Giant Conductivity Modulation and Chemical Neuromodulation via Proton-Electron Coupling in a Hydrogen-Bonded...

Mixed protonic-electronic conductors (MPECs) have been developed to maximize static conductivity for electrochemical applications, but emerging applications that leverage proton-electron coupling (PEC) require dynamic conductivity control. To achieve this, we propose a "de-doping" strategy in a hydrogen-bonded coordination polymer {[Co(DMF)₂(H₂O)₂(bipy)](NO₃)₂·2(DMF)}_n (bipy = 4,4'-bipyridine, DMF = N,N-dimethylformamide) named Co-BAND. By isostructural substitution of Ni(II) (d⁸) in the established Ni-BAND with Co(II) (d⁷), we designed Co-BAND to suppress the intrinsic conductivity while preserving proton transport and PEC. As a result, Co-BAND exhibits a giant conductivity modulation (1.15 × 10⁶) in response to humidity changes and implements complex brain-like learning rules. We also demonstrate chemical control of synaptic plasticity via solvent vapor exposure. This biomimetic neuromodulation tunes transport and learning rules based on vapor polarity, proticity, and steric effects. This work establishes conductivity modulation as an important design metric for MPECs and highlights their potential as designable platforms for stimuli-responsive applications.