Solvent as electron donor: Donor/acceptor electronic coupling is a dynamical variable

We combine analysis of measurements by femtosecond optical spectroscopy, co mputer simulations, and the generalized Mulliken-Hush (GMH) theory in the s tudy of electron-transfer reactions and electron donor-acceptor interaction s. Our focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state accepters. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin accepters reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 ( 7-(dimethylamino)-4-(trifluoromethyl)coumarin), and reductive quenching dyn amics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene, Applying a combination of molecular dyn amics trajectories, semiempirical quantum mechanical calculations (of the r elevant adiabatic electronic states), and GMH theory to the C152/DMA photor eaction, we calculate the electron donor/acceptor interaction parameter H-D A at various time frames. H-DA is strongly modulated by both inner-sphere a nd outer-sphere nuclear dynamics, leading us to conclude that H-DA must be considered as a dynamical variable.