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.

The thesis is divided into two parts. One is about the preparation of discotic liquid crystals Acid-6. The other is about the growth of Acid-6 thin film by thermal evaporation on silicon oxide surfaces and modified silicon oxide surfaces such as self-assembled monolayer(SAM) in different temperature. The surface morphology and molecular orientation of the thin film were studied by Atomic Force Microscopy(AFM) , X-ray Diffraction (XRD) , and then they were applicated to organic thin film transistor and measured properties by Semiconductor Parameter Analyzer. In the second part of our research, our expectative characteristics was not observed in different temperature and substructure. In the other side, we guessed that because discotic liquid crystals Acid-6 is negative semiconductor materials, so it is susceptible to hydrosphere, thus we can¡¦t observe the electric characteristic of OTFT in the atmosphere. In addition, due to discotic liquid crystals Acid-6 have biggish moleculer weight, thus its viscosity was so big that cause the diameter of Acid-6 crystals to be too small. Therefore, it influenced the carrier mobility. Finally, from the aspect of procedure about fabrication of the devices we can discuss whether this parameter of this device can apply to OTFT.

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We take the electron deficient heterocyclic hexaazatriphenylene (HAT) as our central core and readily synthesized by the condensation of hexaketo- cyclohexane with the respective 1,2-bis-alk-oxy-4,5-diaminobenzene. We use the polarised optical microscopy (POM) and differential scanning calorimetry (DSC) to study the mesophase range.These mesophases are identified as columnar phases by diffraction (XRD).

This dissertation describes the study of organic thin-film solar cells in pursuit of affordable, renewable, and environmentally-friendly energy sources. Particular emphasis is given to the molecular ordering found in liquid crystalline or polycrystalline films as a way to leverage the efficiencies of these types of cells. Maximum efficiencies estimated based on excitonic character of organic solar cells show power conversion efficiencies larger than 10% are possible in principle. However, their performance is often limited due to small exciton diffusion lengths and poor transport properties which may be attributed to the amorphous nature of most organic semiconductors.Discotic liquid crystal (DLC) copper phthalocyanine was investigated as an easily processible building block for solar cells in which ordered molecular arrangements are enabled by a self-organization in its mesophases. An increase in photocurrent and a reduction in series resistance have been observed in a cell which underwent an annealing process. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements suggest that structural and morphological changes induced after the annealing process are related to these improvements.In an alternative approach, p-type pentacene thin films prepared by physical vapor deposition were incorporated into heterojunction solar cells with C60 as n-type layers. Power conversion efficiencies of 2.7 % under broadband illumination (350-900 nm) with a peak external quantum efficiency of 58 % have been achieved with the broad spectral coverage across the visible spectrum. Analysis using an exciton diffusion model shows this efficient carrier generation is mainly due to the large exciton diffusion length of pentacene films. Joint XRD and AFM studies reveal that the highly crystalline nature of pentacene films can account for the observed large exciton diffusion length. In addition, the electrical characteristics are studied as a function of light intensity using the equivalent circuit model used for inorganic pn-junction solar cells. Dependences of equivalent-circuit parameters on light intensity are further investigated using a modified equivalent circuit model, and their effects on the overall photovoltaic performance are discussed.

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Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-07-21T16:17:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ATUALIZADA DISSERTAÇÃO_ARTHUR_UFPE_.pdf: 6640779 bytes, checksum: 54162674f1fcaee2b4fef8836f21cd72 (MD5) / Made available in DSpace on 2016-07-21T16:17:26Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ATUALIZADA DISSERTAÇÃO_ARTHUR_UFPE_.pdf: 6640779 bytes, checksum: 54162674f1fcaee2b4fef8836f21cd72 (MD5) Previous issue date: 2016-03-30 / CNPQ / O estudo das propriedades de materiais orgânicos tem chamado atenção devido sua versatilidade estrutural e de composição que podem moldar suas propriedades físicas e químicas. Neste trabalho preparamos seis cromóforos rígidos contendo o heterociclo tiazolo[5,4-d]tiazol (Thz) como espaçador aromático, e grupos terminais piridínicos ou carboxílicos. Desta forma trabalhamos com duas linhas de pesquisa: foto-eletroquímica para os derivados piridínicos e síntese e caracterização de cristais líquidos (CLs). Investigamos as propriedades fotoquímicas e processos redox das bipiridinas X,X'-(tiazolo[5,4-d]tiazol-2,5- dil)bis(piridil) (X,X’ = 2,2’; 3,3’ ou 4,4’). Em solução, apresentaram propriedades acidocrômica via foto- e eletrodissociação de solventes clorados. A seguir, preparamos sais de trifluoracetato dos bipiridínio (viologens), que apresentaram propriedades fotocromáticas via transferência de elétron quando expostos à radiação UVB. Utilizamos os derivados carboxílicos como centros rígidos para a preparação de cristais líquidos. Escolhemos o grupo carboxilato como precursor sintético dos conectores orgânicos: éster, amida e 1,3,4-oxadiazol. Planejamos os cristais líquidos contendo tais conectores e cadeias alquílicas dodeciloxi (-OC12H25), obtendo materiais com estrutura geral: centro rígido + conectores + cadeias alcóxi. De acordo com a estrutura dos centros rígidos, preparamos treze mesógenos calamíticos (ácido tiazolo[5,4- d]tiazol-2,5-dicarboxílico), das quais seis apresentaram mesofases calamítica (comportamento esperados) e três apresentaram mesofases discóticas. O fotocromismo apresentado pelos sais de bipiridinas frente à radiação UVB nos permite sugerir aplicações como dosimetria desta radiação, presente na luz solar. As propriedades mesomórficas ainda estão em estudo. No entanto, conseguimos obter CL’s discóticos a temperatura ambiente e uma mesofase discótica nemática, bastante rara. / The study properties of organic materials has drawn attention due to its structural versatility and composition versatility, which can shape their physical and chemical properties. In this work, we prepared six rigid chromophores containing the heterocycle thiazolo[5,4-d] thiazole (Thz) as aromatic spacers, and pyridyl or carboxylic terminal groups. Hence, we have worked with two research lines: photo-electrochemistry for the pyridine derivatives and synthesis and characterization of liquid crystals (LCs). We investigated the photochemical properties and redox processes of the bipyridines X,X'-(thiazolo[5,4-d] thiazole-2,5-diyl)bis(pyridyl) (X,X' = 2,2 '; 3,3' or 4,4 '). In solution, these compounds showed acidochromic properties via photonand electrodissociantion of chlorinated solvents. Next, we prepare bipyridinium trifluoroacetate salts (viologens), which exhibited photochromic properties through electron transfer when exposed to UVB radiation. We used the carboxylic derivatives as rigid centers for the preparation of liquid crystals. We chose the carboxylate group as a synthetic precursor of organic connectors: esther, amide, and 1,3,5-oxadiazole. We plannned the liquid crystal containing these connectors and the alkoxy chains dodecyloxy (-OC12H25), obtaining materials with general structure: rigid center + connectors + alkoxy chains. According to the rigid center structure, we obtained thirteen calamitic (acid thiazolo [5,4-d] thiazole-2,5-dicarboxylic acid), six of which had mesophases calamítica (expected behavior) and three had discóticas mesophases. The photochromic presented by bipyridinium salts when exposed of UVB radiation allows suggest applications such as dosimetry of sunlight radiation. The mesomorphic properties are still under study. However, we obtained room temperatures discóticos LCs, as well as a nematic discótica mesophase which are quite rare.

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No description available.