viii TABLE OF CONTENTS CHAPTER NO. TITLE PAGE NO. ABSTRACT iii LIST OF TABLES xv LIST OF FIGURES xviii LIST OF SYMBOLS AND ABBREVIATIONS xxix 1. INTRODUCTION 1 1.1 INTRODUCTION TO LIQUID CRYSTALS 1 1.2 HISTORY OF LIQUID CRYSTALS 2 1.3 CLASSIFICATION OF LIQUID CRYSTALS 4 1.3.1 Lyotropic Liquid Crystals 4 1.3.2 Thermotropic Liquid Crystals 5 1.4 SHAPE OF MOLECULES AND THEIR MESOPHASES 6 1.4.1 Conventional Shaped Liquid Crystal 6 1.4.1.1 Calamitic liquid crystals 7 1.4.1.2 Discotic liquid crystals 11 1.4.2 Non-Conventional Shaped Liquid Crystals 12 1.5 (ANTI) FERROELECTRICITY AND SWITCHING MECHANISM 15 1.6 CHIRALITY IN LIQUID CRYSTALS 18 1.7 BENT-CORE LIQUID CRYSTALS 20 1.7.1 B 1 Mesophase 20 1.7.1.1 Variants of B 1 mesophase 23
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viii
TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
ABSTRACT iii
LIST OF TABLES xv
LIST OF FIGURES xviii
LIST OF SYMBOLS AND
ABBREVIATIONS xxix
1. INTRODUCTION 1
1.1 INTRODUCTION TO LIQUID CRYSTALS 1
1.2 HISTORY OF LIQUID CRYSTALS 2
1.3 CLASSIFICATION OF LIQUID CRYSTALS 4
1.3.1 Lyotropic Liquid Crystals 4
1.3.2 Thermotropic Liquid Crystals 5
1.4 SHAPE OF MOLECULES AND
THEIR MESOPHASES 6
1.4.1 Conventional Shaped Liquid Crystal 6
1.4.1.1 Calamitic liquid crystals 7
1.4.1.2 Discotic liquid crystals 11
1.4.2 Non-Conventional Shaped Liquid Crystals 12
1.5 (ANTI) FERROELECTRICITY AND
SWITCHING MECHANISM 15
1.6 CHIRALITY IN LIQUID CRYSTALS 18
1.7 BENT-CORE LIQUID CRYSTALS 20
1.7.1 B1 Mesophase 20
1.7.1.1 Variants of B1 mesophase 23
ix
CHAPTER NO. TITLE PAGE NO.
1.7.2 B2 Mesophase 24
1.7.2.1 Variants of B2 mesophase 27
1.7.3 B3 Mesophase 28
1.7.4 B4 Mesophase 28
1.7.5 B5 Mesophase 29
1.7.5.1 Variants of B5 mesophase 30
1.7.6 B6 Mesophase 30
1.7.7 B7 Mesophase 31
1.7.7.1 Variants of B7 mesophase 33
1.7.8 B8 Mesophase 34
1.7.9 SmCG Phase 34
1.8 STRUCTURE PROPERTY RELATIONSHIP
IN BENT-CORE LIQUID CRYSTALS 34
1.8.1 Central Unit 36
1.8.2 Connecting Groups 37
1.8.3 Lateral Substitution 39
1.8.4 Terminal Chains 41
1.9 APPLICATIONS AND IMPORTANCE
OF LIQUID CRYSTALS 43
1.10 BENT-CORE LIQUID CRYSTALS –
A SURVEY 48
1.10.1 Effect of Central Unit Variation in
Mesophase 48
1.10.2 Effect of Linking or Connecting
Groups (X & Y) Variation in Mesophase 55
1.10.3 Effect of Lateral Substitution in
Mesophase 58
x
CHAPTER NO. TITLE PAGE NO.
