Masaru Yoshida

Photochemically Reversible Liquefaction and Solidification of Single Compounds Based on a Sugar Alcohol Scaffold with Multi Azo‐Arms

Sugar alcohol derivatives with multi azobenzene arms are photochemically and isothermally liquefied from a powdered solid upon irradiation with ultraviolet light at room temperature, and then solidified on irradiation with visible light, where the transition between solid and liquid are reversible. These compounds possess similar chemical structures to comb-like liquid crystalline oligomers.

Viscoelastic and Photoresponsive Properties of Microparticle/Liquid-Crystal Composite Gels: Tunable Mechanical Strength along with Rapid-Recovery Nature and Photochemical Surface Healing using an Azobenzene Dopant

We investigated viscoelastic and photoresponsive properties of the microparticle/liquid-crystal (LC) composite gels. The mechanical strength of the colloidal gels can be widely tuned by varying particle concentrations. With increasing particle concentration, a storage modulus of the particle/LC composite gels increased and reached over 10(4) Pa, showing good self-supporting ability. We demonstrated for the first time that the particle/LC composite gels exhibited rapid and repetitive recovery of the mechanical strength after large-amplitude oscillatory breakdown. In addition, photoresponsive properties of the composite gels were investigated by the cis-trans photoisomerization of the azobenzene compound doped into the host LCs. The photochemical gel-sol transition could be repeatedly induced by changing the phase structure of the host LCs between nematic and isotropic, using the photoisomerization. The particle/LC composite gels can be applied to optically healable materials by the site-selective gel-sol transition based on the photochemical modulation of the phase structures of the host LCs.

Molecular theory of solvation for supramolecules and soft matter structures: application to ligand binding, ion channels, and oligomeric polyelectrolyte gelators

We combine the statistical–mechanical 1D/3D-RISM-KH molecular theory of solvation with DFT electronic structure calculations and MD and coarse-grained DPD simulations, and apply them to study association phenomena in synthetic organic soft matter and biomolecular systems. This combined approach from electronic to molecular structure and coarse-graining allows us to address complex processes occurring in solution on very long timescales, such as protein–ligand binding, distributions of electrolyte solution species in ion channels, and oligomeric polyelectrolyte gelation. The statistics of rare events involving supramolecular solute and solvent is accounted for analytically within the 3D-RISM-KH molecular theory of solvation. The hybrid MD/3D-RISM-KH method for molecular dynamics of the biomolecule in the potential of mean force obtained with the molecular theory of solvation has been implemented in the Amber package. The 3D molecular theory of solvation also replaces MM/GB(PB)SA post-processing using empirical treatment of non-polar contributions with MM/3D-RISM-KH evaluation of the solvation thermodynamics. The 3D-RISM-KH theory accurately yields the solvation structure for biomolecular systems as large as the GroEL chaperonin complex, GLIC ion channel, and 3D maps of ligand binding affinity of antiprion compound to mouse PrPC prion protein at once without phenomenological approximations. We apply the DFT/1D-3D-RISM-KH/DPD multiscale approach to investigate the structural and dynamical properties and gelation ability of oligomeric polyelectrolyte gelators, towards understanding of the gelation mechanism.

Control of the Orientation and Photoinduced Phase Transitions of Macrocyclic Azobenzene

Photoinduced phase transitions caused by photochromic reactions bring about a change in the state of matter at constant temperature. Herein, we report the photoinduced phase transitions of crystals of a photoresponsive macrocyclic compound bearing two azobenzene groups (1) at room temperature on irradiation with UV (365 nm) and visible (436 nm) light. The trans/trans isomer undergoes photoinduced phase transitions (crystal-isotropic phase-crystal) on UV light irradiation. The photochemically generated crystal exhibited reversible phase transitions between the crystal and the mesophase on UV and visible light irradiation. The molecular order of the randomly oriented crystals could be increased by irradiating with linearly polarized visible light, and the value of the order parameter was determined to be -0.84. Heating enhances the thermal cis-to-trans isomerization and subsequent cooling returned crystals of the trans/trans isomer.

