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Microwave-Assisted Synthesis, Characterization, and Photophysical Properties of New Rhenium(I) Pyrazolyl-Triazine Complexes

Description: The reaction of the chelating ligand 4-[4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-yl]-N,N-diethyl-benzenamine, L, with pentacarbonylchlororhenium by conventional heating method produces the complexes fac-[ReL(CO)3Cl2] and fac-[Re2L(CO)6Cl2] in a period of 48 hours. The use of microwaves as the source of heat and the increase in the equivalents of one of the reactants leads to a more selective reaction and also decreases the reaction time to 1 hour. After proper purification, the photophysical properties of fac-[ReL(CO)3Cl] were analyzed. The solid-state photoluminescence analysis showed an emission band at 628 nm independent of temperature. However, in the solution studies, the emission band shifted from 550 nm in frozen media to 610 nm when the matrix became fluid. These results confirm that this complex possess a phenomenon known as rigidochromism.
Date: May 2010
Creator: Salazar Garza, Gustavo Adolfo
Partner: UNT Libraries

Design, Synthesis and Screening of Homoleptic and Heteroleptic Platinum(ii) Pyridylazolate Complexes for N-type Semiconducting and Light-emitting Devices

Description: A series of heteroleptic and homoleptic platinum(II) complexes has been synthesized and characterized towards their use in thin film devices such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs). Pyridylpyrazolate- and pyridyltetrazolate-containing ligands were selected due to their structural rigidity and ease of functionalization. Single-crystal x-ray diffraction studies of two selected heteroleptic complexes show strong aggregation with preferential stacking into vertical columns with a varying degree of overlap of the neighboring square planar molecular units. It is shown that the close proximity of the molecules to one another in the stack increases semiconducting character, phosphorescence quantum yields, and shorter radiative lifetimes. The potential for these materials towards incorporation into high-efficiency doping free white OLEDs (DFW-OLEDs) for solid-state lighting and display applications has been realized and will be expanded upon by present and future embodiments of materials in this thesis.
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Date: August 2012
Creator: Oswald, Iain William Herbert
Partner: UNT Libraries

Synthesis of Tethering Group on Borylazadipyrromethene Dyes to Apply to Photogalvanic Dye-sensitized Solar Cells

Description: This is my thesis research on the preparation of borylazadipyrromethene (azaBODIPY) dyes bearing an anchoring group, such as a carboxylic acid group, at the β-pyrrolic position of the azadipyrromethene scaffold. Carboxylate groups form covalent bonds to oxide semiconductors such as TiO2 (n-type) or Cu2O (p-type) in dye-sensitized solar cells (DSCs) or photogalvanic dye-sensitized solar cells (P-DSCs). Oxide-binding azaBODIPY dyes can be used to investigate the rate and mechanism of electron injection from the dyes to the semiconductors. Two different types of azaBODIPY (difluoroboryl and dialkynylboryl) were prepared by following previously developed methods. To convert difluoroborylazaBODIPY to the final dyes having a carboxylic acid in the β-pyrrolic position, several distinct synthetic routes were designed, adopting various reactions, such as halogenation, Sonogashira coupling, Knoevenagel condensation, Grignard reagents, Vilsmeir-Haack, and Steglich esterification. Some of these reactions were successful, but the overall synthesis to the targeted final molecule couldn’t be accomplished. Even though further studies on the synthesis of oxide-binding azaBODIPYs are needed, at least my thesis research suggests what reactions can be implemented to complete this synthesis in the future. Proton NMR (nuclear magnetic resonance) and carbon NMR were commonly used to confirm the synthesized compounds, and sometimes crystallographic information was obtained by XRD (X-ray diffraction) whenever crystals of sufficient size and quality were grown. NMR spectra, interpreted by SpinWorks 3 software, and crystal structures will be introduced in each chapter.
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Date: August 2014
Creator: Park, Eunsol
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A New Chromophoric Organic Molecule Toward Improved Molecular Optoelectronic Devices

