Dinuclear Ru/Ni, Ir/Ni, and Ir/Pt complexes with bridging phenanthroline-5,6-dithiolate: synthesis, structure, and electrochemical and photophysical behavior.

We report the synthesis and full characterization of dinuclear complexes with the bridging ligand phenanthroline-5,6-dithiolate (phendt(2-)) featuring the Ru(bpy)2 or Ir(ppy)2](+) fragment at the diimine donor center and the Ni(dppe) or Pt(phen) complex moiety at the dithiolate group. The molecular structures of the mononuclear complexes [(C5H5)2Ti(S,S'-phendt)] and (ppy)2Ir{N,N'-phendt-(C2H4CN)2} as well as the dinuclear complex (C5H5)(PPh3)Ru(phendt)Ni(dppe) determined by X-ray diffraction (XRD) studies are compared. Photophysical studies with mononuclear (bpy)2Ru{phendt-(C2H4CN)2} and (ppy)2Ir{phendt-(C2H4CN)2} as well as dinuclear (bpy)2Ru(phendt)Ni(dppe) and (ppy)2Ir(phendt)Ni(dppe) uncovered an effective luminescence quenching in the dinuclear complexes. Lifetime measurements at room temperature, steady-state measurements at low temperature, electrochemical investigations, and DFT calculations provide evidence for a very efficient energy transfer from the Ru/Ir to the Ni complex moiety with a rate constant k > 5 × 10(9) s(-1). In comparison, the [Ru]phendt[Ni] complex displays a higher quenching efficiency with reduced excited state lifetime, whereas the [Ir]phendt[Ni] complex is characterized by an unaltered lifetime of the thermally equilibrated excited state.