Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido-Annulated N-Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors.

Synthetic strategies to access high-valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e. g. amide or oxide) or σ donating electropositive atoms (e. g. boryl or hydride). Besides the η5 -(methyl)cyclopentadienyl derivatives, high-valent η1 carbon-ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all-carbon-ligated anionic bis(CCC-pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido-annulated N-heterocyclic carbene (dpa-NHC) IrIII complex allowed a stepwise 4e- oxidation sequence. The first 2e- oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC-tetradentate ligand. A further 2e- oxidation allowed isolation of a high-valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon-ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties.

Isolation and characterization of blackish-brown BY2-melanin accumulated in cultured tobacco BY-2 cells.

The tobacco BY-2 cell line is one of the most utilized plant cell lines. After long-term culture, the cells turn brown to black, but the causal pigment is unknown. We successfully isolated a blackish-brown pigment from BY-2 cells cultured for 3 weeks. Morphological and spectroscopic analyses indicated that the pigment had similar features to a melanin-like substance reported previously. Furthermore, physicochemical analyses revealed that this pigment possessed most of the properties of melanin-like pigments. In addition, the high nitrogen content suggested that it differed from common plant melanins classified as allomelanins, suggesting a novel eumelanin-like pigment: "BY2-melanin". This is the first example showing that eumelanin-like pigments are produced in the cultures of plant cells for which the accumulation of melanin has not been reported. This tobacco BY-2 cell culture technique may represent a customizable and sustainable alternative to conventional melanin production platforms, with significant potential for industrial and pharmacological applications.

Density estimations and comparisons of a fragmented single fiber using X-ray computed tomography.

A commercial X-ray computed tomography (CT) apparatus using a quasi-monochromatic beam was utilized for density estimations and comparisons of a fragmented single fiber. The validation of quasi-monochromaticity of the X-ray source was investigated by radiograph measurements. For the case of a transmittance higher than 50%, the contribution of Cu Kα characteristic X-rays was dominant. To realize a sufficient statistical quality, an attempt to increase the number of averaged voxels was demonstrated using the neighboring slices of the 3D-CT image. A minimum value of the coefficient of variation (CV) was achieved using multiple images rather than using a single image. The observed values of the inverse of the transmitted X-ray intensity (CT value) of the polymers showed a fairly good relationship with their density. An analytical curve derived from measurements of reference samples of known densities could provide the relative density of an unknown fragmented fiber down to the size of 30 µm in diameter and 35 µm in length. The CV of the estimated density was from 1.5 to 2%, which was estimated from the CV of CT values. Moreover, the correlation of CT values was improved with the linear absorption coefficient than the density. A better performance of discrimination of polymers including fibers might be realized with the difference of linear absorption coefficients for X-rays.

Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor.

Fluorinated analogs of polyhedral hydrocarbons have been predicted to localize an electron within their cages upon reduction. Here, we report the synthesis and characterization of perfluorocubane, a stable polyhedral fluorocarbon. The key to the successful synthesis was the efficient introduction of multiple fluorine atoms to cubane by liquid-phase reaction with fluorine gas. The solid-state structure of perfluorocubane was confirmed using x-ray crystallography, and its electron-accepting character was corroborated electrochemically and spectroscopically. The radical anion of perfluorocubane was examined by matrix-isolation electron spin resonance spectroscopy, which revealed that the unpaired electron accepted by perfluorocubane is located predominantly inside the cage.

Non-destructive analysis of hollow-shaped single fibers using X-ray computed tomography.

A commercial high-resolution X-ray computed tomography (CT) was utilized for non-destructive analysis of single fibers. The micro-CT apparatus was employed because it is applicable to both colored and colorless fibers. A sample preparation using adhesive sheets was demonstrated, and the method is similar to typical tape-lift sample collection method in crime cases. Different cross-sectional shapes of nylon and polyester single fibers were non-destructively distinguished, and the method is applicable to all types of fibers. Cross-sectional areas, aperture ratios, and volumes of individual fibers were directly and automatically measured using the open-source software. The observed parameters were within a coefficient of variation of 3%. In addition, a mass of a single fragment of a fiber can be estimated when the local density is given.

Feasibility Studies of X-Ray Computed Tomography for Forensic Examination of Single Fibers.

Non-destructive observations of cross-sectional shapes of acrylic single fibers using X-ray computed tomography (CT) were performed. A commercial X-ray CT apparatus (Rigaku nano3DX) was employed because of its micrometer-scale spatial resolution and remarkable image contrast for soft matter. We assessed two types of sample support, a paraffin strip and a nylon string, for single fiber samples in terms of easy handling and sample recovery. Fixed individual single fibers were loaded into a narrow polyimide tube in both cases, and the tube ensured that the sample remained in the field of view during the CT measurements. In both cases, the cross-sectional shapes of individual single fibers could be distinguished, with a circular shape for one sample and a triangular shape for the other. However, the support using a nylon string was found to be more suitable for further analysis. The cross-sectional profile of the obtained tomographic image showed a clear difference between polyimide and nylon. The intensity ratio or the image contrast corresponded to that of the local densities. It was also found that the effect of the artifact appeared at around the boundaries of the objects, but the local density could still be utilized for examining individual single fibers.

Thermal Stability Change of Insoluble Sulfur by a Heat Treatment and Its Mechanism Study.

Insoluble sulfur (IS), used as a vulcanizing reagent of rubber, is prepared by the thermal ring-opening polymerization of sulfur (S8). Enhancing its thermal stability and content ratio (yield) is important for the industrial production of IS. The post-heating process at a high temperature of 70 or 90°C of the mixture of IS and S8 enhanced the thermal stability of IS and reduced the yield of IS. Further, the process at 30°C enhanced its thermal stability and maintained its yield. Since the thermal stability of IS is considered to be closely related to the chain length of polymer sulfur, a method for determining the chain length of IS was investigated by quantifying the amount of electron spin of radicals from sulfur, estimated from electron spin resonance (ESR) measurements. We confirmed that the long-period post-heating process at 30°C induced high thermal stability without reducing the yield of IS due to growth of the sulfur polymer chains.

Condensed ferric dimers for green photocatalytic synthesis of nylon precursors.

Although iron oxides have been extensively studied as photocatalysts because of their abundance and environmental compatibility, their performance is notoriously low due to factors such as low photoinduced charge-separation efficiency. Iron oxides, thus, must be modified with expensive and/or toxic materials to attain higher performances, which devalues their appeal as sustainable materials. Here, we design an iron oxide exhibiting an unprecedentedly high photocatalytic performance unrealized by previous photocatalysts such as TiO2 for reactions including the selective oxidation of cyclohexane to industrial nylon precursors. The iron oxide photocatalyst consists of ferric dimers, otherwise extremely unstable, formed via etching of Fe and O sites from ferric oxide nanoparticles immobilized within porous silica. We demonstrate a remarkably high photoinduced charge-separation efficiency (long lifetime of active species) of the ferric dimers due to their electronic structure and the potential of this supported photocatalyst for many more reactions.

Effect of Dispersants on Photochromic Behavior of Tungsten Oxide Nanoparticles in Methylcellulose.

Tungsten oxide-based photochromic films that change reversibly in air between colorless-transparent in the dark and dark blue under UV irradiation were prepared by using methylcellulose as a film matrix and various dispersants. Alpha-hydroxyl acid such as glycolic acid (GA) or glyceric acid (GlyA) is the best dispersant because it can make the film transparent by adding a small quantity much less than that of 3-hydroxypropionic acid or ethylene glycol. Fourier-transform infrared spectra and Raman spectra indicate that a strong interaction exists between WO3 and GA or GlyA. The coloration and bleaching processes of the prepared films were investigated to clarify the effect of the dispersants and the moisture contents. The bleaching rate remarkably decreased in the films containing GA or GlyA but accelerated by increasing the contact with O2. Measurements of electron-spin resonance reveals that GA and GlyA as dispersants stabilize the W5+ state. This paper shows that the coloring rate and the period for keeping the blue-colored state are tunable by changing the dispersants. The photochromic films containing α-hydroxyl acid as the dispersant have the potential for application as rewritable film on which information displayed with blue-colored state can be clearly readable for longer times compared with other dispersants.

Mesoporous TiO2 Embedded with a Uniform Distribution of CuO Exhibit Enhanced Charge Separation and Photocatalytic Efficiency.

Mixed metal oxide nanoparticles have interesting physical and chemical properties, but synthesizing them with colloidal methods is still challenging and often results in very heterogeneous structures. Here, we describe a simple method to synthesize mesoporous titania nanoparticles implanted with a uniform distribution of copper oxide nanocrystals (CuO@MTs). By calcining a titanium-based metal-organic framework (MIL-125) in the presence of Cu ions, we can trap the Cu in the TiO2 matrix. Removal of the organic ligand creates mesoporosity and limits phase separation so that tiny CuO nanocrystals form in the interstices of the TiO2. The CuO@MTs exhibits superior performance for photocatalytic hydrogen evolution (4760 µmol h-1) that is >90 times larger than pristine titania.

Unprecedentedly enhanced solar photocatalytic activity of a layered titanate simply integrated with TiO2 nanoparticles.

We report a simple, low-cost methodology for unprecedentedly enhancing the photocatalytic activity of layered inorganic semiconductors. A layered titanate with a lepidocrocite-type structure scarcely showed photocatalytic activity for a test reaction, the oxidative decomposition of formic acid in water into CO2, under simulated solar light, but it showed highly enhanced photocatalytic activity upon mixing with a much smaller amount (approximately 10 wt%) of commercially available TiO2 nanoparticles (P25) in water. The photocatalytic activity of the mixture was approximately 5 times that of P25, a benchmark photocatalyst. From various analyses, the enhancement resulted from the transfer of photoexcited electrons from the layered titanate to P25 at their particle interfaces and retardation of charge recombination. When applied to a photocatalyst for H2 production from water containing methanol under simulated solar light, the layered titanate/P25 mixture showed considerably enhanced activity and the apparent quantum yield was 23% (at 320 nm). By replacing P25 with Pt co-catalyst-loaded P25, the apparent quantum yield of the mixture increased from 23 to 73%, although an extremely small amount (below 0.06%) of Pt was used in the system.

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

Preparation of tetrabutylammonium salt of a mono-Ru(III)-substituted α-Keggin-type silicotungstate with a 4,4'-bipyridine ligand and its electrochemical behaviour in organic solvents.

The tetrabutylammonium (TBA) salt of a mono-ruthenium(III)-substituted α-Keggin-type silicotungstate with a 4,4'-bipyridine (bipy) ligand, TBA5[α-SiW11O39Ru(III)(bipy)] (1), which is soluble in various organic solvents, was prepared by a cation exchange reaction of Cs5[α-SiW11O39Ru(III)(bipy)] with tetrabutylammonium bromide. Compound 1 was characterised using IR, (1)H-NMR, elemental analysis, single crystal X-ray analysis, X-ray absorption near-edge structure (XANES) analysis (Ru L3-edge), electron spin resonance (ESR), cyclic voltammetry (CV) and UV-Vis. Single crystal X-ray analysis of 1 revealed that the Ru(III) unit was incorporated into the α-Keggin-type silicotungstate framework and coordinated by a bipy molecule through a Ru-N bond. CV indicated that the incorporated Ru(III)-bipy was reversibly oxidised to the Ru(IV)-bipy derivative and reduced to the Ru(II)-bipy derivative in organic solvents. The redox potential of Ru(IV/III)-bipy was found to be affected by organic solvents. Moreover, the Ru(V)-bipy derivative was observed in acetonitrile.

Dye-sensitized solar cells based on D-π-A fluorescent dyes with two pyridyl groups as an electron-withdrawing-injecting anchoring group.

D-π-A fluorescent dye with two pyridyl groups as an electron-withdrawing-injecting anchoring group possessing a high coordinate bonding ability to Lewis acid sites on the TiO2 surface, which can lead to high dye loading on the TiO2 film and efficient electron injection, has been developed as a new type of D-π-A dye sensitizer for dye-sensitized solar cells.

Intermolecular distances of carboxylated TEMPO derivatives on TiO2 evaluated by spin-probe ESR.

Nearest-neighbor intermolecular distances of molecules adsorbed on the surface of nanocrystalline TiO(2) particles were evaluated by the electron spin resonance (ESR) technique with molecules having a nitroxide radical and a carboxyl group as a spin probe to clarify their aggregation behaviors on TiO(2) and the influence of coadsorbates.

Development of a simple method for fabrication of transparent conductive films with high mechanical strength.

We have developed a simple method of fabricating transparent conductive films with a high mechanical strength on glass and indium tin oxide substrates. It does not require a large excess of organic solvents and polymerization catalysts and can yield smooth films by spin-coating of a mixture of a commercially available aqueous dispersion of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) and a neat liquid of tetraethyl orthosilicate. Preparation conditions such as feed ratio, kinds of additives, and annealing temperature and time were optimized to give highly conductive, transparent and mechanically strong films.

Dye-sensitized solar cells based on donor-π-acceptor fluorescent dyes with a pyridine ring as an electron-withdrawing-injecting anchoring group.

A new-type of donor-acceptor π-conjugated (D-π-A) fluorescent dyes NI3-NI8 with a pyridine ring as electron-withdrawing-injecting anchoring group have been developed and their photovoltaic performances in dye-sensitized solar cells (DSSCs) are investigated. The short-circuit photocurrent densities and solar energy-to-electricity conversion yields of DSSCs based on NI3-NI8 are greater than those for the conventional D-π-A dye sensitizers NI1 and NI2 with a carboxyl group as the electron-withdrawing anchoring group. The IR spectra of NI3-NI8 adsorbed on TiO(2) indicate the formation of coordinate bonds between the pyridine ring of dyes NI3-NI8 and the Lewis acid sites (exposed Ti(n+) cations) of the TiO(2) surface. This work demonstrates that the pyridine rings of D-π-A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO(2) surface are promising candidates as not only electron-withdrawing anchoring group but also electron-injecting group, rather than the carboxyl groups of the conventional D-π-A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO(2) surface.

Fluorescence PET (photo-induced electron transfer) sensors for water based on anthracene-boronic acid ester.

Anthracene-boronic acid ester as a new class of fluorescence PET sensors for detection of a trace amount of water in organic solvents has been designed and developed.

Detection of water in organic solvents by photo-induced electron transfer method.

A new class of fluorescence sensor for detection of water in organic solvents based on photo-induced electron transfer (PET) of anthracene coupled with an amino acid has been designed and developed.