Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Crystal-face-selective adsorption of Au nanoparticles onto polycrystalline diamond surfaces

Kondo Takeshi, Aoshima Shinsuke, Hirata Kousuke, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Langmuir 24 ( 14 ) 7545 - 7548 2008.07

ISSN 0743-7463

Crystal-face-selective adsorption of Au nanoparticles (AuNPs) was achieved on polycrystalline boron-doped diamond (BDD) surface via the self-assembly method combined with a UV/ozone treatment. To the best of our knowledge, this is the first report of crystal-face-selective adsorption on an inorganic solid surface. Hydrogen-plasma-treated BDD samples and those followed by UV/ozone treatment for 2 min or longer showed almost no adsorption of AuNP after immersion in the AuNP solution prepared by the citrate reduction method. However, the samples treated by UV/ozone for 10 s showed AuNP adsorption on their (111) facets selectively after the immersion. Moreover, the sample treated with UV/ozone for 40-60 s showed AuNP adsorption on the whole surface. These results indicate that the AuNP adsorption behavior can be controlled by UV/ozone treatment time. This phenomenon was highly reproducible and was applied to a two-step adsorption method, where AuNPs from different batches were adsorbed on the (111) and (100) surface in this order. Our findings may be of great value for the fabrication of advanced nanoparticle-based functional materials via bottom-up approaches with simple macroscale procedures. © 2008 American Chemical Society.

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Sensitive electrochemical detection of oxalate at a positively charged boron-doped diamond surface

Kondo Takeshi, Niwano Yu, Tamura Akira, Ivandini Tribidasari A., Einaga Yasuaki, Tryk Donald A., Fujishima Akira, Kawai Takeshi

Electroanalysis 20 ( 14 ) 1556 - 1564 2008.07

ISSN 1040-0397

Allyltriethylammonium bromide (ATAB) was covalently attached to the surface of hydrogen-terminated boron-doped diamond (BDD) thin films using a photochemical method to fabricate positively charged electrode surfaces. The anodic current for oxalate oxidation both in cyclic voltammetry and in flow-injection analysis with amperometry was found to be up to two times larger at ATAB-modified BDD (ATAB-BDD) than at an unmodified BDD electrode, which may be based on the electrostatic interaction between the oxalate anion and the electrode surface. In addition, the stability of the electrochemical detection of oxalate was improved at the ATAB-BDD electrode compared to the unmodified electrode. © 2008 Wiley-VCH Verlag GmbH&Co. KGaA.

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Photo-control of adhesion properties by detachment of the outermost layer in layer-by-layer assembled multilayer films of Preyssler-type polyozometalate and polyethyleneimine

Nagaoka Yasutaka, Shiratori Seimei, Einaga Yasuaki

Chemistry of Materials 20 ( 12 ) 4004 - 4010 2008.06

ISSN 0897-4756

The ability to generate small-scale structures and assemble functional substances in the fields of micro electronics and optoelectronics continues to support advances in information technology. Here we present a novel type of "layer-by-layer" assembled films, whose surface properties can be controlled by UV irradiation in aqueous solution. We have designed a photochromic multilayer film of Preyssler-type polyoxometalate, (NaP₅W₃₀) and polyethyleneimine (PEI) by using the layer-by-layer method. We found that the outermost PEI layer could be detached by UV irradiation in aqueous solution, and that this process could then cause inversion of the zeta potential. Furthermore, we achieved reversible-control of the surface properties first by UV irradiation, which induced the detachment of the outermost PEI layer, and by subsequent dipping into a PEI solution, which attached a new PEI layer. Finally, we successfully prepared photopatterned films with highly site-selective adsorption abilities by image-wise UV exposure. © 2008 American Chemical Society.

