Electrostatic complementarity and interlayer coupling modulation in halogen-modified covalent organic frameworks for enhanced photocatalytic oxygen reduction.

Covalent organic frameworks (COFs) are promising for solar-driven hydrogen peroxide (H2O2) photosynthesis but are limited by inefficient charge transfer and O2 adsorption. This study introduces a halogen-functionalized COF material that uses dipole-dipole interactions of halogen groups to adjust interlayer spacing, enhance π-π coupling, and form a "π-π conjugated electron transport bridge," significantly improving charge transfer efficiency. Density functional theory (DFT) calculations show that halogen atoms (e.g., F atom) reduce the electron density of the modified benzene rings, increasing π-orbital delocalization and creating the electron transport bridge. The interlayer orbital overlap follows the trend: F-COF (maximum overlap) > Cl-COF (significant overlap) > Br-COF (low overlap) > H-COF (negligible overlap). Additionally, the electronic polarization effect of halogen atoms locally induces charge polarization, creating a δ+-δ--δ+ charge distribution complementary to the δ--δ+-δ- distribution of O2 molecules, which significantly enhances O2 adsorption. Due to the synergistic effect of π-π coupling and charge distribution complementary, F-COF demonstrates excellent catalytic performance with a rate of 2547.7 μmol g-1 h-1 and a quantum efficiency of 10.2%. This study provides a new strategy for optimizing electronic distribution to regulate charge transport and O2 adsorption sites.