Targeted identification of cyanide and fluoride ions utilizing dansyl-derived fluorescent probes: a deprotonation-driven sensing mechanism

In this study, we present the detection of hazardous cyanide (CN−) and fluoride (F−) anions using six dansyl-derived fluorescent probes (L1–L6) specifically designed for rapid and highly sensitive detection in organic media. Through a combination of UV–Vis absorption and fluorescence titrations in acetonitrile, all ligands exhibited a distinct and selective “turn-off” fluorescence response upon exposure to CN− and F−, while remaining unresponsive to common halides such as Br− and Cl−. Quantitative analysis using HypSpec confirmed a consistent 1:1 binding stoichiometry across the series, with L4 emerging as the top performer, displaying low limits of detection of 2 μM and 4 μM for CN− and F−, respectively, and association constants (Log Kass) of 6.37 for CN− and 5.66 for F−. NMR and LC–MS titration studies further revealed a deprotonation-based recognition mechanism, with CN− inducing proton abstraction at sub-stoichiometric levels, while F− required up to 10 equivalents. The high affinity and rapid responsiveness of these dansyl-based systems establish them as potent fluorescent tools for the non-invasive, real-time monitoring of the toxic anions cyanide and fluoride in organic-based samples.