No description available.

This work was devoted to synthesis of new antiferroelectric liquid crystalline materials in series of chiral I-methylheptyI4'-(4-n-alkyloxybenzoyloxy)biphenyl-4-carboxylates. 9 new types of materials were synthesised and their chemical, mesomorphic and electrooptical properties were investigated in the homologous series. The chemical structure of each material synthesised was proved through IHNMR and IR spectroscopy studies, mass spectrometry, optical rotation measurements and analytical HPLC technique. The mesomorphic properties of the final products were investigated by the DSC method and textural observations in polarising light microscope. The electrooptical experiments were done in thin planar cells by applying AC triangular wave field of various voltages and frequencies. The electrooptical response measured was plotted as a function of the external voltage and the resulting curves were analysed in detail. Apart from the investigation into mesomorphic behaviour of the compounds prepared, the effect of V -shaped switching was described for some of the homologues. The switching parameters were determined and conclusions were reached on the origins of the V -shaped electrooptical response. The studies on a new type of the twist grain boundary phase with local anti ferroelectric structure were described in separate chapter.

The properties of specifically designed nanocomposites are currently of high interest to scientists as they are different to those of materials in bulk. Of special interest are nanocomposites made up of gold nanoparticles and liquid crystalline materials. Since most applications of metal nanoparticles are based on their assemblies, controlling their self–assembly opens the potential to synergistic property combination of these composites, most actively discussed are currently those of optical metamaterials. Here the results of the investigation of gold nanoparticle (AuNP)- and gold nanorod (AuNR)- side-chain liquid crystalline polymer chains (SCLCPs) are presented. The synthesis of these nanoystems were explored systematically. The preparation of SCLCPs, either by grafting to the NPs or by polymerisation from the preparation of an Au-NP macroinitiator were explored. The mode of polymerisation either free radical polymerisation or atom transfer radical polymerisation (ATRP) was varied. Firstly, the AuNPs and AuNRs were synthesised and fully characterised. The sizes of AuNPs investigated were 2 nm and 3 nm while the average dimension of AuNRs investigated was 26 nm x 8 nm, with an aspect ratio of 3. These nano species were either functionalized directly with the LC thiol and/or functionalized with initiator and used as a macroinitiator in the polymerisation of different monomers. The mesogenic compound used in the investigation was 4ˈ-undecycloxybiphenyl-4-yl 4-octyloxy-2-(pent-4-en-1-yloxy) benzoate. The alkene end of the mesogen was converted to polymerisable end group through a range of chemical reactions. The polymerisation of these polymers were investigated first by free radical polymerisation, before been polymerised using AuNP/AuNR-initiator modified to act as macroinitiators to obtain the targeted composites. For polymer/nano composites, the optimum structural control of the composite was achieved by preassembling the inorganic nanoparticles with the organic polymer. With accurate compositional specification of the final composite, different methods were used for the synthesis which includes grafting of a polymer chain to the surface through a covalently linked monomer, or grafting polymer chains from polymerisation initiators-modified surfaces. Based on these points, liquid crystalline polymeric composites were synthesised using both ‘grafting from’ and ‘grafting to’ methods. Disulfide functional initiator was prepared followed by methacrylate which was attached to the mesogen and polymerised. The Cu(I)Br/2,2’-bipyridine mediated atom transfer radical polymerisation of the methacrylate was first investigated and the polymer obtained fully characterised. The polymerizations of the methyacrylate mesogenic compounds were then investigated. The disulfide- containing polymers were cleaved to obtain active thiol-polymers which were coupled to the NPs to afford the composites. The initiator-coupled AuNPs and AuNRs were used as the macroinitiator in the polymerization of the methacrylate mesogenic monomers in the ‘grafting from’ method. The mesogen, nanoparticles and the composites were analysed by TLC, 1H NMR, 13C NMR, mass spectrometry, elemental analysis and SEM while the liquid crystalline properties of the mesogens were further determined by DSC, XRD and OPM techniques. The average gold nanoparticle size/distribution was determined by GPC and TEM. The properties of polymers were determined by GPC, mass spectrometry and NMR.

