Browsing by Author "Bechtold, Ivan Helmuth"

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    Efeitos de diferentes extratos de Bidens pilosa L. e da radiação luminosa no processo de isomerização da bilirrubina.
    (2020) Figueiredo, Bruna Inez Carvalho de; Santos, Orlando David Henrique dos; Bianchi, Rodrigo Fernando; Santos, Orlando David Henrique dos; Fontes, Elita Scio; Bechtold, Ivan Helmuth; Coelho, Bruno Nazário; Souza, Gustavo Henrique Bianco de
    A icterícia neonatal, ou hiperbilirrubinemia, ocorre em aproximadamente 60% dos neonatos a termo e 80% dos neonatos prematuros nas primeiras semanas de vida. A icterícia é a manifestação clínica de uma disfunção hepática, onde há o acúmulo de bilirrubina no organismo do recém nascido, podendo ocasionar em síndrome com lesão cerebral irreversível, conhecida como kernicterus. Apesar de décadas de estudos sobre o uso da fototerapia para o tratamento de icterícia neonatal, ainda hoje há um longo caminho a se percorrer em relação à otimização e padronização do tratamento. Neste contexto, o presente estudo busca compreender o efeito dos diferentes comprimentos de onda na isomerização da bilirrubina e avaliar a contribuição da planta Bidens pilosa para a otimização da fototerapia. Os resultados mostraram que a luz azul, quando comparada à luz verde e vermelha, apresentou eficácia superior na cinética de isomerização da bilirrubina. Além disso, foi demonstrado que as luzes vermelha e verde quando utilizadas em diferentes combinações não contribuíram para redução na concentração de bilirrubina. Também foram realizados testes com o intuito de comparar a eficácia da luz azul contínua em relação à luz azul pulsada/intermitente. Os resultados mostram que a luz pulsada apresenta uma eficácia superior à luz contínua, quando submetidas ao mesmo tempo de irradiação, e eficácia equivalente quando a luz intermitente é exposta à metade do tempo da luz contínua. Conclui-se que o intervalo de tempo na irradiação parece influenciar de forma positiva no processo de isomerização da bilirrubina, ocorrendo de forma mais rápida. Além disso, foi possível mostrar o importante papel da espécie Bidens pilosa na otimização da cinética de isomerização da bilirrubina, de forma que seu uso concomitante à fototerapia revelou uma melhora expressiva neste processo. Dessa forma, os resultados indicam a viabilidade de se realizar um tratamento diferenciado, principalmente no que diz respeito ao consórcio da fototerapia com a fitoterapia, otimizando o tratamento e contribuindo para a redução de casos de morbidade e mortalidade decorrentes da hiperbilirrubinemia.
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    High rectification in organic diodes based on liquid crystalline phthalocyanines.
    (2015) Apostol, Petru; Eccher, Juliana; Dotto, Marta Elisa Rosso; Costa, Cassiano Batesttin; Cazati, Thiago; Hillard, Elizabeth A.; Bock, Harald; Bechtold, Ivan Helmuth
    The optical and electrical properties of mesogenic metal-free and metalated phthalocyanines (PCs) with a moderately sized and regioregular alkyl periphery were investigated. In solution, the individualized molecules show fluorescence lifetimes of 4–6 ns in THF. When deposited as solid thin films the materials exhibit significantly shorter fluorescence lifetimes with bi-exponential decay (1.4–1.8 ns; 0.2–0.4 ns) that testify to the formation of aggregates via p–p intermolecular interactions. In diode structures, their pronounced columnar order outbalances the unfavorable planar alignment and leads to excellent rectification behavior. Field-dependent charge carrier mobilities are obtained from the J–V curves in the trap-limited space-charge-limited current regime and demonstrate that the metalated PCs display an improved electrical response with respect to the metal-free homologue. The excited-state lifetime characterization suggest that the p–p intermolecular interactions are stronger for the metal-free PC, confirming that the metallic centre plays an important role in the charge transport inside these materials.
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    Highly luminescent liquid crystals by connecting 1,3,4-oxadiazole with thiazolo[5,4-d]thiazole units.
    (2021) Santos, Arthur Bernardo de Souza; Manfredi, Alex Molina; Salla, Cristian Andrey Momoli; Farias, Giliandro; Girotto, Edivandro; Eccher, Juliana; Westphal, Eduard; Curcio, Sergio Fernando; Cazati, Thiago; Malvestiti, Ivani; Falcão, Eduardo Henrique Lago; Bechtold, Ivan Helmuth; Gallardo, Hugo
    The direct bonding between a thiazolo[5,4-d]thiazole and two 1,3,4-oxadiazole units allowed us to create a new and versatile rigid core for luminescent liquid crystal, which showed interesting and variable mesomorphic and photophysical properties. From the 5-bis(5-phenyl-1,3,4-oxadiazol-2-yl)thiazolo[5,4-d]thiazole new core, three molecules with different number of alkoxy chains were synthesized and had their properties correlated with the molecular structure. The molecule with two chains showed a smectic C mesophase, while the mesogens with four and six chains presented hexagonal columnar mesomorphism, which was confirmed by POM and XRD measurements. In addition, the molecule with six chains presented liquid crystalline behavior close to room temperature. In solution, the molecules presented strong photoluminescence ranging from blue to yellow, with quantum yields higher than 0.6. Excited state lifetimes allowed to correlate the fluorescence component associated to the different emitting species to the molecular organization in spin coated films. The molecular energy levels, together with thermal stability and possible charge carrier transport due to molecular packing, suggest that these molecules are promising for optoelectronic applications. Overall, this work contributes to the development of the use of thiazolo[5,4-d]thiazole in liquid crystals, demonstrating its great efficiency and versatility.
