211 |
Espectroscopia ultrarrápida do polímero semicondutor luminescente MEH-PPV com excitação no ultravioleta / Ultrafast spectroscopy of the luminescent semiconducting polymer MEH-PPV with ultraviolet excitationMarcelo Meira Faleiros 17 August 2012 (has links)
A indústria optoeletrônica passa por um período de transformação em que os materiais inorgânicos estão sendo substituídos pelos orgânicos, oligômeros e polímeros, na fabricação de alguns tipos de dispositivos. No entanto, fatores como baixa eficiência e tempo de vida impedem que os aparelhos com base nos polímeros entrem definitivamente no mercado. Para resolver estas questões, é necessário um conhecimento profundo da estrutura eletrônica desses materiais. Apesar do avanço científico, ainda existem pontos a esclarecer. Por exemplo, não existe um consenso sobre a natureza das excitações óticas primárias e dos processos não radiativos nos polímeros conjugados, principalmente com excitação no ultravioleta. Tais processos limitam a eficiência e podem influenciar nos processos fotoquímicos, determinando o tempo de vida de um dispositivo. Esses fenômenos ocorrem em alguns picossegundos e, portanto, a espectroscopia ultrarrápida é a técnica mais adequada para o seu estudo. Neste trabalho, foi implementado o aparato para espectroscopia de bombeio e prova em filmes finos de polímeros conjugados, no qual podem ser usados dois métodos de aquisição de dados, sensível à fase e pulso-a-pulso. O primeiro é o método padrão citado na literatura, no qual o feixe de excitação é modulado por um chopper e os sinais são medidos por amplificadores lock-in. No segundo, o condicionamento de sinais é feito por circuitos amplificadores e o processamento dos sinais é feito pulso-a-pulso. É um método que a princípio fornece melhor estatística, pois as flutuações do laser são normalizadas pulso-a-pulso, e não na média. Além disso, apresenta menor custo e torna o experimento de bombeio e prova mais simples, pois os únicos procedimentos críticos passam a ser a sobreposição dos feixes na amostra e a determinação do atraso zero entre bombeio e prova. Foi projetado e construído o circuito eletrônico de condicionamento de sinais e o software de aquisição foi desenvolvido em linguagem LabVIEW. Entretanto, o método pulso-a-pulso forneceu uma sensibilidade inadequada para o estudo de filmes poliméricos, (ΔT⁄T ~ 0,7%, limitada pelo ruído elétrico na amplificação dos pulsos detectados), em contraste com ΔT/T ~ 0,1% que foi alcançada pelo método sensível à fase. Desta maneira, foi usado o último método para o estudo da evolução do espectro e da dinâmica de emissão estimulada de um filme de MEH-PPV, com excitação no visível e no ultravioleta, permitindo o estudo da dinâmica de relaxação dos estados de mais alta energia. Os resultados no visível são compatíveis com os da literatura, o que demonstra a confiabilidade do aparato quanto à sensibilidade e resolução temporal e espectral. Os resultados com excitação no UV indicam que a transferência de energia de bandas mais energéticas para a banda π - π∗ (conversão interna) ocorre em aproximadamente 300 fs, confirmando as suposições da literatura quanto à relaxação energética ultrarrápida (regra de Kasha), além de sugerir a existência de bandas ainda mais energéticas do que as já conhecidas. Pretende-se futuramente determinar a eficiência de tal transferência energética, pois ela pode ser um fator limitante na eficiência de fotoluminescência em polímeros conjugados com excitação no ultravioleta. / The optoelectronics industry is currently undergoing a transition period in which inorganic materials are being replaced by organic materials, oligomers and polymers, in the fabrication of some types of devices. However, factors such as low efficiency and low lifetime prevent polymer based devices on entering the market definitely. The solution of these issues requires a thorough knowledge of the electronic structure of these materials, but despite of scientific advances, there are still points to be clarified. For example, there is no consensus on the nature of the primary optical excitations and non-radiative processes in conjugated polymers, specially with ultraviolet excitation. Such processes limit the efficiency and can influence the photochemical processes, determining the device lifetime. These phenomena occur on a femtosecond timescale and therefore, ultrafast spectroscopy is the most appropriate technique for their study. In this work, we implemented the apparatus for pump-probe ultrafast spectroscopy on thin films of conjugated polymers, which can be used with two methods of data acquisition, phase-sensitive and shot-by-shot. The first is the standard method reported in the