Metal-organic frameworks (MOFs) are a class of highly crystalline nanoporous materials that self-assemble from inorganic metal oxide clusters and multitopic organic linkers. MOFs can be altered in terms of the types of metals and structures of organic linkers used, allowing for a high degree of customization and manipulation of the synergistic chemical or physical properties that arise from the precise coordination of their molecular components, including exceptionally large surface area and pore size. Zirconium-based MOFs, called UiOs in honor of their conception at the University of Oslo, also show remarkable chemical stability in both acidic and basic environments, making them excellent candidates for biomedical applications as drug delivery systems, where they can either function as molecular cargo ships, with drugs packed into their pores, or as controlled release systems, in which drug molecules are directly attached to their ligands for precise delivery. The objective of this work is to prepare water-stable MOFs whose linkers are decorated with functional groups that have potential compatibility in drug delivery systems and to explore the efficacy of certain synthesis conditions in terms of the crystallinity of the MOF product. Thus, we hope to establish a basis for the ligation of anticancer drugs and fluorescent tags to MOFs for their controlled release at a specified location within the body. These targeted release mechanisms represent new therapeutic possibilities in terms of cancer treatment as their specificity would mitigate damage to healthy tissues, thereby addressing one of the greatest weakness of present treatment options.

The rational design and construction of Metal-Organic Frameworks (MOFs) with intricate structural complexity are of prime importance in reticular chemistry. However, the design of intricate structures that can practically be synthesized is very difficult, and the suitable targeted intricate nets are still unexplored. Evidently, it is of great value to build the fundamental theory for the design of intricate structures. This dissertation is focused on the exploration of cutting-edge design methodologies in reticular chemistry. This research shows the design and synthesis of several MOF platforms (hex, fcu, gea and the) based on rare earth polynuclear clusters. Furthermore, this research unveils the latest addition, named merged nets approach, to the design toolbox in reticular chemistry for the rational design and construction of intricate mixed-linker MOFs. In essence, a valuable net for design enclosing two edges is rationally generated by merging two edge-transitive nets, spn and hxg. The resultant merged net, named sph net, offers potential for the deliberate design and construction of highly symmetric isoreticular intricate mixed-linker MOFs, sph-MOF-1 to 4, which represent the first examples of MOFs where the underlying net is merged from two 3-periodic edge-transitive nets. Furthermore, the underlying principle of the merged net approach, the fundamental merged net equation, and two key parameters are disclosed. Also, we discovered three analysis methods to check and validate corresponding signature nets in an edge-transitive net. Based on these analysis methods, a signature map of all edge-transitive nets was established. This map showing the systematic relationship among edge-transitive nets will help the material chemist to comprehend more about the underlying nets in reticular chemistry. Based on the revealed map, we systematically described the nine types of merging combination and 140 merged nets based on two edge-transitive nets. Among these enumerated nets, only 18 of them was shown on the RCSR database before. These enumerated merged nets significantly increased the designable targets in reticular chemistry. Using an example of enumerated sub net, we show how this approach can be utilized to design and synthesis mixed-linker porous materials based on the intricate sub-MOF platform, which presents one of the most intricate MOF structures synthesized by design.

