BIBLIOGRAPHY

A. N. Terenin, Photochemistry of Dyes and Related Organic Compounds. Publishing House of the Academy of Sciences of the USSR, Moscow—Leningrad, 1947. 353 pp. Price 23 rubles.

For anyone who is far removed from contemporary photochemistry, the title of this book may give occasion to think that it deals with a narrow, specialized, or perhaps technical subject.

In reality this is not at all the case. In order to form a clear idea of the full significance of the problem of the photochemistry of dyes, one need only recall first of all those fields in which photochemical phenomena in dyes play a fundamental role. These are photosynthesis in plants with the participation of the dye chlorophyll; the problem of photosensitization of photographic emulsions; and, finally, the bleaching (fading) of dyes. But this, so to speak, “applied” side by no means exhausts all the interest and importance of the problem. Dyes are complex organic compounds, characterized optically by the presence of extraordinarily strong absorption bands in the visible part of the spectrum. This, however, is only a special case of the enormous class of hydrocarbons possessing equally strong absorption bands located in the ultraviolet. Therefore, from the point of view of the photochemistry and chemical kinetics of the phenomena observed with dyes, they are of far broader interest.

The photochemistry of dyes is a most important chapter in the photochemistry of complex molecules. Dyes, owing to their exceptional optical properties and their outstanding significance throughout natural science and technology, have attracted great interest and have been studied better. But there is no doubt that the results of this study are of extraordinarily great significance not only for those phenomena in which the presence of absorption in the visible part of the spectrum plays the main role, but also for a much wider range of problems.

In A. N. Terenin’s book, the photochemistry of dyes is presented precisely from this broad physico-chemical point of view. This book is therefore at the same time a foundation for the photochemistry of dyes and is consequently of equal interest to the physicist-optician, to the physical chemist interested in the problem of the chemical bond, to the photochemist, to the biologist, and, finally, to the technologist. The author has done an enormous job in selecting from the countless mass of articles scattered through a wide variety of scientific and technical journals the most essential material, and in bringing all these diverse facts into an orderly system on the basis of modern conceptions of the nature of the chemical bond and of the mechanism of photochemical processes. Being one of the most outstanding specialists in the field of photochemistry, he has, naturally, given an exhaustive critical analysis of all the facts and theories he considers. His book is not a review and not a collection of reviews, but an integral work presenting the entire field under consideration from a single point of view.

BIBLIOGRAPHY

The book is divided into two parts unequal in size. The first part—Photophysical Processes in Dyes—occupies 88 pages; the second part—Photochemical Reactions of Dyes—constitutes, naturally, the main content of the book. Although the first part is introductory in character, it is of considerable independent interest to a wide circle of readers.

In the extensive second chapter—The Structure and Spectrum of Dyes—not only are the necessary structural-chemical data relating to dyes presented, but the modern quantum theory of the chemical bond is also set forth. In doing so, the author leaves aside the cumbersome computational part and focuses all attention on the physical essence of the ideas being expounded.

The third chapter—Energetics of the Dye Molecule—is very interesting; there the Franck–Condon principle is presented in an original manner, the statistical laws of emission and absorption are considered, and a brief survey is given of various processes of conversion of the energy absorbed by a dye. Here, in particular, the assumption is justified of an intermediate unstable excited state of dyes, which plays the principal role in photochemical processes, as a triplet metastable state. This point of view, later expressed also by Gilbert N. Lewis, may now evidently be regarded as confirmed by direct experiments. The final chapter of this part is devoted to the structure and variability of the absorption bands of dyes.

The second and main part of the book is Photochemistry of Dyes. After a brief formulation of the fundamental laws of photochemistry, the author systematizes the various types of photochemical reactions in dyes as follows: 1) photodecomposition; 2) photorearrangement; 3) photoaddition (photodimerization, photooxidation, by which the author means the addition of \(O_2\)); 4) photoelectron transfer
\[ (A^{*}+X \to A^{+}+X^{-},\quad A^{*}+Y = A^{-}+Y^{+}), \]
i.e. photooxidation or photoreduction of the particle \(A\); 5) photosensitization. In the following chapters all the processes listed are considered and discussed consecutively. In a brief review it is, of course, impossible to reveal all the richness of the content of this part. Let us note the extremely interesting Chapter VII—Photoreactions of Addition of Molecular Oxygen—where, in particular, the works of Kautsky on quenching of fluorescence by oxygen, which at one time aroused great interest, are analyzed in detail, and the modern points of view on processes of destructive fading of dyes are set forth. In Chapter IX—Inhibition of Photoreactions of Dyes—the works of S. I. Vavilov and his school on quenching of fluorescence in solutions are considered. In Chapter X—Photoreactions of Dyes on the Surface of Solid Bodies—the question of the mechanism of photosensitization and desensitization of photographic emulsion is examined. The last chapter of the book is devoted to photoelectrochemical effects of dyes. Here effects are considered which the author calls, respectively, photovoltaic and photogalvanic: the first consists in the appearance of an electromotive force upon illumination of a zone of dye solution adjoining one of two identical electrodes; the second is the Becker effect proper, sensitized by the dye. These still little-investigated effects probably have a great future.

The book by A. N. Terenin, written as a survey of what is known about the photochemistry of dyes, represents a substantial contribution to the development of this important problem. It not only critically sums up what has already been found, but also gives new interpretations and poses new problems.

All the main points of view are formulated with great clarity, and the author’s argumentation is logically structured and transparent. If a reader less familiar with the subject of the book should have to work somewhat

BIBLIOGRAPHY

over it, he will be rewarded with a wealth of new facts and ideas that he will draw from this splendid book.

The book undoubtedly represents a significant event in world scientific literature.

E. Shpolsky