title: Triplet Excitation Transfer between Carotenoids in the LH2 Complex from Photosynthetic Bacterium Rhodopseudomonas palustris.
abstract: We have studied, by means of sub-microsecond time-resolved absorption spectroscopy, the triplet-excited state dynamics of carotenoids (Cars) in the intermediate-light adapted LH2 complex (ML-LH2) from Rhodopseudomonas palustris containing Cars with different numbers of conjugated double bonds. Following pulsed photo-excitation at 590 nm at room temperature, rapid spectral equilibration was observed either as a red shift of the isosbestic wavelength on a time scale of 0.6-1.0 mus, or as a fast decay in the shorter-wavelength side of the T(n)<--T(1) absorption of Cars with a time constant of 0.5-0.8 mus. Two major spectral components assignable to Cars with 11 and 12 conjugated double bonds were identified. The equilibration was not observed in the ML-LH2 at 77 K, or in the LH2 complex from Rhodobacter sphaeroides G1C containing a single type of Car. The unique spectral equilibration was ascribed to temperature-dependent triplet excitation transfer among different Car compositions. The results suggest that Cars of 11 and 12 conjugated bonds, both in close proximity of BChls, may coexist in an alpha,beta-subunit of the ML-LH2 complex.
authors.affiliation: The State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, 1st North Street, Haidian District, Beijing, 100080, P. R. China.
authors.forename: Juan
authors.initials: J
authors.lastname: Feng
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Yi-Shi
authors.initials: YS
authors.lastname: Wu
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Ai
authors.forename: Xu-Jia
authors.initials: XJ
authors.lastname: Zhang
authors.forename: You-Guo
authors.initials: YG
authors.lastname: Huang
authors.forename: Xing-Kang
authors.initials: XK
authors.lastname: Zhang
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang