Thermoluminescence in photosynthesis. 4. Influence of energy transfer processes.

Thermoluminescence (TL) emission arising from charge recombination in photosynthetic reaction centres was examined considering the energy transfer between antenna chlorophylls and the reaction centre. The energy transfer processes were shown to decrease the width and change the temperature of the maximum glow of the TL band profiles when the rate constant of direct recombination between the oxidized primary electron donor and reduced primary acceptor (pheophytin or bacteriopheophytin) did not exceed 10(6) s-1. The primary radical pair lifetime of 3.10(-9)-10(-8) s was shown to minimize the influence of energy transfer on the TL band profiles and, therefore, the energy transfer can be neglected when the TL band profiles are calculated. The profile of the TL band arising from charge recombination in the photosystem 2 state S2QB.- was shown to depend considerably on the temperature-dependent rate constant of direct recombination between QB.- and S2 state of the photosystem 2 donor site.