| Summary: | A series of three bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand with terminal triphenylamine (TPA) substituents have been synthesized and characterized for insight into electron transfer reactions at TiO₂ surfaces. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(H₃tctpy)] (pbpy = 6-phenyl-2,2’-bipyridine; H₃tctpy = 4,4’,4”-tricarboxy-2,2’:6’,2”-terpyridine), where an electron-donating group (EDG) or an electron-withdrawing group (EWG) is installed about the anionic ring of the pbpy ligand and methyl groups surrounding the TPA-thiophene bridge. Modification of the anionic ring of the pbpy chelated with EDGs and EWGs enables the modulation of the Ru(III)/Ru(II) redox potential over 140 mV. This property offers the opportunity to turn on and off intramolecular hole transfer. Pulsed light laser excitation of the sensitized thin film resulted in rapid excited state injection and in some cases hole transfer to TPA [TiO₂(e⁻)/Ru(III)−TPA → TiO₂(e⁻)/Ru(II)−TPA･⁺. The rate constants for charge recombination of [TiO₂(e⁻)/Ru(III)−TPA → TiO₂/Ru(II)−TPA and TiO₂(e⁻)/Ru(II)−TPA･⁺ → TiO₂/Ru(II)−TPA] were drastically affected by modification of the bridging unit and can be modulated over 5.2 – 6.2×10⁵ s ⁻¹ and 1.7 – 5.1×10⁴ s⁻¹ respectively. === Science, Faculty of === Chemistry, Department of === Graduate
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