Fluorescence Sensor for pH Tracing Based on Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials. Herein, we prepare HOFs (PFC-1) and develop a facile pH-responsive fluorescent system, since they contain organic ligands with acid–base sensitive groups (H4TBAPy). Upon the addition of alkali, the carboxyl groups undergo deprotonation, and intramolecular charge transfer (ICT) is inhibited, which induces hydrogen bond reconstruction, widens the band gap, and enhances the restricted intramolecular motion (RIM) effect. These changes result in blue shift and significant enhancement of fluorescence emission. We also employ HOFs as excellent pH indicators to analyze histamine and protamine concentrations. The fluorescent system is further applied to monitor food spoilage, since PFC-1 materials exhibit a distinct fluorescent color change upon the generation of biogenic amines. This study thus provides a promising example for designing pH-responsive HOFs, laying a solid foundation for their further applications in food safety, environmental monitoring, and biomedical sensing fields.