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School of Chemistry and Biochemistry
School of Chemistry and Biochemistry
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ItemDoping of Organic Semiconductors: Effects of Crosslinking and Dopant Substituents(Georgia Institute of Technology, 2021-12-15) Saeedifard, FarzanehDoping is the process of addition of dopants to host semiconductors to improve their conductivity and charge transport behavior. Organic solids are held together by weak van der Waals interactions between the molecules and Coulombic attractions between the charged species. Because of these weaker interactions in organic materials, the molecules themselves have higher mobilities within the host material, and therefore, have a higher tendency to move. In most of the devices, the diffusion of the dopants in device stacks is detrimental and therefore, minimizing dopant diffusion within device interlayers is a very important topic to be consider. Considering the widespread usage of DMBI-H derivatives for doping of organic semiconductors, this work will focus on two aspects of doping; investigation of different approaches to address the diffusion of DMBI-H derivatives and studying the effect of dopant substituents on charge transport behavior. The first and second chapters of this thesis, will focus on crosslinking as new approaches for minimizing the dopant diffusion in the solid state. Chapter 2 will discuss electrostatic crosslinking in which the restriction of dopant ion movement by forming multiple electrostatic sites between the multiply charged ions and ionized host segments. Chapter 3 will discuss chemical crosslinking and chemical bond formation to decrease the diffusion of dopant and the corresponding dopant ions. Chapter 4 will focus on a study in which the effect of a polar side chain on DMBI-H for doping of a donor-acceptor polymer. The final chapter summarizes the findings of the thesis, puts them in a broader perspective, and suggests future directions
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ItemSynthetic Strategies Toward Heterocyclic Seven Membered Ring Systems: Building Libraries of Privileged Scaffolds for Medicinal Chemistry and Forensic Analysis(Georgia Institute of Technology, 2021-12-14) Parker, Ariel N.Natural products are often the inspiration for many pharmaceutical compounds as they are found to have drug-like properties. Many times, these compounds exhibit structural commonalities and are therefore referred to as “privileged structures.” Synthetic organic chemists have devoted significant time and effort into developing efficient methods to access these privileged scaffolds for the construction of diverse libraries. This thesis explores novel synthetic strategies to access the privileged scaffolds: cyclohepta[b]indole and the 1,4-benzodiazepine, flubromazepam. The protocols designed to access these heterocyclic seven-membered ring systems include: 1) a formal [5+2] cycloaddition between alkenes and indole fused alkylidenes, 2) a Friedel-Crafts transformation and 3) a nucleophilic arylation. Additionally, through the development of these modular protocols new discoveries were made providing new insights in medicinal chemistry and forensic analysis.
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ItemSpecialized side chain influence on arrangement of conjugated macromolecules in organic electronics(Georgia Institute of Technology, 2021-12-13) Hicks, TheodoreSpecialized side chain influence on arrangement of conjugated macromolecules in organic electronics Theodore Hicks 171 Pages Directed by Dr. Seth R. Marder This dissertation focuses on the design, synthesis, and characterization of pi-conjugated small molecules and 2D polymers of potential interest for organic electronic applications. An investigation of the structure-property relationships that effect two different classes of conjugated macromolecules, covalent organic frameworks (COFs) and small-molecule electron acceptors, is conducted by synthesis of new materials and characterization of the resulting optical, electronic and physical properties. Chapter 2 describes two different approaches toward development of a generalizable method for synthesizing 2D crystalline polymer monolayers. The findings include a remarkable tolerance of interlayer stacking in imine-linked COFs composed of isoindigo as well as the development of air-water polymerization methods to generate monolayer films. The characteristics of the COF materials are demonstrated using a variety of spectroscopic and microscopy techniques. Chapter 3 details the synthesis and characterization of small molecules designed for use in organic photovoltaics. The new compounds are evaluated for electronic and optical suitability before incorporation into test devices. Chapter 4 gives a perspective on the impact of synthetic complexity on organic electronic devices and contains an investigation of new synthetic methods based on ultra-efficient catalysis of precursors required for organic semiconductors.
