研究者詳細 - 山本　崇史

論文 - 山本　崇史

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Thermoresponsive, Freezing-Resistant Smart Windows with Adjustable Transition Temperature Made from Hydroxypropyl Cellulose and Glycerol

Nakamura C., Yamamoto T., Manabe K., Nakamura T., Einaga Y., Shiratori S.

Industrial and Engineering Chemistry Research （Industrial and Engineering Chemistry Research） 58 （ 16 ） 6424 - 6428 2019年04月

共著, ISSN 08885885

© 2019 American Chemical Society. A thermoresponsive smart window that can switch its transmittance to control heating from sunlight is attracting great attention. Such windows made from a hydrogel of a thermoresponsive polymer such as poly(N-isopropylacrylamide) (PNIPAm) or hydroxypropyl cellulose (HPC) have been successful and can switch their transmittance at room temperature. However, such hydrogels occasionally freeze in cold places, degrading their transmittance. Thus, a thermoresponsive hydrogel that can be used in various geographical regions is desired. Here, we produced a thermoresponsive smart window with freezing resistance made from HPC and glycerol. We could adjust its switching temperature by simply changing the amount of added glycerol, letting us easily change it to room temperature for practical use. These smart windows show high cyclic performance, freezing resistance, and heat shielding, demonstrating great potential.

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In situ spectroscopic study on the surface hydroxylation of diamond electrodes

Kasahara S., Ogose T., Ikemiya N., Yamamoto T., Natsui K., Yokota Y., Wong R., Iizuka S., Hoshi N., Tateyama Y., Kim Y., Nakamura M., Einaga Y.

Analytical Chemistry （Analytical Chemistry） 91 （ 8 ） 4980 - 4986 2019年

研究論文（学術雑誌）, 共著, ISSN 00032700

© 2019 American Chemical Society. Carbon-based materials are regarded as an environmentally benign alternative to the conventional metal electrode used in electrochemistry from the viewpoint of sustainable chemistry. Among various carbon electrode materials, boron-doped diamond (BDD) exhibits superior electrochemical properties. However, it is still uncertain how surface chemical species of BDD influence the electrochemical performance, because of the difficulty in characterizing the surface species. Here, we have developed in situ spectroscopic measurement systems on BDD electrodes, i.e., in situ attenuated total reflection infrared spectroscopy (ATR-IR) and electrochemical X-ray photoelectron spectroscopy (EC-XPS). ATR-IR studies at a controlled electrode potential confirmed selective surface hydroxylation. EC-XPS studies confirmed deprotonation of C-OH groups at the BDD/electrolyte interface. These findings should be important not only for better understanding of BDD's fundamentals but also for a variety of applications.

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High-temperature cooperative spin crossover transitions and single-crystal reflection spectra of [Fe^III(qsal)₂](CH₃OSO₃) and related compounds

Takahashi K., Yamamoto K., Yamamoto T., Einaga Y., Shiota Y., Yoshizawa K., Mori H.

Crystals （Crystals） 9 （ 2 ） 2019年

共著, ISSN 2073-4352

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. New Fe(III) compounds from qsal ligand, [Fe(qsal) 2 ](CH 3 OSO 3 ) (1) and [Fe(qsal) 2 ](CH 3 SO 3 )·CH 3 OH (3), along with known compound, [Fe(qsal) 2 ](CF 3 SO 3 ) (2), were obtained as large well-shaped crystals (Hqsal = N-(8-quinolyl)salicylaldimine). The compounds 1 and 2 were in the low-spin (LS) state at 300 K and exhibited a cooperative spin crossover (SCO) transition with a thermal hysteresis loop at higher temperatures, whereas 3 was in the high-spin (HS) state below 300 K. The optical conductivity spectra for 1 and 3 were calculated from the single-crystal reflection spectra, which were, to the best of our knowledge, the first optical conductivity spectra of SCO compounds. The absorption bands for the LS and HS [Fe(qsal) 2 ] cations were assigned by time-dependent density functional theory calculations. The crystal structures of 1 and 2 consisted of a common one-dimensional (1D) array of the [Fe(qsal) 2 ] cation, whereas that of 3 had an unusual 1D arrangement by π-stacking interactions which has never been reported. The crystal structures in the high-temperature phases for 1 and 2 indicate that large structural changes were triggered by the motion of counter anions. The comparison of the crystal structures of the known [Fe(qsal) 2 ] compounds suggests the significant role of a large non-spherical counter-anion or solvate molecule for the total lattice energy gain in the crystal of a charged complex.