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Inorganic nano- and micromaterials (NMMs) exhibit unique properties including high surface areas, tunable optical and electronic properties, low densities, thermal and chemical robustness, and catalytic capabilities, among others. One of the more novel subclasses of NMMs, metal-organic frameworks (MOFs), are crystalline porous coordination polymers consisting of metal nodes connected by organic linkers to form one-, two-, or three-dimensional frameworks. While the mechanism of MOF formation is complex, tuning the metal:ligand ratios, reaction temperature and vessel pressure, ligand concentration, modulator concentration, and H+ activity impacts particle size, morphology, dispersity, and isotropy of these materials. MOFs also exhibit post-synthetic modification capabilities, which, along with their tunable synthetic nature, make them promising candidates for composite materials such as functionalized nanofillers for reverse osmosis (RO) desalination. The work described herein investigates synthetic parameters of a zirconium-based porphyrinic MOF, PCN-222, to selectively control its crystal size, aspect ratio, and dispersity. Size-constrained PCN-222 was post-synthetically modified with fatty acids and zwitterions to be used as RO thin-film composite (TFC) membranes with improved membrane flux, salt rejection, and anti-fouling properties. The synthetic parameters of MOFs were also considered for the commercial scale-up of CO2 direct air capture (DAC) solid sorbents, including UiO-66, MIL-101-Cr, and Mg-MOF-74, to preserve CO2 uptake capacities between lab and industrial scales. / Doctor of Philosophy / Metal-organic frameworks (MOFs) are unique, highly porous materials that have garnered attention for their potential in many applications, including catalysis, drug delivery, energy, and gas storage. In this work, MOFs were produced for environmental applications, particularly for the conversion of salt water to drinkable water in a process known as reverse osmosis (RO) desalination. RO uses a thin membrane to separate dissolved salt, as well as organic materials such as decomposed organisms, from water. Though RO membranes are widely used commercially, they suffer from high costs and short lifetimes; however, their performance is improved through the incorporation of extremely small materials known as nanoparticles. MOF nanoparticles were grown small enough to be dispersed in the polymer matrix of the thin membrane, then functionalized to improve salt rejection and flux, or the speed at which clean water is produced from RO processes. They were also modified to improve lifetimes by preventing the build-up of organic materials on the surface. Besides clean water, MOFs were also prepared for capturing the greenhouse gas, CO2, directly from the air. Because MOFs can be made with many different functionalities, they are promising materials for many different research fields.

A key component of natural photosynthesis are the antenna chromophores (chlorophylls and carotenoids) that capture solar energy and direct it towards the reaction centers of photosystems I and II. Highlighted by highly-ordered crystal structures and synthetic tunability via crystal engineering, metal–organic frameworks (MOFs) have the potential to mimic the natural photosynthetic systems in terms of the efficiency and directionality of energy transfer. Owing to their larger surface areas, MOFs have large absorption cross sections, which amplifies the rate of photon collection. Furthermore, MOFs can be constructed using analogues of chlorophyll and carotenoids that can participate in long-range energy transfer. Herein, we aimed to design photoactive MOFs that can execute one of the critical steps involved in photosynthesis - photon collection and subsequent energy transfer. The influence of spatial arrangement of chromophores on the efficiency and directionality of excitation energy transfer (EET) was investigated in a series of mixed-ligand pyrene- and porphyrin-based MOFs. Due to the significant overlap between the emission spectrum of 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy) and the absorption spectrum of meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP), the co-assembly of these two ligands in a MOF should enable facile energy transfer. Bearing this in mind, three TBAPy-based MOFs with markedly different network topologies (ROD-7, NU-901, and NU-1000) were chosen and a small number of TCPP units were incorporated in their backbone. To gain insight into the photophysical properties of mixed-ligand MOFs, we conducted time-resolved and steady-state fluorescence measurements on them. Stern-Volmer analysis was performed on the fluorescence lifetime data of mixed-ligand MOFs to determine the quenching constants. The quenching constant values for ROD-7, NU-901, NU-1000, and TBAPy solution were found to be 15.03 ± 0.82 M-1, 10.25 ± 0.99 M-1, 8.16 ± 0.41 M-1, and 3.35 ± 0.30 respectively. In addition, the ratio of the fluorescence intensities of TCPP and TBAPy was used to calculate the EET efficiencies in each of the three MOFs. EET