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 [Rux(phen)2x(L)]^2x+ (x = 1 or 2) type, where L is a bpy (4,4ʹ-dimethyl-2,2ʹ-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 photocleavage 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 1O2, via a type II mechanism.