Architectural Evolution Unlocks the Functional Potential of Buried Sites in Covalent Organic Frameworks.

In covalent organic frameworks (COFs), how framework architecture regulates the functional accessibility of chemically present yet spatially confined sites remains poorly understood. Here, by subtly modifying one building unit, we synthesized three chemically related imine-linked COFs that span an architectural sequence from layered 2D kgm and 2D sql frameworks to an entangled 3D sql framework. This architectural evolution disrupts extended planar packing, reduces confinement around the imine linkages, and generates an interconnected, water-accessible pore network. Consistent with these architectural features, the entangled 3D COF exhibits a proton conductivity approximately 5 orders of magnitude higher than those of the two layered analogues, despite only a modest increase in total water uptake. Subsequent mild oxidation of imine linkages to amide linkages further enhanced proton transport while largely preserving the crystallinity of the entangled framework. This work demonstrates that architectural evolution can activate the latent functionality of buried polar linkages, providing a design principle for functional porous materials.