Teses / dissertações sobre o tema "Discotic molecules"

Dans un contexte de transition énergétique, la demande de dispositif de stockage de l'énergie s'est considérablement accrue. La batterie à ions lithium est devenue un acteur emblématique de la transition énergétique. Toutefois, les électrodes constitutives de ces dernières sont exclusivement composé d'élément métallique et donc non renouvelable. Afin de rendre la transition énergétique pérenne, il est nécessaire de développer de nouvelles technologies moins impactantes et moins couteuses environnementalement parlant. Les électrodes organiques ont fait l'objet de nombreuses recherches et semblent être une alternative intéressante pour parvenir à cet objectif. Toutefois, un frein reste à lever : la faible conductivité électrique des matériaux organiques. Ce problème induit la nécessité d'ajouter de grandes quantités d'additif conducteur au sein de l'électrode, diminuant sa densité énergétique. Cette thèse a eu pour objectif de développer un nouveau type de matériaux organiques d'électrodes pouvant surmonter cette difficulté. Notre première piste de recherche s'est portée sur les pérylènes diimide (PDI), dont leurs coeurs polyaromatiques induisent une conformation planaire à la molécule. Cette propriété permet à ce type de molécules de "s'auto-assembler" sous la forme d'un matériau colonnaire par le biais de fortes interactions π,π. Cette organisation dote le matériau de propriétés semi-conductrices. Le premier chapitre de cette thèse a été marqué par la synthèse d'une large gamme de PDI et l'étude de leurs propriétés électrochimiques en configuration demi-pile. Par la suite, une étude approfondie de la réactivité électrochimique du meilleur candidat a été menée par diverses méthodes de caractérisation (microscopie électronique, infrarouge, diffractions aux rayons X, ...) afin de comprendre le mécanisme électrochimique de ce matériau pendant un cycle de charde/décharge. Il a été observé que la réduction du matériau engendre un phénomène de déstructuration de l'empilement colonnaire du matériau induisant une perte progressive de la conductivité électronique. Sur cette base, deux grands axes se sont ouverts, l'augmentation de la taille du coeur et l'externalisation de fonction électroactive. Le troisième chapitre traite de l'élargissement du coeur polyaromatique avec 4 nouvelles cibles moléculaires pouvant présenter des propriétés intéressantes. Ce chapitre y décrit leurs synthèses ainsi que les résultats électrochimiques préliminaires obtenus. Enfin, le dernier chapitre porte sur l'externalisation des fonctions électroactives en dehors du coeur de pérylène à travers deux approches. La première consiste à conserver la structure du PDI avec une substitution TEMPO permettant de travailler à haut potentiel et ainsi ne pas affecter les fonctions imides liées au coeur. La seconde est la création d'une plateforme moléculaire à partir d'un coeur de pérylène présentant des extrémités chlorées pouvant être modifiées par l'ajout de molécule organique électroactive déjà présentes dans la littérature
In a context of energy transition, the demand for energy storage devices has increased considerably. The lithium-ion battery has becom an emblematic player in the energy transition. However, the constitutent electrodes of the latter are exclusively composed of metallic elements and therefore non-renewable. In order to make the energy transition sustainable, it is necessary to develop new technologies that are less impactfull and less costly environmentally speaking. Organic electrodes have been the subject of much research and seem to be an interesting alternative to achieve this objective. However, an obstacle remains to be removed : the low electrical conductivity of organic materials. This problem induces the need to add large quantities of conductive additive within the electrode, reducing its energy density. This thesis aimed to develop a new type of organic electrode materials that could overcome this difficulty. Our first line of research focused on perylene diimide (PDI), whose polyaromatic cores induce a planar conformation to the molecule. This property allows this type of molecules to "self-assemble" in the form of a columnar material through strong π,π interactions. This organization endows the material with semiconductor properties. The first chapter of this thesis was marked by the synthesis of a wide range of PDIs and the study of their electrochemical properties in half-cell configuration. Subsequently, an in-depth study of the electrochemical reactivity of the best candidate was carried out by various characterization methods (electron microscopy, infrared, X-ray diffractions, etc.) in order to understand the electrochemical mechanism of this material during a charge/discharge cycle. It was observed that the reduction of the material generates a phenomenon of destructuring of the columnar stack of the material, inducing a progressive loss of electronic conductivity. On this basis, two main axes have opened up, the increase in the size of the core and the externalization of electroactive function. The third chapter deals with the enlargement of the polyaromatic core with 4 new molecular targets that may present interesting properties. This chapter describes their syntheses as well as the preliminary electrochemical results obtained. Finally, the last chapter focuses on the externalization of electroactive functions outside the perylene core through two approaches. The first consists of retaining the structure of the PDI with a TEMPO substitution allowing it to work at high potential and thus not affect the imide functions linked to the heart. The second is the creation of a molecular platform from a perylene core with chlorinated ends that can be modified by the addition of electroactive organic molecules already present in the literature

