Topologically Designed Cylindrical and Spherical Building

TOPOLOGICALLY DESIGNED CYLINDRICAL AND SPHERICAL BUILDING

BLOCKS TO CONSTRUCT MODULAR-ASSEMBLED STRUCTURES IN GIANT

SHAPE-AMPHPHILES

A Dissertation

Presented to

The Graduate Faculty of The University of Akron

In Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy

Jing Jiang

May 2018 TOPOLOGICALLY DESIGNED CYLINDRICAL AND SPHERICAL BUILDING

BLOCKS TO CONSTRUCT MODULAR-ASSEMBLED STRUCTURES IN GIANT

SHAPE-AMPHPHILES

Jing Jiang

Dissertation

Approved: Accepted:

Advisor Department Chair Dr. Stephen Z. D. Cheng Dr. Coleen Pugh

Committee Chair Dean of the College Dr. Toshikazu Miyoshi Dr. Eric J. Amis

Committee Member Dean of the Graduate School Dr. Tianbo Liu Dr. Chand K. Midha

Committee Member Date Dr. Yu Zhu

Committee Member Dr. Chrys Wesdemiotis

ABSTRACT

Giant shape amphiphiles with isobutyl polyhedral oligomeric silsesquioxane (BPOSS) cages as the periphery at two discotic trisubstituted derivative of benzene cores were specifically designed and synthesized. Depending upon the number of BPOSS cages, these molecules first assembled into either cylindrical or spherical units via π-π interactions among the core unites. The packing of the molecules is mandated by the steric hindrance of the BPOSS cages at the periphery with hydrogen bonding interactions. If the space-packing is allowed, the cylindrical building block can form. Otherwise, the cylindrical building block will be forced to interrupt periodically and to form spherical building blocks. These units can further modular assemble into supramolecular structures.

The cylindrical units form columnar structures with both hexagonal and rectangular packing, while the spherical units construct a Frank-Kasper A15 phase, similar to the metal alloy structures. In addition, based on the mechanism proposed by this work, five more giant shape amphiphiles with high steric hindrance on the periphery were synthesized, these giant shape amphiphiles successfully formed A15 phases with precisely size control,

iii validating the reliability of this strategy. Formation of A15 phase based on nano-spherical building blocks offers a new pathway to design and construct new supramolecular phases and further functionalizes these structures.

ACKNOWLEDGEMENTS

First of all, I wish to express my deepest gratitude to my advisor, Prof. Stephen Z. D.

Cheng for offering great opportunity for me to work as a graduate assistant in his group. I really appreciate his long-term encouragement, support, and inspiration. He is a person full of vision and led me towards the field I’ve never reached before. Instead of Polymer

Science, I majored in Organic Chemistry during my undergraduate study, which is related to fundamental synthetic theories about small molecules. I never involved in any area related to the polymeric materials before he took me to be his student. In spite of the large gap between my background and his research directions, Dr. Cheng has always showed great confidence in me through those years, which was very important for me to conquer any difficulties in my experiments. He is always full of enthusiasm for the science. The way how he conducts himself also gave me a lot of inspiration. What I learn from him is that to be a professional researcher, one should continuously pursue mystery in science, not only focus on the basis of the problems but should also possess a keen insight into the frontier. This project was completely under his supervision and firmly support. From the

v molecular design, sample preparation to data analysis, he gave me tremendous of advices and assistance. I also appreciate that he gave me enough guidance as well as equal level of freedom to choose my research directions and to design experiments. He is a considerate professor who will intentionally let you think about things instead of tell you how to do directly. Without his tremendous guidance and supports, none of the interesting results and conclusions in this dissertation can be possible. His great powder helped a lot of his students includes me. My sincere gratitude is expressed to him.

I am very grateful to the dedicated committee members: Prof. Toshikazu Miyoshi,

Prof. Tianbo Liu, Prof. Yu Zhu and Prof. Chrys Wesdemiotis. I truly appreciate their attendances in my Research Presentation and Defense, and their valuable comments and assistance that guided my research in this dissertation.

I would like to express my deep gratitude especially to Prof. Bernard Lotz for his patient guidance of my research in crystallography. He is a teacher worth his salt. No matter how small the problem is, he will explain it to me clearly full of passion. Although he discussed with me for less than twenty times, his knowledge in crystal structure analysis had a huge influence on me and encouraged me to investigate the crystal structures. About one year ago, that is a hard time for me, I felt very depressed and worried about the possibility of finishing these projects. During that time Dr. Lotz visited our group during that time and talked to me very patiently. He has shown a very positive

vi attitude to both of the research and life. Inspired by his spirits, I started to find a balance for me to solve problems instead of subjected to the worries. He is a person combined professional in science and enjoy of life together, I felt very lucky to have the chance discussing with him.

I would also like to thank my group members, in particular, Dr. Kan Yue for sharing synthetic skills, Dr. Mingjun Huang for sharing physical analysis techniques, Dr.

Chih-Hao Hsu for sharing structure determination and simulation skills during the beginning of my research. Special thanks are given to Dr. Yu Wang, Dr. Wei Zhang, and

Mr. Shuailin Zhang for discussing the details in the project described in chapter four.

Thanks Dr. Tao Li for shearing Synchrotron SAXS experiment beam time, Mr. Shan Mei for preparing carbon coated copper grid, Mr. Bo Ni for sharing microtome skills, Ms.

Jialin Mao for the MALDI MS measurement, and Mr. Wenbin Yin for the IR measurement.

Finally, I would like to thank my family members and friends for their endless supports, encouragement, and understanding during my pursuit of Ph.D. degree. I am deeply grateful to my parents and grandparents. Due to the One Child Policy in China, I am the only child in my family, my parents and grandparents give me selfless love since I was born. When I told them my plan to study abroad, my parents respected my choice and given me the best support immediately. For my grandparents, in spite of the fact that they

vii do not want me to go so far away from home and these years I missed a lot of important things in their lives including the 80th birthday of my grandfather, they still love me. This gives me great power to overcome difficulties in finishing this dissertation. I am also deeply grateful to my boyfriend, Shuailin Zhang, for his support during my writing of this dissertation. When I felt upset and struggling with the tedious problems with myself, he is the person come and talk to me by sharing with his positive thoughts and some even worse situations, which made me feel not that bad.

In summary, the journey of my pursuing the Ph.D. degree in the University of

Akron is full of all kinds of explorations, challenges, improvements and love. I am very grateful to all the people that paricaipated in this important stage of my life.

viii

TABLE OF CONTENTS

Page

LIST OF SCHEMES ...... xiv

LIST OF FIGURES ...... xvi

CHAPTER

I. INTRODUCTION ...... 1

II. BACKGROUND ...... 5

2.1 Building from the Bottom Up ...... 5

2.1.1 Bottom-up Approach ...... 5

2.1.2 Soft Material ...... 6

2.1.3 Bottom-up Construction of Soft Material ...... 8

2.2 Modular Giant Molecule ...... 11

2.2.1 Nanoparticle – “Giant Atom”...... 11

2.2.2 Giant Surfactant ...... 14

2.2.3 Giant Polyhedra ...... 16

2.2.4 Giant Shape Amphiphile ...... 19

2.2.5 Precise Synthesis through Click Reactions ...... 20 ix

2.3 Disc Shape Molecule ...... 24

2.3.1 π interaction Among Disc-shape Molecules ...... 24

2.3.2 Liquid Crystal (LC) Mesogens ...... 26

2.3.3 Physical Properties and Applications ...... 34

2.3.4 Triethynyl Benzene (TEB) ...... 42

2.3.5 Tris-(1, 2, 3-triazol)Benzene (TAB) ...... 44

2.4 Frank-Kasper(F-K) Phase ...... 47

2.4.1 Topological Close Packing ...... 47

2.4.2 Square-triangle Tiling of F-K Phase ...... 49

2.4.3 Examples of F-K Phase ...... 52

2.4.4 F-K Phases in Soft Materials ...... 54

III. EXPERIMENTAL TECHNIQUES ...... 64

3.1 Chemical Reaction Toolbox ...... 64

3.1.1 Corner-Capping Reaction ...... 64

3.1.2 Hydrosilylation Reaction ...... 65

3.1.3 Staudinger Reaction ...... 66

3.1.4 Copper-catalyzed Azide-alkyne Cycloaddition (CuAAC) ...... 68

3.1.5 Sonogashira Reaction...... 69

3.2 Inert Atmosphere Techniques ...... 70

3.3 High Vacuum Line Technique ...... 70

3.4 Schlenk Line Techniques ...... 71

3.5 Chemical Characterization Methods ...... 72

3.5.1 Nuclear Magnetic Resonance (NMR) Spectroscopy ...... 72

3.5.2 Matrix-assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectroscopy ...... 73

3.6 Physical Characterization Methods...... 73

3.6.1 Thermal Gravimetric Analysis (TGA) ...... 75

3.6.2 Differential Scanning Calorimetry (DSC) ...... 75

3.6.3 Small-Angle X-ray Scattering (SAXS) ...... 76

3.6.4 Wide Angle X-ray Diffraction (WAXD) ...... 76

3.6.5 Transmission Electron Microscopy (TEM) ...... 77

3.6.6 Density Measurements ...... 77

IV. FROM CYLINDRICAL TO SPHERICAL PACKED SUPRASTRUCTURES BY TOPOLOGICALLY DESIGNED GIANT SHAPE AMPHIPHILES ...... 79

4.1 Molecular Design ...... 79

4.2 Synthesis and Characterization ...... 82

4.3 Thermal Stability of BPOSS-based Giant Shape Amphiphiles ...... 102

4.4 Sample Preparation ...... 103

4.5 Phase Behavior of Four Disc-POSS Giant Shape Amphiphiles ...... 105

4.6 Hierarchical Structure Analysis of TEB-BPOSS3 ...... 107

4.6.1 Columnar Structure with Less Ordered to Ordered Intracolumnar Packing ...... 107

4.6.2 Thermal Expansion Analysis Help to Separate X-ray Peaks Related to Hierarchical Structure ...... 113

4.6.3 Ordered Columnar Phase Determined by 2D Fiber Pattern...... 115

4.7 Columnar Phases of TEB-BPOSS3 and TAB-BPOSS3 ...... 117

4.7.1 Structure Analysis ...... 117

4.7.2 Phase Morphologies of TEB-BPOSS3 and TAB-BPOSS3 ...... 120

4.8 Spherical Phase of TEB-BPOSS6 and TAB-BPOSS6 ...... 123

4.9 Discussion ...... 125

4.10 Conclusion ...... 128

V. CONSTRUCTING SPHERICAL MOTIFS WITH PRECISE LENGTH

CONTROL:LINKER LENGTH EFFECT ON THE TAB-CnBPOSS6 A15 STRUCTURE ...... 130

5.1 Molecular Design ...... 130

5.2 Synthesis and Characterization ...... 131

5.3 Self-assembled Structures of n=3-8 Determined by SAXS and TEM ...... 152

5.4 Conclusion ...... 160

SUMMARY ...... 161

xii

REFERENCE ...... 163

APPENDIX ...... 173

xiii

LIST OF SCHEMES

Scheme Page

4.1 Chemical structures of designed four giant shape amphiphiles with corresponding relationships...... 81

4.2 Hypothesis of the molecular packing...... 81

4.3 Synthetic route for the preparation of four designed giant shape amphiphiles,

TEB-BPOSS3, TEB-BPOSS6, TAB-BPOSS3 and TAB-BPOSS6...... 84

4.4 Chemical structure of BPOSS-I ...... 85

4.5 Chemical structure of BPOSS2-I ...... 86

4.6 Chemical structure of BPOSS-N3 ...... 86

4.7 Chemical structure of BPOSS2-N3 ...... 87

4.8 Chemical structure of TEB-BPOSS3 ...... 88

4.9 Chemical structure of TEB-BPOSS6 ...... 89

4.10 Chemical structure of TAB-BPOSS3 ...... 90

4.11 Chemical structure of TAB-BPOSS6 ...... 92

4.12 Experimental geometry of fiber sample X-ray test ...... 115

5.1 Chemical structure of BPOSS-H ...... 134

5.2 Chemical structure of BPOSS-C2-Br ...... 134 xiv

5.3 Chemical structure of BPOSS-C4-NH2 ...... 135

5.4 Chemical structure of BPOSS-C5-Br ...... 135

5.5 Chemical structure of BPOSS-C6-Br ...... 136

5.6 Chemical structure of BPOSS-C8-Br ...... 137

5.7 General procedure for synthesizing BPOSS-Cn-N3 from BPOSS-Cn-Br ...... 137

5.8 Chemical structures of BPOSS-Cn-N3 (n = 2, 5, 6, 8) ...... 138

5.9 General procedure for synthesizing BPOSS-Cn-NH2 from BPOSS-Cn-N3 (n = 2, 5, 6, 8) ...... 139

5.10 Chemical structures of BPOSS-Cn-NH2 (n = 2, 5, 6, 8) ...... 139

5.11 General procedure for synthesizing (BPOSS-Cn)2-N3 (n = 2, 3, 4, 5, 6, 8) by amidation reaction ...... 140

5.12 Chemical structure of (BPOSS-Cn)2-N3 (n = 2, 3, 4, 5, 6, 8) ...... 141

5.13 General procedure for synthesizing TAB-CnBPOSS6 (n = 2, 3, 4, 5, 6, 8) by copper (I)-catalyzed alkyne-azide cycloaddition (CuAAC) “click” reaction ...... 142

5.14 Chemical structure of TAB-Cn-BPOSS6 ...... 143

LIST OF FIGURES

Figure Page

2.1 Great wall of China and Pantheon in Athens1 ...... 6

2.2 Double helix structure of DNA5 ...... 9

2.3 Phase structures and diagram of diblock copolymer6 ...... 10

2.4 Stoichiometry-controlled reaction and tether-directed remote functionalization7 .... 12

2.5 Corner-capping reaction of POSS nanoparticle14 ...... 13

2.6 Thiol-ene reaction of octabinyl POSS14 ...... 14

2.7 Molecular model of giant surfactants14 ...... 15

2.8 Molecular models of giant polyhedra14 ...... 16

2.9 Molecular models of giant shape amphiphiles14 ...... 19

2.10 Model reactions of the "click" route for molecular POSS nanoparticle48 ...... 22

2.11 Methodology for the synthesis of sequenced giant molecules developed from orthogonal "click" reactions with "click" adaptors55 ...... 23

2.12 Nucleobase stacking by aromatic ring in folding structures of biomolecules56 ...... 24

2.13 Possible aromatic stacking arrangements...... 26

2.14 Top view along the column direction of the 2D lattices in hexagonal (a), rectangular (b-d), and oblique (e) columnar mesophases58 ...... 27

xvi

2.15 SAXS profile of (a) isotropic melt and (b) hexagonal columnar phase58 ...... 28

2.16 (10) and (11) planes in 2D hexagonal lattices from top view58 ...... 28

2.17 Typical textures for liquid-crystalline phase in POM...... 29

2.18 Symmetry breaking transition from (a) hexagonal, to (b) rectangular columnar phase58 ...... 31

2.19 SAXS variation from (a) hexagonal to (b) rectangular columnar phase58 ...... 32

2.20 Formation process of electronic band from single molecule to the column ...... 35

2.21 Chemical structures of triphenylene derivatives58...... 35

2.22 Set up of time-of-flight (TOF) experiments58 ...... 36

2.23 Set up of the PR-TRMC experiments58 ...... 38

2.24 Index ellipsoids for uniaxial positive (a), and negative (b) liquid crystals ...... 42

2.25 Chemical structures of trisamides 1, (S)-2, and (R)-365 ...... 43

1 65 2.26 Concentration-dependent H NMR spectra of trisamides 1 in CDCl3 ...... 44

2.27 Schematic assembly of propeller-like TAB core66 ...... 45

2.28 Chemical structures of compound 1 and 266 ...... 45

2.29 DSC thermogram of of compound 1 and 266 ...... 45

2.30 X-ray profiles of compound 1...... 46

2.31 X-ray profiles of compound 2...... 46

2.32 Three 12-atom coordination clusters (top) and polyhedra (bottom) for (a) hcp, (b) fcc, (c) icosahedral configurations67 ...... 47

xvii

2.33 The F-K polyhedra (a) CN = 12; (b) CN = 14; (c) CN = 15; and (d) CN = 1667 ...... 48

2.34 Voronoi cells of F-K polyhedra71 ...... 48

2.35 Square-triangle tiling construction of secondary lays of Z16-free (a, b, c) and Z16-included (d, e, f) sites72...... 49

2.36 Square-triangle tiling modes of several typical F-K phases71 ...... 51

2.37 Unit cell in (a) close-packed model, (b) ball-and-stick model, and (c) CN12 coordination polyhedron of Nb atoms about Sn75 ...... 52

2.38 (001) Planes in the A15 structure (a) 2-uniform 3262 tiling at z = 0, and structure projected into a (111) plane (b). Icosahedra surrounding B atoms (c). and their stacking (d)75 ...... 52

2.39 Structure of CrFe (a) ball-and-stick and (b) space-filling model; (c)primary layer 2-uniform tiling at the z = 0 (001) plane; (d) a secondary layer of M(5) atoms near z = 1/4; (e) primary layer at z = 1/2; and (f) a secondary layer of M(5) atoms near z = 3/475 ...... 53

2.40 The phase structures (a) and phase diagrams (b) of diblock copolymers6 ...... 55

2.41 Reported spherical packing structures obtained by block copolymers ...... 56

2.42 Structures of F-K C14 and C15 phases77...... 57

2.43 Chemical structures of dendronized cyclotriveratrylenes82 ...... 58

2.44 A15 structure formed by CVT dendrimer82 ...... 58

2.45 Sigma phase structure formed by CVT dendrimer82 ...... 59

2.46 Chemical structures of dendronized triphenylenes83 ...... 59

2.47 SAXS profiles of (3,4,5)12G1-Tp at different temperatures83 ...... 60

xviii

2.48 SAXS profiles of (3,4-3,5)12G2-Tp at different temperatures83 ...... 60

2.49 Chemical structures of giant surfactant with hydrophilic head and multiple polystyrene tails84 ...... 61

2.50 The SAXS profiles (d-f) and the corresponding TEM images (g-i) of giant surfactant with hydrophilic head and multiple Polystyrene tails, which represent the A15(d, g), sigma(e, h), and DQC(f, i) phases84 ...... 62

2.51 F-K A15 Phase Formed by Giant Tetrahedra85...... 63

3.1 Corner-capping Reaction of T7 POSS86 ...... 65

3.2 Karstedt’s catalyst100...... 66

3.3 Mechanism of Staudinger Reaction101 ...... 67

3.4 Example of Staudinger Reaction89 ...... 67

3.5 Proposed mechanism of CuAAC102 ...... 68

3.6 Mechanism of Sonogashira reaction103 ...... 69

3.7 Example of Sonogashira cross-coupling90 ...... 70

3.8 Typical high vacumm line. Image courtesy of Dr Jimmy W. Mays91 ...... 71

3.9 Typical Schlenk line with parts labelled92 ...... 72

3.10 Techniques used to determine structures including TGA, DSC, POM, TEM, SEM, AFM, WAXD, SAXS, GIXS, ED, density measurement and simulation ...... 74

1 4.1 H NMR characterization of BPOSS-I (a), precursor for TEB-BPOSS3 (A) ...... 93

1 4.2 H NMR characterization of BPOSS2-I (b), precursor for TEB-BPOSS6 (B) ...... 94

1 4.3 HNMR characterization of BPOSS-N3(c), precursor for TAB-BPOSS3(C) ...... 95

xix

1 4.4 H NMR characterization of BPOSS2- N3 (d), precursor for TAB-BPOSS6 (D) ...... 96

1 13 4.5 H NMR and C NMR characterization of TEB-BPOSS3 (A) ...... 97

1 13 4.6 H NMR and C NMR characterization of TEB-BPOSS6 (B) ...... 98

1 13 4.7 H NMR and C NMR characterization of TAB-BPOSS3 (C) ...... 99

1 13 4.8 H NMR and C NMR characterization of TAB-BPOSS6 (D) ...... 100

4.9 MALDI-ToF spectra of (A) TEB-BPOSS3, (B) TEB-BPOSS6, (C)

TAB-BPOSS3 and (D)TAB-BPOSS6。 ...... 101

4.10 GPC characterization of (A) TEB-BPOSS3, (B) TEB-BPOSS6, (C)

TAB-BPOSS3 and (D) TAB-BPOSS6 proves the neat synthesis of giant molecules at volume exclusive level. Elution solvent is THF...... 102

4.11 TGA analysis showing the 5% weight loss temperature of (A) TEB-BPOSS3,

(B) TEB-BPOSS6, (C) TAB-BPOSS3 and (D) TAB-BPOSS6 at 400.1℃, 376.8℃, 370.1℃ and 379.5℃, respectively...... 103

4.12 DSC thermograms showing the phase transition temperature of (A)-(D)...... 107

4.13 Columnar structures with ordered to less ordered intracolumnar packing achieved by three treatment methods...... 108

4.14 Two dimensional hexagonal packing of TEB-BPOSS3 supramolecular columns...... 109

4.15 Simulated SAXS pattern for 2D hexagonal packing: a = b, γ =120°. The model inserted to each pattern was built by atoms in Crystal maker...... 110

4.16 In-situ temperature resolved SAXS pattern of TEB-BPOSS3...... 112

4.17 Temperature resolved in-situ SAXS and WAXD results for TEB-BPOSS3 upon heating and cooling, respectively...... 113

4.18 Thermal expansion coefficient analysis...... 114

4.19 Two dimensional SAXS pattern of TEB-BPOSS3 fiber sample (Sample prepared by Method 3)...... 116

4.20 Two dimensional WAXD pattern of TEB-BPOSS3 fiber sample (Sample prepared by Method 3) and the molecular packing model indicated by this pattern...... 117

4.21 Columnar phase formation of TEB-BPOSS3 and TAB-BPOSS3...... 119

4.22 POM textures of the Colh phase of TEB-BPOSS3 treated by 3 different methods...... 121

4.23 POM textures of Colr phase (a), (b) and Colh phase(c) of TAB-BPOSS3...... 122

4.24 A15 phase formation of TEB-BPOSS6 and TAB-BPOSS6...... 123

4.25 Non-covalent interactions in the self-assembled structure...... 126

5.1 Molecular design and chemical structures of TAB-CnBPOSS6, n=2, 3, 4, 5, 6, 8 (A)-(F)...... 131

5.2 Synthetic route for the preparation of six designed giant shape amphiphiles with

different linker length, (A)-(F)...... 133

1 13 5.3 H NMR and C NMR spectrum of TAB-C2BPOSS6 (A)...... 146

1 13 5.4 HNMR and CNMR spectrum of TAB-C4BPOSS6 (C)...... 147

1 13 5.5 HNMR and CNMR spectrum of TAB-C5BPOSS6 (D)...... 148

1 13 5.6 HNMR and CNMR spectrum of TAB-C6BPOSS6 (E)...... 149

1 13 5.7 HNMR and CNMR spectrum of TAB-C8BPOSS6 (F)...... 150

5.8 MALDI-ToF spectra of TAB-C2BPOSS6, TAB-C3BPOSS6, TAB-C4BPOSS6,

TAB-C5BPOSS6, TAB-C6BPOSS6 and TAB-C8BPOSS6...... 151

xxi

5.9 GPC characterization of TAB-C2BPOSS6, TAB-C3BPOSS6, TAB-C4BPOSS6,

TAB-C5BPOSS6, TAB-C6BPOSS6 and TAB-C8BPOSS6 proves the neat synthesis of giant molecules at volume exclusive level...... 152

5.10 A15 phases of TAB-CnBPOSS6. n=4, 5, 6, 8...... 153

5.11 Summary for the sizes of the A15 phase of TAB-CnBPOSS6 changing with their linker length...... 154

5.12 In-situ SAXS of TAB-C3BPOSS6 upon heating up...... 155

5.13 In-situ SAXS of TAB-C4BPOSS6 upon heating up...... 156

5.14 In-situ SAXS of TAB-C5BPOSS6 upon heating up...... 157

5.15 In-situ SAXS of TAB-C6BPOSS6 upon heating up ...... 158

5.16 In-situ SAXS of TAB-C8BPOSS6 upon heating up ...... 159

xxii

CHAPTER I

INTRODUCTION

From bottom up approach to achieve nanomaterials, molecules will packs into supramolecular structure and further gives hierarchical nano architectures. It is well known that discotic small molecules can stack into 1D columns, and these columns can further packs into 2D rectangular or hexagonal hierarchical structures1. The charge transport ability along the columnar structures has been widely applied to semiconducting areas1, 3.

Their optical property is useful for making optical compensator for LC displays. The self-assembly of 1, 3, 5-triethylene benzene derivatives have been studied by Dr. Sanchez and Meijer’s group1, they found these derivatives can form columnar phase in solution or even in the solid state. The self-assembled structure of 1, 3, 5-tristriazole benzene derivatives were recently studied by Cho’s group, they found those molecules stacked from ordered to disordered columnar phase as temperature increased2.The columnar phase are stabilized by two factors, unidirectional interaction along the column and periphery steric requirements help stabilizing the columns 6.

Phase structures of traditional block copolymers, especially the diblock copolymers, have been well studied. Various phase diagrams of block copolymers have been investigated for predicting the phase formation of block copolymers5. Unlike the conventional phases which can be predicted in the phase diagrams, Frank-Kasper phases are mainly discussed in metal alloys and rarely investigated in soft materials. Dr. Percec and Ungar have done a lot of work about Frank-Kasper architectures mainly in dendrimers since 19987. For studying the formation of Frank-Kasper phases, more precisely modular work is needed. Different from the flexible dendrimers whose physical property mainly rely on molecular weight and volume fraction of different parts, the molecules we designed have precise size and incompressible shapes and their physical properties can be controlled by chemical functionalization.

Nano building blocks that possess precisely defined chemical structures and diverse functionalities have been widely used to fabricate nano-scale suprastructures4. By introducing rigid and shape persistent chemical segments into the periphery of small discotic molecules, both the discotic chemical structure and the periphery shape effects can be amplified. Size-magnified molecules offer more possibilities to modify the factors and exhibit faster kinetics of ordering in self-assemblies and much less defects in those assembled structures, providing a strategy to study the relationship between molecular structures, molecular interaction and their self-assembled structures.

Frank-Kasper phase are made from spherical packing. Each sphere in the F-K phase is topologically close packed. Every other F-K phase can be formed from combining the A15 phase, Z phase and C14 (C15) phase. A15 is one of the most basic Frank-Kasper phases.

According to the literatures, there are mainly four types of molecules can forming A15 phase, dendrimers, asymmetric block copolymers, giant tetrahedral of POSS cages and giant surfactants7. In these 4 types of molecules, the supramolecular spheres are self-assembled from cone shape molecules. Here we proposed the 5th type of molecules, discotic molecules, to achieve A15 phase, and the unit shape forming the supramolecular spheres are discs.

In our work, we introduced BPOSS as the periphery of 1, 3, 5-tri ethynyl benzene

(TEB) core or triazole benzene (TAB) core to enlarge the molecular size and serve as a steric component. BPOSS number was increased from three to six to introduce steric hindrance along the column axis, competing with the non-covalent π-π interactions of discotic cores. By accurately variables-controlled comparison, we found that if the steric hindrance was caused by three BPOSSs on the periphery, columnar phase would remain. It is because the core can be tilted to offer enough space for the rigid cages. However, tilting of the core perpendicular to the column axis cannot make enough room when the number of BPOSSs was increased to six. In this case the BPOSSs have to scrub up and down due to the exclusion, which blocks the π-π interaction along the column and forms a spherical

3 building block. Columns cannot be stabilized by only π-π interactions, which in consequence lead to the formation of supramolecular spheres and further forming spherical packing structure such as A15 phase. Not only steric hindrance but also core type will affect the assembled structures. When the core at the center was changed from TEB to TAB, the limitation of tilting of the triazole arms leads to the tilting of the molecular plane, orientational inequivalent leads to ellipse columns, and in sequence gives rectangular 2D columnar packing. However, there are other possibilities such as the molecular packing inside different columns has obvious difference will also cause the rectangular 2D lattice, so the inside-columnar details need to be solved in the future. The interesting thing is no matter which core type is, six BPOSSs on the periphery will give A15 phase. That clearly shows steric hindrance is the key factor for the A15 phase formation of this type of discotic molecules. (May indicate this triazole ring is more likely to form distorted spheres than

Sonogashira products) Further investigation was conducted on the intermolecular

H-Bonding and π-π interactions to explain the self-assembly process. We established a model to achieve A15 phase from discotic molecules base on nano-building blocks, which may offers a strategy for fabricating unconventional phases in the future.

CHAPTER II

BACKGROUND

2.1 Building from the Bottom Up

2.1.1 Bottom-up Approach

Bottom-up approach, as the name implies, represents an approach piecing together simple systems to give rise to a more complex system. Nature, in this case, is the best teacher for us considering the world it builds up from one atom and one molecule. Looking at the materials it makes such as crystals, wood, collagen, silk and minerals, everyone will be shocked and thus inspired to mimic the way Nature “designs” these materials.1

“When nature finishes to produce its own species, man begins using natural thing in harmony with this very nature to create an infinity of species.”

----Leonardo da Vinci

Actually, in the past several centuries, people were keeping using the bottom-up principle everywhere in the world. The constructions of the Great Wall of China and the

Pantheon in Athens are both good examples when we try to figure out how the very basic brick blocks assemble to these miracles.

Figure 2.1 Great wall of China and Pantheon in Athens.1

Much like the construction of a house which is prefabricated and assembled according to architectural plans, we can apply similar principles to construct materials and devices, through the so-called bottom-up approach.

2.1.2 Soft Material

In the early ages of human history, the materials human used were almost occupied by hard materials, from stones and woods which are most readily to collect, to iron and steel which is the milestones of the improvement of processing technology.2 Although our investigations and understanding of these hard materials is well advanced in past several centuries, we are just standing at the very early stage of the learning the story of “soft” materials.

The concept of “soft materials” was first proposed by Professor de Gennes in 1992 to describe the molecular systems exhibiting very large response to tiny foreign stimuli.3 The term “soft” comes from macroscopic mechanical properties of these systems. This concept could also find many prototypes in Nature. In biological world, the basic components are able to self-assemble into soft segments to perform products with different specific 6 functions with high precision and ultra-sensitivity. The major difference between soft and hard materials is their ability to self-assemble into functional complexes, as directed by non-covalent interactions. In addition to these direct descriptions of soft matter, a clear scientific definition of soft matter could be also derived from their structure and dynamics characteristics.

These scientific descriptions of soft matter are summarized as Table 2.1 below.

Comparisons with liquid and solid states are listed in table as well.

Table 2.198

*kB: Boltzmann constant; kBT: thermal energy at temperature T.

As the concepts shown in the Table 2.1, the physical structure and dynamic characteristics of soft materials can be understood according to their interaction energy. In this case we compare this term of each kind of material with the thermal energy at room temperature. It is well-known that actually there are few perfect long-range positional and bond/molecular orientational orders as found in a crystalline solid. However there is always certain combination of long-range and short-range orders in structure. In this sense, they are quite different from the liquid which theoretically speaking possesses a Newtonian flow behavior. It should be also noticed that the long-range order or the short-range order

7 cannot be distinguished only based on their sizes but rather the way their order decays. The largest challenge in many practical acres nowadays is to acquire ordered structures with periodicity on the length scale of 2-100 nm.4 In soft materials, the self-assembled structures usually possess periodicities in several different dimensions and across many length scales

– they are hierarchically ordered structures. While they are similar to crystalline solids built from atoms and molecules, the building blocks here are supramolecular motifs held together via non-covalent bonds. The molecules inside these motifs could be short-range ordered. The advantages of soft materials are thus evident. First, they facilitate processing to generate material structures with specifically designed long-range and short-range order.

The nature of self-assembly provides opportunities to generate materials that are self-healable, viable, and durable. Second, versatile structures with specifically desired order and symmetry possess different “soft” properties, such as modulus, reflectivity, conductivity, etc., and may be suitable for various applications. Third, the phase transitions in these ordered structures can be triggered relatively easily by small foreign stimuli, since these transitions are mostly entropy-driven. This is the basis for today’s modern devices and sensory technologies. It can be imagined that, if functional materials, such as fullerenes, are incorporated into soft materials to capture these advantages, the scope of fullerene functional materials can be greatly extended, while their properties can be tuned and optimized for target applications.

2.1.3 Bottom-up Construction of Soft Material

Designing and constructing new materials in soft matter usually includes the molecular self-assembly. Molecular self-assembly involves mostly weak and non-covalent 8 interactions, which are individually quite insignificant. However, in all biological structures, these weak interactions play an indispensable role. The DNA double helix is perhaps the best example for this issue.

Figure 2.2 Double helix structure of DNA.5

Inspired by this grand example, the weak non-covalent interactions such as hydrogen bonds, van de Waals interactions, hydrophobic interactions and π-π interactions are gradually introduced to the programmed design and engineering of materials.

Self-assembly has recently emerged as a new approach in chemical synthesis, nanotechnology, polymer science, materials science, and engineering. Molecular self-assembly systems lie at the interface of these disciplines and many self-assembling systems have been developed. These systems range from bi- or tri-block copolymers,

9 complex DNA structures, and lipids to simple or complex peptides and proteins.

Self-assembly systems represent a significant advance in the engineering of simple molecular building blocks useful for a wide range of applications.

Hereon, we just present an example of diblock copolymers and their phase behaviors. Diblock copolymer is, as its name indicates, a kind of polymer consisting of two types of different monomers A and B.

Figure 2.3 Phase structures and diagram of diblock copolymer.6

The same as almost all the thermodynamic systems, the entropic factor and enthalpic factor competes with each other to minimize the free energy. At high temperature, the entropy factor dominates and the polymer is disordered. When below a certain temperature, the polymer melt forms ordered structure and result in a periodic distribution of A and B.

The A and B segments of each copolymer chain will assemble together and thus display macroscopic order.

2.2 Modular Giant Molecule

Generally speaking, the self-assembly behavior of the soft matter, such as polymers, dendrimers, and surfactants is initiated by the micro- or nano-phase separation of incomparable parts in those molecules. Since the minimization of molecular packing frustration is favored in this process, the packing modes of these materials are prominently influenced by the molecular conformation standing for the entropic term and minimization of overall free energy contribution to the enthalpic term. In this case, the size-magnified giant molecules which are impressive by their volume- and shape-persistence can act as a good complement to small molecules. The faster kinetics and much less defects in the assembled structures make these kind of molecule good candidate for the construction of supramolecular structures.7

2.2.1 Nanoparticle – “Giant Atom”

To obtain the modular size-magnified macromolecules, corresponding to the atoms in the small molecules, molecular nanoparticles (MNPs) are selected as “zoomed-in” atoms.

Considering the various MNPs with different functional groups, molecular sizes, geometry and symmetry, two typical nanoparticles, polyhedral oligomeric silsesquioxane (POSS) and [60]fullerene (C60), were used in our group’s previous work because of their potential to be further functionalized. The MNPs such as polyhedral oligomeric silsesquioxane

(POSS) and [60] fullerene (C60) can be held by covalent bonds and usually persist cage-like 11 shape. Both these two nanoparticles have well-defined molecular structure and possibility to be precisely chemically modified.

Fullerenes are one set of carbon allotropes which were discovered last century. C60, as a member of this family, is the smallest stable one with a spherical geometry and Ih symmetry.8 Based on extensive studies on the fullerenes since their discovery, strategies to functionalize them have been thoroughly developed. So far many methods like Prato reaction,9 Bingel-Hirsch reaction,10 and azide addition11 have become available to functionalize fullerenes especially C60.

Figure 2.4 Stoichiometry-controlled reaction and tether-directed remote functionalization.7

One straightforward method is controlling reaction stoichiometry. It is usually used to prepare monosubstituted C60. However, due to the high symmetry of C60, there are still [5,

6] - and [6, 6]-isomers for the monoadducts.12 Another kind of functionalizing strategy is regioselective multi-addition. Although it is more complex than the former, it has been well established in C60 system. Methods such as topo chemically controlled solid-state reaction, template-mediated multiaddition and tether-directed remote functionalization are usually used to synthesize mutiadducts.8

Polyhedral oligomeric silsesquioxane (POSS) is a family of silica cage compounds with a variety of sizes and symmetries. Among this family, a cubic cage named as T8 is most commonly used by researchers. POSS cages are generally prepared by the condensation of a silane or silanol precursor. If the condensation is complete the POSS cage will have very high symmetry otherwise a precursor which can be transferred to heterofunctionalized POSS will form. However, the commercial POSS products’ side groups are still limited to some very simple substituents such as isopropyl, isooctyl, cyclopentyl, phenyl, vinyl, perfluorinated alkyl, and chloropropyl groups. Driven by the aspiration to selectively functionalize the POSS cage, many practical methods have been developed. Starting from a precursor POSS cage with modifiable side groups such as phenyl and vinyl group is an often used strategy. For example, Feher et al. used the monohydroxylation of octavinyl POSS to prepare VPOSS-OH, which is a versatile intermediate.13 Recently, Cheng et al showed that thiol-ene chemistry can be used with controlled stoichiometry to achieve monoaddition.

Figure 2.5 Corner-capping reaction of POSS nanoparticle.14

Figure 2.6 Thiol-ene reaction of octabinyl POSS.14

2.2.2 Giant Surfactant

While polymer chains are usually flexible and can be treated as tails, the MNPs can be viewed incompressible heads because of their volume- and shape-persistence. The combination of this two structure unit offers a new class of “giant surfactant”.15 Giant surfactants possesses the essential structural features of small-molecule surfactants but have magnified sizes even up to several nanometers, which is comparable to that of the common block copolymers. Similar to small-molecule surfactants, various different kinds of giant surfactants with different geometries such as giant bola-form surfactants, giant gemini surfactants, giant multiheaded, and giant multitailed surfactants can be designed and developed16-17. Within each subcategory of giant surfactants, further structural variation can be made based on the choice of tails and MNPs.

Figure 2.7 Molecular model of giant surfactants.14

To speak strictly, the tethered polymer chains should be mono-dispersed which means the molecular weight of each chain is exact the same. But a single molecular-weight polymer is still a daunting challenge in polymer chemistry. In this case, narrowly dispersed polymers are used as a close approximation and can be conveniently synthesized in large quantities by various living/controlled polymerization techniques such as anionic polymerization or atom-transfer radical polymerization. When the giant surfactants have relatively long tails, they may be able to tolerate some molecular heterogeneity on their chain lengths. However, it should be kept in mind that the self-assembly of those with relatively short tails would be very sensitive to the exact length and the molecular weight distribution even if the difference may be as small as only several repeating units. Recently, our group has traversed the self-assembly behaviors of libraries of giant surfactants.18

Although those giant surfactants have certain polydispersity in their tails, the self-assembly behaviors are versatile in the bulk, solution, and thin film states. In particular, the phase behaviors of those giant surfactants were found to possess a duality of small-molecule

15 surfactants and block copolymers. This class of materials build a bridge over the gap between the two traditional self-assembling materials and possesses advantages of both at an intermediate length scale of ∼10 nm.18

2.2.3 Giant Polyhedra

Generally speaking, there are two types of giant polyhedra. The first type is a faceted

MNP who can display a polyhedron itself including higher diamondoid molecules, graphene nanoribbons, and large molecular clusters.19-21 The second type is a giant polyhedron built upon several smaller MNP units. The latter are constructed by placing

MNPs on the apexes of a specific polyhedron to create a faceted giant molecule with larger scale, reminiscent of the classic small-molecule VSEPR structures.

Figure 2.8 Molecular models of giant polyhedra14

For example, when four POSS cages are linked to the apex of a tetrahedron, we obtain a giant tetrahedron. Depending on the linkers, it can be either a soft giant polyhedron or a

16 rigid giant polyhedron. The difference in the shape persistence can largely affect the self-assembly behaviors and will give different ordered structures. The MNPs here in the giant polyhedra may possess different surface functionalities and therefore establish different kinds of driving force for assembly.22 It is well-known that geometric and energetic terms are the most intuitive factors that determine the self-assembly of materials into ordered structures. When the sizes increased, the shape and shape persistency of these

“nanoatoms” in giant molecules increase the importance in determining the final structure formation as long as the interactions among them are strong enough to stabilize the structures. While experiments have shown thermodynamic equilibrium structures for nanoparticle polyhedra, simulation has predicted the formation of even more diverse structures, including liquid crystals, plastic crystals, quasi-crystals, and crystals, from various polyhedra.22-23 Directional enthalpic and entropic driving forces are believed to guide the ordering of faceted polyhedra.24 Therefore, we envision that the molecularly precisely defined giant polyhedra are exciting research targets. Amphiphilic giant polyhedra are also called nano-Janus grains. The term “Janus grain” was proposed by Prof.

De Gennes in his Nobel lecture and refers largely to colloidal particles with asymmetric surface chemistry.3 In general, the symmetry breaking occurs in two ways: geometrically or chemically. Symmetry breaking in geometry refers to the change of overall molecular symmetry upon functionalization (such as the regioselective mono- and multifunctionalization of MNPs). Symmetry breaking in chemistry refers to the introduction of functional groups that possess different interactions from the rest of the molecule. Nano-Janus grains are nanosized molecules built upon MNPs with rigid 3D conformation and symmetry breaking in both chemistry and geometry. The first type of 17 nano-Janus grain has asymmetric surface chemistry on the same MNPs and thus may be considered as a “patchy MNP”. In fact, there are various examples based on C60.

Monofunctionalized C60 derivatives may be arguably regarded as the smallest patchy

MNPs and have been known to generate various nanoaggregates by self-assembly.25

Regioselective C60 penta-adducts can self-assemble into complex structures such as a

26 double-layered vesicle. [5:1], [4:2], or [3:3] mixed hexakis-adducts of C60 are perhaps much more like “patchy particles”.8

The second type of nano-Janus grains is the ones obtained by closely linking together two or more MNP units with distinct surface functional groups. For example, a

POSS-fullerene conjugate (BPOSS-C60) is a nano-Janus grain since the surface chemistries

27 on BPOSS and C60 are drastically different. Similarly, a dumbbell-shaped Janus particle can also be prepared by the conjugation of one hydrophobic POSS having isobutyl side groups and the other hydrophilic POSS possessing carboxylic acid side groups

(BPOSS-APOSS).28 This BPOSS-APOSS nano-Janus grain formed a unique bilayered structure that further packs into crystals with a nanometer-scale superlattice in the bulk. At lower temperatures, the BPOSS within each layer further organized to pull APOSS into the crystalline lattice. At higher temperatures, only the hydrophilic/hydrophobic bilayered structure was maintained to form a supramolecular liquid crystal phase. It can be envisioned that other nano-Janus grains, such as “snowman” type (e.g., one large hydrophilic/hydrophobic POSS connected with one small hydrophobic/hydrophilic POSS) or “Mickey Mouse” type (e.g., one large hydrophilic/hydrophobic POSS connected with two small hydrophobic/hydrophilic POSSs in the given geometry), may be similarly designed and synthesized.29 18

2.2.4 Giant Shape Amphiphile

Shape amphiphiles are the molecules built upon molecular segments of specific shapes and competing interactions.30-31 The term shape amphiphile was first created to describe a discotic-rod liquid crystal mesogen and later described by Glotzer et al. as a broad class of emerging materials.31-32 The building blocks that comprise shape amphiphiles have distinct 3D shapes with persistent geometry, symmetry, and preferred packing mode. This property provides many additional parameters which is tunable for structural engineering design.

Figure 2.9 Molecular models of giant shape amphiphiles.14

Having tremendous kinds of geometries in our mind, we can image numerous ways to combine components of different shape and symmetry, such as sphere-cube, sphere-disk, sphere-rod, and cube-disk dyads. These molecules provide huge potential to engineer diverse self-assembled structures. It should be noted that the components here are not limited to MNPs only, but also include gold nanoparticles, nanorods, single-chain cross-linked nanoparticles, etc.33-34 The shape amphiphiles built up from MNPs are named as “giant shape amphiphiles” in accord with the broad class of giant molecules shown in

19 previous words. Actually, the giant surfactants can also be treated as shape amphiphiles because the MNP possesses specific shape.35 According to the extensive simulation studies on the self-assembly of shape amphiphiles, a variety of unusual phase behaviors and hierarchal superstructures have been predicted.36-38 With MNPs, a series of giant shape amphiphiles can be synthesized and studied in detail. These giant shape amphiphile molecules include C60-POSS shape amphiphile (sphere-cube), C60-oligofluorene shape amphiphile (sphere-rod), C60-porphyrin shape amphiphile (sphere-square),

POSS-triphenylene shape amphiphile (cube-triangle), C60-perylene diimide (PDI) shape amphiphile (sphere-rectangle), POSS-PDI-POSS shape amphiphile (cube-rectangle-cube), and POSS-terthiophene-POSS shape amphiphile.27, 39-45

2.2.5 Precise Synthesis Through Click Reactions

“Click Chemistry” is a term that was introduced by K. B. Sharpless in 2001 to describe reactions with high yield, wide scope, and few byproducts.46 They are usually stereospecific, simple to perform, and can be conducted in very readily steps and mild conditions. This concept was developed parallel in many different fields such as the chemical synthesis, material science, and other industries because of the ability for generating large libraries of compounds.47 It also paves the road to giant molecules by offering modular, robust, and efficient ways that would greatly simplify the material synthesis. Directed by this philosophy, sequential “click” reactions are of great importance as a methodology in the precise synthesis of giant molecules.48-50

2.2.5.1 “Click” Reactions.

Huisgen azide-alkyne 1, 3-dipolar cycloaddition is perhaps the most popular “click” reactions used nowadays.51 At the very beginning, the reaction is proceeded by thermal heating. However, the thermal Huisgen 1, 3-dipolar cycloaddition of alkynes and azides produces mixtures of two regioisomers at elevated temperature when the alkyne is asymmetric. So it fails to be a true “click” reaction in this case. Fortunately, a copper-catalyzed variant developed later allows only 1, 4-disubstitued regioisomers and therefore complies fully with the definition of the “click” chemistry. In recent years, besides the copper-catalyzed azide-alkyne cycloaddition (CuAAC), copper-free, strain-promoted azide-alkyne cycloaddition (SPAAC) has attracted considerable interest as a highly reactive, bio-orthogonal “click” reaction.52 Thiol-ene chemistry,one kind of highly efficient reactions of thiol with reactive carbon-carbon double bonds, is another commonly used prototype “click” reaction. The reaction between the relatively weak sulfur-hydrogen bonds of thiols and the carbon-carbon double bonds can give nearly quantitative yields under mild conditions.53-54

Figure 2.10 Model reactions of the "click" route for molecular POSS nanoparticle.48

In Figure 2.10, a general synthetic scheme of functionalization of our giant molecules is listed.48 Taking mono-substituted vinyl-POSS (VPOSS-OH) as an example, the -OH group is decorated with carbon-carbon triple bond to be a synthon for a CuAAC reaction.

This gives a potential possibility to connect this nano-atom with other chemical segment we want to involve. At the same time, the rest vinyl groups can be functionalized by a thiol-ene reactions with various thiol derivatives such as 3-mercaptopropane-1,2-diol,

2-mercaptoethan-1-ol and 2-mercaptoacetic acid.

2.2.5.2 “Click” Adaptors.

To further broaden the scope of the sequential “click” approaches, a small gadget, called the “click adaptor”, is developed by chemists. It usually contains one “clickable”

22 functional group and another kinds of functionalities which are orthogonal to the previous

“click” reactivity.16

Figure 2.11 Methodology for the synthesis of sequenced giant molecules developed from orthogonal "click" reactions with "click" adaptors.55

One good example of the application of the “click adaptor” in giant molecule synthesis is conducted by Dr Wei Zhang in our group.55 As shown in Figure 2.11, the copper free strain-promoted azide-alkyne cycloaddition (SPAAC) and oxime ligation are selected as two orthogonal reactions. Two kinds of small-molecule “click adaptors” are used to convert one click functionality to another without the need for protection and deprotection. This strategy allows us to sequentially arrange the “nanoatoms” by simply using click adaptors with different geometry.

2.3 Disc Shape Molecule

2.3.1 π Interaction Among Disc-Shape Molecules

Chemically speaking, π stacking refers to an attractive and non-covalent interaction between aromatic rings. This interaction is of great importance in nucleobase stacking within DNA and RNA molecules, protein folding, and molecular recognition. Despite extensive experimental and theoretical studies, there is still no unified description of the factors that contribute to π stacking interactions.

Figure 2.12 Nucleobase stacking by aromatic ring in folding structures of biomolecules.56

In the early 1990s Hunter and Sanders established a widely accepted model that offers a qualitative description for aromatic–aromatic interactions, based on the assumptions that

π systems resulted from polarized and derived electrostatic arguments. They described that

π electron density on most aromatic rings will create a quadrupole moment with partial 24 negative charge above both aromatic faces and a partial positive charge around the periphery. Two such quadrupole moments in proximity should aviod face-centered parallel stacking in favor of perpendicular edge-to-face interactions or off-centered parallel stacking.

Benzene and toluene are used as the prototypical aromatic molecules and therefore extensively examined in both the solid and liquid states. In the solid state, benzene is predominantly in a perpendicular, edge-to-face arrangement, while solid toluene forms an off-center parallel stacking mode with a staggered arrangement. For benzene, the edge-to-face ‘‘t-shaped dimer’’ was found to be less stable than parallel offset pairs and the

‘‘y-shaped’’ edge-to-face geometry (Figure 2.13).

Sherrill has carried out comprehensive calculations on benzene and its derivatives.

Their calculations predict that the t-shaped and parallel-offset configuration are the most stable and nearly energetic identical. Gervasio et al. noted a growing consensus that toluene is a more appropriate model for in biological environments. Toluene therefore possesses a dipole, introducing asymmetry that makes stacking in an offset mode more favorable than t-shaped patterning.

Figure 2.13 Possible aromatic stacking arrangements. (a) Parallel face-centered. (b) Parallel offset. (c) Perpendicular t-shaped. (d) Perpendicular y-shaped. (e) Parallel offset for toluene.57

2.3.2 Liquid Crystal (LC) Mesogens

Discotic liquid crystal was first discovered in 1977 by Chandrasekhar et al.58 The self-assembly of the disc-like molecules into LC crystal phases is usually driven by the anisotropy in the intermolecular interactions. When the short molecular axes of discotic mesogens align along the n, a nematic ND phase is formed. Besides ND phase, if the discotic mesogens pile up into some one-dimensional (1D) columns that align with column axes parallel to each other, another kind of columnar nematic phase Nc is obtained. depending on the details of the intracolumnar interactions, columns with different types of stacking can be observed: “disordered columns” with an irregular stacking of the disks,

“ordered columns” in which the cores are stacked in a regular ordered (equidistant) fashion while the flexible tails are still disordered, and “tilted columns” where the cores of the disks are tilted with respect to the column axis. These extended supramolecular columns are generally considered as 1D fluids because none of these types has perfect translational order. Considering the symmetry of the two-dimensional (2D) intercolumnar lattice, the

2D crystalline structures can be thought as hexagonal, rectangular and oblique columns.

Figure 2.14 Top view along the column direction of the 2D lattices in hexagonal (a), rectangular (b-d), and oblique (e) columnar mesophases.58

2.3.2.1 Hexagonal Columnar Mesophase Colh

The planar space group of a hexagonal columnar mesophase is P6/mmm. For an unorientated (powder) sample of a Colh mesophase, a few distinct peaks which result from the long-range intercolumnar order can be observed in the small-angle regime.

Figure 2.15 SAXS profile of (a) isotropic melt and (b) hexagonal columnar phase.58

Figure 2.16 (10) and (11) planes in 2D hexagonal lattices from top view.58

The d spacings of the (10) and (11) reflections exhibit the ratio of 1:1/√3. And further geometric considerations lead to the characteristic ratios of 1: 1/√3: 1/√4: 1/√7: 1/√9:

1/√12: 1/√13 for the d spacings of the (10), (11), (20), (21), (30), (22), and (31) planes of the 2D hexagonal lattice in the small angle regime. If the corresponding sample is extracted as a fiber, these 2D hexagonal reflection signals in small angle regime will be found on the

28 equator. On the meridian there will be the wide angle halo which related to the diffuse. The halo in the wide angle regime results from the short distance correlation of the reflections corresponding to the alkyl chains’ liquid-like order. There may also be a second relatively narrow diffuse ring in the wide angle regime and this is usually related to the stacking of the mesogenic cores along the column direction.

Figure 2.17 Typical textures for liquid-crystalline phase in POM. (a) Fan-shaped focal conic texture (R=C7H15), (b) Focal conic texture (R=COC12H25), (c) Spherulitic-like texture with Maltese Crosses (R=C16H33). (d) The straight linear defects are characteristic 58-60 for ordered columnar mesophases (R=COC11H23).

In a polarizing microscope (between crossed polarizers) each mesophase shows a typical pattern (“texture”). These textures result from the symmetry-dependent elasticity of

29 the liquid-crystalline phase in combination with defects and the surface conditions of the sample. For Colh mesophases, conic fan-shaped (pseudofocal conic) and focal textures

(Figure 2.17 (a) and (b), respectively) are characteristic. Mosaic and dendritic textures are not as common. When dendritic textures grow in all directions from one point, “flowerlike” texture are formed. Furthermore, relatively rare spherulitic-like (Figure 2.17 (c)) and fingerprint textures are known. It is important to note that these fingerprint textures do not bear analogy to those of cholesteric mesophases, in which the equidistant stripes are related to the periodicity of the chirality-induced helical modulation. On the other hand, fingerprint textures of columnar hexagonal phases can be described as broken focal conics.

Textures of an ordered hexagonal columnar mesophase typically exhibit straight linear defects (Figure 2.17 (d)). However, the problem often occurs that only small domains are formed that could not be attributed to a typical texture.

2.3.2.2 Rectangular Columnar Mesophase Colr

Three different columnar rectangular mesophases Colr have been identified (Figure

2.14(b)–(d)). In general the molecules are tilted with respect to the column axis, whereby the cross section, orthogonal to the long axis of a column, is elliptic.

Figure 2.18 Symmetry breaking transition from (a) hexagonal, to (b) rectangular columnar phase.58

The symmetries of the 2D lattices are specified by three different planar space groups

P21/a, P2/a, and C2/m, belonging to the subset of space groups without any transitional periods in the direction of the principal symmetry axis (that is, the direction of the columns). As a result of the elliptical projection of the molecules in the plane, the symmetry of the Colr phases deviates from a proper hexagonal arrangement. Rectangular phases sometimes are also called pseudo-hexagonal. However, stronger core–core interactions are needed for the formation of Colr mesophases than for the formation of hexagonal phases because the cores of one column have to “know” how they must be tilted with respect to the cores of the neighboring columns. Therefore, crossover from columnar rectangular to hexagonal mesophases with increasing side-chain lengths has often been observed.

Figure 2.19 SAXS variation from (a) hexagonal, to (b) rectangular columnar phase.58

The 2D X-ray patterns resemble those of a columnar hexagonal mesophase with a diffuse halo in the wide-angle regime and sharp reflections in the small-angle regime.

However, a closer look to the SAXS profiles reveals certain differences (Figure 2.19). The

(10) peak of the Colh mesophase splits into the (20) and (11) reflections of the Colr phase.

This observation is explained in Figure 2.18. Here, in a hexagonal lattice a rectangular unit cell with the lattice constants a’ and b’ is shown (Figure 2.18 (a)). Since δ =30° in a hexagonal arrangement, b’ = a’/√3, and thus d11’ = d20’, since for a rectangular lattice,

Equation 2.1 is valid.

Equation 2.1

1 h2 k2 2 = 2 + 2 dhkl a b

As soon as the lattice deviates from perfect hexagonal symmetry that is, δ ≠ 30°

(Figure 2.18 (b)), the degeneracy of d11 and d20 is broken and two separate reflections appear in the small-angle regime. The indexation of a columnar rectangular mesophase and the determination of the lattice structure (space group) are complex and often not completely unambiguous. Since only a quite limited number of reflections are actually observed, in practice an unequivocal determination of the symmetry is questionable.

Furthermore, it can be helpful to consider the lattice constants a and b, which can be calculated from Equation 2.1, in relation to the molecular dimensions obtained, for example, by molecular modeling.

Two-dimensional X-ray patterns of aligned samples can be most helpful to further clarify the symmetry of rectangular phases. The angle in the azimuthal scattering directions of adjacent small-angle reflections deviates from 60° from that expected for a perfect six-fold symmetry (cf. Colh mesophase). Donnio et al. interpreted the origin of this arrangement of the Bragg spots. Moreover, Billard et al. and Morale et al. give further examples of X-ray analyses of columnar rectangular mesophases. As a result of the minor differences in the structures, textures known for Colh phases (Figure 2.17) can also be observed for Colr phases. However, broken fan-shaped and mosaic textures are more common for columnar rectangular mesophases than for columnar hexagonal ones.

2.3.2.3 Oblique Columnar Mesophase Colob

Figure 2.14 (e) shows the arrangement of the columns in a columnar oblique mesophase, in which the tilted columns are represented by elliptic cross sections. The symmetry of this 2D lattice corresponds to the space group P1. Examples for columnar oblique mesophases are rare because strong core–core interactions are required. Since P1 is a primitive planar space group, there are no reflection conditions and therefore all peaks

(hk) are allowed.

2.3.3 Physical Properties and Applications

2.3.3.1 Electrical Conductivity

Considering the inter-core distances of about 3.5 Å in the columns assembled from the discotic aromatic cores, it is possible for the π*–π* LUMOs (lowest-unoccupied molecular orbitals) to overlap and lead to a conduction band for charge transport along the column direction (Figure 2.20).

Figure 2.20 Formation process of electronic band from single molecule to the column.58

The columns would form molecular wires with conductive channels surrounded by insulating peripheral chains, so that the columnar liquid crystal may display photoconductivity. Model systems for conductivity studies were based on triphenylene derivatives, which do not usually possess intrinsic charges.

Figure 2.21 Chemical structures of triphenylene derivatives.58

To investigate the charge transport along the columns, charges were created by doping or through photogeneration. Vaughan et al. doped 44b with iodine, which increased the

61-62 conductivity by several orders of magnitude. Boden et al. used 35b with AlCl3, which transformed the insulating 35b into a p-doped semiconductor, in which the conduction along the columns was three orders of magnitude greater than in the perpendicular direction.63-64 This result clearly proves the high anisotropy in the column structure and that the columnar phase can be regarded as a one-dimensional conductor along the columnar axis.

To study the charge transport in discotic liquid crystals, the time-of-flight (TOF) technique, is most widely used. Charges are generated by light irradiation of discotic films in a typical sandwich-cell configuration (Figure 2.22).

Figure 2.22 Set up of time-of-flight (TOF) experiments.58

A light pulse with a narrow wavelength and a short period is sent to make sure the absorption of light and the following charge generation process occurs in a very thin layer at only the interface. An electric field is applied to induce a drift of the generated charges.

In this electric field, holes or electrons will move across the sample, thus generating a transient current, which is recorded in an external circuit. The time that these charges take to traverse between the electrodes allows the mobility μ to be estimated. In fact, μ largely relies on the applied voltage V and transit time t according to Equation 2.2, where v is the drift velocity, d is the film thickness, and E is the applied electric field.

Equation 2.2

v d2 μ= = E Vt

However there is still a disadvantage in the TOF method: it requires a monodomains with the columns aligned perpendicular to the electrodes. Any defect in the path will have a strong influence on the mobility. Thus the values can underestimate the true transport potential of the material. Discotic mesogens that do not align perfectly might be impossible to investigate with the TOF method.

When samples cannot be properly aligned, the pulse-radiolysis time-resolved microwave conductivity technique (PR-TRMC) has been used. An illustration of the

PR-TRMC method (Figure 2.23) indicates the two main stages of creation of the charges and detection of the conductivity.

Figure 2.23 Set up of the PR-TRMC experiments.58

Charges are uniformly created in the whole sample by irradiation by a high-energy electron pulse from a Van de Graaff accelerator. Microwaves are then sent to and propagate through the sample through and reflect back at the opposite side. The observed change in power of the reflected microwaves is connected to the induced change in conductivity in the material. This change is in turn related to the charge mobility μi and the induced charge-carrier concentration Ni in the sample Equation 2.3.

Equation 2.3

∆σ(t)=e ∑[Ni(t)μi]

The effect of the type and size of the core is investigated by PR-TRMC with a comparative study of the mobility of five different cores (triphenylene, porphyrin, azocarboxyldiimidoperylene, phthalocyanine, hexa-perihexabenzocoronene). Data of

38 derivatives with various peripherally substituted alkyl chains for each family were also extensively studied. The peripheral chains influence the phase-transition temperatures from crystalline to liquid crystal as well as from liquid crystal to isotropic. For phthalocyanine and triphenylene, the chains have very little influence on the mobility in the mesophase. In contrast, the element that connects the core to the chains plays an important role. For example, if oxygen is used as the linking atom, a mobility lower than with direct coupling (for example, through a methylene moiety) or through a sulfur atom results. This decrease in conductivity is attributed to the fact that the oxygen atom is less bulky and thus allows higher mobility, which in turn gives higher intracolumnar disorder, detrimental for charge transport. As a general finding, the bigger the core size, the higher the mobility-probably due to better p-orbital overlap and/or higher intermolecular forces that increase the columnar stability. For all the compounds studied, the highest mobility values were measured in the crystalline phase, but this phase is not attractive because of the formation of domains with subsequent creation of charge traps at the domain boundaries.

In contrast, liquid-crystalline phases avoid this limitation through the formation of columns and possessing the unique feature of self-annealing of defects. The values measured with the PR-TRMC technique can be useful to optimize the desired molecular structure, and to determine which structure gives the highest mobility within few molecular stacks. In macroscopic samples measuring with DC fields, these values could be expected only in case of a well ordered monodomain. Notably, while molecules with big cores have higher stability and conductivity, they are often more difficult to process, which can be cumbersome for applications where macroscopically aligned films are needed. A quantum-chemical approach was used to correlate structure with properties, considering 39 four molecular structures (triphenylene, hexaazatriphenylene, hexaazatrinaphthylene and hexabenzocoronene). The proposed model is based on a hopping mechanism, which describes the rate of charge hopping from one site to the nearest in terms of the molecular reorganization energy and of the intermolecular transfer integral. On studying the reorganization energy, first its reduction was found when the size of the core was increased.

Second, while alkylthio chains only slightly affect the energy, the alkoxy chains decrease the energy, thus adversely affecting the charge transport. Another indicator of the efficiency of transport is the intermolecular transfer integral that is related to the electronic coupling between molecules. The impact of the possible movements that occurred, such as molecular rotation, variation of the intermolecular distance, and translations were evaluated. Although small variations of distance do not have a great effect, rotations do have an effect, independent of the core size, with the complication that the change as a function of the angle is not really predictable. This makes it impossible to estimate the effect of rotation from just the molecular structure. However, in case of bigger molecules, the effect of translational movements is smaller. The theory predicted that transport occurs predominantly by holes, in agreement with the common experimental finding. On the other hand, for hexaazatrinaphthylene derivatives, a substantial electron transport as well as a charge-carrier mobility of an order of magnitude higher than in triphenylene was predicted.

2.3.3.2 Optical Properties

Liquid crystals (LCs), because of their obvious anisotropic structure, are also optically anisotropic in general cases. The optical properties, as the word “anisotropic” suggests, highly depend on the direction in the medium. The optical properties of a material can be 40 visualized using a geometrical representation of the dielectric tensor, known as the index ellipsoid. The intercepts of the ellipsoid surface with its three principal axes give the principal refractive indices of the medium. If the system is isotropic, that is, the properties are independent of direction， the index ellipsoid becomes a sphere. The most common liquid-crystalline phases have one optic axis (they are optically uniaxial), with two principal refractive indices no and ne (the ordinary and the extraordinary refractive index, respectively). The index ellipsoid in this case is an ellipsoid of revolution. Moreover, liquid crystals are most often uniaxial positive, which indicates that the value of no (the refractive index of the light propagating along the optic axis) is lower than that of ne (the refractive index of the light propagating perpendicular, but with polarization parallel, to the optic axis). Many discotic LC phases, like the nematic and the columnar phases, are optically uniaxial, but with negative anisotropy, that is, no > ne, which makes the index ellipsoid oblate (Figure 2.24). This property has been fundamental for the application of discotic films as optical compensators for LC displays.

Figure 2.24 Index ellipsoids for uniaxial positive (a), and negative (b) liquid crystals.58

2.3.4 Triethynyl Benzene (TEB)

1, 3, 5-triethynyl benzene (TEB) is a C3-symmetrical small molecule that can be viewed as a benzene ring with extended carbon-carbon triple bond. Because of the high reaction activity of the triple bond, it can further be functionalized by many methodologies such as Sonogashira reaction with aromatic halo group or CuAAC reaction with terminal azide group. Sanchez et al. in 2011 reported a set of samples obtained by the Sonogashira reaction.65

Figure 2.25 Chemical structures of trisamides 1, (S)-2, and (R)-365.

Upon the geometry relaxation, the TEB center remains almost planar. The proton

NMR signal of aromatic group of the samples displayed strong concentration-dependence.

It indicated a considerable π-π stacking interaction can be provided by the TEB core.

1 65 Figure 2.26 Concentration-dependent H NMR spectra of trisamides 1 in CDCl3 .

2.3.5 Tris-(1, 2, 3-triazol)Benzene (TAB)

Besides the Sonogashira reaction which maintains the carbon-carbon triple bonds of

TEB, CuAAC reaction can also be a candidate to introduce different side groups to the original core. However, due to the formation of triazole five-membered rings, the carbon-carbon triple bonds are broken. Therefore the newly formed TAB core is no longer a perfect plane but a C3-symmetric propeller with tilted triazole rings.

Figure 2.27 Schematic assembly of propeller-like TAB core.66

Cho et al. utilized this propeller-like TAB as a core of a C3-symmetric liquid crystal mesogen.66 This mesogen will give a sequential phase transition from a helical to ordered to disordered hexagonal columnar structure as temperature changes.

Figure 2.28 Chemical structures of compound 1 and 2.66

Figure 2.29 DSC thermogram of compound 1 and 2.66

Figure 2.30 X-ray profiles of compound 1. (a) SAXS profiles of sample 1 at 30℃ and 160℃ in bulk state; (b) WAXS data of sample 1 at different temperatures.66

Figure 2.31 X-ray profiles of compound 2. (a) SAXS profiles of sample 2 at 30℃ and 160℃ in bulk state; (b) WAXS data of sample 2 at different temperatures.66

This unusual phase behavior is attributed to the interdigitated stacking of the propeller-like mesogen.

2.4 Frank-Kasper (F-K) Phase

Frank-Kasper (F-K) phases are an important set of crystalline structures existing in many inter-metallic alloys. Different from simple metallic systems which often generated hcp or fcc structures with few atoms per unit cell, many intermetallic alloys with F-K phase have intricate structures and usually large number of atoms in unit cell.

2.4.1 Topological Close Packing

It is well-known that atoms in both fcc and hcp structures have local 12-fold coordinated structures. For fcc this structure is the cuboctahedron and the hcp it is twinned cuboctahedron. There is actually another icosahedral configuration as shown in Figure

2.32 (c).

Figure 2.32 Three 12-atom coordination clusters (top) and polyhedra (bottom) for (a) hcp, (b) fcc, (c) icosahedral configurations.67

Sir Charles Frank demonstrated that this 12-fold icosahedral coordination could yield lower total energy than the fcc and hcp arrangements.68 This is because the exclusive tetrahedral interstices in icosahedral configuration provide the most efficient packing of

47 atoms. The packing mode which has exclusively tetrahedral interstices is therefore called topological close packing (TCP). To maintain the TCP structure, this distorted icosahedra needs to pack with other polyhedra with larger coordination numbers and atoms. This requires that all the faces on the coordination polyhedra are triangules.69-70 All the possible polyhedra are shown in Figure 2.33, with coordination number of 12, 14, 15 and 16.

Figure 2.33 The F-K polyhedra (a) CN = 12; (b) CN = 14; (c) CN = 15; and (d) CN = 16.67

Canonically these polyhedra can be called Zp cells (p is the coordination number).

They can also be shown in a so-called “Voronoi cell” as Figure 2.34 below. It is very easy for us to find that Voronoi cells have 12 pentagons and p-12 hexagons on their surface.

Figure 2.34 Voronoi cells of F-K polyhedra.71

2.4.2 Square-triangle Tiling of F-K Phase

F-K phases, interestingly, have specific periodic 2D tiling mode made of triangles and squares. Based on this tiling mode and some construction rules, the F-K phases can be generalized and characterized by the tiling mode.71 These construction processes can be classified as two kinds: Z16-free (a, b, c) and with Z16 sites (d, e, f). There are three types of tile interface : triangle-triangle (a, d), triangle-square (b, e) and square-square (c, f).72

Figure 2.35 Square-triangle tiling construction of secondary lays of Z16-free (a, b, c) and Z16-included (d, e, f) sites72.

For the Z16-free sites, sites located on the secondary layers at z = 1/4 and 3/4 sit at the tile vertices (painted as grey sphere). The decoration of primary layer (at z = 1/2) can be formed following the rules below. There are two sets of edges as marked by dark or light grey edges. The classification depends on their angular values. Edges of a given triangle will belong to one of the two sets, while vicinity edges of a square will alternate among the two sets. There are two different primary layer decoration rules (called rules I and II), at the vertical of a triangle of the secondary layer, depending on the triangle color, and whether

49 the primary layer is at height 0 or 1/2. This point will appear more clearly in Figure 2.36.

The figure displays rule I, on the primary layer at height 1/2, with atoms inside triangular prisms (with the triangles being of light-grey color), or square prisms. These atoms are shown in blue (color on line), with the piece of disclination network to which they belong.

They fall in the middle of the triangles, in the middle of the dark grey edges and displaced from the middle of the light grey edges by 1/4 of the square edge length. Rule II applies when the triangles have dark edges, in which case the decoration adds atomic sites on top of the edge centers. Sites located on primary layers at height 0 are also shown (in red with color on-line). Note that these two rules for triangle decoration drive the decoration on top of the squares, with atomic sites on top of dark edges and slightly displaced for the light ones. Sites at height 1/2 in the triangular prism middle are Z15 sites, connected to Z14 sites through a triangle-square interface. Sites falling on the dark grey mid-edge are Z12 sites.

Finally, grey sites on the secondary layers are all Z14 sites, connected by vertical disclination lines. Now, for the primary layer at height 0, the decoration is similar, but with rules I and II reversed with respect to the edge coloring. Let us turn now to the layer decoration with Z16 sites, shown on the right part (d, e, and f). As said in the text, some edges are now “double edges” separating stripes. Across these double edges, rules I and II are reversed. This leads to connecting the disclination lines between two primary layers (in blue and red on-line). A formerly Z15 (resp. a Z14) site is turned into a Z16 (resp. a Z15) site.

One can distinguish several families of Frank-Kasper phases. A first main difference refers to whether or not atoms can be gathered into simple planes (called, in the F-K terminology, “primary layers”, tiled with triangles, hexagons or pentagons, and “secondary layers”, with squares and/or triangles), see for instance. We shall describe here the atomic 50 positions, and disclination network, by focusing on the three types of tile interfaces in the secondary layers, either triangle-triangle, square-square and triangle-square (see Figure

2.36). A nice example of a non-layered F-K phase is provided by the Bergman structure, which shows, around symmetrical sites, an interesting nested sequence of clusters with icosahedral symmetry. Among the layered F-K phases, another criterion distinguishes between principal layers containing only hexagons and triangles (like A15, Z and σ phase), and those in which there are also pentagons (leading to the presence of Z16 sites, as discussed below, like in the C15 and C14 Laves phases.

Figure 2.36 Square-triangle tiling modes of several typical F-K phases.71

2.4.3 Examples of F-K Phase

2.4.3.1 A15 Phase

The A15 phase is a very important intermetallic structure in F-K phase because some

73 superconductors such as Nb3Sn, Nb3Zr and Nb3Ti exhibit this structure. The A15 phase has an A3B stoichiometry with A atoms in a 14-fold coordination polyhedron and the B atoms in 12-fold icosahedral coordination.74 The average coordination number of A15 phase is 13.5.

Figure 2.37 Unit cell in (a) close-packed model, (b) ball-and-stick model, and (c) CN12 coordination polyhedron of Nb atoms about Sn.75

In Figure 2.37, the A15 structure of Nb3Sn is shown in (a) close-packed model and (b) ball-and-stick model. The compounds belong to the space group of Pm3̅n.

Figure 2.38 (001) Planes in the A15 structure (a) 2-uniform 3262 tiling at z = 0, and structure projected into a (111) plane (b). Icosahedra surrounding B atoms (c). and their stacking (d).75

The A15 structure can be also understood in terms of the tiling discussed above.75 As shown in Figure 2.38, we can see the 2-uniform 3262 tilings are stacked along the [001] with 44 secondary layer at z = 0.25. By considering the projections into a (111) plane, the

A15 structure can be decomposed as (b). The edge-sharing icosahedra, connected in chains along [010] directions are shown as (c).

2.4.3.2 Sigma Phase

The sigma (σ) phase is another important intermetallic phase.76 With an AB stoichiometry, sigma phase is determined to have space group P42/mnm. Taking a prototypical sigma phase CrFe alloy as an example, the tetragonal structure has the unit cell as a = 0.8800 nm and c = 0.44544 nm.

Figure 2.39 Structure of CrFe (a) ball-and-stick and (b) space-filling model; (c)primary layer 2-uniform tiling at the z = 0 (001) plane; (d) a secondary layer of M(5) atoms near z = 1/4; (e) primary layer at z = 1/2; and (f) a secondary layer of M(5) atoms near z = 3/4.75

The CrFe σ-phase in ball-and-stick and space-filling models are illustrated in Figure

2.39. There are five atomic sites M(1), M(2), M(3), M(4) and M(5) illustrated using increasingly darker shades of grey.75

2.4.4 F-K Phases in Soft Materials

Although F-K phases are initially observed in and usually considered as inter-metallic alloys structures, they have also been identified in soft-matter systems, including block copolymers, dendrimers and based on the giant molecule concept, giant surfactant and giant tetrahedral.

2.4.4.1 Block Copolymers

Block copolymers are well-studied after the explosion of polymer last century. The phase diagram of AB diblock copolymer is very familiar to almost every polymer student during their polymer physics course.

Figure 2.40 The phase structures (a) and phase diagrams (b) of diblock copolymers.6

Before 2010, it was widely accepted that the spherical packing phases of AB diblock copolymers are dominated by the hexagonal close packing (hcp) and body-centered cubic

(bcc) structures.

Figure 2.41 Reported spherical packing structures obtained by block copolymers.77-81

Upon these classical phase behaviors, Bates et al. later reported various complex spherical packing phases with experimental evidence of novel designed copolymers. They observed a stable Frank-Kasper sigma phase in poly(isoprene-b-lactide) (IL) diblock copolymers and in the poly(isoprene-b-styrene)-b-isoprene-bethelene oxide (SISO) tetrablock copolymers.77 Subsequent experimental studies have firmly established the emergence of a number of nonclassical spherical packing phases in the F-K phases such as sigma and A15 phase.78-80 Surprisingly the C14 and C15 phase which are very unique in

F-K phases because of the Z16 cells in their packing structures are reported for the first time in soft materials in 2017.81

Figure 2.42 Structures of F-K C14 and C15 phases77.

2.4.4.2 Dendrimers

In 2009, Percec et al. reported the first spherical dendritic supramolecular dendrimers by two different dendritic systems.82 The first set of dendrimers used a relatively rigid cyclotriveratrylene (CTV) crown in the center and several dendrimers with different chemical structures and generations as periphery. The dendritic crowns can then self-assemble into superical supramolecular dendrimers which then further self-assembled into cubic (Pm3̅n) and tetragonal (P42/mnm) lattices. In the nomenclature of F-K phases the former is A15 phase and the latter is sigma phase.

Figure 2.43 Chemical structures of dendronized cyclotriveratrylenes82

Figure 2.44 A15 structure formed by CVT dendrimer82

Figure 2.45 Sigma phase structure formed by CVT dendrimer.82

The second dendronized systems replace the CVT center with a triphenylene (Tp) disc-like plane.83 The dendronized Tp, different from the crown ones, displayed phase transition behavior along the temperature.

Figure 2.46 Chemical structures of dendronized triphenylenes.83

For example, the molecule (3, 4, 5)12G1-Tp is hexagonal columnar lattice at room temperature and then switches to a tetragonal lattices with space group P42/mnm (sigma

59 phase in F-K phases) If the temperature is further increased to like 95℃, the superstructure changes to a cubic lattice with space group Pm3̅n which is named as A15 in F-K phase.

Figure 2.47 SAXS profiles of (3,4,5)12G1-Tp at different temperatures.83

Figure 2.48 SAXS profiles of (3,4-3,5)12G2-Tp at different temperatures.83

Interestingly, the phase behavior will further change if the generation of dendrimer is increased. For example, the sample (3,4-3,5)12G2-Tp is glassy state at room temperature

60 instead of hexagonal lattice. Although it also has two phase transition as temperature increases, it will have a dodecagonal quasicrystal phase instead of sigma phase before the temperature reaches the range of A15.

2.4.4.3 Giant Surfactant

Utilizing the nanophase separation between the hydrophilic POSS cages and the hydrophobic PS tails, highly ordered nanostructures in the bulk with feature sizes around

10 nm are formed by giant surfactants, especially the DPOSS-4PSm samples with PS tails

84 longer than PS6 which can show A15, sigma and dodecagonal quasicrystal phases.

Figure 2.49 Chemical structures of giant surfactant with hydrophilic head and multiple polystyrene tails.84

Figure 2.50 The SAXS profiles (d-f) and the corresponding TEM images (g-i) of giant surfactant with hydrophilic head and multiple Polystyrene tails, which represent the A15(d, g), sigma(e, h), and DQC(f, i) phases.84

2.4.4.4 Giant Tetrahedron

In 2015, a giant tetrahedral molecule whose symmetry was broken as one hydrophilic and three hydrophobic heads was reported by our group. The crystallization process of it will provide a frustrated lamellae structure. After melting and annealed at the temperature

85 slightly below the Tm, the A15 F-K phase will form.

Figure 2.51 F-K A15 Phase Formed by Giant Tetrahedra.85

This giant tetrahedron reveals that rigid, single component soft-matter system can provide good potential for constructing supramolecular “metal alloy analogs”. The competition between the tendency to persist molecular geometry and the deformability resulting from interaction terms dictates the selective assembly of the giant tetrahedra.

Different from the metal alloys whose motifs consist of atoms, the building block molecules in soft materials first self-assemble into spherical motif and the motifs further organize into F-K supramolecular lattices.

CHAPTER III

EXPERIMENTAL TECHNIQUES

To successfully achieve the goals mentioned in previous sections, both chemical synthesis and physical characterization parts are of great importance. In the following sections we will exhibit the chemical and physical techniques used to achieve modular molecular design and synthesis and the structure determination.

3.1 Chemical Reaction Toolbox

Several crucial reactions in this thesis are selected and exhibited below. The POSS corner-capping reaction86 and hydrosilylation reaction88 are used to generate a functionalizable POSS cage and the Staudinger reduction101 is used to transfer an azide group to an amine group. Copper-catalyzed azide-alkyne cycloaddition (CuAAC) 102 and

Sonogashira reaction103 are used to connect the cores and BPOSS peripheries together.

3.1.1 Corner-Capping Reaction

Corner-Capping reaction is an approach that generates fully condensed POSS nanoparticle from the incompletely condensed R7Si7O9(OH)3 POSS. Feher et al developed this method in 1986 as an methodology to synthesize monofunctionalized siloxane cages.86

Since the three silanol groups of R7Si7O9(OH)3 is highly active to R’SiCl3, the condensation reaction can process very quickly.

Figure 3.1 Corner-capping Reaction of T7 POSS.86

Subsequent transformation reactions can be performed to the products until the goal

87 synthon is obtained. For example, when the R’ is a -H hydrogen group, the R7R’ POSS product can react with carbon-carbon double bond by hydrosilylation reaction (will be mentioned in next section). If the R’ is a haloalkane, it can be further converted to a variety of modifiable groups such as azide group, hydroxyl group, and amine group.

