Methylation-Induced Permanent Charge Polarization in Covalent Organic Frameworks for Visible Light-Driven Water...

Covalent organic frameworks (COFs) show promise for photocatalytic environmental remediation and antibacterial applications; however, their efficiency is often constrained by strong excitonic effects that impede charge separation. Here, a targeted in situ methylation strategy is reported to engineer permanent cationic centers within a robust non-substituted quinoline-linked COF (NQ-COF_S1). Methyl grafting at the nitrogen sites generates quaternary ammonium groups, inducing pronounced local charge polarization and a strong built-in electric field. This modification drastically reduces the exciton binding energy from 41 to 33 meV, thereby promoting highly efficient charge separation. In synergy with electron-rich thiophene units, the resulting NQ-COF_S1-Me exhibits outstanding photocatalytic activity, characterized by strong reactive oxygen species generation. It achieves > 95% inactivation of Gram-positive, Gram-negative, and drug-resistant bacteria within 10 min, and 96.84% degradation of chloramphenicol-38.72 times faster than NQ-COF_S1. These findings demonstrate that methylation-induced permanent charge polarization offers a powerful strategy for developing high-performance photocatalytic COFs with broad potential in environmental and public health applications.