title: Ligand-selective photodissociation from [Ru(bpy)(4AP)4]2+: a spectroscopic and computational study.
abstract: The new complex [Ru(bpy)(4AP)(4)](2+) (1), where bpy = 2,2'-bipyridine and 4AP = 4-aminopyridine, undergoes selective photodissociation of two 4APs upon light excitation of the metal-ligand-to-ligand charge-transfer (MLLCT) band at 510 nm. The photoproducts of the reaction are mer-[Ru(bpy)(4AP)(3)(H(2)O)](2+) (2a) and trans-(4AP)[Ru(bpy)(4AP)(2)(H(2)O)(2)](2+) (3a). Photodissociation occurs in two consecutive steps with quantum yields of phi(1) = (6.1 +/- 1.0) x 10(-3) and phi(2) = (1.7 +/- 0.1) x 10(-4), respectively. Complex 1 was characterized by combined spectroscopic and theoretical techniques. EXAFS experiments at the Ru K-edge (22 117 eV) of 1 in an aqueous solution gave a Ru-N distance of 2.09 +/- 0.01 A. Photoproducts were characterized by electronic spectroscopy, 1D and 2D NMR, and mass spectrometry. Singlet and triplet excited states of 1 were studied by density functional theory (DFT) and time-dependent DFT for characterizing the optical properties of the complex. In the singlet state, (1)MC (metal-centered) dissociative states lie 0.65 eV above the main (1)MLLCT transition in the visible region of the UV-vis absorption spectrum. In the triplet state, the energy difference between these states is not reduced. However, potential energy curves of singlet and triplet excited states of 1 along the Ru-N(axial 4AP) and Ru-N(equatorial 4AP) stretching coordinates show that the release of the first 4AP may occur from the triplet state by mixing of (3)MLLCT and (3)MC dissociative states. This mixing is favored when the Ru-N(equatorial 4AP) bond is elongated, explaining the formation of the photoproduct 2a.
authors.affiliation: Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.
authors.forename: Luca
authors.initials: L
authors.lastname: Salassa
authors.forename: Claudio
authors.initials: C
authors.lastname: Garino
authors.forename: Giovanni
authors.initials: G
authors.lastname: Salassa
authors.forename: Carlo
authors.initials: C
authors.lastname: Nervi
authors.forename: Roberto
authors.initials: R
authors.lastname: Gobetto
authors.forename: Carlo
authors.initials: C
authors.lastname: Lamberti
authors.forename: Diego
authors.initials: D
authors.lastname: Gianolio
authors.forename: Ranieri
authors.initials: R
authors.lastname: Bizzarri
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Sadler
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D008024:Ligands; D008027:Light; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000528:radiation effects*; D055668:Photochemical Processes; D012428:Ruthenium / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D015082:2,2'-Dipyridyl; D012428:Ruthenium