Physical Sciences and Mathematics Commons^™

Excited State Processes In Radical Elaborated Platinum Donor-Acceptor Complexes, Sangita Paudel

Chemistry and Chemical Biology ETDs

Organo-transition metal complexes are being widely studied to understand their photophysical properties for their wide range of applications as efficient emitters in organic light emitting diodes (OLEDs), light emitting electrochemical cells (LEECs), etc. Cyclometalated organo-transition metal complexes such as cyclometalated square planar platinum(II) complexes are becoming suitable candidates for such applications because of their highly efficient luminescence. Understanding the excited properties of such complexes is useful in designing highly efficient and color tunable phosphors with desired excited state lifetimes. We aim to explore the influence of radical substituents on electronic structure, luminescence quantum efficiencies, and excited state lifetimes by synthesizing …

Syntheses And Characterization Of Photoactive Ruthenium And Iron Polypyridyl Complexes, Rajani Thapa Magar

Chemistry and Chemical Biology ETDs

Within this dissertation, two distinct classes of metal complexes have been discussed that bear significance in the field of solar energy conversion, photo redox catalysis and memory devices. The first class of the metal complexes is a series of photochromic Ruthenium polypyridyl N-heterocyclic carbene tethered sulfoxide complexes that are reported to undergo unusually slow isomerization from S-bonded to O-bonded and unusually fast thermal reversion from O-bonded to S-bonded configuration. The role of NHC in the excited state dynamics of these complexes have been discussed in detail in Chapter 3.

For the first time in two decades, structural information of the …

Synthesis And Reactivity Of Heteroatom Embedded Cycloalkynes In Spaac, Nickel Catalyzed Alkylarylation Of Alkenes, And Carbofluorination Of Alkynes, Namrata Khanal

Chemistry and Chemical Biology ETDs

Part I covers Chapters 1, 2, and 3

cycloaddition reactions, that is utilized in biorthogonal chemistry. This metal free version The strain promoted azide-alkyne cycloaddition (SPAAC) reaction is one of the popular 1,3-dipolar of click reaction offers advantage over copper catalyzed click reaction. Since it eliminates the use of copper that is toxic to cells, it is considered favorable for biocompatible reaction. Due to the increased reactivity with dipoles without the use of metal catalyst, cycloalkynes, in particular cyclooctynes, have been employed as the biorthogonal reagent in biorthogonal chemical reaction for the study of a biological processes in vivo. The …

Photophysical Properties Of Synthetic Oligomeric Phenylene Ethynylene, Hugh F. Fritz Jr.

Chemistry and Chemical Biology ETDs

Oligomeric Phenylene Ethynylenes (OPEs) are a class of synthetically prepared compounds with the basic structure of phenylene rings connected by triple-bonded carbon atoms, also known as an ethyne link. This structure can be modified by incorporating functional groups onto one or more of the phenylene rings. The addition of functional groups, such as sulfoxide or imidazole, may alter the photophysical properties in detectable ways. The photophysical techniques used in this report include fluorescence, spectroscopy in the ultraviolet and visible light range (UVVIS), and photon-based excitation using a photo chamber.

One attractive function of OPEs is their antimicrobial property. Previously published …

Methods Of Magneto-Optical Spectroscopy And Analysis For Porphyrins And Polymer Thin-Films, Emigdio E. Turner

Chemistry and Chemical Biology ETDs

This dissertation describes the construction of two high precision magneto-polarimeters for performing Faraday rotation and Magnetic Circular Dichroism (MCD) measurements of polymer thin-films. There is a focus in materials science on the development of thin-film magneto-optically active materials. These materials could allow for the construction of a thin-film optical diode, an important device for next-generation photonic technology. Upon completion of the Faraday rotation spectrometer, two publications were generated from Faraday rotation measurements of novel polymer thin-film materials.

With growing interest by materials scientists in magneto-optically active transition-metal containing materials, an MCD spectrometer was constructed to study these materials. This spectrometer …

Mechanisim Of Plasmon-Driven Photochemical Reactions, Hamed Kookhaee

Chemistry and Chemical Biology ETDs

Understanding a photocatalytic reaction condition that selectively leads to a desired product on metal surfaces is a longstanding research problem in heterogeneous catalysis. Here, using plasmon enhanced N-demethylation of methylene blue (MB) as model reaction, we show that high degree of product selectivity can be achieved by switching the mechanism from charge transfer to adsorbate electronic excitation and vice versa using surface ligands. In the presence of cetyl trimethyl ammonium bromide (CTAB) surface ligand on gold nanoparticles, MB is selectively transformed to thionine at 633 nm excitation wavelength that overlaps with the electronic transition of the adsorbate. At resonant excitation …

