Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2005. / Kippelen, Bernard, Committee Member ; Brand, Oliver, Committee Chair ; Allen, Mark G., Committee Member. Includes bibliographical references.

Thesis (M.S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008. / Committee Chair: Marder, Seth; Committee Member: Bredas, Jean-Luc; Committee Member: Tolber, Laren. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Ceramic and Materials Science and Engineering." Includes bibliographical references.

Thesis (Ph. D.)--School of Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Bredas, Jean-Luc, Committee Member ; Kippelen, Bernard, Committee Member ; Marder, Seth, Committee Chair ; Bunz, Uwe, Committee Member ; Perry, Joseph, Committee Member.

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In-vitro electronic devices are promising to dynamically monitor minute-changes in biological systems. Electronic devices based on conducting polymers such as poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) provide suitable and attractive substrates for biointerfacing. The soft polymer surface acts as a cushion for the living systems to interface while electronically detecting their properties. However, to this date, most bioelectronics devices have been fabricated via multi-step lithography techniques, which do not allow for mass fabrication and hence high throughput biosensing. Inkjet printing presents an alternative to fabricate organic bioelectronic devices. Besides being low-cost, inkjet printing allows to fabricate several devices in a short time with flexible design patterns and minimal material waste. Here, using inkjet printing, we fabricated PEDOT:PSS based organic electrochemical transistors (OECTs) for biomembrane interfacing. We optimized the deposition of various inks (silver nanoparticles (AgNPs), PEDOT:PSS, and the dielectric SU-8) used during the fabrication of these devices. We characterized the electrical characteristics of all-printed OECTs with various geometries and identified the high-performing ones. Due to the flexibility of ink optimization and design patterns, these all inkjet-printed electronic devices provide an alternative for mass production of biointerfacing platforms.

The development and implementation of biosensors as an integral and growing part of our modern world has prompted the push for precision health as the next step in medicine. Adapted from aircraft engine monitoring, where an array of sensors is used to build a digital twin to preemptively predict problems, precision health requires an increase in molecular monitoring. Organic thin-film transistors (OTFTs), as sensitive, low-cost, and adaptable devices are well suited to meet this need. Phthalocyanines (Pcs), as an organic semiconducting layer for OTFTs, are easily synthesized and highly tunable small molecules which can be deposited through both solution and physical vapor deposition techniques, enhancing their utility. This work presents Pc-based OTFTs for cannabinoid sensing and chemotyping to meet the quality control needs of a growing Canadian and International cannabis industry, and to broadly demonstrate the sensitivity and selectivity attainable with Pc-based OTFTs incorporating molecular analyte sensors. Spectroelectrochemistry is established as a screening technique for Pc-based OTFT sensors and, in combination with thin-film characterization, is used to propose a mechanism for Pc-cannabinoid interactions and OTFT cannabinoid sensitivity with and without a cannabinoid-sensitive chromophore. Thin-film morphologies and polymorphs, pre- and post-analyte exposure, are demonstrated as key drivers of Pc-based OTFT sensing responses and are further explored through controlled deposition conditions and post deposition annealing techniques. Through material screening and thin-film engineering, part-per-billion cannabinoid sensitivity is achieved with Pc-based OTFTs. This report documents several strategies for sensitizing Pc-based OTFT sensors to organic analytes, and the results herein serve as a basis for continued development of Pc-based OTFT biosensors.

Perylene and perylene diimide (PDIs) are widely used for organic optical electronic materials due to their outstanding thermal stability, visible light absorption and high molar absorption coefficients. To tailor perylene and PDI’s optical and electronic properties for specific applications, molecular contortion and bay-functionalization have been proved as effective methods. In this thesis, these strategies will be applied to perylene and PDI to develop novel optical and electronic materials. In the first chapter, the molecular contortion strategy is applied to perylene to tune singlet and triplet energies and successfully turn on singlet fission in thin films of contorted perylene. Perylene does not undergo singlet fission in its planar form. The tuning of the energetics that control singlet fission through molecular contortion can be applied to a large repertoire of established molecular chromophores. In the second chapter, novel bay-functionalization reactions of PDI, which are base-assisted direct amination and N-heteroarylation, are discussed. The reactions are able to achieve up to 70% yield for mono N-heteroarylation. UV-Vis and EPR spectroscopy suggest that these reactions are mediated through PDI radical anions that are thermally induced by strong bases. An intriguing small-molecule white-light-emitter is constructed from this reaction. In the third chapter, contorting PDIs to form chiral helicenes for Chiral Induced Spin Selectivity (CISS) is discussed. CISS allows for selective transportation of one electron spin and filtration out of the other spin, exhibiting great potential applications in spintronics, spin-polarized light-emission, and spin-controlled catalysis. However, the mechanism of CISS remains unclear and it is necessary to develop a molecular system that allows for the investigation of CISS effect at the atomic level. PDI-based helicenes could be an ideal model system for the investigation of CISS effect due to their chiroptical properties. The chirality of PDI-based helicene dimers is resolved without chiral HPLC separation by converting helicene enantiomers into diastereomers, where Prep TLC is used to separate the helicene diastereomers at a relatively large scale.

