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Electronic localization in organic conjugated polymers.

Silva, Rodrigo Ramos da; Caldas, Marilia Junqueira
Fonte: Sociedade Brasileira de Pesquisas em Materiais.; Campos do Jordão Publicador: Sociedade Brasileira de Pesquisas em Materiais.; Campos do Jordão
Tipo: Conferência ou Objeto de Conferência
ENG
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Conjugated polymers are promising organic materials for the development of photovoltaic devices, and the main opto-electronic features are currently under intense study. Concerning the effects induced by disorder effects, conjugation break and localization are supposed to be determinant in the observed properties. As expected the localization of electronic states has dramatic counterparts in the charge carrier mobility and in the exciton formation/dissociation processes.

"Fotoluminescência excitada no ultravioleta em polímeros conjugados"; Photoluminescence excited in the ultraviolet in conjugated polymers

Faleiros, Marcelo Meira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/02/2007 PT
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Os polímeros conjugados luminescentes são materiais com grande potencial tecnológico, mas apesar de estudados desde a década de 80, algumas de suas propriedades óticas ainda não foram totalmente entendidas. Por exemplo, ainda persistem dúvidas quanto à natureza das suas excitações primárias. Nesse sentido foi feito um estudo da fotoluminescência do poli[2-metoxy-5-(2-etil-hexiloxi)-1,4-fenileno vinileno] (MEH-PPV), polímero semicondutor luminescente cujas propriedades ópticas já foram muito investigadas. Além da banda de absorção principal na região visível do espectro, ele possui três bandas no ultravioleta. O objetivo deste trabalho é investigar a fotoluminescência do MEH-PPV quando excitado na região do ultravioleta. Após fotoexcitação no ultravioleta, observou-se apenas a fotoluminescência usual no visível. A intensidade da emissão depende fortemente da energia de excitação, da temperatura e da estrutura morfológica do sistema polimérico, determinada pelo método de preparação das amostras. Os resultados indicam que os estados excitados no ultravioleta relaxam rapidamente de forma não-radiativa até os estados de menor energia, de onde então ocorre a luminescência. Entretanto, a eficiência da fotoluminescência excitada no ultravioleta é consideravelmente reduzida...

Correlação entre polarização da luminescência e orientação molecular em polímeros conjugados; Correlation between luminescence polarization and molecular orientation in conjugated polymers

Maia, Francisco Carlos Barbosa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/08/2006 PT
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Nesta dissertação, visamos o entendimento de processos intermediários que regem a transferência de energia e determinam as propriedades ópticas de polímeros conjugados, a fim de encontrar meios para aumentar a eficiência de emissão e o tempo de vida dos ?LED?s? orgânicos. Estudamos especificamente o polímero PPV, poli(p-fenileno vinilideno), sintetizado através de novo método desenvolvido no Grupo de Polímeros do Instituto de Física de São Carlos, por Marletta e colaboradores[1], na forma de filmes finos depositados pelas técnicas ?spincast? e de automontagem (LbL). Para o trabalho utilizamos técnicas espectroscópicas de luminescência, excitação seletiva e absorbância. Por meio de técnicas de engenharia molecular e através do ordenamento induzido da rede polimérica, avaliamos o peso que têm os eventos intermediários à emissão. Estiramos gradualmente filmes de PTHT/PPV depositados sobre Teflon, sob um eixo preferencial, e constatamos a dependência da polarização da luz emitida com processos de transferência de energia e com a anisotropia da matriz polimérica. Realizamos a separação das cadeias do copolímero a fim de analisar separadamente a transferência de energia entre os segmentos conjugados pertencentes a cadeias distintas (processos intercadeia) ou ao longo da cadeia (processos intracadeia). Esta separação intercadeia e intracadeia resultaram em um significativo aumento da eficiência da emissão...

Estudo atomístico da desordem eletrônica em filmes amorfos de polímeros conjugados; Atomistic Study of Electronic Disorder on Amorphous Films of Conjugated Polymers

Silva, Rodrigo Ramos da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/10/2014 PT
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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...

