論文 - 山本　崇史

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

　概要を見る

© 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

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© 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

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© 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

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© 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

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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

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

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

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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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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

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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

Preparation of Dihydroquinazoline Carbohydrazone Fe(II) Complexes for Spin Crossover

Shen Fu-Xing, Huang Wei, Takashi Yamamoto, Einaga Yasuaki, Wu Dayu

New Journal of Chemistry （ROYAL SOC CHEMISTRY）  40 （ 5 ） 4534 - 4542 2016年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1144-0546

　概要を見る

Dihydroquinazoline FeII complexes, namely [Fe(pq-R)(2)](X)(2)center dot CH3OH center dot yCH(3)CN center dot zH(2)O (R = 2-py: X = ClO4-, x = 1, y = 0, z = 2 (1), BF4-, x = 0, y = 2, z = 1.75 (2), CF3SO3-, x = 1, y = 1, z = 0 (3); and X = ClO4-: R = 2-OCH3, x = 0, y = 0, z = 1 (4), R = 3-OCH3, x = 0, y = 0, z = 1 (5)), were prepared and the effects of the solvent, counteranion and ligand substituent on spin crossover properties were discussed. Comparison of X-ray diffraction data for these complexes revealed the sole presence of high-spin FeII at 298 K and the bond distances around the FeII center at low temperature fall much closer to those at high temperature, which is consistent with variable-temperature dc magnetic susceptibility data. However, the loss of solvent induced a significant change in the spin state of complexes 1 and 2. Moreover, fits to magnetic data of the desolvated samples provide crossover temperatures of T-1/2 = 182.9(6), 157.0(8) and 138.3(5) K for 1-des (ClO4-), 2-des (BF4-) and 3-des (CF3SO3-), respectively, indicative of the anion-dependent transition temperature. The cooperativity operating in the complexes is thought to be mainly from the intermolecular pi center dot center dot center dot pi interactions between dihydroquinazoline rings on the neighboring molecules. The ligand substituent effect was also investigated on Fe-II SCO properties. This work revealed the spin crossover properties of new types of dihydroquinazoline Fe(II) complexes, including the transition temperature, the degree of completion and the cooperative nature of the transition, which can be optimally designed when developing new spin-crossover materials.

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Co-Fe Prussian Blue Analogue Intercalated into Diamagnetic Mg‒Al Layered Double Hydroxides

Zhang Cuijuan, YAMAMOTO Takashi, Einaga Yasuaki

Nanomaterials and Nanotechnology （InTech Europe）  6 （ 1 ） 26-7pp 2016年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1847-9804

　概要を見る

A heterostructure of diamagnetic magnesium-aluminium layered double hydroxides (Mg-Al LDHs) and photomagnetic cobalt-iron Prussian Blue analogue (Co-Fe PBA) was designed, synthesized and then designated as LDH-PB. The cyanide-bridged Co-Fe PBA was two-dimensionally intercalated into the Mg-Al LDH template by the stepwise anion exchange method. LDH-PB showed ferrimagnetic properties with in-plane antiferromagnetic exchange interactions, as well as small photo-induced magnetization by visible light illumination due to the low dimensional structures and the characteristic photo-induced electronic states of the mixed valence of FeIII(low spin, S = 1/2)-CN-CoII(high spin, S = 3/2)-NC-FeII (low spin, S = 0).

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New Family of Anionic Fe^III Spin Crossover Complexes Featuring a Weak-Field N₂O₄ Coordination Octahedron

Takahashi Kazuyuki, Kawamukai Kiko, Okai Mitsunobu, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari

Chemistry A European Journal 22 （ 4 ） 1253 - 1257 2015年12月

研究論文（学術雑誌）, 共著, 査読有り

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Novel Fe(II) Spin Crossover Complexes Involving Chalcogen-Bond and π-Stacking Interactions with a Paramagnetic and Nonmagnetic M(dmit)2 Anion (M = Ni, Au; dmit = 4,5-dithiolato-1,3-dithiole-2-thione)

Okai Mitsunobu, Takahashi Kazuyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Journal of Materials Chemistry C （Royal Society of Chemistry）  3 （ 30 ） 7858 - 7864 2015年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2050-7526

　概要を見る

To introduce both an inter-sulphur atom and p-stacking interaction between a spin crossover (SCO) cation and paramagnetic anion, we designed and synthesised two novel Fe(II) SCO compounds involving a terpyridine-type thiazole containing ligand with the paramagnetic Ni(dmit)(2) and nonmagnetic Au(dmit)(2) anion (dmit = 4,5-dithiolato-1,3-dithiole-2-thione). The temperature variations of magnetic susceptibility and Mossbauer spectroscopy revealed that both complexes exhibited an almost complete SCO conversion, and moreover, the Ni(dmit)(2) anion was in a paramagnetic state down to 2 K. The crystal structures for the Ni(dmit)(2) complex at 213 and 400 K indicated that the chalcogen-bond and p-stacking interaction would be enhanced by the electrostatic interaction between the cation and anion, preventing the p-radicals from dimerising. The light-induced excited spin state trapping effect was observed at 5 K.

