Optical modulation of the physical properties of materials is important for future development of optical memories and switches, optoelectronics, and smart surfaces. Incorporation of an optically bistable photochromic compound into an electronically bifunctional material is a promising strategy for a development of photoswitchable materials. Photochromic spirooxazine ligands undergo light-induced ring-opening and closure between the closed-spirooxazine (SO) and open-photomerocynanine (PMC) forms. The structural reorganization leads to accompanying changes in electronic structure which can lead to a change in the oxidation/reduction potentials and spin state of a bound metal center. Changes in the ligand field about a metal center in turn can lead to “non-classical” photoinduced magnetic (PIM) effects. The “non-classical” PIM effect is an effect that occurs through ligand-centered processes via the metal center, rather than direct excitation at the metal center. The structural change of the photochromic compounds also results in a change in the frontier orbital energies and donor-acceptor character, which may lead to optically-gated charge-transfer and energy-transfer processes. In this dissertation, the structural factors that govern thermal relaxation of spirooxazines, as optical control units, was investigated toward controlling the photostationary states of this important class of photochromes. The electronic structure of the PMC form of azahomoadamantyl-based spirooxazines was found to control the thermal coloration/decoloration rates of photochromic spirooxazines. A significant charge-separated character of the PMC form was correlated with the slow thermal coloration/decoloration rates in spirooxazines. This concept was then extended to an investigation of the effect of Lewis-acidic metal complexation. Solution study of the charge-separated character of the PMC form via metal complexation of the photochromic spirooxazines supported the correlation between the charge-separated character of the PMC form and the rate of the thermal coloration/decoloration. The studies provide a potential pathway for modulating PMC thermal relaxation rates through optimization of the structure of the spirooxazines and metal complexation. The studies were then extended to an investigation of the photomodulation of charge-transfer processes in cobalt multinuclear clusters by photoisomerization of photochromic spirooxazines. Incorporation of optically bistable phenanthroline-spirooxazine ligands into a magnetically bistable cobalt-dioxolene valence tautomeric cluster resulted in large magnetic moments in the solid and solution states. This study suggests that the redox-isomeric behavior of the cobalt dioxolenes can be coupled to isomerization of the photochromic ligand in the solution state when the π-acceptor ability of the photochromic ligands align with the direction of charge transfer of the cobalt dioxolene components. The potential of these cobalt multinuclear clusters to enhance the relaxivity of water in MRI for biological imaging was investigated. A cobalt tetranuclear cluster was prepared and found to exhibit high magnetic moments in solution at room temperature, and large relaxivities relative to commercially available gadolinium based MRI contrast agents. Lastly, the photomodulation of ionic doping of graphene organic field-effect transistors (OFETs) by photochromic spirooxazines was investigated. The electron donor or acceptor nature of the photochromic isomers modulates the direction and magnitude of ionic doping of graphene, and in turn the gate voltages of graphene OFETs, leading to optical modulation of OFET gate voltages for data processing and memory technologies. / Graduate / 2020-02-08

Cette thèse démontre le potentiel d'utilisation du graphène pour la fabrication de transistors à effet de champ à couche mince. Celui-ci est préparé par exfoliation en phase liquide et co-déposé avec un polymère semiconducteur du type n. Cette stratégie montre que le graphène améliore le comportement ambipolaire du polymère et plus particulièrement le transport des trous ce qui renforce l'application des matériaux composites au graphène dans les circuits logiques.Par la même approche de mélange, de nouveaux nanorubans de graphène dispersés en solution, ont été utilisés pour améliorer la performance des dispositifs basés sur un polymère amorphe de type p. Ces nanorubans forment une voie de percolation pour les charges améliorant ainsi la performance des dispositifs dans l'obscurité ainsi que sous illumination. Finalement, les dispositifs photosensibles multifonctionnels ont été examinés par l'introduction de molécules photochromiques avec différents substituants au sein des films semi-conducteurs à base de polymère ou de molécules de petite taille qui ont été trouvés influer la photocommutation. / This thesis demonstrates that graphene produced by liquid-phase exfoliation can be co-deposited with a polymerie semiconductor for the fabrication of thin film field-effect transistors. The introduction of graphene to the n-type polymeric matrix enhances not only the electrical characteristics of the devices, but also the ambipolar behavior and the hole transport in particular. This provides a prospective pathway for the application of graphene composites for logic circuits.The same approach of blending was adopted to enhance the electrical characteristics of an amorphous p-type polymer semiconductor by addition of an unprecedented solution processable ultra-narrow graphene nanoribbon. GNRs form percolation pathway for the charges resulting in enhanced deviee performance in daras weil as under illumination therefore paving the way for applications in (opto)electronics.Finally, multifunctional photoresponsive devices were examined by introducing photochromic molecules exposing different substituents into small molecule or polymeric semiconductor films that were found to affect the photoswitching behavior.