Processos ópticos em semicondutores híbridos formados por nanofios heteroestruturados de AlGaAs/GaAs e polímero conjugado com potencial aplicação em dispositivos fotovoltaicos; Optical processes in hybrid semiconductor nanowires formed by heterostructures of GaAs/AlGaAs / GaAs and conjugated polymer with potential application in photovoltaic devices

Caface, Raphael Antonio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/07/2015 PT
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Dispositivos fotovoltaicos híbridos baseados em polímeros conjugados e semicondutores inorgânicos estão sendo utilizados nos últimos anos para a produção de células de energia solar com baixo custo. Para que haja uma alta eficiência é necessária dissociação eficiente de éxcitons, por isso é importante conhecer os níveis de energias dos componentes do dispositivo fotovoltaico. O presente estudos mostra que o sistema híbrido formado por nanofios cilíndricos preparados com heteroestrutura radial de camadas alternadas de GaAs/AlGaAs/GaAs recobertas com polímero conjugado poli-fenileno vinileno (PPV) forma uma opção alternativa para a fabricação de dispositivos fotovoltaicos. Os nanofios foram fabricados por Epitaxia por Feixe Molecular (MBE). Tanto potencial interno radial e modulação energética axial produzem a separação eficiente de elétrons e buracos fotoexcitados, que gera emissões de natureza e origem distintas e singulares nos nanofios: emissões envolvendo a impurezas aceitadoras no centro do núcleo de GaAs, bem como éxcitons indiretos presos a interface WZ e BZ e a interface da barreira estreita de AlGaAs na casca do nanofio. Medidas do decaimento temporal da emissão mostram uma forte dependência tempo de vida com o comprimento de onda...

Effect of the length of alkyl side chains in the electronic structure of conjugated polymers

Oliveira, Eliezer Fernando; Lavarda, Francisco Carlos
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: 0-0
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Computational modeling studies of conjugated polymers have been shown to present many challenges. One such challenge is to find ways to reduce the computational cost for these studies without compromising the quality of the results. An approach longly used in the literature for this purpose is replacing long alkyl side chains (with six or more carbons) with a methyl group. This work reports on a theoretical study conducted with the conjugated polymer poly(3-hexylthiophene), which contains a hexyl side chain attached to the monomer, to verify the influence of the size of the alkyl side chain on its electronic structure. The results indicated that, for polymers containing long alkyl side chains, replacement with a propyl group offered full saturation of all properties under review, showing it to be a good approach.

Modelling the effect of non-planarity on luminescence energy of conjugated polymers

Correia, Helena M. G.; Barbosa, Helder M. C.; Ramos, Marta M. D.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /06/2006 ENG
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We present theoretical investigations of structural and electronic properties of ground-state and low-lying excited singlet states in isolated chains of conjugated polymers using a self-consistent quantum molecular dynamics method. With this approach, we have determined the energy of both states as function of the twist angle between two planar segments of the same polymer chain, for polymer chains with variable length. The conjugated polymers investigated here are poly(para-phenylene vinylene) (PPV) and polydiacetylene (PDA). Our results show that the energy of the excited-state increases more than that of the ground-state, as the twist angle increases up to 90º degrees. The change in the twist angle of both polymers leads to a blueshift in luminescence transition energy, the effect being stronger in PPV when the planar segments have similar sizes. The predicted blueshift in both polymers is dependent on the chain length, the effect being more pronounced for shorter-chains.; Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional “Ciência , Tecnologia, Inovação” – POCTI/CTM/41574/2001, CONC-REEQ/443/2001 e SFRH/BD/11231/2002; Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER)

Solventless processing of conjugated polymers - a review

Brandão, Lúcia; Viana, Júlio; Bucknall, David G.; Bernardo, Gabriel
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2014 ENG
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The molecular mobility of polymers in their solid or molten states allows their processing without the need for toxic, “non-friendly” solvents. In this work, the main features of solvent-free processing methods applied to conjugated polymers are reviewed taking into consideration that these materials are largely used in a broad range of (opto-)electronic applications, including organic field-effect transistors, polymer light-emitting diodes and polymer photovoltaic devices. This review addresses the main advantages of processing such materials in their solid state offering an alternative fabrication scheme for several opto-electronic devices. Moreover, the properties of polymer-based opto-electronic devices are largelydependent on the conformations and orientations of polymer molecules in the corresponding polymer thin film layers; especially the ordering of conjugated polymer molecules in the active layer has beena topic of intense research in organic electronics. Therefore, this review also highlights the control of conjugated polymer molecule ordering when using solvent free processing techniques. Finally, conclusions and perspectives of solventless processed conjugated polymer molecules in organic electronics are addressed.; This work was supported by FCT (Foundation for Science and Technology-PORTUGAL) through the program PEst-C/CTM/LA0025/2013 (Strategic Project—LA 25-2013–2014) and by the European Regional Development Fund (FEDER) through the program COMPETE (project PTDC/CTM-POL/120843/2010). L. Brandão is grateful to FCT for the post-doc grant(SFRH/BPD/41233/2007).

