Yutaka Kuwahara

Induction of Strong and Tunable Circularly Polarized Luminescence of Nonchiral, Nonmetal, Low-Molecular-Weight Fluorophores Using Chiral Nanotemplates

A new strategy is described for generating strong circularly polarized luminescence with highly tunable emission bands through chiral induction in nonchiral, totally organic, low-molecular-weight fluorescent dyes by chiral nanotemplate systems. Our approach allows the first systematic investigation to clarify the correlation between the circular dichroism and circularly polarized luminescence intensities. As a result, a dilute solution system with the highest circularly polarized luminescence intensity achieved to date and a dissymmetry factor of over 0.1 was identified.

Thermal and Photochemical Control of Molecular Orientation of Azo‐Functionalized Polymer Liquid Crystals and Application for Photo‐Rewritable Paper

A photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PA6Az1) and poly(vinyl alcohol) (PVA) has been prepared on a glass substrate by alternate spin coating of the polymer solutions. The reflectivity of the multi-bilayered film disappears by annealing at 80 °C. The disappearance of the reflection by the annealing is related to the thermal out-of-plane molecular orientation of PA6Az1 even in the multi-bilayered film, which leads to a very small difference in refractive indices between PA6Az1 and PVA. The reflectance of the multi-bilayered film is increased again by UV irradiation because of the transformation from the out-of-plane orientation to an in-plane random orientation. In this way, on-off switching of the reflection is achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PA6Az1 comprising the multi-bilayered film.

Photocontrolled manipulation of a microscale object: a rotational or translational mechanism.

In this paper the photocontrolled manipulation of solid materials on the surface of a liquid crystalline thin film is described. Three different types of films namely cholesteric liquid crystal (ChLC), compensated nematic liquid crystal (NLC) and nematic LC were used. The rotational and translational manipulation of the microscale solid object was induced by irradiation of light and mode of manipulation (either translational or rotational) was changed by changing the isomer of the azobenzene compound used to make the film. Rotational motion of the object was observed on the ChLC and compensated NLC films containing chirally pure azobenzene compound. The direction of rotational motion was controlled either by changing the optical isomer of the chiral azobenzene or by changing the irradiating light (from ultraviolet to visible). When racemic mixture of the chiral azobenzene compound was used, a translational motion of the object was observed. Even though the direction of the translational motion can be controlled by controlling irradiation position, more facile and precise manipulation of the objects was possible by spatially controlled irradiation of Ar(+) laser and diode UV laser.

Modulation of Polymer Refractive Indices with Diamond Nanoparticles for Metal-Free Multilayer Film Mirrors

Modulation of the refractive index of a polymer was achieved by combining it with diamond nanoparticles (NDs). The increase in the refractive index was controlled by the amount of NDs added, according to the Lorentz-Lorenz equation. The refractive index of poly(vinyl alcohol) (PVA), which was used as the base polymer, increased from 1.52 to 1.88. A multilayer film consisting of alternating layers of ND-PVA composite and poly(methyl methacrylate) exhibited ca. 80% reflectance with 10 bilayers.

Crystallographic structure and solid-state fluorescence enhancement behavior of a 2-(9-anthryl)phenanthroimidazole-type clathrate host upon inclusion of amine molecules

An anthrylphenanthroimidazole-type clathrate host, which exhibits fluorescence enhancement behavior with the blue and red shift of the emission maximum upon formation of clathrates with amines, has been developed. The crystals of the title fluorescent clathrate compound with two fluorophores exhibit very different fluorescence behavior with different amines molecules. The crystal structures of the clathrate compounds have been determined by X-ray analysis. On the basis of the spectral data, the fluorescence lifetime and the crystal structures, the effects of the enclathrated guest on the solid-state photophysical properties of the clathrate compounds are discussed.