The field of organic electronics is recently emerging in modern electrical applications. Organic light emitting diodes have been developed and are implemented in commercially available products. The novel materials are also used in sensor applications, utilizing their intrinsic physical, chemical and electrical characteristics. Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonic acid) (PEDOT:PSS) is one of the most successful organic conductive materials. Developed as antistatic coating, it is now used in other fields as well such as in electro-optical devices as transparent electrodes. One of the reasons for its widely spread use is that water-based dispersions in high quality are available. In addition, it is considered highly stable, resisting degradation under typical ambient conditions. For this work, the usability of PEDOT:PSS as active layer for electromechanical sensor applications was investigated. The electrical properties of the material were characterized including temperature dependencies and environmental influences. A piezoresistive effect with negative sign was found. It is small in magnitude and of the same order as the change in resistance due to geometrical effects. The piezoresistive effect is temperature dependent and increasing in magnitude with higher temperatures. An average longitudinal piezoresistive coefficient pi_l of -5.6x10-10 Pa-1 at room temperature has been evaluated. The transverse effect under the same conditions is opposite in sign and two thirds in magnitude of the lateral effect. The hole mobility of PEDOT:PSS follows an Arrhenius function and thus the resistivity has a negative temperature coefficient. Some other thermally induced effects have been observed such as de-doping of the material resulting in an irreversibly lowered conductivity. Due to the low thermal conductivity of the substrate material used, Joule heating of the samples played an important role during the characterization and was utilized to investigate the temperature dependencies. The change of resistance caused by an applied stress to the sample is small, with a gage factor smaller than one.

<p>   Organic electronics has been a highly researched field owing to the low cost, biocompatibility, mechanical flexibility, and superior performance relative to their inorganic counterparts in some applications. Significant advancement has been achieved across various device platforms including organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic solar cells, for instance. Recently, soft materials that can conduct both charge and ions simultaneously (i.e., organic mixed conductors) have been a major catalyst in the fields of biosensors and energy storage. Extensive research efforts in the organic electronics field are being invested to establish the relevant structure-property relationships to design and develop higher performing organic mixed conductors. Simultaneously, these materials are utilized in developing prototype biosensors with the aim of superior performance, lower cost, and better patient comfort and outcomes than currently available technologies. Following suit, this dissertation is dedicated to furthering organic electronics on both fundamental and applied fronts. Specifically, this work examines a novel class of redox-active macromolecules, radical polymers, as the organic electrochemical transistor (OECT) active layer. In addition, wearable ocular biosensors utilizing soft materials to realize design innovation are presented.</p> <p>   For the first part of the present dissertation, radical polymer-based blends are evaluated for mixed electron and ion conduction in OECTs. Traditional macromolecular design motifs for OECT active layer materials have been a closed-shell macromolecular backbone for electron conduction with charge-neutral hydrophilic side chains (e.g., triethylene glycol) for ion conduction. When poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) is blended with poly(3-hexylthiophene) (P3HT), 2,2,6,6-tetramethylpiperidin-N-oxy (TEMPO) radicals in PTEO act as an independent voltage regulator that modulates the ionic and hence electronic transport of the OECT devices. Electrochemical analysis of the blend films reveals that the ionic transport and hence electrochemical doping of the P3HT phase occur when the applied bias matches the onset oxidation potential of TEMPO radicals in PTEO even though that of P3HT is lower than that of TEMPO oxidation. By optimizing the blend ratio, figure-of-merit (i.e., μC*) values over 150 F V–1 cm–1 s–1 at loadings as low as 5% PTEO (by weight) are achieved, placing the performance on the same order as top-performing conjugated polymers despite the mediocre performance of pristine P3HT (<10 F V–1 cm–1 s–1). These findings suggest that introduction of open-shell moieties in the OECT active layer as a secondary redox-active species may significantly improve OECT performance metrics and offer a new paradigm for future macromolecular designs.</p> <p>   In the second part of the dissertation, novel design strategies for wearable ocular electroretinography (ERG) sensors are presented. Typically, wearable sensors are custom-made contact lenses fabricated in a bottom-up fashion where the pre-fabricated sensor component is either embedded in the contact lens body or sandwiched between two. The present work instead utilizes commercially available contact lenses, and the corneal electrode is integrated via electropolymerization of poly(3,4-ethylenedioxythiophene):iron(III) p-toluenesulfonate (PEDOT:Tos) on the lens surface. Electrochemical analysis of the PEDOT:Tos reveals that the measured impedance is several orders of magnitude lower than that of noble metals (e.g., Au) used as the working electrode in commercial electrodes. The mechanical and chemical stability along with the soft form factor of the present design strategy enables high-fidelity recording of ERG signals in human subjects without the need for topical anesthesia.</p> <p>   Following the similar strategy, a new seamless wearable ocular sensor integration strategy utilizing polydopamine (PDA) conformal coating is demonstrated. In this work, we utilize its strong adhesive property originating from the van der Waals interactions between catechol moieties of PDA and various hydrophilic functional groups (e.g., hydroxy, ether, etc.) already present in commercial contact lens materials. The facile integration demonstrates high peeling strength (> 55 J m-2), chemical and mechanical stability. A series of <em>in vivo</em> assessments demonstrates high accuracy, reliability, and user comfort of the fabricated wearable sensor in both animal and human subjects. The findings suggest that the PDA-assisted integration strategy may be applied in designing various future-generation wearable ocular electrophysiological sensors.</p>