The breadth of scientific and technological interests in the general topic of photochemistry is truly enormous and includes, for example, such diverse areas as microelectronics, atmospheric chemistry, organic synthesis, non-conventional photoimaging, photosynthesis, solar energy conversion, polymer technologies, and spectroscopy. This Specialist Periodical Report on Photochemistry aims to provide an annual review of photo-induced processes that have relevance to the above wide-ranging academic and commercial disciplines, and interests in chemistry, physics, biology and technology. In order to provide easy access to this vast and varied literature, each volume of Photochemistry comprises sections concerned with photophysical processes in condensed phases, organic aspects which are sub-divided by chromophore type, polymer photochemistry, and photochemical aspects of solar energy conversion. Volume 34 covers literature published from July 2001 to June 2002. Specialist Periodical Reports provide systematic and detailed review coverage in major areas of chemical research. Compiled by teams of leading authorities in the relevant subject areas, the series creates a unique service for the active research chemist, with regular, in-depth accounts of progress in particular fields of chemistry. Subject coverage within different volumes of a given title is similar and publication is on an annual or biennial basis.
Photochemistry Volume 8
A Review of the Literature Published between July 1975 and June 1976
By D. Bryce-SmithThe Royal Society of Chemistry
Copyright © 1977 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-075-6Contents
Introduction and Review of the Year By D. Bryce-Smith, iii,
Part I Physical Aspects of Photochemistry,
Chapter 1 Developments in Instrumentation and Techniques By M. A. West, 3,
Chapter 2 Photophysical Processes in Condensed Phases By K. Salisbury, 60,
Chapter 3 Gas-phase Photoprocesses By D. Phillips, 105,
Part II Photochemistry of Inorganic and Organometallic Compounds By J. M. Kelly,
1 Photochemistry of Transition-metal Complexes, 167,
2 Transition-metal Organometallics and Low-oxidation-state Compounds, 196,
3 Metalloporphyrins and Related Compounds, 225,
4 Water, Hydrogen Peroxide, and Anions, 226,
5 Main-group Elements, 228,
Part III Organic Aspects of Photochemistry,
Chapter 1 Photolysis of Carbonyl Compounds By W. M. Horspool, 237,
Chapter 2 Enone Cycloadditions and Rearrangements: Photo reactions of Cyclohexadienones and Quinones By W. M. Horspool, 262,
Chapter 3 Photochemistry of Olefins, Acetylenes, and Related Compounds By W. M. Horspool, 314,
Chapter 4 Photochemistry of Aromatic Compounds By A. Gilbert, 362,
Chapter 5 Photo-reduction and -oxidation By H. A. J. Carless, 413,
Chapter 6 Photoreactions of Compounds containing Heteroatoms other than Oxygen By S. T. Reid, 455,
Chapter 7 Photoelimination By S. T. Reid, 503,
Part IV Polymer Photochemistry By D. Phillips,
1 Introduction, 541,
2 Photopolymerization, 541,
3 Optical Properties and Luminescence of Polymers, 545,
4 Photochemical Reactions in Polymers, 549,
5 Appendix: Review of Patent Literature, 554,
Part V Photochemical Aspects of Solar Energy Conversion By M. D. Archer,
1 General Reviews, 571,
2 Photochemistry, 572,
3 Photoelectrochemistry, 575,
4 Photochemistry in Vesicles, Micelles, and Artificial Membranes, 582,
5 Photosynthesis, 583,
6 Photovoltaic Cells, 586,
Part VI Chemical Aspects of Photobiology By G. Beddard,
1 Introduction, 593,
2 Photosynthesis, 593,
3 Vision, 607,
Author Index, 612,
CHAPTER 1
Part I
PHYSICAL ASPECTS OF PHOTOCHEMISTRY
1
Developments in Instrumentation and Techniques
BY M. A. WEST
1 Introduction
Although the progressive trend is for more and more physics to enter into chemical applications, a state of affairs which has attracted comment by analytical chemists (Aiialyt. Chem., 1975, 47, 2073), photochemists must surely welcome the application of lasers and electro-optic developments to aid their research. Fields such as absorption and emission spectroscopy, chemical kinetics, and more recently, preparative chemistry, have all benefited through higher spectral resolution, selectivity, sensitivity, etc.
