Direct visualization of exciton reequilibration in the LH1 and LH2 complexes of Rhodobacter sphaeroides by multipulse spectroscopy |
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| Authors: | Cohen Stuart Thomas A Vengris Mikas Novoderezhkin Vladimir I Cogdell Richard J Hunter C Neil van Grondelle Rienk |
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| Institution: | †Faculty of Sciences, Free University of Amsterdam, de Boelelaan, Amsterdam, The Netherlands;‡Vilnius University, Faculty of Physics, Quantum Electronics Department, Vilnius, Lithuania;§A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia;¶Microbial Photosynthesis Laboratory, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow, United Kingdom;‖Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom |
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| Abstract: | The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. |
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