Delayed Fluorescence by Triplet–Triplet Annihilation from Columnar Liquid Crystal Films

Delayed fluorescence (DF) by triplet–triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO–LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF. In contrast to the DF from the monomeric imidoester in solution, DF of the imide occurs from dimeric aggregates in the blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal molecule as the emitting layer

Preliminary studies of the cytotoxicity and photoprotective properties of Benzophenone and Lactone derivatives.

A Radia??o solar ultravioleta(RUV) pode induzir efeitos ? pele devidos a sua a??o direta ou indireta, por meio da gera??o de radicais livres. Esses efeitos podem provocar diversas les?es na pele humana como o c?ncer de pele. Como medida de prote??o da pele contra os efeitos da radia??o solar pode-se citar o uso de protetores solares, produtos t?picos adicionados de filtros solares UV sint?ticos com propriedades de absor??o e reflex?o de raios solares.Um fotoprotetor org?nico ideal deve proteger a pele contra os raios UVB (290-320 nm) e UVA (320-400 nm), possuir um fator de prote??o solar (FPS) seguro, ser fotoest?vel e n?o ser fotot?xico. Este trabalho objetiva em estudos preliminares de fotoprote??o dos derivados das Benzofenonas e Lactonas. Os produtos obtidos foram sintetizados e caracterizados por t?cnicas espectrosc?picas usuais e foram submetidos a ensaios de viabilidade celular frente ao MTT e determina??o do valor de prote??o solar (FPS) in vitro pelo m?todo espectrofotom?trico UV/VIS. Os espectros de IV, RMN de 1 H e RMN de 13C mostraram bandas e sinais em conformidades com as estruturas propostas para os compostos estudados. Os compostos 1 e2 apresentaram um FPS proporcional ? concentra??o analisada, ou seja, quanto maior a concentra??o, maior ? o Fator de Prote??o, por?m o composto 3 apresentou fator prote??o menor em concentra??es mais elevadas. No estudo de viabilidade celular, os compostos 1 e 2 n?o foram citot?xicos nas concentra??es avaliadas neste trabalho.Ultraviolet solar radiation can generate free radicals that damage skin and cause skin lesions or skin cancer. Sunscreens are a protective measure against the effects of solar radiation that protects the skin by absorbing or reflecting solar rays. Ideally, the sunscreen should protect the skin against UVB (290-320 nm) and UVA (320-400 nm) rays, be photostable and non-toxic. This work describes a preliminary study on the SPF of a benzophenone and a lactone derivative. The synthesized compounds were characterized by spectroscopic techniques, submitted to cell viability assays against MTT and SPF determined in vitro by UV/VIS spectroscopy measurements. The spectroscopic data was in agreement with the proposed structures of the compounds studied. The SPF was proportional to concentration, and in one case, the sun protection factor was lower at higher concentrations. The benzophenone derivatives were evaluated for toxicity by a cell viability study, and found to be non-cytotoxic at the tested concentrations

Preparation and characterization of a quercetin-tetraethyl ether-based photoprotective nanoemulsion.

Although Quercetin absorbs in the UVA/UVB electromagnetic region, it is limited for applications as a UV filter due to its low lipophilicity and capacity to penetrate the epidermis. In order to overcome this limitation, we synthetized and evaluated the photo protective properties of a derivative obtained from Quercetin. The derivative was prepared by alkylation of Quercetin with iodoethane and characterized by IR and NMR spectroscopy. The in vitro Solar Protection Factor was determined by the Mansur method and the cytotoxicity was evaluated using hepatocellular cell (Hep G2) cells. Finally, Quercetin and the corresponding derivative were incorporated in nanoemulsions. Nanoemulsions with particles sizes between 53 and 73 nm were obtained, and polydispersity indexes were around 0.1, indicating good homogeneity of the nanoemulsion particles. The cell viability study for the Quercetin derivative indicated a very low cytotoxicity profile. The chemical modification of Quercetin resulted in a promising compound with improved properties desirable for skin penetration and incorporation into sunscreen formulations

