Energy Transfer in Ordered and Unordered Photochemical Systems

A review is presented of the various mechanisms by which light energy absorbed by one moleculemay be tranformed or transferred to other molecules.It comprises examination of the processes occurring in fluid nonordered systems, followed by characterization of the changes necessary to carry over the basic concepts so introduced to a condensed and ordered system.Examples of model systems are presented.Finally, these concepts are applied to biological materials, especially particulate material derived from green plants.Photoinduced electron spin resonance signals have been observed in isolated chloroplasts and other green plant mateials; their growth time is not affected by reducing the temperature to -140 C. The luminescence of these materials has also been investigated under a variety of conditions.The results of these studies have been shown to be consistent with a mechanism involving the recombination of electrons and holes trapped in a quasi-crystalline lattice.Some details of such a mechanism have been proposed that suggest the mode of entry of the light energy into the photosynthetic pathway.