We consider electron exchange between a metal electrode and an attached molecular wire with a redox center at its end. A model Hamiltonian based on a tight-binding scheme is proposed, which contains the coupling of the redox system to the solvent. The corresponding Green's function is calculated exactly, and the time dependence is derived from its Fourier transform. For the case of photo-exited transfer we calculate current transients for a few representative cases. In addition, we calculate the rate of electron transfer for thermal electron transfer from the redox center to the electrode following a potential step. (C) 2011 Elsevier Ltd. All rights reserved.