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Evidence of the chemical uniaxial strain effect on electrical conductivity in the spin-crossover conducting molecular system

Takahashi Kazuyuki, Cui Heng Bo, Okano Yoshinori, Kobayashi Hayao, Mori Hatsumi, Tajima Hiroyuki, Einaga Yasuaki, Sato Osamu

Journal of the American Chemical Society 130 ( 21 ) 6688 - 6689 2008.05

ISSN 0002-7863

A novel spin-crossover molecular conductor, [Fe(qnal)₂][Pd(dmit)₂]₅·acetone, was prepared and characterized. The crystal structural analyses of both the low- and high-temperature phases revealed that the supramolecular π-π interactions between the spin-crossover Fe(qnal)₂ cations as well as the cation contraction play an important role in the uniaxial lattice deformation which will modulate the electrical conductivity of the conducting Pd(dmit)₂ layer. Copyright © 2008 American Chemical Society.

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Selective determination of dopamine on a boron-doped diamond electrode modified with gold nanoparticle/polyelectrolyte-coated polystyrene colloids

Wei Min, Sun Li Guo, Xie Zhuo Ying, Zhii Jin Fang, Fujishima Akira, Einaga Yasuaki, Fu De Gang, Wang Xue Mei, Gu Zhong Ze

Advanced Functional Materials 18 ( 9 ) 1414 - 1421 2008.05

ISSN 1616-301X

Negatively charged gold nanoparticles (AuNPs) and a polyelectrolyte (PE) have been assembled alternately on a polystyrene (PS) colloid by a layer-by-layer (LBL) self-assembly technique to form three-dimensional (Au/PAH)₄/(PSS/PAH)₄ multilayer-coated PS spheres (Au/PE/PS multilayer spheres). The Au/PE/PS multilayer spheres have been used to modify a boron-doped diamond (BDD) electrode. Cyclic voltammetry is utilized to investigate the properties of the modified electrode in a 1.0M KCl solution that contains 5.0 × 10^-3 M K₃Fe(CN)₆, and the result shows a dramatically decreased redox activity compared with the bare BDD electrode. The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) on the bare and modified BDD electrode are studied. The cyclic voltammetric studies indicate that the negatively charged, three-dimensional Au/PE/PS multilayer sphere-modified electrodes show high electrocatalytic activity and promote the oxidation of DA, whereas they inhibit the electrochemical reaction of AA, and can effectively be used to determine DA in the presence of AA with good selectivity. The detection limit of DA is 0.8 × 10^-6M in a linear range from 5 × 10^-6 to 100 × 10^-6M in the presence of 1×10^-3M AA. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

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Anodic stripping voltammetry of inorganic species of As³⁺ and As⁵⁺ at gold-modified boron doped diamond electrodes

Yamada Daisuke, Ivandini Tribidasari A., Komatsu Motoharu, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 615 ( 2 ) 145 - 153 2008.04

ISSN 0022-0728

Electrochemical detection of mixture solutions of As³⁺ and As⁵⁺ has been investigated by stripping voltammetry at gold-modified diamond electrodes. The method was performed based on stripping oxidation of As⁰ deposited at the electrode surface. Whereas As³⁺ can be deposited by simple electrochemical reduction of As³⁺ to As⁰ at -0.4 V (vs. Ag/AgCl), much higher potential is required to overcome the activation energy of As⁵⁺ reduction. However, in such a high potential, hydrogen evolution also occurs. Consequently, one more step should be added to release the hydrogen gas adsorbed at the electrode surface during the reduction step. During the deposition of As⁵⁺, As³⁺ species was also simultaneously deposited. Therefore, to differentiate As³⁺ and As⁵⁺ quantification in a mixture solution, both stripping voltammetry methods should be performed and calculated mathematically. Comparison of stripping voltammograms of both methods for As³⁺ solution in the absence of As⁵⁺ demonstrated similar peak shapes and current intensities, confirming that error calculation of As⁵⁺ concentration in the mixture solution with As³⁺ can be avoided. Good linear responses were observed for each standard solution of As³⁺ and As⁵⁺. Linear calibration curve could also be achieved for a series concentrations of 100-1000 ppb As⁵⁺ in a mixture solution with 100 ppb As³⁺ (r² = 0.99) and for a series concentrations of 5-30 ppb As³⁺ in a mixture solution with 100 ppb As⁵⁺. Detection limits of 5 and 100 ppb can be achieved for As³⁺ and As⁵⁺ in a mixture solution, respectively. The reproducibility was shown for stripping voltammetry of As³⁺ and As⁵⁺ with an RSD (n = 8) of 7.5% and 8.4%, respectively. Good stability of gold-modified diamond electrodes before and after arsenic detection was also evaluated by SEM image. Application of the method for real sample analysis was performed for arsenic detection in Yokohama tap water. © 2008 Elsevier B.V. All rights reserved.

