Organometallic networks based on 2,2′-bipyridine-containing poly(p-phenylene ethynylene)s

Conjugated polymers that comprise 2,2'-bipyridine moieties as part of the macromolecular backbone represent versatile precursors for the formation of conjugated metallo-supramolecular networks, which are readily accessible via ligand-exchange reactions. Poly{2,2'-bipyridine-5,5'-diylethynylene[2,5-bis(2-ethylhexyl)oxy-1,4-phenylenelethynylene} (BipyPPE(1)) and a statistical copolymer comprising 5,5'diethynyl-2,2'-bipyridine and 1,4-diethynyl-2,5-bis(alkyloxy)benzene moieties (BipyPPE(2)) were synthesized via the Pd-0-catalyzed cross-coupling reaction of 1,4-diethynyl-2,5-bis(octyloxy)benzene, 1,4-bis[(2-ethylhexyl)oxy]-2,5-diiodobenzene, and 5,5'-diethynyl-2,2'-bipyridine. Complexation studies involving these polymers and a variety of transition metals suggest that ligand exchange leads to three-dimensional networks, which feature BipyPPE-metal-BipyPPE cross-links and display interesting optoelectronic properties. It is found that complexes with group 12 d(10) ions (Zn2+ and Cd2+) are emissive, while other transition metals such as Cu+, Co2+, and Ni2+ form nonradiative metal-to-ligand charge-transfer complexes with the polymers.