Employment of Alkoxy Sidechains in Semicrystalline Semiconducting Polymers for Ambient-Stable p‑Doped Conjugated Polymers

Electrical properties arising from doped conducting polymers offer various applications in organic electronics. Recently, sequential chemical doping of semiconducting polymers has attracted attention owing to its capability of being a full solution process, controllable doping level, high electrical properties, and obtaining crystalline conducting polymers. Although the sequentially doped conducting polymers are promising for high electrical conductivities and solid-state physics studies, they show issues of ambient stability due to competitive dedoping. Taking redox reactions with adsorbed water molecules into account as the major dedoping mechanism in p-doped conducting polymers, the fine-tuning of energy levels is a way to improve the ambient stability. In this work, we synthesized two poly­(2,5-bis­(thiophene-2-yl)­thieno­[3,2-b]­thiophene) regioisomers functionalized with alkoxy side chains to lower the ionization potential by the electron-donating alkoxy groups. After sequential p-doping, the two isomers demonstrated high crystallinities and electrical conductivities on the order of 1 × 102 S cm–1 in air. In addition, the p-doped alkoxy isomers exhibited ionization potentials smaller than the alkyl analogue by ∼0.1 eV, which led to a competition with the redox potential of water. As a result, the stability was remarkably improved, particularly under a high-humidity condition. Therefore, the alkoxy sidechains are promising as a molecular design strategy for conducting polymers with excellent ambient stability.