1.10.4 Effect of Terminal Chains (R1 & R2)
Variation in Mesophase 59
1.11 SCOPE AND OBJECTIVES 66
2. EXPERIMENTAL 70
2.1 MATERIALS 70
2.2 PURIFICATION OF SOLVENTS 71
2.2.1 Benzene 71
2.2.2 Dichloromethane 71
2.2.3 Chloroform 71
2.2.4 Ethylacetate 71
2.2.5 Ethanol 72
2.2.6 Methanol 72
2.2.7 Acetone 72
2.2.8 N,N -Dimethylformamide 72
2.2.9 Thionyl Chloride 72
2.2.10 Water 73
2.3 SYNTHESIS OF KEY INTERMEDIATES 73
2.3.1 Synthesis of 4-(10-Undecenoyloxy)
biphenyl-4-carboxylic Acid (1) 73
2.3.2 Synthesis of 4-(Alkyloxy)benzoic
Acids (2a-2g) 74
2.3.3 Synthesis of 4-(4-n-Alkyloxybenzoyloxy)
benzaldehydes (3a-3g) 75
2.3.4 Synthesis of 4-(4-n-Alkyloxybenzoyloxy)
benzoic Acids (4a-4g) 76
2.3.5 Synthesis of Resorcinolmonobenzyl
ether (5) 77
xi
CHAPTER NO. TITLE PAGE NO.
2.3.6 Synthesis of 4-((3-(Benzyloxy)
phenoxy)carbonyl)phenyl-4-(alkyloxy)
benzoates (6a-6g) 77
2.3.7 Synthesis of 4-((3-Hydroxyphenoxy)
carbonyl)phenyl-4-(alkyloxy)
benzoates (7a-7g) 78
2.3.8 Synthesis of 3-(4-(4-(Alkyloxy)benzoyloxy)
benzoyloxy)phenyl-4-formyl
benzoates (8a-8g) 79
2.3.9 Synthesis of 4-(Alkyloxy)
acetanilides (9a-9g) 80
2.3.10 Synthesis of 4-(Alkyloxy)
anilines (10a-10g) 81
2.4 SYNTHESIS OF TARGET COMPOUNDS 82
2.4.1 Synthesis of 1,3-Substituted
Phenylenebis(4-(10- undecenoyloxy)-
1,1'-biphenyl-4-carboxylate)s (Ia-Ie) 82
2.4.2 Synthesis of 3-(4-(4-(alkyloxy)benzoyloxy)
benzoyloxy)phenyl-4'-(10-undecenoyloxy)
biphenyl-4-carboxylates (IIa-IIg) 83
2.4.3 Synthesis of 3-(4-(4-(alkyloxy)benzoyloxy)
benzoyloxy)phenyl-4-((4-(alkyloxy)
phenylimino)methyl)benzoates (IIIa-IIIg) 84
2.4.4 Synthesis of 3-(4-(4-(alkyloxy)benzoyloxy)
benzoyloxy)phenyl-4-((4-(decyloxy)
phenylimino)methyl)benzoates (IVa-IVg) 85
xii
CHAPTER NO. TITLE PAGE NO.
2.5 CHARACTERIZATION OF COMPOUNDS 85
2.5.1 Fourier Transform-Infrared
Spectroscopy 86
2.5.2 Nuclear Magnetic Resonance
Spectroscopy 86
2.5.3 Differential Scanning Calorimetry 87
2.5.4 Polarizing Optical Microscope 88
2.5.5 X-Ray Diffraction Measurements 89
2.5.6 Electro-Optical Investigations 90
3. RESULTS AND DISCUSSION 92
3.1 BACKGROUND OF THE STUDY 92
3.2 SYNTHESIS 94
3.2.1 Synthesis of Compounds Ia-Ie (Series I) 94
3.2.2 Synthesis of Compounds IIa-IIg (Series II) 95
3.2.3 Synthesis of Compounds IIIa-IIIg
and IVa-IVg (Series III & IV) 97
3.3 SPECTRAL TECHNIQUES OF KEY
INTERMEDIATES AND COMPOUNDS 98
3.3.1 Fourier Transform-Infrared
Spectroscopy 98
3.3.21H-Nuclear Magnetic Resonance
Spectroscopy 120
3.3.3 13
C- Nuclear Magnetic Resonance
Spectroscopy 144
xiii
CHAPTER NO. TITLE PAGE NO.