Synthesis, Characterization And Spectroscopic Studies Of Novel Donor-Acceptor Complexes, Shiyue Gao

Chemistry and Chemical Biology ETDs

Square-planar compounds of the (dichalcogenolene)Pt(diimine) series are possess unique photophysical properties that include long-lived excited state lifetimes, which result in their being potential candidates for numerous applications. These applications include solar energy conversion, photocatalysis, nonlinear optics, and photoluminescent probes of biological systems. The most interesting feature of the (dichalcogenolene)Pt(diimine) series of molecules is the bpydichalcogenolene ligand-to-ligand charge transfer (LL’CT) band. To better understand their photoluminescent decay mechanism, and understand their excited dark state properties, we have synthesized and characterized new compounds that include (Thp-bpy)Pt(CAT), (Thp2-bpy)Pt(CAT), (Thp-bpy)Pt(bdt), and (Thp2-bpy)Pt(bdt). Through interpretation of electronic absorption, resonance Raman, XAS, photoluminesce spectroscopy, in addition …

Toward The Yeast Surface Display Of Microviridin B, Jillian Leigh Stafford

Chemistry and Chemical Biology ETDs

Humans have turned to natural products for medicinal therapeutics for millennia. In recent years, the ribosomally synthesized and post-translationally modified peptide (RiPP) class of natural products have garnered a lot of attention due to their ability for heterologous expression, relative ease of mutation, and vast biological activates. Microviridins are a family of RiPPs that contain a tricyclic cage-like structure through the formation of two lactone rings and one lactam ring catalyzed by two ATP-grasp ligase family enzymes. Microviridins are potent inhibitors of serine proteases and mutational studies of a small number of residues indicates the potential of peptide engineering protease …

Theoretical Studies Of Molecule-Surface Interactions And Dynamics, Yingqi Wang

Chemistry and Chemical Biology ETDs

Gas-surface scattering involves the conversion of energy in different forms in the impinging molecule, possible bond breaking and forming, and the energy transfer across gas-solid interface. Possible energy dissipation channels include adiabatic energy transfer to the motion of surface phonons and non-adiabatic interactions with surface electron-hole pairs. A complete understanding of the interplay of energy dissipation and physical/chemical changes in the molecule is vital for many important applications such as materials fabrication and heterogenous catalysis.

Gas-surface encounters may occur where non-adiabatic effects are negligible. Two such systems were investigated, both with ample experimental data. One is concerned with the scattering …

Computational, Synthetic And Spectroscopic Studies On Donor Acceptor Transition Metal Complexes, Ranjana Dangi

Chemistry and Chemical Biology ETDs

Fundamental advances in our ability to design and construct electronic components at the nanoscale will require new design paradigms. One proposed nanoscale electronic component is the molecular rectifier. Molecular and molecule-based electronic components are advantageous due to their ease of synthetic manipulation, and the fact that the size dimensions of molecules are inherently at the nanoscale (0.5 - 3nm). Our group has shown how the Donor-Bridge-Acceptor biradical approach can be used to derive key structure-property relationships that allow insight into the choice of bridge fragments for molecular rectification by using constitutional isomers of the donor-bridge-acceptor biradical (NN-Th-Py-SQ) (S=1/2 ortho-semiquinonate, …

Spin Interactions In New Donor-Acceptor Complexes, Ju Chen

Chemistry and Chemical Biology ETDs

Transition metal complexes ligated by Donor-Acceptor (D-A) biradicals are of interest for probing the degree of electronic coupling between chemically biased radical fragments. The unique nature of their electronic coupling has allowed these systems to serve as ground state analogues of charge separated excited states generated by photoexcitation. We have been interested in how the nature of the acceptor radical affects the magnitude of the electronic coupling matrix element in these biradicals. As such, we have synthesized a new series of D-A semiquinone-verdazyl (SQ-VD) biradical ligands and their transition metal complexes. We have characterized these new complexes by x-ray crystallography, …

Approaches In Molecular Engineering To Optimize The Desired Properties Of Photoactive Molecules, Douglas Joseph Breen

Chemistry and Chemical Biology ETDs

Within this dissertation, photochemical systems that bear significance to next-generation photonic materials and devices are explored. Notable advances in the design, synthesis, and characterization of three distinct groups of photoactive molecules are achieved through molecular design and spectroscopic analysis. First, novel ruthenium sulfoxide complexes bearing substituted phosphine ligands are found to provide extraordinary control over photoisomerization quantum yields. A comparison of these complexes reveals ground-state characteristics that are instrumental in this reactivity, while a novel spectroscopic technique provides rare structural evidence for an O-bonded metastable isomer. Ruthenium complexes bearing chelating carbene-sulfoxide ligands rapidly thermally revert from the O-bonded metastable isomer …

