-sensitized i r r a d i a t i ~ n . ~ ' , ~ Irradiation' ~ of the enol benzoate (94) in the presence of acid yields the isoquinolinone (95) in good yield by a mechanism involving cyclization, elimination and ~xidation.~' Matrix-isolated diene (96) undergoes photochemical transformation into the isomeric compounds (97) and (98) as the primary photo product^.^^ Maier and his coworkers have observed the photoisomerization of the cyclobutadiene dimer (99) into the pentacyclic compound The U.V. irradiation of the Dewar benzene (101) affords the paracyclophane (102, 13%).75 The prismane (103) can be produced by the irradiation of the Dewar benzene (104). The intermediacy of the benzene (105) in the transformation is likely.76 Considerable attention has been focussed, in the past year, on the photochemical transformation of steroidal dienes. Several of these reports have been lodged as patents. Thus the irradiation of the androstadienediols (106) brings about ring opening and the formation of the triene isomer (107).77 The conversion of the diene (108) to the open chain triene (109) yields a product used in enzyme immunoassay procedures.78 Irradiation of the provitamin D derivatives (110) at 254-300 nm and 310-350 nm gives the previtamin D derivatives (111) in 85% yield. This product is accompanied by small ~ (112) yield the trienes (113) amounts of tachysterols and l u m i ~ t e r o l s . ~Androstadienes and (114) on irradiation." Dauben et af. have reported the synthesis of 6-fluoro vitamin D, by a sequence involving the photoisomerization of the dehydro- cholesterol (115) to the previtamin D, (116).81 An antimony-doped lamp can be used in the preparation of the lumisterols by the photoisomerization of 7-dehydrocholesterol.'' Irradiation of hydroxypyrylium cations (117) in sulphuric acid brings about photo-transposition. The yield of the rearranged products (118) and (119) is dependent
Photochemistry
252
(97 1
(90)
(100)
(99)
"2*
M
e
O
2
H
eC 0 2 M e
But
BU'
C02Me C02M e
But BuJ%
BU'
C02Me
BU'
(104)
(103)
HO
d
(105)
& \" p 2
HO
(107)
f
CO2 H
253
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
(110) R 1 =
H, alkyl, acyl, trialkylsilyl R 2 = H, HO, acyloxy, alkoxy, trialkylsiloxy R3 = CH=CHCHMeCHMez, CHzCH2CH2CHMc2
C02 H
(109)
R'O (111 1 Me
Me
02CBu'
AcO (112 1
AcO
-
iso-octy I
HO
@ F (115 1
is? octyl
@ F
(116)
Photochemistry
254
OH
Me
Scheme 9
Me Me
R3
CO2Me (128)
$-R -2-
R3
Me
R! =C02Me, R2 =H, R3 =Me ( 5 4 : 4 6 ) R' =C02Me, R 2 =H, R3 =But ( 3 5 : 6 5 )
R ' =CC+H, R 2 =H, R3 =Me ( 5 6 : 4 4 )
C02Me (129)
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
255
upon the concentration of the acid with transposition products predominant in 100% sulphuric acid and at a minimum in 50% sulphuric acid. At these lower concentrations of acid the ring contraction product (120) is formed to ca. 100%. At O°C in 50% sulphuric acid the cyclopentenone diol (121) is produced from the irradiation of pyrylium salt (122). Product (121), at higher temperature, thermally rearranges to the acetyl furan (123). This route to the ring contracted products is operative in all the pyrylium salts studied.83 Several products are obtained on irradiation (at 254 or 300 nm) of thymol in trifluoro methane sulphonic acid. The analysis of the mixture indicates that four competitive paths are operative involving the ions (124) and (125) formed by protonation of the phenol in its excited state. The isolation of umhiiulone (126) from this complicated mixture of products is of interest and arises by a cross-conjugated dienone type A rearrangement as shown in Scheme 9.84 Other references describing the rearrangement of cross-conjugated cyclohexadienones can be found in Part 111, Chapter 2, Section 4 of this volume. A study of photochemical 1,7-hydrogen migrations. within the cycloheptatriene derivatives (127) has been reported.85 Hansen and his coworkers have demonstrated that irradiation of the heptalenes (128) brings about reversible isomerization into a mixture of isomers composed of (129) and starting material (128). To some extent, the ratio of photo-product : starting material is dependent upon the substitution as indicated by the yields shown under the appropriate structure.86 Laaxhoven et a/. report that irradiation of (130) in methanol or hexane yields (131) by the route illustrated in Scheme A mechanism involving radicals is proposed to for the transformation of P-methyl-2-vinyl stilbene into account 1-(l-indany1)-l-phenylethene on irradiation.88 Calculations have been carried out in an analysis of the photo isomerization of naphthvalene into na~hthalene.~’Photocyclization of the 2-vinylbiphenyls (132) under both direct and xanthone-sensitized irradiation conditions has been studied.” The tetraene (133) is isomerized into (134) on irradiation?’ Tochtermann et a/. have reported the photochemical conversion of the oxepine derivatives (135) into the tricyclic aldehydes (136).”
4 (2f2) Intramolecular Additions Cristol has published a short review of the syntheses of quadri~yclanes?~The photochemical cyclization of norbornadiene to quadricyclane has been achieved using acridinones and benzo-fused acridinones as sensitizers. The reaction is thought to involve an exciplex between the sensitizer and the norbornadiene.% The photoformation of quadricyclanes from norbornadienes is still one of the main approaches by organic photochemists to a workable sunlight energy storage system. Research has continued on this in the past year as seen by the several patents which
Photochemistry
256
have been lodged dealing with this process such as the synthesis of some norbornadienes of use in energy storage photocyclizations to quadricylanes has been patentedg5 A patent has been lodged dealing with the formation of the quadricyclanes (137) by irradiation of the norbornadiene derivatives (138) using acetophenone sensitization.% Novel examples, using intramolecular sensitization, have also appeared involving the norbornadiene/benzophenone derivatives (139) 97 and (140). This latter cyclization is of interest since it can be brought about in high yield by solar irradiati~n.'~ Solar irradiation is also effective in the formation of the quadricyclane (141) from the corresponding norbornadiene. Again the chemical yields are high." The photocyclization of other norbornadienes (142)loo and (143)lo' also yield the corresponding quadricyclanes.
A detailed study of the photochemical cyclization of norbornadiene to quadricyclane The quadricyclane (144) is using aryl phosphine copper(1) halides has been reported."' formed on irradiation of the norbornadiene (145) at 366 nm. The quantum yield (0.68) for the process is high. The influence of triplet sensitizers ( metal complexes, biacetyl = 0.1). The authors suggest that and acetophenone) were found to be less efficient ( the lowest singlet state of norbornadiene is much more reactive than the triplet ~tate.1'~
+
Both the acid induced and the photochemical rearrangement of the norbornadiene derivative (146) affords the hydroxynaphthalene (147). The photo-process is not affected by triethylamine and it is thought to involve benzylic-allylic G O bond cleavage. No evidence was put forward for the intermediacy of a q~adricyclane.~'~ Prinzbach and his coworkers have reported the synthesis of the oxanorbornadienes (148) and their photoconversion into the corresponding oxaquadricyclane derivatives (149) on irradiati~n."~ The azaquadricyclanes (150) have been prepared by the irradiation of the corresponding norbornadiene derivatives (151).lO6 Xanthone-sensitized irradiation of the triene (152) affords the cage compound (153) which can be converted into the benzene dimer (154) by treatment with t-butyl 1ithi~m.l'~ A synthesis of pentaprismane (155) has been developed using the photochemical ring closure of (156) to the cage compound (157) as the key step. This compound (157) can be readily converted to the corresponding ketone (158) which was elaborated to yield pentaprismane."' The cage photoproduct (159) is formed efficently (98%) by acetone- sensitized cyclization of the bis -alkene (16O).lm Paquette et a/. have synthesized the highly strained cage compound (161) by acetone-sensitized cyclization of the diene (162).110 Compound (163) is formed on irradiation of the pentaene (164) establishing the syn-arrangement of the two dicyano-alkene moieties."' In connection with cage compounds Prinzbach et a/. have also studied the photoequilibrium in the diary1 systems (165).l12 Interest in the photochemical additions in constrained systems has continued and Prinzbach and his collaborators have reported
257
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
hu
(1301
(131 1 Scheme 10
(133)
(134)
(132) n = 1 - 4
G!Yo-o-"ph ( 139 1
(140)
258
Photochemistry
(142) R' and R4- R*
= ti, alkyl, a r y l
( 1 4 3 ) R' =Ph,COZEt R2 = M e , H R3 = M e , P h
& RR (148) R = H, CF3,0Me, COZMe
R'
R
& '(149)
(151)
(150) R2
R3
R4
H H COzMe COZMe
p-TOS
H
H
p -TOS
H
CI
H CI CH20CH2CSCH H H COzCHzCH=CHz H p -TOS p-Tos
COzMe
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
259
that the direct and acetone-sensitized irradiation of the imine (166) results in the formation of the cage structure (167).l13 Both direct and acetophenone-sensitized irradiation of the diene lactones (168) have been carried out. In the direct irradiation, three reactions occur in competition namely decarbonylation, cyclization, and the formation of the bicycloheptenones (169). Triplet sensitized irradiation yields the bicycloheptenones (169) exclusively. The cyclization of (168~)to (169c) is in competition with phenyl migration processe~."~ Salomon and his coworkers have over the years studied the influence of copper(1) triflate on the cyclization of non-conjugated dienes. In the present example the diene (170) is converted readily on irradiation in the presence of the catalyst and affords the alcohol (171). This is oxidised to the corresponding ketone.ll5 The intramolecular cyclization of the diene (172), using a copper triflate catalyst, affords the straight (2+2) adduct (173). This cyclization was used as an approach to the synthesis of Robustadial B. However, it was shown that the proposed structure of the natural product was wrong and that the robustadiah should have the camphane moiety in their structure as shown in (174).'" A mechanistic study of the (2+2)-cycloaddition reaction of the dicinnamates (175) has been reported.'"
5 Dimerization and Intermolecular Cycloadditions Acrylonitrile and methyl acrylate can be dimerised to afford trans - 1,2-cyclobutanes using (ethylene) bis -(triphenylphosphine) nickel or bis -(triphenylphosphine) Photodimerization of the coloured styrylpyrylium nickelacyclopentane as the salts (176) and (177) in the crystalline state has been reported.'" The (2+2)-photocycloadditions of 4-dimethylaminostyrene with other styrenes has been examined.12' A theoretical investigation of the mercury sensitized (2+2)-additions of penta-lY4-dienes and hexa-1,Sdienes has been reported.12' Irradiation of the cyclohexadiene / zeolite / methylene chloride system yields a mixture of the two Diels-Alder dimen, (178) and (179), of cyclohexadiene.122 Photochemical addition of alkenes to C=N systems has been studied and interpreted by means of perturbation MO theory.la3 (2+2)-Cycloadducts (180) and (181) are formed on irradiation of the isoxazoline (182) in the presence of indene.la4 The dimerization of acenaphthylene yielding head to head and head to tad dimers is dependent on the polarity of the solvent in which the irradiation is carried out. Mayer et a/. report that the dimerization in micelles produces the same ratios of products to those obtained from reaction in polar s01ution.l~~
Photochemistry
260 H
2%
Ph -/-0
0 4 - p
M
~
(159 1
NC NC’ N*
0
6
0
(160 1
CN
(163)
e
261
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
R2
0
(168) a ; R' = R Z = Me b ; R' = H, R2 = Pr' c ; R' = H o r M e , R 2 = P h
(167)
Go 2:: OH
H
(169)
(171 1
(170)
OMe CHPr'OH
Me0
Me0
OMe (172)
OMe (173)
OH
CH-Pr'
HO Me
Me Me
Photochemistry
2 62
Ar
Bu'
(175) R' = R 2 = H R1 = W e , R * = H R1 = H , R 2 = O M e n = 3 , 1 , 5 or 6
Ph
H
(1 79)
H
(181) a; 11 % b; 4%
(180) a; 64'10 b; 57'10
(182) a; Ar = 4-CNC6H4 b ; Ar = 4-CsHhC02Me
-
(183 ) R = 1 naphthyl , 9- phenanthryl
/SiMe3
IIIN: Photochemistry of Alkenes, Alkynes and Related Compounds
263
6 Miscellaneous Reactions Salt effects ( addition of lithium tetrafluoroborate and magnesium perchlorate) have been evaluated in the photochemical electron transfer reaction between 9,10-dicyanoanthracene and 1,2-bis -(Qmethoxyphenyl) cyclopropanes.12' Direct irradiation of the cyclopropanes (183) results in fission into alkene and dimethylcarbene as the minor reaction path. The major process encountered is ring opening to afford a butene d e r i ~ a t i v e . ' ~ ~ Adam and his coworkers have carried out a detailed study of the irradiation of cyclobutene, bicyclo(l.l.0)butane,128 and of bicyclo(2.l.O)pentane at 185 nm.12' The influence of electron transfer reagents on the photochemical behaviour of cis -1,2-diphenylcyclobutane has been assessed. In the main, the photoreactions give styrene, tram -1,Z-diphenyl cyclobutane, and l-phenyltetralin. However, change of solvent from benzene to acetonitrile leads to a decrease in the quantum yields and a diminished yield of the tetralin.13' Selective bond fission has been reported in the photoinduced electron transfer reactions of the cyclobutanes (184).131 The behaviour of the cation radicals derived from bicyclobutane systems has been under intensive study by Gassman and his coworkers. Currently they have observed that the substituted derivative (185) photorearranges in good yield, using l-cyanonaphthalene as the electron acceptor, to the isomer (186). Although this product can be synthesized independently by the photocyclization of the diene (187) the authors argue that this route is not in operation. The formation of the product (186) follows the one electron transfer path with subsequent rearrangement within the radical cation ( I M ) . ' ~ ~ The photochemical reactivity of the epoxides (189) and ( 1 9 0 ) ~ and ~ ~ (191)134 have been studied. A detailed examination of the photo-ring opening of the epoxides (192) Laser flash photolysis of to yield carbonyl ylides has been reported by George et the epoxide (193) has been carried out and a study of the resultant ylide has been r e ~ 0 r t e d . l ~ 'The related spirooxaziridines (194, 195) are also photoreactive and yield the lactams (196, 197).137 Irradiative (185 nm) conversion of the dihydrofurans (198) affords the cyclopropyl aldehydes (199).138 The photochemical fragmentation of the adduct (200) yields benzene and the photolabile dimer (201) which can also be converted into benzene on further irradiation. 13' Mariano has used his iminium salt approach as part of a synthesis of erythrina alkaloids as outlined in Scheme ll.'*'
264
Photochemistry
(192) R' =
R2 = H = H; R 2 = OMe,Me R1 = Me, OMe,CN; R2 = H R 1 =CN; R 2 = OMe R1
(195)
265
lIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
Rge
a R M e
Me
A
R'2
1198) R = C02Mc,
(199) R ' = CHO; R2:H
CH(OMe),
R' = H;
R2 = CHO
Me0
Meo%vc%Et TMs
Scheme 11
QX
X
(203) a; X = I b; X = Br
OMe ( 204)
Photochemistry
266
Davidson et a/. have reviewed the photochemistry of aryl halides.141 The corresponding ethers and carbinols are formed from the irradiation of 2-phenyl ethylbromide in the lower alcohols.142 A study of the photochemical debromination of meso -1,2-dibromostilbene in multiphase systems has been r e ~ 0 r t e d . l ~ Interest ~ in the generation of vinyl cations by irradiation of vinyl halides and related compounds has received sporadic attention over the years. In the present report Sonawane et al. have compared the photo behaviour of the dihalides (202a,b) with the mono halides (203a,b). Thus the irradiation of (202a) in methanol affords the ether (204) and the mono halide
(203a). Mono halide (203a) can be converted into the hydrocarbon (202c) on further irradiation. Lowering the temperature of the irradiation enhanced the formation of the product (204) from the ionic reaction path but suppressed this type of reactivity in the dibromo compound (202b). Interestingly no products of ionic reaction . were obtained from the irradiation of the mono halides (203)either at room temperature or at -20°C.'44 Irradiation of cyclohexyl iodide in the presence of aromatic compounds affords products of aromatic cyclohexylation by a process involving the cyclohexyl cation.14'j Cristol has continued his studies on the photo- Wagner-Meerwein processes in compounds of the type shown in (205). In this instance the influence of aryl substitution was examined.146 Other studies have reported the photochemical behaviour of the dibenzeoctadiene (206)14' and the octadienes (207).148 The photochemical reported. 14'
behaviour
of
2-aryl-1,3-diphenyl propenyl anions
(205) a; R' = CI, RZ = CI, methylsulphmy or acetoxy, R 3 = H or OMe b; R1 = H, R3 = MeO, R 2 = CI, ace t oxy or me thy lsul phoxy
&J I
(206)
has
been
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
267
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Photochemistry
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R. Ahmed-Schofield and P. S. Mariano, J. Org. Chem., 1985, 50, 5667.
141. R. S. Davidson, J. W. Goodin, and G. Kemp, Adv. Php. Org Chem., 1984, 20, 191. 142. V. K. Bhalerao, B. S. Nanjundiah, H. R. Tetrahedron, 1986, 42, 1487. 143.
Sonawane, and P. M. Nair,
R. Maidan and I. Willner, J. Am. Chem. Soc., 1986, 108, 1080. D. Panse, Tetrahedmn Lett.,
144. H. R. Sonawane, B. S. Nanjundiah, and M. 1985, 26, 3507. 145.
M. Kurz and M. Rodgers, J. Chem. Soc.,Chem. Commun., 1985, 1227.
146. S. J. Cristol and E. 0. Aeling, J. Or8 Chem., 1985, 50, 2698. 147. S. J. Cristol and R. J. Opitz, J. Org. Chem., 1985, 50, 4558. 148. S. J. Cristol, R. J. Opitz, and E. A. Aeling, J. Org. Chem., 1985, 50, 4834. 149. L. M. Tolbert and M. Z. Ali, J. Or8 Chem., 1985, 50, 3288.
Photochemistrv of Aromatic Comnounds BY A. GILBERT Photo-induced c h e m i c a l change o f a r o m a t i c chromophores c o n t i n u e s t o be w i d e l y s t u d i e d and as i n p r e v i o u s y e a r s , t h e a r e a s of s u b s t i t u t i o n and c y c l i z a t i o n p r o c e s s e s a t t r a c t t h e g r e a t e s t i n t e r e s t . The r e a c t i o n s of ground s t a t e a r e n e s w i t h p h o t o g e n e r a t e d r a d i c a l s are o u t s i d e t h e p r e s e n t s c o p e b u t i n t r a m o l e c u l a r c y c l i z a t i o n s r e s u l t i n g from t h e l o s s o f h a l o g e n a c i d are c o n s i d e r e d h e r e as t h e s e p r o c e s s e s have s y n t h e t i c a p p l i c a t i o n s and are complementa r y t o t h e o x i d a t i v e c y c l i z a t i o n s described i n Section 4 of t h i s Chapter. Few r e v i e w s have a p p e a r e d d u r i n g t h e y e a r b u t L a b l a c h e Combier h a s d i s c u s s e d t h e photo-induced r e a r r a n g e m e n t , a d d i t i o n , s u b s t i t u t i o n , d i m e r i z a t i o n , and c y c l i z a t i o n r e a c t i o n s of t h i o p h e n e s i n a u s e f u l and w e l l - r e f e r e n c e d a r t i c l e . 1 1 Isomerization Reactions The p h o t o c o n v e r s i o n of 9 - t - b u t y l a n t h r a c e n e t o i t s Dewar i s o m e r (1) c o n t i n u e s t o a t t r a c t a t t e n t i o n and R u s s i a n w o r k e r s r e p o r t t h a t a l t h o u g h t h e f l u o r e s c e n c e o f t h e a n t h r a c e n e i s quenched by a n i l i n e and P J , g - d i m e t h y l a n i l i n e , t h e quantum y i e l d o f i t s p h o t o i s o m e r i z a t i o n i s u n a f f e c t e d . 2 From t h e s e o b s e r v a t i o n s i t i s deduced t h a t t h e f o r m a t i o n of (1) o c c u r s from a n o n - r e l a x e d Franck-Condon s t a t e . I t i s of i n t e r e s t here t o n o t e t h a t t h e r e v e r s e process of photoi n d u c e d c o n v e r s i o n o f D e w a r isomers t o a r e n e s h a s been u s e d t o s y n t h e s i z e C51 p a r a c y c l o p h a n e which i s t h e s m a l l e s t p a r a - b r i d g e d 3 compound s o f a r r e p o r t e d . I t was r e p o r t e d l a s t y e a r t h a t Dewar t h i o p h e n e c o u l d b e t r a p p e d a s i t s f u r a n a d d u c t from room t e m p e r a t u r e i r r a d i a t i o n e ~ p e r i m e n t s ,b~u t t h a t t h e c o r r e s p o n d i n g a d d u c t from Dewar f u r a n w a s not obtained. F u r t h e r e x p e r i m e n t s i n v o l v i n g i r r a d i a t i o n of t h i o p h e n e and f u r a n i n a r g o n matrices a t 1 0 K have, however, p r o v i d e d i n f r a r e d s p e c t r o s c o p i c e v i d e n c e f o r t h e f o r m a t i o n of b o t h Dewar isomers:6 a l l e n e s and c y c l o p r o p e n e s a r e a l s o formed, t h e l a t t e r by p h o t o r e a r r a n g e m e n t o f t h e Dewar isomer a t w a v e l e n g t h s l o n g e r t h a n 320 nm. Although n e i t h e r g- n o r 3-(trimethylsily1)pyrroles undergo p h o t o r e a r r a n g e m e n t r e a c t i o n s , i r r a d i a t i o n o f t h e 2- i s o m e r i n deg a s s e d p e n t a n e g i v e s an 84% y i e l d of t h e 3- i ~ o m e r . The ~ process
273
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274
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IIIl4: Photochemistry of Aromatic Compounds
275
is reasonably interpreted in terms of the photoformation of the Dewar isomer ( 2 ) which undergoes a 1,3-shift followed by ring opening. Since 1973 several accounts have appeared which describe the phototransposition reactions of 4-hydroxy- to 2-hydroxy-pyrylium cations.8 It is now reported that those cations which undergo this isomerization in concentrated sulphuric acid yield ring contraction products when the reaction is carried out in 50% sulphuric acid. 9 At O°C the initial product of irradiation of the 2,3-dimethyl cation (3) is the 4,5-dihydroxycyclopent-2-enone (4) which can be isolated following neutralization, At higher temperatures a secondary acid catalyzed thermal process of ( 4 ) occurs to give acetylfurans (5). Within the year, two groups have reported on the photochemical transformations of phenols and one of these studies has led to a one-step synthesisof umbellulone (6) from thymol (7) albeit in only The reaction is carried out in trifluoromethanesul10% yield.'' phonic acid solution with either 254 or 300 nm radiation and gives nine products as well as ( 6 ) . From characterization of eight of the products, four competing photoprocesses are deduced to operate for protonated thymol: these involve rearrangement to (6), formal C2 + C3 transposition giving ( 8 ) , intermolecular transalkylation to yield the di-isopropylphenols (9), (10) and (11) and formation of piperitenone (12) by hydrogen abstraction. Other workers have examined the photoreactions of dichloromethane solutions of complexes of methyl substituted phenols with aluminium The position of the methyl groups on the phenol deterbromide." mines whether the oxonium (13) or 0x0 (14) complex will be favoured in the equilibrium and only the latter species undergo photoisomerization. The initial product is a complexed bicyclor3.1.Olhexenone which can be hydrolized to give (15) or undergo further photoreaction to give an isomeric phenol. The photoisomerization also occurs under heterogeneous conditions and irradiation of a stirred slurry of aluminosilicate in 2,3,5,6-tetramethylphenol solution leads to the formation of 2,3,4,6-tetramethylphenol. The bicyclic ketones were, however, only observed in the presence of aluminosilicate in the absence of solvent. It is of interest to note here that irradiation between 280-350 nm of the anionic form of 2chlorophenol induces an efficient ring contraction and the fornThe reaction has been - ation of cyclopentadiene carboxylic acids.12
276
Photochemistry R
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IIIl4: Photochemistry of Aromatic Compounds extended t o s u b s t i t u t e d 2-chlorophenolates
277 and d i - and t r i - c h l o r o -
p h e n o l a t e s a n d a l s o o c c u r r e d i n n e u t r a l s o l u t i o n b u t i n t h i s case p h o t o h y d r o l y s i s t o form, f o r example, c a t e c h o l from t h e 2-chloro compound, a l s o o c c u r s . E a c h y e a r t h e r e a p p e a r r e p o r t s o f p h o t o r e a c t i o n s of aromatic Such compounds w h i c h o c c u r via n o n - a r o m a t i c i n t e r m e d i a t e s . rearrangements and p h o t o e n o l i z a t i o n o f r e a c t i o n s as di-n-methane aromatic c a r b o n y l compounds are c o n s i d e r e d e l s e w h e r e i n t h i s Volume a n d t h e l i t e r a t u r e c i t e d h e r e is i n t e n d e d t o e x e m p l i f y o t h e r t y p e s The p h o t o i s o m e r i z a t i o n o f 2 , 2 - d i p h e n y l - 1 , 4 , 4 o f process. triphenyl-3-azabut-3-en-l-one ( 1 6 ) t o ( 1 7 ) a n d (18) i s c o n s i d e r e d t o p r o c e e d by a 1 , 5 - m i g r a t i o n t o y i e l d ( 1 9 ) a n d t h e n c e t h e nonaromatic i n t e r m e d i a t e ( 2 0 ) , l 3 a n d i r r a d i a t i o n of 5 - c h l o r o - l , 4 dihydro-9-methylnaphthalen-l,4-imine (21) i n cyclohexane, y i e l d s 22% l - c h l o r o n a p h t h a l e n e a n d 1 0 a n d 12% r e s p e c t i v e l y o f t h e i s o m e r i c d i h y d r o c y c l o b u t Cbl i n d o l e s ( 2 2 ) a n d ( 2 3 ) . l4 The n o n - a r o m a t i c i n t e r m e d i a t e ( 2 4 ) is s u g g e s t e d i n t h e l a t t e r r e a c t i o n a n d t h i s p r o c e s s c o n t r a s t s i n t e r e s t i n g l y w i t h t h a t r e p o r t e d f o r nonc h l o r i n a t e d d e r i v a t i v e s ( 2 5 ) which are r e p o r t e d t o g i v e ( 2 6 ) a s t h e major p r o d u c t . l5 S e v e r a l r e p o r t s f r o m C r i s t o l a n d c o - w o r k e r s d e s c r i b e t h e p h o t o r e a c t i o n s of v a r i o u s d e r i v a t i v e s o f 2 , 3 : 6 , 7 - d i b e n z o 16-20 bicycloC3.2.1locta-2,6-dienes a n d of s i m i l a r C 2 . 2 . 2 l o c t a d i e n e s . I n t r a m o l e c u l a r c y c l i z a t i o n t o g i v e non-benzenoid i n t e r m e d i a t e s is t h e k e y s t e p i n p h o t o Wagner-Meerwein r e a r r a n g e m e n t s of s u c h s y s t e m s a n d i n t h e u n p r e c e d e n t e d r e a c t i o n t o form p h e n a n t h r e n e s a n d 9,lO-dihydrophenanthrenes f r o m ( 2 7 ) .I6 The f o r m a t i o n o f t h e p h e n a n t h r e n e s i s a t r i p l e t s t a t e p r o c e s s a n d is promoted by t h e p r e s e n c e of a n u c l e o f u g a l g r o u p a t C-8. The mechanism i s c o n s i d e r e d t o i n v o l v e i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r from t h e e x c i t e d
s t a t e of a n aromatic r i n g t o t h e C - n u c l e o f u g a l bond t o f o r m a z w i t t e r i o n i c b i r a d i c a l which o n l o s s o f t h e n u c l e o f u g e y i e l d s t h e intermediates outlined i n ( 2 8 ) a n d h e n c e t h e p h e n a n t h r e n e &y Scheme 1. 2 Addition Reactions I t i s twenty y e a r s s i n c e t h e first r e p o r t s a p p e a r e d d e s c r i b i n g t h e i n t r i g u i n g p r o c e s s o f meta p h o t o c y c l o a d d i t i o n o f e t h y l e n e s t o t h e b e n z e n e r i n g which c o n v e n i e n t l y y i e l d s t h e d i h y d r o s e m i b u l l v a l e n e s k e l e t o n ( 2 9 ) .21 Numerous p u b l i c a t i o n s c o n c e r n e d w i t h b o t h t h e m e c h a n i s t i c a n d s y n t h e t i c a s p e c t s of t h e r e a c t i o n h a v e a p p e a r e d a n d w h i l e t h e l a t t e r h a v e b e e n , a n d c o n t i n u e t o he, over t h e years
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IIIi4: Photochemistry of Aromatic Compounds
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Photochemistry
e x p l o i t e d , t h e r e are s t i l l d e t a i l s o f t h e mechanism which r e m a i n t o b e c l a r i f i e d . D i f f e r e n c e s between a d d e n d i o n i z a t i o n p o t e n t i a l w ( A 1 . P . ) have i n t h e p a s t been used t o p r e d i c t p r e f e r r e d arenee t h y l e n e r e a c t i o n modes,22 b u t M a t t a y h a s now p r o p o s e d t h a t t h e f r e e e n t h a l p y o f e l e c t r o n t r a n s f e r (ACI) between t h e r e a c t a n t s p r o v i d e s a c o n v e n i e n t method w i t h f e w e r e x c e p t i o n s t h a n t h a t involving A 1 . P . f o r determining and r a t i o n a l i z i n g favoured pathw a y ~ .Thus ~ ~ f o r s y s t e m s i n which t h e e l e c t r o n t r a n s f e r becomes e x e r g o n i c , t h a t is t o s a y A G is l e s s t h a n 0 , t h e n s u b s t i t u t i o n i s p r e f e r r e d a n d c y c l o a d d i t i o n o c c u r s when AG i s g r e a t e r t h a n 0. T h i s s i t u a t i o n i s w e l l - i l l u s t r a t e d by t h e p h o t o r e a c t i o n s o f a , a , a - t r i f l u o r o t o l u e n e w i t h v a r i o u s d i o x o l e s and v i n y l e n e carbone x a m p l e , 2 5 4 nm i r r a d i a t i o n o f t h e a r e n e w i t h 2 , 2 , 4 , 5 a t e ~ .F o~r ~ d i m e t h y l - l , 3 - d i o x o l e ( A G < O ) y i e l d s t h e p r o d u c t o f s u b s t i t u t i o n by t h e e t h y l e n e a t t h e -CF3 g r o u p whereas w i t h v i n y l e n e c a r b o n a t e ( A G > O ) meta c y c l o a d d u c t s are t h e p r i n c i p a l p r o d u c t s . For addend p a i r s which h a v e AC_ a p p r o x i m a t e l y e q u a l t o 0 t h e p r o d u c t r a t i o i s m a r k e d l y i n f l u e n c e d by s o l v e n t p o l a r i t y a n d w h i l e t h e s u b s t i t u t i o n process is l a r g e l y u n a f f e c t e d t h e e f f i c i e n c y of c y c l o a d d i t i o n f a l l s a p p r e c i a b l y o n c h a n g e from c y c l o h e x a n e t o a c e t o n i t r i l e as t h e s o l v e n t . F u r t h e r , from examination o f a c o n s i d e r a b l e range o f a r e n e - e t h y l e n e s y s t e m s i t i s n o t e d t h a t a s t h e A G v a l u e between t h e a d d e n d s i n c r e a s e s t h e n t h e r a t i o o f meta t o o r t h o c y c l o a d d i t i o n a l s o i n c r e a s e s 2 5 b u t i t i s e v i d e n t from t h e s e a n d p r e v i o u s s t u d i e s o n t h i s a s p e c t of t h e s e p h o t o c y c l o a d d i t i o n r e a c t i o n s t h a t n e i t h e r A 1 . P . n o r a b s o l u t e v a l u e s o f AG_ c a n p r e d i c t s u c h r a t i o s f o r a l l systems and a u n i v e r s a l l y a p p l i c a b l e measure o f t h e p o l a r f a c t o r s s t i l l a w a i t s d i s c o v e r y . Over t h e y e a r s , s e v e r a l mechanisms h a v e b e e n c o n s i d e r e d f o r t h e meta p h o t o c y c l o a d d i t i o n b u t t h a t which seems t o r a t i o n a l i z e a l l t h e e x p e r i m e n t a l r e s u l t s i n v o l v e s t h e i n t e r m e d i a c y o f t h e s p e c i e s ( 3 0 ) a s t h e immediate adduct p r e c u r s o r and a t l e a s t i n t h e case o f t h e a d d i t i o n s of d i o x o l e s t o b e n z e n e a n d t o l u e n e t h i s i n t e r m e d i a t e r e s u l t s from c o l l a p s e o f a n S1 a r e n e - S o e t h y l e n e e x c i p l e x . 2 6 I n a n a t t e m p t t o g a i n f u r t h e r i n f o r m a t i o n o n which bond ( s ) i n t h e meta c y c l o a d d u c t i s ( a r e ) formed i n t h e p r i m a r y s t e p , and which bond f o r m a t i o n is r a t e d e t e r m i n i n g , C o r n e l i s s e and co-workers have measured deuterium i s o t o p e e f f e c t s on t h e r e a c t i o n o f t o l u e n e and a n i s o l e w i t h c y c l o p e n t e n e . 27 R e p l a c e m e n t o f m e t h y l h y d r o g e n by d e u t e r i u m g i v e s e f f e c t s which are i n a g r e e m e n t w i t h t h e a b o v e g e n e r a l mechanism b u t
IIIl4: Photochemistry of Aromatic Compounds
28 1
t h e a u t h o r s n o t e t h a t normal e f f e c t s o b s e r v e d w i t h 3,5- a n d 2 , 6 -
d e u t e r a t i o n of t h e a r e n e c a n n o t be r e a d i l y e x p l a i n e d , I t i s , however, deduced t h a t s i n c e t h e s e e f f e c t s c a n be measured i n intermolecular competition experiments, t h e formation o f t h e cyclop r o p a n e r i n g i n t h e i n t e r m e d i a t e species ( 3 0 ) i s t h e r a t e d e t e r m i n i n g s t e p . The e x t e n t o f p o l a r i t y i n t h e r e a c t i o n i n t e r m e d i a t e ( 3 0 ) \and i n d e e d e v i d e n c e f o r i t s i n v o l v e m e n t i n t h e r e a c t i o n , are p o i n t s o f c u r r e n t c o n c e r n . The r e g i o c h e m i s t r y o f t h e a d d i t i o n o f c y c l o p e n t e n e t o 3- a n d 4 - c y a n o a n i s o l e s i s r e p o r t e d t o be c o n s i s t e n t w i t h a mechanism i n v o l v i n g a d i p o l a r s p e c i e s and i n t h i s same a c c o u n t it is a l s o n o t e d t h a t p o s i t i o n a l a d d u c t i s o m e r s c a n be both thermally a n d p h o t o c h e m i c a l l y i n t e r c o n v e r t e d : 28 t h i s makes mechani s t i c d e d u c t i o n s based o n p r o d u c t r a t i o s from G . C , a n a l y s i s a n d / o r from p r o l o n g e d i r r a d i a t i o n somewhat d u b i o u s . For example, t h e isomers (31) and ( 3 2 ) i n t e r c o n v e r t by a n e t h e n y l c y c l o p r o p a n e c y c l o p e n t e n e r e a r r a n g e m e n t and t h e e q u i l i b r i u m p o s i t i o n f a v o u r s t h e f o r m e r isomer t h e r m a l l y and t h e l a t t e r p h o t o c h e m i c a l l y . Such p r e v i o u s l y u n r e c o g n i s e d l a b i l i t i e s o f meta p h o t o c y c l o a d d u c t s may well a c c o u n t f o r t h e r e p o r t t h a t t h e r e l a t i v e y i e l d s o f t h e p a r a a n d meta a d d u c t s (33) and ( 3 4 ) r e s p e c t i v e l y from c y c l o n o n a - 1 , 2 ~ ~ the d i e n e and benzene a s d e t e r m i n e d by n . m . r . s ~ e c t r o s c o p yare r e v e r s e o f t h o s e based on G.C. a n a l y s i s . 30 The s t e r e o c h e m i s t r y of t h e meta a d d u c t s from i r r a d i a t i o n o f a n i s o l e a n d benzene w i t h 2-methyl-1,3-dioxole are s i m i l a r l y i n t e r p r e t e d i n terms of p o l a r i t y w i t h i n t h e i n t e r m e d i a t e ( 3 0 ) . 3 1 The predominance o f t h e exo a d d u c t s (35) from b o t h s y s t e m s is c o n s i d e r e d t o r e f l e c t t h a t r e p u l s i o n between t h e n e g a t i v e l y c h a r g e d p - o r b i t a l s o f t h e d e l o c a l i z e d a l l y l i c s y s t e m i n (30) and t h e o r b i t a l s o f t h e oxygen i n h i b i t s a n endo a p p r o a c h o f t h e addends. The a u t h o r s a l s o n o t e t h a t by t h e t i m e t h e o r i e n t a t i o n of t h e addend i s d e t e r m i n e d , t h e d i p o l a r c h a r a c t e r of t h e 6-membered r i n g i s a l r e a d y d e v e l o p e d . A p r e v i o u s a t t e m p t t o g e n e r a t e a r a d i c a l s p e c i e s ( 3 0 ) by a n i n d e p e n d e n t thermal r o u t e was u n s u c c e s ~ f u lb~u t~ i t is now r e p o r t e d t h a t d i r e c t and s e n s i t i z e d i r r a d i a t i o n o f t h e a z o compounds (36) and ( 3 7 ) which are r e s p e c t i v e l y formed from t h e meta p h o t o c y c l o a d d u c t s ( 3 8 ) and (39) of c y c l o p e n t e n e and m_-xylene, y i e l d s t h e two meta c y c l o a d d u c t s i n t h e same r a t i o a s t h a t o b s e r v e d i n t h e p h o t o a d d i t i o n r e a c t i o n . 3 3 T h i s r e s u l t i s s u p p o r t e d by t h a t from t h e c y c l o p e n t e n e - 2 - x y l e n e s y s t e m and h e n c e t h e s e d a t a are c o n s i d e r e d t o p r o v i d e direct e v i d e n c e f o r t h e i n t e r m e d i a c y o f t h e b i r a d i c a l
Photochemistry
282
(37)
(40)
9" i
(231
(44)
(45)
I (46)
(47)
(48)
IIIl4: Photochemistry of Aromatic Compounds
283
s p e c i e s i n t h e meta p h o t o c y c l o a d d i t i o n p r o c e s s . D e t a i l s of t h e H ' n.m.r. s p e c t r a l d a t a o f t h i r t y meta p h o t o c y c l o a d d u c t s o f 34 benzenoid compounds and e t h y l v i n y l e t h e r have been p u b l i s h e d : t h e s e d a t a w i l l be much a p p r e c i a t e d by o t h e r w o r k e r s i n t h i s a r e a . Wender and co-workers c o n t i n u e t o make e l e g a n t s y n t h e t i c u s e o f t h e i n t r a m o l e c u l a r meta p h o t o c y c l o a d d i t i o n o f p h e n y l e t h e n y l non-conjugated b i c h r o m o p h o r i c s y s t e m s and t h i s y e a r d e s cribe t h r e e such a p p l i c a t i o n s o f t h e r e a c t i o n . The s y n t h e s i s o f ( + ) - s i l p h i n e n e ( 4 0 ) , t h e f i r s t member of a new f a m i l y of t r i q u i n a n e n a t u r a l p r o d u c t s , h a s been a c h i e v e d i n t h r e e s t e p s and i n v o l v e s t h e i n t r a m o l e c u l a r p h o t o c y c l o a d d i t i o n o f t h e bichromop h o r e (41) a s t h e k e y r e a c t i o n . 3 5 I r r a d i a t i o n of ( 4 1 ) i n p e n t a n e y i e l d s ( 4 2 ) and ( 4 3 ) i n a 1:l r a t i o by t h e two p o s s i b l e modes of c y c l o p r o p a n e f o r m a t i o n i n t h e i n t e r m e d i a t e s p e c i e s ( 4 4 ) and as f o r some o t h e r s y n t h e t i c a p p l i c a t i o n s of t h i s r e a c t i o n o n l y one i s o m e r , i n t h i s case ( 4 2 ) , h a s t h e r e q u i r e d s t r u c t u r e f o r e l a b o r a t i o n t o t h e t a r g e t compound. C o n t r o l o v e r t h e d i r e c t i o n of c y c l o p r o p a n e f o r m a t i o n i n meta p h o t o c y c l o a d d i t i o n would d o u b t l e s s improve t h e a c c e p t a b i l i t y o f t h e p r o c e s s as a s y n t h e t i c p r o c e d u r e p a r t i c u l a r l y f o r a s y s t e m which y i e l d s a d d u c t s t h a t are n o t c o n v e n i e n t l y a n d / o r e f f i c i e n t l y i n t e r c o n v e r t e d t h e r m a l l y or p h o t o The p h o t o p r o d u c t s ( 4 5 ) and ( 4 6 ) formed i n a resp e c t i v e r a t i o of 1:1.88 from t h e bichromophore ( 4 7 ) a r e , however, r e p o r t e d t o b e p h o t o - i n t e r c o n v e r t e d a l t h o u g h competing decomposit i o n d o e s o c c u r . 3 6 The minor isomer ( 4 5 ) is c o n v e r t e d i n 6-7 s t e p s i n t o ( + ) - s i l p h i p e r f o l - 6 - e n e ( 4 8 ) and (?)-7aH- ( 4 9 ) and (+)-7@H-(50)-silphiperfol-5-enes i n o v e r a l l y i e l d s of 8 . 4 , 5 . 0 , and 6 . 0 % r e s p e c t i v e l y . The s u c c e s s which h a s a l r e a d y been a c h i e v e d i n t h e a p p l i c a t i o n of t h i s i n t r a m o l e c u l a r c y c l o a d d i t i o n p r o c e s s i s r e m a r k a b l e and t h e p o t e n t i a l u t i l i t y o f t h e r e a c t i o n is f u r t h e r emphasised by i t s e x t e n s i o n t o f o r m a t i o n o f seven-membered r i n g s w i t h t h e f i r s t t o t a l s y n t h e s i s of t h e a n t i l e u k e m i c a g e n t The bichromophore (52) y i e l d s a r e s p e c t i v e ( ? ) - r u d m o l l i n (51). 37 r a t i o o f 2 . 3 : l of t h e two i n t r a m o l e c u l a r a d d u c t s ( 5 3 ) and ( 5 4 ) and w h i l e c o n v e r s i o n t o a common p r o d u c t from s u c h i s o m e r s h a s t o o c c u r by bromine-induced c l e a v a g e of p r e v i o u s l y been shown t h e i n t e r n a l c y c l o p r o r a n e r i n g , i n t h e p r e s e n t c a s e , f o r m a t i o n of t h e r e q u i r e d a l c o h o l ( 5 5 ) is a c h i e v e d from e i t h e r ( 5 5 ) o r ( 5 4 ) by t h e i r t r e a t m e n t w i t h m e r c u r i c acetate. The c o n v e r s i o n o f ( 5 5 ) t o ( 5 1 ) is a c h i e v e d i n f i f t e e n s t e p s . The f e a s i b i l i t y of u s i n g t h e
Photochemistry
284
(49) R = H, R1 = Me (50) R =Me, R’ = H
OH OMe
(57)
(56)
(58) R = OMe (60) R = CHN2 (611 R = OCO *CH2CHMe2
Me
C0,Me
(59)
F5 (62) X = O (64) X = 5
(63)
285
IIii4: Photochemistry of Aromatic Compounds
(68)
(65)
Y - s h i f t
(6 7)
&
Me
0
Me0
(70)
(69)
(75)
(72) R = CN (74) R = -CH=CH,
X =OorS
(71)
Y = 0, NH, or NMe
R = M e or H
Photochemistry
286
Me
(77)
(78) R = H, Me, or Ph
(79)
R
Me
(80)
(81)
f+ 0
(84)
(85)X-Y (86)X-Y (87)X-Y
= -NMe-
= -NMe-
CH(Me)--CH(Me)-
= -CH(Mel-CH(Mc)-NMc-
11114: Photochemistry of Aromatic Compounds
287
i n t r a m o l e c u l a r meta c y c l o a d d i t i o n a s a k e y s t e p t o w a r d s ( 5 . 5 . 5 . 5 ) f e n e s t r a n e s h a s b e e n p r e v i o u s l y i n v e s t i g a t e d by Keese a n d cow o r k e r ~a n~d ~ t h e same g r o u p now r e p o r t s s u c c e s s i n t h i s a p p r o a c h b y t h e s y n t h e s i s o f t h e f e n e s t r a - d i e n o n e ( 5 6 ) . 3 9 The s t a r t i n g m a t e r i a l i s t h e b i c h r o m o p h o r e ( 5 7 ) which on i r r a d i a t i o n i n d e g a s s e d hexane and i n a c c o r d w i t h s t e r i c and c o n f o r m a t i o n a l c o n s i d e r a t i o n s u n d e r g o e s 1 , 3 - c y c l o a d d i t i o n a s t h e major r e a c t i o n t o g i v e t h e two i s o m e r s ( 5 8 ) a n d ( 5 9 ) i n a r e s p e c t i v e y i e l d o f 3 : 4 . Isomer (58) is r e a d i l y c o n v e r t e d t o ( 5 6 ) by t r e a t m e n t of t h e d i a z o k e t o n e (60), p r o d u c e d f r o m t h e mixed a n h y d r i d e ( 6 1 ) , w i t h t r i f l u o r o a c e t i c acid. Intramolecular ortho-cycloaddition
of benzene-ethylene systems
h a s o n l y been p r e v i o u s l y r e p o r t e d f o r s y s t e m s i n which t h e t w o c h r o m o p h o r e s a r e h e l d i n a f a v o u r a b l e ~ r i e n t a t i o n . ~ ' I t is now, h o w e v e r , r e p o r t e d b y w o r k e r s who h a v e c o n t r i b u t e d much t o t h e understanding of t h e photoreactions of f l u o r i n a t e d benzenes, t h a t 254 nm i r r a d i a t i o n o f pentafluorophenyl-prop-2-enyl e t h e r ( 6 2 ) i n cyclohexane r e s u l t s i n t h e formation of t h e 1,2-cycloadduct I n c o n t r a s t tetrafluoropyridyl-prop-2-enyl
(63).
41
i s s t a b l e u n d e r t h e same
c o n d i t i o n s a n d t h e t h i o e t h e r ( 6 4 ) u n d e r g o e s C-S bond c l e a v a g e t o g i v e p e n t a f l u o r o t h i o p h e n o l a n d cyclohexylpentafluorophenyl s u l p h i d e . The p h o t o r e a r r a n g e m e n t of ( 6 5 ) t o ( 6 6 ) h a s p r e v i o u s l y been proposed t o arise & y
a [ 3 , 5 l s i g m a t r o p i c s h i f t , 4 2 b u t f r o m a re-
e x a m i n a t i o n o f t h e r e a c t i o n i t i s now s u g g e s t e d t h a t t h e mechanism
-
i n v o l v e s a n i n t r a m o l e c u l a r S1 a r e n e So e t h y l e n e e x c i p l e x which Rather than yield t h e intramol-
collapses t o t h e species (67).43
e c u l a r o r t h o cycloadduct, ( 6 7 ) is considered t o undergo c y c l i s a t i o n
t o ( 6 8 ) which by a 1 , 3 - s h i f t y i e l d s ( 6 6 ) . The p h o t o r e a c t i o n o f 1 , 3 - d i e n e s w i t h b e n z e n o i d compounds t y p i c a l l y y i e l d s c o m p l e x m i x t u r e s of p r o d u c t s a n d t h e r e a c t i o n o f (69) w i t h b e n z e n e is s e e m i n g l y no e x c e p t i o n . 4 4
The 1 , 4 - 1 ' , 4 ' -
adduct ( 7 0 ) i s , however, i s o l a t e d and i n f o u r f u r t h e r s t e p s , one of which i n v o l v e s x a n t h o n e - s e n s i t i z e d
photocyclization,
pentacyclo
C6.4.0. 0 2 ' 7 0 3 9 1 2 0 6 J 9 1 d o d e c a - 4 , 1 0 - d i e n e (71) is obtained, a l b e i t i n o n l y 2% y i e l d . The p h o t o r e a c t i o n o f f u r a n w i t h b e n z e n e a l s o g i v e s a v a r i e t y of a d d u c t s , b u t by t h e u s e of c o n j u g a t i v e s u b s t i t u e n t s o n t h e a r e n e , t h e a d d i t i o n p r o c e s s h a s been r e n d e r e d r e g i o - a n d s t e r e o - s p e c i f i c . 45 T h u s i r r a d i a t i o n o f b e n z o n i t r i l e i n t h e p r e s e n c e o f f u r a n p r o d u c e s t h e 2,6-2'5'-e= adduct (72) e x c l u s i v e l y a n d t h i s is c o n s i d e r e d t o r e s u l t f r o m a n i n t e r a c t i o n b e t w e e n t h e
Photochemistry
288
cyano s u b s t i t u e n t a n d t h e f u r a n which p r o d u c e s t h e o r i e n t a t i o n (73).
A similar d i r e c t i n g e f f e c t is observed f o r t h e r e a c t i o n
w i t h p h e n y l a c e t y l e n e a n d i t would a p p e a r t h a t e v e n t h e v i n y l g r o u p h a s some c o n t r o l s i n c e s t y r e n e and f u r a n , d e s p i t e an e x p e c t e d non-ideal
a l i g n m e n t f o r a d d i t i o n t o t h e b e n z e n e ring, g i v e ( 7 4 ) a s
w e l l as t h e 2 ? ~ + 2 7p~r o d u c t ( 7 5 ) on i r r a d i a t i o n . The s e n s i t i z e d p h o t o c y c l o a d d i t i o n o f maleic a n h y d r i d e d e r i v a t i v e s t o thiophenes to give t h e
exo
a d d u c t s ( 7 6 ) h a s b e e n known f o r
some t i m e a n d t h e r e a c t i o n h a s now been s u b j e c t e d t o a m e c h a n i s t i c study.46
I t would a p p e a r f r o m t h e p r e s e n t r e s u l t s t h a t t h e e n e r g y
a c c e p t o r s i n t h i s p r o c e s s can be t h e a n h y d r i d e , t h e t h i o p h e n e , and
a c h a r g e - t r a n s f e r complex b e t w e e n t h e a d d e n d s . The p h o t o r e a c t i v i t y o f n a p h t h a l e n e d e r i v a t i v e s w i t h e t h y l e n e s i s v e r y d e p e n d e n t o n t h e p o s i t i o n of t h e a r e n e s u b s t i t u e n t a n d t h e p a r t i c u l a r e t h y l e n e employed. Thus w h i l e t h e c a p t o d a t i v e e t h y l e n e , a - m o r p h o l i n o a c r y l o n i t r i l e ( 7 7 ) g i v e s 55-72% of t h e 1 , 4 - c y c l o adduct ( 7 8 ) w i t h l - a c y l n a p h t h a l e n e s , 2-acetonaphthone i s u n r e a c t S i m i l a r p r o d u c t s t o ( 7 8 ) a r e , however, formed from Me3CSC( : CH2)CN a n d 1- and 2 - n a p h t h a l d e h y d e s a n d t h e t r i p l e t s t a t e of t h e a r e n e i s i m p l i c a t e d i n t h e a d d i t i o n r e a c t i o n . The r e s u l t s o f f u r t h e r s t u d i e s i n t o t h e d i v e r s e a d d i t i o n r e a c t i o n s o f N,methylnaphthalene dicarboximides have been p u b l i s h e d .
A t wave-
l e n g t h s l o n g e r t h a n 320 nm, a l k e n e s u n d e r g o r e g i o s p e c i f i c p h o t o a d d i t i o n t o t h e 1 , 8 - i m i d e ( 7 9 ) t o g i v e , f o r e x a m p l e , ( 8 0 ) i n good y i e l d s a n d 1 , 3 - d i e n e s b e h a v e s i m i l a r l y t o p r o d u c e ( 8 1 ) . 4 8 I n cont r a s t , t h e p h o t o r e a c t i o n of ( 7 9 ) w i t h f u r a n p r o d u c e s ( 8 2 ) and ( 8 3 ) i n approximately equal y i e l d s *,it
is suggested, t h e oxetan ( 8 4 ) ,
and t h e 1,2-dimide
(85) with a l k e n e s undergoes photo-induced CO-NMe i n s e r t i o n t o g i v e ( 8 6 ) a n d ( 8 7 ) . 4 9 The same w o r k e r s h a v e
a l s o shown t h a t i n m e t h a n a l s o l u t i o n a n d i n t h e p r e s e n c e of 1 , l - d i p h e n y l e t h y l e n e , ( 7 9 ) a c t s as a t y p i c a l e l e c t r o n t r a n s f e r p h o t o s e n s i t i z e r f o r t h e anti-hlarkovnikoff a d d i t i o n and 2,2d i p h e n y l e t h y l m e t h y l e t h e r i s formed i n 70% y i e l d w i t h 93% o f ( 7 9 ) 50 being recovered. The p h o t o r e a c t i o n s o f a n t h r a c e n e i n t h e p r e s e n c e o f t r a n s t r a n s hexa-2,4-diene
have been re-examined.
The p r o d u c t s from t h e
r e a c t i o n a r e t h e a n t h r a c e n e d i m e r , t h e two isomers ( 8 8 ) a n d ( 8 9 ) o f C4+4lcycloaddition t o t h e 9 , l O - p o s i t i o n s of t h e a r e n e , and a 51 C2+41 a d d u c t ( 9 0 ) as w e l l as s e v e r a l u n i d e n t i f i e d m i n o r a d d u c t s . D i m e r i z a t i o n of t h e a r e n e i s r e d u c e d by t h e d i e n e r a t h e r t h a n enhanced, and a Diels-Alder r e a c t i o n of t h e s t r a i n e d t r a n s
IIII4: Photochemistry of Aromatic Compounds
289
e t h y l e n e i n t h e m a j o r a d d u c t (88) a n d a n t h r a c e n e t o g i v e ( 9 1 ) a c c o u n t s f o r t h e h i g h a r e n e l o s s w h i c h h a d been p r e v i o u s l y c o n s i d -
ered t o a r i s e f r o m t h e d i m e r i z a t i o n p r o c e s s .
These f i n d i n g s sub-
s t a n t i a t e t h e e a r l i e r q u a l i t a t i v e r e s u l t s and c o n c l u s i o n s o f Kaupp a n d T e ~ f e l . The ~ ~ a d d u c t s ( 8 8 ) , ( g o ) , a n d ( 8 9 ) are f o r m e d i n r e s p e c t i v e y i e l d s o f S l X , 1 4 % , a n d < 5% f r o m t h e s i n g l e t e x c i p l e x w h e r e a s t r i p l e t q u e n c h i n g a n d s e n s i t i z a t i o n s t u d i e s show t h a t ( 9 0 ) i s t h e major p r o d u c t f r o m t h e t r i p l e t p a t h w a y which a l s o y i e l d s a n a d d u c t o f unknown s t r u c t u r e . P h o t o a d d i t i o n o f a l i p h a t i c a m i n e s t o benzene53 a n d n a p h t h a l e
n
e w~a s ~r e ~p o r t e d many y e a r s a g o b u t t h e p r o c e s s i n v o l v i n g
ammonia a n d v a r i o u s p r i m a r y a m i n e s w i t h p h e n a n t h r e n e , a n t h r a c e n e and n a p h t h a l e n e h a s been examined i n t h e p r e s e n c e o f 2-dicyanob e n z e n e . 55
R e a c t i o n s are i n a c e t o n i t r i l e - w a t e r m i x t u r e s and y i e l d s
o f t h e a m i n a t e d a r e n e s ( 9 2 ) , ( 9 3 ) , a n d ( 9 4 ) are b e t w e e n 48-95%. The mechanism f o r t h e p h o t o - a m i n a t i o n
is r e a s o n a b l y s u g g e s t e d t o
i n v o l v e n u c l e o p h i l i c a t t a c k o f t h e amine on t o t h e c a t i o n r a d i c a l o f t h e a r e n e w h i c h i s g e n e r a t e d by p h o t o - i n d u c e d e l e c t r o n t r a n s f e r
t o t h e dicyanobenzene.
I r r a d i a t i o n at wavelengths longer than
500 nm of d i c h l o r o m e t h a n e s o l u t i o n s o f t h e c h a r g e - t r a n s f e r
com-
plexes of various anthracenes with tetranitromethane leads t o rapid b l e a c h i n g o f t h e s o l u t i o n and r e g i o - and s t e r e o - s p e c i f i c f o r m a t i o n of t h e a d d u c t s ( 9 5 ) i n h i g h y i e l d . 5 6
Again t h e r e a c t i o n i s c o n -
s i d e r e d t o p r o c e e d b y e l e c t r o n t r a n s f e r and t h e m u l t i - s t e p p a t h w a y involving t h e g e m i n a t e s p e c i e s [Ant C(N02)3- NO;]
is discussed.
Two f u r t h e r p h o t o a d d i t i o n s t o aromatic r i n g s r e p o r t e d w i t h i n t h e y e a r are t h e f o r m a t i o n o f a d i a s t e r e o i s o m e r i c m i x t u r e o f ( 9 6 ) produced from i r r a d i a t i o n o f t h e 9-(B-D-ribofuranosyl)
purine (97)
i n methanol,57 and t h e c o n v e r s i o n o f n a p h t h o l s and a n t h r o l s i n t h e
t o t h e corresponding quinone The l a t t e r p r o c e s s makes u s e o f t h e e n h a n c e d a c i d i t y o f t h e s i n g l e t e x c i t e d s t a t e o f p h e n o l s t o c a u s e d i s s o c i a t i o n of t h e N - n i t r o s o compound i n n e u t r a l salts.
presence of g-nitrosodimethylamine mono-oxime
3
i n c h e m i c a l y i e l d s o f 64-84%.58
Substitution Reactions
Each y e a r it i s e v i d e n t t h a t p h o t o s u b s t i t u t i o n p r o c e s s e s o f aromatic s y s t e m s c a n n o t r e a d i l y be c l a s s i f i e d a n d a g a i n t h e o r d e r of reviewing the l i t e r a t u r e i n t h i s Section is largely arbitrary. F u r t h e r d e t a i l s and a p p l i c a t i o n s have appeared o f t w o r u l e s which w e r e f i r s t p r o p o s e d i n 1984 t o r a t i o n a l i z e t h e r e g i o c h e m i s t r y o f
Photochemistry
290
(92)
(91)
NHZ
(95) R = NO,, CN, CHO, C02Me, COMe CI, Br, H, Ph or OCOMe
(93)
hv
MeOH
AcoG AcO
AcO (97)
OAC
(96)
OAc
IIIl4: Photochemistry of Aromatic Compounds
291
p h o t o - i n d u c e d n u c l e o p h i l i c aromatic s u b s t i t u t i o n . 5 9 The r u l e s a r e based on f r o n t i e r m o l e c u l a r o r b i t a l t h e o r y and c o n s i d e r e d t o be widely a p p l i c a b l e .6 o I n n u c l e o p h i l i c p h o t o s u b s t i t u t i o n s proceeding by a a-complex formed i n o n e s t e p from i n t e r a c t i o n between t h e e x c i t e d a r e n e a n d n u c l e o p h i l e , t h e r e g i o c h e m i s t r y is r e p o r t e d t o be c o n t r o l l e d by t h e HOMO of t h e s u b s t r a t e w h e r e a s r e a c t i o n s i n v o l v i n g t h e e l e c t r o n t r a n s f e r t o a n i t r o a r o m a t i c from a n u c l e o p h i l e a n d c o m b i n a t i o n o f t h e r a d i c a l i o n s a r e LUMO-controlled. A s w e l l as a n a l y z i n g v a r i o u s s u b s t i t u t i o n p r o c e s s e s by t h e s e r u l e s , t h e p r o p o s e r s r e p o r t s u p p o r t for t h e s e c o n d o f t h e r u l e s f r o m t h e i r r a d i a t g o n o f 4 - n i t r o n a p h t h y l e t h e r s ( 9 8 ) which y i e l d s The same g r o u p a l s o r e i n f o r c e t h e e a r l i e r t h e isomers ( 9 9 ) . 6 1 p r o p o s a l e 2 t h a t t h e p h o t o - S m i l e s r e a r r a n g e m e n t p r o c e e d s via an i n t r a m o l e c u l a r r a d i c a l i o n p a i r a n d a M e i s e n h e i m e r complex a n d q u a l i t a t i v e l y d e s c r i b e t h e r e a c t i o n p a t h by t h e u s e o f h y p e r s u r 63 f a c e s f o r t h e ground, c h a r g e - t r a n s f e r , and l o c a l l y e x c i t e d states. F u r t h e r s t u d i e s on t h e photo-Smiles r e a c t i o n and r e l a t e d p r o c e s s e s of 6 - ( n i t r o p h e n o x y ) e t h y l a m i n e s (100) by Wubbels a n d c o - w o r k e r s i l l u s t r a t e t h a t t h e r e a r r a n g e m e n t i s m a r k e d l y i n f l u e n c e d by t h e r e l a t i v e p o s i t i o n s of t h e s u b ~ t i t u e n t s . ~ The ~ Smiles r e a c t i o n t o g i v e W( nitrophenyl)-2-aminoethanols ( 1 0 1 ) i s o b s e r v e d f o r t h e 2a n d m_-isomers t h e r m a l l y and o n l y t h e 2-isomer u n d e r g o e s r e a r r a n g e ment p h o t o c h e m i c a l l y . I r r a d i a t i o n of t h e 2- a n d m-isomers a s h y d r o c h l o r i d e s y i e l d s ( 1 0 2 ) a n d ( 1 0 3 ) , a n d (104), ( 1 0 5 ) , a n d ( 1 0 6 ) r e s p e c t i v e l y w h i c h shows t h a t t h e 6-amino g r o u p i n b o t h cases b o n d s a t t h e r i n g C-atom a d j a c e n t t o t h e s i d e c h a i n a n d meta t o t h e n i t r o group. These r e s u l t s c o n t r a s t s h a r p l y with t h o s e 8 o b t a i n e d when t h e -NHPh m o i e t y i s t h e a t t a c k i n g n u c l e o p h i l e . P h o t o n u c l e o p h i l i c s u b s t i t u t i o n o f f l u o r o - and c h l o r o - a n i s o l e s h a s been t h e s u b j e c t o f t h r e e r e p o r t s w i t h i n t h e y e a r . C o r n e l i s s e a n d co-workers h a v e s t u d i e d t h e p h o t o c y a n a t i o n a n d p h o t o h y d r o l y s i s of 4 - f l u o r o - a n d c h l o r o - a n i s o l e s by l a s e r s p e c t r o s c o p y a n d r e p o r t t h a t t h e i n i t i a l s t e p of t h e r e a c t i o n involves formation of a t r i p l e t s t a t e t r a n s i e n t complex composed o f a g r o u n d s t a t e a n d a n e x c i t e d s t a t e aromatic m o l e c u l e . 6 5 Only i n t h e p r e s e n c e of
water d o e s t h e complex y i e l d r a d i c a l i o n s a n d i t is t h i s p r o c e s s which d e t e r m i n e s t h e p r o d u c t quantum y i e l d . The r a d i c a l c a t i o n t h e n reacts w i t h t h e n u c l e o p h i l e t o g i v e a n e u t r a l r a d i c a l which y i e l d s t h e s u b s t i t u t e d a r e n e i n a s i n g l e s t e p . L i u a n d Weiss r e p o r t o n anomalous e f f e c t s d u r i n g p h o t o n u c l e o p h i l i c aromatic s u b s t i t u t i o n o f 2- a n d 4 - f l u o r o a n i s o l e s a n d a l s o on t h e p h o t o -
Photochemistry
292
6 -N
@-OCH2CH2NHI
H C H2CH,OH
tl00)
(1 0 4 )
(103)
OR’
NO*
(106)
(105)
(107) R = OMe, OEt, OCHMc, R’ = Me, Et
(108) R = -CO-(CH, (109) R = H (1101 R = -CO-(CH2),-0
I H
I4-O &NO2 -
’ -P\
McNH
NO,
IIIl4: Photochemistry of Aromatic Compounds
293
h y d r o x y l a t i o n , photobyanation and f l u o r e s c e n c e quenching o f t h e 2 - i s o m e r c o m p l e x e d w i t h c y c l ~ d e x t r i n s . 67 ~ ~ ’In the f i r s t study t h e r e a c t i o n s are i n s o l v e n t m i x t u r e s o f water a n d t - b u t a n o l a n d t h e rate c o n s t a n t r a t i o f o r s u b s t i t u t i o n o f t h e f l u o r i n e b y CN- a n d OH- i s o b s e r v e d t o b e r e m a r k a b l y d e p e n d e n t on t h e c o m p o s i t i o n o f t h e s o l v e n t and on t h e s i t e of r e a c t i o n r e l a t i v e t o t h e methoxy g r o u p . T h u s , f o r e x a m p l e , t h e r a t i o o f 2 - h y d r o x y a n i s o l e t o 2 - c y a n o a n i s o l e from t h e 2 - f l u o r o isomer v a r i e s r e s p e c t i v e l y f r o m 2 . 4 4 : l t o 0 . 6 4 : l a s t h e t - b u t a n o l t o water r a t i o c h a n g e s f r o m 1 : 5 t o 3 : l a n d f o r t h e 4 - f l u o r o isomer t h e c o r r e s p o n d i n g h y d r o x y a n d c y a n o p r o d u c t s are formed i n 0 . 0 6 1 : l a n d 0.018:l r a t i o s w i t h r e s p e c t i v e m i x t u r e s o f t - b u t a n o l a n d water o f 1 : 3 a n d 2 : l . The authors report t h a t t h e i r preliminary s t u d i e s with other alcoholwater m i x t u r e s s u p p o r t t h e g e n e r a l i t y o f t h e s e o b s e r v a t i o n s a n d t h e y p o i n t o u t t h a t a f u l l e x p l a n a t i o n o f t h e s e e f f e c t s must i n c l u d e t h e dynamic i n f l u e n c e o f t h e s o l v e n t s t r u c t u r e on b o t h t h e n u c l e o p h i l e a n d s u b s t r a t e . Complexing o f 4 - f l u o r o a n i s o l e w i t h a- a n d B - c y c l o d e x t r i n s t r o n g l y i n h i b i t s p h o t o c y a n a t i o n a n d p h o t o h y d r o x y l a t i o n p r o c e s s e s b u t t h e r e i s v i r t u a l l y no e f f e c t w i t h y-cyclodextrin. The p h o t o s u b s t i t u t i o n o f t h e 2 - f l u o r o i s o m e r h a s been s t u d i e d and it i s r e p o r t e d t h a t with a - c y c l o d e x t r i n b o t h t h e r e a c t i o n s of water a n d CN- w i t h t h e a r e n e a r e s t r o n g l y i n h i b i t e d b u t t h a t s u r p r i s i n g l y t h e 0-cyclodextrin r e t a r d s t h e photohydroxyl67 a t i o n t o a f a r g r e a t e r e x t e n t t h a n it d o e s t h e c y a n a t i o n p r o c e s s . The p h o t o r e a c t i o n s o f f l u o r o - 6 8 a n d r n e t h o ~ y - ~ ’b e n z e n e s i n t h e p r e s e n c e o f amines had been e a r l i e r d e s c r i b e d b u t t h e s e s u b s t i t u t i o n and a d d i t i o n p r o c e s s e s have been re-examined w i t h d i e t h y l a m i n e as t h e n u c l e o p h i l e i n o r d e r t o i n v e s t i g a t e f u r t h e r t h e mechanism i n v o l v e d . 7 0 The e a r l i e r p r o p o s a l s are s u b s t a n t i a t e d b y t h e l a t e r s t u d y a n d a mechanism i n which t h e S1 a r e n e is q u e n c h e d by t h e amine t o g i v e a n e x c i p l e x i s o u t l i n e d . P r o t o n t r a n s f e r w i t h i n t h e e x c i p l e x and combination o f r a d i c a l s l e a d s t o t h e a c y c l i c a d d i t i o n p r o d u c t s some o f w h i c h u n d e r g o e l i m i n a t i o n o f HF o r m e t h a n o l t o yield the substituted arenes. The p h o t o - i n d u c e d s u b s t i t u t i o n o f t h e methoxy g r o u p of 3n i t r o a n i s o l e a n d o f 3 , 5 - d i n i t r o a n i s o l e s by OH- h a s p r e v i o u s l y b e e n s t u d i e d u n d e r s t e a d y s t a t e condition^,^^ a n d h a s now been 72 i n v e s t i g a t e d by nanosecond t i m e r e s o l v e d a b s o r p t i o n s p e c t r o s c o p y . The s p e c t r a o b t a i n e d i m m e d i a t e l y f o l l o w i n g t h e d i s a p p e a r a n c e o f t h e t r i p l e t s t a t e of t h e n i t r o a n i s o l e showed t h a t f o r m a t i o n o f t h e s u b s t i t u t i o n p r o d u c t i s complete a t t h a t p o i n t and from t h e s e
Photochemistry
2 94 CN
CN
NC
CN
(113)
(112)
(111)
N8 ( Ph 13-
II
NB (Ph
It
qPh 'OH
CN (115)
(114)
HO
qPh
(116)
OH OMe
OMe
NO2
OH
OH
OR
I
Ph (121) R = H (123) R = M e
Ph
(122)
Ph
295
IIIl4: Photochemistry of Aromatic Compounds r e s u l t s i t is c o n c l u d e d t h a t t h e a d d i t i o n o f t h e OH- a t C-1 t h e rate determining s t e p .
is
There i s a l s o a t least one f u r t h e r
r e a c t i o n o f t h e n u c l e o p h i l e w i t h t h e t r i D l e t a r e n e a n d t h i s comp e t e s w i t h t h e a t t a c k a t C - 1 a n d lowers t h e quantum y i e l d o f substi-tution.
The p r o d u c t o f t h i s s i d e r e a c t i o n is a l o n g - l i v e d
s p e c i e s w i t h a n a b s o r p t i o n maximum a t 370 nm.
Marquet a n d c o -
workers have pursued t h e i r i n t e r e s t i n t h e u s e of t h e photon u c l e o p h i l i c a r o m a t i c s u b s t i t u t i o n i n p h o t o a f f i n i t y l a b e l l i n g and r e p o r t a model s t u d y a n d t h e r e a c t i o n o f a c y c l o h e x i m i d e d e r i v a t i v e . 73
From r e s u l t s of 4 - n i t r o c a t e c h o l
e t h e r s (107) with methyl-
a m i n e i t is shown t h a t t h e s u b s t i t u t i o n o c c u r s a t t h e p o s i t i o n
meta t o t h e n i t r o g r o u p a n d so i r r a d i a t i o n o f t h e ester (108) o f t h e i m i d e ( 1 0 9 ) which is a n a n t i b i o t i c o f t h e g l u t a r i m i d e f a m i l y , i n t h e p r e s e n c e of t h e amine y i e l d s ( 1 1 0 ) . The a u t h o r s p o i n t o u t t h a t t h e c o n v e r s i o n o f (108) t o ( 1 1 0 ) i l l u s t r a t e s t h e p o t e n t i a l o f nitrophenyl esters as p h o t o a f f i n i t y probes t o i d e n t i f y b i o l o g i c a l receptor sites. The p h o t o r e a c t i o n s o f d i c y a n o b e n z e n e s w i t h a l l y l s i l a n e s which y i e l d a l l y l a t e d benzenes74 h a s been e x t e n d e d t o dicyano n a p h t h a l e n e s , a n t h r a c e n e s , a n d p h e n a n t h r e n e s . 75 I r r a d i a t i o n s o f t h e a r e n e s a n d a l l y l t r i m e t h y l s i l a n e are c a r r i e d o u t i n a c e t o n i t r i l e w i t h wavel e n g t h s l o n g e r t h a n 290 nm a n d w i t h 1 , 4 - d i c y a n o n a p h t h a l e n e , f o r e x a m p l e , as w e l l a s t h e e x p e c t e d s u b s t i t u t i o n p r o d u c t t w o a d d u c t s ( 1 1 2 ) a n d ( 1 1 3 ) a r e formed:
(111) t h e
as p r e v i o u s l y t h e r e a c t i o n
is c o n s i d e r e d t o p r o c e e d b y e l e c t r o n t r a n s f e r t o t h e a r e n e f r o m t h e silane. S i m i l a r d i c y a n o a r e n e s on i r r a d i a t i o n i n t h e p r e s e n c e o f a l k y l t r i p h e n y l b o r a t e s a l t s g i v e a l k y l s u b s t i t u t e d p r o d u c t s . 76 The b o r a t e s a l t s are c o n s i d e r e d a s a new c l a s s o f p h o t o - o x i d i z a b l e r e a g e n t s which e n a b l e f a c i l e a l k y l t r a n s f e r t o an e l e c t r o n a c c e p t o r t o o c c u r a n d y i e l d s c a n b e e x t r e m e l y good. Thus i r r a d i a t i o n of i n t h e p r e s e n c e o f Me4N+CMeR(Ph) 3 1- i n a c e t o n i t r i l e s o l u t i o n g i v e s 100% o f a m i x t u r e o f 3- a n d 4-methyl-11,4-dicyanonaphthalene
cyanonaphthalenes i n a ratio o f 1 . 4 : l . The r e a c t i o n i s c o n s i d e r e d t o p r o c e e d b y e l e c t r o n t r a n s f e r f r o m t h e b o r a t e s a l t t o t h e S1 a r e n e t o g i v e t h e s p e c i e s ( 1 1 4 ) . Cleavage of t h e boron r a d i c a l produces t r i p h e n y l b o r o n a n d 'CH3 w h i c h t h e n c o m b i n e s w i t h t h e a r e n e r a d i c a l a n i o n t o y i e l d ( 1 1 5 ) a n d (116 ) P r o t o n a t i o n and dehydrocyanat i o n of t h e latter i n t e r m e d i a t e s produces t h e methyl s u b s t i t u t e d arenes. I t w a s r e p o r t e d i n 1 9 8 2 by J a p a n e s e w o r k e r s t h a t i r r a d i a t i o n o f b i p h e n y l a b s o r b e d o n s i l i c a g e l i n t h e p r e s e n c e of s o d i u m n i t r a t e s o l u t i o n produced t h e h y d r o x y l a t e d and n i t r a t e d p r o d u c t s
.
Photochemistry
2 96
Ql+) (121) R (125) R (126) d (127) R
O
R
0
R'
= NH,, R' = H
(128) R = H, F, CI, Br, or I
d'
0 (129) R = Cl, R' = H (130) R = R' = C\ (131) R = Cl, R' = Ph
=NH2,R1=OH =NHCOMc, R1 = H = NHCOMe, R' =NHBu'
(132) R =
0
I
Me
-Q'",
(133) R = H, R'
R'= H
=aR
Me
(1351
(136)
11
1
IIIl4: Photochemistry of Aromatic Compounds
297
(117), (118), and ( I I ~ ) . Runce ~ ~ and co-workers have rei n v e s t i g a t e d t h e p r o c e s s m o s t l y u n d e r homogeneous c o n d i t i o n s i n aqueous m e t h a n o l w i t h t h e o b j e c t i v e of d e t e r m i n i n g t h e mechanism of t h e s u b s t i t u t i o n p r o c e s s e s and r e p o r t t h a t t h e i n i t i a l p r o d u c t s are 0- and p - h y d r o x y b i p h e n y l s which t h e n undergo p h o t o n i t r a t i o n . 78 The p r i m a r y s t e p i s NO; q u e n c h i n g o f t h e b i p h e n y l S1 s t a t e t o g i v e a n e x c i p l e x o r a caged r a d i c a l i o n p a i r w h i c h c o l l a p s e s t o t h e hydroxy compounds. T h r e e r e p o r t s which a p p e a r e d w i t h i n t h e year on t h e p h o t o s u b s t i t u t i o n p r o c e s s e s of hydroxy a r e n e s i l l u s t r a t e a l o n g w i t h t h e a c c o u n t s i n r e f e r e n c e s 10-12 t h e d i v e r s e p h o t o c h e m i c a l i n t e r e s t s i n these s u b s t r a t e s . The p h o t o f o r m y l a t i o n o f a number of p h e n o l s h a v e been d e s c r i b e d , 7 g and i t i s r e p o r t e d t h a t i r r a d i a t i o n o f a 5,l0,15,20-tetraphenylporphyrin-~-~nzoquinone-4-methoxyphenol In the latter s y s t e m l e a d s t o t h e s u b s t i t u t i o n p r o d u c t (120).80 r e a c t i o n t h e e f f i c i e n c y of t h e p r o c e s s i s dependent on t h e concent r a t i o n a n d r e d u c t i o n p o t e n t i a l of t h e q u i n o n e employed and from ESR a n d CIDNP e x p e r i m e n t s t h e mechanism is s u g g e s t e d t o i n v o l v e r a d i c a l c o u p l i n g . I r r a d i a t i o n of 4-phenylazo-l-naphthol (121) i s r e p o r t e d to i n d u c e p h o t o - o x i d a t i v e d i m e r i z a t i o n t o g i v e (122) and t h e r e a c t i o n i s most e f f i c i e n t i n s o l v e n t s w h i c h f a v o u r t h e f o r m a t i o n o f t h e h y d r a z o n e r a t h e r t h a n t h e a z o form o f (121). 81 The i n v o l v e m e n t of k e t o - e n o l t a u t o m e r i s m i n t h e p r o c e s s is s u p p o r t e d by t h e o b s e r v a t i o n t h a t t h e methoxy compound (123) is i n e r t under t h e present conditions. P h o t o s u b s t i t u t i o n r e a c t i o n s of 9,lO-anthraquinones c o n t i n u e t o a t t r a c t i n t e r e s t and t h e s e l e c t i v e p h o t o h y d r o x y l a t i o n and p h o t o a l k y l a m i n a t i o n o f t h e amino d e r i v a t i v e s h a s been d e s c r i b e d . 82 I r r a d i a t i o n o f ( 1 2 4 ) i n t h e p r e s e n c e of t - b u t y l a m i n e w i t h oxygen b u b b l e d t h r o u g h t h e b e n z e n e - e t h a n o l s o l u t i o n g i v e s a 79% y i e l d o f t h e hydroxy compound (125) whereas s i m i l a r t r e a t m e n t of t h e Na c y l a t e d d e r i v a t i v e (126) g i v e s t h e a m i n a t e d compound (127). T h e s e d i f f e r e n c e s are s u g g e s t e d t o r e s u l t from a change i n t h e e n e r g y l e v e l s i n t h e e x c i t e d s t a t e s of t h e two s t a r t i n g materials. As f o r a v e r y wide r a n g e o f a r y l h a l i d e s (see below) l - c h l o r o a n t h r a q u i n o n e s u n d e r g o p h o t o d e c h l o r i n a t i o n r e a c t i o n s . 83 Thus 366 nm i r r a d i a t i o n o f 1,5-dichloroanthraquinone f o r example y i e l d s a n t h r a q u i n o n e via a number of photo-induced s t e p s which i n v o l v e f o r m a t i o n of t h e chloroanthrahydroquinones and t h e i r p h o t o c o n v e r s i o n t o t h e d e c h l o r i n a t e d q u i n o n e . D u r i n g t h e i n v e s t i g a t i o n of t h i s
2 98
Photochemistry
process it w a s observed t h a t i r r a d i a t i o n of t h e c h l o r i n a t e d q u i n o n e s g a v e a s p e c i e s which i n a d a r k r e a c t i o n p r o d u c e d t h e hydroquinone and t h e s t a r t i n g quinone s i m u l t a n e o u s l y . T h i s i n t e r m e d i a t e i s a s s i g n e d t o a complex o f t w o c h l o r i n a t e d a n t h r a s e m i quinone r a d i c a l s . I t is a l s o of i n t e r e s t t o n o t e t h a t although i r r a d i a t i o n of 2-chloroanthraquinone y i e l d s the 2-chloroanthrah y d r o q u i n o n e , h e r e t h e r e a c t i o n s t o p s a n d no c o n v e r s i o n t o t h e d e c h l o r i n a t e d quinone is observed. Photodimerizations of a n t h r a c e n e s (see S e c t i o n 5 ) is n o r m a l l y a v e r y f a c i l e r e a c t i o n b u t i n t h e case o f t h e 9 - t r i m e t h y l s i l y l d e r i v a t i v e t h i s p r o c e s s i s r e p o r t e d t o be n e g l i g i b l e and i r r a d i a t i o n of methanol s o l u t i o n s r e s u l t s i n ~ ~ substid e s i l y l a t i o n a n d t h e f o r m a t i o n o f t h e p a r e n t a r e r ~ e . The t i o n is g r e a t l y e n h a n c e d i n t h e p r e s e n c e o f CC13CH20H a n d i n h i b i t e d i n t-butanol: t h e s e o b s e r v a t i o n s are r a t i o n a l i z e d i n terms of a n H-bonding i n t e r a c t i o n i n t h e e x c i t e d s t a t e r e s u l t i n g from i n t r a m o l e c u l a r c h a r g e - t r a n s f e r i n t h e e x c i t e d s i n g l e t state o f t h e s t a r t i n g material. Again t h i s y e a r t h e r e have been s e v e r a l a c c o u n t s o f p h o t o d e c h l o r i n a t i o n of a v a r i e t y o f a r o m a t i c s u b s t r a t e s . The l a s e r f l a s h p h o t o l y s i s o f chlorobenzene i n p o l a r s o l v e n t s h a s been d i s c u s s e d i n terms o f a s i n g l e t s t a t e s u b s t i t u t i o n r e a c t i o n w i t h a r a d i c a l c a t i o n i n t e r m e d i a t e a n d a s i n g l e t and t r i p l e t h o m o l y t i c C-C1 c l e a v a g e p r o c e s s . 85 T e t r a c h l o r o b e n z e n e s i n a c e t o n i t r i l e water m i x t u r e s u n d e r g o p h o t o - i n d u c e d r e d u c t i v e d e c h l o r i n a t i o n a s t h e p r i n c i p a l r e a c t i o n f r o m b o t h d i r e c t and s e n s i t i z e d i r r a d i a t i o n s , 86 a n d t e t r a - a n d p e n t a - c h l o r o p h e n o l s react s i m i l a r l y b u t i n t h e l a t t e r s e r i e s p r o d u c t s o f m o l e c u l a r f o r m u l a C8H4C13N0 a n d C8H3C14N0 r e s p e c t i v e l y are a l s o f o r m e d . 87 F u r t h e r , t h e i r r a d i a t i o n o f 2,3,5,6-tetrachlorophenol l e a d s t o t h e f o r m a t i o n o f h e x a - , h e p t a - , a n d octa-chlorodihydroxybiphenyls as w e l l a s t h e r e d u c t i o n a n d a d d i t i o n compounds a n d s u c h r e a c t i o n i s u n i q u e t o t h i s p h e n o l . P h o t o d e h a l o g e n a t i o n of c h l o r o b i p h e n y l h a s f o r a number o f y e a r s been o f i n t e r e s t and c o n c e r n l a r g e l y f o r e n v i r o n m e n t a l r e a s o n s . E p l i n g a n d F l o r i o now r e p o r t t h a t t h e d e c h l o r i n a t i o n of t h e s e s u b s t r a t e s 8 8 a n d o f c h l o r o t o l ~ e n e si ~n ~9 : 1 a c e t o n i t r i l e : water s o l u t i o n s is e n h a n c e d by 1 4 - f o l d i n t h e p r e s e n c e o f s o d i u m b o r o h y d r i d e a n d t h a t t h e r a t e o f r e a c t i o n is g r e a t e r by a f a c t o r o f 33 i n m i c e l l a r s o l u t i o n s . T h e s e workers d e d u c e t h a t a f r e e r a d i c a l mechanism d o e s n o t o p e r a t e f o r e i t h e r series of compounds b u t from o t h e r s t u d i e s i t i s s u g g e s t e d t h a t t h e p h o t o d e h a l o g e n a t i o n o f c h l o r i n a t e d p h e n o l s may i n v o l v e a r y l r a d i c a l a n d a r y l c a r b e n e /
M l 4 : Photochemistry of Aromatic Compounds a r y l cation intermediates.
299
The l a t t e r s t u d y h a s b e e n e x t e n d e d
t o a c o n s i d e r a t i o n o f p o l y c h l o r i n a t e d diphenyl e t h e r s and c h l o r o a n i s o l e s a n d a g a i n t h e r e d u c t i o n i s p r o p o s e d t o p r o c e e d via a r y l radicals: i n t e r m e d i a t e s i n t h e photohydrolysis of t h e a n i s o l e s and diphenyl e t h e r s are r e p o r t e d t o be a r y l c a r b e n e s / a r y l c a t i o n s . The p h o t o h y d r o l y s i s of 2 - c h l o r o - 4 - n i
t r o d i p h e n y l e t h e r h a s been
s t u d i e d by R u s s i a n w o r k e r s who n o t e t h a t t h e r e is a l i n e a r r e l a t i o n s h i p b e t w e e n t h e r e c i p r o c a l o f t h e quantum y i e l d a n d b a s e c o n c e n t r a t i o n , a n d t h a t t h e r e a c t i v i t y of t h e e x c i t e d s t a t e correlates w i t h t h e change i n e l e c t r o n d e n s i t y r e s u l t i n g from p h o t o e x ~ i t a t i o n . ~As~ may be e x p e c t e d , t h e e f f i c i e n c y o f p h o t o d e h a l o g e n a t i o n v a r i e s w i t h t h e h a l o g e n s a n d o t h e r p r o c e s s e s may compete.
T h u s i r r a d i a t i o n o f 2-(4-halophenyl)benzoxazoles (128) a t 300 nm i n o x y g e n - f r e e h e x a n e s o l u t i o n r e s u l t s i n d e h a l o g e n a t i o n f o r X = B r a n d I,2.rr+21~h e a d - t o - t a i l d i m e r i z a t i o n f o r X = F , I t is r e p o r t e d t h a t and b o t h p r o c e s s e s a r e observed f o r X = C l . 9 3 t h e d e h a l o g e n a t i o n f o r t h e c h l o r o compound is a s i n g l e t s t a t e
process involving an excimer.
The r e a c t i o n i s c o n s i d e r a b l y
enhanced i n t h e p r e s e n c e o f t h e e l e c t r o n donors,*-piperylene and t r i e t h y l a m i n e , and i n s u c h c i r c u m s t a n c e s p r o c e e d s an T h e p ho t o d e c h l o r i n a t i o n
e x c i t e d s t a t e c h a r g e -t r a n s f e r c o m p l e x ,
p r o d u c t (129) i s o b s e r v e d i n t h e r e a c t i o n m i x t u r e o b t a i n e d from i r r a d i a t i o n o f v i n c l o z o l i n (130) i n methanol but i n benzene s o l u t i o n (130) g i v e s mainly t h e biphenylyloxazolidine
(131).
94
Such p h o t o c o u p l i n g r e a c t i o n s a r e a l s o o b s e r v e d on i r r a d i a t i o n o f 5-bromo-1, 3 - d i m e t h y l u r a c i l g 5 benzenes.
o r 2 - i o d 0 p y r i d i n e ~ ~i n s u b s t i t u t e d
I n t h e f o r m e r case b o t h isomers ( 1 3 2 ) a n d ( 1 3 3 ) are
formed i n a r e s p e c t i v e r a t i o o f approximately 7 : l b u t t h e r e a c t i o n
i s o n l y r e p o r t e d f o r methyl benzenes and a n i s o l e . In contrast a c o u p l i n g r e a c t i o n w i t h t h e p y r i d i n e t o g i v e 2 - a r y l p y r i d i n e s is o b s e r v e d f o r a wide v a r i e t y o f s u b s t i t u t e d benzenes, and A n t o n i o l e t t i and co-workers r e p o r t t h a t t h e photocoupling p r o c e s s o f bromofuran-2-carbaldehyde a n d k e t o n e s w i t h a r e n e s p r o v i d e s good 97,98 derivatives. y i e l d s (60-70%) o f 3- a n d 5 - a r y l - 2 - f u r y 1 Work c o n t i n u e s o n t h e f a c t o r s which c a n a f f e c t t h e p h o t o m e t h o x y l a t i o n of e s t e r s o f p y r i d i n e c a r b o x y l i c a c i d s i n a c i d i c methanol s o l u t i o n s and a remarkable e f f e c t o f atmosphere h a s been r e p o r t e d . 99 Under o x y g e n , m e t h o x y l a t i o n o f , f o r e x a m p l e , (134 ) o c c u r s a t b o t h t h e a - a n d @ - p o s i t i o n s i n a r e s p e c t i v e r a t i o o f 3:s but i n nitrogen degassed s o l u t i o n s ,
substitution occurs specific-
Photochemistry
300 CONH,
CONH,
hv
Me0 12 "1.
3 "I"
17'1"
23 '1.
Scheme 2 Ph
Ph
1
I NH I
co,
I
Q
CHEt
I
fHE' ,NH.
HN
I
Et
C02Et
Et 0,C (1 39)
(138)
(1 3 7)
0
Me
A
1
Me
OACH FH2
I
it
Et (1 41 1
(140)
+
+
(142) R = CI, Br, SMes, BF,; NMe3 OAc, OP(0)(OEt l2 or S02Me
IIIl4: Photochemistry of Aromatic Compounds
301
a l l y a t t h e a-site and i n v o l v e s b o t h methoxylation and m e t h y l a t i o n t o g i v e ( 1 3 5 ) a n d ( 1 3 6 ) i n a 11:l r a t i o r e s p e c t i v e l y .
I t is
suggested t h a t under t h e former c o n d i t i o n s t h e r e a c t i o n proceeds by way o f a t e r p l e x o f two m o l e c u l e s o f t h e p r o t o n a t e d d i e s t e r a n d o n e m o l e c u l e o f oxygen w h i l e u n d e r n i t r o g e n t h e p r o d u c t arises d i r e c t l y from t h e a r e n e e x c i m e r .
The same g r o u p o f w o r k e r s have
e x t e n d e d t h e i r s t u d i e s i n t h i s area t o a n e x a m i n a t i o n o f t h e photoreactions of 3-pyridine
carboxamide i n a c i d i c methanol and
a g a i n r e a c t i o n s o f m e t h o x y l a t i o n a n d m e t h y l a t i o n are r e p o r t e d ( s e e Scheme 2 ) . l o o The e f f e c t s o f q u e n c h e r s o n t h e p r o c e s s a r e s u g g e s t e d t o i n d i c a t e t h a t t h e m e t h y l a t i o n o r i g i n a t e s from o n e e x c i t e d t r i p -
l e t s t a t e a n d t h a t t h e m e t h o x y l a t i o n a r i s e s from t w o d i f f e r e n t e x c i t e d s i n g l e t s t a t e s which are q u e n c h e d by a n e l e c t r o n t r a n s f e r P h o t o s u b s t i t u t i o n o f t h e p y r i d i n e a-position also
mechanism.
o c c u r s o n i r r a d i a t i o n o f 4-benzoyl-~-ethoxycarbonylimino~yridinium
s a l t s ( 1 3 7 ) i n t h e p r e s e n c e o f a l k e n e s . lo'
Thus ( 1 3 7 ) a n d c y c l o -
hexene y i e l d t h e e r y t h r o adduct (138) and s m a l l amounts o f 4b e n z o y l p y r i d i n e , and from trans-hex-3-ene
b o t h t h e t h r e o and
e r y t h r o p r o d u c t s ( 1 3 9 ) are formed i n a r e s p e c t i v e r a t i o o f 5:l. The e f f i c i e n c y o f t h e p r o c e s s is o b s e r v e d t o be o p t i m i s e d i n t h e p r e s e n c e o f c h l o r o f o r m a n d a m u l t i s t e p b i r a d i c a l mechanism i s proposed.
F u r t h e r d e t a i l s have been p u b l i s h e d o f t h e p h o t o -
i n d u c e d f u n c t i o n a l i z e d C - a l k y l a t i o n s i n p u r i n e s y s t e m s . lo2 The r e a c t i o n i n v o l v e s i r r a d i a t i o n o f , f o r example, t h e potassium e n o l a t e o f a c e t o n e i n ammonia s o l u t i o n w i t h 6 - i o d o - 9 - e t h y l p u r i n e ( 1 4 0 ) which g i v e s a f t e r c h r o m a t o g r a p h i c s e p a r a t i o n 70% o f 6acetonyl-9-ethylpurine
(141).
Each y e a r r e p o r t s are p u b l i s h e d which d e s c r i b e p h o t o - i n d u c e d changes within an arene s u b s t i t u e n t .
Examples o f s u c h p r o c e s s e s
which may n o t be c o n v e n i e n t l y c o n s i d e r e d e l s e w h e r e i n t h i s Volume are b r i e f l y m e n t i o n e d h e r e t o i l l u s t r a t e t h e t y p e o f r e s e a r c h currently of i n t e r e s t .
Hexamethylbenzene a n d m e r c u r i c t r i f l u o r o -
a c e t a t e form a g r o u n d s t a t e complex which e x h i b i t s c h a r g e - t r a n s f e r a b s o r p t i o n a n d i r r a d i a t i o n w i t h i n t h i s band y i e l d s p e n t a m e t h y l benzyl t r i f l u o r o a c e t a t e . The same p r o d u c t is o b t a i n e d from i r r a d i a t i o n o f t h e complex i n b o t h d i c h l o r o m e t h a n e a n d t r i f l u o r o -
acetic a c i d s o l u t i o n s . A r n o l d and c o - w o r k e r s h a v e s t u d i e d t h e h o m o l y t i c v e r s u s h e t e r o l y t i c c l e a v a g e f o r a wide v a r i e t y o f l-naphthylmethyl d e r i v a t i v e s (142) i n methanol s o l u t i o n F o r R=C1, Rr, SMei, under d i r e c t and s e n s i t i s e d c o n d i t i o n s .
photo-induced
Photochemistry
302
* Q (yCH & CH20Ac
QCH20H
Me (143)
\
+
Me
/
(1 4 4 )
(145)
X
0 ( 1 4 9 ) R = CHZOH (150)R = H
(147) R = H ( 1 4 8 ) R = Me
(146)
WPh (154) A l l rings aromatic
R (153) R = B r (156) R = H
5 \' \ 0
(155) R = Br (157) R = H
IIIt4: Photochemistry of Aromatic Compounds
3 03
B F i , a n d SO 2Me i n ( 1 4 2 ) , t h e c l e a v a g e i s s e n s i t i z e d by x a n t h o n e b u t e v i d e n c e i s p r e s e n t e d which i n d i c a t e s t h a t f o r t h e f o r m e r f o u r compounds e x c i p l e x f o r m a t i o n occurs r a t h e r t h a n t r i p l e t e n e r g y A u s e f u l semi q u a n t i t a t i v e scale o f p h o t o f u g a c i t i e s o f transfer. t h e s u b s t i t u e n t groups i n t h e e x c i t e d s i n g l e t state is given. W i t h i n t h e r e v i e w p e r i o d Wan a n d c o - w o r k e r s h a v e d e s c r i b e d t h e g e n e r a t i o n and subsequent r e a c t i o n s o f charged s p e c i e s from i r r a d i From p h o t o s o l v o l y s i s a t i o n of v a r i o u s aromatic compounds. '05-'07 a n d M e ) i n n e u t r a l and a c i d i c s t u d i e s o f m- a n d E-RC~H~CH~OH(R=F media it h a s b e e n shown t h a t t h e m-isomers react p r e d o m i n a n t l y by a h e t e r o l y t i c r o u t e c a t a l y s e d by H30+ t o y i e l d t h e b e n z y l cat i o n s . I n c o n t r a s t t h e p - i s o m e r s react more s l o w l y a n d i n v o l v e r a d i c a l i n t e r m e d i a t e s and t h e s e d i f f e r e n c e s are a s s i g n e d t o t h e a b i l i t i e s of t h e R - s u b s t i t u e n t s t o s t a b i l i s e t h e p o s i t i v e charge developing at t h e benzylic p o s i t i o n of t h e s i n g l e t e x c i t e d s t a t e o f t h e a r e n e . The p r o d u c t s f r o m (143), for e x a m p l e , are ( 1 4 4 ) a n d ( 1 4 5 ) i n t h e p r e s e n c e o f a c e t i c a c i d . The p h o t o r e a c t i o n s o f 9-phenyl-xanthen-9-01 ( 1 4 6 ) have been s t u d i e d i n some d e t a i l and evidence h a s been p r e s e n t e d t h a t t h e a r e n e undergoes a d i a b a t i c p h o t o d e h y d r o x y l a t i o n i n a q u e o u s s o l u t i o n : t h i s f i r s t example o f a new c l a s s of a d i a b a t i c p h o t o r e a c t i o n d o e s n o t o c c u r i n aceton i t r i l e or 95% e t h a n o l s o l u t i o n . From a s t u d y o f r e l a t e d s y s t e m s , a g e n e r a l method h a s been d e s c r i b e d f o r a s s e s s i n g t h e r e l a t i v e s t a b i l i t y of d i b e n z o y l a t e d c a t i o n i c and a n i o n i c s p e c i e s as 107 a f u n c t i o n of t h e number o f n - e l e c t r o n s i n t h e e x c i t e d s t a t e . From i r r a d i a t i o n of ( 1 4 7 ) i n w a t e r - m e t h a n o l s o l u t i o n t h e methoxy d e r i v a t i v e (148) r e s u l t s a n d t h e a n i o n p r o d u c e d from ( 1 4 9 ) g i v e s (150). 4 Intramolecular Cyclization Reactions T h i s S e c t i o n i s concerned w i t h photo-induced c y c l i z a t i o n r e a c t i o n s o f aromatic compounds i n which t h e f i n a l p r o d u c t i s a l s o a n a r e n e . Examples of i n t r a m o l e c u l a r c y c l i z a t i o n i n w h i c h t h e p r o d u c t i s a s t a b l e a l i p h a t i c s y s t e m (e.g. i n t r a m o l e c u l a r meta p h o t o c y c l o a d d i t i o n o f e t h y l e n e s t o b e n z e n e s ) are c o n s i d e r e d i n S e c t i o n 3 o f t h i s C h a p t e r . The p r e s e n t t y p e o f p r o c e s s o c c u r s f o r a w i d e v a r i e t y o f s y s t e m s and may i n v o l v e a r e n e - a r e n e a n d a r e n e e t h y l e n e p h o t o - o x i d a t i v e c y c l i z a t i o n o r r e a c t i o n s p r o c e e d i n g by l o s s o f h a l o g e n a c i d . F o r s e v e r a l y e a r s now o n e o f t h e major i n t e r e s t s i n t h e s e p r o c e s s e s h a s been i n t h e i r u s e a s s y n t h e t i c p r o c e d u r e s a n d a g a i n w i t h i n t h e r e v i e w p e r i o d there h a v e a p p e a r e d a number o f a c c o u n t s which i l l u s t r a t e t h i s f e a t u r e . S t i l b e n e -
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p h e n a n t h r e n e c y c l i z a t i o n s h a v e been o f p a r t i c u l a r u s e i n t h i s r e s p e c t a n d Hopf a n d c o - w o r k e r s
h a v e s u c c e s s f u l l y employed t h e
r e a c t i o n a s a new method f o r t h e s y n t h e s i s o f c o n d e n s e d C2.21 p a r a c y c l o p h a n e s . lo8 T h u s i r r a d i a t i o n o f t h e s t i l b e n e ( 1 5 1 ) i n h e x a n e s o l u t i o n i n t h e p r e s e n c e o f i o d i n e a n d a i r p r o d u c e s t h e C2.21
(1,4)phenanthrenoparacyclophane ( 1 5 2 ) i n 31% y i e l d . T h i s type o f c y c l i z a t i o n h a s p r e v i o u s l y been e x p l o i t e d f o r t h e s y n t h e s i s o f h e l i c e n e s 8 a n d by t h e u s e o f b r o m i n e as a d i r e c t i v e s u b s t i t u e n t 1 09 S u d h a k a r a n d K a t z h a v e d e v i s e d a n i m p r o v e d r o u t e t o C71 h e l i c e n e . The b r o m i n e atom i s f o u n d t o d i r e c t t h e s t i l b e n e c y c l i z a t i o n away f r o m o c c u p i e d p o s i t i o n s a n d t h o s e o r t h o t o t h e s u b s t i t u e n t so t h a t w i t h ( 1 5 3 ) t h e bromo C77 h e l i c e n e ( 1 5 4 ) i s f o r m e d i n 75% y i e l d o n i r r a d i a t i o n o f benzene s o l u t i o n s c o n t a i n i n g i o d i n e , and less t h a n 1 0 % o f t h e p l a n a r a r e n e ( 1 5 5 ) i s o b s e r v e d . S u c h r e s u l t s compare v e r y f a v o u r a b l y w i t h t h o s e from i r r a d i a t i o n o f t h e hydrocarbon ( 1 5 6 ) when e q u a l q u a n t i t i e s o f t h e C71 h e l i c e n e a n d ( 1 5 7 ) are f o r m e d . 'lo
I r r a d i a t i o n o f ( 1 5 8 ) , t h e meta isomer o f ( 1 5 6 ) ,
c y c l i z e s s e l e c t i v e l y w i t h o u t bromine d i r e c t i o n and (159) is formed 111 i n 75% f r o m x y l e n e s o l u t i o n i n t h e p r e s e n c e o f oxygen a n d i o d i n e . The o r i g i n s o f t h i s s e l e c t i v i t y may n o t b e r e a d i l y e v i d e n t a n d it
i s d i f f i c u l t t o a p p r e c i a t e why o f t h e f o u r p o s s i b l e c o n f o r m e r s o f the f i r s t intramolecular
photo-oxidative cyclization product only (160)
undergoes f u r t h e r r e a c t i o n .
