Energy transfer in ordered and unordered photochemical systems.

A rev iew i s p resen ted of the var ious mechanisms by which light energy absorbed b y one molecule m a y b e t rans formed o r t r a n s f e r r e d to other molecu les . It c o m p r i s e s examination of the p roces se s occur r ing in fluid nonordered s y s t e m s , followed by charac te r iza t ion of the changes n e c e s s a r y to c a r r y over the ba s i c concepts s o introduced to a condensed and o rde red s y s t e m . Examples of mode l sy s t ems a r e presented. Finally, these concepts a r e applied to biological ma te r i a l s , especial ly par t icula te m a t e r i a l de r ived f r o m g r e e n plants. Photoinduced e l ec t ron spin resonance s ignals have been observed i n isola ted ch lorop las t s and other g r een plant mateg ia l s ; thei r growth t ime i s not affected by reducing the t empe ra tu r e to 140 C. The luminescence of t he se m a t e r i a l s h a s a l s o been investigated under a var ie ty of conditions. The r e s u l t s of t h e s e s tud ies have been shown to b e consistent with a mechanism involving the recombinat ion of e lec t rons and holes t rapped i n a quas i c rys ta l l ine l a t t i ce . Some de ta i l s of such a mechanism have been proposed that suggest the mode of en t ry of the l ight energy into the photosynthetic pathway.