This research is based on the synthesis and evaluation of liquid crystalline host materials for use in ferroelectric liquid crystal devices. The liquid crystal materials are synthesised by incorporating silane bulky end groups linked by an alkoxy spacer to a fluoroterphenyl molecular core. The main aim of the research is to improve the alignment quality with the ultimate aim of bookshelf alignment. Almost as important is the target of wide temperature range, high tilt, and low melting SmC phase materials, but maintaining the low rotational viscosity of the fluoroterphenyl core. The syntheses are reported of a series of silane compounds with bulky terminal groups attached to mono-, di-, and tri-fluoroterphenyl cores. The initial targets contain a pentamethyldisilane end group, but the route was unsuccessful so simpler targets with a butyldimethylsilane bulky end groups were prepared. The key part of the synthesis involves hydrosilylation, low temperature directed lithiation and Suzuki-Miyaura coupling reactions. The report discusses the syntheses and transition temperatures obtained from DSC and thermal polarising optical microscopy. The trends in the transition temperatures, and tilt angles of derived FLC materials, values are discussed and compared to literature compounds. An exemplar is the addition of a chiral dopant (BE8OF2N) to butyl(6-((4''-((10- (butyldimethylsilyl)decyl)oxy)-2',3'-difluoro-[1,1':4',1''-terphenyl]-4-yl)oxy)hexyl)dimethylsilane 30a produces a high SmC* tilt angle of around 45° which varies little with temperature and there is a step in Ps data. This example 30a is mixed in percentages up to 50% with a model difluoroterphenyl KC1020 substituted in the middle ring. The bulky end group suppresses the N and SmA phase when compared to the dialkyl mesogen. A marked reduction in crystallisation temperature shows eutectic behaviour which is promising for ferroelectric mixture formulation. The same example 30a mixed with KC1019, fluorinated on the end ring, has similar behaviour, but with more support of the SmC phase. Other silane materials are mixed with KC1020 only, and their phase behaviour is discussed. Selected 50% mixtures of 30a+KC1019, 30a+KC1020, and an end ring monofluoroterphenylbutyldimethylsilane 39+KC1020 are doped with 7% w/w of standard dopant BE8OF2N(-S) aimed at the ideal phase sequence I-N*-SmA*-SmC*-C. The SmC* tilt angles are close to the ideal value of 22.5° at room temperature but Ps values vary.

