Enhancement of charge transition from donor to acceptor in organic and biochemical reactions by the intermediate-mode-assisted tunneling mechanism

The intermediate-mode-assisted tunneling mechanism is shown to be relevant for the control of electron (/hole/energy) transfer in donor-bridge-acceptor based symmetric molecular electronic systems. In this case the donor and the acceptor are superpositions of two practically degenerate eigenstates of the system. A molecular eigenstate of the system, which is mainly localized on the bridge, serves as intermediate state. Upon a small symmetry preserving variation of the bridge site geometry this intermediate state is coupled only to one of the two practically degenerate states. Our approach gives the tools to design a molecular switch where 100% ultrafast electron/hole transition occurs. As an illustrative numerical example the electron/hole transition in a cation radical of a polycyclic analogue of norbornadienone (PC-NBDO) molecule is calculated. We observe that, because of a sudden stretch in the CO bond of the bridge site, the electron transfer time has been decreased from infinity to 11 femtoseconds.