title: Unusual photophysical properties of a ruthenium(II) complex related to [Ru(bpy)2(dppz)]2+.
abstract: A new ruthenium polypyridyl complex, [Ru(bpy)(2)(dpqp)](2+) (bpy = 2,2'-bipyridne; dpqp = pyrazino[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline), shows strong luminescence in water at room temperature, a behavior that is strikingly different from that of the nonemissive "DNA light-switch" prototype [Ru(bpy)(2)(dppz)](2+) (dppz = dipyrido[3,2-a:2'-3'-c]phenazine) under similar conditions. Variation of the absorption and emission spectra of [Ru(bpy)(2)(dpqp)](2+) as a function of the pH is consistent with the occurrence of two ground-state protonation steps associated with the dpqp ligand and an apparent pK(a)* of 2.1. Electrochemistry and theoretical calculations indicate that the lowest unoccupied molecular orbital (LUMO) of [Ru(bpy)(2)(dpqp)](2+) is localized on the distal portion of the dpqp ligand and lies at a lower energy than the dppz-based LUMO of [Ru(bpy)(2)(dppz)](2+). The combination of its strong DNA binding affinity and relatively long-lived triplet metal-to-ligand charge-transfer excited state in an aqueous solution results in more efficient DNA photocleavage by [Ru(bpy)(2)(dpqp)](2+) than [Ru(bpy)(2)(dppz)](2+).
authors.affiliation: Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Sun
authors.forename: Sibrina N
authors.initials: SN
authors.lastname: Collins
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Joyce
authors.forename: Claudia
authors.initials: C
authors.lastname: Turro
mesh_terms: D000818:Animals; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D053837:DNA Cleavage; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010777:Photochemistry; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D009942:Organometallic Compounds; D012428:Ruthenium; D004247:DNA; C427203:calf thymus DNA