Porphyrins and metallo-porphyrins are well-known to have unique photochemical and catalytic properties and then have extensively used as a functional molecule in construction of molecular devices. In order to construct molecular devices using porphyrins with higher efficiency, we should control porphyrin ring orientation, namely porphyrin should be flatly adsorbed on the solid substrate surface. Self-assembly (SA) technique is one of the most promising methods to arrange molecule in order on the substrate surface at a molecular level, and then alkylthiol self-assembled monolayers (SAMs) on gold have extensively studied because of their high density, high stability, and high orientation. In this report, a novel porphyrin derivative with 4 thiol groups as surface binding groups to gold and 4 methoxy groups as lateral interaction groups, 5,10,15,20-tetra-(m-mercapto-p-methoxyphenyl) porphyrin (TMP) was newly designed and synthesized, and SA process of TMP on Au(111) single crystal surface was investigated by electrochemical, scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) measurements.After annealing and quenching of Au(111) disk, TMP SAM on Au(111) was prepared by dipping the Au(111) substrate into benzene solution containing 0.05 mM TMP for certain periods. Linear sweep voltammograms (LSVs) of the Au(111) electrodes modified with TMP SAM, which was prepared for several dipping periods, were measured in 0.1 M KOH solution to estimate density, stability, and orientation. Ex situ STM measurement of TMP SAM on Au(111) was performed in air at room temperature to obtain the molecular arrangement. XPS measurement was carried out to study sulfur state of TMP SAM.Based on the experimental results, we found that even at initial stage of SA process, TMP was flatly adsorbed at random and that after the phase change, flatly adsorbed TMP was arranged in order on the Au(111) surface at the final stage.

Structural studies on first-ordered self-assembly process of flatly adsorbed porphyrin derivatives on Au(111)

248th National Meeting (2014)

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