The a u t h o r s s u g g e s t t h a t t h i s f e a t u r e
r e f l e c t s t h a t o f t h e f o u r c o n f o r m e r s ( 1 6 0 ) h a s t h e smallest d e g r e e o f s t e r i c i n t e r a c t i o n s b e t w e e n t h e t w o a r y l moieties.
The p h o t o -
c y c l i z a t i o n s o f h a l o s t i l b e n e s h a v e b e e n e x a m i n e d by o t h e r w o r k e r s who r e p o r t t h a t v a r i o u s o_-chloro a n d bromo-compounds
(161) undergo
o x i d a t i v e c y c l i z a t i o n i n cyclohexane s o l u t i o n i n t h e presence of i o d i n e and dehydrohalogenation i n b a s i c s o l u t i o n .
Thus, f o r
e x a m p l e , ( 1 6 1 ) ( X = B r , R=OMe, R'=H) y i e l d s r e s p e c t i v e l y ( 1 6 2 ) a n d ( 1 6 3 ) u n d e r t h e t w o s e t s of c o n d i t i o n s a n d t h a t t h e f o r m e r p r o c e s s o c c u r s i n y i e l d s u p t o 95% a n d t h e l a t t e r 5 7 % , h a v e e n c o u r a g e d t h e u s e o f t h e r e a c t i o n as a r o u t e t o d e h y d r o - o r c h i n o l
acetate (164) which is a p r e c u r s o r o f t h e f u n g i c i d a l p h y t o a l e x i n orchinol. I r r a d i a t i o n o f (165) i n t h e presence of potassium t - b u t o x i d e g i v e s 60% o f ( 1 6 4 ) a n d n o o t h e r c y c l i z e d p r o d u c t s : t h i s r e p r e s e n t s a s i g n i f i c a n t improvement o v e r p r e v i o u s a t t e m p t s t o o b t a i n (164) from t h e 2-iodo-3-acetoxy derivative. Martin and co-workers
h a v e c o n t i n u e d t h e i r work i n t h i s area a n d h a v e
i n v e s t i g a t e d t h e u s e of t h e s t i l b e n e - p h e n a n t h r e n e t y p e c y c l i z a t i o n a s a r o u t e t o f l u o r o h e l i c e n e s . 114'115 1-Fluoropentahelicene (166)
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a n d r e l a t e d compounds h a v e b e e n s y n t h e s i z e d by p h o t o - o x i d a t i v e dehydrocyclization of 3-styrylphenanthrenes and of l,Z-bis(ZFor e x a m p l e , i r r a d i a t i o n o f ( 1 6 7 ) y i e l d s naphthyl) ethylenes. ( 1 6 8 ) a n d ( 1 6 9 ) b u t i n some cases t h e p r o d u c t u n d e r g o e s f u r t h e r c y c l i z a t i o n by e i t h e r t h e l o s s o r m i g r a t i o n o f t h e f l u o r i n e atom: t h i s i s i l l u s t r a t e d by t h e f o r m a t i o n o f t h e b e n z o p e r y l e n e s ( 1 7 0 ) a n d ( 1 7 1 ) f r o m i r r a d i a t i o n o f t h e s t y r y l p h e n a n t h r e n e ( 1 7 2 ) . By t h e u s e o f s i m i l a r p r o c e d u r e s t h e same w o r k e r s s y n t h e s i z e d l - f l u o r o h e x a h e l i c e n e and l - f l u o r o h e p t a h e l i c e n e and t w e l v e o f t h e i r d e r i v a t i v e s from t h e i r r a d i a t i o n o f l - f l u o r o - l l - s t y r y l b e n z o t c l p h e n a n t h r e n e s ( 1 7 3 ) a n d l-fluoro-13-styrylpentahelicenes ( 1 7 4 ) r e s p e c t i v e l y b u t a g a i n t h e c y c l i z a t i o n s were a c c o m p a n i e d b y a dehydrofluorS t i l b e n e s w h i c h are c o n s t r i c t e d i n t o a, cis ination reaction. geometry undergo p h o t o - o x i d a t i v e c y c l i z a t i o n r e a d i l y and f r e q u e n t l y i n good c h e m i c a l y i e l d s . S p a n i s h w o r k e r s h a v e a c h i e v e d t h i s n e c e s s a r y c o n f o r m a t i o n a l r i g i d i t y by means o f t h e c y c l o p h a n e s ( 1 7 5 ) w h i c h on i r r a d i a t i o n i n e t h e r s o l u t i o n w i t h i o d i n e a n d o x y g e n a n d i n t h e a b s e n c e o r p r e s e n c e o f C u ( I 1 ) d e c a n o a t e g i v e s good y i e l d s o f ( 1 7 6 ). '16 The p h e n a n t h r e n e s are r e a d i l y o b t a i n e d f r o m ( 1 7 6 ) by r e d u c t i v e c l e a v a g e and u s i n g t h i s p r o c e d u r e on t h e dimetho x y compound ( 1 7 7 ) w h i c h u n d e r g o e s s i m u l t a n e o u s r e d u c t i o n o f t h e 9 , 1 0 - b o n d , c a n n i t h r e n e I1 ( 1 7 8 ) i s c o n v e n i e n t l y o b t a i n e d . C y c l i z a t i o n o f f i x e d c i s - s t i l b e n e h a s also been o b s e r v e d by K l e t t and Johnson d u r i n g t h e i r s t u d i e s i n t o t h e photorearrangement o f t r i - a n d t e t r a - p h e n y l a l l e n e i n a p r o t i c s o l v e n t s . '17 R o t h a l l e n e s y i e l d p h e n y l a t e d i n d e n e s among t h e p r i m a r y p r o d u c t s a n d ( 1 7 9 ) f r o m t h e t e t r a p h e n y l compound c y c l i z e d p h o t o c h e m i c a l l y t o t h e p h e n a n t h r e n e (180) d i r e c t l y whereas t h e p r e c u r s o r of t h e phenanthrene (181) w a s f o r m e d i n a s e c o n d a r y r e a c t i o n f r o m t r i p h e n y l a l l e n e . The p h o t o p r o c e s s e s o f v i n y l s t i l b e n e s ( 1 8 2 ) c o n t i n u e s t o b e o f i n t e r e s t and t h e product formation and r e l a t i v e r e a c t i o n rates o f compounds h a v i n g a l k y l s u b s t i t u e n t s o n t h e v i n y l g r o u p h a v e b e e n ~ r e p o r t e d . '18 The u s u a l r e a c t i o n p r o d u c t f r o m ( 1 8 2 ) i s a 5 phenylbenzohicyclo~2.l.lJhex-2-ene (183) a n d it i s d e d u c e d t h a t where r e l e v a n t t h e v i n y l m o i e t y must h a v e a n g - c o n f i g u r a t i o n w h e r e a s t h a t o f t h e s t i l b e n e m o i e t y h a s no e f f e c t o n p r o d u c t f o r m a t i o n . The mechanism f o r t h e f o r m a t i o n o f (183) i s r e g a r d e d as i n v o l v i n g a n i n t r a m o l e c u l a r t r a p p i n g of t h e t w i s t e d s i n g l e t b i r a d i c a l of t h e s t i l b e n e by t h e v i n y l g r o u p a n d c o n s i s t e n t w i t h t h i s i n t e r p r e t a t i o n 2 - ( 1- c y c l o h e p t e n y l ) st il b e n e ( 1 8 4 ) y i e l d s 1,6-pen t ame t h y l e n e -5 -ex0 phenylbicycloC2.1.11hex-2-ene ( 1 8 5 ) : t h i s c o n v e r s i o n i s a l s o n o t e -
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w o r t h y f o r i t s quantum y i e l d o f 0 . 9 . The p h o t o r e a c t i o n s o f 2v i n y l s t i l b e n e a n d of 1 , 2 - d i s t y r y l b e n z e n e (186) a n d 2 , 2 ' d i s t y r y l b i p h e n y l ( 1 8 7 ) a d s o r b e d o n s i l i c a g e l h a v e been i n v e s t i g a t e d a n d t h e i n f l u e n c e of g r o u n d - s t a t e c o n f o r m e r s o n t h e f o r m a t i o n of p h o t o p r o d u c t s h a s been d i s c u s s e d . Under s u c h c o n d i t i o n s t h e v i n y l s t i l b e n e g i v e s s e v e r a l p r o d u c t s i n c l u d i n g d e r i v a t i v e s of n a p h t h a l e n e a n d i n d e n e as w e l l as t h e a n d endo-5-phenylbicycloC2.1.1lhex-2-enes which are t h e o n l y p r o d u c t s i n s o l u t i o n . T h i s c o n s i d e r a b l e d i v e r g e n c e of r e a c t i o n pathway i s c o n s i d e r e d t o a r i s e from v a r i a t i o n s i n t h e p h o t o r e a c t i v i t i e s o f t h e v i n y l s t i l b e n e c o n f o r m e r s a n d t h e r e d u c e d m o b i l i t y of t h e b i r a d i c a l p r e c u r s o r s o f t h e bicycloE2.l.llhex-2-enes when t h e s e i n t e r m e d i a t e s are a d s o r b e d on t h e s i l i c a s u r f a c e . D i m e r s are e s s e n t i a l l y t h e s o l e p r o d u c t f r o m i r r a d i a t i o n of s o l u t i o n s o f ( 1 8 6 ) b u t o n a s i l i c a s u r f a c e , t h e s e are accompanied by 5 - e ~ , 6 - e n d o - d i p h e n y l b i c y c l o C 2 . 1 . 1 l h e x e n e (188) a n d t h e i n d e n e d e r i v a t i v e ( 1 8 9 ) w h e r e a s ( 1 8 7 ) p r o d u c e s ( 1 9 0 ) a n d ( 1 9 1 ) i n t h e same r a t i o i n s o l u t i o n and i n the surface reaction. Castle a n d L e e h a v e c o n t i n u e d t h e i r s t u d i e s i n t o t h e u s e o f t h e s t i l b e n e - p h e n a n t h r e n e t y p e c y c l i z a t i o n f o r t h e s y n t h e s i s of p o l y n u c l e a r a r e n e s h a v i n g t h i o p h e n e u n i t s a n d have d e s c r i b e d t h e p r e p a r a t i o n of p e n t a - a n d h e x a - c y c l i c t h i o p h e n e s b y p h o t o - o x i d a t i v e c y c l i z a t i o n of (ary1vinyl)benzothiophenes a n d - d i b e n z o t h i o p h e n e s . 120'121 Thus i r r a d i a t i o n o f ( 1 9 2 ) g i v e s a 73% y i e l d o f benzotriphenylenothiophene ( 1 9 3 ) l 2 O a n d s i m i l a r l y 52% of benzoc h r y s e n o t h i o p h e n e ( 1 9 4 ) is o b t a i n e d f r o m t h e ( n a p h t h y l v i n y 1 ) 121 dibenzothiophene (195). L a s t y e a r R a w a l a n d Cava gave a p r e l i m i n a r y a c c o u n t o f t h e i r s t u d i e s i n t o t h e p h o t o c y c l i z a t i o n of 1,2-dipyrrolyl-ethylenes a n d related systems and p o i n t e d o u t t h a t such p h o t o - o x i d a t i v e c y c l i z a t i o n may be employed as t h e k e y s t e p t o t h e t r i c y c l i c r i n g 122 s t r u c t u r e p r e s e n t i n t h e a n t i t u m o u r a n t i b i o t i c d i p e p t i d e CC-1065. The same w o r k e r s have r e p o r t e d f u r t h e r o n t h e p h o t o c h e m i s t r y o f s u c h s y s t e m s a s ( 1 9 6 ) a n d described t h e i r c y c l i z a t i o n t o ( 1 9 7 ) u n d e r non - o x i d a t i v e c o n d i t i o n s . 123 The r e a c t i o n s are p e r f o r m e d under n i t r o g e n i n a c e t o n i t r i l e s o l u t i o n c o n t a i n i n g 2-nitrobenzoic a c i d a n d t r i e t h y l a m i n e i n t h e p r e s e n c e o f a c a t a l y t i c amount o f palladium on c h a r c o a l as t h e oxidant and under t h e s e c o n d i t i o n s , t h e d i p y r r o l y l compound, f o r e x a m p l e , g i v e s a n 85% y i e l d of a 3 : l m i x t u r e of t h e b e n z o d i p y r r o l e a n d 1,2-di(2-g-methylpyrrolyl) e t h a n e r e s p e c t i v e l y . These workers have also pursued f u r t h e r
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Ph
(210)
H
&
(212 1
IPh Ph
qphd Ph
Scheme 3
Photochemistry
312
/ \
/
\
R h v , Xon t h one
Ph (217) R = H or Ph
CQ
* hv
Ph
(220)
w1 5-
Shift
Ph
(219)
Ph ( 2 1 8)
IIIi4: Photochemistry of Aromatic Compounds
313
t h e i r o b j e c t i v e o f t h e development of a g e n e r a l a n d f l e x i b l e r o u t e f o r t h e s y n t h e s i s of t h e i n d i v i d u a l m o i e t i e s of t h e d i p e p t i d e CC-1065 a n d a n a l o g u e s and r e p o r t t h e s y n t h e s i s o f t h e B and C u n i t s ( 1 9 8 ) and ( 1 9 9 ) . 124
The k e y s t e p o f p h o t o c y c l i z a t i o n i n c o r -
p o r a t e s t h e u s e o f t h e above p a l l a d i u m m e d i a t i o n o f t h e p r o c e s s and by s u c h a p r o c e d u r e ( 2 0 0 ) i s c o n v e r t e d i n t o ( 2 0 1 ) i n 82% y i e l d . By t h i s a p p r o a c h t h e B and C u n i t s are s y n t h e s i z e d i n o n l y t e n s t e p s s t a r t i n g from p y r r o l e s and i n o v e r a l l y i e l d s of > 20%. A r y l g r o u p s s e p a r a t e d by m o i e t i e s o t h e r t h a n e t h y l e n e a l s o undergo f a c i l e photo-oxidative
c y c l i z a t i o n and t h i s t y p e o f
r e a c t i o n h a s been u s e d t o p r o v i d e t h e r e g i o s p e c i f i c s y n t h e s i s of
2,3,6,7,10,11-hexasubstituted t r i p h e n y l e n e s from 3 , 3 " , 4 , 4 ' , 4 " , 5 ' h e x a s u b s t i t u t e d 1,l' : 2 ' , l " - t e r p h e n y l s . 125 I r r a d i a t i o n o f t h e dimethoxy compound ( 2 0 2 ) i n benzene s o l u t i o n i n t h e p r e s e n c e of i o d i n e g i v e s ( 2 0 3 ) i n 72% y i e l d a n d t h e hexa s u b s t i t u t e d compound ( 2 0 4 ) is s i m i l a r l y formed from ( 2 0 5 ) .
The c o n t r o l of t h e r e g i o -
c h e m i s t r y of t h e p r o c e s s is c o n s i d e r e d t o a r i s e from s t e r i c factors.
The p h o t o c y c l i z a t i o n o f 1 , 2 - d i a r y l p y r r i d i n i u m compounds
i s a w i d e l y a p p l i c a b l e and f r e q u e n t l y h i g h y i e l d r o u t e t o compounds o f t y p e ( 2 0 6 ) . 12' F u r t h e r s t u d i e s on m e c h a n i s t i c a s p e c t s o f t h e p r o c e s s have been d e s c r i b e d and d i h y d r o s p e c i e s a re p r o p o s e d a s r e a c t i o n i n t e r m e d i a t e s . 127
The p h o t o c h e m i s t r y o f t h e b i s
p y r i d i n i u m s a l t ( 2 0 7 ) h a s been examined and q u a n t i t a t i v e y i e l d s o f t h e c y c l i s e d p r o d u c t ( 2 0 8 ) are r e p o r t e d . 12'
The i r r a d i a t i o n o f 2,2,6,6-tetraphenylcyclohexanone is known t o y i e l d ( 2 0 9 ) a n d ( 2 1 0 ) v i a N o r r i s h Type I c l e a v a g e and d e c a r b o n y l a t i o n . J o h n s t o n and S c a i a n o have u s e d t h i s r e a c t i o n t o g e n e r a t e t h e b i r a d i c a l ( 2 1 1 ) 130 and have t h e n s t u d i e d t h e p h o t o c h e m i s t r y o f t h i s s p e c i e s ( ~ z l p s ) . I n b e n z e n e s o l u t i o n a t room t e m p e r a t u r e t h e e x c i t e d s t a t e of ( 2 1 1 ) h a s ~ = 2 . 5 n sa n d t h i s d e c a y s t o a n i n t e r m e d i a t e which a b s o r b s s t r o n g l y a t 480 nm a n d which is b e l i e v e d t o be ( 2 1 2 ) . The f i n a l p r o d u c t from i r r a d i a t i o n o f t h e b i r a d i c a l ( 2 1 1 ) i s ( 2 1 3 ) and t h i s i s r a t i o n a l i z e d by t h e 1 , 5 - s h i f t s a n d r i n g o p e n i n g r e a c t i o n s o u t l i n e d i n Scheme 3. T h i s s t u d y e l e g a n t l y d e m o n s t r a t e s t h e p r o d u c t d i f f e r e n c e s a c h i e v a b l e i n one- and two-photon p r o c e s s e s . I n t r a m o l e c u l a r p h o t o - i n d u c e d c y c l i z a t i o n between a r y l and e t h y l e n e m o i e t i e s is a common r e a c t i o n o b s e r v e d f o r a v a r i e t y o f m o l e c u l a r s t r u c t u r e s . The f o r m a t i o n o f 9,lO-dihydrophenanthrene from i r r a d i a t i o n o f 2 - v i n y l b i p h e n y l s h a s been a s o u r c e o f i n t e r e s t f o r some y e a r s , 131and Lapouyade and co-workers now r e p o r t on t h e s t e r e o c h e m i s t r y of t h e c y c l i z a t i o n . 13' The s i n g l e t e x c i t e d s t a t e
Photochemistry
314
Ph (225)
(221)
1" Maleic
0 0 (226)
(227 1
Me
0
0
Me
Me H \
(228 1
10,
R'
R'
R
O
(230)R's = H o r OMe
(231)
IIIl4: Photochemistry of Aromatic Compounds
315
of t h e c y c l o a l k e n e s (214) ( n = 1 , 2 , 3 , and 4 ) y i e l d s s o l e l y t h e
, 1 0 - d i h y d r o p h e n a n t h r e n e s ( 2 1 5 ) which are a l s o t h e e x c l u s i v e p r o d u c t s f r o m t h e t r i p l e t s t a t e of ( 2 1 4 ) f o r n = l a n d 2. The t r i p l e t s t a t e o f ( 2 1 4 ) f o r n=3 a n d 4 , however, y i e l d s b o t h ( 2 1 5 ) a n d t h e c o r r e s p o n d i n g cis isomers ( 2 1 6 ) which
t r a n s 9,10-cycloalkano-9
are c o n s i d e r e d t o a r i s e from t h e c y c l i z a t i o n of t h e p e r p e n d i c u l a r t r i p l e t of t h e cycloheptenylbiphenyl and from both t h e t r a n s and t h e p e r p e n d i c u l a r t r i p l e t i n t h e case o f t h e c y c l o - o c t e n y l biphenyl.
The mechanism of t h e x a n t h o n e s e n s i t i z e d r e a c t i o n
of t h e 2 - v i n y l b i p h e n y l s
( 2 1 7 ) h a s been s t u d i e d by laser f l a s h
p h o t d l y s i s a n d i t is c o n c l u d e d t h a t t h e f i r s t s t e p i n t h e r e a c t i o n
t o ( 2 1 8 ) is a n a d i a b a t i c p r o c e s s t o g i v e t h e c y c l i z e d p d l y e n e ( 2 1 9 ) i n t h e t r i p l e t s t a t e : 133 T h i s s p e c i e s h a s a l i f e t i m e of 550-750 n s .
F o r compounds i n w h i c h a 90'
t w i s t of the vinylic
bond i s f e a s i b l e , t h e r e s u l t i n g p e r p e n d i c u l a r t r i p l e t l e a d s t o a non-stereospecific
cyclization.
Previous s t u d i e s of t h e i r r a d i -
a t i o n o f l-phenyl-lJ2-dihydronaphthalene
( 2 2 0 ) had been c a r r i e d o u t
i n a p r o t i c s o l v e n t s u s i n g a b r o a d s p e c t r u m lamp and a p a r t f r o m
exo
4-phenyl-benzobicycloC3.l.Olhex-2-ene ( 2 2 1 ) was t h e s o l e p r o d u c t 134 The same r e s e a r c h group h a v e re-examined t h e photo-induced p r o c e s s e s of (220) i n methanol s o l u t i o n i n t h e a b s e n c e or p r e s e n c e of a c i d a n d u s i n g 254 nm r a d i a t i o n now r e p o r t t h a t u n d e r s u c h c o n d i t i o n s t h e sole p r o d u c t i s c i s - d i b e n z o b i c y c l o C3.3.Olocta-2 , 7 - d i e n e ( 2 2 2 ) w h i c h is c o n s i d e r e d t o a r i s e the p e n t a e n e ( 2 2 3 ) a n d t h e c y c l i z e d compound ( 2 2 4 ) . 135 T h i s r e a c t i o n o f f e r s a n a t t r a c t i v e r o u t e t o ( 2 2 2 ) as t h e o v e r a l l y i e l d f r o m n a p h t h o l i s a c h i e v e d i n 65%. The s t e r e o c h e m i c a l c o u r s e of t h e p r e v i o u s l y r e p o r t e d r e d u c t i v e p h o t o c y c l i z a t i o n o f g-cyclohex-le n y l b e n z a m i d e ( 2 2 5 ) t o t h e lactam ( 2 2 6 ) i n t h e p r e s e n c e o f sodium borohydride h a s been e l u c i d a t e d from a n x-ray c r y s t a l l o g r a p h i c s t u d y o f t h e maleic a n h y d r i d e D i e l s - A l d e r a d d u c t ( 2 2 7 ) this r e s u l t s u p p o r t s t h e earlier deductions on t h e s t r u c t u r e of t h e 137 p ho t o p r o d u c t s I t h a s b e e n known f o r o v e r t w e n t y y e a r s t h a t t h e l - a r y l b u t 1 , 3 - d i e n e u n i t i s p h o t o c h e m i c a l l y v e r y r e a c t i v e and u n d e r g o e s f a c i l e c y c l i z a t i o n t o y i e l d n a p h t h a l e n e d e r i v a t i v e s . 13' F u r t h e r a c c o u n t s a n d a p p l i c a t i o n s of t h i s p r o c e s s h a v e b e e n r e p o r t e d i n t h e r e v i e w p e r i o d a n d t h e o x i d a t i v e c y c l i z a t i o n o f 5 - s t y r y l - 1 ,3d i m e t h y l u r a c i l (228) i n d i l u t e a c e t o n i t r i l e s o l u t i o n t o (229) h a s b e e n d e s c r i b e d . 13' Q u e n c h i n g a n d s e n s i t i z a t i o n s t u d i e s i n d i c a t e polymer,
.
316
Photochemistry
I
1,5 shift
OMe
A NEt,
OMe -MeOH
N E12
(235)
(236)
(237)
(238)R =CI, R' = H (239) R = H, R' = C I
(240)
IIIl4: Photochemistry of Aromatic Compounds
317
t h a t t h e c y c l i z a t i o n i s a s i n g l e t s t a t e p r o c e s s but y i e l d s o f t h e p r o d u c t are improved i n t h e p r e s e n c e o f benzophenone s i n c e t h e e f f i c i e n c y of t h e n e c e s s a r y E t o c o n v e r s i o n o f ( 2 2 8 ) i s improved. T h i s t y p e o f c y c l i z a t i o n h a s been o b s e r v e d f o r 2 - s t y r y l i s o f l a v o n e s (230) and p r o v i d e s t h e k e y s t e p i n a f a c i l e s y n t h e s i s o f 5 - a r y l 12H-benzotalxanthen-12-ones (231 ). Over t h e years Heller and co-workers have d e v e l o p e d and e x p l o i t e d t h e p h o t o r e a c t i o n s o f s t e r i c a l l y crowded l - a r y l b u t - 1 , 3 - d i e n e s a s photochromic s y s t e m s and t h e i r s t u d i e s of 16 compounds from t h i s class o f p h o t o l a b i l e s y s t e m s have been described. 14' F o r example, 366 nm r a d i a t i o n o f (232) i n toluene y i e l d s t h e deep blue solvatochromic 1,8ad i h y d r o n a p h t h a l e n e ( 2 3 3 ) which u n d e r g o e s a t h e r m a l 1 , 5 - s h i f t t o t h e c o l o u r l e s s 1 , 2 - d i h y d r o n a p h t h a l e n e as w e l l as t h e r m a l d i s r o t a t o r y r i n g o p e n i n g . The c y c l i z a t i o n i s a l s o r e v e r s e d by w h i t e l i g h t and t h e i m i d e s c o r r e s p o n d i n g t o ( 2 3 2 ) show s i m i l a r p h o t o p r o p e r t i e s . A n o v e l example o f t h i s t y p e of p h o t o c y c l i z a t i o n is o b s e r v e d on i r r a d i t i o n o f benzene s o l u t i o n s o f t h e y-methoxyiminoa , @ - u n s a t u r a t e d carboxamide ( 2 3 4 ) . 142 The i s o l a t e d p r o d u c t is t h e q u i n o l i n e carboxamide (235) b u t t h i s is r e a s o n a b l y p r o p o s e d t o be formed t h e c y c l i z e d i s o m e r ( 2 3 6 ) which e l i m i n a t e s t h e e l e m e n t s o f methanol. I n t r a m o l e c u l a r c y c l i z a t i o n r e s u l t i n g from t h e p h o t o c h e m i c a l l y i n d u c e d l o s s o f h a l o g e n a c i d s i s a common p r o c e s s and o b s e r v e d f o r a wide v a r i e t y o f d i f f e r e n t t y p e s o f compound. Two g r o u p s have r e c e n t l y r e p o r t e d t h e f o r m a t i o n of p h e n a n t h r i d o n e ( 2 3 7 ) by i r r a d i a t i o n of c h l o r i n a t e d d e r i v a t i v e s o f b e n z a n i l i d e , 143 and now Korean w o r k e r s have d e s c r i b e d t h e c y c l i z a t i o n o f t h e same compounds and of t h e bromo- and m e t h o x y - s u b s t i t u t e d d e r i v a t i v e s The r e a c t i o n i s c o n s i d e r e d t o p r o c e e d y& t h e t r i p l e t s t a t e and is e f f i c i e n t f o r t h e 2 - c h l o r o b e n z a n i l i d e ( 2 3 8 ) b u t a p p r e c i a b l y less so f o r t h e 2 ' - c h l o r o isomer ( 2 3 9 ) w h i c h is s u g g e s t e d t o r e f l e c t t h e a s s i s t a n c e g i v e n by t h e N-Ph g r o u p t o t h e l o s s of c h l o r i n e from t h e Ph-CO group: t h i s i s s u p p o r t e d by t h e o b s e r v a t i o n t h a t e l e c t r o n d o n a t i n g g r o u p s i n t h e former m o i e t y accelerate t h e reaction. The c y c l i z a t i o n rate o f 2-methoxybenzanilide i s enhanced i n t h e p r e s e n c e of oxygen and t h i s is i n t e r p r e t e d i n terms of s i n g l e t s t a t e i n t e r m e d i a t e s . I r r a d i a t i o n o f (240) i s r e p o r t e d t o y i e l d (241) which is a f u r t h e r example o f photoi n d u c e d d e h y d r o h a l o g e n a t i o n o f 3-chloronaphthothiophenes t o y i e l d n o v e l naphthothienoquinolines,145 a n d i r r a d i a t i o n of t h e 2-bromo-
Photochemistry
318
( 2 4 2 ) as t h e h y d r o c h l o r i d e
2 ' -iodo-5-benzyl-6-phenethylamine l e a d s t o t h e iododibenzazocine
( 2 4 3 ) . 146
The l a t t e r t y p e o f
r e a c t i o n is a l s o o b s e r v e d f r o m i r r a d i a t i o n o f 1 - ( h y d r o x y p h e n y l -
ethyl)-3-(bromophenyl)propionamides
( 2 4 4 ) u n d e r basic c o n d i t i o n s
when t h e 11-membered r i n g lactams ( 2 4 5 ) a n d ( 2 4 6 ) a r e o b t a i n e d i n 5-46% y i e l d . 147 The p h o t o c h e m i s t r y of t h e g - c h l o r o a c e t y l compound ( 2 4 7 ) h a s b e e n e x a m i n e d w i t h t h e a i m o f f i n d i n g a convenient r o u t e t o t h e p e n t a c y c l i c r i n g system of Strychnos indole I t w a s hoped t h a t i r r a d i a t i o n o f ( 2 4 7 ) would l e a d a l k a l o i d s . 148
t o a dehydrohalogenation and c y c l i z a t i o n a t t h e i n d o l e 3 - p o s i t i o n b u t a l t h o u g h c y c l i z a t i o n d i d o c c u r t h e p r o c e s s i n v o l v e d t h e benzo I r r a d i a t i o n o f 1r i n g a n d ( 2 4 8 ) w a s i s o l a t e d i n 40% y i e l d . chlom-2-phenylethane i n alcohols y i e l d s t h e corresponding carbinols a n d e t h e r s b u t 1 - c h l o r o - 4 - p h e n y l b u t a n e u n d e r g o e s c y c l i z a t i o n t o give t e t r a l i n as w e l l a s f o r m a t i o n o f n - h u t y l b e n z e n e a n d 4 - p h e n y l b u t 1 49 1-ene A wide d i v e r s i t y o f 2-aryl s u b s t i t u e n t s r e s u l t i n c y c l i z a t i o n products on i r r a d i a t i o n . R e p r e s e n t a t i v e examples o f t h i s t y p e o f r e a c t i o n f r o m t h e c u r r e n t l i t e r a t u r e are g i v e n h e r e f o r i l l u s t r a t i v e purposes. Japanese workers have s t u d i e d t h e i r r a d i a t i o n o f s e v e r a l 2- a n d E - s u b s t i t u t e d aromatic p o l y c a r b o n y l compounds a n d f r o m t h e t r i - i s o p r o p y l compound ( 2 4 9 ) i n b e n z e n e s o l u t i o n , h a v e i s o l a t e d t h e b e n z o c y c l o b u t e n e ( 2 5 0 ) . 150 L a s t y e a r Wagner a n d co-
.
w o r k e r s r e p o r t e d s e v e r a l cases o f i n t r a m o l e c u l a r c y c l i z a t i o n i n v o l v i n g a c e t o p h e n o n e s a n d b e n z o p h e n o n e s a n d h a v e now d e s c r i b e d t h e q u a n t i t a t i v e conversion of 2-t-butylbenzophenone dimethyl-1-indanol
t o 1 - p h e n y l - 3 ,3-
( 2 5 1 ) i n t h e s o l i d s t a t e o r s o l u t i o n from
77K t o room t e m p e r a t u r e . 15'
A s i m i l a r p r o c e s s occurs w i t h
when ( 2 5 2 ) i s f o r m e d both i n e t h y l 152 acetate s o l u t i o n or i n c r o s s l i n k e d e t h y l e n e - v i n y l acetate beads, a n d Dspp a n d c o - w o r k e r s h a v e d i s c u s s e d s t r u c t u r e - r e a c t i v i t y c o r r e l a t i o n i n v o l v e d i n t h e c o n v e r s i o n of c e r t a i n 2 - n i t r o - t b u t y l b e n z e n e s t o ( 2 5 3 ) . 153 I n t h e l a t t e r s t u d y t h e m o l e c u l a r s t r u c t u r e o f t h e s t a r t i n g material h a s been determined by x - r a y c r y s t a l l o g r a p h y and t h e p h o t o r e a c t i v i t y o f t h e n i t r o a r e n e i n t h e s o l i d s t a t e is r a t i o n a l i z e d i n t e r m s of i n t r a m o l e c u l a r g e o m e t r i c a l parameters a n d i n t e r m o l e c u l a r p a c k i n g c o n s i d e r a t i o n s . 4-Substituted 2 ' -hydroxychalcones (254) undergo s e l e c t i v e photo154 c y c l i z a t i o n i n p o l a r a p r o t i c s o l v e n t s t o y i e l d flavanones (255). The e f f i c i e n c y o f t h e p r o c e s s is l o w a n d h y d r o x y l i c s o l v e n t s which
a-(2-methylphenyl)acetophenone
lIIl4: Photochemistry of Aromatic Compounds
319
(241)
(243)
RibcH2
\
R2
CH2
I
NH
R3@cH:H2 A4
(244) R's = H, OH, OMe
(245)
0
(246)
320
Photochemistry
Ar
Ar
(255)
Scheme 4
Ar
321
IIIl4: Photochemistry of Aromatic Compounds
Si (SiMe3I3
1 c=o
Me
Me
Me
Me
7%
si 's
$' -
Me
OSi Me3
Me
b- Ph
Me3Si
Si Me,
Fh
%Me,
S,i Me3
hv
Si Me,
Ph
SiMe3
a,y /
Y-x
(264)
(266)X-Y
X
=
>o
Photochemistry
322
i n h i b i t f o r m a t i o n o f t h e c y c l i c i n t r a m o l e c u l a r H-bond markedly retard
t h e r e a c t i o n which i s c o n s i d e r e d t o p r o c e e d
the
i n t e r m e d i a t e s o u t l i n e d i n Scheme 4. As may be e x p e c t e d i n t r a m o l e c u l a r c y c l i z a t i o n of 2 - d i s u b s t i t u t e d photo-induced
a r e n e s c a n be i n i t i a t e d by
e l i m i n a t i o n of h a l o g e n a c i d and f o r example ( 2 5 6 )
is among t h e p r o d u c t s f r o m i r r a d i a t i o n o f t h e a - c h l o r o compound ( 2 5 7 ) . 155 Tulo g r o u p s have d e s c r i b e d p h o t o c y c l i z a t i o n r e a c t i o n s of o r g a n o s i l a n e s . Canadian w o r k e r s have o b s e r v e d a two-photon p r o c e s s from m e s i t o y l tris(trimethylsily1)silane ( 2 5 8 ) which y i e l d s y t h e i n t e r m e d i a t e s i l e n e (260 ) : 156 t h e b e n z o c y c l o b u t e n e (259) & t h e c y c l i z a t i o n p r o c e s s t o (259) i n v o l v e s a photo-induced
insert-
i o n of t h e C=Si m o i e t y i n t o a r e l a t i v e l y u n a c t i v a t e d C-H bond. The second r e p o r t i s concerned w i t h t h e p h o t o r e a c t i o n s o f t h e l-silaeyclobut-2-ene
( 2 6 1 ) . 157
The i r r a d i a t i o n i s c a r r i e d o u t
i n d r y benzene u n d e r n i t r o g e n and y i e l d s t h e l - s i l a c y c l o p e n t a - 2 , 4 d i e n e (262)
e, i t is p r o p o s e d ,
t h e l-silabicycloC2.1.0lpent-3-
ene intermediate (263). 5 Dimerization Reactions P h o t o d i m e r i z a t i o n i s common for a n t h r a c e n e s , less s o f o r n a p h t h a l e n e s , and u n t i l t h i s y e a r o n l y o n e example o f t h i s r e a c t i o n w i t h a b e n z e n o i d compound had a p p e a r e d . Thus i r r a d i a t i o n o f
diheteraC3.3lmetacyclophanes y i e l d s ( 2 6 4 ) and f u l l d e t a i l s of t h i s A somewhat more s i m p l e example of p h o t o d i m e r i z a t i o n of benzene r i n g s h a s , however, now been d e s c r i b e d by P r i n z b a c h and co-workers. 159 I r r a d i a t i o n (254 nm) of ( 2 6 5 ) and (266) i n i s o - o c t a n e i n d u c e s a C6+6lbenzo-benzo c y c l o a d d i t i o n and t h e f o r m a t i o n o f ( 2 6 7 ) . The retro a d d i t i o n i s a l s o i n i t i a t e d under t h e c o n d i t i o n s of formation of t h e i n t r a m o l e c u l a r dimer and hence t h e r e a c t i o n r e a c h e s a p h o t o e q u i l i b r i u m w i t h r a t i o s of ( 2 6 5 ) t o ( 2 6 7 ) of 1:l t o 2 : 5 r e s p e c t i v e l y dependent on t h e s u b s t i t u e n t s . The same group have also examined t h e u s e of s u c h m o l e c u l a r c o n s t r a i n t s as i n ( 2 6 5 ) t o o r i e n t t h e benzo and azo (and a z o x y ) chromophores and t h e r e b y r e n d e r C6+21 c y c l o X-Ray c r y s t a l l o g r a p h i c d a t a f o r ( 2 6 8 ) a d d i t i o n s v e r y l i k e l y . 160 show t h a t t h e geometry is i n d e e d f a v o u r a b l e for t h e c y c l o a d d i t i o n b u t 254 nm or w a v e l e n g t h s l o n g e r t h a n 280 nm i r r a d i a t i o n o f t h e bichromophore i n methanol o r a c e t o n e s o l u t i o n a t -5OOC s i m p l y i n i t i a t e s t h e s l o w e l i m i n a t i o n of n i t r o g e n and f o r m a t i o n of ( 2 6 9 ) . The azoxy d e r i v a t i v e of ( 2 6 8 ) u n d e r s i m i l a r c o n d i t i o n s y i e l d s (268) and t h e n c e (269).
p r o c e s s have now been p u b l i s h e d . 158
IIIl4: Photochemistry of Aromatic Compounds
(270) R-R = bond (272) R = H
323
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Photochemistry
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(277)
c$J$ R’
R2
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(278) R = R’ = R 2 = H (280) R = R’ = CI, R 2 = H (281) R = H, R’ = R 2 = C I
(279) X = -C H, -CHz(282) X = S i M e 2 (283) X =GeMe2
67
(0
0
(284)
IIIl4: Photochemistry of Aromatic Compounds
325
Over t h e y e a r s t h e r e have been many r e p o r t s t h a t photoreactions, particularly dimerization processes, carried out i n m i c e l l e s , m i c r o e m u l s i o n s , and c y c l o d e x t r i n c a v i t i e s f r e q u e n t l y show a higher s e l e c t i v i t y and o c c u r a t a greater r a t e t h a n t h e corresponding process i n simple s o l u t i o n . I t i s , t h e r e f o r e , of i n t e r e s t b u t no g r e a t s u r p r i s e t o n o t e t h a t t h e p h o t o d i m e r i z a t i o n of w a t e r - s o l u b l e a n t h r a c e n e s s u c h a s 2 - a n t h r a c e n e s u l p h o n a t e i n aqueous s o l u t i o n i s a c c e l e r a t e d i n t h e p r e s e n c e o f B and y c y c l o dextrins. The s e l e c t i v i t y of t h e p r o c e s s i s , however, markedly dependent on t h e p a r t i c u l a r h o s t m o l e c u l e and w h i l e t h e f o u r c o n f i g u r a t i o n a l i s o m e r s of t h e 9 , l o - , 9',10' -photodimer were o b t a i n e d i n t h e p r e s e n c e o f y - c y c l o d e x t r i n i n r a t i o s similar t o t h o s e o b s e r v e d i n h o s t - f r e e s o l u t i o n , i n t h e p r e s e n c e o f B-cyclod e x t r i n o n l y one o f t h e isomers was formed. These r e s u l t s a g a i n i l l u s t r a t e t h e ' f i n e t u n i n g ' which may be imposed on p h o t o r e a c t i o n s by t h e u s e of h o s t - g u e s t s i t u a t i o n s . I t was r e p o r t e d l a s t y e a r t h a t 1-(9-anthry1)-2-phenylacetylene p h o t o d i m e r i z e d t o g i v e ( 2 7 0 ) i n 70% y i e l d . 162 The same g r o u p have a l s o examined t h e photo-induced r e a c t i o n s o f t r a n s - l - ( g - a n t h r y l ) 2 - p h e n y l e t h y l e n e ( 2 7 1 ) , and w h i l e t h e dimer ( 2 7 2 ) c o r r e s p o n d i n g t o ( 2 7 0 ) is t h e major p r o d u c t , 9,10-,9',10'-dimerization t o g i v e ( 2 7 3 ) and C B ~ ~ + 6 1 ~ l c y c l o a d d i tri eo snu l t i n g i n t h e f o r m a t i o n o f (274) and ( 2 7 5 ) are a l s o o b s e r v e d . 163 The r e s p e c t i v e r a t i o o f ( 2 7 2 ) , ( 2 7 3 ) , ( 2 7 4 ) , and ( 2 7 5 ) i s 2 0 : 2 : 2 : 1 and a s t h i s r a t i o i s c o n s t a n t i t i s deduced t h a t a l l p r o d u c t s a r i s e d i r e c t l y from ( 2 7 1 ) . I t i s a l s o r e p o r t e d t h a t t h e m a j o r p r o d u c t ( 2 7 2 ) i s o m e r i z e s t o (274) and u n d e r g o e s c y c l o r e v e r s i o n on direct i r r a d i a t i o n and w i t h b i a c e t y l s e n s i t i z a t i o n forms ( 2 7 5 ) : t h e quantum y i e l d s f o r t h e s e p r o c e s s e s are 0 . 1 , 0 . 0 3 , and 0 . 0 1 r e s p e c t i v e l y . 9,10-,9',10'-Photodimers o f a n t h r a c e n e s undergo p h o t o r e t r o a d d i t i o n and i n t h e past t h i s has been a l s o a c h i e v e d w i t h c h l o r a n i l and d i c y a n o a n t h r a c e n e a s s e n s i t i z e r s . 164 F u r t h e r s t u d i e s on similar s y s t e m s have now been r e p o r t e d and a r a n g e o f head-to-tail d i m e r s of s u b s t i t u t e d a n t h r a c e n e s have been monomerized by i r r a d i a t i o n w i t h i n e i t h e r of t h e 165 t w o c h a r g e - t r a n s f e r b a n d s of t h e dimer-tetracyanoethylene complex. The r e c e n t i n t e r e s t i n t h e p h o t o c h e m i s t r y of l i n k e d a n t h r a c e n e s y s t e m s c o n t i n u e s . The syn[2.2.l(1,4)anthracenophane ( 2 7 6 ) and i t s photodimer ( 2 7 7 ) had been p r e v i o u s l y d e s c r i b e d i n 1972,166 and now t h e same workers have c o n f i r m e d these s t r u c t u r e s by Z-ray c r y s t a l l T h e d i m e r i z a t i o n o c c u r s w i t h 374 nm r a d i a t i o n and ogr aphy .167 is r e v e r s e d w i t h 254 nm r a d i a t i o n o r a t 22OoC. Two r e p o r t s O f
326
Photochemistry
1,2-,9',10'-dimerization of l i n k e d a n t h r a c e n e s have a p p e a r e d r e c e n t l y , 1687169 and f u r t h e r s t u d i e s i n v o l v i n g t h e p r o c e s s f o r 1 , 2 - d i ( g - a n t h r y l ) e t h a n e ( 2 7 8 ) have been d e s c r i b e d . 1709171 B i a c e t y l s e n s i t i z e d i r r a d i a t i o n o f ( 2 7 8 ) l e a d s e x c l u s i v e l y t o t h e 1 , 2 - , 9',10'dimer ( 2 7 9 ) w i t h a quantum y i e l d o f 0 . 1 and a c h e m i c a l y i e l d o f 62% whereas d i r e c t i r r a d i a t i o n p r o d u c e s t h e 9 , 1 0 - , 9 ' , 1 0 ' - d i m e r . T h e d i m e r i z a t i o n p r o c e s s e s a r e , n o t s u r p r i s i n g l y , i n f l u e n c e d by g e o m e t r i c a l e f f e c t s and f o r example, w h i l e t h e t e t r a c h l o r o compound ( 2 8 0 ) b e h a v e s a n a l o g o u s l y t o t h e hydrocarbon ( 2 7 8 ) i n b o t h d i r e c t and b i a c e t y l s e n s i t i z e d i r r a d i a t i o n s , o n l y t h e 9 , 1 0 - , 9 ' , 1 0 ' dimer i s formed from t h e t e t r a c h l o r o isomer ( 2 8 1 ) u n d e r b o t h sets of c o n d i t i o n s . Bouas-Laurent and co-workers r e c e n t l y r e p o r t e d t h a t w i t h a -Si(Me)2- u n i t c o n n e c t i n g t h e two a n t h r a c e n e s a t t h e 9 - p o s i t i o n s , t h e p h o t o d i m e r i z a t i o n r e a c t i o n is d i r e c t e d e x c l u s i v e l y
t o t h e 1 , 2 - , 9 ' , 1 0 ' - p o s i t i o n s t o y i e l d (282). Japanese workers have a l s o o b s e r v e d t h i s p r o c e s s and now d e s c r i b e t h e i r own s t u d i e s which a r e s i m i l a r t o t h o s e r e p o r t e d e a r l i e r b u t which a l s o i n c l u d e t h e f o r m a t i o n o f ( 2 8 3 ) from t h e germanium compound. 172 An e l e g a n t example o f t h e u s e o f c a t i o n s t o d i r e c t t h e p h o t o p h y s i c s and p h o t o c h e m i s t r y o f l i n k e d a n t h r a c e n e s h a s been d e s c r i b e d f o r t h e anthraceno-crown e t h e r ( 2 8 4 ) . 173 I r r a d i a t i o n a t w a v e l e n g t h s l o n g e r t h a n 330 nm o f ( 2 8 4 ) i n d e g a s s e d methanol s o l u t i o n y i e l d s t h e 9,10-,1',4'-intramolecular dimer ( 2 8 5 ) and t h e a b s e n c e o f t h e c l a s s i c a l 9,10-,9',10'-dimer ( 2 8 6 ) i s r a t i o n a l i z e d i n terms o f e l e c t r o n i c r e p u l s i o n between t h e l o n e p a i r s o f t h e oxygen atoms a t these positions. I n t h e p r e s e n c e o f sodium i o n s , however, t h e p h o t o p r o d u c t i s deduced t o be ( 2 8 6 ) and a l t h o u g h t h i s i s n o t i s o l a t e d t h e evidenCe f o r i t s f o r m a t i o n i s c o m p e l l i n g . I t i s s u g g e s t e d t h a t t h e change of d i r e c t i o n i n t h e p h o t o d i m e r i z a t i o n r e s u l t s from a d e c r e a s e i n t h e oxygen l o n e p a i r r e p u l s i o n on comp l e x a t i o n and t h i s r e s t o r e s t h e normal r e g i o c h e m i s t r y o f t h e r e a c t i o n . T h i s change i n t h e p o s i t i o n s o f d i m e r i z a t i o n i s accompani e d by s i g n i f i c a n t d i f f e r e n c e s i n t h e f l u o r e s c e n c e o f (284) i n t h e a b s e n c e and p r e s e n c e of sodium i o n s : i n t h e former case b o t h s t r u c t u r e d monomer and u n s t r u c t u r e d excimer e m i s s i o n are o b s e r v e d b u t when complexed t h e l a t t e r band is r e d s h i f t e d and i n c r e a s e s Intrachain i n i n t e n s i t y a t t h e e x p e n s e o f t h e monomer band. p h o t o d i m e r i z a t i o n of t h e a n t h r a c e n e m o i e t i e s of 9 - a n t h r y l m e t h y l m e t h a c r y l a t e - m e t h y l m e t h a c r y l a t e copolymers i n d i o x a n e s o l u t i o n h a s been s t u d i e d by R u s s i a n w o r k e r s who c o n c l u d e t h a t t h e r e a c t i o n a r i s e s from t w o mechanisms which g i v e s d i m e r s h a v i n g d i f f e r e n t
lIll4: Photochemistry of Aromatic Compounds
327
s t r u c t u r e s . 174 A c r i d i z i n i u m s a l t s a l s o undergo C4+41 d i m e r i z a t i o n t o y i e l d ( 2 8 7 ) and a s p e c t s of t h e i n t r a m o l e c u l a r i n t e r a c t i o n and r e a c t i o n of t h e a r e n e chromophores i n compounds o f t y p e (288) w i t h n=1-6 and 8 have been 176 The quantum y i e l d s o f t h e r e v e r s i b l e i n t r a m o l e c u l a r d i m e r i z a t i o n have been d e t e r m i n e d i n s e v e r a l s o l v e n t s and are r e p o r t e d t o depend upon t h e v a l u e of g . Formation of t h e dimer a r i s e s from t h e i n t r a m o l e c u l a r excimer and a common p e r i c y c l i c t r a n s i t i o n s t a t e i s assumed f o r t h e forward and back reactions. 6 L a t e r a l - N u c l e a r Rearrangements Arenes of t h e t y p e Ar-X-Y i n which t h e X-Y bond i s r e a d i l y c l e a v e d h o m o l y t i c a l l y undergo f a c i l e l a t e r a l - n x c l e a r r e a r r a n g e m e n t . The a r c h e t y p a l example o f t h i s p r o c e s s i s t h e p h o t o - F r i e s r e a r r a n g e ment which o c c u r s w i t h a r y l e s t e r s and a n i l i d e s and s e v e r a l r e p o r t s o f t h e s e r e a c t i o n s have a p p e a r e d w i t h i n t h e r e v i e w p e r i o d . S e v e r a l b e n w y l o x y n a p h t h a l e n e s , q u i n o l i n e s , and b e n z e n e s have been p h o t o r e a r r a n g e d t o t h e c o r r e s p o n d i n g C-benzoyl p r o d u c t s and t h e m a g n e t i c i s o t o p e and e x t e r n a l m a g n e t i c f i e l d e f f e c t s upon t h e 178 p h o t o - F r i e s r e a c t i o n o f l - n a p h t h y l acetate have been r e p o r t e d . The y i e l d o f 2 - a c e t y l - l - n a p h t h o l , t h e i n - c a g e p r o d u c t from 1n a p h t h y l acetate, show an e x t e r n a l m a g n e t i c f i e l d e f f e c t f o r t h e e s t e r l a b e l l e d w i t h m a g n e t i c a l l y a c t i v e 1 3 C b u t none f o r t h e 1 2 C e s t e r . T h i s f e a t u r e is e x p l a i n e d i n terms o f a r a d i c a l p a i r mechanism from a c o n s i d e r a t i o n of h y p e r f i n e c o u p l i n g between t h e H' and 1 3 C and t h e u n p a i r e d e l e c t r o n on t h e a c e t y l r a d i c a l . Two g r o u p s t h i s y e a r have d e s c r i b e d f e a t u r e s of t h e p h o t o - F r i e s r e a c t i o n of a r y l c i n n a m a t e s . 179J180 I t h a s been p r e v i o u s l y r e p o r t e d t h a t p h e n y l cinnaniate g i v e s 20-308 y i e l d s of 2 ' -hydroxyc h a l c o n e s , 18' b u t now I n d i a n w o r k e r s have examined t h e p h o t o r e a r r a n g e m e n t of t h e c i n n a m a t e s ( 2 8 9 ) i n micellar environment and o b s e r v e an e f f i c i e n t and h i g h y i e l d s y n t h e s i s o f t h e c o r r e s p o n d i n g 2'-hydroxy c h a l c o n e s ( 2 9 0 ) . 17' The 4 ' - i s o m e r ( 2 9 1 ) i s a l s o formed and a l t h o u g h t h e r a t i o of t h e two p r o d u c t s depends on t h e a r y l s u b s t i t u e n t s , t h e t o t a l y i e l d s o f r e a r r a n g e m e n t a r e between 'ZO and 90%. The o t h e r s t u d y of t h e p h o t o c h e m i s t r y of c i n n a m a t e s h a s been c o n c e r n e d w i t h a comparison between t h e r e a c t i o n s o f ( 2 8 9 ) The l a t t e r undergo t h e p h o t o - F r i e s and a r y l d i h y d r o c i n n a m a t e s .
'*'
r e a c t i o n more e f f i c i e n t l y t h a n ( 2 8 9 ) and y i e l d t h e 2'-hydroxyd i h y d r o c h a l o n e s ( 2 9 2 ) so t h a t i t a p p e a r s b e n e f i c i a l t o c o n s i d e r
Photochemistry
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Photochemistry
330
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(305) R = OMe, R’ = H (307)
R = H,
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d e h y d r o g e n a t i o n of ( 2 9 2 ) t o ( 2 9 0 ) i n t h e s y n t h e s i s o f f l a v o n e s ( 2 9 3 ) r a t h e r t h a n u s e t h e more d i r e c t r o u t e i n v o l v i n g r e a r r a n g e m e n t of t h e cinnamates. D u r i n g an i n v e s t i g a t i o n o f t h e p h o t o c h e m i c a l r e a r r a n g e m e n t o f a l l e n i c ester t o c y c l o b u t e n o n e s , it h a s been o b s e r v e d t h a t f o r t h e p h e n y l ester ( 2 9 4 ) a p h o t o - F r i e s r e a c t i o n o c c u r s 182 Y i e l d s are low ( 4 % ) and as e x p e c t e d t h e p r o d u c t ( 2 9 5 ) is accompanied by p h e n o l .
.
A c e t a n i l i d e s have been known f o r many y e a r s t o undergo p h o t o F r i e s r e a r r a n g e m e n t s , 182 and s u c h p r o c e s s e s w i t h b e n z a n i l i d e s have r e c e i v e d f u r t h e r comment. 183 The 2- and 2 ' - m e t h y l b e n z a n i l i d e s b o t h y i e l d t h e e x p e c t e d F r i e s p r o d u c t s and t h e e f f i c i e n c y o f t h e former i s g r e a t e r i n non-polar and non-viscous s o l v e n t s t h a n i n p o l a r and v i s c o u s media. The c o r r e s p o n d i n g n i t r o b e n z a n i l i d e s are p h o t o i n e r t which is c o n s i d e r e d t o r e f l e c t t h e lower e n e r g y o f t h e e x c i t e d s t a t e r e s u l t i n g from t h e p r e s e n c e of t h e s u b s t i t u e n t . Both N,_N-dibenzoyl and _N,N-di-(2-chlorobenzoyl) a n i l i n e s undergo t h e photo-Fries r e a c t i o n . The o b s e r v a t i o n o f t h e p r o c e s s i n t h e l a t t e r c a s e i s s u r p r i s i n g i n view o f t h e r e p o r t e d f a c i l e photode144 h y d r o h a l o g e n a t i o n and c y c l i z a t i o n o f 2 - c h l o r o b e n z a n i l i d e . F u r t h e r d e t a i l s have a p p e a r e d o f t h e p h o t o r e a r r a n g e m e n t of Pl,O_-diacyl-N-phenylhydroxylamines ( 2 9 6 ) . 184 The m i g r a t i n g s p e c i e s i n t h i s c a s e is 'OCOR' ( r a t h e r t h a n 'COR) and b o t h o r t h o and p a r a i s o m e r s ( 2 9 7 ) and ( 2 9 8 ) r e s p e c t i v e l y are formed as w e l l as RCONHPh, R'C02H, and R ' H . The mechanism o f t h i s p r o c e s s h a s been derivative i n v e s t i g a t e d u s i n g t h e g-(l-naphthoyl)-Q-(p-toluoyl) and i t i s r e p o r t e d t h a t t h e r e a c t i o n i s s e n s i t i z e d by benzophenone b u t t h a t t h e r e a r r a n g e m e n t from d i r e c t i r r a d i a t i o n o c c u r s e x c l u s i v e l y from t h e S1 s t a t e : 185 t h i s is r a t i o n a l i z e d by t h e l a r g e e n e r g y gap between t h e S1 and TI s t a t e s of ( 2 9 6 ) . Two examples o f r i n g e x p a n s i o n by l a t e r a l - n u c l e a r r e a r r a n g e ment have b e e n r e p o r t e d w i t h i n t h e y e a r . J a p a n e s e w o r k e r s have given a f u l l e r account of t h e i r earlier r e p o r t e d o b s e r v a t i o n s c o n c e r n i n g t h e p h o t o r e a r r a n g e m e n t o f 2-aryl-1,2-benzisothiazolino n e s ( 2 9 9 ) which w i t h 340 nm r a d i a t i o n i n benzene s o l u t i o n g i v e 13% of (300),186 and T u r r o and co-workers have d e s c r i b e d t h e forma t i o n o f p a r a c y c l o p h a n e s (301) from t h e i r r a d i a t i o n o f l a r g e r i n g 2-phenylcyclanones ( 3 0 2 ) . 187 T h i s l a t t e r r e a c t i o n o c c u r s f o r 1 0 , 1 1 , 1 2 , and 15-membered r i n g c y c l a n o n e s and a r i s e s an u n p r e c e d e n t e d c o m b i n a t i o n p r o c e s s o f b i r a d i c a l s . A t < 15% conv e r s i o n , t h e CI1 compound g i v e s a 94% y i e l d of t h e cyclophane w i t h a quantum y i e l d o f 0 . 6 and t h e s t u d y h a s been e l e g a n t l y and
332
Photochemistry
successfully extended to the formation of the biradicals in the intracrystalline supercage of a NaX zeolite: the cyclanone is absorbed, photolyzed, and gives the paracyclophane trapped by a 'ship in bottle' strategy. The photorearrangement of azoxybenzenes to hydrazobenzenes is a well-studied process but one which continues to attract attention. The reaction has now been studied for methoxy and dimethylamino azoxybenzenes and the rearrangement is observed with 188 varying efficiency for all but the disubstituted derivatives. The intermediate is considered to be (303) which either reverts to starting material or yields the 2-hydroxy compound (304) by either acid or base catalysis. Rates of reaction are very dependent on positions of the substituents and while the conversion of (305) to (306) is efficient, the corresponding process of (307) proceeds slowly. Introduction of dimethylamino substituents markedly reduces the photoreactivity of the azoxybenzene and products derived from intramolecular hydrogen abstraction and cleavage of M=N or C=N bonds become evident. The conversion of (305) to (307) is reported to be a general one-way process for these systems and the azoxy isomer formed is always that with the -N-oxide function far from the arene moiety which has the stronger electron donating substituent. Irradiation of sulphonium salts (308) in acetonitrile solution has been shown to lead to lateral-nuclear rearrangement and the 189 formation of l-(methylthi0)-2-~ubstituted alkylnaphthalenes (309). The quantum yield of product formation varies between 0 . 2 4 and 0.1 but bond cleavage to yield 1-naphthyl methyl sulphide also occurs and MeCONH-CH2-R is a by-product of the migrating group and the solvent. The steric crowding in Ctris(trimethylsilyl)methyll benzene (310) is considered to be the origin of its photolability and on irradiation it efficiently yields (311), (312), and five isomers of (310) in a respective approximate ratio of 13:1:6: a trace of phenyltrimethylsilane is also formed. The reaction is acid catalyzed and with DC1, all the deuterium is incorporated at the benzylic position of (311). The observations are rationalized by a radical combination within a cage to give (313) which on protonation (deuteration) gives (314) and thence either (311) or (312) by deprotonation or loss of Me3Si+respectively.
IIIl4: Photochemistry of Aromatic Compounds
333
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Photochemistry L.J.Johnston and J.C.Scaiano, J.Amer.Chem.Soc., 1986, 108, 2349. See for example A.Padwa, C.Doubleday, and A.Mazzu, J.Org.Chem., 1977, 42, 3271. R.Lapouyade, C.Manigand, and A.Mourmamode, Canad.J.Chem., 1985, 63, 2192. S.Lazare, R.Lapouyade, and R.Bonneau, J.Amer.Chem.Soc., 1985. 107,6604. J.J.M.Lamberts and W.H.Laarhoven, Rec1.Trav.Chim.Pays-Bas, 1984, 103, 131. W.H.Laarhoven, F.A.T.Lijten, and J.M.M.Smits, J.Org.Chem., 1985, 50, 3208. T.Naito, I.Ninomiya, M.Doi, and M.Inoue, Heterocycles, 1985, 23, 1215. T.Naito, Y.Tada, Y.Nishiguchi, and I.Ninomiya, J.Chem.Soc.Perkin Trans.1, 1985, 487. G.J.Fonken, Chem.and Ind., 1962, 1327. S.C.Shim, E.J.Shin, and B.S.An, J.Photochem., 1986, 32, 369. B.V.Maliaiah, G.L.D.Krupadanam, and G.Srimannarayana, Indian J.Chem.Sect.B, 1985, E , 862. P.J.Darcy, H.G.Heller, S.Patharakorn, R.D.Piggott, and J.Whittal1, J.Chem.Soc.Perkin Trans.1, 1986, 315. V.H.M.Elferink and H.J.T.Bos, J.Chem.Soc.Chea.Com., 1985, 882. J.Grimshaw and A.P.de Silva, J.Chem.Soc.Perkin Trans.11, 1982, 857; M.Orlic-Nuber, G.Karminski-Zamola, L.Fiser-Jakic, and J.Jakopcic, Glas.Hem.Drus.Beograd., 1983, 48, 409. Y .T. Park, S.R. Do, and K.D. Lee, Taehan Hwahakhoe Chi. , 1985, 3, 426 (Chem.Abstr. , 104,108 729). H.Kudo, R.N.Castle, and M.L.Lee, J.Heterocycl.Chem., 1985, 22, 211. S.Kobayashi, M.Kihara, and Y.Miyake, Heterocycles, -1985, 2, 159. O.Hoshino, H.Ogasawara, A.Takahashi, and B.Umezawa, Heterocycles, 1985, 23, 1943. J.Bosch, M.Amat, E.Sanfeliu, and M.A.Miranda, Tetrahedron, 1985, 41, 2557. V.K.Bhalerao, B.S.Nanjundiah, H.R.Sonawane, and P.M.Nair, Tetrahedron, 1986 , 42, 1487. Y.Ito, N.Kawatsuki, B.P.Giri, M.Yoshida, and T.Matsuura, J.Org.Chem., 1985, 50, 2893. P.J.Wagner, B.P.Giri, J.C.Scaiano, D.L.Ward, E.Gabe, and F.L.Lee, J.Amer.Chem.Soc., 1985, 107, 5483. J.E.Guillet, W.K.MacInnis, and A.E.Redpath, Canad.J.Chem., 1985, 63, 1333. K.Padmanabhan, D . d p p l K.Venkatesan, and V.Ramamuthy, J.Chem.Soc.Perkin Trans.11, 1986, 897. R.Matsushima and H.Kageyama, J.Chem.Soc.Perkin Tians.11, 1985, 743. W.R.Bergmark, C.Barnes, J.Clark, S.Paparian, and S.Marynowski, J.Org.Chem., 1985, 50, 5612. A.G.Brook and H.J.Wessely, Organometallics, 1985, 2, 1487. M.Ishikawa, H.Sugisawa, S.Matsuzawa, K.Hirotsu, and T.Higuchi, Organometallics, 1986, 5, 182. H.Higuchi, E.Kobayashi, Y.Sakata, and S.Miswni, Tetrahedron, 1986, 42, 1731. G.Sedelmeier, W-D.Fessner, C.Grund, P.R.Spurr, H.Fritz, and H.Prinzbach, Tetrahedron Letters, 1986, 27, 1277. G.Fischer, E.Beckmann, and H.Prinzbach, Tetrahedron Letters, 1986, 27, 1273. T.Tamaki and T.Kokubu, J.Inclusion Phenom., 1984, 2, 815. H-D.Becker and K.Andersson, J.Photochem., 1984, 26, 75. 3913. H-D.Becker, K.Andersson, andJ.Org.Chem., 1985, R.A.Barber, P.de Mayo, K.Okada, and S.K.Wong, J.Amer.Chem.Soc., 1982, 104, 4995. J.M.Masnovi and J.K.Kochi, J.Amer.Chem.Soc., 1985, 107, 6781. T.Otsubo, Y.Sakata, and S.Misumi, Tetrahedron Letters, 1972, 1731.
so,
IIIl4: Photochemistry of Aromatic Compounds 167. 168. 169. 170. 171. 172.
337
T.Toyoda, N.Kasai, and S.Misumi, Bull.Chem.Soc.Jap., 1985, 58, 2348. H-D.Becker and K.Sandross, Tetrahedron Letters, 1983, 24, 3273. M.Daney, C.Vanucci, J-P.Desvergne, A.Castellan, and H.Bouas-Laurent, Tetrahedron Letters, 1985, 2, 1505. H-D.Becker and K.Andersson, Tetrahedron Letters, 1985, 3,6129. H-D.Becker andK.Andersson, Tetrahedron, 1986, 42, 1555. H.Sakurai, K.Sakamoto, A.Nakamura, and M.Kira, Chemistry Letters, 1985, 497.
173. 174, 175. 176. 177. 178. 179. 180. 181. 182. 183. 184.
H.Bouas-Laurent, A.Castellan, M.Daney, J-P.Desvergne, G.Guinand, P. Marsau, and M-H.Riffaud, J.Amer.Chem.Soc., 1986, 108,315. S.P.Koze1, G.I.Lashkov, M.G.Krakovyak, M.G.Shelekhov, and S.S.Skorokhodov, Khim.Fiz., 1985, 4, 56. J.Wagner, J.Bendig, and D.Kreysig, J.Prakt.Chem., 1984, 326, 747. J.Wagner, J.Bendig, and D-Kregsig, J.Prakt.Chem., 1984, 326, 757. P.K.Sharma and R.N.Khanna, Monatsh.Chem., 1985, 116,353. R.Nakagaki, M.Hiramatsu, T.Watanabe, Y.Tanimoto, and S.Nagakura, J.Phys.Chem. , 1985, 89, 3222. A.K.Singh and T.S.Raghuraman, Tetrahedron Letters, 1985, 26, 4125. H.Garcia, S.Iborra, and M.A.MBiranda, Heterocycles, 1985, 23, 1983. V.T.Ramakrishna and J.Kagan, J.Org.Chem., 1970, 35, 290. L S Trifonov, A.S Orahovats , R Prewo , J .H.Bieri, and H Heimgartner, J.Chem.Soc.Chem.Comm., 1986, 708. Y.T.Park, H.C.Yun, S.R.Do, and Y.D.Kim, Taehan Hwahakhoe chi., 1985, 29, 441 (Chem.Abstr.,*, 68 329). T.Sakurai, H.Yamamoto, S.Yamada, and H.Inoue, Bull.Chem.Soc.Jap.,
..
.
.
.
1985, 58, 1174.
187.
T.Sakurai, H.Sukegawa, and H.Inoue, Bull.Chem.Soc.Jap., 1985, 58, 2875. N.Kamigata, S.Hashimoto, M,Kobayashi, and H.Nakanishi, Bull.Chem.Soc.Jap., 1985, 58, 3131. X.Lei, C.E.Doubleday, M.B.Zimmt, and N.J.Turro, J.Amer.Chem.Soc.,
188. 189. 190.
A.Albini, E.Fasani, M.Moroni, and S.Pietra, J.Org.Chem., 1986, 51, 88. F.D.Saeva, B.P.Morgan, and H.R.Luss, J.Org.Chem., 1985, 50, 4360. H.Sakurai, H.Yoshida, and M.Kira, J.Chem.Soc.Chem,Comm., 1985, 1780.
185. 186.
1986, 108,2444.
5
Photo-reduction and -oxidation BY A. COX 1
Introduction
Reviews
have appeared of the solid-state dimer isation of
the photooxidat ion of sulphur compounds,
thiones,
photochemistry,
thiocarbonyl
the DCA sen8 it ized photooxygenat ion of olef ins,
and of the role of intersystem crossing steps in singlet oxygen chemistry. Redu ction of the Carbonvl Grouq
2 Mutual
effects
of
nuclei
on
proton
CIDNP
formation
in
benzophenone photoreduct ion using var ious hydrogen donors such as cyclohexane, observed.6
aliphatic
alcohols
and
triethylamine have
been
The pH dependence of the lifetime of the Norrish type
I I biradical derived from y-phenylbutyrophenone has been studied from which it seems that biradical lifetimes may be determined by several
subtle
and
finely balanced
Alkyl
factors.
phenyl
ketones of the type PhCOCRzCHzRo (R=H, RI-Me, Bu; R-R'-Me) been absorbed on to zeolites NaA, Nay, NaX, Na-Mordenite
intermediate
is
favoured
cyclobutanols by more than 50:l. permitting are
greater
c 1.
mobility,
(HOCH,) ,CO,
MeCOCHMeCH,OH
,
and
On Silicalite, fragmentation of the
Silicalite and photolysed. biradical
have
cyclisation
to
However, on Nay, a zeolite
f ragmentat ion-cyclisat ion rat ios
MeCOCHMeOH,
MeCOCH,CMe,OH
over
,
and
MeCOCMe,OH, MeCO (CH, ) ,OH,
PrCOCHPrOH I have
been
irradiated in heptane or PrCN and the a-hydroxyketones found to decompose by a Type I mechanism. by
H-0
intramolecular
The p-hydroxyketones decompose
H-abstraction 338
and
reactions
of
the
IIIi5: Photo-reduction and -oxidation resulting biradicals intramolecular H
.'
An
339
2-quinonoid intermediate resulting from
abstract ion has
-O-substituted 2-nitrobenzylic
been
observed
for
several
compounds in THF solution. In 8ome
cases, both the triplet excited state and the 2-quinonoid are observed at early times and the p-quinonoid intermediate is formed from the singlet excited state at a rate much faster than triplet decay.1°
A
further report of the photocyclisation of
-o-tert-butylbenzophenone s-hydrogen existing
abstraction in
a
accounts for the very observed,
conformation
in
ideal
terms €or
rapid tr iplet the
compound
internal
hydrogen
of
abstraction, and suggests that this may represent tunne1ling.l' Details of the photoenolisation reactions of some acyclic a,p-unsaturated
ketones
have
appeared
and
competing
reketonisation mechanisms used to rationalise the wide variation in the photochemical deconjugation reactivity of enones. l2 A study of the photoenolisation of 4-benzyl-2-methyl-6-methoxy-5-phenylacetophenone has appeared13 and use of the photoenoliaation of 9-methylacetophenone as a synthetic tool has been investigated. l4 Photoenolisation of the chlorine
containing
compound
2,5-Me,C,H3COCHMeC1
2,6-dimethylindan-l-one, 5,2-Me(MeOCH,)C,H,COEt,
and
2,5-Me,C,H3CHMeC0,Me.
gives
2,5-MezC,H3COEt,
The first two products arise by
H
abstraction followed by C1 loss, and the latter two from initial C1 loss.15 (3-MeCoH,CH0 but not o-MeC,H,COMe
photoenol in var ioua gas matrices.
is observed to give a
2,5- and 2,4-MezC,H,CHO
also
produce enola, and it is concluded that the matrix environment, by
imposing
conformational constraints on
intermediates and
starting materials, can determine the course of reactions-l6 A
method of photocyclising a-(2-toly1)acetophenone dissolved
Photochemistry
340 in small crosslinked polymer beads has been described.
Despite
the high internal viscosity of the beads, the efficiency of this intramolecular photocyclisation is not impaired and the procedure may be
useful for
carrying out
a variety of
photochemical
reactions by means of solar radiation.l7 Some aliphatic and alicyclic ap-unsaturated nitro compounds are also reported to undergo
a
light-induced
E o s in-sens it ized
intramolecular
photoreduction
l-benzyl-l,4-dihydronicotinamide
of
cyclisation.l8 benz i 1
with
involves participation of both
an excited triplet state and an unquenchable excited singlet state; initiation seems to occur by electron-transfer.I9 Interest continues to be shown in photodeconjugation reactions and a study has been reported of the synthetic utility of adding base. ap-unsaturated
esters
RCR' :CRZCOzEt(R=Ph,
RI-Me,
R=R'=R2=Me; R=Me, R1=Rr-H; R=R2-Me, R1=H), Me,C:CHCO,Mej all
(2)
of
inefficiently &-unsaturated Aliphatic
which are
undergo
found
to
photochemical be
efficiently
The RL-H;
(1), or
deconjugation converted
to
isomers in the presence of 1,2-dimethylirnidaz0le?~
thiols
have
been
observed
to
catalyae
the
photoreduction of aromatic carbonyl compounds having a lowest '(nn*) mines.
state by
primary,
secondary, and
The mechanism involves abstraction by an aminyl radical
of H from
S
of the thiol, followed by abstraction of H from the Ca
of the aminyl radical by the thiyl radical. in
tertiary aliphatic
competition with
d isproport ionat ion
of
These processes are ketyl and
aminyl
radicals which have a retarding effect.21 A time-resolved ESR investigation of the photodecomposition of dibenzyl ketone in micellar solution has revealed the existence of a CIDEP effect which
is
cons istent
with
phenacyl-benzyl
radical
pair
lIIL5: Photo-reduction and -oxidation interactions, but interaction.
34 1
little
if
any
benzyl-benzyl radical pair
The micelle thus s e e m to be acting as a "super
cage" which allows strong interactions between both initial and subsequent geminate radical pairs. 22 The intramolecular hydrogen abstraction of tetradecyl anthraquinone-2-carboxylate in aerated 1,1,2-trichlorotrifluoroethane has been found to show a magnetic
field
effect.
This
is
attributed
to
reduction
of
the
tr iplet-singlet intersystem crossing rate which in turn brings about
a
reduction
application of
in
spin
the
cage product yield.23
trapping
to
the
study
of
The a
first
magnetic
field-dependent photochemical reaction has been demonstrated in the case of the photoreduction of naphthoquinone in SDS micellar solution.24 The role of micelle-bound L-ascorbic acid in the photoreduct ion of micelle-solubilized 2-acetoxymethyl-9,10-anthraquinone has been studied and it has been found that only those L-ascorbic acid molecules directly associated
with
the
nonionic
micelles
are
involved
in
photoreduct ion. 25 Complex format ion between exc ited z inc ( I I ) m - t e t r a k i s [ 1-( 3-sulphonatopropyl)-4-pyr idiniolporphyrin
and
anthraquinone-2,6-disulphonate leads to quenching by the quinone
acceptor and -its reduction26 and quinones such as dutoquinone and sodium ant.hraqu inone-2-su 1 phonat-a can be photor educed to their radical anions in a propan-2-01 water mixture in the presence of triethanolamine and eosin Y.27
The effect of the nature of
reagents and solvents on the rate of photoreduction of 2-quinones in the presence of aminee has alao been discuesed, and the relative
rate
constants
found
to
increase
with
increasing
electron-donor ability of the m i n e and electron-acceptor ability of
the
gu inone. 28
Radical
intarmed iatee, obtained
in
the
Photochemistry
342 of
photor educt ion
2,6-dimethyl-y-pyrone
and
y-pyrone-2,6-dicarboxylic acid and its anion have been identified
by ESR measurements.29 3
Reduct ion of N itroaen-containina COmDOUndS
Irradiation of methyl viologen in the presence of simple dicarboxylic or polycarboxylic acids brings about their reduction by a photoinduced electron transfer process.
This depends upon
the appearance of a long wavelength absorption associated with viologen carboxylate ion-pairs, the medium pH, and the excitation wavelength.30 In SDS reversed micelles the benzophenone ketyl radical is found to reduce methyl viologen at a rate which is leas than that observed in their absence, and this is thought to be a consequence of
the
lower rate of
quenching of
benzophenone
triplets by the alcohol medium.31 The same authors also report the effects of salts on the methyl viologen reduction rate in micelles and interpret the results quantitatively by an equation for the second approximation of the Debye-Htckel theory.3z It has also been
suggested that
eosin-sensitized photoreduction of
methyl viologen by di-Na EDTA in micelles in the presence of anthracene may serve as a model for photosystem I in a
SDS
micellar
system
containing
triethanolamine and
In zinc
tetraphenylporphyrintrisulphonate, the rate of photoreduction of
methyl viologen reaches a constant value: this is explained by depr ess ion of
complexation between the por phyr in and methyl
~iologen.~*Methylene blue has also been photoreduced in SDS micelles using 10-dodecyl(acridine orange) (DAO')
as sensitizer.
Singlet-singlet and triplet-triplet energy transfer from DAO' to
MB'
and electron transfer from triplet DAO' to MB'
to
be
important primary
processes.35
were all found
Isopropanol has
been
IIII.5: Photo-reduction and -oxidation
as
described
an
343
efficient
anthraquinone-2-eulphonate
reagent
sens it ized
for
the
sodium
of
methyl
reduct ion
v i ~ l o g e nand ~ ~ photochromism of the crystalline viologen (3) has been
attributed
to
the
formation
of
radical
cations,37
Irradiation of methyl viologen containing tetraphenylporphin or various metal derivatives as sensitizer, and EDTA as electron donor, induces its reduction.38 Net viologen reduction has been observed on
excitation of
the CT
complexes formed between
methylviologen and electron donors such as aniline, aniline derivatives, and
naphthalenes,
and
the
yields
of
electron
transfer are dependent on the excitation ~avelength.~’A laser flash photolysis study has been carried out on the photoreduction of the lumiflavin triplet state in the pH range 3-14 using various donors and only one electron equivalent transfer was found to be significant.
However, several secondary reactions
were observed including back reaction to starting materials, transfer
of
a
second
disproportionation
electron the
of
from
donor
to
flavin,
f lavosemiquinone
and
radical.4o
Photochemical deoxygenation of triphenodioxazine y-oxides has also been descr ibed.41 A singlet state-dr iven photogalvanic cell based
on
chloride
the
photoreduct ion
(oxonine)
by
of
Pe( I I )
3,7-diaminophenoxazinylium
has
been
descr ibed42
and
g-arylidenamines have been reduced to the corresponding m i n e s by irradiation in benzene solution under nitrogen.
The reaction
also occur8 in the solid state, and a two-phase system has been successfully tested far recycling an NADH model for photoreduction of &arylideneanilines been
used
as
using sunlight. 43 Aromatic aminea have
sensitizers
for
cls-5,6-dihydroxy-5,6-dihydrothymine
the in
photoreduction aqueous
of
solution;
Photochemistry
344
2x-
( 3 ) X = 4-MeC6H,S03-,
BF4'
C02Me
Qd
C02Me
O Me w Me he
M
e
@io2Me @Jo2Me
8
C02Me
CO2Me (6)
(7)
345
IIIL5: Photo-reduction and -oxidation 6-hydroxythymin-5-yl radicals are involved as intermediates. 44 4
Miscellaneous Reductions
HMPT has been reported to be a useful solvent for the photoreduction of esters. For example, perf luor inated esters give def luor inated esters as well as the corresponding alkane45 ,46 and alkyl esters give alkanes alone,47 in processes which involve electron-transfer
from
HMPT
to
RO,SMe(R=S-cholesten-3p-y1,
ester.
Methanesulphonates,
4,4-dimethyl-3p-cholestanyl,
3~-cholestanyl, n-nonyl) can also be photoreduced in the same solvent .48 Colloidal platinum catalysts have been prepared by hydrogen- and photo-reduction of
chloroplatinic acid
in the
presence of surfactants and these have been found to be highly active
catalysts
Acetone-sensitized
for
hydrogenation
photolysis
of
1,2,3,4-,
1,2,4,5-tetrachlorobenzene at htrr>285 nm
reductive dechlor inat ion.
’*
of
olef ins. 49
1,2,3,5-,
and
leads principally to
In the presence of certain dyes,
3-methyl-2-aryl- or alkyl-2,3-dihydrobenzothiazoles are reported to be capable of reducing activated halides, sulphonium salts?
and certain pyr idiniurn salts under completely neutral conditions. An electron transfer chain as established in similar reactions of
1,4-dihydropyridines is probably involved. 51 Aqueous solutions of 9-phenylxanthen-9-01 undergo adiabatic photodehydroxylation and as such are the first reported example of this new class of adiabatic photochemical reaction. 52 Photoreduction of water to hydrogen has been catalysed using an aqueous suspension of poly(_p-phenylene) in the presence of Et,N as electron donor, and is the first report of hydrogen evolution photocatalysed by an
organic semiconductor
in sacr if ic ial systems. 53
The
use
of
inclusion complexes of hydrophobic viologens to protect the
Photochemistry
346
pyr idinium moiety from hydrogenation in photochemical hydrogen formation has been descr ibed. 54 Singlet Oxvaen
5 Singlet
oxygen
has
been
produced
non-transition metal oxides such as A1,0,
by
irradiation
of
and MgO in an oxygen
atmosphere. A n energy-transfer mechanism involving 0 and excitons on the metal oxide surface appears to be ~perating.’~A new series of Rosc Bcngals has been described in which the Rose Bengal molecules may aggregate.
The quantum yield of singlet
oxygen formed using such a sensitizer is reported to be dependent on the number of Rose Bengal units attached to the polymer chain. 5 6
Thermal decomposition of
tr iphenylphosphite ozonide
leads to an efficient generation of singlet oxygen with yields of 70-903
depending on reaction conditions.57 Similarly, thermal
decomposition of
1,4-dimethylnaphthalene endoperoxide in CC1,
also leads to expulsion of O,( Microheterogeneous ox idat ion ref era
to a photosens it ized
ox idat ion whose ef f ic iency is enhanced beyond that of d if f us ion
control by the covalent bonding of a sensitizer to a ligand.
A
paper has appeared citing several examples of this phenomenon and suggest ing that chemical organiaat ion in a photochemical system must have a significant effect on the rate of a photosensitized process.59 Singlet oxygen luminescence has been used as a probe of the stilbene triplet surface6’ and a quantum mechanical study of mechanisms of photosens itizat ions, luminescence and quenching of O,(‘ag)
in solution has appeared.
The MINM3/3 method is used
to evaluate the collis ion- induced trans it ion moments for the collision complexes between ethylene and 0, and it is found that during the collision there ia an appreciable strengthening of the
IIIt.5: Photo-reduction and -oxidation S,-T, interconversion. transition
moment
347
This is caused by a large rise in dipole
during
the
collision.61
Singlet
oxygen
generated in the flash photolysis of 0, can be quenched by atomic oxygen.
A two-step mechanism involving formation of a transient
excited 0; complex has been suggested.62
c-Phenyl-N-tert-butylnitrone primarily by
a
is reported to deactivate
reversible electron-transf er
O,('%)
mechanism63 and
quantitative aspects of the quenching of a l l - w - r e t i n o l
by
.
singlet and tr iplet oxygen have been described 64 Intermolecular perturbation and elucidate
the
electron-rich
CI
calculations have
attacking olefins.
mode8 The
of
been
O,('a,)
crucial
interactions, exciplex formation, and
carried out on
roles
allylic
played
to and
by
CI
ionic dissociation are
emphasised.65 Reaction of singlet oxygen with (lB,4E)- (lE,43)and (1~,4~)-1,4-di-tert-butoxybuta-l,3-diene leads to dioxetana rather than to the expected (4+2)-cycloadducts. Two mechaniama, namely a concerted 2,
+
2, cycloaddition and a ptocesa involving a
zwitter ionic intermediate have been advanced, and solvent effect and kinetic data presented in support of the suggestions.66f67 The chemilumineacence intensity at A-1270 for the H,O, reaction and corresponding to the
'A,-,
.)
+
NaOCl
c i transition of 0, ha8
been measured as a function of the concentration8 of H,O,
and
NaOCl. 68 6
Comr>ounds
Oxidation of -tic
Photooxidation of
C,,
and
C,,
studied in the NO-air
C,
cycloalkanes has been
and as part of an investigation
of the chemistry of small ring compound8 the
cyclopropylidenecycloalkane8,
cyclopropylideneadamantane
cyclopropylidenecyclohexane
have
been
oxidised
using
and
singlet
Photochemistry
348 oxygen.
Mechanisms of,
processes
have
been
and
possible
discussed.70
It
intermediates is
also
in these
reported
that
2,3-dimethylbut-2-ene undergoes a novel photooxygenation in an oxygen matrix when excited at the contact charge-transfer band by W-vis
light.71 Some simple alkenea have been oxidised using
various cyanoanthracenes as sensitizer ,72 a reactivity order of singlet oxygen towards conjugated dienes and double bonds has appeared,73 and a study made of the photosensitized oxidation of
.
subst ituted oleates 74 Sen8 it ized photooxygenat ion of thujopsene proceeds by a singlet oxygen mechanism but in the presence of added biphenyl electron transfer occurs to give (4), presumably by
a
radical
cation ~ n e c h a n i s m . ~Cyclic ~
olefins
have
been
photooxidised using FeC1, and the reaction has found application in the synthesis of exo-brevicomin. 76 Detail8 of the singlet oxygenation of
COT
and
of
its methoxy,
methyl,
and
phenyl
der ivat ives ,77 and of the sen8 it ized photooxygenat ion of methyl substituted
1,2-diphenylcyclobutenes have been reported. 78 In
these latter reactions methylene blue sensitized photooxidation of
1,2-diphenylcyclobutenes
the
to
ring
functionalised
cyclopropanea is thought to occur by initial [4+2] cycloaddition to the
styryl
unit
to give
an
endoperoxide.
The
comstock
mealybug pheromone has also been synthesised by an oxidative procedure starting from 2,6-dimethylhepta-2,5-diene. 79 a-Pinene has been photooxidised*O and a study of the competition between the ene reaction and a 1,4-cycloaddition of O , ( ' h g ) l-vinylcycloalkenea
@=5-10,12)
and
in a series of
isopropylcycloalkenes
(IJ-6-8) described.81 Methyl 5,8,11,14,17-eicosopentaenoate gives
only
dihydroperoxide
methylene
isomers
blue-sensitized
as
the
secondary
photooxidation. 8 2
products Two
on
dimer ic
1111.5: Photo-reduction and -oxidation
epidioxides
are
formed
349
on
reaction of
l-~-butylcyclohexa-1,3-diene
Ph,C+EF,
and
83
sen8 it ized
triplet
oxygen with
in a phOtOpKoCeS8 catalysed by
photooxygenat ion
of
[2 , 6 ]
the
spirocycloheptatriene (5) with singlet oxygen gives (6) and (7). This and other work suggests that (5) does not equilibrate with .its
valence
Stereoselect ive
isomer. 84
photooxidat ion
of
isocembrol at the C, double bond gives a aeries of epimeric d
and ant itumour -act ive photochemical ox idat ion products of
provitamin D have been prepared. 86 Photosensit ized oxygenat ion of
us ing var ioua
3,4-dihydro-2H-pyran
cyanoanthracenes
has
been
investigated. The mechanism involves electron tranafer between the excited singlet state of the sensitizer and the substrate, followed
by
reaction
of
singlet
oxygen
as
the
reactive
intermediate in subsequent proces8es. 87 Two stable hydroperoxides are
formed
in
the
photooxygenation acid
3,4-dihydro-6-methyl-2H-pyran-5-carboxylic
transformations
which
of
give
The mechanism
intermediates. 88
of
other
ethyl
of ester,
monooxygenated
the chain process
forming
hydrogen in the photooxidation of formaldehyde and the effect of 89 temperature on the photooxidation of formaldehyde in oxygen-lean atmospheresg0 have been described and a mechanistic study of the photooxidat Ion of a-diketones involving interact ion of tr iplet carbonyl
compound
with
oxygen
has
appeared.
Two
reaction occur competitively, the formation of Oz('%)
types
of
by energy
~~ transfer to 0, and the addition of 0, to triplet d i k e t ~ n e .The effect
of
reactivity
substituents, of
the
photooxygenat ion
solvent,
and
temperature
zwitterionic peroxides of
arising
2-(methoxymethylidene)-
on
the
from
the and
2-(phenoxymethylidene)adamantane and other enol ethers have been
Photochemistry
350 descr ibed92,’93 and methionineg4 general
the results of. photooxidation
studies on
and ketoglutar ic acidg5 have also appeared.
method
for
the
of
synthesis
a-keto
derivatives
A
of
lactones, esters, amides lactams and ketones and involving the dye-sens it ized photooxygenation of enamino carbonyl systems has appeared .96
7
Oxidation of Aromatic COmDOUndS
The 9,lO-dicyanoanthracene sensitized 1,4-dimethylnaphthalene media
gives
the
photooxygenation
is solvent dependent and endoperoxide
of
in non-polar
exclusively.
Mechanisms
incorporating a radical ion pair and a singlet exciplex have been proposed
to
explain
these
solvent
effects .97
W o
reaction
channels are found to be open to the photoexcited 1,4-bridged endoperoxide of 1,4-dimethoxy-9,10-diphenylanthracene, both of which start from upper excited states.98 Only excited oxygen and Photolysis of
the ground state parent anthracene are formed.
dipotassium anthracen-9,lO-ylene disulphate in water or ethanol gives anthraquinone and anthrone, and in deoxygenated solution 9,lO-anthracenediol intermediate.99
has
been
Studies
benzophenone-sens it ized
detected
on
ox idat ion
the of
as
a
long
mechanism
lived
of
the
9-phenylxanthene
with
oxygen us ing inhibitors, quenchers, and a s inglet sent3 it izet , suggest that the reaction occurs by a type I non-chain processloo and
photooxygenat ion
of
the
glycosylf ur an
(R-2,3-O-isopropylidene-p-D-erythrofuranot3yl,
( 8)
,
R’=CH (0H)Me)
followed by reaction with hydrazine gives the
erythrofuranosylpyridazine (9) (same R, RZ=CH(OH)Me) .lol Electron transfer photooxygenat ion of sensitized
by
9,lO-dicyanoanthracene
gives
Ph,C-C-CPh,
in MeCN
benzophenone
and
ML5: Photo-reduction and -oxidation
351
Replacement of MeCN by acetone as solvent leads to
polymer.
increased yields of product in a transformation which occurs v i a Ph,C(OOH)COC(OOH)Ph, Ph,&C(OO-) :CPh,
and
formed
as
an
intermediate
from
tetraphenylcyclopropane.Io2 Electron-donor
1,2-diazylcyclopropanes undergo an ef f icient photooxygenat ion to give 3,5-diaryl-l,2-dioxolanes in polar
solvents and
presence of
These processes are
DCA
as
electron acceptor.
in the
accelerated by addition of some aromatic hydrocarbons and metal salts but
are
DABCO. Io3
completely quenched by Cosens it ized
addition of
Et,N
and
photooxygenation
of
1,l-diphenyl-2-vinylcyclopropane in oxygen-saturated MeCN with
biphenyl
and
9 , l O -d icyanoanthracene
3,3-diphenyl-5-vinyl-l,2-dioxolane,
Ph,CO,
gives
and buta-1,3-diene.
1,2-Cycloaddition with singlet oxygen is not obaerved.lo4 A n investigation of the role of cosensitizers such as biphenyl in 9,lO-dicyanoanthracene-sensitized
cis-trans
reactions
has
appeared."'
a-and
Photoisomerisation and photooxygenation of
tzans-1,2-bis(4-methoxyphenyl)cyclopropaes
are
sensitized
by
9,10-dicyanoanthracene, and the efficiencies of these reactions are enhanced by the addition of inorganic salts such as LiBF, and Mg( CLO,)
,. lo6
The
same
authors
have
also
discussed
the
photochemical oxidat ion of styrylcyclopropanes in the presence of Cu(BF,),. lo7 Unsaturated substrates such as PhChCR Ph,C=CPh,,
w-PhCH-CHPh,
2,3-diphenyldihydro-l,4-dioxine
(R-Ph,H),
PhCMe*CH, , undergo
oxidation
and using
2,4,4,6-tetrabromocyclohexa-2,4-dienone as electron acceptor in a process in which the intermediate radical cation reacts with 0,
through a
radical cation chain mechanism.lo8 DCA-sensitized
photooxidation of 1,4-diphenylbuta-1,3-diene
in MeCN gives an
Photochemistry
352 Me
R
Me
(11)
Me
(14)
Me
R’
1115: Photo-reduction and -oxidation
353
epoxide, ozonide, the cleavage products PhCHO and PhCH-CHCHO, and the endoperoxide. transfer
process
The mechanism appears to be involving
O;.lo9
Ce( IV)
an electron
will
induce
the
photochemical side-chain nitroxylation of alkylbenzenes probably via the nitrate radica1,l.l'
and Fe(I1I) is reported to increase
the rate and quantum yields of photoinitiated hydroxylation of salicylic acid by
Some f lavin analogues have been
HzO,.
reported to catalyse the photooxidation of p-methylbenzyl alcohol by oxygen in the presence of Mg2+ or Znz+ in acetonitrile.l12 Electron transfer photooxygenation of 2,3-diaryl-2,3-dimethyloxiranes
in the presence of DCA gives a
mixture of cis- and grans-ozonides and the observations have been interpreted In terms of the addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides. '13
Dye-sensitized
photooxygenation of PhNHCSNHPh gives the corresponding urea which ( 1141 undergoes photorearrangement to 2-H,NC,H4C,H,NHCHO-2 and sensitized photooxygenation of isorhamnetin-4',5-dimethyl ether is reported to lead to the depside (10).l15
. . ComDoun& Oxidation of Nitroaen-containina
B
It is reported that although enamines (11) and (12) undergo photosens it ized
ox idat ion
in toluene to give the ox idat ion
product normally expected, in methanol the pr inc ipal products are the
oxetans
( 13 )
and
( 14)
r espect ively .116
Photochemical
oxidative dehydrogenation of cyclic enamino diketones of the 8-azasteroid ser ies ha8 been described.'17 PhCOCHPhNR,
Compounds such as
(NR,-morpholino or piperidino) and PhCH(OH)CHPhNR,
(NR,-morpholino)
which
contain potentially
labile C-C
bonds
adjacent to the m i n e have been prepared.
Irradiation in the
presence
electron
of
Ru[4,4'-COZEt(bpy) ],(PF,),
as
acceptor
354
Photochemistry
induces C-C bond cleavage and radical formation.
Methylene
blue
sensitized
photooxidation of
ser ies of
a
Schif f bases
-
derived from p-substituted benzaldehydea and 3-alkoxycarbonyl- or 3-acyl-4-amino-5-aryl-2-methylpyrrole8 can proceed via one of two
reaction channels.
These involve fission of the pyrrole ring to
give enamidonitriles and rearrangement to 4-aroyl-2-aryl-5-hydroxy-6-methylpyr imidines .'I9 C,F ,CH=NC,F
,
has
been
peracetic acid or H20, [C,F,NHCH(C,F,) sen8 it ized
ox id ised
C,F ,CH (OOH)NHC,P
,
us ing
in CHC1, and which on irradiation gives
]202.120 Low
temperature
photooxygenat ion
Me,C(OOH)N:NH
to
The Schif f base
of
in l o w yield.121
acetone
tetraphenylporphyrin hydrazone
produces
Irradiation of acidic methanolic
solutions of 2,4- and 3,4-pyridinedicarboxylic acids under an oxygen atmosphere causes methoxylat ion at the w p o s it ion of the
r ing,
pyridine
whereas
a-methoxylation occurs. decrease
a
under
nitrogen
atmosphere
It has been suggested that the observed
in methoxylation at
the a-poeition
is
not
due
to
quenching of the excimer by oxygen but rather to participation of another excited complex.
