Emissive conjugated polymers, namely PPV, PPP, polyfluorenes, etc, have gained considerable attention in recent times, specifically because of their potential application in the fields of PLED’s, displays, FET’s and sensors. The main target of the present work is the synthesis and utilization of dithiocarbamate (DTC) precursor polymers for: (a) generation of segmented conjugated polymers of poly[2-methoxy-5-((2'-ethylhexyl)oxy)-1,4- phenylenevinylene], MEHPPV-x, for color control and the study of their thermal elimination kinetics, (b) modulating phase separation and energy transfer in MEHPPV-x blends, (c) generation of tunable two-color patterns of conjugated polymers and (d) modification of the precursor polymer backbone by grafting and the study of its fluorescence modulation in the presence of different probe molecules. In the first part of this work, various dithiocarbamate (DTC) precursor copolymers, MDP-x, containing two types of leaving groups viz. methoxy and diethyldithiocarbamate with precise control over the DTC composition, were synthesized. Thermal elimination of these precursor polymers generated segmented MEHPPV with controlled conjugation, and hence the tuning of color from green to red is achieved (figure 1). These copolymers were synthesized via a modified Wessling’s route previously developed in our laboratory.1 The advantage of the DTC precursor over the acetate and xanthate precursor routes was that the elimination can be carried out at lower temperature (160OC) for the generation of segmented MEHPPV-x.2 (Figure 1) Kinetic parameters, namely activation energy (Ea) and pre-exponential factor (A), associated with the thermal elimination process of MDP-x to MEHPPV-x were determined in solution and as well as in thin films by following the evolution of the absorption spectra during the elimination process (figure 2). It was seen that the activation energy required for the elimination process was similar in both thin film and solution, whereas the pre-exponential factor was two order magnitude higher in thin films.2 This fact holds good for all the DTC compositions investigated. The thermal degradation products, carbon disulphide and diethyl amine, were analyzed using a mass spectrometer coupled with TGA instrument, confirming the selective elimination of the DTC groups. (Figure 2) Phase separation and energy transfer characteristics of segmented MEHPPV blends containing two different distributions of conjugation lengths, namely MEHPPV-8 (LC) and MEHPPV-100 (HC), were investigated using FL, UV and confocal fluorescence microscopic studies (figure 3). The phase separation and energy transfer in blends of the HC and LC were (Figure 3) modulated by addition of selective non-solvent for HC, namely cyclohexane, to the film casting solution. Typically, the extent of energy transfer to HC from LC is reduced in the presence of high volume fraction of cyclohexane.3 A novel way to generate two-color patterned substrates of MEHPPV was developed based on the control of “molecular conjugation length” using standard photo-acid generator based photolithographic methods (figure 4). This approach relies on the use of a single precursor containing controllable amounts of two types of thermally eliminatable groups, only one of which eliminates in the presence of an acid while the other that is labile even in its absence. An important feature of this approach is that the colour of the unexposed regions can be controlled by varying the composition of the MDP-x precursor. (Figure 4) Benzyl diethyl dithiocarbamate (BDTC) is known to act as iniferter (initiator-transfer agent and terminator). MDP-x precursor polymers, which contain similar benzyl dithiocarbamate groups, were used as macro-iniferter for grafting various acrylates, viz, (Figure 5) methyl acrylate, benzoyloxy ethyl acrylate and t-butyl acrylate, on to the precursor backbone, which resulted in MEHPPV-g-polyacrylate after acid catalyzed thermal elimination of the residual methoxy groups (figure 5).4 The t-butyl acrylate-grafted precursor polymers, namely, MDP-g-PtBA on thermal elimination in presence of acid underwent simultaneous acid-catalyzed thermal elimination as well as the complete hydrolysis of the t-butyl groups, leading to the formation of water soluble MEHPPV-grafted with polyacrylic acid chains, namely MEHPPV-g-PAA (figure 6). These PAA-grafted MEHPPV’s were shown to respond to various probe molecules and their optical responses were studied using fluorescence spectroscopy. These polymers could sense methyl viologen at very low concentrations. Single-tail ammonium surfactants and non-ionic surfactant, like triton-X-100, caused a dramatic enhancement of fluorescence in solution, due to the modulation of the conjugated backbone conformation, and as a consequence the break up of intra-chain inter-chromophore excitons (figure 6). (Figure 6) Fof figures and molecular formula pl see the original thesis)