literature in which the excitation beam is modulated by a chopper and the signals measured by lock-in amplifiers. In the second, the detector signal conditioning is done by conventional amplifier circuits, followed shot-to-shot signal processing. This method provides the best statistics, in principle, because the laser fluctuations are normalized for each pulse, instead of using the average. In addition, the apparatus has a lower cost and the experiment is simpler, having as critical procedures the alignment of the beams on the sample and the determination of zero delay, with all other procedures done via software. The electronic circuitry for signal conditioning was designed and built and data acquisition software that enables measurements with both methods was developed in the LabVIEW programming language. However, the shot-by-shot method provided an inadequate sensitivity for the study of polymeric films (ΔT⁄T ~0.7%, limited by electronic noise in the amplification of detector signals), compared with ΔT⁄T ~ 0.1%, which was achieved by the phase sensitive method, and was the goal at the beginning of the project. Thus, the latter method was used to study the evolution of the spectrum and dynamics of stimulated emission of a film of MEH-PPV, with excitation in the visible and UV, allowing the study of the dynamics of higher lying electronic states. The results in the visible are consistent with those reported in the literature, which demonstrates the performance of the apparatus with respect to sensitivity and time/spectral resolution. The results with UV excitation indicate that the energy transfer among the more energetic bands to the π - π* band (internal conversion) occurs in about 300 fs, confirming the assumptions of the literature on the ultrafast energy relaxation processes (Kashas rule), besides suggesting the existence of even more energetic bands than those currently known. As future work, we plan to measure the efficiency of this energy transfer process, since it may be the limiting step in determining the overall photoluminescence efficiency of conjugated polymers with ultraviolet excitation.
|
212 |
Structure and dynamics of poly(9,9-dioctylfluoren-2,7-co-benzothiadiazole) (F8BT) and correlations with its electrical properties / Estrutura e dinâmica molecular do poly (9,9-dioctylfluoren-2,7-diyl-co-benzothiadiazole) (F8BT) e correlações com suas propriedades elétricas.Gregório Couto Faria 16 September 2011 (has links)
The PHD project has two main goals. The first one is specifically related to investigations on molecular dynamics, structural conformations and packing of polyfluorene-based polymers. For this purpose, Wide Angle X-Ray Diffraction (WAXD), Solid-State Nuclear Magnetic Resonance (NMR) and Dynamical-Mechanical Thermal Analysis (DMTA) are being used as the main techniques. The second goal is to correlate molecular phenomena, as characterized in the first part, with opto-electronic properties of polyfluorene when used as active layer in an electronic device, such as a Polymer Light-Emitting Diode (PLED). In the second part, fabrication of devices and their electrical characterization as a function of temperature are the main objectives. Impedance Spectroscopy, Current-Voltage characterization of the devices and Time-Of-Flight (TOF) techniques are among the main techniques to be used in the second part of the project. Therefore, the project combines fundamental studies on molecular dynamics with technological performance of organic electronic. / O projeto de doutorado entitulado \"Correlação das Propriedades Óticas e Elétricas com a Estrutura Física e Dinâmica Molecular de Filmes e Dispositivos de Polifluorenos e Derivados\". O primeiro é especificamente ligado a investigação da dinâmica molecular, conformação estrutural e empacotamento de polímeros derivados do polifluoreno. Para isso, Difração de Raio-X de Alto Ângulo (WAXD)1, Ressonânica Magnética no Estado Sólido (RMN) e Análise Térmica Dinâmico Mecânica (DMTA) serão utilizadas como técnicas principais. O segundo objetivo é o de correlacionar, os fenômenos observados na primeira parte do projeto, com as propriedades opto-eletrônicas dos filmes poliméricos sendo utilizados como camada ativa em dispositivos eletrônicos do tipo Diodo Polimérico Emissor de Luz (PLED). Na segunda parte, a fabricação dos dispositivos e sua caracterização como função da temperatura serão os principais objetivos. Espectroscopia de Impedância, Corrente-Voltagem, Tempo de Vôo (TOF) e Photo-CELIV serão as principais técnicas de caracterização utilizadas. Dessa forma, o projeto combina estudos fundamentais de aspectos moleculares com o desempenho tecnológico de dispositivos optoeletrônicos.
