Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1020. Adviser: Steven C. Zimmerman. Includes bibliographical references (leaves 152-160). Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6809. Adviser: Jeffrey S. Moore. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

<p> This dissertation includes two topics, which are related to each other: (1) Rupture force measurement of single triazole molecule by atomic force microscope (AFM) and (2) Solid phase stepwise synthesis of polyethylene glycols (PEGs). </p><p> The reaction of an alkyne and an azide to form a 1,2,3- triazole has found wide applications. However, the stability of triazole under mechanical stress is unclear. We investigated the cycloreversion at the single molecular level using atomic force microscopy. A mica surface functionalized with a molecule containing a 1,2,3-triazole moiety in the middle and an activated ester at the end was prepared. An AFM tip with amino group was ramped over the surface, which temporarily linked the tip to the surface through amide bond formation. During retraction, the triazole broke and the forces were recorded. Most of the forces were below 860 pN. The resulting alkyne were labeled with gold nanoparticles (AuNPs). AFM imaging revealed AuNPs at the predefined locations, proving that 1,2,3-triazole could rupture with force below 860 pN. </p><p> We used commercially available functionalized polyethylene glycol (PEGs) for functionalizing of mica surface and AFM tip. These PEGs were polydispersed admixtures with different size of tags and not ideal for many applications. There is a need to develop a new method to synthesize a monodispersed PEGs. We believe that if monodisperse PEGs were used, our data would be much better. In addition, monodispersed PEGs can form single molecular conjugates during chemical reactions which allow precise characterization of all PEGs conjugates. This lead us to conceive an idea to prepare monodisperse PEGs. </p><p> Significant efforts have been made in the area, to achieve monodisperse PEGs using solution phase but the drawbacks include the need of multiple column chromatography, low overall yield, and contamination by depolymerized products. To overcome all shortcomings, we have developed a new technology to synthesize monodispersed PEGs on solid support. The Wang resin, which contains the 4-benzyloxy benzyl alcohol function, was used as the support. On this solid support, tetraethylene glycol monomer was added stepwise. Polyethylene glycol (PEG) with eight and twelve glycol units and its derivatives were synthesized. The synthetic cycle consists of deprotonation, Williamson ether formation (coupling), and detritylation. Cleavage of the PEG from solid support was achieved with trifluoroacetic acid. From this method, we prepared highly pure products having different functionalities at the two ends without any chromatographic purification in the entire synthesis.</p><p>

In a highly interdisciplinary field, such as organic photovoltaics (OPVs), developing a predictive understanding of the relationship between molecular structures, morphology of the photoactive layer and the ultimate device performance is the key to unlocking the vast potential of this field. Although isolated examples of high-performance organic molecules are prevalent in the literature, the reasons for their superior performance are not well understood. The function of an OPV device is dependent of four key processes: (i) light absorption, (ii) charge separation, (iii) charge transport, and (iv) charge collection. While the first three are material-dependent factors, charge collection depends on the nature of the interfaces involved. We have thus investigated a new class of semiconductor molecules based on BODIPY dyes with the aim of understanding how variations in the molecular structure affect the optoelectronic and transport properties of the molecules. First-generation pi-conjugated polymers based on the BODIPY core possess broad and intense absorption spectra. Additionally, the frontier molecular orbital (FMO) energy levels of the polymers can be tuned by a judicious choice of the comonomers. Electron-deficient comonomers with electron affinities higher than that of the BODIPY core, predominantly afford n-type polymers. A unique feature of these semiconductors is their panchromatic absorption spectrum that spans throughout the visible region. Thus these polymers can be considered to be potential electron acceptors in all-polymer solar cells. Copolymerization of BODIPY with electron-rich comonomers, on the other hand, only results in p-type semiconductors. Furthermore, the highest occupied molecular orbital (HOMO) of these polymers is found to correlate with the ionization potential of the electron-rich monomer. Having said that, the lowest unoccupied molecular orbital (LUMO) energy level does not change. Thus for the first time, a correlation between theoretical calculations and experimental observations has been demonstrated for predicting the FMO energy levels of BODIPY-based semiconducting polymers. Second-generation copolymers based on an unsubstituted BODIPY core retain the broad absorption characteristics of the first-generation polymers. In addition, due to reduced electron density on the BODIPY core, the HOMO energy level of the resulting polymers is reduced thereby imparting enhanced oxidative stability to these polymers. Charge transport measurements through thick films (∼1 micron) reveal only p-channel activity with hole mobilities comparable to some of the high-performance polymers reported in literature. Preliminary bulk-heterojunction OPV devices fabricated with these polymers show modest power conversion efficiencies. We believe that understanding the morphology of the active layer in relation to the polymer structure will help improve future molecular designs and eventually, device performance.

This dissertation explores the self-assembly of diblock copolymers as a way to control the morphology of photoactive layer in organic solar cells. Heterojunction formation between electron donor and electron acceptor materials needs to be controlled on the nanometer scale to have high power conversion from organic photovoltaic cells. Two approaches were developed to direct the assembly of electron-donors and electron-acceptors into heterojunction structures. The first one involves the synthesis of acid cleavable diblock copolymer to create porous polymer films, which can be used as templates to form well ordered donor-acceptor heterojunctions on the nanometer scale. Here, we demonstrate that nanoporous templates could be prepared under moderate conditions, which do not interfere with photovoltaic device fabrication. The second approach involves the use of conjugated diblock copolymers as the structure directing agents. Incompatible packing of the side chains was investigated to provide microphase segregation in conjugated polymer/fullerene blends. Packing of the materials within the domain has been shown to be a very important parameter for photovoltaic performances.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 0975. Adviser: Jeffrey S. Moore. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Hierarchically structured inorganic materials are everywhere in nature. From unicellular aquatic algae such as diatoms to the bones and/or cartilage that comprise the skeletal systems of vertebrates. Complex mechanisms involving site-specific chemistries and precision kinetics are responsible for the formation of such structures. In the synthetic realm, reproduction of even the most basic hierarchical structure effortlessly produced in nature is difficult. However, through the utilization of self-assembling structures or "templates", such as polymers or amphiphilic surfactants, combined with some favorable interaction between a chosen inorganic, the potential exists to imprint an inorganic material with a morphology dictated via synthetic molecular self-assembly. In doing so, a very basic hierarchical structure is formed on the angstrom and nanometer scales. The work presented herein utilizes the self-assembly of either surfactants or block copolymers with the desired inorganic or inorganic precursor to form templated inorganic structures. Specifically, mesoporous silica spheres and copolymer directed calcium phosphate-polymer composites were formed through the co-assembly of an organic template and a precursor to form the desired mesostructured inorganic. For the case of the mesoporous silica spheres, a silica precursor was mixed with cetyltrimethylammonium bromide and cysteamine, a highly effective biomimetic catalyst for the conversion of alkoxysilanes to silica. Through charge-based interactions between anionic silica species and the micelle-forming cationic surfactant, ordered silica structures resulted. The incorporation of a novel, effective catalyst was found to form highly condensed silica spheres for potential application as catalyst supports or an encapsulation media. Ordered calcium phosphate-polymer composites were formed using two routes. Both routes take advantage of hydrogen bonding and ionic interactions between the calcium and phosphate precursors and the self-assembling copolymer template. Some evidence suggests that the copolymer morphology remained in the composite despite the known tendency for calcium phosphates to form highly elongated crystalline structures with time, as is commonly the case for synthetic hydroxyapatites. Such materials have obvious application as bone grafts and bone coatings due, in part, to the osteoconductive nature of calcium phosphate as well as to the mesoporosity generated through the cooperative assembly of the block copolymer and the inorganic. Future work, including potential experiments to determine osteoconductivity of as-prepared composites, is also presented herein.