Determination of the rate constant of the solvent cage reorientation around a photoexcited molecule using phase modulation fluorometry

Abstract

The fluorescence lifetime and quantum yield of ethylamino-9-methoxy-2-chloro-6-acridine in glycerol solution were measured at three temperatures using the phase modulation technique. The results were interpreted in terms of a relaxation process in the excited state that involved two emitting species: one (designated F) directly excited and one (designate R) resulting from the reorientation of the solvent cage around the F state. The rate constant of this process was evaluated; it was greatly increased on raising the temperature, which also enhanced the radiationless deactivation rate constants of both emitting species, although to a minor extent. At 60 °C, this relaxation process is so fast that the whole fluorescence is emitted from R species.