Significant progress has been made in recent years in modelling liquid crystal phases using the Monte Carlo and molecular dynamics simulation techniques. We describe the technique of molecular dynamics in the microcanonical ensemble that we have used in simulations of liquid crystal systems. A review and discussion of some of the important simulations that have been performed to date on non-spherical hard particle models, soft anisotropic single site models, and realistic atom-atom based models is presented. We report the results of molecular dynamics simulation studies of a system of particles interacting via an anisotropic potential proposed by Luckhurst and Romano, scaled by part of the well depth formulation employed by Gay and Berne. The resultant hybrid Gay-Berne Luckhurst-Romano (HGBLR) potential has an approximately spherical hard core with anisotropic long range attractive interactions with a dependency on the intermolecular vector joining a pair of sites. The spherical hard core nature of individual HGBLR centres notwithstanding we have parameterised single-site HGBLR centres to represent both calarnitic and discotic mesogens. Both systems are shown to exhibit a range of mesophases on cooling from the isotropic liquid to form a crystal, including uniaxial-nematic and columnar-like phases. Unlike previous hard particle studies these ordered phases obtain because of the presence of the long range attractive interactions. A comparison between the different structures formed with the two different parameterisations is presented including graphical representations of the simulation cell . In order to more closely represent the short range anisotropic interactions of real mesogens, a 3-HGBLR-site model has been parameterised to represent the mesogen para-terphenyl. Details of the parameterisation are discussed. Two versions of this model, a twisted central site 3-HGBLR-site site model obtained from a molecular mechanics minimum energy conformation of para-terphenyl, and an all coplanar 3-HGBLR-site site model have been studied using the molecular dynamics technique. The resultant models are found to be biaxial unlike previous anisotropic single site studies utilising soft potentials. Both models appear to exhibit a variety of uniaxial and biaxial mesophases but inclusion of the twisted site appears to promote the formation of biaxial phases. A comparison of the two models is made.

In 1970, Freiser made the theoretical prediction that a biaxial nematic phase could exist. In auniaxial nematic, only one particle axis is aligned but with a biaxial nematic, all three molecular axes are aligned. This phase is expected to occur for particle whose shape is intermediate between that of a disc and a rod. Board and bent-core particles are examples of such structures. Despite extensive experimental investigation, however, very few biaxial nematic systems have been found. Yu and Saupe [21] have shown the occurrence of a biaxial nematic phase generated for a lyotropic system. Similarly van der Pol observed a biaxial nematic phase in a colloidal suspension of board-like goethite particles [22]. For thermotropic, molecular systems, however, the situation is less clear-cut. Merkel et al., [23] and Figueirinhas et al., [24] claim that Tetrapodes have can exhibit a biaxial nematic phase, whilst Acharya et al., [25] and Prasad et al., [26] have also suggested the occurrence of this same phase with bent-core molecules, though experimental uncertainty still exist. With regards to theoretical predictions of the biaxial nematic transition, one notes in particular the work of Taylor and Herzfeld [13] on hard sphero-platelets, which predicts a rich phase diagram, notably containing an unusual discotic smectic phase. To date there are few simulations of board-like models, such as Vanakaras et al., [27] being arecent exception, developing a phase diagram for hard board-like colloids. Similarly, Escobedo[28] has produced a phase diagram of hard cuboids. We present molecular dynamics simulation results on a short range repulsive fused-hexagonmodel, somewhat resembling hard boards. Depending on the geometry of the board, we observe uniaxial and biaxial nematics, smectics A and C, a biaxial smectic phase and a columnar phase. Possibly the most interesting result is the existence of the theoretically predicted discoticsmectic. We further investigated the effect of applying both external fields and shears to several of the structures. The former, among other things, aided the alignment of the particles in the phase, removing dislocations. The shear was also seen to increase biaxial ordering, however, it also demonstrates an ability to introduce clear layer fractures, seen when shearing forces became overly dominant. An applied electrical field was able to induce isotropic!biaxial nematic and biaxial smectic switching. Finally we consider briefly less-symmetric arrangements of fused hexagons, including chiral particles. These systems proved hard to equilibrate but discotic nematic phases were observed for certain structures. Chiral clusters were also observed, however, no globally chiral phase was found. Columnar structures were also seen, but showing a weak overall alignment as columnstended to point along several directions.

