<p>Despite tremendous achievements, the field of conjugated polymers is still in its infancy, mimicking the more mature inorganic, i.e. silicon-based, technologies. We may though look forward to the realisation of electronic and electrochemical devices with exotic designs and device applications, as our knowledge about the fundamentals of these promising materials grow ever stronger. </p><p>My own contribution to this development, originating from an idea first put forward by my tutor, Professor Magnus Berggren, is a design for a switchable polymer-based diode. Its architecture is based on a modified version of a recently developed highly-rectifying diode,12 where an intermediate molecular layer has been incorporated in the bottom contact. Due to its unique ability to switch its internal resistance during operation, this thin layer can be used to shift the amount of (forward) current induced into the rectifying structure of the device, and by doing so shift its electrical characteristics between an insulating and a rectifying behaviour (as illustrated below). Such a component should be of great commercial interest in display technologies since it would, at least hypothetically, be able to replace the transistors presently used to address the individual matrix elements. </p><p>However, although fairly simple in theory, it proved to be quite the challenge to fabricate the device structure. Machinery errors and contact problems aside, several process routes needed to be evaluated and only a small fraction of the batches were successful. In fact, it was not until the very last day that I detected the first indications that the concept might actually work. Hence, several modifications might still be necessary to undertake in order to get the device to work properly.</p>

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Fizik Anabilim Dalı, 2008. / Kaynakça var.

Conjugated polymers hold tremendous potential as low-cost, solution processable materials for electronic applications such organic light-emitting diodes and photovoltaics. While the concerted efforts of many research groups have improved the performance of organic electronic devices to near-relevant levels for commercial exploitation over the last decade, the overall performance of organic light-emitting diode and organic photovoltaic devices still lags behind that of their traditional, inorganic counterparts. Realizing the full potential of organic electronics will require a comprehensive, molecular-level understanding of conjugated polymer photophysics. Studying pure, well-defined, and reproducible conjugated polymer materials should enable these efforts; unfortunately, conjugated polymers are typically synthesized by metal-catalyzed step-growth polycondensation reactions that do not allow for rigorous control over polymer molecular weight or molecular weight distribution (i.e., dispersity). Chain-growth syntheses of conjugated polymers would not only allow for precise control over the aforementioned polymer metrics such as molecular weight and dispersity, but could also potentially create new applications by enabling the preparation of more advanced macromolecular structures such as block copolymers and surface grafted polymers. Our efforts toward realizing these goals as well as toward exploiting chain-growth methodologies to better understand fundamental conjugated polymer photophysics and self-assembly will be presented. / text

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

For several decades, the field of magneto-optics (MO) has demonstrated applications that have impact on every day applications such as in optical data storage, magnetic field sensing, crucial for magnetoencephalography and magnetocardiography; and compact and efficient optical isolators, among others. In the past, many of these applications and the devices designed for them have heavily relied on inorganic materials. Organic materials with a high MO response represent an interesting alternative to the inorganic equivalent by not only being a more cost efficient solution, but also by allowing the user to modify a number of variables to control and optimize the MO performance depending on the application and level of performance desired. In this dissertation I discuss the MO properties of novel organic materials, starting with polythiophene, which has been of interest due to the strong relationship between its high MO performance and its lamellar structure and regioregularity. I will also be discussing another material system that provides several degrees of MO tunability: magnetite based nanocomposites. A unique and novel synthetic approach described in this dissertation yields both highly transparent and MO responsive polymer films. I will be describing a systematic approach that indicates a strong influence of the size of the nanoparticle as well as the nanoparticle concentration in the MO performance of the bulk polymer, while maintaining high optical quality with minimal scattering and absorption in the visible and near infrared. Finally, I will be discussing the implementation of both a magnetite nanocomposite and a cobalt ferrite based nanocomposite in a free space magnetic field system and demonstrate the proof-of-principle operation of a sensing system.

