Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Steady state reflectance and emission characteristics of anthracene adsorbed on silica gel and titania-silica mixed oxides have been investigated as a function of sample loading. Titania-silica mixed oxides with 1, 3, 5 and 10 wt. % TiO2 were prepared by two different methods: a dropwise method and a sol-gel route. Ground state diffuse reflectance and fluorescence emission spectra of anthracene adsorbed on titania-silica surfaces show a dependence on titania content. The absorption peaks of anthracene are difficult to resolve at higher titania content due to the increasing red-shift of the titania absorption edge. The absorption edge of titania is shifted to longer wavelengths and the band gap energy decreases with increasing the titania loading. Diffuse reflectance laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene and gives relevant information regarding the photochemical transients and the kinetics details of the surface photochemical processes. Energy dependence studies confirm the monophotonic nature of the triplet production, whereas the anthracene radical cation is formed by monophoton or multiphoton ionisation in the mixed titania-silica systems. Energy and electron transfer reactions of anthracene co-adsorbed with azulene as electron donor on silica sol-gel and titania-silica mixed oxides prepared by the sol-gel method with different titania content have been studied using the time-resolved diffuse reflectance laser flash photolysis technique. The fluorescence of excited anthracene adsorbed on silica sol-gel is quenched by the addition of azulene, while co-adsorption of azulene on titania-silica mixed oxides resulted in a decrease in the fluorescence intensity of the adsorbed anthracene due to the formation, at the same time, of anthracene radical cation and Ti3+ species on the titania-silica surface. Triplet-triplet energy transfer from the excited anthracene to ground state azulene and electron transfer from azulene to the anthracene radical cation have been investigated using a time-resolved diffuse reflectance laser flash photolysis technique following laser excitation at 355 nm. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been obtained. Kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene concentration. This indicates that the rate of energy and electron transfer reactions increases as a function of azulene concentration and decreases with increasing titania content in titania-silica mixed oxides, whereas the observed rate of reaction on silica sol-gel is predominantly governed by the rate of diffusion of azulene. Electron transfer reactions in a ternary system using azulene for hole transfer between 9-anthracenecarboxylic acid radical cation as electron acceptor and perylene as electron donor were also studied in order to demonstrate the mobility of radical cations on the silica sol-gel and titania-silica surfaces. The co-adsorption of azulene as a molecule shuttle with 9-anthracenecarboxylic acid and perylene on both silica sol-gel and titania-silica systems has been shown to enhance the rate of electron transfer in this ternary system. Activation energies for energy and electron transfer on photoinduced bimolecular and termolecular processes on silica sol-gel and titania-silica mixed oxides have been measured. In bimolecular anthracene / azulene systems, at higher azulene loadings, the activation energies and the pre-exponential factors on titania-silica surfaces are the same for both energy and electron transfer and are comparable with the parameters extracted for azulene diffusion on silica Davisil suggesting that azulene diffuses across the silica Davisil and titania-silica mixed oxides surfaces, while at lower azulene loadings, ion-electron recombination dominates and the activation energy extracted is for this process. In a ternary 9-anthracenecarboxylic acid / azulene / perylene system, the activation energy for perylene diffusion is higher than that observed for the anthracene / azulene system, reflecting the lower mobility of the perylene molecule. In this study, a series of titania-silica samples with different loadings of titania (1 10 wt. %) prepared by the sol-gel method and also the pure TiO2 P25 Degussa have been used to study the photocatalytic degradation of 4-chlorophenol in aqueous solution under UV light irradiation. The absorption peak of 4-chlorophenol at 280 nm decreases with increasing titania content and finally disappeared suggesting that titania has a positive influence on the degradation of 4-chlorophenol. The investigated titania-silica mixed oxides prepared by the sol-gel method are less efficient photocatalysts for the degradation of 4-chlorophenol than TiO2 P25.