Grace à leurs propriétés d’auto-réparation et d’auto-organisation, les matériaux pi-conjugués liquide-cristallins (LCs) présentent un grand intérêt pour l’élaboration de matériaux semi-conducteurs à hautes performances. Ils peuvent être utilisés pour différents types d’applications en électronique organique telles que les cellules solaires (OPV), les diodes électroluminescentes (OLED) et les transistors à effet de champs (OFET). Dans ce travail, nous avons conçu et préparé une nouvelle famille de LCs combinant des entités pi-conjuguées de type calamitique et discotique au sein d’une architecture moléculaire unique. Plus particulièrement, nous avons imaginé trois différentes architectures telles que des dyades et triades linéaires et des triades ramifiées, incluant des dérivés discotiques de pérylène ou de triphénylène et des dérivés calamitiques de terthiophène, de benzothienobenzothiophène ou encore de pyromellitique. L’objectif était d’étudier leurs comportements liquide-cristallins et leurs propriétés d’auto-organisation et de transport de charges.Les résultats obtenus ont montré que ces matériaux donnent des auto-assemblages complexes formant des arrangements multi-lamellaires de bicouches, dans lesquelles les entités calamitiques et discotiques présentent une organisation dans le plan. De plus, en choisissant judicieusement les entités pi-conjuguées calamitiques et discotiques (type-p ou type-n), nous avons démontré que ce type de matériaux auto-organisés peut présenter des propriétés de transport de charge ambipolaire en formant des chemins distincts pour chaque type de charge (trou et électron) par nano-ségrégation de ces entités de type p et de type n
Due to their self-healing ability and their self-organization property, pi-conjugated liquid crystals (LCs) are materials of great interest to prepare high performance semiconducting materials. They can be used in different types of organic electronic applications such as solar cells (OPV), Organic Light-Emitting Diodes (OLED) and Organic Field-Effect Transistors (OFET). In this work, we were interested in designing and preparing a novel family of LCs combining π-conjugated discotic and calamitic moieties in a unique molecular architecture. More particularly, we designed three different molecular architectures based on a linear dyad, triad and a branched triad, which include discotic triphenylene or perylene and calamitic terthiophene, benzothienobenzothiophene or pyromellitic moieties. The objective was to study their liquid crystalline behaviors and their self-organization and charge transport properties.Based on our results, we demonstrated that these materials can form complex self-assemblies in the bulk such as multi-lamellar arrangements presenting bilayered lamellar phases with in-layer organization of both calamitic and discotic species. In addition, based on the appropriate choice of the disk- and rod-like π-conjugated cores (p-type or n-type), we showed that this kind of self-organized materials could exhibit ambipolar charge transport properties, presenting a spontaneous nanosegregation of p-type and n-type entities in bulk, and leading to well-defined distinct conductive channels for each type of charge carriers (hole and electron)

