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We have synthesized several nitronyl nitroxides (NNs) to study their crystal packing and magnetic properties. These were characterized by ESR spectroscopy, and most by IR and mass spectrometry. Dominant magnetic interactions were studied by magnetic susceptibility studies performed on 2-(3,5-difluorophenyl)-NN and 2-[3,5-bis-(trifluoromethyl)-phenyl)-NN crystals. Structural information was used from X-ray studies to elucidate magnetic interactions present in the NN crystals. The synthesis of the precursors for nitronyl nitroxides was optimized in most of the cases by using triethylamine as the base during the condensation of aryl aldehydes with 2,3-dihydroxylamino-2,3-dimethylbutane (DHAB). 2-Aryl-substituted benzimidazole-3-oxide-1-oxyls (BNNs) were explored as possibly useful building blocks for organic magnetic materials. We analyzed spin delocalization in these systems by examining their ESR hyperfine coupling constants. These studies revealed substantial spin delocalization onto the benzenoid ring of the benzimidazole fragment, which may be responsible for their limited stability. B3LYP-6-31G* level density functional computations on 2-H-substituted BNN confirm that about 30% of spin is delocalized onto the benzenoid ring. The ESR studies also show that there is very little spin delocalization onto a phenyl ring attached at 2-position. Experimental hyperfine coupling constants are affected only by 2–4% with different substituents on the 2-phenyl ring nitrogen, further demonstrating the limited interaction between the 2-phenyl and the BNN unit. We synthesized new heterospin systems comprised of phenyl nitrene substituted NN or BNN molecules in order to investigate the effects of heteroatom substitution, connectivity and conformation. Low temperature ESR, UV-vis spectroscopic studies, and UB3LYP–6-31G* level computations were used to study 2-(4-nitrenophenyl)-NN, 2-(3-nitrenophenyl)-NN and 2-(4-nitrenophenyl)-BNN. The spectroscopic studies show the presence of quartet species resulted from arylnitrene-radical interaction. ESR zero-field-splittings reflected mostly the connectivity of the molecules, and varied only very little with the structure. The UV-vis studies supported the presence of some quinonoidal character in the para-linked nitreno-radicals. Computations show little difference in nitrene delocalization between the para- and meta-linked systems, but find a relatively higher stability of the high spin, planar structures over the low spin state in para-linked nitreno-radicals by comparison to meta-linked analogs.

Tetrahydro-2-methylbenz[e]indanone (5) and tetrahydro-2-methyl benz[f]indanone (11) were produced from the reaction of 2-bromoisobutyryl bromide with tetralin, contrary to what has been previously published in the literature. Indanones 5 and 11 were readily converted into their corresponding indene derivatives tetrahydro-2-methylbenz[e]indene (6) and tetrahydro-2-methylbenz[f]indene (12), respectively. Two new half sandwich titanium trichlorides based on 6 and 12 were synthesized and were shown to polymerize styrene to s-PS with activities in the low 107 range. Two efficient synthetic routes to the novel titanatrane complexes, indenyl titanatrane (19) and 2-methylbenz[e]indenyl titanatrane ( 20) have been presented. These new titanatranes along with the known titanatranes, Cp titanatrane (17) and Cp* titanatrane ( 18) were tested as potential catalyst precursors for the polymerization of styrene and ethylene. Complex 17 was a very efficient catalyst for the polymerization of ethylene at 0°C, exhibiting a 100 fold increase over its corresponding trichloride derivative (CpTiCl3) Complex 18 proved to be the most versatile catalyst producing very high activities in the polymerization of styrene and moderate activities in the polymerization of ethylene. A new versatile synthetic route to substituted alkyl bridged bis-indanones and bis-indenes was developed. In addition, these bis-indenes can be employed as useful ligands in the synthesis of ansa-titanocenes. Ansa-titanocene complexes 22 and 63 were active in catalyzing the polymerization of olefins when activated by MAO, exhibiting activities of ca. 1 × 107 for the polymerization of ethylene and ca. 1.5 × 104 in catalyzing the polymerization of propylene. Four new C1 symmetric metallocenes containing a substituted indenyl moiety were synthesized. Metallocenes 68– 70 and 72 were active for both the polymerization of ethylene and propylene when activated with MAO. In general, diphenylsilylene-bridged catalysts produce polymers of higher molecular weights than do dimethylsilylene-bridged catalysts. Overall, one obtains a higher activity but polymers of lower molecular weights with ethylene-bridged catalysts versus silylene-bridged catalysts. In addition, four new C1 symmetric metallocenes containing 2,7-disubstituted fluorenyl moieties were synthesized. Three of the four metallocenes, 86–88, were highly active for the polymerization of both ethylene and propylene. In general, the most sterically hindered catalysts were more active and produced polymers of higher molecular weights than do their less hindered counterparts.

