In the Mars atmosphere, reactivity of trace components is as relevant as that of the major compounds if formation of complex molecules is considered. These are of great importance concerning the existence of a past or future life on Mars. In this context, the gas-phase chemistry of alkylcarbonate and alkyloxalate ions and radicals, ROCOO–/• and ROCOCOO–/•, is investigated for different alkyl substituents R (H, CH3, C2H5, i-C3H7, and t-C4H9). This study describes the structures, stability, and unimolecular dissociation behavior of these species and is achieved by means of mass spectrometric methods and ab initio calculations. Standard heats of formation of the ions and radicals are determined via computational methods, using atomization energies and bond-separation reactions. Vertical charge-transfer experiments are performed to provide evidence for the existence of the radicals under study and the NIDD (ion and neutral decomposition difference) method is employed to determine their reactivity. Typical processes observed involve direct bond cleavages leading to elimination of carbon dioxide. Concerning anionic compounds, classical metastable ion (MI) and collisional activation (CA) experiments enable the determination of their gas-phase behavior. This, in contrast to radicals, is not only constituted by direct bond cleavages, but also by hydride-transfer reaction or carbon monoxide expulsion involving formation of ion-neutral complexes as intermediates. Translational energy loss spectra are also employed to gain more insights concerning the dissociation energetics of CH3OCOO• and CH3OCOO+ formed by vertical charge-transfer of methylcarbonate. This rather unusual method for such study implies a careful evaluation of the error caused by the instrument which may otherwise generate dramatic deviations of the results compared to theory.

Some interesting electronic and dynamic properties of semiconductor nanocrystal heterostructures have been investigated using various spectroscopic methods. Semiconductor nanocrystal heterostructures were prepared using colloidal synthesis techniques. Ultrafast transient absorption spectroscopy was used to monitor the relaxation of hot electrons in CdS/HgS/CdS quantum dot quantum wells. Careful analysis of the hot electron relaxation in CdS/HgS/CdS quantum dot quantum wells reveals an energy dependent relaxation mechanism involving electronic states of varying CdS and HgS composition. The composition of the electronic states, combined with the layered structure of the nanocrystal permits the assignment of CdS localized and HgS localized excited states. The dynamic effect of surface passivation is then shown to have the strongest influence on excited states that are localized in the HgS layer. New quantum dot quantum well heterostructures of different sizes and compositions were also prepared and studied. The dynamic properties of CdS/CdSe/CdS colloidal quantum wells suggest simultaneous relaxation of excited electrons within the CdS core and CdSe shell on the sub-picosecond time scale. Despite the very different electronic structure of CdS/CdSe/CdS compared to CdS/HgS/CdS, the time scales of the relaxation and electron localization were very similar. Enhancement of trap luminescence was observed when CdS quantum dots were coated with silver. The mechanism of the enhancement was investigated using time-resolved spectroscopic techniques.

Long-distance radical cation transport was studied in DNA condensates where linearized pUC19 plasmid was ligated to an oligomer and transformed into DNA condensates with spermidine. DNA condensates were detected by Dynamic Light Scattering and observed by Transmission Electron Microscopy. Introduction of charge into the condensates causes long-distance charge migration, which is detected by reaction at the remote guanines. The efficiency of charge migration in the condensate is significantly less than it is for the corresponding oligomer in solution. This result is attributed to a lower mobility for the migrating radical cation in the condensate, caused by inhibited formation of charge-transfer-effective states. Radical cation transport was also studied in DNA condensates made from an oligomer sandwiched between two linearized plasmids by double ligation. Unlike the single ligated plasmid condensates, the efficiency of charge migration in the double ligated plasmid-condensates is high, indicative of local structural and conformational transformation of the DNA duplexes. Organic monomer units having extended ð-conjugation as part of a long conducting polymer was synthesized and characterized. The monomer units were covalently attached to particular positions in DNA oligonucleotides by either the convertible nucleotide approach or by phosphoramidite chemistry. Successful attachment of the monomer units to DNA were confirmed by mass spectral analysis. The DNA-conjoined monomer units can self assemble in the presence of complementary sequences which act as templates that can control polymer formation and structure. By this method the para-direction of the polymer formation can be enforced and may be used to generate materials having nonrecurring, irregular structures.