Fluorescence energy transfer from poly(9,9-dioctylfluorene) to polymeric energy acceptors that include head-to-tail regioregular poly(3-hexylthiophene or P3HT) and poly(2-methoxy-5(2 -ethylhexyloxy)-1,4-phenylenevinylene) or MEH-PPV and monomeric acceptor meso-tetraphenylporphyrin or TPP was studied and correlated with the underlying morphology when the donor-acceptor blends were prepared as drop-coated films or breath-figure structures. It was found that the phase-separate morphology in films and breath figures was influenced by a number of factors, including material transport dynamics, solubility of the blend components in a solvent, interaction of the solvent with the substrate, and the diffusion rate of the blend components.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Na investigação científica, o desenvolvimento de novas técnicas de produção de filmes com boas propriedades físicas é de grande importância para áreas de pesquisas como a eletrônica orgânica. No entanto, as implicações causadas por campo elétrico, temperatura e pressão positiva em materiais orgânicos constitui um dos pontos importantes a serem bem compreendidos a fim de evitar problemas na eficiência de emissão em diodos emissores de luz poliméricos (PLEDs). Entender e esclarecer os efeitos de interfaces eletrodo/polímero e polímero/polímero, bem como também a aplicação de pressão externa sobre a estabilidade óptica e elétrica dos dispositivos são passos essenciais para a compreensão, e consequentemente desenvolvimento de dispositivos com melhores desempenhos.1 Por este ângulo, neste trabalho investigamos os efeitos de processos externos como: campo elétrico, temperatura e pressão externa sobre a eficiência de emissão do polímero poli(2-metoxi-5-(2'- etil-hexiloxi)-1,4-fenilenovinileno) (MEH-PPV) em filme na estrutura de PLED. Foi possível correlacionar a dependência da fotoluminescência (PL) para diferentes polarizações do laser (linear ou circular), polarização da tensão aplicada (direta ou reversa) e sobre as temperaturas de relaxação molecular (Tß ~220K e Tα ~330K). Além disso, foram investigados os efeitos induzidos pela aplicação de pressão positiva sobre o dispositivo na temperatura próximo da Tß do MEH-PPV, demonstrando uma quebra na simetria de filme amorfo de MEH-PPV spin- coated, cujo efeito pode ser evitado através de tratamentos de annealing dos dispositivos (T > Tg) ou alterando a interface polímero/polímero. Também investigamos o efeito do campo elétrico na estabilidade térmica de dispositivo PLED utilizado o polímero luminescente poli(9,9'-n-dihexil-2,7-fluorenodiilvinileno-alt-1,4-fenilenovinileno) (LAPPS16) como camada ativa. Demonstramos que os perfis dos espectros da fotoluminescência e eletroluminescência são semelhantes, mostrando que os mecanismos envolvidos na geração dos estados excitados não mudam significativamente o processo de recombinação radiativa. No entanto, apesar de terem o mesmo processo fotofísico, mostramos que os processos não radiativos ativados termicamente são bastante diferentes entre a PL e EL, demonstrando que esses dois processos de emissão não são diretamente relacionados. Por fim, realizamos caracterizações ópticas e elétricas de filmes finos, transparentes e flexíveis de seleneto de cobre (Cu2-XSe) demonstrando que é possível sua aplicação como eletrodo injetor de buraco em dispositivos PLEDs apresentando boas propriedades, sendo obtidos através de técnicas simples e de baixo custo. Os diodos emissores foram processados utilizando o Cu2-XSe como eletrodo ânodo e como camada ativa utilizamos o polímero MEH-PPV. Demonstramos que o filme de Cu2-xSe apresentou boa estabilidade elétrica com valores de resistência de folha de ~148 Ω/❑ e energia de bandgap de ~2,3eV, cujos valores são propícios para aplicações em dispositivos eletrônicos. Também mostramos via fotoluminescência e eletroluminescência que os filmes de Cu2-xSe possuem propriedades de emissão e através dos PLEDs utilizando o Cu2- xSe como eletrodo investigamos a barreira de energia para os portadores de carga na interface eletrodo/polímero e analisamos os mecanismos de transportes de cargas presentes nestes dispositivos. / Scientific research to development of new film production techniques with good physical properties is of great importance to research areas such as organic electronics. However, the implications caused by electric field, temperature and positive pressure on organic