|
213 |
Síntese e caracterização espectroeletroquímica de derivados eletrocrômicos e fluorescentes de polipirrol e politiofeno / Synthesis and spectroelectrochemical characterization of electrochromic and fluorescent derivatives of polypyrrol and polythiopheneAlmeida, Andresa Katherinne Albuquerque de 29 November 2016 (has links)
The electrochemical and optical properties of poly[3-(N-pyrrolyl)propyl dansylglicinate] (PDGP) films prepared by electrochemical polymerisation in acetonitrile (CH3CN)/boron trifluoride diethyl eterate (BFEE) were investigated. The PDGP films presented electrochromic behaviour, changing their colour from greenish-yellow to greyish-blue at the neutral and oxidised states, respectively, being fluorescent properties with emission in λ = 562 nm in dichloromethane CH2Cl2 solution. The poly[2-(3-thienyl)ethyl dansylglycinate] (PDGTE) deposited onto ITO by casting were also electrochromic, with colour varying from yellow to bluish-grey at the neutral and oxidised states, respectively, besides present yellow light emission (λ = 547 nm) in CH2Cl2 solution. Therefore, the properties presented by PDGP and PDGTE films make them potential candidates for application in displays and optoelectronic devices. Besides that, an unprecedented monomer and its respective polymer, the 3-(1-pyrrolyl)propyl-N-(2-[4-(dimethylamino) phenylazo benzoate] (MRPy) was synthesised with 57 % yield. The polymer PMRPy was chemically synthesised by using an usual polymerisation route involving the monomer oxidation with FeCl3. The PMRPy was also prepared by electrochemical polymerisation in CH3CN/ BFEE. The monomer and polymer were characterised by conventional methods of analysis of organic compounds, as 1H NMR, 13C NMR and FTIR. The films of polypyrrole (PPy) and PPy doped with Methyl red (PPy/MR) were prepared in order to compare their electrochromic properties with the films of PMRPy. It was observed colour changes for the PMRPy films, from the yellow color in the reduced state to dark magenta in the oxidised state, whilst the PPy/MR films showed colour variation from yellow in the reduced state to magenta in the neutral state, and a bluish-gray color in the oxidised state. The colour changes PMRPy films were also investigated after exposure to HCl vapours presented dark magenta color fading to yellow when immersed in 0.1 mol L-1 NaOH solution. The characteristics presented by the PMRPy film make this material a good candidate for application as active layers in optoelectronic devices, pH sensors, as well as magenta-colored films derived from polypyrrole, very limited in the literature. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As propriedades eletroquímicas e ópticas dos filmes de poli[dansilglicinato de 3-(N-pirrolil)propila] (PDGP) preparados a partir da polimerização eletroquímica em meio de acetonitrila (CH3CN)/dietil eterato de trifluoreto de boro (BFEE) foram investigadas. Os filmes de PDGP mostraram comportamento eletrocrômico, com mudança de coloração entre amarelo esverdeado e azul acinzentado nos estados neutro e oxidado, respectivamente. O filme de PDGP apresenta propriedades fluorescentes com emissão em λ = 562 nm em solução de diclorometano (CH2Cl2). Os filmes de poli[dansilglicinato de 2-(3-tienil)etila] (PDGTE) preparados por casting apresentaram eletrocromismo, com mudança de coloração entre amarelo e cinza azulado nos estados neutro e oxidado, respectivamente, além de apresentar emissão de luz amarela (λ = 547 nm) em solução de CH2Cl2. Sendo assim, as características apresentadas pelos filmes de PDGP e PDGTE tornam esses materiais candidatos em potencial para aplicação em displays e em dispositivos optoeletrônicos. Além disso, foi sintetizado um monômero inédito e seu respectivo polímero, o benzoato de 3-(1-pirrolil)propil-N-(2-[4-(dimetilamino) fenilazo] (MRPy) com rendimento de 57 %. O polímero PMRPy foi sintetizado quimicamente a partir de uma rota usual de polimerização envolvendo a oxidação do monômero com FeCl3. O PMRPy também foi preparado a partir da polimerização eletroquímica em meio de CH3CN/BFEE. O monômero e o polímero foram caracterizados através de métodos convencionais de análise de compostos orgânicos, tais como RMN1H, RMN13C e FTIR. Os filmes de polipirrol (PPy) e polipirrol dopado com Methyl red (PPy/MR) foram preparados para comparar suas propriedades eletrocrômicas com os filmes de PMRPy. Foi observado uma mudança de cor para os filmes de PMRPy, da cor amarela clara no estado reduzido para a magenta escura no estado oxidado. Enquanto os filmes de PPy/MR mostraram uma variação de cor partindo do amarelo no estado reduzido, magenta no estado neutro, e azul para cinza no estado oxidado. As mudanças de cores dos filmes de PMRPy também foram investigadas após exposição a vapores de HCl apresentando uma cor magenta escura passando para amarelo quando mergulhado em solução 0,1 mol L-1 de NaOH. As características apresentadas pelo filme de PMRPy tornam esses materiais candidatos em potencial para aplicação como camada ativa em dispositivos optoeletrônicos, sensores de pH, bem como filmes de cor magenta derivadas de polipirrol, ainda bastante limitada na literatura.
