Yoko Matsuzawa

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 ]

Macrocyclic amphiphiles. Part 2.†—Multi-point adsorptivity of the crown conformer of calix[4]resorcinarenes and their derivatives on surfaces of amorphous polar substrates

The adsorption behavior of the crown conformer of calix[4]resorcinarenes (CRAs), cyclic tetramers of resorcinol and aliphatic aldehydes, and theirO-carboxymethoxylated and O-hydroxyethyloxylated derivatives on a quartz surface was investigated. The adsorption of the macrocyclic amphiphiles from solutions of less polar solvents such as toluene at concentrations of >10–3 mol dm–3 obeyed the Langmuir equation to give monomolecular layers. The absorption equilibrium constant for CRA was two orders of magnitude greater than that of the corresponding resorcinol. Such efficient adsorptivity of the macrocyclic compounds arises from their characteristic structures which possess eight hydrogen-donating polar residues on the same rim of the cylindrical molecular skeleton. CRA molecules are also adsorbed on the surface of a poly(vinyl alcohol) thin film, suggesting that these cyclic tetramers provide a general procedure to give monomolecular layers deposited on polar surfaces of amorphous solids.

Spontaneous aggregation of octaalkoxyphthalocyanine metal complexes at an air–water interface

Abstract 1,4,8,11,15,18,22,25-Octaalkoxyphthalocyanine metal complexes were synthesized and spread on a pure water surface to reveal the properties of monolayer films using π – A isotherm measurements, UV–visible absorption spectroscopy and Brewster angle microscopy. The results indicated that self-aggregation of the macrocycles occurs in monolayers spontaneously, even when no compression is applied. The mode of self-aggregation was influenced substantially by the alkoxy chain length and central metal ions.

Preparation of soluble tetrabenzoporphyrins with substituents at the peripheral positions

Abstract The preparation of 1,4,8,11,15,18,22,25-octamethyltetrabenzo[b,g,l,q]porphinatonickel(II) having substituents at the peripheral positions was performed by the cyclotetramerization of a 5-substituted 1,3,4,7-tetramethylisoindole, which was prepared by the condensation of 3-substituted hexane-2,5-dione with 2,5-dimethylpyrrole. It was found that the products consist of mixtures of macrocycles with different numbers of peripheral substituents. This resulted from the ring-opening reaction of 2,5-dimethylpyrrole to form unsubstituted 2,5-hexanedione during the isoindole synthesis. The acidolytic side reaction of the dimethylpyrrole was suppressed by employing hexadecane 7,10-dione so that purified tetrabenzoporphinatonickels with hexyl residues at the ‘β’-position were obtained. The macrocycles thus prepared displayed excellent solubility in organic solvents.

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.

Characteristics of monolayers of calix[4]resorcinarenes derivatives having azobenzene chromophores

The adsorption behavior of calix[4]resorcinarenes (CRAs) and their O-carboxylmethylated and O-hydroxyethylated derivatives (CRA-CMs and CRA-HEs) from solutions was studied, aiming at the fabrication of self-assembled monolayers on polar surfaces of amorphous solid such as silica. These macrocyclic amphiphiles displayed considerably enhanced adsorption constants, due to the contribution of their multi-site adsorptivity, to form densely packed monolayers simply by immersing a silica plate in dilute solutions of the amphiphiles. CRA and CRA-CM bearing four azobenzene moieties at the lower rim of the cylindrical skeleton were prepared to modify a silica surface with photo-reactive monolayers by the surface adsorption technique. Adsorbed monolayers exhibited efficient E-to-Z photoisomerizability and applied to the photocontrol of alignment of liquid crystals and of dispersibility of colloidal silica.

