Synthesis, electrochemistry and photo-induced electron transfer of unsymmetrical dinuclear ruthenium osmium 2,2′-bipyridine complexes

Four unsymmetric dinuclear ruthenium and osmium complexes, Os(bpy)3-viologen-Ru(bpy)3 (1; bpy = 2,2′-bipyridyl), Ru(bpy)3-viologen-Ru(bpy)(dcbpy)2 (2; dcbpy = 4,4′-dicarboxyl-2,2-bipyridyl), Os(bpy)3-viologen-Ru(bpy)(dcbpy)2 (3) and rotaxane 1⊂CB[7] (CB[7] = cucurbit[7]uril), were successfully synthesized. The NMR, electrochemistry and photochemistry studies of these complexes were performed in non-aqueous solutions. The results show that the CB[7] host mainly locates at the butyl linker part of the osmium side in an acetonitrile solution. This binding lowers the oxidation potential of osmium whereas the oxidation potential of ruthenium does not change. The oxidation potential of ruthenium in complexes 2 and 3 is higher due to the electron withdrawing property of carboxylic anchor groups. Analysis with UV–vis spectra shows the viologen radical formation and reversed process of these complexes in non-aqueous solutions.