Synthesis and Electrochemical Properties of Novel Aromatic Poly(amine−amide)s with Anodically Highly Stable Yellow and Blue Electrochromic Behaviors

Abstract

A new triphenylamine-containing aromatic diamine, 4,4′-bis[4-aminophenyl(4-methoxyphenyl)amino)]-4′′-methoxytriphenylamine (5), was successfully synthesized by the Ullmann reaction of 4,4′-dibromo-4′′-methoxytriphenylamine (2) with 4-methoxy-4′-nitrodiphenylamine (3), followed by palladium-catalyzed hydrazine reduction of the dinitro (4) intermediate. A series of novel polyamides having inherent viscosities of 0.22−0.64 dL/g were prepared via the direct phosphorylation polycondensation from the diamine 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 polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high softening temperature (200−244 °C), 10% weight-loss temperatures in excess of 460 °C, and char yields at 800 °C in nitrogen higher than 55%. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Oxidation of compound 4 was proved by using an optically transparent thin-layer electrode (OTTLE) cell coupled with UV−vis/NIR spectroscopy. Reversibility of the first oxidation was up to 99%, second oxidation was 94%, and third oxidation was 80%. Polyamide Ic shows the reversibility of the first oxidation was up to 100%, second oxidation was 99%, and third oxidation was 75%. Cyclic voltammograms of the polyamide films cast onto an indium−tin oxide (ITO)-coated glass substrate exhibited three reversible oxidation redox couples (E1/2) at 0.39−0.47, 0.64−0.72, and 1.02−1.13 V vs Ag/AgCl in acetonitrile solution, and polyamide Ie showed additional fourth reversible oxidation redox couples at 1.07 V. The polyamide films revealed excellent reversible stability of anodic electrochromic characteristics with a color change from the colorless or pale yellowish neutral form to yellow and blue oxidized form at applied potentials ranging from 0.00 to 0.80 V. These electrochromic materials not only showed good coloration efficiency of yellow (CE = 203 cm2/C) and blue (CE = 194 cm2/C) but also exhibited high contrast of optical transmittance change (ΔT %) up to 59% at 443 nm for yellow and 79% at 1080 nm for blue. After over 500 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.