Selective Detection of Phosgene via a Fluorescence Activation Mechanism Employing a Synthetic Coumarin‐Derived Molecular System

ABSTRACT The rapid and reliable detection of phosgene is important due to its high toxicity and widespread industrial use. In this study, we report a coumarin‐based fluorescent probe for the selective detection of phosgene generated in situ from triphosgene. The probe remains weakly emissive in its native state but exhibits a pronounced fluorescence “turn‐on” response upon interaction with phosgene, resulting in a strong emission signal. A gradual increase in fluorescence intensity was correlated with increasing concentration of the generated phosgene, demonstrating a linear response and enabling detection at nanomolar concentrations. The probe also displayed high selectivity, with a significant fluorescence enhancement only in the presence of phosgene compared with other tested species. For practical applications, a simple TLC strip‐based method was developed for the visual detection of phosgene vapor. In addition, the sensing response could be quantified through RGB color analysis using a smartphone combined with a portable UV lamp. These results highlight the potential of the developed probe as a convenient and sensitive platform for the detection of phosgene.