FEMTOSECOND INTERMOLECULAR ELECTRON-TRANSFER BETWEEN DYES AND ELECTRON-DONATING SOLVENTS

Ultrafast intermolecular electron transfer (ET) is discussed for the system of various xanthene dyes in diffusionless weakly polar electron donating solvents. ET was observed by fluorescence quenching dynamics. It gives a non-exponential process in case of dyes in aniline. ET rate is determined by mutual displacement of the reactants and by the solvent relaxation. In case of dyes in N,N-dimethylaniline, ET quenching gives very different dynamics and shows a single exponential decay with a rate constant as fast as 10(13) s-1. Ultrafast ET, which is much faster than solvent relaxation time, requires a new mechanism for a cause of ET.and its rate constant may be determined by nuclear motion. rather than controlled by solvent dynamics.