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  Partner: UNT Libraries
 Degree Discipline: Chemistry
 Degree Level: Doctoral
 Collection: UNT Theses and Dissertations
Rational Design of Metal-organic Electronic Devices: a Computational Perspective

Rational Design of Metal-organic Electronic Devices: a Computational Perspective

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Date: December 2012
Creator: Chilukuri, Bhaskar
Description: Organic and organometallic electronic materials continue to attract considerable attention among researchers due to their cost effectiveness, high flexibility, low temperature processing conditions and the continuous emergence of new semiconducting materials with tailored electronic properties. In addition, organic semiconductors can be used in a variety of important technological devices such as solar cells, field-effect transistors (FETs), flash memory, radio frequency identification (RFID) tags, light emitting diodes (LEDs), etc. However, organic materials have thus far not achieved the reliability and carrier mobility obtainable with inorganic silicon-based devices. Hence, there is a need for finding alternative electronic materials other than organic semiconductors to overcome the problems of inferior stability and performance. In this dissertation, I research the development of new transition metal based electronic materials which due to the presence of metal-metal, metal-?, and ?-? interactions may give rise to superior electronic and chemical properties versus their organic counterparts. Specifically, I performed computational modeling studies on platinum based charge transfer complexes and d10 cyclo-[M(?-L)]3 trimers (M = Ag, Au and L = monoanionic bidentate bridging (C/N~C/N) ligand). The research done is aimed to guide experimental chemists to make rational choices of metals, ligands, substituents in synthesizing novel organometallic electronic materials. Furthermore, the ...
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Investigating Molecular Structures: Rapidly Examining Molecular Fingerprints Through Fast Passage Broadband Fourier Transform Microwave Spectroscopy

Investigating Molecular Structures: Rapidly Examining Molecular Fingerprints Through Fast Passage Broadband Fourier Transform Microwave Spectroscopy

Date: May 2011
Creator: Grubbs, Garry Smith, II
Description: Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of Molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation o, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 s) than the molecular relaxation (≈100 s). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, ...
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Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Date: May 2010
Creator: Pierpont, Aaron
Description: Methane and dinitrogen are abundant precursors to numerous valuable chemicals such as methanol and ammonia, respectively. However, given the robustness of these substrates, catalytically circumventing the high temperatures and pressures required for such transformations has been a challenging task for chemists. In this work, computational studies of various transition metal catalysts for methane C-H activation and N2 activation have been carried out. For methane C-H activation, catalysts of the form LnM=E are studied, where Ln is the supporting ligand (dihydrophosphinoethane or β-diketiminate), E the activating ligand (O, NCH3, NCF3) at which C-H activation takes place, and M the late transition metal (Fe,Co,Ni,Cu). A hydrogen atom abstraction (HAA) / radical rebound (RR) mechanism is assumed for methane functionalization (CH4 à CH3EH). Since the best energetics are found for (β-diket)Ni=O and (β-diket)Cu=O catalysts, with or without CF3 substituents around the supporting ligand periphery, complete methane-to-methanol cycles were studied for such systems, for which N2O was used as oxygen atom transfer (OAT) reagent. Both monometallic and bimetallic OAT pathways are addressed. Monometallic Fe-N2 complexes of various supporting ligands (LnFe-N2) are studied at the beginning of the N2 activation chapter, where the effect of ligand on N2 activation in end-on vs. side-on N2 isomers ...
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Sensitization of Lanthanides and Organic-Based Phosphorescence via Energy Transfer and Heavy-Atom Effects

Sensitization of Lanthanides and Organic-Based Phosphorescence via Energy Transfer and Heavy-Atom Effects

Date: May 2010
Creator: Arvapally, Ravi K.
Description: The major topics discussed are the phosphorescence sensitization in the lanthanides via energy transfer and in the organics by heavy atom effects. The f-f transitions in lanthanides are parity forbidden and have weak molar extinction coefficients. Upon complexation with the ligand, ttrpy (4'-p-Tolyl-[2,2':6',2"]-terpyridine) the absorption takes place through the ligand and the excitation is transferred to the lanthanides, which in turn emit. This process is known as "sensitized luminescence." Bright red emission from europium and bright green emission from terbium complexes were observed. There is ongoing work on the making of OLEDs with neutral complexes of lanthanide hexafluoroacetyl acetonate/ttrpy, studied in this dissertation. Attempts to observe analogous energy transfer from the inorganic donor complexes of Au(I) thiocyanates were unsuccessful due to poor overlap of the emissions of these systems with the absorptions of Eu(III) and Tb(III). Photophysics of silver-aromatic complexes deals with the enhancement of phosphorescence in the aromatics. The heavy atom effect of the silver is responsible for this enhancement in phosphorescence. Aromatics such as naphthalene, perylene, anthracene and pyrene were involved in this study. Stern Volmer plots were studied by performing the quenching studies. The quenchers employed were both heavy metals such as silver and thallium and lighter ...
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Phosphorescent Emissions of Coinage Metal-Phosphine Complexes: Theory and Photophysics

