Mononuclear and binuclear ruthenium(II) heteroleptic complexes based on 1,10-phenanthroline ligands.: Part II:: Spectroscopic and photophysical study in the presence of DNA

Photophysical and photochemical properties of a series of mononuclear and binuclear ruthenium(II) complexes of phen (phen = 1,10-phenanthroline), in the absence or in the presence of calf-thymus DNA have been investigated by steady-state as well as time-resolved methods. The complexes of this series (see Fig. 1) are [Ru-x(phen)(2x)(L)](2x+) (x = 1 or 2) type, where L is a bpy (4,4'-dimethyl-2,2'-bypiridine, with x = 1) or a bis-bpy covalently linked by flexible chains including either polymethylene groups or polyamine functions (with x = 2). Upon addition of DNA, the most important increasing luminescence and change of emission maxima wavelength are observed for the bimetallic compounds having amine functions in their spacer. A biexponential decay in luminescence is found with emission lifetimes of the complexes upon binding to DNA. Moreover, these complexes induce efficient photo-cleavage of DNA by irradiation at 450 nm. This efficiency is particularly important when the binuclear complexes include amino groups. Topoisomerization experiments have pointed out a similarity between the DNA cleaving ability of these complexes and their intercalation into DNA. Scavenging experiments have shown that the oxidative species involved in DNA cleavage was mainly 10,, via a type 11 mechanism. (C) 2004 Elsevier B.V. All rights reserved.