An ultrafast one-photon and two-photon transient absorption study of the solvent-dependent photophysics in all-trans retinal

Ultrafast transient absorption has been measured for all-trans retinal in hexane and ethanol with 150 fs time resolution. Excitation by one-photon absorption at 400 nm or two-photon absorption at 800 nm allows selection of the initially populated state. One-photon excitation leads to decays in 300 fs to 2 ps in hexane and about 2 ps in ethanol. On a longer time scale, intersystem crossing is observed in about 30 ps in both solvents even though the order of the two lowest excited singlet states is reversed. A model of the photophysics of all-trans retinal in both solvents is presented.