4 research outputs found
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
Competition between the Direct Exchange Interaction and Superexchange Interaction in Layered Compounds LiCrSe<sub>2</sub>, LiCrTe<sub>2</sub>, and NaCrTe<sub>2</sub> with a Triangular Lattice
Physical properties of new <i>S</i> = 3/2 triangular-lattice compounds LiCrSe<sub>2</sub>,
LiCrTe<sub>2</sub>, and NaCrTe<sub>2</sub> have been investigated
by X-ray diffraction and magnetic measurements. These compounds crystallize
in the ordered NiAs-type structure, where alkali metal ions and Cr
atoms stack alternately. Despite their isomorphic structures, magnetic
properties of these three compounds are different; NaCrTe<sub>2</sub> has an A-type spin structure with ferromagnetic layers, LiCrTe<sub>2</sub> is likely to exhibit a helical spin structure, and LiCrSe<sub>2</sub> shows a first-order-like phase transition from the paramagnetic
trigonal phase to the antiferromagnetic monoclinic phase. In these
compounds and the other chromium chalcogenides with a triangular lattice,
we found a general relationship between the Curie–Weiss temperature
and magnetic structures. This relation indicates that the competition
between the antiferromagnetic direct <i>d</i>-<i>d</i> exchange interaction and the ferromagnetic superexchange interaction
plays an important role in determining the ground state of chromium
chalcogenides
Pickering Emulsions Prepared by Layered Niobate K<sub>4</sub>Nb<sub>6</sub>O<sub>17</sub> Intercalated with Organic Cations and Photocatalytic Dye Decomposition in the Emulsions
We investigated emulsions stabilized with particles of
layered
hexaniobate, known as a semiconductor photocatalyst, and photocatalytic
degradation of dyes in the emulsions. Hydrophobicity of the niobate
particles was adjusted with the intercalation of alkylammonium ions
into the interlayer spaces to enable emulsification in a toluene–water
system. After the modification of interlayer space with hexylammonium
ions, the niobate stabilized water-in-oil (w/o) emulsions in a broad
composition range. Optical microscopy showed that the niobate particles
covered the surfaces of emulsion droplets and played a role of emulsifying
agents. The niobate particles also enabled the generation of oil-in-water
(o/w) emulsions in a limited composition range. Modification with
dodecylammonium ions, which turned the niobate particles more hydrophobic,
only gave w/o emulsions, and the particles were located not only at
the toluene–water interface but also inside the toluene continuous
phase. On the other hand, interlayer modification with butylammonium
ions led to the formation of o/w emulsions. When porphyrin dyes were
added to the system, the cationic dye was adsorbed on niobate particles
at the emulsion droplets whereas the lipophilic dye was dissolved
in toluene. Upon UV irradiation, both of the dyes were degraded photocatalytically.
When the cationic and lipophilic porphyrin molecules were simultaneously
added to the emulsions, both of the dyes were photodecomposed nonselectively
Magnetic–Nonmagnetic Phase Transition with Interlayer Charge Disproportionation of Nb<sub>3</sub> Trimers in the Cluster Compound Nb<sub>3</sub>Cl<sub>8</sub>
We
grew large single crystals of the cluster magnet Nb<sub>3</sub>Cl<sub>8</sub> with a magnetic triangular lattice and investigated
its magnetic properties and crystal structure. In Nb<sub>3</sub>Cl<sub>8</sub>, the [Nb<sub>3</sub>]<sup>8+</sup> cluster has a single unpaired
spin, making it an <i>S</i> = 1/2 triangular lattice anti-ferromagnet.
At low temperatures, Nb<sub>3</sub>Cl<sub>8</sub> exhibits a magnetic–nonmagnetic
phase transition driven by a charge disproportionation, in which the
paramagnetic [Nb<sub>3</sub>]<sup>8+</sup> clusters transform into
alternating layers of nonmagnetic [Nb<sub>3</sub>]<sup>7+</sup> and
[Nb<sub>3</sub>]<sup>9+</sup> clusters. The observed exotic phenomenon
with the strong correlation between the magnetism and structure are
based on the nature of the cluster magnetism