A 35-fs time-resolved absorption study of all-trans retinal in a nonpolar solvent: Ultrafast photophysics revisited

Ultrafast relaxation processes in the excited singlet states of all-trans retinal in cyclohexane solution was investigated by time-resolved absorption spectroscopy with 35-fs time resolution. The observed transient absorption signal consists of three components, including a fully time-resolved ultrafast component having a lifetime of 56 ± 20 fs. The obtained result is consistent with a cascading electronic relaxation (S3(ππ*,Bu) → S2(ππ*,Ag) → S1(nπ*)) occurring after photoexcitation. The time-resolved absorption anisotropy was also measured, and it showed that the transition moments of the transient absorption from these three excited states are nearly parallel to the long axis of the molecule.