3.4 POLARIZED OPTICAL MICROSCOPY
STUDIES 165
3.4.1 Mesomorphic Property of
Compounds Ia-Ie 166
3.4.2 Mesomorphic Property of Intermediates
of Series (II) and Compounds IIa-IIg 167
3.4.3 Mesomorphic Property of
Compounds IIIa-IIIg 171
3.4.4 Mesomorphic Property of
Compounds IVa-IVg 172
3.5 DIFFERENTIAL SCANNING
CALORIMETRY 176
3.5.1 Differential Scanning Calorimetric
Study of Compounds Ia-Ie 177
3.5.2 Differential Scanning Calorimetric
Study of Compounds IIa-IIg 179
3.5.3 Differential Scanning Calorimetric
Study of Compounds IIIa-IIIg
and IVa-IVg 182
3.6 X-RAY DIFFRACTION STUDIES 187
3.6.1 X-Ray Diffraction Measurements
for Compounds IIa-IIg 187
3.6.2 X-Ray Diffraction Measurements for
Compounds IIIa-IIIg 189
3.7 ELECTRO-OPTICAL MEASUREMENT
AND SWITCHING ANALYSIS 192
3.7.1 Electro-Optical Switching Analysis
of Compounds IIa-IIg 193
xiv
CHAPTER NO. TITLE PAGE NO.
3.7.2 Electro-Optical Study and Spontaneous
Polarization Analysis of Compounds
IIIa-IIIg and IVa-IVg 196
4. CONCLUSION 207
4.1 SCOPE FOR FUTURE STUDY 211
REFERENCES 213
LIST OF PUBLICATIONS 233
VITAE 234
xv
LIST OF TABLES
TABLE NO. TITLE PAGE NO.
1.1 Current applications for liquid crystal displays 45
3.1 FT-IR spectral data of 4-n-(alkyloxy)benzoic
acids (2a-2g) 100
3.2 FT-IR spectral data of 4-(4-n-alkyloxy)benzoyloxy
benzaldehydes (3a-3g) 102
3.3 FT-IR spectral data of 4-(4-n-alkyloxybenzoyloxy)
benzoic acids (4a-4g) 103
3.4 FT-IR spectral data of 4-((3-(benzyloxy)phenoxy)
carbonyl)phenyl-4-(alkyloxy)benzoates (6a-6g) 106
3.5 FT-IR spectral data of 4-((3-hydroxyphenoxy)carbonyl)
phenyl-4-(alkyloxy)benzoates (7a-7g) 108
3.6 FT-IR spectral data of 3-(4-(4-(alkyloxy)benzoyloxy)
benzoyloxy)phenyl-4-formylbenzoates (8a-8g) 110
3.7 FT-IR spectral data of 4-(alkyloxy)
acetanilides (9a-9g) 111
3.8 FT-IR spectral data of 4-(alkyloxy)anilines (10a-10g) 113
3.9 FT-IR spectral data of compounds Ia-Ie 114
3.10 FT-IR spectral data of compounds IIa-IIg 117
3.11 FT-IR spectral data of compounds IIIa-IIIg 119
3.12 FT-IR spectral data of compounds IVa-IVg 120
3.13 1H-NMR spectral data of compounds 2a-2g 123
3.14 1H-NMR spectral data of compounds 3a-3g 124
3.15 1H-NMR spectral data of compounds 4a-4g 127
3.16 1H-NMR spectral data of compounds 6a-6g 130
3.17 1H-NMR spectral data of compounds 7a-7g 132
xvi
TABLE NO. TITLE PAGE NO.
