4 research outputs found

    Enhancing the Photoelectric Effect with a Potential-Programmed Molecular Rectifier

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    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

    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

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    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

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    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>

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    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
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