Deactivation of an excited charge-transfer complex I. Influence of solvent polarity on radiative and radiationless transitions

The influence of solvent polarity on the fluorescence of charge-transfer complexes of pyromellitic dianhydride with some methylated benzenes has been investigated. Quantum yields and decay times of fluorescence, in mixed solvents of different polarities, have been measured. It was shown that with increasing solvent polarity the quantum yield of fluorescence is mainly decreasing owing to the decrease of the radiative transition probability k_f is due to the increasing degree of solvent-induced changes in the electronic and geometrical structure of the equilibrium excited state and increasing solvation of the components of the complex. Emissive properties of charge-transfer complexes are compared with emissive properties of heteroexcimers.