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Normal photochromism of spiropyran in montmorillonite interlayer

Saso Naoki, Yamamoto Takashi, Umemura Yasushi, Einaga Yasuaki

Colloids and Surfaces A: Physicochemical and Engineering Aspects 317 ( 1-3 ) 309 - 315 2008.03

ISSN 0927-7757

Spiropyran-montmorillonite hybrid materials have been fabricated by the Langmuir-Blodgett (LB) and an intercalation method. The LB method using clay minerals could be applied to fabricate hybrid ultrathin films consisting of a non-amphiphilic spiropyran. It is confirmed that hybrid LB films possess the layered structure and exhibit "normal photochromism" without any changes in the layered structure. In case of the intercalation method, hybrid compounds also possess the layered structure. Interestingly, intercalation hybrid compounds exhibit "reverse photochromism". It is suggested that a different process in formation of the layered structure influences the observed photochromism. © 2007 Elsevier B.V. All rights reserved.

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Development of amperometric immunosensor using boron-doped diamond with poly(o-aminobenzoic acid)

Preechaworapun Anchana, Ivandini Tribidasari A., Suzuki Akane, Fujishima Akira, Chailapakul Orawon, Einaga Yasuaki

Analytical Chemistry 80 ( 6 ) 2077 - 2083 2008.03

ISSN 0003-2700

An alternative method of a protein immunosensor has been developed at boron-doped diamond (BDD) electrode material. In order to construct the base of the immunosensor, o-aminobenzoic acid (o-ABA) was electropolymerized at an electrode by cyclic voltammetry. The poly-o-ABA-modified BDD was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The XPS result found that carboxyl groups were formed at the electrode surface. The carboxyl groups were then used to covalently attach protein probes. The amperometric sensing of mouse IgG (MIgG) was selected as the model at the pory-o-ABA-modified BDD to compare to the pory-o-ABA-modified glassy carbon (GC) at the same condition. An antimouse IgG from goat (GaMIgG) was covalently immobilized at a pory-o-ABA-modified BDD electrode which used a sandwich-type alkaline phosphatase (ALP) catalyzing amperometric immunoassay with 2-phospho-L-ascorbic acid (AAP) as substrate. The ALP enzyme conjugated at the immunosensor can generate AAP to the electroactive species of ascorbic acid (AA), which can be determined by amperometric detection. The signal was found to be proportional with the quantity of MIgG. The limits of detection (LODs) of 0.30 (3 SD) and 3.50 ng mL^-1 (3 SD) for MIgG at BDD and GC electrodes were obtained. It also was found that the dynamic range of 3 orders of magnitude (1-1000 ng mL^-1) was obtained at BDD, whereas at GC, the dynamic range was more narrow (10-500 ng mL^-1). The method was applied to a real mouse serum sample that contains MIgG. © 2008 American Chemical Society.

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Direct electrochemical oxidation of proteins at conductive diamond electrodes

Chiku Masanobu, Ivandini Tribidasari A., Kamiya Akihide, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 612 ( 2 ) 201 - 207 2008.01

ISSN 0022-0728

Direct oxidation peaks relating to proteins have been clearly observed by exploiting H-terminated boron-doped diamond (BDD) electrodes. Hydrogen generation by reduction treatment was enabled to provide the possibility of using BDD. The pH dependence of bovine serum albumin (BSA) oxidation suggested that the oxidation involved of at least three redox-active amino acid residues (cysteine, tryptophan and tyrosine). Furthermore, the electrochemical detection of not only BSA but also immunosuppressive acidic protein (IAP, a cancer marker) was demonstrated by using cyclic voltammetry and flow injection analysis. A linear dynamic in the concentration range of 5 and 3000 mg/dl (r² = 0.9) with a lower detection limit (LOD) of 5 mg/dl was achieved for BSA. In the case of IAP, the calibration curve was linear over the concentration range from 200 to 800 μg/ml, with an experimental LOD of 100 μg/dl. Excellent reproducibility was also demonstrated, suggested that direct electrochemical detection using BDD electrodes can be performed with advantages in terms of simplicity, sensitivity and stability. © 2007 Elsevier B.V. All rights reserved.

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Tuning of electronic properties of one-dimensional cyano-bridged Cu^II-Ni^II, Cu^II-Pd^II, and Cu^II-Pt^II bimetallic assemblies by stereochemistry of ligands

Akitsu Takashiro, Einaga Yasuaki

Inorganica Chimica Acta 361 ( 1 ) 36 - 42 2008.01

ISSN 0020-1693

Preparations, XPS and electronic spectroscopy, and magnetism of seven new one-dimensional cyano-bridged coordination polymers, chiral [Cu(RR-chxn)₂][Pd(CN)₄] · 2H₂O (1), [Cu(trans-chxn)₂][M(CN)₄] · 2H₂O (2, 4, and 6 for M = Pd, Ni, and Pt), and [Cu(cis-chxn)₂][M(CN)₄] · 2H₂O (3, 5, and 7 for M = Pd, Ni, and Pt) (RR-chxn = cyclohexane-(1R,2R)-diamine, trans-chxn = racemic trans-cyclohexane-(1,2)-diamine, and cis-chxn = racemic cis-cyclohexane-(1,2)-diamine) have been reported in view of tuning of their electronic properties by stereochemistry of chxn ligands and metal-substitution. Comparison of Cu 2p_1/2 and 2p_3/2 peaks of XPS and broad d-d bands around 18 000 cm^-1 of electronic spectra are described systematically for 1-7. Variable-temperature magnetic measurement shows that complexes 1-7 indicate weak antiferromagnetic interactions via cyano-bridges. Because of semi-coordination coupled with pseudo Jahn-Teller elongation and electrostatic interaction for 1, the axial Cu-N coordination bond distances of 2.330(7) and 3.092(8) Å are considerably longer than those of equatorial ones in the range from 2.016(6) to 2.030(6) Å. The former bond distances of 1 are intermediate values among the related Ni (2.324(6) and 3.120(8) Å) and Pt (2.34(1) and 3.09(1) Å) complexes. © 2007 Elsevier B.V. All rights reserved.

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Electrochemical detection of free chlorine at highly boron-doped diamond electrodes

Murata Michio, Ivandini Tribidasari A., Shibata Mamoru, Nomura Satoshi, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 612 ( 1 ) 29 - 36 2008.01

ISSN 0022-0728

The quantitative determination of free chlorine based on its oxidation current was studied using cyclic voltammetry (CV) with highly boron-doped diamond (BDD) electrodes. The voltammograms exhibited well-defined anodic peaks and a good linear relationship in the concentration range of 20-100 mg Cl L^-1 using BDD electrodes without any pretreatment. Excellent reproducibility was demonstrated by an RSD of 2.56% (n = 10). The electrochemical behavior of free chlorine at different pH values suggests the optimum condition to be pH 8. Observations with the BDD electrodes terminated with either hydrogen or oxygen suggest that the active species in the anodic reaction was ClO^-. Interference of limited concentration of chloride ion was not observed, whereas exceeded concentration was found to accelerate the electron transfer on chlorine oxidation. Flow injection analysis (FIA) with amperometric detection was used to estimate lower concentrations of free chlorine. A linear relationship (r² = 0.96) was found for the concentration range of 0.1-2 mg L^-1 and the low detection limit (S/N = 3) was estimated to be 8.3 μg L^-1. The results suggest that BDD electrodes are more than adequate for determining the concentration of free chlorine. © 2007 Elsevier B.V. All rights reserved.

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Characterization and electrochemical properties of CF₄ plasma-treated boron-doped diamond surfaces

Kondo Takeshi, Ito Hiroyuki, Kusakabe Kazuhide, Ohkawa Kazuhiro, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Diamond and Related Materials 17 ( 1 ) 48 - 54 2008.01

ISSN 0925-9635

The effect of CF₄ plasma etching on diamond surfaces, with respect to treatment time, was investigated using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. SEM observations and Raman spectra indicated an increase in surface roughening on a scale of 10-20 nm, and an increase in crystal defect density was apparent with treatment time in the range of 10 s to 30 min. In contrast, alteration of the diamond surface terminations from oxygen to fluorine was found to be rather rapid, with saturation of the F/C atomic ratio estimated from XPS analysis after treatment durations of 1 min and more. The redox kinetics of Fe(CN)₆^3-/4- was also found to be significantly modified after 10 s of CF₄ plasma treatment. This behavior shows that C-F terminations predominantly affect the redox kinetics compared to the effect on the surface roughness and crystal defects. The double-layer capacitance (C_dl) of the electrolyte/CF₄ plasma-treated boron-doped diamond interface was found to show a minimum value at 1 min of treatment. These results indicate that a short-duration CF₄ plasma treatment is effective for the fabrication of fluorine-terminated diamond surfaces without undesirable surface damage. © 2007 Elsevier B.V. All rights reserved.

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Comparison of boron-doped diamond and glassy carbon electrodes for determination of procaine hydrochloride

Wei Min, Zhou Yanli, Zhi Jinfang, Fu Degang, Einaga Yasuaki, Fujishima Akira, Wang Xuemei, Gu Zhongze

Electroanalysis 20 ( 2 ) 137 - 143 2008.01

ISSN 1040-0397

The electrochemical oxidation of procaine hydrochloride (PC·HCL, 2-diethylaminoethyl 4-aminobenzoate hydrochloride) was investigated at as-deposited boron-doped diamond (ad-BDD) electrode, anodically oxidized BDD (aoBDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well-defined cyclic voltammograms were obtained for PC·HCL oxidation with high signal-to-background (S/B) ratio, low tendency for adsorption, good reproducibility and long-term stability at ad-BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao-BDD and GC electrode. At 100 μM PC·HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad-BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC·HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad-BDD, ao-BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10-1000 mV s^-1 in 10 μM PC·HCL solutions, indicating that the oxidation process was diffusion-controlled with negligible adsorption at an ad-BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y = 0.03517x + 0.65346 (r = 0.999), and the detection limit was 0.5 μM for oxidation of PC·HCL at the adBDD electrode. The ad-BDD electrode could maintain 100% of its original activity after intermittent use for 3 months. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

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Pressure effects and Mössbauer spectroscopic studies on a 3D mixed-valence iron spin-crossover complex with NiAs topology

Bai Yue Ling, Tao Jun, Huang Rong Bin, Zheng Lan Sun, Zheng Shao Liang, Oshida Kazuyoshi, Einaga Yasuaki

Chemical Communications ( 15 ) 1753 - 1755 2008

ISSN 1359-7345

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Reversible phototuning of ferromagnetism at Au-S interfaces at room temperature

Suda Masayuki, Kameyama Naoto, Suzuki Motohiro, Kawamura Naomi, Einaga Yasuaki

Angewandte Chemie - International Edition 47 ( 1 ) 160 - 163 2008

ISSN 1433-7851

Out of nowhere: Significant photoinduced changes in ferromagnetism have been observed at the interfaces between gold nanoparticles (Au NPs) and azobenzene-derivatized thiols. These photomagnetic effects could be attributed to photoinduced changes in d-charge losses resulting from the photoisomerization of the azo ligands (see picture), which are accompanied by the inversion of surface dipoles to the opposite sign. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

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Fabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detection

Suzuki Akane, Ivandini Tribidasari A., Yoshimi Kenji, Fujishima Akira, Oyama Genko, Nakazato Taizo, Hattori Nobutaka, Kitazawa Shigeru, Einaga Yasuaki

Analytical Chemistry 79 ( 22 ) 8608 - 8615 2007.11

ISSN 0003-2700

Highly boron-doped diamond (BDD) was deposited on chemically etched micrometer-sized tungsten wires using microwave plasma assisted chemical vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diameter (about 5 μm) and 250 μm in length could be made successfully. In addition to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidation of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a constant current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanalysis. © 2007 American Chemical Society.

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Fabrication of covalent SAM/Au nanoparticle/boron-doped diamond configurations with a sequential self-assembly method

Kondo Takeshi, Aoshima Shinsuke, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Journal of Physical Chemistry C 111 ( 34 ) 12650 - 12657 2007.08

ISSN 1932-7447

An attempt was made to make use of chemical modification of the diamond surface to control the adsorption of Au nanoparticles (AuNPs) on this surface via self-assembly. AuNPs prepared with a citrate reduction method (c-AuNP) and mercaptoacetic acid (MAA)-modified AuNPs (MAA-AuNP) were not adsorbed onto hydrogen-terminated and oxygen-terminated boron-doped diamond (BDD) surfaces. On the other hand, c-AuNP and MAA-AuNP were found to be adsorbed in a homogeneous, well-dispersed fashion on NH₂-terminated and SH-terminated BDDs prepared with the silane coupling method. It was also found that the adsorption of c-AuNP on SH-BDD was more stable than that on NH₂-BDD versus immersion in various thiol aqueous solutions used to form self-assembled monolayers (SAMs) on the Au surface, without desorption of the AuNP from the BDD surface. Immersion of the c-AuNP/SH-BDD sample in a ferrocenylalkanethiol/ ethanol solution was found, by cyclic voltammetry, to result in chemisorption of the thiol to the Au surface. Facile electronic communication through the ferrocenyl moiety to the BDD substrate suggests that SAM/AuNP/BDD configurations based on SH-BDD fabricated by a self-assembly method can be applied to possible molecular electronic and electrochemical devices. © 2007 American Chemical Society.

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Structure of cyano-bridged Eu(III)-Co(III) bimetallic assembly and its application to photophysical verification of photomagnetic phenomenon

Akitsu T., Einaga Y.

Chemical Papers 61 ( 3 ) 194 - 198 2007.06

ISSN 0366-6352

New crystal structure of Eu(DMF)₄(H₂O) ₃Co(CN)₆•H₂O (DMF = N,N′- dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) Å³, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited ⁵ D ₀ → ⁷ F ₂ and ⁵ D ₀ → ⁷ F ₁ luminescence bands at 16300 cm^-1 and 16900 cm^-1, respectively at 298 K (λ_ex = 360 nm (27000 cm^-1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states. © Institute of Chemistry, Slovak Academy of Sciences 2007.

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Photomagnetic hybrid ultrathin films

Yamamoto Takashi, Einaga Yasuaki

Journal of Solid State Electrochemistry 11 ( 6 ) 781 - 790 2007.06

ISSN 1432-8488

Two novel types of photomagnetic hybrid ultrathin film (film A and B) of metal cyanides have been fabricated by means of the modified Langmuir-Blodgett method using a smectite clay mineral. Film A is composed of an amphiphilic azobenzene cation, a montmorillonite, and Prussian Blue in which photocontrol in the magnetization was realized by the photoisomerization of azobenzene chromophore. The observed photomagnetic efficiency was large (ca. 11%) due to the well-organized structure of the ultrathin film. Film B is composed of a quaternary ammonium salt, a montmorillonite, and Co-Fe Prussian Blue in which the photoinduced magnetization caused by the electron transfer exhibited an anisotropic response with regards to the direction of the applied magnetic field. This phenomenon is ascribed to the unique structure of Co-Fe Prussian Blue formed onto the clay layer. © Springer-Verlag 2007.

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Photochromism induced magnetization changes in Prussian Blue ultrathin films fabricated into the Langmuir-Blodgett films composed of an amphiphilic azobenzene and a deoxyribonucleic acid

Yamamoto Takashi, Umemura Yasushi, Nakagawa Masaru, Iyoda Tomokazu, Einaga Yasuaki

Thin Solid Films 515 ( 13 ) 5476 - 5483 2007.05

ISSN 0040-6090

A photomagnetic ultrathin film consisting of an azobenzene, a deoxyribonucleic acid, and Prussian Blue has been fabricated by the Langmuir-Blodgett method. Prussian Blue layers in the films were a two-dimensional structure with the height of 50 Å and the average coherence length of 210 Å. Reversible photoisomerization of the azobenzenes was observed even in the films. The films exhibit the long-range ferromagnetic order below 4.2 K and moreover, upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 1.0%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization. © 2007 Elsevier B.V. All rights reserved.

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