Boron, a group 13 element, has several characteristic structural and electronic features: 1) trivalent boron compounds usually adopt a trigonal planar geometry; 2) due to the presence of a vacant p-orbital, effective orbital interaction with π-conjugated compounds is possible; 3) the presence of a vacant p-orbital is furthermore responsible for high Lewis acidity; 4) the boryl group acts as a π-electron-accepting group particularly in the excited state. The consequent exploitation of these characteristic features of boron in the molecular design enables us to produce sophisticated π-functional materials with attractive photophysical and electronic properties. This account article illustrates our systematic studies on the molecular design and the development of functional π-electron materials using boron as a key element.
The exploitation of several characteristic features of boron in the molecular design enables us to produce sophisticated π-functional materials with attractive photophysical and electronic properties. This account article illustrates our systematic studies on the molecular design and the development of functional π-electron materials using boron as a key element.
Providing both electronic conduction paths and buffer space for the large volume change between LixSi and Si are considered to be the key of development of high-performance Si-based anodes. Si and SiOx nanoparticle-embedded nanoporous carbons were synthesized by Mg thermal reduction of a SiO2 opal–carbon nanocomposite precursor followed by HCl and HF treatments, and the interstitial space in carbon nanopores was systematically controlled by NaOH-etching of the precursor. The electrochemical charge–discharge capacity and its retention with cycling of obtained samples were increased with increasing the nanopore volume and decreasing the loading amount of active material per pore volume. It was also found that dispersive loading of Si and SiOx nanoparticles in the carbon nanospace enhances the reactivity of Si and SiOx nanoparticles. The relationship between the composite structure and the charge–discharge properties were discussed in detail.
Si and SiOx nanoparticles-embedded nanoporous carbons were successfully synthesized by the following procedure. Control of carbon nanospace and dispersive loading of Si and SiO2 nanoparticles in nanoporous carbon were effective to enhance the charge–discharge performance.
We propose a novel method to enhance the THz emission from CuxO/metal nano thin film by using columnar-structured microsized porous silicon (MS-PSi) as the substrate. THz emission was improved several times higher than that from the planar substrate due to the decreased optical reflectance and enlarged surface area.
Palladium(0)-catalyzed insertion/annulation sequence between aryl silylethynyl ethers and internal alkynes was found to proceed through activation of ortho-C–H bonds assisted by alkynoxy groups and gave stereoselectively (Z)-2-silylmethylenechromenes. These products could be easily converted into 2,2-alkylated 2H-chromene derivatives, an important structural motif in medicinal chemistry and materials science. Various aryl silylethynyl ethers and alkynes can be transformed under the reaction conditions, and a wide range of chromenes is thus accessible. When unsymmetric alkynes are employed, a regioselective annulation takes place, especially those containing aryl and/or bulky substituents. Catalytic systems based on palladium(0), such as Pd(OAc)2/PCy3/Zn, [Pd(dba)2]/PCy3, or Pd(PCy3)2 exhibit excellent catalytic activity, and the best performance is observed for Pd(PCy3)2 in combination with Zn(OAc)2 as an additive. Substituents on the aryl group in the alkynyl aryl ethers rarely affect the reaction rate. Deuterium-labeling experiments suggest that the ortho-hydrogen atom migrates to the 2-methylene position in the chromene products. The cleavage of the C–H bond is considered to be the rate-determining step in these reactions.
Effects of magnetic fields on thermal convection in conductive aqueous solutions at ambient temperatures have been studied through heat transport measurements. The suppression of thermal convection by a magnetic field in conductive paramagnetic aqueous solutions of copper nitrate was observed and confirmed as an effect of the Lorentz force by comparing with diamagnetic aqueous solutions of ammonium sulfate. The effect of the Lorentz force and magnetic force on the thermal convection in conductive fluids was separately evaluated by changing the magnetic field environment. The results obtained show that the behavior of liquid metals under magnetic field can be investigated by using electrolyte aqueous solutions combined with a superconducting magnet.
