Implications for multidimensional effects on isomerization dynamics: Photoisomerization study of 4,4′-dimethylstilbene in n-alkane solvents

Studies of the photoisomerization of 4,4′-dimethylstilbene in n-alkane solvents are reported. As with similar studies it is possible to identify an activation barrier to isomerization and the viscosity dependence of the isomerization is not adequately explained by a one-dimensional hydrodynamic Kramers equation. Comparison of the isomerization rates with those of other stilbenes suggests that the use of a frequency dependent friction for the solvent does not consistently explain the data. These results and those of other stilbenes can be explained by a two-dimensional isomerization coordinate where the reaction trajectory is linked to the solvent viscosity.