Synthesis and Characterization of Amide and Urea Receptor Systems for Anion and Metal Complexation and the Synthesis and Use of Block Copolymers for Optoelectronic Crystal Growth

The content of this dissertation is divided into two parts, as a result of projects from two research groups during the course of my research at the University of Kansas. The first five chapters detail my work with Dr. Bowman-James which has focused on host-guest chemistry ranging from ligand synthesis to anion and metal binding. I joined the Bowman-James group after my fourth year at KU and have been a member from 2015 to 2017. Ditopic pyrazine pincers or “duplex” pincers were synthesized and investigated for both their anion binding and their metal binding merit. Chapter 2 will investigate duplex hosts as anion binding hosts, the duplex receptors were synthesized with R group functionalizations that permit a range of solubilities in various solvents. Their anion binding capabilities will be discussed in comparison to their monotopic counterparts. The duplex pincers were also studied for transition metal binding capabilities which will be detailed in Chapter 5. Palladium complexes were made and characterized with the duplex pincers and some of the interesting features of these compounds will be discussed. Aside from the duplex hosts, urea macrocyclic receptors were also synthesized and characterized for their anion host capabilities, which will be discussed in Chapter 3. Variations in macrocycle size and urea components were explored and binding merit was determined on these receptor complexes. The final two chapter of this dissertation highlight one of my projects in the Ren group from my first year of graduate school in 2011 up through my fourth year in 2015. I joined the Bowman-James group after Dr. Ren moved to Temple University. Chapter 6 will include a review on the field of organic photovoltaic and optoelectronic devices. Chapter 7 will detail my work synthesizing block copolymers for use as compatibilizing agents for P3HT and C60 interfaces. These organic photovoltaic devices exhibited an interesting magnetoconductive behavior that can be observed at room temperature in these charge transfer systems

Exciton diffusion in semiconducting single-wall carbon nanotubes studied by transient absorption microscopy

Spatiotemporal dynamics of excitons in isolated semiconducting single-walled carbon nanotubes are studied using transient absorption microscopy. Differential reflection and transmission of an 810-nm probe pulse after excitation by a 750-nm pump pulse are measured. We observe a bi-exponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. By spatially and temporally resolving the differential reflection, we are able to observe a diffusion of excitons, and measure a diffusion coefficient of 200 cm2/s at room temperature and 300 cm2/s at lower temperatures of 10 K and 150 K.Comment: 6 pages, 4 figure

Exciton diffusion in semiconducting single-walled carbon nanotubes studied by transient absorption microscopy

This is the publisher's version, also available electronically from http://journals.aps.org/prb/abstract/10.1103/PhysRevB.86.205417.Spatiotemporal dynamics of excitons in isolated semiconducting single-walled carbon nanotubes are studied using transient absorption microscopy. Differential reflection and transmission of an 810-nm probe pulse after excitation by a 750-nm pump pulse are measured. We observe a biexponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. By spatially and temporally resolving the differential reflection, we are able to observe a diffusion of excitons, and measure a diffusion coefficient of 200±10 cm2/s at room temperature and 300±10 cm2/s at lower temperatures of 10 K and 150 K

Nanocarbon-Based photovoltaics

Carbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells - namely solution processable, potentially flexible, and chemically tunable - but with significantly increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using ab-initio density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC70BM fullerene, semiconducting single-walled carbon nanotubes and reduced graphene oxide. It achieves a power conversion efficiency of 1.3% - a record for solar cells based on carbon as the active material - and shows significantly improved lifetime than a polymer-based device. We calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the superior photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells

Caught Red-Handed:Corporate Labor Practices and the Investigatory Media, a New Look at Corporate Social Responsibility

Firm self-regulation with regards to illegal and unethical labor practices has become a significant trend recently, as firms face possible negative exposure from the investigatory media. This paper provides a theoretical analysis of the determinants corporate labor practices and the role played by the investigatory media in firm selfregulation. The model finds that firms, when facing a media investigation, are no more likely to use unethical labor regardless of how cost effective it is. Instead, the firm is actually driven towards certain labor choices based upon the parameters of the investigatory media’s profitability. This communicates the importance of outside monitoring bodies on the road towards improved global labor standards.Honors thesis, Department of Mathematic