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Electrochemical Pinacol Coupling of Acetophenone Using Boron-Doped Diamond Electrode

Nakahara K., Naba K., Saitoh T., Sugai T., Obata R., Nishiyama S., Einaga Y., Yamamoto T.

ChemElectroChem （ChemElectroChem） 6 （ 16 ） 4153 - 4157 2019年

共著, ISSN 2196-0216

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An electrochemical pinacol coupling reaction of acetophenone using a boron-doped diamond (BDD) electrode has been reported. This transformation is driven by the one-electron reduction of acetophenone on the BDD cathode, followed by an intermolecular radical coupling. Owing to the BDD's outstanding electrochemical properties, the pinacol-type compound has been obtained in good conversion yield. The roles of a supporting electrolyte and solvent were addressed; (1) lithium ions contribute to increase in the reactivity of the radical intermediate. (2) Addition of water promotes the electron transfer process at the BDD surface. The reaction is relatively tolerant to para-substituted acetophenone derivatives. Since electric current is directly employed as reducing reagents to generate a radical intermediate, the reaction is metal-free, sustainable, and inherently safe.

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Oxidative Cleavage of the Acyl-Carbon Bond in Phenylacetone with Electrogenerated Superoxide Anions

Zhang, Y., Sugai, T., Yamamoto, T., Yamamoto, N., Kutsumura, N., Einaga, Y., Nishiyama, S., Saitoh, T., Nagase, H.

ChemElectroChem （ChemElectroChem） 6 （ 16 ） 4194 - 4198 2019年

共著, 査読有り, ISSN 2196-0216

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An oxidative cleavage reaction of the acyl−carbon bond in phenylacetone derivatives under cathodic reduction is reported. This particular transformation is driven by the cathodic reduction of dissolved molecular oxygen to superoxide anions. Various cathode materials were examined, and we discovered that boron-doped diamond (BDD) enables highly efficient molecular conversion, owing to BDD's outstanding electrochemical property for utilizing the small amounts of molecular oxygen effectively. The scope of the reaction is broad and can be applied to a variety of substrates, ranging from ketones to esters and amides. As an electric current is directly employed to generate the superoxide anion, the reaction is metal- and catalyst-free. Electro-organic synthesis using the carbon-based BDD electrode thus provides access to sustainable molecular transformations.

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Controlled decoration of boron-doped diamond electrodes by electrochemical click reaction (e-CLICK)

Yamamoto Takashi, Akahori Miku, Natsui Keisuke, Saitoh Tsuyoshi, Einaga Yasuaki

CARBON （Carbon） 130 350 - 354 2018年04月

ISSN 0008-6223

© 2017 Elsevier Ltd Controlled surface functionalization of electrode materials is an important technique in various fields such as analytical chemistry, molecular electronics, and molecular recognition in biological systems. In this work, we report the control decoration of boron-doped diamond (BDD) electrodes by electrochemically driven copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of alkyne and azide (e−CLICK) in which the catalyst is produced by electroreduction of copper(II) species. As the e−CLICK strategy enabled to tune the produced amount of the copper(I) catalyst electrochemically, the alkyne-terminated BDD electrodes were decorated with azide-terminated ferrocene in a controlled manner.

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Molecular engineering of Rashba spin-charge converter

Nakayama H., Yamamoto T., An H., Tsuda K., Einaga Y., Ando K.

Science Advances （Science Advances） 4 （ 22 ） eaar3899-1 - eaar3899-7 2018年03月

共著, 査読有り, ISSN 2375-2548

© 2018 American Association for the Advancement of Science. All rights reserved. In heterostructures with broken inversion symmetry, the electrons' motion is coupled to their spin through interface-driven spin-orbit coupling: the Rashba effect. The Rashba effect enables the interconversion between spin and charge currents, offering a variety of novel spintronic phenomena and functionalities. However, despite the significant progress in Rashba physics, controlling the spin-charge conversion in metallic heterostructures remains a major challenge. We show that molecular self-assembly provides a way to engineer the Rashba spin-charge converters. We demonstrate that magnetoresistance and voltage generation originating from the spin-charge conversion in metallic heterostructures can be manipulated by decorating the surface with selfassembled organic monolayers through the cooperative molecular field effect. We also demonstrate reversible phototuning of the spin-charge conversion through light-driven molecular transformations using a molecule that can photoisomerize between the trans and cis states. These findings, with the almost-infinite chemical tunability of organic monolayers, pave the way toward molecular engineering of spin-orbit devices.

