Extended Potential-Gradient Architecture of a Phenylazomethine Dendrimer

A dendritic nanoshell based on rigid phenylazomethine units was synthesized up to fifth generation around a zinc porphyrin core. Due to the finely organized sparse architecture, accessibility to the core can be discriminated by the size of the molecules and ionic species. By using this function, the lifetime of the photochemically produced radical ion pair can be extended over 200 times longer along with a good quantum yield

Enhancing the Photoelectric Effect with a Potential-Programmed Molecular Rectifier

Dendrimer-based electron rectifiers were applied to photoconducting devices. A remarkable enhancement of the photocurrent response was observed when a zinc porphyrin as the photosensitizer was embedded in the dendritic phenylazomethine (DPA) architecture. The dendrimer-based sensitizer exhibited a 20-fold higher current response than the non-dendritic zinc porphyrin. In sharp contrast, a similar application of the dendrimer with poly­(vinylcarbazole) as the electron donor resulted in a decreased response. This is consistent with the idea that the DPA facilitates electron transfer from the core to its periphery along a potential gradient, as predicted by density functional theory calculations

Control of Single Molecular Nanodot Patterns of Phenyl Azomethine Dendrimers by Statistical Simulation

Precisely synthesized subnanometer particles of metals or metal oxides can be prepared using dendritic polyphenyl azomethines as the template. With a goal of their arrays to a surface using a simple and quick process, such as spin-casting, statistical analyses were applied to a nanodot array of the dendrimers to obtain the relationship between the experimental condition and the results such as size, spacing, or its standard deviations. The dot patterns of a single molecular dendrimer on a substrate were able to be predicted with numerical values of the experimental parameters associated with the spin coat (concentration of the dendrimer, physical properties of solvent, the spin coating recipe, temperature of the solution, relative humidity­(RH)) as the inputs for the statistical analysis

Magic Number Pt₁₃ and Misshapen Pt₁₂ Clusters: Which One is the Better Catalyst?

A relationship between the size of metal particles and their catalytic activity has been established over a nanometer scale (2–10 nm). However, application on a subnanometer scale (0.5–2 nm) is difficult, a possible reason being that the activity no longer relies on the size but rather the geometric structure as a cluster (or superatomic) compound. We now report that the catalytic activity for the oxygen reduction reaction (ORR) significantly increased when only one atom was removed from a magic number cluster composed of 13-platinum atoms (Pt₁₃). The synthesis with an atomic-level precision was successfully achieved by using a dendrimer ligand as the macromolecular template strictly defining the number of metal atoms. It was quite surprising that the Pt₁₂ cluster exhibited more than 2-fold catalytic activity compared with that of the Pt₁₃ cluster. ESI-TOF-mass and EXAFS analyses provided information about the structures. These analyses suggested that the Pt₁₂ has a deformed coordination, while the Pt₁₃ has a well-known icosahedral atomic coordination as part of the stable cluster series. Theoretical analyses based on density functional theory (DFT) also supported this idea. The present results suggest potential activity of the metastable clusters although they have been “missing” species in conventional statistical synthesis

Non-Functionalized Subnanometer Copper Nanoparticles for Low-Temperature Methane Activation

Subnanostructured particles (SNPs) have recently attracted attention as potential materials to activate inert molecules such as methane. Copper-based SNPs particularly have been focused on activating methane at low temperatures. However, conventional SNPs have often been prepared starting from multinuclear metal complexes stabilized by organic ligands or single-site heterogeneous catalysts in porous materials to avoid aggregation of the SNPs, and the reasons for enhancement of reactivities with a decrease in the particle size have been uncleared by a variety of factors involving the ligand effect. The reactivities of SNPs without organic ligands or cages have not been revealed to date. Herein, we present the precise preparation and unique atomic configuration of naked subnano copper minerals, which were not covered with any protecting ligands. Methane activation was achieved with naked copper SNPs under mild conditions. These results highlight the structural reasons in the copper SNPs for reactivities that provide significant enhancement of the reactivity of methane molecules with molecular oxygen