The interest in conjugated polymers has been two-fold. A rich variety of intriguing physical phenomena, combined with its immense technological implications in the area of molecular electronics, sensors etc. has inspired the researchers all over the globe. The work presented in this thesis is focussed on one of the most widely studied conjugated polymers, namely polyaniline (PANI), which is well known for its high conductivity and remarkable stability in the proton-doped form. The thesis is divided into two chapters and each chapter is further divided into several parts. In the first chapter, we take a look at some novel systems based on PANI that exhibit interesting electrical and optical properties. To begin with, we report the synthesis and characterization (Part I, Chapter 3) a new class of highly conducting polyaniline doped with electron deficient Lewis acids, namely the boron trihalides (BX3, X = F, Cl, and Br). We discuss the various attributes of this interesting class of materials that set it apart from the conventional proton-doped PANI systems. It is known that the conductivity in doped PANI is greatly influenced by the presence of structural disorder. Previous studies have associated the conductivity in doped PANI with the partial crystallinity that is achieved upon proton doping. At the same time, the amorphous regions that have a high degree of disorder were believed to suppress the metallic nature in these doped systems. In view of this "higher-crystallinity-higher-conductivity" picture, it is interesting to note that the BX3 doped PANI remain absolutely amorphous despite being more conducting than previously known samples. Through our investigation, we have been able to address some of the most important and long-standing questions pertaining to the nature of the charge carriers and the role of disorder in doped PANI. A detailed study of the transport properties in Part II, Chapter 3 helps us to understand the mechanism of charge transfer in these novel systems. With the help of our results, we establish that the present systems do not belong to the family of quasi one-dimensional conductors, in stark contrast to the conventional proton-doped samples. Instead, our systems are best described as granular metals, where the conduction mechanism is controlled by the size of the conducting grains and the nature of the grain boundaries. Through a comprehensive study of the magnetic properties based on d. c. magnetic susceptibility and EPR spectroscopy, we further establish that the intrinsic conductivity of these samples are much higher than the previously known systems. By studying the interaction of the mobile charge carriers and the localized spins in the systems, we have established that our samples are far less disordered, and therefore qualify as superior systems when compared to the more conventional proton-doped PANI. One of the serious disadvantages of the conventional protonated PANI lies in its thermal instability. On heating above 75 ±C in air, the polymer backbone undergoes an irreversible aerial oxidation that disrupts the extended conjugated structure. This is marked by a rapid drop in conductivity by a few orders of magnitude. BF3-doped PANI, which has the highest conductivity sample among the present series of samples, exhibits a remarkable thermal stability in air (Part III, Chapter 3). Upon heating, the conductivity initially increases and then reaches a saturation value. The polymer can be heated at temperatures as high as 225 ±C, without any signs of degradation. With the help of temperature dependent conductivity, XPS and FTIR spectroscopy we have tried to understand this unexpected phenomenon. In Part IV, Chapter 3, we report the synthesis and characterization of a novel class of functionalized PANI that exhibit an intense deep-blue photoluminescence. A de- tailed characterization based on absorption, photoluminescence, XPS, NMR and FTIR spectroscopy has been carried out to study the chemical state of this new class of light- emitting polymers. Further, we note that the synthetic procedure followed in this work can provide a very general route to the synthesis of diversely useful derivatives of PANI. In Chapter 4, we have investigated the microscopic origin of conductivity in doped PANI. Among the several factors that can influence the conductivity of doped polymers, one is the microstructural order. To understand this better, we carried out a detailed investigation, based on scanning tunneling microscopy (STM) and spectroscopy (STS) of undoped and doped PANI films (Part I, Chapter 4). We have shown for the ¯rst time that solution processed thin films of undoped PANI has an abundance of PANI anorods self organized over very large areas. Further, we observe that this ordered orphology is Preface vii very sensitive to the choice of dopants and the doping procedure. We have shown that the morphological order can greatly influence the electronic structure and therefore the properties of these systems. To understand the role of dopant-polymer interaction in controlling the conductivity of doped PANI, we carried out x-ray photoelectron spectroscopy (XPS) studies on a large number of partially and fully doped samples (Part II, Chapter 4). We find an interesting trend in the higher binding energy feature and the asymmetry of the N and C 1s spectra, which correlates directly with the respective conductivities of different samples. The analysis of these spectra brings out interesting facts about the chemical state and the electronic structure of these samples. In summary, we have reported new PANI based systems with improved electrical and interesting optical properties, and have studied various factors that influence the properties of these as well as some of conventional doped PANI systems.

<p>Polymer electrochromism on PEDOT coated fibres was successfully achieved. The electrochromic property of the PEDOT polymer is an excellent property. This feature gives way to many more research works at present and in the future also. The electrochromic property of the PEDOT polymer is utilized in this thesis work to design an electrochromic display pixel.</p><p> </p><p>The polymer coating over the fibres were obtained by using In-situ polymerization technique. The coated-fibres were used to design a display-pixel. Electrochemistry is performed successfully on the designed pixel to study electrochromism over the pixels. An electrochemical fibre transistor is designed successfully using the polymer coated fibres.</p> / Polymer Electrochromism on PEDOT coated fibres

<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.

The design, synthesis and characterization of novel conjugated polymers are described. Using a coupling reaction recently developed within our labs, polymers were constructed through triazene linkages generated by joining N-heterocyclic carbenes (NHCs) with organic azides. This triazene reaction produced polymer of sufficiently high molecular weight as to be spin-coated and rendered conductive upon doping with iodine. The reaction also has potential for executing post-polymerization modifications. This was evidenced through rapid functionalization of poly(4-methylazido-styrene) via triazene formation using a commercially available N-heterocyclic carbene (NHC). A formal anion metathesis of benzobis(imidazolium)s was used to transform neutral block copolymers into block ionomers. Further investigation of the block ionomers revealed their solvent mediated self assembly. The gradual change of organic to aqueous media caused the adoption of a three-dimensional micelle conformation as determined by transmission electron microscopy and dynamic light scattering. Through the exploitation of carbene-carbon disulfide adducts, new chain transfer agents were generated. After 2-dithiocarboxylate-imidazolium adduct formation, alkylation was performed with benzyl bromide. The resulting charged chain transfer agent was tested for its ability to moderate radical addition fragmentation (RAFT) polymerizations of styrene. A considerable increase in transfer kinetics as compared to that of commonly used RAFT agents was observed whilst retaining low polydispersity and molecular weight control. The rate enhancement is presumably due to the electron withdrawing imidazolium activating the thionyl towards the nucleophilic radical while retaining effective fragmentation. Ion coordinating macrocycles were affixed to a poly(methacrylate) scaffold for employment as electrolyte extractants. Polymer bound calix[4]pyrrole was found to complex fluoride and chloride with sufficient strength as to extract tetrabutylammonium salts from water. Enhanced extraction abilities were observed when calix[4]pyrrole was used in conjunction with benzo-15-crown-5. Methacrylate polymers containing both macrocycles affected the removal of aqueous potassium fluoride from a biphasic water/dichloromethane mixture. To provide evidence for the presence of potassium fluoride within the dichloromethane layer, ¹⁹F NMR and flame emission spectroscopy were used. / text

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

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