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Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged Fe^II Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine

Takahashi K., Okai M., Mochida T., Sakurai T., Ohta H., Yamamoto T., Einaga Y., Shiota Y., Yoshizawa K., Konaka H., Sasaki A.

Inorganic Chemistry （Inorganic Chemistry） 57 （ 3 ） 1277 - 1287 2018年02月

研究論文（学術雑誌）, 共著, ISSN 00201669

© 2018 American Chemical Society. A series of [FeII(L)2](BF4)2 compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2′ upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2′ demonstrated two-step and one-step abrupt SCO transitions, respectively. An X-ray single-crystal structural analysis revealed that one-dimensional and two-dimensional Fe cation networks linked by π stacking and sulfur-sulfur interactions were formed in 1 and 3, respectively. A thermodynamic analysis of the magnetic susceptibility for 1, 2′, and 3 suggests that the enthalpy differences may govern SCO transition behaviors in the polymorphic compounds 2′ and 3. A structural comparison between 1 and 3 indicates that the SCO behavior variations and crystal structure transformation in the present [FeII(L)2](BF4)2 compounds can be interpreted by the relationship between the lattice enthalpies mainly arising from Coulomb interactions between the Fe cations and BF4 anions as in typical ionic crystals.

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A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol

Yamamoto T., Riehl B., Naba K., Nakahara K., Wiebe A., Saitoh T., Waldvogel S., Einaga Y.

Chemical Communications （Chemical Communications） 54 （ 22 ） 2771 - 2773 2018年02月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 13597345

© 2018 The Royal Society of Chemistry. A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is easy to use, suitable for scale-up, and inherently safe.

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Spin-Singlet Transition in the Magnetic Hybrid Compound from a Spin-Crossover Fe(III) Cation and π-Radical Anion

Takahashi Kazuyuki, Sakurai Takahiro, Zhang Wei-Min, Okubo Susumu, Ohta Hitoshi, HYamamoto Takashi, HR, Einaga Yasuaki, Mori Hatsumi

Inorganics 5 （ 3 ） 54-1 - 54-14 2017年08月

共著, 査読有り

Gigantic Photomagnetic Effect at Room Temperature in Spiropyran-Protected FePt Nanoparticles

HYamamoto Takashi, HR, Yurieva Elena A, Tsuda Kento, Hosomi Tomoko, Aldoshin Sergey M, Einaga Yasuaki

Physica Status Solidi - Rapid Research Letters 11 （ 9 ） 1700161-1 - 1700161-5 2017年07月

共著, 査読有り

Photo-modulation of superconducting and magnetic properties

Takashi Yamamoto, Keisuke Natsui, Yasuaki Einaga

Photon-Working Switches （Springer Japan） 285 - 299 2017年05月

In this chapter, photo-modulation of superconducting and magnetic properties is described. First, the superconducting property of a boron-doped diamond is investigated, in which the critical current density varies dramatically between the hydrogen- and oxygen-terminated diamond. Second, the superconducting diamond is modified with an azobenzene molecular layer to modulate the superconductivity upon photoirradiation. In this composite superconductor, the critical current density is reversibly amplified by 55% upon photoisomerization of the azobenzene layer. Third, Prussian Blue, a coordination polymer, is integrated with the semiconducting titanium oxide nanosheets to modulate the magnetic property upon photoirradiation. In this magnetic heterostructure, photoinduced magnetic phase transition of Prussian Blue is present by injecting photoexcited electrons from titanium oxide nanosheets.

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Cooperative Spin-crossover Transition from Three-dimensional purely π-Stacking Interactions in a Neutral Heteroleptic Azobisphenolate Fe^III Complex with N₃O₃ Coordination Sphere

Murata Suguru, Takahashi Kazuyuki, Mochida Tomoyuki, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Dalton Transactions 46 （ 18 ） 5786 - 5789 2017年03月

共著, 査読有り

Cooperative Spin-crossover Transition from Three-dimensional purely π-Stacking Interactions in a Neutral Heteroleptic Azobisphenolate FeIII Complex with N3O3 Coordination Sphere

Murata Suguru, Takahashi Kazuyuki, Mochida Tomoyuki, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Dalton Transactions （Royal Society of Chemistry） 46 （ 18 ） 5786 - 5789 2017年

査読有り, ISSN 1477-9234

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Single-crystal-to-single-crystal transformation in hydrogen-bond-induced high-spin pseudopolymorphs from protonated cation salts with a π-extended spin crossover Fe(III) complex

Suguru Murata, Kazuyuki Takahashi, Tomoyuki Mochida, Takahiro Sakurai, Hitoshi Ohta, Takashi Yamamoto, Yasuaki Einaga

Polyhedron 2017年

査読有り

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Enhancement of the Coercivity in Co–Ni Layered Double Hydroxides by Increasing Basal Spacing

Zhang Cuijuan, Tsuboi Tomoya, Namba Hiroaki, Einaga Yasuaki, YAMAMOTO Takashi

Dalton Transactions （Royal Society of Chemistry） 45 （ 34 ） 13324 - 13331 2016年06月

共著, 査読有り, ISSN 1477-9234

The magnetic properties of layered double hydroxides (LDH) containing transition metal ions can still develop, compared with layered metal hydroxide salts which exhibit structure-dependent magnetism. In this article, we report the preparation of a hybrid magnet composed of Co-Ni LDH and n-alkylsulfonate anions (Co-Ni-CnSO3 LDH). As Co-Ni LDH is anion-exchangeable, we can systematically control the interlayer spacing by intercalating n-alkylsulfonates with different carbon numbers. The magnetic properties were examined with temperature- and field-dependent magnetization measurements. As a result, we have revealed that the coercive field depends on the basal spacing. It is suggested that increasing the basal spacing varies the competition between the in-plane superexchange interactions and long-range out-of-plane dipolar interactions. Moreover, a jump in the coercive field at around 20 Å of the basal spacing is assumed to be the modification of the magnetic ordering in Co-Ni-CnSO3 LDH.

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Highly Sensitive Detection of Influenza Virus by Boron-Doped Diamond Electrode Terminated with Sialic Acid-Mimic Peptide

Matsubara Teruhiko, Ujie Michiko, HYAMAMOTO Takashi, HR, Akahori Miku, Einaga Yasuaki, Sato Toshinori

Proceedings of the National Academy of Sciences of the United States of America 113 （ 32 ） 8981 - 8984 2016年06月

研究論文（学術雑誌）, 共著, 査読有り

The Role of Coulomb Interactions for Spin Crossover Behaviors and Crystal Structural Transformation in Novel Anionic Fe(III) Complexes from a π-Extended ONO Ligand

Murata Suguru, Takahashi Kazuyuki, Sakurai Takahiro, Ohta Hitoshi, YAMAMOTO Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari

Crystals （MDPI AG） 6 （ 5 ） 49-16pp 2016年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2073-4352

To investigate the pi-extension effect on an unusual negative-charged spin crossover (SCO) FeIII complex with a weak N2O4 first coordination sphere, we designed and synthesized a series of anionic FeIII complexes from a pi-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from pi-stacking interactions between pi-ligands of the FeIII complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2' may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and pi-stacking interactions induces a significant distortion of coordination structure of 2.

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Charge-Transfer Phase Transition of a Cyanide-Bridged Fe^II/Fe^III Coordination Polymer

Zhang Kuirun, Kang Soonchul, Yao Zi-Shuo, Nakamura Kazusa, YAMAMOTO Takashi, Einaga Yasuaki, Azuma Nobuaki, Miyazaki Yuji, Nakano Motohiro, Kanegawa Shinji, Sato Osamu

Angewandte Chemie International Edition 55 （ 20 ） 6047 - 6050 2016年04月

研究論文（学術雑誌）, 共著, 査読有り

Charge-Transfer Phase Transition of a Cyanide-Bridged FeII/FeIII Coordination Polymer

Zhang Kuirun, Kang Soonchul, Yao Zi-Shuo, Nakamura Kazusa, Yamamoto Takashi, Einaga Yasuaki, Azuma Nobuaki, Miyazaki Yuji, Nakano Motohiro, Kanegawa Shinji, Sato Osamu

Angewandte Chemie International Edition 55 （ 20 ） 6047 - 6050 2016年04月

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山本 崇史

論文 - 山本 崇史

山本　崇史

論文 - 山本　崇史