Multi-Stimuli-Responsive Polyamides Containing Benzophenothiazine Being Sensitive to TNP, Acid, Voltage, and Light

To explore the key factors on the stimuli-responsive behavior of polyamides (PAs), TPA-7-BPT series with TPA-12-BPT series for comparison were synthesized by polycondensation of two kinds of diamines containing benzophenothiazine (BPT) groups fused to triphenylamine (TPA) at different positions and various dicarboxylic acid monomers, respectively. PAs exhibit significant multi-stimuli-response behavior to stimulus sources such as 2,4,6-trinitrophenol (TNP), acid, voltage, and light. The photoluminescence (PL) of TPA-7-BPT-CA and TPA-12-BPT-CA (CA-PAs) can be quenched by TNP effectively with high selectiveness (detection limit for TNP: 138 and 168 nM, respectively). Besides, the PL intensity of TPA-7-BPT-CA could be used for detection of trifluoroacetic acid (TFA) (detection limit of 2.52 μM). Interestingly, the colorless TPA-7-BPT series of polymer films turn blue after acid vapor fumigation. All PA films exhibit electrochromic properties, especially the color of the TPA-12-BPT-OA film maintained electrochemical stability during 3000 s continuous cycles under a potential range of 0–1.1 V with changing back and forth between colorless and deep blue. Furthermore, photoelectronic response occurs in all PA films under xenon lamp irradiation, and the switch ratio Ion/Ioff of TPA-12-BPT-CA is about 30. The multifunctional responsive PAs show a promising application in photoelectric sensors, explosion detectors, memristors, and smart window fields.