Electronic structures, DNA-binding and related properties of complexes [Ru(bpy) 2L] 2+ (L=ip, pip, hpip)

Abstract

Theoretical and experimental studies on the electronic structures, trend in DNA-binding and related properties of a series of Ru(II) polypyridyl complexes [Ru(bpy) 2L] 2+ (L=ip, pip, hpip) have been carried out (bpy=2,2′-bipyridine; ip=imidazo[4,5-f] [1,10]-phenanthroline; pip=2-phenylimidazo [4,5-f][1,10]-phenanthroline; hpip=2-(hydroxyphenyl)imidazo[4,5-f] [1,10]-phenanthroline). The theoretical calculations were performed applying the density functional theory (DFT) method, and the DNA-binding and the related properties of the complexes were measured with an electronic absorption, emission spectroscopy, cyclic voltammetry and so on. Some interesting electronic structural characteristics of these complexes were revealed. First, the electronic structures of complexes [Ru(bpy) 2pip] 2+ 2 and [Ru(bpy) 2hpip] 2+ 3 are quite different from those of the well-known parent complex [Ru(bpy) 3] 2+ and [Ru(bpy) 2ip] 2+ 1 in the occupied frontier molecular orbitals. Second, the HOMO and NHOMO energies of the complexes obviously increase from 1 to 3, whereas their LUMO energies are not obviously varied. Third, the effect of intra-molecular hydrogen bond in complex 3 plays a very important role, it not only enlarges the planarity area of its main ligand, but also makes its LUMO energy reduce to be lower than that of 2. These electronic structural characteristics can be used to reasonably explain the experimental trend in DNA-binding affinities, as well as spectral and electrochemical properties of the complexes.