Effects of quencher concentration on bimolecular reaction rate in solution

Fluorescence decay curves of Coumarin 151 quenched by N,N-dimethylaniline in anisole for a wide range of quencher concentrations have been measured by using a time correlated single photon counting as well as a fluorescence up-conversion technique at room temperature. At low quencher concentrations the observed decay curves can be analyzed well by a simple diffusion model with the Smoluchowski equation. At higher quencher concentrations, however, both the simple diffusion model and the nonadiabatic sink term model with distance-dependent reaction rate under a random initial quencher distribution failed to explain the experimental data, which showed a rapid decay of fluorescence on a picoseconds time scale followed by a slower decay on a longer time scale. A radial distribution function estimated by a Lennard-Jones potential between fluorescer and quencher was introduced as an initial distribution of quencher to reproduce the experimental decay profiles. The theoretical prediction at high concentrations of quencher was improved significantly by using the diffusion coefficient obtained at low quencher concentrations. (C) 1997 Elsevier Science S.A.