Thesis (Ph.D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Not embargoed. Vita. Bibliography: 198-212.

In this thesis, an experimental and theoretical study of two and three vector correlations in the inelastic scattering of NO(X) with various rare gas atoms is presented. Vector correlations for a selection of rare gas systems were determined experimentally, and the observations were interpreted using a variety of classical and quantum mechanical models. The experiment is able to provide state-to-state resolution of the dynamics by means of an electrostatic hexapole and 1+1' resonantly enhanced multi-photon ionisation (REMPI). The simplest vector correlation of interest is the differential cross section (DCS), given by the <b>k</b>-<b>k</b>' correlation. The DCSs were determined experimentally for the NO(X)--Kr and NO(X)--Xe collision systems, both characterised by the relatively deep (&asymp;140cm^-1) attractive well and large extent of the attractive potential. The agreement between the experimental angular distributions and quantum mechanical DCS is very good for both systems. Classical calculations fail to correctly reproduce the form and magnitude of the DCS for either system, reflecting the inherently quantum mechanical nature of the collision. The classical calculations do however provide mechanistic insight into regions where the attractive part of the potential plays an important role in determining the dynamics. In order to investigate narrow angular features in the forward scattered direction, several experimental improvements to molecular beams and the detection ion-optic stack were made. Investigation into these structures revealed a strong contribution from molecular diffraction into the classical shadow of the NO(X), and the simple Fraunhofer model revealed a preference for scattering from an individual m&rarr;m' sub-state. Such measurements are in a region of the DCS where scattering is forbidden classically, and reveal the purely quantum nature of the collision interaction in the forward scattered direction. The low order <b>k</b>-<b>k</b>' correlation was then extended by using linearly or circularly polarised laser excitation. The interaction of the light with the molecular dipole allows the measurement of the <b>k</b>-<b>k</b>'-<b>j</b>' correlation. When linearly polarised light was used for the excitation laser, two of the rank two p^{2}_q(&theta;) renormalised polarisation dependent differential cross sections (PDDCSs), which describe rotational alignment, were obtained. With circularly polarised light, the rank one p^{1}_1-(&theta;) renormalised PDDCSs describing rotational orientation were determined. The collision induced alignment in NO(X)--Xe scattering was found to be well reproduced by classical and impulsive theories, highlighting the fact that the alignment is dominated by the propensity for the projection of <b>j</b> onto the kinematic apse to be conserved. The attractive part of the potential does augment the alignment renormalised PDDCSs, and this is most evident in states with strong features of the attractive part of the potential such as ℓ-type rainbows. The orientation is more strongly influenced by the attractive part of the potential and is also influenced by parity. In addition to the parity effect, there exist two limiting classical mechanisms which govern the orientation, one caused by attraction and the other repulsion. Finally, the bond axis of the NO(X) can be oriented by means of hexapole state selection combined with adiabatic orientation using a set of guiding rods. The integral steric effect, an <b>r</b>-<b>k</b> correlation, was measured for the NO(X)--Kr and NO(X)--Ar spin-orbit changing systems. There are large oscillations in the sign of the steric asymmetry which occur for scattering with the various rare gases. There are also large differences between the rare gases as the potentials become more attractive, and more isotropic. The steric asymmetry is well reproduced by quantum mechanics, however, a classical mechanism becomes dominant at high &Delta;j.