Effect of the length of alkyl side chains in the electronic structure of conjugated polymers

Oliveira,Eliezer Fernando; Lavarda,Francisco Carlos
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2014 EN
Relevância na Pesquisa
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Computational modeling studies of conjugated polymers have been shown to present many challenges. One such challenge is to find ways to reduce the computational cost for these studies without compromising the quality of the results. An approach longly used in the literature for this purpose is replacing long alkyl side chains (with six or more carbons) with a methyl group. This work reports on a theoretical study conducted with the conjugated polymer poly(3-hexylthiophene), which contains a hexyl side chain attached to the monomer, to verify the influence of the size of the alkyl side chain on its electronic structure. The results indicated that, for polymers containing long alkyl side chains, replacement with a propyl group offered full saturation of all properties under review, showing it to be a good approach.

Recent Advances in Conjugated Polymers for Light Emitting Devices

AlSalhi, Mohamad Saleh; Alam, Javed; Dass, Lawrence Arockiasamy; Raja, Mohan
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 21/03/2011 EN
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A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore...

Molecular Engineering of Amphiphilic Pyridine Incorporated Conjugated Polymers for Metal Ion Sensors

Vetrichelvan, Muthalagu; Valiyaveettil, Suresh
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 409386 bytes; application/pdf
EN_US
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Recent developments in the synthesis and structure-property investigation studies of conjugated polymers have led to the design of novel polymeric materials with tailored properties for advanced technological applications. A promising development in this direction involves the fabrication of conducting polymer based sensors for the detection of metal ions and small organic molecules. Herein, we designed, synthesized and studied a series of amphiphilic copolymers containing alternate phenylene and 2,5- or 2,6- or 3,5-substituted pyridine rings. The basic N-atom of the pyridine ring and the adjacent –OH group from the phenyl ring provide binding sites for metal ions. Thermal properties, and optical properties of polymers in presence of acid, base and metal ions are investigated. A few target polymers showed high sensitivities for metal ions in solution.; Singapore-MIT Alliance (SMA)

Optimizing the excited state processes of conjugated polymers for improved sensory response; Optimization of energy migration in conjugated polymers for improved sensory response

Rose, Aimee, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 125 p.; 4414783 bytes; 4414590 bytes; application/pdf; application/pdf
ENG
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Conjugated polymers exhibit useful and interesting electrical and optical properties. We exploit the wandering excitons produced after photoexcitation for chemosensory applications. By sampling many sites in a polymer film, the excitation has a greater chance to encounter an analyte, such as 2,4,6 trinitrotoluene (TNT), electrostatically poised to induce non-radiative decay. The result is attenuation of the fluorescence signal characteristic of these bright polymers. Because energy migration is responsible for the amplification of sensory response, we sought to augment this migration by integrating chromophores with long-lived excited states into the polymer backbone. The first chromophore we targeted, triphenylene, has a symmetrically-forbidden ground state transition, resulting in a long excited state lifetime. Chapter 2 describes the synthetic incorporation of triphenylene into conjugated polymer backbones, and Chapter 3 details the spectroscopic interrogation of these materials. We demonstrate that lifetime extension is universal to all triphenylene-containing polymers. The longer excited state lifetimes are then correlated with increased energy migration through polarization spectroscopy. In Chapter 4, we extend this paradigm for elongating energy migration in conjugated polymers to several other systems. Unique polymers with symmetric...

Molecular Engineering of Conjugated Polymers for Sensor Applications

Vetrichelvan, Muthalagu; Valiyaveettil, Suresh
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 174577 bytes; application/pdf
EN
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In recent years, the application of fluorescent conjugated polymers for sensing chemical and biological analytes has received much attention from many researchers. A promising development in this direction was the fabrication of conducting polymer-based sensors for the detection of metal ions, small organic molecules and biomolecules. Herein, we have designed, synthesized and studied a series of copolymers containing alternate phenylene and 2,5- or 2,6-substituted pyridine rings. The basic N-atom of the pyridine ring and the adjacent –OH group from the phenyl ring provide binding sites for metal ions. Another series of water-soluble conjugated polymers with propoxy sulfonate side chains are investigated for biosensor applications. Significant quenching of the polymer fluorescence upon addition of viologen derivatives was also observed. The quenching effect on the polymer fluorescence confirmed that the newly synthesized polymers can be useful in the application of metal and biological sensors.; Singapore-MIT Alliance (SMA)