3.18 1H-NMR spectral data of compounds 8a-8g 134
3.19 1H-NMR spectral data of 4-(alkyloxy)
acetanilides (9a-9g) 135
3.20 1H-NMR spectral data of 4-(alkyloxy)
anilines (10a-10g) 136
3.21 1H-NMR spectral data of compound Ia-Ie 138
3.22 1H-NMR spectral data of compounds IIa-IIg 140
3.23 1H-NMR spectral data of compounds IIIa-IIIg 142
3.24 1H-NMR spectral data of compounds IVa-IVg 143
3.25 13C-NMR spectral data of compounds 2a-2g 145
3.26 13C-NMR spectral data of compounds 3a-3g 147
3.27 13C-NMR spectral data of compounds 4a-4g 148
3.28 13C-NMR spectral data of compounds 6a-6g 151
3.29 13C-NMR spectral data of compounds 7a-7g 153
3.30 13C-NMR spectral data of compounds 8a-8g 155
3.31 13C-NMR spectral data of compounds 9a-9g 156
3.32 13C-NMR spectral data of compounds 10a-10g 157
3.33 13C-NMR spectral data of compounds Ia-Ie 159
3.34 13C-NMR spectral data of compounds IIa-IIg 161
3.35 13C-NMR spectral data of compounds IIIa-IIIg 162
3.36 13C-NMR spectral data of compounds IVa-IVg 164
3.37 Transition temperatures ( C) and associated
enthalpies (J/g) observed in DSC for Ia-Ie 179
3.38 Transition temperatures ( C) and associated
enthalpies (J/g) for compounds IIa-IIg 180
3.39 Transition temperatures ( C) Tm and Ti
for compounds IIa-IIe 181
xvii
TABLE NO. TITLE PAGE NO.
3.40 Transition temperatures (ºC) and associated
enthalpies (J/g) for the compounds of series III 184
3.41 Phase transition temperatures (ºC) and
associated enthalpies (J/g) for the compounds
of series IV 185
3.42 Small angle Bragg reflections (Å) and their
mesophase of compounds IIa-IIg 189
xviii
LIST OF FIGURES
FIGURE NO. TITLE PAGE NO.
1.1 Schematic representation of molecular
arrangement 2
1.2 Schematic representation of the aggregation
of amphiphiles into micelles 5
1.3 Schematic representation for classification
of thermotropic liquid crystals and its polarizing
optical microscopy image 6
1.4 (a) A general template for molecular structure of
calamitic LC and (b) an example of a calamitic LC 7
1.5 Representation of (a) nematic phase and
(b) smectic A phase 9
1.6 Representation of (a) cholesteric phase, (b) chiral
smectic C phase (SmC*) and (c) the angle in
director in subsequent layers 9
1.7 (a) General molecular structure of hexa-n-
alkanoyloxy benzenes and (b) schematic
representation of the columnar structure 11
1.8 Molecular structures of different types of
non-conventional LCs 14
1.9 Bistable switching under influence of an
electric field 16
1.10 Two types of layer organization for bent-core
molecules (a) ferroelectric and (b) antiferroelectric 17
1.11 Two types of polar switching (a) around a cone and
(b) around the molecule 18
xix
FIGURE NO. TITLE PAGE NO.
1.12 Comparison of calamitic and bent-core molecules
and their organization in the smectic layers 19
1.13 Schematic representation of the frustrated
structure of B1 mesophase 22
1.14 Proposed structures of (a) B1 and (b) B1rev 24
1.15 Pictorial representation of the geometry of a
smectic layer in the B2 (SmCPA) phase 25
1.16 Schematic representation of the arrangement of
BC molecules in racemic and chiral states of an
antiferroelectric mesophase and the corresponding
field induced ferroelectric states 27
1.17 Pictorial representation of in-plane molecular
packing in the B5 phase 29
1.18 Schematic representation of the arrangement
of BC molecules in the B6 phase 31
1.19 General scheme of a bent-shaped molecule 35
1.20 Schematic representations on usage of liquid
crystal in various fields 44
1.21 Molecular structure of target compounds
series I-IV 68
2.1 Synthesis of compound 1 73
2.2 Synthesis of compound 2a 74
2.3 Synthesis of compound 3a 75
2.4 Synthesis of compound 4a 76
2.5 Synthesis of compound 5 77
2.6 Synthesis of compound 6a 77
2.7 Synthesis of compound 7a 78
2.8 Synthesis of compounds 8a 79
xx
FIGURE NO. TITLE PAGE NO.
