Vibrational energy relaxation of S1 perylene in solution

Vibrational energy relaxations of S-1 perylene and S-1 12-(3-perylenyl)dodecanoic acid (PD) in 2-methyltet-rahydrofuran at room temperature were investigated by using a Franck-Condon analysis of femtosecond time-resolved fluorescence spectra. Vibrational energy relaxation from \2), v' = 2 level of v(7) mode, occurs not only via successive route, \2> --> \1> followed by \1> --> \0>, but also via direct route, \2> --> \0>. The vibrational energy relaxation times were obtained as 2.7 ps for \2> --> \1> 1.8 ps for \1> --> \0>, and 700 fs for \2> --> \0> in perylene and 1.9 ps for \2> --> \1>, 1.2 ps for \1> --> \0>, and 500 fs for \2> --> \0> in PD. An average-matrix-element treatment proposed by Fourmann et al. (Chem. Phys. 1985, 92, 25) was employed to account for these relaxation times in the Fermi's golden rule. Two parameters of the average-matrix element were estimated to be V-o = 0.59 cm(-1) and 0.46 < (alpha < 0.55 in our analysis, which were in reasonable agreement with Fourmann's analysis, V-o = 0.65 cm(-1) and (alpha = 0.3, for fluorescence spectra of perylene in supersonic jet. To discuss the energy flow in the v(7) mode, transient vibrational temperatures were also calculated at each time. Intramode thermal equilibriums in the v(7) mode both for perylene and for PD are not established while the vibrational temperature is higher than room temperature.