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 (phendt2–) featuring the [Ru­(bpy)2]2+ or Ir­(ppy)2]+ fragment at the diimine donor center and the [Ni­(dppe)]2+ or [Pt­(phen)]2+ 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}]­(PF6) as well as the dinuclear complex [(C5H5)­(PPh3)­Ru­(phendt)­Ni­(dppe)]­(PF6) determined by X-ray diffraction (XRD) studies are compared. Photophysical studies with mononuclear [(bpy)2Ru­{phendt-(C2H4CN)2}]2+ and [(ppy)2Ir­{phendt-(C2H4CN)2}]+ as well as dinuclear [(bpy)2Ru­(phendt)­Ni­(dppe)]2+ 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 × 109 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.