Intramolecular and lateral intermolecular hole transfer at the sensitized TiO2 interface

Ke Hu, Kiyoshi C.D. Robson, Evan E. Beauvilliers, Eduardo Schott, Ximena Zarate, Ramiro Arratia-Perez, Curtis P. Berlinguette, Gerald J. Meyer

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53 Citations (Scopus)

Abstract

Characterization of the redox properties of TiO2 interfaces sensitized to visible light by a series of cyclometalated ruthenium polypyridyl compounds containing both a terpyridyl ligand with three carboxylic acid/carboxylate or methyl ester groups for surface binding and a tridentate cyclometalated ligand with a conjugated triarylamine (NAr3) donor group is described. Spectroelectrochemical studies revealed non-Nernstian behavior with nonideality factors of 1.37 ± 0.08 for the Ru III/II couple and 1.15 ± 0.09 for the NAr3 •+/0 couple. Pulsed light excitation of the sensitized thin films resulted in rapid excited-state injection (kinj > 10 8 s-1) and in some cases hole transfer to NAr3 [TiO2(e-)/RuIII-NAr3 → TiO 2(e-)/RuII-NAr3•+]. The rate constants for charge recombination [TiO2(e -)/RuIII-NAr3 → TiO2/Ru II-NAr3 or TiO2(e-)/Ru II-NAr3•+ → TiO2/Ru II-NAr3] were insensitive to the identity of the cyclometalated compound, while the open-circuit photovoltage was significantly larger for the compound with the highest quantum yield for hole transfer, behavior attributed to a larger dipole moment change (Δμ = 7.7 D). Visible-light excitation under conditions where the RuIII centers were oxidized resulted in injection into TiO2 [TiO 2/RuIII-NAr3 + hν → TiO 2(e-)/RuIII-NAr3•+] followed by rapid back interfacial electron transfer to another oxidized compound that had not undergone excited-state injection [TiO2(e -)/RuIII-NAr3 → TiO2/Ru II-NAr3]. The net effect was the photogeneration of equal numbers of fully reduced and fully oxidized compounds. Lateral intermolecular hole hopping (TiO2/RuII-NAr3 + TiO 2/RuIII-NAr3•+ → 2TiO 2/RuIII-NAr3) was observed spectroscopically and was modeled by Monte Carlo simulations that revealed an effective hole hopping rate of (130 ns)-1.

Original languageEnglish
Pages (from-to)1034-1046
Number of pages13
JournalJournal of the American Chemical Society
Volume136
Issue number3
DOIs
Publication statusPublished - 22 Jan 2014

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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