Publications by authors named "Shun Dekura"

Article Synopsis
  • - Chiral molecular assemblies are studied for their unique physical properties, particularly in spin-selective electron transport, and the research focuses on cation-anion salts of azolium cations with chiral camphorsulfonate and their racemic forms.
  • - The study found that while cations with triazolium showed better proton conductivity and lower activation energy in homochiral forms, imidazolium cations displayed similar conductivity in both homochiral and racemic forms.
  • - The differences in molecular motion were significant: the homochiral triazolium exhibited coupled rotational and translational motion, while its racemic counterpart had steady rotational motion, highlighting how controlling molecular movements in chiral crystals can enhance
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  • Mixed-stack complexes made up of alternating donor and acceptor materials generally have poor electrical conductivity due to either being neutral or highly ionic, leading to a lack of conductive carriers.
  • This study successfully synthesized mixed-stack complexes at the neutral-ionic boundary, using specific donors and acceptors with compatible energy levels and orbital symmetry.
  • The resulting single-crystal complexes displayed greatly enhanced room-temperature conductivity, which is the highest reported for this type under normal conditions, and revealed significant changes in their electrical and optical properties based on temperature.
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  • Bent ligands with heteroatoms are important in creating supramolecular structures, but typically divalent group 16 elements are favored due to sterics.
  • This study focuses on metal-organic frameworks (MOFs) created with dipyridinoarsoles (DPAs), where one MOF type showed dynamic behavior and stable structure while another collapsed upon solvent removal.
  • It also highlights the differences in performance between arsenic-based and phosphorus-based ligands in MOFs, marking the first exploration of how these factors influence the properties of such materials.
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  • - Conductive polymers, like doped PEDOT, are widely used in organic electronics but suffer from structural inhomogeneity, making it hard to control their conductivity and structure.
  • - Low-molecular-weight materials have well-defined structures but limited conductivity control, leading researchers to create oligomer-based conductors that blend the benefits of both polymers and low-molecular-weight materials.
  • - By studying various oligoEDOT analogs, the researchers developed conductors with tunable conductivities, including some reaching metallic states at room temperature, while identifying charge-transfer interactions as the key factor influencing conductivity.
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  • Modern organic conductors can be classified into low-molecular-weight and polymer-based materials, each with their own challenges in controlling conductive properties due to structural limitations.
  • Research focused on using single-molecular-weight oligomers as an alternative, specifically modeling a structure similar to doped poly(3,4-ethylenedioxythiophene) (PEDOT) to optimize electrical conductivity.
  • By creating a tetramer with a specific mixed sequence, the researchers achieved a significant increase in conductivity (36 S cm), the highest reported for single-crystalline oligomer conductors, and observed metallic behavior above room temperature for the first time in oligoEDOT.
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  • Organic semiconductors have high charge carrier mobility that greatly depends on the π-orbital overlap between neighboring molecules.* -
  • The study focused on how slight changes in molecular arrangements (without chemical modifications) affect charge carrier mobility by synthesizing disulfonic acid and organic salts with butylamine isomers.* -
  • While the overall structure of the organic salts was similar, variations in steric hindrance influenced the photoconductivity, leading to a two-fold difference despite similar arrangements and theoretical charge carrier mobilities. *
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Utilizing molecular motion is essential for the use of anhydrous superprotonic molecular proton conductors (σ beyond 10  S cm ) as electrolytes in hydrogen fuel cells. However, molecular motion contributing to the improvement of intrinsic proton conduction has been limited and little clarified in relation to the proton conduction mechanism, limiting the development of material design guidelines. Here, a salt with a three-dimensional (3D) hydrogen-bonded (H-bonded) phosphate network with imidazolium cations installed inside was studied, whose components are known to exhibit molecular motions that contribute to proton conduction.

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Proton-electron-coupled reactions, specifically proton-coupled electron transfer (PCET), in biological and chemical processes have been extensively investigated for use in a wide variety of applications, including energy conversion and storage. However, the exploration of the functionalities of the conductivity, magnetism, and dielectrics by proton-electron coupling in molecular materials is challenging. Dynamic and static proton-electron-coupled functionalities are to be expected.

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The conjugation length is a unique structural factor for oligomer-based π-conjugated conductors as it modulates their electronic structures. Herein, we demonstrated the conjugation length effects on conductivity by comparing a dimer and trimer of single-crystalline oligo(3,4-ethylenedioxythiophene) radical cation salts. The dimer showed a uniform-stacked columnar structure, while the trimer showed stacked columns of the π-dimerized donor and weaker intracolumnar interactions.

