An effective fluorescent probe for detection of phosgene based on naphthalimide dyes in liquid and gaseous phases

•A fluorescent probe was developed for the detection of phosgene based on 1,8-naphthalimide, of which o-diaminobenzene was used as the recognition moiety.•The probe reacts rapidly with phosgene via an intramolecular cyclization reaction with a low detection limit (0.23 nM).•This probe has excellent selectivity for phosgene against competing interference analytes and, in the form of probe-loaded test paper, is an extremely sensitive method for phosgene sensing in the gas phase below 1 ppm concentrations.