13C high-resolution NMR study of doped polyacetylene

¹³C high resolution NMR spectra of doped trans polyacetylene, (CH)_x, have been measured. A spectrum of (CH)_x doped with AsF₅ shows a downfield shift, while that with potassium an upfield shift. The charge distribution and the existence of sp³ hybridized carbon on halogen-doped (CH)_x chains are discussed.     

Isomerization mechanisms from cis to trans form in polyacetylene

Mechanisms of cis-trans irreversible isomerizations occurring in both thermal treatment and doping of polyacetylene are presented and examined by means of MINDO/3 molecular orbital calculations on some finite polyenes. It is predicted that the thermal isomerization proceeds along the internal rotation of (-CH=CH-) unit around two carbon-carbon double bonds via the transition state having a biradical nature. Meanwhile, the isomerization by doping is rationalized by the mechanism that the cis segment between two doping sites is converted into the trans-cisoid form which rotates easily around two single bonds to yield some trans forms in (CH)_x chain.     

METHYLMERCURY: PHOTOCHEMICAL TRANSFORMATION OF MERCURIC SULFIDE INTO METHYLMERCURY IN AQUEOUS SOLUTIONS1

Abstract. The photochemical reaction of mercuric sulfide was studied in aqueous solutions. The photo-solubilization of mercuric sulfide occurred under irradiation with light of ≤650nm and was enhanced in the presence of oxygen and electrolytes. The resultant mercuric ions were easily methylated in the presence of acetate ions via the photosensitized reaction by the simultaneously produced "photo-sulfur" under irradiation with light of ≤420nm. The photoelectrochemical studies of mercuric sulfide electrode revealed that black mercuric sulfide was an n -type semiconductor and the photo-current due to the dissolution as mercuric ions was observed on anodic polarization. The photo-solubilization of mercuric sulfide may be interpreted in terms of the local-cell mechanism.     

Weighted energy-dissipation functionals for doubly nonlinear evolution

This paper is concerned with the Weighted Energy-Dissipation (WED) functional approach to doubly nonlinear evolutionary problems. This approach consists in minimizing (WED) functionals defined over entire trajectories. We present the features of the WED variational formalism and analyze the related Euler-Lagrange problems. Moreover, we check that minimizers of the WED functionals converge to the corresponding limiting doubly nonlinear evolution. Finally, we present a discussion on the functional convergence of sequences of WED functionals and present some application of the abstract theory to nonlinear PDEs.     

Suspension of layered particles: an optimum electrorheological fluid for d.c. applications

 A comparison is made between two types of solid particles used in electrorheological fluids: particles with homogeneous electrical properties versus layered particles with a semi-conducting core surrounded by an outer layer of lower conductivity. Rheological measurements of these suspensions under steady shear and d.c. electric field show that the layered particle system produces the same yield stress but with a substantially reduced electric current. X-ray spectroscopic analysis confirms that these particles have a thin layer of SiO_x on the outer surface which causes the reduction in conductivity. Measurement of the dielectric permittivity followed by analysis using the Maxwell-Wagner model of polarization indicates that the conductivity of the outer layer is about 0.62 times that of the core region. Received: 13 January 1999 Accepted: 26 July 1999     

A head‐to‐head isomer of di‐μ‐pivalamidato‐κ4N,O‐bis­[(1,10‐phenanthroline‐κ2N,N′)­platinum(II)] dinitrate dihydrate

In the title compound, [Pt₂(C₅H₁₀NO)₂(C₁₂H₈N₂)₂](NO₃)₂·2H₂O, the intradimer Pt—Pt distance is relatively short [2.8489 (17) Å], which must be due to the strong intramolecular π–π‐stacking interactions between the phenanthroline moieties. The dimers stack along the c axis, forming one‐dimensional columns in which very intriguing d–d, π–π and d–π interactions exist. Although the dimer–dimer Pt...Pt distances are very long [4.340 (2) and 4.231 (2) Å], some short interdimer Pt...C contacts leading to strong interdimer associations are found [3.325 (19) and 3.402 (19) Å].     

Morphological alignment of liquid crystalline conducting polyacetylene derivatives

We have synthesized novel liquid crystalline conducting polymers by introducing liquid crystalline group into acetylene monomer and polymerizing them with Ziegler-Natta [Fe(acac)₃ - AlEt₃] and metathesis [M0Cl₅ - Ph₄Sn] catalysts. The liquid crystalline group is composed of a phenylcyclohexyl (PCH) or biphenyl (BP) moiety as a mesogenic core, a trimethylene chain [-(CH₂)₃-] as a spacer, and an alkyl chain (-C_nH_2n+1, n = 2, 3, 5 ∼ 8) as a terminal group. The polymers are abbreviated as PPCHn03A and PBPn03A. All polymers prepared exhibited solubility in organic solvents and smectic liquid crystallinity characterized with fan-shaped texture in polarizing optical microscopy. Phase transitions and the corresponding enthalpy changes were also evaluated by means of differential scanning calorimetry (DSC). Macroscopic alignments of the polymers were performed in the liquid crystalline phase by shear-stress or magnetic force field of 0.7 − 1.0 tesla, which resulted in an enhancement by two orders in electrical conductivity of iodine-doped cast films. Changes of the electronic and geometrical structures of the polymer upon the iodine-doping were elucidated by examining the effective conjugation length of a polyene chain, cis and trans thermal isomerization, and spin distribution of unpaired electrons through ultraviolet / visible (UV-Vis) and electron spin resonance (ESR) measurements.