Phosphorescent Emissions of Coinage Metal-Phosphine Complexes: Theory and Photophysics

Date: December 2009
Creator: Sinha, Pankaj
Description: The major topics discussed are all relevant to the bright phosphorescent emissions of coinage metal complexes (Cu(I), Ag(I) and Au(I)) with an explanation of the theoretical background, computational results and ongoing work on the application in materials and optoelectronic devices. Density functional computations have been performed on the majority of the discussed complexes and determined that the most significant distortion that occurs in Au(I)-phosphine complexes is a near and beyond a T-shape within the P-Au-P angle when the complexes are photoexcited to the lowest phosphorescent excited state. The large distortion is experimentally qualified with the large Stokes' shift that occurs between the excitation and emission spectra and can be as large as 18 000 cm-1 for the neutral Au(I) complexes. The excited state distortion has been thoroughly investigated and it is determined that not only is it pertinent to the efficient luminescence but also for the tunability in the emission. The factors that affect tunability have been determined to be electronics, sterics, rigidity of solution and temperature. The luminescent shifts determined from varying these parameters have been described systematically and have revealed emission colors that span the entire visible spectrum. These astounding features that have been discovered within studies of ...
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Interaction of learning approach with concept integration and achievement in a large guided inquiry organic class.

Interaction of learning approach with concept integration and achievement in a large guided inquiry organic class.

Date: August 2009
Creator: Mewhinney, Christina
Description: A study was conducted to investigate the relationship of students' concept integration and achievement with time spent within a topic and across related topics in a large first semester guided inquiry organic chemistry class. Achievement was based on evidence of algorithmic problem solving; and concept integration was based on demonstrated performance explaining, applying, and relating concepts to each other. Twelve individual assessments were made of both variables over three related topics - acid/base, nucleophilic substitution and electrophilic addition reactions. Measurements included written, free response and ordered multiple answer questions using a classroom response system. Results demonstrated that students can solve problems without conceptual understanding. A second study was conducted to compare the students' learning approach at the beginning and end of the course. Students were scored on their preferences for a deep, strategic, or surface approach to learning based on their responses to a pre and post survey. Results suggest that students significantly decreased their preference for a surface approach during the semester. Analysis of the data collected was performed to determine the relationship between students' learning approach and their concept integration and achievement in this class. Results show a correlation between a deep approach and concept integration and a ...
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Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase.

Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase.

Date: August 2009
Creator: Alecu, Ionut M.
Description: The gas phase reactions of atomic chlorine with hydrogen sulfide, ammonia, benzene, and ethylene are investigated using the laser flash photolysis / resonance fluorescence experimental technique. In addition, the kinetics of the reverse processes for the latter two elementary reactions are also studied experimentally. The absolute rate constants for these processes are measured over a wide range of conditions, and the results offer new accurate information about the reactivity and thermochemistry of these systems. The temperature dependences of these reactions are interpreted via the Arrhenius equation, which yields significantly negative activation energies for the reaction of the chlorine atom and hydrogen sulfide as well as for that between the phenyl radical and hydrogen chloride. Positive activation energies which are smaller than the overall endothermicity are measured for the reactions between atomic chlorine with ammonia and ethylene, which suggests that the reverse processes for these reactions also possess negative activation energies. The enthalpies of formation of the phenyl and β-chlorovinyl are assessed via the third-law method. The stability and reactivity of each reaction system is further rationalized based on potential energy surfaces, computed with high-level ab initio quantum mechanical methods and refined through the inclusion of effects which arise from the ...
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Predicting Chemical and Biochemical Properties Using the Abraham General Solvation Model

Predicting Chemical and Biochemical Properties Using the Abraham General Solvation Model