Description: The characterization of 2,3,6,7,10,11-hexabromotriphenylene, Br6TP, is presented toward its potential use as an n-type organic semiconductor and metal-free room temperature phosphor. The crystal structure shows both anisotropic two-dimensional BrBr interactions and inter-layer ?-stacking interactions. Photophysical characteristics were evaluated using solid-state photoluminescence and diffuse reflectance spectroscopies, revealing significantly red-shifted excitations in the visible region for the yellow solid material (compared to ultraviolet absorption bands for the colorless dilute solutions). Correlation of spectral, electrochemical, and computational data suggest the presence of an n-type semiconducting behavior due to the electron-poor aromatic ring. The material shows excellent thermal stability as demonstrated by thermogravimetric analysis and infrared spectra of a thin film deposited by thermal evaporation. The potential for Br6TP and its analogues toward use in several types of photonic and electronic devices is discussed.
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Date: December 2012
Creator: Halbert, Jason Paul
Partner: UNT Libraries

Free Radical Chemistries at the Surface of Electronic Materials

Description: The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.
Date: August 2010
Creator: Wilks, Justin
Partner: UNT Libraries

Synthetic, Mechanistic, and Structural Studies of Polynuclear Metal Clusters and Hydrazido-Substituted Tantalum(V) Compounds

Description: A combined experimental and computational study on the reversible ortho-metalation exhibited by the triosmium cluster Os3(CO)10(dppm) (dppm = 1,1-bis(diphenylphosphino)methane is reported. The conversion of nonacarbonyl cluster HOs3(CO)9[-PhP(C6H4)CH2PPh2] to Os3(CO)10(dppm) is independent of added CO and exhibits a significant inverse equilibrium isotope effect (EIE). Reductive coupling of the C-H bond in HOs3(CO)9[-PhP(C6H4)CH2PPh2] leads to the formation of agostic C-H and two distinct aryl-π species prior to the rate-limiting formation of the unsaturated cluster Os3(CO)9(dppm). Heating the unsaturated dimer H2Re2(CO)8 with Cp*Rh(CO)2 (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) at elevated temperature affords the new trimetallic clusters H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6, and the spiked-triangular cluster HRhRe3Cp*(CO)14. H2Re2(CO)8 reacts with Cp*2Rh2(CO)2 under identical conditions to furnish H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6 as the principal products, in addition to the tetrahedral cluster H2Rh2Re2Cp*2(CO)8. H2RhRe2Cp*(CO)9 undergoes facile fragmentation in the presence of halogenated solvents and the thiols RSH (where R = H, C6H4Me-p) to afford the structurally characterized products Cp*Rh(-Cl)3Re(CO)3, S2Rh3Cp*(CO)4, Cp*Rh(-Cl)(-SC6H4Me-p)2Re(CO)3, and Cp*Rh(-SC6H4Me-p)3Re(CO)3. The new hydrazido-substituted compounds TaCl(NMe2)3[N(TMS)NMe2] (TMS = tetramethylsilyl) and Ta(NMe2)4[N(TMS)NMe2] have been synthesized and their structures established by X-ray crystallography. The latter product represents the first structurally characterized octahedral tantalum(V) complex containing a single hydrazido(I) ligand in an all-nitrogen coordinated environment about the metal center. The fluxional properties of the amido and hydrazido ligands in these new compounds have been established by VT 1H NMR spectroscopy (VT = variable temperature). Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD (ALD = atomic layer deposition) precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.
Date: December 2010
Creator: Huang, Shih-huang
Partner: UNT Libraries

Biocompatible Hybrid Nanomaterials Involving Polymers and Hydrogels Interfaced with Phosphorescent Complexes and Toxin-Free Metallic Nanoparticles for Biomedical Applications

