Acceptor Backbone Cationization via B ← N Functionalization Enables High-Performance Porous n-Type Organic Mixed...

The advancement of high-performance n-type organic mixed ionic-electronic conductors (OMIECs) is pivotal to advancing organic electrochemical transistors (OECTs) for next-generation bioelectronics. While current design strategies predominantly center on non-ionic conjugated polymers, their inherently hydrophobic backbones lead to suboptimal ionic transport characteristics. To address this challenge, we introduce an ionic acceptor design strategy of backbone cationization via B ← N functionalization within bipyridine and bipyrazine frameworks. Leveraging these cationic acceptors, we synthesized two n-type ionic polymer OMIECs, PBPyBF₃, and PBPzBF₃, which exhibit low-lying LUMO levels as low as -4.0 eV, elevated backbone torsional barriers, and ordered microstructures. Most critically, backbone cationization via B ← N coordination significantly enhances hydrophilicity by inducing a distinct porous film morphology, facilitated by hydrogen bonding with processing solvents. This structural evolution translates to a dramatically improved volumetric capacitance of 581 F cm^-3. Consequently, OECTs based on cationic polymer PBPzBF₃ exhibit an exceptional normalized transconductance of 38.9 S cm^-1 and figure of merit of 215.9 F cm^-1 V^-1 s^-1, ranking among the highest values reported for n-type OMIECs to date. Notably, electrocardiogram sensors integrated with PBPzBF₃-OECTs exhibit high signal-to-noise ratios and superior sensitivity. This work establishes fundamental structure-property relationships governing ion-electron coupled transport in conjugated polymers.