Ultrafast studies on intramolecular charge transfer and solvation dynamics

Abstract

Much of the recent activity on the study of fast charge (electron) transfer ET reactions stems from the growing appreciation that the rates of ET can be affected by solvent dynamics in contrast to traditional theories of ET which are based on a quasi—equilibrium assumption. Our work has emphasized femtosecond studies of the excited state, S1 small barrier, ultrafast ET reactions of aromatics, including BA, ADMA, derivatives of ADMA, and several other molecules. We have shown theoretically that emission dynamics at the short wavelength edge of the fluorescence band accurately measures the decay of the prepared (reactant’s) concentration. Results on the solvent dependence of <τET> demonstrate that the ET kinetics of the various molecules are controlled by solvation dynamics, see Table 1. However, we have shown that simple continuum models for solvation dynamics (when combined with theories of ET) do not correctly predict ET rates. Rips and Jortner have analyzed our data and shown that the MSA model (combined with ET theory) more accurately agrees with experiments. This emphasizes the importance of molecular interactions in dynamic solvent effects on chemical reactions.