Nanosecond time-resolved resonance Raman investigation of the radical cation of 4,4′-dibromobiphenyl and the T1→Tn transition of 4,4′-dibromobiphenyl

We have taken nanosecond time-resolved resonance Raman spectra of the T1→Tn transition of 4,4′-dibromobiphenyl in cyclohexane solution and of the radical cation of 4,4′-dibromobiphenyl in acetonitrile solution. The resonance Raman spectrum of T1 4,4′-dibromobiphenyl is consistent with a planar quinoidal structure. The C–Br bond appears stronger in the T1 state than in the S0 ground state and this is in agreement with photochemistry studies done for 4-bromobiphenyl that indicate that the T1 state must be further excited by excimer formation and/or electron transfer with an appropriate donor prior to a debromination reaction.