High contrast ratio and rapid switching electrochromic polymeric films based on 4-(dimethylamino)triphenylamine-functionalized aromatic polyamides

A series of electroactive aromatic polyamides with 4-(dimethylamino)triphenylamine [(NMe2)TPA] units in the backbone were prepared from a newly synthesized diamine monomer, 4,4'-diamino-4 ''-(dimethylamino)triphenylamine, and various aromatic dicarboxylic acids via the phophorylation polyamidation reaction. These polyamides are readily soluble in many organic solvents and can be solution-cast into tough and amorphous films. They had useful levels of thermal stability associated with relatively high glass-transition temperatures (277-298 degrees C), 10% weight loss temperatures in excess of 500 degrees C, and char yields at 800 degrees C in nitrogen higher than 67%. The polymer films showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency, high contrast ratio, and rapid switching time. The optical transmittance change (Delta%T) at 640 nm between the neutral state and the fully oxidized state is up to 88%, and the coloration efficiency is as high as ca. 261 cm(2)/C with high optical density change (delta OD) up to 0.94. The polymers also displayed low ionization potentials as a result of their (NMe2)TPA moieties. Cyclic voltammograms of the polyamide films on the indium-tin oxide (ITO)-coated glass substrate exhibited a pair of reversible oxidation waves with very low onset potential of 0.35 V (vs Ag/AgCl) in acetonitrile solution.