Photophysics of Bis-bipyridyl Nitro Complexes of Ruthenium(II) with Pyridine Ligands: Substituent Effects

Emission, excitation spectra, quantum yields, and emission lifetimes are reported for the mixed ligand, bis-(2,2'-bipyridine)ruthenium(II) complexes cis-[Ru(bpy)(2)(L)(NO2)](+) with 4-substituted pyridines as ligands L [isonicotinamide (isnc), 4,4'-bipyridine (bipy), pyridine (py), 4-phenylpyridine (phpy), 1,2-bis(4-pyridyl)ethane (bpa), 4-picoline (mepy), 4-aminopyridine (apy), and 4-dimethylaminopyridine (ampy)] in EtOH-MeOH, 4:1 (V:V), at 77 K. Radiative, k(r,) and nonradiative, k(nr), decay rate constants were determined for the series of complexes, and a linear dependence of In k(nr) on E-00, with E-00 as the 0-0 energy gap determined by emission spectral fitting, was obtained with a slope of -(3.35 +/- 0.23) x 10(-4) cm(-1). A linear correlation of E-00 for cis-[Ru(bpy)(2)(L)(NO2)](+) complexes and Hammett substituent constant c is found.