臺灣博碩士論文加值系統

本研究主要是在說明旋光性層列相液晶其結構與性質之間的關係，以 (S)-lactic acid 為起始物合成一系列旋光性液晶材料，並分別探討（i）非旋光末端烷鏈長度’m’、（ii）旋光末端醚氧烷鏈長度’n’ 變化及（iii）在硬核中心導入氟側邊取代基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：三系列液晶材料 I(m=8~12)、II(m=8~12)、III(m=8~12)均出現SmA*和SmC*兩種液晶相。（i）改變非旋光末端烷鏈長度’m’，發現隨著非旋光末端烷鏈長度’m’的增加，液晶相的溫度範圍隨之降低，即澄清點溫度隨著降低、結晶點溫度隨著升高；（ii）改變旋光末端醚烷鏈長度’n’時，澄清點及結晶點溫度則會下降；(iii) 在硬核中心的苯環上導入氟側邊取代基會降低相轉移溫度、熔點、澄清點溫度及自發性極化值。
三系列液晶化合物在SmC*液晶相進行光電量測時顯示在改變溫度和頻率下可得到V型轉換行為，而電流轉換行為的量測結果則不會受到非旋光末端烷鏈長度’m’ 的改變和在硬核中心導入氟側邊取代基而有太大的差異。自發性極化值最大值介於19.89~43.93 nC/cm2。
綜合以上結果得知：苯環第二位置氟側邊取代之乳酸衍生旋光性液晶材料，具有寬廣溫度範圍，熔點可達室溫範圍的誘電性液晶相及具有低Ps值並且在光電量測產生V型光電轉換行為。此項發現提供了V-LCD的應用材料上一項新的參考價值。

The primary of this research work was an attempt to elucidate the correlation between structure and property in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-lactic acid has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by (i) the nonchiral peripheral methylene chain length ‘m’, (ii) the chiral tailed ether alkyl chain length ‘n’ and (iii) lateral 2-fluoro substitution in the core.
Chiral materials of three series I (m=8~12), II (m=8~12), and III (m=8~12), displayed enantiotropic mesophases of the SmA* and SmC* phases. (i)With the increasing nonchiral methylene chain lengths ‘m’, the temperature range of the mesophase decreases. It says that the clearing point decreases and the crystal point increases. (ii) When the chiral tailed ether alkyl chain length ‘n’ increase, the clearing point and crystal point decreases. (iii) The materials with lateral 2-fluoro substitutents in the phenyl ring of core could depress the formation of mesophase, lowering the transition temperature, melting point, clearing point and Ps values.
The electro-optical response in the series of chiral materials in the SmC* phase displayed typical ferroelectric hysteresis loop or hysteresis-free, V-shaped switching property upon various applied frequencies and temperatures. The maximum Ps values of I（m=8~10）, II（m=8~10）, III（m=8~10）vary form 19.89~43.93 nC/cm2. The variations of peripheral chain length ‘m’ in the tree series of compounds, have no remarkable effect on switching behavior in the SmC* phase.
In conclusion, the results indicated that the chiral tailed ether alkyl chain materials derived from (S)-lactic acid with the lateral 2-fluoro substitution in the phenyl ring of core are favorable for the formation of the wide temperature range of the ferroelectric phase. V-shaped switching behaviors appear in the SmC* phase of the chiral materials of the three series. This finding may provide a new way of assessing the nature of the V-shaped switching for display application.

