Evidence for Dynamical Solvent Effects on the Photoisomerization of 4,4'-Dimethoxystilbene

Article abstract of DOI:10.1021/j100314a023

The photoisomerization dynamics of 4,4'-dimethoxystilbene have been studied in n-alkanes and n-alkyl alcohols as a function of temperature at ambient pressure.By comparison with unsubstituted stilbene results the influence of the methoxy group, both intramolecular and intermolecular, on the isomerization process has been evaluated.The studies in n-alkane solvents reveal larger barrier heights and a weaker viscosity dependence for dimethoxystilbene compared to those of stilbene.This observation is in agreement with earlier ideas concerning frequency-dependent solvent effects but contrary to free volume models of solute-solvent friction.The studies in n-alkyl alcohol solvents demonstrate the inability of separating intramolecular from intermolecular effects.The potential energy surface associated with the reaction is strongly coupled with solvent dynamics, hence time dependent.These results demonstrate the importance of understanding microscopic friction and dielectric interactions on ultrashort time scales.