In organischen Solarzellen resultiert die photovoltaische Aktivität aus dem das Sonnenlicht absorbierenden Donor-Akzeptor-Heteroübergang. Die Grenzfläche zwischen den beiden organischen Materialien dient der effizienten Ladungsträgertrennung. Die vorliegende Arbeit leistet einen Beitrag im Verständnis zum Wirkungsmechanismus und der zu optimierenden Parameter in diesen Solarzellen. In Bezug auf die Anpassung des Donor-Akzeptor-Heteroübergangs wird neben dem Mechanismus der Ladungsträgergeneration an der Grenzfläche die erzielbare Leerlaufspannung in den Solarzellen diskutiert. Ein wesentliches Kriterium zur Erhöhung der Leerlaufspannung ist die Anpassung der Energieniveaus am Heteroübergang. Eine effiziente Ladungsträgertrennung wird durch eine hinreichende Stufe im Ionisationspotenzial sowie in der Elektronenaffinität am Heteroübergang erreicht. Zur Maximierung der Leerlaufspannung muss diese Überschussenergie, d.h. die Energiedifferenz zwischen photogeneriertem Exziton und freiem Ladungsträgerpaar, auf das notwendige Minimum reduziert werden. Eine Reihe von Dicyanovinyl-Oligothiophenen (DCVnT, n=3-6) wurden als Donor im Heteroübergang zu Fulleren C60 verwendet. Das Ionisationspotenzial der DCVnT nimmt mit zunehmender Kettenlänge ab, während die Elektronenaffinität, die weitestgehend durch die Dicyanovinyl-Endgruppen bestimmt wird, von der Kettenlänge nahezu unabhängig ist. Mittels photoinduzierter Absorptionsspektroskopie und zeitaufgelöster Fluoreszenzmessung wurde der Energie- und Elektronentransfer zwischen DCVnT und C60 entlang der homologen Reihe der DCVnT untersucht. Eine wesentliche Feststellung ist die Korrelation zwischen Rekombination in den Triplettzustand und der Leerlaufspannung. So konnte unter anderem gezeigt werden, dass durch die Verwendung angepasster Heteroübergänge unter bestimmten energetischen Voraussetzungen die indirekte Triplettbesetzung einen bislang nicht beachteten Verlustmechanismus für organische Solarzellen darstellt. Für organische Solarzellen ist demnach ein Kompromiss zwischen möglichst hoher Leerlaufspannung und effizienter Ladungsträgerdissoziation unter Vermeidung dieser Triplettrekombination zu erzielen. Weiterhin wird ein Konzept zur Nutzung dieser indirekten Triplettrekombination diskutiert. Dieses basiert auf der Tatsache, dass die Lebensdauer der Exzitonen im Triplettzustand gegenüber denen im Singulettzustand um 3-6 Größenordnungen höher ist. Damit wird eine höhere Diffusionslänge erwartet, was in einer dickeren und damit stärker absorbierenden aktiven Schicht genutzt werden könnte.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 114-127).

