設計與合成新型未氟化和氟化旋光基衍生之誘電及反誘電性液晶材料

Design and Synthesis of New Non-fluorinated and Fluorinated Chiral Alcohols for the Development of Ferroelectric and Antiferroelectric Liquid Crystal Materials

林卓瑩(Cho-Ying Lin)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/博士(2007年)

摘要

中文摘要

反誘電液晶顯示器(AFLCD)具有寬廣的視角，高解析度，很好的影像品質及全彩化的優良特性，但目前為止仍無法被商品化，這其中液晶材料的相關參數不夠清楚是很重要的關鍵。為了進一步了解結構與其旋光性液晶相之間的關係，本研究以 (S)-propylene oxide 為起始物合成一系列旋光性液晶材料，並分別探討(i)旋光末端未氟化、氟化氧烷鏈及旋光末端燕尾型結構結構變化 (ii)在硬核中心導入側邊取代基及(iii)硬核結構上的變化對於液晶相及物理光電特性的影響，以建立分子結構與旋光液晶相的關係。
實驗結果顯示：在第一部分之第一系列未氟化氧烷鏈材料I(m, n; m=8-12, n=0-3)出現SmA* 和SmC* 液晶相，然而在第二系列氟化氧烷鏈材料 II(m, n; m=8-12, n=1-3)卻出現SmA*、SmC*及SmCA*液晶相，此結果說明氟化烷鏈誘導出SmCA*相。第三系列燕尾型液晶材料中III(m, p; p=0, m=8-12)具有SmA*、SmC*及SmCA*液晶相，但延長旋光鏈長III(m, p; p=1, m=8-12)的系列中，SmCA*液晶相會消失而只出現SmA*和SmC*液晶相。比較其自發性極化值Ps及傾斜角θ發現具反誘電性液晶相的系列材料II(m, n)及III(m, 0)有較高的Ps及θ值。而I(10, 2)及III(10, 1)在SmC*液晶相下進行光電的量測時顯示在特定的溫度和頻率下可得到V形轉換行為，然而I(10, 2)及III(10, 0)在SmCA*相下進行光電的量測時可得到典型反誘電性液晶雙遲滯的三穩定狀態。
第二部份材料IV(m, X, Y)和V(m, X, Y)發現SmCA*相集中出現在非旋光烷鏈8至10之間，而在硬核中心導入側邊取代基會降低相轉移溫度、熔點及自發性極化值但會增加其傾斜角。比較不同原子之取代基發現氯取代基降低相轉移溫度及自發性極化值之幅度最大。比較不同位置取代之效應可得知在苯環第二位置之取代基因部份相轉移溫度受到遮蔽效應的影響明顯的高於苯環上第三位置取代基的化合物，而第二位置取代基亦有較高的自發性極化值及傾斜角。
第三部份材料VI(m)和VII(m)亦發現 SmCA*相集中出現在非旋光烷鏈8至10之間，比較三系列不同硬核結構液晶材料II(m, 2), VI(m) 和VII(m)系列可得知硬核具PhPhCOOPh結構最有利於SmCA* 相的形成，而VI(m)系列有較高的自發性極化值，但硬核改變對傾斜角並無太大影響。在以肉桂酸衍生之材料VIII(m)-XIII(m)系列中可歸納出：結構中至少要有三個苯環才能形成SmCA* 相，而兩個苯環的硬核結構材料只有SmC*相的生成，然而具有兩個苯環的材料其自發性極化值及傾斜角皆高與三個苯環的液晶材料。硬核結構的改變亦有利於出現一些sub-phases，例如SmCα*及SmCγ*相。
在混合液晶材料的研究中指出室溫型反誘電液晶材料可藉由混合兩個反誘電性液晶獲得。在以80%的V(8, H, Cl)和20%XIV(10)做混合的材料中，在室溫25℃下施加26V及60Hz量應答時間，其上升時間為586.7 μs 而下降時間為109.5μs。
本研究利用高純度(S)-propylene oxide所衍生之旋光燕尾及半氟化醇合成出大量的反誘電性液晶材料並建立起結構與反誘電性液晶相之間的關係。此結果在學術上：提供給後續反誘電性液晶材料的設計與合成上的新的參考。在應用上：本研究之混合液晶材料為顯示器的研發上提供一個新的參考價值。

