Functional group engineering in metalloporphyrin-based covalent organic frameworks for enhancing sensing performance

Covalent organic frameworks (COFs) face intrinsic limitations in chemiresistive gas sensing due to low carrier concentration and poor charge mobility. In this work, we report a functional group engineering strategy to enhance the performance of porphyrin-based Cu-COF-366 by modulating donor-acceptor (D-A) interactions. By introducing electron-donating/withdrawing groups into the building units, the separation efficiency of photogenerated electron-hole pairs is significantly improved, leading to increased free carrier density and reactive oxygen species generation under visible-light irradiation. The optimized Cu-COF-366-OCH₃ exhibits an ammonia response of 825.9%, representing a 25.9-fold improvement over Cu-COF-366-H. The response of Cu-COF-366-OCH₃ toward NH₃ is at a moderate level among all reported MOF/COF-based sensors. This breakthrough stems from the synergistic effects of methoxy-induced electron enrichment, which improves charge mobility and increases the number of reactive oxygen species as sensing active sites. The material also demonstrates excellent selectivity, repeatability, and long-term stability. This work establishes a mediator-free molecular design paradigm for COF-based sensors, advancing high-performance gas detection technologies.