Soichiro Yoshimoto

Kumamoto University, Kumamoto, Kumamoto Prefecture, Japan

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Publications (69)290.77 Total impact

  • Hiroyuki Ueda, Katsuhiko Nishiyama, Soichiro Yoshimoto
    Electrochemistry Communications 06/2014; · 4.29 Impact Factor
  • Soichiro Yoshimoto, Hiroto Ogata, Katsuhiko Nishiyama
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    ABSTRACT: The electrodeposition of gold and platinum complexes at the electrochemical interfaces on the coronene-modified Au(111) surface was investigated. Scanning tunneling microscopy revealed the spontaneous deposition of gold and platinum complexes, suggesting that the coronene adlayer plays an important role in the electroreduction of these complexes.
    Dalton Transactions 08/2013; · 4.10 Impact Factor
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    Soichiro Yoshimoto, Kingo Itaya
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    ABSTRACT: We describe the history of electrochemical scanning tunneling microscopy (STM) and advances made in this field during the past 20 years. In situ STM allows one to monitor various electrode processes, such as the underpotential deposition of copper and silver ions; the specific adsorption of iodine and sulfate/bisulfate ions; electrochemical dissolution processes of silicon and gold single-crystal surfaces in electrolyte solutions; and the molecular assembly of metalloporphyrins, metallophthalocyanines, and fullerenes, at atomic and/or molecular resolution. Furthermore, a laser confocal microscope, combined with a differential interference contrast microscope, enables investigation of the dynamics of electrochemical processes at atomic resolution.
    Annual Review of Analytical Chemistry (2008) 06/2013; 6(1):213-35. · 7.81 Impact Factor
  • Soichiro Yoshimoto
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    ABSTRACT: The stability and phase transitions of adlayers of two cobalt(ii) porphyrins, 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(ii) (CoTPP) and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine cobalt(ii) (CoOEP), formed on Au(100) were investigated under electrochemical conditions. In situ scanning tunneling microscopy (STM) was employed to investigate the structure of CoTPP and CoOEP adlayers in 0.1 M HClO4. The CoTPP and CoOEP adlayer structures were varied with the modification time and the concentration. The in situ STM observations showed that the underlying reconstructed atomic structure was lifted to a (1 × 1) atomic arrangement by either the adsorption of CoTPP/CoOEP during modification in a benzene solution or positive potential manipulation in 0.1 M HClO4. Ordered CoTPP arrays with two different hexagonal and square packing arrangements were found on an Au(100)-(1 × 1) surface, along with characteristic Au islands. The CoOEP molecules also formed a close-packed hexagonal structure on an Au(100)-(hex) surface; CoOEP molecules were arranged in a semi-square structure on the Au(100)-(1 × 1) surface by the lifting of reconstruction. The results of this study showed that the interaction between the cobalt porphyrins and the Au(100) substrate depended on the modification conditions and the electrochemical potential.
    Physical Chemistry Chemical Physics 05/2013; · 4.20 Impact Factor
  • Soichiro Yoshimoto, Katsuhiko Nishiyama
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    ABSTRACT: A redox-active adlayer consisting of cobalt ions and terpyridine ligands, 4′,4′′′′-(1,4-phenylene)bis(2,2′:6′,2′′-terpyridine), was prepared on a Au(111) surface by a stepwise coordination method. The obtained adlayer produced a well-defined, stable redox wave associated with cobalt ions coordinated to 4′,4′′′′-(1,4-phenylene)bis(2,2′:6′,2′′-terpyridine), as compared to a tetra-2-pyridinyl-pyrazine adlayer, for which no redox wave was observed. In situ scanning tunneling microscopy revealed a structural change in the redox-active adlayer consisting of 4′,4′′′′-(1,4-phenylene)bis(2,2′:6′,2′′-terpyridine) and cobalt ions. It was found that the ability of cobalt ions to coordinate on Au(111) was clearly dependent on the chemical structure of the ligand, suggesting that ligand coordination with metal ions on the Au surface is determined by the molecular orientation and configuration of the ligand when the ligand is adsorbed on a Au substrate.
