Mononuclear and binuclear ruthenium(II) heteroleptic complexes based on 1,10-phenanthroline ligands: Part I: synthesis, spectroscopic and photophysical study

A series of mononuclear and binuclear ruthenium(II) heteroleptic complexes as potential sensitizers for DNA photocleavage has been synthesized and characterized. This series based on 1,10-phenanthroline (phen) ligands is of the type [Rux(phen)2x(L)]2x+ (x=1 or 2). L is dmbpy (dmbpy=4,4′-dimethyl-2,2′-bipyridine) or a bridging ligand of bis-bpy type linked by a polymethylene or polyamine chain (see Scheme 1). The spectroscopic and photophysical properties determined in Tris buffer and ethanol as well as the redox potentials are not affected by the complex nuclearity. Therefore, the two metallic sites of the binuclear complexes are not electronically coupled neither in the ground state nor in the excited state. The results also show that the luminescence properties of the complexes in Tris buffer solution are sensitive to the presence of amine functions in the linker chain. In particular, the 3MLCT excited state is better stabilized in the case of the binuclear complex including three amine groups. Improvement of binding with the possibility of a double-interaction of these systems with DNA is discussed.