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In this study, a synthetic, water soluble cavitand octa acid (OA) is used as medium for conducting photochemical reactions. The cavitand octa acid is soluble in water in slightly basic conditions. OA forms different types of complexes with variety of organic guest molecules. Remarkably, in presence of a hydrophobic guest, two of these OA molecules self assemble to form a capsular complex (guest@(OA)2). The confined inner phase of the cavitand can be utilized to control both photochemistry and photophysics of organic guest molecules. Stilbene derivatives undergo cis/trans (Z/E) photoisomerization in organic solvents. The results of our studies with stilbenes@(OA)2 suggest that the available free volume for encapsulated guest stilbenes could be manipulated by changing the number and position of the substituent methyl groups which has a significant influence on the photoisomerization process. Further, energy transfer from caged donor ((fluorenone)2@(OA)2) to caged acceptor ((stilbene)@(OA)2) was explored. It is also demonstrated that photoinduced electron transfer (PET) between acceptor (cationic) present outside the OA capsule to donor (a stilbene) present within the capsule is feasible and occurs at a higher than diffusion controlled rate. The PET in the above supramolecular system could be controlled by employing another cavitand, cucurbit[7]uril (CB7) to complex with cationic acceptor. Also, studies with carefully chosen guest molecules suggest that selective photocyclodimerization can be carried out within the inner phase of OA.

Thesis advisor: Jeffery A. Byers / Thesis advisor: Chia-Kuang Tsung / Host-guest chemistry provides a unique platform for catalysis by combining the specificity of homogeneous catalysts with the stability and recyclability of heterogeneous catalysts. Metal-Organic Frameworks (MOFs), such as UiO-66 are ideal hosts for host-guest catalysis. The vast porous network UiO-66 forms is chemically and thermally stable and the individual cages that make up the crystals can be modified by simple organic syntheses. The method developed in our group provides a mild, synthetically simple route for non-covalent organometallic guest encapsulation that decouples host synthesis from guest encapsulation. In this study, the so-called aperture opening encapsulation method is tested using an unstable class of iron-based carbon dioxide hydrogenation catalysts. The study results in launching an extensive investigation into the driving force behind aperture opening encapsulation with the goal of increasing guest loadings. Various methods to achieve this goal are explored including synthesizing novel UiO-66 linkers and taking advantage of factors such as columbic force. In conclusion, the information gained from a bigger picture examination of aperture opening encapsulation directly leads to guest loadings high enough to utilize useful characterization techniques. Accordingly, a standard protocol for characterization of iron catalysts encapsulated in UiO-66 is developed. / Thesis (MS) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Abstract This research work details a systematic study of the structure and function of supramolecular host-guest systems. Host-guest inclusion complexes were formed between β-Cyclodextrin (β-CD) and its copolymers (as hosts), with several types of guest molecules both in aqueous solution and the solid state. The research is divided into two themes; (1) structural characterization and dynamic properties of the inclusion compounds of β-CD with various guest systems in aqueous solution and the solid phase, and (2) heterogeneous adsorption and structural studies of β-CD based copolymers with various guest systems in aqueous solutions. The guest systems include alkyl and perfluoroalkyl carboxylates, perfluoroalkyl sulfonate, and p-nitrophenol (PNP) at variable experimental conditions. In the first theme (chapter 2-5), host-guest complexes in the solid state were prepared using dissolution and slow cool methods at variable host/guest mole ratios (i.e., 1:1 and 2:1). The complexes were further characterized using 19F/13C DP/MAS and CP/MAS solid-state NMR spectroscopy. The solution state complexes were prepared in D2O for structural characterization using 1H/19F NMR spectroscopy. The NMR studies were complemented using FT-IR, thermal analyses (DSC, and TGA), and powder X-ray diffraction (PXRD). Evidence for the formation of host-guest inclusion compounds (ICs) was provided using CP/MAS solids NMR spectroscopy and complexation-induced chemical shift (CIS) values of 1H/19F nuclei in aqueous solution. The β-CD/PFC ICs displayed variable guest geometry and hydration states as determined by the host-guest stoichiometry and the conformation of the guest. PFOA and SPFO form 1:1 and 2:1 ICs with β-CD, wherein the guest adopts a range of gauche and trans conformations, respectively. 1:1 host-guest complexes were concluded for short perfluorocarbon chains (i.e., PFBA) where the gauche conformation of the PFC guest in the bound state was favoured. In the second theme (chapters 6–8), β-CD based copolymers were used as host materials. The structural characterization of a soluble poly-CD material (known as HDI-1) revealed that the solution behaviour of such polymeric hosts are sensitive to the presence of guest compounds such as p-nitrophenol (PNP) (i.e. chemo-responsive), as well as temperature variations (i.e. thermo-responsive). The host-guest chemistry of the soluble poly-CD material, as studied by 2-D solution NMR and induced circular dichroism (ICD) spectroscopy, indicates that PNP was bound within the cavity sites of β-CD and the interstitial domains of the copolymer (cf. Scheme 1.6 and chapter 6). The observed responsive nature of such polymeric host materials to temperature variation and chemical potential resembles behaviour characteristic of ‘smart materials’. Herein, ‘smart materials’ refer to systems which are responsive to external stimuli (e.g. temperature and chemical). The adsorption properties of the soluble (HDI-1) and insoluble (HDI-3 and -6) poly-CD adsorbents with octyl and perfluorooctyl carboxylate and sulfonate anions were estimated using the Sips and BET models. The hydrocarbon (HC) and fluorocarbon (FC) anions form monolayer and multilayer structures at the surface of the polymeric adsorbents, respectively. The formation of layered structures was controlled by the relative hydrophobicity of the alkyl/perfluoroalkyl chains and their mutual miscibility with the adsorbent surface. Other factors include the inductive effects of the alkyl/perfluoroalkyl head groups and their interactions with aqueous solvent or dipolar domains of the adsorbent surface. The adsorbed species at the liquid-solid interface were characterized using FT-IR spectroscopy, thermal analyses, and contact angle.

