Redox-active and electrochromic aromatic poly(amide-imide)s with 2,4-dimethoxytriphenylamine chromophores

A dicarboxylic acid monomer with two built-in imide rings, namely 4,4′-bis(4-carboxyphthalimido)-2″,4″-dimethoxytriphenylamine, was synthesized and then directly polymerized with aromatic diamines leading to new series of aromatic poly(amide-imide)s (PAIs) containing the redox-active 2,4-dimethoxy-substituted triphenylamine (TPA) unit. These PAIs were highly soluble in many organic solvents and could be solution-cast into flexible and strong films. The polymers showed excellent thermal stability, up to 400 °C, and displayed glass transition in the range of 266–294 °C. It is noted that the PAIs have an ambipolar character (n- and p-doping processes) and are capable of repeated, stable electrochemical cycling between a neutral form and an oxidized state. For the PAIs containing the TPA unit on both the imide and amide sides, they showed two pairs of reversible oxidation couples and displayed multi-colored electrochromic behavior: pale yellow in the neutral state, yellowish-green in the semioxidized state, and cyan in the fully oxidized state.