Manipulation and assembly of small objects in liquid crystals by dynamical disorganizing effect of push-pull-azobenzene-dye

The phase transition of a nematic liquid crystal containing a push-pull azobenzene dye could be induced efficiently during irradiation with visible light. The dynamical disorganizing effect of the push-pull azobenzene dye on the liquid crystalline order through its trans-cis-trans photoisomerizaion cycle under visible light was contributed to the efficient phase transition. Then, the effects of light irradiation on the motion of small objects dispersed in the liquid crystals containing the push-pull azobenzene were explored, and the manipulation and assembly of those objects were successfully achieved in the nematic phase but also in the smectic phase. The combination of the photo-controlled dynamical change in the liquid crystalline order and the intrinsic self-assembly property of a liquid crystal is promising for use in technologies that require not only the organization of small objects but also the photo-driving of nano- and micro-sized mechanical materials.

A remarkable enhancement of selectivity towards versatile analytes by a strategically integrated H-bonding site containing phase.

A double β-alanylated L-glutamide-derived organic phase has been newly designed and synthesized in such a way that integrated H-bonding (interaction) sites make it very suitable for the separation of versatile analytes, including shape-constrained isomers, and nonpolar, polar and basic compounds. The β-alanine residues introduced into two long-chain alkyl group moieties provide ordered polar groups through H-bonding among the amide groups.

Nanosecond pulsed laser ablation of copper in supercritical carbon dioxide

A copper target in supercritical CO2 was ablated using nanosecond Nd:YAG laser pulses for a variety of different laser irradiation times, temperatures and pressures. The irradiated copper surface was evaluated by scanning electron microscopy and laser microscopy. Experiments were also conducted in atmospheric conditions with air and liquid hexane to evaluate the environmental dependence of ablation. The results demonstrated that laser ablation of a metal target in high pressure was affected by the pressure and the surrounding environment. An ablation crater with a depth of 6.9 µm was produced by ablating at a temperature of 40 °C, a pressure of 25 MPa, and an irradiation time of 500 s.

On/off switching of structural color by using multi-bilayered films containing copolymers having azobenzene and biphenyl side groups

In this paper, the change in structural color of multi-bilayered films fabricated by stacking copolymers, PMAz–PMBP (m : n), consisting of azobenzene and biphenyl side chain groups, and polyvinyl alcohol (PVA) alternately, was investigated. The multi-bilayered films consisting of polyacrylates having an azobenzene side chain group and PVA were found to reflect a light of specific wavelength, and to show reversible change in the reflection intensity by thermal annealing and irradiation with non-polarized ultra violet (UV) light. However, a long irradiation time was required for the change in reflection intensity of the multi-bilayered films. Therefore, we synthesized PMAz–PMBP (m : n), consisting of azobenzene and biphenyl side chain group having no absorbance over 300 nm, and the PMAz–PMBP (m : n)/PVA multi-bilayered films were fabricated. All the multi-bilayered films showed reversible change in the reflection intensity by thermal annealing and irradiation with non-polarized UV light. The re-coloration speed of PMAz–PMBP (75 : 25)/PVA 20-multibilayered film was faster than others fabricated in this study. It is related to penetration depth of light into the films. The effect of the introduction of the biphenyl side groups in the copolymers on the response behavior of the change in the structural color will be discussed.

Functionalization of a polymer using nanoparticles immobilized in supercritical carbon dioxide

We demonstrated the immobilization of functional nanoparticles onto a poly(ethylene terephthalate) (PET) polymer using supercritical CO2 (SCCO2). Gold nanoparticles (AuNPs) and cadmium sulfide nanoparticles (CdSNPs) were prepared in accordance with a previously reported method. Both of the PET polymer and the nanoparticle dispersion solution were treated in SCCO2. Treatment was carried out at various temperatures and pressures. The optical properties of the treated films were observed by UV–visible (vis) absorption spectroscopy or emission spectroscopy. For the UV–vis absorption spectra of the PET films treated with AuNPs of ca. 3 nm diameter (3-AuNPs), a surface plasmon band appeared at about 550 nm, which characterized gold nanoparticles or its aggregates. For the emission spectra of the PET films treated with CdSNPs of ca. 4 nm diameter (4-CdSNPs), an emission peak appeared at about 600 nm. We found that the PET films could be functionalized using 3-AuNPs or 4-CdSNPs immobilized in SCCO2 (50 °C, 20 MPa, 2 h).