Myelin Sheath-Inspired Fluorocarbon Hydrophobic Bridges for Stable n-Type Organic Mixed Ionic-Electronic Conductors

Operationally stable n-type organic mixed ionic-electronic conductors (OMIECs) remain a critical bottleneck for organic electrochemical transistors (OECTs) for application in bioelectronic and neuromorphic devices. However, several state-of-the-art n-type OMIECs suffer from performance decay and poor stability when operated in aqueous media. Inspired by myelin sheaths, we challenge the conventional "π-backbone + hydrophilic side-chain" design and propose a molecular architecture with fluorocarbon hydrophobic bridges to spatially segregate, at the molecular level, ionic and electronic pathways. By tuning the fluorocarbon bridge chain length in fluorocarbon-ethylene glycol chain substituents [-CH2(CF2)nCH2(OCH2CH2)5OMe = 2nFG; n = 1, 2, 3, 4, 6] of a DPP-CNTVT polymer series (2nFG-P), we balance electron transport, ion exchange, redox chemistry efficiency, and water incorporation. Extensive in situ spectroelectrochemistry, EIS, Raman, EQCM-D, AFM, and GIWAXS characterization reveals that tuning the length of the hydrophobic bridge enables good electron transport, suppresses excessive water incorporation, and enhances stability. Thus, the polymer with a mid-length bridge, 8FG-P (n = 4), achieves the greatest electron transport (μC* ∼ 157 F cm-1 V-1 s-1, μ ∼ 1.22 cm2 V-1 s-1), fastest response (τon/τoff = 2.6/1.5 ms), and retains >90% of the initial performance after 10,000 s of operation in water, a result independent of the polymer molecular weight. This strategy potentially expands OMIECs design principles and offers useful insights toward stable n-type OECT semiconductors.