materials is an important point to be understood in order to avoid problems in the emission efficiency of polymer light emitting diodes (PLEDs). Understand and clarify the effects of electrode/polymer and polymer/polymer interfaces as well as the application of external pressure on the optical and electrical stability of the devices are essential steps towards understanding, and consequently the development of devices with better performances.1 In this sense, this study we investigated the effects of external processes such as: electric field, temperature and external pressure on the emission efficiency poly (2- methoxy-5- (2'-ethyl-hexyloxy) -1,4-phenylenevinylene) (MEH-PPV) film in PLED structure. It was possible to correlate the photoluminescence (PL) depends for different laser polarization (linear or circular), on the polarization voltage (forward and reverse) and on MEH-PPV molecular ß-relaxation (Tß~ 220K) and α-relaxation (Tα ~ 330K) temperatures. Furthermore, we investigated the effects induced by application of positive pressure on device at next temperature Tß MEH-PPV, it showing a break in the symmetry of amorphous film of MEH-PPV spin-coated, the effect can be avoided by annealing treatment the device (T> Tg) or altering the polymer/polymer interface. We also investigated the effect of electric field in the thermal stability of PLED device based on light-emitting polymer poly[(9,9-dihexyl-9H- fluorene-2,7diyl)-1,2-ethenediyl-1,4-phenylene-1,2-ethenediyl] (LAPPS16) as active layer. We showed that profiles of the photoluminescence and electroluminescence spectra are similar, showing that mechanisms involved in the generation of excited states do not significantly change the radiative recombination process. However, despite they have the same photophysical process, we showed that non-radiative processes thermally activated are quite different between the PL and EL, demonstrating that these two emission processes are not directly related. Finally, we performed optical and electrical characterization of thin films, transparent and flexible copper selenide (Cu2-xSe) demonstrating that it is possible its application as hole injector electrode for PLEDs devices exhibiting good properties, being obtained through simple techniques at low cost. Emitting diodes were processed using the Cu2-xSe as anode electrode and as active layer we use the MEH-PPV polymer. We showed that Cu2-xSe film exhibited good electrical stability with sheet resistance values of ~148 Ω/□ and bandgap energy of ~2,3eV, whose values are suitable for applications in electronic devices. We also showed through photoluminescence and electroluminescence that Cu2-xSe films have emission properties and by PLEDs using Cu2-xSe as electrode, we investigated the energy barrier for charge carriers at electrode/polymer interface and we analyzed charge transport mechanisms present in these devices. / Tese (Doutorado)

No description available.

Background: Measurement of carbon monoxide in expired air samples (ECO) is a non-invasive, cost-effective biochemical marker for smoking. Cut points of 6. ppm-10. ppm have been established, though appropriate cut-points for pregnant woman have been debated due to metabolic changes. This study assessed whether an ECO cut-point identifying at least 90% of pregnant smokers, and misidentifying fewer than 10% of non-smokers, could be established. Methods: Pregnant women (N=167) completed a validated self-report smoking assessment, a urine drug screen for cotinine (UDS), and provided an expired air sample twice during pregnancy. Results: Half of women reported non-smoking status early (51%) and late (53%) in pregnancy, confirmed by UDS. Using a traditional 8. ppm. +. cut-point for the early pregnancy reading, only 1% of non-smokers were incorrectly identified as smokers, but only 56% of all smokers, and 67% who smoked 5. + cigarettes in the previous 24. h, were identified. However, at 4. ppm. +, only 8% of non-smokers were misclassified as smokers, and 90% of all smokers and 96% who smoked 5. + cigarettes in the previous 24. h were identified. False positives were explained by heavy second hand smoke exposure and marijuana use. Results were similar for late pregnancy ECO, with ROC analysis revealing an area under the curve of 95 for early pregnancy, and 94 for late pregnancy readings. Conclusions: A lower 4. ppm ECO cut-point may be necessary to identify pregnant smokers using expired air samples, and this cut-point appears valid throughout pregnancy. Work is ongoing to validate findings in larger samples, but it appears if an appropriate cut-point is used, ECO is a valid method for determining smoking status in pregnancy.