Description: The major topics discussed are all relevant to interfacing brightly phosphorescent and non-luminescent coinage metal complexes of [Ag(I) and Au(I)] with biopolymers and thermoresponsive gels for making hybrid nanomaterials with an explanation on syntheses, characterization and their significance in biomedical fields. Experimental results and ongoing work on determining outreaching consequences of these hybrid nanomaterials for various biomedical applications like cancer therapy, bio-imaging and antibacterial abilities are described. In vitro and in vivo studies have been performed on majority of the discussed hybrid nanomaterials and determined that the cytotoxicity or antibacterial activity are comparatively superior when compared to analogues in literature. Consequential differences are noticed in photoluminescence enhancement from hybrid phosphorescent hydrogels, phosphorescent complex ability to physically crosslink, Au(I) sulfides tendency to form NIR (near-infrared) absorbing AuNPs compared to any similar work in literature. Syntheses of these hybrid nanomaterials has been thoroughly investigated and it is determined that either metallic nanoparticles syntheses or syntheses of phosphorescent hydrogels can be carried in single step without involving any hazardous reducing agents or crosslinkers or stabilizers that are commonly employed during multiple step syntheses protocols for syntheses of similar materials in literature. These astounding results that have been discovered within studies of hybrid nanomaterials are an asset to applications ranging from materials development to health science and will have striking effect on environmental and green chemistry approaches.
Date: August 2011
Creator: Marpu, Sreekar B.
Partner: UNT Libraries

Computational Investigation of Molecular Optoelectronic and Biological Systems

Description: The scope of work in this dissertation has comprised several major investigations on applications and theoretical studies of ab initio quantum mechanics and density functional theory where those techniques were applied to the following: (i) investigation of the performance of density functionals for the computations of molecular properties of 3d transition metal containing systems; (ii) guidance for experimental groups for rational design of macrometallocyclic multinuclear complexes with superior π-acidity and π-basicity that are most suitable for p- and n-type semiconductors of metal-organic molecules and nanomaterials; (iii) investigation of the metallo-aromaticity of multi-nuclear metal complexes; (iv) investigation of the kinetics and thermodynamics of copper-mediated nitrene insertion into C-H and H-H bond; and (v) accurate computations of dissociation energies of hydrogen-bonded DNA duplex moieties utilizing the resolution of identity correlation consistent composite approach (RI-ccCA).
Date: August 2011
Creator: Tekarli, Sammer M.
Partner: UNT Libraries

Photophysics and Photochemistry of Copper(I) Phosphine and Collidine Complexes: An Experimental/Theoretical Investigation

Description: Copper(I) complexes have been studied through both experimental and computational means in the presented work. Overall, the work focuses on photophysical and photochemical properties of copper(I) complexes. Photophysical and photochemical properties are found to be dependent on the geometries of the copper(I) complexes. One of the geometric properties that are important for both photochemical and photophysical properties is coordination number. Coordination numbers have been observed to be dependent on both ligand size and recrystallization conditions. The complexes geometric structure, as well as the electronic effects of the coordination ligands, is shown both computationally as well as experimentally to affect the emission energies. Two-coordinate complexes are seen to have only weak emission at liquid nitrogen temperature (77 K), while at room temperature (298 K) the two-coordinate complexes are not observed to be luminescent. Three-coordinate complexes are observed to be luminescent at liquid nitrogen temperature as well as at room temperature. The three-coordinate complexes have a Y-shaped ground (S0) state that distorts towards a T-shape upon photoexcitation to the lowest lying phosphorescent state (T1). The geometric distortion is tunable by size of the coordinating ligand. Luminescence is controllable by limiting the amount of non-radiative emission. One manner by which non-radiative emission is controlled is the amount of geometric distortion that occurs as the complex undergoes photoexcitation. Bulky ligands allow for less distortion than smaller ligands, leading to higher emission energies (blue shifted energies) with higher quantum efficiency. Tuning emission and increasing quantum efficiencies can be used to create highly efficient, white emitting materials for use in white OLEDS.
Date: August 2011
Creator: Determan, John J.
Partner: UNT Libraries

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

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 metal like potassium. Dynamic quenching as the predominant phenomenon was noticed.
Date: May 2010
Creator: Arvapally, Ravi K.
Partner: UNT Libraries

Processing, structure property relationships in polymer layer double hydroxide multifunctional nanocomposites

