Thermal Cis-Trans Isomerlzatlon of Solvatochromic Merocyanlnes: Linear Correlations between Solvent Polarity and Adiabatlc and Diabatic Transition Energies
نویسندگان
چکیده
The correlation between solvatochromy and the solvent-polarity-dependent rate constant k, 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,, varies over 7 orders of magnitude, decreasing with increasing solvent polarity. It has been demonstrated that the first transition energy AEand the free activation enthalpy AG*, of thermal cis-trans isomerization are linearly correlated with each other and with Dimroth’s solvent polarity parameter ET. These observations and the solvent-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.
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