|
214 |
Estudo atomístico da desordem eletrônica em filmes amorfos de polímeros conjugados / Atomistic Study of Electronic Disorder on Amorphous Films of Conjugated PolymersRodrigo Ramos da Silva 10 October 2014 (has links)
O emprego de polímeros conjugados e blendas como camada ativa de diodos emissores de luz ou células fotovoltaicas é foco de intenso desenvolvimento científico na atualidade. O desempenho eletro-ótico de tais dispositivos é fortemente dependente das características estruturais e eletrônicas dos componentes poliméricos ou moleculares, que são difíceis de serem quantificadas, demandando a integração de resultados experimentais e modelagem teórica. A desordem intrínseca desses materiais também dificulta a modelagem e a simulação, sendo necessário o emprego de diferentes e complementares métodos e técnicas de física computacional. O presente trabalho tem como objetivo o estudo, em nível atomístico, da correlação entre propriedades morfológicas e eletrônicas de filmes poliméricos com alta desordem de: I) poli-para-fenileno-vinileno (PPV); II) poli-3-hexil-tiofeno (P3HT) e sua blenda com fulereno (C60). Empregamos modelagem por Dinâmica Molecular Clássica dos sistemas desordenados em temperatura finita; implementamos para tal adaptações específicas no Campo de Forças Universal, baseadas em cálculos quânticos de primeiros princípios. Para obtermos a estrutura eletrônica de modelos selecionados utilizamos método de Hartree-Fock semiempírico. O sistema de PPV é estudado com respeito à variação das propriedades morfológicas ao longo do processo de deformação uniaxial. Estabelecemos correspondência entre os efeitos do estiramento e o surgimento de anisotropia no espectro de fotoluminescência observado experimentalmente. Para os sistemas de P3HT simulamos diferentes tipos de empacotamento, estudamos as propriedades morfológicas e calculamos os estados eletrônicos relevantes ao transporte de buracos pelo polímero. Vemos como majoritária a ocorrência de estados com comprimento conjugado de quatro e cinco meros; além disso, com a desordem estrutural os níveis eletrônicos localizados passam a exibir grande proximidade em energia, com pouca relação ao comprimento de conjugação. Isso resulta no surgimento de uma Densidade de Estados gaussiana com largura de aproximadamente 100meV que se mostra independente das diferenças morfológicas entre os modelos simulados. / The use of organic conjugated polymers and blends as active layers of light emitting diodes and photovoltaic cells has been the focus of intense scientific development in recent years. The electro-optical performance of such devices depends strongly on the structural and electronic properties of the polymeric or molecular components, and is of difficult characterization, demanding integration of experimental results and theoretical modeling. A complicating factor to the theoretical modeling is the intrinsic disorder in these materials, which demands the use of different and complementary techniques and methods of computational physics. The goal of the present work is to study at the atomistic level the correlation between morphological and electronic properties of highly disordered films of: I) poly-para-phenylene-vinylene (PPV); II) poly-3-hexyl-thiophene (P3HT) and blends with fullerenes (C60). We applied Classical Molecular Dynamics to model the disordered systems at finite temperature employing the well-known Universal Force Field, to which we implemented specific corrections based on first-principles quantum calculations. For selected models we calculated the electronic structure through semiempirical Hartree-Fock. The PPV system was studied focusing on the effect of uniaxial stretching on morphological properties. We have established a connection between morphology effects and the anisotropy of light emission detected experimentally. For P3HT systems we simulated different packing systems and studied morphological properties, and the electronic structure of the localized states relevant to hole transport in the polymer film. We found higher occurrence of 4- and 5-mer long conjugated electronic states. Moreover, the structural disorder affects the electronic levels, reducing the energy separation of conjugated segments of different lengths. This makes possible the occurrence of a gaussian Density of States of approximately 100meV width, regardless of the different morphological signatures of the different simulated models.
