Dynamical solvation effects on the cis-trans isomerization reaction: photoisomerization of merocyanine 540 in polar solvents

Abstract

The fluorescence quantum yield, Φ f , of merocyanine 540 in n-alkyl alcohol and n-alkanenitrile solvents was measured as a function of temperature and solvent shear viscosity at ambient pressure. The Strickler-Berg equation was used to calculate the radiative rate, k r , from the absorption and fluorescence spectra. Te values of Φ f and k r were used to obtain the rate of photoisomerization, k iso . This rate is consistent with the Smoluchowski limit of the Kramers theory for activated barrier crossing. The intrinsic barrier height, which is taken to be equal to the difference between the single-solvent activation energy and the viscosity activation energy, is lower in alcohols than in nitriles