Synthesis and characterization of light-emitting main-chain metallo-polymers containing bis-terpyridyl ligands with various lateral substituents

A series of conjugated monomers (5a-5d) with various lateral substituents were symmetrically synthesized by the Sonogashira coupling reaction, in which central aromatic units (i.e. 9,9-dipropylfluorenes) were linked to 2,2′:6′,2′-terpyridyl (tpy) units via phenylene/ethynylene fragments. These light-emitting monomers were further reacted with zinc(II) ions and subsequently anion exchanged to produce supramolecular main-chain metallo-polymers (6a-6d). The formation of polymers 6a6d was confirmed by the increased viscosities (up to 1.5-1.83 times) relative to those of their analogous monomers. The results of ¹H NMR titration and UV-Vis spectral titration revealed a detailed complexation process of metallo-polymers by varying the molar ratios of zinc(II) ions to monomers. After coordination with zinc(II) ions, the luminescent and thermal properties of the polymers were enhanced by the formation of metallo-supramolecular structures in contrast to their monomer counterparts. PLED devices employing these metallo-polymers as emitters gave yellow to orange electroluminescence (EL) emissions with turn-on voltages around 6 V. The maximum power efficiency, external quantum yield, and brightness of the PLED device containing polymer 6c were 0.33 cd A^-1 (at 14 V), 1.02%, and 931 cd m^-2 (at 14 V), respectively.