Ce travail porte sur l'étude de nanoparticules scintillatrices qui sont capables, par définition, de convertir un rayonnement ionisant en lumière visible ou proche UV. Si le processus de scintillation est actuellement bien connu dans le cas des matériaux macroscopiques, les perturbations susceptibles d'apparaître pour des nanomatériaux le sont moins. En effet, des modifications peuvent être induites par le confinement spatial et les spécificités de structure propres aux nanomatériaux. L'étude de ces perturbations constitue l'objet de cette thèse. Le manuscrit se divise en trois parties. La première vise à quantifier la fraction d'énergie qui se dépose dans une assemblée de nanoparticules après interaction avec un photon haute énergie (X ) ou en réalisant des simulations Monte Carlo basées sur le code de calcul Geant4. La deuxième partie présente un travail expérimental exploratoire qui consiste à comparer des mesures de spectroscopie résolue en temps pour des nanoparticules et un monocristal afin d'extraire des informations sur les étapes de thermalisation et de recombinaison radiative spécifiques aux nanoparticules. La dernière partie de ce manuscrit présente l'étude d'une application novatrice des nanoscintillateurs comme agents thérapeutiques. Ils sont alors utilisés pour activer sous excitation X l'effet photodynamique, base d'une thérapie anti-cancéreuse actuellement limitée au traitement de lésions superficielles / This work deals with scintillating nanoparticles, material able to convert ionizing radiations into visible or Ultra-Violet light. The scintillation process is currently well-known for bulk materials. However, for nanomaterials, several steps of the scintillation process are likely to be slightly modified mainly because of the spatial confinement of charges and the structure specificities in nanomaterials. The study of such perturbations is the aim of this thesis. The manuscript is divided into three parts. The first one aims to quantify the amount of deposited energy within a set of nanoparticles after the interaction with a high energy photon (X or –rays). We thus developed Monte Carlo simulations with the Geant4 toolkit to quantify this energy. The second part presents an exploratory experimental study that consists in comparing time resolved spectroscopy measurements for nanoparticles and a single crystal. The aim is to extract a few tendencies on the thermalization and on the radiative recombination processes specific to nanoscintillators. The last part of this thesis presents an application of nanoscintillators as therapeutic agents. In that case, they are used to activate the photodynamic effect under X-ray irradiation. This last effect is the basis of the photodynamic therapy, an anticancer treatment currently limited to superficial tumors

xvi, 218 p. : ill. (some col.) / Our theoretical studies involve the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation. Our control strategy is based upon the fact that, following impulsive electronic excitation, nuclear motion acts to change the instantaneous energy difference between site-excited electronic states and thereby influences short-time electronic excitation transfer (EET). By inducing coherent intramolecular vibration in one of the chromophores prior to short-pulse electronic excitation, we exert external control over electronic dynamics. As a means to monitor this coherent control over EET, we propose using multidimensional wave-packet interferometry (md-WPI). Two pairs of polarized phase-related femtosecond pulses following the control pulse would generate superpositions of coherent nuclear wave packets in optically accessible electronic states. Interference contributions to the time- and frequency-integrated fluorescence signal due to overlaps among the superposed wave packets provide amplitude-level information on the nuclear and electronic dynamics. We test both the control strategy and its spectroscopic investigation by calculating pump-probe difference signals for various combinations of pulse polarizations. That signal is the limiting case of the control-influenced md-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference signals for a variety of systems including a simplified model of the covalent dimer dithia-anthracenophane (DTA) in which we treat only the weakly Franck-Condon active ν 12 anthracene vibration at 385 cm -1 . We further present calculated nl-WPI difference signals for an oriented DTA complex, which reveal amplitude-level dynamical information about the interaction of nuclear motion and electronic energy transfer. We also present pump-probe difference signals from a model system in which a CF 3 group, whose torsional angle is strongly Franck-Condon active, has been added to the anthracene monomers which make up DTA. We make use of electronic structure calculations to find the torsional potential of the monomer, from which we calculate the spectroscopic signals of the dimer. We show that a significant measure of control over short-time EET is achievable in this system. This dissertation includes previously published coauthored material. / Commitee in charge: Dr. Michael E. Kellman, Chair; Dr. Jeffrey A. Cina, Advisor; Dr. David R. Herrick; Dr. Andrew H. Marcus; Dr. Daniel A. Steck

