Master of Science, The Ohio State University, 2024, Chemistry

The increasing energy demand and effects of climate change have led to the need for more effective and reliable renewable energy sources. Solar energy has been a major focus for many scientists because of the large number of photons that reach the Earth. One of the current ways to harness the energy of sunlight is through the use of dye-sensitized solar cells (DSSCs); however, a major drawback is their reliance on second-row transition metals, such as rhodium and ruthenium, which are scarce and expensive. These heavy metal complexes often exhibit a metal-to-ligand charge transfer (MLCT) with excited states lifetimes in the hundreds of nanoseconds. Recently, similar complexes using first-row transition metals have been developed that also possess MLCT states. However, the latter complexes typically exhibit MLCT lifetimes that are too short to serve as effective photosensitizers for DSSCs. The present thesis focuses on the synthesis and characterization of the ground- and excited-state properties of a new heteroleptic Cu(I) complex. [Cu(dptpy)(pyphen)][PF6], where dptpy = 2,2':6',2''-terpyridin]-4'-yl)-N, N-diphenylaniline and pyphen = 2-(pyridin-2-yl)-1,10-phenanthroline. The dptpy ligand is easily oxidized, making it a strong electron donor, while the pyphen is expected to act as an electron acceptor. The photophysical and redox properties of [Cu(dptpy)(pyphen)][PF6] are complexed to the corresponding homoleptic complexes, [Cu(dptpy)2][PF6] and [Cu(pyphen)2][PF6] to aid in the assignments. [Cu(dptpy)(pyphen)][PF6] holds promise to provide the first example of a first-row transition metal complex with an LLCT excited state that could be used in DSSC.

Committee: Patrick Woodward (Committee Member); Claudia Turro (Advisor) Subjects: Chemistry

PhD, University of Cincinnati, 2021, Arts and Sciences: Chemistry

Mankind's sustainable development not only requires the capture and conversion of renewable energies but also necessitates the production of chemical goods from renewable carbon sources. Biomass is the only accessible and renewable carbon source. One major class of biomass is degradative small molecules, among which 5-hydroxymethylfurfural (HMF) is considered as a platform chemical and it can serve as a starting material to produce various upgrading compounds, e.g., the oxidation products, 2,5-furan dicarboxylic acid (FDCA), and 2,5-diformylfuran (DFF), can act as biopolymer precursors. In this dissertation, we successfully demonstrated that ultrathin Ni/CdS nanosheets can be efficient photocatalyst to produce value-added bioproducts (e.g., furoic acid, DFF, and FDCA) from biomass-derived molecules. Even more desirable is that the oxidative biomass upgrading can be integrated with H2 production. Besides biomass-derived small molecules, another major class of biomass is non- degradative polymers. One representative is lignin, which has attracted increasing attention as it can be transformed to small aromatics. However, its recalcitrant structure renders it challenging to be depolymerized. The primary hurdle of lignin valorization is the selective and effective cleavage of the linkages connecting aromatic units. Within this context, we have reported the photocatalytic oxidation and cleavage of lignin model compounds to yield three types of products with very high selectivity on ultrathin metal/CdS nanosheets. By judiciously modulating the solvent mixture and alkalinity, we demonstrated that it was possible to selectively achieve oxidized 2-phenoxy-1-phenylethanone or cleaved products, acetophenone, and phenol. Thanks to the advance in molecular photosensitizers and organometallic catalysts, light-driven C-C bond formation has attracted increasing attention. The traditional methodologies typically require the substrates with leaving groups. To improve the atom e (open full item for complete abstract)

Committee: Yujie Sun Ph.D. (Committee Chair); Hairong Guan (Committee Member); Michael Baldwin Ph.D. (Committee Member) Subjects: Chemistry

Master of Science (MS), Bowling Green State University, 2021, Biological Sciences