Synthetic Approaches to Flexible Fluorescent Conjugated Polymers

Vokata, Tereza
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
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Conjugated polymers (CPs) are intrinsically fluorescent materials that have been used for various biological applications including imaging, sensing, and delivery of biologically active substances. The synthetic control over flexibility and biodegradability of these materials aids the understanding of the structure-function relationships among the photophysical properties, the self-assembly behaviors of the corresponding conjugated polymer nanoparticles (CPNs), and the cellular behaviors of CPNs, such as toxicity, cellular uptake mechanisms, and sub-cellular localization patterns. Synthetic approaches towards two classes of flexible CPs with well-preserved fluorescent properties are described. The synthesis of flexible poly(p-phenylenebutadiynylene)s (PPBs) uses competing Sonogashira and Glaser coupling reactions and the differences in monomer reactivity to incorporate a small amount (~10%) of flexible, non-conjugated linkers into the backbone. The reaction conditions provide limited control over the proportion of flexible monomer incorporation. Improved synthetic control was achieved in a series of flexible poly(p-phenyleneethynylene)s (PPEs) using modified Sonogashira conditions. In addition to controlling the degree of flexibility...

Femtosecond pump-push-probe and pump-dump-probe spectroscopy of conjugated polymers: new insight and opportunities

Kee, T.W.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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Conjugated polymers are an important class of soft materials that exhibit a wide range of applications. The excited states of conjugated polymers, often referred to as excitons, can either deactivate to yield the ground state or dissociate in the presence of an electron acceptor to form charge carriers. These interesting properties give rise to their luminescence and the photovoltaic effect. Femtosecond spectroscopy is a crucial tool for studying conjugated polymers. Recently, more elaborate experimental configurations utilizing three optical pulses, namely, pump–push–probe and pump–dump–probe, have been employed to investigate the properties of excitons and charge-transfer states of conjugated polymers. These studies have revealed new insight into femtosecond torsional relaxation and detrapping of bound charge pairs of conjugated polymers. This Perspective highlights (1) the recent achievements by several research groups in using pump–push–probe and pump–dump–probe spectroscopy to study conjugated polymers and (2) future opportunities and potential challenges of these techniques.; Tak W. Kee; Publication Date (Web): September 3, 2014

Transient absorption spectra of triplet states and charge carriers of conjugated polymers

Burrows, H. D.; Miguel, M. da G.; Monkman, A. P.; Hamblett, I.; Navaratnam, S.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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The use of pulse radiolysis to study transient species in conjugated polymers in solutions is discussed, with particular reference to poly(2-methoxy-5-(2'-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV). The excited triplet state is specifically generated by energy transfer on radiolysis of benzene solutions in the presence of suitable sensitisers, and its spectrum is reported. The presence of vibronic structure suggests a localised triplet state. By varying the energy of the sensitiser, it is possible to determine the energy of the lowest triplet state. Results are also presented for the triplet-triplet absorptions and energies of five other common [pi]-conjugated polymers. The MEH-PPV triplet absorption, produced on radiolysis, does not increase linearly with either polymer concentration or radiation dose. This is suggested to be due to the presence of multiple triplet excitations on the isolated polymer chains. Intrachain triplet-triplet annihilation is observed, and is seen to lead to delayed fluorescence. Spectra are also reported for the positive and negative charge carriers of MEH-PPV and the other polymers specifically produced by pulse radiolysis of the polymers in chloroform or tetrahydrofuran solutions.; http://www.sciencedirect.com/science/article/B6TGS-435M5SD-6/1/35fa76e4ff83689ba132587736150e3a

Triplet state spectroscopy of conjugated polymers studied by pulse radiolysis

Monkman, A. P.; Burrows, H. D.; Miguel, M. da G.; Hamblett, I.; Navaratnam, S.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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Using the technique of pulse radiolysis we have elucidated the energies and kinetics of triplet states in soluble luminescent conjugated polymers. Using poly(2-methoxy,5-(2'-ethyl-hexoxy)-p-phenylenevinylene) MEH-PPV as an example we explain this technique and show how it can be used to study the triplet states in conjugated polymers. Triplet energy transfer is used to determine 11Ag-13Bu energy gaps and the kinetics of triplet-triplet absorption yields triplet lifetimes. In the case of MEH-PPV, at concentrations up to 50 mg/l, the triplet decay rate shows no change, indicating self-quenching of triplets is not significant. However, if very high electron beam doses are used, high intra chain triplet concentrations can be generated. In this high concentration regime triplet-triplet annihilation becomes effective, as determined by the onset of delayed fluorescence.; http://www.sciencedirect.com/science/article/B6TY7-41XMFCG-P/1/21372c53eea4a9fc396cc3fa02a342f0

Processos radiativos e não radiativos em polímeros conjugados emissores de luz.; Radiactive and non-radiactive processes in light-emitting conjugated polymers.

