Synthesis, characterization, and field-effect transistor performance of carboxylate-functionalized polythiophenes with increased air stability

Synthetic strategies to access both regiorandom and regioregular polythiophenes containing electronwithdrawing carboxylate substituents have been developed. Although these polymers have extended conjugation lengths, they provide better oxidative doping stability than conventional polythiophenes due to the lowering of the HOMO energy levels by approximately 0.5 eV. These materials are highly crystalline and exhibit very small π-π-stacking distances in the solid state. High charge mobilities are observed as a result of the close ordering of the polymer chains, and top-contact organic thin-film transistors (OTFTs) fabricated entirely in air had measured mobilities averaging 0.06 cm ²/V̇s with on/off ratios >10 ⁵. Off currents in these devices remained low over a period of months, demonstrating the low propensity of these materials toward p-doping by molecular oxygen.