Applications of photochemistry

An important characteristic of all the photochemical reactions is the quantum yield. In photochemistry it is defined as the ratio of the number of excitations to the number of molecules undergoing the reaction (e.g. photolysis). In fluorescence it is defined as the proportion of the excited molecules decaying by emission of radiation. 

It was emphasized above that flash photolysis is a prime example which demonstrates that the number of intermediates resolved in a reaction is open ended it is dependent on the time resolution of the technique. From the equation 

Luminescence, which is the emission of light, can result from chemical reactions or exdtation by light. The former can be artifidal (for instance the reaction of luminol plus hydrogen peroxide) or the response of the stimulation of natural reactions of photoproteins (see the discussion of the kinetics of aequorin in section 4.2). The form of luminescence of most general interest for kinetic studies is that obtained in response to exdtation by light (fluorescence and phosphorescence). All forms of luminescence are due to the emission of photons from electronically excited states. In the singlet exdted state the electron in the higher orbital has opposite spin 

Fluorophores of interest in the study of the behaviour of biological molecules can be intrinsic or extrinsic. The principal intrinsic ffuorophores are the aromatic amino acids tryptophan, tyrosine and phenylalanine (with decreasing quantum yields in that order) and the cofactors NADH and riboffavin. Extrinsic ffuorophores are introduced as reporter groups either 

The fact that the quantum yield in fluorescence is less than one is due to the return of some molecules to the ground state via radiationless energy transfer (see p. 289) and to thermal (collisional) quenching. In photolysis a number of additional factors depending on the reaction mechanism can 

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Wayne, R. P, "Principals and Applications of Photochemistry." Oxford University Press, New York, 1988. 

Principles and Applications of Photochemistry Brian Wardle 2009 John Wiley Sons, Ltd... 

The aim of this book is to provide an introduction to the principles and applications of photochemistry and it is generally based on my lectures to second and third-year undergraduate students at Manchester Metropolitan University (MMU). 

R. Roberts, R. P. Ouellette, M. M. Muradaz, R. F. Cozens and P. N. Cheremisinoff, Applications of Photochemistry, Technomic Publishing Co. 11984). Whilst weak on basic principles, this book gives a good brief overview of biomedical and technological applications of photochemistry, including uses of lasers. 

Some of the major industrial applications of photochemistry are found in the various imaging processes which include photography, photopolymerization/ photodepolymerization, photochromism and electrophotography— the process used in photocopying machines. 

Photochemical reactions cover a most extensive range of chemical processes, some of which are totally beyond the realm of dark reactions. Industrial applications of photochemistry to the large scale synthesis of chemicals are however relatively unimportant, and this can be traced to the high cost of... 

There are however a few important synthetic applications of photochemistry, and we shall consider here three representative examples. 

We shall begin with a closer look at electronic excitation, some aspects of which were discussed in Section 9-9. Because transfer of electronic energy from one molecule to another is a basic process in photochemistry, we will discuss energy transfer also before giving an overview of representative photochemical reactions. The closely related phenomena of chemiluminescence and bioluminescence then will be described. Finally, there will be a discussion of several important applications of photochemistry. 

RP Wayne. Principles and Applications of Photochemistry. Oxford Oxford University Press, 1980. 

Fig-1 The several routes to loss of electronic excitation. The use of the symbols, f, and J is only intended to illustrate the presence of electronic excitation and not necessarily differences in states. One or both of the products of processes i—iii may be excited. (Reproduced from R.R Wayne, Principles and applications of photochemistry, Oxford University Press, Oxford, 1998. By permission of Oxford University Press]... 

At the end of this section, we wish to mention the reasons that this photoin-duced deracemization is interesting. The deracemization is interesting itself, of course. Besides, this reaction is of considerable interest from the point of view of photochemistry, because both the highly reducing ability of the photosensitizer and the highly oxidizing ability of the one-electron oxidized photosensitizer are utilized in the reaction. This type of photoreaction provides a wider application of photochemistry. 

Bottcher H (ed.) (1991) Technical Applications of Photochemistry, Deutscher Verlag fur GrundstofFindustrie, Leipzig. 

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