The influence of molecular conformation on electronic relaxation processes. The excitation-wavelength dependence of the radiative and nonradiative rates of biphenyl

Abstract

The temperature and excitation-wavelength dependence of the fluorescence quantum yield, the phosphorescence quantum yield, and the phosphorescence lifetime of biphenyl in propylene glycol have been studied. The S 1 → T i intersystem-crossing rate and the T 1 → S 0 radiative rate are enhanced with increasing excitation energy, but the T 1 → S 0 nonradiative rate is unaffected. It was concluded that the S 1 → T i intersystem-crossing rate constant and the T 1 → S 0 radiative rate constant are much faster in twisted biphenyl than in planar biphenyl.