    Journal of Inorganic and Organometallic Polymers and Materials 01/2013; 23(1). · 1.08 Impact Factor
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    ABSTRACT: The 2D molecular assemblies of chloride-coordinated mixed-valence diruthenium complexes, each possessing phenyl, naphtyl, or anthracenyl moieties, were examined on an Au(111) at electrochemical interface. In situ scanning tunneling microscopy images revealed a clear dependence of the molecular assembly on both the nature of the aryl functional groups and on the redox state of the dinuclear ruthenium complex, either chloride-coordinated RuII/RuIII or noncoordinated RuII/RuII. At potentials where the RuII/RuIII and RuII/RuII redox states were in equilibrium, two distinct redox states were clearly identified at the single-molecular level. We found that manipulating both the electrochemical potential and the aryl functional group substitution was important for controlling the 2D molecular assembly of a chloride-coordinated diruthenium complex on an Au(111) surface.
    The Journal of Physical Chemistry 12/2012;
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    Kingo Itaya, Soichiro Yoshimoto
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    ABSTRACT: In this review, we focus on history and advances made in the past 20 years in the field of electrochemical scanning tunneling microscopy (EC-STM). It is demonstrated that in situ STM makes it possible to monitor with atomic and/or molecular resolution a wide variety of electrode processes such as underpotential deposition of copper and silver ions, the specifically adsorption of iodine and sulfate/bisulfate ions, electrochemical dissolution process of silicon and gold single crystal surfaces in electrolyte solution, and molecular assembly of metalloporphyrins, metallophthalocyanines and fullerenes. Furthermore, laser confocal microscope combined with a differential interference contrast microscope (LCM-DIM) investigation allows us to investigate dynamics of electrochemical processes with the capability of atomic layer resolution. Expected final online publication date for the Annual Review of Analytical Chemistry Volume 6 is June 15, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for ...
    08/2012;
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    ABSTRACT: The influence of the alkyl chain length of the bis(trifluoromethylsulfonyl)imide-based ionic liquids 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-methyl-3-octylimidazolium, and 1-decyl-3-methylimidazolium cation on the potential window was investigated with low-index Au single crystal electrodes by cyclic voltammetry. The potential window of the electrical double-layer region was found to depend on the crystallographic orientation of Au, which indicated a difference in the strength of cation adsorption on the Au substrate. The potential window of the electrical double-layer region was also dependent upon the alkyl chain length of the imidazolium cation.
    Electrochemistry Communications 07/2012; 20:26–28. · 4.29 Impact Factor
  • Soichiro Yoshimoto
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    ABSTRACT: Unique molecular assemblies of a porphyrin derivative are prepared on Au(111) by controlling the protonation/unprotonation of the pyridine groups. The porphyrin derivative, driven by the protonation of the pyridine groups, can provide characteristic assemblies with specific molecular conformations on an Au(111) surface at the electrochemical interface. In situ scanning tunneling microscopy images revealed clear differences in the adlayer structures for the unprotonated and the protonated forms of the molecules that depended upon the electrochemical potential.
    Chemical Communications 05/2012; 48(38):4612-4. · 6.38 Impact Factor
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    ABSTRACT: In situ scanning tunneling microscopy (STM) was employed to examine the surface structures of Au(111), Au(100), and Au(110) single crystals in propylene carbonate (PC) containing tetrabutylammonium perchlorate (TBAP). All three electrodes exhibited potential-induced phase transition between the reconstructed and unreconstructed (1 × 1) structures at negative and positive potentials, respectively. The potential-induced phase transition of the Au electrode surfaces is attributed to the interaction of the TBA cation and the perchlorate anion at the electrode surface, which is similar to that which takes place in aqueous solutions. In addition to static atomic structures, dynamic processes of both the reconstruction and the lifting of the reconstruction were investigated by means of in situ STM. The lifting of reconstructed Au(111)-(√3 × 22) on Au(111) to the (1 × 1) structure is completed within 1 min at a positive potential. The diffusion of Au atoms on the Au(100) plane in the PC solution proceeds more rapidly than that in the aqueous solution, suggesting that the PC solvent plays an important role in accelerating the diffusion of Au atoms.
