Determination of the bimolecular rate constant of photoinduced charge separation in the energy gap region where the reaction is diffusion controlled — analysis of the transient effect in the course of fluorescence quenching reaction

Abstract The photoinduced intermolecular charge separation (CS) rate constant ( k CS ) at the encounter in acetonitrile solution has been evaluated for various donor—acceptor pairs by analyzing the transient effect in the fluorescence decay curves, in the energy gap region −Δ G 0 =0.37–2.21 eV, where the reaction is diffusion controlled. Although the obtained k CS values are larger than the diffusion rate constant, they do not show the typical bell-shaped −Δ G 0 dependence as observed in the charge recombination reaction of the geminate ion pairs produced by fluorescence quenching reaction, but show a rather flat shape.