Conjugated polymers (CPs) are intrinsically fluorescent materials that have been used for various biological applications including imaging, sensing, and delivery of biologically active substances. The synthetic control over flexibility and biodegradability of these materials aids the understanding of the structure-function relationships among the photophysical properties, the self-assembly behaviors of the corresponding conjugated polymer nanoparticles (CPNs), and the cellular behaviors of CPNs, such as toxicity, cellular uptake mechanisms, and sub-cellular localization patterns. Synthetic approaches towards two classes of flexible CPs with well-preserved fluorescent properties are described. The synthesis of flexible poly(p-phenylenebutadiynylene)s (PPBs) uses competing Sonogashira and Glaser coupling reactions and the differences in monomer reactivity to incorporate a small amount (~10%) of flexible, non-conjugated linkers into the backbone. The reaction conditions provide limited control over the proportion of flexible monomer incorporation. Improved synthetic control was achieved in a series of flexible poly(p-phenyleneethynylene)s (PPEs) using modified Sonogashira conditions. In addition to controlling the degree of flexibility, the linker provides disruption of backbone conjugation that offers control of the length of conjugated segments within the polymer chain. Therefore, such control also results in the modulation of the photophysical properties of the materials. CPNs fabricated from flexible PPBs are non-toxic to cells, and exhibit subcellular localization patterns clearly different from those observed with non-flexible PPE CPNs. The subcellular localization patterns of the flexible PPEs have not yet been determined, due to the toxicity of the materials, most likely related to the side-chain structure used in this series. The study of the effect of CP flexibility on self-assembly reorganization upon polyanion complexation is presented. Owing to its high rigidity and hydrophobicity, the PPB backbone undergoes reorganization more readily than PPE. The effects are enhanced in the presence of the flexible linker, which enables more efficient π-π stacking of the aromatic backbone segments. Flexibility has minimal effects on the self-assembly of PPEs. Understanding the role of flexibility on the biophysical behaviors of CPNs is key to the successful development of novel efficient fluorescent therapeutic delivery vehicles.

In this dissertation, three aspects about surface and interface engineering of conjugated polymers and nanomaterials will be discussed. (i) There is a significant promise for electroactive conjugated polymers (ECPs) in applications of electrochemical devices including energy harvesting, electrochromic displays, etc. Among these, ECPs has also been developed as electroactive materials in electrochemical supercapacitors (ESCs). Compared with metal oxides, ECPs are attractive because they have good intrinsic conductivity, low band-gaps, relatively fast doping-and-undoping process, the ease of synthesis, and tunable electronic and structural properties through structural modifications. Here, Multiple-branch-chain 3,4-ethylenedioxythiophene (EDOT) derivatives was designed as crosslinkers in the co-electropolymerization of EDOT to optimize its morphology and improve the cycling stability of PEDOT in the supercapacitor applications. High-surface-area π-conjugated polymeric networks can be synthesized via the electrochemical copolymerization of the 2D (trivalent) motifs benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene (BTT) and tris-EDOT-benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene (TEBTT) with EDOT. Of all the material systems studied, P(TEBTT/EDOT)-based frameworks achieved the highest areal capacitance with values as high as 443.8 mF cm-2 (at 1 mA cm-2), higher than those achieved by the respective homopolymers (PTEBTT and PEDOT) in the same experimental conditions of electrodeposition (PTEBTT: 271.1 mF cm-2 (at 1 mA cm-2); PEDOT: 12.1 mF cm-2 (at 1 mA cm-2). (ii) In electrochemical process, the suitable choice of appropriate electrolytes to enlarge the safe working potential window with electrolyte stability is well known to improve ECPs’ performance in ESCs applications. Ionic liquids (ILs) are ion-composed salts and usually fluid within a wide temperature range with low melting points. There are many unique characteristics for these intrinsic ion conductors, including high ionic conductivity, wide electrochemical voltage windows in neutral conditions, fast ion mobility in redox reaction process (>10-14 m2 V-1 s-1), low vapor pressure, and environmental stability. These properties qualified ambient-temperature ILs to be applied as supporting medium for various devices and materials processing applications in both industry and academia, overcoming