We hope to achieve the goal of improving molecule nature of the liquid crystal by change the functional group or the symmetry of the molecule. In the thesis, the derivatives of dibenzophenazine are synthesized and their mesogenic properties are investigated. Polarised optical microscopy (POM) and differential scanning calorimetry (DSC) studies show all these compounds to exhibit a very wide mesophase range. These mesophases are identified as columnar hexagonal phases by X-ray diffraction (XRD).

Discotic liquid crystal (LC) molecules have a structure that is comprised of a rigid aromatic core with side-chain molecules. Intermolecular £k-£k interactions force the tube to orient and form one-dimensional columnar structures which can act as molecular wires. In recent years, discotic LC molecules have been deposited on surfaces from solution to create the solid-state electronic elements used widely in solar cells, organic light-emitting diodes (OLED), organic photovoltaic, field-effect transistors (FET), and molecular wires. Different stacking morphologies can change the behavior of the material and thus will have potential for different applications. Hence, effective control over the stacking of the LC molecules on surfaces is important for optimizing the performance and effectiveness of LC-based electronic components and devices. This study has focused on LC molecules with acid and ester containing functional groups, and how these groups influence the stacking behavior on surfaces. Here, the self-aggregation behavior of the discotic LC ester in solution was investigated quantitatively by determining the concentration dependence of the 1H NMR chemical shifts. Our results showed that discotic LC ester has different self-aggregation behavior in CH2Cl2, THF and Benzene organic solvents. THF solvent showed the highest degree of aggregation, followed by CH2Cl2, and then benzene. We also studied the effects of (i) different solvents (THF, CH2Cl2, and Benzene), (ii) different surface functional groups (OH, CH3, NH2, SH, and diphenyl), and (iii) temperature, on the stacking phenomenon of discotic LCs on silicon surfaces. In part (i) our results showed that discotic LC ester had different morphologies on silicon surfaces due to differences in solvent polarity and evaporation rate. In part (ii), we observed that different surface functional groups did not affect the intermolecular interaction between either the ester- or acid-type LC molecules. For the acid-type LC, strong hydrogen bonding interactions with the surface caused the crystals to form rod-like fiber structures. However, the ester-type LC molecules formed ribbon-like stacks on the surfaces. For functional groups containing CH3 (more hydrophobic surfaces), we observed no LC molecules on the surface, which was likely due to the poor wettability of the solvents on OTS. In part (iii), we observed that both acid and ester discotic LCs formed large aggregates on the surfaces due to a ¡§ripening effect¡¨. With increased temperature, the molecules were able to overcome the wetting interaction with the surface and self-aggregate into three-dimensional clusters.

This dissertation focuses on structural and electrical characterization of self-organizing discotic molecular materials, specifically alkoxy and thioether side chain modified copper phthalocyanines, both in bulk and at organic/dielectric and organic /metal interfaces. A great deal of effort has been focused on understanding the self-organizing nature in these materials since molecular ordering is believed to control the intrinsic physical as well as electrical properties of these molecular aggregates. It was determined that side chains in these Pcs have a significant impact on the general ordering in these materials: alkoxy side chain modification favors a columnar hexagonal phase with a cofacial intracolumn alignment; thioether side chain modification, however, favors a tilted intracolumn alignment and much rigid columnar packing, driven by sulfur-sulfur interactions among adjacent molecular disks. Incorporation of styrene functionality in the side chain has been shown to enable photopolymerization. An optimal hexagonal columnar packing has been proved to be stabilized via photolysis at the mesophase. It is critical to explore the molecular ordering as well as the charge transport characteristics at interfaces since the organic/dielectric interface controls the charge accumulation in organic field-effect transistors (OFETs) and the metal/organic interface determines the charge injection in devices such as organic photovoltaic cells (OPVs). Two analytical tools have been developed in this dissertation work that successfully address these interfacial issues from a molecular level. 1) Probing interfacial structures at the organic/dielectric interface with X-ray reflectometry (XRR). Surface chemistry has shown a drastic impact on the ordering of the initially deposited materials. Surface engineering strategies, i.e. chemical modification, have been shown to significantly improve the coherence of molecular assemblies thereby optimizing charge transport properties of these molecular materials in an OFET platform. 2) Exploring charge injection and transport characteristics at molecular junctions with conductive-probe AFM (C-AFM). Charge injection processes at the metal/organic molecular junction have shown a strong dependence on the microstructure of these molecular materials. Thermionic emission and field emission were shown to be competing processes at these junctions. One dimensional charge transport is realized only with the appropriate molecular ordering in these discotic materials at metal/organic junctions. 3) Exploring structural and electrical properties of ITO with C-AFM. The ITO surfaces have shown both structural and electrical heterogeneity at the nanometer scale. A tunneling model has been proposed and the presence of thin insulating layers was believed to be the cause of electrically inactive regions of ITO. Aggressive chemical etching protocols have been developed and shown to improve the percentage of surface electrically active area, thereby, enhancing the electrode performance.

