PhD, University of Cincinnati, 2012, Arts and Sciences: Physics

In this thesis, linear and non-linear optical properties of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and of tris(8-hydroxyquinolinato)aluminum (Alq3)films have been investigated using various experimental methods. The films were grown using the technique of organic molecular beam deposition (OMBD). The dispersion of the in-plane and normal refractive index in PTCDA waveguides has been studied using the m-line technique. The PTCDA waveguides were grown on Pyrex substrates. TE and TM mode coupling at excitation wavelengths ranging from 633 to 910 nm has been accomplished using a Rutile prism. The derived refractive index values are in good agreement with existing ellipsometric data, which emphasizes the high structural quality of our waveguides. The nonlinear absorption (two-photon absorption) of PTCDA and Alq3 films has been investigated using the z-scan technique. The films were grown on Pyrex substrates and a high repetition rate (80 MHz) laser was used as excitation source. Various methods have been utilized to minimize laser induced damaging of the soft organic films and to improve the signal-to-noise ratio. In addition, nonlinear fluorescence (two-photon induced fluorescence) measurements have been performed on Alq3 films to further investigate nonlinear absorption processes in this material. The singlet-singlet annihilation (nonlinear bimolecular quenching) of excitons in disordered quasi-amorphous Alq3 films has been investigated using both time-resolved and continuous wave (cw) spectroscopic techniques at temperatures ranging from 15 K to 300 K. A significant decrease of the PL efficiency with increasing exciton density (excitation intensity), especially at low temperatures, has been observed which is attributed to bimolecular quenching of excitons that are funneled into low-energy traps. This effect is different from the known diffusion based singlet-singlet annihilation in Alq3. To explain both the intensity and temperature dependence (open full item for complete abstract)

Committee: Hans Peter Wagner PhD (Committee Chair); Young Kim PhD (Committee Member); Leigh Smith PhD (Committee Member); L.C.R. Wijewardhana PhD (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2007, Food Science and Nutrition

Riboflavin is a photosensitizer to produce singlet oxygen. The compound formed from riboflavin under light was positively identified as 2,3-butanedione by a combination of gas chromatographic retention time, mass spectrum and odor evaluation of authentic 2,3-butanedione. The addition of sodium azide, a singlet oxygen quencher, minimized the formation of 2,3-butanedione from riboflavin. The 2,3-butanedione was formed from the reaction between riboflavin and singlet oxygen. The effects of 0, 100, 200, 300, 500, and 1000 ppm of alpha-, beta-, gamma-, and delta-tocotrienol on the oxidation of lard in the dark at 55°C for 7 days were determined by measuring headspace oxygen and peroxide value. The 100 ppm alpha- or beta-tocotrienol was the most effective antioxidant. Gamma- or delta-tocotrienol at all concentrations significantly lowered the oxidation of lard. The antioxidative activities were in delta- > gamma- > beta- > alpha-tocotrienol. The selection of type and optimum concentration of tocotrienol can minimize the oxidation of lipids and be economically important. Samples of 0.1, 0.25, or 0.4 M lard in methylene chloride containing 4.4 × 10 -6M chlorophyll b and 0, 0.3, 0.6, or 0.9 mM alpha-, beta-, gamma-, or delta-tocotrienol were prepared and stored at 3,000 lux for 4 hours to study the quenching mechanisms of tocotrienols on the chlorophyll photosensitized oxidation of lard. The steady state kinetic study showed that tocotrienols acted as singlet oxygen quenchers. The reaction rate of singlet oxygen with lard was 6.5 × 10 4M -1sec -1. The singlet oxygen quenching rates of alpha-, beta-, gamma-, and delta-tocotrienol were 2.16 × 10 7, 1.99 × 10 7, 2.05 × 10 7, and 0.80 × 10 7M -1sec -1, respectively. Alpha-tocopherol in foods is oxidized during the processing and storage. The effects of 0, 250, 500, 1000 and 1500 ppm of oxidized alpha-tocopherol on the oxidation of purified soybean oil in the dark at 55°C for 6 days were studied. The oxidized alpha-tocopherol act (open full item for complete abstract)

Committee: David Min (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2002, Food Science and Nutrition

