Abstract: A novel thin film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with molecular-level control over thickness and multilayer architecture. This new self-assembly process opens up vast possibilities in applications which require large area, ultrathin films of conducting polymers and more importantly in applications that can take advantage of the unique interactions achievable in the complex, supermolecular architectures of multilayer films. In in situ polymerized polypyrrole (PPy), the deposition process strongly depends on the nature of the substrate surface. That is, for a surface that is negatively charged, there is a linear correspondence between dipping time and the amount of PPy deposited on the substrate. However, in the case of a positively charged surface, there is an apparent rest period of approximately 10-20 min, during which no PPy is deposited. From optical absorption spectroscopy and photoelectron emission studies etc., it became clear that oligomers of pyrrole were adsorbed on the positively charged surface during the rest period, as a result the polymerization reaction of PPy could proceed. ? 2005 Elsevier B.V. All rights reserved.

Abstract: It has been shown that the maskless dye-diffusion technique is applicable to a conjugated polymer poly(9,9-dioctylfluorene). The introduction of Coumarin 6 and Nile red results in green and white emission, with the increased onset voltage for the both cases. It has also been confirmed that the heat treatment effect during the maskless dye diffusion technique results in not the increase but the decrease of the onset voltage, indicating that the dye plays a role of carrier trap in the polymer. Copyright ? 2006 The Institute of Electronics, Information and Communication Engineers.

Abstract: A polypyrrole (PPy) film electrochemically grown in a thin slab vessel consisting of poly(tetrafluoroethylene) walls exhibits a notable anisotropy along the thickness direction. This anisotropy allows the film to bend in a regular direction upon electrochemical undoping and revert upon doping. In this study, the size effect, i.e. the length dependence of reduction current, of the actuator has been studied. The length was changed by trimming the tip of the actuator, 12 mm of which was initially soaked in an electrolyte. It has been clarified that current saturates when the actuator exceeds a certain length. This may reflect the reduction in the conductivity of PPy upon undoping, which makes the tip of the actuator almost insulated from the power source. It is also found that the width of the actuator and the electrolyte do not influence the size effect. ? 2006 IOP Publishing Ltd.

Abstract: The suspension-based preparation of conjugated polymer film can generate a nanostructured conjugated film. A simple technique, injecting polymer solution into non-solvent, is applicable for many soluble conjugated polymers. The collection of colloidal particles in suspensions can be done by electrophoretic deposition. In comparison with traditional spin-coating technique, in which most of material used is blown out, the polymers can be efficiently collected. Two types of applications of this technique, polymer light-emitting devices as artificial finger print devices and preparation of conjugated polymer-fullerene nanocomposites, are mentioned. ? 2005 Elsevier B.V. All rights reserved.

Abstract: A phosphorescent metal complex, iridium (III) bis[2-(2��-benzothienyl) pyridinato-N,C3��] (acetylacetonate) (Btplr), was introduced in poly(9,9-dioctylfluorene) (PDOF) films through a dry process for local dye doping into a film, the maskless dye-diffusion technique. A light-emitting device with a PDOF film with Btplr diffusion for 80 s showed red emission originating from the dye with superior quantum efficiency compared to a device with a pristine PDOF film. The effect of heat treatment on PDOF films was also studied to confirm that the enhanced quantum efficiency was attributable not to the heat treatment effect but to that of the phosphorescent nature of Btplr. ? 2006 American Institute of Physics.

Abstract: A simple technique of maskless dye diffusion into polymer films on prepatterned electrodes is developed and three-color polymer light-emitting devices were successfully fabricated on a glass plate. In this method, prepatterned electrodes beneath precoated receiver film are utilized as heaters for activating dye molecules. Upon doping with three types of dye, 1,1,4,4-tetraphenyl-1,3-butadiene, coumarin 6 and Nile red into poly(N-vinylcarbazole) by the present diffusion method, blue, green and red emission were obtained. It is found that the onset voltage of emission does not depend on the type of dye. The maskless dye diffusion technique can be applicable to a variety of devices such as photovoltaic devices. ? 2005 Elsevier B.V. All rights reserved.

Abstract: The preparation of colloidal suspension through a simple method, injection of a small amount of toluene solution of target materials into non-solvent acetonitrile, has been successfully demonstrated for C60 and various conjugated polymers such as poly(3-alkylthiophene), polyfluorene derivative and MEH-PPV. The colloidal suspension of mixtures of MEH-PPV and C60 with almost equivalent weight ratio has also been obtained through the same process. The electrophoretic deposition from these suspensions results in nanostructured polymer film, as indicated by the AFM observation. Since the polymer films obtained through this process has worked as emission layer in a light-emitting device, the film obtained through this process will also be able to work in photocells. ? 2004 Elsevier B.V. All rights reserved.

Abstract: A novel route to obtain donor-acceptor nanocomposite by using electrophoretic deposition has been proposed. Suspensions containing MEH-PPV and C60 nanoparticles are made by mixing suspensions of individual components. The film obtained by the electrophoretic deposition in the suspension shows notable quenching of photoluminescence, indicating the photoinduced charge transfer between donor MEH-PPV and acceptor C60. This results suggests that the donor-acceptor nanocomposite obtained through the electrophoretic deposition in the mixture of suspensions is a promising material for organic photocells. ? 2004 Elsevier B.V. All rights reserved.

Abstract: Tuning the emission color of polymer light-emitting devices (PLEDs) based on a conjugated polymer poly(9,9-dioctylfluorene) (PDOF) through the maskless dye diffusion technique has been studied. The introduction of a green-light-emitting dye, Coumarin 6, into PDOF through this technique results in green light emission from the PLEDs without notable alteration of the external quantum efficiency. On the other hand, the introduction of a red-light-emitting dye, Nile red, which generates pure red light in a poly(N-vinylcarbazole) matrix, results in a white light emission from the PLEDs with an external quantum efficiency smaller than the original device. The onset voltages of emission were almost doubled for both cases, suggesting that both dyes play a role of carrier trap in the polymer. For emission mechanisms, it was suggested that the former case be governed by the efficient energy transfer from PDOF to Coumarin 6 or the direct recombination in Coumarin 6, while the latter case may include exciplex formation. ? 2005 The Japan Society of Applied Physics.

Abstract: Recent new technologies of electromechanical conversion devices have been reviewed. Especially, the electrochemical properties of anisotropic actuators using polypyrrole have been reported in detail and the realization of the bimorph (or bending-beam) structure without artificial adhesive agent is introduced. ? 2004 Elsevier B.V. All rights reserved.

Abstract: Nanostructured films of various conjugated polymers can be obtained through electrophoretic deposition process. Unlike the conventional deposition techniques based on the solutions of conjugated polymer, the methods employing colloidal suspensions like one proposed here make it to possible to separate the solidification of material from the film formation and drying steps. This unique feature provides nanostructure in the films deposited. A simple method, pouring a dilute solution of target material into an excess of non-solvent liquid, was used to obtain suspensions of conjugated polymers. Since this method is similar to a step of purification of the polymers after polymerization and does not use any additives such as surfactant, the polymers in the suspension and therefore the films obtained through the electrophoretic deposition may keep at least the purity of the original material. The unique morphology found in the electrophoretically deposited films opens up the new application of polymer light-emitting devices other than displays, the artificial fingerprint devices for anti-forging technology applicable to smartcards. Additionally, a unique process to obtain polymer-fullerene nanocomposite for photovoltaic application through the electrophoretic deposition is also proposed. ? 2005 Elsevier B.V. All rights reserved.

Abstract: The size effect, the length dependence of actuation behavior, of anisotropic polypyrrole (PPy) film obtained by electrochemical polymerization in a thin slab vessel consisting of PTFE walls has been studied. It was found that the active area of the actuator is limited within 3 mm from the electrolyte surface when it is simply soaked in the electrolyte. The active area is doubled by electrically insulating the actuator from the electrolyte surface. These results suggest that the active area of the PPy actuator is mainly limited by two factors, the enhancement of electrochemical reaction rate at the electrolyte surface and the reduction of electrical conductivity of the actuator upon undoping.

Abstract: Tuning the emission color of polymer light-emitting devices (PLEDs) based on a conducting polymer poly(9,9-dioctylfluorene) (PDOF) through the maskless dye-diffusion technique has been attempted. Introduction of green-emitting dye Coumarin 6 into PDOF through this technique results in green emission from the PLEDs without notable alteration of the external quantum efficiency, although the onset voltage for emission has much increased. This result suggests that Coumarin 6 plays a role of carrier trap in the polymer.

Abstract: A device structure for polymer Schottky diode, which has the glass chimney as a dopant reservoir enabling the reduction of series resistance without cathode corrosion, has been proposed. Doping with the acetonitrile solution of FeCl3 in the device resulted in the increase in the forward-bias current by one order of magnitude without notable increase in reverse-bias current, suggesting that the doping reduced the series resistance. It is found that the penetration speed depends on the solvents. Short time doping with the nitromethane solution of FeCl3 resulted in the increase by three orders of magnitude. However, doping for a long period yielded the considerable increase in the reverse-bias current due to the complete penetration of dopatn solution. When the upper opening of glass chimney of device is left opened and the sample after doping stored in air, the forward-bias current of the device reduced rapidly due to the undoping and/or degradation of polymer. It is possible to protect the degradation of device characteristics after doping, by sealing the chimney and storing the device in vacuum.

Abstract: Conjugated polymers doped with fullerenes show excellent photoconversion efficiencies. However, due to the poor solubility of pure C60 in common organic solvents, it was thought that some chemical modifications to C60 were required in order to load conjugated polymers with comparable weights of fullerene. Here, we report a novel way to load large amounts of unmodified C60 fullerene into the conjugated polymer poly(2-methoxy-5-(2��-ethylhexoxy)-1,4-phenylenevinylene), MEH-PPV. The principle of our approach is to separate the film-deposition stage from the material-solidification stage. That is, materials are quickly solidified from dilute solution into colloidal particles, which are large enough to be collected by electrophoretic deposition. Deposition from a mixture of separate suspensions of MEH-PPV and C60 fullerene resulted in films consisting of isolated particles. In contrast, by using a suspension made of a dilute solution of MEH-PPV and C60, which was so dilute that traditional techniques such as spin-coating were not applicable, an MEH-PPV film doped with 20 mol-% C60, corresponding to an almost 1:1 ratio by weight of molecularly dispersed C60, was easily obtained. To the best of our knowledge, this is the first report on the successful loading of an equivalent weight ratio of unmodified C60 molecules into MEH-PPV.

Abstract: Recent new technologies of electro-mechanical conversion devices have been reviewed. Especially, the electrochemical properties of anisotropic actuators using polypyrrole have been reviewed in detailed and the realization of the bimorph (or bending beam) structure without artificial adhesive agent is introduced.

Abstract: In in situ polymerized polypyrrole (PPy), the deposition process strongly depends on the nature of the substrate surface, That is, for a surface that is negatively charged, there is a linear correspondence between dipping time and the amount of PPy deposited on the substrate. However, in the case of a positively charged surface, there is an apparent rest period of approximately 10-20 min, during which no PPy is deposited. From optical absorption spectroscopy and photoelectron emission studies etc., it became clear that oligomers of pyrrole were adsorbed on the positively charged surface during the rest period, as a result the polymerization reaction of PPy could proceed.

Abstract: We have investigated a method of preparing a large-size anisotropic polypyrrole (PPy) film using a slab vessel consisting of poly(tetrafluoroethylene) (PTFE) walls as well as its actuation abilities. The PPy film can be grown along one side of the PTFE walls and exhibits morphological anisotropy of the PPy packing density along the thickness direction. A piece bends in a regular direction (the surface in contact with the PTFE wall) and reverts during a redox cycle without the use of any additional processes such as lamination. The actuation properties of the anisotropic PPy actuator strongly depend on the size of the cation in the driving electrolyte, and the bending behavior of this actuator at room temperature becomes slower for larger cations. On investigating the temperature dependence of actuation properties, the arrival time of the actuator (the time required for the tip of the actuator to touch the electrolyte surface upon stepwise potential change) was found to become shorter in all electrolyte solutions with different electrolytes. This result can be understood in terms of the thermally activated microscopic movement of the PPy main chains. Such behavior based on electrochemical stimulus not only provides information related to ionic transfer and storage but also suggests that the anisotropic PPy film can be put to practical use as an electrochemical actuator for artificial muscle which directly converts electrical energy into mechanical energy. ? 2004 Wiley Periodicals, Inc.

