Multifunctional Polyamide Containing Carbazole and Triphenylamine for Electrochromic Smart Windows and TNP Detection

A diamine containing carbazole (Cz) and triphenylamine (TPA) groups, N-(4-(dibenzocarbazol-7-yl) phenyl)-N-(4-aminophenyl) benzene-1,4-diamine (DC7TPA-NH2), is designed and used to form three polyamides (PAs): DC7TPA-SA, DC7TPA-CA, and DC7TPA-OA through linear condensation with three dicarboxylic acids. The photophysical properties including UV–visible absorption spectra and photoluminescence (PL) emission spectra of three PAs are measured. Among them, DC7TPA-CA exhibits an intense PL emission. Upon comparison of UV–visible absorption spectra and PL emission spectra of DC7TPA-CA in diverse solvents, a consistent red shift in the PL emission peak is observed with increasing solvent polarity. Most notably, electrochromic (EC) performance testing revealed that this series of PA films exhibit optical contrast exceeding 90% and have good cycling stability. Specifically, the DC7TPA-SA film shows the highest optical contrast, reaching an impressive 95%. Meanwhile, due to the presence of ether oxygen bonds stabilizing free radicals, DC7TPA-OA demonstrates the best cycling stability among the three PAs. To further investigate its potential for application in EC smart windows (ECSWs), DC7TPA-OA is fabricated into an EC device (ECD). Testing reveals a maximum (initial) optical transmittance change (ΔT) of 88% with only a 3% decay after 240 cycles. Compared to other ECSWs, device of DC7TPA-OA consistently ranks among the top in terms of ΔT performance across all-most categories, whether inorganic ECDs, organic ECDs, COF-based ECDs or composite ECDs, and also demonstrates excellent response times and coloring efficiency (CE). Furthermore, the three PAs exhibit distinct color-changing behaviors, and DC7TPA-CA and DC7TPA-OA maintain a colorless neutral state. This property meets diverse application requirements, especially for ECSWs. Additionally, DC7TPA-CA possesses a high PL quantum efficiency (φ) and sensitivity to trinitrophenol (TNP), making it a promising candidate for nitroexplosive detection.