Description: Dan Beaty (1937-2002) was a prolific composer, pianist, researcher, educator, and writer. His large compositional output included chamber works, choral works, songs, orchestral pieces, electronic music, and keyboard works. Beaty was well versed in traditional Western music as well as the more avant-garde and perplexing idioms of the twentieth century. Beaty's compositions reflect the many fascinating, if not always popular, musical trends of his time. His music encompasses styles from serial to jazz, shows compositional influences from Arnold Schoenberg to Indonesian music, and demonstrates thought-provoking and highly intellectual craftsmanship. This document explores several of Beaty's songs through a discussion of the composer's life and compositional process. Songs included in this document are Three Weeks Songs, October, November, A Sappho Lyric, Love Song, That Night When Joy Began, and War Lyrics. This document was written to accompany the author's DMA Lecture-Recital at the University of North Texas. Unfortunately, Beaty's vocal music was never published and is mostly unknown. One goal of the project was to initiate interest in Beaty's songs. Through this document, Lecture-Recital, and additional performances, considerable strides have been made to bring Beaty's songs to new audiences throughout the United States. In addition, the author has received permission from the Beaty family to publish Dan Beaty's songs.
Date: August 2009
Creator: Ogbomo, Sunny Minister
Partner: UNT Libraries

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

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 coinage metal phosphorescent complexes are an asset to applications ranging from materials development to electronics.
Date: December 2009
Creator: Sinha, Pankaj
Partner: UNT Libraries

Triimine Complexes of Divalent Group 10 Metals for Use in Molecular Electronic Devices

Description: This research focused on the development of new metal triimine complexes of Pt(II), Pd(II), and Ni(II) for use in three types of molecular electronic devices: dye sensitized solar cells (DSSCs), organic light-emitting diodes (OLEDs), and organic field effect transistors (OFETs). Inorganic complexes combine many advantages of their chemical and photophysical properties and are processable on inexpensive and large area substrates for various optoelectronic applications. For DSSCs, a series of platinum (II) triimine complexes were synthesized and evaluated as dyes for nanocrystalline oxide semiconductors. Pt (II) forms four coordinate square planar complexes with various co-ligands and counterions and leads to spanning absorption across a wide range in the UV-Vis-NIR regions. When those compounds were applied to the oxide semiconductors, they led to photocurrent generation thus verifying the concept of their utility in solar cells. In the OLEDs project, a novel pyridyl-triazolate Pt(II) complex, Pt(ptp)2 was synthesized and generated breakthrough OLEDs. In the solution state, the electronic absorption and emission of the square planar structure results in metal-to-ligand charge transfer (MLCT) and an aggregation band. Tunable photoluminescence and electroluminescence colors from blue to red wavelengths have been attained upon using Pt(ptp)2 under different experimental conditions and OLED architectures. In taking advantage of these binary characteristics for both monomer and excimer emissions, cool and warm white OLEDs suitable for solid-state lighting have been fabricated. The OFETs project represented an extension of the study of pyridyl-triazolate d8 metal complexes due to their electron-transporting behavior and n-type properties. A prescreening step by using thermogravimetric calorimetry has demonstrated the stability of all three M(ptp)2 and M(ptp)2(py)2 compounds and their amenability to sublimation. Preliminary current-voltage measurements from simple diodes has achieved unidirectional current from a Pt(ptp)2 neat layer and demonstrated its n-type semiconducting behavior.
Date: August 2010
Creator: Chen, Wei-Hsuan
Partner: UNT Libraries

Novel Semi-Conductor Material Systems: Molecular Beam Epitaxial Growth and Characterization

