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.

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.

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