Conjugated polymers are widely used and rapidly developed in practical polymer-based light-emitting electronic devices. Understanding the electrochemical reaction of conjugated polymer has become essential in the design and operation of devices such as electrochemical light-emitting diodes. In particular, we have studied the dynamics and kinetics of oxidation/reduction behavior of conjugated polymer single-molecules and nanoparticles in order to obtain the molecular level properties of deeply trapped holes in organic semiconductor devices. Theoretical calculations suggest the penetration of ions and solvent molecules effectively stabilizes the injected charges, which allows homogeneous charge distribution and further hole injection. The formation and decay of deep traps have been explored by changing the charging rate and duration. We found that the laser excitation significantly promotes the untrapping of deep holes. Electrogenerated chemiluminescence of single nanoparticles has been investigated to unravel the effects due to particle heterogeneity, which are masked in bulk electrochemical studies of nanoparticles. Bigger particles showed more intense light and longer duration time than smaller ones. Co-reactant, tripropylamine can facilitate the formation of electrogenerated chemiluminescence as well as alleviate the polymer oxidation and following irreversible electrochemical reaction. Electrochemically generated light waves from the conjugated polymer thin films have been visualized to obtain microscopic level understanding on the complex reaction mechanism. Electrochemical reaction occurs at local defects and propagates isotropically over macroscopic distances with a sharp wave front. The initially injected holes (oxidized polymers) drag counter-ions into the film, thereby induce a phase-transition-like swelling that enhances transport of ions and solvent and move forward the double layer and corresponding propagation of the wave. / text

Organic photovoltaic cells (OPV’s), renewable energy devices that can convert sunlight into electricity, have a bright future. Most OPV’s are made of conjugated polymers since they can absorb light and have semiconducting properties. However, the low power conversion efficiency (PCE) of OPV’s is a challenge in their development. The main structure of OPV’s includes three main parts: an electron donor, an electron acceptor, and electrodes. To improve the PCE of an OPV, many factors need to be considered, such as light absorption, the fundamental gap, the optical gap, and the OPV’s film thickness. The addition of heteroatoms to conjugated polymers is a way to change the electronic properties of the donors and may improve the PCE. This thesis describes the use of computational methods to determine how oxygen and sulfur atoms affect the electronic properties of a conjugated polymer. The data suggest that the fundamental gaps and binding energies decrease after replacing oxygen with sulfur. Additionally, the results also suggest that incorporating a sulfur atom into the conjugated polymer can increase the dipole moment change, which may lead to accelerated charge dissociation and may reduce charge recombination.

We plan to prepare conjugated polymers containing £k-excessive thiophene and £k-deficient oxadiazole group in the main chain, and introduction of phenyl or alkoxy groups on the side chain. The NMR, IR, TGA, DSC, GPC, stability, and other optical properties will be examined.

