文摘
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 卤 0.08 for the RuIII/II couple and 1.15 卤 0.09 for the NAr3鈥?/0 couple. Pulsed light excitation of the sensitized thin films resulted in rapid excited-state injection (kinj > 108 s鈥?) and in some cases hole transfer to NAr3 [TiO2(e鈥?/sup>)/RuIII鈥揘Ar3 鈫?TiO2(e鈥?/sup>)/RuII鈥揘Ar3鈥?]. The rate constants for charge recombination [TiO2(e鈥?/sup>)/RuIII鈥揘Ar3 鈫?TiO2/RuII鈥揘Ar3 or TiO2(e鈥?/sup>)/RuII鈥揘Ar3鈥? 鈫?TiO2/RuII鈥揘Ar3] 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 (螖渭 = 7.7 D). Visible-light excitation under conditions where the RuIII centers were oxidized resulted in injection into TiO2 [TiO2/RuIII鈥揘Ar3 + h谓 鈫?TiO2(e鈥?/sup>)/RuIII鈥揘Ar3鈥?] followed by rapid back interfacial electron transfer to another oxidized compound that had not undergone excited-state injection [TiO2(e鈥?/sup>)/RuIII鈥揘Ar3 鈫?TiO2/RuII鈥揘Ar3]. The net effect was the photogeneration of equal numbers of fully reduced and fully oxidized compounds. Lateral intermolecular hole hopping (TiO2/RuII鈥揘Ar3 + TiO2/RuIII鈥揘Ar3鈥? 鈫?2TiO2/RuIII鈥揘Ar3) was observed spectroscopically and was modeled by Monte Carlo simulations that revealed an effective hole hopping rate of (130 ns)鈭?.