Enhancement of Luminescence Lifetimes of Mononuclear Ruthenium(II)-Terpyridine Complexes by Manipulation of the (sigma)Donor Strength of Ligands

The synthesis and characterization of mixed ligand 2,2ʹ;6ʹ,2"-terpyridine (tpy) ruthenium complexes with 2,6-bis([1,2,4]triazol-3-yl)pyridine, 2,6-bis(5-phenyl-[1,2,4]triazol-3-yl)pyridine, and 2,6-bis([1,2,3,4]tetrazol-5-yl)pyridine are reported. The species are characterized by HPLC, 1H NMR, UV/vis, and emission spectroscopy. The photophysical properties of the complexes are investigated as a function of temperature over the range 80-320 K. The emission lifetime observed for the fully deprotonated compounds at room temperature is about 80 ns. This increase by 2 orders of magnitude with respect to the parent "[Ru(tpy)2]2+" complex is rationalized by an increase in the energy of the metal based d(sigma) orbital, rather than by manipulation of the (pi)* orbitals on the ligands. The acid-base and electrochemical properties of the compounds are reported also.