The Profound Photophysical Effects Of Organic Chromophore Connectivity And Coupling, David J. Walwark Jr

Nanoscience and Microsystems ETDs

Through-bond and through-space interactions between chromophores are shown to have wide-ranging effects on photophysical outcomes upon light absorption in organic molecules. In collapsed poly(3-hexylthiophene), through-space coupling creates hybrid chromophores that act as energy sinks for nearby excitons and favorable sites for molecular oxygen to dock. Upon excitation with visible light the highly-coupled chromophores react with the docked oxygen and subsequently do not quench nearby excitons as efficiently. In tetramer arrays of perylene diimide chromophores the central moiety through-bond connectivity is synthesized in two variants which exhibit vastly different single-molecule blinking behavior and theoretically-predicted electronic transition character. In the more-connected tetramer …

A Compendium Of Inorganic Photochemistry: Synthetic And Spectroscopic Discoveries, Sebastian B. Vittardi

Chemistry and Chemical Biology ETDs

This dissertation reports and examines contributions made in the advancement of inorganic photochemistry. Empirically driven assessments are allotted to the interplay between ligand sets, excited states, and photochemistry observed in metal complexes. A methodical spectroscopic examination is provided for oligothiophene-sensitized lanthanides. Their excited state dynamics were elucidated by femtosecond pump-probe spectroscopy and used to develop a model explaining their wavelength-dependent dual functionality. Iron (II) cyanide and isocyanides are evaluated to identify the efficacy of strong-field ligands in promoting charge-transfer excited states. Fundamentals of ligand field theory helped conceptualize the synthetically tunable parameters and effects transposed to their absorption dynamics. Transition …

Mitochondrial Proteins In Mediating Colon Cancer And Potential Theraputics, Kunlun Yin

Chemistry and Chemical Biology ETDs

Cancer is one of the biggest threatens to human health. Colon cancer is one of the leading causes of new incidence and mortality in the whole world. It is important to understand the mechanism of tumorigenesis and development. Based on the mechanisms, we may develop new therapeutics to improve survival rate.

In Chapter 2, we discussed the PINK1 function in suppression colon cancer. We found that PINK1 can activate its substrate P53, which activates its downstream targets during mitophay. At the same time, PINK1 is also involved in metabolism, we showed that PINK1 can reduce Acetyl-CoA by inhibiting PDHE1ɑ. Cells …

Pt-Containing Conjugated Polymers And Small Molecules For Bhj Photovoltaic Devices, Yunjeong Kwon

Chemistry and Chemical Biology ETDs

The current state of organic photovoltaic (OPV) devices involve series of small molecular or polymeric systems that can absorb light from the solar spectrum in concert with another material that acts as an acceptor material. Together these materials serve to generate and split bound excitation species then transport the separate charges to their respected electrode. Several limitations have restricted the widescale use of these materials. Since these devices have their genesis in organic materials the OPV devices inherit short exitonic lifetimes, narrow absorption window and a lack of precise control over the morphology. To overcome these limitations, additional molecular engineering …

Petrology And Geochemistry Of Evolved Achondrites: Planetesimal Mantles And Crusts, Zoltan Vaci

Earth and Planetary Sciences ETDs

Melting and differentiation are fundamental to early solar system evolution on planetary bodies that accreted enough material to heat up radioactively or through impacts and breach their solidi. Partially and fully melted material is present in the meteorite record in the form of primitive achondrites and achondrites, which are fragments of planetesimals that underwent heating events in the first few million years of solar system history. Although the vast majority of this material is mafic or ultramafic, new evolved samples, recovered in the last few decades, are pushing the petrologic and geochemical boundaries of planetesimal melting, differentiation, and crust formation. …

Effects Of Environmental Change On Ancestral Pueblo Fishing In The Middle Rio Grande, Jonathan W. Dombrosky Dr.

