Doctor of Philosophy / Department of Chemistry / Viktor Chikan / Ever depleting sources of fossil fuel has triggered more research in the field of alternate sources of energy. Over the past few years, CdSe nanoparticles have emerged as a material with a great potential for optoelectronic applications because of its easy exciton generation and charge separation. Electronic properties of CdSe nanoparticles are highly dependent on their size, shape and electronic environment. The main focus of this research is to explore the effect of different electronic environments on various spectroscopic properties of CdSe nanoparticles and link this to solar cell performance. To attain that goal, CdSe quantum dots (QDs) and nanorods (NRs) have been synthesized and either doped with metal dopants or embedded in polymer matrices. Electronic properties of these nanocomposites have been studied using several spectroscopic techniques such as absorption, photoluminescence, time-resolved photoluminescence, confocal microscopy and wide field microscopy. Indium and tin are the two metal dopants that have been used in the past to study the effect of doping on conductivity of CdSe QDs. Based on the photoluminescence quenching experiments, photoluminescence of both indium and tin doped samples suggest that they behave as n-type semiconductors. A comparison between theoretical and experimental data suggests that energy levels of indium doped and tin doped QDs are 280 meV and 100 meV lower than that of the lowest level of conduction band respectively. CdSe nanorods embedded in two different polymer matrices have been investigated using wide field fluorescence microscopy and confocal microscopy. The data reveals significant enhancement in bandedge luminescence of NRs in the vicinity of a conjugated polymer such as P3HT. Photoactive charge transfer from polymers to the surface traps of NRs may account for the observed behavior. Further study shows anti-correlation between bandedge and trap state emission of CdSe NRs. A recombination model has been proposed to explain the results. The origin of traps is also investigated and plausible explanations are drawn from the acquired data.

Doctor of Philosophy / Department of Chemistry / Christer Aakeröy / Physical properties of bulk solids are typically governed by the molecular arrangement of individual building blocks with respect to each other in the crystal lattice. Thus the ability to synthesize molecular crystals with pre-organized connectivities allows for the rational design of functional solids with desirable and tunable physical properties. A thorough understanding of the various intermolecular interactions that govern the solid-state architectures is an important pre-requisite for the rational design of molecular solids. In order to understand the role of molecular geometric complementarity in the design of solid-state architectures, we explored the structural landscape of two isomeric pyridine based acceptors (3N and 4N) with binding sites oriented along different directions, i.e. parallel and at angle of 60° respectively, with a series of even chain diacid (colinear binding sites) and odd chain diacid (binding sites oriented along 120°) using co-crystallization technique. The results obtained shows a striking correlation between the observed solid state architecture and geometric complementarity of interacting species. Combinations of 3N with odd and 4N with even chain diacid produced 1-D chains whereas 3N with even and 4N with odd chain diacid generated 0-D ring architectures. In order to exploit the possibility of fine-tuning physical properties using co-crystallization techniques, solubility measurements were performed on 3N and 4N co-crystals with the diacids. The results show that the solubilities of 3N and 4N in the co-crystal form were very different from their solubility in the pure form. Also, there was a strong correlation observed between the solubility of the co-crystals and their corresponding co-formers, i.e. diacids. To explore the dependence of crystal structure on a physical property such as melting point, we synthesized co-crystals of 3,3‟-azopyridine and 4,4‟-azopyridine with a series of even chain diacids. Structural consistency was obtained within the two groups of co-crystals. In both groups, 1-D chains were formed with the diacid as the primary building block. However, In the series of 3,3‟-azopyridine co-crystals, the co-crystal with succinic acid showed a different solid-state packing arrangement (although the primary building block was same as others) compared to the others in the same series. This difference is also reflected as a deviation in the melting point, while the others in the series showed a perfect correlation between the structural consistency and melting point behavior. It was also observed that the co-crystals of 4,4‟-azopyridine displayed higher melting points than co-crystals of 3,3‟-azopyridine which could be due to the differences in the overall packing of the crystal which is a combination of different intermolecular interactions that exist between molecules in the solid state. Using bi-functional donors (with both hydrogen and halogen bond donors on same backbone), we investigated the relative strengths of hydrogen and halogen bond donors in the presence of two isomeric acceptors, 3,3‟-azopyridine and 4,4‟-azopyridine, which exhibit geometric bias in their binding-site orientation. Based on the crystal structures, we noticed a preferential binding of hydrogen bond donors with 3,3‟-azopyridine and both hydrogen and halogen bond donors with 4,4‟-azopyridine. This shows that the two types of donors are very comparable and their binding preference is governed by the geometric complementarity between the donor-acceptor pair. Finally, we explored the scope of using co-crystallization for tuning the physical properties of two agrochemicals, cyprodinil and terbuthylazine. The crystal structures of the actives with a series of even chain diacids displayed structural consistency in the primary motifs within the two groups, while few differences were observed in the packing arrangement and secondary interactions. By forming co-crystals we were able to improve the solubility and melting point of cyprodinil, while ensuring that the hygroscopicity of the active was unaltered.

