EFFECT OF VISCOSITY AND ROTOR SIZE ON THE DYNAMICS OF TWISTED INTRAMOLECULAR CHARGE-TRANSFER

Picosecond emission spectroscopy is used to examine the kinetics of twisted intramolecular charge transfer in a series of symmetric bis((N,N-dialkylamino)phenyl) sulfones, DRAPS (R = methyl, propyl, and butyl), in alcohol solutions. Within a given solvent, the dynamics of charge transfer are not dependent on changes in the size of the rotating group; however, for a single molecule in the series of n-alcohols, the rate of charge transfer correlates with the inverse of the solvent viscosity. These seemingly contradictory observations are reconciled by taking into account polarity effects on the reaction barrier, thereby revealing that the rate of reaction for a single molecule in the series of alcohols is independent of changes in solvent viscosity. © 1990 American Chemical Society.