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Spectroscopic Studies of Nanomaterials with a Liquid-Helium-Free High-Stability Cryogenic Scanning Tunneling MicroscopeKislitsyn, Dmitry 01 May 2017 (has links)
This dissertation presents results of a project bringing Scanning Tunneling Microscope (STM) into a regime of unlimited operational time at cryogenic conditions. Freedom from liquid helium consumption was achieved and technical characteristics of the instrument are reported, including record low noise for a scanning probe instrument coupled to a close-cycle cryostat, which allows for atomically resolved imaging, and record low thermal drift. Subsequent studies showed that the new STM opened new prospects in nanoscience research by enabling Scanning Tunneling Spectroscopic (STS) spatial mapping to reveal details of the electronic structure in real space for molecules and low-dimensional nanomaterials, for which this depth of investigation was previously prohibitively expensive.
Quantum-confined electronic states were studied in single-walled carbon nanotubes (SWCNTs) deposited on the Au(111) surface. Localization on the nanometer-scale was discovered to produce a local vibronic manifold resulting from the localization-enhanced electron-vibrational coupling. STS showed the vibrational overtones, identified as D-band Kekulé vibrational modes and K-point transverse out-of plane phonons. This study experimentally connected the properties of well-defined localized electronic states to the properties of associated vibronic states.
Electronic structures of alkyl-substituted oligothiophenes with different backbone lengths were studied and correlated with torsional conformations assumed on the Au(111) surface. The molecules adopted distinct planar conformations with alkyl ligands forming cis- or trans- mutual orientations and at higher coverage self-assembled into ordered structures, binding to each other via interdigitated alkyl ligands. STS maps visualized, in real space, particle-in-a-box-like molecular orbitals. Shorter quaterthiophenes have substantially varying orbital energies because of local variations in surface reactivity. Different conformers of longer oligothiophenes with significant geometrical distortions of the oligothiophene backbones surprisingly exhibited similar electronic structures, indicating insensitivity of interaction with the surface to molecular conformation.
Electronic states for annealed ligand-free lead sulfide nanocrystals were investigated, as well as hydrogen-passivated silicon nanocrystals, supported on the Au(111) surface. Delocalized quantum-confined states and localized defect-related states were identified, for the first time, via STS spatial mapping. Physical mechanisms, involving surface reconstruction or single-atom defects, were proposed for surface state formation to explain the observed spatial behavior of the electronic density of states.
This dissertation includes previously published co-authored material.
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Synthèse et caractérisation photophysique et électrochimique d'une nouvelle classe de composés à base de fluorène et 2-thiophènePérez Guarín, Sergio Andrés January 2007 (has links)
No description available.
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Estudo da adsorção de tiofeno e propanotiol em zeólitas MY (M=H+, Na+, Ag+, Cu+ e Zn2+) com métodos híbridos de química computacionalOLIVEIRA, Paulo McMiller Crisostomo de 23 August 2013 (has links)
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Previous issue date: 2013-08-23 / FACEPE / A adsorção de compostos organossulfurados está se tornando um processo
importante na remoção de enxofre de combustíveis derivados de petróleo. Neste
contexto, realizamos modelagem molecular com método de química
computacional da adsorção de compostos orgânicos sulfurados alifáticos
(propanotiol) e aromáticos (tiofeno) em zeólita Y com os cátions de compensação
de carga H+, Na+, Ag+, Cu+ e Zn2+. As estruturas e as energias de adsorção foram
obtidas com cálculos de química quântica empregando o método ONIOM com
três (PBE1PBE:HF:UFF=QEQ) e duas (PBE1PBE:UFF=QEQ) camadas,
respectivamente, para simular a contribuição do ambiente químico da estrutura
cristalina com um modelo extenso contendo 1473 átomos, denominado, Z40-nT,
com n = 3, 5, 6, 7 e 12 sendo o número de tetraedros SiO4 e AlO4 utilizados nas
vizinhanças da adsorção. Constatou-se que as estruturas obtidas possuem boa
concordância entre si e que fornecem os modos de interação entre o composto
sulfurado e a zeólita. No caso do tiofeno, o modo de coordenação η1S, apesar
de ser menos estável, em que o enxofre do anel interage diretamente cátion foi
aquele que forneceu os melhores resultados com relação aos valores das
energias de adsorção. Disso advém a suposição de que há uma preferência
maior por esse modo de adsorção num sistema real. As zeólitas estudadas
demonstraram alta capacidade de interação com os compostos sulfurados,
justificando assim a potencialidade do uso desses materiais no processo de
dessulfurização adsortiva de combustíveis derivados do petróleo. Para a
adsorção do tiofeno os valores da energia de adsorção crescem em função do
cátion na ordem: H+ < Na+ < Ag+ < Cu+ < Zn2+, para o sítio de adsorção SIII. No
sítio SII as interações com os cátions dos metais de transição são similares.
