Vibrational relaxation pathways in the electronic excited state of carotenoid

Abstract

The intra- and inter-molecular vibrational relaxation in the electronic excited state (1B u +) of spheroidene derivative (the number of conjugated double bonds, n = 8 ) has been investigated at room temperature by means of femtosecond time-resolved fluorescence spectroscopy based on an optical-Kerr-gate technique. Depending on the photo-excitation either to the 1 B u + ( v = 1 ) or 1 B u + ( v = 2 ) vibronic level, remarkable differences were observed in hot luminescence spectra related to the vibrational relaxation process of high- and low-frequency modes. Under the excitation to the 1 B u + ( v = 2 ) state hot luminescence from the 1 B u + ( v = 1 ) state was observed as a dominant feature of the time-resolved spectra while the dynamic Stokes shift originating from the low-frequency-modes dynamics was clearly observed under the excitation to the 1 B u + ( v = 1 ) . These observations of the excitation energy dependence of time-resolved fluorescence spectra were discussed by analyzing the Franck–Condon factors of transitions from v = 0 , 1 , and 2 levels of high-frequency modes.