Boosting Built-in Electric Field via COF Molecular Quadrupole Gradients for Efficient H₂O₂ Photosynthesis

Covalent organic frameworks (COFs) are promising photocatalysts for hydrogen peroxide (H₂O₂) generation using only water, air, and light. The intrinsic polarization, typically evaluated by the dipole moment of the photocatalyst, can induce a built-in electric field to promote exciton dissociation and carrier migration. However, the dipole moment is negligible in a symmetric and periodic COF structure, which hinders the regulation of the built-in electric field and efficient photocatalysis. In this work, we modulate the quadrupole moment by molecular engineering at specific COF sites to enhance the local electric field, achieving a remarkable H₂O₂ photosynthesis rate of 8.32 mmol g^-1 h^-1 in pure water without any sacrificial agent. The local electric field and carrier dynamics studies unveil that the quadrupole moment gradient tunes the intrinsic carrier decay, fluorescence reabsorption, and exciton binding energy to optimize carrier utilization efficiency. Moreover, the stronger quadrupole moment can stabilize the adsorbed ^·OOH intermediate through polarization and electron redistribution. This work provides a molecular engineering strategy for local electric field manipulation and reveals fundamental relationships between the quadrupole moment and photocatalytic processes in non-polar COF photocatalysts.