Development of Semiconducting Polymers with Acid-Cleavable Side Chains for Size-Selective Gas Sensors Based on Organic Thin-Film Transistors

Abstract

Organic thin-film transistor (OTFT) based gas sensors have gained research interests due to their promising performance and potential for integration into flexible and wearable electronic devices, characterized by low cost, light weight, and ease of fabrication. Herein, a series of novel semiconducting polymers with acid-cleavable side chains were synthesized for application as OTFT based gas sensors employing a size-selective approach. We first established a cost-effective and simple synthetic route to obtain acetal substituted thiophene based polymers. Subsequent conversion of acetal side chains to aldehydes was achieved through a simple acid treatment process applied to the coated polymer film by HCl vapor to generate nanopores. The pore sizes could be tuned by varying the lengths of the acetal side chains used. Screening of suitable polymer structures with desired pore sizes and adequate performance was accomplished by altering the acetal side chain lengths and the comonomer units. Overall results revealed that the aldehyde substituted polymer generated by acid treatment to OC21T polymer demonstrated the least sacrifice in OTFT performance upon side chain cleavage and the best stability under ambient conditions, which makes it the optimal candidate for OTFT based gas sensor material among all the polymers synthesized. The resulting aldehyde substituted thiophene based polymer (OCH1T) showed great sensitivity to methanol and ethanol vapors. Slight sensitivity of OCH1T polymer toward isopropanol vapor was also observed, which could be attributed to the grain boundaries of the polymer film. The promising size-selective effect was further confirmed by exposure of the device to other volatile organic compound vapors with various molecular sizes.