Using bacteria in cancer therapies is an emerging area of research. Certain bacteria can target tumors, and therapy can involve either the direct (colonize, invade, and deplete metabolic nutrients) or indirect action (deliver a therapeutic payload or "uncloak" the tumor to the immune system) of the bacteria. However, many of the best-suited bacterial species are pathogenic and require extensive genetic engineering to reduce or eliminate their pathogenicity before they can be used therapeutically. The facultative anoxygenic photoautotroph Rhodobacter sphaeroides is non-pathogenic, and has been shown to target tumors. We have been investigating its use as a vector for delivering 5-aminolevulinic acid (ALA) to tumors, where it functions as a prodrug in photodynamic therapies. ALA is a precursor in the formation of heme, and elevated concentrations delivered to tumor cells leads to overproduction of all products in the heme biosynthetic pathway, including precursor tetrapyrroles. In the presence of oxygen and therapeutic wavelengths of light, these molecules generate reactive oxygen species that destroy the tumor cells. R. sphaeroides naturally produces copious amounts of ALA for heme and bacteriochlorophyll synthesis needed to support photosynthetic growth. Prior studies have already shown that it is possible to engineer these bacteria to produce and excrete ALA in amounts that are suitable for photodynamic therapy (Zeilstra-Ryalls, 2013, unpublished results). A survey of wild type strains to identify which one grows best phototrophically under simulated intratumoral conditions was performed. By disrupting the genes in the optimal strain that code for ALA synthase enzymes a mutant was created that relies upon exogenous ALA for growth. Its minimal ALA requirement, as well as its ability to tolerate the presence of high concentrations of ALA under phototrophic conditions was then assessed. The latter was necessary in order to determine wheth (open full item for complete abstract)

Committee: Jill Zeilstra-Ryalls Ph.D (Advisor); Raymond Larsen Ph.D (Committee Member); Vipaporn Phuntumart Ph.D (Committee Member) Subjects: Biology; Biomedical Research; Microbiology; Molecular Biology; Oncology

Master of Science (M.S.), University of Dayton, 2019, Chemistry

The projects described in this thesis were focused on studying two aspects of singlet oxygen. The first is the ability of singlet oxygen to be generated by photosensitizers for use in photodynamic therapy and the second is the ability of singlet oxygen to be quenched with β-carotene. Photodynamic therapy (PDT) is a medical technique which utilizes a photosensitizing drug, light of a certain wavelength and molecular oxygen to generate singlet oxygen, a toxic oxidizing species. When present, singlet oxygen will rapidly react with surrounding biomolecules, causing cellular damage that ultimately leads to cell death. To the ends of creating a photosensitizer for PDT, a new pi-extended dipyrrin containing isoquinolpyrrole has been synthesized by solvent free reactions with trifluoroacetic acid (TFA) as a catalyst. The borondipyrrin (Bodipy) of the isoquinolpyrrole was synthesized by standard procedures followed by synthesis of the bis-ruthenium(II) Bodipy analog. The spectroscopic properties of this complex show the typical intra-ligand charge transfer transitions (ILCT) along with the Ru(π) to ligand(π*) metal to ligand charge transfer (MLCT) transitions. An intense transition at 608 nm with molar absorptivity greater than 100,000 M-1 cm-1 associated with the ππ* transition of the Bodipy core is observed. In acetonitrile solutions the bis-Ru(II)-Bodipy complex generates significant singlet oxygen when irradiated with low energy light. In aqueous solutions the complex is capable of photo-nicking plasmid DNA when irradiated within the photodynamic therapy (PDT) window of 600 to 850 nm. β-carotene (βC) is an orange pigment present in the photosynthetic reaction center (PRC) of green plants, where it plays a vital role in photosynthesis: It quenches singlet oxygen before it damages chlorophyll and other components of the PRCs. During photosynthesis, βC temporarily converts from its native orange–450 state to a pink–515 state via the so–called 515nm Effect. Because of (open full item for complete abstract)

