Département de chimie moléculaire

New tridentate polypyridine ligands, made of terpyridine chelating subunits connected to various substituted 2-pyrimidinyl groups, and their homoleptic and heteroleptic Ru(II) complexes were prepd. and characterized. The new metal complexes are [(R-pm-tpy)Ru(tpy)]2+ and [Ru(tpy-pm-R)2]2+ (tpy = 2,2':6',2''-terpyridine; R-pm-tpy = 4'-(2-pyrimidinyl)-2,2':6',2''-terpyridine with R = H, Me, Ph, perfluorophenyl, chloride, and cyanide). Two of the new metal complexes also were characterized by x-ray anal. In all the R-pm-tpy ligands, the pyrimidinyl and terpyridyl groups are coplanar, allowing an extended delocalization of acceptor orbital of the metal-to-ligand charge-transfer (MLCT) excited state. The absorption spectra, redox behavior, and luminescence properties of the new Ru(II) complexes were studied. In particular, the photophys. properties of these species are significantly better compared to those of [Ru(tpy)2]2+ and well comparable with those of the best emitters of Ru(II) polypyridine family contg. tridentate ligands. Reasons for the improved photophys. properties lie at the same time in an enhanced MLCT-MC (MC = metal centered) energy gap and in a reduced difference between the min. of the excited and ground states potential energy surfaces. The enhanced MLCT-MC energy gap leads to diminished efficiency of the thermally activated pathway for the radiationless process, whereas the similarity in ground and excited-state geometries causes reduced Franck Condon factors for the direct radiationless decay from the MLCT state to the ground state of the new complexes in comparison with [Ru(tpy)2]2+ and similar species. [on SciFinder(R)]