COHERENCE, FRICTION, AND ELECTRIC-FIELD EFFECTS IN PRIMARY CHARGE SEPARATION OF BACTERIAL PHOTOSYNTHESIS

New electron transfer patterns have been revealed by the dynamics of the special pair chforophyll, the auxiliary chlorophyll, and pheophytin in primary bacterial photosynthetic charge separation. We address here several of these charge transfer features for which new elements of electron transfer theory, disregarded in common theoretical approaches to photosynthetic electron transfer, are needed. These features are, first, an auxiliary chlorophyll state weakly off-resonance relative to the special pair and pheophytin states. Common superexchange views fail in this case, and incorporation of continuous vibrational manifolds in all three electronic states is essential. Secondly, external electric fields may induce transitions between the superexchange and sequential electron transfer modes where the vibrational manifolds ensure that mild resonances rather than divergence appear in the rate constant at resonance. The sequential mode finally incorporates a variety of frictional patterns ranging from vibrationally almost relaxed transitions to strongly dynamically coupled, coherent transitions.