Control of solid state ordering in conjugated small molecules is paramount to the continued development and implementation of organic materials in electronic devices. However, there exists no reliable method on which to predicatively determine how a change to the molecular structure will impact the solid-state packing. As such, the molecule must be synthesized before its solid-state packing can be definitively evaluated. However, once the packing structure of a material is known there exist both qualitative structure- function relationships derived from the literature, as well as quantitative computational methods that can be employed to suggest if a material will perform well in a given device. This type of bottom-up strategy is used in Chapter 2 to design and synthesize a high performance material for organic field effect transistors. A core molecule is synthesized, and through rigorous optimization of pendant and solubilizing groups a material with exceptional solid-state packing is developed and its performance in an organic field effect transistor is discussed. Chapter 3 discusses the use of conjugated organic molecules in conjunction with inorganic materials to develop hybrid organic/inorganic materials. A scalable synthesis is developed so derivatives can be rapidly synthesized and their properties evaluated. Two classes of materials are developed and synthesized: tetracene-based ligands for quantum dots and diammonium-substituted anthracene and tetracene derivatives for 2D-perovskites. Initial results for both classes of materials are presented. Chapter 4 discusses the topochemical photopolymerization of heptacene [4+4] dimers. Multiple derivatives were synthesized in order to give the ideal alignment of molecules in the crystal, followed by irradiation of crystals to give crystal templated polymerization. In Chapter 5, triarylmethane derivatives are synthesized and their performance as radiochromic sensors is evaluated. Chapter 6 involves the development of a robust synthetic scheme toward a difficult to attain π- extended regioisomer of pyrene. Photophysical characterization reveals that the direction of π-extension from the pyrene core has a profound effect on electron delocalization.

A high aspect ratio epoxy mask has been built with Taiyo PSR4000BN on chemical sensing array chip. Thickness up to 200 and #61549;m and aspect ratio up to 16:1 have been achieved with this material. It is demonstrated that this material satisfies the mechanical and chemical requirements. A three-electrode system has been designed and built for electrochemistry in micro-cell on chip. Tests with poly(phenylenesulfide-phenyleneamine) (PPSA) demonstrates that it is possible to precisely tune the properties (Work function and resistance) of conducting polymer that has been cast on chip surface. A new test platform GT03 has been fabricated and used to characterize the chemical effects on organic electronics. It is demonstrated that the chemical species in ambient environment can affect organic electronics properties on bulk, interface and electric contact. The contact resistance in organic field-effect transistors (OFETs) has been characterized with modified interdigitated structure (IDS). It is demonstrated that drain and source contact resistances can be calculated separately with modified four-point-probe measurements, and contact resistance and material bulk resistance are actually modulated by the gate electric field. Furthermore, the influence from oxygen doping in poly(3-hexylthiophene) (P3HT) based OFETs has been investigated. A new model of oxygen doping has been suggested and it is demonstrated that oxygen doping can affect all the resistance components in P3HT OFETs.

In this dissertation novel work is presented showing the performance and device physics of Organic Field Effect Transistors (OFETs) and bulk heterojunction Organic Photovoltaic (OPV) devices fabricated using novel acceptor small molecules. Pentacene and N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN₂) were used as the active layer in p-channel and n-channel Organic Field Effect Transistors (OFETs), respectively, and novel pulsed voltage transient measurements were developed in order to extract transient mobilities and carrier velocities from the transistor response of the device, which were well correlated with the corresponding DC OFET characteristics. A distributed RC network was used to model the OFET’s channel and the transient and DC characteristics of the devices were successfully reproduced. Temperature dependent studies of the DC field effect mobilities and transient mobilities of these two materials were carried out and the results used to extract information on charge carrier transport in the materials at varying time scales. Open-circuit voltages of the OPV devices are correlated with the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) levels various acceptor small molecules and donor polymers comprising the active layers of the devices. / text