Photooxidation and photosensitized oxidation on the formation of volatile compounds in linoleic acid, milk, and lard were studied by a combination of solid-phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS) and headspace oxygen content. Photooxidation is the oxidation under light in the absence of photosensitizers such as chlorophyll and riboflavin. Photosensitized oxidation is the oxidation under light in the presence of photosensitizers. Total volatile compounds in linoleic acid without added chlorophyll under light and in the dark did not increase for 48 hr at 4 °C. Total volatile compounds in linoleic acid with added 5 ppm chlorophyll under light at 4 °C for 0, 6, 12, 24, and 48 hr, increased from 8.9 to 11.6, 21.7, 26.1, 29.3 (*10000) in electronic counts, respectively. 2-Pentylfuran, an undesirable reversion flavor compound in soybean oil, 2-octene-1-ol, 2-heptenal, and 1-octene-3-ol were formed by photosensitized oxidation only. Light excited photosensitizers like chlorophyll can generate singlet oxygen from ordinary triplet oxygen. 2-Pentylfuran, 2-heptenal, and 1-octene-3-ol can come from C10, C12, and C10 hydroperoxide of linoleic acid, respectively, which can be formed by singlet oxygen oxidation but not by triplet oxygen oxidation on linoleic acid. The singlet oxygen oxidation mechanisms for 2-pentylfuran, 2-heptenal, 1-octene-3-ol, and 2-octene-1-ol from linoleic acid were proposed. Milk with or without added riboflavin, ascorbic acid, sodium azide, and butylated hydroxyanisol (BHA) was stored at 4 °C under light and in the dark. Pentanal, dimethyl disulfides, hexanal, and heptanal were formed only in the light stored milk and increased significantly as the added riboflavin concentration increased from 5 to 10, 50 ppm (P<0.05). As fat content in milk increased from 0.5 to 1.0, 2.0, and 3.4%, pentanal, hexanal, and heptanal increased significantly (P<0.05) but dimethyl disulfide concentration did not change. BHA and ascorbic acid (open full item for complete abstract)

Committee: David Min (Advisor); Howard Zhang (Other); Polly Courtney (Other); Hua Wang (Other) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2022, Chemistry and Biochemistry (Arts and Sciences)

Carbon monoxide (CO) is a toxic gas that has been known as the “silent killer” for decades. At high concentrations, CO reacts with hemoglobin, impairing its ability to transfer oxygen throughout the body. At low concentrations, however, CO has anti-cancer and anti-inflammatory effects. CO has also been shown to increase the sensitivity of certain types of cancer cells to the reactive oxygen species (ROS) produced by chemotherapeutics, thereby reducing drug resistance. One way to deliver CO in a controlled and safe manner is through the use of photoCORMs, or photoactivated CO releasing molecules. Transition metal-based photoCORMs are a class of molecules that release CO by breaking the M-CO bond upon exposure to light. In Chapters 2 and 3, my research study the effect of ligand set variation (both electronically and sterically) around the Mn(I) metal center on the photophysical and photochemical properties, as well as the assignment of photochemical intermediate formation during visible light irradiation. In Chapter 4, we designed a system that combined photo-activated CO delivery and singlet oxygen (1O2). The photophysical and photochemical properties of two Mn(I)-based photoCORMs sensitized with a luminescent BODIPY, as well as their ability to generate singlet oxygen during visible light irradiation were investigated.iv In Chapter 5, my focus was on water-soluble 3D supramolecular coordination cages (SCCs). The internal cavity incorporated in these structures allows them to encapsulate various guest molecules. Water-soluble Ln(III)-based SCCs are scarce, and the arrangement of water molecules inside the cavity, as well as the recognition properties of the latter, are mostly unknown. The study of such interactions would be of interest to the growing field of SCCs. To this end, we designed and synthesized a water-soluble Eu(III)-based supramolecular coordination cage with the general formula of Eu2L3 and a triplestranded helicate structure. T (open full item for complete abstract)

Committee: Eric Masson (Advisor) Subjects: Chemistry

Doctor of Philosophy (PhD), Ohio University, 2022, Chemistry and Biochemistry (Arts and Sciences)

The goal of this research was to design and study new systems of light activated molecules to deliver therapeutic agents. The impact of structural variation on spectroscopic properties as well as changes in photoinduced release of therapeutic molecules is reported herein. Chapter 2 reports complexes with the general structure [(bpy)2Ru(BL)Mn(CO)3Br](PF6)2 where the BL = 2,3-bis(2-pyridyl)pyrazine (dpp) and 2,2ʹ-bipyrimidine (bpm) and bpy = 2,2ʹ-bipyridine. Each of the bidentate bridging ligands exhibit different degrees of π-accepting ability when bridging two metal cations. The impact of the choice of bridging ligand on the photoactivated release of both CO and singlet oxygen (1O2) is reported. This report is the first example of a Ru(II),Mn(I) bimetallic complex with photoactivity in the phototherapy window (600 – 900 nm). The complexes were found to be stable in the dark and only released CO and singlet oxygen upon exposure to visible light. Chapter 3 extends the types of photoactivity of the complexes to include photoactivated DNA intercalation, along with CO release and 1O2 production. The framework used in this study was [(bpy)2Ru(tpphz)Mn(CO)3Br](PF6)2 where bpy = 2,2ʹ-bipyridine and tpphz = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′j]phenazine. The previously studied [Ru(bpy)2(tpphz)](PF6)2 complex has the ability to intercalate between the base pairs of DNA, which can inhibit cell proliferation, as well as a high production efficiency of singlet oxygen when exposed to light. This study used the framework studied in chapter 2 and incorporated the tpphz as a bridging ligand component. The purpose of this study was to test if the addition of the Mn moiety would continue to allow interaction of the tpphz to DNA or inhibit it. The study found that the complex is stable in the dark and inhibits DNA intercalation in the dark. When exposed to visible light, the Mn component dissociates from the complex, freeing the tpphz to then intercalate into DNA. To the (open full item for complete abstract)

