Bithiophene-bithiazole copolymers and their metal complexes

This paper describes the synthesis, electrochemistry, and electronic properties of 5,5'-di(2-thienyl)-2,2'-bithiazole, 5,5'-di(2-thienyl)-4,4'-dimethyl-2,2'-bithiazole, and 5,5'-bis(3-methoxy-2-thienyl)-4,4'-dimethyl-2,2'-bithiazole, their complexes with Ru(bpy)(2)(2+) and Os(bpy)(2)(2+), and electrochemically prepared polymer films of these free and complexed ligands. The uncomplexed ligands and their polymers have electrochemical and electronic properties that are similar to the corresponding thiophene homo-oligomers and polymers, with the substituents exhibiting predictable effects. The metal complexes exhibit reversible M(III/II) electrochemistry and ligand based reductions, and can be electrochemically polymerized under suitably anhydrous conditions. BF(3)-Et(2)O was found to facilitate polymerization, either as the electrochemical solvent or when added to a CH(3)CN based solution. The resulting metallopolymers exhibit reversible M(III/II) electrochemistry with no indication of electronic coupling between metal sites. Oxidation of the polymer backbone results in a rapid loss of conjugation, but does not significantly affect the metal and bipyridine based electrochemistry, nor the reductive electrochemistry of the backbone. It is concluded that polymer oxidation is localized on the bithiophene linkages, while its reduction is localized on the bithiazole segments. The evident localization of the backbone pi -orbitals is presumed to be responsible for the lack of significant electronic coupling of metal centres through the polymer backbone.