https://scholarworks.unist.ac.kr/handle/201301/18 2026-04-08T00:28:23Z 2026-04-08T00:28:23Z Cho, Youngsang https://scholarworks.unist.ac.kr/handle/201301/90923 2026-03-26T13:13:36Z 2026-01-31T15:00:00Z

Title: Novel Functional Polymers via Ring-Opening Metathesis Polymerization (ROMP) and Post-ROMP Modification Author(s): Cho, Youngsang Abstract: Functional polymers play a pivotal role in advanced materials research owing to their diverse applications in electronics, optics, and other research and industrial fields. The ability to design and synthesize polymers with precisely tailored structures and properties is therefore of central importance. Among the various synthetic methodologies, ring-opening metathesis polymerization (ROMP), in combination with post-polymerization modification (PPM), has emerged as a versatile and powerful strategy for constructing novel functional polymeric systems. The research presented in this thesis centers on the use of ROMP and PPM in the controlled synthesis of new functional polymers and the study of their structural and physical properties. In Chapter 1, an overview of ROMP and PPM is provided with emphasis on their application to the synthesis of various functional polymeric materials. Chapter 2 describes the study on a novel chlorine-substituted poly(acetylene). As a monomer, cis-3,4-dichlorocyclobutene, was prepared and subsequently polymerized using a ruthenium-based olefin metathesis catalyst (the Grubbs 3rd generation catalyst). The resulting poly(cis-3,4- dichlorocyclobutene) underwent elimination to afford the chlorine-substituted poly(acetylene). The electrical conductivity of the chlorine-substituted poly(acetylene) was measured and determined to be on the order of 10–5 Ω−1 cm−1, a value comparable to those reported for organic semiconductors. In addition, both block and random copolymers were also synthesized and characterized, exhibiting good solubility in organic solvents along with valuable electronic properties. Chapter 3 describes the synthesis and study of new norbornene-based sulfur-containing polymer derivatives, poly(thianorbornene dicarboximide). A series of exo-7-thiabicyclo[2.2.1]hept-5- ene-2,3-dicarboximides were synthesized and polymerized using molybdenum-based olefin metathesis catalyst (Schrock’s catalyst). The ROMP reactions of these monomers proceeded in a controlled manner, enabling the tailoring of molecular weight and chain extension. The polymers were characterized using various techniques, and their refractive indices were found to have higher value than those of poly(norbornene) derivatives. To further demonstrate the monomer versatility, copolymerization reactions with norbornene were carried out and analyzed. As a PPM, treatment with base led to ring- opening hydrolysis, affording a polymer soluble in aqueous media. Major: Department of Chemistry

2026-01-31T15:00:00Z Choi, Huijeong https://scholarworks.unist.ac.kr/handle/201301/90921 2026-03-26T13:13:35Z 2026-01-31T15:00:00Z

