Picosecond-nanosecond time-resolved resonance Raman study of the structure and dynamics of the excited states of 5-dibenzosuberene derivatives

Structures and dynamics of the excited electronic states, S1 and T1, and cation radical R+• of 5-dibenzosuberene (DBCH) and its derivatives were investigated in the picosecond–nanosecond time domain using time-resolved resonance Raman spectroscopy with the aid of time-resolved absorption spectroscopy. For both 5-dibenzosuberene and 5-dibenzosuberenol (DBCH-5-ol) the effect of vibrational cooling or vibrational relaxation in S1 was detected in both the Raman and absorption spectra in the 0–40 ps time region; the time constant of this effect was estimated to be about 13 ps for both DBCH and DBCH-5-ol. The expected conformational change in the S1 state of DBCH-5-ol was not clearly observed in the resonance Raman spectra. It was observed, however, that the central ethylenic C=C bond was weakened considerably in S1, but the degree of the weakening was considerably less than that of T1 and was very similar to that of R+•. The dynamics of S1 of 5-dibenzosuberenone were complicated, possibly owing to the existence of a carbonyl group, and are not discussed. © 1998 John Wiley & Sons, Ltd.