Control of long-range electron transfer in dynamically disordered molecular systems by an external periodic field

The influence of a strong periodic held on the long-range electron transfer is studied theoretically within the driven spin-boson model extended by a dichotomically fluctuating tunneling coupling. Applying the noninteracting blip approximation, a set of coupled kinetic equations is derived. It describes the time-development of the electronic population difference between the donor and acceptor states averaged with respect to the stochastic process, the quantum fluctuations of the bath and over the fast oscillating held. The strength of the periodic field is taken into account:in a nonperturbative manner. A detailed analysis is carried out for the case of a strong coupling of the transferred electron to a specific reaction coordinate. Analytical expressions for the effective transfer rate are obtained and their numerical analysis is presented. For the case of adiabatically controlled (gated) transfer the existence of a transfer regime is demonstrated where the strong external field does not influence the effective transfer rate, however, it can completely revert the direction of the transfer. Finally, it is shown that the periodic held can induce transitions between the quasi-adiabatic (gated) and the nonadiabatic regime of electron transfer. (C) 1997 American Institute of Physics.