A possibility here may be an excited
terplex consisting of two molecules of protonated heterocycle and
of
one
oxygen. 122
Base- induced
oxygenat ion
of
the
3,6-disubatituted pyr idazines (15; R-H, Ph; R'=RZ-OH, C1, OCMe,, OMe;
R1-C1, R'-OCMe,)
using
MesCOK
in
Me,SO
proceeds
with
chemiluminescence. This transformation may be a suitable model for
lum ino1
chemiluminescence.123
FeC1,-H,O-catalysed
photooxidation of the benzylpyrazine (16; R-R'-H, RZ-Ac) leads to (16: RR'=O, R'=Ac;
R-H, R'-OAc,
OH, RZ-Ac), a compound which on
hydrolysis gives products (16; Rz=H) related to the biologically active
metabolite
septor ine.
4( 1H)-Quinolinones
undergo
IlIf5: Photo-reduction and -oxidation
355
-
M e O e C R R '
Me Me
Me Me
(17) OOSiMe, 1 02
Me
Me CN
R = Me, R' IMe,CH R=H,R'=Me Scheme 1
Photochemistry
356 oxidative
cleavage
to
the
2-acylaminobenzoic
acids
on
dye
sensitized photooxygenation in MeOH-aq NaOH, and in some cases to the derived useful
2-aminobenzoic
route
to
derivatives .12'
This may be an alternative
acid.
nuclear
substituted
anthranilic
acids
and
Acr idine and Acr idine yellow are decolour ised in
the presence of Fe(II1) on irradiation at h>360 nm in a process brought about by Ht) radicals. This process has found use in the determination Qu inolines
of have
indole-3-acetic
micro
amounts
been
prepared
acids
and
conversion through N-1-C-2
of
iron,
by
F-and
photooxygenat ion
indole-3-acetaldehydes
and
of this
fission by singlet oxygen may have
significance as a model experiment for the biomimetic synthesis of
alkaloids. 127
quinine
1,1,3,3-tetramethylindan-2-one
Photooxygenation
of
triphenylphosphazine leads to a
carbonyl oxide intermediate and also to chemiluminescence via a zwitter ionic intermediate.
The same workers also report the
first direct observation of the 3-phospha-l,2-dioxa-4,5-diazine (17) by high field 'P
NMR.129 Flash photolysie of lumif lavin in
the presence of C(N02)+ leads to a transient assigned as the one-electron oxidised radical130 and tr imethylsilyl nitr ile is
to
reported
be
a
trapping
intermediates (Scheme 1) oxygen
in methanolic
inc lud ing
agent
for
dipolar
peroxide
Benzimidazole reacts with singlet
solution to give
2,4'-bibenzimidazole,
a
range
of
products
2 , 5 ' -bibenzimidazole
benzimidazolone and 2 (3H)-oxobenzimidazole. 132 The steady state photochemical behaviour of N_,N,N_:N_'-tetramethylbenzidine (TMB) in SDS anionic micelles and on the effect of protonation on the photoionisation of TMB has been
of
diphenylamine
by
hydroxyl
and the oxidation radicals
investigated. 134
IIIl5: Photo-reduction and -oxidation Photooxygenation
of
357
the
pos it ions
benzylic
var i o u s
of
nitroaromatic compounds has been achieved and interpreted in terms of
the greatly enhanced
C-H
acidity of
the benzylic
methylene hydrogens on photochemical excitation,135 and singlet oxygen
is
thought
photodegradation
of
to
an
play
methyl
orange
important in
role
micellar
in
the
solution. 136
N-Vinylcarbazole has been photooridised in a functionalised oil-in-water microemuls ion using bis (hexadecyltrimethylarrpnonium) peroxydisulphate
in
an
electron
transfer
process
The
one-electron photooxidation of E-ethylcarbazole in the presence of
has
CC1,
been
discussed.138
photooxidised in methanol under
(-)
-p-Narcotine
has
been
air,139 and a synthesis of
(*)-sibiricine from the corresponding protoberberine using a photooxygenation procedure has been developed.
9
Mifmllaneous
Oxidation@
Oxidation of t-butanol by benzophenone triplets leads to a number of side products including formic acid, acetone, and at long radiation t imes, Norr ish type-I fragmentation products of benzophenone.141 Laser-induced n-butane and
CO
vibrational photooxidation
of
has been studied142 as has the photooxidation of
1,5-dithiacyclooctane using benzophenone.143 This latter prOC888 involves a two-electron relay and a radical cation intermediate. Radical
anions
have
been
prepared
by
two
complementary
procedures, photooxidation of an electron richer species as for example in the case of tetrabenzocyclooctatetraene dianion, and light-induced electron transfer from a stable carbanion, such as
,'F
to a neutral compound.144 Diacussione have appeared of the
photolysis of m e t h a n e t h i ~ l l and ~ ~ of dimethyl dieulphide in the presence of oxygen,146 and rate constant8 for the photooxidation
Photochemistry
358 of R,S
(R-Me, Et, Pr, CHMe,, determined. 147
been
Bu, CH,CHMe,,
Fluorescence
CMe,)
by O,('A~) have
quenching
processes
of
9,lO-dicyanoanthracene by organic sulphides have been examined and an assessment made of the evidence supporting an electron transfer mechanism. 148 Photooxidation of
the
sodium salt
4,4'-dimethyl-6,6'-dichlorothioindigobissulphonate
of
leuco dye sol
in microheterogeneous media leads to replacement of both OS0,Na groups by
0 groups, 149
and
photooxidat ion of
thiones gives the corresponding reaction
occurring
chromophore.
by
@-unsaturated
ketone as the only product,
attack of
O,('%)
on the thiocarbonyl
Selected and stereospecif ic hydroxylation a to
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f i t
6
Photoreactions of Compounds containing Heteratoms other than Oxygen BY S.T. REID 1
N i t r o g e n - c o n t a i n i n g Compounds
R e a r r a n g e m e n t s . - Examples o f L , E - p h o t o i s o m e r i z a t i o n i n i m i n e s h a v e a g a i n b e e n r e p o r t e d . The p h o t o i s o m e r i z a t i o n s o f m e t h a n i m i n e ' a n d o f f l u o r i n a t e d m e t h a n i m i n e s ' have b e e n examined a n d t h e s t u d y o f t h e p h o t o i s o m e r i z a t i o n o f p r o t o n a t e d and unprotonated imines of 9-*-, ll-%-, 13-*-, and a l l t r a n s - r e t i n a l s h a s a t t r a c t e d a t t e n t i o n i n v i e w o f t h e c o n t i n u i n g i n t e r e s t i n t h e mechanism o f t h e v i s u a l p r o c e s s .3 Evidence from f l a s h p h o t o l y s i s s t u d i e s i n d i c a t e s t h a t t h e p h o t o i s o m e r i z a t i o n of t h e E-hydrazone (1) t o t h e A-hydrazone ( 2 ) may p r o c e e d by way o f a n a z o i n t e r m e d i a t e . 4 Reversible 2,lj-photoisomerization h a s been r e p o r t e d i n 2 , 2 ' dihydroxy-1 - n a p h t h a l d a z i n e , and s h o r t - l i v e d phototautomers have been d e t e c t e d on i r r a d i a t i o n o f t h e same n a p h t h a l d a z i n e ' a n d various salicylideneanilines. 6
'
The quantum y i e l d f o r t h e p h o t o i s o m e r i z a t i o n o f E - a z o benzene h a s been determined, and analogous c o n v e r s i o n s have been r e p o r t e d f o r 1- (phenylazo) -2-naphthols .8 F u r t h e r s u p p o r t f o r t h e i n v o l v e m e n t o f a n i n v e r s i o n mechanism i n s u c h t r a n s f o r m a t i o n s h a s b e e n o b t a i n e d f r o m a s t u d y o f 4-(dimethylamino)-4'-nitroazoS u r p r i s i n g l y , an o x i d a t i v e dimer i s t h e only product o f benzene.' i r r a d i a t i o n of 4-phenylazo-1-naphthol i n t h e p r e s e n c e of oxygen. 1 0 New p h o t o r e s p o n s i v e crown e t h e r s i n c o r p o r a t i n g a n a z o b e n z e n e m o i e t y h a v e b e e n p r e p a r e d . The b i n d i n g p r o p e r t i e s of t h e crown e t h e r ( 3 ) c o n t a i n i n g an i n t r a a n n u l a r 4-methoxyphenylazo s u b s t i t u e n t Photoa r e s i g n i f i c a n t l y a l t e r e d on E + L p h o t o i s o m e r i z a t i o n . l l 13 i n d u c e d a g g r e g a t i o n changes"-and photocontrol of s o l u b i l i t y have been observed f o r poly(L-glutamic a c i d ) , and poly[N-(phenyla z o b e n z o y 1 ) - L - l y s i n e ] s i m i l a r l y shows p r o m i s e a s a p h o t o r e s p o n s i v e s y s t e m . l 4 New a z o b e n z e n e p h o t o r e s p o n s i v e c o m p l e x e s c o n t a i n i n g two i m i n o d i a c e t i c a c i d u n i t s o r e t h y l e n e d i a m i n e u n i t s h a v e a l s o been p r e p a r e d . 1 5 Examples o f p h o t o r e a r r a n g e m e n t a r i s i n g by a 4 ~ ie l e c t r o c y c l i c pathway have b e e n d e s c r i b e d . The low quantum e f f i c i e n c e s
368
IIIJ6: Photoreactions of Compounds containing Heteroatoms other than Oxygen 0
Ph
I
I
Ph
Ph
0Q+R
I R’ (5)
= 3 - , 4 -, =Me,R2= H
( 4 ) R’ = H, R’ R’
R’ = Et or CH=CH,
(6)
5 -, or 6 - M e
, RZ= H
(7)
369
370
Photochemistry
(0.01 - 0.07) r e p o r t e d f o r t h e p h o t o i s o m e r i z a t i o n o f a l k y l a t e d p y r i d i n e s ( 4 ) t o t h e azabicyclo[2.2.0]hexene.s ( 5 ) h a v e b e e n a t t r i b u t e d t o s h o r t - l i v e d s i n g l e t s t a t e s . l 6 The c o m p e t i n g LT4 + T 4 ] photodimerizations a r e believed t o involve preliminary association
v i a a s t r o n g d i p o l e - d i p o l e i n t e r a c t i o n r a t h e r t h a n hydrogen-bonded pairing. Stereospecific photocyclization of the diazepine (6) t o t h e t r i c y c l e ( 7 ) 1 7 and c o n v e r s i o n of t h e 4-pyrimidones (8) i n t o t h e diazabicyclo[Z.Z.O]hexenes t h e p h o t o h y d r a t e s (9) and ( 1 0 ) ( 1 1 ) on i r r a d i a t i o n i n a q u e o u s s o l u t i o n 1 8 h a v e b e e n r e p o r t e d . In a s i m i l a r f a s h i o n , t h e n o v e l 2,6-diazabicyclo[2.2.O]hexane-3,5d i o n e s ( 1 2 ) c a n be p r e p a r e d i n h i g h y i e l d by i r r a d i a t i o n o f t h e c o r r e s p o n d i n g p y r i m i d i n i u m - 4 - o l a t e s ( 1 3 ) i n a c e t o n i t r i l e ' and B-lactam d e r i v a t i v e s a r e o b t a i n e d o n i r r a d i a t i o n o f 3 - d e a z a u r i d ines." The h i g h l y s u b s t i t u t e d p y r i d i n e s ( 1 4 ) h a v e b e e n i d e n t i f i e d a s i n t e r m e d i a t e s i n t h e p h o t o r e a r r a n g e m e n t o f Dewar p y r i d i n e s ( 1 5 ) t o t h e i s o m e r s ( 1 6 ) ; 2 1 t h e same p y r i d i n e d e r i v a t i v e s ( 1 4 ) were s e p a r a t e l y c o n v e r t e d i n t o t h e i d e n t i c a l azabicyclo[2.2.0]hexenes ( 1 6 ) o n i r r a d i a t i o n i n c h l o r o f o r m . The mechanism o f t h e f o r m a t i o n o f Dewar s p e c i e s i n t h e s i n g l e t p h o t o i s o m e r i z a t i o n o f p y r i d i n e , p y r i d a z i n e , p y r i m i d i n e , and p y r a z i n e h a s been d i s c u s s e d . 2 2 P h o t o c h e m i c a l l y i n d u c e d IT e l e c t r o c y c l i c r e a c t i o n s o f t h e stilbene-to-dihydrophenanthrene t y p e a r e common i n n i t r o g e n c o n t a i n i n g systems. Oxidative p h o t o c y c l i z a t i o n of t h e s t y r y l - 1 , 3 d i m e t h y l u r a c i l ( 1 7 ) , f o r example, proceeds from t h e lowest e x c i t e d * s i n g l e t IT,^ s t a t e a n d a f f o r d s t h e n a p h t h a l e n e ( 1 8 j a s shown i n Scheme 1 . 2 3 , 2 4 A s i m i l a r s t r a t e g y h a s b e e n employed i n t h e s y n t h e s i s of two b e n z o [ l Y 2 - b ; 4 , 3 - b ] d i p y r r o l e f r a g m e n t s o f t h e p o t e n t a n t i - t u m o u r a g e n t CC-1065 . 2 5 An a n a l o g o u s e l e c t r o c y c l i z a t i o n h a s b e e n o b s e r v e d o n i r r a d i a t i o n i n b e n z e n e o f t h e y-methoxyimino-aB-unsaturated carboxamide (19) t o g i v e , a f t e r e l i m i n a t i o n of methanol, t h e f u s e d q u i n o l i n e carboxamide ( 2 0 ) . 2 6 P r o t o n a t e d 2-azabuta-lY3-dienes s i m i l a r l y undergo o x i d a t i v e p h o t o c y c l i z a t i o n t o 1 , l -diphenyl-3-arylisoquinolin-4-ones ,27 a n d t h e p h o t o c y c l i z a t i o n o f 1 , 2 , 4 - t r i a r y l p y r i d i n i u m c a t i o n s h a s b e e n shown t o p r o c e e d via d i h y d r o i n t e r m e d i a t e s . 2 8 y 2 9 More s u r p r i s i n g i s t h e r e p o r t e d c o n v e r s i o n o f t h e N-a-cyanoamine ( 2 1 ) i n t o t h e 2-0x0-1 , 2 , 2a,ll-tetrahydrobenzo[3,4-~]imidazolo[3,4-~]quinoline(22) o n i r r a d i a t i o n i n methanol i n t h e p r e s e n c e of potassium hydroxide and p o t a s s i u m i o d i d e ; 3 0 no s a t i s f a c t o r y e x p l a n a t i o n h a s y e t b e e n p r o p o s e d t o a c c o u n t f o r t h i s t r a n s f o r m a t i o n which h a s b e e n shown t o involve i n c o r p o r a t i o n of methanol.
IIIi6: Photoreactions of Compounds containing Heteroatoms other than Oxygen R'
R''N
-1
A \N
hv
(8) R' = F$= Me, R3 = M e or But R'
-$ =
(11)
, R3 = But
(CH,),
+
Rz\
N
H'
R3
(13)
R
= C0,Et
R'
RZ
R3
Ph
H
Ph
Ph
Me
H
Ph
Me
Me
Ph
Me
Ph
Me
SEt
Ph
or CN
(12)
371
372
Me \ 0A
Photochemistry
+
0
NI
Me
Me (17)
0
0
[OI
+---
Scheme
1
OMe
OMe h'V ___)
NEtz (19)
.1
-MtOH
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
hY, MeOH
KOH, K I
H H (21)
MeX)&o
Me0
hV
v NaBH,
(25)
A?
(26)
LQ H
hV
c
0 (27) Ar
=
Ph , o
p
(28)
- MeOC6H4, p - MeOC,H,,
- CIC,H,,
o r d -nclphthyl
373
374
Photochemistry
Novel synthetic applications of the photocyclization of enamides have been reported. Preparation of the fused quinolone (23) from the enamide (24) was achieved by photocyclization and subsequent elimination of a suitably positioned methoxyl group.31 Reductive photocyclization of enamides, usually carried out in the presence o f sodium borohydride, is of particular value in the synthesis of alkaloids. Cyclization of the enamide (25) to the furanoquinolizine (26), for example, has been employed in the synthesis of ipecac and heteroyohimbine alkaloids.32 2,3,9,10Tetraoxygenated protoberberine alkaloids can similarly be converted into 2,3,10,11-protoberberine alkaloids by a sequence of reactions which includes oxidative cleavage, reductive photocyclization in the presence of sodium borohydride , and deoxygenation.33 The stereochemistry of the lactam obtained by reductive photocyclization of N-cyclohex-1-enylbenzamide has been confirmed by a crystal structure determination of the Diels Alder adduct with maleic anhydride. 34 An unusual photocyclization has been observed in the bicyclic dienamides (27) and affords the spiro compounds (28) ;3s there is little precedent for this transformation and the precise mechanism is still uncertain. In contrast to this behaviour, monocyclic dienamides have been shown to undergo a photochemically induced 1 ,3-acyl migration. The reverse process, the electrocyclic ring cleavage of azacyclohexadienes, can also be effected photochemically. Evidence that ring opening of %-substituted 1,Z-dihydroquinolines proceeds from the lowest triplet excited state has been published. 36 The formation of homoadamantano [4,5-<] imidazoles (29) to (31) from the homoadamantano[4,S-~]-5',6'-dihydropyrazines (32) is considered to arise by photochemically induced ring cleavage followed by an alternative cyclization and proton transfer.3 7 Electrocyclic ring opening may also be involved in the photodecomposition of 3-phenyl-2H-1,4-benzoxazin-2-one to Z-phenylbenzoxazole and carbon monoxide. 38 Further studies of photochromic ring opening in spiro [ 2H,1 -benzopyran-2,2' -indolines]39 940 and in related compounds41 have been described. The non-oxidative photocyclization of the N-arylenamine ( 3 3 ) to the hexahydrocarbazole (34) has been investigated using flash photolysis .42 The related aryl vinyl ether photocyclization has been employed in the synthesis o f the benzodihydrofuran ( 3 5 ) from the ether (36) and provides remote control of the stereo-
IIIl6: Photoreactions of Compounds containing Heteroatorns other than Oxygen
(32) R'= $ = $= H R'
R'
(29)
(31) R3 = H
(30)
= R3 = H, R 2 t Me
- R2=(CH,),,R3=H
R' = H , R2= R 3 r Me
- 0-b
Q,k>
hV
I *
I
ph
Ph
(33)
(34)
hV
A.2
Ph
+ hV
Ph
(37) Ar
P
Ph or p -MeC6H,
'""&. Ar
/
\
(38)
Ph +
H?N&
0-
\
(39)
375
376
Photochemistry
c h e m i s t r y a t C-9 i n t h e r e s u l t i n g morphine r i n g s y s t e m . 43 R e a r r a n g e m e n t p r o d u c t s d e r i v e d by 1 , 3 - a n d 1 , s - a r o y l o x y l m i g r a t i o n s were f o u n d o n i r r a d i a t i o n o f N,G-diacyl-N-phenylhydroxyamines . 4 4 C r o s s o v e r e x p e r i m e n t s s u p p o r t an i n t r a m o l e c u l a r pathway i n t h e s e t r a n s f o r m a t i o n s . P h o t o - F r i e s r e a r r a n g e m e n t p r o d u c t s were o b t a i n e d on i r r a d i a t i o n o f c e r t a i n s u b s t i t u t e d b e n z a n i l i d e s . 4 5 The n i t r o g e n atom a p p e a r s t o p l a y a key r o l e i n t h e u n u s u a l 1 , 5 benzoyl m i g r a t i o n observed on i r r a d i a t i o n of t h e 2 , 2 - d i a r y l - 1 , 4 , 4 triphenyl-3-azabut-3-en-l-ones ( 3 7 ) . 4 6 The t e r m i n u s o f t h e m i g r a t i n g group i s t h e phenyl r i n g and t h e p r o d u c t s o b t a i n e d a r e t h e i s o m e r s ( 3 8 ) a n d ( 3 9 ) . A mechanism i n v o l v i n g a n e l e c t r o n t r a n s f e r s t e p has been proposed. I n c o n t r a s t , 4-acyloxy-Z-azabuta1,3-dienes undergo novel photorearrangement t o g i v e dihydroo x a z o l e s i n h i g h y i e l d . 4 7 The c o n v e r s i o n i n v o l v e s a f o r m a l [ 1 , 2 1 a r o y l m i g r a t i o n a n d c y c l i z a t i o n . An o x a - d i - n - m e t h a n e pathway h a s t e n t a t i v e l y been proposed t o account f o r t h i s t r a n s f o r m a t i o n and t h e d e t a i l s a r e o u t l i n e d f o r t h e pentaphenyl d e r i v a t i v e (40) i n Scheme 2 . The f i r s t example o f a n a z a - d i - n m e t h a n e r e a r r a n g e m e n t i n a c y c l i c imines h a s been r e p o r t e d ; 4 8 t h e c y c l o p r o p y l imines (41) were o b t a i n e d i n t h i s way by i r r a d i a t i o n o f l - a z a p e n t a - 1 , s - d i e n e s (42). A t r i p l e t e x c i t e d s t a t e i s involved. Di-n-methane p h o t o r e a r r a n g e m e n t s h a v e a l s o b e e n o b s e r v e d i n 2,6-dimethyl-3,5-dicarbe t h o x y - 1 , 4 - d i h y d r o p y r i d ine4’ a n d i n 5 , 8 - d i h y d r o - 5 , 8 -me t h a n o i s o 50 quinoline derivatives. N i t r i l e y l i d e s a r e r e a d i l y g e n e r a t e d by p h o t o d e c o m p o s i A wide r a n g e o f p o t e n t i a l l y t i o n o f t h e c o r r e s p o n d i n g 2:-azirines. u s e f u l 3 - o x a z o l i n e s h a v e b e e n p r e p a r e d i n t h i s way by a d d i t i o n o f photochemically generated n i t r i l e y l i d e s t o carbonyl containing c o mp oun d s ; 5 1 , 5 2 i r r a d i a t i o n o f t h e a z i r i n e ( 4 3 ) i n t h e p r e s e n c e o f 4-dimethylaminobenzaldehyde ( 4 4 ) , f o r e x a m p l e , g a v e t h e 3-OXaZOli n e ( 4 5 ) . Azomethine y l i d e s h a v e s i m i l a r l y b e e n o b t a i n e d by Intramolecular trapping i n i r r a d i a t i o n of s u b s t i t u t e d a z i r i d i n e s . t h e y l i d e ( 4 6 ) formed on i r r a d i a t i o n o f a z i r i d i n e ( 4 7 ) i s r e s p o n s i b l e f o r t h e f o r m a t i o n o f t h e c y c l o b u t e n e ( 4 8 ) . 5 3 The a z e p i n e ( 4 9 )
i s a l s o a p r o d u c t o f t h i s p h o t o r e a c t i o n . Azomethine y l i d e s h a v e b e e n d e t e c t e d on l a s e r f l a s h p h o t o l y s i s o f t h e l - a z i r i n y l - 1 , 2 d i b e n z o y l a l k e n e s ( 5 0 ) ;54 two r e a c t i o n p a t h w a y s h a v e b e e n o b s e r v e d on s t e a d y - s t a t e i r r a d i a t i o n o f t h e s e a z i r i d i n e s , t h e f i r s t l e a d i n g t o t h e ring-expanded p y r r o l i n e s (51) and t h e second t o t h e isoxa-
111l6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
Scheme 2
R
= Ph, PhCH,, PhCHMe, PhCH,CH,,
or MezCH
377
378
Photochemistry
(47)
Me
(46)
Me Me
+ Me
c" Me
R'
0 (50)
(53 1
1".
I Ph
Ph
1
Ph
(51)
=
R'
o
Ph, R 2
R'
o
H, R2 = Ph
H or CH2Ph
R' = Ck!,Ph, R 2 = H
Scheme 3
IIIi6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
R hV
Et02C-N J - l I N
Et0,C-N
N
NHCOzEt
I
CO,E t (56) R = H or Me
(57)
hV
CHO
R (59) R
0
H, Me, OMe, C I , or F
'0-
hY +
EtOH
0 (60)
(61 1
379
380 z o l e 1521
Photochemistry
via
t h e n i t r e n e ( 5 3 ) a s shown i n Scheme 3 .
N e w examples o f p h o t o r e a r r a n g e m e n t i n five-membered
n i t r o g e n h e t e r o c y c l e s have been r e p o r t e d . P h o t o i s o m e r i z a t i o n of 2 ( t r i m e t h y l s i l y 1 ) p y r r o l e t o t h e 3-isomer h a s been d e s c r i b e d , 5 5 and t h e i s o m e r i c o x a z o l e ( 5 4 ) i s one o f t h e p r o d u c t s o f i r r a d i a t i o n o f 3-methylisoxazolo[4,5-dlpyridazine (55) i n carbon t e t r a c h l o r i d e s o l u t i o n . 56 I r r a d i a t i o n i n d i e t h y l e t h e r , however, a f f o r d s r i n g c l e a v a g e p r o d u c t s d e r i v e d by an i n i t i a l n i t r o g e n - o x y g e n bond homolysis. Photoinduced r i n g cleavage i s p r e f e r r e d i n t h e p y r a z o l e s ( 5 6 ) and y i e l d s t h e n i t r i l e s ( 5 7 ) , presumably by way o f The o x a z i n e s ( 5 8 ) a r e n i t r o g e n - n i t r o g e n bond h o m o l y s i s . 5 7 r e p o r t e d t o be t h e major p r o d u c t s o f i r r a d i a t i o n o f t h e 2 , 7 - d i o x a 3-azabicyclo[3.3.0]oct-3-enes ( 5 9 ) i n p o l a r s o l v e n t s . 58
No r e p o r t s of any s i g n i f i c a n c e have been p u b l i s h e d on t h e photochemistry of n i t r o n e s during t h e y e a r . Further i n v e s t i g a t i o n s on t h e p h o t o r e a r r a n g e m e n t o f h e t e r o a r o m a t i c !-oxides and r e l a t e d s y s t e m s h a v e , however, been d e s c r i b e d i n t h e l i t e r a t u r e . Debate on t h e p o s s i b l e i n t e r m e d i a c y o f o x a z i r i d i n e s i n t h e s e t r a n s f o r m a t i o n s c o n t i n u e s . A s t u d y of t h e e f f e c t of a magnetic (60) i n f i e l d on t h e p h o t o r e a r r a n g e m e n t of i s o q u i n o l i n e !-oxide e t h a n o l i n d i c a t e s t h a t c o n v e r s i o n i n t o t h e l a c t a m (61) d o e s n o t i n v o l v e a n o x a z i r i d i n e i n t e r m e d i a t e b u t p r o c e e d s via a s i n g l e t hydrogen-bonded r a d i c a l - i o n p a i r . 59 In contrast, the singletd e r i v e d p h o t o i s o m e r i z a t i o n o f 1 - c y a n o i s o q u i n o l i n e !-oxide (62) t o t h e 1 , 3 - o x a z e p i n e ( 6 3 ) was n o t a f f e c t e d by an e x t e r n a l l y a p p l i e d m a g n e t i c f i e l d , a n o b s e r v a t i o n which i s i n agreement w i t h t h e i n t e r m e d i a c y o f t h e o x a z i r i d i n e ( 6 4 ) . The r e v e r s i b l e f o r m a t i o n o f two i s o m e r i c o x a z i r i d i n e s h a s been p r o p o s e d t o a c c o u n t f o r t h e o b s e r v e d p h o t o r e a r r a n g e m e n t o f 1-methoxyphenazine I j , N ' - d i o x i d e i n p r o t i c and a p r o t i c s o l v e n t s . 6 0 T r i p h e n y l d i o x a z i n e !-oxides, how61 e v e r , undergo r a p i d d e o x y g e n a t i o n on i r r a d i a t i o n i n c h l o r o f o r m , and p h o t o c h e m i c a l l y i n d u c e d oxygen t r a n s f e r , o b s e r v e d i n p y r i m i d o [ 5 , 4 - g ] p t e r i d i n e !-oxide, h a s been employed i n t h e h y d r o x y l a t i o n of b e n z e n e , t o l u e n e , and a n i s o l e .62 R a d i c a l s a r i s i n g by hydrogen a b s t r a c t i o n from s o l v e n t have been i d e n t i f i e d by e . s . r . s p e c t r o scopy on i r r a d i a t i o n of v a r i o u s h e t e r o a r o m a t i c Ij," - d i o x i d e s .63 9 6 4 A d e t a i l e d e x a m i n a t i o n o f t h e photo-Wallach r e a r r a n g e m e n t o f c e r t a i n methoxyl and dimethylamino d e r i v a t i v e s o f azoxybenzene h a s b e e n r e p ~ r t e d . ~ 'The r e a c t i v e s t a t e h a s been i d e n t i f i e d a s a T , T * c h a r g e - t r a n s f e r complex; a c o m p e t i n g and l i t t l e known l Y 2 - o x y g e n s h i f t was a l s o o b s e r v e d .
IIIt6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
qN+CjQ '0-
EtOH hV
381
0
NC
CN
( 6 41
(62)
CN
(63)
(66)
(65) n = l or 2
hV +
OR
OR
'OF (67) R = Me or RR = CH,
Scheme 4
382
Photochemistry
The photochemistry of oxaziridines has been independently investigated. Regiospecific photorearrangements of spiro-oxaziridines derived from 2-methylindan-1-one, 2-methyltetral-1-one and 1 -methyltetral-2-one have been reported.66 The oxaziridines (651, for example, are converted on irradiation in ethanol into the lactams ( 6 6 ) . A one-photon pathway resulting in ring cleavage and amide formation has also been observed in the gas-phase irradiation o f N-isopropyldimethyloxaziridine .67 An unusual photochemical ring expansion has been reported for the protopine !-oxides (67) and is shown in Scheme 4 ’ The 1-iminopyridinium ylide (68) undergoes photorearrangement to the 1,2-diazepines (69) and (70) via a well-established pathway involving initial photocyclization to the diaziridine intermediates ( 7 1 ) and (72) .68 In contrast, the fused N-iminopyridinium ylide (73) is regiospecifically converted, via an alternative cleavage of the intermediate diaziridine (74), into the 4-aminoimidazo[4,5-~]pyridine (75). Photorearrangement of incorporated N-iminopyridinium ylides has been used to vary the surface characteristics of organized assemblies such as micelles and liposomes; the less polar 1,2-diazepines are the major products of irradiation at 3 0 2 ~ ~ r n . ~ ’ A diaziridine intermediate has also been proposed in the photochemically induced ring contraction o f pyridazin-3-one 1-ethoxycarbonyl imide (76) to the azamaleimide 70 (77) Studies of intramolecular hydrogen abstraction in 0nitrobenzyl systems have again been reported.7 1 Bis-2-nitrobenzyl acetals have been used in this way for the photoreversible protection o f aldehydes and ketones.72 The photo-Smiles rearrangement of 8-(m-nitrophenoxy)ethylamine (78) to the alcohol (79) has been shown to proceed from the triplet excited state;73 the 0and 2-nitro derivatives, however, do not undergo this rearrangement, the major product of irradiation of the 2-isomer (80) being the oxazine (81). Rearrangement in nitrogen-containing carbonyl compounds merits brief discussion in this section as well as in Part 111, Chapter 1. Type I1 photocyclizations are of particular value and have in the past been extensively used in the construction o f nitrogen heterocycles. Competitive y - and 6-hydrogen abstractions have been observed in the a-alkyl-B-oxoamides (821, the former leading to benzoylacetamides (83) via Type I1 photoelimination and
P7
-
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen COzEt
I N
NHC0,Et ‘aNHCOzEt
-
C0,E t
I
(69)
(71)
COzEt
I -N
NHCOzEt NHCO2 Et
EtOzC -
N
O
(72)
NHCO2Et
NHCO2 E t
NHCOZEt
NHCOZEt
a
(70)
3 83
Photochemistry
384
hv
4
HN'
g
H
hU
HzO. NaOH
OCH,CH, NH,
(78)
(79)
(811
(80)
0
-*
0
PhU N / C H Z R 1
I
CON ( c H, R' 1,
CH,~
(83)
N(CH,R' 1,
Ph
NH C H, C H,OH
-
OH
hV
0
I
CH#
(85)
hV --+
I
CH,
(84)
(82) R'
= H , Me, or
R~
=H
Ph
or M ~ P
R3 = H or Me Scheme 5
R'
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
385
. 1
Et
- ox:x: I
I
hV
O 0 X : xI :
0
I
it
Et
(87)
(86)
CH,Ph
(88)
CH 111 N
i j N
R ' (91) R
3:
0-
R '
N
+
R '
CH,Ph, Pri, or But Me Ph+Me
0 Scheme 6
"\
0
(92) n = 1 or 2
I C-
+
111
N+
I
R
386
Photochemistry
t h e l a t t e r t o t h e 3 - a l k y l p y r r o l i d i n o n e s ( 8 4 ) a s shown i n Scheme 5 . 7 4 No e v i d e n c e was f o u n d f o r c y c l o b u t a n o l f o r m a t i o n . F u r t h e r i r r a d i a t i o n o f t h e benzoylacetamides (83) gave t h e a l t e r n a t i v e The d i a s t e r e o s e l e c t i v e s y n t h e s i s o f 3-hydroxypyrrolidinones (85). p r o l i n e s h a s b e e n a c h i e v e d i n a s i m i l a r f a s h i o n by i r r a d i a t i o n o f The c o n v e r s i o n o f d i a p p r o p r i a t e l y s u b s t i t u t e d amino k e t o n e s ? ’ e t h y l p i p e r a z i n e t e t r o n e ( 8 6 ) i n t o t h e 1,4-diaza-7-oxabicyc10[4.3.0]nonane ( 8 7 ) h a s a l s o b e e n e x p l a i n e d i n t e r m s o f a 1 7 4 - b i r a d i c a l i n t e r m e d i a t e . 76 The p h o t o c y c l i z a t i o n i n h e x a n e o f t h e y 6 - u n s a t u r a t e d amine ( 8 8 ) t o t h e p y r r o l i n e s ( 8 9 ) a n d ( 9 0 ) h a s b e e n d e s c r i b e d and i s t h o u g h t t o i n v o l v e e l e c t r o n - p r o t o n t r a n s f e r f r o m a n i n t r a m o l e c u l a r c h a r g e - t r a n s f e r e x c i p l e x , a pathway known t o be r e s p o n s i b l e f o r r e m o t e h y d r o g e n t r a n s f e r by t h e e x c i t e d c a r b o n y l g r o u p . 7 7 5-(Ij7~-Dibenzylamino)-2-phenylpent-l-ene s i m i l a r l y u n d e r g o e s p h o t o c y c l i z a t i o n via a 1 , 7 - h y d r o g e n s h i f t . An e l e c t r o n t r a n s f e r mechanism may a l s o b e i m p l i c a t e d i n t h e p h o t o r e a c t i o n s o f t h e a l d i m i n e s ( 9 1 ) which u n d e r g o p h o t o c h e m i c a l l y i n d u c e d c l e a v a g e t h~e p r o p o s e d pathway i s o u t l i n e d i n rather than c y ~ l i z a t i o n ; ~ Scheme 6 . The p h o t o c y c l i z a t i o n o f ! - s u b s t i t u t e d phthalimides continues t o a t t r a c t a t t e n t i o n . Photochemically induced i n t r a molecular hydrogen a b s t r a c t i o n i s r e s p o n s i b l e f o r t h e conversion of t h e amides (92) i n t o t h e hydropyrazines (93; g = l ) and t h e h y d r o - l , 4 - d i a z e p i n e s ( 9 3 ; g = 2 ). 7 9 1 l - M e t h y l - 6 ~ - i s o i n d o l o [ 2 ~ 1 - ~ 1 indol-6-one (94) can be o b t a i n e d i n a similar f a s h i o n i n 64% y i e l d by i r r a d i a t i o n o f N-(2-ethylphenyl)phthalimide ( 9 5 ) f o l l o w e d by a c i d - c a t a l y s e d dehydration. 8o In c o n t r a s t an e l e c t r o n t r a n s f e r mechanism h a s b e e n p o s t u l a t e d t o a c c o u n t f o r t h e c o n v e r s i o n o f N-substituted phthalimides possessing a terminal thioether f u n c t i o n i n t o t h i a z a c y c l o a l k a n o l d e r i v a t i v e s o n i r r a d i a t i o n . 81 A number o f a p p a r e n t l y u n r e l a t e d p h o t o r e a r r a n g e m e n t s have b e e n r e p o r t e d f o r n i t r o g e n c o n t a i n i n g compounds. E x p e r i m e n t a l d e t a i l s f o r t h e conversion of N-ethylsuccinimide (96) i n t o t e t r a h y d r o - lH-azepine-2,S-dione ( 9 7 ) have been p u b l i s h e d , 8 2 and t h e stereochemistry of t h e photorearrangement of proaporphines t o a p o r p h i n e s h a s b e e n d i s c u s s e d . 83 P h o t o r e a r r a n g e m e n t h a s a l s o b e e n o b s e r v e d i n s a l u t a r i d i n e . 84 A d d i t i o n R e a c t i o n s . - I n t e r m o l e c u l a r a n d i n t r a m o l e c u l a r [82 + 8 2 ] p h o t o c y c l o a d d i t i o n s t o c a r b o n - c a r b o n d o u b l e bonds i n n i t r o g e n
387
IIIf6: Photoreactions of Compounds containing Heteroatoms other than Oxygen 0
HZNOC
CONHz
(Y+
CH2 =CHCN
H
@--CN
1
I"
CH2
I
C"2
I
Ph
Ph
(99)
(98)
H ' 0
0
+
+;
,-CN
I H
H
CH*
I
Ph
(100)
388
Photochemistry
containing systems have been reported. [a2 + 21 Photodimers have been obtained from 2 - p h e n y l - ~ - t r i a z o l o [ l , 2 - ~ ] p y r i d a z i n e - l , 3 - d i o n e and from pyridazino[ 1,2-b]phthalazine-6,11- d i ~ n eand ~ ~thymidine is converted in a similar fashion on acetone-sensitized irradiation into six configurationally distinct dimers of the same type. 86 l-Benzyl-1,4-dihydronicotinamide (98), previously reported to undergo photodimerization, readily adds stereospecifically to acrylonitrile on irradiation to give the regioisomeric adducts (99) and (100) .87 Cyclobutane derivatives are similarly obtained on irradiation of 1,4,5,8-tetraazaphenanthrene with trans-1,2-dichloroethylene, vinyl bromide, acrylonitrile and 2-chloroacrylonitrile;88 a triplet excited state of phenanthrene i s implicated. The use of 1,l-dichloroethylene in photoaddition is preferred to ethylene in some cases for ease of handling; the photoadduct (101) of 3 m e t h o x y i s o q u i n o l i n - 1 - o n e (102) and 1,l-dichloroethylene, for example, can readily be converted into the desired 192-dihydrocyclobut[GI isoquinoline ( 1 0 3 ) by reductive removal of chlorine and elimination of methan01.~’ Irradiation of the chiral lactam (104), derived from (5)-valinol, in the presence of ethylene gave the 90 [ n 2 + T2] adduct (105) in a diastereoisomeric ratio of 12:l. This approach has subsequently been employed in an asymmetric synthesis of the boll-weevil phermone (-)-grandisol. Other related LS2 + n2] photoadditions reported include the reaction of 4-dimethylaminostyrene with 1-vinylpyrene or ~ t y r e n e , ~ ’the reaction of trans-cinnamanonitrile with 2 , 3 dimethylbut-2-ene992 and the formation of the adduct (106) by irradiation of a mixture of 8-methoxypsoralen and thymidine.93 The photocycloaddition of enaminecarbaldhydes to alkenes is of particular value in the synthesis of 1,4-dihydropyridines. This approach has now been employed in the synthesis of 4,4-disubstituted 1,4-dihydropyridines;94 irradiation of enaminecarbaldehydes (107) and alkenes (108) in acetonitrile gave the 2-hydroxytetrahydropyridines (109) in almost quantitative yield. The cyclobutane derivatives (110) are presumed to be intermediates in this transformation. Details of a theoretical study of this photoaddition have been pub1 ished. Analogous intramolecular cycloadditions have been reported. The 9-acyl-9-azatricyclo[S.Z.l . O 1 *6]decan-2-ones (1111, for example, are the major products of irradiation of the 2[lj-acyl-N-(prop-2-enyl)amino]cyclohex-Z-enones (1 1 2 ) . 96 Similarly, irradiation ( A = 350nm) of the 2-alkenylisoquinolin-l(2H) -ones
ZIZl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
Me
389
Me
OMe
""'e;l OH
(106)
~~1;;' M t0,C
R'
I
+
H
~
R3
R4
R
hV
~ MeO& OHC
C02Me
i
R'
(-H,O
R3
"8 C0,Me
HO
I
R'
Photochemistry
390
COR'
hV
R2 H
R' =OMe or Ph, R2
(112)
R'
=H
(111)
= Ph, R2 = Me
0
0
(113) n = 2 or 3
(1141
hV
1
300 nm
R' I
R'
I R3
(116)
(117)
R2
R3
R4
P-tos
H
H
H
- tos - tos
H
CI
H
CI
R'
p p p
- tos
C 0,CH2C H=CH,
CH,0CH2C3CH H
H C02Me
H
C0,Me
H
COzMe
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
1
- qMe Hp
Nc>==(“ NC (122)
NHZ
NC
,,YN
t--
Nc@Me NC
CN
CN
(126)
(1251
Scheme 7
391
Photochemistry
3 92
( 1 1 3 ) gave t h e c y c l o a d d u c t s ( 1 1 4 ) ; 9 7 c y c l o r e v e r s i o n o f t h e s e a d d u c t s was o b s e r v e d on f u r t h e r i r r a d i a t i o n ( A = 300nm) a n d gave t h e 2-vinylbenzamide d e r i v a t i v e s (115) r a t h e r t h a n t h e o r i g i n a l isoquinolin-l(2~)-ones. Intramolecular photocycloaddition of thymine t o hypoxanthine and t o imidazole h a s been observed i n m o l e c u l e s i n which t h e two a d d e n d s a r e s e p a r a t e d by a t r i m e t h y l e n e c h a i n g 8 a n d a s i m i l a r a p p r o a c h h a s b e e n employed i n t h e s y n t h e s i s o f 1 1 - a z a p e n t a c y c l o [ 6 . 2 . 1 .02 7 0 4 l o o 5 "1 d e c a n e 9 9 The a z a q u a d r i -
.
c y c l a n e s ( 1 1 6 ) were o b t a i n e d by d i r e c t o r s e n s i t i z e d i r r a d i a t i o n o f 7 - a z a n o r b o r n a d i e n e s ( 1 1 7 ) . l o o The i n i t i a l f o r m a t i o n o f i n t r a molecular c y c l o a d d u c t s h a s a l s o been proposed t o account f o r t h e c o n v e r s i o n o f 2 - a l l y l a t e d a n i l i n e s i n t o 2 - i n d a n o l s on i r r a d i a t i o n i n p r o t i c s o l v e n t s . 101 [a2 + 2 1 Photocycloaddition o f t h e carbon-nitrogen d o u b l e bond t o a l k e n e s i s r a r e . The r e m a r k a b l e r e g i o s e l e c t i v i t y o b s e r v e d i n s u c h a d d i t i o n s h a s b e e n e x p l a i n e d by means o f p e r t u r b a t i o n m o l e c u l a r o r b i t a l t h e o r y . l o 2 The 1 , 3 - d i a z e t i d i n e ( 1 1 8 ) i s t h e m a j o r p r o d u c t o f i r r a d i a t i o n o f t h e 2-(4-fluorophenyl)benzoxazole (119); '03 photodehalogenation competes w i t h p h o t o d i m e r i z a t i o n i n t h e corresponding 2-(4-chlorophenyl) d e r i v a t i v e and i s observed 3-Aryl-2-isoxazoe x c l u s i v e l y i n t h e 2-(4-bromophenyl)benzoxazole. l i n e s w i t h e l e c t r o n - w i t h d r a w i n g s u b s t i t u e n t s on t h e 3 - a r y l m o i e t y r e a c t r e g i o s p e c i f i c a l l y w i t h i n d e n e t o g i v e a m i x t u r e o f syn- a n d a n t i - c y c l o a d d u c t s ; l o 4 t h e f o r m a t i o n of a c h a r g e t r a n s f e r complex may b e i m p o r t a n t f o r t h e s u c c e s s o f t h i s a d d i t i o n . An e q u i v a l e n t i n t r a m o l e c u l a r c y c l o a d d i t i o n h a s b e e n a c c o m p l i s h e d i n 8 5 % y i e l d by i r r a d i a t i o n of t h e imine (120) i n acetone o r a c e t o n i t r i l e t o g i v e 105 the azetidine (121). The u n u s u a l f o r m a t i o n of 2-amino-1,l-dicyanopropene (122) on i r r a d i a t i o n o f t e t r a c y a n o e t h y l e n e (123) i n a c e t o n i t r i l e (124) i s t h o u g h t t o p r o c e e d by way o f a n e l e c t r o n t r a n s f e r pathway l e a d i n g The a d d i t i o n o f t o t h e c y c l o a d d u c t (125) a s shown i n Scheme 7 . a drop of water t o t h e r e a c t i o n mixture s i g n i f i c a n t l y i n c r e a s e s t h e y i e l d of product and i s presumably r e s p o n s i b l e f o r t h e h y d r o l y s i s o f t h e i n t e r m e d i a t e imine ( 1 2 6 ) . The p h o t o r e a c t i o n s o f I j - a l k y l p h t h a l i m i d e s w i t h a l k e n e s have been e x t e n s i v e l y i n v e s t i g a t e d . O8 Two c o m p e t i t i v e p a t h ways h a v e b e e n e s t a b l i s h e d f o r N - m e t h y l p h t h a l i m i d e ( 1 2 7 1 , t h e f i r s t i n v o l v i n g [ a 2 + n 2 ] c y c l o a d d i t i o n a n d l e a d i n g u l t i m a t e l y t o Z-benza z e p i n e - 1 , s - d i o n e s ( 1 2 8 ) and t h e s e c o n d p r o c e e d i n g by way o f e l e c t r o n t r a n s f e r and r e s u l t i n g i n t h e formation of r a d i c a l c a t i o n -
3 93
IIIJ6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
-I
L
w:e (129)
Me
Me
\=/
benzene
hV
\
0
0
(132)
(130)
+ 0 (1311
a
3 44
Photochemistry
radical anion pairs which can be trapped as the adducts (129) with methanol. Ring-enlarged products are preferred on reaction with electron-poor alkenes and solvent-incorporated products on reaction with electron-rich alkenes. lo8 The regioisomeric naphthazepinediones (130) and (131) are stereospecifically formed in the same way on irradiation of N-methyl-1,2-naphthalenedicarboximide (132) with G - b u t - 2 - e n e,''-but in contrast , the photoaddition of Emethylnaphthalene-l,8-dicarboximide t o alkenes takes a different course and yields cyclobutane and oxetane derivatives. 110 N-Alkenylphthalimides undergo analogous intramolecular phototransformations. Full experimental details for the conversion of phthalimide (133) into pyrrolo[l,2-b] [2]benzazepine-5,10-dione (134) have been published,'" and the same reaction has been employed in the synthesis of certain pyrrolo[l,4]benzodiazepine ant itumour antibiotics . l 2 Benzazepine-5,lO-dione formation has also been found to predominate on irradiation of various N-alk-4enyl- and P J - a l k - 5 - e n y l - p h t h a l i m i d e s , although irradiation of the vinyl ether (135) in methanol gave the solvent-incorporated Methanol-incorporated photocyclizaproducts (136) and (137). tion products have similarly been obtained on irradiation of F j - [ w (cycloalken-1-yl)alkyl]phthalimides' l 4 and of E- (3-phenylallyl)Surprisingly, photoaddition of !-methylarenedicarboximides. 11' phthalimide (138) to the 8-acylindoles (139) gave the spirooxetanes and 1 -methy lp iper id in- 6-one- 2- sp iro - 2 ' - ( 3 ' ,3 ' -dimethyl( 1 4 0) , oxetane) was obtained in 7 5 % yield by photochemically induced addition of N-methylglutarimide to isobutene. 117 Few examples of photocycloaddition of the nitrogennitrogen double bond to alkenes are known and these are usually restricted to molecules in which the double bonds are held in close proximity to each other. A hitherto unknown [ 6 + 2 1 intramolecular addition to a benzene ring has been reported in the azoalkane (141) which i s converted on irradiation into the 1,2-diazetidine (142). 118 Irradiation of 4-phenyl-4~-1,2,4-triazole-3,5-dione (143) in the presence of naphthalene, however, affords the [4 + 21 photoadduct (144) which on further irradiation undergoes triplet-sensitized 119 di-r-methane rearrangement to the urazole (145). Other miscellaneous photocycloaddition reactions which have been studied include the [4 + 21 photoadditions of l-acylnaphthalenes to a-morpholinoacrylonitrile' 2 o and of 2-quinones t o triarylketenimines,12' and the photoadditions of lY3-dimethyluracil and 1,3-dimethyl-6-azathymine to dimethylacetylene
''
$
IZZl6: Photoreactions of Compounds containing Heteroatorns other than Oxygen
hV
l2
@-(CH2
-0 -CH=CH2
0
MeOH
395
\
0 (136) MeOH2C\
(135)
0 (137)
R'SCOMe, R Z = H , R 3 = M e
R' = COzMe or COMe, R2-
Me
4 (141l
(140) R 3 = (CH,),
hV
CDCI,
@
Me Me
(142)
396
Photochemistry
d i c a r b o x y l a t e and t o prop-2-yn-1-01
i n ethanol. 1 2 2
The s t r u c t u r e s
o f t h e [ n 4 + 8 4 ] d i m e r s o b t a i n e d by s o l i d s t a t e i r r a d i a t i o n o f t h e 2 ( 1 H ) - p y r a z i n o n e s (146) have been shown t o have t h e syn, t r a n s s t e r e o c h e m i s t r y ( 1 4 7 ) ; 2 3 i n t r a m o l e c u l a r [ n 4 + *4] p h o t o a d d i t i o n h a s a l s o been o b s e r v e d i n a , w - b i s (9-acridiniumy1)alkanes. 1 2 4 Examples o f t h e p h o t o a d d i t i o n o f s o l v e n t and o t h e r s i m p l e m o l e c u l e s t o n i t r o g e n - c o n t a i n i n g s y s t e m s have been d e s c r i b e d . P o l a r a d d i t i o n o f m e t h a n o l accompanies r e a r r a n g e m e n t on i r r a d i a t i o n o f l-(2,6-dichlorobenzyl)-l,4-dihydronicotinamide (148) a n d y i e l d s 125 i n a d d i t i o n t o o t h e r p r o d u c t s t h e e t h e r s (149) and ( 1 5 0 ) ; i n i t i a l c a r b o n - n i t r o g e n bond h o m o l y s i s i s t h o u g h t t o be r e s p o n s i b l e f o r t h e f o r m a t i o n of t h e s e p h o t o p r o d u c t s . N u c l e o p h i l i c p h o t o a d d i t i o n of a l c o h o l s t o t h e benzene r i n g of p h t h a l i m i d e d e r i v a t i v e s y h a s a l s o been o b s e r v e d on i r r a d i a t i o n . l Z 6 A d d i t i o n of a l c o h o l s & a p h o t o i n i t i a t e d r a d i c a l pathway a r e more common. I r r a d i a t i o n o f 9 - ( 2 , 3 , 5 - t r i - ~ - a c e t y l - B - D - r i b o f u r a n o s y l ) p u r i n e ( 1 5 1 ) i n methanol, f o r e x a m p l e , gave a d i a s t e r e o i s o m e r i c m i x t u r e o f a d d u c t s ( 1 5 2 ) ; 1 2 7 doubt h a s been c a s t on t h e r e c e n t c l a i m t h a t p h o t o a d d i t i o n of methanol t o n e b u l a r i n e p r o c e e d s w i t h h i g h s t e r e o s e l e c t i v i t y . I n i t i a l hydrogen a b s t r a c t i o n i s u n d o u b t e d l y i n v o l v e d i n t h e con(153) i n t o t h e a l c o h o l s v e r s i o n o f !,!-dimethylimidazolidinetrione ( 1 5 4 ) i n t o l u e n e , methanol o r c y c l o h e x a n e ,"* a n d hydroxymethyla t i o n of 1 , 3 - d i m e t h y l u r a c i l h a s been a c h i e v e d i n h i g h y i e l d , p r o b a b l y via an e l e c t r o n t r a n s f e r mechanism, on i r r a d i a t i o n i n I o n i c and r a d i c a l pathways methanol i n t h e p r e s e n c e of EuC13. 12' a r e r e s p e c t i v e l y i n v o l v e d i n t h e p h o t o c h e m i c a l l y i n d u c e d methoxyla t i o n and m e t h y l a t i o n of 3-pyr i d i n e c a r b o x a m i d e i n m e t h a n o l . 130 M e t h y l a t i o n i s t h o u g h t t o o c c u r from t h e e x c i t e d t r i p l e t s t a t e whereas m e t h o x y l a t i o n a r i s e s from two d i f f e r e n t e x c i t e d s i n g l e t states. E l e c t r o n t r a n s f e r i s i m p l i c a t e d i n t h e a d d i t i o n o f amines t o a r e n e s 1 3 1 and t o a l k e n e s .132s 1 3 3 S e l e c t i v e p h o t o a l k y l a m i n a t i o n o f a m i n o a n t h r a q u i n o n e s a n d t h e i r N - a c y l a t e d d e r i v a t i v e s h a s been a c h i e v e d by i r r a d i a t i o n i n t h e p r e s e n c e of a l k y l a m i n e s . 34 Photor e a c t i o n o f N-methylphenanthrene-9,lO-dicarboximide (155) w i t h a pathway d i e t h y l a m i n e gave t h e r i n g - o p e n e d p r o d u c t ( 1 5 6 ) *13' , i n v o l v i n g i n i t i a l N-H hydrogen a b s t r a c t i o n by a ITIT*e x c i t e d t r i p l e t s t a t e o f t h e imide h a s been p r o p o s e d a n d i s o u t l i n e d i n Scheme 8 . E l e c t r o n t r a n s f e r - i n i t i a t e d p h o t o a d d i t i o n s t o iminium s a l t s have a g a i n been r e p o r t e d . I r r a d i a t i o n o f 1-methyl-2-phenyl-
'
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
0
(143)
(144)
Jhv 0 (145)
Me
Me
.rye R
'
h3
Me0
(146)
R * Ph or R-R
(147)
=(CH,),
CONH, McOH
I
R
Me0
I
I
H
H
(149)
(150)
397
Photochemistry
398
hJ
4 MeOH
AcoTi Aco9 OAc
AcO
AcO
OAc
(152)
(151)
$4.0" h3
Me
*
RH
Me'
N wN\Me
0
0 RH = toluene,
(153)
(154)
methanol,
or cyc lohexane
HO NEt, d NHEt2
benzene
0 (155)
(156)
Scheme 8
. I
Me (157)
I
Me
ClO,' (158)
R = C Y O H , CHMeOH, or CMezOH
(159)
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen 1-pyrrolinium
399
p e r c h l o r a t e ( 1 5 7 ) i n t h e p r e s e n c e o f a-hydroxy-
a l k a n o a t e a n i o n s ( 1 5 8 ) l e d , i n t h i s way, t o t h e 2 - ( h y d r o x y a l k y 1 ) p y r r o l i d i n e a d d u c t s ( 1 5 9 ) . 136 E l e c t r o n t r a n s f e r from t h e a n i o n i s f o l l o w e d by e f f i c i e n t d e c a r b o x y l a t i o n . Sequential electron t r a n s f e r - d e s i l y l a t i o n i n such systems h a s been u s e d t o g e n e r a t e b i r a d i c a l s which have been employed i n t h e c o n s t r u c t i o n of p r o t o b e r b e r i n e and s p i r o b e n z y l i s o q u i n o l i n e a l k a l o i d s ’ 3 7 and a s p a r t of a r o u t e t o E r y t h r i n a a l k a 1 0 i d s . l ~ ~I r r a d i a t i o n o f t h e iminium s a l t s ( 1 6 0 ) , f o r example, gave t h e s p i r o compounds ( 1 6 1 ) i n y i e l d s r a n g i n g from 1 7 t o 8 8 % . P h o t o a d d i t i o n of a d e n o s i n e t o 5,7-dimethoxycoumarin gave t h e a d d u c t ( 1 6 2 ) i n c o n t r a s t t o p y r i m i d i n e b a s e s which u s u a l l y The c h a r g e t r a n s f e r - i n i t i a t e d y i e l d [ a 2 -t n21 c y c l o a d d u c t s . 13’ p h o t o a d d i t i o n of t e t r a n i t r o m e t h a n e t o 9 - s u b s t i t u t e d a n t h r a c e n e s h a s been d e s c r i b e d . 140 M i s c e l l a n e o u s R e a c t i o n s . - E x c i t e d s t a t e a l k y l n i t r i t e s undergo competing n i t r o g e n - o x y g e n bond homolysis and exchange by l a b e l l e d n i t r i c o x i d e . 1 4 ’ The s i n g l e t and t r i p l e t e x c i t e d s t a t e e n e r g i e s o f N-nitrosodimethylamine and I j - n i t r o s o p i p e r i d i n e have been d e t e r m i n e d . 42 Under n e u t r a l c o n d i t i o n s , N - n i t r o s a m i n e s undergo n i t r o g e n - n i t r o g e n bond h o m o l y s i s ; i n t h e absence of r a d i c a l s c a v e n g e r s , r e c o m b i n a t i o n i s r a p i d . The s i n g l e t e x c i t e d s t a t e of a n N - n i t r o s a m i n e - a c i d complex b u t n o t t h e t r i p l e t undergoes e f f i c i e n t d i s s o c i a t i o n t o t h e aminium r a d i c a l and n i t r i c o x i d e . N i t r o s a t i o n o f n a p h t h o l s can be e f f e c t e d by i r r a d i a t i o n i n t h e p r e s e n c e o f N - n i t r o s o d i m e t h y l a m i n e . 1 4 3 Three n i t r o x i d e r a d i c a l s have been d e t e c t e d by e . s . r . s p e c t r o s c o p y a s i n t e r m e d i a t e s i n t h e 144 photodecomposition of c a r y o p h j - l l e n e n i t r o s i t e . I r r a d i a t i o n of 1,2,4,5-tetracyanobenzene ( 1 6 3 ) i n a c e t o n i t r i l e i n t h e p r e s e n c e of N - m e t h y l p y r r o l i d i n e (164) gave s u b s t i t u t i o n p r o d u c t s (165) and (166) i n a d d i t i o n t o 1 , 2 , 4 - t r i c y a n o b e n z e n e . 14’ The o r i g i n of t h e amino group i n p r o d u c t (165) h a s n o t been f u l l y e s t a b l i s h e d , but t h e r e i s evidence f o r a photoamination pathway i n v o l v i n g a c e t o n i t r i l e . Reductive d e c y a n a t i o n on i r r a d i a t i o n of p y r a z i n e d i c a r b o n i t r i l e s i s t h e r e s u l t of e l e c t r o n t r a n s f e r from a t e r t i a r y amino group. 46 P h o t o c h e m i c a l l y induced hydrogend e u t e r i u m exchange i n b i o l o g i c a l l y i m p o r t a n t i n d o l e d e r i v a t i v e s 147 i s c o n t r o l l e d by an ammonium group i n t h e s i d e c h a i n . The r a t e of photodecomposition o f p y r i d i n e h a s been shown t o i n c r e a s e w i t h pH. 4 8 Photodecompositions o f N- (1 - n a p h t h o y l l - 0 -
Photochemistry
400
+
HO
OH
1
+
SiMeJ
OH
I
n
(163)
(164)
(165)
(166)
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
&OH
H
CH2S0,Ph
(169)
(170)
(i$p
OMe
OMe
I
CHZ
Me0
I
Ph
Me
(172)
(171)
Me
R'xj33p A
Me
R3
(173)
R
Me
R2 (174)
OMe
401
Photochemistry
402
150 ( p - t o l u o y l ) -Ij-phenylhydroxylamine, substituted benzanilides, and phenazone d e r i v a t i v e s ’ 51 , l S 2 h a v e a l s o been examined. S e v e r a l 7 - d i a l k y l a m i n o c o u m a r i n s u n d e r g o m o d e r a t e l y e f f i c i e n t mono-y-dealkyl153 a t i o n on i r r a d i a t i o n i n benzene i n t h e p r e s e n c e o f n i t r o b e n z e n e , and N - t o s y l a m i n e s u n d e r g o d e t o s y l a t i o n on i r r a d i a t i o n i n t h e p r e s e n c e of an e l e c t r o n - d o n a t i n g a r e n e . 54 P h o t o h y d r o x y n i t r a t i o n o f b i p h e n y l by n i t r a t e i o n h a s been r e p o r t e d , l S 5 a n d photo-oxygena t i o n and p h o t o i s o m e r i z a t i o n have been employed i n a s t e r e o s e l e c t 156 i v e s y n t h e s i s of t h e a l k a l o i d s i b i r i c i n e . 2
S u l p h u r - c o n t a i n i n g Compounds
There i s , i n t h e p e r i o d c o v e r e d by t h i s r e p o r t , a n u n u s u a l l y h i g h l e v e l of i n t e r e s t i n t h e p h o t o c h e m i s t r y of s u l p h u r - c o n t a i n i n g compounds a n d i n p a r t i c u l a r i n t h e p h o t o r e a c t i o n s of t h i o n e s . A d e t a i l e d r e v i e w o f t h e p h o t o c h e m i s t r y of o r g a n o s u l p h u r compounds h a s been p u b l i s h e d . l S 7 The ? - v i n y l s u l p h i d e (167) i s c o n v e r t e d i n t o t h e g - i s o m e r (168) on i r r a d i a t i o n ; 58 b o t h i s o m e r s undergo f u r t h e r i o d i n e - c a t a l y s e d p h o t o c y c l i z a t i o n t o give t h e 1,3-oxat h i a n e s (169) and ( 1 7 0 ) . The mechanism of t h i s c y c l i z a t i o n i s under i n v e s t i g a t i o n . Oxidative p h o t o c y c l i z a t i o n of t h e thiophene (171) gave t h e b e n z o [ b ] t h i o p h e n e ( 1 7 2 ) , l S 9 and 2 - t h i a - 1 0 , l l - d i a z a [3.2]metacyclophan-lO-ene was s i m i l a r l y c o n v e r t e d i n t o 1 , l o - ( 2 thiapropano)-SY6-phenanthroline. 160 Novel n a p h t h o [ Z ’ , 1 ‘ : 4 , 5 ] t h i e n o 161 [ 2 , 3 - c ] q u i n o l i n e s were p r e p a r e d by t h e photoenamide c y c l i z a t i o n . The indolinespirobenzothiopyrans (173) show p h o t o c h r o m i c b e h a v i o u r and y i e l d t h e c o l o u r e d i s o m e r s ( 1 7 4 ) on i r r a d i a t i o n ; 1 6 2 a d r a m a t i c r e d s h i f t o f 1 0 0 nm i s o b s e r v e d i n comparison w i t h t h e oxygen analogue. The p h o t o c h e m i c a l r e a c t i o n s of t h i o p h e n e and i t s d e r i v a t i v e s have been r e v i e w e d . 1 6 3 Dewar t h i o p h e n e (175) h a s been i s o l a t e d and i d e n t i f i e d on a r g o n m a t r i x i r r a d i a t i o n o f t h i o p h e n e (176) a t 10 K ; 1 6 4 a l s o formed a r e t h e a l l e n e ( 1 7 7 ) and t h e t h i o c a r b o x a l d e h y d e ( 1 7 8 ) . I n i t i a l n i t r o g e n - s u l p h u r bond h o m o l y s i s as shown i n Scheme 9 i s t h o u g h t t o be r e s p o n s i b l e f o r t h e p h o t o r e a r r a n g e ment o f t h e 2-naphthyl-1,2-benzisothiazolinone (179) t o t h e whereas t h e n i t r e n e s (181) have been t h i a z e p i n o n e (180) ,16’ proposed a s i n t e r m e d i a t e s i n t h e conversion of t h e 1 A 4 , 2 - t h i a z i n e s (182) i n t o t h e i s o m e r i c p y r r o l e s ( 1 8 3 ) . 6 6 P h o t o c h e m i c a l l y i n d u c e d 1 , 3 - ~ i g m a t r o p i c r e a r r a n g e m e n t h a s been o b s e r v e d i n n a p h t h y l ( a l k y l ) sulphonium s a l t s 1 6 7 and i n a b e n z y l t h i o - 1 , 3 , 4 - t h i a d i a z -
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
+ (176)
(175)
+
CH,=C=CH-CHS
(177 1
403
F C H S
(176)
(179)
I 0
Scheme 9
. a
(182) X
R'
RZ
S
Me
COzEt
S S
Ph Ph
COZEt COMc
S
Ph
CHO
0
Ph
COzEt
C =C
Ph
C02Et
C+R. SR'
(183)
-
1 LQR2 H
SR'
Photochemistry
404
o l e . 1 6 8 A n o v e l r e a r r a n g e m e n t w i t h i n c o r p o r a t i o n of methanol t o g i v e t h e Z-isopropenyl-1,3-thiazine (184) o c c u r s i n low y i e l d on i r r a d i a t i o n of t h e 3-cephem ( 1 8 5 ) ; t h e r e a c t i o n may be i n i t i a t e d by c a r b o n - s u l p h u r bond homolysis. F u r t h e r examples of [ n 2 + 2 1 p h o t o a d d i t i o n of 2 , s d i h y d r o t h i o p h e n e 1 , l - d i o x i d e t o a 6 - u n s a t u r a t e d c y c l i c k e t o n e s and a n h y d r i d e s have been r e p o r t e d . 1 7 0 The p h o t o a d d i t i o n o f p h e n y l (phenylsulphony1)acetylene (186) t o a l k e n e s s u c h a s norbornene (187) t a k e s an u n u s u a l c o u r s e , however, and y i e l d s t h e 1,Z-adduct ( 1 8 8 ) . ' 7 1 An i n t e r m e d i a t e r a d i c a l i o n p a i r may be r e s p o n s i b l e f o r t h i s unprecedented transformation. Intramolecular [n2 + * 2 ] p h o t o a d d i t i o n t a k e s p l a c e i n t h e a l l y l d i h y d r o t h i o p h e n e ( 1 89) t o g i v e a 91 % y i e l d o f t h e t h i a t r i c y c l o - o c t a n o n e (190) 7 2 w h i l e o t h e r 2 , 3 - d i h y d r o - 3 - t h i o p h e n e a c e t a t e s can be d i r e c t l y p r e p a r e d by photoa d d i t i o n of (E)-4-mercapto-2-butenoates t o a l k y n e s . 1 7 3 A d d i t i o n o f s u l p h u r t o cyclohexene t o y i e l d t h e f u s e d t h i i r a n e h a s been a c h i e v e d by i r r a d i a t i o n w i t h a p u l s e d l a s e r (266 nm). 1 7 4 Two d e t a i l e d r e v i e w s of t h e p h o t o c h e m i s t r y of t h i o c a r b o n y l compounds have been p u b l i s h e d . 7 5 ' 1 76 The p h o t o a d d i t i o n of t h i o n e s t o a l k e n e s i s an i m p o r t a n t r o u t e t o t h i e t a n e s . The c y c l o a d d i t i o n of 1,1,3-trimethyl-2-thioxo-ly2-dihydronaphthalene (191) t o e l e c t r o n - d e f i c i e n t a l k e n e s o c c u r s from t h e S 2 e x c i t e d s t a t e and i s s t e r e o s p e c i f i c and r e g i o s p e c i f i c ; 1 7 7 r e a c t i o n w i t h a c r y l o n i t r i l e i n benzene , f o r example, g i v e s t h e t h i e t a n e ( 1 9 2 ) . An a n a l o g o u s p h o t o a d d i t i o n o f t h i o n e s t o k e t e n e a c e t a l s h a s been o b s e r v e d , b u t r e a c t i o n w i t h bromoketene a c e t a l s t a k e s a d i f f e r e n t c o u r s e and y i e l d s t e t r a h y d r o t h i o p h e n e and l Y 3 - d i t h i o l a n e d e r i v a t i v e s 78 T h i e t a n e s were r e a d i l y o b t a i n e d by p h o t o a d d i t ion o f c y c l i c t h i o i m i d e s t o a l k e n e s . T h i e t a n e s (193) and (1941, f o r example, a r e t h e major p r o d u c t s o f i r r a d i a t i o n of N-methylmonot h i o p h t h a l i m i d e (195) i n t h e p r e s e n c e of t h e s t y r e n e d e r i v a t i v e s ( 1 9 6 ) . ' 79 1 , 2 - D i t h i a n e f o r m a t i o n was a l s o o b s e r v e d . N-Methylt h i o p h t h a l i m i d e , I j - m e t h y l d i t h i o p h t h a l i m i d e and x a n t h e n e - 9 - t h i o n e s i m i l a r l y undergo p h o t o a d d i t i o n t o d i p h e n y l k e t e n e t o y i e l d s p i r o t h i e t a n - 2 - o n e s , and t h i o i m i d e s add t o diphenyl-N-(p-tolyllketenimine t o g i v e analogous 2 - i m i n o t h i e t a n e s . 1 8 0 A d e t a i l e d examinat i o n o f t h e p h o t o a d d i t i o n of d i t h i o i m i d e s t o a l k e n e s h a s e s t a b l i s h ed t h a t t h i e t a n e s a r e formed e x c l u s i v e l y ; 1 8 ' Type I and Type I 1 r e a c t i o n s were n o t o b s e r v e d . The f o r m a t i o n o f t h e Z-(Z-mercaptoa l k y 1 ) p y r i d i n e s ( 1 9 7 ) by p h o t o a d d i t i o n of t h e 2 - t h i o p y r i d o n e s (198) t o a l k e n e s (199) i s b e l i e v e d t o a r i s e by i n i t i a l f o r m a t i o n of t h e
,'
.
IIIi6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
405
H
g&e
hJ + McoH
0 C0,Me
(183)
(186)
(18 4)
(187)
hJ
(189)
(190)
CN
(191 1
(192)
Photochemistry
406
eRZ R' = R Z = H
\
+
R'
0
t
Me or Ph, R Z = H
R' = H, RZ = Me, Ph,CN, or COMC
(196 1
(195)
Ph
0
0
(193)
(194)
H
I RZ
+
hJ
HzC=C ' 4 'R3
(198)
(199)
I?'-H or OH
R2=Me, R3 = COzMe or CN R 2 = H , R 3 = C N or Ph
(200)
1 (197)
(201) R = H or Me
n = l or 2
(202 1
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
407
s p i r o t h i e t a n e s (200). 182 I n t r a m o l e c u l a r p h o t o a d d i t i o n h a s been r e p o r t e d i n 3 allyldithiosuccinimides183 and i n 8-alkenyldithiosuccinimides (201) t h e l a t t e r b e i n g c o n v e r t e d i n t o t h e f u s e d t h i e t a n e s ( 2 0 2 ) . 184 S u r p r i s i n g l y , however, i r r a d i a t i o n of [N- ( 4 - p h e n y l b u t - 3 - e n y l ) 3 t h i o p h t h a l i m i d e ( 2 0 3 ) l e a d s t o t h e f o r m a t i o n of a p r o d u c t ( 2 0 4 ) a r i s i n g by i n t r a m o l e c u l a r hydrogen a b s t r a c t ion r a t h e r t h a n t h e
,
e x p e c t e d c y c l o a d d u c t . 18’ Type I1 p h o t o c y c l i z a t i o n h a s a l s o been r e p o r t e d i n N-w-phenylalkyl-thio- o r - d i t h i o - p h t h a l i m i d e s , ’ 86 and t h e monoimide ( 2 0 5 ) i s c o n v e r t e d on i r r a d i a t i o n i n benzene i n t o t h e 8 - l a c t a m ( 2 0 6 ) and thiobenzamide ( 2 0 7 ) by competing Type I 1 p h o t o c y c l i z a t i o n and c l e a v a g e pathways. 1 8 7 T h i s t r a n s f o r m a t i o n i s t h e f i r s t example of a y-hydrogen a b s t r a c t i o n i n a t h i o i m i d e and p r o v i d e s an a t t r a c t i v e r o u t e t o s u l p h u r 3-Acyl-2-thiotetrahydro-l,3-thiazines ( 2 0 8 ) containing 8-lactams. were s i m i l a r l y c o n v e r t e d i n t o t h e B-lactam d e r i v a t i v e s ( 2 0 9 ) by low-temperature i r r a d i a t i o n f o l l o w e d by t r e a t m e n t w i t h a c e t y l I n c o n t r a s t , i r r a d i a t i o n of E- ( d i a l k y l a m i n o m e t h y l ) chloride. 88 t h i o p h t h a l i m i d e s l e d t o c l e a v a g e and t h e f o r m a t i o n o f N - ( t h i o f o r m y l ) d i a l k y l a m i n e s r a t h e r t h a n t h e e x p e c t e d p r o d u c t s of i n t r a m o l e c u l a r hydrogen a b s t r a ~ t i o n !R~e~g i o s e l e c t i v e a - c l e a v a g e h a s been o b s e r v e d i n t h e arylalkylcyclopropenethiones ( 2 1 0 ) l e a d i n g i n methanol t o A pathway \ria t h e f o r m a t i o n of t h e t h i o l a t e e s t e r s ( 2 1 1 ) . t r i p l e t t h i o k e t e n e c a r b e n e s ( 2 1 2 ) h a s been p r o p o s e d and i s shown i n Scheme 1 0 . The p h o t o r e a c t i o n s o f t h i o k e t e n e s d i f f e r from t h o s e o f k e t e n e s and a r e b e l i e v e d t o p r o c e e d by way of 191 t h i i r a n y l i d e n e c a r b e n e and z w i t t e r i o n i c i n t e r m e d i a t e s . O x i d a t i o n p r o d u c t s a r e formed a l m o s t e x c l u s i v e l y on i r r a d i a t i o n of in the and he t e r ocyc 1i c !-a1 ky 1t h i o amide s pte r i d i n et h ione s
’
p r e s e n c e o f oxygen. 3
Compounds c o n t a i n i n g O t h e r Heteroatoms
Much of t h e i n t e r e s t i n t h i s s e c t i o n i s a g a i n c e n t r e d around t h e p h o t o r e a c t i o n s of s i l i c o n - c g n t a i n i n g compounds. S i l a n e p h o t o c h e m i s t r y h a s been reviewed. 1 9 4 P h o t o c h e m i c a l l y induced c l e a v a g e of h e x a - t - b u t y l c y c l o t r i s i l a n e ( 2 1 3 ) a f f o r d s d i - t - b u t y l s i l a p e d i y l (214) and t e t r a - t b u t y l s i l e n e ( 2 1 5 ) , b o t h of which can be t r a p p e d a s a d d u c t s ( 2 1 6 ) C r y s t a l s t r u c t u r e s of two and ( 2 1 7 ) w i t h p h e n y l a c e t y l e n e l g 5
.
i s o m e r i c c y c l o t r i s i l a n e s , c i s , c i s - and cis,trans-1,2,3-tri-t-butyl-
Photochemistry
408 S
0 (204)
(203)
i
+
Ph-C-NH-Ph
R' SH
R2pJ
R' hJ
d
0
1
MeCOCI, EtJN
(212)
(210)
R
=~
/eOH
c , ~Pr, t ,or Pr'
"eoqoMe - 'qL H
I01
Ph
Ph
S (211)
Scheme 10
S
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
409
BU' \si/Bu'
But -Si But /
But
BU'
/ \ Si-Bu' -
-!!!!+
'But
'si=si 0
+
'/'si:
Bu
,But
But
(215) PhCSCH
PhCzCH
But But
BU
I
I
But -Si-SSi--Bu' Ph
(216)
Me
(Me, Si), Si-CO Me' (218 1
Ph (217)
1
But
410
Photochemistry
the 1,2,3-trimesitylcyclotrisilanes, have been determined;lg6 preference exhibited in photofragmentation to E- and 5-1,2-t-butyl1,2-dimesityldisilenes has been discussed in terms of these structures, Fluorescence from tetraneopentyldisilene, obtained in the same way from h e x a n e o p e n t y l c y c l o t r i s i l a n e , has been detected.l g 7 The generation and reactions of silenes have attracted attention. Photoisomerization of the mesitoylsilane (218) affords the silene (219) which is converted into the benzocyclobutane (220) on further irradiation. 98 Addit ion of dimethylsilylene, Me2Si, to this silene (219) yields the disilacyclopropane (221), the first such example of addition to a silene. The silene (222) obtained in the same way from the acylsilane (223) undergoes novel photorearrangement to the isomeric silene (224),* 99 the mechanism of this remarkable transformation is uncertain although a silylene may be an intermediate. The 1-silabicyclo[2.1 .O]pent-3-ene (225), however, has been shown to be an intermediate in the photorearrangement of the 1-silacyclobut-2-ene (226) to the 1-silacyclopenta-2,4diene (227) .200 Evidence for the primary formation of a benzyl-silyl radical pair in the photochemistry of the acyloxymethyl(benzy1)dimethylsilanes (228) has been reported.201 Products obtained include the dioxasilolanes (229) and the isomers (230) and the'ir likely origin is outlined in Scheme 1 1 . A free radical mechanism has also been proposed for the photorearrangement of [tris(trimethylsilyl)methyl]benzene . 202 Dimethylsilanediyl, generated by photodecomposition of d o d e c a m e t h y l c y c l o h e x a s i l a n e , readily abstracts chlorine from carbon tetrachloride,203 whereas irradiation of d o d e c a m e t h y l c y c l o h e x a s i l a n e in carbon t e t r a c h l o r i d e - d i c h l o r o m e t h a n e solution in the presence of 9,lO-dicyanoapthracene affords 1,6204 d i c h l o r o d o d e c a m e t h y l h e x a s i l a n e in 70% yield. Photocycloaddition to silicon-containing alkenes occurs efficiently and is a valuable synthetic procedure. The photoaddition of lY2-bis(trimethylsiloxy)cyclobutene to cyclohex-2-en-1-ones, for example, has been employed in the stereocontrolled synthesis of various sesquiterpenoids and diterpenoids.2 0 5 Similarly, irradiation of 1-trimethylsilyl-hexa-1,s-dien-3-one (231) gave the intramolecular adducts (232) and (233) , 2 0 6 and both di(9-anthryl) dimethylsilane and the corresponding germane derivative gave novel Photoproto[4 + 21 intramolecular adducts on irradiation.'07
IIII6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
Me37i 8
McaSi-Ti
-C
M e 3 S i\
,C10H15
-C,0H,5
Bu
But
M e j S i O\
,C10H15
Si =C Me/
'Si (224)
Me$"'
' 0 s iMe3
411
Photochemistry
412
Me
Me
I
I + Me-Si.
h3
Ph-CH2-Si-CH,-O-C-R
Ph-iH,
II
I
\\C-R
I / CHz-0
0
Me
0
(228) R
5
Me or But
Me
.
I
Me
I
+
Me-Si-0
Me
Me
Ph
-CH2-CH2-Si
I
I
-0 - C
Me
II 0
-R+Ph-CH2
Scheme 11
(231)
1232)
+
Me-Si
1
-0 1FH2 >-R
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
CH,S iMe
CHzS iMe h9
413
Photochemistry
414
d e s i l y l a t i o n h a s been o b s e r v e d on i r r a d i a t i o n of 9 - t r i m e t h y l s i l y l a n t h r a c e n e i n m e t h a n o l ,208 and e l e c t r o n t r a n s f e r p r o c e s s e s a r e involved i n t h e r e g i o s e l e c t i v e p h o t o a l l y l a t i o n of dicyanoarenes w i t h a l l y t r i m e t h y l ~ i l a n ea n~d~ ~ i n t h e photorearrangement of t h e t r i c y c l o h e p t a n e (234) t o t h e b i c y c l o h e p t e n e ( 2 3 5 ) . 2 1 0 Evidence s u p p o r t i n g a c o n c e r t e d [ l , 3 ] s i g m a t r o p i c pathway i n t h e n o v e l p h o t o r e a r r a n g e m e n t of 3-phenylprop-2-enylgermanes t o l - p h e n y l p r o p 2-enylgermanes h a s been d e s c r i b e d . 21 1 P h o t o r e a c t i o n s have a l s o been r e p o r t e d i n organophosphoru s , o r g a n o s e l e n i u m a n d o r g a n o b o r o n compounds. P h o t o c h e m i c a l l y i n d u c e d v a l e n c e i s o m e r i z a t i o n h a s been o b s e r v e d i n 1 , 8 - b i s ( p h o s phano)octa-1 , 3 , 5 , 7-tetraenes'l a n d a c y l p h o s p h i n e o x i d e s undergo p r e f e r e n t i a l a - s c i s s i o n t o g i v e phosphonyl r a d i c a l s on i r r a d i a t i o n i n s o l u t i o n . 2 1 3 p 2 1 4 P h o t o i n i t i a t e d a d d i t i o n of phosphorus t r i b r o m i d e t o d i m e t h y l a c e t y l e n e h a s been r e p o r t e d . 2 1 Irradiation of t h e s e l e n i u m - c o n t a i n i n g p y r a z o l o n e ( 2 3 6 ) i n t h e p r e s e n c e o f oxygen gave t h e b i c y c l e (237) a l o n g w i t h o t h e r p r o d u c t s o f p h o t o oxidation. The p h o t o d e c o m p o s i t i o n o f a z a b o r e t i d i n e s h a s been s t u d i e d , 2 1 7 and a n o v e l p h o t o c h e m i c a l a l k y l m i g r a t i o n h a s been o b s e r v e d i n d i a l k y l b o r y l a c e t o a c e t o n a t e complexes. 2 1 8 The a l k y l a t i o n o f dicyanoarenes with a l k y l t r i p h e n y l b o r a t e s a l t s can 219 be i n d u c e d p h o t o c h e m i c a l l y .
'''
Reference s 1 2 3 4 5 6
7 8 9 10 11
12 13 14 15 16 17
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145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187
Y-L-Chow and Z.Z.Wu,
A. A-Freer, D.K.MacAlpine,
103,
2,
102,
108,
19,
118,
108,
-
-
67,
24,
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen 188 189 190 191 192 193 194 195 196 197 198 199 200
201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219
419
M.Sakamoto, H.Aoyama, and Y.Cmote, Tetrahedron Lett., 1986, 27, 1335. J-D.Coyle and P.A.Rapley, J. Photochem., 1985, 3, 387. S.Singh and V.Ramamurthy, J. Org. Chem., 1985, 50, 3732. S. Singh, H-Nimmesgern, E-Schaumann, and V.Ramamurthy, J. Org. Chem., 1985, 50, 4799. A.Hecke1 and W-Pfleiderer, Helv. Chim. Acta, 1986, 69, 708. A.Hecke1 and W.Pfleiderer, Helv. Chim. Acta, 1986, 69, 704, J.C.Dalton, Org. Photochem., 1985, 1, 149. A.Sch'ifer, M.Weidenbruch, and S.Pohl, J. Organomet. Chem., 1985, 282, 305. J.C.Dewan, S.Mukakami, J.T.Snow, S.Collins, and S.Masamune, J. Chem. S o c . , Chem. Commun., 1985, 892. H. Shizuka, HeTanaka, K.Okazaki, M. Kato, H. Watanabe, Y.Nagai, and M. Ishikawa, J. Chem. SOC., Chem. Commun., 1986, 748. A.G.Brook and H. -J. Wessely, Organometallics, 1985, A, 1487. A.G.Brook, K.D.Safa, P-D-Lickiss,and K.M.Baines, J. Am. Chem. SOC., 1985, 107, 4338. M. Ishikawa, H.Sugisawa, S.Matsuzawa, K.Hirotsu, and T-Higuchi, Organometallics, 1986, 5, 182. M.Kira, H.Yoshida, and H.Sakurai, J. Am. Chem. Soc., 1985, 107, 7767. H.Sakurai, H.Yoshida, and M.Kira, J. Chem. SOC., Chem. Commun., 1985, 1780. R.Nakao, K.Oka, T.Dohmaru, Y.Nagata, and T.Fukumoto, 3. Chem. SOC., Chem. Commun., 1985, 766. Y.Nakadaira, N-Komatsu, and H. Sakurai, Chem. Lett., 1985, 1781. D.De Keukeleire, M.Van Audenhove, L.Van Hijfte, F.Audenaert, and M. Vandewalle, J. Photochem., 1985, 28, 165. P.Wilson, S.Wolff, and W.C.Agosta, Tetrahedron Lett., 1985, 26, 5883. H.Sakurai, K.Sakamoto, A.Nakamura, and M.Kira, Chem. Lett., 1985, 497. J. -P.Desvergne, H. Bouas-Laurent, A. Castellan, J. Kowalski, E.Yurek, and A.de Haut de Sigy, J. Chem. SOC., Chem. Commun., 1986, 82. K.Mizuno, K.Terasaka, M. Ikeda, and Y.Otsuji, Tetrahedron Lett., 1985, 26, 5819 P-GaGassman and B.A.Hay, J. Am. Chem. SOC., 1985, 107, 4075. M-Kobayashi and M.Kobayashi, Chem. Lett., 1986, 385. G.MZrkl, B.Alig, and E.Eck1, Tetrahedron Lett., 1985, 26, 5285. T.Sumiyoshi, W.Schnabe1, and A.Henne, J. Photochem., 1986, 32, 119. T.Sumiyoshi, W.Schnabe1, and A-Henne, J. Photochem., 1986, 32, 191. S.A.Shilov, M.V.Sendyurev, A.M.Taber, and B.I.Ionin, Zh. Obshch. Khim., 1985, 55, 224 (Chem. Abstr., 1985, 103, 6434). N.I.Rtishchev, A-V-El'tsov, I.Ya.Kvitko, and L.V.Alam, Zh. Obshch. Khim., 1985, 55, 2258 (Chem. Abstr., 1986, 105, 5945). D.Maennig, C.K.Narula, H.Noeth, and U.Wietelmann, Chem. Ber., 1985, 3748. K.Okada, Y-Hosoda, and M.Oda, J. Am. Chem. Soc., 1986, 108, 321. J.Y.Lan and G.B.Schuster, J. Am. Chem. SOC., 1985, 107, 6710.
-
-
s,
7 Photoelimination BY S. T. REID This Chapter i s p r i n c i p a l l y concerned with t h e photochemically i n d u c e d f r a g m e n t a t i o n o f o r g a n i c compounds, accompanied by t h e formation of s m a l l molecules such a s n i t r o g e n , carbon d i o x i d e and s u l p h u r d i o x i d e . P h o t o d e c o m p o s i t i o n s r e s u l t i n g i n t h e f o r m a t i o n of two o r more s i z a b l e f r a g m e n t s a r e r e v i e w e d i n t h e f i n a l s e c t i o n . F r a g m e n t a t i o n s a r i s i n g by N o r r i s h Type I a n d I 1 r e a c t i o n s o f c a r b o n y l - c o n t a i n i n g compounds a r e c o n s i d e r e d i n P a r t 111, C h a p t e r 1 , 1
E l i m i n a t i o n o f N i t r o g e n f r o m Azo-compounds
The p h o t o e l i m i n a t i o n o f n i t r o g e n f r o m a c y c l i c a z o a l k a n e s p r o v i d e s an e a s y a n d c o n v e n i e n t r o u t e t o a l k y l r a d i c a l s . Few r e s u l t s o f a n y s i g n i f i c a n c e have, however, been r e p o r t e d i n t h i s a r e a i n t h e p e r i o d c o v e r e d by t h i s r e p o r t . The p h o t o d e c o m p o s i t i o n of a r y l a z o p h o s p h o n a t e s a n d arylazoalkylphosphonates h a s b e e n s t u d i e d , a n d c y c l o h e x y l o x y r a d i c a l s h a v e b e e n g e n e r a t e d by p h o t o l y s i s o f d i c y c l o h e x y l h y p o n i t r i t e C6H1 , 0 N 2 0 C 6 H 1 Much a t t e n t i o n h a s b e e n d e v o t e d t o t h e s t u d y o f t h e p h o t o e l i m i n a t i o n o f n i t r o g e n f r o m c y c l i c a z o a l k a n e s . The p h o t o d e c o m p o s i t i o n of d i a z i r i n e s i s known t o p r o c e e d 9c a r b e n e intermediates r a t h e r than b i r a d i c a l i n t e r m e d i a t e s ? but d e t a i l s of t h e mechanism o f f o r m a t i o n of t h e s e s p e c i e s a r e n o t known w i t h c e r t a i n t y . A t h e o r e t i c a l s t u d y of t h e decomposition h a s been undertaken. P h e n y l c h l o r o c a r b e n e ( 1 1 , g e n e r a t e d by i r r a d i a t i o n o f p h e n y l c h l o r o d i a z i r i n e ( Z ) , h a s been c h a r a c t e r i z e d s p e c t r o s c o p i c a l l y warming t h e m a t r i x t o 3 3 K i n t h e i n an a r g o n m a t r i x a t 1 0 K ; 4 p r e s e n c e o f oxygen gave t h e c a r b o n y l o x i d e ( 3 ) . D i r e c t s p e c t r o s c o p i c i d e n t i f i c a t i o n o f b i s (trifluoromethyl)carbene5 a n d m e t h o x y c h l o r o c a r b e n e 6 o b t a i n e d i n t h e same way f r o m b i s ( t r i f 1 u o r o m e t h y 1 ) d i a z i r i n e and m e t h o x y c h l o r o d i a z i r i n e r e s p e c t i v e l y , h a s a l s o been r e p o r t e d , and evidence f o r t h e e x i s t e n c e and photochemically i n d u c e d i n t e r c o n v e r s i o n o f cis- a n d t r a n s - i s o m e r s o f phenoxyc h l o r o c a r b e n e , g e n e r a t e d by p h o t o e l i m i n a t i o n o f n i t r o g e n from The r e a c t i v i t y o f phenoxychlorodiazirine, h a s been published.
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422
benzylchlorocarbene
( 4 ) , o b t a i n e d i n a s i m i l a r manner f r o m b e n z y l -
c h l o r o d i a z i r i n e ( S ) , h a s been examined; an a c t i v a t i o n b a r r i e r of 6 . 4 k c a l mol-’ h a s b e e n a s s i g n e d f o r 1 , 2 - H m i g r a t i o n , 8 a n d
E-
and Z - c h l o r o s t y r e n e s d e c o m p o s i t i o n i n t h e p r e s e n c e of H C 1 gave ( 6 ) by 1 , 2 - H m i g r a t i o n a n d 1-phenyl-2,2-dichloroethane ( 7 ) by The s t e r e o c h e m i s t r y of d i r e c t r e a c t i o n of t h e c a r b e n e w i t h H C l . ’ such 1 , 2 - H s h i f t s i n s i n g l e t c h l o r o - and phenyl-carbenes h a s been examined. Benzylchlorocarbene h a s a l s o been r e p o r t e d t o undergo a d d i t i o n t o t h e e l e c t r o n - d e f i c i e n t a l k e n e d i e t h y l f u m a r a t e , l 1 and t h e energy b a r r i e r f o r 1,Z-hydrogen m i g r a t i o n i n t h e r e l a t e d b e n z y l b r o m o c a r b e n e h a s b e e n shown t o be 4 . 7 k c a l mol-’ l 2 P h o t o e l i m i n a t i o n o f n i t r o g e n from 1- p y r a z o l i n e s can be
.
used t o g e n e r a t e 1 , 3 - b i r a d i c a l s and p r o d u c t s d e r i v e d therefrom. T r i p l e t 1 , 3 - c y c l o p e n t a d i y l , o b t a i n e d i n t h i s way by benzophenones e n s i t i z e d p h o t o d e c o m p o s i t i o n o f 2,3-diazabicyclo[2.2.llhept-2-ene, h a s been t r a p p e d i n e s s e n t i a l l y q u a n t i t a t i v e y i e l d w i t h molecular o x y g e n . 1 3 The l i f e t i m e s o f t r i p l e t b i r a d i c a l s o b t a i n e d f r o m t h i s a n d o t h e r a z o c y c l o a l k a n e s h a v e b e e n compared. l 4 I n t r a m o l e c u l a r 1 , 3 - d i y l t r a p p i n g on i r r a d i a t i o n o f a z o a l k e n e ( 8 ) t o g i v e t h e t r i c y c l o a l k e n e ( 9 ) i s t h e key s t e p i n a r e c e n t s y n t h e s i s o f (?Ic o r i ~ l i n , ’a n ~d t h e b i r a d i c a l i n t e r m e d i a t e ( 1 0 ) h a s b e e n p r o p o s e d t o a c c o u n t f o r t h e c o n v e r s i o n o f t h e a z o a l k e n e (11) i n t o t h e The p o s s i b l e i s o m e r i c b i c y c l o [ Z . l . O ] p e n t e n e s ( 1 2 ) a n d ( 1 3 ) .I6 intermediacy of diazenyl r a d i c a l s i n such photoelimination r e a c t i o n s h a s b e e n d i s c u s s e d w i t h r e f e r e n c e t o 2,3-diazabicyclo[2.2.1]h e p t - 2 - e n e a n d spiro[cyclopropane-l,7’-[2,3ldiazabicyclo[2.2.1]h e p t - 2 - e n e ] l 7 The d i f f e r e n c e i n t h e p h o t o c h e m i c a l b e h a v i o u r o f
.
4 , 5 - d i a z a t r i c y c l o [ 4 . 3 . 0 .03y7]non-4-en-8-one and t h e corresponding c y c l i c e t h y l e n e a c e t a l h a s b e e n e x p l a i n e d i n t e r m s o f i n i t i a l onebond c l e a v a g e s l e a d i n g t o d i a z e n y l r a d i c a l s ? The r e l a t e d a z o a l k a n e , 4 , s - d i a z a t r i c y c l o [ 4 . 3 . 0 . O 3 7 ] n o n a - 4 , 8 - d i e n e ( 1 4) , u n d e r g a e s competing e l i m i n a t i o n t o t h e t r i c y c l o h e p t e n e (1 5 ) and r e a r r a n g e the aziridine ment t o t h e a z i r i d i n e ( 1 6 ) on d i r e c t i r r a d i a t i o n ; ” i s o b t a i n e d e x c l u s i v e l y on benzophenone-sensitized i r r a d i a t i o n . 1 , 5 - B i r a d i c a l s b e l i e v e d t o b e i n v o l v e d i n t h e m e t a - p h o t o a d d i t i o n of a r e n e s t o a l k e n e s h a v e b e e n i n d e p e n d e n t l y p r e p a r e d by p h o t o Direct e l i m i n a t i o n of n i t r o g e n from t h e a p p r o p r i a t e azoalkanes.
