Kazuya Tada

Actuator based on doping/undoping-induced volume change in anisotropic polypyrrole film

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.

The Optical Properties of Porous Opal Crystals Infiltrated with Organic Molecules

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.

Optical Properties and Blue and Green Electroluminescence in Soluble Disubstituted Acetylene Polymers

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 negligible. 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.

Photoinduced charge separation in photovoltaic cell with heterojunction of p- and n-type conjugated polymers

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/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.

Nanostructured Conjugated Polymer Films by Electrophoretic Deposition

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.

Conducting polymer color sensor

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.

Polymeric Bipolar Thin-Film Transistor Utilizing Conducting Polymer Containing Electron Transport Dye.

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.

Three-Color Polymer Light-Emitting Devices Patterned by Maskless Dye Diffusion onto Prepatterned Electrode

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.

Photoinduced modification of photoluminescent and electroluminescent properties in poly(p-phenylene vinylene) derivative

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 Al cathode drops upon photoirradiation of the device in air and eventually disappears. This indicates that the Al electrode is so thin and the atmospheric oxygen can pass thro...

Characteristics of poly(p-pyridyl vinylene)/poly(3-alkylthiophene) heterojunction photocell

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.