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Ultrafast Dynamics of meso-Tetraphenylmetalloporphyrins: The Role of Dark States

Authors

  • Dr. Yu Liang,

    1. Institute for Physical Chemistry and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 2, 76131 Karlsruhe (Germany)
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  • Maximilian Bradler,

    1. Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität, Oettingenstraße 67, 80538 München (Germany)
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  • Dr. Melanie Klinger,

    1. Institute for Physical Chemistry and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 2, 76131 Karlsruhe (Germany)
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  • Dr. Oliver Schalk,

    1. Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität, Oettingenstraße 67, 80538 München (Germany)
    2. Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, 106 91 Stockholm (Sweden)
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  • Mihaela Carmen Balaban,

    1. Institute for Nanotechnology and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT) (Germany)
    2. Present address: Aix Marseille Université, CNRS, iSm2 UMR 7313, 13397 Marseille (France)
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  • Prof. Dr. Teodor Silviu Balaban,

    1. Institute for Nanotechnology and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT) (Germany)
    2. Present address: Aix Marseille Université, CNRS, iSm2 UMR 7313, 13397 Marseille (France)
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  • Prof. Dr. Eberhard Riedle,

    1. Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität, Oettingenstraße 67, 80538 München (Germany)
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  • Dr. Andreas-Neil Unterreiner

    Corresponding author
    1. Institute for Physical Chemistry and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 2, 76131 Karlsruhe (Germany)
    • Institute for Physical Chemistry and Center for Functional Nanostructures, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 2, 76131 Karlsruhe (Germany)

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Abstract

Studying the relaxation pathways of porphyrins and related structures upon light absorption is crucial to understand the fundamental processes of light harvesting in biosystems and many applications. Herein, we show by means of transient absorption studies, following Q- and Soret-band excitation, and ab initio calculations on meso-tetraphenylporphyrinato magnesium(II) (MgTPP) and meso-tetraphenylporphyrinato cadmium(II) (CdTPP) that electronic relaxation following Soret-band excitation of porphyrins with a heavy central atom is mediated by a hitherto disregarded dark state. This accounts for an increased rate of internal conversion. The dark state originates from an orbital localized at the central nitrogen atoms and its energy continuously decreases along the series from magnesium to zinc to cadmium to below 2.75 eV for CdTPP dissolved in tetrahydrofuran. Furthermore, we are able to directly trace fast intersystem crossing in the cadmium derivative, which takes place within (110±20) ps.

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