title: Photoinduced energy transfer coupled to charge separation in a Ru(II)-Ru(II)-acceptor triad.
abstract: The bichromophoric system Ru-Ru(C)-PI ([(bpy)3Ru-Ph-Ru(dpb)(Metpy-PI)][PF6]3, where bpy is 2,2'-bipyridine, Hdpb is 1,3-di(2-pyridyl)-benzene, Metpy is 4'-methyl-2,2':6',2' '-terpyridine and PI is pyromellitimide) containing two Ru(II) polypyridyl chromophores with a N6 and a N5C ligand set, respectively, was synthesized and characterized. Its photophysical properties were investigated and compared to those of the monochromophoric cyclometalated complexes Ru(C)-PI ([Ru(dpb)(Metpy-PI)][PF6]), Ru(C)-phi-PI ([Ru(dpb)(ttpy-PI)][PF6], ttpy is 4'-p-tolyl-2,2':6',2' '-terpyridine), Ru(C)-phi ([Ru(dpb)(ttpy)][PF6]), and Ru(C) ([Ru(dpb)(Metpy)][PF6]). Excitation of the Ru(C) unit in the dyads leads to oxidative quenching, forming the Ru(C)(III)-phi-PI*- and Ru(C)(III)-Pl.- charge-separated (CS) states with k(f)(ET) = 7.7 x 10(7) s(-1) (CH3CN, 298 K) in the tolyl-linked Ru(C)-phi-PI and k(f)(ET) = 4.4 x 10(9) s(-1) (CH2Cl2, 298 K) in the methylene-linked Ru(C)-PI. In the Ru-Ru(C)-PI triad, excitation of the Ru(C) chromophore leads to dynamics similar to those in the Ru(C)-PI dyad, generating the Ru(II)-Ru(C)(III)-PI*- CS state, whereas excitation of the Ru unit results in an initial energy transfer (k(EnT) = 4.7 x 10(11) s(-1)) to the cyclometalated Ru(C) unit. Subsequent electron transfer to the PI acceptor results in the formation of the same Ru(II)-Ru(C)(III)-PI*- CS state with k(f)(ET) = 5.6 x 10(9) s(-1) that undergoes rapid recombination with k(b)(ET) = 1 x 10(10) s(-1) (CH2Cl2, 298 K). The fate of the Ru(II)-Ru(C)(III)-PI*- CS state upon a second photoexcitation was studied by pump-pump-probe experiments in an attempt to detect the fully charge-separated Ru(III)-Ru(C)(II)-PI*- state.
authors.affiliation: Department of Photochemistry and Molecular Science, BMC, Uppsala University, BOX 579, 751 23 Uppsala, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Borgström
authors.forename: Sascha
authors.initials: S
authors.lastname: Ott
authors.forename: Reiner
authors.initials: R
authors.lastname: Lomoth
authors.forename: Jonas
authors.initials: J
authors.lastname: Bergquist
authors.forename: Leif
authors.initials: L
authors.lastname: Hammarström
authors.forename: Olof
authors.initials: O
authors.lastname: Johansson
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004563:Electrochemistry; D004735:Energy Transfer; D007202:Indicators and Reagents; D008027:Light; D013058:Mass Spectrometry; D010777:Photochemistry; D017785:Photons; D012428:Ruthenium / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D007202:Indicators and Reagents; D012428:Ruthenium