Fully Conjugated Sp² Carbon-Linked Covalent Organic Frameworks Enables Accelerated Exciton Process for Superior...

Photocatalytic oxygen (O₂) activation via energy transfer offers a sustainable approach for singlet oxygen (¹O₂) synthesis, while its performance suffers from the ultrafast exciton dissociation and sluggish intersystem crossing (ISC) process. Up to date, exciton regulation is still in its infancy. Here, via linkage engineering of covalent organic frameworks (COFs), we propose a fully conjugated sp² carbon-linked COFs (sp²c-Py-Bpy COFs) with strong exciton interaction and fast ISC for boosted ¹O₂ photosynthesis. The sp²c-Py-Bpy COFs delivers a record-high ¹O₂ yield (624 µM min^-1) with 100% selectivity, which is ca. eight times that of the traditional imine-bridged COFs (Im-Py-Bpy COFs, ca. 95.8% selectivity), outperforming documented systems. Transient absorption spectroscopy and theoretical investigations demonstrate that the fully conjugated sp² carbon linkage of sp²c-Py-Bpy COFs can enhance Coulomb interaction, promote ISC and push forward the transfer of triplet exciton to the O₂ adsorption sites throughout the COFs matrix, jointly facilitating the energy transfer process for efficient ¹O₂ photosynthesis and bypassing the traditional electron transfer process. Hence, sp²c-Py-Bpy COFs can selectively degrade acetaminophen within minutes under visible light irradiation and enables stable degradation of emerging pollutants in a continuous flow membrane reactor (20 × 30 × 2 cm) utilizing natural sunlight and dissolved O₂.