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ItemAssessment of Mars Analogue Instruments and Biosignatures in Icelandic Mars Analogue Environments: Implications for Astrobiology(Georgia Institute of Technology, 2021-12-13) Tan, George K.To search more efficiently for a record of past life on Mars, it is critical to know where to look and thus maximize the likelihood of success. Large-scale site selection for the Mars 2020 mission has been completed, but small (meter to 10 cm)-scale relationships of microenvironments will not be known until the rover reaches the surface. This thesis aims to study different Icelandic Mars analog environments to simultaneously look at all domains of life interpreted in the context of the underlying mineralogical and geochemical environment. The overarching premise for this work is a comprehensive understanding of the geological and biological characteristics of terrestrial basaltic systems to better develop strategies to help guide the life-detection mission and sampling location selection to ensure best scientific return. This dissertation include 1) a study to describe an analogue mission in low biomass Mars analogue environments comparing the effectiveness, spatial variation, and inter-correlations of life-detection techniques and implications for Mars sampling selection 2) an examination of spatial distributions and levels of biosignatures in Icelandic Mars analogue environments 3) a study exploring the composition of microbial communities at different spatial scales in apparently homogenous environments, 4) final study linking biological indicators to physical characteristics including bulk chemical composition, spectral signatures of mineralogy, and grain size. The last chapter of the thesis will summarize major findings and present several recommendations for continued research.
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ItemProbing Heme Signaling Dynamics Using Fluorescent Heme Sensors(Georgia Institute of Technology, 2021-12-13) Moore, CourtneyLong considered to be a static protein cofactor, a growing body of evidence suggests that heme may function as a dynamic signaling molecule. To elucidate heme-based signal transduction, a library of genetically encoded fluorescent heme sensors with a wide range of heme binding affinities was developed. Moreover, new targets of heme signaling, namely the ubiquitin-proteasome system (UPS), were characterized and a novel role for heme oxygenase-2 (HO-2) in regulating heme availability independent of its role in catalyzing heme degradation was discovered. Together, the results reported herein expand the toolkit of reagents available to probe heme signaling, revealed novel heme homeostatic mechanisms, and demonstrated that heme plays important roles in signaling beyond its canonical function as an enzyme cofactor.
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ItemTailoring optically modulated fluorescent proteins for sensitive fluorescence imaging(Georgia Institute of Technology, 2021-12-10) Peng, BaijieThe continuous development and advancement have made fluorescence microscopy one of the most indispensable tools in life science. Fluorescent proteins (FPs) are highly specific and biocompatible. Therefore, they are widely used in fluorescence microscopy, which enables spatio-temporal analysis of complex biological processes. However, cellular metabolites generate autofluorescence background, which blends with the target FP fluorescence and results in reduced sensitivity or even inconsistent results, especially under low FP copy numbers. On the other hand, some FPs transiently reside in µs- to ms-lived dark electronic states after photoexcitation, which can be rapidly depopulated back to the fluorescent states by a lower energy coillumination. Optical modulation modulates the coillumination intensity, which dynamically alters the dark state population, thereby modulating the fluorescence intensity. Those FPs are named optically modulated fluorescent proteins (OMFPs). Synchronously amplified fluorescence image recovery (SAFIRe) developed by the Dickson group utilizes those modulatable fluorescence tags. SAFIRe uses Fourier transform to selectively recover the light signal from only the target of interest. It greatly suppresses the background and significantly improves the imaging contrast. SAFIRe holds great potentials in not only improving cellular imaging sensitivity but also enabling new paradigms of qualitative and quantitative analysis. Currently, there are only a few OMFP variants engineered and reported, albeit their great potentials in a wide array of applications. Herein, we assess the modulatability of various FPs that possess interesting photophysical characteristics. We also worked with the Fahrni lab at Georgia Institute of Technology to perform mutagenesis on several FPs to generate novel modulatable mutants. Notably, we have successfully engineered, identified, and characterized optically modulated yellow fluorescent proteins with unique modulation profiles even with single mutation. Further experimentation and analysis on some OMFPs revealed unique optically activated delayed fluorescence (OADF), which not only elucidates the triplet nature of the short-lived dark state among some OMFPs but also demonstrates great potential in developing expeditious background-free and reference-free imaging methodologies. Our meticulous characterization of photophysics in the YFP family yields highly accurate photophysical and photochemical parameters, which can be used to generate rate matrices based on corresponding Jablonski diagrams. OMFP fluorescence simulation based on excitation and decay rates coupled to the experimental conditions yields simulated modulation and OADF agree strongly to our experimental results. Continuous research on OMFPs since their discovery inspires us to develop novel high-sensitivity fluorescence imaging methodologies. Utilizing those well-engineered and well-characterized OMFPs in cellular imaging will greatly increase the target contrast. Continuous development of new fluorescence microscopic paradigms will enable qualitative and quantitative analysis of targets of interest.