3.1.2 Hydrosilylation Reaction

The hydrosilylation reaction, which enables the addition of silicon hydrides to C–C multiple bonds, is an efficient method to form organosilicon compounds with Si-C bonds and represents one of the most important reactions in silicon chemistry.88 The process is widely applied to produce industrial products such as silane coupling agents and silicone polymers.

The hydrosilylation reactions can also produce various organosilicon reagents used in fine chemical synthesis for stereospecific oxidation, cross-coupling reactions.

The first hydrosilylation reaction was reported in 1947 by Sommer. In the late 1950s, hexachloroplatinic acid [H2PtCl6]·H2O was found to be a very effective homogeneous transition metal catalyst (Speier's catalyst), in which system the selectivity was improved to a large extent.99 An important breakthrough has been made in early 70's. Thus, in 1973, Karstedt developed the platinum(0) complex containing vinyl-siloxane ligands (Karstedt's catalyst, Figure 3.2 ), which exhibits extremely improved activity and selectivity as well as high solubility in polysiloxane compositions.100

Figure 3.2 Karstedt’s catalyst.100

3.1.3 Staudinger Reaction

The Staudinger reaction is a very useful chemical reaction that can convert an azide group to an amine group as a synthon. It was discovered by and named after H. Staudinger.

The reaction is very fast and has almost quantitative yield. As shown in the mechanism in

Figure 3.3, the Staudinger reaction process in two steps: the triphenylphosphine first reacts with the azide to form a phosphazide; the intermediate phosphazide then undergoes a hydrolysis with water to produce the amine product and phosphine oxide. The structure of the azide part can be widely varied and expended. And not only hydrolysis process, the iminophosphorane is also versatile synthetic intermediates in other reactions: 1) inter- or intramolecular reaction with carbonyl compound towards imines; 2) with carboxylic acid towards N-substituted amides; 3) with acyl halides towards imydoyl halides. 66

Therefore, the Staudinger reaction plays an important role to convert the azide group to various functional groups with great potential for further functionalization.

Figure 3.3 Mechanism of Staudinger Reaction101

A very good example of the application of Staudinger reaction is the antiviral marine natural product (-)-hennoxazole A conducted by F. Yokokawa et al.89 The secondary alkyl azide was carried out in a THF/water mixture. The corresponding amine was collected in very good yield.

Figure 3.4 Example of Staudinger Reaction.89

3.1.4 Copper-catalyzed Azide-alkyne Cycloaddition (CuAAC)

The 1, 3-dipolar cycloaddition reaction was first known as the Huisgen reaction, a thermally promoted reaction that usually gives a mixture of 1, 4- and 1, 5- regioisomers. In

2002, the reaction was re-discovered independently by two groups to be highly robust and efficient under the catalysis of Cu (I) to give only the 1, 4-regioisomer. It was thus recognized as the first “click” chemistry and soon gained its popularity. Using different catalysts, such as ruthenium complexes, it can also afford exclusively the 1,5-regioisomer through a different mechanism. The pros of CuAAC are its high reliability and ease of operation; the cons are, in certain cases, the generation of a bulky, polar triazole linkage between functional groups, which sacrifices elegance in molecular design and add complication and modification to molecular properties.

Figure 3.5 Proposed mechanism of CuAAC.102

3.1.5 Sonogashira Reaction

Sonogashira reaction, also called Sonogashira cross-coupling, is a copper-palladium catalyzed coupling of terminal alkynes with aryl and vinyl halides to afford enynes. The reaction is usually processed at or slightly above room temperature. This makes it a very good alternative to the Castro-Stephens coupling which requires very forcing condition.

Moreover, the catalytic amounts of copper (I) salt successfully avoids the explosive copper acetylides. Since the solvents and reagents don’t need to be rigorously dried, it can undergo well both large and small scale.

The mechanism of the Sonogashira reaction has an oxidative addition-reductive elimination pathway. By reduction with the alkyne substrate a unsaturated Pd(0) species formed from Pd(II) complex. The Pd(0) then processes oxidative addition with aryl or vinyl halide. By further transmetallation with copper (I)-acetylide and reductive elimination, the coupled product is generated.

Figure 3.6 Mechanism of Sonogashira reaction.103

In the total synthesis of the (-)-heliannuol E by K. Shishido, a 3-arylpropargyl alcohol is prepared by the Sonogashira cross-coupling of a substituted aryl iodide with a propargyl alcohol.90

Figure 3.7 Example of Sonogashira cross-coupling.90

3.2 Inert Atmosphere Techniques

To meet the requirements involved in organic synthesis, especially in the operation of highly reactive organometallic compounds and the air- and moisture-sensitive materials, two inert atmosphere techniques were used in our laboratory: the high vacuum line and the

Schlenk line.

3.3 High Vacuum Line Technique

The high vacuum line was developed to meet the extremely stringent requirements to exclude traces of oxygen and moisture from the system to allow the operation of highly reactive organolithiums and to achieve precise control in anionic polymerization. A typical set-up for a high vacuum line is shown in Figure 3.8.

Figure 3.8 Typical high vacuum line. 91

With the help of an oil diffusion pump, a vacuum as low as ~10-3 torr could be achieved. The quality of the vacuum was be tested by a Tesla coil. If vacuum was lower than ~10-3 torr, the Tesla coil would be quiet when placed close to the line surface.

Otherwise, it would create purple-colored electrical discharges with noise. When manipulating chemicals on the line, the liquid nitrogen can be cooled to -78 ℃ and pumped to remove trace amounts of air.

3.4 Schlenk Line Techniques

Schlenk techniques are commonly used for handling air/moisture sensitive compounds under conditions less stringent than anionic polymerization. A typical Schlenk line (Figure 3.9) was built from Pyrex® glass and consisted of a glass manifold containing two-way taps (one for vacuum and one for inert gases). At the end of the line, a pressure

71 release, oil bubbler was attached to monitor the pressure in the inert gas line. The chemicals were usually handled with gas-tight syringes and with degassed solvents.

Figure 3.9 Typical Schlenk line with parts labelled.92

3.5 Chemical Characterization Methods

3.5.1 Nuclear Magnetic Resonance (NMR) Spectroscopy

1 13 H and C NMR spectra of the samples were collecte in CDCl3 (Sigma-Aldrich, 99.8%

D) solvents utilizing either Varian Mercury 300 MHz NMR or 500 MHz NMR

1 spectrometer. H NMR spectra were referenced by the residual proton impurities in CDCl3

13 13 at δ 7.26 ppm and C NMR spectra were referenced by CDCl3 at δ 77.00 ppm.

3.5.2 Matrix-assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass

Spectroscopy

MALDI-TOF mass spectra of the samples were conducted by a Bruker Ultraflex III

TOF/TOF mass spectrometer (Bruker Daltonics, Billerica, MA), equipped with a Nd:YAG laser emitting at a wavelength of 355 nm.

Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenyli-dene]-malononitrile (DCTB,

Aldrich, >98%) served as the matrix. Samples were dissolved in THF at a concentration of about 5 mg/mL for measurement on Bruker Ultraflex III instrument.

3.6 Physical Characterization Methods

To determine the supramolecular structure, generally there will be four steps in this process: thermal analysis, phase determination, lattice characterization, and motif packing determination.93 The experimental techniques corresponding to each step have been summarized in Figure 3.10.

Figure 3.10 Techniques used to determine structures including TGA, DSC, POM, TEM, SEM, AFM, WAXD, SAXS, GIXS, ED, density measurement and simulation93.

Thermal analysis can, at first step, help us understand the thermodynamic phase behavior and kinetics during the phase transitions. Since most of the phase behaviors are not at thermodynamic equilibrium, these measurements need specific careful concerns.

The lattice information and the related space groups can then be extracted by small-angle

X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD), and electron diffraction

(ED) techniques. Finally, the packing details of motifs in a lattice can be investigated via computer simulation based on experimental diffraction patterns and measured densities.

3.6.1 Thermal Gravimetric Analysis (TGA)

Thermal gravimetric analysis is usually used to monitor the mass change of sample as temperature changes. It can provide the information about both chemical and physical phenomena such as thermal decomposition, chemisorption, phase transitions and desorption. By doing TGA experiments for our samples, we can have an overview of the thermal stability of the samples.

The decomposition experiments of TGA were carried out in a thermal gravimetric analysis instrument (Model Q50) protected by nitrogen atmosphere. For each run of the experiments, initial mass of the sample used was about 5 mg, scanned within the temperature range of 30 to 650 °C with a heating rate of 10 °C/min.

3.6.2 Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry is a technique that can be used to trace the phase behaviors as a function of temperature. Since more or less heat needs to flow in or out of the system during the phase transitions, these processes can be detected by the heat flow of either exothermic or endothermic effect.

All the samples were characterized utilizing a PerkinElmer PYRIS Diamond DSC instrument. The temperature and heat flow scales were calibrated at different heating and cooling rates (10 °C/min) using a series of standard materials. For each test of the sample, about 5-10 mg samples was used under nitrogen flow.

3.6.3 Small-Angle X-ray Scattering (SAXS)

Samples for Small angle X-ray scattering (SAXS) were prepared by thermal annealing under N2 atmosphere at corresponded temperatures for several hours. The experiments were recorded on a micromax003+ machine. The wavelength of the X-ray is

0.154 nm. The working voltage is 50 kV and current is 0.6 mA.

3.6.4 Wide Angle X-ray Diffraction (WAXD)

While the SAXS can provide the give the information about the phase behaviors by characteristic distances of ordered domains, the relatively large d spacing size cannot offer enough details on the packing mode in angstrom scale. Wide Angle X-ray Diffraction

(WAXD) herein is used to determine to structural details. Also it is very convenient to justify whether there is crystalline structure using WAXD, which can help explain the phase formation process.

WAXD experiments were conducted on the instrument equipped with a Rigaku Rapid

II sealed tube generator. The working voltage and current used were 40 kV and 30 mA, with the wavelength of the X-ray is 0.154 nm. The instrument was calibrated using silicon powders with 2θ value of 28.4° under Cu Kα radiation in the high angle range and silver behenate in the low angle range. With a two-dimensional cylindrical image film detector, the 2D pattern can be recorded. This 2D pattern makes it easier to analyze a “fiber”-shape sample with the separated equator and meridian information.

3.6.5 Transmission Electron Microscopy (TEM)

Transmission electron microscopy (TEM) uses the beam of electrons to transmit the sample specimen to form images. Because of the much smaller de Broglie wavelength of electron comparing with visible light, the resolution of TEM is much higher than that of light microscopes. This enables TEM to be a capable technique for structure and morphology determination.

The samples in this thesis were all characterized by a JEOL-1230 TEM instrument with an accelerating voltage of 120 kV to collect the bright field (BF) images. The BF TEM images were collected on a digital CCD camera and processed with the accessory digital imaging system.

Two sample preparation methods adopted to process TEM samples are drop-casting and microtome. For drop-casting method, the solution of sample in THF with concentration at 0.5~1.0 mg/mL was dropped onto the carbon-coated copper grids (400 mesh). The casted copper grids were then annealed at corresponding temperature before

TEM measurement. The microtome operation was carried by the Leica EM UC7

Microtome machine.

3.6.6 Density Measurements

While the lattice parameter can be determined by diffraction or scattering techniques such as SAXS, WAXD and TEM, the detailed packing structure at the bottom layer in hierarchical superstructures is hard to describe by these methods due to the resolution limit.

Density measurement is therefore used to provide indirect information about information such as molecule number in each unit cell. 77

The sample was first placed in a vial with water followed by ultrasonication to remove the air bubbles embedded within the sample. Saturated potassium iodide aqueous solution was then added drop-wise into the vial to gradually increase the solution density at the interval of more than 30 min. The density of solution is identical with sample when the sample started to suspend in the middle of the solution.

CHAPTER IV

FROM CYLINDRICAL TO SPHERICAL PACKED SUPRASTRUCTURES BY

TOPOLOGICALLY DESIGNED GIANT SHAPE AMPHIPHILES

In this chapter, we reported four specifically designed shape amphiphiles constructed by two different 1, 3, 5-substituted derivatives of benzene cores with isobutyl polyhedral oligomeric silsesquioxane (BPOSS) cages at the periphery of the molecules. The number of BPOSS cages was selected to be either three or six. These selections are based on two reasons: (1) the molecules are symmetric and can construct the columnar phase via the π-π interactions of discotic cores if no enough steric hindrance at periphery caused by BPOSS cages; (2) when the number of POSS cages increases, its steric hindrance becomes dominant and therefore competes with the π-π interactions of discotic cores which might periodically disturb, interrupt and finally break the column along the columnar axis to construct building blocks with different shapes. New phase structures may be formed.

4.1 Molecular Design

Discotic liquid crystals have been studied for more than 40 years since it was first report in 1977.94 Besides traditional columnar phases by this kind of discotic LC mesogens, some unconventional structures can also be built based on the disc-shaped building blocks.

Here, four giant molecules with isobutyl polyhedral oligomeric silsesquioxane (BPOSS) 79 cages as the periphery at two discotic tri-substituted derivative of benzene core were designed and synthesized. Specifically, two different discotic cores have been chosen: 1, 3,

5-triethynyl benzene (TEB) and 1, 3, 5-tritriazole benzene (TAB), both of which will construct columnar phases when decorated with alkyl chains as LC mesogens.

Furthermore, BPOSS are introduced at the periphery of these discotic cores to generate suitable steric hindrances. As shown in Scheme 4.1, different numbers of BPOSS cages are tethered onto the discotic cores to generate different steric hindrance. For better understanding, a simplified cartoon was drawn for each molecule besides its chemical structure.

The red spheres represents the BPOSS bulk balls and the triangles in the center represents trisubstituted C3 symmetric discotic cores, green represents TEB and orange represents TAB, respectively. The discotic core in the chemical structure has also been colored according to the cartoon. Between the core and BPOSS cages, there is a short linker including an amide group to generate possible hydrogen bonding. The amide group was colored with blue color for emphasize. From the relationship scheme, TEB-BPOSS3 and TEB-BPOSS6 possess the identical TEB core but two different periphery BPOSS numbers (three versus six). Ideally, if the molecules are viewed to be as a planer shape, they hold more or less a C3 symmetry. Similarly, TAB-BPOSS3 and TAB-BPOSS6 have the same relationship between them.

Scheme 4.1 Chemical structures of designed four giant shape amphiphiles with corresponding relationships. Simplified cartoons are drawn for these giant molecules, red spheres represent BPOSS cages, green triangle is TEB discotic core and orange triangle is the TAB type core.

Scheme 4.2 Hypothesis of the molecular packing. The final motif type will be controlled by the periphery steric hindrance caused by BPOSSs (Red spheres) competing with the non-covalent π-π stacking of center core (Blue cylinders).

As shown in Scheme 4.2, the diameter of rigid TAB or TEB core is about 2.6 - 2.8 nm

(see appendix) and they can stack along their C3 rotation axis byπ-π interaction whose typical distance is 0.3 - 0.4 nm in the columnar phase. While the BPOSS cages have a diameter of 1.1-1.2 nm and the perimeter of the rigid core is about 8nm, there can only accommodate about eight BPOSSs if linked tightly. Considering there is a short flexible alkyl linker between the rigid core and rigid POSS cages, surrounded BPOSSs that can be accommodated may reach a bit higher number. The short linker also includes an amide group to generate hydrogen bonding. In order to generate different steric hindrance at the peripheries of these molecules, different numbers of BPOSS cages are tethered on to the discotic cores.

4.2 Synthesis and characterization

AminopropylIsobutyl POSS (BPOSS-C3-NH2) and TriSilanolIsobutyl POSS were purchased from Hybrid Plastics. Trichlorosilane, 2-bromoethyltrichlorosilane,

4-aminobutyltriethoxysilane, 4-amino-3, 3-dimethylbutyltrimethoxysilane,

5-bromopentyltrichlorosilane were purchased from Gelest, Inc. Tetrahydrofuran (THF,

Fisher Scientific) was refluxed over sodium and distilled. Dichloromethane (DCM, Fisher

Scientific) was refluxed over CaH and distilled. Ethyl acetate (Fisher Scientific), methanol

(MeOH, Fisher Scientific, reagent grade), hexanes (Fisher Scientific, Certified ACS) was used as received. Copper (I) bromide (98%, Acros Organics), N, N, N’, N’’,

N’’-pentamethyldiethylenetriamine (PMDETA, 99%, Sigma-Aldrich) need to be stored in refrigerator and avoid oxygen. N, N´-diisopropylcarbodiimide (DIPC, 99%, Aldrich),

1-hydroxybenzotriazole (HOBT, 95+%, Aldrich), 82

N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC, 99%, Aldrich),

4-Dimethylaminopyridine (DMAP) was used as received.

The precursors of BPOSS-I (a), BPOSS2-I (b), BPOSS-N3 (c) and BPOSS2-N3 (d) are achieved by a sequence of corner-capping reaction, azidation, Staudinger reduction and amidation reaction. The final product of TEB-BPOSS3 (A) and TEB-BPOSS6 (B) are prepared by Sonogashira coupling with the iodo-functionalized BPOSSn-I (n=1, 2) with the terminal alkyne groups on the TEB core. Similarly, for preparation of TAB-BPOSS3 (C) and TAB-BPOSS6 (D), CuAAC click reactions are applied to azo-functionalized

BPOSSn-N3(n=1,2) with the alkyne groups on the TEB to obtain the final TAB core. As shown in Scheme 4.3, several steps are proceeded to obtain the final product.

Scheme 4.3 Synthetic route for the preparation of four designed giant shape amphiphiles, TEB-BPOSS3, TEB-BPOSS6, TAB-BPOSS3 and TAB-BPOSS6. Reaction conditions i: 1) HCl H2O 2) NaNO2 3) KI (X=I) or NaN3 (X=N3) ii: DCC/HOBt, CH2Cl2, rt, 12h. iii: All reactions in this step were carried out under an inert atmosphere of N2 with Schlenk techniques. When X=I, Pd (PPh3) Cl2, CuI/Et3N, rt, 12h; when X=N3, CuBr / PMDETA, THF, rt, 24h.

Detailed synthetic procedures are stated as follows. 4-iodobenzoic acid,

4-azidobenzoic acid, 5-iodoisophthalic acid and 5-azidoisophthalic acid are synthesized as literatures.95-98

Scheme 4.4 Chemical structure of BPOSS-I.

BPOSS-I. (a) To a mixture of 437 mg (1.76 mmol) 4-iodobenzoic acid, 2.0 g (2.29 mmol) BPOSS-C3-NH2, and 309 mg (2.29 mmol) HOBt in 100 mL anhydrous CH2Cl2, 471 mg (2.29 mmole) DCC in CH2Cl2 was added dropwise at 0℃. The resulting solution was then stirred at room temperature for 12 h. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of CH2Cl2: EA = 40: 1. 1H NMR (500 MHz, CDCl3, ppm, δ): 7.74(d, 2H,

NHCO-Aro-H),7.48(d, 2H, NHCO-Arm-H), 6.16 (t, 1H, CH2CH2NHCO), 3.41(q, 2H,

SiCH2CH2CH2NHCO), 1.86(m, 7H, SiCH2CHC2H6), 1.53 (m, 2H, SiCH2CH2CH2NHCO),

0.96 (d, 42H, SiCH2CHC2H6), 0.67-0.61 (m, 16H, SiCH2CH2CH2NHCO +

SiCH2CHC2H6). GPC: Molecular Weight Calc. for C38H74INO13Si8: 1105. Found: 922

(Mn).

Scheme 4.5 Chemical structure of BPOSS2-I.

BPOSS2-I. (b) To a mixture of 728 mg (2.49 mmol) 5-iodoisophthalic acid, 2.0 g

(2.29 mmol) BPOSS-C3-NH2, and 337 mg (2.49 mmol) HOBt in 100 mL anhydrous

CH2Cl2, 514 mg (2.49 mmol) DCC in CH2Cl2 was added dropwise at 0℃. The resulting solution was then stirred at room temperature for 12 h. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel

1 with eluate of CH2Cl2: EA = 40: 1. H NMR (500 MHz, CDCl3, ppm, δ): 8.20(s, 2H,

NHCO-AroH-I), 8.10(s, 1H, NHCO-AroH-NHCO), 6.14 (t, 2H, CH2CH2NHCO), 3.46(q,

4H, SiCH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CHC2H6), 1.53 (m, 4H, SiCH2CH2CH2N-

-HCO), 0.97 (d, 84H, SiCH2CHC2H6), 0.67-0.61 (m, 32H, SiCH2CH2CH2NHCO+SiCH2-

CHC2H6). GPC: Molecular Weight Calc. for C70H143IN2O26Si16: 2005.2 Found: 1661(Mn).

Scheme 4.6 Chemical structure of BPOSS-N3.

BPOSS-N3. (c) To a mixture of 229 mg (1.41 mmol) 4-azidobenzoic acid, 1.6 g (1.83 mmol) BPOSS-C3-NH2, and 247 mg (1.83 mmol) HOBt in 100 mL anhydrous CH2Cl2 ,

377 mg (1.83 mmole) DCC in CH2Cl2 was added dropwise at 0℃. The resulting solution was then stirred at room temperature for 12 h. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of CH2Cl2: EA = 40: 1. 1H NMR (500 MHz, CDCl3, ppm, δ): 7.77(d, 2H,

NHCO-Aro-H),7.08(d, 2H, NHCO-Arm-H),6.04 (t, 1H, CH2CH2NHCO), 3.44(q, 2H,

SiCH2CH2CH2NHCO),1.85(m, 7H, SiCH2CHC2H6),1.71 (m, 2H, SiCH2CH2CH2NHCO),

0.96 (d, 42H, SiCH2CHC2H6), 0.68-0.61 (m, 16H, SiCH2CH2CH2NHCO +

SiCH2CHC2H6). GPC: Molecular Weight Calc. for C38H74N4O13Si8: 1020. Found:

822(Mn).

Scheme 4.7 Chemical structure of BPOSS2-N3.

BPOSS2-N3. (d) To a mixture of 5-azidoisophthalic acid (1 eq), BPOSS-C3-NH2 (2.2 eq), HOBt (2.4 eq) in anhydrous CH2Cl2 , DCC (2.4 eq) in CH2Cl2 was added dropwise at

0℃. The resulting solution was then stirred at room temperature for 12 h. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was purified by column 87 chromatography on silica gel with eluate of CH2Cl2: EA = 40: 1.1H NMR (500 MHz,

CDCl3, ppm, δ): 7.68(s, 1H, NHCO-AroH-NHCO),7.54(s, 2H, NHCO-AroH-N3), 6.18 (t,

2H, CH2CH2NHCO), 3.45 (q, 4H, SiCH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CHC2H6),

1.72 (m, 4H, SiCH2CH2CH2NHCO), 0.96 (d, 84H, SiCH2CHC2H6), 0.68-0.61 (m, 32H,

SiCH2CH2CH2NHCO + SiCH2CHC2H6). GPC: Molecular Weight Calc. for

C70H143N5O26Si16: 1920. Found: 1684(Mn).

Scheme 4.8 Chemical structure of TEB-BPOSS3.

TEB-BPOSS3 (A). Sonogashira coupling was used to synthesize the TEB-derivatives.

Oxygen free operation was required. A mixture of 1, 3, 5-triethynyl benzene (1eq),

BPOSS-I (3.5eq), was added into 15ml EtN3. The solution was sealed in an Schleck flask and do freeze-pump-thaw for 3 times before adding Pd(PPh3)Cl2(0.03eq) and CuI(0.03eq).

After adding the catalysts under N2 protection, seal the Schleck flask again and do freeze-pump-thaw for one more time. The mixture was stirred under room temperature for

12 hours. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was

88 purified by column chromatography on silica gel with eluate of Hexane: EA = 6: 1. Further purification including running an THF-HPLC column and precipitating the first eluate with

THF/MeOH gives product as white solid. Yield is 60%. 1H NMR (500 MHz, CDCl3, ppm,

δ): 7.75 (d, 6H, NHCO-Aro-H), 7.70 (s, 3H,-C ≡ C -AroH-C ≡ C -), 7.60 (d, 6H,

NHCO-Arm-H), 6.11 (t, 3H, CH2CH2NHCO), 3.47 (q, 6H, SiCH2CH2CH2NHCO), 1.86(m,

21H, SiCH2CHC2H6), 1.74 (m, 6H, SiCH2CH2CH2NHCO), 0.96 (d, 126H,

SiCH2CHC2H6), 0.69-0.61 (m, 48H, SiCH2CH2CH2NHCO + SiCH2CHC2H6). 13C NMR

(125 MHz, CDCl3, ppm, δ): 166.63, 134.67, 131.79, 126.94, 125.78, 123.80, 89.68, 42.36,

25.67, 23.82, 23.03, 22.48, 9.52. MS (MALDI-TOF, m/z): Calc. for C126H225N3O39Si24:

3078.02. Found: 3099.09 (M+Na)+.

Scheme 4.9 Chemical structure of TEB-BPOSS6.

TEB-BPOSS6 (B). Sonogashira coupling was used to synthesize the TEB-derivatives.

Oxygen free operation was required. A mixture of 1, 3, 5-triethynyl benzene (1eq),

2BPOSS-I(3eq), was added into 15ml EtN3. The solution was sealed in an Schleck flask and do freeze-pump-thaw for 3 times before adding Pd(PPh3)Cl2(0.03eq) and CuI(0.03eq).

After adding the catalysts under N2 protection, seal the Schleck flask again and do freeze-pump-thaw for one more time. The mixture was stirred under room temperature for

12 hours. The precipitate was filtered by running a fast silica column with eluate of THF.

After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of Hexane: EA = 7:1. Further purification of running a THF-HPLC column generates a transparent thin film. The product was

1 precipitated with THF/MeOH gives white solid. Yield is 42%. H NMR (500 MHz, CDCl3, ppm, δ): 8.15 (s, 3H, NHCO-AroH-CONH), 8.06 (s, 6H, NHCO-AroH-C≡ C-), 7.66 (s, 3H,

-C≡ C-AroH-C≡ C −), 6.26 (t, 6H, CH2CH2NHCO), 3.48 (q, 12H, SiCH2CH2CH2NHCO),

1.86(m, 42H, SiCH2CHC2H6), 1.74 (m, 12H, SiCH2CH2CH2NHCO), 0.96 (d, 252H,

13 SiCH2CHC2H6), 0.69-0.61 (m, 96H, SiCH2CH2CH2NHCO + SiCH2CHC2H6). C NMR

(125 MHz, CDCl3, ppm, δ): 165.61, 135.55, 132.54, 125.24, 123.83, 89.15, 42.73, 25.66,

23.81, 23.05, 22.49, 9.59. MS (MALDI-TOF, m/z): Calc. for C222H432N6O78Si48: 5781.94.

Found: 5804.28 (M+Na) +.