Abstract: In this paper, we have proposed to apply a combinatorial approach to investigate the Schottky diode based on electrochemically polymerized conjugated polymer. The concept of combinatorial approach was emerged in the biochemical field and lately used in the materials science to screen a number of experimental conditions efficiently. Some tips for designing the polymerization bath suitable for our purpose, such as the way to suppress the interference of polymerization currents, have been described. In the case of Schottky diodes based on poly (3-methylthiophene), the system chosen to test our idea, the effects of polymer thickness and the supporting salt on the device characteristics have been surveyed clearly and rapidly. The map or library of the relationship between the polymerization condition and device characteristic may be useful to tune the device characteristics as desired. Our preliminary result has shown that the combinatorial approach proposed here can be a powerful tool to investigate the conjugated polymer devices by electrochemical polymerization such as electrochromic devices.

Abstract: In this paper, a method to prepare large anisotropic PPy films using a thin slab vessel consisting of PTFE films is proposed. Our recent studies show that polypyrrole (PPy) films grown in a slender pipe of poly(tetrafluoroethylene) (PTFE) have a considerable vertical anisotropy (anisotropy along thickness), and therefore is available as a self-organized bending-beam actuator. However, poor productivity is one of the main problems of this method. It has been found that the thickness of the slab vessel considerably affects the morphology of the resulted film. The obtained PPy films bend and revert during redox cycles, as PPy films grown in a slender PTFE pipe do. ? 2003 Elsevier Science S.V. All rights reserved.

Abstract: Photoirradiation effects of poly(p-pyridyl vinylene), PPyV/poly(3-hexylthiophene), P3HT and polypyridine, PPy/poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene), MDOPPV heterostructure photoelectric conversion devices have been investigated. The photovoltaic characteristics of the heterostructure photoelectric conversion device are considerably improved from those in a single-layer photoelectric conversion device. Quenching of photoluminescence both in the PPy V layer film and in the P3HT layer film has been observed in the PPyV/P3HT heterostructure film. The observed photoirradiation effects of the heterostructure device have been discussed in terms of interfacial photoinduced charge transfer between P3HT and PPyV. ? 2002 Elsevier Science B.V. All rights reserved.

Abstract: A method of preparing a large-size anisotropic polypyrrole (PPy) film using a slab vessel consisting of poly(tetrafluoroethylene) (PIPE) walls as well as its actuation properties is reported. The PPy film can be grown along one side of the PTFE walls and exhibits a morphological anisotropy along the thickness direction. A piece of it bends and reverts in a regular direction during a redox cycle without the use of any addditional processes such as lamination. The actuation characteristics of the anisotropic PPy film strongly depend on the size of the cation in the driving electrolyte. The bending of this actuator at room temperature becomes slower for larger cations. The temperature dependence of the characteristics of the anisotropic PPy film as actuator has been investigated. As the temperature increases, the arrival time of the actuator becomes shorter in all electrolyte solutions. This can be understood in terms of the thermally activated microscopic movement of polymer chains. It is also found that this actuator can lift an object which weighs more than 25 times of the weight of the actuator itself.

Abstract: Poly(3-alkylthiophene)s (PATs) are conducting polymers possessing high processabilities such as solubility and fusibility. Most conducting polymers known to be p-type, or hole transporting semiconductors. PATs are also known as p-type semiconductors in the solid state. Previous studies have suggested that the dominant photocarrier inverts from positive to negative in the liquid state in PAT with relatively long alkyl side chain. In this study, we tried to confirm the sign inversion of the photocarrier in regiorandom poly(3-octadecylthiophene) (PAT18) by means of the time-of-flight method. It was found that the hole mobility decreases with increasing temperature. At the temperature near the solid-liquid phase transition, the hole mobility decreases drastically, and eventually the melting temperature, it was impossible to evaluate the hole mobility from noisy transient photocurrent. On the other hand, transient photocurrents based on electron transport are observed above the melting point. The negative carrier mobility was evaluated in the range from 10-6 to 10-5 cm2/Vs, which is comparably the hole mobility at solid state. This fact suggests that the same mechanism, for example interchain hopping limits carrier transport, and the negative carrier is electron. This unique phenomenon is interpreted as modulation of electronic energy state caused by conformational change of the main chain. ? 2003 Elsevier Science B.V. All rights reserved.

Abstract: A novel electrode preparation technique for free-standing semiconductor polymer films compatible with reel-to-reel production, the peeling-off transfer technique, has been proposed. This technique can remove the flipping process from the preparation of sandwich-type devices with a free-standing semiconductor polymer film, and can provide easier positioning between upper and lower electrodes. It has been shown that the Schottky junction devices using the conjugated polymer poly(3-hexylthiophene) made through this technique have essentially identical characteristics to those made by direct vacuum deposition techniques. Although we used a conjugated polymer film to test our idea, this technique can easily be applied to any flexible semiconductor films with adequate surface and mechanical properties.

Abstract: In this paper, the preparation of nanostructured films of a conjugated polymer, poly(3-octadecylthiophene), through electrophoretic deposition from colloidal suspension is described. The morphology of the film observed by an atomic-force microscope, indicated that the film consists of nanoparticles. It is suggested that the deposition, as well as drying of the film in the non-solvent atmosphere is a key to obtain nanostructured film. A light-emitting device fabricated from the nanostructured conjugated polymer film has emitted light, directly indicating that pin-hole free nanostructured film can be obtained. ? 2003 Elsevier Science B.V. All rights reserved.

Abstract: The preparation of acetonitrile-toluene suspension and the electrophoretic deposition of poly(9,9-dioctyl-fluorenyl-2, 7-yleneethynylene) have been carried out. It was found that the size of colloidal particles in the acetonitrile-toluene suspension increases with decreasing toluene content. Atomic force microscopy (AFM) observation clearly indicated that a polymer film deposited from a suspension with a low toluene content consists of large particles, reflecting the colloidal size in the parent suspension. A simple recipe for controlling average size of the colloidal particles in the nanostructured film mentioned here, which involves changing the nonsolvent:solvent ratio, may be useful for controlling the nanoporosity of the film, which is very important in optoelectronic, electronic, and electrochemical applications.

Abstract: Polymer light-emitting devices from nanostructured poly(3-octadecylthiophene) film obtained by electrophoretic deposition from a colloidal suspension have been prepared. The atomic force microscope image of the film surface shows a pronounced nanostructured morphology. Despite the porosity of the nanostructured polymer film, the device made by the simple vacuum deposition of a metal cathode on the polymer film deposited on an transparent electrode emits light. The nanostructured conjugated polymer films have no macroscopic porosity. The inhomogeneous emission was found to be a result of the roughness of the polymer film. Since the emission pattern is neither controllable nor duplicable, this device can be used as artificial fingerprints for polymer smart cards.

Abstract: A device structure of polymer Schottky diodes enabling selective doping of polymer has been proposed. The device has a Ni grid anode with a chimney as a reservoir of dopant solution at the back of the cathode. The forward-bias current of the device was enhanced two orders of magnitude upon doping by nitromethane solution of FeCl3 for 10 min, while the reverse-bias current remained unchanged, indicating considerable reduction of series resistance of the device upon selective doping. It has also been found that the penetration depth of dopant depends significantly on the solvent, i.e. nitromethane eventually gives complete doping of a 50 ��m thick PAT6 film, to induce cathode corrosion, while acetonitrile gives only shallow penetration. The device structure and doping procedure proposed may also be useful in reducing the series resistance of polymer photovoltaic devices.

Abstract: The thermochromic behavior of poly(2,5-dialkoxy-p-phenylene vinylene)s (ROPPVs) and poly(2,5-alkyl-p-phenylene vinylene)s (RPPVs) have been studied. The temperature dependence of optical properties and the variation of properties with the side chain length have been compared with those of poly(3-alkylthiophene)s (PATs). The difference of bandgap energy between PPV derivatives and PATs can be tentatively interpreted in terms of the main chain structure. The photoluminescence intensity of ROPPVs and RPPVs decrease monotonically with increasing temperature. To explain this mechanism, we speculate on the separation of the excited species due to the reduction of distance between polymer main chains and the enhancement of the overlap of ��-electrons with the twist of polymer main chain. Furthermore, the interaction between polymer main chain and the oxygen atoms of alkoxy side chain plays an important role for the optical properties of ROPPVs. ? 2003 Elsevier Science B.V. All rights reserved.

Abstract: Photoirradiation effects on polymer light-emitting devices (PLEDs) based on poly(3-dodecylthiophene) and poly(3-octadecylthiophene) have been studied. The PLEDs used have a semitransparent Al cathode to make the photodegradation rate of the polymer film in PLED comparable to that of a naked polymer film. Upon photoirradiation in air using an incandescent lamp (150 W), the electroluminescence from the devices rapidly diminished and was weakened so as to be undetected within several minutes. The quantum efficiency of electroluminescence as well as that of photoluminescence also dropped rapidly due to photoirradiation. These results imply that the photoinduced creation of defects acting as luminescence quenchers plays a crucial role in the photodegradation of PLEDs based on poly(3-alkylthiophene) (PAT), rather than the degraded carrier-transport nature of the polymer due to scission of the main chain. On the other hand, the optical absorption due to ��-��* transition of the polymer film shows little change under the same photoirradiation condition. This indicates that most ��-conjugation systems of polymer main chains survived photodegradation, which suggests a long diffusion length of excitons or a strong interchain interaction in PAT.

Abstract: Poly(2-methoxy, 5-(4-decyloxy-biphenyl-4��-(1,10-dioxydecane))-p-phenylene vinylene), MDBD-PPV, with a long side chain containing alkoxybiphenyl mesogenic unit has been synthesized and its electrical and optical properties have been investigated. This polymer showed a microscopic texture typical to the liquid-crystalline phase and a sharp X-ray diffraction peak due to the smectic layer structure. The band gap of MDBD-PPV in the liquid-crystalline phase has been estimated to be about 2.3 eV. An electroluminescent (EL) device has been fabricated using this liquid-crystalline polymer, MDBD-PPV, as an emissive layer and the polarity effect has been observed in the emission spectra of this EL device. ? 2001 Scripta Technica, Electr. Eng. Jpn.

Abstract: Photoirradiation effects on the polymer light-emitting devices (PLEDs) with a semitransparent-Al cathode have been studied. A light-emitting polymers, a poly (p-phenylene vinylene) derivative MDOPPV has been used in this study. Upon photoirradiation, the emission intensity at a constant voltage was rapidly decreased. However, the quantum efficiency of electroluminescence remained constant, indicating the spatial separation between recombination zone and photooxidized defects. On the other hand, the quantum efficiency of photoluminescence rapidly dropped upon similar photoirradiation. These can be understood by taking the difference in the spatial distribution and the origin of excitons between electro- and photo-luminescence processes. It was also found that the photooxidation rate of the polymer film whose thickness is ca. 100 nm does not have thickness dependence, suggesting that the photooxidation of the polymer proceeds uniformly throughout the device.

Abstract: The emission properties of the polymer light-emitting devices (PLEDs) fabricated by the maskless dye diffusion technique in correlation with the diffusion degree have been studied. It has been found that the emission intensity at a constant voltage slightly increased by the dye diffusion, however, at this stage, no improvement was observed in the external quantum efficiency. The emission color of the devices can be tuned to pure color from the dye diffused at a certain diffusion degree, but further diffusion induces critical damage to the device, indicating that a certain optimum diffusion degree exists. These observations suggest that the optimal condition for the maskless dye diffusion must be considered not only from the heating condition but also from the dye concentration in the reservoir film. ? 2002 Elsevier Science B.V. All rights reserved.

Abstract: The electrophoretic deposition of nanostructured films from colloidal suspensions of a conjugated polymer poly(3-octadecylthiophene) (PAT18), as well as the preparation of the suspension by a simple mixing method, is reported. A colloidal suspension of PAT18 was prepared by pouring a toluene solution of the polymer into acetonitrile, which is not a solvent for the polymer. It was found that the suspension obtained was stable for more than two weeks, and the stability was related to the concentration of the polymer therein. In comparison with a toluene solution of PAT18, the colloidal suspension shows a considerable red-shift in the optical absorption and photoluminescence spectra, as well as a quenched photoluminescence, indicating the solidification of PAT18 in the suspension. The electrophoretic deposition of a PAT18 film from the colloidal suspension was successfully carried out. The film shows almost the same optical absorption and photoluminescence spectra as those of a spin-coated film. On the other hand, an atomic force microscopy study revealed a nanostructured surface morphology of the electrophoretically deposited films. Such nanostructured films are expected to be promising materials for electrochemical and sensor applications.