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Novel P-tert-butylcalix[4]arene derivatives (L-3-10) containing mixed donor atoms (O, N, S) have been synthesised in a two stage reaction, the first part of which involves the preparation of L-2 using 18-crown-6 as a phase transfer catalyst and K2CO3 as a weak base. These conditions lead to the removal of two distal protons from the lower rim, allowing the 1,3-bis-niethylethylthio ether derivative (L-2) to be synthesised in a reduced reaction time with greater yield and purity than previously published. The final two protons were removed using NaH, sites to which a variety of amine, amide and thiophene moieties were introduced. This thesis reports investigations on these new compounds detailed as follows, i) 1H and 13C NMR characterisation of these derivatives. In two cases, X-ray crystallograpliic structures have been determined, showing distortions from the symmetrical cone conformation of p-tert-butylcalix[4]arene caused by steric interactions of the lower rim substituents. ii) Solubility and derived Gibbs energies of these ligands in various solvents at 298.15 K. Using acetonitrile and methanol as reference solvents, Gibbs energy of transfer are calculated. iii)The acid-base properties of ligands L-3,4,6-8 were investigated by potentiometry. Equilibrium constants for the dissociation processes reveal relative proton affinities in methanol at 298.15 K. Data of individual species present as a function of pH are presented in diagrams. iv) Conductimetric measurements. These data are used to derive the stoichiometry of metal cation complexes of L-4 in methanol. v) 1H NMR studies of the complexation of L-4 with metal cations in CD3OD at 298 K. These reveal conformational change in the macrocycle cyclic structure as the substituents' arrangements are altered to accommodate the guests cations. vi) Determination of Gibbs energy of complexation for ligand L-4 and Ag+, Pb+2, Cd2+ and Cu2+ metal cations in methanol at 298.15 K, using a competitive potentiometric method. Cation selectivities are discussed.

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Ions play pivotal roles both biologically and environmentally. The effects felt from the impact of ions, much like their relative charge, can be positive or negative. Ions are responsible for catalyzing and executing precise control over many of the essential processes that occur in our bodies. Ions can also be major contributors as environmental pollutants having catastrophic effects. There is a great deal of interest in better understanding the role and effect of ions in the surrounding environments. The ability to study ions of interest relies on efficient recognition and sensing of these targets. The field of supramolecular chemistry is particularly well suited for this task as it utilizes non-covalent molecular interactions in much the same way natural system involving ions operate. Broadly, this body of research seeks to explore the subtle interactions of various targeted ions with supramolecular receptors. This research is an effort to further understand the nature of these interactions for potential recognition and sensing applications as well as better understanding the highly complex systems found in biology. Chapter I provides a brief overview of various mechanisms of ion coordination in supramolecular chemistry and emphasizes some key examples demonstrating the importance of the various types of coordination as it pertains to the research presented herein. Chapter II highlights a unique class of phosphine oxide-based tripodal ditopic receptors and presents studies on their interactions with alkali metals and halides. Chapter III covers the synthesis and study of anionic binding trends for a series of heteroaromatic-containing urea-based receptors and discusses the influence of anion binding on receptor conformation. Chapter IV provides preliminary results on the application of the bipyridal bisurea-based anion receptor, presented in Chapter III, as ligand for metal salts. Chapter V focuses on a series of pyridal bisurea-based receptors with regard to their ability to serve as chloride sensitive probes in cellular environments. This dissertation contains both previously published and unpublished co-authored material. / 10000-01-01