Fully Conjugated Sp2 Carbon-Linked Covalent Organic Frameworks Enables Accelerated Exciton Process for Superior Singlet Oxygen Photosynthesis for Water Remediation.

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. 8 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.