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 ont o bulk Au has been indirectly quantified from the adsorbate solution b y liquid chromatography. A study of the kinetics of monolayer formatio n and exchange of these adsorbants has been carried out. Using chromat ographic 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 observ ed, with 2-naphthalenethiol as the sole product, suggesting that excha nge involves proton transfer at the Au surface rather than monolayer d esorption followed by addition. Exchange of the aryl monolayers with d idecyl disulfide is much slower and yields decyl 2-naphthyl disulfide. A comparison of the coverage of the aryl monolayers obtained by chrom atography has been made with voltammetric reductive desorption. Confir mation of reductive thiolate desorption by voltammetry is obtained by in situ ultraviolet-visible spectroscopy. Thiolate oxidation of the po lycyclic aromatic monolayers under aerobic conditions was not observed . Estimates of the free energies of adsorption for aliphatic and aroma tic thiols provide similar values, indicating no strong preference by Au for either type of thiol. Similar conclusions are reached concernin g the respective disulfides.