探討具有萘環液晶材料中旋光基氟化烷鏈長度對液晶相及其光電性質的影響

Study on the Effect of Semi-fluorinated Alkyl Chain Length on the Mesomopic Phase of Chiral Liquid Crystals containing Naphthalene Core

謝秉宏(Bing-hung Sie)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/碩士(2008年)

摘要

以(S)-butylene oxide與氟化醇類在鹼性環境下反應合成出具有光學活性的醇類(S)-1-(2,2,2-trifluoroethoxy)-2-butanol, (S)-1-(2,2,3,3,3-pentafluoropropoxy)-2-butanol, and (S)-1-(2,2,3,3,4,4,4-heptafluorobutoxy)-2-butanol。再以上述醇類合成五系列旋光性氟化材料,在旋光基氟化烷鏈長度對誘電性液晶相與反誘點性液晶相的影響。探討五系列旋光性液晶材料I(m=8-12, n=1, q=1), Ⅱ (m=8-12, n=1, q=3), III(m=8-12, n=2, q=1), IV(m=8-12, n=2, q=2) and V(m=8-12, n=2, q=3)結果如下:
藉由偏光紋理圖及DSC的鑑定可分別得知液晶相及相轉移溫度的變化，經
由電流轉換行為及介電性質的量測可進一步鑑定誘電性及反誘電性液晶相的存在。
實驗結果指出: 旋光側邊具有乙基與具有甲基的液晶材料相比，結果顯示,第一系列(q=1)生成室溫型誘電性液晶相,卻抑制反誘電性液晶相的生成。再第二系列(q=3)生成室溫型反誘電液晶相,卻縮短反誘電性液晶相的範圍。半氟化液晶材料 II, III, IV 具有雙向性的SmA*與SmCA*﹔旋光末端之半氟化烷鏈的長度由-CF3,-CF2CF3 增加至-CF2CF2CF3，結果顯示液晶相熱穩定度會隨之增加，尤其是對反誘電性液晶相。硬核結構由單苯環延長為雙苯環時,結果顯示增加熔點與澄清點及液晶相的熱穩定性,並且改變了反誘電性液晶相由單向性液晶變成雙向性液晶。
在物理性質量測方面結果顯示:比較結構類似的液晶材料可發現隨著旋光中心的側邊由具有甲基延長到具有乙基時， 最大自發性極化值增加。旋光末端氟化烷鏈長度的增加，最大自發性極化值增加。顯示出光學傾斜角不會受到氟化烷鏈長度、旋光中心側邊長度與硬核結構的延長而改變。

關鍵字

誘電性液晶 ； 半氟化旋光性液晶材料 ； 反誘電性液晶

並列摘要

Optically active alcohols, (S)-1-(2,2,2-trifluoroethoxy)-2-butanol, (S)-1-(2,2,3,3,3-pentafluoropropoxy)-2-butanol and (S)-1-(2,2,3,3,4,4,4-heptafluorobutoxy)-2-butanol, were designed and synthesized by the treatment of (S)-butylene oxide with fluorinated alchols under basic condition. Five novel homologous series of chiral fluorinated materials derived from these alcohols, (R)-1-(2,2,2-trifluoroethoxy)-2-butanol, (R)-1-(2,2,3,3,3-pentafluoropropoxy)-2-butanol, and (R)-1-(2,2,3,3,4,4,4-heptafluorobutoxy)-2-butanol, were than synthesized for the investigation concerning the effect of the extent of fluorination at the chiral group of the molecule on the formation of SmC* and SmCA* phases. The results obtained from the study of five series of chiral materials, I(m=8-12, n=1, q=1), Ⅱ (m=8-12, n=1, q=3), III(m=8-12, n=2, q=1), IV(m=8-12, n=2, q=2) and V(m=8-12, n=2, q=3) can be summarized as follows:
The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric and antiferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'.
Comparing semi-fluorinated liquid crystal materials possessing ethyl substituent to that possessing methyl substituen at the aymetric carbont, the former suppress the formation of antiferroelectric phase. Compounds III(m=8-12, n=2, q=1), IV(m=8-12, n=2, q=2 and V(m=8-12, n=2, q=3) possess enantiotropic SmA* and SmCA* phases.The extension of semi-fluorinated chiral alkanes increase from -CF3, -CF2CF3 to -CF2CF2CF3 resulted in an enhancement of the stability of mesophases, especially, the SmCA* phase. Extending phenyl ring to biphenyl ring in the core of the molecules could result in increasing melting point, clear point and thermal stability of mesophases, and changing the formation of antiferroelectric SmCA* phase from monotropic to enantiontropic mesophase.
The physical properties of the chiral materials in ferroelectric SmC* and antiferroelectric SmCA* phases were also measured. The magnitudes of maximum Ps values are decreased with the extension of the lateral group at the asymmetric carbon atom from methyl to ethyl group, as compared to the corresponding structural similar chiral materials. The magnitudes of maximum Ps values are increased with the extension of chiral fluorinated alkyl chains from –CF3, -CF2CF3 to CF2CF2CF3. The magnitudes of apparent tilt angle (θ) values show that there is no significant correlation to the extension of fluorinated alkyl chain lengths, lateral alkyl substituent from methyl to ethyl group and addition ring at core structure.

並列關鍵字

antiferroelectricity ； semi-fluorinated chiral liquid crystal ； ferroelectricity

參考文獻

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