title: Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy.
abstract: We have observed that an assembly of the bacteriochloropyll a molecules into B850 and B875 groups of cyclic bacterial light-harvesting complexes LH2 and LH1, respectively, results an almost total loss of the intra-molecular vibronic structure in the fluorescence spectrum, and simultaneously, an essential enhancement of its phonon sideband due to electron-phonon coupling. While the suppression of the vibronic coupling in delocalized (excitonic) molecular systems is predictable, as also confirmed by our model calculations, a boost of the electron-phonon coupling is rather unexpected. The latter phenomenon is explained by exciton self-trapping, promoted by mixing the molecular exciton states with charge transfer states between the adjacent chromophores in the tightly packed B850 and B875 arrangements. Similar, although less dramatic trends were noted for the light-harvesting complexes containing chlorophyll pigments.
authors.affiliation: Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.
authors.forename: Margus
authors.initials: M
authors.lastname: Rätsep
authors.affiliation: Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.
authors.forename: Mihkel
authors.initials: M
authors.lastname: Pajusalu
authors.affiliation: Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.
authors.forename: Juha Matti
authors.initials: JM
authors.lastname: Linnanto
authors.affiliation: Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia and Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu, Estonia.
authors.forename: Arvi
authors.initials: A
authors.lastname: Freiberg
mesh_terms: D025541:Bacteriochlorophyll A / Q000737:chemistry*; D004583:Electrons; D060739:Phonons; D052979:Phycobiliproteins / Q000737:chemistry*; D012241:Rhodopseudomonas / Q000201:enzymology; D013050:Spectrometry, Fluorescence; D014732:Vibration
chemical_list: D025541:Bacteriochlorophyll A; D052979:Phycobiliproteins