Single-walled carbon nanotubes (SWNTs) are envisioned as one of the most promising materials for next-generation electronic devices such as field-effect transistors, photovoltaics, new power sources and bio/chemical sensors. In particular, solution processable SWNT networks are of great interest for flexible and stretchable electronics. However, most of these applications specifically require pure semiconducting (sc-) or metallic (m-) SWNTs. However, large scale synthetic methods for SWNTs always produce a mixture of semiconducting and metallic carbon nanotubes. In recent years, several biochemical separation techniques such as DNA assisted separation, density gradient ultracentrifugation, and gel chromatography techniques have been utilized to separate semiconducting and metallic SWNTs. Although these methods can be used for sorting SWNTs according to their chiralities, they are either time-consuming or not easily scalable. In addition, the supramolecular functionalization of SWNTs with conjugated polymers has received a great deal of attention due to its capability to extract sc-SWNTs via simple sonication and centrifugation steps within a few hours. Furthermore, π-conjugated polymers can be modified by suitably changing monomers and/or comonomers, and it is also easy to control molecular weight and solubility of resulting polymers in organic solvents and aqueous media. There is also the possibility for selectively extracting specific chirality (n, m) nanotubes using specifically designed macromolecular structures. Except for its application to the separation of SWNTs, the supramolecular complexes of π-conjugated polymer and SWNTs have potential applications in many research areas such as new composite materials. After a brief overview of the current work related to the investigation of the supramolecular interaction between various conjugated polymers and SWNTs (chapter 1), synthesis of a series of different types of fluorene-based conjugated copolymers and their supramolecular complex formation properties with SWNTs are described (chapter 2, 3, 4, 5 and 6). In order to understand the effect of conjugated polymer backbone and side-chain structure on formation of supramolecular complexes with SWNTs, several crucial factors were investigated by: (1) altering the polymer backbone composition; (2) introducing different solubilizing (functional) groups while the polymer backbone remains the same; (3) changing the side-chain functional groups, and (4) introducing different polymer repeat units with varying physical and chemical properties. The experimental results indicated that all of the resulting polymer-SWNTs complexes possess excellent (or moderate) solution stability in organic solvents such as tetrahydrofuran (THF), toluene, and xylene. It was also demonstrated that the interaction between the conjugated polymers and SWNTs is strongly influenced by polymer structure; even minor changes on side-chains have a significant effect on the selectivity of the polymers in dispersing specific SWNT structures. This investigation highlights the potential importance of incorporating different types of heterocyclic aromatic rings (electron rich or electron poor), and introducing side chains with varying electronic and geometric structure on selective solubilization of SWNTs. Polymer molecular weight and solvent properties also strongly influence the π-conjugated polymer assisted dispersion of specific chirality SWNTs. Although some progress has been made, the search for a conjugated polymer that selectively solubilizes specific SWNT chiralities on large scale remains a challenge. / Thesis / Doctor of Philosophy (PhD)

This thesis is dedicated to the study of fluorescent conjugated polymers made of fluorene labelled with rylene moieties. Those polymers are important candidates for use in Organic Light Emitting Devices (OLEDs). The dyes present in the polymers were studied at the single-molecule level. The first part of the work is devoted to the construction and validation of an epi-fluorescent confocal/widefield/Total Internal Reflection microscope. The ensemble properties of the samples are first measured in solution. The combination of steady-state and time-resolved spectroscopies allows us to unravel the photophysics of the conjugated polyfluorene polymer containing perylenediimides in its backbone. Energy transfer is found to occur between the polyfluorene and the perylenediimide units. Beside energy transfer, a photoinduced electron transfer is also supposed to take place. Widefield microscopy is used to measure the end-to-end distance in single polymer chains. From those measurements the polymer is shown to present a quasi linear shape inside its host matrix. From the simulation of the end-to-end distance distribution, a conjugation length of 4-6 fluorene units is found. The introduction of a new subtraction method associated with defocused imaging allows us to study a more complicated polymer containing more perylenediimide units. The location and the 3D orientation of the incorporated dyes were measured at the same time by this new technique named SPIDER. Finally, the sequential two-color measurements allow us to get useful informations concerning the energy transfer occurring between polyfluorene backbone and perylenediimide units at the single molecule level.

In recent years, application of fluorescent conjugated polymers to sense chemical and biological analytes has received much attention owing to its technological significance. Water soluble conjugated polymers are interesting towards the developing sensors for biomolecules. In this present contribution, we describe the syntheses and characterization of a series of water soluble conjugated polymers with sulfonic acid groups in the side chain. Such anionic conjugated polymers are designed to interact with biomolecules such as cytochrome-C. All polymers are water soluble and showed strong blue emission. Significant quenching of the fluorescence from our functionalized PPP was observed upon addition of viologen derivatives or cytochrome -C. / Singapore-MIT Alliance (SMA)

