Novel aromatic polyimides with pendent triphenylamine units: Synthesis, photophysical, electrochromic properties

A new triphenylamine-containing aromatic diamine, N-(4-triphenylamine-phenyl)-3,5-diaminobenzamide, was synthesized from 4-aminotriphenylamine and 3,5-dinitrobenzoyl chloride. A series of novel aromatic polyimides with pendent triphenylamine units were prepared from the newly synthesized diamine and various aromatic tetracaboxylic acid dianhydrides via polycondensation. These polyimides have inherent viscosities of 0.36–0.47 dl/g. They are readily soluble in many organic solvents, such as NMP, DMAC, DMF and DMSO. They can be solution-cast into transparent, tough, and brittle films with good mechanical properties. These aromatic polyimides display outstanding thermal stabilities, i.e. 10% weight-loss temperatures in excess of 540 °C under nitrogen. Cyclic voltammograms of the polyimide films on an indium-tin oxide (ITO)-coated glass substrate exhibit one pair of reversible redox couple at half-wave oxidation potentials (E1/2) around 0.82–0.850 V, respectively, versus Ag/AgCl in acetonitrile solution. The electrochromic properties were examined by spectroelectrochemical methods. All the polymer films reveal good electrochemical and electrochromic stability by repeatedly switching electrode voltages, with coloration change from the green neutral state to the red or blue oxidized state.