Title: Understanding Structure‒Property Relationships of Photoactive Materials for Efficient and Stable Organic Photovoltaics Author(s): Choi, Huijeong Abstract: Organic photovoltaics (OPVs) have gained great attention as next-generation photovoltaic technologies due to their lightweight nature, mechanical flexibility, tunable optical properties, and compatibility with low-cost, solution-based fabrication. These advantages enable their use for both outdoor and indoor energy harvesting, such as powering low-power Internet of Things (IoT) devices. Over the past few decades, the remarkable efficiency improvements in OPVs, now exceeding 20%, have been driven primarily by advances in molecular design of photoactive materials. While the development of advanced p-type polymer donors and n-type non-fullerene acceptors (NFAs) has driven notable efficiency gains, key challenges remain in terms of device stability, green-solvent processability, and large-area scalability for practical applications. Achieving these advances demands a molecular- level understanding of how structural variations influence optoelectronic properties, blend morphology, and device performance. Therefore, rational design of both n-type and p-type materials is essential. A deep understanding of their structure‒property‒performance relationships is critical for realizing highly efficient and stable OPVs. In this dissertation, I aim to develop both n-type and p-type materials for efficient and stable OPVs, and to elucidate the structure‒property relationships that guide the rational design of next-generation organic semiconductors. Firstly, an asymmetric NFA named IPC-BEH-IC2F, incorporating a tricyclic pyrazine-based IPC unit, was designed to strengthen π-π intermolecular interactions and stabilize blend morphology. The resulting IPC-BEH-IC2F devices exhibited higher power conversion efficiency (PCE) and excellent long-term stability compared to the symmetric IC2F-BEH-IC2F-based devices. This demonstrates the effectiveness of asymmetric structural modification and the tricyclic IPC unit in enhancing crystallinity and suppressing Ag electrode-induced degradation pathways. Secondly, long alkyl chains and halogen-functionalized IPC-based end groups were introduced to finely tune light absorption, energy levels, and miscibility with polymer donors under non-halogenated solvent processing. Eight asymmetric NFAs—IPCnF-BBO-IC2X and IPCnCl-BBO-IC2X (where n = 1 and 2, X = F and Cl)—enabled efficient and additive-free devices processed from o-xylene. They achieved over 15% PCEs and maintained more than 94% of the initial performance over 2000 hours without encapsulation. These results demonstrate that incorporating halogenated IPC units into asymmetric NFAs provides an effective route to efficient, stable OPVs that are compatible with eco-friendly fabrication. Finally, PB2FQxn (n = 5, 10, and 15) terpolymers were developed via random terpolymerization of PM6 with a bulky quinoxaline-based B2FQx unit to achieve high-performance indoor OPVs (IOPVs). Incorporation of the B2FQx unit weakened pre-aggregation and improved miscibility with NFA L8-BO. This resulted in deeper highest occupied molecular orbital (HOMO) levels, reduced non-radiative energy losses, and enhanced VOC under indoor light conditions. As a result, PB2FQx15-based IOPVs achieve a PCE of up to 31% under LED illumination (1000 lx), outperforming the reference PM6-based IOPVs. Collectively, this dissertation highlights the importance of rational molecular design in developing efficient, stable, and environmentally sustainable OPVs. By systematically establishing correlations between molecular structure, morphology, and device performance, this work provides valuable design guidelines for next-generation photoactive materials that can achieve both high efficiency and long- term stability for practical outdoor and indoor applications. Major: Department of Chemistry

2026-01-31T15:00:00Z Sun, Seungwon https://scholarworks.unist.ac.kr/handle/201301/90922 2026-03-26T13:13:36Z 2026-01-31T15:00:00Z

Title: Activation and Delivery of Small Molecules by Transition Metal Complexes Author(s): Sun, Seungwon Abstract: In nature, the activation and delivery of biologically relevant small molecules such as nitrite (NO2−), nitric oxide (NO•), and dioxygen (O2) represent fundamental processes that play a central role in catalytic reactions and cellular signaling pathways mediated by metalloenzymes. The biological transformations and signaling events are tightly regulated by diverse metalloenzymes to support essential physiological functions. To gain deeper insight into the reactivity and mechanisms of metalloenzymes, synthetic coordination and bioinorganic chemistry have sought to elucidate the fundamental principles of small molecule activation and delivery, while also developing biomimetic complexes capable of reproducing or modulating such reactivity in a controlled manner. This thesis explores the mechanisms not only for the activation and transformation of NO2− and O2 but also for the spatiotemporal delivery of NO•, as observed in biological systems. In chapter 1, a mononuclear iron(II)-nitrite complex is shown to mediate the 2H+/1e− reduction of NO2− to NO• via the {FeNO}6 species proposed as a key reaction intermediate. Spectroscopic and kinetic studies reveal the formation of {FeNO}6 intermediate, including evidence for heterolytic N–O bond cleavage and the involvement of a transient Fe(II)···ONOH2+ adduct. Chemical reduction of {FeNO}6 confirms the generation and release of NO•, providing insight into the stepwise pathway of NO2− reduction relevant to enzymatic and catalytic NO• production. Chapter 2 investigates the photoinduced dissociation of NO• from a nonheme {FeNO}7. In-situ photocrystallographic experiments on crystalline {FeNO}7 provide direct structural evidence of Fe–NO bond elongation under visible light irradiation, capturing real-time snapshots of the excited-state of the {FeNO}7 species. Combined with solution-phase reactivity studies and multiconfigurational CASSCF calculations, the results reveal that NO• release is induced via metal-to-ligand charge transfer (MLCT). Furthermore, electronic modulation of supporting ligand by para-substituted Cl enhances photodissociation efficiency, elucidating key design principles for NO-delivering photoactive systems. Chapter 3 describes a functional model of quercetin 2,4-dioxygenase based on a well-defined nickel(II)-flavonolate complex. Structural, spectroscopic, and computational analyses demonstrate that the complex mimics the enzymatic O2 activation chemistry. Notably, the electronic configuration exhibits SOMO-HOMO inversion, highlighting the flavonolate ligand as the initial site of oxidation. Thermal decomposition of the complex after O2 activation yields benzoic and salicylic acid, supporting an oxygenation mechanism that parallels natural flavonoid degradation pathways. Taken together, all investigations in this thesis demonstrate how transition metal complexes can mediate the activation and delivery of small molecules through finely tuned electronic and structural features. The findings provide a deeper mechanistic understanding of metal-mediated activation and delivery chemistry. Major: Department of Chemistry

