|其它题名: ||Studies of biaxial nematic, supramolecular, and chiral discotic liquid crystals|
|作者: ||陳秀慧;Chen, Hsiu-hui|
|关键词: ||液晶;雙軸;板形;盤形;筒型;螺旋;Liquid Crystals;boardlike;biaxial;discotic;hydeogen-bonded;helical columnar|
|上传时间: ||2010-01-11 02:39:18 (UTC+8)|
首先在光學雙軸向列型液晶材料的開發，利用分子幾何形狀設計介於皆為單軸之桿形與盤形分子間，合成出以苯環為中心外接四個炔基聯苯的罕見板形結構一系列化合物，除了利用偏光顯微鏡(optical microscope)證實均具有向列型液晶相外，並利用錐光偏振鏡檢法(conoscopy observation)、自由立膜法(free standing film)以及在外加磁場配向下之粉末X光繞射實驗確認其光學雙軸性。
In this thesis, four liquid crystalline systems are explored, i.e. biaxial board-like nematic, hydrogen-bonded discotic supramolecular, chiral columnar, and helical columnar liquid crystals. The synthesis and properties of these four systems are described in details. Except the biaxial liquid crystals, all other systems are discotic mesogens.
For the exploration of biaxial nematic liquid crystalline materials, the molecular shape was designed to be between calamitic and discotic by replacing the peripheral phenyls in reported board-like 1,2,4,5-tetrakis(phenylethynyl)benzene with biphenyls. These materials exhibited nematic phases by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The optical biaxiality of these nematic phases were detected by conoscopic studies as well as by their optical textures of free-standing films. Moreover, biaxiality of these nematic phases were confirmed by powder X-ray diffraction (PXRD) studies under magnetic field.
Based on the reported discotic nematogen, hexakis(alkoxyphenylethynyl)- benzene, replacing one of the alkoxyphenyl with a pyridine and with a benzoic acid afforded two new compounds, a hydrogen bonding acceptor and a hydrogen donor respectively. Mixing the two afforded a new disc dimer by generating hydrogen bonding interaction between the pyridine and carboxylic acid. The hydrogen bonding interactions were identified by infrared spectroscopy and differential scanning calorimeter. The liquid crystalline temperature range of the dimer was significantly widened to be ca. two fold of that of the pyridyl disc monomer.
In the third system, chiral chains were introduced onto columnar hexakis(dialkoxyphenylethynyl)benzene. Studies by circular dichroism and scanning tunneling microscopy (STM) confirmed intramolecular and intermolecuar chiral inductions Intramolecularly, the chiral chains have induced helical conformation of other sidearms within the molecule by STM studies. On the other hand, intermolecular chiral induction was detected by CD signal amplification when a chiral discogen was doped into a non-chiral discogen.
The last system utilized steric hindrance for the design of a new helicene based on hexabenzocoronene (HBC). Incorporation of the helical conformation onto the HBC has imposed more ordered intracolumnar molecular packing evidenced by PXRD studies than the reported planar HBC analogues that slippage of discs within columns are very likely to occur.