the limitation of volatile organic compounds (VOCs). Especially, ILs have been utilized as superior medium to electrodeposit metals, alloys, semiconductors and ECPs in the application of supercapacitors. Electropolymerization of EDOT and its derivative 4,4'-dimethoxy-3,3'-bithiophene (BEDOT) have been studied in three kinds of imidazolium-based ionic liquids and conducting salt in VOCs with different anions both as the growth medium and the supporting electrolyte, to assess the influence of these anions on their morphology and electrochemical activity. It is found these thiophene polymers grown in ILs with higher viscosity and lower diffusion shows much slower growth rate and orderly morphologies than in Tetrabutylammonium hexafluorophosphate (TBAPF6) dissolved in acetonitrile (ACN), and gives better electrochemical performance via cyclic voltammetry (CV) and galvanostatic charge-and-discharge (CD) studies. Polymers displayed multiple redox peaks in several cases, the possible reasons and origins are discussed. The synthesized polymer can be affected greatly by both the ILs with different anion/cation, and its mutal interation with targeted monomer.. As far as known, there is no systematic study on how the anions of ILs and common organic solution could play a role as a medium both for polymerization and post-polymerization electrolyte for PEDOT and its derivatives. This study can be used as an easy reference and provide experimental diagnositc data when selecting ionic liquids to investigate and optimize thiophene-based electrochemical systems, such as batteries and supercapactiors. (iii) Another aspect about interface chemistry of direct functionalization of nanodiamond with maleimide has also been addressed. Functional nanodiamonds are promising candidates for extensive practical applications in surface science, photonics and nanomedicine. Here, a protocol of direct functionalization is described by which maleimide-derivatized substituents can be appended to the outer shell of thermally annealed nanodiamonds through Diels-Alder reaction. This protocol can be carried out in room temperature, ambient atmosphere, without catalyst, and provide functionalized nanodiamonds with good solubility in organic solution. Also, this method can be applied for other maleimide derivatives,e.g.m aleimide-fluorescene, which can be applied in fluorescence labeling, sensing, and drug delivery. A series of techniques, especially Fourier transform infrared spectroscopy (FTIR), and Solid State Nuclear Magnetic Resonance (SS-NMR) was conducted for the analysis of surface chemistry and the investigation of the two-point binding strategy in details.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20410号 / 工博第4347号 / 新制||工||1674(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 松田 建児, 教授 杉野目 道紀 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Since the development and optical study of conjugated (conducting) polymers it has become apparent that chain conformation and aggregation at the molecular scale result in complex heterogeneous nanostructured bulk materials for which a detailed insight into morphological, spectroscopic as well as optoelectronic properties and mechanisms is overwhelmingly difficult to obtain. Nanoparticles composed of the conjugated polymer poly (MEH-PPV) and nanocomposite nanoparticles consisting of MEH-PPV doped with 1-(3-methoxycarbonylpropyl)-1-phenyl-C61 (PCBM) were prepared as model systems to study these materials at the length scale of one to a few domains. The MEH-PPV and PCBM doped nanoparticles were analyzed by single imaging/particle spectroscopy (SPS) and revealed molecular scale information on the structure-property relationships of these composite materials. The data obtained from SPS were investigated in terms of spectral difference between doped and undoped nanoparticles. The doped nanoparticles are blue shifted by approximately 5-10 nm, have an additional blue shoulder, and show different vibronic structure than the undoped nanoparticles. Specifically, relative intensity of the 0-1 transition is lower than for the undoped nanoparticles. These data are indicative of differences in molecular order between both nanoparticle systems, detected at the molecular scale. In addition, the effect of electrical fields present in devices on the interfacial charge transfer properties was evaluated. Furthermore, these nanoparticles were incorporated into the lipid nanotubes to study the diffusion process of the single MEH-PPV nanoparticles inside the lipid nanotubes. Our data shows a clear proof of concept that diffusion of nanoparticles inside the hollow lipid nanotubes can be studied on a single particle basis, which will allow us to study diffusion processes quantitatively and mechanistically within the framework of developing a biocompatible drug and gene delivery platform.

