Study On Highly Efficient Fluorescent Sensors Of Chemical Warfare Agents And Their Sensing Mechanisms

Chemical warfare agents(CWAs)are a general term for chemical substances,which are are used in related military or terrorist attacks to produce toxic effects on human body and make people quickly incapacitated or even dead.Among them,the two most representative substances are nerve agent sarin and the blister agent sulfur mustard.In recent years,chemical warfare and chemical terrorist attacks from sarin and sulfur mustard have frequently caused casualties for soldiers and civilians,posing serious threats and harms to national defense and public security,thus it is particularly important to detect them quickly.Since the production and use of chemical warfare agents have been strictly banned by the international community,diethylchlorophosphate(DCP)and 2-chloroethyl ethyl sulfide(2-CEES)with less toxic and similar chemical properties are commonly used as mimics to sarin and sulfur mustard.Due to the advantages of low cost,simple operation,good mobility,high sensitivity and selectivity,fluorescence analysis method has made some progress in the detection of DCP and 2-CEES.However,the performanceses of reported fluorescence sensing materials are not still satisfactory,for example,it is difficult to achieve highly sensitive and selective detection of DCP and 2-CEES at very low concentrations.In particular,the examples of fluorescence detection of sulfur mustard are still very limited,the relevant research work has been carried out for less than ten years.At present,there are many problems that need to be overcome,such as long response time,complex detection strategy and harsh detection conditions,so there are still great challenges in practical application.To solve the above problems,several novel nitrogen-containing heterocyclic organic fluorescent materials were designed,synthesized and used as fluorescent sensors to achieve highly efficient,rapid detection of DCP and 2-CEES.Moreover,multifunctional fluorescent sensor that can simultaneously detect nitro-aromatic explosive gas,peroxide-based explosive gas and nerve agent simulant gas was developed.At the same time,their sensing mechanism is studied deeply by experimental and theoretical calculation methods.The main research contents are as follows:1.Based on the“molecular wire effect”of fluorescent polymer,we designed and synthesized a novel organic fluorescent conjugated polymer P1,P1 consists of carbazole group with electron-donor and 4H-1,2,4-triazole group with electron-acceptor.No matter in solution or in solid film,its fluorescence emission is located in the blue region.P1 not only exhibited high luminescence efficiency,but also has typical ICT characteristics.It was found that P1 sensor showed instantaneous fluorescence response to DCP both in solution and in vapor.After cantacting DCP,the emission peak rapidly shifted from blue to green,and the detection limits were as low as 2.3 n M and0.7 ppb,respectively,which is lower than the Immediately Dangerous to Life or Health concentration of sarin(IDLH concentration,30 ppb).Furthermore,deprotonation through water treatment,P1 sensor can be reused for many times.At the same time,P1sensor also demonstrated high selectivity,which was mot interfered by other organophosphorus compounds.We conducted an in-depth study on the sensing process through using nuclear magnetic experiments and theoretical calculations,and confirmed the key role of 4H-1,2,4-triazole group as recognition unit in the detection of DCP.This work provides a new idea for the design and development of high-performance DCP fluorescence conjugated polymer sensors.2.Furthermore,in order to improve sensitivity and detect DCP at low concentration,we introduced terpyridine groups with multiple active sites.Two low-cost and easy-synthesize organic fluorescent small molecules T1 and T2 based on terpyridine group were designed and synthesized.By conjugating of electron-acceptor terpyridine groups with electron-donor carbazole/phenothiazine groups,T1 and T2 not only had high luminescence efficiency,but also displayed typical ICT properties.Furthermore,the sensing behavior of the two sensors to DCP both in liquid and in gas phase was studied,we found that T1 and T2 sensors showed instantaneous colorimetric and fluorescence two-channel response to DCP,and detection limits as low as 0.5 ppb and 0.43 ppb,respectively,which are among one of the most sensitive sensors so far.At the same time,T1 and T2 sensors also showed high selectivity and anti-interference.By adding triethylamine,the two sensors realize reversible detection to DCP.Furthermore,sensing mechanism was proved by using flurescence spectrum test,the nuclear magnetic resonance experiments and theoretical calculation methods,the electron distribution and charge transfer process before and after the reaction of T1 and T2 with DCP were well discussed,the reason why substituents with different electron donating ability output different fluorescence signals has also been revealed.This study provides a new strategy for the design of novel fluorescent sensors with different response signals for detection of nerve agents.3.In order to realize the simultaneous detection of DNT vapor,peroxide explosive TATP vapor and DCP vapor by a single sensor.We designed and synthesized a D-A-D type organic fluorescent material TTPA-TAZ with 4H-1,2,4-triazole group and triphenylamine(TPA)group as the skeleton.The large conjugated structure can not only reduce the fluorescence quenching caused by the aggregation state,but also ensure the high luminescence efficiency.Moreover,the introduction of TPA group with typical pyramidal conformation is beneficial to the construction of spin-coating film with better permeability,which is conducive to the diffusion of gas molecules.Based on three different mechanisms of PET,intermolecular hydrogen bond and ICT,TTPA-TAZ film respectively realizes the rapid and efficient detection to DNT vapor,H₂O₂ vapor,and DCP vapor in different fluorescence channels,which effectively avoids the crosstalk problem of fluorescence output signals.And this method realizes the purpose of integrated detection of"explosion-proof"and"chemical-proof".At the same time,TTPA-TAZ film showed high sensitivity and selectivity,excellent repeatability for the three kinds of hazardous analyte vapors.This work provides a new design strategy for developing a novel multifunctional integrated-fluorescent-film sensors.4.We designed and synthesized a D-A-D type of organic fluorescent material NDTAZ with AIEE property.NDTAZ consists of a central 4H-1,2,4-triazole(TAZ)group as“core”,two electron-donating N-phenyl-1-naphthylamine(NPN)group connected at 3 and 5-position of TAZ as"arms",and a naphthalene ring connected at 4-position of TAZ as the"head".The NDTAZ film enabled instantaneously visual detection of 2-CEES vapor at room temperature.In addition,NDTAZ film also showed high sensitivity and selectivity,and the detection limit is 0.55 ppm,which is lower than the acute exposure guideline levels(AEGL-1)concentration of sulfur mustard(0.6ppm).The sensing mechanism is proved in detail by various experimental methods and theoretical calculation,we found both the electron-acceptor TAZ group and electron-donating NPN group jointly participated in the N-alkylation reaction mediated by 2-CEES,and reaction product a new ICT characteristic,corresponding to the longer-wavelength fluorescence emission.In addition,a simple paper-based sensor was developed successfully to monitor the leakage of 2-CEES vapor in real time.This work not only provides a fluorescence sensor with excellent performance for practical detection of sulfur mustard vapor,but also provides a new design strategy for developing a novel and efficient fluorescence sensor for sulfur mustard.