’’
o b s e r v a t i o n o f t h e p r e v i o u s l y unknown t h e r m a l l y l a b i l e 7 - n o r b o r n a d i e n o n e ( 1 7 ) h a s b e e n a c h i e v e d on i r r a d i a t i o n o f t h e 1 - p y r a z o l i n e 21 (18) o r t h e 1 , 2 - a z e t i n e ( 1 9 ) i n 3 - m e t h y l p e n t a n e a t 1 0 K . S i m i l a r l y , Dewar b e n z e n e h a s b e e n p r e p a r e d by p h o t o e l i m i n a t i o n o f
IIIi7: Photoelimination
423
N=N'
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] o c t - 7 -ene , and n i t r o g e n from 7 ,8 - d i a z a t e t r a c y c l o [ 3 . 3 . 0 0 4 0 d i r e c t P y r e x - f i l t e r e d i r r a d i a t i o n of t h e 1 - p y r a z o l i n e ( 2 0 ) i n 23 methanol gave t h e v i n y l c y c l o p r o p a n e ( 2 1 ) i n q u a n t i t a t i v e y i e l d . S u c c e s s i v e p h o t o e l i m i n a t i o n s of n i t r o g e n have been o b s e r v e d i n t h e b i s a z o a l k a n e ( 2 2 ) l e a d i n g i n i t i a l l y t o t h e a z o a l k a n e (23) and t h r e e o t h e r s t e r e o i s o m e r i c a z o a l k a n e s w i t h no e v i d e n c e f o r t h e i n t e r m e d i a c y o f a t e t r a r a d i c a l . 2 4 F u r t h e r i r r a d i a t i o n gave t h r e e s t e r e o i s o m e r i c bi-5,5'-bicyclo[2.1.Olpentanes. 2,3-Diazabicyclo[2.2.2]oct-2-enes undergo p h o t o c h e m i c a l l y i n d u c e d e l i m i n a t i o n o f n i t r o g e n l e s s e f f i c i e n t l y and h i g h e r t e m p e r a t u r e s a r e o f t e n r e q u i r e d t o e f f e c t r e a c t i o n . Slow e l i m i n a t i o n o f n i t r o g e n l e a d i n g t o t h e b i c y c l o [ 2 . 2 . 0 ] h e x a n e ( 2 4 ) was t h e o n l y r e a c t i o n o b s e r v e d on i r r a d i a t i o n of a z o a l k a n e ( 2 5 ) i n methanol o r a c e t o n e s o l u t i o n . 25 P h o t o r e a c t i v i t y c a n be enhanced by t h e i n t r o d u c t i o n of s u i t a b l y p o s i t i o n e d c y c l o p r o p y l g r o u p s . I n t h e 2,3-diazabicyclo[2.2.2]oct-2-ene ( 2 6 1 , f o r example, c y c l o p r o p y l c a r b i n y l r e a r r a n g e m e n t l e a d i n g t o c y c l o a l k e n e s ( 2 7 ) , ( 2 8 ) a n d (29) s u c c e s s f u l l y competes w i t h r i n g c l o s u r e a n d s c i s s i o n o f t h e i n t e r m e d i a t e l Y 4 - b i r a d i c a l ( 3 0 ) which g i v e r e s p e c t i v e l y t h e 26 bicyclo[2.2.0]hexane (31) and t h e hexadiene (32). E l i m i n a t i o n of n i t r o g e n i s t h e major r e a c t i o n pathway o b s e r v e d on i r r a d i a t i o n ( A = 185 nm) o f g- o r ~ - 1 , 2 - d i a z a c y c l o i s p r e f e r r e d on i r r a d i a o c t - l - e n e , whereas 2,:-photoisomerization t i o n a t l o n g e r w a v e l e n g t h s (A = 350 nm) . 2 7 The t r i p l e t b i r a d i c a l , 2-methylenecyclohept-3-en-ly5-diyl, i s formed and h a s been i d e n t i f i e d by e . s . r . s p e c t r o s c o p y on i r r a d i a t i o n o f 6,7-diaza-Z-me28 thylenebicyclo[3.2.2]nona-3,6-diene i n a g l a s s y m a t r i x a t 77K. The a n a l o g o u s c o n v e r s i o n o f 3H-pyrazoles i n t o c y c l o p r o p e n e d e r i v a t i v e s i s known t o p r o c e e d via c y c l i z a t i o n o f a t r a n s i e n t v i n y l c a r b e n e . The c y c l o p r o p e n e ( 3 3 ) , f o r example, h a s been o b t a i n e d i n t h i s way i n e x c e l l e n t y i e l d by i r r a d i a t i o n o f t h e 3H-pyrazole (34) . 2 9 The f u s e d 3 H - p y r a z o l e s ( 3 5 1 , however , behave d i f f e r e n t l y a n d t h e b i r a d i c a l i n t e r m e d i a t e s (36) c a n be t r a p p e d w i t h f u r a n t o g i v e t h e a d d u c t s ( 3 7 ) . 30 A z i r i d i n e s c a n s i m i l a r l y be o b t a i n e d by p h o t o e l i m i n a t i o n of n i t r o g e n from l Y 2 , 3 - t r i a z o l i n e s . T h i s a p p r o a c h h a s been u s e d i n t h e s y n t h e s i s o f h e t e r o [ 4 . 2 . l ] p r ~ p e l l a n e s . ~1~, 2 , 3 - T r i a z o l e s , however, undergo p h o t o d e c o m p o s i t i o n i m i d o y l c a r b e n e s . The t r i a z o l e s ( 3 8 ) , f o r example, a r e c o n v e r t e d i n t h i s way i n t o t h e e x p e c t e d b e n z i n d o l e s (39) . 3 2 S u r p r i s i n g l y , t h e i s o m e r i c t r i a z o l e s
425
IIIl7: Photoelimination
(2 4)
(25)
t
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426
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R' = C02Et, R 2 = H R1 = C 0 2 M e or CN, R2 = H or Me
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( 4 0 ) gave t h e same b e n z i n d o l e s ( 3 9 ) t o g e t h e r w i t h s m a l l e r amounts Intermediate 1I-J-azirines ( 4 2 ) a s of t h e e x p e c t e d b e n z i n d o l e s ( 4 1 ) . shown i n Scheme 1 a r e p r o p o s e d t o a c c o u n t f o r t h e s e o b s e r v a t i o n s . 4aH-Carbazoles ( 4 3 ) a r e b e l i e v e d t o be i n t e r m e d i a t e s i n t h e photochemically induced conversion of ? - s u b s t i t u t e d l-arylbenzot r i a z o l e s ( 4 4 ) i n t o c y c l o p e n t a q u i n o l i n e s ( 4 5 ) ;33 t h e r e a c t i o n
s e q u e n c e which i n v o l v e s p h o t o e l i m i n a t i o n o f n i t r o g e n f o l l o w e d by p h o t o c h e m i c a l l y i n d u c e d a z a - d i - r - m e t h a n e r e a r r a n g e m e n t i s shown i n Scheme 2 . Benzo d e r i v a t i v e s o f 4 a - m e t h y l - 4 a g - c a r b a z o l e have 34 been i s o l a t e d from a n a l o g o u s r e a c t i o n s . Examples o f p h o t o e l i m i n a t i o n of n i t r o g e n from t e t r a z o l e s have a l s o been r e p o r t e d . The diazacyclopentadienonimines (46) were o b t a i n e d on i r r a d i a t i o n o f t h e i m i d a z o [ l , 5 - ~ J ] t e t r a z o l e s ( 4 7 ) . 3 5 The i m i n o t e t r a z o l e s (48) a r e s i m i l a r l y c o n v e r t e d via t h e 36 t r i s ( i m i n o ) m e t h a n e b i r a d i c a l i n t o t h e 2-aminobenzimidazole ( 4 9 1 , and d i a r y l n i t r i l i m i n e s have been i d e n t i f i e d a s p r o d u c t s o f p h o t o 37,38 e l i m i n a t i o n of n i t r o g e n from a r y l - s u b s t i t u t e d 2 I - J - t e t r a z o l e s . 2
E l i m i n a t i o n o f N i t r o g e n from Diazo-compounds
C a r b e n e s a r e r e a d i l y o b t a i n e d by t h e p h o t o d e c o m p o s i t i o n o f d i a z o compounds. The r e a c t i o n s of c a r b e n e s g e n e r a t e d i n t h i s way i n r i g i d m a t r i c e s a t low t e m p e r a t u r e s have been r e v i e w e d . 39 A d d i t i o n of s i n g l e t methylene t o a c e t o n i t r i l e a f f o r d s t h e n i t r i l e y l i d e + + MeC=N-CH2, 4 0 and d i d e u t e r i o f o r m a l d e h y d e g - m e t h y l i d e , C D 2 =0-CHZ , h a s s i m i l a r l y been shown t o be a n i n t e r m e d i a t e i n t h e r e a c t i o n o f 41 photochemically generated dideuteriomethylene with formaldehyde. C o n f l i c t i n g r e s u l t s o b t a i n e d on p h o t o d e c o m p o s i t i o n of d i a z o c y c l o p e n t a d i e n e i n t h e p r e s e n c e o f oxygen have been r e c o n c i l e d by t h e i d e n t i f i c a t i o n of two p r o d u c t s , c y c l o p e n t a d i e n o n e 2 - o x i d e and t h e i s o m e r i c d i o x i r a n e . 4 2 T r i p l e t ground s t a t e c y c l o h e p t a t r i e n y l i d e n e ( S O ) h a s been p r e p a r e d by i r r a d i a t i o n o f a r g o n m a t r i x - i s o l a t e d diazocycloheptatriene(51) and c h a r a c t e r i z e d s p e c t r o s c o p i c a l l y ; 43 f u r t h e r i r r a d i a t i o n i s thought t o a f f o r d e i t h e r bicyclo[4.1.0]but there h e p t a - 2 , 4 , 6 - t r i e n e o r bicyclo[3.2.0]hepta-l,3,6-triene, i s no e v i d e n c e f o r t h e r m a l o r p h o t o c h e m i c a l f o r m a t i o n o f c y c l o heptatetraene. P a r t i c u l a r a t t e n t i o n h a s been d e v o t e d t o t h e c h a r a c t e r i z a t i o n and t o t h e r e a c t i o n s of a r y l c a r b e n e s . Energy d i f f e r e n c e s between s i n g l e t and t r i p l e t ground s t a t e c a r b e n e s a r e u s u a l l y
429
IIIl7: Photoelimination R1 = R 2 = H or Me R1 = H, R 2 = M e
Me
Me (45)
Scheme 2
R
R
A N-N
N’ Me0,C
hv
MN,i I
-N2
M e 0,C -NPh
Ph ( 4 7 ) R = Me or Ph
(46)
430
Photochemistry
s m a l l a n d a r e d e p e n d e n t on c h e m i c a l s t r u c t u r e . A t r i p l e t g r o u n d s t a t e h a s been d e t e c t e d i n t h e carbene d e r i v e d photochemically from 2,3-benzo-1 l - d i a z ~ f l u o r e n e ! ~w h e r e a s s i n g l e t g r o u n d s t a t e s a r e e n e r g e t i c a l l y p r e f e r r e d i n 9-xanthylidene4’ and i n 3,6-dimethoxyfluorenylidene . 4 6 R e s u l t s o b t a i n e d from a s t u d y of t h e photodecomposition of phenyldiazomethane i n cyclohexane and i n c y c l o h e x e n e a r e c o n s i s t e n t w i t h t h e i n v o l v e m e n t of s i n g l e t r a t h e r t h a n t r i p l e t p h e n y l c a r b e n e .47 The e n e r g y s e p a r a t i o n b e t w e e n s i n g l e t and t r i p l e t d i a r y 1 c a r b e n e s h a s been c o r r e l a t e d w i t h s t r u c t u r e . 4 8 The p h o t o l y s e s o f d i a r y l d i a z o m e t h a n e s h a v e a l s o b e e n 49 examined u s i n g p o l a r i z e d l i g h t . U n l i k e p h e n y l d i a z o m e t h a n e which i s c o n v e r t e d on i r r a d i a t i o n i n t o cyclohepta-1,2,4,6-tetraene, t h e c a r b e n e s ( 5 2 ) g e n e r a t e d by p h o t o d e c o m p o s i t i o n of t h e n a p h t h y l d i a z o m e t h a n e s ( 5 3 ) u n d e r g o r e a r r a n g e m e n t t o t h e benzobicyclo[4.1.O]hepta-2,4,6-trienes ( 5 4 ) . 50 Hydrogen a b s t r a c t i o n by t r i p l e t d i p h e n y l c a r b e n e i s o b s e r v e d on photodecomposition of diphenyldiazomethane i n cyclohexane, whereas s i n g l e t - d e r i v e d s o l v e n t i n s e r t i o n r e a c t i o n s compete w i t h h y d r o g e n a b s t r a c t i o n i n t h e analogous r e a c t i o n o f photochemically generated 51 fluorenylidene. A s t u d y o f t h e e f f e c t o f t e m p e r a t u r e on t h e photodecompo s i t i o n of diphenyldiazomethane i n methanol s u p p o r t s t h e p r e v i o u s view t h a t diphenylcarbene i n s e r t i o n t o g i v e t h e corresponding e t h e r i s s i n g l e t - d e r i v e d . 5 2 An a d d i t i o n a l s t e p i n v o l v i n g t h e r e v e r s i b l e f o r m a t i o n o f a n y l i d e h a s b e e n p r o p o s e d . The 0 - H i n s e r t i o n s e l e c t i v i t y of o t h e r photochemically generated carbenes i s influence d by t h e p r e s e n c e of 1 , 4 - d i o x a n e which h a s t h e a b i l i t y t o s t a b i l i z e s i n g l e t c a r b e n e s by c o m p l e x i n g w i t h t h e l o n e p a i r of e l e c t r o n s on o x y g e n , 53 a n d t h e r e a c t i o n s o f c a r b e n e s d e r i v e d f r o m 4 - s u b s t i t u t e d and 4 , 4 ’ - d i s u b s t i t u t e d diphenyldiazomethanes with m e t h a n o l i s e n h a n c e d by p - m e t h y l s u b s t i t u e n t s a n d r e t a r d e d by p - e l e c t r o n - w i t h d r a w i n g s u b s t i t u e n t s . 54 The f o r m a t i o n o f a n e n a n t i o m e r i c a l l y p u r e p r o d u c t on p h o t o d e c o m p o s i t i o n o f d i p h e n y l diazomethane i n s o l i d S-(+)-butan-2-01 i s thought t o a r i s e a t r i p l e t - d e r i v e d r a d i c a l p a i r i n which t h e r e i s no r o t a t i o n a l movement.55 A c o n c e r t e d s i n g l e t pathway d o e s n o t a p p e a r t o b e i n v o l v e d . Analogous i n t r a m o l e c u l a r h y d r o g e n a b s t r a c t i o n i s undoubtedly r e s p o n s i b l e f o r t h e formation of t r i p l e t b i r a d i c a l s (55) on i r r a d i a t i o n o f t h e n a p h t h y l d i a z o m e t h a n e s ( 5 6 ) i n r i g i d g l a s s e s a t 77 K.56
43 1
IIIl7: Photoelimination
(48) R 1 = R 2 = Me, R 3 = Ph R2 = Ph, R1 = R 3 = M e
R
I
CRN,
R
hv
(53) R = H.or D
(52)
R
(56) R = H, Cl, Br, I , SPh, or SOzPh
(54)
R
(55)
432
Photochemistry
Reactions of photochemically generated a r y l carbenes with o t h e r s p e c i e s have a l s o been s t u d i e d . The mechanism o f a d d i t i o n o f c a r b e n e s t o a l k e n e s i s of c u r r e n t i n t e r e s t . A n o n - c o n c e r t e d pathway w i t h a r e v e r s i b l e f i r s t s t e p h a s been shown t o be i n v o l v e d i n t h e a d d i t i o n s of t r i p l e t f l u o r e n y l i d e n e and diphenylmethylene t o fumarate e s t e r s . 57 Nitrogen-laser e x c i t a t i o n of diazofluorene ( 5 7 ) i n a c e t o n e a t room t e m p e r a t u r e a f f o r d s t h e c a r b o n y l y l i d e ( 5 8 ) 58 which undergoes f u r t h e r p h o t o r e a r r a n g e m e n t t o t h e o x i r a n e ( S S ) , and l o n g - l i v e d t h i o c a r b o n y l y l i d e s have been i d e n t i f i e d i n t h e r e a c t i o n s of f l u o r e n y l i d e n e and d i p h e n y l c a r b e n e w i t h d i - t - b u t y l t h i o k e t o n e and adamantanethione. 59 The benzylamines ( 6 0 ) and t h e amines ( 6 1 ) a r e t h e major p r o d u c t s o f i r r a d i a t i o n of a r y l d i a z o methanes (62) i n d i e t h y l a m i n e ; t h e y a r i s e r e s p e c t i v e l y by N-H and C-H c a r b e n e i n s e r t i o n r e a c t i o n s .60 Hydrogen a b s t r a c t i o n p r o d u c t s were formed a t t h e expense o f i n s e r t i o n p r o d u c t s on i r r a d i a t i o n of p-nitrophenyldiazomethane under t h e same c o n d i t i o n s . P o s s i b l e e x p l a n a t i o n s f o r t h i s d i f f e r e n c e i n r e a c t i v i t y have been o f f e r e d . P h o t o c h e m i c a l l y g e n e r a t e d a r y l c a r b e n e s have been i n t e r c e p t e d w i t h carbon monoxide" and w i t h oxygen. Benzophenone 2-oxide h a s been d e t e c t e d s p e c t r o s c o p i c a l l y on i r r a d i a t i o n ( 5 1 5 nm) o f d i p h e n y l diazomethane a t 8 K i n t h e p r e s e n c e of oxygen,62 b u t t h e r e i s no e v i d e n c e f o r c a r b o n y l o x i d e f o r m a t i o n on p h o t o e l i m i n a t i o n o f n i t r o g e n from phenyldiazomethane under i d e n t i c a l c o n d i t i o n s . 6 3 Benzoic a c i d and benzaldehyde have been i d e n t i f i e d a s p r o d u c t s . The photochemical g e n e r a t i o n o f a r y l c a r b e n e s f o r p o t e n t i a l u s e a s o r g a n i c f e r r o m a g n e t s h a s been r e p o r t e d . 6 4 9 6 5 The e l e c t r o p h i l i c c a r b e n e , 4 g - i m i d a z o l y l i d e n e (631, h a s 66 (64). been p r e p a r e d by photodecomposition of 4-diazo-4€j-imidazole R e a c t i o n w i t h cyclohexane a f f o r d s t h e C-H i n s e r t i o n p r o d u c t , 4(5)c y c l o h e x y l i m i d a z o l e ( 6 5 ) , whereas r e a c t i o n w i t h benzene y i e l d s 4 ( 5 ) - p h e n y l i m i d a z o l e ( 6 6 ) . Analogous a d d i t i o n of 4 5 - i m i d a z o l y l i d ene t o d e r i v a t i v e s of benzene i s i n f l u e n c e d by t h e p r e s e n c e and n a t u r e of t h e s u b s t i t u e n t s . - a - D i a z o a c e t a t e s and r e l a t e d e s t e r s a r e a u s e f u l s o u r c e of c a r b e n e s . I r r a d i a t i o n of t h e c h o l e s t e r o l diazopcetate (67) i n 67 c y c l o h e x a n e , f o r example , gave t h e C-H i n s e r t i o n p h d u c t ( 6 8 ) , and a d d i t i o n of t h e c a r b e n e s i m i l a r l y g e n e r a t e d from d i m e t h y l diazomalonate t o bis[trimethylsilyllacetylene a f f o r d e d t h e c o r r e s p o n d i n g 2 , 3 - d i s i l y l a t e d c y c l o p r o p e n e . 6 8 The r e a c t i o n s o f t h e same c a r b e n e w i t h c y c l i c d i s u l p h i d e s have been examined.
69
IIIl7: Photoelimination
Ar -CH
=Nz
43 3
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1
cyclohexane
,Me
(66)
434
Photochemistry
a-Diazo k e t o n e s and r e l a t e d s p e c i e s r e a d i l y undergo l-Diazo-3-(l-methylcyclopenta-2,4-diphoto-Wolff r e a r r a n g e m e n t . eny1)propan-2-one (691, f o r e x a m p l e , i s c o n v e r t e d i n t h i s way on d i r e c t i r r a d i a t i o n i n t o t h e k e t e n e ( 7 0 ) ; 70 i n c o n t r a s t , i n t r a m o l e c u l a r c a r b e n e a d d i t i o n i s p r e f e r r e d on b e n z o p h e n o n e - s e n s i t i z e d O t h e r examples o f t h e i r r a d i a t i o n y i e l d i n g t h e adduct ( 7 1 ) . a p p l i c a t i o n of t h e p h o t o c h e m i c a l l y i n d u c e d Wolff r e a r r a n g e m e n t t o a c y c l i c d i a z o k e t o n e s have been r e p o r t e d . 7 1 - 7 4 Of p a r t i c u l a r i n t e r e s t i s t h e m i g r a t i o n o f a carbomethoxy group o b s e r v e d on i r r a d i a t i o n i n e t h a n o l of methyl 3-diazo-2-oxopropionate ( 7 2 ) t o g i v e e t h y l m e t h y l m a l o n a t e ( 7 3 ) a s shown i n Scheme 3 . 7 4 P h o t o i n d u c e d Wolff r e a r r a n g e m e n t i n c y c l i c a - d i a z o k e t o n e s i s f r e q u e n t l y accompanied by r i n g c o n t r a c t i o n . Thus, diazodimedone ( 7 4 ) i s c o n v e r t e d i n t o t h e c y c l o p e n t a n o n e s ( 7 5 ) on i r r a d i a t i o n i n t h e p r e s e n c e o f o p t i c a l l y a c t i v e a l c o h o l s . 7 5 An a n a l o g o u s r i n g c o n t r a c t i o n h a s been r e p o r t e d f o r 5 - d i a z o - 2 , 2 - d i m e t h y l - 4 , 6 - d i o x o - l , 3 - d i o x a n e , 76 and t h e p h o t o d e c o m p o s i t i o n o f u n s y m m e t r i c a l l y s u b s t i t u t e d 4-diazopyrazolidine-3,5-diones h a s been used i n t h e s y n t h e s i s of aza-B-lactams. 7 7 Examples of p h o t o e l i m i n a t i o n of n i t r o g e n from o t h e r r e l a t e d s y s t e m s have been r e p o r t e d . The A3-phosphinocarbene ( 7 6 ) , o b t a i n e d by p h o t o d e c o m p o s i t i o n o f t h e a - d i a z o p h o s p h i n e ( 7 7 ) , h a s been i n t e r c e p t e d w i t h d i m e t h y l a m i n e t o g i v e t h e t e r t i a r y amine (78) , 7 8 and i r r a d i a t i o n o f t h e t o s y l h y d r a z o n e ( 7 9 ) a f f o r d s t h e t r i e n e ( 8 0 ) and t h e c y c l o p r o p e n e ( 8 1 ) by way o f a c a r b e n e i n t e r m e d i a t e a s shown i n Scheme 4 . 79 I n t r a m o l e c u l a r c a r b e n e a d d i t i o n h a s been o b s e r v e d on i r r a d i a t i o n o f t h e q u i n o n e d i a z i d e (82) t o g i v e t h e spiro-cyclopropane-cyclohexadienone ( 8 3 ) ;80 oxygen t r a n s f e r from t h e sulphonamido g r o u p i s a c o m p e t i n g p r o c e s s . The p h o t o d e c o m p o s i t i o n o f 2-benzoquinone d i a z i d e i t s e l f h a s b e e n examined i n a p i p e r y l e n e o l i g o m e r m a t r i x a t 7 7 K , 8 1 a n d f u r t h e r s t u d i e s o f t h e p h o t o l y s i s o f a r e n e d i a z o n i u m s a l t s have been described. 8 2 83 3
E l i m i n a t i o n of N i t r o g e n from A z i d e s
The p h o t o r e a c t i o n s o f a z i d e s c a n i n most c a s e s b e r a t i o n a l i z e d i n t e r m s of t h e f o r m a t i o n of i n t e r m e d i a t e n i t r e n e s which t h e n undergo r e a r r a n g e m e n t , i n s e r t i o n , o r a d d i t i o n . A t h e o r e t i c a l s t u d y o f t h e p h o t o d e c o m p o s i t i o n o f m e t h y l a z i d e h a s been r e p o r t e d . 84
IIIi7: Photoelimination
435
(731
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Scheme 3
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Pri N ‘P-?-SiMeg Pri2N’
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436
Photochemistry
P h o t o e l i m i n a t i o n of n i t r o g e n from f l u o r o a l k y l a z i d e s gave t h e c o r r e s p o n d i n g f l u o r o i m i n e s by r e a r r a n g e m e n t o f s h o r t - l i v e d i n t e r m e d i a t e n i t r e n e s . 8 5 Dimeric p r o d u c t s o b t a i n e d on i r r a d i a t i o n of 9-azido-10-methyltriptycene (84) a r i s e via t h e i n i t i a l l y formed b r i d g e h e a d imine ( 8 5 ) . 8 6 A v a r i e t y o f r e a c t i o n s have been r e p o r t e d f o r a n a l o g o u s l y formed p h o s p h i n o n i t r e n e s . 8 7 I r r a d i a t i o n o f t h e phosphine a z i d e (86) i n m e t h a n o l , f o r example, gave t h e p r o d u c t (87) by a d d i t i o n of s o l v e n t t o t h e t r a n s i e n t oxo-iminophosphorane ( 8 8 ) . P h o t o e l i m i n a t i o n of n i t r o g e n from t h e d i a z i d e d i m e t h y l d i a z i d o s i l a n e h a s been shown t o y i e l d d i m e t h y l s i l y l e n e , 8 8 and s u c c e s s i v e l o s s of n i t r o g e n h a s been o b s e r v e d on i r r a d i a t i o n o f 2 , 3 - d i a z i d o - 1 , 3 - b u t a 89 (90). d i e n e (89) t o g i v e t h e b i s - 2 H - a z i r i n - 3 - y l S t u d i e s of t h e p h o t o r e a c t i o n s of a r y l and h e t e r o a r y l a z i d e s have a l s o been d e s c r i b e d . N i t r o - s u b s t i t u t e d a r y l a z i d e s a r e of i n t e r e s t b e c a u s e o f t h e i r p o s s i b l e u s e i n p h o t o a f f i n i t y The r e a c t i v i t i e s of r o t a m e r i c a p - and s p - 3 , 5 dimethyl-2-(9-fluorenyl)phenylnitrenes, o b t a i n e d by p h o t o l y s i s o f t h e c o r r e s p o n d i n g a z i d e s , have been c o m p a r e d Y g 2and d i o x o a n t h r a [ 1 , 2 - d ] p y r a z o l i n e s have been p r e p a r e d by i r r a d i a t i o n of l - a z i d o - 2 [ ( d i a l k y l a m i n o ) m e t h y l ] -9 ,1 0 - a n t h r a q u i n o n e s . 9 3 H e t e r o a r y l a z i d e s f r e q u e n t l y undergo r i n g e x p a n s i o n on p h o t o e l i m i n a t i o n of n i t r o g e n ; f u s e d a z i r i n e i n t e r m e d i a t e s have been p r o p o s e d . I r r a d i a t i o n of t h e 4 - a z i d o i s o q u i n o l i n e s ( 9 1 ) , f o r example, gave i n t h e p r e s e n c e o f sodium methoxide t h e 1!-2,4b e n z o d i a z e p i n e s ( 9 2 ) . 9 4 The l i k e l y pathway i s o u t l i n e d i n Scheme 5 . Analogous r i n g e x p a n s i o n s have been r e p o r t e d f o r 5 - a z i d o - , 8 - a z i d o - , 6-azido-8-methoxy- and 8-azido-6-methoxy-quinolines i n a l c o h o l a l k o x h e - d i o x a n e s o l u t i o n c o n t a i n i n g 18-crown-6 . 9 5 I r r a d i a t i o n of t h e 2-substituted 3-azidopyridines ( 9 3 ) , again in t h e presence of sodium m e t h o x i d e , l e d t o t h e f o r m a t i o n o f t h e n o v e l 2 H - l Y 4 - d i a z e p i n e s (94) a s shown i n Scheme 6 , whereas 2 - u n s u b s t i t u t e d and 2 , 4 d i s u b s t i t u t e d 3 - a z i d o p y r i d i n e s a r e c o n v e r t e d i n t o t h e known 5H1 , 3 - d i a ~ e p i n e s . ~No~ r i n g e x p a n s i o n p r o d u c t s were d e t e c t e d on i r r a d i a t i o n of 3- and 4 - a z i d o p y r i d i n e l - o x i d e s i n n u c l e o p h i l i c s o l v e n t s . 9 7 P h o t o c h e m i c a l l y i n d u c e d d e c o m p o s i t i o n o f 3-azido-2v i n y l t h i o p h e n e s l e a d s t o t h e f o r m a t i o n of t h i e n o [ 3 , 2 - b l p y r r o l e s .98 9 9 The a z i d e ( 9 5 ) , f o r example, i s c o n v e r t e d on i r r a d i a t i o n i n a c e t o n i t r i l e i n t o t h e p y r r o l e ( 9 6 ) ; t h e p r o p o s e d mechanism, which involves i n i t i a l formation of a n i t r e n e , 1,5-electrocyclization t o t h e f u s e d 2 H - p y r r o l e , and s i g m a t r o p i c m i g r a t i o n o f t h e Z - s u b s t i t u e n t , i s shown i n Scheme 7 . 2 - A z i d o s t y r e n e s have s i m i l a r l y been
IIIt7: Photoelimination
437
GTs hv
Me
NaH
*
hv
-Nz
* Me
Me
/
(79)
& + L y Me
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Scheme 4
CH I
=CH2
4+:
SO, Me
MeCONH
hv
___j
-N2
‘S02Me MeCONH
0
0
(82)
hv
(84)
4
’/
(85)
Photochemistry
438
(89)
(90)
k (91 1
(92 1
R = H, Me, Ph, OMe, or Cl Scheme 5
hV
(93)R = Me or C I
(941 Scheme 6
lI1/7: Photoelimination
43 9
.. hv
C
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C
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M
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"2
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C0,E t
(951
&cozE'
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mo hv
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(97)
C H, = C H (CH (1 00)
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-
hv, co, MeCN
~
O Y0 K " (102) R' = Ph, Et, Pr! or CH2Pri, R2 = H R' = R 2 = Ph
(101)
Me
Photochemistry
440
converted into indoles. 4
P h o t o e l i m i n a t i o n o f Carbon D i o x i d e
Photochemically induced decarboxylations o f (phenyla1koxy)acetic a n d of a c i d s i n t h e p r e s e n c e o f m e r c u r y (11) o x i d e and iodine1'' t h r e o - a l e u r i t i c a c i d i n t h e p r e s e n c e o f l e a d t e t r a a c e t a t e and iodine"' have been r e p o r t e d . Carbon d i o x i d e i s o n e o f many p r o d u c t s o b t a i n e d by g a s - p h a s e p h o t o l y s i s o f d i m e t h y l o x a l a t e . 102 Carbon d i o x i d e i s a l s o e l i m i n a t e d on i r r a d i a t i o n o f t h e l a c t o n e (97) t o g i v e 1 - m e t h y l n a p h t h a l e n e (98) i n h i g h y i e l d . l o 3 S e l e c t i v e mixed c o u p l i n g h a s b e e n o b s e r v e d on p h o t o d e c o m p o s i t i o n o f unsym* l o 5 t h e p e r o x i d e (99), f o r e x a m p l e , metrical diacyl peroxides; i s c o n v e r t e d i n 61% y i e l d i n t o t h e a l k e n e ( l o o ) , and c y c l o p e n t a decanone a n d c y c l o t e t r a d e c a n e h a v e s i m i l a r l y b e e n p r e p a r e d by p h o t o e l i m i n a t i o n of carbon d i o x i d e from t h e a p p r o p r i a t e c y c l i c 106 tetraacyl diperoxide The s y n t h e s i s of 1 - a z a b i c y c l o b u t a n e s ( 1 0 1 ) h a s b e e n a c c o m p l i s h e d i n r e a s o n a b l e y i e l d by i r r a d i a t i o n o f t h e c y c l i c 107 carbarnates (102) i n a c e t o n i t r i l e i n t h e p r e s e n c e of p y r i d i n e . E l i m i n a t i o n o f c a r b o n d i o x i d e h a s a l s o b e e n o b s e r v e d on i r r a d i a t i o n ring o f t h e [1,2,4]oxadiazolo[2,3-clquinazolinazolin-2-one ( 1 0 3 ) ; l o 8 cleavage p r o d u c t s ( 1 0 4 ) and (105) were o b t a i n e d and t h e proposed pathway i s o u t l i n e d i n Scheme 8 . @-Lactams (106) h a v e b e e n o b t a i n e d i n t h e same way by p h o t o d e c o m p o s i t i o n o f t e t r a h y d r o - 1 , 2 oxazine-3,6-diones (107) , l o g and photochemically induced n i t r o g e n n i t r o g e n bond h o m o l y s i s f o l l o w e d by l o s s o f c a r b o n d i o x i d e h a s been used i n t h e s y n t h e s i s of 1 , 2 , 4 - o x a d i a z o l e s from N-nitroso-N-acetyla-amino a c i d s . l o P r o d u c t s c o n s i s t e n t w i t h a pathway i n v o l v i n g s e q u e n t i a l e l e c t r o n t r a n s f e r were o b t a i n e d on p h o t o l y s i s o f t h e p e p t i d e t r i g l y c i n e . 111 D e t a i l e d s t u d i e s of t h e photoinduced decarboxylative 112 rearrangement of thiohydroxamic e s t e r s have been undertaken. C r o s s o v e r e x p e r i m e n t s i n d i c a t e t h e p h o t o d e c o m p o s i t i o n t o be a r a d i c a l c h a i n p r o c e s s a s shown i n Scheme 9 . 1 1 3 P e r f l u o r o a c i d
.
e s t e r s of Ij-hydroxypyridine 2-thione a l s o undergo decarboxylative r e a r r a n g e m e n t on i r r a d i a t i o n t o g i v e 2-perfluoroalkylthiopyridines i n h i g h y i e l d . ' 1 4 The c a r b o n r a d i c a l s t h u s formed h a v e b e e n t r a p p e d with e l e c t r o n - r i c h a l k e n e s . Alkyl r a d i c a l s d e r i v e d i n a s i m i l a r f a s h i o n add r e a d i l y t o p v i n y l sulphone and v i n y l - h e n .y l phosphonium bromide" a n d t o p r o t o n a t e d h e t e r o a r o m a t i c compounds
IZZi7: Photoelimination
44 1
0
0
I
(103)
(104)
(105)
Scheme 8
hv
0
-cog
0
(1 06)
(1071 R = Ph or CHMePh
OYO R
Scheme 9
Photochemistry
442
c o n t a i n i n g a b a s i c methine n i t r o g e n . l 6 ( L ) -Glutamate e s t e r s of h a v e b e e n shown t o u n d e r g o t h e same d e c a r b o x y l a t i v e r e a r r a n g e m e n t a s t h e i r t h i o - a n a l o g u e s . 117
N-hydroxy-2-selenopyridine
5
F r a g m e n t a t i o n of O r g a n o s u l p h u r Compounds
C a r b o n - s u l p h u r bond h o m o l y s i s i s r e s p o n s i b l e f o r many p h o t o c h e m i c a l l y i n d u c e d d e c o m p o s i t i o n s o f o r g a n o s u l p h u r compounds. P e n t a fluorophenylprop-2-enyl t h i o e t h e r (108) undergoes carbon-sulphur bond c l e a v a g e on i r r a d i a t i o n i n c y c l o h e x a n e t o g i v e t h e t h i o l (109) Photoelimination of and t h e cyclohexyl t h i o e t h e r (110). l 1 methanethiol i s t h e p r i n c i p a l r e a c t i o n observed i n t h e d i t h i o a c e t a l ( 1 1 1 1 and l e a d s t o t h e Z,E-stereoisomeric b e n z o t h i a z o l e s (1 1 2 ) . ’ l 9 A r y l p h e n a c y l s u l p h i d e s u n d e r g o c a r b o n - s u l p h u r bond h o m o l y s i s on i r r a d i a t i o n , t h e major p r o d u c t s b e i n g t h e corresponding methyl k e t o n e s a n d d i s u l p h i d e s . 1 2 0 A wide v a r i e t y o f s u b s t i t u t e d t h i o a l d e h y d e s , o b t a i n e d by p h o t o d e c o m p o s i t i o n o f t h e a p p r o p r i a t e phenacyl s u l p h i d e s , have been t r a p p e d a s t h e d i h y d r o t h i o p y r a n s by r e a c t i o n w i t h d i e n e s . 1 2 ’ An example o f t h i s c o n v e r s i o n , which
i s t h o u g h t t o i n v o l v e a Type I 1 f r a g m e n t a t i o n , i s shown i n Scheme 1 0 . a - S c i s s i o n h a s a l s o b e e n o b s e r v e d o n i r r a d i a t i o n of ( 2 , 4 , 6 t r i m e t h y l b e n z o y l ) diphenylphosphine s u l p h i d e , 2 2 and t h e c - a l k y l S - p h t h a l y l g l y c y l x a n t h a t e s ( 1 1 3 ) u n d e r g o d e c o m p o s i t i o n on i r r a d i a 123 t i o n i n benzene t o g i v e t h e a l k y l x a n t h a t e s ( 1 1 4 ) . E x t r u s i o n o f s u l p h u r f r o m s u l p h i d e s by i r r a d i a t i o n i n t h e presence of t r i m e t h y l o r t r i e t h y l p h o s p h i t e h a s a g a i n been used i n s y n t he s i s . The f i r s t [ 2 . 1 ] p h a n e , 6 , 7 - d i hy d r o b e n zo [&I n a p h t ho [ 2 ,1 , 8 g h i l o x e c i n e ( 1 I S ) , h a s b e e n o b t a i n e d i n t h i s way f r o m t h e s u l p h i d e 125 ( 1 1 6 ) . 2 4 D i t h i a [ 3.31 - a n d [ 2 . 2 1 - a z u l e n o ( 2 , 6 ) p y r i d i n o p h a n e s and isomeric b i s (methoxycarbonyl) [ 2 . 2 1 (2,S)pyridinophanes’ 26 have been s i m i l a r l y p r e p a r e d . I r r a d i a t i o n of t h e Z-thioxo-1,3-dithiole ( 1 1 7 ) i n t h e p r e s e n c e o f t r i e t h y l p h o s p h i t e , h o w e v e r , gave t h e t e t r a t h i o f u l v a l e n e (1 1 8 ) ; 2 7 p h o t o i n d u c e d e l e c t r o n t r a n s f e r f r Q m
’
t h e phosphite appears t o a c c e l e r a t e t h e formation of zwitterion intermediate (119). I r r a d i a t i o n of t h e aB-unsaturated sulphine ( 1 2 0 ) i n c h l o r o f o r m gave a s i n g l e p r o d u c t , t h e k e t o n e ( 1 2 1 1 , i n 9 0 % y i e l d . ’ 2 8 An o x a t h i i r a n e i n t e r m e d i a t e i s p r o b a b l y i n v o l v e d in t h i s transformation. Bis(trifluoromethy1)sulphine i s s i m i l a r l y 129 c o n v e r t e d w i t h e x t r u s i o n of s u l p h u r i n t o h e x a f l u o r o a c e t o n e .
IIIl7: Photoelimination
443
S
SH
FQF F
Fl$F
+
hv cyc lo hexone)
F$F
/o
F
F
F
i
I
Ph
(112)
(111)
0
0
It
McCCH2-S-CHZ-C-Ph
0
It
0
II
+
MeCCH=S
II
Me-C-Ph
Me
Schema 10
0
S
S benzene
0 (113) R
I
@N
-CCHz-S-C-OR
0 E t , Pr", P r ' , Bun, or Bu'
II
Photochemistry
444
9
0
S
hV
Me Me
Me
Me Me
_I_) hv
Me
Me
c'" My
WcN
M e Me
Me
-:o
+
Me
and
445
IlIt7: Photoelimination
p b'
Me
(125)
lhv
+ Me Me
!Lo
Me
Me*O
hv
___)
tie
Me
(1 27)
(128)
Photochemistry
446
6
Miscellaneous Decomposition and E l i m i n a t i o n Reactions
Fragmentation and e l i m i n a t i o n r e a c t i o n s t h a t cannot be included i n any of t h e above c a t e g o r i e s a r e b r i e f l y r e v i e w e d i n t h i s S e c t i o n . I t has not proved p o s s i b l e t o c l a s s i f y t h e s e p r o c e s s e s , but l i k e r e a c t i o n s a r e grouped t o g e t h e r . Carbon-oxygen bond h o m o l y s i s i s r e s p o n s i b l e f o r t h e f o r m a t i o n o f some of t h e p r o d u c t s o b t a i n e d on p h o t o d e c o m p o s i t i o n o f l i q u i d 1 , 3 - d i o x a n e , ' 30 a n d t h e n u c l e o p h i l i c a d d i t i o n of primary a l c o h o l s t o N-methylacridinium c h l o r i d e t o give N-methyl-9-alkoxyacridans i s r e v e r s e d on i r r a d i a t i o n a t 7 7 K . 131 P r o d u c t s of i r r a d i a t i o n o f o x i r a n e s a r e d e r i v e d a number o f d e c o m p o s i t i o n p a t h w a y s . Both t h e c a r b o n y l y l i d e ( 1 2 2 ) a n d t h e c a r b e n e (123) a r e i m p l i c a t e d i n t h e e x c i t e d s i n g l e t s t a t e r e a c t i o n s of t h e a 8 - u n s a t u r a t e d y6-epoxy n i t r i l e ( 1 2 4 ) . 32 I n t r a m o l e c u l a r a d d i t i o n of a photochemically generated vinyl carbene i s a l s o r e s p o n s i b l e f o r t h e c o n v e r s i o n o f t h e two e p o x y d i e n e s ( 1 2 5 ) i n t o t h e c y c l o p r o p e n e ( 1 2 6 ) . 33 B i r a d i c a l i n t e r m e d i a t e s have b e e n proposed t o account f o r t h e formation of t r i p l e t - d e r i v e d products of o t h e r 5 , 6 - e p o ~ y - l , 3 - d i e n e s , ~a~n~d f u r t h e r s t u d i e s o f t h e p h o t o c h e m i s t r y of c a r b o n y l - c o n t a i n i n g o x i r a n e s have b e e n r e p o r t e d . 135137 Oxygen-oxygen bond h o m o l y s i s i s t h e i n i t i a l s t e p i n t h e p h o t o r e a r r a n g e m e n t of 9,10-dimethyl-9,10-dihydro-9,lO-epidioxya n t h r a c e n e (127) t o t h e d i m e t h y l a c e t a l ( 1 2 8 ) . 1 3 * Cyclohexanone 139 p e r o x i d e s have s i m i l a r l y been c o n v e r t e d t o c a r b o x y l i c a c i d s , and h y d r o x y l r a d i c a l s a r e g e n e r a t e d on i r r a d i a t i o n o f u n s a t u r a t e d f a t t y a c i d h y d r o p e r o x i d e s . 1 4 0 The u n s t a b l e 2 - a z a c a r b a p e n e m s ( 1 29) 141 a n d (130) were p r e p a r e d by p h o t o l y s i s o f t h e o z o n i d e ( 1 3 1 ) . P h o t o d e a l k y l a t i o n o f amines i s a well-documented r e a c t i o n p-Dimethylamino-p'-nitrodiphenylethyne h a s b e e n shown t o u n d e r g o t h i s decomposition e x c l u s i v e l y on i r r a d i a t i o n i n t o l u e n e , e t h e r o r acetone. 142 Numerous e x a m p l e s o f p h o t o c y c l i z a t i o n accompanied by e l i m i n a t i o n of H C 1 , H B r o r H I have a g a i n been d e s c r i b e d a l t h o u g h i n most c a s e s d e t a i l s o f t h e r e a c t i o n mechanism a r e n o t c l e a r . Noteworthy e x a m p l e s i n c l u d e t h e c o n v e r s i o n o f t h e I j - ( h y d r o x y p h e n y l ethyl)-3-(bromophenyl)propionamide (132) i n t o t h e 11-membered l a c t a m ( 1 3 3 ) ' 4 3 and t h e s y n t h e s e s o f 4 , 5 , 7 a Y 8 - t e t r a h y d r o - 1 ,2d i m e t h o x y p h e n a n t h r o [ 1 0 , l -&I a z e p i n - 6 (7H) -one1 4 4 a n d (+I - c a t h a r a n t b A key s t e p i n t h e s y n t h e s i s of c r a s s i f o l a z o n i n e i s t h e i n e 14' u n u s u a l p h o t o c y c l i z a t i o n u n d e r a l k a l i n e c o n d i t i o n s o f t h e bromo
.
447
lIIl7: Photoelimination
OH
Meo&N"
-
0
KOH,hv+ MeOH
QJ0
Me0
OMe
(132)
OMe
(133)
OH
OH
MeotLA
Meo*
HowNH &:: \
hv
______j
KOH, MeOH
Me0
OMe (134)
(136)
(137) R = Me or OMe
(135)
(139)
(138)
448
Photochemistry
compound (134) i n t o t h e i n d o l i n e ( 1 3 5 1 , a p r o c e s s which i s t h o u g h t t o o c c u r by n u c l e o p h i l i c a t t a c k o f amide a n i o n on t h e a r y l 146 radical. I n t e r m o l e c u l a r p h o t o e l i m i n a t i o n o f HX h a s b e e n employed i n t h e s y n t h e s i s of 2 - a r y l p y r i d i n e s 4 - h e t e r o a r y l p y r i d i n e s , 148 a n d c y c l o h e x y l a r e n e s . 51 I r r a d i a t i o n o f 5-bromoa r y l f u r a n s 14’ ’’ 1 , 3 - d i m e t h y l u r a c i l (136) i n t h e p r e s e n c e o f s u b s t i t u t e d b e n z e n e s (137) s u r p r i s i n g l y a f f o r d s t h e 6 - a r y l d e r i v a t i v e s (138) a s w e l l a s t h e e x p e c t e d 5 - a r y l i s o m e r s ( 1 39) ; ’ 5 2 d i f f e r e n t r e a c t i o n mechanisms may b e i n v o l v e d . The s y n t h e s e s o f 5 - a l k y l p y r i m i d i n e a n d 5 - a l k y 1- a n d 5 - h e t e r o a l ky 1- p y r i m i d i n e nuc l e o s i d e s n u c l e o t i d e ~h a~v~e ~b e e n a c h i e v e d i n a s i m i l a r manner u s i n g 2 - i o d o e t h a n o l . The p h o t o c h e m i s t r y o f a r y l h a l i d e s h a s b e e n r e v i e w e d . 155 Much i n t e r e s t h a s b e e n shown i n t h e s t u d y a n d u s e o f p h o t o i n i t i a t e d SRNl r e a c t i o n s . 1 5 6 - 1 6 7 I n p a r t i c u l a r , t h e p r o c e s s h a s b e e n employed i n t h e c o n s t r u c t i o n o f b e n z o [ ~ l p h e n a n t h r i d i n e s a n d benzo [ c l p h e n a n t h r i d o n e s , 1 6 8 o f 3 - b e n z a z e p i n e s a n d 3-benzoxep170,171 i n e s , I 6 ’ and of f u n c t i o n a l i z e d 6 - a l k y l a t e d p u r i n e s . Many o t h e r p h o t o c h e m i c a l l y i n d u c e d d e c o m p o s i t i o n s a r i s e by c a r b o n - h a l o g e n bond c l e a v a g e . The m a j o r i t y o f t h e s e r e a c t i o n s a r e r a d i c a l p r o c e s s e s w i t h l i t t l e photochemical s i g n i f i c a n c e and a r e t h e r e f o r e n o t reviewed i n d e t a i l i n t h i s Report. Interest is evident i n photochemically generated vinyl r a d i c a l c y c l i z a t i o n . I r r a d i a t i o n i n benzene of t h e v i n y l a z e t i d i n o n e
(1401, f o r
e x a m p l e , gave t h e l a - m e t h y l c a r b a p e n a m ( 1 4 1 ) t o g e t h e r w i t h t h e r e d u c t i o n p r o d u c t ( 1 4 2 ) . ’ 7 2 P r o d u c t s d e r i v e d by b o t h r a d i c a l and i o n i c pathways have been o b t a i n e d from 2-phenylethyl and 174 4 - p h e n y l - 1 - b u t y l h a l i d e s , ’ 7 3 f r o m w-bromo-w-phenylcamphene, a n d f r o m v i n y l i d e n e d i h a l i d e s d e r i v e d f r o m camphene. 17’ Benzyl c a r b o c a t i o n s , h o w e v e r , a r e formed e x c l u s i v e l y on i r r a d i a t i o n of benzyl c h l o r i d e o r benzyl a c e t a t e i n aqueous methanol,176 and t h e t r i a r y l c h l o r o a l l e n e s (143) a r e photochemically c o n v e r t e d i n t o t h e 1,3,3-triaryl-3-methoxypropynes ( 1 4 4 ) i n m e t h a n o l , s u g g e s t i n g the i n t e r v e n t i o n of t r i a r y l a l l e n y l c a t i o n s . 77 Photochemically i n d u c e d Wagner-Meerwe i n r e a r r a n g e m e n t s h a v e b e e n r e p o r t e d i n c h l o r o - s u b s t i t u t e d d i b e n z o b i c y c l o [ 2 . 2 . 2 1 o c t a - 2 , S - d i e n e s , ’ 78 i n 179 c i s - a n d trans-7,8-dichlorodibenzobicyclo[2.2.2]octadienes, and i n syn- and anti-8-chloro-2,3:6,7-dibenzobicyclo[3.2.llocta2 , 6 - d i e n - 4 - y l s y s t e m s . 8o 2 , 4 - D i n i t r o - 6 - (pheny1iodonio)phenolate ( 1 4 5 ) r e a d i l y u n d e r g o e s p h o t o r e a c t i o n w i t h n u c l e o p h i l e s ; 18’ w i t h
IIIl7: Photoelimination
449
H
$ 2
0
hv benzene
__i)
0
(140)
R2
R2
R’
)c=c=c, R2
hV MeOH
/
CI
1
R ~ - C-CEC-R’
1
OMe (143) R1 = R 2 = P h R1 = Ph, R 2 = p-MeC6H4 R1 = p-MeOC&,R2 = Ph
(145)
(146)
0
I
py ridine
0’ (151) S c h e m e 11
CHO (150)
Photochemistry
450
p h e n y l t h i o c y a n a t e , f o r e x a m p l e , t h e o x a t h i o l e (146) i s o b t a i n e d . P h o t o c h e m i c a l l y i n d u c e d n i t r o g e n - h a l o g e n bond c l e a v a g e i s r e s p o n s i b l e f o r t h e c o n v e r s i o n o f N,N-dihalo-1,l-difluoroamines i n t o t h e c o r r e s p o n d i n g d i a z e n e s , 18' a n d f o r t h e f o r m a t i o n o f t h e 1 , l - a d d u c t ( 1 4 7 ) a n d t h e 1 , Z - a d d u c t ( 1 4 8 ) o b t a i n e d on photodecompo s i t i o n of 1,4-dibromo-Z,5-piperazinedione ( 1 4 9 ) i n t h e p r e s e n c e of 1 8 3 The p h o t o l y s i s o f h y p o i o d i t e s c o n s t i t u t e s 3,4-dihydro-Z!-pyran. a v a l u a b l e a p p r o a c h t o a l k o x y r a d i c a l s . The f o r m a t i o n o f t h e
f o r m a t e (150) by i r r a d i a t i o n o f t h e l a c t o l ( 1 5 1 ) i n t h e p r e s e n c e o f HgO-IZ a s shown i n Scheme 1 1 i s a k e y s t e p i n t h e c o n v e r s i o n o f 5 a - c h o l e s t a n - 6 - o n e i n t o 6 - o x a - 5 a - c h o l e s t a n e . 1 8 4 The mechanism o f t h e f o r m a t i o n o f oxa s t e r o i d s from 3 - h y d r o x y - A s - s t e r o i d h y p o i o d i t e s has been i n v e s t i g a t e d . 18' P h o t o l y s i s of s e v e r a l s t e r o i d a l l a c t o l s i n t h e p r e s e n c e of i o d o s o b e n z e n e d i a c e t a t e a n d i o d i n e a l s o l e a d s t o t h e p r o d u c t i o n o f a l k o x y r a d i c a l s , 18' a n d i o d o s o b e n z e n e d i a c e t a t e h a s b e e n shown t o b e a n e f f i c i e n t r e a g e n t f o r t h e p h o t o c h e m i c a l l y i n d u c e d o x i d a t i v e d e c a r b o x y l a t i o n o f c a r b o x y l i c a c i d s . 187 References 1
2 3 4 5 6
7 8 9 10
11 12 13 14 15 16 17 18 19 20 21 22 23 24
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IIIl7: Photoelimination
45 1
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(w.
-
c,
Photochemistry
452 69 70 71 72 73 74 75 76
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114
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27,
103,
27, 27,
-
104, 2,
117,
s,
. 107,
-
108,
108,
8 ,
104,
2,
17,
3,
42,
107,
IIIi7: Photoelimination
453
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-
-.,
*,
-
454
Photochemistry
159 G.A.Russel1 and D.F.Dedolph, J. Org. Chem., 1985, 2, 2378. 2498. 160 G.A.Russel1 and D.F.Dedolph, J. Org. Chem., 1985, 1 6 1 4.B.Pierini, A.B-Penenory, and R.A.Rossi, J. Org. Chem., 1985, 2, 2739. 162 G.F.Meijs, J. Org. Chem., 1986, 51, 606. 163 A.T.O.M.Adebayo, W.R.Boman, and W.G.Salt, Tetrahedron L e t t . , 1986, 27, 1943. 4147. 164 S.M.Palacios, R.A.Alonso, and R.A.Rossi, Tetrahedron, 1985, 165 R.Beugelmans and M.Bois-Choussy, Tetrahedron, 1986, 42, 1381. 166 J.F.Bunnett, E.Mitche1, and C.Galli, Tetrahedron, 1985, 41, 4119. 16 7 M.Mayer, A.Samat, and M.Chanon, H e t e r o c y c l e s , 1986, 24, 1013. 168 R. Beugelmans, J. Chastane t, H,Ginsburg L. Quintero-Cortes, and G. Rous s i , J. Org. Chem., 1985, 50, 4933. 169 R.Beugelmans and H.Ginsburg, H e t e r o c y c l e s , 1985, 23, 1197. 5069. 170 V.Nair and S.D.Chamberlain, J. Org. Chem., 1985, 0 9 1985, 218317 1 V.Nair and S.D.Chamberlain, and R.Southgate, J. Chem. SOL, Chem. Cornmun., 1 7 2 J.Knight, P.J.Parsons, 1986, 78. 173 V. K.Bhalerao, B. S. Nanjundiah, H.R. Sonawane, and P. M.Nair, Tetrahedron, 1986, 42, 1487. 174 H.R.Sonawane, B.S.Nanjundiah, M.Udaykumar, and M.D.Panse, I n d i a n J. Chem. , Sect. B , 1985, 202. 175 H.R. Sonawane, B, S.Nanjundiah, and M.D.Panse, Tetrahedron L e t t . , 1985, 26, 3507 176 S . J a a r i n e n , J - N i i r a n e n , and J . K o s k i k a l l i o , I n t . J. Chem. Kinet., 1985, 925. 1 7 7 T. Kitamura, S.Miyake, S.Kobayashi, and H.Taniguchi, Chem. L e t t . , 1985, 929. 2698. 178 S . J . C r i s t o 1 and E.O.Ael.ing, J. Org. Chem., 1985, 4558. 179 S . J . C r i s t o 1 and R.J.Opitz, J. Org. Chem., 1985, 180 S.J.Cristo1, R.J.Dpitz, and E.O.Aeling, J. Org. Chem., 1985, 50, 4834. 18 1 S.P. Spyroudis, L i e b i g s Ann. Chem., 1986, 947. 4459. 18 2 M.Geise1, A. Waterfeld, and R.Mews, Chem. Ber., 1985, 18 3 K.Itoh and A.Sera, B u l l . Chem. SOC. Jpn., 1986, 59, 479. 184 H.Suginome and S.Yamada, J. Org. Chem., 1985, 2, 2489. 18 5 H.Suginome, Y.Seki, S.Yamada, K.Orito, and N.Miyaura, J. Chem. SOC., P e r k i n Trans. 1, 1985, 1431. M.S.Rodriguez, and E.Su&ez, Tetrahedron L e t t . , 186 R.Freire, J.J.Marrero, 1986, 383. 18 7 J. I.Concepcion, C.G. F r a n c i s c o , R. F r e i r e , R. Hernandez, J. A. S a l a z a r , and E.Suirez, J. Org. Chem., 1986, 51, 402.
2,
2,
,
2,
107,
24,
17,
2, 2,
118,
27,
Part IV POLYMER PHOTOCHEMISTRY By N. S. ALLEN
Polymer Photochemistry BY N. S. ALLEN
1
Introduction This report follows the same format as the previous one. A s in previous years academic and industrial interest in
this field continues to grow at a steady rate with radiation curing now firmly established in many technological areas such as lithography and printing, the electronics and computer industries. The optical and luminescence properties of polymers, particularly aromatic and heterocyclic types remain an area of strong academic interest not only as a means of probing molecular structure and the motion of polymer chains but as a means of investigating the potential of the future plastics “solar cell”. Polymer photodegradation and stabilisation continues to be an active and complex field of study with much emphasis on the search for not just in;proving the stability of plastics but for methods of rapidly assessing and predicting durability and performance in various envirunments. The dyestuff and pigment fields are unfortunately a very much neglected area in terms of eg. dye fading phenomena, particularly when these materials now have many important applications such as photochrowics,liquid crystals and printing electrophotography where stability to ambient light is important. 2
Photopolymerisation Activity in the field of photopolymerisation and radiation curing continues to be high and this is yet again reflected in the large number of reviews which have A nurnber of articles have concentrated on various properties and characteristics of both ultra-violet and electron-beam curable systems. These include a comparison of industrial processes, thermosetting resins, reactive diluents, and inks7 ’ 8 . photosensitive polymers, coatings5 p 6
457
Photochemistry
458
Application areas for radiation curing have been reviewed and include optical disks and printed circuit^,^'^^ surface 14,15 modif ication of polymers, , l2 adhesives13 and wood coatings. On the more mechanistic side reviews have concentrated on photochemical reactivity of resins, charge-transfer a -methyl-styrene/ polymerisations,l7 butadiyne derivatives, cyclohexene oxide,"triary lsulphonium salts2o 21, peroxydisulphate ion22, p h o t o c h r ~ m i c sand ~ ~ silicones24. Other selected 25 topics of interest include low temperature ultraviolet curing, 9
epoxy resins by cationic initiators26, performance of photo29 initiators,27 manufacture of acrylate resins,28 photoresists and microwave curing lamps.30 At a recent conference in Stockholm a number of reviews of interest have appeared. These include the photochemistry of acylphosphine oxides and derivatives3' which are particularly useful for pigmented coatings, the photobehaviour of monomers containing electron donor-acceptor pairs32, general photoinitiation of polymerisation,33 synthesis o f block copolymers,34 photoinitiation by transition metal complexes35 and unwanted reactions in the photopolymerisation of coatings.36 The latter article is particularly interesting to industrial workers concerned with such problems as degradation, yellowing, colour and gloss change. 2.1 Photoinitiated Addition Polymerisation This last twelve months has seen an abundance of articles dealing with novel photoinitiators, resins/monomers and methods. One particularly interesting system claimed to be effective for inducing the polymerisation of epoxides is based on a composite of an aluminium compound with o-nitrobenzyl triphenylsilyl ether 3 7 The first step in the polymerisation is represented by Scheme 1 which shows the photogeneration of silanol from the ether. The second step shows the polymerisation of epoxides by the photogenerated catalyst and can proceed in the absence of light. Scheme 2 shows a possible reaction pathway f o r the formation of the silanol from the ether. The first step is oxidation of the methylene. bridge by the adjacent aromatic nitro group. The resulting hemi-acetal then decomposes to give the silanol. Although
459
IV: Polymer Photochemistry Step 1 Photodecomposition of catalyst
Aluminum
compound
I Step 2 Initation of polymerization
Scheme 1
& PhjSiOH
Ph3SiO-CH2Q
$
+
(a
N = N g ) '
COOH
No*
+
I1
\ (hemiacetal structure)
Ph,SiO-CH H
A
1
Ph3SiOH
'/
P
[ r
+
2 COOH
+ Proposed
photodecomposition 2
COOH
others
reaction mechanism of
Scheme
COOH
others
ONBSi
*
460
Photochemistry
the reaction scheme shows other products only the latter was identified in this particular case. One particular problem in photopolymerisation is oxygen quenching and on this point one attempt to minimise this effect has involved the use of long aliphatic structures built onto the initiator such as in (1). 38 Use of such structures however, are limited since high concentrations for effective polymerisation is offset by poor adhesion. Furthermore, structures such as 1 can be very expensive commercially from a cost-efficiency point-ofview. Attempts to change the photopolymerising efficiency of aromatic carbonyl initiators has recently involved the use of mixtures with cationic photoinitiators such as benzophenone with p-chlorobenzenediazonium tetrafluoroborate,39 phenanthrene quinone4' and benzoin methyl ether'' with triarylsulphonium and iodonium salts. In this case quenching of the lowest excited triplet state of the quinone by the monomer is reduced due to the greater efficiency of electron transfer from the quinone to the cation. Triphenylamine has been found to induce the photopolymerisation of vinyl monomers4z by a mechanism which involves the formation of a phenyl and diphenylamino radical. The latter will then abstract a hydrogen atom from the solvent to give diphenylamine which itself then reacts with the phenyl radical to give a phenylamine radical. Aniline is the final product (Scheme 3). Other workers43 claim a crystal violet and ascorbic acid mixture is similarly very effective in inducing the photopolymerisation of vinyl monomers. The photoinduced emulsion polymerisation of styrene with sodium dodecyl sulphate as a surfactant and dibenzyl ketone as the initiator has been found to be enhanced in the presence of La3+ and Mg2+ ions in a magnetic field of 2000G.44 The effect was explained on the basis of a combination of salt effects on unicellar structure and magnetic effects on the reaction of geminate triplet radicals in the micelles. The presence of the salt apparently increases the size of the micelles which, in turn, results in a reduction in the efficiency of freeradical migration from the micelle. The photopolymerisation of acrylamide by a new photosensitiser 4-benzoyl-N,N,lj-
46 1
ZV: Polymer Photochemistry CF, (CFZ1.I SO, NEt CHzCH,OCHzCH(OH)CH,
I
PhCMe2C-0
II 0
(1)
hY
H
O
i
+
I
H
S
H
-
N
Scheme 3
NH,
+
S'
462
Photochemistry trimethylbenzenemethanaminium chloride is enhanced by the addition of a reducing agent such as EDTA45 while 2,4,6trimethylbenzyldiphenylphosphine oxide is a relatively stable and effective photoinitiator, giving polymers with little or no y e l l ~ w i n g . Mixtures ~~ of anthracene with cationic photoinitiators are effective for inducing the photopolymerisation of vinyl while tungsten hexacarbonyl is an effective photoinitiator for acetylene48 and organo-titanium compounds are better photoinitiators than 49,50 zirconium compounds for the polymerisation of vinyl monomers. Bis(4-tert-butylphenyl) iodinium chloride has been found to be effective in enhancing the free radical, photo-polymerisation of vinyl monomers induced by a-phenylbenzoin/acrylamine compound mixtures5' while on the otherhand a new initiator l-benzyl-1,4-dihydronicotinamide initiated the photopolymer53 isation of styrene but not acrylonitrile.52 Other workers have successfully prepared a 13C derivative of 2,a-azobispropionitrile in order to determine spin-lattice relaxation times and chemical shifts of homopolymers prepared from this compound when used as a photoinitiator. Several new monomers/polymers have been prepared. These include 2-trifluoromethyl-4,6-bis(4-iodo-2-oxa-hexafluorobutyl)s-triazine which after photo-polymerisation has good thermal stability,54 2,5-bis( 4-hydroxy-3-methoxybenzylidene)-cyclopentanone which produces photocurable terpolymers with bisphenol A , 55 di-ethyl-p-phenylenediacrylate which gives an amorphous polymer in the s o l i d - ~ t a t eand ~ ~ copolymers of 2-hydroxyethyl methacrylate with 4-nitrophenylmethacrylate followed by condensation with cinnamoyl chloride.57 Polymeric photoinserters of the general structure (2) have been prepared and were found to give living free radical fragments 58 while an electrically conducting alternating copolymer p-diethynylbenzene-p-benzenedithiol has been prepared.59 Vinyl acetate has been successfully copolymerised with ethyl acrylate using a C02 laser6' and poly(a-methylolbenzoin methyl ether acrylate) has been prepared and found to
N:Polymer Photochemistry
463
have enhanced photopolymer activity compared with that of simple benzoin derivatives,61 Block copolymers of E-acryloylL-validine and vinyl monomers have been prepared and characterised62 while the photopolymerisation of 2,4-hexadiyne1,6-diolbis(toluene-sulphonate) under hydrostatic pressure gives a biradical dimer which was determined by time-resolved absorption spectroscopy.6 3 The photochemically induced high pressure polymerisation of ethylene and resulting molecular weight distribution patterns have been accounted for on the basis of ethylene entropy64 while the molecular weight of a maleic anhydride-styrene copolymer prepared by low energy photoinitiation increases linearly up to 4 molar concentration but thereafter diverges.65 The physical state of the matrix has been shown to be important in polymer photoreactions66 and laser flash photolysis has been shown to be particularly useful for evaluating the individual 67 rate constants during a free-radical induced polymerisation. In another kinetic study an estimation of the non-monochromaticity of light during photopolymerisation can apparently eliminate the discrepancy between the calculated and experimental dependence of the initial reaction rate on photoinitiator concentration.68 Using laser nephelometry the kinetics of free radical photoinduced polymerisation of acrylate monomers has been found to show a less than first-order dependence of oxygen inhibition with the reciprocal of the light intensity indicating that the oxygen is consumed by a free radical chain peroxidation mechanism.69 70 Kinetic chain lengths of between 1.6 and 16 were evaluated depending very much on the light intensity. Using calorimetry the photoinduced polymerisation of (2,2-dimethyl)-1,3-dioxdan4-yl) methyl methacrylate has been found to follow first order kinetics up to ~ 4 0 %c o n ~ e r s i o n . ~On ~ further irradiation chain degradation processes dominated. I
Tri( 2,2l-bipyridine) ruthenium (11) dichloride has been found to induce the photopolymerisation of acrylamide in the presence of an electron donor such as triethylamine.72 It was interesting to note that the addition of an electron
Photochemistry
464
acceptor such as methylviologen impaired the polymerisation and that the addition of potassium thiocyanate restored the reaction. g-Ethylmaleimide has been copolymerised with several acrylate monomers with very high efficiency and was accounted for on the basis of complex formation.73 Layer by layer photopolymerisation of acrylates was possible by altering the intensity of i l l u m i n a t i ~ nwhereas ~~ for very thin layers the rate of photopolymerisation of acrylates has been found to be proportional to the square root of the initiator concentration.75 Microwave dielectric measurements have been found to be particularly valuable for the measurement 76 of energy changes during the photopolymerisation of acrylates while methyl-2-methoxyacrylate has been studied and found to studies be unsuitable as a model acrylate ~ u b s t r a t e . Other ~~ of interest include a dilatometric study in oli&ocarbonate dimethacrylates,78 dimerisation of anthracene units in 79 9-anthrylmethyl methacrylate-methyl methacrylate copolymer and the effect of sulphites and chromates on the photopolymerisation of acrylates . Poly( 1-vinylpyrene) has been successfully prepared using a photoelectrochemical method on a gallium arsenide semi-conductor.81
*'
Photoreactions of carbonyl compcunds and the involvement of charge-transfer complexes in polymerisation continues to attract much interest, Biacetyl in methanol gives an a-substituted alkanone which is a very effective photoinitiator for vinyl pyrrolidene and vinyl acetate.82 Alkanone production is associated with partial keto group solvation by the methanol (Scheme 4 ) . The photophysical properties of a range of substituted thioxanthones has been studied and related to their photopolymerisation activity of n-butyl methacrylate.83 Polymerisation activity in the presence of a secondary amine synergist was associated with electron transfer from the amine and this was confirmed using micro-second flash photolysis where a new transient absorption was observed at wavelengths above 400 nm which was associated with the radical anion of the thioxanthone. In a similar study by the same workers84 on a range of
465
ZV: Polymer Photochemistry Ar [CH2SC(: S) NEt,
Ix
(2) Ar = Ph x =1-4
0 0
0
0-R
OH
Scheme 4
Formation of f r e e radicals:
+ H,O
PO;'-
HPOi-
+
6H
and 6 H
(Here PO;'-
Initiation : WH
+R
kl
W'
k:
W ' + M-WM'
Propagation:
Termination : WML
+
S -+
G r a f t copolymer
Scheme
5
= R')
Photochemistry
466
conventional aromatic carbonyl photoinitiators micro-second flash photolysis was used to identify the benzoyl radical produced from several of the photofragmenting benzoin derivatives. In particular benzil appeared to exhibit similar photoreactions to that of a photofragmenting type initiator and no evidence for hydrogen atom abstraction, as has previously been suspected, was found. The photopolymerisation of methyl methacrylate by various disulphides decreases in the order p-MeC H SS C H Me-p > t-Bus2 > 6 4 6 4 Ph CH2 SSCH2Ph = (C12H25)2S2 = Et2NCH2 CH2 SSCH2 CH2 NEt 2i5 the rates being comparable with those for benzoin ethers. In a similar study86 for acrylonitrile and various di and triphenyl compounds of N,P,As,Sb and Bi the order of initiation activity decreased Ph3P > Ph3S >Ph3N > Ph20 > Ph3As z Ph3Sb > Ph3Bi. This order agrees with increasing atomic radius and decreasing electronegativity of the 0 , N , S and P. Remaining with the same monomer the same group of workers87 found the following order of activity for a series of aryl ethers thus -p-HzNC6H4 Ome > 2-naphthyl Me ether > -pMe OC6H40Me >
-p-Br
OC6H40Me. In this case exiplex formation was tentatively proposed as the active intermediate. Surfactants such as alkylammonium carboxylates have been found to enhance the photopolymerisation of methyl methacrylate in the presence of triethylamine.88 Here the molecular structure and concentration of the surfactant were found to be critical factors as well as their ability to destroy hydroperoxides. Other studies on activity relationships have shown the following order for benzoin alkyl ethers in the polymerisation of butyl methacrylate thus: benzoin methyl ether > benzoin ethyl ether > benzoin iso-propyl ether > a-hydroxymethylbenzoin methyl ether > benzoin > benzil ethylene ketal,89 In this case activities were related to conjugation effects of the a-substituted groups.Phenothiazine initiates the polymerisation of acrylonitrile via an exciplex intermediate90 as does benzophenone and phenazine,91 benzophenone and dieth~lenetriamine’~ and benzil with triethylamine.9 3
IV: Polymer Photochemistry
467
A uuinoline--brorinecharge transfer complex has been found to
be particularly effective for producing copolymers of styrene and acrylonitrile with ethyl methacrylate at mole ratios similar to that of the monomer starting compositiong4 while 2,2,6,6-tetramethylpiperidinyloxy radical inhibited the polymerisation of the acrylonitrile-triphenylphosphine system.95 Phosphonyl radicals have been identified in the photoinduced polymerisation of methyl methacrylate by acylphosphine oxidesg6 and their high activity is associated with their tetrahedral structure while free radicals are formed from photoinitiators such as benzil by a 1st-order reaction.97 Photoinitiated cationic polymerisations continue to show promise in a number of areas. A group of workers at IBM research have developed a new technique for the surface modification of polymers based upon the properties of thistype 98 of photoinitiator. Bulk plastics when doped aith catjonic initiators and irradiated develop surface properties that can allow the interfacial polymerisation SJf monomers in a very controlled manner. The growth kinetics are non-linear and display an initial induction period, a rapid growth period, followed by a plateau where polymerisation ceases. Polymers that have crown ether groups as cation binding sites and cinnamic acid ester groups as photodimerizable groups have been prepared by the cationic polymerisation of monomers of the structures (3)” and (4)100, The binding abilities of the phototransformed polymers for alkali and alkaline earth metal cations were higher than those of the native polymer and they were also less-temperature sensitive. A series of cationic photoinitiators have been prepared which contain 2 and 3 photoactive trisylsulphonium groups in the same molecule1o1 and were found to be effective in the polymerisation ofdl-limonene dioxide. In the cationic polymerisation of a-methylstyrene by trityl salts the 9-phenylfluorenyl cation is the major product in the early stages of photolysis and is primarily responsible for the regeneration of the trityl cation.lo2 Other studies of interest include the cationic polymerisation of
468
Photochemistry
II
RO-CCHZCH
CH, :CMeCO,(CH,),O,CC
H=CH
L
A n -An (dimer)
An-OOt PCH,CH-CH, (endoperoxide) Is/
4
0 ( P = polymer)
Scheme 6
Me \ '6"5
/
C = NOSO,
(6) R = - M e
-R
i3No (8) R = -Me
IV: Polymer Photochemistry
469
N-vinylcarbazole by
triphenylsulphoniumhexafluoroantimonate saltslo3 and epoxy resins by onium salts.lo4
2.2.
Photografting Photochemical grafting of monomers/molecules onto substrates continues to show interest in terms of improving property requirements. Dyes have been effectively photografted onto polypropylene and nylon 6 films using 1,2-diphenyl-2,2dimethoxyethanonelo5 while methacrylic acid and acrylamj.de bave been successfully photografted onto polypropylene sheets using benzophenone as a sensitiser in order to modify the surface of the polymer from a hydrophobic to a hydrophilic one.lo6 A styrene-2,2,6,6-tetramethyl-4-piperidinyl methacrylate copolymer has also been successfully photografted onto polypropylenelo7 as has bromine into atactic polypropylene.lo8 Acrylamide has been photografted onto polyester fibres using benzophenone as an initiator in order to improve the cationic dyeability of the fibres”’ while methyl methacrylate has been grafted onto wool using peroxydiphosphate as an initiator.110 In the latter case the overall mechanism for the reaction is shown in Scheme 5 indicating that the active free radicals are phosphate ion and hydroxide radicals that interact v i a hydrogen abstraction with amino, carboxy and thiol groups on the wool cleaning active graft sites. With regard to work on the photografting of styrene and maleic anhydride onto polyethylene,evidence for the sensitisation of the styrene graft by maleic anhydride has been obtained. Vinyl monomers have been successfully photografted onto brominated polyacrylonitrile using dimethylsulphoxide as a solvent.’12 In this case the graft yield was monitored by measuring the bromine concentration spectrophotometrically. The diffusion properties of polypropylene toward oxygen and nitrogen gases may be carefully controlled by grafting 1,6-hexanediol diacrylate onto its surface113 while composites of low density polyethylene have been prepared by the photografting of sorbed vinyl monomers/initiator into the suface layers of the polymer. Chloromethylated polystyrene has been photografted onto polymethylmethacrylate by quaternising
Photochemistry
470
the former with pyridine.'l5 The graft yield was very much solvent dependent decreasing in the order methanol > acetonitrile > dichloromethane. Polyacrylonitrile has been grafted with acrylamide in strong sodium thiocyanate solution116 whereas in other studies perf luorination of polyethylene and polystyrene has been achieved by exposure to plasmas containing fluorine gas, inorganic solids have been grafted with vinyl monomers by treating them with 138 and by using an alkyl trichlorometa chlorinated silane hyl-manganese carbonyl system.119 2.3
Photocrosslinking Mixtures of diethylene glycol diacrylate and poly(methy1methacrylate) cure effectively on ultraviolet irradiation 120 with wavelengths<300 nm in the absence of any photoinitiator 121 while the addition of 9-phenylacridine acts as an accelerator. The photocrosslinking of poly(2,3-epithiopropyl methacrylate) occurs by the oxidation of the pendant episulphide groups when anthracene or benzoyl peroxide are present as initiators.122 In the former case singlet oxygen generated by energy transfer from triplet anthracene to ground state molecular oxygen oxidises the episulphide groups by Scheme 6. Solvents also had a dramatic effect on this reaction and this was correlated with the lifetime of the singlet oxygen. Poly(2,3-epoxypropyl methacrylate) films photocrosslink rapidly in the presence of imino-sulphonates of the general structures 5-8.123 In this case crosslinking efficiency decreased in the order 7 > 5 > 8 > 6 and their mechanism of photolysis shown in Scheme 7 for structure 7 shows that a sulphonic acid and associated free radicals are active species responsible for the insolubilisation of the polymer. Using a conventional carbonyl photoinitiator no insolubilisation was observed and led the authors to suspect the involvement of a cationic type mechanism. Concentration-cure profiles have been determined for acrylate resins using alkoxyacetophenone initiators124 and infra-red 125 analysis has been used to assess the degree of cure.
N:Polymer Photochemistry
I ,
hV
47 1
8+
OSo2
lRH M e \ O S/ O 3 "
-N
Scheme 7
Q
or
or
isomers
isomers
(13)
(12)
or isomers
* C-C-N-C-CHZw
II II I I1
O
O
H
O
472
Photochemistry
Epoxy resins have been cured using a tris(ethy1 acetoacetato) aluminium complex and tris (4-chloro-phenyl) (o-nitrobenzoyloxy) silane.126 Resins produced by this catalyst mixture were found to have desirable electrical characteristics. N-vinyl-2-pyrrolidone is claimed to be a much superior resin than several acrylate diluents for photocured coatings in terms of cure speed, tensile strength and hardness properties127 while photocrosslinking resins onto textile fabrics causes a reduction in dye lightfastness but an improvement in wash fastness .128 An automatic control process has been developed for the photocuring of acrylatd coatings onto leather substrates12g and electrophoretic coatings have been prepared from the photocuring of resins containing 1,3-dioxolane groups such as 2-isobutyl-2methyl-l,3-dioxolan-4-y1 methacrylate.I 3 O The photosensitivity of polyamic acid photoresists have been improved by the addition of acrylamide and a benzoin ethyl ether initiator131 and laservision disks have been made by photocuring 1,6-hexandiol diacrylate and mixtures of g-vinylpyrrolidone and tripropylene glycol diacrylate.132 Several other property studies relate to hardness measurements in relation to initiator concentrations,133 electrochemical 135 properties of photocured resins,134 adhesion of acrylates, morphology and phase separation of poly(styrene/see-Bu malcate) and trimethylolpropane triacrylate,136 influence of diluent on strength and modulus,137 comparison of glycol ethers with hydrocarbon dials,138 influence of inhibitor on cure rates of acrylates, 13’reduction in ahrinkage properties using diluent epoxy resins14* as well as improvements in flexibility.14’ Mixtures of anti-oxidants and hindered piperidine light stabilisers have been found to dramatically improve the thermal stability of ultraviolet cured epoxy diacrylates while having little o r no influence on the cure rate142 and DSC has been used to monitor the 143 curing of acrylate resins.
-
Polymers with cinnamate ester groups continue to attract interest. The nature of the substituent (CL,Br,Me,N02,
IV: Polymer Photochemistry
473
in substituted cinnamate esters of bisphenol AMe0 e&) epichlorohydrin copolymers significantly influences photosensititivity 144 Electron donating groups which increased the long wavelength absorption of the polymers’were ,important. The cation binding ability of cinnamoyl containing acrylates has been monitored using a fluorescent probe namely 8-anilinol-naphthalene ~ u l p h o n a t e lwhile ~~ in another study the photocuring of cinnamoyl containing vinyl ethers was monitored using infra-red analysis.14‘ Dimerisation processes in trans-poly(viny1cinnamate) have been monitored by fluorescence analysis and found to be substantially faster in the S2 than the S1 state.147 In another study148 the rates of photodimerisation of cinnamate ester moieties were found to obey first-order kinetics and were jmarkedly influenced by the polymer skeleton and presence of sensitising groups. Photosensitive resins of maleic anhydride/styrene with 2-hydroxyethyl cinnamate have been prepared and photocured with benzophenone and Michler ’ s ketonL?’
.
Secondary amines have been found to accelerate the air saturated photocuring of lf6-hexanediol diacrylate resin150 associated with the former giving alkylamino radicals which scavenge the oxygen. The photosensitivity of a series of polyester resins to an argon ion laser has been found to depend on the longest wavelength absorption property in relation to the output of the laser.15’ The photocrosslinking efficiencies of a series of methacrylate resins has also been found to be related to their absorption properties 152 while the degree of crosslinking of polyethylene by a series of benzophenone derivatives correlated with the quantum yields of photoreduction of the initiators. The crosslinking of vinylsilane rubbers with tetramethylsilanes has been 154 successfully carried out using carbonyl initiators and polyvinyl alcohol has been made resistant to boiling water by crosslinking with photosensitisers.155 Free radical concentrations in radiochemical polymerisations have been found to be 3-10 times greater than in photoinduced polymer is at ion^'^^ suggesting uneven distribution
Photochemistry
474
ie
of the initiators in the matrix present in isolated microregions. Finally, some new electrophoretic paints have been developed based on alkyl acrylates with alkyl methacrylates followed by electrodeposition on an aluminium anode at a pH of 7-8.157 3
Optical and Luminescent Properties Of all the subject areas in the field of polymer photochemistry this one remains by far the most prolific and is yet the least practical from a commercial point-of-view. Several reviews of interest have appeared, one, in particular, is a critical article on the characterisation of polymers by luminescence s p e c t r o ~ c o p y .Here ~ ~ ~ it is concluded that whilst this technique has the advantages of simplicity and sensitivity it is strongly lacking in terms of specificity and has adapted itself only in highly specialised areas of interest. This reporter not only supports these comments but would like to alter the comment on simplicity since on a more practicalbasis this may not be so and in some cases the precision of the method can be very poor (+lo%). On the theoretical side Phillips15' has edited an excellent book on the subject of polymer photophysics. Included are chapters by Mannerie'" on dynamic depolarisation, PhillipslG1 on an introduction to polymer luminescence, Webber'" on phosphorescence and delayed emissions, David and Baeyens-V~lant"~ on fluorescence of the solid-state, Nobbs and Ward164 on polarised luminescence, Roberts and Soutar"' on luminescence in fluid solutions of polymers and Solaro et ~ ~ on 1optically 1 ~ ~ active polymers. Another excellent book which encompasses many aspects of the photophysics and photochemistry of polymers has been written by Guillet.167 The use of fluorescence anisotropy in the study of polymers has been reviewed168 as has polarised luminescence for studying polymer structure. The applications of photoresponsive polymers170' 17' and conductive polymers172 are more specialised subject areas including reviews on polymeric donor175 acceptors , thermo1uminescence and photochromism
' ' '
.
IV: Polymer Photochemistry
475
The luminescence of polymers in relation to their degradation and stabilisation has been covered11ir6as has one author's specialised interests on the laser photochemistry of polymers.'lir7 In the Stockholm131 proceedings there are reviews on intramolecular energy transfer11ir8,antenna effects in polymers,'lir9 equilibria and molecular dynamics 181 in polymers180 and polymers in solar energy applications. The lumineqcence properties of commercial polymers continues to attract dnterest particularly with regard to the involvement of the chromophores in thermal and photochemical oxidation. Using combined luminescence, TLC and GC-mass spectrometry Allen and Harrison182 identified the presence of several types of fluorescent and phosphorescent chromophores in nylon 6,6. The fluorescence was associated with the presence of structures (9) and (10) while the phosphorescence was a mixture of all (9) to (14) thus accounting for the marked variation in emission lifetimes with wavelength. All the chromphores were further identified as aldol condensation products of cyclopentanone which is itself a product of the degradation of nylon 6,6 polymer. Bound fluorescent structures are also present in nylon 6,6 and are associated with a-keto-imides of the structure (15) as was confirmed recently by Smirnova et al.183 On irradiation polyethylene gives rise to new longer wavelength fluorescence emission bands which are tentatively associated with polyunsaturated centres wheras polypropylene exhibits no such phenomenon.184 Luminescence analysis of sulphonated polyethylene and polytetrafluoroethylene indicate that micropolarities of ionic clusters in the polymers are quite dynamic and vary with the nature of the polymer chain and the water content.185 The luminescence of polyacetylene has attracted some interest. The distribution of *-segments in Durham polyacetylene has been determined by luminescence and lower Raman analysis186 and the low fluorescent quantum yield is associated with self quenching by electronphoton coupling by the second nearest neighbour.181ir The same mechanism caused a fundamental alteration of impurity level locations in trans-polyacetylene188 while for laser
476
Photochemistry degraded polymer the existing-energy dependence of the luminescence is associated with energy selective excitation of randomly distributed defect levels.18’ For fully polymerised polydiacetylene the luminescence originates Po1yacenaphtha1ene from recombination at extrinsic sites. ’O apparently shows more fine structure in its photoelectron emission spectrum than that of poly~inylnaphthalene~~~ and the cure rate of epoxy resins has been measured using a fluorescent probelea as well as mixture absorption.lg3 The luminescence of doped polymers still continues to attract interest. Dimethylterephthalate quenches the delayed fluorescence of polyvinylcarbazole containing pyrene and this is associated with some charge-transfer interaction with the polymer. lg4 In poly (vinylidene fluoride) containing spin probes both ESR and fluorescence polarisation studies lg5 shows that two well defined relaxation processes are present. These include the lower temperature y-process and the higher temperature 8-process. In this work however, the latter was found to consist of two processes namely BL and Bu molecular relaxations. In various polymers of differing glass transitions the erythisine dye sensitised photolysis of 4-diethylaminoazabenzene diazonium salt and 2-diazo-l-oxo-k,2-dihydronaphthalene varies quite considerably. In the case of the former the efficiency of quenching of the delayed fluorescence of the dye increases with the decreasing glass transition of the polymer while in t h e case of the latter the effect is reversed.lg6 These results are associated with the fact that the former is quenched &v the singlet excited state while the latter is quenched via its lowest excited triplet state. The decay kinetics of various aromatic carbonyl phosphorescence emissions in various polymers was very much temperature dependent displaying generally non-exponential kinetics up to 323K and was tentively associated with the involvement 198 of hydrogen atom abstraction.lg7 In a similar study on benzophenone in polystyrene and polycarbonate the decay kinetics of the benzophenone phosphorescence shared a strong dependence on the glass transition temperatures of the
IV: Polymer Photochemistry
477
polymers and was again non-exponential. Singlet energy migration has been observed in naphthalene doped polymethylmethacrylate and was found to be quenched by the addition of anthracene.lg9 Stern-Volmer kinetics were obeyed and delayed fluorescence was observed. On a more practical note some workers have used the oxygen sensitivity of 9,lOdiphenylanthracene fluorescence as a means of measuring 200 dissolved oxygen in silicone fluids. Conformational arrangement in polyampholytes have been determined using 201 and toluene - sulphonic acid as a fluorescent probe excimer formation in phenanthrene doped polymer layers has 202 been used to measure the depth of phase mixing. The substitution in polymer-fluorescent dye-competitor systems has been investigated by fluorescence analysis and depending on their ability to substitute dyes competitors were arranged in the order polyelectrolyes nonionic polymers > surfactants > metal ions.203 The distribution of copper I1 ions in polyvinylpyridine was found to be non-uniform as measured by the non-Stern-Volmer dependence of the ions on the quenching of the polymer fluorescence204 while the fluorescence decay of photobleached Rhodamine 6G has been studied by the Moire technique and fringes were estimated by this method at 0.24.205 Luminescence analysis has been found particularly useful for studying ionic-clusters in a Nafion membrane using fluorescence probes such as pyrene.206 The cluster phase was found to be very much dependent on the water content and the presence of a hydrophilic counterion.The binding of sulphonated fluorophores t o copper (11) complexes of pol (ethylenimine) 20: has been studied by fluorescence analysis. For pyrene sulphonates the amount of binding exceeded that required for electroneutrality under certain conditions and was explained by the predominantly hydrophobic and territorial character of the Cu(I1) ion which shields the bound counterion from the charge on the metal ion. The fluorescence of 1-anilino-8-naphthalenesulphonic acid increased in 208 the presence of poly(dimethyldial1yammonium chloride)
478
Photochemistry and icne-type polymers containing viologen units exhibit photochromism209 ' 210 while other workers have studied the laser induced flash photolysis of polymer-containing spiropyran units.211 On the conformational side a study on 9,lO-dialkyanthracene probes both bound and free within polybutadiene has shown that the dynamic behaviour of the probe does not change212 Radical initiated copolymers of ( - ) menthyl acrylate with trans-4-vinylstilbene exhibit trans-= photoisomerisation of the side-chain stilbene groups which contrary to the low molecular weight analogue does not exhibit first-order kinetics.213 This effect is associated with interactions of the trans-cis mechanism of the stilbene side-chains and the locally ordered trans segments along the polymer backbone. The colouration of spiropyran in polycarbonate film has been measured on the nanosecond time scale using a single pulsed laser.214 The kinetics of the photochromism and its dependence on temperature showed strong deviations from exponentiality associated with an inhomogeneous distribution of free volume change in the polymer. New optically active copolymers prepared from ( - ) menthyl vinyl ether and E-vinylcarbazole have been characterised and found to possess a blacklike syndiotactic structure215 while the colour decay of tdu.ene solutions of a homopolymer of structure (16) obeys firstorder kinetics, the half-life being a linear function of the 216 average molecular weight of difference fractions the polymer. Bisindolinos-pirobenzopyrans have been synthesised and their photochromic properties examined217 and photoresponsive polypeptides membranes containing azobenzene side chains have been prepared and found to undergo complete reversible trans-cis photoisomerisation.218 Trans-4-( phenylazo) methacryl-anilide-styrene copolymer undergoes reversible gelation in carbon disulphide solution when photoisomerised to the L o form219 and circular dichroism studies have been carried out on optically active poly a-olefins in the far u.v. region?20 The solubility of polystyrene in cyclohexane has been found to change reversibly on ultraviolet irradiation when it contains %2 mole % of spirobenzopyran pendant
479
IV: Polymer Photochemistry Me
Iz
H,C =CMeCO,(CH,
X
X
OH
OH’
Scheme
-C-CH,J;;
8
(WCH=CH-CH=CH-)
lhY=
w C H2-CH
CH n~
(2)J
-CH-CH=CH-
Scheme 9
480
Photochemistry groups.221 Interestingly, at higher mole percentages of spirobenzopyran groups the polymer behaves as an excellent photoresist with a high contrast. Diffusion coefficients and molecular/ionic interactions between polymers and other species appear to have attracted some interest, particularly with regard to polyions. Quantitative information on coil size and associated changes therein together with the degree of aggregation in blends of polymers and copolymers has been shown to be possible using fluorescence depolarisation measurements.222 Using copolymer blends of vinylnaphthalene and methyl methacrylate in poly (methyl methacrylate) and poly(ethy1 methacrylate) blends at low guest concentrations could be measured. At higher blend concentrations, particularly where phase separation occurs,there is an increased rate of fluorescence depolarisation associated with increased excitation energy transport and a concurrent decreased fluorescence lifetime due to trapping effects. For the theoretically minded this is a novel approach to the study of polymer blend structure. Complex formation between polyacrylic acid and polyoxyethylene has been investigated by labelling the former with fluorescent dansyl groups.223 Adding a high molecular weight polyoxyethylene to the polyacrylic acid did not produce any significant increase in fluorescent emission suggesting that the latter is stretched out and is in contact with the former only in widely separated regions. Quasi-elastic light scattering and fluorescence photobleaching recovery methods have been used to study molecular dynamics of poly(bysine) in water and its dependence on in concentration (in this case K C a ) . 224 Fluorescence change indicated conformational transitions due to both polyionsmall ion and polyion-polyion interactions. The kinetics of fluorescence quenching of phenanthyryl groups bound to polyelec$rolytes has been studied225 and found to be highly dependent on the concentration of the phenanthryl groups while the luminescence of the porphyrin group in an acrylic acid - (10, 15, 20,-tritolyl porphin-5-yl) phenyl
N:Polymer Photochemistry
481
methacrylate-2-isopropenylanthraquinone copolymer is quenched intramolecularily by the anthraquinone group.226 The interaction between cellulosic polycations and polcations has been investigated using fluorescence polymerisation by labelling the polymers with dansyl groups.227 Crystalisation was found to be highly pH dependent. Evanescent wave-induced fluorescence has been used for the study of the interfacial depletion layer between a polymer solution and a solid barrier228 while fluorescence polarisation has been used to study the configuration of adsorbed polymerions on Self-diffusion coefficients have calcium carbonate.229 been measured for dye-labelled polystyrene230 and interactions between cations and anions in latex particles have been measured by luminescence quenching using a carbazole Curing reactions in epoxy-based labelled latex system.231 232 networks have been ministered using fluorescence analysis. Intra-molecular exciplexes have been observed to be formed in vinyl polymers containing phenanthrax and ,N ,N1-dimethylaniline moieties 233 as well as in 4-(dimethylamino) Chain conformation and styrene-l-vinylpyrene copolymer.234 steric effects were obviously important in both cases. End-to-end cyclisation is still a topic of some interest and for dimethylaniline and pyrene labelled polystyrene intra-molecular exciplexformation has been observed with rate constants that were very much solvent dependent.235 In cyclohexane, for example, the rate constant for exciplex formation was found to be identical to that of excimer formation for pyrene end-terminated polystyrenes. In tolerence simplex formation was much faster and was preceded by electron-transfer. In the case of a-anthrylpolystyrene end to end dimerisation was found to be diffusion controlled since the rate constants for different solvents were inversely proportional to the solvent viscosity.236 Fluorescent recovery experiment in polystyrene have indicated that some polymer molecules are imobile after initial photobleaching.237 On subsequent photobleaching total recovery was observed.
Photochemistry
482
Excimer f o r m a t i o n a n d e n e r g y m i g r a t i o n a n d i t s r e l a t i o n s h i p toward an u n d e r s t a n d i n g of molecular m o b i l i t y i n polymers r e m a i n s t o b e t h e n o s t p r o l i f i c area of s t u d y i n luminescence a n a l y s i s .
Measurements on e x c i m e r f l u o r e s c e n c e
from c o p o l y m e r s o f p o l y s t y r e n e w i t h v a r i o u s a c r y l a t e j h a s shown t h a t excimer
f o r m a t i o n is d i r e c t l y r e l a t e d t o t h e
s t a t i s t i c a l f r a c t i o n of l i n k a g e s between t h e s t y r e n i c g r o u p s , 238
In a n o t h e r s t u d y excimer formation a t t h e c o i l
globule t r a n s i t i o n p o i n t f o r p o l y s t y r e n e i n cyclohexane showed a s t r o n g d e p e n d a n c e on e x c i m e r
format ion a s s o c i a t e d
w i t h d i s t a n t chromophoresdue t o c o i l collapse239 w h i l e o t h e r w o r k e r s h a v e shown t h a t t h e r o t a t i o n a l e f f e c t o f t h e phenyl groups i n polystyrene i n s o l u t i o n has only a n e g l i g i b l e e f f e c t o n b o t h t h e monomeric a n d d i m e r i c f l u o r e s c e n c e d e c a y k i n e t i c s . 240
Q u e n c h i n g e f f e c t s on p o l y s t y r e n e e x c i m e r
f l u o r e s c e n c e have been found t o f o l l o w t h e o r d e r n a p h t h a l e n e > t o l u e n e > b e n z e n e . 241
Poly
(E,N_-dimet hy l a m i d e )
c o n t a i n i n g pendant triphenylmethane leucohydroxide r e s i d u e s 242 undergoes a p h o t o - r e v e r s i b l e v i s c o s i t y change i n methanol. This i n t e r e s t i n g e f f e c t is associated with t h e r e v e r s i b l e leuco -triphenylmethyl
c a t i o n e q u i l i b r i u m shown i n Scheme 8
which a l s o g i v e s r i s e t o an i n t e n s i v e c o l o u r c h a n g e .
Local m o t i o n s o f a , w - b i s ( 1 - p y r e n e )
a l k a n e s and pyrene
-
l a b e l l e d poly(methy1 m e t h a c r y l a t e ) i n s o l u t i o n have been m e a s u r e d by p i c o - s e c o n d e x c i m e r
fluorescence spectroscopy.
243
I n t h i s s t u d y t h e formation of t h e polymers d u r i n g p o l y m e r i s a t i o n c o u l d b e a c c u r a t e l y m a i n t a i n e d by m e a s u r i n g excimer f l u o r e s c e n c e l i f e t i m e .
The p h o t o p h y s i c a l p r o p e r t i e s
of p o l y ( N - v i n y l c a r b a z o l e ) h a v e b e e n i n t e r p r e t e d on t h e b a s i s o f a s t u d y i n d i a s t e r e o i s o m e r s of 2 , 4 - d i ( ~ - c a r b a ~ o l y l ) $ ~ ~ I n t h i s work i t is c o n c l u d e d t h a t 95% o f t h e e x c i t a t i o n e n e r g y occurs w i t h chromophoresassociated w i t h s p e c i f i c excimer sites.
Excimer f o r m a t i o n i n v a r i o u s p o l y v i n y l c a r b a z a l e
s t r u c t u r e s h a s been found t o b e d i r e c t l y connected w i t h t h e T h u s , a n enhancement p h o t o c o n d u c t i v i t y of t h e p o l y m e r s . 245
i n excimer forming s i t e s g i v e s rise t o reduced c a r r i e r g e n e r a t i o n c a p a b i l i t y and hence a lower p h o t o c o n d u c t i v i t y .
IV: Polymer Photochemistry
483
PolyCN-(viny1oxy)carbonyl carbazole] has been prepared and found t o g i v e rise t o t w o d i s t i n c t t y p e s o f t r i p l e t e x c i m e r e m i s s i o n s 246 w h i l e i n p u r e p o l y ( 2 4 i n y l n a p h t h a l e n e ) t r a n s p o r t theory normally a p p l i c a b l e t o
t h e 3-dimensional
polystyrene for a s p a t i a l p e r i o d i c lattice d i d not apply i n t h i s case d u e t o a h i g h e r t r a n s p o r t r a t e i n t h e case of t h e f o r m e r . 247
The a c t i v a t i o n e n e r g y f o r r a d i a t i o n l e s s
d e c a y processes i n isobutylene-naphthylmethyl m e t h a c r y l a t e methyl methacrylategraft
copolymer h a s been found t o
c o r r e s p o n d t o t h a t a s s o c i a t e d w i t h r o t a t i o n o f t h e a-methyl g r o u p . 248
Relaxation t i m e s i n anthracene labelled
poly(E-vinylacetamide),poly ( & - v i n y l c a p r o l a c t a m ) End p o l y (N-vinylpYrolidine)have been found t o decrease markedly i n an o r g a n i c s o l v e n t owing t o t h e loss o f h y d r o p h o l i c i n t e r a c t i o n s i n t h e m o l e c u l e s . 249 I n t h e case o f a s c e n a p h t h a l e n e amylnitride and 2-vinylnaphthalene copolymers excimer formation is a s s o c i a t e d with next t o n e a r e s t neighbours
250
w h i l e i n n a p h t h a l e n e and a n t h r a c e n e labelled methyl methacrylate-acrylic
acid copolymers i n t r a m o l e u c l a r s i n g l e t
energy migration w a s s i g n i f i c a n t l y enhanced i n aqueous media 251 when c o m p a r e d w i t h n o n - a q u e o u s m e d i a . The e f f e c t o f s o l v e n t v i s c o s i t y o n t h e r a t e c o n s t a n t o f
eximer f o r m a t i o n h a s b e e n s t u d i e d f o r p y r e n e t e r m i n a t e d Two classes o f c o n f o r m a t i o n a l t h e o r y
p o l y a c r y l a t e s . 252
were r e q u i r e d t o e x p l a i n t h e r a t e c o n s t a n t b a s e d o n d i f f u s i o n a l and non-diffusional
effects.