Estes resultados estão de acordo com o que é observado dos dados
experimentais disponíveis. Para adsorção de propanotiol obtivemos a ordem Na+
< H+ < Ag+ < Cu+ < Zn2+ e esses resultados são inéditos na literatura. / The adsorption of organosulfur compounds is becoming an important process in
desulfurization of fossil fuels. In this context, we performed molecular modeling,
through computational chemistry method, the adsorption of aliphatic
(propanethiol) and aromatic (thiophene) organosulfur compounds in faujasites
zeolites (Y) with four compensation charges: H+, Na+, Ag+, Cu+ and Zn2+. The
structures and adsorption energies were obtained by quantum chemical
calculations employing ONIOM with three (PBE1PBE:HF:UFF=QEQ) and two
(PBE1PBE:UFF=QEQ) layers, respectively, to simulate the chemical
environment contribution of the crystalline structure with a model containing 1473
atoms called Z40-nT, where n = 3, 5, 6, 7 and 12 is the number of tetrahedral
SiO4 and AlO4 used in the site of adsorption. It was found that the structures
obtained showed good agreement between themselves and provide the modes
of interaction between the sulfur compound and the zeolite. For the thiophene,
the coordination mode η1S, although less stable, wherein the sulfur ring interacts
directly with the cation, was that which gave the best results for the values of the
adsorption energies. Thus it comes the assumption of that coordination mode has
a higher preference for adsorption in a real system. Zeolites studied showed a
high capacity for interaction with sulfur compounds, thus justifying the potential
use of these materials in the adsorptive desulfurization of petroleum fuels. For
thiophene, the adsorption energy values, according to the cation, grow in order:
H+ < Na+ < Ag+ < Cu+ < Zn2+ for the adsorption site SIII. On the site SII,
interactions with cations of transition metals are similar. These results are
consistent in good quantitative agreement with the available experimental data.
For adsorption of propanethiol we obtained the order Na+ < H+ < Ag+ < Cu+ < Zn2+
and these results are unpublished in the literature.
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Estudo de adsorÃÃo de tiofeno em carbono ativado / Study thiophene adsorption in activated carbonAna VÃvian Parente Rocha 29 January 2010 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A qualidade do ar e a preocupaÃÃo com o meio ambiente e a saÃde da populaÃÃo tÃm influenciado as regulamentaÃÃes de emissÃes veiculares. A exemplo de ÃrgÃos governamentais em todo o mundo, a AgÃncia Nacional do PetrÃleo, GÃs Natural e BiocombustÃveis (ANP) do Brasil tem estabelecido cronogramas de reduÃÃo drÃstica de sulfurados no diesel e na gasolina nos Ãltimos anos. A hidrodessulfurizaÃÃo (HDS) à o processo classicamente utilizado atualmente para reduzir o teor de enxofre em correntes de hidrocarbonetos. No entanto, o processo HDS à caro, pois requer elevadas temperaturas e pressÃes e hidrogÃnio, podendo levar à saturaÃÃo de compostos olefÃnicos, o que compromete a octanagem da gasolina. Dessa forma, atenÃÃo especial vem sendo dada ao uso da adsorÃÃo para remoÃÃo de compostos sulfurados que poderà complementar ou â em alguns casos â substituir os processos existentes de hidrotratamento (HDT). Esse processo de adsorÃÃo pode ser realizado a temperatura e pressÃo ambiente. Neste trabalho foi realizado um estudo de remoÃÃo de enxofre a partir de soluÃÃes tiofeno/n-hexano, tiofeno/n-octano e tiofeno/tolueno/n-octano e um estudo de seletividade tiofeno/tolueno utilizando como adsorvente o carbono ativado 830 W da Norit (Holanda). O material foi caracterizado texturalmente por adsorÃÃo de N2 a 77 K. Os resultados indicaram ser um material microporoso. A adsorÃÃo do tiofeno em n-hexano e a seletividade tiofeno/tolueno foi avaliada usando a tÃcnica experimental de banho finito com cromatografia headspace. A isoterma de adsorÃÃo obtida em headspace apresentou um comportamento desfavorÃvel para o tiofeno e o adsorvente estudado foi seletivo pelo tolueno em relaÃÃo ao tiofeno, sendo observado um ponto de saturaÃÃo em razÃes lÃquido/sÃlido inferiores a 4%. Jà a adsorÃÃo do tiofeno em n-octano e em n-octano/tolueno foi avaliada atravÃs de um estudo dinÃmico de adsorÃÃo usando uma coluna de leito fixo com uma vazÃo de 0,5 mL/min a duas temperaturas