Scattering angle dependence has been experimentally examined for inelasticity effect on the intramolecular interference term observed from the time-of-flight neutron diffraction method. Internuclear distance and its root-mean-square displacement for liquid pure D2O, C6D6 and CCl4, have been determined from the least squares fitting analysis of the observed total interference term in the high-Q region. Although “apparent shrinkage” in the intramolecular distance has been observed obviously for the light nuclei pair at large scattering angle data (2θ > ca. 70°), it has been revealed that the apparent shrinkage in the D•••D distance for D2O and C6D6, in which the inelasticity effect is expected to be most significant, is found to be suppressed well within ca. 1% for the data observed for the scattering angle below ca. 2θ < ca. 50°. Structural parameters determined have been compared with those determined from the gas-phase electron diffraction method in order to obtain insight of the effect of intermolecular interaction to molecular geometry in the liquid phase.
Persistent phosphors show contentious luminescence even after ceasing excitation light. This unique phenomenon is caused by several processes such as carrier generation, trapping and detrapping. Based on the mechanism, persistent luminescence can be designed by controlling the carrier transportation. By utilizing the vacuum referred binding energy diagram of lanthanoid and transition metal ions for the prediction of the trap levels in host compounds, new persistent phosphors have been developed successfully. This design guides for persistent phosphors are introduced, and the analyzing methods for persistent phosphors are also explained.
The current mandates of a sustainable society and circular economy lead to the request that materials chemistry, but also chemistry as such, become significantly redesigned. Changes include the commonplace as the glassware we use, the minimization of wastes and side products or replacement strategies in the materials choice, among others. In this context, “carbons” are very versatile and already have found their place in a myriad of applications for a “carbon-neutral” society. They already take key enabling positions for sensors and biomaterials preparation, as energy conversion and storage electrodes, or as effluent remediation sorbents. Herein, we describe how carbon chemistry can be again re-designed to outperform benchmark materials in a number of fields, especially in energy storage, (electro)catalysis, as sorbents, but also in a new chemistry of the confined state.
Properties of protein-based O/W emulsions are influenced by various factors including species and concentration of the protein, oil content, and employed homogenization technique, which make it difficult to establish suitable conditions to prepare stable emulsions. To address this issue, two proteins, bovine serum albumin (BSA) and ovalbumin (OVA), were used as emulsifiers in a wide concentration range to disperse n-hexadecane, and necessary conditions to prepare reasonably stable, submicron-size emulsions were explored. A two-step homogenization process, premixing with a rotor-stator mixer followed by either sonication or high-pressure homogenization, was employed, and volume-weighted average droplet diameter (d43), adsorption density of proteins (Γ), and coalescence stability of oil droplets were measured. For sonicated emulsions in the emulsifier-rich regime, d43 was ca. 1 µm for both BSA and OVA, and Γ was ca. 2–3 mg m−2 (over 15 mg m−2) for BSA (OVA). The high-pressure homogenization could reduce d43 down to 0.4 µm provided BSA (OVA) concentration was 5 g L−1 (15 g L−1) or higher. These submicron-size emulsions were stable for several days only for BSA emulsions with the concentration ≥ 15 g L−1, otherwise coalescence proceeded. These results suggested that the adsorbed OVA films are more easily broken than the BSA films.
The miniaturization of boron-doped diamond (BDD) electrodes is an important requirement for application to the study of electrochemical processes in living beings. In this work, we describe the fabrication and characterization of BDD electrodes with micrometer dimensions, with a particular emphasis on micro needle electrodes. As a result of the combination of the microelectrode size effect and the intrinsic properties of the diamond films, these electrodes showed not only a significantly lower background current than diamond macroelectrodes, but also an ability for use in analytical sensing in low conductive media. Accordingly, a wider range of experiments including in vivo measurements could be performed.
Regiodivergent carbene/alkyne metathesis for the selective synthesis of 2-alkylidenebicyclo[4.1.0]heptanes and 1-alkenylbicyclo[3.1.0]hexanes from common 1,6-enynes precursors was demonstrated. The cyclization mode could be switched by simple addition of diamine ligands to control the relative orientation of the approaching chromium Schrock carbene equivalents generated in situ from gem-dichromiomethanes toward triple bonds.
