PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION IN LIQUIDS - ANALYTICAL THEORY AND MONTE-CARLO SIMULATIONS

Photoinduced electron transfer and geminate recombination in liquid solution are addressed with analytical theory and Monte Carlo simulations. The time-dependent probabilities of the donor being excited and of an ion pair existing are obtained for a system of a donor and many accepters undergoing diffusive motion. Multiparticle simulations are modeled as a Markov chain and are shown to agree with the analytical formalism presented previously. The calculations are performed using both a simple exponential form of the distance dependence of the transfer rate and using the more general Marcus distance-dependent transfer rate. For a static donor, in the absence of acceptor-acceptor excluded volume, theory and simulations provide identical results, confirming the accuracy of the analytical method. For the calculation of properties of real systems in which both the donor and accepters diffuse, to make the mathematics tractable, the donor is held static and each acceptor is given a Fick diffusion constant equal to the sum of the diffusion constants of the donor and acceptor, D=D-d+ D-a. The validity of this approximation is examined in the absence of acceptor-acceptor excluded volume and found to work extremely well under all conditions. It is also examined with acceptor-acceptor excluded volume. In this case, the static donor approximation is found to work generally well up to moderately high acceptor concentrations, <5% packing fraction. However, the results suggest that at even higher packing fractions, the static donor approximation loses its validity. (C) 1995 American Institute of Physics.