Poly(3-alkoxythiophene)-Based Block Copolymer as Organic Electrochemical Transistor Material

In recent years, there had been a burgeoning interest in organic electrochemical transistors in due to their unique ability to modulate charge carrier conductivity upon electrochemical doping, rendering these devices useful in bio-analyte detection, neuromorphic computing, electrocardiographic sensing and many other biomedical applications ^[1]. To enhance ionic affinity in aqueous electrolyte, many OECT-active polymers, such as pgBTTT ^[2] and polylactam-based P75 ^[3], are grafted with oligoethylene glycol side chain to facilitate ion penetration. Glycolation has been established as a successful strategy for OECT material design, but heavily glycolated polymers have been reported to undergo irreversible swelling during device operation, impose limited solubility in the polymerisation solvent and result in less-ordered microstructure compared to alkylated analogues ^[4]. Side-chain free polyarenes such as BBL ^[5] and PBFDO ^[6] have been explored, but processing and fabrication of these materials generally requires overcoming their limited solubility in common organic solvents.<br/>Herein, we developed a series of novel block copolymers comprising an electroactive poly(3-alkoxythiophene) (P3OAT) block and a flexible polymer block. Serendipitously, pristine P3OAT can be electrochemically doped in aqueous electrolyte, possibly owning to its high lying HOMO energy level and mesoporous film structure. However, its operation in OECT device is not very reversible and possesses a slow turn-on time (τ_on). PEGylation of poly(3-alkoxythiophene) was shown to enhance its hydrophilicity and ionic affinity, resulting in faster τ_on and higher volumetric capacitance, but slightly lowering carrier mobility due to its insulating nature. In addition, we explored the anchorage of base-labile poly(lactide) block. Following etching, the fabricated film possesses microstructure with large pores to mediate ion entry, with pore dimensions controlled by the degree of polymerization (DP) of labile block.<br/>[1] Nature Reviews Materials 3 (2), 1-14<br/>[2] J. Am. Chem. Soc. 2021, 143, 29, 11007–11018<br/>[3] Angew. Chem. Int. Ed. 2022, 61, e202113078<br/>[4] Nature Materials 19, 491–502<br/>[5] J. Am. Chem. Soc. 2023, 145, 3, 1866–1876<br/>[6] Nature 611, 271–277