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      Two-Photon Study on the Electronic Interactions between the First Excited Singlet States in Carotenoid−Tetrapyrrole Dyads

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      The Journal of Physical Chemistry A
      American Chemical Society (ACS)

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          Abstract

          Electronic interactions between the first excited states (S(1)) of carotenoids (Car) of different conjugation lengths (8-11 double bonds) and phthalocyanines (Pc) in different Car-Pc dyad molecules were investigated by two-photon spectroscopy and compared with Car S(1)-chlorophyll (Chl) interactions in photosynthetic light harvesting complexes (LHCs). The observation of Chl/Pc fluorescence after selective two-photon excitation of the Car S(1) state allowed sensitive monitoring of the flow of energy between Car S(1) and Pc or Chl. It is found that two-photon excitation excites to about 80% to 100% exclusively the carotenoid state Car S(1) and that only a small fraction of direct tetrapyrrole two-photon excitation occurs. Amide-linked Car-Pc dyads in tetrahydrofuran demonstrate a molecular gear shift mechanism in that effective Car S(1) → Pc energy transfer is observed in a dyad with 9 double bonds in the carotenoid, whereas in similar dyads with 11 double bonds in the carotenoid, the Pc fluorescence is strongly quenched by Pc → Car S(1) energy transfer. In phenylamino-linked Car-Pc dyads in toluene extremely large electronic interactions between the Car S(1) state and Pc were observed, particularly in the case of a dyad in which the carotenoid contained 10 double bonds. This observation together with previous findings in the same system provides strong evidence for excitonic Car S(1)-Pc Q(y) interactions. Very similar results were observed with photosynthetic LHC II complexes in the past, supporting an important role of such interactions in photosynthetic down-regulation.

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          Author and article information

          Journal
          The Journal of Physical Chemistry A
          J. Phys. Chem. A
          American Chemical Society (ACS)
          1089-5639
          1520-5215
          April 28 2011
          April 28 2011
          : 115
          : 16
          : 4082-4091
          Article
          10.1021/jp1122486
          21417489
          c4fea22b-306e-4f18-8d07-83a516fdef37
          © 2011
          History

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