Conjugated polymers represent a class of semi-conducting materials with numerous applications in optoelectronic devices, including organic light-emitting diodes, field-effect transistors, and photovoltaics. Because of the numerous advantages of macromolecular systems, including solution processing and mechanical flexibility, conjugated polymers have become a burgeoning field of research with the hopes of producing cost-effective solution-based electronics. Importantly, optoelectronic device performance is heavily influenced by conjugated polymer backbone orientation and overall thin film morphology. As such, the processing conditions of these systems are important to the construction of high- performance optoelectronics. Polythiophenes are model conjugated polymers that have been studied extensively in halogenated organic solvents. However, the self- assembly of these systems from dilute solution to the solid state remains ambiguous for solvents with high dielectric constants. Here, two derivative compounds of poly(3-hexylthiophene) are correspondingly investigated in high dielectric solvents by way of ultraviolet-visible absorption and fluorescence spectroscopy, Fourier transform infrared spectroscopy, small-angle X-ray scattering, polarized optical microscopy, and four- point probe conductivity measurements. In dilute solutions, both systems are found to undergo self-assembly when exposed to various stimuli, including temperature, solvent composition, and side-chain characteristics. The kinetics of these transitions are investigated, and a model is put forth to explain contrasting self-assembly mechanisms. At higher concentrations, both systems form lyotropic liquid crystalline phases. Characteristics of the liquid crystalline phases are found to be heavily influenced by dilute solution self-assembly mechanisms and processing. Through the application of a mechanical shear force along still-wet liquid crystal films, alignment of the polythiophene long axis is attained. This morphological characteristic is found to carry over to the solid-state for both systems, and clear optoelectronic anisotropy of the thin films is observed. As such, these methodologies may provide a route to the production of environmentally friendly high-performance optoelectronic devices.

No description available.

Single-walled carbon nanotubes (SWNTs) have attracted extensive research effort since their discovery nearly 30 years ago. Their impressive mechanical, optical, thermal, and electronic properties make them promising candidates for incorporation into a variety of applications. Depending on the method used for SWNT synthesis, different diameter ranges can be produced. Within these diameter ranges, a heterogeneous mixture of semiconducting and metallic species are present. The combination of these electronic species, as well as their minimal solubility in common solvents, hinders their incorporation into electronic devices, providing reasons for the development of scalable purification techniques. Although, some impactful purification strategies have been developed in recent literature, the use of conjugated polymers is considerably more scalable, less expensive, and offers processability of the final purified material. At the time of this thesis, the purification of semiconducting SWNTs has been realized using electron-rich conjugated polymers such as polyfluorenes, polycarbazoles, and polythiophenes. For metallic SWNTs, less progress has been made. When enriched, metallic SWNTs could act as an effective replacement for common metals in conductive applications. The objective of this work is to develop an efficient and scalable technique for the dispersion of metallic SWNTs and to shed light on the effect of polymer electronics on SWNT dispersion selectivity using nitrated poly(fluorene-co-phenylene)s and cationic poly(fluorene-co-pyridine)s. These investigations lead to the development of novel techniques using multiple conjugated polymers to yield enriched metallic SWNT samples. A secondary objective of this work is to investigate the gentle removal of the polymer, post-purification using UV-irradiation to cleave the polymer linkages of a poly(carbazole-co-terephthalate). Characterization of the polymer-SWNT composites is carried out using absorbance, photoluminescence, and Raman spectroscopy techniques to evaluate their electronic purity. / Thesis / Doctor of Philosophy (PhD)

