5 research outputs found
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 polyÂ(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 humidityÂ(RH))
as the inputs for the statistical analysis
Magic Number Pt<sub>13</sub> and Misshapen Pt<sub>12</sub> 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 (Pt<sub>13</sub>). 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 Pt<sub>12</sub> cluster exhibited
more than 2-fold catalytic activity compared with that of the Pt<sub>13</sub> cluster. ESI-TOF-mass and EXAFS analyses provided information
about the structures. These analyses suggested that the Pt<sub>12</sub> has a deformed coordination, while the Pt<sub>13</sub> 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