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

The synthesis and characterization of mixed ligand 2,2‘;6‘,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 dσ orbital, rather than by manipulation of the π* orbitals on the ligands. The acid−base and electrochemical properties of the compounds are reported also.