In this thesis, the interface between the electron donor polymer and the electron acceptor fullerene in organic photovoltaic devices is studied. Starting from a bilayer system of donor and acceptor materials, the proximity of polymer and fullerene throughout the bulk of the devices is improved by inducing an interdiffusion of the two materials by heating the devices in the vicinity of the glass transition temperature of the polymer. In this manner, a concentration gradient of polymer and fullerene throughout the bulk is created. The proximity of a fullerene within 10 nm of any photoexcitation in the polymer ensures that the efficient charge separation occurs. Measurements of the absorption, photoluminescence, and photocurrent spectra as well as I-V characteristics are used to study the interdiffusion and its influence on the efficiency of the photovoltaic devices. In addition, the film morphology is studied on a microscopic level with transmission electron microscopy and with Auger spectroscopy combined with ion beam milling to create a depth profile of the polymer concentration in the film. Initial studies to induce an interdiffusion were done on poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) as the electron donor polymer and the buckminsterfullerene C60 as the electron acceptor. Interdiffused devices show an order of magnitude photoluminescence quenching with concomitant increase in the photocurrents by an order of magnitude. Variation of the polymer layer thickness shows that the photocurrents increase with decreasing thickness down to 70 nm due to charge transport limitation. The choice of layer thickness in organic photovoltaic devices is critical for optimization of the efficiency. The interdiffusion process is also monitored in situ and a permanent increase in photocurrents is observed during the heat treatment. Transmission electron microscopy (TEM) studies on cross sections of the film reveal that C60 interdiffuses into the MEH-PPV bulk in the form of >10 nm clusters. This clustering of C60 is a result of its tendency to crystallize and the low miscibility of C60 in MEH-PPV, leading to strong phase separation. To improve the interdiffusion process, the donor polymer is replaced by poly(3-octylthiophene-2,5-diyl) (P3OT), which has a better miscibility with C60. Again, the photocurrents of the interdiffused devices are improved significantly. A monochromatic power conversion efficiency of 1.5 % is obtained for illumination of 3.8 mW/cm2 at 470 nm. The polymer concentration in unheated and interdiffused films is studied with Auger spectroscopy in combination with ion beam milling. The concentration profile shows a distinct interface between P3OT and C60 in unheated films and a slow rise of the P3OT concentration throughout a large cross-section of the interdiffused film. TEM studies on P3OT/C60 films show that C60 still has some tendency to form clusters. The results of this thesis demonstrate that thermally-controlled interdiffusion is a viable approach for fabrication of efficient photovoltaic devices through nanoscale control of composition and morphology. These results are also used to draw conclusions about the influence of film morphology on the photovoltaic device efficiency and to identify important issues related to materials choice for the interdiffusion process. Prospective variations in materials choice are suggested to achieve better film morphologies. / Ph. D.

An in-depth study of concentration gradients in thermally-interdiffused polymer – fullerene photovoltaic devices, with a focus on thickness and heat treatments, is presented in this thesis. Device performance is improved from the bilayer by the creation of a concentration gradient of the donor and acceptor materials throughout the active layer of the device. Concentration gradients are expected to improve device performance by optimizing the charge transfer, transport and collection processes. This is achieved through heat-induced interdiffusion of the two materials at temperatures above the glass transition temperature of the polymer. Investigation of the poly(3-octylthiophene) (P3OT) – C₆₀ system show a three-fold improvement in the external quantum efficiencies (EQE) as compared with bilayer devices. Auger spectroscopy, combined with argon-ion beam milling, serves to record the concentration depth profile and identify concentration gradients in the device through detection of the sulfur in the P3OT backbone. Concentration gradients are optimized to yield the best devices through a thickness variation study conducted on the P3OT – C₆₀ system for fixed thermal interdiffusion conditions at 118 °C for 5 minutes. An optimum thickness of 40 to 60 nm is obtained for the two materials that yields the ideal morphology of a concentration gradient as recorded by Auger spectroscopy. For such devices, the concentration gradient is seen to extend through the device, ending in a thin layer of pure material at each electrode. A monochromatic power conversion efficiency of 2.05% is obtained for 5.3 mW/cm²⁺ illumination at 470 nm. A brief study is also presented to optimize the concentration gradient profile through variations of the thermal parameters. The dependence of the concentration gradient on the interdiffusion time and temperature is investigated. The merits of heat treatment on the crystallinity of P3OT and the overall device performance are also discussed. It is shown in some case that devices with annealed