Previous studies of single-molecule magnets (SMMs) have interpreted their low-temperature (below 8 K) magnetic measurements on the basis of X-ray crystal structures measured at 100 K or even room temperature. The work presented herein describes the first structural measurements performed on SMMs in the temperature regime in which magnetisation studies are performed. The ultra-low temperature (2 K) crystal structure of the prototypical SMM [Mn12O12(O2CMe)16(H2O)4]⋅2MeCO2H⋅4H2O (Mn12-acetate, 1) was determined by using single-crystal X-ray and neutron diffraction. We have observed an additional hydrogen-bonding interaction in the disordered region of 1 that backs up the link between solvent disorder and disorder in the position of an acetate ligand. Two new desolvated species [Mn12O12(O2CMe)16(H2O)4]⋅4H2O (2) and [Mn12O12(O2CMe)16(H2O)4] (3) were formed from 1 by single-crystal to single-crystal (SCSC) transformations and lead to the conclusion that the acetic acid of crystallisation in 1 is responsible for positional disorder in an acetate ligand. Another new {Mn12} derivative [Mn12O12(O2CMe)16(CH3CH2OH)4]•CH3CH2OH (4) is formed by exposing the desolvated species to ethanol vapour. The structure of the SMM [Mn3O(Et-sao)3(ClO4)(MeOH)x(H2O)3-x] (5, Et-saoH2 = C6H4-1-CH(C2H5)N(OH)-2-OH) at 2 K is also reported from a combination of single-crystal neutron and X-ray diffraction experiments. There is linked disorder in the identity of the coordinated solvent (methanol or water) and in the position of the ethyl substituent in the Et-sao2- ligand. This leads to a number of possible isomers present in a single-crystal and is consistent with the observation of transverse anisotropy in 5 previously recorded by high-frequency- and high-field-electron paramagnetic resonance (HF-EPR) spectroscopy. The crystal structure of the triangle intermediate [Mn3O(O2CEt)6(py)3](ClO4) (6, py = pyridine) formed during the synthesis of the SMM [Mn4O3Cl4(O2CEt)3(py)3]⋅4MeCN (7) is reported for the first time. Additionally a related new compound [Mn4O3Cl7(O2CEt)3](C5H5NH)3 (8) that crystallises in the same space group as 7 is also reported. The structure of the SMM [Ni4(dea)4Cl4]⋅4MeCN⋅0.6H2O (9, deaH = (HOCH2CH2)2NH) is reported at 1.7 K by using single-crystal neutron diffraction. The isostructural bromide complex [Ni4(dea)4Br4]⋅6MeCN (12) was synthesised for the first time and its structure is reported at 30 K. Methanol solvates of each species are also reported (10 and 13) and crystallise in the lower symmetry P-1 space group. 13 displays similar low-temperature (sub-3 K) magnetic behaviour to that reported for 9, as well as an additional slow relaxation process at 4-6 K. Mass spectrometry is consistent with the formation of {Ni4} cubanes with N-substituted diethanolamine ligands, N-phenyl-deaH and triethanolamine (teaH); the former with chloride ligands and the latter with bromide ligands. Another new solvothermally-derived {Ni4} cubane species is described with a slightly different cubane core, [Ni4(dea)4Br2(H2O)2]Br2 (14). We attempted to investigate two species based on a {Ni10} supertetrahedron (16 and 17); unfortunately the single-crystal neutron diffraction experiment carried out on these compounds was unsuccessful. The structure of the SMM (C(NH2)3)8[Co4(cit)4]⋅4H2O (18, H4cit = (HO2CCH2)2C(OH)CO2H) was determined at 2 K using high-resolution neutron powder diffraction, single-crystal X-ray diffraction and single-crystal neutron diffraction. The former two measurements offer some evidence for disorder in the hydrogen bonding between the {Co4} clusters, guanidinium cations and solvent of crystallisation; however, the latter measurement does not support this. A series of inelastic and polarised neutron scattering measurements are presented for a deuterated sample of 18 (denoted 19) and allow observation of scattering related to magnetic excitations.

The work presented in this thesis represents the study of the polymorphism exhibited by several molecular, organic solid-state systems. In-situ techniques are used to explore aspects of the polymorphism and crystallization behaviour displayed by these systems. The crystal structures of new polymorphs and other solid phases are determined directly from powder X-ray diffraction data. Chapter 1 provides background information on the phenomenon of polymorphism and the importance of its study. In addition, the range of in-situ techniques that have been used to study crystallization and solid-state systems is described. Chapter 2 gives details on the experimental techniques used in the work presented in this thesis. These include powder X-ray diffraction (including the methodology behind structure determination from powder X-ray diffraction data), solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy, thermal analysis techniques and dynamic vapour sorption. Chapter 3 explores the polymorphism of m-aminobenzoic acid, resulting in the discovery and characterization of three new polymorphs. The crystallization of m-aminobenzoic acid from solution is studied via in-situ solid-state NMR spectroscopy and this in-situ technique is expanded to allow the evolution of both the solid and liquid phases during the crystallization process to be studied. Chapter 4 investigates the crystallization behaviour of triphenylphosphine oxide and methyldiphenylphosphine oxide from solution using in-situ solid-state NMR spectroscopy. Evidence is found for transient, unknown solid phases formed during the crystallization process. Chapter 5 reports new insights into the crystallization behaviour of polymorph II of the drug rac-ibuprofen. Differential scanning calorimetry and in-situ powder X-ray diffraction experiments demonstrate that previous assumptions about the crystallization behaviour of this polymorph were incorrect. Finally, Chapter 6 explores the crystalline phases of the amino acid L-phenylalanine. A new polymorph and two hydrate phases are discovered and their hydration/dehydration behaviour.

