The main focus of this thesis is on the aromaticity of the ground state and electronically excited states of π-conjugated molecules and polymers, as well as how aromaticity is connected to their properties. The electronic structures of polybenzenoid hydrocarbons (PBHs) were explored through density functional theory (DFT) calculations and the π-component of the electron localization function (ELFπ). The study revealed how the π-electronic structure is influenced by the fusion of double bonds or benzene rings to the PBHs. We also demonstrated that the π-electrons of benzene extend to accommodate as much aromaticity as possible when bond length distorted.   The aromatic chameleon property displayed by fulvenes, isobenzofulvenes, fulvalenes, bis(fulvene)s, and polyfulvenes were investigated using DFT calculations. The tria-, penta-, and heptafulvenes were shown to possess ionization energies and electron affinities which can be tuned extensively by substitution, some of which even outperform TTF and TCNQ, the prototypical electron donor and acceptor, respectively. The singlet-triplet energy gap of pentafulvenes can be tuned extensively by substitution to the point that the triplet state is lower than the singlet state and thus becomes the ground state. The ELFπ of isobenzofulvene shows that the benzene ring in an electronically excited state can be more aromatic than the corresponding ring in the ground state. We have shown that the 6-ring of [5.6.7]quinarene is influenced by a Hückel aromatic resonance structure with 4n+2 π-electrons in the excited quintet state. The bis(fulvene)s which are composed of a donor type heptafulvene and an acceptor type pentafulvene, retain the basic donor-acceptor properties of the two fragments and could function as compact donor-acceptor dyads. A few of the designed polyfulvenes were found to have band gaps below 1 eV at the PBC-B3LYP/6-31G(d) level. Various 2,7-disubstituted fluorenones and dibenzofulvenes were synthesized and their excited state properties were investigated by absorption spectroscopy and time-dependent DFT calculations. It was found that the 1A → 1B transition of ππ* character can be tuned by substitution in the 2,7-positions. The 2,7-bis(N,N-dimethyl) derivatives of fluorenone and dibenzofulvene displayed low energy transitions at 2.18 and 1.61 eV, respectively, in toluene.

To better understand the physical and electronic properties of donor and acceptor-based structures used in organic electronic applications, a variety of oligothiophene and naphthalene diimide-based small conjugated molecules were designed, synthesized, and characterized. The materials were initially synthesized using oxidative copper-chloride coupling reactions, palladium-catalyzed amination reactions, Friedal-Crafts acylations, Negishi coupling reactions, and Stille coupling reactions. Once isolated, the physical properties of the compounds were characterized through a combination of X-ray crystal structure, thermogravimetric analysis, differential scanning calorimetry, UV-vis. absorption spectroscopy, cyclic voltammetry, and differential pulse voltammetry, along with comparison to quantum-chemical calculations. In some cases, the radical cations or radical anions were generated by chemical oxidation and analyzed by vis-NIR spectroscopy. Furthermore, the electronic properties of the materials were investigated through incorporation as solution-processed active layers in organic field-effect transistors. Multiple examples exhibited hole- and / or electron-transport properties with electron mobility values of up to 1.5 cm²V⁻¹s⁻¹, which is among the highest yet reported for an n-channel OFET based on a solution-processed small molecule.

The synthesis and characterization of two donor acceptor type conjugated polymers were investigated. The electrochemical properties were examined using cyclic voltammetry, spectroelectrochemistry and kinetic studies. The increase in the alkyl chain length attached to the fluorene unit was investigated by the corresponding electrochemical characteristics. The synthesis was carried out via Stille coupling of 4,7- dibromo-4&#039 / -(tert-butyl)spiro[benzo[d]imidazole-2,1&#039 / cyclohexane] and 2,5- bis(tributylstannyl)thiophene with 9,9-dihexyl-9H fluorene and 9,9-didodecyl-9H fluorene respectively. Both of the polymers were neutral state green polymers. They had optical band gaps of 2.46 and 2.54 eV respectively. Increasing the chain length resulted in an increase in solubility and processibility of the polymer but also an increase in the band gap. This was due to the increased bulkyness of the alkyl group, leading to a decrease in the effective conjugation and planarity. They both had distinctive &pi / -&pi / * transitions, band structure and backbone that provides oxidative doping. P1, with the shorter alkyl chain had a lower oxidation potential than P2. Neither of the polymers was capable of being n-doped. They were both multichromic, revealing colors from neutral state green to doped state blue.