The increasing environmental impact of society has created the need for the modification of current and the implementation of new industrial processes which are less environmentally harmful. However, these new or modified processes must be less material-, time-, and cost-intensive such that they are more economically beneficial than the processes they are to supplant. The described research was inspired by these two ideas and is comprised of two projects, both focused on the creation of recyclable, CO2-switchable methods of separating organic compounds. The development and optimization of switchable water, a CO2-switchable ionic strength aqueous solvent is described. The solvent system, an amine/aqueous mixture, had the ability to switch from low to high ionic strength via the application and removal of CO2. This solvent system was able to achieve salting-out of water-miscible organics in comparable amounts to several inorganic salts typically used for salting-out. The switchable water system was explored for use in several industrial applications. A homogeneous catalysis recycling system was developed for the hydroformylation of styrene. A catalyst was able to be recovered and recycled five times with minimal loss of activity. The use of switchable water to expedite the settling of clay suspensions was also explored. Switchable water, when used as process water did not settle bulk clay solids as quickly as a CO2-only treatment, but did however increase the settling rate of small clay fines resulting in lower turbidities of the supernatant. The solvent could be recovered from settled clay suspensions and recycled up to three times. Finally, efforts towards the realization of CO2-switchable chiral resolving agents are presented. It is hypothesized that chiral nitrogenous bases could be used as switchable resolving agents by forming diastereomeric salt pairs with racemic alcohols via the application of CO2. After separation of the diastereomers, removal of CO2 would afford the resolved alcohol enantiomers and the chiral base. Efforts towards the synthesis of a library of chiral nitrogenous bases and the screening of their reactivity with CO2-treated alcohols are described. Several bases were generated, but the necessary reactivity between the bases and the racemic alcohols in the presence of CO2 was not observed. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-12-20 16:26:50.635

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / A series of nanoparticle synthesis methods were devised with the aim of controlling shape. CuO nanorods were synthesized by a hydrothermal treatment with different chemical combinations. Physical parameters: concentration, temperature, and aging time greatly affected the size, morphology and the composition of nanorods. These CuO nanomaterials were reduced to metallic copper at elevated temperature by 4% H[subscript]2 diluted in helium while preserving the morphology. The CuO and Cu nanomaterials were employed for near infra-red (NIR) diffuse reflectance. Among them, CuO nanorods were found to be the best NIR diffuse reflectors, indicating potential application as NIR obscurants. Cu[subscript]2O and its composite samples with different morphologies, some with unique morphologies, were synthesized by reducing Cu[superscript]2[superscript]+ precursors without using any surfactant. The effects of change of Cu-precursors, reducing agents, and other physical conditions such as temperature and pressure were investigated. Since Cu[subscript]2O is a semiconductor (E[subscript]g ~ 2.1 eV), these samples were used as photocatalyst for the degradation of methyl violet B solution under UV-vis light and as dark catalysts for decomposition of H[subscript]2O[subscript]2 to investigate the effect of morphology. The photocatalytic activity was found to be morphology dependent and the dark catalytic activity was found to be dependent on both surface area and morphology. Mixed oxides of MgO and TiO[subscript]2 with different ratios, and pure TiO[subscript]2 were synthesized by two methods—flame synthesis and aerogel. These mixed oxides were employed as photo-catalysts under