Unveiling distinct hydrogen-bonding mechanisms: A catechol-derived probe for selective cyanide and fluoride detection

Catechol-derived Schiff bases serve as versatile platforms for anion sensing, where intramolecular hydrogen bonding governs recognition and photophysical behavior. We report a catechol-based probe, PyCt, capable of discriminating cyanide (CN^-) and fluoride (F^-) via distinct hydrogen-bonding modes. Spectroscopic analyses reveal that CN^- forms hydrogen bonds with the phenolic -OH without full deprotonation, while F^- induces complete deprotonation, disrupting the hydrogen-bonding network. These interactions yield pronounced fluorescence enhancements at 535 nm (CN^-) and 544 nm (F^-), attributed to enhanced intramolecular charge transfer (ICT) that stabilizes the excited state and promotes radiative decay. Job's plot, ¹H NMR and DFT studies confirm a 1:1 binding stoichiometry, with detection limits of 0.42 μM (CN^-) and 1.20 μM (F^-). PyCt demonstrates reversible recognition, high selectivity, and reliable sensing in real food samples. Furthermore, smartphone-assisted RGB analysis enables facile F^- quantification, underscoring the probe's practical applicability.