Ultrafast Energy Transfer in Dinuclear Complexes with Bridging 1,10-Phenanthroline-5,6-Dithiolate

We report herein the preparation and characterization of dinuclear complexes with the bridging ligand 1,10-phenanthroline-5,6-dithiolate (phendt^2–) bearing Ru­(bpy)₂ or Ir­(ppy)₂ at the diimine moiety and Ni­(dppe), Ni­(dppf), CoCp, RhCp*, and Ru­(p-Me-ⁱPr-benzene) at the dithiolate unit. In comparison with the mononuclear precursors used in the synthesis, all dinuclear complexes were characterized by absorption and photoluminescence spectroscopy as well as cyclic voltammetry. Because of the beneficial spectral and electrochemical properties of the Ir/Co complex for a light-driven charge separation, this complex was investigated in detail by time-resolved luminescence {nanosecond (ns)-resolution} and transient absorption spectroscopy {femtosecond (fs)-resolution}. All measurements supported by DFT calculations show that the observed effective luminescence quenching by the dithiolate coordinated metal is caused by an ultrafast singlet–singlet Dexter energy transfer.