ABSTRACT BIOACTIVE SURFACE DESIGN BASED ON CONDUCTING POLYMERS AND APPLICATIONS TO BIOSENSORS Ekiz, Fulya M. Sc., Department of Biotechnology Supervisor: Prof. Dr. Levent Toppare Co-Supervisor: Prof. Dr. Suna Timur June 2012, 88 pages An underlying idea of joining the recognition features of biological macromolecules to the sensitivity of electrochemical devices has brought the concept of biosensors as remarkable analytical tools for monitoring desired analytes in different technological areas. Over other methods, biosensors have some advantages including high selectivity, sensitivity, simplicity and this leads to solutions for some problems met in the measurement of some analytes. In this context, conducting polymers are excellent alternatives with their biocompatibility and ease of applicability for an efficient immobilization of biomolecules in preparing biosensors. Using several materials and arranging the surface properties of the electrodes, more efficient and seminal designs can be achieved. In this thesis, it is aimed to create new direct biosensors systems for the detection of several analytes such as glucose and pesticides thought to be harmful to the environment. Recently synthesized conducting polymers (polyTBT) / (poly(2-dodecyl-4,7-di(thiophen-2-yl)-2H-benzo[ d][1,2,3]triazole) and (poly(TBT 6 -NH2 ) / poly(6-(4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazol-2-yl)hexan-1-amine) were utilized as a matrices for biomolecule immobilization. After successful electrochemical deposition the polymers on the graphite electrode surfaces, immobilization of glucose oxidase (GOx) and choline oxidase (ChO) were carried out. Amperometric measurements were recorded by monitoring oxygen consumption in the presence of substrates at -0.7 V. The optimized biosensors showed a very good linearity with rapid response times and low detection limits (LOD) to glucose and choline. Also, kinetic parameters, operational and storage stabilities were determined. Finally, designed biosensor systems were applied for glucose and pesticide detection in different media.

Conjugated polymers and oligomers are great materials for use in the next generation devices namely organic field effect transistors, light emitting diodes and polymeric solar cells. Apart from having the potential for developing power-efficient, flexible, robust and inexpensive devices, conjugated polymers can also be tuned by molecular design to optimize device characteristics. One key problem for the full commercial exploitation of conjugated polymers is that the charge carrier mobility of the state-of-the-art polymer semiconductors is much lower than required for many applications. The performance of the devices is strongly dependent on the molecular structure and supermolecular assembly of the conjugated polymer chains. This thesis covers our attempts to design molecular structure to control and improve the solid state properties of conjugated polymers. The relative placement of side chains along the backbone has a great influence on the solid state ordering of conjugated polymers. Poly(2,5-disubstituted-1,4-phenylene ethynylene)s (PPE)s, an important class of conjugated polymers, are generally synthesized by Pd-catalyzed coupling polymerizations of appropriately substituted diiodo and diethynyl benzenes (i.e., A-A and B-B type monomers). In asymmetrically substituted PPEs, this results in an irregular substitution pattern of the side chains along the polymer backbone. We report a new synthetic approach to prepare regioregular unsymmetrically substituted PPEs by polymerization of 4-iodophenylacetylenes (i.e., A-B type monomer). We provide a detailed discussion of various approaches to the synthesis of PPEs with different regioregularities and provide a description of the differences between regioregular and regiorandom analogs. The effect of regioregularity becomes even more important when the two side chains are very dissimilar or amphiphilic. We explore the effect of relative placement hydrophobic (dodecyloxy) / hydrophilic (tri(ethylene glycol) and hydrophobic (dodecyloxy)/fluorophilic (fluoroalkyl) side chains along the poly(1,4-phenylene ethynylene) backbone. We found that the regioregular substitution of the polymer backbone provides a structure in which the side chains segregate to afford a Janus-type structure. The regioregular polymer chains pack more densely in a monolayer at the air-water interface, and pack into a bilayer in the solid state to form a highly crystalline material. Pentacenes are very important organic molecules for use as semiconductor in oFETs due to their low band gap and high field effect mobility. One approach to reduce the bandgap of a polymeric system and improve performance is to include low bandgap small molecules into the conjugated backbone. A new copolymer system consisting of pentacene and terthiophene was developed and its optical and electronic properties along with its stability were evaluated. We report the use of ultrasonication of P3HT as a novel operationally-simple process to significantly improve the field effect mobility of P3HT-based FETs, thereby potentially eliminating the need for dielectric surface modifications or further processing of the device. Investigation of the sonicated polymer samples by number of characterization techniques indicates that ultrasonication leads to aggregation and ordering of the P3HT chains resulting in increase in the mobility.