Magister Scientiae - MSc (Chemistry) / Nanoscience and nanotechnology are known to be interdisciplinary, crossing and combining various fields and disciplines in pursuit of desirable outcomes. This has brought about applications of nanoscience and nanotechnology in multitudes of industries, spanning from the health, pharmaceutical to industrial industry. Within the health industry, the medical field has seen much advancement through nanoscience and nanotechnology. The importance of finding cures to diseases is top priorities within the medical field, along with advancements in understanding and diagnosing diseases. Due to these outcomes, we see the emergence of imaging techniques playing a crucial role. The work covered in this thesis looks at a prospective luminescent agent applicable in the medical field for bio-imaging, but also at a possible phthalocyanine sensitizer for treatment of cancer through photodynamic therapy. Another area where nanoscience and nanotechnology are found is in industry, where nanoparticles are utilised as catalysts in many synthetic reactions. Highly desirable catalysts in industry are those involved in oxidative reactions where we explore a metal nanoparticle catalyst within this work.

abstract: Photosystem I (PSI) is a multi-subunit, pigment-protein complex that catalyzes light-driven electron transfer (ET) in its bi-branched reaction center (RC). Recently it was suggested that the initial charge separation (CS) event can take place independently within each ec2/ec3 chlorophyll pair. In order to improve our understanding of this phenomenon, we have generated new mutations in the PsaA and PsaB subunits near the electron transfer cofactor 2 (ec2 chlorophyll). PsaA-Asn604 accepts a hydrogen bond from the water molecule that is the axial ligand of ec2B and the case is similar for PsaB-Asn591 and ec2A. The second set of targeted sites was PsaA-Ala684 and PsaB-Ala664, whose methyl groups are present near ec2A and ec2B, respectively. We generated a number of mutants by targeting the selected protein residues. These mutations were expected to alter the energetics of the primary charge separation event. The PsaA-A684N mutants exhibited increased ET on the B-branch as compared to the A-branch in both in vivo and in vitro conditions. The transient electron paramagnetic resonance (EPR) spectroscopy revealed the formation of increased B-side radical pair (RP) at ambient and cryogenic temperatures. The ultrafast transient absorption spectroscopy and fluorescence decay measurement of the PsaA-A684N and PsaB-A664N showed a slight deceleration of energy trapping. Thus making mutations near ec2 on each branch resulted into modulation of the charge separation process. In the second set of mutants, where ec2 cofactor was target by substitution of PsaA-Asn604 or PsaB-Asn591 to other amino acids, a drop in energy trapping was observed. The quantum yield of CS decreases in Asn to Leu and His mutants on the respective branch. The P700 triplet state was not observed at room and cryogenic temperature for these mutants, nor was a rapid decay of P700+ in the nanosecond timescale, indicating that the mutations do not cause a blockage of electron transfer from the ec3 Chl. Time-resolved fluorescence results showed a decrease in the lifetime of the energy trapping. We interpret this decrease in lifetime as a new channel of excitation energy decay, in which the untrapped energy dissipates as heat through a fast internal conversion process. Thus, a variety of spectroscopic measurements of PSI with point mutations near the ec2 cofactor further support that the ec2 cofactor is involved in energy trapping process. / Dissertation/Thesis / Doctoral Dissertation Biochemistry 2014

abstract: Sunlight, the most abundant source of energy available, is diffuse and intermittent; therefore it needs to be stored in chemicals bonds in order to be used any time. Photosynthesis converts sunlight into useful chemical energy that organisms can use for their functions. Artificial photosynthesis aims to use the essential chemistry of natural photosynthesis to harvest solar energy and convert it into fuels such as hydrogen gas. By splitting water, tandem photoelectrochemical solar cells (PESC) can produce hydrogen gas, which can be stored and used as fuel. Understanding the mechanisms of photosynthesis, such as photoinduced electron transfer, proton-coupled electron transfer (PCET) and energy transfer (singlet-singlet and triplet-triplet) can provide a detailed knowledge of those processes which can later be applied to the design of artificial photosynthetic systems. This dissertation has three main research projects. The first part focuses on design, synthesis and characterization of suitable photosensitizers for tandem cells. Different factors that can influence the performance of the photosensitizers in PESC and the attachment and use of a biomimetic electron relay to a water oxidation catalyst are explored. The second part studies PCET, using Nuclear Magnetic Resonance and computational chemistry to elucidate the structure and stability of tautomers that comprise biomimetic electron relays, focusing on the formation of intramolecular hydrogen bonds. The third part of this dissertation uses computational calculations to understand triplet-triplet energy transfer and the mechanism of quenching of the excited singlet state of phthalocyanines in antenna models by covalently attached carotenoids. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2016

