Photo sensitizer definition

Photoresponsive polymers so far described change their properties in proportion to the number of photons that they absorb. Thus, when they contain more photo-chromic chromophores, which undergo an isomerization by absorbing a definite number of photons depending on the quantum yield, their properties change more. To make a sensitive photoresponsive polymer, i.e. one which responds more effidently to a fewer photons, we have to introduce an amplification mechanism into the system. A convenient way to achieve this end is to utilize the phase transition of polymers. 

In this chapter we have used the term sensitization in a generic sense to denote a process in which a Cu(I) compound (the sensitizer) accelerates the rate of an olefin photoreaction with at least one photon being required per product molecule formed. Within this rather broad definition, the preceding section provides examples of three general classes of sensitization process these are depicted in Scheme 4, where the symbol Cu(I) is taken to represent some Cu(I) compound, an asterisk signifies an excited electronic state, and a prime indicates that the olefin has undergone a photo-induced transformation. 

Sensitization was another word requiring definition and correct application. Thus, a stable molecule could be made photosensitive by the additirai of a small amount of another molecule, but this might involve different phenomena, as illustrated by Berthoud [62]. These ranged from the photochemical formation of a reactive compound to that of a catalyst. Atoms could be generated and transfer their energy to other species, as demonstrated for atoms of mercury or of oxygen [63]. Noyes pointed out to the reaction of molecules, e.g., NO2, at an irradiated mercury surface, and on the differences and similarity between photochemistry and photo-ionization [64]. 

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