Comparison of two models for bridge-assisted charge transfer

Based on the reduced density matrix method, we compare two different approa ches to calculate the dynamics of the electron transfer in systems with don or, bridge, and acceptor. In the first approach a vibrational substructure is taken into account for each electronic state and the corresponding state s are displaced along a common reaction coordinate. In the second approach it is assumed that vibrational relaxation is much faster than the electron transfer and therefore the states are modeled by electronic levels only. In both approaches the system is coupled to a bath of harmonic oscillators bu t the way of relaxation is quite different. The theory is applied to the el ectron transfer in H2P-ZnP-Q with free-base porphyrin (H2P) being the donor , zinc porphyrin (ZnP) being the bridge and quinone (Q) the acceptor. The p arameters are chosen as similar as possible for both approaches and the qua lity of the agreement is discussed. (C) 1999 Elsevier Science B.V. All righ ts reserved.