Charge transport below the mobility edge, where the charge carriers are hopping between localized electronic states, is the dominant charge transport mechanism in a wide range of disordered materials. This type of incoherent charge transport is fundamentally different from the coherent charge transport in ordered crystalline materials. With the advent of organic electronics, where small organic molecules or polymers replace traditional inorganic semiconductors, the interest for this type of hopping charge transport has increased greatly. The work documented in this thesis has been dedicated to the understanding of this charge transport below the mobility edge. While analytical solutions exist for the transport coefficients in several simplified models of hopping charge transport, no analytical solutions yet exist that can describe these coefficients in most real systems. Due to this, Monte Carlo simulations, sometimes described as ideal experiments performed by computers, have been extensively used in this work. A particularly interesting organic system is deoxyribonucleic acid (DNA). Besides its overwhelming biological importance, DNA’s recognition and self-assembly properties have made it an interesting candidate as a molecular wire in the field of molecular electronics. In this work, it is shown that incoherent hopping and the Nobel prize-awarded Marcus theory can be used to describe the results of experimental studies on DNA. Furthermore, using this experimentally verified model, predictions of the bottlenecks in DNA conduction are made. The second part of this work concerns charge transport in conjugated polymers, the flagship of organic materials with respect to processability. It is shown that polaronic effects, accounted for by Marcus theory but not by the more commonly used Miller-Abrahams theory, can be very important for the charge transport process. A significant step is also taken in the modeling of the off-diagonal disorder in organic systems. By taking the geometry of the system from large-scale molecular dynamics simulations and calculating the electronic transfer integrals using Mulliken theory, the off-diagonal disorder is for the first time modeled directly from theory without the need for an assumed parametric random distribution.

A novel polymer semiconductor with side chains thermally cleavable at a low temperature of 200 °C was synthesized. The complete cleavage and removal of the insulating 2-octyldodecanoyl side chains were verified with TGA, FT-IR, and NMR data. The N-H groups on the native polymer backbone are expected to form intermolecular hydrogen bonds with the C=O groups on the neighboring polymer chains to establish 3-D charge transport networks. The resulting side chain-free conjugated polymer is proven to be an active p-type semiconductor material for organic thin film transistors (OTFTs), exhibiting hole mobility of up to 0.078 cm2V-1s-1. This thermo-cleavable polymer was blended with PDQT to form films that showed a higher performance than the pure individual polymers in OTFTs. MoO3 or NPB was used as a hole injection buffer layer between the metal electrodes and the polymer semiconductor film layer in OTFT devices. This buffer layer improved hole injection, while its use in the OTFT, improved the field-effect mobility significantly due to better matched energy levels between the electrodes and the polymer semiconductor.

In this diploma work, organic electrochemical transistors based on PEDOT:PSS have been studied, focusing on the influence of the geometry and physical dimensions on the transistor characteristics. The geometrical parameters studied are the area ratio between the gate and channel, the channel width and the channel length. Each parameter has been varied in five steps with each step containing three identical transistors. Results concerning the geometrical influence of the linear region resistance, the saturation current (density) and the on/off ratio are presented and discussed. Also, empirical curve-fits of the geometrical influence on the linear region resistance and the saturation current have been performed. In addition, tentative results of the locus of the saturation current versus saturation voltage for specific transistors have been obtained.

Structural evolution and its effect on optical absorption/emission behavior of derivatives of PFs upon heat treatment at different temperatures were studies by means of a combination of x-ray diffraction, transmission electron microscopy and molecular simulation. The main physical characteristics from results of this study over a series of PFs with alkyl side-chains may be summarized as the following: (1) The crystal structure of poly (9,9-di-n-octyl- 2,7-fluorene, PF8) and poly(9,9-bis(2- ethylhexyl)- 2,7-fluorene, PF26) are determined via a combination of selected area electron diffraction and molecular simulation. In PF8 case, there are 8 chains in an orthorhombic unit cell with dimensions a = 2.56 nm, b = 2.34 nm, c (chain axis) = 3.32 nm, space group P212121, and calculated density of 1.041 gcm-3. On the other hand, in PF26 case, there are 3 chains in a trigonal unit cell with dimensions a = 1.67 nm, b = 1.67 nm, c (chain axis) = 4.04 nm, space group P3, and calculated density of 0.991 gcm-3. (2) All the simulation results indicate that branched side-chains in the case of PF26 tend to fill the space among backbones. In contrast, the linear side-chains in the case of PF8 appear to embrace the neighboring backbone, favoring formation of layered structure. (3) As a consequence, co-planrity of PF backbones is decreased by the attached alkyl side-chains. This in turn results in lowered conjugation length, and in favor of blue light emission.

