Adlayers of 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) and copper(II) (CoTPP and CuTPP) formed on a Au(111) electrode by immersion into a benzene solution containing either CoTPP or CuTPP were investigated in 0.1 M HClO4 by cyclic voltammetry and in situ scanning tunneling microscopy (STM). Highly ordered arrays of CoTPP and CuTPP molecules were observed on the Au(111) surface. Highresolution STM images revealed the characteristic shape, internal molecular structure, and molecular orientation of individual CoTPP and CuTPP molecules in ordered arrays. The adlayers of CoTPP and CuTPP formed on Au(111) were in an identical packing arrangement with the same orientation. The center cobalt ion in CoTPP appeared as the brightest spot in the STM image, whereas the copper ion in CuTPP was dark. On the adlayers of highly ordered CoTPP and CuTPP molecules, O 2 reduction was carried out in 0.1 M HClO4 saturated with O2. Voltammetric results indicated that CuTPP did not catalyze the reaction, whereas the highly ordered CoTPP adlayer on Au(111) enhanced the two-electron reduction of O2 to H2O2.

Characteristic properties of the coronene layer formed on Au(111) for the epitaxial growth of various fullerenes are described. The electrochemical behavior of the coronene adlayer prepared by immersing a Au(111) substrate into a benzene solution containing coronene was investigated in 0.1 M HClO4. The as-prepared coronene adlayer on Au(111) revealed a well-defined (4 x 4) structure. Structural changes of the array of coronene molecules induced by potential manipulation were clearly observed by in situ scanning tunneling microscopy (STM). Supramolecularly assembled layers of fullerenes such as C60, C70, C60-C60 dumbbell dimer (C120), C60-C70 cross-dimer (C130), and C60 triangle trimer (C180) were formed on the well-defined coronene adlayer on the Au(111) surface by immersing the coronene-adsorbed Au(111) substrate into benzene solutions containing those molecules. The adlayers thus prepared were characterized by comparison with those which were directly attached to the Au(111) surface. The C60 molecules formed a honeycomb array with an internal structure in each C60 cage on the coronene adlayer, whereas C70 molecules were one-dimensionally arranged with the same orientations. The dimers, C120 and C130 molecules, formed an identical structure with c(11 x 4 radical3)rect symmetry. For the C130 cross-dimer molecule, C60 and C70 cages were clearly recognized at the molecular level. It was difficult to identify the adlayer of the C180 molecule directly attached to Au(111); however, individual C180 molecules could be recognized on the coronene-modified Au(111) surface. Thus, the adlayer structures of those fullerenes were strongly influenced by the underlying coronene adlayer, suggesting that the insertion of a coronene adlayer plays an important role in the formation of supramolecular assemblies of fullerenes.

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In situ scanning tunneling microscopy (STM) revealed that highly ordered adlayers of fullerene monomer (C60) and [2 + 2]-type dimer (C120) were formed on Au(111) by immersing the surface in benzene solution containing C60 or C120 molecules. High-resolution STM images allowed us to determine packing arrangements of C60 and C120 on a Au(111) surface in an aqueous HClO4 solution. The (2 3 × 2 3)R30°and the so-called in-phase structures of the C60 adlayer were found on the Au(111) surface, whereas the (2 3 × 4 3)R30°a nd (2 3 × 5 3)R30°structures were observed for the C120 dimer. Each C120 dimer was imaged in a dumbbell shape by in situ STM.