Grace à leurs propriétés d’auto-réparation et d’auto-organisation, les matériaux pi-conjugués liquide-cristallins (LCs) présentent un grand intérêt pour l’élaboration de matériaux semi-conducteurs à hautes performances. Ils peuvent être utilisés pour différents types d’applications en électronique organique telles que les cellules solaires (OPV), les diodes électroluminescentes (OLED) et les transistors à effet de champs (OFET). Dans ce travail, nous avons conçu et préparé une nouvelle famille de LCs combinant des entités pi-conjuguées de type calamitique et discotique au sein d’une architecture moléculaire unique. Plus particulièrement, nous avons imaginé trois différentes architectures telles que des dyades et triades linéaires et des triades ramifiées, incluant des dérivés discotiques de pérylène ou de triphénylène et des dérivés calamitiques de terthiophène, de benzothienobenzothiophène ou encore de pyromellitique. L’objectif était d’étudier leurs comportements liquide-cristallins et leurs propriétés d’auto-organisation et de transport de charges.Les résultats obtenus ont montré que ces matériaux donnent des auto-assemblages complexes formant des arrangements multi-lamellaires de bicouches, dans lesquelles les entités calamitiques et discotiques présentent une organisation dans le plan. De plus, en choisissant judicieusement les entités pi-conjuguées calamitiques et discotiques (type-p ou type-n), nous avons démontré que ce type de matériaux auto-organisés peut présenter des propriétés de transport de charge ambipolaire en formant des chemins distincts pour chaque type de charge (trou et électron) par nano-ségrégation de ces entités de type p et de type n
Due to their self-healing ability and their self-organization property, pi-conjugated liquid crystals (LCs) are materials of great interest to prepare high performance semiconducting materials. They can be used in different types of organic electronic applications such as solar cells (OPV), Organic Light-Emitting Diodes (OLED) and Organic Field-Effect Transistors (OFET). In this work, we were interested in designing and preparing a novel family of LCs combining π-conjugated discotic and calamitic moieties in a unique molecular architecture. More particularly, we designed three different molecular architectures based on a linear dyad, triad and a branched triad, which include discotic triphenylene or perylene and calamitic terthiophene, benzothienobenzothiophene or pyromellitic moieties. The objective was to study their liquid crystalline behaviors and their self-organization and charge transport properties.Based on our results, we demonstrated that these materials can form complex self-assemblies in the bulk such as multi-lamellar arrangements presenting bilayered lamellar phases with in-layer organization of both calamitic and discotic species. In addition, based on the appropriate choice of the disk- and rod-like π-conjugated cores (p-type or n-type), we showed that this kind of self-organized materials could exhibit ambipolar charge transport properties, presenting a spontaneous nanosegregation of p-type and n-type entities in bulk, and leading to well-defined distinct conductive channels for each type of charge carriers (hole and electron)

Abstract: Osteoarthritis (OA) affects 250 million people worldwide. Currently, no targets for disease-modifying osteoarthritis drugs exist. Matrix metalloproteinase-13 (MMP-13) would make it an ideal target; however, its broad biological effects restrict its application as a target enzyme of inhibitory drugs in the treatment of OA. The expression and activation of discoidin domain receptor 2 (DDR2) is increased in human OA tissues and mouse models of OA and was co-localized with elevated expression of MMP-13 in degenerative articular cartilages. In healthy articular cartilage, DDR2 is kept inactivated by the pericellular matrix, which separates the receptor from its ligand, type II collagen. Once enzymes capable of degrading the pericellular molecules expose chondrocytes to type II collagen, DDR2 is activated and induces expression of MMP-13 leading to degradation of type II collagen and proteoglycans resulting in joint destruction and OA. We tested the hypothesis that complete removal of Ddr2 from the knee joint of mouse adult articular cartilage can delay progression of osteoarthritis prior to or after initiation of articular cartilage degeneration. To accomplish this goal, conditional knock out techniques were used with Aggrecan-CreERT2 mice and floxed Ddr2 mice, Ddr2 was removed from articular cartilage of knee joints in mice at 8 weeks of age via intraperitoneal Tamoxifen injection (2mg/10g body weight) for 5 consecutive days (Group A). Mice were subjected to destabilization of the medial meniscus (DMM) or sham surgery at 10 weeks of age. An additional experimental group was subjected to DMM or sham surgery at 10 weeks of age and then DDR2 was removed by intraperitoneal Tamoxifen injection 8 weeks later (Group B). Knee joints from mice in Group A and their corresponding controls were harvested at 8 weeks or 16 weeks post-surgery and mice from Group B and their controls were harvested at 16 weeks post surgery. Histology was performed and the OARSI Modified Mankin Score was used to evaluate articular cartilage degeneration. Statistically significant differences were determined via T-test. We found the average modified score for Group A 8 week control was 1.64 (n=7) whereas with Ddr2 removed was 0.64 (n=7) [P<0.05]. 2) The average modified score for Group A 16 week control was 4.67 (n=7) and with Ddr2 removed was 1.27 (n=9) [P<0.05]. 3) The average modified score for Group B was 1.1 (n=5). In conclusion, conditional removal of Ddr2 in articular cartilage attenuated articular cartilage degeneration in mature knee joints of mouse models of OA.

