Effect of the solvent environment on the spectroscopic properties and dynamics of the lowest excited states of carotenoids

The spectroscopic properties and dynamics of the lowest excited singlet sta tes of peridinin, fucoxanthin, neoxanthin, uriolide acetate, spheroidene, a nd spheroidenone in several different solvents have been studied by steady- state absorption and fast-transient optical spectroscopic techniques. Perid inin, fucoxanthin, uriolide acetate, and spheroidenone, which contain carbo nyl functional groups in conjugation with the carbon-carbon pi-electron sys tem, display broader absorption spectral features and are affected more by the solvent environment than neoxanthin and spheroidene, which do not conta in carbonyl functional groups. The possible sources of the spectral broaden ing are explored by examining the absorption spectra at 77 K in glassy solv ents. Also, carotenoids which contain carbonyls have complex transient abso rption spectra and show a pronounced dependence of the excited singlet stat e lifetime on the solvent environment. It is postulated that these effects are related to the presence of an intramolecular charge transfer state stro ngly coupled to the S-1 (2(1)A(g)) excited singlet state. Structural variat ions in the series of carotenoids studied here make it possible to focus on the general molecular features that control the spectroscopic and dynamic properties of carotenoids.