Abstract: In situ polymerization of polypyrrole (PPy) in various alcohols and water/methanol mixture solvents has been studied. The deposition rate in alcohols has been found to be slower than that in aqueous solution with the same composition, approximately 1-2 nm/min, by two orders of magnitude. On the other hand, the electrical conductivity of PPy films deposited in alcohols ranged from approximately 10-6 S/cm to approximately 1 S/cm, depending on the solvent, while that in aqueous solution was approximately 100 S/cm. These results suggest that the replacement of the solvent water with alcohols induces drastic deactivation of FeCl3 as an oxidizer. The surface morphologies of the PPy films deposited in alcohol solutions mimic those of PPy films deposited in aqueous solutions. For in situ polymerization of PPy in water/methanol mixture solvents, it has been found that the electrical conductivity as well as the deposition rate is continuously and monotonically tunable by changing the methanol content. This indicates that the utilization of a mixture solvent is a promising way to control the electrical conductivity as well as the deposition rate.

Abstract: A polymer light-emitting device (PLED) with a semitransparent metal electrode drastically reduces its emission intensity upon photoirradiation in air, because the electrode does not prevent the penetration of atmospheric oxygen into the polymer layer. By using such PLEDs, we have studied the photooxidation mechanism of PLEDs. It has been found that the mechanism of the PLED based on a PPV derivative is substantially different from that of the device based on poly(3-alkylthiophene). Application of such PLED to optically patternable devices is also proposed. The importance of the metal thickness to the patternability of the device has also been found.

Abstract: We studied the photoexcitations in films of disubstituted polyacetylene, a ��-conjugated polymer with degenerate ground state. We found that the polymer in its pristine form supports charged and neutral topological soliton excitations. Photo-oxidized films or polymer/C60 blends show, in addition, polaron excitations. At the same time the polymers show a strong emission band with high quantum efficiency, which leads to stimulated emission in thin films and lasing in cylindrical ��-cavities. These excitation properties are unique among polymers of both degenerate and non-degenerate ground state.

Abstract: Photoirradiation effects of a polypyridine, PPy/poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene), MDOPPV heterostructure photoelectric conversion device have been investigated. The photovoltaic characteristics of the heterostructure photoelectric conversion device are considerably improved from those in single-layer photoelectric conversion devices. Quenching of photoluminescence both in the PPy layer film and in the MDOPPV layer film has also been observed in the PPy/MDOPPV heterostructure film. The observed photoirradiation effects of the heterostructure device indicate that a photo-induced charge transfer occurs between PPy and MDOPPV. However, the photo-induced charge transfer between these polymers cannot be explained by the bulk electronic energy states of the polymers. A possible mechanism, which takes modulation of electronic energy states at the interface due to a local lattice distortion into account, has been proposed. ? 2001 Elsevier Science B.V. All rights reserved.

Abstract: The novel features of electrochemical actuators fabricated from a cylindrical polypyrrole (PPy) pipe prepared by the electrochemical polymerization techniques have been described. This cylindrical PPy pipe was cut into a rectangular film and its electrochemical and electrical properties were measured. When the inner surface of the PPy film (surface in contact with electrolyte when PPy was polymerized) was insulated and redox was carried out, the PPy film bent toward the outer surface (surface in contact with a slender Teflon pipe when PPy was polymerized) upon reduction and returned to its original shape upon oxidation. However, the bending was not completely accomplished by redox when the outer wall side of the PPy film was insulated. Although such an anomalous bending in the PPy film actuator cannot be explained satisfactorily at this stage, we speculate that the bending phenomena are due to steric effects from cation insertion and extraction.

Abstract: In this paper, the photooxidation effect on the organic electroluminescent devices based on a ��-conjugated polymer, poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene) (MDOPPV) is reported. The devices used have a semitransparent Al cathode, which enables atmospheric oxygen to penetrate into the polymer layer in the device, and therefore extensive photooxidation takes place upon photoirradiation in air. It was confirmed that when the Al cathode is sufficiently thin (with an optical transmittance of ?30% at �� = 500 nm), the photooxidation rate of the polymer is independent of whether the Al film exists or not. Therefore, the electroluminescence (EL) data obtained from such a device irradiated for a period of time can be directly compared with the photoluminescence (PL) data obtained from a naked polymer film irradiated for a similar period. We have found that the external quantum efficiency of EL for the device based on MDOPPV does not change on photooxidation in air for a few minutes, while the quantum efficiency of PL rapidly decreases upon such photooxidation. This means that the optically generated luminescent species are efficiently quenched by photooxidized defects, but the electrically generated luminescent species are not, suggesting that the recombination zone for the electroluminescent process is spatially separated from the photooxidized defects, or excitons 'dodge' the defects. ? 2001 Elsevier Science B.V. All rights reserved.

Abstract: The molecularly doping is known as an efficient way to improve various properties of polymers. For example, the conversion performance of polymer photocells can be drastically enhanced by incorporation of appropriate molecules. In polymer light-emitting device, the emission color is tunable by doping appropriate dyes into emission layer. However, the molecularly doping by conventional method based on mixing the solutions of polymer and dopant should not be compatible to the patterning of the emission color, which is requisite for full-color display. Here, we show a novel molecularly doping method for polymer devices, the maskless dye diffusion technique. In this method, the highly doped and non-doped polymer films are brought into contact, and the electrode beneath the non-doped polymer film is heated by means of Joule heating. Then, the thermally activated dopant molecules diffuse into the non-doped polymer films. The most important feature of the present method is that the doping region can be limited near the electrode. That is, the doped region directly reflects the shape of electrode. With this technique, three-color (RGB) polymer light-emitting devices have been successfully integrated on a glass substrate. The application of this technique to a color-sensing device is also proposed. ? 2001 Elsevier Science B.V. All rights reserved.

Abstract: We propose an actuator using the cylindrical polypyrrole (PPy) film, with an anisotropy of morphology and conductivity, can be polymerized electrochemically in a Teflon slender pipe. The PPy actuator bends and reverts in a regular direction upon electrochemical undoping/doping. The bending speed becomes faster as the undoping potential is increased, but the magnitude of displacement depends not on the undoping potential but on the amount of charge or dopant concentration. The bending behavior strongly depends on the type of supporting salt in the electrolyte solutions, suggesting that cation transport into and out of the PPy plays a key role in the bending behavior and the size of the cation is a critical factor. It was also found that, the shape of the transient reduction current strongly depends on the type of cation and that the current does not follow the diffusion law. A bending mechanism based on the cation insertion and extraction, as well as on the anisotropic volume change upon doping/undoping, is proposed. ? 2001 Elsevier Science B.V. All rights reserved.

Abstract: We have found that a polypyrrole (PPy) film with anisotropy of conductivity and morphology bends in a regular direction and reverts during redox cycles. That is, the anisotropic PPy film acts as an actuator or a "bending machine". The PPy film can be prepared electrochemically as a fiber in a slender Teflon pipe. The response speed of the PPy fiber actuator depends on the speed and amount of dopant insertion and extraction; namely, it becomes faster when the reduction potential is more negative or the electrolyte concentration is higher. The bending behavior strongly depends on the type of supporting salt in the electrolyte solutions, suggesting that cation transport into and out of PPy plays a key role in the bending behavior and that the size of the cation is also a critical factor. A bending behavior mechanism based on cation insertion and extraction, as well as on the anisotropic volume change upon doping/undoping, is proposed. ? 2000 The Japan Society of Applied Physics.

Abstract: Optically patternable light-emitting devices based on conducting polymers were fabricated and were characterized. The cathode of the devices is made with a semitransparent Al film, which enables to photoinduced degradation of the polymers in air. The optically patternable devices were successfully made with poly (2-methoxy-5-dodecyloxy-p-phenylene vinylene) (MDOPPV), as well as with poly (3-dodecylthiophene) (PAT12). However, optical absorption study indicated that the patterning mechanism of the MDOPPV device is considerably different from that of the PAT12 device.

Abstract: Emission characteristics of polymer light-emitting devices (PLED) with a configuration of indium-tin-oxide/poly(3-dodecylthiophene)/semitransparent-Al changed drastically upon photo-irradiation in air. After photo-irradiation to PLED, current passing through the device decreased by about one order of magnitude and emission disappeared within several minutes. Patterned emission from PLED utilizing this effect was also demonstrated. The observed modification should originate from slight photo-oxidation at the polymer/Al interface and/or the polymer layer. The optical patterning method mentioned here can be applied onto the completed devices, in contrast to other methods such as ink-jet printing technology, in which the patterning of the polymer must be carried out before deposition of the metal electrode.

Abstract: The characteristics of a photovoltaic device based on a heterostructure consisting of poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene) (MDOPPV) and polypyridine (PPy) have been studied. The heterostructure device shows a significant enhancement of the photovoltaic properties compared to the single-layer devices based on MDOPPV or PPy. For example, the device shows a significantly larger photocurrent than a device consisting only of MDOPPV. Moreover, notable quenching of the photoluminescence of the two polymers due to lamination has also been observed. These results indicate that a photoinduced charge transfer occurs between MDOPPV and PPy. However, the photoinduced charge transfer between these polymers cannot be explained by the bulk electronic energy structure of the polymers estimated from the optical absorption and the atmospheric photoemission spectra. A possible mechanism, which takes modulation of electronic energy structure at the interface due to a local lattice distortion into account, has been proposed. Another possible mechanism of the enhanced carrier generation based on the polarization at the MDOPPV/PPy interface is also mentioned. ? 2000 The Japan Society of Applied Physics.

Abstract: The thermochromic behaviors of poly(2,5-dialkoxy-p-phenylene vinylene)s (ROPPVs) have been studied. The temperature dependence of electrical and optical properties and the variation of properties with the side chain length have been compared with those of poly(3-alkylthiophene)s (PATs). The band-gap energy of ROPPV16 increases gradually from about 2.2 eV at room temperature to about 2.4 eV at 200��C. This temperature dependence of band-gap energy is different from those of PATs, and the difference can be tentatively interpreted in terms of the main chain structure. The photoluminescence intensities of ROPPVs decrease monotonically with increasing temperature. To explain this mechanism, we speculate on the separation of the excited species due to the reduction of distance between polymer main chains and the enhancement of the overlap of ��-electrons with the twist of polymer main chains. The ionization potentials of ROPPVs decrease slightly with increasing temperature. However, the origin of this temperature dependence is not clear at this stage. ?2000 The Japan Society of Applied Physics.

Abstract: The photoirradiation effect on the characteristics of a polymer light-emitting diode with a semitransparent metal cathode is studied. The electroluminescence intensity as well as the photoluminescence quantum efficiency decreases due to photoirradiation in air, while the external quantum efficiency of electroluminescence does not change. This suggests that not the formation of quenching defects but the degraded carrier transport/injection nature of the polymer mainly affects the emission property of the device and that the recombination zone is separated from the photo-oxidized defects. Two models of the separation, the layer model and the scattering model, are proposed. The validity of the two models depends on the penetration depth of oxygen in the polymer. ? 2000 American Institute of Physics.

Abstract: By exposing low-density polyethylene to an atmosphere of fuming sulfuric acid, sulfonated low-density polyethylenes (SPE) were prepared and the degree of surface sulfonation for treated film was determined as the weight-increase per unit area. Polypyrrole (PPy) films on the surface of SPE were grew using a molecular self-assembly process. The electrochemical properties of PPy/SPE composite films have been investigated and their functional applications have also been proposed.

Abstract: The percolation threshold concentration of the donor-acceptor conducting polymer composite can be experimentally determined by characterizing the field-effect transistors with the composite as a channel layer. In this study, poly(3-alkylthiophene)s doped with an electron transporting dye are used as an example of donor-acceptor composites. The dye concentration dependence of the mobilities are clarified and discussed in terms of the percolation model.

Abstract: By exposing low-density polyethylene to an atmosphere of fuming sulfuric acid, sulfonated low-density polyethylene (SPE) was prepared and the degree of surface sulfonation for the treated films was determined as the weight-increase per unit area. Polypyrrole (PPy) films were grown on the surface of SPE using the molecular self-assembly process and the properties of PPy/SPE composite films have been investigated. Functional applications of PPy/SPE composite films have also been proposed and in particular, the movement properties of actuators using PPy/SPE composite films have been mentioned.

