臺灣博碩士論文加值系統

過去對於藍相(BP)液晶單一材料的報導並不多見，而且溫度範圍都很狹窄(1-2

℃)，主要因為藍相(BP)為一種挫敗相(frustrated)，也因此分子結構與藍相(BP)

生成的關係從未被建立。因此設計開發具藍相(BP)液晶相的材料並建立分子結構與

藍相(BP)生成的關係，近幾年來成為本實驗室研究的方向，所以本研究以具有光學

活 性 的 醇 類 為 起 始 物 ， 合 成 六 系 列 液 晶 材 料 I-RS(m=6-10), II-SS(m=6-10),

III(m=6-9, n=2, p=1), IV(m=6-9, n=2, p=2), V(m=6-9, n=3, p=3) and VI(m=6-9, n=4,

p=2) ，主要分為兩個部分進行探討(i)非旋光烷鏈長度(m)、(ii)旋光烷鏈長度(n)

及(p)，對於藍相(BP)液晶相生成的影響，藉以建立分子結構與藍相(BP)液晶生成的

關係。

第一部份結構如下 :







I-RS(m=6-10)







II-SS(m=6-10)

第二部份結構如下:






III (m, n, p; m=6-9, n=2, p=1)

`VI






IV (m, n, p; m=6-9, n=2, p=2)
V (m, n, p; m=6-9, n=3, p=3)
VI (m, n, p; m=6-9, n=4, p=2)


第三部分的研究是探討混合液晶對於藍相液晶的穩定性，將兩液晶化合物依不

同重量百分比的比例混合(100/0, 80/20, 65/35, 50/50, 35/65, 20/80, 0/100)以觀察藍相

(BP)液晶相溫度範圍的變化，其分子結構如下:







I-RS(m=8)






II-SS(m=8)

實驗結果顯示: 六系列化合物中，可以觀察到 BP, N*, TGBA*, SmA*和 SmC*液晶

相，挫敗相(BP 和 TGB*)的產生顯示出化合物具有高旋光性。兩光學同分異構物

I-RS(m=6-10)與 II-SS(m=6-10)對藍相生成並無顯著的影響。化合物隨著旋光末端烷

鏈長度(n, p)增長，藍相的穩定度隨之增加。其中，當旋光末端烷鏈長度相同時(n=p)，

類似於燕尾型，有最寬廣的藍相溫度範圍。

光學同分異構物的混合液晶實驗中，發現了藍相(Blue Phase)液晶消失，而出

現了膽固醇型液晶相。推測的原因是藍相的雙螺旋結構中，其中一個方向的螺旋互

相抵消，只剩一個方向的螺旋，所以觀察到的是膽固醇型液晶相。

綜合以上研究結果顯示，非旋光末端烷鏈的鏈長’m’的改變，對藍相液晶相的溫


`VII






度範圍無顯著規則性。旋光末端烷鏈的鏈長(n=p)相等時，類似於燕尾型結構有較寬

廣的藍相溫度範圍，隨著旋光末端烷鏈鏈長(n, p)的增加也會有較寬廣的藍相溫度範

圍。六系列化合物中，V (m, n, p; m=8, n=3, p=3)具有最寬廣的雙向性藍相液晶相(約

為 13.9 度 C)。

A few of liquid crystal materials exhibiting blue phases have been reported in a

single compound, moreover, the blue phases in the materials possess a very small

temperature range (cal.1-2℃), mainly because of the blue phases are frustration phases.

Thus, in order to find more of blue phase liquid crystal materials and shed light on the

relationship between molecule structure and the formation of blue phases, in this work,

the optically active alcohols, (S, S)-1-(2-methylbutyloxy)-2-propanol and (R,

S)-1-(2-methylbutyloxy)-2-propanol were designed and synthesized by reacting

(R)-propylene oxide or (S)-propylene oxide with (S)-2-methyl-1-butanol under basic

condition as the chiral moieties for synthesizing chiral liquid crystal materials. The other

optically active alcohols, 2-alkylalkyl (S)-2-hydroxypropanoate were designed and

synthesized by the reaction of (L)-lactic acid with alcohols. Consequently, six

homologous series of chiral compounds, (R,

S)-6-[1-methyl-2-(2-methylbutoxy)ethoxy]-2-naphthyl 4-(alkyloxy)benzoate,

I-RS(m=6-10), and (S, S)-6-[1-methyl-2-(2-methylbutoxy)ethoxy]-2-naphthyl

4-(alkyloxy)benzoate, II-SS(m=6-10), and 2-alkylalkyl

(R)-2-[4-(4’-alkoxyphenylcarbonyloxy)biphenyloxy]propionates, III(m=6-9, n=2, p=1),

IV(m=6-9, n=2, p=2), V(m=6-9, n=3, p=3) and VI(m=6-9, n=4, p=2), were prepared for

the study.