In this work we generalize existing theory of low-energy collisions of atomic hydrogen with its anion. We extend the non-local resonance model for this system by adding new discrete state and two continua that are coupled with it. We calculate numerically cross sections for associative electron detachment process that is important for models of early universe. We add cross section for collision detachment and show spectra of outgoing electrons. We show how the isotopic effect is involved in studied collision. We also calculate charge transfer, elastic scattering cross sections, and reaction rates for hydrogen collisions with deuterium anion. We compare our results with recent experiments and we discuss their reliability. Powered by TCPDF (www.tcpdf.org)

Submitted by Maike Costa (maiksebas@gmail.com) on 2016-05-11T11:38:41Z No. of bitstreams: 1 arquivo total.pdf: 5689290 bytes, checksum: 55be9a3cf14a111bd7b7407cbca5df8e (MD5) / Made available in DSpace on 2016-05-11T11:38:41Z (GMT). No. of bitstreams: 1 arquivo total.pdf: 5689290 bytes, checksum: 55be9a3cf14a111bd7b7407cbca5df8e (MD5) Previous issue date: 2015-08-07 / The photoluminescence efficiency in compounds of lanthanide ions is a result of the complex balance between absorption of photons, energy transfer and quenching mechanisms, among which the multiphonon decay and suppression mediated by low energy ligand-to-metal charge transfer states (LMCT) which might be generated by ligands that have a low oxidation potential, for instance the NCS–. Less than a decade ago, this process was described mainly in terms of the energy transfer between 4f states and LMCT states, not being considered the participation of intraligands states. In the present study, we investigated the photoluminescent properties of new lanthanide isothiocyanates coordination complexes with N-acetyl-2-aminopyridine, N-benzoyl-2-aminopyridine and N-benzoyl-2- aminopyrimidine as ligands. We also synthesized the well-known complexes of formulas [Ln(NCS)3(phen)3] (H2O), and [Ln(NO3)3(Phen)2] with phen = 1,10-phenanthroline. The complexes were characterized via CHN elemental analysis, vibrational spectroscopy, complexometric titration and thermogravimetric analysis. Their spectroscopic properties were investigated via molecular diffuse reflectance, excitation and emission spectroscopy along with time decay of the emitting states. The results from the analysis of emission spectroscopy and photoluminescence excitation, as well as the lifetimes measurements of the emitting states of the investigated complexes provided what we believe to be the most expressive experimental demonstration of the luminescence quenching via triplet-LMCT energy transfer process in Eu(III) complex so far. / A eficiência na fotoluminescência em compostos de íons lantanídeos é o resultado de um balanço complexo entre absorção de fótons, transferência de energia e mecanismos supressores, dentre os quais se destacam o decaimento multifônon e a supressão mediada por estados de transferência de carga ligante-metal (TCLM) de baixa energia, que pode ser gerado por ligantes que apresentam baixo potencial de oxidação, a exemplo do NCS–. Há menos de uma década, este processo era descrito essencialmente em termos da transferência de energia entre estados 4f e os estados TCLM, não sendo considerada a participação dos estados intraligantes. Neste trabalho, investigamos as propriedades fotoluminescentes de novos compostos de coordenação de isotiocianatos de lantanídeos com os ligantes N-acetil- 2-aminopiridina, N-benzoil-2-aminopiridina e N-benzoil-2-aminopirimidina. Sintetizamos, também, os complexos já conhecidos, de fórmulas gerais [Ln(NCS)3(phen)3] (H2O) e [Ln(NO3)3(phen)2] com phen= 1,10-fenantrolina. Os complexos foram caracterizados por análise elementar de CHN, espectroscopia vibracional na região do infravermelho, análise termogravimétrica e titulação complexométrica e suas propriedades espectroscópicas foram investigadas por espectroscopias molecular de reflectância difusa e de excitação e emissão bem como os tempos de decaimento dos estados emissores. Os resultados obtidos a partir das análises de espectroscopia de emissão e excitação da fotoluminescência, assim como as medidas de tempos de vida dos estados emissores dos complexos investigados proporcionaram o que acreditamos ser a demonstração experimental mais expressiva, até então, do processo de supressão da luminescência mediada pelo processo de transferência de energia tripleto-TCLM em complexos do íon Eu(III).