Solvent-mediated self-assembly of nanoparticles is an effective and efficient way for the bottom-up organization of functional structures. The primary object of this work is to build up a model system for the study of suspensions of disk-shaped nanoparticles, and use it for the study of self-assembly and discotic liquid crystal phase transitions of discotic particles. The work was introduced by the control over the size and polydispersity of zirconium phosphate (ZrP) disks through synthesis. Systematic experiments revealed that regular-shaped α-zirconium phosphate crystalline disks with a size-to-thickness ratio from 1 to 50 and size polydispersity as low as 0.2 can be obtained through hydrothermal treatment in 3 M to 15 M phosphoric acid solutions. Transmission and scanning electron micrographs revealed that the growth of the disks is mediated by oriented attachment, which happened continuously throughout the hydrothermal treatment between various sized disks. Ostwald ripening is effective in improving the regularity of the shape of the disks, especially under prolonged hydrothermal treatment. Under the microwave assisted hydrothermal conditions, the rate of attachment on the flat surfaces of the disks is accelerated, which leads to the formation of the column-shaped crystals. With the ability to adjust the size, aspect ratio, and polydispersity of ZrP disks, the study on self-assembly behavior and the discotic liquid crystal phases was enabled. Firstly, liquid crystal phases of aqueous suspensions of ZrP disks were investigated. Iridescent smectic phase and the critical points of phase transitions were found. Moreover, monolayer ZrP nanosheets with extremely high aspect ratio, which were achieved by exfoliating the ZrP crystals, were also used in this study. The high aspect ratio of nanosheets produces a laminar phase at low nanosheet concentration. Chiral liquid crystal phases were demonstrated when increased the concentration of the nanosheets. The competition between the chirality and layering leads to twisted and layered structures. For the final part, solvent-mediated self-assembly of disks and nanosheets via undulation of liquid crystal phases showed an interesting approach for bottom-up design of functional nano-structures.

Disc like molecule which was formed by fused polyaromatics was found to be with discotic liquid crystal properties. So it has been researched thoroughly. We take 5,6,11,12,17,18-hexaazatrinaphthylene (HTN) as our central core and synthesize Hexa-O-substituted hexaazatriphenylene, a new molecule with discotic liquid crystal properties successfully.

Because of the unique physical properties of liquid crystal molecules, such as: light, electricity, magnetic anisotropy, they exhibit different values, the most known current application on displays in our life. As the liquid crystal molecules can be modified through the functional groups, thereby affecting its physical properties, it caused great interests in synthetic chemists. In this thesis, we synthesized liquid crystal based on dibezo[a,c]phenazine core and the dioxole skeleton was also induced into dove-tail alkyl chain functional group surrounding the central aromatic core . Moreover, we also change the chain length of alkyl chain to explore stacking arrangement structure of the mesophase. By the various instruments to explore the nature of stacking, we preliminary assumed that the mesophase might exhibit the helical stacking with excellent charge mobility, which could be good candidates for optical and electrical applications.

Part 1. Discotic liquid crystals are a relatively new class of mesogens in which the molecules self assemble in the melt state to form highly ordered columnar stacks. The ability of the molecules to display this type of mesomorphic behavior is a function of their shape; a semi-rigid core with flexible "arms" gives the necessary flatness and broad diameter conducive to columnar stacking. We first set out to make discotic liquid crystals by synthesizing a series of three-armed aryloxy-s-triazines with aromatic Schiff's base moieties at the molecular periphery and investigate the thermal and optical behavior of these compounds. We discovered that these molecules were in fact rigid rod, or calamitic, liquid crystals based on the optical textures and X-ray diffraction patterns in the mesophase. This is in direct conflict with published but unsubstantiated reports of the "discotic” behavior of similar compounds. The failure of these compounds to give crystals suitable for X-ray crystal structural analysis prompted us to utilize electron microscopy to look at the microstructures formed when dilute solutions were evaporated onto different substrates. Surprisingly, these aryloxy-s-triazines in several different solvents formed well defined microtubules of varying dimensions on both copper and polymeric substrates. Hole diameters of up to 10³ Å and lengths of up to 0.5 cm were commonly seen using both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Finally, we understood via molecular modeling studies that the aryloxy-s-triazines adopted a rod shape in the mesophase due to the inherent flexibility of the ether linkages at the triazine core. By substituting 1,3,5-triphenylbenzene cores in place of the s-triazine we hoped to rigidify the molecules and prompt them to stack in a discotic or columnar fashion in the melt state. This plan was successful based on the X-ray diffraction patterns and optical textures observed with these compounds in the mesophase. Part 2. α-Aminonitriles and their derivatives have played an important role in the synthesis of enantiomerically pure and racemic α-amino acids for almost ninety years. Much less studied is the alkylation behavior of this particular class of compounds. The ability of the aminonitrile moiety to be deprotonated with a base and reacted with various electrophiles allows for the placement of carbonyl functionalities virtually anywhere in a synthetic system through hydrolysis of this aminonitrile group after alkylation. Using this "umpolung”, or reversed polarity, approach we have demonstrated the utility of this class of compounds by reacting them with several activated aromatic dihalides and aliphatic dihalides to produce high molecular weight poly(bis-α-aminonitrile)s which were in turn hydrolyzed under mild conditions to afford the corresponding polymeric ketones. This ability to form both wholly aromatic and mixed aliphatic/aromatic polyketones is extremely powerful and unprecedented in the literature to date. During the course of this research, it was also discovered that some of these α-aminonitriles underwent side reactions which were undesirable for polymerization but which produced interesting compounds in their own right. These enaminonitriles and quinodimethanes which resulted from dehydrocyanation were studied extensively in order to exploit the possible polymerization of these reactive intermediates. Finally, another route to ketones is through the reaction of enamines with appropriate electrophiles followed by acid hydrolysis. Research towards polymeric ketones was Carried out using monomeric di(enamine)s and aromatic diacid chlorides with the hope of producing high molecular weight polymeric 1,3-diketones. Unfortunately, the extent of reaction was not high enough to produce high molecular weight polymers. / Ph. D.