There is significant need to improve the sensitivity and selectivity for detecting chemical and biological agents. This need exists in a myriad of human endeavors, from the monitoring of production of consumer products to the detection of infectious agents and cancers. Although many well established methodologies for chemical and biological sensing exist, such as mass spectrometry, gas or liquid phase chromatography, enzymelinked immunosorbent (ELISA) assays, etc., it is the goal of the work described herein to outline aspects of two specific platforms which can add two very important features, low cost and portability. The platforms discussed in this dissertation are organic semiconductor field-effect transistors (OFETS), in various architectural forms and chemical modifications, and ion channels immobilized in tethered lipid bilayers integrated with solid state devices. They take advantage of several factors to make these added features possible, low cost manufacturing techniques for producing silicon and organic circuits, low physical size requirements for the sensing elements, the capability to run such circuits on low power, and the ability of these systems to directly transduce a sensing event into an electrical signal, thus making it easier to process, interpret and record a signal. In the most basic OFET functionality, many types of organic semiconductors can be used to produce transistors, each with a slightly different range of sensitivities. When used in concert, they can produce a reversible chemical "fingerprint". These OFETS can also be integrated with silicon transistors - in a hybrid device architecture - to enhance their sensitivity while maintaining their reversibility. The organic semiconductors themselves can be chemically altered with the use of small molecule receptors designed for specific chemicals or chemical functional groups to greatly enhance the interaction of these molecules with the transistor. This increases both sensitivity and selectivity for discrete devices. Specially designed nanoscale OFET configurations with individually addressable gates can enhance the sensitivity of OFETS as well. Finally, ion channels can be selected for immobilization in tethered lipid bilayer sensors which are already inherently sensitive to the analyte of choice or can be genetically modified to include receptors for many kinds of chemical or biological agents. / text

This work reports the various aspects of the application of atomic force microscopy (AFM), for the characterization of organic semiconductors and DNA-based arrays, for organic electronics and biological applications. On these soft surfaces, the amplitude modulation AFM mode was chosen. This choice is argued by a study of dissipative processes, performed on a particular sample, a DNA chip. We showed the influence of experimental parameters on the topographic and phase image quality. By calculating the dissipative energy, it was shown that the dissipation on the DNA chip was mainly induced by a viscoelastic tip-sample interaction.The AFM study of the "thickness-driven" pentacene growth was made to link the morphology to the nature of the substrate and to the electrical performance of created pentacene-based Organic Field Effect Transistor (OFET). Deposited on two polymer substrates, parylene and benzocyclobutene (BCB), pentacene has been characterized for nanoscale film thicknesses between 6 and 60nm. It has been shown that the larger grains were created for a deposited thickness of 30nm. Spectroscopic AFM mode was used as an alternative to the method of contact angles, to measure local surface energy. Decrease of surface energy is characteristic of a more ordered surface and was measured for a thickness of 30 nm of pentacene deposited on both substrates. Models of statistical analysis of spectral images, based on the Power Spectrum Distribution (PSD) have been used to explain the morphology of pentacene films. In addition, these models have provided a comprehensive description not only of the accessible surface of the sample, but also of its internal structural properties. Highlighted in the models, the critical thickness of 30 nm corresponds to a transition from the orthorhombic phase to the triclinic phase for pentacene molecules deposited on parylene. Similarly, a polymorphic transition occurs on the BCB. On OFETs, based on pentacene on BCB, the largest mobility of 3.1x10-2 cm²/Vs corresponds to the pentacene layer of 30nm, that shows a better ordering of the orthorhombic molecular packing in comparison with the triclinic packing.The molecular arrangement of X and Y structures based on DNA was observed, by AFM, in air and in two buffer solutions of Tris and HEPES on a mica substrate. It was shown that the treatment of the mica by Ni2 + ions increases the strength of the DNA/substrate interaction and reduces the diffusivity of the molecules. In air, wired macromolecules containing one double-stranded structure are observed on untreated mica and macromolecules with a 2D geometry on pretreated mica. Onto a non-treated, the greater thermal motion of weakly bounded to mica DNA molecules leads to the rupture of intermolecular bonding and the forming structures are more simple and not branched. The organization is different in solutions of Tris and HEPES. In the Tris solution, containing Mg2+ cations, the arrangement leads to a well-organized 2D architecture. In the HEPES solution, containing Ni2+ cations, the ionic strength is 10 times lower, this leads to a breaking of the bonds previously formed between DNA and mica. However, DNA molecules are near each other due to a partial substitution of already adsorbed Mg2 + cations by Ni 2 + cations of higher affinity with the mica. These results show that the two liquids promote a 2D assembly. In air, the networks are not stable and the few observed ones remain in a dendritic structure on the surface of pretreated mica and as a linear macromolecule on the untreated mica.

This thesis demonstrates that graphene produced by liquid-phase exfoliation can be co-deposited with a polymerie semiconductor for the fabrication of thin film field-effect transistors. The introduction of graphene to the n-type polymeric matrix enhances not only the electrical characteristics of the devices, but also the ambipolar behavior and the hole transport in particular. This provides a prospective pathway for the application of graphene composites for logic circuits.The same approach of blending was adopted to enhance the electrical characteristics of an amorphous p-type polymer semiconductor by addition of an unprecedented solution processable ultra-narrow graphene nanoribbon. GNRs form percolation pathway for the charges resulting in enhanced deviee performance in daras weil as under illumination therefore paving the way for applications in (opto)electronics.Finally, multifunctional photoresponsive devices were examined by introducing photochromic molecules exposing different substituents into small molecule or polymeric semiconductor films that were found to affect the photoswitching behavior.

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

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