Cette thèse s’est focalisée sur le développement de nanocristaux semi-conducteurs luminescents, i.e. des boîtes quantiques (quantum dots, QDs), pour des applications photo-induites. Ces nanomatériaux possèdent des propriétés optiques très intéressantes qui dépendent de leur taille et sont prometteurs pour des applications dans divers domaines.Les QD sont généralement hydrophobes mais de nombreuses applications intéressantes requiert une compatibilité avec l'eau ou du moins avec un environnement polaire. Cela, nécessite donc un traitement post-synthétique afin de modifier leur solubilité.Au cours de cette thèse, une nouvelle méthode pour transférer les QDs d'un solvant apolaire vers un solvant polaire a été développée en les fonctionnalisant avec l'acide lipoïque, un tensioactif complexant.L'acide lipoïque est une molécule chirale générant donc un effet de dichroïsme induit qui a pu être étudier, ainsi que sa dépendance vis-à-vis la taille des nanocristaux.Un objectif clef de ces recherches était le développement de QDs présentant un transfert d'énergie électronique réversible (REET). Il s’agit d’un transfert d'énergie bidirectionnel entre les QDs photoexcités et des unités chromophores appropriées fixées sur leur surface, dont la conséquence la plus importante est l'allongement de la durée de vie de luminescence du QD.Enfin, un nouveau protocole pour le dépôt de QDs chargés sur un substrat vitreux localement polarisé a été développé en collaboration avec le Dr Marc Dussauze de l'Université de Bordeaux. / This thesis focuses on the development of luminescent semiconductor nanocrystals quantum dots (QDs) for photoinduced applications. QDs are promising nanomaterials with size-dependent optical properties and are attractive for applications in several fields.However, QDs are commonly hydrophobic and many interesting applications require their compatibility with water or at least with a polar environment, meaning a post-synthetic treatment is required to confer a different solubility.During these studies, a new method for transferring QDs from an apolar solvent to another one polar has been successfully developed, by exploiting lipoic acid, as a versatile surface capping agent. Moreover, lipoic acid is a chiral molecule so a possible induced dichroism effect has been also investigated, as well as its dependence on the size of nanocrystals.A major aim of this research was the development of QDs exhibiting reversible electronic energy transfer (REET). Such a process is a bidirectional energy transfer between the photoexcited QDs and suitable chromophoric units attached on their surface, whose most important consequence is the elongation of the luminescence lifetime of the QD. Strong experimental evidence for REET and accompanying modifications of the photophysical properties has been obtained. Such a process to our knowledge has never been observed in QD-based systems.Finally, a novel protocol for depositing charged QDs on a locally polarized glassy substrate has been developed in collaboration with Dr. Marc Dussauze of the University of Bordeaux.