The effects of conjugated linoleic acid (CLA) on lipogenesis and preadipocyte proliferation in young pigs were evaluated in two separate experiments. The first compared dietary effects of linoleic acid, beef tallow, and CLA on composition, lipogenesis, and DNA synthesis. Eighteen pigs weaned at 17 d of age were allotted randomly to corn-based diets supplemented with 1.5% corn oil, 1.5% tallow, or 1.5% CLA. The second experiment evaluated the effects of CLA included with diets high in polyunsaturated fat or beef tallow. Twenty-four pigs weaned at 17 d of age were allotted randomly to one of four corn-based diets supplemented with: 15% corn oil, 12% corn oil + 3% CLA, 15% tallow, and 12% tallow + 3% CLA. The piglets in both trials were fed a basal diet for 7 d and their respective diet for 35 d. [U-14C]Glucose incorporation into total lipids was (experiment 1): 10.64, 11.04, 13.64; (experiment 2): 21.15, 17.54, 21.34, and 19.52 nmol/(105 cells per h) for subcutaneous (s.c.) adipose tissue from corn oil, tallow, CLA; corn oil, corn oil + CLA, tallow, and tallow + CLA-fed piglets, respectively. Tritiated thymidine incorporation into DNA was not different in s.c. adipocytes across treatment groups, but was 5,581, 2,794, 6,573, and 3,760 dpm/(105 cells per h) in s.c. stromal vascular cells from corn oil, corn oil + CLA, tallow, and tallow + CLA-fed piglets, respectively (CLA main effect p<0.034). Additionally, there was a greater proportion of s.c. adipocytes in the smaller, 180-pL cell fraction from the corn oil + CLA-fed pigs (p<0.0074). CLA in the diet increased the s.c. adipose tissue concentration of 18:0 and decreased 16:1 and 18:1 (p<0.05), suggesting depression of stearoyl-coenzyme A desaturase (SCD) enzyme activity in the CLA-fed pigs. The concentration of CLA isomers was raised only slightly in s.c. adipose tissue with the addition of CLA to the diets even though the CLA oil contained 62% CLA isomers. No effects on the growth of young pigs were observed. However, CLA caused a more saturated fatty acid composition and may suppress preadipocyte proliferation, apparent SCD activity, and lipid filling of smaller cells.

Fully conjugated heterocyclic aromatic rod-like polymer poly-p-phenylene- benzobisoxazole (PBO) and coil-like poly-(3-hexylthiophene) (P3HT) were applied as opto-electronically active layer. The two polymers mixed with nano-carbon particles, having excellent optical absorption and electric conductivity, of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) or esterified multi-wall carbon nano-tube (MWNT-COOC10H21) as well as a hole transporting layer of PEDOT:PSS. Photovoltaic (PV) cells of indium-tin-oxide (ITO)/PEDOT:PSS/nano-carbon particle:fully conjugated polymer/Al were fabricated for optical and electrical characterizations. Tri-layered structure of ITO/PEDOT:PSS/PBO/PCBM/Al produced a straight current-voltage relation showing no PV effects. Upon changing the active layer into PCBM doped P3HT layer (PCBM:P3HT), it produced good PV effects suggesting that the doped layer had a penetrating network to facilitate the PV effects. When PCBM or MWNT-COOC10H21 was doped into P3HT, the device PV effects were increased significantly with nano-carbon particle concentration. The direct-current electric conductivity parallel to the film surface (£m¡ü)was increased with the nano-carbon particle concentration. By changing the thickness of hole transporting PEDOT:PSS and of opto-electronically active layers, it was found that when the PEDOT:PSS layer was decreased from 90 nm to 32 nm, there was a slight increase of PV cell efficiency. The active layer of PCBM:P3HT with a thickness of 99 nm had the best optical absorption and charge transport leading to an increase of PV cell efficiency.

