Kazuyuki Nobusawa

Chemical-Stimuli-Controllable Circularly Polarized Luminescence from Anion-Responsive π-Conjugated Molecules

Introduction of a BINOL-boron moiety to dipyrrolyldiketones as precursors of anion-responsive π-conjugated molecules results in the formation of a chiral environment in the form of anion-free receptors and anion-binding complexes. Conformation changes by inversion (flipping) of two pyrrole rings as a result of anion binding can control the chiroptical properties of the anion receptors. In particular, appropriate pyrrole β-substituents induce distorted receptor π-planes and, as a result, give larger circularly polarized luminescence (CPL), which can be tuned by chemical stimuli (anions). This is the first example of chemical-stimuli-responsive CPL properties.

Facile Synthetic Route to Highly Luminescent Sila[7]helicene

A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large g value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules.

Stiffness- and Conformation-Dependent Polymer Wrapping onto Single-Walled Carbon Nanotubes

This work reports the effect of stiffness and conformation of chain-like polymers on wrapping behaviors around single-walled carbon nanotubes (SWNT). As a model of chain-like polymers, three kinds of poly(dialkylsilane) (PSi)s with random-coiled, flexible, and semiflexible main chains were employed. Complexes of PSi and SWNT were prepared using mechanochemical high-speed vibration milling (HSVM). Stiffness-dependent polymer wrapping behaviors were investigated using combinational analyses with a differential scanning calorimeter, transmission electron microscopy, and atomic force microscopy. Furthermore, the conformational behaviors of the PSis wrapped onto SWNTs were characterized spectroscopically with ordinary UV spectroscopy. Random-coiled and flexible PSis were successfully wrapped onto small bundles of SWNTs, in which their conformations were changed to fit the surface curvatures of the SWNTs. However, semiflexible PSi could not form a complex with SWNTs, and its conformation remained unchanged even after the same HSVM process. Knowledge gained from this study may lead to a new approach to molecular design of chain-like polymers for efficient wrapping materials for SWNTs.

Synthesis and Properties of [7]Helicene-like Compounds Fused with a Fluorene Unit

[7]Helicene-like compounds with a fluorene unit were successfully synthesized using a platinum-catalyzed double cyclization reaction. Crystal structures and photophysical properties of these compounds were also studied. In particular, they were found to exhibit a high fluorescence quantum yield and a relatively large g value (dissymmetric factor) of circularly polarized luminescence (CPL) for small molecules.

pH responsive smart carrier of [60] fullerene with 6-amino-cyclodextrin inclusion complex for photodynamic therapy

A new pH responsive smart carrier of C60 was prepared with 6-amino-γ-cyclodextrin (ACD) for photodynamic therapy. C60 was rapidly released from its inclusion complex with ACD at pH 6.7, due to electrostatic repulsion between ammonium groups, followed by a rapid C60 release at slightly acidic cancer cell surfaces.

Reversible solubilisation and precipitation of carbon nanotubes by temperature and pH control in water

Single-walled carbon nanotubes (SWNTs) were dissolved in a basic aqueous (NaOH) solution through the formation of a complex with folic acid. Water-solubilisation of SWNTs by folic acid is superior to that by guanosine 5′-monophosphate (GMP). The addition of diluted hydrochloric acid to the folic acid–SWNT mixture resulted in the precipitation of SWNTs from the basic solution. The precipitate was then redissolved by the addition of the basic solution without the need for sonication. Although the solubilisation of SWNTs was also controllable by changing temperature, sonication for 2 h was required to redissolve the SWNTs.

[70]Fullerenes Assist the Formation of Phospholipid Bicelles at Low Lipid Concentrations

The incorporation of neutral [70]fullerenes (C70) led to bicelle formation in a relatively low lipid concentration range from neutral lipid mixtures (DMPC/DHPC). Furthermore, C70 addition resulted in the formation of large bicelles with a radius of ca. 100 nm, in contrast to C70-free bicelles that were formed from anionic lipid mixtures (DMPC/DHPC/DMPG). The stabilization of these bicelles was attributed to C70 incorporation into the membranes.

NMR spectroscopic study of the complexation behaviors of deuterated cyclodextrins and [60]fullerene.

Cyclodextrins (CDxs) have been selectively deuterated using a Ru/C-catalyzed H-D exchange reaction in D2O. The structures of the deuterated CDxs barely changed and their (1)H NMR spectra became very simple, which made it possible for the deuterated CDxs to be applied to the analysis of CDx complexes. Furthermore, the deuterated CDxs allowed for the existence of the equilibrium between free and complexed CDx to be confirmed, even at rt.

Field Electron Emission from Carbon Nanotube/ZnO Composite Films Prepared by Electrodeposition

Multi-walled carbon nanotube (MWNT)/ZnO composite films were fabricated by electrodeposition using water-soluble MWNTs prepared by a high-speed vibration milling (HSVM) technique. Raman scattering spectroscopy and scanning electron microscopy revealed that the MWNTs were incorporated into the ZnO films in different manners depending on the deposition temperature. Field emission (FE) of electrons from the MWNT/ZnO films was investigated with a conventional FE device and a side-electron emission device (SEED). The MWNTs embedded horizontally in the ZnO films exhibited superior FE characteristics with luminance beyond 4000 cd/m2 for the SEED.

Fabrication of Carbon Nanotube/Zinc Oxide Composite Films by Electrodeposition

Carbon nanotube/zinc oxide (CNT/ZnO) composite films were fabricated by electrodeposition with aqueous solution of ZnCl2 and water-soluble CNTs prepared using a high-speed vibration milling technique. The experimental results of secondary ion mass spectroscopy and Raman scattering spectroscopy clearly showed that the CNTs were embedded in the ZnO films. The field electron emission was observed from selectively-etched CNT/ZnO composite films.