Conjugated polyrotaxanes incorporating mono- or divalent copper complexes

A conjugated polyrotaxane poly[Cu(1.2)(+)] has been synthesized via copper(I)-templated strategy and electropolymerization. The polymer backbone contains alternating quaterthiophene moieties and 1,10-phenanthroline complexes. It is threaded by coordinating cyclic units. Copper(I) binding was reversible only if lithium cation was present during copper removal, as a labile scaffolding, maintaining the topography of the free coordinating sites and of the organic matrix, as demonstrated by H-1 NMR studies on monomer precursors. Electrochemistry has been coupled with X-ray absorption spectroscopy at the Cu K edge to study the interactions between the complexed copper centers and the conjugated backbone. The spectra of poly[Cu(1.2)(n+)] in various oxidation states have been analyzed and compared with those of monomeric model compounds. For all of the samples four nitrogen atoms are the closest neighbors. No dramatic geometric and electronic differences exist between monomeric and polyrotaxane Cu(I) binding sites. However, for the copper(I) rotaxane the closest neighbors were unambiguously split into two subshells of two nitrogen atoms, reflecting higher steric constraints around the copper center in the polymetallorotaxane. For the divalent complexed copper-rotaxane, these steric constraints partially prevent the flattening of the coordination tetrahedron expected when passing from Cu(I) to Cu(II) and the Cu(II)-N distances are significantly longer in the polymer (2.04 Angstrom) than in the model compound (2.00 Angstrom).