Isotopological Modulation of Entanglement in 3D Covalent Organic Frameworks Unlocks a Fully Open Catalytic Architecture.

Rational control over structural entanglement in three-dimensional covalent organic frameworks (3D COFs) is essential for optimizing catalytic-site accessibility and substrate transport in heterogeneous catalysis. However, conventional thermodynamically governed crystallization often produces interpenetrated architectures that restrict permanent porosity and hinder active-site exposure. Here, we report a symmetry-breaking molecular design that enables isotopological modulation of entanglement within a bcu topology by repositioning a single substituent on the linker. This subtle perturbation induces spatial steric asymmetry that suppresses interpenetration during crystallization, affording noninterpenetrated, mesoporous, porphyrin-based microcrystals (PCOF-23) with uniform particle sizes of ∼2 μm. After iron incorporation, PCOF-23-Fe exhibits substantially enhanced electrocatalytic nitrate reduction performance, achieving a Faradaic efficiency of 88.1% and an ammonia yield rate of 10.9 mol gcat.-1 h-1, more than twice that of its interpenetrated analogue. Multiscale investigations attribute these improvements to the fully open pore system, which promotes accelerated reactant adsorption and mass transport. Furthermore, PCOF-23-Fe serves effectively as a cathode in a rechargeable zinc-nitrate battery. This work establishes a paradigm for suppressing interpenetration in 3D COFs and highlights their potential in energy-related electrocatalysis.