Design,Synthesis And Self-assembly Of Bent-shaped Liquid Crystalline Molecules

Liquid crystals（LCs）have developed rapidly since they were discovered.Initially,the scientists mainly studied the relationship between their structures and properties.Later,the scientists have found that besides the well known application as display,there are many other applications of liquid crystals,such as photonic band gap materials,light modulators,organic light emitting diodes,photovoltaic devices,organic field effect transistors etc.The combination of order and mobility in the LC state provides the unique property which is also the basic requirement for self-assembly and structure formation in bio-systems.Among the classic liquid crystalline molecules,rod-like molecules and disk-like molecules can self-assemble into the nematic phase,the smectic phase and the columnar phase.In order to discover liquid crystalline phases with new nano-structures,it is necessary to design and synthesize new types of liquid crystalline molecules,such as bent-shaped molecules,dendritic molecules,bola amphiphilic molecules and polycatenar molecules etc.Such unconventional liquid crystalline molecules can self-assemble into new and complex liquid crystalline phases.Recently,bent-shaped molecules,where ferroelectricity and spontaneous achiral symmetry breaking emerge in well ordered,but still fluid systems,have attracted much attention.Therefore,in order to obtain the complex liquid crystalline phases and develop new application properties in the bent-shaped molecules,this thesis mainly studies the design,synthesis and self-assembly behavior of three types of unconventional bent-shaped liquid crystalline molecules.Through the changes of the molecular structure parameters（linking groups,flexible chain,and functional group modifications）,the influence of changes in the structural parameters on the self-assembly structures of these molecules was studied.And this thesis is divided into five chapters.In chapter 1,the following five parts are reviewed:research progress of dendrimers;research progress of triazole compounds;research progress of polycatenar amphiphilic compounds;research progress of Janus compounds and research progress of bola amphiphilic compounds.In chapter 2,a series of novel bent-shaped polycatenar molecules consisting of bisphenylsulfone central core and 1,2,3-triazole dendritic wings were synthesized by copper（I）-catalyzed azide-alkyne cycloaddition（CuAAC）reaction.The liquid crystalline properties of the synthesized bisphenylsulfone based bent-shaped polycatenar compounds were studied by polarizing optical microscopy（POM）,differential scanning calorimetry（DSC）and small angle X-ray scatting（SAXS）.These compounds can self-assemble into liquid crystalline phases with hexagonal columnar structure and Pm3n cubic structure,even more complex 3D liquid quasicrystal（LQC）structure by increase the number of the dendritic generations.Additionally,the compound IC³/14 could self-assemble into organogels with different morphologies in1,4-dioxane with aging time.Interestingly,the SEM study reveals that the gel shows the formation of three dimensional networks of nanofibers can transform into microspherical morphologies composing of entangled fibers.XRD date demonstrats that the compound could self-assemble into a layer structure in the gel state.Furthermore,the gels show good mechanical performance and stability and can be established to remove I₂,Fe³⁺,rhodamine B（RhB）from wastewater.In chapter 3,a novel Janus dendrimer JD-I bearing a bisphenylsulfone central core,with a hydrophobic 3,4,5-tridodecyloxybenzylether dendron at one side and a hydrophilic trioligoethylene oxide benzyl triazoly dendron at another side has been synthesized via stepwise copper（I）-catalyzed azide-alkyne cycloaddition（CuAAC）reaction.The pure compound JD-I can not self-assemble into liquid cystalline phase.But JD-I can display SmA₂ phase triggered by the addition of 0.3-1.5 eq alkali metal ions.The conductivity of the doped system（JD-I:LiOTf）is 4.0×10^-8 S cm^-1.The JD-I could gel in both ethanol and aqueous ethanol.The SEM study reveals that such gel can formed helical nanostructure.The XRD displays that the JD-I can self-assemble into a monolayer structure which has a small tilt angle in the layers.Furthermore,the gel system can be established to remove iodine from water.Additionally,JD-I can recognize Fe³⁺with lower detection limit in aqueous ethanol(V_water:V_ethanol=1:1).Finally,JD-I can self-assemble into micelles in aqueous solution,and the critical micelle concentration CMC was determined to be 0.002 mg.mL^-1 with the diameter of the spherical micelles about 15-20 nm.In chapter 4,bolaamphiphiles consisting of a bent 1,3-bis（phenylethynyl）benzene core,two terminal glycerol units,with a long,flexible nonpolar chain（n-alkyl chain,branch chains or semiperfluoroalkyl）attached to the bay region and different group at the apex（CN,Br,NO₂,COOCH₃,COOH,CONH₂）of the central 1,3-substituted benzene ring have been synthesized via Sonogashira coupling reactions as key steps.These compounds can self-assemble into two distinct types of hexagons,3-hexagons and 6-hexagons,leading to p3m1 and p6mm lattices,respectively.Furthermore,the compound I-CN/C₆F₄ with polar group（CN）at the apex can self-assemble into supramolecular columns.In addition,the SHG experiment shows the compound I-CONH₂/C₆F₄ with p3m1 space group has the nonlinear optical property;and under the fluorescence microscopy,the microtube formed by compound ICN-2C5 in EE/PE exhibits blue emission,with very bright luminescence at both tips and relatively weaker emission from the body of the tube,which indicates that the microtube of compound ICN-2C5 migth have optical waveguide property.In chapter 5,the detail synthesis steps of the intermediate products and target compounds,as well as the corresponding experimental data including NMR spectra,XRD and DSC etc are presented.