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.

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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)

Latently-reactive conjugated polymer-coated single-walled carbon nanotubes / Single-walled carbon nanotubes (SWNTs) are intensely investigated nanomaterials that exhibit intriguing physical and optoelectronic properties. Although SWNTs are highly regarded in terms of their potential societal impact, commercialization of SWNT applications has been dampened by the difficulty in SWNT processability and purification. Current commercially viable carbon nanotube syntheses produce complex mixtures of metallic and semiconducting SWNTs, as well as amorphous carbon and metal catalyst particles. Furthermore, the ability to decorate carbon nanotube surfaces to modulate their properties is non-trivial, especially if concurrent preservation of optoelectronic properties is desired. To date, the issues of SWNT solubilization, sorting, and functionalization have been approached in a piecemeal fashion. Conjugated polymers, which are macromolecules that possess extended π-systems, have the potential to address all of these issues simultaneously. In my Thesis, I explore conjugated polymer structures to investigate (i) factors that influence dispersion selectivity, and (ii) the decoration of polymer-SWNT complexes by incorporating reactive moieties into the polymer structure. The work presented in this Thesis begins by examining the ability of conjugated polymers to sort SWNTs. To date, the selective dispersion of metallic SWNTs is unrealized. In Chapter 2, I examine the effect of the electronic nature of the conjugated backbone on the selective dispersion of SWNTs by preparing SWNT dispersions pre- and post-methylation of a pyridine-containing conjugated polymer. In doing so, I prepare a series of polymers with identical degrees of polymerization and dispersity (to minimize extraneous selectivity factors) and find that electron rich π-systems disperse only semiconducting SWNTs, while electron poor π-systems disperse relatively more metallic SWNTs. In Chapter 3, I challenge the conventional wisdom that complete backbone conjugation is required to selectively disperse semiconducting SWNTs by introducing non-conjugated linkers into the polymer backbone and demonstrating that nanotube sorting is still possible. I next examine conjugated polymers as tools that can simultaneously sort SWNTs and impart reactivity to the polymer-SWNT complex, while preserving SWNT optoelectronic properties. In Chapter 4, I incorporate azides into polyfluorene side chains and perform solution-phase Strain-Promoted Azide-Alkyne Cycloaddition (SPAAC). I show that the polymer-SWNT complex can be rapidly decorated with strained cyclooctyne derivatives, and that only pre-clicked polymer enables for sorting of semiconducting SWNTs. The sorted SWNT population can then be made water soluble post-SPAAC, enabling for the study of SWNT emission in solvents with very different polarity. In Chapter 5, I examine the reactivity of azide-containing polymer-SWNT thin films and show that thin film properties can be drastically altered. Interfacial chemistry enables for the spatially-resolved patterning of a Janus polymer-SWNT thin film containing both hydrophilic and hydrophobic regions. In Chapter 6, I devise a system to perform aqueous solution-phase chemistry on the polymer-SWNT complex. The water soluble polymer-SWNT complex allows for functionalization of the hydrophobic SWNT scaffold with polar and charged molecules. Clicking an acidochromic switch onto the polymer-SWNT surface enables for control over the SWNT emission properties. Lastly, in Chapter 7 I develop a conjugated polymer whose backbone can be functionalized using visible light. The visible-light mediated photoclick coupling of a conjugated polymer backbone enables for rapid polymer modification and is the first example of spatially-resolved conjugated polymer backbone functionalization. / Thesis / Doctor of Philosophy (PhD) / Carbon nanotubes are cylindrical shells of carbon that possess fascinating physical, optical, and electrical properties. Commercial syntheses of carbon nanotubes produce complex mixtures of impure material, and raw carbon nanotube samples further suffer from insolubility. A grand challenge preventing commercialization of carbon nanotube applications is simultaneously solubilizing, sorting, and functionalizing carbon nanotube structures while avoiding damage to the nanotube properties. To date, these issues have been tackled in a piecemeal fashion. In my Thesis, I explore conjugated polymer coatings as a solution to address these problems all at once. I investigate how modifying conjugated polymer structure can (i) influence carbon nanotube purification and (ii) produce latently-reactive polymer-nanotube complexes that can be used to decorate carbon nanotubes without damaging nanotube properties.