Submitted by ANA KARLA PEREIRA RODRIGUES (anakarla_@hotmail.com) on 2017-08-07T15:46:16Z No. of bitstreams: 1 arquivototal.pdf: 5525294 bytes, checksum: b7714e7665b3af997613f352395d6e2b (MD5) / Made available in DSpace on 2017-08-07T15:46:16Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 5525294 bytes, checksum: b7714e7665b3af997613f352395d6e2b (MD5) Previous issue date: 2014-09-03 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This work reports spectroscopic and structural investigations of the complexes presenting the formulas [Ln(TTA)3L2], [Ln(DBM)3L], [Ln(TTA)2(NO3)L2], [Ln(DBM)2(NO3)L2] and [Ln(DBM)(NO3)2(HMPA)2], where Ln: Eu3+ or Tb3+, TTA: 2-thenoyltrifluoroacetonate, DBM: dibenzoylmethanate and L: HMPA (hexamethylphososphoramide) or TPPO (Triphenylphosphine oxide). The compounds were characterized by complexometric and elemental analysis and single crystal X-ray diffraction. The spectroscopic properties of the complexes were studied by diffuse reflectance and luminescence spectroscopies. Formation of positronium in the complexes were also investigated. In order to obtain a synergy between theory and experiment, DFT calculations were performed, for geometry optimization and to obtain DBM triplet states energies, using B3LYP, B97D, M06-2X, PBE1PBE, CAM-B3LYP and ω-B97XD functionals, in both gas phase and in acetone solvent. X-ray data showed that the replacement of DBM molecules by nitrate ions promotes stronger intramolecular interactions, which influence the compounds melting points. The diffuse reflectance and excitation spectra suggest the presence of ligant-to-metal charge transfer states (LMCT) of low energy in DBM containing Eu3+ complexes. The replacement of DBM ligands by nitrate ions decrease the energy of these LMCT states. This decrease is duo to the lower polarizability of the nitrate ion which promotes a greater charge donor effect on the other ligands, reducing the energy of the LMCT state. Positron annihilation results showed that positronium formation in compounds containing both DBM and phosphine oxides decreases when the former are replaced by nitrate ions, due to the increase of electron density donation from the ligands to the metal center, decreasing the phosphinoxides positronium formation capacity. DFT calculation provided relatively satisfactory results for geometry optimization and in obtaining DBM triplet states energies. These results indicate that the replacement of B-diketonate ligands by less polarizable species, such as nitrate, has a great influence on the structural and spectroscopic properties of the investigated compounds. / Este trabalho reporta investigações espectroscópicas e estruturais de complexos de fórmulas [Ln(TTA)3L2], [Ln(DBM)3L], [Ln(TTA)2(NO3)(TPPO)2], [Ln(DBM)2(NO3)L2] e [Ln(DBM)(NO3)2(HMPA)2], em que Ln: Eu3+ ou Tb3+, TTA: 2-tenoiltrifluoroacetonato, DBM: dibenzoilmetanato e L: HMPA (hexametilfosforamida) ou TPPO (Trifenilfosfinóxido). Os compostos foram caracterizados por análises complexométricas e elementar e difração de raios X de monocristal. As propriedades espectroscópicas dos complexos foram estudadas através de espectroscopia de reflectância difusa e de luminescência. O processo de formação de positrônio nos complexos também foi investigado. No intuito de obter uma sinergia teoria-experimento, foram realizados cálculos DFT, para otimização de geometria e obtenção de estados tripletos do DBM, utilizando os funcionais B3LYP, B97D, M06- 2X, PBE1PBE, CAM-BγLYP e ω-B97XD, em fase gasosa e no solvente acetona, Os dados de estruturas de raios X mostraram que a substituição de moléculas de DBM por íons nitrato promove a existência de interações intermoleculares mais fortes o que tem uma influência sobre o ponto de fusão dos compostos. Os espectros de reflectância difusa e de excitação sugerem a presença de estados de transferência de carga ligantemetal (TCLM) de baixa energia em complexos de Eu3+ contendo o ligante DBM, com um abaixamento na energia desses estados à medida que os ligantes DBM são substituídos por íons nitrato. Isso é explicado considerando que a menor polarizabilidade do íon nitrato provoca um maior efeito doador de carga nos outros ligantes, diminuindo a energia do estado TCLM. Os resultados de aniquilação de pósitron mostraram que a formação de positrônio em compostos com ligantes DBM e fosfinóxidos diminui quando os primeiros são substituídos por íons nitrato, devido ao aumento da doação de densidade eletrônica dos ligantes para o centro metálico, diminuindo a capacidade formadora dos fosfinóxidos. Os cálculos teóricos DFT forneceram resultados relativamente satisfatórios para a otimização de geometrias dos complexos e para a obtenção de energias dos estados tripletos do ligante DBM. Esses resultados indicaram que a substituição de ligantes B-dicetonatos por espécies menos polarizáveis, como o nitrato, tem grande influência nas propriedades estruturais e espectroscópicas dos compostos estudados.

