Vibrational Energy Relaxation of S1 Perylene in Solution

Abstract

Vibrational energy relaxations of S1 perylene and S1 12-(3-perylenyl)dodecanoic acid (PD) in 2-methyltetrahydrofuran 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 ν7 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 V0 = 0.59 cm-1 and 0.46 < α < 0.55 in our analysis, which were in reasonable agreement with Fourmann's analysis, V0 = 0.65 cm-1 and α = 0.3, for fluorescence spectra of perylene in supersonic jet. To discuss the energy flow in the ν7 mode, transient vibrational temperatures were also calculated at each time. “Intramode” thermal equilibriums in the ν7 mode both for perylene and for PD are not established while the vibrational temperature is higher than room temperature.