Committee: Jessica White (Committee Member); Eric Masson (Advisor) Subjects: Chemistry; Inorganic Chemistry

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Nanoparticles are defined as particulate materials with sizes ranging between 1-1000 nm. Because of the development of nanotechnology-based science, many significant milestones have been achieved for sensors and therapeutics in recent years. When it comes to sensors, not only has nanotechnology enhanced the selectivity and sensitivity in the detection of various analytes, but it has also enabled the development of simpler, faster, and portable devices. The development of nanoparticles for therapeutics is not far behind. Nanomaterial-based therapeutics have enhanced drug targeting, delivery, and specificity, which has led to significant improvements in the efficacy of treatments while keeping toxicity at low levels. Despite all the significant achievements obtained already by the incorporation of nanotechnology into sensors and therapeutics, these fields could benefit further from employing the next generation of nanoparticles. The focus of the research described here was on the synthesis, characterization, and better understanding of new nanoparticle-based sensors and therapeutics. More specifically, in Chapter 2, the use of a paramagnetic nanoparticle to detect oligonucleotides through nuclear relaxation was explored. The proof-of-concept presented in Chapter 2 widened the application of nuclear relaxation to different biotargets, such as enzymes and cells. Moreover, due to its simplicity, sensitivity, robustness, and portability, if further developed, the sensing scheme described in Chapter 2 has the potential to improve point-of-care diagnostics. Chapter 3 comprises the design, synthesis, and characterization of a singlet oxygen sensor based on the Singlet Oxygen Sensor Green (SOSG) working principle. In the presence of the target molecule, the fluorescence properties of the designed probe were changed, indicating its sensing capability. Despite the preliminary nature of the results presented in Chapter 3, they already provide a better un (open full item for complete abstract)

Committee: David Smithrud Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member); Michael Baldwin Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2019, Physics

This thesis is mainly focused on three topics: Majorana excitations in a number-conserving model, manipulation of quasi-particle excitations in quantum Hall systems, and a new machine learning algorithm to find the ground states of a general Hamiltonian. In condensed matter physics, Majorana fermions are emergent excitations which are candidates for quantum memory and topological quantum computation. The first and simplest model revealing these excitations does not conserve particle number. Its experimental realization in solid state materials is difficult and still under debate. In comparison, cold atoms provide an alternative platform to realize these exotic excitations. However, cold atoms experiments require the system to be number-conserving. Theoretically, it is not yet clear whether there is a model realizable in cold atoms that also hosts these exotic excitations. In this thesis, we investigate such a number-conserving model and show that it has the same phase diagram and very similar excitations. Although the ground state degeneracy, as one of the signature properties of the original Majorana model crucial for quantum memory, is not present when the total particle number is fixed, one can recover the degeneracy by allowing tunnelling to change the total particle number. As for the quantum Hall system, we discuss how to control quasi-hole excitations with sharp external potentials where the system has integer filling factor. The eigen wavefunctions of the quasiholes are discussed in details. Our motivation is that most discussions or experiments regarding quantum Hall systems mainly focus on transport properties, but topological quantum computation may require one to have more precise control over the quasiparticle excitations. Although the ultimate goal is to control the non-Abelian excitations predicted in fractional quantum Hall systems, our results, especially in the situation with contact interactions, pave a way to explore this problem analytical (open full item for complete abstract)

Committee: Tin-Lun Ho (Advisor); Nandini Trivedi (Committee Member); Rolando Valdes Aguilar (Committee Member); Eric Braaten (Committee Member) Subjects: Physics

PhD, University of Cincinnati, 2018, Arts and Sciences: Physics

Organic materials have proved very useful for many devices, ranging from organic light emitting diodes (OLED) to waveguiding structures. One such organic material is tris(8-hydroxyquinoline)aluminum (Alq3), whose high emission efficiency and electron mobility make it ideal for efficient high-quality OLED displays. However, a complete picture of the exciton dynamics responsible for Alq3 fluorescence is still up for debate. With a better understanding of these dynamics we will have the potential to make OLEDs even more efficient than those capable today. For this reason, the singlet exciton lifetime of Alq3 films is investigated using time-integrated (TI-) and time-resolved photoluminescence (TR-PL) measurements for temperatures between 20 and 300 K. By adjusting the laser excitation pulse repetition and energy fluence, the dynamics of bimolecular quenching processes between singlets and triplets can be observed. Furthermore, the quasi-amorphous structure of Alq3 creates local traps, which not only account for an increase in singlet and triplet annihilation rates, but also explains the decrease in PL efficiency above 180 K, where singlets can be thermally freed from their traps and recaptured by non-radiative centers. In addition to their emission properties, organic materials make ideal waveguides insofar that they can be better integrated into opto-electronic computing devices because of their ability to be deposited on various substrates without the need of lattice matching, unlike traditional crystalline semiconductors. As will be shown, the inclusion of magnetic layers within an organic waveguide allows the structure to act as an optical mode switch. In order to create such a device with efficient mode conversion, there must be perfect index matching (PIM) between transverse electric (TE) and transverse magnetic (TM) waveguide polarizations. Thus, several Alq3 – perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) multilayer waveguides are fabricated an (open full item for complete abstract)

