PHOTOPHYSICS OF BIFUNCTIONAL RU(II) COMPLEXES BEARING AN AMINOQUINOLINE ORGANIC UNIT - POTENTIAL NEW PHOTOPROBES AND PHOTOREAGENTS OF DNA

[Ru(BPY)(2)POQ-Nmet](2+) and [Ru(TAP)(2)POQ-Nmet](2+) (1 and 3) are bi functional complexes composed of a metallic unit linked by a flexible chain to an organic unit. They have been prepared as photoprobes or ph otoreagents of DNA. In this work, the spectroscopic properties of thes e bifunctional complexes in the absence of DNA are compared with those of the monofunctional analogues [Ru(BPY)(2)Phen](2+), [Ru(BPY)(2)acPh en](2+), [Ru(TAP)(2)Phen](2+), and [Ru(TAP)(2)acPhen](2+) (2 and 4). T he electrospray mass spectrometry and absorption data show that the qu inoline moiety exists in the protonated and nonprotonated form. Althou gh the bifunctional complex containing 2,2'-bipyridine (BPY) ligands e xhibits photophysical properties similar to those of the monofunctiona l compounds, the bifunctional complex with 1,4,5,8-tetraazaphenanthren e (TAP) ligands behaves quite differently. It has weaker relative emis sion quantum yields and shorter luminescence lifetimes than the monofu nctional TAP analogue when the quinoline unit is nonprotonated. This i ndicates an efficient intramolecular quenching of the (MLCT)-M-3 (meta l to ligand charge transfer) excited state of the TAP metallic moiety. When the organic unit is protonated, there is no internal quenching. In organic solvent, the nonquenched excited metallic unit (bearing a p rotonated quinoline) and the quenched one (bearing a nonprotonated org anic unit) are in slow equilibrium as compared to the lifetime of the two emitters. In aqueous solution this equilibrium is faster and is ca talysed by the presence of phosphate buffer. Flash photolysis experime nts suggest that the intramolecular quenching process originates from a photoinduced electron transfer from the nonprotonated quinoline to t he excited Ru(TAP)(2)(2+) moiety.