Ultrafast Charge Separation in ADMA Experiment, Simulation, and TheoreticalIssues

摘要

Excited state intramolecular charge separation in organic electron donor/acceptor(D-A) compounds has become an important model reaction for studying the mechanism of small barrier electron transfer (et) reactions. In this paper we present new ultrafast fluorescence measurements on the excited states of dynamics of 4-(9-anthryl)-N,N'-dimethylaniline (ADMA), especially on the excited state et process (D-A* = D+ -A-, conventionally denoted by LE= CT). Employing an extension of the semi-empirical model of Kang et al. (Chem. Phys. 149 81 (1990)), the results have been analyzed leading to several conclusions. First, the variation in the static absorption and emission spectra of ADMA, as a function of solvent, is primary due to simple solvent coordinate effects, rather than large intramolecular structural changes. Second, in polar solvents the excited state et (LE = CT) of ADMA is in the Marcus inverted regime. Third, there are two distinct et kinetic components, a faster (<150 fs) component which is not solvent controlled and probably involves intramolecular bath states: and a slower solvent controlled component with a limiting rate constant.