The results of the works are divided into two part for discussion, and the results for

discussions are in term of the effect of (i) achiral terminal alkyl chain length (m) of the

materials, (ii) chiral terminal alkyl chain length (n) and (p) of the materials, on the

generation of blue phase liquid crystals.


`II






Six series of the materials for the study with the general formulas are depicted

below.



The first part of materials is depicted as follow







I-RS(m=6-10)







II-SS(m=6-10)

The second part of materials is depicted as follow






III (m, n, p; m=6-9, n=2, p=1)
IV (m, n, p; m=6-9, n=2, p=2)
V (m, n, p; m=6-9, n=3, p=3)
VI (m, n, p; m=6-9, n=4, p=2)

The third part of the works is to investigate whether the binary mixture of the blue

phase materials could enhance the thermal stability of the blue phase. Thus, binary

mixtures (I) with the weight percentage ratios of 100/0, 80/20, 65/35, 50/50, 35/65, 20/80,

0/100 of the compounds were prepared for the investigation. The corresponding

molecular structures of the target compounds are depicted below:




`III











I-RS(m=8)







II-SS(m=8)

The results from the study of these six series of chiral compounds show that,

depending on the molecular structure, various mesomorphic phases: BP, N*, TGBA*,

SmA* and SmC* phases can be found. The appearance of frustrated phases (BP and TGB*

phase) indicate that most of these compounds possess high chirality. The results from the

study of two diastereomers; I-RS(m=6-10) and II-SS(m=6-10) on the formation of blue

phase shows that the formation of blue phases have no obvious correction to the isomers.

As extending alkyl lengths (n, p) at the chiral tail of the compounds, the stability of BP

phases increases. In addition, when the lengths of “n” and “p” are in the same number

resemble to the swallow-tail like, the compounds has the wider temperature range of BP

phase.

In the study of the binary mixture of diastereomers, surprisingly, it is found that

mixing of diastereomers results in the disappearance of blue phase. This result may be

due to that one of helix in the double helix of the blue phase in diastereomers is in the

opposite sense with nearly the same pitch, such that diminishes one of the helix in the

mixtures and remains other helix that exhibiting chiral nemetic phase.

In conclusion, our results show that the change of achiral alkyl chain length ‘m’ has

no correlation to the temperature range of blue phase. Chiral tails length (n=p) along with

`IV






the increase of n and p, which is resemble to the swallow-tail like, has wider temperature

range of blue phase. Among all compounds, compound V (m, n, p; m=8, n=3, p=3) has the widest temperature range of enantiotropic blue phases (cal. 13.9℃).

ACKNOWLEDGEMENTS I
ABSTRACT II
中文摘要IV
TABLE OF CONTENTS IX
LIST OF SCHEME XII
LIST OF TABLES XIII
LIST OF FIGURES XIV
CHAPTER 1 1
INTRODUCTION 1
1.1. Overview 1
1.2. Cholesteric (Ch) or chiral nematic (N＊) phase 3
1.3. Chiral smectic phases 5
1.3.1. Chiral smectic A phase (SmA*) 5
1.3.2. Chiral smectic C phase (Ferroelectric phase, SmC*) 6
1.4. Frustrated phases 11
1.4.1. Blue phases 11
1.4.2. Twist grain boundary phase 15
1.4.2.1. The TGBA* phase 16
1.5. Motivation of study 19
CHAPTER 2 24
EXPERIMENTAL 24
2.1. Preparation of materials 24
2.1.1. Synthesis of 4-alkoxybenzoic acid chloride, 1(m=6-10) 27
2.1.2. Synthesis of 6-hydroxy-2-naphthyl 4-alkyloxybenzoate, 2(m=6-10)27
2.1.3. Synthesis of 4-hydroxybiphenyl 4’alkoxybenzoate, 3(m=6-9) 28
2.1.4. Synthesis of (S, S)-1-(2-methylbutyloxy)-2-propanol, I-4 28
2.1.5. Synthesis of (R, S)-1-(2-methylbutyloxy)-2-propanol, II-4 29
2.1.6. Synthesis of (S, S)-2-methylbutyl 2-hydroxypropanoate III-4 29

