Photoinduced energy transfer coupled to charge separation in a Ru(II)-Ru(II)-acceptor triad

Magnus Borgström, Sascha Ott, Reiner Lomoth, Jonas Bergquist, Leif Hammarström, Olof Johansson

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Abstract

The bichromophoric system Ru-Ruc-Pl ([(bpy)3Ru-Ph- Ru(dpb)(Metpy-Pl)][PF6]3, where bpy is 2,2′-bipyridine, Hdpb is 1,3-di(2-pyridyl)-benzene, Metpy is 4′-methyl-2,2′:6′,2″-terpyridine and Pl is pyromellitimide) containing two Ru(II) polypyridyl chromophores with a N 6 and a N5C ligand set, respectively, was synthesized and characterized. Its photophysical properties were investigated and compared to those of the monochromophoric cyclometalated complexes Ruc-Pl ([Ru(dpb)(Metpy-Pl)][PF6]), Ruc-φ-Pl ([Ru(dpb)(ttpy-Pl)][PF6], ttpy is 4′-p-tolyl-2,2′: 6′,2″-terpyridine), Ruc-φ ([Ru(dpb)(ttpy)][PF 6]), and Ruc ([Ru(dpb)(Metpy)][PF6]). Excitation of the Ruc-unit in the dyads leads to oxidative quenching, forming the RucIII-φ-Pl•- and Ru cIII-Pl•- charge-separated (CS) states with kfET = 7.7 × 107 s-1 (CH3CN, 298 K) in the tolyl-linked Ruc-φ-Pl and k fET = 4.4 × 109 s-1 (CH 2Cl2, 298 K) in the methylene-linked Ruc-Pl. In the Ru-Ruc-Pl triad, excitation of the Ruc chromophore leads to dynamics similar to those in the Ruc-Pl dyad, generating the RuII-RucIII-Pl•- CS state, whereas excitation of the Ru unit results in an initial energy transfer (k EnT = 4.7 × 1011 s-1) to the cyclometalated Ruc unit. Subsequent electron transfer to the Pl acceptor results in the formation of the same RuII-Ru cIII-Pl•- CS state with kf ET = 5.6 × 109 s-1 that undergoes rapid recombination with kbET = 1 × 1010 s -1 (CH2Cl2, 298 K). The fate of the Ru II-RucIII-Pl•- CS state upon a second photoexcitation was studied by pump-pump-probe experiments in an attempt to detect the fully charge-separated RuIII-Ruc II-Pl•- state.

Original languageEnglish
Pages (from-to)4820-4829
Number of pages10
JournalInorganic Chemistry
Volume45
Issue number12
DOIs
Publication statusPublished - Jun 12 2006

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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