| Phosgene and its substitutes(diphosgene and triphosgene)are important chemical materials and play important roles in the fields of medicine,pesticides,polymer materials and others.However,they are highly toxic chemical reagents,which can severely stimulate the lungs to cause pulmonary edema,breathing difficulties,or even death.In the industrial process,it would pose a great threat to human health and environmental safety if there were not warnings on the leakage accidents.Therefore,it is necessary to develop convenient and efficient detection methods to deal with these high risk events.This paper focuses on the design and synthesis of 1,8-naphthalimide-based fluorescent probes,and studies their applications in the detection of phosgene and its substitutes.Compared with the "turn-on" probe,whose single emission signal is easily interfered by various external factors(e.g.,intensity of the excitation light,slit width,test sample thickness,probe concentration),the ratiometric fluorescent probe which provide built-in correction by simultaneously measuring two different emission signals,improve the accuracy of fluorescence readouts.So,the ratiometric fluorescent probe Phos-1 for the detection of phosgene was designed and synthesized.Phos-1 could be used for highly selective and visual detection of phosgene in solutions and in gas phase by using peri-diamine as the response site.Moreover,the proposed sensing mechanism was confirmed by using NMR spectroscopy and mass spectrometry:twice acylation reactions occurred between phosgene and peri-diamine to give ureal end-products.(See chapter 2 for details)Phos-1 could be used to detect phosgene,but the long response time(20 min)limited its practical application.For this reason,the "turn-on" fluorescent probe Phos-2 for detection of phosgene and its substitutes was developed.Compared with Phos-1,Phos-2 has shorter response time(10 min)by using 3,4-diamine as the response site.By the usage of UV-vis and fluorescent spectroscopic methods,the second-order rate constants of Phos-2 reacting with phosgene,diphosgene and triphosgene were measured(the ratio was 40:4:1),in addition,the sensing mechanism was further investigated:the carbamylation between phosgene agents and 3-amine of Phos-2 is the rate-determining step and the subsequent intramolecular cyclization(that is,the secondary carbamylation with 4-amine)is a fast process.What's more,the test paper containing Phos-2 was fabricated to selectively and sensitively(the limit of detection is 0.1 ppm)detect the phosgene agents in the gas phase.(See chapter 3 for details)Although the sensitivity of Phos-2 for detecting phosgene agents is considerably improved versus Phos-1,the response time is still long(10 min in liquid phase,30 s in gas phase).To further shorten the response time,the fluorescent probe Phos-3 for real-time detecting phosgene was synthesized.Different from the response site(diarylamino groups)in Phos-1 and Phos-2,the aliphatic amine is introduced to work as the response site for phosgene,at the same time,the pentacyclic moiety was used to limit the rotation of C-N bond to accelerate the response to phosgene in liquid phase(about 1 min).In addition,we used electrospinning to fabricate the test paper for the detection of gases and the nanofiber membranes covering its surface could significantly increase the contact areas between gases and probes.So,it can realize the real-time(?1 s)detection for phosgene in gas phase.(See chapter 4 for details)Phosgene and triphosgene have different harmful effects on the environments and human bodies.Thus,it is necessary to discriminate them.Phos-1,Phos-2 and Phos-3 can be used to achieve this objective in short time based on the activity difference between phosgene and triphosgene.However,a long analysis time of triphosgene would lead to similar fluorescent response with phosgene.In other words,these three probes can not discriminate between phosgene and triphosgene effectively in fact.Therefore,the fluorescent probe Phos-4 was developed.Phos-4 used 2-(2-amino phenyl)imidazol as the recognition site.There was only once carbamylation reaction between triphosgene and non-fluorescent Phos-4 to form blue fluorescent products,but there were twice carbamylation reactions for phosgene to give yellow-green fluorescent products.The maximum fluorescence emission wavelengths of the two response products are significantly different,so the dual-emission channel can be used to discriminate between phosgene and triphosgene effectively.Similarly,the test paper containing Phos-4 was prepared by electrospinning and could be used for selective and visual detection of phosgene in the gas phase,besides,the response time was not over 10 seconds and the detection limit could be as low as 42 ppb.(See chapter 5 for details)... |
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