Scheme 4.10 Chemical structure of TAB-BPOSS3.

TAB-BPOSS3 (C). CuAAC reaction was used to synthesize the TAB-derivatives.

Oxygen free operation was required. A mixture of 1, 3, 5-tri triazole benzene (1eq),

BPOSS-N3 (3.5eq), CuBr (0.1eq) was added into 15ml THF. The solution was sealed in a

Schleck flask and does freeze-pump-thaw for 3 times before adding PMDETA (0.04eq) under N2 protection. Seal the Schleck flask and do freeze-pump-thaw for one more time before stirring under room temperature for 24 hours. The Cu salt was filtered by running a fast silica column with eluate of THF. After removal of solvent under reduced pressure, the residue was purified by flash column chromatography of silica gel with eluate of Hexane:

EA = 5:1. Further purification including running a Bio-Beass S-X Resin column and precipitating the first eluate with THF/MeOH. Product is white solid. Yield is 89%. 1H

NMR (500 MHz, CDCl3, ppm, δ): 8.32(s, 3H,triazole-AroH-triazole),8.30(s, 3H, triazole-H), 7.79 (d, 6H,triazole-AroH-CONH),7.73(d, 6H, triazole-ArmH-CONH),6.68(t,

3H, CH2CH2NHCO),3.54(q, 6H, SiCH2CH2CH2NHCO),1.88(m, 21H, SiCH2CHC2H6),

1.82(m, 6H, SiCH2CH2CH2NHCO), 0.98(d, 126H, SiCH2CHC2H6), 0.76-0.63 (m, 48H,

13 SiCH2CH2CH2NHCO + SiCH2CHC2H6). C NMR (125 MHz, CDCl3, ppm, δ): 166.62,

147.55, 138.24, 135.31, 131.04, 128.49, 122.44, 119.26, 117.33, 42.63, 25.66, 23.84, 22.50,

9.65.MS (MALDI-TOF, m/z): Calc. for C126H228N12O39Si24: 3207.07. Found: 3232.92

(M+Na)+.

Scheme 4.11 Chemical structure of TAB-BPOSS6.

TAB-BPOSS6 (D). CuAAC reaction was used to synthesize the TAB-derivatives.

Oxygen free operation was required. A mixture of 1, 3, 5-tri triazole benzene (1eq),

2BPOSS-N3 (3.5eq), CuBr (0.1eq) was added into 15ml THF. The solution was sealed in a

Schleck flask and does freeze-pump-thaw for 3 times before adding PMDETA (0.04eq) under N2 protection. Seal the Schleck flask and do freeze-pump-thaw for one more time.

The mixture was stirred under room temperature for 24 hours. The precipitate was filtered by running a fast silica column with eluate of THF to remove the Cu salt. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of Hexane: EA = 5:1. Further purification of running a Bio-Beass S-X

Resin column generates a transparent thin film. Precipitating the product with THF/MeOH gives white solid. Yield is 71%. 1H NMR (500 MHz, CDCl3, ppm, δ): 8.64 (s,

3H,triazole-AroH-triazole), 8.55 (s, 3H, triazole-H), 8.46 (s, 6H, triazole-AroH-CONH),

8.31 (s, 3H, triazole-ArmH-CONH), 6.45(t, 6H, CH2CH2NHCO), 3.53 (q, 12H,

SiCH2CH2CH2NHCO), 1.87(m, 42H, SiCH2CHC2H6), 1.78 (m, 12H,

SiCH2CH2CH2NHCO), 0.97 (d, 252H, SiCH2CHC2H6), 0.72-0.62 (m, 96H,

13 SiCH2CH2CH2NHCO + SiCH2CHC2H6). C NMR (125 MHz, CDCl3, ppm, δ): 164.92,

148.11, 137.39, 136.95, 131.49, 125.22, 123.38, 121.05, 118.40, 42.94, 25.67, 23.82, 23.02,

22.49, 9.65. MS (MALDI-TOF, m/z): Calc. for C222H435N15O78Si48: 5908.95. Found:

5936.19 (M+Na) +.

In order to follow up the synthetic procedure, 1HNMR spectrum was used to trace each step as follows.

1 Figure 4.1 H NMR characterization of BPOSS-I (a), precursor for TEB-BPOSS3 (A).

The appearance of peak d (SiCH2CH2CH2NHCO) at δ = 3.41ppm indicates the success of amidation reaction.

1 Figure 4.2 H NMR characterization of BPOSS2-I (b), precursor for TEB-BPOSS6 (B).

The ratio of two peaks b and a on the aromatic phenyl ring is about 2 to 1 and the H resonance from amide group (δ = 6.14ppm) to H resonance from peak a is about 2 to 1, indicating the success dual functionalization of the isophthalic acid.

1 Figure 4.3 HNMR characterization of BPOSS-N3(c), precursor for TAB-BPOSS3(C).

The appearance of peak d (SiCH2CH2CH2NHCO) at δ = 3.44 ppm indicates the success of amidation reaction.

1 Figure 4.4 H NMR characterization of BPOSS2- N3 (d), precursor for TAB-BPOSS6 (D).

The ratio of two peaks b and a on the aromatic phenyl ring is about 1 to 2 and the H resonance from amide group (δ = 6.18ppm) to H resonance from peak a is about 2 to 1, indicating the success dual functionalization of the isophthalic acid.

1 13 Figure 4.5 H NMR and C NMR characterization of TEB-BPOSS3 (A).

Only one substituted arm on the 1, 3, 5- trisubstituted benzene was drawn detailed structure for clear demonstration of the chemical environment. Other arms have the same chemical structures and therefore with the same chemical shift as the arm shown on the spectrum. Those arms are abbreviated by two wavy lines.

1 13 Figure 4.6 H NMR and C NMR characterization of TEB-BPOSS6 (B).

Detailed structure was drawn for only one of the three substituted arms on the 1, 3, 5- trisubstituted benzene to show the chemical environment more clearly. The three arms have the same chemical structures and therefore with the same chemical shift. Those arms are abbreviated by two wavy lines.

1 13 Figure 4.7 H NMR and C NMR characterization of TAB-BPOSS3 (C).

Detailed structure was drawn for only one of the three substituted arms on the 1, 3, 5- tri-substituted benzene to show the chemical environment more clearly. The three arms have the same chemical structures and therefore with the same chemical shift. Those arms are abbreviated by two wavy lines.

1 13 Figure 4.8 H NMR and C NMR characterization of TAB-BPOSS6 (D).

100

From NMR characterization, every peak can be assigned to corresponding chemical sections, indicating the chemical structures of these shape amphiphiles are correct. In order to verify the sample mass and purity of these four giant molecules, matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and gel permeation chromatography (GPC) were also used to confirm the final products.

Figure 4.9 MALDI-ToF spectra of (A) TEB-BPOSS3, (B) TEB-BPOSS6, (C)

TAB-BPOSS3 and (D)TAB-BPOSS6。

All the samples show a single peak with same observation mass as calculated mass, which proves the successful synthesis of these molecules.

101

Figure 4.10 GPC characterization of (A) TEB-BPOSS3, (B) TEB-BPOSS6, (C) TAB-BPOSS3 and (D) TAB-BPOSS6 proves the neat synthesis of giant molecules at volume exclusive level. Elution solvent is THF. Calculated Mn=3868(A), 5464(B), 4552(C), 5470(D).

4.3 Thermal Stability of BPOSS-based Giant Shape Amphiphiles

Thermogravimetric analysis (TGA) is one kind of thermal analysis method that measure sample mass over time as the temperature changes. This method can be applied to analysis of thermal stability, oxidation and/or combustion, thermogravimetric kinetics and so on. Here, the thermogravimetric analysis (TGA) at a heating rate of 10oC/min was used to verify the thermal stability of these prepared four giant molecules and the TGA curves are shown in Figure 4.11. From the TGA curve we found the 5% weight loss temperature of all these molecules are all above 370oC, which may benefits from the good thermal stability of BPOSS. 102

Figure 4.11 TGA analysis showing the 5% weight loss temperature of (A) TEB-BPOSS3, (B) TEB-BPOSS6, (C) TAB-BPOSS3 and (D) TAB-BPOSS6 at 400.1℃, 376.8℃, 370.1℃ and 379.5℃, respectively.

4.4 Sample Preparation

All powder samples are originally precipitated out from poor solvent (usually methanol). Based on the TGA results, all the samples are thermally stable before 300℃, so chemical structure will preserve during thermal treatment of the bulk sample.

For X-ray experiments, to prepare thermally treated sample without crystalline, the thermal annealed sample of TEB-BPOSS3 were prepared by three different methods.

Different treatment method will result in the different intracolumnar order level. For example, if the sample is heated above its melting temperature to remove thermal history and then cooled to the room temperature immediately by directly quenched in liquid

103 nitrogen, then intracolumnar short-range order can be removed. It will be discussed in the next section. TEB-BPOSS6 was prepared by melting the molecule and then cooling to the room temperature naturally. However, only thermally annealing it above the BPOSS melting temperature cannot give such ordered structure. It may result from the energy barrier that needs to be overcome before forming ordered structure. TAB-BPOSS3 and

o TAB-BPOSS6 were prepared by annealing the sample at 180 C for 2-3 hours. Increasing the temperature above melting temperature and then cooling down to room temperature at a rate of 10℃/min or directly quench the samples in liquid nitrogen gives the same structure.

The reason for different sample preparation method comes from the TEB core and

TAB core effect. It will be discussed later in the structure analysis.

For TEM experiments, all samples can be prepared by fast evaporating 1 drop of 0.5 mg/ml solution directly from carbon coated cooper grid before further treatment. Thermal annealing the thin film sample at 180℃ for overnight will give the prepared thin film of samples suitable for TEM experiments. Thin film samples can also be prepared by utilizing

Reichert Ultracut S (Leica) microtome on the annealed sample and transfer slices to the carbon coated copper grids. The latter method can be used to obtain pre-treated and relatively flat thin slices along preferred directions.

IR was conducted in situ with protection of inert Helium atmosphere. Samples are precipitated from poor solvent and dry for overnight in vacuum chamber to avoid H2O absorption.

104

Thermal treated and fresh precipitated samples are used to obtain the SSNMR spectrums to detect the different chemical environments of the center aromatic core, in order to estimate the formation of π-π interaction before and after phase formation.

Samples for UV experiments are prepared by dropping a solution in chloroform with concentration of 10 mg/ml and then fast evaporating on a piece of quartz plate. Thermal anneal the thin film sample at 180℃ for overnight is processed before UV experiment. All thermal treatments before characterization is under protection of N2.

4.5 Phase Behavior of Four Disc-POSS Giant Shape Amphiphiles

Traditionally, columnar phase is one kind of ordered packing in liquid crystal area.

Discotic molecules prefer to form columnar LC phase with uni-directional interaction helping stabilizing the columns. Most often, the mesogen contains π-π stacking core with insulating periphery. The charge transfer ability along the column axis offers potential applications in the semiconducting area of this kind of materials. In our system, instead of flexible alkyl chains, rigid and bulky POSS was introduced into the periphery of disc shape core. Different shape and geometry properties between alkyl chains and POSS may lead to quite different phase behaviors in bulk state. The primary difference is the steric hindrance brought by the 1nm rigid POSS cage. It will either help to stabilize the column if the steric hindrance are endured or break the column into fragments if the steric hindrance is too much. The second issue is the crystallization tendency of BPOSS. If BPOSS crystallized, which prefers to form flat interface, it will most likely destroy the columnar phase. The third thins is the thermal stability of BPOSS. As BPOSS itself has very good thermal stability, introducing of BPOSS will enhance the the whole molecular thermal stability, 105 which has been proved by TGA. There are also some other factors will be brought by the

BPOSS to the molecules that affect their self-assembly behaviors. For example, the rigidity of the whole molecule will be increased and will affect the packing mode at molecular level.

The differential scanning calorimetry (DSC) is one kind of thermoanalytical techniques in which the difference of the sample and reference heat flow is measured upon heating or cooling. The result of a DSC experiment is represented as a curve of heat flux versus temperature or time. In our conventions, an exothermic reaction in the sample is represented by negative peak. This curve can be used to calculate enthalpies of transitions (|∆퐻|) by integrating the peak area. The thermal diagrams of compound A-D were collected for 2nd heating and 1st cooling at a scan rate of 10℃/min in Figure 4.12.

Upon heating, the transition temperature of A, C (1st transition) and C (2nd transition) are

214oC, 234.3oC and 253℃, respectively. Latent heats were measured as 19.6 KJ/mol for

A，23.0 KJ/mol for C (1st transition) and 1.3 KJ/mol for C (2nd transition). Above these temperatures, compound A enters the isotropic liquid state (I), while compound C firstly enters a nematic columnar phase (Phase II) and then enters the isotropic state (I). Upon cooling, both compound A and C exhibit enantiotropic behavior with almost identical latent heats. No phase transition is observed for compound B and D. The phase behavior of compound A and C is similar to the reference, in which TEB and TAB with alkyl chains on the periphery. It indicates that the presence of the BPOSS didn’t obviously change the thermal property of A and C but did for compounds B and D.

106

Figure 4.12 DSC thermograms showing the phase transition temperature of (A)-(D). (a) TEB-BPOSS3 Tm=214℃ (|∆H|=19.6 KJ/mol), Tc=165.8℃ |∆H| = 15.4 KJ/mol) (b) TEB-BPOSS6 No obvious enthalpy change has been observed (c) TAB-BPOSS3 TphaseI-phaseII = 234.3℃ (|∆H| = 23.0 KJ/mol), TphaseII-isotropic = 253.0℃ (|∆H|=1.3 KJ/mol) T isotropic-phaseII = 245.9℃(|∆H|=1.3 KJ/mol),TphaseII-phaseI = 201.6℃ (|∆H| = 14.5 KJ/mol) (d) TAB-BPOSS6 No obvious enthalpy change has been observed.

4.6 Hierarchical Structure Analysis of TEB-BPOSS3

4.6.1 Columnar Structure with Less Ordered to Ordered Intracolumnar Packing

Based on the DSC results, samples were thermally annealed below the melting temperature and above the BPOSS crystallization temperature which is about 150℃. Not only the temperature fluctuation will influence the final structure, but also the pre-treatments of the samples will affect the order of structure. For example, for

107

TEB-BPOSS3, there are mainly three different methods was used for obtaining different ordered structures.

Figure 4.13 Columnar structures with ordered to less ordered intracolumnar packing achieved by three treatment methods. Method 1: Quench the sample from its melt states to room temperature by liquid nitrogen. Method 2: Thermal anneal the sample at 180℃ for 12 hours and cooled to room temperature at a rate of 10℃/min. Method 3: Extrude the sample into a fiber at high temperature and thermal anneal the fiber at 180 oC for 12hours.

As shown in Figure 4.13, three different methods were used to treat the compound

TEB-BPOSS3. If the sample is rapidly quenched, there will be no crystalline peaks in the

WAXD regime, indicating that the BPOSS crystallization is avoided while a two dimensional (2D) hexagonal lattice is remained. However, after thermal annealing the sample at 180℃, whether cooling down or not, the 2D hexagonal lattice remains but a relatively broad peak whose d spacing is near 1 nm and small crystalline peaks show up in

WAXD regime. It indicates the intracolumnar order increases at high temperature.

108

Shearing the sample into fiber sample results into an even more ordered packing, which consists of the same hexagonal arrays of columns with a periodic, positional intracolumnar order.

Motif arrangement instead of details within crystal unit cell is more concerned in this work. So the calculations in later comparison with the rest three molecules are based on the sample prepared by Method 1.

Figure 4.14 Two dimensional hexagonal packing of TEB-BPOSS3 supramolecular columns.

The first three diffractions possess a q ratio of 1:√3: √4, corresponding to planes of

(10) (11) and (20) in a hexagonal columnar lattice. The two-dimensional (2D) lattice parameters can be determined as a = b = 3.83 nm, γ = 120°. Other diffractions in the small angle area can also be indexed by this 2D lattice as shown in Table 4.1. The peak

109 corresponding to (10) plane has weak intensity than (11) or (20), which is not normal in the traditional columnar phase. Different from traditional columnar phase formed by discotic

LC mesogens that have flexible chains filling into the columns, columns formed by our giant molecules have lower density in the center but higher density at the periphery. This is caused by the rigidness of BPOSS.

Figure 4.15 Simulated SAXS pattern for 2D hexagonal packing: a = b, γ =120°. The model inserted to each pattern was built by atoms in Crystal maker. Traditional columnar packing is analogy to the model in (a). To compare the atom position effect on the diffracted peak intensity, three more models (b) (c) and (d) were built.

The lower intensity of the first diffraction peak is mainly due to the core-shell structure. According to the simple atomic simulation in Figure 4.15, the intensity of the diffracted peaks is related to the atom position on this plane. In model (b), most of the atoms are on (10) plane, giving high (10) intensity. Instead in model(c), most of the atoms

110 are on (20) plane, giving high (20) intensity. Thus fewer atoms in one plane will result in lower intensity of the diffracted peak of this plane. If forming columnar phases, the center core of the giant shape amphiphile with low electron density is on the (10) plane, but the periphery BPOSS with high electron density is not always on the (10) plane, similar to the condition in model showed in Figure 4.15 (d), resulting in the lower intensity of (10) than

(11).

Table 4.1 Indexing of the SAXS peaks of TEB-BPOSS3 prepared by Methond 1.

-1 q/Å d/Å (hk) Intensity（*100%）

0.1894 33.2 (10) 0.404

0.3294 19.1 (11) 0.545

0.3799 16.5 (20) 0.394

0.5026 12.5 (21) 0.488

0.5465 11.5 (30) 0.595

0.6578 9.6 (22) 0.496

0.6918 9.1 (31) 0.534

0.7599 8.3 (40) 0.320

Based on the indexing from Table 4.1 Indexing of the SAXS peaks of TEB-BPOSS3 prepared by Methond 1, all of the peaks in Figure 4.16 can also be indexed by the similar lattice parameters except two dissociative broad peaks X and Y.

111

Figure 4.16 In-situ temperature resolved SAXS pattern of TEB-BPOSS3. Peak X and Y cannot be indexed by the two dimensional hexagonal lattice.

These peaks may contain the information of intracolumnar packing. Upon temperature increasing, peak X and peak (30) are seperated, indicating the molecular packing is more ordered at high temperature.

112

4.6.2 Thermal Expansion Analysis of Hierarchical Structure

Figure 4.17 Temperature resolved in-situ SAXS and WAXD results for TEB-BPOSS3 upon heating and cooling, respectively.

It is well known that most of the solid materials will expand or draw back upon heating or cooling. The length change can be expressed as ∆l. The relationship between the length change and the temperature change can be expressed as ∆l/l0 = αl ∆T. l0 represents the original length, and αl represents the length coefficient of thermal expansion. Since all dimensions will be affected by temperature change, so the volume change with relation to temperature change can also be expressed ∆V/V0 = αv ∆T. αv represents the volume 113 coefficient of thermal expansion. However, the expansion along different dimensions are mostly anisotropic, depending on the crystallographic directions, so the difference of thermal expansion coefficient can be used to determine the peaks related to different directions and help to separate the peaks from hierarchical structures.

To compare the thermal expansion coefficient of TEB-BPOSS3 from different directions, the in-situ X-ray scattering peaks shown in Figure 4.17 have been assigned to

1-10, d-spacing of each peaks were collected at 30oC, 100℃, 120℃, 140℃, 160℃, 180℃,

200℃, 220℃ and 230℃ during heating up. The change of d- spacing of each peaks are proportional to the temperature change. For instance, the relationship between the d-spacing and temperature of peak 1 in SAXS (S1) can fit into a linear curve and the slope is the thermal expansion coefficient α1 calculated from peak 1 as shown in Figure 4.18 (a).

Figure 4.18 Thermal expansion coefficient analysis. (a) Thermal expansion coefficient calculation of S1. (b) Linear fit curve of thermal expansion coefficient calculated from d-pacing of S1 to S10. S1-S10 are scattering peaks from TEB-BPOSS3 in-situ SAXS (Sample treated by Method 2).

114

Similarly, thermal expansion coefficient was calculated for each peak from the SAXS data and their values were listed in the up left corner inserted table of Figure 4.18. Every peak can be nicely fitted to a linear curve except 2 peaks: Peak 5 and peak 7 have dramatically different thermal expansion coefficient from other peaks, which are the peaks

X and Y caused by the intracolumnar order as we speculated in Figure 4.16. Here, the difference in thermal expansion indicating two set of crystallographic directions, further proves the hierarchical packing of TEB-BPOSS3.

4.6.3 Ordered Columnar Phase Determined by 2D Fiber Pattern

More direct evidence for hierarchical structure is from the 2D X-ray pattern for fiber sample prepared by Method 3, which will clearly demonstrates peak X and Y are from different direction with the columnar packing.

Scheme 4.12 Experimental geometry of fiber sample X-ray test.

115

Figure 4.19 Two dimensional SAXS pattern of TEB-BPOSS3 fiber sample (Sample prepared by Method 3). (a) Two dimensional SAXS pattern (b) Meridional (Red) and equatorial (Blue) plots from the 2D diffraction pattern shown in (a), in other words, the integration along the direction parallel to the fiber (red dashed line cut in (a)) and perpendicular to the fiber (blue dashed line cut in (a)) was plotted. Numerical values denote their Miller indices and d-spacing, respectively.

Oriented fiber sample was obtained by extruding the melt sample from a 0.5 mm fiber-extrusion molder with diameter of 0.5 mm. The fiber successfully displayed a distinct

2D SAXS pattern (Figure 4.19(a)) and 2D WAXD pattern (Figure 4.20(b)) featuring a set of diffuse spots along the fiber direction and perpendicular to the fiber direction. In the direction perpendicular to the fiber (Figure 4.19(b), blue), those spots can be indexed as

(10), (11) and (20) planes of a 2D hexagonal lattice, similar to sample prepared by Method

1, with a lattice parameter of a = 3.73 nm. This hexagonal lattice indicates columnar packing with columns oriented parallel to the fiber direction and hexagonally packed with an inter-core distance of 3.73nm (Figure 4.20(b)). This distance is reasonable considering that the size of the rigid core is about 2.6 nm with 1nm BPOSS cages on the periphery.

Meanwhile, along the fiber axis of TEB-BPOSS3, distinct diffraction arcs with d-spacing 116 of 1.1nm (Figure 4.19(b), red) and 0.37nm (Figure 4.20(b)) was observed. Taking into account the molecular structure and dimensions of π-π stacking, this diffraction pattern is attributed to a intracolumnar structure illustrated in Figure 4.20(b), where the molecules stacks on top of each other inside the column to maximize the intermolecular π-π interaction and H-Bonding.

Figure 4.20 Two dimensional WAXD pattern of TEB-BPOSS3 fiber sample (Sample prepared by Method 3) and the molecular packing model indicated by this pattern. (a) two dimensional WAXD pattern. (b) Illustration of intercolumnar packing and intracolumnar packing with respect to the fiber axis and X-ray beam direction. Intercolumnar distance and intracolumnar d-spacing have been denoted in the picture respectively.

4.7 Columnar Phases of TEB-BPOSS3 and TAB-BPOSS3

4.7.1 Structure Analysis

From the hierarchical structure analysis of TEB-BPOSS3, the columnar phase of

TAB-BPOSS3 can also be determined following the same procedure. X-ray pattern of

TAB-BPOSS3 treated by three different methods is attached in the appendix. Here, data was collected for thermal annealed sample (Method 2) to compare the columnar phase of

TAB-BPOSS3 and TEB-BPOSS3. 117

Figure 4.21 shows a small angle X-ray scattering (SAXS) pattern of TEB-BPOSS3 after thermally annealed at 180 ºC for 12 hours. As the structure determination procedure demonstrated for TEB-BPOSS3 in Figure 4.14, the first three diffractions possess a q-ratio of 1:√3: √4, corresponding to planes of (10) (11) and (20) in a hexagonal columnar lattice.

The low intensity of (10) is due to few atoms were contribute to the ordered of this lattice pane. The two-dimensional (2D) lattice parameters can be determined as a = b =

3.73 nm, γ = 120°. Other diffractions in the SAXS pattern can also be indexed based on this 2D lattice. In order to verify this assignment, transmission electron microscopy (TEM) experiments were carried out after the sample was annealed without staining. Figure 4.21 are Fourier filtrated (FT) bright field TEM images along the columnar axis and [10] zone, respectively. In Figure 4.21, a hexagonal columnar packing can be clearly seen with inter-column d-spacing of 3.6 nm, with a good agreement of the calculated d-spacing (3.73 nm) based on the SAXS pattern. Here, the darker part in the image is attributed to the

BPOSS cages and the light dots are discotic cores, indicating that both of the cores and

BPOSS cages are nano-phase separated. The size of the light dot is about 2.4 nm, matching the diameter of the disk core (rigid part 2.6nm), and the darker part is about 1.2 nm, since the BPOSS cage is about 1nm, we speculate that the BPOSS cages at the periphery sharing the 1.2 nm space with the neighboring columns. The inter-column d-spacing in Figure

4.21(c) is 3.1 nm, indicates it’s the projection along the [10] zone, corresponding to the d-spacing of (10) plane (X-ray 3.23 nm).

For TAB-BPOSS3, its SAXS pattern is shown in Figure 4.21(d). The diffraction peaks with q-ratio of √3: √4: √7 can be identified and assigned as the (01) (11) (21) in a 2D rectangular lattice with lattice parameters of a = 6.88 nm and b = 3.99 nm. The bright field 118

TEM image of TAB-BPOSS3 shown in Figure 4.21(e) proves the assignment of this rectangular lattice. Although The angles between the columns within one lattice cell shown in Figure 4.21(e) is not exactly 60°.As shown in the Figure 4.21(e), this lattice parameters are 6.6 nm and 3.9 nm, in good agreement with the values obtained from the SAXS results

(6.88 nm and 3.99 nm). It is speculated that the rectangular lattice formation may result from the slight titling of discotic giant molecules. This tilting made the suprastructure deviated from the circular shape of the columns. This projection of the column along the column axis may thus be in an elliptical shape and gives rise to the 2D rectangular columnar packing.

Figure 4.21 Columnar phase formation of TEB-BPOSS3 and TAB-BPOSS3. Hexagonal columnar packing of TEB-BPOSS3 is indicated by (a) Small angle X-ray scattering pattern and computer-reconstructed TEM images (obtained by Fourier filtration (b) along and (c) perpendicular to the column axis along (10) plane. Rectangular columnar packing of TAB-BPOSS3 is indicated by (d) Small angle X-ray scattering pattern and computer-reconstructed TEM images (obtained by Fourier filtration (e) along and (f) perpendicular to the column axis. Peak X and Y denoted by red color are short correlation peaks of intracolumnar packing along column axis.

