title: Effects of Molecular Symmetry on the Electronic Transitions in Carotenoids.
abstract: The aim of this work is the verification of symmetry effects on the electronic absorption spectra of carotenoids. The symmetry breaking in cis-β-carotenes and in carotenoids with nonlinear π-electron system is of virtually no effect on the dark transitions in these pigments, in spite of the loss of the inversion center and evident changes in their electronic structure. In the cis isomers, the S2 state couples with the higher excited states and the extent of this coupling depends on the position of the cis bend. A confrontation of symmetry properties of carotenoids with their electronic absorption and IR and Raman spectra shows that they belong to the C1 or C2 but not the C2h symmetry group, as commonly assumed. In these realistic symmetries all the electronic transitions are symmetry-allowed and the absence of some transitions, such as the dark S0 → S1 transition, must have another physical origin. Most likely it is a severe deformation of the carotenoid molecule in the S1 state, unachievable directly from the ground state, which means that the Franck-Condon factors for a vertical S0 → S1 transition are negligible because the final state is massively displaced along the vibrational coordinates. The implications of our findings have an impact on the understanding of the photophysics and functioning of carotenoids.
authors.affiliation: Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University , Gronostajowa 7, 30-387 Kraków, Poland.
authors.forename: Leszek
authors.initials: L
authors.lastname: Fiedor
authors.affiliation: Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University , Gronostajowa 7, 30-387 Kraków, Poland.|Ma Chung Research Center for Photosynthetic Pigments, Ma Chung University , Villa Puncak Tidar N-01, Malang 65151, Indonesia.
authors.lastname: Heriyanto
authors.affiliation: Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University , Gronostajowa 7, 30-387 Kraków, Poland.|Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology , Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Fiedor
authors.affiliation: Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University , Gronostajowa 7, 30-387 Kraków, Poland.|Faculty of Chemistry, Jagiellonian University , Ingardena 3, 30-060 Kraków, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Pilch
mesh_terms: D002338:Carotenoids / Q000737:chemistry*; D004579:Electron Transport; D015394:Molecular Structure
chemical_list: D002338:Carotenoids