title: Deconstructing the excited-state dynamics of β-carotene in solution.
abstract: The femtosecond to nanosecond dynamics of the all-trans β-carotene carotenoid dissolved in 3-methylpentane is characterized and dissected with excitation-wavelength and temperature-dependent ultrafast dispersed transient absorption signals. The kinetics measured after red-edge (490 nm) and blue-edge (400 nm) excitation were contrasted under fluid solvent (298 K) and rigid glass (77 K) conditions. In all four measured data sets, the S* population kinetics was resolved prompting the development of a modified multicompartment model. The temperature-dependent and excitation wavelength-dependent S* quantum yield is ascribed to a competition of population surmounting a weak (55 cm(-1)) energy barrier on the S(2) state to favor S(1) generation and rapid internal conversion that favors S* generation. When cooled from room temperature to 77 K, the S* decay time scale shifted significantly from 30 to 400 ps, which is ascribed to small-scale structural relaxation with a 115 cm(-1) energy barrier. For the first time under low-energy excitation conditions, the triplet state is observed and confirmed to not originate from S* or S(1), but from S(2). The interconnectivity of the S* and S(1) populations is discussed, and no observed population flow is resolved between S* and S(1). Comparison of samples obtained from different laboratories with different purity levels demonstrates that sample contamination is not the primary origin of the S* state.
authors.affiliation: Department of Chemistry, University of California Davis, One Shields Avenue, Davis, California 95616, United States.
authors.forename: Askat E
authors.initials: AE
authors.lastname: Jailaubekov
authors.forename: Mikas
authors.initials: M
authors.lastname: Vengris
authors.forename: Sang-Hun
authors.initials: SH
authors.lastname: Song
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kusumoto
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
mesh_terms: D018360:Crystallography, X-Ray; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012996:Solutions; D013696:Temperature; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D012996:Solutions; D019207:beta Carotene