Conjugated polymers comprise some of the most promising materials for new technologies such as organic field effect transistors, solar light harvesting technology and sensing devices. In spite of tremendous research initiatives in materials chemistry, the potential to optimize device performance and develop new technologies is remarkable. Understanding relationships between the structure of conjugated polymers and their electronic properties is critical to improving device performance. The design and synthesis of new materials which self-organize into ordered nanostructures creates opportunities to establish relationships between electronic properties and morphology or molecular packing. This thesis details our progress in the development of synthetic routes which provide access to new classes of conjugated polymers that contain dissimilar side chains that segregate or dissimilar conjugated blocks which phase separate, and summarizes our initial attempts to characterize these materials. Poly(1,4-phenylene ethynylene)s (PPEs) have been used in a variety of organic electronic applications, most notably as fluorescent sensors. Using traditional synthetic methods, asymmetrically disubstituted PPEs have irregular placement of side chains on the conjugated backbone. Herein, we establish the first synthetic route to an asymmetrically substituted regioregular PPEs. The initial PPEs in this study have different lengths of alkoxy side chains, and both regioregular and regiorandom analogs are synthesized and characterized for comparison. The design of amphiphilic structures provides additional opportunities for side chains to influence the molecular packing and electronic properties of conjugated polymers. A new class of regioregular, amphiphilic PPEs has been prepared bearing alkoxy and semifluoroalkoxy side chains, which have a tendency to phase separate. Fully conjugated block copolymers can provide access to interesting new morphologies as a result of phase separation of the conjugated blocks. In particular, donor-acceptor block copolymers that phase separate into electron rich and electron poor domains may be advantageous in organic electronic devices such as bulk heterojunction solar cells, of which the performance relies on precise control of the interface between electron donating and accepting materials. The availability of donor-acceptor block copolymers is limited, largely due to the challenges associated with synthesizing these materials. In this thesis, two new synthetic routes to donor-acceptor block copolymers are established. These methods both utilize the catalyst transfer condensation polymerization, which proceeds by a chain growth mechanism. The first example entails the synthesis of a monofunctionalized, telechelic poly(3-alkylthiophene) which can be coupled to electron accepting polymers in a subsequent reaction. The other method describes the first example of a one-pot synthesis of a donor-acceptor diblock copolymer. The methods of synthesis are described, and characterization of the block copolymers is reported.

[pt] Nos últimos anos, polímeros conjugados ganharam muita atenção na eletrônica orgânica por seu uso na fabricação de dispositivos flexíveis e de baixo custo. Como resultado, diferentes tipos de dispositivos têm sido desenvolvidos como: diodos emissores de luz orgânicos (OLEDs), células fotovoltaicas orgânicas (OPVs) e transistores de efeito de campo orgânicos (OFETs). Em particular, para os OFETs seu desempenho depende da interface isolante/semicondutor, principalmente, devido ao acúmulo de portadores de carga. Além disso, as propriedades da interface afetam fortemente o transporte de carga através do canal de dispositivo. Por estas razões, a pesquisa de novos polímeros semicondutores e novos materiais dielétricos é um fator chave para aprimorar o desempenho dos dispositivos. Neste trabalho, os polímeros PMMA, PVA, FORMVAR e PU foram investigados como materiais dielétricos. Inicialmente foram fabricados capacitores de placas planas paralelas do tipo ITO/dielétrico/Al para determinar a constante dielétrica dos isolantes, as curvas JxV e a capacidade por unidade de área. Desenvolveu-se OFETs tipo Top-Gate/Bottom-Contacts (TGBC) com a estrutura Au/P3HT/PMMA/Ag e Au/P3HT/PU/Ag. No trabalho, a espessura dos dielétricos foi variada para aprimorar o desempenho dos dispositivos. Para os OFETs de PMMA obteve-se resultados concordantes com os da literatura. Os novos OFETs de PU apresentaram tensões de operação menores que 5V, que é um requisito para a integração destes OFETs em aplicações da eletrônica orgânica. A mobilidade obtida nestes OFETs de PU foi de 1.25 cm(2)/V.s, com uma tensão limiar de 0.02 e uma razão On/Off de 100. / [en] In the last years, conjugated polymers have received much attention in organic electronics for their use in the fabrication of low cost and flexible devices. As a result, different types of devices have been developed e.g. organic light emitting diodes (OLEDs), photovoltaic devices (OPVs) and field effect transistors (OFETs). For the OFETs in particular, their performance depends primarily on insulator/semiconductor interface, mainly due to charge carrier accumulation. Moreover, the interface properties strongly affect the charge transport through the device channel. For these reasons, the research for new semiconductor polymers and new dielectric materials is key to advancing the performance improvement of devices. In this work, the polymers PMMA, PVA, FORMVAR and PU were used as dielectric materials. Initially, parallel plate capacitors of the structure ITO/dielectric/A1 were made, in order to determine the dielectric constant of the insulators, get the curves JxV and the capacity per unit area. It was used to develop Top-Gate/Bottom-Contacts (TGBC) OFETs with structures of Au/P3HT/PMMA/Ag and Au/P3HT/PU/Ag. The thicknesses of the dielectric materials were varied to improve the performance of the devices. For the PMMA OFETs, the results obtained were concordant with those of the existing literature. The new PU OFETs presented with operating voltages of less than 5V, appropriate for applications of these OFETs in organic electronics. The mobility of the PU OFETs was 1.25cm(2)/V.s, the threshold voltage 0.02V and the On/Off ratio 100.