efficiencies were in the following order: ROD-7 > NU-901 > NU-1000 > TBAPy-solution. Based on the trends observed for quenching constants and EET efficiencies, two conclusions were drawn: (1) the ligand-to-ligand energy transfer mechanism in MOFs outperforms the diffusion-controlled mechanism in solution phase, (2) energy transfer in MOFs is influenced by their structural parameters and spectral overlap integrals. The enhanced EET efficiency in ROD-7 is attributed to shorter interchromophoric distance, larger orientation factor, and larger spectral overlap integral. Directionality of energy transfer in these MOFs was assessed by calculating excitonic couplings between neighboring TBAPy linkers using the atomic transition charges approach. Rate constants of EET (kEET) along different directions were determined from the excitonic couplings. Based on the kEET values, ROD-7 is expected to demonstrate highly anisotropic EET along the stacking direction. In order to explore the mechanistic aspects of EET in porphyrin-based MOFs, we studied the energy transfer characteristics of PCN-223, a zirconium-based MOF containing TCPP ligands. After performing structural characterization, the photophysical properties of PCN-223 and free TCPP were investigated using steady state and time-resolved spectroscopy. pH-dependent fluorescence quenching experiments were performed on both the MOF and ligand. Stern-Volmer analysis of quenching data revealed that the quenching rate constants for PCN-223 and TCPP were 8.06 ± 1011 M-1s-1 and 2.71 ± 1010 M-1s-1 respectively. The quenching rate constant for PCN-223 is, therefore, an order of magnitude larger than that for TCPP. Additionally, PCN-223 demonstrated a substantially higher extent of quenching (q = 93%) as compared to free TCPP solution (q = 51%), at similar concentrations of quencher. The higher extent of quenching in MOF is attributed to energy transfer from neutral TCPP linkers to N-protonated TCPP linkers. Using the Förster energy transfer model, the rate constant of EET in PCN-223 was calculated. The magnitude of rate constant was in good agreement with the kEET values reported for other porphyrin-based MOFs. Nanosecond transient absorption measurements on PCN-223 revealed the presence of a long-lived triplet state (extending beyond 200 μs) that exhibits the characteristic features of a TCPP-based triplet state. The lifetime of MOF is shorter than that of free ligand, which may be attributed to triplet-triplet energy transfer in the MOF. Lastly, femtosecond transient absorption spectroscopy was employed to study the ultrafast photophysical processes taking place in TCPP and PCN-223. Kinetic analysis of the femtosecond transient absorption data of TCPP and PCN-223 showed the presence of three distinct time components that correspond to: (a) solvent-induced vibrational reorganization of excitation energy, (b) vibrational cooling, and (c) fluorescence. Materials that allow control over the directionality of energy transfer are highly desirable. Core-shell nanocomposites have recently emerged as promising candidates for achieving long-distance, directional energy transfer. For our project, we aim to employ UiO-67-on-PCN‐222 composites as model systems to explore the possibility of achieving directional energy transfer in MOF-based core-shell structures. The core–shell composites were synthesized by following a previously published procedure. Appropriate amounts of Ruthenium(II) tris(5,5′-dicarboxy-2,2′-bipyridine), RuDCBPY, were doped in the shell layer to produce a series of Ru-UiO-67-on-PCN‐222 composites with varying RuDCBPY loadings (CS-1, CS-2, and CS-3). The RuDCBPY-doped core–shell composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) imaging, Nitrogen adsorption-desorption isotherms, and diffuse reflectance spectroscopy. Efforts are currently underway to quantify RuDCBPY loadings in CS-1, CS-2, and CS-3. After completing structural characterization, the photophysical properties of CS-1, CS-2, and CS-3 will be investigated with the help of time-resolved and steady-state fluorescence spectroscopy. / Doctor of Philosophy / The pigment−protein complexes in natural photosynthetic units (also known as light harvesting antennas) efficiently capture solar energy and transfer this energy to reaction centers that carry out water splitting reactions. The collective chromophoric behavior of antennas can be replicated by metal-organic frameworks (MOFs). MOFs are crystalline, self-assembled materials composed of metal clusters connected by organic molecules. In this dissertation, we study the factors that govern the energy transfer and light harvesting capabilities of MOFs. In chapter 2, we examined the role of 3D structure of MOFs in energy transfer. In chapter 3, we investigated the influence of pH and temperature on the photophysical properties of MOFs. In chapter 4, we explored the possibility of energy transfer in novel MOF-on-MOF composites. This work is intended to pave the way for the construction of highly efficient MOF-based materials that can serve as the light harvesting and energy-transfer components in solar energy conversion devices.