Anthropology ETDs

It has long been assumed that fishes were unimportant in the diet of past Pueblo people in the U.S. Southwest. Yet, small numbers of fish remains are consistently recovered from Late pre-Hispanic/Early Historic archaeological sites in the Middle Rio Grande of New Mexico. The end of drought conditions may have impacted food choice and fishing decisions during this time. I use behavioral ecology to understand how fishing could have been an optimal food-getting strategy for Ancestral Pueblo farmers. Stable isotope analysis offers a way to account for environmental change. I provide a refined ¹³C Suess correction model to support …

Studies Of The Rectification Behavior Of The Pdt Ligand And The Active Site Of Msrp, Laura J. Ingersol

Chemistry and Chemical Biology ETDs

Molybdenum (Mo) is an essential element that plays an important role in global nitrogen, carbon, and sulfur cycles with a critical role in human metabolism and ecological balance. It becomes catalytically active when complexed with the pyranopterin dithiolene ligand (PDT), forming the nearly ubiquitous molybdenum cofactor (Moco). The complex biosynthetic pathway of Moco, its presence in all three domains of life, and its role as a constituent cofactor in the last universal common ancestor (LUCA) all point toward the importance of the PDT in the development of life on Earth. Molybdoenzymes catalyze the two-electron oxidation or reduction of substrates that …

Synthesis And Characterization Of Regioregular Cross-Conjugated Poly(Thienylene Vinylene)S, Yousef M. Katba Bader

Chemistry and Chemical Biology ETDs

Poly(thienylene vinylene)s (PTVs) is special a class of conjugated polymers (CPs) that show remarkable optoelectronic properties and promising applications. The main reason that hinders their application, is the lack of synthetic methodologies for preparing new derivatives with various functionality. Developing new PTVs with improved structures based on structure-property relationships increases the potential of utilizing this type of polymers in advanced applications. Most available preparation methods lead to regio-random PTVs (ra-PTVs) structures due to the different placement of the sidechain in the polymer backbone, which results in reduced crystallinity. In this study, we developed a novel strategy that produces a series …

Understanding The Role Of Atom Trapping In The Evolution Of Hydrocarbon Transformation Catalyst Morphology, Griffin Canning

Chemistry and Chemical Biology ETDs

Converting alkanes to other, more chemically and economically valuable molecules requires catalysts that can survive elevated temperatures and highly reducing environments. These environments can cause many metal-nanoparticle based catalysts to sinter rapidly, causing a loss of activity. They must also tolerate the coke formation, as well, since coke can restrict access to active sites by gas phase molecules, thus lowering catalytic activity. While there are routes to improve both the sinter and coke resistance of catalysts, an alternative strategy is to develop a protocol for regenerating the activity of the catalyst in question when coke formation or sintering becomes problematic. …

Atom Trapping And Its Role On The Nucleation & Growth Of Platinum Nanoparticles, Deepak Kunwar

Chemistry and Chemical Biology ETDs

Diesel oxidation catalysts deactivate due to Pt sintering, a major problem in automotive industries. To make sure they operate effectively throughout the lifetime of the vehicle, automotive industries are putting an excessive amount of Pt. There is a need to develop a catalyst that serves long term performance with minimal use of Pt. Jones et al^.1 demonstrated that ceria traps Pt atoms. His work generated some logical and valid questions such as what is the mechanism for the formation of anomalously large Pt particles? What is the upper limit of Pt metal loading in the form of single atoms …

Radial Basis Densities And The Density Functional-Based Atom-In-Molecule: Designing Charge-Transfer Potentials, Godwin Amo-Kwao

Nanoscience and Microsystems ETDs

Classical potentials that are capable of describing charge transfer and charge polarization in complex systems are of central importance for classical atomistic simulation of biomolecules and materials. Current potentials—regardless of the system—do not generalize well, and, with the exception of highly-specialized empirical potentials tuned for specific systems, cannot describe chemical bond formation and breaking. The charge-transfer embedded atom method (CT-EAM), a formal, DFT-based extension to the original EAM for metals, has been developed to address these issues by modeling charge distortion and charge transfer in interacting systems using pseudoatom building blocks instead of the electron densities of isolated atoms. CT-EAM …

Small Molecule Analog Studies Of Paramagnetic Dmso Reductase Enzyme Family Intermediates, Khadanand Kc

Chemistry and Chemical Biology ETDs

Pyranopterin molybdenum and tungsten enzymes are expressed in numerous organisms from all domains of life. These enzymes catalyze a variety of atom, hydride, and electron transfer reactions. The enzymes are of great importance in the biogeochemical cycles of nitrogen, carbon, and sulfur. In recent years, chemists have investigated applications for some of these enzymes as industrial biocatalysts. The dimethylsulfoxide reductase (DMSOr) enzyme family is the broadest family of pyranopterin Mo enzymes. The first coordination sphere of the Mo or W-containing active site for each member of this family is made up of 4 sulfur donors from the two pyranopterin dithiolenes …

Charge Transfer And Plasmon-Pumped Molecular Excitation Mechanisms In Surface Enhanced Photochemistry, Tefera Entele Tesema

Chemistry and Chemical Biology ETDs

Photochemistry that can be driven at low incident photon flux on optically excited plasmonic nanoparticles is attracting increasing research interest because plasmon-driven reactions offer new pathways for efficient conversion of the abundant solar energy into fuel. The confinement of the electromagnetic field by plasmonic metal nanoparticle and consequent field enhancement gives a dual advantage of ultrasensitive in situ and operando spectroscopic methods to monitor enhanced field-driven photochemical transformation. Charge carrier driven either via direct or indirect excitation mechanism are well-established pathways in plasmon-driven reactions to date. However, the excitation mechanism via plasmon-pumped electron transition from an occupied molecular orbital (HOMO) …

Design And Applications Of Charge-Separated Metal-Organic Frameworks, Sheela Thapa

Chemistry and Chemical Biology ETDs

Ionic tetrapodal ligands with colinear coordinating arms are very effective for designing hybrid porous materials with unusual structure and properties. The novelty of this research work lies in the utilization of a unique borate ligand that leads to charge-separated MOF structure with tailor designed properties. Borate ligands being tetrahedral afford 3D materials and the negative charge of borate anion can compensate the positive charge of metal ion in the framework. The borate ligands designed in this research consists of quaternary ammonium cation and anionic borate with four pyridine arms. These ligands upon coordination with Cu(I), Cu(II), Ag(I) and Co(II) metal …

Self-Assembly, Integration, Characterizations And Applications Of Plasmonic And Excitonic Nanomaterials, Bijesh Kafle

Chemistry and Chemical Biology ETDs

Plasmon on metal nanoparticles can efficiently confine, amplify light at the nanoscale. This property is beneficial for different applications such as harvesting energy of the broad solar spectrum, highly sensitive spectroscopy, photocatalysis, and many other optoelectronic applications. For plasmonic applications, it is necessary to understand the fundamental physical properties of the individual, coupled plasmonic nanomaterials, and their interaction with the surrounding environment, which is not fully understood yet. In this dissertation, the chemical and optical interaction in plasmonic interfaces has been investigated. Plasmon-enhanced photochemistry of p-aminothiophenol as a model molecule is investigated using highly sensitive surface-enhanced Raman spectroscopy (SERS). The …

Development Of Ni-Catalyzed Alkene Dicarbofunctionalization Reactions, Shekhar Kc

Chemistry and Chemical Biology ETDs

Alkenes serve as one of the most important feedstocks for organic synthesis, having two vicinal sites for bond formation. In alkenes, both vicinal sites can be functionalized with two reagents in a process commonly known as alkene difunctionalization, which results in the formation of two new bonds. A number of alkenes difunctionalization reactions, such as diamination, dioxygenation, carboamination and carbooxygenation, are known. However, difunctionalization of alkenes with two carbon-based entities, termed alkene dicarbofunctionalization, is relatively less common. Development of such a process could provide a powerful method to introduce two different carbon fragments across an alkene in a regioselective manner, …

Triplet Population Dynamics And Excited State Relaxation In Chalcogenophene Polymers, Benjamin D. Datko

Chemistry and Chemical Biology ETDs

The conventional understanding of intersystem crossing in multichromophoric conju- gated polymers is usually depicted via a pure electronic model, neglecting contributions of vibrations or conformational order. Obtaining accurate structure-function correlations on spin-conversion processes involving photogenerated singlet excitons to triplet excitons and the excited state dynamics requires sensitivity to the subtle conformational ordering within conjugated polymers. This dissertation seeks to understand the kinetics of multi-exciton singlet-triplet interactions and the excited state relaxation of chalcogen containing (S, Se) conjugated polymers. Utilizing single molecule modulation spectroscopy allows determi- nation of triplet formation of individual conjugated polymer chains and aggregates. This technique resolves triplet-induced …

Nanostructuring Organic/Inorganic Multicomponent Composites For Solution Processable Solar Cells, Brad Watson

Chemistry and Chemical Biology ETDs

The current state of organic photovoltaics is centered on systems of polymeric donors and some type of acceptor molecule (i.e. fullerene) formed into an active layer that adopts a bulk-heterojunction morphology. Although these devices have come a far way from where they were when they were first discovered in the 1980’s much work is still needed to make them a viable technology. Two of the limitations of this type of devices revolve around the relatively narrow absorption window of the components and lack of control over the morphology after the film is cast. To overcome these shortcomings there are several …