Functional Structural Disorder Governing Efficient Proton Transport in Non‐Porous Phosphonic‐Acid‐Based HOFs

ABSTRACT Efficient proton transport in hydrogen‐bonded organic frameworks (HOFs) is widely assumed to require permanent porosity and well‐defined conduction channels. This work demonstrates that dynamic structural disorder can play a central role in governing proton dynamics, even in essentially non‐porous systems. We report the synthesis and comparative analysis of three positional isomers of pyridinediyldiphosphonic acid 2,6‐, 2,5‐, and 3,5‐ – providing a systematic platform for investigating structure–property relationships. Among them, the 2,5‐isomer exhibits an outstanding proton conductivity of S at room temperature and 97% relative humidity, despite its essentially non‐porous nature (BET ). A humidity‐driven decrease in activation energy from 0.46 to 0.15 eV reveals a transition from vehicle‐assisted transport to a Grotthuss‐type proton‐hopping mechanism. Crystallographic analysis demonstrates pronounced positional and dynamic disorder, while ATR–FTIR spectroscopy reveals a Zundel‐type continuum indicative of highly polarized and delocalized protons. We show that structural disorder enables adaptive reorganization of hydrogen‐bond networks upon hydration, generating efficient proton‐conduction pathways without permanent pores. These findings challenge the prevailing paradigm that permanent porosity is essential for proton‐conducting HOFs and establish dynamic disorder as a powerful design principle for solid‐state proton conductors.