Understanding structure-property relationship of molecules is imperative for designing efficient materials for organic semiconductors. Organic semiconductors are based on π-conjugated molecules, either small molecules or macromolecules such as dendrimers or polymers. Charge transport through organic materials is one of the most important processes that drive organic electronic devices. We have investigated the charge transport properties in various molecular designs based on dendrons, dendron-rod-coil molecular triads, and conjugated oligomers. The charge transport properties were studied using bottom contact field effect transistors, in which the material was deposited by spin coating. In case of dendrons, their generation and density of charge transporting functionalities were found to play a significant role in influencing the charge transport properties. In case of macromolecules such as dendron-rod-coil molecules, the solid state morphology plays a significant role in influencing the charge transport properties. While these molecules exhibit only electron transporting behavior in field-effect transistor measurements, ambipolar charge transport is observed in the diode configuration. Short conjugated oligomers, based on donor-acceptor-donor design, provide model systems for conjugated polymers. Effect of varying the donor functionality on optoelectronic and charge transport properties was studied in short donor-acceptor-donor molecules. While donor-acceptor-donor molecules are well known in the literature, the effect of molecular composition on the charge transport properties is not well understood. We designed molecules with 2,1,3-benzothiadiazole as the acceptor and thiophene based donor functionalities. These molecules exhibit a reduced bandgap, good solution processability and charge mobility making them interesting systems for application in organic photovoltaics. Cyclopentadithiophene (CPD) based materials have been widely utilized as organic semiconductors due to their planar nature which favors intermolecular charge transport. While most CPD based materials are hole transporting, incorporation of electron withdrawing fluorinated substituents imparts n-type behavior to these molecules. This change in charge transport properties has often been attributed to the lowering of the LUMO energy level due to the increased electron affinity in the molecule. We designed CPD based semiconductors in which the bridgehead position was functionalized with electron withdrawing ketone or dicyanomethylene group and the -positions were substituted with phenyl or pentafluorophenyl groups. Both the phenyl substituted molecules are p-type materials, even though the dicyanomethylene group lowers the LUMO by 500 meV as compared to the carbonyl compound. The pentafluorophenyl substituted molecules are n-type materials even as their LUMO energy levels are about 300 meV higher than the corresponding phenyl substituted molecules. This indicates that charge transport behavior is not an exclusive function of the frontier orbital energy levels.

This dissertation utilizes the power of organic synthesis to construct novel chiral and achiral π-conjugated organic molecules/materials that serve as platforms for single molecule chiroptical studies, to develop optical sensors and solar thermal fuels. The first section of the dissertation describes the synthetic methodologies employed to obtain chiral bridged triarylamine helicene scaffolds with well defined molecular orientation (relative to the surface) on a surface, to address the fundamental question: What is the role of molecular orientation on the magnitude of chiroptical response of a chiral molecule? Next, we investigated bridged triarylamine chromophores for optical sensing. We developed a novel bridged triarylamine helicene that shows turn-on sensory response towards toxic nerve agent mimics such as dichloroethylphosphate (DCP). The final section of this dissertation addresses the question: Can mechanical energy induce a change in configuration from cis-azobenzene to trans-azobenzene? For this purpose, we developed an azobenzene-functionalized polymer and showed that ultrasound-induced mechanical energy isomerizes the azobenzene moiety within the polymer from cis to trans configuration without cleaving the azo bond.