Committee: Shawn Swavey PhD (Committee Co-Chair); Mark Masthay PhD (Committee Co-Chair); Jeremy Erb PhD (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Physical Chemistry

Master of Science (M.S.), University of Dayton, 2017, Chemistry

Two new bridging ligands have been synthesized by combining substituted benzaldehydes with phenanthrolinopyrrole (php), resulting in new polyazine bridging ligands. The ligands have been characterized by 1H NMR, mass spectroscopy, and elemental analysis. These new ligands display ϖ-ϖ* transitions above 500 nm with modest molar absorptivities. Upon excitation at the ligand-centered charge-transfer transition, weak emission with a maximum wavelength of 612 nm is observed. When coordinated to two ruthenium (II) bis-(2,2'-bipyridine) groups, the new bimetallic complexes generated give an overall 4+ charge. The electronic transitions of the bimetallic ruthenium (II) complexes display traditional ϖ-ϖ* transitions at 287 nm and metal-to-ligand charge-transfer transitions at 452 nm with molar absorptivities greater than 30000 M-1 cm-1. Oxidation of the ruthenium (II) metal centers to ruthenium (III) occurs at potentials above 1.4 V versus the Ag/AgCl reference electrode. Spectroscopic and electrochemical measurements indicate that the ruthenium (II) moieties behave independently. Both complexes are water-soluble and show the ability to photo-nick plasmid DNA when irradiated with low-energy light above 550 nm. In addition, one of the complexes, [Ru(bpy)2php]2Van4+, shows the ability to linearize plasmid DNA and gives evidence, by gel electrophoresis, of photoinduced binding to plasmid DNA. Coordination of two Osmium(II) bis-(bipyridine) complexes to the peripheral phenanthroline of (4-hydroxy-3- methoxyphenyl)diphenanthropyrromethane ligand yields the bimetallic Os(II) complex. The spectroscopic properties are similar to those of [Os(bpy)3]2+ with ligand-centered ϖ-ϖ* transitions in the UV region of the spectrum and three metal-to-ligand charge-transfer (1MLCT) transitions in the visible region. A broad 3MLCT is observed stretching from 550 to 700 nm with modest intensity. Binding studies with calf thymus DNA (ctDNA) show binding constants as high as 105 M–1 indicati (open full item for complete abstract)

Committee: Shawn Swavey (Committee Chair); Kevin Church (Committee Member); Mark Masthay (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

In this dissertation, I first developed and optimize an upconversion nanoparticles-based DNA detection scheme on different target DNA sequences, and then I explored the syntheses and characterizations of a nanomaterial-photosensitizer platform used for photodynamic therapy of cancer cells and bacteria in vitro. In the first project, a novel ligase-assisted signal-amplifiable DNA detection scheme is demonstrated based on luminescent resonance energy transfer between upconversion nanoparticles and the intercalating dye, SYBR Green I. Target DNA serves as a template for two DNA probes, one of them covalently attached to upconversion nanoparticles, to be joined into a long, hairpin-forming DNA by ligase. The number of the resulting DNA strand, which brings SYBR Green I close to the upconversion nanoparticles, is amplified through thermal cycling. The method was proven to display high sensitivity and specificity for DNA detection. Factors affecting the detection specificity and sensitivity, including ligation temperature, the amount of ligase, and the number of thermal cycles, have been investigated to optimize the performance of the detection method. Based on our result, the detection scheme can easily differentiate the BRAF V600E mutation from the wild-type sequence with a mutant-to-wild-type ratio of 1:1000. A detection limit of 1 fmole BRAF V600E mutation is achieved. While for the target sequence of EGFR T790M, the differentiate ratio is 1:100. The results show that 0.01 pmole of EGFR T790M mutant can be readily detected. In the second project, I report a hybrid singlet oxygen production system, where strong resonance coupling between silver nanoparticles and photosensitizing molecules results in exceptionally high singlet oxygen production under both visible light and near-infrared light excitation, even for the photosensitizing molecules without near-infrared absorption. Also, our results indicate that the hybrid photosensitizers display low cytotoxicity wi (open full item for complete abstract)