Temperature
e f f e c t s o n t h e f l u o r e s c e n c e a n i s o t r o p y d e c a y of a n t h r a c e n e 253 l a b e l l e d polybutadiene have been measured i n t h e m e l t u s e d t h e r e s u l t s showed t h a t l o c a l o r i e n t a t i o n a l m o t i o n s f o l l o w e d t h e same t e m p e r a t u r e l a w a s f o r t h e m a c r o s c o p i c For p h e n y l mechanical p r o p e r t i e s o f t h e polymer. terminated polybutadiene, fluorescence' quenching i n s o l u t i o n h a s b e e n f o u n d t o b e d i f f u s i o n c o n t r o l l e d . 254 The composition o f s e v e r a l flavin-containing p o l y e l e c t r o l y t e s h a s been found t o i n f l u e n c e markedly t h e s t a t i c a n d dynamic p r o p e r t i e s of t h e f l u o r e s c e n c e e m i s s i o n o f t h e f l a v i n m o l e c u l e . The d e c a y of t h e a n i s o t r o p i c e m i s s i o n w a s f o r e x a m p l e , r e s o l v e d i n t o t w o relaxation t i m e s , t h e longest corresponding with
484
Photochemistry polymer chain motions whilst the shortest is associated Chiroptical with rotat ion of the flavin molecule.255 spectroscopy has been found t o be a powerful technique for the elucidation of complex excited-state interactions in 256 . For example, in novel arowatic chromophar ic polymers poly(a-aminoacids) such as poly(L-1-pyrenealanine) strong ground-state interactions between pyrenyl groups were observed to be in a helical arrangement along the polypeptide chain. Two excimericspecies were observed by fluorescence analysis, one with a negative circularily polarised fluorescence dissymmetry at 460 nm while the other had positive dissymmetry The latter was found to be dominant at wavelengths >500 nm. at lower temperatures. Fluorescence anisotropy decay measurements have been carried out on a series of 9,lO-dialkylanthracenes in polybutadiene with alkyl substituents rangingin the power from 6 to 16 methylene Such a study allowed a striation of the groups.257 orientation autocorrelation functions which were found to increase with an increase in the alkyl chain length. For fourteen carbon atoms or more this function corresponded closely to that for the 1 - 3 diffusion found in long-chain labelled polymers. Intra-coil sensitisation of the singlet excited state of 9,lO-diphenylanthracene and fluorescence tagged pOly(viny1pyrrolidone)has been found to depend 258 strongly on the size of the polymer coil in solution. Analysis of the fluorescence decay curves in water indicated that the intracoil process is static and that anthryl aggregation induces non-exponentiality in the fluorescence decay associated with a dynamic equilibrium between the singlet diphenyl-anthracene and a non-fluorescent dimer state. Further evidence was also presented to show that these polymers self-organise into hydrophobic and hydrophilic regions Energy migration in alternative and random copolymers of 2-vinylnaphthalene and methyl methacrylate/methacrylic acid was found to vary fitting into a single exponential in the former case and a three segmental fitting in the latter.259 Spectral and time dependent fluorescence analysis of meso and meso and r s - b i s c and =-2,4-di(l-pyrenyl)pentane 1-( 1-pyrenylIetherJether have shown that these compounds are
ZV: Polymer Photochemistry
485
excellent models for isotactic and heterotactic diads of poly(1-vinylpyrene). 260 No evidence for triplet excimer formation has been found on laser flash photolysis of diastereoisomers of bis [l-( l-and 2-naphthyl) ethyllethers.261 Stereoisomers that exhibit strong excimer fluorescence show a corresponding reduction in the quantum yield of intersystem crossing. Photophysical models and experimental techniques have been developed to allow the determination of the ratio of the intrinsic quantum yields of excimerto monomer emission Apparently to apply this method the in polymer blends.262 host matrix must be miscible with the guest fluorescent polymer at low concentrations and a suitable small probe molecule must be available to model the polymer monomer signal. The singlet and triplet state properties of poly (dimethyl- silylene-co-methyl( l-naphthy1)silylenel have 263 been characterised and found to be highly solvent dependent. Strong excimerfluorescence is seen at room temperature in THF but at 77 K in methyltetrahydrofuran strong dimer emission is observed. The rate of energy migration in a photo-Fries reaction in naphthyl methacrylate copolymers is Fluorescence decays did not considered to be small.264 match those of the predicted Fryer model and was associated with inhomogeneous distribution of quenchers produced by the photo-Fries reaction. The phosphorescence emission properties of copolymers of poly(viny1benzophenone) closely match those of benzophenone itself apart from some E-type No triplet energy migration could delayed fluorescence.265 be observed. Changes in fluorescence depolarisation have been used to determine the coil-globule transitions for, anthryl labelled poly( styrene-maleic anhydride)266 and The depolarisation pyvinyl-labelled poly(viny1 acetate). 267 of fluorescence resulting from the transport of electronic excitations in chromophore containing polymers has been investigated as a technique for detecting non-ideal chain statistics268 and kinetic modelling of the 3-pulse dynamics of a monomer excimer pair has been attempted in the presence Segmented orientation of energy migration and detrapping.269 in polyisoprene networks has been maintained by fluorescence ~ lrevised his own work polarisat ion270 and Mor a w e t ~ ~has
486
Photochemistry on applications of synthetically labelled polymers. Chemiluminescencefrom polymers continues to attract wide-spread interest. The technique has been used as a sensitive monitor for the extent of Oxidation which occurs during the radiation sterilisation of In a similar respect plastic medical components.272 the technique has been used for measuring the extent of physical property changes in electron-beam irradiated polypropylene.273 The kinetics of aging of cellulosic materials has been correlated with their chemiluminescence 274’275 and in one study the presence of low molecular weight phenolics and hydrolysable hydrocarbons were assumed to play a minimal role in the chemiluminescence properties of hydrolysed wood material276 which in another study singlet oxygen was concluded to be important.2 77 Variations in the chemiluminescence emission from hydrolysed wood pulp have been associated with the intermittent decomposition of peroxides and hydroperoxides. 278 ’ 279 The chemiluminescence of poly [ 9-phenyl-l0-( 4vinylpheny1)anthracenel films has been found to be similar to that of 9,lO diphenylanthracene itself showing that the polymer backbone has little if any influence on this phenomenon !80 Other studies of interest include the chemiluminescence of weakly degraded polyethylene glycol ,281 residual initiators in PVC,282 polymer equipment 283 and a-tocatrienyl acetate.284 The radiothermoluminescence of polyethylene is associated with orientation of the tie molecules in the amorphous regions of the polymer285 while radiolysis products of hexabromotetrakisl(allyloxycarbony1)diphenyl oxide 286 quenched the radiothermoluminescence of this polymer. This type of emission has been used to investigate the cross-linking in butadiene rubber287 and also peel strength of polymer films.288 Thermoluminescence glow curves of butadiene-styrene rubber were associated with two processes, the first being independent and the second dependent on molecular relaxations289 which in doped polymethylmethzrylate containing anthracene and pyrene this emission was associated
IV: Polymer Photochemistry
487
with the recombination of polymer cations and aromatic Electroluminescence from polyethylene in anions.290 an electric field is associated with a double carrier injection mechanism acting at the metalpolymer interface. Spectra were directly related to the molecular structure of the polymer. Electroluminescence has also been observed from degassed (W,) and SF6 impregnated polyethylene when subjected to a divergent electric field and is associated with electron-hole recombination at luminescent centres present as deep traps between amorphous and crystalline regions.292 The electroluminescence of polyethyleneterephthalate has been found to be only weakly dependent upon temperature and is associated with electron injection from the electrode through the interfacial barrier and subsequent deactivation of the excited Ir.olecules to their groundA similar mechanism was proposed for state.293 polyethylene and polystyrene.294
,''
4
Photodegradation and Photooxidation Processes Interest in polymer photodegradation and oxidation processes is still widespread. Several reviews in this area have 295 appeared covering initiation mechanisms in polypropylene, kinetics and mechanisms in all polymers 296 coatings 297 and biphenol-type polymers.298 Other articles of topical interest include computer simulation of polymer weathering 299 photooxidation of polymer containing jet ESR as an early detection method of resin oxidation3'l and a comparison of light sources for weathering polymers.302 Polyolefins These continue to be the most widely studied materials. Detailed spectroscopic and mechanical testing studies on polyethylene have shown that whilst pre-crosslinking of the polymer gives enhanced oxygenated products, the mechanical properties are improved.303 Limitation of the photodegradation of crosslinked polyethylene is
4.1
488
Photochemistry associated primarily with diene chromophors and proceeds in an oxygenation process involving peroxy radicalsas shown In the case of silane crosslinked in Scheme 9.304 polyethylene hydroperoxidation rates during photoooxidation have been found to be the same as for normal low density Oriented polypropylene films have on grade polymer.305 the otherhand been found to exihibit better stability compared with that of unoriented film30' The reinforcing effect of crystalline films in the former case is attributed to the improvement in polymer stability. The photooxidation kinetics of branched polyethylenes has been found to be strongly influenced by processing history307 and the incorporation of poly(2,6-dimethyl-l,4-phenylene acid) has been found to suppress double bond formation during photooxidation.308 ESCA studies 309 on photooxidised low density polyethylene shows that oxidation rapidly 0 declines in the top 150 A of the surface . Using sandwich layers of polymer oxidation at the vinyl surface is found The to be twice as great as that at a 20 pm depth. mechanisms of thermal and photooxidation in octene-1 linear low density polyethylene have been found to be the same as those found for normal low density polyethylene.310 During photooxidation both isolated and parallel hydroperoxides are produced, the former being stable whilst the latter are fairly unstable at a temperature of 85OC. Surprisingly, variations in branching are concluded to have no effect on photooxidation rate. Uniaxial deformation of polyethylene and related polymers has been found to improve photostability of the polymers311 due to reduced oxygen permeability. This would be difficult to visualise particularly in view of ESCA work where photooxidation is a maximum on the surface of the polymer. Photooxidation of poly(4-methyl-l-pentene) results in oxidation of both the main chain as well as the pendant side chains. 312 Water transmission rates of polyethylene films have been altered by the photochemical irradiation of blendsof the polymer with acrylic monomers.313
IV: Polymer Photochemistry
489
D e t a i l e d ESR s t u d i e s on t h e p h o t o o x i d a t i o n of i s o t a c t i c p o l y p r o p y l e n e a t d i f f e r e n t t e m p e r a t u r e s showed t h a t d e c o m p o s i t i o n of t e r t i a r y h y d r o p e r o x i d e s is t h e key s t e p
i n i n i t i a t i o n and t h a t t h e N o r r i s h t y p e I p h o t o c l e a v a g e o f k e t o n e s is o n l y a minor c o n t r i b u t i o n t o f r e e r a d i c a l p r o d u c t i o n . 314
The photo-induced
c r o s s l i n k i n g of
p o l y e t h y l e n e by a n t h r a q u i n o n e h a s been a s s o c i a t e d n o t o n l y w i t h i t s p h o t o r e d u c t i o n by hydrogen atom a b s t r a c t i o n b u t a l s o by p r o d u c t s o f t h e p h o t o r e d u c t i o n p r o c e s s .
315
4 . 2 Poly(viny1 h a l i d e s )
P h o t o t h e r m a l d e h y d r o c h l o r i n a t i o n of PVC as s t u d i e d by derivative
u l t r a v i o l e t a b s o r p t i o n and f l u o r e s c e n c e
a n a l y s i s t e c h n i q u e s h a s shown t h a t c a r b o n y l and h y d r o p e r o x i d e g r o u p s a r e more i m p o r t a n t i n t h e i n i t i a t i o n s t e p s t h a n r e s i d u a l d o u b l e bonds. 316
O t h e r w o r k e r s however, have
shown t h a t r e s i d u a l u n s a t u r a t i o n i s p r i m a r i l y i m p o s s i b l e f o r t h e p r o d u c t i o n of h y d r o p e r o x i d e s and e v e n t u a l l y a , @ - u n s a t u r a t e d c a r b o n y l g r o u p s by Scheme 1 0 , t h e l a t t e r
317
b e i n g p r i m a r i l y r e s p o n s i b l e f o r t h e f l u o r e s c e n c e emission. The c o n c e n t r a t i o n of t h e l a t t e r s p e c i e s were a l s o found t o c o r r e l a t e c l o s e l y w i t h t h e p h o t o o x i d a t i v e s t a b i l i t y of t h e polymer.
The SbC13 c a t a l y s e d p h o t o c h e m i c a l
d e g r a d a t i o n of PVC h a s been a s s o c i a t e d w i t h an i o n i c i n t e r a t i o n between t h e SbC13 a n d p o l y e n e s e q u e n c e s .
318
C a t i o n i c p o l y e n i c s e q u e n c e s w i t h absorpti-on maxima from 500-900 c m were i d e n t i f i e d i n t h e polymer. Lubricants have been found t o p l a y l i t t l e , i f a n y , r o l e i n t h e p h o t o i n d u c e d o x i d a t i o n of PVC, 319 a l t h o u g h it s h o u l d b e pointed out t h a t o t h e r important a d d i t i v e s such a s metal c a r b o x y l a t e s t a b i l i s e r s w e r e n o t c o n s i d e r e d and i n commercial r e a l i t y s y n e r g i s t i c e f f e c t s may p r e v a i l . Low m o l e c u l a r weight waxes were found t o b e weak sensitisers.
The p h o t o s t a b i l i t y of p l a s t i c i s e d PVC i s
improved i n t h e p r e s e n c e of m e t a l o x i d e , p a r t i c u l a r l y Zn0.320 D i b a s i c l e a d p h o s p h i t e was found t o b e e x c e p t i o n a l l y good.
O t h e r w e a t h e r i n g s t u d i e s on
p l a s t i c i s e d PVC have examined l o s s of p l a s t i c i s e r ,321 ESR
Photochemistry
490
pO' -CH=CH-CH-CH2W
+
wCH=CH-C-CH,
HO ,
II
I
0
Scheme 10
-
CH2-
-
C H z-
CH -NH -C0 -CH2-
( P H)
X
1
ihv(hr340nm) -
CH2- NH
CO
I
hv (observed at
r*
CH
I
I
J . 1
1-+1- f -
/ c r 0t 0n i2 at i 0n
\h:o2
-CH2COOH
CHz-~H-NH-CO-CH2~
-
CH
(Po)
1
O2
CH
i
-N H -C0-CHz~
00.
1+pH
*OH
+
CHz-CO-NH-CO-
~CH2-CH-NH-CO-CHZ-
I
?
J.
-CH2-CH0
h = 3 4 0 nm)
pH
+ NHz-CO-CH2~
Scheme 11
CH
IV: Polymer Photochemistry
491
a n a l y s i s o f c o p o l y m e r s 3 2 2 a n d g e n e r a l p h o t o a g i n g .3 2 3 The s e n s i t i s e d p h o t o c h e m i c a l o x i d a t i o n o f PVC f i l m s h a s b e e n c h a r a c t e r i s e d by t h e f o l l o w i n g f e a t u r e s namely
-
(1) a l i n e a r d e p e n d e n c e o f o x i d a t i o n r a t e on l i g h t intensity;
(2) l o w h y d r o p e r o x i d e quantum y i e l d s ; (3) h i g h c a r b o n y l y i e l d s ; ( 4 ) l i n e a r g r o w t h of c a r b o n y l i c g r o u p s ; (5) short-links i n t h e oxidative chain; (6) f i r s t - o r d e r decay of peroxy r a d i c a l s ; (7) v a l e n c y m i g r a t i o n s o v e r v e r y l o n g d i s t a n c e s 324 i n t h e s o l i d polymer. ,
The t r a p p i n g of hydroxy r a d i c a l s was c o n s i d e r e d t o b e t h e b e s t way o f p r o t e c t i n g t h e p o l y m e r .
In another study i t was f o u n d t h a t PVC p h o t o o x i d a t i o n w a s a n o n - u n i f o r m
process involving photooxidation a t t h e s u r f a c e and photodehydrochlorination i n t h e h u l k . 325
4 . 3 Polyacrylates The quantum y i e l d o f t h e u l t r a v i o l e t l i g h t i n d u c e d photolysis
of polymethyl methacrylate has been found 326 t o be 0.03 chain emissions p e r absorbed photon. I n d e t a i l e d k i n e t i c s t u d i e s t h e p r e s e n c e of oxygen was f o u n d t o b e u n i m p o r t a n t i n t h e i n i t i a t i o n of t h e p h o t o x i d a t i o n of p o l y m e t h y l m e t h a ~ r y l a t ea n~d~ t~h e s e r v i c e l i f e of t h e polymer c o u l d b e p r e d i c t e d w i t h r e a s o n a b l e a c c u r a c y . 328 I r r a d i a t i o n of p o l y m e t h y l
m e t h a c r y l a t e w i t h an excimer l a s e r a t 1 9 3 nm p r o d u c e d a b l a t e d particles with temperatures
S 3000K. 329
4 . 4 P o l y a m i d e s a n d Copolymers The p h o t o o x i d a t i o n of n y l o n s 6 , 1 1 a n d 1 2 h a v e b e e n
e amined u n d e r b o t h s h o r t <300 nm a n d l o n g w a v e l e n g t h ‘t Intermediate i r r a d i a t i o n >300 nm c o n d i t i o n s . 330 p h o t o p r o d u c t s are i n d e p e n d e n t o f t h e s t r u c t u r e of t h e p o l y a m i d e a n d i n t h e f o r m e r case C-N bond s c i s s i o n of
Photochemistry
492
t h e amide g r o u p i s t h e key i n i t i a t i o n s t e p i n v o l v e d . A t l o n g e r w a v e l e n g t h s up t o 340 nm it is c l a i m e d t h a t
i n i t i a t i o n is t h e same a s t h a t f o r s h o r t - w a v e l e n g t h i r r a d i a t i o n w h e r e a s a t w a v e l e n g t h s >340 nm p h o t o o x i d a t i o n o f t h e p o l y m e r s i s i n d u c e d s o l e l y by i m p u r i t i e s s u c h a s carbonyl o r hydroperoxide groups.
B e t w e e n 300-340 nm a d u a l mechanism i n v o l v i n g b o t h C-N bond s c i s s i o n a n d i m p u r i t y chromophores is invoked.
Scheme 11 o u t l i n e s
t h e v a r i o u s o x i d a t i o n pathways involved.
I n t h e case of
t h e polyether-block-polyamides t h e p o l y e t h e r s e c t i o n s a r e highly prone t o r a d i a t i o n t o give hydroperoxides vhich a r e u n s t a b l e a b o v e 6 O o C a n d breakdown t o g i v e h e m i a c e t a l s which t h e m s e l v e s breakdown t o g i v e a l c o h o l a n d a l d e h y d e s 331 t h u s p r o t e c t i n g t h e polyamide s e c t i o n of t h e c h a i n . O t h e r w o r k e r s u s i n g l i g h t w a v e l e n g t h s >360 nm h a v e p r o p o s e d t h a t p o l y a m i d e s p h o t o x i d i s e i n t h e p r e s e n c e of 332,333 a-ketoimide groups.
4.5
P o l y s t y r e n e s a n d Copolymers
Weir h a s r e v i e w e d s p e c i f i c mechanisms,phenomena a n d u n s o l v e d p r o b l e m s i n t h e p h o t o d e g r a d a t i o n of p o l y s t y r e n e s 3 3 4 I n d e p t h s t u d i e s i n t h e d e g r a d a t i o n p r o d u c t s of p o l y s t y r e n e and t h e i r involvement i n i n d u c i n g p r o p e r t y changes h a s l e d
some w o r k e r s t o c o n c l u d e t h a t lower m o l e c u l a r w e i g h t f u n c t i o n s a r e more s u s c e p t i b l e t o o x i d a t i v e a t t a c k . 335 Quantum y i e l d s o f c h a i n s c i s s i o n p r o c e s s e s i n p o l y s t y r e n e s have been measured i n solution336 w h i l e o t h e r w o r k e r s h a v e examined t h e i n f l u e n c e o f d e g r a d a t i o n p r o d u c t s o n p h o t o d e g r a d a t i o n r a t e s m e a s u r e d by u l t r a v i o l e t a b s o r p t i o n s p e c t r o s c o p y .337
O p t i c a l f i l t e r e f f e c t s by
t h e p r o d u c t s o n t h e m e a s u r e d r a t e had t o b e c o r r e c t e d a n d s u i t a b l e e x p r e s s i o n s were d e r i v e d f o r t h i s p u r p o s e .
The r o l e of s i n g l e t oxygen i n t h e p h o t o o x i d a t i o n of s t y r e n e b u t a d i e n e c o p o l y m e r s h a s b e e n examined i n some d e p t h , 338-340 A n t h r a c e n e a n d 9 - m e t h y l a n t h r a c e n e were f o u n d t o b e e f f e c t i v e p h o t c s e n s i t e r s of t h e o x i d a t i o n of t h e copolymer a n d w a s a s s o c i a t e d w i t h t h e f o r m a t i o n of s i n g l e t oxygen
IV: Polymer Photochemistry
493
produced from the quenching of the lowest triplet excited state of the sensitiser by ground-state molecular oxygen. The singlet oxygen will then attack the double bond in the butadiene moiety. In the absence of any sensitiser the initiation of the photooxidation of the copolymer was accounted for on the basis of singlet oxygen formation via. a copolymer oxygen complex.340 Methane production through the depth of a film of poly(p-methoxy-styrene) on long wavelength irradiation ( X ' s > 3 0 0 nm) has been used in an attempt to provide information on depth profiles of polymer photodegrations.341
-
4.6
Polyesters Photodegradation of poly(ethyleneterephtha1ate) has been found to cause dramatic changes in the electrical properties of the polymer342 while in another study water extractable phthalate residue were f o ~ n d 3The ~ ~adhesion properties of poly(ethy1ene terephthalate) have been 344 and infrafound to increase during photodegradation red changes in the photooxidation of vinyl acetate copolymers has indicated that hydroperoxide groups are the key photoinitiators.345 The photothermal oxidation of segmented copoly (etheresters) have been found to behave like two polymers with different portions of polyether. 346 The polymers of the general structure(17) apparently photooxidise in the a-position with respect to oxygen of the polyether segment to give hydroperoxides of the structure.'l8)The latter will then proceed to photolyse by the overall Scheme 12 to give esters, hemi-acetals and formates as products.
Photochemistry
494
OOH
I
Q
C-0-CH,
I
-
H
(18)
OOH
I
- C -0-C
H,
Q
I
H
6 I
+ HOa
-C-O-CH,I
I
H
J
- CO-O-CH,-
Esters
OH
I
*C-O-CH,
I
H
*
Hemiacetal
S c h e m e 12
Formates
IV: Polymer Photochemistry 4.7
495
Bisphenol A Polymers Bisphenol A-polycarbonate
does n o t undergo a photo-Fries
r e a r r a n g e m e n t when e x p o s e d t o l o n g
wavelength l i g h t i n
n i t r o g e n o r oxygen a t m o ~ p h e r e s ? ~ ~t hI ne a b s e n c e o f oxygen a n d w i t h l i g h t of w a v e l e n g t h s <315-320
nm c r o s s
l i n k i n g was t h e dominant p r o c e s s a n d b i s p h e n o l A w a s an i d e n t i f i a b l e and e x t r a c t a b l e product.
U s i n g FTIR
ather workers have found t h a t i r r a d i a t i o n of polycarbonate w i t h l i g h t i n t h e r e g i o n 254-365 nm r e s u l t s i n t h e r e g i o n 254-365 nm r e s u l t s i n t h e f o r m a t i o n o f p h e n y l s a l i c y l a t e , dihydroxybenzophenone,
Iiiono a n d d i -
hydroxybiphenyl and hydroxydiphenyl e t h e r groups.
348
None of t h e s e p r o d u c t s c o n t r i b u t e t o w a r d s t h e i n i t i a t i o n o f p h o t o o x i d a t i o n of t h e p o l y m e r o t h e r t h a n h a v i n g some U.V.
antioxidant action.
On l o n g - w a v e l e n g t h
( 3 6 5 pm) p h o t o i n i t i a t i o n o c c u r s
V
J
irradiation
i m p u r i t y chromophore
w h e r e a s w i t h l i g h t of w a v e l e n g t h s s h o r t e r t h a n 300 nrn d i r e c t e x c i t a t i o n of t h e d i p h e n y l c a r b o n a t e u n i t o c c u r s . Two d i s t i n c t m e c h a n i s t i c p a t h w a y s h a v e b e e n p r o p o s e d o n t h e b a s i s o f t h e r e s u l t s o b t a i n e d a n d t h e y are shown i n Schemes13 a n d 1 4 f o r s h o r t a n d l o n g w a v e l e n g t h i r r a d i a t i o n conditions.
A l l t h e p r o d u c t s shown were i d e n t i f i a b l e .
At
h i g h h u m i d i t y t h e k i n e t i c s of t h e p h o t o o x i d a t i o n o f p o l y c a r b o n a t e i s i n f l u e n c e d t o some e x t e n t i n t h a t on s h o r t - w a v e l e n g t h i r r a d i a t i o n o n l y p r o d u c t s which a r e s o l u b l e i n water a p p e a r t o b e p r o d u c e d .
Furthermore, t h e
p r e s e n c e of t h e m o i s t u r e h a s a n a c c e l e r a t i n g e f f e c t on p h o t o d e g r a d a t i o n of t h e p o l y m e r .
The l i f e e x p e c t a n c y of
s t a b i l i s e d polycarbonate is expected t o be a t least t h r e e y e a r s o u t - o f -doors349
and product formation
strongly influences
p r o p e r t y changes d u r i n g photoo x i d a t i o n o f p o l y c a r b o n a t e s . 350 Wet a n d d r y w e a t h e r i n g
of epoxy r e s i n s b a s e d o n b i s p h e n o l A h a s b e e n c a r r i e d 351 out. 4.8
Miscellaneous Polymers I n t h e p h o t o i n i t i a t e d o x i d a t i o n o f poly(ethy1ene-co-
Photochemistry
496
P C ( h m a x =2 6 4 n m ) hv
1
excitation of diphenylcarbonate units
0
photo- Fries rearrangement
3 hv,O,
1
\
A
Ll(hmax= 320 n m ) I R : 169Ocm-'
//
\
acid groups
recombination
chain brcakings
do"
T
h"+'p!$
p h e no1 ic extremities
HO
L2 (hmax=355
nm)
I R : 1629 cm-l
HO
/
4 t y p t s of chain groups
I L, :phenolic groups nm 1 IR :3550 and 3500 cm-'
(Amax=284
3
PHOTO-OXIDATIVE PRODUCTS
Scheme 13
1
497
IV: Polymer Photochemistry
3. X
hv, o2
excitation of defects or impurities
rYrO;)
*r*o-i-o+
pc
0
CH3
3
hydrogen abstraction
-CH,
II
+\+o-c-o--
0
CH3
3
isomerizotion
-c-o0
0-C -0-
CH3-C
II
0
00
I
-
hv
CPC
1
photolysis
0 II
\ p- scission
+
+
I R 1 3490 cm-'
ACID GROUPS
p
+ PA
c A0 2 -----..--)+OH
\i
aromatic Ketones IR :1688cm-'
(hm,,=284nrn) IR:3550and
3500 crn-1
Scheme 14
I R : 1860 cm-'and
1840cm-1
498
Photochemistry carbon monoxide) copolymers the main chain ketonic groups are considered to be ineffective initiators.352 In the case of phenylvinylketone copolymers photodegradation rates were found to be more dependent on temperature than structure. 353 Novel poly (1-( 4-carboethoxyphenyl)-2propene-1-one) has been prepared and its photochemistry characterised.354 Of particular interest was its high rate of photodegradability when compared with other known polymer materials. A novel poly (bis(4-benzoylphenoxy) phosphazene) has also been synthesised and found to be an extremely efficient and very stable triplet energy donor.355 In the photooxidation of wood the photochemical reactions of phlobaphene are believed to be similar to those of catechin shown in Scheme 15356Here singlet oxygen generated by the quenching of excited catechin by ground-state molecular oxygen attacks the catechin ring system to give ring opening carboxylic acid products. The synthesis and photochemical properties of several novel polymeric 357,358 derivatives of rose bengal have been described. The polymeric derivates are made from poly(styrene-covinylbenzyl chloride) by nucleophilic displacement using the C - 2 ' carboxylate group of the dye. These polymeric dye derivatives are highly efficient singlet oxygen sensitisers and could have a number of potentially useful scientific applications. Maximum singlet oxygen generation is achieved at a ratio of one dye molecule per thirty chain units whereafter there is a strong built-in quenching effect. On prolonged irradiation these derivatives cross-link and involve the usual triphenylmethane dye intermediate radicals and radical ions. New photosensitive polymers with pendant dimethylmaleimide groups have been prepared359 as well as several styrylpyridine based polymers.360 The latter were found to undergo the usual photo-Fries rearrangement. g-acetyl amino acids have been studied and
IV: Polymer Photochemistry
X
I
0
0
499
GI
I
I
0
0
i
0 0
0
7 I S 0
0
0
r
I +
X
I
0
0
% 0
- 0 = '0
1
0
I
4
0
r
500
Photochemistry found n o t t o b e a p p r o p r i a t e models f o r poly(amino a c i d s ) . Laser
361
Raman s p e c t r o s c o p y h a s been found t o b e v e r y u s e f u l
f o r t h e s t u d y of t h e p h o t o d e g r a d a t i o n o f alkyd-based v a r n i s h e s . 362
The t e c h n i q u e p r o v i d e s e v i d e n c e f o r c r o s s -
l i n k i n g a t d o u b l e bonds,
l o s s of methylene g r o u p s due
t o c h a i n s c i s s i o n and t h e u s u a l f o r m a t i o n of c a r b o n y l i c g r o u p s and a s s o c i a t e d d e c o m p o s i t i o n of h y d r o p e r o x i d e s . The p r e s e n c e o f t i t a n i u m d i o x i d e i n t h e a l k y d r e s i n f i l m s
i s concluded t o play a n important r o l e i n t h e p h o t o c a t a l y t i c A number of a r t i c l e s have a p p e a r e d on t h e laser a b l a t i o n u s e r of polymers and t h e d e c o m p o s i t i o n of t h e l a t t e r s p e c i e s .
p h o t o d e c o m p o s i t i o n p r o d u c t s . 363-366 t h e i n t e n s i t y of
In controlled etching
t h e l a s e r is extremely important f o r
i n t r o d u c i n g r e a c t i v e s u r f a c e f u n c t i o n a l groups.
Intense
l a s e r p u l s e s w h i l s t t h e y c a u s e a b l a t i o n do n o t g i v e t h e polymer r a d i c a l s t i m e enough t o r e a c t w i t h oxygen.
Product
d i s t r i b u t i o n s a l s o v a r y enormously depending on t h e polymer structure.
For example, w i t h p o l y ( m e t h y 1 m e t h a c r y l a t e ) a t 1 9 3 nm, 18% of t h e a b l a t e d polymer is monomer w h i l e a t 248 nm l e s s t h a n 1%monomer is produced.
I n t h e p h o t o o x i d a t i o n of CC14- s o l u t i o n s of c i s - 1 , 4 Inf ra-red a n a l y s i s of t h e e a r l y s t a g e s of t h e p r o d u c t s i n d i c a t e t h a t h y d r o p e r o x i d a t i o n i s a key s t e p i n t h e g e l l a t i o n p r o c e s s . I n t h e case o f p o l y ( 2 , 6 - d i m e t h y l - 1 , 4 - p h e n y l e n e ) photooxidation i n s o l u t i o n produces r a d i c a l - c a t i o n polymeric c h a i n s and s u p e r o x i d e i o n s . 368 The p h o t o d e g r a d a t i o n of n i t r o c e l l u l o s e h a s shown t h a t NO2 g r o u p s a t C6 d e g r a d e 369 more r a p i d l y t h a n a t C2 and Cg of t h e p y r a n r i n g . Photodegraded polyether-polyurethanes a r e r a p i d l y crossl i n k e d when immersed i n sodium d i c h r o m a t e s o l u t i o n whereas undegraded m a t e r i a l is u n a f f e c t e d . 370 Hydroperoxide g r o u p s produced i n t h e f o r m e r c a s e may b e i m p o r t a n t h e r e a l t h o u g h no mention of t h i s f a c t is made i n t h e p a p e r . In t h e photolysis of p o l y s i l a n e s i n s o l u t i o n s i l y l radicals371 a r e produced whereas i n t h e T i 0 2 p h o t o c a t a l y t i c o x i d a t i o n of p o l y v i n y l a l c o h o l i n aqueous media hydroxvl r a d i c a l s p o l y b u t a d i e n e g e l l a t i o n is dominant. 367
IV: Polymer Photochemistry
501
are considered to be of primary importance.372 Other miscellaneous studies of interest include the photodegradation 373 of glycidyl-methacrylate~n~ethyl isopropenyl ketone , radiation-curable resins,374 polymeric reinforced concrete,375 Kapt~n~'~, plastic components377, and general laser effects.378 5
Photostabilisation Processes Several reviews in polymer stabilisation have appeared. These 379 include new aspects of the stabilisation of polyolefins,, mechanisms of orthohydroxybenzophenones and hindered piperidines,38Thotoantioxidant mechanisms381 and new The po 1ymer isab1e ortho-hydroxyph eny 1benz ot riaz o 1e 8 photostabilisation of nylon 6,6,6and 12 polymers have been reviewed 383 as has polypropylene in some depth384 as well as polyolefins generally,385 Hindered piperidines and their stabilising mechanisms and activity continue to be extensively reviewed and include their photoanti-oxidant 388 action,386 usage over the last ten years,387 progress, interactions,389 and recent trends.390 Other reviews of interest include coupling agents3g1 and ways of optimising the activity of stabilisers.392 Hindered piperidines, their mechanisms, behaviour and performance continue to reign as highly effective stabiliers for a wide range of polymeric materials. Detailed ESR studies 393-395 on 2,2,6,6- tetramethylpiperidine molecules have presented some new insights into the mode of action of these types of stabilisers. Free radical processes induced by t-butoxy radicals393 have shown that in the case of an unsubstituted molecule abstraction of the amino hydrogen is the dominact step, Studies on the structure (19) in acrylat$melamine coatings have shown that the rate of production of nitrcxyl free radicals is strongly enhanced by humidity but decreased by intense light sources.394, 395 In the case of acrylic/urethane coatings humidity has little or no effect. In the former case
Photochemistry
502
IMe Me
.NMe ;->oi(cH24]Me
2
(19)
Me
4
'Me
Me
MHDPN
ROOH
ROO'
Scheme 16
S c h e m e 17
ZV: Polymer Photochemistry
503
increasednitroxylradical p r o d u c t i o n is a s s o c i a t e d w i t h a from
h i g h r a t e o f r e g e n e r a t i o n of t h e o r i g i n a l amine
n i t r o x i d e r a d i c a l s i n t h e melamine b a s e d c o a t i n g .
Also, i n
g r o u p were f o u n d t o b e c o n v e r t e d t o
t h e l a t t e r s y s t e m , amine
g r o u p s , a g a i n a f u n c t i o n o f t h e melamine.
methylamine
The s u b s t i t u t i o n o f &-acyl g r o u p s i n t o t h e s e c o n d a r y amine function i n hindered p i p e r i d i n e molecules generally suppresses t h e i r s t a b i l i s i n g a c t i v i t y i n polypropylene.
396
The e x c e p t i o n s t o t h e r u l e were 2 - a c r y l o y l a n d g - b e n z o y l g r o u p s .
-N - a c y l a t e d
h i n d e r e d amines
were f o u n d t o b e e f f e c t i v e i n
inducing t h e decomposition of hydroperoxidesmore e f f e c t i v e l y t h a n t h e s e c o n d a r y amine i n isooctane
functionality.
Solution studies
on t h e mode o f a c t i o n o f h i n d e r e d p i p e r i d i n e s
h a v e shown t h a t r a d i c a l t e r m i n a t i o n i n v o l v e s i n h i b i t i o n of peroxy
r a d i c a l s i n t h e c h a i n r e a c t i o n . 397
s c a v e n g i n g by t h e t e t r a m e t h y l p i p e r i d i n e
Peracid radical
derivatives was
also considered t o be a very important process. 2,2,6,6-
tetramethyl
-
4
-
A styrene
-
p i p e r i d i n y l m e t h a c r y l a t e copolymer
h a s b e e n f o u n d t o p o s s e s s good
and
imparted 2 , 2 , 4 , 4 , 6 - pentamethylhexahydro--pyrimidine e x c e l l e n t s t a b i l i t y t o i s o t a c t i c p o l y p r o p y l e n e . 400 Other
a r t i c l e s o f i n t e r e s t i n c l u d e n i t r o s y l s and oxamides as s t a b i l i s e r s f o r p o l y a m i d e s , 401 w e a t h e r - r e s i s t a n c e of s t a b i l i s e d a u t o m o b i l e p a i n t s , 402 e n h a n c e d p e r f o r m a n c e w i t h anti-oxidants403 and p r o p e r t y changes and s u r f a c e changes i n 404 s t a b i l i s e d polystyrene. The i n t e r a c t i o n o f h i z d c r c d p i p e r i d i n e s t a b i l i s e r s w i t h o t h e r a d d i t i v e s c o n t i n u e s t o a t t r a c t some i n d e p t h a p p r o a c h e s . Allen e t a l f o 5 have c a r r i e d o u t a wide r a n g i n g s t u d y i n p o l y p r o p y l e n e on t h e i n t e r a c t i o n b e t w e e n v a r i o u s a n t i o x i d a n t s and h i n d e r e d p i p e r i d i n e l i g h t s t a b i l i s e r s i n b o t h thermal and photochemical o x i d a t i o n . Generally, phenolic a n t i - o x i d a n t s were f o u n d t o a n t a g o n i s e t h e p e r f o r m a n c e of h i n d e r e d p i p e r i d i n e compound i n p h o t o c h e m i c a l o x i d a t i o n a n d is a s s o c i a t e d w i t h t h e f o r m e r d e s t r o y i n g o r p r e v e n t i n g t h e f o r m a t i o n o f h y d r o p e r o x i d e s which a r e e s s e n t i a l f o r t h e conversion of t h e p i p e r i d i n e t o a p i p e r i d i n e - g -
oxy r a d i c a l .
504
Photochemistry Removal of the latter in the cyclic regeneration mechanism of piperidine stabilisers by reaction with hindered phenol radical intermediates is also believed to be important in antagonism. During thermal oxidation the interactions were more favourable and synergism prevailed due here to the complementary behaviour of nitroxyl free radicals and antioxidant radicals in free radical scavenging processes. Organic sulphides are important secondary anti-oxidants in polyolefin stabilisation but also antagonise the performance of hindered piperidine light stabilisers. In one detailed study all organicsulphideswere found to be antagonistic in poly (1,4-butadiene).406 The mechanism for this antagonism is complicated and involves various processes. Firstly, the ability of hindered piperidines to destroy hydroperoxide prevents the organic sulphides from forming acidic catalysts which are important stabilising entities. Secondly, another important interaction is the formation of products between sulphide and nitrosyl radicals. Ultraviolet absorbers such as o r t h o h y d r o x y b e n z o p h e n o n e s and benzotriazoles a l s o antagonise the performance of hindered piperidine stabilisers although here there is an enhancement in performance. The interactions are again complex and involve several processes. Intra-molecular hydrogen banding is the main feature which is disrupted by the piperidine nitroxyl radicals. Here the nitroxyl radical reacts with the intermediate phenoxy radical in the intramolecular keto-enol tautomerim of the absorbers thus imparing the performance of both systems.407 Phenolic nitrones are effective photoanti-oxidants which have been studied recently in polypropylene and operate in a similar way to that of the hindered piperidine compounds.408 An appropriate modified reaction Scheme 16 is shown and involves the regeneration of nitrone radicals. Unsaturation is believed to be important here although it could not be identified but this is believed to be due to the rapid addition of nitrones with unsaturation by a 1,3- addition on processing.
505
IV: Polymer Photochemistry Some
new s t a b i l i s e r s o f i n t e r e s t a r e 4-tert-butyloxocalix(n)-
a r e n e s w h i c h o p e r a t e a s e f f e c t i v e a b s o r b e r s by a k e t o - e n o l t a u t o r n e r i s r n shown i n Scheme 1 7 . 409 T h e s e s t a b i l i s e r s are e f f e c t i v e i n PVC.
I n p o l y e t h y l e n e some new 3 , 4 - d i h y d r o - l J 3 -
b e n z o x a z i n e s of s t r u c t u r e ( 2 0 ) a r e c l a i m e d t o b e e f f e c t i v e a n d d e p e n d e n t on t h e e l e c t r o n d o n a t i n g a b i l i t y o f R . 410
Vogl
a n d c o - w o r k e r s 411 412 c o n t i n u e t h e i r i n t e r e s t i n g work on new 2(2-hydroxyphenyl)-2H-
b e n z a t r i a z o l absorbers and t h e i r
i n c o r p o r a t i o n i n t o condensation polymers.
The p h o t o s t a b i l i t y
is d r a m a t i c a l l y i m p r o v e d by t h e i n c o r p o r a t i o n o f c o p p e r complexes413 a n d p o l y ( p h e n y l e n e - 1 , 3 ,4o x a d i a z o l e s ) a r e s t a b i l i s e d by t h e i n c o r p o r a t i o n o f 3% manganese c h l o r i d e . 414 A c o m m e r c i a l p h e n o l i c a n t i - o x i d a n t of dyed polyamids
h a s been found t o p h o t o s t a b i l i z e styrene-butadiene c o p o l y m e r by s c a v e n g i n g a l k o x y f r e e r a d i c a l s a n d q u e n c h i n g s i n g l e t o x y g e n . 415 The p e r f o r m a n c e a n d mode o f a c t i o n o f a corn-ercial n - a l k y l s u h s t i t u t e d p - h g d r o x y b e n z o a t e h a s
-
b e e n s t u d i e d i n l i n e a r low d e n s i t y p o l y e t h y l e n e .
416
Here, a l t h o u g h p r o c e s s i n g h i s t o r y h a d a d e t r i m e n t a l e f f e c t on p o l y m e r s t a b i l i t y it i m p r o v e d t h e l i g h t s t a b i l i t y o f t h e stabiliser.
T h i s i n t e r e s t i n g e f f e c t was a s s o c i a t e d w i t h t h e
a b i l i t y o f t h e r e s i d u a l c a t a l y s t s i n t h e polymer t o c a t a l y s e t h e d e c o m p o s i t i o n of h y d r o p e r o x i d e s on p r o c e s s i n g w h i c h r e d u c e s polymer s t a b i l i t y b u t improves t h e s t a b i l i s e r stability. I n t h e l a t t e r case t h e r e a r e f e w e r a l k o x y a n d hydroxy f r e e r a d i c a l s t o react w i t h t h e s t a b i l i s e r . This particular light s t e b i l i s e r also exhibited excellent s y n e r g i s m w i t h h i n d e r e d p i p e r i d i n e s t a b i l i s e r s a n d t h i s is a s s o c i a t e d w i t h i t s i n a b i l i t y t o g i v e an i n t e r m e d i a t e a c t i v e q u i n o n e . Cadmium s t e a r a t e s t a b i l i s e s PVC b u t a c c e l e r a t e s d o u b l e bond f o r m a t i o n i n t h e p o l y m e r . 417’418
Co-stabilisers
a r e b e l i e v e d t o g i v e a p o s i t i v e e f f e c t w i t h t h i s compound i n o r d e r t o reduce u n s a t u r a t i o n as w e l l a s carbonyl formation. Calcium s t e a r a t e p l a y s an i m p o r t a n t r o l e i n t h e s t a b i l i s i n g a c t i o n o f metal c h e l a t e s i n p o l y p r o p y l e n e , p a r t i c u l a r l y t h e i r interaction with hindered piperidine s t a b i l i s e r s .
419
For e x a m p l e , n o t o n l y d o e s t h e c a l c i u m s t e a r a t e r e d u c e a c i d i t y b u t i t w i l l d i s p l a c e t h e n i c k e l i n metal c o m p l e x e s
Photochemistry
506
to give more efficient calcium complexes. Thio-organo tin stabilisers on the other handhave been found to sensitise the photooxidation of polystyrene.420 The employment of a ligand and nickel stearate mixture is claimed to be more effective for stabilising polypropylene than using the original stabiliser complex.421 Stilbene and coumarin compounds have been found to be highly efficient stabilisers for polyurethanes422 and salicyloyl -3,5 - di - tert -butyl -4- hydroxybenzylamine is efficient in polyethylene.423 Other articles of interest include l o s s of plasticizer in PVC,424 the efficiency of 2-hydroxybenzalacetophenones in PVC,425 mechanical property changes in stabilised polystyrene,426 spectrosconic analysis of stabilised polystyrene-cross1inked polyesters427 nylon 6 stabilised with l,l-diphenyl-3-p-tolylurea, 428 metal stearates in PVC,429 synergism between absorbers in polypropylene430 and recycled stabilised polyethylene with carbon black.431
-
6
Photochemistry of Dyed and Pigmented Polymers The photochemistry of dyes, particularly with regard to fading phenomena is sadly a neglected area. Only two reviews have appeared on dye fading phenomena.432 433 Colour difference measurements have been found to be particularly sensitive for monitoring the fading of vat dyed fabrics434 and Wilkinson and c o - w o r k e r ~have ~ ~ ~demonstrated that the photochemistry of dyed fabrics and films can be studied directly using diffuse reflectance flash photolysis. In the latter study energy transfer between the dye and polymer fibre appeared to dominate the photophysics. The photo fading of a series of mono-azo dyes has been studied in both solution and polymer film$?6 Aggregation was considered to be an important factor in controlling dye stability even in solution although generally dye structure and the nature of the polymer substrate were the most important criteria. Substratesof high polarity apparently favoured aggregation. Vat dyes have been found to deaggregate in poly(viny1 alcoh%!J iodide has been observed to and diethylthiadicarbozyanine 9
IV: Polymer Photochemistry
507
a g g r e g a t e i n s o l u t i o n u s i n g pico-second s p e c t r o s c o p y . 438
absorption
Dyes g e n e r a l l y are c l a i m e d t o f a d e less i n
n y l o n f i l m s t h a n i n a c r y l i c o r wool a l t h o u g h t h e l a t t e r are c l a i m e d t o b e more s t a b l e m e c h a n i c a l l y . 439 i s o m e r i s a t i o n i n t h e case o f 4 - p h e n y l a q o
-
Cis-trans 1
-
naphthol is
r e s t r i c t e d i n polymer s u b s t r a t e b u t a c c e l e r a t e d i n t h e p r e s e n c e o f m o i s t u r e 440 w h i l e i n t h e case o f cyamine d y e s t h e c i s - t r a n s i s o m e r i s a t i o n is b e l i e v e d t o i n v o l v e a n u n s t a b l e p h o t o i s o r r e r w i t h a h i g h l y t w i s t e d s t r u c t u r e formed t h r o u g h an adiabatic
r e a c t i o n p a t h w a y . 441
Cyanine dyes have been
o b s e r v e d t o b e formed f r o m t h e p h o t o l y s i s o f 4 - ( d i m e t h y l a m i n o ) a - h a l o s t i l b e n e s i n a c e l l u l o s i c matrix.442
For a series of
mono-a&o d y e s t h e m e t h y l e n e b l u e s e n s i t i s e d p h o t o f a d i n g r a t e s
were f o u n d t o b e d e p e n d e n t on t h e a b i l i t y o f g e n e r a t e d 443 s i n g l e oxygen t o react w i t h t h e a n i o n f o r m o f t h e d y e . Indigo dyes have been found t o e x h i b i t d u a l e l e c t r o n donor a n d a c c e p t o r p r o p e r t i e s . 444
T h i s was c o n f i r m e d by t h e f a c t
t h a t t h e s e dyes can form an e l e c t r o n donor-acceptor with i t s e l f .
complex
I n t h i s case t h e s t a b i l i t y o f t h e d y e s were
found t o decrease w i t h i n c r e a s i n g c o n c e n t r a t i o n .
In
s o l u t i o n t h i a i n d i g o i d d y e s were f o u n d t o h a v e e n h a n c e d s t a b i l i t y i n t h e p r e s e n c e o f oxygen i n d i c a t i n g t h a t s i n g l e t oxygen may n o t b e i m p o r t a n t i n f a d i n g . 445
Photofading
s t u d i e s on c r y s t a l v i o l e t i n s o l u t i o n h a v e shown t h a t e l e c t r o n t r a n s f e r is a n i m p o r t a n t s t e p i n t h e p r o c e s s . The a b s o r p t i o n a n d e r r i s s i o n
446
p r o p e r t i e s o f a series o f 3-
h e t e r o c o u m a r i n s h a v e b e e n r e c o r d e d 4 4 7 a n d a new m o d i f i e d Parisier-Pass-Pople
m o l e c u l a r o r b i t a l method h a s b e e n
d e v e l o p e d f o r p r e d i c t i n g t h e f l u o r s c e n c e maxima 448 organic dyes.
of
S e v e r a l a t t e m p t s h a v e b e e n made t o improve t h e p h o t o s t a b i l i t y of dyes i n polymer s u b s t r a t e s .
One g r o u p o f w o r k e r s
449-451
h a v e shown t h a t a wide v a r i e t y o f d y e s are p h o t o p r o t e c t e d by v a r i o u s n i c k e l s a l t s and complexes.
These i n c l u d e n i c k e l
toluenesulphonate, s u l p h a t e and diethyldithiocarbarnate compounds a n d a l l a r e b e l i e v e d i n some way t o q u e n c h s i n g l e t
Photochemistry oxygen. The metal content in 1:2 premetallised dyes has been found to be important in controlling the photostability of the dyes in wool 4 5 2 and ultraviolet absorbers protect the fading of dyes used in automobile textiles.453 Ethyleneurea improves the photostability of reactive dyes on 454 cellulose and 4-aminonaphthalic acid phenylimide is a good luminophore for phthalocyanine pigments where stability light is required.455 Finally, the photostability of triphenylpyrazolines have been studied and found to vary significantly with the nature of the solvent and oxygen solubility.456 Structurally, they all faded at similar rates.
509
IV: Polymer Photochemistry References
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126,
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442) M. Pulst, M. Weissenfels and F. Dietz , Z. Naturforsch., B: Anorg. Chem.Org. Chem., (1985), 40 B, 585 443) H. Mustroph, J. Potocnak and N. Grossman, J. Prakt. Chem., (1984), 326, 979 444) J. Pouliquen, V. Wintgens, V. Toscano and J. Kossanyi, Dyes and Pigments, (19851, 6 , 163 445) H. Langbein B. Kirchhof and R. Koche, Z.Chem., (1984), 24, 439 446) M.A.Y. Naguib, S.G. Cohen and C . Steel, J.Am. Chem. Soc.,(1986),108,128 447) N.K. Chodankar and S. Seshadri, Dyes and Pigments, (1985),6, 331448) W. Fabian, Dyes and Pigments, (1985), 5, 341 449) N. Kuramoto, I Satake, K. Yamamoto, M. Hirota, K. Natsukamo, H. Shiozaki, Y. Murakami, T. Kitao and R. Yamamoto, Sen'i,(1985), 37, 49, idem - ibid, (1985), 37, 197 450) G. Oda and T. Kitao, J. SOC. Dyers and Colourists, (1985), 101, 177. 451) K. Nakamura, I. Okagawa, T. Katayama, M. Noda, F. Sakane, and S. Nakanishi, Sen'i, (1985), 37, 155 452) L. Benisek, G. Edmondson and J.W.A. Matthews, Tex.Res.J., (1985), 55, 256 453) R. Eichler, P. Richter and P. Vonhoene, Textilveredlung, (1985), 2, 126 454) A. Vig, G.E. Krichevskii, V.M. Anisimov and O.N. Karpukhin, Przegii Wlok., (1985), 3,168 455) L.N. Sal'vitokaya, D.G. Peruyenlova and M.Ya.Zabara, Plast. Massy, (19851, . . _ 6 -, 29 456) R.S. Davidson, D. King, D.M. Lewis and S.K.R. Jones, J. SOC. Dyers and Colourists, (1985), 101, 291
Part V PHOTOCHEMICAL ASPECTS OF SOLAR ENERGY CONVERSION By A. HARRIMAN
Photochemical Aspects of Solar Energy Conversion BY A. HARRIMAN INTRODUCTION
1
’his h a s been a q u i e t , r a t h e r s e d a t e y e a r w i t h no m a j o r breakthroughs o r s i g n i f i c a n t d i s c o v e r i e s .
Attention has centred
m o s t l y on fundamental a s p e c t s of the s u b j e c t , e s p e c i a l l y t h e mechanism of photo-induced
e l e c t r o n t r a n s f e r i n p o l a r media, and
t h e p r a c t i c a l s i d e of t h e f i e l d h a s been l a r g e l y i g n o r e d .
The
g e n e r a l s u b j e c t of s o l a r e n e r g y c o n v e r s i o n and s t o r a g e h a s been reviewed by s e v e r a l a u t h o r s , c o n s i d e r i n g both homogeneous’ ’ and h e t e r o g e n e o u ~ ~photosys -~ terns.
Particular attention has
been g i v e n t o t h e u s e of t r a n s i t i o n m e t a l complexes6-8 and t h e p o t e n t i a l importance of o r g a n i s e d a s s e m b l i e s h a s been s t r e s s e d on numerous o c c a s s i o n s .
’’
lo
O t h e r workers h a v e s u g g e s t e d
i m p o r t a n t r o l e s f o r s y n t h e t i c polymers”
and f l a v i n s 1 2 i n s o l a r
energy s t o r a g e devices. A s i n p r e v i o u s y e a r s , t h e o r e t i c a l l i m i t s of s o l a r energy
c o n v e r s i o n h a v e been c o n s i d e r e d .
F o r s i n g l e band-gap
semiconductor systems based upon w a t e r c l e a v a g e , t h e p r a c t i c a l e f f i c i e n c y l i m i t a t i o n h a s been c a l c u l a t e d t 3 t o be less t h a n 10% b u t t h e u s e of d u a l band-gap semiconductor systems could g i v e higher efficiency.
An a n a l y s i s of t h e k i n e t i c f a c t o r s involved
i n photoredox r e a c t i o n s aimed a t s o l a r energy c o n v e r s i o n h a s
also been published14 and c a l c u l a t i o n of e x c i t e d s t a t e redox p o t e n t i a l s h a s been 0 u t 1 i n e d . l ~ ’Ihe r o l e of hydrogen i n s o l a r e n e r g y s t o r a g e d e v i c e s 1 6 and some of t h e e n g i n e e r i n g problems a s s o c i a t e d w i t h o p e r a t i o n of such d e v i c e s 1 7 h a v e been 523
Photochemistry
524 cons i d e r e d .
S e v e r a l a u t h o r s 1 8 - 2 1 h a v e n o t e d t h e importance of
r e a c t o r d e s i g n and geometry i n d e t e r m i n i n g t h e e f f i c i e n c y of l a r g e - s c a l e photochemical p r o c e s s e s .
'Ih i s is an i m p o r t a n t and
o f t e n n e g l e c t e d p a r t of p h o t o c h e m i s t r y and it is w o r t h w h i l e i n v e s t i n g some time i n t h e c a r e f u l c o n s t r u c t i o n of r e a c t o r s t h a t o p t i m i s e s o l a r energy c o n v e r s i o n . I n t e r e s t i n g c o n c l u s i o n s a r e r a i s e d by a l l t h e s e s t u d i e s b u t none h e l p i n t h e d e s i g n of new photosystems. Hydrogen p r o d u c t i o n from p h o t o e l e c t r o c h e m i c a l c e l l s c o n t i n u e s t o a t t r a c t a t t e n t i o n 2 2 9 2 3 and i t is known t h a t such s y s t e m s can o p e r a t e w i t h h i g h e f f i ~ i e n c y . l~h~e complete p h o t o d i s s o c i a t i o n of water i n t o H 2 and O2 u s i n g p a r t i c u l a t e semiconductor p h o t o c a t a l y s t s h a s been claimed f o r s e v e r a l d i f f e r e n t systems.
Thus , semiconducting o x i d e s p r e p a r e d from
mercury,24 niobium,25 s i l v e r , 2 6
and vanadium28 h a v e
been r e p o r t e d t o p h o t o c l e a v e w a t e r upon i r r a d i a t i o n w i t h UV o r visible light.
These r e p o r t s merit c l o s e but c a u t i o u s
inspection. R e p o r t s d e s c r i b i n g the p h o t o c l e a v a g e of water under homogeneous c o n d i t i o n s are n o t so numerous but two such systems have appeared.
Thus , t h e p h t h a l o c y a n i n e p h o t o s e n s i t i s e d
decomposition of water h a s been r e p o r t e d 2 ' d a t a are f a r from c o n v i n c i n g .
but the experimental
More r e a l i s t i c r e s u l t s a r e
p r o v i d e d f o r t h e p h o t o c l e a v a g e of water u s i n g hydrous o x i d e s as electron relays.30
This is a n o v e l and e x t r e m e l y i n t e r e s t i n g
525
V: Photochemical Aspects of Solar Energy Conversion system and it s h o u l d be examined i n some d e t a i l .
‘Ihe mechanism
of the p h o t o l y s i s of c h l o r o c u p r a t e ( 1 ) i o n s i n a c i d i c s o l u t i o n h a s been r e p o r t e d 3 ’ and t h e system h a s been o p t i m i s e d f o r H 2 generat ion. I n t e r e s t is growing r a p i d l y i n t h e a p p l i c a t i o n of UV and v i s i b l e l i g h t t o water p u r i f i c a t i o n systems.
S e v e r a l such
s y s t e m s have been d e s c r i b e d r e c e n t l y 32-37 and it is c l e a r t h a t p h o t o c h e m i s t r y c a n o f f e r g e n u i n e a d v a n t a g e s o v e r more conventional approaches.
T h i s s u b j e c t seems c e r t a i n t o g a i n i n
p o p u l a r i t y and importance i n coming y e a r s .
Reports concerning
t h e p h o t o a s s i s t e d o x i d a t i o n of H15r38 and t h e p h o t o r e d u c t i o n of c a r b o n d i o x i d e h a v e appeared3’
but their involvement i n solar
e n e r g y c o n v e r s i o n sys tems i s minimal. 2
H(EI
OGENEoUS PHOTOSYSTEMS
Valence Isomerism Photochemical e n e r g y s t o r a g e v i a t h e p h o t o s e n s i t i s e d v a l e n c e isomerism of n o r b o r n a d i e n e d e r i v a t i v e s h a s i n c r e a s e d i n popularity in recent years.
The c h e m i c a l s t o r a g e p o t e n t i a l o f
such s y s tems h a s been reviewed4” 4 1 and t h e r e l a t i v e e f f i c i e n c y
of many d i f f e r e n t p h o t o s e n s i t i s e r s h a s been ~ o m p a r e d . ~ ~ l h-e~ ~ r e a c t i o n mechanism h a s been determined f o r s e v e r a l systems and t h e importance of e l e c t r o n t r a n s f e r h a s been
The
r o l e of t h e n o r b o r n a d i e n e s i n g l e t e x c i t e d s t a t e i n t h e o v e r a l l isomerism p r o c e s s h a s been c o n s i d e r e d . 48 An i n t e r e s t i n g development 4 9 - 5 1 i n t h i s f i e l d h a s been t h e
Photochemistry
526
d e s i g n of m o l e c u l a r u n i t s i n which t h e n o r b o r n a d i e n e and t h e p h o t o s e n s i t i s e r a r e j o i n e d by c o v a l e n t l i n k a g e s .
Such systems
a v o i d t h e need f o r d i f f u s i o n a l c o l l i s i o n between s e n s i t i s e r and a c c e p t o r m o i e t i e s and a p p e a r t o have s i g n i f i c a n t a p p l i c a t i o n s i n p r a c t i c a l devices.
W a t e r - s o l u b l e d i e n e and ~ ~ ~ cyclodextrin
i n c l u s i o n complexes53 h a v e been d e s c r i b e d and t h e i r p o t e n t i a l u s e i n s o l a r energy s t o r a g e systems h a s been c o n s i d e r e d .
Only
economics l i m i t t h e u t i l i t y o f t h e s e s i m p l e d e v i c e s . P h o t o s e n s i t isers C o n s i d e r a b l e e f f o r t h a s been expended i n t r y i n g t o l o c a t e e f f i c i e n t and s t a b l e p h o t o s e n s i t i s e r s t h a t a r e u s e f u l i n homogeneous w a t e r s p l i t t i n g photosystems.
Ihe emphasis h a s been
p l a c e d m a i n l y on v e r s a t i l i t y and l i g h t a b s o r b i n g p r o p e r t i e s and l i t t l e thought h a s been g i v e n t o c o s t o r t o x i c i t y .
Most
a t t e n t i o n 54-56 h a s c e n t r e d on d e r i v a t i v e s of t r i s ( 2 , 2 ' -
bipyridyl)ruthenium(II).
I t h a s been shown by s e v e r a l groups57-
5 9 t h a t mixed l i g a n d complexes p o s s e s s i n t e r e s t i n g photoredox
properties.
I h e most promising complexes a p p e a r t o be ones
based upon p o l y a z i n e l i g a n d s 6 0 - 6 2 which e x h i b i t h i g h redox p o t e n t i a l s f o r o n e - e l e c t r o n o x i d a t i o n , a b s o r b s t r o n g l y around 440-480 nm and r e t a i n r e a s o n a b l y l o n g - l i v e d t r i p l e t s t a t e s .
Such compounds h a v e been shown t o f u n c t i o n as e f f i c i e n t p h o t o s e n s i t i s e r s f o r t h e r e d u c t i o n of v i o l o g e n s i n aqueous solution. M e t a l l o p o r p h y r i n s , by v i r t u e of t h e i r involvement i n t h e
V : Photochemical Aspects of Solar Energy Conversion
527
n a t u r a l p h o t o s y n t h e t i c p r o c e s s and t h e i r a t t r a c t i v e l i g h t absorbing c h a r a c t e r i s t i c s , continue t o receive a t t e n t i o n .
'Ihe
f i e l d h a s been reviewed63 and rhodium p o r p h y r i n s h a v e been found 64 t o be good p h o t o c a t a l y s t s f o r t h e d e h y d r o g e n a t i o n of a l c o h o l s . Several p h t h a l ~ c y a n i n e s ~ h a~v-e ~ found ~ u s e as p h o t o s e n s i t i s e r s f o r t h e r e d u c t i o n of v i o l o g e n s i n water and a z i n c p o r p h y r i n c o v a l e n t l y bound t o a v i o l o g e n h a s been used68 t o g e n e r a t e H2. This l a t t e r system r e p r e s e n t s an i n t e r e s t i n g v a r i a t i o n t o t h e
normal homogeneous approach.
I t is r e p o r t e d 6 8 t h a t t h e v i o l o g e n
l i n k e d p o r p h y r i n , when d i s p e r s e d i n T r i t o n X-1 00 m i c e l l e s , p r o d u c e s H2 upon i r r a d i a t i o n i n t h e p r e s e n c e of a s a c r i f i c i a l e l e c t r o n donor and h y d r o g e n a s e o r P t .
' h e s y n t h e s i s and photoredox p r o p e r t i e s of i n d i g o dyes h a v e as have t h e photochemical r e a c t i o n s of
been xanthene
The a b i l i t y of z i n c d i t h i o l e n e s t o p h o t o r e d u c e
v i o l o g e n s h a s been r e p o r t e d 7 2 D 7 3 and some a t t e n t i o n h a s been g i v e n t o t h e p o s s i b l e u s e of tris(2,2'-bipyridyl)rhodium(III)
as
a p h o t o ~ e n s i t i s e r . ~S e~v e r a l o t h e r i n o r g a n i c complexes h a v e been p o s t u l a t e d as u s e f u l p h o t o s e n s i t i s e r s 75-81 b u t , o v e r a l l ,
l i t t l e p r o g r e s s h a s been made w i t h r e g a r d t o d e v e l o p i n g s t a b l e and s e l e c t i v e s e n s i t i s e r s .
H2 P h o t o p r o d u c t i o n C o n v e n t i o n a l p h o t d y s t e m s f o r t h e v i s i b l e l i g h t induced d e h y d r o g e n a t i o n of o r g a n i c m a t e r i a l s are now w e l l e s t a b l i s h e d . M e t a l l o p o r p h y r i n based photosystems have been reviewed63 and it
Photochemistry
528
h a s been shown t h a t such systems a r e a b l e t o e x t r a c t H2 from a wide v a r i e t y of o r g a n i c and i n o r g a n i c s u b s t r a t e s .
The r o l e of
t h e redox c a t a l y s t i n t h i s t y p e of photosystem h a s been d e s c r i b e d , 82 w i t h s p e c i a l emphasis p l a c e d on k i n e t i c a s p e c t s . Perhaps t h e b e s t documented s a c r i f i c i a l H2-evolving photosystem c o n c e r n s t h e i r r a d i a t i o n of t r is ( 2 , 2 ' - b i p y r i d y l ) ruthenium ( I I ) i n aqueous s o l u t i o n c o n t a i n i n g methyl v i o l o g e n as e l e c t r o n r e l a y ,
ethylenediaminetetraacetic a c i d as s a c r i f i c i a l e l e c t r o n donor and c o l l o i d a l P t as c a t a l y s t .
This system h a s been s t u d i e d i n
c o n s i d e r a b l e d e t a i l s 3 84 and t h e H2 e v o l u t i o n p r o c e s s h a s been optimised.
Replacing the p h o t o s e n s i t i s e r with the corresponding
tris(2,2'-bipyrazine) e f f i c i e n t system.
complex85J86 g i v e s a s l i g h t l y more
One major problem a s s o c i a t e d w i t h t h i s work
c o n c e r n s t h e tendency of t h e v a r i o u s i n g r e d i e n t s t o complex e l e c t r o s t a t i c binding.
T h i s complexation 87-92 h a s a
c o n s i d e r a b l e e f f e c t upon t h e o v e r a l l mechanism and makes o p t i m i s a t i o n of t h e system a d i f f i c u l t and t e d i o u s t a s k .
I t is
a u n i v e r s a l problem i n t h is t y p e of work and, t o a l a r g e d e g r e e , i t c o n t r o l s t h e e f f i c i e n c y of t h e photosystem.
As a
consequence, t h e importance of t h e i o n i c s t r e n g t h and p o l a r i t y o f t h e medium and t h e o v e r a l l c h a r g e s on t h e r e a c t a n t s cannot be o v e r s t r e s s e d . 92 'Ihe most p o p u l a r e l e c t r o n r e l a y i n t h e s e photosystems c o n t i n u e s t o be methyl v i o l o g e n a l t h o u g h it is w e l l e s t a b l i s h e d t h a t t h i s material is u n s t a b l e w i t h r e s p e c t t o h y d r o g e n a t i o n
529
V: Photochemical Aspects of Solar Energy Conversion under operating conditions.
O t h e r v i o l o g e n s h a v e been t r i e d g 3 -
96 b u t t h e fundamental problem s t i l l remains.
C o b a l t cage
complexes have been proposed as p o s s i b l e a l t e r n a t i v e r e l a y s and t h e r e s u l t s a r e q u i t e i n t e r e s t i n g .
97 - 99
Simple m e t a l c a t i o n s a r e
prone t o h y d r o l y s i s i n aqueous s o l u t i o n s o t h a t t h e i r v e r s a t i l i t y i n H2-evolving photosystems is s e v e r e l y r e s t r i c t ed 100
.
Although c o l l o i d a l P t p a r t i c l e s a r e by f a r t h e most e f f e c t i v e c a t a l y s t s f o r H2 e v o l u t i o n from w a t e r t h e y are n o t s e l e c t i v e and tend t o c a t a l y s e most redox r e a c t i o n s .
The n a t u r e
o f t h e p r o t e c t i v e a g e n t p r e s e n t on t h e c o l l o i d s u r f a c e can i n f l u e n c e the s e l e c t i v i t y o f t h e c a t a l y s t .
S e v e r a l groups h a v e
d e s c r i b e d t h e p r e p a r a t i o n and t e s t i n g of P t c o l l o i d s p r o t e c t e d by s u r f a c t a n t s ” ’
o r polymerised s u r f a c t a n t s l o 2 ’ l o 3 w h i l s t t h e
v i t u e s of d i s p e r s i n g t h e P t o n t o an o x i d e s u p p o r t h a v e been conf inned. l o 4 nickel,
Other m e t a l c o l l o i d s , i n c l u d i n g i r i d i u m , 105
c o p p e r , l o 6 * l o 7 and molybdenum, l o 7 h a v e been p r e p a r e d
and used as m i c r o e l e c t r o d e s .
A l s o , complex t u n g s t a t e s h a v e been
shown t o s t o r e many e l e c t r o n s on a s i n g l e m o l e c u l e l o 8 and t o r e d u c e w a t e r t o H2 w i t h o u t the need f o r an added c a t a l y s t . I n a d d i t i o n t o t h e f i o t o s e n s i t i s e d e v o l u t i o n of H2 t h e above s y s t e m s a r e r e a d i l y a d a p t e d f o r o t h e r u s e f u l chemical p r o c e s s e s . Thus, t h e h y d r o g e n a t i o n of e t h y l e n e and a c e t y l e n e h a s been reported”’
and t h e p h o t o s e n s i t i s e d c l e a v a g e of a c e t y l e n e t o
methane is p o s s i b l e . ’ ”
’he f u n c t i o n a l i s a t i o n of a l k a n e s ’ ”
aqd
Photochemistry
530
t h e p h o t o c h e m i c a l d e h y d r o g e n a t i o n of o r g a n i c s u b s t r a t e s h a s been described'
O2
u s i n g p o l y o x o m e t a l a t e s as @ o t o s e n s i t i s e r s .
Photoproduction
A s a l w a y s , t h e p h o t o o x i d a t i o n of water t o O2 h a s r e c e i v e d
much less a t t e n t i o n t h a n t h e much e a s i e r p h o t o r e d u c t i o n of w a t e r t o H2.
However, some n o t a b l e a c h i e v e m e n t s h a v e a p p e a r e d and
g e n u i n e p r o g r e s s h a s been made. w a t e r by m e t a l l o p o r p h y r i n s l
'
Ihe mechanisms f o r o x i d a t i o n of
and c o b a l t ( I I 1 ) ammines' l 4 have
been s t u d i e d , w i t h p a r t i c u l a r a t t e n t i o n b e i n g g i v e n t o k i n e t i c parameters.
S e v e r a l new 0 2 - e v o l v i n g c a t a l y s t s h a v e been
proposed. ' 1 5 - ' 1 9
Of t h e s e , two merit s p e c i a l n o t i c e .
nus, a
s i m p l e manganese(1V) S c h i f f - b a s e complex h a s been found" o x i d i s e water t o O2 u n d e r n e u t r a l c o n d i t i o n s .
to
T h i s system needs
c a r e f u l e v a l u a t i o n i n view o f i t s p o s s i b l e s i g n i f i c a n c e t o t h e n a t u r a l 0 2 - e v o l v i n g enzyme.
An e f f e c t i v e homogeneous 02-
e v o l v i n g c a t a l y s t h a s been o b t a i n e d "
from t r i s ( 2 , 2 ' - b i p y r i d y l -
4 , 4 ' - d i c a r b o x y l i c a c i d ) r u t h e n i u m ( I I ) which p e r m i t s d e t a i l e d s t u d y of t h e mechanism o f water o x i d a t i o n .
Both r e p o r t s s h o u l d
be c l o s e l y s c r u t i n i s e d and, h o p e f u l l y , they w i l l lead t o a c l e a r e r u n d e r s t a n d i n g of t h e whole p r o c e s s of water o x i d a t i o n . The p h o t o o x i d a t i o n of water t o O2 u n d e r n o n s a c r i f i c i a l c o n d i t i o n s h a s been r e p o r t e d . 120
mis
system employs t r i s ( 2 , 2 ' -
b i p y r i d y l ) r u t h e n i u m ( I I ) as p h o t o s e n s i t i s e r , i r o n ( 111) o r m e r c u r y ( I 1 ) as e l e c t r o n a c c e p t o r , and a c o l l o i d a l Ru02 c a t a l y s t . Oxygen g e n e r a t i o n is r e s t r i c t e d t o a c i d i c s o l u t i o n s and t h e
531
V: Photochemical Aspects of Solar Energy Conversion t o t a l y i e l d of 02 is s e t by k i n e t i c l i m i t s .
Even s o , t h e i n i t i a l
quantum e f f i c i e n c y f o r O2 e v o l u t i o n is about 48% with i r o n ( I I 1 ) a s acceptor.
Such systems r e p r e s e n t t h e f i r s t r e a l approach
towards achieving t h e complete p h o t o d i s s o c i a t i o n of water under homogeneous c o n d i t i o n s . Charge Separation Homogeneous systems r e l y on a photoinduced e l e c t r o n t r a n s f e r r e a c t i o n t o i n i t i a t e the o v e r a l l energy s t o r a g e process.
I t is
necessary t h a t t h i s r e a c t i o n occurs with high e f f i c i e n c y and t h a t it g e n e r a t e s a t l e a s t one h i g h l y e n e r g e t i c redox product. Consequently, c o n s i d e r a b l e a t t e n t i o n h a s been given t o the design of photosystems h i c h undergo e f f i c i e n t charge s e p a r a t i o n upon e x c i t a t i o n with v i s i b l e l i g h t .
Many s t u d i e s have
concentrated on systems t h a t r e t a i n a s much of t h e i n i t i a l e x c i t a t i o n energy a s p o s s i b l e w h i l s t o t h e r s have been concerned with t r y i n g t o maximise t h e y i e l d of s e p a r a t e d redox products. Related s t u d i e s have t r i e d t o i n h i b i t back e l e c t r o n t r a n s f e r between t h e redox products, thus i n c r e a s i n g t h e chances of doing some u s e f u l chemistry with the system. Much fundamental work, concerned mostly with t h e mechanism and k i n e t i c s of photoinduced e l e c t r o n t r a n s f e r i n p o l a r medium, h a s been reported t h a t h e l p s i n t h e design of new s o l a r energy s t o r a g e systems.
General t r e a t m e n t s of e l e c t r o n t r a n s f e r
p r o c e s s e s , with p a r t i c u l a r r e f e r e n c e t o back e l e c t r o n t r a n s f e r , 124 have been given.12'-' 23 The a p p l i c a t i o n of magnetic f i e l d s
Photochemistry
532
and s o l v e n t e f f e c t s 1 2 5 f o r o p t i m i s a t i o n of redox i o n p r o d u c t y i e l d s h a s been d e s c r i b e d .
Most s t u d i e s have employed
i n t r a m o l e c u l a r systems i n which t h e two r e a c t i v e s i t e s a r e j o i n e d by c o v a l e n t bonds.
The u s e of c o v a l e n t l y l i n k e d
donor/acceptor u n i t s permits t h e excited s i n g l e t state of t h e chromophore t o f u n c t i o n i n redox r e a c t i o n s , h e n c e a l l o w i n g t r a n s i e n t s t o r a g e of a h i g h f r a c t i o n of t h e e x c i t a t i o n energy. With f l e x i b l e b r i d g e s , c o n f o r m a t i o n a l p a r a m e t e r s become imp0 r t an t 1 2 6 - 1 2 9 and t h e k i n e t i c s f o r t h e e l e c t r o n t r a n s f e r s t e p are difficult to interpret.
R i g i d bonding, 30-134 a l t h o u g h
g i v i n g more problems with the s y n t h e s i s , a l l o w s more e x a c t s t u d i e s t o be made.
Recent work h a s d e s c r i b e d such s t u d i e s
where the d i s t a n c e between t h e two r e a c t a n t s is f i x e d r e a s o n a b l y w e l l . 1 3 3 D 1 3 4 From such work, t h e t h e o r y o f photoinduced e l e c t r o n t r a n s f e r p r o c e s s e s can be extended and r e f i n e d . The r a t e of back e l e c t r o n t r a n s f e r can be c o n t r o l l e d , a t l e a s t t o some d e g r e e , by t h e environment.
Obviously, solvent
v i s c o s i t y 3 5 J 36 and e l e c t r o s t a t i c f o r c e s between t h e reactants'37 play important r o l e s i n determining t h e r a t e of the back r e a c t i o n .
Even more d r a m a t i c e f f e c t s can be o b t a i n e d by
i n c o r p o r a t i n g one o r more of t h e r e a c t a n t s i n a m i c e l l e
138-143
o r v e s i c l e . 144 S i m i l a r e f f e c t s can be r e a l i s e d by a t t a c h i n g one r e a c t a n t t o a p o l y e l e c t r o l y t e and t h i s h a s become a p o p u l a r method f o r modifying t h e r a t e s of forward and back e l e c t r o n t r a n s f e r s . l45-' 5'
m e s e e l e c t r o s t a t i c factors play a c r u c i a l
V: Photochemical Aspects of Solar Energy Conversion
533
r o l e i n f i x i n g t h e y i e l d of charge separated redox products, e s p e c i a l l y i n w a t e r , and by c a r e f u l choice of t h e r e a c t i o n system t h e y i e l d can approach 100%. This year h a s seen increased employment f o r polymer bound
reactants
.
Both sens i t iser
-'
51 54 u s u a l l y t r i s ( 2 2 ' -
b i p y r i d y l ) r u t h e n i m ( I I ) , and e l e c t r o n relayJ155-159 u s u a l l y a viologen d e r i v a t i v e , have been a t t a c h e d t o a polymer backbone. In most cases it is d i f f i c u l t t o compare the polymer-bound and t h e monomeric systems so t h a t t h e r e a l b e n e f i t s of t h e polymeric systems a r e not c l e a r .
Probably, they a r e minimal.
Long range
e l e c t r o n t r a n s f e r between monomeric reagents embedded i n a polymer matrix h a s been demonstrated. 160,161 3
HETEROGENEOUS PHOTOSYSTR'SS
The study of heterogeneous photosystems involving UV o r v i s i b l e l i g h t i r r a d i a t i o n of suspensions of semiconductor powders o r c o l l o i d s h a s abated somewhat t h i s year although t h e photochemistry of T i 0 2 remains popular.
The p h o t o d i s s o c i a t i o n
o f water no longer dominates t h e f i e l d and many d i f f e r e n t photoreactions have been described i n which a semiconducting powder is used t o induce changes i n s t r u c t u r e of organic materials.
Much of t h i s work is r e l e v a n t t o s o l a r energy
s t o r a g e but only i n a few cases h a s the semiconductor powder been w e l l c h a r a c t e r i s e d .
lhis o b s e r v a t i o n is p a r t i c u l a r l y
important i n view of t h e f a c t t h a t most s t u d i e s involve t h e use of doped o r modified
(u.p l a t i n i s e d )
semiconductors.
Photochemistry
534
The scope of t h e p h o t o c a t a l y t i c r e a c t i o n s t h a t can be accomplished w i t h naked o r m o d i f i e d T i 0 2 h a s been reviewed162 i n depth.
S u s p e n s i o n s of T i 0 2 , u n d e r UV i l l u m i n a t i o n , h a v e been
u s e d t o ox i d i s e e t h a n e , 63 t o decompose ch l o r o p h e n o l s , 64 and t o o x i d i s e phenol. 1 6 5 The p h o t o a d s o r p t i o n of O2 o n t o t h e s u r f a c e o f T i 0 2 powders h a s been r e p o r t e d i n
The i m p o r t a n c e
o f pH, s u r f a c e s t a t e s , f l u o r i d e i o n s and i o n i c s t r e n g t h h a s been recorded.
Examination of t h e r e a c t i o n mechanism by which T i 0 2
p h o t o o x i d i s e s m a t e r i a l s is growing i n p o p u l a r i t y . 167,168 I r r a d i a t i o n of small p a r t i c l e s of T i 0 2 i n aqueous s u s p e n s i o n is r e p o r t e d t o r e s u l t i n f o r m a t i o n of h y d r o x y l r a d i c a l s , 16' d e t e c t e d by e p r t e c h n i q u e s .
as
O t h e r w o r k e r s ' 70 h a v e determined
t h e a v e r a g e l i f e t i m e s of e l e c t r o n s and h o l e s i n i r r a d i a t e d Ti02 c o l l o i d s under a v a r i e t y of c o n d i t i o n s .
Using f l a s h p h o t o l y s i s
methods, i t h a s been p o s s i b l e t o r e c o r d a b s o r p t i o n s p e c t r a f o r t h e long-lived c a r r i e r s trapped a t the interface. I n a l m o s t a l l c a s e s , t h e p h o t o a c t i v i t y of T i 0 2 i s enhanced by d e p o s i t i n g a small amount of a c a t a l y t i c a l l y a c t i v e material o n t o t h e s u r f a c e of t h e s e m i c o n d u c t o r . S e v e r a l methods a r e a v a i l a b l e f o r the p r e p a r a t i o n of the p h o t o c a t a l y s t 171-174 and
some of t h e materials175 h a v e been w e l l c h a r a c t e r i s e d .
The
g e n e r a l e f f e c t of p l a t i n i s a t i o n upon t h e e l e c t r o c h e m i c a l b e h a v i o u r of T i 0 2 h a s been d e s c r i b e d , 1 7 6 w i t h p a r t i c u l a r S i m i l a r s t u d i e s have 177 been performed f o r T i 0 2 l o a d e d w i t h s u r f a c e l a y e r s of Pd. r e f e r e n c e t o the H2 e v o l u t i o n p r o c e s s .
V: Photochemical Aspects of Solar Energy Conversion
535
P l a t i n i s e d T i 0 2 h a s been used t o p h o t o o x i d i s e s u l p h u r o u s a c i d , 17'
glucose,17'
b e n z e n e , 180 p o l y e t h y l e n e o x i d e , 1 8 1 and
'
a r o m a t i c primary m i n e s , 82 amongst o t h e r t h i n g s . The @ o t o d i s s o c i a t i o n of water w i t h s u s p e n s i o n s of p l a t i n i s e d T i 0 2 c o n t i n u e s t o a t t r a c t a t t e n t i o n and some i n t e r e s t i n g r e p o r t s h a v e appeared.
The e f f e c t s of v a r i o u s
'
c a t a l y t i c depos i t s h a v e been s t u d i e d . 83-1 86
Thus, complete
w a t e r vapour c l e a v a g e h a s been o b s e r v e d l a 3 w i t h a l k a l i t r e a t e d Ti02/Rh p h o t o c a t a l y s t s w i t h a f o r m a l quantum y i e l d of 29%.
The
e f f e c t s of p r e s s u r e and s t o i c h i o m e t r y h a v e been s t u d i e d ' 84 f o r t h e T i 0 2 / P t p h o t o c l e a v a g e of water u n d e r ambient c o n d i t i o n s .
It
h a s been r e p o r t e d ' 8 5 t h a t O2 e v o l u t i o n is enhanced c o n s i d e r a b l y i f Ru02 i s a l s o d e p o s i t e d o n t o t h e s u r f a c e .
I n aqueous
s o l u t i o n , an o p t i c a l t o c h e m i c a l c o n v e r s i o n e f f i c i e n c y o f 0.7% h a s been claimed' 86 f o r water c l e a v a g e w i t h p l a t i n i s e d Ti02. Under t h e s e c o n d i t i o n s , water o x i d a t i o n l e a d s t o f o r m a t i o n of s u r f a c e bound p e r o x i d e s n o t O2 l i b e r a t i o n .
However, t h e
p e r o x i d e can be scavenged by a d d i t i o n of barium s a l t s and t h e r e s u l t a n t i n s o l u b l e barium p e r o x i d e can be decomposed by h e a t i n g I n an i n t e r e s t i n g m o d i f i c a t i o n , T i 0 2 h a s been 187 c o u p l e d t o h y d r o g e n a s e and H 2 e v o l u t i o n observed. a t 200-300°C.
The p h o t o c a t a l y t i c a c t i v i t y of T i 0 2 c a n also be m o d i f i e d by b u l k doping w i t h i n o r g a n i c materials.
Doping'88 w i t h C r o r Mn
i o n s i n c r e a s e s t h e f r a c t i o n of the s o l a r spectrum t h a t can be c o l l e c t e d by t h e p h o t o c a t a l y s t .
Doping w i t h a l k a l i metal
Photochemistry
536 cations18’
changes t h e p r o d u c t s e l e c t i v i t y f o r t h e
p h o t o s e n s i t i s e d r e a c t i o n between w a t e r and methanol.
Using
b i n a r y o x i d e s of T i 0 2 / S i 0 2 1 9 0 o r Ti02/M03191 l e a d s t o marked changes i n t h e c r y s t a l s t r u c t u r e and t h i s can have a pronounced e f f e c t upon t h e r a t e of s u r f a c e recombination.
In p a r t i c u l a r ,
doping w i t h M 0 3 seems t o c a u s e s u r f a c e d e p o s i t s of molybdate which lowers t h e p h o t o a c t i v i t y of the m a t e r i a l .
T i 0 2 doped w i t h
n i t r o g e n o x i d e is p a l e yellow’ 92 and e x h i b i t s p h o t o c a t a l y t i c a c t i v i t y under v i s i b l e l i g h t i r r a d i a t i o n .
S u r f a c e doping w i t h 195 p y r e n e , 93 ruthenium complexes, 94 o r c o b a l t p h t h a l o c y a n i n e g i v e s c o l o u r e d m a t e r i a l s b u t t h e i r a b i l i t y t o f u n c t i o n as u s e f u l p h o t o c a t a l y s t s seems s u s p e c t . The photochemical p r o p e r t i e s of T i 0 2 m o d i f i e d w i t h a v a r i e t y
of s e c o n d a r y o x i d e s have been r e p o r t e d .
’Ittus , t h e e f f i c i e n c y
f o r water r e d u c t i o n is i n c r e a s e d markedly by t h e i n c o r p o r a t i o n l g 6 of s m a l l amounts ( c a . 1 % ) of N i O .
Efficient
p h o t o c a t a l y s t s f o r water d i s s o c i a t i o n a r e a l s o o b t a i n e d from S r T i 0 3 / N i 0 b i n a r y o x i d e s .27
The p h o t o a s s i s t e d d e c o m p o s i t i o n of
w a t e r h a s been r e p o r t e d ’ 97 f o r l e a d z i r c o n a t e / t i t a n a t e systems wh i l s t s e v e r a l new n i o b a t e s h a v e been w a t e r under ambient c o n d i t i o n s .
t o pho t o c l e a v e
Water decomposition h a s a l s o
been claimed26 € o r a system employing s u s p e n s i o n s of both T i 0 2 and Ag20. The p h o t o e l e c t r o c h e m i c a l p r o p e r t i e s of many o t h e r o x i d e s
h a v e been i n v e s t i g a t e d .
I n p a r t i c u l a r , ZnO h a s been s t u d i e d by
V : Photochemical Aspects of Solar Energy Conversion
537
'
s e v e r a l groups 98-202 b u t t h e poor l i g h t a b s o r b i n g c h a r a c t e r i s t i c s of t h i s m a t e r i a l p r e v e n t i t s d i r e c t u s e i n s o l a r P h o t o a d s o r p t i o n of O2 o n t o t h e s u r f a c e
e n e r g y s t o r a g e systems.
of Mg0203 and A1203204
h a s been r e p o r t e d and t h e photochemical
p r o p e r t i e s of Fe20g c o l l o i d s 2 o 5 p 2 o 6h a v e been d e s c r i b e d . S e v e r a l r e p o r t s 28p207p208h a v e been concerned w i t h t h e p h o t o c h e m i s t r y of V205 powders.
A report describing the cyclic
decomposition of water with vanadium o x i d e systems28 is n o t c o n v i n c i n g b u t t h e u s e of s i l v e r loaded z e o l i t e s t o p h o t o o x i d i s e 20 9 c h l o r i d e i o n s a p p e a r s t o be c o m p l e t e l y a u t h e n t i c . 'Ihe photodecomposition of H2S w i t h modified CdS h a s a t t r a c t e d considerable a t t e n t i o n in recent years. t h e CdS p h o t o c a t a l y s t on ion-exchange r e s i n 2 ' '
Immobilising
does n o t improve
t h e e f f i c i e n c y of t h e system b u t l o a d i n g s m a l l m o u n t s of Ru02 o n t o the s u r f a c e g i v e s 2 1 1 a v e r y e f f e c t i v e photosystem. Improvements can be made by r e p l a c i n g the Ru02 d e p o s i t w i t h Rh21 2 o r Ag2S.'13 Such systems are a b l e t o c o n v e r t s u n l i g h t i n t o chemical energy with an o v e r a l l e f f i c i e n c y of about 2-3%. The u s e of h e p t e n e t o remove t h e h i g h l y r e a c t i v e s u l p h u r atoms h a s been suggested214 b u t this is n o t t o be recommended. n-Type CdS h a s a l s o been used t o g e n e r a t e H2 under s a c r i f i c i a l conditions p21 decompose methanol.217
t o i s o m e r i s e s t i l b e n e s 2 1 6 and t o A r e p o r t 2 1 8 t h a t CdS loaded w i t h P t and
Ru02 s u r f a c e d e p o s i t s can photoreduce N2 t o ammonia h a s been published.
'Ihe same system is claimed t o be a b l e t o
Photochemistry
538 p h o t o d i s s o c i a t e w a t e r i n t o H2 and 02report2'
UnfortunatelY,
this
l a c k s c o n v i c t i o n and t h e e x p e r i m e n t a l d e t a i l s a r e
woefully inadequate.
Indeed, d e t a i l e d experiments have
concluded t h a t CdS is i n c a p a b l e of e v o l v i n g O2 from w a t e r . 21 9
'his r e p o r t should be c o n s i d e r e d c a r e f u l l y i n l i g h t o f t h e many p r e v i o u s c l a i m s , a l l u n s u b s t a n t i a t e d , t h a t CdS can a f f o r d w a t e r cleavage
.
The p h o t o e l e c t r o c h e m i c a l p r o p e r t i e s of RuS2 h a v e been described.220
' h i s n-type m a t e r i a l seems t o be an e x t r e m e l y
good O2 e v o l v i n g anode and, when d e p o s i t e d o n t o t h e s u r f a c e of CdS, i t promotes e f f i c i e n t c l e a v a g e of H2S.
'he
photodecomposition of H2S can a l s o be achieved221 w i t h V2S5 loaded with Ru02 a l t h o u g h the e f f i c i e n c y is low.
4
PHOTOELECTROCHEM ICAL CELLS
Research i n t o t h e p h o t o g a l v a n i c e f f e c t h a s h a r d l y p r o g r e s s e d i n r e c e n t y e a r s and t h e f i e l d is i n u r g e n t need of a f r e s h impetus.
I r r a d i a t i o n of an a c e t o n i t r i l e s o l u t i o n of
tetrabutylamrnonim d e c a t u n g s t a t e i n a c e l l equipped w i t h P t and C e l e c t r o d e s is r e p o r t e d 2 2 2 t o y i e l d a p h o t o p o t e n t i a l of about
650 mV and a c o n v e r s i o n e f f i c i e n c y of 1%.
'Ihe r e a c t i o n h a s been
o p t i m i s e d and i t is b e l i e v e d t h a t a two photon mechanism operates.
A similar p h o t o g a l v a n i c e f f e c t h a s been observed
upon i r r a d i a t i o n of oxonine i n water c o n t a i n i n g i r o n ( I 1 ) .
223 Here,
t h e c o n v e r s i o n of l i g h t (578 nm) i n t o e l e c t r i c i t y o c c u r s w i t h about 3 x
efficiency.
'Ihe n o v e l f e a t u r e of this system is
V : Photochemical Aspects of Solar Energy Conversion
t h a t , u n l i k e the popular t h i o n i n e / i r o n photogalvanic c e l l , t h e p h o t o c h e m i s t r y t a k e s p l a c e from t h e s i n g l e t e x c i t e d s t a t e of the dye.
With r e g a r d t o t h i o n i n e , it h a s been r e p o r t e d 2 2 4 t h a t the
quantum y i e l d f o r f o r m a t i o n of t h e t r i p l e t e x c i t e d s t a t e of a s u r f a c t a n t d e r i v a t i v e of t h i o n i n e approaches u n i t y i n aqueous microemulsions.
I h i s is a l a r g e i n c r e a s e w i t h r e s p e c t t o
aqueous s o l u t i o n and t h e quenching by i r o n ( I 1 ) r e t a i n s similar b e h a v i o u r i n t h e two e n v i r o n m e n t s .
The p h o t o g a l v a n i c e f f e c t h a s
n o t y e t been demonstated i n t h e m i c r o h e t e r o g e n e o u s medium but it s h o u l d be e a s i l y o b s e r v a b l e .
S u l p h o n a t e d a n t h r a q u i n o n e s are
a l s o known t o f u n c t i o n i n p h o t o g a l v a n i c and photochemical f u e l c e l l s . 225, 226
In t h e l a t t e r a r r a n g e m e n t , an o r g a n i c compound,
such as an a l c o h o l , is used as a s a c r i f i c i a l donor. Ihe g e n e r a t i o n of a p h o t o c u r r e n t upon i l l u m i n a t i o n of a dye
c o a t e d o n t o a metal e l e c t r o d e h a s long been a t o p i c of r e s e a r c h interest.
S e v e r a l porphyrin-based
s y s t e m s h a v e been r e p o r t e d
r e c e n t l y 227 ,228 b u t t h e o v e r a l l o p t i c a l t o e l e c t r i c a l c o n v e r s i o n e f f i c i e n c i e s remain e x t r e m e l y low.
S t a b l e photoanodes f o r water
o x i d a t i o n h a v e been formed from doped s t r o n t i u m o x i d e 2 2 9 and from indium o x i d e . 230
n e l a t t e r system is e s p e c i a l l y
i n t e r e s t i n g i n t h a t t h e quantum e f f i c i e n c y f o r the photoanode is claimed t o be e s s e n t i a l l y 100% f o r i r r a d i a t i o n a t 310 nm. As
mentioned e a r l i e r , t h e r e is a growing i n t e r e s t i n the
p o s s i b i l i t y of d e v e l o p i n g a Fhotochemical method f o r water purification.
S e v e r a l r e p o r t s 231 232 h a v e d e s c r i b e d i n t e r e s t i n g
539
Photochemistry
540
photoelectrochemical approaches.
F i n a l l y , a p h o t o c e l l h a s been
c o n s t r u c t e d 2 3 3 t h a t is c a p a b l e of the c a t a l y t i c r e d u c t i o n of CO w i t h modest e f f i c i e n c y .
5
LW INESCENCE SOLAR COLLECTORS
I n t e r e s t i n luminescence s o l a r c o l l e c t o r s (LSC) h a s been m a i n t a i n e d and r e c e n t developments i n t h e f i e l d h a v e been reviewed, w i t h p a r t i c u l a r emphasis b e i n g p l a c e d on t h e fundamental p r i n c i p l e s of such d e v i c e s .234 e v a l u a t i o n of LSC p r o t o t y p e s h a s ' b e e n
An o u t d o o r and t h e e f f e c t s of
w e a t h e r c o n d i t i o n s upon t h e e f f i c i e n c y of a t y p i c a l d e v i c e h a v e been monitored.
The e f f e c t of g e o m e t r i c s h a p e on t h e o v e r a l l
c o n v e r s i o n e f f i c i e n c y h a s been c o n s i d e r e d 2 3 6 and t h e a d v a n t a g e s o f u s i n g m u l t i p l e l a y e r s have been s t r e s s e d . 237
m e use238 o f
an LSC f o r c o n v e r s i o n of s o l a r energy i n t o t h e r m a l energy h a s a l s o been d e s c r i b e d .
Somewhat r e l a t e d work h a s shownz3'
that
t h e u s e of i o d i n e i n a f l a t p l a t e c o l l e c t o r can i n c r e a s e t h e maximum a t t a i n a b l e t e m p e r a t u r e . Most LSC d e v i c e s employ a l u m i n e s c e n t o r g a n i c dye d i s p e r s e d i n a p l a n a r p l a s t i c s h e e t t o c o l l e c t i n c i d e n t s u n l i g h t and c o n c e n t r a t e the e m i t t e d l i g h t a t the edges.
Many o r g a n i c dyes
a r e known t o f u n c t i o n i n such d e v i c e s and i t h a s now been r e p o r t e d 2 4 0 t h a t t r a n s - t h i o i n d i g o is t h e most e f f i c i e n t dye tested to date.
m u s , the e f f i c i e n c y of an a t t a c h e d S i s o l a r
c e l l was i n c r e a s e d by about 1 . 7 % u s i n g a t h i o i n d i g o - b a s e d LSC. 240
Inorganic materials, with t h e i r inherent h i g h e r
54 1
V: Photochemical Aspects of Solar Energy Conversion s t a b i l i t y , can a l s o be used a s t h e luminescent dye and many of 241 242 Other t h e r a r e e a r t h s have been t e s t e d i n L S C d e v i c e s . I
workers243 h a v e employed ruby i n such s y s t e m s , a g a i n w i t h some d e g r e e of s u c c e s s . 1.