Oligo(ethylene glycol) groups have been used as substituents in poly(p-phenyleneethynylene)s (PPEs) to provide solubility, and to boost quantum yield. Properties such as water-solubility and increased quantum yield in aqueous solution make these conjugated systems promising for biosensory applications. In this thesis, a PPE containing a branched ethylene glycol side chain is synthesized as part of a polymer array for glycan biosensing. I also report that the same side chain can be put to use in a red-emissive polymer to lend water solubility. Another monomeric unit, containing ethylene glycol chains, is incorporated into a PPE to create an ampiphilic polymer. The versatility of these polymers allows them to be used for a variety of purposes, some of which will be described herein.

The field of molecular electronics includes the study of conjugated oligomers and polymers that have significant potential for use in devices such as light emitting diodes (LEDS), field effect transistors (FETS), and photovoltaic solar cells. These materials may replace inorganic semiconductors in these devices, Achieving better device performance through lowering the band-gap and achieving higher field effect mobilities will benefit from a greater fundamental understanding of charge transfer through the aromatic subunits. π-stacking of segments of conjugated polymers has been identified as a key feature that influences the charge transfer through semiconducting organic materials. Optimizing the molecular architecture of conjugated polymers has the potential to provide materials with better charge mobility. While devices might benefit from materials that take advantage of π-stacking, access to π-stacked structures presents a synthetic challenge. 1,8-Disubstituted naphthalenes may serve as simple covalent bridging scaffolds which might hold conjugated oligomers in a π-stacked arrangement. The research described in this thesis focuses on the synthesis of well-defined phenylene ethynylene oligomers coupled to naphthalene to serve as experimental models of closely π-stacked aromatic units in conjugated polymers. The π-stacked molecules reported in this dissertation are characterized by NMR, IR, and mass spectrometry. The effects of π- stacking on the structure and behavior of conjugated oligomers are determined by X-ray crystallography, spectroscopy, and electrochemistry.

<p>Microcontact printing using elastomeric stamps is a technique used in finding new and efficient ways to produce biodetection chips. Microcontact printed, with poly(dimetylslioxane) (PDMS) stamps, patterns of antibodies have been evaluated using fluorescence microscopy, imaging ellipsometry and atomic force microscopy. Fluorescent conjugated polyelectrolytes form non-covalent molecular complexes with Immunoglobulin-γ type antibodies, antigen binding to the tagged antibody result in spectroscopic shifts. Four different conjugated polyelectrolytes (POWT, POMT, PTT, PTAA) in complex with human serum albumin antibodies (aHSA) have been tested with fluorescence spectroscopy. Complexes of POWT and aHSA gave rise to thelargest wavelength shift when exposed to human serum albumin.</p><p>Several types of commercially available fluorescent antibodies and antigens were used to test the specificity of microcontact printed antibodies to different antigen solutions. Using fluorescence microscopy it could not be shown that printed antibody patterns promote specific adsorption of corresponding antigen. It is proposed however that changed surface characteristics of the substrate due to PDMS residues transferred during printing is the main driving force behind antigen adsorption.</p><p>POMT - poly (3-[(s)-5-amino-5-methoxylcarboxyl-3-oxapentyl]-2,5-thiophenylenehydrochloride)</p><p>POWT - poly (3-(s)-5-amino-5-carboxyl-3-oxapentyl]-2,5-thiophenylenehydrochloride)</p><p>PTAA - polytiophene acetic acid</p><p>PTT - poly (3-[2,5,8-trioxanonyl] thiophene)</p>

<p>In this diploma work, organic electrochemical transistors based on PEDOT:PSS have been studied, focusing on the influence of the geometry and physical dimensions on the transistor characteristics. The geometrical parameters studied are the area ratio between the gate and channel, the channel width and the channel length. Each parameter has been varied in five steps with each step containing three identical transistors. Results concerning the geometrical influence of the linear region resistance, the saturation current (density) and the on/off ratio are presented and discussed. Also, empirical curve-fits of the geometrical influence on the linear region resistance and the saturation current have been performed. In addition, tentative results of the locus of the saturation current versus saturation voltage for specific transistors have been obtained.</p>