Spectroscopic and Electrochemical Properties of Dimeric Ruthenium(II) Diimine Complexes and Determination of Their Excited State Redox Properties

Article abstract of DOI:10.1021/ja00243a023

The complexes Ru(bpy)2(ppz)²⁺ and <(bpy)2Ru(ppz)Ru(bpy)2>⁴⁺, where ppz is the planar ligand 4',7'-phenanthrolino-5',6':5,6-pyrazine, have been prepared and characterized.Resonance Raman spectra establish that the visible spectra of Ru(bpy)2L²⁺ and <(bpy)2Ru-L-Ru(bpy)2>⁴⁺ complexes, where L is a bis-diimine, in general, are composed of MLCT transitions which terminate in the ?^* orbitals localized on the different ligands.The luminescence, which is detectable at room temperature in fluid solutions of both the mono- and bimetallic complexes, can be assigned as a L(?^*) - Ru(II) t2 transition.An approximate but general correlation between the lower energy MLCT absorption maximum and the emission maximum suggests that in many other bimetallic complexes of Ru(II) the emission energy is shifted beyond usual detection limits.Analysis of the emission and electrochemical data indicates that the MLCT states of bridged 2,3-dipyridylpyrazine (dpp) and ppz dimeric complexes are weak reductants but very strong oxidants.The implications of this general pattern of excited state redox potentials are discussed.