Photophysics of the adsorbed bipyridyl complexes of ruthenium(II) with phosphines

Luminescence of the ruthenium(II) complexes cis-Ru(bpy)2(CN)2 (I), cis-[Ru(bpy)2(PPh3)CN](BF4) (II), and cis-Ru(bpy)(dppe)(CN)2 (III)[bpy=2.2′-bipyridyl, PPh3=triphenylphosphine, dppe=1,2-bis(diphenylphosphino)ethane], adsorbed on silicon oxide (Aerosil) were studied at a temperature of 77 K. The luminescence spectra, decay times, and quantum yields were measured, and the intermolecular rate constants of radiative transitions and nonradiative decay of the excited electronic state with the metal-to-ligand charge transfer (MLCT) were determined. It is found that the adsorption of the complex is accompanied by a decrease in the energy of the radiative MLCT state and by a considerable acceleration of its nonradiative decay. It is concluded that the interaction of the complexes with the surface adsorption centers occurs via formation of a strong hydrogen bond with a hydroxyl-hydrate cover, the interaction of complexes in the 3MLCT state being stronger than in the ground state. The additive (in the number of phosphorus atoms coordinated to the central ruthenium ion), a shift of the absorption and luminescence bands to shorter wavelengths in the sequence of complexes I–III, is retained when the complexes transform from solutions to the absorbed state.