Influence of solvent permittivity on excited state photoisomerization rates of stilbene in n-alcohols

The dependence of the activation energy for trans-stilbene photoisomerization on solvent permittivity has been determined in n-alcohols via fits of the isomerization rates across the alcohol series at constant solvent permittivity to Kramers expression. The results of this procedure indicate that the internal barrier to isomerization in these solvents is considerably larger than that indicated by isoviscosity Arrhenius plots and predicts a strong dependence of the barrier height on temperature and alcohol chain length.