Conjugation length dependence of relaxation kinetics in β-carotene homologs probed by femtosecond Kerr-gate fluorescence spectroscopy

Ultrafast dynamics of the optically allowed S 2 ( 1 1 B u + ) state in all-trans-carotenoids with a number of conjugated double bonds, n = 7–15, has been investigated by femtosecond Kerr-gate fluorescence spectroscopy. The lifetime of the S2 state is determined eliminating effect of excess vibrational energy. The lifetime has a maximum for n = 9 and shows anomalous dependence on the energy gap between the S2 and S1 states.