Excited states and electrochromism of radical cation of the carotenoid astaxanthin

Radical cations of the carotenoid astaxanthin were generated by chemical oxidation with Fe(Cl)3, and their absorption and electroabsorption (Stark) spectra at temperatures about 150 K were recorded in the spectral range from 5900 to 26000 cm−1 (380 to 1700 nm), covering two absorptive electronic transitions from D0 (ground) to D1 and D2 excited states. The changes in static polarizability are negative and equal −40±10 A3 for D0→D1 and −105±15 A3 for D0→D2, pointing that dominant contribution to polarizabilities results from the coupling of D1 and D2 with the ground state. An approximate localization of the next excited state with ground-state parity is estimated based on arguments from perturbation theory.