Abstract: Electroluminescence (EL) and photoluminescence (PL) have been studied in polyacetylene derivatives with various substituents. Intense green and blue ELs are observed in poly(diphenylacetylene)s and in poly(1-alkyl-2-phenylacetylene)s, respectively. While, red PL and EL in mono-substituted polyacetylene derivatives are much weaker. Detailed dependence of EL and PL on molecular structure of substituents have been discussed. Spectral narrowing of PL and lasing have also been realized with intense excitation.

Abstract: The novel features of electrochemical actuators fabricated using cylindrical polypyrrole (PPy) fibers prepared by electrochemical polymerization techniques are described. A Ni wire with a Teflon-made slender pipe was used as a working electrode. If the inner wall side (contacting surface with electrolyte when PPy was polymerized) was insulated and the redox was carried out, the PPy fiber bends toward the outer side, but the bending was not completely observed when the outer wall side was insulated. Although such an anomalous bending in PPy-fiber actuator can't be explained satisfactorily at this stage, we speculate that the bending phenomena are due to the difficulty of dopant transfer between the inner and outer wall sides.

Abstract: Optically patternable polymer light-emitting devices with an indium-tin-oxide/poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene)/semitransparent-Al structure are fabricated and characterized. When the optical transmittance of the Al electrode is about 30% at a 500 nm wavelength, the emission from the device is rapidly reduced by photoirradiation in air, and the emission is completely suppressed after irradiation for 5 min. Considerable bleaching of the optical absorption of the polymer film of the devices due to photoirradiation is also observed. These effects originate from photooxidation of the polymer by the atmospheric oxygen passing through the semitransparent-Al electrode. It is also shown that these effects are considerably moderated by using a thicker Al electrode, indicating the importance of the Al electrode thickness on the patternability of the emission.

Abstract: We studied the excitation dynamics in films of disubstituted polyacetylene, a degenerate ground-state conjugated polymer, using psec transient and steady-state spectroscopies. The polymer is found to support charged and neutral topological soliton excitations concurrent with a strong intrinsic photoluminescence band with quantum efficiency, �� ? 50%. This leads to stimulated emission in thin films and lasing in cylindrical �� cavities. The seeming contradiction of a degenerate ground-state polymer with high �� is explained by the lowest excited-state ordering. ? 1999 The American Physical Society.

Abstract: Photocell with poly(3-alkylthiophene) (PAT6) / poly(p-pyridyl vinylene) (PPyV) heterojunction is fabricated and characterized. PL of the both polymers are quenched by making heterojunction. The photovoltaic characteristics such as short-circuit photocurrent of the heterojunction device are improved from the single-PAT6-layer device. These characteristics are discussed in terms of photoinduced charge transfer between PAT6 as donor and PPyV as acceptor.

Abstract: Ionization potentials of metal/conducting polymer interfaces and conducting polymer/poly(p-pyridyl vinylene), PPy V, interfaces have been evaluated by low-energy photoelectron spectroscopic method and nano-interfacial electronic states were determined. At all the measured interfaces, shift of the vacuum level was observed, showing the formation of an interfacial electric dipolar layer. The shifts of the ionization potential at the interface could be expressed as a linear function of work function of the contact metal. But, for conducting polymers/ITO, interfaces, nano-interfacial electronic states could not be determined, because of observed novel ionization potential behavior in these systems. The present results have clearly demonstrated that sufficient clarification of the interfacial electronic states is necessary for understanding the properties of the organic electronic devices.

Abstract: Physical properties and electronic structure of new molten conducting polymer, poly(2,5-dialkoxy-1,4-phenylene-alt-2,5-thiophene) (ROPPT) are investigated. The electronic states of ROPPT remarkable changes at the solid-liquid phase transition. Thermochromic behavior observed in ROPPT is a little different from poly(3-alkylthiophene) (P3AT), which are discussed by taking differences in molecular structures into account. The interfacial electronic energy diagrams of conducting polymer/metal interfaces were evaluated by the photoelectron spectroscopy. The shifts of the vacuum level were observed at all the measured interfaces and could be expressed as a linear relationship of work function of the metal, showing the formation of an interfacial electric dipole layer. For good understanding the properties of the organic electronic devices such as electroluminescent devices and organic photovoltaic cells, it is extremely important to directly clarify the interfacial electronic structures by non-contact technique such as photoemission spectroscopy.

Abstract: A simple technique of maskless dye diffusion into polymer films on prepatterned electrodes is developed and three-color polymer light-emitting devices were successfully fabricated on a glass plate. In this method, prepatterned electrodes beneath precoated receiver film are utilized as heaters for activating dye molecules. Upon doping with three types of dye, 1,1,4,4-tetraphenyl-1,3-butadiene, coumarin 6 and Nile red into poly(N-vinylcarbazole) by the present diffusion method, blue, green and red emissions were obtained. It is found that the onset voltage of emission does not depend on the type of dye. The maskless dye diffusion technique can be applicable to a variety of devices such as photovoltaic devices.

Abstract: Carbonized materials with flexibility have been prepared by a heat treatment of conducting poly-(1,4-naphthalene vinylene) films. The electrical and structural properties of the carbonized films have been investigated. From the x-ray diffraction pattern for 2400��C-treated film the material consists of the regions with different degree of carbonization. It may originate from a multi-phase graphitization. And the obtained films are highly porous and disordered carbonized materials.

Abstract: Electronic energy states of various fusible conducting polymers in liquid state were studied by the atmospheric UV photoemission spectroscopy. The energy of the conduction band top or HOMO of poly(3-alkyl-thiophene)s (PATs) shows anomalous temperature dependence. That is, PATs with alkyl side chain length shorter than hexadecyl (C16H33) show higher photoemission threshold energy in liquid state than those in solid state, while the PATs with longer side chain length show the opposite behavior, although the main chain structure and thus ��-electron system of these polymers are thought to be almost the same. The electronic energy states of other conducting polymers whose main chain structure differs from PAT as well as anomalous features observed in the optical and electronic properties such as photoluminescence and photoconductivity of the conducting polymers in liquid state were also discussed.

Abstract: The novel features of electrochemical actuators fabricated from a cylindrical polypyrrole (PPy) pipe prepared by the electrochemical polymerization technique have been described. This cylindrical PPy pipe was cut into a rectangular film and its electrochemical and electrical properties were measured. When the inner surface of the PPy film (surface in contact with electrolyte when PPy was polymerized) was insulated and redox was carried out, the PPy film bent toward the outer surface (surface in contact with a slender Teflon pipe when PPy was polymerized) upon reduction and returned to its original shape upon oxidation. However, the bending was not completely accomplished by redox when the outer wall side of the PPy film was insulated. Although such an anomalous bending in the PPy-film actuator cannot be explained satisfactorily at this stage, we speculate that the bending phenomena are due to the difficulty of dopant transfer between inner and outer surfaces.

Abstract: We have observed the electronic states at conducting polymer/conducting oxide interfaces using a low-energy photoelectron spectroscopic method. The electronic states of conducting polymer/ indium tin oxide (ITO) interfaces were different from those of conducting polymer/metal interfaces. The electron transfer from a conducting polymer to ITO occurred at the interfaces, and is not related to the difference of the ionization potential between conducting polymers and ITO. Although the origin of this electron transfer is not clear at this stage, we speculate that the surface states of ITO play a major role. Moreover, the electron transfer at the interfaces is enhanced at higher temperatures. Other conducting oxides such as indium oxide (In2O3) and tin oxide (SnO2) also show a similar tendency to that of ITO. ? 1999 American Institute of Physics.

Abstract: Ionization potentials of conducting polymer/metal interfaces and conducting polymer/ poly(p-pyridyl vinylene), PPyV, interfaces were evaluated by a low-energy photoelectron spectroscopic method, and interfacial electronic states were determined. At all the measured interfaces, a shift of the vacuum level was observed, and was attributed to the formation of an interfacial electric dipolar layer. The shifts of the ionization potential at the interface could be expressed as a linear function of the work function of the contact metal. However, for conducting polymers/indium-tin-oxide interfaces, interfacial electronic states could not be determined. This may be related to the novel ionization potential behavior in those systems. The present results clearly demonstrate that characterization of the interfacial electronic states is necessary for a complete understanding of the characteristics of organic electronic devices. ? 1999 American Institute of Physics.

Abstract: Creeping discharge characteristics on negative polarity of a composite gas/solid insulating system with N2/SF6 mixed gas have been studied by inserting a solid insulator between a needle electrode and a plane electrode. In the case of the shorter creeping distance, the flashover voltage on the negative needle increased with increasing SF6 gas content, which was a positive effect of the SF6 gas mixture. When creeping distance was increased, a considerable decrease in the flashover voltage on the negative needle under the gas pressures P of 0.2 MPa and 0.3 MPa was observed by the addition of a small amount of SF6 into N2. The effect of SF6 gas mixture for the flashover voltage on the negative needle changed from positive to negative at a threshold creeping distance. Furthermore, the threshold creeping distance depended on the gas pressure. ? 1999 Publication Board, Japanese Journal of Applied Physics.

Abstract: Modification of photoluminescent and electroluminescent properties due to photoirradiation in air of a poly(p-phenylene vinylene) derivative, poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene), and their application to the patterning of the emission from polymer light-emitting device (PLED) are mentioned and discussed. The observed change of the photoluminescence spectrum upon irradiation can be divided into two stages. At the first stage, the photoluminescence intensity rapidly drops to about 40% of initial intensity while the spectrum shape is unchanged. On the other hand, the intensity is unchanged while the spectrum is considerably blue shifted by further irradiation. This result is discussed in terms of photoinduced defect creation and scission of main chain due to photo-oxidation. The emission from the PLED with semitransparent A1 cathode drops upon photoirradiation of the device in air and eventually disappears. This indicates that the A1 electrode is so thin and the atmospheric oxygen can pass through the A1 film and react with the polymer during photoirradiation. The importance of thickness of the A1 electrode to the patternability of the device is also mentioned. ? 1999 American Institute of Physics.

Abstract: Photoluminescence (PL) and electroluminescence (EL) in polymer mixture of blue emissive poly(1-hexyl-2-phenylacetylene) (PHxPA) and green emissive poly(1-phenyl-2-p-n-butylphenylacetylene) (PDPA-nBu) were studied. Both PL and EL in the polymer mixture change from blue to green by the addition of a small amount of PDPA-nBu into PHxPA. This fact has been interpreted as a result of energy transfer from the larger band gap PHxPA to the smaller band gap PDPA-nBu. PL and EL in the polymer mixture are found to be deconvoluted into PL1 and PL2 peaks originating from PDPA-nBu and PHxPA, respectively. PL1 of PDPA-nBu shifts to a higher energy upon introduction of PHxPA, while PL2 of PHxPA also shifts to a higher energy by adding a small amount of PDPA-nBu. From this change in luminescence, molecular conformation at the excited state in the mixture is interpreted to be distorted, depending on the molar ratio of PDPA-nBu and PHxPA. A similar change in PL and EL spectra with molar ratio implies that in this mixture the energy relaxation process is nearly the same for both the cases and does not strongly depend on whether the excited state is produced by photoexcitation or charge injection.

Abstract: The experimental studies on photophysical properties of a new C60-derivative (2,2-dimethyl-5-spiro-cyclohexanyl-3,4-fulleropyrrolidine-1-oxyl) (DSCFPO) and its composite with poly(3-dodecylthiophene) (P3DDT) are presented. Good solubilities in organic solvents and good thin film formation capabilities are found. The quenching of photoluminescence in a composite thin film of the new C60-derivative and poly(3-dodecylthiophene) are observed, which could be due to the electron transfer from the polymer to the C60-derivative molecule. Transport properties of charge carriers of DSCFPO-doped P3DDT film are determined by the disorder effects induced in the polymer matrix by large DSCFPO molecules. The new C60-derivative can be considered as a promising acceptor photodopant in polymer composites because of its good solubility. ? 1998 Published by Elsevier Science Ltd.

Abstract: Current-voltage characteristic and electroluminescence (EL) have been observed in a heterojunction device using a conducting polymer, poly(2-methoxy-5-dodecyloxy-1,4-phenylenevinylene) (MDDO-PPV), and a diamond film prepared by microwave plasma chemical vapor deposition with Al/MDDO-PPV/diamond/Si structure. These results can be interpreted in terms of the hole injection from diamond into MDDO-PPV and occurrence of radiative recombination in MDDO-PPV. The electronic energy structure evaluated from electrochemical and photoelectrochemical measurements suggests that the diamond film is suitable for hole injection in the conducting polymers, being consistent with the current-rectifying characteristics of the EL device. The observed photocurrent spectra suggest the important roles of surface and/or interface effects of the diamond films. ? 1998 American Institute of Physics.