2026-01-31T15:00:00Z Choi, Solbee https://scholarworks.unist.ac.kr/handle/201301/90920 2026-03-26T13:13:35Z 2026-01-31T15:00:00Z

Title: Development of a Chemoproteomic Phosphohistidine Probe and Identification of Phosphohistidine Regulated Proteins Author(s): Choi, Solbee Abstract: Protein post-translational modifications (PTMs) and small-molecule metabolites serve as fundamental mechanisms for dynamically regulating protein structure, activity, and signaling across biological systems. Among the diverse PTMs, histidine phosphorylation (pHis) is a chemically labile and historically underexplored posttranslational modification due to the intrinsic instability of its phosphoramidate bond. To overcome the limitations of conventional proteomics, a chemoproteomic platform was established using a stable pyrazole-based τ-pHis analog (pPyp-BP) conjugated to a photocrosslinker and alkyne handle for visualization and enrichment of labeled proteins. This probe enabled selective covalent labeling and enrichment of pHis-recognizing proteins under native conditions. Application to Escherichia coli lysates revealed 13 high-confidence candidate pHis acceptors, many of which participate in central carbon metabolism. Comprehensive biochemical validation demonstrated distinct regulatory behaviors among these targets. Phosphofructokinase (PfkA) was identified as a bona fide pHis-regulated enzyme. His249 phosphorylation by the phosphotransferase system, PtsI–PtsH cascade, and dephosphorylation by phosphatase SixA establish a reversible signaling axis that couples carbon source availability to glycolytic flux. In contrast, phosphoglucomutase (GlmM) and citrate synthase (GltA) showed probe reactivity but provided limited evidence for functional pHis regulation in vivo. Pyruvate kinase II (PykA) was phosphorylated at the previously unannotated His41, a residue essential for catalytic activity, although its phosphorylation appeared independent of the phosphotransferase system, indicating an alternative upstream regulator. In parallel, this thesis explored whether endogenous metabolites could drive covalent protein modification. Ascorbic acid- and melatonin-derived chemical probes were designed to mimic reactive metabolites. While melatonin- and AMK-based alkyne probes were successfully synthesized, neither melatonin nor AMK probes produced specific protein labeling in cellular or lysate experiments. Ascorbic acid-based probe synthesis was hindered by instability during key coupling steps, preventing downstream biological evaluation. These findings highlight the need for systematic interrogation of the biological conditions under which metabolite-derived covalent modifications occur, as well as the development of chemically rigorous and synthetically reliable strategies to enable metabolite-based probe synthesis. Together, this work provides an integrated chemical biology framework for investigating two complementary modes of protein regulation, reversible pHis-dependent signaling and potential metabolite-driven covalent modification. The chemoproteomic strategy developed here expands the toolkit available for studying labile PTMs and uncovers a previously uncharacterized pHis regulatory mechanism governing bacterial glycolysis. In addition, the exploratory metabolite-probe efforts outline foundational steps toward mapping covalent interactions between cellular metabolites and protein targets. This thesis underscores the value of chemical approaches in revealing hidden layers of metabolic and signaling regulation across biological systems. Major: Department of Chemistry

2026-01-31T15:00:00Z