Study On Highly Efficient Nerve Agent Fluorescent Film Probes And The Sensing Mechanisms

Organophosphorus-based nerve agents are extremely toxic and potent acetylcholinesterase(ACh E)inhibitors,which can interrupt the normal transmission of nerve impulses and lead to death within several minutes.Recent attacks involving nerve agents highlight the need for rapid detection.Due to the extreme toxicity of nerve agents,diethylchlorophosphate(DCP)and diethylcyanophosphate(DCNP)are typically employed as simulants for their similar chemical structure and lower toxicity.At present,some progresses have been made in the detection of nerve agent simulants.Among them,fluorescent film probes have the advantages of ultra-high sensitivity,selectivity and repeatability,which are more practical in the detection of nerve agent simulant vapors.However,the material systems used in the reported fluorescent film probes are very limited,and the sensitivity of the probes is not satisfactory;although nitrogen-based fluorescent probes have been reported to be the most sensitive,false positives from acids due to the protonation of nitrogen-containing group is likely to be a major issue.So far,all the fluorescent probes in this field are closed-shell materials,the performance of open-shell systems such as organic luminescence radicals in the detection of nerve agent simulants have never been explored.To solve the above problems,several novel nitrogen-containing heterocyclic materials with intramolecular charge transfer(ICT)characteristics were designed and synthesized in this paper.The fluorescent film probes realized the rapid and efficient selective detection of nerve agent simulants vapor;The luminescent radicals-based film probes were development for the first time.We have also studied the sensing mechanisms of the probe through a variety of methods.The main works are as follows:1.We have designed and synthesized a novel polymer,PS-TPy,with polystyrene as main chain,triphenylamine as donor and terpyridine as acceptor,with obvious ICT characteristics.When the PS-TPy probe solution was exposed to DCP,the absorption and emission spectra were significant red-shifted,the limit of detection was 0.51?M.The fluorescence of PS-TPy film probe was quenched quickly after exposed to DCP vapor(the response time was less than 5 s),and can be reused for many times.The detection limit of the film probe was 0.32 ppb,which is much lower than the Immediately Dangerous to Life or Health concentration of sarin(IDLH concentration,30 ppb).We also studied the sensing mechanism of PS-TPy by spectral test,¹H NMR and ³¹P NMR,and confirmed that the ICT characteristics of the polymer is enhanced,ultimately leading to the red shift of the absorption and emission spectra.This work laid the experimental and theoretical foundation for the subsequent DCP fluorescent probes based on pyridine.2.Pyridine-based DCP fluorescent probes often interfered by volatile acids.In order to solve this problem,we prepared a novel organic-inorganic hybrid nanomaterial using 1,8-naphthalenediamine-pyridine derivate and hydrophilic silica nano particles(NIPy-Si O₂).The NIPy-Si O₂ film probe is porous and rough,enabling rapid and efficient detection of various nerve agent simulants.Exposure of the film probes to DCP and DCNP vapors leading a significantly enhanced and redshift of the absorption and emission spectra,the limit of detections are 2.4 ppb and 67.8 ppb,respectively.Most importantly,the fluorescence of NIPy-Si O₂ films is quenched rapidly after exposure to a variety of acids.This diverse fluorescence signal variation mechanism distinguishes nerve agent simulants from volatile acids effectively.After confirmed by ¹H NMR,³¹P NMR and infrared spectroscopy,we proposed that the pyridine hydrochloride product formed after the pyridine group nucleophilic attack DCP and DCNP leads to the enhancement of the ICT characteristics of the material,which in turn makes the fluorescence emission redshift and enhanced.This study not only provides a highly selective fluorescent probe that can simultaneously detect multiple nerve agent simulants but also provides a new strategy for the design of other multi-functional fluorescent probes.3.To further expand the material system of fluorescent probes for DCP detection,for the first time we have prepared two fluorescent film probes based on organic luminescent radical(TTM-?Py ID and TTM-?Py ID).With different carbolines as electron donors,TTM-?Py ID and TTM-?Py ID are not only highly luminescent and photostable,the doped films also have pure red emission.Exposure of the radical film probes to DCP vapor leads to obvious blue-shift,which is very rare in both luminescent radicals and DCP fluorescent probes.In addition,the two film probes have good sensitivity to DCP and the limit of detections are 3.5 ppb and 2.7 ppb,respectively.By studying the photophysical properties of the radicals and combining theoretical calculations,we confirmed that the carbazoline group of the radicals have been protonated once exposed to DCP.After protonation,the radicals showed broader energy gaps,the dihedral angle between donor and acceptor increases,resulting in a weaken and blue-shifted of emission.Most intriguingly,the electron cloud distribution between the electron donor and acceptor of the protonated radicals are completely opposite,and the transition of the doublet first excited state is between the radical and the protonated carbazoline groups.This is not only the first radical fluorescent film probe,but also provides ideas for the development of new materials and new mechanisms for nerve agent fluorescent probes.