title: Resonance Raman spectra and electronic transitions in carotenoids: a density functional theory study.
abstract: Raman and electronic absorption spectra corresponding to the S0-S2 electronic transition of various carotenoid and polyene molecules are theoretically analyzed using the density functional theory (DFT) approach. The results demonstrate the linear dependence between the frequency of the so-called ν1 band corresponding to the C═C stretching modes in the Raman spectra and the S0-S2 electronic transition for molecules of different conjugation lengths. From these calculations the following relationship have been identified: (i) the effective conjugation length shortens in conformers of carotenoids containing β-rings whereas it increases in polyene upon s-cis isomerization at their ends, (ii) methyl groups connected to the conjugated chain of carotenoids induce a splitting of the ν1 band in the Raman spectra, (iii) the effective conjugation lengths of all-trans-polyenes and corresponding all-trans-carotenoids are the same as follows from the Raman ν1 frequency, but they are different as defined from S0-S2 electronic transition energies. The results well correlate with the experimental observations.
authors: Theoretical Physics Department, Faculty of Physics, Vilnius University , Saulėtekio al. 9, LT-10222 Vilnius, Lithuania.
authors: Mindaugas
authors: M
authors: Macernis
authors: Juozas
authors: J
authors: Sulskus
authors: Svetlana
authors: S
authors: Malickaja
authors: Bruno
authors: B
authors: Robert
authors: Leonas
authors: L
authors: Valkunas
mesh_terms: D002338:Carotenoids / Q000737:chemistry*; D003198:Computer Simulation; D004560:Electricity; D016014:Linear Models; D008958:Models, Molecular; D011090:Polyenes / Q000737:chemistry; D013059:Spectrum Analysis, Raman
chemical_list: D011090:Polyenes; D002338:Carotenoids