Role of twisted intramolecular charge-transfer states in the decay of 2-(2′-hydroxyphenyl)benzothiazole following excited-state intramolecular proton transfer

Abstract
The photophysics of 2-(2′-hydroxyphenyl)benzothiazole in non-polar and alcoholic solution is reported for temperatures in the range 96–298 K. In all solvents a rise in both fluorescence quantum yield and lifetime is observed as the temperature is decreased. It is proposed that a viscosity-dependent non-radiative process leading to a non-emissive, twisted excited state accounts for these observations. Results of quantum chemical calculations are consistent with this interpretation.