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Polímeros conjugados têm sido tema de várias pesquisas devido à sua potencial idade de aplicação em dispositivos optoeletrônicos. Esses materiais apresentam propriedades luminescentes que envolvem processos fotofísicos ainda pouco compreendidos devido à grande variedade morfológica assumida por suas cadeias poliméricas. Neste trabalho, apresentamos os resultados que evidenciam a influência da morfologia molecular (ordenamento e empacotamento) no estado final da polarização da luz emitida (luminescência) pelos filmes de poli(p-fenileno vinileno) (PPV). Foram preparados filmes de PPV com diferentes ordenamentos moleculares, obtidos a partir dos seguintes métodos e técnicas de montagem de filmes: Casting, Spin-Coating (SC), Langmuir-Blodgett (LB) e Self-Assembly (S.A). As propriedades ópticas dos filmes foram investigadas através das medidas de absorção (UV-VIS) polarizada, de fotoluminescência (PL) em diferentes temperaturas (10 K a 300 K) e da análise da polarização da luz emitida. As medidas ópticas de absorção e de emissão de luz polarizada revelaram que os filmes obtidos por Langmuir-Blodgett, Casting e SelfAssembly com estiramento mostraram-se anisotrópicos, emitindo luz com polarização na direção do estiramento ou de imersão (quando preparados por LB), independente da direção de polarização da luz de excitação. Os filmes obtidos por Casting e SpinCoating, por outro lado, mostraram-se isotrópicos, emitindo luz com polarização na direção da polarização da luz de excitação. Os resultados obtidos da medida da polarização da luz emitida evidenciaram a ocorrência de transferência de energia entre moléculas. Deste modo, utilizou-se a teoria de Forster (radiação dipolo-dipolo) para explicar os resultados obtidos para os diferentes filmes de PPV, permitindo correlacioná-la com as propriedades ópticas e com o ordenamento molecular dos filmesSince the first report of polymer light-emitting diodes (PLEDs), there have been considerable efforts to understand the emission process in luminescent polymers. However, many aspects related to this process are still under investigation, as the influence of morphology assumed by the polymeric chains. In this work we studied the influence of the molecular morphology, as ordering and packing, on the polarized light emitting of poly(p-phenylenevinylene) - PPV films. It was obtained films with different molecular arrangements from different assembly techniques, as Casting, Spin-Coating (SC), Langmuir-Blodgett (LB), and Self-Assembly (S.A). The optical property was investigated by absorption spectroscopy (UV-VIS), photoluminescence spectra (PL), and polarized light-emitting. The optical measurements disclosed that LB-PPV films, Casting-PPV and S.A-PPV stretched films were optically anisotropic, where the direction of the light-emitting is the same of the stretched direction or dipping preparation. In the other hand, Casting-PPV and Spin-Coating did not have such behavior, i.e., the emitted polarized light propagated in the same direction of the polarization of the excitation light. These data acquired from the optical measurements indicate a relation between morphology and photophysical process involving energy transfer via Forste

Photoconduction effect in single layer diodes based on PPV derivatives.

Esta tese de doutorado é resultado do estudo da fotocondutividade em materiais poliméricos, com particular enfoque em diodos poliméricos com camada ativa de derivados do poli (p-fenileno vinileno) (PPV): OC10-PPV, SY e MEH-PPV, em estrutura tipo sanduíche (ITO/polimérico/Metal) de camada única, utilizando eletrodos metálicos com diferentes funções trabalho depositados sobre o mesmo filme. Para isso, foi necessária a realização de todas as etapas de fabricação de dispositivos orgânicos, como descritas neste trabalho, para obter resultados com o máximo de reprodutibilidade, bem como o domínio das técnicas de caracterização. As propriedades ópticas dos filmes poliméricos foram analisadas através dos espetros de absorção e de fluorescência estacionária na região do visível. O comportamento fotocondutivo dos dispositivos foi realizado através de medidas de corrente-tensão (I-V) e da espectroscopia de fotocorrente no estado estacionário em regime dc sob incidência de luz com diferentes comprimentos de onda, ora através do ITO, ora através dos eletrodos metálicos semitransparente, para o dispositivo sob diferentes valores de tensões aplicadas. A variação desses parâmetros permitiu verificar como estes influenciam na fotogeração e no transporte de portadores de cargas e assim adaptar e aplicar um modelo teórico que levasse em consideração o campo elétrico aplicado para ajustar a fotocorrente obtida experimentalmente, obtendo informações sobre as propriedades de fotocondutividade dos materiais estudos.This thesis is a study about photoconductivity in polymeric materials, in particular diodes with single-layer sandwich structure derivates of poly(para-phenylene vinylene) (PPV): OC10-PPV, SY and MEH-PPV. Different metallic electrodes were deposited on the same polymeric layer. Therefore, it was necessary to realize the devices fabrication process step by step as well to dominate the characterization techniques. The optical properties of polymeric film were analyzed through the absorption and emission spectrum in the visible region. The photoconductivity behavior was studied by dc current-voltage (I-V) and photocurrent action spectra through the absorption and emission spectrum in the visible region. The photoconductivity behavior was studied by dc current-voltage (I-V) and photocurrent action spectra through the both side of device under applied voltages. The variation of these parameters allowed verifying how are influencing in the charge carrier photo-generation and the charge transport and then to adapt and apply a theoretical model wich considers the electric field applied to fit the photocurrent action spectra of devices. The values of the parameters allow to survey important about photoconductivity properties of the material