Devido à escassez de dados espectroscópicos sobre as interações de aminas aromáticas com SO2 e devido também à importância que complexos de transferência de carga assumem numa série de processos, inclusive biológicos, realizou-se um estudo objetivando a caracterização dessa interação através de várias técnicas espectroscópicas, como a espectroscopia Raman, no Infravermelho, no visível-ultravioleta e de Ressonância Magnética Nuclear. A partir dos dados obtidos nesses estudos concluímos que ocorre transferência de carga da amina para o SO2 ; essa transferência ocorre a partir do orbital ocupado de maior energia da amina , localizado principalmente no átomo de nitrogênio, para o orbital vago de mais baixa -energia do SO2 (π * ) localizado no a-tomo de enxofre. Os espectros vibracionais mostram que não é possível correlacionar as frequências de estiramento do SO2 complexado com o pKb (ou potencial de ionização) da base e sugerem que fatores estéricos podem ser importantes, influenciando o recobrimento dos orbitais do doador e do aceptor. No caso particular da ANI.SO2 , alterações na região de estiramento N-H do espectro no infravermelho , indicam que muito provavelmente ocorre a formação de ligações de hidrogênio entre a amina e o SO2 além da interação através do átomo de nitrogênio. ° comportamento termocrômico dos complexos foi investigado através de espectroscopia Raman à baixa temperatura. As informações preliminares obtidas sugerem que o desaparecimento da côr é devido a uma depopulação dos estados vibracionais excitados, a partir dos quais se efetuam as transições eletrônicas com fatores de Franck-Condon muito favoráveis / The shortage of spectroscopic data on the interactions between amines and SO2, together with the relevance that molecular complexes have in several process, including biological ones, stimulated us to study these systems by Raman, Infrared, Visible-Ultra violet and NMR spectroscopic techniques. From the data obtained, it\'s possible to conclude that there is charge transfer from the HOMO of the amines, which is localized mainly at the nitrogen atom, to the LUMO of SO2, localized at the sulfur atom. The vibrational spectra show that it is impossible to correlate any of the SO2 vibrational bands to the pKb of the donor and suggest that steric hindrance may play an important role in such interations, affecting the overlap of donor and aceptor orbitals; in the case of ANI.SO2 , the band shape in the N-H stretching region led us to conclude that hidrogen bonding between the amine and SO2 occurs, together with the specific interation through the nitrogen atom. The complexes show Pré-Resonance Raman Effect and from its study one concludes that SO2 belongs to the chromophoric group. The thermochromism that the complexes present was investigated by Raman Spectroscopy at low temperature. The informations obtained strongly suggest that the vanishing of its colour may be atributed to a depopulation of an vibrational excited state from which the charge transfer eletronic transition can occur with apreciable Franck-Condon factors.

