Instruments Microanalysis (C, H, and N) was carried out with a Perkin-Elmer 240Q elemental analyzer. 1 H NMR spectra were recorded on a Varian-500 spectrometer at 25 o C. All chemical shifts are given relative to tetramethylsilane (TMS). Electrospray mass spectra (ES-MS) were recorded on a LCQ system (Finnigan MAT, USA). UV-Vis spectra were recorded on a Perkin-Elmer Lambda 850 spectrophotometer. Emission spectra were recorded on a PerkineElmer LS 55 spectrofluorophotometer at room temperature.

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... Time-resolved emission measurements were conducted on an FLS 920 combined fluorescence lifetime and steady state spectrometer. Quantum yields of luminescence at room temperature were calculated according to literature procedures 1 , compared to [Ru(bpy) 3 ] 2+ (Φ = 0.028 in aerated aqueous solution). 2 Materials EtBr, DAPI, DOPE, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Calf thymus DNA (CT-DNA) were purchased from Sigma. The plasmid pBR322 DNA from MBI Fermentas, the plasmid pEGFP DNA was from Clonetech, and the plasmid pGL3 control vector and luciferase kid were from Promega. Unless otherwise stated, the DNA concentration was expressed in base pairs. All samples were prepared using distilled water that had been passed through a Millipore-Q ultra-purification system. Syntheses The compounds [Ru(bpy) 3 ]Cl 2 ⋅2H 2 O 3 , Ru(DMSO) 4 Cl 2 4 and Ru(bpy) 2 (H 2 bpib)Cl 2 ⋅2H 2 O 5 were Electronic Supplementary Material (ESI) for Chemical Communications This journal is