119

3 The density of TAB-BPOSS3 is 1.15g⁄cm , slightly larger than the TEB-BPOSS3 sample (1.12g⁄cm3) treated by same method.

As shown in Scheme 4.2, with three BPOSS cages tethered onto the core, the π-π stacking of the cores can be accommodated by the BPOSS cages at the periphery via certainly degrees of rotation of the cores.

4.7.2 Phase Morphologies of TEB-BPOSS3 and TAB-BPOSS3

Although X-ray and TEM already provide definitive means for the columnar phases formed by TEB-BPOSS3 and TAB-BPOSS3, Polarized optical microscope offers an opportunity to see morphologies for these structures macroscopically. Phase morphology of the Colh phase of TEB-BPOSS3 is shown in Figure 4.22. The samples was prepared by drop casting on the glass slides and thermally treated by 3 methods as discussed before. For example, (a) and (c) are prepared by heated to the I phase and cooled down by dipping into the liquid nitrogen. Due to the dramatically temperature change, the sample in (a) breaks into small pieces and (b) is the enlarged graph of a piece in (a). According to the X-ray pattern, hexagonal columnar phase will formed under this method, however, due to the cooling rate is too fast, the domains are too small that large macroscopic morphology was not obtained. Method 2 can give better quality of morphologies than method 1. (d), (g) is prepared by heated to the I phase and cool to 180℃ at cooling rate of 10℃/min and annealed at 180℃ for 12 hours and cool down to room temperature at cooling rate of

10℃/min. The birefringent conical fan shape optical texture of (d) (g) and (i) under the polarized optical microscope (POM) is typically found in the columnar LC phase of discotic LCs. In (e) and (h) spherullite texture with Maltese cross was displayed, indicating 120 packing of semicrystalline lamellars, suggests that the growth rate along and perpendicular to the column axis are different. The sheared and annealed sample gives more information about the growth rate parallel with and perpendicular to the columns. (h) shows ribbon-like texture perpendicular to the shear direction, indicating the growth rate along the columns are much lower than the growth rate in the columnar packing plane. The ribbons have uniform width, indicate the columns inside the sample prepared by method 3 have length limit to about 500nm.

Figure 4.22 POM textures of the Colh phase of TEB-BPOSS3 treated by 3 different methods. Method 1: Quench the sample from its melt states to room temperature by liquid nitrogen. Method 2: Thermal anneals the sample at 180 ℃ for 12 hours and cooled to room temperature at a rate of 10℃/min. Method 3: Shear the sample along one direction on the surface of a glass slide and thermal anneal the glass side at 180 ℃ for 12hours. Scale bars inserted to each graph is corresponding to 10 μm standard scale. 121

Phase morphology of the columnar phase of TAB-BPOSS3 is shown in Figure 4.23.

The samples preparation methods are shown under the micrograph. Figure 4.23(a) is taken for sample prepared by heated to the 200℃ (Phase I, Colr) and anneal at 200℃ for 12 hours and cool to room temperature at cooling rate of 10oC/min. The birefringent focal conitropic optical texture under the polarized optical microscope (POM) suggesting the presence of the smectic liquid crystal phases. Quench down instead of normal cooling will not destroy this texture. This type of texture will change into mosaic texture if annealed at 260oC and quench down, indicates the Colr to Colh phase transition.

Figure 4.23 POM textures of Colr phase (a), (b) and Colh phase(c)s of TAB-BPOSS3. (a) Sample was prepared by annealing the sample on glass slide at 200oC(Phase I) for 12 hours and cool down to room temperature at a cooling rate of 10oC/min. (b) Sample was prepared by annealing the sample on glass slide at 200℃ (Phase I) for 12 hours and quench the sample to room temperature by liquid nitrogen. (c) Sample was prepared by annealing the sample on glass slide at 260℃ (Phase II) for 12 hours and quench the sample to room temperature by liquid nitrogen. Scale bars inserted to each graph is corresponding to 10 μm standard scale.

122

4.8 Spherical Phase of TEB-BPOSS6 and TAB-BPOSS6

Figure 4.24 A15 phase formation of TEB-BPOSS6 and TAB-BPOSS6. Cubic A15 packing is indicated by Small angle X-ray scattering pattern of (a) TEB-BPOSS6 and (b) TAB-BPOSS6. Fourier filtrated (FT) and color inversed bright field TEM image of (c) 4 TEB-BPOSS6 and (d) TAB-BPOSS6 revealed a clear view of the 2D 4 tiling along <100> direction. Only square decorated tiles was observed for these Pm3̅n structure.

Changing from the three to six BPOSS cages at the periphery, the self-assembled supramolecular structures are completely different. For annealed TEB-BPOSS6 and

TAB-BPOSS6 samples, both of SAXS patterns shown in Figure 4.24(a) and (b) possess q-ratios of √3: √4: √5 , indicating a 3D Frank-Kasper A15 phase with spherical motifs

(space group Pm3̅n). Those diffraction peaks are indexed as (200) (201) and (121) of this

A15 lattice. No sharp diffractions can be observed in WAXD patterns, revealing that

BPOSS cages are not crystallized (see Figure 4.25). The unit cell parameters can be determined as a = b = c = 5.95 nm, and  =  = γ = 90 for TEB-BPOSS6, and a = b = c =

6.59 nm,  =  = γ = 90 for TAB-BPOSS6, respectively. Other diffractions in the SAXS

123 patterns can also be all indexed as show in Figure 4.24(a) and (b). Again, TEM bright field images taken along the [001] direction show clearly 44 tiling patterns in Figure 4.24(c) and

(d) for both of the samples, further confirming a spherical packed A15 structure. The cartoons drawn on the TEM images are for better understanding.

Hereon, the question is why in TEB-BPOSS3 and TAB-BPOSS3 case, the columnar phases are observed, while in TEB-BPOSS6 and TAB-BPOSS6 case, the spherical packed

F-K A15 cubic phases can form? The most reasonable explanation is that with three

BPOSS cages at the periphery, there is enough space to accommodate the cages, therefore the columns can be maintained via the π-π interaction of the cores. However, with the number of BPOSS cages increasing to six, the cages are crowded enough to generate high steric hindrance at the periphery. The columns resulted from the π-π interaction can no longer to be maintained while tolerating the steric hindrance. They are thus periodically broken down along the column axis as shown in Scheme 4.12.

By measuring the densities of both A15 phases, the densities of these two samples can

3 3 be determined as 1.10 g/cm for TEB-BPOSS6 and 1.08 g/cm for TAB-BPOSS6.

Combining the unit cell information gained from SAXS data, we concluded that there would be 24 molecules in one unit cell of TEB-BPOSS6, and 30 molecules in one unit cell of TAB-BPOSS6. Since there are eight spherical motifs in each lattice cell of the A15 structure, the average numbers of the molecules in each spherical motif are three to four molecules for TEB-BPOSS6, and TAB-BPOSS6. We thus concluded that the π-π interaction of the discotic cores can only be upheld between three to four molecules, the column will then break down periodically to form spherical motifs.

124

4.9 Discussion

Based on the previous results, we may explain why these series of molecules need different methods to afford the ordered packing without crystalline. It probably because the

TEB core is flat, with amide group at the arm, it is very likely to forming H-bonding by slightly rotate the molecules at the disc plane, which further helps long range order packing at the molecular level. On the contrary, the propeller shape of the TAB core will lead to close interdigitating of the molecule; result in limitation of tilting of the molecular plane and restriction of the H-bonding formation than TEB core. What’s more, BPOSS is very likely to form crystal with itself, quenching down very fast will lock the liquid-like order at the temperature before quenching, thus will help avoiding BPOSS crystallization. Only π-π interaction and BPOSS shape effect will influence its molecular packing, above the

BPOSS melting temperature, BPOSS got a lot of mobility so the packing is easy to adjust.

125

Figure 4.25 Non-covalent interactions in the self-assembled structure. WAXD patterns of (a) TAB-BPOSS3 and (b) TAB-BPOSS6. Voigt fitting separate both curve into 2 peaks. (c) In-situ FTIR of TEB-BPOSS3, presenting a clear N-H stretch vibration change during thermotropic phase formation. (d)The intensity ratio of isolated N-H bond to H-Bonded N-H bond changes along with the temperature.

Apart from the steric hindrance, we are interested in what happened to the non-covalent interactions which are supposed to help stabilizing the traditional columnar phase.

The intracolumnar interaction was studied by WAXD and FT-IR. According to the literature, there are π-π interactions in the columnar phase formed by TEB/TAB core. Here, as shown by WAXD characterization in Figure 4.25(a) and (b), Voigt fitting of the 126 scattering curve gives two diffuse halos at about 5Å and 3.8-3.9 Å. The diffuse halo indicates not very ordered structure around this d-spacing range. Broad peak at about 0.5 nm is corresponding to the mean distance of aliphatic chains as pointed out by Levelut, since there’s no long aliphatic chains in our molecule, it may refers to the distance of isobutyl groups on the BPOSS in our system. The other halo with 3.6 - 3.8 Å is the typical d-spacing for π-π stacking of the TEB/TAB core. The Lorentzian width of this fitted peak is relatively broad in TAB-BPOSS6, than in TAB-BPOSS3, suggests the π-π interaction along the columns is stronger than in the spherical motif. It is reasonable because the columns are stacked by more than 6 molecules per column but in the spherical motif just

3-4 molecules cannot produce as much π-π interactions as in the columnar system.

Apart from π-π interactions, hydrogen-bonding may also affect the phase formation.

There are some amide groups in the arm outside of the rigid core, offers possibility for forming H-Bonding. There are intramolecular H-Bonding and intermolecular H-Bonding, here, only intermolecular H-Bonding will be considered. The role of H-bonding in self-assembly can be determined by synthesizing a molecule without amide group but keep the other chemical structures the same. If the H-Bonding doesn’t help the phase formation, the phase will be still formed without amide group. Here H-Bonding percentage in the formed structure were investigated by in-situ FTIR (Full spectrum see Apendix). As shown in Figure 4.25(c), single peak at ~3450cm-1 refers to free N-H stretch and broad band at

~3280cm-1 refers H-Bonded N-H stretch (see evidence from Appendix). After heating up above the phase formation temperature, the disappearance of ~3450cm-1 peak indicates

N-H inside the TEB-BPOSS3 is clearly all H-Bonded. Calculate the intensity ratio between the isolated N-H peaks to H-Bonded N-H peak will give clearly view of the percentage of 127

H-Bonded N-H groups in each phase. From Figure 4.25(d), iso/HB ratio of N-H intensity in the columnar phase is lower than in the spherical phase, but obvious change was observed for TEB-BPOSS3 and TAB-BPOSS6. It indicated that in the spherical phase, there is less H-Bonding percentage of N-H than in the columnar phase. Combining the information obtained above, we can speculate that H-Bonding works with π-π interactions together to stabilize the columnar phase but contributes less to the formation of spherical phase.

4.10 Conclusion

In our work, we introduced BPOSS as the periphery of 1, 3, 5-tri ethynyl benzene

(TEB) core or triazole benzene (TAB) core to enlarge the molecular size and serve as a steric component. By accurately variables-controlled molecular design, BPOSS number was increased from three to six to introduce steric hindrance along the column axis, competing with the non-covalent π-π interactions of discotic cores. We found that if there are three BPOSSs on the periphery, columnar phase would remain because periphery space is enough for enduring the rigid cages. However, tilting of the core perpendicular to the column axis cannot make enough room when the number of BPOSSs was increased to six.

In this case the BPOSSs have to scrub up and down due to the exclusion, which blocks the

π-π interaction along the column and forms a spherical building block, in consequence leads to the formation of supramolecular spheres and futher forming spherical packing structure such as A15 phase.

Not only steric hindrance but also core type will affect the assembled structures.

When the core at the center was change from TEB to TAB, the limitation of tilting of the 128 triazole arms leads to the tilting of the molecular plane, orientational inequivalent leads to ellipse columns, and in sequence gives rectangular 2D columnar packing. The interesting thing is no matter which core type is, six BPOSSs on the periphery will give A15 phase.

That clearly shows steric hindrance is the key factor for the A15 phase formation of this type of discotic molecules. Further investigation was conducted on the intermolecular

H-Bonding and π-π interactions to explain the self-assembly mechanism. Hence, we established a model to achieve A15 phase from discotic molecules base on nano-building blocks, which may offers a strategy for fabricating unconventional phases in the future.

129

CHAPTER V

CONSTRUCTING SPHERICAL MOTIFS WITH PRECISE LENGTH

CONTROL:LINKER LENGTH EFFECT ON THE TAB-CnBPOSS6 A15 STRUCTURE

In last chapter, we demonstrated a modular work to form A15 phase by giant shape amphiphiles with disc-shape core and BPOSS cage periphery. Based on this study, we can easily manufacture A15 phase by controlling of the periphery BPOSS number. In this chapter we manufactured A15 phase with five different sizes controlled by the length of linkers between core and BPOSS peripheries.

5.1 Molecular Design

Base on the study in previous chapter, the columnar phase can be disrupted into spherical motif when the periphery steric hindrance introduced by BPOSS is enhanced.

When there are six BPOSS on the periphery, the columnar motifs will no longer be stable.

Instead of cylindrical structure, spherical motifs will form. Utilizing this strategy as a modular method, we designed five more TAB-CnBPOSS6 molecules with different linker length (n=2, 4, 5, 6, 8) for constructing spherical packed phases. To control the variables, all the chemical structures except the length of alkyl chains were kept the same. The flexible linker length was increased from 3 carbons to 4, 5, 6 and 8. It will introduce more space to accommodate the 6BPOSS cages on the periphery. This change will affect the size 130 of the spherical motif and there may have a limit that linker length beyond that limit will dramatically change the sphericity of the spherical motif and leading to another phase.

Figure 5.1 Molecular design and chemical structures of TAB-CnBPOSS6, n=2, 3, 4, 5, 6, 8 (A)-(F). The POSS cage has been simplified as a red sphere in this figure, all of these giant molecules have 6 BPOSSs on the periphery, and the number of CH2 inside brackets will increase from 2 to 8.

5.2 Synthesis and Characterization

All the giant molecules are prepared by high efficient click reaction in the last step. To prepare the precursors with different linker length, reactions such as corner-capping 131 reaction, hydrosilylation, azidation，Staudinger reduction reactions were used. Since

5-azidoisophthalic acid has been synthesized as described in previous chapter,

BPOSS-Cn-NH2 with different linker lengths react with carboxyl groups on the

5-azidoisophathalic acid to achieve the (BPOSS-Cn) 2-N3, (n=2, 3, 4, 5, 6, 8), and these precursor react with TEB core by CuAAC click reaction to fabricate TAB-CnBPOSS6 with linker length equals to 2, 3,4,5,6 and 8 as shown in Figure 5.2.

132

Figure 5.2 Synthetic route for the preparation of six designed giant shape amphiphiles with different linker length (A)-(F). Reaction conditions: i: Et3N, THF, 0℃, rt, 12h. ii: DMF, THF, NaN3,rt,24h. iii: 1). THF,PPh3,2h 2) H2O, rt, 24h.iv: Toluene, Karstedt o catalyst, 90 C, 24h. v: DCC/HOBt, CH2Cl2, rt, 12h. vi: CuBr / PMDETA, THF, rt, 24h. Reactions in step iv and vi were carried out under an inert atmosphere of N2 with Schlenk techniques. 133

Detailed synthetic procedures are stated as follows. AminopropylIsobutyl POSS

(BPOSS-C3-NH2) and TriSilanolIsobutyl POSS were purchased from Hybrid Plastics.

Trichlorosilane, 2-bromoethyltrichlorosilane, 4-aminobutyltriethoxysilane, 4-amino-3,

3-dimethylbutyltrimethoxysilane, 5-bromopentyltrichlorosilane were purchased from

Gelest, Inc.

Scheme 5.13 Chemical structure of BPOSS-H.

BPOSS-H To a solution of 8.3 g (10.5 mmol) trisilanolisobutyl POSS and 5.1 g Et3N in 70 mL of THF at ice bath, 1.1 mL trichlorosilane were added and the resulting solution is stirred overnight. The mixture was filtrated and the filtrate was collected and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel

1 with CH2Cl2. H NMR (CDCl3, 300MHz, ppm, δ) 4.10(s, 1H, -SiH), 0.96 (m, 42H,

SiCH2CH(CH3)2), 0.67-0.61 (m, 14H, SiCH2CH(CH3)2).

Scheme 5.14 Chemical structure of BPOSS-C2-Br. 134

BPOSS-C2-Br To a solution of 3 g (2.8 mmol) trisilanolisobutyl POSS and 1.27 g

Et3N in 20 mL of THF at ice bath, 1.1 g (4.1 mmol) of 2-bromoethyltrichlorosilane were added and the resulting solution is stirred overnight. The mixture was filtrated and the filtrate was collected and evaporated under reduced pressure. The residue was purified by

1 column chromatography on silica gel with CH2Cl2. H NMR (CDCl3, 300MHz, ppm, δ)

3.54(t, 2H, -CH2CH2Br), 1.86(m, 7H, - SiCH2CH(CH3)2), 0.96 (m, 44H,

-CH2CH2Br+SiCH2CH(CH3)2), 0.67-0.61 (m, 14H, SiCH2CH(CH3)2).

Scheme 5.15 Chemical structure of BPOSS-C4-NH2.

BPOSS-C4-NH2 To a solution of 2 g (2.5 mmol) trisilanolisobutyl POSS in 20 mL of

THF at 25℃, 0.62 g (2.6 mmol) of 4-aminobutyltriethoxysilane were added. After addition

+ - of 0.1 mL Et4N OH (35% solution in water), the resulting solution is stirred overnight. The resulting cloudy solution is mixed with 50 mL MeOH and filtrated. The residue is washed with 20 mL MeOH and product is obtained as white powder. 1H NMR (CDCl3, 300MHz, ppm, δ) 2.68(t, 2H, -CH2CH2NH2), 1.86(m, 9H, -CH2CH2NH2+SiCH2CH(CH3)2), 1.46 (m,

2H, SiCH2CH2CH2CH2NH2), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H,

SiCH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

Scheme 5.16 Chemical structure of BPOSS-C5-Br. 135

BPOSS-C5-Br To a solution of 3.75 g (4.8 mmol) trisilanolisobutyl POSS and 1.60 g

Et3N in 20 mL of THF at ice bath, 1.62 g (5.7 mmol) of 5-bromopentyltrichlorosilane were added and the resulting solution is stirred overnight. The mixture was filtrated and the filtrate was collected and evaporated under reduced pressure. The residue was purified by

1 column chromatography on silica gel with CH2Cl2. H NMR (CDCl3, 300MHz, ppm, δ)

3.39(t, 2H, -CH2CH2NH2), 1.86(m, 9H, -CH2CH2NH2+SiCH2CH(CH3)2), 1.48-1.34 (m,

4H, SiCH2CH2CH2CH2CH2NH2), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H,

SiCH2CH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

Scheme 5.17 Chemical structure of BPOSS-C6-Br.

BPOSS-C6-Br A mixture that consisted of 2.58 g BPOSS-H, 25 mL toluene, 1.03 g

6-bromo-1-hexene was placed in a 50 mL schlenk bottle. After addition of 36 μL Karstedt catalyst under N2 atmosphere, the mixture was heated up to 90℃ and stirred for 24h. Then the solvent was evaporated under reduced pressure and the residue was purified by column

1 chromatography on silica gel with eluate of CH2Cl2: Hexane = 1: 3. H NMR (CDCl3,

300MHz, ppm, δ) 3.41(t, 2H, -CH2CH2Br), 1.86(m, 9H,

SiCH2CH2CH2CH2CH2CH2Br+SiCH2CH(CH3)2), 1.54-1.20 (m, br, 6H,

SiCH2CH2CH2CH2CH2CH2Br), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H,

SiCH2CH2CH2CH2CH2CH2Br + SiCH2CH(CH3)2).

136

Scheme 5.18 Chemical structure of BPOSS-C8-Br.

BPOSS-C8-Br A mixture that consisted of 4.08 g BPOSS-H, 25 mL toluene, 1.91 g

8-bromo-1-octene was placed in a 50 mL schlenk bottle. After addition of 56 μL Karstedt catalyst under N2 atmosphere, the mixture was heated up to 90℃ and stirred for 24h. Then the solvent was evaporated under reduced pressure and the residue was purified by column

1 chromatography on silica gel with eluate of CH2Cl2: Hexane = 1: 3. H NMR (CDCl3,

300MHz, ppm, δ) 3.40(t, 2H, -CH2CH2Br), 1.86(m, 9H,

SiCH2CH2CH2CH2CH2CH2CH2CH2Br +SiCH2CH(CH3)2), 1.54-1.20 (m, br, 10H,

SiCH2CH2CH2CH2CH2CH2CH2CH2Br), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m,

16H, SiCH2CH2CH2CH2CH2CH2CH2CH2Br + SiCH2CH(CH3)2)

Scheme 5.19 General procedure for synthesizing BPOSS-Cn-N3 from BPOSS-Cn-Br.

General procedure for synthesizing BPOSS-Cn-N3 from BPOSS-Cn-Br (n = 2, 5, 6, 8).

To a solution of 2.5 g BPOSS-Cn-Br in 10 mL DMF and 10 mL THF, 1.5 g sodium azide was added and then stirred for 24h under room temperature. Solvent were then evaporated under reduced pressure and the residue was extracted with CH2Cl2/H2O. The organic layer was evaporated and the product was obtained as white powder.

137

Scheme 5.20 Chemical structures of BPOSS-Cn-N3 (n = 2, 5, 6, 8).

1 BPOSS-C2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 3.34(t, 2H, -CH2CH2N3), 1.86(m,

7H, - SiCH2CH(CH3)2), 0.96 (m, 44H, -CH2CH2N3+SiCH2CH(CH3)2), 0.67-0.61 (m, 14H,

SiCH2CH(CH3)2).

1 BPOSS-C5-N3 H NMR (CDCl3, 300MHz, ppm, δ) 3.25(t, 2H, -CH2CH2N3), 1.86(m,

9H, -CH2CH2N3+SiCH2CH(CH3)2), 1.48-1.34 (m, 4H, SiCH2CH2CH2CH2CH2NH2), 0.96

(d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H, SiCH2CH2CH2CH2CH2N3 +

SiCH2CH(CH3)2).

1 BPOSS-C6-N3 H NMR (CDCl3, 300MHz, ppm, δ) 3.25(t, 2H, -CH2CH2N3), 1.86(m,

9H, SiCH2CH2CH2CH2CH2CH2N3+SiCH2CH(CH3)2), 1.54-1.20 (m, br, 6H,

SiCH2CH2CH2CH2CH2CH2N3), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H,

SiCH2CH2CH2CH2CH2CH2N3 + SiCH2CH(CH3)2).

1 BPOSS-C8-N3 H NMR (CDCl3, 300MHz, ppm, δ) 3.26(t, 2H, -CH2CH2N3), 1.86(m,

9H, SiCH2CH2CH2CH2CH2CH2CH2CH2N3+SiCH2CH(CH3)2), 1.54-1.20 (br, 10H,

SiCH2CH2CH2CH2CH2CH2CH2CH2N3), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m,

16H, SiCH2CH2CH2CH2CH2CH2CH2CH2N3 + SiCH2CH(CH3)2).

138

Scheme 5.21 General procedure for synthesizing BPOSS-Cn-NH2 from BPOSS-Cn-N3 (n = 2, 5, 6, 8).

General procedure for synthesizing BPOSS-Cn-NH2 from BPOSS-Cn-N3 (n = 2, 5, 6,

8). To a solution of 2.5 g BPOSS-Cn-N3 in 20 mL THF, 3 g triphenylphosphine was added.

After 2h stirring, 1 mL H2O was added and the mixture was stirred for another 24h under room temperature. Solvent were then evaporated under reduced pressure and the residue was extracted with MeOH/Hexane. The hexane layer was collected and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel with eluate of CH2Cl2: MeOH = 10: 1.

Scheme 5.22 Chemical structures of BPOSS-Cn-NH2 (n = 2, 5, 6, 8).

1 BPOSS-C2-NH2 H NMR (CDCl3, 300MHz, ppm, δ) 2.85(t, 2H, -CH2CH2NH2),

1.86(m, 7H, - SiCH2CH(CH3)2), 0.96 (m, 44H, -CH2CH2NH2+SiCH2CH(CH3)2),

0.67-0.61 (m, 14H, SiCH2CH(CH3)2).

1 BPOSS-C5-NH2 H NMR (CDCl3, 300MHz, ppm, δ) 2.68(t, 2H, -CH2CH2NH2),

1.86(m, 9H, -CH2CH2NH2+SiCH2CH(CH3)2), 1.48-1.34 (m, 4H, SiCH2CH2CH2CH2CH2

139

NH2), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H, SiCH2CH2CH2CH2CH2NH2 +

SiCH2CH(CH3)2).

1 BPOSS-C6-NH2 H NMR (CDCl3, 300MHz, ppm, δ) 2.68(t, 2H, -CH2CH2NH2),

1.86(m, 9H, SiCH2CH2CH2CH2CH2CH2NH2+SiCH2CH(CH3)2), 1.54-1.20 (m, br, 6H,

SiCH2CH2CH2CH2CH2CH2NH2), 0.96 (d, 42H, SiCH2CH(CH3)2), 0.67-0.61 (m, 16H,

SiCH2CH2CH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

1 BPOSS-C8-NH2 H NMR (CDCl3, 300MHz, ppm, δ) 2.69(t, 2H, -CH2CH2NH2),

1.86(m, 9H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2+SiCH2CH(CH3)2), 1.54-1.20 (br,

10H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2), 0.96 (d, 42H, SiCH2CH(CH3)2),

0.67-0.61 (m, 16H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

Scheme 5.23 General procedure for synthesizing (BPOSS-Cn) 2-N3 (n = 2, 3, 4, 5, 6, 8) by amidation reaction.

General procedure for synthesizing (BPOSS-Cn) 2-N3 (n = 2, 3, 4, 5, 6, 8) by amidation reaction. To a mixture of 5-azidoisophthalic acid (1 eq), BPOSS-Cn-NH2 (2.2 eq), HOBt (2.4 eq) in anhydrous CH2Cl2, DCC (2.4 eq) in CH2Cl2 was added dropwise at

0℃. The resulting solution was then stirred at room temperature for 12 h. The precipitate was filtered and the filtrate was washed with water and dried by anhydrous Na2SO4. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of CH2Cl2: EA = 40: 1.

140

Scheme 5.24 Chemical structure of (BPOSS-Cn) 2-N3 (n = 2, 3, 4, 5, 6, 8).

1 (BPOSS-C2)2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 7.88(s, 1H,

NHCO-AroH-NHCO),7.53(s, 2H, NHCO-AroH-N3), 6.22 (t, 2H, CH2CH2NHCO), 3.56 (q,

4H, SiCH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CHC2H6), 0.96 (d, 84H, SiCH2CH(CH3)2),

0.68-0.61 (m, 32H, SiCH2CH2NHCO + SiCH2CH(CH3)2).

