Sono Sasaki

π-Conjugated Nickel Bis(dithiolene) Complex Nanosheet

A π-conjugated nanosheet comprising planar nickel bis(dithiolene) complexes was synthesized by a bottom-up method. A liquid-liquid interfacial reaction using benzenehexathiol in the organic phase and nickel(II) acetate in the aqueous phase produced a semiconducting bulk material with a thickness of several micrometers. Powder X-ray diffraction analysis revealed that the crystalline portion of the bulk material comprised a staggered stack of nanosheets. A single-layer nanosheet was successfully realized using a gas-liquid interfacial reaction. Atomic force microscopy and scanning tunneling microscopy confirmed that the π-conjugated nanosheet was single-layered. Modulation of the oxidation state of the nanosheet was possible using chemical redox reactions.

Amphiphilic Molecular Design as a Rational Strategy for Tailoring Bicontinuous Electron Donor and Acceptor Arrays: Photoconductive Liquid Crystalline Oligothiophene−C60 Dyads

For tailoring solution-processable optoelectronic thin films, a rational strategy with amphiphilic molecular design is proposed. A donor-acceptor dyad consisting of an oligothiophene and C60, when modified with a hydrophilic wedge on one side and a paraffinic wedge on the other (1Amphi), forms over a wide temperature range a photoconducting smectic A liquid crystal having bicontinuous arrays of densely packed donor and acceptor units. In contrast, when modified with only paraffinic wedges (1Lipo), the dyad forms a smectic A liquid crystalline mesophase, which however is poorly conductive. As indicated by an absorption spectral feature along with a synchrotron radiation small-angle X-ray scattering profile, 1Lipo in the lamellar structure does not adopt a uniform head/tail orientation. Such defective donor and acceptor arrays likely contain a large number of trapping sites, leading to short-lived charge carriers, as observed by a flash photolysis time-resolved microwave conductivity study.

Large-Area Three-Dimensional Molecular Ordering of a Polymer Brush by One-Step Processing

Bend It, Stretch It Materials (such as those found in some artificial muscle systems) that are used for stimulus-controlled bending or stretching, require long-range ordering so that local chemical triggers will result in long-range bending or flexing motions. Hosono et al. (p. 808) observed that a sandwich of a polymethacrylate between uniaxially stretched Teflon sheets develops three-dimensional ordering. Upon hot pressing, the main chains of the polymer brushes aligned homeotropically to the film plane, whereas the side chains, containing azobenzene groups, oriented horizontally along the drawing direction of the Teflon sheets. With some azobenzene groups, alternate irradiation with ultraviolet and visible light made the composites bend and stretch reversibly. The main and side chains of a polymer align in different directions when heated and pressed between Teflon plates. Rational molecular design and processing, enabling large-area molecular ordering, are important for creating high-performance organic materials and devices. We show that, upon one-step hot-pressing with uniaxially stretched Teflon sheets, a polymer brush carrying azobenzene-containing mesogenic side chains self-assembles into a freestanding film, where the polymer backbone aligns homeotropically to the film plane and the side chains align horizontally. Such an ordered structure forms through translation of a one-dimensional molecular order of the Teflon sheet and propagates from the interface macroscopically on both sides of the film. The resultant wide-area bimorph configuration allows the polymer film to bend rapidly and reversibly when the azobenzene units are photoisomerized. The combination of polymer brushes with hot-pressing and Teflon sheets provides many possibilities in designing functional soft materials.

Oriented Salts: Dimension‐Controlled Charge‐by‐Charge Assemblies from Planar Receptor–Anion Complexes

