Abstract

We have observed ultrafast non-exponential fluorescence quenching of 7-aminocoumarin dyes in electron donating solvents by means of femtosecond fluorescence up-conversion technique [1]. We regarded this fluorescence quenching as an ultrafast intermolecular electron transfer (ET) from the solvent to the excited dye. When the carbon chain on the amino group becomes longer, the rate of ET becomes slower, and when the amino group is fixed by hexagonal carbon ring, it becomes the slowest. Some of the fast reactions occur much faster than the diffusive solvent relaxation process. The fastest reaction with a time constant of ~200 fs was observed for coumarin 151 (C151) in N,N-dimethylaniline (DMA). In such a case, some dynamics faster than diffusive orientational polarization of the solvent is required to induce the reaction.

© 1994 Optical Society of America