Thermal Cis-Trans Isomerization of Solvatochromic Merocyanines: Linear Correlations between Solvent Polarity and Adiabatic and Diabatic Transition Energies

Article abstract of DOI:10.1021/j100326a017

The correlation between solvatochromy and the sovent-polarity-dependent rate constant k_ct of thermal cis-trans isomerization (solvatokinetic behavior) has been investigated for a stilbazolium-type merocyanine and an amphiphilic analogue in a polarity series of eight neat solvents (protic and aprotic).At room temperature k_ct varies over 7 orders of magnitude, decreasing with increasing solvent polarity.It has been demonstrated that the first transition energy ΔEmax and the free activation enthalpy ΔG(excit.)_ct of thermal cis-trans isomerization are linearly correlated with each other and with Dimroth's solvent polarity parameter E_T.These observations and the sovent-polarity-dependent increase of absorption band width are explained in terms of a model emphasizing the strong coupling between molecular conformation, electronic charge distribution, and solvent polarization.