The 1Bu-type singlet state of β-carotene as a precursor of the radical cation found in chloroform solution by sub-picosecond time-resolved absorption spectroscopy

Generation of the radical cation from 1Bu-type states (1Bu+ and/or 1Bu−) of all-trans-β-carotene in chloroform was demonstrated by sub-picosecond time-resolved absorption spectroscopy. In the visible region, ground-state absorption bleaching completely recovered in n-hexane but not in chloroform. In near-infrared, broad transient absorptions from 1Bu+ and 1Bu− states appeared and decayed within 1 ps in both solvents, while weak transient absorption ascribable to the cation appeared and stayed until 40 ps after excitation in chloroform, but not in n-hexane. In chloroform, direct transformation from the 1Bu-type singlet state to the radical cation had a time constant 0.14±0.03 ps.