Yoko Tatewaki

Organization of single-walled carbon nanotubes wrapped with liquid-crystalline π-conjugated oligomers

Two oligo(phenylenevinylene)s with cyanobiphenyl terminates were synthesized as non-covalent modifiers of single walled carbon nanotubes (SWNTs). The wrapping of SWNTs with synthesized oligomers enhanced the dispersibility in CHCl3 by the dissociation of SWNT bundle structures. It was found that the addition of oligomers caused self-organized precipitation from a homogeneous dispersed solution of SWNT complexes. The self-organized precipitates exhibited thermotropic liquid-crystalline properties.

Intramolecular axial ligation of zinc porphyrin cores with triazole links within dendrimers.

Stable ligation: A series of dendritic porphyrins, such as that depicted in which benzyl ether dendrons were linked to a porphyrin core through 1,2,3-triazole links, was synthesized. Absorption and fluorescence spectra showed a stable axial ligation at the zinc center of the porphyrin core by triazole links in dendritic wedges and indicated that the position of the triazole links strongly affected the stability of the axial ligation within the dendrimer.A series of dendritic porphyrins 7-9 and 12, in which benzyl ether dendrons were linked to a porphyrin core through 1,2,3-triazole links, were synthesized by Cu(I)-catalyzed cycloaddition of azides and alkynes. Absorption and fluorescence spectra showed a stable axial ligation at the zinc center of the porphyrin core by triazole links in dendritic wedges and indicated that the position of the triazole links strongly affected the stability of the axial ligation within the dendrimer. When the porphyrin core was surrounded by aryl ether dendrons having anionic termini and triazole linkers, a significant rate enhancement for photoinduced electron transfer was observed compared with a similar water-soluble dendritic zinc porphyrin lacking triazole linkers. These triazole links constituted a direct pathway within the dendrimer architecture for electron transfer between the zinc porphyrin core and peripheral electron acceptors.

Wrapping of self-organized fluorescent nanofibers with a silica wall.

Amphiphilic compounds 1 and 2, composed of an aromatic pyrene core and an amphiphilic three-branched unit, were synthesized and investigated for their self-organizing process in solution by UV-vis, fluorescence spectra, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and fluorescence microscopes. While 2 formed spherical objects in a mixed solvent of methanol and water, 1 assembled into long, flexible, and fluorescent fibers through pi-pi stacking of pyrene cores and hydrogen bonding among amide groups. The fluorescence spectra and morphologies strongly depended on the concentration and solution temperature. The fibrous assemblies were wrapped with an ultrathin silica wall by the acidic sol-gel polymerization of tetraethoxysilane (TEOS). A transmission electron microscopy (TEM) image after the sol-gel polymerization showed discrete fibrous structures with a uniform diameter of 3.5 nm and several micrometers in length. The thickness of the silica wall and the inner diameter of one fiber were estimated to be 0.5 nm and 2.5 nm, respectively. The observed inner diameter of the fiber was almost compatible with the width of the cylindrical assembly made of 1. The pyrene unit in 1 can interact with the sidewall of single-walled carbon nanotubes (SWNTs) through pi-pi interaction, and the adsorption of 1 onto the surface of SWNTs could disrupt the formation of bundles. The accumulation of oligomeric silica species at the hydrophilic surface created organic-inorganic nanoscopic fibers containing electronic conductive SWNTs.

Aminostilbazolium Derivatives Substituted by Hydroxyethyl Groups for Second-Order Nonlinear Optics

As DAST (1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium p-toluenesulfonate) derivatives for improved crystal stability and inhibition of crystal water inclusion, 1-(2-hydroxyethyl)-4-(2-{4-[bis(2-hydroxyethyl)amino]phenyl}ethenyl)pyridinium salts 2 (2a–2l) and 1-(2-hydroxyethyl)-4-{2-[4-(diethylamino)phenyl]ethenyl}pyridinium salts 3 (3a–3l) were synthesized and their properties were investigated. Salts 3 were found to have no crystal water, and the cation with one hydroxyethyl group was effective to eliminate water inclusion in the crystals. Although the melting points of 2 were lower than those of the corresponding 3, decomposition temperatures of these chromophores were above 250°C indicating their good thermal stability. Crystals of m-nitrobenzenesulfonate salt 3f was obtained without crystal water and showed SHG activity.

Synthesis and nanostructures of several tetrathiafulvalene derivatives having the side chains composed of chiral and hydrogen-bonding groups and their charge-transfer complexes

Tetrathiafulvalene (TTF) derivatives TTF-Bor, TTF-2UM and TTF-4UM having chiral urethane groups were prepared. Among them, TTF-2UM, TTF-4UM and their charge-transfer (CT) complexes with F4TCNQ organized the nanowires. The intermolecular hydrogen bonding of the chiral urethane groups and π-stacking of TTF moieties or the formation of CT complexes resulted in a long one-dimensional nanowires. The chiral moieties were responsible for the molecular orientation of TTF cores to give helical structures. Electronic conductivity of the films of nanowires composed of TTF-2UM and TTF-4UM with F4TCNQ were determined to be 8.0 × 10(-2) and 3.2 × 10(-2) S cm(-1), respectively.

