A subpicosecond, subnanosecond and steady-state study of diffusion-influenced fluorescence quenching

Subpicosecond and subnanosecond time resolved experiments are combined with steady-state fluorescence measurements to examine the diffusion influenced fluorescence quenching reaction of rhodamine B and ferrocyanide. The classic models of Smoluchowski, and Collins and Kimball are unable to consistently explain both the rapid initial decay and the slower decay seen at long times (>1 ns) in the experimental data. Neither the short nor the long time data can be reconciled with the steady-state data using these models. Better agreement is found between the data and a simple model incorporating a position dependent intrinsic reaction rate [A. Szabo, J. Chem. Phys. 93, 6929 (1989)] in addition to a diffusional rate. This model suggests a rate of electron transfer for the rhodamine B–ferrocyanide system of (27.5±4 ps)−1. Use of a bare Coulomb potential between reactants is found to be inappropriate in all of the models investigated.