Salts, ionic compounds comprising cations (positive ions) and anions (negative ions), are essential materials for biotic activities. They are also utilized as inorganic minerals for industry. The appropriate arrangement of charged species through electrostatic interactions is a significant issue for constructing ordered nanoscale architectures in various states. For example, most inorganic, organic, and inorganic–organic hybrid salts use electrostatic interactions between ions to form organized three-dimensional (3D) crystal structures. The 3D structures defined herein include not only crystals of isomeric space groups in a cubic system but also non-isomeric crystals. Appropriate pairs of cations and anions yield ionic liquids, which are partially ordered but essentially nondimensional (0D) states. In ionic liquids, bulky geometries of both the cationic and the anionic species effectively prevent crystallization owing to significantly weaker ionic interactions. In contrast to crystals and liquids from ions, soft materials formed by electrostatic interactions between charged components have been reported as liquid crystals on the basis of ionic mesogens. 4] For example, Kato et al. reported various ionic liquid crystals comprising alkyl-substituted imidazolium salts, which afford columnar structures and have ionic conduction. Compared to such ionic mesophases, in which the locations of either cations or anions cannot be confirmed, more rigidly organized structures with a certain level of mobility in their building subunits are also useful for various applications such as ferroelectric materials. In contrast to bulky components, planar cationic and anionic molecules effectively interact with each other and form charge-by-charge assemblies composed of alternately stacking charged components. Aided by supplementary van der Waals interactions along with electrostatic and p–p interactions, dimension-controlled charge-by-charge assemblies will form not only crystals but also soft materials such as supramolecular gels, liquid crystals, and other organized structures. In comparison to p-conjugated cations, which are often based on sp-hybridized planar geometries, p-conjugated planar anionic species are required to delocalize their excess electrons, for example by depositing them in aromatic systems, to prevent them from suffering an electrophilic attack. Focusing on these perspectives, one of the strategies for forming planar anions is the complexation of electronically neutral p-conjugated anion receptors and spherical halide anions. As p-conjugated planes for associating with halide anions, BF2 complexes of 1,3-dipyrrolyl-1,3-propanediones efficiently bind spherical anions with inversion of pyrrole rings (1 and 2 ; Scheme 1 a). 8] Receptor 1 affords single crystals, which are composed of 1D columnar structures of alternately stacking chloride and bromide complexes and tetrapropylammonium (TPA) countercations, and are prepared from a hydrocarbon solvent. In contrast to these crystal states, an alkyl-substituted receptor 2 exhibits the formation of anion-responsive supramolecular octane gel, which is temporally transformed into a solution state by the addition of tetrabutylammonium (TBA) salts owing to the formation of soluble ion pairs comprising fairly aliphatic TBA cations and receptor–anion complexes. 9] Therefore, the introduction of planar cations in place of bulky TBA cations may form fine-tuned supramolecular organized structures as soft materials using p–p stacking and electrostatic interactions along with van der Waals forces. Herein, we present the [*] Y. Haketa, Prof. Dr. H. Maeda College of Pharmaceutical Sciences, Institute of Science and Engineering, Ritsumeikan University Kusatsu 525–8577 (Japan) Fax: (+ 81)77-561-2659 E-mail: maedahir@ph.ritsumei.ac.jp

Prominent Electron Transport Property Observed for Triply Fused Metalloporphyrin Dimer: Directed Columnar Liquid Crystalline Assembly by Amphiphilic Molecular Design

A triply fused copper porphyrin dimer, when site-specifically modified on its periphery with hydrophobic and hydrophilic wedges (1C12/TEG), self-assembles into a columnar liquid crystalline (LC) mesophase over a wide-temperature range from -17 to 99 degrees C but gives rise to an amorphous solid when modified with only hydrophobic (1C12/C12) or hydrophilic wedges (1TEG/TEG). A LC film of 1C12/TEG displays at 16 degrees C a top-class one-dimensional electron mobility (0.27 cm2/V x s), as evaluated from its maximum flash-photolysis time-resolved microwave conductivity.

Crystalline Graphdiyne Nanosheets Produced at a Gas/Liquid or Liquid/Liquid Interface

Synthetic two-dimensional polymers, or bottom-up nanosheets, are ultrathin polymeric frameworks with in-plane periodicity. They can be synthesized in a direct, bottom-up fashion using atomic, ionic, or molecular components. However, few are based on carbon-carbon bond formation, which means that there is a potential new field of investigation into these fundamentally important chemical bonds. Here, we describe the bottom-up synthesis of all-carbon, π-conjugated graphdiyne nanosheets. A liquid/liquid interfacial protocol involves layering a dichloromethane solution of hexaethynylbenzene on an aqueous layer containing a copper catalyst at room temperature. A multilayer graphdiyne (thickness, 24 nm; domain size, >25 μm) emerges through a successive alkyne-alkyne homocoupling reaction at the interface. A gas/liquid interfacial synthesis is more successful. Sprinkling a very small amount of hexaethynylbenzene in a mixture of dichloromethane and toluene onto the surface of the aqueous phase at room temperature generated single-crystalline graphdiyne nanosheets, which feature regular hexagonal domains, a lower degree of oxygenation, and uniform thickness (3.0 nm) and lateral size (1.5 μm).