Abstract: Emission characteristics of a polymer light-emitting device (PLED) with an indium-tin-oxide/poly(3-hexylthiophene)/semitransparent-Al structure are drastically changed upon photo-irradiation in air. After the photo-irradiation of PLED, current passing through the device decreased by about one order of magnitude and the emission disappeared. Patterned emission from the PLED utilizing this effect is demonstrated. The observed modification should originate from a slight photo-oxidation at the polymer/Al interface and/or polymer layer. The optical patterning method mentioned here can be carried out after completing the device fabrication, in contrast to other methods such as ink-jet printing technology, in which the patterning of the polymer must be carried out before deposition of the metal electrode.

Abstract: Creeping discharge characteristics of a composite gas/solid insulating system have been studied by inserting a solid insulator between a needle electrode and a plane electrode. Considerable differences have been found in the creeping discharge behaviors of N2/SF6 and CO2/SF6 systems. With the addition of three-percent of SF6 gas to CO2 gas, the creeping discharge of the CO2/SF6 gas mixture was clearly seen to be strongly affected by the nature of SF6 gas, as revealed by photon emission measurements in a corona and observations using an ultrahigh-speed digital imaging system. On the other hand, the addition of a small amount of SF6 to N2 caused a significant decrease in the flashover voltage and a peculiar creeping corona extension. The creeping discharge characteristics of N2/O2 mixtures are similar to that observed in N2/SF6 mixtures. Both an electronegative gas (negative ion) and nitrogen play important roles in this behavior.

Abstract: Photoluminescence (PL) intensity and spectrum are strongly dependent on substituents of conducting polymers, such as polyacetylene derivatives. Intense PL and electroluminescence (EL) have been observed in di-substituted polyacetylene derivatives. Novel EL characteristics have also been found in EL devices with aligned conducting polymers and also of various electrode configurations. Spectral narrowing and lasing have been observed in conducting polymers with micro-ring structures and also in photonic crystals upon relatively low optical excitation. ? 1998 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

Abstract: Unique characteristics such as quenching of photoluminescence and improvement of photovoltaic effect were observed in acceptor polymer, (cyano-substituted poly(p-phenylene vinylene)), CN-PPV/donor polymer (poly(3-hexylthiophene), P3HT composites. By taking account of the difference in electronic energy states of both CN-PPV and P3HT, these characteristics are interpreted in terms of photoinduced charge transfer between CN-PPV and P3HT and formation of fractal network.

Abstract: A poly(p-pyridyl vinylene) (PpyV)/poly(3-hexylthiophene) (P3HT) heterojuction photovoltaic cell was fabricated and its photoirradiation effects have been investigated. Quenching of photoluminescence both in the PPyV and P3HT layers has been observed in the PPyV/PSHT heterojunction film. The photovoltaic characteristics of the heterojunction photovoltaic cell are also greatly improved from those in a P3HT monolayer photovoltaic cell. Its photoresponse gives evidence of the photoinduced charge transfer between PPyV and P3HT. These results are discussed by taking account of the difference in electronic states of both PPyV and P3HT. ? 1998 Elsevier Science S.A. All rights reserved.

Abstract: Unique characteristics such as quenching of photoluminescence and improvement of photovoltaic effect were observed in donor polymeracceptor polymer composites, PAT6-CNPPV system and PDPATPSi-CNPPV system. Electronic energy structures of these polymers were determined and these characteristics are interpreted in terms of photoinduced charge transfer between donor polymer (PAT6 and PDPATPSi) and acceptor polymer (CNPPV) and formation of fractal network.

Abstract: The electrical characteristics and photoirradiation effects of a conducting polymer/C60 heterojunction device with C60 doped conducting polymer layer were investigated in contrast to those of non-doped device. The C60 doping to conducting polymer layer should be effective not only to improve short circuit photocurrent but also to reduce the serial resistance of the conducting polymer layer. Both effects can be interpreted in terms of photoinduced charge transfer between conducting polymer and C60.

Abstract: Thin film field-effect transistors (TFTs) utilizing poly(3-hexylthiophene) (PAT6) doped with the electron transporting molecule N,N��-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylene dicarboximide (BPPC), have been fabricated and characterized. Bipolar transport characteristics have been found in these TFTs, for which the mobilities of both the hole and the electron have been evaluated. Observed unique BPPC concentration dependence of the field-effect electron mobilities has been interpreted in terms of the percolation model.

Abstract: Electroluminescence (EL) in various conducting polymers (CP) based on poly(phenylene ethynylene) (ROPPE) which have C-C triple bond in their main chains were studied. EL in Al/CP/ITO structure utilizing copolymer based on ROPPE and pyridine as CP was blue-green and stronger than that in same structure utilizing well-known poly(dialkoxy-p-phenylene vinylene) (ROPPV). However, weaker red EL was observed in same structure utilizing copolymer based on ROPPE and anthracene. These result suggests that the increased band gap energy and improve exciton confinement efficiency, due to shortened conjugate length, were realized by introduction of C-C triple bonds in main chain of conducting polymers such as ROPPV, while these effects of C-C triple bonds are suppressed by introduction of electron-rich moiety such as anthracene which should increase effective conjugation length. Electrochemical studies on these copolymers also confirmed this interpretation.

Abstract: The low-field microwave absorption in poly(3-alkylthiophene) composites with fullerene C60 doped by alkali metals revealed multipeak spectra, with two signals appearing at different critical temperature. The superconducting phase consists of three components: out-of-phase, narrow in-phase and broad in in-phase. The behavior of the out-of-phase component with microwave power is in good agreement with the overheating model of a Josephson junction system. The narrow in-phase signal observed at low microwave power at the lowest temperatures supports the existence of ��-junctions. The behavior of the peak position of the broad in-phase signal with temperature and microwave power is explained by the RSJ model, which suggests that the broad in-phase signal originates from a S-N-S junction.

Abstract: The effect of annealing on the optical properties and dopability of pristine and C60 - intercalated poly (3 -octadecylthiophene) (P3ODT) have been studied. After heat treatment of thin films of P3ODT increased structuring in the optical absorption spectra and also significant change in Franck-Condon factors in photoluminescence spectra were observed. The shape of PL spectra of heated P3ODT become more wide. It is explained by better ordering and concentrating of polymer chains with long side groups (n=18) due to a "zipper effect". The PL of P3ODT(C60)y (with y=0.01) thin film after moderate annealing was recovered to initial intensity and the shape of spectra was changed to the original one of pristine P3ODT. This behavior is explained by aggregation of C60 molecules into large clusters, so that PL quenching effect of single C60 molecules is suppressed.

Abstract: Photoluminescence (PL) of poly[(disilanylene)quaterphenylene] (PDSiQP) has been markedly quenched upon introduction of several mol% of C60, whereas photoconductivity of PDSiQP has been drastically enhanced upon doping with a small amount of C60 at the excitation with a photon energy exceeding the band gap energy of PDSiQP. We interpreted these results taking the electronic energy states of both PDSiQP and C60 and the role of oligophenyl units in the main chain of PDSiQP into consideration.

Abstract: A fluorescent dye and a photochromic dye were infiltrated into polycrystalline samples of porous opal in order to determine the effects of opal repeat dimension on the optical properties of the dyes. These opals consist of faulted face-centered-cubic arrays of monodispersed, nanoscale SiO2 spheres. The observed absorption and fluorescence of tris(8-hydroxyquinoline) aluminum (Alq3) depended on the lattice constant of the opal. The Alq3 exhibited a blue shift of the absorption edge and a decrease of fluorescence intensity with decreasing lattice constant. Also, the stability of the photochromic behavior of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethene (CMTE) increased remarkably inside the opal matrix. These characteristics are possibly due to the interaction between the nano-structure-confined dyes and the surfaces of the SiO2 spheres.

Abstract: Properties of conducting polymers, especially optical properties, have been found to be strongly influenced by doping of molecular dopants such as C60, aromatic molecules, photo chromic dyes and different structures of conducting polymers, which are interpreted in terms of dynamics of photo-excited electrons, holes and excitons by taking electronic energy states of both conducting polymer and molecular dopants into consideration. Novel characteristics have also been observed upon double doping, superconductivity and ferromagnetism upon doping of Alkali metal and TDAE into C60 doped conducting polymer, respectively. Molecular doped conducting polymers also have exhibited novel junction characteristics such as high efficiency of photovoltaic effects, light sensitive FET characteristics and voltage and its polarity dependent electroluminescence.

Abstract: A novel thin film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with molecular-level control over thickness and multilayer architecture. This new self-assembly process opens up vast possibilities in applications which require large area, ultrathin films of conducting polymers and more importantly in applications that can take advantage of the unique interactions achievable in the complex, supermolecular architectures of multilayer films.

Abstract: Photoirradiation effects of a poly(p-pyridyl vinylene) (PPyV)/poly(3-hexylthiophene) (PAT6) heterojunction photocell have been investigated. The photovoltaic characteristics of the heterojunction photocell are considerably improved from those in a single-PAT6-layer photocell. Quenching of photoluminescence both in the PAT6 layer and in the PPyV layer has also been observed in the PPyV/PAT6 double layer. The observed photoirradiation effects of the heterojunction have been discussed in terms of interfacial photoinduced charge transfer between PAT6 and PPyV.

Abstract: Substituent dependences of electroluminescence (EL) and photoluminescence (PL)in disubstituted polyacetylene derivatives such as poly(1-methyl-2-phenylacetylene) (PMePA), poly(1-ethyl-2-phenylacetylene) (PEtPA), poly(1-n-hexyl-2-phenylacetylene) (PHxPA) and poly(1-methyl-2-naphthylacetylene) (PMeNA) have been studied. Blue light emission was observed from EL devices utilizing PEtPA and PHxPA, and blue-green light emission was observed from those utilizing PMePA and PMeNA. EL intensity, relative EL efficiency and PL intensity increase by one or two orders of magnitude on increasing the alkyl chain length. EL intensity, EL efficiency and PL intensity of PMeNA are higher than those of PMePA. The results are discussed in terms of substituent-dependent interchain interaction and electronic energy states.

Abstract: Poly [�¿-(bithiophene-5,5'-diyl)- (p- (heptyloxy)benzylidene)-co-(�¿-bithiopheue quinodimethane-5.5'-diyl)] (PBTHBQ), which is obtained from precursor poly[�¿-(bithiopheue-5.5'-diyl)-(p-(heptyloxy)benzylidene)] (PBTHB) by oxidative dehydrogenation with 2,3-dichloro-5,6-dicyano-p-benzoquinone and contains alternating aromatic and quinoid thiophene rings in its main chain, has an optical absorption edge at about 1.4eV, while the band gap of PBTHBQ was evaluated to be about 2.6eV from the short-circuited photocurrent spectrum. The electrochemical and optical properties of PBTHBQ and PBTHB have been investigated by cyclic voltammetry, in situ optical absorption spectroscopy, photoconduction spectra measurements and electron spin resonance measurements. From these experimental results, electronic energy states of PBTHBQ and PBTHB were estimated. PBTHBQ was also found to be made from PBTHB by an electrochemical cycle.

Abstract: An organic heterojunction utilizing conducting polymer, poly(2-methoxy-5-dodecyloxy-1,4-phenylenevinylene) (MDDO-PPV), and diamond film with the structure of Al/MDDO-PPV/diamond/Si has been fabricated. The device exhibits current rectification characteristics. The electroluminescence (EL) from MDDO-PPV on the diamond film has been observed. The rectifying junction and EL characteristics have been revealed and explained by taking hole injection from diamond film into consideration.

Abstract: Optical absorption spectrum, photoluminescence (PL) and electroluminescence (EL) in poly[(tetraalkyldisilanylene)-p-oligophenylene]s (PDSiOP) are found to be dependent on the length of the oligophenylene but not on the length of the short alkyl substituents such as methyl and ethyl substituents. Spectral narrowing of the blue PL was observed in poly[(tetraalkyldisilanylene)-p-oligophenylene]s upon intense optical excitation due to stimulated emission. PL quenching and photoconductivity (PC) enhancement upon C60 doping are commonly observed in these polymers. These characteristics were explained taking the important role of oligophenylene units in the main chain into consideration.

