Theoretical study on excitation dynamics of 5-dibenzosuberene and its derivatives

The present study theoretically investigated structures and dynamics of 5-dibenzosuberene (DBCH), 5-dibenzosuberenol (DBCH-5-ol), and 5-dibenzosuberenone (DBCH-5-one) in the excited states, in order to clarify specific behavior of transient species of DBCH-5-one in picosecond time region. The theoretical results confirm that the transient species observed in picosecond time-resolved absorption spectra of DBCH and DBCH-5-ol correspond to the S₁ state and those in nanosecond ones to the T₁ state. On the other hand, both picosecond and nanosecond transient species of DBCH-5-one are shown to be the T₁ state, which means that the lifetime of S₁ transient species is shorter than the picosecond order. Furthermore, the short lifetime of the S₁ transition species is found to be due to large transition probability of S₁→T₁ intersystem crossing. Since the S₁ state has n-π* character and the T₁ state π-π* one, the spin-orbit coupling and, therefore, the transition probability between the S₁ and T₁ states are large, which corresponds to El-Sayed rule.