Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Tolbert, Laren, Committee Member ; Perahia, Dorva, Committee Member ; Perry, Joseph, Committee Member ; Collard, David, Committee Member ; Bunz, Uwe, Committee Chair.

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Quick and early detection of abnormalities in the body's metabolism is of paramount importance to monitor, control, and prevent the associated diseases and pathologies. Biosensors technology is rapidly advancing, from the first electronic biosensor reported by Clark and Lyons in 1962 for blood glucose monitoring to today’s devices that can detect multiple metabolites in bodily fluids continuously and simultaneously within seconds. This rapid growth in point-of-care devices promises for the development of novel devices with different form factors and the ability to detect a wide range of biomarkers. These advancements mainly stem from the development of electronic materials that have properties better aligning with the biotic interface compared to the traditional metal electrodes. A promising class of electronic materials for biosensors is conjugated polymers. Conjugated polymers are carbon-based, organic semiconducting materials made of long chains comprising conjugated repeat units. The fundamental property that makes these materials so attractive is, however, not their electronic conductivity, but their ionic conductivity. As living organisms use ionic fluxes to relay signals, materials that can conduct ionic currents are believed to facilitate the communication between the electronics and living systems. This communication happens at various levels: organs, complex tissues, cells, cell membrane, proteins, and small biomolecules. Besides, the inherently soft nature of these materials facilitates mechanical conformity with soft biological systems. The field of organic bioelectronics has experienced tremendous growth over the past two decades, thanks to the design of new conjugated polymers customized for the biotic interface. While hole conducting (p-type) polymers have been widely investigated, electron conducting (n-type) counterparts are relatively new. This dissertation aims to explore the capabilities of n-type conjugated polymers for bioelectronics applications. Chapter 1 overviews the key properties of conjugated polymers and the resulting electronic devices that leverage these properties for specific applications in bioelectronics. Chapter 2 presents microfabricated metabolite (lactate and glucose) sensors based on an n-type polymer in combination with enzymes, and how this communication can enable energy production from bodily fluids. Finally, Chapter 3 reports the development of engineering and design strategies to enhance the performances of n-type polymers in bioelectronics.

Mostly new acetylene based monomers were prepared. All monomers were prepared by the means of standard spectroscopic methods. All monomers were successfully polymerized using standard metathesis TaCl5 based catalyst. Prepared polymers were characterized by the means of GPC/GPC-MALLS chromatography and standard spectral methods. Fluorescence properties of all prepared compounds were also studied: quantum fluorescence yields were determined and excitation and emission fluorescence spectra were recorded. Polymerization on modern metathesis Grubbs-Hoveyda catalytic systems of all prepared monomers was also tested. These reactions were only partially successful and only low molecular weight oligomers in mediocre yields were obtained.

ABSTRACT SYNTHESIS OF MONOMERS FOR NEW CONJUGATED POLYMERS This dissertation addresses the problem of synthesis of different monomers for donor and acceptor polymers in photovoltaic applications. In general, functionalization of conjugated polymers and understanding of molecular packing of electron donors and electron acceptors are very important to produce efficient solar cells. As a result, it is important to design and synthesize novel monomers which will require making new π-conjugated donors and acceptors polymers and understand the influence of these new polymers in bulk heterojunction to design polymer solar cells. In this study, two different monomers were synthesized. The first monomer was designed and synthesized to investigate the effect of π-conjugated linker directly attached to the polymer backbone where the polymer backbone was based on thiophene unit and conjugated linker was 1,2,3-triazole. In a different study, a conjugated monomer based on benzthiadiazole was designed and synthesized in order to synthesize new acceptor homopolymers and alternating copolymers. Two different monomers with different alkyl side chains based on benzthiadiazole were synthesized and subject to Suzuki and Stille polymerization to get respective polymers.

Conjugated tetrazine-containing polymers that undergo Inverse Electron Demand Diels-Alder (IEDDA) reactions with trans-cyclooctenes are interesting not only for their intrinsic optoelectronic properties, but also their interactions with π-conjugated surfaces. Here, we prepared a series of poly(fluorene-co-tetrazine) polymers and carried out IEDDA reactions to decorate them with hydroxyl, hexadecyl, or triethylene glycol side chains. The polymers were investigated pre- and post-IEDDA coupling in terms of their ability to disperse single-walled carbon nanotubes (SWNTs) in organic solvent. It was found that polymer molecular weight, side chain structure, and degree of conjugation all impacted the quality of SWNT dispersions. While the starting poly(fluorene-co-tetrazine) polymer produced concentrated dispersions, the post-IEDDA polymer containing dihydropyridazine groups did not produce dispersions of equal concentration. However, upon oxidation to the fully aromatic pyridazines, the polymers regained their ability to form concentrated dispersions. Furthermore, the post-IEDDA polymers exhibited increased selectivity toward metallic SWNTs relative to the starting polymer. In addition, due to the efficiency of the IEDDA reaction, it was possible to perform modification of the polymer-SWNT dispersion formed with poly(fluorene-co-tetrazine) to modify the polymer structure while on the SWNT surface. Overall, this work demonstrates the first use of reactive polytetrazines to disperse SWNTs and to rapidly modify the solubility of polymer-nanotube complexes. / Thesis / Master of Science (MSc)

Thesis (Ph.D.) - University of St Andrews, November 2007.