Background: Measurement of carbon monoxide in expired air samples (ECO) is a non-invasive, cost-effective biochemical marker for smoking. Cut points of 6. ppm-10. ppm have been established, though appropriate cut-points for pregnant woman have been debated due to metabolic changes. This study assessed whether an ECO cut-point identifying at least 90% of pregnant smokers, and misidentifying fewer than 10% of non-smokers, could be established. Methods: Pregnant women (N=167) completed a validated self-report smoking assessment, a urine drug screen for cotinine (UDS), and provided an expired air sample twice during pregnancy. Results: Half of women reported non-smoking status early (51%) and late (53%) in pregnancy, confirmed by UDS. Using a traditional 8. ppm. +. cut-point for the early pregnancy reading, only 1% of non-smokers were incorrectly identified as smokers, but only 56% of all smokers, and 67% who smoked 5. + cigarettes in the previous 24. h, were identified. However, at 4. ppm. +, only 8% of non-smokers were misclassified as smokers, and 90% of all smokers and 96% who smoked 5. + cigarettes in the previous 24. h were identified. False positives were explained by heavy second hand smoke exposure and marijuana use. Results were similar for late pregnancy ECO, with ROC analysis revealing an area under the curve of 95 for early pregnancy, and 94 for late pregnancy readings. Conclusions: A lower 4. ppm ECO cut-point may be necessary to identify pregnant smokers using expired air samples, and this cut-point appears valid throughout pregnancy. Work is ongoing to validate findings in larger samples, but it appears if an appropriate cut-point is used, ECO is a valid method for determining smoking status in pregnancy.

No description available.

A presente tese de doutorado deu início a uma nova linha de pesquisa no grupo de Síntese de Polímeros Condutores do IQ-USP, que consiste nos estudos relacionados a sensores de gases para equipamentos do tipo narizes eletrônicos, confeccionados com polímeros condutores. Para isso, foram sintetizados eletroquimicamente sete polímeros da família dos poli(p-fenileno vinileno)s, dos quais cinco inéditos, substituídos por grupos receptores e doadores de elétrons.Todos os polímeros, incluindo seus precursores, foram caracterizados espectroscopicamente (RMN de 1H, IV e UV-Vis). Estudos de análises térmicas (TG e DSC) e de cromatografia por exclusão de tamanho (SEC) foram realizados com os polímeros que possuíam grupos alifáticos de cadeias longas, tendo sido um desses polímeros usado na confecção de dispositivos metal/polímero/metal, cujas medidas de corrente vs. tensão permitiram determinar a mobilidade dos portadores de carga. Sensores de gases foram feitos com os polímeros sintetizados, mostrando boa seletividade quando testados com vapores de uma série de solventes orgânicos polares e apolares. / In this thesis we describe the electrosynthesis of seven difterent poly(p-phenilenevinylene)s, PPVs, bearing long and short, electron donating and withdrawing side groups. These polymers are aimed for our recent interest in gas sensors based on conducting polymers and their application in electronic noses. Five out of the seven polymers are novel materials, hence never described before. The polymers were characterized spectroscopically. Those with long side chain were also submitted to thermal analyses and size exclusion chromatography. Electrical measurements (I x V) in metal/polymer/metal sandwich devices led to the determination of the charge carrier mobility of one of the polymers. Gas sensors, having thin films of the synthesized polymers as active layers, have shown good selectivity towards several organic solvent vapors and water as well.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / In this work we made a theoretical study of absorption line-shape of poly (pphenylene vinylene) (PPV). The model was applied in films processed by techniques: spin-coating (SC), layer-by-layer (LbL), and Langmuir-Blodgett (LB). The probability of electronic transitions was calculated based on the molecular model of excitons, Franck-Condon states, Gaussian distribution of non-entangled chains with conjugate degree n, semi-empirical parameterization of energy gap, electric dipole moment, and electron-vibrational mode coupling. Based on the approach of the energy gap functional dependence 1/n, the inclusion of the non-homogeneity energy dispersion 1/n2 is essential to obtain good experimental data agreement, mainly, where the absorption spectra display peaks width of about 65 meV. For unresolved absorption spectra, such as those observed for a large number of conjugated polymers processed via spin-coating technique, for example, the non-homogeneity energy dispersion parameterization is not significant. We develop a model to describe the possible chemical reactions of conversion of poly(xylyliden tetrahydrothiophenium chloride) (PTHT) monomers to PPV monomers and PPV monomers in others monomers of different degrees of conjugation. The dependence 