J E. coli On-Off &ldquo, &rdquo, °, &ndash The specific objectives of the work presented in this dissertation are to design novel molecular sensors based on fluorescence resonance energy transfer (FRET) between fluorophore (donor) and polydiacetylene (PDA, acceptor) for selective detection of biomolecules in solution. The work described in this dissertation is divided into three sections. In the first section, we report here two novel systems where the rate of energy transfer is based on changes in the spectral overlap between the emission of the donor and the absorption of the acceptor (J) as well as changes in the quantum yield of the acceptor. In the second section, we discuss modified these high sensitive molecular sensors based on FRET by using different receptors for selective detection of biomolecules such as proteins or bacteria in solution. The third section develops reversibility studies on FRET based sensors in solution or solid state. In the Chapters two and three, conjugated polydiacetylene (PDA) possessing stimuli-responsive properties have been intensively investigated for developing efficient sensors. Sensors based on FRET between conjugated polymers and fluorophores can be more sensitive than colorimetric based sensors. We use the fluorophore dansyl as the donor and polydiacetylene (PDA) as the acceptor to demonstrate the modulation of FRET efficiency through conformationally induced changes in the PDA absorption spectrum following thermal treatment that converts the PDA backbone of the liposome from the blue form to the red form. We have used steady-state electronic absorption, emission and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). Energy transfer was found to be significantly more efficient from dansyl to the red-form PDA. This is due to large increase in the J values between dansyl emission and absorption red-form of PDA. We also have found that the monomer ratio of acceptor to donor (Rad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. A decrease in Rad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. Increase in Rad led to increase probability of FRET from donor to acceptor as larger number of acceptors are present around a given donor. The competition between donor for energy transfer increases with decrease in Rad that contributed to lower FRET efficiency between donors and acceptors. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to the insertion of dansyl in the bilayer of the liposomes which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. Much larger emission amplification for FRET was observed as compared to direct-excitation of PDA. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. These findings support the basis of a new sensing platform that utilizes J-modulated FRET as an actuating mechanism. A FRET based protein sensor by using sulforhodamine 101 as donor and PDA as acceptors was developed. This novel FRET based system primarily utilizes changes in J values (the spectral overlap between the emission of the donor and absorption of the acceptor) for the modulation of FRET efficiency between donors and acceptors. These FRET based sensors can be modified by tagged receptors (for proteins, viruses, and bactria) onto PDA liposomes which can interact with ligands present on proteins or bacteria. The biotin-streptavidin interactions were used as a sensing model system to test our FRET sensor response. In chapter 4, four different biotin-tagged lipids were used as receptors to investigate the effect of interactions between ligand-receptors on the FRET efficiency. The biotin was covalently linked to the liposome surface when using biotin-tagged diacetylene; whereas the biotin-tagged lipids with hydrophobic chains but without diacetylene functionalities provided non-covalently inserted lipids in liposomes. These studies were used to elucidate the effect of molecular interactions on FRET sensor response. The conjugated polymerized liposomes consisted of sulforhodamine-tagged-diacetylene and receptors linked lipids in different molar ratios. The characterization of the liposomes and sensing mechanism was investigated using UV-Vis and steady-state emission spectroscopy. The liposome solution yielded a weak donor emission (sulforhodamine 101) from after photo-polymerization of diacetylene monomers. This is due to energy transfer from the donor to PDA backbone chains (acceptors). The addition of streptavidin which interacted with biotin receptors resulted in increase in the sulforhodamine 101 emissions. The stress, due to interactions between biotin and streptavidin, induced the chromatic shift in the absorption spectrum of PDA which led to a decrease in the spectral overlap (J) between the emission spectra of donor and the absorption spectra of acceptor, leading to a decrease in the FRET efficiency from sulforhodamine 101 to PDA. These sensors, thus, show an "On-Off" type optical mechanism based on FRET between fluorophores and PDA where the donor emission was highly quenched in the "Off" state but was turned "On" due to receptor-ligand interactions. Large electronic absorbance and emission intensity differences between covalently and non-covalently bound biotin liposome systems were observed which indicated that the molecular interactions between biotin and PDA backbone play a crucial role in the FRET sensor response. In Chapter 5, we also developed FRET sensor for the detection of E. coli in aqueous media. Two glucose-based receptors were used in this study: (1) glucose-tagged lipid which can be inserted non-covalently in the bilayer of liposome, and (2) glucose-tagged diacetylene monomer in which the receptors were covalently bound to the backbone of the PDA liposome. The steady-state UV/Vis absorbance and fluorescence emission spectroscopy, and the fluorescence microscopy analysis of the receptors-containing liposomes were investigated for the detection of E. coli. The blue shift in the absorption spectrum of the conjugated PDA backbone induced through the interactions between receptors and bacteria resulted in decrease in the spectral overlap between the emission of SR-101 (donor) and the absorption of PDA (acceptor). This, ultimately, led to change in FRET efficiency between SR-101 and PDA after glucose - E. coli binding and caused increase in the emission intensity of SR-101. Polydiacetylenes have been exploited because of their sensitivity to external stimuli, such as temperature, pH, ions, and ligands. Unfortunately, the majorities of the sensors developed are not reversible but used as a one-time use. Here we report our preliminary results of a benzoic acid monomer of polydiacetylene (PDA-mBzA) to investigate reversible FRET characteristics between fluorophore and PDA. The LS films containing dansyl-tagged-diacetylene monomers and m-aminobenzoic acid derivatized- diacetylene monomers in different molar ratios were self-assembled and polymerized. The UV/Vis and steady-state fluorescence emission analysis of these LS films were investigated. These systems have shown partial reversible FRET over many "on-off" cycles. We believe that this incomplete FRET reversibility is due to liposomes preparation conditions used for liposomes which decreased PDA-mBzA amount in liposomes. We also reported reversible FRET studies on the liposome solutions, made from the monomer of m-aminobenzoic acid derivatized-10,12-pentacosadiynoic acid (PDA-mBzA) monomers and 11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid (DAUDA) or dansyl-tagged diacetylene. After photo-polymerization, the solution appeared blue in color at room temperature. Heating and cooling cycles (between 25 ºC and 95 ºC temperature range), illustrated a visible color change from blue to red and a complete return to blue over many thermal cycles. Our preliminary reversible absorption and emission measurements showed that there exist opportunities for reversibility in FRET response. We are now performing more experiments to increase the FRET reversibility in these experiments. Although our system does not display full reversibility, the preliminary absorption and emission measurements strongly suggest that there exist opportunities for fully reversible selective and sensitive FRET-based sensors after further optimization of the system.