We have been aiming to reduce the amount of platinum (Pt) needed in catalysts for automobile exhaust-gas purification and fuel cell electrodes. To achieve this, we have attempted to: 1) establish simple methods for synthesizing ligand-protected ∼1-nm-sized Pt clusters with a narrow distribution in the number of constituent atoms; 2) load these clusters onto supports, while retaining their number of constituent atoms, to prepare supported ∼1-nm-sized Pt clusters; and 3) elucidate the catalytic activity of each type of supported ∼1-nm-sized Pt cluster. These studies have revealed that: 1) ligand-protected ∼1-nm-sized Pt clusters stable in the atmosphere can be isolated with high purity by a combination of polyol reduction and ligand-exchange reaction; 2) ∼1-nm-sized Pt clusters can be loaded onto the support without aggregation when the clusters are adsorbed on the support and then calcined at an appropriate temperature; and 3) Pt17 clusters loaded onto γ-alumina exhibit high activity and durability for exhaust-gas purification, whereas Ptn clusters (n = ∼35, ∼51, or ∼66) loaded onto carbon black exhibit high activity and durability for the oxygen reduction reaction (which occurs at fuel cell electrodes). This account describes our previous studies and explores future prospects for supported ∼1-nm-sized Pt clusters.
Binary colloids of two morphologically different particle species cause phase separation containing liquid crystalline phases. Although electric alignment of colloidal nanosheets has been investigated for colloidal systems consisting of single nanosheet species, that of binary nanosheet colloids has scarcely been examined. We report herein the electric alignment of aqueous binary colloids composed of niobate (NB) nanosheets from K4Nb6O17 and commercially available graphene oxide (GO) platelets. The NB–GO binary colloids show multiphase coexistence involving liquid crystalline phases induced by the NB nanosheets, whereas the employed GO particles do not contribute to the liquid crystallinity. The NB nanosheets in the binary colloids are electrically aligned in parallel to an AC voltage (1 kV cm−1 peak to peak, 50 kHz) applied to the sample. When the concentration of GO in the binary colloids is low enough, the GO particles are also electrically aligned although they hardly respond to electric field in the absence of NB nanosheets. Combined optical microscopy of bright-field, polarized, and fluorescence observations demonstrates that isolated GO particles are dragged by the aligning motion of the NB nanosheets forming liquid crystalline domains. The results indicate that collective motions of colloidal nanosheets can induce participation of isolated particles.
During the synthesis of CdTe quantum dots (QDs) by the hydrothermal method, a CdS shell layer is naturally formed by the thermal decomposition of thiol ligands, and CdTe/CdS core/shell QDs are produced. Herein, we investigate the selective synthesis of CdTe and CdTe/CdS QDs to control the thermal decomposition of thiol ligands by changing the Te/Cd molar ratio of the precursor solutions. From the experimental results of X-ray photoelectron spectroscopy and optical properties of absorption and photoluminescence (PL) spectra and PL decay profiles of the synthesized colloidal QDs, it was found that the formation of the CdS shell can be controlled by varying the Te/Cd ratio of the precursor solution. Thus, the selective synthesis of CdTe and CdTe/CdS QDs with the same PL energy but different PL decay times is possible.
Multiple (or multivalent) interaction is the key in many biological systems. One of the most important (photo-)chemical reactions, photosynthesis, is driven by regularly aligned molecules by multiple interactions between proteins and molecules. A grand challenge of modern chemistry therefore includes the construction of supramolecular assemblies and control of their functions for mimicking nature and beyond. While most synthetic systems depend on covalent, coordination and hydrogen bonds between molecules, my approach focuses on multiple electrostatic interactions with two-dimensional clay mineral nanosheets. I here summarize my recent work on manipulation of precise molecular arrangements and photochemical properties via multiple electrostatic interactions. This Account mainly consists of the three parts; 1: manipulation of photochemical properties of molecules and new emission enhancement phenomenon (chapters 2–7), 2: efficient photochemical reactions and artificial photosynthesis model (chapters 8–14), and 3: molecular-scale understanding by means of electron microscopy (chapters 15–17).