Metal-organic frameworks (MOFs) are a class of hybrid materials that offer a promising platform for a range of catalytic reactions. Due to their complex structure, MOFs offer unique opportunities to serve as novel catalysts, or as host to improve the properties of previously studied species. However, while other catalytic approaches have been studied for many decades, the recency of their discovery means that significant work is still needed to develop MOFs as a viable option for large scale application. Herein, we aimed to advance the field of MOFs as both novel catalysts, and as host platforms for other catalytic species. To this end, we studied synthetic pathways to produce favorable MOF properties such as higher porosity and active site concentration through introduction of defects and macromorphological control, as well as utilization of molecular catalysts imbedded in the MOF structure for multicomponent, light driven reactivity. Chapter 1 introduces the history MOFs and the pursuit of the stable structures commonly associated with MOF chemistry. The synthesis process for zirconium-based MOFs will be discussed, with specific attention given to the modulated synthesis process which can harnessed to change MOF properties and improve catalysis. Two specific reactions will be introduced which serve as a basis for study in this work. First, the hydrolysis of organophosphate nerve agents by MOFs acting as novel catalysts will be introduced. The mechanism of reaction, as well as previous work in this field will be discussed. Finally, water oxidation as part of artificial photosynthesis through incorporated molecular catalysts will be introduced. Chapter 2 presents a modulator screening study on a zirconium-based MOF, UiO-66. One of the most commonly studied MOFs, UiO-66 provides an excellent platform for synthetic modulation. Particle size and defect level were measured of 26 synthetic variations and synthetic conditions were found to isolate changes in defect level and particle size, which typically change coincident with each other. Hydrolysis of the organophosphate compound dimethyl 4-nitrophenylphosphate (DMNP) was used to study the impact of particle size and defect level on reactivity. The reaction was found to be surface limited, even at high levels of missing linker defects. In Chapter 3, the macromorphology of three zirconium-based MOFs were tuned through synthesis modification. MOF powders and xerogels were prepared and characterized to highlight the desirable properties obtained through the gelation process. The materials were compared in the hydrolysis of DMNP and significant enhancement was observed for UiO-66 and NU-1000 xerogels. This was largely attributed to the introduction of mesoporosity and nanocrystalline particle sizes, which significantly increase the number of reactive sites easily accessible for catalysis. In Chapter 4 the authors examine MOFs as a host for molecular catalysts for use in photoelectrochemical water oxidation. A ruthenium-based catalyst [Ru(tpy)(dcbpy)]2+ was incorporated into UiO-67 through a mixed linker synthesis and grown on a WO3 substrate (Ru-UiO-67/WO3). Previous work from our group demonstrated Ru-UiO-67 retained the catalytic activity as the molecular species, while improving the recyclability of the material. In this work, addition of WO3 as a light harvester allowed for the reaction to be driven at a photoelectrochemical underpotential, a first for MOF-based water oxidation. Finally, Chapter 5 offers a perspective of the field of MOF-based artificial photosynthesis. Particular attention is given to issues of diffusion, selectivity, stability, and moving towards integration of multiple components rather than the study of half-reactions. / Doctor of Philosophy / Catalysts are a key component of chemistry that has a major impact on everyday life. From biological examples to industrial settings, catalysts are used to facilitate chemical conversions to new products and compounds. Because of the high demand, development of new catalysts with improved reactivity is a significant scientific challenge. A new class of materials known as metal-organic frameworks (MOFs) have been recently shown to acts as new catalysts or improve the properties of existing catalysts. Herein, we discuss the use of MOFs as catalysts for both development of new catalysts and improving known species. MOF-based catalysts have been used in a range of reactions from destruction of toxic chemical weapons to the production of renewable energy through artificial photosynthesis. This work is intended to highlight the potential for MOF-based catalysts and the next steps to further realize their potential.

