The Influence Of Weak Interaction On Performance Of Supramolecular Fluorescent Sensing System And Its Application In Detection Of Nitroaromatic Compounds

As the energetic materials,nitroaromatic compounds（NACs）have been widely used in the fields of blasting and military,but they have also become important sources of dangerous pollution because of their high toxicity and high risk.With the enhancement of awareness of environmental protection and occupational health,effective and real-time detection of NACs pollutants is imminent.They are mostly electrical neutral molecules and have various kinds with similar structures.The interacting force between them with the sensor receptor is relatively weak.Then it is difficult to achieve high selectivity and high sensitivity by conventional fluorescence sensing technology.Supramolecular fluorescence sensors not only have the advantage of fluorescence sensing,but also have the simplicity and diversity of synthetic methods.The performance is very adjustable,so it has become a new research hotspot.Either self-assembly based construction or the application process is essentially a process based on weak interactions.Only in depth understanding of these weak interactions,it can be manipulated effectively and it is possible to aim at preparing sensors with specific structures and functions,and use them effectively.The main functional groups in the fluorescent sensor are fluorophore and receptor.This paper used the naphthalimide fluorophore 4-methoxy-N-ethyl-1,8-naphthalimide and pyridine urea base receptor N,N’-bis-（3-pyridyl）ethylene-bis-urea,through the theoretical calculation methods,from the micro level,studied the effects of solute-solvent weak interaction on the optical properties and receptor recognition performance of sensor;Based on the possible regulatory effect of heterogeneous metal interaction on detection selectivity,with silver nitrate（AgNO₃）,ammonium thiocyanate（NH₄SCN）and magnesium nitrate（Mg（NO₃）₂）and calcium nitrate（Ca（NO₃）₂）as the main raw materials,Mg-Ag and Ca-Ag coordination polymer fluorescence sensors had been synthesized.Further their luminescent properties and detection performance of NACs had been studied.The results show that both of the two complexes can selectively detect TNP by fluorescence quenching method and their selective performance had been compared.Main results are as follows:（1）We used a polarizable continuous medium model（PCM）,combined with the density functional（DFT）method with a periodic explicit solvent model,to study influence of solvent polarity on the optical properties of fluorophore and recognition selectivity of receptor.The molecular dynamics simulation（MD）method was used to study the specific weak interactions between solute and solvent molecules.A widely used naphthalimide fluorophore,4-methoxy-N-ethyl-1,8-naphthalimide was selected as the research object.With the enhancement of the polarity of the solvent,the maximum absorption wavelength of the compound is red shift and the quantum yield is gradually reduced.The effect of the solvent polarity on the excited state electronic structure had been studied in a variety of solvents with different polarity.The optical physical properties of the fluorophores（especially the fluorescence intensity）varying with the solvent had been discussed in detail.And from the ground state to the excited state,the change of the intermolecular interaction sites between the solute and solvent molecules and the inactivation of the excited states caused by the weak interactions had also been discussed;A typical multipoint receptor N,N’-bis-（3-pyridyl）ethylene-bis-urea（BPEBU）,in gas（ε=1.0）and acetone（ε=20.7）and ethanol（ε=25.7）solutions was chosen to study that the effect of solvent polarity on the geometric and electronic structure and the intermolecular interaction of syn-anti conformation in acetone and ethanol solutions.Implicit/explicit solvent model was used to optimize the structure of solute-solvent supramolecular cluster,and the structures were compared with that of the MD results to further study hydrogen bonding interaction between molecules.The results show that the weak interaction between molecules will have a great impact on the sensing properties of fluorescent sensing materials.The influence of solvent molecules is not only from the polarity,but also from the solute-solvent specific weak interaction.These weak interactions can make the major optical properties,such as quantum yield and fluorescence lifetime of the sensing material change.When acting on the multipoint receptor,weak interactions can change the relative competitive ability of each action sites and affect the molecular recognition performance and self assembly process of supramolecular sensing system.（2）For the influence of the weak interaction of heterogeneous metals on selective recognition,we used AgNO₃,NH₄SCN and Mg（NO₃）₂ as the main raw materials to synthesize the Mg-Ag coordination polymer fluorescent sensing material[Mg（DMF）₄Ag₂（SCN）₄]_n.The coordination polymer can emit strong fluorescence and selectively detect TNP with fluorescence quenching in DMF and aqueous media.Compared with other NACs,it showed high sensitivity for TNP,and after five cycles,the luminescence intensity and PXRD of the sample are all consistent with the original samples,indicating that the complex may be a promising practical TNP sensor;AgNO₃,NH₄SCN and Ca（NO₃）₂ were used as the main raw materials to synthesize the Ca-Ag coordination polymer fluorescent sensing material[Ca（DMF）₄Ag₂（SCN）₄]_n.The complex also has strong emission and high quenching constant and low detection limit for the detection of TNP with fluorescence quenching.The synthesis cost is lower than the Mg-Ag complex.It can be used as a high sensitivity sensor for TNP.Because the emission spectra of the Mg-Ag and Ca-Ag complexes are highly overlapped with the absorption spectra of TNP,the mechanism of their sensing may lie in the energy transfer between TNP and the complexes.The comparative study shows that the crystal structure of the two is similar,but in the detection application,in addition to the highest TNP sensitivity,the selectivity of the other NACs is different.It indicates that the weak interaction between the heterogeneous bimetallic centers in the coordination polymer can produce cooperative effect.With different metal centers,the selective recognition performance of the system for the guest molecules is changed,and the selectivity and sensitivity of the sensor are regulated.Through the above research on the weak interaction of supramolecular system,it provides a theoretical basis for the synthesis design and application of new sensors.The comparative study of heterogeneous metal coordination polymers provides a new way for the development of highly selective sensors.