Synthesis And Properties Regulation Of Stimuli-responsive Fluorescent Tetraphenylethylene Materials

Stimulus-responsive organic fluorescent material is a kind of smart material that the photophysical properties of the compound in the solid state highly change under external stimuli(molecules,ions,mechanical forces,acid/base,light or heat).This material has received extensive attention of many researchers due to the potential applications in pressure sensor,memory chip,information security,recording media,data recording,security ink,etc.In recent years,a large number of efficiently and sensitively stimulus-responsive organic fluorescent materials,such as piezochromism or mechanofluorochromism,vapochromism,thermochromism and acid/base chromism have been developed by researchers.However,the materials with excellent properties are relatively scarce.The perspicuous design strategies are lack and the mechanism of stimulus-response behaviors are needed to be in-depth explored,which are important for developing excellent stimulus-responsive fluorescent materials.Thus,it is significance to develop stimulation-responsive fluorescent materials with excellent performance,and to further study the internal relationship between molecular microstructures and macroscopic properties.Tetraphenylethylene(TPE)with"propeller"structure is a"star molecule"in the field of aggregated and solid-state luminescence material studied and often used for designing excellent stimulation-responsive fluorescent materials because of the high stability,simple synthesis,easy modification,and good AIE properties.In this thesis,a series of organic stimulus-responses fluorescent materials are designed and synthesized by choosing the TPE unit as the core.The molecular structures and conformations are rationally optimized to adjust the steric hindrance and molecular stacking patterns in aggregate state.And the intrinsic relationship between the molecular structure and fluorescence stimulus-response performance is investigated in detail.The primary research contents are as follows:1.Four pyrazoline-modified tetraphenylethylene derivatives with different substituents(TPEB,TPEN,TPEF and TPECN)were synthesized and characterized by FTIR,HR-MS,¹H and ¹³C NMR.The molecules have obvious intramolecular charge transfer(ICT)properties and aggregation-induced emission(AIE)properties by UV-Vis absorption spectra and fluorescence emission spectra.And it has excellent fluorescence emission performance in solid state.The compounds show obvious AIE property with high emission efficiency in solid state.The fluorescence spectra of compounds TPEB,TPEN and TPEF are red-shifted(green-yellow)under external stimulation.The quantum yields of TPEB,TPEF and TPEN are significantly increased and that of TPECN was slightly reduced after grinding.X-ray powder diffraction(XRD)and differential scanning calorimetry(DSC)analysis showed that the compounds transformed from microcrystalline state to amorphous state before and after grinding.According to single crystal structure analysis,intermolecular?-?interaction of compounds TPEB,TPEN and TPEF was destroyed after grinding,resulting in the increment of fluorescence intensity.While,the molecular planarization of compound TPECN after grinding resulted in the formation of weak interaction between molecules,resulting in the reduction of fluorescence intensity.2.Three cyclohexyl modified tetraphenylethylene derivatives(TPATPE,TPETPE and TPETPA)have been designed and synthesized.The results of optical physical properties and density functional theory studies show that the molecules are typical intramolecular charge transfer(ICT)compounds.In addition,compound TPATPE shows high emission efficiency in monomolecular and aggregation state.While,compound TPETPE and TPETPA exhibit obvious AIE characteristic.In the solid state,the fluorescence of compounds TPATPE,TPETPE and TPETPA successively red-shifted and the fluorescence intensities decreased.Moreover,the superb utilization of compounds had been executed as fluorescence probes for detecting explosive picric acid in aqueous medium with high quenching efficiency.3.A series of multi-stimulus responsive materials(G2,G3,G4,L-G2,L-G3and L-G4)based on functionalized tetraphenylethylene and arylimidazole unit were designed and synthesized.The photophysical properties and molecular conformation were changed by fine-tuning the molecular distorted conformation and the position of pyridyl group.It was found that compounds G2,G3,G4,L-G2,L-G3 and L-G4showed significant solvatochromic effects,AIE characteristics and could be used for mechano-responsive,PA explosive and acid/base recognition.Under the force stimulation,the fluorescence peaks of all compounds were red-shifted and the fluorescence intensity was still high enough,but which was just slightly reduced compared to the pristine sample.After treated by ethanol,the grinding sample could easily convert to pristine state.The fluorescence color change is driven by the planarization of molecular conformation,which leads to the increase of molecular conjugation.According to theory calculations and crystal structure analysis,the molecules are highly distorted and with weak intermolecular interactions.The loose packing results in the only slight reduction of emission peak after grinding.Moreover,the compound G2,G3,G4,L-G2,L-G3 and L-G4 is high sensitivity and selectivity for PA recognition in 90%THF/H₂O solution.The limit of detection of G2,G3,G4,L-G2,L-G3 and L-G4 for PA is evaluated to be 257 n M,564 n M,155 n M,308 n M,344 n M,232 n M,respectively.Additionally,the fluorescence of all the compounds in90%THF/H₂O mixture solution could be strongly quenched by trifluoroacetic acid(TFA).