Language：Others  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.1c03498

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpcc.1c00738

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/D0CP04659K

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.0c00758

Language：Others  

This chapter describes the emission behavior of molecules on the surface of layered materials. Emission properties of molecules depend on their surrounding environment. Even in homogeneous environments, this emission behavior depends on solvent effects such as viscosity, permittivity, polarity, and so on. While the chemical reaction media provided by layered materials is the analog of solvent effects, the effect of layered materials induces important changes in the properties of the molecule. For example, the emission intensity could be enhanced 100 times by the complex formation with layered materials. Despite the drastic effect of layered materials on the photochemical properties of molecules, the use of layered materials is limited due to some factors. One of these factors is the complicated complex formation behavior of molecules on layered materials. This sometimes includes segregation and aggregation that induce changes in photochemical properties. In recent decades, the intrinsic photochemical properties of molecules on layered materials were clarified by the progress in techniques to prepare complexes between molecules and layered materials. These examples will be described in this chapter.

DOI： 10.1007/430_2020_58

Language：English   Publishing type：Research paper (scientific journal)  

We have recently pioneered per-cationized molecular gold (Au) cluster compounds. Herein, we present a new series of per-cationized Au cluster compounds, Au-144(SR+)60, which is the largest reported compound with the most stable and studied Au clusters. Although it is typically difficult to obtain a single composition of a Au-144 cluster due to the existence of similar-sized quasi-stable compounds, optimized thermal etching and selective precipitation made strict size focusing into a single Au-144 composition possible and produced Au-144(SR+)(60) with high atomic precision. In positive-mode high-resolution ESI-MS, per-cationized Au-144(SR+)(60) clusters with different numbers of PF6- counteranions for the +12- to +21-charged states were observed. The Au-144(SR+)(60), 60(+) termini distributed over a spherical surface of radius similar to 2.5 nm, presented here, is, to the best of our knowledge, the most polycationic molecular compound reported thus far.

DOI： 10.1021/acs.jpcc.9b05319

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201908905

Language：Others   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.langmuir.8b02226

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpcc.8b05371

Language：English   Publishing type：Research paper (scientific journal)  

We herein present the preparation of short, bulky cationic thiolate (thiocholine)-protected fluorescent Au nanoclusters via sputter deposition over a liquid polymer matrix. The obtained Au nanoclusters showed near-infrared fluorescence and had an average core diameter of 1.7 ± 0.6 nm, which is too large compared to that of the reported fluorescent Au nanoclusters prepared via chemical means. We revealed the mechanism of formation of this unique material using single-particle electron microscopy, optical measurements, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography fractionations. The noncrystallized image was observed via single-particle high-angle annular dark-field scanning transmission electron microscopy observations and compared with chemically synthesized crystalline Au nanoparticle with the same diameter, which demonstrated the unique structural characteristic speculated via XPS. The size fractionation and size-dependent fluorescence measurement, together with other observations, indicated that the nanoclusters most probably contained a mixture of very small fluorescent species in their aggregated form and were derived from the sputtering process itself and not from the interaction between thiol ligands.

DOI： 10.1021/acs.langmuir.8b00067

Language：English   Publishing type：Research paper (scientific journal)  

Microwave induced plasma in liquid has become a green and effective method for preparation of metallic nanoparticles (NPs). In our research, we have introduced yttrium oxide (Y2O3) coated stainless steel electrodes to address impurity problems of resulting NPs due to the loss of electrode materials. We have proposed using [Ag(NH3)(2)](+) complex as an alternative precursor and L-arginine as the stabilizing agent to synthesize highly uniform Ag NPs with an average diameter of around 5 nm. [Ag(NH3)(2)](+) complex was chosen as it can allow the reaction proceed at high pH for higher reaction yield compared with using AgNO3 whereas L-arginine can stabilize Ag NPs to attain highly uniform and small sizes. The influence of the selection of initial precursor on the reduction of metal precursor during the plasma irradiation, the particle size and size distribution of Ag NPs, and influence of the amount of L-arginine, were investigated.

DOI： 10.1246/bcsj.20170327

Language：English   Publishing type：Research paper (scientific journal)  

Au/Ag alloy nanoparticles (NPs) were successfully prepared by a one step synthesis using HAuCl4 and [Ag(NH3)2]+ as the corresponding precursors in a microwave-induced plasma in liquid process (MWPLP) without the addition of any organic protecting or reducing agents. The time dependent reduction and particle formation during the 140 min plasma discharge were studied with TEM, UV-vis extinction spectra, and ICP-OES. After 140 min, the HAADF-STEM and EDX results indicated that the obtained Au/Ag NPs were alloy NPs. Varying the input molar ratios of the metal precursors allowed for control of the composition of the Au/Ag alloy NPs.

DOI： 10.1039/C7NJ05154A

Language：English   Publishing type：Research paper (scientific journal)  

We herein report the first real-space investigation of Förster resonance energy transfer (FRET) in two different types of quantum dot (QD) supramolecular assemblies by observing their three-dimensional (3D) configurations through high-resolution electron tomography. Owing to its critical role in photosynthesis, artificial light-harvesting antennas, and investigation of protein-protein interactions, the mechanism of FRET has been intensively studied by monitoring its excited-state dynamics via various spectroscopic techniques. The utilized electron tomography technique allowed the direct localization of 3D coordinates of individual QDs in self-assembled nanostructures and theoretical estimation of the FRET efficiency of a single fluorophore, domain, or supramolecular assembly. Moreover, the experimental value of the FRET efficiency determined by fluorescence spectroscopy was in good agreement with the magnitude obtained via electron tomography. We believe that the described strategy can be used in single-molecule FRET studies and will help to create a new bridge between material science and molecular/supramolecular photochemistry.

DOI： 10.1021/acs.jpcc.7b10628

Language：English   Publishing type：Research paper (scientific journal)  