Fluorescence Spectroscopic Properties of Nitro-Substituted Diphenylpolyenes: Effects of Intramolecular Planarization and Intermolecular Interactions in Crystals

The steady-state absorption and fluorescence properties of (E,E,E)-1,6-diaryl-1,3,5-hexatrienes (2, aryl = 2-nitrophenyl; 3, aryl = 3-nitrophenyl; 4, aryl = 4-nitrophenyl) have been investigated in solution and in the crystalline state. The solid-state absorption spectra of 2-4 shifted to longer wavelengths than those in solution. A combination of theoretical calculations and single-crystal X-ray structure analyses shows considerable planarization of molecules in the solid state, which is mainly responsible for the spectral red shifts. The effects of intermolecular interactions on the absorption spectra appeared to be relatively small in these crystals. This is consistent with the monomeric origin of the solid-state emission. Molecule 2 was nonfluorescent in all solvents studied, probably due to the efficient nonradiative deactivation from ionic species produced by excited-state intramolecular proton transfer (ESIPT) along the C-H...O-type hydrogen bonds. The fluorescence of 3, observed only in medium polar solvents, originated from an intramolecular charge transfer (ICT*) state, while that of 4 derived from locally excited (LE*) and/or ICT* states depending on the solvent polarity. All three molecules exhibited LE* fluorescence in the solid state. No observation of ICT* emission in crystals strongly suggests the twisted geometries for ICT* (TICT) of 3 and 4 in solution. The measurable fluorescence from crystal 2 can be attributed to the restricted torsional motions in the solid excited state.

Doubly-dendronized linear polymers

Doubly-dendronized polymers were synthesized by grafting polybenzyl ether dendrons onto a poly(hydroxy) styrene polymer with polyaliphatic esters.

Photoinduced Dispersibility Tuning of Carbon Nanotubes by a Water‐Soluble Stilbene as a Dispersant

Although single-walled carbon nanotubes (SWNTs) exhibit superior mechanical and electrical properties, [ 1 ] the industrial applications of SWNTs have been hindered by their insolubility in many conventional solvents. Bundled aggregates due to strong intertubular van der Waals interactions cause the poor solubility, which acts as an obstacle to both the purifi cation and handling of the SWNTs. In order to improve the solubility and to expand the potential application areas of the SWNTs, various approaches including covalent and noncovalent modifi cations have been reported. [ 2 ] In particular, noncovalent methods using solubilizing agents are of particular of interest because well-dispersed SWNTs can be easily prepared without a signifi cant decrease in the intrinsic electronic properties. Recently, a number of such dispersants with stimuli responsibility have been reported because tuning of the dispersibility of the SWNTs is desirable in many applications including switching devices, sensors, and drug delivery systems. For example, such dispersion or release control of the SWNTs has been examined using a metal complex, [ 3 ] a natural product, [ 4 ] and stimuli-responsive polymeric dispersants. [ 5 , 6 ]

Functional transformation of poly(dialkylaminotrimethyldisilene) prepared by anionic polymerization of the masked disilenes. The preparation of a true polysilastyrene

Abstract The SiN bond of the amino-substituted polysilane, poly[1,1,2-trimethyl-2-(dibutylamino)disilene] yields chloro-substituted polysilanes. Substitution with some nucleophiles, such as a Grignard reagent, organolithium reagents, hydrides, and alcohols, yields a new class of polysilanes. This synthetic route provides a true polysilastyrene with a head-to-tail structure.

Cation‐Tuned Stimuli‐Responsive and Optical Properties of Supramolecular Hydrogels

Hierarchical self-assembly of an amphiphilic tris-urea in aqueous media is shown. A mixture of the amphiphilic tris-urea and an alkaline solution gave a viscous solution composed of fibrous aggregates. This viscous solution transformed into supramolecular hydrogels, which are capable of hierarchically organizing into higher-order aggregates in response to several cationic triggers. The resulting supramolecular hydrogels were relatively stiff and their storage moduli attained over 10(3)  Pa. The stimuli-responsive and optical properties of the resulting hydrogels were influenced by the cationic trigger. Proton and calcium ion triggers gave pH- and chemical stimuli-responsive hydrogels, respectively. A terbium ion trigger also provided a highly luminescent hydrogel through energy transfer from the tris-urea to terbium.

Light-driven modulation of fluorescence color from azobenzene derivatives containing electron-donating and electron-withdrawing groups

We report a simple preparation and color-tunable fluorescence of a series of azobenzene derivatives. The introduction of an electron-withdrawing or electron-donating group at the X position of azobenzenes (1–8) containing a biphenyl unit makes it possible to modulate the fluorescence color of the UV-exposed azobenzene solutions from blue to yellow, which correlates with the electron-donating abilities of the respective substituents. Theoretical calculations suggest that changes in both the dihedral angles between two phenyl rings of the biphenyl unit and the dipole moments between the trans and cis forms depending on the substituents seem to be important factors in determining the photochemical properties of chromophores.