No description available.

Il est actuellement bien connu que les molécules non sphériques peuvent former des mésophases (ou cristaux liquides), c'est-à-dire des phases dont les propriétés sont intermédiaires entre celles des liquides et celles des cristaux. La mésophase la plus connue est la phase nématique. Il s'agit d'une phase caractérisée par une distribution aléatoire des centres de masse des molécules, mais dans laquelle l'orientation des molécules présente une direction préférentielle, désignée par un vecteur unité appelé le directeur du nématique. Une telle phase possède donc la fluidité d'un liquide tout en présentant, tel un cristal, une biréfringence. C'est cette dernière propriété qui est exploitée dans les applications technologiques, principalement dans les dispositifs d'affichage. Dans un tel dispositif, le liquide nématique est contenu dans une cellule (il y a une cellule par pixel), et son directeur est manipulé à l'aide d'un champ extérieur, électrique ou magnétique. Pour une bonne compréhension du fonctionnement de ce dispositif, il est essentiel de connaître le profil du directeur à travers la cellule en l'absence de champ extérieur. Dans le cadre de ce travail, nous avons étudié un nématique torsadé, c'est-à-dire dont le directeur décrit une hélice à travers la cellule. Ce profil est déterminé principalement par les propriétés d'ancrage du liquide nématique sur les parois solides de la cellule. En effet, celles-ci peuvent posséder une direction d'ancrage privilégiée, qui favorise l'alignement du directeur dans une direction particulière. Nous avons considéré ici le cas de directions d'ancrage planaires, c'est-à-dire que le directeur est dans le plan des parois. Alors que l'ajout de parois identiques dans le système induit toujours une non-uniformité spatiale dans la densité du nématique (en comparaison avec un nématique en coeur de phase), l'utilisation de directions d'ancrage différentes induit une non-uniformité orientationnelle dans le directeur du nématique; dans notre cas une torsion. C'est principalement ce profil de directeur torsadé qui nous intéresse ici. L'objectif général de ce travail consiste donc à étudier les propriétés d'ancrage d'une phase nématique confinée et torsadée, d'une part par une théorie microscopique (théorie de la fonctionnelle de la densité), et d'autre part sur le plan de simulations de Monte Carlo, en particulier dans le cas où les molécules ont la forme de disques (discotiques).

Discotic liquid crystals (DLCs), which consist of disc-like molecules, are known to be able to form nematic and columnar mesophases through self-assembly. Because of the high electric charge mobility in one-dimension, DLCs are found to have uses in making electronic and photonic devices, such as organic light emitting diode, photovoltaic and molecular wires. In order to achieve better performance of these applications, it is essential to obtain the desired alignment of the DLCs. The purpose of this study is to investigate the stacking of disk-like molecules and to control their alignment. The materials used in the present studies are HDBP-8 and LC10. In this thesis, we will show that the stack of disk-like molecules is strongly influenced by temperature. We will also discuss how the molecules stacking is influenced by surface free energy. The disk-like molecules tend to stack with face-on when the surface free energy of the substrates is high. On a surface with lower surface free energy, molecules tend to stack with edge-up. In the latter part of the research, substrates are specially treated to have different surface free energies, and molecular stack on these substrates is observed.