| Liquid crystal is a soft matter which has both order of crystal and mobility of liquid. It has been existed for 128 years since liquid crystal was first discovered. Nowadays, the liquid crystal has been widely used as liquid crystaline display, GPS navigation systems, panel computer, smart mobilephone, digital camera, projector, domestic appliance and large industrial equipment and so on. Modern life will be unimaginable without liquid crystals. Therefore, it is an urgent need of the modern society to reduce costs, save raw materials, and get more effcient liquid crystal materials. Designing simple and novel liquid crystal molecules, discovering new liquid crystal phase, and exploring the relationship between structures and properties of the liquid crystal molecules are currently great interest in the field of liquid crystal. These results will help to deepen the understanding of self-assembly of soft material forming liquid crystal functional materials.This thesis is composed of six chapters:In chapter 1, the research progress on cholesterol-azobenzene compounds was reviewed. Symmetrical trimesogens incorporating two cholesteryl groups as terminal groups at a central azobenzene core unit were often reported as multiresponsive gelation system. Unsymmetrical cholesterol-azobenzene couples were reported mostly as mesogens which could form chiral mesophases, including blue phases (BP), chiral nematic (N*), twist grain boundary (TGB), and chiral smectic C (SmC*). The research progress on heterocyclic liquid crystal compounds was reviewed, including 1,2,3-triazole ring,1,3,4-thiadiazole ring,1,3,4-oxadiazole ring,2,5-diphenyl thiophene, and the terphenyl liquid crystal compounds. It has been reported based on the heterocyclic liquid crystal compounds, most of these compounds can form nematic phase, smectic phase and column phase. Finally, this chapter introduced the research situations on imidazolium ionic liquid crystal compounds and fluorenone liquid crystal compounds.In chapter 2, a series of azo compounds with a CN group at one end and a cholesteryl carbonate attached via different spacer unit to the opposite end were synthesized in this chapter. The liquid crystalline, photo responsive and gelling properties as well as chiral induction and chiral amplification properties were demonstrated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscope (AFM), and affected by UV irradiation. These compounds are reversible photoresponsive chiral liquid crystal, and show a chiral nematic phase (N*) and a smectic C phase (SmC*). These compounds have good solubility in 4’-pentyl-4-cyanobiphenyl (5CB), and can act as chiral mesogenic dye dopants to induce a high helical-twisting chiral phase in the common nematic phase of 5CB. These compounds can show reversible photoresponsive properties in solution, the liquid crystalline state and the gel state. The gelation test revealed that the compounds with shorter spacer unit could form multiple stimuli-responsive organogels in medium polarity organic solvents. The gels formed in organic solvents have multiple stimuli-responsive behavior upon exposure to a number of environmental stimuli, including temperature, light and shear forces. SEM and AFM reveal that the gelator molecules self-assemble into fibers with helical conformation forming three-dimensional networks.In chapter 3, the research on ABC type triblock liquid crystal compounds containing heterocyclic was summarized. First of all, three series of triblock polyphiles consisting of a rigid 4-phenyl-1,2,3-triazole or 1,4-diphenyl-1,2,3-triazole core, with three lipophilic and flexible alkoxyl chains at one end and a polar glycerol group at the opposite end were synthesized via copper-catalyzed azide-alkyne click reaction(CuAAC). Depending on alkyl chain length and core-length, a transition from hexagonal columnar to Pm3n-type cubic phases was observed. In the cubic phases, the molecules organized into spherical objects. Remarkably, compounds with a longer core unit have a higher tendency to form these cubic phases and their stability is strongly enhanced compared to those of the compounds with a shorter core, despite longer cores provide a smaller cone angle and therefore would be expected to disfavor the formation of spherical objects. There is a large difference of the number of molecules involved in the spherical aggregates formed by compounds with long and short cores. Whereas the aggregates in the cubic phases of the compounds with short rod units are small and could be regarded as micellar, the long-core compounds form much larger aggregates which are considered as a kind of monolayer vesicular aggregates.Secondly, this chapter introduced the 1,3,4-thiadiazole ring and 1,3,4-oxadiazole ring liquid crystal compounds. Triblock polyphiles containing 1,2,3-triazole ring have been reported in the previous works. In order to further explore whether the