Borges, Célio Aécio Medeiros
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/11/2001 PT
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O presente trabalho tem como objetivo estudar os processos radiativos e não radiativos em filmes automontados de poli(p-fenileno vinileno), ou PPV, sintetizados e processados no Grupo de Polímeros Prof. Bernhard Gross (GPBG) do IFSC. Além de adquirir conhecimento das propriedades ópticas fundamentais, tais como, os mecanismos básicos responsáveis pela emissão de luz, foram investigados os efeitos da temperatura, da redução da dimensionalidade através do tamanho efetivo de conjugação, das impurezas e dos defeitos estruturais. Foram realizados estudos das propriedades ópticas desse material através das seguintes técnicas espectroscópicas: fotoluminescência (PL), absorção óptica, fotoluminescência por excitação seletiva (PLE). As propriedades estruturais e de superfícies do PPV foram estudadas por infravermelho (IR) e microscopia de força atômica (AFM). A adsorção de camadas alternadas do polímero precursor poli(cloreto de tetrahidrotiofeno de xilideno) (PTHT) e do íon de cadeia longa dodecilbenzenosulfônico (DBS) propiciou a formação de filmes finos com controle de monocamada. A introdução do DBS permitiu a conversão rápida (~10min) destes filmes em PPV a temperaturas muito mais baixas (~100 'graus'C) e com baixa incorporação de defeitos do que aquelas usadas convencionalmente. A boa qualidade estrutural e o alto grau de conjugação destes filmes de PPV foram responsáveis pela boa resolução dos espectros de absorção e emissão...

Quantum molecular dynamics simulations of conjugated polymers

Almeida, A. M.; Ramos, Marta M. D.; Cadilhe, A. M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /05/2002 ENG
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The softness of conjugated polymers leads to strong coupling between polymer's electrons and lattice vibrations. Therefore, it is necessary to perform quantum molecular dynamics computer simulations in order to study their electronic and optical properties at molecular level. We have used self-consistent molecular dynamics calculations with interatomic forces evaluated from quantum mechanical calculations at the complete neglect of differential overlap level to discuss some of the issues relating to the electronic processes involved in polydiacetylene and poly(p-phenylene vinylene). Specifically addressed are the charge induced structural changes of the polymer chains and the intra-molecular charge mobility. The change in the chemical potential of individual polymer strands at zero temperature is also discussed. Our results suggest a geometrical distortion in the bond length distribution relative to the uncharged chains which is accompanied by changes in atomic charges at the distortion site. The charge carrier mobility is predicted to depend on the strength of the electric field, in accordance with experiments.

Synthesis and applications of electron deficient conjugated polymers

Kim, Youngmi, Ph. D
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 235 leaves; 9155748 bytes; 9170987 bytes; application/pdf; application/pdf
ENG
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Chapter 1. In this introductory chapter, we present the general properties of conjugated polymers for sensory and electronic applications, with a special emphasis placed on electron-deficient materials. Chapter 2. In this chapter is presented the synthesis, characterization, and applications of a series of electron-deficient poly(p-phenylene vinylene)s (PPVs) homopolymers and copolymers. Poly(p-phenylenevinylene)s containing trifluoromethyl substituted aromatic rings (CF3- PPVs) exhibited high photooxidative stability to give robust materials suitable for molecular electronic device applications. Chapter 3. Hyperconjugative and Inductive Perturbations in Poly(p-phenylene vinylenes) New approaches that produce high fluorescence quantum yields and also tune electron affinity of conjugated polymers are presented. Novel three-dimensional poly(phenylene vinylenes) having [2.2.2] bicyclic ring system were synthesized to give highly efficient solid- state fluorescence and hyperconjugative and inductive electronic perturbations. The ability of hyperconjugative and inductive perturbation to tune the polymers' sensory applications was determined by investigating the fluorescence quenching responses to electron-rich and electron-deficient analytes in solution and solid thin films. Chapter 4. High Ionization Potential Conjugated Polymers In this chapter is presented a series of poly(p-phenylene ethynylenes) (PPEs) with high ionization potentials. Their photophysical properties were investigated using steady-state and time-resolved fluorescence techniques.; (cont.) The ionization potentials of the polymer thin films were determined using ultraviolet photoelectron spectroscopy (UPS)...