TABLE OF CONTENTS

CHINESE ABSTRACT.………….….……………………………..…….…………….i
ENGLISH ABSTRACT………….…………..…………..………………...………..ii
ACKNOWLEDGMENTS…..…………………………………………...……………iv
TABLE OF CONTENTS……………………..………………..…………….…….......v
LIST OF SCHEME………………………………………………………………. viii
LIST OF TABLES……………………….……………………………..….…………. ix
LIST OF FIGURES………………..…………………………………………………..x
CHAPTER
I INTRODUCTION……………………………….…………………..………1
1.1 Overview.………………………………………………………………..…1
1.2 Chiral Smectic Phases…………………………………………….………………...1
1.2.1 Chiral Smectic A Phase……..………………….…………………1
1.2.2 Chiral Smectic C Phase (Ferroelectric phase)……………………...3
1.2.3 Antiferroelectric phase……………………………………………8
1.3 Motivation of Study……….……………………………………….…...13
II EXPERIMENTAL………………..……………………….……..……16
2.1 Preparation of Materials……..……………….……………………...….16
2.1.1 Synthesis of 2-fluoro-4-hydroxybenzoic acids, I-1…..……….…16
2.1.2 Synthesis of 2-fluoro-4-methoxycarbonyloxybenzoic acid, I-2 .....17
2.1.3 Synthesis of (S)-2-alkoxyethyl 2-hydroxypropionate, I-3, II-3, III-3
…………………………………………………………………….17
2.1.4 Synthesis of 2-alkoxyethyl (S)-2-[2’-fluoro-4-methoxycarbony-
loxy) phenylcarbonyloxy]propionates, I-4, II-4, III-4.……..…….19
2.1.5 Synthesis of 2-alkoxyethyl (S)-2-(2’-fluoro-4-hydroxyphenylcar-
bonyloxy) propionates, I-5, II-5, III-5………..…….……. ….…..20
2.1.6 Synthesis of 4-(4’-alkoxyphenyl)benzoic acids, I-6………....…21
2.1.7 Synthesis of 2-alkoxyethyl (S)-2-[2’-fluoro-4-(4’-alkyloxybiphenyl-
carbonyloxy)phenylcarbonyloxy]propionates I-7, II-7, III-7…......21
2.2 Physical properties……………………………………...….….………22
2.2.1 Mesophase identification………....………………..…………...22
2.2.2 Preparation of homogenous cells……….…………………….23
2.2.3 Alignment of liquid crystals in SSFLC cells……….............…….23
2.2.4 Spontaneous polarization measurement…..……………….……..23
2.2.5 Optical response measurement………...….……………..………24
III RESULTS AND DISCUSSION…………………………………..………26
3.1 Chemical structure identification.……………………………....………26
3.2 The effect of peripheral chain length; I (m=8~12)……………….……..27
3.2.1 Transition temperatures and mesomorphic properties……..….…27
3.2.2 Differential scanning calorimetry (DSC)…..……….……..……..35
3.2.3 Switching behavior……..…………….….…..…………………..39
3.2.4 Spontaneous polarization (Ps)……..…….………………………39
3.2.5 Electro-optical responses………..………..…………...…..……..39
3.3 The effect of peripheral chain length; II (m=8~12)…..………..….….....40
3.3.1 Transition temperatures and mesomorphic properties……….…44
3.3.2 Differential scanning calorimetry (DSC).……….....….…..……..44
3.3.3 Switching behavior…………………………....…………….….46
3.3.4 Spontaneous polarization (Ps)………….………………….……46
3.3.5 Electro-optical responses…………………...…….……….……51
3.4 The effect of peripheral chain length; III (m=8~12).…...............……….54
3.4.1 Transition temperatures and mesomorphic properties..…………54
3.4.2 Differential scanning calorimetry (DSC)………………………..54
3.4.3 Switching behavior…………………..………………………..…55
3.4.4 Spontaneous polarization (Ps)…………………………………....60
3.4.5 Electro-optical responses……………...………..………………..60
3.5 A comparison of in mesomorphic properties for the compounds I, II,
III (m=8)……...…...........……..……….……….………………....……61
3.6 A comparison of in Spontaneous polarization for the compounds I, II,
III (m=8)…..….......................………….…….….….……......................61
3.7 A comparison of in tilt angle for the compounds I, II, III (m=8)………62
IV CONCLUSIONS……………………….……………………………….…69
REFERENCES…………………………..………..……...…………………………70















LIST OF SCHEME

Scheme 2.1 Synthetic procedures for the target compounds, I (m=8~12, n=1),
II (m=8~12, n=3), and III (m=8~12, n=4)…….…………..….…….....18























LIST OF TABLES

Table 2.1 The boiling points and yields for lactates I-3, II-3 and III-3….….……....19
Table 3.1 Chemical shifts of 1H-NMR spectra for I (m=8~12)………………..….…30
Table 3.2 Chemical shifts of 1H-NMR spectra for II (m=8~12).....…………...…31
Table 3.3 Chemical shifts of 1H-NMR spectra for III (m=8~12).………...…..….32
Table 3.4 Results of elemental analysis for the final compounds I (m=8~12),
II (m=8~12), and III (m=8~12).…………………….……………………33
Table 3.5 The transition temperatures and associated enthalpy data for the
I (m=8~12)……...….........…..…………………….……….………………37
Table 3.6 The transition temperatures and associated enthalpy data for the
II (m=8~12)…..….….…...…….…….………………………….…..……...48
Table 3.7 The transition temperatures and associated enthalpy data for the
III (m=8~12)………......…....…..…….…………………………….………58













