Self-assembled monolayers of an aryl thiol: Formation, stability, and exchange of adsorbed 2-naphthalenethiol and bis(2-naphthyl) disulfide on Au

The adsorption of 2-naphthalenethiol and bis(2-naphthyl) disulfide onto bulk Au has been indirectly quantified from the adsorbate solution by liquid chromatography. A study of the kinetics of monolayer formation and exchange of these adsorbants has been carried out. Using chromatographic retention times and diode array spectroscopy, the products of desorption and exchange have been identified directly. For both aryl-derived monolayers, desorption in pure solvent yields bis(a-naphthyl) disulfide. Exchange of both aryl monolayers with decanethiol is observed, with 2-naphthalenethiol as the sole product, suggesting that exchange involves proton transfer at the Au surface rather than monolayer desorption followed by addition. Exchange of the aryl monolayers with didecyl disulfide is much slower and yields decyl 2-naphthyl disulfide. A comparison of the coverage of the aryl monolayers obtained by chromatography has been made with voltammetric reductive desorption. Confirmation of reductive thiolate desorption by voltammetry is obtained by in situ ultraviolet-visible spectroscopy. Thiolate oxidation of the polycyclic aromatic monolayers under aerobic conditions was not observed. Estimates of the free energies of adsorption for aliphatic and aromatic thiols provide similar values, indicating no strong preference by Au for either type of thiol. Similar conclusions are reached concerning the respective disulfides.