Nanoscale Supramolecular Chemistry—interfacing molecular recognition and nanosized inorganic materials was explored in this work. Initial work focused on the incorporation of molecular recognition elements into the monolayers of gold nanoparticles, allowing for the creation of entities capable of partaking in multivalent interactions with solution phase guests. The effect of the radial nature of monolayers formed on nanoparticles was explored; here, increased packing density near the nanoparticle surface allowed for the increased effectiveness of multivalent binding sites. Molecular recognition element functionalized nanoparticles can also be designed to interact with polymers functionalized with complimentary recognition elements, enabling a “Bricks-and-Mortar” nanoparticle self-assembly process. Control over either assembly size or particle spacing is possible when either diblock copolymers or dendrimers, respectively, are employed as the “Mortar”. Finally, monolayer chemistry of γ-Fe 2O3 nanoparticles was also described, and the application of “Bricks-and-Mortar” assembly to the fabrication of magnetic materials was accomplished.

Nanotechnology promises to revolutionize the way we think about, but more importantly create new materials. The key to making this promise a reality is a commitment to fundamental research in critical areas including synthesis, fabrication, and characterization of nanoscale components. Nanoparticles have attracted wide attention as such components due to their unique size dependent properties including, superparamagnetism, chemilumiescents, and catalysis. To fully harness the potential capabilities of nanoparticles we need to develop new methods to assemble them into useful patterns or structures. Directed self-assembly using noncovalent interactions can be used to achieve this goal. This dissertation outlines experiments demonstrating several methods of polymer-mediated assembly of gold and iron oxide nanoparticles. Directed self-assembly using various polymer architectures provided a direct means to: (1) control the overall size of nanoparticle aggregates, (2) control interparticle spacing between particles, (3) control the collective behavior in nanoparticle ensembles.

Bionanotechnology provides an attractive and unique arena for chemists, biologists and physicists due to its interdisciplinary nature. This thesis work has focused on using synthetic chemical tools to functionalize nanoparticles for biological applications. To this end, a ligand system featuring poly(ethylene glycol) (PEG) segments and chain-end functionalities was developed. These ligands were utilized to functionalized nanoparticles with different cores, including metallic (Au), semiconductor (CdSe and CdSe/ZnS), and magnetic (FePt and iron oxide) materials. Using these surface tailored nanoparticle scaffolds, surface binding of nanoparticles with enzyme α-chymotrypsin (ChT) was systematically studied. The ChT-nanoparticle interaction was characterized as electrostatically driven and reversible. Importantly, control over ChT structure and function was demonstrated on three levels: no binding, binding and denaturation, and binding without denaturation, dictated by the nanoparticle surface monolayer composition. The monolayer of nanoparticles can be tailored to not only control protein (ChT)-nanoparticle interactions, but also impact enzyme-substrate interactions, which results in enhanced ChT chemoselectivity towards substrates with different charges. In addition, the PEGylated nanoparticles have been explored to stabilize enzyme to stresses found in real-world bio-catalysis. The combination of the unique attributes of the nanoparticle cores and the function of the monolayer periphery provides numerous opportunities in creation of multi-functional nano-materials that are useful in biological and material applications.