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Author Index In this index the numbers in parentheses are the Part and, where applicable, Chapter numbers of the citation and are followed by the reference number or numbers of the relevant citations within that Chapter, e.g., (3.2) 14 Part I11 Chapter2 ref. 14
Aartsma, T.J. (1) 193, 243 Abadic, M.J.M. (4) 143 Abakumov, G.A. (3.5) 28 Abdel-Magid, A. (3.1) 17; (3.2) 65 Abdon, L.A. (4) 436 Abdul, M.H. (3.1) 51 Abdullah, K.A. (1) 163, 454 Abdullin, M.I. (4) 282, 429 Abe, T. (1) 165 Abeleke, B.B. (3.5) 29 Abelt, C.J. (3.3) 62; (5) 46 Aberti, A. (3.2) 158 Abett, C.J. (1) 156 Abeysekara, B.F. (3.2) 22 Ableev, R . I . (4) 282 Abraham, W. (1) 161; (2.3) 48, 49; (3.3) 85 Abraham, J. (2.1) 23; (5) 172 Abramovitch, R.A. (3.7)
(3.6) 88, 125 Adriaens, P. (1) 201 Adzuma, S. (5) 181 Aeling, E.A. (3.3) 146, 148; (3.4) 18, 20; (3.7) 178, 180 Afonichev, D.D. (2.1) 222 Agamalieva, M.M. (4) 410 Agarwal, H.K. (4) 273 Agha, B. (3.4) 126 Agosta, W.C. (3.2) 1, 2 , 17, 67; (3.6) 206 Agrawal, M.L. (1) 381 Ah, K. (4) 61 Ahmed-Schofield, R . (3.3) 140; (3.6) 138 Aibara, K. (1) 357 Aida, H. (4) 73 Aikawa, N. (5) 168 Aime, S. (2.2) 81, 99 Ait-Ichou, I. (2.1) 26 Ait-Lyazidi, S. (1) 162 Aizenshtat, Z. (2.1) 117 Ajo, D. (2.2) 80, 81 Akahori, Y. (3.2) 114 Akasaka, T. (3.5) 128, 97 Abrams, L. (3.1) 6 129 Akesson, E. (1) 242 Abramson, S. (5) 38 Akhmed-Zade, D.A. (4) 423 Abrieva, Z.K. (1) 392 Akhrem, A.A. (3.5) 117 Ache, H . J . (1) 194, ,195 Akid, R. (2.1) 64; (5) 79 Acierno, D. (4) 306 Acuna, A.U. (1) 130 Akimoto, H. (3.5) 69, 71 Adachi, G. (2.1) 200 Akiyama, T. (2.2) 83, 84, Adam, W. (1) 494; (3.1) 97; (5) 77 14; (3.2) 86; (3.3) 43, Al-Abbasi, M.A. (5) 239 Alam, L.V. (3.6) 216 128, 129; (3.5) 77; (3.7) 13, 14, 17-19, Alberti, A. (2.3) 18 Albertson, A.C. (4) 382, 24, 27 412 Adebayo, A.T.O.M. (3.7) Albini, A. (3.4) 188; 163 (3.5) 72; (3.6) 65 Adeleke, B.B. (3.2) 164 Alcala, J . R . (1) 24 Adembri, G. (3.2) 39; 555
Alcock, N.W. (2.1) 196 Aldoshin, S.M. (3.6) 40 Al-Ekabi, H. ( 1 ) 314; (3.3) 14 Aleksandrov, A.P. (4) 325 Aleksankina, M.M. (1) 472 Alekseeva, L.N. (4) 183 Al-Emara, K. (2.1) 37; (5) 28, 221 Alfano, R.R. (1) 32, 377, 382 Alfassi, Z.B. (1) 424 Alford, P.C. (1) 102 Alfsen, A. (1) 399 Al-Hassan, K.A. (1) 125, 265 Ali, K. (2.3) 39 Ali, M.B. (3.7) 57 Ali, M.Z. (3.3) 46, 149; (3.4) 16, 17 Ali, S . I . (2.1) 59 Ali, S.M. (1) 41 Aliev, M.Kh. (4) 423 Alig, B. (3.6) 212 Aliwi, S.M. (2.1) 37; (5 28, 221 Al-Khalil, S . I . (3.7) 15 Alland, M. (4) 15 Allen, N.S. (4) 83, 84, 182, 295, 317, 380, 384, 405, 416, 419 Almond, M.J. (2.3) 38 Aloise, G.G. (1) 227 Alonso, R.A. (3.7) 164 Al-Sayyed, G.H. (5) 180 Alt, H.G. (2.2) 22 Altomare, A. (4) 213 Altona, C. (3.2) 99 Aly, M.M. (3.4) 79 Amadelli, R. (2.2) 99 Amarasekara, A. (3.2) 35 Anmt, M. (3.4) 148
Author Index
556 Amat-Guerri, F. (1) 130 Ameloot, M. (1) 42, 43, 48 Amemiya, S. (4) 210; (5) 155 Amera, A . B . (4) 434 Ames, D.P. (4) 192, 193 Ameta, S.C. (3.5) 94 Amick, T . J . (3.7) 66 Amir, D. (1) 362, 374 Amirov, A. (1) 117 Amouyal, E. (2.1) 10, 128; (5) 59, 83, 84 Amserve, D. (4) 228 An, B.S. (3.4) 139; (3.6) 23 Anand, R.C. (4) 308 Anba, F.E. (3.7) 87 Anderson, B.E. (1) 324 Anderson, F.R. (2.2) 106 Anderson, H.C. (4) 268 Anderson, S.A. (1) 355 Andersson, K. (3.4) 162, 163, 1?0, 171 Ando, W. (2.3) 20, 22; (3.5) 2, 128, 129, 151; (3.7) 69 Andolfatto, G. (2.2) 34 Andre, J.C. (2.1) 30 Andrei, C. (4) 345 Andrews, L. (2.3) 37, 51 Andrianov, A . K . (4) 118, 119 Androkites, A. (5) 34 Anfinrud, P. (1) 258 Angel, S.M. (2.1) 48 Anisimov, V.M. (4) 454 Anklam, E. (3.2) 6 ; (3.6) 172, 173 Anpo, M. (2.1) 244; (5) 167-169, 190, 202 Ansari, P. (2.1) 215 Ansell, G.B. (2.2) 93 Antipin, V.A. (2.1) 249 Antonioletti, R. (3.4) 97, 98; (3.7) 149, 150 Antsyshkina, A.S. (2.2) 37 Anufrieva, E.V. (4) 169, 249 Anzai, J. (4) 170 Aoe, K. (3.6) 183 Aon, M. (4) 130, 157 Aono, S. (2.1) 231-233; (3.5) 34; (5) 66, 68, 89, 90, 94, 95, 140 Aoyagui, S. (2.1) 35 Aoyama, H. (3.1) 37; (3.2) 123, 134; (3.3) 3; (3.6) 77, 78, 187, 188 Aoyama, Y. (2.2) 1 1 7
Appelt, B.K. (4) 143 Appleyard, J.H. (4) 419 Arai, T. (1) 188, 439 Arain, M.F. (3.5) 83 Arakawa, S . (3.6) 162 Arakawa, Y. (3.2) 110 Araki, T. (3.2) 143, 148, 153-157; (3.4) 48-50; (3.6) 109, 110, 113, 115, 135 Aramendia, P.F. (2.3) 41, 56 Arata, Y. (3.1) 41; (3.2) 122; (3.3) 3; (3.6) 75, 78 Arce, R. (3.5) 133 Archer, A.J. (5) 33 Argitis, P. (2.1) 65 Ariaans, G.J.A. (3.2) 7 Ariel, A. (3.1) 34 Arikawa, Y . (2.1) 144 Armesto, D. (3.2) 75-78; (3.3) 41, 42, 72; (3.4) 13; (3.6) 27, 46-48, 79 Armiri, A.S. (4) 264 Arnason, J.T. (1) 419 Arnaud, R. (4) 310, 312 Arndt-Jovin, D.J. (1) 73 Arnikar, H.J. (1) 504 Arnold, B. (3.4) 104 Arnout, L.G. (1) 2 Aroba, K.J.S. ( 3 . 7 ) 120 Arora, K.S. (1) 271; (4) 44 Arreozzi, A. (4) 141 Arutyunyan, V.I. (5) 229 Arvidson, E. (1) 84 Asada, S. (4) 304 Asafu-Adjaye, E.B. (1) 66 Asai, K. (3.6) 37 Asai, N. (3.2) 154; (3.6) 115 Ashizawa, M. ( 1 ) 442 Ashmawy, F.M. (2.1) 66 Askerov, D.B. (3.1) 25 Asocka, S. (1) 83 Assemian, Y. ( 1 ) 192 Astik, R.R. (3.4) 38 Atabekyan, L.S. (1) 507 Atasoy, B. (3.5) 84 Atherton, S.J. (1) 389 Atovmayan, 1.0. (3.6) 40 Atreyi, M. ( 1 ) 336 Atta-ur-Rahman. (3.2) 111; (3.6) 85 Audenhart, F. (3.2) 27; (3.6) 205 Auerbach, R.A. (2.1) 80, 84; (5) 57 Augugliaro, V. ( 5 ) 19 Auld, D.S. (1) 352 Auty, A.R. (1) 319
Avnir, D. (1) 310, 311 Axelrod, B. (1) 505 Azumi, T. (1) 429; (2.1) 57, 173, 174 Baader, W.J. (1) 494, 497 Baaij, J.P.B. (3.2) 165; (3.6) 121 Babaeva, S.G. (4) 423 Baceiredo, A. (3.7) 78, 87 Bachowska, B. (3.7) 97 Baciocchi, E. (3.5) 110 Back, M. ( 4 ) 301 Back, R.A. (3.2) 116, 117 Baddour, F.R. (4) 117 Badr, M.Z.A. (3.4) 79 Baeckstroem, P. (3.3) 84; (3.4) 10; (3.5) 79 Baer, L. (2.1) 176 Baes, M. (3.4) 110 Baessler, H. (4) 63 Baevisuyl, D. (4) 188 Baeyens-Volant, D. (4) 163 Baeza, J. (4) 356 Bagdasar'yan, Kh.S. (5) 217 Bahnemann, D. (2.1) 18; ( 5 ) 170, 219 Bai, F. (1) 267; (4) 259 Bain, A.J. (1) 15 Baines, K.M. (2.3) 19; (3.3) 4; (3.6) 199 Bajgur, C.S. (2.2) 6 Balaban, R.S. (1) 402 Balai, M. (3.5) 84 Balard, H. (5) 204 Balashev, K.P. (2.1) 91, 182, 183 Baldwin, J.E. (3.7) 72 Baldwin, L.J. (3.4) 120 Baldwin, S.W. (3.2) 37 Ball, P. (4) 440 Ball, R.C. (4) 187 Balla, R.J. (3.5) 145, 146 Ballardini, R. (2.1) 92, 103, 178; (5) 91 Ballinger, R.F. (5) 56 Balogh-Nair, V. (1) 377 Balzani, V. (2.1) 78, 79, 93, 103, 104, 130, 142, 150, 175; (5) 55, 58, 91, 99, 123 Bamezai, S. (3.7) 108 Bamford, C.H. (4) 35 Bando, Y. (3.2) 91; (3.4) 95; (3.7) 152 Bandow, H. (3.5) 69 Bandyopadhyay, R. (4) 92
557
Author Index B a n e r t , K . (3.7) 89 B a n i j i , S.R. ( 4 ) 292 Bapacios, S.M. (3.7) 164 Baral, S. ( 2 . 1 ) 160 Baral-Tosh, S. ( 1 ) 111 Baran, J. ( 1 ) 19 Barba, C. ( 4 ) 321 Barbara, P.F. ( 1 ) 134, 223, 231, 232; ( 3 . 2 ) 52 Barbay, N. ( 1 ) 468 B a r b e n i , M. ( 2 . 1 ) 22; ( 5 ) 212 B a r b e r , R.A. ( 3 . 4 ) 164 B a r b i e r , M. ( 3 . 5 ) 124 B a r b o o t i , M.M. ( 5 ) 239 Barbush, M. ( 3 . 5 ) 121 Bard, A.J. ( 4 ) 280; ( 5 ) 179 Bardez, E. (1) 305 Bardy, J . E . ( 1 ) 6 B a r e t z , B.H. ( 1 ) 304 B a r i g e l l e t t i , F. ( 1 ) 81; ( 2 . 1 ) 78, 79, 130; ( 5 ) 55, 58 B a r i k , R. ( 3 . 6 ) 54 Barkley, M.D. ( 1 ) 344 Barltrop, J.A. (3.4) 54, 69 Barmasov, A.V. ( 5 ) 29 Barnes, C. (3.1) 46; ( 3 . 4 ) 155; (3.5) 15 Baron, U. ( 3 . 6 ) 42 B a r r e r a , M. ( 2 . 2 ) 85 Barrow, D.A. ( 1 ) 275 B a r t e l t , G. (3.6) 42 B a r t l e t t , P.D. ( 3 . 3 ) 104 B a r t n i k , R . ( 3 . 1 ) 55; ( 3 . 7 ) 107 B a r t o c c i , C. ( 1 ) 227; (2.1) 71; ( 2 . 2 ) 99 B a r t o n , D.H.R. ( 3 . 1 ) 24; ( 3 . 4 ) 129; ( 3 . 7 ) 112117 B a r t o n , J.K. (1) 386 B a r t o n , T.J. ( 3 . 4 ) 7 ; ( 3 . 6 ) 55 Bartoszek-Loza, R . ( 4 ) 134 B a s c e t t a , E. ( 3 . 5 ) 74 Basheer, R. ( 4 ) 81 B a s h i r , M. ( 3 . 2 ) 111; ( 3 . 6 ) 85 Bassler, H. ( 1 ) 272, 449 Batlogg, B. ( 2 . 1 ) 165 Bats, J.W. (3.2) 103 B a t t e n , R . J . ( 3 . 1 ) 19 B a u d i e r , J . ( 1 ) 335 Bauer, D.R. ( 4 ) 394, 395 Bauer, I. ( 3 . 3 ) 76 Bauld, N.L. ( 3 . 3 ) 6 7 , 122 Baumann, H. ( 3 . 7 ) 83; ( 4 ) 3 9 , 4 0 , 51
Baumann, M. ( 2 . 1 ) 209 ( 3 . 7 ) 31 Baurngart, K.-D. Baxte, E.W. (3.7) 80 Bayer, E. ( 1 ) 225 Baynham, R.F.G. (2.2) 8 Bazhin, N.M. ( 2 . 1 ) 191 Beaman, R.A. ( 1 ) 19 Beaudry, Y. ( 5 ) 35 Beaumont, P.C. ( 1 ) 389 Bebedix, R. (2.1) 72 Bechara, J . (2.3) 32 Beck, G. ( 1 ) 92 Beck, K. ( 3 . 6 ) 118 Becker, H.-D. (1) 110; ( 3 . 4 ) 162, 163, 168, 170, 171 Becker, H.G.O. ( 3 . 7 ) 83 Becker, P. ( 2 . 1 ) 209 Becker, R.S. (1) 224, 225, 233, 508-510; (3.6) 3 Beckmann, E. ( 3 . 4 ) 160; ( 3 . 7 ) 25 Beddows, C.G. ( 4 ) 111 Bednar, B. ( 4 ) 223 Bednar, W.M. ( 3 . 3 ) 66; ( 3 . 6 ) 132 Beechem, J.M. (1) 4 2 , 43, 333 Beever, R.G. (2.2) 40 Begmark, W.R. ( 3 . 4 ) 155 B e i e r , S. (3.1) 16 B e i n , T. ( 2 . 2 ) 6 8 B e i n e r t , G. (1) 264; ( 4 ) 235 Bekturov, E.A. ( 4 ) 203, 208 Be1 Bruno, J.J. ( 1 ) 128; ( 3 . 6 ) 67 B e l ' g i b a e v a , Z.K. ( 4 ) 203, 208 B e l l , G.A. ( 3 . 7 ) 6 1 B e l l , T.N. ( 2 . 3 ) 1 2 Bellabono, I . R . ( 4 ) 105, 113 B e l l a s , M. ( 3 . 4 ) 53 B e l l e n g e r , V. ( 4 ) 420 B e l l o n i , J. ( 5 ) 106 B e l o t t i , D. (3.2) 55 Belousov, V.M. ( 2 . 1 ) 1 9 ; ( 5 ) 207 Belser, P. ( 2 . 1 ) 78, 79, 9 3 , 130; ( 5 ) 55, 58, 123 B e l y i , A . A . ( 5 ) 107 Ben, I. (3.4) 116 Ben Arnotz, D. ( 1 ) 204 Bendic, C. ( 3 . 4 ) 92 Bendig, J. ( 3 . 4 ) 1 7 5 , 176; ( 3 . 6 ) 124 Benisek, L. ( 4 ) 452 Benn, R . ( 2 . 2 ) 4
Bensasson, R.V. (3.2) 47 Bentz, D.P. ( 4 ) 328 Benz, G. ( 4 ) 343 Berg, K. ( 2 . 2 ) 4 Bergamini, P. ( 2 . 2 ) 3 Bergaya, F. ( 2 . 1 ) 137; (5) 30, 117 Bergmann, A. (3.2) 38; (3.6) 94 Bergmark, W.R. ( 1 ) 216; (3.1) 46; (3.5) 15 Berhard, W. ( 3 . 3 ) 86 B e r k e s s e l , A. (3.1) 1 4 ; (3.3) 43 Berkowitz, W.F. (3.2) 35 B e r l i n e r , L.J. (1) 353 Berman, H.A. (1) 356 Berman, M.C. ( 1 ) 370 Bernard, G. ( 3 . 1 ) 32 B e r n a r d i n e l l i , G. ( 3 . 5 ) 93 Bernauer, K. (3.6) 51, 52 B e r n e r , G. ( 4 ) 402 B e r r i d g e , J.C. (3.4) 30 B e r r y , N.M (3.2) 34 Berson, J . A . ( 3 . 2 ) 119 B e r t a i n a , C. ( 3 . 6 ) 174 B e r t h i e r , G. ( 1 ) 418 B e r t o , J . R . ( 1 ) 317 B e r t r a n d , G. (3.7) 78, 8 7 B e r t s c h , A. ( 3 . 3 ) 139 B e r t u c c i , C. ( 4 ) 220 Berube, M. (5) 34 B e r z i n , M.P. ( 4 ) 156 B e t z , E. ( 1 ) 115, 255 Beugelmans, R. ( 3 . 7 ) 1 6 5 , 168, 169 Beyer, G. ( 3 . 1 ) 22 B h a l e r a o , V.K. ( 3 . 3 ) 142; (3.4) 149; (3.7) 1 7 3 Bhardwaj, C. ( 5 ) 218 Bhardwaj, R.C. ( 5 ) 218 Bhaskar, V.U. ( 4 ) 404 B h a t t a c h a r y y a , K. (1) 111, 455, 463, 473, 487; ( 3 . 5 ) 64 Bibinov, N.K. ( 2 . 3 ) 4 3 B i c k e l h a u p t , F. ( 3 . 3 ) 75; (3>4) 3 B i d d l e t J . R . (5) 1 7 Bideau,' M. ( 1 ) 192; ( 5 ) 163 B i e r i , J.H. (3.2) 68; ( 3 . 4 ) 182 B i g l e r , P. (3.4) 38 Bignozzi, C.A. (2.1) 92 B i l a l , B.A. ( 2 . 1 ) 209 (3.2) B i l l h a r d t , U.-M. 103, 104 Binana-Lirnbele, W. (1) 282 Bingmann, H . ( 3 . 3 ) 105,
Author Index
558 106; (3.6)
100
Binkley, R.W. (3.1) 52 Birch, D. (3.2) 120; (3.7)
111
Birch, D . J . S . (1) 27, 55 Birney, D.M. (3.2) 119 Biryukov, V.P. (4) 429 Bisby, R.H. (1) 145, 398 Bischofberger, N. (3.1) 35; (3.3) 133, 135
133; (3.7)
Biseau, M. (2.1) 20 Bishop, A.R. (4) 188 Bitai, I. (4) 67 Bityurin, M.N. (4) 378 Bjerring, P. (3.2) 101 Bjoerkling, F. (3.5) 79 Blagov, S.N. (4) 429 Blaha, J.P. (2.2) 87, 92 Blais, N.C. (2.3) 34 Blanchard, D . J . (1) 17 Blanco, M. (4) 321, 424 Blaney, D.G. (2.1) 98; ( 5 ) 96 Blasse, G. (2.1) 1 Blatt, E. (1) 351 Blazej, A. (3.3) 12 Blenkinsop, R.E. (5) 15 Blinov, 1.1. (2.1) 182 Blornqvist, K. (3.7) 102 Blondeel, G. (5) 127 Blount, J.F. (3.1) 17;
Bolognese, A. (3.5)
41;
(3.6) 61
Bolte, M. (2.1) 53, 54 Bolton, J . R . (4) 226; (5) 13, 126, 128, 132
Bombieri, G. (2.2) 126 Bonacic-Koutecky , V. (3.6)
1
Bondybey, V.E. (1) 120 Bong, P.-H. (1) 234, 444; (3.3)
28
Bon Hoa, G.H. (1) 365 Bonneau, R . (1) 500; (3.2) (3.4)
105; (3.3) 9; 133 Bonsal, W.R. (1) 467 Bootsma, J.P.C. (4) 255 Borden, P.G. (4) 55 Borgarello, E. (2.1) 22, 178; (5) 211, 212 Borisevich, Y.E. (1) 471 Borkman, R.F. (1) 332 Borovik, A.S. (2.2) 137 Bortolus, P. (4) 314, 355, 393 Bos, F.C. (1) 422 BOS, H.J.T. (3.2) 70, 149, 165; (3.3) 94; (3.4) 142, (3.6) 26, 121, 180; (5) 43 Bosch, J. (3.4) 148 Bosch, P. (5) 151 Bott, D.C. (4) 186 (3.2) 65 Blow, D. (4) 190 Bottcher, H. (4) 196 Blumen, A. (1) 249 Bouas-Laurent , H. (2.3) 17; (3.4) 84, 169, 173; Bocarsley, A.B. (2.1) (3.6) 208 185; (2.2) 46 Bochu, C. (3.6) 35 Bouchard, D.A. (5) 112 Boeger, B.E. (1) 281 Bougeard, P. (2.2) 110 Boehm, H.P. (2.1) 28; (5) Boukouvalas, J. (3.5) 92, 93 178 Boens, N. (1) 36, 213; Boule, P. (3.4) 12 Bourdeaux, M. (1) 159 (4) 260 Boente, J.M. (3.7) 146 Bourdelande, J.L. ( 5 ) 93 Boettcher, W. (2.1) 108 Bourgin, D. (3.2) 133 Bogdantsaliev, J. (4) 353 Bowen, M. (3.2) 138, 139 Boghillo, V.I. (1) 472 Bowman, W.R. (3.7) 158, Bohne, C. (1) 497 163 Boikov, V.N. (2.1) 218 Boyd, M.K. (3.4) 106; Boileaus, S. (4) 246 (3.5) 52 Bois-Choussy, M. (3.7) Bragatssvilli, V.N. (2.3) 46 165 Boivin, S. (4) 246 Branca, S . J . (3.3) 108 Bojarski, C. (4) 238, 240 Brand, L. (1) 42-45, 321, Bokadia, M.M. (3.5) 95, 333 Brandt, 0. (1) 292 114 Bokobza, L. (3.5) 97 Brasitus, T.A. (1) 400 Boldridge, D.W. (1) 121 Braslavsky, S.E. (1) 60, Bolivar, R.A. (3.1) 44, 479 45; ( 3 . 4 ) 4 6 ; ( 3 . 5 ) 13, Brauer, H.D. (3.5) 98 14 Braun, C. (2.1) 30 Bolletta, F. (2.1) 104 Braun, D. ( 4 ) 120, 1 2 1
Braun, M. (2.1) 122 Braunschweig, F. (4) 63 Bravar, M. ( 4 ) 335, 342 Braven, B. (4) 363 Bray, B.L. (3.7) 145 Bray, R.G. (2.2) 52 Brearley, A.M. (1) 223, 232
Brecht, E. (1) 197 Breckenridge, W.H. (2.2) 12
Breen, P.J. (1) 359 Brenner, H.C. (1) 448 Brenner, K. (1) 446 Brewer, K.J. (2.1) 129; (5) 60
Briere, R. (2.2) 75 Briggs, L.M. (4) 394, 395 Bright, F.V. (1) 40 Brillante, A. (1) 112 Brillas, E. (5) 93 Brink, P.R. (1) 410 Brisirnitzakis, A.C. (3.2) 107
Brittain, H.G.
(2.1) 203, 205, 206, 210-213, 215 Brodbeck, H. (3.2) 133
Brokatzky-Geiger, J . (3.3)
105, 106; (3.6)
100 Bromberg, A. (1) 140; (3.5)
134
Bronstein-Bonte, I. (1) 221
Brook, A.G.
(2.3) 19; 4; (3.4) 156; 198, 199 Brooke, G.M. (3.4) 42 Brookfield, R.L. (1) 218 Brouwer, A.M. (3.3) 56; (3.7) 79 Browett, W.R. (2.1) 239 Brown, D.W. (1) 246 Brown, P.E. (1) 295; (3.3) 23 Brown, T.L. (2.2) 64 Briiggemann, K. (3.6) 94 Brugger, P. (3.3) 86 Bruice, T.C. (2.1) 52 Brummer, J . G . (2.1) 56 Brune, H.A. (3.3) 51-55 Bruno, G. (2.2) 126 Brunschwig, B.S. (2.1) 109 Brus, L.E. (1) 316 Bryant, L.R.B. (3.2) 141 Bryce-Smith, D. (3.4) 21, 22, 53 Buchachenko, A.L. (3.1) 25 Buchardt, 0. (3.2) 101 Buchholz, H. (3.1) 4 2 ; (3.3) (3.6)
559
Author Zndex ( 3 . 6 ) 76
Buchler, J.W. ( 2 . 1 ) 135 Buckland, S.J. ( 3 . 7 ) 30 Buechler, J. ( 2 . 1 ) 242; ( 5 ) 73
Buenzli, J.C.G. ( 2 . 1 ) 1 9 6 , 197
Buerbanner, J. ( 4 ) 269 Buffel, D.K. ( 3 . 4 ) 5 7 ; ( 3 . 6 ) 127
Cameron, R.E. ( 2 . 1 ) 1 8 5 ; ( 2 . 2 ) 46
Campa, C. ( 5 ) 151 Camparini, A. ( 3 . 6 ) 56 Campillo, A.J. ( 1 ) 6 4 , 65 Camps, J. ( 5 ) 9 3 , 151 Canas, L.R. ( 5 ) 42 Canonica, L. ( 3 . 2 ) 64 Canonica, S . ( 1 ) 2 8 , 9 4 , 119
Cava, M.P. ( 3 . 4 ) 122-124; ( 3 . 6 ) 2 5 , 159
Cavanagh, R.R. ( 4 ) 243 Cavatorta, P. ( 1 ) 390 Cavazza, M. ( 3 . 2 ) 1 9 Cazeau, P. ( 1 ) 162 Cazeau-Dubroca, C. ( 1 ) 162
Cebulska, 2. ( 3 . 1 ) 5 5 ; ( 3 . 7 ) 107
Cecchi, L. ( 5 ) 20 Cech, F. ( 3 . 2 ) 103 67 Celander, D.W. ( 3 . 4 ) 62 Buku, A. (1) 334 Cellucci, T.A. ( 2 . 1 ) 69 Bulgakov, R.G. ( 2 . 3 ) 57 95 Bulinski, A.T. ( 4 ) 292 Cao, Y. ( 3 . 3 ) 11, 8 7 , 109 Cen, J. ( 4 ) 399 Cerfontain, H. ( 3 . 2 ) 6 9 , Buma, W.J. ( 1 ) 422 Capponi, M. ( 3 . 2 ) 129 102 Bunce, N.J. ( 3 . 4 ) 6 9 , 7 0 , Capps, N.K. ( 3 . 6 ) 169 Cernak, V. ( 4 ) 9 7 , 133 Carassiti, V. ( 2 . 1 ) 7 1 ; 7 8 ; ( 3 . 6 ) 155 Cesca, S. ( 4 ) 141 ( 2 . 2 ) 99 Buono-Core, G.E. ( 2 . 1 ) Cha, J.K. ( 3 . 7 ) 72 Cardenas, J. ( 3 . 2 ) 49 168 Cha, Y. ( 3 . 7 ) 4 0 , 52 Burbo, E.M. ( 3 . 5 ) 3 1 , 32 Ca-rdona, R. ( 2 . 2 ) 136 Chadda, S.K. ( 3 . 4 ) 11 Cargill, R.L. ( 3 . 2 ) 25 Burger, U. ( 3 . 6 ) 1 1 9 ; Carless, H.A.J. ( 3 . 1 ) 1 9 , Chae, K.H. ( 1 ) 2 3 4 , 4 4 4 ; ( 3 . 7 ) 70 ( 3 . 2 ) 94; ( 3 . 3 ) 28; Burghardt, T.P. (1) 4 0 5 , 49 412 Carlini, C. ( 4 ) 213 ( 3 . 6 ) 24 Chae, Y.M. ( 3 . 2 ) 1 2 ; Burkhart, R.D. ( 4 ) 246 Carlsson, D.J. ( 4 ) 3 7 9 , Burlov, A.S. ( 2 . 1 ) 188 ( 3 . 6 ) 93 386 Burnett, J.F. ( 3 . 7 ) 1 5 7 , Carmely, Y. ( 3 . 5 ) 90 Chai, C.K. ( 4 ) 186 Chakraborty, K.B. ( 4 ) 408 166 Carpendale, N. ( 5 ) 34 Challa, G. ( 4 ) 255 Burns, V.W. ( 1 ) 385 Carr, P.W. ( 1 ) 6 Challal, D. ( 2 . 1 ) 1 3 7 ; Carrascosa, M. ( 5 ) 2 3 5 , Burshtein, A.I. ( 1 ) 2 5 1 ,
Bukhtiyarov, V.K. ( 2 . 1 )
252
Bursten, B.E. ( 2 . 2 ) 92 Buser, C.A. (1) 229 Bushby, R.J. ( 3 . 4 ) 1 2 5 ; ( 3 . 7 ) 28
Busse, R. ( 1 ) 310 Busulini, L. ( 4 ) 355 Butler, A.P. ( 1 ) 394 Buttafava, A. ( 4 ) 314,
Cao, D. ( 2 . 3 ) 30 Cao, H. ( 3 . 6 ) 7 Cao, W. ( 4 ) 8 6 , 8 7 , 9 0 ,
2 36
Carraway, E.R. ( 1 ) 34 Casal, B. ( 2 . 1 ) 137; ( 5 ) 117
Casal, H.L. ( 1 ) 8 0 , 461,
465; ( 3 . 1 ) 8 Casarin, M. ( 2 . 2 ) 8 1 Casey, C.P. ( 2 . 2 ) 9 4 Caspar, J.V. ( 2 . 1 ) 1 3 , 1 3 4 ; ( 2 . 2 ) 124 393 Butter, R.J. ( 4 ) 134 Cassano, A.E. ( 1 ) 7 0 Castedo, L. ( 3 . 4 ) 1 1 6 ; Buys, T.S.V. ( 3 . 2 ) 69 ( 3 . 7 ) 146 Castel, N. ( 1 ) 230 Cabaness, W.R. ( 4 ) 250 Castellan, A. ( 2 . 3 ) 1 7 ; ( 3 . 4 ) 8 4 , 169, 173; Cadet, J. ( 3 . 2 ) 9 9 ; ( 3 . 6 ) 87 ( 3 . 6 ) 208 Caffieri, S. ( 3 . 2 ) 48 Castello, A. ( 3 . 4 ) 7 3 Cai, 2. ( 2 . 1 ) 225 Castelvetro, V. ( 2 . 1 ) 150 Calalini, L.H. ( 1 ) 494 Casti, T.E. ( 5 ) 145 Calderwood, T.S. ( 2 . 1 ) 52 Castle, R.N. 1 2 0 , 1 2 1 , Caldwell, R.A. ( 2 . 1 ) 6; 1 4 5 ; ( 3 . 6 ) 161 Castleman, A.W. ( 2 . 3 ) 2 (3.5) 7 ; ( 5 ) 8 Caldwell, W.E. ( 3 . 2 ) 25 Catalan, J. ( 1 ) 130 Calgari, S . ( 4 ) 105 Catalina, F. ( 4 ) 8 3 , 84 Calhorda, M.J. ( 2 . 2 ) 35 Cater, R.S. ( 3 . 4 ) 7 0 , 7 8 ; Callender, R.H. ( 1 ) 377 ( 3 . 6 ) 155 Callis, P.R. ( 1 ) 324 Cato, C. ( 1 ) 95 Calo, V. ( 3 . 5 ) 108 Caucik, P. ( 4 ) 403 Calvin, M. ( 5 ) 145 Caufield, C.E. ( 3 . 2 ) 7 3 , Calzaferri, G. ( 5 ) 4 , 209 74
( 5 ) 3 0 , 117
Challiner, J.F. ( 3 . 2 ) 141 Chamberlain, G. ( 3 . 2 ) 28 Chamberlain, S.D. ( 3 . 4 ) 1 0 2 ; ( 3 . 7 ) 1 7 0 , 171
Chambers, S. ( 4 ) 125 Chambron, J.C. ( 2 . 1 ) 1 2 8 ; ( 5 ) 59
Chan, C.K. Chan, K.H. Chan, M.G. Chan, S.S.
( 2 . 1 ) 205 ( 4 ) 386 ( 4 ) 142 (2.1) 27; ( 5 )
191
Chan, Y. ( 3 . 5 ) 88 Chance, M.R. ( 1 ) 367 Chander, K. ( 4 ) 308 Chandrasekaran, K. ( 2 . 1 ) 248; ( 5 ) 193
Chandross, E.A. ( 1 ) 174 Chang, C.-H. ( 1 ) 267, 395; ( 4 ) 259
Chang, H.C. ( 3 . 1 ) 1 0 , 11 Chang, L.C.P. ( 4 ) 223 Chang, M.C. ( 1 ) 20 Chang, Z. ( 4 ) 8 5 , 88 Chanon, M. ( 2 . 1 ) 1 8 0 ; ( 3 . 7 ) 167
Chapman, O.L. ( 3 . 7 ) 4 3 , 50
Charpiot, B. ( 3 . 1 ) 2 4 ; ( 3 . 4 ) 129
Author Index
560 Chasey, K.L. ( 3 . 3 ) 91 Chassot, L. ( 2 . 1 ) 175, 176
Chastanet, J. ( 3 . 7 ) 168 Chattopadhyay, N . ( 1 ) 133 Chattopadhyay, S.K. ( 1 ) 111, 476, 490
Chauveau, F. ( 5 ) 222 Chauvet, J . D . (1) 381 Che, M. ( 5 ) 168 Chelibanov, V.P. ( 2 . 3 ) 42 Chen, C.C. ( 3 . 3 ) 6 3 Chen, J. ( 3 . 5 ) 8 7 , 109 Chen, L.X.-Q. ( 1 ) 328 Chen, R.F. (1) 71 Chen, S. ( 4 ) 191 Chen, W.Y. ( 4 ) 297 Chen, Y. ( 3 . 5 ) 38; ( 4 ) 12 Cheng, C.-C. ( 1 ) 464; (3.1) 6
Cheng, C.P. ( 2 . 2 ) 6 2 , 63 Cherek, H. ( 1 ) 132, 348, 456
Cherkasov, V.K. ( 3 . 5 ) 28 Chermette, H . ( 2 . 1 ) 180 Chernysh, Yu.E. ( 3 . 6 ) 4 1 Cherry, W.R. ( 1 ) 283; (2.1) 84-86
Chervenkova, V. ( 3 . 5 ) 139 'Cheskis,S.G. ( 2 . 3 ) 35, 36
Chesnokov, S.A. ( 3 . 5 ) 28 Chetwynd-Talbot, J. (2.2) 8
Chevalier, J.L. ( 5 ) 20 Chevalier, Y. ( 5 ) 141 Chevychelor, V.A. ( 4 ) 56 Chew, J.-F.A. ( 1 ) 417 Chiao, Y.C. ( 4 ) 201 Chiba, M. ( 2 . 1 ) 145 Chiba, T. ( 3 . 2 ) 4 1 Chiba, Y. ( 3 . 5 ) 54 Chibisou, A.K. ( 1 ) 507 Chiellini, E. ( 4 ) 215 Chigladge, L.G. ( 5 ) 107 Childs, R.F. ( 3 . 4 ) 11 Chin, I.J. ( 4 ) 232 Chiorboli, C. (2.1) 92 Chirinos-Padron, A.J. ( 4 ) 295, 384, 419
Cho, J.-H. ( 3 . 4 ) 38 Cho, K . ( 4 ) 409 Cho, T.H. ( 3 . 2 ) 100; ( 3 . 6 ) 139
Chockalingam, K. ( 3 . 7 ) 144
Chodankar, N.K. ( 4 ) 447 Chodosh, D.F. ( 3 . 6 ) 170 Choi, I.S. ( 4 ) 237 Choi, J.H. ( 2 . 1 ) 4 3 Choi, K . Y . ( 2 . 1 ) 208 Chondhary, V. ( 4 ) 404
Chou, P.T. (1) 77, 193; ( 3 . 5 ) 58 Choudhry, G.G. ( 3 . 4 ) 86, 8 7 ; ( 3 . 5 ) 50 Chow, Y.L. (1) 8 6 ; ( 2 . 1 ) 168; ( 3 . 4 ) 58; ( 3 . 6 ) 142, 143; ( 3 . 7 ) 110 Chowdhury, M. ( 1 ) 133 Christensen, P . A . ( 2 . 1 ) 102, 240; ( 5 ) 113, 120 Christensen, R . L . ( 1 ) 26, 84 Christensen, S. ( 3 . 5 ) 78 Christl, M. ( 3 . 7 ) 22 Chu, C.H. ( 4 ) 45 Chu, D . Y . ( 2 . 1 ) 121 Chu, G . ( 1 ) 196 Chu, W.T. ( 4 ) 45 Chuang, C. ( 3 . 7 ) 46 Chuang, J.C. ( 4 ) 127 Chukovskaya, E.Ts. ( 2 . 2 ) 61 Chung, D.G. (1) 396 Chung, J.J. ( 2 . 1 ) 4 3 Chupka, E.I. ( 4 ) 274-279 Church, S.P. ( 2 . 2 ) 1 5 , 7 3 Ci, X. ( 3 . 5 ) 118 Ciano, M. ( 2 . 1 ) 142; ( 5 ) 99 Ciardelli, F. ( 3 . 6 ) 1 2 , 13; ( 4 ) 213, 220 Cik, G. ( 3 . 3 ) 12 Cilento, G. (1) 494 Claesens, F. (1) 30 Clark, J. ( 3 . 1 ) 46; ( 3 . 4 ) 155; ( 3 . 5 ) 15 Clark, S.F. ( 2 . 1 ) 155; ( 2 . 2 ) 112 Clark, T. ( 3 . 4 ) 94 Claudel, R. (1) 192 Clement, A. ( 3 . 4 ) 6 ; (3.6) 164 Clennan, E.L. ( 3 . 5 ) 67 Cloke, F.G.N. ( 2 . 2 ) 4 8 , 66 Closs, G.L. ( 1 ) 502 Coburn, J.T. ( 1 ) 33 409 Coghlan, M.J. ( 3 . 3 ) 47; (3.6) 50 Cohen, H. ( 2 . 1 ) 166 Cohen, R.E. ( 4 ) 117 Cohen, S.G. ( 3 . 5 ) 2 446 Colin, H. ( 3 . 1 ) 18 Collart, P. ( 4 ) 260 Collier, J.R. ( 3 . 7 ) 120 Collin, G.J. ( 3 . 3 ) 5 , 6 Collins, S. ( 2 . 3 ) 29; ( 3 . 6 ) 196 Comba, P. ( 2 . 1 ) 47 Come, J.H. ( 3 . 2 ) 11
Comi, D. ( 4 ) 113 Commes, K. ( 1 ) 341 Concepcion, J.I. ( 3 . 7 ) 187
Condie, C.C. ( 1 ) 337 Condorelli, G. ( 2 . 1 ) 70 Conesa, J.C. ( 5 ) 166 Connolly, J . S . ( 2 . 2 ) 112; ( 5 ) 1 3 , 126
Conte, J.C. ( 1 ) 257 Cook, D.R. ( 5 ) 126 Cooke, J . M . ( 4 ) 273 Cooksey, C.J. ( 2 . 2 ) 110 Cooper, S.L. ( 4 ) 137 Corbin, D.R. ( 3 . 1 ) 6 Corbin, G.A. ( 4 ) 117 Cornelisse, J. ( 1 ) 8 9 ; ( 3 . 4 ) 2 7 , 28, 31, 3 4 , 6 5 , 71 Correa da Silva, P.A. ( 2 . 1 ) 192 Cosito, C. ( 1 ) 404 Cossy, J. ( 2 . 3 ) 9; (3.2) 55 Costa, J. ( 3 . 6 ) 148 Costa, S.M.B. ( 2 . 2 ) 35 Costanzo, L.L. ( 2 . 1 ) 70 Cotsaria, E. ( 5 ) 134 Cottrell, C.E. ( 3 . 3 ) 47; ( 3 . 6 ) 50 Coulon, D.A. ( 4 ) 101 Courbon, H. ( 5 ) 175 Courtney, S.H. ( 1 ) 20; (3.3) 17 Couture, A. ( 3 . 6 ) 35 Cowlen, M.S. (1) 320 Cox, M.E. ( 4 ) 200 Coyle, J . D . ( 3 . 1 ) 2 ; ( 3 . 2 ) 1 2 0 , 141, 149, 150; (.3.3) 37; ( 3 . 6 ) 175, 180, 185, 189; ( 3 . 7 ) 111 Cozman, I . P . (3.7) 1 Crackel, R.L. ( 1 ) 313 Cragg, J.E. ( 3 . 2 ) 141 Craig, D.P. ( 1 ) 1 Creaser, 1.1. ( 2 . 1 ) 47, 110; ( 5 ) 9 8 Creed, D. ( 2 . 1 ) 6 ; ( 3 . 5 ) 42; ( 5 ) 8, 223 Creighton, J.R. ( 2 . 2 ) 30 Creutz, C. ( 2 . 1 ) 1 4 , 109 Crich, D. ( 3 . 7 ) 112, 113, 117 Crimmins, M.T. ( 3 . 2 ) 4 Cristol, S.J. ( 3 . 3 ) 4 6 , 93, 146-148; ( 3 . 4 ) 1620; (3.7) 178-180 Crivello, J . V . ( 4 ) 20, 21, 101 Croncher, M.D. ( 4 ) 202 Crosby, G.A. ( 1 ) 466;
561
Author Index ( 2 . 1 ) 5 6 , 162, 229; ( 2 . 2 ) 114 Cross, A.J. ( 1 ) 20 Croucher, M.P. ( 4 ) 248 Cruces Blanco, C. ( 1 ) 124 Csongar, C. ( 3 . 7 ) 3 7 , 38 Cuendet, P. ( 5 ) 187 Cuevas, A. ( 4 ) 424 Cui, G. ( 3 . 5 ) 1 4 7 , 148 Cuivas, A. ( 4 ) 321 Cukier, R.I. ( 1 ) 8 , 9 Culp, S.J. ( 3 . 3 ) 6 6 ; ( 3 . 6 ) 132 Cundall, R.B. ( 1 ) 101, 1 4 5 , 166, 398 Cuniberti, C. ( 4 ) 267 Cunningham, J. ( 5 ) 180 Cunningham, P.D. ( 3 . 2 ) 8 ; ( 3 . 4 ) 43 Cuppen, T.J.H.M. ( 3 . 4 ) 118 Currell, L.J. ( 1 ) 240; ( 3 . 3 ) 26 Cusso, F. ( 5 ) 235, 236 Cusumano, M. ( 2 . 2 ) 126 Cutler, A.R. ( 2 . 2 ) 125 Czochralsk, B. ( 1 ) 323
Dabestani, R. ( 3 . 4 ) 51 Daems, D. ( 1 ) 36 Dagen, A.J. ( 1 ) 382 Da Graca, M. ( 2 . 1 ) 216 Dai-Ho, G. ( 3 . 6 ) 137 Dailey , W.P ( 3 . 3 ) 7 3 Daino, Y. ( 3 . 3 ) 6 8 , 69 Dale, R.E. ( 1 ) 398 Dall-Acqua, F. ( 3 . 2 ) 48 Dallinger, R.F. ( 2 . 1 ) 88 Dalores Baena, M. ( 1 ) 369 Dalton, J.C. ( 2 . 3 ) 1 ;
.--
( 3 . 6 ) 194
Dalton, J.R. ( 3 . 2 ) 25 Daltrozzo, E. ( 1 ) 210 Daney, M. ( 2 . 3 ) 1 7 ; ( 3 . 4 ) 1 6 9 , 173
Daniel, C. ( 2 . 2 ) 103 Danieli, B. ( 3 . 2 ) 64 Danielsen, P.L. ( 4 ) 187 Danielzik, B. ( 4 ) 329 Danko, S . ( 1 ) 376 Dankowski, M. ( 3 . 7 ) 139 Danziger, J.L. ( 1 ) 331 Daraji, R.R. ( 3 . 2 ) 1 5 2 ; ( 3 . 7 ) 123
Darbarwar, M. ( 1 ) 199 Darcy, P.J. ( 3 . 4 ) 141 Dardoux, M. ( 2 . 1 ) 2 0 ; ( 5 ) 163
Darey, M.C.P. ( 3 . 2 ) 34 Darlak, K. ( 1 ) 350 Darmanyan, A.P. ( 3 . 5 ) 63
Darwent, J.R. ( 2 . 1 ) 6 4 ; (5) 79
Das, P.K. ( 1 ) 1 1 1 , 315, 455, 487, 124; 136; 136
463, 473, 476, 490; ( 3 . 2 ) 6 3 , ( 3 . 3 ) 6 4 , 135, (3.6) 54; (3.7)
Das, S. ( 2 . 1 ) 194 da Silva, A.G. ( 1 ) 257 Daub, G.H. ( 1 ) 100 Dauben, W.G. ( 3 . 2 ) 3 ; ( 3 . 3 ) 7 7 , 81
Daudey, J.P. ( 2 . 2 ) 8 0 D'Auria, M. ( 3 . 4 ) 9 7 , 9 8 ; ( 3 . 7 ) 149, 150
Dave, V. ( 3 . 2 ) 21 Davenport, L. ( 1 ) 4 4 , 4 5 , 321, 398
David, C. ( 4 ) 163 David, P.G. ( 2 . 1 ) 192 Davidson, G.A. ( 1 ) 370 Davidson, R.S. ( 1 ) 1 7 3 , 475; ( 2 . 1 ) 2 3 ; ( 3 . 3 ) 141; ( 3 . 5 ) 105; (3.7) 155; ( 4 ) 456; ( 5 ) 172, 206 Davies, A.N. ( 1 ) 19 Davies, G.M. ( 3 . 6 ) 169 Davies, H.G. ( 3 . 1 ) 30 Davis, H.F. ( 3 . 2 ) 63 Davoust, J. (1) 75 Davydov, E.Ya. ( 3 . 7 ) 81 Day, J.P. ( 2 . 2 ) 66
Deal Olivera, M.E.C.D. (1) 145 DeArmond, M.K. ( 2 . 1 ) 48 de Bernardez., E.R. ( 1 ) 70
De Boer, T.J. ( 3 . 5 ) 70 De Bruyn, V.H. ( 3 . 4 ) 6 4 ; ( 3 . 6 ) 74
Decicco, C. ( 3 . 2 ) 28 Dedolph, D.F. ( 3 . 7 ) 1 5 9 , 160
Defay, N. ( 3 . 4 ) 115 Degani, Y. ( 1 ) 3 0 2 ; ( 2 . 1 ) 125; ( 3 . 5 ) 2 6 ; ( 5 ) 1 0 9 , 110 Degl ' Innocenti, A. ( 2 . 3 ) 18 DeGraff, B.A. ( 1 ) 3 4 ; (2.1) 112 Degrief, H. ( 1 ) 201 De Guidi, G. ( 2 . 1 ) 70 de Haas, M.D. ( 1 ) 109 de Haut de Sigy, A. ( 3 . 4 ) 8 4 ; ( 3 . 6 ) 208 Deibel, M.R. (1) 344 Deiker, C. ( 4 ) 69 De Kanter, F.J.J. ( 3 . 4 ) 3 De Keukeleire, D. ( 3 . 2 )
2 7 ; ( 3 . 6 ) 205; ( 5 ) 127
De Lange, W.G.J. ( 2 . 2 ) 58 de la Rosa, F.F. ( 5 ) 12 De la Rosa, M.A. ( 3 . 5 ) 40; ( 5 ) 12
Delcourt, M.O. ( 2 . 1 ) 1 6 4 ; ( 5 ) 105, 106
De Leeuw, F.A.A.M.
(3.2)
99
Delfini, M. ( 4 ) 215 Del Giacco, T. ( 3 . 5 ) 110 Dell'Amico, M. ( 1 ) 159 Dellonte, S. ( 1 ) 8 1 , 90 DeLoach, J.A. ( 3 . 2 ) 4 De Lucchi, 0 . ( 3 . 2 ) 8 6 ; ( 3 . 6 ) 1 5 8 , 171; ( 3 . 7 ) 18 De March, P. ( 5 ) 9 3 , 151 Demas, J.N. ( 1 ) 3 4 ; ( 2 . 1 ) 112 de Mayo, P. (1) 5 1 , 312, 314; ( 3 . 1 ) 3 2 ; ( 3 . 2 ) 21; (3.3) 14, 21; ( 3 . 4 ) 164; ( 5 ) 216 Demchenko, A.P. ( 1 ) 278 De Mico, A. ( 3 . 4 ) 9 7 , 9 8 ; ( 3 . 7 ) 1 4 9 , 150 Demmer, D.R. ( 1 ) 339 Dempsey, M.E. ( 1 ) 320 Demuth, M. ( 3 . 2 ) 8 8 , 89 Demuynck, J. ( 2 . 2 ) 103 Denisov, V.Ya. ( 3 . 2 ) 166 Den Ouden, B. ( 3 . 3 ) 9 4 ; ( 5 ) 43 Densley, R.J. ( 4 ) 292 Deodhar, D.J. ( 3 . 7 ) 120 De Oliveira, S.M. ( 2 . 2 ) 69 De Paoli, M.A. ( 2 . 2 ) 6 9 ; ( 4 ) 313 Depew, M.C. ( 3 . 2 ) 164 Derker, C. ( 4 ) 70 Derrick, J.M. ( 2 . 1 ) 44 Dervan, P.B. ( 5 ) 131 De Ryck, P.H. ( 2 . 3 ) 52 Deschaux, M. ( 2 . 1 ) 207
De Schryver, F.C. (1) 3 6 , 201, 213, 330, 346; ( 2 . 1 ) 8 9 ; ( 4 ) 244, 260, 261 Deshayes, H. ( 3 . 5 ) 47 de Silva, A.P. ( 3 . 4 ) 143 Desilvestro, J. ( 2 . 1 ) 100; ( 5 ) 119 Deslauriers, H. ( 3 . 3 ) 5 , 6 Desvergne, J.P. ( 2 . 3 ) 1 7 ; ( 3 . 4 ) 8 4 , 169, 1 7 3 ; ( 3 . 6 ) 208 de Vaal, P. ( 3 . 4 ) 27 De Ville, G.Z. ( 3 . 4 ) 126 Devys, M. ( 3 . 5 ) 124
Author Index
562 Dewar, J.C. ( 2 . 2 ) 9 2 ; (3.6) 196
Dewey, T.G. ( 1 ) 373 de Wolf, W.H. ( 3 . 3 ) 75; (3.4) 3
De Zeeuw, P. (3.3) 88 Dhawan, S.N. (3.5) 7 Dias, A.R. ( 2 . 2 ) 35 Diaz, E. ( 3 . 1 ) 3 1 ; (3.2) 49
Dibenedetto, J. ( 2 . 1 ) 4 Dickens, B. (49 328 Dickinson, J.T. ( 4 ) 288 Di Cocco, M.E. ( 4 ) 215 Dietz, F. ( 1 ) 3, 241; ( 4 )
Donnigue, R.P. ( 4 ) 222 Donohue, T. ( 2 . 1 ) 224 Dopp, D. ( 3 . 4 ) 4 7 , 153 Dordet, Y. ( 5 ) 243 Dore, P. ( 2 . 1 ) 226 Dorofeev, Yn.1. ( 4 ) 327 Dorr, G. (5) 62 Doshi, S.V. ( 1 ) 504 Dote, T. ( 1 ) 239; ( 3 . 3 ) 29
Dotsenko, V.P. ( 4 ) 80 Doubleday, C.E. ( 1 ) 143,
144; ( 3 . 1 ) 27; (3.4) 131, 187 Doukas, A.G. ( 1 ) 377 Dovbii, E.V. ( 4 ) 414 441, 442 Diez-Masa, J.-C. ( 3 . 1 ) 18 Dowling, S.D. ( 4 ) 207 DiGiambattista, M. ( 1 ) Downs, A.J. ( 2 . 3 ) 38 Dracy, P.J. ( 3 . 2 ) 126 404 Dignam, M.J. ( 5 ) 230 Drake, J.M. (1) 200 Dikareva, L.M. ( 2 . 2 ) 37 Drake, R.C. ( 1 ) 26 Dillinger, R. ( 2 . 2 ) 4 1 Dreeskamp, H. ( 1 ) 149; (3.1) 13 Dillon, S.B. ( 5 ) 34 Dilung, 1.1. ( 1 ) 472; Dreher, B. (2.3) 4 8 , 49 (2.1) 55; ( 4 ) 9 1 Dressel, J. ( 3 . 3 ) 91 Ding, Y.S. ( 4 ) 137 Dressick, W.J. ( 2 . 1 ) 134 Dirk, N.A. ( 4 ) 205 Dreyfus, R.W. ( 4 ) 363 Disanayaka, B.W. ( 3 . 2 ) 32 Druliner, J.D. ( 3 . 7 ) 2 Disdier, J. ( 5 ) 175 Duan, Y. ( 2 . 1 ) 220 Dittrich, U. ( 3 . 6 ) 160 Dubey, R. ( 3 . 5 ) 9 4 , 9 5 , Dixon, D.A. ( 2 . 3 ) 7 114 Dixon, D.W. ( 3 . 5 ) 121 Dubois, D.L. ( 2 . 2 ) 112 Dmitrieva, N.B. ( 2 . 1 ) 136 Ducasse, A . ( 1 ) 286 Dmitrieva, S.Yu. ( 4 ) 323 Duchgne, K.-H. ( 3 . 7 ) 124 Do, S.R. ( 3 . 4 ) 144, 183; Dudeja, P.K. ( 1 ) 400 Dudek, M. ( 2 . 1 ) 60 (3.6) 45 Doany, F.E. ( 1 ) 236; Dudkiewicz, J. ( 1 ) 248 Duerner, G. ( 3 . 2 ) 103, ( 3 . 3 ) 24 Dobashi, S. ( 3 . 5 ) 73 104 Dobrov, E.N. (1) 392 Duerr, H. ( 5 ) 62 Dobvescu, V. ( 4 ) 345 Duesler, E.N. ( 3 . 2 ) 140; Dodsworth, E.S. (2.1) 131 ( 3 . 6 ) 126 Dopp, D. ( 3 . 6 ) 120, 153 Duhaime, R.M. ( 3 . 5 ) 20 Dogan, B.M.J. ( 3 . 3 ) 111 Dunford, H.B. (1) 497 Dogra, S.K. ( 1 ) 127, 136, Dung, D. ( 2 . 1 ) 100; ( 5 ) 137 119 Doherty, N.M. (2.2) 38 Dunkin, I.R. ( 3 . 7 ) 42, Dohmaru, T. ( 2 . 3 ) 28; 49, 61 ( 3 . 6 ) 203 Dunn, R . ( 4 ) 200 Doi, E. ( 3 . 6 ) 31 Dunn, D.A. ( 1 ) 500; ( 3 . 2 ) Doi, M. ( 3 . 4 ) 136; ( 3 . 6 ) 105 Dupuy, C. ( 2 . 1 ) 40 34 Doi, T. ( 4 ) 34 Duran, M. ( 5 ) 1 6 3 Domen, K. ( 2 . 1 ) 33; ( 5 ) Duran, N. ( 1 ) 413; ( 2 . 1 ) 2 5 , 27, 190 20; ( 4 ) 356 Domenech, J. ( 5 ) 201 Dureja, P. ( 3 . 3 ) 31, 32 Dominey, R.N. ( 3 . 3 ) 22 Durmis, J. ( 4 ) 386, 403 Dominguez, D. ( 3 . 7 ) 146 Durocher, G. ( 3 . 5 ) 138 Donald, L. ( 3 . 4 ) 104 Dutch, A. ( 1 ) 55 Donaldson, E.E. ( 4 ) 288 Dvornikov, I.V. ( 3 . 5 ) 6 2 Donati, D. ( 3 . 2 ) 3 9 ; Dzau. V.J. ( 1 ) 341 ( 3 . 6 ) 88, 125 Dzhabiev, T:S. ( 3 . 5 ) 31-
33; ( 5 ) 1 4 3
Dzhafarov, A.S. ( 4 ) 410 Dziemionowicz, T.S. ( 4 ) 273
Eaton, B. (2.2) 107 Eaton, D.F. ( 1 ) 150 Eaton, P.E. (3.3) 108 Ebara, N. (1) 485 Ebbesen, P. ( 3 . 2 ) 101 Ebbesen, T.W. (1) 154, 188, 423; (3.4) 85
Eberbach, W. ( 3 . 3 ) 105, 106; ( 3 . 6 ) 100
Eberlein, T.H. ( 3 . 7 ) 121 Eckert, P. (3.7) 86 Eckl, E. (3.6) 212 Ecoto, J. (3.1) 18 Ediger, M.D. (4) 222 Edmondson, G. ( 4 ) 452 Eftink, M.R. (1) 340 Egan, L.S. ( 4 ) 202 Egana, H. ( 4 ) 122 Egorochkin, A.N. ( 2 . 2 ) 27 Eguchi, S. ( 3 . 6 ) 37 Egusa, C. (3.2) 155; ( 3 . 6 ) 135
Eichenberger, H. ( 3 . 2 ) 57 Eichler, R. ( 4 ) 453 Eisenberg, M. ( 1 ) 403 Eisenberg, R. ( 2 . 2 ) 120 Eisenthal, K.B. ( 1 ) 226 Eisinger, J. ( 1 ) 54 Elbanowski, M. ( 2 . 1 ) 202 El-Bayoumi, M.A. (1) 125 Elferink, V.H.M. (3.2) 70; ( 3 . 4 ) 142; ( 3 . 6 ) 26
Elger, W. ( 3 . 1 ) 16 Elizarova, L.E. ( 4 ) 428 Elliott, C.M. ( 2 . 1 ) 97, 98; ( 5 ) 96
Ellis, A.B. ( 2 . 1 ) 217; ( 2 . 2 ) 138
Ellis, R.W. ( 3 . 7 ) 4 1 Ellul, H. ( 1 ) 218; (2.1) 247
Elofson, R.M. ( 5 ) 214 Elsaesser, A. ( 3 . 7 ) 129 Elsaesser, T. ( 1 ) 206 El-Sayed, M.A. (1) 58 Elschenbroich, C. ( 2 . 2 ) 38
El-Tamany, S. ( 3 . 4 ) 108 El'tsov, A.V. ( 3 . 3 ) 1 2 ; ( 3 . 6 ) 216
Emeren, A. ( 5 ) 215 Encinas, M.V. ( 1 ) 147, 288, 458; (3.5) 9
Endicott, J.F. (2.1) 7 , 49. 111
Endo; A. (2.2) 8 4
563
Author Index Endoh, M. ( 3 . 2 ) 122 Enea, 0. ( 5 ) 179 Eneinas, M.V. ( 4 ) 82 Eng, K.K. ( 3 . 1 ) 28; ( 3 . 7 )
127, 128; ( 3 . 6 ) 2 8 , 29
Feitelson, J. ( 1 ) 468 Fekarurhobo, G.K. ( 3 . 1 ) 49
Felberg, J.D. ( 3 . 7 ) 41 Engel, K. ( 2 . 2 ) 5 Felder, B.N. ( 4 ) 397 Engel, P.S. ( 3 . 7 ) 26 Felder, P. ( 2 . 3 ) 33 Engelhardt, H.E. ( 2 . 2 ) 22 Feldhues, M. ( 3 . 7 ) 104106 Engh, R.A. ( 1 ) 328 Feldkamp, L.A. ( 1 ) 411 Engst, P. ( 2 . 3 ) 45 Epling, G.A. ( 3 . 4 ) 8 8 , 89 Feldman, K.S. ( 3 . 2 ) 11 Felisberti, I.M. ( 4 ) 114 Epperlein, J. ( 3 . 6 ) 8 Equsa, S . ( 4 ) 256 Felker, P.M. ( 3 . 3 ) 20; ( 5 ) 131 Erbs, W. ( 2 . 1 ) 102; ( 5 ) Fellow, R. ( 3 . 6 ) 174 120 Fendler, J.H. (1) 292; Erker, C. ( 2 . 2 ) 4 , 5 ( 5 ) 215 Erman, B. ( 4 ) 270 Feng, L. ( 3 . 6 ) 63 Ernst, L. ( 3 . 4 ) 108 Ershov, Yu.A. ( 4 ) 414 Feng, S . ( 4 ) 106 Feng, X. ( 3 . 5 ) 80; ( 4 ) Ertl, P. ( 3 . 6 ) 2 85-88, 90,. 95 Eryavec, G. ( 2 . 1 ) 131 Fenzion, B. (5) 38 Escudero, J.L. ( 1 ) 169 Fernandez, A. ( 2 . 1 ) 242, Esplugas, S . ( 3 . 6 ) 148 243; ( 5 ) 7 2 , 73 Esquivel, B. ( 3 . 2 ) 49 Fernandez, P.F. ( 2 . 3 ) 40 Euler, K. ( 3 . 3 ) 74 Fernandez Martin, J.-A. Evans, C. ( 1 ) 419 Evans, S. ( 3 . 1 ) 34, 36 ( 3 . 3 ) 4 1 , 42; ( 3 . 6 ) 48 Evseev, A.M. ( 3 . 7 ) 102 Ferraudi, G. ( 1 ) 470; ( 2 . 1 ) 194; ( 2 . 2 ) 6 5 , Eychmuller, A. ( 3 . 6 ) 42 134 Eyring, E.M. ( 2 . 2 ) 60 Ferri, A. ( 2 . 1 ) 71 Ferrier, R.J. ( 3 . 2 ) 60 Fery-Forgues, S. ( 3 . 4 ) Fabian, W. ( 3 . 3 ) 123; 23
( 3 . 6 ) 9 5 , 102; ( 4 ) 448 Fabricius, N. ( 4 ) 329 Fagan, M.H. ( 1 ) 373 Fagan, P.J. ( 2 . 2 ) 94 Fakazawa, Y. ( 3 . 7 ) 125 Fan, F.R. ( 4 ) 280 Fan, M. ( 3 . 6 ) 122 Fan, P. ( 3 . 6 ) 122 Fanghaenel, E. ( 3 . 7 ) 82 Fanter, D.L. ( 4 ) 351 Fanton, E. ( 4 ) 310 Farwaha, R. ( 3 . 2 ) 21 Fasani, E. ( 3 . 4 ) 188; ( 3 . 6 ) 65 Fassler, D. ( 3 . 3 ) 7 9 ; ( 3 . 5 ) 9 9 , 149 Fatinikun, K.O. ( 4 ) 317 Fatti, G. ( 4 ) 220 Faucitano, A. ( 4 ) 314, 393 Faulkner, L.R. ( 1 ) 186 Faure, L. ( 1 ) 192 Fauri, J. ( 4 ) 69 Fawcett, N.C. ( 3 . 5 ) 4 2 ; ( 5 ) 223 Fayer, M.D. ( 1 ) 438; ( 4 ) 222 Federici, J. ( 1 ) 31 Feigel'man, V.M. ( 3 . 4 )
9 3 ; ( 3 . 6 ) 103
Fissi, A. ( 3 . 6 ) 1 2 , 13 Fisz, J.J. ( 1 ) 11 Fizeb, M. ( 4 ) 69 Flamigni, L. ( 1 ) 81 Flammersheim, H.J. ( 4 ) 4 1 , 71
Fleming, G.R. ( 1 ) 2 0 , 328; ( 3 . 3 ) 17
Fleming, S.A. ( 3 . 2 ) 2 0 ; (3.3) 60, 61; (3.6) 9
Fletcher, S.C. ( 2 . 2 ) 95 Fletcher, T.R. ( 2 . 2 ) 11 Flom, S.R. ( 1 ) 223, 231 232
Flores, J. ( 1 ) 54 Floret-David, D. ( 1 ) 462 Florio, E. ( 3 . 4 ) 8 8 , 89 Fojtik, A. ( 1 ) 240; ( 3 . 3 ) 26
Fok, N.V. ( 4 ) 51 Fokin, E.P. ( 3 . 2 ) 167 Folcher, G. ( 2 . 1 ) 221; ( 5 ) 135, 222
Fonken, G.J. ( 3 . 4 ) 138 Font, J. ( 5 ) 9 3 , 151 Fontanges, R. ( 5 ) 35 Foote, C.S. ( 1 ) 8 4 ; ( 3 . 5 ) 4 , 125
Forat, F.P. ( 5 ) 35 Ford, P.C. ( 2 . 1 ) 4 , 153, 159; ( 2 . 2 ) 122
Formenti, M. ( 2 . 1 ) 2 6 ; (5) 3
Formosinho, S.J. ( 1 ) 2 ,
Fessenden, R.W. ( 1 ) 487 296; ( 2 . 1 ) 216 Fessner, W.-D. ( 3 . 3 ) 112; Fornasiero, D. ( 1 ) 202, ( 3 . 4 ) 159
Fetizon, M. ( 3 . 1 ) 1 8 ; ( 3 . 2 ) 36
Fetterolf, M.L. ( 2 . 1 ) 83 Field, M. ( 1 ) 400 Fields, R.A. ( 2 . 1 ) 41 Fife, D.J. ( 2 . 2 ) 1 3 5 ; ( 3 . 3 ) 102; ( 5 ) 44
Figge, H. ( 3 . 7 ) 16 Findak, D.C. ( 3 . 6 ) 168 Findsen, E.W. (1) 367 Finey, P.A. ( 1 ) 74 Fink, J. ( 3 . 6 ) 21 Finter, J. ( 4 ) 359 Firl, J. ( 3 . 7 ) 140 Fischer, A.B. ( 1 ) 221 Fischer, E. ( 1 ) 228, 230 Fischer, G. ( 3 . 2 ) 104-
393
Forrester, J. ( 3 . 4 ) 30 Forster, L.S. ( 2 . 1 ) 42 Fouassier, J.P. ( 1 ) 461, 462; ( 4 ) 16
Foulger, B.E. ( 3 . 4 ) 30 Fournier, J. ( 1 ) 418 Foust, D.F. ( 2 . 2 ) 9 Fox, M.A. ( 2 . 1 ) 9 6 ; ( 2 . 2 ) 136;' ( 3 . 3 ) 63; ( 4 ) 81
Fozard, H.A. ( 1 ) 400 Francisco, C.G. ( 3 . 7 ) 187 Frank, A.J. ( 2 . 1 ) 179 Frank, C.W. ( 1 ) 266; ( 4 ) 247, 257, 262, 268
Frank, P. ( 4 ) 326 Frankel, E.N. ( 2 . 2 ) 28 Frankel, R.B. ( 2 . 2 ) 92 Frankowski, A. ( 3 . 6 ) 69 106, 113; ( 3 . 4 ) 160; Franz, L.H. ( 3 . 2 ) 159 ( 3 . 6 ) 105; ( 3 . 7 ) 25 Fratev, F. ( 1 ) 126 Fischer, J.W. ( 3 . 3 ) 109 Frauenrath, H. ( 3 . 3 ) 138 Fischer, R.T. ( 1 ) 320 Freas, R.B. ( 2 . 2 ) 10 Fischman, D.A. ( 1 ) 406 Fredrickson, G.H. ( 4 ) 268 Fisera, L. ( 3 . 6 ) 58 Fiser-Jakic, L. ( 3 . 4 ) 143 Freedman, K.A. ( 1 ) 224, 225, 233: ( 3 . 6 ) 3 Fisher, K. ( 3 . 4 ) 37
Author Index
5 64 Freeman, M.J. ( 2 . 2 ) 40 F r e e r , A.A. ( 3 . 6 ) 144 F r e e r , J. ( 4 ) 356 F r e i , B. ( 3 . 1 ) 35; ( 3 . 2 ) 56; ( 3 . 2 ) 57; ( 3 . 3 ) 70, 71, 133; ( 3 . 7 ) 133-135, 137 F r e i , H. (1) 77; ( 3 . 5 ) 58 F r e i l i c h , S.C. ( 1 ) 501 F r e i r e , R . ( 3 . 7 ) 186, 187 F r e i s e r , B.S. ( 2 . 2 ) 7 F r e i t a g , B.-J. ( 3 . 2 ) 103 F r e i t a g , R.A. ( 2 . 1 ) 9 7 , 98; ( 5 ) 9 6 F r e y e r , A.J. ( 3 . 2 ) 11, 111; (3.6) 85 Friedman, J.M. ( 1 ) 367 F r i e d r i c h , C. ( 4 ) 195 F r i n g s , R.B. ( 4 ) 147 F r i n k , M.E. ( 1 ) 470; ( 2 . 1 ) 153, 159 F r i p i a t , J. ( 2 . 1 ) 137; ( 5 ) 30, 117 F r i t z , H. ( 3 . 3 ) 106, 112, 113; ( 3 . 4 ) 159; ( 3 . 6 ) 1 7 , 100, 105 F r i t z , M.J. ( 3 . 7 ) 56 Frolow, F. ( 3 . 1 ) 1 1 Fryde, C.A. ( 4 ) 347 Fryzuk, M.D. ( 2 . 2 ) 121 Fu, S. ( 4 ) 382, 411 Fu, W.K. ( 2 . 2 ) 96 F u c a l o r o , A.F. ( 2 . 1 ) 42 F u e k i , K. ( 4 ) 303, 304 Fueno, T. ( 3 . 5 ) 6 5 F u j i e , H . ( 5 ) 94 F u j i h a r a , M. ( 2 . 1 ) 35 F u j i i , N. ( 4 ) 112 F u j i m o r i , T. ( 3 . 6 ) 106 Fujimoto, M. ( 2 . 1 ) 6 8 F u j i n a m i , M. ( 3 . 2 ) 31 F u j i o k a , T. ( 2 . 1 ) 21 F u j i t a , T. ( 4 ) 396; ( 5 ) 17 F u j i w a r a , M. ( 5 ) 118 F u j i w a r a , T. ( 5 ) 69 Fukaya, C. ( 3 . 2 ) 110 Fukishima, T. ( 4 ) 375 Fukuda, H. ( 4 ) 130, 157 Fukuda, Y. ( 1 ) 452 Fukumoto, K. ( 3 . 5 ) 127 Fukumoto, T. ( 2 . 3 ) 28; (3.6) 203 Fukumura, H. ( 1 ) 6 3 Fukunaga, T . ( 3 . 3 ) 130 Fukushima, M. (1) 457 Fukuzumi, S. ( 3 . 5 ) 112 Fu-Mian L i ( 4 ) 32 F u r a k o s h i , N . ( 3 . 6 ) 39 Furlong, D.N. ( 1 ) 297; ( 2 . 1 ) 114 Furue, M. ( 4 ) 233; (5)
Gasyna, Z. ( 2 . 1 ) 239 G a t e c h a i r , L.R. ( 4 ) 13 G a u g l i t z , G. (1) 244 Gautron, R. (1) 434 Gauvin, P. ( 4 ) 331 G a v r i l i n a , L.M. ( 4 ) 277 G a v r i l y u k , R.P. ( 4 ) 370 Gazel, A. ( 4 ) 305 Gaziev, S.A. ( 2 . 1 ) 219 G e b i c k i , J. ( 3 . 5 ) 1 6 Geenevasen, J.A.J. ( 3 . 2 ) 6 9 , 102 Gabe, E. ( 3 . 1 ) 39; ( 3 . 4 ) G e h r i s c h , R. ( 4 ) 120, 121 151; ( 3 . 5 ) 11 G e i g e r , D. ( 2 . 2 ) 6 5 , 134 G e i r s s o n , J. ( 3 . 5 ) 116 G a b r i e l , R. ( 3 . 5 ) 98 Gaceva-Bogreva, G. ( 4 ) Geisel, M. ( 3 . 7 ) 182 Genkin, V.N. ( 4 ) 325, 378 109 Gadd, G.E. ( 2 . 2 ) 14 Geoffroy, G.L. ( 2 . 2 ) 44; Gafney, H.D. ( 2 . 1 ) 122; ( 4 ) 48 George, C.A. ( 2 . 3 ) 24, ( 2 . 2 ) 42 25; ( 4 ) 158 Gahan, L.R. ( 2 . 1 ) 4 7 , George, M.V. ( 1 ) 487; 110; ( 5 ) 9 8 G a i r n s , R.S. (3.6) 166; ( 3 . 2 ) 6 3 , 124; (3.3) 135; (3.6) 54; ( 3 . 7 ) (3.7) 98, 99 G a l k i n , B.Ya. (2.1) 227 136 G a l l a g h e r , M . J . ( 3 . 3 ) 39; Georgieva, T. ( 4 ) 353 ( 3 . 7 ) 142 Geraghty, N.W.A. ( 3 . 2 ) 8 ; G a l l e g o , M.G. ( 3 . 2 ) 75, (3.4) 43 76; (3.4) 13; ( 3 . 6 ) 46 G e r a l d , R . (1) 175 G a l l h u b e r , E. ( 2 . 1 ) 81 Gerard, D. (1) 335, 358 G a l l i , C. (3.7) 157, 166; Gerasimenko, Yu.E. (3.2) ( 4 ) 166 168 Gerasimova, T.N. ( 3 . 5 ) G a l l u c c i , R.R. ( 3 . 7 ) 74 120 Gandhi, P. ( 3 . 5 ) 9 4 , 9 5 , 114 Gergely, J. ( 1 ) 363, 364 G a n d o l f i , M.T. ( 2 . 1 ) 103; G e r h a r t z , W. ( 2 . 2 ) 1 7 G e r l o c k , J.L. ( 4 ) 394, (5) 91 Ganjoo, A. ( 1 ) 467 395 G e r r a r d , D.L. ( 4 ) 186 G a n r i a , E.S. ( 4 ) 119 Ganz, A.M. (1) 281 G e r s d o r f , J. ( 3 . 1 ) 1 2 ; Ganzer, G.A. (3.7) 4 ( 3 . 4 ) 24 Gershuni, S. ( 2 . 1 ) 118; Gao, Z. ( 4 ) 106 Garacia Sahchez, F. ( 1 ) 166 Gethner, J.S. ( 2 . 2 ) 52 124 G e t o f f , N. ( 5 ) 22 Garbuz, N.I. ( 3 . 5 ) 117 Geue, R . J . ( 2 . 1 ) 110; ( 5 ) Garcia, B. (3.7) 116 Garcia, H. ( 3 . 4 ) 180 98 Gezalov, Kh.B. ( 4 ) 294 G a r c i a , J. ( 3 . 2 ) 49 Ghiggino, K.P. (1) 5 2 , Garcia, N.A. ( 1 ) 479 G a r d e t t e , J.L. ( 4 ) 346 53, 228, 237 Ghiron, D.A. ( 1 ) 168 G a r n e r , A . (3.2) 95 G a r r i d o , J. ( 4 ) 8 2 Ghosh, S. (1) 488; (3.2) G a r r i s o n , J . B . ( 4 ) 366 113; ( 3 . 3 ) 115, 122 Gasanov, R.G. ( 2 . 2 ) 61 Ghosh, T. (3.3) 104 Giamello, E. (5) 168 Gasanova, L.V. (3.5) 31; 32 G i a n n o t t i , C. (1) 220; Gasdaska, J . R . ( 3 . 7 ) 40 (2.1) 221; (3.5) 118; Gasking, D . I . ( 2 . 3 ) 1 4 ( 5 ) 70 Gassman, P.G. (3.3) 132; Giasson, R . (3.5) 10; ( 3 . 6 ) 210 ( 3 . 6 ) 72 Gaston-Bonhomme, Y. ( 5 ) Gibson, D.H. (2.2) 32 Giesse, R. ( 4 ) 114, 313 20
152 F u r u s a k i , A. ( 3 . 2 ) 4 0 , 42 F u r u t a , H. (3.4) 80 F u r u t a , T. ( 3 . 2 ) 81, 8 2 , 85 Furuya, Y. ( 3 . 4 ) 81; ( 3 . 6 ) 10 F u s i , S. ( 3 . 2 ) 39; (3.6) 88, 125 F u s s , A. ( 3 . 7 ) 36
Author Index G i l , M.H. ( 4 ) 111 G i l b e r t , A. ( 3 . 4 ) 2 1 , 2 2 , 3 0 , 4 5 , 5 3 , 68 G i l b e r t , B.C. ( 3 . 7 ) 48 G i l l , S. ( 3 . 5 ) 43 G i l l , U.S. ( 2 . 2 ) 86 G i l l b r o , T. ( 1 ) 214, 242; ( 3 . 3 ) 1 6 ; ( 4 ) 438 G i l p i n , R.W. ( 5 ) 34 G i l y a n o v s k i i , P.V. ( 2 . 1 ) 188 Gimenez, M. ( 5 ) 21 G i n i g e r , R. ( 1 ) 117 Ginsberg, A. ( 1 ) 360 Ginsburg, A.P. ( 2 . 1 ) 165 Ginsburg, D. ( 3 . 3 ) 111 Ginsburg, H. ( 3 . 7 ) 1 6 8 , 169 G i o r g e t t i , A. ( 2 . 1 ) 1 9 6 , 197 G i r i , B.P. ( 3 . 1 ) 3 9 , 4 0 , 47; ( 3 . 4 ) 150, 151; ( 3 . 5 ) 11 Gismondi, T.E. ( 2 . 2 ) 5 4 ; ( 4 ) 374 Gitzel, J. ( 2 . 1 ) 2 3 3 ; ( 5 ) 66 G i u f f r i d a , S. ( 2 . 1 ) 7 0 Glasser, N. ( 1 ) 167 Gleiter, R. ( 1 ) 93 G l e i x n e r , G. ( 4 ) 67 Glenneberg, J. ( 3 . 2 ) 103 G l e n t o , G. ( 1 ) 497 Gleria, M. ( 4 ) 355 Gliemann, G. ( 2 . 1 ) 1 7 6 ; ( 2 . 2 ) 41 G l i e s i n g , S. ( 3 . 3 ) 7 9 G l i n c h i k o v , S.V. ( 5 ) 114 Glinski, R.J. (2.3) 7 Glock, V. ( 3 . 7 ) 16 G l o v e r , S.A. ( 3 . 5 ) 1 0 0 ; ( 3 . 7 ) 100 G l o v e r , S.G. ( 2 . 1 ) 42 Gnanaguru, K. ( 3 . 2 ) 4 3 , 45 Goan, K. ( 3 . 3 ) 8 Godburt, E. ( 4 ) 216 Goedeweeck, R. ( 1 ) 330, 346 Goedken, V.L. ( 2 . 2 ) 1 3 9 ; ( 3 . 4 ) 51 G o e l l e r , G. ( 1 ) 210 C o r n e r , H. ( 1 ) 238, 240, 4 4 3 ; ( 2 . 1 ) 242, 243; ( 3 . 3 ) 1 5 , 25-27; ( 5 ) 72, 73 G o e t z b e r g e r , A. (5) 238 G o z l e r , B. ( 3 . 6 ) 8 4 Gohre, K. ( 3 . 5 ) 55 Gold, J.S. ( 2 . 1 ) 82 Goldener, U. ( 3 . 3 ) 7 0 , 7 1 ; ( 3 . 7 ) 134
565 G o l ' d f a r b , E.I. ( 3 . 7 ) 1 Golding, S.L. ( 3 . 7 ) 100 Goldman, A.S. ( 2 . 2 ) 4 7 , 100, 101 Gole, J.L. ( 2 . 3 ) 7 Golikov, I.V. ( 4 ) 156 G o l l n i c k , K. ( 1 ) 481; ( 3 . 5 ) 102 Golombek, M. ( 1 ) 7 9 Golovanov, S.P. ( 2 . 1 ) 136 Golovina, A.P. ( 2 . 1 ) 136 Gomes, A.G.L. ( 1 ) 212 Gomez, P.M. ( 4 ) 411 Gomez-Fernandez, J.C. ( 1 ) 369 Gondo, Y. ( 1 ) 440 Gong, B. ( 4 ) 131 Gonzalez, L.A. ( 4 ) 320 Gonzalez, R. ( 3 . 4 ) 46 Gonzalez-Elipe, A.R. ( 5 ) 166 Gooden, R. ( 4 ) 352 Goodin, J.W. ( 3 . 3 ) 141 Goodman, J.L. ( 1 ) 152 Goodwin, D. ( 1 ) 4 7 5 ; ( 3 . 5 ) 105 Goodwin, J.W. ( 3 . 7 ) 155 Goodwin, K.V. ( 2 . 1 ) 11 G o o i j e r , C. ( 1 ) 116 Goosen, A. ( 3 . 5 ) 1 0 0 ; ( 3 . 7 ) 100 Gopidas, K.R. ( 1 ) 4 8 7 ; (3.2) 63 Gorman, A.A. ( 1 ) 4 2 0 , 474; ( 3 . 5 ) 6 0 Gornostaev, L.M. ( 3 . 7 ) 93 Gorodetsky, G. ( 4 ) 365 Gorodova, L.V. ( 5 ) 107 Gorovkov, A.T. ( 4 ) 369 Gorsane, M. ( 3 . 4 ) 1 1 4 , 115 Gorshkov, N.G. ( 2 . 1 ) 219 Gosh, P. ( 4 ) 92 Goswami, P.C. ( 3 . 1 ) 32 G o t t h a r d t , H. ( 3 . 2 ) 1 1 2 ; ( 3 . 6 ) 19 G o t t s c h a l k , P. ( 1 ) 478 Gould, I . R . ( 1 ) 1 4 3 , 289, 304, 4 6 4 , 4 9 2 ; ( 3 . 1 ) 7 ; ( 3 . 7 ) 4 0 , 52 Goursot, A. ( 2 . 1 ) 180 Goyal, I . C . ( 1 ) 379 G o z l e r , B. ( 3 . 2 ) 109 Grabarek, Z. ( 1 ) 364 Grabielle-Madelmont, C . ( 1 ) 399 Grabowski, Z.B. ( 1 ) 435 G r a e t z e l , C.K. ( 3 . 5 ) 137 Graetzel, M. ( 2 . 1 ) 2 2 , 100; ( 3 . 5 ) 1 3 7 ; ; ( 5 ) 119, 186. 1 8 7 , 194. 206; 2 1 1 ; 2 2 4 -
Graham, D.J. ( 1 ) 450 G r a i f e r , A.Yu. ( 5 ) 200 Gramain, J.C. ( 3 . 5 ) 141 Granchak, V.M. ( 4 ) 153 Grancludon, P. ( 3 . 6 ) 35 Granger, R. ( 2 . 2 ) 34 Granozzi, G. ( 2 . 2 ) 8 0 , 8 1 Granshak, V.M. ( 4 ) 9 1 G r a n t , E.R. ( 2 . 2 ) 8 8 G r a n t , H.G. ( 3 . 5 ) 9 2 G r a n t , R.D. ( 3 . 5 ) 18 Grasse, P.B. ( 3 . 7 ) 44 G r a t t i n i , F. ( 4 ) 3 1 4 , 393 G r a t t o n , E. ( 1 ) 2 4 , 3 8 , 3 9 , 260 G r a v e l , D. ( 3 . 5 ) 1 0 ; ( 3 . 6 ) 7 2 , 73 Gray, A.B. ( 3 . 2 ) 10 Gray, H.B. ( 2 . 1 ) 149 Gray, T.H. ( 1 ) 203 Grayson, D.H. ( 3 . 2 ) 33 Grayson, M.A. ( 4 ) 351 Grebenik, P. ( 2 . 2 ) 8 Green, J.C. ( 2 . 2 ) 48 Green, K.E. ( 3 . 3 ) 110 Green, M. ( 2 . 2 ) 4 0 ; ( 5 ) 214 Green, M.L.H. ( 2 . 2 ) 48 Green, P.N. ( 4 ) 8 3 , 8 4 Green, W.A. ( 4 ) 8 3 , 8 4 Greenberg, D.B. ( 5 ) 42 Greene, B . I . ( 1 ) 1 5 3 , 2 1 9 , 236; ( 3 . 3 ) 24 G r e g o i r e , F. ( 5 ) 21 Gregory, M.F. ( 2 . 2 ) 98 Grellmann, K.-H. (3.1) 5 3 ; ( 3 . 6 ) 3 8 , 42 G r e s a l f i . N.J ( 2 . 2 ) 19 Gretz, J: ( 5 ) 16 G r e v e l s , F.W. ( 2 . 2 ) 1 5 , 1 7 , 73 Griesser, F. 1 ) 273 G r i f f i n , G.L. ( 2 . 1 ) 2 7 ; ( 5 ) 191 G r i f f i n , G.W. ( 3 . 3 ) 1 3 6 ; ( 3 . 5 ) 78 G r i f f i n g , B.F. ( 4 ) 326 G r i g o r e v a , G.L. ( 4 ) 286 G r i g o r o v , I . ( 1 ) 323 G r i l l e r , D. ( 3 . 7 ) 4 8 , 49 Grime. W. ( 3 . 3 ) 139 Grimshaw, J. ( 3 . 4 ) 143 G r i s k i n a , A.D. ( 4 ) 173 G r i t s a n , N.P. ( 2 . 1 ) 1 9 1 ; ( 3 . 2 ) 167 Grosch, W. ( 3 . 7 ) 140 Grossman, N. ( 4 ) 443 Gruen, H. ( 3 . 3 ) 27 Grutzmacher, H.-F. ( 3 . 6 ) 160 Grummt, U.-W. (3.5) 99; (3.6j 5, 6 , 8
566 Grund, C. ( 3 . 3 ) 112; ( 3 . 4 ) 159 G r u t s c h , P . A . ( 2 . 2 ) 129 Gryczynski, I. ( 1 ) 348, 350, 384, 456 Grzonka, Z. ( 1 ) 350 Gu, B. ( 5 ) 186 Guard-Friar, D. ( 1 ) 261 G u a r r , T. ( 5 ) 160 Gudgin Templeton, E.F. ( 1 ) 123 Gudzera, S.S. ( 4 ) 6 8 , 75 Guedel, H.U. (2.1) 51 Guenther, U. ( 3 . 3 ) 51 Guenzburger, D.J.R. (2.2) 69 Guerry-Butty, E. ( 1 ) 91 Guesten, H. ( 1 ) 194, 195 Gugliemo, G. ( 2 . 2 ) 126 Gugumus, F.L. ( 4 ) 389 G u i g l i a n o , R.P. ( 1 ) 128; ( 3 . 6 ) 67 G u i l l e t , J.E. (3.4) 152; (3.5) 17; ( 4 ) 1 6 7 , 179; 226, 251, 299, 354 Guinand, G. (3.4) 1 7 3 Guinaudeau, H. ( 3 . 2 ) 109; (3.6) 84 G u l o t t y , R . J . ( 1 ) 20 Gulyakevich, O.V. ( 3 . 5 ) 117 Gunstone, F.D. ( 3 . 5 ) 74 Guo, L.W. ( 2 . 2 ) 6 3 Gupta, A . ( 4 ) 382, 411 Gupta, B.P. ( 1 ) 379 Gustav, K. (3.6) 4 Gut, I. ( 3 . 2 ) 129 G u t h r i e , J.T. ( 4 ) 111, 124, 125 Guyon, C. ( 3 . 4 ) 1 2
H a l e v i , E . A . ( 3 . 3 ) 89 Hall, D.O. ( 5 ) 187 Haller, K . J . ( 2 . 2 ) 94 H a l t o n , B. ( 3 . 7 ) 30 Halverson, A.M. ( 3 . 4 ) 6 4 ; ( 3 . 6 ) 74 Hamada, T. (3.6) 154 Hamada, Y. ( 2 . 3 ) 22 Hamaguchi, H. ( 1 ) 439 Hamanoue, K. ( 1 ) 189, 190; ( 3 . 4 ) 83 Hamazaki, H. ( 3 . 6 ) 146 Hamblett, I. ( 1 ) 420 Hambley, T.W. ( 3 . 5 ) 83 Hambright, P . ( 2 . 1 ) 160 Hamer, N.K. ( 3 . 2 ) 118 Hamidi, A . ( 4 ) 405 Hamiotis, Z. ( 4 ) 359 Han, P. ( 4 ) 8 6 Hanaoka, M. (3.5) 140; ( 3 . 6 ) 33, 156 Hancock, L.E. (1) 261 Handa, T. (3.5) 136 Haneda, T. ( 3 . 6 ) 20 Hanfland, M. ( 1 ) 112 Hanly, N.M. ( 3 . 2 ) 8; (3.4) 43 Hannaby, M. ( 3 . 3 ) 2 Hannak, D. ( 1 ) 225 Hannemann, K. ( 3 . 7 ) 13, 1 4 , 24 Hansen, C.M. ( 4 ) 36 Hansen, H.-J. (3.3) 8 6 ; ( 3 . 6 ) 101 Hansen, J . B . ( 3 . 2 ) 101 Hansen, L. ( 1 ) 110 H a n z l i k , C . A . ( 1 ) 261 Har, G. ( 4 ) 398 Harada, H. ( 2 . 1 ) 24; ( 5 ) 1 7 1 , 173, 174, 185 H a r a s h i n a , H. ( 3 . 2 ) 13 Hardy, C. ( 3 . 4 ) 125 Haas, E. ( 1 ) 362, 374 Hargreaves, J . S . ( 4 ) 258 Haas, 0. ( 5 ) 228 Harle, I . L . ( 3 . 2 ) 140 Haber, H. ( 3 . 1 ) 42; ( 3 . 6 ) H a r r i g a n , L. ( 1 ) 8 4 76 Harriman, A . ( 1 ) 218 Haber-Patz, U. ( 3 . 3 ) 76 ( 2 . 1 ) 9 , 102, 160, 240, Hace, D. ( 4 ) 335 247; (5) 63, 113, 115, Hada, H . ( 5 ) 198, 199 120, 127 Hadel, L . M . ( 3 . 7 ) 54 Harris, C.B. ( 1 ) 204 Haga, M. ( 2 . 1 ) 131 Harris, R . A . ( 1 ) 401 Hagaman, K . A . (1) 340 Harris, R.L. ( 2 . 1 ) 165 Hageman, H . J . ( 4 ) 77 H a r r i s o n , M.J. ( 4 ) 182 H a r r i s o n , W.D. ( 2 . 1 ) 196 Hagiwara, H. ( 1 ) 457; ( 3 . 3 ) 114 Harrop, R . ( 4 ) 229 Hagiwara, S. (3.3) 6 8 , 69 H a r r o w f i e l d , J.M. ( 2 . 1 ) 47 Hagiwara, T. ( 4 ) 151 Hahn, L . R . ( 3 . 1 ) 31 Hart, D.E. ( 1 ) 258 H a i m , A . (2.1) 9 5 , 108 H a r t a n , H.-G. (3.2) 159 H a i n d l , E. (2.1) 41 H a r t l e y , R . J . ( 1 ) 186 Hakushi, T. ( 3 . 3 ) 8, 6 8 , Hartmann, M. ( 4 ) 108 69 Hartmann, W. ( 3 . 6 ) 178
Author Index Harwood, L.M. (3.2) 10, 34 Hasegawa, M. ( 3 . 2 ) 13 Hasegawa, T. (3.1) 41; ( 3 . 2 ) 121, 122; (3.3) 21; (3.6) 75; ( 5 ) 216 Haselbach, E . ( 1 ) 1 7 3 Hashem, M.M. ( 4 ) 127 H a s h i , T. ( 1 ) 452 Hashida, T. (2.2) 29 Hashimoto, S. ( 1 ) 274, 298, 307; ( 3 . 4 ) 186; (3.5) 71; (3.7) 131 Hashimoto, T. ( 4 ) 1 7 4 , 209; ( 5 ) 159 Hashimoto, Y. (1) 388 Hassan, M.E. (3.7) 153, 154 Hasselbach, H.-J. (3.7) 126 Hassinen, E. (3.7) 102 Hata, N. ( 3 . 6 ) 5 9 Hata, Y. ( 1 ) 83 Hatakeyama, Y. ( 2 . 1 ) 147 Hatanaka, Y. (3.2) 135, 140, 142; ( 3 . 6 ) 81, 83, 126 H a t s u i , T. ( 3 . 2 ) 15; ( 3 . 5 ) 75 Haubs, M. ( 3 . 6 ) 70 H a u e n s t e i n , B.L. ( 1 ) 34 Hauge, R.H. (2.2) 8 2 Haupt, J . ( 2 . 1 ) 77 Hauqing, W. ( 3 . 6 ) 64 Hauser, M. (1) 349 Havranek, A . ( 4 ) 289 Hawecker, J. (2.1) 124 Hawkins, M. ( 2 . 3 ) 37, 38, 51 H a w s , E.J. ( 3 . 2 ) 141 Hay, B.A. (3.3) 132; ( 3 . 6 ) 210 Hayakawa, K. (3.2) 132; (5) 53 Hayase, S. ( 4 ) 10 Hayashi, H. ( 2 . 1 ) 198; ( 2 . 3 ) 55 Hayashi, K. (4) 19 Hayashi, S. ( 4 ) 37, 126 Hayenes, R.K. ( 3 . 5 ) 83 Hayes, W. ( 4 ) 190 He, H. ( 3 . 5 ) 57 He, X. ( 4 ) 86, 95 He, Y. ( 4 ) 89 Hebeish, A . ( 4 ) 436 Heckel, A . (3.6) 192, 193 Hedstrom, J.F. ( 1 ) 258 Heelis, P.F. (3.5) 40, 130 Hegedus, L.S. ( 2 . 2 ) 25 H e i c k l e n , J. (3.5) 145, 146; ( 3 . 6 ) 141
567
Author Index Heimgartner, H. ( 3 . 2 ) 6 8 ; ( 3 . 4 ) 182
Heisel, F. ( 1 ) 1 5 7 , 158 Heitele, H. ( 5 ) 133 Heldal, J.A. ( 2 . 2 ) 28 Heldt, J. ( 1 ) 107 Heller, H.G. ( 3 . 2 ) 126; ( 3 . 4 ) 141
Hellman, M.Y. ( 4 ) 352 Helman, W.P. ( 1 ) 31 Helwic, N. ( 2 . 1 ) 44 Hemmila, I. ( 1 ) 69 Hemmingsen, T.H. ( 3 . 7 ) 138
Henderson, D. ( 3 . 1 ) 16 Henderson, L.J. ( 2 . 1 ) 85 Hendrich, M.P. ( 3 . 7 ) 44 Henglein, A. ( 2 . 1 ) 1 8 ; ( 5 ) 170
Henin, F. ( 3 . 1 ) 4 3 ; ( 3 . 2 ) 62
Henlin, J.-M. ( 3 . 7 ) 141 Henman, T.J. ( 4 ) 295, 384 Henne, A. ( 3 . 6 ) 213, 214 Henner, A. ( 4 ) 46 Hennig, H. ( 2 . 1 ) 7 2 ; ( 2 . 2 ) 3 1 , 33
Henning, H.G. ( 3 . 1 ) 4 2 ; ( 3 . 6 ) 76
Henre, A. ( 1 ) 427 Hensler, G. ( 2 . 1 ) 8 1 Heppener, M. ( 5 ) 134 Herbert, D . J . ( 3 . 2 ) 22 Hermanies, E. ( 4 ) 154 Hermann, H. ( 2 . 2 ) 1 5 , 7 3 Hernandez, R. ( 3 . 7 ) 187 Hernandez, S. ( 2 . 2 ) 85 Heropoulos, A. ( 1 ) 341 Herreman, W. (1) 48 Herrmann, J.M. ( 5 ) 175 Hertl, W. ( 5 ) 225, 226 Herve', Y. ( 3 . 7 ) 117 Hervet, H. ( 4 ) 228 Herz, W. ( 3 . 5 ) 81 Hesabi, M.M. ( 3 . 7 ) 120 Hesse, K. ( 3 . 3 ) 119 Hessler, D. ( 2 . 1 ) 132 Hetrick, R.E. ( 5 ) 231 Hettich, R . L . ( 2 . 2 ) 7 Heuffer, J. ( 3 . 6 ) 153 Heyward, I.P. ( 4 ) 142 Hibbard, L.B. ( 1 ) 332 Hidaka, H. ( 5 ) 171 Higgins, B.E. ( 2 . 2 ) 60 Highland, R.G. ( 1 ) 4 6 6 ; ( 2 . 1 ) 229
Higuchi, H. ( 3 . 4 ) 158 Higuchi, T. ( 2 . 2 ) 2 9 ; ( 2 . 3 ) 26; ( 3 . 4 ) 157; ( 3 . 6 ) 200 Hikada, T. ( 1 ) 1 4 2 , 442 Hikasa, M. ( 3 . 4 ) 8 2 ;
( 3 . 6 ) 134
