Effect of Acetylenic Chain Length on the Tuning of Functional Properties in Fluorene-Bridged Polymetallaynes and Their Molecular Model Compounds

We describe for the first time thermally stable and high-molecular-weight group 10 platinum(II) and group 12 mercury(II) polyyne polymers consisting of 2,7-bis(buta-1,3-diynyl)-9,9-dihexylfluorene linking units trans -[ Pt(PBu 3 ) 2 (C⋮C) 2 R(C⋮C) 2 ] n and [ Hg(C⋮C) 2 R(C⋮C) 2 ] n (R = 9,9-dihexylfluorene-2,7-diyl). The optical absorption and photoluminescence spectra of these carbon-rich metallopolymers were examined and compared with their dinuclear model complexes trans -[Pt(Ph)(PEt 3 ) 2 (C⋮C) 2 R(C⋮C) 2 Pt(Ph)(PEt 3 ) 2 ] and [MeHg(C⋮C) 2 R(C⋮C) 2 HgMe] as well as the group 11 gold(I) congener [(PPh 3 )Au(C⋮C) 2 R(C⋮C) 2 Au(PPh 3 )]. The regiochemical structures of the polymers were studied by NMR spectroscopy and ascertained by single-crystal X-ray structural analysis for the model platinum(II) compound. The heavy-atom effects of group 10−12 transition metals in triplet light energy harvesting and the influence of the C⋮C chain length on the spatial extent of singlet and triplet excitons in metalated systems of the form [ M(C⋮C) m R(C⋮C) m M ] n (M = Pt, Au, or Hg chromophore; m = 1, 2) are systematically characterized. The dependence of the optical energy gap as a function of the acetylenic chain length for the platinum system was probed by both optical methods and molecular orbital calculations, and a linear correlation was derived between the highest occupied molecular orbital−lowest unoccupied molecular orbital gap and 1/ m 2 . An extension of the C⋮C unit gives rise to a state of lower triplet energy and is accompanied by a decrease in the triplet quantum yield and lifetime, in accordance with the energy gap law for the triplet states in metal polyynes.