Cette thèse est consacrée à l’étude de films minces ouverts de cristaux liquides colonnaires sur un substrat solide. Ces matériaux, capables de s’auto-organiser en de larges domaines orientés, sont généralement obtenus à partir de molécules discotiques dérivées de colorants aromatiques. Ces différentes caractéristiques, associées à une bonne mobilité de charges, permettent d'envisager l'utilisation des cristaux liquides colonnaires en film mince dans des dispositifs photovoltaïques. Afin de bénéficier de leurs bonnes propriétés optoélectroniques, les cristaux liquides colonnaires doivent être déposés en film mouillant, d’épaisseur inférieure à 100 nm, et leur orientation contrôlée. Ainsi, pour des applications photovoltaïques, un alignement homéotrope (colonnes normales au substrat) est requis. Inversement, l’orientation planaire uniaxe (colonnes parallèles au substrat), est quant à elle requise pour une utilisation de ces composés dans les polariseurs ou dans les transistors organiques à effet de champ. Dans ce travail, différentes méthodes permettant de contrôler l’alignement de films minces ouverts de cristaux liquides colonnaires ont été développées, permettant d’obtenir aussi bien un ancrage homéotrope par traitement thermique spécifique, qu’un ancrage planaire uniaxe par dépôt préalable d’une couche de téflon. Le contrôle de l’orientation a ainsi permis d’une part de produire un film mince (e ? 50 nm) mouillant en ancrage homéotrope ouvrant la voie vers des cellules solaires organiques efficaces, et d’autre part de déterminer l’ensemble des propriétés optiques (indices complexes anisotropes) de ces matériaux cristallins liquides colonnaires. La dynamique du démouillage et l’état d’équilibre d’un film mince ouvert de cristal liquide colonnaire ont également été étudiés. Les résultats expérimentaux révèlent la formation de gouttelettes anisotropes et la présence d’un film nanométrique lors du démouillage de ce film mince
This thesis deals with columnar liquid crystal studied in the geometry of open supported thin films. Columnar liquid crystals are usually made of disk-shaped molecules derived from aromatic dyes. They are efficient charge transporters with the added capacity to self-assemble in large oriented domains. Consequently, such materials may be used in photovoltaic devices. In order to benefit from their good uniaxial charge mobility, their organization has to be controlled in uniform oriented thin films in the range of thicknesses of typically 100 nm. Homeotropic alignment (columns normal to the interface) is required for solar cells whereas uniaxial planar anchoring (columns parallel to the interface) is needed for applications such as polarizers or organic field effect transistor. Different methods to monitor the alignment in open thin films have been developed in this work, which make possible to achieve either homeotropic anchoring by a specific thermal treatment, or uniaxial planar orientation using a Teflon layer. Based on these orientation skills, a uniform ultra-thin film, free of dewetting and homeotropically oriented, is achieved (down to 50 nm thick) opening the way towards efficient solar cells, and a complete study of the optical properties has been performed (with the determination of the anisotropic complex indices) for different columnar liquid crystals. The dynamics of dewetting and the equilibrium state of a thin supported film have also been investigated. Experimental results show the formation of anisotropic droplets and reveal a nanometric film during dewetting

Grâce à leurs remarquables qualités de transport de charges et d'autoorganisation, les cristaux liquides colonnaires formés de molécules discotiques dérivées de colorants aromatiques sont des candidats prometteurs pour la réalisation de dispositifs photovoltaïques. Pour profiter à bien de ces propriétés, il est indispensable de maîtriser leur organisation en films minces. Un ancrage homéotrope avec les colonnes perpendiculaires au substrat est ainsi nécessaire pour conduire efficacement les charges aux électrodes. Cet alignement a été obtenu par transition d'ancrage entre un substrat solide et une cathode d'argent permettant d'obtenir des films ultra-minces (environ 25 nm d'épaisseur) homogènes orientés. Par ailleurs, une bicouche de composés discotiques intégralement alignée en ancrage homéotrope a été élaborée. A notre connaissance, ce travail constitue la première preuve de faisabilité d'une hétérojonction donneur - accepteur orientée constituée de cristaux liquides colonnaires.

