Branching relaxation pathways from the hot S2 state of 8′-apo-β-caroten-8′-al

Abstract

We present infrared and visible transient absorption measurements of 8'-apo-beta-caroten-8'-al following one-photon excitation at 405 nm. An excess vibrational energy of approximately 4000 cm(-1) in the S(2) state is created with 405 nm excitation. Relaxation from this vibronic region shows distinct relaxation pathways from those observed for 490 nm excitation which excites S(2) near its origin. Infrared and visible transient absorption measurements show long-lived transient signals that persist longer than 1 ns. These transient spectra are identical to those observed in previous two-photon excitation measurements at 1275 nm. Our results are consistent with at least two minima on the S(1) surface and a branched decay from hot S(2) molecules to at least two of these minima.