Synthesis of electroactive and electrochromic poly(amide-imide)s containing diphenylpyrenylamine moieties

A novel dicarboxylic acid monomer bearing two built-in imide rings, namely N,N-bis(4-trimellitimidophenyl)-1-aminopyrene, was synthesized from the condensation of N,N-di(4-aminophenyl)-1-aminopyrene and two equivalent amount of trimellitic anhydride. New poly(amide-imide)s (PAIs) with diphenylpyrenylamine segments were prepared by the direct phosphorylation polyamidation reactions from the newly synthesized diimide-diacid monomer with two different aromatic diamines or from N,N-di(4-aminophenyl)-1-aminopyrene with four different imide ring-preformed dicarboxylic acids. All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. These PAIs showed glass-transition temperatures (Tgs) in the range of 211–352 °C, and they did not show significant weight-loss before 500 °C. Cyclic voltammograms of the PAI films cast onto the indium-tin oxide (ITO)-coated glass substrate revealed reversible electrochemical oxidation processes accompanied with strong color changes from the pale yellow neutral state to the purplish blue oxidized state and the orange reduced state, respectively. Incorporating the diphenylpyrenylamine unit on the amide side of PAIs led to lower oxidation potentials and higher redox reversibility and, thus, better electrochromic performance such as high coloration efficiency, fast switching speed, and high electrochromic stability.