UV-vis light to oxidize acetaldehyde. The mixed oxides with low content of MgO (~ 2 mole %) were found to be more UV active photo-catalysts for the degradation of acetaldehyde than the degradation by TiO[subscript]2. The mixed oxides prepared by the aerogel method were found to be superior photo-catalysts than the mixed oxides of equal ratio prepared by flame synthesis. Silica aerosol gels were prepared by two methods: detonation and flame synthesis. Hexamethyldisiloxane (HMDSO) was used as a precursor during the detonation at different conditions. Interestingly, spherical silica nanoparticles were found to be formed by the detonation. Relatively smaller silica nanoparticles with larger volume fraction were found to be favorable for the formation of silica aerosol gels. During the flame synthesis, the silicon precursors, dimethoxydimethylsilane (DMDMS) and HMDSO, were used. Different shapes—spherical, oval, and non-spherical—and sizes of silica particles were formed. These silica nanomaterials were almost amorphous, and they might have many potential applications.

While the catalytically powerful [Cu,Zn] superoxide dismutase (SOD1) possesses great potential as a therapeutic, unfavorable properties in circulation limit its use in clinical medicine. The small, water soluble dimer is rapidly excreted by the kidney. Previous initiatives have been used to increase the mass of the enzyme (PEGylation, liposome encapsulation). This has resulted in highly heterogeneous mixtures of modified SOD1, which are difficult to characterize. Furthermore, these modified proteins have utilized foreign material that has shown to elicit an inflammatory response. We developed an improved strategy that creates a homogenous high molecular weight SOD1 based on combinations of the protein itself. This was accomplished through the addition of a site-specific, azide functionalized cross-linker to unmodified SOD1, followed by the conjugation of SOD dimers using CuAAC and a bis-alkyne linker to form a 64 kDa SOD tetramer. The final product, bis-SOD, presents the fully catalytic activity of the combined proteins.

While the catalytically powerful [Cu,Zn] superoxide dismutase (SOD1) possesses great potential as a therapeutic, unfavorable properties in circulation limit its use in clinical medicine. The small, water soluble dimer is rapidly excreted by the kidney. Previous initiatives have been used to increase the mass of the enzyme (PEGylation, liposome encapsulation). This has resulted in highly heterogeneous mixtures of modified SOD1, which are difficult to characterize. Furthermore, these modified proteins have utilized foreign material that has shown to elicit an inflammatory response. We developed an improved strategy that creates a homogenous high molecular weight SOD1 based on combinations of the protein itself. This was accomplished through the addition of a site-specific, azide functionalized cross-linker to unmodified SOD1, followed by the conjugation of SOD dimers using CuAAC and a bis-alkyne linker to form a 64 kDa SOD tetramer. The final product, bis-SOD, presents the fully catalytic activity of the combined proteins.

Electron transport and recombination are two competing factors within Dye-Sensitized Solar-Cells (DSSCs) which have a great influence on their performance. By drastically increasing the speed of electron transport to the electrode, it is believed that these cells could reach new record efficiencies. To achieve this result, an all-in-one integrated DSSC was attempted, in which the electrode material is extended into the active area of the solar cell material. The research conducted can be separated into two stages. The first stage is the production of a three-dimensional macroporous electrode. The second stage is the production of an all-in-one DSSC by a simplified co-casting technique. The structures and materials presented were examined using electron microscopy, X-ray Diffraction, 4-point and 2-point probe electrical measurements as well as experimentally by the testing of solar cells. The methods of fabrication, characterization, experimental results and future directions are also presented.

