# Conjugation Lock-In Reinforced Sulfur-Heteropolycyclic Covalent Organic Frameworks with Asymmetric Electron Distribution for Photocatalytic Aerobic Oxidation Reactions

## TL;DR

Scientists created a new type of material that improves photocatalytic reactions by reinforcing its structure and electron distribution.

## Contribution

A postcyclization strategy using sulfur incorporation to enhance COFs for photocatalytic aerobic oxidation.

## Key findings

- Modified COF shows a 3-fold increase in H2O2 evolution rate compared to the precursor COF.
- Achieves complete benzylamine conversion in 1 hour under mild blue LED light.
- Modified COF outperforms most organic and inorganic competitors in photocatalytic activity.

## Abstract

The development of robust heterogeneous photocatalysts
capable
of operating under harsh chemical conditions remains a critical yet
challenging goal in materials science. Here, we present a postcyclization
strategy based on conjugation lock-in reinforcement to construct sulfur-heteropolycyclic
covalent organic frameworks (COFs) with asymmetric electron distribution
for superior photocatalytic reactions, which is achieved through a
consecutive thionation–cyclization–oxidation transformation
of N-acylhydrazone precursors using Lawesson’s
reagent. Systematic characterization reveals that sulfur incorporation
endows the framework with enhanced chemical stability, localized asymmetric
electron density, rapid charge carrier migration, efficient exciton
dissociation, extended π-conjugation, and a well-defined donor–acceptor
architecture, collectively leading to significantly improved photocatalytic
activity and durability compared to the original hydrazone-linked
COF. Consequently, the modified COF exhibits a H2O2 evolution rate of 5270 μmol g–1 h–1 in pure water, representing a 3-fold enhancement
over the precursor COF (1878 μmol g–1 h–1) and surpassing most reported organic and inorganic
competitors. Moreover, it achieves complete conversion of benzylamine
within 1 h under mild blue light-emitting diode irradiation, demonstrating
high efficiency in aerobic oxidation catalysis. These findings establish
the lock-in reinforcement strategy coupled with electronic structure
modulation as a versatile route to designing durable and highly active
photocatalysts for demanding synthetic and energy-conversion applications.