distintas com concentraÃÃo de alimentaÃÃo na faixa de 275 a 1000 ppm. As isotermas de equilÃbrio assim obtidas encontram-se na regiÃo de Henry (linear) com a constante de adsorÃÃo K = 3,7 e 3,0 para temperaturas de 30 ÂC e 45 ÂC, respectivamente. Obteve-se para concentraÃÃo de 1000 ppm sem tolueno uma quantidade adsorvida de 0,035 mmolS/gads, que se reduz para 0,020 mmolS/gads na presenÃa do aromÃtico (20 % vol.). Pode-se observar que â em toda a faixa de concentraÃÃes de sulfurado estudada â a quantidade de tiofeno adsorvida diminuiu consideravelmente na presenÃa do tolueno. Curvas de breakthrough do tiofeno em n-octano foram simuladas segundo um modelo matemÃtico que considera fluxo axialmente disperso e transferÃncia de massa descrita por uma aproximaÃÃo de forÃa motriz linear (LDF). O modelo foi resolvido numericamente por colocaÃÃo ortogonal em elementos finitos, utilizando o software comercial gPROMS. O modelo matemÃtico proposto representou razoavelmente os dados experimentais, especialmente para concentraÃÃo de 1000 ppm. A constante de tempo de transferÃncia de massa foi o parÃmetro de ajuste entre as simulaÃÃes e os dados experimentais, estimando-se valores mÃdios de 3,3 e 2,2 min-1 a 30 e a 45 ÂC, respectivamente. / Concerns with environmental protection and human health have had a remarkable impact on vehicle emissions regulations. Following similar policies of governmental agencies worldwide, Brazilian AgÃncia Nacional do PetrÃleo, GÃs Natural e BiocombustÃveis (ANP) has established a timetable for drastic reduction of sulfur content in diesel and gasoline in the last few years. Hydrodesulfurization (HDS) is the industrial process being currently employed for this matter. However, the HDS process is costly and, to achieve deeper desulfurization levels, it would require higher hydrogen pressure, which may eventually lead to the saturation of olefinic compounds, causing a decrease in gasoline octane number. Therefore, special attention has been given to the use of adsorption for additional removal of sulfur compounds from effluent streams of existing hydrotreatment (HDT) plants. Adsorption processes may operate under mild temperature and pressure conditions. In the present work, desulfurization in thiophene/n-hexane, thiophene/n-octane and thiophene/toluene/n-octane mixtures were conducted, together with a study of thiophene/toluene selectivity, all experiments using activated carbon 830 W by Norit (Netherlands) as sorbent. The adsorbent was characterized texturally by adsorption/desorption of N2 at 77 K and results showed it to be a microporous material. Adsorption of thiophene from n-hexane solutions and thiophene/toluene selectivity were carried out using the experimental technique of headspace chromatography finite bath. Adsorption isotherms thus obtained showed unfavorable behavior and the adsorbent selectively adsorbs toluene as compared to thiophene, reaching maximum selectivity on liquid/solid ratio of less than 4%. Adsorption of thiophene in n-octane and n-octane/toluene (4:1 vol.) was assessed by fixed bed experiments performed under a flow rate of 0.5 mL/min, two different temperatures and sulfur concentration in the feed ranging from 275 to 1000 ppm. Adsorption isotherms thus measured fall within the Henryâs Law region (linear) with dimensionless adsorption constants of 3.7 and 3.0 at 30 ÂC and 45 ÂC, respectively. For the feed concentration of 1000 ppm in n-octane, the measured dynamic adsorption capacity was 0.035 mmolS/gads, which was reduced to 0.020 mmolS/gads when toluene was present. Regardless the inlet sulfur concentration, the amount of adsorbed thiophene decreased considerably in the presence of the aromatic compound. Breakthrough curves of thiophene in n-octane were simulated according to a mathematical model that assumed axially dispersed flow and mass transfer described by a linear driving force approximation (LDF). The model was solved numerically by orthogonal collocation in finite elements, using the commercial solver gPROMS. The proposed model matched experimental data reasonably well, especially for the feed concentration of 1000 ppm. The LDF time constant was the tunable parameter between simulations and experimental data and the best average values were found to be 3.3 and 2.2 min-1 at 30 and 45 ÂC, respectively.
