Vibrational energy relaxation of perylene in supercritical alcohols

Abstract

The time resolved fluorescence spectra of perylene in sub- and supercritical methanol have been measured by using a streak camera in the lower-pressure region than 10 MPa and an optical Kerr gate spectroscopic method in the higher-pressure region than 10 MPa. The lineshape of the fluorescence spectrum has been found to be dependent on the time. By comparing the excess energy dependence of the fluorescence lineshape in vapour perylene without energy dissipation process, the spectral change was assigned to the vibrational energy relaxation process in the S1 state. The vibrational energy relaxation time at each solvent density in supercritical region was determined by the time-profile at the 0-0 band peak position in the fluorescence spectrum. The vibrational energy relaxation rate scaled by the square root of the temperature has been compared with the hydrogen-bonding degree between solvent molecules estimated by the NMR measurement (Hoffmann M M and Conradi M S 1998 J. Phys. Chem. B 102 263).