Diborane (B2H6) is a hydride gas often employed in high-purity industrial surface processes such as chemical vapor deposition or epitaxial layer growth. The use of diborane at industrial scales is complicated by the formation of higher-order borane contaminants in pure diborane gas via a complex series of gas-phase reactions. An advanced, rationally designed sorbent could stabilize diborane through interfacial interactions, dramatically reducing the decomposition rate without permanently trapping the molecule. However, the design of such a sorbent would require a nuanced understanding of diborane's fundamental surface chemistry, about which little is known. In the work presented in this thesis, a novel ultra-high vacuum (UHV) system was designed and employed to characterize the fundamental interactions of diborane with a variety of surfaces. In situ Fourier-transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD) experiments were used in conjunction with density-functional theory (DFT) calculations to elucidate binding geometries and interaction mechanisms. On non-functionalized model surfaces such as CaF2 or amorphous carbon, diborane adsorbed only at cryogenic temperatures. Hydroxylated surfaces such as amorphous silica (SiO2) adsorbed significantly more diborane, which remained at slightly higher temperatures. FTIR spectra indicated the presence of hydrogen bonding between diborane and surface hydroxyl groups. DFT calculations revealed that the interaction takes the form of a novel bifurcated dihydrogen bond. In contrast with previous reports, diborane exhibited only weak interactions with the surface hydroxyl groups of silica. DFT calculations further elucidated that the irreversible reaction of diborane with surface hydroxyls is only possible in the presence of a second nucleophile (such as adventitious water). On the metal-organic framework (MOF) UiO-66 NH2, unique chemistry was observed in which diborane reacted with the –NH2 groups of the MOF linkers, yielding stable surface-bound products. DFT calculations determined the reaction mechanism to be dissociative adsorption of diborane, resulting in two amine-bound –BH3 moieties. Importantly, it was found that these fragments persisted at room temperature and could only leave the surface via the reverse reaction. The discovery that diborane can be stored as separate fragments that re-combine to yield the parent molecule has important implications for the development of new diborane sorbents. We hypothesize that surfaces designed with fixed, precisely spaced nucleophiles could enable the reversible storage of diborane. / Doctor of Philosophy / Diborane (B2H6) is a useful but hazardous gas employed in both academia and industry, often in processes that require ultra-high-purity source gases. However, diborane reacts with itself at room temperature, making the contamination of pure diborane very difficult to avoid. This problem could potentially be solved with a specially designed solid material that would sequester diborane without destroying it, but the design of such a material would require a much better understanding of diborane's chemistry with surfaces than currently exists. In this work, we employed ultra-high vacuum (UHV) methods to study the interactions between diborane and a variety of surfaces, with the ultimate goal of determining guiding principles for the design of diborane-stabilizing sorbents. Among the materials we studied were inorganic carbon, silica (SiO2), and a class of advanced microporous materials known as metal-organic frameworks (MOFs). Inorganic materials were found not to interact meaningfully with diborane. A novel hydrogen bond was discovered between diborane and the surface of silica, but the interaction was found to be too weak to provide significant stabilization. Most MOFs behaved similarly to silica. The MOF UiO-66-NH2, however, was found to react with diborane. Through a combination of computer simulations and UHV experiments, the precise nature of the reaction was determined. On the surface of UiO 66 NH2, diborane splits into two surface-bound BH3 molecules, where it is trapped until the reaction reverses. Importantly, it was found that BH3 can only leave the surface by recombining into diborane—effectively storing diborane on the surface to be released later. We hypothesize that this useful chemistry is due to the fixed distance between chemical groups on the MOF surface. This discovery suggests a promising strategy for the design of advanced diborane sorbents.

Many applications of metal-organic frameworks (MOFs) are highly dependent on their structures. The type and consistency of structure inform their properties. Zinc-based MOFs are applicable in different fields because of the low toxicity of zinc materials and are therefore also useful for catalysis. While MOF-5, a zinc-based MOF with carboxylate linkers is moisture intolerant, a variant of this is moisture tolerant. The introduction of a nitrogen-based linker in the zinc MOF which renders the structure moisture-tolerant. This material has not been explored as much, despite its multifunctional properties. Furthermore, the growth of Zn-based bimetallics of this MOF has not yet been explored. In this work, I studied the synthesis of this zinc-based moisture-tolerant MOF-5 as a thin film using a simple, fast, and cost-effective layer-by-layer wet synthesis method on different substrate surfaces. I successfully synthesized a series of bimetallics of this MOF as thin films on an untreated silicon wafer substrate. The successful synthesis of these materials was confirmed using X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy techniques. Additionally, some software data analysis tools were used for the characterization of the surface of the thin films to quantify the chemical composition. Future applications of these materials will be as sorbent materials for the capture of CO2 and its subsequent conversion to CO which is a synthesis gas for different useful materials like fuel and other chemical materials.