|
215 |
ESTABLISHING THE OPTOELECTRONIC INTERACTIONS BETWEEN CONJUGATED POLYMERS AND ORGANIC RADICALSDaniel A Wilcox (9116285) 28 July 2020 (has links)
<div> Design rules and application spaces for closed-shell conjugated polymers have been well established in the field of organic electronics, and this has allowed for significant breakthroughs to occur in myriad device platforms [e.g., organic field-effect transistors (OFETs) and organic light-emitting devices (OLEDs)]. Conversely, organic electronic materials that are based on the emerging design motif that includes open-shell stable radicals have not been evaluated in such detail, despite the promise these materials show for charge transfer, light-emission, and spin manipulation platforms. Moreover, recent results have demonstrated that the materials performance of hybrid systems will allow for future applications to harness both of these platform design archetypes to generate composites that combine the performance of current state-of-the-art conjugated polymer systems with the novel functions provided by open-shell species. Thus, establishing the underlying physical phenomena associated with the interactions between both classes of materials is imperative for the effective utilization of these soft materials.</div><div><br></div><div> In the first part of this work, Förster resonance energy transfer (FRET) is demonstrated to be the dominant mechanism by which energy transfer occurs from a common conjugated polymer to various radical species using a combination of experimental and computational approaches. Specifically, this is determined by monitoring the fluorescence quenching of poly(3hexylthiophene) (P3HT) in the presence of three radical species: (1) the galvinoxyl; (2) the 2phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO); and (3) the 4-hydroxy-2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) radicals. Both in solution and in the solid-state, the galvinoxyl and PTIO radicals show quenching on par with that of a common fullerene electronaccepting derivative. Conversely, the TEMPO radical shows minimal quenching at similar concentrations. Using both ultrafast transient absorption spectroscopy and computational studies, FRET is shown to occur at a significantly faster rate than other competing processes. These findings suggest that long-range energy transfer can be accomplished in applications when radicals that can act as FRET acceptors are utilized, forming a new design paradigm for future applications involving both closed- and open-shell soft materials.</div><div><br></div><div> Following this, addition of the galvinoxyl radical to P3HT is shown to alter the thin film transistor response from semiconducting to conducting. This is accompanied by a modest enhancement in electrical conductivity. This interaction is not seen with either the TEMPO or PTIO radicals. While an increase in charge carrier concentration is observed, the interaction is not otherwise consistent with a simple charge-transfer doping mechanism, due to the mismatched reduction and oxidation potentials of the two species. Additionally, no freeze-out of charge carriers is observed at reduced temperatures. It is also not due to parallel conduction through the radical fraction of the bulk composite, as the radical species is non-conductive. Hole mobility is enhanced at lower concentrations of the radical, but it decreases at higher concentrations due to the reduced fraction of conductive material in the polymer bulk. Despite the increase in mobility at lower concentrations, the activation energy for charge transport is increased by the presence of the radical. This suggests that the radical is not improving the charge transport through filling of deep trap states or by reducing the activation energy for the charge transport reaction; however, the galvinoxyl radical is likely filling shallow trap states within the P3HT for the composite thin film.