Abstract: Intense photoluminescence (PL) is observed in di-substituted polyacetylene derivatives even though solitonic mid-gap absorption is observed upon doping, contrary to non-substituted trans-polyacetylene and mono-substituted polyacetylene in which strong PL is not observed. Intense green and blue electroluminescence (EL) is realized utilizing poly (diphenylacetylene) derivatives and poly (1-alkyl-2-phenylacetylene) derivatives, respectively. Greenish-blue emission is also observed in poly (1-chloro-2-phenylacetylene) derivatives. The dependence of wavelength and intensity of PL and EL on the molecular structure of substituents is clarified in detail. The effects of molecular alignment and layer structure on the EL characteristics are also discussed. Upon intense light excitation, remarkable spectral narrowing due to stimulated emission is also observed in these di-substituted polyacetylene derivatives. ?1997 Elsevier Science S.A.

Abstract: Interest in organic photocells was significantly renewed a few years ago due to discovery of extremely fast photo-induced charge transfer (CT) from conducting polymer (CP) to fullerene C60 molecules in CP(C60) composites. This allowed creation of interfacial junction photocells with relatively high efficiencies. It has been recognized that those are not conventional p/n type semiconducting junction devices, but are so called donor-acceptor (D-A) photocells, reminiscent of reaction centers of natural photosynthetic systems. Even more efficient photovoltaic devices have recently been fabricated with interpenetrating D-A networks which allow electron-hole separation to take place throughout the bulk of the device. In the present paper we demonstrate how these photocells can be further improved; we describe new experimental results, give general discussion of the efficiency of such devices, and analyze strategies for design of better D-A type photocells. Our recent experimental results on sensitization by inserting an excitonic layer between donor and acceptor layers multilayered structures, and by doping the D-layer by A-molecules in D(A)/A cells are briefly discussed. The organic photocell, which consists of the multilayer structure: ITO/poly(2,5-dioctyloxy-p-phenylenvinylene) (OOPPV)/octaethylporphine (OEP)/C60/Al, has been fabricated. Photocurrent yield spectra are interpreted by light absorption at OEP layer, exciton migration, and charge generation at both organic heterojunctions. That is, double heterojunctions of OOPPV/OEP and OEP/C60 contribute to the charge generation by excitonic dissociation. We also report a new type of "fractal network" photovoltaic devices made of two conducting polymers, particularly D and A derivatives of poly(phenylene vinylene). Conceptual theoretical work and modeling have been carried out to understand the ways for improvement of the device performance. Strategies to improve each step involving selective doping have been suggested to improve each step. Selective doping can provide low serial resistance and create internal electric fields for the collection of charges, while in the undoped parts excitons are effectively photogenerated. Ways to increase the effective use of absorbed photon energy and filling factor are also suggested. ? 1997 IEEE.

Abstract: Intense green photoluminescence (PL) in the wavelength range of 520 to 540 nm was observed in many poly(diphenylacetylene) (PDPA) derivatives. The band gap energy and the highest occupied molecular orbital (HOMO) energy of these polymers were estimated to range from 2.6 to 2.7eV and -5.6 to -5.9eV depending on the substituent. Green electroluminescence (EL) was observed from EL devices fabricated utilizing these polymers. Among these PDPA derivatives. poly(1-phenyl-2-m-(trimethylsilyl)phenylacetylene) (PDPA-mSiMe3) with the smallest band gap energy exhibited the weakest PL and EL of longest wavelength. Polymers with bulkier and/or longer substituents exhibited stronger PL and EL. The results are interpreted in terms of a steric hindrance effect and the interchain interaction depending on the molecular structure of the substituents. In addition, upon electrochemical doping, these light emissive polyacetylene derivatives exhibited evolution of new single midgap absorption suggesting formation of solitons.

Abstract: A color sensor device using conducting polymer poly(3-hexylthiophene) (PAT6), has been fabricated and characterized. The device consists of two photocells made of the same conducting polymer with different polymer thicknesses, and which exploits the difference in the photocurrent spectrum of the photocells. The color of the irradiated light can be detected by measuring the ratio of the short-circuit photocurrent of two photocells with different PAT6 thicknesses. The color sensor proposed here is suitable for large-area sensor systems such as the integrated image sensor device because of its simple structure.

Abstract:

Abstract: We studied spontaneous and stimulated optical emission in films of di-substituted trans-polyacetylene (t-PA). We found that di-substitution of t-PA drastically changes the polymer optical emission properties, so that photo-generation of exciton and photoluminescence (PL) quantum yields become much higher than those measured in unsubstituted and mono-substituted t-PA. The strong PL is accompanied by high optical gain and emission spectral narrowing at high excitation intensities; the emission spectrum changes from a broad PL band of 100 nm at low intensities to a narrow stimulated emission band of ? 8 nm at high intensities. These properties show that di-substituted t-PA films can be good candidates for laser medium in the green and blue spectral ranges.

Abstract: Optical properties and electronic structure of a new fusible and soluble conducting polymer based on poly(p-phenylene), poly(1,4-bis(2-thienyl)-2,5-dialkoxy phenylene) (ROPBTP), are investigated. From the optical absorption edge, the band gap of ROPBTP has been evaluated to be about 2.3 eV. The electronic structure of ROPBTP is similar to that of poly(2,5-dialkoxy-p-phenylene vinylene) (ROPPV). Electrochromism from orange to blue is observed in ROPBTP upon electrochemical oxidation and strong yellowish-green emission as strong as that from ROPPV is observed in an electroluminescence device with AI/ROPBTP/ITO structure. The thermochromic behaviour of ROPBTP is a little different from that of poly(3-alkylthiophene) (PAT), which difference is discussed by taking differences in molecular structures into account.

Abstract: Heterostructure multilayer thin films of electroactive polymers such as protonated poly(p-pyridyl vinylene) (PHPyV) and sulphonated polyaniline (SPAn) have been fabricated via processes based on the spontaneous self-assembly of conjugated poly-ions on to a substrate. The heterostructure thin films formed from these polymers exhibited a perfectly linear relationship between the absorbance and the number of SPAn/PHPyV bilayers deposited. A greenish-yellow electroluminescent (EL) diode utilizing a SPAn/PHPyV multilayer thin film has been fabricated and the EL properties of this device are discussed. The EL emission of this device can be qualitatively interpreted in terms of radiative recombination of the singlet polaron exciton formed by the injection of electrons and holes. The EL intensity of this light-emitting diode is weak. This result is discussed in terms of the quenching centre of cationic sites on the PHPyV polymer's main chain at the heterojunction. The Stokes shift due to the absorption and emission of a phonon is clearly observed in the EL spectrum of this device. A small shift between the EL and PL spectra of SPAn/PHPyV is observed. It was assumed that the EL emission takes place in a narrow region at the interface whereas the PL emission probes the bulk of the film. The SPAn/PHPyV monolayer LED emits yellow light, but the SPAn/PHPyV multilayer LED emits greenish-yellow light and there is a slight shift between the two spectra of these devices. These results can be interpreted in terms of the effect of confinement of carriers in the superlattice structure constituting the SPAn/PHPyV multilayer system.

Abstract: Hetrostructure multilayer thin films of electroactive polymers such as protonated poly(p-pyridyl vinylene), PH-PyV, and sulfonated polyaniline, SPAn, have been successfully fabricated via a process based on the spontaneous self-assembly of conjugated polyions on a substrate. The heterostructure thin films formed by these different polymers exhibited a perfectly linear relationship between the absorbance and the number of a SPAn/PHPyV bilayer, SPAn/PHPyV(b), deposited. A greenish-yellow electroluminescent (EL) diode utilizing an SPAn/PHPyV multilayer thin film, SPAn/PHPyV(m), has been produced, and the EL properties of this device are discussed. The EL emission of this device can be qualitatively interpreted in terms of a radiative recombination of the singlet polaron exciton formed by the injection of electrons and holes. The EL intensity of this light-emitting diode is weak. This result is discussed in terms of the quenching centers associated with cationic sites on PHPyV polymer main chain at the heterojunction. The Stokes shift due to the absorption and emission of a phonon is clearly observed in the EL spectrum of this device. A small shift between the EL and PL spectra of SPAn/PHPyV(m) is observed. It was assumed that the EL emission takes place in a narrow region at the interface while the PL emission probes the bulk of the film. The SPAn/PHPyV(b) (LED) emits yellow light, but SPAn/PHPyV(m) emits greenish-yellow light, and there is a slight shift between the two spectra of these devices. These results can be interpreted in terms of the confinement effect of carriers in the superlattice structure of the SPAn/PHPyV (m) system.

Abstract: The in-phase and out-of-phase low field microwave absorption (LFMA) signals in a PAT12(C60)0.05Rbx composite, consisting of superconducting granular Rb3C60 grains embedded in host poly(3-alkyltiophene) (PAT12) matrices, are investigated as functions of temperature and the intensity of trapped field. Temperature dependence of the peak field Hp of the out-of-phase and in-phase LFMA obeys the relation Hp?{1 - (T/Tc2)}1/4 and Hp?{1 - (T/Tc1)4}1/2 respectively, where Tc2 ( = 22 K) and Tc1 (=26 K) is the critical temperature of respective phase. Threshold field of the flux trapping in the out-of-phase and in-phase LFMA is nearly zero and 150 G respectively. These results support the previous models proposed for the origins of two phases presented in the K-doped CP-C60 composites. ? 1997 Elsevier Science Ltd.

Abstract: Doping effects of conducting polymer (CP)-C60 composites by n-type dopants, namely, by alkali metals, are investigated, emphasizing the electron spin resonance (ESR) spectroscopy together with conductivity changes upon K-doping of poly(3-alkylthiophene) (PAT)-(C60)y composites at various fullerene concentrations y. The ESR shows two types of lines: one from polarons on PAT chains, and the other from K3C60 clusters and monomolecular C60 radicals. The evolution of conductivity suggests that, at comparatively large C60 content y = 0.05, the composite can be viewed as a network of C60 clusters in the PAT host matrix at the initial K-doping stage. K3C60 metallic islands are formed, while the PAT matrix is still insulating so that increase of conductivity is slower than in the pure PAT case. These results are consistent with the granular nature of superconducting phases found by us in PAT(C60)yKx at y?0.005 by low-field microwave absorption (LFMA).

Abstract: The processes of charge transfer (CT) between fullerene and conducting polymer (CP), both intrinsic photoinduced CT and extrinsic CT due to strong n-type (alkali-metal) dopants, are analyzed from a general point of view and illustrated by new experimental results. The origin of strongly suppressed backward recombinative CT is discussed in terms of polaronic effects on C60 spheres and CP chains, as due to the orientational self-trapping barrier caused by modulation of ��-�� overlapping. Upon external CT provided by alkali-metal doping, the superconducting (SC) phase is found in poly (3-alkylthiophene)-C60-K composite: PAT-(C60)y-Kx at y > 0.005. The SC transition temperature Tc ranges from 12 to 17 K depending on y and x. Exceptionally strong low field microwave absorption (LFMA) shows phase reversal just below Tc in SC composites with large C60 content (y > 0.025), indicating the granular nature of the SC phase in which K3C60 clusters are weakly coupled through Kx-PAT intergranular barriers. The anomalous phase of LFMA and the paramagnetic Meissner effect, which are found at T �á Tc for certain values of y, suggest the existence of Josephson intergrain ��-junctions. Spin-carrying polarons P+ in chains of PAT separating K3C60 granules are suggested as the possible origin of such ��-junctions. The possibility of a two-component SC phase in which electrons of CP chains are actively involved in SC pairing induced via hybridization with C60 molecules (which play a role of negative U centers) is analyzed and strategies for the search of such a two-component SC phase are discussed.

Abstract: Novel electrical and optical characteristics have been observed in conducting polymers doped with molecular dopants such as fullerenes (C60, C70 etc.), photochromic dyes and another (guest) conducting polymer. Highly effective photo-induced charge transfer results in various effects such as photoluminescence quenching, photoconductivity enhancement, electroluminescence quenching and persistent photoconductivity which have been observed in fullerene-doped conducting polymers. Unique photo-sensitive characteristics have also been found in conducting polymer/fullerene systems. Photoluminescence and photoconductivity in conducting polymers doped with photochromic dyes have been changed dramatically by photo-induced isomerization of photochromic dyes and memory effects in both dark conductivity and photoconductivity have been observed. We also present here some results on conducting polymer-conducting polymer mixtures and discuss general features of such composites. These characteristics can be explained by the asymmetry of the relative electronic energy states of conducting polymer and molecular dopants on account of self-trapping effects. Superconductivity evolved upon alkali metal doping of C60-conducting polymer composites, and has been confirmed by low-field microwave absorption (LFMA) and SQUID magnetometry measurements. The origin of superconducting phases in this doubly doped conducting polymer is discussed.

