<p> Thin films (~100 nm) have been prepared of the prototypical spin-crossover complex Fe(phen)₂(NCS)₂ (phen = 1,10-phenanthroline). Initial attempts to prepare these films by direct vapor deposition yielded films of a different material. Through extensive FT-IR, Raman, UV-Vis, and x-ray photoelectron spectroscopy it is shown that these as-deposited films are the ferroin-based tris complex [Fe(phen)₃](SCN)₂. Structural characterization by AFM and powder XRD reveals them to be smooth and amorphous. When heated, the [Fe(phen)₃](SCN)₂ films are converted first to Fe(phen)₂(SCN)₂ and then to a third species postulated to be Fe(phen)(NCS)₂ which is likely a one-dimensional coordination polymer. On the other hand, deposition from Fe(phen)₂(NCS)₂ onto heated substrates produces a mixture of these three materials. The identity of the Fe(phen)₂(NCS)₂ films is proved by additional spectroscopic, structural, and magnetic characterization. Magnetometry reveals them to remain spin-crossover active albeit with a more gradual and incomplete spin-transition than the bulk material. The films are found to be granular in nature and deep crevices were observed at the grain boundaries. Within the optical microscope, the coloring of the grains is seen to be dependent upon sample orientation. Powder XRD indicates texturing of crystalline domains where the crystallographic c-axis is parallel to the surface normal. This represents a new process for production of Fe(phen)₂(NCS)₂ films.</p><p> With the aim of realizing the potential for spin-crossover materials to modulate electrical conduction and vise versa, electrical characterization has been performed as a function of temperature on vertical junction devices incorporating the prepared Fe(phen)₂(NCS)₂ films. In order to prevent penetration of the top electrode through the cracks and crevices in the organometallic layer, a multiple sequential deposition and annealing process was developed to produce films with a continuous surface topography. A small change in the weak electrical conductivity of these devices appears at the spin transition temperature, demonstrating for the first time in this important material a coupling of the electrical conductivity and magnetic spin state. Here, the HS state has a higher electrical conductivity. Incorporation of LiF interfacial layers between the Fe(phen)₂(NCS)₂ and the metal electrodes improves conduction slightly but tunneling still appears to be the current-limiting mechanism. Electrical measurements were also performed on devices made with the related complex [Fe(phen)₃](SCN)₂. Such films were much more conductive&mdash;as good as other typical organic semiconductor materials. All together, this work establishes the potential for this family of complexes to be incorporated into thin-film based electrical devices whose operation is based on the spin-crossover effect or otherwise.</p>

Water pollution is a major concern worldwide. Bacteria, viruses and fungi present in drinking water cause various diseases as a result of poor hygienic conditions in developing countries. Similarly, presence of microorganisms in drinking water is a threat to public health in developing world due to poor hygienic condition. Numerous disinfectants and biocides are used for inhibiting the growth of pathogenic microbial contamination, producing carcinogenic by-products which are dangerous to human health. This work involved the synthesis, characterisation and application of novel multifunctional nanocomposites by the modification of cost effective available materials for antimicrobial treatment of contaminated water and the detection of specific DNA associated with water-borne bacteria. A series of multifunctional nanocomposites composed of commercially available carbon (activated charcoal and multi-walled carbon nanotubes), and silica-based materials such as diatomeous earth, celatom-80 and celatom-14 were modified with silver and iron oxide nanoparticles via a simple one-pot synthesis protocol in order to incorporate antimicrobial and superparamagnetic properties. The resultant materials have been tested for antimicrobial efficiency using model water system containing Gram-negative Escherichia coli (E. coli) K12 and Gram-positive Staphylococcus. aureus (S. aureus) microorganisms. It was found that all materials ranging from 10 to 200 μg/mL produced excellent inhibition of S. aureus and E. coli. All nanocomposites have been fully characterised by several physico-chemical techniques such as Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Fluorescence (XRF), Energy Dispersive X-ray Analysis (EDAX), Fourier Transform Infrared Spectroscopy (FT-IR), Nitrogen gas adsorption and (BET) surface area analysis. Surface area of the materials measured in range of 5 to 560 m2/gm. XRF along with EDAX/SEM analyses have been used for the confirmation of silver and iron oxide presence in the nanocomposite materials. TEM images showed nano-sized silver particles with an average diameter of 15-17 nm and iron oxide (magnetite) nanoparticles with an average diameter of 30 nm embedded into the nanocomposites. FT-IR spectroscopy measurement confirmed the presence of Fe-O bonding of iron oxide nanoparticles due to a characteristic stretching vibration at 570 cm-1. Powder X-ray Diffraction (XRD) measurements confirmed the crystalline structure of the iron oxide nanocomposite mostly magnetite (Fe3O4). Nitrogen gas adsorption-desorption experiments suggests the presence of average pore diameter 28 to 79 Å, micropore volume: 0.01 to 0.16 cm³/g, and surface area 5 to 560 m2/g. Gram-negative E. coli K12 and Gram-positive S. aureus bacteria were used for anti-bacterial activity study where the nutrient agar was used for the growth of the bacteria. The antimicrobial effect of the nanocomposites was quantified by counting the number of colonies (colony forming unit, CFU/mL) grown on the media compared with a blank solution. Different concentrations (0.2 µg/mL to 300 µg/mL) of the nanocomposite materials were used for this study. MBC of QM1-3 and QM2-3 was found 10 µg/mL for the S. aureus and 30 µg/mL for E. coli K12, while other samples of QM3-3, QM4-3 and QM5-3 were higher such as 30 µg/mL for the S. aureus and 100 to 200 µg/mL for E. coli. All experiments were performed in triplicate and the data presented are the mean values of triplicate experiments ± standard deviation. Detection of water-borne microorganisms is the second application of the developed nanocomposites via surface modification with specific oligonucleotides sequences of E. coli gene followed by hybrid capture with complementary sequence. It was observed that multi-walled carbon nanotubes, activated charcoal and diatomeous earth gave good and satisfactory results (0.384 to 0.400 nmol/mg) in hybrid capture of complementary oligonucleotides sequences in model assay. Surface modified optimum materials (carbon nanotubes and activated carbon) with efficient hybrid capture were also efficient in detecting amplicon of 97 base pairs (bp) of E. coli specific genome by PCR experiment.

