π-Conjugated Ligand Polymers Entwined around Copper Centres

Abstract

We describe conjugated polymers entwined around Cu1 with alternating alpha-quaterthienyl (poly[Cu(T2)2]) or 3',4',3'''',4''''-tetrahexyl-alpha-sexythienyl (poly[Cu(T3)2]) moieties and 1,10-phenanthroline complexing sites. Our strategy is to synthesise the 2,9-bis(oligothienyl)-1,10-phenanthroline precursors, then to assemble these ligands by means of Cu1 templating followed by electropolymerisation. Poly[Cu(T2)2] shows separate electroactivities for Cu redox centres and conjugated backbones, whereas the electroactivities overlap in the case of poly[Cu(T3)2]. An X-ray absorption study on these polymers in their reduced state at the Cu-K edge identifies, in both cases, four nitrogen atoms as the closest copper(I) neighbours. For poly[Cu(T2)2], the Cu1 environment is a distorted tetrahedron similar to a monomer model compound, but with a slightly higher number of steric constraints. The Cu1 environment for poly[Cu(T3)2] is a less distorted tetrahedron with an unusually short Cu1-N average bond length. Cu1 removal in poly[Cu(T2)2] induces an irreversible collapse of the structure, whereas the reversibility of Cu1 binding is almost perfect for poly[Cu(T3)2], as the hexyl chains prevent irreversible gliding of the wires after copper removal. Combined electrochemical and resistance measurements reveal that the Cu centres in poly[Cu(T2)2] play the role of mechanical support for the structure with no significant electronic interactions with the conjugated backbone, whereas in the case of poly[Cu(T3)2] copper centres contribute to the conductivity of the structure.