Hiromasa Goto

Synthesis and properties of liquid crystalline polyacetylene derivatives

Abstract We have synthesized mono-substituted acetylenes with a liquid crystalline group and then poylmerized them with Ziegler-Natta and metathesis catalyts. The liquid crystalline group in the side chain of the polymer is composed of a cyclohexylphenoxy (PCH) or biphenoxy (BP) moiety as a mesogenic core, a methylene chain [-(CH 2 ) 3 -] as a spacer, and an alkyl chain as a terminal group. The polymers are abbreviated as PPCHn03A (n = 2, 3, 5 ∼ 8) or PBP503A. All polymers exhibited a fan-shaped texture in the polarizing microscope that is characteristic to smectic liquid crystalline phase, consistent with DSC measurements. Spectroscopic characterizations were carried out by means of IR, UV-VIS, 1 H- and 13 C-NMR, as well as evaluations of molecular weights by GPC and electrical conductivities upon iodine doping before and after magnetically forced alignment.

Vortex fibril structure and chiroptical electrochromic effect of optically active poly(3,4-ethylenedioxythiophene) (PEDOT*) prepared by chiral transcription electrochemical polymerisation in cholesteric liquid crystal

Chiroptical electroactive poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically synthesised in a cholesteric liquid crystal (CLC) electrolyte solution from the terEDOT monomer. PEDOT synthesised from terEDOT was found to enable the formation of a fibril structure. In contrast, the EDOT monomer produced PEDOT without fibrils. Electrochemical polymerisation using this method provides a polymer with a distinct fibril structure and vortex texture. This indicates that the individual main chains are arranged by the topological transcription of structural chirality in the epitaxial electrochemical polymerisation in CLC as a one-handed helically twisted matrix. The polymer was confirmed to exhibit chiroptical electrochromism, diffraction, and the generation of a charge carrier in a chiral environment. This suggests formation of helical polarons of PEDOT.

Synthesis and properties of Photo-responsive liquid crystalline polyacetylene derivatives

Abstract New crystalline conjugated polymer, poly(mono-substituted acetylene) was synthesized by introducing an azobenzene moiety as a mesogen core into side chain. Polymerization of the liquid crystal-substituted acetylene monomer was carried out using a Rh-based or Fe-based catalyst. Polarizing microscope studies demonstrated that the monomer exhibits a“droplets” texture characteristic of a nematic phase, and the polymer a polygonal texture assignable to a smectic phase. Photo-induced reversible cis-trans isomerization of the azobenzene moiety as well as thermal irreversible isomerization from cis to trans form of the polymer backbone were elucidated.

Dichroic fluorescence of liquid crystalline polythiophene and polythienylenevinylene derivatives

We report magnetically forced alignment of novel liquid crystalline polythiophene and polythienylenevinylene derivatives that were synthesized to develop dichroic luminescence as well as electrical anisotropy. Macroscopic alignment of the polymers was confirmed by X-ray diffraction analysis. The aligned polymers exhibited not only anisotropic electrical conductivity but also dichroic fluorescence. indicating that the present LC conjugated polymers are feasible for linearly polarized luminescent materials.

In situ monitoring of reflection high-energy electron diffraction oscillation during the growth of gallium nitride films by gas-source molecular beam epitaxy

Abstract Reflection high-energy electron diffraction (RHEED) specular intensity oscillations have been observed during the growth of gallium nitride (GaN) films by gas-source molecular beam epitaxy (GS-MBE) for the first time. The GaN films were grown on sapphire substrates using metal gallium and ammonia as source materials, following the deposition of a GaN buffer layer at lower temperature. The incident electron beam was parallel to the GaN [1 1 00] azimuth direction and the signal intensity was measured with a photo-multiplier via an optical fiber fixed on the specular spot. The total thickness of the film was 1700 A which includes the 180 A buffer layer. RHEED oscillations during growth were observed on the sapphire (0001) substrate. Comparing the period of the RHEED intensity oscillations with those calculated from the growth rate, we found that a single period of the RHEED intensity oscillation corresponds to a monolayer growth of GaN.