Neste trabalho, o método de Monte Carlo e a resolução da Equação Mestra foram utilizados para simular o processo de difusão espectral da excitação em um sistema polimérico emissor de luz. A metodologia utilizada incorpora a relaxação energética intramolecular, a migração de energia incoerente entre segmentos conjugados e o processo final radiativo (luminescência). O principal objetivo é comparar os resultados da simulação e de experimentos envolvendo medidas de absorção, de excitação óptica e de luminescência realizadas no IFSC ao longo dos últimos anos ou provenientes da literatura especializada. Além disso, a simulação pretende elucidar a natureza dos processos fotofísicos em semicondutores orgânicos e testar a validade de teorias analíticas existentes, o que é essencial para a aplicação dessa classe de materiais como dispositivos no futuro. Especial atenção é dada na análise do comportamento temporal da difusão espectral em sistemas homogêneos em que o acoplamento dipolar na transferência de energia é realizado entre uma matriz de segmentos conjugados distribuídas aleatoriamente. A temperatura foi incorporada ao modelo. A comparação dos resultados da simulação com os resultados experimentais permitiu comprovar a validade do modelo proposto, do programa utilizado e entender melhor características de parâmetros não conhecidos em polímeros conjugados, como a influência da forma da distribuição energética dos estados eletrônicos e a distribuição e da temperatura no processo de migração do éxciton. Foi possível reproduzir com sucesso os espectros de luminescência e de absorção em polímeros conjugados descritos na literatura. Além disso, a simulação permitiu explicar resultados relacionados a sistemas poliméricos homogêneos anisotrópicos como polímeros estirados por uma tensão mecânica e materiais não homogêneos híbridos contendo polímero conjugado emissor de luz e nanopartículas. A maior contribuição foi o entendimento do efeito da temperatura nas propriedades de emissão como deslocamento espectral e alargamento homogêneo. Efeitos anômalos, como o deslocamento da emissão com a temperatura e o alcance da difusão com o tempo, foram explicados em termos da termalização do estado excitado e frustração da migração. Por fim, foi possível estudar os processos fotofísicos envolvidos em heteroestruturas orgânicas contendo gradiente energético que permitem o controle da migração direcional do éxciton e suas propriedades de emissão a partir dos processos de transferência de energia tipo Förster (dipolo-dipolo). O controle sobre os processos fotofísicos do polímero luminescente foi realizado através da alteração tanto da orientação como do tamanho de conjugação do material de polimérico. / In the present work, the Monte Carlo method and the direct numerical integration of the Master Equation were employed to simulate the excitation spectral diffusion process in light emitting polymeric systems. The methodology employed a competition among the internal intra-molecular relaxation, the inter-molecular incoherent energy transfer via Förster mechanism and the final process that may be a radiative emission or a non radiative relaxation through a suppression center. This works main objective is to compare the simulation results with the experiments of absorption, optical excitation and luminescence carried out in our group, throughout the last years or from the specialized literature. Moreover, the simulation intends to elucidate the nature of the photophysical processes in organic semiconductors and to test the validity of existing theories, what is essential for the application of this class of materials to devices in the future. Special attention is given to the analysis of the time dependence and the effect of temperature in homogenous systems, where the energy transfer and spectral diffusion were carried out through a matrix of randomly distributed conjugated segments coupled by dipole interaction. The comparison of the simulation results with the experimental ones allowed to prove the validity of the model, the computational program and to better understand characteristic of parameters for conjugated polymers which are still studied. Different energy distributions of electronic states, molecular position and orientation are used in order to simulate molecular configurations obtained by various sample preparation methodologies. With the simulation, it was possible to reproduce with success the experimental luminescence and absorption spectra in polymers conjugated described in literature. Besides, the simulation allowed to explain the exciton migration and properties related to temperature, such as the red shift and broadening of the spectral lines of conjugated polymer emission. The non exponential characteristics of the emissions time resolved intensity curves have been reproduced. The simulation was used to understand effects of temperature on the spectral diffusion as well. Anomalies related to spectral shift emission spectra with temperature and the mean diffusion length with time were explained with the thermalization and frustration of the migration at sufficiently low temperatures and at long relaxation times. Finally, it was possible to study the photophysical processes present in organic heterostructures having energy gradient, as well as the control of the properties of emission via changing the Förster type energy transfer processes between emitting polymers. The control over the photophysical process of the luminescent polymer was accomplished by changing both orientation and mean conjugation length of the polymer material.