1/n of the functional energy gap was compared with experimental data oligomers and calculations optimized geometry by Density Functional Theory (DFT). Effects of exciton confinement were considered in the transition dipole moment functional. Simulations to calculate the oscillator strength of the absorption spectra in PPV oligomers indicate that the HOMO-LUMO state prevails over other excited states. Results obtained from the use of the distribution of the random walk are as good as those achieved by the use of Gaussian distribution of conjugated segments in simulations of absorption spectra of the PPV. The use of transition dipole moment functional, which includes the effect of exciton confinement together with the distribution of the random walk provide good results in adjustments theoretical absorption spectra of PPV with more consistent physical parameters. / Nesse trabalho fizemos um estudo teórico da forma de linha de absorção do poli(p-fenileno vinileno) (PPV). O modelo foi aplicado em filmes processados pelas técnicas: spin-coating (SC), layer-by-layer (LbL) e Langmuir-Blodgett (LB). A probabilidade de transição eletrônica foi calculada com base no modelo do exciton molecular, estados de Franck-Condon, distribuição Gaussiana de cadeias não emaranhadas com grau de conjugação n, parametrização semi-empírica do gap de energia, do momento de dipolo elétrico e do acoplamento eletrônico vibracional. Baseamos na aproximação do funcional do gap de energia de dependência 1/n, a inclusão da dispersão de energia não homogênea 1/n2, que é essencial para se obter uma boa concordância com os dados experimentais, principalmente em casos, onde o espectro de absorção apresenta picos com largura de aproximadamente 65 meV. Em espectros de filmes pouco definidos, tais como os processados pela técnica spin-coating, a dispersão de energia não homogênea não é significativa. Desenvolvemos um modelo para descrever as possíveis reações químicas de conversão de monômeros de poli- (cloreto de xilideno tetrahidrotiofeno) (PTHT) em PPV e de monômeros de PPV em outros de diferentes graus de conjugação. A dependência 1/n do funcional do gap de energia foi comparada com dados experimentais de oligômeros de PPV e cálculos otimizados da geometria pela Teoria do Funcional da Densidade (DFT). Efeitos de confinamento de exciton foram considerados no funcional do momento de dipolo de transição eletrônica. Simulações feitas para calcular a força de oscilador no espectro de absorção em oligômeros de PPV indicam que o estado HOMO-LUMO prevalece sobre outros estados excitados. Resultados obtidos pelo uso da distribuição do passeio aleatório são tão bons quanto aos realizados pelo uso da distribuição Gaussiana de segmentos conjugados em simulações de espectros de absorção do PPV. O uso do funcional do momento de dipolo de transição, que inclui efeito de confinamento de excitons, junto com a distribuição do passeio aleatório propiciam bons resultados nos ajustes teóricos de espectros de absorção do PPV com parâmetros físicos mais consistentes. / Doutor em Física

A presente tese de doutorado deu início a uma nova linha de pesquisa no grupo de Síntese de Polímeros Condutores do IQ-USP, que consiste nos estudos relacionados a sensores de gases para equipamentos do tipo narizes eletrônicos, confeccionados com polímeros condutores. Para isso, foram sintetizados eletroquimicamente sete polímeros da família dos poli(p-fenileno vinileno)s, dos quais cinco inéditos, substituídos por grupos receptores e doadores de elétrons.Todos os polímeros, incluindo seus precursores, foram caracterizados espectroscopicamente (RMN de 1H, IV e UV-Vis). Estudos de análises térmicas (TG e DSC) e de cromatografia por exclusão de tamanho (SEC) foram realizados com os polímeros que possuíam grupos alifáticos de cadeias longas, tendo sido um desses polímeros usado na confecção de dispositivos metal/polímero/metal, cujas medidas de corrente vs. tensão permitiram determinar a mobilidade dos portadores de carga. Sensores de gases foram feitos com os polímeros sintetizados, mostrando boa seletividade quando testados com vapores de uma série de solventes orgânicos polares e apolares. / In this thesis we describe the electrosynthesis of seven difterent poly(p-phenilenevinylene)s, PPVs, bearing long and short, electron donating and withdrawing side groups. These polymers are aimed for our recent interest in gas sensors based on conducting polymers and their application in electronic noses. Five out of the seven polymers are novel materials, hence never described before. The polymers were characterized spectroscopically. Those with long side chain were also submitted to thermal analyses and size exclusion chromatography. Electrical measurements (I x V) in metal/polymer/metal sandwich devices led to the determination of the charge carrier mobility of one of the polymers. Gas sensors, having thin films of the synthesized polymers as active layers, have shown good selectivity towards several organic solvent vapors and water as well.