# Methylation‐Induced Permanent Charge Polarization in Covalent Organic Frameworks for Visible Light‐Driven Water Decontamination and Disinfection

## TL;DR

A methylation strategy improves COFs for water decontamination by enhancing charge separation and photocatalytic activity.

## Contribution

A methylation-induced permanent charge polarization strategy is introduced to enhance COF photocatalytic performance.

## Key findings

- Methylation reduces exciton binding energy from 41 to 33 meV, improving charge separation.
- NQ-COFS1-Me achieves >95% bacterial inactivation within 10 minutes and 96.84% chloramphenicol degradation.
- The material degrades chloramphenicol 38.72 times faster than the unmodified COF.

## Abstract

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‐COFS1). 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‐COFS1‐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‐COFS1. 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.

A targeted in situ methylation strategy is developed to engineer cationic centers in a quinoline‐linked COF (NQ‐COFS1‐Me), creating a strong built‐in electric field, which effectively suppresses excitonic effects and promotes charge separation. The optimized material demonstrates powerful photocatalytic ROS generation for rapid bacterial inactivation and efficient degradation of antibiotic pollutants.