Substituents and Resonance Effects on the Electrochemical Stability of Polyelectrochromic Triarylamine-Based Polymers

Abstract

Two polyamides (PAs) (PA1 and PA2) with three electroactive nitrogen atoms within triphenylamine (TPA)-containing structures were synthesized from two diamine monomers, 4,4′-bis[(2,4-dimethoxyphenyl)(4-aminophenyl)amino]-2″,4′′-dimethoxytriphenylamine (1-NH2) or 4,4′-bis(4-aminophenyl(4-methylphenyl)amino)-4′-methyltriphenylamine (2-NH2), and dicarboxylic acids via a phosphorylation polyamidation technique. PA1 exhibited highly integrated electrochromic performances, including multiple color changes (colorless to grass green, green, and blue), fast response speed (7.7/2.6 s at 422 nm for the first electrochromic process), high contrast of optical transmittance change (ΔT = 54% at 422 nm at the first oxidation stage), and excellent electrochromic stability. Introducing electron-donating ortho and para methoxy substituents and three electroactive nitrogen centers could effectively increase the electrochromic stability of the resulting PA1. At the first oxidation stage, PA1 exhibited the highest electrochromic stability (only 4.1 and 2.5% decay of its coloration efficiency (CE) at 422 and 1252 nm after 15,000 switching cycles, respectively) compared to all other TPA-based polymers. It was noteworthy for the first time that the polymers containing more electroactive nitrogen centers reveal longer wavelength absorption in the near-infrared (NIR) region at the first oxidation stage due to cation radical delocalization. The delocalization could facilitate electrochromic stability, and the relationship between the structures and electrochromic stability for these TPA-based polymers was also investigated. In addition, these PAs exhibited good solubility in many solvents and could be solution-cast into flexible films. They showed good thermal stability with glass transition temperatures ranging from 236 to 278 °C and 10% weight loss in nitrogen at temperatures above 425 °C.