Showing papers by "Hideki Shirakawa published in 1990"

The one‐dimensional intersoliton electron tunneling conduction in doped polyacetylene: Semiconductor‐metal transition

Abstract: The one-dimensional intersoliton electron tunneling conduction model in doped polyacetylene, which is a semiconductor-metal transition mechanism, is proposed. With this model, the observed two transition concentrations (y = 0.001 and y = 0.05) can be estimated correctly. In the lightly doped regime (y 0.05), the pinned soliton wave function can overlap each other forming a soliton liquid. In this stage, the bond alternation of the trans-polyacetylene chain vanishes being equivalent to the uniform bond length chain. Therefore, the metallic conductivity and finite Pauli susceptibility are expected consistent with the observed experimental results. However, since this metallic state is formed by the soliton liquid it is not a single particle like metal. The internal vibrational modes and other signals characteristic to the soliton can persist in the metallic polyacetylene.

Geometrical and electronic structures of polyacetylene chlorinated via prolonged chemical doping

Abstract: Geometrical and electronic structures of chlorinated polyacetylene, (CHCl)x, a precursor of one-dimensional conjugated polyyne, have been investigated through experimental and theoretical approaches. Uniaxially oriented (CHCl)x films prepared by means of prolonged FeCl3-doping of mechanically stretched polyacetylene films have been subjected to analyses. Polarized infrared absorption spectra showed a dichroism to confirm an orientation of the (CHCl)x films. On the basis of x-ray diffraction analysis, a fiber period of the (CHCl)x has been determined to be 5.2 ± 0.1 A. Ab initio crystal orbital calculations have been performed on structural models of infinite polymer systems for the (CHCl)x. Energy gradient optimization afforded a relative stability of three different configurational structures of poly-1,2-dichloroethylene which is assumed to be a planar zigzag all-trans conformation with respect to carbon-carbon single bonds, i.e., di-syndiotactic (dst) > erythro-di-isotactic (e-dit) > threo-di-isotactic (t-dit) structures. In addition, the fiber period of the ist structure was calculated to be 5.2 A, coinciding with the experimental value of the (CHCl)x. In consequence, it has been demonstrated that the prolonged FeCl3-doping of polyacetylene causes a stereospecific chlorination to yield a stereoregular dst structure of the (CHCl)x. The present results imply that a usage of this sort of chlorination through the chemical doping should provide a novel reaction design, especially to control a stereospecificity of chlorination reaction.