Hilary, J.L. ( 4 ) 195 Hild, E.K. ( 1 ) 359 Hild, G. ( 4 ) 237 Hildenbrand, K. ( 3 . 3 ) 43 Hilgers, G. ( 3 . 1 ) 2 2 , 33 Hilinski, E.F. ( 1 ) 172 Hill, C.L. ( 5 ) 111, 112 Hill, D.J.T. ( 4 ) 361 Hill, J. ( 3 . 7 ) 120 Hill, K. ( 3 . 2 ) 8 6 ; ( 3 . 7 ) 1 8 , 19
Hill, R.R. ( 3 . 7 ) 111 Hiller, W. ( 2 . 2 ) 24 Hine, K. ( 4 ) 198 Hinsken, W. ( 3 . 2 ) 89 Hinzmann, G. ( 3 . 5 ) 99 Hirai, H. ( 3 . 5 ) 4 9 ; ( 5 ) 101, 102
Hiraki, K. ( 2 . 2 ) 104 Hiramatsu, M. ( 1 ) 1 9 1 ; ( 3 . 4 ) 6 3 , 1 7 8 ; ( 3 . 5 ) 23
Hirao, K. ( 1 ) 211 Hirase, S. ( 3 . 4 ) 8 3 Hiratsuka, H. ( 1 ) 142 Hirayanagi, K. ( 4 ) 236 Hirokami, S . ( 3 . 2 ) 9 2 ; ( 3 . 6 ) 18
Hirota, K. ( 3 . 6 ) 62 Hirota, M. ( 4 ) 449 Hirota, N. ( 1 ) 1 2 2 , 441 Hirotsu, K. ( 2 . 2 ) 29; ( 2 . 3 ) 2 6 ; ( 3 . 4 ) 157; ( 3 . 6 ) 200 Hitchcock, P.B. ( 3 . 6 ) 169 Ho, C.N. ( 1 ) 62 Ho, P.P. ( 1 ) 32 Ho, T.F. ( 5 ) 1 2 6 , 132 Ho, T.I. ( 3 . 6 ) 133 Hobert, K. ( 3 . 7 ) 75 Hochstrasser, R.M. ( 1 ) 235, 236; ( 3 . 3 ) 24 Hoegberg, H.E. ( 3 . 5 ) 79 Hoel, E.L. ( 2 . 2 ) 93 Hoenes, G. ( 1 ) 349 Hoerhold, H.H. ( 4 ) 41 Hoffman,,M.Z. ( 2 . 1 ) 9 4 , 1 3 2 ; ( 5 ) 8 5 , 8 6 , 92 Hoffmann, M.R. ( 5 ) 195 Hoffmeyer, H. ( 2 . 3 ) 8 Hofmann, M. ( 2 . 3 ) 2 Hofstraat, J.W. ( 1 ) 116 Hofzumahaus, A . ( 2 . 3 ) 31 Hoganson, C.W. ( 1 ) 205 Hogea, I. ( 4 ) 345 Hogiguchi, R. ( 1 ) 105 Holden, D.A. ( 4 ) 264 Hollebone, B.R. ( 2 . 1 ) 140 Holler, J.F. ( 2 . 1 ) 8 8 ; ( 5 ) 56 Hollingsworth, W.E. ( 2 . 2 ) , l
L
Holroyd, R.A. (1) 82 Holt, E.M. ( 2 . 2 ) 96 Holton, G.R. ( 1 ) 235 Holzwarth, A.R. ( 1 ) 453 Honda, H. ( 3 . 3 ) 44 Honda, K. ( 2 . 3 ) 20 Honda, Y. ( 2 . 1 ) 189 Hong, A.P. ( 5 ) 195 Hong, S. ( 4 ) 149 Honi, K. ( 4 ) 214 Hontzopoulos, E. ( 2 . 1 ) 170; ( 5 ) 76
Hooker, R.H. ( 2 . 2 ) 7 0 Hoornweg, G.P. ( 1 ) 116 Hopf, H. ( 1 ) 432, 4 3 3 ; ( 3 . 4 ) 108
Hopfield, J.J. ( 5 ) 131 Hopkins, J.B. ( 1 ) 1 4 , 9 8 , 99
Horak, M. ( 2 . 3 ) 45 Horie, K. ( 1 ) 9 6 , 211, 270; ( 4 ) 1 7 5 , 236
Horie, 0. ( 2 . 3 ) 8 Horiuchi, T. ( 2 . 2 ) 29 Horner, M.G. ( 3 . 3 ) 1 0 7 ; ( 3 . 4 ) 44
Horowitz, A. ( 3 . 5 ) 90 Horowitz, P.M. ( 1 ) 345, 354
Horrocks, W.D. ( 1 ) 359 Horspool, W.M. ( 3 . 1 ) 3 ; ( 3 . 2 ) 75-78; ( 3 . 3 ) 4 1 , 42, 72; (3.4) 13; (3.6) 2 7 , 46-48, 79 Horvath, 0 . ( 2 . 1 ) 1 8 7 , 190; ( 5 ) 31 Hoser, H. ( 1 ) 210 Hoshi, B. ( 3 . 2 ) 80 Hoshi, N. ( 3 . 3 ) 114 Hoshino, M. ( 2 . 1 ) 1 3 8 ; ( 2 . 2 ) 5 9 , 113, 1 1 5 , 116, 139 Hoshino, 0 . ( 3 . 4 ) 1 4 7 ; ( 3 . 7 ) 143 Hosoda, M. ( 4 ) 242 Hosoda, Y. ( 2 . 3 ) 6 ; ( 3 . 6 ) 218 Hosseini, M.W. ( 2 . 1 ) 150 Hou, H. ( 2 . 1 ) 225 Houben, J.L. ( 3 . 6 ) 1 2 ; ( 4 ) 213 Houlding, V.H. ( 2 . 1 ) 179 Hoyle, C.E. ( 4 ) 150 Hrllovic, P. ( 4 ) 354 Hruska, F.E. ( 3 . 2 ) 9 9 ; ( 3 . 6 ) 87 Hsu, W.L. ( 2 . 2 ) 32 Hu, C. ( 4 ) 54 Hu, J. ( 2 . 1 ) 220 Hu, Q. ( 3 . 3 ) 4 8 ; ( 3 . 6 ) 49 Hu, X. ( 4 ) 399 Huang, B. ( 4 ) 54
568 Huang, D. ( 1 ) 203 Huang, S. ( 2 . 3 ) 47 Huang, W. ( 4 ) 54 Huang, X. ( 3 . 3 ) 48; (3.6) 49 Huang, Y. ( 4 ) 223 Huber, D.M. ( 1 ) 409 Huber, J . R . ( 2 . 3 ) 33 Huber, W. ( 3 . 5 ) 144 Hubesch, B. ( 2 . 1 ) 158; (5) 74, 104 Hubig, S. ( 1 ) 244 Hubmann, B. ( 4 ) 189 Hucker, J. ( 1 ) 433 Hudson, A. ( 3 . 2 ) 158 Huelskaemper, L. ( 3 . 1 ) 51 Hunig, S. (3.3) 119; ( 3 . 6 ) 118 Hug, D.H. ( 1 ) 343, 495 Hug, G.L. ( 1 ) 31, 487 Hui, Y. (3.3) 22 Huizer, B.H. ( 1 ) 88, 109, 179 H u l t , A. ( 4 ) 38, 98 Humphrey-Baker, R . ( 1 ) 217 Hunter, E.P.L. ( 1 ) 18 Hunton, D.E. ( 2 . 3 ) 2 Huppert, D. ( 1 ) 120, 138 Hurley, J . ( 5 ) 34 H u r t u b i s e , R . J . (1) 426 Husain, A . (1) 351 Hush, N.S. ( 5 ) 134 Hussmann, G.P. ( 3 . 4 ) 7 ; (3.6) 55 Huston, A.L. ( 1 ) 6 4 , 65 Hutchinson, J . A . (1) 233 H u t z i n g e r , 0. ( 3 . 4 ) 87 Hwang, K.K.S. ( 4 ) 137 Hyla-Kryspin, I. ( 2 . 2 ) 103 Hynes, J.T. (1) 7 I b a r z , A . ( 3 . 6 ) 148 I b o r r a , S. (3.4) 180 Ibrahim, M. ( 4 ) 434 I c h i n o s e , N. (3.3) 126; (3.5) 103, 106; ( 5 ) 47 I d e , H. ( 3 . 5 ) 44 I d e , J.P. ( 1 ) 280 I g a , R. ( 4 ) 219 I g a r i s h i , T. ( 1 ) 511 I h , K.J. ( 4 ) 6 1 Ihama, M . ( 2 . 1 ) 126 I h a r a , M. ( 3 . 5 ) 127 I'Haya, Y.J. ( 1 ) 460 I i t a k a , Y. ( 3 . 1 ) 48 I i z a w a , T. ( 4 ) 146, 148 I i z u k a , H. (3.6) 165 I k a , K . V . ( 4 ) 417 I k e d a , K. ( 4 ) 112
Author Index I k e d a , M . (2.3) 1 0 ; (3.4) I t a g a k i , H. ( 1 ) 96 74, 75; (3.6) 96, 209 I t a y a , A. (5) 165 I t o , K. (2.2) 29 I k e d a , Y. (3.5) 65 Ikekawa, N. ( 3 . 7 ) 67 I t o , S. ( 1 ) 263; ( 3 . 7 ) Ikemoto, I. (5) 203 125 Ikemoto, N. (1) 376 I t o , T. ( 2 . 2 ) 139; (5) Ikeyama, T. ( 1 ) 429 203 Ikezawa, H. (3.3) 103; I t o , Y. (1) 239; ( 3 . 1 ) 47; ( 3 . 3 ) 29; ( 3 . 4 ) 150 ( 5 ) 48 I k e z u , S. ( 3 . 3 ) 118 I t o h , H. ( 3 . 4 ) 100; ( 3 . 6 ) I l g e , H.D. ( 3 . 2 ) 125; 130 I t o h , K. (3.4) 81; (3.6) ( 3 . 3 ) 79 I l i c h , P. ( 1 ) 324 10; ( 3 . 7 ) 64, 183 I l l i s k o v i c , N. ( 4 ) 341 I t o h , M . ( 1 ) 135, 141, Imaeda, K. ( 4 ) 281 388; (3.2) 40; ( 3 . 5 ) 2 3 Imamura, T. ( 2 . 1 ) 68 Itokawa, H. ( 3 . 1 ) 4 8 I m a n i s h i , Y. ( 4 ) 256 Ivanov, V.F. ( 5 ) 158, Imhof, R.E. ( 1 ) 27, 55 324, 430 I n a g a k i , S. ( 3 . 7 ) 10 Ivanova, L.V. ( 2 . 2 ) 6 1 Inamoto, N. ( 2 . 2 ) 29 I v e s , J.L. ( 3 . 5 ) 96 Iwabuchi, S. ( 3 . 5 ) 25 I n d e l l i , M . T . ( 2 . 1 ) 92 I n g o l d , K.U. ( 3 . 1 ) 24; Iwahama, K. ( 4 ) 189 I w a h a s h i , M. ( 1 ) 401 (3.4) 129 Inou, Y. (5) 197 Iwai, J. (2.2) 49, 50, 59 Inoue, H. ( 2 . 1 ) 248; Iwai, K . ( 4 ) 72, 233 Iwamoto, H. ( 3 . 2 ) 161, ( 3 . 4 ) 184, 185 ( 3 . 6 ) 44, 149 162 Inoue, M. ( 3 . 4 ) 136; Iwamoto, M. ( 3 . 6 ) 15 ( 3 . 6 ) 34 Iwamura, H. ( 2 . 1 ) 21; Inoue, T. ( 4 ) 245 ( 3 . 7 ) 6 4 , 92 I n o u e , Y. (3.3) 8 , 6 8 , 69 Iwasa, K. (3.6) 6 8 Inouye, Y. ( 3 . 2 ) 9 I w a s a k i , H. ( 3 . 7 ) 6 5 I o g a n s e n , A . A . (2.3) 35, I w a s a k i , K . (3.5) 1 2 3 36 I w a s a k i , N. ( 1 ) 105 I o n i n , B.I. ( 3 . 6 ) 215 Iwase, K. (3.7) 10 Ionov, S . I . ( 2 . 3 ) 46 Iwata, K. ( 4 ) 151 I q b a l , M. (2.2) 86 Iwayanagi, T. ( 4 ) 221 I q b a l , R. ( 2 . 3 ) 39 Iweibo, I. (1) 165 I r i e , M. ( 4 ) 209, 219, Iyoda, J. ( 4 ) 152 221, 242; (5) 159 I y o d a , M. ( 3 . 2 ) 29-31 I r i e , T. ( 3 . 3 ) 47; ( 3 . 6 ) Izawa, Y. (3.5) 123; 50 ( 3 . 7 ) 10, 39, 53, 60 I r n g a r t n e r , H. ( 3 . 3 ) 74, Izumridov, V . A . ( 4 ) 204 76 I r v i n e , M. ( 1 ) 420 I s a k o v , I . V . ( 4 ) 56 J a a r i n e n , S. (3.7) 176 I s e n o r , N.R. ( 2 . 3 ) 3 Jackson, W.R. (1) 216 I s h i b a s h i , I. (3.6) 96 J a c o b i , M. ( 4 ) 46 I s h i d a , A . ( 2 . 1 ) 201; J a c o b s , H.J.C. (3.3) 56; ( 3 . 3 ) 36; ( 3 . 6 ) 129 ( 3 . 7 ) 79 I s h i d a , H. ( 4 ) 1 2 3 J a c o b s , P.A. ( 2 . 2 ) 6 8 I s h i i , K. ( 3 . 3 ) 134; J a c o b s s o n , U. ( 3 . 3 ) 84; ( 3 . 4 ) 8 2 ; ( 3 . 6 ) 134; ( 3 . 4 ) 10 ( 3 . 7 ) 132 J a c q u e s , P. ( 1 ) 461, 462 Ishikawa, M. ( 2 . 3 ) 26; J a e g e r , W. ( 4 ) 208 ( 3 . 4 ) 157; ( 3 . 6 ) 197, J a f f r e z i c , N . ( 5 ) 175 200 J a g g i , D. ( 3 . 5 ) 92 Ishikawa, Y. ( 3 . 2 ) 121 J a h n , R. ( 3 . 3 ) 76 I s h i t a n i , 0. ( 2 . 1 ) 126 J a i n , S. ( 3 . 5 ) 114 I s h i z a k a , S. ( 1 ) 139 J a k o p c i c , J. (3.4) 1 4 3 I s k a h o r , N . I . ( 4 ) 94 Jakoubkova, M . ( 2 . 3 ) 45 I s o b e , K. ( 2 . 2 ) 39 James, D.R. ( 1 ) 49-51,
Author Zndex 3 2 5 , 3 2 9 , 339
Jameson, D.M. ( 1 ) 2 4 , 39 Janic, I. ( 1 ) 209 Janovia, Z. ( 4 ) 412 Jans, A.W.H. ( 3 . 4 ) 34 Janzen, E.G. ( 2 . 1 ) 245 Jaque, F. ( 5 ) 2 3 5 , 236 Jardon, P. ( 1 ) 434 Jarecki, C. ( 3 . 7 ) 28 Jarosiewicz, M. ( 1 ) 87 Jawad, H. ( 2 . 2 ) 2 3 , 24 Jefford, C.W. ( 3 . 5 ) 9 2 , 93
Jeffries, P.R. ( 3 . 3 ) 77 Jeffs, G.E. ( 3 . 2 ) 1 2 0 ; ( 3 . 7 ) 111
Jeganathan, M.B. ( 4 ) 124 Jeger, 0 . ( 3 . 1 ) 3 5 ; ( 3 . 2 )
569 Jones, R.D. ( 1 ) 324 Jones, R.G. ( 4 ) 103 Jones, R.J. ( 3 . 4 ) 1 2 3 ; ( 3 . 6 ) 159
Jones, S.B. ( 2 . 2 ) 6 Jones, S.K.R. ( 4 ) 456 Jones, W.D. ( 2 . 2 ) 67 Jones, W.J. ( 1 ) 1 9 Jones, W.M. ( 2 . 2 ) 9 0 , 91 Jong, D.-J. ( 1 ) 16 Joran, A.D. ( 5 ) 131 Joranovic, D. ( 4 ) 367 Jordan, K. ( 4 ) 264 Jorritsma, R. ( 3 . 2 ) 102 Joshi, N. ( 1 ) 372 Joussot-Dubien, J. ( 1 ) 106
Jovanovic, S. ( 4 ) 64 Jovin, T.M. ( 1 ) 7 3 56, 57; ( 3 . 3 ) 7 0 , 7 1 , 1 3 3 ; ( 3 . 7 ) 133-135, 137 Jug, K. ( 3 . 7 ) 3 Jenden, C.M. ( 4 ) 362 Junnarkar, M.R. ( 1 ) 377 Jenkins, A.D. ( 4 ) 7 0 Juo, R.R. ( 3 . 5 ) 8 1 Jennesken, L.W. ( 3 . 4 ) 3 Jurgens, A. ( 3 . 4 ) 104 Jenny, B. ( 5 ) 175 Juris, A . ( 2 . 1 ) 7 8 , 7 9 , Jensen, B.L. ( 3 . 7 ) 144 1 3 0 ; ( 5 ) 5 5 , 58 Jensen, N.-H. ( 1 ) 421 Justus, B.L. ( 1 ) 6 4 , 65 Jesion, G . ( 1 ) 411 Jian, S.Z. ( 4 ) 4 0 6 , 427 Jiang, F.-B. ( 1 ) 387 Kabaivanov, V. ( 4 ) 353 Jiang, L. ( 3 . 3 ) 127 Kabanov, V.A. ( 4 ) 1 1 9 , Jian-hu, X. ( 3 . 2 ) 7 3 204 Jin, T. ( 2 . 1 ) 6 8 Kabasawa, Y. ( 3 . 2 ) 8 1 , Jingui, M. ( 1 ) 1 0 3 , 442 8 2 , 85 Jirakova-Audouin, L. ( 4 ) Kabir, S.E. ( 2 . 2 ) 77 Kabumoto, A. ( 3 . 5 ) 53 4 20 Jirousek, M. ( 3 . 5 ) 137 Kachan, A.A. ( 4 ) 1 5 3 , 315 Jitsumatsu, T. ( 4 ) 28 Kaczmarck, H. ( 4 ) 322 Johansen, 0 . ( 2 . 1 ) 1 1 4 ; Kaddouri, A. ( 1 ) 418 Kadota, H. ( 3 . 4 ) 8 2 ; (5) 71 Johansson, L.B.-A. ( 1 ) 47 ( 3 . 6 ) 134 Johnson, B.V. ( 2 . 2 ) 32 Kafafi, Z.H. ( 2 . 2 ) 82 Johnson, C.R. ( 2 . 1 ) 206 Kagan, J. ( 3 . 4 ) 181 Johnson, G.P. ( 3 . 3 ) 1 3 7 ; Kageyama, H. ( 3 . 2 ) 5 1 ; ( 3 . 6 ) 66
( 3 . 4 ) 154
Johnson, I.D. ( 1 ) 166 Johnson, M.D. ( 2 . 2 ) 110 Johnson, R.P. ( 3 . 3 ) 57-
Kagi, J.H.R. ( 1 ) 342 Kagiya, T. ( 3 . 5 ) 4 4 ; ( 4 )
5 9 , 6 5 ; ( 3 . 4 ) 2 9 , 117 Johnson, T.J. ( 2 . 1 ) 162 Johnston, L.J. ( 1 ) 465, 499; ( 3 . 1 ) 9 , 24, 26; ( 3 . 4 ) 1 2 9 , 130 Jolidon, S. ( 3 . 6 ) 101 Jolliet, P. ( 2 . 1 ) 175 Jones, A.C. ( 1 ) 319 Jones, D.J. ( 2 . 2 ) 72 Jones, G. ( 1 ) 216; ( 2 . 1 ) 9 9 ; ( 3 . 5 ) 30, 39, 143; ( 5 ) 8 7 , 8 8 , 137 Jones, G.R. ( 1 ) 101 Jones, J. ( 4 ) 65 Jones, M. ( 3 . 7 ) 7 4
Kahlow, M.A. ( 1 ) 223 Kaiser, G. ( 3 . 2 ) 128 Kaiser, W. ( 1 ) 2 0 6 , 378 Kaizu, Y. ( 2 . 1 ) 228 Kaji, N. ( 2 . 1 ) 232; ( 3 . 5 )
372; ( 5 ) 182
34; ( 5 ) 68, 89, 9 0 , 94, 9 5 , 140 Kajitani, M. ( 2 . 2 ) 8 3 , 8 4 ; ( 5 ) 77 Kajiwara, Y. ( 1 ) 189 Kakisawa, H. ( 3 . 2 ) 9 Kakitani, K. ( 1 ) 146 Kakitani, T. ( 5 ) 121 Kakiuchi, K. ( 3 . 2 ) 2 3 ; (3.4) 3
Kalashmik, A.T. ( 4 ) 414 Kalbas, C . ( 2 . 2 ) 55 Kaliaguine, S. ( 2 . 1 ) 63 Kalinnikov, V.T. ( 2 . 2 ) 37 Kalisky, Y. ( 4 ) 211 Kalkar, C.D. ( 1 ) 504 Kallfass, D. ( 3 . 3 ) 7 6 Kalliorinne, K. ( 3 . 7 ) 102 Kallir, A.J. ( 1 ) 437 Kalontarov, I.Ya. ( 4 ) 428 Kalyanasundaram, K. ( 1 ) 217; ( 2 . 1 ) 1 7 7 ; ( 5 ) 82
Kamat, P.V. ( 4 ) 8 1 , 263 Kambayashi, M. ( 4 ) 7 3 Kametani, T. ( 3 . 5 ) 127 Kamigata, N. ( 3 . 4 ) 1 8 6 ; ( 3 . 6 ) 165
Kaminsika, A. ( 4 ) 322 Kamiya, M. ( 3 . 2 ) 114 Kamiyama, N. ( 3 . 5 ) 103 Kamogawa, H. ( 3 . 5 ) 3 7 ; ( 4 ) 210; ( 5 ) 155
Kamphuis, J. ( 3 . 2 ) 1 4 9 , 165; ( 3 . 6 ) 1 2 1 , 180
Kan, S.L. ( 3 . 2 ) 99; ( 3 . 6 ) 87
Kanai, M. ( 3 . 4 ) 9 9 ; ( 3 . 5 ) 122
Kanakarajan, K. ( 3 . 7 ) 47 Kananiaru, N. ( 1 ) 326 Kanaoka, Y. ( 3 . 2 ) 1 3 5 , 1 4 0 , 1 4 2 , 145-147, 1 5 1 ; ( 3 . 4 ) 96 ( 3 . 6 ) 8 0 , 8 1 , 83, 114, 116, 126, 128, 179, 1 8 1 , 183, 1 8 4 , 1 8 6 ; ( 3 . 7 ) 1 4 7 , 148 Kanatomi, H. ( 1 ) 511 Kane, C . ( 1 ) 31 Kane, V.V. ( 2 . 2 ) 7 9 Kaneko, C. ( 3 . 2 ) 2 4 , 4 1 ; ( 3 . 6 ) 2 0 , 9 0 , 97 Kaneko, M. ( 2 . 1 ) 1 2 0 ; ( 5 ) 1 1 , 1 5 3 , 154
Kane-Maguire, N.A.P. ( 2 . 1 ) 4 4 , 46
Kanematsu, K. ( 3 . 2 ) 132 Kanemoto, A. ( 1 ) 447 Kang, H.K. ( 3 . 2 ) 9 8 ; ( 3 . 6 ) 93
Kang, W.S. ( 4 ) 32 Kang. Z.H. ( 1 ) 196 Kanno, H. ( 2 . 1 ) 2 4 ; ( 5 ) 173
Kano, K. ( 1 ) 274; ( 3 . 7 ) 131
Kanofsky, J.R. ( 1 ) 505 Kanoktanaporn, S. ( 1 ) 216 Kanstrup, A. ( 3 . 2 ) 101 Kapinus, E . I . ( 1 ) 472 Kaplan, A.M. ( 5 ) 34 Kaplan, L. ( 3 . 4 ) 21 Kaplan, R. ( 1 ) 75
570 Karasev, V.E. ( 2 . 3 ) 5 Karatsu, K. ( 1 ) 188, 439 Karavaev, A.D. ( 2 . 1 ) 106 Karle, I . L . ( 3 . 6 ) 126 Karlivam, V. ( 4 ) 286 Karminski-Zamola, G. (3.4) 143 Karnaukh, A.P. ( 4 ) 75 Karplyuk, V.A. ( 4 ) 370 Karpukhin, O.N. ( 4 ) 454 Kartuzhanskii, A.L. ( 2 . 1 ) 195 Karup, G. ( 3 . 2 ) 101 Karuyama, K. (3.4) 80 Karvas, M. ( 4 ) 403 Kasai, N. (3.4) 167 Kashuba, E.V. ( 5 ) 207 Kasprzyk, P.G. ( 1 ) 360 Kastening, B. ( 5 ) 219 Katagiri, N. ( 3 . 6 ) 20, 97 Katakis, D. ( 2 . 1 ) 170; ( 5 ) 76 Katayama, T. ( 4 ) 451 Kato, H. ( 4 ) 28 Kato, K. ( 3 . 5 ) 8 2 Kato, M. ( 2 . 2 ) 139; (2.3) 27; (3.3) 50; (3.5) 123; ( 3 . 6 ) 197; ( 4 ) 23, 27, 172; ( 5 ) 203 Kato, N . ( 3 . 2 ) 1 4 Kato, S. ( 5 ) 148 Kato, T. ( 3 . 2 ) 81-83, 85 Katritzky, A.R. (3.4) 126 Katsukura, Y. (3.5) 8 6 Katz, T.J. (3.4) 109 Kauffmann, H.F. ( 4 ) 269 Kaufman, S . J . ( 1 ) 7 3 Kaufmann, F. (3.6) 51 Kaupp, G. ( 3 . 4 ) 52; ( 3 . 7 ) 119 Kawaguchi, H. (5) 164 Kawaharada, Y. (2.2) 8 4 Kawai, K. ( 5 ) 199 Kawamura, T. (2.2) 56 Kawamura, Y. ( 3 . 3 ) 124; (3.6) 104 Kawanishi, Y. ( 2 . 1 ) 90, 127; ( 5 ) 61, 122 Kawase, K. ( 3 . 3 ) 95; ( 5 ) 53 Kawata, H. ( 3 . 6 ) 60 Kawata, K. (2.1) 200 Kawata, S. ( 2 . 1 ) 147 Kawato, T. (1) 511 Kawatsuki, N. ( 3 . 1 ) 47; (3.4) 150 Kawski, A. ( 1 ) 209, 350, 384, 456 Kayak, Ya.A. ( 4 ) 344 Kayakawa, Y. (3.3) 9 5 Kazachkova, O.L. ( 4 ) 344 Kazakov, V.P. ( 2 . 1 ) 106,
Author Index 222, 249; ( 2 . 3 ) 57 Kazama, S. (3.2) 114 Kazuya, M. ( 3 . 3 ) 117 Kazyaka, T.G. ( 4 ) 365 Keene, J.P. (1) 480 Keese, R. (3.4) 38, 39 Keghouche, N. (2.1) 164; (5) 105 Keller, B.A. ( 2 . 3 ) 33 Keller, R.A. ( 1 ) 68 Kelley, C.K. ( 2 . 2 ) 127: (5) 45 Kelley, D.F. ( 1 ) 1 6 Kellog, R.M. ( 3 . 5 ) 51 Kelly, J.M. ( 2 . 2 ) 7 3 Kemp, G. (3.3) 141; ( 3 . 7 ) 155 Kemp, T.J. ( 1 ) 1 6 3 , 454 Kenig, S. ( 4 ) 349 Kenimov, M.K. ( 4 ) 294 Kenji, F. ( 4 ) 141 Kenkre, V.M. ( 1 ) 247 Kennedy, J. ( 1 ) 417 Kennelly, T. (2.1) 122 Kenney, J.W. ( 2 . 2 ) 114 Kenney, M.I.S. ( 2 . 2 ) 114 Kenney-Wallace, G.A. (1) 79, 123 Kerr, S.R. ( 4 ) 138 Kessel, D. ( 1 ) 416, 480 Kesselmayer, M.A. ( 3 . 7 ) 6, 7 Kevan, L. ( 1 ) 300; ( 3 . 5 ) 133 Keys, D.E. ( 3 . 7 ) 26 Keyser, P. (5) 34 Khac, D.D. ( 3 . 2 ) 36 Khamzamulina, R.E. ( 4 ) 203, 208 Khan, A . Y . ( 2 . 3 ) 39 Khan, J . D . (3.5) 21 Khan, M.M. ( 5 ) 218 Khanna, R . N . ( 3 . 4 ) 177 Khanova, L.A. (5) 227 Kharitonov, A.P. (2.3) 44 Khimich, N.N. ( 3 . 7 ) 76 Khokhlova, V.P. ( 2 . 1 ) 222 Kholmanskii, A.S. (3.6) 40 Kholmogorov, V.E. ( 5 ) 29 Kholodova, N.V. ( 3 . 4 ) 128; (3.6) 29 Khripach, V.A. ( 3 . 5 ) 117 Khristova, N.N. ( 4 ) 129 Khvorostovskii, S.N. (2.3) 42 Khvostova, V.P. (2.1) 136 Kido, K. ( 3 . 2 ) 132 Kido, M. (3.6) 9 6 Kiesewetter, R. (3.2) 66 Kieu, H.T. ( 2 . 3 ) 4 Kihara, M. ( 3 . 4 ) 146
Kikkawa, M. ( 2 . 1 ) 147 Kikuchi, K. ( 1 ) 6 3 , 208, 447, 493; ( 3 . 5 ) 35 Kilhoffer, M.-C. ( 1 ) 358 Kim, D.H. ( 1 ) 376, 469 Kim, H.J. ( 1 ) 234; ( 3 . 3 ) 28 Kim, H.S. ( 4 ) 149 Kim, J.H. (2.1) 146 Kim, K . J . ( 4 ) 149, 150, 24 1 Kim, W. ( 4 ) 194 Kim, Y. (2.1) 127; ( 5 ) 61 Kim, Y.D. (3.4) 183; ( 3 . 6 ) 45 Kimoto, M. ( 1 ) 189 Kim-Thuan, N. ( 1 ) 461 Kimura, E. ( 1 ) 131 Kimura, M. ( 2 . 1 ) 101, 105, 123 Kimura, S. ( 2 . 2 ) 39 Kincaid, J . R . (2.1) 88; ( 5 ) 56 King, D. ( 4 ) 456 King, J.A. ( 2 . 2 ) 107 King, R.B. (2.2) 96 King, R.K. ( 3 . 2 ) 73, 74 Kinoshita, S. ( 1 ) 29 Kinoshita, T. ( 4 ) 218 Kira, M. ( 2 . 3 ) 15, 1 6 ; ( 3 . 4 ) 172, 190; ( 3 . 6 ) 201, 202, 207 Kirchhof, B. (3.5 149; ( 4 ) 445 Kirchhoff, J . R . ( 2 . 1 ) 11 Kirk, A.D. ( 2 . 1 ) 4 2 , 45 Kirk, N.J. ( 1 ) 332 Kirsch, B. ( 1 ) 21 Kirschenheuter, G.P. ( 3 . 5 ) 78 Kiryukhin, Yu.1. ( 5 ) 217 Kisch, H. ( 2 . 1 ) 242, 243; ( 5 ) 72, 7 3 Kisilev, A . (2.1) 199 Kislinger, J. (2.1) 135 Kissinger, P.T. ( 1 ) 33 Kita, H. ( 2 . 1 ) 29; ( 5 ) 176 Kita, T. (2.1) 232; ( 3 . 5 ) 34; (5) 8 9 , 94. 9 5 , 140 Kitaigorodskii, A . N . ( 2 . 2 ) 132 Kitami, S. ( 3 . 2 ) 31 Kitamura, A . ( 1 ) 486; ( 3 . 7 ) 26 Kitamura, N. ( 1 ) 506; (2.1) 90, 127; ( 5 ) 61, 122 Kitamura, S. ( 2 . 2 ) 104 Kitamura, T. ( 3 . 7 ) 177 Kitani, T. (5) 148 Kitao, T. ( 4 ) 449, 450;
Author Index ( 5 ) 69
Kivana, D. ( 2 . 1 ) 20 Kiwi, J. ( 5 ) 186, 206 Klabunovskii, E . I . ( 5 ) 144
Klarner, F.-G.
(3.3) 111; ( 3 . 7 ) 16 Klafyer, J. ( 1 ) 249 Kleijn, M. ( 2 . 1 ) 100; ( 5 ) 119 Kleiner, E. ( 3 . 2 ) 103 Klemm, E. ( 4 ) 41, 71 Klett, M.W. ( 3 . 3 ) 5 9 ; ( 3 . 4 ) 117 Kliger, D.S. ( 2 . 1 ) 8 2 , 152; ( 3 . 2 ) 96 Klimenko, B.B. ( 3 . 1 ) 25 Klimenko, L.S. ( 3 . 2 ) 167 Klock, A. ( 1 ) 184 Kloosterboer, J.G. ( 4 ) 132 Klotzbuecher, W.E. ( 2 . 2 ) 1 7 , 73 Klug, G. ( 3 . 5 ) 77 Klunder, A.J.H. ( 3 . 2 ) 7 Klvana, D. ( 5 ) 163 Kmelinskii, I . V . ( 2 . 1 ) 191 Kneuper, H.J. ( 2 . 2 ) 38 Knight, J. ( 3 . 7 ) 172 Knoesel, R. ( 4 ) 265 Knoester, J. ( 1 ) 1 2 ; 279 Knoll, P. ( 4 ) 189 Knothe, L. ( 3 . 3 ) 105, 106; ( 3 . 6 ) 100 Knox, C.N. ( 1 ) 477 Knox, R . S . ( 1 ) 261 Knox, S.A.R. ( 2 . 2 ) 38 Knudsen, P.H. ( 3 . 2 ) 101 Knutson, J . R . ( 1 ) 4 4 , 4 5 , 321 Knyazhanskii, M . I . ( 2 . 1 ) 188; ( 3 . 4 ) 126-128; ( 3 . 6 ) 28, 29 Kobayashi, E. ( 3 . 4 ) 158; ( 4 ) 59 Kobayashi, H. ( 2 . 1 ) 228; ( 3 . 3 ) 50 Kobayashi, K. ( 3 . 2 ) 4 0 ; ( 3 . 5 ) 76 Kobayashi, M. ( 3 . 4 ) 186; ( 3 . 6 ) 165, 211 Kobayashi, S. ( 3 . 4 ) 1 4 6 ; ( 3 . 7 ) 177 Kobayashi, T. ( 1 ) 164, 269; ( 2 . 2 ) 49-51, 5 9 ; ( 4 ) 225; ( 5 ) 148 Kober, E.M. ( 2 . 1 ) 134 Koch, H. ( 3 . 1 ) 1 Koch, R. ( 3 . 5 ) 99; ( 4 ) 445 Kocherov, A.V. ( 4 ) 129
57 1 Kochi, J . K .
(1) 172, 182; ( 3 . 4 ) 56, 103, 165; ( 3 . 6 ) 140 Kodama, S. ( 2 . 1 ) 244; ( 5 ) 190, 202 Koek, J.H. ( 3 . 2 ) 72 Koffi, P. ( 2 . 1 ) 128; ( 5 ) 84 Koga, K. ( 3 . 2 ) 5 Kogan, V.A. ( 2 . 1 ) 188 Kohjiya, S . ( 4 ) 209; ( 5 ) 159 Kohler, B. ( 3 . 3 ) 81 Kohmoto, K. ( 1 ) 452 Kohmoto, S . ( 3 . 5 ) 9 2 , 93 Kohzu, M. ( 3 . 5 ) 140; ( 3 . 6 ) 156 Koike, T. ( 1 ) 208 Koizumi, H. ( 1 ) 83 Kojima, A. ( 3 . 2 ) 30 Kojima, K. ( 3 . 5 ) 25; ( 4 ) 293 Kojima, M. ( 3 . 3 ) 13 Kojima, N. ( 3 . 6 ) 32 Kojima, T. ( 2 . 1 ) 181; (3.2) 9 Kokado, H. ( 4 ) 245 Kokkes, M.W. ( 2 . 2 ) 5 7 , 58 Kokubu, T. ( 3 . 4 ) 161 Kokubun, H. ( 1 ) 6 3 , 208, 447, 493; ( 3 . 5 ) 3 5 ; ( 3 . 6 ) 60 Kokunova, V.N. ( 2 . 1 ) 133 Koleski, J . V . ( 4 ) 26, 104 Kolling, E. ( 1 ) 378 Kolodziej, R.M. ( 2 . 2 ) 18 Komatsu, N. ( 3 . 6 ) 204 Komiyama, K. ( 3 . 2 ) 16 Komorowski, S.J. ( 1 ) 435 Komozin, P.N. ( 2 . 1 ) 133 Konak, C. ( 4 ) 239 Konaka, R. ( 3 . 5 ) 24 Konarski, J. ( 2 . 1 ) 202 Konda, H. ( 3 . 6 ) 162 Kondo, A. ( 2 . 2 ) 8 3 , 8 4 ; ( 5 ) 77 Kondo, K. ( 3 . 5 ) 73 Kondo, M. ( 3 . 2 ) 5 3 ; 3 . 6 ) 123 Kondow, T. ( 1 ) 491 Konijnenberg, J. ( 1 ) 89 179; ( 3 . 4 ) 65 Konopikova, M. ( 3 . 6 ) 58 Konstantatos, J. ( 2 . 1 170; ( 5 ) 76 Konstantinova, A.V. ( 3 . 2 ) 167 Koob, R.D. ( 2 . 3 ) 24, 25 Koolhaas, W.E. ( 3 . 4 ) 3 Kopelman, P. ( 4 ) 199 Koper, N.W. ( 1 ) 176; ( 5 ) 125
Kop'eva, L.G. ( 2 . 3 ) 42 Korobitsyna, I.K. ( 3 . 7 ) 76
Korolev, G.V. ( 4 ) 156 Korotkikh, O.A. ( 2 . 3 ) 5 Korotkov, V . I . ( 5 ) 29 Korovin, Yu.V. ( 2 . 1 ) 214 Koshiba, M. ( 4 ) 137 Koshima, H. ( 2 . 1 ) 39 Koskikallio, J. ( 3 . 7 ) 102, 176
Kosmider, B.J. ( 3 . 2 ) 11 Kossanyi, J. ( 1 ) 94; ( 4 ) 444
Kostermans, G.B.M.
(3.3)
75
Kosugi, N. ( 2 . 1 ) 33; ( 5 ) 27
Kotani, M. ( 1 ) 139 Kotzian, M. ( 2 . 2 ) 21 Kouchi, N. ( 1 ) 83 Kougo, Y. ( 2 . 3 ) 27 Koulkes-Pujo, A.M. ( 5 ) 135
Koutek, B. ( 3 . 3 ) 8 4 ; ( 3 . 4 ) 10
Kovacevic, V. ( 4 ) 335 Kowalski, J. ( 3 . 4 ) 8 4 ; ( 3 . 6 ) 208
Koya, G. ( 2 . 1 ) 186 Koyama, H. ( 1 ) 511 Koyama, K. ( 3 . 6 ) 81 Kozel, S.P. ( 3 . 4 ) 174; ( 4 ) 79
Koz'menko, M.V. ( 3 . 4 ) 2 Kraakman, P.A. ( 3 . 4 ) 3 Kracke, G. ( 1 ) 372 Kraft, G. ( 2 . 2 ) 55 Krakovyak, M.G. ( 3 . 4 ) 174; ( 4 ) 7 9 , 169, 249
Kramarenko, A.S. ( 4 ) 327 Kramer, A. ( 2 . 2 ) 25 Kramer, H.E.A. ( 1 ) 210 Kranovskii, V.A. ( 4 ) 74 Krantz, A. ( 3 . 5 ) 16 Krausz, E. ( 2 . 1 ) 87 Kreiter, C.G. ( 2 . 2 ) 21, 26, 53
Kremer, E.B. ( 4 ) 183 Kresins, E. ( 4 ) 285 Krespan, C.G. ( 3 . 7 ) 85 Krestonosich, S. ( 3 . 4 ) 68 Kretzschmar, G. (3.7) 112 Kreysig, D. ( 2 . 3 ) 4 8 , 49; ( 3 . 3 ) 8 5 ; ( 3 . 4 ) 175, 176; ( 3 . 6 ) 124 Krichevskii, G.E. ( 4 ) 454 Krieger, C. ( 3 . 7 ) 126 Krishnan, C.V. ( 2 . 1 ) 109 Krishnan, S. ( 4 ) 343 Krishnan, V. ( 1 ) 177; ( 5 ) 129
Author Index
572 Kriss, E. ( 2 . 1 ) 67 K r i s t e n s e n , 0. ( 1 ) 30 Krogh, K. ( 3 . 4 ) 107 Krok, K. ( 4 ) 290 Krone, K.P. ( 1 ) 76 K r o n f e l d , K.P. ( 3 . 7 ) 8 3 Krongauz, V. ( 4 ) 216 Kropp, P.J. (3.3) 1 Kriiger, C. ( 2 . 2 ) 5; ( 3 . 3 ) 106; ( 3 . 4 ) 47; ( 3 . 6 ) 100, 120 Krupadanam, G.L.D. ( 3 . 4 ) 140 K r u p i t s k i i , S.V. ( 2 . 1 ) 227 Krusic, P.J. (2.2) 72, 75; ( 3 . 7 ) 2 Kryszewski, M. ( 4 ) 307 Kryukov, A . I . (2.1) 6 2 , 67 Ku, H.S. ( 3 . 6 ) 168 Kubiak, C.P. ( 2 . 2 ) 125 Kubichi, A. ( 1 ) 209 Kubo, M. ( 4 ) 3 Kubo, Y. ( 3 . 2 ) 136, 143, 144, 148, 153-157; ( 3 . 4 ) 48-50; ( 3 . 6 ) 108111, 113, 115, 117, 135 Kubokawa, Y. ( 2 . 1 ) 244; (5) 167-169, 1 9 0 , 202 Kubota, H. ( 4 ) 42 K u c h i t s u , K. ( 1 ) 491 Kuchmii, S.Ya. ( 2 . 1 ) 62 Kudo, A. ( 2 . 1 ) 33; ( 5 ) 25, 27 Kudo, H. ( 3 . 4 ) 121, 145; ( 3 . 6 ) 161 Kuehnle, W. ( 5 ) 124 Kugler, K . J . ( 1 ) 76 Kuhnert, L. ( 2 . 1 ) 107 Kulagina, L.V. ( 3 . 5 ) 62 Kulagowski, J.J. ( 3 . 7 ) 33, 34 Kuleshov, S.P. ( 2 . 3 ) 57 Kuliev, A.M. ( 4 ) 410 Kulikowska, E. ( 3 . 2 ) 97 Kulkar, M.G. ( 3 . 2 ) 18 K u l l b e r g , M.L. ( 2 . 2 ) 125 K u l l n i g , R.K. ( 3 . 1 ) 28; (3.7) 23 Kumagai, T. ( 3 . 3 ) 4 4 , 4 5 , 124; ( 3 . 6 ) 60, 104 Kumamoto, S. ( 3 . 2 ) 50 Kumamoto, Y. ( 3 . 7 ) 69 Kumar, C . V . (1) 386, 476, 490; ( 3 . 2 ) 6 3 , 124; ( 3 . 3 ) 135; ( 3 . 6 ) 54; ( 3 . 7 ) 136 Kumar, S. (1) 336 Kume, H. ( 1 ) 35 Kun, H.B. (1) 506 Kundu, T. ( 1 ) 133
( 3 . 4 ) 1; (3.6) 35, 163; ( 4 ) 177 Lach, P. (3.3) 51-55 Lacher, B. (3.7) 114 L a c o s t e , J. ( 4 ) 312 Laczko, G ( 1 ) 348 Ladouceur, G. ( 3 . 6 ) 7 3 L a e u f e r , M. (3.1) 13 Lagnov, V.M. ( 4 ) 156 Lahav, M. ( 3 . 1 ) 1 0 , 11 L a i , Z. ( 3 . 2 ) 46 Lakin, D.C. (3.5) 7 8 Lakowicz, J . R . ( 1 ) 38, 132, 348 L a l , K. (3.3) 116 L a l a n d i , M. ( 1 ) 72 Lalanne, J . R . ( 1 ) 286 L a l o , C. ( 3 . 5 ) 142 La-Mantia, F.P. ( 4 ) 306 Lamberts, J.J.M. ( 3 . 4 ) 134 Lamette, M. ( 1 ) 106 Lami, H. ( 1 ) 167 Lammel, U. ( 4 ) 39 Lamos, M.L. ( 1 ) 391 Lampe, F.W. (2.3) 11 Lan, A . J . Y . ( 3 . 6 ) 137 Lan, J . Y . ( 3 . 4 ) 7 6 ; ( 3 . 6 ) 219 Lan, M.R. (1) 196 Land, E.J. ( 1 ) 477, 480 Landahl, P.S. ( 4 ) 188 Landon, S . J . ( 2 . 2 ) 44 L a n f r a n c h i , M. (3.5) 119 Lang, J . ( 1 ) 284, 287 Langa, F. (3.3) 72; ( 3 . 6 ) 27 Langbein, H. (3.5) 9 9 ; ( 4 ) 445 Lange, G.L. (3.2) 26, 28 Langford, C.H. ( 2 . 1 ) 140 L a n g k i l d e , F.W. ( 1 ) 421 Langley, A . J . ( 1 ) 19 L a n t r i p , D.A. ( 1 ) 33 Lanz, K. (3.2) 159 Lapcik, L. (3.3) 1 2 L a p i n , S.C. ( 3 . 7 ) 44-46 Laplane, J . P . ( 5 ) 21 L a P l a n t e , J.P. ( 1 ) 417 Lapouyade, R. ( 1 ) 162; ( 3 . 3 ) 90; ( 3 . 4 ) 132, 133 L a r a , S. ( 4 ) 355 L a r r y , R.E. ( 4 ) 230 Lashkov, G . I . (3.4) 17 ( 4 ) 79 L a t t , S.A. ( 1 ) 72 Lau, M.P. ( 1 ) 8 6 ; ( 3 . 6 Laarhoven, W.H. ( 3 . 3 ) 8 7 , 142 Lau, S. (3.2) 6; ( 3 . 6 ) 88; ( 3 . 4 ) 118, 119, 134, 135 172 Lau, W. ( 3 . 4 ) 103 L'Abbe, G. ( 3 . 7 ) 35 Lablache-Combier, A. L a u f e r , A.G.E. (1) 149
Kunin, A . J . (2.2) 120 Kunisch, F. (3.7) 75 Kunkel, L.M. (1) 72 Kunkely, H. (2.1) 5 Kuntyi, 0.1. ( 2 . 1 ) 6 1 Kuntz, R.R. ( 1 ) 168 Kunyama, A. ( 4 ) 58 Kunze, U . (2.2) 23, 24 Kunzer, H. ( 3 . 3 ) 110 KUO, P.-L. ( 1 ) 289, 290 Kuo, Y.H. ( 3 . 5 ) 131 Kupfer, M. ( 1 ) 161; ( 3 . 3 ) 85 Kurahashi, K. ( 2 . 1 ) 161; ( 5 ) 64 Kuramto, N. ( 4 ) 433, 449 Kurauchi, Y. ( 3 . 3 ) 3 4 ; ( 3 . 6 ) 136 Kurbako, V.Z. ( 3 . 5 ) 117 K u r i t a , J . (3.6) 5 7 , 71 K u r i t a , S. ( 2 . 1 ) 181 Kuroda, H. (2.1) 33; ( 4 ) 184; ( 5 ) 27 Kuroda, K. ( 3 . 5 ) 7 3 Kuroda, R. ( 1 ) 452 Kuroda, S. ( 3 . 5 ) 112 Kurokawa, H. ( 1 ) 388 Kurokawa, K. ( 1 ) 164 Kurtenbach, K. ( 1 ) 371 K u r t z , I. ( 1 ) 402 Kurucsev, T. ( 1 ) 202, 393 Kururnada, T. ( 4 ) 388, 396 Kurz, M. ( 3 . 3 ) 145; ( 3 . 7 ) 151 Kushida, T. ( 1 ) 29; ( 3 . 2 ) 31 Kushner, A.S. ( 3 . 4 ) 40 Kusumoto, Y. (1) 308 K u t a l , C. ( 2 . 1 ) 12; ( 2 . 2 ) 6 5 , 127, 129; ( 3 . 3 ) 103; ( 5 ) 7 , 4 0 , 4 5 , 48 Kuwabara, A. ( 2 . 1 ) 235; ( 5 ) 150 Kuwabara, H. ( 2 . 3 ) 27 Kuwano, A. ( 4 ) 112 Kuz'min, M.G. ( 1 ) 148; (3.4) 2 Kuzmin, V . A . ( 1 ) 471, 489 Kuz'min, V . G . ( 5 ) 227 Kuz'mina, N.A. ( 2 . 2 ) 61 Kuzmoney, H. ( 4 ) 189 Kuznetsov, E . I . (5) 107 Kuznetsova, I . M . ( 1 ) 338 K v i t k o , I.Ya. ( 3 . 6 ) 216 Kwon, I . C . ( 4 ) 6 1
573
Author Index Launikonis, A. ( 2 . 1 ) 110, 114, 141; ( 5 ) 9 7 , 98 L a u p r e t r e , F. ( 4 ) 195 Laurenson, P. ( 4 ) 305 L a u r e n t , A. (3.1) 55; ( 3 . 7 ) 107 L a u r e n t , C. ( 4 ) 291 Lavabre, D. ( 5 ) 21 L a v a l l e e , D.K. (2.1) 8 L a v i a l l e , F. (1) 399 L a v i e r i , F.P. ( 3 . 2 ) 8 7 , 106 Lavrikova, T.I. ( 3 . 7 ) 93 Lawrance, G.A. ( 2 . 1 ) 47 Laws, W.R. (1) 333, 334 Lawton, G. (3.7) 77 Lawton, J.B. ( 4 ) 227 Lay, P.A. ( 2 . 1 ) 110, 141; (5) 97, 98 L a z a r e , S. (3.4) 133; ( 4 ) 364 Lazarenko, E.T. ( 4 ) 80 Lazarev, L.N. ( 2 . 1 ) 227 L e a v i s , P.C. (1) 363, 364 LeBlanc, B.F. (3.1) 56; (3.7) 21 Lechner, J . A . ( 4 ) 328 Ledwith, A. ( 4 ) 166 Lee, C.Y. ( 2 . 2 ) 78, 8 6 Lee, F.L. ( 3 . 1 ) 39; (3.4) 151; (3.5) 11 Lee, H.W.H. ( 1 ) 438 Lee, J. ( 1 ) 183 Lee, J.L. ( 4 ) 20, 101, 241 Lee, K.D. (3.4) 144 Lee, K.H. ( 2 . 1 ) 146 Lee, K.W. (2.2) 64 Lee, L. (2.1) 155 Lee, L.Y.C. ( 1 ) 220; (3.5) 118; (5) 70 Lee, M. ( 1 ) 235; (3.2) 26 Lee, M.L. (3.4) 120, 121, 145; (3.6) 161 Lee, 0. ( 4 ) 246 Lee, S.W. (2.2) 6 2 Lee, Y.T. ( 3 . 3 ) 38 Leeming, S.A. ( 3 . 2 ) 10 Lees, A.J. (2.2) 18-20 Lefkowitz, S.M. ( 1 ) 448 Legros, B. ( 5 ) 39 Lehn, J . M . (2.1) 1 2 4 , 150 Lehr, G.F. (1) 304; ( 3 . 7 ) 2 L e i , X. ( 1 ) 492; ( 3 . 1 ) 6, 27; (3.4) 187 Leigh, W . J . ( 1 ) 451, 484 L e i g h t o n , P. (2.1) 241; (5) 130 Leihkauf, P. (3.7) 3 7 , 38 Leinwand, D.A. ( 1 ) 448 L e i s e r o w i t z , L. ( 3 . 1 ) 10,
11 Leismann, H. ( 3 . 1 ) 1; (3.4) 26 Leland, B.A. ( 5 ) 131 Lemaire, F. (3.6) 174 Lemaire, J . (2.1) 53, 54; ( 3 . 4 ) 12; ( 4 ) 298, 305, 310, 312, 330, 331, 348 Lemmetyinen, H. (1) 89; (3.4) 65 Lempereur, F. (3.5) 142 Lempers, E.L.M. ( 3 . 4 ) 28 Lenka, S. ( 4 ) 43, 110 Lenoble, C. (1) 508-510 L e n t s n e r , B.I. ( 5 ) 227 L e n t z , B.R. (1) 275, 277 Leonard, C. (4) 195 Leonova, G.V. ( 4 ) 274 Lerebours, B. (5) 141 Le ROUX, D. (2.1) 234; ( 5 ) 138 Le ROUX, P. ( 1 ) 299 Lesclaux, R. ( 3 . 5 ) 89 L e s h i n a , T.V. (3.5) 6 Leska, J. ( 3 . 6 ) 2 Lesma, G. (3.2) 6 4 L'Esperance, R.P. (3.5) 6 6 , 67 L e t a , S. ( 2 . 2 ) 93 L e t c h e r , R.M. (3.4) 113 Letokhov, V.S. (1) 392 Leung, H. (3.5) 88 Leung, M.S. (4) 376 L e v e n t i s , N, ( 2 . 2 ) 4 3 Lever, A.B.P. (2.1) 2, 131; ( 5 ) 6 Levin, V.S. ( 4 ) 431 Levin, Ya.A. (3.7) 1 Levine, A. ( 1 ) 182 L e v i t z , P. ( 1 ) 309 Levy, A. ( 1 ) 311 Levy, D.H. (1) 327 Levy, R.L. ( 4 ) 192, 1 9 3 Lewin, M . J . (2.2) 110 Lewis, D.M. ( 4 ) 456 Lewis, F.D. (3.3) -64 L e w i s , J.W. ( 2 . 1 ) 8 2 Lewis, P.N. ( 1 ) 396 Leyendecker, M. (2.2) 53 L i , G. ( 4 ) 4 9 , 50 L i , J. ( 4 ) 421 L i , M. ( 4 ) 85, 88, 89 L i , Q. (3.5) 57 L i , S. ( 4 ) 373 L i , X. ( 2 . 1 ) 161; (5) 64 L i , Y. ( 4 ) 373; ( 5 ) 177 L i , Z . ( 4 ) 217, 223 L i a n g , D. (3.2) 46 Liang, T.-Y. ( 3 . 7 ) 9 1 Liang, X. (3.5) 38 Liang, Z. ( 4 ) 89 Liauw, S. (5) 132
L i b e r t i n i , L.J. ( 1 ) 361 L i c i n i , G. (3.6) 1 7 1 L i c k i s s , P.D. ( 2 . 3 ) 19; (3.3) 4 ; (3.6) 199 Lieberman, R.A. ( 4 ) 139 L i g h t , J.R.C. (2.2) 79 L i j t e n , F.A.T. ( 3 . 3 ) 8 7 ; (3.4) 135 Limy B.T. (1) 151 Limy E.C. ( 1 ) 113, 151 L i n , C. ( 3 . 6 ) 170 L i n , C.H. ( 2 . 2 ) 78 L i n , 1,s. ( 4 ) 127 L i n , S.B. ( 4 ) 137 L i n , T.H. ( 1 ) 283 L i n , Z. (2.2) 74 Lindberg, B. ( 4 ) 36 Lindeman, T.G. (2.3) 2 Lindenberg, K. (1) 245, 246 L i n d q v i s t , L. ( 1 ) 323 L i p p i t s , G.J.M. ( 4 ) 132 L i s , S. ( 2 . 1 ) 202 Lisko, J . R . ( 2 . 2 ) 9 0 L i s s i , E.A. ( 1 ) 147, 288, 291, 458; ( 3 . 5 ) 9 ; ( 4 ) 82 L i t s o v , N.I. ( 4 ) 153; 315 L i t t l e , R.D. ( 3 . 7 ) 15 L i u , C.F. ( 3 . 2 ) 42 L i u , C.S. (2.2) 7 8 L i u , D. ( 4 ) 4 9 , 50 Liu, H.J. (3.2) 18 L i u , J.H. (3.4) 6 6 , 6 7 L i u , M.T.H. ( 3 . 7 ) 4 , 8, 9 , 11, 1 2 L i u , P. ( 4 ) 6 0 L i u , W. (2.1) 204; (3.6) 7 L i u , Y.C. (2.1) 27; ( 5 ) 191 L i u , Y.S. ( 1 ) 51 Lodder, G. ( 1 ) 180; ( 3 . 4 ) 27 Loder, J . W . ( 2 . 1 ) 114 Loeb, S.E.S. ( 3 . 4 ) 111 L o f r o t h , J.-E. ( 1 ) 46 Loffelman, F.F. ( 4 ) 405, 416 Loginov, A.V. (2.2) 108 Lohray, B.B. ( 3 . 2 ) 63 Lohse, F. ( A ) 359 Lohse, V. (3.7) 37, 38 Lombardo, D . A . ( 3 . 5 ) 20 London, S.J. ( 4 ) 4 8 Lopez, L. ( 3 . 5 ) 108 Lopez-Aparicio, F.J. (3.5) 101 Lopez-Arbeloa, F. ( 1 ) 330 Lopez-Campillo, A . ( 1 ) 169 Lopez-Espinoza, M.T.P.
Author Index
574 (3.5) 101
Lorch, E. (3.6) 51 Lorenzoni, E. (2.2) 80 Lougnot, D.J. (1) 461, 462
Louis, C. (5) 168 Lowry, R.E. (4) 237, 243, 252
Lozoskaya, E.L. (4) 430 Lu, H. (4) 60 Lu, s. (4) 373 Lu, x. (2.2) 74 Lu, Z.X. (1) 366 Lucchini, V. (3.6) 158 Luc-Gardette, J. (4) 298 Luciano, A3 (5) 20 Lucki, J. (4) 406, 407, 427
Luduena, R.F. (1) 345, 354
Ludwick, A.G. (4) 142 Luettke, W. (1) 206 Lugtenburg, J. (3.2) 72 Lukac, I. (4) 354 Lukomskaya, I.S. (4) 332 Luk'yanenko, L.V. (4) 78 Luk'yanov, B.S. (3.6) 41 Lunak, S. (3.5) 111 Lunt, E. (3.4) 126 Luss, H.R. (3.4) 189;
McCown, L.B. (1) 25, 40 McCullough, J.J. (1) 150 Macda, T. (4) 25 McDerrnott, G.A. (2.2) 46 MacDonald, P. (4) 405, 416
MacDonald, S.A. (4) 98 McEvoy, A.J. (2.1) 16; (5) 220
McGirnpsey, W.G. (3.2) 158; (3.7) 54, 58, 59
McGrath, W.D. (2.3) 32 McGuigan, C. (3.4) 57; (3.6) 127
McGuire, M. (1) 155; (5) 160
Machado, R. (3.1) 44, 45; (3.4) 46; (3.5) 13, 14
Machida, K. (2.2) 56 Machida, L. (3.6) 186 Machida, M. (3.2) 145-
147, 151; (3.6) 80, 114, 116, 179, 181, 183, 184 Macielag, M. (3.2) 106 Macinnis, W.K. (1) 150; (3.4) 152; (3.5) 17 McIntosh, A.R. (4) 226; (5) 126 Mackay, R.A. (5) 224 (3.6) 167 McKenna, G.B. (4) 237 Lutz, P. (4) 237 McKenna, W.P. (2.2) 60 Lux, B. (1) 335 Mackor, A. (3.3) 94; (5) Ly, C. (3.4) 24 43 Lyashenko, L.V. (2.1) 19; McLendon, G. (1) 155; (5) (5) 207 160 Lydon, J.D. (2.1) 110; McMahon, R.J. (3.7) 43, 50 (5) 98 Lyle, T.A. (1) 100 McMillin, D.R. (2.1) 11 Lytle, F.E. (1) 33, 409 McMorrow, D. (1) 243 McMullan, R.K. (3.1) 11 MacNeil, P.A. (2.2) 121 Ma, 2 . ( 4 ) 107, 398 Macrov, S.B. (4) 136 Maassen, J.A. (1) 404 Madge, D. (2.1) 40 McAllister, W.A. (2.1) Maekawa, Y. (1) 142 203 Miirkl, G. (3.6) 212 MacAlpine, D.K. (3.6) 144 Maertin, R. (4) 41 McArdle, P . J . (3.2) 8; Maestri, M, (2.1) 93, (3.4) 43 175; (5) 123 McAuliffe, C.A. (2.1) 66 Maglione, R. (3.5) 41; McCaffery, A.J. (1) 15 (3.6) 61 MacCallurn, J.R. (4) 296 Maguire, J.A. (2.2) 67 McCarthy, M.G. (2.1) 110; Mah, S. (4) 19 Mahaguchi, H. (1) 95 (5) 98 McCarthy, N.J. (4) 104 Mahgoub, S . A . (3.4) 79 McClanahan, S.F. (2.1) Mahieu, B. (2.1) 158; (5) 88; (5) 56 74, 104 McCleland, C.W. (3.5) Mahler, W. (3.1) 7 100; (3.7) 100 Maidan, R. (3.3) 143 McClelland, B.J. (1) 4 Maier, G. (3.2) 159; McClure, C.K. (3.7) 121 (3.3) 74, 76; (3.7) 68 Maier, V.E. (5) 103 Maccoll, R. (1) 261
Maiya, G.B. (1) 177; (5) 129
Majoral, J.P. (3.7) 87 Makarov, S.P. (3.4) 127; (3.6) 28, 36
Makhmadrnurodov, A. (5) 210
Makhonina, E.V. (5) 114 Maki, A.H. (1) 488, 496 Maki, Y. (3.6) 62 Makowska, B. (2.1) 202 Makunchi, K. (4) 272 Malati, M.A. (5) 188 Malba, G. (5) 88 Malba, V . (2.1) 99; (3.5) 39, 143; (5) 137
Maldotti, A. (2.1) 71 Malet, P. (5) 166 Maliaiah, B.V. (3.4) 140 Maliwal, B.P. (1) 38 Malkhasian, A.Y.S. (2.1) 140
Malkin, Ya.N. (3.6) 36 Malliaris, A. (1) 282, 284, 287
Mallory, C.W. (1) 229; (3.4) 111
Mallory, F.B. (1) 229; (3.4) 111
Maloney, V.M. (3.7) 54 Mal'tsev, A.K. (3.7) 5 Maltthys, E.F. ( 4 ) 300 Mamantov, A. (3.4) 90, 91 Marniche-Afara, S. (5) 230 Man, A.W.-H. (1) 297; (4) 280
Manabe, 0. (2.1) 189; (3.6) 11, 15
Mandal, K. (2.1) 94; (5) 92
Manfrin, M.F. (2.1) 150 Manh, D.D.H. (3.1) 18 Mani, J. (3.4) 38, 39 Manigand, C. (3.3) 90; (3.4) 132
Manning, L.E. (1) 187 Mansour, A.F. (5) 240, 204
Manuel, G. (3.7) 87 Marcandalli, B. (4) 113 Marcantonatos, M.D. (2.1) 207
Marchaj, A. (2.1) 50 Marchand, G.R. (3.3) 9 Marchant, M.J. ( 3 . 4 ) 110 Marchioro, C. (3.6) 158 Marciniec, B. (3.6) 151, 152
Marcinkowska, K. (2.1) 63 Marconi, G. (1) 90 Marden, M.C. (1) 365 Mardian, J.K.W. (1) 394
575
Author Index Mazzu, A. (3.4) 131 Mardirosyan, Z. (3.5) 139 Masuda, K. (3.1) 41; Mazzucato,, U. (1) 227 (3.6) 75 Margareth, J.C.M. (3.2) Meador, M.A. (1) 484; Masuda, T. (3.2) 15; 69 (3.1) 40 (3.4) 81; (3.6) 10; (4) Margaretha, P. (3.2) 6, Meallier, P. (1) 383; 123 17, 66; (3.6) 172, 173 (2.1) 246 Masude, H. (2.2) 56 Margerum, L.D. (5) 157 Meares, C.F. (1) 395 Masuhara, H. (1) 85 Margolin, A.L. (4) 431 Mechkovskii, S.A. (2.1) Masumo, K. (1) 485 Margrave, J.L. (2.2) 82 143 Mariano, P.S. (3.3) 140; Masumoto, Y. (3.7) 10 Meech, S.R. (1) 319 Mataga, N, (1) 85, 146, (3.6) 137, 138 Mehrotra, A. (3.1) 54; 259; (5) 121 Marignier, J.L. (5) 106 (3.7) 101 Mathews, R.W. (5) 36, 37 Mariotti, S. (1) 355 Mehrotra, K. (3.1) 54; Mathies, P. (3.1) 35; Markert, J. (3.3) 105, 106; (3.6) 100
Markovits, D. (1) 280 Marples, B.A. (3.3) 137; (3.6) 66
Marquet, J. (3.4) 73 Marrero, J.J. (3.7) 186 Marsau, P. (3.4) 173 Marsh, K.L. (5) 126 Marshall, J.L. (2.1) 134 Marsman, H.J.B. (1) 75 Martin, C.N. (4) 185, 206 Martin, C.R. (1) 293 Martin, G.F. (3.2) 37 Martin, J.W. (4) 328 Martin, L.L. (2.1) 47 Martin, R.H. (3.4) 110, 114, 115
Martinelli, M. (4) 76 Martinez-Lozano, C. (3.5) 126
Martinho, J.M.G. (1) 158, 257
Martinotti, F. (4) 314, 393
Martonosi, A. (1) 372 Marty, A. (1) 159 Marutani, M. (3.6) 33 Maruya, K. (5) 25 Maruyama, K. (3.2) 136, 143, 144, 148, 161-163; (3.6) 108, 111, 113 Maruyama, Y. (1) 105 Marx, J. (4) 196 Marynovski, S. (3.1) 46; (3.4) 155; (3.5) 15 Masaji, 0. (2.3) 6 Masamune, S. (2.3) 29; (3.6) 196 Masanet, J. (3.5) 142 Mashirov, L.G. (2.1) 219 Mashraqui, S.H. (3.5) 51 Mashyuk, A.F. (4) 74 Maslov, A.V. (2.1) 148; (5) 78 Masnovi, J.M. (1) 1 7 2 , 182; (3.4) 56, 165; (3.6) 140 Mason, J.D. (3.3) 1 Masotti, L. (1) 390
(3.3) 70; (3.7) 135
Matko, J. (1) 347 Matsuda, H. (4) 409 Matsuda, M. (4) 231 Matsuda, Y. (2.1) 39 Matsueda, S. (3.5) 86 Matsuhara, H. (4) 176 Matsumoto, M. (3.5) 73 Matsumoto, T. (3.4) 55; (3.6) 131
Matsuo, T. (5) 139, 156 Matsushima, R. (3.2) 51, 93; (3.4) 154; (3.6) 16 Matsushita, T. (5) 118 Matsuura, T. (1) 239; (3.1) 47; (3.2) 90; (3.3) 29; (3.4) 150; (3.5) 131; (3.6) 147 Matsuzawa, H. (4) 151 Matsuzawa, S. (2.3) 26; (3.4) 157; (3.6) 200 Mattauch, B. (3.7) 22 Mattay, J. (3.1) 12; (3.4) 23-26, 31 Mattei, P.L. (3.1) 17; (3.2) 65 Matthews, J.W.A. (4) 452 Matthews, R.S. (3.4) 42 Mattice, W.L. (1) 283 Mau, A.W.H. (2.1) 47, 110, 114, 141; (5) 71, 97, 98 Maukai, T. (3.3) 131 Maunnig, D. (3.6) 217 Maurizi, M.R. (1) 360 Mauzerall, D. ( 1 ) 32 Mayake, H. (5) 80 Mayer, E. (5) 62 Mayer, H. (3.3) 125 Mayer, J. (4) 290 Mayer, M. (3.7) 167 Mayer, W.J.W. (5) 38 Mayoux, C. (4) 291 Mayr, A. (2.2) 46 Mazur, D.J. (3.7) 121 Mazura, J. (4) 133 Mazzariello, R.G. (4) 26 Mazzocchi, P.H. (3.2) 137-139; (3.6) 107, 112
(3.7) 101
Mehta, G. (3.2) 84 Meier, K. (4) 359 Meijs, G.F. (3.7) 162 Meisel, D. (1) 140; (3.5) 134
Meissner, D. (5) 219 Melcher, R.L. (4) 365 Melikyan, V.V. (5) 229 Mel'nikov, M.Ya. (4) 51 Memarian, H.R. (3.4) 47; (3.6) 120
Memming, R. (5) 219 Mendenhall, G.D. (1) 503; (4) 273
Meng, L. (4) 50 Menghini, M. (2.1) 226 Mentha, Y. (3.6) 119 Menzel, R. (1) 205 Merola, F. (4) 253 Mes, G.F. (1) 176; (5) 125
Meseguer, F. (5) 235, 236 Meshkova, S.B. (2.1) 214 Messmer, C.H. (1) 342 Metui, H. (1) 315 Meunier-Piret, J. (2.1) 158; (5) 74
Mews, R. (3.7) 182 Meyer, T.J. (2.1) 13, 134; (2.2) 102; (5) 157
Meyer, V. (3.4) 38 Meyers, A . I . (3.2) 20; (3.6) 91
Meyerstein, D. (2.1) 166 Mialocq, J.C. (1) 299; (2.1) 234; (5) 135, 138
Michael, B.D. (1) 18 Michael, M.N. (4) 436 Michalczyk, M.J. (2.3) 2 1 Micheau, J.C. (5) 21 Michel-Beyerle, M.E. (5) 133
Michels, E. (2.2) 26 Michelsen, H.A. (1) 128; (3.6) 67
Michl, J. (2.3) 13, 21; (3.7) 88
Miehg, J.A. (1) 157, 158
576 Migita, Y. (3.2) 142 Miguel, M.G.M. (1) 296; ( 2 . 1 ) 216 Mihailov, S. (1) 198 Mihammad, M. (2.3) 39 Mihashi, S. (3.1) 48 Mikawa, H. (4) 17 Milazzani, Q.G. (5) 99 Milder, S.J. (2.1) 82, 151, 152; (3.2) 96 Miler, R . J . (1) 502 Miles, W.H. (2.2) 94 Milgrom, L.R. (5) 127 Mil'khiker, P.P. (4) 437 Milkie, T.H. (4) 337 Millar, D.P. (1) 226 Millard, R.R. (1) 219, 236 Miller, G.C. (3.5) 55 Miller, M.E. (2.2) 88 Miller, R.D. (3.7) 73; (4) 371 Miller, S.S. (2.1) 95 Millers, D. (4) 286 Milone, L. (2.2) 99 Milosavljevic, B.H. (2.1) 115, 116; (5) 161 Minaev, B.F. (3.5) 61 Minai, Y. (2.2) 71 Minamikawa, S. (3.2) 137, 139; (3.6) 107 Minana, M. (5) 106 Minemater, Y. (4) 302 Ming, Y. (3.3) 11; (3.5) 87, 109 Minkin, V . I . (3.6) 41 Minnesgern, H. (3.6) 191 Minsker, K.S. (4) 282, 4 29 Minto, F. (4) 355 Minton, K.W. (1) 337 Miranda, M.A. (3.4) 148, 180 Mirbach, M.F. (2.2) 16 Mirbach, M.J. (2.2) 16, 89 Miroshnichenko, I . V . (2.1) 133 Misawa, H. (3.5) 2 7 , 36 Mishakov, G.V. (2.3) 46 Mishin, K.Ya. (2.1) 227 Mishra, A . K . (1) 127, 136 Mishra, S.P. (1) 380 Miskowski, V.M. (2.1) 149 Mislavskii, B.V. (4) 119 Misumi, S. (3.4) 158, 166, 167 Mita, I. (1) 96, 211, 270; (4) 175, 198, 214, 236 Mitchel. E. (3.7) 166 Mitchell, G. (3.7) 32
Author Index Mitchell, S. (2.2) 110 Mitina, V.G. (3.2) 44 Mitra, S.B. (4) 343 Mitsuzuka, M. (1) 493; (3.5) 35 Miwa, T. (3.3) 50 Miyagawa, K. (1) 460 Miyajima, M. (4) 439 Miyake, S. (3.7) 177 Miyake, Y. (3.4) 146 Miyama, H. (2.1) 235; (4) 112; (5) 150, 197 Miyama, Y . (3.5) 128 Miyamoto, T. (3.6) 150 Miyasaka, H. (1) 85 Miyashita, A. (3.3) 118 Miyata, 0. (3.6) 31, 32 Miyauchi, Y. (2.1) 126 Miyaura, N . (3.7) 185 Miyazaki, K. (3.6) 11 Mizera, F.P. (4) 376 Mizoguchi, T. (3.2) 142; (3.6) 82 Mizumoto, K. (3.5) 53 Mizuno, K. (2.3) 10; (3.1) 41; (3.3) 126; (3.4) 74, 75; (3.5) 103, 106, 107; (3.6) 75, 209; (5) 47 Mizutani, T. (3.3) 23 Mlynek, C. (3.4) 108 Moan, J. (1) 415 Mochida, K . (2.3) 55 Modak, S.K. (4) 93 Modena, G. (3.6) 158 Modinos, A . (1) 4 Mobius, K. (2.1) 41 Moeller, W. (1) 404 Moger, G. (3.5) 63 Moggi, L. (2.1) 3, 142, 150; (5) 54, 99 Mohanty, I . B . (4) 43 Mohri, T. (1) 375 Molla, A.H. (2.2) 76 Molla, M.E. (2.2) 76, 77 Momose, Y. (3.2) 41 Monnerie, L. (4) 160, 168, 195, 212, 253, 257, 270 Monnier, E. (1) 305 Monnoret, J. (4) 205 Montavon, F. (3.6) 52 Montoro, T. (1) 169 Moody, C.J. (3.6) 166; (3.7) 33, 34, 77, 98, 99 Mooney, W. (2.1) 221 Moore, D.E. (3.5) 7 Moore, R.A. (1) 183 Moore, W.M. (2.2) 135; ( 3 . 3 ) 102; ( 5 ) 44 Mooring, A.M. (3.7) 50
Moorman, A.r. (3.6) 168 Morabito, P. (3.6) 141 Morales, P. (2.1) 226 Moralev, V.M. (2.3) 54 Morantz, D.J. (4) 197 Morawetz, H. (4) 180, 223, 271 Moreno-Manas, M. (3.4) 73 Morgan, B.P. (3.4) 189; (3.6) 167 Mori, A. (3.2) 160 Mori, Y. (1) 142, 442 Morii, M. (1) 376 Morinaka, A . (3.6) 39 Morisaki, M. (3.7) 67 Morishima, Y. (1) 269; (4) 225; (5) 148 Morishita, K. (4) 198 Morita, M. (1) 83 Morita, S. (3.3) 34 Moriyama, H. (5) 80 Morizur, J.P. (3.1) 15 Morley, C.P. (2.2) 48 Moroi, R. (3.2) 41 Moroni, M. (3.4) 188: (3.6) 65 Morrison, C.L. (2.1) 23; (5) 172, 206 Morrow, T. (2.3) 32 Morse, D.L. (2.2) 42 Morse, K.W. (2.2) 135; (3.3) 102; (5) 44 Mortezaei, R. (3.1) 4 3 ; (3.2) 62 Morton, C.E. (2.2) 40 Morton, G.H. (3.2) 25 Morton, J.R. (2.2) 123 Mos, G.H.M. (3.3) 8 2 Mosetti, F. (1) 227 Moshenberg, R. (3.6) 86 Moskovkin, A.S. (2.1) 133 Motherwell, W.B. (3.1) 24; (3.4) 129 Motohashi, K. (4) 375 Motyka, L.A. (3.3) 49; (3.4) 14 Mourmamode, A. (3.4) 132 Mozzanega, M.N. (5) 175 Msayib, K . J . (4) 318 Muller, E.P. (3.2) 58; (3.6) 53 Muller, H.K, (4) 387, 392 Muller, U. (3.6) 4; (4) 24 Muller, W. (1) 407 Muller-Remmers, P.L. (3.7) 3 Mugmer, J. (1) 260 Mugnier, J. (5) 243 Mujashita, T. (4) 231 Mukai, C. (3.6) 33 Mukai, T. (3.3) 44, 45,
577
Author Index Nagorski, H. (2.2) 16, 89 Naguib, M.A.Y. ( 4 ) 446 Nagy, R. (1) 347 Nahor, G.S. ( 2 . 1 ) 230 Nahr, U. (3.7) 36 Naikenova, G.P. ( 4 ) 350 Nair, P.M. (3.3) 142; ( 3 . 4 ) 149; ( 3 . 7 ) 173 Nair, V. (3.4) 102; (3.7) 170, 171 N a i t o , S. ( 2 . 1 ) 32; (5) 189 N a i t o , T. (3.2) 41; (3.4) 136, 137; ( 3 . 6 ) 31, 32, 34, 9 0 Nakadaira, Y. (3.6) 204 Nakagaki, M. ( 3 . 5 ) 136 Nakagaki, R. (1) 191; ( 3 . 4 ) 59-61, 63, 178; (3.5) 2 3 Nakagawa, H. ( 3 . 5 ) 131 Nakagawa, K. ( 4 ) 115 Nakagawa, Y. ( 3 . 6 ) 145 Nakahima, N. ( 3 . 6 ) 1 2 3 Nakahira, T. (3.5) 25 Nakai, H. (3.2) 142; ( 3 . 6 ) 82 Nakajima, N. ( 3 . 2 ) 53, 54 Nakamura, A. ( 2 . 3 ) 16; ( 3 . 4 ) 172; (3.6) 207 Nakamura, H. (3.3) 6 8 Nakamura, J . ( 2 . 1 ) 163; (3.4) 62 Nakamura, K. ( 3 . 3 ) 109; ( 4 ) 451 Nakamura, S. ( 3 . 4 ) 6 3 ; ( 3 . 6 ) i5 Nakamura , ( 1 ) 83; ( 2 . 2 ) 39 N a k a n i s h i , H. (3.4) 186 Nakanishi, S. ( 4 ) 451 Nakao, R . 2.3) 28; (3.6) 203 Nakashima, M. ( 3 . 6 ) 15 Nadtochenko, V . A . ( 3 . 5 ) Nakashima, N. ( 1 ) 234, 33; ( 5 ) 143 319, 444 ( 3 . 3 ) 28 Nagagawa, K. ( 5 ) 199 Nagai, Y. ( 2 . 3 ) 27; ( 3 . 6 ) Nakashima. Y. ( 4 ) 157 197 Nakashira; T. ( 5 ) 194 Nagakura, S. ( 1 ) 191; Nakayama, T. ( 1 ) 189 , ( 3 . 4 ) 6 2 , 178; (3.5) 23 190; ( 3 . 4 ) 83 Nagamura, T. (5) 139, 156 Nakazawa, N. ( 1 ) 215 Nakazawa, T. ( 1 ) 103, 442 Nagarajan, S. (3.5) 115 Nagarajan, V. (1) 223, N a l l y , J. ( 3 . 2 ) 130; 231, 232 ( 3 . 7 ) 109 Naman, S.A. ( 2 . 1 ) 37; ( 5 ) Nagase, S. ( 2 . 2 ) 29 28, 221 Nagata, A . ( 4 ) 152 Namasivayan, C. ( 2 . 1 ) 45 Nagata, M. ( 3 . 2 ) 92; Nanjundiah, B.S. ( 3 . 3 ) (3.6) 18 Nagata, Y. ( 2 . 3 ) 28 33, 142, 144; ( 3 . 4 ) Nagaya, S. ( 4 ) 303 149; (3.7) 173-175 Nagishiwara Rao, B. (1) Naqvi, M.K. ( 4 ) 385 455 N a i i a n , M. ( 3 . 2 ) 138
124; (3.6) 104 Mukakami, S. (3.6) 196 Mukerjee, S.K. (3.3) 31, 32 Mulazzani, Q.G. ( 2 . 1 ) 104, 142 Mullakhmetov, I . N . ( 4 ) 282 Muller, F.W. ( 4 ) 196, 255 M u l l i n , J.L. ( 4 ) 207 Munro, H.S. ( 4 ) 309 Munuera, G. ( 5 ) 166 Murai, H. ( 1 ) 460 Murakami, S. (2.3) 29 Murakami, Y. ( 2 . 1 ) 39; ( 4 ) 449 Muraki, H. ( 2 . 1 ) 35 Muramatsu, S. (3.6) 147 Murata, I. ( 1 ) 103 Murata, S. (3.7) 92; ( 5 ) 174, 185 Murphy, W.R. (2.1) 129; ( 5 ) 60 Murray, R.W. ( 5 ) 157 Murray, S. (3.6) 7 3 Murtaza, 2. (2.1) 5 9 Murty, B.A.R.C. ( 3 . 2 ) 124 Muruyama, K. ( 3 . 4 ) 50; (4) 388 Musci, G. ( 1 ) 353 Musso, H. ( 3 . 2 ) 128 Mustafeva, S.K. ( 4 ) 423 Mustroph, H. ( 4 ) 443 Mutai, K. ( 1 ) 191; (3.4) 59-63 Mutoh, A. ( 4 ) 281 Muzart, J. ( 2 . 2 ) 128; (2.3) 9 ; (3.1) 43; (3.2) 62 Myasnikov, I.A. ( 5 ) 200, 208
.
N a r i n , T. (3.5) 79 Narula, C.K. (3.6) 217 Nasimento, M.G. ( 4 ) 356 N a t a r a j a n , L.V. (1) 312 N a t a r a j a n , P. (1) 268 Natsukamo, K. ( 4 ) 449 Naumann, A. (3.5) 116 Naumer, R. (2.2) 24 Navarro, J.A. (5) 1 2 Navio, A. (5) 166 Nayak, P.L. ( 4 ) 43, 110 Nayak, U.R. (3.1) 20 Nayaya, H. (5) 190 Nazran, A.S. (3.7) 48, 49 Nazuka, R. ( 4 ) 302 Neckers, D.C. (1) 478, 482; ( 3 . 5 ) 56, 59; ( 4 ) 357, 358 Neef, G. ( 3 . 1 ) 16 Nefedov, O.M. (3.7) 5 Nehrings, A. ( 3 . 1 ) 50 Neier, R . (3.2) 133 Nemeth, E.F. (1) 408 Nenkov, G. ( 4 ) 353 Neta, P. ( 2 . 1 ) 160, 240; ( 5 ) 113, 115 N e t t o - F e r r e i r a , J.C. ( 1 ) 451, 459 N e u r e i t e r , M. (1) 210 Newhouse, E . I . ( 4 ) 199 Ngai, R. ( 2 . 1 ) 169 Ngata, Y. (3.6) 203 Nguyen, M.T. (3.7) 8 4 Nguyen, T.L. ( 4 ) 311 N i c h o l l s , C.H. ( 4 ) 440 N i c k o l ' s k i i , V.G. ( 4 ) 287 N i e l s e n , P.E. ( 3 . 2 ) 101 N i g a z i , F.F. ( 4 ) 428 N i i k u r a , H. ( 4 ) 57 N i i n i s t o , L. ( 2 . 1 ) 215 N i i r a n e n , J . (3.7) 176 Niizuma, S. (3.6) 60 N i k i t a e v , A.T. ( 2 . 2 ) 133 N i k i t i n a , G.N. ( 2 . 1 ) 55 Nikogosyan, D.N. ( 1 ) 392 Nikolaev, V . A . ( 3 . 7 ) 76 Nikolov, P. ( 1 ) 126 Nikol'skii, A.B. (2.1) 193 Niles, W.D. (1) 403 Ninayawa, A. ( 4 ) 409 Ninomiya, I. (3.4) 136, 137; ( 3 . 6 ) 31, 3 2 , 3 4 N i s h i b a t a , Y. ( 3 . 6 ) 183 N i s h i d a , A. ( 3 . 6 ) 1 4 ; ( 3 . 6 ) 154 N i s h i d a , S. ( 2 . 1 ) 101, 105, 1 2 3 N i s h i g u c h i , Y. ( 3 . 4 ) 137 N i s h i j i m a , Y. (1) 263; ( 3 . 3 ) 120; ( 3 . 6 ) 9 2 ; ( 4 ) 234
578 Nishikubo, T. ( 4 ) 57, 146, 148 Nishimoto, S. (3.5) 44; ( 4 ) 372; ( 5 ) 181, 182 Nishimura, N. ( 1 ) 83; (3.3) 7 ; (3.6) 9 Nishio, T. (3.2) 53, 54; (3.6) 123, 182 Nittono, T. ( 3 . 3 ) 45 Nivorozhkin, L.E. (3.6) 41 Nixdorf, M. ( 3 . 3 ) 74 Nixon, E.R. (2.1) 69 Nizova, G.V. (2.2) 132, 133 Nobbs, J.H. ( 4 ) 164 Nobudsada, N. (3.3) 7 Nobuhara, H. (3.3) 34; (3.6) 136 Noda, H. (2.2) 49-51, 59 Noda, K. ( 3 . 3 ) 10 Noda, M. ( 4 ) 451 Noe, L.J. ( 1 ) 233 Noel, C. ( 4 ) 195 Noel, S. ( 4 ) 291 Noerdin, H. (3.3) 39; (3.7) 142 Noeth, H. (3.6) 217 Noguchi, K. (3.5) 127 Nohara, M. ( 3 . 2 ) 13 Nohira, H. ( 3 . 3 ) 118 Nomura, M. ( 4 ) 432 Nonaka, T. ( 4 ) 122 Noomen, A . ( 4 ) 140 Norden, B. ( 3 . 2 ) 101 Norin, T. (3.3) 84; (3.4) 10 Norinder, U. (3.3) 30 N o r r i s , R.K. (3.7) 156 N o r t h c o t t , D.J. (3.7) 49 Nosaka, Y. (2.1) 235; ( 5 ) 150 Noth, D. (1) 133 Nouchi, G. (1) 162 Nourmamode, A. (3.3) 90 Nowaezyk, K. ( 1 ) 456 Nowakowska, M. ( 4 ) 338340, 415 Nozakura, S. ( 1 ) 269; ( 4 ) 225, 233; ( 5 ) 148, 152 Nunn, D.S. ( 3 . 2 ) 37 Nurmukhametov, R.N. ( 4 ) 437 NUSS, M.C. (1) 378 Oba, K. (1) 35 Obata, K. (3.5) 131 O'Connor, D.V. ( 1 ) 26 O'Connor, L.H. (2.1) 213 Oda, G. ( 4 ) 450 Oda, K. (3.2) 145, 151;
Author Index (3.6) 114, 179, 181, 183, 184, 186 Oda, M. (3.2) 29-31; (3.6) 218 Odaira, Y. (3.2) 23; (3.4) 3 O'Donnell, J.H. ( 4 ) 361 O'Donnell, P.S. (1) 343 Oertel, U. ( 4 ) 40, 47 O e s t e r h e l t , D. ( 1 ) 378 Oevering, H. (5) 134 Offen, H.W. (1) 294; ( 2 . 1 ) 83 Ogasawara, H. (3.4) 147; ( 3 . 7 ) 143 Ogata, K. (3.2) 8 3 Ogawa, T. (3.2) 136, 143; (3.6) 113, 117 Ogiwara, T. (1) 131; ( 4 ) 42 Ogneva, T.M. ( 4 ) 414 Ogoshi, H. (2.2) 117 Ogura, K. ( 5 ) 233 Ohama, Y. (2.2) 104 Ohashi, M. (3.4) 1 5 ; (3.6) 106, 145; ( 3 . 7 ) 127 Ohashi, Y. (2.1) 163 Ohga, K. (3.3) 34; (3.6) 136 Ohgo, Y. (2.2) 111 Ohjura, K. (3.7) 147 Ohkawa, K. (2.1) 25; ( 5 ) 116 Ohkubo, K. ( 2 . 1 ) 144, 145, 186 Ohkura, K . ( 3 . 2 ) 91; (3.4) 95, 96; (3.7) 148, 152 Ohno, K. (3.6) 179 Ohno, M. ( 1 ) 388 Ohno, 0. (2.1) 228 Ohno, T. (2.1) 156, 157; ( 5 ) 148 Ohnota, M. (3.2) 134; (3.6) 77 Ohsaku, M. (3.3) 121 Ohsawa, H. ( 4 ) 396 Ohsawa, K. ( 4 ) 281 Ohsawa, M. ( 4 ) 231 Ohta, K . ( 4 ) 1, 2 , 6 , 7 Ohta, N. ( 1 ) 300 Ohtani, B. ( 4 ) 372; (5) 181, 182 Ohtani, H. ( 1 ) 164; (2.2) 49-51, 59 Ohtsuki, T. (3.3) 130 Ohyashiki, T. ( 1 ) 375 Oikawa, T. (3.5) 76 Oka, K. (2.3) 28; (3.6) 203 Oka, M. (3.2) 121
Okada, K. (2.3) 6; (3.4) 164; (3.6) 218 Okada, Y. (2.1) 181 Okagawa, I. ( 4 ) 451 Okai, M. (5) 199 O k a i s h i , K. (3.2) 16 Okajima, H. (3.2) 135; ( 3 . 6 ) 83 Okajima, S. ( 1 ) 151 Okamoto, K. ( 5 ) 165 Okamoto, M. ( 1 ) 171, 436 Okamoto, T. ( 1 ) 211 Okamoto', Y. (3.3) 10 Okarma, P . J . (3.3) 7 3 Okawa, T. ( 2 . 3 ) 27 Okazaki, H. (3.4) 77 Okazaki, K. (3.6) 197 Okazaki, M. (3.5) 24 Okeda, Y. ( 3 . 7 ) 127 Okubo, T. (4) 115 Okuda, T. (3.3) 117 Okuno, Y. (3.5) 54 Okura, I . (2.1) 231-233; ( 3 . 5 ) 34; (5) 6 6 , 68, 8 9 , 90, 94, 95, 140 Olah, G.A. (3.7) 41 Olaj, O.F. ( 4 ) 67 Olba, A. ( 1 ) 318 O l b r i c h , G. ( 1 ) 126 Olea, A. ( 1 ) 291, 458 Olenin, A.V. ( 4 ) 118, 119 O l i n s , D.E. ( 1 ) 394 Olken, M.M. (2.1) 217 O l l i n o , M. (2.1) 8 4 , 86 O l l i v o n , M. ( 1 ) 399 Olsen, R.J. (3.4) 112 Omata, M. (2.2) 83; (5) 77 Omata, Y. ( 1 ) 357 Omishi, Y. ( 4 ) 37 Omkaram, N. (3.1) 32, 34, 36 Omote, Y. (3.1) 37; (3.2) 53, 5 4 , 123, 134; (3.3) 3 ; ( 3 . 6 ) 77, 78, 123, 182, 187, 188 Ondrias, M.R. (1) 367 O n i s h i , M. ( 2 . 2 ) 104 Onishi, T. ( 2 . 1 ) 33; ( 5 ) 25, 27, 190 O n i s h i , Y. ( 4 ) 126 Onuki, S. ( 1 ) 270 Ooms, P.H.J. ( 3 . 6 ) 178 Op den Brouw, P.M. (3.3) 88 O p i t z , R . J . (3.3) 147, 148; (3.4) 18, 19; (3.7) 179, 180 Opnya, V . Y a . ( 4 ) 370 Oppenlander , T. (3.3) 128, 129; ( 3 . 7 ) 17, 27 O r , Y.S. ( 3 . 3 ) 108
579
Author Index Oraevsky, A.A. ( 1 ) 392 Orahovats, A.S. ( 3 . 2 ) 6 8 ;
Pac, C . ( 2 . 1 ) 126; ( 3 . 3 )
130; ( 3 . 4 ) 5 5 ; ( 3 . 5 ) 53; ( 3 . 6 ) 131 ( 3 . 4 ) 182 Paci, M. ( 4 ) 215 Ordsmith, N.H.R. ( 3 . 2 ) Packard, B.S. ( 1 ) 276 130; ( 3 . 7 ) 109 Paczkowski, B. ( 4 ) 358 Orekhovskii, V.S. ( 2 . 1 ) Paczkowski, J. ( 1 ) 482; 188 ( 3 . 5 ) 5 6 , 59; ( 4 ) 144, Orger, B.H. ( 3 . 4 ) 21, 22 357, 358 Orikata, T. ( 4 ) 30, 99 Paczkowski, M.A. ( 3 . 5 ) 22 Orito, K. ( 3 . 7 ) 185 Paddon-Row, M.N. ( 5 ) 134 Orlandi, G. ( 1 ) 81 Orlic-Nuber, M. ( 3 . 4 ) 143 Padmanabhan, K. ( 3 . 4 ) 153 Padwa, A. ( 3 . 4 ) 131; Orlowska, B. ( 3 . 1 ) 5 5 ; ( 3 . 7 ) 29, 40 ( 3 . 7 ) 107 Paik, Y.H. ( 5 ) 149 Orpen, A.G. ( 2 . 2 ) 40 Paillous, N. ( 3 . 4 ) 9 3 ; Ors, J . A . ( 1 ) 262 ( 3 . 6 ) 103 Ortega, A. ( 3 . 2 ) 49 Ortega, J.J. ( 4 ) 321, 424 Pak, C.S. ( 4 ) 279 Palmer, T.F. ( 1 ) 102, 428 Ortigosa, K. ( 2 . 2 ) 109 Palmisano, G. ( 3 . 2 ) 64 Ortiz, J . V . ( 2 . 3 ) 40 Ortiz, M.J. ( 3 . 2 ) 7 7 , 7 8 ; Palomino, E. ( 3 . 5 ) 113 Pan, J. ( 4 ) 107, 398, 421 ( 3 . 3 ) 7 2 ; ( 3 . 6 ) 27, 47 Panattoni, M. ( 4 ) 213 Ortmann, W. ( 3 . 7 ) 82 Pancatelli, G. ( 3 . 4 ) 97 Osa, T. ( 4 ) 170 Pancry, P.J. ( 4 ) 361 Osawa, Z. ( 4 ) 184, 422 P m d e y , B. ( 3 . 2 ) 88 Osborne, J . H . ( 2 . 1 ) 165 Panicheva, M.V. ( 2 . 2 ) Osella, D. ( 2 . 2 ) 99 Panse, M.D. ( 3 . 3 ) 33, Oshima, S. ( 1 ) 491 144 Oshima, T. ( 3 . 1 ) 48 Panse, M.D. ( 3 . 3 ) 3 3 ; Oskam, A. ( 2 . 2 ) 4 5 , 5 7 , ( 3 . 7 ) 174, 175 58 Pantar, A.V. (1) 336 Osman, A.H. ( 2 . 1 ) 5 Panzone, G. ' ( 3 . 5 ) 119 Osselton, E.M. ( 3 . 4 ) 2 8 , Paoli, M.A. ( 4 ) 114 31, 34 Paonessa, R.S. ( 2 . 2 ) Osterhoff, P. ( 4 ) 77 Papaconstantinou, E. Ostrikova, V.N. ( 2 . 2 ) 37 ( 2 . 1 ) 6 5 ; ( 5 ) 108 Osuka, A. ( 3 . 2 ) 161, 162 Paparian, S. (3.1) 46 O'Sullivan, A. ( 3 . 2 ) 5 6 ; ( 3 . 4 ) 155; ( 3 . 5 ) 15 ( 3 . 7 ) 137 Papendicik, U. ( 4 ) 196 Otsu, T. ( 4 ) 5 8 , 62 Papier, E. ( 5 ) 204 Otsubo, T. ( 3 . 4 ) 166 Papkov, S.P. ( 4 ) 414 Otsuji, Y. ( 2 . 3 ) 1 0 ; Papp, S . ( 1 ) 347; 372; ( 3 . 3 ) 126; ( 3 . 4 ) 7 4 , ( 2 . 1 ) 187, 190; ( 5 ) 31 7 5 ; ( 3 . 5 ) 103, 106, Pappas, S.P. ( 4 ) 33 107; ( 3 . 6 ) 209; ( 5 ) 47 Paquette, L.A. ( 3 . 3 ) 4 7 , Otsuki, N. ( 3 . 5 ) 44 91, 109, 110; ( 3 . 6 ) 50 Otsuki, T. ( 3 . 2 ) 163 Pardee, J . D . ( 1 ) 406 Ottenbrite, R.M. ( 4 ) 65 Parenti, R.A. ( 1 ) 277 Otterburn, M.S. ( 4 ) 124, Paris, J. ( 5 ) 222 125 Parish, R.V. ( 2 . 1 ) 66 Ottolenghi, M. ( 1 ) 310, Park, C.-H. ( 1 ) 100 31 1 Park, J.M. ( 3 . 7 ) 49 Otvos, J.W. ( 5 ) 145 Park, J.W. ( 5 ) 149 Oucharenko, V.V. ( 4 ) 369 Park, K.K. ( 2 . 1 ) 208 Ounsworth, J. ( 3 . 1 ) 38 Park, S.K. ( 3 . 3 ) 35; Overum, T. ( 4 ) 77 ( 3 . 6 ) 89 Owen, E.D. ( 4 ) 318 Park, S.-M. (1) 100, 387 Owens, P.A. ( 2 . 2 ) 110 Park, Y.T. ( 1 ) 327; ( 3 . 4 ) Owers, R . J . ( 3 . 4 ) 54 144, 183; ( 3 . 6 ) 45 Oxman, J . D . ( 3 . 4 ) 6 4 ; Parkinson, A. ( 4 ) 416 ( 3 . 6 ) 74 Parmar, S . S . ( 1 ) 428 Ozaki, Y. ( 3 . 7 ) 53
Parmon, V.N. Parris, P.E. Parshin, G.S. Parsons, B . J .
