Synergistic Topology and Node Engineering in Mesoporous COFs for Efficient H ₂ O ₂ Photosynthesis

ABSTRACT

Covalent organic frameworks (COFs) represent a promising class of metal‐free photocatalysts. However, the synergistic optimization of exciton dissociation and mass/charge transport still remains a significant challenge. Herein, a synergistic topological and electronic engineering strategy was implemented in COFs to decrease exciton dissociation energy during photocatalysis, while planar‐locking and mesopore engineering in COF frameworks enhanced mass/charge transport properties. Isomeric carbazole‐based COFs (COF‐Cz‐kgd‐v versus COF‐Cz‐hcb) with distinct topologies and node‐site hybridization states (sp ² ─NH─ in COF‐Cz‐hcb versus sp ³ ─CH ₂ ─ in fluorene‐based COF‐Flu‐hcb) have been prepared. Theoretical and experimental studies indicated that the enhanced spatial separation efficiency of the frontier orbitals from COF‐Cz‐kgd‐v, COF‐Cz‐hcb to COF‐Flu‐hcb would result in a decreasing exciton binding energy (59.35, 57.47 to 42.46 meV) and prolonging photogenerated charge migration. Inspired by this, the H ₂ O ₂ photogeneration was investigated, and its rates were elevated from 49.5 mmol g ⁻¹ h ⁻¹ for COF‐Cz‐kgd‐v, 66.3 mmol g ⁻¹ h ⁻¹ for COF‐Cz‐hcb to 97.9 mmol g ⁻¹ h ⁻¹ over COF‐Flu‐hcb in an O ₂ ‐pre‐saturated benzylamine‐acetonitrile system. A two‐step indirect 2e ⁻ oxygen reduction pathway mediated by *OOH intermediates, coupled with a hole‐driven dehydrogenation of benzylamine on donor‐acceptor sites, also contributed to their high photosynthetic performance.