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    Molecular 5,8-π-extended quinoxaline derivatives as chromophores for photoluminescence applications.
    (2019) Aguiar, Leonardo de Oliveira; Lima Junior, Adalberto Santana; Bechtold, Ivan Helmuth; Curcio, Sergio Fernando; Cazati, Thiago; Alves, Tiago Vinicius; Vieira, André Alexandre
    The 5,8-π-extended quinoxaline derivatives are widely studied due to their wellknown photophysical and electrochemical properties. In order to investigate the structure-property relationship, a novel series of fluorescent calamitic liquid crystals based on the quinoxaline heterocycle was successfully synthesized and characterized. The final molecules presented calamitic mesomorphism with nematic and smectic phases. These compounds displayed intense green photoluminescence under UV light excitation in solution and in the solid state. In chloroform solution, the fluorescence quantum yields (ΦFL= 0.54–0.62) of the quinoxaline-based derivatives were significantly higher than those previously described for similar benzothiadiazoles. The maximum emission peaks were between 511-520 nm with singlet excited-state lifetimes in the nanosecond timescale. The solvatochromism studies showed a significant dependence of the emission on the polarity of the solvent. Doping of the quinoxalines with fullerene C60 suggests a charge transfer process, this being dependent on the π-conjugate core. The energy band gaps predicted with DFT calculations are in excellent agreement with the experimental data.
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    New boron(III) blue emitters for all-solution processed OLEDs : molecular design assisted by theoretical modeling.
    (2019) Salla, Cristian Andrey Momoli; Santos, Jéssica Teixeira dos; Farias, Giliandro; Bortoluzzi, Adailton João; Curcio, Sergio Fernando; Cazati, Thiago; Izsák, Róbert; Neese, Frank; Souza, Bernardo de; Bechtold, Ivan Helmuth
    Luminescent boron(III) complexes have recently been employed as emitters in organic light-emitting diodes (OLEDs) with reasonable success. They are easy to prepare and sufficiently stable to be used in such devices, being of great interest as a simple molecular emissive layer. Although emitters for this class with all colors have already been reported, highly efficient and stable blue emitters for applications in solution processed devices still pose a challenge. Here, we report the design, synthesis, and characterization of new boron complexes based on the 2-(benzothiazol-2-yl)phenol ligand (HBT), with different donor and acceptor groups responsible for modulating the emission properties, from blue to red. The molecular design was assisted by calculations using our newly developed formalism, where we demonstrate that the absorption and fluorescence spectra can be successfully predicted, which is a powerful technique to evaluate molecular photophysical properties prior to synthesis. In addition, density functional theory (DFT) enables us to understand the molecular and electronic structure of the molecules in greater detail. The molecules studied here presented fluorescence efficiencies as high as Φ = 0.88 and all solution processed OLEDs were prepared and characterized under an ambient atmosphere, after dispersion in the emitting layer. Surprisingly, even considering these rather simple experimental conditions, the blue emitters displayed superior properties compared to those in the present literature, in particular with respect to the stability of the current efficiency.
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    Reducing lifetime in Cu(I) complexes with thermally activated delayed fluorescence and phosphorescence promoted by chalcogenolate-diimine ligands.
    (2020) Farias, Giliandro; Salla, Cristian Andrey Momoli; Heying, Renata da Silva; Bortoluzzi, Adailton João; Curcio, Sergio Fernando; Cazati, Thiago; Santos, Paloma Lays dos; Monkman, Andrew P.; Souza, Bernardo de; Bechtold, Ivan Helmuth
    Luminescent copper(I) complexes have drawn attention due to their promising performance as alternative optoelectronic materials to the well-known heavy transition metals complexes. Herein, we report the synthesis of six luminescent Cu(I) complexes with phosphines and 1,10-phenanthroline-derived ligands with thiadiazole and selenodiazole groups in order to evaluate the effect of heavy atom on their photophysical properties. Steady-state and time-resolved spectroscopy confirmed delayed fluorescence emission via a thermally activated delayed fluorescence mechanism in all cases. The experimental spectroscopic data was analyzed with detailed quantum-chemical calculations. Interestingly, these complexes did not show the expected “heavy atom effect”, that enhances the spin-orbit coupling matrix elements, but nevertheless the addition of the heavier chalcogens contributed to reduce the photoluminescence lifetime to roughly 800 ns, which is the lowest reported so far for such TADF materials
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    Triplet exciplex electroluminescence from two columnar liquid crystal perylene derivatives.
    (2016) Eccher, Juliana; Almeida, Ana Cláudia Batista; Cazati, Thiago; Seggern, Heinzvon; Bock, Harald; Bechtold, Ivan Helmuth
    Double layers and mixed single layers of two electronically complementary columnar liquid crystals show enhanced performances in light emitting diodes compared to devices made from single layers of only one of the materials. A shift from green to red electro luminescence is observed between single-material and two-material devices, assigned as resulting from triplet exciplexes in the electroluminescence of the two- material films, where as singlet exciplex states contribute to the photoluminescence of the mixture and double layer films.