Design, Synthesis And Bio-imaging Of Photocrosslinkable Tetraphenylethylene Molecules

As a prominent aggregation induced emission(AIE)luminogen,tetraphenylethylene(TPE)had been widely studied and applied because of its simple structure,convenient synthesis and easy modification.However,there are still some problems that need to be further studied and solved.For example,the separation of E/Z isomers of TPE derivatives and the preparation of small size AIE nanoparticles and their specific labelling imaging.In this paper,we will focus on the two problems.In order to separate the E/Z isomers of TPE,we designed oxetane-substituted TPE(TPE-OXE)in the third chapter and separated pure isomers by simple column chromatography with high yields,as confirmed by Mass spectrometry,IR and NMR spectroscopy.Their geometry structures were confirmed by 2D NMR spectroscopy.The isomerization of two isomers can occur by photo-and thermo-activation.Importantly,Z-TPE-OXE isomer solid shows bathochromic emission with a quantum yield 5 times higher than that of E-TPE-OXE.The differences in emission wavelength and quantum yield are derived from distinct emission mechanisms of locally excited(LE)state emission of E-TPE-OXE and charge transfer(CT)state emission of Z-TPE-OXE.The two isomers are also good piezochromic luminescent materials and have high contrast,which have not only obvious emission color shift,but also significant enhanced luminescence brightness by external force.They also can return to the initial state.Besides,E-TPE-OXE solids show self-healing ability,which can crystallize spontaneously from ground amorphous state.The higher brightness of Z-TPE-OXE can be retained in solution,so there are obvious brightness differences between the two kinds fluorescent AIE nanodots prepared from the two isomers.Cell labelling experiments also show that Z-TPE-OXE AIE dots have higher labelling brightness as compared to the E-TPE-OXE isomer.So we realized the macroscopic separation of TPE isomers by simple reaction.The synthesis and distinct properties of E/Z isomers are beneficial to further development of new TPE derivatives for various applications.In the forth chapter,we designed and synthesized three kinds oxetane substituted TPE derivatives with blue,green,and red emission.The maxima wavelengths for three molecules are 479 nm,503 nm and 612 nm,respectively.All molecules exhibited evident AIE characteristic.The solid powders of the three molecules exhibit strong fluorescence,the quantum yields are 69%,63%,and 57%,respectively.The nanoparticles were prepared by nanoprecipitation,which have small size(?16 nm),good stability and high brightness.The oxetane groups in the nanoparticles can be photocrosslinked.There are newly covalent frameworks in the photocrosslinked nanoparticles,the stability of nanoparticles can be dramatically improved.So the crosslinked nanoparticles have good stability in a variety of physiological conditions and even in the organic solvent.The size of the nanoparticles can be maintained after crosslinking.Due to the high brightness,small size and good stability,the three kinds nanoparticles aqueous solution can be used as a fluorescent ink in inkjet printers to realize fluorescence printing and fluorescence security.In the biological imaging,successful bioconjugation produces AIE dots-streptavidin probes that specifically label cell-surface markers by antigen-antibody interaction.We realized the first example of AIE dots for subcellular microtubules labeling with high resolution.More importantly,we achieved the stimulated emission depletion(STED)super-resolution imaging by the AIE nanoparticles.The full width at half maximum decreased from 190 nm to 95 nm,the imaging resolution has been significantly improved.Finally,the photostability of the AIE dots are greatly improved by the oxygen scavenging system,which is beneficial to wider applications of AIE dots in long-term bio-imaging.In conclusion,we designed and synthesized a series of oxetane-modified tetraphenylethylene derivatives.Based on the structural characteristics of oxetane,we achieved the macroscopic separation of E/Z isomers of tetraphenylethylene.E/Z isomerization is closely related to molecular properties,which is benefical for the design and synthesis of TPE derivatives in future.Using the photocrosslinking properties of oxetane,we developed a new method for the preparation of AIE nanoparticles,and prepared small size,high brightness and ultra-stable AIE nanoparticles.We realized the specific labelling of cell surface proteins and subcellular microtubules by bio-functionalization.The resolution of imaging was further improved by super-resolution fluorescence imaging.