Preparation,Structural Regulation And Properties Of Fluorescent Covalent Organic Polymers

Fluorescent covalent organic polymers have attracted wide interest for their various advantages,such as high fluorescence quantum efficiency,diverse structure,good stability,function adjustability,strong processability and easy synthesis.They have shown potential applications in the fields of fluorescence sensing,photoelectric devices and adsorption.The properties of fluorescent covalent organic polymers depend not only on the framework structure of the polymer itself but also on their internal aggregation structure and micro-morphology.A series of fluorescent covalent organic polymers with uniform micro-morphology can be synthesized by a purposeful selection of building monomers,reference to reasonable design strategies and appropriate preparation methods,and even covalent organic frameworks with ordered and predictable structures can be obtained,so that the optical properties and application performance of the polymers can be effectively improved.Although many fluorescent covalent organic polymer materials with different properties have been developed,we still lack in-depth research on the relationship between the properties of these materials and their structure.In recent years,many fluorescent molecules have been synthesized and polymorphs of them have been developed in our group.By adjusting the molecular structure and aggregation structure of these materials,the structure-property relationship has been studied.Based on this,we think that the skeleton structure and microstructure of fluorescent polymers can be regulated,which can provide a direct and effective argument for revealing the relationship between structure and properties of fluorescent covalent organic polymer.Herein,this thesis focuses on the design and synthesis of different fluorescent covalent organic polymer materials,as well as the regulation of the skeleton structure and microstructure in them by adjusting the construction unit structure or the synthesis conditions.The intrinsic relationship between the fluorescent properties and application properties of these materials is explored,and new functions of these fluorescent polymers are also expanded.The main contents are as follows:1.The fluorescent polymer hollow nanospheres constructed by aggregation-induced luminescence units and flexible linkers,named HS,are designed and synthesized.The polymer can be obtained by simple synthesis method in solution,which presents uniform hollow spherical morphology and admirable dispersion in solution through a variety of microscopic observation methods,and the hollow structure can provide a high contact area and plenty of cavities for explosive molecules.Due to the high fluorescence quantum efficiency and morphology advantages,polymer HS exhibit super amplified fluorescence quenching effect and good selectivity for nitrophenol explosives in ethanol solution,the quenching constant(K_SV)of HS for 2,4,6-trinitrophenol(TNP)can be as high as 9.67×10⁵ M^-1,and the detection limit can be as low as 0.084?M.Furthermore,the handy test paper coated with hollow nanospheres was prepared and showed a good response toward TNP solutions and vapor.These results indicate that the hollow spherical morphology is beneficial to improve the fluorescence sensing properties of the polymers.2.Three kinds of azine-linked fluorescent covalent organic polymers with different morphologies are designed and synthesized through regulating the synthetical condition,including covalent polymer nanosheets(A-NS),conjugated microporous polymers(A-CMP)and covalent organic frameworks(A-COF).All of these polymers exhibit uniform structure and good stability,and the materials present high fluorescence quantum efficiency due to the introduction of AIE-active building units,as well as sensitive fluorescence quenching response to TNP.Compared with A-CMP and A-COF,A-NS has higher fluorescence efficiency and the best TNP sensing performance with the detection limit of0.09?mol/L.We not only obtained fluorescent covalent polymers with different morphologies based on the same building units by changing the synthesis conditions,but also showed that the nanosheets morphology reduced the?-?stacking between fluorescent molecules and increased the contact possibilities with analytes,which was conducive to improving the properties of the polymers.3.Two covalent organic frameworks(Pythz-COF and Pyurea-COF)are designed and synthesized,and their applications in trace water detection and water adsorption are studied in detail.We choose the same knot(Py)and different linkers(Thz and Urea)to construct two COFs with high crystallinity,high BET surface area and good thermal/chemical stability.The COFs display a positive solvatochromic effect and obvious fluorescence quenching response after adding trace water in various organic solutions,and the detection limit of Pythz-COF and Pyurea-COF in acetonitrile can be as low as 0.09%and 0.02%,respectively.The more sensitive detection effect of pyurea COF can be attributed to the more conjugated structural feature of Pyurea-COF which promotes the charge transfer process compared with Pythz-COF.More importantly,the COFs also show good hydrolytic stability and recycling utilization ability,which can be recycled at least 5 times for trace water sensing.Moreover,the COFs exhibited prominent water adsorption capacity and excellent reusability.When the relative humidity is 90%,the water absorption capacity of Pythz-COF can reach 83.2%.Because of the larger pore volume and surface area of Pythz-COF,it has better water absorption capacity than Pyurea-COF.In this work,we not only synthesized two kinds of covalent organic frameworks by adjusting the building units and explored the influence of material structure changes on trace water detection and water adsorption performance,but also broadened the application of covalent organic frameworks in trace water fluorescence sensing and water harvesting.4.Two covalent organic framework isomers(Py T-1 and Py T-2)with different structures are designed and synthesized based on the same building units.By adjusting the solvent conditions and the stoichiometric ratio of monomers,we make the monomers connected by[4+2]and[4+4]condensation pathway to form Py T-1 and Py T-2,respectively.Both two COFs exhibit good crystallinity and stability,and the differences in their crystal structure and micro morphology are carefully analyzed.In addition,it can be found that the two COF isomers also have a fluorescence quenching response to trace water in organic solvents,which can be used as trace water detection probes.Because the skeleton of Py T-1 contains strong electron-withdrawing aldehyde group,Py T-1 has a better detection effect than Py T-2 and the detection limit is 0.049%.In this work,we not only synthesized two COF isomers based on the same building units by adjusting the synthesis conditions,studied the relationship between the polymer structure and the fluorescence sensing performance for trace water,but also broadened the application scope of COF isomers in the field of fluorescence sensing.