Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory

Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be beta =1 Angstrom (-1), data were fit to a single parameter, the coupling matrix element at contact, J(0). The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J(0). Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J(0) are very similar for all solvents. (C) 2000 American Institute of Physics. [S0021- 9606(00)01846-8].