Shozo Yamanaka

Design of polymers with metallic properties: Substituted polyperylene and poly(p-phenylene)

Abstract A design of novel synthetic polymers possessing metallic properties is studied on the basis of the one-dimensional tight-binding self consistent field-crystal orbital (SCF-CO) method. The idea presented here is to utilize crossing π bands of polyperylene (PP) and poly( p -phenylene) (PPP) by controlling the number of π electrons in the polymer skeletons. It is suggested that nitrogen-substituted PP, nitrogen-substituted PPP and boron-substituted PPP can be candidates for showing intrinsic metallic properties.

Intersoliton hopping in lightly doped polyacetylene: assistance by vibrational motion of the dopant

The rate of intersoliton hopping associated with the interchain conduction mechanism in lightly doped polyacetylene has been studied explicitly including a certain vibrational motion of the dopant molecule. The model system which was used consists of a neutral soliton and a charged soliton alternating between these chains. Conventional time‐dependent perturbation theory was applied to the effective Hamiltonian developed here to study the system. We find that, under the assistance of the vibrational motion of the dopant along the axis between the two soliton sites, the rate of this intersoliton hopping is largely accelerated up to the order of that of the vibrational motion.

A stability condition for the Hartree-Fock solution of the infinite one-dimensional system

A simplified stability condition for the Hartree–Fock (HF) solution giving the self‐consistent field crystal orbitals (SCF‐CO) of the infinite one‐dimensional system is derived. Since the present formulation, particularly for the systems having nearly or entirely degenerated highest occupied and the lowest unoccupied COs, contains only two physical parameters, that is, the density of states and the Coulomb repulsion integrals both at the Fermi level, it is tractable to examine the stability of the HF solutions of such polymers as well as the ordinary molecular systems. An example of its application to metallic trans‐type polyacetylene is also shown.

Anderson localization in a polyacetylene chain with sp3 carbon defects

Abstract The electronic structure of a model for a polyacetylene chain with a random distribution of sp3 carbon defects is studied by the tight-binding molecular orbital theory. The dependence of the Anderson transition near the band centre (levels around the Fermi level) and in the band wings (levels near the lowest occupied and the highest unoccupied levels) on the number of sp3 carbons introduced is examined. Even one sp3 carbon in a chain leads to localization at the band edge. Near the centre of the band, both the extended and the localized states co-exist densely even if the number of sp3 carbons increases. It is concluded that conduction π electrons delocalize over a chain at a finite temperature as a result of the mixing of the states near the Fermi level.

Design of polymers with metallic properties: electronic structures of diborines and boron-substituted poly(p-phenylene)

Abstract The electronic structures of boron-containing systems are studied theoretically using the ab initio molecular orbital (MO) method and the one-dimensional tight-binding self-consistent field-crystal orbital (SCF-CO) method, and are compared with the results previously reported by Tanaka et al. (Synth. Met., 20 (1987) 333). It is suggested that poly( p -2,6-diboraphenylene) could also be a candidate for showing metallic properties.

A.c. impedance of polyacenic semiconductor electrode

Abstract Electrochemical a.c. impedance measurement has been performed with respect to a polyacenic semiconductor (PAS) material which was prepared by pyrolytic treatment of phenol-formaldehyde resin. The ionic relaxation model has been applied to analyze the experimental results. It has been concluded that a large portion of dopants interact with the PAS electrode very weakly in the electrochemical reaction.

Electronic structures of polymetacyclophanes

Abstract The electronic structures of two kinds of polymetacyclophanes, each consisting of a biphenol and biphenoquinone plane, have been theoretically studied using the one-dimensional tight-binding SCF-CO (self consistent field-crystal orbital) method. Emphasis has been put on the search for the path of the electrical conduction carriers in these polymers. It has been confirmed that the path is made up of the through-space overlapping of stacked longitudinal π AOs (atomic orbitals) of each cyclophane plane. The formation of an auxiliary path through the methylene bridges (CH 2 CH 2 ) between the planes has been discussed. Furthermore, the effect of extrinsic atoms inserted between the planes has also been examined.

Electrochemical a.c. impedance measurement of the electrode fabricated by polyacenic semiconductive material

Abstract Electrochemical a.c. impedance measurement is carried out for polyacenic semiconductive (PAS) materials prepared by pyrolytic treatment of phenol-formaldehyde resin in order to investigate the electrochemical doping mechanism at the interface between electrode and electrolyte. The ionic relaxation model is introduced to understand the present results. It is concluded that more than half of the dopants are trapped in the PAS electrode with relatively weak interaction, the relaxation time of which is 53 s. This is closely connected with the fact that the PAS battery possesses rapid charge-discharge characteristics.

Localization in a polyacetylene chain with sp3 carbon defects

Abstract The electronic structure of a model for a polyacetylene chain with sp 3 carbon defects is studied by the tight-binding molecular orbital theory. There are two types of localization of wavefunctions, on-defect type and in-chain-fragment type. The localized states in the band wings consist of the former type whereas those inside the band the latter type. Existence of sp 3 carbon defects induces the localization of in-chain-fragment type around the Fermi level and, in other words, reduces the conjugation length of a chain, which is consistent with general idea hitherto ambiguously considered.