Organic light-emitting devices (OLEDs) have attracted significant attention because of their unique advantages for flat panel display applications. However, the relatively limited electroluminescence (EL) stability of blue emitting OLEDs continues to limit the commercialization of full color OLED displays. In most cases, the decrease in EL efficiency is also accompanied by a loss in blue color purity. Thus, the understanding of the degradation mechanisms of both the EL efficiency loss and color purity loss and the corresponding solutions to device degradation are required. In this thesis, electrical aging mechanism in anthracene-based OLEDs is investigated by using a number of techniques, including delayed EL measurements. The studies reveal that electrical aging is associated with an increasing concentration of an intermolecular species with a weak characteristic luminescence at around 535 nm. This species is capable of trapping charges, and thus plays a role as an electron-hole recombination center with prolonged electrical driving. Weak green luminescence from this species leads to an increased green/blue emission ratio, and causes the color purity loss in aged devices. The results also suggest that this species is also efficient in dissipating excitation energy non-radiatively, hence is capable of quenching singlet excitons in anthracene-based OLEDs, contributing to the observed efficiency loss with electrical aging. Moreover, the photo-stability of the organic/metal cathode interface in OLEDs is studied. Irradiating OLEDs by external illumination is found to result in a gradual increase in driving voltage and decrease in EL efficiency. This photo-induced degradation in device performance is found to be caused by changes at the organic/metal cathode interface that lead to a deterioration in electron injection. Evidence of photodegradation of the same interface, inherently, by device own EL, is also reported. The results uncover an important degradation mechanism in OLEDs and shed the light on a phenomenon that might limit the stability of other organic optoelectronic and photovoltaic devices.

<strong>Chapter 1</strong> introduces the concept of spin, how spins interact, and how the spin state in a radical pair can affect the outcome of a chemical reaction between the unpaired electrons. The computational methodology for simulating such radical pairs is also discussed. <strong>Chapter 2</strong> discusses anisotropy in the singlet recombination yield of a radical pair in a carotenoid-porphyrin-fullerene triad, containing many hyperfine couplings. The singlet yield was calculated as a function of the direction of an applied magnetic field, using symmetry in the molecule to reduce the size of the problem. The symmetry reduction was partially successful, however it was not possible to include all the hyperfine couplings in the molecule. <strong>Chapter 3</strong> introduces a radical pair located on a flavin ligand and a tryptophan residue in the protein cryptochrome, and discusses the spin-relaxation mechanism of singlet-triplet dephasing. Magnetic field effect curves, describing the formation of a secondary radical pair as a function of applied magnetic field, were found to be broader in longer-lived radical pairs, due to dephasing caused by spin-selective recombination to the singlet ground state. Additional singlet-triplet dephasing may occur due to hopping of one of the unpaired electrons, between a zone of strong exchange interaction and a zone of negligible exchange interaction, although this is an incomplete description of the spin-relaxation. <strong>Chapter 4</strong> discusses the effect of rotational tumbling on spin-relaxation in the flavin-tryptophan radical pair in cryptochrome. Simulations indicated that the resulting modulation of anisotropic hyperfine couplings contributed modestly to spinrelaxation during transient absorption measurements, but was insufficient to explain the lack of an experimental low-field effect, or to explain the width of the experimental magnetic field effect curves as a function of magnetic field strength. <strong>Chapter 5</strong> discusses magnetic field effects on the mutual annihilation of a pair of triplet excitons in tetracene and anthracene crystals. The experimental singlet recombination yield was found, for the first time, to be modulated as a function of the direction of a applied magnetic field as weak as 2 mT. Simulations indicated that this anisotropy arose due to the zero field splitting of the electronic state in each triplet exciton. The direction of the external magnetic field altered the singlet component of the eigenstates of the Hamiltonian, and therefore altered the timeaverage of the singlet probability of a triplet exciton pair. This is different to the already established mechanism under a strong magnetic field, where the anisotropy arises from level crossings of eigenstates.

