Ryu-ichi Sugimoto

Preparation and Properties of Conducting Heterocyclic Polymer Films by Chemical Method

Heterocyclic conducting polymer films are prepared by the oxidative cationic polymerization of thiophene, pyrrole and furan. Electrical and optical properties of these polymer films are similar to those using electrochemically prepared polythiophene, polypyrrole and polyfuran.

Fusibility of Polythiophene Derivatives with Substituted Long Alkyl Chain and Their Properties

Conducting polythiophene derivatives with substituted long alkyl chain such as poly(3-octylthiophene), poly(3-dodecyl-thiophene) and poly(3-dococylthiophene) etc. Have for the first time been found to be fusible by heating in a relatively low temperature range. The film formed by the hot press method at a temperature above the softening point from the powder sample exhibits a drastic change of properties upon doping just as in the case of conducting polymer films prepared by other methods.

Electrical and optical properties of poly(3-alkylthiophene)

Abstract Poly(3-alkylthiophene) has been found to be fusible at relatively low temperature. Films and fibers prepared by molding and melt-spinning methods, respectively, demonstrate also an insulator-metal transition upon doping. Reversible absorption spectrum change of poly(3-alkylthipphene) films with temperature and anomalous temperature dependence of luminescence have been also observed. By the application of hydrostatic pressure, the spectrum at high temperature turns into that of low temperature. Drastic change of electrical conductivity and optical properties have been also found at the melting point. These novel characteristics are tentatively explained in terms of the remarkable conformation change and its influence on the conjugation system.

Thermochromism, photochromism and anomalous temperature dependence of luminescence in poly(3-alkylthiophene) film

Thermochromism and anomalous temperature dependence of emission spectra have been observed in poly(3-alkylthiophene) films, and are explained in terms of the transition of poly(3-alkylthiophene) conformation. The spectral change by laser irradiation and its memory have also been confirmed. The application of this phenomenon as an optical active element is proposed.

Anomalous dependences of luminescence of poly (3-alkylthiophene) on temperature and alkyl chain length

Abstract Photo-luminescence of poly(3-alkylthiophene) film is found to increase with increasing temperature and after indicating maximum at a melting point it again decreases in the liquid phase. Photo-luminescence also increases with increasing alkyl chain length. These results are discussed in terms of the changes of the effective conjugation length due to the introduction of a large torsion angle between neighbouring thiophene rings and the inter-chain interaction which influence on the dynamics of excited spices and recombination.

Photoconductivity and carrier transport process in poly(p-phenylene vinylene) film

Abstract Anisotropic photoconductivity of an oriented form of poly(p-phenylene vinylene) (PPV) has been studied. The photocurrent spectrum for the light polarized parallel to the chain direction is much enhanced in lower photon energy compared with that for the light polarized perpendicular to that direction. Also, the dependences of the carrier mobility in PPV films on the heat-treatment temperature have been studied. The carrier mobility is found to increase with the increase of the heat-treatment temperature.

Dependence of Absorption Spectra and Solubility of Poly(3–alkylthiophene) on Molecular Structure of Solvent

Solvatochromic shifts of spectra of solutions of poly(3-hexylthiophene) and poly(3-docosylthiophene) have been analyzed in terms of Taft linear solvation energy relationships. Color changes of solutions of the former at 25°C are primarily due to changes in normal solute-solvent interactions. On the other hand, color changes of solutions of poly(3-docosylthiophene) appear to be due to configurational changes of the polymer chain. Solubility of the polymer is affected by solvation of the alkyl groups, electron donating or Lewis basicity properties of the solvent, polarity, and molecular volume of solvent molecules.

Absorption and Emission Spectral Changes in a Poly(3-Alkylthiophene) Solution with Solvent and Temperature

A remarkable change of the absorption spectrum has been observed in poly(3-alkylthiophene) solutions with changing temperature, which is tentatively interpreted in terms of a conformation change of polymer chains such as a rod-coil transition due to the change of the entanglement of alkyl chains with temperature. The emission intensity has been found to decrease remarkably at low temperature due to this transition.

Effect of Polymer Elongation on the Absorption Spectrum of Poly(3-alkylthiophene)

A remarkable absorption spectral change has been observed in ethylene propylene elastomer (EPR) films containing elongated poly(3-alkylthiophene). This change is explained in terms of the formation of new torsioned bonds between thiophene rings on the main polymer chains. This interpretation is also consistent with the anisotropy of the polarization dependence of absorption.

Large Change of Electrical Conductivity and Absorption Spectrum of Poly(3-alkylthiophene) at the Solid-Liquid Phase Transition

Electrical conductivity of poly(3-alkylthiophene) such as poly(3-dodecylthiophene) and poly(3-docosylthiophene) decreases in a step-wise manner at the melting point. The absorption spectra also changes rapidly at the phase transition. These phenomena are discussed in terms of the increased energy band gap in the liquid state due to the decrease of the co-planarity of thiophene rings accompanied by remarkable conformation changes. Large hysteresis was also observed in the temperature dependence of conductivity and absorption spectra. Thermochromism in the premelting region can be explained by effective shortening of the conjugation length due to the introduction of torsion of the thiophene rings at several points on a conjugated chain.