Description: Semi-conductor industry relies heavily on silicon (Si). However, Si is not a direct-band gap semi-conductor. Consequently, Si does not possess great versatility for multi-functional applications in comparison with the direct band-gap III-V semi-conductors such as GaAs. To bridge this gap, what is ideally required is a semi-conductor material system that is based on silicon, but has significantly greater versatility. While sparsely studied, the semi-conducting silicides material systems offer great potential. Thus, I focused on the growth and structural characterization of ruthenium silicide and osmium silicide material systems. I also characterized iron silicon germanide films using extended x-ray absorption fine structure (EXAFS) to reveal phase, semi-conducting behavior, and to calculate nearest neighbor distances. The choice of these silicides material systems was due to their theoretically predicted and/or experimentally reported direct band gaps. However, the challenge was the existence of more than one stable phase/stoichiometric ratio of these materials. In order to possess the greatest control over the growth process, molecular beam epitaxy (MBE) has been employed. Structural and film quality comparisons of as-grown versus annealed films of ruthenium silicide are presented. Structural characterization and film quality of MBE grown ruthenium silicide and osmium silicide films via in situ and ex situ techniques have been done using reflection high energy electron diffraction, scanning tunneling microscopy, atomic force microscopy, cross-sectional scanning electron microscopy, x-ray photoelectron spectroscopy, and micro Raman spectroscopy. This is the first attempt, to the best of our knowledge, to grow osmium silicide thin films on Si(100) via the template method and compare it with the regular MBE growth method. The pros and cons of using the MBE template method for osmium silicide growth are discussed, as well as the structural differences of the as-grown versus annealed films. Future perspectives include further studies on other semi-conducting silicides material systems in terms ...
Date: December 2013
Creator: Elmarhoumi, Nader M.
Partner: UNT Libraries

Water-soluble Phosphors for Hypoxia Detection in Chemical and Biological Media

Description: Water-soluble Pt(II) phosphors exist predominantly for photophysical studies. However, fewer are known to be candidates for cisplatin derivatives. If such a molecule could exist, it would be efficient at not only destroying the cancerous cells which harm the body, but the destruction would also be traceable within the human body as it occurred. Herein, research accomplished in chemistry describes the photophysical properties of a water-soluble phosphor. Spectroscopically, this phosphor is unique in that it possesses a strong green emission at room temperature in aqueous media. Its emission is also sensitive to the gaseous environment. These properties have been expanded to both analytical and biological applications. Studies showing the potential use of the phosphor as a heavy metal remover from aqueous solutions have been accomplished. The removal of toxic heavy metals was indicated by the loss of emission as well as the appearance of a precipitate. The gaseous sensitivity was elicited to be used as a potential cancerous cell biomarker. In vivo studies were accomplished in a wide variety of species, including bacteria (E. coli), worms (C. elegans), small crustaceans (Artemia), and fish (D. rerio and S. ocellatus). The phosphor in question is detectable in all of the above. This fundamental research lays the foundation for further expansion into bioinorganic chemistry, and many other possible applications.
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Date: December 2012
Creator: Satumtira, Nisa Tara
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Modeling Transition Metal Catalysts for Small Molecule Activation and Functionalization

Description: There is a high demand for the development of processes for the conversion of ubiquitous molecules into industrially useful commodities. Transition metal catalysts are often utilized for the activation and functionalization of small organic molecules due to their diverse nature and proven utility with a myriad of chemical transformations. The functionalization of methane (CH4) and dinitrogen (N2) to methanol (CH3OH) and ammonia (NH3) respectively is of particular interest; however, both methane and dinitrogen are essentially inert due to the inherit strength of their bonds. In this dissertation a series of computational studies is performed to better understand the fundamental chemistry behind the functionalization of methane and the activation of dinitrogen in a homogeneous environment. A catalytic cycle is proposed for the oxy-functionalization of methane to methanol. The cycle consists of two key steps: (1) C-H activation across a metal-alkoxide bond (M-OR), and (2) regeneration of the M-OR species through an oxy-insertion step utilizing external oxidants. The C-H activation step has been extensively studied; however, the latter step is not as well understood with limited examples. For this work, we focus on the oxy-insertion step starting with a class of compounds known to do C-H activation (i.e., Pt(II) systems). Computational studies have been carried out in an attempt to guide experimental collaborators to promising new systems. Thus, the majority of this dissertation is an attempt to extend transition metal mediated C-O bond forming reactions to complexes known to perform C-H activation chemistry. The last chapter involves a computational study of the homogeneous cleavage of N2 utilizing iron-?-diketiminate fragments. This reaction has been studied experimentally, however, the reactive intermediates were not isolated and the mechanism of this reaction was unknown. Density functional theory (DFT) calculations are carried out to elucidate the mechanism of the reductive cleavage of N2 via the sequential addition ...
Date: May 2013
Creator: Figg, Travis M.
Partner: UNT Libraries

