Azonia‐Naphthalene: A Cationic Hydrophilic Building Block for Stable N‐Type Organic Mixed Ionic‐Electronic Conductors**.

Conjugated polymers that can efficiently transport both ionic and electronic charges have broad applications in next‐generation optoelectronic, bioelectronic, and energy storage devices. To date, almost all the conjugated polymers have hydrophobic backbones, which impedes efficient ion diffusion/transport in aqueous media. Here, we design and synthesize a novel hydrophilic polymer building block, 4a‐azonia‐naphthalene (AN), drawing inspiration from biological systems. Because of the strong electron‐withdrawing ability of AN, the AN‐based polymers show typical n‐type charge transport behaviors. We find that cationic aromatics exhibit strong cation‐π interactions, leading to smaller π–π stacking distance, interesting ion diffusion behavior, and good morphology stability. Additionally, AN enhances the hydrophilicity and ionic‐electronic coupling of the polymer, which can help to improve ion diffusion/injection speed, and operational stability of organic electrochemical transistors (OECTs). The integration of cationic building blocks will undoubtedly enrich the material library for high‐performance n‐type conjugated polymers. [ABSTRACT FROM AUTHOR]