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 (–NO 2, –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 cm 2 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.