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

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 calculations presented here propose novel ways to tune the geometric, electronic, spectroscopic, and conduction properties in semiconducting materials. In addition to novel material development, electronic device performance can be improved by making a judicious choice of device components. I have studied the interfaces of a p-type metal-organic semiconductor viz cyclo-[Au(µ-Pz)]3 trimer with metal electrodes at atomic and surface levels. This work was aimed to guide the device engineers to choose the appropriate metal electrodes considering the chemical interactions at the interface. Additionally, the calculations performed on the interfaces provided valuable insight into binding energies, charge redistribution, change in the energy ...
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Date: December 2012
Creator: Chilukuri, Bhaskar
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Computational Studies of Inorganic Systems with a Multiscale Modeling Approach: From Atomistic to Continuum Scale

Description: Multiscale modeling is an effective tool for integrating different computational methods, creating a way of modeling diverse chemical and physical phenomena. Presented are studies on a variety of chemical problems at different computational scales and also the combination of different computational methods to study a single phenomenon. The methods used encompass density functional theory (DFT), molecular dynamics (MD) simulations and finite element analysis (FEA). The DFT studies were conducted both on the molecular level and using plane-wave methods. The particular topics studied using DFT are the rational catalyst design of complexes for C—H bond activation, oxidation of nickel surfaces and the calculation of interaction properties of carbon dioxide containing systems directed towards carbon dioxide sequestration studies. Second and third row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity, and which are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of non-innocent and/or very high-field ligands? Using DFT, the impact of these electronic features upon methane C—H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo and carbene complexes (M = Fe, Co, Ni, Cu; E = O, NMe, CMe2). To promote a greater understanding of the process and nature of metal passivation, first-principles analysis of partially oxidized Ni(111) and Ni(311) surface and ultra-thin film NiO layers on Ni(111) was performed. A bimodal theoretical strategy that considers the oxidation process using either a fixed GGA functional for the description of all atoms in the system, or a perturbation approach, that perturbs the electronic structure of various Ni atoms in contact with oxygen by application of the GGA+U technique was applied. Binding energy of oxygen to the nickel ...
Date: August 2013
Creator: Olatunji-Ojo, Olayinka A.
Partner: UNT Libraries

Biological Applications of a Strongly Luminescent Platinum (Ii) Complex in Reactive Oxygen Species Scavenging and Hypoxia Imaging in Caenorhabditis Elegans

Description: Phosphorescent transition metal complexes make up an important group of compounds that continues to attract intense research owing to their intrinsic bioimaging applications that arise from bright emissions, relatively long excited state lifetimes, and large stokes shifts. Now for biomaging assay a model organism is required which must meet certain criteria for practical applications. The organism needs to be small, with a high turn-over of progeny (high fecundity), a short lifecycle, and low maintenance and assay costs. Our model organism C. elegans met all the criteria. The ideal phosphor has low toxicity in the model organism. In this work the strongly phosphorescent platinum (II) pyrophosphito-complex was tested for biological applications as a potential in vivo hypoxia sensor. The suitability of the phosphor was derived from its water solubility, bright phosphorescence at room temperature, and long excited state lifetime (~ 10 µs). The applications branched off to include testing of C. elegans survival when treated with the phosphor, which included lifespan and fecundity assays, toxicity assays including the determination of the LC50, and recovery after paraquat poisoning. Quenching experiments were performed using some well knows oxygen derivatives, and the quenching mechanisms were derived from Stern-Volmer plots. Reaction stoichiometries were derived from Job plots, while percent scavenging (or antioxidant) activities were determined graphically. The high photochemical reactivity of the complex was clearly manifested in these reactions.
Date: December 2015
Creator: Kinyanjui, Sophia Nduta
Partner: UNT Libraries