Photoresponsive monolayers on water and solid surfaces

Abstract Organic photochromic units and molecules can be regarded as light-driven nano molecular machines. Once such molecules are aligned at a surface, the supramolecular organization provides an efficient macroscopic mechanical response in a collective way. Amphiphilic polymers having an azobenzene (Az) side chain are the favorable materials for observation of such effects since they show marked photomechanical response with essentially full reversibility. An in situ Brewster angle microscopic observation showed marked morphological and rheological photoinduced changes in the molecular films. Moreover, we have newly found that the identical photosensitive molecular film transferred on to a solid mica surface shows large morphological changes under highly humid conditions as proven by atomic force microscopy (AFM). It is supposed that the molecular film is driven in the same mechanism both on water and water-adsorbed mica surfaces. These microscopic observations provide new insights of the photomechanical response in photochromic monolayers.

Effects of surfactant concentration on formation of high-aspect-ratio gold nanorods.

The effects of surfactant concentration in a growth solution on the elongation of gold nanorods were examined. Gold nanorods were synthesized in solutions with different concentrations of hexadecyltrimethylammonium bromide (HTAB): 100, 200, 300, 400, 500, and 600 mM. The nanorods grown in a solution with higher surfactant concentrations were longer (aspect ratio ~30) than those grown in that with lower concentrations (aspect ratio <10). The self-assembled surfactant structures in the solutions were analyzed using viscosity measurement and small-angle X-ray scattering. These results showed a decrease in the inter-micellar distance with increasing surfactant concentration. Taking the chemical equilibrium for the complex formation between Au ions and HTAB micelles into account, we found that the free Au ion concentration decreases accompanied with the increase in the surfactant concentration. This decrease in the free Au ion concentration suppresses undesirable secondary nucleation of gold crystals in a growth solution, resulting in gold nanorod elongation.

Structure of Hybrid Langmuir-Blodgett Films of Amphiphilic Cyclodextrin and Water-Soluble Azobenzene

Amphiphilic alkylamino cyclodextrins(CDs-NH)in the Langmuir films had strong intermolecular interaction with sodium salt of p-methyl red(p-MR)in the subphase. Molecules of p-MR were incorporated in CDs-NH LB films fabricated from subphases containing p-MR. Deconvolution of the polarized UV/vis absorption spectra ofα-CD-NH/p-MR LB films revealed the existence of both monomeric and H-aggregated p-MR. The AFM image of a single-layerα-CD-NH/p-MR LB film showed three-dimensional dendrites, probably due to H-aggregated p-MR. We concluded thatα-CD-NH/p-MR LB films consisted of three components:(1)α-CD-NH without p-MR,(2)α-CD-NH with monomeric p-MR in the CD cavity, and(3)H-aggregated p-MR outside the CD cavity.

Stable spherical hollow particles composed of bola-form amides via non-covalent interactions

Dipeptide-based bola-form amides, which self-assemble into fibrous structures under usual conditions, formed stable micrometer-sized hollow spheres directed by hydrophilic interfaces in aqueous solution. The chemical structure of the bola-form amide and the surface properties of the substrate proved to significantly affect the self-assembly process. Bis(N-α-amide-L-valyl-L-valine)1,n-alkane dicarboxylate (n = 10: (Val)2C10, 12: (Val)2C12) and bis(N-α-amide-L-isoleucyl-L-isoleucine)1,n-alkane dicarboxylate (n = 10: (i-Leu)2C10) produced hollow spheres, whereas (Val)2Cn (n = 7–9, 11) and bis(N-α-amide-L-valyl-L-methionine)C10 ((Val/Met)2C10) formed no spheres. Static light scattering measurements revealed that the rod-like micelles of (Val)2C10, (Val)2C12 and (i-Leu)2C10 were converted to the hollow spheres via vesicle-like intermediates. The vesicle-like intermediates gathered together to form the spherical hollow particles with the aid of the surface of hydrophilic glass substrates. On the other hand, (Val)2Cn (n = 7–9, 11) and (Val/Met)2C10 directly self-assembled into fibrous structures from rod-like micelles without passing through the vesicle-like intermediates. The carbon number of the spacer, bulkiness of the head groups and surface properties of the substrate played critical roles in determining the self-assembly. FT-IR, XRD and DSC measurements revealed that the packing of the bola-form amides in the hollow spheres differed from that in the fibrous assembly. Molecules in the spheres were more tightly packed, as in the crystalline state, than those in fibrous structures.