    Physical Chemistry Chemical Physics 02/2012; 14(7):2286-91. · 4.20 Impact Factor
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    ABSTRACT: Molecular adlayers of doubly C(60)-conjugated phthalocyanine derivatives ((C(60))(2)NiPc) were examined on bare and zinc(II) octaethylporphyrin (ZnOEP)- and coronene-modified Au(111) surfaces. Electrochemical scanning tunneling microscopy (EC-STM) has revealed the structure of the (C(60))(2)NiPc adlayer at single molecular level. The (C(60))(2)NiPc adlayer is strongly influenced by the underlying organic layers, i.e., a disordered, a packed structure of (C(60))(2)NiPc was found on a clean Au(111) surface because of the strong interaction between (C(60))(2)NiPc molecule and Au(111) substrate, whereas a single (C(60))(2)NiPc molecule was clearly distinguished both on ZnOEP and coronene adlayers at a low coverage of (C(60))(2)NiPc molecules. The obtained results in the present study suggest that the underlying organic adlayers play an important role in the formation process of the (C(60))(2)NiPc molecule adlayer.
    Journal of inorganic biochemistry 11/2011; 108:178-81. · 3.25 Impact Factor
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    ABSTRACT: The direct assembly of single component 4',4''''-(1,4-phenylene)bis(2,2' : 6',2''-terpyridine) (PTPy) and Co(2+) and PTPy mixed arrays was examined on a Au(111) surface by a simple immersion method. A redox active 2D adlayer consisting of a bisterpyridine derivative and cobalt ions was found to form directly on Au(111) from solution, suggesting that new nanostructures and/or adlayers with electrochemical activity can be precisely designed and controlled by selection of the metal ion and ligand.
    Physical Chemistry Chemical Physics 11/2010; 12(43):14442-4. · 4.20 Impact Factor
  • Soichiro Yoshimoto, Nagao Kobayashi
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    ABSTRACT: The “bottom-up” strategy is an attractive and promising approach for the construction of nanoarchitectures. Supramolecular assemblies based on noncovalent interactions have been explored in an attempt to control the surface properties. In this chapter, we focus on advances made in the past 5 years in the field of scanning tunneling microscopy (STM) on supramolecularly nanostructured phthalocyanines and porphyrins on single-crystal surfaces. The design of supramolecular nanoarchitectures consisting of phthalocyanines and porphyrins, supramolecular traps of C60 and coannulene, direct metallation on phthalocyanines and porphyrins adlayers, direct synthesis of porphyrin oligomers at surfaces, axial coordination of phthalocyanines and porphyrins, and nanoapplications induced by tip manipulation at surfaces were clearly visualized by STM. KeywordsMetal single-crystal surface-Phthalocyanines-Porphyrins-Scanning tunneling microscopy (STM)-Supramolecular assembly
    02/2010: pages 137-167;
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 41(1).
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    ABSTRACT: Self-assembled monolayers (SAMs) of 4-pyridineethanethiol (4-PyEtS) formed on a Au surface was investigated by cyclic voltammetry (CV), surface enhanced infrared spectroscopy (SEIRAS), and in situ scanning tunneling microscopy (STM). On the basis of reductive desorption for 4-PyEtS on Au(111), the peak potential was observed at -0.86 V vs. Ag/AgCl (sat. KCl). The surface excess was calculated to be 5.4 × 10-10 mol cm-2 from the CV. High-resolution STM images revealed that p(5 × √3 R−30å) lattice including two molecules was found in 0.1 M NaClO4, whereas the 4-PyEtS-SAMs formed p(10 × √3 R−30å) lattice constituted from four molecules in 0.05 M HClO4. By the analysis of SEIRA spectra, the b axis of pyridine ring of 4-PyEtS-SAMs formed on an evaporated Au film electrode in 0.1 M NaClO4 was tilted to the electrode. In contrast, that in 0.1 M HCl was parallel to the surface.
    ECS Transactions 08/2009; 16(46).
  • Soichiro Yoshimoto, Takahiro Sawaguchi
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    ABSTRACT: Cationic tetraphenyl porphyrin with two carboxyphenyl moieties in cis-position (cis-H4DCPP2+) was investigated to control the structure of the two-dimensional supramolecular assembly in 0.05 M H2SO4. In situ scanning tunneling microscopy (STM) images revealed the formation of supramolecularly organized nanostructures of cis-H4DCPP2+ such as dimer, trimer, and tetramer on the (√3 × √7) sulfate/bisulfate (SO42-/HSO4-) adlayer, suggesting the importance of both electrostatic interaction between cationic porphyrin core and SO42-/HSO4- adlayer and the hydrogen bond formation between carboxyl groups of the nearest neighbor cationic porphyrins. In contrast, when 0.1 M HClO4 was used as an electrolyte solution, only a disordered array was observed. The results indicate that the (√3 × √7) SO42-/HSO4- adlayer formed on Au(111) plays a significant role as a template in the control of electrostatically assembled cis-H4DCPP2+.
    ECS Transactions 08/2009; 16(46).
  • Koji Suto, Soichiro Yoshimoto, Kingo Itaya
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    ABSTRACT: Adlayers consisting of two components selected from the group of cobalt(II) tetraphenylporphyrin (CoTPP), copper(II) tetraphenylporphyrin (CuTPP), and zinc(II) tetraphenylporphyrin (ZnTPP) were prepared by immersing Au(111) substrate in a benzene solution containing those molecules. The bimolecular adlayers thus prepared were investigated in 0.1 M HClO4 by electrochemical scanning tunneling microscopy (EC-STM). The mixed adlayers consisting of CoTPP and CuTPP formed structurally ordered but compositionally disordered arrays on Au(111). The ratio of CoTPP to CuTPP molecules in the mixed adlayer was proportional to the ratio of CoTPP to CuTPP molecules in the solution phase. Accordingly, the composition of CoTPP and CuTPP in the adlayer on the Au(111) surface was independent of absolute concentrations of these species in the solution and immersion time. In contrast, the structural feature of the mixed adlayer consisting of CoTPP and ZnTPP was similar to that of the mixed adlayer of CoTPP and CuTPP when these adlayers were prepared in solutions containing those mixtures at a total concentration of 100 microM, whereas when the total concentration was lower, adsorption was site-selective depending on the coordinated metal ion. This finding indicates that the herringbone structure of reconstructed Au(111) served as a template for the bimolecular assembly of CoTPP and ZnTPP. The characteristic phase separation of CoTPP and ZnTPP molecules assisted by reconstructed Au(111) surface can be controlled by the subtle balance between kinetics and thermodynamics.
    Journal of Nanoscience and Nanotechnology 02/2009; 9(1):288-94. · 1.34 Impact Factor
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    ABSTRACT: Self-assembled monolayers (SAMs) of 4-pyridineethanethiol (4-PyEtS) formed on a Au(111) surface were investigated in aqueous electrolyte solutions by cyclic voltammetry and in situ scanning tunneling microscopy (STM). On the basis of reductive desorption of 4-PyEtS on Au(111), the reduction peak potential was found to be -0.86 V vs. Ag/AgCl (sat. KCl). The surface excess was calculated from the reductive desorption peak area to be 5.4 x 10(-10) mol cm(-2). High-resolution STM images revealed that a p(5 x radical3 R-30 degrees ) lattice including two molecules was found in 0.1 M NaClO(4), whereas the 4-PyEtS-SAMs formed a p(10 x radical3 R-30 degrees ) lattice constituting four molecules in 0.05 M HClO(4). The transition from a p(10 x radical3 R-30 degrees ) to a p(5 x radical3 R-30 degrees ) in the 4-PyEtS-SAMs was directly observed by changing pH of the electrolyte solution, indicating that the conformational change in 4-PyEtS-SAMs is driven by protonation/deprotonation. The present results obtained by STM observation are also supported by the clear pH dependence of the pyridine moiety in the surface-enhanced infrared spectrum.
    Physical Chemistry Chemical Physics 01/2009; 10(46):6935-9. · 4.20 Impact Factor
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    ABSTRACT: Until the mid 1980’s, there had been only few in situ methods available for structural determination of an electrode surface in solution at atomic and monolayer levels. Nowadays, many powerful in situ techniques, such as electrochemical scanning tunneling microscopy (EC-STM), infrared reflection absorption spectroscopy (IRAS), surfaceenhanced Raman scattering (SERS), and surface-enhanced infrared reflection absorption spectroscopy (SEIRAS), second harmonic generation (SHG), sum frequency generation (SFG), and surface X-ray scattering (SXS) have been widely employed to characterize the electrode surfaces under potential control with atomic and/or molecular resolution. The object of this review is to highlight some of the progress on in situ methods at solid-liquid interface with atomic and molecular levels. Several selected topics are focused on, specifically adsorbed anions on metal surface, electrocatalysis of the carbon oxide oxidation and dioxygen reduction, and direct observation of single crystal electrode surfaces.
    Electrochemistry -Tokyo- 01/2009; 77(1):2-20. · 0.98 Impact Factor
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    Soichiro Yoshimoto, Takahiro Sawaguchi
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    ABSTRACT: Two different cationic tetraphenyl porphyrins, one with two carboxyphenyl groups in cis-position and the other in trans-position (cis- and trans-H(4)DCPP(2+)), have been examined to control the structure of their 2D supramolecular assemblies in 0.05 M H(2)SO(4) at electrochemical interfaces. Electrochemical scanning tunneling microscopy (EC-STM) images revealed the formation of supramolecularly organized nanostructures of cis-H(4)DCPP(2+) such as dimer, trimer, and tetramer on the (square root(3) x square root(7)) sulfate/bisulfate adlayer, suggesting the importance of both electrostatic interaction between cationic porphyrin core and sulfate/bisulfate adlayer and the hydrogen bond formation between carboxyl groups of the nearest neighbor cationic porphyrins. Trans-H(4)DCPP(4+) ions were also found to be aligned in the square root(3) direction of the sulfate/bisulfate adlayer. The structure of these cationic porphyrin adlayers was found to depend upon the electrode potential; i.e., when the potential was changed in the negative direction, the (square root(3) x square root(7)) sulfate/bisulfate adlayer disappeared, and no ordered arrays were formed. In contrast, when 0.1 M HClO(4) was used as an electrolyte solution, only a disordered array was observed. The results of the present study indicate that the (square root(3) x square root(7)) sulfate/bisulfate adlayer formed on Au(111) in 0.05 M H(2)SO(4) plays a significant role as a nanorail template in the control of electrostatically assembled diacid porphyrin dicarboxylic acid derivative. In addition, the high-resolution STM clearly distinguished between cis-H(4)DCPP(2+) ion and cis-H(2)DCPP molecule. The cis-H(2)DCPP molecules on Au(111) provided an adlayer structure and an electrochemical behavior which are different from those of cis-H(4)DCPP(2+) ions.
    Journal of the American Chemical Society 12/2008; 130(47):15944-9. · 11.44 Impact Factor

Publication Stats

864 Citations
290.77 Total Impact Points

Institutions

  • 1999–2013
    • Kumamoto University
      • • Priority Organization for Innovation and Excellence
      • • Department of Applied Chemistry and Biochemistry
      Kumamoto, Kumamoto Prefecture, Japan
  • 2010
    • Hokkaido University
      • Catalysis Research Center
      Sapporo, Hokkaidō, Japan
  • 2002–2009
    • Tohoku University
      • • Department of Applied Bioorganic Chemistry
      • • Department of Applied Chemistry
      • • School of Engineering
      Sendai-shi, Miyagi-ken, Japan
  • 2007
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
  • 2004
    • Northeast Institute of Geography and Agroecology
      • Institute of High Energy Physics
      Beijing, Beijing Shi, China