Committee: Hans Peter Wagner Ph.D. (Committee Chair); Philip Argyres Ph.D. (Committee Member); Carlos Bolech Ph.D. (Committee Member); Leigh Smith Ph.D. (Committee Member) Subjects: Condensation

Doctor of Philosophy, The Ohio State University, 2017, Chemistry

In this work, we outline the development, testing, and application of a novel electronic structure method for computing the properties of excited states of molecular aggregates. The method is an ab-inito realization of the molecular exciton model, proposed a long time ago by Frenkel and Davydov to describe excited states of molecular crystals, and is called the Ab-Initio Frenkel Davydov Exciton Model (AIFDEM). The AIFDEM ansatz follows the traditional exciton model by expanding the supersystem excited state wavefunction as a linear combination of excitations that are localized on the component molecules. Our method is a truly ab-inito implementation of this model as the requisite fragment excited states and the exciton Hamiltonian matrix are computed rigorously, including exact Coulomb and Hartree-Fock exchange interactions, without any neglect of overlap, nearest neighbor, or other common approximations. We have tested this method and found that it can reproduce excitation energies of water clusters, DNA bases, and organic chromophores within ~0.1 eV. A charge embedding scheme is able to reduce the scaling of this method to only quadratic with the number of fragments and provides near perfect parallel performance without reducing the accuracy, significantly outperforming traditional approaches. The method was utilized to investigate the excitation energy transfer dynamics of a napthalene-diimide nanotube where it was found that model systems beyond the scope of traditional methods are necessary for a fully detailed mechanistic picture, including the role of quantum coherence. Analytic derivatives of the AIFDEM Hamiltonian are derived and implemented and these provide access to non-adiabatic couplings as well as Holstein and Peierls electron-phonon coupling constants. This is applied to the challenging electronic structure of the singlet exciton fission process to identify vibrational modes key to the mechanism. Dynamics simulations, using parameters computed via th (open full item for complete abstract)

Committee: Sherwin Singer (Advisor); Heather Allen (Committee Member); Terry Gustafson (Committee Member) Subjects: Physical Chemistry

Doctor of Philosophy, Case Western Reserve University, 2017, Chemistry

Sulfur-substituted purine and pyrimidine nucleobases—also known as thiobases—are among the world's leading prescriptions for chemotherapy and immunosuppression. Long-term treatment with some of the purine derivatives of these drugs has recently been correlated with the photo-induced formation of carcinomas. Establishing an in-depth understanding of the photochemical properties of these thiobase drugs may provide a route to overcoming these carcinogenic side effects, or, alternatively, may provide a basis for developing highly-effective compounds for targeted photochemotherapy. In this thesis work, a broad investigation is undertaken, surveying the excited-state dynamics and photochemical reactions of nearly every sulfur-substituted analog of the canonical DNA and RNA nucleobases. The thiobase derivatives are investigated using time-resolved absorption and emission spectroscopies in the femtosecond (10-15 s) to microsecond (10-6 s) time window. Coupling these experiments with quantum chemical calculations, we have developed a molecular-level understanding of how sulfur-substitution so drastically perturbs the photochemical properties of the nucleobases. The structure-property relationships established by this work demonstrate the impact of site-specific sulfur substitution on the population and reaction dynamics of the excited triplet state. Some of the most photoreactive derivatives identified are applied to human epidermoid carcinoma cells and shown to effectively decrease their proliferation upon exposure to a low dose of light. The results presented in this body of work demonstrate the utility of fundamental photochemical investigations for driving the development of next-generation photochemotherapeutics, while simultaneously elucidating overarching principles for the impact of sulfur substitution (thionation) on the photochemical properties of organic chromophores.

