Time-resolved resonance Raman spectra of the triplet state and the radical cation of 5-dibenzosuberenol and its photoionization mechanism

Abstract

Time-resolved resonance Raman spectra are obtained for the lowest excited triplet state T 1 and the radical cation of 5-dibenzosuberenol (DBCH-5-ol). It is concluded, based on the large downshifts of the Raman bands assignable to the CC stretch of the central ring, that the CC bond is weakened markedly both in the T 1 state and in the radical cation; the weakening is much more pronounced in the T 1 state. Dependence on the intensity and wavelength of the pump laser pulse indicates that the production of the radical cation is biphotonic via the S 1 state and that the intersystem crossing from S 1 to T 1 is much slower from low vibrational levels than from higher vibrational levels, resulting in the very small yield of the T 1 state when photolysed by 340 nm UV light.