title: Interfacial electron transfer dynamics following laser flash photolysis of [Ru(bpy)2((4,4'-PO3H2)2bpy)]2+ in TiO2 nanoparticle films in aqueous environments.
abstract: Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru(bpy)(2)(4,4'-(PO(3)H(2))(2)bpy)](2+) surface-bound to TiO(2) (TiO(2)-Ru(II)). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, <τ(bet)>, were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO(2)(e(-))-Ru(3+) → TiO(2)-Ru(2+). The appearance of pH-dependent decreases in the efficiency of formation of TiO(2)-Ru(3+) and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond-microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA. kyleb@email.unc.edu
authors.forename: M Kyle
authors.initials: MK
authors.lastname: Brennaman
authors.forename: Antonio Otávio T
authors.initials: AO
authors.lastname: Patrocinio
authors.forename: Wenjing
authors.initials: W
authors.lastname: Song
authors.forename: Jonah W
authors.initials: JW
authors.lastname: Jurss
authors.forename: Javier J
authors.initials: JJ
authors.lastname: Concepcion
authors.forename: Paul G
authors.initials: PG
authors.lastname: Hoertz
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Traub
authors.forename: Neyde Y Murakami
authors.initials: NY
authors.lastname: Iha
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
mesh_terms: D002384:Catalysis; D004579:Electron Transport; D007834:Lasers; D053758:Nanoparticles / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010777:Photochemistry / Q000379:methods*; D010782:Photolysis; D011720:Pyrazoles / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D011720:Pyrazoles; D011725:Pyridines; D014867:Water; C009495:titanium dioxide; D012428:Ruthenium; D014025:Titanium