Regioisomeric Covalent Organic Frameworks with Precisely Engineered Spatial Arrangement of Active Sites Enable...

Covalent organic frameworks (COFs) offer precise spatial control over catalytically active sites due to their ordered, crystalline structures. This control directly governs site accessibility and interfacial charge transfer, both critical for electrochemiluminescence (ECL) via multistep energy conversion. To decouple and systematically investigate spatial effects independent of chemical composition, we introduce an isomeric COF design strategy, yielding two structurally distinct yet chemically identical frameworks: BTT-DAPQ and BTT-DAAQ. These feature ortho- and para-positioned ketone groups on the same diamine linker, respectively, thereby enabling atomic-level control over active-site distance, relative orientation, and local cooperative microenvironment. In BTT-DAPQ, the ortho-ketone motif promotes dipole-driven antiparallel π-stacking, which enhances intralayer charge delocalization and increases surface exposure of redox-active carbonyl sites. This synergistic structural advantage strengthens interfacial interaction with the coreactant S2O82-, facilitating its efficient activation and subsequent sulfate radical (SO4•-) generation. Consequently, BTT-DAPQ delivers a 7.12-fold higher ECL intensity than its para-isomeric counterpart. Leveraging this amplified signal transduction, we further developed a selective uranyl ions (UO22+) sensing platform: the strong Lewis acidity of UO22+ drives preferential coordination to oxygen-rich sites in the framework, competitively inhibiting S2O82- activation and inducing up to 96.23% ECL quenching. The assay exhibits a broad linear dynamic range (10-5000 nM) and an ultralow detection limit of 2.53 nM. Collectively, this study establishes that nanoscale spatial organization, not merely chemical identity, is a decisive factor in governing ECL mechanisms.