Ultrafast fluorescence study on the excited singlet-state dynamics of all-trans-retinal

The femtosecond time-resolved fluorescence of all-trans-retinal in hexane was measured by using the fluorescence up-conversion method. It was found that the fluorescence consists of ultrafast (tau = 30 +/- 15 fs and lambda(max) approximate to m 430 nm), fast (tau = 370 +/- 20 fs and lambda(max) approximate to 440 nm), and slow (tau = 33.5 ps and lambda(max) approximate to 560 nm) components. These three components were assigned to fluorescences from the B-1(u), (1)A(g), and (1)n pi* states, respectively, which are successively populated during the relaxation process in the singlet: manifold after photoexcitation. The oscillator strengths of the three excited singlet states were determined to be 1.0 (B-1(u)), 0.024 ((1)A(g)), and 0.0018 ((1)n pi*) on the basis of the obtained lime-resolved fluorescence data. The state ordering in the singlet manifold, as well as quantitative characterization of the three low-lying excited singlet states, is discussed.