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Nouveaux oxydes nanostructurés pour la désulfuration : cinétique et mécanismes d'interaction avec le sulfure d'hydrogène et le thiophène / New nanostructured oxides for the desulfurization : kinetic and interaction mechanisms towards hydrogen sulfur and thiopheneSkrzypski, Jonathan 17 March 2011 (has links)
Ce travail de thèse s’inscrit dans le contexte de la désulfuration par absorption des gaz utilisables dans des technologies émergentes comme les piles à combustible ou le procédé Fischer-Tropsch. Cette purification peut être réalisée à des températures modérées (200-300°C) sans régénération d'échantillon. L’absence de traitements à haute température permet d'envisager l'utilisation des solides nanostructurés qui devraient montrer naturellement une réactivité élevée. En fonction du schéma précis du procédé, on pourra être amené à éliminer des molécules de nature différente : H2S ou des molécules réfractaires comme mercaptans ou thiophènes. Pour répondre à ces exigences, la thèse s'est déroulée en deux parties. Dans la première partie des échantillons à base de nanoparticules de ZnO pur et dopé (M0,03Zn0,97O, M=Fe, Co, Ni, Cu) ont été préparés, caractérisés et leur réactivité vis-à-vis d’H2S a été étudiée. Il a été trouvé que le cuivre est le dopant qui permet d’améliorer le plus les performances de l’échantillon. L'étude du mécanisme de sulfuration par MET, DRX in situ et XPS a permis de conclure que la diffusion des ions O2- à travers la couche de ZnS est l'étape limitante de la sulfuration. Son accélération en présence de cuivre serait due à la formation d'une solution solide Cu2S-ZnS riche en lacunes anioniques. La deuxième partie du travail a été consacrée à l'élimination du thiophène. Un nouveau solide nanocomposite 2,8NiO-H1,8Ni0,6(OH)MoO4 a été mis au point. Sa structure ouverte sous forme de feuillets et sa capacité à se réduire facilement en présence d’H2 créent des conditions propices pour l'interaction avec le thiophène et permettent ainsi d'augmenter considérablement sa vitesse de sulfuration en comparaison avec l'échantillon classique à base de Ni/ZnO. Sa haute réactivité avec le thiophène en fait un excellent candidat pour éliminer les traces d’autres espèces sulfurées (COS, CS2, mercaptans). / This work focuses on the desulfurization by absorption of gases which can be used inemerging technologies such as fuel cells or Fischer-Tropsch process. This purification canbe achieved at low temperatures (200-300°C) without regeneration of the sorbent. Theabsence of high temperature treatment allow to use nanostructured solids wich can normallymust exibit higher reactivity. Depending on the process chosen, we will have to eliminatemolecules of different nature : H2S or molecules like mercaptans or thiophene. To answerthese requirements, the thesis work consisted of two parts. In the first part, nanoparticles ofpure and doped ZnO (M0,03Zn0,97O, M=Fe,Co,Ni,Cu) were synthesized and characterized,and their reactivity towards H2S was investigated. It was found that copper is the dopandwhich allow to improve considerably the performances of the sorbent. The study ofsulfidation mechanism by TEM, in situ XRD and XPS allow to conclude that diffusion ofO2- ions trough the ZnS layer is the rate limiting step of sulfidation. The acceleration in thepresence of copper may be due to formation of a solid solution Cu2S-ZnS rich in anionicvacancies. The aim of the second part of this work was to eliminate thiophene. A newnanocomposite solid 2,8NiO-H1,8Ni0,6(OH)MoO4 was prepared. Its layered open structureand its ability to be easily reduced create favorable conditions for interactions withthiophene, and in this way, allow to increase considerably its sulfidation rate (in comparisonwith the sulfidation rate of the classical sample Ni/ZnO). Its high reactivity with thiophenemakes it an excellent candidate for the elimination of other sulfure containing molecules(COS, CS2, mercaptans).