( 5 ) 107, 210 ( 1 ) 247 ( 2 . 1 ) 249 ( 3 . 5 ) 130;
( 3 . 7 ) 172
Pasman, P. ( 1 ) 176; ( 5 ) 125
Pasquato, L. ( 3 . 6 ) 171 Pasynskii, A.A. ( 2 . 2 ) 37 Paszyc, S. ( 1 ) 384 Patel, D . I . ( 3 . 7 ) 95 Patharakorn, S . ( 3 . 2 ) 126; ( 3 . 4 ) 141
Patonay, G. ( 1 ) 62 Patterson, F.G. ( 1 ) 438 Patterson, L.K. ( 1 ) 31, 38 1
Paulsen, H. ( 1 ) 397 Paulus, E.F. ( 3 . 2 ) 103 Pavker, F. ( 1 ) 37 Pavlik, J.W. ( 3 . 3 ) 8 3 ; (3.4) 9
Pavlopoulos, T.G. ( 1 ) 431 Pavlov, N.N. ( 4 ) 350 Pavlovski, V . I . ( 2 . 1 ) 139 Peacock, J . A . ( 3 . 6 ) 144 Peak, D. ( 1 ) 331 Pearce, E.M. ( 4 ) 360 Pearson, C.J. ( 3 . 7 ) 77 Pearson, K.H. ( 2 . 1 ) 213 Pedulli, G . F . ( 2 . 3 ) 1 8 ; ( 3 . 2 ) 158
Peirigua, A. ( 1 ) 162 Pekcan, 0. ( 4 ) 248 Pelizzetti, E. ( 2 . 1 ) 2 2 , 178; ( 5 ) 9 , 211, 212
Pelizzi, G. ( 3 . 5 ) 119 Pellerean, B. ( 4 ) 310 Penenory, A.B. ( 3 . 7 ) 161 Penico, A. ( 4 ) 267 Penigault, E. ( 2 . 1 ) 180 Pereira,, V.R. ( 1 ) 257 Pereira, L.C. ( 1 ) 145 Peretti, J. ( 2 . 1 ) 77 Perez-Ossorio, R. ( 3 . 2 ) 75-78; ( 3 . 3 ) 4 1 , 4 2 , 7 2 ; ( 3 . 4 ) 1 3 ; ( 3 . 6 ) 27, 46-48, 79 Perez-Ruiz, T. ( 3 . 5 ) 126 Perichet, G. ( 1 ) 383; ( 2 . 1 ) 246 Perry, D.A. ( 3 . 7 ) 121 Perry, D.L. ( 2 . 1 ) 215 Persy, G. ( 1 ) 103 Perumattarn, J. ( 3 . 2 ) 35 Perutz, R.N. ( 1 ) 7 8 ; ( 2 . 2 ) 8 , 17 Peruyenlova, D.G. ( 4 ) 455 Pestanov, V.Yu. ( 2 . 3 ) 36 Pete, J.-P. ( 2 . 2 ) 128; ( 2 . 3 ) 9 ; ( 3 . 1 ) 43; ( 3 . 2 ) 55, 6 2 ; ( 3 . 5 ) 46-
580 256 Rao, D.N. ( 1 ) 483 Rao, K.K. (5) 187 Rao, M.V.R. ( 1 ) 336 Rao, V.B. ( 3 . 2 ) 2 , 1 7 Rao, V.P. ( 1 ) 473; (3.5) 150; ( 3 . 6 ) 177; (3.7) 128 Rapley, P.A. ( 3 . 2 ) 149, 150; (3.6) 180, 185, 189 Rappan, M. ( 4 ) 341 Rappoldt, P.M. ( 3 . 3 ) 8 2 Rau, H. ( 2 . 1 ) 113; ( 5 ) 142 Raabe, G. ( 2 . 3 ) 13; ( 3 . 7 ) Raucher, S. ( 3 . 7 ) 145 88 Rabani, J. ( 2 . 1 ) 117-119, Rauhut, M. ( 4 ) 405, 416 166, 167, 230; ( 5 ) 146, Rausch, M.D. ( 2 . 2 ) 9, 54 R a w a l , V.H. ( 3 . 4 ) 122147 124; ( 3 . 6 ) 25 Rabek, J.F. ( 4 ) 11, 181, Razuvaev, G.A. ( 3 . 5 ) 28 316, 319, 406, 427 Reber, J.F. ( 5 ) 213 Raby, P. ( 1 ) 420 Raghuraman, T.S. ( 3 . 2 ) Reddoch, A.H. ( 3 . 7 ) 49 Reddy, A.R. (1) 199 71; ( 3 . 4 ) 179 Redmond, R.W. (1) 480 Rahrnan, A.N. ( 5 ) 240 Redpath, A.E. ( 3 . 4 ) 152; R a i n e s , D.E. ( 2 . 1 ) 112 (3.5) 17 Rakunov, Yu.P. ( 4 ) 129 Redwine, O.D. ( 1 ) 502 Raldugin, V.A. ( 3 . 5 ) 85 Ram, A. ( 4 ) 349 Reed, J.L. ( 2 . 1 ) 169 Ramachandran, P.V. ( 3 . 7 ) Reedich, D.E. ( 3 . 4 ) 3 3 ; ( 3 . 7 ) 20, 103 108 Ramaiah, D. (3.3) 135; R e e n t s , W.D. ( 2 . 2 ) 10 Rees, C.W. ( 3 . 6 ) 166; (3.7) 136 ( 3 . 7 ) 32-34, 9 8 , 99 Ramakrishna, V.T. ( 3 . 4 ) R e g i t z , M. ( 3 . 6 ) 21 181 Rehak, V. ( 1 ) 303 Ramamurthy, V. (1) 301, Rehm, D. ( 3 . 2 ) 103 455, 473; ( 3 . 1 ) 4 ; Rehms, A.A. ( 1 ) 324 (3.2) 43, 45; (3.4) Rehorek, D. ( 2 . 1 ) 245 153; ( 3 . 5 ) 1, 3 , 150; Reichenbaecher, M. ( 3 . 3 ) (3.6) 176, 177, 190, 191; ( 3 . 7 ) 128; ( 5 ) 10 79 Reimann, B. ( 2 . 3 ) 8 Ramanan, S.V. ( 1 ) 410 Ramaraj, R. (1) 268 R e i n h a r d t , G. ( 3 . 3 ) 139; Ramasubbu, N . ( 3 . 2 ) 4 3 , ( 4 ) 413 R e i n i s c h , G. ( 4 ) 208 45 Reinking, M.K. (2.2) 125 Ramazemova, M.R. ( 4 ) 249 R e i s e n a u e r , H.P. ( 3 . 2 ) Ramesh, V . ( 1 ) 301; ( 5 ) 159 10 R e i s f e l d , R. ( 2 . 1 ) 199; Ramey, C.E. ( 4 ) 400 (5) 241, 242 Ramnath, N. ( 1 ) 301; Rejnek, J. ( 2 . 3 ) 45 (3.1) 32; (5) 10 Rembold, M. ( 4 ) 402 Ramos, A. ( 3 . 6 ) 79 Rempp, P. ( 4 ) 237 Ramos, E.L. ( 3 . 7 ) 56 Remuson, R. ( 3 . 5 ) 141 Rampi, M.A. (2.1) 92 R e n d a l l , W.A. ( 3 . 4 ) 4-6; Ramsay, P.J. ( 4 ) 224 Ranade, A.C. (2.2) 136 ( 3 . 6 ) 164; ( 4 ) 251 Renge, I . V . ( 1 ) 471 Ranby, B. ( 4 ) 38, 316, 319, 406, 427 Renneke, R.F. (5) 111 Rentsch, S.K. ( 1 ) 241; Randolph, C.L. ( 2 . 2 ) 92 ( 4 ) 441 Raneeze, D. ( 4 ) 420 Ranganathan, D. ( 3 . 7 ) 108 R e n t z e p i s , P.H. ( 1 ) 14, Rangel-Zamudia, L . I . ( 1 ) 9 8 , 9 9 , 120, 138, 156,
Qin, Q. ( 2 . 1 ) 225 Quanten, E. (1) 201 Quast, H. ( 3 . 7 ) 36, 86 Quay, S.C. ( 1 ) 337, 341 Q u e s l e l , J . P . ( 4 ) 270 Qui, L. ( 2 . 1 ) 223 Quinga, E.M.Y. ( 1 ) 503 Q u i n k e r t , G. ( 3 . 2 ) 103, 104 Quintero-Cortes, L. ( 3 . 7 ) 168 Q u i t e v i s , E.L. ( 1 ) 123
Author Index 172 Rest, A.J. (2.2) 70 R e t t i g , S . J . ( 2 . 2 ) 121 R e t t i g , W. (1) 93, 174, 184, 265; (2.1) 81 R e v e r t e , J.M.A. (1) 317 R e v i n s k i i , Yu.V. ( 2 . 1 ) 188 Rey, P. ( 2 . 2 ) 75 Reynolds, D.W. (3.3) 67 R i a h i , A. ( 2 . 2 ) 128; (2.3) 9 R i c a r d , R. ( 3 . 2 ) 59; (3.5) 12 Ricci, A . ( 2 . 3 ) 18 Rice, J . A . ( 2 . 3 ) 53 R i c e v u t o , V. ( 2 . 2 ) 126 Richardson, F.S. (1) 59 R i c h e r t , R. (1) 449 Richman, R.M. ( 2 . 1 ) 76 Richoux, M.C. ( 2 . 1 ) 240, 247; ( 5 ) 113, 115 R i c h t e r , P. ( 4 ) 453 R i d e r , E.S. ( 4 ) 56 Ridge, D.P. (2.2) 10 R i e d e , J . ( 2 . 2 ) 22 R i e g e r , P.T. (2.1) 112 R i e g l e r , M. ( 4 ) 189 K i e h l , J.P. ( 1 ) 59, 250 R i e k e r , J. ( 1 ) 210 Riepponen, P. ( 3 . 7 ) 102 R i f f a u d , M.-H. (3.4) 173 R i g h e t t o , L. ( 4 ) 113 R i g l e r , R. (1) 30 R i h s , G. ( 3 . 7 ) 2 5 R i m a , J. ( 1 ) 106 R i n g s d o r f , H. ( 3 . 6 ) 70 Rinke, M. ( I ) 194, 195 R i v a s , C. ( 3 . 1 ) 45; ( 3 . 4 46; (3.5) 14 R i v a t o n , A. ( 4 ) 298, 348 R i v e r a , S. ( 2 . 1 ) 210 R i v e r s , D.S. ( 2 . 1 ) 76 Rives-Arnau, V. (2.1) 36 (5) 166 Rizzo, T.R. ( ) 327 Robbins, D . J . ( 1 ) 344 Roberge, P.C. (2.1) 6 3 Robert, B. ( 2 1 ) 53, 54 Robert-Nicoud M. ( 1 ) 7 3 R o b e r t s , A . J. ( 4 ) 165 R o b e r t s , S.M. (3.1) 30 Robins, M.J. 3 . 4 ) 57; ( 3 . 6 ) 127 Robinson, G.W. ( 1 ) 183, 222 Robles Diaz, R. (3.5) 101 Robson, N.S. (3.4) 42 ROCCO, V.P. ( 3 . 2 ) 3 Roche, G. ( 4 ) 305 Rodewald, H. (3.3) 76 Rodewald, W.J. ( 3 . 3 ) 80
58 1
Author Index
48 Peteanu, L.A. (1) 327 Peteres, K. (3.1) 14 Peters, A.W. (4) 229 Peters, E.-M. (3.1) 14; (3.2) 86; (3.3) 43, 92; (3.5) 77; (3.7) 18, 24 Peters, K. (3.2) 86; (3.3) 43, 92; (3.5) 77; (3.7) 18, 24 Peters, K.S. (1) 152, 187, 501 Petersen, J.D. (2.1) 129, 155; (5) 60 Petersen, J . L . (2.2) 6 Peterson, D.B. (5) 17 Peterson, J.R. (2.1) 177 Peterson, K . A , (4) 222 Peterson, L.K. (2.2) 34 Peterson, M.W. (2.1) 76 Petit, J. (1) 399 Petit-Ramel, M. (1) 383; (2.1) 246 Petrak, K.L. (4) 29 Petrenko, N.I. (3.5) 120 Petrich, J . W . (1) 20 Petrin, M. (1) 488 Petrov, G. (4) 109 Petter, W. (3.1) 35; (3.7) 135 Pettit, T.L. (2.1) 96 Pfeifer, D. (3.7) 83 Pfleiderer, G.P. (1) 349 Pfleiderer, W. (3.6) 192, 193 Pfoertner, K.-H. (3.6) 51, 52 Phaff, R. (3.1) 35; (3.7) 135 Phifer, J . E . (2.1) 46 Philipart, J.L. (4) 331, 346 Phillips, D. (1) 26, 319; (4) 159, 161 Phillips, G.O. (3.5) 40, 130 Phillips, P. (4) 190 Phillips, R.B. (3.3) 77 Phillips, S.D. (2.1) 162 Phillips, T. (3.3) 138 Phillpot, S.R. (4) 188 Piancatelli, G. (3.4) 98; (3.7) 149, 150 Pichat, P. (5) 162, 175, 204 Pickett, J.E. (4) 368 Pienta, N . J . (3.3) 66; (3.6) 132 Pierini, A.B. (3.7) 161 Pieroni, 0. (3.6) 12, 13 Piers, E. (3.2) 22 Pietra, F.'(3.2) 19
Pietra, S. (3.4) 188; (3.6) 65 Piggott, R.D. (3.2) 126; (3.4) 141 Pileni, M. (5) 141 Pill Soon Song, (1) 413 Pin, N.E. (1) 196 Pina, F. (2.1) 142; (2.2) 35; (5) 99 Pincock, J . A . (3.4) 104 Pinhey, J.T. (3.5) 18 Pinther, P. ( 4 ) 108 Pipe, E. (3.7) 141 Pirogova, N . A . (3.2) 166 Pirrung, M. (3.1) 29 Piserchio, M. (2.3) 11 Pisulina, L.P. (3.2) 168 Piszezek, L. (1) 87 Plachenov, B.T. (2.1) 195 Plato, M. (2.1) 41 Platz, M.S. (3.7) 47, 51, 54, 55, 90 Pleskov, Yu.V. (5) 227 Plyusnin, V.F. (2.1) 191 Podoplelov, A.V. (2.3) 54 Pohl, S. (2.3) 23; (3.6) 195 Polansky, O.E. (1) 126 Polewski, K. (3.5) 68 Poliakoff, M. (2.2) 14, 95, 98 Polinski, A.S. (4) 204 Politi, M.J. (1) 292 Polo, J.S. (3.7) 110 Polokoff, M.A. (1) 401 Poluektov, N.S. (2.1) 214 Polyakov, N.E. (3.5) 6 Polyanina, N . A . (4) 429 Pommier, B. (2.1) 26 Ponder, M. (1) 168 Ponomarev, O.A. (3.2) 44 Ponticelli, F. (3.2) 39; (3.6) 56, 88, 125 Popisil, J. (4) 289 Popovitz-Biro, R. (3.1) 10, 11 Porai-Koshits, M.A. (2.2) 37 Port, H. (1) 115, 255 Porte, A.L. (3.6) 144 Portella, C. (3.2) 55; (3.5) 45-48 Postnikov, L.M. (4) 332, 333, 401, 431 Potapov, I . A . (5) 114 Potier, P. (3.7) 113, 117 Potocnak, J. (4) 443 Pottel, H. (1) 48 Pottier, R. (1) 417 Potziger, P. ( 2 . 3 ) 8 Pouaet. - . J. (5) 243 Pouligny, B; (1) 286
Pouliquen, J. (1) 94; (4) 444 Pouyet, B. (1) 383; (2.1) 246 Povazzaneova, M. (4) 403 Powell, M.H.A (2.2) 8 Poznyak, A. L. (2.1) 139, 143 Pradervand, .G 0. (2.1) 196 Pramauro, E. 2.1) 22 Prasad, A.R.S (1) 345, 354 Prasad, D.R. 1) 199; (2.1) 94, 1 2; (5) 85, 86, 92 Prasad, G. (3.5) 113 Prasad, P.N. (1) 483 Pratapan, S. (3.2) 124 Pratt, J.E. (1) 475; (3.5) 105; (4) 261 Pravednikov, A . N (5) 158 Prementine, G.S. (4) 53 Preses, J.M. (1) 82 Presser, D.W. (3 5) 42; (5) 223 Preston, K.F. (2 2) 123 PrevitaLI, C.M. 1) 154, 188, 423, 424, 445 ; (3.4) 85 Prewo, R. (3.2) 68; (3.4) 182 Price, J.D. (3.3) 58 Prieto,,A. (5) 201 Prieto, N.E. (1) 293; ( 4 ) 185, 206 Prignano, A.L. (2.2) 131 Prince, R.C. (5) 15 Prinzbach, H. (3.3) 105, 106, 112, 113; (3.4) 159, 160; (3.6) 100, 105; (3.7) 25 Priola, A . (4) 141 Pritchard, R.B. (4) 435 Pritze, B. (2.3) 48, 49 Procter, G . (3.2) 130; (3.7) 109 Prout, K. (3.2) 10 Pruett, S.R. (3.4) 112 Pshenichnyi, V . N . (3.5) 117 Puaux, J.-P. (1) 192 Puig, S. (3.2) 108 Pulst, M. (4) 442 Purbrick, M.D. (4) 29 Purich, D.L. (1) 355 Pushpa, S . (5) 26 Puthraya, K.H. (2.1) 172 Putnins, E. (5) 229 Pyshchev, A.I. (3.4) 128; (3.6) 29 Pyun, C.-H. (1) 387
Author Index
582 Rodgers, J. ( 1 ) 114 Rodgers, M. (3.3) 145; ( 3 . 7 ) 151 Rodgers, M.A.J. ( 1 ) 74, 474; ( 3 . 5 ) 60 R o d i g h i e r o , G. ( 3 . 2 ) 48 Rodrigo, L. ( 2 . 1 ) 6 3 Rodriguez, F. ( 4 ) 45 Rodriguez, M.S. ( 3 . 7 ) 186 Rodriguez-Hahn, L. (3.2) 49 Rodwell, P.W. ( 3 . 4 ) 45 Roe, D.C. ( 2 . 2 ) 72 R o e l a n d t s , R . ( 1 ) 201 Roesle, A. (3.3) 81 Roewkamp, M. ( 4 ) 329 Roffey, C.G. ( 4 ) 22 Roger, A . ( 4 ) 330 Rogers, E.C. ( 4 ) 311 Rohatgi-Mukerjee, K.K. (1) 463 Rohde, R. (3.1) 16 R o j a s , G.E. (2.1) 4 0 R o j a s , N. ( 4 ) 356 Rol, C. (3.5) 110 R o l i a , P.A. ( 4 ) 76 Roman, E. (2.2) 8 5 Roman Ceba, M. ( 1 ) 124 Romano, S. ( 3 . 3 ) 72; ( 3 . 6 ) 27 Romkina, J. ( 4 ) 77 Roncel, M. (5) 1 2 Rondelez, F. ( 4 ) 228 R o n d i n e l l a , M.A. ( 4 ) 45 ROOS, G. ( 4 ) 128 Rosenberg, A. (1) 347 Rosenfeld, R.N. ( 2 . 2 ) 11 Ross, J.B.A. ( 1 ) 333, 334 Rossbroich, G. ( 1 ) 479 R o s s e t t i , R . (1) 316 R o s s i , R . A . ( 3 . 7 ) 161, 164 Rostch, C . J . ( 4 ) 400 Roth, H.D. ( 1 ) 156; ( 3 . 3 ) 62; ( 5 ) 46 R o u l e t , R. ( 2 . 2 ) 80 R o u n d h i l l , D.M. ( 2 . 2 ) 130 R o u s s e l , P. ( 3 . 5 ) 8 9 R o u s s i , G. (3.7) 168 Rozenkevich, M.B. (5) 100, 114 Rozploch, F. ( 4 ) 322 R t i s h c h e v , N . I . ( 3 . 3 ) 12; (3.6) 216 Rubin, H.D. ( 2 . 2 ) 46 Rubin, M.B. (3.2) 115 Rubtsov, I . V . ( 3 . 5 ) 33; ( 5 ) 143 Rudinskaya, G.V. ( 4 ) 414 Rufs, A . M . ( 3 . 5 ) 9 Ruggeri, R. (3.7) 121 Rughooputh, S.D.D.V. ( 4 )
190 Ruiz-Hitzky, E. ( 2 . 1 ) 137; ( 5 ) 117 Rumbach, T. (3.4) 24 Runkasova, J. ( 1 ) 303 Runov, V.K. (2.1) 136 Runsink, J. ( 3 . 1 ) 50; ( 3 . 4 ) 24 Rusek, M. ( 5 ) 213 R u s h f o r t h , D.S. ( 1 ) 256 R u s l i n g , J.F. (5) 232 R u s s e l l , G.A. ( 3 . 7 ) 159, 160 R u s s e l l , J . C . ( 1 ) 285, 295; ( 3 . 3 ) 23 R u s s e l l , P.M. ( 4 ) 343 R u t t e n s , F. ( 1 ) 330 R u t t e r , A. ( 3 . 2 ) 164 Ruziewicz, Z. ( 1 ) 446 Rychla, L. ( 1 ) 494 S a a , J . M . ( 3 . 4 ) 116 Saad, A.D. (1) 406 S a b i , Z.S. ( 4 ) 9 4 S a c k s , S.L. ( 3 . 2 ) 131; ( 3 . 6 ) 99 S a d o v s k i i , N.A. (1) 148 S a d r i d d i n o v , B.B., ( 4 ) 9 4 Sadvakasova, S.K. ( 2 . 1 ) 136 S a e k i , Y. ( 5 ) 148 Saeva, F.D. ( 3 . 4 ) 189; ( 3 . 6 ) 167 S a f a , K.D. ( 2 . 3 ) 1 9 ; ( 3 . 3 ) 4 ; (3.6) 199 Safarazadeh-Amisi, A. ( 1 ) 160 Sagdeev, R.Z. ( 2 . 3 ) 54; (3.5) 6 Saha, S. ( 3 . 2 ) 113 Sahn, G. ( 4 ) 110 Sahota, R.I.K. (3.5) 43 S a i g o , K . ( 3 . 2 ) 13 S a i t o , I. ( 3 . 2 ) 90; ( 3 . 5 ) 131; ( 3 . 6 ) 147 S a i t o , K. ( 2 . 1 ) 58, 147 S a i t o , Y. ( 2 . 1 ) 5 7 , 161; ( 2 . 2 ) 118, 119; ( 5 ) 6 4 , 75, 80, 81 S a i t o h , K. ( 3 . 6 ) 33 S a i t o v i t c h , E.M.B. ( 2 . 2 ) 69 S a j i , T. ( 2 . 1 ) 35 Sakaguchi, Y. ( 2 . 1 ) 198; ( 2 . 3 ) 55 S a k a i , H. (3.6) 57 S a k a i , M. ( 3 . 5 ) 136 S a k a i t a n i , M. ( 3 . 2 ) 30 S a k a k i , S. ( 2 . 1 ) 186 Sakamoto, K. ( 2 . 3 ) 16; ( 3 . 4 ) 172; ( 3 . 6 ) 207
Sakamoto, M. (3.1) 37; ( 3 . 2 ) 1 2 3 , 134; (3.3) 134; (3.6) 77, 187, 188; (3.7) 132 Sakamoto, S: ( 2 . 1 ) 39 Sakamoto, T. (5) 156 Sakane, F. ( 4 ) 451 S a k a t a , S. (3.5) 24 S a k a t a , Y. ( 3 . 4 ) 158, 166 S a k h a r o v s k i i , Yu.A. ( 5 ) 100, 114 Sakhnovskaya, E.B. ( 4 ) 423 S a k i , H. ( 5 ) 182 Sako, M. ( 3 . 6 ) 62 S a k o t a , N. ( 4 ) 52 S a k u r a g i , H. ( 1 ) 486; ( 3 . 3 ) 13; (3.5) 27, 36 S a k u r a i , H. (2.3) 15, 1 6 ; ( 3 . 3 ) 130; (3.4) 172, 190; ( 3 . 6 ) 201, 202, 204, 207 S a k u r a i , K. ( 2 . 2 ) 117 S a k u r a i , T. (3.4) 184, 185; ( 3 . 6 ) 44, 149 Sakurovs, R. ( 1 ) 52 Salamon, Z. ( 1 ) 272 S a l a z a r , J . A . (3.7) 187 S a l l e t , D. ( 4 ) 330, 348 Salmeen, I. ( 1 ) 411 Salomon, R.G. (3.3) 115, 116 S a l t , W.G. ( 3 . 7 ) 1 6 3 S a l t i e l , J. ( 1 ) 229; ( 3 . 3 ) 9; ( 3 . 4 ) 51 S a l v a d o r i , P. ( 4 ) 220 S a l v e r i d e s , C. ( 4 ) 227 S a l ' v i t o k a y a , L.N. ( 4 ) 455 Samanta, A. ( 1 ) 133 Samat, A. (3.7) 167 Samol, S. ( 4 ) 110 Samotus, A. ( 2 . 1 ) 60 Samuel. E. (2.2) 5 Sanchez, I . Z . (1) 317 Sandarova, S.A. ( 4 ) 410 S a n d e r , W. ( 3 . 7 ) 6 2 , 6 3 S a n d e r s , J.K.M. ( 2 . 1 ) 241; (5) 130 S a n d i s o n , M. ( 3 . 5 ) 113 S a n d r i n i , D. (2.1) 93, 175; ( 5 ) 123 Sandros, K. ( 3 . 3 ) 30; ( 3 . 4 ) 163, 168 S a n f e l i u , E. ( 3 . 4 ) 148 Sano, K. ( 3 . 5 ) 1 2 3 San Roman, E. ( 2 . 3 ) 56 S a n t a m a r i a , J. ( 3 . 5 ) 97 Santhanam, M. ( 2 . 2 ) 129 Sanz, J. ( 5 ) 166 S a r a v a r i , 0. ( 1 ) 506 S a r g e s o n , A.M. (2.1) 4 7 ,
Author Index 110, 141; (5) 97, 98 S a r i y a r , G. (3.2) 109; (3.6) 84 S a r k i s o v , O.M. (2.3) 35, 36 S a r k i s y a n , A.G. (5) 229 S a s a k i , T. (3.6) 37; (4) 272 S a s a k i , Y. (2.1) 57, 58, 147 S a s h i d a , H. (3.7) 94 S a s s e , W.H.F. (1) 297; (2.1) 47, 110, 114, 141; (5) 71, 97, 98 Sassoon, R.E. (1) 10; (2.1) 117-119; (5) 146, 147 S a t a k e , I. (1) 308; (4) 449 S a t o , E. (3.6) 128 S a t o , F. (2.1) 186 S a t o , H. (1) 96; (2.2) 71 S a t o , K. (3.3) 114; (5) 197 S a t o , M. (3.2) 50; (4) 218 S a t o , R. (3.5) 128, 129 S a t o , S. (2.1) 31; (3.4) 15; (5) 183, 184, 192 S a t o , T. (3.4) 77; (3.5) 76; (4) 62 S a t o , Y. (3.2) 142; (3.6) 82, 183 S a t y a n a r a y a n a , N. (3.1) 20 S a u c i e r , A.C. (1) 355 S a u e r , G. (3.1) 16 S a u e r , J. (3.3) 125 Sauvage, J.P. (2.1) 128; (5) 59 Sauvage, P. (3.2) 59; (3.5) 12 S a v i n o , T.G. (3.7) 47, 51 Savinov, E.N. (5) 107, 210 Savinova, E.R. (5) 107 Savory, B. (1) 322 S a v v i n , N.N. (5) 200 Sawada, K. (3.4) 83 Sawaki, Y. (2.1) 21; (3.5) 91 S a w a n i s h i , H . (3.7) 94, 96 Sawyer, W.H. (1) 351 S c a i a n o , J . C . (1 80 419, 451, 459, 461, 465, 484, 498, 499 ; (3.1) 8, 9, 24 26, 39, 40; (3.4) 129, 130, 151; (3.5) 11; (3.7) 54, 58, 59 S c a n d o l a , F. ( 2 . 1 92,
583 178 S c a r l a t t a , S.F. (1) 262 S c a r p a , A. (1) 408 S c e t t r i , A. (3.4) 97, 98; (3.7) 149, 150 Schaap, A.P. (3.5) 113 S c h a d t , M.J. (2.2) 19, 20 S c h a f e r , A. (2.3) 23; (3.6) 195 S c h a f e r , H.J. (3.7) 104106 S c h a e f f e r , C.D. (2.2) 32 S c h a f f n e r , K. (2.2) 15, 73; (3.2) 88 Schanze, K.S. (1) 220; (2.2) 102; (3.4) 51; (5) 70 S c h a r f , G. (1) 425 S c h a r f , H.-D. (3.1) 1, 22, 33, 50; (3.4) 26 Schaumann, E. (3.6) 191 S c h e f f e r , J . R . (3.1) 32, 34, 36, 38; (3.2) 131; (3.6) 99 S c h e l l e r , M.E. (3.3) 70 Schenk, K.-H. (3.2) 112; (3.6) 19 S c h i a v e l l o , M. (5) 5 S c h i e b e r l e , P. (3.7) 140 S c h i r s a , R. (1) 207 S c h i s a n o , M.I. (2.1) 226 S c h i s s e l , D.N. (3.3) 40 Schlimper, R. (4) 154 Schmehl, R . H . (2.1) 80, 84; (5) 57, 136 Schmid, A.A. (1) 119 Schmidt, F. (2.2) 68 Schmidt, J. (1) 422 Schmidt, J.A. (5) 128 Schmidt, K.H. (3.5) 134 Schmidt, R. (3.5) 98 Schmidtberg, G. (3.3) 52, 54, 55 Schmieder, K.R. (3.2) 103 S c h m i t t , U. (3.6) 42 S c h n a b e l , W. (1) 427; (3.6) 213, 214; (3.7) 31, 96, 122, 147 S c h n a t t e r e r , A. (1) 481; (3.5) 102 Schneck, R. (1) 72 Schneckenburger, H. (1) 37 Schoenecker, B. (3.3) 79 S c h o l e s , G. (3.2) 95 S c h o l l , B. (3.6) 101 S c h o l l e r , D. (3.5) 47 S c h o n h i l z e r , P. (3.3) 86 Schoonheydt, R.A. (2.1) 89 Schreckenbach, J. (2.2) 31, 33
Schrock, A.K. (3.7) 46 S c h r o d e r , C. (3.2) 17 Schroeder, F. (1) 320 S c h r o f , W. (1) 115 S c h r o t h , G. (2.2) 4 S c h u b e r t , U. (2.2) 55 Schuchmann, H.P. (3.7) 130 Schuda, A.D. (3.6) 112 S c h u e t z , H. (3.2) 125 Schulman, P.M. (2.2) 44 S c h u l t e - F r o h l i n d e , D. (1) 443; (3.3) 25 S c h u l t e n , K. (1) 57 S c h u l t z , A.G. (3.1) 28; (3.2) 87, 106, 108; (3.6) 43; (3.7) 23 Schumacher, H.J. (2.3) 41 Schumacher, L.C. (5) 230 Schumann, D. (3.5) 116 S c h u s t e , G.B. (3.7) 46, 91 S c h u s t e r , D . I . (1) 500; (3.2) 79, 105, 107 S c h u s t e r , F. (3.3) 125 S c h u s t e r , G.B. (3.4) 76; (3.6) 219; (3.7) 44, 45 Schwan, L.O. (2.1) 8 1 Schwartz, E. (3.7) 121 S c l a f a n i , A. (5) 5 Scopes, D.I.C. (3.7) 95 S c o t t , C.H. (1) 71 S c o t t , G. (4) 381, 408 S c o t t , G.W. (1) 121 S c o t t , T.L. (1) 368 S c o t t , T.W. (1) 367 Scrimgeour, C.M. (3.5) 74 S c r i v e n , E.F.V. (3.7) 95 Scyfong, R. (1) 115 S c y p i n s k i , S. (1) 200 S c z o s t a k , A. (3.3) 92 S e a r s , D.F. (1) 229 S e b a s t i a n i , G.V. (3.5) 110 S e d e l m e i e r , G. (3.3) 112; (3.4) 159 Sedlacek, B. (4) 239 S e d l a k , P. (3.5) 111 S e e g e r , D.E. (4) 363 S e h r o f , W. (1) 255 S e i d l e r , P.F. (2.2) 52 S e i f e r l i n g , B. (3.7) 86 S e i j a s , J . A . (3.4) 116 S e i t z , R.W. (4) 207 S e k i , H. (2.2) 116 S e k i , K. (3.2) 9:; (3.4) 95, 96; (3.7) 147, 148, 152 S e k i , Y. (3.7) 185 S e k i g u c h i , A. (2.3) 20, 22 S e k i n e , T. (2.1) 38
Author Index
584 Sekutowski, J . C . ( 3 . 3 ) 106; ( 3 . 6 ) 100 S e l l i , E. ( 4 ) 105, 113 Semchishen, V . A . ( 2 . 3 ) 46 Semenishin, D . I . ( 2 . 1 ) 6 1 Semerak, S.N. ( 1 ) 266; ( 4 ) 247 Sendyurev, M.V. ( 3 . 6 ) 215 Sengupta, P.K. ( 4 ) 9 3 Sennikov, P . G . ( 2 . 2 ) 27 S e n t a , M. ( 3 . 6 ) 171 S e n t h i l n a t h a n , V.P. ( 1 ) 426; (3.7) 51 S e r a , A. ( 3 . 7 ) 183 Serdobov, M.V. ( 2 . 2 ) 132 Serdyukova, T . I . ( 2 . 1 ) 62 Sergeev, A.D. ( 4 ) 275, 277 S e r i e s , I . ( 1 ) 347 Serpone, N. ( 2 . 1 ) 22, 104, 132; ( 5 ) 211, 212 S e r v a a s , P.C. ( 2 . 2 ) 45 S e s h a d r i , S. ( 4 ) 447 S e s i l e t s , D . J . ( 1 ) 33 S e t o , J . ( 3 . 6 ) 162 S e t s e r , D.W. ( 2 . 3 ) 30 S e t s u n e , J. ( 5 ) 69 S e x t o n , D.A. ( 2 . 1 ) 40 Seymour, P. ( 2 . 1 ) 131 Seymour, R.B. ( 4 ) 391 Shade, J.E. ( 2 . 2 ) 32 S h a f i r o v i c h , V.Ya. ( 5 ) 103, 144 Shagisultanova, G . A . (2.1) 9 1 , 148, 182, 183; ( 2 . 2 ) 108, 109; ( 5 ) 78 Shah; A ( 3 . 2 ) 152; ( 3 . 7 ) 123 S h a k r a , s. ( 4 ) 434 Shamma, M. ( 3 . 2 ) 109, 111; 3.6) 8 4 , 85 Shankar B.K.R. ( 3 . 3 ) 108 Shannon P . J . ( 3 . 6 ) 4 3 Shaphel L. ( 5 ) 170 ShaDiro G. (3.2) 3 S h a i i h a n , H. ' ( 1 ) ~387 Sharma, D.K. (3.5) 10; ( 3 . 6 ) 72 Sharma, P.K. ( 3 . 4 ) 177 Sharma, T.C. ( 3 . 5 ) 9 4 , 95 Sharma, V . K . ( 3 . 5 ) 4 3 S h c h e r b a t s k a , N . V . (1) 278 S h e c h t e r , H . ( 3 . 7 ) 66 S h e l d r i c k , W.S. (2.2) 26 Shelekhov, M.G. (3.4) 174; ( 4 ) 79 Shen, C.C. ( 2 . 2 ) 137 Shen, S. ( 2 . 1 ) 236, 238; ( 3 . 5 ) 19; ( 5 ) 6 7 Shen, W. ( 4 ) 131
Shen, X.A. ( 4 ) 288 S h e p e l i n , E.V. (5) 217 Sheradsky, T. ( 3 . 6 ) 86 S h e r i d a n , R.S. ( 3 . 1 ) 56; ( 3 . 4 ) 32, 33; (3.7) 4 , 6 , 7 , 20, 21, 103 S h e r s t y u k , V.P. (2.1) 55; ( 4 ) 80 Sherwood, A . G . ( 2 . 3 ) 1 2 S h i , H. ( 2 . 1 ) 204 S h i , Q.-L. ( 1 ) 366 S h i e l d s , C . J . ( 3 . 7 ) 42 S h i g a , A . (1) 486 S h i g a , T. ( 3 . 5 ) 24 Shigematsu, K . ( 2 . 1 ) 189 S h i l l i n g , R.D. ( 1 ) 148 S h i l o v , A.E. ( 5 ) 144 S h i l o v , S.A. ( 3 . 6 ) 215 Shim, H.K. ( 3 . 2 ) 100; ( 3 . 6 ) 139 Shim, S.C. ( 1 ) 234, 444; ( 2 . 1 ) 146; ( 3 . 2 ) 1 2 , 9 4 , 9 8 , 100; ( 3 . 3 ) 28, 35; ( 3 . 4 ) 139; ( 3 . 5 ) 104; ( 3 . 6 ) 23, 24, 8 9 , 93, 139 Shima, K . ( 3 . 4 ) 55; ( 3 . 6 ) 131 Shima, T. ( 5 ) 169 Shimada, K. ( 3 . 6 ) 62 Shimazaki, I . ( 3 . 6 ) 150 Shimizu, K. ( 2 . 2 ) 8 4 Shimizu, Y. ( 2 . 1 ) 173 Shimo, T. ( 3 . 2 ) 50 Shimoda, E. ( 1 ) 388 Shimomura, N. ( 3 . 2 ) 41 S h i n , E.J. ( 3 . 2 ) 94; ( 3 . 4 ) 139; ( 3 . 6 ) 23, 24 S h i n k a i , S. ( 2 . 1 ) 189; ( 3 . 6 ) 11, 15 Shinoda, S. ( 2 . 1 ) 161; ( 2 . 2 ) 118, 119; ( 5 ) 6 4 , 75, 80, 81 Shinoda, T. ( 2 . 1 ) 25; ( 5 ) 116 S h i n o h a r a , I. ( 4 ) 171 S h i n o z a k i , A . ( 5 ) 25 S h i n s a k a , K . ( 1 ) 83 Shiokawa, J . ( 2 . 1 ) 200 S h i o z a k i , H. ( 4 ) 449 S h i r a i , H. ( 4 ) 372; ( 5 ) 181 S h i r a i , M. ( 4 ) 9 9 , 100, 123, 145 Shiraawa, M. ( 5 ) 203 S h i r o t a , V. ( 4 ) 1 7 Shizuka, H. (1) 129, 131, ( 1 ) 308, 457; (3.6) 197 S h l y a p i n t o k h , V.Ya. ( 4 ) 430, 431 Shono. T. (5) 118 s h u , X. ( 4 j $0
Shudo, K. ( 1 ) 388 Shudok, C. (3.2) 103 Shugar, D. ( 3 . 2 ) 9 7 S h u k l a , S.S. ( 5 ) 232 Shukun, L. ( 3 . 6 ) 6 4 Shulman, P.M. ( 4 ) 4 8 S h u l ' p i n , G.B. ( 2 . 2 ) 132, 133 S h u l t z , A.R. ( 4 ) 326 S h v e t s , D . I . ( 2 . 1 ) 67 Sicard, G. (3.7) 78 S i c i n s k i , R.R. (3.3) 80 S i d d i q u i , S. (3.5) 113 Sidebottom, H.W. ( 2 . 3 ) 53 S i d h u , K.S. (1) 467 S i d k y , M.M. ( 3 . 5 ) 132 S i d r a c h d e Cardona, M. ( 5 ) 235, 236 S i e g e l , J . A . ( 1 ) 61 Siegmund, M. ( 3 . 7 ) 37 Siemiarczuk, A . ( 5 ) 126, 128, 132 S i e n i c k i , K . ( 4 ) 238, 240 S i e r o c k a , M. ( 4 ) 144 S i h l e r , R. ( 3 . 3 ) 51 S i m i c , M.G. (1) 18 Simoff, D.A. ( 4 ) 352 Simon, F.R. ( 1 ) 401 Simon, R.C. ( 2 . 2 ) 42 Simon, T.J. ( 1 ) 401 Simpson, A . F . ( 2 . 2 ) 1 4 Simpson, M.B. (2.2) 1 4 S i n c l a i r , A.M. ( 1 ) 264; ( 4 ) 235 Sindew, E.I. ( 4 ) 78 S i n d o , Y. ( 4 ) 236 S i n g a l , K . K . ( 3 . 6 ) 30 S i n g e r , L.A. ( 1 ) 489 Singh, A . K . ( 3 . 2 ) 71; ( 3 . 4 ) 179 Singh, B. (3.6) 30 S i n g h , S. ( 3 . 5 ) 43; (3.6) 190, 191 S i n g h , S.K. ( 3 . 4 ) 36 S i n h a , H.K. ( 1 ) 137 S i n i t s y n , N.M. ( 2 . 1 ) 133 S i n i t s y n a , Z.A. ( 5 ) 217 S i p , B. ( 1 ) 253 S i r e r a , Y. ( 3 . 4 ) 7 3 S i r o t a , V.G. (2.3) 42 S i r o t k i n , N . I . ( 2 . 2 ) 27 S i s i d o , M. ( 4 ) 256 Sivyakova, L.N. ( 3 . 6 ) 22 S k a l s k i , B. ( 1 ) 384 Skeean, R.W. ( 3 . 2 ) 61 S k e l t o n , B.W. ( 1 ) 110 S k e t , B. (3.4) 41; ( 3 . 7 ) 118 S k i b s t e d , L.H. ( 2 . 1 ) 15, 153, 154 S k i l t o n , P.F. ( 1 ) 53. 228 S k i n n e r ; I . A . (315) 20
Author Index
585
Skorina, J . ( 5 ) 34 Skorokhodov, S.S. ( 3 . 4 ) 174; ( 4 ) 79
Skowronski, T.A.
( 4 ) 316,
319
Skripkin, Yu.V. ( 2 . 2 ) 37 Skurat, V.E. ( 4 ) 327 Slama-Schwok, A. ( 2 . 1 ) 1 6 6 , 167
I
Slifkin, M.A. ( 1 ) 41 Small, E.W. ( 1 ) 361 Smalley, R.K. ( 3 . 7 ) 95 Smart, J . C . ( 2 . 2 ) 112 Smedarchina, Z. ( 1 ) 3 ; ( 3 . 3 ) 18
Smets, G. ( 4 ) 3 4 , 66 Smirnov, R . F . ( 4 ) 428 Smirnova, E.I. ( 4 ) 183 Smirnova, N.B. ( 4 ) 287 Smit, K . J . ( 1 ) 237 Smith, C.M. ( 3 . 2 ) 11 Smith, D.E. ( 3 . 2 ) 52 Smith, G.F.H. ( 3 . 3 ) 1 Smits, J.M.M. ( 3 . 3 ) 8 7 ; ( 3 . 4 ) 135
Soutar, I. ( 4 ) 165 Southgate, R. ( 3 . 7 ) 172 Sowa, T. ( 2 . 2 ) 56 Spada, A.P. ( 3 . 3 ) 8 3 ; (3.4) 9 Spadaro, G.S. ( 4 ) 306 Spahni, W. ( 5 ) 209 Spajer, M. ( 4 ) 205 Spanhel, L. ( 2 . 1 ) 18 Spaulding, L. ( 2 . 1 ) 2 1-
Stibranyi, L. ( 3 . 6 ) 58 Stiegman, A.E. ( 2 . 2 ) 1 Stierman, T . J . ( 3 . 3 ) 5 7 , 5 8 ; ( 3 . 4 ) 29
Still, I . W . J . ( 3 . 6 ) 157 Stillman, M . J . ( 2 . 1 ) 239 Stiver, S . ( 3 . 1 ) 2 1 , 23 Stochel, G . ( 2 . 1 ) 73-75 Stoesser, R. ( 2 . 3 ) 4 8 , 49 Stohler, F . R . ( 4 ) 383 Stoiljkovic, D. ( 4 ) 64 213 Spears, K.G. ( 1 ) 1 8 5 , 203 Stone, G.B. ( 3 . 7 ) 7 1 Storp, S . ( 4 ) 301 Speckhardt, T.A. ( 4 ) 37 Spikes, J . D . ( 1 ) 414 Stothers, J . B . ( 3 . 2 ) 21 Stramel, R.D. ( 5 ) 205 Spiro, T.G. ( 1 ) 469 Spreti, S . ( 3 . 5 ) 72 Strandjord, A.J.G. ( 1 ) 1 3 4 ; ( 3 . 2 ) 52 Sprinkle, C.R. ( 2 . 1 ) 165 Spurlin, S . R . ( 2 . 1 ) 1 2 9 ; Strat, G . ( 4 ) 425 Strausz, O.P. ( 3 . 4 ) 4-6; (5) 60 ( 3 . 6 ) 1 6 4 ; ( 4 ) 201 Spurr, O.K. ( 4 ) 104 Streith, J. ( 3 . 4 ) 1 0 1 ; Spurr, P.R. ( 3 . 3 ) 1 1 2 ; ( 3 . 6 ) 17
( 3 . 4 ) 159
Spyroudis, S.P. ( 3 . 7 ) 181 Streith, S . ( 3 . 7 ) 141 Stretzkowski-Marden, F. Srimannarayana, G. ( 3 . 4 ) ( 1 ) 365
140
Smolenski, I . N . ( 4 ) 401 Snead, T.E. ( 3 . 2 ) 8 7 ;
Srinivasan, R . ( 4 ) 363-
(3.3) 83; (3.4) 9 Snow, J . T . ( 2 . 3 ) 2 9 ; ( 3 . 6 ) 196 Snow, M.R. ( 2 . 1 ) 47 Snyder, R. ( 1 ) 8 4 Snyder, S.W. ( 2 . 1 ) 112 Sobczynski, A. ( 5 ) 196 Sobukawa, M. ( 3 . 7 ) 125 Soga, 0 . ( 3 . 2 ) 1 6 1 , 162 Sokolov, V.N. ( 4 ) 325, 429 Sokolova, B.T. ( 2 . 1 ) 195 Sokolyuk, N.T. ( 3 . 2 ) 168 Solaro, R. ( 4 ) 1 6 6 , 215 Solomitz, K.S. ( 4 ) 224 Solozhenkin, P.M. ( 5 ) 210 Somekawa, K. ( 3 . 2 ) 50 Somersall, A.C. ( 4 ) 299 Somogyi, B. ( 1 ) 347 Sonawane, H.R. ( 3 . 3 ) 3 3 , 142, 144; ( 3 . 4 ) 149; ( 3 . 7 ) 173-175 Song, J.S. ( 3 . 5 ) 104 Song, X. ( 2 . 1 ) 204; ( 3 . 6 ) 7 Sonnichsen, F. ( 3 . 3 ) 92 Soria, J. ( 5 ) 166 Soriano-Garcia, M. ( 3 . 1 ) 3 1 ; ( 3 . 2 ) 49 Sorita, K. ( 2 . 1 ) 200 Sorokina, A.V. ( 4 ) 431 Sorrell, T.N. ( 2 . 2 ) 137 Sostero, S. ( 2 . 2 ) 3 Soto-Garrido, G. ( 2 . 3 ) 12 Soumillion, J.P. ( 5 ) 39
Srivastava, T.S. ( 2 . 1 )
366 172
Staab, H.A. ( 3 . 7 ) 126 Stadler, K.H. ( 2 . 1 ) 2 8 ; ( 5 ) 178
Staerk, H. (5) 124 Stahl, W. ( 5 ) 2 3 4 , 238 Stamm, E. ( 3 . 4 ) 38 Standen, M.C. ( 1 ) 420 Stanforth, S . ( 3 . 1 ) 2 4 ;
Stricker, R. ( 1 ) 75 Stringate, R. ( 3 . 6 ) 174 Strobel, F. ( 2 . 2 ) 10 Strub, H. ( 3 . 4 ) 101 Struckler, S.J. ( 5 ) 13 Struve, W.S. ( 1 ) 2 5 8 , 313 Stuart, J . G . ( 3 . 4 ) 120 Studzinskii, O.P. ( 2 . 1 ) 195
Stueben, K.C. ( 4 ) 135 Stufkens, D . J . ( 2 . 2 ) 4 5 , 57,
58
Stuhl, F. ( 2 . 3 ) 31 Stults, J.S. ( 3 . 7 ) 121 Stanovik, B. ( 3 . 7 ) 30 Stunnenberg, F. ( 3 . 2 ) 6 9 Starczewski, I. ( 4 ) 144 Staryi, V.P. ( 1 ) 472 Su, S.C. ( 2 . 3 ) 54 Stasicka, 2. ( 2 . 1 ) 7 3 , 75 Su, S.Y. ( 1 ) 66 Susrez, E. ( 3 . 7 ) 1 8 6 , 187 Staskun, B. ( 3 . 5 ) 125 Suau, R. ( 3 . 4 ) 116 Statman, D. ( 1 ) 222 Subrahmanyam, D. ( 3 . 2 ) 8 4 Steel, C. ( 4 ) 446 Subramanian, G.B.V. ( 3 . 1 ) Steer, R . P . ( 1 ) 339 5 4 ; ( 3 . 7 ) 101 Steinberg, H. ( 3 . 5 ) 7 0 Subramanian, R . ( 3 . 7 ) 9 , Steinmetz, K.M. ( 1 ) 185 1 1 , 12 Steinmetzer, H.-C. ( 3 . 2 ) Suckling, I . D . ( 3 . 2 ) 22 103 Suddaby, B.R. ( 1 ) 2 9 5 ; Steinmueller, F. ( 2 . 1 ) ( 3 . 4 ) 129
( 3 . 3 ) 2 2 , 23
1 1 3 ; ( 5 ) 142
Stel'mashok, V.E.
(2.1)
143
Stelzer, E.H.K. ( 1 ) 75 Stemple, T.W. ( 4 ) 377 Stenstrom, Y. ( 2 . 2 ) 91 Stepanek, P. ( 4 ) 239 Stepanenko, V . I . ( 2 . 1 ) 1 9 Stewart, G.M. ( 2 . 2 ) 12 Stevart. D.W. ( 1 ) 156 Steiowski, J.JI ( 1 ) 210
Sudhakar, A. ( 3 . 4 ) 109 Sueishi, Y. ( 3 . 3 ) 7 ; (3.6) 9
Suetinov, A.P. ( 2 . 3 ) 44 Sugawara, T. ( 3 . 7 ) 92 Sugihara, Y. ( 1 ) 103 Sugimori, A . ( 2 . 2 ) 8 3 ; (2.2) 84, 97; (3.4) 99, 100; ( 3 . 5 ) 122; ( 3 . 6 ) 1 3 0 ; (5) 77
Author Index
586 Suginome, H. ( 3 . 2 ) 4 0 , 4 2 ; ( 3 . 7 ) 1 8 4 , 185 Sugisawa, H. ( 2 . 3 ) 2 6 ; ( 3 . 4 ) 157; ( 3 . 6 ) 200 Sugiura, M . ( 3 . 6 ) 6 8 Sugiura, T. ( 3 . 7 ) 10 Sugiyama, H. ( 3 . 6 ) 147 Sugiyama, T. ( 3 . 4 ) 9 9 ; ( 3 . 5 ) 122 Suglobov, D.N. (2.1) 219 Suguira, K. ( 1 ) 190 Suguwara, Y. ( 3 . 7 ) 65 Suh, I.S. ( 2 . 1 ) 208 Suijker, J . L . G . (1) 88 Sukale, R. ( 3 . 1 ) 4 2 ; ( 3 . 6 ) 76 Sukegawa, H. ( 3 . 4 ) 1 8 5 ; ( 3 . 6 ) 149 Sullivan, B.P. ( 2 . 1 ) 134 Suluimanov, B.A. ( 4 ) 294 Sumi, K. ( 5 ) 152 Sumiyesgu, T. ( 4 ) 96 Sumiyoshi, T. ( 1 ) 4 2 7 ; ( 3 . 6 ) 213, 214; ( 3 . 7 ) 1 2 2 ; ( 4 ) 31 Sundahl, M. ( 3 . 3 ) 30 Sundberg, R.J. ( 3 . 7 ) 80 Sundermeyer, W. ( 3 . 7 ) 129 Sundstrom, V. ( 1 ) 214, 242; ( 3 . 3 ) 1 6 ; ( 4 ) 438 Sung, C.S.P. ( 4 ) 232 Suppan, P. ( 1 ) 5 , 9 1 , 1 7 0 , 173 Surya Prakash, G.K. ( 3 . 7 ) 41 Suschitzky, H. ( 3 . 7 ) 95 Susi, P.V. ( 4 ) 4 0 5 , 416 Suter, G.W. ( 1 ) 437, 446, 453 Sutherland, J.C. ( 1 ) 333, 334 Sutherland, R.G. ( 2 . 2 ) 86 Sutin, N. ( 2 . 1 ) 1 4 , 109 Suto, M. ( 3 . 2 ) 1 5 3 , 1 5 7 ; ( 3 . 4 ) 4 8 ; ( 3 . 6 ) 110 Suzuki, J. ( 3 . 4 ) 77 Suzuki, K. ( 4 ) 422 Suzuki, N. ( 3 . 5 ) 7 5 , 123 Suzuki, S . ( 3 . 6 ) 145; ( 4 ) 3 7 , 126 Suzuki, S.S. ( 3 . 4 ) 77 Suzuki, T. ( 2 . 1 ) 6 8 ; ( 3 . 5 ) 37 Svenberg, C.E. ( 1 ) 382 Svorcik, V. ( 4 ) 417, 418 Swayambunathan, V. ( 1 ) 113 Sweany, R.L. ( 2 . 2 ) 1 3 , 36 Syassen, K. ( 1 ) 112 Sydnes, L.K. ( 3 . 7 ) 138 Symons, M.C.R. ( 3 . 7 ) 158 Szabo, A.G. ( 1 ) 390
Szeimies, G. ( 3 . 7 ) 31 Szentirmay, M.N. ( 1 ) 293; ( 4 ) 1 8 5 , 206
Szezepanski, J. ( 1 ) 107 Szyclinski, J. ( 1 ) 87 Tabankia, M.H. ( 4 ) 346 Tabata, Y. ( 1 ) 9 6 , 1 9 0 , 211
Tabayashi, K. ( 3 . 7 ) 6 0 Taber, A.M. ( 3 . 6 ) 215 Tabuchi, K. ( 4 ) 5 2 , 115 Tada, M. ( 3 . 6 ) 146 Tada, Y. ( 3 . 4 ) 137 Taen, S . ( 1 ) 440 Taga, T. ( 2 . 2 ) 56 Tagawa, S . ( 1 ) 9 6 , 1 9 0 , 211
Taghizadeh, N. ( 1 ) 192 Tajima, E. ( 4 ) 422 Taka, M. (1) 375 Takagi, H. ( 3 . 5 ) 6 9 Takagi, K. ( 2 . 1 ) 21 Takagi, M. ( 5 ) 233 Takahara, S. ( 1 ) 486 Takahashi, A. ( 3 . 4 ) 1 4 7 ; ( 3 . 7 ) 143
Takahashi, E. ( 4 ) 5 7 , 1 4 6 , 148
Takahashi, M. ( 3 . 6 ) 9 6 Takahashi,.T. ( 1 ) 208; (2.2) 119; ( 3 . 2 ) 9 2 ; (3.5) 49; ( 3 . 6 ) 18; ( 5 ) 8 1 , 1 0 1 , 102 Takahashi, Y. ( 4 ) 226 Takakubo, M. ( 1 ) 2 9 9 ; ( 2 . 1 ) 234; ( 5 ) 138 Takamuku, S. ( 2 . 1 ) 2 0 1 ; ( 3 . 3 ) 3 6 ; ( 3 . 6 ) 129 Takao, N. ( 3 . 6 ) 6 8 Takarik, Z.G. ( 4 ) 80 Takase, I. ( 4 ) 73 Takashima, M. ( 1 ) 1 3 5 ; ( 3 . 5 ) 23 Takata, T. ( 3 . 5 ) 2 , 1 5 1 ; ( 3 . 7 ) 69 Takayama, K. ( 3 . 6 ) 7 1 , Takayama, M. ( 4 ) 8 Takechi, H. ( 3 . 2 ) 1 4 6 , 1 4 7 ; ( 3 . 6 ) 8 0 , 116 Takei, M. ( 3 . 4 ) 8 1 ; ( 3 . 6 ) 10 Takemura, F. ( 4 ) 7 2 , 233 Takenaka, S . ( 3 . 4 ) 9 9 ; ( 3 . 5 ) 122 Takenchi, A . ( 4 ) 303 Takeshita, H. ( 3 . 2 ) 141 6 , 1 6 0 ; ( 3 . 5 ) 75 Takeuchi, S . ( 2 . 2 ) 111 Takibsev, Zh.S. ( 5 ) 23 Takizawa, A. ( 4 ) .218
Takubo, Y. ( 1 ) 211 Takui, T. ( 3 . 7 ) 6 4 Takuwa, A. ( 3 . 2 ) 1 6 1 , 162 Talapatra, G.B. ( 1 ) 483 Tale, I.A. ( 4 ) 289 Taleb, A.M. ( 5 ) 239 Taljaard, B. ( 3 . 5 ) 100 Tal'roze, V.L. ( 4 ) 327 Tamai, N. ( 1 ) 259 Tamaki, T. ( 3 . 4 ) 161 Tamazaka, T. ( 1 ) 142 Tames, J. ( 2 . 1 ) 6 6 Tamiaka, H. ( 3 . 2 ) 163 Tamilarsan, R. ( 1 ) 268; ( 2 . 1 ) 111
Tamminga, J.J. ( 3 . 4 ) 71 Tamura, N. ( 4 ) 272 Tamura, Y. ( 3 . 5 ) 1 5 1 ; ( 3 . 6 ) 96
Tan, P. ( 3 . 6 ) 63 Tan, S.L. ( 3 . 2 ) 28 Tanaka, A. ( 5 ) 25 Tanaka, F. ( 1 ) 1 7 1 , 436; ( 4 ) 266
Tanaka, H. ( 3 . 6 ) 1 9 7 ; ( 5 ) 165
Tanaka, H.K. ( 2 . 1 ) 5 7 , 58 Tanaka, I. ( 1 ) 215 Tanaka, J. ( 1 ) 326 Tanaka, K. ( 5 ) 1 7 4 , 185 Tanaka, M. ( 1 ) 215; (2.1) 181; ( 3 . 2 ) 5 ; ( 3 . 3 ) 117; ( 4 ) 9 9 , 100, 122, 1 2 3 , 145; ( 5 ) 165 Tanaka, N. ( 3 . 3 ) 45 Tanaka, S . ( 4 ) 5 , 122 Tanaka, T. ( 3 . 5 ) 1 1 2 ; (3.6) 9 Tanaka, Y. ( 1 ) 9 6 ; ( 2 . 1 ) 1 7 3 , 174 Tanemura, H. ( 5 ) 198 Tang, C.P. ( 3 . 1 ) 1 0 , 11 Tang, Z. ( 4 ) 155 Tanida, H. ( 3 . 3 ) 4 7 ; ( 3 . 6 ) 50 Taniguchi, H. ( 3 . 7 ) 177 Taniguchi, Y. ( 4 ) 221 Tanirnoto, Y. ( 3 . 4 ) 1 7 8 ; ( 3 . 5 ) 23 Tanner, M. ( 1 ) 498 Tantravaki, V. ( 1 ) 7 2 Tao, T. ( 1 ) 363 Taoda, H. ( 3 . 3 ) 9 5 ; ( 5 ) 53 Tarasevich, M.R. ( 5 ) 227 Tarasov, V.F. ( 3 . 1 ) 25
Tardieu de Maleissye, J. ( 3 . 5 ) 142
Tarzia, G. ( 3 . 5 ) 119 Tasayco, M.L. ( 3 . 4 ) 46 Tasumi, M. ( 1 ) 9 5 . 439 Tatikolov, A.H. (1) 489
Author Index Tauer, E. (3.1) 53; (3.6) 38, 42 Taylor, D.G. (1) 431 Taylor, J . R . (1) 212 Taylor, P. (1) 356 Taylor, R.S. ( 1 ) 198 Tazuke, S. (1) 506; (2.1) 90, 127; (4) 245; (5) 61, 122 Teashima, M. (3.7) 148 Tedeschi, P. (3.6) 56 Tedjamulia, M.L. (3.4) 120, 121 Teh, C.E. (3.6) 99 Teh, C.Z. (3.2) 131 Teichner, S.J. (2.1) 26; (5) 3 Teki, Y. (3.7) 64 Tempczyck, A. ( 1 ) 384 Tennakone, K. (2.1) 34; (5) 24 Tera, F.M. (4) 436 Terada, K. (3.2) 93; (3.6) 16 Teranishi, H. ( 1 ) 171, 189, 190, 436; (3.4) 83 Terasaka, K . (3.4) 75; (3.6) 209 Terashima, M. (3.4) 96; (3.7) 147 Teratani, S. (2.2) 51 Terazima, M. ( 1 ) 122, 441 Ternansky, R.J. (3.4) 35 Terner, J. (1) 58, 469 Tero-Kubota, S. (2.2) 139 Tersawa, T. (3.7) 67 Teruel, J.A. ( 1 ) 369 Teufel, E. (3.4) 52 Theis, W. (3.7) 73 Thewalt, U. (2.2) 22 Thiel, W. (3.3) 89 Thielen, A.P.G.M. ( 1 ) 404 Thierry, J. (3.7) 117 Thirunamachandran, T. (1)
(5) 223 Thomson, A. (3.4) 69 Thorel, P.J. (3.6) 119 Ticke, B. ( 4 ) 18 Tietze, L.-F. (3.2) 38; (3.6) 94 Tikhomirov, V.V. (2.1) 133 Tiltina, I. ( 4 ) 286 Timofeeva, T.V. (5) 158 Timpe, H.-J. ( 1 ) 303: (3.6) 4, 58; (3.7) 83; (4) 24, 39, 40, 47, 51, 154 Tinnemans, A.H.A. (3.3) 94; (5) 43 Tirrell, D.A. ( 4 ) 53 Titov, A . A . (2.3) 35, 36 Tiwari, L.B. ( 1 ) 380 Tkachenko, Z.A. (2.1) 67 Tobe, Y. (3.2) 23; (3.4) 3 Tobita, S. (1) 442 Tochtermann, W. (3.3) 92 Toda, R. (3.2) 153, 156; (3.4) 49; (3.6) 109 Toda, T. (4) 388, 396 Todesco, R.V. ( 4 ) 263 Togo, H. (3.7) 115, 116 Toi, K. (5) 203 Toivonen, J. (2.1) 215 Tojo, G. (3.4) 116 Tojo, S. (3.2) 153, 157; (3.4) 48; (3.6) 110 Toki, S. (2.1) 201; (3.3) 36; (3.6) 129 Tokuda, T. (5) 203 Tokumaru, K. (1) 141, 188, 439, 486; (3.3) 13; (3.5) 27, 36 Tol, A . J . W . (3.4) 119 Tolbert, L.M. (3.3) 149; (3.7) 57 Tolman, C.A. (3.7) 2 Tolstikov, G.A. (2.1) 1 106; (2.3) 57 Thistlethwaite, P. (1) Tomai, N. (1) 35 53, 273 Tho, N.D. (3.2) 36 Tomas, V. (3.5) 126 Tomaschewski, G. (3.7) Thomas, A.C. (2.2) 138 37, 38 Thomas, B. (3.5) 130 Thomas, E.W. (1) 145, 166 Tomasik, P. (3.7) 97 Thomas, J.K. (1) 92, 298, Tombari, E. (4) 76 Tominaga, T. (2.2) 7 1 307; (2.1) 115, 116, Tomioka, H. (3.7) 10, 39, 121; (4) 229; ( 5 ) 161, 193, 205 53, 60 Thomas, J.W. ( 4 ) 262 Tomioka, K. (3.2) 5 Thomas, P. (2.2) 31, 33 Tomita, H. (3.2) 121 Thomas, W.R.L. (5) 237 Tomokiyo, K. (2.1) 200 Thomas-David, G. ( 1 ) 383; Toms, M. (3.7) 40 Toncheva, V. (4) 102 (2.1) 246 Thompson, N.L. (1) 412 Tondello, E. (2.2) 81 Thompson, R.L. (3.5) 42; Toney, C.G. (2.1) 46
587 Tooburg Jenson, J.P. (4) 386 Toppet, S. (3.7) 35; (4) 260 Toptygin, D.Ya. (3.7) 81 Toribio, F. (1) 130 Torikai, A. (4) 303, 304 Toriumi, M. (1) 83 Torkelson, J.M. (4) 254 Torrent, A.O. (1) 317 Torres, M. (3.4) 4-6; (3.6) 164; (3.7) 90 Toscano, A. (3.2) 49 Toscano, R.A. (3.1) 31 Toscano, V. (4) 444 Toshima, N. (3.5) 49; (5) 101, 102 Totrajada, J. (3.1) 15 Townsend, D.E. (3.4) 51 Toyoda, T. (3.4) 167 Trammell, G.L. (3.2) 61 Tran-Thi, T.H. (5) 135 Traverso, 0. (2.1) 71; (2.2) 3 Treacy, J.J. (2.3) 53 Trebert, Y. (3.7) 140 Trefonas, P. ( 4 ) 371 Treichel, r. (5) 124 Triandos, P. ( 1 ) 273 Tricot, Y.-M. (1) 297; (5) 215 Trifinov, L.S. (3.2) 68; (3.4) 182 Tripathi, G.N.R. ( 1 ) 97 Tritthart, H.A. (1) 407 Trkula, M. (1) 68 Troe, J. (3.3) 19 Trogler, W.C. (2.2) 131 Trojan, D. (3.4) 51 Trotter, J. (3.1) 34, 36 Truscott, T.G. ( 1 ) 477, 480 Tsao, L. (2.1) 215 Tsay, S.Y. ( 4 ) 137 Tsay, Y.-H. (2.2) 5; (3.4) 47; (3.6) 120 Tschamber, T. (3.6) 17; (3.7) 141 Tse, A. (3.2) 131; (3.6) 99 Tseung, A.C. ( 5 ) 206 Tsivenko, V . I . (5) 208 Tsnooka, M. (4) 122, 1 2 3 Tsoi, S.C. (3.6) 166 Tsuchida, A. (3.3) 120; (3.6) 92; (4) 234 Tsuchiya, J. (3.7) 125 Tsuchiya, T. (1) 35; (3.6) 57, 71; (3.7) 94, 96 Tsujimoto, K. (3.6) 106; (3.7) 127
Author Index
588
Tsujita, Y. ( 4 ) 218 Tsukamoto, M. ( 4 ) 1 9 8 , 214
Tsuzuki, K. ( 3 . 6 ) 146 Tuckerman, R.T. ( 2 . 3 ) 50 Tueling, M.B. ( 4 ) 376 Tung, C.H. ( 1 ) 306 Turkenburg, L.A.M. ( 3 . 4 ) 3
Turley, W.D. ( 1 ) 294 Turnbull, J.H. ( 1 ) 322 Turner, D.H. ( 1 ) 391 Turner, J.J. ( 2 . 2 ) 1 4 , 9 5 , 98
Urabe, S. ( 4 ) 439 Urachem, M.N. ( 4 ) 91 Ushiki, H. ( 1 ) 270; ( 4 )
Van Stappen, P. ( 3 . 7 ) 35 Van Steenwinkel, R. ( 2 . 1 )
2 3 6 , 266 Usui, M. ( 1 ) 388 Usui, Y. ( 1 ) 4 9 3 ; ( 3 . 5 ) 35 Uyehara, T. ( 3 . 2 ) 81-83, 85
van Tol, M.W. ( 1 ) 88 Vanucci, C. ( 2 . 3 ) 1 7 ;
Vaida, V. ( 2 . 2 ) 2 Vaillet, P. ( 1 ) 159 Vainshtein, A.B. ( 4 ) 286,
Turoverov, K.K. ( 1 ) 338 344 Turro, N.J. ( 1 ) 1 4 3 , 1 4 4 , Valat, P. ( 1 ) 9 4 ( 1 ) 2 7 1 , 289, 2 9 0 , 3 0 4 , Valeeva, T.G. ( 3 . 7 ) 1 386, 464, 4 9 2 ; ( 3 . 1 ) 6 , Valeur, B. ( 1 ) 260, 305 7 , 2 7 ; ( 3 . 4 ) 1 8 7 ; ( 3 . 5 ) Valiev, K.A. ( 4 ) 327 5 , 8 , 2 2 ; ( 3 . 7 ) 4 0 , 5 2 ; van Arkel, B. ( 3 . 4 ) 34 Van Audenhove, M. ( 3 . 2 ) ( 4 ) 44 2 7 ; ( 3 . 6 ) 205 Tverskoi, V.A. ( 5 ) 158 Tyler, D.R. ( 2 . 2 ) 1 , 4 7 , VanEik, H. ( 2 . 3 ) 1 3 ; 1 0 0 , 101
( 3 . 7 ) 88
Tyler, P.C. ( 3 . 2 ) 6 0 Tymyanskii, Ya.R. ( 3 . 4 )
Van Damme, H. ( 1 ) 3 0 9 ;
126-128; ( 3 . 6 ) 2 8 , 29 Tyrrell, H.M. ( 3 . 4 ) 22
Vandendriessche, J. ( 4 )
( 2 . 1 ) 1 3 7 ; ( 5 ) 3 0 , 117 244
Van den Heuvel, C.J.M. ( 3 . 5 ) 70
Uasugi, M. ( 4 ) 72 Uchida, K. ( 4 ) 152 Uchido, J. ( 4 ) 148 Uchino, T. ( 3 . 6 ) 96 Uchiyama, K. ( 3 . 6 ) 9 7 ; ( 4 ) 281 Uda, H. ( 3 . 2 ) 8 0 ; ( 3 . 3 ) 114 Udagawa, M. (1) 141 Udaykumar, M. ( 3 . 3 ) 3 3 ; ( 3 . 7 ) 174 Ueda, A. ( 4 ) 1 0 0 , 145 Ueda, H. ( 2 . 1 ) 38 Ueda, K. ( 3 . 2 ) 23 Ueda, T. ( 5 ) 171 Uehara, M. ( 3 . 5 ) 23 Ueno, F.B. ( 2 . 1 ) 147 Ueno, Y. ( 1 ) 357; ( 3 . 5 ) 82 Ueyama, T. ( 3 . 5 ) 123 Ukdova, E.M. ( 4 ) 118 Ullah, S.S. ( 2 . 2 ) 7 6 , 77 Umezawa, B. ( 3 . 4 ) 1 4 7 ; ( 3 . 7 ) 143 Umrigar, P.P. ( 3 . 5 ) 78 Unsoeld, E. ( 1 ) 37 Uosaki, K. ( 2 . 1 ) 2 9 ; ( 5 ) 176 Uozo, Y. ( 1 ) 239; ( 3 . 3 ) 29 Upadhyaya, V. ( 1 ) 380 Upmacis, R.K. ( 2 . 2 ) 14
van den Zegel, M. ( 1 ) 36 van der Auweraer, M. ( 1 ) 213, 346
Van der Kelen, G.P. ( 2 . 3 ) 52
van der Loop, E.A.R.M. (3.2) 7
van der Meer, B.W. ( 1 ) 48 van der Veen, J.M. ( 3 . 2 ) 7 9 , 107
Van der Werf, S. ( 4 ) 77 Van der Wielen, F.W.M. ( 3 . 4 ) 87
van der Zegel, M. ( 1 ) 213 van der Zwan, G. ( 1 ) 7 Vandewalle, M. ( 3 . 2 ) 2 7 ; ( 3 . 6 ) 205
Van Dijk, H.K. ( 2 . 2 ) 45 Van Duyne, R.P. ( 1 ) 256 van Eijk, L.M.J. ( 1 ) 1 8 1 ; ( 3 . 4 ) 72
Van Eldik, R. ( 2 . 1 ) 184 van Ginkel, F.I.M. ( 1 ) 180
Van Hemelryck, B. ( 3 . 1 ) 15
Van Hiftje, L. ( 3 . 2 ) 2 7 ; ( 3 . 6 ) 2 0 5 ; ( 3 . 7 ) 15
Van Himbergen, J.E. (1) 1 2 , 279
Van Hoek, A. ( 1 ) 67 Vannikov, A.V. ( 4 ) 173
77 ( 3 . 4 ) 169
van Zeijl, P.H.M. ( 1 ) 1 8 1 ; ( 3 . 4 ) 72
Varani, G. ( 2 . 1 ) 92 Vareux, J. ( 4 ) 128 Varfolomeev, S.D. ( 5 ) 14 Varie, D.L. ( 3 . 7 ) 121 Varkhede, R.S. ( 1 ) 504 Varma, C.A.G.O. ( 1 ) 8 8 , 8 9 , 1 0 9 , 179-181; ( 3 . 4 ) 6 5 , 7 1 , 72 Varma, I.K. ( 4 ) 3 0 8 , 404 Varshovski, L. ( 1 ) 362 Vasina, E.R. ( 3 . 2 ) 44 Vauthey, E. ( 1 ) 173 Vaz, C. ( 3 . 5 ) 7 8 Vechkanov, G.N. ( 4 ) 183 Vedejs, E. ( 3 . 7 ) 121 Veillard, A. ( 2 . 2 ) 103 Velichkov, V.A. ( 4 ) 431 Velichkova, R. ( 4 ) 102 Velikov, C.V. ( 4 ) 327 Velthorst, N . H . ( 1 ) 116 Venema, R.C. ( 1 ) 495 Venkataraman, V.R. ( 3 . 5 ) 115 Venkatesan, K. ( 3 . 2 ) 4 3 , 4 5 ; ( 3 . 4 ) 153 Venturi, M. ( 2 . 1 ) 1 0 4 , 142; ( 5 ) 99 Veprek-Siska, J. ( 3 . 5 ) 111 Verbovaya, S.N. ( 4 ) 75 Verdonck, L. ( 2 . 3 ) 52 Verdu, J. ( 4 ) 420 Verhoeven, J.W. ( 1 ) 1 7 6 ; ( 5 ) 1 2 5 , 134 Verjovski-Almeida, S . ( 1 ) 37 1 Verral, R.E. ( 1 ) 339 Verschoor, C.M. ( 2 . 1 ) 217 Vershal, V.V. ( 4 ) 2 7 6 , 278 Vert, F.T. ( 1 ) 317 Vettermann, S . ( 3 . 5 ) 149 Veyret, B. ( 3 . 5 ) 89 Vichutinskaya, E.V. ( 4 ) 3 3 2 , 401 Vidal, C.J. ( 1 ) 369 Vieira Ferreira, L.F. ( 1 ) 254 VSg, A . ( 4 ) 454 Villalain, J. ( 1 ) 369 Vinogradov, I.P. ( 2 . 3 ) 43 Vinogradov, S.A. ( 2 . 1 ) 183 Viovy, J.L. ( 1 ) 1 0 8 ; ( 4 )
Author Index 168, 212, 253, 257 Virag, L. (3.4) 92 Virgili, A. (5) 151 Visser, A.J.W.G. (1) 23, 67; (4) 255
Visser, P.C. (3.2) 102 Visser, R.-J. (1) 109; 179, 180
Vliers, D.P. (2.1) 89 Vo-Dinh, T. (1) 118, 437 VVogel, E. (3.3) 111 Vogel, F.R. (3.5) 100 Vogel, P. (2.2) 5 Vogl, 0. (4) 382, 411, 412
Vogler, A. (2.1) 5, 135 Voightman, E. (1) 2 1 Voituriez, L. (3.2) 99; (3.6) 87
Volkov, O.G. (2.2) 37 Vollhardt, K.P.C. (2.2) 107
Voltz, R. (1) 253 Von der Linde, D. (4) 329 Von Gustorf, E.A.K. (2.2) 17
Vonhoene, P. (4) 453 von Kan, P.J.H. (1) 109 von Schnering, H.G. (3.1) 14; (3.2) 86; (3.3) 43, 92; (3.5) 77; (3.7) 18, 24 Von Sonntag, C. (3.7) 130 von Wartburg, B. (3.2) 57 Vonwiller, S.C. (3.5) 83 Von Zelewsky, A. (2.1) 78, 79, 93, 130, 175, 176; (5) 55, 58, 123 Vorotnikov, A.P. (3.7) 81 Vos, J.G. (5) 228 Voyakin, I . V . (2.2) 109 Vrachnou-Astra, E. (2.1) 170; (5) 76 Vretsena, N.B. (2.1) 61 Vuilleumier, J.J. (2.1) 207 Vymazal, Z. (4) 417, 418 Vymazalova, Z. (4) 417 Vysotskii, Yu.B. (3.6) 22
Wacholtz, W.F. (2.1) 80, 84: (5) 57
Wachs, I.E. (2.1) 27; (5) 191
Wada, I. (1) 270 Wada, M. (3.2) 142; (3.6) 82; (4) 37, 126
Wagner, G.S. (2.3) 3 Wagner, J. ( 3 . 4 ) 175, 176; (3.6) 124
589
Wagner, P.J. (1) 484; (2.2) 43; (3.1) 39, 40; (3.4) 151; (3.5) 11 Wagner, R. (4) 24, 154 Wahiduzzaman, S.M. (2.2)
Wayner, K. (4) 45 Webber, S.E. (1) 267; (4)
258, 259, 261; (5) 162, 178, 194 Weber, M.A. (2.2) 65 Weber, R.H. (3.3) 86 77 Weber, W. (2.1) 184; Wahl, P. (1) 56 (3.7) 122 Wakabayashi, S. (1) 103 Webster, G.R.B. (3.4) 86, Wakao, S. (3.6) 179 87; (3.5) 50 Wakashima, Y. (4) 130 59; (3.5) 1 2 , 20; (5) Wakefield, B.J. (3.1) 30 Wakisaka, A. (3.5) 27, 36 126, 128, 132 Weers, J.G. (1) 496 Waksman, D. ( 4 ) 328 Weetall, H.H. (5) 225, Wallace, J. (1) 408 226 Wallace, S.C. (1) 79 Wehry, E.L. (1) 22 Walsh, E.J. (3.7) 7 1 Weidenbruch, M. (2.3) 23; Walters, E.A. (2.3) 40 (3.6) 195 Waltz, W. (2.1) 180 Weider, R. (3.3) 111 Wamhoff, H. (3.5) 132 Weill, G. (4) 265 Wan, C.S.K. (3.2) 59; Weir, D. (1) 419, 498 (3.5) 12; (5) 132 Weir, N.A. ( 4 ) 334, 337 Wan, J.K.S. (3.2) 158, Weisenborn, P.C.M. (1) 164; (3.5) 22 109, 179 Wan, P. (3.4) 105-107; Wan, P. (3.5) 8 , 52, 135 Weiss, R.G. (3.4) 66, 67 Weissenfels, M. (4) 442 Wandelt, B. (4) 307 Weitz, E. (3.3) 64 Wang, D. (3.5) 57 Weixelbaumer, D.W. ( 4 ) Wang, E. (49 85, 88 269 Wang, F.W. (4) 230, 237, Welch, G.R. (1) 347 252 Wang, H. (2.2) 105; (3.6) Weller, A. (5) 124 Weller, H. (3.6) 42 63 Wang, L. (3.2) 79; (4) 89 Wellner, E. (1) 310 Welzel, P. (3.7) 75 Wang, T. (2.1) 223 Wen, Z. (4) 399 Wang, X. (3.5) 38 Wender, P.A. (3.4) 35-37 Wang, Y. (1) 178; (2.2) 63; (3.2) 108; (3.6) 7; Weng, Y. (2.1) 1 7 Wennerstroem, 0. (3.3) 30 (4) 60, 217 Wannamaker, M.W. (3.7) 29 Wensel, T.G. (1) 395 Wenska, G. (3.6) 98 Ward, D.L. (3.1) 39; Werner, T.C. (1) 114, 331 (3.4) 151; (3.5) 11 Wessely, H.-J. (3.4) 156; Ward, I . M . (4) 164 (3.6) 198 Ware, W.R. (1) 49-51, West, B.J. (1) 245, 246 312, 325, 329 West, P.R. (3.7) 50 Warman, J.M. (1) 109 West, R. (2.3) 13, 21; Warner, I . M . (1) 62 (3.7) 88; (4) 371 Warren, S. (3.3) 2 Weston, R.E. (1) 82 Wasgestian, F. (2.1) 50 Weyerstahl, P. (3.1) 51 Washida, N. (3.5) 69 Weyna, I. (1) 209 Washio, M. (1) 96, 190, White, A.H. (1) 110 211 Wasielewski, M.R. (1) 175 White, D.A. (1) 118 Wasserman, H.H. (3.5) 96 White, J.D. (3.2) 61 Whitharn, G.H. (2.3) 14 Watabiki, 0. (3.6) 145 Whiting, M.C. (2.2) 79 Watanabe, H. (2.3) 27; Whittaker, A.K. (4) 361 (3.6) 197 Whittall, J. (3.2) 126; Watanabe, T. (3.4) 178; (3.4) 141 (3.5) 23 Whitten, D.G. (1) 220, Waterfeld, A. (3.7) 182 285, 295; (2.1) 248; Watkins, D.A.M. (3.4) 94 (3.3) 2 2 , 23; (3.5) Watts, R.J. (2.2) 112
Author Index
5 90 118; ( 5 ) 70
( 3 . 6 ) 126
Witkowski, K. ( 4 ) 336 Whittle, E. ( 2 . 3 ) 50 Wittenberger, S . ( 3 . 7 ) Whyman, R. ( 2 . 2 ) 14 121 Wiberg, K.B. ( 3 . 3 ) 73 Wickramaaratchi, M.A. ( 1 ) Wittwer, V. ( 5 ) 238 Wi Wang, F. ( 4 ) 243 82 Wickramanayake , S . ( 2 . 1 ) Wodtke, A.M. f 3 . 3 ) 38 Woehrle, D . ( 2 . 1 ) 233, 3 4 ; ( 5 ) 24 Wiechert, R. ( 3 . 1 ) 16 ( 5 ) 66 Woessner, G. ( 1 ) 210 Wietelmann, U. ( 3 . 6 ) 217 Wolf, B. ( 3 . 7 ) 68 Wietfeld, B. ( 3 . 2 ) 88 Wolf, C . J . ( 4 ) 351 Wigley, J.W. ( 4 ) 197 Wijnaundts van Resandt, Wolf, D.E. ( 1 ) 276 Wolf, H.C. ( 1 ) 1 1 5 , 255 R.W. ( 1 ) 75 Wolf, H.R. ( 3 . 2 ) 57 Wilbrandt, R. ( 1 ) 421 Wolff, C.R. ( 2 . 2 ) 46 Wild, U.P. ( 1 ) 2 8 , 9 4 , 1 1 9 , 2 8 5 , 4 3 7 , 4 4 6 , 453 Wolff, S. ( 3 . 2 ) 1 , 2 , 1 7 , Wilda, J. ( 3 . 7 ) 38 6 7 ; ( 3 . 6 ) 206 Wilde, R.G. ( 3 . 7 ) 121 Wolinski, L. ( 4 ) 336 Wiles, D.M. ( 4 ) 3 7 9 , 386 Wong, D . F . ( 3 . 2 ) 5 9 ; Wilkinson, F. ( 1 ) 4 6 5 ; ( 3 . 5 ) 12 Wong, K.-M. ( 3 . 4 ) 113 ( 3 . 1 ) 9 ; ( 4 ) 435 Wong, K.S. ( 4 ) 190 Williams, A.C. ( 1 ) 352 Williams, D . J . ( 4 ) 211 Wong, S.K. ( 3 . 4 ) 164 Williams, J . R . ( 3 . 1 ) 1 7 ; Wong, W.K. ( 5 ) 188 Wong, Y.-F. ( 3 . 1 ) 32 ( 3 . 2 ) 6 5 ; ( 3 . 6 ) 170 Williams, P.J.K. ( 4 ) 186 Woodin, R.L. ( 2 . 2 ) 52 Woods, J. ( 4 ) 1 2 4 , 125 Willig, F. ( 1 ) 213 Wooler, J. ( 4 ) 317 Willner, I. ( 1 ) 302; Worman, H.J. ( 1 ) 400 ( 2 . 1 ) 125; ( 3 . 3 ) 143; Wostratzky, D.' ( 4 ) 13 ( 3 . 5 ) 2 6 ; ( 5 ) 1 0 9 , 110 Wright, T . A . ( 3 . 7 ) 156 Willsher, C . J . ( 1 ) 4 6 5 ; Wrighton, M.S. ( 2 . 2 ) 8 7 , ( 3 . 1 ) 9 ; ( 4 ) 435 9 2 , 106 Willson, C.G. ( 4 ) 98 Willson, J.M. ( 3 . 4 ) 7 8 ; Wroblenski, J. ( 1 ) 240; ( 3 . 6 ) 155
Wilson, B.A. ( 2 . 2 ) 92 Wilson, J.R.H. ( 3 . 2 ) 33 Wilson, P. ( 3 . 2 ) 1 , 1 3 7 ; ( 3 . 6 ) 107, 206 (3.7) 13, 1 4 , 24 Wilson, W.L. ( 1 ) 438 Wilzbach, K.E. ( 3 . 4 ) 21 Winders, J . A . ( 3 . 1 ) 30 Windisch. H. ( 1 ) 407 Windsor, M.W. ( 1 ) 205 Winefordner, J.D. ( 1 ) 2 1 , 425 Wink, D.A. ( 2 . 2 ) 122 Winnik, M.A. ( 1 ) 264; ( 4 ) 202, 235, 248 Winscom, C.J. ( 2 . 1 ) 41 Winslow, F . H . ( 4 ) 352 Wintermeyer, W. ( 1 ) 397 Wintgens, V. ( 1 ) 9 4 ; ( 4 ) 444 Wirth, M . J . ( 1 ) 17 Wirz, J. ( 1 ) 1 0 3 ; ( 3 . 2 ) 1 2 9 ; ( 3 . 7 ) 25 Withnall, R. ( 2 . 3 ) 51 Witkop, B. ( 3 . 2 ) 140;
Wilson, R.M.
Yablonskaya, E.E. ( 5 ) 144 Yabuta, M. ( 2 . 1 ) 244; ( 5 ) 202
Yaegashi, H. ( 3 . 3 ) 131 Yaghmour, H. ( 4 ) 408 Yagi, M. ( 1 ) 430 Yakota, N. ( 3 . 3 ) 117 Yakovlev, V.N. ( 2 . 3 ) 57 Yakshin, V.V. ( 2 . 1 ) 222 Yakunichev, M.V. ( 5 ) 208 Yamabe, T. ( 2 . 2 ) 56 Yamada, A. ( 2 . 1 ) 1 2 0 , 231; ( 5 ) 9 0 , 1 5 3 , 154
Yamada, J. ( 3 . 2 ) 8 3 , 85 Yamada, S . ( 3 . 4 ) 1 5 , 1 8 4 ;
(3.6) 44, 145; ( 3 . 7 ) 1 8 4 , 185 Yamada, T. ( 3 . 5 ) 8 2 ; ( 3 . 6 ) 97 Yamada, Y. ( 2 . 1 ) 1 8 1 ; ( 2 . 2 ) 71 Yamaguchi, K. ( 3 . 5 ) 65 Yamaguti, K. ( 2 . 1 ) 3 1 ; ( 5 ) 1 8 3 , 184 Yamakawa, T, ( 5 ) 80 Yamakita, H. ( 3 . 3 ) 9 5 ; ( 5 ) 53 Yamamoto, A. ( 3 . 6 ) 147 Yamamoto, H. ( 2 . 2 ) 1 1 8 ; (3.4) 184; (3.6) 1 4 , 4 4 ; ( 5 ) 75 Yamamoto, I. ( 3 . 6 ) 150 Yamamoto, K. ( 3 . 3 ) 10; ( 4 ) 2 3 3 , 449 Yamamoto, M. ( 1 ) 2 6 3 ; (3.3) 120; (3.6) 92; ( 3 . 3 ) 26 ( 4 ) 234 Wronka, J. ( 2 . 2 ) 10 Yamamoto, R. ( 4 ) 449 Wu, E.S. ( 4 ) 2 3 0 , 237 Wu, G. ( 3 . 1 ) 5 ; ( 3 . 3 ) 127 Yamamoto, S . ( 3 . 2 ) 1 1 6 , 117; (3.6) 9 Wu, S . ( 3 . 5 ) 80, 1 4 7 , 1 4 8 ; ( 4 ) 106 Yamamoto, Y. ( 2 . 1 ) 2 4 , 171; ( 4 ) 1 9 ; ( 5 ) 165, wu, ( 3 . 3 ) 11 WU, Z.-Z. ( 1 ) 8 6 ; ( 3 . 4 ) 173 Yamane, K. ( 3 . 2 ) 1 5 6 ; 5 8 ; ( 3 . 6 ) 1 4 2 , 143 Wubbels, G.G. ( 3 . 4 ) 6 2 , ( 3 . 4 ) 4 9 ; ( 3 . 6 ) 109 Yamanouchi, K . ( 3 . 2 ) 110 6 4 ; (3.6) 74 Wyssbrod, H.R. ( 1 ) 3 3 3 , Yamaoka, M. ( 4 ) 284 Yamaoka, T. ( 4 ) 4 , 9 334 Yamashita, K. ( 1 ) 2 6 3 ; ( 2 . 1 ) 145 Yamashita, M. ( 2 . 1 ) 123 Xiao, X. ( 2 . 1 ) 2 3 7 ; ( 3 . 5 ) Yamashita, S . ( 1 ) 4 3 6 ; 5 7 ; ( 5 ) 65 ( 4 ) 209; ( 5 ) 159 Xie, X. ( 4 ) 155 Yamashita, T. ( 3 . 4 ) 5 5 ; Xu, B. ( 3 . 5 ) 1 4 7 , 148 ( 3 . 6 ) 131 Xu, D. ( 3 . 5 ) 1 4 7 , 148 Yamashita, Y. ( 3 . 3 ) 1 3 1 ; XU, H. ( 2 . 1 ) 2 2 0 , 236( 3 . 4 ) 8 2 ; ( 3 . 6 ) 134 238; ( 3 . 5 ) 1 9 ; ( 5 ) 6 5 , Yamashito, H. ( 1 ) 215 67 Yamauchi, R. ( 3 . 5 ) 82 Xu, H . J . ( 1 ) 306 Yamauchi, S . ( 1 ) 1 2 2 , 441 Xu, J. ( 3 . 1 ) 5 Yamauchi, T. ( 3 . 2 ) 29 Xue, F. ( 3 . 6 ) 63 Yamazaki, H. ( 2 . 1 ) 1 7 1 ;
w.
Author Index ( 2 . 2 ) 5 1 , 116, 129; ( 3 . 3 ) 103; ( 5 ) 48 Yamazaki, I . ( 1 ) 3 5 , 259 Yamazaki, T. ( 3 . 2 ) 9 2 ; ( 3 . 6 ) 18 Yamazaki, Y. ( 1 ) 259 Yan, R. ( 2 . 2 ) 105; ( 3 . 6 ) 63 Yanagida, S . ( 3 . 3 ) 130; ( 3 . 5 ) 53 Yanagisawa, T. ( 4 ) 422 Yang, C . S . ( 2 . 2 ) 6 2 , 63 Yang, F. ( 4 ) 116 Yang, N.C. ( 1 ) 175; ( 3 . 3 ) 107; ( 3 . 4 ) 44 Yang, Y, ( 4 ) 106 Yanuck, M.D. ( 5 ) 136 Yarmolenko, N.S. ( 3 . 2 ) 44 Yaroshenko, N.I. ( 3 . 5 ) 85 Yarrazaki, M. ( 4 ) 302 Yartsev, V.P. ( 4 ) 426 Yashioka, T. ( 4 ) 396 Yashirin, A.V. (49 429 Yasuda, M. ( 3 . 4 ) 55; ( 3 . 6 ) 131 Yasuda, S . ( 3 . 5 ) 140; ( 3 . 6 ) 156 Yasufuku, K. ( 2 . 2 ) 49-51, 5 9 , 113, 115, 116; ( 5 ) 48 Yates, K. ( 3 . 4 ) 106; ( 3 . 5 ) 52 Yates, P. ( 3 . 1 ) 2 1 , 23 Yau, H.J. ( 4 ) 360 Ye, D. ( 4 ) 4 9 , 50 Yeates, S . ( 1 ) 420 Yersin, H. ( 2 . 1 ) 81 Yesaka, H. ( 2 . 2 ) 49 Ygge, B. ( 3 . 2 ) 101 Yguerabide, J. ( 1 ) 356 Yi, H. ( 4 ) 116 Yijun, C. ( 2 . 2 ) 25 Yip, R.W. (1) 1 3 , 8 6 ; ( 3 . 5 ) 10; ( 3 . 6 ) 7 2 , 142 Yo, A. ( 4 ) 131 Yokoyama, K. ( 3 . 2 ) 110; ( 3 . 4 ) 6 2 , 83 Yoneda, R. ( 2 . 1 ) 29; ( 5 ) 176 Yonemitsu, 0. ( 3 . 5 ) 54; ( 3 . 6 ) 154 Yonemura, M. ( 2 . 1 ) 38 Yonezawa, T. ( 2 . 2 ) 56 Yonezawa, Y. ( 5 ) 198, 199 Yoon, S . K . ( 3 . 2 ) 1 2 ; ( 3 . 6 ) 93 Yoshi, F. ( 4 ) 272 Yoshida, A . ( 3 . 2 ) 41 Yoshida, C. ( 3 . 4 ) 9 6 ; ( 3 . 7 ) 147 Yoshida, E. ( 3 . 6 ) 179, 181
591 Yoshida, H. ( 2 . 3 ) 1 5 ; ( 3 . 4 ) 1 9 0 ; ( 3 . 6 ) 201, 202 Yoshida, K. ( 3 . 4 ) 8 2 ; ( 3 . 6 ) 134 Yoshida, M. ( 3 . 1 ) 4 7 ; ( 3 . 4 ) 150 Yoshida, N. ( 1 ) 135 Yoshida, T. ( 2 . 2 ) 117; ( 3 . 6 ) 39 Yoshida, Z. ( 5 ) 41 Yoshifuji, M. ( 2 . 2 ) 29 Yoshihara, K. ( 1 ) 234, 444; ( 3 . 3 ) 28 Yoshihara, N. ( 3 . 1 ) 4 1 ; ( 3 . 6 ) 75 Yoshimi, Y. (1) 83 Yoshino, K. ( 3 . 5 ) 53 Yoshioka, K. ( 3 . 5 ) 107 Yoshioka, M. ( 3 . 2 ) 121, 122 Yosufuku, K. ( 3 . 3 ) 103 Young, A.L. ( 4 ) 326 Young, D.W. ( 3 . 6 ) 169 Youngs, W.J. ( 3 . 3 ) 116 Yu, H.S. ( 4 ) 254 Yu, W.C. ( 4 ) 232 Yuan, L.C. ( 2 . 1 ) 52 Yuasa, S. ( 3 . 5 ) 25 Yue, P.L. ( 5 ) 18 Yughakova, O.A. ( 4 ) 56 Yukitani, M. ( 4 ) 390 Yumoto, T. ( 3 . 3 ) 9 5 ; ( 3 . 6 ) 150; ( 5 ) 53 Yun, H.C. ( 3 . 4 ) 183; ( 3 . 6 ) 45 Yun, S.S. ( 2 . 1 ) 208 Yurek, E. ( 3 . 4 ) 8 4 ; ( 3 . 6 ) 208 Yutani, Y. ( 4 ) 62
17
Zarate, E.A. ( 3 . 3 ) 116 Zard, S.Z. (3.7) 114-116 Zastrow, A. ( 5 ) 234 Zavoduik, V.E. ( 4 ) 56 Zawadzki, Z. ( 3 . 2 ) 97 Zayas, J. ( 3 . 7 ) 5 5 , 90 Zayed, M.F. ( 3 . 5 ) 132 Zeiri, L. ( 1 ) 104 Zelent, B . ( 3 . 5 ) 138 Zellweger, D. ( 3 . 7 ) 70 Zengerle, K. ( 5 ) 62 Zerilli, L. ( 3 . 5 ) 119 Zet, Y.Z. ( 1 ) 192 Zeug, N. ( 2 . 1 ) 242; ( 5 ) 73
Zewail, A.H. ( 3 . 3 ) 2 0 ; ( 5 ) 131
Zhang, B. ( 3 . 3 ) 1 1 ; ( 3 . 5 ) 8 0 , 8 7 , 109
Zhang, C. ( 4 ) 107, 398 Zhang, F. ( 2 . 1 ) 204 Zhang, J. ( 4 ) 217; ( 5 ) 177
Zhang, L. ( 2 . 2 ) 7 4 ; ( 3 . 5 ) 57; ( 4 ) 116
Zhang, P. ( 4 ) 12 Zhang, R. ( 2 . 1 ) 220 Zhang, S. ( 2 . 1 ) 223 Zhang, X. ( 2 . 1 ) 220 Zhang, Y. ( 4 ) 85 Zhang, Z. ( 4 ) 60; ( 5 ) 177 Zhao, R. ( 3 . 6 ) 63 Zhen, Z. ( 1 ) 306 Zhi, L. ( 3 . 5 ) 80 Zhil'tsova, E.E. ( 2 . 2 ) 27 Zhon, X. ( 4 ) 399 Zhou, B. ( 1 ) 274; ( 3 . 7 ) 131
Zhou, Q. ( 2 . 1 ) 236, 238; ( 5 ) 67
Zabala, F.T.I. ( 1 ) 318 Zabara, M.Ya. ( 4 ) 431, 455
Zachariasse, K . A . (1) 149, 310
Zacmanidis, P. ( 1 ) 411 Zahir, K. ( 2 . 1 ) 95 Zahn, K. ( 2 . 1 ) 108 Zai, L. ( 4 ) 116 Zaitsev, V.N. ( 1 ) 338 Zakov, A . N . ( 4 ) 274 Zakrzewski, A. ( 4 ) 144 Zamaraev, K . I . ( 5 ) 1 , 2 Zamotaev, P.V. ( 4 ) 153, 315
Zamzam, S.A. ( 4 ) 250 Zana, R. ( 1 ) 282, 284, 287
Zander, M. ( 1 ) 432, 433 Zang, G. ( 3 . 3 ) 128; ( 3 . 7 )
Zhou, Q.F. ( 4 ) 260 Zhou, Y. ( 3 . 6 ) 122 Zhou, Z. ( 2 . 1 ) 220 Zhu, C. ( 3 . 5 ) 88 Zhu, J. ( 3 : 2 ) 46 Zhu, L. ( 4 ) 399 Zhu, P. ( 2 . 3 ) 11 Zhu, Q. ( 2 . 3 ) 47 Zhu, Y. ( 2 . 1 ) 237; ( 5 ) 65 Zhuravlev, M.A. ( 4 ) 324 Ziada, B . A . ( 5 ) 239 Zielenkiewicz, W. ( 1 ) 435 Zielinski, S . (5) 196 Ziessel, R. ( 2 . 1 ) 124 Zilber, 0. ( 4 ) 349 Zilinskas, B.A. ( 1 ) 382 Zimmermann, G. ( 3 . 2 ) 103 Zimmermann, H.E. ( 3 . 1 ) 52; (3.2) 73, 74; (3.3 4 0 , 6 0 , 61 Zimmt, M.B. ( 1 ) 143, 144
Author Index
592 304, 464, 492; ( 3 . 1 ) 7 , 27; ( 3 . 4 ) 1 8 7 ; ( 3 . 5 ) 22 Zimnyakov, A . M . ( 2 . 1 ) 91 Zinth, W. ( 1 ) 378 Zisk, M.B. ( 3 . 5 ) 30; (5) 87 Zlatkevich, L. ( 4 ) 283
ZU, Q.-Y. ( 1 ) 366 Zubanev, V.E. ( 4 ) 51 Zubov, V.P. ( 4 ) 1 1 8 , 119 Zuchowcz, I. ( 4 ) 290 Zuev, P.s. ( 3 . 7 ) 5 Zumbrunnen, H.R. ( 5 ) 228
Zumofen, G. ( 1 ) 249 Zupan, M. ( 3 . 4 ) 4 1 ; ( 3 . 7 ) 118 Zupancic, J.J. ( 3 . 7 ) 44 Zupancic, N. ( 3 . 4 ) 4 1 ; ( 3 . 7 ) 118 Zwanenburg, B. ( 3 . 2 ) 7