P3OT layers show almost twice the EQE as non-annealed P3OT layer devices. Potential alternatives for C₆₀ in interdiffused devices with P3OT have been presented. [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), a well-investigated acceptor for blend devices, is studied as an acceptor in concentration gradient devices. A method for spin-coating uniform bilayers of P3OT and PCBM, without solution damage to either layer, is presented. A thermal variation study of the interdiffusion conditions on this system indicated higher interdiffusion temperatures and times are preferred for P3OT – PCBM systems. For interdiffusion at 150 °C for ten minutes, EQE values approaching 35 % at 500 nm are obtained. Auger spectroscopy studies on this system yielded the same conclusions about the concentration gradient device morphology that gives optimum device output. 1:1 and 1:2 blends of P3OT – PCBM are also studied. The influence of various thermal treatments on these devices is described. The endohedral fullerene Sc₃N@C₈₀ is introduced as a new acceptor material. The endohedral fullerene consists of Sc₃N cluster enclosed in a C₈₀ cage. An order of magnitude increase is seen in device performance upon sublimation of these molecules on a P3OT layer confirming its effectiveness as an acceptor. Preliminary studies done on this system indicated the need for greater thermal treatment to produce optimum concentration gradients. An in depth study for varying temperatures and times is presented. The best device performance was seen for interdiffusion at 160 °C for 25 minutes. The endohedral fullerene devices also show a long-term deterioration and so best result are presented from a set of devices fabricated within the same time period. The study of these three donor-acceptor systems confirms that the conclusions on the thickness dependence and device performance study conducted for the P3OT – C₆₀ system extend to other acceptors. A model of EQE for varying thicknesses based on absorption in the interdiffused concentration gradient regions is also presented. This model effectively highlights the influence of P3OT layer thickness on the trends observed in the EQE. It did not, however, reproduce the experimental thickness variation results for varying C₆₀ thicknesses. Incorporation of the effects of the electric field intensity distribution is expected to correct for this. Suggestions have been given on how this might be achieved. / Ph. D.

This thesis presents a study of lasing properties and optical amplification in semiconducting conjugated polymers and dendrimers. Configured as surface-emitting distributed feedback lasers, the effect of incorporating wavelength-scale microstructure on the output of the devices is examined along with the ability to create such structures using simplified fabrication processes such as soft lithography. Conjugated materials have received a great deal of interest due to their broad spectral absorption, emission, ability to exhibit gain and ease of processing from solution. As a result, they show great potential for a variety of applications such as photovoltaics, displays, amplifiers and lasers. To date however, there has only been one demonstration of a polymer optical amplifier. A broadband, solution based polymer amplifier is presented where the gain overlaps with the transmission window of polymer optical fibres. The effect of transitions that reduce the availability of gain in conjugated polymers is also examined by studying saturation of absorption in thin films. Producing wavelength scale microstructure is traditionally a slow, expensive technique. Here, solvent assisted micromoulding is used to pattern polymer films in less than two minutes. The effect of the variations in the pattern transfer on the laser characteristics is examined. The micromoulding technique is then applied to fabricating novel device types such as circular gratings and flexible plastic lasers. Encapsulation of the micromoulded laser is then shown to improve the lifetime of the device by over three orders of magnitude. The degradation effects witnessed during this extended operation are characterised quantitatively, an area of study where little data exists in the literature. A novel class of branched dendrimer materials whose properties can be independently tuned due to their modular architecture are configured as blue-emitting distributed feedback lasers. The ability to tune the emission wavelength by varying the film thickness is demonstrated. By changing the chemical groups contained within the molecule, further tuning of the emission can be obtained along with the demonstration of a highly efficient blue-emitting dendrimer laser. Chemosensing using dendrimer lasers is presented by demonstrating the incredibly sensitive response of the laser device to trace vapours of nitro-benzene compounds. The future application of which could be highly beneficial in the detection of explosives.