Bio‐Transport Regulation Inspired 5‐Fluorouracil Keto to Enol Tautomerism Achieving High Proton Conductivity

Abstract The strategic modulation of proton transport kinetics and precise control of migration energy barriers in metal‐organic frameworks (MOFs) are essential for developing next‐generation proton conductors. Inspired by biological proton channels, this study introduces a dynamic regulation strategy by keto‐enol tautomerism to reconcile the intrinsic trade‐off between low activation energy ( E a ) and sustained proton mobility. We successfully construct a hierarchical proton conductive system (denoted as FU@MOF‐808‐SO 3 H ) by integrating 5‐fluorouracil (5‐FU) molecules into sulfonic‐functionalized MOF‐808 through a two‐step post‐synthetic modification. The enol tautomer of 5‐FU reconfigures hydrogen‐bond networks under humidity variations, synergizing with anchored ─SO 3 H groups to establish proton transport pathways along ordered ionic channels (─SO 3 H···H 2 O···5‐FU) and tautomerism‐driven delocalization via reversible keto‐enol isomerization. The optimized compound FU@MOF‐808‐SO 3 H exhibits a high proton conductivity of 7.15 × 10 −2 S cm −1 at 353 K and 95% RH, representing an approximate 300‐fold enhancement over pristine MOF‐808 , a 15‐fold improvement versus the 5‐FU‐encapsulated analogue FU@MOF‐808 , and the sulfonated framework MOF‐808‐SO 3 H . Density functional theory (DFT) calculations elucidate an ultra‐low formation energy barrier (9.05 and 1.59 kcal mol −1 ) from keto to enol conversion, attributed to sulfonic acid stabilization of protonated transition states. Furthermore, the proton conductive mechanism is visually corroborated by molecular dynamic (MD) simulation, suggesting Grotthuss‐dominated proton migration within hydrated nanochannels, aligning with experimental results.