Amy Keirstead - Energy transfer, excited-state deactivation, and exciplex formation in artificial caroteno-phthalocyanine light-harvesting antennas.

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      Publication Details (including relevant citation   information):

      Rudi Berera,   Ivo H M van Stokkum,   Gerdenis Kodis,   Amy E Keirstead,   Smitha Pillai,   Christian Herrero,   Rodrigo E Palacios,   Mikas Vengris,   Rienk van   Grondelle,Devens Gust,   Thomas A Moore,   Ana L Moore,   John T M Kennis

      The journal of physical chemistry. B. 06/2007; 111(24):6868-77.

      Abstract:

      We present results from transient absorption spectroscopy on a   series of artificial light-harvesting dyads made up of a zinc   phthalocyanine (Pc) covalently linked to carotenoids with 9, 10,   or 11 conjugated carbon-carbon double bonds, referred to as dyads   1, 2, and 3, respectively. We assessed the energy transfer and   excited-state deactivation pathways following excitation of the   strongly allowed carotenoid S2 state as a function of the   conjugation length. The S2 state rapidly relaxes to the S* and S1   states. In all systems we detected a new pathway of energy   deactivation within the carotenoid manifold in which the S* state   acts as an intermediate state in the S2-->S1 internal   conversion pathway on a sub-picosecond time scale. In dyad 3, a   novel type of collective carotenoid-Pc electronic state is   observed that may correspond to a carotenoid excited state(s)-Pc   Q exciplex. The exciplex is only observed upon direct carotenoid   excitation and is nonfluorescent. In dyad 1, two carotenoid   singlet excited states, S2 and S1, contribute to singlet-singlet   energy transfer to Pc, making the process very efficient   (>90%) while for dyads 2 and 3 the S1 energy transfer channel   is precluded and only S2 is capable of transferring energy to Pc.   In the latter two systems, the lifetime of the first singlet   excited state of Pc is dramatically shortened compared to the 9   double-bond dyad and model Pc, indicating that the carotenoid   acts as a strong quencher of the phthalocyanine excited-state   energy.

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