Submitted by ANA KARLA PEREIRA RODRIGUES (anakarla_@hotmail.com) on 2017-08-02T13:41:04Z No. of bitstreams: 1 arquivototal.pdf: 3866821 bytes, checksum: 1b8fc11ea5100eea54ea37850025d528 (MD5) / Made available in DSpace on 2017-08-02T13:41:04Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3866821 bytes, checksum: 1b8fc11ea5100eea54ea37850025d528 (MD5) Previous issue date: 2016-02-29 / This work reports the synthesis, characterization and the investigation of photoluminescence properties of systems [Ln(DPM)2(NO3)(L)2] and [Ln(L)3(NO3)3] (where L = THPO or TPPO and Ln3+ = Tb3+, Gd3+ or Eu3+), and the dimeric compounds [Eu2(DPM)6] and [Tb2(DPM)6]. The compounds were characterized by elemental analysis of CHN, vibrational spectroscopy in the infrared region, thermogravimetric analysis and their spectroscopic properties were investigated by molecular diffuse reflectance, excitation and emission as well as decay times of emitting states. The experimental data of CHN analysis and complexometric titrations of the synthesized complexes are in agreement with theoretical data for their respective formulas. The absorption spectra in the infrared region show that the coordination of β-diketonate and phosphine oxide ligands to the Ln3+ ions occurs by the oxygen atoms of carbonyl groups and P=O, respectively. The structural behavior of complexes [Eu(DPM)2(NO3)(TPPO)2] and [Tb (DPM)2(NO3)(TPPO)2] is significantly different from those dimeric ones [Eu2(DPM)6] and [Tb2(DPM)6]. In addition, the complex [Tb(DPM)2(NO3)(TPPO)2] presented fractoluminescence phenomenon, emitting green light when its crystals are broken. The presence of metal ligand charge transfer state (TCLM) of low energy in compounds of Eu3+ was also investigated. The luminescent properties studies showed that the bis-DPM systems Eu3+, an increase occurs in the energy state of TCLM, contributing to an increase in luminescence intensity of these compounds, when compared with dimeric complexes. This observation is evidenced by the luminescence at room temperature observed for the first compound, which is not observed for the second. The geometries of complexes [Ln2(DPM)6] and [Ln(DPM)2(NO3)(L)2] with Ln = Tb3+ or Eu3+ were optimized using SPARKLE/RM1 method, the first having a coordination polyhedron described by a monocapped trigonal prism trigonal and the second as distorted dodecahedron. / O presente trabalho envolve a síntese, caracterização e a investigação das propriedades fotoluminescentes dos complexos de fórmulas [Ln(DPM)2(NO3)(L)2] e [Ln(L)3(NO3)3], em que L = triciclohexilfosfinóxido (THPO) ou trifenilfosfinóxido (TPPO) e Ln3+ = Tb3+, Gd3+ ou Eu3+, além dos compostos diméricos [Eu2(DPM)6] e [Tb2(DPM)6]. Todos os sistemas foram caracterizados por análise elementar de CHN e Lantanídeo (Ln), espectroscopia vibracional na região do infravermelho, análise termogravimétrica e suas propriedades espectroscópicas foram investigadas por espectroscopia molecular de reflectância difusa, de excitação e emissão, assim como por medidas de tempos de decaimento dos estados emissores. Os dados experimentais das análises de CHN e titulações complexométricas dos complexos sintetizados estão em concordância com os dados teóricos calculados para as suas respectivas fórmulas. Os espectros de absorção na região do infravermelho evidenciam que a coordenação dos ligantes β-dicetonatos e fosfinóxidos aos íons Ln3+ ocorre por meio de átomos de oxigênio dos grupos carbonila e P=O, respectivamente. O comportamento estrutural dos complexos [Eu(DPM)2(NO3)(TPPO)2] e [Tb(DPM)2(NO3)(TPPO)2] é significativamente diferente daqueles complexos diméricos, [Eu2(DPM)6] e [Tb2(DPM)6]. Além disso, o complexo [Tb(DPM)2(NO3)(TPPO)2] apresentou o fenômeno de fractoluminescência, emitindo luz verde quando seus cristais são quebrados. A presença de estados de transferência de carga ligante-metal (TCLM) de baixa energia nos compostos de Eu3+ também foi investigada. Os estudos das propriedades luminescentes mostraram que nos sistemas bis-DPM de Eu3+, ocorre um aumento na energia do estado de TCLM, contribuindo para um aumento na intensidade de luminescência destes compostos, quando comparados com os complexos diméricos. Esta observação é evidenciada pela luminescência à temperatura ambiente observada para o primeiro composto, que não é observada para o segundo. As geometrias dos complexos [Ln2(DPM)6] e [Ln(DPM)2(NO3)(L)2] com Ln = Tb3+ ou Eu3+ foram otimizadas usando o método SPARKLE/RM1, o primeiro apresentando um poliedro de coordenação descrito como prisma trigonal monoencapuzado e o segundo como dodecaedro distorcido.

Made available in DSpace on 2014-10-09T12:53:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:43Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP