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-β-caroten-8′-al following one-photon excitation at 405 nm. An excess vibrational energy of ∼4000 cm⁻¹ in the S₂ 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 S₂ 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 S₁ surface and a branched decay from hot S₂ molecules to at least two of these minima.