PRIMARY ELECTRON-TRANSFER IN PHOTOSYNTHETIC REACTION CENTERS

A simple model is presented for the primary step in the photoinduced electron transfer in the photosynthetic reaction centers of Rps. viridis and Rb. sphaeroides. The interaction of the chromophore system (consisting of photoexcited donor P, conduction intermediate BL, and acceptor HL) with the environment is assumed to be negligible until vibronic deexcitation takes place resulting in a stochastically perturbed adiabatic electron transfer. This process constitutes a three-level problem. It is shown that this problem, in the present case, can be approximated by a two-level problem which can simply be solved. The energy level of |BL-〉 is found to be 0.06 eV above the level of |P* 〉. The unidirectionality of the electron flow is explained by coincidence of energy levels in the L branch due to evolutionary constraint. © 1990 American Chemical Society.