Design, Synthesis, and Characterization of Aqueous Polymeric Hybrid Composites and Nanomaterials of Platinum(ii) and Gold(i) Phosphorescent Complexes for Sensing and Biomedical Applications

Description: The two major topics studied in this dissertation are the gold(I) pyrazolate trimer {[Au(3-R,5-R’)Pz]3} complexes in aqueous chitosan polymer and phosphorescent polymeric nanoparticles based on platinum(II) based complex. The first topic is the synthesis, characterization and optical sensing application of gold(I) pyrazolate trimer complexes within aqueous chitosan polymer. A gold(I) pyrazolate trimer complex, {[Au(3-CH3,5-COOH)Pz]3}, shows high sensitivity and selectivity for silver ions in aqueous media, is discussed for optical sensing and solution-processed organic light emitting diodes (OLEDs) applications. Gold(I) pyrazolate trimer complexes are bright red emissive in polymeric solution and their emission color changes with respect to heavy metal ions, pH and dissolved carbon dioxide. These photophysical properties are very useful for designing the optical sensors. The phosphorescent polymeric nanoparticles are prepared with Pt-POP complex and polyacrylonitrile polymer. These particles show excellent photophysical properties and stable up to >3 years at room temperature. Such nanomaterials have potential applications in biomedical and polymeric OLEDs. The phosphorescent hybrid composites are also prepared with Pt-POP and biocompatible polymers, such as chitosan, poly-l-lysine, BSA, pnipam, and pdadmac. Photoluminescent enhancement of Pt-POP with such polymers is also involved in this study. These hybrid composites are promising materials for biomedical applications such as protein labeling and bioimaging.
Date: December 2015
Creator: Upadhyay, Prabhat K.
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Photochemical and Photophysical Properties of Mononuclear and Multinuclear Closed Shell D10 Coinage Metal Complexes and Their Metallo-organometallic Adducts

Description: This dissertation covers the studies of two major topics: the photochemistry of mononuclear and multinuclear gold(I) complexes and synthetic approaches to tailor photophysical properties of cyclic trinuclear d10 complexes. First a detailed photochemical examination into the photoreactivity of neutral mononuclear and multinuclear gold(I) complexes is discussed, with the aim of gold nanoparticle size and shape control for biomedical and catalysis applications. Next is a comprehensive systematic synthetic approach to tailor the photophysical properties of cyclic trinuclear d10 complexes. This synthetic approach includes an investigation of structure-luminescence relationships between cyclic trinuclear complexes, an examination into their π-acid/π-base reactivity with heavy metal cations and an exploration into the photophysical properties of new heterobimetallic cyclic trinuclear complexes. These photophysical properties inspections are used to screen materials for their employment in molecular electronic devices such as organic light-emitting diodes (OLEDs) and thin film transistors (OTFTs).
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Date: December 2013
Creator: McDougald, Roy N., Jr.
Partner: UNT Libraries

Synthesis and Characterization of Two and Three Coordinate Gold (I) Conjugated and Rigid Metallodendrimers

