Design and synthesis of novel angular 4,5-pyranocoumarin fluorescent probes for detecting hydrazine and their applications

Novel structured 4,5-pyranocoumarin-based fluorescent probes (2b and 3c) were designed and synthesized for the selective detection of hydrazine hydrate (N₂H₄). The probes feature an extended conjugated system via a 3-aryl-substituted pyranocoumarin skeleton, with ester groups serving as recognition sites for N₂H₄. Probe 3c demonstrated superior performance, exhibiting a 494% fluorescence enhancement at 460 nm with a detection limit of 0.03 μM, surpassing most reported coumarin-based fluorescent probes for hydrazine detection and the EPA safety threshold. Both probes exhibited high selectivity against 17 interferents (ions/biomolecules) and functioned effectively in complex matrices, including food samples (lettuce, rice) and vapor-phase detection via test strips. Probe 3c achieved rapid (<5 min), pH-stable (pH 6–10) responses with visible color transitions (blue-green to green), while 2b operated across a broader pH range (1–12). This work highlights pyranocoumarin scaffolds as promising platforms for designing intensity-responsive probes, combining synthetic novelty, sensitivity, and practicality for environmental and food safety.