Site Specific Electropolymerization To Form Transition-Metal-Containing, Electroactive Polythiophenes

We report a series of novel bis(salicylidene) metal complexes that undergo oxidative electropolymerization to afford polymers comprised of three different backbone constitutions and a variety of film colors. The ligand architecture, being either N, N ‘-bis(salicylidene)-3,4-diaminothiophene (SALOTH) or N, N ‘-bis(salicylidene)-3‘,4‘-diamino-2,2‘:5‘,2‘‘-terthiophene (BTh−SALOTH), is based upon a thiophene or 2,2‘:5‘,2‘‘-terthiophene core with the imine functionalities attached at the 3-, 4-, or 3‘-,4‘-positions, respectively. This monomer design possesses two switchable polymerization sites that yield phenylene-linked backbones with unblocked salicylidene rings or polythiophenes with the use of methyl blocking groups. As expected with metal centers in direct electronic communication with the polymer chains, the metal type has a dramatic influence over electrochromic properties, with colors unique to each metal being achieved. For example, the Ni-containing films exhibit an orange-to-green redox transition while the Cu-containing analogues display a light green/dark green pair. Details of monomer synthesis as well as full electrochemical details for the monomers and polymers are presented.