Toshinori Iwasa

Electrochemical Characteristics of Poly(trans‐1,2‐di(2‐thienyl)ethylene) and Its Battery Application

The electrochemical characteristics of poly(trans‐1,2‐di(2‐thienyl)ethylene) and its battery characteristics have been studied. Poly(trans‐1,2‐di(thienyl)ethylene)s prepared from both trans‐1,2‐di(thienyl)ethylene and cis‐1,2‐di(thienyl)ethylene show reversible doping‐undoping behavior and excellent charge‐discharge characteristics such as a coulombic efficiency greater than 99% and a stable electrode potential even under a large charge‐discharge current. A higher charge‐discharge capacity is observed in nitrobenzene solution than in propylene carbonate solution. The dependence of the charge‐discharge characteristics on the configuration of the monomer used in the polymer synthesis has been discussed in terms of the difference in diffusion coefficient of dopant ion in the polymer films obtained by polymerization of each monomer.

Optical recording utilizing conducting polymers, poly(p-phenylene vinylene) and its derivatives

Optical recording has been performed successfully by the preirradiation of light upon the precursor of a conducting polymer such as poly(p-phenylene vinylene) and its derivatives and subsequent thermal treatment and washing with water. The effect has been tentatively interpreted in terms of the deterioration of the irradiated area of the precursor film in which polymerization is suppressed. The application of this phenomenon for lithography has been also proposed.

Electrochemical preparation of conducting poly(trans-1,2-di(2-thienyl)ethylene) and poly(1,4-di(2-thienyl)-1,3-butadiene) and their properties: comparison with polythiophene

The electrochemical and optical properties in poly(trans-1,2-di(2-thienyl)ethylene), (trans-PTE), and poly(1,4-di(2-thienyl)-1,3-butadiene) (PTB), in comparison with those of polythiophene (PT), during electrochemical p-type doping have been investigated by cyclic voltammetry and in situ optical-absorption-spectrum measurements. The evolution of localized states is evidenced by the spectral change associated with doping. These results are discussed in terms of polaron and/or bipolaron models. The band gap of trans-PTE and PTB was evaluated to be both about 1.9 eV and smaller than that of PT by about 0.2 eV. This result can be interpreted in terms of a conformation change in the molecular structure, such as a change in the torsion angle between neighbouring thiophene rings. The polaron states in trans-PTE appear in the band gap, about 0.65 eV above the valence band but about 0.6 eV below the conduction band. The polaron states in PTB appear at about 0.7 and 0.6 eV below and above the conduction and valence bands respectively. The top of the valence band of both trans-PTE and PTB is located at a higher-energy state than that of PT by about 0.2 eV. This result satisfactorily explains the stability of p-type dopants in trans-PTE and PTB compared with PT. The bottom of the conduction band of both trans-PTE and PTB is in almost the same position as that of PT and successful n-type doping in trans-PTE and PTB is expected.

The electrochemical properties of poly(2,5‐thienylene vinylene) synthesized via water‐soluble precursor polymer

The electrochemical, optical, and magnetic properties in poly(2,5‐thienylene vinylene), PTV, in comparison with those of polythiophene, PT, during electrochemical p‐type doping have been investigated by cyclic voltammetry, optical absorption spectrum, and electron spin resonance (ESR) measurements. The evolution of localized states is evidenced by the spectral change associating with doping. In the lightly doped state only two absorption peaks originating from the transitions between two gap states and the valence band appear within the gap region at about 0.6 and 1.2 eV. The spin susceptibility increased by about 1 order of magnitude from 3.7×10−7 to 2.6×10−6 emu/mol upon doping up to a dopant concentration of about 2.8 mol %. With further increasing dopants concentration, the spin susceptibility decreases slightly. The spin density evaluated from the susceptibility was inconsistent with the polaron density assumed to be formed by dopants of 2.8 mol %. Namely, even at lightly doped state, the newly devel...

IN SITU ABSORPTION SPECTRA MEASUREMENTS IN POLY(1,4-NAPHTHALENE VINYLENE) DURING ELECTROCHEMICAL DOPING

The electrochemical and optical properties of poly(1,4-naphthalene vinylene) (PNV) during electrochemical p-type doping have been investigated by the cyclic voltammetry and in situ optical absorption spectrum measurements. The evolution of localized states is evidenced by the spectral change with electrochemical doping. These results are discussed in terms of polaron and/or bipolaron models. The band gap of PNV was evaluated to be about 2.3 eV and that of poly(p-phenylene vinylene) (PPV) to be smaller by about 0.4 eV. This result can be interpreted in terms of a more effective resonance interaction between the naphthalene unit and the vinylene unit. The electronic band structure of PNV was determined. The polaron states in PNV appear in the band gap: about 0.5 eV above the valence band and about 0.5 eV below the conduction band. The bottom of the conduction band of PNV is about 0.3 eV lower than that of PPV and successful n-type doping in PNV is expected.

