Bi-1,10-phenanthrolines and Their Mononuclear Ru(II) Complexes

A series of four biphen (phen = 1,10-phenanthroline) ligands, 2,2‘-biphen (1), 3,3‘-biphen (2), 2,2‘-dimethylene-3,3‘-biphen (3), and 2,3‘-dimethylene-3,2‘-biphen (4), is prepared by coupling and Friedländer methodology. The corresponding mononuclear Ru(II) complexes, [Ru(1−4)(Mebpy)2]2+ where Mebpy = 4,4‘-dimethyl-2,2‘-bipyridine, are prepared. These complexes show long wavelength electronic absorptions at 441−452 nm and emissions at 622−641 nm. Metal-based oxidations occur in the range 1.18−1.21 V, and ligand-based reductions, at −1.20 to −1.30 V. The addition of Zn2+, Cd2+, or Hg2+ ions results in a strong enhancement and red shift of the luminescence of complex Ru-3. Alkali and alkaline earth metal ions barely affect the luminescence of Ru-3 while transition metal ions such as Co2+, Cu2+, Ni2+, and Mn2+ lead to efficient quenching of the Ru-3 luminescence. The luminescence of Ru-2 and Ru-4 is quenched in the presence of Zn2+ because of a conformationally induced reduction in electronic communication between the two phen halves of the ligand. The addition of Zn2+ has only a slight effect on the luminescence of Ru-1 because of steric hindrance toward complexation.