EXAMINATION OF THE VIABILITY OF THE COLLINS-KIMBALL MODEL AND NUMERICAL-CALCULATION OF THE TIME-DEPENDENT ENERGY-GAP LAW OF PHOTOINDUCED CHARGE SEPARATION IN POLAR SOLUTION

Viability of the analysis using the Collins-Kimball model for the rate constant of photoinduced charge separation reactions in polar solutio ns is investigated, In the Collins-Kimball model, it is assumed that t he reaction occurs only at a specified distance in the encounter betwe en donor and acceptor molecules under mutual diffusional motion while in real systems the reaction can occur over a range of distances, By c omparing the fluorescence decay curve obtained by the Collins-Kimball model with the decay curve calculated numerically using the model inco rporating a suitable distance dependence of the reaction rate, we foun d that the Collins-Kimball model is viable with some reservation. Usin g the numerically calculated distance distribution function of donor a nd acceptor molecules, we calculated time-dependent energy gap laws of photoinduced charge separation reactions. The calculated energy gap l aw for t=0 fits well the experimental data obtained by a transient eff ect analysis of the fluorescence decay curve (S. Nishikawa, T. Asahi, T. Okada, N. Mataga and T. Kakitani, Chem. Phys. Letters 185 (1991) 23 7). The calculated energy gap law for t-->infinity fits very well the experimental data obtained by the stationary state fluorescence quench ing measurements (D. Rehm and A. Weller, Israel J. Chem. 8 (1970) 259) .