Committee: Peng Zhang Ph.D. (Committee Chair); William Heineman Ph.D. (Committee Member); Pearl Tsang Ph.D. (Committee Member) Subjects: Nanotechnology

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

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

PhD, University of Cincinnati, 2015, Arts and Sciences: Chemistry

This dissertation is mainly based on the works of synthesis and characterization of self-assembling polymers using hydrogen bonding or hydrophobic interactions. Firstly, N-alkyl urea peptoid oligomer was synthesized as backbone of supramolecular polymers through three step repetition cycles with high yield. One N-alkyl urea peptoid precursor was explored to simplify the synthetic process. 4 different functional groups were converted from one precursor. Then 2-ureido-4[1H]-pyrimidinone (UPy) group which is a quadruple hydrogen bonding system was incorporated to N-alkyl urea peptoid oligomers to generate supramolecules. With the experience of UPy unit, we further explored UPy containing monomer to make organogelators. Three different monomers with different Tg values were copolymerized using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Organogels were afforded in both chloroform and dichlorobenzene. Critical gelation concentration and mechanic properties of organogels were examined. Cooperating another novel monomer containing pyrene unit to the above copolymers, fluorescent organogels were achieved which were suitable for potential up-conversion applications. In addition to pyrene, anthracene is another molecule which shows great up-conversion property. A series of Poly[(9-anthrylmethyl methacrylate)-co-(methyl methacrylate)] (Poly(AnMMA-co-MMA)) with different AnMMA ratios were synthesized via RAFT polymerization, resulting in tunable inter-chromophore distances. These polymers can serve as emitters, with PtOEP as sensitizer, in triplet-triplet annihilation up-conversion (TTA-UC) systems. TTA-UC intensity of the Poly(AnMMA-co-MMA)/PtOEP mixtures displays interesting dependence on the AnMMA ratio in the polymer. Interactions between chromophores on the same polymer chain play the key role in affecting the TTA-UC intensity in these systems. It is critical to minimize intra-chain chromophore quenching in order to achieve high UC intensity. H (open full item for complete abstract)

Committee: Neil Ayres Ph.D. (Committee Chair); David Smithrud Ph.D. (Committee Member); Peng Zhang Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2005, Chemistry

Both nanosecond and ultrafast laser flash photolysis with UV-visible and infrared detection were used to observe the transient species generated photochemically from a number of photosensitizers. The reactions of these transient species were monitored spectroscopically with the aid of theoretical computation.In the study of photochemical reactions of riboflavin and nucleosides, it was found that triplet riboflavin can be quenched by a silylated guanosine derivative. TRIR spectroscopy demonstrated that a hydroflavin radical is formed by an electron transfer-proton transfer mechanism. This sequential electron transfer-proton transfer between triplet riboflavin and guanosine derivative provides the direct observation of the photoinduced oxidative damage of riboflavin to the DNA nucleobase. The triplet states of isoquinoline N-oxide and benzocinnoline N-oxide react sluggishly with electron, proton and hydrogen atom donors. These triplets will react with hydroquinone by hydrogen atom transfer (proton coupled electron transfer). Triplet 4-nitroquinoline N-oxide reacts readily with electron donors to from the radical anions as previously reported. The radical anion is protonated on the oxygen atom of the N-oxide group to from a neutral radical. The three N-oxides of this study are not expected to serve as photochemical sources of hydroxyl radical. Singlet states of tirapazamine and desoxytirapazamine were identified by picosecond time-resolved absorption spectroscopy. The lifetimes of the S1 states and fluorescence quantum yields of aromatic N-oxides were found to be controlled by reversible cyclization to an oxaziridine. The S1 states of TPZ and dTPZ are reduced to radical anions by KSCN, KI and NaN3. Using LFP-based methodology, we have determined the rate coefficients for the reaction of hydroxyl radical with a number of monocyclic and polycyclic aromatic hydrocarbons in acetonitrile. We observed the reactivities of hydroxyl radical in acetonitrile. For simple aromatic (open full item for complete abstract)

