Nanodomains of Juglonethiol on Au(111): Relationship between Domain Size and Electrochemical Properties

The electrochemical properties of 5-hydroxy-3-butanedithiol-1,4-naphthoquinone (juglonethiol) depend on the gold electrode nature and on its crystalline organization, suggesting a long-range order due to the presence of physical oligomers. On an Au(111) substrate, nanodomains of juglonethiol are formed by the replacement of weakly adsorbed dodecanethiol molecules in a self-assembled monolayer by juglonethiol. By means of scanning tunneling microscopy, we show that domains a few nanometers to tens of nanometers in size grow along the grain boundaries of the dodecanethiol monolayer; their redox behavior is compared with that of a complete grafted monolayer. Modeling shows the presence of hydrogen-bonded oligomers of juglonethiol and accounts for the variation of redox potential with the coverage, that is, with the oligomer size. These nanostructured domains are better than a complete monolayer for the detection of oligodeoxynucleotide hybridization.