Abstract: The expansion of global industries results in the release of harmful volatile acid vapors into the environment, posing a threat to various life forms. Hence, it's crucial to prioritize the development of swift sensing systems capable of monitoring these volatile acid vapors. This initiative holds great importance in safeguarding a clean and safe environment. This paper presents the synthesis and characterization of pyrene-based covalent organic frameworks (COFs) demonstrating exceptional crystallinity, thermal stability, and intense fluorescence. Three COFs—PP-COF, PT-COF, and PE-COF—were synthesized, showcasing large surface areas and robust thermal stability up to 400 °C. The fluorescence properties and intramolecular charge transfer within these COFs were significantly influenced by their Schiff base bonding types and π-stacking degrees between COF layers. Notably, PE-COF emerged as the most fluorescent among the three COFs and exhibited exceptional sensitivity and rapid response as a fluorescent chemosensor for detecting HCl in solution. The reversible protonation of imine bonds in these COFs allowed for the creation of highly sensitive acid vapor sensors, showcasing a shift in spectral absorption while maintaining structural integrity. This research highlights the potential of COFs as reliable and reusable sensors for detecting harmful acid vapors, addressing environmental concerns arising from industrial activities.