Thermotropic liquid crystalline conjugated polymers, poly(cyclohexylphenoxyacetylenes) - synthesis and properties

Summary form only given. A, series of poly(cyclohexylphenoxyacetylenes) that are mono-substituted polyacetylenes with liquid crystalline group in the side, chain have been synthesized to elucidate systematically phase transition behaviors and optical and electrical properties of the polymers. Since the side chain of the, polymers consists of cyclohexylphenoxy moiety as a rigid mesogen, a methylene chain as a spacer, and a terminal alkyl group as a flexible moiety, the polymers are abbreviated as PPCHn03A ( n = 2, 3, 5, 6, 7, and 8). The polymerizations are carried out using not oaly Ziegler-Natta and metathesis catalysts but also rhodium complex catalyst. Special attention has been paid to the identification of liquid crystalline states of the substituted acetylene monomers and polymers during observation of optical textures in the polarizing microscope and also DSC measurement. Charge transfer interaction between the polyene main chain and iodine, used Es a chemical dopant is elucidated by means of UV-Visible absorption spectra. Macroscopic alignment of die polymer due to the external force such as shear stress or magnetic force has been focused in relation to enhancement of electrical conductivity upon iodine doping.

Ferroelectric liquid crystalline polythiophene derivatives

Chiral liquid crystalline (LC) substituent with fluorine-containing asymmetric moiety was introduced into the 3-position of thiophene ring. Polythiophene derivatives were fusible and soluble in ordinary organic solvents. Phase transition behaviors of the polymers and monomers were examined by differential scanning calorimetry, polarizing optical microscope, and X-ray diffraction. The polymers showed several types of smectic phases in the heating and cooling processes. Besides, one of the polymers exhibited a chiral smectic C phase (Sc*), which is indispensable for ferroelectricity. The ferroelectric behavior was also confirmed by examining the temperature dependence of dielectric constant of the polymer.

Syntheses and properties of small-bandgap liquid crystalline conjugated polymers

Abstract We present syntheses and properties of thermotropic liquid crystalline conducting polymers with small-bandgaps. The polymers consist of aromatic and quinoid units in the polymer backbone and a methine-bridge substituted with a liquid crystalline group. We adopted a thienylene or pyrrolylene ring as a heteroarylene unit and a phenylcyclohexyl moiety as a mesogenic core in the liquid crystalline group. The thienylene-based polymers exhibited smectic E or smectic A phases. The bandgaps evaluated for these polymers were 1.45~1.54 eV and 2.48 eV, depending on an intramolecularπ-electron resonance interaction between the main chain and the liquid crystalline side chain.

Dynamically Controllable Emission of Polymer Nanofibers: Electrofluorescence Chromism and Polarized Emission of Polycarbazole Derivatives

Electrochemical polymerization of a series of N-alkyl-2,7-di(2-thienyl)carbazoles in acetonitrile was performed to obtain conjugated polymers with fluorescence. Scanning electron and atomic force microscopies revealed that the surface morphology of the polymer films significantly depends on the alkyl chain lengths of the polymers. Particularly, a homopolymer bearing hexyl groups and copolymers with an average alkyl chain length of six carbon atoms show nanofiber morphology. The polymer nanofibers were stacked on a substrate electrode. The fluorescence of the polymer nanofiber film was tunable with application of voltage, with good repeatability. The X-ray diffraction pattern of the fibers showed the structural order. The polymer nanofibers thus prepared showed an electrochemically driven change in polarized photoluminescence.

Synthesis and properties of novel ferroelectric liquid crystalline polyacetylene derivatives

Abstract Novel liquid crystalline (LC) polyacetylene derivatives were synthesized to develop advanced LC conducting polymers with abilities of quick response to an electric field used as an external force. In practice we synthesized ferroelectric LC conducting polymers by introducing fluorine — containing chiral LC groups into side chains of polyacetylenes. Phase transition behaviors of these polymers were examined by differential scanning calorimeter and polarizing optical microscope. Mesophases as well as higher order structures were evaluated with X-ray diffraction measurements. One of the polymers synthesized showed chiral nematic (N * ) and chiral smectic C (Sc * ) phases in the heating and cooling processes. Observation of the Sc * phase allows us to expect that the polymer should exhibit the ferroelectricity.