Microscopic lamellar organization in high-density polyethylene banded spherulites studied by scanning probe microscopy

Surface topography and lamellar aggregation structure of high-density polyethylene (HDPE) banded spherulites were investigated by scanning probe microscopy. HDPE films were prepared by isothermal crystallization at various crystallization temperatures from the melt. Polarizing near-field scanning optical microscopic (NSOM) observations for the HDPE films revealed submicron-scale correlation between surface topography and birefringence of banded spherulites. The height profile of the film surface along the spherulitic radius periodically changed corresponding to the intensity profile of transmitted light along the radius of the extinction ring. This correlation was more clearly observed in the topographic and NSOM images of permanganic etched PE films. Therefore, it was apparently suggested that the crystallographic c-axis of the orthorhombic unit cell was parallel and perpendicular to the film surface at the peak and the valley in the surface corrugation of the banded spherulite, respectively. The band spacing obtained by polarizing NSOM and atomic force microscopy (AFM) was comparable to that determined by polarizing far-field optical microscopic observation under crossed nicols. The band spacing and the peak-to-valley height difference in the corrugation increased with an increase in isothermal crystallization temperature. AFM observations directly indicated local lamellar orientation and stacking manner.

Structural changes in the ordering process of polymers as studied by an organized combination of the various measurement techniques

Abstract Structural changes occurring in the ordering process of crystalline polymers have been investigated by combining various such kinds of techniques as X-ray scattering, infrared and Raman spectroscopy, etc. The methods to perform the time-resolved measurements under quick and stable temperature jumping process between two fixed temperatures, for example, were reviewed. Application of these techniques was made for the structural studies of isothermal crystallization of polyethylene, solvent-induced crystallization of syndiotactic polystyrene, photo-induced solid-state polymerization of muconate ester, polymerization reaction of 4-vinyl pyridine on the electrode surface, gelation process of syndiotactic polystyrene and poly(vinylidene fluoride), and so on. Usefulness of simultaneous measurements of different types of apparatus has been shown for the various cases of phase transition. Concrete examples were given for the simultaneous measurements of X-ray diffraction and Raman scattering, small-angle and wide-angle X-ray scatterings, and infrared spectra and viscoelastic property.

Relationship between morphological change and crystalline phase transitions of polyethylene-poly(ethylene oxide) diblock copolymers, revealed by the temperature-dependent synchrotron WAXD/SAXS and infrared/Raman spectral measurements.

The phase transition behaviors of low-molecular-weight polyethylene-poly(ethylene oxide) (PE-b-PEO) diblock copolymers with the monomeric units of PE/PEO = 17/40 and 39/86 have been successfully investigated through the temperature-dependent measurements of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), infrared and Raman spectra, as well as thermal analysis. These diblock copolymers had been believed to show only order-to-disorder transition of lamellar morphology in a wide temperature region, but it has been found here for the first time that this copolymer clearly exhibits the three stages of transitions among lamella, gyroid, cylinder, and spherical phases in the heating and cooling processes. The WAXD and IR/Raman spectral measurements allowed us to relate these morphological changes to the microscopic changes in the aggregation states of PEO and PE segments. In the low-temperature region the PEO segments form the monoclinic crystal of (7/2) helical chain conformation and the PE segments of planar-zigzag form take the orthorhombic crystalline phase. These crystalline lamellae of PEO and PE segments are alternately stacked with the long period of 165 Angstroms. In a higher temperature region, where the PEO crystalline parts are on the way of melting but the PE parts are still in the orthorhombic phase, the gyroid morphology is detected in the SAXS data. By heating further, the gyroid morphology changes to the hexagonally packed cylindrical morphology, where the orthorhombic phase of PE segments is gradually disordered because of thermally activated molecular motion and finally transforms to the pseudohexagonal or rotator phase. Once the PE segments are perfectly melted, the higher-order structure changes from the cylinder to the spherical morphology. These morphological transitions might relate to the thermally activated motions of two short chain segments of the diblock copolymer, although the details of the transition mechanism are unclear at the present stage.

Room-temperature nanoimprint lithography for crystalline poly(fluoroalkyl acrylate) thin films

A mold with a line pattern was imprinted onto a thin film of poly{2-(perfluorooctyl)ethyl acrylate} with long crystalline fluoroalkyl groups (PFA-C8), and the nanoimprinting characteristics of PFA-C8 thin films were investigated. It was revealed that nanostructures could be imprinted on PFA-C8 at room temperature because of the weak interaction among the fluoroalkyl groups in crystallites. The nanotextured PFA-C8 film with a line pattern exhibited anisotropic wetting behavior. The anisotropic wetting behavior was attributed to the difference between the energy barriers of wetting in the direction parallel and orthogonal to the lines. Fabricated nanostructures were stable for annealing below its melting point and were stable at room temperature (RT) for several months.