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    题名: 雙軸性液晶、超分子液晶材料及掌性盤狀液晶之研究
    其它题名: Studies of biaxial nematic, supramolecular, and chiral discotic liquid crystals
    作者: 陳秀慧;Chen, Hsiu-hui
    贡献者: 淡江大學化學學系博士班
    徐秀福;Hsu, Hsiu-fu
    关键词: 液晶;雙軸;板形;盤形;筒型;螺旋;Liquid Crystals;boardlike;biaxial;discotic;hydeogen-bonded;helical columnar
    日期: 2009
    上传时间: 2010-01-11 02:39:18 (UTC+8)
    摘要: 本論文主要內容分為四個部分,分別是光學雙軸向列型板形液晶材料、氫鍵盤形超分子材料、掌性筒型液晶材料、具螺旋結構的筒型液晶材料之開發及研究。這四個主題除了板形材料外,其餘均以盤形分子為設計主軸,利用其多共軛系統輔助分子進行高秩序性堆疊。
    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。
    氫鍵盤形超分子材料是將氫鍵的概念引入盤形液晶分子的設計中,以快速且有效達到核面積擴大的效果,也就是材料均一性的概念。本論文是以六炔苯基苯為氫鍵單體的主結構,分別以羧酸根及吡啶當作氫給體及氫受體形成氫鍵超分子結構,利用紅外線光譜儀確認氫鍵的存在外,也探討氫鍵對盤形液晶之性質影響。
    最後兩個主題均是將結構螺旋的概念引入分子的設計上,並藉以引導螺旋分子堆疊,以進一步增加筒型分子堆疊之有序性。一個是以六炔苯基苯為出發點,利用引入具掌性側鏈,使無序偏轉之外環傾向特定螺旋偏轉之分子結構;另一個則是於合成過程中加入立體效應概念製備具螺旋構形之并合共軛環。此二分子螺旋構形設計對於引導分子間堆疊之影響,已利用圓二色光譜儀證實其分子螺旋確實可以轉映至分子間螺旋堆疊。
    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.
    显示于类别:[化學學系暨研究所] 學位論文

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