碩士
淡江大學
化學學系碩士班
101
The first part of series one is make use of hexakis(phenylethynyl)benzene derivatives as the central core, and introduced o-fluorophenyl, m-fluorophenyl, p-fluorophenyl as one of side arm, respectively. Expectations by introducing fluorine atoms in different positions can make molecules arrange due to steric effect and differ in dipole orientation to become different types of arrangement. The results of the introduction of a single fluorine atom different locations in hexakis(phenylethynyl)benzene derivatives, neither liquid crystal. The second part replaced the para position of monofluorine atom to chlorine and bromine. Because introducing different halogen atoms, can affect the molecular dipole moment. The properties of the liquid crystal can be adjusted and changed with different moment. And the successful introduction of only one halogen atom, alter nematic liquid crystal molecules to a high order of the columnar liquid crystal molecules. In series two, a compound which introducd fluorine atom onto 1, 3, 5 position and the benzene jointed terminal pentane onto 2, 4, 6 position of hexabenzocoronene central core as the target product. It’s anticipated that the repulsion of fluorine atoms between molecules twisted the whole molecules. Therefore, the distances between disc-disc arranged closer and increased the contact area of the central core, for the purpose of raising current density in the columns of the photovoltaic devices. In addition, C3 symmetry enhanced solubility and reduced its clearing point. However, only the precursor, hexaphenylbenzene derivatives, was successfully synthesized.

Controlling the assembly of amphiphilic molecules and micron-sized, disk-shaped particles at different length scales into ordered structures enables bottom-up organization which is of great interest to emerging technologies based on structured materials. The primary object of this work is the investigation of structure forming components - Zirconium phosphate (ZrP) discotic particles and polymersomes/ amphiphiles on their self-assembly and interactions. The effect of bilayer architecture of polymersomes on surface reactivity was investigated via fluorescent probing method. Established through complementary experiments, correlation between reactivity and molecule diffusivity in polymer-rich environment revealed the mechanism of reduced reactivity when tethered reactive groups are located deeper within the hydrophilic polymer layer. The phase diagram of charged nanoplatelets was constructed as a function of particle concentration, surface cation moiety, and ionic strength. Influence of surface cation on the isotropic-nematic transition was done by measuring the transition boundaries of discotic suspensions prepared by acid-base exfoliation reaction with a series of exfoliating agents. Furthermore, a novel phase transition was found, where platelet-platelet interaction was influenced synergistically by ionic strength and ion exchange. At low pH, directional inter-platelet attractions lead to the formation of low volume fraction colloidal gels. Alternative surface modification approaches, including biomolecule deposition and alkyl chain grafting were explored. Finally, self-assembly of platelets in emulsions and oil-water interface was examined. Surface modification was applied to link surface properties to stable emulsion-forming ability in mixed surfactant-particle system. Emulsion uniformity was achieved by microfluidic flow focusing method. Surface engineering and interaction control was demonstrated throughout this work to be viable approaches to the fundamental understanding of collective behaviors of individual building blocks.

This dissertation reports a study of three kinds of liquid crystals using modern solid state NMR techniques: chiral rod-like liquid crystals, bent-core mesogens and disc-like liquid crystals. The properties and structures of liquid crystals are first introduced in Chapter 1. To understand the principles of different NMR phenomena, quantum mechanical theory is adopted to study different nuclear spin interactions and NMR techniques in Chapter 2. In the next part of this dissertation (Chapter 3-6), deuterium NMR methods are used to investigate the dynamics and structures of some liquid crystal phases. This is first done using the spin relaxation study. The parameters obtained from the model simulation can describe the molecular motion and internal dynamics in the fast motion region. Secondly, we investigate the dynamic process of discotic mesophases and unwound smectic C* phase using the line shape simulation study. 2D deuterium NMR exchange experiments are then performed to study the jump process in TGBA* phase and SmC* phase. The above investigation has demonstrated some powerful NMR methods for the dynamic study of liquid crystals. The third part of the dissertation (Chapter 7-9) is concerned with C-13 NMR techniques. After we introduce the quantum theory of different pulse sequences, theoretical models are presented to fit observations such as chemical shifts and dipolar splittings. Moreover high resolution liquid C-13 NMR experiments are introduced to study some bent-core molecules. They are useful to assist the carbon peak assignments of these molecules. The structure and ordering information of liquid crystals can be determined in their mesophases. Finally, a brief summary of the dissertation is given in the last chapter.
October 2007

