ESIPT‐Active Naphthalene‐Based Hydroxyoxime Fluorescent Chemodosimeters for Rapid and Sensitive Phosgene Sensing in Solution and Polymer Films

C NMR, FT-IR spectroscopy, and HRMS methods. Among the two probes, HNOX-6 exhibits exceptional sensing performance with an ultralow detection limit of 0.042 nM and an ultrafast response time of <5 s, whereas HNOX-7 responds within 10 s with a detection limit of 47.7 nM. Specifically, the reaction involves phosgene-promoted cyclisation of the hydroxy-oxime functional group, leading to the formation of fluorescent isooxazoles, ISOX-6 and ISOX-7, which generate the signal. For practical gas-phase detection, probe-loaded poly(ε-caprolactone) (PCL) films were developed as solid-state sensing platforms. HNOX-7 embedded films exhibited a prominent naked-eye fluorescence change from yellow to cyan upon phosgene exposure, showing superior performance compared to HNOX-6. The gas-phase LOD was found to be 0.34 ppm for HNOX-7 embedded polymer film. SEM studies further confirmed effective probe-phosgene interactions through pronounced surface morphological changes after gas exposure.