Takahiro Nishioka

IR and ram-an studies in three polyanilines with different oxidation levels

Summary form only given. FT-IR and non-resonance FT-Raman spectra have been measured in three kinds of polyanilines (PANIs) chemically synthesized, i.e., leucoemeraldine base (LB), emeraldine base (EB) and pernigraniline base (PB) with different oxidation levels. In Raman spectra shown in Fig. 1, the peaks at about 1600 cm/sup -1/ and 1176 cm/sup -/ are attributed to benzenoid unit (B), while the peak at 1380 cm/sup -1/ are to benzenoid unit (Q). In IR spectra, we also observed several characteristic peaks in three PANIs, which are attributed to N-H stretching (3380 cm/sup -1/), C=C and C-C streching and bending modes (B : 1600, 1500, 1150 cm/sup -1/, Q : 1380, 1300 cm/sup -1/). The variations of oscillator strength at each IR and Raman peak among three PANIs are consistently interpreted in the viewpoint of the ratio of benzenoid and quinoid moieties.

Electrooptical Study of an In-Plane Switching Mode Using a Uniaxial Medium Model

A new modeling method using a uniaxial medium model has been proposed to obtain a simple and quantitative expression for the transmittance of an in-plane switching (IPS) mode. In this model, the effective birefringence (Δneff) and the apparent optic axis rotation angle (app) are used instead of the original birefringence and the director profile, and Δneff changes when an electric field is applied to the IPS mode cell. The dependences of Δneff (measured as a retardation) and app on the applied voltage have been evaluated first by experiment. Δneff was reduced to 80% of the original value and app rotated 45° at the maximum transmittance (Tmax). It has been confirmed that the transmittance can be reproduced satisfactorily by employing the models expression using the observed Δneff and app values. Theoretical simulation has also been executed and the results supported the experimental results. The simulation has also shown that both the Δneff–Δn ratio and app at Tmax are almost constant and do not depend on either the cell gap or liquid-crystal properties. Tmax can be easily calculated using the uniaxial medium model.

Novel Pretilt Angle Measurement Method for Twisted-Nematic Liquid-Crystal Cells by Apparent Retardation Measurement

We have proposed a novel pretilt angle measurement method for twisted-nematic (TN) liquid-crystal (LC) cells. In this method, the dependence of the apparent retardation of the TN cell on the cell rotation angle is analyzed by the simple mathematic equations derived here to determine the pretilt angle and the gap. This method can be applied to the TN LC display panel. The necessary range of the cell rotation angle is from -3° to 3°. This provides an advantage for both constructing a compact measurement system and measuring a small-size pixel.

2Ag Exciton State below 1Bu Exciton State in Trans-Polyacetylene Observed by Second-Harmonic-Generation Spectroscopy

We measured second-harmonic-generation spectra of centrosymmetric trans-polyacetylene films. A resonance peak was observed and assigned to the electric-quadrupole transition to the 2Ag exciton state at about 0.96 eV, which is located below the 1Bu exciton state at about 1.5 eV. We have also discussed the relative magnitude of the transition dipole between the excited states by comparing the various nonlinear optical spectra.

Photoexcited states in directly synthesized trans-polyacetylene films studied by photocurrent measurement

Abstract A trans -polyacetylene film was directly synthesized to reduce defects introduced during usual thermal isomerization treatment. A photocurrent excitation spectrum of this film showed very low efficiency around a reflection peak which was accompanied with phonon side bands. This strongly indicates that the lowest optically allowed state of trans -polyacetylene is a 1 1 B u exciton state like other conjugated polymers, such as polydiacetylenes. Misinterpretations of the experimental results under the SSH model, because of the use of a film of low quality, are pointed out and reinterpretations are made according to the present conclusion.

Direct synthesis of trans-polyacetylene films: dependence on polymerization conditions

Abstract We tried to prepare trans-polyacetylene films without thermal treatment to obtain the films with conjugated system of long average length and narrow distribution. Polymerization was carried out at room temperature on various conditions. It has been clealy suggested that the decrease in polymerization rate particularly by decreasing aging temperature is effective for the preparation of trans-polyacetylene films without thermal treament.

Blurring and Broadening of Reflection Spectra Due to Structural and Alignment Changes of Conjugated Chains Caused by Isomerization and Stretching in Trans-Polyacetylene

An optimized thermal isomerization condition has been established to produce trans-(CH)x films which show the reflection spectra with well-resolved vibronic structure peaking at the lowest subband. The conjugation lengths with about 100 and 150 double-bond (C=C) units are estimated to be responsible for the 1.56 eV peak of as-grown (CH)x and the 1.51 eV peak of trans-(CH)x, respectively. The 0.05 eV peak shift accounts for the extension of the trans-part by 50% of the initial length. The effect of mechanical stretching for alignment on the reflection spectra has also been studied by paying particular attention to the conjugation-length distribution. The reflection spectra obtained using light polarized parallel and perpendicularly to the stretching direction indicate that the shorter chains align more easily than the longer ones; the observed perpendicular reflection does not arise from the reflection with light polarized perpendicularly to the (CH)x chains but from the reflection with light polarized parallel to the longer ones which remain unaligned. It appears the real dimensionality of trans-(CH)x must be reconsidered by taking account of the distribution of conjugated chain lengths.

Photocarrier generation in directly synthesized trans-polyacetylene

The direct photocarrier generation edge of directly synthesized trans-polyacetylene was studied by means of electric field, temperature and excitation photon energy dependence of photocarrier generation efficiency. We found that the excited states have an energy barrier to generate the charged carrier at the absorption edge and the direct barrierless photocarrier generation starts at about 1.7 eV. These results strongly support the existence of the exciton state at the absorption edge in trans-polyacetylene.

Optical studies of directly synthesized trans-polyacetylene films

Summary form only given. We study the electronic states, including the dipole forbidden ones, of a directly synthesized trans-polyacetylene film. 1 ) A main peak of reflection spectra of this film shifts to the lower energy side by more than 0.3 eV and becomes narrower than that of an ordinary thermoisomerized film, as seen in Fig. 1. This fact indicates that the conjugation length has long average length and narrow distribution width. Resonance Raman spectra also support this conclusion. We are in the process of studying luminescence excited near absorption edge and electro-reflectance by using such a film.

Simple Method of Measuring Alignment Directions and Retardation of Liquid Crystal Cells

We developed a simple method of measuring alignment directions and retardation of twisted nematic liquid crystal cells. Our method is particularly suitable for the distribution measurement of such cell parameters of the in-plane switching and fringe-field switching panels. The normalized Stokes parameters of light passing through the cell, i.e., S1 and S2, show a special property wherein a point of (S1,S2) in the S1–S2 plane of the Poincare sphere moves on a circle by rotating the cell. A twist angle and retardation of the cell can be evaluated from the center of the circle separately from an alignment direction at a substrate interface. The alignment direction at the substrate interface can be evaluated by explicit calculation using the evaluated twist angle and an angle between the S1-axis and a line from the center of the circle to the point of (S1,S2).