Concept of Triphenylamine Main Chains with Dual Electroactive Nitrogen Centers toward Record-High Stable Electrochromic Polyamides

Two novel electrochromic (EC) polyamides (PAs) with dual electroactive nitrogen sites, IA and IB, were synthesized from 4,4′-dicarboxydiphenyl ether with N,N′-bis(4-aminophenyl)-N,N′-bis(2,4-dimethoxyphenyl)benzene-1,4-diamine (2) and N,N′-bis(4-aminophenyl)-N,N′-bis(4-methoxyphenyl)-2,5-dimethoxybenzene-1,4-diamine (4), respectively. IA demonstrated superior EC performances, including multiple color changes, intense absorption in the near-infrared (NIR) region, fast switching speed, and exceptional EC stability (after 16,000 switching cycles in the first oxidation stage, only 4.0% coloration efficiency (CE) decay at 1016 nm). The high EC stability of IA could originate from the resonance effect between the different redox states and the effect of electron-donating dimethoxy substituents. Although the isomeric IA and IB contain the same number of electron-donating methoxy substituents and electroactive nitrogen centers, IA⁺ is significantly more stable than IB⁺ due to the steric hindrance of the ortho-substituents (methoxy groups) at the electroactive nitrogen centers, which hinders the resonance effect of the electroactive centers for IB⁺. The steric hindrance for IB increases the oxidation potential and a broader NIR absorption. Notably, the resonance effect of the oxidized electroactive centers plays a crucial role in stabilizing cation radicals. Moreover, IA and IB exhibit strong absorption properties in the NIR and visible regions in the first oxidation state, indicating their substantial potential applications in smart windows, EC displays, and other high-performance optoelectronic devices.