Lattice-Matched Bimetallic CuPd-Graphene Nanocatalysts for Facile Conversion of Biomass-Derived Polyols to Chemicals

A bimetallic nanocatalyst with unique surface configuration displays extraordinary performance for converting biomass-derived polyols to chemicals, with potentially much broader applications in the design of novel catalysts for several reactions of industrial relevance. The synthesis of nanostructured metal catalysts containing a large population of active surface facets is critical to achieve high activity and selectivity in catalytic reactions. Here, we describe a new strategy for synthesizing copper-based nanocatalysts on reduced graphene oxide support in which the catalytically active {111} facet is achieved as the dominant surface by lattice-match engineering. This method yields highly active Cu-graphene catalysts (turnover frequency = 33–114 mol/g atom Cu/h) for converting biopolyols (glycerol, xylitol, and sorbitol) to value-added chemicals, such as lactic acid and other useful co-products consisting of diols and linear alcohols. Palladium incorporation in the Cu-graphene system in trace amounts results in a tandem synergistic system in which the hydrogen generated <i>in situ</i> from polyols is used for sequential hydrogenolysis of the feedstock itself. Furthermore, the Pd addition remarkably enhances the overall stability of the nanocatalysts. The insights gained from this synthetic methodology open new vistas for exploiting graphene-based supports to develop novel and improved metal-based catalysts for a variety of heterogeneous catalytic reactions

Pyrazinetetracarboxamide: A Duplex Ligand for Palladium(II)

Tetraethylpyrazine-2,3,5,6-tetracarboxamide forms a dipalladium­(II) complex with acetates occupying the fourth coordination sites of the two bound metal ions. Crystallographic results indicate that the “duplex” dipincer has captured two protons that serve as the counterions. The protons lie between adjacent amide carbonyl groups with very short O···O distances of 2.435(5) Å. In the free base, the adjacent carbonyl groups are farther apart, averaging 3.196(3) Å. While the dipalladium­(II) complexes stack in an ordered stepwise fashion along the <i>a</i> axis, the free base molecules stack on top of each other, with each pincer rotated by about 60° from the one below

Nanocarbon-Based Photovoltaics

Carbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and maintain superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells, namely, solution processable, potentially flexible, and chemically tunable, but with increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using <i>ab initio</i> density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC₇₀BM fullerene, semiconducting single-walled carbon nanotubes, and reduced graphene oxide. This active-layer composition achieves a power conversion efficiency of 1.3%a record for solar cells based on carbon as the active materialand we calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells employing PCBM as the acceptor. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the high photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells

Characterizing Hydrogen-Bond Interactions in Pyrazinetetracarboxamide Complexes: Insights from Experimental and Quantum Topological Analyses

Experimental and topological analyses of dipalladium­(II) complexes with pyrazinetetracarboxamide ligands containing tetraethyl (<b>1</b>), tetrahexyl (<b>2</b>), and tetrakis­(2-hydroxyethyl) ethyl ether (<b>3</b>) are described. The presence of two very short O---O distances between adjacent amide carbonyl groups in the pincer complexes revealed two protons, which necessitated two additional anions to satisfy charge requirements. The results of the crystal structures indicate carbonyl O---O separations approaching that of low barrier hydrogen bonds, ranging from 2.413(5) to 2.430(3) Å. Solution studies and quantum topological analyses, the latter including electron localization function, noncovalent interaction, and Bader’s quantum theory of atoms in molecules, were carried out to probe the nature of the short hydrogen bonds and the influence of the ligand environment on their strength. Findings indicated that the ligand field, and, in particular, the counterion at the fourth coordination site, may play a subtle role in determining the degree of covalent association of the bridging protons with one or the other carbonyl groups