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Antiferromagnetic Transition in a Novel Star-Shaped High-Spin Fe(III) Tetranuclear Cluster from a Mononuclear Coordination Anion Featuring π-Extended Schiff Base Ligands

Takahashi Kazuyuki, Kawamukai Kiko, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Mori Hatsumi, Shimura Yasuyuki, Sakakibara Toshiro, Fujisawa Takumi, Yamaguchi Akira, Sumiyama Akihiko

Chemistry Letters （The Chemical Society of Japan）  44 （ 6 ） 840 - 842 2015年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0366-7022

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A novel star-shaped high-spin Fe(III) tetranuclear cluster was unexpectedly obtained by the reaction of an [Fe-III(phsal)(2)](-) anion with an Fe(III) coordination cation (H(2)phsal: N-(2-hydroxyphenyl)salicylaldimine). Despite a star-shaped Fe(III) tetranuclear structure similar to reported Fe(III) single molecule magnets, the present compound exhibited a bulk antiferromagnetic transition at 0.6 K due to a magnetic exchange coupling through intercluster pi-stacking interactions.

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Photochromism-Induced Amplification of Critical Current Density in Superconducting Boron-Doped Diamond with an Azobenzene Molecular Layer

NATSUI Keisuke, YAMAMOTO Takashi, AKAHORI Miku, EINAGA, Yasuaki

ACS Applied Materials & Interfaces （American Chemical Society）  7 （ 1 ） 887 - 894 2014年12月

共著, 査読有り,  ISSN  1944-8244

　概要を見る

A key issue in molecular electronics is the control of electronic states by optical stimuli, which enables fast and high-density data storage and temporal-spatial control over molecular processes. In this article, we report preparation of a photoswitchable superconductor using a heavily boron-doped diamond (BDD) with a photochromic azobenzene (AZ) molecular layer. BDDs electrode properties allow for electrochemical immobilization, followed by copper(I)-catalyzed alkyne-azide cycloaddition (a click reaction). Superconducting properties were examined with magnetic and electrical transport measurements, such as field-dependent isothermal magnetization, temperature-dependent resistance, and the low-temperature voltage-current response. These measurements revealed reversible amplification of the critical current density by 55% upon photoisomerization. This effect is explained as the reversible photoisomerization of AZ inducing an inhomogeneous electron distribution along the BDD surface that renormalizes the surface pinning contribution to the critical current.

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Synergistic Spin Transition between Spin-Crossover and Spin-Peierls-Like Singlet Formation in the Halogen-bonded Molecular Hybrid System: [Fe(Iqsal)₂][Ni(dmit)₂]•CH₃CN•H₂O

Kappei Fukuroi, Kazuyuki Takahashi, Tomoyuki Mochida, Takahiro Sakurai, Hitoshi Ohta, Takashi Yamamoto, Yasuaki Einaga, Hatsumi Mori

Angewandte Chemie International Edition （WILEY-V C H VERLAG GMBH）  53 （ 7 ） 1983 - 1986 2014年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1433-7851

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To introduce halogen-bond interactions between a cation and an anion, a novel Fe-III complex from iodine-substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of -spins and played a crucial role in the synergistic magnetic transition between d- and -spins. In addition, the compound showed the light-induced excited spin state trapping effect.

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Structure-Distortion-Induced Photomagnetic Effect in Azobenzene/Polyoxometalate Langmuir–Blodgett Films

Takashi Yamamoto, Yasushi Umemura, Yasuaki Einaga

Dalton Transactions （ROYAL SOC CHEMISTRY）  42 （ 45 ） 16014 - 16020 2013年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1477-9226

　概要を見る

We have prepared photomagnetic Langmuir-Blodgett films composed of an amphiphilic azobenzene and a magnetic polyoxometalate. The obtained film possesses a well-organized layered structure where polyoxometalate anions are sandwiched by azobenzene cations in a single-layered manner. Reversible photoisomerization of azobenzene was achieved even at low temperature, accompanying intensity changes in the d-d transition of polyoxometalate anions. The photomagnetic effect was observed reversibly upon alternate UV and visible light irradiation. Based on polarized spectroscopy, the observed photomagnetic effect is ascribed to the structure-distortion of polyoxometalate layers.

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