Highly Stable Anodic Electrochromic Aromatic Polyamides Containing N,N,N‘,N‘-Tetraphenyl-p-Phenylenediamine Moieties:  Synthesis, Electrochemical, and Electrochromic Properties

A new triphenylamine-containing aromatic diamine, N,N-bis(4-aminophenyl)-N‘,N‘-di(4-methoxylphenyl)-1,4-phenylenediamine (4), was successfully synthesized by the cesium fluoride-mediated condensation of 4-amino-4‘,4‘ ‘-dimethoxytriphenylamine with 4-fluoronitrobenzene, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediate. A series of novel polyamides with pendent 4,4‘-dimethoxy-substituted triphenylamine (TPA) units having inherent viscosities of 0.28−0.80 dL/g were prepared via the direct phosphorylation polycondensation from the diamine (4) and various dicarboxylic acids. All the polymers were amorphous with good solubility in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into tough and flexible polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high softening temperature (242−282 °C), 10% weight-loss temperatures in excess of 510 °C, and char yields at 800 °C in nitrogen higher than 63%. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium−tin oxide (ITO) coated glass substrate exhibited two reversible oxidation redox couples at 0.47−0.51 and 0.82−0.86 V vs Ag/AgCl in acetonitrile solution. The polyamide films revealed excellent stability of electrochromic characteristics, with a color change from colorless or pale yellowish neutral form to green and blue oxidized form at applied potentials ranging from 0.00 to 0.98 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good coloration efficiency of green (CE = 285 cm2/C) and blue (CE = 272 cm2/C) but also exhibited high contrast of optical transmittance change (ΔT %) up to 60% at 430 nm and 73% at 1035 nm for green, and 86% at 850 nm for blue. After over 1000 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.