Abstract: Optical characteristics of poly(2,5-dialkoxy-1,4-phenylene diethynylene-co-2,5-pyridinylene) (ROPPE-Py) were investigated. Intense blue-green electroluminescence (EL) emission was observed in light emitting diode (LED) with Al/ROPPE-Py/indium-tin-oxide (ITO) structure. This result suggests that triple bonds in the main chain are responsible for the blue shift and enhancement of EL, due to the shortening the effective conjugation length and effective confinement of excitons or exciton-polarons. However, the effects of triple bonds were suppressed by the introduction of electron-rich moieties in the main chain such as poly(2,5-dialkoxy-1,4-phenylene diethynylene-co-9,10-anthracenylene) (ROPPE-An). Electronic energy structures obtained from optical absorption spectra and cyclicvoltammetry measurements confirmed the effect of the electron-rich moieties, which is due to the delocalization of ��-electrons and the enhancement of interchain interactions.

Abstract: Charge transfer in the ground state has been observed in poly(3-octadecylthiophene) (PAT-18), doped by C60. ESR studies of PAT-18-C60 composite reveal for the first time two ESR signals without photoexcitation. For the detection of two ESR signals an increase of microwave power is important. Only then can the two ESR signals be resolved: one with g1 = 2.0022 and �¢HPP = 3.5 G, corresponding to positive polaron P+ in PAT-18 chains, and the second with g2 = 1.9993 and �¢HPP = 1.5 G, corresponding to the C60- anion. The microwave power dependence of the intensity of these two ESR signals differs significantly due to different mechanisms of spin relaxation in C60 and PAT-18. The ESR study of PAT-18-C60 composite, additionally doped by I2, shows at the initial stage the disappearance of the C60- anion signal due to the further step of charge transfer (CT) from C60- to I2 at a low doping level and then, after heavy doping in I2 vapor, the increase of the polaronic P+ polymer signal due to strong CT doping of PAT-18 by I2.

Abstract: The fabrication of multilayered conducting polymer hetero-structures and their optical and electrical properties are studied. A unique self-assembly technique allows to form ultra-thin layers of negatively charged conducting polymer, poly(3-�¿-carboxylmethyl thiophene), and positively charged conducting polymer, poly-(dihexyldipropargyl ammonium bromide). Photovoltaic effect is enhanced and photoluminescence of a conducting polymer is quenched markedly in the multilayered hetero-structure system, which is explained in terms of photoinduced charge separation at the interfaces of conducting polymers taking energy states of the conducting polymers into consideration.

Abstract: A using multilayered conducting polymer heterostructure is fabricated by the self-assembly technique with a negatively charged conducting polymer, poly(3-�¿-carboxylmethylthiophene), and a positively charged conducting polymer, poly(dihexyldipropargyl ammonium bromide), and its optical and photovoltaic properties are studied. Photoluminescence from the positively charged conducting polymer is quenched markedly in the multilayered heterostructure system. The enhanced photovoltaic effect observed in a junction device with Al and ITO electrodes is explained in terms of photoinduced charge separation at the interface of conducting polymers.

Abstract: Intense photoluminescence (PL) was observed in soluble disubstituted polyacetylenes such as poly(1-phenyl-2-p-adamantylphenyl acetylene (PDPA-Ad) at 530 nm, poly(1-phenyl-2-p-triphenylsilylphenyl acetylene) (PDPA-TPSi) at 530 nm and poly(1-hexyl-2-phenyl acetylene) (PHxPA) at 455 nm, although they are considered to be derivatives of trans-polyacetylene. In monosubstituted acetylene polymers such as poly(o-trimethylsilylphenyl acetylene) (PTMSiPA), PL was neglible. Green and blue light emissions were observed from an electroluminescent (EL) device having soluble poly(diphenyl acetylene) (PDPA) derivatives (PDPA-Ad and PDPA-TPSi) and PHxPA as emission layers, respectively. EL emission is clearly observable under normal room illumination conditions. The electronic energy structures of the disubstituted PA derivatives are also discussed to interpret PL and EL characteristics.

Abstract: Novel properties of recently developed conducting and insulating polymers and their composites are discussed. Properties of conducting polymer whose main chains are composed of unsaturated ��-bonds depend strongly on the main chain structure, substituent and also molecular dopants. Various applications of conducting polymers such as electroluminescence (EL) elements, electrolyte capacitors, photoconductors, photovoltaic cells, superconductors and insulators at cryogenic temperature, are discussed by taking effects of molecular dopants such as C60 into consideration. A new type of insulating polymer, syndiotactic polypropylene prepared by newly developed metallocene catalysts has been studied and found to exhibit much superior electrical, thermal and mechanical characteristics compared with those of conventional isotactic polypropylene, atactic polypropylene and polyethylene. These excellent characteristics originate from lower crystallinity, smaller spherulites and different crystal lattice than in isotactic polypropylene. Negligible degradation of syndiotactic polypropylene by contact with copper is interpreted in terms of difference of catalysts and suppression of diffusion of copper cation. New types of conducting polymer, insulating polymer composites were prepared. Their conductivity was controlled over more than 10 orders of magnitude by small amounts of a conducting polymer, polypyrrole, which can be interpreted in terms of the percolation model depending on the shape and density of polypyrrole coated insulating polymer particles. Nonlinear current-voltage characteristics were also studied. ? 1996 IEEE.

Abstract: A polymeric bipolar TFT with a single channel layer has been successfully realized. In the present TFT, a single interpenetrating network channel layer, consisting of PAT12 and electron transport dye, was formed by spin-coating. The current-voltage characteristics of the TFT are qualitatively similar to those of a heterostructure bipolar TFT. The interpenetrating network TFT has some advantages in fabrication compared with the heterostructure TFT.

Abstract: Superconducting (SC) phases in poly(2,5-dioctyloxy-p-phenylene vinylene) (OO-PPV) composite with fullerene C60 are found upon alkali-metal A (= K and Rb) vapor doping by sensitive low-field microwave absorption (LFMA) and proved by SQUID. LFMA of OO-PPV(C60)yKx at small y < 0.005 shows a "normal out-of-phase" shape, and appears at Tc = 11 K. At larger C60 content 0.01 < y < 0.1, the LFMA revealed unusual multipeak spectra, with two components appearing at different Tc's. At Tc1 = 12-13 K for K dopant (and Tc1 = 21.5 K for Rb) the broad component appears with anomalous phase, which we assign to SC A3C60 grains weakly linked into Josephson media, containing �� junctions. By SQUID measurements the paramagnetic Meissner effect has been observed, supporting the existence of �� junctions. Below Tc2 = 6.5-8.5 K (for K) and Tc2 = 11 K (for Rb) the narrow component with a normal phase and hysteresis appeared in the LFMA spectra. The structure found by SQUID measurements at the same Tc2 supports this assignment to a second SC2 phase. One possible origin of SC2 is discussed in terms of nonstoichiometric AxC60 grains (with x �� 3), and C60 induced superconductivity, in which electrons of conducting polymer chains are actively involved in SC pairing via hybridization with C60 may be another origin for SC2. Alternative explanations for multipeaked LFMA are also discussed.

Abstract: The drastic changes of structure and resistance of a pyropolymer (graphite) prepared by pyrolysis at 2800��C have been investigated in an electrochemical cell with 1M LiClO4 in a 7:3 volume mixture of propylene carbonate and 1,2-dimethoxyethane. Two characteristic X-ray diffraction peaks originated from the electrolyte decomposition in graphite bulk phase due to the cointercalation of solvent and lithium ions have been clearly observed in in-situ X-ray diffraction measurement during the 1st discharge. Upon addition of 12 crown 4 into the electrochemical cell, the excessive electrolyte decomposition responsible to the two diffraction peaks has been suppressed considerably and the reversibilities of changes in resistance and structure of the electrode material and also the capacity of the cell have been much improved.

Abstract: Optical properties of a soluble conducting polymer, perfluoroalkylated poly(diphenylacetylene) (PFPDPA) were clarified. The band-gap energy was evaluated to be about 2.7 eV. Relatively strong fluorescence was observed in PFPDPA, while poly(diphenylacetylene) (PDPA) is considered to be a conducting polymer with a degenerated ground state in which a soliton is considered to play an important role. A light-emitting diode (LED) with In-Mg/PFPDPA/indium-tin-oxide (ITO) configuration was fabricated and green light emission was observed.

Abstract: The C60 / poly(isothianaphthene) (PITN) heterojunction device was fabricated and its electrical characteristics and photoirradiation effects were investigated. This device has current-rectifying function. Upon photoirradiation, both forward and backward currents were enhanced, and photovoltaic effects was also appeared. These results were discussed in terms of charge transfer between C60 and PITN in the ground state and photoexcited state.

Abstract: At the interfaces of three-layered molecular structure of donor-absorber-acceptor (D-M-A) the polarization double barriers (PDB) may be formed due to a large difference in polarization energies of charge carriers in each layer: PD,PA < <PM. Such PDBs are originated from solid state effect of intermolecular interactions. Properly designed PDB at account of single molecular properties of D,A and M layers may lead to selective separation of photogenerated charge carriers enhancing the efficiency of D-M-A photocell.

Abstract: Optical properties of conducting polymers such as absorption spectrum, photoluminescence, electroluminescence, photo-magnetic effect, photoconductivity, non-linear optical phenomena and their dynamics change drastically upon doping of small amount of fullerene. Electrical and optical characteristics of junctions based on conducting polymers and fullerenes are also anomalous. It should be mentioned that these unique photophysical properties and their dynamics are dependent on the molecular structure of conducting polymer (non-degenerated polymers such as polythiophene derivatives or degenerated polymers such as polyacetylene derivatives) and also on fullerenes (C60, C70). These novel results are discussed in terms of photoexcitation in both conducting polymers and fullerene, photoinduced excitons, solitons, polarons, also their transfers between conducting polymers and fullerene, capture of carriers by C60, influence of C60 on inter-chain charge transport by taking into account the electronic energy states of conducting polymers and fullerenes.

Abstract: We have tried to confirm the sign inversion of electronic photocarrier in a fusible conducting polymer, regiorandom poly(3-octadecylthiophene), PAT] 8 associated with the solid-liquid phase transition by means of the time-of-flight (TOF) method. It was found that the hole mobility decreases with increasing temperature. At the temperature near the solid-liquid phase transition, the hole mobility decreases drastically, and eventually the melting temperature, it was impossible to evaluate the hole mobility from noisy transient photocurrent On the other hand, transient photocurrent based on electron transport are observed above the melting point The negative carrier mobility was evaluated in the range from 10-6 to 10-5cm2/Vs, which is comparably the hole mobility at solid state. This fact suggests that the same mechanism, for example interchain hopping limits carrier transport, and the negative carrier is electron. This unique phenomenon is interpreted as modulation of electronic energy state caused by conformational change of the main chain. That is, the drastic conformational change of polymer backbone induced by the thermal activation of side chain vibration, which is responsible for the thermochromism in poly(3-alkylthiophene)s, may play a key role for this unique phenomenon. ? 2005 IEEE.

Abstract: The electrophoretic deposition of nanostructured films from colloidal suspensions of a conjugated polymer poly(3-octadecylthiophene), PAT18, as well as the preparation of the suspension by a simple mixing method, is reported. A colloidal suspension of PAT18 was prepared by pouring a toluene solution of the polymer into acetonitrile, which is not a solvent for the polymer. It was found that the suspension obtained was stable for more than two weeks, and the stability was related to the concentration of the polymer therein. In comparison with a toluene solution of PAT18, the colloidal suspension shows a considerable red-shift in the optical absorption and photoluminescence spectra, as well as a quenched photoluminescence, indicating the solidification of PAT18 in the suspension. The electrophoretic deposition of a PAT18 film from the colloidal suspension was successfully carried out. The film shows almost the same optical absorption and photoluminescence spectra as those of a spin-coated film. On the other hand, an atomic force microscopy study revealed a nanostructured surface morphology of the electrophoretically deposited films. Such nanostructured films are expected to be promising materials for electrochemical and sensor applications.

Abstract: A simple technique for molecular doping to polymer films, the maskless dye diffusion, is developed. In this method, prepatterned electrodes beneath precoated receiver film are utilized as heaters for activating dye molecules. Upon doping with three types of dye, 1,1,4,4-tetraphenyl-1,3-butadiene, coumarin 6 and Nile red into poly(N-vinylcarbazole) by the present diffusion method, blue, green and red emissions were obtained. By applying this technique three times on a glass substrate, RGB light-emitting devices were successfully integrated on the glass plate. It is found that the onset voltage of emission does not depend on the type of dye. It is also found that the condition for dye diffusion was independent of dye.