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ItemSynthesis and Characterization of Solid-State and Molecular Quantum Magnetic Materials(Georgia Institute of Technology, 2021-12-09) Jiang, NingxinF-element magnetic materials are crucial for the next-generation applications, such as the design of the single-molecule magnets, topological insulators, the heavy-fermion superconductors, and high-coercivity hard magnets. However, compared to first-row transition metals, f-elements have more complications including degenerate ground states and significant spin-orbit coupling. This latter phenomenon is the basis of their application in both hard magnets and in the quantum condensed matter since it induces significant magnetic anisotropy. The large ionic radii of f-elements normally lead to high coordination number and low local symmetry of f-element magnetic materials which also prevents the in-depth understanding of the physical properties of f-elements based exchange-coupled systems. In this dissertation, the design and synthesis of novel exchanged-coupled magnetic systems were described and the impact of structural imperfection and local symmetry change on the magnetic properties of these systems were also studied. The first chapter provides an introduction to quantum spin liquid and single molecule magnet. Chapter two and three details the synthesis of two layered triangular ytterbium-based antiferromagnets. The lack of long-range magnetic ordering down to 0.1 K in both compounds was observed. Chapter four describes the synthesis and physical property studies of (CH3NH3)2NaTi3F12 with perfect kagome layer and several quantum-spin-liquid behaviors. Chapter five outlines the synthesis of (CH3NH3)2NaV3F12 which is a rare S = 1 antiferromagnet with perfect kagome layer and the magnetic characterization of this compound suggests a spin-glass state at low temperature. Chapter six details the structural and physical property studies of (CH3NH3)2KTi3F12 with slightly distorted kagome layers. Comparison between the physical properties of (CH3NH3)2KTi3F12 and (CH3NH3)2NaTi3F12 was also provided. Chapter seven outlines the development of two isomeric titanocene terbium chloride molecules. Dramatically different magnetic behaviors suggest the importance of local symmetry to the magnetic properties of small molecules. This chapter also provided a useful design strategy for the synthesis of high-performance single molecule magnets. The final chapter summarizes the research results in the thesis and provides a perspective on the design of novel solid-state and molecular magnetic materials.
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ItemSynthesis, reactivity and polymerization of bridged bicyclic twisted amides(Georgia Institute of Technology, 2021-12-08) Xu, MizhiAmides are generally robust and hydrolytically resistant due to the nN-to-π*C=O conjugation. Twisted amides represent an unusual subclass of amides containing distorted, non-planar amide bonds as a consequence of geometric, steric or electronic effects. The most common approach to twisting the amide bond involves geometric constraint in the bridged bicyclic amide structure. Due to the disrupted amide resonance, twisted amides feature distinct reactivities compared to normal amides, including enhanced N-nucleophilicity, carbonyl-electrophilicity and “amino-ketone” reactivity. Despite the unusual structure and unique reactivity of twisted amides, their potential as monomers in polymerization has rarely been explored. In this dissertation, the polymerization of a [3.3.1] bicyclic twisted amide system is described through the halide-rebound (Chapter 2) and ring-opening metathesis strategies (Chapter 4). In addition, the remote substituent effects on modulating the geometry and reactivity of this twisted amide framework are investigated via computational and kinetic studies (Chapter 3). Finally, a new halide-abstraction strategy is disclosed in the synthesis of a highly strained [3.2.1] bicyclic twisted amide (Chapter 5).