Date: May 2009
Creator: Mintz, Christina
Description: Several studies were done to illustrate the versatillity of the Abraham model in mathematically describing the various solute-solvent interactions found in a wide range of different chemical and biological systems. The first study focused on using the solvation model to construct mathematical correlations describing the minimum inhibitory concentration of organic compounds for growth inhibition towards the three bacterial strains Porphyromonas gingivalis, Selenomonas artemidis, and Streptococcus sobrinus. The next several studies expand the practicallity of the Abraham model by predicting free energies of partition in chemical systems. The free energy studies expand the use of the Abraham model to other temperatures and properties by developing correlations for the enthalpies of solvation of gaseous solutes of various compounds dissolved in water, 1-octanol, hexane, heptane, hexadecane, cyclohexane, benzene, toluene, carbon tetrachloride, chloroform, methanol, ethanol, 1-butanol, propylene carbonate, dimethyl sulfoxide, 1,2-dichloroethane, N,N-dimethylformamide, tert-butanol, dibutyl ether, ethyl acetate, acetonitrile, and acetone. Also, a generic equation for linear alkanes is created for use when individual datasets are small. The prediction of enthalpies of solvation is furthered by modifying the Abraham model so that experimental data measured at different temperatures can be included into a single correlation expression. The temperature dependence is directly included in the model ...
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Metallization and Modification of Low-k Dielectric Materials

Metallization and Modification of Low-k Dielectric Materials

Date: December 2008
Creator: Martini, David M.
Description: Aluminum was deposited onto both Teflon AF and Parylene AF surfaces by chemical vapor deposition of trimethylaluminum. This work shows that similar thin film (100 Angstroms) aluminum oxide adlayers form on both polymers at the low temperature dosing conditions used in the studies. Upon anneal to room temperature and above, defluorination of the polymer surfaces increased and resulted in fluorinated aluminum oxide adlayers; the adlayers were thermally stable to the highest temperatures tested (600 K). Angle-resolved spectra showed higher levels of fluorination toward the polymer/adlayer interface region. Copper films were also deposited at low temperature onto Teflon AF using a copper hexafluoroacetylacetonate-cyclooctadiene precursor. Annealing up to 600 K resulted in the loss of precursor ligands and a shift to metallic copper. As with aluminum adlayers, some polymer defluorination and resulting metal (copper) fluoride was detected. Parylene AF and polystyrene films surfaces were modified by directly dosing with water vapor passed across a hot tungsten filament. Oxygen incorporation into polystyrene occurred exclusively at aromatic carbon sites, whereas oxygen incorporation into parylene occurred in both aromatic and aliphatic sites. Oxygen x-ray photoelectron spectra of the modified polymers were comparable, indicating that similar reactions occurred. The surface oxygenation of parylene allowed enhanced reactivity ...
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Preparation of flat dendrimers and polycyclic aromatic hydrocarbons connected via 1,3,5-triethynylbenzene core.

Preparation of flat dendrimers and polycyclic aromatic hydrocarbons connected via 1,3,5-triethynylbenzene core.

Date: December 2008
Creator: Jung, Jiyoung
Description: Flat dendrimers, consisting of a hexavalent aromatic core and rigid ethynyl units locked in place by ether connections were developed based upon the divergent synthetic method. Alternating functional groups were adopted on each site of the hexa-substituted benzene, in order to avoid undesired cyclization pathways. The flat structures of conjugated dendrimers would allow investigation on the discotic liquid crystal properties. In addition, these ethylnyl dendrimers are expected to show directed energy and electron transfer with a highly conjugated system, and thus are effective in the preparation of photoreactive materials such as electronic sensors or light harvesting materials. Conjugated polycyclic aromatic hydrocarbons, consisting of naphthalene, anthracene, pyrene, and phenanthrene groups connected via 1,3,5-triethynylbenzene cores, were synthesized. These molecules exhibited luminescence properties and the π-complexation with a mercury trifunctional lewis acid are expected to enhance the phosphorescence in the presence of the heavy metal due to the spin-orbit coupling. Besides, owing to the presence of heavy metal atom in the Au (I) complexes linked by s-bonded triethynyltriphenylene luminophore, the phosphorescence occurs from a metal-centered emission. The conjugated organic luminophores have been developed to produce excellent quantum efficiencies, brightness, and long lifetimes.
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