Major efforts have been spent during recent years in worldwide attempts to achieve an electronic paper technology; the common name for novel flexible displays utilizing substrates such as paper, plastics or thin metal sheets. Various kinds of technology are available that potentially will be used for an electronic paper, which differs from each other mainly with respect to the choice of active materials, substrates and manufacturing techniques. There are many applications for electronic paper technology, ranging from high-resolution displays used in electronic books to updateable large-area billboards. The latter suggests a novel electronic display function that could extend the utilization of cellulose-based paper, which is one of the most common materials ever produced by mankind, by using the paper as a thin and flexible carrier. The requirement for fast update speed in such large area applications would probably be a bit more relaxed compared to traditional display technologies, while low-power consumption and bi-stability are among the factors that should be further emphasized, together with the utilization of well-established printing techniques to enable low-cost manufacturing of the displays. The choice of active materials is therefore crucial in order to reach these objectives in reality and this paves the way for printable conjugated polymers with electrochromic properties. Chemical synthesis of these materials during the last decades has resulted in a vast variety of electrochromic polymers with custom-tailored functionality covering a broad range of optical absorption and electrical conductivities. This thesis review the studies done on the electrochemical switching of poly(3,4-ethylenedioxythiophene) (PEDOT). For this material both the electrical conductivity and the optical absorption is controlled by the oxidation state. Active matrix addressed displays that are printed on flexible substrates have been obtained by arranging electrochemical smart pixels, based on the combination of electrochemical transistors and electrochromic display cells, into cross-point matrices. The resulting polymer-based active-matrix displays are operated at low voltages and the same active material can be used in electrochemical transistors and conducting lines and in electrochromic display cells employing the electronic and the opto-electonic properties of the material, respectively. In addition to this, a switchable optical polarizer is briefly discussed. This is a device utilizing electrochromism of stretch-aligned polyaniline (PANI). The combination of two identical devices in a vertical architecture, orthogonally oriented with respect to each other, results in a filter in which the orientation of the polarized optical absorption is governed by the voltage polarity applied to the device. / Report code: LiU-TEK-LIC- 2006:18