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Polímeros conjugados têm sido tema de várias pesquisas devido à sua potencial idade de aplicação em dispositivos optoeletrônicos. Esses materiais apresentam propriedades luminescentes que envolvem processos fotofísicos ainda pouco compreendidos devido à grande variedade morfológica assumida por suas cadeias poliméricas. Neste trabalho, apresentamos os resultados que evidenciam a influência da morfologia molecular (ordenamento e empacotamento) no estado final da polarização da luz emitida (luminescência) pelos filmes de poli(p-fenileno vinileno) (PPV). Foram preparados filmes de PPV com diferentes ordenamentos moleculares, obtidos a partir dos seguintes métodos e técnicas de montagem de filmes: Casting, Spin-Coating (SC), Langmuir-Blodgett (LB) e Self-Assembly (S.A). As propriedades ópticas dos filmes foram investigadas através das medidas de absorção (UV-VIS) polarizada, de fotoluminescência (PL) em diferentes temperaturas (10 K a 300 K) e da análise da polarização da luz emitida. As medidas ópticas de absorção e de emissão de luz polarizada revelaram que os filmes obtidos por Langmuir-Blodgett, Casting e SelfAssembly com estiramento mostraram-se anisotrópicos, emitindo luz com polarização na direção do estiramento ou de imersão (quando preparados por LB), independente da direção de polarização da luz de excitação. Os filmes obtidos por Casting e SpinCoating, por outro lado, mostraram-se isotrópicos, emitindo luz com polarização na direção da polarização da luz de excitação. Os resultados obtidos da medida da polarização da luz emitida evidenciaram a ocorrência de transferência de energia entre moléculas. Deste modo, utilizou-se a teoria de Forster (radiação dipolo-dipolo) para explicar os resultados obtidos para os diferentes filmes de PPV, permitindo correlacioná-la com as propriedades ópticas e com o ordenamento molecular dos filmesSince the first report of polymer light-emitting diodes (PLEDs), there have been considerable efforts to understand the emission process in luminescent polymers. However, many aspects related to this process are still under investigation, as the influence of morphology assumed by the polymeric chains. In this work we studied the influence of the molecular morphology, as ordering and packing, on the polarized light emitting of poly(p-phenylenevinylene) - PPV films. It was obtained films with different molecular arrangements from different assembly techniques, as Casting, Spin-Coating (SC), Langmuir-Blodgett (LB), and Self-Assembly (S.A). The optical property was investigated by absorption spectroscopy (UV-VIS), photoluminescence spectra (PL), and polarized light-emitting. The optical measurements disclosed that LB-PPV films, Casting-PPV and S.A-PPV stretched films were optically anisotropic, where the direction of the light-emitting is the same of the stretched direction or dipping preparation. In the other hand, Casting-PPV and Spin-Coating did not have such behavior, i.e., the emitted polarized light propagated in the same direction of the polarization of the excitation light. These data acquired from the optical measurements indicate a relation between morphology and photophysical process involving energy transfer via Forste

Influence of intensive light exposure on the complex impedance of polymer light-emitting diodes.

In this work we investigated the effect of visible radiation on the electrical properties of poly[(2-methoxy-5 hexyloxy)-p-phenylenevinylene]– MH-PPV films and light emitting diodes. Complex impedance measurements of (Au or ITO)/MH-PPV/(Au or Al) samples were carried out at room temperature and exposed to white light. Over the frequency range from 100 mHz to 2 MHz, the electrical results of Au/MH-PPV/Au was dominated by the Cole-Cole approach, where the electrode influence is negligible. However, some additional influence of the interface was observed to occur when Al was used as electrode. These effects were observed under both dark and visible-light illumination conditions. A simple model based on resistor-capacitor parallel circuits was developed to represent the complex impedance of the samples, thereby separating bulk and interface contributions. We observed that the polymer electrical resistivity decreased while the dielectric constant of the polymer and the thickness of the Al/MH-PPV layer were almost constant with increasing light intensity. The decrease of the polymer layer resistance comes from a better charge injection due to a light induced dissociation of positive charge carriers at the electrode