1 (BPOSS-C3)2-N3 H NMR (500 MHz, CDCl3, ppm, δ): 7.86(s, 1H,

NHCO-AroH-NHCO),7.53(s, 2H, NHCO-AroH-N3), 6.19 (t, 2H, CH2CH2NHCO), 3.45 (q,

4H, SiCH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CHC2H6), 1.72 (m, 4H,

SiCH2CH2CH2NHCO), 0.96 (d, 84H, SiCH2CH(CH3)2), 0.68-0.61 (m, 32H,

SiCH2CH2CH2NHCO + SiCH2CH(CH3)2). GPC: Molecular Weight Calc. for

C70H143N5O26Si16: 1920. Found: 2059 (Mn).

1 (BPOSS-C4)2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 7.86(s, 1H,

NHCO-AroH-NHCO),7.53(s, 2H, NHCO-AroH-N3), 6.10 (t, 2H, CH2CH2NHCO), 3.45 (q,

4H, SiCH2CH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CH(CH3)2), 1.67(m, 8H,

SiCH2CH2CH2CH2NH2), 0.96 (d, 84H, SiCH2CH(CH3)2), 0.67-0.61 (m, 32H,

SiCH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

1 (BPOSS-C5)2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 7.86(s, 1H,

NHCO-AroH-NHCO), 7.54(s, 2H, NHCO-AroH-N3), 6.18 (t, 2H, CH2CH2NHCO), 3.45

(q, 4H, SiCH2CH2CH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CH(CH3)2), 1.67-1.51 (m, br,

141

12H, SiCH2CH2CH2CH2CH2NHCO), 0.96 (d, 84H, SiCH2CH(CH3)2), 0.68-0.61 (m, 32H,

SiCH2CH2CH2CH2CH2NHCO + SiCH2CH(CH3)2).

1 (BPOSS-C6)2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 7.86(s, 1H,

NHCO-AroH-NHCO),7.53(s, 2H, NHCO-AroH-N3), 6.16 (t, 2H, CH2CH2NHCO), 3.45 (q,

4H, SiCH2CH2CH2CH2CH2CH2NHCO), 1.86(m, 14H, SiCH2CH(CH3)2), 1.60-1.38 (m, br,

16H, SiCH2CH2CH2CH2CH2CH2NH2), 0.96 (d, 84H, SiCH2CH(CH3)2), 0.67-0.61 (m,

32H, SiCH2CH2CH2CH2CH2CH2NH2 + SiCH2CH(CH3)2).

1 (BPOSS-C8)2-N3 H NMR (CDCl3, 300MHz, ppm, δ) 7.86(s, 1H,

NHCO-AroH-NHCO), 7.86(s, 1H, NHCO-AroH-NHCO),7.53(s, 2H, NHCO-AroH-N3),

6.16 (t, 2H, CH2CH2NHCO), 3.45 (q, 4H, SiCH2CH2CH2NHCO), 1.86(m, 14H,

SiCH2CH(CH3)2), 1.60-1.38 (m, br, 24H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2), 0.96

(d, 84H, SiCH2CH(CH3)2), 0.67-0.61 (m, 32H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2 +

SiCH2CH(CH3)2).

Scheme 25.13 General procedure for synthesizing TAB-CnBPOSS6 (n = 2, 3, 4, 5, 6, 8) by copper (I)-catalyzed alkyne-azide cycloaddition (CuAAC) “click” reaction.

General procedure for synthesizing TAB-CnBPOSS6 (n = 2, 3, 4, 5, 6, 8) by copper

(I)-catalyzed alkyne-azide cycloaddition (CuAAC) “click” reaction. CuAAC click was used to synthesize the TAB-derivatives. Oxygen free operation was required. A mixture of

142

1, 3, 5-tri triazole benzene (1eq), (BPOSS-Cn) 2-N3 (3.5eq), CuBr (0.1eq) was added into

15ml THF. The solution was sealed in a Schlenk flask and does freeze-pump-thaw for 3 times before adding PMDETA (0.04eq) under N2 protection. Seal the Schlenk flask and do freeze-pump-thaw for one more time. The mixture was stirred under room temperature for

24 hours. The precipitate was filtered by running a fast silica column with eluate of THF to remove the Cu salt. After removal of solvent under reduced pressure, the residue was purified by column chromatography on silica gel with eluate of Hexane: EA = 3:1-7:1.

Further purification of running a Bio-Beass S-X Resin column generates a transparent thin film. Precipitating the product with THF/MeOH gives white solid. Yield is 71%.

Scheme 26 Chemical structure of TAB-Cn-BPOSS6..

1 TAB-C2BPOSS6 (A). H NMR (500 MHz, CDCl3, ppm, δ): 8.66(s, 3H, H-Ar),

8.51(s, 6H, NHCO-AroH-N3), 8.48(s, 3H, N-CH=C), 8.33(s, 31H, NHCO-AroH-NHCO),

6.56 (t, 6H, CH2CH2NHCO), 3.63 (q, 12H, SiCH2CH2CH2NHCO), 1.86(m, 424H,

SiCH2CHC2H6), 0.96 (d, 264H, SiCH2CH2NHCO+SiCH2CH(CH3)2), 0.68-0.61 (m, 84H,

SiCH2CH(CH3)2). MS (MALDI-TOF, m/z): Calc. for C222H435N15O78Si48: 5847.84. Found:

5851.82 (M+Na) +.

143

TAB-C3BPOSS6 (B). This molecule has been synthesized according to the procedure described in Chapter VI.

1 TAB-C4BPOSS6 (C). H NMR (500 MHz, CDCl3, ppm, δ): 8.62(s, 3H, H-Ar), 8.52(s,

3H, N-CH=C) ,8.44(s, 6H, NHCO-AroH-N3), 8.29(s, 3H, NHCO-AroH-NHCO), 6.46 (t,

6H, CH2CH2NHCO), 3.52 (q, 12H, SiCH2CH2CH2CH2NHCO), 1.86(m, 42H,

SiCH2CH(CH3)2), 1.75(m, 24H, SiCH2CH2CH2CH2NH2), 0.96 (d, 252H,

SiCH2CH(CH3)2), 0.67-0.61 (m, 96H, SiCH2CH2CH2CH2NH2 + SiCH2CH(CH3)2). MS

+ (MALDI-TOF, m/z): Calc. for C222H435N15O78Si48: 6016.03. Found: 6019.19 (M+Na) .

1 1 TAB-C5BPOSS6 (D). H NMR (500 MHz, CDCl3, ppm, δ): H NMR (CDCl3,

300MHz, ppm, δ) 8.48(s, 3H, H-Ar),8.36(s, 6H, NHCO-AroH-N3), 8.35(s, 3H, N-CH=C),

8.23(s, 3H, NHCO-AroH-NHCO), 6.78 (t, 6H, CH2CH2NHCO), 3.54 (q, 12H,

SiCH2CH2CH2CH2CH2NHCO), 1.86(m, 42H, SiCH2CH(CH3)2), 1.70-1.48 (m, m，36H,

SiCH2CH2CH2CH2CH2NHCO), 0.96 (d, 252H, SiCH2CH(CH3)2), 0.68-0.61 (m, 96H,

SiCH2CH2CH2CH2CH2NHCO + SiCH2CH(CH3)2). MS (MALDI-TOF, m/z): Calc. for

+ C222H435N15O78Si48: 6100.13. Found: 6105.06 (M+Na) .

1 TAB-C6BPOSS6 (E). H NMR (500 MHz, CDCl3, ppm, δ): 8.41-8.30(s, 12H, H-Ar,

NHCO-AroH-N3, N-CH=C), 8.30(s, 3H, NHCO-AroH-NHCO), 7.02 (t, 6H,

CH2CH2NHCO), 3.52 (q, 12H, SiCH2CH2CH2CH2CH2CH2NHCO), 1.86(m, 42H,

SiCH2CH(CH3)2), 1.72-1.43 (m, br, 48H, SiCH2CH2CH2CH2CH2CH2NH2), 0.96 (d, 252H,

SiCH2CH(CH3)2), 0.67-0.61 (m, 96H, SiCH2CH2CH2CH2CH2CH2NH2 +

SiCH2CH(CH3)2). MS (MALDI-TOF, m/z): Calc. for C222H435N15O78Si48: 6184.22. Found:

6187.40 (M+Na) +.

144

1 TAB-C8BPOSS6 (F). H NMR (500 MHz, CDCl3, ppm, δ): 8.45-8.33(s, 12H, H-Ar,

NHCO-AroH-N3, N-CH=C), 8.21(s, 3H, NHCO-AroH-NHCO), 6.72 (t, 6H,

CH2CH2NHCO), 3.54 (q, 12H, SiCH2CH2CH2NHCO), 1.86(m, 42H, SiCH2CH(CH3)2),

1.73-1.38 (m, br, 72H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2), 0.96 (d, 252H,

SiCH2CH(CH3)2), 0.67-0.61 (m, 96H, SiCH2CH2CH2CH2CH2CH2CH2CH2NH2 +

SiCH2CH(CH3)2). MS (MALDI-TOF, m/z): Calc. for C222H435N15O78Si48: 6352.41. Found:

6356.38 (M+Na) +.

While n=3, TAB-C3BPOSS6 has been fully characterized in last chapter, here,

1HNMR and 13CNMR spectrum were used to confirm the chemical structure of the other giant molecules TAB-CnBPOSS6，n=2, 4,5,6,8 as follows.

145

1 13 Figure 5.3 H NMR and C NMR spectrum of TAB-C2BPOSS6 (A). For clear demonstration, only one arm on the trisubstituted benzene core has been draw, the other two arms are simplified by two wavy lines

146

1 13 Figure 5.4 HNMR and CNMR spectrum of TAB-C4BPOSS6 (C). For clear demonstration, only one arm on the trisubstituted benzene core has been draw, the other two arms are simplified by two wavy lines

147

1 13 Figure 5.5 HNMR and CNMR spectrum of TAB-C5BPOSS6 (D). For clear demonstration, only one arm on the trisubstituted benzene core has been draw, the other two arms are simplified by two wavy lines.

148

1 13 Figure 5.6 HNMR and CNMR spectrum of TAB-C6BPOSS6 (E). For clear demonstration, only one arm on the trisubstituted benzene core has been draw, the other two arms are simplified by two wavy lines

149

1 13 Figure 5.7 HNMR and CNMR spectrum of TAB-C8BPOSS6 (F). For clear demonstration, only one arm on the trisubstituted benzene core has been draw, the other two arms are simplified by two wavy lines.

From NMR characterization, every peak can be assigned to the molecular structure, indicating the chemical structures of these TAB-CnBPOSS6 giant molecules are correct. In order to verify the sample mass and purity of these four giant molecules, matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and gel permeation chromatography (GPC) were also used to help characterizing the final product.

150

Figure 5.8 MALDI-ToF spectra of TAB-C2BPOSS6, TAB-C3BPOSS6, TAB-C4BPOSS6, TAB-C5BPOSS6, TAB-C6BPOSS6 and TAB-C8BPOSS6. All the samples show a single peak with same observation mass as calculated mass, proves the successful synthesis of these molecules.

151

Figure 5.9 GPC characterization of TAB-C2BPOSS6, TAB-C3BPOSS6, TAB-C4BPOSS6, TAB-C5BPOSS6, TAB-C6BPOSS6 and TAB-C8BPOSS6 proves the neat synthesis of giant molecules at volume exclusive level. Elution solvent is THF. Calculated Mn =4522(n=2), 5070(n=3), 5447(n=4), 5567(n=5), 5850(n=6), 6232(n=8).

5.3 Self-assembled structures of n=3-8 determined by SAXS and TEM

TAB-C3BPOSS6 was proven having an A15 phase with unit cell parameter a determined as 6.59nm in last chapter. Here, after successfully synthesis of TAB-CnBPOSS6 with n=4, 5, 6, 8 these samples were prepared for X-ray structure determination by thermally annealed at 180℃ for overnight. Sample for TEM thin slices was prepared by drop casting 0.75 mg/ml TAB-CnBPOSS6 solution directly on the carbon coated copper grid and thermally annealed at 180℃ for overnight.

152

The Small Angle X-ray Scattering pattern for TAB-CnBPOSS6, (n=4, 5, 6, 8) all presenting three strong peaks with same scattering vector ratio √3: √4: √5 , which is the characteristic ratio for F-K A15 phase (Pm3̅n cubic packing). Those peaks can be indexed as (200) (201) and (121) of the A15 lattice. All these samples forming A15 phase, the only difference is the lattice parameter.

(a)

(b)

Figure 5.10 A15 phases of TAB-CnBPOSS6. n=4, 5, 6, 8. (a). SAXS pattern of TAB-C4BPOSS6, TAB-C5BPOSS6, TAB-C6BPOSS6, TAB-C8BPOSS6 thermal annealed samples. (b). TEM bright field images (Obtained by Fourier filtration). 153

The d-spacing of first peak was used to calculate the lattice parameter. It is the d-spacing of (200) plane so a=2d1. The unit cell parameter was determined as 6.58nm,

6.82nm, 7.52nm and 7.72nm for TAB-CnBPOSS6, n= 4, 5, 6, 8 respectively as shown in

Figure 5.11. TEM bright field images along the [001] direction show clearly 44 tiling patterns for n=4, 6, 8 in Figure 5.10 (b), proves the A15 packing symmetry.

Figure 5.11 Summary for the sizes of the A15 phase of TAB-CnBPOSS6 changing with their linker length.

For better understanding the molecular packing in each sphere of A15 phase, the density should be measure to calculate how many molecules per spherical motif. For more detailed comparison for the A15 phase for each molecule, in-situ SAXS pattern for each giant shape amphiphile were listed here in Figure 5.12 to Figure 5.16.

154

Figure 5.12 In-situ SAXS of TAB-C3BPOSS6 upon heating up.

The order is appeared at 150 ℃ and will disappear at 240 ℃. The red line marks the temperature gap that above this gap will lead to the decreasing of d-spacing. The black arrow with dash line shows the trend of the first peak of A15 phase with the change of temperature.

The q value and d-spacing of the first peak in SAXS pattern has been marked as q1 and d1 for each temperature, their values has also been given in Figure 5.12. The d1 increases while heating up from room temperature. The lattice parameter varies from 6.72 nm to 6.84 nm while temperature changing. While T>195oC, further increasing the temperature will result in decreasing of d-spacing of the first peak in SAXS pattern. Considering the order will disappear at 240℃, the decreasing may due to the loss of order.

155

Figure 5.13 In-situ SAXS of TAB-C4BPOSS6 upon heating up.

The order is appeared at 130 ℃ and will disappear at 280 ℃. The red line marks the temperature gap that above this gap will lead to the decreasing of d-spacing. The black arrow with dash line shows the trend of the peak value of (200) plane with the change of temperature.

The values of q and d-spacing of the first peak in SAXS pattern have been given in

Figure 5.13. The lattice parameter varies from 6.74 nm to 6.88 nm while temperature changing. While T>190℃, further increasing the temperature will result in decreasing of d-spacing of the first peak in SAXS pattern. The decreasing may due to the loss of order or the formation of new phase.

156

Figure 5.14 In-situ SAXS of TAB-C5BPOSS6 upon heating up.

The order is appeared at 120 ℃ and will disappear at 280 ℃. The red line marks the temperature gap that above this gap will lead to the decreasing of d-spacing. The black arrow with dash line shows the trend of the first peak of A15 phase with the change of temperature.

The d-spacing of the first peak in SAXS pattern d1 increases while heating up from room temperature. The lattice parameter varies from 7nm to 7.34nm while temperature changing. While T>180℃, further increasing the temperature will result in decreasing of d-spacing of the first peak in SAXS pattern. The decreasing may due to the loss of order or the formation of new phase.

157

Figure 5.15 In-situ SAXS of TAB-C6BPOSS6 upon heating up.

The order is appeared at 120℃ and will disappear at 280℃. The red line marks the temperature gap that above this gap will lead to the decreasing of d-spacing. The black arrow with dash line shows the trend of the first peak of A15 phase with the change of temperature.

The d-spacing of the first peak in SAXS pattern increases while heating up from room temperature. The lattice parameter varies from 7.34nm to 7.46nm while temperature changing. While T>170℃, further increasing the temperature will result in decreasing of d-spacing of the first peak in SAXS pattern. The decreasing may due to the loss of order or the formation of new phase.

158

Figure 5.16 In-situ SAXS of TAB-C8BPOSS6 upon heating up.

The order is appeared at 150 ℃and will disappear at 280 ℃. The black arrow with dash line shows the trend of the first peak of A15 phase with the change of temperature.

The lattice parameter varies from 7.72nm to 7.86nm while temperature changing.

Comparing to other molecules in this system, contrary to n=4 molecule, the d1 will continually decreasing from the A15 was formed at 150℃ until order was lost.

By the studies above, there are some differences in A15 phase formed by each

TAB-BPOSS6 with different linker length. Firstly, the temperature that start to form the phase varies, A15 phase formed at about 150℃ for n=3, 8, 130oC for n=4 and 120oC for 5,

6. The highest temperature that the A15 phase can keep also varies, for n=3, the A15 phase can only be stable under 240℃, while the temperature increased to 280oC while increasing

159 the linker length from 3 to 4, 5, 6 or 8. Thus, the TAB-C3BPOSS6 have the smallest interval of temperature that can form A15 phase while TAB-C5BPOSS6 or TAB-C6BPOSS6 having the largest. Most of the samples (n=3, 4, 5, 6) will have a temperature gap that above the gap temperature, d-spacing will not increase with the temperature. It may indicate the formation of new phase or just caused by the loss of order. Sample with longer time thermal annealing above the gap temperature gave less ordered SAXS pattern, suggests the decreasing of the d-spacing is due to the loss of order, at a very slow rate. The starting of the order loss begins at 195 ℃, 190℃, 180 ℃, 175 ℃, and 150 ℃ for n=3, 5, 6, and 8 respectively, indicating the A15 phase becomes much less stabled during the increasing of linker length. Further increasing the linker length will much likely to form another phase.

5.4 Conclusion

In conclusion, based on the modular mechanism we proposed in chapter 4, we established a molecular library that each molecule possessing the A15 phase with precise nanoscale sizes, offers more insight of the F-K A15 phase.

160

SUMMARY

In this dissertation, we reported four specifically designed shape amphiphiles constructed by two different cores via isobutyl polyhedral oligomeric silsesquioxane

(BPOSS) cages at the periphery of the molecule in chapter four. We found the columnar phase can be easily disrupted into spherical packing while increasing the periphery steric hindrance introduced by BPOSSs. When there are six BPOSS on the periphery, the columnar motifs will no longer be stable, instead spherical motifs of A15 phase formed.

Steric hindrance is the key factor for the A15 phase formation of this type of discotic molecules. Our work established a model to achieve A15 phase from discotic molecules and offers a strategy for fabricating unconventional phases in the future.

Base on the study in chapter four, we designed five more giant shape amphiphiles with different linker length and six BPOSSs on their periphery for constructing spherical phase. To control the variables, all the other chemical structures are kept the same including the existence of amide groups. The increased flexible linker length will introduce more space to accommodate the six BPOSS cages on the periphery. This change will affect the size of the spherical motif. Based on our work, we established a molecular library that each molecule possessing the A15 phase with precise nanoscale sizes, offers more insight of the F-K A15 phase.

161

In the future, much longer linker will be investigated to find the limit of A15 phase and open a window to another phase. The BPOSS number should be changed to four or five to study the steric hindrance effect more roughly and gradually. In addition, other types of core will also be tried, considering the H-Bonding may cooperate with π-π interaction, the amide group should be removed to see the role of H-Bonding in formation of spherical phase in the following work.

162

REFERENCES

1. Zhang, S., Building from the bottom up. Materials Today 2003, 6 (5), 20-27.

2. Wikipedia contributors. (2018, February 21).Materials science. In Wikipedia, The Free Encyclopedia. Retrieved 20:08, March 7, 2018, from https://en.wikipedia.org/w/index.php?title=Materials_science&oldid=826944814. Wikipedia, The Free Encyclopedia 2018.

3. de Gennes, P.-G., Soft Matter (Nobel Lecture). Angewandte Chemie International Edition in English 1992, 31 (7), 842-845.

4. Cheng, S. Z. D., Design and engineering of polymer/macromolecular structures on the 2–100 nm length scale: A personal view on structural research. Journal of Polymer Science Part B: Polymer Physics 2005, 43 (23), 3361-3364.

5. Wikipedia contributors. DNA. Retrieved from https://en.wikipedia.org/wiki/DNA#/media/File:DNA_orbit_animated_static_thumb.png.

6. Feng, H.; Lu, X.; Wang, W.; Kang, N.-G.; Mays, W. J., Block Copolymers: Synthesis, Self-Assembly, and Applications. Polymers 2017, 9 (10).

7. Zhang, W.-B.; Yu, X.; Wang, C.-L.; Sun, H.-J.; Hsieh, I. F.; Li, Y.; Dong, X.-H.; Yue, K.; Van Horn, R.; Cheng, S. Z. D., Molecular Nanoparticles Are Unique Elements for Macromolecular Science: From “Nanoatoms” to Giant Molecules. Macromolecules 2014, 47 (4), 1221-1239.

8. Hirsch, A.; Brettreich, M., Parent Fullerenes. In Fullerenes, Wiley-VCH Verlag GmbH & Co. KGaA: 2005; pp 1-48.

9. Maggini, M.; Scorrano, G.; Prato, M., Addition of azomethine ylides to C60: synthesis, characterization, and functionalization of fullerene pyrrolidines. Journal of the American Chemical Society 1993, 115 (21), 9798-9799.

10. Camps, X.; Hirsch, A., Efficient cyclopropanation of C60 starting from malonates. Journal of the Chemical Society, Perkin Transactions 1 1997, (11), 1595-1596.

163

11. Prato, M.; Li, Q. C.; Wudl, F.; Lucchini, V., Addition of azides to fullerene C60: synthesis of azafulleroids. Journal of the American Chemical Society 1993, 115 (3), 1148-1150.

12. Han, A.; Bai, J.; Murata, Y.; Komatsu, K., Synthesis and characterization of the fullerene–terthiophene dyads. Heteroatom Chemistry 2011, 22 (1), 72-78.

13. J. Feher, F.; D. Wyndham, K.; K. Baldwin, R.; Soulivong, D.; W. Ziller, J.; D. Lichtenhan, J.; D. Lichtenhan, J., Methods for effecting monofunctionalization of (CH2[double bond, length half m-dash]CH)8Si8O12. Chemical Communications 1999, (14), 1289-1290.

14. Abdelrahman, O. A.; Park, D. S.; Vinter, K. P.; Spanjers, C. S.; Ren, L.; Cho, H. J.; Zhang, K.; Fan, W.; Tsapatsis, M.; Dauenhauer, P. J., Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran. ACS Catal. 2017, 7, 1428.

15. Yu, X.; Zhong, S.; Li, X.; Tu, Y.; Yang, S.; Van Horn, R. M.; Ni, C.; Pochan, D. J.; Quirk, R. P.; Wesdemiotis, C.; Zhang, W.-B.; Cheng, S. Z. D., A Giant Surfactant of Polystyrene−(Carboxylic Acid-Functionalized Polyhedral Oligomeric Silsesquioxane) Amphiphile with Highly Stretched Polystyrene Tails in Micellar Assemblies. Journal of the American Chemical Society 2010, 132 (47), 16741-16744.

16. Yue, K.; Liu, C.; Guo, K.; Wu, K.; Dong, X.-H.; Liu, H.; Huang, M.; Wesdemiotis, C.; Cheng, S. Z. D.; Zhang, W.-B., Exploring shape amphiphiles beyond giant surfactants: molecular design and click synthesis. Polymer Chemistry 2013, 4 (4), 1056-1067.

17. Wang, Z.; Li, Y.; Dong, X.-H.; Yu, X.; Guo, K.; Su, H.; Yue, K.; Wesdemiotis, C.; Cheng, S. Z. D.; Zhang, W.-B., Giant gemini surfactants based on polystyrene-hydrophilic polyhedral oligomeric silsesquioxane shape amphiphiles: sequential "click" chemistry and solution self-assembly. Chemical Science 2013, 4 (3), 1345-1352.

18. Yu, X.; Yue, K.; Hsieh, I. F.; Li, Y.; Dong, X.-H.; Liu, C.; Xin, Y.; Wang, H.-F.; Shi, A.-C.; Newkome, G. R.; Ho, R.-M.; Chen, E.-Q.; Zhang, W.-B.; Cheng, S. Z. D., Giant surfactants provide a versatile platform for sub-10-nm nanostructure engineering. Proceedings of the National Academy of Sciences 2013, 110 (25), 10078.

19. Dahl, J. E.; Liu, S. G.; Carlson, R. M. K., Isolation and Structure of Higher Diamondoids, Nanometer-Sized Diamond Molecules. Science 2003, 299 (5603), 96.

20. Dössel, L.; Gherghel, L.; Feng, X.; Müllen, K., Graphene Nanoribbons by Chemists: Nanometer-Sized, Soluble, and Defect-Free. Angewandte Chemie International Edition 2011, 50 (11), 2540-2543.

164

21. Claridge, S. A.; Castleman, A. W.; Khanna, S. N.; Murray, C. B.; Sen, A.; Weiss, P. S., Cluster-Assembled Materials. ACS Nano 2009, 3 (2), 244-255.

22. Damasceno, P. F.; Engel, M.; Glotzer, S. C., Predictive Self-Assembly of Polyhedra into Complex Structures. Science 2012, 337 (6093), 453.

23. Shevchenko, E. V.; Talapin, D. V.; Murray, C. B.; O'Brien, S., Structural Characterization of Self-Assembled Multifunctional Binary Nanoparticle Superlattices. Journal of the American Chemical Society 2006, 128 (11), 3620-3637.

24. Damasceno, P. F.; Engel, M.; Glotzer, S. C., Crystalline Assemblies and Densest Packings of a Family of Truncated Tetrahedra and the Role of Directional Entropic Forces. ACS Nano 2012, 6 (1), 609-614.

25. Takashi, N., Hierarchically organized soft-materials based on fullerenes. Journal of Physics: Conference Series 2009, 159 (1), 012005.

26. Zhou, S.; Burger, C.; Chu, B.; Sawamura, M.; Nagahama, N.; Toganoh, M.; Hackler, U. E.; Isobe, H.; Nakamura, E., Spherical Bilayer Vesicles of Fullerene-Based Surfactants in Water: A Laser Light Scattering Study. Science 2001, 291 (5510), 1944.

27. Sun, H.-J.; Tu, Y.; Wang, C.-L.; Van Horn, R. M.; Tsai, C.-C.; Graham, M. J.; Sun, B.; Lotz, B.; Zhang, W.-B.; Cheng, S. Z. D., Hierarchical structure and polymorphism of a sphere-cubic shape amphiphile based on a polyhedral oligomeric silsesquioxane-[60]fullerene conjugate. Journal of Materials Chemistry 2011, 21 (37), 14240-14247.