TiO2–heteroTCNQ surface complexes between TiO2 and 2,5-bis(dicyanomethylene)-2,5-dihydrofuran, 2,5-bis(dicyanomethylene)-2,5-dihydrothiophene, and 2,5-bis(dicyanomethylene)-2,5-dihydroselenophene (furanTCNQ, thiopheneTCNQ, and selenopheneTCNQ, respectively) were designed using the redox potential of heteroTCNQ molecules. The tendency of the calculated redox potentials was in good agreement with the experimental results. We assumed the chemical adsorption structure of the TiO2–heteroTCNQ surface complexes that formed an O–C bond as well as that of previously reported TiO2–TCNQ surface complex. These surface complexes showed light absorption in the visible to near-IR region via interfacial charge-transfer transitions at longer wavelengths, as assessed using a TD-DFT calculation. This indicates that these surface complexes, as well as the TiO2–TCNQ surface complex, are applicable to the development of solar cells.
Photochemical behaviors which depend on the pentamethylene conformations of fluorene-based light-driven molecular rotary motor (denoted by M5-PCPF) have been examined by ab initio complete active space self-consistent-field calculations. In the conical intersection region where the ethylenic rotary axis is perpendicularly twisted, the stable geometries in S1 which are distinguished from each other by the pentamethylene conformations are separated by a low energy barrier. In consequence, conformational interchanges are allowed on the S1 surface in the conical intersection region. Two conical intersections (CIXs) are located in the region where the fluorene stator wags to the negative and positive directions against the ethylenic rotary axis, respectively. After electronic relaxation at CIX for a forward rotation, M5-PCPF with some conformations directly goes to P′-helical isomer, whereas M5-PCPF with other conformations is trapped in the M′-helical region and no longer reaches the P′-helical region thermally. The former types of conformers exhibit unidirectional rotation through the direct photochemical P–P′ and P′–P photochemical conversions, whereas the latter exhibit oscillatory photochemical behavior between P- and M′-helical (and P′- and M-helical) isomers. However, the conformation with oscillatory behavior can interchange into another conformation with unidirectional rotation in the conical intersection region. Therefore, M5-PCPF exhibits a net unidirectional rotation.
Nanoporous Co-VSB-5 and Fe-VSB-5 are prepared by isomorphous substitution of nickel ions in the framework with Co and Fe ions. The included nickel phosphate Ni-VSB-5 is employed as the active components for the catalytic reduction of NO by hydrogen in the absence of oxygen. Enhanced catalytic activities and selectivity are observed on the substituted samples compared with that of pure nickel phosphate VSB-5. A large amount of NO can be adsorbed in the nanopores of these materials and confirmed by in-situ FTIR. The possible active components for the reaction are discussed and the reaction mechanism is proposed.
Carbon–nitrogen bond-forming cross-coupling reaction of haloarenes with N-trimethylsilyl (TMS)-substituted secondary and primary arylamines proceeded with the aid of a palladium catalyst and a fluoride activator. Various TMS-N(aryl)2, TMS-NH(aryl), and TMS-N(alkyl)2 reacted to give the corresponding coupled products in high yields. Multi-TMS-amine nucleophiles such as N,N-(TMS)2-aniline and N,N′-Ph2-N,N′-(TMS)2-p-phenylenediamine also participated in this C–N coupling to give multiply C–N coupled products in high yields. The novel C–N cross-coupling reaction was successfully applied to C–N bond-forming polymerization. Relative rates of the cross-coupling of p-bromotoluene with N-TMS-substituted primary and secondary amines showed that N-TMS-diphenylamine reacted faster than N-TMS-N-methylaniline or N-TMS-aniline, and N-TMS-morpholine was the least reactive, indicating that the low basicity of the nitrogen nucleophile is the key for the smooth coupling.
Gelation properties of aprotic low-molecular-mass organic gelators (LMOGs) based on a gemini 4-[2-(perfluoroalkyl)ethylsulfanyl]phenoxy derivative unit are described. These LMOGs without hydrogen-bonding functional groups produced physical gels in several organic solvents such as ethanol, 1-octanol, acetonitrile, DMF, DMSO, propylene carbonate, and γ-butyrolactone at low concentration below 1 wt %. From the results of microscope observation and nuclear magnetic resonance spectroscopy, these aprotic LMOG molecules were aggregated into tape-shaped molecular nanofibers, and formed three-dimensional networks. In addition, the self-diffusion coefficient of the solvent molecules in these networks was similar to that of neat, although these solvent molecules have non-fluidity by gelation.
Novel terbium nanoparticles (TbX: terbium oxide (Tb2O3), terbium fluoride (TbF3), and terbium oxyfluoride (TbOF)) have been prepared and their magneto-optical properties reported. The TbX nanoparticles were synthesized by the thermolysis of Tb(III) complexes, used as single-source precursors, in oleylamine. The temperature used for the decomposition was estimated from using the thermogravimetric analysis (TGA) measurements. The as-prepared TbX nanoparticles were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). Large Faraday rotations were observed from poly(methyl methacrylate) (PMMA) thin films containing TbX nanoparticles under magnetic field (15000 Oe). TbX nanoparticles with magneto-optical properties have been prepared for the first time.
Biomimetic approaches for growth control of inorganic crystals in aqueous media have been applied to that of organic crystals in organic media. Morphology and orientation of organic crystals, such as 2,3,6,7,10,11-hexahydroxytriphenylene hydrate (HHTP) and 9-vinylcarbazole (VCz), were controlled on the surface-modified substrates with gradual evaporation of the solvents. The polyhedral and dendritic morphologies of HHTP and VCz crystals were obtained on the substrates with changes of the growth conditions. Solvents, surface-modified substrates, and additive molecules play important roles for growth control of organic crystals in organic media. The present results indicate that biomimetic approaches can be applied to growth control of organic crystals in organic media.
Theoretical studies of substituent R-effects on intermolecular resonance-assisted hydrogen bonds (RAHBs) of R-thymine/R-COOH, R-adenine/R-COOH complexes, and R-thymine/R-adenine base pairs have been made via Taft–Topsom treatment and natural bond orbital analysis, using density functional theory at the M06-2X/aug-cc-pVDZ level. Dimerization energy arising from constituent double H-bonds is essentially dependent on the nature of π-resonance of a substituent, i.e. π-electron-donating and -accepting properties. For monosubstituted base complexes with reference formic acid, π-donor (−R) substitution enhances π-delocalization of conjugated amide/amidine frames and activates the corresponding electron-donor site whereas π-acceptor (+R) substitution quenches the system via the same site, depending on their potentialities |σR+| and |σR−| of π-resonance effect. When both π-donor and π-acceptor substituents coexist in the complexes and base-pairs, they are activated under the support of mutual π-potentialities from counter molecules. Accordingly, one H-bond is significantly enhanced through cooperative electron push–pull interaction by substituents whereas the other being quenched due to the π-resonance effects in the opposite direction. Since bare thymine and adenine bases are actually found π-donating in nature against the amide/amidine frames of RAHBs, π-acceptor substitution of the counter molecule causes cooperative electron push–pull interaction on the corresponding H-bond and actually influences the dimerization energy depending on relative contribution of the constituent H-bonds.
Solid surfaces often serve as a reaction field for organic molecules. If a surface has chirality, it could play a significant role as an enantioselective catalyst. Electrodeposition in magnetic fields (magnetoelectrodeposition; MED) has potential to produce enantioselective metal surfaces, however, the exploration of chiral formation conditions has not been sufficient in previous MED experiments. Here we show the chiral behaviors of copper film surfaces prepared by galvanostatic MED. We found that the chiral sign depends on both the deposition current and the polarity of magnetic field. Furthermore, we found that the specific adsorption of chloride ions on the film surfaces brings about drastic influence on the chiral formation in MED. At certain chloride concentrations chiral symmetry breaking was observed for the polarity of magnetic field. These findings imply that magnetohydrodynamic micro-vortices and the rate-limiting steps are responsible for the chiral surface formation.
Soot combustion performance of K-containing perovskite oxides, La0.8K0.2MnO3 (LKM82), was evaluated under tight- and loose-contact conditions. The perovskite oxides were prepared by evaporation-to-dryness methods using malic acid or citric acid as the complexing reagents. Catalyst surface area, surface K concentration, and morphology of the LKM82 catalysts can be controlled by changing the preparation conditions. The temperature of soot combustion decreased with increasing catalyst surface area and surface K concentration of the LKM82 catalysts, indicating that these are important factors controlling the soot combustion performance. The increase in surface area and surface K concentration of the LKM82 catalysts improved soot ignition activity and promoted the soot combustion reaction after ignition. In the loose-contact mode, the ratio of the amount of catalytically combusted soot to that of non-catalytically combusted soot increased with an increase in catalyst surface area and surface K concentration of the LKM82 catalysts. The apparent activation energy of the catalytic soot combustion with the perovskite oxides that have both high surface area and high surface K concentration was much lower than that of non-catalytic soot combustion.
In recent years, the partitioning of food and pharmaceutical materials in ionic liquid-based aqueous two-phase systems (ATPSs) has attracted the attention of researchers to itself as a new approach. A new type of these aqueous two-phase systems is based on cholinium chloride. Cholinium chloride is a type of vitamin B, which is an appropriate and biocompatible ionic liquid (IL) for the processes of the extraction and separation in the food and pharmaceutical industries. In this study, with respect to the effective development of aqueous two-phase systems in vanillin separation, an aqueous two-phase system containing cholinium chloride and potassium phosphate salt has been used. The effect of the variables such as the temperature, salt weight fractions, ionic liquid weight fractions, and vanillin concentration on the partitioning coefficient of vanillin was evaluated. The results indicated that by increasing the salt weight fraction and decreasing the cholinium chloride weight fraction, the partition coefficient of vanillin increased. Nevertheless, in all stages the vanillin showed a tendency to migrate toward the ionic liquid-rich phase. The recovery percentage of vanillin showed that the cholinium chloride-based systems have the ability to improve the vanillin recovery in the ionic liquid-rich phase.
Particle size dependence in the H2 production from formic acid was investigated over Pd/C catalysts with nanoparticle sizes ranging from 2.7 to 5.5 nm. A volcano type relationship between catalytic activity and nanoparticle size was obtained and the average size of 3.9 nm exhibited the highest activity under mild reaction conditions.
Measurement of the quenching rate constant (kQ) of singlet oxygen (1O2) by α-tocopherol was performed in ethanol solution including four kinds of alkali and alkaline earth metal salts (NaClO4, Mg(ClO4)2, MgCl2, and CaCl2) by varying concentrations of metal salts. A remarkable effect of metal salts on the kQ value of α-tocopherol was observed. The 1O2-quenching rate constant (kQ) decreased notably with increasing concentrations of metal salts, and reached a constant value for each salt at high concentration of the salt. For example, the kQ value (9.48 × 107 M−1 s−1) obtained in the presence of 20 mM of Mg(ClO4)2 was 46% of that (2.06 × 108 M−1 s−1) in the absence of metal salt. The kQ value decreased in the order of no metal salt > NaClO4 > CaCl2 > MgCl2 ≈ Mg(ClO4)2 at the same concentration of the metal salts. The metal salts having a smaller ionic radius and a larger charge of the cation gave a smaller kQ value. Effects of anions were negligible. These metal cations coexist with α-tocopherol in foods and biological systems, suggesting that the metal cations may give a notable effect to the 1O2-quenching rate constant (kQ).