A theoretical explanation for quantum yield failure in bacterial photosynthetic reaction centers Original Research Article

A new theoretical model addresses the reduction in the quantum yield for primary charge separation in bacterial photosynthetic reaction centers (RCs) in an applied electric field. The electric field dependence of the internal conversion rate constant for the primary donor is proposed to act as a drain that competes with primary charge separation. The field dependence of the internal conversion process is based on experimental data that have shown that the excited state of the primary donor has a large polarizability suggesting that the excitonic basis of the primary donor is mixed with charge transfer (CT) basis states. The model provides analytic expressions for the electric field dependence of the primary charge separation rate constant, prompt and delayed fluorescence, and predicts an effect on the intersystem crossing rate constant. The model provides a mechanism for a reduction of the quantum yield and an explanation for the lack of a concomitant increase in either prompt or delayed fluorescence.