Deuterium nuclear magnetic resonance (NMR) spectroscopy was used to explore molecular motions in the mesophases of calamatic liquid crystals 4-' n'-pentyloxybenzylidene-4'-heptylaniline (50.7), ' '-(methoxybenzylidine)-'p'-n-butylaniline(MBBA or 10.4), 4-'n'-hexyloxy-4'-cyanobiphenyl (60CB), a mixture of 60CB and 4-'n'-octyloxy-4'-cyanobiphenyl (80CB), and discotic liquid crystals hexakis('n'-hexyloxy)triphenylene(HAT6). The Zeeman and quadrupolar spin--lattice relaxation times were measured as a function of temperature at 15.1 MHz and 46 MHz using a broadband multiple--pulse sequence. In addition, quadrupolar splittings were measured for 60CB, 60CB/80CB mixture and columnar phase of HAT6. The TZ model was used to interpret the deuteron relaxation of biaxial molecules in the uniaxial medium. For 50.7, the analysis of the relaxation data in the nematic and smectic A phases supports a model which includes director fluctuations and rotational diffusion of an asymmetric rigid rotor in a biaxial potential of mean torque. The molecular biaxiality of the molecule is found, based on the relaxation data, to give a small positive molecular biaxial order parameter 'S'' xx'-'Syy'. In addition, the activation energy for the tumbling motion of the molecule is found to be larger than that for the spinning motion. For MBBA, the zero-frequency spectral densities ' J'0(0) data is quantitatively interpreted using a model that includes director fluctuations and rotational diffusion of symmetric rotors in a nematic phase. The contribution to 'J'0(0) from director fluctuations has mainly a second-order component, whereas the first-order contribution to 'J'1([omega]) is suppressed in the megahertz region (Larmor frequencies are 15.1 and 46 MHz) due to the high-frequency cutoff, which is estimated to be around 3-10 MHz for MBBA. For 60CB and 60CB/80CB mixture, the data analyses were carried out for both samples in order to achieve a consistent physical picture. The additive potential method is employed to model the quadrupolar splittings of 60CB, from which the potential of mean torque is parametrized, and the order parameter tensor for an "average" conformer is determined. A decoupled model is used to describe correlated internal motions of the end chain, which are independent of the molecular reorientation. The latter motion is treated using the small-step rotational diffusion model of Tarroni and Zannoni, while the former motion is described using a master rate equation.

碩士
國立臺北科技大學
有機高分子研究所
91
The first part of this thesis is to analyze the molecular arrangement of bis[1-3´,4´,5´-trioctyloxyphenyl-3-(4´-octyloxphenyl) propane-1,3-dionate] palladium (II) (Pd(II)BPOC8) and bis[1-3´,4´,5´-trihexadecyloxyphenyl-3-(4´-hexadecyloxy-ph- enyl)-propane-1,3-dionate] palladium (II) (Pd(II)BPOC16), two discotic metallomeso- gens, on the basal plane of HOPG. Experimentally, it was observed by scanning tunnelling microscopy (STM) with near molecular resolution that these molecules form regular and cognate surface structures upon adsorption on HOPG. However, the expansion of 2D array is not proportionate in two unit vectors, suggesting that the Pd(II)BPOCn assembling process is correlated with the conformation structure of alkoxy substitution which might affect the way molecules interdigitate. Using molecular simulation technique, a simplified model for the molecular packing pattern of Pd(II)BPOC16 on HOPG has been deduced and compared to that of Pd(II)BPOC8. The second part of this thesis is to synthesize the derivatives of newly designed rod-like liquid crystal molecules (compound 1, n= 3, 6, and 16), by means of the following reaction scheme : The resulting compounds were characterized using NMR, IR, EA, MASS, DSC, and POM. For n=3 and n=6, the molecules show nematic liquid crystal phase, while for n=16, only smetic C phase was observed. A complete discussion for the variation of mesophase as a function of chain length is also given in this thesis.