Electron transport and recombination are two competing factors within Dye-Sensitized Solar-Cells (DSSCs) which have a great influence on their performance. By drastically increasing the speed of electron transport to the electrode, it is believed that these cells could reach new record efficiencies. To achieve this result, an all-in-one integrated DSSC was attempted, in which the electrode material is extended into the active area of the solar cell material. The research conducted can be separated into two stages. The first stage is the production of a three-dimensional macroporous electrode. The second stage is the production of an all-in-one DSSC by a simplified co-casting technique. The structures and materials presented were examined using electron microscopy, X-ray Diffraction, 4-point and 2-point probe electrical measurements as well as experimentally by the testing of solar cells. The methods of fabrication, characterization, experimental results and future directions are also presented.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / The work presented in this thesis has demonstrated that supramolecular synthons can be used to make multicomponent crystals, and various synthons can be combined to make supermolecules. The synthons can also be used to construct nanoscale assemblies. Molecules containing single and multiple hydrogen-bond (HB) and halogen-bond (XB) acceptor sites have been synthesized in an effort to carry out supramolecular synthesis in order to establish a reliable hierarchy for intermolecular interactions. Pyrazole-based molecules have been made, combined with various carboxylic acids, and characterized using infrared (IR) spectroscopy to give a success rate of 55-70%. Reactions that gave a positive result were converted to solution experiments, and crystals were grown and characterized using single-crystal X-ray diffraction (XRD). The co-crystals display infinite 1-D chains with the intended stoichiometry and structural landscape on 6/6 occasions. The salts, on the other hand, display unpredictable stoichiometry and structural landscape on 5/5 occasions. Furthermore, the electrostatic charge on the primary hydrogen-bond acceptor, N(pyz), can be altered by adding a nitro, R-NO2, covalent handle to the backbone of the pyrazole molecule. Addition of a strongly electron withdrawing group significantly lowered the charge on the pyrazole nitrogen atom and, in turn, lowered the supramolecular yield to 10%. Ditopic molecules containing pyrazole and pyridine on the same molecular backbone were synthesized and characterized using 1H NMR. The molecules were co-crystallized with carboxylic acids, and the resulting solids were characterized using IR spectroscopy. The solids could then be classified as co-crystal or salt using specific markers in the IR spectrum. Single-crystal XRD was used to observe the intermolecular interactions in the co-crystals and salts, and the co-crystals were assigned to two groups: Group 1 (2) and Group 2 (2). The salts (4) show more unpredictability with stoichiometry and structural landscape. A library of ditopic molecules containing triazole and pyridine acceptor sites were synthesized and characterized using 1H and 13C NMR. The molecules were co-crystallized with carboxylic acids and the resulting solids were characterized using IR spectroscopy which demonstrated a 100% supramolecular yield whenever a pyridine moiety was present, consistent with results from Chapter 3. Single-crystal XRD was used to identify the intermolecular interactions in the co-crystals (2) and salt (1), and the results show that triazole can compete with pyridine for hydrogen bond donors. A library of ditopic molecules was also used for halogen-bonding (XB) studies with a series of activated iodine and bromine-based donors. The results show that iodine donors have a higher success rate range (12.5-75%) compared to bromine donors (16.7-50%) based on results obtained from IR spectra. Furthermore, the results from the XRD show that pyrazole nitrogen atoms can compete with pyridine for forming XB, and two groups of supramolecular synthons were observed. Finally, relatively weak non-covalent interactions, HB and XB, can influence the assembly of nanoparticles based on IR spectroscopy and TEM images. The assembly of the particles is influenced by specific capping ligands, which were synthesized and characterized using 1H, 13C and 19F NMR. The results demonstrate that relatively weak non-covalent interactions based on HB and XB interactions can influence nanoparticle assembly.