2.9 Synthesis of compound 9e 80
2.10 Synthesis of compounds 10e 81
2.11 Synthesis of compounds Ia-Ie 82
2.12 Synthesis of compounds IIa-IIg 83
2.13 Synthesis of compounds IIIa-IIIg 84
2.14 Synthesis of compounds IVa-IVg 85
2.15 Block diagram showing the X-ray diffraction
experimental set-up 90
2.16 Block diagram of a circuit used for the measurement
of polarization 92
3.1 Synthesis of compounds Ia-Ie (series I) 95
3.2 Synthesis of compounds IIa-IIg (series II) 96
3.3 Synthesis of compounds IIIa-IIIg & IVa-IVg
(series III & IV) 97
3.4 FT-IR spectrum of compound 1 99
3.5 FT-IR spectrum of 4-(hexyloxy)benzoic acid (2a) 100
3.6 FT-IR spectrum of 4-(4-n-heptyloxybenzoyloxy)
benzaldehyde (3b) 101
3.7 FT-IR spectrum of 4-(4-n-heptyloxybenzoyloxy)
benzoic acid (4b) 102
3.8 FT-IR spectrum of 4-(4-n-nonyloxybenzoyloxy)
benzoic acid (4d) 103
3.9 FT-IR spectrum of resorcinol monobenzylether (5) 104
3.10 FT-IR spectrum of 4-(4-n-octyloxybenzoyloxy)
phenyl monobenzylether 3-benzoate (6c) 105
3.11 FT-IR spectrum of 4-((3-(benzyloxy)phenoxy)
carbonyl)phenyl-4-(dodecyloxy) benzoate (6g) 105
xxi
FIGURE NO. TITLE PAGE NO.
3.12 FT-IR spectrum of 4-((3-hydroxyphenoxy)
carbonyl)phenyl-4-(heptyloxy)benzoate (7b) 106
3.13 FT-IR spectrum of 4-((3-hydroxyphenoxy)carbonyl)
Phenyl-4-(undecyloxy)benzoate (7f) 107
3.14 FT-IR spectrum of 4-((3-hydroxyphenoxy)
carbonyl)phenyl-4-(dodecyloxy)benzoate (7g) 107
3.15 FT-IR spectrum of 3-(4-(4-(heptyloxy)benzoyloxy)
benzoyloxy)phenyl-4-formylbenzoate (8b) 108
3.16 FT-IR spectrum of 3-(4-(4-(nonyloxy)benzoyloxy)
benzoyloxy)phenyl-4-formylbenzoate (8d) 109
3.17 FT-IR spectrum of 3-(4-(4-(dodecyloxy)
benzoyloxy) benzoyloxy)phenyl-4-formyl
benzoate (8g) 109
3.18 FT-IR spectrum of 4-(nonyloxy)acetanilide (9d) 110
3.19 FT-IR spectrum of 4-(decyloxy)acetanilide (9e) 111
3.20 FT-IR spectrum of 4-(heptyloxy)aniline (10b) 112
3.21 FT-IR spectrum of 4-(octyloxy)aniline (10c) 112
3.22 FT-IR spectrum of 4-(decyloxy)aniline (10e) 113
3.23 FT-IR spectrum of compound Ia 114
3.24 FT-IR spectrum of compound IIa 115
3.25 FT-IR spectrum of compound IIb 115
3.26 FT-IR spectrum of compound IIe 116
3.27 FT-IR spectrum of compound IIf 116
3.28 FT-IR spectrum of compound IIIf 117
3.29 FT-IR spectrum of compound IIIg 118
3.30 FT-IR spectrum of compound IVe 118
3.31 FT-IR spectrum of compound IVg 119
3.321H-NMR spectrum of compound (1) 121
xxii
FIGURE NO. TITLE PAGE NO.
3.331H-NMR spectrum of 4-(hexyloxy)benzoic acid (2a) 122
3.341H-NMR spectrum of 4-(decyloxy)benzoic acid (2e) 122
3.351H-NMR spectrum of 4-(4-n-octyloxybenzoyloxy)
benzaldehyde (3c) 124
3.361H-NMR spectrum of 4-(4-n-hexyloxybenzoyloxy)
benzoic acid (4a) 125
3.371H-NMR spectrum of 4-(4-n-heptyloxybenzoyloxy)
benzoic acid (4b) 126
3.381H-NMR spectrum of 4-(4-n-octyloxybenzoyloxy)
benzoic acid (4c) 126
3.391H-NMR spectrum of resorcinol monobenzylether (5) 127