</div><div><br></div><div> Finally, a novel analysis technique for polymer relaxation is investigated through dielectric spectroscopy of model polyalcohols. An understanding of relaxation phenomena and the physics of amorphous solids in general remains one of the grand open challenges in the field of condensed matter physics. This problem is particularly relevant to organic electronics as many organic electronic materials are found in the amorphous state, and their physical relaxation can lead to undesirable effects such as hysteresis and instability. Current procedures describe relaxation phenomena in terms of empirical functions, but the physical insights provided by this representation are limited. The new approach instead represents the dielectric response as a spectrum of Debye processes. Rather than varying the spectral strength at fixed time points as traditional spectral analysis implicitly does, this approach instead varies the characteristic time of each spectral element while the strength remains fixed. This allows the temperature dependence on relaxation time of each spectral element to be determined, and the <i>α</i>- and <i>β</i>-relaxation are interpreted in light of this analysis. </div><div> </div>
|
216 |
Synthèse d'oligo- et polythiophènes pontés pour augmenter la dimensionnalité du transport de charges / Synthesis of bridged oligo- and polythiophenes to increase the dimensionality of charges transportJenart, Maud 10 November 2014 (has links)
Un nouveau domaine de recherche a vu le jour à la fin du XXe siècle, celui de l’électronique organique provenant de l’union des propriétés de l’électronique avec celles des matériaux semiconducteurs organiques. Les principaux avantages technologiques des matériaux organiques proviennent de leur facilité de mise en œuvre (par exemple :l’impression à pression et température ambiantes) et de leur flexibilité mécanique en comparaison au silicium qui est le matériau semiconducteur le plus utilisé au monde. En raison de ces avantages, de nombreuses perspectives d’applications ont été envisagées telles que les écrans flexibles, l’éclairage à partir de grandes surfaces ou encore les cellules photovoltaïques flexibles. Les performances des semiconducteurs organiques sont actuellement moins bonnes que celles du silicium, mais ont fait des progrès spectaculaires depuis ces dernières années. Les performances des semiconducteurs organiques dépendent de l’efficacité avec laquelle les charges se déplacent dans les matériaux π-conjugués ;le paramètre clé qui caractérise le transport de charges est la mobilité, µ. En raison de l’extraordinaire diversité de structures moléculaires accessibles par la synthèse organique, les performances peuvent espérer un jour approcher celles du silicium, car il n’existe à ce jour pas de limite supérieure imposée à la mobilité des charges dans les matériaux organiques. Dans ce contexte, la contribution des chimistes consiste à développer de nouvelles molécules et macromolécules organiques donnant lieu à des matériaux aux performances toujours accrues. Un aspect important à améliorer est la dimensionnalité du transport de charges qui est comprise entre 1 et 3. En effet, plus celle-ci est faible, plus le transport de charges sera sensible aux défauts. <p><p>Au cours du présent travail, nous nous sommes intéressés à l’amélioration du transport de charges en augmentant la dimensionnalité de ce dernier. Cette approche est basée sur les études théoriques du Dr Antoine Van Vooren relevant du couplage électronique par un pont covalent, mais non conjugué entre des systèmes π tels que les oligothiophènes. En effet, selon ces travaux, le couplage électronique entre deux systèmes π est plus important lorsqu’ils sont reliés par un pont éthylène que lorsqu’ils sont isolés. Le pont permet dès lors le transport de charges dans une nouvelle dimension, favorisant ainsi le transport de charges. L’objectif principal de cette thèse consiste à réaliser la synthèse d’oligo- et polythiophènes pontés par des liens éthylènes et d’en étudier les propriétés afin de contribuer à la démonstration expérimentale qu’un pont covalent entre systèmes π aide au transfert de charges. L’étude a porté sur deux systèmes :le système 1 dans lequel le noyau aromatique est un 2,2’:5’,2’’:5’’,2’’’-quaterthiophène et le système 2 dans lequel le noyau aromatique est un 2,5-bis(thiophèn-2-yl)thiéno[3,2-b]thiophène. Les dimères D1 et D2, servant de systèmes modèles, sont étudiés dans le deuxième chapitre tandis que les polymères P1 et P2, permettant de conclure sur l’effet du pont, sont étudiés dans le chapitre trois. <p><p>Une stratégie de synthèse menant au dimère D1, à l’échelle du gramme, a été développée et les quantités recueillies ont permis d’étudier les propriétés de ce dimère. Cependant, nous n’avons pas pu obtenir de monocristaux D1, faillant ainsi à l’étude de la conformation du pont. Une stratégie de synthèse menant au dimère D2 a été développée bien que les quantités recueillies fussent faibles. Le