Photophysical and photochemical properties of a family of isoelectronic tris chelated ruthenium(ii) aza-/azo-aromatic complexes

We have investigated the electrochemical, spectroscopic and electroluminescent properties of a family of aza-aromatic complexes of ruthenium of type [Ru(bpy/phen)2(L)] 2+ (4d) with three isomeric L ligands, where, bpy 1⁄4 2,20-bipyridine, phen 1⁄4 1,10-phenanthroline and the L ligands are 3-(2-pyridyl) [1,2,4]triazolo[1,5-a]pyridine (L), 3-(2-pyridyl[1,2,3])triazolo[1,5-a]pyridine (L) and 2-(2-pyridyl)[1,2,4] triazolo[1,5-a]pyridine (L). The complexes display two bands in the visible region near 410–420 and 440–450 nm. The complexes are diamagnetic and show well defined H NMR lines. They are electroactive in acetonitrile solution and exhibit a well defined Ru/Ru couple near 1.20 to 1.30 V and 1.40 to 1.50 V due to ligand reduction versus Saturated Calomel Electrode (SCE). The solutions are also luminescent, with peaks are near 600 nm. All the complexes are electroluminescent in nature with peaks lying near 580 nm. L and L ligated complexes with two bpy co-ligands show weak photoluminescence (PL) but stronger electroluminescence (EL) compared to corresponding L ligated analogues.