Conjugated polymers are promising candidates for applications in all kinds of organic optoelectronic devices: OLEDs, organic field-effect transistors (OFETs) and organic photovoltaic cells. The main goal of this work was to investigate transport features of photogenerated electrical charge in pi-conjugated polymers by means of novel technique based on time-resolved electric field-induced second harmonic generation (TREFISH). TREFISH measurement setup was implemented in the laboratory of Molecular compounds physics, and applicability of the method has been verified. Measurements were performed on three different model polymers: methyl substituted ladder-type poly(para-phenylene) (MeLPPP), poly(fluorene-co-benzothiadiazole) (F8BT) and poly(spirobifluorene-co-benzothiadiazole) (PSF-BT), having different morphological and chemical structure. It has been found that motion of photogenerated charge carriers in π-conjugated polymer films experiences rapid dynamics after excitation. Different time domains of charge transport were distinguished. Initial fast transport of photogenerated charge carriers corresponds to the carrier motion along the single polymer chain or conjugated segment of the polymer chain. Slowest carrier motion phase is well described by the stochastic drift, which is attributed to interchain jumps and determines the macroscopic equilibrium mobility. Thus, the equilibrium mobility value is not applicable to the transport on nanometer scale up to tens of nanometers... [to full text] / Konjuguotieji polimerai kaip funkcinės medžiagos gali būti panaudoti įvairiuose prietaisuose: organiniuose šviestukuose, organiniuose lauko tranzistoriuose, organiniuose saulės elementuose. Šio darbo tikslas - nustatyti fotogeneruotų krūvininkų pernašos dėsningumus π – konjuguotuose polimeruose panaudojant naują žadinimo-zondavimo metodą pagrįstą išoriniu elektriniu lauku indukuota antrosios optinės harmonikos generacija. Pagrindinis dėmesys buvo skiriamas pernašos dinamikai. Molekulinių darinių fizikos laboratorijoje buvo įrengta matavimų schema ir įvertintas metodo tinkamumas krūvio pernašos tyrimams. Buvo atlikti krūvio pernašos matavimai trijuose skirtinguose konjuguotuosiuose polimeruose. Nustatyta, kad fotogeneruotų krūvininkų judris tuoj po sužadinimo yra daug didesnis lyginant su stacionaria judrio verte, o krūvio pernašos dinamiką lemia konjuguoto polimero struktūrinė hierarchija, krūvininkų judėjimas yra daugialypis, susidedantis iš greito judėjimo viena polimero grandine ar konjuguotais polimero grandinės segmentais ir lėto šokavimo tarp atskirų polimero grandinių Pirmą kartą detaliai išnagrinėta šviesa sugeneruotų krūvininkų pernašos dinamika konjuguotuose polimeruose. Darbo rezultatai suteikia žinių apie fundamentalius krūvininkų pernašos mechanizmus konjuguotuose polimeruose, kurios gali būti panaudotos kuriant organinius elektronikos prietaisus.

The synthesis and biological sensing applications of novel water soluble poly(para-phenyleneethynylene)s (PPEs) are presented. The ease of synthesis, synthetic variability, and dramatic chromicity of PPEs makes them well suited for biological and sensing applications. Molecular recognition and signal transduction can be achieved by using PPEs as sensory materials. By incorporating biological functional groups (e.g. sugars), PPEs can efficiently detect the presence of toxic heavy metals, proteins, and bacteria through either fluorescence quenching or enhancement. Rapid, precise, and convenient sensory arrays for the detection of biological analytes are possible through the formation of gold nanoparticle-PPE constructs.

Thesis (Ph.D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008. / Committee Chair: Tolbert, Laren; Committee Member: Collard, David; Committee Member: Lyon, Andrew; Committee Member: Srinivasarao, Mohan; Committee Member: Wilkinson, Angus

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

Conjugated Polymers have attracted a great deal of research interest in recent years due to their optoelectronic properties which makes them suitable for applications in organic light-emitting devices (OLEDs) and organic photovoltaics. Their properties are strongly dependent on the electron-electron and electron-nuclear interactions as well as the disorder which is present in almost all systems at finite temperatures. In this thesis the optical properties of electronically neutral conjugated polymers will be investigated. The results obtained are general and applicable to a wide range of parameters. In order to compare these to experiment the optical properties of poly( paraphenylene), poly(para-phenylene vinylene), and derivatives have been calculated. In these polymers the primary photoexcitations are Frenkel excitons which can be described by the Frenkel-Holstein Hamiltonian, which explicitly takes into account the exciton-nuclear coupling. Disorder can be introduced into this model both as diagonal and off-diagonal disorder within the Hamiltonian. First the optical transitions in ordered, linear conjugated polymers are investigated. It is found that the length of the polymer has a direct spectroscopic signature in the emission spectrum. When off-diagonal disorder is introduced the excitons localise on portions of the chain and the length of these portions, the conjugation length, then shows a clear emission signature. As such, a disordered polymer can be described theoretically as a chain of shorter segments, which define chromophores in a polymer context. Following from these calculations the role of conformation was investigated and effects were observed that greatly determine the optical properties of non-linear polymers. Most notable the Herzberg-Teller effect, which renders symmetrically forbidden transitions weakly allowed and greatly affects the absorption and emission spectra. The signatures observed in these spectra allow the determination of the (coarse grained) conformation of the polymer, something that has been difficult to measure directly.