Selective Ion Exchange in Supramolecular Channels in the Crystalline State.

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li2 ([18]crown-6)3 [Ni(dmit)2 ]2 (H2 O)4 (1) in an aqueous solution containing K+ , we succeeded in complete ion exchange of the Li+ ions in 1 with K+ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K+ was selectively conducted even in mixed solutions containing K+ as well as Na+ /Li+ . Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.

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.

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.

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.

Radical-initiator-Induced solid-state polymerization of butadiyne nanocrystals in water and their dispersion stabilization.

Butadiyne nanocrystals in water are usually polymerized by UV or gamma-ray irradiation to give polydiacetylene (PDA) nanocrystals. In this study, we confirmed that solid-state polymerization of 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD) and 5,7-dodecadiyn-1,12-diyl bis[N-(butoxycarbonyl-methyl)carbamate] (4BCMU) could be stimulated by water-soluble radical initiators. The radical initiators used were potassium peroxodisulfate, three kinds of azo-type compounds and a redox initiator. In all cases, the solid-state polymerization was confirmed by color change into blue indicating that PDA modified by the radical residues at the end was formed. However, nanocrystal cohesion occurred especially when the concentration of the initiators was high or the dispersion was kept for a long time. In order to improve the dispersion stability, two kinds of surfactants, i.e., sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTMAC), were added to the DCHD nanocrystal aqueous dispersion. As a result, when anionic SDS was added, the solid-state polymerization of nanocrystals proceeded without coagulation and quantitative conversion was confirmed for all initiators. Cationic DTMAC has no effect on dispersion stabilization. PDA nanocrystal surfaces in water are negatively charged in nature and electric interaction of nanocrystals with the cations results in decrease of surface charge and aggregation of nanocrystals.

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.

Conductive nanoscopic fibrous assemblies containing helical tetrathiafulvalene stacks.

Tetrathiafulvalenes (TTF) S-TTF and R-TTF having four chiral amide end groups self-organize into helical nanofibers in the presence of 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyano-p-quinodimethane (F(4)TCNQ). The intermolecular hydrogen bonding among chiral amide end groups and the formation of charge-transfer complexes results in a long one-dimensional supramolecular stacking, and the chirality of the end groups affects the molecular orientation of TTF cores within the stacks. Electronic conductivity of a single helical nanoscopic fiber made of S-TTF and F(4)TCNQ is determined to be (7.0+/-3.0)x10(-4) S cm(-1) by point-contact current-imaging (PCI) AFM measurement. Nonwoven fabric composed of helical nanofibers shows a semiconducting temperature dependence with an activation energy of 0.18 eV.

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.