Excited-state dynamics of trans,trans-distyrylbenzene: transient anisotropy and excitation energy dependence

We report a study of excited-state dynamics of trans,trans-distyrylbenzene in hexane solution with femtosecond two-color transient absorption spectroscopy. A consistent model of two distinct excited states, S1 and X, connected by the 10 ps dynamics is proposed with the support from the analysis of excited-state anisotropy. An investigation on the 10 ps dynamics with varying excitation energy has been also conducted. In the assumption of fast intramolecular vibrational redistribution, a dependence of this nonradiative 10 ps process on intramolecular temperature in the S1 state has been analyzed. We have found that an effective mode of approximately 1270 cm-1 is responsible for the 10 ps dynamics. The analysis of both anisotropy and pump-dependent results further implies that a distribution of rotamers may exist in the X state. The result indicates a drastic different excited-state relaxation pathway than that of trans-stilbene.