Synthesis And Stimuli-Responsive Performance Of Acrylonitrile Derivatives With Aggregation-Induced Emission Character

Stimuli-responsive fluorescent materials can generate reversible/irreversible photophysical or photochemical changes under external stimuli,which are mainly manifested in changes of color and fluorescence emission intensity/band.These materials have been widely used in intelligent optoelectronic devices,optical information storage,chem-/bio-sensors,and other fields.Stimuli-responsive fluorescent materials are required strong light-emitting properties in solution or solid state,however,conventional fluorophores emit strong fluorescence in dilute solutions and exhibit aggregation caused quenching?ACQ?phenomena,which limits its application range.In recent years,the discovery and development of aggregation-induced emission?AIE?and aggregation-induced enhanced emission?AIEE?materials have broken through the limitation of traditional fluorescent molecules in practical applications and opened up a new door for stimuli-responsive fluorescent materials.To date,a great number of stimuli-responsive AIEgens have been designed and synthesized.However,most of them still suffer from some difficulties due to the lack of a comprehensive understanding of the correlation between structure and properties,such as relatively complex molecular structures,complicated synthesis precedure,expensive consumables and limited in applications.According to international research of stimuli-responsive AIEgens and combined with the previous work in my lab,we have designed and synthesized a series of acrylonitrile derivatives with AIE/AIEE character.The photophysical and stimuli-responsive properties of the as-prepared acrylonitrile derivatives have been studied in detail including mechanical force,ions,and acids/bases.The correlation between molecular structure and stimuli-responsive fluorescent performance has been explored in depth.The main research contents are as follows:1.Two tetraphenylethylene-modified carbazole acrylonitrile derivatives?abbreviated as TPECZ and TPECZBr?were designed and synthesized through introducing bromine atom in the molecular structure to investigate the photophysical properties and mechanofluorochromism.The photophysical properties indicated that TPECZ and TPECZBr exhibited intramolecular charge transfer?ICT?and AIE character.Meanwhile,their photophysical properties were similar in solution and aggregated states.However,the fluorescence quantum yield of them in the solid state was significantly different(?_TPECZ=11.2%,?_TPECZBr=28.3%).Crystal structure analysis confirmed that the two compounds showed different molecular packing patterns caused from bromine atom.Upon grinding the crystalline powders of TPECZ and TPECZBr,their fluorescence emission colors changed from yellow to orange,which can be restored to its original state under ethanol steam.The results indicated reversible mechanofluorochromic performance of them.Moreover,the effect of bromine atom was unconspicuous on the molecular stimulus response.The results of powder x-ray diffraction?PXRD?and differential scanning calorimetry?DSC?analysis showed that the mechanofluorochromic mechanism of TPECZ and TPECZBr was related to a decrease of crystallinity.2.Four bromo-carbazole acrylonitrile derivatives?named as 2BrCZ-N,2BrCZ-H,2BrCZ-Br,and 2BrCZ-CN?were designed and synthesized with different substituent groups.The effects of terminal substituents and bromine atoms on the response to external force stimuli were inquired in combination with the crystal structure.2BrCZ-N showed ACQ effect,while 2BrCZ-H,2BrCZ-Br and2BrCZ-CN displayed AIE activity.With the enhancement of the electron donating ability of the terminal group,the fluorescence emission of these compounds in the solid state shifted from bright yellow?588 nm?of 2BrCZ-CN to red?618 nm?of2BrCZ-N.After grinding the crystalline powders of the four compounds,the fluorescence emissions were red-shifted with varying degrees and the fluorescence quantum yields were reduced?2BrCZ-N:9.3%?1?2.2%?.The phenomenon can be restored to its original state under ethanol steam,indicating that these four compounds have reversible mechanofluorochromic performance.PXRD and scanning electron microscopy?SEM?analysis revealed that the conversion of crystalline state to amorphous state was the main reason for the change in the band and relative intensity of their fluorescence emission under the stimulation of external force.Meanwhile,crystal structure analysis confirmed that larger distorted molecular configurations and fewer intermolecular interactions were more conducive to sensitive mechanofluorochromic behavior.3.A diaryl substituted acrylonitrile derivative?CN-Si?modified with tert-butyldiphenylsilyl oxide?TPDBSO?was designed and synthesized.CN-Si can selectively detect F^-by different affinity of fluorosilicon?the bond energy of Si-F=582 kJ/mol?and oxysilicon?the bond energy of Si-O=472.5 kJ/mol?.Adding F^-promoted the dissociation of silicon-oxygen bonds,which resulted in the intramolecular ring-closure reaction and forming aminocoumarin derivatives.Consequently,it can greatly alter the photophysical properties of the dyes and achieve F^-selectivity identify.CN-Si showed AIEE characteristics in THF/H₂O solution,which exhibited“turn-on”fluorescence response to F^-with high selectivity,sensitivity and fast response?THF/H₂O solution,1:1 ratio in v/v?.The detection limit was as low as 0.203 ppm.4.A D-?-A-?-D type TBDPS-functionalized dye?TPEOSi?with highly red-light emission and multi-stimuli-responsive property was designed and synthesized,in which tetraphenylethylene and 4-diethylaminosalicylaldehyde units acted as electron-donor?D?,malononitrile unit as electron-acceptor?A?.Under external force,TPEOSi exhibited high-contrast mechanofluorochromic?MFC?performance with a red-shift in emission wavelength?603 nm?1?631 nm?and a significantly quenched quantum yield?27.25%?1?2.34%?,which can be recovered after ethanol treatment.The MFC effect can be attributed to increased molecular conjugation induced by planarization of molecular conformation,along with the enhanced intermolecular?-?interaction.Furthermore,TPEOSi showed high sensitivity and selectivity to detect fluoride ion in aprotic solvents in both colorimetric and fluorescent modes with detection limits of 0.11?M and 0.39?M,respectively.In addition,the as-formed TPEOSi-F^-system was extremely sensitive to protons and can measure trace water in aprotic solvents with the detection limit of 1.78×10^-3?v/v?.