Committee: Matthew Platz (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2002, Chemistry

The work described in this thesis describes steps towards building a zeolite-membrane based photochemical assembly, which can be used for developing a hydrogen evolving artificial photosynthetic system. We adopted the membrane system of natural photosynthesis in our artificial photosynthesis system to separate photochemically generated redox species. For photochemical applications, membranes without any inter crystal pinholes and grain boundaries are preferred since these defects introduce non-shape selective pathway for molecules to pass through the membrane. Also the membrane needs to be mechanically stable for assembly and operation of the system. To prepare zeolitic membranes for artificial photosynthestic systems, hydrothermal synthesis of zeolitic membranes was studied and an optimized synthesis procedure was developed. The films formed were typically 10 micron thick and made up of 4-5 micron spherical zeolitic crystals. However, intercrystalline defects were observed in zeolitic films made by hydrothermal synthesis and the films were not mechanically stable for photochemical applications. To address these issues, novel secondary treatment method to prepare zeolitic membranes was developed. Positive-type photoresist was used to fill nano to micrometer size pinholes that are generated during zeolite membrane casting. With this method, membrane leaking was reduced to 0.05% while zeolitic surface and pores were still accessible to molecules. For photochemical studies, photoresist-coated zeolitic membrane was used as a host for electron acceptor molecules and provided a route for charge propagation by electron hopping across the membrane. Since acceptor molecules are separated from donor molecules by a membrane, back electron transfer is prohibited and permanent charge separation can be achieved. Ruthenium dyad molecules were utilized as photosensitizers in our artificial photosynthetic system. To improve the efficiency of synthesis and photo electron transfer rea (open full item for complete abstract)

Committee: Prabir Dutta (Advisor) Subjects:

Doctor of Philosophy, Miami University, 2003, Chemistry and Biochemistry

The first project is development of a 5.5 µL spiral micro-flow chemiluminescence (CL) cell that allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light for flow injection (FI) using a 25 µL/min flow rate for luminol and a 50 µL/min buffer carrier flow rate. The detection limit of 1.5 µM achieved by using a spiral flow cell is 24 times lower than that obtained from a conventional FI system with a premixing tee and a straight 12 µL flow cell. This luminol FI method is applied to the enzymatic determination of L-lactate from 5–50 µM using polyethyleneglycol-stablized lactate oxidase. The second project is development of a quinine-sensitized photo-oxidation and quenched CL detection method for phenols using FI and LC. This method is based on the decrease of light emission from the luminol CL reaction due to the photo-oxidation of phenols that scavenge the photogenerated reactive oxygen species. On-line photo-oxidation is achieved using a coil photo-reactor made from FEP tubing coiled around a mercury UV lamp. This method is applied for the FI determination of ten phenolic compounds, mostly nitro- and chloro-phenols, and the LC determination of phenol, 4-nitrophenol and 4-chlorophenol with detection limits of about 1 µM. The third project is development of an indirect fluorescence (FL) detection method via the shielding effect on the UV-photolysis of 2-phenylbenzimidazole-5-sulfonic acid (PBSA). Compounds that have a strong UV absorbance at 217 nm and/or are reactive toward the photogenerated oxygen species can possess such a shielding effect. This method is applied for both the FI determination of thirteen aromatic compounds, mostly non-fluorescent nitro compounds, and the LC determination of salicylate, nitrofurantoin, 4-nitroaniline, 2-nitrophenol, and 4-nitrophenol with detection limits of about 0.2 µM. The fourth project is separation of ionic organic compounds by reversed phase ion-pair LC with MS detection. tert-Octylamine (open full item for complete abstract)

Committee: Neil Danielson (Advisor) Subjects: Chemistry, Analytical