Sensitive and Selective Detection of Phosgene, Diphosgene, and Triphosgene by a 3,4-Diaminonaphthalimide in Solutions and the Gas Phase.

Phosgene and its substitutes, diphosgene and triphosgene, are highly toxic and widely used chemicals, so it is necessary to investigate their reactivity and develop facile, sensitive, and specific methods for detecting them. In this work, we have developed a new 1,8-naphthalimide-based fluorescent chemosensor, Phos-2, which exhibits high sensitivity (detection limits: 0.2-0.7 nm), high selectivity to phosgene and its substitutes over nitric oxide (NO), various acyl chlorides, and nerve agent mimics in solutions. Based on investigation of the reaction kinetics of Phos-2 with phosgene and its substitutes, a two-step sensing mechanism was clarified. The second-order rate constants (k2 ) of Phos-2 reveal that the relative rate constants of phosgene, diphosgene, and triphosgene are 40:4:1. Moreover, a Phos-2 test paper has been fabricated as a low-cost, sensitive (≈5 ppm from observation by the naked eye or 0.1 ppm from a measurement), and efficient method for visual detection of a low concentration of phosgene in the gas phase.