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  • - The study investigates the proton conduction mechanisms in anhydrous organic crystalline materials with imidazolium hydrogen succinate (Im-Suc), which are promising for solid electrolytes in fuel cells due to their high proton conductivity above 100 °C.
  • - Quantum chemical calculations were employed to analyze changes in hydrogen bonding and molecular rotation, helping to characterize the local structures essential for effective proton conduction.
  • - Findings indicate that proton transfer between imidazole and succinic acid is a key rate-limiting step in proton transport, revealing that proton conduction operates through a combination of proton transfer and molecular motion in a Grotthuss-type mechanism.
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Ferroelectric spin crossover (SCO) behavior is demonstrated to occur in the cobalt(II) complex, [Co(FPh-terpy) ](BPh ) ⋅3ac (1⋅3 ac; FPh-terpy=4'-((3-fluorophenyl)ethynyl)-2,2':6',2''-terpyridine) and is dependent on the degree of 180° flip-flop motion of the ligand's polar fluorophenyl ring. Single crystal X-ray structures at several temperatures confirmed the flip-flop motion of fluorobenzene ring and also gave evidence for the SCO behavior with the latter behavior also confirmed by magnetic susceptibility measurements. The molecular motion of the fluorobenzene ring was also revealed using solid-state F NMR spectroscopy.

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Invited for the cover of this issue is the group of Tomoko Fujino and Hatsumi Mori at the University of Tokyo. The image depicts the structural information of doped PEDOT uncovered by the single-crystalline EDOT dimer model. Read the full text of the article at .

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Although doped poly(3,4-ethylenedioxythiophene) (PEDOT) is extensively used in electronic devices, their molecular-weight distributions and inadequately defined structures have hindered the elucidation of their underlying conduction mechanism. In this study, we introduce the simplest discrete oligomer models: EDOT dimer radical cation salts. Single-crystal structural analyses revealed their one-dimensional (1D) columnar structures, in which the donors were uniformly stacked.

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Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br](SO)·32HO (dach: (1R, 2R)-(-)-1,2-diaminocyclohexane; bpy: 4,4'-bipyridine).

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We investigated the relationship between crystalline disorder and electronic structure deviations of Pd nanoparticles (NPs) and their hydrogen storage properties as a function of their particle diameter (2.0, 4.6 and 7.

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One of the key issues for an upcoming hydrogen energy-based society is to develop highly efficient hydrogen-storage materials. Among the many hydrogen-storage materials reported, transition-metal hydrides can reversibly absorb and desorb hydrogen, and have thus attracted much interest from fundamental science to applications. In particular, the Pd-H system is a simple and classical metal-hydrogen system, providing a platform suitable for a thorough understanding of ways of controlling the hydrogen-storage properties of materials.

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We report a hybrid solid system, UMOM-100-a and UMOM-100-b, synthesized by incorporation of Cu-based metal-organic polyhedra (MOPs) into a porous metal-organic framework (MOF) host, PCN-777. The MOP guests have acid (SO) functional groups, acting as functionalized nanocages, whereas the porosity is still maintained for proton conductivity. The key parameter for the UMOM-100 series is the number of MOPs inside a MOF, which controls the ratio between meso- and micropores, polarity, and finally proton conductivity.

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The palladium-hydrogen system is one of the most famous hydrogen-storage systems. Although there has been much research on β-phase PdH(D) , we comprehensively investigated the nature of the interaction between Pd and H(D) in α-phase PdH(D) (x<0.03 at 303 K), and revealed the existence of Pd-H(D) chemical bond for the first time, by various in situ experimental techniques and first-principles theoretical calculations.

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The synthesis of a new ionic plastic crystal, tetraethylammonium-d d-10-camphorsulfonate, is reported. The crystal has three solid phases, the structures of which were determined by single-crystal X-ray diffraction (XRD). XRD analysis revealed a phase transition from nonpolar space group P222 to polar space group P2 with increasing temperature.

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Understanding the role that crystal imperfections or defects play on the physical properties of a solid material is important for any application. In this report, the highly unique crystal structure of the metal-organic framework (MOF) zirconium 2-sulfoterephthalate is presented. This MOF contains a large number of partially occupied ligand and metal cluster sites which directly affect the physical properties of the material.

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Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state (2)H NMR and hydrogen pressure-composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response.

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