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeröy / A series of four bifunctional ligands based on β-diketonate moieties bearing methyl, chloro, bromo and iodo substituents and their corresponding Cu(II) complexes were synthesized and crystallographically characterized in order to explore the possibility of using relatively weak halogen…halogen contacts for the directed assembly of predictable architectures in coordination chemistry. The four ligands have characteristic O–H...O intramolecular hydrogen bonds, and the structures of the halogenated ligands contain extended 1-D architectures based on C-O...X halogen bonds, which can be explained on the basis of electrostatic considerations. The corresponding Cu(II) complexes show a constant coordination chemistry for all the ligands, wherein the metal ion sits in a slightly distorted square-planar pocket, without any coordinated or uncoordinated solvent molecules. Furthermore, the absence of halogen-bonds in the coordination complexes is due to the depleted charge on the potential halogen-bond acceptors. As a result, the halogen-bonds are unable to compete with the inherent close packing in the crystal lattice, and thus display a head to head close-packed motif for methyl, chloro, and bromo, substituted Cu(II) complexes. The enhanced polarizability of the iodine atom, produces a more electropositive surface which means that this structure cannot accommodate a linear head-to-head arrangement due to electrostatic repulsion, and thus a unique close-packed structure very different from the three iso-structural complexes is observed for the iodo substituted Cu(II) complex.(1) Oximes offer great opportunities in supramolecular chemistry (hydrogen-bond donors), as well as in coordination chemistry (strong coordinating ligands). Hence, we established a versatile and robust mechanochemical route to aldehyde/ketone–oxime conversions for a broad range of aldehydes(2) and ketones(3) via a simple mortar–pestle grinding method. The relative reactivity of aldehydes vs. ketones under these conditions was also explored, along with an examination of the possible connection between reactivity and electronic substituent effects. The growing interest in the oxime (RR′C═N–OH) functionality, and a lack of the systematic examinations of the structural chemistry of such compounds, prompted us to carry out analysis of intermolecular oxime···oxime interactions, and identify the hydrogen-bond patterns for four major categories of oximes (R′ = −H, −CH3, −NH2, −CN), based on all available structural data in the CSD, complemented by three new relevant crystal structures.(4) It was found that the oximes could be divided into four groups depending on which type of predominant oxime···oxime interactions they present in the solid-state: (i) O–H···N dimers (R22(6)), (ii) O–H···N catemers (C(3)), (iii) O–H···O catemers (C(2)), and (iv) oximes in which the R′ group accepts a hydrogen bond from the oxime moiety catemers (C(6)). In order to explore and establish a hierarchy between hydrogen (HB) and halogen (XB) bonds in supramolecular architectures, we designed and synthesized two ditopic HB/XB donors, and screened them with a series of 20 HB acceptors. IR was used as a preliminary and reliable tool to gather information on the presence/absence of HB/XB in the different cases. We were able to get the solved single-crystal data for three of the 40 reactions. In two out of two cases with symmetric ditopic acceptors, both HB and XB were present leading to 1-D infinite chains, which suggests that in a system of “equal opportunities”, both these interactions can be tolerant of each other. In the only case with asymmetric ditopic acceptor, the HB donor binds to the best acceptor, whereas XB donor binds to the second best acceptor. This selectivity can be rationalized on the basis of electrostatic considerations, where the HB donor was shown to have a higher molecular electrostatic potential than the XB donor. Finally, we designed and synthesized a versatile and dynamic metallomacrocycle based on the 2,2'-bipyridyl backbone capable of controlling the metal-metal distance within the macrocycle cavity. The macrocycle was synthesized by high-dilution method and characterized by several spectroscopic techniques (IR, NMR, Mass, UV-Visible). Also, the macrocycle:Cu(II) stoichiometric ratio was determined by Job’s continuous variation method using UV-Visible spectroscopy, and was found to be 1:2, respectively. (1) Aakeröy, C. B; Sinha, A. S.; Chopade, P. D.; Desper, J. Dalton Trans. 2011, 40, 12160. (2) Aakeröy, C. B.; Sinha, A. S.; Epa, K. N.; Spartz, C. L.; Desper, J. Chem. Commun. 2012, 48, 11289. (3) Aakeröy, C. B.; Sinha, A. S. RSC Adv. 2013, 3, 8168. (4) Aakeröy, C. B.; Sinha, A. S.; Epa, K. N.; Chopade, P. D.; Smith, M. M.; Desper, J. Cryst. Growth Des. 2013, 13, 2687.