Synthesis and Properties of Chromophores with a Pyrroline-Type Acceptor for Electro-Optic Polymers

We synthesized four electro-optic (EO) chromophores, which contained an aniline donor and an acceptor of 4-cyano-5-dicyanomethylene-2-oxo-3-pyrroline (CDCOP) with alkyl groups and/or oxyethylene chains terminated by an acrylate group as the three substituents. Photopolymerization of the mixture composed of the CDCOP derivatives, a liquid acrylate monomer and a radical photoinitiator was performed, and the chromophore fixation by crosslinking was achieved although about 30% of the chromophores were degraded by the radical attacks during crosslinking. Corona poling of these CDCOP derivatives in PMMA as a matrix polymer was successful regardless of the substituents. However, poling of the CDCOP derivatives in the liquid acrylate monomer matrix during photocrosslinking was difficult, and the poling conditions should be optimized.

Quick and selective synthesis of Li6[α-P2W18O62]·28H2O soluble in various organic solvents

Herein we report the synthesis of α-Dawson type POM, Li6[α-P2W18O62]·28H2O, directly from the use of Li2WO4 as the tungstate source. The salt obtained was soluble not only in water but also in a range of polar and non-polar organic solvents, such as benzene.

Study of molecular arrangement of organized molecular films of charge–transfer complexes containing 1,3-dithiole-2-thione-4,5-dithiolate by in-plane and out-of-plane X-ray diffractions

We investigated the molecular arrangement and surface morphology of organized molecular films of alkylammonium-M bis(1,3-dithiole-2-thione-4,5-dithiolate) ((dmit)(2), M = Ni, Au, and Pd) charge-transfer complexes using the surface pressure-area (pi-A) isotherm, polarized visible spectroscopy, in-plane and out-of-plane X-ray diffractions (XRD), and atomic force microscopy (AFM). Since Langmuir-Blodgett films of alkylammonium-M(dmit)(2) generally exhibit superconductivity, it may be possible to develop novel electronic molecular devices on the subnanometer scale. In the bulk state, several alkylammonium-M(dmit)(2) molecules could not form a highly ordered layered structure along the c-axis and a subcell structure of the alkyl chain in the ab-plane; however, almost all molecules formed a layered structure in the film multilayers. Monolayers of alkylammonium-M(dmit)(2) molecules on the water surface were extremely condensed. Out-of-plane and in-plane XRD measurements revealed that over a long period, systematic changes occurred in the two-dimensional lattice structure of alkylammonium-M(dmit)(2) molecules and not in their bulk state. These structural changes appear to be caused by enhancement of the van der Waals interaction among long hydrocarbons and the pi-pi interaction among (dmit)(2) units arranged two dimensionally. In addition, both the molecular arrangement and the structural morphology of the films showed dependence on the hydrocarbon chain length, number of long alkyl chains, and kind of central metal. In particular, the molecular arrangement of materials having didecyl chains changed drastically and (dmit)(2) units were highly oriented in the ab-plane. Such structural formations are suggested to significantly influence the stacking of functional dmit units presiding over the conductive properties.

Effective polar orientation of organic polar nanocrystals and their fixation in polymer matrices

Nanocrystals of 1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium p-toluenesulfonate (DAST) with a size of about 130 nm were prepared by the reprecipitation method, in which an ethanol solution of DAST and additives was injected into volatile hydrocarbons. Since the DAST crystal belongs to a polar space group, the nanocrystals dispersed in hydrocarbons could be aligned in a polar orientation by applying a DC electric field. A more efficient orientation was achieved by the initial application of a DC electric field followed by a DC magnetic field. By changing the dispersion medium from a hydrocarbon to a liquid monomer with a photoinitiator and a crosslinker, the polar orientation could be fixed after photocuring.

Morphological transition of a conductive molecular organization with non-covalent from nanonetwork to nanofiber.

The formation of nanofiber morphology at a mesoscopic scale, and molecular level stacking of a tetrathiafulvalene (TTF) derivative with a chiral group were investigated by the one-dimensional growth method in interfacial molecular films. Monomolecular films of a TTF derivative with a chiral borneol group display a two-dimensional phase transition at the air/water interface. At high surface pressures, nanonetwork domains are formed, where the TTF molecular planes are densely packed with an interlayer distance of 4.1 Å. The formation of this network is attributed to the organized aggregation of the TTF derivatives, which is a result of strong intermolecular interactions. Subsequently, the growth of morphology is encouraged by the application of the one-dimensional growth method at low surface pressure conditions, varying compression speeds, and subphase temperatures. At low surface pressure and a subphase temperature of 15 °C, the TTF derivatives aggregated as nanofibers with close packing of molecules. Upon raising the subphase temperature, the thickness of the nanofibers was found to increase and hence, spontaneous morphogenesis at the air/water interface was achieved.