Synthesis And Investigation On Multi-responsive Fluorescence Switching Of α-cyanostilbene Based Luminescent Liquid Crystals

In recent years,fluorescent liquid crystal materials are gradually receiving widespread attention in the fields of light-emitting diodes,information storage,sensors,and one-dimensional semiconductors.The α-cyanostilbene unit can be used as a mesogen to construct liquid crystal materials,and its derivatives have Aggregation-induced-emission(AIE)properties.Their fluorescence intensity and color can be correlated with the external environment changes,such as temperature,pressure,light,pH,and solvent vapor.In this work,a series of monomers,polymers and a dendritic molecule containing α-cyanostilbene unit were designed.Their liquid crystal properties,fluorescence properties and multiple fluorescence response behaviors were studied systematically.Photoreversible fluorescence conversion behaviors can be implemented in the three systems.The main contents of the thesis include the following aspects:1.A series of α-cyanostilbene monomers M-(Z)-345,M-(Z)-34,M-(Z)-35 and M-(Z)-4,as well as M-(E)-345 and M-(E)-34 containing a norbornene moiety and different number of tail chains were designed and synthesized.The molecular structures were verified by 1H NMR,13C NMR,COSY and ROESY,HR-MS and EA characterizations.The corresponding side-chain luminescent liquid crystalline polymers,including P-(Z)-345,P-(Z)-34,P-(Z)-35,P-(Z)-4,P-(E)-345 and P-(E)-34,were then prepared by ROMP.Combined with POM,DSC and SAXS,it has been shown that the Z-isomer monomers and polymers are mesomorphic,while the E-isomer monomers and polymers are not.Among them,P-(Z)-345 forms a hexagonal columnar phase structure.P-(Z)-4,P-(Z)-34,and P-(Z)-35 form smectic phase structures.2.The fluorescence response behaviors of monomers and polymers in solid,solution and film were studied by UV-vis absorption spectra,fluorescence emission spectra,1H NMR,mass spectrometry,powder X-ray diffraction and so on.Both Z-monomers and polymers are AIE-active.M-(Z)-345 and M-(Z)-34 have mechanochromism and solvatochromism phenomena.The photo-triggered fluorescence switching has been found in this system and the mechanism is invesitaged.When the film was irradiated via 365 nm UV light,Z/E isomerization and[2+2]cycloaddition(head-to-head and head-to-tail)occurred,which induced fluorescent color change in the film.Then the fluorescent color can be returned to their original state by subsequent 254 nm UV illumination.The polymer films retain this photo-triggered reversible fluorescence switches like monomers and their fluorescence properties are more stable.3.The dendritic POSS-8CN with polyhedral oligomeric silsesquioxane(POSS)as the core and α-cyanostilbenic liquid crystal moiety as the arm was synthesized.The molecular structure was verified by 1H NMR,13C NMR,MALDI-TOF MASS and EA.DSC,POM,and temperature-variable SAXS were used to study the liquid crystal property and phase transition behavior.POSS-8CN can form an ordered smectic structure and a crystalline ordered structure at room temperature.The photo-triggered fluorescence switches in solution and film states were investigated by UV-vis absorption spectra,fluorescence emission spectra and 1H NMR.The dendrimer can undergo Z/E isomerization in solution and cross-linking reaction in film under 365 nm UV illumination.The reversible fluorescence changes in film can be achieved under 254 nm UV illumination.