Fast vs. Slow: Electrolyte and Potential Dependent Adlayer Switching of an Oligopyridine on Au(111)

The structure of an oligopyridine (3,3′-bis(terpyridine) (3,3′-BTP)) monolayer at the Au(111)|electrolyte interface shows a strong dependence on type of electrolyte and pH. Neutral phosphate buffer, sulfuric acid, sodium sulfate and perchloric acid were employed as electrolytes. Structure transitions are fast and fully reversible under acidic conditions, while an extremely slow process in the range of hours could be observed in phosphate buffer. These findings are attributed to the relative weakness of (weak) hydrogen bonds in comparison to Coulomb interactions in buffer. The slow process allows time-dependent investigations of structure formation. The systems were investigated by cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM).