Excited state dynamics of β-carotene explored with dispersed multi-pulse transient absorption

The excited-state dynamics of β-carotene in hexane was studied with dispersed ultrafast transient absorption techniques. A new excited state is produced after blue-edge excitation. Pump–repump–probe and pump–dump–probe measurements identified and characterized this state, termed S‡, which exhibits a blue-shifted spectrum with a longer lifetime than S1. We establish the independent co-existence of the S‡ and S1 states following the relaxation of S2 and demonstrate that S‡ is an electronically excited state and not a vibrationally excited ground-state species. Our data support the premise that S‡ is formed directly from S2 and not via preferential excitation of ground-state sub-populations.