This two-year review (July 1974 to June 1976) discusses most of the obvious advances in instrumentation and techniques in photochemistry, photophysics, and related spectroscopy as well as referring to fringe and other developments which have potential for, or have yet to be applied to, studies on the interaction of light with matter. With such a wide subject content, it is not possible to be very critical of publications or to include all publications within the confined space of this chapter. Furthermore, although subjects have been arbitrarily separated into 10 sections, some areas could be equally well placed in several sections, for example, two-photon absorption in sections dealing with pulsed lasers, absorption, or even emission spectroscopy.
Several key developments have taken place recently in a number of relatively new techniques. Photoacoustic spectroscopy, though discovered 95 years ago, has benefited considerably by recent research which shows its considerable potential for absorption spectrometry of solids and semi-solids. Preparative photochemistry using i.r. lasers is already proving itself as a powerful technique for isotopic separations and for producing specific products. The time resolution in transient absorption measurements has now been pushed back to femtoseconds, beyond which, chemistry, as we know it, does not exist because of the uncertainty principle.
A list of recommended terms for spectroscopy was tabulated in a previous volume (Vol. 6, p. 62) and was reputably based on the S.I. system of units. Unfortunately, inconsistencies in these terms have been indicated by Mielenz, who recommends use of more logical adjectives and nouns to describe quantities and terms which are based on the transport of energy according to the laws of geometrical optics. For example, by defining absorbance as the negative logarithm to base ten of internal transmittance, it should be clear that this refers to the transmittance of an absorbing material exclusive of losses at boundary surfaces and effects of interreflection between them. Any instrument used for the measurement of spectra should simply be called a spectrometer. The word spectrophotometer, though commonly used, is a misnomer since a photometer is an instrument that measures luminous flux. Since the adjective 'luminous' implies the integral effect of visual radiation as perceived by the human eye, the spectral analysis of luminous flux has no physical meaning. It is certainly more accurate and logical to use the term absorption spectrometer and in the same way the confusion over spectrofluorimeters and spectrofluorometers would be eliminated by the term fluorescence spectrometer. One suggestion unlikely to find acceptance by photochemists, however, is replacement of the firmly established quantum yield by radiant yield or photon yield.
2 Plasma Sources
The low-pressure mercury lamp so commonly used for photochemistry has been studied recently and the intensity of the 253 nm line examined as a function of Hg pressure, tube radius, and operating current. The intensity rises to a peak at about 7 mTorr pressure and falls at higher Hg pressures and, at constant pressure, increases linearly with current. A useful review emphasizing the chemical developments of inorganic phosphors discusses their applications in changing the output wavelength of an Hg lamp. Instabilities in the output of an HPK mercury lamp have been overcome by operation from an optically stabilized supply resulting in a drift of 0.1% h-1 over a 30 h period.
The amount of obnoxious and hazardous ozone generated by xenon short arc lamps is reduced considerably by passing the normal cooling air through a baffled aluminium chamber containing iron oxide. This 'filter' decomposes the ozone to oxygen with high efficiency, but only after a warm-up time of 30 — 40 min. A comparison of Xe–Hg, D2 arc, and H2 hollow-cathode lamps has been made in an evaluation of a suitable source for background correction in atomic absorption spectrometry.' At shorter wavelengths, a new type of source generating the line radiation of the rare gas ions achieves an enhanced ion flux by incorporating a charged particle arrangement. Intense line spectra are obtained from the He, Ne, and Ar ions, affording a convenient windowless source of He(II) (30.4 and 25.6 nm) and Ne(II) (46 nm) suitable for photoelectron spectroscopy. A microwave-discharge U.V. light source has been reported to yield...
