Electrochemical and spectroscopic studies of nitrophenyl moieties immobilized on gold nanoparticles

Electrochemical and spectroscopic studies of gold nanoclusters passivated by a mixed monolayer of n-hexanethiolates (C6S) and p-nitrothiophenolates (NTP) were reported. Multiple copies of NTP were incorporated into the cluster monolayers by a surface exchange reaction, where the final surface composition was determined by (1)H NMR, and further characterized by infrared (FTIR) study. UV-vis spectroscopic study of the exchanged particles showed a surface-plasmon (SP) band position at ca. 504 nm. The blue shift of the SP energy relative to that of the (unexchanged) hexanethiolate-protected clusters, 520 nm, was attributed, in part, to the interactions between the gold cores and the nitrophenyl functional groups. Electrochemical measurements of the cluster solutions in dried CH(2)Cl(2) exhibited two (quasi-)reversible voltammetric waves within the potential range of -1.0 to -1.6 V (vs Ag/AgCl), which were ascribed to the successive single-electron-transfer processes related to the nitrophenyl moieties, with the corresponding reduction products being the anion radical and dianion, respectively. In addition, in the potential range of +1.0 to -0.8 V, multiple reversible voltammetric waves were observed, which were interpreted based on the quantized capacitance charging of nanoparticle double layer. The peak spacings were found to decrease slightly compared to those without NTP exchange, corresponding to a small increase of the particle capacitance due to the more polar NTP ligands.