Prompt fluorescence from biphenylene in liquid solution: Absence of detectable S2→S0 fluorescence and its implications, vibrational structure and polarization of S1→S0 fluorescence, and orientational relaxation of molecules in S1

摘要

The prompt emission from S0→S2 photoexcited biphenylene in 3-methylpentane has been investigated. No prompt S2→S0 fluorescence has been observed. The implications of this negative result are discussed. It is shown that lengthening of the radiative lifetime of S2 due to intermediate strong S2-S1 coupling is the likely cause of the absence of detectable S2-S0 fluorescence. The observable resonance Raman lines of biphenylene can be assigned to totally symmetric vibrations. The position of S1,0 is determined by a vibrational analysis of the S1→S0 fluorescence. The polarization degree P of the S1→S0 fluorescence is positive. From the dependence of P on temperature and viscosity, orientational relaxation times of biphenylene in S1 are determined with Perrin's formula.