28. Li, Y.; Zhang, W.-B.; Hsieh, I. F.; Zhang, G.; Cao, Y.; Li, X.; Wesdemiotis, C.; Lotz, B.; Xiong, H.; Cheng, S. Z. D., Breaking Symmetry toward Nonspherical Janus Particles Based on Polyhedral Oligomeric Silsesquioxanes: Molecular Design, “Click” Synthesis, and Hierarchical Structure. Journal of the American Chemical Society 2011, 133 (28), 10712-10715.

29. Li, Y. Giant Molecular Shape Amphiphiles Based on Polyhedral Oligomeric Silsesquioxanes: Molecular Design, "Click" Synthesis and Self-Assembly. University of Akron, 2013.

30. Coronado, E.; Gómez-García, C. J., Polyoxometalate-Based Molecular Materials. Chemical Reviews 1998, 98 (1), 273-296.

31. Date, R. W.; Bruce, D. W., Shape Amphiphiles: Mixing Rods and Disks in Liquid Crystals. Journal of the American Chemical Society 2003, 125 (30), 9012-9013.

32. Glotzer, S. C., Some Assembly Required. Science 2004, 306 (5695), 419.

165

33. Park, S.; Lim, J.-H.; Chung, S.-W.; Mirkin, C. A., Self-Assembly of Mesoscopic Metal-Polymer Amphiphiles. Science 2004, 303 (5656), 348.

34. Wen, J.; Yuan, L.; Yang, Y.; Liu, L.; Zhao, H., Self-Assembly of Monotethered Single-Chain Nanoparticle Shape Amphiphiles. ACS Macro Letters 2013, 2 (2), 100-106.

35. Zhang, W.-B.; Li, Y.; Li, X.; Dong, X.; Yu, X.; Wang, C.-L.; Wesdemiotis, C.; Quirk, R. P.; Cheng, S. Z. D., Synthesis of Shape Amphiphiles Based on Functional Polyhedral Oligomeric Silsesquioxane End-Capped Poly(l-Lactide) with Diverse Head Surface Chemistry. Macromolecules 2011, 44 (8), 2589-2596.

36. Horsch, M. A.; Zhang, Z.; Glotzer, S. C., Self-Assembly of Laterally-Tethered Nanorods. Nano Letters 2006, 6 (11), 2406-2413.

37. Iacovella, C. R.; Glotzer, S. C., Complex Crystal Structures Formed by the Self-Assembly of Ditethered Nanospheres. Nano Letters 2009, 9 (3), 1206-1211.

38. Horsch, M. A.; Zhang, Z.; Glotzer, S. C., Self-Assembly of Polymer-Tethered Nanorods. Physical Review Letters 2005, 95 (5), 056105.

39. Wang, C.-L.; Zhang, W.-B.; Hsu, C.-H.; Sun, H.-J.; Van Horn, R. M.; Tu, Y.; Anokhin, D. V.; Ivanov, D. A.; Cheng, S. Z. D., A supramolecular structure with an alternating arrangement of donors and acceptors constructed by a trans-di-C60-substituted Zn porphyrin derivative in the solid state. Soft Matter 2011, 7 (13), 6135-6143.

40. Wang, C.-L.; Zhang, W.-B.; Sun, H.-J.; Van Horn, R. M.; Kulkarni, R. R.; Tsai, C.-C.; Hsu, C.-S.; Lotz, B.; Gong, X.; Cheng, S. Z. D., A Supramolecular “Double-Cable” Structure with a 12944 Helix in a Columnar Porphyrin-C60 Dyad and its Application in Polymer Solar Cells. Advanced Energy Materials 2012, 2 (11), 1375-1382.

41. Wang, C.-L.; Zhang, W.-B.; Van Horn, R. M.; Tu, Y.; Gong, X.; Cheng, S. Z. D.; Sun, Y.; Tong, M.; Seo, J.; Hsu, B. B. Y.; Heeger, A. J., A Porphyrin–Fullerene Dyad with a Supramolecular “Double-Cable” Structure as a Novel Electron Acceptor for Bulk Heterojunction Polymer Solar Cells. Advanced Materials 2011, 23 (26), 2951-2956.

42. Cui, L.; Collet, J. P.; Xu, G.; Zhu, L., Supramolecular Self-Assembly in a Disk-Cube Dyad Molecule Based on Triphenylene and Polyhedral Oligomeric Silsesquioxane (POSS). Chemistry of Materials 2006, 18 (15), 3503-3512.

43. Baffreau, J.; Ordronneau, L.; Leroy-Lhez, S.; Hudhomme, P., Synthesis of Perylene-3,4-mono(dicarboximide)−Fullerene C60 Dyads as New Light-Harvesting Systems. The Journal of Organic Chemistry 2008, 73 (16), 6142-6147.

166

44. Ren, X.; Sun, B.; Tsai, C.-C.; Tu, Y.; Leng, S.; Li, K.; Kang, Z.; Horn, R. M. V.; Li, X.; Zhu, M.; Wesdemiotis, C.; Zhang, W.-B.; Cheng, S. Z. D., Synthesis, Self-assembly, and Crystal Structure of a Shape-Persistent Polyhedral-Oligosilsesquioxane-Nanoparticle-Tethered Perylene Diimide. The Journal of Physical Chemistry B 2010, 114 (14), 4802-4810.

45. Araki, H.; Naka, K., Syntheses and properties of dumbbell-shaped POSS derivatives linked by luminescent π-conjugated units. Journal of Polymer Science Part A: Polymer Chemistry 2012, 50 (20), 4170-4181.

46. Kolb, H. C.; Finn, M. G.; Sharpless, K. B., Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angewandte Chemie International Edition 2001, 40 (11), 2004-2021.

47. Iha, R. K.; Wooley, K. L.; Nyström, A. M.; Burke, D. J.; Kade, M. J.; Hawker, C. J., Applications of Orthogonal “Click” Chemistries in the Synthesis of Functional Soft Materials. Chemical Reviews 2009, 109 (11), 5620-5686.

48. Yue, K.; Liu, C.; Guo, K.; Yu, X.; Huang, M.; Li, Y.; Wesdemiotis, C.; Cheng, S. Z. D.; Zhang, W.-B., Sequential “Click” Approach to Polyhedral Oligomeric Silsesquioxane-Based Shape Amphiphiles. Macromolecules 2012, 45 (20), 8126-8134.

49. Su, H.; Zheng, J.; Wang, Z.; Lin, F.; Feng, X.; Dong, X.-H.; Becker, M. L.; Cheng, S. Z. D.; Zhang, W.-B.; Li, Y., Sequential Triple “Click” Approach toward Polyhedral Oligomeric Silsesquioxane-Based Multiheaded and Multitailed Giant Surfactants. ACS Macro Letters 2013, 2 (8), 645-650.

50. Li, Y.; Wang, Z.; Zheng, J.; Su, H.; Lin, F.; Guo, K.; Feng, X.; Wesdemiotis, C.; Becker, M. L.; Cheng, S. Z. D.; Zhang, W.-B., Cascading One-Pot Synthesis of Single-Tailed and Asymmetric Multitailed Giant Surfactants. ACS Macro Letters 2013, 2 (11), 1026-1032.

51. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B., A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation” of Azides and Terminal Alkynes. Angewandte Chemie International Edition 2002, 41 (14), 2596-2599.

52. Agard, N. J.; Prescher, J. A.; Bertozzi, C. R., A Strain-Promoted [3 + 2] Azide−Alkyne Cycloaddition for Covalent Modification of Biomolecules in Living Systems [J. Am. Chem. Soc. 2004, 126, 15046−15047]. Journal of the American Chemical Society 2005, 127 (31), 11196-11196.

53. Hoyle, C. E.; Bowman, C. N., Thiol–Ene Click Chemistry. Angewandte Chemie International Edition 2010, 49 (9), 1540-1573. 167

54. Kade, M. J.; Burke, D. J.; Hawker, C. J., The power of thiol-ene chemistry. Journal of Polymer Science Part A: Polymer Chemistry 2010, 48 (4), 743-750.

55. Zhang, W.; Huang, M.; Su, H.; Zhang, S.; Yue, K.; Dong, X.-H.; Li, X.; Liu, H.; Zhang, S.; Wesdemiotis, C.; Lotz, B.; Zhang, W.-B.; Li, Y.; Cheng, S. Z. D., Toward Controlled Hierarchical Heterogeneities in Giant Molecules with Precisely Arranged Nano Building Blocks. ACS Central Science 2016, 2 (1), 48-54.

56. Stacked base pairs cause aromatic-aromatic interactions in DNA. http://www.chem.ucla.edu/~harding/IGOC/A/aromatic_aromatic_interaction.html.

57. Martinez, C. R.; Iverson, B. L., Rethinking the term "pi-stacking". Chemical Science 2012, 3 (7), 2191-2201.

58. Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hägele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M., Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics. Angewandte Chemie International Edition 2007, 46 (26), 4832-4887.

59. Ito, S.; Wehmeier, M.; Brand, J. D.; Kübel, C.; Epsch, R.; Rabe, J. P.; Müllen, K., Synthesis and Self-Assembly of Functionalized Hexa-peri-hexabenzocoronenes. Chemistry – A European Journal 2000, 6 (23), 4327-4342.

60. Eshdat, L.; Hoffman, R. E.; Fechtenkötter, A.; Müllen, K.; Rabinovitz, M., Stereodynamics and Characterization of the Hexa(4-n-dodecylbiphenylyl)benzene Hexaanion that Includes a Twisted Benzene Core. Chemistry – A European Journal 2003, 9 (8), 1844-1851.

61. Bushby, R. J.; Lozman, O. R., Photoconducting liquid crystals. Current Opinion in Solid State and Materials Science 2002, 6 (6), 569-578.

62. Vaughan, G. B. M.; Heiney, P. A.; McCauley, J. P.; Smith, A. B., Conductivity and structure of a liquid-crystalline organic conductor. Physical Review B 1992, 46 (5), 2787-2791.

63. Boden, N.; Bushby, R. J.; Clements, J.; Jesudason, M. V.; Knowles, P. F.; Williams, G., One-dimensional electronic conductivity in discotic liquid crystals. Chemical Physics Letters 1988, 152 (1), 94-99.

64. Boden, N.; Bushby, R. J.; Clements, J., Electron transport along molecular stacks in discotic liquid crystals. Journal of Materials Science: Materials in Electronics 1994, 5 (2), 83-88.

168

65. García, F.; Viruela, P. M.; Matesanz, E.; Ortí, E.; Sánchez, L., Cooperative Supramolecular Polymerization and Amplification of Chirality in C3-Symmetrical OPE-Based Trisamides. Chemistry – A European Journal 2011, 17 (28), 7755-7759.

66. Park, S.; Cho, B.-K., Sequential phase transformation of propeller-like C3-symmetric liquid crystals from a helical to ordered to disordered hexagonal columnar structure. Soft Matter 2015, 11 (1), 94-101.

67. Marc De Graef, M. E. M., Structure of Materials: An Introduction to Crystallography, Diffraction and Symmetry.

68. Frank, F. C., Supercooling of liquids. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences 1952, 215 (1120), 43.

69. F. C. Frank, J. S. K., Complex Alloy Structures Regarded as Sphere Packings. I. Definitions and Basic Principles. Acta Cryst. 1958, 11, 7.

70. F. C. Frank, J. S. K., Complex alloy structures regarded as sphere packing: 2. Analysis and classfication of representative structures. Acta Cryst. 1959, 12, 483-499.

71. Shoemaker, C. B.; Shoemaker, D. P., Concerning systems for the generating and coding of layered, tetrahedrally close-packed structures of intermetallic compounds. Acta Crystallographica Section B 1972, 28 (10), 2957-2965.

72. Sadoc, J.-F.; Mosseri, R., Quasiperiodic Frank–Kasper phases derived from the square–triangle dodecagonal tiling. Structural Chemistry 2017, 28 (1), 63-73.

73. Pande, C. S., Microstructural Aspects of High and Low Tc Superconductors. Materials Physics and Mechanics 2000, 2, 1-9.

74. Sinha, A. K., Topologically close-packed structures of transition metal alloys. Progress in Materials Science 1972, 15 (2), 81-185.

75. Marc De Graef, M. E. M., Structure of Materials: An Introduction to Crystallography, Diffraction and Symmetry. Cambridge University Press: United States of America by Cambridge University Press, New York, 2012.

76. Pearson, W. B.; Christian, J. W.; Hume-Rothery, W., New Sigma-Phases in Binary Alloys of the Transition Elements of the First Long Period. Nature 1951, 167, 110.

77. Lee, S.; Bluemle, M. J.; Bates, F. S., Discovery of a Frank-Kasper σ Phase in Sphere-Forming Block Copolymer Melts. Science 2010, 330 (6002), 349.

169

78. Zhang, J.; Bates, F. S., Dodecagonal Quasicrystalline Morphology in a Poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) Tetrablock Terpolymer. Journal of the American Chemical Society 2012, 134 (18), 7636-7639.

79. Lee, S.; Leighton, C.; Bates, F. S., Sphericity and symmetry breaking in the formation of Frank–Kasper phases from one component materials. Proceedings of the National Academy of Sciences 2014, 111 (50), 17723.

80. Gillard, T. M.; Lee, S.; Bates, F. S., Dodecagonal quasicrystalline order in a diblock copolymer melt. Proceedings of the National Academy of Sciences 2016, 113 (19), 5167.

81. Kim, K.; Schulze, M. W.; Arora, A.; Lewis, R. M.; Hillmyer, M. A.; Dorfman, K. D.; Bates, F. S., Thermal processing of diblock copolymer melts mimics metallurgy. Science 2017, 356 (6337), 520.

82. Percec, V.; Imam, M. R.; Peterca, M.; Wilson, D. A.; Heiney, P. A., Self-Assembly of Dendritic Crowns into Chiral Supramolecular Spheres. Journal of the American Chemical Society 2009, 131 (3), 1294-1304.

83. Percec, V.; Imam, M. R.; Peterca, M.; Wilson, D. A.; Graf, R.; Spiess, H. W.; Balagurusamy, V. S. K.; Heiney, P. A., Self-Assembly of Dendronized Triphenylenes into Helical Pyramidal Columns and Chiral Spheres. Journal of the American Chemical Society 2009, 131 (22), 7662-7677.

84. Yue, K.; Huang, M.; Marson, R. L.; He, J.; Huang, J.; Zhou, Z.; Wang, J.; Liu, C.; Yan, X.; Wu, K.; Guo, Z.; Liu, H.; Zhang, W.; Ni, P.; Wesdemiotis, C.; Zhang, W.-B.; Glotzer, S. C.; Cheng, S. Z. D., Geometry induced sequence of nanoscale Frank– Kasper and quasicrystal mesophases in giant surfactants. Proceedings of the National Academy of Sciences 2016, 113 (50), 14195.

85. Huang, M.; Hsu, C.-H.; Wang, J.; Mei, S.; Dong, X.; Li, Y.; Li, M.; Liu, H.; Zhang, W.; Aida, T.; Zhang, W.-B.; Yue, K.; Cheng, S. Z. D., Selective assemblies of giant tetrahedra via precisely controlled positional interactions. Science 2015, 348 (6233), 424.

86. Feher, F. J., Polyhedral oligometallasilsesquioxanes (POMSS) as models for silica-supported transition-metal catalysts. Synthesis and characterization of (C5Me5)Zr[(Si7O12)(c-C6H11)7]. Journal of the American Chemical Society 1986, 108 (13), 3850-3852.

87. Ruffieux, V.; Schmid, G.; Braunstein, P.; Rosé, J.; Braunstein, P.; Rosé, J., Oligosilsesquioxane8-OSS-Ethyldiphenylphosphine: A New Functional Oligosilsesquioxane Ligand. Chemistry – A European Journal 1997, 3 (6), 900-903.

170

88. Nakajima, Y.; Shimada, S., Hydrosilylation reaction of olefins: recent advances and perspectives. RSC Advances 2015, 5 (26), 20603-20616.

89. Yokokawa, F.; Asano, T.; Shioiri, T., Total Synthesis of the Antiviral Marine Natural Product (−)-Hennoxazole A. Organic Letters 2000, 2 (26), 4169-4172.

90. Sato, K.; Yoshimura, T.; Shindo, M.; Shishido, K., Total Synthesis of (−)-Heliannuol E. The Journal of Organic Chemistry 2001, 66 (1), 309-314.

91. Mays, J. W. High Vacuum Line.,https://www.chem.utk.edu/mays/research.

92. Complete Schlenk line set-up. http://www.chemistryviews.org/details/education/3728881/Tips_and_Tricks_for_the _Lab_Air-Sensitive_Techniques_1.html.

93. Hsu, C.-H.; Cheng, S. Z. D., The Deconstruction of Supramolecular Structures Based on Modular Precise Macromolecules. Macromolecular Chemistry and Physics 2018, 219 (3), 1700390-n/a.

94. Chandrasekhar, S.; Sadashiva, B. K.; Suresh, K. A., Liquid crystals of disc-like molecules. Pramana 1977, 9 (5), 471-480.

95. Isaad, J., Acidic ionic liquid supported on silica-coated magnetite nanoparticles as a green catalyst for one-pot diazotization-halogenation of the aromatic amines. RSC Advances 2014, 4 (90), 49333-49341.

96. Wu, X.; Hu, L., Design and synthesis of peptide conjugates of phosphoramide mustard as prodrugs activated by prostate-specific antigen. Bioorganic & Medicinal Chemistry 2016, 24 (12), 2697-2706.

97. Wang, H.; Deng, T.; Cai, C., Fluorous bis(oxazolines) ligand: Synthesis and application in Kabachnik-Fields reaction. Journal of Fluorine Chemistry 2014, 168, 144-150.

98. Ganguly, S.; Pachfule, P.; Bala, S.; Goswami, A.; Bhattacharya, S.; Mondal, R., Azide-Functionalized Lanthanide-Based Metal–Organic Frameworks Showing Selective CO2 Gas Adsorption and Postsynthetic Cavity Expansion. Inorganic Chemistry 2013, 52 (7), 3588-3590.

99. John L. Speier, James A. Webster, and Garrett H. Barnes The Addition of Silicon Hydrides to Olefinic Double Bonds. Part II. The Use of Group VIII Metal Catalysts J. Am. Chem. Soc. 1957, 79, 4, 974-979

171

100. Judith Stein, L. N. Lewis, Y. Gao, and R. A. Scott In Situ Determination of the Active Catalyst in Hydrosilylation Reactions Using Highly Reactive Pt(0) Catalyst Precursors J. Am. Chem. Soc. 1999, 121, 15, 3693-3703

101. Wikipedia contributors. Staudinger reaction. Retrieved from https://en.wikipedia.org/wiki/Staudinger_reaction

102. Meldal, M.; Tornoe, C. W. Cu-Catalyzed Azide-Alkyne Cycloaddition Chem. Rev. 2008, 108, 2952-3015

103. Wikimedia contributors. Sonogashira reaction mechanism. Retrieved from https://commons.wikimedia.org/wiki/File:Sonogashira_reaction_mechanism.png

172

APPENDIX

Appendix 1. Core size of TAB and TEB measured by Material Studio.

1.3 nm 1.1 nm

1.4 nm 1.2 nm

Figure A1. Rod and sphere mode of TEB and TAB core rigid part with center to arm distance measured.

173

The amide group was included in this calculation. The radius of the TEB core was measured as 1.3 nm with three arms and 1.1nm with six arms. The radius of the TAB core is measured as 1.4nm and 1.2 nm with three and six arms, respectively. The slightly different in the core size for three arms and six arms are resulted from the different positions of amide groups on the outside benzene ring.

174

Appendix 2. X-ray pattern of TAB-BPOSS3 treated by three different methods.

Simliar to TEB-BPOSS3, TAB-BPOSS3 has also been treated by three differetnt method. Based on the DSC results, there are two ordered phases were can be formed by increasing the temperature, the phase we are going to determine here is phase I so the

o annealing temperature should be lower than the TphaseI-phaseII (234.3 C)and above the

BPOSS crystallization temperature(150oC).Here we choose 180 oC as our thermal annealing temperature.

2X X

Figure A2. Columnar structures with ordered to less ordered intracolumnar packing achieved by three treatment methods. Method 1: Quench the sample from its melt states to room temperature by liquid nitrogen. Method 2: Thermal anneals the sample at 180 oC for 12hours and cooled to room temperature at a rate of 10oC/min. Method 3: Extrude the sample into a fiber at high temperature and thermal anneal the fiber at 180 oC for 12 hours.

175

As show in Figure A2, three different methods have been applied for preparing samples for X-ray structure determination. Method 1 gives scattering peaks that belongs to

2D rectangular lattice. SAXS pattern for sample prepared by method 2 have 2 peaks with the 2D rectangulararrays remaining. Those new peaks may result from the quasi-long range order along and inside the column, indicating hierarchical structures. The rectangular lattice parameter can be determined and the indexes of peaks are listed in Table A1. In traditional rectangular columnar phase, the split of (11) (20) peak and indicate the rectangular symmetry instead of hexagonal symmetry. Different from traditional rectangular phase, here the appearance of (01) and (21) diffractions indicate it is not hexagonal packing. Based on the indexing from Table A1, all of the peaks in can also be indexed by the similar lattice parameter except two new and relatively broad peaks X and

2X(q ratio is two times over X peak).

Table A1. Indexing of the SAXS peaks of TAB-BPOSS3 (Method 2)

-1 q/Å d/Å (hk) dcal/Å

0.1576 39.9 01 39.9

0.1824 34.4 20 11 34.5, 34.4

0.2411 26.1 21 26.1

0.2790 22.5 X

0.3147 20.0 02 31 20.0 19.9

0.3251 19.3 12 19.2

0.4701 13.4 03 13.3

176

0.4827 13.0 13 42 51 13.1 13.0

0.5040 12.5 23 12.4

0.5587 11.1 2X

0.6323 9.9 04 62 14 10.0 9.9

Shear the sample into fiber sample result into an even more ordered packing, consists of the same rectangular arrays of columns with a periodic, positional intracolumnar order.

(The partial missing of the higher ordered (hk0) peaks of the fiber sample is due to the detector has a rectangular profile, results in absence of peaks of q >0.4 while integrating along the equator of the 2D fiber pattern).

177

Appendix 3. Hierarchical Columnar Phase Determined by 2D Fiber Pattern.

Figure A3. Two dimensional SAXS pattern of TAB-BPOSS3 fiber sample (Sample prepared by Method 3). (b) Meridional (Red) and equatorial (Blue) plots from the 2D diffraction pattern shown in (a), in other words, the integration along the direction parallel to the fiber (red dashed line cut in (a)) and perpendicular to the fiber (blue dashed line cut in (a)) was plotted. Numerical values denote their Miller indices and d-spacing, respectively.

More direct evidence for hierarchical structure is from the 2D X-ray pattern for fiber sample prepared by Method 3, clearly demonstrates peak X and 2X are from different direction with the columnar packing. Oriented fiber sample was obtained by same extruding method as TEB-BPOSS3. The fiber successfully displayed a distinct 2D SAXS pattern (FigureA3 (a)) and 2D WAXD pattern (FigureA4 (a)) featuring a set of diffuse spots along the fiber direction and perpendicular to the fiber direction. In the direction perpendicular to the fiber (FigureA3 (b) blue), those spots can be indexed as (01), (11) and

(20), (21) planes of a 2D rectangular lattice. Along the fiber axis of TAB-BPOSS3, distinct diffraction arcs with d-spacing of 1.1nm (Figure A3 (a) red) and 0.37nm (Figure A4 (a))

178 was observed. Taking into account the molecular structure and dimensions ofπ-π stacking, this diffraction pattern is attributable to a intracolumnar structure as illustrated in Figure

4.21 (b), where the molecules stacks on top of each other inside the column to maximize the intermolecular π-π interaction and H-Bonding.

(a) (b)

Figure A4. (a) Two dimensional WAXD pattern of TAB-BPOSS3 fiber sample (Sample prepared by Method 3). (b) Integration along the fiber axis (black) and perpendicular to the fiber (blue) was plotted. Numerical values denote their Miller indices and d-spacing, respectively.

179

Appendix 4. X-ray characterization of π-π interaction.

Figure A5. WAXD study of (a) TEB-BPOSS3, (b) TEB-BPOSS6, (c) TAB-BPOSS3, (d) TAB-BPOSS6. (e) and (f) are the Voigt fitting of (b) and (d). 2 fitted peaks with d-spacing of 5.0−5.1 Å and 3.9 Å are separated. 5.0−5.1 Å are the typical d spacing for aliphatic chains and 3.9 Å is π-π interactions between the discotic cores. The Lorentzian width of the 2nd peak of molecules with 6BPOSS on the periphery is relatively broader than molecules with 3BPOSS on the periphery.

180

Appendix 5. H-bonding investigation by in-situ FTIR.

Free N-H stretching vibration frequency can be derived from FT-IR spectrum by concentration-resolved experiments as shown in Figure A6.

Figure A6. Concentration resolved FT-IR spectrum for (a) TEB-BPOSS3 (b) TEB-BPOSS6. -1 The solvent is CDCl3. We can clearly see a small peak appeared at about 3450 cm when the solution is very dilute for both (a) and (b), indicating the isolated N-H stretch wavelength is at about 3450 cm-1. This peak disappeared at high concentration for TEB-BPOSS3 indicate the N-H of this molecule is very likely to form H-Bonding with C=O group when concentration getting thicker. From picture (b), as long as the solution concentration increasing, the peak intensity at 3155 cm-1 is decreasing, it was assigned to the vibration of CDCl3.

181

Figure A7. In-situ FTIR characterization of (a) TEB-BPOSS3, (b) TEB-BPOSS3, (c) -1 TAB-BPOSS3, (d) TAB-BPOSS6. Wavenumber at ~3450cm refers free N-H stretch and Wavenumber at ~3280cm-1 refers H-Bonded N-H stretch. Red arrow means heating up and blue arrow means cooling down.

182

Appendix 6. H-Bonding formation in the solution of TEB-BPOSS3, characterized by

HNMR at different concentrations.

1 Figure A8. The HNMR spectrum chemical shifting of N-H in CDCl3 for TEB-BPOSS3 at 1M, 3M, 10M and 20M. Chemical shift moving to lower field indicates the H-bonding formation of N-H upon increasing the concentration.

183

Appendix 7. TEM bright field images original data.

184

Figure A9. Original TEM Bright Field images of TEB-BPOSS3 (a)(b) and TAB-BPOSS3(c)(d), projection from zone [001] and [100], respectively. (e) and (f) are the original images of <100> projection of A15 phase of TEB-BPOSS6(e) and TAB-BPOSS6(f). The inset is the FFT pattern of each image.

Figure A10. Original TEM Bright Field images of TAB-CnBPOSS6 n=4, 6, 8, projection from zone [001]. The inset is the FFT pattern of each image.

185