Spectroscopy and photophysics of binuclear ruthenium(II) complexes with nitrogen-containing heterocyclic bridging ligands

The absorption spectra at room temperature and the spectra, the quantum yields, and the decay times of the luminescence at 77 K of binuclear complexes [X(bpy)2Ru(BL)Ru(bpy)2Cl]2+ (bpy = 2,2′-bipyridyl; X = Cl, BL = pyrazine, 4,4′-bipyridyl, trans-1,2-bis(4-pyridyl)ethylene, and trans-1,2-bis(4-pyridyl)ethane and X = NO2, BL = 4,4′-bipyridyl) in alcoholic (4: 1 EtOH-MeOH) solutions are studied. It is shown that the interaction between the metal centers (MCs) of the complexes affects the characteristics of the electronically excited states (EESs) of each of them and facilitates increasing the transition dipole moment Ru(dπ)→BL(π*). The deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer (3MLCT) state of the complexes are determined. In an asymmetric binuclear complex, the energy transfer from MC(NO2) to MC(Cl) is revealed, with the rate constant of this transfer being not smaller than 3.2 × 1010 s−1.