The "push-pull" electronically substituted polymers poly(2 (5) -bromo-5 (2) -n-hexyloxy-1,4-phenylene vinylene), poly(2 (5) -chloro-5 (2) -n-hexyloxy-1,4-phenylene vinylene) and poly(2 (5) -fluoro-5 (2) -n-hexyloxy-1,4-phenylene vinylene) were synthesized by a soluble precursor method and were used to fabricate light emitting diode (LED) devices. Thermal elimination of the polyether precursors gives final conjugated polymers as flexible red films. Precursor polymers can be spin-cast from solutions onto indium/tin oxide (ITO) pretreated quartz plates, then thermally converted to the final red polymers. Light emitting diode fabrication is then completed by the thin film vapor deposition of calcium, followed by aluminum. LED devices of the "push-pull" polymers give light emission in the 620-635 nm range. Two fluorinated polymers, poly(2-fluoro-1,4-phenylene vinylene) and poly(2,5-difluoro-1,4-phenylene vinylene) were investigated for their electroluminescent (EL) properties. LED's using these materials as emissive layers show substantial EL wavelength shifts (560 nm and 600 nm, respectively) relative to emission from unsubstituted poly(1,4-phenylene vinylene) (565 nm). These differences in EL emission can be attributed to the electronic effects of fluorine substitution. Synthetic strategies were developed for copolymeric materials based on poly(1,4-phenylene vinylene). The alternating block copolymer, poly (1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene- 3,5-dimethoxy-1,4-phenylene) was synthesized by a modified Wittig polymerization utilizing trialkyl phosphonium salts. This resulted in a regiospecific trans-olefination reaction when compared to polymeric materials synthesized through the use of common triaryl-phosphonium salts. Harsh post-Wittig isomerization procedures using I$\sb2$ were bypassed as a result of the high trans-cis ratio of the final copolymer. It was fully characterized using the standard spectroscopic techniques as well as elemental analysis. Light-emitting single-layer diodes using the soluble, processible copolymer as the emitting layer gives green light with an electroluminescence maximum at 513 nm.

Seven nondisjoint dinitrenes were produced in order to determine the length of chain conjugation that would still allow effective inter-nitrene exchange communication. The dinitrenes were generated in frozen matrices of 2-methyltetrahydrofuran by photolysis of appropriate diazides by a 1000-Watt xenon arc lamp and studied by electron spin resonance (ESR) spectroscopy. Conjugation lengths varied from 17 to 29 atoms between spin sites. In each case, it was determined by variable temperature analysis that the high-spin quintet state was the ground state. Six other dinitrenes were also produced which surprisingly exhibited quintet state spectra at 77 K, despite having possible quinoid biradical resonance structures. Possible reasons for the latter observation include conformational torsion effects, combined with a preference to retain benzenoid sextet resonance structures. In addition to the molecules produced in this lab, numerous samples of mono-, di-, and tri-azidopyridines were jointly studied with Dr. Sergei Chapyshev of the Russian Institute of Chemical Physics. These systems were studied by ESR spectroscopy. The effect of the pyridine heteroatom upon the ESR spectroscopy of these systems was found to be considerable, relative to simpler aryl nitrenes. Several of the triazide of systems were deemed to be ground state septet systems.

Acylated aminopyridines provide models for specific flavoenzyme-cofactor interactions, allowing isolation and observation of the effects of hydrogen bonding on flavin NMR. To determine the relative hydrogen bond affinities of O(2) and O(4) of the flavin, a 2-aminopyridine based receptor was investigated. Additionally, this receptor allowed the effects of hydrogen bonding at O(2) and O(4) on the electron distribution in the flavin nucleus to be determined using $\sp{13}$C NMR. A new family of receptors for flavins based on 6-aryl-2,4-(acyldiamino)-s-triazines was synthesized. In these synthetic hosts, systematic variation of the spatially remote substituents on the 6-aryl ring altered the hydrogen bond donating abilities of the amide functionality and the hydrogen bond accepting properties of the triazine N(3). This variation resulted in a strong modulation of the efficiency of flavin binding, with association constants for the receptor flavin complexes ranging over an 8-fold range. In addition, the communication of electronic information over extended distances was also investigated. Polymers can provide relevant media for the modeling of biological processes, including molecular recognition. To explore this possibility, a diaminotriazine-functionalized polymer was synthesized, starting from Merrifield's peptide resin. This polymer selectively bound a flavin derivative through hydrogen bonding, efficiently extracting it from a chloroform solution, as monitored by UV-vis extraction studies. The temperature profile of this polymer-flavin binding was also investigated and compared to the analogous solution-phase triazine-flavin dyad. Hydrogen bonding and aromatic stacking are fundamental interactions in molecular recognition. These interactions are sensitive to the redox states of the components of the host-guest complex. To explore the interplay of recognition and redox processes, a system consisting of two hosts and one guest, where guest binding interactions (hydrogen bonding and aromatic stacking) were modulated via choice of redox state was examined. Proper choice of receptors then provided a device where the competition between the two hosts was controlled by the redox state of the guest. The efficient reversal of host preference in this assembly provided an electrochemically-controlled three-component, two-pole, molecular switch.