Committee: Carlos Crespo-Hernández (Advisor); Mary Barkley (Committee Chair); Clemens Burda (Committee Member); Geneviève Sauvé (Committee Member); Nancy Oleinick (Committee Member) Subjects: Analytical Chemistry; Biochemistry; Chemistry; Experiments; Molecules; Pharmaceuticals; Physical Chemistry; Quantum Physics

PhD, University of Cincinnati, 2016, Arts and Sciences: Chemistry

The objective of my research is to develop multifunctional nanoparticles for sensing and photodynamic therapy applications. Ethylenediaminetriacetic acid (EDTA)-functionalized silica nanoparticles were synthesized by microemulsion method. The EDTA groups on the nanoparticle surface have the role to chelate with metal ions to form paramagnetic nanoparticles in aqueous solution, which would reduce the relaxation rate of water protons. In this study, SiO2@TMS-EDTA@Fe3+ NPs and SiO2@TMS-EDTA@Gd3 NPs were used for detection of dopamine and phosphate ion, respectively. The results demonstrate that paramagnetic nanoparticles can be integrated into relaxation based detection schemes while avoiding the aggregation problem commonly associated with more widely used superparamagnetic nanoparticles. Lanthanide-based NaYF4:Yb3+,Tm3+ upconversion nanoparticles were synthesized in the presence of polyacrylicacid (PAA) via solvothermal method. This is an one step synthesis method to get uniform, reproducible and biocompatible NaYF4:Yb,Tm upconversion nanoparticles with –COOH surface functional groups. In this study, we designed a ligase-assisted signal-amplifiable DNA biosensor based on NaYF4:Yb3+,Tm3+ UCNPs with high sensitivity and specificity. Silver nanoparticles captured by mesoporous silica nanoparticles with photosensitizer (Ag@MS@HPIX) were synthesized using silver nitrate as the silver source, formaldehyde as the reducing agent, CTAB as the template/stabilizer, TEOS/TMS-EDTA as the silane source, sodium hydroxide as the catalyst, and HPIX as the loading photosensitizer. Ag@MS@HPIX NPs show strong enhanced singlet oxygen generation because of the strong resonance coupling between surface plasmon Ag nanoparticles and the photosensitizing molecules, consequently demonstrating highly efficient photodynamic inactivation (PDI) efficacy against both gram-positive and gram-negative bacteria. In this study, PDI efficacy of Ag@MS@HPIX NPs was tested against a multidrug- (open full item for complete abstract)

Committee: Peng Zhang Ph.D. (Committee Chair); William Heineman Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member); Thomas Ridgway Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2016, Arts and Sciences: Chemistry

In this dissertation, we explored the syntheses and characterizations of silver nanoparticles and its application in fluorescence, Raman and singlet oxygen generation. In the first project, we report the observation of significantly enhanced fluorescence from molecules placed inside a silver nanocavity, as compared to those without the silver coating. Meso-tetra(4-carboxyphenyl) porphine (TCPP) is used as the fluorophore molecule. The fluorophores werefirst embedded in the porous TiO2 colloid nanoparticles. Then additional TiO2 was used as a spacer layer, onto which a controlled amount of silver is deposited. The final nanostructure consisted of a TiO2–TCPP core, a pure TiO2 layer and a silver nanoshell. In essence, the fluorophores (TCPP molecules) were placed inside a metallic nanocavity. The result shows the observation of >50-fold fluorescence enhancement for fluorophores trapped inside a silver nanocavity. In the second project, we report a quantitative SERS measurement scheme based on the magnetic microspheres and AgNPs to detect target DNA. This detection displays both high sensitivity (down to 10 nM) and high specificity (differentiating single-base mismatched targets). The use of magnetic microspheres facilitates rapid, efficient and reproducible sample preparation. The results demonstrate great potential of using SERS for quantitative DNA detection. In the third project, we report the synthesis of the general platform for singlet oxygen production which significantly increased the singlet oxygen production of the photosensitizers, in some cases by up to 26 times. It is observed that the presence of silver core in Ag@SiO2@mSiO 2@HP core-shell structure would significantly increase the singlet oxygen generation, and the thickness of either solid SiO 2 shell or mesoporous SiO2 could affect the singlet oxygen generation as well.

Committee: Peng Zhang Ph.D. (Committee Chair); Hairong Guan Ph.D. (Committee Member); James Mack Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2016, Arts and Sciences: Chemistry

In this dissertation, we explored the syntheses and characterizations of water dispersible hybrid photosensitizers by combining metal nanoparticles and organic photosensitizers. In the first project, we reported a novel metal enhanced singlet oxygen production and fluorescence quenching phenomenon based on the conjugates between gold nanoparticles and rose bengal. When rose bengal covalently conjugated to the surface of average ~ 50 nm gold nanoparticles, the fluorescence was dramatically quenched; however, singlet oxygen production was implied to be enhanced by measuring its phosphorescence at ~ 1280 nm. Singlet oxygen quantum yield of the novel hybrid photosensitizer was calculated as to be 0.75 by using rose bengal as reference photosensitizer. In the second project, we discussed the employing of carboxylic modified silver nanoparticles, 6-mercaptohexanoic acid stabilized silver nanoparticles, to conjugate with toluidine blue O to form a novel hybrid photosensitizer. The silver nanoparticles were prepared by a modified Brust's method with an average size ~ 5 nm. The covalent conjugation between silver and toluidine blue O quenched the fluorescence and enhanced the singlet oxygen production according to the spectroscopic results. The presence of singlet oxygen and the enhancement of singlet oxygen production were demonstrated by the photodecomposition of 1,3-diphenylisobenzofuran. Singlet oxygen quantum yield of the hybrid photosensitizer was calculated as 0.78. In the third project, thiol-modified amphiphilic block copolymer, poly(N-isopropylacrylamide-block-styrene), was synthesized and characterized. Then, a novel hybrid photosensitizer based on poly(N-isopropylacrylamide-block-styrene) stabilized silver nanoparticles and entrapped hydrophobic photosensitizer (hematoporphyrin) was prepared. The water dispersible hybrid photosensitizer demonstrated enhanced singlet oxygen production with broadened excitation profile by monitoring phosphorescence at ~12 (open full item for complete abstract)

