Fabrication Of Functional Liquid Crystalline Gels

Low molecular weight organogels(LMOGs)are a type smart materials that respond to external stimuli.Fluorescent gel not only have the advantages of LMOGs,but also undergo fluorescence changes when phase transitions occur under external stimuli.Therefore,it can be used for the design and synthesis of sensors and fluorescent probes.Liquid crystals(LC)are used as photoelectric materials because their unique physicochemical and optical properties.Two important moieties in the supramolecular chemistry of LC are azobenzene and cholesterol.The azobenzene unit is well known for its clean,fast and controllable photo-responsiveness.Cholesterol groups are special because of both its chirality and gelation properties.Based on this,we designed and synthesized functional LC gelators and studied its self-assembly behavior and performance in detail.(1)A series of cholesterol derivatives modifying azobenzene and tetraphenylethylene(TPE)has been designed and synthesized by changing the carbon chain length between azobenzene and cholesterol(Cn-Chol,n =1,3,5).Through the gel performance test,it was found that C3-Chol and C5-Chol molecules can form a stable gel by ?-? stacking force in single and mixed solvents,while C1-Chol cannot be gel in the tested solvents,indicating carbon chain plays a crucial role in the gelation process.Then the scanning electron microscopy(SEM)was used to study the micro?morphology of gelators.We found that the two molecules can self-assembly a variety of chiral helical structures in the gelation solvent.Furthermore,the supermolecular chirality was preliminary exploration by circular dichroism spectra(CD).Both of two compounds were accompanied by fluorescence enhancement during the gelation process.Meanwhile,results show that such gelators happened gel-sol phase transition under ultraviolet light irradiation,which was further characterized by nuclear magnetic resonance(NMR)and UV-Vis spectroscopy.(2)Duing to the introduction of TPE into azobenzene and cholesterol liquid crystal(LC)primitives,the liquid crystal and luminescence behavior of the synthesized gelators were investigated.The phase transition temperature was obtained by differential scanning calorimetry(DSC),the LC texture was observed by polarized light microscopy(POM),and small-angle and wide-angle X-ray scattering(SAXS and WAXS)finally determined the LC phase and the LC self-assembled structure.The results display that three synthesized molecules can become smectic A phase LC,and the LC phase of C3-Chol and C1-Chol can be stable at room temperature.While there is no LC phase during heating for C5-Chol,and two LC phases existing on the cooling process.In addition,three molecules have AIE behaviors,suggesting a class of AIE LC molecules were successfully constructed.