Regioisomerism‐Driven Microenvironment Modulation in Three‐Dimensional Covalent Organic Frameworks for Selective H 2 O 2 Photosynthesis

ABSTRACT Internal microenvironment within covalent organic frameworks (COFs) is essential for photocatalytic performance. Nevertheless, retaining the chemical composition of building blocks hinders precise control over internal charge distribution. Herein, a regioisomerism‐driven strategy was adopted to engineer the framework microenvironment by modulating the α/β‐connectivity of cyclooctatetrathiophene (COTh) cores. Two isostructural 3D COFs, JUC‐701 (symmetric) and JUC‐702 (asymmetric), were constructed via the condensation of specific COTh regioisomers with tetrathiafulvalene (TTF) nodes, yielding frameworks with identical chemical compositions and pts topologies. Experimental and theoretical investigations reveal that the asymmetric α/β‐linkage in JUC‐702 breaks the local structural symmetry, amplifying the intrinsic molecular dipole and charge polarization. This induces a robust built‐in electric field within the 3D channels, optimizing the local electronic structure for thermodynamically favorable two‐electron oxygen reduction reaction (2e − ORR). Moreover, the separation and interfacial transfer kinetics of photogenerated carriers was facilitated. Consequently, JUC‐702 achieves an exceptional H 2 O 2 production (6724 µmol g −1 h −1 ) in a sacrificial‐agent‐free pure water system, which is superior to other 3D COFs in such a system. This work highlights the pivotal role of positional isomerism in modulating the intrinsic properties of 3D COFs, offering a versatile blueprint for the precision engineering of local electrostatic landscapes.