Molecular assemblies of functional molecules on gold electrode surfaces studied by electrochemical scanning tunneling microscopy: Relationship between function and adlayer structures

In this research, molecular assembly and function of aromatic thiols, porphyrins, phthalocyanines, and fullerenes on gold single crystal surfaces was studied by electrochemical methods and scanning tunneling microscopy (STM). Surface functions of promoter molecules such as pyridinethiols, pyrimidinethiols, and benzenethiol for cytochrome c electrochemistry were characterized by electrochemical techniques. Adlayer structures of those molecules were investigated by in situ STM, and molecular orientations for each molecule on the Au surfaces were clarified at molecular level. Adlayers of porphyrins and phthalocyanines for electrocatalytic reduction of dioxygen were examined to elucidate the relationship between activity and adlayer structure. Stable two-dimensional arrays of cobalt porphyrins indicated two-electron reduction of O-2 to H2O2, whereas two-step four-electron reduction of O-2 to H2O occurred because of highly mobile porphyrinatoiron molecules on the surface. Furthermore, well-defined adlayers of crown-substituted phthalocyanine for host-guest interface and binary array consisting of porphyrin and phthalocyanine for the design of supramolecular nanoarchitectures were clearly visualized by STM. Finally, a unique approach for controlling molecular orientation was found by the formation of supramolecular assemblies consisting of porphyrin and fullerene. The electrochemical redox reaction of carbonyl and ferrocene moieties was promoted by using the simple method for the construction of a 1:1 supramolecular assembled film consisting of C-60 derivative and octaethylporphyrinatometal on Au single crystal surfaces.