Committee: Peng Zhang Ph.D. (Committee Chair); Hairong Guan Ph.D. (Committee Member); William Heineman Ph.D. (Committee Member) Subjects: Chemistry

MS, University of Cincinnati, 2012, Arts and Sciences: Chemistry

In recent years scientists are more interested in studying reactive intermediates like triplet carbenes and triplet nitrenes. Those molecules have unpaired electrons and have high spin properties. By considering the magnetic properties of these organic molecules scientists attempt to build organic magnets. Even though they have extensively studied reactive intermediates like carbenes, less attention has been paid to investigations of nitrenes, specially the vinylnitrenes. Several research groups have proposed triplet vinylnitrene formation from different precursors. Isoxazoles, azirine derivatives and vinyl azides are the some of these precursors to triplet vinylnitrenes. In this work, I studied the photoreactivity of 3,5-diphenylisoxazole (1) and 3-benzoyl-2-phenylazirine (2) as precursors to triplet vinylnitrene. Irradiation of both compounds in acetonitrile solution with 308 nm laser lead to give triplet vinylnitrene (4) with lifetime of 1.7-1.8 µs. Triplet vinylnitrene (4) shows an abroad absorption with λmax at ∼ 350 nm and 415 nm which trails further out towards 500 nm. Furthermore 2 forms ylide (5) which absorbs with λmax 460 nm with life time of 13 µs. In oxygenated-saturated solution I observed an efficiently trapping of 4 with oxygen and formed a peroxide radical which intersystem cross to decay the singlet surface. Then this peroxide radical auto oxidizes to give benzoic acid and benzamamide as photoproducts. Calculations (B3LYP/6-31+G(d) illustrate that T1 of 1 is located 63 kcal/mol above the S0 of 1. Comparatively, T1 of 2 is located 65 kcal/mol above the S0 of 2. The calculated transition state energy barrier to form 4 from 1 is 12 kcal/mol above T1 of 1. Similarly the transition state energy barrier to yield 4 form 2 is only 2 kcal/mol above T1K of 2. Spin density calculations show that 4 has 1,3-carbon iminyl biradical character which explains the efficient reactivity of 4 with oxygen. In addition to the triplet reactivity, 2 shows singlet rea (open full item for complete abstract)

Committee: Anna Gudmundsdottir PhD (Committee Chair); Bruce Ault PhD (Committee Member); James Mack PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2011, Chemistry

Molecule based electronics and devices are an increasingly popular area of research in chemistry. These molecular-based devices largely rely on the separation of charge from (solar cell, LED) or movement of charge through (wires) a molecular unit. Largely, it is desirable for these materials to be easily fabricated, absorb throughout the visible/NIR spectrum or emit certain wavelengths. Organic systems generally provide good fabrication properties while the incorporation of metals can provide more easily tunable physical properties. Metallo-organic paddlewheel compounds involving quadruple bonds have previously been made into soluble, linear polymers with tunable absorption and have been incorporated into an LED to show electroluminescence. In terms of device performance, it is important to know how well charge can be expected to flow through the material. In devices that rely upon photon absorption, charge transport ability is dependent on charge delocalization and rates of transport. As a first step in these regards a series of complexes which represent simple monomeric analogs to the individual repeating units of the polymer have been studied. They serve as model complexes to the polymeric and a better understanding of their fundamental properties should relate to better design of polymeric materials. This dissertation uses both electronic and vibrational spectroscopies to characterize photoexcited states, determine their lifetimes, and evaluate the electronic delocalization within these states. Theoretical calculations also supported the results. Four molecules constitute limiting cases across a wide set of properties and are the focus of this work. Chapters 2 describes the molecules M2(O2CTiPB)2(O2C-C6H4-C≡N)2 (2a and 2b) and 3 describes the molecules M2(O2CCH3)2(NiPr)2C-C≡C-C6H5]2 (3a and 3b), where M = Mo (a) or W (b), each focusing on results from electronic spectroscopy. In particular, assignments for the photophysical excited states were made as well as s (open full item for complete abstract)

Committee: Malcolm Chiholm Prof. (Advisor); Terry Gustafson Prof. (Advisor); Claudia Turro Prof. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2010, Chemistry

Photodynamic therapy (PDT) is a cancer therapy that operates with greater selectivity than conventional chemotherapy by the combination of a photosensitizer and visible light irradiation. Localization of irradiation allows for specificity by selectively activating the photosensitizer in the tissue of interest, while leaving healthy cells undamaged. However, PDT drawbacks remain and in this document the photophysical properties and DNA interactions of dirhodium, ruthenium, and osmium complexes are investigated for their abilities to address some of the shortcomings of current cancer photochemotherapies. A series of dirhodium(II,II) complexes of the type cis-[Rh2(μ-O2CCH3)2(dppn)(L)]2+, where dppn = benzo[i]dipyrido-[3,2-a:2′,3′-h]quinoxaline and L = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-f:2′3′-h]quinoxaline (dpq), dipyrido[3,2-a:2′,3′-c]phenazine (dppz), and dppn, was synthesized and its photophysical properties investigated. The ability of the complexes to bind and photocleave DNA was also probed, along with their toxicity and photocytotoxicity toward human skin cells. Nanosecond time-resolved absorption measurements established that the lowest energy excited state in the series is dppn-localized 3ππ* in DMSO. All complexes except the bis-dppn complex photocleave DNA efficiently via a mechanism that is mostly mediated by reactive oxygen species. The DNA photocleavage by the bis-dppn complex is significantly lower than that measured for the others, however, it exhibits the largest increase between toxicity and photocytotoxicity within the series. A discussion of three new complexes [Ru(bpy)2(dpqp)]2+ (dpqp = pyrazino[2′,3′:5,6]pyrazino-[2,3-f][1,10]phenanthroline), [Ru(bpy)2(dppn)]2+, and [Os(bpy)2(dppn)]2+ is also presented. These complexes provide improvement to current PDT shortcomings by utilizing longer lifetimes, dual mechanisms of reactivity, and longer wavelengths of absorption, respectively. [Ru(bpy)2(dpqp)]2+ exhibits strong lu (open full item for complete abstract)

Committee: Claudia Turro PhD (Advisor); Terry Gustafson PhD (Committee Member); Yiying Wu PhD (Committee Member); Christopher Adin DVM (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2009, Ohio State Biochemistry Program

Photodynamic therapy (PDT) is a promising clinical modality for killing unwanted cells,especially cancer cells by the combined use of light, photosensitizers and molecular oxygen.In the process of PDT,energy flows from light-activated triplet state photosensitizers to the triplet ground state molecular oxygen by the type II pathway,converting it to singlet oxygen,which can damage cancer cells by directly reacting with nearby biomolecules,or indirectly by destroying tumor vasculature and invoking systemic immune responses.To improve the efficiency of PDT in clinical practice, we studied photodynamic damage to important nuclear proteins involved in DNA replication/repair, and identified the [Ru(tpy)(pydppn)]2+complex as a very promising photosensitizer.PCNA,p53,SV40 large T-antigen,topoisomerase I and lamin B were identified as cellular protein targets for photodynamic damage caused by proflavine and visible light. Following photodynamic damage, p53 was detected in a distinct covalent crosslinking profile, with p53 tetramers and dimers being the predominant forms; SV40 large T-antigen was mainly crosslinked into a hexamer while lamin B was crosslinked to dimers, trimers and tetramers. [Ru(tpy)n(pydppn)2-n]2+ (n = 0,1)complexes have been reported to be capable of photosensitizing the generation of singlet oxygen with near 100% efficiency in vitro.In our study,[Ru(tpy)(pydppn)]2+ caused efficient covalent oligomerization of cellular PCNA and p53 in light.In the cell lysates, both [Ru(tpy)(pydppn)]2+ and [Ru(pydppn)2]2+ were able to produce efficient PCNA and p53 photodynamic crosslinking.Cellular PCNA photocrosslinking caused by [Ru(tpy)(pydppn)]2+ increased linearly with [Ru(tpy)(pydppn)]2+ concentration,time of uptake, or visible light exposure.The inclusion of azide,a singlet oxygen quencher, led to significant suppression of p53 photocrosslinking,suggesting that singlet oxygen is the reactive agent causing p53 photocrosslinking.[Ru(tpy)(pydppn)]2+ caused efficient p (open full item for complete abstract)

Committee: Robert M. Snapka (Advisor); Marshall V. Williams (Committee Member); Donald H. Dean (Committee Member); Charles E. Bell (Committee Member) Subjects: Biochemistry