other heterocycle contained block molecules can also form the monolayer vesicular aggregates. Triblock compounds containing 2,5-diphenyl-1,3,4-oxadiazole or 1,3,4-thiadiazole ring were synthesized in this chapter to study the structure and self-assembled relationship. Their mesophase behavior was studied by POM, DSC and XRD. Depending on alkyl chain length, and a transition from hexagonal columnar to Pm3n-type cubic phases was observed. Compounds with a 1,3,4-oxadiazole ring have a higher tendency to form these cubic phases. UV absorption spectra and fluorescence emission spectra showed that these compounds have better optical and electrical properties compared to triblock polyphiles containing 1,2,3-triazole ring. These compounds have broad application prospects as functional luminescent materials.Finally, the 2,5-diphenyl thiophene and the terphenyl contained liquid crystals were Synthesized. In order to further explore the regular of forming cubic phase. Block compounds containing linear terphenyl,2,5-diphenyl thiophene have smaller dipole moment and compounds contining thiophene acetylene units have a longer core. The compounds containing terphenyl units can only form hexagonal columnar phases. A transition from Pm3n-type cubic to Cub/Im3 m phases was observed for block compounds containing 2,5-diphenyl thiophene. Despite compounds containing thiophene acetylene units have a longer core, a transition from hexagonal columnar to Pm3n-type cubic phases was also observed. Therefore, the bending angle, the dipole moment and hydrogen bonding ability, all are very critical for the formation of complex three-dimensional cubic phase. This result provides a good way for deepening the understanding of the relationship between the design of structure and self-assembly structure of the liquid crystal molecules.Chapter 4 contains the synthesis and liquid crystal properties of imidazolium ionic liquid crystals was observed. In the previous works, we have systematically studied the structure-property relation of nonthiophene imidazolium salts with different linking groups. In order to further explore their new applications and relevant new properties, the rigid core is further elongated by inserting one or two thiophenes between imidazol and phenyl rings of the parent triple chain ether nonthiophene imidazoliums, leading to two new series of oligothiophene imidazolium salts with longer rigid core, monothiophene imidazolium bromides and bisthiophene imidazolium bromides. Due to the special properties of thiophene units, elongation of the rigid core by inserting thiophene units into the rigid core leads to the nonlinear shape of the molecules, and lower melting points and higher clear points and therefore broader region of LC phases, SmA-Colhex-CubI/Pm3n was also found in these oligothiophene ILCS upon decreasing the length of the N-terminal chain or by increasing the length of the triple C-terminal chains. It is interesting that the columnar phase can occur above and below the cubic phase upon rising the temperature for monothiophene imidazolium bromides and columnar phases are dominant for bisthiophene imidazolium bromides.Chapter 5 contains the synthesis and liquid crystal properties based on fluorenone derivative was prepared. Three series of symmetrical fluorenone derivative with flexible alkoxyl chains at both ends were synthetized. All the compounds can form Colhex/p6mm, and the Colhex/p6mm formed at lower temperature and the cubic phase formed at high temperature are also observed in the compound with four alkoxyl chains. The melting point and the clearing point were reduced by the increase of the number of alky1 chains. When the number of alkyl chains is the same, the compounds with a benzylether linking groups have a lower melting point and higher clearing point compared to the compounds with a ester linking groups. This result may be due to the greater flexibility of benzylether. The compounds with thiophene units have a lower melting point and higher clearing point compared to the compounds without thiophene units, this may be due to the introduction of the thiophene ring and the conjugate property of the rigid core increases. Photophysical properties show that the maximum absorption peak gives rise to red-shifted with the increasing of the number of thiophene rings in the rigid core, and the maximum absorption peak has little change with the change of the length of the alkyl chain. The energy gaps (2.46-2.95 eV) of these compounds are calculated by UV absorption spectroscopy and density functional theory, which indicated that these compounds could be used as potential organic semiconductor materials.Chapter 6 contains the detail synthesis steps of the intermediate products and target compounds, as well as the corresponding experimental data including NMR spectra, XRD and DSC were provided. |
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