The work in this dissertation focused on two topics which are typically encountered in organic based magnetic materials: (1) the self-assembly of molecules in the solid state to provide viable interelectronic exchange pathways and (2) the use of spin density distribution and radical communication in high spin molecules to provide a better understanding of the interelectronic exchange pathways that are encountered in (1). To study the effects of crystal packing and exchange behavior in hydrogen bonded systems, compounds 5NNBIm, 6UrIN, 35diBu4HOPhNN, and 35diBu4HOPhIN were all synthesized and their solution and solid state properties were analyzed. Compound 5NNBIm, was synthesized and found exhibit antiferromagnetic interactions between spin units. The crystal structure revealed a water of molecule was incorporated into the structure, providing NH(imidazole)......O(H)H......:N(imidazole) chains of hydrogen bonds. The magnetic data was fit to 1D and 2D Heisenberg chain models for spin exchange, both of which gave excellent fits to the data. The crystal structure of 6UrIN, revealed a dimer structure which formed between two uracil portions of the molecule. The magnetic data was fit to a Bleaney-Bowers dimer model for spin pairing and showed overall antiferromagnetic interactions between spin units. The crystal structure of 35diBu4HOPhNN revealed extended hydrogen bonded chains formed between the phenolic OH and a NO of the nitronyl nitroxide portion of the molecule. The magnetic data was fit to a 1D Heisenberg model for exchange and showed strong antiferromagnetic interactions between spin units. Compound 35diBu4HOPhIN was found to have disorder in its crystal structure making the magnetic analysis very difficult. To study the effects of spin density distribution and radical communication in high spin molecules, compounds BTNIT, 5azaBABI, pNPhIN, mNPhIN, 35diBu4OPhNN, and 35diBu4OPhIN were synthesized and their solution state properties analyzed. Compounds BTNIT and 5azaBABI were prepared to determine what effect heteroatom substitution would have on the spin density distribution in BABI. Electron spin resonance (ESR) and computational results determined sulfur substitution in BTNIT played a significant role in increasing the spin density onto the benzenoid portion of the molecule, while nitrogen substitution in 5azaBABI did not significantly affect the spin density on the nitroxide portion of the molecule. The ground state spin multiplicities in compounds pNPhIN, mNPhIN, 35diBu4OPhNN, and 35diBu4OPhIN were all determined using ESR and/or theoretical computations. Heteroatom substitution, within the spin bearing portions of the molecule, was determined to reverse the expected ground state spin multiplicities that were expected based on traditional spin polarization and parity connectivity models.

A series of 2,6-di-tert-butylphenols with para aza-heterocyclic rings and fluorinated was synthesized. These phenols were oxidized to the corresponding persistent phenoxyl radicals and their EPR spectra (spin density distribution) and kinetic decay rates were studied. The varying electron spin delocalizations in the phenoxyl radicals were studied using EPR spectroscopy and UB3LYP/6-31G* spin density computations. Kinetic studies showed that the attachment of different heterocyclic rings results in varying degrees of the persistence of the 2,6-di-tert-butylphenoxyl radicals. The phenolic compounds themselves were tested for antioxidant activity, and were sent to the National Cancer Institute for in-vitro cell culture assays of their anticancer effect. The crystal structures and IR spectra of the phenols revealed phenolic OH---N hydrogen-bonding pattern despite the steric hindrance caused by tert-butyl groups. Conjugated nitroxide radicals have been widely used for molecular magnetism. The delocalization of the spin density over the entire molecule makes a larger variety of magnetic interactions possible. The way the spins interact with each other can lead to paramagnetic, antiferromagnetic or ferromagnetic interactions. By examining the crystal structures of a number of nitroxides and nitronyl nitroxides bearing heteroatom substituents the relationship can be studied between close crystallographic contact spin sites and the resulting magnetic behavior is investigated. 2-(4,5,6,7-Tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5,dihydro- 1H-imidazole-3-oxide-1-oxyl (F4BImNN) was synthesized and shown to be the first ferromagnetically coupled purely organic radical synthesized in the Lahti group. 1-(4-(N-[para-Methoxyphenyl]- N-hydroxylaminoxyl) phenyl)pyrrole (MNPP) was made and found to be a very rare example of a stable diarylnitroxide. It shows two-dimensional square planar antiferromagnetic exchange behavior, which is very unusual in purely organic electronic materials. 1-(4-[N-tert-Butylaminoxyl]-2,3,5,6-tetrafluorophenyl)pyrrole (BNPPF4) was made as the first fluorinated nitroxide subjected to magnetostructural analysis to our knowledge. Its crystal structure suggests possible one-dimensional antiferromagnetic interactions. However it interestingly shows magnetic behavior that is more consistent with a spin-pairing model.

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The process of self-assembly provides unique opportunities for designing novel materials at the nano-scale. The development of such processes involves fine-tuning of chemical structures and effective use of the non-covalent forces that controls such molecules. This thesis discusses a new design of an amphiphilic species that can undergo self-assembly, directed by solvophobic/solvophilic interactions. The building block of the system contains a polar and an apolar unit, embedded within the same monomer. Amphiphilic dendrimers and homopolymers were built on this basic structure. The self-assembly of these macromolecules were studied in solvents of widely different polarities. The biphenyl based dendrimers showed aggregation behavior in the solvents, which was hitherto unknown for those. Along with their host-guest properties in solution, the preferential location of the amphiphilic functionalities were probed, in order to fundamentally understand the dendritic systems. The same design principle, applied to homopolymers also led to the formation of micelle-like and inverted micelle-like assemblies. The detailed characterization of such systems is discussed along with their behavior in a heterogeneous solvent mixture. The polymeric systems hold promise in applications such as separation nanotechnology and protein sensing.