Oxygen-bearing functionalities enhancing NO2, NH3, and acetone electronic response and response variation by polythiophenes in organic field-effect transistor sensors

Abstract

We investigated the enhanced vapor responses and altered response ratios of a series of thiophene (co)polymers with oxygenated side chains (CH₂OH, linear polyethylene glycol, and crown ether), including the novel poly(3-hydroxymethylthiophene) (PTOH) and other newly synthesized polymers. Hydroxymethyl-containing copolymers had higher mobility compared to poly(3-hexylthiophene) (P3HT). The larger crown ether moiety promotes transistor characteristics of P3HT while the smaller one impairs them. Incorporating different oxygen bearing functionalities increased responses of thiophene polymers to NO₂, NH₃, and acetone. For example a polyether side chain increases the NO₂ response sensitivity of copolymers of both P3HT and PTOH, but sensitivity towards gas analytes was more prominent for glycol-based functionalities rather than the crown ethers. PTOH is very sensitive to NO₂ and the response likely includes a contribution from conductive protons on the OH group. The lack of correlation among the rank-ordered gas sensitivities imparted by each functional group was found to be useful for designing a selective sensor array. We specifically showed high classification accuracy for all the polymer responses to NO₂ and acetone vapors, both of which gave increased device currents but with response ratios different enough to allow highly classifying discriminant functions to be derived.