`IX






2.1.7. Synthesis of 2-alkylalkyl (S)-2-hydroxypropanoates, IV-4, V-4, VI-4 29
2.1.8. Synthesis of (R, S)-6-[1-methyl-2-(2-methylbutoxy)ethoxy]-2-naphthyl
4-(alkyloxy)benzoate, I-RS(m=6-10) 30
2.1.9. Synthesis of (S, S)-6-[1-methyl-2-(2-methylbutoxy)ethoxy]-2-naphthyl
4-(alkyloxy)benzoate, II-SS(m=6-10) 31
2.1.10. Synthesis of (S)-2-methylbutyl (R)-2-[4-(4’-alkoxyphenylcarbonyloxy)b
iphenyloxy]propionates, III(m=6-9, n=2, p=1) 31
2.1.11. Synthesis of 2-ethylbutyl (R)-2-[4-(4’-alkoxyphenylcarbonyloxy)b
iphenyloxy]propionates, IV(m=6-9, n=2, p=2) 32
2.1.12. Synthesis of 2-propylpentyl (R)-2-[4-(4’-alkoxyphenylcarbonyloxy)b
iphenyloxy]propionates, V(m=6-9, n=3, p=3) 32
2.1.13. Synthesis of 2-ethylhexyl (R)-2-[4-(4’-alkoxyphenylcarbonyloxy)b
iphenyloxy]propionates, VI(m=6-9, n=4, p=2) 32
2.1.14. Preparation of the binary mixture 33
2.2. Physical properties 33
2.2.1. Chemical structure identification 33
2.2.2. Mesophase identification 33
2.2.3. Preparation of homogenous cells 34
2.2.4 Dielectric constant measurement 34
CHAPTER 3 36
RESULTS AND DISSCUSSION 36
3.1. Chemical structure identifications 36
3.1.1. Mesophase studies 36
3.2. The effect of diastereomers and the peripheral chain length on the formation of
mesophases for compounds I-RS(m=6-10) and II-SS(m=6-10) 36
3.2.1. Optical microscopy observations and phase transition behaviors of chiral
compounds I-RS(m=6-10) 37
3.2.2. Dielectric property measurements for the compounds I-RS(m=9) 45
3.2.3. Optical microscopy observations and phase transition behaviors of chiral
compounds II-SS(m=6-10) 46

3.2.4. Dielectric property measurements for the compounds II-SS(m=10) 52
3.3. The effect of achiral and chiral chain length on the mesomorphic properties of chiral compounds III(m=6-9, n=2, p=1), IV(m=6-9, n=2, p=2), V(m=6-9, n=3,p=3), VI(m=6-9, n=4, p=2) 55
3.3.1. Optical microscopy observations and phase transition behaviors for the
chiral compounds III(m=6-9, n=2, p=1) 55
3.3.2. Optical microscopy observations and phase transition behaviors for the chiral compounds IV(m=6-9, n=2, p=2) 63
3.3.3. Optical microscopy observations and phase transition behaviors for the chiral compounds V(m=6-9, n=3, p=3) 69
3.3.4. Optical microscopy observations and phase transition behaviors for the chiral compounds VI(m=6-9, n=4, p=2)75
3.4. Comparison of mesomorphic properties among structurally similar molecular structures82
3.4.1. The influence of the diasteromers on mesophase properties for compounds IVN-II(m=7-9, n=4), I-RS(m=7-9) and II-SS(m=7-9) 82
3.4.2. The influence of the lateral alkyl chain length on mesophase properties for compounds III(m=8, n=2, p=1), IV(m=8, n=2, p=2), V(m=8, n=3, p=3) and VI(m=8, n=4, p=2) 82
3.5 The study of binary mixtures of diasteromers 85
3.5.1 Optical microscopy observations and phase transition temperatures for the binary mixture, I 85
CHAPTER 4 91
CONCLUSIONS 91
REFERENCES 92
APPENDIX 95

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