History of photochemistry

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

In 1979 G.R. De Mare replaced S.G. Bone as co-Editor of the Newsletter with H.J. Kuhn. In 1982 H. Durr joined them as the third co-Editor. The Newsletter became more and more attractive with the publication of the series History of Photochemistry (pioneers and trends), Photochemistry in Europe, Technical Reports, Topical Articles, the news about Glossary of Terms used in Photochemistry (from the lUPAC Commission) and regular news from the sister Societies (lAPS and IP A). Nevertheless, in the July 1986 issue, the Editors of the Newsletter published a complaint against the scarce contributions received from the EPA members asking for more active participation from the silent members , estimated to be 95%. 

The photoreduction of benzophenone is one of the oldest and most thoroughly studied photochemical reactions. Early in the history of photochemistry, it was discovered that solutions of benzophenone are unstable in light when certain solvents are used. If benzophenone is dissolved in a "hydrogen-donor" solvent, such as 2-propanol, and exposed to ultraviolet light, hv, an insoluble dimeric product, benzpinacol, will form. 

As a matter of fact, the applications of photochemistry are so rich and diverse that the relation with a common basic discipline tends to be lost. This is unfortunate, because the abovementioned central role of photochemistry is a continuous source of inspiration and there is much to gain from conserving a unified point of view. In this sense, some historic knowledge is helpful, as always in science. The present volume is not a proper history of photochemistry, but rather a discussion of some turning points drrring the formation of the basic postulates of photochemistry and an attempt to present some directions of future development. 

As mentioned, the observation of chemical effects of light is as old as mankind itself. Accounts of the earlier history of photochemistry have been presented by several authors. Long erudite lists of reference are of little usefulness, however. Here, it has been chosen to present a brief historic profile based on a document itself of historic value, the introduction written by a great authority, professor Ivan Plotnikov. This well-known Russian-bom scientist published in 1910 a book on photochemistry which was followed in 1936 by a second, much extended, edition of over 900 pages. The view he had on this science, or at least on some aspects of it, in particular the unconditioned refusal of the Stark-Einstein equivalence law, appeared obsolete at the time of the second edition, as it is discussed in Sect. 2.3. However, Plotnikov can certainly not be accused of insufficient knowledge of the matter or of insufficient exploration of the literature and his book is a rich mine of data and thoughts [7]. 

A high point in the history of photochemistry corresponds to the first years of the twentieth century. As it may be seen in Chap. 3, most elements of the theoretical framework of this discipline were available and a consistent picture was beginning to take form in these years, although it would require at least 20 years to arrive at a satisfactory formulation [1]. However, as it happens not rarely in chemistry, it seemed that the discovery of reactions and their application may precede theory. In fact, intense work, though carried out in a small number of laboratories, called attention by the international community to this discipline and by 1910 photochemistry seemed well established as one of the most promising fields of chemistiy. 

With the increased sophistication in experiment and interpretation since that time, photochemists have made substantial progress in achieving the fundamental objective of photochemistry elucidation of the detailed history of a molecule that absorbs radiation. The scope of this objective is so broad and the systems to be studied are so many that there is little danger of exhusting the subject. We hope that this series will reflect the frontiers of photochemistry as they develop in the future. 

There have been two books devoted to the chemistry of iron, " and many reviews devoted to various aspects of its coordination chemistry, including structures and photochemistry (iron(III)). Iron complexes appear in a multi-author volume on the history of coordination chemistry, but there is disappointingly little about iron—just a brief mention of hexacyanoferrates in connection with pigments—in an otherwise excellent overview of the history of chemistry. ... 

Progress in photochemistry could only be made following progress in spectroscopy and, in particular, the interpretation of spectra in at least semiquantitative terms, but history has shown that this was not enough. The arrival of new methods of analysis which permit determination of small amounts of products, the development of flash photolysis, nuclear magnetic resonance, and electron spin resonances which can yield valuable information about the natures of intermediate excited states, as well as of atoms and radicals, all have permitted the photochemist to approach the truly fundamental problem of photochemistry What is the detailed history of a molecule which absorbs radiation ... 

In short, although the history of anthropogenic perturbations to the stratosphere is much shorter, it is clear that these are also important. Indeed, such perturbations are expected to affect the chemistry of the troposphere as well for example, increased UV radiation will alter photochemistry at the earth s surface. 

Most of the latest experimental techniques have been applied to the study of the photodissociation dynamics of these molecules. Part of the reason for the great interest in these molecules is a result of their long history in photochemistry and partly because there is a low lying absorption that is accessible to the available lasers. Formaldehyde is particularly important since it is the simplest molecules in the group and has been studied theoretically. 

In the rather short history of organic photochemistry, the geometrical E-Z photoisomerization has been exceptionally intensively studied for half a century and a number of reviews have been published [11-18], Although the geometrical isomerization of alkenes can be effected thermally, catalytically, and photochemically, one of the unique features of photoisomerization is that the photostationary EfZ ratio is independent from the ground-state thermodynamics but is instead governed by the excited-state potential surfaces, which enables the thermodynamically less-stable isomers... 

Photochemistry has expanded enormously since those first days. A serious percentage of the papers in any single volume of the Journal of the American Chemical Society, for instance, can rightly fall in its purview. The emergence of the laser and the evolution of theoretical methods strongly influenced research. With new computational methodology almost no intermediate lives too short a time to be detected and its dynamics characterized. The fundamental objective of our field, elucidation of the history of a molecule that absorbs radiation, is now within reach in even the most complicated cases. We hope that the series continues to reflect the frontiers of photochemistry as it evolves into the future. 

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