Exciton equilibration induced by phonons: Theory and application to PS II reaction centers

In this paper we compare calculations of the rates of excitation energy transfer within reaction center of photosystem II, with transient absorption measurements of the same dynamics. The theory that we apply is based on the assumption that exciton-phonon interaction is fairly weak. In this way we can study the effect of exciton coherence as well as the relaxation toward thermal equilibrium of an excitonically coupled system. The theory correctly predicts the experimentally observed differences in rates for transfer between two degenerate states in the vicinity of 680 nm and transfer between red and blue electronic states.