An unexpected discovery of a one-pot synthesis for carbazole-based diamine and the electrochromic properties of the derived polymers

Unexpected carbazole-based diamine monomers with a hydroxyl group (E-Cz) or carbonyl group (K-Cz) were successfully synthesized via the hydrogenation reaction of TPA-OBz in one pot, wherein three different kinds of reactions could happen simultaneously, the reduction of the nitro group, the deprotection of the benzyl group, and the coupling reaction of triphenylamine (TPA). The TPA structure thoroughly transforms into two different carbazole structures depending on the hydrogen source, as characterized by IR, NMR, and HRMS analyses. In addition, three related triarylamine-based polyamides (TPA-PA, E-Cz-PA, and co-OH-PA) were also prepared to investigate their electrochromic (EC) performance. The hydroxyl groups of E-Cz provide active sites for the in situ sol-gel reaction with the metal oxide precursor to form hybrid films. The resulting polyamide hybrid films showed effectively improved EC behaviors during the redox process by accelerating the charge transfer due to the donor-acceptor system. Consequently, the polyamide hybrid films possess a lower driving potential, more negligible charge transfer resistance (R-ct), and shorter switching and bleaching response times. The hybrid film (co-Zr20-PA) could be further fabricated into an electrochromic device (ECD) and it demonstrated highly stable switching reversibility over one hundred cyclic switches.