Synthesis And Self-assembly Behavior Of Oligothiophene-based Bolaamphiphiles And Benzothiadiazole-based Polycatenar Compounds

Since liquid crystals (LCs) was discovered in1888, this area has been developed rapidly. LCs combine the order of the crystal and the fluid of the liquid in the molecular level, which leads to the self-healing, adaptive, and stimuli-responsive properties of these supramolecular systems. These unique properties made LCs system the quintessential self-assembling molecular materials of the current science area. The research of the driving force of LCs microscopic self-assembly and the relationship between the structure and the self-assembled structure of the liquid crystalline molecules has become the focus of the scientific research community. Moerover, it is the most essential goal to design novel liquid crystalline molecules which can self-assemble into more complex microscopic ordered structures.Bolaamphiphiles and polycatenar molecules are two important LCs systems, which can form a series of complex nanostructures with different dimensions by molecular self-assembly. In order to achieve the application of these LCs system, oligothiophene unit and2,1,3-benzothiadiazole (BTD) unit, which possess excellent optoelectronic properties, were introduced into both LCs systems respectively. We hope that these compounds will give rise to not only novel liquid-crystalline structures and new LCs self-assembly principles but also can be applied as electrooptical matierals.In chapter1, the research progress on bolaamphiphile-and BTD-based LCs were summarized. Firstly the research work on bolaamphiphile-based LCs was reviewed the effects of rigid core and terminal polar group as well as the length/number/kind of lateral non-polar chains to the self-assemble behaviour of bolaamphiphiles are highlighted and some novel columnar phase and lamellar phases as well as cubic phase formed by bolaamphiphiles were listed. Then, the progress on benzothiadiazole-based liquid crystals was reviewed, including both non-symmetrical and symmetrical liquid crystals (LCs) containing one or two BTD units. The relationship among molecular structure, mesophase behavior and the electrooptic property is highlighted.In chapter2, the synthesis and liquid-crystalline property of dithiophene-based bolaamphiphiles were investigated. The results showed that with the increasing of the length of lateral chain(s), SmA+phase and square honeycombs columnar phase (Co\squ/p4mm) with double molecular wall were formed by T-shaped dithiophene-based bolaamphiphiles, while an isotropic phase (Iso) and square honeycombs columnar phase (Colsqu/p4mm) with single molecular wall were formed by X-shaped dithiophene-based bolaamphiphiles. Interesting, a stable ColhexNp6mm phase was formed by adding water to the Iso phase, which demonstrated that the transition from triangular cylinder phase to a square cylinder phase could go through a disordered isotropic state upon reaching a critical lateral chain length. This finding will encourage us to explore the complex self-assemble structure between triangular and square cylinder phase by modification of the dithiophene rigid core.In chapter3, on the basis of chapter2, a series of X-shaped5,5’-bis(phenylethynyl)-2,2’-bithiophene-based bolaamphiphiles with longer regid core has been synthesized and their liquid-crystalline properties were investigated. The results showed that by increasing the length of the lateral chains, a transition from defective triangular cylinder phase (ColhexNp6mm) to square cylinder phase (Colsqu/p4mm) was observed. Additional acetylene units enabled the formation of triangular cylinder phase, but cannot provide a proper degree of rigid core to form the complex intermediate phase and even liquid-crystalline superstructure combining triangular and square cells. The reason may be that the rigid linear structure of C=C bond leads to an enhanced zigzag-shape which reduce the orientational order of rigid aromatic cores.In chapter4, in order to find the complex intermediate phases between ColhexNp6mm phase and Colsqu/p4mm phase, a series of tetrathiophene-based and sexithiophene-based bolaamphiphiles with longer rigid core were synthesized and investigated. The reasearch showed that these compounds could form the defected ColhexA/p6/mm phases. By elongation of the lateral chains, there is a trend of increasing the stability of liquid crystalline phase. But the intermediated phases were not found in these compounds, the reason may be ascribed to the increasing the number of the lateral chains leading to the difficulty of the XRD investigation for these compounds. In addition, the spectrum data and DFT calculation results showed that sexithiophene-based bolaamphiphiles have a lower optical band gap (Egopt=2.39-2.60eV) and there is a strong intramolecular charge transfer along the π-conjugated oligothiophene core.In chapter5, the synthesis and liquid-crystalline properties of a series of2,1,3-benzothiadiazole-based polycatenar molecules have been investigated. The results showed that the compounds without thiophene spacers only exhibited monotropic hexagonal columnar phases (Colhex/p6mm). By introducing thiophene spacer, enantiotropic rectangular phase with clmm lattice (Colrec/c2mm) was found in the compound with short alkyl chains while enantiotropic hexagonal columnar phase (Colhex/p6mm) was found in the compound with long alkyl chains. It was demonstrated that the volume of peripheral alkyl chains and the length of aromatic core had significant impacts on the self-assembly behavior of polycatenar molecules. Additionally, the spectrum data and DFT calculation results demonstrated that there was a strong intramolecular charge transfer in2,1,3-benzothiadiazole-based polycatenar molecules with thiophene spacer and an enhanced absorbance at long wavelength (λmax≈504nm) with a lower optical band gap (Egopt=1.99-2.19eV).In chapter6, the detail synthetic procedures of eight types of target compounds and the corresponding experimental data for each compound were provided.