Cette thèse est porté sur l'étude du transport électronique dans différents matériaux organiques semi-conducteurs, considérés comme candidats potentiels pour des applications en Electronique de Spin Organique. Pour rendre possible la diffusion d'un courant polarisée en spin à l'intérieur d'un semi-conducteur (injection-transport-détection), le mécanisme de transport et la mobilité des porteurs de charge, ainsi que la nature et la valeur de la résistance de contact de l'interface séparant matériau organique et électrodes métalliques ferromagnétiques, doivent répondre à des critères très stricts. Tous les dispositifs sont en géométrie latérale. Nous étudions trois matériaux organiques différents: des fibres supramoléculaires auto-assemblées, une encre de nana-flocons de graphene exfolié en phase liquide et un polymère semi-conducteur fortement dopé en forme de couche mince. Nos résultats montrent que les conditions sont partiellement respectées, mais que des défis demeurent. / In this thesis, we study the electronic charge transport properties in different high mobility organic semiconductors considered as possible candidates for applications in Organic Spintronics. Stringent conditions are needed to make possible the diffusive transport of a spin-polarized current through an organic spacer (injection-transport-detection): the mechanism of charge transport and the carriers mobility, as well as the interface between the organic semiconductor and the ferromagnetic metallic electrodes, should meet special criteria. Our devices are in lateral geometry. We investigate three organic materials, all compatible with wet processing of organic electronics: supramolecular fibers self-assembled by light irradiation, an ink of liquid-phase exfoliated graphene nano-sheets and a conjugated polymer semiconductor thin film exposed to strong electrochemical doping. We observe that the criteria are partially matched, but some challenges are still present.

It is well established that the morphology and physical properties of an organic semiconducting (OSC) material regulate its electronic properties. However, structure-function relationships remain difficult to describe in polymer-based OSC, which are of particular interest due to their robust mechanical properties. If relationships among the molecular and bulk levels of structure can be found, they can aid in the design of improved materials. To explore and detail important structure-function relationships in polymer-based OSC, this work employs molecular dynamics (MD) simulations to study various π-conjugated polymers in different environments. Two independent investigations are discussed in this work. One investigation examines how the purposeful disruption of the π-conjugated backbone to increase the chain flexibility impacts the chain structure and packing in the condensed phase. This is done by adding a conjugation break spacer (CBS) unit of one to ten carbons in length into the monomer structure of diketopyrrolopyrrole-based polymers. It is found that trends in the folding and glass structure follow the increase and the parity (odd versus even) of the CBS length. The second investigation analyzes a variety of polymers and small molecule acceptor (SMA) blends to observe the effects of changing the shape of either component and the physical properties of the material, as well as the structure of the polymer chains. It is found that the conjugated core, the side chains, and the planarity or sphericity each influence the density and diffusion of the materials made.