An in depth study of the performance of thermally interdiffused concentration gradient polymer photovoltaic devices is carried out with particular attention to the effect of the thickness and the thermal treatments on the power conversion efficiency, short circuit current, open circuit voltage and other key electrical properties. Bilayer films of sequentially spin-cast donor and acceptor materials are exposed to various heat treatments in order to induce the interdiffusion. The depth profiles show concentration gradients in the donor and acceptor as a result of interdiffusion and these devices show an order of magnitude increase in the device performance compared to the bilayer devices. Dual spin-cast poly (3-octylthiophene-2,5-diyl) (P3OT)- [6,6] phenyl C61 butyric acid methyl ester (PCBM) and poly (3-hexylthiophene-2,5-diyl) (P3HT)-PCBM interdiffused devices are studied in detail by varying the thickness of the donor and acceptor layers as well as the annealing conditions for initial polymer layer and the time and temperature of the interdiffusion process. Auger spectroscopy and X-ray photoelectron spectroscopy along with ion beam milling are used to investigate the concentration gradient formed as a result of the interdiffusion. The sulfur signal present in the P3OT and P3HT backbone is detected to identify the concentration profiles in the P3OT-PCBM and P3HT-PCBM devices. The interdiffusion conditions and thickness of the active layers have been optimized to obtain the highest power conversion efficiency. The best device performance of the P3OT-PCBM interdiffused devices is achieved when the interdiffusion is carried out at 150°C for 20 minutes and the P3OT thickness is maintained at 70 nm and the PCBM thickness at 40-50 nm. The highest efficiency achieved for P3OT-PCBM interdiffused devices is 1.0% under AM1.5G solar simulated spectrum. In order to further increase the efficiency, P3OT is replaced by (P3HT) which has higher hole mobility. P3HT- PCBM based concentration gradient devices show improved device performance over P3OT-PCBM devices. Power conversion efficiency of the order of ~3.0% is obtained for P3HT-PCBM interdiffused devices when the interdiffusion is carried out at 150°C for 20 minutes. For both P3OT:PCBM and P3HT:PCBM devices, the optimum performance occurs when the concentration gradient extends across the entire film and is correlated with an increase in the short circuit current density and fill factor as well as a decrease in the series resistance. The results demonstrate that an interdiffused bilayer fabrication approach is a novel and efficient approach for fabrication of polymer solar cell devices. In addition, porphyrin derivative 5, 10, 15, 20-Tetraphenyl-21H, 23H-porphine zinc (ZnTPP) is studied as a new donor material for organic solar cells. ZnTPP: PCBM blend devices are investigated in detail by varying the weight ratio of the donor and acceptor materials in blend devices. The devices with ZnTPP: PCBM in 1:9 ratios showed the best device performance and the efficiency of the order of 0.2% is achieved under AM1.5G solar simulated conditions. Trimetallic Nitride Tempelated (TNT) endohedral fullerenes are also examined in this thesis as the novel acceptor materials. Bulk heterojunction or blend devices are fabricated with P3HT as the donor material and several TNT endohedral fullerenes as the acceptor material. Y3N@C₈₀PCBH based devices which are annealed both before and after the electrode deposition show improvement in the device performance compared to devices that are only annealed before the electrode deposition. The highest power conversion efficiency achieved for TNT endohedral fullerene devices is only 0.06%, suggesting that substantial additional work must be done to optimize the compatibility of the donor and acceptor as well as the device fabrication parameters. / Ph. D.

Different optical and calorimetric techniques were utilized to gain a better understanding of aggregated macromolecules. This research looked at two different macromolecules: poly(9,9'-dioctylfluorene), a conjugated polymer that forms aggregates in organic solvents; and bovine insulin, which forms amyloid fibrils. Conjugated polymers are of increasing interest due to their thermal stability and ease of solution processing for use in devices. A member of the polyfluorene family, poly(9,9'-dioctylfluorene) (PFO), has been studied due to its blue-emitting spectral properties. However, PFO has been found to form aggregates in solution, which is detected by the presence of a red-shifted absorption peak. This peak is caused when a section of the backbone planarizes forming the [beta]-phase. The [beta]-phase can be removed from the solution upon heating and will not return until the solution is cooled, making it a non-equilibrium process. The dissolution and reformation of the -phase were monitored using absorption spectroscopy and differential scanning calorimetry. Atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM) were able to probe the aggregates in films. It is important to understand polymer properties in solution in order to understand film morphology. Amyloid fibrils contribute to over 20 different neurodegenerative diseases, in which cures have yet to be found. The fibrils form when a soluble protein misfolds and self-assembles to form insoluble protein aggregates, and the cause of the fibril formation in vivo has still yet to be determined. Spectroscopy studies have been made possible with the use of fluorescent dyes: thioflavin T (ThT), BTA-2, and Congo red (CR). These dyes bind to amyloid fibrils and exhibit changes in their spectral properties. However, the exact mechanism for the binding of these dyes has only recently been studied. Through the use of calorimetry, the forces involved with binding of ThT and CR to amyloid fibrils can be determined. Absorption and fluorescence spectroscopy techniques were employed to study the spectral properties of these dyes. Polarized NSOM was used to determine the ThT or BTA-2's orientation with an individual fibril. Understanding how these dyes bind to fibrils will enable researchers to use spectroscopy to study the early stages of fibril formation. / text

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

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.