N-Type doping properties and electronic states of poly(2,5-thienylene vinylene)

Evidence for electrochemical n-type doping of poly(2,5-thienylene vinylene) (PTV) is obtained from in situ measurements of a cyclic voltammogram, optical absorption spectrum and electron spin resonance. Bipolaron levels in the gap states appear upon n-type doping and the electronic band scheme of PTV is discussed.

Secondary Battery Characteristics of Poly(p-phenylene vinylene) Derivatives

Electrochemical characteristics of poly(2, 5-diethoxy-p-phenylene vinylene) film are investigated for use as a rechargeable electrode active material for a secondary battery. The Coulombic efficiencies in constant current chargedischarge cycles are nearly 100% allowing the estimation of a maximum energy density of as high as 240 wh/kg. The Coulombic efficiency showed no marked dependency upon the number of cycles below the 1000 th cycle in repetitive chargedischarge tests. The electrolyte dependence of the battery performance is also investigated.

In Situ Optical and Magnetic Measurements of Conducting Poly (trans-1,2-di(2-thienyl) ethylene) Prepared by the Electrochemical Polymerization of cis-1,2-di(2-thienyl) ethylene

Preparation of high quality conducting poly( cis -1,2-di(2-thienyl)ethylene), cis -PTE from the electrochemical polymerization of cis -1,2-di(2-thienyl)ethylene was tried. However, synthesized polymer was not cis -PTE but trans -PTE. The electrochemical, optical, and magnetic properties in the trans -PTE in comparison with those of polythiophene, PT, during electrochemical p -type doping have been investigated. These results are discussed in terms of polaron and/or bipolaron models. The band gap of trans -PTE was evaluated to be about 2.1 eV and almost the same as that of PT. The polaron states in trans -PTE appear in the band gap: ca. 0.5 eV above the valence band but ca. 0.8 eV below the conduction band. This result satisfactorily explains the stability of p -type doped trans -PTE compared with that of PT. Since the energy level of the bottom of conduction band in trans -PTE is higher than that in PT by ca. 0.2 eV, and successful n -type doping in trans -PTE is not expected.

In situ optical absorption spectra and electron spin resonance measurements of poly(1,4-naphthalene vinylene) during electrochemical n-type doping

The electrochemical, optical and magnetic properties in poly(1,4-naphthalene vinylene) (PNV) during electrochemical n-type doping have been investigated by cyclic voltammetry, optical absorption spectroscopy, and electron spin resonance (ESR) measurements. Evidence for electrochemical n-type doping of this polymer and evolution of localized states is obtained from measurements of a cyclic voltammogram and is demonstrated by the spectral change associated with doping. In the lightly doped state only two absortpion peaks originating from the transitions between two gap states and the conduction band appear within the gap region at 1.1 and 1.7 eV. The spin susceptibility increases by about two orders of magnitude from 5.9*10-8 to 6.1*10-6 emu mol-1 upon doping up to a dopant concentration of about 2.8 mol.%. With a further increase in dopant concentration the spin susceptibility decreases slightly. The spin density evaluated from the susceptibility was inconsistent with the polaron density assumed to be formed by dopants of 2.8 mol.%. That is, even at lightly doped slates the newly developed species turn into n-type spinless bipolarons. The ESR linewidth decreases by doping from about 9.9 G to 0.4 G. The g factor of 2.0031 at the neutral state shifts upon doping to the smaller value 2.0028, which corresponds to the nearly free electron g factor. These results are discussed in terms of bipolaron models.

Electrochemical properties and battery characteristics of poly(dithienyl ethylene)s

Abstract Electrochemical characteristics of poly(dithienyl ethylene)s and their battery characteristics are studied. Poly(1,2-dithienyl ethylene)s which have trans-type vinylene groups have been prepared by electrochemical polymerizations of both trans- and cis-1,2-dithienyl ethylenes, indicating isomerization during the electrochemical polymerization process of the cis-isomer. Charge-discharge properties of the conducting polymer prepared from the cis-type monomer were superior to that prepared from the trans-monomer. Diffusion coefficient of dopant ion within the polymers and morphology of the polymer surface have been studied. A rechargeable test Li battery shows excellent high coulombic efficiency and cycling behavior. Photochemical doping of the polymer has also been studied as a method of photo-induced charging of the electrode active material.