title: Electronic absorption and ground state structure of carotenoid molecules.
abstract: Predicting the complete electronic structure of carotenoid molecules remains an extremely complex problem, particularly in anisotropic media such as proteins. In this paper, we address the electronic properties of nine relatively simple carotenoids by the combined use of electronic absorption and resonance Raman spectroscopies. Linear carotenoids exhibit an excellent correlation between (i) the inverse of their conjugation chain length N, (ii) the energy of their S0 → S2 electronic transition, and (iii) the position of their ν1 Raman band (corresponding to the stretching mode of their conjugated C═C bonds). For cyclic carotenoids such as β-carotene, this correlation is also observed between the latter two parameters (S0 → S2 energy and ν1 frequency), whereas their "nominal" conjugation length N does not follow the same relationship. We conclude that β-carotene and cyclic carotenoids in general exhibit a shorter effective conjugation length than that expected from their chemical structure. In addition, the effect of solvent polarizability on these molecular parameters was investigated for four of the carotenoids used in this study. We demonstrate that resonance Raman spectroscopy can discriminate between the different effects underlying shifts in the S0 → S2 transition of carotenoid molecules.
authors.affiliation: Institute of Biology and Technology Saclay, CEA, UMR 8221 CNRS, University Paris Sud , CEA Saclay 91191 Gif sur Yvette, France.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Mendes-Pinto
authors.forename: Elodie
authors.initials: E
authors.lastname: Sansiaume
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Pascal
authors.forename: Andrew
authors.initials: A
authors.lastname: Gall
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
mesh_terms: D002338:Carotenoids / Q000737:chemistry*; D004583:Electrons; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D019207:beta Carotene / Q000737:chemistry
chemical_list: D019207:beta Carotene; D002338:Carotenoids