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Nouvelle méthode de fonctionnalisation d'hétérocycles et des composés benzéniques par voie organimétallique : déprotonations par des magnésiates, réactions avec des électrophiles et couplages / New Functionalisation Methodology of Heterocycles and Benzene Derivatives Using Magnesates Bases : deprotonations, Reaction with Electrophiles and Cross CouplingsBayh, Omar 27 June 2008 (has links)
Ce travail a eu pour objectif l’étude d’une nouvelle méthodologie de fonctionnalisation aromatique basée sur la déprotonation par les bases magnésiates (alkyl- et/ou amidomagnésiates de lithium) à température ambiante encore très peu étudiée et l’examen de la réactivité nucléophile et dans le couplage croisé catalysé par un métal de transition des complexes (hétéro)arylmagnésiates générés. La première partie a été centrée sur la déprotonation des hétérocycles à 5 chaînons (furane, thiophène, benzoxazole et oxazole) qui a été réalisée avec succès en utilisant essentiellement la base Bu3MgLi. Les complexes hétéroarylmagnésiates dont les formes ouvertes issues de la déprotonation de l’oxazole et du benzoxazole ont révélé d’une part une bonne réactivité nucléophile vis à vis d’agents de deutération, d’halogénation, de sylilation et des aldéhydes aromatiques pour conduire aux hétérocycles substitués avec de bons rendements. D’autre part les complexes magnésiates ont été engagés avec succès dans le couplage croisé avec des partenaires bromo(hétéro)aromatiques catalysé par PdCl2(dppf). La seconde partie a été consacrée à l’étude de l’ortho-fonctionnalisation des dérivés benzéniques. Les conditions d’ortho-magnésiation par les bases tri(tétra)alkylmagnésiates de (di)lithium des oxazolyl-, carboxamido-, pivaloylamino-, et alkoxybenzènes ainsi que du benzène sulfoxyde ont été mises au point. Les complexes arylmagnésiates générés ont révélé d’une part une bonne réactivité nucléophile vis à vis d’agent de deutération, d’halogénation, de sylilation et du méthyloxirane. Seule la réactivité vis-à-vis des aldéhydes s’est révélée moindre mettant à jour deux réactions compétitives, l’addition d’un groupement butyle et la réduction concurrente de la fonction carbonyle. D’autre part, les nouveaux complexes arymagnésiates à l’exception de ceux issus de la déprotonation du benzène sulfoxyde ont été couplés avec succès avec des dérivés (hétéro)aromatiques bromés. De façon plus générale, la méthodologie de fonctionnalisation par déprotonation par les bases magnésiates s’est révélée efficace et apporte de nouveaux avantages par rapport aux méthodes classiques tels que d’une part la déprotonation au voisinage de la température ambiante pour les applications industrielles et d’autre part l’utilisation d’une nouvelle classe de réactifs organométalliques utilisables aussi bien pour le piégeage électrophile que pour le couplage croisé catalysé par un métal de transition. / This present work reports the development of a novel versatile aromatic functionnalization methodology based upon deprotonation with magnesiate bases (lithium alkyl- and /or amidomagnesiates) at room temperature, currently poorly studied and the use of the novel arylmagnesiates complexes formed as nucleophilic agents and organometallic partners in the cross-coupling reaction. The deprotonation of the five-membered heterocycles (furan, thiophene, benzoxazole and oxazole) was first successfully accomplished using mainly Bu3MgLi as base. The arylmagnesiates thus obtained, including the expected ring-opened magnesiate complexes obtained from deprotonation of benzoxazole and oxazole, proved to be effective in several reactions as deuteration, halogenation, silylation and nucleophilic addition on aromatic aldehydes leading to the corresponding substituted heterocycles. Futhermore the heteroarylmagnesiates complexes revealed to be efficient in cross-coupling reaction with bromo(hetero)aromatics catalyzed by PdCl2(dppf). In a second part, works were directed toward the study of the ortho-functionnalization of benzene derivatives. Thus, the deprotonation of oxazolyl-, carboxamido-, pivaloylamino- and methoxybenzenes as well as benzene sulfoxyde was achieved using mainly (di)lithium tri(tetra)magnesiate bases. The arylmagnesiates complexes showed a good nucleophilic reactivity toward deuterative, halogenative and silylative agents and methyloxirane whereas reactions with aromatic aldehydes occurred in more moderate yields due to two side processes, addition of a butyle group and reduction of the aldehyde function. The arylmagnesiates excepted from benzene sulfoxyde could be coupled with bromo(hetero)aromatics under PdCl2(dppf)-catalysis. In summary, the novel aromatic functionnalization based upon the use of magnesiate bases proved to be particularly efficient and represents many advantages compared to classical methods such as metalation at room temperature for direct industrial application as well as the use of a new class of organometallic reagents possessing a good nucleophilic reactivity and directly valuable in the transition metal-catalyzed cross-coupling reaction.
