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-(PBu3)(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) (PEt3)(2)(C C)(2)R-(C C)(2)Pt(Ph)(PEt3)(2)] and [MeHg(C C)(2)R(C C)(2)HgMe] as well as the group 11 gold(I) congener [(PPh3)-Au(C C)(2)R(C C)(2)Au(PPh3)]. 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.