<p> In this thesis I present the synthesis and characterization of materials exhibiting frustrated magnetism. In Chapter 1 I describe magnetic frustration and some of the magnetic states that can arise from it followed by the background on iridates and platinates with honeycomb structures and rare earth pyrochlores. </p><p> In Chapter 3 I discuss my work on the synthesis and properties of ternary sodium iridates with formulas Na_xM_2/3Ir_1/3O₂ and Na_xM_1/3Ir_2/3O₂ (M = Mn, Fe, Co, Ni, Cu, Zn). The ternary iridates are based on the honeycomb compound Na₂IrO₃ but show more disorder in the honeycomb layer than the parent. The six new compounds are all spin glasses but show distinct magnetic properties from one another. </p><p> In Chapter 4 I continue my work on honeycombs by exploring new ternary sodium platinates. These three new compounds with formulas Na₃MPt₂O_6+x (M = Mg, Cu, Zn) are structurally very similar to the iridates discussed in Chapter 2 but have non-magnetic Pt⁴⁺ in place of magnetic Ir⁴⁺. The Mg and Zn variants are non-magnetic while the Cu variant is paramagnetic at 2 K. </p><p> Chapter 5 is a synchrotron X-ray diffraction study of the magnetically frustrated rare earth pyrochlores Ho₂Ti₂O₇, Er₂Ti₂O₇ and Yb₂Ti₂O₇. Previous neutron scattering studies have shown reflections that are forbidden by the assigned space group <i>Fd-3m,</i> therefore high intensity, high resolution X-ray diffraction data was collected to determine if the reflections are present. Slight variations in sample stoichiometry were studied to account for possible sample variation. The forbidden reflections are absent from the X-ray diffraction patterns, providing strong evidence that the extra reflections in neutron scattering experiments are not structural in origin.</p>

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 253-268).

<p> Metal&ndash;organic frameworks are a rapidly expanding family of crystalline porous materials and have shown great promise to address various challenges such as gas storage and separation due to their well-defined pore size and unprecedented tunability in both composition and pore geometry. Here, we have synthesized and structurally characterized a number of new metal- organic framework materials and studied the effects of ligands and metal types on the construction and properties of metal&ndash;organic frameworks. To probe the effects of functional groups on ligands, two zinc-based three-dimensional frameworks have been synthesized. They consist of zinc-triazolate layers pillared by dicarboxylates with different functional groups. In addition, a very unusual magnesium metal-organic framework material has been made. It consists of novel magnesium acetate chains crosslinked by 1,4-benzenedicarboxylate into a three-dimensional framework with large channels. The phase purity and structures of these materials have been determined by powder and single-crystal X-ray diffraction. Their thermal stability and sorption a properties for gas molecules such as N₂, H₂, and CO₂ have also been studied. </p><p>