Noble metal nanoclusters are believed to be the transition between single metal atoms, which show distinct optical properties, and metal nanoparticles, which show characteristic plasmon absorbance. The interesting properties of these materials emerge when the particle size is well below 2 nm, such as photoluminescence, which has potential application particularly in biomedical fields. These photoluminescent ultrasmall nanoclusters are typically produced by chemical reduction, which limits their practical application because of the inherent toxicity of the reagents used in this method. Thus, alternative strategies are sought, particularly in terms of physical approaches, which are known as "greener alternatives," to produce high purity materials at high yields. Thus, a new approach using the sputtering technique was developed. This method was initially used to produce thin films using solid substrates; now it can be applied even with liquid substrates such as ionic liquids or polyethylene glycol as long as these liquids have a low vapor pressure. This revolutionary development has opened up new areas of research, particularly for the synthesis of colloidal nanoparticles with dimensions below 10 nm. We are among the first to apply the sputtering technique to the physical synthesis of photoluminescent noble metal nanoclusters. Although typical sputtering systems have relied on the effect of surface composition and viscosity of the liquid matrix on controlling particle diameters, which only resulted in diameters ca. 3-10 nm, that were all plasmonic, our new approach introduced thiol molecules as stabilizers inspired from chemical methods. In the chemical syntheses of metal nanoparticles, controlling the concentration ratio between metal ions and stabilizing reagents is a possible means of systematic size, control. However, it was not clear whether this would be applicable in a sputtering system. Our latest results showed that we were able to generically produce a variety of photoluminescent monometallic nanoclusters of Au, Ag, and Cu, all of which showed stable emission in both solution and solid form via our matrix sputtering method with the induction of cationic-, neutral-, and anionic-charged thiol ligands. We also succeeded in synthesizing photoluminescent bimetallic Au-Ag nanoclusters that showed tunable emission within the UV-NIR region by controlling the composition of the atomic ratio by a double-target sputtering technique. Most importantly, we have revealed the formation mechanism of these unique photoluminescent nanoclusters by sputtering, which had relatively larger diameters (ca. 1-3 nm) as determined using TEM and stronger emission quantum yield (max. 16.1%) as compared to typical photoluminescent nanoclusters prepared by chemical means. We believe the high tunability of sputtering systems presented here has significant advantages for creating novel photoluminescent nanoclusters as a complementary strategy to common chemical methods. This Account highlights our journey toward understanding the photophysical properties and formation mechanism of photoluminescent noble metal nanoclusters via the sputtering method, a novel strategy that will contribute widely to the body of scientific knowledge of metal nanoparticles and nanoclusters.

DOI： 10.1021/acs.accounts.7b00470

Language：English   Publishing type：Research paper (scientific journal)  

Herein, we report a novel positively charged photoluminescent Au-Ag bimetallic nanocluster synthesized using 11-mercaptoundecyl-N,N,N-trimethylammonium bromide as the capping ligand by means of green double-target sputtering method on a biocompatible polymer matrix. The photoluminescent Au-Ag bimetallic cluster showed emission tunability from blue to near infrared (NIR) regions with respect to change in the composition.

DOI： 10.1021/acs.langmuir.7b02011

Language：English   Publishing type：Research paper (scientific journal)  

For the first time, investigation on the effect of lowering the synthesis temperature below room temperature (10 to -10 degrees C) and increasing the viscosity of the reaction solution at certain temperatures has been used to trigger the formation of single-crystalline ss-Sn nanorods (NRs) in a chemical synthesis using an organic solvent. These two parameters govern the energy of the particles in the solution, thereby mediating the selective attachment to the nuclei and the preferential growth of Sn along the c-axis. The length and aspect ratio of the NRs were inversely proportional to the synthesis temperature and directly proportional to the viscosity of the reaction solution. In addition, we found that poly(vinylpyrrolidone) with a high molecular weight aided the formation of longer and higher aspect ratio NRs via the bridge flocculation effect.

DOI： 10.1021/acs.cgd.7b00227

Language：English  

Production of oxygen-deficient tungsten oxide nanoparticles with a diameter of around 10 nm have been successfully developed using a microwave-induced plasma in liquid technique. The prepared blue-green nanoparticles exhibit strong absorption in the visible region; thus, these could be efficient visible-light photocatalysts. The high-angle annular dark-field images revealed the dislocation of tungsten, which causes oxygen deficiencies.

DOI： 10.1021/acsomega.7b00986

Language：English   Publishing type：Research paper (scientific journal)  

This study demonstrates a novel synthesis of cationically charged photoluminescent noble metal nanoclusters of Au, Ag, and Cu; these are known plasmonic elements utilizing 11-mercaptoundecyl-N,N,N-trimethyl ammonium bromide as a stabilizing and capping ligand via sputtering deposition over a liquid polymer matrix.

DOI： 10.1039/c7nj01369h

Language：English   Publishing type：Research paper (scientific journal)  

The microwave-induced plasma in liquid process (MWPLP) has been attractive as a unique preparation method of metal nanoparticles. In this study, we investigated the effect of H2O2 on gold nanoparticles prepared using the MWPLP. Au nanoparticles were obtained without aggregation when the Au and H2O2 concentrations in the reaction solution were 0.3 mM and 0.03 mM, respectively. When the H2O2 concentration was lower or higher than the optimum range, aggregated particles were obtained. The results show that the addition of H2O2 had a great influence on the reduction rate and the dispersibility, and that Au nanoparticles prepared under optimum conditions were not aggregated and exhibited a high dispersibility. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2017.02.009

Language：English   Publishing type：Research paper (scientific journal)  

Many thiolate-protected molecular Au clusters, of different cluster sizes and with varying neutral or anionic thiolate ligands, have been reported over the past two decades. Despite this abundance of information, to date there has been no report of atomically pure cationized molecular Au clusters that are protected with cationic thiolates. We herein present a novel, facile and high-yield synthetic approach towards producing a new series of thiolate- protected molecular Au clusters: a fully cationized Au-25(SR+)(18) cluster with atomic precision. The simple "charge neutralization strategy" presented enables treatment of the cationic thiols as neutral thiols, thus the well-established method for preparing Au-25 clusters with neutral thiolates can be adopted for cationic Au-25 clusters at a very high synthetic yield. We believe that this report will widen the spectrum of gold cluster chemistry and also help in the further development of cationized molecular clusters with various metals, core sizes, and ligand structures.

DOI： 10.1002/cnma.201700012

Language：Others  

Language：English   Publishing type：Research paper (scientific journal)  

We have been investigating complexes composed of nano-sheet with anionic charges such as clay nanosheets and molecules such as cationic organic dyes. Photochemical properties of organic dyes are much affected by the complex formation with nano-sheet in many cases. Especially, a strong fluorescence enhancement behavior of dyes was frequently observed on the nano-sheet surface. Based on the mechanism, we name this unique effect "S-Fixation Induced Emission (S-FIE)". The examples for fluorescence enhancement are shown and the mechanism is discussed in detail. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2017.01.013

Language：English   Publishing type：Research paper (scientific journal)  

We have developed a novel physical approach for size-controlled synthesis of metal nanoparticles via sputtering deposition over liquid matrix. Here we report a novel water-dispersible, negatively charged fluorescent silver nanoparticles through this method with a very short anionic thiolate ligand. Our previous result showed that multiple hydrogen bonds between carboxylic groups in surface ligands resulted in a very poor dispersilibity of formed nanoparticles, however neutralized sodium 3-mercaptopropionate used in this work could overcome this limitation. We successfully obtained NIR fluorescent, water-dispersible silver nanoparticles for the first time among physical-based approach. Results presented here therefore will widen the spectrum of novel and environmental-friendly strategy for functionalized metal nanoparticles or fluorescent clusters. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2017.01.022

Language：English   Publishing type：Research paper (scientific journal)  

A straightforward method for synthesizing single-crystalline SnO micro particles in an organic medium using tin acetylacetonate as the precursor and oleylamine as the capping ligand is proposed. For the first time, well-defined four-petal starfish-like SnO sheets were obtained in the organic medium. In addition, the shape of the particles could be reproducibly tuned such that their structures varied from cubes to squares and then to starfish-like sheets by simply changing the concentration of oleylamine. The underlying mechanism of this process was found to be closely related to the interaction of the stabilizing agent with the SnO crystal planes. Changing the concentration of the stabilizing agent could modify this interaction, leading to the preferential growth of certain crystal planes of SnO particles which determined the particle shape. This synthesis approach is advantageous in terms of allowing control over the particle shape as well as for its simplicity and short reaction time. Our results yield crucial insights regarding the shape evolution of SnO particles.

DOI： 10.1039/c5ra25676c

Language：English   Publishing type：Research paper (scientific journal)  

A modified magnetron sputtering technique using pentaerythritol tetrakis(3-mercaptopropionate) (PEMP) as a stabilizing agent and liquid dispersion medium was developed to generate photoluminescent copper nanoclusters. The results reveal that, over time, the as-prepared blue emitting copper nanoclusters were converted to red-emitting copper sulfide nanoclusters. The formation of copper oxide as an intermediate during the conversion of copper to copper sulfide nanoclusters was demonstrated. Furthermore, based on the mechanism of formation of copper sulfide, the kinetics of the conversion process could be controlled via ultraviolet (UV) irradiation of the as-synthesized dispersion. These findings shed light on the formation and conversion of nanoclusters obtained via sputtering into liquid, demonstrating that the method is highly versatile for producing metal nanoclusters and compounds with tailorable composition and optical properties.

DOI： 10.1021/acs.langmuir.6b03017

Language：English   Publishing type：Research paper (scientific journal)  

Tin nanoparticles (Sn NPs) are of considerable interest for conductive printing because of their low melting temperature and low cost. In the present study, polyvinylpyrrolidone (PVP) stabilized metallic Sn NPs were synthesized by a polyol process and the size of Sn NPs was controlled from 15 to 89 nm by adjusting the amount of PVP. For the first time, we demonstrated that conductive patterns fabricated from the inks of metallic Sn NPs were achieved readily at room temperature under N-2 without reducing gases or additives. The lowest obtained resistivity was 1.1 x 10 (3) Omega cm, which was 100 times higher than that of bulk Sn. The size of Sn NPs, the amount of the stabilizing agent, and the low melting temperature of Sn NPs were found to be the main factors controlling the conductivity of the obtained Sn pattern in room temperature sintering. This study offers a new approach for the room temperature fabrication of conductive electronics using the printing technique.

DOI： 10.1039/c6tc00161k

Language：English   Publishing type：Research paper (scientific journal)  

Although many thiolate-protected Au clusters with different numbers of Au atoms and a variety of thiolate ligands have been synthesized, to date there has been no report of a fully cationized Au cluster protected with cationic thiolates. Herein, we report the synthesis of the first member of a new series of thiolate-protected Au cluster molecules: a fully cationized Au-25(SR+)(18) cluster.

DOI： 10.1021/acs.jpclett.6b01725

Language：English   Publishing type：Research paper (scientific journal)  

We report detailed aggregation mechanisms of sputtered silver nanoparticles in a viscous thiolate liquid matrix. Fluorescent silver nanoparticles were prepared by the sputtering deposition over pentaerythritol tetrakis(3-mercaptopropionate) (PEMP). The dependences of extinction, fluorescence and particle size on time were discussed in terms of two possible aggregation mechanisms. The main aggregation process was secondary aggregation, with primary aggregation (core coalescence) making a small contribution. The four thiol groups in the PEMP structure are the driving force determining the predominance of secondary aggregation. Finally, we successfully prepared a thiourethane resin by the polymerization of a thiolate matrix, and complete immobilization of nanoparticles in the resin resulted in no observable degradation of the photophysical properties. The demonstrations presented here will be beneficial in understanding the detailed aggregation mechanism and optical properties of nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2016.05.035

Language：English   Publishing type：Research paper (scientific journal)  

Plasma-in-liquid process (PLP) has become a hot topic in green synthesis of metal nanoparticles (NPs). In order to overcome one of the current challenges associated with the impurity produced from metal electrodes, this study utilized a ceramic-coated electrode to prepare pure Au NPs stabilized by L-arginine. Using this electrode, the reduction of Au ions during the plasma irradiation, the formation of Au NPs, their size and size distribution as a function of the pH were investigated. Our results show that a bimodal NP size distribution was obtained at pH 3.5-12.0. The fraction of small sized Au NPs becomes significant at pH 6.0 and 12.0 while that of big sized Au NPs is dominant at pH 3.5. The results in the present study suggested that this change in the size distribution of Au NPs was governed by the reduction rate of gold ion at different pH under plasma generated in water.

DOI： 10.1166/jnn.2016.12923

Language：English   Publishing type：Research paper (scientific journal)  

Sputtering deposition of gold over a liquid matrix containing different ligands with thiolate, amine, or carboxy groups resulted in the formation of spherical gold nanoparticles (Au NPs) in the range of 2.1 to 6.7 nm, and the diameters gradually decreased as the affinity of the ligands for Au increases.

DOI： 10.1246/bcsj.20160187

Language：English   Publishing type：Research paper (scientific journal)  

Here we report a novel physical approach for thiolate-protected fluorescent gold nanoparticles with a controlled size of the order of a few nanometers. This approach is based on a sputtering of gold into a liquid matrix containing thiolate ligand as a stabilizer at various concentrations, thus no reductant was used. The size of the gold nanoparticles was successfully controlled to range from 1.6 to 7.4 nm by adjusting the thiol concentrations. Surface plasmon absorption was observed in larger nanoparticles, but it was not observed in smaller ones. Such smaller nanoparticles fluoresced at around 670 nm with a small spectral shift according to their size, however, the diameter (1.6-2.7 nm) was very strange to show such red emission compared with photophysical characteristics of reported gold cluster or nanoparticles synthesized by chemical method. By detailed investigations using TEM, HAADF-STEM, XPS, and TGA, and size fractionation by size exclusion chromatography, we finally arrived at the plausible mechanism for the origin of unusual fluorescence property; the obtained gold nanoparticles are not single-crystal and are composed of aggregates of very small components such as multinuclear gold clusters or complexes.

DOI： 10.1038/srep29928

Language：English   Publishing type：Research paper (scientific journal)  

A sputtering deposition of metals over liquid matrixes has been investigated as a novel and environmentally friendly method to generate stable colloidal metal nanoparticles. We have expanded this method by using the liquid monomers with mercapto groups in order to prepare more stable, uniform and size controllable nanoparticles. Here we report the systematic investigation on the growth mechanism of silver nanoparticles on pentaerythritol tetrakis(3-mercaptopropionate) (PEMP) matrix under the varied viscosities controlled by temperature. The diameter of obtained nanoparticles increased from 1.8 to 2.3 nm as the viscosity of the liquid matrix increased, and at higher viscosity region we obtained a thin deposited film on the liquid surface but no nanoparticles formed. The effect of viscosity on the particle diameter was much smaller than previous works using ionic liquids or polyethylene glycol, and then the phenomenon was understood by the structure of these matrixes where PEMP has four mercapto groups however ionic liquids or polyethylene glycol does not have any functional groups that introduce strong interaction with metals. These demonstrations suggest that the sputtering over mercaptan liquid matrix is a more favorable method for the stable preparation of uniform very small nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2016.03.044

Language：English   Publishing type：Research paper (scientific journal)  

A transparent resin containing titanium oxide nanoparticles ( NPs) was prepared using a molten matrix sputtering ( MMS) technique. The low vapour pressure of the liquid, pentaerythritol ethoxylate ( PEEL) substrate permits the use of this vacuum technique directly with liquid PEEL under stirring conditions in order to obtain uniform dispersions of NPs. We found that it is possible to synthesize titanium oxide, TiOx, NPs with diameters of less than 5 nm with a controlled composition by simply adjusting the sputtering atmosphere. Furthermore, as the electronic structure of the TiOx NPs changes depending on the particle size, crystallinity and degree of oxidation, we were able to modify the optical properties of PEEL and the resin by embedding TiOx NPs in the matrix. The enhancement of the refractive index of a resin containing TiO2 NPs was also demonstrated. This synthetic method is promising for the advanced preparation of high purity TiOx NPs without using a reducing agent and leaving by-products for various applications in optical devices, energy conversion, and light harvesting in the UV visible region.

DOI： 10.1039/c6nj01624c

Language：English   Publishing type：Research paper (scientific journal)  

A novel positively charged fluorescent gold nanocluster was successfully synthesized using the shortest cationic thiol, thiocholine. Effective control of electrostatic repulsion by the introduction of an anionic surfactant afforded a nanocluster that showed blue fluorescence emission.

DOI： 10.1039/c6cp00538a

Language：Japanese  

Photochemical Reaction in Two Dimensional Assemblies of Functional Dyes on Inorganic Nanosheets
In recent years, it has been revealed that light-harvesting systems (LHSs) are composed of beautifully aligned chlorophyll molecules; the regulated alignment of chlorophylls is responsible for the efficient and selective light-harvesting energy transfer processes in purple bacteria. This finding led to the construction of regularly arranged assemblies of functional dyes as a step toward fabricating artificial LHSs. While most researchers use molecular interactions such as covalent, coordination, and hydrogen bonds to produce dye assemblies, our approach involves guest-host interactions using an inorganic nanosheet as a host material. This short review presents the construction of a 2D dye assembly and its effective utilization in artificial light-harvesting applications. Owing to the highly stable and uniform 2D alignment of functional dyes on inorganic nanosheets, nearly 100% singlet-singlet energy transfer and efficient light-harvesting were achieved.

DOI： 10.1295/koron.2015-0051

Language：English   Publishing type：Research paper (scientific journal)  

For the first time, magnetron sputtering of copper onto liquid was investigated for the preparation of stable blue-fluorescent copper nanoclusters. The fluorescent intensity increased linearly with an increase of mercaptan. Our finding casts light on the formation mechanism of metal photoluminescent nanoclusters via sputtering onto liquid.

DOI： 10.1039/c6ra17291a

Language：English   Publishing type：Research paper (scientific journal)  

Stable room-temperature phosphorescence of guest aromatic molecules was achieved by the effective suppression of oxygen quenching. The organic capsule (first wall) suppressed static oxygen quenching by enclosing a guest molecule, and dynamic quenching via the capsule opening-closing process was well suppressed and manipulated by the intercalation of this capsule into the restrictive space between clay nanosheets (second wall).

DOI： 10.1039/c6pp00124f

Language：English   Publishing type：Research paper (scientific journal)  

To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions.

DOI： 10.1039/c5cp06984j

Language：English   Publishing type：Research paper (scientific journal)  

De Novo Synthesis of Gold-Nanoparticle-Embedded, Nitrogen-Doped Nanoporous Carbon Nanoparticles (Au@NC) with Enhanced Reduction Ability

DOI： 10.1002/cctc.201501020

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel method to enhance the THz emission from CuOx/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.

DOI： 10.1246/bcsj.20150173

Language：English   Publishing type：Research paper (scientific journal)  

Knowledge on the synthesis of cationically charged fluorescent gold nanoparticles (Au NPs) is limited because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs (usually less than ca. 2 nm) during nucleation in solvents. We herein propose a novel methodology for a synthesis of water-dispersible, cationic-thiolate protected fluorescent Au NPs by the sputtering of Au into liquid matrix containing thiolate ligands. By controlling mercaptan concentration the size and photophysical characteristics of Au NPs were directly controlled, resulting in near IR fluorescence with a 0.9% of absolute quantum yield. Cationically charged fluorescent metal NPs are promising, especially in biological fields, and this work provides a novel methodology towards the synthesis of a new series of functional metal NPs.

DOI： 10.1038/srep15372

Language：English   Publishing type：Research paper (scientific journal)  

We herein report a novel synthesis of black TiO2 nanoparticles by using a microwave-induced plasma over Ti complex aqueous solution. The resultant TiO2 nanoparticles showed very strong reflectance over the whole visible light region. Detailed HAADF-STEM analysis of the obtained particles revealed that this plasma method enables doping of W ions inside the TiO2 crystal structure.

DOI： 10.1246/cl.150531

Language：English   Publishing type：Research paper (scientific journal)  

A nanoisland-structured SiOx (x <= 2)/CuxO (x <= 2) composite was prepared from a Cu-deposited Si wafer by electrochemical anodization in a hydrofluoric acid (HF) and ferric nitrate (Fe(NO3)3) electrolyte. The surface of the nanoisland comprised Cu, Cu oxides, Si nanoparticles and Si oxides. The distribution of elemental Cu on the surface was uniform. Cracks and native Cu-oxides in the deposited Cu layer are the two main factors for the formation of the nanoisland-structured surface. Different from the single red photoluminescence (PL) band emitted from the electrochemical anodized bare Si wafer, a dualvisible PL band with comparable intensities at red and blue ranges was observed. The red PL quenching did not occur in this Cu-ion-doped nanostructured Si due to the different distribution areas of Cu+ and the red PL centre. The red PL originates due to oxygen defects in the band gap of Si nanoparticles/Si oxides; the blue PL is the consequence of the band-to-band transitions between 3d(10) and 3d(9)4s(1) of Cu+ ions and the intra d -> d band transition of Cu2+ ions in the interstitial vacancies of Si oxides. Compared with the electrochemical anodized bare Si sample with a single PL band, the nanoisland-structured SiOx/CuxO composite emitting a dual-PL-band is more promising for fabricating white light emitters.

DOI： 10.1039/c5tc01685a

Language：English   Publishing type：Research paper (scientific journal)  

A column-shaped porous silicon (PSi) sample was successfully prepared by electrochemical anodization in a hydrofluoric acid (HF) containing electrolyte. The PSi exhibited an unstable red photoluminescence (PL). The PL arose from surface oxygen defects under quantum confinement effects and degraded as the exposure time in air increased. After hydrofluoric acid treatment and 2 min Cu sputtering coating, the PL-degraded aged column-shaped PSi showed dual PL bands in the blue and yellow ranges. Cu-coated fresh PSi without aging and Cu-coated aged PSi without HF treatment did not show this result. The PL intensity of these two bands was greater than that of the fresh column-shaped PSi. These two emissions also showed relatively good stability, as determined from the fact that they had the same intensities after air treatment for three months. The improvement of PL can be attributed to the surface unstable SiO that combines with the sputtered Cu, forming new Cu related defect sites and surface nanostructures. The method in this study does not require any heating treatment, because SiO is very unstable, particularly in a high-moisture environment.

DOI： 10.1039/c5nj00909j

Language：English   Publishing type：Research paper (scientific journal)  

Here we report a novel method for modifying commercially available TiO2 nanoparticles by a microwave-induced plasma technique. After the plasma treatment TiO2 nanoparticles showed enhanced visible absorption due to the doped W atoms, and the photocatalytic methylene blue degradation above 440 nm was successfully improved.

DOI： 10.1039/c5cp03400k

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a novel methodology to synthesize highly fluorescent gold nanoparticles (NPs) with a maximum quantum yield of 16&#37;, in the near-infrared (IR) region. This work discusses the results of using our (previously developed) matrix sputtering method to introduce mercaptan molecules, alpha-thioglycerol, inside the vacuum sputtering chamber, during the synthesis of metal NPs. The evaporation of alpha-thioglycerol inside the chamber enables to coordinate to the nucleation stage very small gold nanoclusters in the gas phase, thus retaining their photophysical characteristics. As observed through transmission electron microscopy, the size of the Au NPs obtained with the addition of alpha-thioglycerol varied from approximately 23 nm to approximately 5 nm. Plasmon absorption varied with the size of the resultant nanoparticles. Thus, plasmon absorption was observed at 2.4 eV in the larger NPs. However, it was not observed, and instead a new peak was found at approximately 3.4 eV, in the smaller NPs that resulted from the introduction of alpha-thioglycerol. The Au NPs stabilized by the alpha-thioglycerol fluoresced at approximately 1.8 eV, and the maximum wavelength shifted toward the red, in accordance with the size of the NPs. A maximum fluorescent quantum yield of 16&#37; was realized under the optimum conditions, and this value is extremely high compared to values previously reported on gold NPs and clusters (generally similar to 1&#37;). To our knowledge, however, Au NPs of size >2 nm usually do not show strong fluorescence. By comparison with results reported in previous literature, it was concluded that these highly fluorescent Au NPs consist of goldmercaptan complexes. The novel method presented in this paper therefore opens a new door for the effective control of size, photophysical characteristics, and structure of metal NPs. It is hoped that this research contributes significantly to the science in this field.

DOI： 10.1021/acs.langmuir.5b00294

Language：English   Publishing type：Research paper (scientific journal)  

Herein we report for the first time the synthesis of octadecanethiol-capped gold nanoparticles (Au NPs) by sputtering of Au over a liquid matrix (silicone oil). Au NPs prepared in silicone oil showed plasmon absorption; however, those prepared in the presence of 1-octadecanethiol did not show plasmon absorption but fluoresced in the near IR region.

DOI： 10.1039/c5nj01011j

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel synthetic approach for cationic charged platinum nanoparticles via the autocatalytic hydrolysis of acetylthiocholine. This method can be extended to the platinum group of metals.

DOI： 10.1039/c5nj00420a

Language：English   Publishing type：Research paper (scientific journal)  

Metallic copper fine particles were prepared by chemical reduction of CuO in the presence of thermally degradable poly-1,4-butanediol-divinylether (BDVE). Because a BDVE thin layer formed on the particle surfaces, the obtained copper particles were stable and did not undergo obvious oxidation under ambient conditions. The ether groups of BDVE were hydrolyzed with protons, and this generated small fragment molecules. The BDVE-stabilized copper fine particles and their pastes can be therefore sintered at 150 degrees C in the presence of protons. Electro-conductive films with a relatively low resistivity of 8.5 x 10(-5) Omega cm were obtained on a alumina substrate in the presence of formic acid, and hot pressed conductive pellets with a resistivity of 2.9 x 10(-5) Omega cm were also obtained without any pre-oxidative annealing in the presence of proton generator molecules at very low temperatures. The hot pressed pellets show a high anti-oxidative ability and their corrosion tests revealed their good anti-corrosion property.

DOI： 10.1039/c5ra21402e

Language：English   Publishing type：Research paper (scientific journal)  

We herein propose a novel methodology to synthesize silver nano-particles with precisely controlled diameters in single nano-meter orders by sputtering into a liquid matrix (polyethylene glycol) containing mercaptans (11-mercaptoundecanoic acid) as an environmental friendly preparation without reductants.

DOI： 10.1039/c5nj00294j

Language：English   Publishing type：Research paper (scientific journal)  

In recent years, excellent research has revealed that light-harvesting systems (LHSs) are composed of beautifully aligned chlorophyll molecules; the regulated alignment of chlorophylls is responsible for the efficient and selective light-harvesting energy transfer processes in purple bacteria. This finding led to the construction of a regularly arranged assembly of functional dyes as a step toward fabricating artificial LHSs. While most approaches toward the construction of dye assemblies have depended on molecular interactions such as covalent, coordination, and hydrogen bonds, my approach involves guest-host interactions using an inorganic nanosheet as the host material. This short review presents the construction of a 2D dye assembly and its effective utilization in artificial light-harvesting applications. Owing to the highly stable and uniform 2D alignment of functional dyes on inorganic nanosheets, nearly 100 &#37; singlet-singlet energy transfer and efficient light-harvesting were achieved. I believe that the results presented herein will contribute to the construction of efficient photochemical reaction systems in supramolecular host-guest assemblies, which may facilitate the realization of artificial photosynthesis.

DOI： 10.1515/pac-2014-0906

Language：English  

By decreasing the water content in an NH4F and glycerol-water electrolyte, the transition from single-wall to double-wall TiO2 nanotube arrays was successfully achieved using an anodization method. The double-wall TiO2 nanotube structures exhibited better photocatalytic activity than the typical single-wall structures. After modification with platinum nanoparticles, the photocatalytic activity of both the single- and double-wall TiO2 nanotubes was improved further. In situ observations at the annealing temperature of the TiO2 nanotubes were performed using a transmission electron microscopy (TEM) system. A slower structural failure of the nanotubes was obtained with the introduction of oxygen gas into the TEM column compared with the structural changes observed under high-vacuum conditions without the introduction of oxygen gas. These behaviors suggest that oxygen injection is an important factor in stabilizing the TiO2 nanotubes during the in situ TEM annealing process. The high-magnification TEM images of the double-wall TiO2 nanotubes revealed that the sintering of the inner wall can draw a clear distinction between the inner and outer walls.

DOI： 10.1021/am505333v

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a unique phenomenon of the strong enhancement in the fluorescence quantum yield (phi(f)) and the excited lifetime (tau) of tetra-cationic porphyrazine dye (Pz) upon a complexation with inorganic nanosheets. Although Pz does not strongly fluoresce in a bulk solution ((phi(f) = 0.01, tau = 0.1 ns), phi(f) and tau increased up to 19 and 34 times by an intercalation into stacked clay nanosheets. Steady-sate and time-resolved fluorescence measurements revealed that this strong enhancement in phi(f) and tau is derived from the suppression of nonradiative deactivation pathways of Pz by a complexation with day nanosheets. We here name this phenomenon a "Surface-Fixation Induced Emission (S-FIE)". S-FIE can be predicted easier than aggregation-induced emission (AIE) due to its clear mechanism depending on the flat solid surface, and we can thus simply design the photophysically enhanced system. Since photophysical characteristics of organic molecules directly influence the efficiency of objective reactions such as energy or electron transfers and photocatalysis, this study is beneficial to propose a novel strategy to create efficient photochemical reaction systems and photodevices.

DOI： 10.1021/jp506766t

Language：English   Publishing type：Research paper (scientific journal)  

We report the occurrence of efficient energy transfer reaction in a novel host-guest assembly composed of an anionic clay nanosheet, cationic porphyrin, and neutral aromatic molecule encapsulated within a cationic organic cavitand. The supramolecular assembly was prepared by the coadsorption of tetracationic Zn-porphyrin (acceptor) and 2-acetylanthracene (donor) enclosed within cationic organic cavitand (octaamine in its protonated form) on anionic clay nanosheets. In this arrangement under the interguest distance of 2.4 nm, almost 100&#37; efficiency of singlet-singlet energy transfer was achieved. Detailed time-resolved fluorescence measurements revealed that the energy transfer rate constant could be attributed to a single component (1.9 x 10(9) s(-1)). This strongly suggests that the adsorption distribution of porphyrin and cavitand is rather uniform, not segregated. This is a progress from our previous study that involves energy transfer between two encapsulated neutral molecules. The use of Zn-porphyrin as an energy acceptor in this study enables to connect this energy transfer system to charge separation processes in the same manner as natural photosynthetic systems do; moreover, the efficiency of energy transfer reaction improved to almost 100&#37; from 85&#37; in the previous system between two cavitands.

DOI： 10.1021/jp502816j

Language：English   Publishing type：Research paper (scientific journal)  

In Situ Transmission Electron Microscopic Observation of Double-wall TiO₂ Nanotube Arrays at High Temperature
Double-wall TiO₂ nanotube arrays were prepared using an anodization method in a glycerol-containing electrolyte. In situ TEM observation of these samples at high temperature was carried out with and without oxygen injections. With oxygen injection, an improved thermal stability of the nanotubes at high temperature was observed. It may provide more detailed information about the calcination process of TiO₂ nanotubes and assist its morphology and structure modulation.

DOI： 10.1246/cl.140486

Language：English   Publishing type：Research paper (scientific journal)  

We present an efficient synthesis of a modified carbon nitride photocatalyst by using supramolecular complexes of cyanuric acid, melamine, and 2,4-diamino-6-phenyl-1,3,5-triazine as precursors. We combined a self-templating approach for morphology control with the modification of photophysical properties by altering the chemical structure of the material. The resulting carbon nitrides exhibit high surface areas, defined morphologies, and a strong enhancement of light absorption in the visible-light region. A detailed analysis shows that the ratio changes of the three raw monomers resulted in different carbon nitride morphologies, absorption, and emission properties, along with the incorporation of different numbers of phenyl groups in the resulting carbon nitride structures. The modified carbon nitrides exhibit superior activity in the photodegradation of rhodamine B, up to 16 times that of bulk carbon nitride. The pyrolysis of rationally chosen supramolecular hydrogen-bonded precursors constitutes a synthetic pathway for the simple one-pot preparation of efficient, metal-free carbon nitride photocatalysts.

DOI： 10.1021/la404101h

Language：English   Publishing type：Research paper (scientific journal)  

Novel tetra-cationic xanthene derivative (Flu) was synthesized. Its adsorption and photochemical behaviors on the clay surface were investigated. Fluorescence quantum yield (phi(f)) and fluorescence lifetime were 0.50 and 2.9 ns for Flu/clay complex. phi(f) of Flu was enough high (>0.1) even at high density conditions (0.080 molecules nm(-2)). It is supposed that the strong interaction between clay and Flu by the 'Size-Matching Effect' realizes the highly emissive clay complexes at high density adsorption condition by a suppression of a molecular aggregation, which tends to decrease the photochemical activity. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2013.12.072

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes an efficient artificial light-harvesting system in a host-guest assembly composed of functional dyes and inorganic nanosheet. Although we have already reported an efficient energy transfer between two types of porphyrin molecules on inorganic nanosheets (e.g., J. Am. Chem. Soc. 2011, 133, 14280), the number of photons captured by one acceptor molecule (photon-harvesting efficiency: the donor/acceptor ratio when the total energy transfer efficiency is 50&#37; as defined in the main text) was a few. To overcome this low photon-harvesting efficiency, we designed and investigated a new nanosheet type light-harvesting system including phthalocyanine. As a result from steady-state and time-resolved fluorescence measurements, the energy transfer reaction was highly efficient even under the donor excess conditions. The efficiency was almost 100&#37; even under the ratio of donor/acceptor = 1/1-6/1. The most advanced point of this study is the presence of energy transfer between nonadjacent donor-acceptor, and the photon-harvesting efficiency of this system progressed seven times compared to that of the previous porphyrin-porphyrin system. Additionally, the efficient utilization of visible region of sunlight (visible-light-harvesting efficiency: the percentage of visible region of sunlight (380-780 nm), in which the extinction coefficient of the light-harvesting molecules excesses 10(4) M-1 cm(-1)) was realized in the present donor-acceptor combination. The visible-light-harvesting efficiency of the present system reached 86&#37;. Thus, our host-guest system took a step closer to realize an artificial light-harvesting system utilizing the wide-wavelength region of sunlight with high photon-harvesting efficiency, in which a few energy acceptor molecules can harvest the excitation energies from a large number of adjacent and/or nonadjacent donor molecules efficiently.

DOI： 10.1021/jp4022757

Language：English  

Photochemical properties of cationic pyrene derivative and energy transfer reaction between pyrene and porphyrin on the clay surface
1,6-di(N-methyl-pyridinium-3-yl)-pyrene(m-Py^<2+>) was synthesized. Photochemical properties were observed for m-Py^<2+> itself and m-Py^<2+>/clay complexes. Judging from Lambert-Beer plot analysis, m-Py^<2+> molecules adsorb on the clay surface without aggregation up to 60 &#37; versus cation exchange capacity of the clay. m-Py^<2+> molecule emits fluorescence from excimer on the clay surface. An energy transfer reaction from excited singlet m-Py^<2+> to the ground-state p-TMPyP on the clay surface was examined. The maximum energy transfer efficiency was 13 &#37;. These findings indicate that pyrene derivative is expected as energy donor which can absorb shorter wavelength light in the visible region towards the establishment of artificial light-harvesting system.

DOI： 10.11362/jcssjclayscience.17.1_7

Language：English   Publishing type：Research paper (scientific journal)  

We have been investigating complexes composed of nanolayered materials with anionic charges such as clay nanosheets and dye molecules such as cationic porphyrins. It was found that the structure of dye assembly on the layered materials can be effectively controlled by the use of electrostatic host-guest interaction. The intermolecular distance, the molecular orientation angle, the segregation/integration behavior, and the immobilization strength of the dyes can be controlled in the clay-dye complexes. The mechanism to control these structural factors has been discussed and was established as a size-matching effect. Unique photochemical reactions such as energy transfer through the use of this methodology have been examined. Almost 100&#37; efficiency of the energy-transfer reaction was achieved in the clay-porphyrin complexes as a typical example for an artificial light-harvesting system. Control of the molecular orientation angle is found to be useful in regulating the energy-transfer efficiency and in preparing photofunctional materials exhibiting solvatochromic behavior. Through our study, clay minerals turned out to serve as protein-like media to control the molecular position, modify the properties of the molecule, and provide a unique environment for chemical reactions.

DOI： 10.1021/la3034808

Language：English   Publishing type：Research paper (scientific journal)  

A supramolecular host guest assembly composed of a cationic organic cavitand (host), neutral aromatic molecules (guests), and an anionic clay nanosheet has been prepared and demonstrated that in this arrangement efficient singlet singlet energy transfer could take place. The novelty of this system is the use of a cationic organic cavitand that enabled neutral organic molecules to be placed on an anionic saponite nanosheet. Efficient singlet singlet energy transfer between neutral pyrene and 2-acetylanthracene enclosed within a cationic organic cavitand (octa amine) arranged on a saponite nanosheet was demonstrated through steady-state and time-resolved emission studies. The high efficiency was realized from the suppression of aggregation, segregation, and self-fluorescence quenching. We believe that the studies presented here using a novel supramolecular assembly have expanded the types of molecules that could serve as candidates for efficient energy-transfer systems, such as in an artificial light-harvesting system.

DOI： 10.1021/la305148j

Language：English   Publishing type：Research paper (scientific journal)  

Time-resolved fluorescence and steady-state spectroscopic measurements were performed with +4-charged cationic porphyrins adsorbed on an anionic-type clay (Sumecton SA; SSA) surface at a low molecular loading level (10 &#37; vs. cation-exchange capacity of clay) corresponding to an occupied area of ca 50 nm(2) per molecule. Absorption spectra indicated no interaction between transition moments of the porphyrins on the clay surface. An efficient energy-transfer process from donor to acceptor porphyrin was observed on the clay surface even under low porphyrin loading conditions. The efficiency of energy transfer obtained from the steady-state measurement was 65 &#37;. Real-time behavior of the porphyrins was successfully captured during energy transfer. The rate constant of the energy transfer obtained from time-resolved fluorescence measurements was found to be 5.3 x 10(8) s(-1). According to the efficiency and the rate constant, it is proposed that the adsorbed porphyrins did not have a uniform and fixed distribution.

DOI： 10.1007/s11164-012-0647-1

Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a novel methodology to improve noncollisional photochemical reactions such as Forster resonance energy transfer on solid surfaces. Since an excited guest molecule densely adsorbed on the solid surfaces is quenched by an unfavorable interaction between guests in general, the photochemical reactions such as electron and energy transfers tend to be inefficient compared to those in homogeneous systems. In this work, the mechanism of unfavorable quenching process of dyes on the clay surface as a typical solid surface for the photochemical energy transfer was systematically investigated by using a series of porphyrin derivatives. As a result, it was found that the quenching rate constants of excited guest dye determined by the time-resolved fluorescence measurements correlated well with the strengths of coulombic interaction between host and guest. The strong coulombic interaction should suppress the mobility and collision frequency of guests on the clay surface; thus, the collision of guest molecules was revealed as the origin of unfavorable quenching for photochemical reactions on the clay surface. According to this principle, we will be able to construct efficient photochemical reaction systems without any quenching process, such as efficient energy transfers toward an artificial light-harvesting system. In fact, we have already realized almost 100&#37; energy transfer by the suppression of quenching process on the clay surface (e.g., J. Am. Chem. Soc. 2011, 133, 14280-14286).

DOI： 10.1021/jp309502j

Language：English   Publishing type：Research paper (scientific journal)  

Novel tetracationic pyrene derivative (1,3,6,8-tetrakis(N-methylpyridinium-4-yl)pyrene, Py4+) was synthesized. Photochemical properties such as fluorescence quantum yield and fluorescence lifetime were observed for Py4+ and Py4+/clay complexes. Judging from Lambert-Beer plot analysis, Py4+ molecules adsorb on the clay surface without aggregation up to 69&#37; versus cation exchange capacity of the clay. Py4+ molecule emits strong fluorescence from an excited state of monomer, while the emission from excimer was not detected, in spite of high density adsorption condition on the solid surface. It is supposed that strong interaction between host and guest by the 'Size-Matching Effect' inhibits the formation of excimer on the clay surface. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2012.08.079

Language：English   Publishing type：Research paper (scientific journal)  

The mechanism inducing the unique absorption spectral shifts of porphyrin molecules upon adsorption on the clay surface was experimentally confirmed to be the flattening of the meso substituent with respect to the plane of the porphyrin ring. We investigated the spectral shift systematically by using seven types of porphyrin derivatives, differing in their center metal, meso substituent, and number of cationic sites. The aggregation, which usually induces the spectral shift, is suppressed in our clay/porphyrin systems. The adsorption strengths of porphyrin molecules on the clay surface were estimated as the relative adsorption equilibrium constants K-rel. The seven types of porphyrins studied had different values of K-rel, which can be explained by the steric effect and the Coulomb interaction due to the differences in the molecular structure. The obtained K-rel values have interesting information of the photochemical property of the clay/porphyrin complexes. The absorption spectral shifts of the porphyrin Soret bands between those in the bulk solution and those on the clay surface are well related to K-rel values. Like this, by the systematic experiments using the series of porphyrin derivatives, it was directly confirmed that the flattening of the molecule is the dominant mechanism for the spectral shift on the surface of inorganic nanosheets.

DOI： 10.1021/jp300842f

Language：English   Publishing type：Research paper (scientific journal)  

The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was investigated by photochemical energy transfer reaction. Three procedures were examined for the preparation of the clay/porphyrin complexes: (i) coadsorption (CA) method, (ii) sequential adsorption (SA) method, and (iii) independent adsorption (IA) method as described in the text. Efficient and moderate energy transfer reactions were. observed in the CA and SA complexes, respectively. On the contrary, the energy transfer did not occur in the IA complex. These results indicate that the microadsorption structure of the two kinds of porphyrin on the clay Mineral surface resulting from the sample preparation methods, affects the energy transfer efficiency. As a result, it was revealed that (i) the adsorbed porpbyrins can move on the day mineral surface but cannot move from one day surface to another clay sheet, and (ii) the integration structure of two kinds of porphyrin is more stable than the segregation structure in the present system. This unusual,structure originated from an extremely strong electrostatic interaction between the porphyrin and the day mineral as a result Of a "size-matching rule". These unique strongly fixed dye assemblies on the clay mineral surface, in which the aggregation and Segregation of dyes are suppressed, is very promising and attractive for constructing efficient photochemical reaction systems.

DOI： 10.1021/am201465a

Language：English   Publishing type：Research paper (scientific journal)  

Saponite-type days that have different cation exchange capacities were successfully synthesized by hydrothermal synthesis. The structure and properties were analyzed by X-ray diffraction, X-ray fluorescence, Al-27 NMR, FT-IR, thermo-gravimetric and differential thermal analysis, atomic force microscopy, and cation exchange capacity measurement. The inter-charge distances on the synthetic saponite (SS) surfaces were calculated to be 0.8-1.9 nm on the basis of a hexagonal array. The complex formation behavior between SS and cationic porphyrins was examined. It turns out that the average intermolecular distance between porphyrin molecules on the SS surface can be controlled, depending on the charge density of the SS. In the case of tetrakis(1-methylpyridinium-4-yl)porphyrin (H2TMPyP4+), the average intermolecular distances on the SS surface can be controlled from 2.3 to 3.0 nm on the basis of a hexagonal array. It was also found that absorption maxima of porphyrins depend on the charge density of the SS. The adsorption behavior of porphyrin on the SS surface can be rationally understood by the previously reported "size-matching rule". This methodology using host-guest interaction can realize a unique adsorption structure control of the porphyrin molecule on the SS surface, where the gap distance between guest porphyrin molecules is rather large. These findings will be highly valuable to construct photochemical reaction systems such as energy transfer in the complexes.

DOI： 10.1021/la202231k

Language：English   Publishing type：Research paper (scientific journal)  

The quantitative excited energy transfer reaction between cationic porphyrins on an anionic clay surface was successfully achieved. The efficiency reached up to ca. 100&#37; owing to the "Size-Matching Rule" as described in the text. It was revealed that the important factors for the efficient energy transfer reaction are (i) suppression of the self-quenching between adjacent dyes, and (ii) suppression of the segregated adsorption structure of two kinds of dyes on the clay surface. By examining many different kinds of porphyrins, we found that tetrakis(1-methylpyridinium-3-yl) porphyrin (m-TMPyP) and tetrakis(1-methylpyridinium-4-yl) porphyrin (p-TMPyP) are the suitable porphyrins to accomplish a quantitative energy transfer reaction. These findings indicate that the clay/porphyrin complexes are promising and prospective candidates to be used for construction of an efficient artificial light-harvesting system.

DOI： 10.1021/ja204425u

Language：English  

WHAT LOWERS THE EFFICIENCY OF AN ENERGY TRANSFER REACTION BETWEEN PORPHYRIN DYES ON CLAY SURFACE?(TMC2010)
Excited energy transfer reaction from tetrakis(1-methylpyridinium-2-yl) porphyrin (o-TMPyP) to tetrakis(1-methylpyridinium-4-yl) porphyrin (p-TMPyP) on an anionic clay surface was investigated. The energy transfer efficiency and quenching efficiency due to an electron transfer were quantitatively estimated. Both the energy transfer efficiency and quenching efficiency increased as the dye loadings increased. By a comparison with the results of other porphyrin combination systems, it was found that the major factor for lowering the energy transfer efficiency was the self-quenching of the donor porphyrin on the clay surface. Since the self-quenching was effectively suppressed by the strong adsorption of porphyrin on the clay surface due to the Size-Matching Effect, relatively efficient energy transfer was achieved. For constructing an efficient energy transfer system, such as an artificial light-harvesting system, a suppression of the self-quenching of dyes on the clay surface should be important.

DOI： 10.11362/jcssjclayscience.15.4_169

Language：English   Publishing type：Research paper (scientific journal)  

A novel optically transparent membrane composed of porphyrin-clay mineral complexes was developed. Reversible solvatochromism behavior of the membrane seas successfully observed, due to an orientation change of porphyrin in the clay interlayer space. The lambda(max) value of porphyrin seas 423 nm in acetone, while it was 464 nm in hexane. The color of the membrane changed from pink to green through to brown, when Sri porphyrin was used. The mechanism for solvatochromism in the present system is very unique compared to those for conventionally reported materials.

DOI： 10.1021/la1007928

Language：English  

A UNIQUE "FLATTENING EFFECT" OF CLAY ON THE PHOTOCHEMICAL PROPERTIES OF METALLOPORPHYRINS(2010 TMC Special Paper)
Clay-porphyrin complex formation and spectral behaviour of metalloporphyrins containing di-, tri- and tetravalent central metals with synthetic clay were examined. The spectral shift of porphyrin Soret band to higher wavelengths was observed upon the complex formation, where the clay sheets were either exfoliated or stacked in aqueous colloidal suspension. Moreover, the degree of the spectral shift decreased as the valence of porphyrin central metal increased. Since tri- and tetravalent metals have one and two axial ligands, respectively, their steric effect on porphyrin ring plane affected the extent of the "flattening" (i.e. co-planarization of porphyrin ring and peripheral aromatic rings) on the clay surface, thus influencing the spectral shift in porphyrin absorption spectra. These observations support the proposed hypothesis that "flattening" of porphyrin molecules on the clay surface induces the spectral shift of porphyrin Soret band. With this "flattening effect" of the clay surface, the λ_<max> value of Mg(II)TMPyP porphyrin reached up to 500nm in the stacked clay complex. These results indicate that the utilizing a combination of porphyrin with clay turned out to be unique to control the photochemical properties of porphyrins.

DOI： 10.11362/jcssjclayscience.14.6_235

Responsible for pages：総ページ数：v, 208p, 図版 [4] p   Language：Japanese  

Responsible for pages：総ページ数：2, 10, 405, 11p, 図版13p   Language：Japanese  

Responsible for pages：総ページ数：vii, 235p   Language：Japanese  

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Atomic scale imaging of a free-standing monolayer clay mineral nanosheet by aberration corrected scanning transmission electron microscopy

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2013.9

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Event date： 2013

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Event date： 2013

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Event date： 2013

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Event date： 2013

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Event date： 2012.7

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Event date： 2012

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Event date： 2012

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Event date： 2012

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Event date： 2012

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Event date： 2012

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Event date： 2012

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Event date： 2012

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Event date： 2011

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Event date： 2011

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Event date： 2011

Language：Japanese  

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Event date： 2011

Language：Japanese  

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Event date： 2011

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Event date： 2011

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Event date： 2010.9

Language：Japanese  

Country：Other  

Event date： 2010.9

Language：Japanese  

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Event date： 2010.6

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Event date： 2010

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Event date： 2010

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Event date： 2010

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Event date： 2010

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Event date： 2009.9

Language：Japanese  

Country：Other  

Event date： 2009.9

Language：Japanese  

Country：Other  

Event date： 2009.9

Language：Japanese  

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Event date： 2009.9

Language：Japanese  

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Event date： 2009

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Language：Others  

Country：Other  

Language：Others  

Country：Other  

Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Presentation type：Oral presentation (invited, special)  

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Language：Others  

Language：Others  

Language：Others  

Language：Others  

Language：Others  

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Type：Competition, symposium, etc. 

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Type：Competition, symposium, etc. 

Type：Scientific advice/Review 

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Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency