Hu et al. reported that 4-chloro-7-nitrobenzo[c]-[ 1, 2, 5] oxadiazole (NBD) based o-phenylenediamine (OPD) group, are colorimetric gas sensing substances which can swiftly And accurately detect phosgene. [245]. however, NBD-OPD phosgene gas sensors produce HCl as by-products which could result in secondary contamination. to overcome this problem, Hu et al. reported a new ring structure material, and they introduced the synthesized sensor 1, a benzimidazole-fused rhodamine dye that can efficaciously detect phosgene gas. they have plotted the possible reaction mechanism among sensor-1 and phosgene in figure 16a. consistent with the 1H NMR spectrum of the product, the products produced after phosgene gas assay showed that it has a structure as indicated through the ring-opened N-shloroformyl -benzimadazle 2. Senor-1, with a nanofiber platform, showed color alternate and fluorescence upon exposure to phosgene gas. As shown in figure 16c, the test paper based on sensor 1 is white and green in color and fluorescent, After the reactions of the phosgene gas, the color change to darkish pink and emit pink fluorescence. [246]. 
 Hu
 et al. reported that 4-chloro-7-nitrobenzo[c]- 
[ 
1, 2, 5]  
oxadiazole
 ( 
NBD
) based  
o-phenylenediamine
 ( 
OPD
) group, are colorimetric  
gas
 sensing substances which can  
swiftly
 And  
accurately
 detect phosgene. [245].  
however
,  
NBD-OPD
 phosgene  
gas
 sensors produce HCl as by-products which could result in secondary contamination.  
to
 overcome this problem,  
Hu
 et al. reported a new ring structure material, and they introduced the synthesized sensor 1, a  
benzimidazole-fused
  rhodamine
 dye that can  
efficaciously
 detect phosgene  
gas
.  
they
 have plotted the possible reaction mechanism among sensor-1 and phosgene in figure 16a.  
consistent
 with the 1H NMR spectrum of the product, the products produced after phosgene  
gas
 assay  
showed
 that it has a structure as indicated through the ring-opened  
N-shloroformyl
  -benzimadazle
 2. Senor-1, with a  
nanofiber
 platform,  
showed
 color alternate and fluorescence upon exposure to phosgene  
gas
. As shown in figure 16c, the  
test
 paper based on sensor 1 is white and  
green in color
 and fluorescent, After the reactions of the phosgene  
gas
, the color  
change
 to  
darkish
 pink and emit pink fluorescence. [246].