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The Removal of Lead Ions from Water Using Thiophene-Containing Metal-Organic FrameworksGeisse, Alissa Renee 23 August 2019 (has links)
No description available.
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Solution Assembly of Conjugated PolymersBokel, Felicia 01 May 2013 (has links)
This dissertation focuses on the solution-state polymer assembly of conjugated polymers with specific attention to nano- and molecular-scale morphology. Understanding how to control these structures holds potential for applications in polymer-based electronics. Optimization of conjugated polymer morphology was performed with three objectives: 1) segregation of donor and acceptor materials on the nanometer length-scale, 2) achieving molecular-scale ordering in terms of crystallinity within distinct domains, and 3) maximizing the number and quality of well-defined donor/acceptor interfaces.
Chapter 1 introduces the development of a mixed solvent method to create crystalline poly(3-hexyl thiophene) (P3HT) fibrils in solution. Chapter 2 describes fibril purification and approaches to robust and functional fibrils, while chapters 3 and 4 demonstrate the formation of hybrid nanocomposite wires of P3HT and cadmium selenide (CdSe) nanoparticles by two methods: 1) co-crystallization of free and P3HT-grafted CdSe for composite nanowires and 2) direct attachment of CdSe nanoparticles at fibril edges to give superhighway structures. These composite structures show great potential in the application of optoelectronic devices, such as the active layer of solar cells. Finally, ultrafast photophysical characterization of these polymers, using time-resolved photoluminescence and transient absorption, was performed to determine the aggregation types present in suspended fibrils and monitor the formation and decay of charged species in fibrils and donor-acceptor systems
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Systematic Synthesis of Organic Semiconductors with Variable Band GapsScilla, Christopher Thomas 01 May 2012 (has links)
Polymeric materials are attractive candidates for the fabrication of low cost, large area photovoltaic devices. Controlling the band gap of the electroactive polymer is an essential factor in optimizing the resulting devices. In this dissertation, a methodology for the synthesis of well-defined semiconducting materials with tunable band gaps is described. First, the synthesis, characterization, and computational analysis of a variety of trimers consisting of two 3-hexylthiophene units flanking a central moiety consisting of thiophene, or one of the electron donating monomers isothianaphthene or thieno[3,4,b]thiophene will be described. From this analysis the influences of the electronic and steric structure of the materials will be investigated. Several of these trimers will then be used in the synthesis of well-defined, higher order, oligomers of thiophene and isothianaphthene in varying compositions. Polymerization of these oligomers yields polymers of known sequence allowing the band gap of the polymers to be systematically varied. Finally, preliminary investigations into the development of alternate oligomer core units will be described. The control over the band gap that this method affords will be useful in the optimization of polymeric semiconductor devices.
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Stable Hetero-Acene Analogs of Heptacene: The Synthesis and Study of their Conductive Properties in Organic Transistors And The Photo-induced Formation of Quantum Dot – Conductive Polymers (QD:CP) for Application in PhotovoltaicsDe, Puran K. 21 October 2011 (has links)
No description available.
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