peu de dimère D2 obtenu rendit l’étude des propriétés de ce dernier compliquée et lacunaire. Suite à l’absence d’information sur la conformation du pont des systèmes modèles, d’autres systèmes pontés, présentant une structure chimique proche, de celle des dimères ont été développés. L’efficacité des voies de synthèse imaginées pour obtenir ces composés ainsi que leurs capacités à cristalliser ont permis d’étudier la conformation du pont de ces nouveaux systèmes pontés. Nous avons pu en conclure que de faibles changements de la structure chimique engendrent des changements significatifs sur la structure cristalline ;rendant difficile la prédiction des structures cristallines des molécules cibles. <p><p>Une voie de synthèse menant au polymère P1 a été développée par couplage de Stille en guise de polymérisation, suite à d’infructueux essais via le couplage de Yamamoto. Les quantités recueillies ont permis d’étudier les propriétés de ce polymère. Nous avons ainsi pu constater que le polymère P1 présente un large domaine de stabilité thermique, mais qu’il est complètement amorphe. Néanmoins, le niveau de la HOMO fait de lui un bon candidat pour le transport de trous. Le polymère P2 a été synthétisé selon la même voie de synthèse et nous avons pu observer les mêmes propriétés que celles du polymère P1.<p><p>L’analyse des propriétés spectroscopiques des polymères P1 et P2 ne nous a pas apporté de preuve de la délocalisation des charges le long de la chaine de polymère. En effet, nous avons mis en évidence un effet d’agrégation et un effet de couplage excitonique des polymères qui a pour conséquence de modifier les propriétés caractéristiques des spectres d’absorption et d’émission dans le domaine UV-vis. Nous avons ensuite étudié leurs propriétés de transport de charges dans des transistors. Cependant, les résultats furent décevants en raison de l’absence d’un ordre cristallin au sein des polymères, ceci indépendamment de la méthode de déposition utilisée. Au final, nous n’avons pas de preuve définitive de l’effet du pont sur le transport de charges. Nous espérons que les tentatives de cristallisation des polymères porteront leurs fruits afin qu’une conclusion sur l’effet du pont éthylène entre deux systèmes π puisse être tirée dans un avenir proche. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
|
217 |
Studium vlivu fotochromní reakce na optoelektrické vlastnosti organických polovodičů / The influence of photochromic reaction on optoelectrical properties of organic semiconductorsHeinrichová, Patricie January 2009 (has links)
This diploma thesis is focused on study of electric and optoelectric properties of conjugated polymers. The theoretical part describes the relationship between molecular structure of conjugated materials and their chosen macroscopic physical properties like absorption of visible and ultraviolet radiation, electrical conductivity and photoconductivity. This part also describes photochromism and its utilization for construction of light driven current switch. The experimental part studies this switch based on change of photochromic species dipole moment dispersed in conjugated conducting polymer. The active switching unit is represented by photochromic spiropyran 1’,3’-dihydro-1’,3’,3’-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2’-(2H)-indol] which is dispersed in conjugated conducting polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylen]. The influence of the photochromic conversion on the polymer matrix was studied by absorption spectroscopy, current-voltage measurements and spectrally resolved steady state photoconductivity and transient photoconductivity.
|
218 |
Příprava a studium optoelektrických vlastností tenkých vrstev pro organickou fotoniku / Deposition and study of optoelectronic properties of thin films for organic photonicsNagyová, Veronika January 2013 (has links)
This diploma thesis concentrates on the properties characterization of new organic materials for solar cells. In the theoretical part, there is a solar cells themed literature search, there is described a mechanism of conversion of solar energy, factors influencing photovoltaic conversion efficiency and materials using for preparation of organic solar cells. The practical part includes the preparation of solar cells and characterization of optical and electrical properties of the studied materials in thin layers and solutions. Used materials were conjugated polymers and derivatives of fullerenes.