Orientadores: José Barreto Campello Carvalheira, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-16T22:41:20Z (GMT). No. of bitstreams: 1 Lixandrao_RenataRodriguesdosSantos_M.pdf: 9485549 bytes, checksum: e66206316ef01c5412be9d8bb78185ec (MD5) Previous issue date: 2010 / Resumo: O tratamento radioterápico é um procedimento capaz de matar células tumorais, expondo elas a doses pré-calculadas de radiação ionizante. A precisão na entrega da dose é fundamental para se obter um tratamento seguro e eficaz. Com o intuito de minimizar as incertezas referentes ao tratamento, é de extrema importância a implementação de procedimentos de Controle de Qualidade (CQ). O presente trabalho apresenta o desenvolvimento e validação de um sistema de detecção de radiação para CQ de feixes clínicos de fótons de megavoltagem. O dosímetro desenvolvido é composto de uma mistura de antraceno e polímero óptico, inserida num capilar de SiO2. O capilar foi acoplado à uma fibra óptica de poly(methyl methacrylate), PMMA, que conduziu o sinal luminoso até a fotomultiplicadora, localizada exteriormente a sala de irradiação e conectada a um eletrômetro. O sinal medido está relacionado à taxa de dose a qual o dosímetro foi exposto. A remoção do sinal de Cerenkov foi realizada utilizando uma fibra de referência para posterior subtração do sinal. A caracterização e os testes de performance do dosímetro foram realizados utilizando um feixe de fótons de 6 MV de um acelerador linear clínico. O desempenho do dosímetro e alguns parâmetros do feixe foram obtidos, analisados e comparados a uma câmara de ionização tipo Farmer FC65. Resultados obtidos demonstraram que o polímero óptico misturado ao antraceno reduziu os efeitos de espalhamento da luz emitida pelo volume sensível, aumentando a eficiência de detecção do sistema. O volume sensível é cerca de 100 vezes menor que o da câmara FC65. A quantidade de luz emitida pelo cintilador e, consequentemente, as leituras obtidas pelo sistema de detecção, aumentam linearmente com a taxa de dose. Medidas de reprodutibilidade foram validadas utilizando análise de variância (ANOVA). As curvas de Porcentagem de Dose Profunda (PDP) e de perfil de dose estão em concordância com as leituras do sistema de referência. Medidas em tempo real realizadas com o dosímetro são coerentes e confiáveis, tornando-o viável para a utilização em CQ. Devido, principalmente, ao seu tamanho reduzido, apresenta um grande potencial para ser usado em casos onde uma alta resolução espacial é necessária (por exemplo, em radiocirurgia e Radioterapia de Intensidade Modulada) / Abstract: Radiation therapy is a procedure capable of kill tumor cells, exposing them to precalculated doses of ionizing radiation. The precision in dose delivery is essential for obtain a safe and effective treatment. To minimize the uncertainties related to treatment, it is extremely important to implement Quality Control (QC) procedures. This work presents development and validation of a radiation detection system for clinical megavoltage photons beams QC. The designed dosimeter is composed of an anthracene and optical polymer mixture inserted on a SiO2 capillary. The capillary was coupled to a poly (methyl methacrylate), PMMA, optic fiber that led the light signal to the photomultiplier located outside the irradiation room and connected to an electrometer. The signal measured is related to the dosimeter exposed dose rate. Removal of the Cerenkov signal was performed using a reference fiber for signal subtraction. The dosimeter characterization and performance tests were performed using a 6 MV clinical linear accelerator photon beam. The dosimeter performance and some beam parameters were obtained, analyzed and compared to a Farmer type ionization chamber FC65. Results showed that the optical polymer mixed with anthracene reduced volume sensitive scintillation light scattering, increasing the system detection efficiency. The sensitive volume is about 100 times smaller than the FC65 camera. The scintillator light emission and, hence, the system detection readings, increase linearly with dose rate. Reproducibility measures were evaluated using analysis variance (ANOVA). The curves of percentage depth dose (PDD) and dose profile are consistent with the system reference readings. Real-time measurements performed with the dosimeter are consistent and reliable, making it feasible for use in QC. Due, mainly, to its small size, has great potential to be used in cases where a high spatial resolution is required (for example, radiosurgery and Intensity Modulated Radiotherapy) / Mestrado / Ciencias Basicas / Mestre em Clinica Medica