Magnetostructural investigations were carried out on pyrene-1-yl (Pyr) bearing nitronylnitroxide (NN) and iminoylnitroxide (IN) radicals. PyrNN gives two allotropes: one has spin-paired dyads with ΔE = J/k ≈ -178 K, and the other is only half spin-paired with ΔE = J/k ≈ -102 K and the other half paramagnetic. PyrIN also gives two allotropes, an anti conformation that is spin paired in the crystal lattice with ΔE = J/k = -410 K, and a syn conformation that is disordered and paramagnetic. PyrNN also was discovered to co-crystallize with C6F6 in 2:1 ratio to give chains of radical networks linked into networks exhibiting low dimensional 1-D or 2-D antiferromagnetic exchange behavior. Furthermore, PyrNN was discovered to form a 2:1:2 co-crystal with octafluoronaphthalene (OFN) and entrapped solvent dichloromethane (DCM), in which the radical is ``shepherded'' into forming chains of radical-radical contacts on the peripheries of (PyrNN-OFN-PyrNN)n pi-stacks, giving weak, low dimensional inter-radical antiferromagnetic (AFM) exchange interactions. Anthraquinone-substituted nitronylnitroxide radical (AntQNN) was synthesized and found to form two crystal polymorphs. Magnetostructural investigations carried on these indicated that both have antiferromagnetic (AFM) exchange behavior attributed to chain-type inter-radical contacts: one with J1D/k ≈ -3 K, and one with J1D/k ≈-17 K. Five different anthracene nitroxide-type biradicals were synthesized: 27AntdNN, 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Room temperature solution state, and frozen solution state electron spin resonance (ESR) studies were carried on all of these biradicals. Crystallographic packing information was successfully obtained for 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Magnetic susceptibility measurements were carried on 27AntdNN, 27AntdIN, 26AntdIN and 9Br27AntdNN. The NN derivatives showed both ferromagnetic (presumed intramolecular) and antiferromagnetic exchange interactions in the solid state. Four different anthraquinone nitroxide-type biradicals were synthesized: 27AntQdNN, 27AntQdIN, 26AntQdNN, 26AntdIN. ESR studies were carried on these biradicals, and showed that 27AntQdNN is not a stable organic radical. While ESR spectra confirmed that 27AntQdNN, 27AntQdIN are biradicals, ESR spectra with isolated monoradical behavior were obtained for 26AntQdNN, 26AntQdIN. Iodine substituted meta-phenylene nitroxide biradicals, IPhdNN, IPhNNIN, and IPhdIN were synthesized. Room temperature and frozen solution ESR studies showed triplet states with strong intramolecular spin interaction. Magnetic behavior and crystallography for IPhdIN (which incorporates DCM), showed halogen bonding between molecules that assists formation of chains between radical sites.

Geometrically hindered motions of a single large solute (particle or polymer) can be imaged in real time via optical microscopy. The dynamics of fluorescent colloidal particles near surfaces and in porous membranes were monitored using confocal microscopy. A method of analysis to estimate diffusivity of particles in the axial direction by observing their intensity fluctuations was developed. The intensity fluctuations correspond to the Brownian motion of the particles in the axial direction. The method was successful in capturing the hindered diffusion of particles close to surfaces and in pores. This study provides a novel route to monitor the dynamics of particles, including biomacromolecules, near surfaces, through porous substrates and biological tissues. Ionic liquid (IL) as a medium for room temperature preservation of biomacromolecules has been proposed and, to investigate the possibility, physicochemical and enzymatic properties of proteins in the neat hydrophilic IL, ethylmethyl imidazolium ethyl sulfate [EMIM][EtSO4] were studied. Spectroscopic techniques were employed to probe the secondary and tertiary structure of proteins whereas light scattering and viscometry were used to estimate the hydrodynamic size. The secondary structure of the protein was retained in the ionic liquid but the tertiary structure was found to change. Alterations in protein conformation/activity were investigated after transfer of the dissolved protein from the IL to buffer. Further, suitability of ionic liquid gels as protein encapsulation and preservation media was assessed.

