Solvent-assisted intramolecular vibrational energy redistribution of S1 perylene in ketone solvents

We investigated vibrational energy relaxations of S1 perylene at an excess energy of ca. 2800 cm−1 in several ketone solvents by femtosecond time-resolved fluorescence measurements. Temporal evolution of fluorescence emissions occurs on the following distinct timescales: 70–330 fs, 0.6–1.1 ps and 1.8–4.9 ps. The latter two was assigned to the intramolecular vibrational redistribution (IVR), and to the solvent-assisted IVR (SA-IVR), respectively. In SA-IVR, intramolecular vibrational couplings are affected by elastic or quasi–elastic interactions between solute and solvents. Solvent dependence of the SA-IVR rates can be explained qualitatively by the tier V–V coupling mechanism.