Temperature dependence of bianthryl dual fluorescence

The fluorescence of bianthryl in ethyl acetate and acetone has been investigated in dependence on the temperature. The variation of temperature changes the ratio of the locally excited (1LE) and the charge transfer (1CT) fluorescence quantum yields, which parallels the dielectric properties of the solvent. Thermodynamic functions (ΔGCT,ΔSCT) of the excited state charge transfer process of bianthryl in ethyl acetate and acetone have been determined from equilibrium constants (1LE⇔1CT) accessible from the fluorescence data. Charge-transfer induced intersystem crossing occurring in BA is slightly temperature dependent in both solvents, which indicates that the ISC rate constant is mainly governed by the spin inversion in the anthracene subunits of bianthryl.