The unique electronic, magnetic, and optical properties of nanoparticles (NPs) make them useful building blocks for nanodevices and biofabrication. Site-selective immobilization/deposition of NPs on surfaces at desired positions is an important fabrication step in realizing the potential of nanomaterials in these applications. In this thesis, my research has focused on developing new strategies for mono- and multilayered-NP deposition on surfaces, increasing the stability of NP-assembles upon various surfaces for practical use of NP-based devices. Chemically directed dithiocarbamate binding of amine groups to NPs in the presence of CS2 was used for enhancing the robustness of NP assembles. Such patterning methodologies have allowed me to use site-directed NP immobilization in applications as diverse as microcontact printing, nanomolding in capillaries, nanoimprint lithography, and photolithography. Also, I have developed a simple and reliable one-step technique to form robust dendrimer-NP nanocomposites using dithiocarbamate-based chemistry. These composites are able to encapsulate and release various therapeutics, providing controllable sustained release and to separate small molecules and biomacromolecules.

Rheology is a particularly useful tool for elucidating the nature of polymer structures. The polymer at the gel point, the critical gel, has a power-law relaxation modulus, G(t) = St$\sp{-n}$. This simple constitutive equation is an expression of structural self-similarity which evolves as a result of crosslinking. We tested the composition dependence of the critical gel properties--the strength S and the relaxation exponent n--by studying an array a precursor materials, with different chain length, stoichiometry, and diluent concentration. All materials studied exhibited power-law rheological behavior, however, the critical gel properties were found to depend on the precursor composition. Several end-linked polydimethylsiloxanes with various composition yielded n values between 0.18 and 0.92, which is almost the entire possible range (0 $<$ n $<$ 1), while the gel strength varied by over five decades. Series of experiments at different stoichiometry and dilution can be reduced with S = G$\sb0\lambda\sb0\sp{\rm n}$, where G$\sb0$ and $\lambda\sb0$ may be material characteristic constants. The rate of change of the dynamic modulus was found to scale as a power law of frequency. The exponent, termed the dynamic critical exponent, describes the evolution of mechanical properties. It appears to take on a universal value $\kappa$ = 0.21 $\pm$ 0.02. A simple constitutive equation in the form of a stretched exponential can model the evolution of mechanical properties very well.

A novel technique for the production of toughened polymers using LCST behavior as a mechanism for the production of rubbery domains is discussed. The polymer blend of isotactic polyvinylmethylether (PVME) with polystyrene (PS) is used. Synthesis, fractionation and characterization of isotactic PVME is reviewed. Thermodynamic effects of tacticity on miscibility are extensively investigated using light and neutron scattering. A simple critical point analysis is presented which indicates an entropic nature to the tacticity effect in this blend. Flory-Huggins-Staverman (F-H-S) theory is next applied to the tacticity effect. This more elaborate analysis also indicates an entropic nature to the tacticity effect. Accounting for polydispersity results in a predicted fractionation in the phase separated blends which is supported by mechanical data. F-H-S theory was used to generate a functional form for the interaction parameter in terms of the temperature and composition dependence of miscibility. From these functions a dramatic shift in the kinetics of phase separation with tacticity is predicted. Experimental data affirms this prediction. A novel, modified Cahn-Hillard analysis is presented for analysis of intermediate stages. Neutron scattering data yields the composition and temperature dependence of the statistical segment length, b, of tactic PVME. A functional form for b is derived which predicts the equilibrium melting point and melting point depression behavior for the blends. A relationship between b and thermodynamic miscibility from a geometric perspective is discussed. The tacticity effect can be described in terms of an interaction parameter whose change with tacticity in terms of entropy is functionally related to the volume of an interacting group and in terms of enthalpy is functionally related to the surface area of an interacting group. Two related studies are presented. The first pertains to a shift in glass transition of thin PS films with thickness as investigated using ellipsometry. The second study used neutron reflection data to disprove the supporting argument for a minus two thirds dependence of surface tension with molecular weight. An alternative theory for the molecular weight dependence of surface tension is presented.