Neste trabalho foram estudados os complexos de transferência de carga resultantes da interação entre as espécies aceptoras de elétrons tetracianoetileno (TCNE) e 7,7,8,8-tetracianoquinodimetano (TCNQ), com aminas mono, bi e tri aromáticas, como espécies doadoras de elétrons, em solução. Também foram estudadas as reações de substituição eletrofílica aromática que ocorre entre o TCNE e aminas. Para tal estudo, foram utilizadas as técnicas espectroscópicas de absorção UV-VIS e Raman, o que permitiu a caracterização dos complexos de transferência de carga, assim como das espécies participantes da reação de tricianovinilação que ocorre entre aminas e TCNE. Para dar suporte aos dados experimentais, cálculos DFT (Teoria do Funcional da Densidade) e TDDFT (Teoria do Funcional da Densidade dependente do tempo) foram realizados, o que permitiu a obtenção das geometrias otimizadas, valores de frequência Raman e energias de transição dessas espécies. Os espectros eletrônicos dos complexos formados entre TCNE e aminas monoaromáticas mostraram que suas energias de transição são proporcionais à capacidade de doação de elétrons da amina. De fato, as energias de transição puderam ser correlacionadas com os valores de potencial de ionização das aminas, apresentando uma correlação linear de acordo com a regra Mulliken. Os espectros Raman permitiram verificar que os modos vibracionais do TCNE envolvidos no processo de transferência de carga apresentam deslocamento para menores números de onda com a diminuição do potencial de ionização da amina, e analogamente, pôde-se obter uma correlação linear entre esses dois parâmetros. No caso das aminas bi e tri aromáticas, a tendência linear entre energia de transição e potencial de ionização foi observada, mas não para os deslocamentos Raman das bandas do TCNE. Na reação de tricianovinilação, os espectros eletrônicos possibilitaram a identificação das espécies participantes da reação, assim como sua caracterização vibracional por espectroscopia Raman ressonante. Através da espectroscopia Raman ressonante, pôde-se, pela primeira vez, caracterizar as espécies intermediárias da reação de tricianovinilação entre TCNE e aminas aromáticas. Os complexos envolvendo TCNQ e aminas monoaromáticas apresentou tendência semelhante à observada em complexos com o TCNE. As energias de transição desses complexos diminuem linearmente, assim como, os modos vibracionais do TCNQ, que apresentam deslocamentos para menores frequências Raman com a diminuição do potencial de ionização da amina. Por outro lado, complexos formados pelo TCNQ e aminas com mais de um anel aromático em sua estrutura, não apresentam correlação entre potencial de ionização do doador e energia de transição e deslocamentos Raman. Os cálculos dos espectros eletrônicos e vibracionais apresentaram boa concordância com os obtidos experimentalmente, porém algumas limitações ficam evidentes na descrição das interações π nesses sistemas modelo. / In this work the charge transfer complexes resulting from the interaction between tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), as electron accepting species and mono, bi and tri aromatic amines, as electron donating species, were studied in solution. Also the electrophilic aromatic substitution that occurs between the TCNE and amines has been studied. For this study, the spectroscopic techniques of UV-VIS absorption and Raman were used, which allowed the characterization of the charge transfer complexes, as well as of the species involved in the reaction of tricianovinylation that occurs between amines and TCNE. In order to support the experimental data, DFT (Density Functional Theory) and TDDFT (Time-dependent Density Functional Theory) calculations were performed, to obtain the optimized geometries, Raman frequency values and theoretical transition energies of such species. The electronic spectra of the complexes formed between TCNE and monoaromatic amines showed that their transition energies are proportional to the amine electron donation capacity. In fact it could be linearly correlated with the ionization potential values of the amines, following the Mullikens rule. The Raman spectra allowed to verify that the vibrational modes of the TCNE involved in the process of charge transfer, were displaced to lower wavenumbers with the reduction of the ionization potential of the amine, and analogously, a linear correlation between these two parameters could be obtained. In the case of bi and tri aromatic amines, the linear trend between transition energy and ionization potential was observed, but not for the Raman shifts of the TCNE bands. In the reaction of tricianovinylation, the electronic spectra enabled the identification of the participating species in the reaction, and their vibrational characterization by resonance Raman. Using resonance Raman spectroscopy, it was possible to characterize the intermediate species of the tricianovinylation reaction between TCNE and aromatic amines for the first time. The complexes involving TCNQ and monoaromatic amines showed a similar trend to that observed in complexes with TCNE. The transition energies of these complexes decrease linearly, as well as the vibrational modes of the TCNQ, which present shifts to lower Raman frequencies with the decrease of the ionization potential of the amine. On the other hand, complexes formed by TCNQ and amines with more than one aromatic ring in their structure do not present correlation between donor ionization potential and transition energy and Raman displacements. The calculations of the electronic and vibrational spectra presented good agreement with those obtained experimentally, however some limitations were evidenced in the description of the π interactions in these model systems.