X-ray diffraction techniques have been used to examine the structural chemistry of three compounds of Group II metals. The crystal structures of all three compounds were solved by the heavy atom method and refined, with three dimensional data, by the method of least squares.

No description available.

This thesis presents a study of colloidal particles dispersed in thermotropic liquid crystals. It has a specific focus on colloids in the presence of an interface between the liquid crystal and an isotropic fluid. Three systems are studied: colloids trapped at a planar interface between a cholesteric liquid crystal (CLC) and an isotropic oil, nematic emulsions with interfacial colloids and the influence of colloids on the phase transition kinetics of the cholesteric blue phase. Experiments are carried out using polarising optical and confocal microscopy. By combining these techniques, the director field of the liquid crystals could be imaged in combination with precise observation of the colloid locations. Custom image analysis algorithms are developed to extract the information. In the first system, we create an interface between a cholesteric liquid crystal and an isotropic liquid. Homeotropic anchoring leads to a well aligned cholesteric layer and the formation of the fingerprint texture. Fluorescent colloidal particles with planar surface anchoring are dispersed in the CLC. A majority of these particles decorate the interface. The final distribution of particles perpendicular to the interface has a clear dependence on the particle size. In the plane of the interface, surface defects form a template for the colloids. The second system is a particle dispersion within a short pitch CLC which exhibits a blue phase. The colloidal particles and associated defects act as nucleation sites for the blue phase in the cholesteric to blue phase transition. Colloidal particles cause localised melting from the blue phase to the isotropic phase and lead to a larger temperature range for coexistence between isotropic and blue phases. Furthermore, the isotropic regions can be faceted, their shape and size is controlled by the blue phase elasticity. In the final system, a nematic emulsion is created. Droplets of nematic LC are dispersed in water. Colloidal particles initially mixed into the liquid crystal decorate the interface between the two fluids. The addition of a surfactant switches the liquid crystal alignment at the fluid-fluid interface from planar to homeotropic. This forces a change in defect structure, from two boojums at the poles to a hedgehog defect in the droplet centre. The presence of colloids affects the switching dynamics and alters the final liquid crystal alignment preventing the droplets from forming a central radial defect. There is a symbiotic relationship between the particle properties - size and anchoring at the surface - and the elastic properties of the liquid crystal in the bulk and in the presence of an interface with an isotropic fluid. How the systems respond when the balance of these factors is altered is explored throughout the thesis.

Organic co-crystals are a class of promising materials in industries such as pharmaceuticals and energy industry. The work described in this thesis is the result of studying a series of organic co-crystals, which are synthesized by several different crystallization methods, and includes structures determined by single-crystal X-ray diffraction and powder X-ray diffraction. Chapter 1 is a general introduction to organic co-crystals and the phenomenon of polymorphism in organic crystalline materials. The importance of intermolecular interactions such as hydrogen bonding and π-π stacking interactions for the design of organic co-crystals are also highlighted. Chapter 2 describes the experimental techniques which have been used for studying organic co-crystals. These include co-crystallization methods and characterization methods such as single-crystal X-ray diffraction, powder X-ray diffraction, thermal analysis techniques and solid-state nuclear magnetic resonance. Chapter 3 reports two novel polymorphic co-crystal systems of trimesic acid (TMA) and tert-butylamine (TBA) with different stoichiometric ratios and analyses the crystal structures of the two polymorphic systems. Apart from the phenomenon of polymorphism of co-crystals of TMA and TBA, the structural diversity of other co-crystals of TMA and TBA are discussed in Chapter 4. In this chapter, all co-crystals of TMA and TBA are classified into four families based on the stoichiometric ratio between TMA and TBA, and the structural features of each family are investigated from the view point of hydrogen bonding with graph set notation. Chapters 5 and 6 demonstrate the processes of structure determination of co-crystals of TMA and ʟ-arginine (Chapter 5) and the co-crystal of pillar[5]quinone and 1,1,2,2-tetrachloroethane (Chapter 6) from powder X-ray diffraction data.