Drug-resistant pathogens are emerging rapidly and thwart the treatment of common bacterial infectious diseases that can lead to death. Many contagious diseases remain difficult to treat because of acquired drug resistance. Compared to small antibiotics, which interrupt the intracellular biochemical processes, antimicrobial polymers with relatively high molecular weights offer a promising strategy to overcome drug resistance by disrupting the physical integrity of the membrane. Because of the unique mechanism, bacteria need a much longer time to develop resistance. A new class of antimicrobial polymer in which the positive charge and hydrophobic/hydrophilic units are linearly connected in the amidinourea backbone was designed, synthesized, and tested for various bacteria including methicillin-resistant Staphylococcus aureus (MRSA). We evaluated the effects of hydrophobicity and polymer molecular weights on antimicrobial activity by measuring minimum inhibitory concentrations (MIC) and hemolytic activities (HC50). Amidinourea antimicrobial polymers exhibit a promising MIC90 value (13 μg/mL) with low HC50, resulting in high selectivity (HC50/MIC90) against MRSA. Many bacteria have developed resistance against Ciprofloxacin. To overcome the antibiotic resistance associated with Ciprofloxacin, we hypothesized that a steady release of Ciprofloxacin at the bacteria membrane can overcome the drug resistance because the local drug concentration can be overwhelmingly high to suppress the drug efflux pump expressed on the membrane. A series of homo and di-block copolymers containing Ciprofloxacin, as the form of prodrugs, was synthesized using ring-opening metathesis polymerization (ROMP), and we evaluated their antimicrobial efficacy.While homo polymers only containing Ciprofloxacin were inactive against almost all bacteria tested, di-block copolymers containing Cipro and triphenylphosphine exhibited some antimicrobial activity against wild type M. smegmatis. Modulation of chemical environments at the positively charged polymeric materials can significantly influence the biophysical properties required for efficient cellular interaction and subsequent entry. Using intrinsic fluorescent conjugated polymers (CPs), we have demonstrated that the modulated guanidine group with various hydrophilic or hydrophobic moieties dramatically changed their cellular behaviors. We prepared a series of modified guanidine-containing CPs and examined their cellular behaviors by using confocal microscopic imaging. Details of the modification chemistry and modification-dependent cellular behaviors and a knockdown of a target protein in primary cells were discussed.

<p>Since the discovery in 1977 that conjugated polymers can be doped to achieve almost metallic electronic conduction, the research field of conducting polymers has escalated, with applications such as light emitting diodes, solar cells, thin film transistors, electrochemical transistors, logic circuits and sensors. The materials can be chemically modified during their synthesis in order to tailor the desired mechanical, electronic and optical properties of the final product. Polymers are also generally possible to process from solution, and regular roll-to-roll printing techniques can therefore be used for manufacturing of electronic components on flexible substrates like plastic or paper. On top of that, the nature of conjugated polymers enables the creation of devices with novel properties, which are not possible to achieve by using inorganic materials such as silicon.</p><p>The work presented in this thesis mainly focuses on devices that utilize two rather unique properties of conducting polymers. Conducting polymers are generally electrochromic, i.e. they change color upon electrochemical oxidation or reduction, and can therefore be used as both conductor and pixel element in simple organic displays. As a result of the electrochemical reaction, some polymers also alter their surface properties and have proven to be suitable materials for organic electronic wettability switches. Control of surface wettability has applications in such diverse areas as printing techniques, micro-fluidics and biomaterials.</p><p>The aim of the thesis is to briefly describe the physical and chemical background of the materials used in organic electronic devices. Topics include molecular properties and doping of conjugated polymers, electrochromism, surface tension etc. This slightly theoretical part is followed by a more detailed explanation of device design, functionality and characterization. Finally, a glance into future projects will also be presented.</p> / ISRN/Report code: LiU-TEK-LIC-2005:50