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ItemTunable Magnetic Properties of Spinel Ferrite Nanoparticles: Ferromagnetic Resonance and Physical Model of Magnetic Permeability(Georgia Institute of Technology, 2021-12-07) Cao, YiSpinel ferrite nanoparticles have been widely applied in high frequency applications such as microwave absorption, signal filter, etc. The design of spinel ferrites with various properties has been a hot topic to satisfy different application requirements. The goal of this dissertation is to explore the tunability of magnetic properties especially at high frequencies with the manipulation of size, chemical composition, magnetic couplings, and super exchange interactions. Chapter 2 studies the magnetic coupling, cation distribution, and magnetic properties (susceptibility, hysteresis, FMR spectrum, etc.) of hard and soft spinel ferrite nanoparticles. The hard (CoFe2O4) and soft (MnFe2O4, MgFe2O4, and ZnFe2O4) nanoparticles show discrepancy on magnetic properties due to spin-orbit coupling strength difference. The magnetic property difference among soft nanoparticles has been demonstrated to be attributed to the variation of cation distribution. Chapter 3 investigates the effect of Al3+ substitution in MnAlxFe2-xO4 and CoAlxFe2-xO4 nanoparticles. It has been demonstrated that the magnetic properties under DC and AC applied field are size dependent. Composition dependent study reveals the preference of Al3+ on octahedral sites, which consequently affect the number of super exchange interactions and magnetic behavior. Chapter 4 explores the tunability of superparamagnetic and ferromagnetic resonance properties of CoxMg1-xFe2O4 and MnxMg1-xFe2O4 nanoparticles. The incorporation of Co2+ is proved to have significant influence on the magnetic properties of CoxMg1-xFe2O4 nanoparticles, which is mainly caused by magnetic coupling and magnetic anisotropy change. Broad tunability of magnetic properties has been achieved in CoxMg1-xFe2O4 series of nanoparticles. Chapter 5 reveals the effect of annealing process on the cation distribution and FMR spectrum of ZnFe2O4 nanoparticles. As-prepared ZnFe2O4 nanoparticles are demonstrated to have high inversion degree of 0.46, which decreases with higher annealing temperature. The number of super exchange interaction diminishes with smaller inversion degree. Chapter 6 develops a physical model for complex magnetic permeability of spinel ferrite nanoparticles using DC SQUID magnetometer and FMR data. The model reveals the intrinsic permeability information over broad range of frequency and applied field. In Chapter 7, the complex permeability of spinel ferrite nanoparticles with various chemical compositions is simulated and compared. The correlation of saturation magnetization, magnetic anisotropy, and FMR behavior with magnetic permeability has been found.
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ItemUnprotected Carbohydrate Conversion to Polyhydroxyalkyl Furans and Dihydrofurans: Improvement, Expansion, and Interruption of the Garcia Gonzalez Reaction via Homogeneous and Heterogeneous Catalysis(Georgia Institute of Technology, 2021-11-18) Ronaghi, NimaBiomass conversion of carbohydrates will lay the foundation for the future of materials, chemicals, and fuels. The Garcia Gonzalez reaction, an undervalued reaction coupling carbon nucleophiles with aldose sugars, can be an integral part of the carbohydrate conversion world, given the high yields, ease of tunability, mild conditions, and ease of setup. The improvement of the homogeneous catalysis of the Garcia Gonzalez reaction, using zirconium chloride as the catalyst, allows for more mild, facile synthesis of polyhydroxyalkyl and C-glycosyl furans. The expansion of the catalysts to a well-defined metal-organic framework, specifically UiO-66, showcases an example of heterogenizing a catalyst for a reaction system, as well as tuning the catalytic and morphological properties. Finally, interruption of the Garcia Gonzalez reaction is displayed by accessing a polyhydroxyalkyl dihydrofuran, rather than the polyhydroxyalkyl furans synthesized in the previous chapters, by using a cheap, recyclable magnesium oxide catalyst.