Synthesis And Properties Of Stimuli-Responsive Fluorescent Tetraphenylethylene Materials With Intramolecular Change Transfer Character

Organic fluorescent materials have become popular research topics in the scientific community due to their wider luminous color range,relatively simple manufacturing process,and wide selection of materials.Traditional organic fluorescent materials are limited by the aggregation-caused quenching(ACQ)effect.The high fluorescence quantum yield of aggregation-induced emission(AIE)materials in the aggregated state overcome the problems of the traditional fluorescent materials and expands the development of organic fluorescent materials.Tetraphenylethylene(TPE)is a"star molecule"in the field of aggregated luminescence due to its high thermal stability,simple synthesis,easy modification,and strong aggregation-induced luminescence properties,especially in the field of stimulus-responsive fluorescent materials.The"paddle-wheel"structure makes its intermolecular interactions weak,and it has a flexible three-dimensional molecular geometry and self-assembly mode.Under the external environmental stimulus,the change of different molecular three-dimensional(3D)geometric structure and self-assembly mode will cause the change of the spectral signal of the material,thereby realizing the fluorescence response to the external stimulus.So far,a large number of TPE derivatives with different structures have been reported and are widely used in the fields of biological probes and imaging,chemical sensors,explosives detection and optoelectronic devices.However,it is necessary to further investigate the relationship relationship among the properties,molecular structure and molecular self-assembly of TPE derivatives.In this paper,a series of TPE derivatives with AIE propertity were designed and synthesized,and their photophysical properties and mechanofluorochromic(MFC)behavior are systematically studied.Combined with crystal structure analysis and theoretical calculations,the correlation between structure and properties are explored,and research some application in information date storage and explosives detection.The main research contents are as follows:1.Designed and synthesized two D-?-A tetraphenylethylene derivatives with mechanofluorochromic(TPEDA and TPEPL),malononitrile as accept group(A),and diethylamino and tetrahydropyrrole as donor groups(A),respectively.The results show that TPEDA and TPEPL have significant AIE effects and intramolecular charge transfer characteristics.In addition,the solid fluorescence quantum yields(?_F)of the compounds TPEDA and TPEPL show great differences,the original states were 15.67%and 2.53%,respectively.Through the analysis of the single crystal structure,it was found that there is a strong intermolecular interaction between the molecules of TPEPL(C-H????,C-H???N and weak?-?interactions),resulting in a lower solid fluorescence quantum yield;Diethylamino,which has a large resistance,weakens the interaction between TPEDA molecules,and the non-close-packed self-assembly makes it have a higher solid fluorescence quantum yield.Moreover,TPEDA and TPEPL show obvious MFC properties.Under pressure grinding stimulation,their fluorescence emission peaks are red shifted by 25 nm(from 619 nm to 644nm)and 10 nm(from 647 nm to 657 nm),respectively.Moreover,the grinded sample were recovered to the original ones,whereas after treatment by ethanol,indicating excellent reversibility of MFC behavior.Time-resolved fluorescence spectra,powder X-ray diffraction(PXRD),and differential scanning thermal analysis(DSC)of different solid states show that the mechanism of MFC is the transition between crystalline and amorphous states.2.Five kinds of intramolecular charge-transfer tetraphenylethylene derivatives(TPEN,TPEH,TPEF,TPEIZ,and TPECN)were designed and synthesized by changing the type of the para-phenyl substituent at the terminal benzene ring.The AIE properties,MFC behavior and detection picric acid(PA)of these compounds were studied.TPEN exhibits the ACQ effect,TPEH,TPEF,TPEIZ,and TPECN exhibit the AIE effect.Under grinding stimulus,these compounds exhibit unique MFC behavior due to the different substituents.After grinding,the fluorescence peak position of TPEN is hardly changed,and its solid fluorescence quantum yield is reduced by 0.38 times.Under external force stimulation,the fluorescence emission peak positions of TPEH,TPEF,TPEIZ,and TPECN were red-shifted by 34 nm,33 nm,64 nm,and 26 nm,respectively,and different degrees of change in solid?_F were occured.The solid?_F of TPEH and TPEF were enhanced to 1.23 and 2.45times,but the solid?_F of TPEIZ and TPECN were reduced to 0.52 and 0.83 times,respectively.The analysis of the crystal structure shows that the?-?interaction is destroyed after grinding TPEH and TPEF,resulting in an increase in?_F;after grinding of TPEN,TPEIZ,and TPECN,the molecular conformation is flattened to form?-?interactions,which causes a decrease in?_F.Based on its excellent MFC properties,it was applied to date storage.In addition,based on the photo-induced electron transfer mechanism,TPEH,TPEF,TPEIZ,and TPECN can specifically recognize picric acid(PA)in the aqueous media,and their detection limits are 7.58?M,458 nM,634 nM,and 4.62?M,respectively.3.Four arylimidazole-modified tetraphenylethylene derivatives(S1,S2,S3,and S4)were synthesized by Debus-Radziszewski and Knoevenagel reaction.Among them,S1 and S2,S3 and S4 are positional isomers of each other with the same molecule skeleton.The photophysical properties in different solvents show that S1,S2,S3,and S4 have intramolecular charge transfer properties,and density functional theory calculations verify the change in the electron cloud density distribution during the excitation process.By studying the luminescent behavior in THF-water mixture,the fluorescence intensity of S1 and S2,S3and S4 showed a clear increasing trend with the increase of water content.At f_w=90%,the intensity was increased by 13,75,12 and 51 times,respectively.In addition,compounds S1,S2,S3 and S4 exhibit reversible MFC behavior with mechanical-induced emission enhancement(MIEE),the fluorescence emission peak were red shifted by 43 nm,30 nm,12nm,and 11 nm,respectively.At the same time,the solid?_F was enhanced to 4.96,2.66,1.78,and 1.61 times,respectively.The time-resolved fluorescence spectrum,PXRD and the scanning electron microscope(SEM)under different solid states revealed that the mechanism of the stimuli-responsive fluorescence discoloration was the transition between microcrystalline and amorphous states.In addition,compounds S1,S2,S3 and S4 can specifically recognize PA in aqueous phase,and their detection limits are 69.7 nM,73.5 nM,93.8 nM,and 96.9 nM,respectively.The detection mechanism was PET and energy transfer mechanism,which was verified by ~1H NMR proton titration experiments and density functional theory calculation.