Cobalt and nitrogen co-doped carbon (Co/N/C) catalysts prepared by pyrolysis are promising electrocatalysts for hydrogen evolution reaction (HER). Construction of Co–Nx active sites is an important strategy for improving HER activity. We developed a method for thermally controlled construction of the Co–Nx active sites by applying a bottom-up synthetic methodology using an N-doped graphene nanoribbon (N-GNR). Preorganized aromatic rings in the precursors assist graphitization during generation of N-GNR which has N2 sites that coordinate to a cobalt ion. Atomically dispersed Co–Nx sites in the catalysts are observed by electron microscopy. Moreover, the amount of Co–Nx sites increases up to 0.31 wt% as confirmed by XPS and elemental analysis. The Co/N/C catalyst prepared from the precisely designed precursor forming an N-GNR shows HER activity with a low overpotential of 258 mV (in 1.0 M HClO4aq) and 311 mV (in 0.1 M HClO4aq) at 10 mA·cm−2, and with a long-term stability.
Triskelion-shaped π-fluorophores bearing coumarins with nitrogen-containing donor groups (1a, 1b, and 1c) were successfully synthesized via intramolecular Ullmann coupling. X-ray crystal structure analysis revealed that 1a and 1b adopt curved propeller-shaped structures similar to that of parent compound 1-H. A theoretical study suggested that compounds 1a–1c possess two different molecular surfaces, as do Janus-type molecules. The emission spectra of 1a–1c in toluene showed broad emission bands at 570, 599, and 600 nm with a large Stokes shift at 4430–5930 cm−1. Although compounds 1a and 1b exhibited more intense fluorescence emission compared with that of parent compound, the emission intensity decreases in high-polarity solvents due to broken symmetry resulting from the twisting of the donor groups. Conversely, compound 1c showed weak emission in all tested solvents. These curved and triskelion-shaped fluorophores were found to form nanoaggregates in THF/H2O mixtures and demonstrated outstanding aggregation-induced emission enhancement (AIEE) properties.
Neutron reflectometry (NR) has been utilized to study the electric double layer (EDL) of ionic liquids (ILs), however, further improvement of the sensitivity toward interfacial structure would be desirable. We recently proposed two ways to improve the NR sensitivity toward the EDL structure at the IL/electrode interface (J. Phys. Chem. C, 123 (2019) 9223). First, as the electrode, a thin film of metal (Nb) was used with the scattering length density (SLD) and thickness controlled to sensitively analyze the potential dependent EDL structure. Second, the IL cation and anion were chosen so that they have large size and large SLD difference, both of which also increase the sensitivity. In the present study, we have further explored this rational material design for the sensitivity enhancement, by changing the film metal from Nb to Bi whose SLD is closer to those for two bulk materials: Si and the IL used, trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide. We successfully observed not only the first ionic layer in the EDL but also the overlayers, revealing that the IL cation is specifically adsorbed on the electrode and that the cation-rich first layer induces overscreening in the overlayers up to the third ionic layer.
Dialkyl-diphosphenes and -distibenes of the type RTrp*2E2 (E = P, Sb; R = H, n-Pr) were synthesized and isolated using the steric protection of extended triptycyl groups (Trp*). The solubility of these diphosphenes and distibenes can be increased by installing a propyl group onto the bridgehead position of the triptycyl core (n-PrTrp*).
A nickel–cobalt-modified boron-doped diamond (NiCo-BDD) electrode was prepared by chronoamperometry. A Ni/Co ratio of 4:1 in solution was determined as the optimum ratio for the urea oxidation reaction. Results showed that the Ni and Co particles were homogeneously deposited on the BDD surface and deposited without any interaction between the particles. The prepared NiCo-BDD electrode for a urea fuel cell exhibited optimum performance with a 0.1 M KOH and 0.50 M urea solution as the anode electrolyte and a 2.0 M H2O2 and 2.0 M H2SO4 solution as the cathode electrolyte. An open-circuit voltage of 0.817 V with a power density of approximately 0.632 mW cm−2 at room temperature and excellent stability after 6 h of application were achieved. NiCo-BDD significantly enhanced the catalytic activity of UOR compared with the Ni plate, unmodified BDD, Ni-BDD, and Co-BDD.
Multi-dimensional coordination frameworks whose charge states are controllable by the sophisticated chemical modification of the components or by the application of stimuli are fascinating targets for the design of electronic/magnetic functional materials. A simple way to design such frameworks is to assemble electron donor (D) and electron acceptor (A) units in a DmAn ratio with electronically conjugated linkages; we call this type of framework a D/A metal–organic framework (D/A-MOF). In this account article, our previous studies on D/A-MOFs composed of carboxylate-bridged paddlewheel-type diruthenium units ([Ru2]) and polycyano organic molecules such as N,N′-dicyanoquinodiimine (DCNQI) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as the D and A subunits, respectively, are summarized. In this family of D/A-MOFs, the charge distribution between the internal D and A subunits can be precisely tuned by varying their electronic structure, i.e., depending on what kind of D and A we choose. Crucially, the diverse charge states, as well as anisotropic framework and often porous nature, of D/A-MOFs are well correlated with their bulk electronic and magnetic properties.
Mesoionic 1,3-dialkyltetrazolium-5-thiolates can be prepared in good yields by alkylation of 1-alkyltetrazole-5-thiols with secondary alcohols in concentrated sulfuric acid. The thiolates are transformed into the corresponding olates through S-alkylation followed by hydrolysis. The olates were found to be liquid at room temperature and to work effectively as polar solvents. The use of a smaller amount of sulfuric acid led to drastically different products; S-bridged dimers linked by 1,2-dimethylethylene were formed as the major products.
A visible-light mediated, catalyst-free hydroalkylation of electron-deficient alkenes was achieved using benzothiazoline as a radical transfer reagent. The photoreaction proceeded under household LEDs. Mechanistic studies elucidated the formation of an electron-donor-acceptor complex between benzothiazoline and electron-deficient alkenes.
We investigated the morphology of binary monolayers of palmitic acid and behenic acid using atomic force microscopic observations. The monolayers exhibited a phase-separated morphology composed of meandering domains with a width of nanometer order, which is probably due to fixation of the monolayer morphology at a stage on the way to phase separation.
When a crystalline 1,3-diphosphacyclobutane-2,4-diyl bearing a 3,5-dichloro-2,4,6-triazine substituent was irradiated with muon beam, two paramagnetic species showing muon hyperfine coupling constants (hfcs) of 4.5 MHz and 6.5 MHz were produced via addition of muonium. These observed paramagnetic species are consistent with the cis and trans isomers of the C-muoniated 1,3-diphosphacyclobutane-2,4-diyl.
Computational approaches to elucidate the phase transitions in lanthanide complexes will support understanding their electronic structure changes by weak stimuli such as gas adsorptions. There are no examples as molecular models of Ln complexes for defining parameters, due to various molecular shapes with unexpected coordination numbers resulting in different packings with different Ln ions. Here, we succeeded in determining molecular force field parameters (van der Waals; vdW for Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm; and torsion parameters of the ligand) to apply the structural optimization of a series of Ln complexes taking uniform helicate for ten Ln ions with the same ligand, L, which reported previously as LnL. SmL, ErL, and TmL were newly synthesized for this calculation and the structure and luminescence properties experimentally determined. The coordination distances surrounding Ln are along the lanthanoid contraction. It is the first case to clarify the lanthanoid contraction in a 10-coordination system of a series of Ln ions. The applied optimized structures with these parameters for Eu well exhibit correspondence to observed results for four analogous of EuL. This work will strongly push development of luminescent Ln complexes with soft-crystalline behaviour.