Effects of Electron-Withdrawing Substituents (−NO ₂ , −F, and −CN) on Thieno[3,2- b ]thiophene and Benzothiadiazole Polymers for Low-Voltage Organic Transistor and Sensor Applications

OFET-based gas sensors are of significant interest as they offer low-power, flexible, and highly sensitive platforms for real-time gas detection, which make them highly suitable for next-generation environmental and healthcare monitoring applications. Conjugated polymers play a key role in these devices owing to their tunable electronic structures, allowing efficient modulation of charge transport in response to gas exposure. In this study, three thienothiophene (TT)- and benzothiadiazole (BTD)-based donor–acceptor (D–A) conjugated polymers, P1–P3, with different electron-withdrawing groups (–NO2, –F, and –CN), were designed and synthesized. Their optical and electronic properties were systematically investigated using spectroscopic techniques. The polymers were employed as active layers in bottom-gate top-contact (BGTC) OFETs and as sensing layers in ethanol vapor sensors utilizing a natural dielectric, Khaya gum, which enabled low-voltage and low power operation. The p-type polymers exhibited a maximum hole mobility of up to 0.14 cm2 V−1 s−1, while the lowest limit of detection (LOD) toward ethanol reached as low as 430 ppb. These findings underscore the potential of TT- and BTD-based conjugated polymers for high-performance, low-voltage OFET-based gas sensors, offering a promising pathway toward practical real-time gas sensing applications.