Intramolecular electron transfer and solvation

The intramolecular charge transfer reaction and solvation dynamics of 4,4′-dimethylaminophenyl sulphone in alcohols are measured using picosecond time-resolved emission spectroscopy. The results are compared to theoretical models that treat the solvent as a dielectric continuum. In alcohol solvents, the value for τ_L^-1(τ_L = τ_DE∞/E_s) using either n₂ or E _mv for E∞ do not provide a good gauge for the intramolecular electron transfer rate. These results are discussed in terms of the importance of vibrational contributions to the reaction rates and the applicability of the parameter τ_L in gauging the solvent dynamics. In addition, the time-resolved emission data clearly show that the charge transfer state is formed out of equilibrium with the surrounding solvent structure. The measured time scales for the ensuing solvent relaxation are significantly longer than the hydrodynamic continuum model prediction of τ_L. The discrepancy between the observed rates and those predicted by models based on a dielectric continuum description of the solvent reveal the importance of the underlying molecular aspects of the role of the solvent in both intramolecular charge transfer and solvation.