Vibrational relaxation in the state of carotenoids as determined by Kerr-gate fluorescence spectroscopy

Subpicosecond time-resolved fluorescence spectra of all-trans-neurosporene and spheroidene, upon excitation above the 1 B u + (v = 2) and 1 B u + (v = 3) vibronic levels, respectively, were recorded by means of Kerr-gate spectroscopy. The spectral data matrices were analyzed by singular-value decomposition followed by global-fitting by the use of a sequential model. A pair of species-associated difference spectra thus obtained in each carotenoid was ascribed to fluorescence from the 1 B u + (v = 1) and 1 B u + (v = 0) vibronic levels down to the ground 1 A g - (v = 0, 1 and 2) levels. The lifetimes of the 1 B u + (v = 1) and 1 B u + (v = 0) states were determined to be 50 and 260 fs in neurosporene and 25 and 260 fs in spheroidene.