|
219 |
Synthesis of a polar conjugated polythiophene for 3D-printing of complex coacervatesHeimonen, Johanna January 2021 (has links)
The aim of this thesis was to synthesize a functionalized polar conjugated polythiophene that could be (3D-) printed into form-stable structures for bio-interfacing. The material design rationale aimed for a water-processable polymer that had the capability of electronic and ionic conduction, by using a thiophene backbone and oligoethylene side chains. Functionalization of the oligoethylene side chains with carboxylate groups created a polyanion, which allowed for a bio-inspired approach to combine printability and form-stability through formation of complex coacervates. The synthesis of the conjugated monomer and polymer was optimized to provide a more sustainable and material efficient synthesis route. Combined structural analysis with 1H-NMR, FT-IR and UV-vis revealed successful synthesis of the target polymer. Spectro electrochemistry revealed that the polymer was optically and electrochemically active in both the protected and deprotected form. The obtained material is processable from water, and initial tests revealed that crosslinking can be achieved through formation of acid dimers, ionic crosslinks with Ca2+ ions and complex coacervation with a polycation. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>
|
220 |
Development of new approaches for characterising DNA origami-based nanostructures with atomic force microscopy and super-resolution microscopyFischer, Franziska Elisabeth 17 April 2019 (has links)
DNA nanotechnology has developed a versatile set of methods to utilise DNA self-assembly for the bottom-up construction of arbitrary two- and three-dimensional DNA objects in the nanometre size range, and to functionalise the structures with unprecedented site-specificity with nanoscale objects such as metallic and semiconductor nanoparticles, proteins, fluorescent dyes, or synthetic polymers. The advances in structure assembly have resulted in the application of functional DNA-based nanostructures in a gamut of fields from nanoelectronic circuitry, nanophotonics, sensing, drug delivery, to the use as host structure or calibration standard for different types of microscopy. However, the analytical means for
characterising DNA-based nanostructures drag behind these advances. Open questions remain, amongst others in quantitative single-structure evaluation. While techniques such as atomic force microscopy (AFM) or transmission electron microscopy (TEM) offer feature resolution in the range of few nanometres,
the number of evaluated structures is often limited by the time-consuming manual data analysis.
This thesis has introduced two new approaches to quantitative structure evaluation using AFM and super-resolution fluorescence microscopy (SRM). To obtain quantitative data, semi-automated computational image analysis routines were tailored in both approaches.
AFM was used to quantify the attachment yield and placement accuracy of poly(3-tri(ethylene glycol)thiophene)-b-oligodeoxynucleotide diblock copolymers on a rectangular DNA origami. This work has also introduced the first hybrid of DNA origami and a conjugated polymer that uses a highly defined polythiophene derivative synthesised via state-of-the-art Kumada catalyst-transfer polycondensation. Among the AFM-based studies on polymer-origami-hybrids, this was the first to attempt near-single molecule resolution, and the first to introduce computational image analysis. Using the FindFoci tool of the software ImageJ revealed attachment yields per handle between 26 - 33%, and determined a single
block copolymer position with a precision of 80 - 90%. The analysis has pointed out parameters that potentially influence the attachment yield such as the handle density and already attached objects. Furthermore, it has suggested interactions between the attached polymer molecules.
The multicolour SRM approach used the principles of single-molecule high-resolution co-localisation (SHREC) to evaluate the structural integrity and the deposition side of the DNA origami frame “tPad” based on target distances and angles in a chiral fluorophore pattern the tPads were labelled with. The computatinal routine that was developed for image analysis utilised clustering to identify the patterns in a sample’s signals and to determine their characteristic distances and angles for hundreds of tPads simultaneously. The method excluded noise robustly, and depicted the moderate proportion of intact tPads in the samples correctly. With a registration error in the range of 10 -15 nm after mapping of the colour channels, the precision of a single distance measurements on the origami appeared in the range of 20 - 30 nm.
By broadening the scope of computational AFM image analysis and taking on a new SRM approach for structure analysis, this work has presented working approaches towards new tools for quantitative analysis in DNA nanotechnology. Furthermore, the work has presented a new approach to constructing hybrid structures from DNA origami and conjugated polymers, which will open up new possibilities in the construction of nanoelectronic and nanophotonic structures.
|
Page generated in 0.1107 seconds