Nucleophilic substitution reactions at silicon are frequently thought to occur through the formation of pentacoordinated or hexacoordinated intermediates or transition states. Pentacoordinated compounds have geometries ranging from trigonal bipyramidal to square or rectangular pyramidal. Interconversion from one geometry to another occurs via Berry pseudorotation. Hexacoordinated compounds have geometries ranging from octahedral to bicapped tetrahedral. Silicon compounds which achieve higher coordination as a result of intramolecular coordination are useful model compounds for the intermediates in nucleophilic substitution reactions. Group 14 and 15 elements are the donor atoms commonly found to behave in this regard. Six compounds which incorporate both sulfur and silicon atoms into an eight-membered ring system are synthesized. In addition, a disiloxane with two eight-membered ring systems is obtained as a hydrolysis product. Si-S coordination is observed in the five crystal structures that are obtained. Steric and electronic effects on the degree of coordination are compared. The degree of coordination is measured by calculating the distortion of the geometry around the silicon atom from a tetrahedral to a trigonal bipyramidal geometry. Four other organosilanes that have the sulfur atom as part of a dangling moiety attached to the eight-membered ring are also synthesized. No coordination was observed in this type of system, with the silicon atom retaining a tetrahedral geometry. The 29Si NMR spectra of all 11 organosilanes are indicative of the nature of the substituents on the silicon atom. A total of seven zwitterionic silicates are synthesized. Four of these zwitterions are obtained from an organosilane that is thought to be either penta- or hexacoordinated as a result of intramolecular nitrogen donation. A pentacoordinated organosilane, which models a proposed intermediate for this reaction, is shown to form one of the zwitterions. Cleavage of a Si-C bond occurs in the formation of these zwitterions, and a mechanism for their formation is proposed. Three other zwitterions have two nitrogen atoms on the alkyl chain, with one of the nitrogen atoms capable of coordination. No further coordination is observed, and the 29Si NMR spectra for all the zwitterions. are consistent with the retention of a pentacoordinate structure. Hydrogen-bonding is present in all of these zwitterions. Crystal packing effects are responsible for the observed geometries of these compounds, which are found to span the Berry coordinate from a TBP to an RP.

Gold nanoparticles (AuNPs) hold a great promise for biomedical applications. The inert inorganic core provides a scaffold to hold organic ligands and their payloads, while the diversity of monolayers provide a means to tailor AuNP surface properties for particular purposes. Based on our synthethic approach to ligand fabrication, our group has been able to control the chemical properties of AuNPs at the nanoscale level. These properties have made AuNPs an excellent scaffold for delivery applications. In this dissertation, it has been demonstrated how the properties of monolayers play a crucial role in achieving a desired biological goal. In each case, the monolayer of AuNPs has been tailored using organic synthesis as a strategy to afford stable and biocompatible biological tools. These engineered AuNPs demonstrate numerous biomedical applications, including a controlled release of payload, cellular uptake, gene regulations, cytosolic delivery, and cytotoxicity.

Engineering nanostructures with complete control over the shape, composition, organization of the surface structures, and function remains a major challenge. In my work, I have fabricated nanostructures using functional polymer motifs and nanoparticles (NPs) via supramolecular and non-supramolecular interactions. In one of the approaches to generate nanostructures, I have integrated top-down approaches such as nanoimprint lithography, electron-beam lithography, and photolithography with the self-assembly (bottom-up) of NPs to provide nanostructures with tailored shape and function. In this strategy, I have developed a geometrically assisted orthogonal assembly of nanoparticles onto polymer features at precisely defined locations. This versatile NP functionalization method can be used to fabricate protein resistant patterned surfaces to provide essentially complete control over cellular alignment, making them promising biofunctional structures for cell patterning. In another approach, I have utilized self-assembly of dendrimers and NPs without preformed templates to generate nanostructures that can be used as chemoselective membranes for the separation of small and biomacromolecules.

The detection of chemical explosives is an important problem that poses unique challenges for chemists. Common explosives such as nitro-organics and peroxides lack chromophores, and differ greatly in chemical structures and properties. A family of Zn(salicylaldimine) (ZnL) complexes were prepared, and investigated for fluorescence sensory applications. ZnLs are strong fluorophores, Φ = 0.3, with sub-nanosecond lifetimes and highly reducing excited states. The fluorescence of ZnL is effectively quenched by both nitroaromatics and nitroalkanes. Quenching occurs via photoinduced electron transfer from the phenolate ring of ZnL, creating a phenoxyl radical species that was observed with EPR. ZnL was synthetically varied with electron withdrawing and donating substituents, and Stern-Volmer quenching experiments revealed mixed quenching pathways, depending upon the steric bulk of the substituent. The energetic contributions from the electron withdrawing or donating substituents changed the driving force for electron transfer, and high steric bulk favored dynamic quenching over the static pathway. The kinetics of dynamic quenching were treated with Marcus theory, predicting a modest reorganization energy, λ = 24 kcal/mol, governed by solvent effects. A sensor array was formulated for the discrimination of structurally similar nitro-organic compounds. Fingerprint patterns were generated for each quencher based on the unique interactions with each ZnL. Using statistical analysis, 100% of unknown samples were accurately identified. Solid state structural investigations reveal a penta-coordinate Zn with solvent bound axially. The axial ligand, EtOH, THF and pyr, influenced the degree of π-stacking in the unit cell, and shifted the solid state λ em. Preliminary investigations into solid state sensors involved formation and characterization of polycrystalline structures, ZnL doped thin films, and ZnL polymers. Fluorescence turn-on methods are highly sensitive compared to fluorescence quenching. A fluorescence turn-on sensor was developed for peroxide based explosives using the oxidative deboronation of a masked prochelator to form H2L, which chelated Zn2+ and produced fluorescent ZnL. The rate of fluorophore formation was limited both by peroxide concentration and structure of the diamine backbone of the prochelator. Limits of detection for H2O2, benzoyl peroxide and triacetone triperoxide, a highly energetic peroxide-based explosive, were below 10nM in solution.

The steric nature of the new topology created by the starburst polymer has been studied by $\sp{13}$C and $\sp2$H dynamic nuclear magnetic resonance (NMR) relaxation measurements. For two series of poly(amidoamines), PAMAM, (one OH terminated, the other NH$\sb2$ terminated), $\sp{13}$C correlation times ($\tau$) of the terminal carbons were found to be almost independent of the number of end groups; $\tau$ varied from 1.0 $\times$ 10$\sp{-11}$ to 6.3 $\times$ 10$\sp{-11}$, and no evidence of dense-packing of the end groups was observed. The $\tau$'s of the methylene carbons on the interior of the dendrimers were found to increase with molecular weight, indicative of a progressive increase in local monomer density within the polymer. No significant differences in relaxation parameters of the internal carbons were observed for the NH$\sb2$ terminated PAMAM compared to the OH terminated analogues, in either D$\sb2$O or DMSO-d$\sb6$. Thus, the results reflect topological effects, and are not due to specific solvent or end group behavior. Larger relaxation times were observed for both series when measured in D$\sb2$O. While the differences in polymer behavior in the two solvents indicate that the polymer chains are more flexible in D$\sb2$O than in DMSO-d$\sb6$, intrinsic viscosities were determined to be comparable in the two solvents (0.04-0.10 dl/g). The difference in the NMR behavior is thus attributed to strong H-bonding between the polymer and DMSO, resulting in an increase in the hydrodynamic volume of the mobile unit. The relaxation behavior of the terminal carbon, in D$\sb2$O, differed upon changing the end group. The terminal carbon of the OH terminated PAMAM was observed to be less mobile than the corresponding carbon atom in the NH$\sb2$ terminated PAMAM. $\sp2$H NMR relaxation measurements were used in a more extensive study of the mobility of amine terminated PAMAM chains as a function of molecular weight and positions. The $\tau$'s were found to increase with molecular weight, irrespective of the location of the labelling. In the last generation the $\tau$'s were found to increase as the number of termini increases from 3($\tau$ = 1.7 $\times$ 10$\sp{-12}$s) to 384 ($\tau$ = 2.2 $\times$ 10$\sp{-11}$s), and were smaller than the $\tau$'s observed when the polymers were labelled at interior positions. No significant difference in relaxation parameters was observed when the label was located in the interior repeat units, irrespective of chain length following deuteration. No evidence of radial gradients was observed.

Studies of the properties of metal cyclopentadienyl compounds were made by infra-red spectroelectrochemistry, electrochemistry, synthesis and $\sp{103}$Rh nuclear magnetic resonance spectrometry. A cell capable of simultaneously recording IR spectra of the region near the electrode surface during electrochemical experiments was developed, and characterized using ferricyanide. The absorbance-time response to potential step and potential sweep experiments was investigated and the experimentally determined response compared to a digital simulation of the response at different distances from the electrode surface. This allowed the distance from the electrode surface to the point of observation to be estimated. The capabilities of the cell were applied to the elucidation of the electrochemical behavior of titanocene dichloride and iron pentacarbonyl. Titanocene dichloride was reduced under an atmosphere of carbon monoxide to titanocene dicarbonyl and ultimately to the anion (CpTi(CO)$\sb4$) $\sp{-}$. No evidence for the formation of a titanium(III) carbonyl species was found. In contrast, reduction of titanocene dichloride in the presence of 2,6-dimethylphenylisocyanide led to the formation of titanium(III) and titanium(II) products, in which one and both of the chloride ligands had been replaced by the isocyanide, respectively. Electrochemical and chemical reduction of fulvalene-dititanium cyclopentadienyl compounds led to the breakage of the carbon-carbon bond linking the two five-membered rings of the fulvalene ligand. The electrochemical properties of a series of ferrocene-containing polyesters in solution was investigated using various stationary and rotating solid electrode techniques. The oxidised form of the polyesters coated the electrode surface in an uneven fashion allowing solution and surface processes to occur simultaneously. Evidence for the nature of this coating was gathered using X-ray photoelectron spectroscopy. The effect of substituents on a series of ring-substituted (h$\sp5$-cyclopentadienyl)dicarbonylrhodium complexes was investigated by means of changes in C-O stretching frequencies as well as $\sp{103}$Rh NMR chemical shifts. The effect of the substituents was found to be neither a purely resonance or inductive phenomenon, but best described by a substituent parameter which took both effects into account.

The roles that nickel plays in biological systems appear to be largely dependent on the ligand environment. Non-redox active Ni-containing proteins have a predominantly O/N ligand donor environment. In contrast, Ni-containing redox active enzymes contain S-donor ligands. This study was undertaken to investigate the roles of the Ni ligands in the redox active enzyme, hydrogenase, and the isomerase, glyoxalase-I. An X-ray absorption spectroscopic (XAS) study of the Ni site of Chromatium vinosum hydrogenase during reductive activation, CO binding, and photolysis is presented. The results indicate that Forms A, B, and C are formally Ni(III), whereas Forms SIu and SIr are formally Ni(II). In addition, the Ni site undergoes changes in the coordination number and geometry that are consistent with five-coordinate Ni sites in Forms A, B, and SIu; distorted four-coordinate sites in SIr and R; and a six-coordinate Ni site in Form C. The loss of a short Ni-O bond, and a shortening of the Ni-Fe distance, accounts for the change in coordination number from five to four that accompanies formation of SIr. Comparison of Forms C and L rules out the presence of H2 or H− binding in Form C, whereas analysis of the SI-CO complex reveals the presence of Ni-CO ligation. A hydrogenase modeling study of complexes containing thiolate ligands indicate the importance of S-donor ligands. Modification of the thiolates by protonation and alkylation leads to changes in the redox behavior of the model complexes without inducing large structural changes. This is similar to the behavior exhibited in hydrogenases. Escherichia coli glyoxalase-I is maximally activated by Ni2+, unlike other known glyoxalase-I enzymes that are active with Zn2+. An XAS study of the active site Ni and Zn-substituted glyoxalase-I indicated metal sites consistent with Ni(Glu)2(His) 2(OH2)2 and Zn(Glu)2(His)2(OH 2) structures, respectively. A similar study using Ni-glyoxalase-I and complexes formed with the product and various inhibitors was conducted. The results indicated interaction of S-D-lactoylglutathione (product) or octylglutathione with the enzyme did not change the structure of the Ni site nor did incorporation of SeMet for Met. However, the addition of an hydroxamate inhibitor results in a Ni site where the hydroxamate substitutes for both water molecules and a Glu ligand. In contrast, the SeMet-substituted enzyme hydroxamate complex loses both water molecules, but retains both histidine and glutamate ligands. The results are suggestive of a mechanism that involves both water molecules.

This thesis describes the synthesis and characterization of segmented, triblock and star block copolymers with mesogenic hard segments and long flexible spacers. This thesis explores two important aspects of structure-property relationships of phase separated block copolymers: (1) the effect of soft segment structure on the polymer thermal phase behavior; (2) the effects of hard segment structure and soft segment topology on polymer properties. The first part tests the hypothesis that the soft segment substituents that are adjacent to the hard segment lower the polymer thermal transitions temperatures. Copolymers with pentad hard segments and soft segments with varying degrees of substitution were synthesized to test this hypothesis. Pentad copolymers with completely substituted soft segments showed the lowest melting transition and exhibited no liquid crystallinity. When the substituents are separated from the hard segment, the polymer exhibits higher melting transitions and liquid crystalline behavior. In the second part, efforts were concentrated to synthesize block co-oligomers that behave as high polymers at ambient temperatures but have low melt viscosities. As part of this study, block co-oligomers with dyad esteramide and bisamide hard segments and amine terminated poly(propylene glycol)s of linear and star topologies were synthesized. The block co-oligomers showed that variations in the hard segment structure have a dramatic effect on both the melting temperature and the stability of the liquid crystalline phase. Topology of the soft segment does not effect the thermal transitions, but does affect hard segment organization. In general, star block co-oligomers showed better organization than their linear counterparts.