The reduction of 1,2-catecholatochloroboron by lithium in liquid ammonia/dimethoxyethane produces a reactive mixture containing multiple products. Formation of complexes with 12-crown-4 allows the isolation of one of these, (12-C-4)LiB(O$\sb2$C$\sb6$H$\sb4)\sb2.$ This complex was characterized by chemical analyses, multinuclear NMR, and single crystal x-ray diffraction. Chemical and spectroscopic data suggest that the remainder of this mixture contains boron in an asymmetric electronic environment and a low oxidation state. Reaction of this mixture with TiCl$\sb4$ forms an air stable complex with the formula TiB$\sb2{\cdot2}$((12-C-4)$\cdot$Ti(O$\sb2$C$\sb6 $H$\sb4)\sb2$). $\sp{11}$B and $\sp{47,49}$Ti NMR measurements of this complex indicate that boron and titanium inhabit a highly asymmetric electronic environment possibly with a considerable B-Ti interaction. The complex TiB$\sb2{\cdot}$((dme)$\cdot$Ti(SC$\sb2$H$\sb5)\sb2$(NH$\sb2)\sb2\rbrack,$ was prepared in a similar way. Reaction of this complex with bidentate protic species produced a series of polymeric complexes. TGA of theses polymers showed that mass loss was essentially complete by 400-600$\sp\circ$C. Pyrolysis of this series to 1000$\sp\circ$C formed green ceramic products that were characterized by volatiles analysis, chemical analysis, $\sp{11}$B MAS-NMR, XPS and powder diffraction. Annealing the green products at 1650$\sp\circ$C caused a carbothermic reduction that removed oxide impurities and formed crystalline TiB$\sb2$/TiC. However, this reduction only occurred when the green ceramic contained $>$5% amorphous carbon. In all other cases, the annealed ceramics contained TiBO$\sb3$/TiC. Pyrolysis of TiB$\sb2{\cdot}2$((dme)$\cdot$Ti(O$\sb2$C$\sb6$H$\sb4)\sb2\rbrack$ in a fluidized bed reactor produced a green ceramic with a minimum particle size of 100 nm. For this product, formation of TiB$\sb2$/TiC by carbothermic reduction was complete by 800$\sp\circ$C, 450$\sp\circ$C lower that conventional preparations. Reaction of a boryl-titanium complex with solid supports containing surface hydroxide groups led to thin films of titanium boride.

Evaluation of stress transfer mechanisms is critical in the design of composite structures and laminates. Due to anisotropy incurred during production, assessment of stress transfer processes is crucial for polymeric materials. In this study, two cases are evaluated in which parameters governing stress transfer play a critical role. These are: (1) Single fiber composites, and (2) Coatings. The first case examines the consequences of transferring stress from an isotropic matrix to embedded orthotropic fibers. The second case assesses the transferring of stress from anisotropic coatings to isotropic substrates. Fibers used in this investigation are highly oriented high-density polyethylene, poly (paraphenylene terephthalamide), and polydiacetylene (poly(2,4-hexadiyne-1,6-diol bisphenyl urethane)) single crystals. Poly (4,4$\prime$-oxydiphenylene pyrromellitimide), known as PMDA-ODA polyimide, is used as the coating material. The investigation of stress transfer was carried out using finite element analysis and analytical solutions. Elastic constants utilized for the analysis were obtained by molecular simulation methodologies. Crystalline and orientational order of the polymeric coating are characterized. This characterization was accomplished using wide-angle X-ray diffraction, electron diffraction, infrared spectroscopy, and Raman spectroscopy. Also, an external reflection infrared spectroscopic study of ultra-thin polyimide films revealed that molecular anisotropy remained higher and molecular packing lower for films thinner than 150 A. Results from these two case studies indicate that stress transfer observed at the ends of fibers or at the edges of coatings, is influenced by increases in the degree of material anisotropy. Assumptions of isotropy in polymeric materials undergoing analysis may lead to serious error in the characterization of stress transfer. Stress transferred from the isotropic matrix to anisotropic fibers leads to a state of radial compression near the fiber ends. Transverse stresses approach the value of the transverse strength of anisotropic fibers when strained uniaxially. For coatings, a complicated state of stress develops at the edges, at which out-of-plane and shear stresses are significant. Shear stress distributions near the ends, and equal in-plane stress, exhibit a slower decay when the degree of anisotropy is higher.