Conjugated polymers and oligomers have been widely studied based on their wide range of useful properties and applications. Given the importance of self-assembly and charge transfer in the development of conjugated materials for use in electronic applications, it is crucial to: (i) prepare functional materials by molecular design, (ii) evaluate the structure-property relationships of new materials, and (iii) develop fundamental understanding of electronic structure and charge transport behavior. The use of conjugated polymeric materials in electronic applications relies on control of the assembly and orientation of the polymer chains in the solid state. Conjugated polymers with liquid crystalline behavior could be used to implement an additional level of control over orientation and resultant properties. Substitution of the conjugated polythiophene backbone with semifluoroalkyl side chains (i.e., the diblock -(CH2)m(CF2)nF) has afforded materials with unusual properties. The mutual immiscibility of the aromatic backbone, the alkyl side-chain segments, and the fluoroalkyl side-chain termini provides control over supramolecular packing. A series of eight polymers has been synthesized, in which the lengths of the alkyl (m) and fluoroalkyl (n) segments are varied. One regiorandom analogue and two poly(3-alkylthiophene)s were also synthesized for comparative purposes. The structure, molecular weight, and regioregularity of the polymers were evaluated using a variety of techniques. The semifluoroalkyl-substituted polymers have been systematically studied to determine the effect of side chain length and m:n block ratios on their solution state, liquid crystalline, and solid state properties. The effect of side chains on conjugation was determined, where solubility allowed, by solution-state UV-visible and fluorescence spectroscopy. The thermal and liquid crystalline properties of the homopolymers were evaluated by DSC, variable-temperature X-ray diffraction, and polarized optical microscopy. Several semifluoroalkyl-substituted polythiophene homologues show liquid crystalline behavior. Molecular packing and charge transport are key factors governing the use of conjugated materials in electronic applications. A wide variety of oligomers have been studied as models for charge migration in conjugated polymers. One-dimensional models do not adequately represent two-dimensional charge transport; thus, a variety of two-dimensional, covalently-linked models have been developed. Previous work by our group, and others, led to the proposal of bis(oligothienyl) compounds as models to study the interaction of the ð-conjugated chains. Previous reports by other researchers described the synthesis and characterization of hydrogen-terminated analogues of 1,8-bis(oligothienyl)naphthalenes. However, these materials proved to be unsuitable for use as charge transport models, as they were subject to irreversible polymerization upon oxidation. Installation of methyl groups at the terminal a-positions of 1,8-bis(oligothienyl)naphthalenes allowed us to create a series of models in which conjugated chains are held in close proximity. This provides access to multiple redox states, and future systems based on these molecules may be used as models for charge transport or as functional materials for incorporation into devices.

Novel organic conjugated materials have led to new technologies in the field of flexible electronics, with applications in the area of sensors, field effect transistors, or photovoltaic devices. Several material parameters and properties come into play in these devices, including energy of the frontier molecular orbitals, thin film morphology, and charge transport. These properties can be controlled by the chemistry of organic materials, and through processing conditions. In particular, this dissertation focuses on the isoindigo unit as an electron deficient unit to tune polymer light absorption, charge separation, charge transport in the first part of this dissertation, and morphology control in organic photovoltaic (OPV) devices in a subsequent section. The first part of this dissertation introduces the synthesis and properties of isoindigo-containing polymers as n-type, p-type, or ambipolar semiconductors, and their application in all-polymer or polymer:fullerene blends OPV active layers. It is found that polymers with phenyl linkages along the backbone tend to have broader light absorption than polymers with alternating phenyl-thiophene rings; however, steric hindrance in the former leads to low charge mobilities, and poor device performance. In addition, this section highlights the importance of controlling phase separation in OPV devices by focusing on all-polymer blends, which show large phase separation, and polymer:fullerene blends, where the morphology can be controlled through processing additives generating a two-fold increase in device efficiency. Looking at poly(oligothiophene-isoindigo) polymers as model systems, emphasis is placed on photovoltage losses in these devices due to a decrease in effective energy gap between the polymers and fullerene as the oligothiophene donating strength is increased, as well as explanation of the device parameters through description of morphology as solubility is varied. The second portion of this dissertation focuses on solution properties of polymers and their correlation to thin film morphology. A first study investigates the influence of alkyl side chains on solubility, molecular packing, and phase separation in blends of poly(terthiophene-alt-isoindigo) with fullerenes. Specifically, as side chains are lengthened, solubility is increased, but with limited impact on the blends morphology. On the other hand increased backbone torsion leads to variations in energy levels, polymer packing and large phase separation in blends with fullerenes. These thermodynamic parameters are to put in perspective with the kinetic control of film formation during the coating process. This is discussed in a second study, which looks at the mechanism of thin film formation when processing additives are used. In particular, this study highlights the interactions that provide a driving force for polymer crystallite formation, depending on the mechanism followed when aliphatic and aromatic additives are used. These observations are then used to predict the morphology in spin-coated thin films.

published_or_final_version / Chemistry / Master / Master of Philosophy