<p> &beta;-Diketones are well known to form metal complexes with practically every known metal and metalloid. Metal complexes of fluorinated &beta;-diketones generally exhibit increased volatility and thermal stability compared to the non-fluorinated analogues, and thus are used extensively in various chemical vapor deposition (CVD) processes for the deposition of metal, simple or mixed metal oxides, and fluorine-doped metal oxide thin films. Furthermore, the electron-withdrawing nature of the fluorinated ligand enhances the Lewis acidity of a coordinatively unsaturated metal center which facilitates additional coordination reactions. The physical and structural properties of fluorinated &beta;-diketonate complexes are discussed in Chapter 1 and a few key application examples are given.</p><p> The focus of this work is the synthesis and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated metal complexes of bis(pentafluorobenzoyl)- methanide (L, C₆F₅COCHCOC₆F₅^-). In Chapter 2, we present the preparation and isolation of the unsolvated complex [Cu(L)₂] in pure crystalline form for the first time. We subsequently investigated the reaction of unsolvated [Cu(L)₂] with sodium hexafluoroacetylacetonate [Na(hfac)] in a solvent-free environment. This reaction allowed the isolation of the first heterometallic Na&ndash;Cu diketonate [Na₂Cu₂(L)₄(hfac)₂] structurally characterized by single crystal X-ray crystallography. Thermal decomposition of [Na₂Cu₂(L)₄(hfac)₂] was investigated for its potential application in MOCVD processes. In the final chapter, we present the first exploration of the anhydrous synthesis of Co(II) complexed with bis(pentafluorobenzoyl)methanide in order to produce a complex without ligated water. Single crystal X-ray crystallographic investigations revealed the isolation of the ethanol adduct, [Co₂(L)₄(C₂H₅OH)₂], and following the removal of ethanol, a 1,4-dioxane adduct, [{Co₂(L)₄}₂(C₄H₈O₂)]. </p><p> In this work, we have provided the first investigation of the synthesis, isolation and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated Cu(II) and Co(II) complexes of bis(pentafluorobenzoyl)methanide ligand. These studies demonstrate how the electrophilicity of a coordinatively unsaturated metal complexed to highly-fluorinated &acirc;-diketone ligands can be utilized for the formation of new adducts or new and interesting heterometallic complexes. This body of work provides a basis upon which future research into unsolvated and unligated bis(pentafluorobenzoyl)methanide metal complexes can expand.</p><p>

<p> In the past, we have demonstrated that 1,8-anthraquinone-18-crown-5 (1) and its heterocyclic derivatives act as luminescent hosts for a variety of cations of environmental and clinical concern. We report here a series of heteroatom-substituted macrocycles containing an anthraquinone moiety as a fluorescent signaling unit and a cyclic polyheteroether chain as the receptor. Sulfur, selenium, and tellurium derivatives of 1,8-anthraquinone-18-crown-5 (<b>1</b>) were synthesized by reacting sodium sulfide (Na₂S), sodium selenide (Na₂Se) and sodium telluride (Na₂Te) with 1,8-bis(2-bromoethylethyleneoxy)anthracene - 9,10-dione in a 1:1 ratio (<b>2,3,</b> and <b>6</b>). These sensors bind metal ions in a 1:1 ratio (<b>7</b> and <b>8</b>), and the optical properties of the new complexes were examined and the sulfur and selenium analogues show that selectivity for Pb(II) is markedly improved as compared to the oxygen analogue <b>1</b> which was competitive for Ca(II) ion. </p><p> Selective reduction of <b>1</b> yields secondary alcohols where either one or both of the anthraquinone carbonyl groups has been reduced (<b> 15</b> and <b>9</b>). A new mechanism for the fluorescence detection of metal cations in solution is introduced involving a unique keto-enol tautomerization. Reduction of <b>1</b> yields the doubly reduced secondary alcohol, <b> 9. 9</b> acts as a chemodosimeter for Al(III) ion producing a strong blue emission due to the formation of the anthracene fluorophore, <b>10,</b> via dehydration of the internal secondary alcohol in DMSO/aqueous solution. The enol form is not the most thermodynamically stable form under these conditions however, and slowly converts to the keto form <b>11.</b> </p><p> Currently we are focusing on cucurbituril derivatives, also described as molecular clips due to their folded geometry used as molecular recognition hosts. We first investigated the synthesis and characterization of aromatic methoxy/catechol terminated cucurbituril units that act as hosts for small solvent molecules, such as CH₂Cl₂, CH₃CN, DMF, and MeOH, through dual pi&hellip;H-C T-shaped interactions. We have calculated the single-point interaction energies of these non-covalent interactions and compared them to the dihedral angle formed from the molecular clip. We have also synthesized a molecular clip that contains terminal chelating phenanthroline ligands. This tetradentate ligand shows 2:3 metal:ligand binding with Fe(II) and 1:2 metal:ligand binding with Co(II) and Ni(II) cations.</p><p>