關鍵字

誘

並列摘要

ABSTRACT
AFLCD display with such good characteristics as: wide screen, high resolution, excellent image quality and full color have been developed. However, so far, display manufacturers have been unable to commercialize AFLC display devices despite continuous efforts. It seems that the appearance of the SmCA* phase and structure-property relationship of AFLC materials are still understood well enough to optimize the material parameters. Thus, in order to ascertain the structure-property correlations and the practical application in electro-optical services, in this work, we attempt to elucidate the structure-property correlation in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-propylene oxide has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by the (i) the structure of the non-fluorunated, fluorinated alkoxy chain length and chiral swallow-tailed structure (ii) lateral halogen substituents in the core and (iii) different core structure of the molecules of the chiral molecules for the study.
Chiral non-fluorinated materials, I(m, n; m=8-12, n=0-3) displayed enantiotropic mesophases of the SmA* and SmC* phases; however, chiral semi-fluorinated materials, II(m, n; m=8-12, n=1-3), exhibited SmA*, SmC* and SmCA* phases. These results demonstrate that the presence of the semi-fluorinated alkyl chain in the chiral tail of the material induces an antiferroelectric SmCA* phase. Chiral swallow-tailed materials, III(m, p; p=0, m=8-12), displayed enantiotropic mesophases of the SmA*, SmC* and SmCA* phases. The materials increasing methylene chain lengths n, III(m, p; m=8-12, p=1), the SmCA* was disappeared and only exhibited SmA* and SmC* phase. In addition, the antiferroelectric liquid crystal materials, II(m, n) and III(m, 0), have higher Ps and θ values than ferroelectric liquid crystal materials, I(m, n) and III(m, 1). The electro-optical response in the series of chiral materials, I(10, 2) and III(10, 1), in the SmC* phase displayed V-shaped switching property; however, in the series of chiral materials, II(10, 2) and III(10, 0), in the SmCA* phase displayed typical antiferroelectric tri-stable state of double hysteresis loop switching behavior .
Chiral semi-fluorinated materials, IV(m, X, Y) and V(m, X, Y), were synthesized and investigating the influence of lateral halogen substituents in the core. The SmCA* phase was generally occurred in the alkyl chain length from m=8 to m=10 of the materials. The materials with lateral substitutents in the core could depress the formation of mesophase, lowering the transition temperature, melting point and Ps values but increasing θ values. Comparing with the materials of different atom substitution, it is seen that the materials with lateral chloro substituents in the core of molecular was most decreasing transition temperature and Ps values. The materials with halogens substuted at 2-position on the ring of the molecule were sterically shielded so that possessed higher transition temperature than that materials at 3-position; however, the materials with halogens substuted at 2-position on the ring of the molecules also enhanced Ps and θ values.
In chiral semi-fluorinated materials, VI(m) and VII(m), the SmCA* phase was also occurred in the alkyl chain length from m=8 to m=10 of the materials. Comparing with different core structure of three series materials, II(m, 2), VI(m), VII(m), it can be found the materials, III(m, 2), with PhPhCOOPh as the core structure of the molecule were favorable for the formation of antiferroelectric SmCA* phase; however, the materials have highest Ps values in those materials. In chiral materials, VIII(m)-XIII(m) which derived firm cinnamatic acid can be found two ring core materials only exhibit ferroelectric SmC* phase; however, three ring core materials favor the formation of antiferroelectric SmCA* phase. Changing the core structure of molecule exhibited some sub-phases such as SmCα* and SmCγ* phases.
Binary mixture study shows that the antiferroelectric mixtures with ambient temperature can be obtained by two antiferroelectric liquid crystals. The response of the optical transmission obtained from the antiferroelectric mixture of 80% V(8, H, Cl) and 20% XIV(10) in SSFLC cell by driving at 60Hz and 26V square wave at 25℃ show that the raise time is 586.7 μs and fall time is 109.5μs.
In conclusion, the chiral swallow-tailed and semi-fluorinated alcohol groups can be prepared by the optically pure (S)-propylene oxide treating with semi-fluorinated or swallow-tailed alcohols. These chiral alcohols are then developed large amount of antiferroelectric liquid crystals, and subsequently, the structure-property correlation for the formation of antiferroelectric liquid crystals is established. The establishment of this correction will be beneficial for the future design and synthesis of more antiferroelectric liquid crystals. A large amount of antiferroelectric liquid crystals developed in the present work demonstrates that there is a potential for the preparation of suitable antiferroelectric mixtures for the display devices.

並列關鍵字

ferroelectric liquid crystals ； antiferroelectric liquid crystals

參考文獻

[6] N. A. Clark, S. T. Lagerwall. Appl. Phys. Lett., 36, 899 (1980).

[12] R. B. Meyer. Mol. Cryst. Liq. Cryst., 40, 74 (1976).

[19] J. Barbera, A . Omenat, J. L. Serrano. Mol. Cryst. Liq. Cryst., 166, 167 (1989).

[22] H. Taniguchi, M. Ozaki, K. Yoshino, N. Yamasaki, K. Satoh. Jpn. J. Appl. Phys., 26, 4558 (1987).

[28] S. T. Nishiyama, Y. Ouchi, H. Takzoe, A. Fukuda. Jpn. J. Appl. Phys., 26, L1787 (1987).