Abstract: A method to prepare large-size anisotropic polypyrrole (PPy) film using a slab vessel consisting of PTFE walls as well as its actuation properties has been reported. The PPy film can be grown along one side of the PTFE walls and has a morphological anisotropy along thickness. A piece of its bends and reverts in a regular direction during a redox cycle without any other processes such as lamination. The actuation characteristics of the anisotropic PPy film strongly depend on the size of cation in the driving electrolyte. The bending of this actuator at the room temperature becomes slower for large cations. The temperature dependence of characteristics of the anisotropic PPy film as actuators has been investigated. The arrival time of actuator becomes shorter in all electrolyte solution with increasing temperature. This can be understood in terms of the thermally activated microscopic movement of polymer chains. It is also found that this actuator can lift an object which weights more than 25 times of the weight of actuator itself.

Abstract: The thermochromic behaviors of poly(2,5-dialkoxy-p-phenylene)s, ROPPVs have been studied. The temperature dependence of electrical optical properties and the variation of properties with the side chain length have been compared with those of poly(3-alkylthiophene)s, PATs. The bandgap energy of ROPPV16 increases gradually from about 2.2eV at room temperature to about 2.4eV at 200��C. This temperature dependence of bandgap energy is different from those of PATs, and the difference can be tentatively interpreted in terms of the main chain structure. The photoluminescence intensities of ROPPVs decrease monotonically with increasing temperature. To explain this mechanism, we speculate on the separation of the excited species due to the reduction of distance between polymer main chains and the enhancement of the overlap of ��-electrons with the twist of polymer main chains. The ionization potentials of ROPPVs decrease slightly with increasing temperature. However, the region of this temperature dependence is not clear at this stage.

Abstract: In this study, the energy states at conducting polymer/electrode interfaces have been observed by methods measuring in the atmosphere. The Fermi level (EF) of the conducting polymer on several electrode materials was estimated using Kelvin probe method, and the ionization potential (IP) was estimated using the atmospheric photoelectron spectroscopy. Based on the observation, the electron transfer at interfaces was related to the difference of the IP between conducting polymers and electrode material. And the dependence of the EF of PAT6 on the film thickness differed depending on electrode materials including indium-tin-oxide (ITO), Ag, and Al.

Abstract: A poly(p-pyridyl vinylene), PPyV / Poly(3-hexylthiophene), P3HT heterojunction photo-voltaic cell was fabricated and its photoirradiation effects have been investigated. Quenching of photo-luminescence both in the PPyV and P3HT layers has been observed in the PPy/P3HT heterojunction film. The photovoltaic characteristics of the heterojunction photovoltaic cell are also greatly improved from those in a P3HT monolayer photovoltaic cell. Its photoresponse gives evidence of the photoinduced charge transfer between PPyV and P3HT. These results are discussed by taking account of the difference in electronic states of both PPyV and P3HT.

Abstract: The photoirradiation effects on the emission characteristics of polymer light-emitting devices (PLEDs) based on conjugated polymer have been studied. In this study, we have used PLEDs with semitransparent Al cathode to accelerate the photooxidation of the emission layer. It was already confirmed that the semitransparent-Al film having optical transmittance ?30% does not reduce the photooxidation rate of underlying polymer film. When poly(2-methoxy-5-dodecyloxy-1,4-phenylene vinylene) (MDOPPV) is used in the emission layer, the emission intensity at a constant voltage drops significantly. It has been also observed that the photoluminescence quantum efficiency of MDOPPV film significantly reduces by similar photooxidation. On the other hand, the electroluminescence quantum efficiency remains constant. These apparently curious results have been explained by taking the difference in the exciton formation sites between electroluminescence and photoluminescence processes into account.

Abstract: Polypyrrole (PPy) pipe was electrochemically polymerized in a Teflon slender pipe. It was found that a PPy film cut from the PPy pipe has anisotropy in conductivity as well as in morphology, and bends and reverts in a regular direction during redox cycles [1]. That is, the anisotropic PPy film can be used as an actuator. We have investigated the bending behavior of the PPy actuator in various electrolytes and have found that incorporation of cations into PPy upon reduction plays a key role in the bending behavior. A mechanism of the bending behavior based on the cations transport as well as the anisotropic volume change upon doping is proposed.

Abstract: By exposing low-density polyethylene to an atmosphere of fuming sulfuric acid, sulfonated low-density polyethylenes (SPE) were prepared. The degree of surface sulfonation of the treated film was determined from the weight increase per unit area. Polypyrrole (PPy) films on the surface of SPE were grown by molecular self-assembly process and the properties of PPy/SPE composite films have been investigated. Functional applications of PPy/SPE composite films have also been proposed.

Abstract: In this article, we report fabrication and characterization of the photovoltaic devices using donor polymer-acceptor polymer composites and heterojunction. Upon mixing the two polymers, quenching of photoluminescence and improvement of photovoltaic properties have been observed. These phenomena have been interpreted in terms of the photoinduced charge transfer between donor and acceptor polymers. Drastic enhancement of photovoltaic effect has been observed also in the heterojunction device consists of donor and acceptor polymers. The charge carrier transport phenomena in polymer donor-acceptor composites have been studied by characterizing the field-effect transistors with the composites, and discussed in terms of the percolation model.

Abstract: Optical properties and electronic structure of new fusible and soluble conducting polymer based on poly(p-phenylene), poly(1,4-bis(2-thienyl)-2,5-dialkoxyphenylene) ROPBTP, and poly(2,5-dialkoxy-1,4-phenylene-alt-2,5-thiophene), ROPPT, are investigated. Thermochromic behavior observed in ROPBTP and ROPPT is a little different from poly(3-alkylthiophene) (P3AT), which are discussed by taking differences in molecular structures into account. The interfacial electronic energy diagrams of conducting polymer/metal interfaces were evaluated by the photoelectron spectroscopy. The shifts of the vacuum level were observed at all the measured interfaces and could be expressed as a linear relationship of work function of the metal, showing the formation of an interfacial electric dipole layer. For good understanding the properties of the organic electronic devices such as electroluminescent devices and organic photovoltaic cells, it is extremely important to directly clarify the interfacial electronic structures by non-contact technique such as photoemission spectroscopy.

Abstract: We have studied resonant and non-resonant Raman scattering spectra in thin films of novel disubstituted acetylene polymers such as poly(1-ethyl-2-phenylacetylene) (PEtPA), poly(1-n-hexyl-2-phenylacetylene) (PHxPA) and poly(1-phenyl-2-p-n-butylphenylacetylene) (PDPA-nBu), which possess high photoluminescence (PL) quantum efficiency. We found that the Raman scattering frequency dispersion is smaller in disubstituted acetylene polymers than in other acetylene polymers, in agreement with many other strongly luminescent polymers. Assuming the model of short polyene conjugation length in these acetylene polymers, we can obtain the conjugation length (N) for each polymer from the respective phonon frequency of the carbon-carbon double bond; we obtained N=7 for PDPA-nBu, and N=5 or 6 for PHxPA and PEtPA. The related energies of 11Bu and 21Ag can be estimated from these N and are in good agreement with the respective absorption and PL spectra of the various disubstituted polymers.

Abstract: Optical properties and electronic energy structures of di-substituted acetylene polymers have been studied. Strong blue and green photoluminescence and electroluminescence have been observed in the poly(diphenylacetylene) (PDPA) derivatives and poly(1-alkyl-2-phenylacetylene) (PAPA) derivatives, contrary to trans-polyacetylene, in which only very weak photoluminescence are observed at infrared region. The dependence of optical properties of the di-substituted polyacetylene derivatives such as photoluminescence intensity and electroluminescence efficiency on the molecular structure of substituents and the change of optical properties upon electrochemical doping and their interpretation by soliton model have also been discussed. Spectral narrowing in photoluminescence of some di-substituted polyacetylenes have also been studied.

Abstract: Optical Properties of poly[(disilanylene)oligophenylenes] such as poly[(disilanylene) terphenylene] (PDSiTP) and poly[(disilanylene) quarterphenylene] (PDSiQP) have been studied and compared with those of poly(methylpropylsilane), p-terphenyl and p-quarterphenyl. Band-gap energies of PDSiTP and PDSiQP were 3.5 eV and 3.3 eV, respectively, which are similar to those of p-terphenyl and p-quarterphenyl. Among various poly[(disilanylene)oligophenylenes], influence of short alkyl substituents such as methyl and ethyl substituents on their properties are relatively small. However, slightly stronger photoluminescence (PL) is observed in ethyl substituted PDSiTP than in methyl substituted PDSiTP. Blue electroluminescence (EL) has been observed in diode of MgIn/PDSiTP/ITO and MgIn/PDSiQP/ITO structures. Spectral narrowing of PL of blue in color due to stimulated emission has been observed both PDSiTP and PDSiQP. Poly[(disilanylene)oligophenylenes] are much more stable than poly(methylpropylsilane) under ultraviolet light irradiation.

Abstract: Organic liquids and polymer liquids with highly extended ��-conjugated electron system in their structures have much smaller band gaps than those of conventional dielectric liquids and therefore exhibit relatively high electrical conductivity and interact with visible light. In these liquids, various anomalous temperature dependences were observed in electrical conductivity, photoconductivity and photoluminescence, which have been discussed in terms of changes of electronic energy states and the inter-chain interaction with temperature. The band gap in the liquid state is found to be larger than in the solid state and fluctuates in the pre-melting region. The top of valence band (HOMO level) in the liquid state is found to be lower in energy than that in the solid state except for poly(3-alkylthiophene) of long alkyl side chains by the measurement of photo-electron emission. Polarity effects of photoconductivity indicates major role of electrons in the liquid state but both electrons and holes play roles in the pre-melting region. Electroluminescence has been studied in these ��-conjugated organic liquids and polymers. Novel characteristics of there ��-conjugated organic molecules and polymers in various solvents such as thermochromism and electro-rheology (voltage dependent viscosity) have also been observed. Unique phenomena at conducting polymer-electrode and conducting polymer-dielectric liquids interfaces have also been studied.

Abstract: The general features of charge transfer processes fullerene/conducting polymer (CP) systems, such as energetics of photoinduced charge transfer (PCT) between C60 and CP ��- electronic states, geometry of ��-�� overlapping and the role of self-trapping effects to polaronic states on C60 and CP chains on the PCT dynamics are analyzed. Persistent photoconductivity and electroluminescence quenching recently found in C60/CP composites additionally to photoconductivity enhancement and photoluminescence quenching observed earlier, indicate that photogenerated C60 radicals may be extremely long living in CP matrices, due to multicharging of C60 as suggested by us accompanied with deep self-trapping to polaron/bipolaron states. The anisotropy of PCT is proposed to arise due to orientational modulation of overlapping between polaronic rings on C60 and CP which strongly suppresses back recombination. The strategy to increase the efficiency of C60CP donor-acceptor (DA) photocells by improving PCT is analyzed, particularly considering multilayered structures with polarization barriers at interfaces, and increased intralayer mobilities of carriers. To increase the efficiency of photons collection in photocells we suggest three layered D-M-A structures, with molecular 'photon pump' layers strongly absorbing photons. The prospects for novel photonic applications of various C60CP systems, such as NLO devices and photomodulated field effect transistors (FETs) are discussed and illustrated by the newest results. New results on superconductivity of C60/CP upon alkali metal doping are presented, and exciting possibilities for novel superconducting phases in this system are discussed.

Abstract: The fabrication of multilayered conducting polymer hereto-structures and their optical and electrical properties are studied. A unique self-assembly technique allows to form ultra-thin layers of negatively charged conducting polymer, poly(3-�¿-carboxylmethyl thiophene), and positively charged conducting polymer, poly-(dihexyldipropargyl ammonium bromide). Photovoltaic effect is enhanced and photoluminescence of a conducting polymer is quenched markedly in the multilayered hereto-structure system, which is explained in terms of photoinduced charge separation at the interfaces of conducting polymers taking energy states of the conducting polymers into consideration.

Abstract: Schottky diodes and Schottky gated field effect transistors (FET) were fabricated utilizing C60 doped conducting polymers. Their characteristics are strongly dependent on the C60 concentration, and marked photo-irradiation effects exist. These results have been discussed taking into account photoinduced charge transfer between C60 and conducting polymer.