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The dependence of excitation energy transfer pathways on conjugation length of carotenoids in purple bacterial photosynthetic antennae

Authors

  • Satoshi Maruta,

    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
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  • Daisuke Kosumi,

    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
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  • Tomoko Horibe,

    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
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  • Ritsuko Fujii,

    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
    2. The Osaka City University Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka 558-8585, Japan
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  • Mitsuru Sugisaki,

    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
    2. The Osaka City University Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka 558-8585, Japan
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  • Richard J. Cogdell,

    1. Glasgow Biomedical Centre, University of Glasgow, G12 8QQ, Scotland, UK
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  • Hideki Hashimoto

    Corresponding author
    1. CREST/JST and Department of Physics, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
    2. The Osaka City University Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka 558-8585, Japan
    • Phone: +81 6 6605 3627, Fax: +81 6 6605 3619
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Abstract

Ultrafast excited state dynamics of carotenoids in solution and bound to pigment–protein complexes have been investigated by femtosecond pump-probe spectroscopic measurements. Possible excitation energy transfer (EET) pathways between carotenoids and bacteriochlorophylls and their efficiency depend strongly on the conjugation length of carotenoids. In the case of Rhodobacter sphaeroides 2.4.1, dual EET channels from carotenoid to bacteriochlorophyll (S2 → Qx and S1 → Qy) upon excitation of carotenoid were observed. In the case of Rhodospirillum rubrum S1, on the other hand, the EET pathway of S1 → Qy upon excitation of carotenoid was closed, whereas reverse energy transfer from bacteriochlorophyll to carotenoid was clearly observed upon excitation of bacteriochlorophyll. The role of carotenoids in the light-harvesting complexes is discussed in terms of their conjugation length.

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