The main theme of this research is to understand the structure-property evolution during crystallization of a semicrystalline thermoplastic polymer. A combination of techniques including rheology, small angle light scattering, differential scanning calorimetry and optical microscopy are applied to follow the mechanical and optical properties along with crystallinity and the morphology. Isothermal crystallization experiments on isotactic poly-1-butene at early stages of spherulite growth provide quantitative information about nucleation density, volume fraction of spherulites and their crystallinity, and the mechanism of connecting into a sample spanning structure. Optical microscopy near the fluid-to-solid transition suggests that the transition, as determined by time-resolved mechanical spectroscopy, is not caused by packing/jamming of spherulites but by the formation of a percolating network structure. The effect of strain, Weissenberg number (We ) and specific mechanical work (w) on rate of crystallization (nucleation followed by growth) and on growth of anisotropy was studied for shear-induced crystallization of isotactic poly-1-butene. The samples were sheared for a finite strain at the beginning of the experiment and then crystallized without further flow (Janeschitz-Kriegl protocol). Strain requirements to attain steady state/leveling off of the rate of crystallization were found to be much larger than the strain needed to achieve steady state of flow. The large strain and We>1 criteria were also observed for morphological transition from spherulitic growth to oriented growth. An apparatus for small angle light scattering (SALS) and light transmission measurements under shear was built and tested at the University of Massachusetts Amherst. As a new development, the polarization direction can be rotated by a liquid crystal polarization rotator (LCPR) with a short response time of 20 ms. The experiments were controlled and analyzed with a LabVIEW™ based code (LabVIEW™ 7.1) in real time. The SALS apparatus was custom built for ExxonMobil Research in Clinton NJ.

Polymeric betaines gain considerable attention for their interesting solution properties, but even more so, for their favorable bio- and haemocompatible properties. When incorporated into materials or used as surface coatings, some of these zwitterionic polymers strongly resist protein absorption due to their hygroscopic nature, making betaines promising candidates for medical diagnostics, drug delivery, and tissue engineering applications. This dissertation introduces novel norbornene-based polybetaines as foundational materials for biological applications, including non-fouling coatings and antimicrobial macromolecules. Sulfo- and carboxybetaines, composed of backbones that do not contain hydrolyzable units under physiological conditions, as well as new polymers that carry a dual functionality at the repeat unit level, coupling a zwitterionic functionality with an alkyl moiety varied to adjust the amphiphilicity of the overall system, are introduced. How structural changes, backbone chemistry, hydrophilicity/amphiphilicity, and coating surface roughness impact their non-fouling properties is investigated.

Co-continuous structures generated from the phase separation of polymer blends present many opportunities for practical application. Due to the large interfacial area in such structures and the incompatibility between the components, such non-equilibrium structures tend to coarsen spontaneously into larger sizes and eventually form dispersed morphologies. Here, we utilize various strategies to kinetically stabilize the co-continuous structures in polymer blend systems at nano- to micro- size scales. In the partially miscible blend of polystyrene and poly(vinyl methyl ether), we took advantage of the spinodal decomposition (SD) process upon thermal quenching, and arrested the co-continuous micro-structures by the addition of nanoparticles. In this approach, the critical factor for structural stabilization is that the nanoparticles are preferentially segregated into one phase of a polymer mixture undergoing SD and form a percolated network (colloidal gel) beyond a critical loading of nanoparticles. Once formed, this network prevents further structural coarsening and thus arrests the co-continuous structure with a characteristic length scale of several microns. Our findings indicate that a key to arresting the co-continuous blend morphology at modest volume fractions of preferentially-wetted particles is to have attractive, rather than repulsive, interactions between particles. For the immiscible blend of polystyrene and poly(2-vinyl pyridine) (PS/P2VP), we presented a strategy to compatibilize the blend by using random copolymers of styrene and 2-vinylpyridine, controlling the degree of immiscibility between PS and P2VP. Based on such compatibilization, co-continuous structured membranes, having characteristic size down to tens of nanometers, were fabricated in a facile way, via the solvent-induced macrophase separation of polymer blend thin films. The feature size was controlled by controlling the film thickness and varying the molecular weight of the PS homopolymer and the random copolymers. As the processing method (solution casting) is simple and the structures are insensitive to the solvent or substrate choices, this approach shows great potential in the large scale fabrication of co-continuous nanoscopic templates on flexible substrates via roll-to-roll processes. Moreover, we proposed a quasi-binary blend system based on the PS/P2VP pair with the addition of a common solvent. An experimentally accessible phase mixing temperature was achieved, and the co-continuous morphologies were generated via thermally induced spinodal decomposition. The addition of solid particles significantly slowed down the coarsening kinetics and, in some cases, arrested the co-continuous structures at ∼6 µm for a short period of time. This study suggests an alternative means to achieve co-continuous structures in polymer solutions and also provides better understanding of the thermodynamics and kinetics of polymer blend phase separation. Our research demonstrates several means of kinetically trapping the non-equilibrium interconnected structures at sub-micron to tens-of-nanometer size scales that are germane to several functions including active layers of photovoltaic cells and polymer-based membranes.