ESIPT-Active Naphthalene-Based Hydroxyoxime Fluorescent Chemodosimeters for Rapid and Sensitive Phosgene Sensing in...

Choking agents such as phosgene, diphosgene, and chlorine pose serious threats to public health due to their extreme inhalation toxicity. Exposure to these gases can cause severe damage to the respiratory system, leading to acute oxygen deprivation, respiratory failure, and potentially fatal outcomes. In this regard, two hydroxy-oxime-based chemodosimetric fluorescent probes, HNOX-6 and HNOX-7, were designed, synthesized, and characterized using ¹H NMR, ^{1 3}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.