A novel NBD-based fluorescent turn-on probe for detection of phosgene in solution and the gas phase

As a highly toxic gas, phosgene (COCl2) is widely used in chemical industry processes. Because of its colorlessness and acute effects, the detection of phosgene is important for public health safety. In this work, we report a novel 7-nitro-2,1,3-benzoxadiazole (NBD)-based fluorescent probe. It is constructed with the 1,4,7-triazacyclononane moiety as the active site, which includes two aliphatic secondary amines and one aromatic tertiary amine. The 1-nitrogen atom connected to the aromatic ring facilitates the intramolecular charge transfer (ICT) process, providing high quality of fluorescence potential. The 4- and 7-nitrogen atoms are used as double-site recognition groups and also as effective photoinduced electron transfer (PET) donors. The NBD-1,4,7-triazacyclononane probe can be bis-carbamylated with phosgene to block the PET effect, which gives a turn-on fluorescence response at 525 nm. The sensing reaction can be achieved within 20 s in solution. The probe's response to triphosgene is highly sensitive and selective, and the detection limit is as low as 1.2 nM to triphosgene in solution. Furthermore, a portable filter paper has been produced for real-time detection of phosgene in the gas phase.