Molecularly Imprinted Semiconducting Polymers for Size- and Interaction-Selective Gas Sensors Based on Organic Thin-Film Transistors

Achieving high selectivity among chemically similar analytes remains a critical challenge for organic thin-film transistor (OTFT)-based gas sensors. We report a molecular imprinting strategy that imparts both size- and interaction-selective sensing by covalently incorporating ethanol molecules into acid-cleavable acetal side chains of the semiconducting polymer TAT-2. Subsequent HCl vapor treatment cleaves these side chains, generating subnanometer pores and free aldehyde groups in the resulting polymer TFT-2, as confirmed by FTIR analysis. These structural features facilitate selective diffusion and hydrogen-bonding interactions with small alcohols. TAT-2 and TFT-2 exhibit HOMO energy levels of -5.29 and -5.37 eV, respectively, rendering them stable p-type semiconductors with hole mobilities of ∼10^-4-10^-3 cm² V^-1 s^-1 in OTFTs under nitrogen and ambient air. While TAT-2 OTFTs responded nonselectively to ethanol and other VOCs, TFT-2 devices demonstrated high sensitivities to ethanol (1.11 × 10^-4 ppm^-1) and methanol (0.61 × 10^-4 ppm^-1), but much lower responses to isopropanol (0.11 × 10^-4 ppm^-1), acetone (0.0057 × 10^-4 ppm^-1), and negligible responses to larger or nonpolar VOCs. Unlike TAT-2 devices, which showed current decreases, TFT-2 devices exhibited current increases upon methanol and ethanol exposure, likely due to pore filling that passivates charge-trapping sites and enhances charge transport. This side-chain engineering approach establishes a new paradigm for molecular imprinting in semiconducting polymers, enabling facile device fabrication with functional microstructures for selective analyte recognition.