Doctor of Philosophy, The Ohio State University, 2009, Chemistry

In this work, a new series of thienyl carboxylate ligated quadruply bonded dimolybdenum and ditungsten compounds have been synthesized. The effect of systematically varying the ligands in terms of number of thienyl rings, rigidity of the thienyl backbone, nature of the carboxylate tethers, and changing the metal content in the dinuclear MM core (from MM = Mo2 to MoW to W2) have been studied. Charge delocalization in the ground state of these compounds have been examined by electrochemical methods. Cyclic voltammetry has revealed MM-δ based reversible oxidations and ligand-π* based quasi-reversible reductions. Further, the electronic communication in the oxidized species has been examined by electron paramagnetic spectroscopy. The UV-Vis absorption spectra and photoluminescence spectra of the compounds show remarkable influence of the overlap between MM-δ orbitals and thienyl based π* orbitals. Intense and broad range metal-to-ligand charge transfer is observed, which is dependent on the nature of ligand as well as on the metal content in the MM dinuclear core. Room temperature dual emission, fluorescence and phosphorescence, is observed for the dimolybdenum compounds. Other photophysical studies, including, nanosecond and femtosecond transient absorption spectroscopy, fluorescence upconversion and emission decay measurements reveal the presence of two excited states, a short lived (τ ~ several ps), and a longer lived (τ ~ several ns to µs) one, for all the compounds in the series. The shorter lived excited state was found to be 1MLCT, which decays by fluorescence and in addition goes on to populate a longer lived triplet excited state, which was found to be 3MMδδ* in the dimolybdenum compounds. In the thienyl carboxylated compounds, when the quadruply bonded dinuclear core has MM = MoW or W2, the triplet excited state was assigned to be a 3MLCT, which decays by non-radiative processes. Electronic structure calculations were carried out, using density functional (open full item for complete abstract)

Committee: Malcolm H. Chisholm PhD (Advisor); Claudia Turro PhD (Committee Member); Terry L. Gustafson PhD (Committee Member) Subjects: Chemistry

Master of Science, The Ohio State University, 2008, Aeronautical and Astronautical Engineering

The present work addresses performance optimization of a small-scale, electric discharge excited, gasdynamic oxygen iodine laser (DOIL). For this, (i) nitric oxide has been added to the laser mixture, and (ii) iodine vapor was dissociated in an auxiliary electric discharge prior to its injection into the laser flow. The addition of NO has a significant effect on the laser performance, increasing small signal gain in the supersonic laser cavity from 0.05 %/cm to 0.08 %/cm. On the other hand, although large iodine dissociation fractions in the laser cavity have been achieved using an auxiliary discharge (up to 50%), only modest increase in gain was detected. The DOIL laser apparatus has been scaled up, with the main electric discharge volume increased by a factor of four and the flow rate through the laser doubled. The scaled-up laser has been tested using a nanosecond pulser / DC sustainer discharge or a capacitively coupled radio frequency discharge (CCRF) sustained at powers up to 2.7 kW and 4.5 kW, respectively. In both these cases, single-delta oxygen yield of up to 3-4% has been measured. Small signal gain up to 0.116 %/cm has been measured in the laser cavity while using the CCRF discharge to generate singlet delta oxygen. Numerical modeling of magnetohydrodynamic deceleration of a low-temperature M=4 flow was conducted using a three-dimensional compressible Navier-Stokes flow code. The results are in good agreement with recent experiments conducted at Ohio State, where flow deceleration by up to 2% has been demonstrated.

Committee: Igor Adamovich (Advisor) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2007, Chemistry

The photochemistry and photophysics of a series of carbenes and nitrenes and their precursors have been investigated using state of the art ultrafast time-resolved spectroscopies and quantum mechanical calculations. Carbene-related photochemistry and photophysics was discussed in Chapters 2 to 9. 1,2-hydrogen shift in the excited states of diazo compounds was discussed in Chapter 2 and the first direct evidence for the Rearrangements in the Excited State (RIES) mechanism was provided. To pursue other RIES examples, we studied Wolff Rearrangement (WR) in the diazo excited states in Chapter 3, along with a detailed discussion of WR for keto and ester carbenes. In Chapter 4, an ultrafast interconversion for a pair of isomeric ketocarbenes was observed. In Chapter 5, we reinvestigated the photochemistry of 9 diazofluorene and directly observed the formation of an excited singlet carbene in solution for the first time. In Chapter 6, we reported the first carbene solvation dynamics and found that the solvation phenomena are more prominent in polar and hydrogen bonded solvents than in non-polar solvents. The Eisenthal group established a rule for intersystem crossing (ISC) rates of aryl carbenes in 1980s, stating carbene ISC rates correlate with solvent polarities. In Chapter 7, we described some remarkable exceptions to this rule and discussed the factors controlling carbene ISC rates. In Chapter 8, we investigated the photochemistry of arylhalodiazirines and concluded that zwitterions are intermediates in the photochemical formation of arylhalocarbenes. Some other ultrfast studies of diarylcarbenes were discussed in Chapter 9. In Chapters 10 to 12, photochemistry and photophysics of nitrenes and their precursors were studied. In Chapter 10, we reported the first spectroscopic observation of azide excited states and measured the lifetimes of some extremely reactive nitrenes, o-biphenylylnitrene, 1-naphthyl and 2-naphthylnitrenes at ambient temperature in solution. 2-napht (open full item for complete abstract)

Committee: Matthew Platz (Advisor) Subjects: