On a subnanometer scale, an only one-atom difference in a metal cluster may cause significant transitions in the catalytic activity due to the electronic and geometric configurations. We now report the atomicity-specific catalytic activity of platinum clusters with significantly small atomicity, especially below 20. The atomic coordination structure is completely different from that of the larger face-centered cubic (fcc) nanocrystals. Here, an electrochemical study on such small clusters, in which the atomicity ranged between 12 and 20, revealed Pt₁₉ as the most catalytically active species. In combination with a theoretical study, a common structure that leads to a high catalytic performance is proposed.

On a subnanometer scale, an only one-atom difference in a metal cluster may cause significant transitions in the catalytic activity due to the electronic and geometric configurations. We now report the atomicity-specific catalytic activity of platinum clusters with significantly small atomicity, especially below 20. The atomic coordination structure is completely different from that of the larger face-centered cubic (fcc) nanocrystals. Here, an electrochemical study on such small clusters, in which the atomicity ranged between 12 and 20, revealed Pt₁₉ as the most catalytically active species. In combination with a theoretical study, a common structure that leads to a high catalytic performance is proposed.

Phenylazomethine dendrimers (DPA) can precisely incorporate metal chlorides onto the imine sites in a stepwise fashion. Such precise dendrimer–metal complexes allow the preparation of size-controlled subnanometer metal particles. We now propose a novel approach for the fabrication of size-controlled subnanometer metal oxide dots isolated on a substrate using two different-type dendrimers. One is a fourth-generation phenylazomethine dendrimer (DPAG4) and the other is a benzylether dendrimer (BzEG3) with a zinc porphyrin core. Even though the diameter of BzEG3 corresponds to that of DPAG4, BzEG3 has no metal-complexing site. Upon dip coating on a highly oriented pyrolytic graphite substrate by the mixed solution of the metal chloride-assembling DPAG4 molecules and BzEG3 molecules, the dendrimer monolayer was immobilized on the substrate. The concentration of the dendrimer mixture was determined in order to separate each DPAG4–metal chloride complex molecule by BzEG3. Monodispersed metaloxide nanodot arrays could be obtained from the dendrimer monolayer in which DPAG4–metal chloride complex molecule is well isolated by the BzEG3 as a spacer after the hydrolysis of metal chlorides followed by the complete removal of dendrimers. Copyright © 2013 John Wiley & Sons, Ltd.

Phenylazomethine dendrimers, which can be used as the template for precise metal nanoparticles, are soluble only in aprotic media. The use of a specific surfactant enabled their solubilization in aqueous solutions. Under dilute condition, they formed discrete micelles with a size close to the that of the dendrimer. Condensation resulted in their aggregation; however, they remained in a homogeneous solution without precipitation. Furthermore, each micelle was well isolated. The triplet-excited state of the zinc porphyrin core in the micelles was significantly stable, suggesting the formation of rigid core-shell micelles preventing any external molecules from approaching to the core.

The aerobic oxidative polymerization of 2,6-difluorophenol (F₂PhOH) catalyzed by copper(II) for assembling dendritic ligands was studied. Although the mono-metallic complex of copper(II) chloride with a dendritic phenylazomethine (DPAG4) efficiently catalyzed this polymerization reaction without any additive bases, a significant increase in the molecular weight of the product polymer was observed when an iron(III) complex was added to the copper(II)–dendrimer system. The synergistic enhancement based on the copper–iron bimetallic system provided a higher molecular weight product polymer in addition to the high yield. Copyright © 2011 John Wiley & Sons, Ltd.

New dendritic poly(phenylazomethine)s (DPAs) with dodecyl end groups (C12DPA) have been synthesized. C12DPA showed stepwise radial complexation with metals as a metal-storage nanocapsule. Through modification with dodecyl, the properties of environmental responsiveness and self-assembly become apparent for C12DPA as a π-conjugated soft material. The dodecyl-modified DPAs (C12DPAG4) were synthesized up to the fourth generation dendrimer, for the first time, which is a nanocapsule with a basic atmosphere for metal complexes in a hydrophobic environment. In addition, we found a suitable structure and conditions for the fibrous self-assembly of DPA through the precise design of its dendritic structure. C12DPA, with an asymmetric structure, showed a fibrous assembly by a solvent drop-casting. The metal-complexed C12DPA showed an assembly different from the fibrous one through metal complexation on DPA imines. Interestingly, the vesicular assembly structure of C12DPA has been observed by the complexation of CuCl₂ in toluene. In this study, we investigated the unique properties of C12DPA as a novel π-conjugated soft material.

The aerobic oxidative polymerization of phenol derivatives can provide poly(phenylene oxide)s, which are known as engineering plastics. This oxidation can be carried out with atmospheric oxygen molecules as the oxidizing reagent in the presence of copper complexes as the catalyst; however, stoichiometric or excess amounts of bases are also generally required. By using a phenylazomethine dendrimer complexed with several equivalent amounts of copper chloride, the additive (base)-free polymerization of 2,6-difluorophenol was successful with a very small amount of the catalyst (0.7 mol % of copper for the monomer) because the dendrimer was composed of many Schiff base units, affording a base and catalyst (copper complex) condensed reaction field. The resulting polymer was nearly linear and the molecular weight was very high. When the equimolar amount of the copper complex in one dendrimer molecule was increased, the polymer obtained under this reaction condition was rather branched, resulting in a higher glass transition temperature.