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Yoshimoto S.,Kumamoto University | Yoshimoto S.,Kumamoto Institute for Photo Electro Organics Phoenics
Physical Chemistry Chemical Physics | Year: 2013

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. This journal is © the Owner Societies 2013.

Jintoku H.,Kumamoto University | Ihara H.,Kumamoto University | Ihara H.,Kumamoto Institute for Photo Electro Organics Phoenics
Chemical Communications | Year: 2012

Here, we present the first application of molecular gel-mediated power-conversion enhancement of solar cells, which is based on the excimer emission from a transparent and colourless polymer film that encapsulates a pyrene nano-fibrillar assembly. © The Royal Society of Chemistry 2012.

Yoshimoto S.,Kumamoto University | Yoshimoto S.,Kumamoto Institute for Photo Electro Organics Phoenics
Chemical Communications | Year: 2012

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. This journal is © The Royal Society of Chemistry 2012.

Tominaga M.,Kumamoto University | Tominaga M.,Kumamoto Institute for Photo Electro Organics Phoenics | Sakamoto S.,Kumamoto University | Yamaguchi H.,Kumamoto University
Journal of Physical Chemistry C | Year: 2012

A jungle-gym structured film of single-walled carbon nanotubes (SWCNTs) was synthesized onto a gold surface according with our protocol, which was used immediately as a working electrode in electrochemistry without pretreatment because of the high electrical conductivity between the SWCNTs and the gold surface. No removal of the SWCNTs from the gold surface in solution was necessary, which completely covered the gold surface. The electrochemical properties of as-grown SWCNTs and SWCNTs treated with UV-ozone and electrochemical oxidation were investigated by use of ferrocenecarboxylic acid (Fc) as a monitor redox species. The redox waves of Fc were analyzed by voltammetric simulation fitting method. In the case of UV-ozone treatment, the side-wall structure of the SWCNTs was well oxidized, but the deeper parts of SWCNTs films were not well-oxidized because the UV-ozone irradiation did not penetrate into the deeper parts of the SWCNT layer. On the other hand, electrochemical oxidation at the side-wall structure of the SWCNTs was performed uniformly. The heterogeneous electron transfer rate constant (k°') values for Fc were as follows: (0.45-1.4) × 10 -3, 7.6 × 10 -3, and 0.45 × 10 -3 cm·s -1 for the as-grown SWCNTs, SWCNTs treated with electrochemical oxidation, and SWCNTs treated with UV-ozone, respectively. The k°' values for the as-grown SWCNTs were similar to those for SWCNTs treated with UV-ozone, which suggests that the UV-ozone irradiation would affect only the surface of the SWCNT layer. The electrochemically active surface areas of the electrochemical oxidized and UV-ozone-treated SWCNTs decreased to 1/ 15- 1/ 30 and 1/ 2, respectively, in comparison with the untreated SWCNTs, because of the decomposition of the sp 2-hybridized carbon structure in the SWCNTs. The simulated voltammograms for Fc at the electrochemically oxidized SWCNTs fitted perfectly, indicating that it was uniformly active at all parts of the electrochemically oxidized SWCNT surface. On the other hand, the observed voltammograms from untreated SWCNTs and UV-ozone-treated SWCNTs did not fit well because of the broad peaks in the voltammograms, which indicated that the electron transfer rate constant was broad at those SWCNT surfaces. © 2012 American Chemical Society.

Tominaga M.,Kumamoto University | Tominaga M.,Kumamoto Institute for Photo Electro Organics Phoenics | Iwaoka A.,Kumamoto University | Kawai D.,Toho Gas Co. | Sakamoto S.,Kumamoto University
Electrochemistry Communications | Year: 2013

The correlation between carbon oxygenated species as a defect in single-walled carbon nanotubes (SWCNTs) and the oxidation reaction behavior of the reduced form of β-nicotinamide dinucleotide (NADH) was investigated. The two main oxidation peaks of NADH at the SWCNTs were due to adsorbed and diffused species, respectively. The peak current ratio showed a good relationship to the intensity ratio of the G-band/D-band obtained from the Raman spectra of the SWCNTs. © 2013 Elsevier B.V.

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