Description: This dissertation is a study of two major topics that involve synthetic strategies for new classes of phosphorescent gold(I)-based metallodendrimers. The phosphorescence of organic and inorganic luminophores originates from spin-orbit coupling owing to internal or external heavy atom effects as well as metal-centered emissions. Previous work in the Omary group entailed systematically designed small molecules, metallopolymers, and unconjugated metallodendrimers that contain d10 and d8 metals, whereas this dissertation aims in part to expand such strategies to the conjugated metallodendrimer regime. In one approach novel synthetic strategies were used to make first-generation phenyl acetylene dendrimers and phosphine derivatives thereof. The phosphine dendrimers are made by tethering one of the phosphines to an unsaturated dendrimer, as such phosphine dendrimers are better chromophores and luminophores due to their structural rigidity and extended conjugation. In another approach, 2- and 3-coordinate Au(I) dendritic complexes are synthesized from these phosphine dendrimers. This study is further extended to study metallodendritic complexes with different cores, for example triphenylene-based metallodendritic complexes with six acetylene branches. The physical properties of the metallodendrimers can be modulated upon proceeding to further dendrimer generations or by using solubilizing groups on the peripheral phosphines, thus allowing better processability for thin-film fabrication as required for molecular electronic devices and higher chance for crystal growth toward accurate structural characterization. Other data produced in this project suggested that some structural alterations led to porous solids that render them suitable for realized and potential applications in energy storage and carbon capture. The interesting luminescence properties of the metallodendrimers and porous extended solids produced in this dissertation are significant toward utilizing such materials for optoelectronic applications such as energy-saving organic light-emitting diodes and optical sensors for environmental pollutants.
Date: August 2012
Creator: Kaipa, Ushasree
Partner: UNT Libraries

Targeted and Metal-loaded Polymeric Nanoparticles As Potential Cancer Therapeutics

Description: Polymeric nanoparticles were designed, synthesized, and loaded with metal ions to explore the therapeutic potential for transition metals other than platinum found in cisplatin. Nanoparticles were synthesized to show the potential for polymer based vectors. Metal loading and release were characterized via Inductively Coupled Plasma Mass Spectrometry (ICP MS), Energy Dispersive X-Ray Spectroscopy (EDX), X-Ray Photoelectron Spectroscopy (XPS), and Elemental Analysis. Targeting was attempted with the expectation of observed increased particle uptake by cancer cells with flow cytometry and fluorescence microscopy. Results demonstrated that a variety of metals could be loaded to the nano-sized carriers in an aqueous environment, and that the release was pH-dependent. Expected increased targeting was inconsistent. The toxicity of these particles was measured in cancer cells where significant toxicity was observed in vitro via dosing of high copper-loaded nanoparticles and slight toxicity was observed in ruthenium-loaded nanoparticles. No significant toxicity was observed in cells dosed with metal-free nanoparticles. Future research will focus on ruthenium loaded polymeric nanoparticles with different targeting ligands dosed to different cell lines for the aim of increased uptake and decreased cancer cell viability.
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Date: May 2014
Creator: Harris, Alesha N.
Partner: UNT Libraries

The Mechanisms of Methane C–H Activation and Oxy-insertion Via Small Transition Metal Complexes: a DFT Computational Investigation

Description: Our country continues to demand clean renewable energy to meet the growing energy needs of our time. Thus, natural gas, which is 87% by volume of methane, has become a hot topic of discussion because it is a clean burning fuel. However, the transportation of methane is not easy because it is a gas at standard temperature and pressure. The usage of transition metals for the conversion of small organic species like methane into a liquid has been a longstanding practice in stoichiometric chemistry. Nonetheless, the current two-step process takes place at a high temperature and pressure for the conversion of methane and steam to methanol via CO + H2 (syngas). The direct oxidation of methane (CH4) into methanol (CH3OH) via homogeneous catalysis is of interest if the system can operate at standard pressure and a temperature less than 250 C. Methane is an inert gas due to the high C-H bond dissociation energy (BDE) of 105 kcal/mol. This dissertation discusses a series of computational investigations of oxy-insertion pathways to understand the essential chemistry behind the functionalization of methane via the use of homogeneous transition metal catalysis. The methane to methanol (MTM) catalytic cycle is made up of two key steps: (1) C-H activation by a metal-methoxy complex, (2) the insertion of oxygen into the metal−methyl bond (oxy-insertion). While, the first step (C-H activation) has been well studied, the second step has been less studied. Thus, this dissertation focuses on oxy-insertion via a two-step mechanism, oxygen-atom transfer (OAT) and methyl migration, utilizing transition metal complexes known to activate small organic species (e.g., PtII and PdII complexes). This research seeks to guide experimental investigations, and probe the role that metal charge and coordination number play.
Date: May 2014
Creator: Prince, Bruce M.
Partner: UNT Libraries