Anthraquinone derivative modified Au clusters with a 2.2 nm core diameter prepared by a substitution reaction of octyl thiolate-covered Au clusters with 1-(1,8-dithiaoctyl)anthracene-9,10-dione (AQS) underwent two-step one-electron reduction in aprotic solvents, and the second reduction potential was significantly more negative than that of free AQS. The magnitude of this potential shift became larger for the clusters in association with increase in the number of exchanged anthraquinone-terminated thiolates due to the electronic interaction between the adjacent anthraquinone moieties on the Au cluster surface. By electrochemical reduction of the anthraquinone moieties, a redox-active Au cluster film was formed on the electrode. The energy of the surface plasmon band of the film on ITO was shifted with the change in the solvent refractive index from nd 20 ) 1.33 to 1.62, and the V-shaped profile of the energy shift vs nd 20 plots is inexplicable by Mie theory. The band was also blue-shifted by 12 nm by changing the potential in the negative direction between -1.0 and -2.0 V vs Ag/Ag + in Bu4NClO4-MeCN. The scanning tunneling microscopy image revealed that spherical Au clusters aggregated to form an organized assembly at the early stage of the electrodeposition process.

The electrodeposition phenomenon of octyl thiolate-stabilized gold nanoparticles with a 2.3 ( 0.5 nm core diameter modified with biferrocene-terminated alkanethiolates on their surface (Au n -BFc) has been investigated using cyclic voltammetry, STM and AFM morphological observation, and electrochemical quartz crystal microbalance (EQCM) of the deposited Au n -BFc film. Consecutive potential scans causing two-step oneelectron oxidation of the biferrocene units of Au n -BFc in CH 2 Cl 2 electrolyte solution produce the adhesive Au n -BFc film on electrode surface. The deposition rate is lower for the biferrocene derivative on one particle θ BFc with a smaller modification number and a kind of electrolyte anion: ClO 4 -∼ BF 4 -. PF 6 -. The STM and AFM images have revealed that the thickness of the Au n -BFc film grows gradually by increasing the number of cyclic scans, forming many monolayer-level domains with ca. 80 nm diameter of the assembled Au n -BFcs. The average interparticle spacing of neighboring Au n -BFcs in the film is 7.5 nm, which is longer than the estimated diameter of whole Au n -BFc species (5.9 nm). Analysis of boron in the film electrodeposited in Bu 4 NBF 4 -CH 2 Cl 2 by the prompt γ-ray neutron activation (PGA) method shows that the BF 4 -ion is incorporated in the film. EQCM measurement suggests that not only ions but also the included CH 2 Cl 2 solvent molecules in the film are moved in and out reversibly in a potential range of E 0 ′ 2 of Au n -BFc. These results indicate that the formation of ionic lattice including Au n -BFc 2+ and counterion is accompanied by the exclusion of CH 2 Cl 2 solvent molecules among the particles in the initial deposition process.