LIST OF FIGURES

Figure 1.1 The melting process of a calamitic (rod-like) liquid-crystalline
material ..……………....……..…………………………………………2
Figure 1.2 The structure of smectic A phase (SmA*)………….……………………5
Figure 1.3 Symmetry operations in the smectic C and chiral smectic C* phase
(SmC*)……………………………...…………………………………..5
Figure 1.4 Helical macrostructure of the chiral smectic C* phase………..….…6
Figure 1.5 Schematic representation of a "surface stabilized FLC" (SSFLC) cell
where the helix is unwound due to the strong interactionin thin cell. The
director of a molecule can be on either side of a cone with an opening angle of 2θ and alternate each other by applying electrical field and vice
versa…………..…..……………………………………………....……..7
Figure 1.6 The structure of the antiferroelectric smectic C* phase ..…….…………10
Figure 1.7 Antiferroelectric switching behaviors……………....…….……...……….10
Figure 1.8 (a) A three-component mixture of compound I, II and III with the mixing
ratio of I:II:III=40:40:20, (b) the observed V-shaped switching (Upper) and the simulated light transmittance as a function of the normalized electrical field and (c) the simplified model of the phase with
thresholdless antiferroelectricity…….……………...……………….…....11
Figure 1.9 Schematic illustration of the molecular orientational structuresand the
simulated light transmittance as function of electrical field in the
three stable states………….………………………..…………………12
Figure 2.1 Optical setup for the transmittance measurement. L, He-Ne laser; P,
polarizer; C, LC sample cell; D, detector; F, function generator; A,
power preamplifier; S, digital oscilloscope………………..………...…...25
Figure 3.1 The 1H-NMR spectra: (a) I-3 and (b) I-4……….……………………….28
Figure 3.2 The 1H-NMR spectrum: I-7…………...……………………..………….29
Figure 3.3 Textures of I (m=11) observed from the polarizing microscope on
cooling process (a) the focal-conic texture of SmA* phase (100 oC;
magnification ×300); (b) the broken focal-conic texture of SmC* phase
(64 oC; magnification×300)…………..……………………….…….…….34
Figure 3.4 DSC thermogram for I (m=11) in heating and cooling runs at a scanning
rate of 5 ℃/min……………………...……………………...…..………….36
Figure 3.5 A plot of transition temperature as a function of terminal alkyl chain
length ‘m’ for compounds I (m=8~12) on cooling process…..…….……..38
Figure 3.6 The switch current of I (m=9) behaviors in SmA* phase at (a) 90 oC,
SmC* phase at (b) 88 oC, (c) 75 oC, (d) 60 oC, (e) 45 oC and (f) 30 oC
in the homogeneously aligned cell with 5 µm thickness…….……………41
Figure 3.7 Magnitudes of the spontaneous polarization plotted as a function of temperature for I (m=8, 9, 10). The Tc is the temperature of SmA*-
SmC* transition………………………..……………..…………………42
Figure 3.8 Transmittance versus electrical field obtained in the SmC* phase of compound I (m=9) at several temperatures on applying triangular wave,
5Hz………………..………………...………………..……...……………43
Figure 3.9 Textures of II (m=11) observed from the polarizing microscope on
cooling process (a) the focal-conic texture of SmA* phase (100 oC;
magnification ×300); (b) the striated focal-conic texture of SmC* phase
(80 oC; magnification ×300)…………..………………………………..45
Figure 3.10 DSC thermogram for II (m=11) in heating and cooling runs at a
scanning rate of 5℃/min……….....…………………………………..47
Figure 3.11 A plot of transition temperature as a function of terminal alkyl chain
length ‘m’ for compounds II (m=8~12) on cooling process…........…..49
Figure 3.12 The switch current of II (m=9) behaviors in SmA* phase at (a) 90 oC, SmC* phase at (b) 80 oC, (c) 75 oC, (d) 60 oC, (e) 45 oC and (f) 30 oC in
the homogeneously aligned cell with 5 µm thickness………..…….….50
Figure 3.13 Magnitudes of the spontaneous polarization plotted as function of temperature for II (m=8, 9, 10). The Tc is the temperature of SmA*-
SmC* transition………….………………………………………..…..52
Figure 3.14 Transmittance versus electrical field obtained in the SmC* phase of compound II (m=10) at several temperatures on applying triangular
wave, 1Hz……………….……………………………………………….53
Figure 3.15 Textures of III (m=10) observed from the polarizing microscope on cooling process (a) the focal-conic texture of SmA* phase (105 oC; magnification × 300); (b) the striated focal-conic texture of SmC*
phase (70 oC; magnification × 300)…………………………………....….56
Figure 3.16 DSC thermogram for III (m=11) in heating and cooling runs at a
scanning rate of 5 ℃/min…………………..………………………….57
Figure 3.17 A plot of transition temperature as a function of terminal alkyl chain
length ‘m’ for compounds III (m=8~12) on cooling process ...……...…....59
Figure 3.18 The switch current of III (m=9) behaviors in SmA* phase at (a) 90 oC, SmC* phase at (b) 75 oC (c) 60 oC (d) 50 oC (e) 40 oC and (f) 30 oC, in
the homogeneously aligned cell with 5 µm thickness………………...…..63
Figure 3.19 Magnitudes of the spontaneous polarization plotted as function of temperature for III (m=8, 9, 10). The Tc is the temperature of SmA*-
SmC* transition……………………………………………….…….…....64
Figure 3.20 Transmittance versus electrical field obtained in the SmC* phase
of compound III (m=10) at several temperatures on applying triangular wave…………………………………………...…………………….…..65
Figure 3.21 A phase diagram of compounds I (m=8), II (m=8), and III (m=8)……...66
Figure 3.22 Magnitudes of the spontaneous polarization plotted as function of temperature for I, II, III (m=8). The Tc is the temperature of SmA*-
SmC* transition……………………………….……………...………….67
Figure 3.23 The temperature dependences of optical tilt angle of compounds I, II, III (m=10). The Tc is the temperature of SmA*-SmC* transition..………….68

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