Evolution of lowest singlet and triplet excited states with transition metals in group 10-12 metallaynes containing biphenyl spacer

A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer trans-[-Pt(PBu ₃)₂C≡C(p-C₆H₄) ₂C≡C-]_n and [-HgC≡C(p-C₆H ₄)₂C≡C-]_n were prepared in good yields by Hagihara's dehydrohalogenation reaction of the corresponding metal chloride precursors with 4,4′-diethynylbiphenyl HC≡C(p-C₆H ₄)₂C≡CH at room temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model complexes trans-[Pt(Ph)(PEt₃)₂C≡ C(p-C₆H₄)₂C≡CPt(Ph)(PEt₃) ₂] and [MeHgC≡C(p-C₆H₄) ₂C≡CHgMe] as well as the group 11 gold(I) counterpart [(PPh₃)AuC≡C(p-C₆H₄)₂C≡ CAu(PPh₃)]. The structural properties of all model complexes have been studied by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) which enables efficient intersystem crossing from the Si singlet excited state to the T₁ triplet excited state.