SILVERLESS PHOTOCHEMICAL IMAGING-SYSTEMS

Starting from the various reaction possibilities of photoexcited organic molecules, a general survey is given of numerous examples of applications taken from the field of unconventional photographic imaging systems. Special attention is given to the photolytic processes wherein a.o. free radicals are set free, which play an important role in the realization of photopolymerisation systems. The colour-forming processes based on the action of free radicals are reviewed as well. Photolysis with molecular fragmentation to carbenes and nitrenes is illustrated thereafter. Photochemical acid generation has led to interesting possibilities since a few years. Diazo photochemistry then closes the series of the photolytic processes. Amongst the photochemical transformations, photocyclodimerisations, hydrogen abstraction and photosubstitution are selected as typical examples. Thereupon the role of photoisomerisation reactions in the photochromism is emphasized. A few important energy- and electron-transfer processes illustrate the fundamental significance of these reactions in imaging systems. Finally, on the basis of typical examples, the role of the radiationless deactivation in optical memories and the possibilities of application of biphotonic transformations are discussed briefly.