Orientador: Sergio Santos Muhlen / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T07:39:48Z (GMT). No. of bitstreams: 1 Onusic_DanielMassaro_M.pdf: 790417 bytes, checksum: 961b20bedda8e7a02cb48b7c666067f6 (MD5) Previous issue date: 2005 / Resumo: Este trabalho descreve a construção de um dispositivo eletrônico para medição de camada semi-redutora em feixes de raios-X de aparelhos de radiodiagnóstico. O dispositivo faz uso de um transdutor constituído por três sensores que utilizam o efeito fotoluminescente do cintilador orgânico antraceno. O sinal luminoso, proporcional à radiação incidente, sensibiliza três fotoresistores que fazem parte de um circuito eletrônico de aquisição e registro de medida. Além das características adequadas de sensibilidade e dependência energética do transdutor construído, é desejável que apresente baixo custo em relação aos transdutores tradicionais. Os resultados obtidos com os protótipos já caracterizados demonstraram a sua viabilidade e encorajam a sua utilização em serviços de campo / Abstract: This work describes the construction and the validation tests of an electronic device able to measure the half value layer in diagnostic X-ray beams. The device utilizes a transducer assembled with three sensors using the photoluminescence of the organic scintillator anthracene. The light signal, proportional to the incident radiation, reaches three photo resistors that are part of the electronic acquisition circuitry and measurement register. Besides adequate features of sensitivity and energy response, it is expected that the assembled transducer present low cost compared to the conventional measurement devices. The results obtained with the characterized prototypes have shown their feasibility and encouraged their use in field services / Mestrado / Engenharia Biomedica / Mestre em Engenharia Biomédica

The gas-phase ion chemistry of hydroxyl- and amino-substituted polycyclic aromatic hydrocarbons (PAHs) and their protonated counterparts were studied using mass spectrometry. Ions were generated using an electron ionization (EI) source and the unimolecular chemistry of metastable ions was studied by performing mass-analysed ion kinetic energy spectrometry (MIKES) experiments with a magnetic sector tandem mass spectrometer. Collision-induced dissociation (CID) experiments were used in conjunction with MIKES experiments to determine ion structure. The ten molecules studied were: 1-naphthol, 2-naphthol, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 1-phenanthrol, 9-phenanthrol, 1-hydroxypyrene and 1-aminopyrene. Since it is believed that larger PAHs, on the order of more than 50 carbon atoms, populate the interstellar medium, the goal of this study was to attempt to extrapolate the results from smaller systems to larger ones. The trends found include: hydroxy-substituted PAH radical cations lose carbon monoxide spontaneously and amino-substituted PAH radical cations lose HCN. Mechanisms for both processes are proposed, and it appears from the present results that this process should extrapolate to larger PAHs. Another trend found was that all the remaining fragment ions were always a closed ring. Protonated amino-substituted PAHs were generated by electrospray ionization using a quadruple time-of-flight mass spectrometer. By protonating 1-naphthol and 2-naphthol using methane in the high-pressure EI source, it was found that they lost exclusively H2O. As for 2-naphthylamine, 1-aminoanthracene and 2-aminoanthracene, it was found that 2-naphthylamine lost NH3 and a hydrogen atom, NH3being the dominant channel. However, as the ion size 3 increases, the hydrogen-loss channel became the dominant channel. This means that larger PAHs will likely lose exclusively a hydrogen atom to reform the parent radical cation.

No description available.

Des récepteurs de barbiturates greffés avec des groupements anthracène photoactifs possédant différentes fonctions d’ancrage ont été synthétisés et caractérisés, en vue de transférer leurs propriétés de reconnaissance photocontrôlable à des substrats par diverses techniques de modification, comme la formation de liaisons amide, de liaisons thioacétate, ou par réaction click. Les propriétés photophysiques et photochimiques de ces récepteurs ont été étudiées en solution, et la fluorescence, la durée de vie et le rendement quantique ont été mesurés à différentes températures. Des surfaces d’or modifiées ont été fabriquées et caractérisées par ellipsométrie, mesure d’angle de contact, AFM et PM-IRRAS. Les résultats montrent qu’il est possible de moduler les propriétés de reconnaissance moléculaire des récepteurs de manière réversible via une combinaison d’irradiation lumineuse (365 nm) et de chaleur (80 °C). / Anthracene-appended photoactive barbiturate receptors possessing various anchoring groups are synthesized and characterized in view of transferring their photocontrolled binding properties onto substrates through various surface grafting techniques, such as amide bond formation, direct thioacetate linkage, or post click reaction modification. The photophysical and photochemical properties of the synthesized receptors were investigated in solution using variable temperature fluorescence, lifetime measurement and reaction quantum yield measurements. Receptor-modified gold substrates were characterized using ellipsometry, contact angle, AFM and PM-IRRAS experiments. The results showed that it is possible to reversibly modulate the binding properties of the anthracene-appended receptors through a combination of the irradiation with light (365nm) and heat (80℃).