title: Improving the photosensitizing properties of ruthenium polypyridyl complexes using 4-methyl-2,2'-bipyridine-4'-carbonitrile as an auxiliary ligand.
abstract: We report in this work the synthesis and spectroscopic, electrochemical, spectroelectrochemical, and photophysical characterization of a novel series of ruthenium polypyridyl complexes with 4-methyl-2,2'-bipyridine-4'-carbonitrile (Mebpy-CN) as an auxiliary ligand of general formula [Ru(bpy)3-x(Mebpy-CN)x](PF6)2 (x = 1-3) (with bpy = 2,2'-bipyridine). A significant increase in the lifetime and quantum yield of emission of the lowest (3)MLCT excited state is disclosed when going from x = 1 to x = 3, evidencing an improvement of the photosensitizing properties with respect to [Ru(bpy)3](PF6)2. Furthermore, quenching by molecular oxygen of (3)MLCT excited states of the three complexes produced singlet molecular oxygen ((1)O2) with quantum yield values higher than that of [Ru(bpy)3](2+) in CH3CN. The structure of the complex with x = 1 has been determined by X-ray diffraction. The photoconductivity of ZnO nanowires covered with this same complex is increased by an order of magnitude, pointing to its feasibility as a component of a DSSC. A new dinuclear complex with Mebpy-CN as a bridging ligand has also been prepared and characterized by physicochemical techniques. The derived mixed-valent species of formula [(bpy)2Ru(II)(Mebpy-CN)Ru(III)(NH3)5](5+) displays a considerable metal-metal electronic coupling due to the delocalization effect of a nitrile group in the 4' position of the bpy ring.
authors.affiliation: INQUINOA-CONICET, Instituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 491, (T4000INI) San Miguel de Tucumán, Argentina.
authors.forename: Juan H Mecchia
authors.initials: JH
authors.lastname: Ortiz
authors.forename: Nadia
authors.initials: N
authors.lastname: Vega
authors.forename: David
authors.initials: D
authors.lastname: Comedi
authors.forename: Mónica
authors.initials: M
authors.lastname: Tirado
authors.forename: Isabel
authors.initials: I
authors.lastname: Romero
authors.forename: Xavier
authors.initials: X
authors.lastname: Fontrodona
authors.forename: Teodor
authors.initials: T
authors.lastname: Parella
authors.forename: F Eduardo Morán
authors.initials: FE
authors.lastname: Vieyra
authors.forename: Claudio D
authors.initials: CD
authors.lastname: Borsarelli
authors.forename: Néstor E
authors.initials: NE
authors.lastname: Katz